Patent GB-666844-A (GB)
Title: An improved injection-molding machine
IPC: B29C45/03
Filed: 1947-03-14
Abstract: 666,844. Hydraulic machines. ALDEN, R. M. March 14, 1947. No. 7180/47. Class 69 (ii) [Also in Group V] A cyclically-operable machine for moulding thermosetting material comprises (a) a chamber in which the loose material is formed into pellets; (b) a heating chamber to which the pellets are transferred and in which they are heated by high frequency electric heating means; (c) an injection chamber to which the heated pellets are transferred; (d) automaticallyoperated means for opening and closing the dies; and (e) means automatically operative in timed sequence with the opening and closing of the dies for forming the material into pellets, heating the pellets for a time less than a complete cycle of the machine and injecting a heated pellet into the die cavity each time the dies are closed. The drawings show a machine in which the operations are performed by hydraulic cylinders, the supply of liquid to which is controlled by valves under the control of solenoids in an electrical circuit. The electrical circuit may be set to perform one cycle automatically, or continuous repetitive cycles automatically, or the various parts of the machine may be operated independently of each other by manually-controlled switches. There are four hydraulic cylinders 26, 46, 51 and 82 which operate respectively pelletting piston 27, injection piston 47, die-closing piston 52 and piston 83. Moulding powder falls from a hopper 1 into an adjustablevolume measuring slide 3 which then moves to the left to the position shown, the powder in the slide dropping into a chamber 16 in front of the pelletting piston 27. This piston then moves to the left to compress the powder into a pellet against a stationary abutment 18 in a chamber formed by a sleeve 17 which is slidable on the abutment. The piston and sleeve later retract to the right and left respectively, and the pellet drops down a shoot 28, first resting on a stop pin 37 and later falling into a chamber 29 in front of an ejector pin 36. At this stage the pellet is in position 41, and a previously-fed pellet is in position 42 where it is being heated by high-frequency means. The pin 36 then moves to the left, pushing the pellet immediately in front of it into the heating position 42. The unheated pellet pushes the heated pellet into a shoot 44, whence the latter falls in front of the injection plunger 47. The pins 36, 37 are supported on a bracket 35 and move together; thus, when pin 36 pushes a pellet from position 41 to position 42, stop pin 37 extends across shoot 28 to support a recently-formed pellet. The bracket 35 is fixed to the sleeve 17 which is directly connected to and reciprocated by a rod 23 attached to one end of a lever 84 fulcrummed at 85. The other end of the lever is pivoted to the piston rod 83 of the hydraulic cylinder 82. The measuring slide 3 also is reciprocated by the rod 23 through the medium of lever 80 and rod 5. The sequence of operations for the whole machine is as follows:-(1) The operator opens and closes a safety gate 62. This operates a switch 61 to energise solenoid 64 which operates valve 66 to allow pressure oil from pump 69 to pass through pipe 67 to cylinder 51 to move die part 49 to the right to closing position. Pump 69 is of the dual type comprising a large volume low pressure pump and a small volume high pressure pump, both pumps applying pressure to the mould part at first, and later the second part only applying pressure. As the die part 49 reaches its closed position a cam 76 thereon operates limit switch 77. (2) Operation of switch 77 energises solenoid 78 to operate valve 79 to move piston rod 83 to the right. Rod 23 is thus moved to the left, pulling sleeve 17 over abutment 18 to allow the pellet to drop into shoot 28, moving pins 36, 37 to effect the operations described above, and pushing the measuring slide from the position shown to its filling position under the hopper. At the end of the leftward travel of sleeve 17 an adjustable dog 86 mounted thereon operates a switch 87. (3) operation of switch 87 results in the following :- (a) The high-frequency generator is switched in, thus starting the heating of the pellet in position 42. The heating means comprises a pair of plates which touch or nearly touch the pellet and may be resiliently mounted, (b) The operating motor of a preheating timer for controlling the duration of high-frequency heating of the pellet is started. (c) The operating motor of a curing timer for controlling the duration of the period during which the die remains closed is started. (d) Solenoid 88 is energised to operate pilotvalve 89 and valve 92 to move injection piston 47 to the left to fill the mould. The piston moves quickly at first, under low pressure, but slows down as pressure builds up, and at the end of its stroke the high pressure pump alone operates to hold the material at high pressure during the curing period. (e) Solenoid 95 operates valve 79 to move piston rod 83 to the left and rod 23 to the right, thus restoring the parts 3, 17, 36, 37 to the position shown, whereupon powder drops from slide 3 into chamber 16 and a pellet drops off pin 37 into chamber 29. As sleeve 17 reaches the end of its rightward travel a dog 99 thereon operates a switch 101. (4) Operation of switch 101 energises solenoid 103 to operate valve 104 which allows pressure to pass through pipe 105 to move pelletting piston 27 to the left to compress the powder. When sufficient pressure has been built up in pipe 105, switch 106 operates. (5) Operation of switch 106 energises solenoid 102 to operate valve 104 to return piston 27 to the right. (6) After the above described operations have been completed, the curing timer continues to operate, and at the end of a measured period acts to de-energise solenoid 88, thus actuating valves 89, 92 to retract injection piston to the right, and to energise solenoid 111 to operate valve 66 to retract die part 49 to the left to open position, the moulded article being stripped out of die part 48 manually or mechanically.. The preheating timer then cuts out, and in so doing cuts out the high-frequency generator. The preheated pellet starts to cool. The cutting-out of the timer initiates operation of a safety timer the function of which is to lock the die part 49 in open position if the preheated pellet in position 42 has been allowed to cool below a certain temperature. Thus, in order to restart the machine, the operator must open and close gate 62, and if he does not do this within a specified time the safety timer acts to lock the solenoid 111, whereupon die part 49 is locked in open position and belated operation of switch 61 by gate 62 fails to shift valve 66. When the safety timer "times out" it may ring a bell. To remove the cold pellet the operator actuates a switch (292, Fig. 8, not shown) which results in an operating cycle of the machine being completed except for the closing of the die parts, whereupon the cool pellet is ejected through exposed die part 48. When thermoplastic material is being moulded the die parts are cooled.