Guangzhou Steel Plate Welding Technology
Guangzhou Steel News: Since the 1980s, Chinese construction steel has been an unprecedented development, construction steel occupies a very important position in the national economy. Steel due to its many advantages, including light weight, short construction period, adaptable, attractive appearance and easy maintenance, which is widely applied. Steel development is closely related to steel production. China has become the world's steel-producing countries in 2006, Chinese steel production reached 410 million t, of which steel output up steel 140 000 000 t, energy, transportation, metallurgy, machinery, chemicals, electric power, building and infrastructure construction and other fields construction industry has become a pillar of the national economy. Our light steel steel, steel space, high-rise steel structures, bridges and other steel structures and steel industry and residential buildings, have sprung up all over the country.
At the same time, construction steel and heavy steel plate to get a lot more use of rolled H-beam flange thickness as Beijing New Poly Plaza project uses to reach 125mm (ASTMA913Gr60), the National Stadium (Bird's Nest) engineering steel Maximum thickness up to 110mm (Q460E-Z35), a large number of steel works thick steel plate, thick steel plate welded to promote the development of technology, but also enrich the scope of construction steel.
Thick plate welding
When the plate, thick plate welding filler metal consumables deposited large, long welding time, high total heat input when welding seam binding member high welding residual stress, stress and deformation after welding. Welding welding process, easy to produce hot cracking and cold cracking.
Thick plate prior to welding, the steel sheet temperature is low at the start of welding, the arc temperature up to 1250 ~ 1300 ℃, in the case of slab sheet temperature cool-heat shock, the uniform temperature distribution, so that the weld heat affected area prone to hardening - martensite weld metal embrittlement tendency to produce cold cracking increases, in order to avoid such occurrences, the slab must be heated before welding.
In the actual manufacturing process, to deal with the welding process control, to prevent weld cracking.
1. Locate welding: positioning welding thick plate construction process is the most prone to the subject site. Since the slab during tack welding, tack welding at the temperature is cooled rapidly around the "cooling medium", resulting in excessive local stress concentration, causing cracks on the material damage. Measures to address the slab during tack welding, preheating temperature progress, increase the length of tack welds and weld leg size.
2. The multi-pass welding: In the thick plate welding process, an important process is to adhere to the principle of multi-pass welding, non-swing-Road. This is due to the large slab groove weld, the weld can not fill a single channel within the groove cross-section, the results of a wide swing-pass welding is caused by base metal weld large restraint stress, the weld strength is relatively weak easily lead to weld cracking or delayed cracking occurred. The multi-pass welding The upside is: before and after a weld on a weld is a "warm-up" process; after a pre-weld on a weld acts as a "heat treatment" process, effectively improve the stress distribution in the welding process, which will help ensure the welding quality.
3. Check the welding process: welding thick plate is different from the sheet, it takes several hours or even several tens of hours to complete a welding member, and therefore strengthen the welding process, intermediate inspection, it is particularly important to facilitate the timely detection of problems, in the middle check can not stop the construction, but the construction side, edge inspection. As slag process, carefully check for cracks. Timely detection and timely treatment.
4. planks butt weld, the weld shall immediately and on both sides of the base material in each local 100 ~ 150mm range of heating, when using infrared heating electric heating plate. After heating to a temperature of 250 ~ 350 ℃ with asbestos Show cover insulation, heat 2 ~ 6h after air cooling. Such heat treatment can make improper or inappropriate cleaning before welding flux baking permeates bath diffusible hydrogen quickly escape, weld and heat affected zone to prevent hydrogen induced cracking occurs.
Ultrasonic testing thick steel after welding should be 48h or longer. As promised progress, but also can be detected again before the member factory to ensure qualified member, so as not to delay the destruction of the crack of the workpiece.
Control welding thick plate welding deformation and stress
During welding, butt welding thick plate deformation after the main angular distortion. Actual production in order to control the deformation, often the first part of the front of the welding bead, flip the workpiece, gouged after gouging weld bead negative, then flip the workpiece, and so forth. Generally, after every three to five welding stand to stand until the full front of each track weld seam. At the same time when the welding should always observe the angle of deformation, welding stand ready at any time to pay attention, in order to minimize the distortion in the welding and weld stresses. In addition, the tire mold fixture set for member constraints to control the deformation, such methods are generally applicable to the slab shaped structure, since the slab shaped structure strange shape, cross section, cross-section of various sizes, in the free state, is difficult to guarantee the dimensional accuracy assembly, positioning, welding, which requires member according to the frame, making the tire mold jig, the member is in a fixed state, thereby to control the welding deformation.
Choice and control reasonable welding sequence, which is effective measures to prevent welding stress, is also one of the most effective measures to prevent welding deformation. According to different welding methods for different welding sequence submerged arc welding generally use the inverse method, regression method; CO2 gas welding and manual welding method using symmetrical, uniform dispersion law; policy preparation reasonable welding sequence is "scattered, symmetrical uniform, reducing the degree of restraint. "
Member generated when the instantaneous welding stress, residual stress after welding, while residual deformation, which is an objective law. Usually in the production process is important to control the deformation, often take measures to increase the rigidity of the member to be welded, in order to reduce the deformation, while at the same time ignoring the increased transient stress and welding residual stress. For rigid, thick plate member, although the residual deformation is relatively small, but it will have an enormous tensile stress, and even lead to cracks. In the absence of cracks, residual stress in the course of internal force structure that is uploaded homogenization often lead to destabilization, deformation or even destruction. Therefore, welding stress control and eradication member in the production process is very important.
Target control stress is to reduce peak stress and uniformly distributed.
In more welding assembly conditions, should be based on component shape and weld arrangement, take the first weld seam shrinkage of large, small amount of shrinkage after welding weld; welding the first large degree of restraint can not free shrinkage weld, post-weld restraint of liberty can shrink smaller and principles of the weld.
In the welding process in order to reduce the excessive loss of weld heat input, the weld avoid cracks in the crystallization process, when the thickness reaches a certain thickness, should be preheated before welding, the weld on the inner periphery of a certain range of heating, heating depending on the temperature and thickness of the base material of carbon equivalent (CE) may be.
When a seam on a preheated welding member, member weld area temperature is very high, along with the progress of the welding seam, the region must produce the phenomenon of thermal expansion and contraction, and the region accounts for only member section a very small part, in addition to part of the base material are in cooling (room temperature) state, whereby the welding area a huge rigid restraint, caused great stress and even crack. If at this time symmetrical parts of the weld area is heated, the temperature slightly higher than the preheating temperature and the heating temperature is always accompanied by welding the whole, the situation will greatly reduce the stress, deformation member will be greatly improved.
Guangzhou Steel course to take certain measures to control welding stress, but most member after welding thick plate remains considerable stress, need to be completed after the member is baked in the weld seam or the back sides to remove residual stress .
China's construction steel welding technology has made considerable progress and development in the physical, chemical, metallurgy, materials, electronics, computer, automatic control and other disciplines rapid development of today, with the new technology, new materials, new equipment, new technology continue to emerge, manufacturing and installation of construction steel welding technology, is bound to get faster and better development. New technologies such as: new digital intelligent inverter welding, laser welding and cutting, high pressure electron beam welding, welding robot systems, steel production 4C control technology, computer aided design (CAD), computer-aided machining (CAM ), computer-aided detection (CAT), computer-aided evaluation (CAE), etc. will gradually get involved in the field of steel construction, so construction steel welding technology level to a new level.
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