Materials and Components
Woods
Wood - the hard fibrous material that forms the main substance of the trunk or branches of a tree or shrub
Trees are cut down and the logs and branches are then worked into sheets of wood, or planks. As a natural product, they are sustainable (if the forest they come from is being re-planted), and have an attractive grain in the wood.
Softwood
Softwoods come from coniferous trees which are evergreen, needle-leaved, cone-bearing trees, such as cedar, fir and pine.
Hardwood
Hardwoods come from broad-leaved, deciduous trees. The main hardwood timbers are ash, beech, birch, elm, mahogany, oak and teak.
| Wood | Category | Colour | Properties | Common Uses |
|---|---|---|---|---|
| Ash | Hardwood | Light brown | Open-grained, tough, flexible | Ladders, sport equipment |
| Pine | Softwood | Pale yellow | Durable, resists swelling | Carpentry |
| Oak | Hardwood | Light brown | Strong, hard, open-grain, corrodes steel | Furniture and interior woodwork |
| Beech | Hardwood | Light brown | Close-grained, hard, warps easily | Furniture, toys |
| Elm | Hardwood | Light brown | Open/interlocking grain, tough, durable in water, resists splitting | Indoor and outdoor furniture |
Composite Woods
Manufactured boards - Man-made boards are those which are produced in factories. They tend to have a uniform appearance, and have unique properties. It is often cheaper and easier to buy composites rather than natural wood.
| Board | Appearance | Properties | Common Uses |
|---|---|---|---|
| Cardboard | Brown | Weak, damaged by rain, cheap | Boxes, prototyping |
| Medium Density Fibreboard (MDF) | Various shades of brown, no grain | Flat, stiff, has no knots, easily machined | Cupboard doors, hidden wood uses |
| Plywood | Comes in different finishes | Strong, Flexible, attractive grain or knots, can be waterproof | Sheds and cladding |
| Chipboard | Brown, with a coarse texture | Various densities: hard or soft, often soak up water and break apart | Furniture, flooring construction |
Plastics
Usually derived from oil, plastics provide a variety of durable materials which can be formed easily into whatever shape is required, and can be highly durable. Their relatively low cost has led to their popularity for use in all manner of every day objects. Unfortunately, plastics tend not to be easily bio-degradable (often taking several hundred years to break down in landfill), and as such need to be recycled wherever possible.
Production
Natural
Natural sources of plastics include:
- Plants - From which cellulose can be extracted
- Trees - From which latex, amber and resin can be extracted
- Animals - From which horn and milk (used to make glues) are obtained
- Insects - From which shellac (used to make polish) is obtained
Synthetic
Synthetic plastics are chemically manufactured from:
- Crude oil
- Coal
- Natural gas
Plastics can be either classed as thermosetting, or thermoplastic (thermosoftening).
When forming them into a shape, thermosetting polymers normally need to be mixed with a curing agent, which allows them to set solid. Once set, they cannot be re-formed into another shape.
Thermoplastics can be repeatedly heated until soft, then cast into a new shape and cooled.
| Plastic | Category | Properties | Common Uses |
|---|---|---|---|
| Acrylic | Thermoplastic | Transparent, weather resistant, scratches easily, brittle in small sections, good electrical insulator | Covers of storage boxes, aircraft canopies and windows, covers for car lights, |
| ABS | Thermoset | High impact resistance, strong, lightweight, durable, available in a range of shapes and colours | Making tubes and structures, children’s toys |
| Polystyrene | Thermoplastic | Light, hard, stiff, transparent, brittle, with good water resistance | Toys, especially model kits, packaging, ‘plastic’ boxes and containers |
| Low density polythene (LDPE) | Thermoplastic | Tough, good resistance to chemicals, flexible, fairly soft, good electrical insulator | Packaging, especially bottles, toys, packaging film and bags |
| High density polythene (HDPE) | Thermoplastic | Hard, stiff, able to be sterilised | Plastic bottles, tubing, household equipment |
| HIPS | Thermoplastic | Maintains strength at high-impact, paintable, recyclable,mouldable | Packaging |
| Polypropylene (PP) | Thermoplastic | High Stiffness, strong, heat resistant | Plastic pipes, school chairs |
| Nylon | Thermoplastic | Tough, resists wear, self-lubricating, good resistance to chemicals and machines | Casings for power tools, hinges for small cupboards, curtain rail fittings and clothing |
LEGO is made used ABS plastic
Metals
Metals come from ores which are dug from the ground, and purified. They can be cast into sheets, or ingots ready for forming into different shapes.
Some metals can be combined with other materials to form alloys, which have new, unique properties. Steel is made by combining iron and carbon, for instance.
Ferrous metals are those which contain iron.
| Metal | Category | Colour | Properties | Common Uses |
|---|---|---|---|---|
| Copper | Non-ferrous | Coppery: red-brown | Excellent electrical and thermal conductor | Wiring, copper piping |
| Mild Steel | Ferrous | Grey | Tough, ductile, malleable, good tensile strength, poor resistance to corrosion | General purpose engineering material |
| Aluminium | Non-ferrous | Grey | Good strength-to-weight ratio, light, soft, ductile | Kitchen equipment, window frames, general cast components |
| Stainless Steel | Ferrous | Grey | Hard and tough, resistant to wear and corrosion | Cutlery, kitchen equipment |
Smart Materials
| Material | Properties | Common Uses |
|---|---|---|
| Smart memory Alloys | Can be bent out of shape, but returns to original shape when heated | Dental braces, glasses frames |
| Piezoelectric materials | Generate an electric charge in response to applied mechanical stress | Mics, speakers, alarm systems |
| Quantum Tunnelling composite | An insulator which becomes a conductor when put under pressure | Membrane switches like those used on mobile phones, pressure sensors and speed controllers. |
| Electroluminescent Materials | Give out light when an electric current is applied to them | Safety clothing, safety lights |
| Thermochromic Materials | Change colour as the temperature changes | Test strips on the side of batteries, food packaging materials that show you when the product is cooked to the right temperature. |
| Photochromic Materials | Change colour according to different lighting conditions | Security markers that can only be seen in ultraviolet light |
Past Paper Questions
June 2010, Q5a. This question is about programming a greenhouse temperature / environmental control system model. The greenhouse model has a heat sensor, and a roof vent that opens and closes to regulate the temperature.
June 2011, Q4a. This question is about a washing machine control system model. The washing machine model is made from plywood and has: -
- a door that opens and shuts
- a button to start the simulated wash
- a door lock to stop the door opening
- a geared motor to turn the wash drum
- an LED that lights to show that the drum is turning.
