Welding repair method for anode steel claw

Abstract

Welding repair of the claw leg of the steel claw is achieved through the electric resistance welding technology, the claw leg does not need to be beveled, welding wires are not needed, the steel surface is in a micro-melting state in an electric heating and resistance heat heating mode, and then certain pressure is applied to enable the claw leg of the steel claw and the cross beam to be welded together. The method is high in welding efficiency and low in cost, and does not need professional welders.

Description

Technical Field

[0001] The invention relates to the repair of an anode steel claw of an aluminum electrolytic cell, in particular to a welding repair method of an anode steel claw. Background Art

[0002] Electrolytic aluminum is a traditional high-energy-consuming enterprise. At present, the electricity consumption of my country's electrolytic aluminum enterprises generally reaches more than 13,600 kWh. The electrolytic aluminum industry is currently calculated based on an operating capacity of 38 million tons, and the electricity consumption per ton of aluminum is calculated based on 13,600 kw.h / ton of aluminum. The annual electricity consumption is 516.8 billion kWh, accounting for about 6.5% of the total social consumption in the country. Energy conservation and emission reduction in the electrolytic aluminum industry are urgent.

[0003] Anode steel claws in the electrolytic aluminum industry are consumables. As the use time increases, their claw legs will gradually become thinner, especially the claw legs on both sides. When they become thinner to a certain extent, the conductivity is poor, and the thinned claw legs need to be repaired before they can be put into use. At present, there are three common methods for repairing anode steel claws in aluminum electrolytic cells: one is two-protection welding, that is, welding the thinned claw legs to make them thicker or sawing and opening the thinned claw legs, and repairing the new claw legs with two-protection welding full-section welding. The second is the wire electrode electroslag welding technology, after cutting the old claw legs, use the new claw legs to support the formwork at the beam and then perform electroslag surfacing welding, the third is the plate electrode electroslag welding technology, after cutting the old claw legs, use the new claw legs to support the formwork at the beam and then perform plate electrode electroslag surfacing welding. In actual use, there are two types of anode steel claws to be repaired: one is a steel claw with an anode guide rod, and the other is a steel claw without an anode guide rod. There are certain problems in repairing steel claws using the above two methods, and the main shortcomings are as follows:

[0004] 1. Low welding efficiency: Secondary welding is used The steel welding wire fills the groove of the crossbeam and the new claw leg for repair. It takes 30 minutes to weld one claw leg. The steel welding wire is used to fill the molds of the beam and claw legs to complete the repair. It takes 20 minutes to weld a claw leg. Plate electrode electroslag welding uses steel plates as filler metal, and it takes 15 minutes to weld a claw leg.

[0005] 2. Poor welding quality: Secondary welding cladding repair is often manual welding, and its quality is greatly affected by the workers' technical level and is unstable. However, due to the large current and long-term welding of electroslag cladding, the metal grains in the heat-affected zone are coarse and the strength is low.

[0006] 3. It is not easy to realize automation: Since the steel claws are washed by aluminum water and electrolyte during use, they are severely deformed and corroded on the surface, and the consistency of the steel claws is very poor. It is not easy to realize automatic repair using the above two methods.

[0007] Chinese patent CN202010917100.6 proposes a surfacing method for electrolytic aluminum anode steel claws, which relates to the technical field of preparation and repair of electrolytic aluminum anode steel claws. The surfacing method includes the following steps: processing trapezoidal grooves on both sides of the bottom of the steel claw crossbeam, which are combined with the steel claw legs to form two V-shaped grooves, and surfacing is performed at the two groove positions at the same time. The surfacing speed, gas volume and wire feeding speed on both sides are kept consistent, and the welding starting point and welding end point are always symmetrical. The implementation process of this invention is extremely complicated. Manual welding on both sides of the two grooves at the same time cannot ensure the same welding quality. There are too many influencing factors, and it is difficult to achieve in tooling production. If robot welding and tooling production are realized, the cost is also very high.

[0008] Chinese patent CN201920290223.4 designs a dual-purpose machine for welding and repairing anode steel claws of electrolytic aluminum, which belongs to the field of electrolytic aluminum technology. The operation steps are: fix the steel claw beam on the turntable through the clamping claw, and then the rotating part drives the tilting module to rotate 90°, clamp and fix the steel claw claw head on the clamping claw at the front end of the positioning rod, and adjust the position of the horizontal slide and the vertical slide to align the position of the steel claw claw head with the steel claw beam. At this time, the steel claw claw head and the steel claw beam are tightly together, and the position of the welding seat is adjusted to align the welding gun with the contact position of the steel claw claw head and the steel claw beam, start the driving part of the turntable, and start the welding gun at the same time to start welding. This invention only realizes the welding of the outer area of ​​the claw leg and the beam on the welding surface, and does not realize the full interface welding of the claw leg and the beam. The conductivity needs to be improved.

[0009] Chinese patent CN201310295520.5 proposes a method for repairing anode steel claws, the operation steps are: cut off a section of the burned steel claw head by gas welding, and the length of the cut section is greater than the length of the burned section from the design length of the steel claw head; prepare a cylindrical steel rod with the same diameter as the steel claw head, vertically weld an auxiliary connecting piece between the cut surface of the steel claw head and the cylindrical steel rod, connect the two, and form two equal semicircular surfacing supplementary spaces between the cylindrical steel rod and the cross section of the steel claw head; fill the surfacing supplementary space with welding meat by surfacing welding, and after the surfacing supplementary space on one side is welded, turn the steel claw over, and use the same welding method to weld the other surfacing supplementary space. This method has low welding efficiency, and it is difficult to realize automated production to improve welding efficiency, and the consumption of welding materials and labor costs are high. Summary of the invention

[0010] The main purpose of the present invention is to solve the problems of low efficiency, unstable welding quality, and difficulty in automation in the repair process of steel claws. The welding repair of the claw legs of the steel claws is achieved through resistance welding technology. The claw legs do not need to be grooved or welded. The steel surface is in a slightly molten state through electric heating and resistance heating. Then a certain pressure is applied to weld the claw legs of the steel claws to the crossbeam. This method has high welding efficiency, low cost, and does not require professional welders.

[0011] To achieve the above object, the technical solution adopted by the present invention is as follows.

[0012] (1) Saw off the scrapped claw legs of the steel claw and prepare new claw legs.

[0013] (2) Put a graphite sheath on the claw leg of the new steel claw, and the inner side of the graphite sheath is 30mm higher than the claw leg of the new steel claw.

[0014] (3) Place an arc-starting block in the graphite sheath and add electroslag. After adding and confirming that there is no slag, turn on the power (current 2800-3100A, voltage 23-28V).

[0015] The main function of electroslag is to generate heat and provide heat and refine metals. By mass, its main components are: CaF2 30%-42%, CaO 26%-30%, Al2O3 28-36%, and the rest is SiO2. Fluoride can reduce the melting point, viscosity and surface tension of slag, promote slag flow, separate slag and metal well, and promote desulfurization and dephosphorization in the smelting process; CaO is the most commonly used alkaline oxide in steel metallurgy; Al2O3 can significantly reduce the conductivity of slag, reduce power consumption, and improve productivity. By adjusting the proportion of slag components and appropriately adding some density-reducing substances, a special slag that is easy to ignite and has a low density can be prepared.

[0016] During the power-on process, the electric slag will gradually melt and quickly heat (within 5 minutes) the new claw leg and the surface to be welded of the sawn part. When both sides melt and reach a micro-melting state (the current is stable at more than 2000A and relatively stable, and the temperature is 1200℃-1300℃), the power is turned off and an external force (30-50 tons) is applied to squeeze the two together to complete the welding.

[0017] Through the principle of electroslag metallurgy, the part to be welded is rapidly melted to a plastic state under the heat of the electrified slag, and the molten metal liquid is refined at the same time. The upper part of the round steel is melted under the action of the slag heat and metal droplets (the amount of melting is controlled by the electrification time). After the steel beam and the round steel are melted, external force is quickly applied from the bottom, so that the steel beam and the round steel are welded together tightly, so that the metal atoms interact with each other to form a reliable welded joint. The external force has the effect of pressing the steel beam and the round steel together and squeezing the liquid slag out of the joint surface of the steel beam and the round steel.

[0018] Beneficial effects of the technology of the present invention

[0019] 1. Improved welding strength: The current research status shows that the finished product welding surface of the current welding repair quality manual welding has coarse grains and a welding strength of 275-350Mpa; the present invention is refined during the welding process, the grains are fine, and the welding strength reaches 400-450Mpa.

[0020] 2. Reduce costs: The present invention realizes steel-steel welding, saves welding wire, welding materials, labor, etc., and realizes cost reduction in the production process.

[0021] 3. Improved welding efficiency: Compared with the traditional welding repair process, it is easy to operate and can achieve full-section welding while greatly improving welding efficiency. Take the three traditional welding methods as an example: Two-way welding is used The steel welding wire fills the groove of the crossbeam and the new claw leg for repair. It takes 30 minutes to weld one claw leg. The steel welding wire is used to fill the mold of the crossbeam and the claw leg to achieve repair. It takes 20 minutes to weld one claw leg. The plate electrode electroslag welding uses a steel plate as a filler metal and takes 15 minutes to weld one claw leg. However, the present invention only takes 5 minutes to weld one claw leg. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a structural schematic diagram of a new type of anode steel claw welding repair embodiment of the present invention. In the figure: 1-lower electrode; 2-claw leg; 3-graphite sheath; 4-cable; 5-electroslag; 6-claw crossbeam; 7-upper electrode; 8-the place where the steel claw crossbeam is to be welded; 9-pressure; 10-main power supply;

[0023] Figure 2 This is a visual weld diagram. DETAILED DESCRIPTION

[0024] Example 1: The claw leg length is 270 mm. The steel claw (cylindrical) is repaired and welded. The specific steps are as follows:

[0025] The first step is to cut off the damaged claw legs with gas welding, and grind the oxide scale on the part of the steel claw beam to be repaired that will be energized so that it can be energized normally. Then hoist it to the welding tooling and fix it. Grinding the oxide scale on the part to be energized is only to improve the conductivity efficiency.

[0026] The second step is to place a new steel claw leg (cylindrical) with the same size and shape as the damaged claw leg (the size and shape before the damaged claw leg was used) at the upper end of the output end of the hydraulic cylinder that can reciprocate up and down, and install an annular graphite sheath (whose inner diameter is 2mm larger than the diameter of the round steel) around the surface to be welded at the upper end of the new steel claw leg (which has the same shape and size as the lower bottom surface of the cylindrical damaged claw leg (the area to be repaired) with a remaining length of 50mm at the lower end of the steel beam). The upper open end of the annular graphite sheath is 30mm higher than the surface to be welded at the upper end of the claw leg. After the installation is completed, a 35*40*40mm volume graphite sheath is placed at the center of the upper end of the new steel claw leg. 3The arc-starting block (i.e. the conductive block composition is CaF2 powder: 60%; Al2O3 powder: 20%; TiO2 powder: 5%; the rest is iron filings) is added with electroslag. The thickness of the electroslag layer is 30mm. The electroslag is added to 5mm below the upper end surface of the arc-starting block. Be careful not to bury the arc-starting block.

[0027] The main function of electroslag is to generate heat and refine metals. Its main components by mass are: CaF2 36%, CaO2 18%, Al2O3 32%, and the rest is SiO2;

[0028] The third step is to control the claw leg base to move to the bottom of the steel beam (damaged claw leg) where it needs to be repaired, and align the center of the new claw leg with the center of the end of the steel beam to be repaired. During the alignment process, ensure that the area of ​​the steel beam (i.e., steel claw beam) where the steel claw needs to be repaired does not touch the graphite ring (i.e., annular graphite sheath).

[0029] Step 4: Turn on the main power supply, control the hydraulic cylinder to move the claw leg upward to contact the steel beam, pass direct current between the energized part of the steel beam and the new steel claw leg, the current is turned on, the arc block is ignited, and the control current is within the range of 2800A and the voltage range is 25V. After 4 minutes, confirm that the electric slag has been completely melted, control the hydraulic cylinder to lift the claw leg upward, and use 30 tons of pressure to squeeze and bond the new claw leg to the repair surface. After an interval of 10s, the hydraulic cylinder can be controlled to move downward to leave the claw leg.

[0030] Step 5. After the operation is completed, turn off the power of the entire equipment, remove the graphite ring, and then lift out the repaired steel claw to obtain the finished welding repair product.

[0031] The quality of the finished product: the surface of the weld between the steel claw and the beam is full and crack-free; the internal slices have no cracks, pores or slag inclusions; the tensile strength test is above 400Mpa;

[0032] The test method is visual method (such as Figure 2 as shown) and the results of the universal electronic tensile testing machine (as shown in Table 1).

[0033] Example 2

[0034] Claw leg length 270mm, The steel claws (cylindrical) are repaired by welding;

[0035] The process and conditions are the same as in Example 1, except that: the upward extrusion bonding force is 50 tons;

[0036] The quality of the finished product: the surface of the weld between the steel claw and the beam is full and crack-free; the internal slices have no cracks, pores or slag inclusions; the tensile strength test is above 400Mpa.

[0037] Comparative Example

[0038] Claw leg length 270mm, The steel claws (cylindrical) are repaired by welding;

[0039] The process and conditions are the same as those of Example 1, except that: the upward extrusion pressure is 5 tons;

[0040] The quality of the finished product: there is unfused surface on the weld between the steel claw and the beam, and there is slag inclusion in the internal slice; the tensile strength test is only 156Mpa.

[0041] Table 1

[0042]

Claims

1. A welding repair method for anode steel claws, characterized in that: The first step is to cut off the damaged claw leg and grind the oxide scale on the part of the steel claw that will be energized above the crossbeam to be repaired so that it can be energized normally; the second step is to place a new steel claw leg with the same size, shape and specification as the damaged claw leg on the upper end of the output end of the hydraulic cylinder that can reciprocate up and down, and set an annular graphite sheath around the surface to be welded at the upper end of the new steel claw leg; the upper opening end of the annular graphite sheath is 25-30mm higher than the surface to be welded at the upper end of the new steel claw leg. After the assembly is completed, an arc-starting block is placed in the middle of the upper end surface of the new steel claw leg of the graphite sheath, and electric slag is added to the upper end surface of the new steel claw leg. The electric slag is added to 3-5mm below the upper end surface of the arc-starting block; Step 3: Move the claw leg of the new steel claw to the part below the steel beam to be repaired, and align the center of the claw leg of the new steel claw with the center of the end of the steel beam to be repaired. During the alignment process, ensure that the area of ​​the steel claw of the steel beam to be repaired does not contact the annular graphite sheath; The fourth step is to control the hydraulic cylinder to move the new steel claw leg upward to contact the steel beam, and pass alternating current between the energized part of the steel beam and the new steel claw leg. The current is conducted and the arc-starting block is ignited. The current is controlled to be between 2800-3100A and the voltage is between 23-28V. After 4-8 minutes, it is confirmed that the electric slag has been completely melted, and then the hydraulic cylinder is controlled to lift the claw leg upward. The new claw leg is squeezed and bonded to the repair surface through a pressure of 30 to 50 tons. After an interval of 10s-30s, the hydraulic cylinder can be controlled to move downward to leave the claw leg to obtain a welded repair product.

2. The method according to claim 1, characterized in that: The components of the conductive block are as follows: CaF2 powder: 60% to 70%; Al2O3 powder: 20% to 25%; TiO2 powder: 3 to 5%; and the rest is iron filings.

3. The method according to claim 1, characterized in that: By mass, the main components of electroslag are: CaF2 25-40%, CaO2 15-30%, Al2O3 30-35%, and the rest is SiO2.

4. The method according to claim 1, characterized in that: The thickness of the electroslag layer is 25-30mm.

5. The method according to claim 1, characterized in that: The distance between the inner wall of the annular graphite sheath and the outer wall of the new steel claw leg is 1-5mm; the upper end of the new steel claw leg and the lower end of the steel beam have the same shape and size as the lower bottom surface of the cylindrical damaged claw leg (area to be repaired) with a remaining length of 35-50mm; the third step is to move until the arc-starting block and the lower bottom surface of the damaged steel claw are in contact.

6. The method according to claim 1, characterized in that: Arc starting block volume (28-35)*(35-45)*40mm 3 .

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