Page 64 - 3D Fibre Reinforced Polymer Composites

Preform Consolidation 53

throughput of resin is large, for example, the automotive or sporting goods industries.
The disadvantages of the multi-valve machines are the greater degree of maintenance
required of the more complex equipment and the possibility of uneven catalysation if
incorrect mixing occurs during impregnation.

Figure 3.4 Megaject RTM-Pro injection machine (photo courtesy of Plastech T.T. Ltd,
UK)

The other main decision affecting the choice of equipment is related to the mechanism
used to inject the resin into the mould and here the choice is between equipment
designed to produce a constant injection pressure or a constant flow rate.
When constant pressure is being used then the flow rate will vary during
impregnation and will decrease with increasing distance from the injection port. The
main advantage of this system is the complete control over pressure during injection.
This system has the obvious disadvantage of limited control over the resin flow rate, but
also the added disadvantages of the pressurisation being limited by available equipment,
for example shop air pressure, and the tact that the resin must be held in a pressurisable