Injection moulding machines

One alternative approach to the two-stage steam moulding process is that in which impregnated beads are fed directly to an injection moulding machine or extruder so that expansion and consolidation occur simultaneously. This approach has been used to produce expanded polystyrene sheet and paper by a tubular process reminiscent of that used with polyethylene. Bubble nucleating... 

Safety at injection moulding machines Safety at blow moulding machines Safety at thermoformmg machines... 

The earliest injection moulding machines were of the plunger type as illustrated in Fig. 4.30 and there are still many of these machines in use today. A predetermined quantity of moulding material drops from the feed hopper into the barrel. The plunger then conveys the material along the barrel where it is heated by conduction from the external heaters. The material is thus plasticised under pressure so that it may be forced through the nozzle into the mould cavity. In order to split up the mass of material in the barrel and improve the heat transfer, a torpedo is fitted in the barrel as shown. 

Fig. 4.31 Typical cycle in reciprocating screw injection moulding machine...

There are a number of important features in reciprocating screw injection moulding machines and these will now be considered in turn. 

Foamed plastic articles may be produced with good results using normal screw-type injection moulding machines (see Fig. 4.43(a)). However, the limitations on shot size, injection speed and platen area imposed by conventional... 

Fig. 4.46 One embodiment of SCORIM where the device (B) for producing shear during solidification, by the action of pistons (D) and (E), is placed between the injection moulding machine barrel (A) and the mould (C) (Courtesy of Brunei University)...

Since the reactants have a low viscosity, the injection pressures are relatively low in the RIM process. Thus, comparing a conventional injection moulding machine with a RIM machine having the same clamp force, the RIM machine could produce a moulding with a much greater projected area (typically about 10 times greater). Therefore the RIM process is particularly suitable for large... 

The steps in the process are illustrated in Fig. 4.48. Initially a preform is injection moulded. This is subsequently inflated in a blow mould in order to produce the bottle shape. In most cases the second stage inflation step occurs immediately after the injection moulding step but in some cases the preforms are removed from the injection moulding machine and subsequently re-heated for inflation. 

These long fibres give better product performance although injection moulding machine modifications may be necessary to prevent fibre damage and reduce undesirable fibre orientation effects in the mould. 

Example 5.2 In a plunger-type injection moulding machine the torpedo has a length of 40 mm, a diameter of 23 mm and is supported by three spiders. If, during moulding of polythene at ITO C, the plunger moves forward at a speed of 13 mm/s, estimate the pressure drop along the torpedo and the shear force on the spiders. The barrel diameter is 25 mm. 

It may be seen from the above analysis and that in Chapter 4 for the calculation of clamping force on an injection moulding machine the Mean Effective pressure (MEP) across the cavity may be obtained from... 

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... 

Some injection moulding machines are designed according to the First-In, First-Out (FIFO) principle. The material first plasticised is also the first material to be injected so that the thermal state of the entire shot volume is identical. 

Injection moulding machines can be in a horizontal or vertical mode, with or without tiebars, or with a C frame structure for easy mould fitting and access. Machines are also available which can deal with two colour/compound injection into the same mould cavity. 

Simple ram machines are cheaper than screw machines having equivalent shot volumes. Although the simple ram injection moulding machine was once quite widely used it was generally obsolescent by 1977. Plasticisation by screw is quicker and more controllable than by heat conduction in simple ram machines. A higher and more uniform compound temperature and thus a more uniform viscosity is achieved. 

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. 

An injection-moulding machine (Figure 5.2) comprises three main parts ... 

By contrast, the processing of HPGF compounds requires no additional investments as it utilizes standard injection moulding machines. 

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. 

PP-structural foam mouldings were produced on an injection moulding machine in a pre-pressurised mould cavity by the classical low-pressure process and an alternative low-pressure process. Melt temperature, injection direction and sprae diameter were varied. Cross-sections cut from the middle of the small cylinder in longitudenal orientation were investigated by site-resolved X-ray scattering. Morphological properties were investigated. 4 refs. 

The use of crosslinked expanded EVA and other crosslinked foamed polymers in shoe soles is discussed, and developments by Main Group in injection moulding machines for the production of soles from such materials are examined. 

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