GB1175905A - Vacuum Sealing Means for Molds - Google Patents

Abstract

1,175,905. Injection moulding. H. R. BUCY. 30 Aug., 1967, No. 39763/67. Heading B5A. [Also in Division B3] A mould for the die casting of metal or the injection moulding of plastics comprises a stationary cover die 4 and a movable ejector die 1, the former having die blocks 5, 5<SP>1</SP> and the latter blocks 2, 2<SP>1</SP> between which a mould cavity 11 is located and to which moulding material is fed via a sprue hole 8, recess 8<SP>1</SP>, the end of a spring-loaded plunger 52 and runners 9, 10 and 12. Three gates 13 lead to three overflow pockets 14. A core 15 provides a central opening in the casting and a tapered opening 16 in the die block provides a breather for the evacuation of air from the mould cavity via passages 16a, 21 and 24 leading to a vacuum pump 25 on the mould. Similar evacuation means each comprising a core 18 extending into a sleeved opening extending through the die blocks in the cover die 4 to a passage at the rear of the die connected to the vacuum pump are provided to ensure that all parts of the mould cavity and its supply passages are evacuated before moulding material is supplied to them. A shallow groove 30 located at the meeting face of the dies 1 and 4 has similar core pins 34, Figs. 8 and 10a, cooperating with bores 34<SP>1</SP> extending to passages at the rear of the cover die; one half of the groove is connected to a vacuum pump 38<SP>1</SP> on the mould. The screws by which the blocks are held in place in the dies have their heads received in counterbores which are interconnected by passages and connected to one or other of the pumps 38, 38<SP>1</SP>. The corners of the die blocks and the rear faces thereof at their edges are slightly bevelled and the spaces thereby formed are connected by bores to the pumps. To prevent air leaking into the mould from the ejector pins 26 of an ejector plate assembly 27, counterbores 26<SP>1</SP>, Fig. 10, are located in the base of the ejector die and around the pins and are interconnected by grooves which lead to a passage connected to a vacuum pump 47 on the mould. The rear faces of the dies 1 and 4 are covered by plates 49 and 22, respectively. Each core pin 34 may be positioned between a pair of ejector pins 44, each of the latter having similar counterbores around them in the ejector die and connected by grooves on to the pump 47. In order to prevent the sprue hole 8 and its associated passages being connected to atmosphere, the end of the spring loaded plunger 52, which closes the sprue hole runner 9 and is forced back by the pressure of the moulding material, has a channel 54 which connects via a runner 66 with a breather passage provided with a core 68. Said passage is connected to a vacuum pump 72 via passages and grooves in the die 4. The plunger may be located between a pair of ejector pins having counterbores in the die 1 as above described and connected to the vacuum pump 47. An operator may initiate a mould cycle when the vacuum within the mould reaches a predetermined value, whereupon the cycle proceeds automatically. Alternatively a vacuum responsive switch may initiate the cycle. In a modification, the assembly includes a core for forming a hole in the side of the casting, the core having a head outside the dies and slidable in a guide; the head has a bore therethrough to receive a pin extending from one of the dies such that when the two dies are brought together the core is slid into the moulding position. An annular groove surrounds the core when in position between the dies and is connected via passages and with a vacuum pump.