Patent GB-622186-A (GB)
Title: Improvements in presses
IPC: B29C45/03
Filed: 1944-05-26
Abstract: 622,186. Injection-moulding machines. FITZPATRICK, H. D. (Clearing Machine Corporation). May 26, 1944, No. 10225. [Class 87 (ii)] [Also in Group XXIX] A press, more particularly for injection moulding, comprises a platen 24, Figs. 4 and 5, having a long stroke and a ram 34 having a short stroke and exerting greater pressure than the platen, and a compression member 50 interposed between the ram and the platen so that the ram may augment the pressure on the platen. The compression member 50 is carried on guides 52 carried by the ram 34 and is interposed between the ram and the platen by a fluid-pressure cylinder 56 when the platen is in its lowest position. The fluid-pressure to the ram is controlled by a valve 49, Fig. 8, and the platen is operated by two fluid-pressure cylinders 29, one on each side. The plastic material is injected into the mould 111, 121, Fig. 4, by a plunger 93 and additional plastic material may be injected by a further plunger 255, Fig. 8, controlled by a hand-controlled valve 260, from an excess supply chamber into which a portion of the material being fed to the mould passes temporarily. The pressure of the ram 34 may be still further augmented by a plunger 79 which reduces the space in the ram cylinder. When completed the moulded article is removed from the upper part 121 of the mould by knockout pins 122 operated by a plate 123 and pins 125 which are adapted to be engaged by pins 130 on the knockout mechanism 129. The mechanism 129, carried on the guides 52, is adapted to be drawn across the top of the platen, to allow pins 130, 125 to register, by a spring catch connection 138, 139 to the compression member 50, when this member is withdrawn by the cylinder 56. The mechanism 129 is locked in. inoperative position by a catch 131 operated by a hand-operated lever 133: The moulding operation may be arranged to take place in two stages by the insertion, by means of fluid-pressure cylinders, of anvils between the platen and the press-bed, these anvils engaging successively steps on members secured to the platen in order to arrest the platen in two positions. The two parts of the mould are connected by means of tapered members 245, Fig. 10, which are adapted to be forced, by levers 247, between ledges 151 on the lower mould part 111 and the hooked ends of members 237 secured to the upper part 121, which is secured to the platen by clamps 229. Passages 144, Fig. 4, for cooling fluid in the mould are supplied from tubes on the platen guides arranged to telescope to allow for movement of the platen and heating passages are provided in a collar 106 surrounding the injection chamber 103, which rests on a bearing 100 adapted to be maintained in lowest position by the engagement of a member 107 on the plunger 93 with collars 109 on rods 108 connected to the bearing. In this position there is an air circulating gap between the upper edge of the chamber 103 and the mould aperture in the press bed 20. Cooling-fluid is supplied through pipes 118 to chamber 97 containing the injection mechanism and overflows through a passage 119a. Air circulates through passages 120. In operation, the platen is raised, the mould placed on the press bed and the platen lowered and secured to the mould. The platen and mould are then raised, the preheated plastic material placed in the injection chamber, the platen and mould are lowered on to the bed again, the compression member 50 interposed and the ram and the plunger 79 operated to exert pressure through the member 50 on the platen and mould. This pressure counteracts internal pressure in the mould. The injection plunger 93 is now operated and allows, by means of the rods 108 and the upward pressure of a resilient member 99, the injection chamber to rise and engage the mould. The plunger then forces plastic material through the sprue 112 to fill the mould. The plunger 79 is then withdrawn, the ram 34 raised, the member 50 withdrawn, the platen 24 raised and the knock-out mechanism 129 releases the moulded article. The fluid-pressure operating system shown in Fig. 8 comprises a pump 152 supplying fluid to a main pipe 155 to operate the various cylinders under control of valves 49, 86, 72 and 117. These valves are double-acting piston valves and are operated by fluid-pressure, supplied by a pump 176 to a pilot pipe 178, and controlled by hand valves 180, 186 191, 195. The platen operating cylinders 29, operated by a fluidpressure from the pipe 155 controlled by a handoperated piston valve 159, are provided with cushioning means at the bottom of the stroke comprising an auxiliary pipe 165 of small diameter which throttles the release of the fluid after the main pipe 32 has been closed by the pistons. An extra supply of fluid is provided for the injection plunger 93 by a pump 219, fluid from which is normally by-passed by a valve 222 to an exhaust pipe 221. When the plunger 93 moves upwardly, it closes a valve 223 controlling the venting line 224 for the valve 222 which thereupon supplies extra fluid to the pipe 155 and the plunger 93. To maintain the operating pistons of the apparatus at the end of their strokes and to obviate loss of full pressure from the pump 152 through the relief valve 201, the pilot line pump 176 is utilised to maintain the necessary pressure through a valve 205 and the pump 152 is adapted to be discharged to exhaust at a low pressure through a supplemental relief valve 202 controlled, through a vent pipe 210, by an electrically operated time-controlled valve 211, which is arranged to operate automatically at a predetermined time in the cycle of operations. An over-riding hand-controlled, by-pass valve 217 allows the valve 202 to be maintained open for a prolonged period when necessary. The valve 205 only opens when the pressure from the pump 176 exceeds the pressure in the main system 155 and comprises a valve member 277a, Fig. 18, adapted to connect pipes 178 and 204 and counterbalanced by the pressure fluid from the pump 176, admitted by the pipe 178 and the pressure fluid from the main system admitted by pipe 204 and also a spring 279. The pressure from the pipe 204 acts both above and below the valve member by passages 282 and 277d respectively. The valve 201 comprises a valve member 285, Fig. 14, controlling communication between the pipe 155 and the exhaust pipe 200, controlled by a piston 284 having a bleed passage 287 which allows the pressure to equalise on both sides of the piston which is then held down by a spring 291. If the pressure above the piston exceeds the spring pressure seating a valve.289 the valve is opened to vent this pressure, thus maintaining a predetermined pressure above the piston. The pressure in the system 155 may be regulated by means of the valve 201 and a manual valve 218, Fig. 8, connected to a passage 294 in the valve 201. In order not to extend unduly the length of the cylinder 56 it comprises two concentric telescoping cylinders, and the member 50 is connected to a cap 62 on the rod of the piston which is in the inner cylinder. The machine may be rendered inoperative by operation of a valve 206 to open the main pipe 155 to exhaust by a valve 207.