| Reaction Injection Molding (RIM)
is the process by which two liquid reactants - an isocyanate
component and a polyol resin mixture - are held in separate tanks at an elevated
temperature with agitators. These liquids are fed through supply
lines at high pressure to the mixhead. When the injection begins, valves
open in the mixhead and the liquids enter a chamber in the mixhead at
high pressures (usually between 1,500 and 3,000 psi) and high
speeds. Here they are mixed by high-velocity impingement.
From the mix chamber, the mixed liquid flows into the mold at
atmospheric pressure and undergoes an exothermic chemical reaction,
forming a polymer in the mold. Reaction time is usually expressed
in seconds. For extremely large parts the reaction time can be
extended to allow for proper filling of the mold.
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