Injection moulding sandwich construction - by using separate extruders for skins and core, and minimum length straight runners so that sprue wastage is minimal and is easily removed

摘要

At least two different component polymers are successively or alternately injected from their extruders through at least one common runner; each product moulded has a core of at least one component polymer and (with the possible exception of a part adjacent to the gate(s) of a runner) a skin of another component polymer. Each polymer is fed from a separately coupled extruder through straight feed bores of minimum length to the runner concerned; the system is designed so that each sprue produced has a minimum cross-section, is easily cut off, and has the minimum volume, and so that when the mould is opened it can be removed quite simply. ADVANTAGE - The process has a minimal energy consumption, minimum sprue, and minimum arrangement needed to remove the sprue. It reduces any problem of heat loss or heat conduction between extruder and mould, even when moulding different materials with different temps