The high-frequency welding process of straight seam steel pipe is completed in the high-frequency welded pipe unit. The high-frequency welded pipe unit is usually composed of rolling forming, high-frequency welding, extrusion, cooling, sizing, flying saw cutting, and other components. The front end of the unit is equipped with a material storage looper, and the rear end of the unit is equipped with a steel pipe turning frame; The electrical part is mainly composed of a high-frequency generator, DC excitation generator, and instrument automatic control device. Thermally expanded straight seam steel pipe refers to the expansion of straight seam steel pipes through diameter expansion technology to meet the needs of customers. There are two processes for straight seam steel pipes: double-sided submerged arc welding and high-frequency welding. Double-sided submerged arc welding can produce straight seam steel pipes with a diameter of about 1500. The expansion we are talking about now mainly refers to high-frequency welded pipes. There are two points The reason is that the production caliber of the high-frequency welded pipe itself is relatively small, so it needs to be enlarged.
There are many kinds of straight seam steel pipes, according to the application: general welded pipe, oxygen-blowing welded pipe, galvanized welded pipe, wire casing, idler pipe, metric welded pipe, automobile pipe, deep well pump pipe, transformer pipe, electric welding special-shaped pipe, electric welding thin-walled pipe.
General welded pipe: General welded pipe is used to convey low-pressure fluid. Made of Q235 grade, L245, and Q235B steel.
Galvanized steel pipe: It is to coat the surface of the black pipe with a zinc layer. Divided into heat and cold. The hot zinc layer is thick, and the cold is cheap.
Oxygen-blowing welded pipe: generally small diameter welded steel pipe, commonly used for steelmaking oxygen blowing.
Wire casing: It is a pipe for a power distribution structure, which is an ordinary electric-welded carbon steel pipe.
Welded thin-walled tube: it is a small-caliber tube used for furniture and lamps.
Roller tube: The electric welded steel tube on the belt conveyor has the required ovality.
Transformer tube: It is an ordinary carbon steel pipe. Used in the manufacture of transformer heat pipes and other heat exchangers.
Requirements for the appearance of straight seam steel pipes:
1. Cracks, unfused, pores, slag inclusions, and splashes are not allowed.
2. The weld surface of pipes whose design temperature is lower than -29 degrees, stainless steel and alloy steel pipes with a large hardening tendency shall not have undercut. The undercut depth of the weld seam of pipes made of other materials shall be greater than 0.5mm, the continuous undercut length shall not be greater than 100mm, and the total length of the undercut on both sides of the weld shall not exceed 10% of the total length of the weld.
3. The surface of the weld seam shall not be lower than the surface of the pipe. Weld seam reinforcement, and not more than 3mm, (the maximum width of the groove after the welding joint is assembled).
4. The wrong side of the welded joint should not be greater than 10% of the wall thickness, and not greater than 2mm.
The method of straight seam steel pipe in preheating deformation:
1. Reasonable material selection. For precision and messy molds, micro-deformation mold steels with good quality should be selected. For mold steels with serious carbide segregation, reasonable casting and quenching and tempering heat treatment should be carried out. For larger mold steels that cannot be cast, solid solution double refinement heat treatment can be carried out. Reasonably select the heating temperature and control the heating speed. For precision and messy molds, slow heating, preheating, and other balanced heating methods can be used to reduce the heat treatment deformation of the mold.
2. Correct heat treatment process operation and reasonable tempering heat treatment process are also useful methods to reduce the deformation of precision and messy molds. The reasons for the deformation of precision and messy molds are often messy, but we only need to grasp the rules of deformation, analyze the causes of its occurrence, and use special methods to prevent the deformation of the mold, which can be reduced and controlled.
3. Pre-heat treatment is required for precision and messy molds to eliminate the remaining stress generated during machining. For precision and messy molds, if conditions permit, try to use vacuum heating and quenching and cryogenic treatment after quenching. Under the premise of ensuring the hardness of the mold, try to use pre-cooling, graded cooling quenching, or a warm quenching process.
4. The design and description of the mold should be reasonable, the thickness should not be too disparate, and the shape should be symmetrical. For molds with large deformation, the deformation rules should be mastered, and machining allowances should be reserved. For large, precise, and messy molds, a combined design can be used. For some precision and messy molds, pre-heat treatment, aging heat treatment, quenching, and tempering nitriding heat treatment can be used to control the precision of the mold. When repairing defects such as mold trachoma, air hole 5, wear, etc., use equipment with small thermal influence such as a cold welding machine to avoid deformation during the repair process.
Hunan Gaoxing Steel Development Zone, No.1888 Purui South Rd, Wangcheng District,Changsha, Hunan, China