What are the common defects found in welding? Explain their causes and remedies. A projection welding of 3 spots is obtained with a current of 35,000 A for a period of 0.01 sec. If the effective resistance of the joint be taken as 120 micro ohms, and if the joint can be considered as a cylinder of 6mm diameter and 2.5 mm in height, calculate the heat distributed to the surroundings. Take heat required for melting steel as 10 J/mm3.