Patent GB-426238-A (GB)
Title: Electric testing apparatus for the verification of the quality of welds
IPC: G01N27/20
Filed: 1934-06-21
Abstract: 426,238. Detecting faults ; hand contact-appliances. SCIAKY, D., 13, Rue Charles-Fourier, Paris. June 21, 1934, No. 18382. Convention date, June 27, 1933. [Classes 37 and 38 (i)] An apparatus for testing sheet metal welds comprises main current electrodes and auxiliary potential electrodes, the main electrodes being movable relatively to one another, but maintained in axial alignment so that the current passes perpendicularly to the faces of the metal sheets when the electrodes are applied to opposite sides of the sheets, the potential electrodes being likewise applied to opposite sides of the sheets, each at a constant distance from the respective main electrode. Parts 1, 2, Fig. 1, connected by a weld 3 are traversed transversely by current from a source 4 passing between main electrodes 5, 6. A galvanometer 11, in series or shunt with a variable resistance 15, is connected to potential electrodes 13, 14 separated from the main electrodes 5, 6 by a fixed distance. If the weld is of good quality, substantially the whole of the main current passes directly between the electrodes 5, 6, otherwise a certain portion is shunted and sets up a potential difference between the electrodes 13, 14. In a modification a battery or other current source is arranged in series or shunt to the galvanometer 11 so that its electromotive force opposes that between the electrodes 13, 14, the whole being regulated so that the galvanometer gives a zero reading when the weld is good. Fig. 3 shows a constructional form of the apparatus. Tongs or clamping means 17 carry the electrodes 5, 6, of which the former is fixed and the latter is carried by, but insulated from, a slide 18 movable by a lever 19. The electrodes 5, 6 are normally maintained apart by means of a spring 23. The electrodes 5, 6 are mounted to move in sockets 26, Fig. 4, a spring 27 being situated between the electrode and the base 28 of the socket. In each electrode is a channel 29 carrying the corresponding potential electrode 14, which is separated from a brass sleeve 30 by an insulating tube. The potential electrode is connected to the galvanometer circuit through a brass button 32. A screw 33 engaging a recess 34 limits the motion of the electrodes. In a modification, each potential electrode is concentric with its corresponding main electrode. Instead of the contacts being mounted on tongs, they may be attached to the arms of a welding machine, e.g. at the side of the welding electrodes, so as to come into operation as soon as a weld is made. For testing an end weld, the main electrodes 5, 6 may be arranged on one of the welded parts and the potential electrodes 13, 14 on the other part. In this case with a weld of good quality, the galvanometer gives a larger deflection than with a weld of bad quality. Several auxiliary electrodes may be employed, so that several voltages can be ascertained simultaneously. The tongs may carry a punch by means of which the operator marks bad welds, the number of which may be registered by a totalizer. The difference of potential between the potential electrodes may be measured by potentiometric methods employing a Wheatstone bridge &c. Alternating current may be supplied to the main electrodes 5, 6, the galvanometer being connected to the potential electrodes through a transformer and copper oxide or other rectifier.