Tandem submerged-arc welding using plasma-arc preheating - giving increased welding speeds combined with increased penetration

摘要

Although the use of electrodes in tandem increases the speed of seam-welding by submerged-arc, the increase is restricted by inadequate penetration. To overcome this problem, a plasma burner is located on an adjustable mounting ahead of the first electrode at a distance of 30-300mm (pref. 100mm); the current supplied to the plasma burner is pref. 70-800A degrees. The pref. arrangement consists of mounting the plasma burner and e.g. three electrodes in tandem on a combined holder which moves along the seam being welded, the plasma-arc being used to heat a zone narrower than the width of the seam to a temp. between 1000 degrees C and the m. pt. of the metal being welded. Instead of the plasma-arc, a tungsten inert-gas arc can be used. In an example with no preheating, three electrodes in tandem with total current of 2800A and welding speed 1.8 m/min. gave a penetration of 8mm.