Reaction injection molding (RIM) technology
The BaySystems polyurethane (PU) systems house in Otterup, Denmark, has joined forces with Isotherm AG in Uetendorf, Switzerland, to develop a cost-effective process for the production of housings and protection for sensitive electronic components. It is based on polyurethane systems from the Baydur E and Bayflex E ranges, which are processed in a single step by reaction injection molding (RIM) technology. In the RIM process, the two main components – isocyanate and polyol – are introduced in liquid form into a countercurrent mixing head via a dosing system. They are then homogenized and injected into a mold at low pressures of up to 6 bar. Here, the material reacts very rapidly to produce polyurethane. Finished parts can usually be removed from the mold in less than two minutes. This leads to a very cost-effective method of combining housing production and electronic encapsulation in a single production line. The polyurethane’s properties can be varied by selecting suitable starting materials. The low viscosity of the polyurethane reaction mixture ensures that even areas of the electronic assemblies that are difficult to reach are enclosed effectively.
To meet the requirements of electronic components, it is important that the polyurethane reaction proceeds very quickly, gently and with little shrinkage, as required. Curing takes place at a maximum temperature of 120°C. Subsequent annealing is not necessary. The thermal conductivity of the polyurethanes, which is very important for the heat dissipation of electronic assemblies, can be raised to high values by adding fillers and is largely independent of the material’s hardness. Motor vehicles in particular are being equipped with an ever-increasing number of electronic applications. The delicate pin contacts of components and assemblies require reliable protection against oxidation caused by weathering. The connecting cables are exposed to constant vibrations, and their insulation must not be damaged in the event of contact with fixed parts. These and other requirements are fulfilled by polyurethane in combination with the RIM process.
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