No. 40 - RIM

Polyurethane reaction injection molding (RIM) technology, developed by Bayer AG in the late 1960s, has evolved into a range of rigid (“structural foam”) and elastomeric forms, as well as reinforced (RRIM) and structural (SRIM) composites. As a relatively low-pressure liquid molding process, it competes with injection molding in applications ranging from auto interiors and exteriors to medical-equipment housings.

The first mention of this process in Plastics Technology was in a review of the 1971 International Plastics Fair in Dusseldorf: “The higher density, integral-skin, structural urethane foams produced by so-called reaction molding are becoming competitive with thermoplastic structural foams.” The process filled a closed mold that could be oriented so that material entered at its lowest point. Liquid components were injected at high pressure (2000 psi) into a chamber where the streams mixed without mechanical assistance.

By the mid-1970s, RIM was gaining prominence in the automotive industry for the production of fascias and body panels. One of the first complete machinery systems for RIM in the U.S. was introduced by Cincinnati Milacron in 1976. The first of these machines were used to produce elastomeric exterior panels for 1977 cars, including GM’s Pontiac.

The late ’70s also saw the development of RRIM using milled glass or mineral fillers. Ford Motor Co. field tested 5000 RRIM fenders for the 1980 Fairmont. The auto industry’s drive for weight reduction then led to the development of SRIM in the mid-’80s. It initially meant dispensing PUR chemicals onto a glass mat or preform. SRIM demonstrated its potential in 2001 in the cargo box for the full-size GM Silverado 1500 pickup truck.

SRIM took a new direction in 1995 with the launch of Krauss-Maffei’s Long-Fiber Injection (LFI) process, which chops and wets out glass fibers inside the mixhead. The mix is sprayed onto an open mold by a robot. Versions of this process soon followed from Hennecke and Cannon.