GB811878A - Improvements in die construction for injection-type molding machines - Google Patents

Abstract

811,878. Injection-moulding machines. COLUMBUS PLASTIC PRODUCTS Inc. Sept. 3, 1956, No. 26938/56. Class 87(2) The mould is in two parts, 8, 9 Fig. 2, meeting at their surfaces 10, that of the part 8 being grooved at 10a to facilitate alignment and separation. The surface of the part 8 where it meets that of a stationary platen 5 is also grooved, at 32, and has slots 33 which register with slots 33a in the platen. Dogs 12, carried by the stationary platen 5, enter recesses 11 in the part 8 and so clamp it. Wedge bars 34 Fig. 4, pass through the slots 33 and fit in slots in the inclined face 36 of a valve-plungercarrying head 37 with a rib and groove engagement. Plungers 41 project from the opposite face of the wedge bar and pass through part 8 to the sprue bushings 24 where, Fig. 7, they seat at 43 in the ends of ports 44 through which the plastic material is forced into the mould cavities. The seating may be conical. The mould part 9 has cavities 26 corresponding to cores 27 which project from a movable core section 28. Dogs 31 enter recesses 30 in the sections 28 and are secured to a platen 6, whereby reciprocation of the platen 6 causes the cores 27 to enter or leave the mould cavities, dowels 61 registering with sockets 62. The hydraulic and electrical circuits which control the apparatus are shown in Figs. 14 and 15. When a master switch MS is closed it sets in operation a timer Tl which energizes a solenoid S1 and causes a valve 94 to direct the pressure fluid into a cylinder 6b whereby a ram 6a advances the platen 6 to the mould-closing position, the cores 27 registering with the cavities 26. The advance of the platen 6 closes a limit switch LS2 whereby the switch MS is shunted and the timer T1 remains energized. When the platen 6 has reached the die-closed position it closes a limit switch LS1, which energizes a second timer T2 which, in turn, energizes the solenoids S2, and S3. Valves 67, 76 are thus operated and direct pressure fluid into the cylinders of rams 39a and 3 respectively. The pressure in the ram 39a causes it to retract the wedge bars 34 and their action withdraws the plungers 41 from their seatings 43. Plastic resin, made fluid by a heating cylinder 2, is forced by the ram 3 from the pressure chamber 13 into a passage 15 of an axial sprue bushing 16, unseating a ball-check valve 19 and spreading through diverging branch passages 22 to the sprue bushings 24. The bushings 24, Fig. 5, have heads 25a which seat on shoulders 25b and can only be removed when the sections 8 and 9 are separated. With the plungers 41 withdrawn to allow plastic material to flow, it occupies the spaces between the cores and mould cavities and when it cures, or cools and hardens, the required hollow articles will be formed. The timer T2 de-energizes the solenoids S2, S3 immediately after the injection stroke to allow springs 74, 81 to reverse the valves 67, 76, thus causing the ram 39a to move the wedge bars 34 to return the pins 41 to their seated positions at the same time as the injection ram 3 is retracted. Thus undesired sprue runners are removed. After a time long enough for the plastic material to have cured or hardened the timer TI de-energizes the solenoid S1, whereupon a spring 98 reverses the valve 94 with the result that the ram 6a retracts the platen 6. At the start of its return stroke the platen operates the limit switch LSI to deenergize the timer T2 which is automatically reset for another cycle. The mould part 9 is interchangeable with other mould parts to form differently shaped hollow articles. Passages 45 in the part 8 conduct heating fluid and passages 46 in the part 9 conduct cooling fluid. Cooling fluid is also circulated in the cores by passages 47 which have baffies 48 to direct it. In a modification, Fig. 9, a sleeve 52 is attached to the wedge bar 34a and the valve-plunger 41a fits in the sleeve, with its forward end 50 of reduced diameter. On the retracting movement of the wedge bar the sleeve 52 moves over the outlet of the passage 22 and shuts off the plastic material. The plunger 41a may be heated to keep the material round its end fluid, e.g. by conduction from the flow of superheated steam through the passages 45.