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ter vacuum is applied.

At constant temperature there is a longer or shorted dwell time which allow the resin flow with little cure.

The pressure is applied to the autoclave and the temperature is increased.

Gelation occurs within an hour.

The temperature and pressure is kept constant at the end of cure and it will take approximately 2-3 hours.

Heating is switched off and the moulding is allowed to cool to room temperature. Some pressure is preserved during cooling process.

Figure 2.4: Autoclave lay-up.

2.2.5 Spray-Up Technique

The spray-up technique is an excellent method of supplying a considerable weight of fibre and resin concurrently to a mould surface using an injection gun. It is mainly used for continuous glass and carbon. The figure below exhibits the process. The roving consists of fibres and these fibres are chopped into small components. The chopper assists for cutting the fibres. The resin and the catalyst are pumped disjointedly to the gun and are mixed inside the gun. The resin and the chopper are sprayed on to the mould surface and required thickness is obtained after the spraying technique. The laminates which are produced by this method will have variable thickness and there is a possibility to have a large number of voids. So this technique is not used regularly.

Figure 2.5 Spray-Up techniques [19].

2.2.6 Continuous Fibres Prepregs

Prepreg is the industry's term for continuous fibre reinforcement pre-impregnated with a polymer resin that is only partially cured. The continuous lamination of reinforced plastic materials involves impregnating various reinforcements with resins on an in-line conveyor. The laminate is then cured and trimmed as it passes through the various conveyor zones. In this method a resin mix is metered on to a bottom carrier film. Chopped glass fibres fall in to the resin mix and are allowed to saturate. A second carrier film is applied to the top of the panel before subsequent curing and forming. The cured panel is then stripped of its films, trimmed and cut to the desired length [19]. Both thermoplastic and thermoset resin are utilised. Carbon, glass and aramid fibres are the common reinforcement. Figure below illustrate the process.

Figure 2.6: Continuous Pre-preg method [19].

2.2.7 Filament Winding Process

Filament winding is a comparatively slow process. The fibre direction can be controlled and the diameter of parts can be varied. During the process, tape is drawn through the resin bath and wind in a rotational mandrel. Filament winding mandrels can be metallic or non-metallic. The mandrel should guarantee the possibility of easy part removal or be dissolvable after curing. The fibre bundle has various dimensions, from several thousand of carbon fibres to several centimetres. The finished part is cured in an autoclave and later is removed from mandrel. When the mandrel is removed, a hollow shape is the result. Variety of parts can be manufactured using this process. Pipes, tubing, pressure vessels; tanks are some of the shapes manufactured with the help of filament winding. The figure given below is the filament winding process [20].

Figure 2.7: Filament Winding [20].

The various ways to remove the filament wound components from the internal mandrel is given