Butt Welding

Butt resistance welding (hereinafter referred to as the butt) is the use of the thermal resistance of the two workpieces simultaneously welded together along the entire end face of a class of resistance welding methods. Butt high productivity, easy to automate, and therefore widely available. 

Butt is divided into two kinds of resistance butt welding and flash butt welding. 
Resistance butt is always pressed the two workpiece face, using resistance heating to heat the plastic state, then quickly forging force is applied to the top (with or without top forging force to maintain only the welding pressure) to complete welding. And spot welding, as the contact resistance of the resistor depends on the surface condition when butt contact surface, temperature and pressure. When the contact resistance significantly oxide or other stolen goods, the contact resistance is large. Increasing the temperature or pressure will increase the effective contact area by leaving the contact resistance is reduced. The beginning of the welding, the current density at the contact point on the great; rear end rapid temperature rise, the contact resistance sharply decreased. Heated to a temperature (600 degrees steel, aluminum alloy 350 degrees), the contact resistance disappeared completely. And spot, as also when the heat resistance of welded heat generated by the resistance welding area. When the resistance welding, the contact resistance very short time of existence, the heat generated is less than 10-15% of total calories. But because part of the heat is generated within a narrow area near the contact surface. Therefore, the temperature will rise rapidly in this area, the internal resistance increases rapidly, even if the contact resistance completely disappeared, the strength of the heat generating region is still higher than elsewhere. 

Flash butt welding can be divided into continuous flash butt welding and flash butt welding preheat. Continuous flash butt welding consists of two main phases: phase flash stage and upset. Preheat flash butt welding flash stage just before the warm-up phase increased. The main role of the flash heating the workpiece. At this stage, the first power, and make slight contact between the two workpiece face, forming many points of contact. Current through the melting point of contact to become liquid metal connection end faces of the crosspieces. As the liquid is too high beam current density, so that over the evaporation of liquid metal beams, lintels blasting. With the slowly advancing dynamic clamp, lintels also continue to produce and blasting. Under the action of electromagnetic force and vapor pressure, the liquid metal particles are ejected from the interface between the continuous. Formation of sparks Rapids - flash. At the end of the flash stage, immediately applying sufficient pressure on top of the workpiece, the lintel fitting clearance decreases rapidly stop blasting, forging stage is entered. Role is upset and liquid metal sealing gap workpiece face lintels left after blasting crater, while the liquid metal and oxide inclusions extrusion end face so clean plastic metal in close contact, and to produce a certain plasticity joint area deformed to promote recrystallization for forming the grains together to obtain a strong joint. The flash butt welding process, although the heating of the molten metal, it is essentially plastic state welding.