GB1160859A - Internal Resistance Heating Apparatus - Google Patents

Abstract

1,160,859. Control systems for electric heating apparatus. CHESTON CO. 16 May, 1968, No. 23386/68. Heading H2H. [Also in Division H5] A control circuit for an internal resistance heating apparatus has a main supply 98, 99 which supplies the primary 91 of a transformer through a saturable reactor 90, the secondary of the transformer being formed by a workpiece not shown, clamped between a pair of fixed electrodes 50, 51 and a pair of movable electrodes 52, 53. When a selector switch 102 is moved to the auto-position shown, a timer 109 is closed, completing an energizing circuit for relay coil 120 from supply terminal 104 through lines 118, 119, 121, stop switch 122, line 123, the normally closed contacts 124 of a timer 125, line 126, to supply terminal 95. Relay coil 120 closes contacts 114, 116 completing a holding circuit. Workpieces are carried on a movable platform which is moved by a solenoid valve 139 to position a workpiece on the fixed electrodes 50, 51. At the end of its positioning movement, limit switch 133 is changed over from the position shown to complete a circuit through the now closed contacts 141, 142 of relay 120 of a relay 144, and to de-energize solenoid valve 139 so that the movable platform returns to collect another workpiece. Relay 144 closes contacts 146, 147 completing the energizing circuit of a relay 148. Closure of the contacts 155, 156 of relay 120 energizes a relay 158 whereupon its contacts 160, 161 close completing an energizing circuit for solenoid valve 162 which moves the movable electrodes 52, 53 into clamping engagement with the workpiece. Energization of relay 148 closes contacts 166, 167 completing an energizing circuit for relay 101 which closes its contacts 100 to connect reactor 90 to supply 98, 99. Energization of relay 148 also closes contacts 182, 183 completing a circuit through contacts 179, 180, tapped coil 97 and rectifier 93 to a control coil 92 of the saturable reactor 90. Near the end of the heating period a timer 178 which is energized through contacts 174, 175 of relay 148 opens its contacts 179, 180 so that the rheostat 172 is inserted in series with control coil 92 and reduces the heating current. The heating operation is terminated when a timer 197 energized through contacts 193, 194 of relay 148 opens contacts 124, thereby de-energizing relay 120 and restoring the circuit to its initial position, whereupon timer 109 recloses to repeat the cycle. The operation in the manual position of the selector 102 is similar.