High pressure closed mold system

In the reinforced RIM (RRIM) process a dry reinforcement preform is placed in a closed mold. Next a reactive plastic system is mixed under high pressure in a specially designed mixing head. Upon mixing, the reacting liquid flows at low pressure through a runner system to fill the mold cavity, impregnating the reinforcement in the process. Once the mold cavity is filled, the plastic quickly completes its reaction. The complete cycle time required to produce a molded thick product can be as little as one minute. 

Large machines operate best when a hybrid clamping system Is used. Here one uses large volume, low pressure hydraulics to activate the toggle system and close the mold. Once the mold Is virtually closed, a low volume, high pressure system applies the clamping force (see Figure 2). 

Mechanics. The RIM process can best be described as a variant of injection molding that uses thermoset systems normally consisting of two hquids that react inside the closed mold to form a solid part (Fig. 5). The two heated liquid streams are metered to precise ratios and placed in intimate contact under high pressure in a mix head. The hquid then enters the mold at a much lower pressure where chemical crosslinkings are completed and a solid part can be removed from the mold. The imphcation of component ratios is that a degree of property tailoring of the final part is achievable by the machine operator. 

The force needed to close the mold can be substantial. This is a particularly important problem for large area molds with a high-fiber loading because the pressure to compact the fibers can be high. In addition, the clamping system must resist the full injection pressure without leakage at the mold seals. 

Resin Transfer Molding (RTM) The RTM system gives high quality surface on both the sides. A relatively low pressure (vacuum to 100 psi) process, RTM makes perfect shapes in 30 min to 1 h. The fabricator generally gel coats one or both mold halves, then lays continuous or chopped strand mat and the core, if used, into the bottom half, and closes the mold. The resin transfers into the mold through injection pressure, vacuum pressure, or both. Cure temperature depends on the resin system used. Heater blankets can heat the mold up to 202°C, if the matrix allows sensors to detect resin flow position in the mold and monitor resin and cure data [98]. 

---