著者

山本 利雄 島田 弥

出版者

社団法人溶接学会

雑誌

溶接学会誌 (ISSN:00214787)

巻号頁・発行日

vol.39, no.11, pp.1171-1179, 1970-11-25

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Various penetration shapes formed in the plates of copper, aluminum, mild steel and stainless steel by the fixed TIG arc at reduced argon pressures are discussed in relation to the electrical and thermal characteristics of the arc mentioned in the previous reports, where the arc is formed between the 2% thoriated tungsten cathode of 4mm in diameter shaped like a pencil form and a directly or indirectly water cooled anode plate under the following conditions. Gas Pressure : 18 to 760mmHg Arc Current : 250,400,450A Arc Length (Distance between Electrodes) : 4,9,15,25mm The facts elucidated are as follows (1) At reduced gas pressure, "cathode zone" (a bright spherical zone) is observed at the neighborhood of the cathode. When the cathode zone touches the anode specimen, the contact zone on the anode surface melts rapidly and a large "conduction type penetration" is formed in the specimen. Then the cathode zone is presumed to have a higher energy density compared to the arc column. (2) In the specimen of low thermal conductivity, the "peripheral type penetration" is formed due to the convectional flow in the molten pool when the energy density of the arc is considerably high. It happens sometimes that the depth of the conduction type penetration formed at small current is deeper than that of the peripheral type penetration of larger current. (3) At higher pressure the molten pool beneath the arc depresses and the "finger type penetration" is formed in this case. For directly water cooled specimen, the shape of the molten pool is conserved down to room temperature and a hollow part is often formed when the arc length is sufficiently long. At the bottom of the hollow part a solid surface is exposed and no solidified layer is observed on it. (4) The penetration in low thermal conducters such as mild steel and stainless steel varies from the "conduction type" to the "peripheral type" and further to the combined type of "peripheral type" and "finger type", with an increase in the energy density and the plasma stream at the specimen surface. For high thermal conductors like copper and aluminum, the "conduction type" is easily formed by the thermal conduction mechanism. Although the "finger type" is likely to appear when the arc energy density is considerably high, no "peripheral type" penetration is observed.