GB1317029A - Method of and apparatus for processing plasticisable material by injection moulding - Google Patents

Abstract

1317029 Valves BUEHLER AG Gebr 5 June 1970 27359/70 Heading F2V [Also in Division G3] In the injection moulding of a hot or cold setting plasticizable material, in mould 1, 2, the axial displacement of injection and plasticizing screw 10 is programmed as a given function of time. A continuous magnetic foil or tape 62 moving at a uniform speed is read by head 63 and provides pulses of variable spacing via amplifier 65 and change-over switch 66 to a stepping motor 70 causing programmed axial displacements of permanent magnet core 85. The movement of core 85 causes output signals in coils 82, 83 fixed to thrust bearing 24, and which, via amplifier 76, lead 110 and pressure regulating valve 45, see also Fig. 4 (not shown), causes a bleed of pressure fluid from line 43 to 38 to cause the coils 82, 83, and hence the injection assembly to follow the core 85. Amplifier 76 has non-linear electrical characteristics to complement those of valve 45. Bidirectional pulse counter 75 indicates the position of the screw 10 and a connection between counter 75 and machine control unit 60 enables travel dependent switching. After injection switch 109 is operated under program control to connect valve 45 to a variable resistor 112, 113 to provide a predetermined pressure for setting, and switch 121 is operated so that any movement during setting is communicated via amplifiers 76 and 65 to motor 70 to keep the core 85 centred. For plasticizing, material is provided via hopper 4 to cylinder 3, and hydraulic motor 11 whose speed is set by variable resistor 96, via gears in housing 12, rotates splined drive shaft 15. Pressure regulating valve 46, see also Fig. 4 (not shown), controls movement of shaft 13 during plasticizing. Limit switches 91, 92 are provided. In the embodiment of Fig. 2 (not shown) a band (146) connected to thrust bearing (24) drives a pulse generator 145, and desired and actual valve pulses respectively are converted to analogue form in d/a converters (137), (147) whose outputs feed a comparator/ amplifier (140) controlling the valves 45, 46 to maintain the respective pulse counts equal. A pressure switch (131) operates upon the rise of pressure at the end of injection, thus connecting valve 45 to the variable resistor 112, 113, for setting, and any movement during this phase, as recorded on counter (75<SP>1</SP>) is communicated to pulse store (136), so that subsequent programmed movements can take account of prior setting movement. Injection can be started only when the mould is locked, and is at the required temperature. In a further modification, Fig. 5 (not shown), the stepping motor 70 sets the axial position of a flow regulating valve (173), and the pressure duct 43 is connected to a housing (171) surrounding the valve, and fixed to the thrust bearing 24. Any movement of the valve (173) enabling passage of fluid through it, produces motion of the screw 10, and the housing (171) to follow it. The passage of fluid controls the pressure in duct 43 either directly or via a pressure regulating valve. Hydraulic system.-Pumps 32, 42 provide fluid under pressure, via non-return valves 34, 44, and a pressure limiting valve 40 (Fig. 3) is provided. Pressure regulating valves, 45, 46 and Fig. 4 (not shown). Each valve has a coil (105) embedded in an iron core (450), and attracting a yoke (451) supporting a valve (452). The current in the coil determines the extent to which the valve (452) can lift to enable passage of fluid from pressure duct 43 to return duct 38. Pressure limiting valve, 40 and Fig. 3 (not shown) remains shut unless fluid pressure, from duct 33 is able to lift valve (411) from its seat, whence piston (401) will rise, relieving the pressure. A direct current motor may be used in place of a stepping motor.