Reaction Injection Molding (RIM) Vs Plastic Injection Molding (PIM)

In the manufacturing process when large quantities of a specific part are required, production companies tend to look towards an injection molding service. Injection molding is a rather straight forward procedure, but there are different kinds of molding, including reaction injection molding and plastic injection molding. To know which process is better for a certain industry, understanding what the difference is between the two methods is necessary.

The Major Difference

In general, the two methods are extremely similar to one another. The main difference though is reaction injection molding uses a thermosetting polymer in the injection process, which needs a curing reaction to take place inside of the mold in order to harden. If this is not added, the injected material is not going to become stiff, rendering the process useless. With a plastic injection process, a hot plastic is injected into the mold, which is then rapidly cooled, causing the plastic to harden without a curing agent.

The Two Injection Methods

In the first stage of the reaction injection process, two elements of the polymer are combined and then injected into the mold. The mold is then allowed to sit in order to cure and harden. Fiberglass and mica are two of the most common materials used in this molding process. With this method, the injectable material does not need to be hot. Instead, the material is usually injected into the mold using a high pressure injector at closer to room temperature. It then requires heat to harden the product into mold. Plastic injection molding uses the exact opposite approach. Plastic pellets are dropped into an injector which heats up the plastic, causing it to liquefy. The liquid plastic is pushed through the injection tube along a moving, spiral (similar to an oversized screw) in order to prevent the liquid plastic from sitting and sticking. The hot, melted plastic is forced out of the nozzle into the mold. Once in the mold it is cooled rapidly (such as dunking the mold in water) in order to harden the plastic. Once the material is hard it is ejected out of the mold and the process is repeated again.

Using the reaction molding process produces a strong, yet flexible material although it usually costs more to use reaction versus plastic simply because the starting material is more expensive than what plastic is going to cost. Either way, the two are similar.

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