Equipment and Mold Design

At the heart of the polyurethane RIM process is a chemical reaction between the two liquid components, which are held in separate, temperature-controlled feed tanks equipped with agitators. From these tanks, the isocyanate and polyol feed through supply lines to metering units that precisely meter both components, at high pressure, to a mixhead device.

Gusmer-Admiral P12 Dispensing MachineWhen injection of the liquids into the mold begins, the valves in the mixhead open. The liquid reactants enter a chamber in the mixhead at pressures between 1,500 and 3,000 psi, and they are intensively mixed by high-velocity impingement. From the mix chamber, the liquid then flows into the mold at approximately atmospheric pressure. Inside the mold, the liquid undergoes an exothermic chemical reaction, which forms the polyurethane polymer in the mold.

Mix Head

The mix head contains injector nozzles which impinge the isocyanate and polyol at ultra-high velocity to provide excellent mixing. Additional mixing is accomplished using an aftermixer, typically constructed inside the mold.

Click to see the Bayer Part and Design Guide

 Mix Head Illustration

Mold Design

To make good polyurethane parts, you must have a good mold. Molds are sometimes referred to as “tools.” A correctly designed mold is the single most important factor in gaining maximum productivity, uniform part quality, and trouble-free production. Improvements in gate, mixing head, and after-mixer designs are continuing to add to part quality and uniformity. RIM Manufacturing can provide assistance with part and mold design and can also provide this Design Guide from Bayer.