At present, ordinary fluid on the market with the general Longitudinal Welded Pipe is generally used in high-frequency resistance welding production, which is characterized by high production efficiency, weld heat affected zone is small, low quality requirements on the bonding surface, but the molding quality requirements, forming process Any change in the shape of the V-shaped opening may cause welding quality problems.
Rolling groove processing is the use of grooved joints as pipe fittings when the pipe pretreatment process. Its operating principle is the use of roll groove rolling machine driven rotating pipe, pipe radial direction of the follow-up pressure roller radial pressure applied to the use of the structure of the pressure roller welded pipe in a fixed position of cold out a specified groove.
A "roll groove cracking" is the root cause of the weld strength is not enough, coupled with rolling groove processing of the severe deformation, resulting in weld stress concentration and tear. Raw material is the source of product quality, production must master its characteristics. From the welding point of view, the impact of raw materials on the quality of the weld is mainly reflected in the welding of the material and the two aspects of organization. Elements of alloying elements and the morphology of the weld quality also affect. The high content of sulfur and phosphorus in the material will easily cause crystallization segregation; the high carbon content will promote the formation of martensite, the embrittlement of the weld metal; the grain size of the metal structure is too large, the direction of the weld crystal will be strengthened; Easy to promote the segregation of impurities. There are non-metallic materials in the inclusion, stratification, width and thickness fluctuations, all kinds of factors may cause weld cracks and reduce weld strength.
ERW steel pipe main welding process parameters are input power, raw production speed, opening angle, welding pressure, induction coil (induction contact) and the location of the impedance and so on. The unreasonable setting of welding parameters is an important reason for the phenomenon of rolling groove cracking. If the input power is not enough, the speed is too fast, the input heat is insufficient, the edge of the steel strip is not completely melted, the end solid oxide can not be extruded out to form the low-temperature welding defect; conversely, the input heat is too large, , Metal splash and return inclusions and other defects. Secondly, the welding pressure is also important. If the welding pressure is not enough, the fusion line on both sides of the metal microstructure flow line is not obvious, welding strength will not meet the requirements; the other hand, the welding pressure is too large, irregular weld lines, metal flow line rise angle is too large, Reduced only when the welding pressure is appropriate should be, the fusion line without distortion, metal streamline angle of 45 °~ 60 °ideal state, the weld strength is guaranteed.
