Paste injection moulding

Paste injection moulding processes have also been developed. In one technique used for applying PVC soles to shoe uppers the paste is injected by gas under pressure into a hot mould, the last and shoe upper forming the top half of the mould. The paste gels in the mould, adheres to the upper in the presence of a suitable adhesive and is stripped hot from the mould. 

The early 1980s saw considerable interest in a new form of silicone materials, namely the liquid silicone mbbers. These may be considered as a development from the addition-cured RTV silicone rubbers but with a better pot life and improved physical properties, including heat stability similar to that of conventional peroxide-cured elastomers. The ability to process such liquid raw materials leads to a number of economic benefits such as lower production costs, increased ouput and reduced capital investment compared with more conventional rubbers. Liquid silicone rubbers are low-viscosity materials which range from a flow consistency to a paste consistency. They are usually supplied as a two-pack system which requires simple blending before use. The materials cure rapidly above 110°C and when injection moulded at high temperatures (200-250°C) cure times as low as a few seconds are possible for small parts. Because of the rapid mould filling, scorch is rarely a problem and, furthermore, post-curing is usually unnecessary. 

In some compositions the PIB is plasticized with ethyl oleate to improve low temp properties. .. Since the propint is a stiff paste it can be inserted into a rocket motor by a type of injection moulding process (Refs 3 5)... 

Cases are now almost exclusively fabricated by injection moulding using synthetic polymers which have replaced the bitumen and hard rubber widely used in the past. Polypropylene has excellent mechanical and... 

Polymer melts cool slowly in contact with air, so it is possible for a weld to form when two sections of melt are pressed together, as in the base of a blow-moulded container. Welds occur in injection mouldings when the melt from neighbouring gates meet (Fig. 5.27), or when the melt stream parts to flow past a hole in the product, and then recombines. Extruded products... 

The rheological properties of the paste control to a large extent the final properties of the extruded or injection moulded part. Different additives, such as dispersants and lubricants, are added to the powder-polymer mixture to promote deagglomeration and reduce the... 

The possibility of making automotive tyres by casting or reaction injection moulding has frequently been discussed in the past, and now appears to be approaching reality. ... 

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