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achieved.

The completed lay-up is squeezed or rolled with grooved rollers to combine the lay-up and remove many of the air bubbles. The moulding is allowed to gel and then harden, either at room temperature or after gelation, removed to an air-oven to speed up the hardening process. The figure given below illustrates the hand lay-up technique.

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Figure 2.1: Ordinary Hand Lay-Up

2.2.2 Compression Moulding

In this method of manufacturing, the moulding material is preheated and placed in an open heated mould cavity. After placing the material, the mould is then closed with a plug member. Pressure is then applied to force the material in to contact with the mould areas. Until the moulding material is cured, the heat is sustained. Complex and high strength fibre glass reinforcements are manufactured using compression moulding as this method is a high volume, high pressure moulding method. The main advantages of compression moulding are its ability to mould large and complicated parts. It is also low cost method. The main disadvantage of this method is that it often provides poor product reliability and is not suitable for some types of parts. The figure below shows the compression moulding process [17].

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Figure 2.2: Compression Moulding [17]

2.2.3 Vacuum Bag Technique

Vacuum bagging uses atmospheric pressure as a clamp to hold the laminate plies together. In this method the laminate is wrapped in an air tight envelope. Within the envelope the airtight mould is on one side and an airtight bag on the other. When the bag is sealed to the mould, the pressure outside and the pressure inside the envelope is equal to the atmospheric pressure which is approximately 29 inches of mercury or 14.7psi. The vacuum pump is important equipment in the vacuum bagging technique. The vacuum pump evacuates air from inside the envelope. As the air is evacuated, the pressure inside the envelope is reduced, while the pressure outside remains 14.7psi. As a result the pressure outside the envelope that is the atmospheric pressure forces the sides of the envelope and everything within the envelope together, putting equal and even pressure over the surface of the envelope 18].

The pressure difference between the inside and outside of the envelope determines the amount of clamping force on the laminate. The maximum possible pressure that can be exerted on the laminate if a perfect vacuum is achieved is one atm. The realistic pressure differential will be 6-12.5psi [18]. The vacuum bagging technique is used in this project for the manufacture of polyester glass fibre. The figure below demonstrates the vacuum bagging equipment.

Figure 2.3: Vacuum Bagging Technique [18]

2.2.4 Autoclave Moulding

Autoclave moulding is similar to vacuum bagging technique. The main difference is that the lay-up is subjected to greater pressure and compact parts are produced. High quality aerospace laminates are manufactured with the help of autoclave curing. Curing is attained through a combination of pressure, temperature and heat under inert conditions in a closed vessel. A typical moulding cycle is as follows.

Temperature is allowed to rise af