Higher Design & Manuacture

Transcription

1 Higher Design & Manuacture Materials Booklet Duncanrig Secondary School

2 Content Material Characteristics Terms page 1 Wood: Timber 2 Softwood 3 Hardwood 4 Manufactured boards 5 & 6 Summary Sheet 7 Metals: Metals 8 Ferrous metal 9 Non-Ferrous metal 10 Alloys 11 Summary Sheet 12 Polymers (plastics): Thermoplastics 13 & 14 Thermosets 15 Elastomers 16 Composites 17 Polymer identification tests 18 Summary Sheet 19 Notes: 20

3 Introduction During the ideas stage of the design process product designers attempt to be as innovative and creative as possible. This divergent thinking often results in a wide range of ideas which must then be narrowed down. It is here during the development and planning for manufacture stages that the product designer needs to be aware of the materials characteristics and the manufacturing processes used to form them. These notes outline the properties of a range of common materials and are intended to assist you, the product designer, make informed choices. This booklet should be read in conjunction with the Manufacturing Process notes. Material Characteristics Terms Before considering different materials it is important that you have an understanding of the terms used to describe their characteristics: Strength - the ability of a material to resist force and suffer no permanent deformation. A strong material requires high loads to permanently deform (or break) it - not to be confused with a stiff material, which requires a large load to elastically (non-permanent) deform it. Stiffness (Young s Modulus) - the ability of a material to resist distortion when a load is applied. A stiff material requires a large load to elastically (non-permanently) deform it - not to be confused with a strong material, which requires a large load to permanently deform or break it. Plasticity - the ability of a material to easily shaped and remain deformed when the load is removed. Ductility - the ability of a material to be stretched and formed without fracturing. Copper, for example, is very ductile and behaves in a plastic manner when stretched. Brittleness - the property of being easily cracked, snapped or broken. It is the opposite of ductility and therefore the material has little plasticity and will fail under loading without stretching or changing shape. Cast iron and glass are examples of a brittle material. Malleability - the ability of a material to be shaped, worked or formed without fracturing. It is closely related to the property of plasticity. Toughness - the ability of a material to absorb sudden loadings without permanent deformation or failure. Tough materials require high elasticity. Hardness - the ability to resist erosion or surface wear. Hard materials are used in situations where two surfaces are moving across or over each other. Testing a specimen sample of material by measuring how it behaves when placed tension. This can determine characteristics such as the stiffness, ductility and brittleness. Duncanrig Secondary School - Materials Booklet Aug

4 Timber It takes many years for trees to grow to a commercially viable size. As the world s forests are presently being depleted, many of the slow growing hardwoods are becoming very scarce. Modern forestry methods use fast growing softwoods (conifer trees) that can be harvested and replanted in a shorter space of time. With careful management it is possible to control the supply and demand of these trees. Modern forestry equipment can fell a tree, de-branch the trunk and then cut the log into standard lengths. These are transporting by lorry to a saw mill for conversion into standard stock sized timber. Selecting Timber Timber suppliers usually stock pine, fir and spruce, the softwoods commonly used for carpentry and joinery. These timbers tend to be sold as dimensioned or dressed stock i.e. sawn or surface planned, to a series of standard sizes. For reasons of convenience and cost it is always a good practice to use the standard stock sized timber and avoid any wasteful and time-consuming machining. Most hardwoods tend to be sold as boards of random width and length but some timbers such as mahogany, teak or oak can be bought as dimension stock. The selection of a particular wood for a design is quite important. Timber is a product of nature; therefore each piece is unique. Each section of wood cut from a tree will be different. It may have the same strength and colour, but is unlikely to have the same grain pattern. It is this diversity of character, strength, colour and workability that makes this material so appealing to use. Selecting timber is therefore a process of balancing its appearance with strength, workability, pliability, weight, cost and availability. Wherever possible you should select standard stock sized timber that can be bought cheaply off-the-shelf and that requires no further processing or machining. When considering wood as a choice of material, the vast range available to the designer falls into three categories: softwoods, hardwoods and manufactured boards. Duncanrig Secondary School - Materials Booklet Aug

5 Softwood Softwood comes from coniferous trees, that is ones with cones and needle shaped leaves. These trees grow quickly which makes their timber inexpensive. Softwoods are easily identified by their light colour and open grain pattern. The following table details some of the more widely used softwoods: Name Characteristics Uses Scots Pine Light coloured, resinous. White yellow to yellow brown. Furniture, construction work, joinery. Red Cedar Relatively soft aromatic timber. Reddish brown to silver grey after long exposure to weathering. Shingles, exterior boarding and cladding, greenhouses, sheds and beehives. Parana Pine Straight grain. Even texture. Light Joinery, furniture, turnery. Spruce (white wood) to dark brown with red streaks. Straight grain. Even texture. Almost white to pale brown. Construction, joinery, boxes, plywood, piano soundboards, violin bellies, ship masts. Pine Overview: Pine is an abundant material which grows in temperate or cool climates. Like most timbers, pine is light and durable - wood has been used for building and construction for thousands of years. Like all woods, pine products must be sawn and machined from felled trees, which places some limits on the range of shapes for which it is suitable. All woods have an internal structure of aligned natural fibres and elongated hollow cells. This structure gives them very low density, and excellent specific properties. Design Issues: high stiffness-to-weight ratio, high strength-to-weight ratio, corrosion resistant, easily recycled, low density, difficult to form. Typical Products: furniture, railway sleepers, pallets, house construction. Process Notes: readily machined to shape by turning, cutting and "milling". Naturally decorative surface, but usually finished by sanding. Very good for use with mechanical fasteners such as screws and nails. Adhesives a common method of joining, especially in high volume goods. Environmental Issues: Pine is a relatively fast-growing timber which is a sustainable resource if wellmanaged. Intensive forestry can lead to environmental damage when trees are cleared without replanting. Woods are naturally biodegradable, or can be shredded and used for wood-fibre products or burnt as fuel. A modern house showing the pine timber frame. This frame has been pre-made in a factory before being transported to the site where it is assembled and then covered with a single layer of brick. Duncanrig Secondary School - Materials Booklet Aug

6 Hardwood Hardwood comes from deciduous trees, that is ones with broad leaves. Deciduous trees tend to be slow growing which makes their wood expensive. Hardwoods tend to be more durable than softwoods and offer a greater choice of texture and colour. Unfortunately, the indiscriminate destruction of the world s rainforests is leading to a severe shortage of tropical hardwoods again adding to the expensive nature of this material. The following table details some of the more widely used hardwoods: Name Characteristics Uses Beech Straight-grained wood. Fine even texture. Whitish brown turning to yellowish brown on exposure. Cabinet making, bent wood furniture, interior joinery, veneer, turnery, plywood. Oak Straight grained. Course texture. Furniture, flooring, boat Ash Mahogany Teak Walnut Balsa Pinkish red. Straight grained. Coarse texture. Whitish to pale brown in colour. Straight or interlocking grain. Medium texture. Reddish brown to deep red. Straight or wavy grained. Course uneven texture with oily feel. Golden to darker brown. Very expensive. Straight to wavy grain. Grey brown with darker streaks. Open straight grain. Very pale beige to pinkish colour. Softest and lightest hardwood. Oak Overview: Oak is a slow-growing hardwood which is abundant worldwide in temperate or cool climates. It has been used for building and construction for thousands of years - particularly for shipbuilding. As one of the harder woods, it has been used extensively for furniture and for woodcarving. Like all woods, oak must be sawn and machined from felled trees, which places some limits on the range of shapes for which it is suitable. All woods have an internal structure of aligned natural fibres and elongated hollow cells. This structure gives them very low density, and excellent specific properties. Design issues: High stiffness-to-weight ratio, high strength-to-weight ratio, corrosion resistant, easily recycled, low density, difficult to shape. Typical Products: Furniture, woodcarvings, decorative flooring. building, veneer. Sports equipment, tool handles, cabinet making, veneer, furniture. Interior panelling, boat planking, carving, pianos, veneer. Interior and exterior joinery, garden furniture, veneer. Furniture, gunstocks, musical instruments, veneers. Insulation, buoyancy aids, model-making, packaging. Process Notes: Readily machined to shape by turning, cutting and "milling". Naturally decorative surface, but usually finished by sanding. Very good for use with mechanical fasteners such as screws and nails. Adhesives a common method of joining, especially in high volume goods. Environmental Issues: Oak is slow-growing, so requires long-term forestry planning if it is to remain a sustainable resource. Woods are naturally biodegradable, or can be shredded and used for wood-fibre products or burnt as fuel. An oak computer unit which uses a mix of solid timber and oak veneered manufactured board. Duncanrig Secondary School - Materials Booklet Aug

7 Manufactured Boards Manufactured boards are a relatively new type of material and are being used more and more in both home and industry. They have several advantages over natural timbers. They have strength in all directions due to criss-crossing of grain in each layer, they are more resistant to changes in temperature and humidity, and they come in large standard sized boards. Manufacturers are constantly developing these materials to improve their quality, ease of working and use of raw materials. This development has given rise to a wide range of boards available. Manufactured boards roughly fall into three categories: laminated, fibre and particle boards. Laminated Boards Plywood is constructed from thin sheets of wood veneer bonded in layers to form a strong, stable board. The grain of each alternate sheet is laid at right angles to the next. This construction produces a stable and warp resisting board. Most plywoods have an odd number of veneers to give a balanced construction, the minimum being three, but four and six ply is also available for use in structural work. Plywood is available in a range of sizes. Blockboard differs from plywood given that the core is made from square strips of pine covered with a layer of veneer on each side. Fibreboards These are constructed from wood that has been reduced to a fibrous state, added to a bonding adhesive and then compressed into boards. Boards of various densities can be produced depending on the pressure applied and bonding material, however, medium density fibreboard is the most common type used. Particleboards These are constructed from flakes or chips of wood bonded together under pressure. Depending on the size of the wood particles various types of board are produced. Chipboard is most commonly used although it will swell if exposed to moisture and will not recover. Moisture resistant types are available. Can be veneered for internal structures. Duncanrig Secondary School - Materials Booklet Aug

8 The following table shows some of the most commonly used manufactured boards: Name Properties & Characteristics Uses Medium Density Fibreboard (M.D.F.) Two smooth surfaces. High strength. Excellent edge quality. Plywood Blockboard Chipboard Hardboard Veneer An odd number of veneers are laid at 90 to each other, with surface parallel to grain. Timber strips laid parallel with veneers glued either side with their grain running crosswise. Wood chips mixed with bonding mixture to create large flat boards. Surface and strength depends on chip particle size. Standard hardboard has one smooth face and the other embossed. Thin sheets of wood cut from a log for constructional or decorative purposes. Wide variety. Usually glued to one of the other types of board before use. Furniture with intricately shaped parts or large smooth surfaces, carcass construction. Interior joinery, carcass construction. Decorative ply is mainly used for panelling. Shelving and worktops. Furniture, flooring, flat roof construction, kitchens and bathrooms. Wall and ceiling linings, panelling, partitions, shop fitting display and exhibition work. Furniture restoration, Wall panelling, furniture making, violin backs. MDF Overview: MDF is the most common fibreboard which is made by compacting wood fibres with a small proportion of polymer resin. Fibreboards are a good way to use up waste wood from sawing and machining of solid timber. As the fibres are chopped into short lengths, the fibre-polymer mixtures can be moulded or pressed into shapes which cannot be made in one piece from wood (such as large panels or doors). Design Issues: high stiffness-to-weight ratio, high strength-to-weight ratio, corrosion resistant, easily recycled, low density, easy to shape, usually needs veneering for a good finish Typical Products: desktops, doors, furniture carcases. Process Notes: may be moulded like a thermoplastic, readily machined to shape by turning, cutting and "milling". Very good for use with mechanical fasteners such as screws and nails. Adhesives a common method of joining, especially in high volume goods. Environmental Issues: Fibreboards largely use waste wood fibre, can be recycled and are mostly biodegradable. Kitchen unit made from chipboard with round moulded MDF doors finished in white melamine polymer laminate. Question Advances in man-made boards, where additives have been introduced, have dramatically expanded the range of options available to designers. State the name of three of these man-made boards and give an example of a product manufacture from each. Duncanrig Secondary School - Materials Booklet Aug

9 Wood: Summary Table Duncanrig Secondary School - Materials Booklet 7

10 Hardwood Softwood Manufactured Board Family Wood Name Cost (relative) Supply Strength General Information Beech Oak Ash Mahogany Teak Walnut Balsa Scots Pine Red Cedar Parana Pine Spruce MDF Plywood Blockboard Chipboard Hardboard Board, rectangular & Square lengths Board, rectangular & Square lengths Board, rectangular & Square lengths Board, rectangular & Square lengths Board, rectangular & Square lengths Board, rectangular & Square lengths Rectangular & Square lengths Board, rectangular & Square lengths A close grained hardwearing timber which is used in kitchen wear, furniture making, work benches, desks, chairs, turnery, tool handles, mallets, veneers and flooring. A hardwearing open grained timber that can be used in or outdoors. It is commonly in furniture making, boat building, barrels and flooring. Similar in appearance to oak but with a more closed grain. It is used in furniture, sports equipment, turnery and plywood. Used in high quality cabinet and furniture making, panelling, pattern making, decorative veneers and plywood. Teak is best finished with oil and the timber can be difficult to glue and it's dust is known to be a skin irritant. It is used in boat building, cabinets, garden furniture, flooring and laboratory benches, decorative veneers. Walnut is an attractive timber that is commonly used in furniture and cabinet making, gun stocks, flooring, snooker tables and veneers. Balsa is the softest and lightest commercial hardwood. It is used in model making, buoyancy in rafts, floats, water sports equipment, and insulation. Scots pine in commonly used in furniture making, joinery, building construction, telegraph poles and plywood. Board, rectangular Red Cedar is used extensively for outdoor uses such as garden sheds, greenhouses, & Square lengths exterior boarding and cladding, fences and posts. Very attractive wood with straight grain, very close density, honey colouring, and very Board, rectangular & Square lengths subdued growth rings. Parana is not a true pine and is used in internal joinery, doors, staircases and plywood manufacture. Board, rectangular Similar to pine but with smaller but more frequent knots. It is lighter and stronger than & Square lengths pine and is commonly used to make staircases and in general building construction. Wood dust glued into a smooth stable board ideal for machining and painting/ It is Sheet (2440 x 1220mm) used in furniture, carcases, pattern making and as a base for decorative veneers. Layers of timber veneer glued with the grain at right angles to produce a stable and Sheet (2440 x 1220mm) very strong board. It is used in furniture making, carcases, cabinet backs, drawer bottoms and panelling. Sheet Made from solid strips of pine sandwiched between a veneer outer layer. It is used in (2440 x 1220mm) table tops, knock-down furniture and carcases. Wood chips glued and pressed into a board. It can be covered with wood veneer or Sheet (2440 x 1220mm) plastic melamine surface (conti board). It is used in Inexpensive knock down furniture and kitchen work tops. Sheet Wood dust pressed into a thin board with a smooth and a textured side. It is used in (2440 x 1220mm) drawer bottoms and cabinet backs. Duncanrig Secondary School - Materials Booklet 8

11 Metal Metals are an extremely versatile design material and the huge variety of metals and their alloys can be used in many applications from jewellery to engine parts. A small cast platinum with gold pendant 6m long ships diesel engine made from cast iron. Compared to all other materials, metals are stiff, strong and tough, but they are heavy. They have a relatively high melting point, allowing some metal alloys to be used at temperatures as high as C. Metals are ductile, allowing them to be shaped by rolling, forging, drawing, and extrusion; they are easy to machine with precision; and they can be joined in many ways. This allows a flexibility of design with metals that is only now being challenged by polymers (plastics). The primary production of metal is energy intensive. Many, among them aluminium, magnesium, titanium, require at least 5 times more energy per unit volume than polymers (plastics). But metals can be recycled, and the energy required to do so is much less than that required for primary production. Metals can be either pure material extracted from ore deposits found buried in the earth s surface or made from a mixture of two or more metals combined with other elements. The latter are called alloys. Duncanrig Secondary School - Materials Booklet 8

12 Ferrous Metals Pure iron is difficult to produce and not often used nowadays. Ferrous metals therefore tend to be alloys of iron and carbon. They tend to rust in moist conditions and are magnetic. Name Properties Uses Cast Iron Iron + 3.5% carbon. Brittle with a hard Machine tools, vices. skin. Casts well. Mild steel Iron + up to 0.35% carbon. Malleable, ductile with a very uniform texture. Nuts, bolts, screws, tubes, small non-cutting tools. High carbon steel Iron + up to 1.5% carbon. Malleable & ductile. Can be hardened and tempered. Cutting tools, files, drills, saws, taps & dies, knives, scribers, lathe tools. Stainless steel High speed steel Iron, carbon with Chromium, Nickel & Magnesium. Hard and tough. Corrosion and wear resistant. Medium carbon steel, tungsten, chromium & vanadium. Very hard. Excellent heat resistance. Cutlery, sink units, dishes, teapots, boat fittings. Tool bits, drills, lathe cutting tools. Steel Overview: Steels are the most important engineering materials, and cover a wide range of alloys based on iron and carbon. The strength of iron-carbon alloys, particularly after heat treatment, has been exploited for thousands of years (since the "Iron Age"). Alloy steels are mostly fairly cheap, covering a range of carbon contents ( %). The medium to high carbon content steels respond well to heat treatment (such as "quenching and tempering") to give very high strength and good toughness for gears, driveshafts, pressure vessels, tools. All steels have a high density and a high stiffness. The strength and toughness of alloy steels can be varied enormously by alloying, working and heat treatment. Alloy carbon steels rust easily, and must be protected by painting or other coatings. Design Issues: high strength with good toughness, high stiffness, mostly very cheap, quite easy to shape, easy to weld, easy to recycle, high density, poor electrical and thermal conductivity Typical Products: structures - oil rigs, railway track, bearings, gears, shafts, cutting tools, hand tools. Process Notes: Powder metal forming is most commonly used with high alloy steels. Rolling, extrusion and sheet forming are only used with low alloy (lower strength alloys). Machining gets more difficult for the stronger alloys (usually those with higher alloy content). Joining - suitable for use with most techniques. Friction welding can be difficult for high alloy steels. Environmental Issues: Steel production uses a lot of energy, but less than most metals. Steel is easily recycled - as it is usually magnetic it is easily sorted from mixed waste. Detail of the steel structure in the Glasgow Science Centre Tower. Duncanrig Secondary School - Materials Booklet 9

13 Non-Ferrous Metals These metals have no iron and therefore withstand moist conditions. Non-ferrous metals are not magnetic. Name Properties Use Aluminium Pure metal from Bauxite ore. Strength to weight ratio good. Casts easily. Copper Tough, ductile and malleable. Good conductor. Expensive. Window frames, food packaging, kitchen utensils. Central heating pipes, electric wires and cables, jewellery. Tin Lead Zinc Heavy and soft material with a low melting point. Very heavy, soft, weak, ductile and malleable. Low melting point and can be cast. Weak and difficult to work. Used extensively in alloys. Surface coating on sheet steel. Roof flashing, plumbing, solder. Surface coating on steel (galvanized). Dustbins, corrugated sheets, castings. Aluminium Overview: Aluminium is a lightweight, reasonably cheap metal widely used for packaging and transport. It has only been widely available and used for the last 60 years. Raw aluminium has low strength and high ductility (ideal for foil). Strength is increased by alloying, e.g. with silicon, magnesium, copper, zinc and heat treatment. Some alloys are cast; others are used for wrought products. Aluminium is quite reactive, but protects itself very effectively with a thin oxide layer. The surface can be "anodised", to resist corrosion and to give decorative effects. Design Issues: high strength-to-weight ratio, high stiffness-to-weight ratio, high electrical and thermal conductivity, easy to shape, easy to recycle, difficult to arc weld. Typical Products: aircraft, bicycles, car engines, "Space frame" car bodies, drinks cans, window frames. Process Notes: Metal forming - easy to use with most metal forming processes. Very suitable for rolling at all thicknesses down to foil. Die casting is the most commonly used casting process. Usually comparatively soft, so readily extruded. Sheet forming is important use for cans. Machining - relatively soft, so readily machined. Joining - suitable for use with most techniques, although difficult to arc-weld and an inert gas is needed. Environmental Issues: Aluminium production uses lots of energy (4% of total US energy consumption!). Aluminium is easily recycled - this only uses 1% of the energy needed to produce the metal. Aluminium use in cars is growing rapidly - low weight means good fuel economy and low emissions metal. The aluminium space fame chassis for Audi s new A8 luxury car. Duncanrig Secondary School - Materials Booklet 10

14 Alloys An alloy is a mixture of two or more metals formed together with other elements such as copper and zinc to create new materials. These new materials tend to have more desirable qualities than pure metals. Name Composition Properties Uses Stainless steel Iron & carbon + Chromium + Nickel + Magnesium Ferrous. Hard and tough. Corrosion and wear resistant. High speed steel Brass Bronze Duralumin Medium carbon steel + tungsten + chromium + vanadium. Copper + zinc Copper + Tin + zinc Aluminium + manganese + magnesium Ferrous. Very hard. Excellent heat resistance. Non-ferrous. Corrosion resistant, hard. Casts well, work hardens. Easily joined, polishes well, good conductor. Non-ferrous. Strong and tough. Wear and corrosion resistant. Non-ferrous. Very good strength to weight ratio. Age hardens. Machines and finishes well. Cutlery, sink units, dishes, teapots, boat fittings. Tool bits, drills, lathe cutting tools. Taps, decorative items, boat fittings, casting. Statues, water fittings, coins. Aircraft parts. Brass Overview: Brass is quite an expensive alloy of copper and zinc. Alloying, working and heat treatment gives it a much better strength than copper and a good corrosion resistance. Design Issues: reasonable strength, corrosion resistant, easy to shape, quite expensive Typical Products: ornamental fittings, plumbing fittings, screws Process Notes: Metal forming - readily extruded because it is quite soft. Rarely rolled, forged or used in sheet forming. Not used much with powder metallurgy as it tends to oxidise. Machining - Readily machined. Joining - Soldering and brazing are important for electrical connection and pipe. Adhesive bonding rarely used. Environmental Issues: Copper and brass production uses quite a lot of energy. Brass is easy to recycle, but the volume in use is small. Question Figure 1 shows a drawing of a Chinese cooking wok, designed for high temperature, fast stir-fry cooking. The body of the wok is manufactured from thin gauge mild steel. Figure 2 shows a drawing of a cast iron saucepan designed for low temperature slow cooking. For each product, explain how the cooking requirements led to: (i) the choice of material; (ii) the method of construction. Duncanrig Secondary School - Materials Booklet 11

15 Ferrous (with iron) Non-ferrous Rotational Casting Die casting Sand casting Pressing Piercing & blanking Forging Extrusion Turning Milling Arc welding Spot Welding Riveting Adhesives Family Metal: Summary Table Manufacturing Process Metal name Cost (relative) Supply General Information Mild Steel High Carbon Steel rod, sheet, bar, tube rod, bar Stainless Steel High speed Steel rod, sheet, bar, tube rod, bar Cast iron Ingot Brass rod, sheet, bar, tube Bronze ingot Aluminium Duralumin Copper Tin Lead Ingot, bar, tube sheet, rod, sheet, bar sheet, wire, tube Ingot, rod, Ingot, sheet Perhaps the most common metal it is used in general structural work, girders, nuts, bolts, screws, non cutting tools and car bodies. Harden and tempered and used in hand tools as the cutting edge is lost at high temperatures. Stainless steel has a high tensile strength and resists abrasion and corrosion because of its high chromium content. It is difficult to cut or file and is used is sinks, kitchenware, pipes and aircraft. High Speed Steel is hardened and tempered and is used in cutting tools for lathes, milling cutters and drill bits where it will retain hardness up to temperatures of 600 C. Cast Iron has a hard skin but soft core and is strong in compression. Used in engine parts, vices, manhole covers and machine tools. An alloy of copper and zinc which is used in castings, boat fittings, ornaments, wood screws, door handles and hinges. Bronze is an alloy of copper, tin, zinc, phosphorus and it is harder than brass. Used in bearings, gears, statues, coins. Aluminium is rarely used as a pure metal and it is usually alloyed with copper to improve strength (duralumin) The most common aluminium alloy used in car bodies, cookware, aircraft, boats, engines, window frames and drink cans. It is malleable, ductile and conducts electricity. Copper roofs become tarnished in the air resulting in a green finish known as verdigris. Used in wire, water pipe, boxes, bowls and rivets. Tin is very soft and is used in soft solder and pewter or to cover sheet steel (tinplate) to prevent rusting. Lead is a soft but poisonous metal used in roof flashing, car batteries or to form alloys. Duncanrig Secondary School - Materials Booklet 12

16 Zinc Ingot, sheet A brittle metal with a low melting point used in dies casting and galvanise steel to prevent rusting Duncanrig Secondary School - Materials Booklet 13

17 Polymers (Plastics) Polymers, commonly called plastics, are synthetic materials produced from refined oil. Plastics provide a versatile material that is extremely suitable for mass production and can be made to suit a wide range of applications by simply altering the chemical structure. There are four main categories of polymer; Thermoplastics, Thermosets, Elastomers and Composites. Thermoplastics Thermoplastics soften whenever heated and harden again when cooled. This allows them to be moulded into complex shapes. When reheated a thermoplastic will return to its original shape, this characteristic is known as plastic memory. Name Characteristics Uses Polythene (Low density) Good electrical insulator, Soft & flexible. Variety of colours. Carrier bags, squeezy bottles, toys, detergent. Polythene (High density) Good chemical resistance. Stiff and Buckets, bowls, milk crates. hard. Variety of colours. Polyvinyl chloride (PVC) Weather resistant. Stiff, hard, tough & lightweight. Pipes, guttering, curtain rails, window frames. Polystyrene (a) conventional (b) expanded (c) Toughened Polyamide (Nylon) Cellulose acetate Acrylic (Perspex) Polypropylene ABS (a) Light, hard, transparent, waterproof. (b) Light, buoyant, good insulator. (c) Good strength Good chemical resistance. Hard, tough & rigid. Machines well. Tough, hard & stiff. Lightweight, Transparent. Weather durable. Stiff & hard. Easily scratched. Variety of colours. Light, hard, impact resistant, and can be sterilized. High impact strength, scratch resistant, durable. (a) Kit models, food containers. (b) Ceiling tiles, insulating boxes. (c) Toys, refrigerator linings. Wheels, gears, machine parts. Pen cases, Spectacle frames, photographic film. Shop signs, display stands. Shampoo bottles, medical equipment, film. Telephones, toys, safety helmets, kitchenware. Polythene Overview: Polythene (polyethylene, PE) is the polymer used in the largest quantities and like all thermoplastics, polythene is easy to shape and join. It comes in various forms, of which LDPE (low density) and HDPE (high density) is the most common. Low density polythene is the only polymer which floats, high density polythene does not. Design Issues: It is very simple polymer structure, so easy to process. Transparent, or easily coloured. Can be drawn to very large elongations, and very thin sheet. Quite expensive. Typical Products: dustbins, water and gas pipes, carrier bags, food packaging, sandwich boxes. Process Notes: Most polymer processes are suitable - injection moulding is the most common. Often extruded for pipes and rotational moulded for large products like dustbins. Blow moulding for bottles and vacuum forming for packaging. It is not compression moulded. It is relatively soft, so readily machined. However, usually formed to shape so little cutting is done in practice. Surface finish usually good enough after moulding, so no polishing required. Adhesive bonding is most common joining technique and fusion (e.g. arc) welding is not suitable, although some hot welding (non-melt) processes are okay - e.g. friction welding for pipes. Environmental Issues: Polymers are derived from hydrocarbons, and require energy to extract and purify them. Thermoplastics can be reheated and reshaped. No toxic fumes when burnt. The HDPE body of the wheelie bin formed rotational moulding. Duncanrig Secondary School Materials Booklet 13

18 Thermoplastics may be recycled after use, indeed EU rules insist that manufacturers collect and recycle their products after their useful life is over. This legal requirement is to help reduce the impact on the environmental but it also has cost savings to the manufacturer through the use of the recycled materials. All major thermoplastic components must now carry the recycling logo with the appropriate polymer code number to ease the sorting and recycling: 1: PET Polyethylene Terephthalate 2: HDPE High Density Polythene 3: PVC Polyvinylchloride 4: LDPE Low Density Polythene 5: PP Polypropylene 6: PS Polystyrene 7: Other Any other thermoplastic Duncanrig Secondary School Materials Booklet 14

19 Thermosets Thermoset plastics usually come in a liquid form which is set solid using a chemical catalyst or with heat. When re-heated thermosets do not melt, they degrade. Thermosets have a greater dimensional stability than thermoplastics; they are used where there is a requirement for high temperature resistance or little or no creep (movement). Thermosets are shaped by compression moulding, casting and injection moulding where they copy exactly the mould finish. Moulding can be adapted to low volume production using low cost moulds; but higher production cycles of up to a million or greater are economical only with expensive moulds that allow fast heating, cooling and extraction. Thermosets cannot be recycled. Name Characteristics Uses Epoxy Resin Good chemical, heat and wear Adhesives, surface coatings. resistance. Melamine Formaldehyde Stiff, hard & strong. Reasonably water-resistant. Scratch, heat & stain resistant. Variety of colours. Kitchen worktops, electrical insulation Urea Formaldehyde Polyester Resin Stiff, hard, strong & brittle. Electrical insulator. Variety of light colours. Stiff, hard & brittle. Heat and chemical resistant. Good electrical insulator. White electrical fittings, adhesives. Chair shells, car bodies, boats reinforced with glass (GRP). Urea formaldehyde Overview: Urea formaldehyde (UF) is a thermosetting polymer. Design Issues: heat resistant, stiff and strong. It has few processing routes and cannot be reshaped or recycled. Typical Products: electrical plugs, household insulation (as foam). Process Notes: compression moulding is the most commonly used, although injection moulding is done on a regular basis as well. Rotational moulding is possible, but not that common. Cycle time is always limited by the need for 'curing'. Machining - readily machined; however, usually formed to shape so little cutting is done in practice. Surface finish usually good enough after moulding, so no polishing required. Joining - adhesive bonding is most common but no welding processes are suitable as UF doesn't soften or melt. Environmental Issues: Polymers are derived from hydrocarbons, and require energy to extract and purify them. As a thermoset it cannot be recycled. Urea formaldehyde plug body made by compression moulding Question Developments in plastics have resulted in their use in furniture design, in place of traditional materials for construction, surfaces, upholstery and fixtures & fittings. For each of these show how designers have taken advantage of the design potential offered by plastics. Duncanrig Secondary School Materials Booklet 15

20 Elastomers Elastomers, unlike all other class of solids, remember their shape when stretched (some up to five times their original length) and return to it when released. Their soft touch textures make them popular with consumers and hence are increasingly used in product design. Elastomers are easy to foam, giving them the comfort of cushions, and increasing even further their ability to conform to whatever shape is pressed against them. Name Characteristics Uses Isoprene Synthetic natural rubber. A thermoset material. Inner tubes, belts, hoses, cable instillation, encapsulation, footwear, sporting goods, water EVA (Ethylene-vinyl-acetate) Natural Rubber Soft flexible and tough. Stiff, hard & strong. Derived from the sap of the rubber tree. It is the most widely used elastomer accounting for more than 50% of all products. It is a thermoset and cannot be recycled which presents major environmental concerns for the disposal of products such as runner car tyres. repellent sealants. Gaskets, gloves, shrink film, laminated film, ice trays, inflatable parts, running shoes. Tyres, hoses seals. EVA Overview: Ethylene-Vinyl-Acetate is an elastomer built around polythene Design Issues: flexible, soft and tough and it retains these properties down to Typical Products: medical tubes, milk packaging, bags, shrink film, deep freezer bags, running shoes. Process Notes: compression moulding is the most commonly used, although injection moulding is done on a regular basis as well. Rotational moulding is possible, but not that common. Environmental Issues: Polymers are derived from hydrocarbons, and require energy to extract and purify them. EVA is a thermoplastic and hence can be recycled. EVA elastomer used in the injection moulded sole of a training shoe. Duncanrig Secondary School Materials Booklet 16

21 Composite Polymers Very often two or more materials are combined to obtain different properties than those available in the original substance. This is true of materials such as concrete, plywood, fibreglass and carbon fibre. These type of materials are known as composites. Composites are usually formed to increase the strength-to-weight ratio, ductility or temperature and shock resistance. Polymer composites are one of the great developments of the late 20 th century. Those with the highest stiffness and strength are made of continuous fibres (glass, carbon or Kevlar) embedded in a thermosetting resin (polyester or epoxy). The fibres carry the mechanical load while the matrix material transmits loads to the fibre and provides ductility and toughness as well as protecting the fibres from damage caused by handling. Polymer composites can be formed by open or closed moulding methods with the lay-up method allowing complete control over the fibre orientation and hence strength. Composite products are labour intensive to manufacture but the moulds can be inexpensive and suitable for one-off or batch production. Name Characteristics Uses GFRP (Glass Fibre Reinforced Polymer) - Fibreglass CFRP (Carbon Fibre Reinforced Polymer) Commonly called Fibreglass, this is lightweight with a high strength and stiffness. Glass fibres are embedded with polyester matrix. It accounts for 98% of the composite products and is less expensive than CFRP. Carbon fibre is the material of sports and aerospace. It is made by embedding carbon in an epoxy matrix. Lighter, stronger but very much more expensive than fibreglass. Boat hulls, train seats, pressure vessels, car body panels, sports equipment, bathroom and kitchen fixtures. Aircraft structure, power boats, racing cars, tennis rackets, fishing rods, golf club shafts, performance bicycles. GFRP Overview: Fibreglass uses epoxy resin and fibres, which are difficult materials to work with, requiring special precautions against toxic fumes, fibre fragments, fire hazards etc. Design Issues: high stiffness and strength-to-weight ratio but it cannot be recycled and it is difficult to shape and join. Typical Products: Sports goods (tennis racquets, golf clubs, fishing rods), boat hulls (yachts, canoes) and bath tubs. Process Notes: All composite techniques are suitable - e.g. hand lay up, spray lay up. Machining it requires special tools to drill and cut. Not used with other machining processes. Joining - usually, made to shape; fasteners rarely used because of risk of cracking at holes; adhesives most common method of joining. Environmental Issues: GFRP mostly uses epoxy resin and fibres, which are difficult materials to work with, requiring special precautions against toxic fumes, fibre fragments, fire hazards etc. A hand laid-up GFRP nose cone of a racing car being removed from the two halves of a split mould. In Formula One racing however, where manufacturers have almost an unlimited budget, CFRP is used instead. Duncanrig Secondary School Materials Booklet 17

22 Polymer Identification Polymers can be identified through a variety of tests, some of which are given in the tables below. In general, most thermoplastics will cut cleanly, become pliable at 200 C or less, and if heating continues will melt to become a thick and sticky liquid. Thermosets will produce powdery fragments when cut with a knife and bubble and disintegrate before softening. Name Does material cut with a sharp knife? Does material bend at room temperature? Polythene Cuts cleanly LD: flexible HD: rigid Polyvinyl chloride (PVC) Cuts cleanly Plasticised: flexible Rigid: stiff What happens in water? LD: Floats HD: sink Sinks Will material scratch with a fingernail? Yes Plasticised: yes Rigid: no Polystyrene Fairly hard Rigid Sinks No Expanded polystyrene Breaks into small Breaks Buoyant Yes fragments Nylon Cuts cleanly Rigid Sinks Yes Acrylic Fragments Breaks Sinks No Polypropylene Cuts cleanly Rigid Floats No Melamine formaldehyde Splinters Very rigid Sinks No Urea Formaldehyde Splinters Very rigid Sinks No Name of material. Effects of Burning Material soften? Material ignite? Polythene Yes Easily Polyvinyl chloride (PVC) Flame colour Blue with a yellow tip. Yes Difficult Yellow Polystyrene Yes Easily Expanded Polystyrene No Easily Nylon No Difficult Acrylic Yes Easily Polypropylene Yes Easily Melamine & Urea Formaldehyde No Difficult Orange/ Yellow Orange/ Yellow Blue with a yellow tip Yellow, with blue base Yellow with a blue base Yellow, blue green edges Nature of the smoke Small amount White with heavy soot. Black with soot Black with soot Small amount No smoke Small amount Small amount Nature of the flame? Burning droplets which go out on surface contact. Smells of candle wax. May drip. Smells of hydrochloric acid. Burning droplets. Smells sweet. Drips continue to burn. Smells sweet. Melts to a liquid and drips carrying a flame. Smells like burning hair. Drips which continue to burn. Bubbles first. Smells strong, sweet and fruity. Burning droplets which go out on surface contact. Smells like candle wax. Swells and cracks, turns white at edges. Smells pungent & burning. Continue to burn? Yes No Yes Yes Yes Yes Yes No Duncanrig Secondary School Materials Booklet 18

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24 Thermoplastic Thermoset Elastomer Composite Injection Moulding Extrusion Rotational Moulding Vacuum Forming Blow Moulding Laminating Compression moulding Joining Family Polymer (Plastic): Summary Table Forming Process Plastic Name (commonly called) Cost General Information Polythene High Density (HDPE) Polythene Low Density (LDPE) PVC Polystyrene (PS) High rigidity and tensile strength but with a low impact strength. Used in water and gas pipes, guttering, buckets, moulded house ware, traffic cones. Flexible, tough and with good chemical resistance. Used in grocery and rubbish bags, hot melt adhesives, wire insulation and blow moulded toys. Used in window frames, cladding, piping, vinyl flooring, clothing, dip coating finishing, car upholstery. A good insulator but degrades under sun (UV) light. A light, flame retardant material with a low impact resistance (brittle). Used in food rays, packaging (Expanded), pens, razors and CD cases Nylon (PA) Fatigue resistant, tough and strong. Used in gears, bearings, textiles, rope, car upholstery. Cellulose Acetate (CA) Polycarbonate (PC) Acrylic (PMMA) Polypropylene (PP) ABS Polyester Epoxy Resin Melamine Formaldehyde (MF) Made from wood pulp to produce a tough, transparent material with a low heat resistance. Used as a film (cellophane), sunglasses, safety glasses, tool handles and combs. Optical transparency, high impact, heat and flames resistant. Uses include safety glasses, CD cases, light diffusers, computer housings. Stiff, strong UV resistant but brittle. Used in baths, aircraft windows, car light lens, shop signs compact discs. Inexpensive and similar to HDPE but can be used at higher temperatures. Used in ropes, hinged containers, garden chairs etc. Hard, rigid and highest impact resistant. plastic. Used in electrical equipment cases, safety hard hats, toys (Lego) etc. The thermoplastic version (PET) is crystal clear and in drinks bottles. When re-cycled it is used in fibres to make clothing and carpets. The thermosetting version reinforces glass or carbon fibres. A hard, rigid and brittle material which is used as an adhesive (Araldite), paint and protective finish or for printed circuit boards. Heat resistant and will not flavour food, hard and abrasion resistant. Used in kitchen work surfaces and table wear. Urea Formaldehyde (UF) A brittle heat resistant material used in electrical fittings, adhesives, laminates. Glass-reinforced plastic (GFRP) Carbon-fibre plastic (CFRP) Rubber Isoprene EVA A lightweight material with high strength and stiffness. Made with a glass woven mat soaked with polyester and used in boat hulls, baths and sports equipment. Epoxy or polyester soaked carbon woven mat used by the sport and aerospace industry for very strong but lightweight components. Natural Rubber to synthetic Isoprene this family is used in tyres, hoses and footwear. A bouncy, flexible and wear resistant material. Synthetic natural rubber used in Inner tubes, belts, hoses, cable instillation, encapsulation, footwear, sporting goods, water repellent sealants. Soft, flexible, tough, stiff, hard & strong. Used in gaskets, gloves, shrink film, laminated film, ice trays, inflatable parts, running shoes. Duncanrig Secondary School - Materials Booklet 19

25 NOTES: Duncanrig Secondary School - Materials Booklet 20