The hand lay-up process

Similarly, special SMC formulations were developed for the ERF Lorry cab, and in the case of the High-Speed Train cab, the hand lay-up process is developed. In the following sections of this chapter various aspects of these processes are discussed at greater length, and some comparisons are made, especially between SMC and the hand lay-up process which may compete with one another. 

This process is economically most suited to producing low quantities of very large GRP mouldings such as boat hulls and building panels, and is highly labour intensive. 

Where drainage of resin down vertical surfaces is likely to occur a 

Before choosing hand lay-up as the GRP moulding process to make a 

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Wet Lay-Up Process. Formulations are impregnated by hand or sprayed into fibers that are in the form of woven, knitted, stitched, or bonded fabrics. This is usually accomplished by rollers or brushes. Spray-up is a partly mechanized version of the hand lay-up process. The thermoset precursor is applied by means of a spray gun to the mold surface simultaneously with the chopped glass-fiber roving. Laminates are left to cure under standard atmospheric conditions. 

The hand lay-up process can be used for fabricating boat hulls, automobile bodies, swimming pools, chemical tanks, ducts, tubes, sheets, and housings, and for building, machinery, and autobody repairs. 

In the spray-up process, a mould is made, just as in the hand-lay-up process. Continuous roving is fed into a chopper gun, which as its name suggests chops the fibres and sprays them onto the mould resin is also sprayed at the same time. The fibre and resin streams meet each other on the mould surface. The laminate is then rolled to remove as much air as possible. The fibre content achieved with this process is typically between 25-35 wt%. This method is rarely used by itself for corrosion-resistant vessels but is used in combination with filament winding for larger vessels. 

Manufacturing and assembly of the individual segments will be done manually to ensure effective quahty control and to be able to accommodate late design and material changes. Instead of a negative form, a positive mall will be used. The hand lay-up process will start with the inner foam layer and work to the top of the complete composite sandwich which will be finalised by applying the inner fibre layer. 

Resin transfer moulding is used to replace the hand lay-up process for better productivity and quahty. In this process, resin is injected into a closed cavity mold that is filled... 

In contrast to the hand lay-up process hot press moulding is ideally suited to long production runs of relatively small components. The moulding operation is as follows ... 

Prior to ERF producing SMC-clad lorry cabs the company had acquired several years experience of moulding GRP panels for their LV series lorry cab. However, these panels were manufactured by the hand lay-up process which has certain limitations, see Chapter 15, PST 4. 

In the hand lay-up process, the reinforcing mat is cut to shape and disposed in the mould manually prior to impregnation with catalysed resin, applied with brush and squeeze-roller. In the spray process, chopped glass fibres are incorporated in a spray of catalysed resin applied to the mould. Both techniques allow the manufacture of large continuous mouldings limited only by the size of the mould. 

The main advantage of this method is that the equipment is portable, therefore on- site fabrication can easily be accomplished. In addition, low cost molds can be used and complex shapes with reverse curves can be formed more easily than the hand lay-up process. 

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