GB709417A - Improvements in apparatus for the injection moulding of thermoplastic materials - Google Patents

Abstract

709,417. Injection moulding machines. PEARCE, G. H. Oct. 19, 1951 [July 21, 1950], No. 18261/50. Class 87 (2) A machine comprises a turret which indexes on a vertical axis into a plurality of stations, moulds mounted on the turret, means on the turret for opening and closing the moulds at certain stations, means for stopping the indexing of the turret if any mould fails to close, means for checking the moulds for complete closure and preventing the filling of any mould not completely closed, means for clamping the mould parts together and injecting plastic material, means for varying the period of dwell underpressure at the injection station, this varying means being operated by .an adjustable member on each mould station on the turret, and means, operated by the indexing of the turret, for removing the moulded articles. The machine shown (Fig. 1, plan, and Fig. 2, elevation) is hydraulically operated under the control of an electric circuit and operates continuously and automatically in cycles. If a mould does not nearly close, an electric switch is operated to stop the machine: but a mould which is very nearly but not quite closed operates another' switch which does not stop the machine but prevents the nearly-closed mould from being filled. The machine comprises a turret 1 which rotates counter-clockwise about an axis 1A. Spaced equidistantly on the turret are six pairs of platens 2, 3 between each pair of which a mould is mounted. The turret rotates intermittently in 60 degree steps, each mould dwelling at six stations a ... f. At a the mould is closed, at b it is filled, at c the material in the mould solidifies, at d the mould opens, at e the article is removed from the mould, and at f mould cleaning, mould changing or loading of inserts or other operation takes place. Each platen 3 is fixed on a rod 50 which is slidable vertically in the turret, and each platen 2 is slidable on that rod 50. The turret carries six mould-closing fluid-pressure cylinders 30, one for each mould. Operation :-(1) When the turret 1 is about to index (counter-clockwise, Figs. 1 and 10), the parts are in the Fig. 10 position. The electrical circuit to a solenoidoperated valve 63 is closed, and this valve supplies hydraulic pressure through line 72 to a cylinder 53 to urge piston 53a to the left, thereby turning the turret through 60 degrees by means of rack 54, pinion 55 and Geneva mechanism 57. A mould which has been closed at a is thereby transferred to injection station b and during the transference it passes three electric switches, 75, 10 and 11. If the mould is not; closed, e.g. due to foreign matter trapped between the mould faces, it moves safety device 9 to' open switch 75, thereby de-energizing valve 63, and further indexing of the turret is stopped. If the mould is not completely closed it opens micro-switch 10 to close valve 64 and prevent continuance of the cycle (see below). Each incompletely-closed mould operates micro-switch 11 to re-set the switchgear to start a cycle for the succeeding cylinder mould. (2) As piston. 53a reaches the left-hand end of its cylinder, an arm 60 on piston rod 53b moves a rod 58 to open switch 62, whereupon valve 63 reverses, pressure passes through line 74 and piston 53a returns idly rightward to the Fig. 10 position, returning rod 58 and closing switch 62: under normal circumstances the piston thus reciprocates continuously. (3) When pressure passes through line 74 it also passes through line 73 and valve 64 (if switch 10 has not been opened) to cylinder 61 to push plunger 13 into recess 51 to lock the turret. If switch 10 has been opened, as soon as piston 53a completes its return stroke it will start another cycle, the mould that opened switch 10 being thus not filled. (4) As plunger 13 moves into locking position it closes switch 65 to energize solenoid-operated valve 66 which admits pressure through line 79 to cylinder 14 to move mould-clamping hooks 15 from the inclined idle position shown to the vertical clamping position, As piston rod 14c moves it opens a switch 68 to de-energize valve 63 and temporarily prevent indexing: a valve 70 delays the return stroke of piston 53a so that switch 68 is opened before switch 62 closes, (5) As hooks 15 move to the clamping position they open valve 69 to admit pressure from valve 66 through line 80 to cylinder 16, whereupon ram 17 rises, thus pushing the mould up into engagement with the injection nozzle 21. The pressure that raises ram 17 acts also through ram 18 on crosshead 19, thus exerting a downward mould-locking .pull on hooks 15. The upward thrust lifting the mould is proportional to the difference in areas of the rams 17, 18. As ram 17 rises it closes valve 20 to prevent piston 14a from retracting hooks 15. As the mould rises it telescopes the injection cylinder over a stationary injection piston 23, material passing through divergent-convergent holes. 52 to fill the mould. The mould dwells in this raised position for a period of time controlled by a timer .27, this timer having been set, during the ascent of the mould, by engagement of an adjustable stem 28 on platen 3 with a lever 29 on the timer. The lever moves through an angle the magnitude of which determines the duration of the dwell, and the angle is determined by the position to which the stem is adjusted in the platen. Each of the six moulds may be different and require a different dwell. (6) When the dwell period has expired the timer opens a switch 81 to de-energize valve 66 to exhaust lines 79, 80, whereupon ram 17 and the mould descend by their own weight. (7) As the ram descends it allows valve 20 to open, whereupon spring 14d retracts the hooks and closes switch 68 to re-energize valve 63. When valve 63 is re-energized line 73 is exhausted and spring 61b withdraws plunger 13. The turret then indexes and the filled mould passes to station c. At station c the mould halves are held together by piston 30<1> whilst (thermoplastic) material cools. Between stations c and d a cam operates valve 4 to raise piston 30<1> and hence platen 2. As platen 2 rises a cable 8 attached thereto pulls up a lever 7 pivoted at 7' on platen 3, thus raising pins 6 to eject the moulded article. At station e the article is removed by means which seize the injection sprue and drop the article into a tray. This sprue-seizing means comprises a pick-up arm 38 which extends between the platens and carries two levers 44 urged together by spring 44a held apart, in the inactive position, by a cam 47. The pick-up arm is carried by a stem 37 on a piston-and-cylinder assembly 36 supported on the outer ends of levers 32 fulcrummed at 33 on a fixed bracket 31. The inner ends of the levers are normally held down by a cam 42 on the turret, this cam acting on the ends through a roller 40 on a part 40<1> of a valve 39, this part having a pin 41 which abuts the ends. When the mould reaches station e the cam allows part 40<1> to rise, the pick-up arm 38 descending to a level (the sprue level) determined by an adjustable roller stop 35. As part 40<1> rises it actuates valve 39 to operate cylinder 43 to rock lever 45 about fulcrum 45a, thus, via rod 46, rotating cam 47 to allow spring 44a to close jaws 44 on the sprue. When lever 45 rocks, a pad 45b thereon actuates valve 48 to operate cylinder 36 to lift-the pick-up arm carrying the sprue and moulded article. When the turret moves away from station e the cam 42 reverses these movements and the article drops into a tray.