GB531100A - Improvements in and relating to injection moulding machines - Google Patents

Abstract

531,100. Injection-moulding machines. BRAUN AKT.-GES., F. July 7. 1939. No. 19888. Convention date, July 7, 1938. [Class 87 (ii)] In an injection-moulding machine, the charge to be admitted to the injection cylinder is controlled by weighing-mechanism. As shown, the supply hopper 7 discharges into a pan 2 on a beam 3 pivoted at 9, an adjustable weight 4 determining the weight of the charge required to tip the balance into the space 14. When the balance starts to tip, a curved shutter 5 closes the hopper 7, the charge, however, remaining in the pan 2 until a depending arm 6 is engaged by a headed rod 10 on a plunger 12 which is forced to the right along a cylinder by pneumatic pressure and is returned by a coil spring. The sequence of operations is controlled by a slide valve 21 in a cylinder, the ends of which are connected to air pressure or atmosphere by interconnected manually-operated valves 16, 17. When the valve 16 admits pressure to the pipe 20; the valve 21 slides to the right and opens a port 22 to admit air pressure behind a piston 24 on a rod 26 carrying a piston 15 which ejects the deposited charge into a shoot 27 leading to the injection cylinder 28. When the piston 24 reaches the end of its stroke, the port 29 is uncovered to pressure which is admitted through the passage 32, groove 34, and pipe 33 to the cylinder Z. The piston 35 is thus moved to the right and operates the injection plunger 36 with pressure which progressively increases by virtue of the toggle connection P, 53. The piston 35 carries a fork 42 which contacts, with lost motion, with stops 57, 43 on a sliding bar 44 carrying a rack 45 meshed with a pinion 46 on a shaft 47 carrying a rotary valve 48. Thus, if, for some reason, the cylinder 28 has been overcharged and the piston 35 prevented from advancing to its end position, the stop 43 will not be contacted and the valve 48 will remain closed. When pressure is admitted to the pipe 50, the valve 21 will move to the left and admit pressure, through the pipe 37, to the space 19, the piston 35 being thus moved to its extreme left position. The passage 49 will remain closed, however, so that the piston 24 will remain stationary and pressure will not be admitted to the piston 12 which ensures that the trip 10 will remain inactive and the pan 12 will not be emptied for the next injection stroke.