The RIM Process (Reaction Injection Molding) can be translated as reaction molding. This molding process consists in the injection into a mold of 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 primarily by the automotive industry. However, one can apply this process in sectors such as industrial equipment, buses, railroads, furniture, among many others.
But how does the RIM Process work?
We can consider that the process presents 5 distinct phases, depending on the quality requirements of the final part:
- Mixing of low viscosity monomers in the chamber;
- Filling the mold;
- Polymerization or curing reaction;
- Extraction of the part;
- Eventually, post-cure operations to obtain better properties.
The process begins when we mix the two raw materials, where one is necessarily a diisocyanate or a pollisocyanate 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. The injection time depends on the type of reactants injected and the amount injected, however it generally lasts between 5 and 35 seconds. For large molds, this time is naturally exceeded.
After injection, for about 60 to 120 seconds the mold remains closed for polymerization, also called the curing reaction, to take place. 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.