AS Resistant Materials Unit one Aims Match a range of products with the appropriate plastic material and manufacturing method. Tasks: 1)For each of the plastic products suggest a suitable plastic material 2) Suggest a suitable shaping or forming method. 3) Give brief reasons why you think these materials and forming processes are suitable. Consider the following: a) What the product and material must do, or be like to be successful. b) The intended scale of production and how this might influence materials and forming methods.

Plastics forming processes or methods Typical usesUsed for thermoset, or thermoplastic Description of process Vacuum forming Yoghurt pots, Chocolates and biscuit package trays. Shaped food containers and packages. School projects. Commonly used for high volume and one off, or batch production or mass production. Thermoplastics (Polystyrene, acrylic, polycarbonate). A heated thermoplastic sheet is pulled down onto a mould or former by a vacuum action. Blow moulding Soft drinks containers, bottles, containers for detergent, washing up liquid bottles. High’ tooling’ costs makes blow moulding unsuitable for small scale production. Thermoplastics such as HDPE or LDPE, or PET begins as a blank cylinder which is heated inside a mould. Hot air is pumped into the blank. Or parison causing it to expand into the mould cavity. Generally used for mostly symmetrical, two part moulds. Injection moulding Used for high volume production of complex plastic casings, containers and enclosures for electrical goods. Very expensive, initial ‘tooling’ costs. Unit costs greatly reduced because of high volume production. Thermoplastics reduced to a liquid state. ABS, HDPE, LDPE, polypropylene, nylon. A thermoplastic is heated and injected into a cavity where it takes on the form of the cavity in the mould. It cools and is finally ejected from the mould by ejector pins as the mould is opened. Injection moulding allows complex objects such as whole chairs to be moulded in one process. Extrusion Plastic drain pipes, roof guttering, Window frame sections, plastic channelling. Anything that is a prism, or uniform in section. ThermoplasticsThermoplastics are heated and plasticised so they can be squeezed through a die or mould. calendering Plastic bags, plastic material for garments. Making flat sheets of thermoplastics to be sold to industry. Can also be used to press a pattern or surface detail into plastics ThermoplasticMaking different thicknesses of thermoplastics by heating and squeezing it through decreasing sized gaps between powerful rollers. Compression moulding Electrical fittings such as plugs and sockets. Cooking pot handles Thermosets such as urea, phenol, or melamine formaldehyde A powdered thermoset is heated and compressed into a mould at the same time. Once it is ‘baked’ it is removed.

Plastics forming processes or methods Typical usesUsed for thermoset, or thermoplastic Description of process Hand building processes Boat building, custom car bodies, fair ground or amusement park rides. Used for one off, or batch production. Not suitable for high volume production. It is more efficient to injection mould a product if it is fairly complex and you want a large number of them. Polyester resin, (a thermoset) and fibre glass, or carbon fibre are used to produce a composite. Produces strong, rigid, lightweight structures especially carbon fibre. An interface of fibre glass or carbon fibre is soaked in polyester resin and pasted into a mould by hand. A catalyst is added to the resin to begin the process of turning from a gel to a solid. Needs a lot of skill to build the moulds in addition to ‘laying up’ the GRP. Rotational casting This unique polymer moulding process affords moulders the ability to produce items ranging from small toy doll components to agricultural tanks that will hold up to 22,500 gallons (85,167 litres) of liquid. A variety of polymer materials can be used to provide specific characteristics to the products. Thermoplastics, Polyethylene (HDPE, LPDE and LLPDE), PVC, Fluorocarbons, Polypropylene, Nylon and Polycarbonate A heated hollow mould is filled with a charge or shot weight of material, it is then slowly rotated (usually around two perpendicular axes) causing the softened material to disperse and stick to the walls of the mould. In order to maintain even thickness throughout the part.

Bottles and containers Seed tray Plastic seat for large scale production Lightweight, see through roofing or green house Drill casing components for high volume production High volume, one piece, moulded shoe Loo seat and lid

11 Prisms or uniform sections Retail display stand Flowerpots Gear and pulley wheels Plugs and electrical casings Small volume production amusement park constructions Kitchen work top coverings Plastic films Custom car bodiesPan handles Moulded casings and luggage Palm pilot or phone casing Sunglasses

Prisms or uniform sections Shoe sole Toothbrush and bristles Biro casing Raincoat and garments Disposable food trays Wheelie bins Motorcycle helmet Pipes and guttering

11) Describe the processes of line bending and drape forming thermoplastics in the workshop. Are these forming methods suitable for high volume or mass production. How could they be speeded up to be more cost effective and efficient. 12) Describe three typical uses for thermoset plastics. Give reasons for their suitabillity. 13) Name four other thermoplastic materials that are not derived from oil or hydrocarbons. 14) Name and describe uses for three thermoset materials other than plastics. 15 Describe the characteristics of each of the following plastic forming processes. What evidence would you look for on the casting or moulding to decide which forming process was used to produce the plastic object. Vacuum forming, injection moulding, rotational moulding, calendering, extrusion, compression moulding. 16) Make a list of the international symbols for polymers, describe a typical use for each. 17) Complete the exercises toward the end of the plastics chapter.

Plastics Plastics are manufactured polymers made from crude oil. Plastic polymers occur in nature in things such as animal horn and shell. Advantages of plastics: Very useful, versatile and available. Much quicker to use industrial plastic forming processes than traditional crafting methods. Plastics are amazing for large quantity production. Plastics are ‘self finishing’. (The colour is built in to the plastic, through addition of coloured pigment at its raw state saving the need for painting, finishing etc.) Good resistance to atmospheric corrosion Good electrical insulator Some have excellent insulation against, or resistance to heat. Most can be recycled and use less energy in their production than glass and metals. Disadvantages of plastics: Waste plastic does not break down or biodegrade. Lot of litter in the form of plastic bags etc. Waste plastic is a biological hazard. Oil and energy are wasted using unnecessary plastics for packaging etc. Plastic manufacturing methods are so successful and efficient that plastic has replaced every other method of making containers, packaging and utensils. Cost is minimised by making huge quantities rather than smaller, more responsible, sustainable quantities.