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Cathode Erosion due to Evaporation in Plasma Arc Cutting Systems

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Abstract

Erosion of a hafnium cathode in Plasma Arc Cutting torch using oxygen as plasma gas is considered. It is shown that approximately 0.001 fraction of the evaporated particles participate in a net erosion, the rest of the evaporated particles return back to the cathode after spending some time in a near-cathode plasma. Along with erosion rate, the suggested equations allow one to the calculate current density at the cathode, the cathode temperature inside the arc attachment and the electron temperature at the cathode-plasma boundary. Comparison of the obtained values with the available information on these parameters shows a reasonable agreement.

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Notes

  1. Variation of the ion fraction of the total current density do not change the results much.

  2. In our previous paper [5], we explained the observed erosion rate dependence on the swirling of the plasma gas by moving of the point of no return away from the cathode. There is another, also important factor: high swirling squeezes the arc attachment. This increases the current density and cathode temperature, thus, increasing the erosion rate.

  3. For example, if the arc attachment covers the most part of the insert surface, and the temperature of the emitter-holder boundary exceeds a certain limit (e.g. holder melting point), the thermal contact between the emitter and the holder deteriorates, cooling condition deteriorates as well, and this leads to a rapid insert erosion. Another explanation: loss of the thermal contact during switching arc on and off.

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  1. Keiser University, Fort Lauderdale, FL, USA

    Valerian Nemchinsky

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  1. Valerian Nemchinsky
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Correspondence to Valerian Nemchinsky.

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Nemchinsky, V. Cathode Erosion due to Evaporation in Plasma Arc Cutting Systems. Plasma Chem Plasma Process 33, 517–526 (2013). https://doi.org/10.1007/s11090-013-9440-1

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  • DOI: https://doi.org/10.1007/s11090-013-9440-1

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