Conditions of steady arc ignition in vacuum and hollow cathode operational life

摘要

Purpose: The aim of this paper is to determine the conditions of steady arc ignition in vacuum and the effect some of the main operating parameters have on the life of tantalum-foil hollow cathodes. Design/methodology/approach: The experiments presented in this paper have been carried out with equipment for vacuum hollow cathode arc processing similar to what is used in the industry. In order to find out if steady arc ignition is possible, a two-level factorial experiment has been conducted helping to establish the corresponding regression dependency between the factors examined and the starting parameter values. The evaluation of hollow cathode operational life is based on three criteria: indirectly, considering their erosion u; establishing possible damage on their surface which leads to plasma-forming gas leakage and 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 necessary minimum amount of the plasma-forming gas for φ 3.5-mm-diameter hollow cathodes is QAr=0/3 l/h, and, for 0 6.0-mm-diameter hollow cathodes, it is QAr=2.4 l/h. It has been established that the operational life of tantalum hollow cathodes can be and even exceed 3 hours. Of all the parameters that have been studied, vacuum level has the most negative effect. It has been confirmed that tantalum-foil hollow cathodes are suitable mainly for current intensity values of about 120 A.Practical implications: The results of the research allow: guaranteed hollow cathode arc ignition regardless of its diameter at the working levels of plasma forming gas; the choice of operating modes ensures the implementation of processes of varying lengths without the need for premature replacement of the hollow cathode.Originality/value: This paper presents the results showing the conditions necessary for steady arc ignition in vacuum with a hollow cathode of the following diameters: 0 3.5 mm and 0 6 mm. The effect of some of the main working parameters on the operational life of hollow cathodes made of tantalum foil is also studied