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.

NamePropertiesUses
Ash AshLight, creamy-brown colour, open-grained [open grain: A wood with visible large pores - eg oak. ], tough [tough: Able to withstand blows or sudden shocks without breaking. ], flexible [flexible: Capable of being bent or flexed many times without breaking. ]Sports equipment, wooden ladders, tool handles
Beech BeechWhite to pinkish-brown in colour, close-grained [close-grained: A wood with no visible large pores - eg beech. ], hard [hard: Able to resist wear, scratching and indentation. ], tough, strong [strong: Able to withstand a force without breaking or bending. ], warps [warps: Bends or twists out of shape, this is common with wood as it dries. ] easilyFurniture, toys, tool handles
Elm ElmLight to medium brown in colour, open and sometimes interlocking grain [interlocking grain: The grains have a weaved structure. For wood this makes it strong, less prone to splitting andn often suitable for bending. ], tough, durable [durability: The ability of a material to withstand wear, especially as a result of weathering. ], resists splitting, durable in waterIndoor and outdoor furniture
Mahogany MahoganyPink to reddish-brown colour, fairly strong, durable, some interlocking grainGood quality furniture
Oak OakLight brown colour, strong, hard, tough, open-grained, corrodes steel screws and fittingsInterior 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 pointProperties and characteristicsPrincipal uses
Cast iron 1200°CHard [hard: 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 rustingParts with complex shapes which can be made by casting
Mild steel 1600°CTough [tough: 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 strength [tensile 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°CEven harder than medium carbon steel and more brittle, can be heat-treated to make it harder and tougherCutting tools, ball bearings
Stainless steel 1400°CHard 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 pointCompositionProperties and characteristicsPrincipal uses
Aluminium 660°CPure aluminiumGood strength [strength: The ability of a material to withstand a force without breaking or bending. ]-to-weight ratio, light, soft, ductile, good conductor of heat and electricityKitchen equipment, window frames, general cast components
Copper 1080°CPure copperMalleable and ductile, good conductor of heat and electricity, resistant to corrosionWater pipes, electrical wire, decorative goods
Brass 900-1000°CAlloyResistant to corrosion, fairly hard, good conductor of heat and electricityOrnaments, cast items such as water taps
Tin 230°CPure tinSoft, weak, malleable, ductile and resistant to corrosionUsually used for coating steel to form tin-plate, soft solder [solder: An alloy used to join metallic parts. ]

Plastics

Sources of plastics

Natural

Two yellow rubber ducks (actually made from plastic) floating on soapy water.

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.

NamePropertiesPrincipal uses
Polyamide (Nylon)Creamy colour, tough [tough: Able to withstand blows or sudden shocks without breaking. ], fairly hard [hard: Able to resist wear, scratching and indentation. ], resists wear, self-lubricating [lubricating: Oiling or reducing friction. A lubricant is anything which reduces the friction between two surfaces. ], good resistance to chemicals and machinesBearings, 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 wellSigns, covers of storage boxes, aircraft canopies and windows, covers for car lights, wash basins and baths
PolypropyleneLight, hard but scratches easily, tough, good resistance to chemicals, resists work fatigue [work 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
PolystyreneLight, hard, stiff, transparent, brittle, with good water resistanceToys, especially model kits, packaging, 'plastic' boxes and containers
Low density polythene (LDPE)Tough, good resistance to chemicals, flexible, fairly soft, good electrical insulatorPackaging, especially bottles, toys, packaging film and bags
High density polythene (HDPE)Hard, stiff, able to be sterilisedPlastic bottles, tubing, household equipment

Thermoset plastics can only be heated and shaped once.

Properties and uses of the thermoset plastics.

NamePropertiesPrincipal uses
Epoxy resinGood electrical insulator, hard, brittle unless reinforced, resists chemicals wellCasting and encapsulation, adhesives, bonding of other materials
Melamine formaldehydeStiff, hard, strong, resists some chemicals and stainsLaminates for work surfaces, electrical insulation, tableware
Polyester resinStiff, hard, brittle unless laminated, good electrical insulator, resists chemicals wellCasting and encapsulation, bonding of other materials
Urea formaldehydeStiff, hard, strong, brittle, good electrical insulatorElectrical 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. MDF [MDF: Medium Density Fibreboard - a type of engineered wood made of compressed wood and fibre particles held together with glue. ] and GRP [GRP: 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 feldspar [feldspar: 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 ergonomic [ergonomics: 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 elasticity [elasticity: 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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