Yan'an medium thick wall Tangshan square tube production
Rectangular tube is a kind of light thin-walled steel tube with hollow square section, also known as steel cold-formed section. It is a shape steel with square section and overall dimension made of Q235 hot-rolled or cold-rolled strip or coil as the base material after cold bending and forming and then high-frequency welding. Hot rolled extra thick wall square tubes, except for the thickening of wall thickness, have corner dimensions and edge straightness to the extent that they exceed the resistance welded cold formed square tubes.
Yan'an medium thick wall Tangshan square tube production
In order to understand the process law of direct squaring, it is necessary to understand the forming principle of bending. Both rectangular tube and round tube are formed by rolling, but there are great differences in the forming object, forming request and forming force between them. In order to understand the principle of direct squaring, the tube forming method is called bending; The forming method of rectangular tube is called bending. (Broadly speaking, bending is also bending. Bending and bending are distinguished here in order to understand that bending changes the curvature during tube forming and bending changes the angle during direct square forming.) Bending and bending are different. (1) Forming object The bending object of different round tubes is a line segment, and the bending object of square tubes is a point (in practice, the bending point of square tubes is a small area where the inner corner R is unfolded); (2) Different requirements for forming - the curvature of the line segment is changed when the circular tube is bent, and the included angle of the adjacent side is changed when the square tube is bent (3) The forming force is different - the forming force for bending is centripetal force, and the forming force for bending is bending moment.
Yan'an medium thick wall Tangshan square tube production
Seamless square tubes pass through the tube blank sawing section of the steel mill, and then are heated - perforated - sized - straightened - cooled - slugged - packaged in the annular furnace to become qualified waste products. Generally, it is impossible to place so many stock items in the consumer workshop when they are sent to the user, which requires dealers to place some stock items. However, dealers generally do not have large indoor warehouses, and some costs are too high, which is not cost-effective. Most of them are outdoor warehouses. If the seamless square tubes are placed outdoors, they will be exposed to the wind and the sun. The so-called floating rust literally means a layer of rust floating on the seamless square tube, which can be removed with a towel or other things. Simply speaking, floating rust is also considered as no rust, which belongs to the normal state. The rusting of seamless square tubes is a long-term problem. At least for more than one year, the seamless square tubes that have been exposed to the wind and the sun outside have large and small pits on them, which is the only difference between the floating rust and rusting of seamless square tubes.
Yan'an medium thick wall Tangshan square tube production
1. During square forming, the corner bending is related to the neutral layer of the strip steel. The inner corner is pressed and the outer corner is pulled. No matter what method you use for square forming, the result of the corner force is that the outer tensile strip steel is thinner. From the physical phenomenon, the metal lattice changes and cold work hardening occurs. Especially when the general pass strip is hard, the corner may be broken. In addition, the dimensional accuracy of the straight square is mostly handled by sizing: first, it increases the equipment load; second, the steel strip also produces local cold work hardening, which affects the internal quality of the profile. 2. During the round to square forming, the main pipe is compressed and deformed in the pass. The pass design considers the elastic limit of the base metal, that is, the pressure must not exceed the elastic limit. If the elastic limit is exceeded, the base metal will "lose stability" and form waste products. It can be seen that the physical phenomenon of round to square forming does not change the strip. In addition, the contour and dimensional accuracy of the round to square shape is guaranteed by the hole type and adjustability, so its contour dimensional accuracy is high. Moreover, because the deformation of round to square is stopped under pressure, the thickness of its corner has an increasing trend instead of thinning, and the load resistance of profiles with the same thickness and the same specification can be significantly improved compared to the straight square.
Yan'an medium thick wall Tangshan square tube production
Under the action of bending moment, during the transition from elastic deformation to plastic deformation of the full section of the cross section at the bending part of the rectangular tube, the outside of the strip steel is pulled, the inside is pressed, and at the same time, it is also affected by the radial pressure. In addition, the rigidity of the roll tool ring angle limits, on the one hand, the neutral layer of the rectangular tube strip steel moves inward, and on the other hand, the thickness of imperial steel is reduced at the bending part. In the process of bending from the outside to the inside to move the neutral layer inward, the circumferential stress is far greater than the radial stress, and the radial strain mainly occurs outside the neutral layer. Therefore, the radial displacement velocity of each layer of fiber outside the rectangular tube is different. At the inner side, due to the small radial strain, the radial displacement velocity of each layer of fiber has little difference, which is almost a constant. Here, the radial displacement velocity inside the neutral layer is treated as a constant.
