© Boardworks Ltd 2004 1 of 14 Topic 1.2 Metals What students need to learn Aesthetic, functional...

© Boardworks Ltd 20041 of 14

Topic 1.2MetalsWhat students need to learn

Aesthetic, functional and mechanical properties, application and advantages/disadvantages of the following ferrous and non-ferrous metals when manufacturing products:•Mild steel, Stainless steel and Carbon steel•Aluminium, Copper, Zinc and Brass.

The composition of mild steel and brass.

Understand and describe the following properties when selecting and using metals in product manufacture:•ductility•malleability•hardness•toughness•elasticity•strength in tension, compression and shear.


Metals and their Properties

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Did you get any of these?

Write down as many common metals as you can.

Take a few minutes to think about some of the metals you already know about. Perhaps they are at home or in the room right now.

Starter activity

Mild steel

Aluminium

Brass

Copper

Zinc

Stainless steel

Carbon steel


Metals are part of the earth’s crust in the form of metal ore. Metal ore is mined and washed to remove other minerals and unwanted materials.

It is heated in a furnace and the pure metal ore is run off. This process is known as smelting. Iron ore is the basis for most steels.

Where do metals come from?


Metals can be broken down into two main categories:

Categories of metals

Non-ferrous Metals don’t contain iron

aluminium, copper, tin and lead are all non-ferrous.

Ferrous Metals contain iron

will corrode unless protected

attracted by a magnet.


Although all metals can be classified as ferrous or non-ferrous, there are some other important groups of metals:


Pure Metals

Metals in their basic form

Aluminium, gold, copper, zinc, tin and lead are all pure metals

Aluminium is the most plentiful of the pure metals, but it has to go through some refining processes to turn it into a usable material.


Alloys

A mixture of two or more metals

Brass is an alloy of 65% copper and 35% zinc

High tensile steel is an alloy of low carbon steel and nickel

Stainless steel is an alloy of steel, chromium, nickel and magnesium.



Examples of metals


When studying materials and especially when selecting materials for a project / design, it is important to understand key properties. The most important properties are outlined below.

STRENGTH

The ability of a material to stand up to forces being applied without it bending, breaking, shattering or deforming in any way. Our technology technician (Ed) demonstrates the ‘strength’ of a material by performing a hand stand on a strong piece of timber (wood). It does not bend even under his weight. He has eaten pies and drunk a large amount of beer for twenty years and yet the strong material does not bend, flex or deform (change shape) in any way.

ELASTICITY The ability of a material to absorb force and flex in different directions, returning to its original position. Our technology technician demonstrates the ‘elasticity’ of a material by springing up and down on a piece of steel rod. Do not try this at home as an accident may result. Ed our technician is an expert at demonstrating this property as it is his hobby.


PLASTICITY The ability of a material to be change in shape permanently. Our technology technician and his twin brother demonstrate the ‘plasticity’ of molten aluminium by pouring it into a mould. Once the aluminium has cooled down, it can be removed from the casting sand. It has a new shape. Our technician is often seen scavenging in dust bins after aluminum drinks cans. He then melts them down to form blocks (ingots) of aluminium to sell to scrap metal dealers.

DUCTILITY The ability of a material to change shape (deform) usually by stretching along its length. Our technician stretches the lead above his head. As it stretches if deforms (changes shape). Ed thinks he is a strong man, little does he realise that lead is a very soft metal and stretches very easily. He performs these tricks in local pubs in an attempt to pass himself off as a ‘hard man’. TENSILE STRENGTH The ability of a material to stretch without breaking or snapping. Our technology technician demonstrates ‘tensile strength’ by stretching a piece of steel until it snaps. Ed thinks he is incredibly strong. However, his friends at work have substituted a sausage in place of the steel


Properties of metals


Working with metals – hand tools


Working with metals – industrial processes

When metals are used to make many identical products, industrial processes are used. These are specialized processes which are used to mass produce products.

CNC Milling Machine

Robotic arm


Materials can be joined temporarily or permanently. Three methods of joining metals are shown below.

Joining metals

RivetingNut, bolt &

washerMIG Welding


Working with metals – finishing techniques

Several surface finishing techniques can be used on metals. The most common ones are detailed below:

Paint

Plastic Coating

Lacquering

Enamelling

Surface must be smooth & de-greasedPrimer requiredHammerite is a good one-coat metal paint.

Suitable for most metalsObject is heated and dipped in a tank of powder paintObject is returned to oven to ensure a smooth, glossy finish.

Helps to prevent corrosion after polishingA layer of cellulose or varnish is appliedOften used on jewellery.

Powdered glass is melted onto the metal surfaceProvides a hard (but brittle) finish with different colours and textures.


Noughts & crosses

© Boardworks Ltd 2004 1 of 14 Topic 1.2 Metals What students need to learn Aesthetic, functional...

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