Standard injection moulding

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

Figures 5.21 and 5.22 show a loudspeaker boxes frame made from ARBOFORM granules on a standard injection moulding machine. The thickness of the spherical boxes is about 10 mm and represents an example of extremely low shrinkage. The injection moulded parts are of high precision, having stable dimensions without dips and tolerances less than 0.1 mm.

During shear flow, polymer chains are deformed and orientate in the direction of flow. (The results of this orientation in standard injection mouldings was discussed in Section 2.1.) The tension of the polymer in the flow direction is called the first normal stress. In contrast to this, flow in other directions is relatively small. First normal stress can be defined by the difierence between the normal stress component in the flow direction and the normal component in the direction of the shear plane. Combinations of some or all of these forces are applied to the molten polymer material dining the moulding process depending upon where on the moulding they are. Analysis using methods such as these, allows material interactions to be better understood. 

The characteristic feature of gas injection moulding technology is the filling of a form with two different materials. Plastic materials form the first component. The second component consists of a gas, generally nitrogen (N2). The two components do not mix. All standard injection moulding machines which are equipped with a device for introducing gas are suitable for the GIT process. The injection of the gas may be performed by a machine nozzle or by a separate injection module in the mould. 

Due consideration of these principles has made it possible to process unplasticised PVC by all the standard melt processes, including injection moulding and bottle blowing, a state of affairs hardly conceivable in the 1950s. 

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. 

Because of their low viscosity the liquid cyclic aliphatic resins find use in injection moulding and extrusion techniques, as used for glass-reinforced laminates. They are also very useful diluents for the standard glycidyl ether resins. 

Most tests will be made on standard test pieces which may be pieces cut from a component or a sheet, or they may have been moulded separately from the same material. Where test pieces or sheet are produced for the trials it is important that they are produced in as near as possible the same way as the product and that the processing conditions are recorded. Different results can be expected from compression and injection moulding or from extrusion (where a choice is possible). Directional properties can result from the conditions of flowing and cooling in a mould. For example, in a study at ERA, the creep strain of unfilled HDPE, either individually moulded or cut from square plaques, varies by up to a factor of two depending on the orientation of flow [40]. This difference becomes even more marked with short fibre reinforcement. 

Very often (since a melt process is to be used) a material for injection moulding or extrusion will be subjected in advance to one or more tests of flow at different temperatures, using relevant equipment and methods from British and international standards or other specifications. 

For estimation of the processability of a moulding polymer melt, the pressure to fill a standard mould has to be measured. Furches and Kachin (1989) have compared the results of several rheological tests often used to evaluate injection moulding polymer melts. 

Biodegradable polymers are similar in terms of their chemical structure to conventional thermoplastics such as polyethylene, polypropylene and polystyrene. They can be processed using standard polymer processing methods such as film extrusion, injection moulding and blow moulding. 

Although hard-rubber containers had been used for many decades (Fig. 12.8), polypropylene (PP) containers and lids, manufactured by injection moulding, became standard from about the 1960s (Figs. 12.1, 12.5). Therefore, at the beginning of the 21st century, the standard SLI battery in a new car still uses the same... 

The different processing steps and the processing conditions are fully described in a previous publication.15 After powder mixing and extrusion, injection moulding is used to produce standard dumbbells. The injected dumbbells are usually equilibrated (54% RH, 23 °C) for 6 weeks before testing. The different composites elaborated are presented in Table 1. 

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