As the saying goes, “the devil is in the detail.” The viscosity of the liquid silicone rubber must be low enough to allow casting at atmospheric pressure without creating any bubbles in the mold. The rubber must also have an adequate processing life, yet still cure to a silicone elastomer as fast as possible in the heated mold at temperatures below 115 °C, as otherwise the GRP pipe would soften and buckle.
Conventional liquid silicone rubbers are unsuitable. “They are far too viscous, must be injected at high pressure and entail expensive injection molds,” explains Dr. Winter. In principle, a different rubber from the WACKER portfolio could be used, namely POWERSIL® 600, which cures at room temperature. It possesses the requisite low viscosity and cures to an elastomer which has excellent technical properties. “The only problem is that the mold needs to be cooled before each filling operation, as otherwise curing would start before it was completely filled,” adds the materials expert. This circumstance had the makers of the hollow-core insulators looking for an alternative.