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Technical operation specification for submerged arc automati

Source of the article:admin popularity:Time of publication:2021-1-3

1 Preparation
(1) Be familiar with the welding process of the parts to be welded, understand the welding position, size and technical requirements, and select the welding method reasonably.
(2) Check the equipment thoroughly. The conductor shall be well insulated, the connecting parts shall not be loose, and the control box and power supply shell shall be grounded. The rubber wheel of the welding trolley shall be well insulated, and the mechanical moving parts shall 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 ℃ for 2 hours before use.
(4) Check the assembly quality of the weldment and the cleaning of the groove. It is required that there shall be no welding slag, oil, rust and other dirt in the groove and within 30mm on both sides.
(5) Install the run on plate and run-off plate, the plate size is 160mm × 150mm × s (length × width × product thickness), the material, thickness and groove form should be the same as the product.
(6) Wear insulating shoes, gloves and goggles during operation. For fixed position, insulation baffle can be added for heat insulation, and good ventilation facilities can be provided.
(7) The welding trolley shall be free of obstacles and the flux shall be dry. If the flux is wet, it should be dried, otherwise it will produce a lot of steam, which will increase the slag splash, easy to cause scald.
(8) In the welding process, attention should be paid to prevent arc radiation caused by sudden stop of flux.
2 welding process
The process parameters of automatic submerged arc welding mainly refer to welding current, arc voltage, welding speed, wire diameter, wire extension length, relative position between wire and weldment surface, type and polarity of power supply, type of flux and groove form of weldment. These parameters affect the shape coefficient and fusion ratio of the weld, thus determine the quality of the weld.
(1) Welding current and arc voltage
The welding current mainly affects the weld penetration and calculated thickness, while the arc voltage mainly affects the weld width. The influence of welding current and arc voltage on the weld formation is too large, the penetration (H) and reinforcement (H) are too large, the weld shape coefficient is reduced, it is easy to produce hot cracks, and even cause burn through in the welding process; too small current is easy to produce defects such as incomplete penetration and slag inclusion.
If the arc voltage is too high, the width of weld (b) will increase significantly, but the penetration (H) and reinforcement (H) will decrease. Because the arc is too long, the arc combustion will be unstable, which is easy to cause weld porosity and undercut defects. At the same time, the amount of flux melting will also increase, resulting in waste. If the arc voltage is too small, the penetration (H) and reinforcement (H) will increase, and the shape factor will decrease.
(2) Welding speed
If the welding speed is too high, the weld width (b) decreases significantly, which will produce defects such as small residual height (H), undercut and porosity; if the welding speed is too slow, the weld pool overflows, which will produce defects such as excessive residual height (H), rough forming, no fusion and slag inclusion.
When the welding speed is high, the penetration (H) decreases with the increase of welding speed; when the welding speed is low, the penetration (H) increases with the increase of welding speed.
(3) Wire diameter and extension length
When the welding current is constant, the diameter of welding wire decreases, the current density increases, the blowing force of arc on the bottom of molten pool increases, the penetration increases correspondingly, and the weld shape coefficient decreases.
In automatic submerged arc welding, the extension length of welding wire is generally 30 ~ 40mm. At the same time, the fluctuation range of welding wire extension length should be controlled in the welding process, which is generally not more than 10 mm.
Abstract: submerged arc welding has the characteristics of strong wind resistance, deep penetration and high welding efficiency. It has good economic benefits when it is applied to the prefabrication and welding construction of pipelines in petrochemical plants. The submerged arc welding technology is mature, there are many welding materials, many welding materials and flux manufacturers, and the welding quality is stable. Submerged arc welding can be operated in the open air without site restrictions, especially suitable for field pipeline automatic prefabrication.
Automatic submerged arc welding is one of the earliest automatic welding methods, which is used in the longitudinal seam welding of large pipelines. After improvement, automatic welding of pipe girth can be realized by configuring pipe driver. When submerged arc welding is used in pipe prefabrication, it is difficult to clean the welding slag. Through practice, it is found that the main reasons for the difficulty are improper adjustment of groove angle, welding current, arc voltage, welding speed and welding position, resulting in mismatching of welding parameters, and eventually resulting in difficulty in slag cleaning and defects such as lack of fusion and slag inclusion. Based on the practical application of submerged arc welding in pipeline prefabrication of Dalian Yisheng PTA project, Ningbo Zhongjin petrochemical, Jiaxing Sanjiang petrochemical and Ordos Zhongtian hechuang coal chemical project, this paper expounds the metallurgical characteristics of submerged arc welding, the influence of welding process parameters on weld quality and welding requirements, so as to prevent defects.
Advantages and disadvantages of submerged arc welding
1.1 advantages of submerged arc welding compared with other welding methods:
1) It can complete butt joint, fillet joint and lap joint of heavy parts with high welding speed and deposition efficiency.
2) Submerged arc flux can deoxidize, reduce and infiltrate alloy into weld metal, which can obtain high quality weld metal with excellent mechanical properties and high compactness.
3) There is no spatter in the process of submerged arc welding, the deposition efficiency is high, and the weld surface is smooth and clean.
4) There is no arc in the welding process, and the working conditions of welders are good.
5) Little smoke and dust are produced during welding.
6) Submerged arc welding can use 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 suitable for field pipeline prefabrication.
1.2 disadvantages of submerged arc welding
1) Submerged arc welding is only suitable for flat welding and horizontal welding.
2) The equipment covers a large area with high one-time investment.
3) Because the welding wire and molten pool can not be seen, it is not easy for the welder to judge the position and width of the weld bead, and it is not easy for the latter weld bead to weld the ideal weld bead.
4) Necessary cooling measures should be taken for the welding of materials requiring strict control of heat input.

Keywords of this article:Technical,operation,specificat