Selection and Thinking of Welding Materials for Bridge Steel Structures

Main products and common welding consumables
Our company is a strong comprehensive enterprise in the domestic railway turnout and bridge manufacturing industry. The bridge steel structure manufacturing level has always led the development of the industry and enjoys a high reputation at home and abroad. It has been hailed as the cradle of China's “steel bridge”. At present, it is undertaking the manufacturing tasks of the Hong Kong-Zhuhai-Macao Bridge, the New York-based Verrazano Strait Bridge and the Yalu River Bridge.
The domestic bridge structural steel is mainly Q370 grade and Q345 grade, and some adopt Q390 grade and Q420 grade steel, which conforms to "low alloy high strength structural steel" (GB/T1591-2008) and "structural steel for bridge" (GB/T714- 2008) Standard, higher strength grades have not been applied in bridge engineering. The welding methods commonly used in the manufacture of bridge steel structures are submerged arc welding and gas shielded welding, and a small number of welding rod arc welding is used. The corresponding commonly used welding materials are shown in the attached table.

According to the different structural forms of steel bridges, the proportion of welding materials used is different: 1 For highway steel box girder bridges, the amount of gas shielded welding is large, accounting for about 85%, and the amount of submerged arc welding is small, accounting for about 15%, electrode arc welding About 2%. 2 For truss bridges, submerged arc welding is used in a large amount, accounting for 58%, gas shielded welding is about 40%, and electrode arc welding is about 2%.
Welding material selection problems encountered in production
(1) The selection range of high-quality welding materials is small. With the continuous improvement of the strength grade and toughness standards of bridge steels, the demand for high-strength, high-toughness and low-hydrogen welding materials is increasing, such as the Q420qE steel plate of Nanjing Dashengguan Yangtze River Bridge. Welded joints require -40°C shock absorption energy ≥48J. For welded joints of Q345qE and Q370qE steel plates, the impact absorption energy of -40°C is ≥47J, and the impact toughness of the butt welds of thin plates with thickness ≤16mm is difficult. From the welding material standard, the general requirement is -40 °C impact absorption energy ≥ 27J or 34J, the welding material standard is lower than the mechanical properties of the product weld. In addition, while requiring high toughness, it is also required that the strength of the weld metal should not exceed the strength of the base metal, that is, the super strength is limited. Take the Nanjing Dashengguan Yangtze River Bridge as an example, the butt weld does not exceed the actual value of the base metal 100 MPa. The fillet weld does not exceed the actual value of the base material by 120 MPa.
With the development of steel bridges in the direction of height, heavy load, full welding and large section manufacturing, higher requirements are imposed on the crack resistance of welding consumables, and the requirements for diffusing hydrogen content are lower. For example, the Hong Kong-Zhuhai-Macao Bridge proposes to use diffusible hydrogen content ≤ 5mL/100g ultra-low hydrogen welding consumables, which puts high demands on the production of flux-cored wire. Due to the high cost of research and development of welding consumables, low dosage and low profit, the research and development of high-quality welding materials in China does not match the development of high-performance steel sheets, and there are few high-quality welding materials.
(2) Welding materials qualification certificates selected for foreign projects are not complete In recent years, our company has successively manufactured steel bridges and hydraulic steel structures in the United States, Germany, Canada and other countries. Due to different welding quality management systems, welding technical standards and welders Qualification requirements are different. For example, EU steel structure products have CE certification for welding consumables. American steel structure products require ABS certification for welding consumables. Canadian structural products have CWB certification for welding consumables, and China's welding consumables generally It has ABS or classification society certification, and there are fewer welding consumables with CE certification. There are fewer welding consumables with CWB certification from Canadian Welding Bureau. The steel structure manufacturers have a small range of selection. Some varieties are not available in China and can only be imported from abroad.
Expectations and suggestions for the future development and development of welding consumables
(1) Reduce dust, sewage, noise and reduce environmental pollution during the production of welding materials.
(2) Improve the processability of the welding consumables, reduce the smoke generated during the welding process, and reduce environmental pollution and welder hazards.
(3) Improve the welding material formulation, improve the welding deposition efficiency, and produce high-efficiency and energy-saving welding materials.
(4) With the popularization and application of welding robots and welding special machines in the field of steel bridge manufacturing, green welding workshops are gradually emerging, and the amount of barreled gas shielded welding consumables for welding robots or welding special machines will increase in the steel bridge manufacturing industry.

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