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Introduction:
RIM was conceived in the laboratories of Bayer AG, Leverkusen, West Germany, about 1964.
The Reaction Injection Molding process is a structural foam molding process. This process is most suited for moderate-volume production of medium-to-large structural parts.
RIM is not a material, it is a process in which two or more liquid components are introduced to each other via high-pressure impingement mixing and then injected into a closed mold at low pressure where they react to form a finished polymer and take on the shape of the mold cavity.
RIM products have uniform shrink and dimensional stability. Low mold temperatures of 130 to 160F help reduce part shrinkage.
Wall thicknesses from 3/16" to 1/4" are recommended. Molded thicknesses can be varied to well over 1/2" without sink marks in the molded surfaces. Most common densities are from 38 to 40 pounds per cubic foot.
Screw threads are attained by inserting brass screw inserts into molded holes after the part in molded.
RIM materials are an excellent choice for product encapsulation techniques. Steel, aluminum and even plastic opjects can be covered with RIM materials.
In mold painting is achived by painting the mold surface before injection occurs. RIM material is injected and chemically bonds with the paint film.
The molds used with the RIM process can be made from a variety of materials. Cast and machined aluminum, composites, sprayed metal, epoxy, nickel shell and steel. The choice is determined by the number of parts to be made, dimensions, shapes and tolerances, surface texture, mold life, mold cost and part performance.
Process:
Liquid plastic, together with a catalyst, is introduced into a closed mold. Catalytic reaction, which creates heat, causes the plastic to expand to fill the mold.
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