gy fluxes (laser radiation, low-temperature plasma flows, and electron-beam technology). Plasma cutting and welding with electric-arc plasmatrons are applied extensively. We shall explore the possibility of using high-temperature jets for case hardening of parts as an alternative to laser or electric-arc treatment with lower equipment costs, smaller size, and a simple treatment process. Problems: • the plasma flow must be focused to obtain a power density of the order of 10–10 W·m, which ensures ultrafast hardening in the solid phase or from the liquid state. The plasma flow may be squeezed by an exit nozzle, but in that case the thermal stability of the nozzle will be severely limited; • the short lifetime of the plasmatron cathodes, which is less than several hours of continuous operation. The cathode erosion is known to depend exponentially on the arc discharge current. This is why it is preferred to have operating conditions in which the Joule heating power IU is attained at high charging voltages U and low arc current I, i.e., electric-field strength E = dν /dz. These problems can be solved by using a special plasmatron design with cathode and anode separated by an interelectrode insert (Fig. 1) of a porous electric insulating material through the walls of which a plasma-forming gas is blown at a rate m [1]. An alternating strong gas flow, acting on the entire arc discharge column can be assumed to cause insulation of the column walls from the walls of the channel and the nozzle and squeezing, i.e., gasdynamic focusing. Moreover, the use of an interelectrode insert to fix the arc length by and the gasdynamic effect on the arc discharge, i.e., turbulization and cooling of the flow increase the electric field strength. That means the plasmatron can operate in a high-voltage mode that ensures a long cathode life. Let us consider the mathematical model and the results of numerical simulation of the operating process in the plasmatron channel when there is a strong blast of plasma-forming gas through the porous wall. In [1], we demonstrated experimentally that the use of a strong blast, when the bulk of the gas flow rate is through the porous wall and the axial gas flow rate G1 is zero or is a small part of the total, the energy release can be accelerated substantially by the higher electric field strength and heat losses in the interelectrode insert can be eliminated by regeneration of heat in the porous wall. In that case, the mass flow rate through a unit surface of the channel is commensurate with the flow rate through a unit area of the cross Chemical and Petroleum Engineering, Vol. 37, Nos. 3–4, 2001
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Mar 1, 2005
M I Sazonov + 1
Open Access