What is an arc blow? How is the arc blow problem taken care-off in welding? Calculate the melting efficiency in case of arc welding of steel with a potential of 20V and current of 200A. The travel speed is 5 mm/sec and the cross-sectional area of the joint is 20 mm2. Heat required to melt steel may be taken as 10J / mm3 and the heat transfer efficiency as 0.85.