Special discussion on flame correction construction method of light steel structure welding deformation Jiangsu Nanling Steel Structure Engineering Co., Ltd. Nan Yi Content: The author introduced the main types of light steel structure welding deformation, flame correction welding deformation based on many years of experience, combined with relevant data at home and abroad The principle and construction method of flame correction for welding deformation.
* Preface At present, light steel structure has been widely used in house construction, and the main components of light steel structure houses are wide flange welded H-shaped steel beams and steel columns. These components need to be welded during the manufacturing process, and welding deformation problems are unavoidable. 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.
After the deformation of the welded structure exceeds the technical requirements, it should be corrected to meet the product quality requirements. Practice has proved that many deformed structures can be corrected. Various methods of correcting deformation are essentially trying to create new deformations to counteract the deformations that have occurred.
The correction methods used in production mainly include mechanical correction, flame correction and comprehensive correction. Flame rectification is a highly empirical work, and improper methods will also cause greater changes in component size. This article makes a specific analysis of the types, correction principles and correction methods of light steel structure welding deformation.
Second, the principle of gas flame correction Metal has the characteristics of thermal expansion and contraction, and the mechanical properties also change with temperature. The relationship between the yield limit Ss and the temperature of the low carbon steel, such as Q235 steel, is shown by the dashed line, and can generally be simplified to a solid line, that is, when the temperature is below 500 *, the yield limit is basically unchanged; when the temperature is above 600 * The yield limit is close to zero. The temperature changes linearly between 500 and 600 *.
When the metal structure is locally heated, the thermal expansion of the metal in the heating zone is prevented by the surrounding cold metal and cannot be freely deformed, and the metal in some parts is plastically compressed. After cooling, the residual local shrinkage allows the structure to obtain the deformation required for correction.
How to use heating and cooling to bend and straighten the steel, the following is a detailed analysis of the principle of hot processing.
The hot-bending method, also known as the linear heating method, was first invented by the Ishikawajima Tokyo Plant in Japan (later the second plant in Tokyo in 1H1) and later widely adopted by the steel structure manufacturing industry. The principle of heating and bending is as shown. After the surface of the steel plate is heated, the surface temperature closest to the heating point rises fastest and expands fastest. The surrounding heat is less affected and the expansion is also very small. After heating stops, the temperature diffuses to the surroundings and the heated part begins to cool. It gradually recovered, but due to the contact of the surface of the board with the air, the heat dissipated quickly, so that the heated part of the surface was fixed before it was restored.
As the cooling process continues, it can be seen that the high temperature on the upper side of the neutralization shaft begins to shrink, and the contraction force causes the plate to bend upward. After the bending is terminated, the two ends of the steel plate are shortened by a / 2, but the volume in the middle is raised by a The volume does not change and the weight does not change.
During the linear heating, cooling, and shrinking process, when the thin plate is heated, the surface heat is quickly transferred to the inside due to the thin plate. The high temperature part penetrates through the entire cross section of the plate. During cooling, the upper and lower surfaces are cooled equally, and the cooling of the neutralization shaft The shrinkage force is also the same, so the expansion of the upper and lower surfaces is left when heated, which causes the entire board to shorten, but it does not bend. If there is no phase change in the organization, the mechanical properties of the metal do not change much. The medium temperature correction method is more commonly used at home and abroad.
Although there is a phase transformation of the metal structure in this temperature range, as steel materials such as As, ASF and 16Mn are cooled in the air, the annealed structure can still be obtained, and the mechanical properties do not change much. However, if the heating temperature is excessive, it will cause austenite grains to grow and cannot be refined during cooling, which will increase the brittleness of the metal and reduce the impact toughness.
It should be noted that for 16Mn steel, water cooling should not be used when heated to the phase transition temperature, otherwise low-carbon martensite will be produced, which will affect the impact toughness.
The heating temperature should also be limited to linear heating below 650T, and point heating should be limited to 750T or less.
The point heating and cooling shrinking process shortens the processing and the position of the heating point is relatively fixed. The processing method that heats both the inside and the outside of the board is called spot heating (usually also called acupuncture). This method is generally used to correct the wave deformation of thin plates.
The mixing ratio of oxyacetylene used for flame correction should be between 1: 1.05 and 1: 1.25, which is more suitable for neutral flame or oxidized flame.
According to the heating temperature of flame correction, it can be divided into low temperature correction, middle temperature correction and high temperature correction. The corresponding heating temperature and cooling medium are shown in the table below.
Classification heating temperature (t low carbon steel color cooling medium low temperature correction is red in bright water temperature correction dark red air and water high temperature correction light pink air according to the relationship between the yield limit of low carbon steel and temperature to 500 ~ 600 y The yield limit of low-carbon steel has been greatly reduced. Heating to this temperature range can serve the purpose of flame correction, while the metallographic structure and mechanical properties remain unchanged. Due to the fast water spray cooling speed, the flame correction efficiency is high. China uses low temperature correction Not many, Japan and other countries adopt this method.
When the heating temperature of the metal in the middle temperature correction is 600 ~ 700 *, the yield limit Ss is closer to zero value, and the effect of flame correction is lower when the temperature correction is higher. The heating temperature is still below the phase transition temperature. The gold three, the types of light steel structure welding deformation and the main components of the flame correction light steel structure are welded H-shaped steel beams and columns.
The three types of flame correction methods used for welding deformation are: (1) linear heating method; (2) point heating method; (3) triangular heating method. The following is a detailed introduction to the construction methods to solve the deformation of different parts.
Correct the welding angle deformation of H-shaped steel beams and columns. The longitudinal linear heating above the flange plate (outside the weld), pay attention to the heating range can not exceed the range controlled by the two welding feet, you can not use water cooling, see. Attention should be paid to linear heating: (1) It should not be heated repeatedly in the same place; (2) Watering is necessary during the heating process. These two points are the general principles of flame correction.
Method one: On the flange plate, facing the longitudinal weld, linear heating from the middle to both ends can be corrected to correct the bending deformation. In order to avoid side bending and distortion, the two heating belts should be synchronized. Low temperature correction method or medium temperature correction method can be adopted. This method is conducive to reducing the internal stress of welding, but this method has a larger lateral shrinkage while shrinking in the longitudinal direction, which is more difficult to master.
The topic of angular deformation discusses the linear heating correction arch (bending) bending method two: linear heating on the wing board, corresponding to the triangular heating on the web, see. Using this method to correct the bending deformation of beams and columns has a significant effect. The transverse linear heating width is usually 20 ~ 90mm. When the plate thickness is small, the heating zone should be narrower. The heating process should extend from the middle of the width to both sides. Linear heating is best done by two people, and then heating the triangle separately. The width of the triangle 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 should start from the top and then extend from the center to both sides, heating layer by layer until the bottom of the triangle. The temperature should not be too high when heating the web, otherwise it will cause the deformation of the depression and it is difficult to repair.
Beam-column side-bending deformation adopts triangle heating to the edge of the wing, eg.
The specific method and requirements of the linear heating correction of the triangle and the transverse diagram are the same as those described in the second method in 2. Use medium temperature correction, less water, such as shower level. In addition, water cooling should not be used for steels with larger thickness or hardening tendency. In order to improve the correction effect and quality, an external force can be applied to clamp the flange plate toward the concave side with a flat tool during the heating process.
4. Wave deformation of beam and column web repair Wave deformation should first find out the protruding peak, use the dot heating method to correct it with a hand hammer, the diameter of the heating dot is 50 (larger plate thickness or wave deformation area) The larger diameter should choose the larger value), or it can be calculated by d = 4S + 10mm (heating point diameter d, plate thickness S). The roasting mouth moves in a spiral shape from the crest, and it is corrected with medium temperature. When the temperature reaches 600 ~ 700, place the hand hammer at the edge of the heating zone, and then hit the hand hammer with a sledgehammer, so that the metal in the heating zone is squeezed, flattened after cooling and shrinking. Pay attention to avoid excessive shrinkage stress. After correcting a dot, heat the second peak point in the same way as before. In order to accelerate cooling, water cooling is allowed for A3 and A3F steel. This correction method belongs to the point heating method, and the distribution of the heating points can be plum-shaped or chain-shaped dense dot-shaped.
5. The concave deformation of the flange connection plate at the end of the beam and column. The beam and column blue plate refer to the beam and connection plate, the beam and column connection plate and the column foot bottom plate.
The concave deformation of the connecting plate is also a common problem. The corrective measures are as follows, see.
The convex "position roasting nozzle moves 4UC linear heating to correct the concave deformation of the connecting plate parallel to the width of the flange on the connecting plate, linear heating from the middle to both ends, the two heating belts should be synchronized. Low temperature correction method or medium temperature correction method can be used.
When using this correction method, it is better to plan the welding seam between the transverse stiffener and the connecting plate and the connecting plate, and then weld it to the connecting plate immediately after the correction. It is difficult to repair the deformation here, and the firework size should be mastered.
4. Conclusion The stress caused by flame correction is the same as the welding stress. Inappropriate correction results in the correction of the internal stress of the snare value. The superposition of the welding internal stress and the load stress will make the total stress of the beam and column to the P area exceed the allowable stress and reduce the load safety factor. Try to adopt reasonable technological measures to reduce deformation during manufacturing, and pay attention to the following points when it is determined that flame correction is required: (1) The location of the fire should not be near the maximum stress section of the main beam; (2) The area of ​​the fire at the correction is at a cross section The upper part should not be too large, and several cross-sections can be selected; (3) It is advisable to use spot heating to improve the stress state of the heating zone;
Pots And Pans Organizer,Pot Lid Organizer,Pan Organizer,Pan Holder
ROYALWIND IMPORT&EXPORT CO.,LTD , https://www.hoombest.com