Moulding method

This is an injection moulding method which permits material costs to be reduced in large mouldings. In most mouldings it is the outer surface of an article which is important in terms of performance in service. If an article has to be thick in order that it will have adequate flexural stiffness then the material within the core of the article is wasted because its only function is to keep the outer surfaces apart. The philosophy of sandwich moulding is that two different materials (or two forms of the same material) should be used for the core and skin. That is, an expensive high performance material is used for the skin and a low-cost commodity or recycled plastic is used for the core. The way that this can be achieved is illustrated in Fig. 4.44. 

The process is attractive for a number of reasons. Firstly, since it is a low pressure process the moulds are generally simple and relatively inexpensive. Also the moulded articles can have a very uniform thickness, can contain reinforcement, are virtually strain free and their surface can be textured if desired. The use of this moulding method is growing steadily because although the cycle times are slow compared with injection or blow moulding, it can produce very large, thick walled articles which could not be produced economically by any other technique. Wall thicknesses of 10 mm are not a problem for rotationally moulded articles. 

An inherent problem with all of the above moulding methods is that they must, by their nature, use short fibres (typically 0.2-0.4 mm long). As a result the full potential of the reinforcing fibres is not realised (see Section 2.8.5). In recent years therefore, there have been a number of developments in reinforced... 

Fig. 4.66 market shares for composite moulding methods in Europe... 

As a result, the merits of fiber fillers for the manufacture of conducting composite materials by extrusion and injection moulding methods can be realized sufficiently. 

Figure 7.2 Blow moulding methods (a) Plax method (b) Mills/Pirelli method (c) Kautex method...

Alternative moulding methods (Section 4.3.4) and inorganic binders (Section 6.5) are considered to have a promising potential for the minimisation of the environmental impact of moulding and casting processes. 

The issue about whether enviromnental eonsiderations play a detrmining role in the basic choice of melting fiimaees and moulding methods, as formulated in Chapter 4 of the dociunent, was earefully eonsidered. There was a general agreement that these choices are complex and should be based on teehnieal reasons and market eonsiderations, on a case-by-case basis. Therefore the issue was not selected as BAT. 

Figure 9.18 Gratings made by a contact moulding method using a bisphenol A epoxy vinyl ester resin and its flame retardant, brominated equivalent. It was installed at the Enichem plant at Gela...

The moulding methods discussed typically require the use of internal release agents. These agents weaken the adhesion and therefore lower the load-bearing capacity of the joint. The use of these agents should be minimised, but can seldom be entirely avoided. 

Plastics recycling has become more and more common for two different reasons [4, 5] the first is driven by cost, which requires the reprocessing of faulty parts and scrap from moulding methods. The second is environmental, which is crucial in the case of commodity plastics due to the large production volume. 

Ribbed bars - manufactured from a combination of a pultrusion and compression moulding method. 

GIM technology is a special injection moulding method for thermoplastic... 

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