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What is Reaction Injection Molding?

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  • Written By: M. McGee
  • Edited By: Lauren Fritsky
  • Last Modified Date: 29 October 2016
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    Conjecture Corporation
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Reaction injection molding is a process of making machine parts and product components. The reaction molding process differs from normal injection molding in one important way—the material used in the molding process requires a curing phase while the material is still in the mold. The forming material used in a reaction injection molding process offers specific advantages over the materials used in normal molding. On the other hand, reaction injection molding requires more time and expensive forming materials.

Injection molding is a common manufacturing process. In most cases, a liquid agent is fed into a holding tank, where it is heated and mixed. The agent is then forced into a pre-made cavity called a mold, where it cools and hardens. The mold is made using a separate machining process and is often removable, allowing one injection machine to make multiple items. The hardened object is removed and placed in an area where it cures and hardens further.

In a reaction injection molding machine, there is an additional phase after the agent is injected into the machine. During this phase, the agent cures while still inside the mold. There are varying ways of doing this, but a common method is through a secondary chemical reactant that is injected along with the agent. Other methods include heat or varying forms of radiation.

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The curing phase separates reaction injection molding from the normal process and gives it a specific set of advantages and disadvantages. The biggest advantage lies in the injected agent itself. The agents used for a reaction injection molding process are thinner and have a lower viscosity than the agents used in a standard process. This allows the agent to fill up small spaces and thin areas.

The in-mold curing process enhances this basic feature. When the part comes out of the machine, it is already cured and nearly in its final shape. This means that the small areas and thin spaces have even less chance to break. As a result, a reactive process is useful when the mold contains very fine sections.

There are two main disadvantages to reaction injection molding; time and money. Since the material needs to cure in the molding machine, that means that less parts are made at any given time. A standard machine may complete several molds and have them all curing at once. In addition, the agents used in the process are very specialized—they are typically more expensive than materials used in a common molding process.

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