Reaction Injection Molding
The Reaction injection molding (RIM) process is an
economical option commonly used for larger, more complex polyurethane plastic and
rigid foam parts produced in small quantity. RIM is used in a number of
commercial and industrial applications, and is employed for the production of
parts such as panels for electrical equipment, enclosures for medical devices, housings
for computer and telecommunications equipment, and in the automotive industry. RIM
is often used to produce larger parts because of low viscosity and low
injection pressures. RIM parts are
sturdy, durable and are resistant to aging and weathering. The RIM process is
used to make parts such as shields for telephone systems, radar antennas and
automobile bumpers.
Instead of using thermoplastics, the main difference between
RIM and standard injection molding is the use of thermoset polymers,
specifically polyurethane. Reaction injection molding is named after the chemical reaction that takes place within
the plastic. Two liquid components-a
polyisocyanate component and a resin mixture-are injected into a mold,
chemically react and then dry, all within 60 seconds. During the chemical reaction, foaming occurs,
forming bubbles which become open or closed cell foam. Because there are so many different design
choices when using RIM, the look may vary considerably. The finished product can be solid and hard, a
foam or elastomeric like rubber. RIM is
useful in the production of parts that need a cosmetic appearance, such as
computer covers. They are low costing
molds and have allow for greater design flexibility, but have a lower
production rate than standard injection molding.