design and metals and technology 8552 alloys

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3 Design and Technology 8552 Metals and alloys Unit 3 Materials and their working properties

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Page 1: Design and Metals and Technology 8552 alloys

3

Design and Technology 8552

Metals and alloys

Unit 3Materials and their working properties

Page 2: Design and Metals and Technology 8552 alloys

Objectives

• Know the primary sources of materials for

producing metals and alloys

• Be able to recognise and characterise different

types of metals and alloys

• Understand how the physical and working

properties of a range of metals and alloys affect

their performance

Page 3: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Starter

• Padlocks are traditionally attached to bridges or

landmarks to signify enduring love and friendship

• How might these padlocks age over time?

Page 4: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Metal

• Metals have been essential in the development

of civilisation

• The word ‘metal’ comes from the ancient Greek word ‘metallum’

which means to mine, excavate or extract from the ground

• Prehistoric man used metals to make tools and weapons

• Which common metals would you find in a domestic kitchen?

Page 5: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Ore

• The Earth’s crust contains many types of rock

• Metallic minerals are found naturally in rock or ore

• Ore is obtained by mining, and the metals contained

within it are extracted

• The method used for extraction depends on the

metal’s reactivity with air, water or acids

• The more reactive the metal, the more expensive it is

to extract

Page 6: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Finding metal

• Some naturally occurring metals are found as lumps

in the rock and don’t require a chemical extraction

• Why is gold expensive in comparison to aluminium?

Page 7: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Extraction processes

• Some metals exist as oxides

• Metals such as copper, iron and zinc are oxides

• Oxides are heated with carbon to extract the metal

• Electrolysis is used to extract metals

such as aluminium

• Are metals a

renewable resource?

• How we man reduce the

speed at which we will run

out of natural resources?

Page 8: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Classification of metals

• Metals are divided into two main categories

• Ferrous metals and Non-ferrous metals

• Ferrous metals contain the element

iron, also known as ferrite (Fe)

• Non-ferrous metals don’t

contain iron

• You also need to know about ferrous

alloys and non-ferrous alloys

• What is an alloy?

Page 9: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Iron ore

• Iron can be extracted from iron ore by using a blast

furnace and the process of smelting

• Smelting extracts common industrial

metals such as iron

• The extreme heat draws off the metals in

a liquid state called ‘hot metal’

• The impurities are removed and the iron

mixed or ‘alloyed’ with a small amount

of carbon to create steel

• The amount of carbon added affects

the strength of the steel

Page 10: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Ferrous metals

• Ferrous metals contain iron and may rust

• Iron and steel can corrode – this is known as rust

• Rust is a compound called iron oxide and is formed when iron

and oxygen react in the presence of moisture or water

• Most ferrous metals are magnetic

• Name two types of protective layer

that could be added to metal

to help prevent rust

Page 11: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Ductility and malleability

• Ductile metals

• Will stretch without being damaged

• Can be drawn or stretched out into long wires

• Copper is highly ductile and can be

drawn into long, thin wires

• Malleable metals

• Can be hammered into a shape

without breaking

• Can be rolled or pressed into sheets

• Will deform under compression

Page 12: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Hard or tough?

• Hardness is the ability to

withstand abrasion

• A very hard metal is likely to crack

or shatter upon impact or force

• Cast iron would be described as

hard but brittle

• Toughness is the ability to

absorb energy and not fracture

• A tough material may scratch

easily on the surface but can

withstand large impacts

Page 13: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Tensile strength

• Tensile strength is the amount of

tensile stress (stretching) a

material can withstand before

breaking or failing

• Testing for tensile strength is crucial

in industry

• Suggest two uses for metals with

high tensile strength

• Why is destructive testing

so important?

Page 14: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Hard as nails

• Steel is a ferrous metal available in different forms

• Stainless steel has a high resistance to corrosion, staining

and friction, suitable for a wide range of applications

• High speed steel is formed by alloying elements

of carbon, tungsten, vanadium, cobalt,

chromium or molybdenum

• Name three everyday

applications for

stainless steel

Page 15: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Material selection

• Ferrous metals have varying properties making them

suitable for different uses

• Low carbon steel is tough, ductile and easily welded

• High carbon steel is very hard wearing, but less ductile

or malleable

• Cast iron is hard and easily cast into shapes, but brittle

• Suggest two items made from each of these metals?

Page 16: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Non-ferrous properties

• Non-ferrous metals don’t contain iron

• They are often more expensive than ferrous metals

owing to their desirable properties which include:

• Lightweight

• Good conductivity

• Ductile and malleable

• Resistant to corrosion

• The process of galvanising adds a

protective coat of zinc to iron and

steel to help prevent rusting

Page 17: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Electrical conductivity

• Conductivity is how easily an electrical current can

flow through a metal

• As copper is such an efficient conductor, it’s most common

use is in electrical cabling

Page 18: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Thermal conductivity

• Thermal conductivity measures the ability of a metal

to conduct heat

• Copper is also an excellent conductor of heat and is

commonly used in air conditioning, water tanks, saucepan

bases and water heaters

• In what environment would it be more appropriate to use

steel than copper?

Page 19: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Non-ferrous metals

• Aluminium, copper, tin and zinc are all

non-ferrous metals

• List a selection of household items that

may be made from non-ferrous metals

• In what way do non-ferrous metals

differ from ferrous metals?

Page 20: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Tin

• Tin is commonly associated with a ‘tin can’

• In fact, the can is steel, with a thin coating of tin,

‘tin plating’, which helps preserve the contents

• Tin is soft, ductile and malleable

• Alloys of tin include pewter, copper, bronze

and soft-solder

• What other non-ferrous metal is

associated with the production

of cans?

Page 21: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Alloys

• Metals are rarely used in their pure form. Alloys are

made by combining two or more elements

• This helps improve the working properties

and appearance

• Brass and steel are common alloys

• Stainless steel is made by combining iron, with

a small amount of carbon and chromium

• This protects the alloy from oxygen –

what will this help prevent?

• What are the advantages of

creating alloys?

Page 22: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Worksheet

• Complete Tasks 1 and 2 on your Worksheet

Page 23: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Uses of metals

• Given the various properties of metals, list as many

metals as you can that are used to make this bicycle

Page 24: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Uses of metals Answers

• A vast range of metals may be used to create

a single product

Frame could be low carbon

steel, aluminium alloy

Aluminium or stainless

steel shopping basket

Aluminium

mud guards

Steel wire in the

tyres, zinc in

the manufacture

of rubber

Twisted strands of steel in the

brake cables, aluminium and

steel in the brake handle

Aluminium alloy

in the pedals

Steel or aluminium

spokes

Fused or welded joints

are usually brass

(a copper / zinc alloy)

High speed steel

in ball bearings,

pedals, wheel

hubs, headstocks,

cranks

Steel springs

Chain made of

carbon steel

Page 25: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Worksheet

• Complete Task 3 of the Worksheet

Page 26: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Everything but tin?

• Tin probably didn’t feature in your bicycle list

• Working with recycled cans is a technique called Kapoaka

• Used in Madagascar by small scale workshops, crafters

make decorative objects and toys for sale

• It has created sustainable employment and helps the poorest

in Africa attain a living from the profits

Page 27: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Oxidisation

• Non ferrous metals such as copper and

bronze, don’t rust, but may oxidise

• Oxidising can be caused by corrosion

or weather exposure over a period of time

• A thin layer of tarnish that appears on the

surface of the metal is known as a patina

• A natural patina occurring on copper

is called Verdigris

• The green hue can be manufactured by

adding acetic acid to copper and is often

used in architecture for aesthetic purposes

Page 28: Design and Metals and Technology 8552 alloys

Metals and alloys

Unit 3 Materials and their working properties

Plenary

• What are metals commonly extracted from?

• Name three ferrous metals

• Which metal would you select for high conductivity?

• Explain the term ‘alloy’

• Describe the difference between hard and tough

• How can you protect metal from oxidisation?

• Justify one metal used to manufacture cutting tools

Page 29: Design and Metals and Technology 8552 alloys

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Metals and alloys

Unit 3 Materials and their working properties