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Resin Transfer Molding (RTM process)

Resin transfer molding is a closed molding process. In this technique, as the name indicates, resin is transferred over the already placed reinforcement.

Reinforcement in terms of either woven mat or strand mat form is placed on the surface of lower half mold. A release gel is applied on the mold surface for easy removal of the composite.

The mold is properly closed and clamped. The clamping can be done either perimeter clamping or press clamping mechanism. The resin is pumped into the mold through ports and air is displaced through other vents. The uniformity of resin flow can be enhanced by using a catalyst as an accelerator and vacuum application. After curing, the mold is opened and composite product is taken out.

Resin transfer molding can incorporate soft or hard mold depending upon the expected duration of run. For soft mold, thermosetting polymers like epoxy and polyester can be used for molding material. For hard mold, materials like steel and aluminium can be used.

The cost of mold varies from very low to high cost mold with short to long life molds. The process can be automated to reduce cycle time. For complex shapes to be produced, preformed fiber reinforcements are used. The viscosity of the resin plays an important role in resin transfer molding process because injection time depends upon viscosity of the resin.

If viscosity of resin is high, high pressure is required which may cause displacement of fibers, known as fiber wash. The raw materials used in resin transfer molding are given in table 1.


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