Introduction to the advantages and disadvantages of submerged arc welding
ALAND WELDING Let you feel the most sincere welding service
1. Concept of submerged arc welding
Submerged arc welding (including submerged arc surfacing and electroslag surfacing, etc.) is a method in which the arc burns under the flux layer for welding. Its inherent advantages of stable welding quality, high welding productivity, no arc light, and little smoke make it the main welding method in the production of important steel structures such as pressure vessels, pipe sections, and box beams and columns. In recent years, although many efficient and high-quality new welding methods have emerged, the application fields of submerged arc welding have not been affected in any way. From the perspective of the weight share of deposited metal by various fusion welding methods, submerged arc welding accounts for about 10% and has changed little over the years.
2. Advantages of submerged arc welding
Submerged arc welding is one of the most efficient mechanized welding methods today. Its full name is submerged arc automatic welding, also known as automatic arc welding under the flux layer. advantage:
(1) High production efficiency
This is because, on the one hand, the conductive length of the welding wire is shortened and the current and current density are increased, so the arc penetration and wire deposition efficiency are greatly improved. (Generally, the penetration depth on one side without beveling can reach 20mm.) On the other hand, due to the heat insulation effect of the flux and slag, there is basically no heat radiation loss on the arc, and there is less spatter. Although the heat loss used to melt the flux is has increased, but the overall thermal efficiency is still greatly increased.
(2) High quality welds
The protective effect of slag in isolating air is good, the welding parameters can be kept stable through automatic adjustment, the technical level of the welder is not high, the composition of the weld is stable, and the mechanical properties are relatively good.
(3) Good working conditions
In addition to reducing the labor intensity of manual welding operations, it has no arc radiation, which is a unique advantage of submerged arc welding.
3. Disadvantages of submerged arc welding
Submerged Arc Welding is a commonly used welding method, but it also has some disadvantages:
(1) High cost: Submerged arc welding equipment is relatively expensive, especially for small-scale production or individual users, which may be a significant investment.
(2) High professional skill requirements: Submerged arc welding requires skilled operation and technical knowledge. Operators require specialized training to ensure welding quality and safety.
(3) Not suitable for small welding: Since the welding wire used in submerged arc welding is thicker, it is not suitable for welding small parts. For thinner materials or projects that require more delicate welds, other welding methods may be more suitable.
(4) Not suitable for vertical or overhead welding: Submerged arc welding is usually suitable for horizontal or nearly horizontal welding positions. When welding vertically or overhead, uneven welding or residual welding slag may occur due to poor fluidity of the solder.
(5) The weld is not easy to inspect: Since the weld is covered under the solder during the welding process, the quality and integrity of the weld are not easy to directly observe. This may require additional non-destructive testing to ensure weld quality.
(6) More waste is generated: Submerged arc welding uses more solder and welding wire, so more waste is generated. This not only increases costs, but also has a certain impact on the environment.
4. Submerged arc automatic welding
(1) Process of submerged arc automatic welding
During automatic submerged arc welding, the processes of igniting the arc, feeding the wire, moving the arc along the welding direction, and finishing the welding are completely completed mechanically.
After the flux 2 flows out from the funnel 3, it is evenly deposited on the assembled workpiece 1. The welding wire 4 is fed into the welding arc zone by the wire feeding mechanism through the wire feeding roller 5 and the contact nozzle 6. The two ends of the welding power source are connected to the contact tip and the workpiece respectively. The wire feed mechanism, flux funnel and control panel are usually mounted on a trolley to realize the movement of the welding arc.
The welding process is automatically controlled by operating the button switch on the control panel. During the welding process, the workpiece is covered with a layer of 30-50mm thick granular flux. The continuously fed welding wire generates an arc between the flux layer and the weldment. The heat of the arc melts the welding wire, workpiece and flux to form a metal. molten pool, insulating them from the air. As the welding machine automatically moves forward, the arc continues to melt the weldment metal, welding wire and flux in front, while the edge behind the molten pool begins to cool and solidify to form a weld, and the liquid slag then condenses to form a hard slag shell. Unmelted flux can be recycled.
The function of welding wire and flux during welding is the same as that of the electrode core and electrode coating of manual arc welding. When welding different materials, welding wires and fluxes of different compositions should be selected. For example, H08A welding wire is often used when welding low carbon steel, and high manganese and high silicon flux HJ431 is used. Welding power sources usually use arc welding transformers with larger capacities.
(2) Advantages of submerged arc automatic welding
The main advantages of submerged arc automatic welding are:
① High productivity The wire extension length of submerged arc welding (the length of the wire from the end of the contact tip to the end of the arc) is much shorter than that of manual arc welding, generally around 50mm, and it is a light wire, which will not cause damage due to increased current. To solve the problem of redness of the electrode coating, a larger current can be used (5-10 times larger than manual welding). Therefore, the penetration depth is large and the productivity is high. For butt welding below 20mm, no grooves and no gaps can be left, which reduces the amount of filler metal.
② High weld quality: The welding pool is well protected and there are fewer impurities in the weld metal. As long as the welding process is properly selected, it is easier to obtain stable and high-quality welds.
③Good working conditions. In addition to reducing the labor intensity of manual operations, the arc light is buried under the flux layer and there is no arc radiation, so the working conditions are good. Submerged arc automatic welding is still the most commonly used welding method in industrial production. Suitable for welding larger batches, thicker and longer straight lines and larger diameter circular welds. It is widely used in the manufacturing of chemical containers, boilers, shipbuilding, bridges and other metal structures.
This method also has shortcomings. If it is not as flexible as manual welding, it is generally only suitable for welds in horizontal positions or with small inclinations. The quality requirements for edge preparation and assembly of workpieces are high and time-consuming. Since it is a submerged arc operation, it cannot be seen. To the formation process of molten pool and weld seam, therefore, welding specifications must be strictly controlled.
5. Submerged arc semi-automatic welding
Submerged arc semi-automatic welding is mainly automatic hose welding, which is characterized by the use of thinner diameter (2mm or less) welding wire, which is fed into the molten pool through a curved hose. The movement of the arc is done manually, while the feeding of the welding wire is automatic. Semi-automatic welding can replace automatic welding for welding some curved and shorter welds. It is mainly used for fillet welds and can also be used for butt welds.
6. Submerged arc welding operation technology
(1) The trolley wheels of the submerged arc automatic welding machine should be well insulated, and the wires should be well insulated. The wires should be straightened out during work to prevent them from twisting and being burned by slag.
(2) The control box and welding machine shell should be reliably grounded (zero) and prevent leakage. The terminal block cover must be closed.
(3) During the welding process, care should be taken to prevent the flux from suddenly stopping supply and causing strong arc light exposure and burns to the eyes. Therefore, ordinary protective glasses should be worn during welding operations.
(4) The welding handle of semi-automatic submerged arc welding should be placed in a fixed place to prevent short circuit.
(5) The components of submerged arc automatic welding flux contain manganese oxide and other substances harmful to the human body. Although welding does not produce visible smoke like manual arc welding, it will produce a certain amount of harmful gases and vapors. Therefore, it is best to have local extraction and ventilation equipment at the work site.
7. Submerged arc welding process
Preparation before welding: Preparations must be made before submerged arc welding, including groove processing of the weldment, surface cleaning of the parts to be welded, assembly of the weldment, cleaning of the surface of the welding wire, and drying of the flux, etc.
①Bevel processing
The groove processing requirements are implemented in accordance with GB 986-1988 to ensure that there is no incomplete penetration or slag inclusion at the root of the weld and to reduce the amount of filler metal. Bevel processing can use edge planing machines, mechanized or semi-mechanized gas cutting machines, carbon arc gouging, etc.
②Cleaning of the parts to be welded
Weldment cleaning is mainly to remove rust, oil and moisture to prevent the occurrence of pores. Generally, sandblasting, shot blasting or manual removal is used, and if necessary, flame is used to bake the parts to be welded. Before welding, the surface of the groove, the 20mm area on both sides of the groove, and the parts to be welded should be cleaned of rust, oxide scale, oil, etc.
③Assembly of weldments
When assembling weldments, ensure uniform gaps, flat heights, and small misalignment. The length of the tack weld is generally greater than 30mm, and the quality of the tack weld is consistent with the quality requirements of the main weld. Use special tooling and fixtures when necessary.
For the assembly of straight seam weldments, arc strike plates and lead-out plates should be installed at both ends of the weld, and then cut off after welding. The purpose is to obtain a normal size weld cross section at the beginning and end of the weld joint, and also to Defects that easily occur in arc starting and closing can be eliminated.
④Cleaning of welding materials
The welding wire and flux used in submerged arc welding have a great influence on the composition, structure and properties of the weld metal. Therefore, oxide scale, rust and oil stains on the surface of the welding wire must be removed before welding. When storing the flux, pay attention to moisture-proof, and it must be dried at the specified temperature before use.
8. Submerged arc welding process parameters
The main welding parameters of submerged arc welding include: welding current, arc voltage, welding speed, wire diameter and extension length, etc.
①Welding current
When other parameters remain unchanged, the effect of welding current on the shape and size of the weld.
Under general welding conditions, weld penetration is proportional to the welding current.
As the welding current increases, the penetration depth and weld reinforcement increase significantly, while the width of the weld does not change much. At the same time, the melting amount of the welding wire also increases accordingly, which increases the reinforcement of the weld. As the welding current decreases, both the penetration depth and the residual height decrease.
②Arc voltage
As the arc voltage increases, the welding width increases significantly, while the penetration depth and weld reinforcement decrease. However, when the arc voltage is too high, it will not only reduce the penetration depth and cause incomplete penetration, but also lead to poor weld formation, difficulty in slag removal, and even defects such as undercuts. Therefore, while increasing the arc voltage, the welding current should also be appropriately increased.
③Welding speed
When other welding parameters remain unchanged and the welding speed increases, the welding heat input decreases accordingly, so that the penetration depth of the weld also decreases. Welding speed that is too high will cause defects such as incomplete penetration. In order to ensure welding quality, a certain amount of welding heat input must be ensured. That is, while increasing the welding speed in order to increase productivity, the welding current and arc voltage should be increased accordingly.
④Welding wire diameter and extension length
When other welding parameters remain unchanged and the diameter of the welding wire increases, the diameter of the arc column increases, that is, the current density decreases, which will cause the width of the weld to increase and the penetration to decrease. On the contrary, the penetration depth increases and the weld width decreases.
When other welding parameters remain unchanged and the length of the welding wire increases, the resistance also increases, the preheating effect on the extended part of the welding wire increases, and the melting speed of the welding wire accelerates. As a result, the penetration depth becomes shallower and the weld reinforcement increases. Therefore, The extension length of the welding wire must be controlled and should not be too long.
⑤Welding wire inclination angle
The tilt direction of the welding wire is divided into forward tilt and backward tilt. The direction and size of the inclination angle are different, and the force and heat effects of the arc on the molten pool are also different, thus affecting the formation of the weld. When the welding wire is tilted back at a certain angle, since the arc points in the welding direction, the weldment in front of the molten pool is preheated, and the arc’s effect on discharging liquid metal in the molten pool is weakened, resulting in a wider weld and shallower penetration. On the contrary, the weld width is smaller and the penetration depth is larger, but it is easy to cause unfusion and undercutting at the edge of the weld, and the weld shape will be deteriorated.
⑥Others
a.Groove shape b. Root gap c. Weldment thickness and weldment heat dissipation conditions.
9. Application scope of submerged arc welding
Currently it is mainly used for welding various steel plate structures. Weldable steel types include carbon structural steel, stainless steel, heat-resistant steel and its composite steel, etc. Submerged arc welding is most widely used in shipbuilding, boilers, chemical containers, bridges, hoisting machinery, metallurgical machinery manufacturing, marine structures, and nuclear power equipment. In addition, submerged arc welding is used to weld wear-resistant and corrosion-resistant alloys or to weld nickel-based alloys. Copper alloys are also ideal.
