Forming plastic hollow shapes, e.g. for air ducts, involves drawing pre-heated sheets to permeable tool walls by suction and then closing tool to seal edges

摘要

Plastic pre-forms containing film of single or multi-layer non-crosslinked polypropylene foam (1, 2) is pre-heated (1a, 2a) and placed in a mold with air permeable walls. A vacuum is applied to draw the film towards the walls, after which the mold is closed to form a seal at the edges. The tool can be of homogeneous porous material or have perforations, e.g. porous resin, sintered metal, wire mesh. Tensioning arrangements can be included to feed material during the deep-drawing process. A lance can be introduced to produce a positive pressure within the molding.