More and more building structures are used in the structure of the steel truss, especially the special type steel frame used in the stadium, exhibition hall and other large architectural structures, which embodies its unique style and has been recognized by the world. At present, there is no uniform standard for fabrication, welding and NDE of steel frames. Most of them are based on the reference of AWS standard in the United States. Truss girder welding machine mainly uses the world's advanced level of five-axis linkage intersecting line CNC cutting machine from Netherlands, Japan and other countries for cutting vehicles. The supporting software can meet the technological requirements (including the length of the inclined web and the various angles of the grooves). And using NC pipe bending machine to bend the head. After bending, the roundness and asymmetry of the head can be effectively controlled and detected. Because the head and diagonal bars and their bevel are all processed on the numerical control equipment, the assembly process id required to realize easily. Butt welding is a conventional welding seam, and the quality of welding is easy to guarantee. However, it is still impossible to achieve full penetration and ultrasonic testing when the branch pipe and the Inclined rod intersect the seam of the main pipe at the same time. This is mainly due to the defects of the inner wall of the inclined belly bar and the 1 2mm failure in the local area. So the welding strength is reduced, and the diameter of the dry rod is less than 159mum, and the CB11345 nondestructive testing can not be used.
The steel truss branch pipe is usually welded by a single arc welding and double sided forming method. This welding method inevitably brings the weld in the tube inner wall concave, or in the weld root part of the local area that does not produce (1-2 mm). And there is no weld allowed to exist according to GB11345 requirements. The defect must be repaired. The defect must be removed by air gouging or grinding wheel and then repaired. And the same defect may still exist after repairing. Moreover, the welding seam is concentrated in one part. After repeated heating, the hot expansion and contraction produces a great stress, which will cause the lamellar tearing of the matrix of the mother tube ( the rolling direction of the matrix is perpendicular to the direction of welding stress), or the residual shrinkage stress in the welding head, and it may result in the tendency of delay cold cracking and therefore the tendencies of the delay cold cracking. So there will be a serious hidden danger in the toughened.
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