GB906762A - Improved injection moulding machine - Google Patents

Abstract

906,762. Injection moulding machines. BRITISH INDUSTRIAL PLASTICS Ltd. March 13, 1961 [March 24, 1960], No. 10541/60. Class 87(2). The pressure on a ram 6 of an injection moulding machine is controlled during the injection stroke so that the full injection pressure is reduced, after the mould 5 has been substantially filled by use of a control rod 30 which is coupled to the ram 6 and moves with it when the pressure on the ram has reached a predetermined pressure e.g. 0À2 of the full injection pressure, the control rod being used to bring about the reduction of the full injection pressure after a predetermined movement with the ram. In the machine shown cold moulding material is fed from a hopper 3 into a heated cylinder 1 and thence into the mould 5 by movement of a piston 4. The piston is coupled to the ram 6, the ram being moved by supply of fluid under pressure into either of the spaces 19, 20 through a main control valve 16, the fluid expelled by movement of the ram escaping through a line 21. The fluid under pressure is normally fed to the valve 16 from a pump 17 through a by-pass valve 13, 18 being a pressure reducing valve. As the piston 4 starts to fill the mould the pressure in the space 19 rises rapidly and this actuates a pre-set pressure sensitive switch 23 which opens an electrically operated valve 25 allowing compressed air to act on a piston 28 in a cylinder 27. Movement of the piston 28 clamps the rod 30 and causes it to move with the ram 6. After a predetermined movement a cam 35 on the rod 30 closes a micro-switch 36 the position of which is adjustable, and this opens an electrically operated valve 38 allowing compressed air to close the by-pass valve 13, so that the pressure applied to the ram 6 is reduced by the pressure reducing valve 18. On completion of the injection stroke the pressure in the space 19 is released and this unclamps the rod 30, which returns to its rest position against a stop 34 under the action of a spring 32. The microswitch 36 is thus opened so that the by-pass valve 13 is again opened. The air operated clamping device 29 may be replaced by an electromagnetic clamping device actuated by the switch 23 and acting directly or indirectly on the rod 30.