Closed molding fabric

The mold in RRIM is similar to resin transfer molding (RTM) (Chapter 15). In the reinforced RIM (RRIM) process reinforcements such as woven or nonwoven fabrics, short glass fibers, glass flakes, milled fibers dry reinforcement preform, etc. are placed in a closed mold. Next a reactive plastic system is mixed under high pressure in a specially... 

Reinforcing fibers are not broken up as they are in closed-mold methods such as transfer and injection. Therefore, the fabricated parts under compression molding may be both stronger and... 

These fabrics are well suited for use in closed molding applications. They allow reduction in both the kit cutting time and the part loading time, by combining all layers of a laminate into one stack. As the marine industry is moving into closed molding, it needs to rethink the laminate composition and move away from a layer-by-layer approach. 

Figure 3.3 Fabrication process (a) measuring the resin (b) the mold (c) the vacuum chamber (d) the closed mold with clamps in the oven for curing (e) block specimens (left - cut specimen right - after compression programming)...

In RTM a low viscosity resin is injected imder low pressure into a closed mold which contains the fiber preforms or fabrics used as reinforcements. RTM has gained increasing importance, because of its potential for making structural components (due to the use of continuous fibers) in a cost-effective manner. 

A diagram of the injection molding process is shown in Figure 6.22. The extruder is similar to other fabrication techniques where the granular resin enters a hopper, where the material is transferred to a heated barrel and a reciprocating screw moves the molten plastic to the molding cavity. The molding cavity is unique to this process. The molten polyethylene is forced xmder pressure into a closed mold that is continually cooled. After the molded part cools, the mold opens and the fabricated part is ejected from the mold. An injection molded article can usually be identified by the ejector pin marks that are usually present on the molded part. 

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