Design & Technology
Materials
The material types used in resistant materials are woods, metals, plastics, ceramics and composites. Each of these has its own characteristic working properties, such as strength, malleability, conductivity, toughness and durability.
Timber
There are two types of timber, called hardwood and softwood. These names do not refer to the properties of the wood: some softwoods can be hard and some hardwoods can be soft.
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, cherry, elm, iroko, mahogany, meranti, oak, obeche, sapele and teak.
Properties and uses of hardwood timbers.
| Name | Properties | Uses |
|---|---|---|
Ash  | Light, creamy-brown colour, open-grainedopen grain: A wood with visible large pores - eg oak., toughtough: Able to withstand blows or sudden shocks without breaking., flexibleflexible: Capable of being bent or flexed many times without breaking. | Sports equipment, wooden ladders, tool handles |
Beech  | White to pinkish-brown in colour, close-grained [close-grained: A wood with no visible large pores - eg beech. ], hardhard: Able to resist wear, scratching and indentation., tough, strongstrong: Able to withstand a force without breaking or bending., warpswarps: Bends or twists out of shape, this is common with wood as it dries. easily | Furniture, toys, tool handles |
Elm  | Light to medium brown in colour, open and sometimes interlocking graininterlocking grain: The grains have a weaved structure. For wood this makes it strong, less prone to splitting andn often suitable for bending., tough, durabledurability: The ability of a material to withstand wear, especially as a result of weathering., resists splitting, durable in water | Indoor and outdoor furniture |
Mahogany  | Pink to reddish-brown colour, fairly strong, durable, some interlocking grain | Good quality furniture |
Oak  | Light brown colour, strong, hard, tough, open-grained, corrodes steel screws and fittings | Interior woodwork, good quality furniture |
Metals
Most metals are extracted from their oresore: An ore is a rock containing enough quantities of a mineral that it is profitable to extract it. using a chemical reaction. Metals are rarely used in their pure form, and are usually mixed with other metals to improve their properties. This is called an alloyalloy: An alloy is a compound of two or more elements, at least one of which is a metal.. Most metals are good conductorsconductor: An electrical conductor is a material which allows an electrical current to pass through it easily. It has a low resistance. A thermal conductor allows thermal energy to be transferred through it easily. and can be recycled.
Ferrous metals
Ferrous metals contain iron. Examples are cast iron, mild steel, medium carbon steel, high carbon steel, stainless steel and high speed steel.
The ferrous metals listed below are all alloys.
Composition, properties and uses of ferrous metals
| Name and melting point | Properties and characteristics | Principal uses |
|---|---|---|
| Cast iron 1200°C | Hardhard: Able to resist wear, scratching and indentation. skin, softer underneath, but brittlebrittle: If something is brittle it is easily broken., corrodes [corrosion: The destruction of a metal by oxidation or chemical action. ] by rusting | Parts with complex shapes which can be made by casting |
| Mild steel 1600°C | Toughtough: Able to withstand blows or sudden shocks without breaking., ductileductile: If a material is ductile it is capable of being drawn into thin sheets or wires without breaking., malleablemalleable: If a material is malleable it is capable of being hammered or pressed out of shape without being likely to break or return to the original shape., good tensile strengthtensile strength: The tension a material can withstand without breaking., poor resistance to corrosion [corrosion: The destruction of a metal by oxidation or chemical action. ] | General purpose engineering material |
| High carbon steel 1800°C | Even harder than medium carbon steel and more brittle, can be heat-treated to make it harder and tougher | Cutting tools, ball bearings |
| Stainless steel 1400°C | Hard and tough, resistant to wear and corrosion | Cutlery, kitchen equipment |
Non-ferrous metals
Non-ferrous metals do not contain iron. Some common non-ferrous metals are aluminium, Duralumin, copper, zinc, brass, gilding metal and tin.
Composition, properties and uses of non-ferrous metals:
| Name and melting point | Composition | Properties and characteristics | Principal uses |
|---|---|---|---|
| Aluminium 660°C | Pure aluminium | Good strengthstrength: The ability of a material to withstand a force without breaking or bending.-to-weight ratio, light, soft, ductile, good conductor of heat and electricity | Kitchen equipment, window frames, general cast components |
| Copper 1080°C | Pure copper | Malleable and ductile, good conductor of heat and electricity, resistant to corrosion | Water pipes, electrical wire, decorative goods |
| Brass 900-1000°C | Alloy | Resistant to corrosion, fairly hard, good conductor of heat and electricity | Ornaments, cast items such as water taps |
| Tin 230°C | Pure tin | Soft, weak, malleable, ductile and resistant to corrosion | Usually used for coating steel to form tin-plate, soft soldersolder: An alloy used to join metallic parts. |
Plastics
Sources of plastics
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
Thermoplastics and thermoset plastics
Plastics are divided into thermoplastics and thermoset plastics.
Thermoplastics can be heated and shaped many times.
Properties and uses of thermoplastics.
| Name | Properties | Principal uses |
|---|---|---|
| Polyamide (Nylon) | Creamy colour, toughtough: Able to withstand blows or sudden shocks without breaking., fairly hardhard: Able to resist wear, scratching and indentation., resists wear, self-lubricatinglubricating: Oiling or reducing friction. A lubricant is anything which reduces the friction between two surfaces., good resistance to chemicals and machines | Bearings, gear wheels, casings for power tools, hinges for small cupboards, curtain rail fittings and clothing |
| Polymethyl methacrylate (Acrylic) | Stiff, hard but scratches easily, durable, brittlebrittle: If something is brittle it is easily broken. in small sections, good electrical insulatorinsulator: Material that is a poor conductor of electricity or heat., machines and polishes well | Signs, covers of storage boxes, aircraft canopies and windows, covers for car lights, wash basins and baths |
| Polypropylene | Light, hard but scratches easily, tough, good resistance to chemicals, resists work fatiguework fatigue: Weakening of a material as a result of prolonged or repeated stress on it. | Medical equipment, laboratory equipment, containers with built-in hinges, 'plastic' seats, string, rope, kitchen equipment |
| Polystyrene | Light, hard, stiff, transparent, brittle, with good water resistance | Toys, especially model kits, packaging, 'plastic' boxes and containers |
| Low density polythene (LDPE) | Tough, good resistance to chemicals, flexible, fairly soft, good electrical insulator | Packaging, especially bottles, toys, packaging film and bags |
| High density polythene (HDPE) | Hard, stiff, able to be sterilised | Plastic bottles, tubing, household equipment |
Thermoset plastics can only be heated and shaped once.
Properties and uses of the thermoset plastics.
| Name | Properties | Principal uses |
|---|---|---|
| Epoxy resin | Good electrical insulator, hard, brittle unless reinforced, resists chemicals well | Casting and encapsulation, adhesives, bonding of other materials |
| Melamine formaldehyde | Stiff, hard, strong, resists some chemicals and stains | Laminates for work surfaces, electrical insulation, tableware |
| Polyester resin | Stiff, hard, brittle unless laminated, good electrical insulator, resists chemicals well | Casting and encapsulation, bonding of other materials |
| Urea formaldehyde | Stiff, hard, strong, brittle, good electrical insulator | Electrical fittings, handles and control knobs, adhesives |
Other materials
Composite materials
Composite materials are formed by combining a reinforcing material such as wood pulp, and a bonding agent, such as glue. The wood pulp is made from the waste from cutting solid wood. MDFMDF: Medium Density Fibreboard - a type of engineered wood made of compressed wood and fibre particles held together with glue. and GRPGRP: Glass-Reinforced Plastic - a strong and versatile material made by combining a plastic (usually polyester resin) with fibres made of glass. are examples of composite materials.
Remember: Alloysalloy: An alloy is a compound of two or more elements, at least one of which is a metal. are not composite materials.
Ceramics
Ceramics are made from clay, sand and feldsparfeldspar: A very common group of hard, crystalline minerals containing silicon.. These materials are ground to a fine powder, mixed together and fired at high temperatures (700-2000°C).
Smart materials
Smart materials are reactive materials. Their properties can be changed by exposure to stimuli, such as electric and magnetic fields, stress, moisture and temperature.
Smart colours
Smart colours are pigments which can be incorporated into paints, dyes, inks and plastics.
- thermochromic pigments react to changes in temperature
- photochromic pigments react to changes in light levels
Photochromatic materials are used in the manufacture of sunglasses. Exposure to sunlight causes the lens of the glasses to darken to protect the eye.
Polymorph
Polymorph is available in small pellets which fuse together when heated to 62˚C. It can be moulded into shape resulting in a very tough polymer. Unused pellets can be re-heated and re-used.
Polymorph is used for:
- manufacturing awkward shapes such as ergonomicergonomics: The science of designing the product to fit the user, or the job to fit the worker. handles
- joining components together
- making moulds for vacuum forming
Smart grease
Smart grease is used to control movement, producing a dampened, slowed down feeling. For example, smart grease is used on volume control knobs and microscope slides.
Conductive polymers
Most plastics are natural insulatorsinsulator: Material that is a poor conductor of electricity or heat.. The advantages of making plastics which are conductorsconductor: An electrical conductor is a material which allows an electrical current to pass through it easily. It has a low resistance. A thermal conductor allows thermal energy to be transferred through it easily. are:
- they are easier to manufacture
- they are lighter and cheaper than metals
- they prevent the build-up of static electricity which can damage microcircuits
Some conductive polymers are also biocompatible [biocompatible: Can be safely used in the body. ], making them suitable for use in medical devices.
Nanomaterials
Nanoparticles improve the mechanical properties of a material, such as stiffness or elasticityelasticity: The ability of a fibre, yarn or fabric to stretch and return to its original shape.. When incorporated into polymers, they can be used as lightweight replacements for metals.
Nanomaterials are used in car manufacturing to create cars that are faster, safer and more fuel efficient. They can also be used to produce more efficient insulation and lighting systems.
Working properties
Different materials exhibit different working properties. Listed below are the key properties which determine how materials behave.
- conductivity is the ability of a material to conduct heat or electrical energy
- strength is the ability of a material to withstand a force without breaking or bending
- elasticity is the ability of a material to bend and then to return to its original shape and size
- plasticity is the ability of a material to permanently change in shape
- malleability is the ability of a material to permanently deform [deforming: Changing an object's shape without losing any material. ] in all directions without cracking
- ductility is the ability of a material to deform, usually by stretching along its length
- hardness is the ability of a material to resist wear, scratching and indentation
- toughness is the ability of a material to withstand blows or sudden shocks without breaking
- durability is the ability of a material to withstand wear, especially as a result of weathering
- fusibility is the ability of a material to change into a liquid or molten state when heated to its melting point
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