GB1512850A - Method of and apparatus for monitoring an arc atmosphere - Google Patents

Abstract

1512850 Automatic control of concentration OSAKA DENKI CO Ltd 29 Dec 1975 [28 Dec 1974(4)] 53054/75 Heading G3R [Also in Divisions B3 and G1] In gas-shielded (with e.g. A, He) arc welding, particularly non-consumable (with filler wire) or, as shown, consumable electrode arc welding, the extent of the shielding function of the arc zone atmosphere is determined by measuring the proportion of nitrogen oxide in said atmosphere. The arc zone atmosphere may be influenced by gas nozzle spatter build up, gas nozzle/workpiece distance and angle, and workpiece shape and disposition, and by variation of gas flow. As shown, shielding gas is fed to the arc zone via a pipe 19, a gas flow adjuster 92 and a nozzle 18. The arc zone atmosphere is collected via a nozzle 27 by a pump 29 and supplied to a nitrogen oxide measuring device 23. In the latter, arc zone atmosphere is reacted, under reduced pressure, at 32 with ozone, from a generator 33, and a photo-electric device 34 detects, by way of an optical filter and multiplier, an infrared ray, radiated with a light emitting intensity proportional to mass flow-rate of NO, to provide an electric output signal which, amplified at 35, is fed to a differential amplifier 91, to be compared with a reference signal which may be set to represent the desired proportion of nitrogen oxide. The output from the differential amplifier may operate an alarm (e.g. buzzer) and may stop the welding power and wire feed device, and automatically controls the shielding gas flow adjuster 92 (e.g. valve). In Fig.9 (not shown), the arrangement is similar to that of Fig.8 but the measuring device output signal is fed to a differential amplifier the output of which acts to vary fume extraction flow, as by varying suction pump rotational speed. The above nitrogen oxide measuring device may be replaced by devices based on NO analysis methods including infrared ray gas analysis and ultraviolet light absorption comparison; NO 2 -proportion measuring methods including methods suitable for NO and constant potential electrolysis, NO + NO 2 analysis methods including naphthylethyldiamine (absorptiometric), constant potential electrolysis, ozone oxide heat analysis and oxygen oxidation; and total-nitrogen analysis methods including phenoldisulphonic acid (absorptiometric) and ozone oxidation-ion electrode.