Injection moulding equipment

Grades reinforced with fibres 10 mm long can be processed on conventional injection moulding equipment by simply adapting the processes to preserve the fibres. 

In practice, a combination of internal and external lubricants may be necessary. Single screw extruders need both types of action, whereas twin-screw machines and most injection moulding equipment depend more on external lubrication. 

There are two types of injection moulding equipment plunger-type (also called ram or piston) and screw-type machines. Linear low-density PE (LLDPE) requires more heat to be moulded than LDPE. These materials are more easily moulded in a screw machine in which the mechanical work of the screw adds considerably to the heat delivered by external electric heaters. 

Monomeric and oligomeric forms of caprolactam modified with a compatible elastomer (such as butadiene) and usually glass-fibre-reinforced, can be conveniently processed using reaction injection moulding equipment to produce block copolymers of PA 6, (e.g. Dutch State Mines Nyrim ). Applications include panels for the underside of snowmobiles. 

Blow moulding process used to make one-piece hollow plastics products, eg bottles. There are various techniques but they are normally based on the use of extrusion or modified injection moulding equipment. 

Both thermoplastics and thermosets can be formed by compression moulding (Fig. 24.5). The polymer, or mixture of resin and hardener, is heated and compressed between dies. The method is well suited to the forming of thermosets (casings for appliances, for instance) and of composites with a thermosetting matrix (car bumpers, for example). Since a thermoset can be removed while it is still hot, the cycle time is as short as 10 seconds for small components, 10 minutes for large tliick-walled mouldings. Pressures are lower than for injection mouldings, so the capital cost of the equipment is much less. 

A substantial part of the market for the ethylene-vinyl acetate copolymer is for hot melt adhesives. In injection moulding the material has largely been used in place of plasticised PVC or vulcanised rubber. Amongst applications are turntable mats, base pads for small items of office equipment and power tools, buttons, car door protector strips and for other parts where a soft product of good appearance is required. Cellular cross-linked EVA is used in shoe parts. 

Polynorbomene is also of interest to the plastics processor since by using a dry blending process for mixing and a modified injection moulding process for fabricating, the use of conventional rubber-processing equipment may be avoided. 

The methacrylic polymer remains a useful glazing material. In aircraft applications it is used extensively on aircraft which fly at speeds less than Mach 1.0. They form the familar bubble body of many helicopters. On land, acrylic sheet is useful for coach roof lights, motor cycle windscreens and in do-it yourself cabins for tractors and earth-moving equipment. Injection mouldings are frequently used for plaques on the centre of steering wheels and on some fascia panelling. 

These polymers may be extruded and injection moulded on standard equipment used for thermoplastics. Typical melt temperatures range from about 230°C for the harder grades down to about 200°C for the softer polymers. Mould temperatures are about 25-30°C. 

Acetal resins may be processed without difficulty on conventional injection moulding, blow moulding and extrusion equipment. The main points to be considered are ... 

Polyaryl ether ketones may be processed on conventional injection moulding and extrusion equipment, providing sufficiently high temperatures can be achieved. Melt temperatures required are typically 370°C for unreinforced PEEK, 390°C for reinforced PEEK and both unreinforced and reinforced PEK and unreinforced PEEKK, and 410°C for reinforced PEEKK. For the latter material a temperature profile from feed zone to nozzle would be... 

Processing temperatures should not exceed 180°C, and the duration of time that the material is in the melt state should be kept to a minimum. At the end of a run the processing equipment should be purged with polyethylene. When blow moulding, the blow pin and mould should be at about 60°C to optimise crystallisation rates. Similarly, injection moulds are recommended to be held at 60 5 C. 

Nylons 6,6 and 6 are the ones usually employed as textile fibres. Where individual monofilaments are used, such as in brushes, sports equipment, or surgical sutures, nylons 6,10 and 11 tend to be used, because of their greater flexibility and water resistance. All nylons can be injection moulded and the resulting articles have found widespread use in engineering applications, such as bearings and gears. 

A method of injection moulding thermoplastics, which makes large-part moulding possible on injection equipment normally capable of moulding only small parts. The injection moulding machine fills the mould at relatively low pressures. See Injection Moulding. 

The form of or act of laying strip material taken off a mill or extruder into a basket in an oscillating manner. Such material is then suitable for subsequent automatic feeding of production equipment such as injection moulding machines. Wild Rubber... 

Control of the temperature of rubber compound whilst being processed in extruders and injection moulding machines is vital if the product from these processes is to be uniform in quality. Failure to control temperatures in processing equipment can lead to scorching of the compound as it emerges from the extruder die or injection machine nozzle. Most modem items of processing equipment are fitted to a temperature control unit using either oil or water as the circulatory medium. 

The upgraded product has to be compatible for use on existing injection moulding and auxiliary equipment. 

A twin-screw extruder is generally preferred for producing rubber-toughened, glass-filled PET compounds for injection moulding applications. The PET and impact modifier are added at the throat while the glass reinforcement is added downstream. The size of the rubber domains will depend on the amount of energy and the capability of the equipment used for dispersion. 

A two-colour automated injection-moulding machine from Husky allows simultaneous-shot injection moulding of a two-colour instrument panel for the 2005 Ford Mustang. The process reduces squeaks and rattles, equipment costs, production time and scrap, and improves scratch resistance. 

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