Moulding processes compression

Note The injection/compression moulding process capability maps 1, 2 and 3 are used for large parts with a major dimension greater than 50 mm typically and/or for large production volumes. Map 4 is for injection moulded parts that have a major dimension less than 150 mm and which are produced in small volumes. 

The setting of these materials after shaping occurs via a chemical process, that of cross-linking. The most common process is moulding but some extrusion, sintering and other miscellaneous processes are also used. A typical compression moulding process is illustrated in Figure 8.12. 

Whilst the injection moulding process has now been widely accepted for phenolics the transition from compression moulding has been less extensive with U-F materials. The basic reason for this is that the U-F materials are more difficult to mould. This has been associated with filler orientation during moulding, which can lead to stress peaks in the finished product which the somewhat brittle resin in less able to withstand than can a phenolic resin. 

The hydrophilic/hydrophobic SIN composition of PDMS with poly(HEMA) and poly(AAC) were proposed as a potential apphcation for high-permeability soft contact lenses. Other sUicone-containing IPNs for contact lenses include polymerization of MMA in the presence of polymerized methacryloxypropyl trimethoxysilane, the cross-linking of a polymeric hydrogel of a copolymer of NVP during the final compression or injection-moulding process. 

Injection is by far the most used moulding process but compression and compression-transfer are used for specific cases. Rotomoulding is specifically used for polyethylene and a few other powdered resins. Slush moulding is broadly used for automotive dashboards. Generally ... 

ECTFE can be processed by conventional molten-state methods such as extrusion, injection, compression, transfer, rotational and blow-moulding processes. 

Injection and blow moulding are by far the most used of the moulding processes but compression is sometimes used for specific cases. 

Processing of LFRT or LFT - long fibre (reinforced) thermoplastics injection, composite insert moulding, compression moulding, extrusion-compression. 

Journal of Cellular Plastics 37, No. 1, Jan. 2001,p.21-42 THERMAL CONDUCTIVITY OF A POLYETHYLENE FOAM BLOCK PRODUCED BY A COMPRESSION MOULDING PROCESS Martinez-Diez J A Rodriguez-Perez M A De Saja J A Arcos y Rabago L O Almanza O A... 

The injection moulding process for producing a microcellular crosslinked EVA has several advantages over the conventional compression moulding process reduced cycle time, labour and scrap. The presence of skin adds aesthetic value and ability to engrave logos in one step. However, the injection moulding process has... 

PE and EVA foams were manufactured by a two-stage heat and chill compression moulding technique, which allowed more efficient utilisation of the platen area than other compression moulding process variants and which was suited to low density foam production. The interrelationships of base polymer type, crosslinking and blowing agent concentrations and physical properties of resultant foams were investigated. 13 refs. 

Three types of moulding processes are available - compression, transfer and injection moulding. In compression moulding the rubber blank is placed directly into the cavity of the mould where it is heated by conduction which causes rubber flow by application of pressure. Transfer moulding uses prewarmed rubber which is heated during transfer and forced through small orifices into the mould cavities in a three-part mould. In the injection moulding process, the rubber compound is pushed under pressure from an injection head where it has been heated and plasticized into a closed heated mould where cure is completed. 

Table 14.1 Comparison of compression, transfer and injection moulding processes...

Thermo set as well as thermoplastic and elastomer binders are used in compression, injection and calendaring process respectively. Extrusion moulding uses elastomers as well as thermoplastic materials such as PVC. Compression and injection moulding processes make only rigid magnets, calendaring makes flexible magnets and extrusion can lead to both states. 

Figure 9.12A shows that this stress release effect for the X-direction of the reference sample (no glassfibres) results in a permanent length decrease, just like the effect shown in Figure 3.1. The same effect was also measured in the Y-direction. In the z-direction (Figure 9.12B), however, an expansion effect is measured. The extent of the measured shrinkage/expansion effects are listed in Table 9.8. These values show that these shrinkage/expansion effects are clearly caused by the compression moulding process the measured effects decrease with increasing glassfibre contents.

As already stated, the shaping of plastics materials is achieved by the application of heat, pressure or both. There are many ways in which this can be done, depending on the nature of the polymer, the type and size of product and the quantity and dimensional accuracy required. The methods to be described here are moulding by compression, transfer, injection and low-pressure processes. 

High performance biocomposites reinforced with glass fibres were prepared by a compression moulding process using vegetable oil-based... 

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