Partially expanded mouldings - with a smooth interior or exterior surface esp self insulating pipe fittings

摘要

Shapes having >=1 internal cavity or passage and produced from a dense undersize moulding of an expansible thermoplastic compsn. subsequently supported on or in a jig with chilled walls and then heated to above the threshold blowing temp. Pref. an ancillary moulding cavity is used to limit the degree of dimensional expansion by blowing. Ancillary chilled sleeves or plugs may be used to prevent some zones of moulding from expanding at all. Esp. for producing plastic conduits or fittings with a smooth bore and controlled joint dia. together with integral partially foamed walls offering better thermal and acoustic insulation than dense walls. Polymers based on PVC, polystyrene, ABS, polyolefins or acrylic resins are suitable for hollow mouldings.