creased as the plasma gas flow rate increased. As can be seen in Fig. 6, the peak value has been significantly increased as the plasma gas flow rate increased, the pressure of the arc plasma was reducing as the arc radius increased, and the pressure mainly distributed within the 2.5 mm radius. Heat Distribution As shown in Table 1, Experiments 4–6 are designed to measure the heat from the arc plasma and electron flow under different conditions. The results are shon in Figs. 7–9. The points on the lines are the measurements. In the Y-axis, the energy output is calculated based on Equations 1 and 2. As illustrated in Fig. 7, the current is applied at seven pairs; and in the Xaxis, the first number represents the CP and the second represents the CG. The sum of the two currents remained 100 A. In all experiments, the arc length was 4 mm. As seen from Fig. 7, as the separated electron flow (the CG) decreases (i.e., toward the right in the current axis in the figure), the heat of the electron flow (the lower curve in the figure) decreases, but the heat of the arc plasma (the upper curve) (as reflected by the temperature elevation of the cooling water) increases because the proportion of the electron flow that is not separated increases. Further, as can be observed, the heat of the arc plasma was greater than the electron flow. The first reason was that the heat being received by the electron flow receiver mainly came from the anode spot and decreased as the separated electron flow (the CG) decreased. The heat of the electron flow receiver decreased as the separated electron flow decreased. WELDING RESEARCH However, when the separated electron flow was zero, the temperature elevation of the cooling water that flowed through the electron receiver was not zero because of the thermal radiation of the arc plasma. Another reason was the heat received by the workpiece mainly comes from the ionized gas, highly compressed and with a high temperature. The ionization starts at the cathode and continues in the arc column. Due to the total current flowing through the plasma torch was unchanged, the ionizability of the ionized gas was unchanged until the electron flow started to separate from the arc plasma. The ionizability of the arc plasma increased as the separated electron flow decreased. With the decrease in the separated electron flow, the electron flow, which is still contained within the arc plasma, increased, and the an- JUNE 2016 / WELDING JOURNAL 223-s Fig. 6 — Arc pressure distribution under different plasma gas flow rates in Experiment 3. CP, 50 A; CG, 50 A; arc length, 4 mm. Fig. 8 — Energy output of the arc plasma and the electron flow under different arc lengths in Experiment 5. CP, 50 A; CG, 50 A; plasma gas flow rate, 3 L/min. Fig. 7 — Energy output of the arc plasma and the electron flow under different currents in Experiment 4. Arc length, 4 mm; plasma gas flow rate, 3 L/min. The current is given as CPCG. Fig. 9 — Energy output of the arc plasma and the electron flow under different plasma gas flow rates in Experiment 6. CP, 50 A; CG, 50 A; arc length, 4 mm.
Welding Journal | June 2016
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