GB558506A - Improvements relating to electric flash welding - Google Patents

Abstract

558,506. Annealing. SINCLAIR, J. M., and YOUNG, W. F. Sept. 21, 1942, No: 13292. [Class 72] [Also in Groups XXII and XXXV] In treating articles in a flash welding machine the article after welding and while still in the welding clamps and after cooling to a temperature below welding temperature is again submitted to the passage of a current so as to maintain it for a time at the lower temperature. This may be effected by using a post-heating current of lower voltage than the welding current. Change in structure of alloy steels due to blast welding is thus avoided. The welding contactor 16, which connects the supply to one of the tappings 18 of primary of the welding transformer is closed by a winding 36 energized when the main switch 54 is closed in a circuit containing a normally closed switch 34. The contactor is mechanically connected to a switch 22 which is opened when the contactor is closed, and tends to close when the contactor opens, the closing being delayed by a dash pot 24. The switch 22 when closed completes a circuit which causes the normally open relay 46 of a timing device to be closed. This circuit also includes a switch 32 which is closed by an adjustable cam 28 on the bar 26 connected to the movable welding head. Just before butting of the parts occurs the switch 32 is closed and when butting takes place the switch 34 is opened by an adjustable cam 30 so as to de-energize the winding 36 and open contactor 16 to cut out the welding current. Adjacent to the work is a photo-sensitive unit 38 responsive to the radiation from the work and connected to the control panel 40 within which is a relay 42 which is closed when the intensity of radiation after cutting out the welding current diminishes to a certain point. A circuit is thus completed through a winding 48, relay 42. relay 46. switch 54 and thus contactor 50 is closed to connect the primary of the transformer via tapping 52 and thus to effect heating of the work with a current at a lower secondary voltage than that employed during welding. The work heats up till the device 38 causes relay 42 to open again and thus re-open the contactor 50 and the cycle of operations is then repeated until the relay 46 opens to break the heating circuit finally. After removal of the work the main switch 54 is then opened to reset the part of the machine. The photo-sensitive device may be replaced by a thermo-couple or other pyrometer. The change of volltage may be effected manually.