The RIM Process

RIM Molding System DiagramThe RIM Molding process begins with two liquid reactants, a polyol component (B) and an isocyante (A). These are contained in separate temperature controlled day (feed) tanks equipped with agitators. When a shot is called for at the mix head at injection, from these tanks, the polyol and isocyanate are fed through individual supply lines to metering units that precisely meter both the A and the B components and supply them to the high pressure mixhead.

When injection begins and valves in the mixhead open, the liquids are impinged upon each other at pressures between 1,500 and 3000 psi beginning the high velocity mixing of the two components. From the mix chamber, the liquid flows into the mold at approximately atmospheric pressure and undergoes an exothermic chemical reaction, starting the foaming process inside the mold cavity and subsequently forming the polyurethane polymer part inside the mold. Shot and cycle times vary, depending on the part size (up to 100 pounds in a single shot) and the type polyurethane system used (rigid, foamed, elastomeric, etc.).