Materials, Smart Materials and Finishing Techniques

What engineers make things from

Choosing the right material is one of the first decisions an engineer makes, because the material shapes what a product can do, how long it lasts and what it costs. Materials fall into families. Metals split into ferrous metals, which contain iron, such as steel, and non-ferrous metals, such as copper and aluminium, which do not. Polymers are the plastics, and they come in two kinds depending on how they behave when heated. Woods and composites, which combine two materials to get the best of both, complete the picture. On top of these sit smart materials that can change in response to heat or light. Once a material is chosen and shaped, it is usually given a finish, a surface treatment that protects it and improves how it looks. This module covers the material families, smart materials, and the main finishing techniques.

Materials and finishing words

Learn these terms before the materials are matched up. They name the ideas used in this topic.

Match each material or finish to what it is

Painting against powder coating

Two of the most common finishes protect a metal product in different ways, and each suits a different job.

Which kind of material is this?

A panel is made by setting strong glass fibres into a hardened resin, giving something light but very stiff. What kind of material is it?

• A composite, made from two materials combined
• A ferrous metal
• A thermoplastic on its own
• An alloy

Materials that respond

Some of the most interesting materials do not just sit there: they react to the world around them. A shape-memory alloy can be bent out of shape when cool, then spring back to its original form when it is warmed, which makes it useful in spectacle frames and in medical devices. A thermochromic pigment changes colour with temperature, so it can turn a mug or a kettle into a heat warning. A photochromic material darkens in bright light, which is how some glasses turn into sunglasses outdoors and clear again inside. These are called smart materials because their behaviour changes with heat, light or force. They let a designer build a response into the product itself, rather than adding extra electronics to do the same job.

Pick what is true about materials and finishes

Select every statement about materials and finishing that is true.

• Ferrous metals contain iron
• A finish protects a product and improves its look
• A smart material can react to heat or light
• A finish makes no difference to how long a product lasts
• Every material is a metal

Order how to apply a paint finish

Put the steps of giving a metal part a good painted finish into a sensible order.

• Clean the surface of grease and dirt
• Rub it down until it is smooth
• Apply a coat of primer
• Apply the top coat of paint
• Leave it to dry and harden

Complete the materials and finishes facts

A metal that contains iron, such as steel, is called a _____ metal. A plastic that can be reheated and reshaped again and again is a _____. A material made by combining two others to get the best of both, such as carbon fibre, is a _____. Coating steel with a layer of zinc to stop it rusting is called _____.

Tap the two smart materials

Read these four materials. Tap the TWO that are smart materials.

• a shape-memory alloy
• a thermochromic pigment
• cast iron
• oak

A coat of paint on a garden fence

Think about why a garden fence gets painted. The wood underneath is perfectly good, but left bare it soaks up rain, swells, splits and slowly rots, and it looks grey and tired within a season. A coat of paint changes all that. It seals the surface so water runs off instead of soaking in, it keeps the sun from bleaching the timber, and it lets you pick a colour that suits the garden. The paint has not changed what the fence is made of at all; it has simply given it a protective, good-looking skin. Every finish an engineer applies does the same two jobs for a product: it guards the surface against wear, rust or weather, and it makes the thing look finished and deliberate rather than raw.

Work out the density

A block of metal has a mass of 60 grams and a volume of 20 cubic centimetres. Density is the mass divided by the volume. Work out the density in grams per cubic centimetre. Give the number only.

Pick the material or finish for the job

Read each situation and choose the best answer.

• A steel gate will live outdoors and must not rust. Which finish suits it best?
• A designer wants a light but very stiff bike frame. Which material fits?
• A kettle should show when it is hot without any electronics. What could its surface use?

Build a materials and finishes point

Choose the word for each gap to complete one point about materials and finishing.

Explain materials, smart materials and finishing

A friend is starting the engineering materials topic. Using what you have learned, explain the material families, smart materials and finishing.

• Explain the difference between ferrous and non-ferrous metals
• Explain what a thermoplastic is and how it differs from a thermoset
• Explain what a composite is, with an example
• Explain what a smart material is, with an example
• Explain why a product is given a finish and name two finishes