Cyclic erosion of a cathode in high-pressure arcs

Nemchinsky, Valerian

doi:10.1088/0022-3727/36/13/322

Cited by 23 publications

(19 citation statements)

References 6 publications

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“…The erosion rates for pure argon were significantly higher than those for pure helium, where 13.5 µg C −1 is obtained for argon and 1 µg C −1 for helium. Nemchinsky [10] tested the hafnium cathode with different working gases: oxygen, nitrogen and noble gases (argon, helium and hydrogen-argon mixture). In this study the erosion in noble gases was higher than that in other gases, where non-noble gases created chemical compounds with hafnium to form a protective layer.…”

Section: Introductionmentioning

confidence: 99%

Experimental study on copper cathode erosion rate and rotational velocity of magnetically driven arcs in a well-type cathode non-transferred plasma torch operating in air

Chau

Hsu

Lin

et al. 2007

J. Phys. D: Appl. Phys.

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The cathode erosion rate, arc root velocity and output power of a well-type cathode (WTC), non-transferred plasma torch operating in air are studied experimentally in this paper. An external solenoid to generate a magnetically driven arc and a circular swirler to produce a vortex flow structure are equipped in the studied torch system, which is designed to reduce the erosion rate at the cathode. A least square technique is applied to correlate the system parameters, i.e. current, axial magnetic field and mass flow rate, with the cathode erosion rate, arc root velocity and system power output. In the studied WTC torch system, the cathode erosion has a major thermal erosion component and a minor component due to the ion-bombardment effect. The cathode erosion increases with the increase of current due to the enhancement in both Joule heating and ion bombardment. The axial magnetic field can significantly reduce the cathode erosion by reducing the thermal loading of cathode materials at the arc root and improving the heat transfer to gas near the cathode. But, the rise in the mass flow rate leads to the deterioration of erosion, since the ion-bombardment effect prevails over the convective cooling at the cathode. The most dominant system parameter to influence the arc root velocity is the axial magnetic field, which is mainly contributed to the magnetic force driving the arc. The growth in current has a negative impact on increasing the arc root velocity, because the friction force acting at the spot due to a severe molten condition becomes the dominant component counteracting the magnetic force. The mass flow rate also suppresses the arc root velocity, as a result of which the arc root moves in the direction against that of the swirled working gas. All system parameters such as current, magnetic field and gas flow rate increase with the increase in the torch output power. The experimental evidences suggest that the axial magnetic field is the most important parameter to operate the straight-polarity WTC plasma torch at high output power with a limited cathode erosion rate. This emphasizes the importance of an external magnetic field on a WTC torch system for reducing the erosion at the cathode.

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Section: Introductionmentioning

confidence: 99%

Experimental study on copper cathode erosion rate and rotational velocity of magnetically driven arcs in a well-type cathode non-transferred plasma torch operating in air

Chau

Hsu

Lin

et al. 2007

J. Phys. D: Appl. Phys.

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“…This enhanced axial gas flow sweeps the evaporated particles away from the cathode and thus increases the net evaporation rate. Another experimental result indicated the importance of the flow pattern close to the cathode [1,10]: The erosion rate decreases with time for long arc duration tests, because there exists a stagnation zone inside the crater of the cathode insert. The probability of the evaporated atom/ion returning to the cathode is increased by the slowing down of the gas flow near the cathode and thus decreases the net erosion rate.…”

Section: Introductionmentioning

confidence: 99%

Numerical investigation of the effect of cathode holder shape on hafnium cathode evaporation for an oxygen plasma cutting arc

Long¹,

Tanaka²,

Uesugi³

et al. 2013

J. Phys. D: Appl. Phys.

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The effects of the cathode holder shape on a plasma cutting arc were investigated using a two dimensional thermo-fluid model developed for arc plasmas with the consideration of the hafnium cathode evaporation. The shape of the cathode holder shape was defined a convex structure which protrudes from the surface of the cathode holder. Results showed that the vortex of gas flow near the hafnium cathode was created by the effect of the convex cathode holder. The temperature of the cathode surface decreased markedly with the higher protrusion of the convex cathode holder by a rapid clockwise rotation of gas flow. The presence of gas flow vortex toward to the cathode surface reduces the mass fraction of hafnium vapor near the surface cathode. Finally, the total amount of mass loss of the hafnium evaporation was predicted to decrease markedly with the effect of the convex cathode holder.

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“…The effects of arc current, pressure, shielding gas flow, and cathode geometry on hafnium erosion were reported. [10][11][12] Hafnium cathode erosion is attributed to the ejection of small liquid metal droplets. 13) The optimization of the initial cathode shape to minimize cathode erosion was attempted.…”

Section: Introductionmentioning

confidence: 99%

Effect of arc current on droplet ejection from tungsten-based electrode in multiphase AC arc

Hashizume

Tanaka

Watanabe

2017

Jpn. J. Appl. Phys.

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The dynamic behavior of droplet ejection from a tungsten electrode was successfully visualized using a high-speed camera and an appropriate band-pass filter. The effect of arc current on droplet ejection was investigated to understand the electrode erosion mechanism in the multiphase AC arc. The rate of erosion by droplet ejection increased with increasing current. This result was examined on the basis of the time variation in forces on a pending droplet at the electrode tip during the AC cycle. The relationship among electromagnetic force, surface tension, and ion pressure on the molten tip during the cathodic period is crucial for controling droplet ejection. The molten tip becomes hemispherical forming the pending droplet with an increase in the instantaneous value of arc current during the AC cycle. The pending droplet detaches from the electrode surface when electromagnetic force becomes the dominant force. Consequently, a higher rate of erosion by droplet ejection with a higher arc current resulted from a stronger electromagnetic force.

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Cyclic erosion of a cathode in high-pressure arcs

Cited by 23 publications

References 6 publications

Experimental study on copper cathode erosion rate and rotational velocity of magnetically driven arcs in a well-type cathode non-transferred plasma torch operating in air

Experimental study on copper cathode erosion rate and rotational velocity of magnetically driven arcs in a well-type cathode non-transferred plasma torch operating in air

Numerical investigation of the effect of cathode holder shape on hafnium cathode evaporation for an oxygen plasma cutting arc

Effect of arc current on droplet ejection from tungsten-based electrode in multiphase AC arc

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