The RRIM process

RRIM polyurethanes are an extension to Reaction Injection Moulding (RIM) which is a relatively recent, but now established, plastics processing technique. Simplified, RRIM is the inclusion of a reinforcement - short glass fibres - into one of the components used in the RIM process. However, the inclusion of glass reinforcement into one of the reactive components, usually the polyol, has meant that certain processing equipment modifications were necessary in order to handle the 

In the RRIM process two fast-reacting liquid streams are precisely metered and mixed using high-pressure impingement mixing. A schematic of a typical process is shown in Fig. 12.1. 

Interest currently centres on high-grade, slightly expanded elastomer systems. By incorporating a blowing agent into one of the reactants and filling the mould cavity to approximately 90% of its total volume a partially expanded product is formed. 

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The RRIM process is limited by the problems associated with dispersing the glass evenly into all areas of the mold. Because of this, it may be difficult to develop adequate strength in key performance areas of the parts such as ribs and bosses. Small changes in processing conditions also open the door to significant part-to-part variation in physical performance. 

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