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ES/S6 – HSC 41094 P0022158

Engineering StudiesHSC CourseStage 6

Lifting devices



Acknowledgments

This publication is copyright Learning Materials Production, Open Training and Education Network – Distance Education, NSW Department of Education and Training, however it may contain material fromother sources which is not owned by Learning Materials Production. Learning Materials Productionwould like to acknowledge the following people and organisations whose material has been used.

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All reasonable efforts have been made to obtain copyright permissions. All claims will be settled ingood faith.

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Edit: John Cook, Jeff Appleby, Stephen Russell

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Copyright in this material is reserved to the Crown in the right of the State of New South Wales.Reproduction or transmittal in whole, or in part, other than in accordance with provisions of theCopyright Act, is prohibited without the written authority of Learning Materials Production.

© Learning Materials Production, Open Training and Education Network – Distance Education,NSW Department of Education and Training, 2001. 51 Wentworth Rd. Strathfield NSW 2135.

Revised 2002



i

Module contents

Subject overview ................................................................................iii

Module overview................................................................................vii

Module components.......................................................................... vii

Module outcomes..................................................................... ix

Indicative time........................................................................... x

Resource requirements............................................................. xi

Icons ..............................................................................................xiii

Glossary ............................................................................................. xv

Directive terms.................................................................................xxi

Part 1: Lifting devices – developments ................................................................1–45

Part 2: Lifting devices – mechanics/hydraulics ................................................... 1–55

Part 3: Lifting devices – materials ......................................................................... 1–45

Part 4: Lifting devices – electricity/electronics .................................................... 1–43

Part 5: Lifting devices – communication .............................................................1–35

Part 6: Lifting devices – engineering report ......................................................... 1–24



ii

Bibliography.......................................................................................25

Module evaluation.............................................................................27



iii

Subject overview

Engineering Studies Preliminary Course

Household appliances examines common appliances

found in the home. Simple appliances are analysedto identify materials and their applications.

Electrical principles, researching methods and

techniques to communicate technical information are

introduced. The first student engineering report is

completed undertaking an investigation of materials

used in a household appliance.

Landscape products investigates engineering

principles by focusing on common products, such as

lawnmowers and clothes hoists. The historical

development of these types of products demonstrates

the effect materials development and technological

advancements have on the design of products.

Engineering techniques of force analysis are

described. Orthogonal drawing methods are

explained. An engineering report is completed that

analyses lawnmower components.

Braking systems uses braking components and

systems to describe engineering principles. The

historical changes in materials and design areinvestigated. The relationship between internal

structure of iron and steel and the resulting

engineering properties of those materials is detailed.

Hydraulic principles are described and examples

provided in braking systems. Orthogonal drawing

techniques are further developed. An engineering

report is completed that requires an analysis of a

braking system component.



vi

Aeronautical engineering explores the scope of the

aeronautical engineering profession. Career

opportunities are considered, as well as ethical

issues related to the profession. Technologiesunique to this engineering field are described.

Mechanical analyses includes aeronautical flight

principles and fluid mechanics. Materials and

material processes sections concentrate on their

application to aeronautics. The corrosion process is

explained and preventative techniques listed.

Communicating technical information using both

freehand and computer-aided drawing is required.

The engineering report is based on the aeronautical

profession, current projects and issues.

Telecommunications engineering examines the

history and impact on society of this field. Ethical

issues and current technologies are introduced.

The materials section concentrates on specialised

testing, copper and its alloys, semiconductors and

optical fibres. Electronic systems such as analogue

and digital are explained and an overview of a

variety of other technologies in this field is

presented. Analysis, related to telecommunication

products, is used to reinforce mechanical concepts.

Communicating technical information using both

freehand and computer-aided drawing is required.

The engineering report is based on the

telecommunication profession, current projects and

issues.

Figure 0.1 Modules



vii

Module overview

Lifting devices investigates the social impact that these devices, from

complex cranes to simple car jacks, have had on our society. The

mechanical concepts are explained, including the hydraulic concepts

often used in lifting apparatus. The industrial processes used to form

metals and the processes used to control physical properties are

explained. Electrical requirements for many devices are detailed.

The technical rules for sectioned orthogonal drawings are demonstrated.

The engineering report is based on lifting devices.

Module components

Each module contains three components, the preliminary pages, the

teaching/learning section and additional resources.• The preliminary pages include:

– module contents

– subject overview

– module overview

– icons

– glossary

– directive terms.

Figure 0.2 Preliminary pages



viii

Figure 0.3 Teaching/learning section

• The teaching/learning parts may

include:

– part contents

– introduction

– teaching/learning text and tasks

– exercises

– check list.

• The additional information may

include:

– module appendix

– bibliography

– module evaluation.

Ad d it ional r esour ces

Figure 0.4 Additional materials

Support materials such as audio tapes, video cassettes and computer

disks will sometimes accompany a module.



ix

Module outcomes

At the end of this module, you should be working towards being able to:

• differentiate between properties of materials and justify the selectionof materials, components and processes in engineering (H1.2)

• determine suitable properties, uses and applications of materials in

engineering (H2.1)

• demonstrate proficiency in the use of mathematical, scientific and

graphical methods to analyse and solve problems of engineering

practice (H3.1)

• use appropriate written, oral and presentation skills in the preparation

of detailed engineering reports (H3.2)

• investigate the extent of technological change in engineering (H4.1)

• apply a knowedge of history and technological change to

engineering-based problems (H4.2)

• appreciate social, environmental and cultural implications of

technological change in engineering and apply them to the anlaysis

of specific problems (H4.3)

• work individually and in teams to solve specific engineering

problems and in the preparation of engineering reports (H5.1)

• demonstrate skills in analysis, synthesis and experimentation related

to engineering (H6.2).

Extract from Stage 6 Engineering Studies Syllabus, © Board of Studies, NSW, 1999.

Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.



x

Indicative time

The Preliminary course is 120 hours (indicative time) and the HSC

course is 120 hours (indicative time).

The following table shows the approximate amount of time you should

spend on this module.

Preliminary modules Percentage of time Approximatenumber of hours

Household appliances 20% 24 hr

Landscape products 20% 24 hr

Braking systems 20% 24 hr

Bio-engineering 20% 24 hr

Elective: Irrigation systems 20% 24 hr

HSC modules Percentage of time Approximatenumber of hours

Civil structures 20% 24 hr

Personal and public transport 20% 24 hr

Lifting devices 20% 24 hr

Aeronautical engineering 20% 24 hr

Telecommunications engineering 20% 24 hr

There are five parts in Lifting devices. Each part will require about four

to five hours of work. You should aim to complete the module within 20

to 25 hours.



xi

Resource requirements

During this module you will need to access a range of resources

including:• actual lifting devices to analyse

• technical drawing equipment

– drawing board, tee square, set squares (30∞ –60∞, 45∞),

protractor, pencils (0.5 mm mechanical pencil with B lead),

eraser, pair of compasses, pair of dividers

• calculator

• rule.



xii



xiii

Icons

As you work through this module you will see symbols known as icons.

The purpose of these icons is to gain your attention and to indicate

particular types of tasks you need to complete in this module.

The list below shows the icons and outlines the types of tasks for Stage 6

Engineering studies.

Computer

This icon indicates tasks such as researching using an

electronic database or calculating using a spreadsheet.

Danger

This icon indicates tasks which may present a danger and

to proceed with care.

Discuss

This icon indicates tasks such as discussing a point or

debating an issue.

Examine

This icon indicates tasks such as reading an article or

watching a video.

Hands on

This icon indicates tasks such as collecting data or conducting experiments.

Respond

This icon indicates the need to write a response or draw

an object.

Think

This icon indicates tasks such as reflecting on your

experience or picturing yourself in a situation.



xiv

Return

This icon indicates exercises for you to return to your

teacher when you have completed the part. (OTEN OLP

students will need to refer to their Learner's Guide for instructions on which exercises to return).



xv

Glossary

As you work through the module you will encounter a range of terms that

have specific meanings. The first time a term occurs in the text it will

appear in bold.

The list below explains the terms you will encounter in this module.

apparent weight difference between actual weight and buoyancyforce; weight it appears to be when submerged

austempering heat treatment process where the austenitised steelis soaked till the structure changes to ferrite andfinely dispersed carbide particles

bainite the product of austempering; ferrite with finelydispersed carbide particles

barelling formation of a shape often found in a ductilespecimen that has been subjected to a compressiveload

billet large ‘block’ of metal used as a start for the rolling process

boom (telescopic) telescopic member hinged to a revolving super-structure that can extend in length

bow’s notation labeling of spaces between applied forces on a non-concurrent force system

brinell type of hardness test that uses steel sphere indentorsand two different loads

brittleness a material that doesn't show much plasticdeformation is seen to be rigid and brittle; thestress/strain graphs for some ceramic materials areonly a straight line with no curve at all

buoyancy force upthrust force exerted by a fluid on a body equal tothe weight of the displaced fluid

centre of buoyancy the centre of mass of the displaced fluid. The buoyancy force acts through this point

centre of gravity a term used to describe the point that is the centrefor the mass of an object



xvi

cherry picker a specialised crane consisting of an enclosed‘bucket’ in which workers are lifted to carry outtasks such as changing street lights etc

cold welding occurs under the extreme pressure of powder

forming when adjacent particles are forced to jointogether

compliance plate metal plate under the bonnet indicating details suchas the mass of a vehicle

compressibility A measure of the extent a fluid volume may bereduced by an increase in pressure

conventionalrepresentation

a shortened and easier method of drawing some partor feature, based upon AS 1100 drawing standards

core solid mixture of sand and resin used to create

shaped cavities inside cast structures.

coring occurs in alloys, under non equilibrium cooling,when the centre of the grain is richer in the higher melting point metal

counterweight weight used to supplement the weight of themachine in providing stability for lifting workingloads – usually attached to the rear of a revolvingsuper-structure

density mass per unit volume

derrick cranes small, simple, fixed cranes consisting of a boomand lifting tackle

derricking angular movement of crane main jib/boom in avertical plane, also called luffing

drum rotating cylinder with side flanges on which therope, used in the machine operation, is wrapped

ductility any stress/strain graph that shows a large area of plastic deformation and possibly a failure point thatis below the ultimate tensile strength (uts) isrepresentattive of a ductile material

elasticity the angle of the straight-line section of the stress-strain graph indicates elasticity; the steeper the line,the stiffer the material

elevators a moving cage or car used to lift people or cargofrom one level in a building to another

escalator a continuous, inclined moving walkway

factor of safety the margin included in all calculations to ensurematerials are not stressed beyond their elastic limit

fillet curve curve used in the design of cast and forgedcomponents to reduce stress concentration at corners



xvii

fine pearlite thin bands of ferrite and cementite formed under faster than equilibrium cooling often found innormalising

fluid liquid or a gas

fly jib extension attached by pins and ropes to the boomhead to provide additional length for handlingspecified loads, it may also be offset from the lineof the boom

forklifts small motorised vehicles with two prongs or ‘forks’at the front designed to lift pallets

funicular polygon method of finding the line of action by adding‘strings’ to a space diagram

governor safety device, found on elevators, that operatesunder centrifugal force to activate emergency

brakes

hardenability the depth to which steel hardens

hydraulic operated by or employing water or other fluid

hydraulics study of pressurised liquid systems

item number a number assigned to a component on an assemblydrawing, used to identify components referred to ina materials or parts list

itemizing the use of numbers or upper case letters to identifycomponents on an assembly drawing

leader thin dark continuous lines drawn from an itemizingcircle or number to the component on an assemblydrawing

lifting motion of raising or lowering of load in a verticaldirection

lifting device a machine that makes it easier to raise somethingeither by reducing the force required or raising the

heights achievable

line of centres a line used to locate the point of contact of touchingcircles by joining the centres of the two circles

low carbon steel an alloy of iron with between 0.15% and 0.35%carbon

luffing angular movement of crane main jib/boom in avertical plane. Also called derricking

machinability the ability of a material to be shaped with variousmachine tools and cutting tips



xviii

manometer gauge for measuring fluid pressure of gases or liquids

martempering heat treatment process where the austenitised steelis held till it is a constant temperature throughout

then quenched in water

mass quantity of matter in a substance

materials list a materials or parts list used on assembly drawingsto show item or part number, the name or description of the parts, the quantity required andthe material specification

non-concurrentforces

forces whose lines of action do not pass through acommon point

outrigger extendable or fixed arms attached to a mounting

base (chassis) which rest on supports at the outer ends to increase stability

patenting heat treatment process where the austenitised steelis cooled in molten lead

piezometer gauge for measuring fluid pressure of liquids

platform lifts any of a range of lifting devices consisting of a flatsurface on which a worker stands, and that may beraised or lowered

pneumatics study of pressurised air systems

prefinished surface finish, such as ‘Colorbonding’, that is plated on the surface before rolling

ram the piston that lifts on a hydraulic jack

ray a radial line from a pole point drawn to theend points of force vectors drawn on a forcediagram

relative density how heavy or light a substance is when comparedwith water

repeated features a regular pattern of features, such as holes or slots,in a component

resilience this is the area under the straight-line sectionof the stress/strain graph; it is a measure of the amount of energy which can be absorbed

by a material without causing plasticdeformation

resultant force single force having the same effect as the originalforce system

Rockwell type of hardness test that uses three different loads

and three different indentors



xix

ropes twisted, multi strand steel cables used in elevatorsand cranes; also refers to twisted cables of naturalor synthetic fibres

sheave rotating wheel with an angled groove for carryingthe rope to operating position

slewing rotary motion of a crane about its vertical axis

space diagram a scaled drawing showing spaces between forcesacting on a body

specific gravity ratio of the density of the substance to the densityof water

specific volume volume per unit mass

strength the amount of force needed to plastically deform thematerial is called the proof or yield strength whilethe 'high point' of the stress/strain graph shows theultimate tensile strength

string lines drawn on funicular polygon to determine lineof action of resultant/equilibrant force. Drawn

parallel to rays on a force diagram

surface tension cohesive force that occurs at the surface of a liquid

tangency circles or arcs in contact with or touching a straightline

tangent a straight line which touches a circle or arc

telescopic extensioncrane

a crane in which the boom can be extended or shortened by retracting within itself

toughness the area under the total curve of the stress/straingraph; it is a measure of the amount of energyrequired to cause failure

tower crane a crane where the operator’s cabin, boom andlifting gear are supported at the top of a very talltower

vacuum gauge pressure below atmospheric pressure

Vickers type of hardness test that uses a standard load and adiamond pyramid indentor.

viscosity resistance to flow



xx



xxi

Directive terms

The list below explains key words you will encounter in assessment tasks

and examination questions.

account account for; state reasons for, report on;

give an account of; narrate a series of events or transactions

analyse identify components and the relationship between

the; draw out and relate implications

apply use, utilise, employ in a particular situation

appreciate make a judgement about the value of

assess make a judgement of value, quality, outcomes,

results or size

calculate ascertain/determine from given facts, figures or

information

clarify make clear or plain

classify arrange or include in classes/categories

compare show how things are similar or different

construct make, build, put together items or arguments

contrast show how things are different or opposite

critically

analyse/evaluate

add a degree or level of accuracy, depth,

knowledge and understanding, logic, questioning,

reflection and quality to analysis/evaluation

deduce draw conclusions

define state the meaning and identify essential qualities

demonstrate show by example



xxii

describe provide characteristics and features

discuss identify issues and provide points for and/or against

distinguish recognise or note/indicate as being distinct or

different from; to note differences between

evaluate make a judgement based on criteria; determine the

value of

examine inquire into

explain relate cause and effect; make the relationships

between things evident; provide why and/or how

extract choose relevant and/or appropriate details

extrapolate infer from what is known

identify recognise and name

interpret draw meaning from

investigate plan, inquire into and draw conclusions about

justify support an argument or conclusion

outline sketch in general terms; indicate the main

features of

predict suggest what may happen based on available

information

propose put forward (for example a point of view, idea,

argument, suggestion) for consideration or action

recall present remembered ideas, facts or experiences

recommend provide reasons in favour

recount retell a series of events

summarise express, concisely, the relevant details

synthesise putting together various elements to make a whole

Extract from The New Higher School Certificate Assessment Support Document ,© Board of Studies, NSW, 1999.




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Part 1: Lifting devices – developments 1

Part 1 contents

Introduction .........................................................................................2

What will you learn?........ ........ ......... ........ ........ ........ ........ ........ ...2

Lifting devices.....................................................................................3

Common lifting devices..............................................................5

Impact of lifting devices on construction methods......................26

Exercises...........................................................................................35

Progress check.................................................................................43

Exercise cover sheet.......................................................................45



2 Lifting devices

Introduction

Welcome to the module on lifting devices.

Lifting devices are machines that have been designed to address two of the

major shortcomings of the human body – that of lack of strength and lack of

reach.

In this part you will look at the historical background behind the

development of a modern lifting device as well as considering the function of

a number of other common lifting devices. Finally you will examine the

influence lifting devices have had on the construction industry.

What will you learn?

You will learn about:

• the historical development of lifting devices

• engineering innovation in lifting devices and their effect on people’s

lives.

You will learn to:

• research the history of technological change in lifting devices

• examine the impact of lifting devices on engineering construction methods.





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Lifting devices

What do you do if you need to lift something that is too heavy for you

to lift on your own?

You could get a group of friends together to give you a hand. That’s

exactly the technique used in many ancient civilisations except thefriends were called slaves. When blocks of stone weighing 2.5 tonnes

each had to be moved into position during the construction of the great

pyramids of Egypt, large teams of people using little more than brute

force were called upon for the job. A more modern solution is to use a

machine, some sort of lifting device, to help.

Machines are devices that help you do work. You would have learnt about

simple machines during the landscape and bio-engineering modules in the

preliminary year. Some machines such as bicycles are speed magnifiers

however the majority of machines are force magnifiers. That is, they have a

mechanical advantage of greater than one. The effort we apply at one partof the machine is not as great as the load we can lift at another part of the

machine.

Pulley systems, levers, hydraulic systems and screw threads are all

examples of simple machines that are used every day to magnify our force

and have been put to use in common lifting devices. A lifting device is a

machine that makes it easier for you to raise something that is difficult to lift

either because it is too heavy or too awkward to lift or in other cases

because the heights involved are beyond your physical capabilities.

Examples of common lifting devices include:

• corkscrews

• cranes

• car jacks and hoists

• elevators and escalators

• conveyor belts

• dry docks for ships

• forklifts

• pulley systems.



4 Lifting devices

Look at the three common corkscrews in Figure 1.1. They all do the

same job – removing corks from wine bottles. They all have a screw

thread that winds down to get a good grip on the cork but after that they

all work in slightly different ways. The corkscrew on the left works on brute force but the other two are simple machines operating as force

magnifiers.

Figure 1.1 Three types of corkscrew

Explain how the middle and right hand corkscrews magnify the force

being applied to them.

___________________________________________________________

___________________________________________________________

___________________________________________________________

Did you answer?

Once the corkscrew has been wound into the cork the force applied by the user is magnified by a first order lever arrangement. The right-hand one is larger buteasier to use because two hands can apply the effort.

When you are looking at any lifting device for this module it is important to

keep in mind a number of important questions.

• What is being lifted and where?

• How is it doing it – what simple machine systems are being used?

• What materials have been used in the construction of the lifting device

and why?



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• What is the power source?

• What would you do if the lifting device was not available?

You will now go on to look at the development of a common lifting device –

the crane. The crane has been chosen because of its long history and thewide variety of designs that have been produced.

Common lifting devices

Cranes

Cranes are one of the bigger lifting devices you may see especially around

large construction sites. Scaled down cranes are mounted on the back of tow

trucks to lift one end of a vehicle so it can be towed away after an accident.

However, most cranes are used to lift things high off the ground, such as for

lifting materials to the upper floors of a building under construction. All

cranes are designed to lift a suspended load from one place to another.

Early cranes

The ancient Greeks developed a hoist system that was the forerunner to

later cranes. This basic hoist consisted of a timber pole or jib, a pulley andrope. The rope was passed over the pulley and attached to the load.

Human power, often lots of it, was used to pull on the rope to raise the

load.

Figure 1.2 An early Greek hoist



6 Lifting devices

The Romans developed the crane further by adding more complex pulley

systems, larger capstans or winding drums for winding the rope around, and

human powered treadmills. The purpose of these innovations was to

increase the lifting capacity of the crane by raising its mechanical advantage.

However, the strength of the timber and natural fibre ropes used in theconstruction of the cranes was still a limiting factor in the overall lifting

capacity.

Figure 1.3 A Roman crane with a human-powered treadmill (viewed from the frontand the side)

© NSW Department of Education

As with many other areas of engineering there was little technological change

from the Roman era through to the start of the industrial revolution in the

18th century. The crane in figure 1.4 was built some 1300 years after the

Roman era but still used timber in its construction and had a human powered

treadmill as the source of motion.

Figure 1.4 A timber-framed crane from the 1300s




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Stronger materials increase the lifting capacity

By the 1800s new steam powered engines and higher strength materials,

such as cast iron and wrought iron, were introduced, which greatly increased

the lifting capacity of the cranes of the time.

Figure 1.5 An early steam powered, metal framed crane from 1879


With the rapid development of the rail and shipbuilding industries heavy,

steam powered, rail mounted cranes began to be used extensively.

The materials and construction techniques used on cranes mirrored theconstruction of bridges of the time, with jibs made from either a truss design

or a solid box girder design. Note the solid construction of the crane in

figure 1.6.

Figure 1.6 A heavy lift crane from the late 1800s




8 Lifting devices

Mobile cranes

The development of the internal combustion engine and lighter, stronger

steels at the start of the 1900s led to a dramatic reduction in the size and

weight of cranes. This in turn improved the cranes versatility. The cranefrom 1922 in figure 1.7 was mounted on the back of a truck to provide

increased mobility.

Figure 1.7 A truck mounted crane from 1922


By 1932 cranes that could move under their own power were developed.

Mass production techniques pioneered in the automotive industry lead to a

reduction in the price of cranes opening the way for even wider use inindustry and greater experimentation with new materials such as high tensile

steels.

Figure 1.8 A mobile crane from 1932




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In 1945 even the largest mobile cranes were capable of lifting only 5 tonnes.

By 1950 mobile cranes were capable of lifting 20 tonnes and by 1963 that

figure had risen to 100 tonnes.

Figure 1.9 The first mobile crane to break the 100 tonne barrier


To increase lift capacity yet maintain mobility lighter high tensile, structural

steels and aluminium alloys have been used in increasing amounts in modern

mobile cranes.

A mobile crane will typically be powered by a diesel engine. The diesel

engine provides the power directly for the lifting motions but will power a

hydraulic pump to provide the luffing motion. Luffing is when the boom

or jib of the crane pivots up or down as seen in figure 1.10.

In some cases an electric motor is used for the lifting operations. In this

system a generator powered by the diesel engine powers the electric motor.

The advantage of using an electric motor is that the rate of lift can be easily

varied without having to use a gearing system or varying the speed of the

diesel motor.



10 Lifting devices

Figure 1.10 A telescopic crane demonstrating luffing


Special purpose cranes

To this stage most cranes had developed along fairly similar lines but in the

1960s two new developments appeared. First was the development of

special purpose cranes.

One of the first purpose built cranes was designed to lift the inter-continental ballistic missiles of the USA defence force. Purpose built cranes are not as

common as multi-purpose machines because the more jobs a crane can do, the

more valuable it is to its owner/operator.

Figure 1.11 A special purpose crane designed to lift missiles




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What are the advantages of using a special purpose built crane for a

lifting operation?

___________________________________________________________

___________________________________________________________

___________________________________________________________

Did you answer?

It will do the job more quickly, more efficiently, more safely. These factorsmay combine to make its use less expensive also.

Two common examples of purpose built cranes are shown in figure 1.12 and

figure 1.13. Mobile container cranes are found at ports around Australia and

are capable of lifting 35 tonnes.

Figure 1.12 A special purpose crane designed to lift shipping containers


A crane designed to lift pallets of bricks from the back of a truck is another

example of a purpose built crane.



12 Lifting devices

Figure 1.13 A special purpose crane designed to lift pallets of bricks


Telescopic extension cranes

The second major innovation in crane design from the 1960s was the

telescopic extension crane. Telescopic cranes have the advantage of being

able to work in confined spaces with the boom extending only as far as

needed. An early example from 1966 is seen in figure 1.14.

Telescopic cranes rely largely on the advantages of hydraulics for their

effectiveness. As you would already know from earlier modules, hydraulic

systems can smoothly transfer forces from one part of a machine to another and can be designed to act as force magnifiers. They also have high

efficiency ratings because there are few moving parts and friction is reduced

by using oil-based fluids. Modern telescopic cranes can reach to heights of

about 60 metres or further if a trussed jib is attached to the final boom

extension.

Figure 1.14 An early telescopic crane from 1966


Turn to the exercise section and complete exercise 1.1



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Tower cranes

A recent innovation is the self-erecting tower crane, as shown in figure

1.15. Tower cranes have very high towers or masts reaching unsupported

heights of 80 metres. Greater heights can be achieved if the mast is tied tothe frame of the building at regular intervals.

Figure 1.15 A tower crane tied to the building

© Tom Brown

Pretend you’re a self-erecting tower crane. Sit down on a chair. Place

your hands by your side onto the seat of the chair. Lift yourself up off

the seat and have someone place a book on the seat of the chair. When

you drop back down onto the chair you will be one book thickness

higher than you were before.

Tower cranes operate in a similar fashion. A climbing frame just below the

cabin uses large hydraulic rams to lift the cabin and jib one mast section

higher. The new mast section is lifted by the crane itself into the position

opened up by the climbing frame. Once the new section is bolted to the

lower portion of the mast the whole operation can continue upwards. When

the crane is no longer required it simply reverses the procedure to dismantle

itself.

Figure 1.16 shows the horizontal boom of a tower crane. On the left is the

hook and sling controlled by the trolley that moves back and forth along the

boom. On the right-hand side of the boom are heavy concrete blocks that

act as counterweights to the load. On the mast below the boom is the

operators cabin. Below the cabin is the climbing frame.



14 Lifting devices

Figure 1.16 A self-supporting tower crane

Tower cranes do not have a high capacity with 20 tonnes being about the

maximum lift rating. Their main function is to move building materials

around the construction site especially to the upper floors of tall buildings.

Some tower cranes have horizontal jibs, which may reach 75 metres or more.This enables then to reach from one side of a building site to the other even

though the crane base remains stationary. When working at the extreme end

of the jib the lifting capacity is reduced by at least half due to the greater

turning effect placed on the crane by the load.

The use of modern radio telecommunication systems is vital to the operation

of a tower crane since in many cases the crane operator is not in direct visual

contact with the loading or unloading area. Their height and reach may even

allow them to lift materials over the top of a building under construction and

down the other side. This would not have been possible in the days prior to

two-way radio when a system of hand signals and whistles was used to passon messages to the crane operator. You may even have seen old photos or

film footage of workers, nicknamed ‘monkeys’, riding up with the load so

they could communicate more clearly with the crane operator. This unsafe

practice is no longer considered acceptable under current Occupational

Health and Safety regulations.

Most tower cranes use high capacity electric motors for their lifting power

source. As the cranes are fixed in position until they are dismantled they

can be wired into the electricity grid of the building. A typical tower crane

with a lift capacity of 20 tonnes would be powered by a 415 volt, 190

kilowatt motor.



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High capacity cranes

It has been pointed out that a mobile crane is generally more versatile than a

fixed or stationary crane but there are times when there is no substitute for

outright strength. Due to the high stresses involved, high capacity cranes areextremely large in size, fixed in position and require large counterweights to

balance the load.

The use of high capacity cranes is limited because of their high cost and lack

of mobility. The hammerhead crane in figure 1.17 was capable of lifting 250

tonnes – that’s about 160 family-size cars in one go. This crane was used at

the Garden Island naval dockyards in Sydney to lift major machinery

components, missile launchers, ship superstructures and even complete

ships out of the water. Due to its age it requires expensive maintenance

work and has not been used since the early 1990s.

Figure 1.17 The Hammerhead crane at Sydney’s Garden Island dockyards


Lifting materials twenty storeys to the top of a building with a tower crane

is a different problem from lifting people twenty storeys to the top of a

building. You will now look briefly at a number of other common lifting

devices.

Turn to the exercise section and complete exercise 1.2



16 Lifting devices

Car jacks and hoists

In Personal and public transport you discovered how important the

motorcar is to everyday living for many people. The engine lift, trolley jack,

car hoist, block and tackle and the simple car jack are all lifting devices thatare associated with the motorcar. There are scissor type-jacks, screw thread

jacks, ratchet type jacks and multi-lift hydraulic jacks. A jack for off road

vehicles has been developed to allow the vehicle to be lifted out of bogs, or

lifted over uneven territory which uses a PVC coated cushion that is inflated

by connecting a tube to the exhaust pipe. Modern racing cars have a jack

built into the frame that is activated by compressed air in the pits to achieve

speed in the lifting operation.

The simple car jack is designed to raise one corner of a car when changing a

wheel. All cars come with their own jack and extreme care must be taken if

using a jack borrowed from another vehicle, as the head of the jack will need

to mate with the designated jacking point under the car.

Always use a jack on firm, level ground and never work under a car

supported only on a car jack.

Since they rely on human effort for the power source car jacks are designed

to have a very high mechanical advantage provided by the screw thread.

Mechanical jacks such as these deliberately have low efficiency ratings so

that the weight of the vehicle won’t force the jack to unwind once the effort

has stopped.

Figure 1.18 A typical car jack from a small modern car



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Figure 1.18 shows a common car jack from a small car rated to lift 850

kilograms. Due to its design, this jack has a variable mechanical advantage.

When first raising the jack, the mechanical advantage is low meaning the jack

will gain height quickly. By the time it is at the height where the load would

normally be applied the mechanical advantage has increased, reducing therate at which the jack gains height but also reducing the effort required to lift

the car.

Look at a car jack and see it differs to the one in figure 1.18.

How could you work out its velocity ratio, mechanical advantage and

efficiency?

A trolley jack is a hydraulically operated jack of high capacity capable of lifting one end of a vehicle off the ground. It is used by mechanics to make

quick inspections under a vehicle. Again never work under a vehicle

supported only by a trolley jack.

The engine lift is a mobile block and tackle system that can be wheeled over

to the vehicle to enable the motor to be lifted and removed from the engine

bay. Most auto workshops will also have a fixed block and tackle mounted

to a strong roofing beam for the same purpose.

To work under a vehicle safely the car hoist is used. The hoist in figure 1.19

is an electrically operated hydraulic system capable of lifting 2 500 kg.



18 Lifting devices

Figure 1.19 Car hoists enable mechanics to work safely under vehicles

Turn to the exercise section and complete exercise 1.3.

Lifting people

When lifting machinery, vehicles or building materials a certain degree of

disregard for the cargo is acceptable but when lifting live cargo, such as

people, the rules change dramatically. Much greater emphasis must be

placed on the needs of the cargo particularly the need for a quick, safe and

comfortable journey.

There are four general types of people lifts:

• elevators

• escalators

• moving ramps and walkways• specialised working platforms.



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Elevators

Elevators, more commonly known in Australia as lifts, are small rooms,

called cars, which travel up and down an elevator shaft. Elevators are

designed to move people and materials from floor to floor in multi-storey buildings. Buildings over three storeys are required to have at least one

elevator. Large buildings will have banks of elevators with some being

dedicated to special tasks. In hospitals for example, some elevators are

dedicated to moving patients between the hospital wards and the operating

theatres while others are reserved for the cleaning staff for waste disposal

and linen transfer.

Why would a hospital have a system of dedicated elevators for specific

tasks? Can you think of any other specialised or dedicated elevators you

may have seen or heard about in other types of buildings?

When designing an elevator system a number of factors need to be taken into

account such as the:

• type of building

• number of floors to be serviced

• floor to floor distance

• number of people using each floor

• maximum peak demand

• load to be moved.

There are two general types of elevator systems:

• electric

• hydraulic.

Electric lifts are the most common type and can be adapted to be used in all

situations. The motors for an electric lift are usually:

• two speed AC motors for car speeds up to 1.0 m/s

• variable speed AC or DC geared motors for speeds up to 2.5 m/s

• direct drive DC or variable speed AC gearless motors for speeds greater

than 2.5 m/s.

Despite common fears of being trapped in an elevator or of the elevator

cables snapping, statistically it is safer to use a lift than to take the stairs.

Elevators have more than one cable to provide greater safety and all have

emergency brakes to slow the car if the cables suddenly snapped. The first

elevators to have an emergency brake were designed by Elisha Otis way

back in 1853. The early elevators designed by Otis were built to carryfreight but in 1856 he developed a ‘vertical railway’ passenger lift.



20 Lifting devices

Around the early 1890s multi-strand steel cables replaced hemp rope for the

elevator cables improving their safety and efficiency. Early elevators used a

top mounted electric motor turning a winding drum with the elevator cable

simply wound around the drum. As the height of the buildings increased, so

did the length of the cable required. This lead to problems with the cable notwinding neatly onto the drum.

Have you had the same problem with your garden hose?

The solution that was developed, and which is still used today, was to have

the electric motor winding a number of high tensile cables to raise and lower

the elevator. One end of each cable is attached to the top of the elevator car

and is then wrapped around the drive shaft – a grooved pulley. The other

ends are attached to a counterweight that slides up and down the shaft on its

own rails. The counterweight, equal to the weight of the car with a half load

of passengers, reduces the effort required from the motor and provides

enough friction at the drive shaft for the cables not to slip. Sailors use a

similar principle on the winch systems on sailing ships.

Winding drum

Elevator car

Elevator shaft

Counterweight

Electric motor

Figure 1.20 Components of a typical electric elevator

Hydraulic elevators are used extensively in low-rise buildings up to five

storeys and where elevator speeds do not exceed 0.75 m/s. The elevator is

pushed up the elevator shaft by a hydraulically controlled piston. To save

space a telescopic piston may be used. Hydraulic elevators do not require

any overhead mounted lifting gear. The pumping unit can be located up to

15 metres away from the shaft and the overall installation and running costs

are less than for an electric drive system.



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Elevator car

Elevator shaft

Hydraulically operatedtelescopic lifting ram

Figure 1.21 Components of a hydraulic elevator


Escalators

For over 60 years the term ‘escalator’ was an Otis Elevator Company

trademark. However, now it has become the standard term for any

continuous moving stairway. Escalators are particularly useful in moving a

large number of people travelling in the same direction. Their main

disadvantage is that they generally only operate to a height equal to one or

two storeys. This can be overcome by placing escalators in ‘series’ so that

the passengers move from one escalator to another. This also provides get

on / get off points for the passengers. A typical application for escalators is

in large multi-storey shopping centres where elevators could not cope with

the large volumes of people moving throughout the centre.


Moving walkways and ramps

While escalators are limited to an incline of 30° from the horizontal, moving

ramps are restricted to a maximum incline of only 12° meaning they have to

be a lot longer to reach the same vertical height. Their main advantage over

escalators is that prams and shopping trolleys can safely be taken on the

ramps. This is a major issue for customers in shopping centres.



22 Lifting devices

Specialised working platforms

When carrying out work high above the ground workers face two major

problems:

• getting up to the operating height quickly and with minimum effort

• being able to move freely and work safely while high off the ground.

Devices such as cherry pickers and scissor lifts provide much greater safety

than using older technology such as working from a ladder. Ladder work is

considered so dangerous that there are now strict guidelines relating to their

use in the workplace. A cherry picker can also be considered as another

example of a specialised crane.

An example of a specialised working platform is shown in figure 1.22



24 Lifting devices

Dry dock

Up until now you have been looking at the lifting of small to medium sized

objects but how could you lift a large ocean-going ship out of the water to

carry out repairs. One solution is to use a floating dock such as the one at Newcastle, shown in figure 1.23. The floating dock is a long ‘U’ shaped

channel structure, which is partially sunk by flooding the ballast tanks in its

hold. The ship to be repaired is sailed into position inside the dock and

propped against the sides to stop it from falling over. The floating dock is

then raised by pumping out the tanks and filling them with air. The ship is

lifted out of the water at the same time as the dock is raised. The floating

dock in Newcastle can handle ships weighing up to 45 000 tonne.

Figure 1.23 The floating dock at Newcastle

Helicopters

Using helicopters as a lifting device is an example of a new application being

found for an existing machine. Basically thought of as a form of air transport, helicopters play a small but increasing role in the lifting and

transferring of cargo.

Helicopters have a significant advantage over other forms of lifting device.

They are fast, highly mobile and most importantly can access areas

inaccessible by other forms of transport. Some heavy lift models such as

the Russian MI-26 have a lifting capacity of up to 20 tonnes.



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Some of the varying lifting applications helicopters have been used for

include :

• winching bushwalkers hurt or trapped in rugged bushland

• rescuing sailors at sea• water bombing bush fires

• lifting and transporting cargo to remote locations

• moving large animals, such as an elephant or rhinoceros out of

inaccessible terrain for the purpose of relocation.

CH53 Sea Stallion heavy lift helicopters are used by the armed forces of the

United States to lug 6 000 litre fuel bladders and 10 tonne equipment

containers to troops in remote combat areas. Australia’s CH47 Chinook

medium lift helicopters are capable of cruising at a speed of over 200kilometres per hour with a 5 tonne slung payload.

Helicopters have been used by the construction industry but usually only

for special one-off jobs where it would not be economical or possible to

erect a crane to do the job. Such jobs include placing air conditioner cooling

towers onto high-rise buildings or placing telecommunication equipment

onto high structures or inaccessible mountains.

One problem that limits their use in the construction industry is the

turbulence below the blades. The downdraft produced by a hovering

helicopter exceeds 160 kilometres per hour. This poses special safety

problems for those working below the helicopter.



26 Lifting devices

Impact of lifting devices on constructionmethods

In this section of the module it is important to consider a number of issues.

• Has a change in lifting device impacted on the type of buildings being

constructed?

• Has the building style remained the same but the method of

construction changed due to the use of new lifting devices?

• How have lifting devices improved safety and productivity in the

construction industry?

In 1871 a huge fire devastated much of the central business district of the

large American city of Chicago. The building boom that followed resulted inthe price of land skyrocketing. The best way to make use of the valuable

land was to build as tall a building as possible.

At this same time a new innovative building system was being trialled

utilising the increased strength of a new material – steel. The new system

relied on the weight of the building being supported by a steel skeleton

instead of the outer masonry walls. These early ‘skyscrapers’ quickly

exceeded the height of the buildings they replaced. One New York building

constructed at the time using the old technique of load bearing walls required

walls three metres thick at the base to support the fourteen-storey structure.

There were two problems that needed to be overcome before architects

could take full advantage of the steel frame building system.

• How to get the materials to the upper floors of the building under

construction.

• How to move people through the building once it had been constructed.

The role of cranes in multi-storey construction

There has always been a need for lifting devices on construction sites. The

challenge for engineers now is how to cope with the increased heights of

modern buildings while at the same time maintaining safe working

procedures and reducing construction times.

On modern multi-storey buildings that use a steel frame, curtain wall

construction method, the steel frame is constructed as soon as the

foundation work is complete. Tall tower cranes and derrick cranes are used

to lift the steel beams and hold them in place until secured. Derrick cranes

are small, fixed, basic cranes similar to the simple Egyptian hoist with safe

working loads of approximately 5 tonnes. They may be assembled on thetop floor of a building under construction. The derrick crane can jack itself



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up to the next level as the building grows in height in a manner similar to that

used by tower cranes. Tower cranes working at extreme heights are ‘tied’ to

the frame of the building to stop the mast from buckling by increasing the

rigidity of the mast.

The walls of steel-framed buildings take very little of the load with their

main function being to close in and protect the building. This is one reason

why modern buildings can have such large expanses of glass windows – the

outer skin is not required to take any weight. It also means that the walls

and windows can be fitted out anytime during the construction process.

The walls of the lower levels don’t need to be in place before work can begin

on the upper levels. Lightweight, pre-fabricated panels are lifted into

position by crane to be bolted or clipped to the supporting frame.

Sections of the walls are deliberately left unfilled to allow the loading and

unloading of materials to the various levels of the building under construction. Loading decks fitted into the vacant spots have been designed

to improve productivity and safety by providing secure platforms for the

cranes to load to, while also providing overhead protection to those working

below. The decks can be retracted when not required so that they don’t

obstruct the rope and load of cranes working in the area.

Figure 1.24 Loading from a crane to a retractable deck

© Preston Australia P/L

When construction has finished, tower cranes can simply disassemble their

mast one section at a time to lower themselves back to street level.

A second method is to use a derrick crane on top of the building to lower the

tower crane. The derrick crane is then completely dismantled and may belowered by a temporary block and tackle system.



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Safety considerations

Lifting devices contribute to improved safety in a number of ways. On a

simplistic level, by reducing the human effort required, they greatly reduce

the chance of back injury, one of the biggest forms of injury amongst

construction workers.

Lifting devices such as cherry pickers and platform hoists provide a more

secure working environment for people working high off the ground.

Figure 1.25 A worker using a cherry picker to inspect street lighting

Also, the curtain wall system of modern multi-storey buildings allows

sections of the wall to remain unfilled during construction to allow access to

the building for delivery of materials and for personnel elevators. These

temporary elevators are a quicker and safer way of moving workers, light

materials and equipment up and down the building during construction.

They free up the cranes for tasks requiring greater lifting capacity.

Properly designed guards and barriers reduce the chance of building materials

falling or being dropped to the ground when using temporary elevatorsimproving the safety for those working below on the construction site. As



30 Lifting devices

with tower cranes the temporary elevators are tied to the framework of the

building to provide greater rigidity. The blank portions of wall are filled in

once the elevator is dismantled.

The lower levels of multi-storey buildings are now usually surrounded byscaffolding and a shade cloth type material to improve the conditions inside

the building under construction by

• stopping swirling wind from stirring up dust

• reducing the chance of tools, equipment and materials being dropped to

lower levels

• providing a visual barrier to stop workers from walking off the upper

levels of the building.

The design and construction of this scaffolding needs to be co-ordinated

with the operating requirements of the cranes, their loading decks and the

temporary elevators that will be working on the site.


Storage of building materials

An ever-increasing range of building materials are being bundled together to

enable them to be stored on pallets or specialised racks. By using forklifts

and platform lifts, hardware and building supply companies can stack their

materials as high as 10 metres off the ground yet still be able to retrieve them

quickly when required. For hardware stores and their customers this has led

to a number of improvements such as:

• a greater range of items can be stored

• materials can be retrieved more quickly – less waiting time

• a warehouse space can hold a greater amount of stored material.

Forklifts and walk-behind pallet lifts are designed to work in narrowwarehouse aisles. One innovation allows a machine to pivot on its own

footprint using a system whereby the driving wheels are controlled

independently to the point where they turn in opposite directions when

maximum manoeuvrability is required.



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Direction of motion

Wheel direction

Figure 1.26 Varying the direction of travel of the driving wheels of a forklift

To reduce the levels of harmful exhaust gases and noise most indoor-based

forklift models operate using battery powered electric motors. Outdoor

forklifts are likely to use Liquid Petroleum Gas (LPG) or small traditional

petrol engines.

Figure 1.27 A modern petrol powered forklift



32 Lifting devices

Safety features common on most modern forklifts include:

• very low centre of gravity to increase stability

• guards to protect the operator from falling objects

• reduced noise levels from the motor

• ergonomically designed controls and seats to reduce operator fatigue

• sprung floors on operator stand-up models

• warning buzzer when reversing.

Lifting devices found on domestic constructionsites

On a domestic building site a number of lifting devices are commonly used.

Forklifts are used to unload palletised materials from the delivery trucks to a

convenient location on site.

Bobcats and front-end loaders are used to lift and carry loose materials such

as sand, soil and gravel.

Pallet cranes are specialised truck mounted cranes used to unload palletised

materials off the truck.

Conveyor belts are used in situations such as to carry tiles to the roof. With

one person loading and two others unloading on the roof the complete roof

of a typical house can be stacked in about two hours. The same job without

the conveyor belts would take the same workers about eight hours. It would

also be significantly more dangerous and demanding, as the workers would

have to carry the tiles up ladders or ramps to the roof.



34 Lifting devices



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Exercises

Exercise 1.1

Explain how each of the following developments in crane design from the

1960s has had a positive impact on lifting efficiency and/or safety.a Specialised cranes

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

b Telescopic extension cranes

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________



36 Lifting devices

Exercise 1.2

Over the past 100 years the relative size and weight of cranes has decreased

compared to their lifting capacity. List four reasons for this decrease in

relative size.a _______________________________________________________

b _______________________________________________________

c _______________________________________________________

d _______________________________________________________

Exercise 1.3

Compare two different lifting devices by completing the table below.

Lifting device No.1 Lifting device No. 2

Type of lifting device(Name of device)

Purpose(What does the devicehave to lift)

Lifting capacity(What is the maximumload it can lift)

Power source(Human power,electric, petrol, orsomething else – specify)

Safety features

(Load limiting sensors,guards, Governmentregulation)

Who would use it(Builder, car mechanic,etc)

Simple machinesystems used(screw thread, pulleys,levers, hydraulics)



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Exercise 1.4

The elevator system for a public building such as a hospital would be

different to the elevator system in a similar sized commercial building.

Identify and describe two main features in the elevator systems in the two

buildings.

a Hospital

i ___________________________________________________

___________________________________________________

ii ___________________________________________________

___________________________________________________

b Commercial building

i ___________________________________________________

___________________________________________________

ii ___________________________________________________

___________________________________________________

Exercise 1.5

a Explain why escalators are more efficient than elevators in moving

people from floor to floor in large shopping centres.

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

b Explain why escalators aren’t used more widely in other types of

buildings by highlighting two of the main restrictions of escalators.

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________



38 Lifting devices

Exercise 1.6

‘Tall multi-storey buildings could not exist without the elevator.’

Explain this statement making reference to the ways that elevators have

made multi-storey buildings more accessible.

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

Exercise 1.7

Describe three ways in which modern lifting devices have improved safety

on construction sites.

1 _________________________________________________________

2 _________________________________________________________

3 _________________________________________________________

Exercise 1.8

List five criteria you would use when deciding on the appropriateness of a

lifting device for a particular task.

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________



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Exercise 1.9

Describe the impact lifting devices have had on construction time and

building height on modern building sites. Give examples to support your

answer.a Construction time

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

b Building height

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

Exercise 1.10

Select the alternative a, b, c, or d that best completes the statement. Circle

the letter.

1 Lifting devices usually have:

a a velocity ratio greater than one and a mechanical advantage less

than one

b a velocity ratio less than one and a mechanical advantage greater

than one

c a velocity ratio and mechanical advantage both greater than one

d a velocity ratio and mechanical advantage both less than one.

2 People use lifting devices because:

a the human body is not very strong or tall

b it saves time and money

c they might hurt their back if they don’t use one

d all of the above



40 Lifting devices

3 The only power source not still commonly used in lifting devices today is:

a human power

b electric power

c petrol power

d steam power.

4 In the period after the Roman era the development of lifting devices did

not progress greatly because:

a the power source did not change

b the materials technology did not improve

c there was no need for an improved lifting device until multi-storey

buildings were designed

d slaves were available to do all the lifting.

5 A specific advantage of telescopic cranes is that:

a they can lift large loads

b they can work in restricted spaces

c they can reach high off the ground

d they are very mobile.

6 Car jacks have low efficiencies because:

a it stops them from winding down under load

b it stops them from costing too much

c they are only small

d they are human powered.

7 The maximum acceleration rate of an elevator is limited by:

a the strength of the elevator cables

b the power of the driving motor

c the effect on the human body

d the stopping power of the elevator braking system.

8 Tower cranes do not have a high lifting capacity because:

a the mast is too thin to support a large load

b electric motors can’t lift large loads

c the counter-weights required to balance the load would be too large

d there is not the demand to lift high capacity loads on a building site.



42 Lifting devices



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Progress check

During this part you examined the development of the crane as a lifting

device and were introduced to other common lifting devices such as

corkscrews, elevators and forklifts.

Take a few moments to reflect on your learning then tick the box which best represents your level of achievement.

❏✓ Agree – well done

❏✓ Disagree – revise your work

❏✓ Uncertain – contact your teacher A g r e e

D i s a g r e e

U n c e r t a i n

I have learnt about:

• the historical development of lifting devices

• engineering innovation in lifting devices and theireffect on people’s lives.

I have learnt to:

• research the history of technological change in liftingdevices

• examine the impact of lifting devices on engineeringconstruction methods.



During the next part you will investigate how engineering mechanics and

hydraulics can be used to solve problems relating to some lifting devices.



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Exercise cover sheet

Exercises 1.1 to 1.10 Name: ______________________________

Check!

Have you have completed the following exercises?

❒ Exercise 1.1

❒ Exercise 1.2

❒ Exercise 1.3

❒ Exercise 1.4

❒ Exercise 1.5

❒Exercise 1.6

❒ Exercise 1.7

❒ Exercise 1.8

❒ Exercise 1.9

❒ Exercise 1.10

Locate and complete any outstanding exercises then attach your responses

to this sheet.

If you study Stage 6 Engineering Studies through a Distance Education

Centre/School (DEC) you will need to return the exercise sheet and your

responses as you complete each part of the module.

If you study Stage 6 Engineering Studies through the OTEN Open Learning

Program (OLP) refer to the Learner’s Guide to determine which exercises

you need to return to your teacher along with the Mark Record Slip.



Part 2: Lifting devices – mechanics/hydraulics 5

Conditions of equilibrium

You will recall that there are three equations of equilibrium that need to

be satisfied.

These equations are also applicable to non-concurrent systems.

SH = 0

SV = 0

SM = 0

For a graphical solution, the force polygon must close.

Resultant of non-concurrent forcesType 1 – Two support reactions

20 N

RA RB

80 N3 m 3 m 4 m

Figure 2.3 Two support reactions

A beam is loaded with two vertical forces. Determine the reactions (R Aand R B)

Solution:

MRA

= 0Â This line states that moment calculations are going to be

performed around the point on the left hand end of the

beam and that the sum of all the moments will equal zero.

Note: In this example, both of the applied forces are vertical, so both

reactions must be vertical. The sum of the forces up must equal the sumof the forces down. It is standard procedure to begin moment

calculations about the pin joint.



6 Lifting devices

MR A= F d F d F d1 1 2 2 3 3¥( ) + ¥( ) + ¥( )

= – – 20 3 80 6 10¥( ) + ¥( ) + + ¥( )RB

R B =( )

+ +60 480

10

= 54 N ≠

MRB= F d F d F d1 ¥( ) + ¥( ) + ¥( )1 2 2 3 3

= 80 4 20 7 10– ¥( ) + ¥( ) + ¥( )RA

RB =( )320 140

10

+

= 46 N

≠ Note: the two reactions add to 100 N≠. This confirms the result, as there

is 100 NØ due to the applied forces.

Often the moment calculation is not completed about each end of the

beam. Instead, once moment calculations have determined the roller

support reaction, a simple 'sum of forces' calculation can be made.

Example:

≠+ SFv = 0

= F F F F1 2 3 4 + + +

= – – 20 80+ + +R RA B

= – – 20 80 54+ + +RA

RA = 46 N ≠

The advantage of this technique is its speed. The disadvantage is that an

error in the moment calculation of the roller support reaction will lead to

an error in the calculation of the other reaction. Therefore, it is often

advisable to do both moment calculations, and then calculate the 'sum of forces' as a check.

Worked example 2

The truss lifting frame shown in figure 2.4 is acted on by three forces.

The 8 kN force acts vertically down and the other two forces act at right

angles to the top chord members. The height of the truss is 2 metres.

Determine the reactions at the two supports at X and Y.



8 Lifting devices

To find XD, consider triangle XBD

tan30∞ =BD

XD

\ XD = BDtan 30∞

=2

tan 30∞

= 3.46 m

XD = DY \ xy = 2 3 46.¥

= 6.92 m

To find AE, XE =

XD

2

= 1.73 m

and tan 30∞ =AE

XE

\ AE = XE tan¥ ∞30

= 1 73 0 577. .¥

= 1.0 m

Now, to solve for the three unknown, RXH , RXV and Ry, apply the three

equations of equilibrium.

Take moments about the pin joint first. That is, apply the equation

Â iMX = 0.

For equilibrium, + SiMX 0

(RY x 6.92) – (5sin60∞ x 1.73) – (8 x 3.46) – (2sin60∞ x 5.19) – (5cos60∞ x 1) + (2cos60∞ x 1) 0

6.92 RY – 7.49 – 27.68 – 8.99 – 2.5 +1 0

6.92 RY 45.66

RY 6.6 kN ≠

+≠ SV 0

RXV + 6.6 – 5sin60∞ - 8 – 2sin60∞ 0

RXV 7.46 kN ≠



22 Lifting devices

Since water is a very commonly used liquid, you should memorise these

facts:

• 1 cubic metre of water has a mass of 1 tonne

• 1 litre of water has a mass of 1 kilogram.

Relative density (RD)

Relative density is the ratio of the density of a substance to the density of

water.

RD (substance) =r

rsubstance

water

( )

( )

Because relative density is a ratio, it has no units.

Worked example 5

The relative density of mercury is 13.6. Calculate its density.

RD (mercury) =r

rsubstance

water

( )

( )

13.6 =r

1000

r = 13 6 103 3. ¥ k g / m

Specific volume ( nn n n)

The word ‘specific’ usually means per unit mass.

The specific volume then is volume per unit mass.

v =V

m

13.6 =1

R

(the inverse of density)

Units for specific volume are m kg3 .

Specific volume is mainly used for gases.

Specific gravity

The specific gravity of a substance is the ratio of the density of the

substance to the density of water R water kg m/ .= ¥( )1 103 3




Pressure (p)

The pressure on an object is the force (F) acting perpendicular to a given

surface area (A).

R =F

A

The unit for pressure is the newton per square metre (N/m2) or pascal

(Pa). The pascal was named in honour of Pascal who formulated much of

fluid mechanics.

1 pascal (Pa) = 1 N/m2

One pascal is a relatively small amount of pressure, roughly equivalent to

the pressure exerted by a five dollar note on a level surface.

It is more usual to express pressure in either kilopascal (kPa) or

megapascal (MPa).

1 MPa = 1 N/mm2

1 MPa is about the weight of an orange (1N) resting on the end of a

vertical matchstick (1mm x 1mm).

Pressure is a scalar quantity, acting with equal magnitude in all

directions.

Gases exert pressure on all sides of the container in which the are

enclosed. A liquid exerts pressure on a container where it touches the

sides and the bottom. Inside a gas or a liquid pressure is exerted in all

direction due to the movement of the molecules.

Solids exert pressure due to their weight pushing down on the surface on

which they sit. But inside the solid, the molecules have no translational

movement, so they cannot exert pressure in other directions.

Atmospheric pressure (patm)

Atmospheric pressure is the pressure associated with the atmosphere due

to the weight of air.

This pressure will vary according to the location and weather conditions.

The average value or ‘normal’ or ‘standard’ atmospheric pressure at sea

level is 101.3 kPa, that is, at the earth's surface the pressure felt by an

object due to the weight of the atmosphere above it is 1 013 105. ¥ Pa or

101.3 kPa. This is also called a pressure of 1 atmosphere.

At higher elevations atmospheric pressure is less.



30 Lifting devices

Pressure, p =F

A

=900

491

= 1.83 Mpa

c Determine the load the jack can lift on the 90 mm diameter

piston when the effort is 90 N.

Area of plunger, A =p d

4

2

=p 90

4

2( )

= 6362 2mm

Pressure, p =

F

A

Load, F = p ¥ A

= 1.83 x 6362

= 11642.5 N

= 11.6 kN

d Determine the mechanical advantage of the hydraulic jack.

Mechanical advantage, MA =Load

Effort

=11642 5

90

.

= 129

Note: this MA is achieved through the MA of the lever and the MA of

the hydraulic system.





Stress and pressure

Stress and pressure are both defined as force per unit area and have the

same units. However, they are two entirely different things and must be

understood separately. Stress is only used with solids, whereas pressuremust only be used with fluids and gases.

Many solid pieces of machines and structures interface with fluids under

pressure.

The difference between stress and pressure is explained by Pascal’s

principle.

Principle 3 (Pascal’s principle)

A pressure applied to an enclosed fluid at rest is transmitted without loss

in all directions throughout the system.

Pascal’s principle applies to fluids, but not to solids. A fluid has the

ability to transfer pressure to all parts of a container equally in all

directions.

It applies for static conditions and neglects the weight of the fluid. If the

fluid is moving, or if the weight of the fluid is not negligible, then

Pascal’s principle must be modified using other principles involving

hydraulics, pneumatics or fluid mechanics.

An important consequence of Pascal’s principle is that a force can be

magnified or reduced by means of fluid pressure. This is the main reason

why pneumatic and hydraulic systems are so widely used.

A relatively small force applied to a piston with a small diameter can

generate a large pressure. As the ram is of much larger diameter, the

same fluid pressure acting over a larger area will magnify the force at the

piston to a much larger force at the ram.

Consider a system of enclosed fluids as shown.



32 Lifting devices

Pressure p

Piston force

Piston

Pressure p

Pressure gauge

Fluid

Gas

Ram forceRam

A

BC

Figure 2.27 Pressure transmission in a fluid

If the piston is held in position, each of the pressure gauges will register a

pressure. These pressures are not necessarily the same.

Pascal’s principle applies to both liquids and gases. In hydraulics, gas in

the system is a nuisance because much of the applied pressure results in

the compression of the gas rather than movement of the ram. To work

properly, the system must be bled to remove any gas before use.

Worked example 8

Consider the system of enclosed fluids in figure 2.27. The piston has adiameter of 12 mm and the ram has a diameter of 75 mm. The pressure

gauge at A registers 70 kPa, and B and C indicate 65 kPa and 60 kPa,

respectively.

A force is applied to the piston after which gauge A reads as 90 kPa.

a Determine the reading on the other two pressure gauges B and C.

Applied pressure will be 90 – 70 = 20 kPa.

By Pascal’s principle, each gauge will register 20 kPa higher.

Gauge B will now read 65 + 20 = 85 kPa and gauge C will read 80kPa.

b Identify the ratio of the force at the ram to the force at the piston.

Remember that the pressure remains constant throughout the system.

Pressure, p, will equal.

Pressure =F

A

\Fpiston = p Apiston ¥

and Fram = p A ram¥




\ Ratio is A:A (as p is constant)

\ :p p d d2 2

4 4

d dRam piston2 2:

75 122 2:

\ :39 1

Worked example 9

What piston rod diameter and bore diameter of a hydraulic cylinder

mechanism must be used for the lifting mechanism of a fork-lift truck if

it must produce at least 35 kN of force on contraction?

The hydraulic pressure is to be 7 MPa. The allowable stress of the piston

rod is 140 MPa. Neglect seal and piston friction.

P

F

Figure 2.28 Hydraulic cylinder mechanism of fork-lift truck

To contract the cylinder mechanism, the pressure p must be applied to

the chamber.

The diameter of the piston rod can be calculated using the stress formula.

s = FA

\ A =3500

140

=p d2

4

\ d2 =3500 4

140

¥p

d = 17.84 mm




1 Perform an activity to measure the weight of an object in air and the

weight of the same object in a liquid. Measure the weight of the

fluid displaced by the submerged object, and analyze the

measurements obtained.

2 Determine the weight of a small metal object. Place the object into

an overflow can. Collect the water displaced from the can and

calculate the volume and weight of the displaced water.

Record the weight of the object when submerged in water, by

attaching it to a spring balance. Determine the weight of the liquid

displaced and compare it to the apparent weight of the submerged

object due to the buoyant force. The weight loss of the submerged

object should be equal to the weight of water displaced.

3 Repeat for an object which floats. Carefully examine how the

apparent loss in weight of a floating object compares to the weight of the liquid it displaces.

Report on your findings.

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________ __________________________________________________________

__________________________________________________________

__________________________________________________________

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38 Lifting devices

4 Place uninflated balloons 30 cm apart around the perimeter of a

rectangular table. Invert a second table face down on the one below,

so that the open ends of the balloons are all protruding out from

between the tables. Invite someone to sit in the middle of the

inverted table. Get as many volunteers as there are balloons. Ask each volunteer to blow into a balloon, to see if they can lift the

inverted table with the person sitting on it.

Turn to the exercise section and complete exercise 2.6 and 2.7.



42 Lifting devices

Exercise 2.3

A mobile crane with the necessary dimensions for a force analysis is

shown in the diagram. The point C represents the centre of mass of the

mobile crane, mass 2.5 tonnes.

Mass6 tonnes

45∞

1500 3000 4000

C

3 5 0 0

7 5 0 0

Hydrauliccylinder

90∞

A B

Figure 2.34 Mobile crane

a For the loading arrangement shown, determine the force on the

hydraulic cylinder.



46 Lifting devices

Exercise 2.4

A hydraulic jack is shown in the sketch below.

50450LoadEffort

PistonØ 90

PlungerØ 25

Fluid

Figure 2.35 Hydraulic jack

A load of 1.3 tonnes is to be lifted with the jack.

Determine the effort that must be exerted at the end of the handle to lift

the load.




10 Atmospheric pressure is

a always equal to 101.3 kPa

b always equal to 760 mm of mercury

c called a vacuum when it is low

d associated with the atmosphere due to the weight of air.



52 Lifting devices





Exercises 2.1 to 2.7 Name: _______________________________

Check!Have you have completed the following exercises?

❐ Exercise 2.1

❐ Exercise 2.2

❐ Exercise 2.3

❐ Exercise 2.4

❐ Exercise 2.5

❐ Exercise 2.6

❐ Exercise 2.7

Locate and complete any outstanding exercises then attach your

responses to this sheet.


Centre School (DEC) you will need to return the exercise sheet and your


If you study Stage 6 Engineering Studies through the OTEN Open

Learning Program (OLP) refer to the Learner’s Guide to determine whichexercises you need to return to your teacher along with the Mark Record

Slip.



Lifting devices

Part 3: Lifting devices –materials



Part 3: Lifting devices – materials 1

Part 3 contents

Introduction..........................................................................................2

What will you learn?...................................................................2

Jacks, elevators, cranes....................................................................3

Testing of materials ................................................................... 6

Heat treatment .........................................................................13

Forming processes..................................................................19

Exercises ...........................................................................................33

Progress check .................................................................................43

Exercise cover sheet........................................................................45




Jacks, elevators, cranes

The following diagrams of lifting devices are included to assist in the

identification of the various component parts.

Floor jacks

Most of the materials used in floor jacks are iron-based alloys. Hydraulic

cylinders are cast iron, pistons are chrome plated low carbon steel, bodies

may be cast steel or fabricated in low carbon steel, lifting arms, pivot

pins and tension screws are low carbon steel, wheels are cast iron and

bleed screws are low carbon steel.

Screw jack

Load cap

Lever bar

Ductile-iron housing

Welded stop

Single chrome-molybdenumball reduces operating friction

Four-way headpermits lever barinsertion at four angles

Figure 3.1 Screw jack




From the information available in previous modules, summarise the steps

in performing a tensile test on a standardised specimen.

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

The graph in figure 3.6 shows the result of a tensile test on a low carbon

steel.

L o a d

( k N )

Extension (mm)

Maximum load

Elastic limit

Failure point

Figure 3.6 Load/extension graph for low carbon steel

The shape of a load/extension graph tells a good deal about the

mechanical properties of the material. These properties include:

• toughness this is determined from the total area under the curve

• resilience this is the area under the straight-line section of the

graph



8 Lifting devices

• elasticity the angle of the straight-line section of the graph

indicates elasticity – the steeper the line, the stiffer the

material

• brittleness a material that doesn't show much plastic deformation

is rigid and brittle – the graphs for some ceramic

materials are only a straight line with no curve at all

• ductility any graph that shows a large area of plastic

deformation and possibly a failure point that is below

the ultimate tensile strength (UTS) is said to be

ductile

• strength the amount of force needed to plastically deform the

material is the proof or yield strength while the 'high

point' of the graph is the UTS.

Before the load/extension graphs for a variety of materials can beaccurately compared, the cross-sectional areas and the original length of

each specimen must be taken into account.

Naturally a telegraph pole will withstand a greater load than a steel guitar

string but that doesn't necessarily mean that timber is stronger than steel.

In fact from our previous learning we know that steel is stronger than

timber.

To allow comparison of tensile test results, the load must be divided by

the cross-sectional area to give the stress (s) and the extension must be

divided by the original length to give the strain (e). Once this is done,

graphs can be directly compared or even drawn on the same set of axes.

Note: different units for strain

S t r e s s ( M P a )

Strain

250

200

150

100

150

0 1 2 3 4 5

Grey cast iron

300

S t r e s s ( M P a )

Strain

250

200

150

100

150

0 10 20 30 40 50

Normalised mediumcarbon steel

Normalised lowcarbon steel

300

Figure 3.7 Tensile test results for common irons and steels




Compare the stress/strain curves in figure 3.7 and suggest which material

has the highest:

Toughness __________________________________________________

Resilience __________________________________________________

Strength____________________________________________________

Ductility ___________________________________________________

Stiffness____________________________________________________

Did you answer?

Medium carbon steel appears to be the strongest and most resilient while lowcarbon steel is the most ductile and grey cast iron is the stiffest. One of thesteels is the toughest, though it might be necessary to calculate the areas under the curves, since it is difficult to assess visually.

Compression test

Many parts involved in lifting devices are subjected to compressive

loads. Hydraulic rams in some cranes, elevators and many modern jacks

are all subject to compressive loads. In all lifting devices some part must be under compression to allow lifting to occur. As a tower crane lifts a

load at a building site, the cables will be in tension but the tower itself

will be under an additional compressive force equal in magnitude to the

tensile force in the cables.

In previous modules, both Preliminary and HSC, some detail has been

given of compression testing.

As with tensile testing, standardised specimens can be used to produce

load/reduction graphs that can then be converted to stress/strain graphs.

The specimen is positioned between two hard and rigid platens and acompressive load is gradually applied. With brittle materials, such as

concrete and stone, there is a definite failure point. In ductile materials,

like those used in lifting devices, there is no definite failure point and

specimens often bulge in the middle. This effect is known as barrelling.

To provide an accurate test result, the ends of the specimen must be

parallel and the specimen must have a large enough cross-sectional area

to prevent it from bending or tipping rather than compressing. This

means the specimen is normally larger than the one used for tensile tests

and consequently the testing machine must be larger and capable of

applying a greater load.



10 Lifting devices

Figure 3.8 Barrelling in ductile materials

Hardness tests

The Brinell, Vickers and Rockwell hardness tests were described in

detail in the preliminary module on Braking Systems.

Complete the table below to provide a summary of three common types

of hardness test, refer back at the previous modules or textbooks if you

need to.

Hardnesstest

Indentor Measured Used On

Brinell

the diameter ofthe circularindentation ismeasured using alow-poweredmicroscope

Vickers

industrial

diamond cut toa square-basedpyramid.

Rockwell

used on a fullrange ofmaterials with awide range ofhardness




Safety systems on elevators, surfaces on gears and pulleys in cranes and

faces of hydraulic cylinders all need to be hard in order to resist wear.

The materials used for these components, the forming processes

employed and any heat treatments applied all contribute to the hardness

of the components.

The data collected from hardness testing can be used to initially select the

correct material or heat treatment for an application and also to assess the

effect of the forming process. These tests are also used on the production

line to provide checks on the quality of the raw materials and production

processes.

Notched-bar impact tests

Jacks, cranes and elevators are usually subjected to a variety of loads

including gradually applied and impact loads. To assess the safe

performance of these lifting devices under impact loads each device must

be thoroughly tested. As the behaviour of materials under impact loads

can be vastly different to their behaviour under gradually applied loads, it

is also important that each of the component materials is tested under

impact or dynamic loads.

Standardised impact tests use a standard specimen with a standard notch

cut into it. The results of dynamic testing of this type are interesting.

The dynamically tested impact strength of an unnotched specimen issimilar to the toughness that is assessed from the area under the curve of

a stress/strain diagram.

The use of notched specimens provides a stress point and even ductile

materials display a brittle type of fracture. The notched-toughness of

dynamically tested materials is much less than the toughness figures

expected from stress/strain diagrams.

Suggest some materials that would have very low notched-toughness.

___________________________________________________________

___________________________________________________________

Did you answer?

Did you suggest brittle materials like white cast iron, grey cast iron andhardened high carbon steel.

Notched-bar impact tests were described in detail in the Preliminary

module on Braking Systems and in the previous HSC module.




Crane hooks and safety chains are commonly subjected to proving tests

before being used and new design concepts in jacks are also subjected to

proving tests under actual loading conditions.

Each of these lifting devices is subject to maximum loads. The number of persons allowed in an elevator is normally clearly indicated on the

control panel. The lifting capacity of jacks and cranes is labelled clearly,

often with a warning about overloading. Obviously manufacturers

understand that people will always stretch lifting devices to their loading

limits so it is important that proving tests overload the devices and

therefore include a factor of safety in the loading limits.


Heat treatment

Various heat treatment processes have been discussed in detail in

previous Preliminary and HSC modules.

Give definitions of the following processes, use information from

previous modules if you need to.

Normalising

__________________________________________________________

Hardening

___________________________________________________________

Tempering

___________________________________________________________

Did you answer?

In summary, normalising involves heating and cooling in still air, hardeninginvolves heating and quenching and tempering is the reheating of a hardenedstructure to reduce some of the brittleness while retaining hardness.

In this part, you will take a closer look at the internal structure that

results from these heat treatment processes and the typical properties that

result.




The final microstructure shows uniformly fine-grained ferrite and pearlite

throughout. As the cooling rate in normalising is faster than equilibrium

cooling, there is less time for the grains of ferrite to form before the

eutectoid reaction takes place. This means there will be more pearlite in

a normalised structure than in an annealed structure of the samecomposition.

Properties resulting from normalising

As previously mentioned, normalising is used to refine grain structure so

it is the same throughout the component (homogenous). It is used to

remove the stresses induced during forming processes and to eliminate

columnar grains and dendritic segregation that sometimes occurs during

casting. Normalising improves the machinability of the component and provides dimensional stability if the component is subjected to further

heat treatment.

Normalising produces harder and stronger steel than annealing due to a

number of factors including:

• the greater amount of pearlite found in the normalised structure

because of the non-equilibrium cooling.

• the pearlite is fine not coarse, as in annealed structures, which means

that there is not as much soft and ductile ferrite separating the plates

of hard and brittle cementite. This tends to stiffen the structureincreasing both the hardness and strength.

Normalising in lifting devices

A number of components found in lifting devices would be normalised.

These include:

• forged and cast steel crane hooks

• cast steel jack bodies

• fabricated steel lifting chains

• forged steel gear blanks

• cast iron pulleys in cranes

• cast brackets used in elevator assemblies.





Did you answer?

Tempering allows some of the carbon in the martensite to diffuse which relievessome of the stresses and reduces brittleness and hardness.

Identify components of jacks, elevators and cranes to suggest some

components of each that you feel would be hardened and tempered.

___________________________________________________________

___________________________________________________________

Did you answer?

Did you suggest parts like the teeth of gears in cranes and mechanical jacks andwear plates in the safety devices in elevators.

Properties resulting from hardening andtempering

The hardness of martensite depends on the carbon content of the steel.

The greater amount of carbon produces maximum strain of the lattice

structure and therefore the greatest hardness and brittleness.

Different quenching media cool the steel at different rates and can be

useful in hardening a variety of steels. Steels with higher carboncontents must be quenched slowly to avoid cracking while lower carbon

steels need very rapid quenching to produce maximum stress in the

lattice structure. Common quenching media from rapid to slow cooling

are:

• hydroxide solution

• salt water (10%) or brine

• agitated.

Hardenability

This term refers to the depth to which steel hardens. When the steel is

quenched the surface cools rapidly but the inside cools at a slower rate.

The depth of martensite, in plain carbon steel, might only be two to three

millimetres with pearlite forming below this depth. Alloy steels have

been developed that, once quenched, show martensite to a depth of

50 mm or more. Other alloys, containing 5% nickel and 1.5 %

chromium, change to martensite even after cooling in still air and are

known as air-hardening steels. Alloy steels are always used when adepth of hardness is required.



18 Lifting devices

A standardised test has been developed that is used to determine the

hardenability of steel. Known as the Jominy end-quench test, it involves

heating a 25 mm diameter, 100 mm long specimen into the austenite

range then quenching it from one end only. Parallel flats are ground on

the sides of the specimen and hardness readings are taken at 1.5 mmintervals along the specimen. The results of this test clearly demonstrate

the hardenability of the specimen.

Test-piece(Ø 25 x 100 mm)

Water jet

Air cooled end

Jig

___ Distance from quenched end (%)0 50 100

H a r d n e s s Al l o y

s t e e l

C a r b o n s t e e l

Figure 3.11 Jominy end-quench test Figure 3.12 Test results

Patenting

This process is peculiar to the wire industry and is used on the wire that

goes to make up the ‘ropes’ found in cranes and elevators. The wire used

is of around 0.65% carbon steel and the patenting process involves it

being heated to the austenitic range then quenched into a bath of molten

lead that is held at 250°C.

The final structure of this process shows both nodular and lamellar pearlite in a ferrite matrix. It responds well to severe deformation and

demonstrates high tensile strength in the direction of drawing.

The mass effect

The change from austenite to martensite involves an expansion of the

structure due to the movement of the carbon caused by the allotropic

change of the iron. As any material cools it contracts and, with steels, it

is possible that while one section of a quenched item is shrinking another section is expanding. The larger the mass of an article the more




pronounced the differences in cooling rates and the more likely the item

is to crack due to quenching.

Two processes, Martempering and Austempering, have been developed

that allow large masses to be cooled without developing quench cracks.

In both these processes, the component to be heat-treated is heated till the

structure is all austenite. The component is then quenched in a lead or

salt bath that is held at a temperature just above the temperature at which

the cooling steel will change into martensite.

In Martempering, the component is held in the bath till it is a uniform

temperature throughout. It is then water-quenched producing a full

martensite structure. The shrinking, due to cooling, and the expansion

due to the austenite-martensite transformation are separated by this

process and cracking is eliminated.

Sketch and label, in figure 3.13, the microstructure of the martensite that

results from martempering.

Figure 3.13 Martensite

In Austempering, the component is held in the ‘bath’ till the austenite has

changed to a ferrite matrix with carbide particles finely dispersed

throughout. This new structure is softer than martensite with similar

carbon content but has greater shock resistance.


Forming processes

Jacks, cranes and elevators all use component parts that have been

manufactured using a variety of forming processes. Each of these

processes alters the structure of the material being formed. These

changes in structure produce properties that are often desirable in these

component parts.



20 Lifting devices

Forging

Both hot and cold forging are used on various parts of lifting devices and

the major reason for using forging is that the component’s strength

properties are all increased in the direction of the forging.

In hot drop forging, a set of special dies are made from hardened and

tempered carbon steel or special alloy steel. The upper-half of the die is

attached to the hammer and the lower half is attached to the anvil. These

dies provide a series of stages to allow the metal to ‘flow’ into the shape

of the final die. The stages in forging are:

• metal blank cut from stock then heated and placed in the lower die

• rough forming is carried out in the first set of dies

• final forming takes place in the finishing dies• trim dies are used to remove flash from the forging.

For ease of forgeability, mild steel is by far the best materials, followed

by aluminium, copper, nickel and stainless steel.

Temperature range for common metals and alloys

Metal Temperature Range °C

Steel low – medium carbon 800 – 1300

Steel high carbon 750 – 1100

Steel alloys (including stainless) 950 – 1200

Copper 450 – 1000

Copper alloys 600 – 800

Aluminium and alloys 325 – 475

Aluminium bronze 800 – 900

Grainflow

When cast stock is hot forged the material is plastically deformed and

then immediately starts to recrystalise. Any cored grains remaining from

the casting process disappear and segregations and slag inclusions are

spread throughout the structure.




The new grain structure is known as ‘grainflow’ or ‘fibre’. The hot

working produces a recrystalised or normalised grain structure and the

forging process forces the original grains into new orientations. The new

grains form from these reorientated grains assuming the flow of the

original grains. Any non-metallic impurites, such as slag and trappedoxides, are aligned in the direction of forging.

Grainflow affects the properties of the forged components. Elastic limit,

ultimate strength, ductility and toughness are all greater when measured

in the direction of grainflow. Gears and cogs cut into forged blanks are

stronger than those machined from cast stock.

Casting

A number of practical and economic factors are taken into account whendeciding whether a component should be cast and what type of casting is

most suitable. In some cases, the shape and size of the component may

be such that casting is the only suitable process even though the grain

structure and mechanical properties will be inferior to those of a forged

product.

List at least four different processes that are used to cast molten metal

___________________________________________________________

___________________________________________________________

Did you answer?

Did you mention sand casting, shell moulding, pressure die-casting andinvestment casting or have you included centrifugal casting or permanent mouldcasting?

Some of the cast components in lifting devices include the following.

Jacks Elevators Cranes

hydraulic cylinder,body, wheels, ram

counterweight sections,motor components, drivesheaves, guide rollers,covers and guards

some hooks, pulleys,housings to supportgears, hydrauliccylinders and rams



24 Lifting devices

Thin vents on the parting line of the mould allow the air to be forced

from the mould, as the metal is injected, without letting the molten metal

squeeze out. Die-cast components typically have a surface that is harder

than the interior due to the faster cooling rate on the surface.

Solidification of cast metals

When metal is cast, the rate of cooling affects the structure of the cast

component that in turn influences the properties.

Outline the stages in the solidification process of metals.

___________________________________________________________

___________________________________________________________ ___________________________________________________________

___________________________________________________________

Grain size in a cast structure is determined both by the rate of nucleation

of the metal and the rate of grain growth. Fast cooling, as in a cold metal

mould, will result in a large number of nuclei being formed and resulting

in a fine grain structure. Under slower cooling, as in sand, shell or heated

mould casting, only a few nuclei form and have a chance to grow into

larger equiaxed grains.

Other factors that may increase the rate of nucleation and produce a fine

grain structure are:

• stirring the molten metal during solidification to break up the crystals

into smaller parts

• impurities in the melt that provide a ‘seed’ for the formation of

crystals.

When molten metal is poured into a mould, the metal ‘skins’ as it hits the

surface of the mould. Once the skin of the casting has formed, the rate of

conductivity of the mould material governs the cooling rate of the

interior.

As metal moulds easily conduct heat, as the molten metal cools many

nuclei form close to the surface of the component and dendrites start to

grow ‘reaching’ into the still molten centre of the component. The

resulting grains are long and thin and are known as columnar grains. If

the casting temperature is not too high the final grains to solidify, in the

centre of the component, will possibly be equiaxed. If the casting

temperature is too high, the columnar grains will meet forming a plane of

weakness at the centre of the casting.




As sand is a poor conductor of heat, the molten metal cools slowly in

conditions that are closer to equilibrium. The resulting structure is

typically a chilled ‘skin’ with fine equiaxed grains in the centre.

You may have noticed that castings don’t have sharp internal corners.The diagram in figure 3.14 shows how the use of fillet curves in corners

prevents the formation of a plane of weakness where the columnar grains

meet.

Chill crystals

Plane ofweakness

Equiaxed grains

Metal mould

Columnar grains

Fillet curve

Figure 3.14 Grain structure in a cold metal mould

Properties of cast metals

As discussed previously, the rate of cooling in cast metals influences the

final structure and therefore the mechanical properties.

The surface of any casting will always cool very rapidly when the molten

metal hits the surface of the mould. This invariably produces a very fine

grain structure and a harder ‘skin’ on the casting. In the case of grey cast

iron, there is insufficient time for the graphite to precipitate from the

cementite so the surface remains as hard and brittle white cast iron. Any

machining to occur must first remove this white cast iron skin. Tools

with very hard cutting tips, such as cemented carbide, must be used.

Generally, fine-grained materials show greater toughness, are more shock

resistant and are harder and stronger than coarse-grained materials.

Components produced by die-casting are generally fine-grained and have

more favourable properties than sand-cast components.

Castings are often heat treated (normalised) after forming. This is carried

out for a number of reasons:

• coring, that can occur when alloys are cooled under faster than

equilibrium conditions, is removed




through the use of a lubricant. One method of lubrication involves the

use of a coating of phosphate salts or glass that melts under the extrusion

temperature and acts as a lubricant. Other metals have much lower yield

strength than steel; aluminium brass, lead, copper, bronze and

magnesium are all fairly easy to extrude.

In elevators, much of the trimming used in the car is extruded. Next time

that you are in an elevator, have a look at the extruded track in which the

doors run, both on the floor and at the top. They are steel extrusions that

have been plated to provide protection from corrosion.

Properties in extrusions

The process of extrusion causes an alignment of the grain structure.This results in grainflow similar to the structure found in forgings. In

cold extrusion, the grains are distorted in the direction of extrusion and

the extruded metal is stronger along its length than across.

In hot extrusion, as in hot forging, the final grain structure will be

equiaxed grains but these equiaxed grains will recrystalise from the

grains that have been forced to ‘flow’ by the extrusion process. This will

also provide directional properties in the direction of extrusion. As the

outer surface of the hot extruded metal cools more quickly than the

centre, the outer layer shows fine equiaxed grains while the grains in the

centre will be larger.

Dimensional accuracy, excellent surface finish and directional properties

are all appealing features of extruded products.

Outer surface

Figure 3.15 Grain structure resulting from extrusion

Rolling

This is the name given to the process that changes the cross-sectional

shape of a piece of metal by passing the metal through suitably shaped

and spaced rollers.



28 Lifting devices

There are two general types of rolling mill:

• sheet, strip and plate mills

• bar, rail and joist mills.

Often, a series of roller sets in tandem form a line to enable the change

from billet to sheet to be a single continuous operation. Rolling increases

the length of the metal while reducing the thickness. The width does not

really change during the rolling process. Rolling is an effective method

of producing long lengths of material with a uniform cross-sectional

shape.

Hot billet

Scale breaker

Roughing rolls

Edging rolls

Finishing train

Coil roll

Live roller table

Finished strip

Figure 3.16 Continuous rolling mill

Some of the rolled components in lifting devices include the following.

Jacks Elevators Cranes

HotRolling

Mainframework/chassisof floor jacks,

Guide rails, safetyrails

Jib structuralmembers, windingdrum supportstructure

ColdRolling

Cover plates,framework of simplecar jacks

Button panels, doorskins

Body panels forcontrol booth.



30 Lifting devices

Powder forming, sometimes known as powder metallurgy, was first used

in modern times, to produce tungsten and platinum wires. Soon after

World War I, Germany used the process to produce cutting tips. It soon

became obvious that powder forming had many applications in

manufacturing.

The production of tungsten wire is a good example of the use of powder

forming. Tungsten melts at 3410°C, that is, beyond the softening

temperature of normal furnace linings. Tungsten powder is produced

from its ore, and compacted at around 1500 Pa. Under this pressure, the

particles of tungsten are ‘cold-welded’ together at the points of contact.

Sintering, at around 1600°C, allows recrystallisation to occur particularly

in the highly stressed region where ‘cold-welding’ has occurred. The

particles become joined as grain-growth occurs across the original grain

boundaries.

Compacting Sintering

Particles oftungsten powder Cold welding

between particles

Pressure Heat

Grain growth

across particleboundaries

Figure 3.17 Stages in a powder-metallurgy process

Again look at the previous module, and list four different types of

products that are commonly produced by powder forming.

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

Some of the main advantages of powder forming include:

• the elimination of machining because the dimensional accuracy and

surface finish after sintering is suitable for most applications

• high production rates as the steps are simple and the process is

highly automated




• scrap is eliminated which is important when forming expensive

materials – pressing, casting and machining can waste up to 50% of

the original metal

• complex shapes can be produced and the density of the part can also

be controlled to allow for porous parts

• materials, metals and non-metals, that normally don’t alloy can be

combined in the full range of proportions.

Some of the main disadvantages of powder forming include:

• the strength properties are inferior to wrought or cast components

due to the lack of directional properties or grainflow

• the dies are expensive because they must be big and made from

expensive alloys to withstand high pressure and severe abrasion

from the powders

• powdered materials are more expensive than cast or wrought

materials but, as there is less scrap and the parts are normally fairly

small, the material cost is not that great

• designs are limited as components must be uniform along one axis

and the length to diameter ratio is limited. The restricted size of

presses also limits the size of components that can be produced.

Properties of powder formed componentsThere are so many variables associated with powdered products it is

difficult to give general information about the properties. The type and

size of powders, pressing pressure, sintering temperature and finishing

treatments will all influence the properties of the component.

Electrical contacts, for example, may blend gold, copper or silver with

tungsten or molybdenum. The gold, copper and silver provide high

conductivity while the tungsten or molybdenum provides resistance to

fusion that can occur through the high arcing temperature. Bearings can

be made porous and may contain from 10 to 40 % voids. These are usedto hold oil and provide lubrication during the service life of the bearing.

True powder forming uses a sintering temperature that is below the

melting point of each of the component materials. Sometimes, however,

the sintering temperature is above that of one of the metal powders. In a

bronze bearing (90% copper and 10% tin) sintered at 800∞C, the tin melts

and flows around the copper particles joining them in a solid mass.

Bearings similar to those described, would be used in the moving parts of

jacks, cranes and elevators.



34 Lifting devices

c Describe with the aid of a sketch, the Charpy notched bar impact test

with the aid of a sketch.

_______________________________________________________

_______________________________________________________

_______________________________________________________

Exercise 3.2

a Briefly discuss the specific types of proving tests that may be used

with jacks, cranes and elevators

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

b Briefly explain the difference between a load-extension curve and astress-strain curve.

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________



36 Lifting devices

d With reference to the structure, explain why steel in the normalised

state is stronger and harder than in the annealed condition.

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

Exercise 3.4

a Complete the table below by suggesting a heat treatment process that

may be undertaken on each of the lifting device components listed.

Component Heat treatment process

Forged gear blank before machining

Steel ‘ropes’ used on cranes

Wear plates on elevator safetydevice

Cast steel jack body

b Describe the process of patenting that is used to heat treat steel

lifting cables used in crane and elevator ‘ropes’.

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

c Explain why Martempering and Austempering are used when heat-

treating components in lifting devices.

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________




Exercise 3.5

a State four stages in forging.

i______________________________________________________

ii______________________________________________________

iii_____________________________________________________

iv______________________________________________________

b Briefly explain why and how grainflow in forged components, like

gear blanks, increases the strength of components.

_______________________________________________________

_______________________________________________________

_______________________________________________________

c Pulleys and rollers used in cranes and elevators are often cast. List

some defects that can occur in sand casting

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

d Explain why fillet curves are used in the design of castings to

overcome weaknesses that may result from non-equilibrium cooling

with the aid of a sketch.

_______________________________________________________

_______________________________________________________




Exercise 3.7

a Discuss the reasons why lubrication may be used to aid the extrusion

process. _______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

b Explain how a powder formed component becomes ‘solid’ with the

aid of sketches.

_______________________________________________________

_______________________________________________________

_______________________________________________________

c Explain why powder formed components normally not as strong as

those made by forging.

_______________________________________________________

_______________________________________________________

d List two variables that may influence the properties of powder

formed products.

i ___________________________________________________

ii ___________________________________________________



40 Lifting devices

Exercise 3.8

Select the alternative a, b, c or d that best answers the question. Circle

the letter.

1 On a stress/strain graph, toughness is indicated by the:

a total area under the graph

b area under the straight line section of the graph

c length of the straight line section of the graph

d the downturn in the graph after the UTS.

2 Strain can be calculated by:

a dividing the load by the extension

b multiplying the load by the cross-sectional area

c dividing the extension by the original length

d multiplying the cross-sectional area by the original length.

3 In compression tests, barrelling occurs

a after brittle materials have failed

b as ductile material is squashed

c when the deforming load is removed

d only on cylindrical specimens.

4 The indentor used in the Vickers hardness test is:

a a combination of spherical and diamond point indentors

b two different sizes of hardened steel spheres

c a diamond cone

d a diamond pyramid.

5 The main reason for normalising is to:

a produce a uniform structure throughout the component

b increase the surface hardness of the component

c make the material softer so it can be cold worked

d change the grain structure to large, equiaxed grains.



42 Lifting devices




Progress check

During this part you examined the basic components of jacks, lifts and

cranes and how the forming processes for these components are used to

produce the most desirable material properties.

Take a few moments to reflect on your learning then tick the box that best

represents your level of achievement.




D i s a g r e e

U n c e r t a i n


• testing of materials used in lifting devices

• structure/property relationships in heat treatmentprocesses

• structure/property relationships in the material formingprocesses.

I have learnt to:

• describe the properties, uses and appropriateness ofmaterials used in lifting devices

• evaluate manufacturing processes for componentsused in lifting devices

• investigate impact testing• experiment with and assess structure/property

relationships, before and after heat treatment

• analyse the structure/property relationship developedthrough forming processes.



During the next part you will investigate electric systems and their

control and electrical safety systems and how these can be applied to

lifting devices.



44 Lifting devices



Lifting devices

Part 4: Lifting devices –electricity/electronics



2 Lifting devices

Introduction

Many lifting devices use electricity as a source of power or energy. Electric

motors are common in lifting devices and electric pumps are often used

together with hydraulic systems.

In this part you will examine the different types of motor that are used inlifting devices and the control systems that enable them to be used

effectively. You will also learn more about electrical safety and its

application to lifting devices.

What will you learn?

You will learn about:

• engineering electricity/electronics

– applications found in appropriate lifting devices;

motors, motor control

– electrical safety

You will learn to:

• describe the basic principles and applications of electrical components

to lifting devices.





4 Lifting devices

'Control'

The term ‘control’ is used in many situations. Control is based around the

notions of ‘inputs’ and ‘outputs’ of a system.

A familiar control problem – a hot shower

Let’s illustrate the principle with a simple but common example – a hot

shower. In this situation, the ‘system’ includes the hot and cold water taps,

the shower rose and the associated plumbing. The ‘inputs’ to the system are

the settings of the hot and cold water taps. The ‘outputs’ from the system

are the temperature and pressure of the stream of water from the shower

rose. Figure 4.1 illustrates the example.

Cold water pressure

Inputs System Outputs

Hot water pressure

Total water pressurePC

PH

Plumbing, tapsand

shower rose Water temperature

PW

TW

Figure 4.1 Inputs and outputs of a control system (in this case, a hot shower)

In controlling the shower, you adjust the inputs (hot and cold water taps) toachieve a desired water temperature and pressure. In this case there are two

inputs, and two outputs.

You want to control the two outputs separately. That is, you might want to

have the water temperature very hot, with low pressure, or very hot water

with high pressure. Similarly you might want to have a cool shower, with

high or low pressure.

Note that the inputs are not directly connected to the outputs: that is, there is

no explicit ‘temperature’ and ‘pressure’ taps. You can only adjust the

pressure of the cold and hot water supplies. The total water pressure is thesum of the two separate pressures, while the temperature is essentially the

difference between the amount of hot water and the amount of cold water

being supplied.

The shower system is known as a multiple input, multiple output, or MIMO,

control system. The relationship between the inputs and outputs is said to

be ‘cross-coupled’, since changing one of the inputs (say the cold tap)

affects both outputs (temperature and pressure).

The simplest control system is a single input, single out, or SISO, system.

In a SISO system, the input and output can be different quantities. For



Part 4: Lifting devices - electricity/electronics 5

example, on a gas cooker you can adjust the flow rate of gas (the input) to

regulate the temperature of the cooking vessel (the output).

Can you think of a simple SISO control system? Can you define the

input? Can you define the output?

Feedback in control systems

There is another important part of a control system that is not shown in

figure 4.1. The missing part is the ‘feedback path’.

The feedback path or feedback signal provides the information by which

you adjust the inputs so that outputs move towards their correct values.

Figure 4.2 shows how the feedback path fits into the control system of figure 4.1.

Desiredtemperature


Total waterpressure

TD

PH Watertemperature

PW

TW

Plumbing,taps and

shower roseDesiredpressure

PD

Human“controller”

PCET

Feedback path

ControlErrorDesiredvalues

EP

Figure 4.2 Key components of a control system (in this case, a hot shower)

You see from figure 4.2 that the system output is compared with (subtracted

from) the desired reference signal. The difference between the current

output and the desired output gives an ‘error’. This error is then used to

adjust the inputs so that the input moves towards the desired value.

If the output is greater than the desired value, the error becomes negative,

and you need to reduce the input to achieve the desired output.

The error signal is zero when the output matches the desired signal. When

this happens, the inputs need not be adjusted any further.

Let’s think about the feedback mechanisms that occur in our example of the

hot shower.

If the temperature or pressure is not correct (too hot, too cold, too light), you

immediately feel it on your back! Quickly, you turn to the taps to make the

appropriate adjustments.



6 Lifting devices

In this case the outputs are measured, or sensed, by the human body. The

desired, or reference, signal against which you compare the output does not

exist as a physical quantity: it is actually our brain that determines what the

ideal water temperature should be. In this context you see that the human

mind/body is an integral part of the shower control system.

The human body is, in fact, a very, very good system controller. Humans

can control systems that are very difficult, if not impossible, for a machine

to manage.

Let’s think about driving a car. With some training, many humans can drive

a car. This involves controlling many interacting inputs and outputs, with

many forms of sensing being required, and many desired outputs to be

achieved simultaneously.

Inputs in a car's control system include steering, accelerator, brake, gears,windscreen wipers, indicators, radio volume and so on. The system outputs

are the speed and position of the car on the road (hopefully!), the

acceleration rate of the car, the cleanliness of the windscreen, volume of the

radio and so on.

Figure 4.3 A highly complicated system to control – a car

It would be virtually impossible to write equations that related all of the

system inputs to the system outputs for control of a motor vehicle. Without

such a set of equations it is extremely difficult to design a machine to drive a

car. Yet many of us can manage it without undue difficulty.

You will see in subsequent examples that humans form an integral part of

many motor control systems.




Types of control systems

Analogue control

The example of the hot shower is one in which you exercise continuous, or

analogue, control over the input variables.

In Part 4 of Personal and public transport you have already used the term

analogue to describe a signal that is continuous in amplitude. In using the

term ‘analogue control’, you refer to a system in which the inputs and

outputs are continuously variable – that is, you can make arbitrarily small

adjustments to the input variables to achieve arbitrarily small changes to the

outputs. The input and output signals are said to be ‘analogue signals’.

Digital control (or switching)

In some control systems, the inputs and outputs are not analogue signals, but

instead take on only a finite number of possible values. This is equivalent to

a digital signal.

Perhaps the most simple example of a digital control system is an electric

light. The input to the system is the light switch (which controls voltage or

current) and the output is the intensity of illumination. In most instances theinput can take only one of two possible values: on or off. (You may

recognise this as a binary system). The corresponding light output is either

illumination, or no illumination.

Another example might be a ceiling fan. Many ceiling fans have two or

three speeds that can be selected to give varying levels of air circulation.

Systems that are regulated by inputs with only a finite number of possible

values are called digital or switched control systems. Note that the use of

the term digital does not (necessarily) imply logical operations (as seen in

digital logic circuits) but rather that the control system is operating withinputs and outputs that can only take on one of a finite set of values.

Can you think of an electrical appliance that has an analogue control

system? Can you think of an electrical appliance that has a digital or

switching control system?

In each case, identify the input/s and output/s of the system.

Turn to the exercise section and complete Exercise 4.1 questions 5 to 7.



10 Lifting devices

Analogue (Continuous) control of motors

In this section you investigate analogue, or continuous, control of various

types of electric motors. You are interested in identifying how you canregulate the speed, torque and/or position of the motors using particular

inputs.

The general configuration of an electrical machine was shown in figure 4.26

of Part 4 of Transport systems, and is reproduced here as figure 4.4.

Torque

Figure 4.4 A generic electrical machine to produce torque

The figure shows two electromagnets whose fields interact to produce

torque on the rotor. You have seen in previous work that the torque produced by the machine is given by:

q S i n N I N I T S S R R ¥¥µ

where

I R and I S are the currents in the rotor and stator coils respectively;

N R and N

S are the number of turns on the rotor and stator coils

respectively; and

q is the angle between the two magnetic fields.

Control of DC motors

The general configuration of a DC machine was seen previously in figure

4.32 of Part 4 of Transport Systems. You saw there that the commutator

structure of the DC machine fixed the angle between the rotor and stator

fields at 90°. This angle maximises the torque produced, since Sin q is at a

maximum when q = 90°




The torque produced by a DC machine is thus:

S S R Rd c N I N I T ¥µ

The number of turns on the stator and rotor coils of a DC machine areinvariably fixed by the manufacturer of the motor. This means that the

variables N R and N S cannot be used (by us) for controlling the motor torque.

Consequently, the torque produced by the DC motor is described by the

more simple expression:

S Rd c I I T ¥µ

That is, the torque produced by the motor is simply proportional to the

product of the rotor and stator currents.

It is common to keep the stator current in a DC motor constant. (This meansthat the stator’s magnetic field is constant.) This is simply achieved by

feeding the stator coils with a constant DC voltage source. See figure 4.5.

DC sourceVS

Figure 4.5 Stator of a DC machine fed by a constant voltage source, givingconstant stator current

The stator current in this case is determined by:

I V

RS

S

S

=

where V S is the stator source voltage and RS is the stator winding resistance.



12 Lifting devices

Small DC motors, such as those found in model cars and video cassette

players are often made with permanent magnet stators. This means that

there is no stator winding, and hence no value of I S .

What do you think determines the torque produced by a permanent

magnet DC motor?

Let’s now consider the rotor circuit in some detail.

Figure 4.6 shows a DC voltage source V C and variable resistor RC feeding

the rotor circuit of a DC motor. You see that the rotor circuit is modelled by

a constant resistance R R in series with a DC voltage source E R.

Rotor of DC motor

Back emfER

External variableresistor RCDC voltagesource VC

Rotor current

Rotor windingresistance RR

Figure 4.6 Equivalent circuit for the rotor of a DC machine

The resistor R R represents the resistance in the wire that makes up the turns

on the rotor coils. This resistance is usually no more than a couple of Ohms,

and in large machines is usually less than one Ohm.

The voltage source E R represents the ‘back electromotive force’, or ‘back

emf’ induced in the rotor winding.

You will recall from the discussion of induction motors in Household

appliances that an electrical conductor that cuts a magnetic field will have a

voltage induced in it. This phenomenon is described by Faraday’s Law.

In a DC machine, the conductors making up the coils on the rotor spin in the

magnetic field produced by the stator. As these conductors break the lines

of magnetic flux, they too have a voltage, or emf, induced in them. The



14 Lifting devices

Figure 4.7 shows the electrical connections for a DC machine to enable

torque control.

DC sourceVs

External variableresistor RC

DC voltagesource VC

Figure 4.7 Electrical connections for controlling a DC motor

Implementing either of these two control strategies allows us to control the

torque produced by the motor. The speed or position of the motor is

generally much more difficult to control, since these outputs are dependent

on the nature of the load attached to the motor.

Figure 4.8 shows the DC machine from a control system perspective.

Rotor source voltage


DC motor

Rotor resistance

Motor torque

VC

RC

TDC

Figure 4.8 Control system view of a DC machine

In many instances, the control of speed or position is left to a ‘human

controller’.

For example, an electric train lifting a load of passengers up the Blue

Mountains is driven by a human. The driver makes adjustments to themotor (rotor) current which varies the torque produced by the machine.




However, the torque produced by the motors is not the important output

variable. The speed and position are more significant: these outputs are the

result of the good judgement of the driver who instinctively varies the

torque to achieve the desired speed and position.

Similarly, a crane driver uses experience and his observations to control the

lifting of very light or very heavy loads, using only the rotor current to

regulate the torque of the winch motor.

An example where direct human intervention is not used is that of a modern

elevator. In an elevator, there is no ‘driver’ using observations and

judgement to control the vehicle. (There was, of course, in older style

elevators.) Instead, the control of the vehicle is handled by a sophisticated

automated system.

The automated system needs to sense where passengers are located (bymonitoring push buttons on respective floors) and where they want to go (by

monitoring push buttons inside the vehicle). Using this information,

together with measurements of vehicle speed and position, the controller

regulates the motor (rotor) current to achieve the desired outputs.

Can you think of an example where a DC motor is used in an appliance or

toy in your home? Is the speed of the motor variable? Who or what

controls the motor speed?

Turn to the exercise section and complete exercise 4.1 questions 8 to 10.

Control of synchronous motors

You have previously read about the principles of synchronous motors.

While synchronous motors are not often used in lifting devices, it is

insightful to contrast their control characteristics with those of the DC

machine examined above.

The stator of a synchronous motor is usually fed by a three-phase supply to

produce a rotating magnetic field. (See Part 4 figure 4.29 of Personal and

public transport .) The key parameter of this supply is its frequency.

You might recall from previous work that the speed of a synchronous motor

is determined by the speed of rotation of the stator field. This means that if

the stator field is supplied by a fixed frequency source (such as mains

electricity) then the speed of the motor is also fixed. If you change the

supply frequency, you can change the speed of the motor.

In order to vary the speed of the machine you must be able to provide a

variable frequency supply to the synchronous motor's stator. In practice the

complexity, and hence cost, of this arrangement discourages its use.



16 Lifting devices

Consequently, synchronous motors are generally only used in constant

speed applications.

The torque produced by a synchronous motor is again determined by:


where

I R and I S are the currents in the rotor and stator coils respectively;

N R and N S are the number of turns on the rotor and stator coils

respectively; and

q is the angle between the two magnetic fields.

In the synchronous motor case, the stator current I S is usually fixed (by the

stator supply voltage V S and stator winding resistance RS , with I V

R S

S

S

= ).

N S and N R are fixed by the motor manufacturer.

In the case of the DC motor, you saw that the torque and speed are related

by the nature of the load and not by the motor itself. For example, a heavy

load requires greater torque for a given speed than does a light load.

In the synchronous motor, the torque and speed are determined by separate

quantities inside the motor: the torque is determined by I R ¥ Sin q ; the

speed is determined by the frequency of the AC supply.

However, you know from physics that the torque and speed must be

matched for a given load.

So how does the synchronous motor ensure that the appropriate torque is

produced for a given load and speed?

The answer is in the Sinq term. The angle q is defined as the angle between

the stator and rotor magnetic fields. This angle can vary between 0o (zerotorque) and 90o (maximum torque). The angle q is not an input variable that

you can control – it is a variable that automatically adjusts itself to match

the torque required by the load.

When the load is relatively light, q adjusts to a small angle, and only a small

torque is produced by the motor. When the load increases, q also increases

towards 90o.

If the load is too heavy for the machine, the angle increases beyond 90o.

The resulting torque then decreases (because of the Sinq term). The motor




experiences what is called ‘pole slipping’ whereby the rotor magnetic field

loses its ‘lock’ on the stator field.

Pole slipping is analogous to a set of slipping gears. Imagine that you had a

small gearbox made up from polymer gears. If you try to transfer too muchtorque through the gearbox the gear teeth will start to slip over each other.

If you reduce the torque, the gears will again start to mesh properly,

transferring the torque.

Given that the Sinq term is not available to us as an input, the only variable

that you can control to regulate the torque is I R.

You can control the rotor current in a synchronous motor in the same way

that you controlled the rotor current in a DC motor: that is, by varying the

DC supply voltage (if possible) or by varying a series resistance if the DC

supply voltage is fixed.

Figure 4.9 shows the electrical connections for a synchronous motor.

AC sourceVS

External variableresistor RC

DC voltagesource VC

Figure 4.9 Electrical connections for controlling a synchronous motor



18 Lifting devices

Figure 4.10 shows the synchronous motor from a control system

perspective.

Rotor source voltage


SynchronousmotorRotor resistance

Motor torque

VC

RCTSynch

Figure 4.10 Control system view of synchronous motor

Turn to the exercise section and complete exercise 4.1 questions 11

and 12.

Control of induction motors

The induction motor is fundamentally different to the DC and synchronous

motors in that it has only one electrical supply. That is, you can only feed

power to the stator of the induction motor, with the power being supplied to

the rotor through an inductive process. This contrasts with DC and

synchronous motors which have separate stator and rotor power supplies.

The single power supply means that the general expression for torque given by:


is not immediately applicable, since you can’t determine what the rotor

current I R and field angle q will be.

(The equation does in fact still hold, but you have to infer I R and q from

known quantities through complicated relationships.)

In the induction motor case, you have a single AC supply. This supply hastwo main parameters: the voltage (or current) and the frequency.

The relationship between the applied voltage and supply frequency (the

system inputs) and the torque of the motor (the system outputs) is quite

complicated. This system is a multiple input, single output (MISO) system.

Figure 4.11 shows an induction motor from a control system perspective.




Source voltage


Synchronousmotor

Source frequency

Motor torque

VS

FS

TInduct

Figure 4.11 Control system view of an induction motor

In practice, you use induction motors in either a controlled, or uncontrolled,

form.

In a controlled form, you need Variable Voltage Variable Frequency

(VVVF) drive system. This is essentially a box of electronics that converts

a fixed frequency fixed voltage supply (from the mains) into a supply that

has adjustable voltage and frequency. These systems are invariablymicroprocessor controlled, and allow us to vary the torque, and hence speed,

of an induction motor.

Unfortunately, VVVF drives are relatively expensive. Thus while induction

motors are relatively cheap amd robust, the addition of a VVVF controller

detracts from the motor's inherent advantage.

In an uncontrolled form, you simply apply a fixed frequency fixed voltage

(from the mains) to the motor. The motor then runs at a speed dictated by

the nature and size of the load.

Obviously uncontrolled motors are much cheaper to use that controlled

motors. The uncontrolled form is actually very common: refrigerators,

washing machines, fans and pumps can all run uncontrolled. The maximum

speed of the induction motor is limited by its supply frequency, and so

induction motors connected to the mains cannot run at excessive speed.

Induction motors make up a large part of the total electrical load of the state.

By far the majority of these motors are uncontrolled!

How many induction motors do you think there may be in and around

your home?

Make a list of the devices that you think contain induction motors.

___________________________________________________________

___________________________________________________________

Did you answer?

Some of the appliances which may contain induction motors include: air

conditioner; washing machine; electric crane and electric lifts.



20 Lifting devices

Are any of these motors controlled by VVVF drives?


Motor control summary

The following table shows a summary of the key parameters for control of

various motor types.

Motor Type NormallyFixed Inputs

ControllableInputs

ControlledOutputs

Notes

DC motor N R , N S , I S ,Sin q

I R T DC Max speed limitedby back emf.Speed set by load.

Synchronousmotor

N R , N S , I S I R T synch Speed set bystator supplyfrequency. Sin q

self adjusting toload.

Inductionmotor

N R , N S V S , frequencyof supply F S

T Induct Max speed limitedby supplyfrequency. Speedset by load.




Digital (Switching) control of electric motors

In the above you have looked at analogue control of DC, synchronous andinduction motors. In these instances you saw you can control the speed

and/or torque of the various motors by continuously variable voltages,

currents, resistances and/or frequencies.

While analogue systems offer very good control of motor performance, such

systems are becoming increasingly expensive, particularly in comparison

with alternatives based on digital devices.

Digital technology is based on a simple on-off switching arrangement. The

approach is simple, cheap, and as you will see, can be very effective.

On-Off (Binary) switching

The concept of switching is simple and familiar to us all. Every day you

switch many devices on and off as you require.

Most of the time, the time lapse between switching on and off varies from a

few seconds to several or many hours. For example, you might use a food

processor for ten seconds at a time; a hair dryer for minutes at a time, and

room lighting for hours at a time.

In some appliances the motor is switched automatically by the appliance's

control system. For example, in a refrigerator, a thermostat monitors the

temperature inside the fridge. If the temperature rises above a preset

threshold, the cooling system (compressor) motor is switched on until such

time as the fridge cools to its correct operating range.

Another example of an automated motor drive is a garage door opener.

Usually you press a switch (on the wall or on a remote controller) to start the

door opening or closing. However, the motor stops driving when the door is

fully open or closed without our intervention. Sensors are used to detectwhen the door is fully open or fully closed and to cut power to the motor

when these limits are reached.

Can you draw a control system diagram for an automatic garage door

when it is closing? What are the system inputs? What are the outputs?

What is the desired setting? How can you generate an error signal?



22 Lifting devices

Pulse Width Modulation (PWM)

Switching control of electric motors is not limited to those applications

when the time between switching is several seconds, minutes or hours.

Many new technologies use a control strategy that switches a device on and

off many times per second in order to emulate a continuously variable, or

analogue, signal. Such systems are often called Pulse Width Modulation, or

PWM, systems.

Suppose you have a single electric lamp in a darkened room.

If the lamp is off, the room is totally dark.

If the lamp is turned on (and left on) we'll say that the room is totally bright.

Now suppose you were able to turn the lamp on and off at around 1 000

times per second. (Don't worry for the moment as to how you could operate

a switch so rapidly, we'll just assume it can be done!)

If the lamp is on for 1 millisecond, and then off for one millisecond, then on

again for one millisecond, off for one millisecond, and so on, the room

would only be half as bright as compared to when the lamp was on all of the

time. This is because only half the amount of light energy is being delivered

into the room.

During this switching, our eyes would not be able to tell that the lamp wasflashing. Our eyes can only detect flicker frequencies up to ten or twenty

Hertz.

(Films shown at the cinema are actually a series of still images, updated at

24 frames per second (24 Hz). Our eyes are not sufficiently sensitive to see

the individual images, hence the resulting image is perceived as one of

continuous motion.)

Suppose now that you turned the lamp on for one millisecond, then off for

three milliseconds, then on for one millisecond, off for three milliseconds,

and so on. The room now is only one quarter as bright as if the lamp wasfully on.

It is clear that you can vary the ratio of on-time to off-time to vary the

average brightness.

The ratio of on-time to off-time is called the ‘duty cycle’ and is measured as

a percentage:

% Duty Cycle(on - time)

(on - time) off - time)=

+¥

(100

By varying the duty cycle, you can in effect approximate an analogue signal.



24 Lifting devices

Time varying pulse width modulation

In the above discussion you assumed that the duty cycle remained constant,

and hence the average output remained constant.

The duty cycle can be made time varying. Varying the duty cycle allows

you to produce a time varying ‘average’ signal. (The term ‘average’ here is

used in inverted commas because you now have to be careful over what

period you do your averaging.) Figure 4.13 shows the effect of varying the

duty cycle in a particular pattern so as to produce a sinusoidally varying

signal.

On

Off

Equivalent (sinusoidal)analogue output

Pulse with modulated output

Switchposition

Figure 4.13 Sinusoidal signal produced by a time varying PWM cycle


Applications of motor control in liftingdevices

In considering motor control in the context of lifting devices, you will try to

categorise the system according to a number of key parameters:

• Motor type – does it use a DC motor, synchronous motor or inductionmotor?

• Is the motor controlled in some sense, or is it simply on/off?

• If controlled, what are the controllable inputs, and what are the

controlled outputs?

• Does the system use automatic feedback, or does it rely on human control?

Electric motors are used in many lifting applications. You will consider a

small number of applications here.



26 Lifting devices

Brick conveyor

A brick conveyor is used to haul individual bricks from ground level up one

or two floors on small building sites on a conveyor belt.

The belt is started with no bricks on it, and then bricks are placed on the

conveyor. This means that the conveyor can start with virtually no load, but

once under way, the load is steadily increased.

• Motor type – does it use a DC motor, synchronous motor or induction

motor?

You would like the motor to be as robust and cheap as possible, so use

an induction motor.

• Is the motor controlled in some sense, or is it simply on/off?

System is controlled by a simple on/off arrangement. The speed of theconveyor is limited by the supply frequency (usually a mains supply),

and slows down as the load increases. Control over torque, speed or

position not really required.

Crane

• Motor type - does it use a DC motor, synchronous motor or induction

motor?

Need variable speed, and high starting torque, so DC or VVVF-fed

induction motor best suited.• Is the motor controlled in some sense, or is it simply on/off?

Motor needs to be closely controlled to allow accurate placement of loads.

• If controlled, what are the controllable inputs, and what are the

controlled outputs?

The main output to be controlled is the position of the load. This

position is closely related to the speed and duration of lift. The speed of

lift is, in turn, dependent on the torque produced by the motor which is

a function of the motor current.

• Does the system use automatic feedback, or does it rely on humancontrol?

The system is highly dependent on skilled operators to translate desired

position into a combination of speed and duration of lift.

Can you categorise the following applications according to the criteria abo

• A motorised garage door opener?

• A constant speed escalator in a shopping mall?

Turn to the exercise section and complete exercise 4.2a to f.



28 Lifting devices

Employers (OH&S Act Section 15)

Employers are responsible for ensuring the health, safety and welfare of

their employees. Employers must ensure that hazard identification and risk

assessments have been done, control measures applied, and safe working practices put in place, before starting work.

All of these precautions must be reviewed on an ongoing basis.

What type of safety measures might you (as an employer) provide if you

expected one of your employees to work (safely) on a roof?

Employers and self employed persons (OH&S ActSection 16)

Employers and self employed people must ensure the health and safety of

people visiting the workplace who are not their employees. This covers all

types of visitors, such as passers by, or likely visitors to each work site.

Why do you think high rise building sites are often cloaked in mesh or

cloth screens? Why would you bother to board up or fence off a building

site in a shopping centre when it would be much easier not to do this?

Supervisors (OH&S Act Section 15)

Supervision is the process of providing guidance and training. An employer

is required to provide whatever supervision may be necessary. The level of

supervision is determined by the need to ensure the work is done safely.

Employees (OH&S Act Section 19)

Employees must comply with any safety procedures prescribed by the

employer. This includes correct use and maintenance of personal protective

equipment, special tools or related safety gear. The employee is also

expected to identify and report workplace hazards as they become known to

ensure they are addressed.

Duty of care

Under the Act, everyone, not just employers and supervisors have a

responsibility not only for their own health and safety while at work, but a

‘duty of care’ for the health and safety of others.

If you noticed an unsafe work practice by a work or school colleague, or

found a dangerous or faulty piece of equipment, what do you think your ‘duty of care’ requires you to do?




Australian standards

The Australian Standards are a large collection of documents that cover

an enormous variety of situations. They prescribe what precautions andmeasures are considered appropriate for anything from paint and building

materials through to electrical appliances. Almost any device, product or

service you can think of is likely to have some components subject to an

Australian Standard.

There are a large number of Standards documents that relate to electrical

equipment and installations. Some of these include:

• AS 3000 – 1994: Electrical installations – buildings, structures and

premises (SAA Wiring Rules).

• AS 2243.7 – 1991: Safety in laboratories Part 7: Electrical aspects,electrical safety in the workplace.

• AS 1674.2 – 1990: Safety in welding and allied processes Part 2:

Electrical.

• AS 3003 – 1999: Electrical installations - patient treatment areas of

hospitals and medical and dental practices.

• AS/NZS 3760 – 1996: In-service safety inspection and testing of

electrical equipment.

These documents prescribe anything from the distance a power point

must be located away from a source of water, to how deep an electricalcable must be buried in the ground. The standards change regularly as

new equipment and methods evolve.

Hazard assessments

Hazard assessment is the process of identifying all the hazards that are

present in a particular working area. These are prioritised in order of

seriousness of potential injury arising from each hazard, from fatal through

to minor injury.

Having listed all of the identified hazards and assessed their potential

severity, the next step is to estimate the exposure: that is the number of

times and/or the length of time in which a worker is exposed to each hazard.

A combination of long or frequent exposure and the possibility of severe

injury would mean the hazard should be placed high on the priority list.

The purpose of prioritising the hazards is only for the order of addressing

them. All hazards must be considered, irrespective of risk. The combination

of potential injury and level of exposure determines the level of risk.



32 Lifting devices

Building elevator

An elevator or lift in a multi storey building is another common example of

an electrical lifting device, and it too has a number of specific additionalsafety features. Commonly the lift is driven up and down by an electric

motor connected through a mechanical gear box and system of steel cables

and counter weights.

Just as with the garage door opener, a lift also automatically detects objects

(or people) caught between its doors as they attempt to close. This can be

done by detecting the door closer current or by a switch bar which contacts

the obstacle before the door does. On detection of an obstacle the door

automatically reverses.

Again, once the doors are closed, what happens if something goes wrong?What happens if there is a power failure with people in the lift?

A lift commonly does not have windows, so in the event of power failure,

the lift is likely to be particularly dark. Lifts (and indeed buildings in

general) will often have an emergency lighting system. A small light,

usually powered by a small battery, automatically comes on if the ambient

light levels fall below a certain threshold or the mains power is removed.

When the mains are operating normally, the battery is kept charged.

Many power failures are relatively short in duration, but what if the power is

off for a significant length of time?

People in the lift will need to be able to contact someone outside for help.

Most elevators contain either an alarm, that can be triggered by people in the

lift to alert those outside to their plight, or a telephone.

Most telephone systems are actually battery powered for this very reason.

Ever noticed that during a power blackout, your telephone at home will still

work?

The telephone network is powered by a large bank of batteries that are kept

charged at your local exchange.

What about the lift drive system itself? What happens if the motor or control

system malfunctions?

Many elevators contain additional safety devices for the event of the hoist

system failing. There are sometimes redundant hoist systems, safety cables,

automated detection of cable breakages, or slack cables, manual overrides to




open doors or to control the elevator hoists directly in the event of a control

system failure.

Elevators and other building electrical systems are often interlocked with a

building fire alarm. Elevator doors will permanently open if the fire alarmis triggered and the lift disabled. Air conditioning systems will often switch

off to prevent smoke from a fire circulating through the building.





11 A synchronous motor can be made to run at variable speed by:

a varying the magnitude of the stator current

b varying the magnitude of the rotor current

c varying the frequency of the stator current

d varying the frequency of the rotor current.

12 Pole slipping in a synchronous machine results from:

a insufficient motor torque to match the given load

b too much motor torque for the given load

c too much grease on the motor shaft

d incorrect meshing of polymer gears.

13 An induction motor:

a has separate stator and rotor power supplies

b uses one power supply connected to both stator and rotor

c doesn't need any power in the rotor

d induces power in the rotor as described by Faraday's Law.

14 An induction motor connected directly to the mains supply will:

a not run at all

b run at a fixed speed

c run at a speed determined by the size and nature of the load

d cause a short circuit and catch fire.

15 PWM is an abbreviation of:

a perfectly wound motor

b perfect width motor

c pulse width modulation

d precisely weighted magnets

16 The principal use of PWM in control systems is to:

a emulate analogue control using switching devices

b blind people with flickering lights

c feature electric motors in cinematography

d confuse Engineering Studies students.




Exercise 4.2

Suppose you are engaged as an engineering consultant to oversee the design

of a moving walkway to be installed in a new international airport. The

proposed walkway is quite long (around 200 metres) and should run at aconstant speed in normal operation.

In considering the following factors, state any assumptions you make about

the walkway, its design or about the people who will use it.

a State the number of electric motors that should be used to power the

walkway and justify the reason for your proposed selection

______________________________________________________

______________________________________________________

______________________________________________________ b Indicate the type/s of motors that should be used for this application and

explain the reason for your choice of these particular motor types.

______________________________________________________

______________________________________________________

______________________________________________________

c State how many output parameters do you need to control in terms of a

control system.

______________________________________________________ ______________________________________________________

d List the input variables do you need to control the motors to achieve the

desired outputs.

______________________________________________________

______________________________________________________

e Indicate if the control system should be fully automatic, or employ

skilled operators to control the walkway.

______________________________________________________ f Indicate if you propose to use analogue or digital techniques to

implement your controller and explain the reasons underlying your

decision.

______________________________________________________

______________________________________________________

______________________________________________________



40 Lifting devices

Exercise 4.3

a Identical who is responsible for the safety of the passengers on the

moving walkway.

_______________________________________________________ b Indicate if you propose to schedule regular and/or routine maintenance

as an integral component of your safety regime and outline maintenance

or checking would you specify.

_______________________________________________________

_______________________________________________________

_______________________________________________________

c Explain how your system should react if too many people crowd on the

walkway overloading it.

_______________________________________________________

_______________________________________________________

_______________________________________________________

d Outline the options that should be available to stop the walkway in case

of an emergency.

_______________________________________________________

_______________________________________________________

_______________________________________________________



42 Lifting devices



Arial Arial bold

Lifting devices

Part 5: Lifting devices –communication



Arial Arial bold

Part 5: Lifting devices – communication 3

Orthogonal projection, AS 1100 standards

Representation of repeated features

When a component contains a regular pattern of repeated features such as

holes or slots, the AS 1100 standard allows these repeated features to beshown as full outline of all of the features or alternatively by a

conventional representation.

Using the conventional representation, one of the holes or slots may be

shown in full outline, and the position of the remainder by centrelines.

The number and size of the holes or slots must be indicated using a note

and leader line.

The method of conventional representation is far quicker to use and also

makes the drawing much simpler. The advantage in using this standard

is a great saving of time, especially in your HSC examination.

Figures 5.01 and 5.02 show the true representation then the conventional

representation of eight drilled and counterbored holes in a circular

locking cap.



4 Lifting devices

4 8 6

60

ON 40 PCD

Figure 5.1 True drawing of the top view of the circular locking cap

4 8 68 x

60

40

5

2 5

20

Figure 5.2 Conventional representation of repeated features



Arial Arial bold


What do the drawings convey to you? What does the dimensioning

mean? Which drawing is the quicker and easier to draw?

While you are considering each drawing you should revise the AS 1100standards used in the drawings; the use of a half-section, the use of full

dimensioning, the standard dimensioning methods and the use of a detail

drawing. These will all be used in Exercise 5.1.

Consider the two views of the circular locking cap and the dimensioning

of the holes. Both top views show a regular pattern of eight,

counterbored, through holes of diameter four millimeter, counterbored

diameter eight millimeters to a depth of six millimeters.

Figure 5.1 shows the true representation of the repeated features,

dimensioned using the symbol methods from AS 1100.101-1992. You

should revise this dimensioning work from your previous module. The

reason for the use of symbols when dimensioning is to avoid the use of

written language, and also to make the drawing simpler to read and

quicker to draw.

Similarly, the conventional representation of the repeated features in the

top view in figure 5.2 makes the drawing simpler to read and quicker to

draw.

To save you time you should learn the standards for this conventional

representation of repeated features. Remember that you must use a note

and leader line to indicate the number of holes or features and the

dimensions required for those holes or features.

Preparing for Exercise 5.1

The following section explains the approach you should use when

attempting Exercise 5.1. You should read the section and then attempt

the exercise. You should also be aware that the exercise number is

shown in the title block for each exercise, not at the top of the page.

Look at Exercise 5.1.

The exercise requires you to draw to a scale of 1:1, a detail drawing of

the Screw Jack Head. You are required to use a top view, incorporating

the conventional representation for repeated features, a half-sectioned

front view, and to completely dimension the drawing.

Your first step should be to consider the shape and size details given on

the drawing. The screw jack head is circular in shape, the top is diameter

75 mm and has twelve 5 mm x 3 mm grooves. The head has a through

25 mm hole, counterbored 36 mm to a depth of 8 mm. A radius of 25



8 Lifting devices

Itemising of parts or components

Item number

An item number is a number assigned to a component on an assembly

drawing. It is used to identify components, enabling information

regarding the components to be referenced from the materials or parts

list.

Capital, that is, upper case letters may be used in addition to numbers

where necessary.

The height of the numbers should be twice the height of dimensioning

used on the drawing.

The item number should be enclosed in a circle to further differentiate itfrom any dimensioning. The circle should be drawn using thin dark lines

and a diameter equal to twice the height of the numbering.

Where no confusion would occur, the number may be drawn without the

use of a circle.

The numbers should be arranged in sequential order to assist in easy

identification of the components, and should be positioned in vertical

columns and/or horizontal rows on the drawing.

Leaders

Leaders are thin dark continuous lines drawn from the itemizing circle or

number to the component or item on the assembly drawing. They are

used to clearly identify the component.

Leaders should:

• not intersect dimension lines or other leaders

• be kept as short as possible

• be drawn at an angle to the itemizing number

• be drawn radially from the itemizing circle

• terminate in an arrow or a dot.

In assembly drawings, dots are the preferred method to be used as

terminators of leader lines. The dots should be;

• of diameter twice the thickness of the leaders they terminate, but not

less than diameter 1 mm

• within the outline of the component.



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Where arrow heads are used to terminate the leaders, the point of the

arrowhead should touch the first point of reference of the component.

Note that on any drawing, all leaders should have the same terminators,

either arrowheads or the preferred method, dots.

2 2 2 2

Figure 5.5 Itemizing methods, using dots and arrowheads

Square screw threads

Where screw threads are used to transmit large forces, such as in lifting

devices, square threads are used rather than the standard v-thread.

To differentiate the representation of the standard v-thread and threads

other than v-threads, a section or other detail view is drawn to illustrate

the thread form.

A square thread is represented by drawing the standard thin dark line for the thread then drawing part of the thread in section to show the profile

of the thread.

Figure 5.6 Standard representation of a square thread



The exercise requires you to draw to a scale of 1:1, an assembly drawing

of the Lifting Screw Assembly. You are required to draw a sectioned

front view of the assembled parts , incorporating the conventional

representation for a square thread, and both a full-section of the head and

a part-section of the top of the lifting screw.



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You have now completed most of the AS 1100 standards appropriate to

your Engineering Studies course. However, you need to practise the

application of these standards. Exercise 5.3 does not introduce any newstandards, but requires you to revise and apply previously covered

standards.


The exercise requires you to draw to a scale of 1:1, an assembly drawing

of the Pulley Block Assembly. You are required to draw a sectioned

front view of the assembled parts.

Your first step again should be to consider the shape and size details

given on the drawing, and the method of assembling the components. Toassemble, the pulley is positioned inside the block and the shaft is pushed

through the diameter 20 mm holes in both the block and the pulley. The

shaft protrudes evenly on both sides of the block.

Care should be taken with the dimensions of the webs; they slope from

the top bosses, a distance of 62 mm apart, to the bottom bosses, 60 mm

apart.

Your next step is to design the drawing, completing a freehand sketch

showing the required sectional front view. Again, you should complete a

quality freehand drawing as practice for your HSC.

Turn to the exercise sheets and complete exercise 5.3 as an accurate

freehand drawing.

Tangency and circles in contact

Many orthogonal drawing exercises involve tangency or circles in

contact, so you would be expected to be able to construct and draw these

exercises.

Tangency involves circles or arcs in contact with, or touching a straight

line. Both tangency, and circles in contact, involve a similar basic

method of construction.

The basic method:

• locate the centre of the arc or circle

• locate the point of contact

• draw the arc or circle.



14 Lifting devices

R 2 5

B D

C

A

B D

C

A

Parallel line, 25mm from BD R 25 arc from A Perpendicular from C R 25 arc

Figure 5.10 Worked example 5.2 – arc touching a point and a straight line

Circles in contact, external circle

To construct an arc or circle to touch a given circle, the same basicmethod applies; locate the centre, locate the contact point then draw the

arc or circle.

To locate the centre for the arc, a concentric circle having a radius equal

to the sum of the radii of the two touching circles is drawn from the

centre of the given circle. Concentric circles have the same centre.

If the arc is to touch the given circle and:

i a given point; the centre is located a distance equal to the radius of

the arc from the given pointii a given straight line; the centre is located on a parallel line, a

distance equal to the radius of the arc from the given line

iii another given circle; the centre is located on a concentric circle

having a radius equal to the sum of the radii of the arc and the

second circle.

Having located the centre in each case, the contact point of the touching

circles is located. The contact point of two touching circles is on the line

of centres of the two circles. Therefore, a line is drawn from the centre

of the given circle to the located centre.

Now the point of contact is located for:

i the point

ii the straight line

iii the other circle, using the appropriate method.

The required arc or circle is now drawn.



16 Lifting devices

To locate the centre for the arc, a concentric circle having a radius equal

to the difference of the radii of the two touching circles is drawn from the

centre of the given circle.

If the arc is to touch the given circle and:i a given point, the centre is located a distance equal to the radius of

the arc from the given point

ii a given straight line, the centre is located on a parallel line a distance

equal to the radius of the arc from the given line

iii another given circle, externally, the centre is located on a concentric

circle having a radius equal to the sum of the radii of the arc and the

second circle

iv another given circle, internally, the centre is located on a concentric

circle having a radius equal to the difference of the radii of the arcand the second circle.

Now having located the centre in each case, the contact point of the

touching circles is located. The contact point of two touching circles is

again on the line of centres of the two circles. Therefore, a line from the

centre of the given circle to the located centre is drawn.

Now locate the points of contact for each exercise and draw the arc.

Worked example 5.4

Drawing an arc of radius 55 mm to internally touch two given circle of

centre A, and centre B.

A

B

R – r arc from A R – r1 arc from B Contact points from C R 55 arc

A

B

C

R –

r

R – r 1

r

r1

Figure 5.13 Worked example 5.4 – arc internally touching two given circles



18 Lifting devices

with an arc of radius 14 + 50, from the R14 centre. Join this point to

the R14 centre to locate the contact point and draw the R50 arc.

vi Now mark out the size of the shaft, diameter 22 mm, height 35 mm,

and draw the peened head.

vii The ‘upset’ collar can now be completed, the R3 rounds finished and

the R3 curve drawn to complete the shape of the hook.

viii Complete the thick dark outline of the drawing.

Turn to the exercise sheets and complete exercise 5.4, using drawing

instruments.


You should now turn to, and attempt Exercise 5.5. The given drawingshows a front view and sectioned right side view of a supporting screw

assembly, drawn to a scale of 1:1. The components have been itemized

and a materials list included.

Turn to the exercise sheets and complete exercise 5.5 answering the

multiple choice questions with reference to the given drawing.



Arial Arial bold


Exercises

Exercises 5.1 to 5.3 require you to represent each object using freehand

orthogonal sketching. AS 1100 standards for representing features must

be applied. Accuracy to within 1 mm would be expected.

Exercise 5.4 is an instrument drawing exercise. Use all technical drawingequipment as required.

Exercise 5.5 requires features on a drawing to be identified and the

correct option (a to d) to be selected.



20 Lifting devices



Arial Arial boldhelvetica

S C R E W J

A C K H E A D S

C A L E 1 : 1

E X 5 . 1

A 4

S h a p e a n d s i z e d e t a i l s o f a s c r e w j a c k h e a d a r e

g i v e n b e l o w i n a p i c t o r i a l

d r a w i n g . D r a

w u s i n g a s c a l e o f 1 : 1 , a d e t a i l d

r a w i n g o f t h e s c r e w j a c k

h e a d .

T h e d e t a i l d r a w i n g m u s t i n c l u d e :

( i ) a t o p v i e w i n c o r p o r a t i n g t h e c o n v e n t i o n a l r e

p r e s e n t a t i o n f o r r e p e a t i n g

f i g u r e s

,

( i i ) a h a l f - s e c t i o n e d f r o n t v i e w ,

( i i i ) f u l l d i m

e n s i o n i n g i n c l u d i n g t h e u s e o f s y m b o l s w h e r e a p p r o p r i a t e .

P a r t 5 : L i f t i n g d e v i c e s – c o m m u n i c a t i o n

2 1




E X 5 . 2

A 4

Q T Y

M A T L

2 3

L I F T I N G S C R E W A

S S E M B L Y

S

C A L E

:

D r a w i n o r t h o

g o n a l p r o j e c t i o n , u s i n g a s c a l e o

f 1 : 1 , a f r o n t v i e w o f t h e

a s s e m b l e d c o

m p o n e n t s , s h o w i n g :

( i )

a f u l l - s e c t i o n o f t h e h e a d ,

( i i )

a p a r t - s e c t i o n o f t h e l i f t i n g s c r e w t o s h o

w d e t a i l s o f t h e M 1 5 x 1

M S s c r e w ,

( i i i )

i t e m i s e t h e c o m p o n e n t s a n d c o m p l e t e t h e m a t e r i a l s l i s t .

I T E M

N A M E O R D E S C R I P T I O N





P U L L E Y B L O C K A S S E M B L Y

S C A L E

1 : 1

E X 5 . 3

A 4

S h a p e a n d

s i z e d e t a i l s o f c o m p o n e n t s f r o m

a c r a n e h o o k p u l l e y

b l o c k a s s e m b

l y a r e g i v e n b e l o w i n a p i c t o r i a l d r a w

i n g . W i t h t h e c o m p o n e n t s

a s s e m b l e d ,

d r a w , i n o r t h o g o n a l p r o j e c t i o n ,

u s i n g a s c a l e o f 1 : 1 , a

f u l l - s e c t i o n e d

f r o n t v i e w o f t h e p u l l e y b l o c k a s s

e m b l y .


2 5




C R A N E H O O K

S C

A L E

1 : 1

E X 5 . 4

A 4

I n s t r u m e n t d r

a w i n g

S h a p e a n d s i z

e d e t a i l s o f a c r a n e h o o k a r e g i v e n

b e l o w i n a d e t a i l d r a w i n g

a n d a p i c t o r i a

l d r a w i n g . D r a w , i n o r t h o g o n a l p r o

j e c t i o n , u s i n g a s c a l e o f

1 : 1 , a f r o n t v i e w o f t h e c r a n e h o o k , w i t h t h e t o p

p e e n e d o v e r a s s h o w n

i n t h e d e t a i l d r a w i n g . S h o w f u l l c o n s t r u c t i o n f o r c e

n t r e s a n d c o n t a c t p o i n t s .


2 7




S U P P O R T I N G S C R E W A

S S E M B L Y

D I S T E D S T U D E N T

S C A L E 1 : 1

E X 5 . 5

A 4

1

S C R

E W J

A C K V E E H E A D

1

C I

2

M 1 0

X 2 H E X L O C K N U T

1

M S

3

M 1 0

X 2 H E X B O L T

1

M S

4

S P I N D L E Ø 4 0 X 6 S Q T H R E A D

1

M S

4 3 2 1

P a r t 5 : L i f t i n g d

e v i c e s – c o m m u n i c a t i o n

2 9



Arial Arial bold


Progress check

During this part you practised freehand sketching and CAD/instrument

drawing using the AS 1100 standards and were introduced to some new

techniques including the standard representation of repeated features and

parts.






D i s a g r e e

U n c e r t a i n


• communication

– Australian Standard AS 1100

– sectioning of orthogonal views

– orthogonal assembly drawings.

I have learnt to:

• produce orthogonal drawings applying appropriate

– australian standard (AS 1100) –computer graphics/computer assisted drawings.

• apply dimensions to AS 1100.



During the next part you will investigate some lifting devices in order to

write your engineering report.



Arial Arial bold



Exercises 5.1 to 5.5 Name: _______________________________

Check!

Have you have completed the following exercises?

❐ Exercise 5.1

❐ Exercise 5.2

❐ Exercise 5.3

❐ Exercise 5.4

❐ Exercise 5.5

Locate and complete any outstanding exercises then attach your responses to this sheet.


School/Centre (DEC) you will need to return the exercise sheet and your


If you study Stage 6 Engineering Studies through the OTEN Open

Learning Program (OLP) refer to the Learner’s Guide to determine which

exercises you need to return to your teacher along with the Mark Record

Slip.



Lifting devices

Part 6: Lifting devices –engineering report



Part 6: Lifting devices – engineering report 1

Part 6 contents

Introduction..........................................................................................2

What will you learn?...................................................................2

Engineering reports............................................................................3

Sample engineering report................................................................9

Exercise .............................................................................................19

Progress check .................................................................................21

Exercise cover sheet........................................................................23

Bibliography.......................................................................................25

Module evaluation ............................................................................27




Engineering reports

Engineering requires compromise. There are always conflicting criteria

and specifications. The design engineer must evaluate and select. Any

design can only be judged as the best solution based on the set criteria. If

the criteria change, so might the best solution change.

What is the best car?

The best car might be:

• the most fuel efficient

• the easiest to manufacture

• the most recyclable

• the fastest

• the one with the most powerful motor

• the best colour

• the most reliable

• the safest

• the most versatile

• the car with the most accessories.

The answer to this question depends entirely on what criteria you select

to base the evaluation.

The list seems endless. If you select more than one criteria to base your

evaluation, the best might be decided on what weight you give to the

criteria. Recyclability might be given a weighting twice that of best

colour.

It is important to remember that an engineering report will be based on

the authors analysis of the collected data, not on a personal opinion. For

instance, to find the best colour, the author would need to carry out

research and collect data, such as sales figures over the past year and a

public survey. The author would report on the data collected, not on

their favourite colour!



4 Lifting devices

Researching an engineering report

You will need to demonstrate in your report that you have used many

types of sources to research information for your report. Include Internet

sites as well as CD ROM journals, phone interviews or industry visitswhere possible, books and the encyclopaedia.

All the references should be listed at the back of the report under the

heading references. Source information should be cited on the relevant

pages in the report where you have used the source.

The engineering report sections

The engineering report should be written under the following headings:• title

• abstract

• introduction

• analysis

• result summary

• conclusions

• acknowledgments

• bibliography

• appendices.

Title page

The title page gives the title of the report, identifies its writer or writers

and the date when the report was completed. You might add a drawing

of the object on the title page.

Abstract

The abstract is a very concise summary of the report. The purpose of the

abstract is to allow a reader to decide if the report contains information

about which they are researching.

The abstract should be no more than two or three paragraphs of text, and

shorter if possible. It should cover the scope of the report (what it is

about), and the approach or approaches used to complete the analysis

(how the information was assembled).



6 Lifting devices

Result summary

This section presents the results concisely (the details can be set out in an

appendix). The results will be used as the basis for your conclusions and

recommendations.

This section should also note any limitations on the results obtained. For

example, if you conduct an experiment to find out the average

temperature in your home, you might measure the temperature every

hour for three days in succession, and then calculate the average. In the

results section, when stating the average temperature for your home, you

should also point out that the figure might be different at other times of

the year due to seasonal variations.

Conclusions

This section requires the writer to draw conclusions based on data

collected. If the purpose of the report was to ‘select the best…..’, then the

selection is now stated and the reason for the selection is explained.

Remember the ‘best’ jack will be determined based on the criteria you

have set to evaluate each jack.

Acknowledgments

The acknowledgment section provides the opportunity to acknowledge,

or thank, other people who have contributed to the completion of thereport. For example, a local mechanic may have demonstrated their

hydraulic jack. While the mechanic may not have helped you directly

with the calculations, without their contribution the investigation would

not have been possible. Hence an acknowledgement would be

appropriate.

Bibliography

This section is most critical for two reasons. Firstly you must

demonstrate that the report is well researched. This can be demonstrated

by including references to the most important sources of informationrelevant to the investigation.

Secondly, it is important to acknowledge the various sources of

information you have used.

Sometimes we think it is cheating to use other people's work. This is not

true. If we did not use other peoples work, and did everything ourselves

from scratch, we would never progress very far. Real progress is made by

building on the work of others.




If you use someone else's work you must reference the fact accordingly.

This is the literal basis for 're-search' : to re-find a result that someone

else discovered. If you use someone else's work without referencing the

fact, you are implicitly claiming it to be your own. This is "cheating", or

as it is more usually called, 'plagiarism'.

The Harvard system is a standard academic method of referencing. A

sample of how to reference this way is given in the following section.

Follow this technique accurately.

Higgins, R.A 1977, Properties of Engineering Materials, Edward

Arnold, Sydney.

Standards for bibliography entries must follow the strict guidelines. All

references must be included.

Appendices

This section contains information that has been separated from the main

body of the report because it is not essential that every reader look at this

information. It is information that enhances the other data. An example

would be engineering drawings of the appliances being compared. The

overall dimensions of the product may not have been part of the report,

but some readers may need this specific information. During the

engineering course this section will always contain a technical drawing

and will often contain pamphlets collected from organisations and

Internet page copies.

As this is the last part of this module you should demonstrate all the

skills you have gained to produce the best possible report.



8 Lifting devices



Lifting devices

Title: Efficiency of lifting jacks

Author/s: Jack Advantage

Date: June 2000

Abstract: This report analyses two different types of lifting jacks, a

caliper screw jack and a hydraulic jack, and compares

their relative efficiency.

Introduction

Car jacks are used to raise the wheels of a vehicle off the ground.

This report analyses two different types of car jack by comparing their

efficiency to lift the front section of a medium sized utility. The

research involved estimating the mechanical advantage and velocity

ratio of both jacks and then using this data to estimate the efficiency

of each device as a percentage. This allowed an objective assessment

to be made regarding the most efficient device.

The jacks analysed are a caliper screw jack and a hydraulic jack.

Details of both of these are shown in the Appendices.

Analysis

The calculations for this report are based on estimating the load lifted

by the jacks and then establishing the Velocity Ratio and Mechanical

Advantage of the two jacks when lifting this load. Once this has been

calculated, the formula for efficiency can be used to make acomparison between the two jacks:

Efficiency = Mechanical Advantage

Velocity Ratio

The load lifted by the jacks is an estimation based on the mass given

under the bonnet of the car on the compliance plate. This is shown as

2350 kg on the vehicle used in this research which was a Toyota Hilux

four wheel drive. The load lifted by the jacks has to be estimated

because the centre of gravity of the utility will be towards the front of the vehicle due to the effect of the motor which is nearer to the front.



As shown below in Figure 6.1 the centre of gravity of the vehicle is

estimated to be 1metre from the centre of the front wheels.

1

2.8

c of g

Figure 6.1 The vehicle and the estimated position of the centre of

gravity

Once the centre of gravity is estimated, a sum of the moments can be

taken about the rear wheels to establish the load lifted by the jacks.

The Mechanical Advantage and the Velocity Ratio can be determined

using the following formulae:

Mechanical Advantage = Load(Newtons) / Effort (Newtons)

Velocity Ratio = Distance moved by Effort / Distance

moved by Load

The approach taken to compare a caliper screw jack to a hydraulic

jack can be summarised as follows:

• establish a common load to be lifted by the jacks

• lift the load by the same distance for both jacks

• establish the mechanical advantage and velocity ratio for both

jacks under the same conditions

• calculate the efficiency of the two jacks.



Caliper screw jack

The caliper screw jack, shown below in figure 6.2, is based on the

principle of a screw thread. As the handle of the jack is turned the

threaded shaft in the centre rotates to bring together the two arms of the jack causing the top to rise and therefore the load to lift. The

turning crank used on the caliper jack is shown in figure 6.3, it has an

offset handle as shown of 140 millimetres giving a turning diameter of

280 millimetres. This adds a lever advantage to this jack. An

orthogonal drawing showing the Front View of a caliper screw jack is

given in the Appendix, figure 6.10.

Figure 6.2 Caliper screw jack

1 4 0 m m

Figure 6.3 The turning crank for the caliper screw jack showing the

turning radius of 140 mm

2.5 mm pitch

Figure 6.4 Details of the square thread on the caliper jack showing a pitch of2.5mm



The hydraulic jack shown below in figure 6.5 is based on the principle

that fluid is incompressible. As the lever is depressed the piston on

the right hand side forces hydraulic fluid through a valve to lift the

ram which causes the load to lift. A sketch showing the operation of a

hydraulic jack is given in figure 6.6.

Figure 6.5 Hydraulic jack

Ram (load)Piston (effort)

Figure 6.6 Schematic diagram of a hydraulic jack

The effort required to lift the load supported by each jack was

calculated by using spring balances, calibrated in N. A picture of

these spring balances in use is shown in figure 6.2 and figure 6.5. The

maximum force measured by the spring balances was 50 N, this

required two spring balances to be arranged in parallel. A reading of

90 N (2 x 45 N) was obtained.



Calculations

Establishing the load lifted by the jacks:

Data

Distance between the axles = 2.8 metres

Mass of the utility = 2350 kgs

If it is assumed that the centre of gravity of the utility is 1 metre from

the front axle, due to the fact that the motor is towards the front, theload lifted by the jacks can be calculated by taking moments about the

rear axle as follows:

23500 N

15107 N 8393 N

1 m

Figure 6.7 Freebody diagram of load lifted by jacks

Weight = m ¥ g

= 2350 ¥ 10

= 23500 N

∑MR = F ¥ d + F ¥ d

= - (23500 x 1.8) + (R F x 2.8)

R F = 15107 N

From the calculations above it is estimated that a load of 15 107

Newtons will be lifted by each jack when it is placed in the position

shown below in figure 6.8.



Figure 6.8 A jack in position lifting the load calculated above

From figure 6.3 it can be seen that the radius of the handle used on the

caliper screw jack is 140 mm. The diameter is thus 280 mm. This

means that the distance moved by the effort is D or the

circumference of the circle the effort will travel in as the jack is

raised. When the thread on the jack is rotated one revolution the

caliper jack shown in figure 6.2 rises 2.5 mm, this is the distance or

lead the thread moves through one revolution of the handle, which is

also equal to the pitch of the thread.

Using the information given above the Velocity Ratio and Mechanical

Advantage and efficiency of a caliper screw jack can be calculated as

follows:

Velocity Ratio = Distance moved by Effort/Distance moved by Load

= D / 2.5 (millimetres)

= x 280 / 2.5

Mechanical Advantage = 351.8

= Load / Effort

= 167.8

Efficiency = Mechanical advantage / Velocity ratio

= 168 / 352

= 47.7 %



Hydraulic jack

The Velocity Ratio of the hydraulic jack needs to be calculated in a

different way to the caliper screw jack as it works on a different

principle. The basic features of the hydraulic jack can be seen infigure 6.6. As the piston on the hydraulic jack is depressed the ram

will move upwards so that the volume of the piston (effort) which is

pushed into the oil must equal the volume of the ram (load) that is

displaced by the oil as it moves upwards, therefore (d2/4)h =

(D2/4)H. Where d= the diameter of the piston, h = distance moved

by the piston and D = the diameter of the ram, H = the distance moved

by the ram.

Therefore:

Velocity ratio = Distance moved by Effort/Distance moved by Load

h / H = (D2/4) / (d

2/4)

= D2/d

2

For the hydraulic jack therefore:

Velocity Ratio = D2

of the ram / d2

of the piston

= 502/ 10

2

= 2500 / 100

= 25

Applied force50 N

Reaction force

560 mm

Apivot

40 mm

Figure 6.9 Freebody diagram of lever forces in the hydraulic jack handle



The force applied to the lever of the jack was found to be 50 Newtons.

The Mechanical Advantage gained by the hydraulic jack occurs in two

stages. Firstly the lever has a mechanical advantage that is applied to

the piston and secondly the hydraulic system creates an M.A. betweenthe piston and the ram of the jack. The effort that is applied by the

lever to the piston can be calculated by taking moments about point A

in figure 6.9, as follows

∑MA = (F ¥ d) + (F ¥ d)

= (F ¥ 0.04) – (50 ¥ 0.56)

F = 28 / 0.04

= 700 N

Mechanical Advantage = Load / Effort

= 15107 / 700

= 21.58

Efficiency = Mechanical Advantage / Velocity Ratio

= 21.58 / 25 ¥ 100

= 86%

Result summary

From the calculations above it can be seen that the caliper screw jack

has an estimated efficiency of 48% whereas for the hydraulic jack it is

86%.

Conclusions

This report on the efficiency of a caliper screw jack as compared to a

hydraulic jack indicates that the hydraulic jack is clearly the most

efficient by a margin of 38%. Therefore, in any situation where

efficiency is required a hydraulic jack should be used.

There are some disadvantages however in that a hydraulic jack ismore expensive than a caliper screw jack and usually heavier due to

the more robust construction and the hydraulic fluid used to operate it.



Also, the caliper screw jack can be compressed into a smaller space

when it is wound in compared to the hydraulic jack allowing it to take

up a relatively smaller space.

In conclusion then, whilst the hydraulic jack is more efficient there are

other factors which may make the caliper jack more suitable in

situations where a lighter load needs to be lifted and space is critical.

The caliper screw jack may be the better choice for example, as an

accessory for a car where it is mainly used when changing tyres.

Glossary

centre of gravity a term used to describe the point

that is the centre for the mass of an object

compliance plate metal plate under the bonnet

indicating details such as the mass

of a vehicle

hydraulic Operated by or employing water

or other fluid

ram the piston that lifts on a hydraulic

jack

Bibliography

Holden, R. 1991, A Guide to Engineering Mechanics,

Science Press, Sydney.

Schlenker, B. McKern, D. 1976, Introduction to Engineering Mechanics,

John Wiley & Sons, Sydney.

<www.motojacks.com/>

<www.bobstools.com/prd0129.htm>

<www.sktoolstore.com/astro/500fc.html>

<www.autoramps.com>

<www.ralmikes.com.catalog/temp_top_right.cfm?Familyid=mv46sj2000>



Appendices

Figure 6.10 Caliper Jack

Handle lever

Ram

Piston

Fluid gates

Reservoir

Figure 6.11 Hydraulic Jack




Exercise

You have read the sample engineering report comparing the efficiency of

two different types of lifting devices. It is now time to begin your

engineering report.

In the sample report, efficiency was the only criteria on which the jacks

were compared. There are numerous qualities that could be used for a

comparison. For instance, you could compare two jacks to find the best

jack for off road conditions. You might therefore include in your criteria

evaluation:

• the initial cost

• the weight

• the reliability

• the maximum height of the lift

• maintenance requirements.

The more criteria you add to your evaluation, the more complex the

analysis becomes. In addition, not all criteria are likely to be of the same

importance. The criteria are therefore weighted on their importance.

The height of the possible lift might be twice as important as

maintenance. A table of the criteria should be created and a score

recorded for each jack in each criteria. The weighting for the criteria is

then calculated. The score for each jack in each criteria is then totalled,

determining the best jack. In the conclusion the author should note how

the criteria and the weighting of criteria would influence the result.

Exercise 6.1

Write an engineering report that compares two lifting devices. The lifting

devices should perform a similar task but use different techniques to

achieve the result. You should compare the devices based on three criteria

that you determine are the most important characteristics/requirements of

the devices. Use a weighting system for the criteria. The results should

show clear evidence of the research completed by the author. Data might

be collected, depending on the criteria, using calculations, surveys,

experimentation and text information.




Progress check

During this part you have examined the structure and format of a typical

engineering report.






D i s a g r e e

U n c e r t a i n

I have learnt about

• engineering report writing.

I have learnt to

• research information

• complete an engineering report based on the analysisand synthesis of information using software andcomputer assisted drawing where appropriate.



Congratulations! You have completed the module on Lifting devices.



22 Part 6: Engineering report for lifting devices



24 Part 6: Engineering report for lifting devices



25

Bibliography

Avner, S.A. 1974, Introduction to Physical Metallurgy , McGraw-Hill,Singapore.

BHP Steel, http://www.ezysteel.com

Board of Studies, 1999, Stage 6 Engineering Stuidies Examination, Assessment

and Reporting , Board of Studies NSW, Sydney.Board of Studies, 1999, Stage 6 Engineering Stuidies Support Document ,

Board of Studies NSW, Sydney.

Board of Studies, 1999, Stage 6 Engineering Stuidies Syllabus ,Board of Studies NSW, Sydney.

Eide, Jenison, Marshaw & Northup, 1998, Introduction to Engineering Design n,McGaw Hill, United States.

Crane (machine), http://encarta.msn.com, Encarta Encyclopeadia Article Titled‘Crane (machine)’

Davis, Troxell, Wiskocil 1964, The Testing and Inspection of Engineering Materials , McGraw-Hill, Tokyo.

DeGarmo, E.P. 1966, Materials and Processes in Manufacturing , Macmillan,New York.

Die Casting in Australia, http://www.diecasting.asn.au/about.html

Drop Forging, http://bdl-mc.qc.ca/processes/mprg/drop_forging.html

General Floor Jacks, http://www.hyjacks.com

Guy, A.G. 1972, Introduction to Materials Science , McGraw-Hill,

Tokyo.Harding, D.W, and Griffiths, L 1970, Materials, Longman,

London.

Hiab Cranes, http://www.redaustralia.com

Higgins, R.A 1987, Materials for the Engineering Technician , Edward Arnold,London.

John, V.B. 1985, Introduction to Engineering Materials , MacMillan,London.

Manufacturing, http://www.wichard-usa.com/manufacture.html



26

National Centre for Excellence in Metalworking Technology, Material Standardsfor Powder Metallurgy Alloys, http://www.ncemt.ctc.com

Otis Elevator Company, http://www.otis.com.html

Otis Elevator Company, Student Information, Otis Pty Ltd,Minto, NSW.

Rochford, J. 1999, Engineering Studies – A Student’s Workbook , K.J.S.Publications, Gosford.

Schlenker, B.R. 1974, Introduction to Materials Science, Wiley, Sydney.

Teaching Resources, 1981, Cranes, lift, loft and slew, Division of Services NSWDepartment of Education

The Correspondence School, 1993, Engineering Science – 2 Unit Cours e,Learning Materials Production Centre, Redfern

Van Vlack, L.H. 1973, A Textbook of Materials Technology , Addison-Wesley,Massachusetts.

Hibbler, R C. 1989, Engineering Mechanics – Statics , Macmillan,Sydney.

Holden, R. 1991, A Guide to Engineering Mechanics , Science Press,Sydney.

Mullins, R K. 1983, Engineering Mechanics , Longman Cheshire, UnitedKingdom.

Rochford, J. 2000, Engineering Studies – Student’s Handbook , KJSPublications, Gosford.

Schlenker, B. McKern, D. 1976, Introduction to Engineering Mechanics , JohnWiley & Sons, Sydney.

Schlenker, B. McKern, D. 1983, Introduction to Engineering Mechanics ,Jacaranda Press, Sydney.

Taylor, A. Barry, O. 1975, Fundamentals of Engineering Mechanics , Cheshire,

Wolf, L. 1990, Statistics and Strength of Materials: a parallel approach to understanding structures , Merrill, New York.

Otis Elevator Company, Otis student package.

http://www.ph.unimelb.edu.au/lecdem/fa1.htm

www.howstuffworks.com (enter ‘hydraulic crane’ into search box)

http://www.sasked.gov.sk.ca/docs/physics/u6c3phy.html

www.motojacks.com

www.bobstools.com/prd0129.htm

www.sktoolstore.com/astro/500fc.html

www.autoramps.com

www.ralmikes.com.catalog/temp_top_right.cfm?Familyid=mv46sj2000



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