Surface temperature measurements for tungsten-based cathodes of high-current free-burning arcs

Haidar, J; Farmer, A. J. D.

doi:10.1088/0022-3727/28/10/014

Cited by 90 publications

(71 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, it is expected to be below the current density range of GTA. It was checked in [26] that for the GTA test cases investigated experimentally in [29,30] with a W-2%wt ThO 2 cathode, secondary emission is negligible compared to electron emission, so that assumption (A2) is satisfied. It should be noticed that, for computational purposes, secondary electron emission might however be convenient to consider.…”

Section: Cathode-modelling Assumptionsmentioning

confidence: 99%

“…3 and 4. Figure 3 compares the calculated cathode surface temperature with the experimental measurements of Haidar and Farmer [30]. At the tip end (located at distance zero in Fig.…”

mentioning

confidence: 94%

“…The electrode to workpiece distance was 5 mm. This test case, which is described in further details in Appendix B, was retained since measurements of both the cathode surface temperature and the electron temperature in the arc were available [29,30], while temperature prediction was the weakness of the modelling approach. Calculation results are plotted in Figs.…”

mentioning

confidence: 99%

See 2 more Smart Citations

Gas tungsten arc models including the physics of the cathode layer: remaining issues

Choquet

2017

Weld World

View full text Add to dashboard Cite

A recent review pointed out that the existing models for gas tungsten arc coupling the electrode (a cathode) and the plasma are not yet complete enough. Their strength is to predict with good accuracy either the electric potential or the temperature field in the region delimited by the electrode and the workpiece. Their weakness is their poor ability to predict with good accuracy these two fields at once. However, both of these fields are important since they govern the heat flux to the workpiece through current density and temperature gradient. New developments have been made since then. They mainly concern the approaches addressing the electrode sheath (or space charge layer) that suffered from an underestimation of the arc temperature. These new developments are summarized and discussed, the modelling assumptions are examined, and important modelling issues that remain unexplored are underlined.

show abstract

Section: Cathode-modelling Assumptionsmentioning

confidence: 99%

“…3 and 4. Figure 3 compares the calculated cathode surface temperature with the experimental measurements of Haidar and Farmer [30]. At the tip end (located at distance zero in Fig.…”

mentioning

confidence: 94%

mentioning

confidence: 99%

See 1 more Smart Citation

Gas tungsten arc models including the physics of the cathode layer: remaining issues

Choquet

2017

Weld World

View full text Add to dashboard Cite

show abstract

“…Our goal in the present paper is to investigate the behaviour of these cathodes over a wide range of arc current intensities. Thoriated tungsten cathodes have been experimentally studied by different authors [1][2][3][4][5][6][7][8][9][10][11], but in most of the studies, the cathodes were operated with only a few current intensities; therefore, the dependences of the cathode parameters on the arc current intensity I were not found.In the present paper, we discuss our experimental investigation of thoriated tungsten cathodes operating in the actual working conditions of an industrial plasma torch. We used arc current intensities ranging from 30 A to 200 A, which allows the investigation of cathode…”

mentioning

confidence: 99%

An experimental study of thoriated tungsten cathodes operating at different current intensities in an atmospheric-pressure plasma torch

Sillero¹,

Ortega²,

Munoz-Serrano³

et al. 2010

J. Phys. D: Appl. Phys.

View full text Add to dashboard Cite

Abstract.Thoriated tungsten cathodes operating in an open-air plasma torch at current intensities between 30 and 200 A were experimentally studied. The morphology and composition of the cathode tip after arcing were investigated by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Three relevant zones were found on the cathode tip (spot zone, thorium-depleted zone and thorium-enriched zone), and their dimensions were measured. For each current intensity, the spot temperature T during arcing was measured by one-colour pyrometry, and the spot current density was determined. Exponential growth was seen for the current density as the spot temperature increased. From the experimental data and the energy balance in the presheath, the dependence of the cathode effective work function ϕ on the arc current intensity and its dependence on T were determined. It was found that ϕ increased from ϕ = 2.64 eV when T 2900 K to ϕ = 3.06 eV when T 3700 K. These values are consistent with the presence in the spot of a layer of thorium atoms on the tungsten matrix during arcing. The atomic surface density of the layer determines the value of ϕ. IntroductionThe investigation of cathodes is important in order to improve the performance of plasma torches due to the essential role of cathodes as electron emitters and the severe erosion of cathodes caused by the high temperatures attained on the cathode surface. Binary cathodes, formed by a tungsten matrix doped with rare-earth oxides, are of particular interest, as they combine the refractory properties of tungsten with the good electron emission characteristics of the dopant. The processes that take place in such cathodes during arcing are complex due to the interaction between the dopant and the tungsten matrix and between both the dopant and the tungsten with the plasma arc. In spite of the progress achieved in the understanding of binary cathodes, there are still fundamental aspects that are not well understood and require further experimental investigation. For instance, the dependence of the cathode work function on the spot temperature has not yet been satisfactorily established.Tungsten cathodes doped with thoria are commonly used in industrial applications of plasma torches. Our goal in the present paper is to investigate the behaviour of these cathodes over a wide range of arc current intensities. Thoriated tungsten cathodes have been experimentally studied by different authors [1][2][3][4][5][6][7][8][9][10][11], but in most of the studies, the cathodes were operated with only a few current intensities; therefore, the dependences of the cathode parameters on the arc current intensity I were not found.In the present paper, we discuss our experimental investigation of thoriated tungsten cathodes operating in the actual working conditions of an industrial plasma torch. We used arc current intensities ranging from 30 A to 200 A, which allows the investigation of cathode

show abstract

“…It is important to clarify the thorium atom behavior in the cathode and that at the surface for the cathode lifetime evaluation. 24,25) Here the cathode lifetime is evaluated by coupling with plasma thermofluid characteristics as calculated previously. In order to derive the governing equations, the following assumptions are introduced.…”

Section: Numerical Conditions and Proceduresmentioning

confidence: 99%

Performance Evaluation of Arc-Electrodes Systems for High Temperature Materials Processing by Computational Simulation

2003

View full text Add to dashboard Cite

Thermofluid analysis of an arc flow and the evaluation of the cathode lifetime have been conducted by a computational simulation for the performance improvement of arc-electrodes systems. The effects of arc current, electrode gap, inlet gas flow rate and cathode vertex angle on the temperature and velocity fields of an arc flow are clarified by parametric computations to optimize the operating conditions and torch geometry. The temperature field by an arc flow model shows the quantitative agreement with the available experimental data in the local thermodynamic equilibrium (LTE) region. The cathode lifetime is evaluated successfully by coupling with the computated thermofluid field of an arc flow. The effects of different operating conditions on the cathode lifetime are also discussed for longer lifetime of the arc-electrodes systems.KEY WORDS: computational simulation; arc; electrode; interaction; lifetime evaluation.Under these assumptions, the governing equations for arc and electrodes regions are presented as follows: The radiation loss Ra from arc is given by the multipleterms approximation as a function of plasma temperature from the experimental data for argon.2) inside the electrode ... (5) Heat flux between arc and cathode, anode are respectively given by neglecting space charge effects 13,14) in the very thin sheath and both electrodes evaporation for simplicity 15) ........ (6) ... (7) where the emission current density j e is given by the Richardson-Dushman equationion current j i is given as follows: Boundary ConditionsIn the previous almost studies, temperature distribution on the electrode surface and the current density at the cathode spot are given in assumptions. [4][5][6][7][8][9] In the present study, the temperature and electric potential conditions are given only at the cooled surfaces of anode and cathode, represented as lines CЈDЈ, FA, in Fig. 1 without assuming the current density and temperature at the electrodes surface, represented as lines CD, FG, GB 11) and neglecting sheath boundary Vol. 43 (2003) conditions for the reduction in computation time. 15,17) Because calculated arc temperature and cathode surface temperature are relatively insensitive to those detailed properties of the sheath. Table 1 shows the discharge configuration and operating conditions referring to Gas Tungsten Arc (GTA) plasma facility. Numerical Conditions and Procedures19) A cylindrical thoriated tungsten cathode (Wϩ 2wt%Th) and a plate copper anode are investigated for lifetime evaluation in the present study. The roots of both electrodes are cooled fixedly at 300 K. The thermofluid field is solved by Semi-Implicit-Method for Pressure Linked Equation (SIMPLE) 20) method using Tri Diagonal-Matrix Algorithm (TDMA). The electromagnetic field is solved by Gauss-Seidel method. Here, the grid has 75ϫ102 meshes in the axial and radial directions, respectively. The thermodynamic and transport properties of argon 21,22) and tungsten and copper 23) are given as a function of temperature. Figure 2 shows a schematic i...

show abstract

Surface temperature measurements for tungsten-based cathodes of high-current free-burning arcs

Cited by 90 publications

References 7 publications

Gas tungsten arc models including the physics of the cathode layer: remaining issues

Gas tungsten arc models including the physics of the cathode layer: remaining issues

An experimental study of thoriated tungsten cathodes operating at different current intensities in an atmospheric-pressure plasma torch

Performance Evaluation of Arc-Electrodes Systems for High Temperature Materials Processing by Computational Simulation

Contact Info

Product

Resources

About