The commonly used correction methods in the production process mainly include mechanical correction, flame correction and comprehensive correction. However, flame correction is a difficult task, and improper method control and temperature control will also cause new and greater deformation of components. Therefore, flame correction should have rich practical experience.
1, steel structure welding deformation types and flame correction
The main components of steel structure are welded H-beam columns, beams and braces. Welding deformation often adopts the following three flame correction methods:
(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 of flame correction (low carbon steel).
Attention: The heating temperature should not be too high during flame straightening, which will cause the metal to become brittle and affect the impact toughness. 16Mn cannot be cooled by water during high temperature correction, including steel with large thickness or hardening tendency.
1. 1 Angular deformation of flange plate
Correct the deformation of H-beam columns, beams and supports.
Longitudinal linear heating (the heating temperature is controlled below 650 degrees) is carried out on the flange (outside the alignment weld), and the heating range cannot exceed the control range of two welding legs, so water is not used for cooling.
Attention should be paid to linear heating:
(1) should not be heated repeatedly in the same position;
(2) Do not water when heating. These two points are the general principles of flame correction.
1.2 Upper arch, lower deflection and bending of columns, beams and braces
First, on the flange plate, facing the longitudinal weld, linear heating from the middle to both ends can correct the bending deformation. In order to avoid bending and deformation, the two heating belts should be synchronized. Low temperature correction or medium temperature correction can be adopted. This method is beneficial to reduce welding internal stress, but it is difficult to master because it shrinks longitudinally and laterally at the same time.
Second, the flange plate is heated linearly and the web plate is heated triangularly.
This method is effective for correcting the bending deformation of columns, beams and braces. The transverse linear heating width is generally 20-90 mm, and the heating width is narrow when the thickness of the plate is small, and the heating process should extend from the middle of the width to both sides.
Linear heating is best carried out by two people at the same time. The width of the triangle heated separately should not exceed twice 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 expands from the center to both sides, and is heated layer by layer until the bottom of the triangle. When heating the web, the temperature should not be too high, otherwise it will cause depression and deformation, which is difficult to repair.
Note: The above triangle heating method is also applicable to the lateral bending correction of members. Proper temperature correction should be adopted when heating, and less water should be used.
1.3 Wave deformation of columns, beams and supporting webs
To correct the wave deformation, we must first find the convex peak, use the point heating method and correct it with a hammer.
The diameter of heating spot is generally 50 ~ 90 mm, and it should be increased when the thickness of steel plate or wave area is large. D = (4 δ+ 10) mm (D is the diameter of the heating point; Delta is the plate thickness).
The baking nozzle moves spirally from the highest point and is calibrated at medium temperature.
When the temperature reaches 600 ~ 700 degrees, put a hammer on the edge of the heating area, then squeeze the metal in the heating area with a sledgehammer, and then flatten it after cooling and shrinking.
Excessive shrinkage stress should be avoided during calibration. After correcting one point, heat the second peak point. The method is as above. In order to speed up the cooling rate, Q235 steel can be cooled by adding water. This correction method belongs to point heating method, and the distribution of heating points can be plum blossom or chain dense points. Be careful not to exceed 750 degrees.
2. Conclusion
The stress produced by flame correction is internal stress and welding internal stress. Improper correction, superposition of internal stress caused by welding internal stress and load stress will make the longitudinal stress of columns, beams and supports exceed the allowable stress, which will lead to a decrease in the safety factor of bearings. Therefore, we must be careful in the production of steel structures, adopt reasonable technological measures as far as possible to reduce deformation, and adopt mechanical correction as much as possible when correcting. When flame correction must be used, the following points should be noted:
(1) The baking position shall not be close to the maximum stress section of the main beam;
(2) The fire area of the correction site should not be too large on one section, and several sections should be selected;
(3) Point heating should be used to improve the stress state in the heating zone;
(4) The heating temperature should not exceed 700 degrees.
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This article is selected from Henan Qianwanjian New Building Materials Co., Ltd.