Patent GB-656415-A (GB)
Title: Injection cylinder assembly for injection moulding machines
IPC: B29C45/53
Filed: 1948-09-08
Abstract: 656,415. Injection - moulding machines. GRAVESEN, C. C. Sept. 8, 1948, No. 23674. Convention date, Sept. 8, 1947. [Class 87 (ii)] In an injection-moulding machine material is fed to the heating chamber 10 from the entrance port 11 by an annular plunger 8 working in a housing 2 and ejected from the chamber through the nozzle 3 by an inner plunger 7 working inside the annular plunger and also supported by ribs 6 projecting inwards from the lining 5 of the injection cylinder 1. In all positions of the two plungers there is free communication in the chamber between the zones in front of and behind the front face of the inner plunger. The feeding plunger works at low power against little resistance and the inner plunger acting directly on the plastic material has little frictional resistance to overcome. The cylinder is heated by an element 12. The Specification as open to inspection under Sect. - 91 describes an injection-moulding machine, Fig. 1 (Cancelled), incorporating the assembly described above. The housing 2 for the plunger 8 is mounted on a fixed cross-head 17 and the cylinder 1 is secured to the housing 2 by nut 38. The cross-head 17 is fixed on a pair of rods 15 on either side of the machine joining end members of the machine frame. The plunger 8 is secured to a cross-head 16 sliding on the rods 15 and moved by a toggle 33 operated through links 34, 35 from the pistonrod 29 of pneumatic cylinder 30. The plunger 7 is operated directly by a pneumatic cylinder 32 fixed to the frame. One mould half is fixed to a cross-head 18 sliding on the rods 15 and is urged to the right by springs 19 bearing against adjustable nuts 25 on threaded portions of the rods 15. Movement of the mould half to the right is limited by hooks 53 engaging the nuts 25. The complementary mould half 21 is fixed on a sliding cross-head 49 which is moved on the rods 15 by a toggle 43 operated through links 44, 45 and rack and gear 48, 47 from the pistonrod 29. On moving to the left the mould half 21 first engages the other mould half and pushes it against the nozzle of the injection cylinder, compressing the springs 19. A rotatable plug valve with four positions is described for controlling the machine. The right-hand sides of both cylinders 30 and 32 are connected to a constant pressure source lower than the full actuating pressure. In position (i) of the valve the left-hand side of cylinder 30 is connected to exhaust to move plunger 8 back to position A; in position (ii) pressure air is admitted to the left-hand side of cylinder 30 to feed material into the heating zone and close the moulds and the left-hand side of cylinder 32 is opened to exhaust to allow plunger 7 to move to position C to provide room for the new material; in position (iii) the right and left sides of cylinder 32 are connected to each other and in position (iv) the left-hand side of cylinder 32 is connected to the pressure air source to inject material into the mould. After injection, on returning to position (iii) the plunger 7 takes up an equilibrium position in the cylinder 1, thus reducing the pressure therein to a low value to avoid spewing from the nozzle on opening the mould. The valve is returned to position (ii) while the material in the mould cools and return to (i) opens the mould and returns plunger 8 to position A. Material is fed to the port 11 by a feed-bar reciprocated between a position under a hopper 61 to a position over the port 11 by a rod 63 moved to and fro by an arm 64 secured to the piston-rod of cylinder 32. Fig. 4, (Cancelled), shows an alternative die having a spring-loaded valve member 83 to close the nozzle orifice 90. The member 83 is moved back against the spring 85 to open the orifice for injection by pressure of the material on its conical surface 91. Heating of the cylinder 1 by electric induction or fluid is referred to. This subject-matter does not appear in the Specification as accepted.