The bending process of the steel tube bending has achieved obvious technical and economic benefits. The main bridge structure of the Beijing-Hangzhou Grand Canal Bridge is a self-anchored CFST mid-supported tied arch bridge with a main arch span of 235m and a vector height of 5875m. For the space catenary form, two main arch ribs are composed of 4-850mm steel tubes, and the cross-section is a parallelogram lattice column. Each rib is composed of four Y850<14mm (Q343C) main chords. Therefore, the linear processing of the main string tube is a key process in the fabrication of the main arch rib of the bridge, and it is also one of the difficulties.
1 The choice of main pipe bending scheme The traditional steel pipe bending process generally includes manual bending, folding bending, cold bending machine bending, medium frequency heating bending, flame heating bending, etc. Manual sanding bending is generally only suitable for small and medium The diameter of a short pipe with a small number of elbows is curved. For the large diameter and long pipe of the main arch rib of the bridge, it is obviously not applicable to continuously bend the determined catenary curve, the quality is not easy to guarantee, and the process requires sand filling. Sand cleaning, heat preservation, time and effort.
The wrinkle bending method is suitable for bending a large-diameter thin-walled tube with a relatively small bending radius, but after bending, the wall will swell a lot of wrinkles, one affecting the appearance, and the second will have a great influence on the strength of the steel structure. Therefore, it is not suitable for the bending of important steel structures of bridges.
As for the bending machine bending tube, the intermediate frequency heating bending tube, the flame heating bending tube, etc., although there is no shortage of a better bending process, but this bending method requires not only a large equipment investment, but also a production and The above-mentioned process is obviously uneconomical in the production of single-piece or small-batch elbows, and the main chord of the bridge is a low-alloy structural steel (Q345C). According to the provisions of GB50205-95, the low-alloy steel should be slowly cooled after heating to prevent embrittlement in the heating zone. The above-mentioned hot-bending pipe process requires water spray cooling immediately after bending, which is obviously not suitable for low-alloy steel pipes. The problem is that the focus of the problem is to find a pipe bending process that does not require the special equipment required for conventional processes.
The main chord tube of this bridge is made into a curved shape. The firework bending process is only required to make a simple tire frame. Several flame cutting torches can be used for several common jacks. 2 Firework bending process 21 Process principle The discussion of the firework elbow refers to the segmentation of the steel pipe to be bent on the special tire frame, and the eccentric heating (the heating zone is biased toward the upper side of the steel pipe), mainly relying on the natural cooling shrinkage of the heating part to cause the steel pipe to sag toward the eccentric heating side, and at the same time A bending process for external bending of the steel tube to promote the final bending of the steel tube. 22 Process method. The tire frame is made of a special frame for the firework. The arrangement spacing of the longitudinal linear template on the tire frame depends on the spacing of the main arch ribs. Double the station spacing and align with the site position. In order to save cost, the tire frame can be repeated so that all the upper (or lower) strings have the same curvature, as long as the main string is in the pipe joint butt ring When the ribs are arranged symmetrically at both ends with the apex of the main arch rib as the center, the two main arch ribs have a total of eight segments of the main chord segment of the same curvature except for a section adjacent to the vault, and the eight segments are used as one round. Available in the same tire carrier After completing the round of the firework elbow, only the longitudinal linear formwork on the tire frame must be repaired, which can be used as the next main chord tube segment. The main chord tube to be bent is about 20m long. Hang the tire carrier with its 180* radial line in the same vertical plane as the longitudinal centerline of the carrier.
Before the upper main frame of the main string tube to be bent, the radial line should be marked on the outside of the tube wall. See the role of the radial line: first, to facilitate the linear crown and position of the steel tube after the firework bending Inspection; second, it is convenient for positioning and precision inspection of the main arch rib body, segment assembly and pre-assembly.
Draw a heating band on the string tube. The position of the heating belt is symmetrical with the cross section of the center of the chord, and gradually spreads toward both ends. The heating belt has a width of about 40 mm and a spacing of about 400 mm (for example), and avoids the joint position of the steel pipe ring seam. The heating zone of each heating belt is arranged such as a jack and a circular clamp, and the arrangement of the circular clamp is arranged to prevent the jack from deforming the cross section of the steel pipe during the pressing process.
The number of double groups (that is, each force å© tropical is arranged on both sides of the steel pipe, and the flame torch is gradually heated from the two ends of the string tube to the middle. At the same time, the jack is controlled to press the pressure in the same pressure, and attention should be paid to each group of personnel. Synchronously symmetrical heating, and control the heating temperature at 600*C~ (when the steel is heated to 800*C, the surface color is light cherry red). After the heat is applied, the natural cooling method is adopted, and forced cooling is not allowed.
After the cold bending of the steel pipe, use the inspection line (not shown) on the tire frame to check the degree of camber and flatness of the 180* radial line on the steel pipe, and check whether the sections are bent in place according to the theoretical value. For a group of 2 thousand jacks and a pair of d), the firefighters use the unreached section again. According to this method / retrospective M section of the main string tube bending molding 23 Note When the tire frame is made, the installation position of the longitudinal line template should consider adding a certain amount of string tube rebound margin because the firework bend is to be supplemented by external forces. When the external force is released, it will inevitably cause a certain amount of rebound of the string tube to be pre-loaded with a certain amount of rebound. After the first string tube is bent, the original main string tube is evaluated according to the actual situation. Before the upper frame is bent, the inner tube wall at both ends of the string tube should be temporarily supported and strengthened to ensure that the string tube port maintains a good roundness after the firework is bent, thereby ensuring that the main string tube is bent after the bending. The wrong dimension accuracy of the interface when the segment is docked.
The heating method must be based on the longitudinal centerline of the steel pipe, and the two ends are symmetrically heated synchronously, otherwise the steel pipe will be laterally bent.
At 600*C, the effect of firework is not great; when it is higher than 900*C, the quality of the steel pipe material will decrease and the pressure and top pressure should be controlled. According to the heating temperature of the steel pipe, the pressure is applied in a timely, slow and uniform manner, otherwise the steel pipe will be partially bent. In severe cases, sharp corners or wrinkles will be formed for 2~3 times of firework, but the fired heating part should avoid overlap. Results The 850mm main chord of the Beijing-Hangzhou Grand Canal has two fire-fighting elbows. It has created a gratifying speed of about ten meters per shift (including rainy days and renovation time of template reuse), which effectively guarantees that the quality of the firework bends during the construction period of the main arch ribs is all qualified by the supervision engineer. . At the same time, the use of fire-fighting pipe bending process, compared with the traditional pipe bending process, saves a lot of equipment and mold capital investment, and achieved good economic benefits.
4 Conclusion Practice has proved that the firework elbow is a steel pipe bending process with small investment, fast bending speed, good quality and easy operation. It is especially suitable for continuous curved bending of single or small batch, large diameter and long pipe. And the relative bending radius is large, the accuracy of the bending line type is not very high, and the V high white body quality is adapted to the competition =
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