Untitled

Abstract

In order to make clear the physical grounds of deviations from local thermodynamic equilibrium (LTE) in atmospheric free-burning argon arcs, the heavy particle temperature, electron temperature and LTE temperature obtained from electron number density were measured by use of line-profile analysis of the laser scattering method without an assumption of LTE. The experimental results showed that the core region of the arc significantly deviated from LTE under both conditions of 50 and 150 A in arc current. As a result, it is suggested that the deviations from LTE in the arc core should be affected strongly by the cathode jet and that aspects of the anode heat transfer were greatly changed by the plasma state in the arc core.

Effect of Anode Heat Transfer on Melted Penetration in Welding Process by Free-burning Argon Arc.

“…[1][2][3] Thus, understanding the relation among the temperatures of the arc plasma, the distributions of current and heat input on the anode, and the results is quite important for the materials processing by the free-burning arcs. However, experimental and theoretical investigations of the temperature of arc plasma, [3][4][5][6][7][8][9] the distributions of current and heat input, 10,11) and results, for example, the weld penetration [12][13][14][15][16] were separately conducted and the relation among them has not been made clear. For example, Nestor 10) measured the distributions of current and heat input on the anode of freeburning arc by using the water-cooled copper anode which consists of two separate blocks.…”

Number Density Distributions of Metal Vapor in Helium Gas Tungsten Arcs

“…Because it is expected that this region consists of metal vapor and information about the concentration of metal vapor is nothing. Fortunately, Tanaka and Ushio [11] found that LTE temperature was in accordance with the electron temperature in the region close to the anode. On the other hand, as showed in Fig.…”

“…The theory of Thomson scattering is explicated by many literatures [7][8][9][10][11]13]. Figure 2 shows the comparison between electron temperature for the pure helium arc with the water-cooled copper anode (left side) and that for the helium arc during welding (right side) under the same condition of 150 A in arc current and 5 mm in arc length.…”

“…Measured scattering signal was the integration of signals for 500 laser pulses. Other details of experimental set up for Thomson scattering is referred to our previous paper [11]. Helium GTA plasma was established between a tungsten cathode with 2% La 2 O 3 (diameter 3.2 mm with tip angle 60°) and stainless steel SUS304.…”

“…Bentley [9] and Murphy [10] also showed deviation from LTE in GTA plasma. Furthermore, Tanaka and Ushio [11] showed non-LTE state in argon GTA and insisted that the non-LTE state in GTA was caused due to the cathode jet induced by arc constriction at the tungsten electrode. In the case of metal contaminated arc, non-LTE result is also expected.…”