PLASMA PARAMETERS NEAR A SMALL ANODE IN A HIGH-PRESSURE ARC (GAS METAL ARC-WELDING)

The size of the arc attachment at the anode of gas metal arc welding (GMAW) is small compared to the arc column. The small anode attachment results in a high current density and high Joule heating near the anode. It is believed that this is the reason why the voltage in such an arc rises with current which is in contrast to an almost current-independent V-I characteristic in the case of a large anode. The equation to describe the distribution of plasma parameters near a small arc anode is presented. Calculations have been performed for an atmospheric pressure arc in argon in the 50 A to 500 A current range and for the anode sizes of 0.5 mm to 2 mm. Calculations showed that: (1) the voltage drop across the anode layer rises with the current, and (2) there is an electron temperature maximum close to the anode. The calculated volt-ampere characteristic of the anode layer is in agreement with experimental data. The calculated heat flux to the anode is slightly higher than that measured. It is believed that this difference is due to anode vaporization. The thermal balance of the anode is discussed.