In recent years, with the rapid development of China's economic construction, cold-formed steel products will gradually be accepted by the market. Cold-formed square rectangular tubes are used as columns and H-beams for building beams. Their good seismic performance and economic advantages will be gradually recognized and valued, and their development potential in the construction of industrial and residential buildings is great. Many domestic manufacturers are also optimistic about the market prospects of structural cold-formed rectangular tubes and other cold-formed steel products for building structures, and new production lines are under construction. Today's developed countries are our tomorrow. Like hot-rolled H-beam products, cold-formed steel products have a very broad application prospect in building steel structures.
Brief introduction of technical characteristics of cold-formed welded pipe production
1 Basic production process of cold-formed square rectangular welded pipe
In the current cold-formed rectangular welded pipe production line, the representative production process is as follows:
Hot rolled coil → uncoiler → straightening machine → cutting head tail machine → head and tail butt welding machine → spiral looper → preforming unit → forming unit → high frequency welding machine → deburring machine → air cooling section → → water cooling section →Sizing machine→milling saw→traveling and falling 垛→packing→stocking and stacking.
2 Main technical features of cold-formed square rectangular welded pipe production
The key technologies for cold-formed square rectangular welded pipe production include: forming technology, high-frequency welding technology, cutting technology and rapid roll changing technology. These technologies directly affect the quality and production efficiency of the cold-formed rectangular welded pipe produced.
1) Forming technology
From the perspective of the production technology of cold-formed steel, the rectangular tubes produced abroad are basically round-shaped. The earlier production is to cold-bend into a circle, and then the tube is heated to the normalizing temperature, and then the rectangular tube is formed in the sizing process. The advantage of this process is that the residual stress of the finished steel tube is small, and the radius of the corner arc is small. However, high energy consumption, high cost and poor surface quality are currently only produced in the UK. At present, foreign countries basically adopt cold-type round-square process. Compared with the direct-formed process of roll bending which is more commonly used in China, the advantage of cold-state round-square is that the product has high dimensional accuracy, good weld quality and corner. The tip and the shape are regular. The disadvantage is that the construction investment is large and the corner work hardening is heavier.
The circular deformation process and the direct square process are divided into roll forming and row roll forming in the forming mode. The main difference is that in the preforming stage, the subsequent production processes are not much different. Roll forming is a traditional forming process that performs cold forming by performing a series of matching roll designs on a roll during the preforming stage and then sizing. Roller forming is an advanced cold-formed rectangular welded pipe forming technology invented by a Chinese American craftsman. It is referred to as Dragon Forming. It is the patented technology of Yoder Company of the United States. Now the main process design of cold-formed square rectangular welded pipe in the world. And the production unit manufacturer, this molding technology is used in the new production line. It is pre-formed in the production line by the preliminary roll bending of 2~3 racks. It adopts a certain number of small rolls and uses the segmented roll design to form the roll forming, which reduces the speed difference and reduces the wear of the rolls. The loss is reduced and the product scratches are reduced. The biggest feature of the roller forming machine is that it can be changed without changing or reorganizing the rolls. The product specifications can be changed by simple adjustment, saving a lot of roll changing time. Flexible commissioning is conducive to the improvement of the yield and the commissioning time is greatly shortened. It is possible to convert the closed steel from the production side and the rectangular tube to the open steel such as C steel and channel steel without changing the mold. When producing thick heavy-duty steel, it can show obvious advantages. The cost of the products produced by the equipment will be the lowest, and the production volume will not be limited, and the production efficiency will be improved.
2) High frequency welding technology
High-frequency welding is divided into induction welding and contact welding according to whether it is in contact with the pipe. Compared with induction welding, contact welding can increase the efficiency by 50%, but it is necessary to change the contacts frequently. It is required to form the pipe well, otherwise it is easy to spark, and the weld is prone to scratches. Especially disadvantageous is that there will be welds. Residual copper, after a long time, the welded pipe is prone to corrosion. Induction welding welds are of good quality, but the welder power required for the same size of welded pipe is nearly doubled. Equipment investment is 50% to 55% higher.
The high-frequency welding machine is divided into two types: vacuum tube type and solid-state type (transistor). The solid-state type is smaller than the vacuum tube type and has high efficiency (15% high), but the reliability and maintainability are not as good as the vacuum tube type. The price of the vacuum tube is also 15% higher. The new large-scale cold-form rectangular rectangular tube production line basically adopts solid-state high-frequency welding machine. The current solid-state high-frequency welding machine technology has developed rapidly, such as the famous EFD high-frequency welding machine, which has the following latest technical features:
EFD high-frequency welding machine adopts a new unique WELDAC G2 electronic matching system, which makes the energy conversion rate as high as 85%~87%. Due to the diode rectification technology, the power factor can be constant at 0.95, no power factor is needed. make up. Frequency range: 50 ~ 500kMz. It adopts independent frequency conversion module design, and the long cable connection between the rectifier and the inverter can continuously match different loads, which has the remarkable features of high efficiency, energy saving and low running cost. The newly-built 200mm×200mm～450mm×450mm/500mm×200mm square rectangular tube production line of Baosteel Iron and Steel Technology Research Institute has selected EFD high frequency induction (maximum induction welding power 700kW) and contact welding dual function welding machine.
3) Welded pipe cutting technology
Cold-welded welded pipe needs to be cut according to the length of the fixed length after the sizing. The traditional cutting is a circular saw. The circular saw cutting has lower production cost and high production efficiency. However, after the circular saw is cut, the end face of the welded pipe has many burrs. The shear deformation is large, and the two welded pipes are not well connected during the construction of the user, and the product is difficult to meet the requirements of the European, American and Japanese standards for product quality. After the 1980s, cold-bending pipe equipment manufacturers used synchronous profiling saws (equivalent to copy milling) in the new cold-welded pipe production line, using two saw blades to simultaneously cut the steel pipe. The trajectory of each saw blade cuts off the cut of half of the pipe. When the variety is changed, the trajectory of the saw blade can be automatically adjusted according to the cross-sectional shape of the pipe. This profiling and cutting saw has smooth and smooth burr-free, low noise during milling and high precision of the fixed length. It is said that the length of the steel pipe with a length of 18m can be up to ±2.5mm. However, the investment in the profile milling machine is high, and the blade is changed every 3 to 4 hours during the production. The blade is scrapped three times and is scrapped, and the production cost is high.
Cold-formed pipe manufacturers need to select sawing equipment according to different product positioning and user requirements.
4) Quick roll change technology
The traditional welded pipe production line carries out a large change of the whole line, which usually takes 8 to 12 hours. According to the requirements of users and the competition, the famous cold-bending pipe manufacturer SMS and the American company Abbey have developed the quick roll change. The technology adopts the quick roll changing system, and the roll change required for the replacement of the variety can be completed by changing the roll car in 90 minutes, which greatly reduces the production preparation time, thereby greatly improving the design capability of the production line. At the same time, through the application of the computer, the roller position adjustment has memory, the roller position can be adjusted quickly and automatically when the product is changed, the time and error of manually adjusting the roller position are reduced, and the precision of the product is improved.
In addition to the above typical cold-bent welded pipe production technology features, some of the newly formed cold-formed steel production lines use URD-equal stiffness forming and welding frames, which can simultaneously withstand similar rolling in horizontal and vertical directions. The force and rigidity are equal, the precision of the produced products is higher, and the frame roller system can be quickly removed horizontally when the roller is changed; some production lines also adopt a new internal burr removal device, and the internal burr removal device is characterized by Deburring can also break the burr to protect the saw blade of the fixed-length milling saw. The height tolerance of the inner surface of the weld after removal of the burr is up to ±0.2 mm.