Patent GB-924852-A (GB)
Title: Improvements in or relating to presses for moulding articles from thermoplastic or thermosetting material
IPC: B29C43/00
Filed: 1959-11-23
Abstract: 924,852. Moulding gramophone records. PHILIPS ELECTRICAL INDUSTRIES Ltd. Nov. 23, 1959 [Nov. 26, 1958], No. 39655/59. Class 87(2). A press for moulding articles from thermoplastic or thermo-setting material, particularly gramophone records, comprises a heated pressing block 2 and a cooled pressing block 4 which are separated by an insulating portion 3 and mounted on the frame of the press and a lifting table 9 adapted to bring pressing dies to the level of the heated or cooled pressing block, each die comprising a pair of plates 12a, 13 hinged at 16 to form a self-contained unit, the lifting table providing three positions for the pressing dies of which the centre position corresponds to the location of the pressing blocks. The slide 12 has projections 24, 25 from its underside which slide in grooves 26, 27 in the table 9 and it is moved by a hydraulic cylinder 30 through a plunger 29. The plates 12a, 13 of each die unit, carrying the dies 17, 18, are connected by spring plates 14, 15 to the hinge 16 and the dies are aligned by a centring stud 19. The die units can be slid sideways on or off the slide 12, the plate 13 being adapted to engage transverse grooves in the slide and the part of the plate 12a, where it projects beyond the dies, engaging cam plates 31 which, as the die unit is moved across the slide, force the plate 12a vertically upwards off the centring stud 19, the spring plates 14 and 15 flexing accordingly. Instead of the cam plates 31, studs may be pushed upwards under the plate 12a, actuated by a hydraulic plunger. Fig. 9 shows means for preheating the dies before the next moulding operation. A heating element 41 is raised by a plunger 40 into contact with the lower die 18 and the upper plate 12a may be swung upwards so that the upper die 17 makes contact with a heating element 42, where it is held by an electromagnet 44 energized by a switch 43. A pushbutton 45 breaks the circuit so that the die can be closed. The heater element 42 can be mounted on a plunger which brings it into contact with the die 17. The heating time may be controlled thermostatically. In position I, Fig. 1, a die unit a is filled with material, e.g. polyvinyl chloride. The lifting table 9 is then raised by hydraulic plungers 10, 11 to position II and a limit switch 46 is operated and causes a hydraulic plunger 6 to retract the heated pressing block 5, i.e. the press opens, enabling the die unit b, in which the moulding operation has just taken place, to be drawn out of the press on to one end of the slide 12. The movement of the die unit b closes a limit switch 50, Fig. 5, which causes the plunger 29 to move the slide 12 to the right, the movement ceasing with the operation of a limit switch 49, position III. The die unit a is then pushed below the pressing block 5 and operates a switch to close the press and to lower the table 9. At the bottom of its travel the table operates a limit switch 47 which causes a hydraulic plunger 8 to lower the cooled pressing block 7, position IV. Removal of a cooled die unit c operates another switch to cause the slide 12 to move to the left until it meets a limit switch 48, position V. This brings the die unit b into place for being pushed above the cooling plate 7 and the movement of the die unit c from the press will have partly opened the unit, so that, in the position V, the dies may be heated as in Fig. 9. Specification 879,774 is referred to.