talon garikayi c056634k-work related learning report for simbi plantwith cover page

CHINHOYI UNIVERSITY OF TECHNOLOGY

FACULTY OF ENGINEERING

DEPARTMENT OF MECHATRONICS ENGINEERING

ATTACHMENT REPORT

FOR

TALON GARIKAYITALON GARIKAYI

REG NO: CO56634K

AT

S.I.M.B.I. PVT. LTD

(STEELMAKERS ZIM PVT LTD GROUP OF COMPANIES) MASVINGO BRANCH

________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

1

TITLE: A WORK RELATED LEARNING REPORT AT STEELMAKERS (PVT)

LTD –SPONGE IRON PRODUCTION DIVISION (SIMBI BRANCH) BY TALON

GARIKAYI (C056634K).

A REPORT SUBMITTED IN PARTIAL FULFILMENT OF THE

REQUIREMENTS OF A BACHELOR OF ENGINEERING HONOURS DEGREE

IN MECHATRONIC ENGINEERING TO THE DEPARTMENT OF

MECHATRONIC ENGINEERING, CHINHOYI UNIVERSITY OF

TECHNOLOGY UNIVERSITY (2008).

__________________________________

INDUSTRIAL SUPERVISOR’S SIGNATURE

MR I. MUCHIMWE

GROUP INSTRUMENTS ENGINEER


2

CONTENTS PAGECONTENTS PAGEContents PagesAcknowledgements iSummary of report iiJob offer letter iiiLetter of recommendation iv

Chapter One1.1 Introduction 11.2 Plant Operations 2

Chapter Two2.0 Instrumentation and Control department 52.1Introduction and objectives of the department 52.2 SCADA and Automation as applied to Sponge Iron Production 82.3 The Drive overview 122.4 The VersaMax PLC 132.5 Inputs and Outputs signals of the PLC 172.6 CPU Details 182.7 The Communication protocol 22

Chapter Three3.0 The Control Phylosophy 293.1 PLC Programming 303.2 Plant Control loop drawings 363.3 The transformer Theory 373.4 Variable Speed Drives 393.5 General structure of a Drive 433.6 Programming a Drive 46

Chapter Four4.0 Activities and tasks Carried out in the Instruments department 484.1 Thermocouple movements 484.2 Cleaning Slip Rings 504.3 Cleaning Belt Conveyor Tail pulley Sensor-ZSS 504.4 Replacing a ZSS 514.5 Cleaning weighfeeders 514.6 Calibration of Weighfeeders 52

Chapter Five5.0Field Instruments 535.1 Kayblower 545.2 Air Compressor 545.3 Schematic representation of valves 565.4 Pressure regulator 565.5 Uninterrupted Power Supply 585.6 Kiln main Drive 585.7VFD Parameter setting 59


3

5.8 Weighfeeder Controller 60

Chapter Six

6.0 Sensors 626.1 Water level sensor 636.2 Water flow sensor 646.3 Zero Speed Sensor 656.4 Gate Valve-Actuator 656.5 Thermocouples 666.6 Temperature Transmitter 676.7 Pressure Transmitter 706.8 Weighfeeder control loop 756.9 Junction Boxes and Weighbridge 77

Chapter Seven

7.1 Information and Technology 80

Chapter Eight

8.0 Telecommunication System 82

Chapter Nine

9.1 Workshop Practices and Processes 849.2 Machining Operations 869.3 Basic machining processes 889.4 Other Types of machining operations 889.5 The Centre Lathe Machine 899.6 The Cutting Tool 909.7 The Cutting Conditions 919.8 The Cutting Fluid 929.9 Turning, Milling and Grinding 95

Chapter Ten

10.0 Maintenance Work at the Mechanical Engineering Dept. 11410.1 Conveyors 11510.2 The Rotary Kiln Section 11610.3 The Rotary Cooler Section 11710.4 Wet Scrapper Section 11810.5 Gearboxes 11910.6 Water Pumps 12010.7 The Crusher 12110.8 Electric Motors 121

Chapter Eleven________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

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11.0 Screen maintenance 12211.1 Double Pendulum Valves (DPV) 12211.2 Welding Process 12311.3 Oxy-Acetylene Welding 12411.4 Acetylene Cylinders 12611.5 Oxygen Cylinders 12611.6 Gas Welding 12711.7 Manual Metal Arc Welding 127

Chapter Twelve

12.0 Introduction to Electrical Engineering Department 12812.1 Safety precautions 13112.2 The 33KV/11KV and 11KV/415V 13112.3 The Motor Control Center 133

Chapter Thirteen:

12.0 Recommendations to the Company 14312.1 Recommendations to the University 144

Chapter Fourteen: Conclusion 145APPENDIX 146


5

Summary of report

The Bachelor of Engineering Honours Degree in Mechatronic Engineering is a four

and half year full-time programme. The programme focuses on Mechanical

Engineering, Electronics, Control Engineering and Computer Science. The

programme also links Applied Science with entrepreneurship. This Degree

programme was new to most industries, thus most companies were not comfortable to

engage us, as they believe it will take months to come up with a training programme.

I did my Attachment at two different locations i.e. the branches of Steelmakers

Zimbabwe. I did my Workshop practices and processes at Steelmakers Kwekwe

branch and finally plant maintenance at Steelmakers (SIMBI)-Sponge Iron Division

in Masvingo as part of Mechanical Engineering Internship.

After finishing Mechanical Engineering training programme I was attached to the

Information and Technology (IT) Department at Kwekwe HQ for four weeks

where I was taught Networking, Programming (C, C++ and Visual basic

programming), hardware and software engineering this improved my computer skills.

As soon as I finished IT I was transferred to SIMBI-Masvingo for my Electrical and

Electronics Engineering internship where I was trained on substation installation,

general plant electrical maintenance and, AC and DC motor installation as D.O.L

motors.

Later on I joined the Instrumentation and Control Engineering Department,

where I was trained on SCADA, PLC, sensors, controllers, transmitters, engineering

design and innovation, telecommunication system and ladder logic programming. It

is during this period I managed to a greater extent prove to the Company Directors

that Mechatronics is a total engineering package for all engineering problems and that

a Mechatronic Engineer is a must at any Automated Industry. I displayed a broader

knowledge base in Mechanical and Control Engineering such that I was promoted to a

Technician Level with all company benefits, the position I still hold.

To a greater extent this report covers all areas that I was trained on.

CHAPTER 1________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

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1.1 Introduction

SIMBI is an acronym, which stands for Sponge Iron Mining Beneficiation Industry

and is a subsidiary of Steel makers Group of companies. It is located in Westview

industrial site in Masvingo along Bulawayo road. SIMBI is currently the only

company in the country involved in the production of SPONGE IRON which is a

metallic product formed when iron ore is directly reduced below the melting point of

iron. The iron ore pellets are reduced directly in the solid state without the material

changing its physical state. SIMBI is capable of producing 100 tones per day of

sponge iron.

The organization is headed by the Managing director who currently resides in Kenya.

On the local scene the top official is the GGM-Group General Manager.

In essence we are a part of the process industry because our final product is used as a

raw material in the fabrication industry for instance where sponge iron is mixed with

various materials to make steel and other alloys.

1.2 Plant Operation

1.2.2 Process overview

The raw materials in sponge iron manufacture are coal, iron ore and limestone. The

coal is a reducing agent and also heats up the raw materials.

Limestone is for desulphurization i.e.: it acts as a fluxing agent.

Iron ore is the main raw material for the production of sponge iron.

These raw materials are conveyed to the SCREEN HOUSE by means of two conveyor

belts. Each of the conveyor belts is driven by electric motors. Proximity sensors are

mounted to monitor the movement of each belt.

At the screen house the raw materials are screened, oversized coal particles are

conveyed back to the CRUSHER where they are crushed to desirable sizes. Fine coal is

conveyed to the INJECTION HUSE where it is used to Aid ignition in the kiln.


7

Fine coal is discarded from the process because there is a danger of fusion at high

temperatures which causes ACCREATIONS in the kiln.

Limestone is fed into the system using the same belt of that of iron ore.

Recommended Particle Size

Feed coal 3mm to 15mm

Injection coal Less than 3mm

Iron ore 5mm to 18mm

Limestone 1mm to4mm

1.2.3 Storage Bins

Raw materials are later stored in storage bins from the raw material section. This

enables a continuous supply of raw materials since the rate of consumption in the kiln

is not the same with the rate of which the raw material are supplied. There are four

different storage bins, which are

Feed coal bin

Charcoal bin

Iron ore bin

Limestone bin

At the storage bin there are weigh feeders for feed-coal, iron and charcoal and one

volumetric feeder for limestone. The weigh-feeders are used to control the tonnage

per hour fed into the kiln using the principle of load cells and the tachometer to

measure the speed of the belt using the formula below.

WEIGHT = LOAD CELL VALUE X SPEED OF BELT

1.2.4 Kiln Section


8

The Kiln is the heart of the plant and is the site of all chemical reactions involving

sponge iron manufacture. The Kiln is 42m and has an internal shell of 2,6m diameter

and external diameter of 3,0m.The kiln in inclined at 15º to facilitate movement. The

retention time is the time taken to flow the material from the feed to the discharge

end. The lining of the kiln is of refractory thickness 250mm. At the various sections

of the kiln are thermocouples to measure the temperatures in the kiln.

The kiln is divided into two zones, which are the pre-heating zone and the reduction

zone.

(a) Preheating Zone

Raw materials are heated using fee gases to the reaction temperatures and several

reactions take pace such as drying of iron ore and coal.

Free gases heat raw materials to a reaction temperature which result in:

Calcinations because of limestone / dolomite.

Drying of Iron ore and Coal.

Release of volatile matter from coal.

(b) Reduction Zone

As temperatures of the charge exceed the carbon gasification of the boundary reaction

becomes available for the reduction reactions. Temperatures of the order 900 to 1000

degrees are maintained in the kiln.

The reaction:

3Fe2O (s) + CO(g) 2Fe3 O4(s) + Co 2(g)

Fe3 O4(s) + CO(g) 3FeO(s) + CO2(g)

FeO(s) + CO(g) Fe(s) + CO2(g)

1.2.5 Cooler section


9

The kiln discharge temperature is around 900-1000. The discharge should be cooled

down to 150-200 degrees before being discharged hence the need for cooler.

The cooler section consists of a steel cylinder of 2.2m diameter and length 12.262m

and rotates at 4rpm. The cooler shell is cooled by circulating cold water around it.

The product is not cooled directly because it can easily reoxidise when it gets in

contact with water.

1.2.6 Product section

The product is transported via a conveyer belt to the intermediate bin where it is

blended (when necessary) with older stock. The product is then sent to the product

house via another belt. In the product house there are magnetic separators which

separate the product into four types:

+ 4mm magnetic Direct reduced Iron

+ 4mm nonmagnetic Charcoal

- 4mm magnetic Direct reduced iron fines

- 4mm non-magnetic Ash

These materials are collected in four different bins and are sent to different markets

around the region.


10

STOCK PILE 1LIMESTONE

STOCK PILE 2IRON ORE

STOCK PILE 3 COAL SHADE

GROUND HOOPERVIBRO FEEDER 1 VIBRO FEEDER 2

DUST EXTRACTOR

CHAPTER 2

2.0Instrumentation and Control Engineering Department

2.1Introduction

This Department is headed by Mr. I. Muchimwe a well known Instruments and

Control Engineer in Masvingo and the Low-veld area of Chiredzi and Triangle. There


11

CONE CRUSHER IMPACTOR

PRIMARY SCREEN

SECONDARY SCREEN

DOUBLE DECKSCREEN

LIMESTONE HOOPER

CHAR BIN LIMESTONE BIN IRON ORE BIN FEED COAL BIN

STOCK HOUSE

WEIGHFEEDERS AND LIMESTONE-VOLUMETRICFEEDER

INJECTIONCOAL BIN

MAGNET

ROTARY KILN

ROTARY COOLER

PRODUCT HOUSEPRODUCT HOUSE

COARSE FRACTION

FINE FRACTION

MAGNETIC SEPERATOR

MAGNETIC SEPERATOR

LUMP SPONGE IRON BIN

COARSE NON-MAGNETIC

FINE SPONGE IRON BIN

FINE NON- MAGNETIC

DOUBLE DECK SCREEN

DCSABCSTACK

ELBOW DUCT GCT

ESP

CHIMNEY

I-FAN

CAP

I-BIN

DUST EXT

are 3 Technicians and six Assistants that is for every shift there is a Technician and an

Assistant. SIMBI is a fully automated plant that uses SCADA and PLC.

Instrumentation is a collective term used to describe the equipment that is used for

measurement, control, data storage, and display of process variables such as:

temperature, pressure, pH, humidity, weight, speed, distance, level, flow, position,

conductivity, turbidity e.t.c. Instrumentation equipment can be installed in the field,

control room and marshalling rooms depending on the purpose and type of

Instrument.

Instrumentation department is there to ensure quality production of Sponge Iron and

the associated byproducts by installation and maintenance of the appropriate

measurement and control instruments in an economic, safe and efficient manner.

Instrumentation department is there to ensure quality production of Sponge Iron and

the associated byproducts by installation and maintenance of the appropriate

measurement and control instruments in an economic, safe and efficient manner.

The main objective of this report is to focus on:

Variable speed drives

PLC programming

Appreciate drive programming keypad operation.

Design a drive programme for a motor for a specified operation.

Appreciate analogue and digital I/O wiring.

Be able to read a ladder logic programme

Use ladder logic on fault finding,

PLC hardware trouble shooting

Procedures for connecting HMI to SCADA

Appreciate SCADA and associated software

Design control logic in ladder language.

Practice loading ladder logic programmes in PC.

Improve production, easy maintenance and cost effective.

Identification of the entire field instrumentation and control room

Instrumentation

The principal of operation and control loops of each instrument.

NB: PLC and AC drive programming dealt in depth at this point.


12

2.1.1Objectives/Roles of Instrumentation Department

Instrumentation department is there to ensure quality production of sponge

Iron and the associated by products by installation and maintenance of the

appropriate measurement and control instruments in an economic, safe and

efficient manner.

Ensures plant and equipment availability at all times by carrying out planned

and preventive maintenance of instruments and attending to breakdowns.

Carry out equipment calibration and checks as per planned schedules or as the

need arises so as to ensure safe and accurate measurement and control of

variables.

To ensure that equipment is user safe bay carrying out appropriate and

standard installations and checks/tests of measurement, safety and other

instrumentation

Interaction with other departments (Engineering, SHE, Administration and

Processing) to form a strong and reliable sponge ion production team.

Offer appropriate training to unskilled workforce and other trainee in order for

them to be a useful asset in the instrumentation field.

Make plans, recommendations and provisions for further plant expansion in

future.

2.1.2Safety Precautions

Next to the Kiln Slip rings for shell thermocouples, there are power rings for

shell air fans and these have very high and dangerous voltages, so extra care

must be taken not to temper around the rings. As a safety measure, any one

entering this area should have company.

Before carrying out any work on proximity, sensors make user the belt has

stopped unless carrying out level 3 maintenance (i.e. cleaning or inspection)

taking care not to interfere with the moving parts of the conveyor.________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

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Avoid putting hands or any other body parts underneath the moving machinery

of weigh feeders.

Make sure power supply is switched off before disconnecting power supply to

the transmitter and sensors. If there is need for power to the transmitter caution

must be taken not to short circuit the power cables.

AC Drives and Weigh feeder Panels have very high and dangerous voltages,

therefore no work is to be carried out on these equipment when energized. If

need arises that work ought to be carried out when energized, caution must be

taken not to interfere with the live parts.

The main kiln temperatures are very high and dangerous, thus when carrying

out thermocouple movements and QRT readings, always wear hand gloves,

apron and safety goggles.


14

2.2SCADA and Automation as applied to SIMBI

Monitoring the Plant using the SCADA

Fig 12.2.1SCADA

SCADA simply means Supervisory Control and Data Acquisition the terms refer to

large-scale distributed measurement and control system. The bulk of the site control is

actually performed automatically by a Remote Terminal Unit or PLC as for SIMBI

most of the control functions are restricted to basic plant override or supervisory level

capability. It includes all HMI controllers, I/O devices; networks and software

(Cimplicity as for SIMBI). It implements a distributed database, which contains data

elements called points.

Hard point representative of actual O&I connected to the system.

Soft point result of mathematical \operations applied to hard and soft points.

The main SCADA Screen of SIMBI Plant________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

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Fig 2

2.2.2Automation

Is the automatic processes done by machines with minimum to no human

interference.

As the name indicates, it is not a full control system, but rather focuses on the

supervisory level. As such it is a purely software package that is positioned on top of

hardware to which it is interfaced, via PLCs. The system collects data from various

sensors in the plant and then sends this data to a central computer that then manages

and controls the data. The plant control logic resides in the PLC and it does all the

logic decisions.

Roles

Aid humans


16

Increase production

Control management

Increase precision.

Characteristics

System must be safe

System must be comprehensive

System must have minimum human interference.

Improve production, easy maintenance and cost effective.

2.2.3Supervisory Control Architecture

Control engineering is the engineering discipline that focuses on the modelling of a

diverse range of dynamic systems (e.g.mechanical systems) and the design of

controlers that will cause these systems to behave in the desired manner. Although

such controllers need not be electrical many are and hence control engineering is

often viewed as a subfield of electrical engineering.


HUMANINTERVENTION

SENSOR

SYSTEMSUPERVISORYCONTROLCOMPUTER

CONTROL

DISPLAY

INTERFACE

17

Electrical circuits, digital signal processors and microcontrollers can all be used to

implement control system. Control engineering has a wide range of applications from

the flight and propulsion systems of commercial airliners to the production of sponge

iron at SIMBI.

Control engineers often utilize feedback when designingcontrol system. For example,

in temperature is continuously monitored and fed back to the system which adjusts the

motor’s speed accordingly. Where there is regular feedback, control theory can be

used to determine how the system responds to such feedback. In practically all such

systems stability is important and control theory can help ensure stability is achieved.

Although feedback is an important aspect of control engineering, control engineers

may also work on the control of systems without feedback. This is known as open

loop control. A classic example of open loop control is a temperature control at

SIMBI that use K type thermocouples on the KILN SECTION.

Other functions of SCADA are:

To generate trends and reports of the plant parameters.

To generate alarms.

To have graphical views of the whole plant.

To provide troubleshooting guides.

So many SCADA packages are currently in use throughout the world. Some of the

most common ones are:

- Wonder ware

- Cites

- Genesis

- RS View

- Cimplicity

At SIMBI, we use CIMPLICITY SCADA. It is important to note that SCADA is not a

controller but simply interfacing software between the controller and the operator’s

panel, the computer.


18

2.3The Drive

2.3.1Human Machine Interface (HMI)

Fig 4

A SCADA system includes a user interface usually controls where the individual can

interface with the SCADA system. The SCADA system communicates with PLCs

throughout the system network and processes information that is easily disseminated

by HMI

At SIMBI we use two computers the Engineering PC and the Station manager PC for

our SCADA system. Also for TUC-4 HMI for communicating with our weigh feeder

TUC-4 controller.

2.4PLC (VersaMax)

2.41Introduction


19

I was trained on how to do fault finding and appreciate the need for a controller in the

processing industry so I compiled the information in this chapter with great caution

since any wrong information could lead to a disastrous future in the control

engineering field. Most of the literature was researched after practicals with the

Instruments engineer. This was one of the most challenging topics of my attachment

since it strongly requires good background of control engineering. Emphasis was on

understanding the principle factors under industrial measurement and control.

The appearance of the PLC at SIMBI Plant

Fig 5

2.4.2Schematic representation o f the PLC


20Mains supply

Power Supply Analogy Input and Output Modules

Detachable Programming device

Digital Input and Output ModulesProcessor

CPUMemory unit

Fig 6

2.4.3General Structure of a PLC consists of the

CPU,

Output and Input modules,

Power supply

Detachable programming device

Expansion transmitter modules

The GE Fanuc* PLC system consist of Ethernet based control processing unit and

total programming for monitoring and controlling the various equipment pertaining to

the plant.

A PLC is a microcomputer based controller that uses stored instructions in

programmable memory to implement logic, sequencing, timing, counting and

arithmetic functions through digital or analogue I/O module for controlling machines

and processes.

The microprocessor is used for automatic distribution of real world process but

designed for an extended temperature ranges dirty or dusty conditions. It is immune to

electrical noise, mechanically more rugged and resistant to vibrations.

2.4.4 Processor

It is the CPU of the programmable controller. It executes the various logic and

sequencing functions by operating on the PLC inputs to determine the appropriate

output signals. It consists of one or more microprocessors designed to facilitate I/O

transmissions. The GE Fanuc* PLC like all PLCs, it has inbuilt facilities like timers

counters, PID loops and parameters like memory bits registers, global bits, temporary


21

bits, and system bits that can be configured as per plant requirements through

programming software for the better monitoring and control of the plant.

The VersaMax solution is a single control product that may be used as I/O, as a PLC,

and/or as distributed control for up to 256 I/O points. With its modular and scaleable

architecture, intuitive features and ease of use, it saves initial costs for machine

builders and life-cycle costs for end users. VersaMax provides reliability and

increased uptime because of its Six Sigma design, intuitive diagnostics, and hot I/O

module insertion. Its broad family offers 34 different I/O modules, powerful PLC

CPU, open networking, and multiple wiring options. Its combination of feature-rich

I/O and powerful CPU provides the performance to meet any industry need

2.4.5 Memory unit

It is connected to the CPU; it contains the programs of logic sequencing and I/O

operations. It also holds data files associated with these programs including I/O status

bits, counter and timer constants, other variables and parameter values. This memory

unit is referred to as the user or application memory because it s contents are entered

by the user. In addition the processor has a system that directs the execution of the

control program and coordinates I/O operations. The contents of the system memory

are entered by the manufacturer and cannot be accessed or altered by the user.

2.4.6 Power supply

A power supply of typically 120VAC is used to drive the PLC some 230VAC .It

converts AC to DC of 5V. It often includes a battery back up that switches on

automatically in he event of an external power source failure. At SIMBI a UPS is

connected in series and there is a 230AC transformer of equal voltage on Primary and

Secondary winding responsible for smoothening the 230ACV. A number of breakers

are installed in the PLC panel for different inputs. These are:

Transformer

PC


22

Digital output signals

Digital input signals

Analogue signals

NB: swichedmode power supply units are the ones in use.

2.4.7 Input/ Output Module

Provides the connectors to the backplane and process that is to be controlled. Inputs to

the controllers are signals from he sensors and other ON/OFF devices. Outputs from

the controller are ON/OFF signals to operate actuators and other devices required to

activate. Many PLCs are capable of accepting continuous signals from analogue

sensors and operate signals suitable for actuators.

2.4.8 Programming device

The PLC is programmed by means of a special programming device. It is detachable

from he PLC cabinet so that it can be shared among the controllers. A PC (as for

SIMBI) can be used, but usually remain connected to serve a process monitoring or

supervision functions related to the process.

2.4.9 Expansion transmitter modules

These modules are responsible for communication between the processor and the

input/output modules. There is a main ETM and is the one responsible for direct

communication and the rest of the ERMs behave as parasites.

2.5.0 Inputs and Output Signals

Digital Inputs

These are real discrete inputs from the field e.g. limit switches, level switches, flow

switches, push buttons, and contactors, overload relays.

Digital input modules are configured to accept these inputs, which are connected to

the same power supply from the CPU.________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

23

The switching mode for digital inputs can either be source mode or sink mode and are

activated on by either a 24 VDC, 110 VAC at 220VAC. The most common are the

source mode, which has a switching signal at the (+) positive.

For sink mode, the switching mode is (-) negative; therefore, the PLC will sink

(switching a mental OV). At SIMBI there are 32 input modules with a 24 VDC

switching voltage (source mode).

2.5.1 Digital Output

Give out a voltage usually 24 VDC to field devices such as relays, contractors,

transistors depending on the type of PLC. Usually the output is a low current, which is

used to switch a higher current.

2.5.2 Analog Output

Gives output commands to field devices such as control valves, transistors, indicators

etc. The signal current operates the current to pneumatic converter.

2.5.3Analogy Inputs

Receives signals from real world analog transducers and transmitters. Most common

type of inputs are: 0 – 20mA; 0,-5V; 0,-10V; 1 – 5V, 1 – 10V and 4 – 20mA. At

SIMBI, the most widely used analog input is the 4 – 20 mA.

Input module/card

Source voltage


24

24VDC

TRANSMITER

+-CH1

+- CH2

+- CH3

+- CHn

Fig 7

NB: The wiring of digital inputs is different from that of analogue inputs. If the 4 – 20

mA is coming from a transmitter, a power supply, in our case, of 24VDC is required.

2.6The CPU (Details)

The CPU at SIMBI is as shown below.

ETM – Expansion Transmitter Module µp-processor

The VersaMax's powerful processor with 12K of memory for application programs,

floating point math, real-time clock, subroutines, PID, Flash memory, and bumpless

run mode provides a powerhouse of versatility in a small package. It includes

automatic I/O addressing - extensive diagnostics with an internal fault table and LEDs

that indicate system faults and I/O forces - freeing up the operator to concentrate on

maintaining the highest quality

The Input and Output modules are connected onto a Backplane; the general structure

is shown below. The Output and Input modules are fitted on the female connectors to

enable communication with the CPU, which is also placed on the back plane. The

power supply of the back plane is to supply some modules with power.

NB: Not all output and input modules get their supply from the power supply in the

PLC, but some input/output modules are supplied from the back plane.


25

SENSOR

POWERSUPPLY

ETM Ethernet card

µp

Each back plane accommodates a specific number of modules and if the required

modules in a plant exceed the maximum number accommodated by a back plane,

there is need for an Expansion Transmitter Module which will enable the CPU on a

certain back plane to communicate with Input and Output Module in another back

plane.

NB: All other modules which are connected on a different back plane from the one

with the CPU need an Expansion Receiver Module (ERM) which receives

instructions or signals from the Expansion Module (ETM). See diagram below.

All Analog Output Modules are powered from the back plane with a 5V supply.

Digital Output sends output to the relays, which will enable switching on of high

currents. There are two types of relays in use, NO (normally open) and NC (normally

closed) Each relay has one digital output from the PLC.

2.6.1The VersaMax PLC Panel


26

Fig 7

2.6.2Hardware Configuration

When assembling a PLC you carry out hardware configuration first i.e.

Choosing the correct type of CPU

Choosing the correct digital input card (32 port)

Selecting the type of mode (SIMBI uses source mode)

Correctly, use slot number and rack number for the PLC to correctly identify

the Input/Output signals.

2.6.3Back Plane

This is the plane where digital/analog modules are mounted. At SIMBI, the back

plane can support up to 9 modules. Some of the output modules take their supply

voltage from the back plane, however at SIMBI most of the output modules are not

supplied from the back plane.

2.6.4Expansion Transmitter Module (MDL 650)


27

It is the main transmitter from the CPU to the output modules. All other ERMs

depend on the ETMs thus; they behave in a parasite manner. For every backplane, we

have the ERM. In addition, when changing modules one should take note of the

codes.

Digital outputs and inputs can be slotted on the same back plane but it is wise for

uniformity to separate them that is using different back planes.

At SIMBI, there are 7 digital output modules, which translate to 7 x 32 output signals

from the PLC. In addition, there are also 17 digital input modules, which translate to

17 x 32 input signals.

NB: Analog Output Modules uses 24VDC from SMPS and Input Modules use 5VDC

from the back plane.

Relays

SIMBI uses 24VDC relays and they are high current rating relays. These are of two

types, Normally Open (NO) and Normally Closed (NC). Each digital output uses one

relay.

LED

The LED ON, on the Modules only signal whether the signal from the instrument is

reaching the PLC. These LEDs are helpful during trouble shooting of an instrument.

Digital outputs have only 2 LEDs for power supply.

Terminal Block Side (TBS)

The blocks are used to connect the cables from the field to the PLC. This reduces the

number of cables into the PLC panel and provides SMART installation. Terminal

blocks on the terminal side also help a lot during troubleshooting. The cables are

given addresses for easy identification e.g.

Analog Outputs AQ0001 (Blue Cable)________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

28

Analog Inputs AI 0001

Digital Outputs R0001 (Blue cable)

Digital Q000I(Yellow cable)

NB: Take note that after expansion of the plant, some of the cables are not labeled

and the terminal side has changed a lot and is not yet updated.

2.7.0 The Communication Protocol

Checking the Ethernet LEDs IC200CPUE05.

For more information about the IC200CPUE05 Ethernet Interface, refer to the next

chapter of VersaMax® PLC User’s Manual – GFK-1503D.

After configuring the Interface, follow the steps below to verify that the Ethernet

Interface is operating correctly.

1. Turn power OFF to the PLC for 3–5 seconds, and then turn the power back ON.

This starts a series of diagnostic tests. During powerup diagnostics, after a brief delay

the STAT LED on the Ethernet side of the CPU module blinks. Both the LAN and

PORT1 LEDs are off. If a fatal diagnostic failure occurs, the failure is indicated by a

two-digit pattern in amber on the STAT LED.

2. After successful power-up, all three LEDs on the Ethernet side turn on briefly.

Then the STAT and LAN LEDs should be green. The LAN LED blinks when there is

traffic.

3. If the STAT LED is amber, check the PLC Fault Table. With the Station Manager

feature, you can also use the LOG command as explained in GFK- 1876, The

VersaMax PLC Ethernet Station Manager Manual.

If a problem occurs during power-up, the Ethernet interface may not begin operating.

Check the Ethernet LEDs, as explained below.

Ethernet LEDs

LAN Off

STAT Off________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

29

PORT 1 Off

Actions

-Make sure the PLC has power

-Look in the PLC Fault Table for problems

-Recheck configuration

-Check module installation

-If the problem persists, replace PLC CPU

Ethernet LEDs

LAN Off

STAT Fast blink green

PORT 1 Off

Indications

Performing powerup diagnostics

Actions

No action necessary; diagnostics will complete within 3 to 10 seconds.

Ethernet LEDs

LAN Off

STAT Blinking amber

PORT 1 Off

Indications

Hardware failure mode.

Actions

STAT: Blinks 2-digit error code:

1 – 2, unexpected interrupt

1 – 3, timer failure

1 – 4, DMA failure

2 – 1, RAM failure

2 – 2, stack error

2 – 3, shared memory interface error

2 – 4, firmware CRC error________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

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3 – 1, unidentified instruction, or divide by 0

3 – 2, unexpected SWI interrupt

3 – 3, prefetch abort error

3 – 4, data abort error

3 – 5, unexpected IRQ request

3 – 6, unexpected FIQ interrupt

3 – 7, reserved exception error

4 – 1, fatal operating system startup or EEPROM error

Actions

-Note error code

-Power cycle or restart Ethernet interface

-If problem persists, replace the PLC hardware.

Ethernet LEDs

LAN Off

STAT Slow blink Green

PORT 1 Off

Indications

Waiting for Ethernet configuration data from CPU.

PORT 1: PLC CPU is controlling Port 1.

Actions

-Use the PLC programmer to update the configuration, then store the configuration to

the PLC.

-Power cycle the PLC.

-Clear faults and press the Restart pushbutton for less than 5 seconds to restart the

Ethernet interface.

Ethernet LEDs

LAN Green / flickering

STAT Slow blink green

PORT 1 Off


31

Indications

Waiting for IP Address, IP address has not been configured, or has been configured as

0.0.0.0 .

LAN: Ethernet interface is online. Flickers during activity.

STAT: IP Address has not been configured.


Ethernet LEDs



PORT 1 Amber

Waiting for IP Address

Indications


0.0.0.0 .



PORT 1: Available for Station Manager use

Ethernet LEDs

LAN Amber


PORT 1 Amber

Indications


0.0.0.0 .

LAN: Ethernet interface is offline. Attempting to recover if possible.




32

Ethernet LEDs

LAN Amber


PORT 1 Amber

Indications


0.0.0.0 .



PORT 1: Available for Station Manager use

Actions

Use the PLC programmer to configure a non-zero IP address.

Ethernet LEDs


STAT Green

PORT 1 Off

Indications

Operational


STAT: No “exception” detected


Ethernet LEDs


STAT Green

PORT 1 Amber

Indications________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

33

Operational



PORT 1: Forced to Station Manager use

Ethernet LEDs

LAN Amber

STAT Green

PORT 1 Off

Indications

Operational




Ethernet LEDs

LAN Amber

STAT Green

PORT 1 Amber

Indications

Operational



PORT 1: Forced to Station Manager use

Actions

If LAN is off, the problem may be:

-Network cable not connected either at the PLC or at the hub.

-Hub disconnected/failed.

-Network cable not properly terminated.

If STAT is amber, an “exception” condition has occurred.________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

34

Ethernet LEDs

LAN Slow blink green, all LEDS blink in unison

STAT Slow blink green, all LEDS blink in unison

PORT 1 Slow blink green, all LEDS blink in unison

Indications

Software Load

Loading new firmware (via CPU serial port)

Actions

No action necessary; the Ethernet interface restarts automatically after loading

CHAPTER 3


35

3.0The Control Philosophy

As an abstract, the plant has been divided into four major segments.

i) Kiln and Cooler Section

ii) Waste Gas Section

iii) Product Separation Section

iv) Raw material handling section

The corresponding signal from every individual section has been connected to the

PLC system through the corresponding Input and Output modules. The CPU is

continuously processing the data as per the program logic and communicating the

SCADA – Graphical interface terminals for equipment status, monitoring and control.

The proposed PLC is user friendly and during the operation, in case of any fault due

to malfunction of any input address, the same can be reset by assigning some other

address from the spare block for ensuring the smooth functioning of the plant.

The necessary interlocks have been incorporated for every equipment to safe guard

from any eventualities and ensuring the smooth operation of the plant.

The system is designed to operate in 3 modes:

i) Manual

ii) Auto

iii) DE INT

Manual Mode

In this mode, the system can be started/stopped through SCADA i.e. from computer.

Here we can start all drives as well as conveyers by clicking the respective icons. All

interlocks are applicable in this mode.

Auto Mode


36

Generally, the system is operated in this mode. Here the system is designed in such a

way that the entire plant can be started with one click or individual major sections can

be started one by one.

DE INT Mode

In this mode, all the drives can be started/stopped independently irrespective of the

interlocks and is generally used for maintenance purposes.

The selection of the control of the plant is achieved by selecting LOCAL/REMOTE

positions in the MCC. To operate the plant in Auto mode all the selector switches

should be in REMOTE mode. When the system is in Auto mode, if any of the selector

switches in a particular group changes to LOCAL mode, then the whole group trips

along with down stream groups.

NB; In case it is necessary to keep one or few drives out of the total sequence of

operation, this is achieved by putting them in DE INT mode.

3.1PLC Programming

Introduction

A program is a set of instructions to execute a certain function. The instructions to be

performed during each scan are coded and inserted into memory with the programs.

Programming is carried out using a programming unit, which provides an interface

between the PLC and the user during program development, start up and trouble

shooting.

What makes a PLC special? PLC's are used to automate machinery in assembly lines.

For our (plant) project, we use the computer link feature that allows a PLC to take

commands and communicate with a host computer. If something goes wrong with the

computer link, the PLC still functions and protecting valuable equipment. This PLC ________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

37

and most others use a language called relay ladder logic programming. Normally in a

programming language things happen in order. The command or line of code on top is

executed before the command on the bottom until you hit the end of a loop. This is

not so in ladder logic. Everything happens at the same time.

So what is ladder logic programming really like? Ladder logic programming looks,

well, like a ladder. It's more like a flow chart than a program. There are two vertical

lines coming down the programming environment, one on the left and one on the

right. Then, you have rungs of conditionals on the left that lead to outputs on the right.

The things you will probably use the most writing Ladder Logic are the relay

conditionals --| |-- ---|/|--- and the output coils --- ( ) ---. These three things basically

make up a kind of IF THEN statement.

Ladder logic is a method of drawing electrical logic schematics. It is now a graphical

language very popular for programming PLCs. It was originally invented to describe

logic made from relays. The name is based on the observation that programs in this

language resemble ladders, with two vertical "rails" and a series of horizontal "rungs"

between them.

A program in ladder logic, also called a ladder diagram, is similar to a schematic for

a set of relay circuits. An argument that aided the initial adoption of ladder logic was

that a wide variety of engineers and technicians would be able to understand and use

it without much additional training, because of the resemblance to familiar hardware

systems. (This argument has become less relevant given that most ladder logic

programmers have a software background in more conventional programming

language, and in practice implementations of ladder logic have characteristics — such

as sequential execution and support for control flow features — that make the analogy

to hardware somewhat imprecise.)

Ladder logic is widely used to program PLCs, where sequential control of a process

or manufacturing operation is required. Ladder logic is useful for simple but critical

control systems, or for reworking old hardwired relay circuits. As programmable logic

controllers became more sophisticated it has also been used in very complex

automation systems.


38

Manufacturers of programmable logic controllers generally also provide associated

ladder logic programming systems. Typically, the ladder logic languages from two

manufacturers will not be completely compatible; ladder logic is better thought of as a

set of closely related programming languages rather than one language (the

IEC61131-3 standard has helped to reduce unnecessary differences, but translating

programs between systems still requires significant work). Even different models of

programmable controller within the same family may have different ladder notation

such that programs cannot be seamlessly interchanged between models.

Ladder logic can be thought of as a rule-based language, rather than a procedural. A

"rung" in the ladder represents a rule. When implemented with relays and other

electromechanical devices, the various rules "execute" simultaneously and

immediately. When implemented in a programmable logic controller, the rules are

typically executed sequentially by software, in a loop. By executing the loop fast

enough, typically many times per second, the effect of simultaneous and immediate

execution is obtained. In this way it is similar to other rule-based languages, like

spreadsheet. However, proper use of programmable controllers requires understanding

the limitations of the execution order of rungs.

Hence a program is a set of instructions to execute a certain function. The instructions

to be performed during each scan are coded and inserted into memory with the

programs. Programming is carried out using a programming unit, which provides an

interface between the PLC and the user during program development, start up and

trouble shooting.

There are four types of programming units

i) Hand held Unit

ii) Video/System programming unit

iii) Graphic programming unit

iv) Personal computers.


39

Where computers are used the manufacturer supply a program for the P.C that usually

allow the computer to, interface with serial input/output module installed in the PLC,

peripheral devices, programming aids and computer interface devices.

Symbols

This --| |-- means closed if energized while --|/|-- means closed if not energized. The

output coil -- ( ) -- basically means then energize this. So the first rung of example one

means that if input 1 is energized and input 2 is not then energize output 1. You

should note that on the T1, the number of a particular input or output is written on the

case of the PLC but for T2's and for some other more advanced PLC's this is not

necessarily the case. To find out what the addresses of your inputs and outputs are you

should refer to the documentation that came with your PLC. Also, in most ladder

logic programming environments you have to specify the address of each of your

inputs and outputs before it will even let you start programming. [The T series can

auto configure]

For example

x0001 x0002 Y0001|---| |-----|/|---------( )-----|| || || x0001 Y002 ||---| |--[01000 TON T012]--( )--|| || || R001 ||--[D0140 = 0001]--------( )--|| || R001 Y004 ||--| |---------------------( )--|| ||-{END}-------------------------|

In Ladder logic programming you do not have variables, you have registers. There

are four kinds of registers: X's that are inputs, Y's that are outputs, D's that are data

that can form integer, hex and real numbers, and finally R's that are internal relays.

X's and Y's are pointers to the actual terminal strip connectors (what you use a screw ________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

40

driver on to connect wires) on the PLC. If you energize an input, let's say 5, then

X0005 will have an on status; also if you give Y0023 an on status then relay 23 will

flick on.

R's are just about the same as X's and Y's except that they don't point to any hardware.

They just hold an on or off value inside of the PLC's memory. R's can be useful. X's

Y's and R's can even hold data besides their on and off states on many PLC's, but

personally I don't recommend it. For data like integers and hexadecimal numbers D's

are used as their addresses.

Delay timer

What this means is that after a specified amount of time after x0001 turns on, y0002

will turn on. You should note that because of the nature of ladder logic you can not

simply put a timer attached directly to the left hand side without a relay conditional

between it. Remember, everything is happening at the same time. PLC's are meant to

run on their own for long periods of time, so you can't just tell it that 10 seconds after

it's first plugged in it should activate something. You have to tell it to start timing

after something in the outside world has occurred, like the energizing or de-energizing

of an input.

In the code --[01000 TON T012]-- there is the parameter 01000 that tells the timer to

wait 1000*10ms or 10 seconds, and the parameter T012 tells the PLC which internal

timer you want to use. Some of the more advanced PLC's have timers with different

accuracy. Most measure time in 10ms intervals but others measure time in single

milliseconds. You should check the documentation on your PLC to see if any of it's

timers measure time in different units than the others. Also you should not use the

same timer for more than one thing.

On rung three of the ladder we have a conditional statement. If the number stored in

D0140 is equal to 1 then energize R001. If you look at the entire circuit you'll note

that there is no where else in it where D0140 is mentioned and you should know that

all data registers are set to 0 at default. You may think that D0140 will never actually

reach the value of 1 and that R001 will never be activated and that rung three and four

are useless garbage code. It's true that during the normal operation of the PLC D0140


41

will never change from zero and the last two rungs before end would be useless.

However, this is where the computer link function comes in. All Toshiba PLC's have

a computer link protocol built into them. This allows a host computer, such as any

sort of DOS, Linux based PC or even a Unix administrator with an RS232 serial port

to send commands to the PLC while it's running and read or write values into its

registers. This includes data, inputs, outputs, and relays.

Suppose that Y004 was attached to equipment that you wanted to turn it on or off at

your pleasure. Suppose it was an air conditioner or maybe some strange contraption

that brought you a coke from the fridge to your seat at a computer. If you can write a

program at your own specialized system that can send ASCII characters with 8 data

bits 1 start bit 1 stop bit and 9600 baud rate with odd parity, then you can manipulate

the registers in the VersaMax PLC 's and toggle d0140 between 1 and zero or 1 and

any other value.

The final rung on the ladder the - {END} - is basically what it says. It's the end

statement. It doesn't really do anything except to say, well, your done programming.

However, no program will work without an end statement and the PLC will ignore

any code put in after an end statement. This shouldn't be a problem for small

programs, just look at the screen and make sure the end is in there and at the bottom.

If you happen to be making a very large and a very complicated relay circuit your

editor will likely force you to write it in separate blocks.

Before attempting to write a very large program you should go to the very last

programming block available to you and put the end statement there and no where

else. The end statement can be used in debugging by ending the program early and

disabling commands that fall after the end statement.

NB: Most of the time on has to draw wiring diagram as shown below so that you can

come up with the Ladder Diagram.


42

3.2 Plant Control Loop drawings

All Drawings had been drawn using AUTOCAD2004 by Talon Garikayi for the

company with the immense help of the Instruments Engineer- Mr. I Muchimwe

Belt Conveyor Control Loop

Gas Conditioning Tower water level Control Loop

Fig 8

Ladder Logic/Diagram


43

NB: In ladder logic a rung is a complete ladder, and the complete circuit when

represented in ladder diagram is called a Project. Every input and output is assigned

an address and at SIMBI, inputs are addressed as % IQ0001

All inputs with the same status as the output are given an address similar to that of the

output.

3.3Basic Induction and Transformer Theory

“Since I had encountered circuits which include Transformers on most power supply

units I decided to include this section.”

When an electric current is applied to a conductor a magnetic field builds around that

conductor. If another conductor is in close proximity so that the building magnet field

"cuts" through that conductor, a current of equal potential is produced with flow in the

opposite direction of the original current. This conductor is called the secondary

circuit and the principal is called induction.

If the number of conductors in the secondary are increased the output potential is

increased in direct proportion. The inverse is also true. This is called transformer

action. It is because of transformer action that a current is created in the rotor

(secondary circuit) of an AC induction motor and a resulting magnetic force, within

and around the rotor, is also created.

If the magnetic field reaches maximum strength and quits growing, the current flow in

the secondary returns to zero regardless of the level of current flow in the primary. In

other words, there is a secondary current generated only when the magnetic field is

changing state.

Magnetism and electricity are the same way. We have some well-accepted theories

that we can use to explain how magnets can move our load but no one really knows

what magnetism and electricity are (regardless of what they say). When it comes to


44

using magnetic force to move our load, how it works just doesn't matter. We do know

that it works. We have even noticed a few peculiar things.

We have noticed that when you wrap a coil of wire around a piece of iron and apply

electric current the piece of iron becomes magnetic. We call this an electro-magnet.

We have noticed a lot of things about electro-magnets that are very important to the

drive application wizard:

After we apply the electric current, the magnet field grows at a finite rate to a

finite size.

After voltage is applied and full current is reached, which always takes a little

time, the field quits growing and becomes a constant size. If we increase the

applied voltage the field grows and becomes stronger, decrease the voltage

and the field weakens and shrinks.

When we remove electric power to the coil the field does not just disappear. It

just decreases in size until it does disappear. It collapses over time so to speak.

The more current our coil draws (which we can force by increasing the applied

voltage level) the stronger and larger our magnetic field becomes. I know I

said it twice. It's that important.

When we increase voltage to our electro-magnet, current will increase directly

proportional up to a point. After that point current increases exponentially.

THIS IS IMPORTANT! Generally accepted theory says that the iron core or

any material, can only conduct a limited amount of magnetic flux. Once that

point is reached current can become very high with a very small increase in

voltage. This is called magnetic saturation and is sometimes seen in motor

applications. Motor life becomes very short when the core reaches saturation -

about 15 seconds in some cases. We will look at this and some of the causes

later.

Some energy is consumed by simply magnetizing the iron core. Different

materials consume different amounts of energy. This is usually considered an

energy loss.


45

Some energy is converted into heat within the iron core. Different materials

convert different amounts of energy. This is also usually considered an energy

loss.

Once a core is magnetized, demagnetization and reverse polarity re-

magnetization consumes more energy and takes quite a long time, relatively

speaking. (Remember, an existing field has to collapse over time.) The amount

of this loss is proportional to the frequency of polarization reversals. This

happens 120 times per second when operating an AC motor at 60 hertz. We

will touch on the importance of this later. (Are you beginning to see where all

this is going?)

3.4Variable Speed AC Drives

Fig 9

The word "drive" is used loosely in the industry. It seems that people involved

primarily in the world of gear boxes and pulleys refer to any collection of mechanical


46

and electro-mechanical components, which when connected together will move a

load, as a "drive". When speaking to these people, an AC drive may be considered by

them as the variable frequency inverter and motor combination. It may even include

the motor's pulley .

People in the electrical field and electrical suppliers usually refer to a variable

frequency inverter unit alone as the "drive" and the motor as the "motor".

Manufacturers of variable frequency drives (VFD) used to refer to the drive as just

that, a "variable frequency drive". More manufacturers are referring to their drive as

an "adjustable speed AC drive". To make matters worse when a motor is included in

the package it may be referred to as an "adjustable speed AC drive system".

A variable frequency drive is an adjustable speed drive. Adjustable speed drives

include all types; mechanical and electrical. Now is it clear? Don't worry about it. It's

not clear to anyone. As you read on, when I refer to the "drive" I am referring to the

variable frequency inverter alone.

3.9 A little about AC drives

Outside the drive panels

Fig 10


47

The main power components of an AC drive have to be able to supply the required

level of current and voltage in a form the motor can use. The controls have to be able

to provide the user with necessary adjustments such as minimum and maximum speed

settings, so that the drive can be adapted to the user's process.

Spare parts have to be available and the repair manual has to be readable. It's nice if

the drive can shut itself down when detecting either an internal or an external

problem. It's also nice if the drive components are all packaged in a single enclosure

to aid in installation but that's about it

Ambiguous Motor Theory

The real action in an AC variable frequency drive system is in the motor. This is

really where it all happens.

To be an AC drive application Wizard one must understand how motors use electric

power. It is essential. I cannot emphasize the importance of this.

All loads moved by electric motors are really moved by magnetism. The purpose of

every component in a motor is to help harness, control, and use magnetic force. When

applying an AC drive system it helps to remember you are actually applying magnets

to move a load.

To move a load fast does not require more magnets, you just move the magnets fast.

To move a heavier load or to decrease acceleration time (accelerate faster) more

magnets (more torque) are needed. This is the basis for all motor applications.


48

Fig 11

Motors are designed so that the electro-magnets are made as strong as possible with

acceptable risk of core saturation. This will maximize the torque capability of the

motor but also means that during normal operation every motor may at some point,

operate close to saturation. How close a motor runs to saturation depends upon the

amount and type of core material used. So naturally, this point varies from

manufacturer to manufacturer. There really is a difference in motors and you get what

you pay for.

When the voltage applied to a motor is increased current to the electro-magnets

increases resulting in higher field strength and increased motor torque output. This is

a commonly used technique, especially in AC drive applications. It is a very good

way to gain torque capability when needed. This technique can cause higher than

normal motor heating resulting in reduced motor life. Close monitoring of the motor

is required. Avoid saturating the core.


49

3.5General Structure

Inside the AC drive Panel

Fig 12

AC drives consists of two sections namely.

i) Rectifier section which converts AC to DC

ii) Inverter section which converts DC to AC

Rectifier Section

This consist of three sections namely

a) AC Choke/Inductor – this is put on the supply side of the drive to

correct/reduce harmonics.

b) Charging circuit – it consist of capacitors which smoothens the charging

voltage. It also helps to reduce the amount of current from the drive phase,

which may damage the capacitors.


50

iii) Rectifier Bridge – usually made of thyristors or a combination of thyristors

and diodes.

NB: Between the rectifier and inverter there is a DC link, which consist of capacitors

and resistors. Capacitors smoothen the voltages and resistors discharge capacitors

Inverter section

Depending on the type of drive, some employ any of the following.

i) Thyristors

ii) Diacs

iii) Triacs

iv) IGBT – This is the one used at SIMBI to drive the AC motors. These

devices either can be individual units or integrated.

Also on the inverter side there are clamping capacitors which clamp (keep it constant)

output voltage at a required level, i.e. setting voltage to a certain load.

For the charging circuit, some use a diode with a resistor . Since during initial

charging of capacitors, they draw a high current, this is also very dangerous when 3

lines are used so voltage is tapped from one phase and used to charge the capacitors

and when fully charged the 3Ф voltage can now pass through. The resistors in parallel

with the capacitors are used during discharging of capacitors. The DC voltage is later

converted to variable AC voltage, which is required by the AC motors.

Rectifier Bridge – It is made of Thyristor only or combination of Thyristor and diodes.

Standard Six Thyristor Bridge

For the set up above where only a resistor is used and no diode but relay B, the

standard six diodes are used. During the operation, current passes through the resistor

charging the capacitor. When the capacitor is fully charged, a signal is send to relay B

and energizes it. The relay then closes the switch.


51

The Six Diodes

AC Drive Control of AC is divided into various circuitries namely :

i) Main Control Board

ii) Input/Output Board

iii) Gate Pulse Board

iv) Interface Board

These can be incorporated into one unit or set as individual units.

How to vary frequency

The rate and mode of switching ON/OFF determines the frequency (varying frequency).

Variable Frequency Drive Operation Parameter Setting that can be set on an AC

Drive. The following example illustrates how to carry an Operation Parameter Setting

when the drive is in REMOTE, LOCAL OR DUAL mode for RPM and ON/OFF

sequence.

General Schematic Representation of the Drive Structure

External Analog Signals in

Analog Signals to external devices

Digital Inputs

Links with the outside world

Communication with other devices

Drives Electric Motor at SIMBI0 - 415V0 – 50HzApplication ________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

52

Analog/ Digital Input/Output Card

Interface Board

Motor Control Board (Program

IGBTTRIACS THYROSTOSTRANSISTORSRESISTORS

Gate Driver Board

i) Main Control Board – It is microprocessor based. It is used for the

program and memory of the control system of the drive.

ii) Input/Output Board – It is an interface between the drive and the outside

world (analog and digital signal parts)

iii) Gate Pulse Board – It gives pulses to the thyristors, IGBT, TRIACS, and

DIACS etc to activate the whole system.

iv) Interface Board – It receives all measured signals as they are send to the

board e.g. supply voltage and current, output current, output voltage,

frequency.

3.6Programming an AC Drive

To program an AC Drive needs a user programme which is in the application control

board. A good example is when you want to run an AC motor using Variable

Frequency Drive (VFD) the following parameters should be considered.

Parameters for AC motor application

i) Motor Parameters

ii) Control Method Parameters

iii) Input/Output Parameters

iv) Preprogrammed Parameters

Motor Parameters

The following are considered:

i) Supply Voltage

ii) Motor Power

iii) Motor Current

iv) Motor Speed

v) Motor Frequency

vi) Power factor correction (Cos Ф)


53

Control Method Parameters

Consider the following

i) Variable frequency

ii) Variable torque

iii) Constant torque

iv) Constant frequency

v) Direct Torque Control (DTC)

Input/Output Parameters

a) Input Parameters are subdivided into two groups.

i) Process Inputs – Includes such factors as speed, flow level.

ii) Digital Inputs: Consider factors like

- Start command

- Stop command

- Reverse/forward command

- Auto/Manual selection command

- Selecting the control method

Output Parameters

i) Analog Output – These are signals representing measured parameters

inside/outside change. Inside parameters include factors such as Output

torque, frequency, current, voltage input signals.

ii) Digital Outputs – these show status of the drive

- Running status

- Power status

- Direction

- Auto/Manual selection

- Control method selection


54

CHAPTER 4

4.0Activities and Tasks in the Instrumentation Department

4.1Thermocouple Movements

4.1.1Reasons for carrying out the task.

The thermocouple (Tc) is housed in a stainless steel protector tube, which is in turn

housed in a thermowell (Tw).

Tc movements are done after every 4 hours during production, when the casted

material in the kiln inner lining is heated; the Tw gained a lot of heat and expands.

The protector tube also expands but due to di8fference in coefficient of expansion of

the two different materials the protector tube tends to stick to the Tw thus Tc

movements are done to create the much-needed clearance.

To a greater extent excretion build up at the tip of the Tw thereby blocking the tip of

the protector tube, which will be exposed to the process/product in the kiln. During Tc

movements these build ups are displaced and the protector tube will be exposed to the

process/product.

Therefore Tc movements are important and technicians are advised to closely monitor

this routine work.

4.1.2 Risk and Possible Dangers.

During Tc movements Technicians and their Assistants are exposed to highly

dangerous temperatures with the central burning area T6 and T7 recording an average

of 3600C and 4870C respectively hence T1 is always greater than 550C hence being

the lowest temperature at the Kiln area. Thus during Tc movements employees are

advised to spend the shortest possible time on this area. Research I had carried out

revealed that the shortest possible time one could spend whilst properly caring out this

task is &minutes. After Tc movements one is advised to drink at least to glasses of

water to compensate for dehydration that could have occurred so as to avoid

unexpected headaches.


55

4.1.3 Safe work procedure

Before leaving the Instruments Workshop one should put on the following safety

clothing:

Leather gloves, which are able to cover up to the elbow.

Safety goggles, which are heat resistant and can avoid dust particles from

entering from the top of the goggles.

A helmet to prevent any falling objects to directly harm you.

Safety shoes and proper clothing.

On moving T1, T2 and T3 ensure that the stand you will be using is properly

positioned; caution has to be taken since the Kiln will be rotating and shell air fans

can easily harm you.

Do not totally remove the Thermocouple since the process can easily have access to

get yet it will be red-hot.

Company is a must when one is carrying out this exercise.

4.1.4 Removing Thermocouple

Do not remove Tc during production if there are other alternatives, Technicians are

advised to seek clearance from the Instruments Engineer or otherwise wait for

shutdown.

Do not add water into the thermowell, this can cause a sudden contraction and may

result on the thermowell cracking. Thus decreasing unnecessarily clearance for the

protector tube thereby causing the thermocouple to stick.

If force is required you are advised not to over apply it on one side since this can

cause the thermocouple to be deformed.

Proper documentation is to be done during this exercise taking note of all serial

numbers.


56

4.2.0 Cleaning slip rings

4.2.1 Reasons for carrying out the task.

The compensation cables from the respective thermocouples are all connected to the

slip rings. These slip rings are also important because if they are dirty we will not be

able to get the correct input mV to the transmitter.

Slip rings for shell thermocouples and QRT signals need regular cleaning

4.2.2 Risk and Possible Dangers

Technicians should note that next to the temperature signal cables there are power

cables for shell air fans and these have very high voltage so extra care must be taken

not to temper around these slip ring cables.

4.2.3 Safe procedure

Always use fine sand paper and dry cotton when cleaning the slip rings.

Under what circumstance do not apply water on the slip rings.

Do not clean the slip rings for shell air fans.

4.3.0 Belt conveyor tail pulley sensors


The status of a belt drive on the SCADA is attained by the status of a Zero Speed

Sensor (ZSS), which is mounted at the tail pulley of the belt conveyor. Most ZSS are

of the Ale Bradley make and model ID18 3005NA.


The maintenance work carried out on these sensors is done when the belt is moving so

the assistants are advised not to interfere with the rotating crossbar. Since company is

not a must when one is doing routine work on these sensors, you are advised to clean

the sensors only.

4.3.3 Safe work procedure

Do not interfere with any moving parts on the tail pulley.

Remove the fuse for the respective sensor before tempering with power supply

cables.


57

Do not apply oil on the shank or threads of the sensor, this will cause dust

particles to stick on the sensor.

Routine check on the ZSS has to e done during the start of every shift and at

the end of every shift.

Documentation on the status of every sensor has to be done on every shift.

The tags on the shank of the sensors or power cables are not suppose to be

removed or exchanged without the Engineer’s approval.

Do not remove the housing of the sensor or exchange them.

4.4.1 Replacing a ZSS-Proximity sensor.

ZSS are in the START/STOP circuit of nearly all conveyor belts, caution has to be

exercised when carrying out any maintenance work while the plant is running.

Remove the fuse before tempering with the power cables of the ZSS, or any

replacement is done.

One has to remember when setting the ID sensor it is not all about lighting the LED

but also setting the correct Sn.

All Technicians must be in a position to interpret the model of every ZSS in the field.

Consider ID18 3005NA

05-is the Sn –detecting distance. Which is 5mm.

ID- means it is an inductive sensor.

18- means the diameter of the sensor is 18mm.

30-means the power supply should be greater than 6V but less than

30V.

N- means its an NPN logic.

A- means its Normally open circuit.

4.5.0 Weighfeeders

4.5.1 Cleaning of weighfeeders

As the name suggest, these instruments are used to feed the measured quantities of the

raw materials into the main conveyor belt BC7 into the kiln. They are 4 weighfeeders

at SIMBI and mostly 3 are always running except for one for feed coal which had

developed some drive faults lately, but we are doing everything in our capacity to

reprograme it in the long run.________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

58


Normally no work is expected to be carried out on moving machinery unless you are

carrying out level 3 maintenance.

4.5.3 Cleaning Safe working procedure

Do not lean or sit on the weighfeeders.

Do not open the load cell box during cleaning.

Avoid disturbing the limit switches during cleaning.

Always use a blower when cleaning since compressed air can penetrate the

awkward positions of the weighfeeders.

NB: When cleaning the weighfeeders do not use wet material, there are electronic

components.

4.5.4 Safe working procedure for general maintenance work

First know the level of your maintenance work (level 1,2 or 3)

Get clearance from the Instruments Engineer.

Put the machinery on LOCAL so as to avoid the situation whereby someone

can run the machinery from REMOTE.

Notify other relevant departments e.g. Electrical and Mechanical about the

breakdown.

4.6.0 Calibration of weighfeeders.


Calibration is always done if and only if:

The process value deviates from the expected value.

The plant is about to be RUN after shutdown jobs are done.

When the Process Operator requested for the procedure.

4.6.2 Procedure

Switch ON the WF.

Clear all errors if any is flagged

Check WF Date/month/year

Press ESC then CL


59

ESCESC CLCL

BBBB

The word “password” will be flagged. (Calculate the password as 10-

(date+month) if the sum of (date+month) is less than 10. or 20-

(date+month) if the sum of (date+month) is greater than 10.

Press as ENTER.

Press to select CALIBRATION.

Press to ZERO the WF.

Press to select SPAN.

Press for SPAN CALIBRATION

TYPE 1800d (1800 are counts) for SPAN after you have confirmed

hat the test weight has been placed.

Press then to escape from calibration

mode.

Press twice so as ton verify whether the counts are

in the 90% range.

Press after selecting the main program.


60

CHAPTER 5

5.0 Field Instruments

5.1 Kayblower

A Kayblower is a positive displacement, constant volume machine that operates

against varying pressure. The Two “8” shaped impellers (involute design) which are

mounted on parallel shafts, rotate in opposite direction and with every movement of

the impeller across the compressor inlet, a definite volume of air is trapped and

carried across the casing to the compressor outlet where this air is discharged.

Design

This allows operation without the need for lubrication inside the air casing.

The compact, sturdy design is engineered for continuous service when operated in

accordance with speed and pressure ratings.

Kayblower Compressor has computer calculated impeller profiles and is precision

machined on the latest CNC equipments assuring close tolerances between the

impellers, casing and side

Diagram

Fig 14

Pipe Sizes


61

Position INSIDE DIAMETER OUTSIDE DIAMETER

mm Inches mm Inches

Kayblower 150 6 160 6.4

CB Fans 150 6 160 6.4

5.2Air compressor

At SIMBI, we use a Centrifugal air compressor -a vane rotating disk or impeller in a

shaped housing forces the gas to the rim of impeller increasing the velocity of the gas.

A diffuser (divergent duct) section converts the velocity energy to pressure energy.

These are used for continuous, heavy industrial uses and are usually stationary.

Their application can be from 100 hp (75 kW) to thousands of horsepower. With

multiple staging, they can achieve extremely high output pressures greater than

10,000 lbf/in² (69 MPa).

I am going to design a pressure control system that will improve productivity and

safety. Fluid-handling devices are not concerned with the modulation of power, but

only with the movement of fluid.

Choosing a fluid-handling valve used to be easy, because each one had its own area of

utility. For on off, full, or no-flow requirements, ball and gate valves were favored;

where tight shutoff was not required, butterfly and slide valves were used.

As a result, beliefs were formed which may inhibit the selection of the best valve for

my design.


62

5.3Schematic representation of the valves

The present set up of the valves

Fig 15

5.4Pressure Regulators

The first pressure regulator has to allow a constant air pressure supply of 140Kpa

(21psi) to be used as an input to the Current-to-Pneumatic converter.

The second pressure regulator has to allow a constant air pressure supply of 140Kpa

(21psi) to be used as an input to the Valve Positioner.

The pressure regulator is a normally open valve and is installed at the START of a

system or before pressure sensitive equipment to regulate or reduce undesirable

higher upstream pressure. Too often, a pressure regulator is installed. In this case, the

pressure regulator will simply stay wide open and just send liquid straight into the

tank without maintaining upstream pressure...just a very expensive fitting.


63

Where an obstruction will benefit everything after the valve, a pressure regulator

should be used so that not all the equipment after it will have excessive pressure. Used

where it should be that is at the beginning of a process, the pressure regulator will

ensure safe downstream pressure. The combination of a pressure regulator at the

beginning of a system, and a backpressure regulator at the end of a system, will

ensure balanced pressure throughout the system. This is a simplification, of course,

and the specifics within any given system can vary greatly.

Calculations.

Using the equation of continuity

Assumption: The flow rate at any point of the system obeys this equation

By varying the area of the opening at the outlet of the regulator we can regulate the

outlet pressure.

Applying Bernoulli Principle, under steady state flow, well developed flow conditions

the total energy of a unit volume of material must be constant at every part of the

system.

By increasing we decrease and increase the pressure thereby regulating

pressure.


64

5.5 Uninterrupted Power Supply (UPS)

The Power Supply is made up of 20,12v batteries. It uses IGBT for inverting and is

used to supply the panels with power when, the main supply is down. It uses the

concept of switched mode power supply (SMPS)

5.6 The Kiln Main Drive

Fig 16

At SIMBI, from the Drive Output the signal is going straight to SCADA via RS 485.


PLC

TACHO METER

MOTOR

SCADA SETPOINTOPERATOR PC

DRIVE CONTROLLER

65

5.8 Variable Frequency Drive Operation Parameter setting that can be set on an

AC Drive.

The following example illustrates how to carry an Operation Parameter Setting when

the drive is in REMOTE, LOCAL OR DUAL mode for RPM and ON/OFF sequence.

1. To operate the Drive in REMOTE MODE

Parameter to set Set Parameter to Operation

Value to set to

b1 – 01 0 RPM setting from screen

on the system.

b1 – 02 0 ON/OFF sequence from

the Screen on the system

2. To operate the Drive in LOCAL MODE

Parameter to set Set parameters to; Operation

b1 – 01 0 RPM setting from digital

Operator on drive panel.

b1 – 02 0 ON/OFF Sequence from

the screen on the system.

3. To operate the Drive in DUAL MODE

Parameter to set Set parameters t Operation

B1 -01 0 RPM setting from the

digital Operator on the drive panel.

B1 -02 1 ON/OFF sequence from

the Screen on the system.


66

4. To increase/decrease the RPM from digital operator on the drive in running

mode.

i) Check the display is in rpm or frequency mode.

ii) The drive LED on the digital operator should be stable if the above

conditions are satisfied, then press: DATA/ENTER. At this point the

Display in Operator Panel starts blinking. By scrolling the Up, Down,

Reset arrow keys on the operator panel, set the required RPM. Then press

ENTER and then ESC.

5.8 Weigh feeder Controllers

There are four weigh feeder controllers in the control room, each for.

i) Feed coal

ii) Iron ore

iii) Charcoal

iv) Injection coal

NB: Weigh feeder controllers are constructed in the same way as AC Drives, thus

most of the information has been covered.

Weigh feeder Control Panel

During programming of the control panel controller, a statement list is used. The

tonnage set point is set from the SCADA. The Digital and Analog Input/Output cards

are used for interfacing with the controller. The control panel shows the status of the

belt. Serial communication is used on control panels and drives.

VFD (telemechanics-it implies hard wired circuit)


67

Fig17

4-20mA DIGITAL

SERIALRS485

Fig 18


68

FIELD DISPLAY

SCADA PLC A/I CARD CONTROLLER

DRIVE COMMAND

A/I..O

CHAPTER 6

6.0Sensors

Introduction

A transducer is a device that is able to convert one form of energy to another. The

signal from a transducer will require undergoing the process of conditioning and

conversion. Transducers can be classified as either passive or active.

i) Active- is one that generates electrical energy directly e.g. moving coil

microphone, since it uses the principle of electromagnetic induction

ii) Passive – require an electrical supply which is then modified in some way

(modules) so as to develop an output e.g. a potentiometer is supplied with

a voltage, a portion of which appears at the wiper according to its position,

thus the output voltage is directly related to the angular or lower position

of the wiper.

Proximity sensors, level sensors and flow sensors

At SIMBI, proximity sensors (ZSS) are used mostly to confirm belt status, ie

running or not running (the, RUN/STOP MODE). The most common type of

proximity sensors in use is the inductive sensor. Again, the same inductive sensors

are used as level sensors (for checking the water level) at the wet scrapper tank

and as flow sensor in the supply pipes at the cooler section.

Inductive sensor principle of operation

The sensors operate on the principle of an inductor producing a wave like output

signal of graphical means, which is used for ON/OFF of an LED at the rear of the

sensor. When a metal is passed near the inductive sensor 9within a detecting distance)

the LED switches on. Thus, the sensors are mounted in such a way that will signal the

presence of a metal within their operating distance.


69

Coding of Inductive Sensors

The most common type of inductive sensors at SIMBI are cylindrical in shape and the

markings are at the rear unthreaded section. Inductive sensors come in different

diameters and each chosen depending on its mode of exploitation. An example of

such a sensor marked as follows:

ID 18 – 3005NA, where

ID – Inductive.

18 – diameter in mm

30 – 6 – 36VDC

05 – Detecting distance

N- NPN

A – Normally Open

6.1Proximity sensor as Water level sensor

High Sensor

Metal bar

Floater

Fig 19


70

6.2 Proximity sensor as a water flow sensor

The Proximity sensor is also used as a water flow sensor after including a mechanical

design on the flow sensing system. The Kayblower is water-cooled and if there is no

signal indicating the flow of water it automatically stop. The Kayblower water flow

sensor is in the start /stop circuit of the injection coal circuit so this will mean the

whole circuit will trip.

This clearly indicates the importance of the water flow sensor; therefore, care must be

taken when dealing with the water flow sensor.

o Common faults

The water flow sensor is positioned in a wet environment hence there is no proper

housing provided so it usually turn off due to obstruction.

There is a fuse in the junction box, which is usually loosely held, and during cleaning

of JB box by Assistants it is often disturbed.

o Diagram

Fig 20


71

6.3Proximity sensor as a Zero Speed Sensor (ZSS)

During this operation the inductive sensors are used as ZSS, thus they signal the status

of the belt as RUN/STOP. There is a cross bar protruding from the pulley center (non-

drive section of the belt. The sensor is then positioned at a determined detecting

distance away from the cross bar.

At this position, it will be able to detect the presence of the metal and sent an impulse

signal to the PLC on the status of the belt. An LED will be either ON or OFF

depending on the presence of the metal. When the belt is moving it will be ON/OFF

on equal intervals, depending on the metal position.

o Detecting RUN/STOP MODE of a belt

Inductive Sensor Nuts

Led cable

Belt Pulley Mounting bracket

Rotating Bars

Fig 21

6.4 Gate valves (actuator)

Include wedge and double-disc valves. Both are typically used in a fully open or fully

closed position because close regulation of flow is not possible.

A gate valve can be used for throttling only when the valve is in an almost shut

position, where most of the flow reduction occurs. The small, crescent-shaped

aperture causes a high flow velocity that can erode seat faces. Repeated movement of

the disc near the point of closure against upstream pressure can create drag between

the seats on the downstream side and may gall or score the seat faces. In addition, the

high-velocity flowing liquid impinging against a partially open disc or wedge

produces vibration that can damage seating surfaces and score the downstream side.


72

Nevertheless, a gate valve is excellent for service that requires either full or no flow.

It has essentially no flow restriction when fully open. The flow area at the point of

control is equal to the full cross-sectional area of the line. Because flow is straight

through the line, pressure drop across a gate valve is only about 1/50 that of a globe

valve of comparable size.

6.5Thermocouples

These are temperature devices, which utilizes the set back effect. They are designed

by joining two dissimilar metals to form two junctions. One junction called a hot

junction is placed at the point where the temperature is to be measured. This junction

is a permanent one, usually formed by welding the two metals together.

The cold junction, since in use has outside controlled environment and is closed by a

load across it where a thermo – electric is developed by the flow of a thermoelectric

current through it. This results from the temperature difference between the two

junctions.

NB; Different materials are used for making various types and each make is

differentiated by useful temperature ranges and tolerances.

At SIMBI thermocouples are used to measure the temperature of the rotary Kiln ABC

and cooler outlet, T/Cs gives out, put in mV, which is converted into mA by a

temperature transmitter. The mA are then send to the PLC for conversion into Celsius.

6.5.1Resistance Temperature Detectors

Those are wire wound and thin film devices that measure temperature because of the

physical principle of the positive temperature coefficient of electrical resistance of

metals. The hotter they are the higher the value of their electrical resistance.

PTs and PT 100 are the most popular RTD type nearly linear over a wide range of

temperatures. Some are small enough to have response times of a fraction of second.

They are the most precise temperature sensors available with resolution and ________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

73

measurement unattainable of 10C or better. Usually RTDs are provided encapsulated

in probes for temperatures sensing and measurement with an external indicator,

controller or transmitter or is enclosed inside other devices where they measure

temperature as a part of the device function such as temperature controller or

precision thermostat.

6.5.2 Temperature Control System

There are 7 thermocouples at the kiln section. These thermocouples are connected to

the slip rings and one 2 wire transmitter. The transmitter is positioned under the main

kiln. The thermocouples measure or detect mV which are transmitted to the

transmitted to the transmitter and the transmitter gives an output 4 – 20 mA. The PLC

will have an input of 4 -20mA, which will be used for control calculation to have an

output temperature in degrees Celsius showing in SCADA.

6.5.3 The Temperature Loop

4– 20 mA

Fig 22

The regulation of temperature at the kiln is achieved by the STACK CAP use, i.e.

opening and closing and INDUCED DRAFT FAN (although it is not in use at the

moment)


74

Process (Kiln) (Sensor)ThermocouplesmV

Temperature2 Wire TransmittersTT 209

SCADAIndicator

PLCController

Junction Box(JB 201)

6.6 Temperature Transmitters (Type K)

Temperature sensors at SIMBI show their reading in mV. However the PLC does

not read signals, which are in mV (unless it is a stand alone controller), hence there

is need to convert the mV into mA, which the controller can read. Thus, a

temperature transmitter is used to convert mV into mA. The mA (4-20 mA) is

converted into degrees Celsius and send as a digital signal to the indicator.(PC).

The XTR108 is a "smart", programmable, 4-20mA, two-wire transmitter designed

for temperature and bridge sensors. Zero, span, and linearization errors in the analog

signal path can be calibrated via a standard digital serial interface, eliminating

manual trimming. Non-volatile external EEPROM stores calibration settings.

The all-analog signal path contains an input multiplexer, auto-zeroed programmable-

gain instrumentation amplifier, dual programmable current sources, linearization

circuit, voltage reference, sub-regulator, internal oscillator, control logic, and an

output current amplifier. Programmable level shifting compensates for sensor DC

offsets. Selectable upscale and downscale output indicates out-of-range and burnout

per NAMUR NE43. Automatic reset is initiated when supply is lost.

6.7.1Calibration of Temperature Transmitter

Sometimes the temperature transmitter gives false readings, hence there is need to

carry out a calibration procedure in order to set it to within operating range

Transmitter Calibration Procedure (Type k Input type

Range: 0 - 1200ºC

Input; 0 - 47,836 mV which corresponds to 4 – 20 mA

For cold junction compensation, adjust to 0mV. For input adjust transmitter to 4,33A

which equals 25ºC.

NB: For 0mV input, the Input channel has to be shorted.

When calibrating always check zero calibration first followed by span calibration and

then the mid ranges.


75

Fig 23

Procedure for calibration

i) Connect the components as shown above

ii) Put the Read/Feed switch to feed.

iii) Switch on your 24VDC

iv) Switch on your calibrator

v) Adjust the coarse/fine mV switches to read zero

vi) Millimeter should indicate 4,33A if not adjust the zero adjustment,

millimeter to indicate 4,33A.

vii) Adjust the coarse/fine mV switches to 47,836mV.

viii) Multimeter should indicate 20mA, if not adjust for span.


76

24VDCPower Supply

Millimeter (PLC)

+ Temperature Transmitter+-

+ -Calibrator(Thermocouple)

Other Mid-Range Adjustments

When calibrating the mid-ranges, 1mV must be subtracted from each value for

temperature compensation.

mV Input m A Output Corresponding

Temperature

0 4,33 25ºC

11,210 8,0 300ºc

25,90 12 600ºC

36,33 16 900ºC

47,830 20 1200ºc

NB: After mid range calibration always check that zero and span have not been offset

Pressure Control System for the kiln section

There is pressure build up in the kiln due to gases formed during the production

process. In addition, the volume of air blown in by the Kay Blower and Central

Burner (CB) fan increases the volume of gases in the kiln. If pressure is not regulated,

it results in temperature increase, which can lead to changes in the dimensions of the

kiln.

6.7.0The pressure transmitter

The pressure control system is open loop. The opening and closing of the STACK

CAP is based on operator’s decision and is not programmed.

NB; It is advisable to take note that even when the control loop for pressure (and

temperature) is open, their output will be used to actuate most of the machinery within

the plant such as ID fan, stack cap, kiln rotation speed and Kay blower speed.

6.7.1Functional Principle

The transmitter is ready for operation immediately after installation. The settable

measuring span corresponds to the specification on the rating plate. If customized

setting is made at the factor, the start of scale are specified o the measuring pate .If


77

necessary, the parameters can also be changed during commissioning by simple

operating procedures.

6.7.2 Design

The device consists of different components depending on what the

customer has specified in the order. The possible variants will be listed

in the operating manual.

The rating plate with the order number is on the side of the housing.

One can determine the optional constructional details and the possible

measuring range (physical properties of the built –in sensor element)

with the specified number and specifications.

6.7.3 Installation

We must not overlook the possibility of condensate freezing in impulse lines to

transmitters measuring gas pressure. Although these components could be heated

similar to water and steam applications, the simplest and best approach is to install

transmitters so that they are self draining. This means that the impulse lines are

connected to the lowest point in the transmitter meter body and the piping is sloped

downward at least one inch per foot. If the transmitter is located below the process

taps, piping must still run downward from the transmitter to the point and then to the

process as shown on the next page.


78

Functional Block Diagram for Transmitter


79

Fig 24

When the transmitter is in its DE mode, the process variable is available for

monitoring and control purposes; and the meter body temperature is also available as

a secondary variable for monitoring purposes only.

6.7.4Effects of pressure on the STACK CAP


80

Fig 25

It is also called the Differential Pressure Transmitter since it utilizes the principle of

difference in pressure. Other types of pressure transmitters are:

i) Differential capacitor

ii) Piezoelectric

iii) Linear Variable Differential Transformer (LVDT)

iv) Servo Motor

6.7.5 Principle of Operation


START KILN

KILN ROTATING

STACK CAPOPENING

DECRESED

ID FAN SPEEDDECREAED

STACK CAPOPENING INCREASED

ID FAN SPEEDINCREASED

BELOW RANGEABOVE RANGE

FINISH

IS

PRESSURE

WITHIN

RANGE

81

The differential pressure is directly proportional to the flow rate,

- Differential pressure

- Flow rate

The differential capacitor is used to achieve the differential pressure due to decrease

or deformation of the diaphragm, which reduces the dielectric field thereby changing

the mV and inducing a new value of capacitance. The mV are then changed to mA (4-

20mA) which is then transmitted to the PLC. A defining equation then changes the

mA to a pressure value, which is then shown on SCADA.

Parallel plate

low pressure High pressure

Using the equation of capacitance we can deduce that any slight change on D, or D2

will cause a change in voltage. Atmospheric pressure D1 = D2, hence the differential

pressure = 0

During calibration O K Pa (when expressed to atmospheric pressure) = 4mA.

A pressure simulation is used to achieve the differential pressure, span = 20mA.

During installation note that P = * so that the height in 8 on which the high pressure

pipe and low pressure pipe are connected must be equal to avoid the creation of

vacuum i.e.

6.7.6 Important facts about Pressure Transmitter

i) When zeroing always make sure you open the equalizing valve so that P1

= P2 and open the two isolation valves


82

ii) When trying to position the pressure transmitter, take note that the

equalizing valve is closed and the isolation valves open.

iii) Drainpipes should be open for flushing.

iv) Always reset transmitter to zero.

NB: If one side of the transmitter is exposed to high pressure, a condition known

as warping results which lead to a permanent deformation of the parallel plate.

High pressure on one side is usually due to a blockage in one of the impulse lines.

6.8.0Weigh feeders

Weigh frames

These mechanical components make up a weigh feeder control system. It is that

position where the load is placed during weighing and there are mechanical links

to the load cells. During calibration of a weigh feeder controller, the desired

weight (test weight) is placed directly on the weigh frame. The weigh frame also

comprises an adjustable bolt and nut mechanism.

6.8.1Weigh feeder Control Loop

Weigh feeders are used for the raw material feed into the kiln to maintain a fixed ratio

which is ideal for optimum reduction of iron ore into sponge iron. Iron ore charcoal,

feed coal and injection coal are the main raw materials used.


83

SCADA OPERATOR SET

PLC

SERIAL COMMUNICATION

Fig 26

To get the material flow rate, the controller multiplies the load on the weigh frame

(Kg/m) by the speed of the conveyor (m/s) i.e. **/m X m/s = k*/s (also expressed

in tons/hr). The flow rate is then compared to the operator set point and a control

output send to the VFL.

NB: There are only 3 control loops at SIMBI

i) Weigh feeder control loop

ii) Temperature system at the kiln section

iii) Control valve at the high-pressure tank. These valves do not use the PLC

but has a standalone controller, which is in the MCC.

6.8.2 Limit Switches and Push buttons

Limit switches at SIMBI show discrete from the position of individual components.

They are powered by a24VDC. This limit switches indicate

i) belt sway

ii) gate valve position (open or close)

iii) Position of the stack cap as it opens and closes

Push buttons also give two states ie ON or OFF. They are used for switching field

electrical and instrumentation machines.________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

84

PROCESS WEIGHFEEDR CONTROLLER

FIELD INDICATOR

LOAD CELL TACHOGEN

AC MOTOR VARIABLE SPEED DRIVE

6.9 Junction Boxes

There are 3 junction boxes within the plant. These are used to connect wires from the

field with those from/to the PLC i.e. a junction box provides termination of field

wires, where signals can easily be traced. It also provides a 24VDC supply to the

individual sensors using the loop system.

One junction box is within the Screen House area and it caters for ZSS (BC1 – BC7),

charcoal, feed coal and iron ore weigh feeders, dust extractor solenoid valves, limit

switches and loud speaker within the area.

The second one is at the elbow of the ABC near the kiln inlet. It has terminations for

the ABC temperatures, wet scrapper temperature and level sensor, kiln inlet pressure

and the ESP area.

The last one is at the kiln outlet, just close to the Central Burner fans and it caters for

the ZSS (BC9 – BC 11), dust extraction solenoid valves for cooler area and product

section, kiln thermocouples, kiln outlet pressure, flow sensor at the cooler, coolant

pressure and cooler discharge temperatures.

It is important to note that there are Analog and Digital sensor signals at the junction

box. There also have different 24V supply lines and do not share common ground

When checking voltage across a fuse, always connect the voltmeter at OV and any

point on the field side. When checking for current, always connect the ammeter in

series with the measured.

NB: Disconnect the fuse before attempting to work on transmitter and check for 24V

supply. On this junction boxes, blue is negative.

Junction boxes are an important termination point for troubleshooting.

The Weighbridge


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At SIMBI we have a weighbridge, which is used to measure all the raw materials to

be used at the plant and also the products of SIMBI before distribution to the

respective customers. It consists of 8 load cells all wired to respective corner boxes.

We have two corner boxes each with 4 load cells. The excitation voltage is 9V and the

output voltage range is 0 to 18mV. The actual mV is the average of the 8 load cells.

Sometimes the colour coding printed on the PCB do not coincide with the polarity of

the load cell so during trouble shooting one has to recheck the wiring. Considering the

weighbridge at SIMBI when measuring the mV we use the Red and White cables at

the corner boxes.

A password is required during calibration. A digital display for HMI with

weighbridge is the L215 but there are different models for specific applications in the

industry.

The weighbridge schematic diagram


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Fig 27

CHAPTER 7


LOADCELL 8

CORNER BOX

1

LOADCELL 1

LOADCELL 2

LOADCELL 6

LOADCELL 5

LOADCELL 3LOADCELL

4

LOADCELL 7

CORNER BOX

2

L215

COMPUTER

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Information and Technology Department

7.1 Introduction

This department is based mainly at our company Headquarters in Kwekwe. The main

objective of this department is to maintain the Information System at Group level of

all other branches nationwide. At each branch there are Technicians responsible for

the day-to-day business of the department. I was trained at Kwekwe HQ then worked

at SIMBI Masvingo for all my practicals. Together with the Hardware Engineer we

did the Network System currently being used at SIMBI Branch in Masvingo.

I also did Basic Software Engineering at an advanced stage. It is from this Department

where I was trained on Telecommunication system with the help of Digital Dynamic

System Pvt Ltd and Commaf as external service providers. I carried out proper

maintenance of all the Computers at the plant up to date, this include System

Administration of the new Broadband network system provided by Ecoweb.

The Network Project

We started this project on 13 May 2008 and finished on 24 May 2008.This was

my first time to take part in a project concerning the IT-Department but I managed

to work well with the whole team.

Constructing a communication cable.

Generally there are two main types of communication cables used in

Networking, i.e. Straight-through and the cross-over cable using RJ45

pins.

The cross-over cable is used when connecting two computers without the

use of a hub. This cable is constructed by using the T568A on one side and

T568B wiring scheme on the other end.

Straight-through cable is used during LAN, whereby the T568A wiring

scheme of CAT 5E is implemented on both ends of the cable.

Important colours.


88

Orange and green are the main colours hence the other colours are for

voice.

Wiring scheme for CAT 5E as T568A.

1-orange/white

2-orange

3-green/white

4-blue

5-blue/white

6-green

7-brown/white

8-brown

Wiring scheme for CAT 5E as T568B.

1-green/white

2-green

3-orange/white

4-blue

5-blue/white

6-orange

7-brown/white

8-brown

Panel components

24 Port CISCO catalyst 2950 series switch

Patch panel- for interfacing with cables so as to avoid direct

conection.

CISCO 1841 Router

Bridge

Radio


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CHAPTER 8

Telecommunication Systems

Overview

I did telecommunication systems practices with an external service provider called

Digital Dynamic Systems based in Masvingo which is responsible for the

maintenances of telecommunication system at Steelmakers Branches country wide.

I was under the guidance of Mr. J Mbirima a Telecommunication Technician with the

same company. I did several types of PABXs at different locations, which include the

following types:

Samsung 24/72

Jupiter 8/48

Siemens 20/84

Connectors

o RJ11- has two wires inside the connector head.

o RJ45- has 4four wires inside and can also have 8 wires for LAN networking.

o BT- for Betacom and also for BT handsets which are an old model.

Communication cards

These cards are categorized using the colour on their handles.

WHITE means two direct lines and two extensions and no executive line.

BLUE you can connect two extensions and one can connect a switchboard or

executive line.

BROWN has only four extensions.

BLACK one direct line, 2 extensions and one executive.

GREEN is the control card or main control board. It controls all the

communication system between peripheral interface, supervises all resources

in the system and control the gain adjustment of PCM signal, generates

stantenous and manage all processes of the system


90


91

CHAPTER 9

Mechanical Engineering Department

9.1 Workshop practices and processes at SIMBI

I want to thank Mr. D Wakasemwa for the encouragement he gave me so that I can

also concentrate on practicals during my Workshop practices and processes at C.U.T.

He was my Lecturer for that Course i never had problems in the Workshop at SIMBI

as I was even a step further during Welding processes as I produced door frames,

window frames and did maintenance work in the plant at a good speed and accuracy

thereby producing attractive work.

The workshop at SIMBI has fully assembled and running lathe machines, heavy duty

milling machines and drilling machines. I had access to all the machines and I was

trained on turning, milling and drilling operations. We had the following machines to

name but a few:

Lathe machine

Milling machine

Drilling machine

Electric grinders (Grinding wheels)

Saw Cutters

Sheet metal cutters

Welding machines (Gas & Electric Arc Welding)

First, I was taught the precautions necessary to take before working on any of these

machines and dangers associated with running machines.

I gained good knowledge and experience to an extent that our company assigned me

to do some external jobs from other nearby companies which include mines, garages

and foundry companies. I did all my workshop operations under the guidance of Mr.

B. Bvunde who is the Workshop Foreman and his Artisan Mr. M Chapukira a well

known lathe operator.


92

On 25 April 2008 the main driving shaft at the Kiln broke and a technical team was

set up to investigate the cause, write a report, design the shaft and machine it. I was

tasked to come up with the AUTOCAD drawings also during research i was made the

team leader that also involved Paul a student on attachment from Production

Engineering-C.U.T currently at Steelmakers Kwekwe branch. We managed to come

up with the shaft, which is 120cm in diameter and 160cm in length consisting of 3-

gear system. We did this project at our Steelmakers Kwekwe Branch.

Safety precautions

(a) Never to start the machines unless I know how to stop them.

(b) Any electrical fault to be reported to qualified personnel.

(c) Avoid spilling oil and grease or placing any obstacle within the working area.

(d) Horseplay within the working area to be avoided.

(e) To use the correct tool for the right job always.

(f) When I’m not sure of what to do on any particular job, I should ask qualified

experienced personnel first.

(g) To carry out regular house keeping and to put on goggles when grinding &

welding hat during welding.


93

Fig 28

9.2 Machining operations

The three principal machining processes are classified as turning, drilling and milling.

Other operations falling into miscellaneous categories include shaping, planing,

broaching and sawing.

Turning operations are operations that rotate the workpiece as the primary

method of moving metal against the cutting tool. Lathe is the principal

machine tool used in turning.

Milling operations are operations in which the cutting tool rotates to bring

cutting edges to bear against the workpiece. Milling machines are the

principal machine tool used in milling.

Drilling operations are operations in which holes are produced or refined by

bringing a rotating cutter with cutting edges at the lower extremity into

contact with the workpiece. Drilling operations are done primarily in drill

presses but not uncommon on the lathes or mills.


94

Miscellaneous operations are operations that strictly speaking may not be

machining operations in that they may not be chip producing operations but

these operations are performed at a typical machine tool. Burnishing is an

example of a miscellaneous operation. Burnishing produces no chips but can

be performed at a lathe, mill, or drill press.

An unfinished workpiece requiring machining will need to have some material cut

away to create a finished product. A finished product would be a workpiece that

meets the specifications set out for that workpiece by engineering drawings or

blueprints. For example, a workpiece may be required to have a specific outside

diameter.

A lathe is a machine tool that can be used to create that

diameter by rotating a metal workpiece, so that a cutting tool

can cut metal away, creating a smooth, round surface matching

the required diameter and surface finish.

A drill can be used to remove metal in the shape of a

cylindrical hole. Other tools that may be used for various types

of metal removal are milling machines, saws, and grinding

tools. Many of these same techniques are used in

woodworking.

More recent, advanced machining techniques include electrical discharge machine

(EDM), electro-chemical erosion, laser, or water jet cutting to shape metal workpiece.

As a commercial venture, machining is generally performed in a machine shop, which

consists of one or more workrooms containing major machine tools. Although a

machine shop can be a stand alone operation, many businesses maintain internal

machine shops which support specialized needs of the business.

Machining requires attention to many details for a workpiece to meet the

specifications set out in the engineering drawings or blueprints. Beside the obvious

problems related to correct dimensions, there is the problem of achieving the correct

finish or surface smoothness on the workpiece. The inferior finish found on the

machined surface of a workpiece may be caused by incorrect clamping, dull tool, or

inappropriate presentation of a tool. Frequently, this poor surface finish, known as


95

chatter, is evident by an undulating or irregular finish, and the appearance of waves on

the machined surfaces of the workpiece.

9.3Basic machining process.

Machining is not just one process; it is a group of processes. The common feature is

the use of a cutting tool to form a chip that is removed from the workpart. To perform

the operation, relative motion is required between the tool and work. This relative

motion is achieved in most machining operation by means of a primary motion, called

cutting speed and a secondary motion called feed. The shape of the tool and its

penetration into the work surface, combined with these motions, produce the desired

shape of the resulting work surface.

9.4Types of machining operation

There are many kinds of machining operations, each of which is capable of generating

a certain part geometry and surface texture.

Turning, a cutting tool with a single cutting edge is used to remove material

from a rotating workpiece to generate a cylindrical shape. The speed motion in

turning is provided by the rotating workpart, and the feed motion is achieved

by the cutting tool moving slowly in a direction parallel to the axis of rotation

of the workpiece.

Drilling is used to create a round hole. It is accomplished by a rotating tool

that is typically has two cutting edges. The tool is fed in a direction parallel to

its axis of rotation into the workpart to form the round hole.

In boring, the tool is used to enlarge an already available hole. It is a fine

finishing operation used in the final stages of product manufacture.

Milling, a rotating tool with multiple cutting edges is moved slowly relative

to the material to generate a plane or straight surface. The direction of the feed

motion is perpendicular to the tool's axis of rotation. The speed motion is

provided by the rotating milling cutter.

The two basic forms of milling are:

Peripheral milling


96

Face milling

Other conventional machining operations include shaping, planing, broaching and

sawing. Also, grinding and similar abrasive operations are often included within the

category of machining.

9.5The Center Lathe

A lathe is a machine tool used principally for shaping pieces of metal, sometimes

wood, or other materials by causing the workpiece to be held and rotated by the lathe

while a tool bit is advanced into the work causing the cutting action. Lathes can be

divided into three types for easy identification: engine lathe, turret lathe, and special

purpose lathes. Some smaller ones are bench mounted and semi-portable. The larger

lathes are floor mounted and may require special transportation if they must be

moved. Field and maintenance shops generally use a lathe that can be adapted to

many operations and that is not too large to be moved from one work site to another.

The Lathe is the most versatile of all machine tools in the workshop. Its main

operations are:

Sliding

Surfacing

Screw cutting

Drilling

Running

Boring

Tapping

Knulling

The Lathe size is given by the distance from the center of the headstock to the lathe

bed or by its overall length. The bed is made from high-grade cast iron. Mounted on

the bed is the headstock, which contains a clutch and the gears, which enable the

correct cutting speeds and feeds to be selected and obtained. The main spindle is

either screwed or flanged to take a chuck or face plate and is hollow to allow for long

bars. The center is tapered to accommodate other centers (live centre, dead centre,

half centre and bell centre for larger diameters).


97

The Tailstock on the machine can be moved to any position on the bed and has a

clapping lever. A hand wheel moves the barrel in or out and the barrel has a nose

tapper to allow for centers, drills and runners.

The carriage comprises the saddle, apron, cross-slide, compound or topside and the

tool post. The saddle rests on the slide of the bed and the apron carries the automatic

controls for moving the cross- slide and for engaging the lead screw. On top of the

cross slide is the compound slide, which can be manually operated and rotated

through 1800 and is useful for boring and tapper turning. Also mounted on the

compound slide is the tool post.

The Lead Shaft enables threads to be cut to desired pitch and the feed shaft enables

the carriage to be engaged automatically for uniform movement of the tool, thus

saving the operator from fatigue.

All Lathe machine have chucks. These can be either 3 –jaw chucks which have jaws

that move together from a single adjusting point and they are self centering. 4 –jaw

chucks are independent and can handle irregular work. Also included is the Face

Plate, which is used to hold work, which cannot be held between centers or in the

chuck.

The engine lathe is ideally suited for this purpose. A trained operator can accomplish

more machining jobs with the engine lathe than with any other machine tool. Turret

lathe and special purpose lathes are usually used in production or job shops for mass

production or specialized parts, while basic engine lathes are usually used for any type

of lathe work.

9.6The cutting tool

A cutting tool has one or more sharp cutting edgesand is made of a material that

harder than the work material. The cutting edge serves to separate chip from the

parent work material. Connected to the cutting edge are the two surfaces of the tool:

The rake face; and

The flank.


98

The rake face which directs the flow of newly formed chip, is oriented at a certain

angle is called the rake angle "α". It is measured relative to the plane perpendicular to

the work surface. The rake angle can be positive or negative. The flank of the tool

provides a clearance between the tool and the newly formed work surface, thus

protecting the surface from abrasion, which would degrade the finish. This angle

between the work surface and the flank surface is called the relief angle.

There are two basic types of cutting tools:

Single point tool; and

Multiple-cutting-edge tool.

Single point tool has one cutting edge and is used for turning. During

machining, the point of the tool penetrates below the original work surface of

the workpart. The point is easily rounded to a certain radius, called the nose

radius.

Multiple-cutting-edge tools have more than one cutting edge and usually

achieve their motion relative to the workpart by rotating. Drilling and milling

uses rotating multiple-cutting-edge tools. Although the shapes of these tools

are different from a single-point tool, many elements of tool geometry are

similar.

9.7Cutting conditions

Relative motion is required between the tool and work to perform a machining

operation. The primary motion is accomplished at a certain cutting speed. In addition,

the tool must be moved laterally across the work. This is a much slower motion,

called the feed. The remaining dimension of the cut is the penetration of the cutting

tool below the original work surface, called the depth of cut. Collectively, speed, feed,

and depth of cut are called the cutting conditions. They form the three dimensions of

the machining process, and for certain operations, their product can be used to obtain

the material removal rate for the process.

Where:

The material removal rate in mm3/s, (in3/s),


99

The cutting speed in m/s, (ft/min),

The feed in mm, (in),

The depth of cut in mm, (in).

Machining operations usually divide into two categories, distinguished by purpose

and cutting conditions:

Roughing cuts, and

Finishing cuts.

o Roughing

These cuts are used to remove large amount of material from the starting workpart as

rapidly as possible, in order to produce a shape close to the desired form, but leaving

some material on the piece for a subsequent finishing operation.

o Finishing

These cuts are used to complete the part and achieve the final dimension, tolerances,

and surface finish. In production machining jobs, one or more roughing cuts are

usually performed on the work, followed by one or two finishing cuts. Roughing

operations are done at high feeds and depths — feeds of .04-1.25 mm/rev (0.015-

0.050 in/rev) and depths of 2.5-20 mm (0.100-0.750 in) are typical. Finishing

operations are carried out at low feeds and depths - feeds of 0.125-0.4 mm/rev (0.005-

0.015 in/rev) and depths of 0.75-2.0 mm (0.030-0.075 in) are typical. Cutting speeds

are lower in roughing than in finishing.

9.8.1Cutting fluid

A cutting fluid is often applied to the machining operation to cool and lubricate the

cutting tool. Determining whether a cutting fluid should be used, and, if so, choosing

the proper cutting fluid, is usually included within the scope of cutting condition.

Lubrication for cutting tools


100

When machining a lot of heat is generated between the tool and the machined

component. If not properly cooled, the cutting tool becomes blunt. The most common

cutting lubricants are

i. Soluble oil and water

ii. Pure oil

iii. Paraffin

The advantages of using lubricant are:

(a) A tool and work are cooled ad higher cutting speeds maybe used.

(b) It helps the rubbing action between the chip and the tip of the tool,

which saves power, lasts longer and promotes a better finishing.

(c) It helps wash away the chips and keeps the cutting point clear

Material and their lubricants

Cast Iron – dry

Brass, Bronze & Aluminum – dry or little paraffin

Steel – Soluble oil and water.

Stages in metal cutting

Roughing cuts are used to remove large amount of material from the starting workpart

as rapidly as possible, in order to produce a shape close to the desired form, but

leaving some material on the piece for a subsequent finishing operation.

Finishing cuts are used to complete the part and achieve the final dimension,

tolerances, and surface finish. In production machining jobs, one or more roughing

cuts are usually performed on the work, followed by one or two finishing cuts.

Roughing operations are done at high feeds and depths — feeds of .04-1.25 mm/rev

(0.015-0.050 in/rev) and depths of 2.5-20 mm (0.100-0.750 in) are typical.


101

Finishing operations are carried out at low feeds and depths - feeds of 0.125-0.4

mm/rev (0.005-0.015 in/rev) and depths of 0.75-2.0 mm (0.030-0.075 in) are typical.

Cutting speeds are lower in roughing than in finishing.

A cutting fluid is often applied to the machining operation to cool and lubricate the

cutting tool. Determining whether a cutting fluid should be used, and, if so, choosing

the proper cutting fluid, is usually included within the scope of cutting condition.

Tool Geometry

The various angles in a single-point cutting tool have importance functions in

machining operations. Different types of angle such as rake angle, side rake angle,

cutting-edge angle, relief angle, nose radius exist and may be different with respect to

the workpiece.

Cutting Tool Selection

An important aspect in lathe machining is the selection on of cutting tools. The

following factors should be considered when choosing a cutting tool.

i. The tool should have a high core of fraction (hardness)

ii. Bending strength must be high.

iii. Should have high compressive strength.

iv. Should have high impact strength.

v. The tool should have the ability to work at elevated temperatures without

loosing its hardness properties (red hardness)

vi. Tool should be able to resist wear (abrasion resistance)

Thus the cutting tool should not be used under the following conditions:

i. High pressure

ii. High friction force

iii. High heat generation

The type of cutting tool material in common use is:

(a) Carbon steel and steels – for machine thread taps and core drills and

for making files.________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

102

(b) Alloy Tool Steels – for making files, core drills & taps

(c) High speed steels

(d) Cemented carbides – twist drills, milling cutters single point tools,

core drills & reamers.

Overview

Machine tools can be operated manually, or under automatic control. Early machines

used flywheel to stabilize their motion and had complex systems of gears and levers

to control the machine and the piece being worked on. Soon after World War 2, the

NC, or numerical control, machine was developed. NC machines used a series of

numbers punched on paper tape or punch cards to control their motion. In the1960,

computers were added to give even more flexibility to the process. Such machines

became known as CNC, or computerized numerical control, machines. NC and CNC

machines could precisely repeat sequences over and over, and could produce much

more complex pieces than even the most skilled tool operators.

Before long, the machines could automatically change the specific cutting and

shaping tools that were being used. For example, a drilling machine might contain a

magazine with a variety of drill bits for producing holes of various sizes. Previously,

either machine operators would usually have to manually change the bit or move the

work piece to another station to perform these different operations. The next logical

step was to combine several different machine tools together, all under computer

control. These are known as machining centers, and have dramatically changed the

way parts are made.

From the simplest to the most complex, most machine tools are capable of at least

partial self-replication since they are machines, and produce machine parts as their

primary function.

Material

Aluminium, copper alloys, steels, stainless steels, high-temperature alloys, refractory

alloys, titanium alloys, cast irons, thermoplastics, thermosets, etc… are examples of

different type of materials used.________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

103

9.9 Turning

Turning is the process whereby a centre lathe is used to produce "solids of

revolution". It can be done manually, in a traditional form of lathe, which frequently

requires continuous supervision by the operator, or by using a computer controlled

and automated lathe which does not. This type of machine tool is referred to as

computer numerical control, better known as C.N.C. and is commonly used with

many other types of machine tool besides the lathe.

When turning, a piece of material (wood, metal, plastic even stone) is rotated and a

cutting tool is traversed along 2 axes of motion to produce precise diameters and

depths. Turning can be either on the outside of the cylinder or on the inside (also

known as boring) to produce tubular components to various geometries. Although

now quite rare, early lathes could even be used to produce complex geometric figures,

even the platonic; although until the advent of C.N.C it had become unusual to use

one for this purpose for the last three quarters of the twentieth century. It is said that

the lathe is the only machine tool that can reproduce itself.

Facing is part of the turning process. It involves moving the cutting tool

across the face (or end) of the workpiece and is performed by the operation of

the cross-slide, if one is fitted, as distinct from the longitudinal feed (turning).

It is frequently the first operation performed in the production of the

workpiece, and often the last- hence the phrase "ending up".

9.9.1 Turning operations

The turning processes are typically carried out on a lathe, considered to be the oldest

machine tools, and can be of four different types such as straight turning, taper

turning, profiling or external grooving. Those types of turning processes can produce

various shapes of materials such as straight, conical, curved, or grooved workpiece. In

general, turning uses simple single-point cutting tools. Each group of workpiece

materials has an optimum set of tools angles, which have been developed through the

years.


104

9.9.2Assigning cutting parameters in turning operations

i. Select the cutting depth, t

ii. Select rate of the feed, s

iii. Select speed, v

NB: Cutting temperature, wear and tool life are influence least by the cutting depth, t

more by the rate of feed, s and most by the cutting speed, v.

The cutting speed should be less than 3 000rpm

Feed rate for roughing: 1,5mm – 25mm/rev or /sec

Feed rate for finishing: 0,5mm – 1mm/rev or/sec

Cutting speed for semi finishing: 500 – 800 rpm

Cutting speed for semi finishing: above 800rpm.

Cutting Tool Clearance

The following are recommended angles or tool rake

Mild steel: 200– 2700

Cast Iron: 10 –800

Brass: 10 – 800

Bronze: 10 –800

Copper: 3000

Aluminum: 4000

Material removal rate

The material removal rate (MRR) in turning is the volume of material removed per

unit time in mm3/min. For each revolution of the workpiece, a ring-shaped layer of

material is removed.

MRR = pi×Davg×d×f×N where

Davg: Average diameter

N: Rotational speed of the workpiece

f: Feed

d: Depth of cut


105

Turning forces

The forces acting on a cutting in turning are important in the design of machine tools.

The machine tool and its components must be able to withstand these forces without

causing significant deflections, vibrations, or chatter during the operation. There are

three principal forces during a turning process: cutting force, thrust force and radial

force.

Cutting force acts downward on the tool tip allowing deflection of the

workpiece upward. It supplies the energy required for the cutting operation.

Thrust force acts in the longitudinal direction. It is also called the feed force

because it is in the feed direction of the tool. This force tends to push the tool

away from the chuck.

Radial force acts in the radial direction and tends to push the tool away from

the workpiece.

Although it requires less-skilled labor, the engine lathes do need skilled labor and the

production is somewhat slow. Moreover, it can be accelerated by using a turret (In a

turret lathe, a longitudinally feedable, hexagon turret replaces the tailstock. The turret,

on which six tools can be mounted, can be rotated about a vertical axis to bring each

tool into operating position, and the entire unit can be moved longitudinally, either

manually or by power, to provide feed for the tools) and automated machines.

Elements of the Cutting process in turning operation

In order to machine part by machining blank, definite motions must be imparted to the

blank and cutting tool. These motions are divided in o

i. Working motions (serves the effects of cutting process)

ii. Auxiliary motions – serves to prepare the machine, work and tool for

cutting process and for completing the operations.

It is important to note that after mounting the blank onto the machines, the speed and

feed should be selected taking into account the type of material to be machined. Thus ________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

106

hard material e.g. steel requires slow speeds and light feeds while soft material such

as brass require high speeds and feeds.

NB Test running the blank to see if its running true is important before any machining

is carried out. This is done to ensure complete removal of material from the work

piece.

Setting Speeds on a Lathe (n)

To select speed on a lathe, you place/put one hand on the face plate or chuck and turn

the lathe spindle slowly by hand, while shifting the lever position. This enables the

levers to engage the gear teeth without clashing.

NB: Never change speed when lathe is running.

Setting Feeds (s)

i. Select the desired feed on the chart.

ii. Move tumbler lever #4 into the hole directly below the selected feed.

iii. Follow the row in which the selected feed is found to the left and set the feed

change levers (No1 &11) to the letter indicated.

iv. Set lever (No111) to disengage the lead screw.

NB: Turn the head stock spindle by hand and see that the feed rod turns to ensure that

all levers are engaged before turning on the lathe.

Analysis of Cutting Parameters.

(a) Cutting Speed – is a travel of a point on the cutting edge relative to the surface of

cut in a unit time e.g. let Dmm be the blank diameter, D0 mm be the machined surface

diameter, N rpm be the rotation speed of the spindle.


107

(b) Rate of feed – is the travel of the cutting edge in the direction of the feed motion

relative to the machined surface in a unit time. The feed can be expressed as

Distance traveled by the tool in a minute i.e. feed (Sm) = mm/min.

Distance traveled by the tool in one revolution of the spindle is S =

mm/min.

Relation between Sm and S is given by

S = Sm/N where N = rpm (angular velocity)

Cutting depth (t) – for external longitudinal turning

Rate of Chip Removal (Q) – this is the volume of chip removed in one minute of

operation.

Q = V.t S cm3/min where s, t&v are expressed in mm, mm/rpm and mm/min

respectively.


108

Fig 17


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9.9.3 Milling Machine

A milling machine is a machine tool used for the shaping of metal and other solid

materials. Its basic form is that of a rotating cutter, which rotates about the spindle

axis (similar to a drill), and a table to which the workpiece is affixed. The cutter and

workpiece move relative to each other, generating a toolpath along which material is

removed. The movement is precisely controlled, usually with slides and leadscrew or

analogous technology. Often the movement is achieved by moving the table while the

cutter rotates in one place, but regardless of how the parts of the machine slide, the

result that matters is the relative motion between cutter and workpiece. Milling

machines may be operated manually or by CNC.

Milling machines can perform a vast number of operations, some of them with quite

complex tool paths, such as slot cutting, planing, drilling, diesinking, rebating,

routing, etc.

Cutting fluid is often pumped to the cutting site to cool and lubricate the cut, and to

sluice away the resulting swarf.

There are various types of milling machines available but at SIMBI, the milling

machine is a Knee type generally known as Universal Milling machine. It is called a

knee type because of the overhanging of he cross slide and the table. This machine

can swing in both directions for helical milling and the spindle can turn in both

directions.

Milling is a machine process whereby a surface is generated with a rotating toothed

cutter. Each tooth takes an individual chip to form a uniform profile.

Milling Machine Parts

The Spindle – provides the drive to the arbor aid cutters.

Arbor – drives and holds the cutters in correct position.

Arbor Support - It fits and clumps to the over atm. Can be secured in any

position to align and support the arbor.________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

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Knee – It is fitted to the column and can manually & automatically moves

vertically up and down.

Dividing Head

An important use of the milling machine is for cutting slots, gloves, teeth and gears

that are to be placed equally around the circumference of a cylinder or disc. A

dividing head is used for such purposes. This unit has a single start worm with a 40:1,

thus the index plate has for a chuck turn.

Index Plate

The object of this plate is to enable one turn of the rank. In the plate are a number of

holes in a circle, each circle containing a different number.

The crank can be adjusted to a radius that will fit any desired circle of holes.

The sector arms can be adjusted to include any remainder on any number of holes.

9.9.5The shaping Machine

The main function of the machine is the production of flat surfaces, which are

obtained by combined line tool cuts with a perpendicular feed. It is preferred for the

quickness with which the work can be set-up and the good standard of accuracy.

Shaper Drive

An electric motor is mounted on a platform at the rear and drives the gearbox pulley

and clutch with a V- belt. The gearbox delivers the power to a pinion, which drives

the stroke wheel. Mounted on the face of the stroke wheel is the crankpin, which is

incorporated with a sliding block working in dovetail slide ways, running across the

face of the wheel.


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A link arm connects a stroke wheel to the ran and is pivoted at the bottom of the

machine. The feature for shaping machine is that for every cutting stroke there is an

idle return. The tool is carried on a holding slide of the tool holder which is attached

to the end of the ran through a circular flange which is graduated in degrees. The feed

is activated by a screw from a handle at the top of the slide.

9.9.5. The Principle of he speed of the Stroke

Quick Return Motion

Although the pivot distance covered in a straight line from A –B is the same from B –

A the peripheral distance is much shorter on the return stroke thereby speeding up the

forward stroke

Mounting of Cutter

The cutter is carried on the arbor being keyed and is supported between collars. It is

essential that the arbor run through in all places i.e. along its length to make full use

of all teeth on the cutter. Milling cutters are made from Hs, hardened and then

ground.

Rotation and Feed.

When operating a cut with a milling cutter the normal relation between the direction

and rotation are of importance. These are also called up cut and down cut milling.

NB: Climbed milling should never be used unless the machine is equipped with

backlash elimination or else a cutter will overrun itself (Climb up or dig in)

Care and Operation of the machine

Cleaning the table after every use.

Oil and greasing the machine regularly.

Always use draw bolt to secure arbor.


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Never loosen or tighten arbor nut without the over –atm support in position

and do not leave spanners on the arbor nut.

Always clamp up the slides when traversing a cut.

Do not drop cutters.

Always clean collar faces before assembly onto the arbor.

Always note the direction of rotation before engaging automatic.

9.9.6Milling as a process

Milling is the process of cutting away material by feeding a workpiece past a rotating

multiple tooth cutter. The cutting action of the many teeth around the milling cutter

provides a fast method of machining. The machined surface may be flat, angular, or

curved. The surface may also be milled to any combination of shapes. The machine

for holding the workpiece, rotating the cutter, and feeding it is known as the milling

machine.

9.9.7Milling operations

Slab milling

In peripheral (or slab) milling, the milled surface is generated by teeth located on the

periphery of the cutter body. The axis of cutter rotation is generally in a plane parallel

to the workpiece surface to be machined.

Face milling

In face milling, the cutter is mounted on a spindle having an axis of rotation

perpendicular to the workpiece surface. The milled surface results from the action of

cutting edges located on the periphery and face of the cutter.

End milling


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The cutter in end milling generally rotates on an axis vertical to the workpiece. It can

be tilted to machine tapered surfaces. Cutting teeth are located on both the end face of

the cutter and the periphery of the cutter body.

9.9.7.1Methods of Milling

Up milling is also referred to as conventional milling. The direction of the cutter

rotation opposes the feed motion. For example, if the cutter rotates clockwise , the

workpiece is fed to the right in up milling.

Down milling

Down milling is also referred to as climb milling. The direction of cutter rotation is

same as the feed motion. For example, if the cutter rotates counterclockwise , the

workpiece is fed to the right in down milling.

However the chip formation in down milling is opposite to the chip formation in up

milling. The figure for down milling shows that the cutter tooth is almost parallel to

the top surface of the workpiece. The cutter tooth begins to mill the full chip

thickness. Then the chip thickness gradually decreases.


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115


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9.9.8Grinding Wheel


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Grinding wheels are as important to any mechanical workshop as any other machine.

They are used for grinding shaping and providing a finish to any work piece. Several

factors are considered when grinding. These are

Material to be ground

Amount of material to be removed and finish desired

Arc of contact

Type of grinding machine

Other influential variable factors in grinding are:

o Wheel speed

o Work speed (speed of work piece)

o Condition of machine

o Skill of workman.

NB: When selecting a grinding wheel for general workshop practice non-ferrous

metals should not be ground on any grinding wheel (material will clog the wheel.

Also important to note is that Green wheel soft wheel should only be used for

grinding tungsten carbide tools.

The following physical properties of material are also important to take into account

when using grinding wheels.

(a) Aluminum oxide grinding wheels should be used for materials of high

tensile strength e.g. carbon steels, alloy steel, Hss, wrought iron and

tungsten.

(b) Silicon carbide grinding wheels are used for materials of low tensile

strength e.g. cast Iron, Chilled Iron, Marble granite, Cementile,

carbides and to a lesser extend non-ferrous groupings.

Factors affecting Selection of Grit of Wheel


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i. Amount of material to be removed, use a course wheel for fast removal.

ii. Finish desired use a fine wheel for time finish. Physical Property of material, -

use course grain for duck file material and finer grain for hard, dense or brittle

material.

Factors affecting the selection of the grade of wheel.

i. Physical properties of a material - use hard wheels for soft materials and soft

wheel for hard materials.

ii. Arc of contact – the shorter the contact the harder the wheel should be.

iii. Wheel speed and work speed – the higher the ration of the wheel speed to

work speed the softer the (grinder) grade.

iv. Condition of machines - machine in poor conditions would normally require

hard wheels.

v. Operators Skill – skillful operators can use softer wheels. Every grinding

wheel has two components: Abrasive that does the cutting & Bond that holds

it together.

Cutting efficiency depends largely upon the abrasive and the grade and hardness

depends upon the relative percentage of the bond used. The functions of the bond are:

i. It holds the abrasive grains together.

ii. It provides a factor of safety at running speeds.

iii. It modifies the hardness or strength of the wheel.

Factors affecting selection of bond on a grinding wheel

i. Dimensions of wheels - wheels subjected to bonding strain should be made

from elastic or rubber bond followed by extremely thin abrasive. NB; Wheels

over 900mm in diameter are usually made from a silicate bond.


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ii. Rate of Cutting – for most rapid cutting, use vitrified wheels and rubber

wheels for speeds above 2000rpm.

iii. The finish desired – Use elastic or rubber wheels best finish and silicate for

cutlery.

Common Abrasive in use

i. Emmery – confined to abrasive paper and cloth

ii. Silicon Carbide (C) - for grinding tungsten tipped tools

iii. Aluminum Oxide (A)

iv. Crushed Diamond

v. Boron Carbide

Types of Bonds

i. Vitrified (V) – this is the most common

ii. Silicate (S) – for large wheels

iii. Shellac (Elastic Bond) E – for thin cut off wheels.

iv. Resinoid (B) –for high-speed wheels.

v. Rubber (R) - for thin cut of wheels.

Grinding wheel marking

The selection of a grinding wheel is affected by these markings.

i. Abrasive type

ii. Grain size

iii. Grade of hardness and strength of bond


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iv. Structure o f spacing of grains

v. The kind of bond

vi. Manufacturers’ record

Mounting of a Grinding Wheel

Before mounting the wheel, it must be checked for cracks. All new wheels should be

run at full speed for I minute before applying work on it, during which time the

operator should stand to one side. Work should never be forced against the cold

wheel but should be applied gradually. Grinding on the flat sides of speed wheels is

often hazardous.

Balancing the Grinding Wheel

The procedures when balancing a wheel are:

i. Balancing it

ii. Mounting it on the machine

iii. Truing it (dressing the wheel)

iv. Balancing it once again.

Truing is carried out with a diamond, which has a shearing action on the abrasive

grains and the bond. It trues the wheel face parallel to the axis of the machine.

Dressing is a process of cleaning and opening up of the face using a star wheel

dresser.

NB: Care must be taken not to traverse too fast when dressing or truing a wheel. A

good flow of coolant must be used to prevent overheating of the stone and the dresser.

Diamond Abrasive Wheels


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These are the most common wheels in use and are made from diamond particles

(diamond dust) held in either a Resinoid or Vitrified bond. These are recommended

for cementite tipped tools, glass, ceramic and stone. The recommended surface speed

are 1500 – 2000rpm.

Rules for Diamond Wheels

i. Mount the wheel so that it turns time.

ii. Keep the wheel in its collect until it is worn out.

iii. Undercut the steel shank on carbide tipped tools.

iv. Lubricate the face of the wheel at all times.

v. Do not dress the wheel with a diamond dresser.

vi. Do not grind or other relatively soft materials.

CHAPTER 10

10.0 The maintenance work that I carried out in the Plant during my attachment

at Mechanical Engineering Department

The mechanical department concern for the plant is ranges from monitoring the plant

itself as well as the process. The plant is comprised of Static and Dynamic machines

the majority being supported on structural frames.

The most notable dynamic machines are:

i. The conveyor belt system

ii. The rotary Kiln and cooler

iii. Wet scraper


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iv. V- belts

Static running (rotating) machines include:

i. Electric motors

ii. Gear boxes

iii. Water pumps

iv. Crusher.

Conveyor Belts

Conveyor belts are made of a carcass to transmit power and carry tension. Sheet metal

covers from blows, abrasion and keep out moisture protect the carcass. Carcass

consists of plies or layers of rubber impregnated fabric or cord. The rubber compound

on the fabric is called friction skims (thin layer of rubber between plies)

Belt Support

These are straight beds, which are narrow hang* platforms of wood, plastic or steel.

Mainly used for carrying objects that requires individual handling. Belts run on idlers.

Belt idlers convey bulk material in volume at medium to high speed. They are made

from pressed steel or steel tubings in anti-friction bearing. Their purpose is to shape or

trough the belt to increase it carrying capacity.

There are 17 conveyor belts at SIMBI plant. A gearbox compiled to an electric motor

drives each. The electric motor here is the source of drive; hence, the size of the

motor used depends on the length of the belt, angle of inclination and the load

carrying capacity of the belt. Thus, the size of the gearbox used is as well differently

proportional to the length of the belt and the load resistance.

BC1 – BC11 are the main conveyor belts and these cover from the raw material

section to the production section. The 11 main conveyor belts are installed in such a

way that they are repairable and adjustable in the unlikely event of a major crack

breaking.


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Within the stock house, there is another belt, smaller in size to the main belts which

runs across the storage bins as it transport charcoal to its storage bin

The remaining 5 belts are for the weighing feeders (4) and one (1) used in the

production house.

NB: It is important to note that BC 4 transports both Iron Ore and Limestone into the

storage bins. Within the storage bins, there is a gate valve, which is used to direct

either Iron Ore or Limestone into its proper storage bin. An assistant from the

mechanical department operates this valve. Therefore, a lot of care must be exercised

not to mix the two raw materials in one bin by opening the valve in the wrong

direction. To avoid the operator limit switches are used to indicate the position of the

valve.

10.1Repair and maintenance carried out on conveyors

i. Check the condition of head and tail pulleys. If excessively worn replace with

a new one. Also greasing the bearings on which these pulleys run.

ii. Checking the condition of bearings and replacing when it collapses.

iii. Checking the condition of rollers on which the belts run. If rollers are

excessively worn out replace them.

iv. Checking for cracks on belts. Joining the belts using special glue.

v. Securing frames which support the belts and all covers.

vi. Checking status of sensors and metal detectors. Adjusting or replacing where

necessary.

10.2 The Rotary Kiln Section


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Fig 18

The rotary Kiln acts as a furnace into which the process of coming up with sponge

iron takes place. I is compiled to a gear box which is driven by a variable speed

electric motor but it normally rotates at a constant speed of 1rev 144 sec.

There is also an auxiliary electric motor, which is used to drive the Kiln when the

main electric motor is fault or when carrying out maintenance work.

The Kiln sits on rollers placed at each end. The rollers are supported by ball and

roller bearings, which resist radial and axial loading respectively.

Around the Kiln shell are 7 air fans with air ducts for air circulation. These fans are

electric motor driven. There are also Thermocouples placed radially along the Kiln

and these are used for temperature measurement.


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Just at the middle of the Kiln, there are slip rings for thermocouple and quick response

Thermocouple (QRTs) temperature mill volts readings. There is also another set of

slip rings, which is used for power supply to the shell air fans. The inlet and the outlet

of the Kiln sit and rotate on a brass lining referred to as hood. In these two areas a lot

of heat is generated hence cooling is provided by a continuous supply of air into the

pockets around.

Repair and Maintenance work carried on the kiln

i. Greasing the hood regularly

ii. Lubricating roller bearings

iii. Cleaning slips rings.

iv. Oiling gearboxes and replacing worn seals and gaskets.

v. Thermocouple movement (this prevents sticking)

vi. Checking the temperature of the electric motors, loose connections, removing

dust and listening to any abnormal noises.

vii. Purging Kiln inlet and outlet pressure impulse lines.

viii. Taking Kiln outside temperature periodically.

ix. Checking for any connections of T/C wires.

10.3 The Cooler

From the Kiln Iron Ore now Sponge Iron goes into the cooler. This is achieved by

free movement due to the angle of inclination. The cooler is constantly supplied with

water, which is speed across the whole surface area. The sponge Iron when it gets

into the cooler has to be cooled from as a high a temperature as 7000c temperatures

below 1200c before it can be transferred to the storage bins.


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The cooler is also driven by a gearbox (smaller as compared to the main Kiln gearbox,

which gets its drive from an electric motor. The water, which is pumped to the

cooler, circulates as the cooling process takes place.

Repair and Maintenance of the Cooler Section

i. Checking the flow rate by observing the flow sensor indicator.

ii. Remove clogging to permit free flow of water.

iii. Welding broken water pipes due to rusting.

iv. Checking electric motor temperature, loose connections and abnormal noises.

v. Changing oil in the gearbox

vi. Checking for oil leaks and level & topping up.

vii. Changing worn oil seals and gaskets.

viii. Lubricating bearings

ix. Checking coition of valve deflector.

10.4 Wet Scrapper Section

During the production process, a lot of dust is extracted and should be disposed off in

ways that are environmentally correct. Also during this extraction period the gases

and dust are very hot such that it is not recommended to dump it as it is hazardous to

both human beings and vegetation. Most of the dust /gases comes out through the

Gas

o Gas Conditioning Tower. The GCT has a constant supply of water, which

mixes with the dust as it tries to escape into the atmosphere. The dust on

mixing with water becomes dense. Instead of going up the tower it goes

down the tower and out through the extraction point. Below this outlet is a

water reservoir where the wet dust settles. Within the water reservoir, there is


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a chain link with blades, which is driven at the other end by a gearbox

coupled to an electric motor at a very slow speed. The blades scrap the wet

dust out of the water.

Repair and Maintenance carried on Water scrapper

i. Checking the status of the water level sensor adjusting sensing distance and

replacing with new one when fault.

ii. Checking condition of floater.

iii. Checking water level, if low opening supply valve. Chain and blades. Replace

worm out blades

iv. Lubricating bearings.

v. Removing scrapped wet material around the area.

10.5 Gearboxes

All gearboxes within the plant were manufactured by Radicon. From my

observations and questioning the gearboxes, seem to be very robust as non has

suffered a breakdown so far.

The gearboxes are used for steeping up or stepping down both speed and torque

depending on the mode of exploitation. At SIMBI, most of the gearboxes are step

down gearboxes the gearboxes are driven by high-speed electric motors, which runs at

speeds ranging between 1000-1300rpm.

The Electra gearboxes have helical gears. Theses offer smooth noise free operation

and can achieve torque without subjecting the gears to high stresses. The bearings,

which support the shafts, are either taper roller or ball bearings. These preferred

because of their ability to sustain high loads and stresses. The gearboxes can be oiled

or greased lubricated.


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Repair and Maintenance on gearboxes

i. Checking oil level s and leaks.

ii. Topping oil.

iii. Replacing worn seals and gaskets.

iv. Replace worn rubber compiling between electric motor & gearbox.

v. Checking and changing bearings.

vi. Lubrication of bearings.

vii. Changing oil

viii. Securing loose mounting bolts.

ix. Checking condition of gear teeth.

10.6 Water pumps

Excluding the ESP, there are currently six water pumps working at plant, and these

are mainly used for cooling purposes. The pumps are:

a) Make up Pumps x 2

b) Cold Water Pumps x 2

c) Hot Water Pumps x 2

The pumps are centrifugal type, single stage (multistage are for the ESA).

* Cold well pumps draw water from a reservoir and supply it under predetermined

pressure to the cooler for cooling purposes of Sponge Iron. Hot Well pumps draw ho

water from another reservoir and pump it to cooling fans where it is cooled before

being pumped again to the cooler.


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Make-up pumps are used to cater for shortfalls results from evaporation, leakages,

spillages when the coolants reaches levels below the normal requirements makeup

pumps are opened and pump in water to cover the loss. Each of the above pumps

delivers a volume of 5litres per revolution and has a lead of 6 meters

I carried an installation of one of the make-up pumps. During installation one should

take note of the normal direction of rotation when in use otherwise incorrect

installation will result in no delivered of water at all also to take note of is the type of

coupling used in this case it is a flange type. This is the most preferred because there

are no shock loads involved. The pump does not need any form of lubrication since

bearings are repacked and sealed.

Repair and Maintenance carried on Water Pumps

i. Replacing seal and packing.

ii. Pining the pump after installation

iii. Checking for misalignment and realigning.

iv. Checking for any bend, crack on section line and repairing as necessary.

v. Checking and removing dirty.

vi. Checking condition of impeter if not damaged.

vii. Checking conditions of bearings and lubricating them.

10.7 Crusher

The coal supplied to SIMBI is sometimes and in most cases large boulders not

suitable for use directly in the production process. It has to be reduced to

recommended size and this is achieved by the use of a jaw crusher. This crusher

consists of fixed jaws and moving jaws. It is driven by an electric motor through V-

belts. During the reciprocal movement of the jaws coal boulders are trapped in

between jaws and are crushed to set size. The crushed coal is taken through screens

where large boulders are returned to the crusher for further reduction.


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Repair and Maintenance of Crusher

i. Checking and adjusting belts tension

ii. Replacing worn jaws.

iii. Adjusting jaws gap size.

iv. Lubricating bearing

10.9 Electric Motors

These are the source of drive power to all machines in the plant. Most of the electric

motors in use are the 3 Induction motors.

Repair and Maintenance of Electric Motors

i. Check for any loose connection.

ii. Dedusting.

iii. Covering the motors.

iv. Listening to any abnormal noises

v. Remove and replace worn bearings.

CHAPTER 11

11.0 Screens

I have mentioned earlier on that raw material are supplied in different sizes and so is

the end product which comes out in different sizes hence some of the material is not

required at all. The unwanted material is separated by means of screening. These

screens are placed at various places within the flow process of raw materials up to the

product house. The screens serve as sieve to select correct sized particles of both raw

materials and sponge iron. These screens are mesh wired and are of different sizes

placed one after the other in accordance to size.


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At the screen house there are 2 screens each for coal and iron ore. Dust and unwanted

particles are disposed off through chutes. At the product house there are 4 screens, all

of different sizes and these separate large particles from correct size particles and dust

with the second screen separating the correct size from dust. All the 3 particle sizes

are directed via different chutes.

Repair and Maintenance carried on screens

i. Inspecting whether correct particles size screening is taking place , if not

remove screens.

ii. Check whether screen are damaged if so repair by welding.

iii. Check whether screening is taking place, if not remove clogging.

11.1 Double Pendulum Valves (DPV)

As the process of screening is carried out, a lot of dust is extracted or removed. All

round the plant there are pipes laid to direct dust to a particular point of collection.

Just below, the screens and other ducts (chutes) (toward the outlet) are doubled

Pendulum valves, which opens and close for extraction of dust. These valves are can

operate and the cans are driven by a single phase (1) motors.

Also incorporated within the working mechanism of DPVs are return springs, which

allow closing of the valves.

Repair and Maintenance of DPV

i. Check the tension of the spring replaces spring when the tension is weak.

ii. Check cam bearings/ bushings condition. Lubricate if necessary or replace

when worn out.

iii. Check cam if in condition.

iv. Inspect for any loose connections on motor, secure monitoring bolts and listen

to any abnormal noises.


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11.2 Welding

During my attachment period at the workshop I was also taught how to weld I did

mainly two types of welding:

o Gas welding

o Arc welding

Having taught that all workshop processes have their specific safety precautions and

safe working procedure to be followed. I was assigned to produce several window

frames and doorframes .I was also made to produce some steel fabricated products

with the guidance of Mr. Neil and Mr. Mugova the senior Boilermaker and Welder

respectively.

Types of joints

Before carrying out any welding, the type of joint best for the job should be

ascertained.

There are 4 types of joints in common use. These are:

o T –joint.

o Butt joins.

o Cuter joint.

o Lap joint.

T- joint

T – Joint mostly used at a flange to weld junction in late girders, branches attached to

main pipe and stiffness welding to panel.

Butt joint

Used for joint where load is transmitted along common axis.


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For joining length of pipes, plates and flanges on bridge girders.

Corner joint

There are normally associated with Box sections

Lap joint

The bond is over a small area of interface as a narrow strip along the length of joint.

Used in sheet fabrications.

11.3 Oxy-Acetylene Welding

An oxygen and acetylene mixture is burnt at the tip of a designed nozzle which is

fitted to a torch body. The welder uses the flame to melt the parent metal to form a

weld pool. Filler metal if required is added separately by manual feeding off a wire

into the bading edge of the welding pool.

Parent Metal Fusion.

To make a weld of good quality the surface of the parent metal has to be melted

before the added electrode or filler metal is allowed to flow into the joints.

Heat input in gas welding

Oxy Acetylene welding depends on a chemical reaction to generate heat which is then

transferred to the work.

The flame has two zones

1. Inner cone

2. Outer enveloped

Inner Cone


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Acetylene (C2 H2) burns in that emerges from the nozzle to give carbon monoxide

(C0) and oxygen heat,

C2 H2 + O2 2CO+H2 + heat

Outer enveloped

Carbon monoxide and hydrogen burns in atmospheric oxygen giving carbon dioxide,

water and heat.

4C+H2 +3O2 4Co2+2H2O+heat

NB: Total quantity of heat produced depends on the amount of acetylene, which is

burnt. If more heat is required, the flow rate of acetylene is increased and oxygen

supply is adjusted to give the correct type of flame.

Types of flames

Carburizing flame

Temperature 21000c

Used when welding aluminum or where excess oxygen on metals would cause

oxidation

Neutral Flame

Temperature –32000c

Used for welding all normal welding on mild steel, cooper and magnesium.

Oxidizing flame

Temperature-32000c


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Used for welding brass and bronze. On an oxidizing flame, temperatures do not

change but due to more oxygen being released, the heat is increased.

Safety measures when using Gas welding

11.4 Acetylene Cylinders

The gas is stored together with a solvent acetone in maroon painted cylinders.

Note that the cylinder valves outlet is screw left-handed.

As the gas is highly inflammable, all joints must be checked for leaks using

soapy water.

Acetylene cylinders must be stored and used in an upright position and

protected from excessive heat and coldness.

Acetylene can form explosive compounds in contact with certain metals and

alloys especially copper and silver. Joint fittings made of copper should never

be used.

The colour of cylinders, valve threads or markings must not be altered or

tempered with in any way.

11.5 Oxygen Cylinders

The gas is stored in black painted cylinders.

Never allow oil or grease to come in contact with oxygen fittings

because spontaneous ignition may take place.

Oxygen must not be used in ease of compressed air.

Do not allow cylinders to come in contact with electricity.

Cylinders must not be roughly, knocked or allowed to fall to the

ground.


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11.6 Gas Welding

When the direction changes to right ward movement, the torch angle becomes 40o-

50o

NB: When lighting or extinguishing the welding torches the manufacturers

instructions should always be followed.

To clean the nozzle use special nozzle cleaners not steel wire.

11.7 Manual Metal Arc Welding

This has become an efficient and reliable means of welding sheet and metal plate. It

is used for welding the heavier gauge metal plates ranging in thickness from 2mm –

75mm. It is used for either mild steel stainless steel and aluminum metals.

Principals of Arc Welding

It is based on the principal that intense heat is obtained from an electric current, which

creates an arc between a metal electrode and the plates which are to be welded. The

heat produced will fuse the edges of the plates at the joint forming a small pool of

molten metal. A small addition of molten metal comes from the tip of the electrode

and is deposited into the molten pool. When it solidifies it forms a very strong

welded joint.

Heat input In Arc Welding

Arc power: Input (watts) (j/s) = Arc Voltage x Arc Current

E.g. Power Input = 20V x 150 A = 3000W.

Input at any given point depends on the travel speed. Hence knowing the energy being

supplied to the arc and travel speed, it is possible to calculate the heat input and to

express it as the amount of heat per unit length of wed run.

NB: Current Range is normally 25-350 Amps


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Heat input is normally 0, 5 – 11kj

Factors governing heat Input

i. Current

ii. Arc voltage

iii. Travel speed

Electrodes To a large extend the degree of success of the welding operation depends

on the coating which is varied to suit different conditions and metals.

Functions of Coating

i. Stabiles the arc and enable the use of arc welding.

ii. Cleans away an impurities

iii. Speed up the welding operation by increasing the rate of melting.

iv. Prevents oxidation by forming a slag over the weld, slow the rate of cooling of

the weld

Electrodes identification

The following codings are used:

i. Strength, toughness and coating (STC) code.

ii. Electrode Dimensions and tolerance.

iii. Electrode and bundle identification.

Essential Factors of Arc welding

i. Correct choice of electrode

ii. Correct arc length


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iii. Correct speed of travel

iv. Correct current.

Welding Accessories

In addition to the welding machines, the following should also be part of the welder

before commencing any work:

i. Electrode holder

ii. Welding earth

iii. Head shield (face screen)

iv. Gloves

v. Leather Aprons

vi. Goggles

vii. Cleaning tools

viii. Welding booth

Arc Welding Positions

Arc welding operations can be carried out with work in every position but the degree

of skill required of the operator will vary considerably depending on the position of

the joint.

i. Flat (downward position)

ii. Horizontal position

iii. Vertical position

iv. Overhead position


139

NB: The successful step towards electric arc welding is learning to strike and

maintain the arc and run a straight bead of weld metal

First set the control unit to correct setting specified for the size of electrode being

used. Then bring the electrode in to contact with the plate by either

i. Tapping

ii. Scratching

Weld Defects: Under – cutting grooves appear in the base metal on

both sides of the bead this results due to high current. Overlapping –

Molten metal fall from the electrode with out fusing with the base

metal. This result when current is set too low.

CHAPTER 12

Electrical Department Internship

12.0 Introduction

The Electrical Engineering Department is one of the production sections which have

its full and committed participation in rendering services in the repair and

maintenance of all electrical faults and machinery at the plant. I however recommend

that most of our courses require more practicals and industrial visits even on-site

learning.

The relationship between Mechatronics and Electrical Engineering has been derived

from the fact that I did the following courses which are a major in the field of

Electrical Engineering:

Electrical Machines which consist of :

o DC Machines

o Transformers

o AC machines

o Generators


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o All types of Electric motor starters

Electrical Principles and Principles of Electronics which consist of :

o All electrical principles and their application in the industry.

o Most electronic components and their application in Design and in the

industry.

Since industrial internship is mainly applying most theoretical knowledge that you

had from the University, it was an easy period of training in this Department as I had

vast knowledge in Electrical Machines.

Mr. Srihari heads the department and the supervisors are Mr. M. Munyariwa and Mr.

Mahove. There are 5 artisans and 8 assistants all committed to offering first class

service in line with the company’s goals. During my first days at the department I

was taken through a rigorous learning process to ensure that I get well acquainted

with the necessary safety precautions, knowledge and procedure of working on

(handling) high voltage.

12.1 Safety Precautions

i. No unauthorized entry into designated high voltages areas such as 33kv, 11kv

substations and the MCC.

ii. No switching without authority.

iii. When switching, you have to know what you are doing.

iv. When entering into the substation, always leave the gates wide open.

v. Fire extinguishers must be installed on accessible points and should always be

in good working conditions.

vi. Before carrying out any work, you must make sure whether power is ON or

OFF. Isolate power when necessary..

vii. Wear proper safety clothing. When switching always put on rubber shoes.

viii. Put dangers warning signs on main switches and if necessary lock.

ix. Work environment must be clean and free of obstacles.

x. Never put sharp objects in the pocket.

12.2 The 33/11kv and 11kv/415v Transformers


141

The Electrical department tasks starts at the supply substation from ZESA which is a

33kv. SIMBI substation receives 33kv from ZESA and steps it down to 11kv through

a 10MVA transformer.

From the 10MVA transformer , power is transferred to a second substation which

steps the 11kv to 415v through a 2MVA transformer. The 2MVA substation is

located closer to the plant. The 415v is fed into the MCC (Motor Control Centre) to

supply the whole plant. The 33kv and 11kv are sometimes referred to as outdoor

transformers.

Within the 33kv substation there are switch gears which are used for grounding

residual electrical power when maintenance work is to be carried out. The two

transformers, 10MVA and 2MVA have four banks with tins each for air cooling the

oil used in the transformers. In every shift of 8hours, winding temperatures and

cooling oil temperature readings are recorded twice . the cooling oil temperature

should always be higher than the winding temperature . This ensures that the

transformer windings are not burnt.


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415V TO MCC

33KVZESA

TRANS-CURRENT

ISOLATOR

TRANS-POTENTIAL

BREAKEROIL CIRCUIT

ISOLATOR

TRANS-33KV/11KV

-

TRANS-POTENTIAL

ISOLATORTRANSCURRENT

CIRCUIT BREAKEROIL VACUUM

2MVA

11KV/415V

P

P

Maintenance Work carried out on outdoor transformers (33/11KV)


143

i. Checking oil level and topping up if necessary.

ii. Recording winding and oil temperatures twice per every shift.

iii. Checking moisture content by observing colour changes of Silica gel (status of

silica gel: Blue –Ok; Red/Pink – fault).

iv. Checking physical conditions of measuring instruments.

v. Checking condition of arcing horns.

vi. Verify all tapping positions such as Isolators.

vii. General checks.

Maintenance Work done on Indoor Substation (33kv & 11kv)

i. Taking meter readings twice every shift

ii. Checking the presence of 33kv and 11kv (Voltage & Amperes)

iii. Checking relay status (for tripping)

iv. Checking enunciator status (fault alarm status)

v. Taking energy meter readings twice every shift.

vi. NB: For 11kv, we check energy consumption after every 8hours and this

includes Diesel Generator.

vii. Checking condition of batteries for substation and emergency lights.

12.3The Motor Control Centre (MCC)

The 415 V from the 2MVA transformer is fed into the MCC from where the whole

plant is supplied. All plant electrical circuit starts from the MCC i.e. the MCC is

where all field drives are controlled. The circuits are divided into 12 sections with the

main circuits being MCC 1; MCC 2 and MCC 3. The diagram below starting from

the MCC.


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50KVAR CAPACITOR BANK

630A 630A 630A 630A 630A 250A 250A 250A 125A 125A 125A 1235A

A3200/5A

0-1600A

0-500V1/55

0-3200A

0-500VCT1-3

MDO ACB1600A 4PMDO ACD

V

AA

VDG PANEL

DG. INCOMER415 SUPPLY

Circuit No 1 Power Factor Correction

It is protected by an 800 A circuit breaker and supplies a 300 kVAR capacitor panel.

The panel has six capacitor banks each supply protected by a 125A circuit breaker.

Each bank consists of 3,50kVAR capacitors connected in Delta configuration. The

bank has an automatic power factor control and the number of banks energized

depends on the inductive loads connected at that particular time.

NB: Each bank is supplied through NO contacts and a relay, which are energized,

by a 110v supply.


145

MCC 12&3 Circuits

These are the main circuits in the plant. Each circuit is supplied by a 630 A circuit

breaker. The circuits are categorized as:

a) MCC 1 – Raw Material Section

b) MCC – Kiln & Cooler Area

c) MCC3 – Production/ Separation Section

MCC 1

630A

Supply for Dedusting Solenoid vales-32A Coal Crusher 3 Induction Motor

Power – 37, 5 KW

Supply breaker – 125 A

This circuit has a total of 22 electric motors (Induction Type) mainly for driving

conveyor belts screens weigh feeder belts, crusher and dust fans. Three of them are

star – delta connected and the rest are direct on line. See Appendices 1

MCC 2

The kiln and cooler are consists of 43 electric motor circuitry. 3 are star – delta

connected, 26 are DOL. In this circuit we have the kiln main drive and cooler main

drive, shell air fans, weigh feeders, all of which are variable speed drives some of

the motor drive DPVs fans Kay Blower dedusting etc. See Appendices 2

MCC 3

The Product separation section has a total of 36 electric motors (Induction) with five

5 of them star – delta connected and 22 are Dol. The motors drive water pumps;

fans, wet scrapper and ABC pumps see Appendices.


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12.4 Motor Starting Circuits

Electric Motors at SIMBI are connected in star – Delta or direct online

configuration. Connecting a motor in star – Delta is done to reduce high starting

currents.

The majority of the motors are DOL due to their small size (1,1kw – 11kww) and

those connected in star - Delta have a power rating of 22kw –55kw.

All the Motors can be switched either in the MCC control room or in plant

depending on the mode selected. In each panel either for DOL or star Delta there is

a selection switch for selecting REMOTE OR LOCAL mode of operation, see

control diagrams for both DOL & S/D REMOTE _ enables starting from Control

room.

LOCAL -enables starting from MCC or plant.

NB: If you select LOCAL or REMOTE, you can only start in the selected mode and

not the other.

13.5 Direct on Line Starter

Electric motors that are bi-directional can run either in forward or reverse direction.

Below is typical Control diagram for a DOL starter circuit at SIMBI. The diagram

also incorporates (show) signals, which go to the controller. These signals show the

selected

i. Mode

ii. Status of motor, whether running or not, whether tripped or not.

iii. Emergency stops, whether tripped or not.

iv. Overload

v. Trip wire (pull cord switches.

Also in this circuit are additional relays KIA (PLA relay and KIB (PLA relay) .

When the drive is running in LOCAL, KIA relay is energized and its NO contacts

will close and NC contacts opens. During this time, when the emergency stop is

disturbed it opens the control circuit and there is no supply to KIA and NO contact

opens, cutting the 24v supply to the PLC. The NO contact KIA supplies J5, which

goes to the PLC.________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

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NB: When running in LOCAL mode one of the KIM No contacts closes to switch

on J3 signal which gives indication to control room that the drive is running in

LOCAL.

When REMOTE is selected, KIB is energized and the indication closes and

switches on J2 and gives an indication for REMOTE selection (PLC input). After

REMOTE selection, the motor can be started from control room. By initiating a

start o the PC in the control room, we are inputting a signal to the PLC. The output

from the PLC wick close the switch indicated PLC O/P in the diagram. This is

achieved by the use of an opt coupler which is in series with the switch.

Reverse DOL

An additional contactor K2M is incorporated in parallel with KIM. Also included

are inter locks which prevent selecting both directions.NB: KIM and K2M are

interlocks connected in PLC can select mode through an opt coupler.

12.6 Star – Delta Connection

Star – Delta circuit can also be started in either LOCAL OR REMOTE mode.

LOCALLL starting is done in the MCC or field and REMOTE starting is done in

control room. Like any other circuit at SIMBI, the parameters monitored for a star –

Delta circuit are :

i. Mode Selection

ii. Run feedback

iii. Overload trip

iv. Emergency trip

The status of mode selection is monitored by KIB relay through its NO contact.

When LOCAL is selected, simply to the REMOTE terminal is open, thus KIB relay

is off. The NO contact of KIB which is in series with J2 will be open and there is

no 24V signal to J2 going to PLC. Absence of 24v shows that REMOTE is not

selected

When REMOTE is selected, KIB relay is energized closing its NO contact, thereby

supplying 24v to J2

Presence of 24v indicates that REMOTE mode is selected.________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

148

The Run feedback is detected by the NO contact of Kim relay, which is the main

(Common) contactor, which supplies the motor. When the motor is running one of

its NO contact, which is in series with J3 closes, thereby supplying 24V to the PLC.

The presence of 24V to the PLC indicates that the motor is running.

When the main contactor is off, its NO contacts opens thereby opening 24v supply

to J3 . Absence of 24v indicates the motor is not running.

NB: This condition is applicable to any mode selected.

Incorporated in this circuit is a timer T1 which closes its NO contracts at the same

time as no contacts at the same time as No contacts for relay K3M closes, switching

on indicating lamp P14. The timer indicates the time it takes for the motor to run in

star before switching to delta.

Overload status is detected by J4, which is connected in series with the NO contact

of the overload (O/L) relay. When the overload trips, its NO contacts closes

supplying 24v to J4. Presence of 24 V indicates to the PLC that O/L trips. When

O/L is not tripped the NO contact is open, hence there is no Supply to J4, which

indicates that the circuit is okay.

Emergency trip is detected by the NO contact of K/A relay. When the machine is

running and the Emergency stop is on, K/A relay is energized closing its NO

contacts, enabling the 24v signal to J5. Presence of 24V indicates that the

Emergency trip is okay and absence of 24v means Emergency trip is off.

NB: The Status of the motor ie emergency trip, on or off can also be seen in the

MCC through indicating lamps.

Control and Power Circuit for Conveyor Belts

The conveyor belts BC1 - BC 11 run at a constant speed and they are connected in

DOL> other belts for weigh feeders vary speed, so they are connected in variable

AC drives.

The diagram for a conveyor belt is similar to any ordinary DOL circuit. What

differs is the control circuit. All the Circuits for conveyors are unidirectional;

hence, they are a forward DOL starter.________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

149

Below is a control diagram for conveyor. Like any other circuit at SIMBI, conveyor

belts can also be started in LOCAL or REMOTE mode.

LOCAL – starting in MCC or plant.

REMOTE – starting from the control room.

Conveyor incorporates a safety mechanism in the form of a pull switch. The pull

cord switch runs in tandem with the belt so that at any point along the belt one can

operate it in case of emergency. When the switch is open, the belt cannot be started

in either mode.

The pull cord is wired in series with the coil of KIC relay, which is wired from the

NO contact of KIC J6, which shows the status of the pull cord switch in the PLC.

Thus when the belt is running, KIC relay is energized and its NO contact enabling

24v to go to the PLC via J6. The presence of 24v to PLC indicates that the pull cord

switch is okay.

When the pull cord switch is tripped, supply to the KIC relay is open, reenergizing it

and the NO contact at J 6 opens, thereby opening he 24v line to the PLC.

Therefore, absence of 24v to the PLC shows that the pull cord switch is off.

For conveyor belts, the PLC indicates the following parameters:

i. Run feedback, J 3

ii. Mode selection J2

iii. Emergency stop feedback J5

iv. Overload trip feedback, J 4

v. Status of pull cord switch, J 6

NB: J2-J6 are cables connecting 24v to the PLC input section.

NO contact of the O/L shows the status of the O/L relay under normal operation

conditions, the NC contact of the O/L allows supply of power onto the control

circuit. When the O?L trips, the NO contacts opens whilst NO contact closes. The

trip indicator J4 is wired in series with the NO contact. During this time, the O/L is

tripped. Thus, when there is no 24 V signal, the O/L is not tripped.________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

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12.7 Diesel Generator

The diesel generator supplies the whole plant with electricity when ZESA power is

cut. It is a 600KVA generator driven by a 600 Horsepower Cummins K19 diesel

engine at 1500rpm.It is manually operated. It supplies the whole plant through a

1600A circuit breaker and has an output voltage of 415 V Ac

When ZESA power supply is cut off, an electrical attendant switches the ZESA

circuit off and switches on the diesel generator circuit. Included within this

switching mechanism are mechanical breaker and diesel Generator Supply breakers)

which ensures that only one-breaker switches at a time

D.G Metering

The DG metering in the MCC shows voltage at 400V and current at 400A when

running at an average speed of 1300rpm.

In the D.G room the following parameters are recorded and at an average speed of

1500rpm,the following readings are obtained:

Current

Voltage

Frequency

Power

KVA

Power Factor

Battery

The source of power for the AC generator is a K19 Cummins engine. This engine

has been chosen because of its problem free and long life span operation. Since the

Kiln is not allowed to stop for more than 15 minutes during the production period, it

is essential that the source of power for the generator does not develop a fault

especially these days when ZESA power cuts are so rampant. As such, the engine is

incorporated with an Electronic Control Panel, which monitors the running

parameters and possible faults for easy identification of a problem. This helps to

ensure the problem is attended, to avoid a major breakdown.________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

151

12.8 Electronic Control Panel

Parameter Problem

Engine Speed (rpm) Engine Over speed

Lube Oil Pressure (ban) Low lube Oil Pressure

Coolant Temp (oc) High Coolant Temp

Intake Air Temp High Intake Air Temp

Engine Run Time Low Coolant level

Battery (V) Battery charging Fault

Fuel Actuator Command (%) High Fuel Actuator

Command

ECP Fault Code ECP Fault Code Detected

NB: The D.G is now manually started after it developed a fault in automatic start.

Therefore, during the day it requires those on duty to quickly notice a ZESA power

cut in order to switch the D.G on.

Also within the D.G room there is a boast charger for Batteries which supplies a

voltage of 35 VDC

The batteries are used for power back up to relays.

12.9Maintenance and Repairs

The following meter readings for Electric Motors and Electric parameters are

recorded

33kV voltage

33kV current

11kV current

Relay status (Amps)

Kay Blower Status (Amps)

Cooler Drive (Amps)

Kiln Main Drive Amps)

Shell Air fans (Amps)________________________________________________________________Talon Garikayi B.Eng Honours Degree in Mechatronic Engineering, Chinhoyi University of Technology- Attachment Report.

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I.D Fan (Amps)

Also at 4hour interval the following checks are carried out

Coal crusher

Cold Well Pump1&2

Gas Conditioning Tower

After Burning Chamber 1&2

Other duties I carried out were

i. Rewiring of emergency lights in MCC & Control room.

ii. Replacement of worn electric motor bearings.

iii. Checking the status of running drives.

iv. Checking the temperature of electric motors

v. Replacement of electric motor covers and securing loose connections.

vi. Listening to any abnormal noises


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CHAPTER 13

Recommendations to the Company

I recommend that the instruments department create a library of books so that even

the newly employed Technicians can use during their research. It was difficult to

extract or share knowledge from fellow technicians, as they were new to this plant at

the same time their previous employers were using a different set up from that at

SIMBI.

The Instruments Engineer was too busy trying to train the whole department as both

Technicians and Trainees show their lack of knowledge about instrumentation at a

processing plant like SIMBI so the training programme was long as I tried to catch up

with the Technicians.

Researching using the Internet is slowly becoming expensive hence as trainees we

don’t have a computer specifically for us. I therefore recommend that a computer be

put in place in the Instruments Laboratory/Workshop.

However I enjoyed this phase of my training since I was being exposed to real plant

faults and was the most challenging of them all.

The Mechanical Department is too centralized at the Headquarters with other

branches only focusing on maintenance thus I was transferred to the HQ for my

training in Workshop practices and Processes. I recommend that new well equipped

workshops be constructed at all branches especially at the Glenlivet and Chiredzi Coal

mine. To a greater extent I enjoyed my training with the Mechanical Engineer who by

now has since left the company.

The fact that the IT department only comprises of one Hardware Engineer and one

Software Engineer made my training difficult as these

Engineers had to also meet the Company demands; I recommend that the Company

employ another two Technicians.


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Recommendations to the Department of Mechatronics

Firstly I would like to thank our Department Staff Members mainly Mrs. Hondoma

and Mr. D Wakasemwa for their tremendous support as I even bothered them after

working hours. I recommend that Workshop practice and process which is done in the

first year have more practicals and a good relationship be forged by the department

between Mechanical Engineering Diploma Students and Mechatronics Students as

this will help a lot on understanding the mechanical engineering principles as applied

to Mechatronics. I recommend that Practicals had to be done on Electronics so that

students won’t be found too theoretical during attachment period.

I however want to thank the Department Staff for accurately selecting the Course

content of most of the Courses that are covered during our First and Second Year, this

enabled us (feedback from other students) to have an upper hand in the industry since

we were trained among Electronics student and Mechanical Engineering students

from other universities.

AUTOCAD proved to be more helpful during Designing both Electrical diagrams and

Mechanical diagrams, if it is possible I recommend that more time be created for

AUTOCAD i.e. it should be applied to second year.

The Industrial and Automation, Control Engineering and Intelligent controllers and

interfacing were not dealt in depth since the late Mr. T Zhuga was hospitalised yet in

the field of Mechatronics these courses proved to be the driving force behind the

establishment of this Engineering discipline in Zimbabwean industries, I therefore

recommend that students be advised on the need of the 75% attendance during

Lectures as this will give them a cutting edge in the industry.

All in all I do believe corrective measures are to be taken from the department to

include on the site learning even during the semester before attachment.


155

CHAPTER 14

Conclusion

The work related period of training was quite a good and successful experience,

though there were ups and downs here and there. I had an opportunity to prove the

theoretical aspect in the real practical environment. The attachment period however

did prepare me for becoming a Mechatronic Engineer and I gained vast experience

and requisite skills. It was quite a helpful experience since it developed me in many

aspects of what the working environment entails. The attachment prepared me well

for the industry that waits after completion of studies.

At first life was difficult at the IT-Department as I was trained alongside Computer

Science students who were a step ahead but later on I managed to improve my

programming skills in Visual Basic, C++ and C+ .

I managed to acquire a certificate in Industrial First Aid from Red Cross after being

trained by the S.H.E Department.

I believe I had a very wonderful training from Steelmakers Pvt Ltd, in return of my

hardworking and ability to be an ambassador for Mechatronics at that company I was

offered a job as an Instrumentation and Control Technician up to graduation day.

Many thanks to the Department of Mechatronics at C.U.T. and may the good Lord

guide you and give you more strength to help us during our final year.


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talon garikayi c056634k-work related learning report for simbi plantwith cover page

Documents

university chapter

control engineering

technology chapter

mechanical engineering

drive chapter

weighbridge chapter

eng honours degree

plant operations chapter