GB700442A - Improvements in or relating to injection moulding machines - Google Patents

Abstract

700,442. Injection-moulding machines. DAVIDSON, R., and BUTTERWORTH, C. March 17, 1952, No. 6790/52. Class 87 (2) An injection moulding machine of the type in which the injection cylinder is moved to effect sealing contact of its discharge nozzle with a diebox on each operative stroke of the ram and in which there are means for holding the diebox is characterized in that the die-box holding means and the ram are operable by pressure fluid, the die-box holding means is automatically releasable at the end of each return stroke of the ram, and the pressure fluid actuating means comprise a double-acting piston and cylinder in respect of the ram of the injection cylinder and a singleacting spring-influenced piston and cylinder in respect of the die-box holding means. The ram 7, fitting in the injection cylinder 2, is associated through a piston-rod 8a with a doubleacting piston 8 in a cylinder 9. The injection cylinder 2, to the forward end of which is screwed a nozzle 4, has lateral projections which are slidable in guides which are held in the walls of the casing 1 by catches to enable the cylinder 2 to be readily removable for maintenance. The cylinder carries a funnel 17 communicating with its bore and when the cylinder is retracted a stop (not shown) positions the funnel under an opening in a cover 12 on the casing 1. The outside of the cylinder 2 carries electrical heaters controlled from a panel as described in Specification 662,957, and inside the cylinder is a torpedo 68 to ensure even heating of the material. Overheating of the ram is prevented by a passage 7a therein which communicates through a passage in the piston-rod 8a with the fluid in the cylinder 9. Underneath the hopper 13 is a measuring slide 14 which, according to the distance it travels, passes material through one or more passages 14a. The member 14 is operated from a vertical arm 16 on the pistonrod 8a through a rod 15 and its travel is adjusted by altering the position of a stop 15b on the rod which the arm 16 meets as the ram advances. The arm 16 also operates a relay valve 60 as later described. The construction of the die-box holder resembles that described in Specification 662,957 except that the jaws 30 are moved by fluid pressure, for which purpose a cylinder 33 is fixed to a plate 27, which is supported from the end plate 1d of the casing, and houses a piston 32 which, acting through a plunger 32a, pushes a pressure plate against the resistance of a spring 38 and thus causes push rods 35 to open the jaws. The fluid-pressure system is controlled from a hand or foot actuated valve 55 through valves 50, 51, which are themselves fluid-pressure operated, and from a relay valve 60 through a fluid-pressure operated valve 54. The relay valve 60, Fig. 8, has a spring-influenced plunger 60a operable either by hand through a lever 65 or by a stud 66 carried by the vertical arm 16. The lever 65 has a portion of reduced thickness 65c, and when this portion is between the plunger 60a and the stud 66 the latter is not long enough to move the plunger and the valve must be hand operated by rotating the lever in its bearing 65a. When the lever 65 is slid in the bearing 65a to the position shown dotted the valve 60 is operated when the piston 8 reaches its rearmost position. When the central valve 55 is moved to effect forward movement of the piston 8 it supplies low pressure fluid through a small diameter pipe 59 which causes the valve 51 to open and admit pressure fluid behind the piston. The cylinder 2 moves forward and brings the nozzle 4 into sealing contact with the inlet of a die-box held in the jaws 30 and the ram 7 continues to move and forces plastic material into the die. At the end of the injection stroke the control valve 55 is moved to' supply low pressure fluid through a small-diameter pipe 58 which causes the valve 50 to open and admit pressure to the other side of the piston 8, thereby retracting the ram 7, the cylinder 2 being retracted by springs 42. The arm 16 operates the relay valve 60, which supplies low pressure fluid through the small-diameter pipe 63 which causes the valve 54 to open and admit pressure fluid to the cylinder 33 to cause the piston 32 to move the push rods 35 to open the jaws and release the die box.