At present, steel structure has been widely used in factory buildings. The primary component of steel structure workshop is welding H-shaped steel column, beam and brace. These components have welding deformation problems in the manufacturing process. If the welding deformation is not corrected, it will not only affect the overall structure, but also reduce the safety and reliability of the project. If the deformation of welded steel structure exceeds the allowable deformation scale of technical design, it shall be corrected to meet the product quality requirements.

　　In the production process, the most common correction methods are mechanical correction, flame correction and inductive correction. However, flame correction is a difficult operation, and improper method control and temperature control will cause new and greater deformation of components. Therefore, we should have rich practical experience in flame correction.

　　1. Types of welding deformation of steel structure and flame correction

　　The primary components of steel structure are welded H-shaped steel columns, beams and braces. The following three flame correction methods are often used for welding deformation:

　　(1) Linear heating method;

　　(2) Point heating method;

　　(3) Triangle heating method.

　　The following describes the construction methods to solve different parts.

　　The following is the heating temperature during flame correction (material is low carbon steel)

　　Caution: the heating temperature should not be too high during flame correction, which will cause metal embrittlement and impact toughness. 16Mn does not need to be cooled with water when it is corrected at high temperature, and it contains steel with a large thickness or hardening tendency.

　　1.1 angular deformation of flange plate

　　Correct the deformation of H-shaped steel column, beam and brace angle.

　　Longitudinal linear heating (heating temperature controlled below 650 ℃) is conducted on the flange plate (aligned with the outside of the weld). Pay attention that the heating scale does not exceed the scale controlled by two welding legs, so no water cooling is required.

　　Pay attention to the following when heating in line:

　　(1) It should not be heated repeatedly in the same direction;

　　(2) Do not spray water during heating. These two points are the general principles of flame correction.

　　1.2 up arch, down deflection and twists of columns, beams and braces

　　1、 On the flange plate, the zigzag deformation can be corrected by linear heating from the middle to both ends against the longitudinal weld. In order to avoid twists and turns, the two heating belts should be carried out simultaneously. Low temperature correction or medium temperature correction can be adopted. This method is beneficial to reduce the internal stress of welding, but it is difficult to grasp because of its great transverse shortening and longitudinal shortening.

　　2、 Linear heating is applied to the flange plate and triangular heating is applied to the web plate.

　　This method can correct the zigzag deformation of columns, beams and braces with remarkable effect. The width of transverse linear heating is generally taken as 20-90mm. When the plate thickness is small, the heating width should be narrower. The heating process should be extended from the middle to both sides of the width.

　　The linear heating should be carried out by two persons at the same time, and the width of the triangle should not exceed 2 times of the thickness of the plate, and the bottom of the triangle is equal to the linear heating width of the corresponding wing plate.

　　The heating triangle starts from the top, then extends from the center to both sides, heating layer by layer until the bottom of the triangle. When heating the web, the temperature should not be too high, otherwise it will cause concave deformation and it is difficult to correct.

　　Note: the above triangular heating method is also applicable to the side bending correction of components. When heating, the medium temperature should be selected for correction, and the watering should be less.

　　1.3 wave deformation of column, beam and brace Web

　　In order to correct the wave deformation, we should first find out the raised wave crest, and use the method of dot heating and hand hammer to correct it.

　　The diameter of the heating circle is generally 50-90mm. When the thickness of the steel plate or the area of the wave shape is large, the diameter should also be enlarged. The heating value can be calculated according to d = (4 δ + 10) mm (D is the diameter of the heating door; δ is the thickness of the plate).

　　The baking mouth moves spirally from the wave crest, and the middle temperature is selected for correction.

　　When the temperature reaches 600-700 degrees, place the hammer on the edge of the heating area, and then hit the hammer with a large hammer, so that the metal in the heating area is squeezed, cooled and shortened, and then flattened.

　　Excessive shortening stress shall be avoided during correction. After one point is corrected, heat the second peak point by the same method. In order to speed up the cooling, Q235 steel can be cooled with water. This correction method belongs to the point heating method, and the distribution of the heating door can be plum shaped or chain dense point shaped. Be careful not to exceed 750 degrees.

　　2, conclusion

　　The stress caused by flame correction is the same as the internal stress in welding. If the internal stress is superposed with welding internal stress and load stress, the longitudinal stress of column, beam and brace will exceed the allowable stress, which will lead to the reduction of bearing safety factor. Therefore, it is necessary to be careful in the fabrication of steel structure, select reasonable process measures as far as possible to reduce deformation, and select mechanical correction as far as possible during correction. When you have to choose flame correction, you should pay attention to the following points:

　　(1) The baking position shall not be near the maximum stress section of the main beam;

　　(2) The baking area at the correction point shall not be too large on one section, and more sections shall be selected;

　　(3) The point heating method should be used to improve the stress state of heating zone;

　　(4) The heating temperature should not exceed 700 ℃