Reaction injection molding (RIM) utilizes thermosetting polymers. The process requires a curing reaction to happen within the mold. Automotive bumpers, air spoilers, and fenders are items successfully made using the RIM technique.
The RIM process involves mixing together two parts polymer. Then the mixture is injected into the mold under high pressure using an impinging mixer. The mixture is held in the mold long enough for it to expand and cure.
The most common RIM processable material is polyurethane. Other materials include polyureas, polyisocyanurates, polyesters, polyepoxides, and nylon 6. The advantage of RIM is that it can produce strong, flexible, lightweight parts. These parts can be easily painted, which make them ideal material for automotive bumpers and fenders, as mentioned above.
There are several advantages to RIM. The first is the quick cycle times contrasted with typical vacuum cast materials. The two component mixture injected into the mold has a significantly lower viscosity than molten thermoplastic polymers, as a result large, light-weight, and thin-walled items are ideal for the RIM process. This thinner mixture also requires less clamping forces, which requires smaller equipment and ultimately lower capital expenditures. Another advantage of RIM processed foam is that a high-density skin is formed with a low-density core.
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