The Injection Moulding Process

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 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... 

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. 

Characteristics of the Hybrid Compound Within the Injection Moulding Process... 

The behaviour and appearance of the rubber compound at different points in the injection moulding process are diagnostic of where scorch is occurring (See Table 3.1). 

Whatever the compound, it is vital that it is produced in such a way that there can be no question as to its composition or processing characteristics. The rubber is often the least understood part of the injection moulding process and will be the first thing to be questioned if injection moulding process problems of any nature are encountered. The best formulations are usually the most simple. The average rubber formulation need contain no more than 11 or 12 ingredients. 

Many similarities exist between SM and SF mouldings. Briefly, both techniques are based on the injection moulding process and the products consist of solid skins with low-density cores. However, two important differences exist between the techniques ... 

The injection-moulding process used has been extensively redeveloped to make it suitable for DMC. 

The components of plastic materials are cut and compacted and again made into plastic products, mainly by the injection moulding process. 

The scope of the injection moulding process has been extended in recent years by some very ingenious elaborations ... 

---