Dapeng Town Industrial Park, Tongshan District, Xuzhou City, Jiangsu Province, China
Welding is commonly used for steel structure connection, and full penetration welding is generally used for some important welds. During the local heating and melting process of metal welding, the temperature of the metal in the heated area and the surrounding parent material is very different, resulting in instantaneous stress during the welding process.
After cooling to the original temperature, the tensile stress area of the entire joint area weld and the near-seam area is balanced with the compressive stress area of the parent material, which generates welding residual stress of the structure itself.
At this time, under the action of welding stress, the welded structure undergoes various forms of deformation. The existence of residual stress and the generation of deformation are mutually transformed. By recognizing the deformation law, it is not difficult to find ways to prevent, reduce and correct deformation.
(1) Thermal effect
During welding, the weld and its surrounding area are rapidly heated, forming a huge temperature difference with the surrounding parent material. This uneven thermal field causes the steel to expand and contract to different degrees, generating thermal stress. When the thermal stress exceeds the yield strength of the steel, it will cause plastic deformation. For example, when welding a steel column, the weld expands at high temperature, while the temperature of the parent material far away is low, causing the steel column to bend or twist.
(2) Weld distribution
If the welds are not distributed symmetrically or evenly on the component, the welding thermal stress will generate a bending moment around the centroid of the component, thus causing deformation. For example, if the flange and web welds of a T-beam are not set properly, the beam is prone to bending or twisting.
(3) Welding sequence
An unreasonable welding sequence will cause the welding residual stresses of various parts of the component to be superimposed, aggravating the deformation. For example, if welding is continuously performed on one side of the steel structure, the component will bend significantly toward the welding side.
(1) Process parameters
Reasonably select welding current, speed and method. For thin plate steel structures, low current and high speed can reduce heat input and prevent burn-through and deformation. In terms of welding methods, gas shielded welding has low heat input and can be used preferentially for components with high deformation requirements.
(2) Welding sequence
Symmetrical welding is used for symmetrical components. For example, for an H-beam, two flange and web welds are welded at the same time, or the flange welds on both sides are welded in sequence to offset each other. Long welds or large components can be de-welded or skipped in sections to disperse the heat. For example, de-welding the vertical welds of large steel columns in sections can reduce longitudinal deformation.
(3) Rigid fixation
Before welding, use a clamp or tack weld to fix the component on a rigid platform to limit deformation. For example, when splicing thin plates, use a clamp to clamp it on the workbench. However, this method will produce large residual stress and require subsequent treatment.
(1) Mechanical correction
Press correction: Applicable to simple bending and deformation components. Place the deformed component on the press workbench and apply pressure on the convex surface to produce reverse deformation. For example, a bent steel beam can be restored to its original shape by this method.
Hammer correction: Use a hammer to hammer the local small deformation area. For convex or concave parts of the weld, hammer it flat, but pay attention to the force and direction to prevent new deformation.
(2) Flame correction
Use flame to heat the steel locally, expand it, and then cool and shrink it to correct the deformation. The heating position, range and temperature should be determined according to the type and degree of deformation. Bending deformation is heated on the convex surface, and twisting deformation is heated in a targeted manner. The temperature is generally controlled at 600-800℃ to prevent damage to the performance of the steel, and attention should be paid to the heating speed and method.
In short, understanding the causes of steel structure welding deformation and taking effective control and correction measures are crucial to ensuring the quality of steel structure welding and improving structural performance, which can ensure the safe and reliable application of steel structures in engineering.
