Flash Butt Welding
The two pieces to be welded are pressed against each other by applying a pressure. To whatever finish the faces are machined, there will be some protuberances which cause contacts. Because of the bridges present, when a high welding current is passed, a high current density results at the contact surface. The bridges get heated upto molten conditions since one work piece is slowly advancing towards the other. After the faces attain a plastic stage upsetting pressure is applied. The molten metal and some of the impurities associated with it are expelled. Depending on the material and contact area preheating and post heating may be warranted.A typical flash butt welding sequence will comprise the following steps. Load machine - clamp work - apply preheating force - preheat - Release preheat force to separate work pieces Contact Contact parts lightly for flashing - apply welding voltage - Flash at high voltage Flash at normal voltage - Cut off welding current - pass up set current - Upset - Cut off upset current - Reclamp and post heat - Pinch off and shear die operation Unclamp work - Return platen and unload.