Abstract : The welding characteristics of the integral joint of Sunkou Yellow River Bridge are introduced. Positioning welding, unequal thickness butt welding, angular welding, fillet welding, and flat joint plate welding technology eliminate the problems of undercuts, grooves, high temperature cracks, burn through and welding deviation caused by angular welding, etc. A reasonable welding sequence ensures the manufacturing accuracy and welding quality of the overall joint.
Key words : Yellow River Bridge; steel bridge; gusset plate; integral joint; welding process; tack welding; butt welding; fillet welding
CLC number: U445.583 Document code: A Article ID: 1003-4722(1999)02-0044-02
1 Introduction
The Sunkou Yellow River Bridge is a railway double-line under-supported vertical truss-type truss-welded continuous truss girder with a span of 4×180 m and a total of 4 links. The whole node is the new structure adopted for the first time in China. It has the advantages of saving steel and high-strength bolts, which is conducive to the construction of the site, and is the future development direction. The overall node structure is complex and the welds are dense. There are butt welds, angular welds and fillet welds. The welding quality is high and the yield strength is tight. In the welding experiment, there are still insufficient butt joints, angular joints, and undercuts. Problems such as high temperature cracking and burn through. With the joint efforts of Baoji Bridge Factory and related units, the problem was solved, the quality of welding was ensured, and it was completed more than one month in advance.
2 Welding technology research of Sunkou Yellow River Bridge
2.1 Main technical indicators of welded joints:
Docking σs(W)=σs(B)+100 (MPa); corner joint σs(W)=σs(B)+120 (MPa); three zones of various welded joints-25°C, AKV≥48J(35J) .
2.2 Welding process research The SM490C steel butt joint, angular joint and corner joint welding process were studied. Welded various welded joints with optimized H08MnT or H10Mn2, H08MnA welding wire, SJ101 flux and welding process. According to the revised technical specifications, it is known that H10Mn2 welding wire can meet the technical requirements of butt joint and angular joint. H08MnA welding wire can meet angular joint. Technical requirements.
In the welding process, the welds with insufficient penetration of the weld depth are improved by changing the groove size, the groove angle and adjusting the welding parameters; the groove and undercut problems of the angular weld are changed by changing the wire inclination Angle and wire alignment position, adjust the welding sequence to solve it; for the high temperature crack generated in the first weld of the angular weld, reduce the welding current, reduce the welding speed, increase the arc voltage by changing the groove size Or use CO2 gas shielded welding to make a solution.
3 Welding of the integral node of the Yellow River Bridge in Sunkou
3.1 Construction of the overall node The overall node of the upper and lower chords of the Sunkou Yellow River Bridge is composed of two webs with nodes, two cover plates, six partition plates and inner support plates, joint plates, and flat joint plates. It is composed of components such as connecting plates. In order to save steel, the cover and the web are made of steel plates of different sizes and thicknesses.
3.2 Welding
3.2.1 Positioning welding
In order to ensure the mutual position of the pre-weld parts, the part is prevented from being tilted and the tack welding is performed. Because the positioning welding bead is short, the cooling speed is fast, and the weld heat affected zone is prone to hardened structure, thereby forming cold cracks. For this reason, the preheating temperature for preventing cold cracks was established by the oblique Y-bevel weld crack test method. The tack welding is performed by E5015, a low-hydrogen type electrode with low hydrogen content and good crack resistance. In order to not affect the penetration depth and prevent the undercut of the small solder fillet, the welding of the inside of the groove and the small solder fillet is performed with a î€Ï†3.2 mm electrode, and the rest is made of î€4 mm electrode. In order to prevent cold cracking of the tack welding, the length of the tack welding of the thick plate must be ≥ 80 mm, and the thickness of the thin plate must be ≥ 50 mm.
3.2.2 Butt welding
The cover and the web of the upper and lower chords of the integral node are formed by butting the steel plates of different sizes and thicknesses. This process was first applied to the chord. To ensure the toughness of the butt joint, î€Ï†5 standard welding wire H10Mn2 and SJ101 flux with high manganese content were selected. Weld a variety of butt joints with optimized welding parameters (see Table 1). The arc test plate data proves that the mechanical properties of various butt joints meet the technical requirements. Butt welding is performed by MZ-1-1000 type welding machine. When the welding machine encounters the tack welding, the arc voltage is constant, the current is automatically reduced, and the tack welding cannot be melted, which seriously affects the penetration of the butt weld and the escape of the pores during the tack welding. Increased measures to clear roots with carbon arc gouging.
Table 1 Butt joint, angular joint, corner joint welding parameters
| Connector type | Composition thickness | Wire diameter Mm | Flux | Welding parameters | |||||||
| Number of weld beads | V strip m*n -1 | I/A | u/V | V car m*n -1 | Preheat / °C | Layer temperature / °C | Wire inclination / (°) | ||||
| Docking | 16+16～18 | 5 | SJ101 | 1 1 | 730±35 | 30±1 | 25 | No ~ ≥ 20 | ≤100 | ||
| Docking | 20+20～36 | 5 | SJ101 | 2 2 | 730±35 | 28±1 31±1 | 25 | No ~ ≥ 20 | ≤135 | ||
| Docking | 24+24～36 | 5 | SJ101 | 2 3 | 730±35 | 28±1 31±1 | 21.5 | No ~ ≥ 20 | ≤135 | ||
| Docking | 28+28～32 | 5 | SJ101 | 2 5 | 730±35 | 28±1 31±1 | 21.5 | ≥20 | ≤135 | ||
| Docking | 32+36 | 5 | SJ101 | 2 5 | 730±35 | 28±1 31±1 | 21.5 | ≥20 | ≤135 | ||
| edges and corners | 24~28 +24～36 | 5 | SJ101 | 1 2 | 710±35 | 28±1 31±1 | 21.5 | No ~ ≥ 20 | ≤135 | 20 | |
| edges and corners | 28+ 32~36 | 5 | SJ101 | 1 2 | 710±35 | 28±1 31±1 | 21.5 | ≥20 | ≤135 | 20 | |
| edges and corners | 20~24 +20～36 | 5 | SJ101 | 1 2 | 710±35 | 28±1 31±1 | 25 | No ~ ≥ 20 | ≤135 | 20 | |
| edges and corners | 16~20 +20～28 | 1.2 5 | SJ101 | 1 1 | 260±20 710±35 | 32±2 31±1 | 21.5 | ≥60 No ~ ≥ 20 | ≤135 | 20 | |
| Corner connection k=12 | 16~32 +16～36 | 5 | SJ101 | 1 1 | 68.5 | 750±35 | 31±1 | 18 | No ~ ≥ 20 | no | |
| Corner connection k=10 | 16~20 +16～28 | 5 | SJ101 | 1 1 | 62.5 | 730±35 | 30±1 | 19.5 | No ~ ≥ 20 | no | |
The angular connection of the integral joint is the first application in China. The standard welding wire H10Mn2 and SJ101 flux with high manganese content are selected. Various angular joints are welded with optimized welding parameters (see Table 1), and all mechanical properties meet the technical requirements. Due to the long angular welds, the cover plate has a machining side bend, the welding of the rods causes the assembly gap to be partially out of tolerance, and because of the composition of the steel plate containing the hot crack sensitive element Nb, a weld deviation occurs in the first weld. Burn through and high temperature cracks seriously affect the quality of the weld. In view of the above problems, careful adjustment of the track and wire alignment position is adopted for the installed rigid track, and the free swing height of the welding head is shortened to prevent the welding deviation. For the gap excess that occurs, the bottom of the partition is manually welded, and the rest is clamped with a clamp to prevent burn-through. By reducing the welding current of the first weld, slowing down the speed, increasing the arc pressure, and improving the weld forming coefficient, the low-melting inclusions in the weld are easy to float and prevent high-temperature cracks. For the problem of insufficient penetration of the deep penetration reserve, the welding rod with î€Ï†3.2 mm is used for the tack welding, and the operation method of the CO2 gas shielded welding is improved and the height of the weld overlay is limited to ensure the penetration.
3.2.4 fillet weld
(1) Submerged arc automatic welding is used to weld the lower flange fillet welds of the upper and lower chords of the integral joint and the upper flange fillet weld of the upper chord. The welding wire is made of H08MnA, the flux is selected by SJ101, and various angular joints are welded with optimized welding parameters. All mechanical properties meet the requirements of technical indicators. The lower flange fillet welds of the upper and lower chords have variable cross-sections, and the MZ1-1000 welder is used for welding and welding, and the alignment of the welding wire is carefully adjusted to prevent it. Angular welds are difficult. In order to reduce the workload of such welds, the angular seams of the upper chord are designed to be replaced by fillet welds. In order to save steel and minimize the height of the extended limb, the factory designed the welder bracket.
(2) Manual welding is used to weld fillet welds such as flat joint plates, baffles, struts and joint plates. The electrode is E5015 and the diameter is î€Ï†4 mm or î€Ï†5 mm.
3.2.5 Welding sequence of the overall node
In order to ensure the weld quality and manufacturing precision of the overall joint and improve the welding efficiency, a reasonable welding sequence has been established. 1 In order to allow the components to shrink freely to reduce the welding residual stress, the cover and the web are docked on the unit. 2 After the upper and lower chords form a trough shape, the fillet welds and the fillet welds at the ends of the welded trough are welded at the ends. In order to reduce the welding deformation, the welding direction is welded from the outside to the inside. 3 After the upper and lower chords are formed into a box shape, in order to ensure the manufacturing precision of the overall joint, the inner side flange flange welds of both ends are welded first, then the angular welds are welded, and the outer flange fillet welds are finally welded. 4 Welding of other components and assembly of the winding gusset plate.
In order to ensure the quality of the weld and the flatness of the cover plate of the gusset plate, the groove size is improved and the outer fillet weld of the joint node is welded first, and then the angle of the inner fillet weld, the flat joint plate and the spreader of the flat joint plate are welded. Weld seam, after welding, re-weld the fillet weld of the cover and the gusset. In order to improve the fatigue strength of the end of the flat joint plate, in addition to smoothing the end portion, the hammering is added.
(1) Various welded joints welded by the preferred welding materials and welding process and a number of measures taken in the production to make the welds look beautiful and the internal quality is good. The pass rate of the butt welds is 99.85%, and the angular welds are The pass rate of seam inspection reached 96.43%, and the pass rate of corner joint welds reached 99.13%. Beyond the best level in history. All mechanical properties meet the requirements of technical indicators.
(2) The hammering of the end of the whole node, the angular joint and the end of the joint plate are the first application in China. This new technology is close to the international advanced level.
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