Patent GB-657552-A (GB)
Title: Improvements in or relating to a press for moulding plastic materials
IPC: B29C33/20
Filed: 1948-01-16
Abstract: 657,552. Control of motors. McNEIL MACHINE & ENGINEERING CO. Jan. 16,1948, No. 1388. Convention date, Feb. 16, 1947. [Class 38(iii)] [Also in Group V] A mechanically-operated press for the vulcanization of articles such as rubber heels &c. has a stationary platen 52, Fig 1, and movable platens 40 and 88 operated by toggle linkage driven through gears from a motor 2. One of the main gear wheels 15 is provided with external grooves having blocks 130-133 set therein, adapted to operate switches 125, 126 and 127, Figs. 15-20, housed in a bracket 124 on the press. A low limit micro-switch 107 opens when the resistance of the material to moulding exceeds a predetermined low limit, and a high, limit micro-switch 109 opens to halt the press closing movement when the material resistance is excessive. When the switch 109 is opened a holding circuit 110 is closed through a relay R, switch 109, line 146, safety switch 147, return line 150. This circuit includes a contactor the plates of which are moved together as soon as the switch 109 is opened, Fig. 16. When the excessive resistance drops, switch 107 is remade and the motor 2, Fig. 1, is again started up. The micro-switches are operated by the small elongation of the press arm 30 under load tension. In Figs. 15-20, the directions in which the switches are moved by the blocks 130 &c. are shown by arrows, and the power circuit for the motor 2 is separate from the control circuit. To close the press from the fully open position the spring-loaded button S, Fig. 15, is moved to the right to connect the line 145 with the return line 150 and energize a coil 152 to close a contactor 154 to complete the power circuit to the motor 2 and also close the plates of the contactor 154 in the circuit shown. The movement of the button S also connects a motor T witha timing device. The movement of the press causes the block 131 to leave the switch 125 which moves to the Fig. 20 position. The current now flows through line 145, contactor 154, switch 109, and line 150. When the press reaches its fully closed position the switch 126 is moved by the block 132 to open position, Fig. 17, and the motor circuit is broken. When the full time for vulcanizing has elapsed the timer acts upon the button S and moves it to the left dotted position, Fig. 20, and the clutch in the timer is disconnected. The motor T however receives current constantly. A circuit is now made through coil 162, line 160, switch 125, to line 150, causing the contactor 163 to complete the power circuit and start the press opening movement. This condition continues until the block 130 opens the switch 125 when the press is partly open for unloading, whereupon the conditions of Fig. 15 are produced, switch 126 having been returned. A spring loaded button S<SP>1</SP> is then pushed by the operator to complete an opening circuit through lines 170, 164, 148, safety switch 147 and switch 126. The button S<SP>1</SP> causes the contactor 163 to operate the press to move the block 130 off the switch 125 to reestablish the press opening circuit, Fig. 20. The safety switch 147 is moved only in case of accident during closing to reverse the motor 2. During vulcanizing the press may be oscillated or "bumped" between an open and closed position in order to release gases given off by the material. When the press is closed. Figs. 17, 18 and a " bumuing switch 175 is closed, an opening circuit is provided through coil 162, lines 160, 164, and switches 175, 126 to line 150. A second circuit leads from line 149 through switch 125, line 165, switch 127, to line 164, which circuit will be established as soon as the contactor 163 is made by coil 162. As soon as switch 175 is closed, Fig. 18, coil 162 is energized and contactor 163 starts the motor 2 to open the press and complete the second circuit. Block 132 then moves to return the switch 126 to its open position, Fig. 19, and breaks the first circuit without affecting the second which permits the press to continue opening. When the block 133 strikes the switch 127 in the second circuit the switch moves to its Fig. 19 position, arresting the movement of the press. In Fig. 19 switch 127 connects to line 180, the plates of a spring biassed contactor 182 being held apart by coil 162 during the opening, but as soon as the opening circuit is broken a temporary circuit is set up through coil 152, line 180, switch 127, line 155, switch 109, and line 150. As soon as this circuit is established, coil 152 is energized to close the press. As the press closes block 133 will release switch 127 and break the closing circuit, but since the regular closing circuit has been re-established through contactor 154 the movement continues until the switch 126 is moved to remake the opening circuit. The press will thus oscillate during the time the switch 175 is closed, which time may be determined by the timer. A change-over switch 141 or a snap switch 184 may be used to byepass the timer if it is so desired. The timer, Figs. 13-14 (not shown), comprises an adjustable cam driven by the motor T, the cam operating a rocker arm to actuate the switch 175.