Thermoset plastics moulding methods

Compression moulding is one of the most common methods used to produce articles from thermosetting plastics. The process can also be used for thermoplastics but this is less conunon - the most familiar example is the production of LP records. The moulding operation as used for thermosets is illustrated in Fig. 4.62. A pre-weighed charge of partially polymerised thermoset is placed in the lower half of a heated mould and the upper half is then forced down. This causes the material to be squeezed out to take the shape of the mould. The application of the heat and pressure accelerates the polymerisation of the... 

The decorative laminates described in the previous chapter are made with selected thermosetting resins while resins of this type can be moulded and extruded by methods similar to those outlined in the present and the next chapter the materials employed for these processes predominantly are thermoplastic. Many such plastics can be moulded and extruded under suitable conditions, the most important in terms of quantities used being those that combine properties satisfactory for the purpose with convenience in pro-cessing-especially the polyolefins (polyethylene and polypropylene), poly(vinyl chloride), and styrene polymers and blends. Other plastics with special qualities, such as better resistance to chemical attack, heat, impact, and wear, also are used—including acetals (polyformaldehyde or polyoxymethylene), polyamides, polycarbonates, thermoplastic polyesters like poly(ethylene terephtha-late) and poly(butylene terephthalate), and modified poly(phenylene oxide),... 

BS2782. Part 9, Method 902A, Methods of testing plastics Compression moulding test specimens of thermosetting materials. British Standards Institute Publication. 1992. 

To make reinforced plastics objects, the resin and fibres must be combined intimately, so that they adhere together and distribute the fibres uniformly, with the desired orientation, with a minimum of porosity and with no dry, resin-free reinforcement. The correct fibre volume fraction must be ensured. In the case of thermosetting resins, there is an additional requirement to ensure that the hardening reaction, or cure, occurs at the right stage of the process and is eventually completed. The methods available depend on the size, overall shape and complexity of the article being produced, the materials involved and the number of mouldings required. 

As has already been stated in Chapter 5, the principal method used for the plastic encapsulation of electronic devices is transfer moulding with thermosetting epoxide resin based moulding compounds. A number of other thermosetting compounds are also occasionally used but until recently no thermoplastic materials capable of being injection moulded were suitable for the encapsulation of electronic components because of the high pressures required. One thermoplastic material that has been successfully developed for the packaging of electronic components is polyphenylene sulphide. 

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