Composite materials VARI moulding

Manufacturing methods for composites vary from manual to fully automated processes, whereby the latter have better quality control than the former. Wet layup, pultrusion, and filament winding are all discussed in some detail, while other techniques such as pull-winding, resin transfer moulding, vacuum bag moulding, and injection moulding are left to specialized composite materials texts. 

Usually, the fibres are not unidirectional oriented in composite materials. Fibres orientation varies in function of the pieces thickness, processing method, and mould geometry. Accepting a random orientation of fibres, or a known and measured orientation, the laminates theory was appealed in order to describe the behaviour of this type of composites. The method allows the determination of the weakest layers, which will be firstly fractured [1285]. The Figure 3.456 illustrates a good agreement between the theory and practice, considering, for comparison, the data furnished by P.E. Chen [1285] and J.K. Lees [1286]. 

Polymers vary widely in their processing characteristics, and it is important to ensure that the design developed can be produced economically and efficient from the chosen material. The most obvious differences in processing behaviour are between thermoplastics and long-fibre composites, but fiiere are also significant variations within each class of materials. To take an extreme example, PTFE has such a high melt viscosity that it cannot be injection-moulded, but has to be formed from powder by... 

Strenuous efforts are being made to market various waste materials as fillers for plastics, with varying degrees of success. They include fly ash from power stations, newsprint and various agrowaste products. In the past five years Asian organisations have promoted empty fruit bunch fibres, oil palm mesocarb fibres, rice husk ash and various nutshells. Scrap rubber crumb from used tyres has also been evaluated by Composite Particles, Inc. for use in mouldings, foams and pipes. 

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