Needle valve for hot runner nozzle to inject thermoplastic into mould - has bored needle containing inner needle whose nozzle end widens out to produce very narrow annular gap for flow of compressed gas feed

摘要

The hot runner nozzle with needle valve, for the injection of thermoplastic melt into moulds, has main body with the runner and a valve mouthpiece at the end with closure needle; the needle is moved axially in a bore of the nozzle body by means of a drive arrangement. The needle itself has a longitudinal internal bore which ends by the nozzle with an outlet with dia. less than 0.1mm; its other end is connected to a pressurised gas supply. The enlarged view of the valve needle shows it (5) as it moves to open/close the mouthpiece in the heated nozzle body. It is moved by a rod which is operated by two hydraulic cylinders. It (5) is bored centrally (14) along its whole length and contains another finer needle (15), the top end of which has a head (16) to close it off. ADVANTAGE - The design enables pressurised gas to be injected into the shot to prevent collapse of thicker parts while they cool in the mould. It can be used even for sprue-less moulding without necessitating insertion of the needle into the thicker parts of the moulding.