ATTEN: Manager Liu
ADD: Longhua Development Zone, Jing County, Hengshui City, Hebei Province
At present, steel structure has been widely used in factory buildings. The main components of steel structure workshop are welded H-shaped steel columns, beams and braces. These components have welding deformation problems in the manufacturing process. If the welding deformation is not corrected, it will not only affect the overall installation of the structure, but also reduce the safety and reliability of the project.
Deformation of welded steel structure is beyond the allowable range of technical design, so it should be corrected to meet product quality requirements. Practice has proved that most deformed components can be corrected. The method of correction is to try to create new deformations to offset the deformations that have already occurred.
In the production process, the main correction methods are mechanical correction, flame correction and comprehensive correction. However, flame rectification is a difficult work to operate, and improper control of method and temperature will result in new and larger deformation of components. Therefore, flame correction should have abundant practical experience. This paper gives a rough analysis of the types and correction methods of welding deformation of steel structures.
1-nbsp; Types of Welding Deformation of Steel Structures and Flame Correction
The main components of steel structure are welded H-shaped steel columns, beams and braces. Three kinds of flame correction methods are often used for welding deformation: (1) linear heating method; (2) point heating method; (3) triangular heating method. The following introduces the construction methods to solve different parts.
The following is the heating temperature of flame correction (made of low carbon steel)
Low temperature correction & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; cooling mode: water;
Medium temperature correction & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; cooling mode: air and water
High temperature correction & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; cooling mode: air
Notes: The heating temperature should not be too high when the flame is corrected. Excessive high temperature will cause brittle metal and affect impact toughness. 16Mn can not be cooled by water during high temperature correction, including steel with high thickness or hardening tendency.
Angular Deformation of 1.1 Flange Plate
Correct H-section steel column, beam, brace angle deformation. In the flange panel (outside the alignment weld), the longitudinal linear heating (heating temperature controlled below 650 degrees), pay attention to the heating range does not exceed the control range of the two welding feet, so water cooling is not used. When linear heating, we should pay attention to: (1) not heating repeatedly in the same place; (2) do not water during heating. These two points are the general principles of flame correction.
1.2 Upper Arch and Downward Deflection and Bending of Columns, Beams and Braces
1. On the flange plate, the bending deformation can be corrected by heating the longitudinal weld line from the middle to both ends. In order to avoid bending and distortion, the two heating belts should be synchronized. Low temperature correction or moderate temperature correction can be adopted. This method is helpful to reduce the internal stress of welding, but it is difficult to master because of its large transverse shrinkage as well as longitudinal shrinkage.
2. Linear heating on the flange plate and triangular heating on the web. This method can rectify the bending deformation of columns, beams and braces with remarkable effect. The horizontal linear heating width is generally 20-90 mm. When the plate thickness is small, the heating width is narrower. The heating process should be extended from the middle of the width to both sides. Linear heating should be operated by two persons at the same time. The width of the triangle should not exceed twice the thickness of the plate separately. The bottom of the triangle is equal to the width of the linear heating on the corresponding wing. The heating triangle starts at the top, then extends from the center to both sides, heating layer by layer until the bottom of the triangle. When heating web, the temperature should not be too high. Otherwise, the depression will be deformed and it will be difficult to repair.
Note: The above triangular heating method is also applicable to the side bending correction of members. Medium temperature correction should be adopted when heating, and less water should be poured.
1.3-nbsp; wave deformation of columns, beams and bracing webs
To rectify the wave deformation, the first step is to find out the protruding peaks, which are rectified by the method of dot heating and hand hammer. The diameter of heating circle is usually 50-90 mm. When the thickness or wavy area of steel plate is large, the diameter should also be enlarged. The value of heating can be calculated according to d=(4 delta+10)mm (d is the diameter of heating point; delta is the thickness of plate). The baking nozzle moves spirally from the peak and is corrected at medium temperature. When the temperature reaches 600-700 degrees, the hammer is placed at the edge of the heating zone, and then the hammer is hit with a big hammer, so that the metal in the heating zone is extruded and flattened after cooling and contraction. Excessive shrinkage stress should be avoided during rectification. After rectifying a circle point, the second peak point is heated. The method is the same as above. In order to accelerate the cooling rate, the Q235 steel can be cooled by adding water. This correction method belongs to the point heating method. The distribution of heating points can be plum blossom or chain dense point. Be careful not to exceed 750 degrees.
2 & nbsp; conclusion
The stress caused by flame correction is the same as that caused by welding. If the internal stress produced by improper rectification is superimposed with the welding internal stress and the load stress, the longitudinal stress of the column, beam and brace will exceed the allowable stress, which will lead to the reduction of the bearing safety factor. Therefore, caution must be taken in the manufacture of steel structure, reasonable technological measures should be adopted to reduce deformation and mechanical correction should be adopted as far as possible. When flame correction has to be adopted, the following points should be paid attention to:
1. Fire location should not be near the maximum stress section of the main beam.
2. The fire area of the rectification should not be too large in one section, and several sections should be selected.
3. Point heating should be used to improve the stress state of heating zone.
4. Heating temperature should not exceed 700 degrees.