GB572177A - Improvements in or relating to the control of electrical billet heating machines - Google Patents

Abstract

572,177. Control systems for resistance heating. ARON, H. Nov. 1; 1943, No. 18020. [Class 40 (iii)] [Also in Groups XI and XXXV] In heating billets 133 by passing current therethrough while held under pressure between anvil electrodes 57, 71 the potential applied is kept relatively low (insufficient to produce local overheating at the contact surface with the electrodes) until when the contact faces of the billet reach or approach softening point, the potential is increased to raise the temperature to the final temperature and the softened ends of the billet are compressed. The secondary 110 of a transformer is connected to the electrodes 57, 71, and connections 116 of the primary to the transformer are altered by electromagnetic switches 123, 131 to increase the secondary voltage during heating by a device 100 sensitive to temperature or heat radiation of the billet, by a hand-operated push-button 149, by a time-delay relay 181, or by a limit switch 157 operated by a cam-rod 151 on a movable electrode holder 70 when the ends of the billet are compressed. The transformer primary is connected at one end to current supply line 112 and has tappings 115 connected to contacts 116, which are connected by bridges 119, 120 (set by hand) to contacts 117, 118 connected through the switches 122, 131 to the other current supply lines 125, 127. Current from switch 122 passes through a switch 124 set by hand to current supply line 125 or to line 127, which is the neutral of a 3-phase supply. The control current for switches 123, 131, which are interlocked through contacts 164, 165, passes through lines 136 to a motor operating a pump driving a hydraulic ram moving the upper electrode 71, and has a branch line 140 connected to hand-operated push-button control box 142. Low-voltage current is started by push-button. 149 and is stopped by push-button 148. High-voltage is started by push-button 147 and is stopped by push-button 148, by limit switch 157 on final compression of the billet throughout or by the heat radiation-sensitive device 100 acting through relay 145. Alternatively low-voltage is stopped by limit switch 157. The heatsensitive device 100 may be set to stop the voltage at a higher temperature than normal to act as a safety device. In a modification, hydraulic pressure for driving the ram passes through a pipe 186 and spring-loaded valves 196, 197 to a piston 198 operating a switch 180 for starting the current arranged in place of the push-button box, in series with the limit switch 157, a two-way time switch 181 and the electromagnetic switches 123, 131. The time switch changes the current to the higher potential, which is such that heating of the billet is completed in normal time. Specifications 135,344, [Class 39 (iii)], 569,120, [Group XXII], and 569,996, [Group XI], are referred to.