Resin Transfer Molding

Principle:

RTM is similar to the traditional transfer molding or reaction injection molding (RIM) with a difference that a reinforcement is molded with the resin. The physical arrangement and type of equipment used in RTM are like RIM.

Material Used:

Thermoset        : Unsaturated polyster resin, Epoxy resin, phenolic resin, polyurethane resin, silicone, alkyd,                

                         DAP, thermoset polyimides.

Thermoplastic   : Nylon, PP, PE, styrenic resin, thermoplastic polyster, flouropolymer, liquid crystal polymers                 

                         and thermoplastic elastomers

Additives Used:

Fillers

Flame retardants
Conductive additives

Catalyst

Accelerator 

U V stabilizers

Release agents-

Reinforcing fibre -Glass fibres in continuous rovings, yarn form and chopped strand mat

They are used as perform which is an arrangement of fibres configured to replicate the shape finished part.

 Process Description:

In the resin Transfer Molding(RTM) process, dry (i.e., unim-pregnated) reinforcement is pre-shaped and oriented into a skeleton of the actual part known as the preform, which is inserted into a matched die mold. The mold is then closed, and low-viscosity thermoset resin is injected into the tool. During this time, the resin "wet out" the fibres and the air is displaced and escapes from vent ports placed at the high point. Heat is applied to the mold to activate the polymerization that solidifies the resin. The resin cure beings during filling and continues after the filling process. Once the part develop sufficient strength, it is removed or de molded.

Process Characteristics:

• Part cost is moderate to high.
• Tooling Cost is low.
• Production Rate is low.
• Part strength is high.
• Parts are easily painted.

Trouble shooting:

Problem	Possible cause
Fibres not fully wetted	Resin viscosity too high, Improper mix ratio of filler
Poor or inadequate cure	Improper temperature Apply proper vacuum to the mold Improper accelerator content Initiator is added to compensate shortage of inhibitor
Part delaminates	Poor resin movement due to high viscosity