The RIM Process (Reaction Injection Molding) can be translated as molding by reaction. This molding process consists of injecting into a mold two liquid components that, when mixed, react with each other and polymerize, in order to produce a material with predetermined structure and properties.
Reaction Molding emerged about two decades ago and began to be used essentially by the automotive industry. However, this process can be applied in sectors such as industrial equipment, buses, railways, furniture, among many others.
But how does the RIM Process work?
We can consider that the process has 5 distinct phases, depending on the quality requirements of the final part:
- Mixture of low viscosity monomers in the chamber;
- Mold filling;
- Polymerization or reaction cure;
- Part extraction;
- Eventually, post-cure operations to obtain better properties.
The process begins when we mix the two raw materials, one of which is necessarily a diisocyanate or polyisocyanate and the other a diol or polyol. Other additives such as colorants or anti-fire additives can also be added.
The purchased solution is injected into a mold.
In the mold cavity, the reacted mixture flows at low pressure, temperature and viscosity. Injection time depends on the type of injected reagents and the amount injected, however it generally lasts between 5 and 35 seconds. For large molds, this time is naturally exceeded.
After the injection, for about 60 to 120 seconds, the mold remains closed for polymerization to occur, also known as the curing reaction. Thus, at low pressure and low temperature the material solidifies and can be removed without damaging it.
It is therefore a quick and low-cost process.