Tools for making large thermo:formed mouldings - using residual mould cavity pressure to develop forming pressures against compression mould face

摘要

Large thermoformed mouldings are made by clamping thermoplastic sheet (4) on to a mould cavity tool having a broad rim, heating the sheet to its thermoforming temp. and then partly evacuating the mould cavity prior to forming the sheet by applying a compression mould tool. The residual air vol. is set to be slightly greater than the residual cavity vol. after the introduction of the compression tool, so that compression of the residual air raises the cavity pressure sufficiently to apply the sheet closely to the compression tool face. Used esp. for making large mouldings, e.g. boat hulls, container panels, partitions, garden ponds, work benches, electroplating baths etc. Avoids need to use large compressors to achieve same effect by vacuum forming or by pneumatic bag consolidation where large moulding surface areas are involved. The consolidation pressure rises progressively as the compression tool enters the cavity.