Welding torch moves from right to left. During the process inner core heats the base material at the joint, and the outer blue flame preheats the unwanted portion. Due to this difference, the temperature at the welding region and un-welding region can be reduced. With this stress developed in the weld joint region can be minimized.
Welding torch moves from left to right. During this process the outer blue flame will post heat on already welded portion. Due to the stress developed in the weld joint region, the stress can be relieved. In the welding of cast iron, if the difference of the temperature in the weld and unweld region is maximum. This is due to presence of carbon that is a free form, which is later converted into carbides, to overcome this preheating done by using fore hand welding technique.
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