阴APP导航

One of the main areas of research at the Canadian Centre for Welding and Joining is the measurement of droplet heat content in free-flight metal transfer in GMAW and related processes. The technique is based on calorimetry of multiple droplets, together with high-speed video, image recognition, and data acquisition. A novel set-up involving a cathode with a hole enables the operation of welding machines using standard settings because the arc attaches to the cathode, yet the molten metal falls through the hole and is captured by the calorimeter. The water-cooled cathode also acts as a secondary calorimeter, discriminating the heat input provided by droplets from that from the arc acting on the cathode. Several iterations of cathode and calorimeter will be discussed, with emphasis on the latest embodiments. Among the findings from this line of research are the direct measurement, for the first time, of a droplet temperature minimum at the transition between globular and spray transfer. This insight has been used to explore the existence of a temperature minimum in tubular Ni/WC wires for wear protection overlays for the oil sands. These overlays are extremely sensitive to degradation if the molten metal temperature is excessive during application. Wire based processes show much promise for practical applications, but are seldom used because of high degradation problems. It will be discussed the exploration of a temperature minimum for tubular wires, including instability of arc attachment, existence of a broad temperature minimum (instead of sharp minimum as in solid wires), and the unexpected non-wetting property of WC powders in molten Ni.