Abstract
The power sources used in cutting arc torches are usually poorly stabilized and have a large ripple factor. The strong oscillatory components in the voltage and arc current produce in turn, large fluctuations in the plasma quantities. Experimental observations on the dynamics of the non-equilibrium plasma inside the nozzle of a 30 A oxygen cutting torch with a 7 % ripple level of its power source are reported in this work.
Highlights
The plasma cutting process is characterized by a transferred electric arc that is established between a cathode, which is a part of the cutting torch, and a work–piece acting as the anode [1]
The strong oscillatory components in the voltage and arc current should produce in turn, large fluctuations in the plasma quantities that vary at the ripple frequency
Since the temporal variations introduced by the ripple are very slow as compared with the characteristic times in the layer, a previously developed steady model [5,10] will be adopted, with the additional assumption that the plasma quantities follows instantaneously the arc current and arc voltage variations
Summary
The plasma cutting process is characterized by a transferred electric arc that is established between a cathode, which is a part of the cutting torch, and a work–piece (the metal to be cut) acting as the anode [1]. [2] to [4]) both from an experimental or a numerical points of view, to understand the dynamics of the plasma flow inside non–transferred arc torches (like spraying torches) In such torches, large plasma jet fluctuations arise either from ripple in the direct–current power supply, or random arc root movement at the anode, or combined effects of gas dynamic and electromagnetic instabilities causing cold gas entrainment. The power sources used in such plasma torches are usually poorly stabilized and have a large ripple factor (with root–mean– square –rms– deviations that vary between o 5 to 10 % of the mean voltage) This is due to the fact that the torch currents are of the order of 100 A, which difficult an effective filtering of the ripple. It is employed a technique previously developed in our laboratory consisting in using the nozzle as a large–sized Langmuir probe [5]
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