RIM Process

Premold Corp is a custom plastic molder specializing in the Reaction Injection Molding (RIM) process. The Reaction Injection Molding (RIM) process allows us to meet your low volume, injection molded plastic part needs.   We use the Reaction Injection Molding (RIM) process to mold rigid polyurethane plastic parts using low molding pressures and low mold temperatures.   These advantages lead directly to low cost injection molds, low energy requirements and low overhead costs.


How does the Reaction Injection Molding (RIM) process work?

Two liquid components, an isocyante and a polyol are placed in holding tanks.   They are conditioned to the correct temperatures (approximately 100 degrees F), pressures and specific gravities.   The dispensing unit pumps the correct amounts and ratios of these liquids into the mold during the injection phase of the molding cycle.   During the molding process, the unit continuously circulates the isocyante and the polyol at low pressures to keep them uniformly conditioned.


Time To Inject

When it is time to inject the two liquids into the mold the dispensing unit switches to a higher pumping pressure.   The isocyanate and the polyol are injected via a special valve called a mix head.   The mix head ensures complete mixing of the two liquids.   At this time the chemical reaction begins as the mold is being filled with liquid polyurethane.   The mold must be filled within 5 to 35 seconds depending on which polyurethane we are using.   There is little if any expansion to most of the polyurethanes we process.   The chemical reaction between the isocyanate and the polyol creates exothermic heat.   Temperatures may reach 250 to 350 degrees momentarily in the mold.   Pressures seldom rise above 25 to 50 psi in the mold.


Shrink Factor

The molded part is allowed to cure or cool in the mold for a minute or several minutes depending on the process parameters required for the part.   The part shrinks a slight amount during the molding process.   This shrink factor is quite predictable and Premold Corp factors it into the mold design.   Part designers do not need to compensate for shrink.   Our resins do not outgas during or after molding.   No post curing is required for the parts.   The parts are immediately ready for use if they are a non-cosmetic part or ready for post processing if painting, decorating or assembly are required.


Numerous Advantages to Reaction Injection Molding (RIM)

The very low molding pressures and temperatures for Reaction Injection Molding (RIM) give it numerous advantages:

  • Low cost tooling that is economical for low production volumes and/or large parts.
  • Economical set-ups for short production runs make Reaction Injection Molding (RIM) well suited to JIT deliveries for even low production volumes and Kan Ban.
  • Designers have more creative opportunities with Reaction Injection Molding (RIM) because it can easily mold thin and thick walls in the same part.
  • Insert molding and encapsulation of delicate components is much easier with Reaction Injection Molding (RIM) because pressures and temperatures are low.   This can reduce your assembly costs, make assemblies tamper-proof or solve sealing problems for you.

Finest Materials Offer UL 94V-0 Flammability Ratings

Premold Corp molds parts in either foamed or solid, rigid polyurethanes.   We process the finest materials on the market: Prism CM200 and Baydur foamed materials  from Bayer Corp and Instant Set Polymers (ISP) from Carpenter Corp.   All of these materials offer UL 94V-0 flammability ratings at thin wall thicknesses.