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Technical specification for automatic submerged arc welding

Part of the article: Popularity:Time:2018-07-03 16:25

1 preparation work
 
(1) be familiar with the welding process of the weldment parts, understand the weld position, size and technical requirements, and choose the welding method reasonably.
 
(2) complete the inspection of the equipment. The conductor should be well insulated, and the connection points must not be loose. The control box and the power supply case should be grounded. The rubber wheel of the welding car should be well insulated and the mechanical parts should be lubricated in time to ensure flexible operation.
 
(3) check whether the grade, specification and quality of welding wire and flux meet the requirements. The flux must be baked at 250 degrees 2H before use.
 
(4) check the assembly quality of the weldment and the cleaning of the groove. It is requested that no slag, oil, rust and other dirt shall be allowed in the groove and within the 30mm range of the two sides.
 
(5) install the arc guide plate and the lead plate. The size of the panel is 160mm * 150mm * s (length * width * product thickness). The material, thickness and groove form should be the same as the product.
 
(6) shoes, gloves and goggles should be worn during operation. For fixed stations, insulation baffles can be insulated and well ventilated.
 
(7) require welding car around barrier free, flux must be dry. If the flux is wet, it should be treated by drying. Otherwise, a lot of steam will be generated, which will increase the spatter of slag and cause burns easily.
 
(8) in the welding process, we should pay attention to prevent the arc radiation from suddenly stopping the flux.
 
2 welding process
 
The technical parameters of submerged arc automatic welding are mainly welding current, arc voltage, welding speed, wire diameter, length of welding wire, relative position of welding wire and weld surface, type and polarity of power supply, kinds of flux and groove form of welding parts. These parameters affect the shape coefficient and fusion ratio of the weld, thus determining the quality of the weld.
 
(1) welding current and arc voltage
 
The welding current mainly affects the penetration depth and the thickness of the weld, while the arc voltage mainly affects the weld width. The effect of welding current and arc voltage on weld formation is too large, H and H are too large, the shape coefficient of weld is reduced, hot cracks are easy to produce, and the welding process even causes burning through, and the current is too small, so it is easy to produce the defects such as non penetration and slag.
 
The arc voltage is too large, the melting width (B) increases significantly, but the melting depth (H) and the residual height (H) will decrease. As the arc is too long, the arc combustion is unstable, it is easy to cause the weld hole and the edge bite defect. At the same time, the flux of flux is also increased, resulting in waste; the arc voltage is too small, the melting depth (H) and the residual height (H) are increased and the shape coefficient drops.
 
(2) welding speed
 
The welding speed is too large and the weld width (B) decreases significantly. The defects such as small Yu Gao (H), edge bite and gas hole will be produced. The welding speed is too slow and the molten pool is overflowing. The defects such as oversize, rough forming, non fusion and slag inclusion will be produced by Yu Gao (H).
 
When the welding speed is large, the penetration (H) decreases with the increase of the welding speed, but when the welding speed is small, the depth of the weld (H) increases with the increase of the welding speed.
 
(3) diameter and extension length of welding wire
 
When the welding current is fixed, the diameter of the wire is reduced, the current density increases, the arc will increase the blowing force at the bottom of the molten pool, the depth of the melt is increased and the shape coefficient of the weld is reduced.
 
When the submerged arc welding is done, the length of the wire is usually 30 ~ 40mm. At the same time, the fluctuation range of welding wire length should not exceed 10mm in the welding process.
 
Abstract: submerged arc welding (submerged arc welding) has the characteristics of strong wind resistance, deep melting and high welding efficiency. It has good economic benefit in the construction of pipeline prefabricated welding of petrochemical plant. Submerged arc welding technology is mature, with many welding materials, many welding and flux manufacturers, and stable welding quality. Submerged arc welding can be operated in open air and is not restricted by site. It is especially suitable for automatic precasting of field pipelines.
 
Automatic submerged arc welding is one of the earliest automatic welding methods, initially used in longitudinal welding of large pipelines. After improvement, the pipe driver can be configured to automatically weld the girth of the pipeline. When buried arc welding is used in pipeline prefabrication, it is difficult to clean up the slag. It is found through practice that the main reasons are the angle of the groove, the welding current, the voltage of the arc, the welding speed, the welding position, the mismatch of the welding parameters, the difficult to lead to the slag and the unmelting and the slag. And other defects. In this paper, the actual application of submerged arc welding in the pipeline prefabrication of Zhongjin petrochemical, Jiaxing Sanjiang petrochemical and Erdos sinicu coal chemical project was applied in Dalian Yisheng PTA engineering transformation project. The metallurgical characteristics of the submerged arc welding, the influence of welding parameters on the weld quality and the welding requirements were expounded, and the defects were prevented.
 
 
Analysis of the merits and demerits of submerged arc welding
 
1.1 advantages of submerged arc welding compared with other welding methods:
 
1) the butt joint, corner joint and lap weld of heavy workpiece can be completed with high welding speed and deposition efficiency.
 
2) the submerged arc flux has the function of deoxidizing and reducing the infiltration of alloy into the weld metal, and the high-quality weld metal with excellent mechanical properties and high compactness can be obtained.
3) there is no splash in the submerged arc welding process. The welding efficiency is high and the surface of the weld is smooth and neat.
 
4) there is no arc light in the welding process, and the welder's working conditions are good.
 
5) little smoke and dust were produced during the welding process.
 
6) submerged arc welding can adopt large welding current, voltage and welding speed, easy to realize automatic welding, wide range of welding parameters adjustment and high production efficiency.
 
7) submerged arc welding is not sensitive to wind, so it is most suitable for field pipe prefabrication.
 
 
1.2 defects of submerged arc welding:
 
1) submerged arc welding is only suitable for flat welding and transverse welding.
 
2) the equipment covers a large area and has a high investment in one time.
 
3) because the welding wire and weld pool can not be seen, it is not easy for the welder to judge the location and width of the bead.
 
4) the necessary cooling measures should be taken for the welding of materials requiring strict control of heat input.

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