Reaction Injection Molding

We see the results of reaction injection molding everywhere! Otherwise known as RIM, you will find the technology in everything from auto parts and tractors to machine parts and tools. The equipment and the products to produce these items have only been around for sixty years or so, and businesses across the US have been in operation for over thirty years. This happened in the 1980’s when the automotive industry began to use more reaction injection molding to make gaskets for panel and radial seal air filters. Because polyurethane, the material used in RIM manufacturing is synthetic, it also has a lower cost than many natural metals that were the former materials to make some of these automotive and machine parts. The toughness and potential flexibility of RIM products, in addition to the wide variety of shapes and sizes that it can make, make polyurethane products an invaluable resource for today’s industries.

How Reaction Injection Molding Works

So many things that we encounter in everyday life are made out of polyurethane. Do we ever think to wonder how they came to get that shape? It had to come from a mold, and a substance had to get into that mold somehow, and that’s how reaction injection molding gets its name. The reaction occurs when two liquid compounds – a polyisocynate component and a resin mixture are fed from separate tanks into a common mixing area. From the two temperature and pressure controlled tanks, they are rapidly “shot” into the mix chamber and undergo a chemical change, and the mixture then flows into the mold. For smaller parts, this can take just seconds per shot of material and the part can be out of the mold in 30-60 seconds, complete. Larger products, such as automotive bumpers, car hoods and even fenders can also be made with reaction injection molding.

Variability of Reaction Injection Molding

Two different techniques for RIM technology are used to produce items. The first is open cast molding. This is typically less expensive to produce, for the urethane mixture can be hand mixed or put into a urethane dispensing machine and then poured into the mold. The other method is centrifugal casting, described above, and is used when the part needs to be built from the center.

These days, your part can be made with different colors and have a varying degree of hardness and flexibility. The four primary colors of red, blue, yellow and black, and the non-color, white, are most likely available from most reaction injection molding manufacturers. Also, depending on the quantity ordered, you can have custom colors mixed to produce the perfect match for your product.

The hardness and durability of an item may be adjusted as well. Bowling balls, a very hard substance, are made with RIM. Products produced with RIM have a durometer rating – which shows the hardness of the material on a number scale, with the higher the number, the harder the material. Along with the number, a letter is added to describe how dense the material is. This is shown as an A for a lower density to a D for a high density product. A 72D is much more hard and dense than a 28A. RIM allows the variation of how hard and how dense a particular item needs to be. The size of the product would be another consideration, and various manufacturers have different availability of sizes of tooling, or molding equipment. Whenever you see a hard, plastic-like urethane material, it may very well have been fashioned with reaction injection molding.