the technological world - mrs. isernhagen's science … coatings: zinc, chrome, gold, silver,...

The Technological

World

Chapter 12

Chapter 12

Manufacturing Technical Objects

There have been many inventions that have improved the quality of our lives. We will refer to these inventions as technical objects.

In this chapter we will look at what must be considered when designing and manufacturing an object:

1. Materials and their properties

2. Technical Drawings

3. Manufacturing of the objects

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12.1 Constraints & Deformations

Stress caused by normal use.

Constraints are the different types of stresses.

1. Compression (crush)

2. Tension (stretch)

3. Torsion (twist)

4. Deflection (bend)

5. Shearing (cut)

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Deformation is the change in shape

caused by a constraint.

1. Elastic (go back to original shape)

2. Plastic (changed into new shape)

3. Fracture (break)

12.2 Mechanical Properties Mechanical properties of a material determine

how it will react when subjected to one or more

constraints.

1. Hardness (resist dents without breaking)

2. Elasticity (return to it’s original shape)

3. Resilience (resist shocks)

4. Ductility (stretches)

5. Malleability (flattened/bent without breaking)

6. Stiffness (keep it’s shape)

7. Resist Corrosion

8. Electrical conductivity (carry current)

9. Thermal conductivity (transmit heat)

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Main

Other

Checkup

Observatory: The Environment

Page 418, Questions 1 and 2

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12.3 Categories of Materials and

their Properties

Let’s have a closer look at the following

materials and their properties:

1. Wood and Modified Wood

2. Ceramics

3. Metals and Alloys

4. Plastics

5. Composites

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Please paste table into notes!

You need to be able

to explain using

these properties

why a certain

material is or is not

a good choice

Degradation and Protection

The degradation of a material is the

decline in some of its properties due to the

effects of the surrounding environment.

The protection of a material is the

application of procedures that prevent or

delay its degradation.

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Wood and Modified Wood

Wood comes from harvesting trees &

processing wood chips.

Hardwood comes from deciduous trees

maple, oak, & birch

Softwood comes from coniferous trees

spruce, pine & fir

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Solid Oak Furniture

Oak Flooring

Maple Baseball bats

Other considerations include:

1. Aesthetic appeal

2. Hardness, elasticity, resilience, and toughness

3. Low thermal and electrical conductivity

4. Ease with which it can be worked

5. Colour

6. Its lightness relative to its strength

Modified Wood

Modified wood

treated wood

wood mixed with other substances

Eg. plywood, particle board & fibreboard

These are sheets, chips, or fibres of wood

that are glued together in sheets.

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Particle Board

Degradation and Protection of Wood

Unprotected wood can degrade swiftly.

Since wood is an organic substance, many fungi, microorganisms, and insects can infest the wood, feed off it and cause it to rot.

Wood can be painted, stained, varnished or treated with other protective coatings to help prevent its deterioration.

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Treated wood is made resistant to rot by:

Dipping it in an alkaline solution containing copper. This wood usually has a greenish colour.

Heating it to a high temperature.

Some woods, such as cedar, have a natural resistance to rot.

Coatings (paint, stain, varnish)

Degradation and Protection of Wood

Treated wood

Cedar Docks and Decks

Ceramics

Ceramics

A ceramic is a solid material obtained by

heating inorganic matter containing

various compounds, usually oxides.

When the raw material is heated, the

water evaporates, and the bonds between

the constituent compounds are

rearranged.

A ceramic is always solid at room

temperature.

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Traditionally, most ceramic objects were

made out of clay and sand. Sand is used

for making glass.

Although other materials are now used,

clay and sand are still widely used as they

are both plentiful and inexpensive.

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Properties of Ceramics Their properties depend on the raw material and

the method of baking.

Ceramics can be a good choice for many objects because:

Low electrical conductivity used as insulators

High degree of hardness building materials & cutting tools

Heat resistance and low thermal conductivity dishes, cookware & thermal insulators

Resistance to corrosion used in ducts for fumes or water

Fragility - very fragile ST

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Terracotta Army Sculptures depicting the armies of Qin Shi Huang,

the first Emperor of China.

It is a form of funerary art buried with the emperor

in 210–209 BC and whose purpose was to protect

the emperor in his afterlife.

discovered in 1974 by some local farmers in

Lintong District, Xi'an, Shaanxi province.

The figures include warriors, chariots and horses.

over 8,000 soldiers, 130 chariots with 520 horses

and 150 cavalry horses, the majority of which are

still buried.

Ceramics can be fragile

The Degradation and Protection of Ceramics

Can be degraded by some acids & bases

A thermal shock (a sudden change in temperature)

can cause damage to a ceramic object.

Glazes can be used to protect the ceramics

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Metals and Alloys A metal is a material extracted from a

mineral ore. Metals are usually shiny in appearance and are good conductors of heat and electricity.

The pure metal is rarely used.

An alloy is a mixture of a metal with one or more other substances, which may be metallic or nonmetallic. The mixture of materials results in more desirable properties.

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Metals and Alloys

Alloy Bike Frames

There are two main types of alloys:

Ferrous alloys whose main component is

iron.

Nonferrous alloys whose main component is

a metal other than iron

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The Degradation and Protection

of Metals & Alloys The main cause for metal and alloy degradation

is oxidation, where the material reacts with

oxygen. This is commonly referred to as rusting.

Metals & Alloys can be protected by coating it

with a substance that isolates it from the oxygen

in the air:

Metallic coatings: zinc, chrome, gold, silver, nickel,

aluminum, lead

Other coatings: paint, enamel, grease, resin

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Please write into notes

Oxidation of Metals

Rustproofing

Techniques to enhance the properties of Metals & Alloys

Steel heat treatments

These methods include: Quench hardening

Atoms are rearranged at high temperatures and then set by

dropping into a cool liquid (water, oil, …)

Hardens the steel but is brittle!

Tempering Atoms are rearranged at lower temperatures than quenching

Hardens the steel (less brittle than above & softer)

Annealing Very slow process!

Restores the properties of steel once they have been modified by welding.

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Plastics

Plastics made from fossil fuels

petroleum and natural gas

Monomers are extracted from the fossil fuels and are arranged into long chains called polymers.

Plastic is a material made of polymers, to which other substances may be added to obtain certain desirable properties.

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Types of Plastics A thermoplastic is a plastic that becomes soft

enough when heated to be molded or remolded and that hardens enough when cooled to hold its shape. Most plastic objects are made of this type.

Most thermoplastics can be recycled

A thermosetting plastic is a plastic that remains permanently hard, even when heated. Often harder and more resilient than thermoplastics

Include melamine and polyesters

Cannot be recycled in Quebec

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The Degradation and Protection of Plastics

Plastics tend to degrade over time.

Slow

Cracks form

Change in colour

Causes & Prevention

Penetration of a liquid

Oxidation

UV

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Write into notes please

Waterproof coating

Add an antioxidant

Add a pigment that absorbs UV

Mythbusters

What is bulletproof

Composites

Composites A composite is formed by combining materials

from different categories to obtain a material with

enhanced properties.

A composite has two main parts: the matrix and

the reinforcement.

The matrix is the body of the material. It

surrounds and supports the reinforcement and

gives the object its shape.

The reinforcement is inserted into the matrix to

strengthen the object.

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Kevlar is a composite

The Degradation and Protection of

Composites

The degradation of composites usually

takes one of two forms: 1. The deformation or fracture of the matrix (body)

or the reinforcement (skeleton).

2. The loss of adherence between the matrix and

the reinforcement.

The speed of degradation depends on

the type of matrix and reinforcement and

the conditions of use.

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Checkup

Observatory: The Environment

Page 418, Questions 3 to 6

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Review

Observatory: The Environment

Page 421, Review Questions A to D

Credits All images are from:

Observatory: The Environment

Editions du Renouveau Pedagogique Inc