Professional car styling products - Aldor Automotive - Netherlands

Polyurethane reaction injection molding (RIM) technology was developed in the late 1960s by Bayer AG. Since then, the technology has evolved dramatically as more and more product designers and manufacturers have learned to tap the unique capabilities and benefits of RIM for an ever-growing range of products. The universal physical characteristics of polyurethane RIM parts are high strength and low weight. Like thermoplastic injection molding, RIM is a plastics-forming process that uses molds to form parts. But the similarity ends there.

 

The polyurethanes begin as two liquid components, compared with the pellet form of most thermoplastics. These liquid components - an isocyanate and a polyol - are developed in two-part formulations, which are often called polyurethane RIM systems. Depending on how the polyurethane RIM system is formulated, the parts molded with it can be a foam or a solid, and they can vary from flexible to extremely rigid. Thus, polyurethane RIM processing can produce virtually anything from a very flexible foam-core part to a rigid solid part. Part density can vary widely, too, with specific gravities ranging from 0.2 to 1.6.



 

At the heart of the polyurethane RIM process is a chemical reaction between the two liquid components, which are held in separate, temperature-controlled feed tanks equipped with agitators. From these tanks, the isocyanate and polyol feed through supply lines to metering units that precisely meter both components, at high pressure, to a mixhead device.

 

When injection of the liquids into the mold begins, the valves in the mixhead open. The liquid reactants enter a chamber in the mixhead at pressures between 1,500 and 3,000 psi, and they are intensively mixed by high-velocity impingement. From the mix chamber, the liquid then flows into the mold at approximately atmospheric pressure. Inside the mold, the liquid undergoes an exothermic chemical reaction, which forms the polyurethane polymer in the mold.

 

Shot and cycle times vary, depending on the part size and the polyurethane system used. An average mold for an elastomeric part may be filled in one second or less and be ready for demolding in 30-60 seconds. Special extended gel-time polyurethane RIM systems allow the processor enough time to fill very large molds using equipment originally designed for smaller molds.