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The end faces of two work pieces are always pressed tightly, heated to the plastic state by resistance heat, and then quickly apply the upsetting pressure (or maintain the welding pressure without upsetting pressure) is called resistance butt welding.
The process parameters of resistance butt welding mainly include the following three items.
(1) Extension length: when deter mining the extension length of the workpiece from the electrode end face of the clamp, the stability ofthe workpiece during upsetting and the heat dissipation to the clampshall be considered.
(2) Welding time and welding current. There are two decisive factors inresistance butt welding, welding time and welding current. The twocan be adjusted accordingly within a certain range. Large current andshort time can be used; Small current and long time can also be used.However, when the matching difference is too large, it will affectthe strength of the welded joint, and it is easy to produce defectssuch as joint oxidation, coarse grain and so on.
(3) Upsetting pressure, welding pressure. Smaller upsetting pressure and larger welding pressure should be used for upsetting during heating
Flashbutt welding
Generally,flash butt welding can be divided into preheating flash butt welding and continuous flash butt welding (continuous flash butt welding isdivided into upsetting stage and flash stage).
1. Flash stage
In the flash stage, power on first, and the main function is to heat the workpiece. Then make the end faces of the two workpieces slightly contact to form many contacts. When the current passes, heat is generated, and the contact is melted and becomes a liquid metallintel connecting both ends. The liquid metal in the lintel evaporates, and the lintel explodes due to the high current density in the liquid metal beam. During operation, the moving clamp is pushed slowly, and blasting will continue to occur during the lintel.Under the action of electro magnetic force, liquid metal particles continue to form sparks and eject from the interface, that is, flash.
2. Upsetting stage
Afterthe flash stage, it is necessary to carry out upsetting pressure onthe work piece immediately, and the interface gap is rapidly reduced,then stop lintel blasting and enter the upsetting stage. The function of upsetting is to squeeze the liquid metal and oxide inclusions onthe end face, close the gap between the end faces of the workpiece,and make the clean plastic metal in close contact to form a firmjoint.
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