著者

西口 公之 松繩 朗 北田 豊文

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.1, pp.55-63, 1970-01-25

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As stated in the previous paper, there found two kinds of the cathode modes, i. e. the cold and hot cathode modes, in a low pressure arc generated between the graphite electrodes. Consumption of a graphite cathode was quite different in each cathode mode. For example, a carbon vapour stream and spattering from the cathode root were ovserved in the cold cathode mode, while no vapour stream nor spattering was seen in the hot one. The consumption characteristics of a graphite cathode and the corelation to the cathode mode were investigated to clarify the cathode mechanism. Experiments were conducted on an arc with a graphite cathode and a water cooled copper anode under the condition of the current range being 10-120Amp and of the pressure 10-100 Torr of hydrogen and 10-60 Torr of helium and argon. Results obtained in this study are as follows. (1) In addition to the cold and hot cathode modes, a new mode which was termed the plasma cathode mode was distinguished in a C(-)-Cu(+) arc at low pressure, regardless of the kinds of gas. This mode which was featured by a bright sphere in front of the cathode tip (cathode plasma ball) appeared as an intermediate stage of the cold and hot cathode modes. The existence of the plasma cathode mode was clearly recognized in the consumption characteristics of a graphite cathode but hardly detected in the electric characteristics of an arc. (2) A cathode plasma ball expaoded its size with the increase of current or the reduction of pressure. In the plasma cathode mode, it was clearly separated from the arc column by a dark space. When the dark space became undetectable, the hot cathode mode emerged. (3) Under the condition of this experiment, specific consumption rate m_C/I (mg/A min) of a graphite cathode ith the cold cathode mode was as hifih as five times or compared with so the one in the hot cathode. Meanwhile, in the plasma cathode mode, m_C/I was a little higher than that in the hot one. In the cold cathode mode, more than 90% of the consumption was the sublimation of carbon at the cathode root, and the spattering loss was less than 10%. (4) In the cold cathode mode, carbon rather than the ambient gas might be preferentially ionized in the cathode fall region. (5) The transition of the cathode mode was determined by the systematic study of the consumption characteristics of a graphite cathode. In this study, three governing factors of the cathode mode (p, I & V_i), which were mentioned in the previous paper, were clearly proved.

著者

岡田 実 西口 公之 丸尾 大 谷 隆之

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.36, no.1, pp.44-52, 1967-01-25

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An excellent dense and oxide free coating of Ni-Cr-B-Si alloy was obtained by the shielded plasma spraying method as shown in the previous report. The present report describes certain effects of spraying conditions, such as spraying atmosphere and preheating of substrate surface, on the quality of coating. And the application of shield nozzle and its effect are also investigated in details. Usually, plasma spraying of Ni-Cr-B-Si alloy in the air makes a porous and oxide inclusive deposit, even with use of pure argon plasma jet. It may be seen that some of these defects were caused by the oxidation of droplets in spraying. Air contamination into the plasma flame up to 90% was detected in the quantitative gas analysis of plasma flame at a distance of 90mm from the torch. Spraying in argon atmosphere gave a somewhat better coated layer compared with the spraying in the air, but is far from being perfect. These results suggest that the protection of particle and substrate from oxidation is necessary but is insufficient for obtaining perfect coating. Furthermore, thermal problems in a process should be considered at the same time. As the result of atmospheric, thermal and kinetic considerations in the processes, shield spraying method has been proposed. In the shielded spraying of this alloy, the preheating of substrate has great effect on the bond between the coated layer and the substrate. For the specimen which is shield-sprayed without any preheating, a little amount of porosity was observed at the boundary. But almost perfeet metallurgical bonding is accomplished with local preheating (300℃) of substrate surface. As for the application of shield nozzle, a series of experiments were carried out to analize the effect of nozzle. Results as follows; (1) Spraying atmosphere is kept perfectly inert. (2) Shield nozzle has an effect of raising the heat transfer from the plasma flame to the particles and substrate, since the contamination of cold gas is completely shout off. (3) Application of shield nozzle makes it easy to preheat the substrate surface with a high effluent of heat flux. (4) Temperature and velocity of particle rise as a result of increase of thermal efficiency and velocity of plasma flame.

著者

岡田 実 西口 公之 丸尾 大 谷 隆之

出版者

JAPAN WELDING SOCIETY

雑誌

溶接学会誌 (ISSN:00214787)

巻号頁・発行日

vol.36, no.1, pp.44-52, 1967

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An excellent dense and oxide free coating of Ni-Cr-B-Si alloy was obtained by the shielded plasma spraying method as shown in the previous report. The present report describes certain effects of spraying conditions, such as spraying atmosphere and preheating of substrate surface, on the quality of coating. And the application of shield nozzle and its effect are also investigated in details.<BR>Usually, plasma spraying of Ni-Cr-B-Si alloy in the air makes a porous and oxide inclusive deposit, even with use of pure argon plasma jet. It may be seen that some of these defects were caused by the oxidation of droplets in spraying. Air contamination into the plasma flame up to 90% was detected in the quantitative gas analysis of plasma flame at a distance of 90 mm from the torch.<BR>Spraying in argon atmosphere gave a somewhat better coated layer compared with the spraying in the air, but is far from being perfect. These results suggest that the protection of particle and substrate from oxidation is necessary but is insufficient for obtaining perfect coating. Furthermore, thermal problems in a process should be considered at the same time. As the result of atmospheric, thermal and kinetic considerations in the processes, shield spraying method has been proposed.<BR>In the shielded spraying of this alloy, the preheating of substrate has great effect on the bond between the coated layer and the substrate. For the specimen which is shield-sprayed without any preheating, a little amount of porosity was observed at the boundary. But almost perfect metallurgical bonding is accomplished with local preheating (300°C) of substrate surface.<BR>As for the application of shield nozzle, a series of experiments were carried out to analize the effect of nozzle. Results as follows;<BR>(1) Spraying atmosphere is kept perfectly inert.<BR>(2) Shield nozzle has an effect of raising the heat transfer from the plasma flame to the particles and substrate, since the contamination of cold gas is completely shout off.<BR>(3) Application of shield nozzle makes it easy to preheat the substrate surface with a high effluent of heat flux.<BR>(4) Temperature and velocity of particle rise as a result of increase of thermal efficiency and velocity of plasma flame.