GB420728A - Improvements in and relating to injection moulding machines for plastic materials - Google Patents

Abstract

420,728. Injection moulding of artificial resins &c. BRAUN AKT.-GES., F., Zerbst, Germany. Dec. 11, 1933, No. 34815. Convention date, Dec. 10, 1932. [Class 87 (ii)] In an injection moulding machine for plastic material of the kind provided with a pump the piston of which is adapted to inject the material into the mould, the driving means for the piston comprises an electric motor and transmission mechanism including a spring coupling the motor and the piston, the driving means being adapted to maintain the pressure on the piston when the motor has come to rest owing to increased resistance to the injection motion of the piston. As shown, the material is fed from a hopper 1 to the cylinder 2 of the injection pump and is forced by the piston 3 into a heated cylinder 4<a> communicating through the nozzle 5 with the mould 9. The rod 10 of the piston 3 slides within a threaded sleeve 11 keyed to the casing 12 and engaged by a threaded bush 13. The bush 13 is formed externally as a worm wheel and meshes with a worm on the shaft of the electric motor A. The end 20 of the sleeve 11 is screwed to a casing 21 containing a spring 23 acting between the end 22 of the casing and a flange 19 on a sleeve 18 secured to the outer end of the piston rod 10. The piston 3 is thus actuated from the motor through the intermediary of the spring 23. The motor A may be of the asynchronous type; the armature winding being continually shortcircuited through an adjustable resistance b, Fig. 3, which is connected to the slip rings and acts to limit the starting current and, by its adjustment, to control the maximum torque of the motor when stalled and thus the pressure on the piston. The terminal w of the scator winding is connected directly to the lead W of the three-phase leads U, V, W, whilst the terminals u, v are connected to an automatic change-over relay o, the timing of which is adjustable and which is mechanically actuated by the closure of the mould. The relay o connects the terminals u, v either to the leads U, V, in which case the motor runs in a direction to advance the piston, or inversely to the leads V, U through the intermediary of a switch N. The switch N acts to limit the return stroke of the piston by cutting out the motor and is actuated by a stop 24 on the casing 21.