Intrusion mould filling for thermoplastic blanks - uses timed filling in sequence with reduced pressure in final filling stage from continuous extruder

摘要

The assembly to produce blanks of thermoplastics, from a continuously operating extruder, uses intrusion moulding in a static assembly with at least two moulds which are filled in succession from a continuous flow of melted material. Before the end of a filling operation of a mould the next mould filling action starts for the next mould, in the time sequence, by release of the molten flow and the remainder of the filling is at a reduced pressure. Pref. the filling pressure is maintained at the mould for the whole filling and cooling phases, with a short interruption for emptying. The moulded blanks are ejected by the pressure of steam formed by the coolant water injected at the heated zone, and/or by compressed air. The moulded blank can also be ejected by the subsequent molten pressure, where the mould and feed closure acts through holding the moulded blank to be ejected. ADVANTAGE - The final filling of the mould is slowed down to avoid a pressure shock. In operation all the feed slides are open until a short closing time in each mould for emptying, the residual pressure remains for the filling time at each mould in the whole array, so that the hollow zone shrinkage is minimised to give uninterrupted extruder working.