Numerical analysis of plasma characteristics of constricted and free-burning arc with a refractory cathode

Abstract

Self-consistent mathematical model of the processes of energy-, mass-and electric transfer in the column and anode region of the electric arc with refractory cathode was used as a basis to perform numerical analysis of thermal, electromagnetic and gas-dynamic characteristics of arc plasma for constricted (plasma) and free-burning argon arc with copper water-cooled anode. Results of calculation of characteristics of arc column plasma show that distributions of electric current density, temperature and velocity of constricted arc plasma can greatly differ from the respective distributions for free-burning arc, depending on arc current, plasmatron nozzle channel diameter and plasma gas flow rate. Characteristics of near-anode layer of plasma arc also differ significantly from the respective characteristics of free-burning arc, depending on the above arcing mode parameters. Thus, by varying arc current, plasmatron nozzle channel diameter and plasma gas flow rate, it is possible to effectively control the characteristics of thermal, electromagnetic and, particularly, dynamic impact of the constricted arc on anode metal surface. 13 Ref., 1 Table, 10 Figures. K e y w o r d s : constricted (plasma) arc, free-burning arc, refractory cathode, water-cooled anode, arc column, anode region, arc plasma characteristics, mathematical modelingApplication of a constricted (plasma) arc instead of free-burning one is one of the methods to improve the effectiveness of electric arc impact on metals, and, consequently, to increase the penetration depth and nonconsumable electrode welding speed. Limitation of transverse dimensions of the column of an arc with refractory cathode by the wall of plasmatron nozzle channel can lead to an essential increase of the density of electric current and heat flow, applied by the arc to the metal being welded, and variation of plasma gas flow rate enables varying in a broad range the dynamic impact of arc plasma flow on weld pool surface. Effective practical application of plasma arc as welding heat source requires having valid information on distributed characteristics of constricted arc plasma, as well as characteristics of its thermal, electromagnetic and gas-dynamic impact on the metal being welded. As experimental determination of such, important in practical terms, plasma arc characteristics as distribution of electric current density, heat flow and gas-dynamic pressure of plasma over the weld pool surface is difficult, because of high values of arc plasma temperature and temperature of the above-mentioned surface, smallness of geometrical dimensions of the arc anode region and a number of other factors, studying the plasma arc by mathematical modeling methods seems highly relevant (see, for instance, [1][2][3][4][5][6]). Therefore, the objective of this work is detailed numerical analysis of distributed characteristics of plasma column and anode region of the constricted arc, depending on its arcing mode, as well as their comparison with the respective characteristics for a free-burning arc.Le...