Conditions of steady arc ignition in vacuum and hollow cathode operational life
Journal Title: Journal of Achievements in Materials and Manufacturing Engineering - Year 2016, Vol 79, Issue 1
Abstract
Purpose: The aim of this paper is to determine the conditions of steady arc ignition invacuum and the effect some of the main operating parameters have on the life of tantalumfoilhollow cathodes.Design/methodology/approach: The experiments presented in this paper have beencarried out with equipment for vacuum hollow cathode arc processing similar to whatis used in the industry. In order to find out if steady arc ignition is possible, a two-levelfactorial experiment has been conducted helping to establish the corresponding regressiondependency between the factors examined and the starting parameter values. The evaluationof hollow cathode operational life is based on three criteria: indirectly, considering their erosion[μ]; establishing possible damage on their surface which leads to plasma-forming gas leakageand makes the arc unsteady; taking into account the critical change in the cathode shape.Findings: It has been established that when a multi-stage arc torch is using the necessaryminimum amount of the plasma-forming gas for Ø 3.5-mm-diameter hollow cathodes isQAr=0/3 l/h, and, for Ø 6.0-mm-diameter hollow cathodes, it is QAr=2.4 l/h. It has beenestablished that the operational life of tantalum hollow cathodes can be and even exceed3 hours. Of all the parameters that have been studied, vacuum level has the most negativeeffect. It has been confirmed that tantalum-foil hollow cathodes are suitable mainly forcurrent intensity values of about 120 A.Practical implications: The results of the research allow: guaranteed hollow cathode arcignition regardless of its diameter at the working levels of plasma forming gas; the choiceof operating modes ensures the implementation of processes of varying lengths without theneed for premature replacement of the hollow cathode.Originality/value: This paper presents the results showing the conditions necessary forsteady arc ignition in vacuum with a hollow cathode of the following diameters: Ø 3.5 mmand Ø 6 mm. The effect of some of the main working parameters on the operational life ofhollow cathodes made of tantalum foil is also studied
Authors and Affiliations
N. V. Ferdinandov, D. D. Gospodinov
Keywords
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