Prodn. of model for forming hollow moulds - by coating model with thin silicon layer, thick layer of silicon and HF sensitive material and filling with silicon and aluminium

摘要

Cavity moulds for compression moulding plastics materials fused by high frequency (HF) dielectric loss heating are made by coating a pattern a) with a thin (0.4-0.7 mm thick) layer of silicone resin deposited from solution (by e.g. spraying), covered with b) a thicker (1-3mm) layer of silicone resin extended with a material (such as polyvinyl acetate, PVC or epoxy resin) having a higher HF loss factor. The second coating compsns should be non-melting up to 200 degrees C. The bulk of the mould body is then cast using a conventional silicone resin/aluminium powder blend. Used esp. for moulds for shaping thin layers (1mm) of material such as flexible PVC coatings on supports for shoe uppers or other artificial leather work. Complementary heat generation at the cavity surface reduces mould cycle times, esp. when gelling thin layers of material relatively susceptible to heat loss to moulds or mould coatings not warmed up by the HF heating. Alternatively allows larger (>1200 cm2) mouldings to be formed using conventionally sized 15-20 kVA generators.