Patent GB-1086722-A (GB)
Title: Moulding apparatus
IPC: B29C45/84
Filed: 1963-05-08
Abstract: 1,086,722. Cleaning injection-moulding apparatus. PENNSALT CHEMICALS. May 8, 1963 [May 9, 1962; March 21, 1963], No. 18272/63. Heading B5A. The feed screw 40 of injection moulding apparatus is retracted and rotated to purge the moulding material, e.g. thermoplastic. Moulding compound is fed from a hopper 42 to a cylinder 38 where it is fed by rotation of screw 40, which at the same time plasticizes the material, to an accumulation zone 46 and from there through a port 51 into transfer pot 50. Heating coils 39 surround the cylinder to prevent heat loss from the material being plasticized and cooling coils 45 surround the zone 46 to prevent polymerization of the plasticized material by overheating. A transfer ram 48 reciprocable within the pot 50 moves up from the position shown in dotted lines to close the port 51 and transfer plasticized material to the mould cavity 18, a clamp ram 20 being moved down to close the moulding press 14, 15. Operation.-The moulding press is open; the transfer ram in position shown in dotted lines and the screw in the advance position. On automatic actuation, a clamp ram timer starts timing and also solenoid 31 is energized causing liquid to flow through conduit 26 to force the clamp ram down to close the press, at which point switch 36 is closed causing a transfer ram timer to start timing and also causing the energizing of solenoid 63 so that liquid flows through conduit 62 to force the transfer ram up to close port 51 and carry plasticized material to the mould. When the transfer ram is fully advanced switch 53 is closed causing solenoid 84 to become energized to rotate the screw and thereby extrude plasticized material into the zone 46, at the same time the transfer ram timer times out de-energizing solenoid 63. As the material is extruded the screw moves hack and trip ring 86 opens switch 88 to deenergize solenoid 84 and stop rotation of the screw. At this point the clamp ram timer times out de-energizing solenoid 31 and energizing solenoid 33 so that liquid flows through conduit 28 causing the clamp ram to rise and close switch 34 whereby solenoid 65 is energized causing liquid to flow through conduit 60 to move the transfer ram down to close switch 54. This de-energizes solenoid 65 and causes solenoid 108 to become energized causing liquid to flow through conduit 104 to advance the screw to force material into the transfer pot 50. When the screw is fully advanced trip ring 86 closes switch 90 to re-energize the clamp ram timer whereby the cycle is repeated. Safety timer.-A safety timer is provided which has a timing period of slightly longer than that of the automatic cycle and resets itself each time the moulding press closes. If the cycle takes longer than it should, the safety timer times out causing de-energization of solenoid 114 which causes (i) liquid to flow through conduits 96 and 95 to retract the extruder and shift the hopper to cut off the supply of moulding compound to the extruder and (ii) to sound an alarm. Thermoplastic material from compartment 43 of the hopper passes into the extruder which when retracted far enough closes switch 120 which energizes solenoid 84 to rotate the screw and purge the moulding compound from zone 46 into a cavity 65. Alternatively the screw may be retracted far enough to expose its threads whereby material can be mechanically removed; the screw may also be rotated in a reverse direction by motor 70 energized by solenoid 85. An electrical circuit is described in Fig. 2 (not shown).