The continuous flash butt welding machine welding cycle consists of flash, upset, hold, rest and other procedures. Flash and upsetting two successive stages constitute the formation process of continuous flash butt welded joint. The hold, rest and other procedures are necessary in the butt welding operation. Preheat flash butt welding has a preheat phase in its welding cycle (before the flash). The essence of the formation of the flash: turn on the power and make the end faces of the two weldments touch slightly. Many small contacts with very small resistance will be formed between the counterparts. Under the heating of a large current density, they will melt instantaneously to form a liquid lintel connecting the two ends of the counterparts. At the same time, under the action of the liquid surface tension radial electromagnetic compression effect force, electromagnetic repulsion force, and electromagnetic attraction force, coupled with strong heating. There is a huge pressure difference between the interior of the lintel and its surface. For example: in low carbon steel flash butt welding, the data show that the current density in the lintel can be as high as 300A/mm2 at the moment of blasting, and the metal vapor pressure at the moment of blasting can reach hundreds of atmospheres. And its temperature is as high as 6000 ℃-8000 ℃, and the liquid metal particles are ejected from the counterpart gap at a temperature of more than 60M/S to form a spark jet-flash. In flash butt welding, in order to obtain a good quality joint, the following three requirements must be met at the end of the flash stage:
(1). The metal at the counterpart should not be oxidized as much as possible. This requires the flash to be carried out stably and intensely. In particular, the welding parts should not be short-circuited during the flashing process, otherwise, the end face will be overheated locally.
(2). Obtain a suitable temperature distribution in the counterpart and its vicinity. The mark heats the end face evenly, obtains a suitable temperature distribution along the length of the weldment, and has a thick liquid metal layer on the end face.
(3). Upset forging is the later stage of flash butt welding, which applies an upsetting force to the weldment to make the burnt end face close contact. And make it to achieve the operations necessary for a high-quality combination. In flash butt welding, in order to obtain high-quality joints, the following requirements must be met at the end of upsetting: that is, enough and appropriate plastic deformation of the butt and its adjacent areas is obtained, and the safe and reliable way is to make those metals oxidized in the flash stage, Use upsetting to squeeze as much as possible into the burr with the liquid metal. The upsetting stage is composed of two parts: electric upsetting and non-electrical upsetting. Electric upsetting is to prevent the liquid metal on the end face from cooling prematurely, so that the opposite heating zone maintains a certain depth. Preheating stage: On the welding machine, the temperature of the end face of the weldment is increased to a suitable value (generally 800℃--900℃ for the chain) by preheating, and then the flashing and upsetting process are carried out. There are two types of preheating processes: resistance preheating and flash preheating. Preheating also has shortcomings, namely, low production efficiency, complex process control, wide preheating zone and poor stability of joint quality. Therefore, many chain manufacturers have recently adopted a strong standard welding process, which saves the preheating stage.
