2013年7月26日星期五

Bridge crane box girder manufacturing

A company has to undertake over a  overhead bridge crane  manufacturing tasks as single girder   gantry crane  span 22In, lifting the quality of 5t. In the absence of large-scale lifting equipment in the case, the use of side edge welding assembly and welding assembly sequence, effective control of welding distortion, box girder solve difficult problems flipping the successful completion of box girder welding to ensure that the technical requirements. Box girder length 361TI, Dimensions: 36000mm ~ l25mm ~ l500mm. By the Q235 welded steel plate, shown in Figure 1. Girder webs and flanges are Class I butt weld seam, the main beam and the web is a combination of Class Ⅱ weld seam; beam camber of 22mm lateral bending ≤ 8mm, twisted ≤ 3mm.
An analysis
Box girder weld quality and require high dimensional accuracy. Section size, rigidity. During the welding process, due to site conditions for lifting the restrictions, unable to box girder repeatedly overturned, only use a reasonable order of assembly and welding deformation control. In the event of deformation after welding can not be corrected, therefore, box girder manufacturing key is to control the manufacturing process in welding deformation.
Girder  bridge crane  requirements in the vertical plane must have some camber. To offset the lower beam deflection when lifting. Arch on value of L/1000, namely 22itlm. Therefore, in the manufacturing process, the use of precast webs arch deformation method to ensure that the main beam camber.

Two manufacturing processes and practices
2.1 welding personnel
Participate welder welding operation should have the appropriate qualifications. In addition. It should also be equipped with specialized technical personnel on-site guidance welding, welding inspection personnel tracking checked.
2-2 welding materials
Electrodes before use must be strictly carried out according to the instructions of the drying. Then placed insulation tube, used with the check. After drying cylinder electrode placed over 4h in the insulation should be re-drying. Drying times shall not exceed 2 times.
2_3 cutting
Automatic cutting flame cutting method.
(A) under the cover material to the upper and lower plate leveler after. Put the butt length of 400mm process margin.
(B) the material web leveler web, the first in the longitudinal direction of the stitching, and the left and right symmetrical cutting the web. On both sides to prevent the main beam webs of different sizes. Cause distortion of the main beam. For there are provisions on the main beam camber in web cutting must have the appropriate camber and camber should be larger than the main beam camber. Web cutting, the need to put 1.5L/1000, ie 33mm margin, and may not have from the center 2ITI at joints, in order to avoid weld concentrated on the lower cover joints should be staggered with the web from not less than 200mm. After cutting the length of the web error _10mm.
(C) the length of the rib cutting the length of the main beam width ribs not only big small (1mm or so). Length dimension may allow a certain degree of error (± 2mm or less). Ribs four corners should be 90. , Especially
Which is on the cover with the coupling ribs at two corners should be strictly kept at right angles to the beam web and the emperor assembly upper cover vertical, while the main beam in the longitudinal direction distortion does not occur.
2.4 Preparation of the groove
Upper and lower cover and web docking forming process can be side welding, bevel angle is 30. ~ 40. , Single-sided V-shaped groove, groove and to reduce post-weld flip workload.
2.5 assemble a welding
2.5.1 assembling a welding sequence
In order to maintain a reasonable girder camber. And effectively control the welding deformation, on the use of prefabricated arch assembly method.
(A) under the cover of the first leveler, then lower cover all the butt weld welding.
(2) the system out on the platform and the web on a consistent camber and lower cover after welding leveling. Tile on the platform, and the mounting position of the boards draw cord.
(3) to the side of the lower fixing point on the cover web, the web and the lower plate taken to ensure the verticality and the draw of the web the location of the partition line.
(4) to draw in the other flanks of the spacer board after position line. And lower cover tack welded together.
(5) the length of the separator and the angle at good position draw lines, respectively, with two webs for tack welded together.
(6) Welding bulkhead with two long vertical slit webs, and the angle fillet with two webs.
(7) assembled on the cover.
(8) under the cover of the first welding of two webs with two longitudinal seam. Welding on the cover again with two webs two longitudinal seam, and finally welded on the cover with the long spacer fillet.
(9) group for the short spacer group after the first weld short vertical separator and two webs seam, then welded on the cover with a short spacer fillet.
2.5.2 Group on clearance
Upper and lower covers and webs in docking, should leave some space, thickness 8mm, gap of 3 4mm, to ensure that the forming side welding. Two webs and lower cover in the group, the group should minimize weld gap. Clearance amount <1.0mm, in order to reduce the welding deformation. Length of the ribs with the upper cover for group, they also should be pressed components, in order to minimize the gap welding team.
2.6 Welding
To ensure the box girder welding quality and reasonable camber, and effective control of the welding deformation. Welding process is critical.
(A) before welding, check the groove and the group of quality, such as the discovery size tolerance. Should be timely treatment after welding.
(2) must be removed before welding and weld groove 20mm wide on each side of the oil, sewage, water, rust and other impurities.
(3) Welding sequence: first welding the upper and lower covers and web butt weld. Then welded two webs and lower cover two longitudinal seam; welding process, should be adopted in two or four welders while welding symmetrically to prevent the main The beams distorted.
(4) reasonable selection of welding parameters: welding method using SMAW, electrode diameter is 4.0mm, the welding current is 160 ~ 200A, arc voltage is 22 ~ 25V.
2.7 Quality Inspection
Box girder quality inspection is mainly in the manufacturing process and the manufacturing process inspection after completion of special inspection. Box girder welding is completed, the joint inspection by the quality inspection department, its geometry, camber and weld quality are in line with quality requirements.

3 Conclusions
For this large bridge box girder cranes, lifting equipment that do not have a large case, the author uses reasonable assembly and welding sequence and process measures, successfully compensate for the shortage of equipment, to avoid repeated for box girder flip, guaranteed box girder welding quality and meet the size requirements.

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