Application of Plasma ARC to Bevel Cutting

This report summarizes our assessment of plasma plate edge preparation. One, two and three torch bevel configurations were evaluated. Special controls were developed which automatically ignite the trailing torches as they pass over the edge of the workpiece, and accurately maintain the torch-to-work distance of the torches during the cut. One and two torch plate edge preparation appears to be practical for shipbuilding applications. Three torch beveling is not practical with the present technology it is impossible to produce a condition which is dross-free. The joint configuration studied in the two torch case was the single bevel with a nose edge preparation. This geometry does have a process limitation The bevel depth cannot exceed a value determined by the bevel angle and the nozzle size kerf width otherwise, dross will appear along the bottom edge of the nose. This does not appear to be a serious constraint on 34, 1, and 1 14-inch plate, but may pose a problem on 1 12-inch plate. The best results for two and three torch plasma plate edge preparation are obtained by cutting the top bevel first, square cut second, and in the case of three torch beveling, the bottom bevel third. This is the reverse of the normal cut sequence employed for oxy-fuel multitorch beveling. Keversing the cut sequence pushes the dross down to the bottom edge rather than washing it over previously cut surfaces. In the case of two torch beveling, the conditions can be adjusted so that the plasma jet developed by the last torch provides sufficient momentum to prevent dross adherence. In the case of three torch beveling, dross formation along the edge of the bottom bevel cannot be avoided.