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Reaction Injection Molding

What is RIM

RIM is a new process way for producing large size and huge quantity products rapidly . RIM process is monomer or pre-polymer (PU materials) in liquid state with a certain proportion which measured by the metering pump mixing in mixing head of a mold . After the mixture be injected into the mold under a low pressure/room temperature environment , it will rapid response and cross-linking curing . After ten more minutes , it will be solidified , and then release it from the mold , that part is RIM product . This process can be simplified as: storage, measurement, hybrid ,mold filling and curing , demould and post-processing.

The process of Reaction Injection Molding

1) Storage
Two raw liquid material used in the RIM process were stored in two reservoir at certain temperatures, reservoir is commonly pressure vessel. In molding , stoste usually in 0.2 ~ 0.3 MPa low pressure in the reservoir, and circulating constantly in the reservoir, heat exchangers and mixing head. As for polyurethane, the average temperature of stoste is 20~40 ℃, the temperature control accuracy is ±1 ℃.
Measurement will be finished by the metering pump , and requirements for measuring accuracy is at least be ± 1.5%, and the best control should at ± 1%.
3) Hybrid
In RIM process , product quality is largely depend on the quality of mixture in the mixing head , so does the production capacity . The normal pressure is about 10 Mpa in order to get the better effect .
4) Mold falling
The characteristic of RIM process is the material flow rate is very high .Then stoste’s viscosity can not be very high .Such as the viscosity of polyurethane mixture is about 0.1 Pa s.and flow rate control at 600 g/s in mold falling .
5) Curing.
Polyurethane two-component mixture have very high reactivity after injected in the mold ,so it complete curing in ten more minutes .But plastic’s conductivity is not good , so most heat can not release from a large chemical reaction condition , so that the outside temperature are higher than inside, so the curing development is from inside to outside .
6) Demold
Demold also means we need release the cured part from the mold , and that part is the RIM product . And more quantity can be produced as the above process .
7) Post-Process
It is according to customers’requirements .

Material for RIM

General common resin : polyurethane resin, vinyl ester, amide ester resin, unsaturated resin, epoxy resin and traditional composite material, etc.
Normally material : HD-PU4210,DCP-RIM,AXSON-RIM 875 ,etc .

PS:The curing time of RIM process is mainly by the molding material formulation and product size decision. In addition, RIM products need going on the second curing after release from the mold . And as RIM process is fast(15-30 minutes/piece) and high-precision , it fit to produce large quantity and huge size products ,and the size of biggest casting part is 2000mmX1200mmX1000mm,for 10KG .