Reaction injection molding foam: A versatile system for a wide variety of parts
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Like thermoplastic injection molding, RIM (reaction injection molding) is a plastics-forming process that uses molds to form foam or solid parts, which can vary from flexible to extremely rigid depending on how the polyurethane RIM system is formulated.
We first developed RIM in the 1960s. What makes this system unique is that it produces polyurethanes using two liquid components - an isocyanate and a polyol - rather than the pellet form of most thermoplastics. These two materials are fed through supply lines to metering units, at high pressure (approx. 150 bar), and on to a mixhead device. The liquid is then injected into a closed mold, where it undergoes an exothermic chemical reaction and forms a polyurethane polymer. Shot and cycle times vary (between 1 to 20 minutes), depending on the part size and the polyurethane system used. An average mold for fast system may be filled in one second or less and be ready for demolding in 30-60 seconds.
Depending on how the polyurethane system is formulated, the parts molded with it can be a foam or a solid, and they can vary from flexible to extremely rigid. Part density can vary widely, too, with specific gravities ranging from 0.2 to 1.6 (filler included). We offer several polyurethane systems applicable for RIM technology for different applications:
Baydur - a rigid integral foam, e.g. for window insulation. Bayflex - an elastomeric integral foam, e.g. for car body parts. Bayfill - a semi-rigid foam, e.g. for instrument panels. Baytherm - a rigid foam, e.g. for appliances.
How RIM works: A step-by-step explanation
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. When 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 100 and 200 bar, 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.
Shot and cycle times vary, depending on the part size and the polyurethane system used. An average mold for an elastomeric part may be filled in one second or less and be ready for demolding in 30-60 seconds. Special extended gel-time polyurethane RIM systems allow the processor enough time to fill very large molds using equipment originally designed for smaller molds.
RIM Product Spectrum: Let's identify the right foam system for your product
We are a single-source supplier of the major polyurethane components for reaction injection molding - isocyanates and polyols. But our real strength is in formulating these separate components into polyurethane systems containing just the right isocyanate and polyol - as well as any filler, internal mold release or other ingredient - to produce the processing and physical properties you need. From structural foam RIM systems to solid polyurethane systems to advanced RIM composite systems, we have a broad range of polyurethane systems to meet virtually any need. Covestro offers a full range of polyurethane RIM systems.
If you need a system that we don't already offer, our chemists and technical service representatives can work with you to develop a formulation tailor-made to your application. Over 60 years’ experience in polyurethane chemistry make us extremely well-qualified to help so, whether you select one of our standard polyurethane RIM systems or need a custom-formulated system, you can leave the chemistry to us while you focus on manufacturing your product.