Fig. 10 — Schematic of the separated plasma transferred arc weld surfacing (SPTAWS) where 1–4 are the plasma gas, powders, powder feeding gas, and shielding gas. Fig. 11 — Appearance of typical deposited bead by conventional PTAWS. Fig. 12 — Appearance of typical deposited bead by SPTAWS. ode spot transfered heat to the arc plasma receiver. Hence, the heat of the arc plasma increased as the separated electron flow decreased. The results from Experiment 5 are shown in Fig. 8. The arc length is at three levels, 4, 6, and 8 mm. The plasma gas flow rate remained 3.0 L/min, and the CP and the CG both remained at 50 A. As shown in Fig. 8, the heat from the arc plasma (the temperature elevation of the cooling water flowing through the arc plasma receiver) exhibited a slow decrease as the arc length increased, while the heat from the separated electron flow illustrated a reversal trend. The increment of the heat from the separated electron flow was smaller than the reduction of the heat from the arc plasma. As the arc length increased, the distance from the orifice exit to the workpiece increased. The travel distance and the radius of the arc plasma both increased. The heat loss through the radiation and air convection both increased. The heat received by the arc plasma receiver thus reduced as the arc length increased. For the electron flow receiver, the separated electron flow (the CG) was unchanged despite the increase in the arc length. The heat from the electron flow was thus unchanged. With the increase in the arc length, the radius of the arc plasma increased. The thermal radiation transfer of the arc plasma thus increased. Hence, the heat received by the electron flow receiver tends to increase, but very slightly. The results from Experiment 6 are shown in Fig. 9. The plasma gas flow rate was applied at five levels, 2.0, 2.5, 3.0, 3.5, and 4.0 L/min. The arc length remained 4 mm. The CP and CG both remained at 50 A. As the plasma gas flow rate increased, the heats from the arc plasma and electron flow (the temperature elevation of the cooling water) both increased. In this case, the ionized gas needed more energy to keep the degree of ionization in the plasma arc flowing through the plasma torch with a fixed diameter, which was attained by increasing the voltage. The arc plasma thus carried additional energy to the arc plasma receiver. Based on the fluid dynamics, the initial velocity and the final velocity of the arc plasma increased as the plasma gas flow rate increased, and the dynamic energy that was transformed into the internal energy of the arc plasma receiver increased. Hence, the heat of the arc plasma receiver increased as the plasma gas flow rate increased. For the electron flow receiver, the heat from the electron flow was unchanged. Due to the arc plasma containing part of the electron flow, the degree of ionization in the arc plasma increased as the plasma gas flow rate increased, and the thermal radiation of the arc plasma increased. Separated Plasma Transferred Arc Weld Surfacing Principle and System As verified previously, the heat input and arc pressure on the base metal can be both reduced from the conventional PAW and adjusted by changing the degree of the separation. A novel process, namely the separated plasma transferred arc weld surfacing (SPTAWS), is thus proposed and developed. Its test platform is shown in Fig. 10. As illustrated, the system includes a power source (transferred arc power source or WELDING RESEARCH 224-s WELDING JOURNAL / JUNE 2016, VOL. 95
Welding Journal | June 2016
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