Reaction Injection Molding (RIM)
What is RIM?
Reaction Injection Molding (RIM) is a new process for the production of large parts in large runs. In the RIM process, a monomer or pre-polymer (PU derivatives) in a liquid state is poured using a dosing pump into the mold head.
The mixture is then injected into the mold at a low ambient temperature and pressure, the crosslinking and curing begin quickly, and after 10 minutes the figure will already be solidified, being able to be removed from the mold
The reaction-injection molding process (RIM)
- Storage: The two liquid raw materials used in the RIM process are stored in two large tanks at a certain temperature, and at an approximate pressure of 0.2 ~ 0.3 MPa. These liquids circulate between heat exchangers and mix-heads in a speedy, continuous loop. As in the case of polyurethane, the average storage temperature is 20 ~ 40 ° C, and the temperature tolerance is ± 1 ° C.
- Measurement: The dosing pump is responsible for the measurement and tolerance requirements are at least ± 1.5%.
- Hybrid: In the RIM process, the quality of the product depends largely on the mixture made in the mix-head. The normal pressure is approximately 10 MPa in order to obtain the best results.
- Deposition in the mold: The characteristic of RIM process is that the material flow rate is very high, so the viscosity cannot be very high. The viscosity of the polyurethane mixture when falling into the mold is approximately 0.1 Pa and frequency control flow is 600 g / s.
- Curing: The mixture of the two polyurethane components has a very high reactivity after being injected into the mold, so a complete cure takes only ten more minutes. The problem is that the conductivity of the plastic is not very high, so the curing process is from the inside out.
- Demolding: Demolding means to remove the finished part from the mold.
- Post-Processing: The treatment or coating requested by the customer is applied to the part.
Materials used in RIM
Resins are generally used: polyurethane resin, vinyl ester, ester-amide resin, unsaturated resin, epoxy resin, traditional composite material, etc.
Commercial materials: HD-PU4210, DCP-RIM, RIM AXSON-875, etc.
PS: The curing time in the RIM process depends mainly on the formulation of molding material and the size of the product. In addition, RIM products need a second cure after the mold removal. Since the RIM process is fast (15-30 minutes / unit) and highly precise, it is suitable for producing large quantities and large products. The size of most casting is 2000mm X 1200mm X 1000mm, for 10KG.
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