Method and device for increasing the production capacity of electroslag remelting

Abstract

This invention relates to a method and apparatus for improving the production capacity of electroslag remelting. The method involves using an induction heating coil to assist heating of the electrodes during the electrode remelting process, thereby increasing the melting rate of the electrodes in the molten slag. The implementation of this invention reduces the overall power consumption of the production system while simultaneously increasing the production capacity of electroslag remelting by 20% to 40% compared to the original electroslag remelting process.

Description

Technical Field

[0001] This invention belongs to the field of electroslag remelting technology, and particularly relates to a method and apparatus for improving electroslag remelting production capacity. Background Technology

[0002] The basic principle of electroslag remelting is that the resistance heat generated by the current passing through the molten slag gradually melts the metal electrodes. The molten metal gathers into droplets, passes through the slag layer, and enters the molten metal pool. Electroslag remelting has a good ability to remove non-metallic inclusions, and steel and alloys produced through electroslag remelting have a high degree of cleanliness. 80-90% of the non-metallic inclusions in steel produced by conventional methods can be removed after electroslag remelting. Electroslag steel ingots are forcibly cooled and solidified in a water-cooled crystallizer, resulting in a dense crystalline structure that generally avoids low-magnification defects such as shrinkage cavities and porosity. Due to these advantages, electroslag remelting has become one of the main methods for producing high-quality steel and alloys. However, the biggest drawback of electroslag remelting is its relatively low production capacity, typically between 0.3 and 0.8 t / h. This is mainly because during electroslag remelting, the electrodes are gradually melted through heat conduction due to the high temperature of the molten slag. This thermal conductivity directly affects the electrode melting rate. To increase the temperature of the liquid slag, the slag system is modified to increase its thermal resistance, thereby accelerating electrode melting. Slag systems with high thermal resistance typically have higher viscosity, which is detrimental to the removal of inclusions from the molten steel. Furthermore, high thermal resistance requires more electrical energy to maintain the high temperature of the liquid slag. Although the power grid system for electroslag remelting has been optimized to reduce line reactance and improve the power factor, the power consumption per ton of steel during electroslag remelting remains relatively high, generally between 1500 and 2000 kWh / t.

[0003] Patent application number 201310166458.X discloses an electroslag remelting slag for smelting plastic mold steel and its preparation method. The slag system is characterized by the following raw material composition and mass percentages: CaF2: 30-45%, Al2O3: 20-30%, CaO: 20-30%, SiO2: 5-10%. This slag system increases the viscosity of the electroslag remelting slag by adding CaO, thereby increasing the slag's resistivity and improving its electrostatic efficiency, thus potentially increasing production capacity. However, this method increases slag electro-remelting consumption by adjusting the slag composition, resulting in additional energy consumption. Furthermore, the added CaO easily absorbs moisture from the air, leading to an increase in the hydrogen content of the electroslag steel ingot. Overall, this application's adjustment of the slag composition is not conducive to low-cost and stable production.

[0004] The reference "Research on Second Generation Electroslag Remelting Technology" (Chinese Journal of Materials and Metallurgy, Vol. 10, Supplement, 2011) provides a comprehensive discussion of current electroslag remelting technology. The reference discusses improving the production efficiency of electroslag remelting and introduces a new method: using electroslag casting, molten steel smelted in an electric arc furnace is poured from the tundish transition trough into a crystallizer containing molten and superheated basic synthetic slag to complete the ingot casting. While this method significantly improves production efficiency compared to traditional electroslag remelting, strictly speaking, it no longer falls under the category of electroslag remelting. This is because it involves directly pouring molten steel from an electric furnace into a slag-filled crystallizer. This process has a significant negative impact on ingot quality. Firstly, it inevitably creates strong agitation of the slag within the crystallizer, easily causing slag entrapment and reducing the cleanliness of the ingot. Secondly, it greatly reduces the contact surface area between the poured molten steel and the slag, hindering the removal of inclusions. Thirdly, the amount of molten steel injected is much larger than in traditional electroslag remelting, negatively affecting the solidification structure of the ingot and easily leading to segregation and porosity defects. Finally, the molten steel from the electric furnace is heated to a very high temperature (a certain degree of superheat) during pouring to prevent freezing. A large portion of this heat is lost through radiation during pouring, representing a waste of energy. From the perspective of a single aspect, it may seem to achieve energy conservation, but when analyzed from the perspective of the energy usage of the entire system, it has not actually achieved the effect of reducing electricity consumption and reducing costs.

[0005] Based on the above background, this invention proposes to preheat the electrodes by means of induction heating, thereby reducing the power consumption of the entire system and increasing the electrode melting rate to improve the production capacity of electroslag remelting. Summary of the Invention

[0006] The purpose of this invention is to provide a method and apparatus for improving the production capacity of electroslag remelting. While reducing the power consumption of the entire production system, it can also improve the production capacity of electroslag remelting, increasing it by 20% to 40% compared with the original electroslag remelting process.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] A method for improving the production capacity of electroslag remelting involves using an induction heating coil to assist heating of the electrode during the electrode remelting smelting operation, thereby increasing the melting rate of the electrode in the liquid slag.

[0009] Specific methods include:

[0010] 1) Install the crystallizer on the bottom water tank and complete the routine process operations.

[0011] 2) Place the induction heating coil above the crystallizer and align the induction heating coil with the center of the crystallizer on the same axis.

[0012] 3) Insert the electrode into the crystallizer from the top of the induction heating coil, and make the gap between the induction heating coil and the electrode uniform;

[0013] 4) Sprinkle ignition slag on the bottom water tank, move the electrode downwards to contact the ignition slag, and then ignite the arc by applying electricity. After the ignition slag has completely melted and the current and voltage have stabilized, feed the slag material into the crystallizer.

[0014] The slag material selected is a ternary slag system of CaF2-Al2O3-NaCl. The advantages of this slag system are its low melting point and good electrical conductivity, which facilitates the removal of inclusions at high temperatures and significantly reduces power consumption, thus lowering costs. The disadvantage is that its resistance heat is relatively low compared to conventional slag materials, which is not conducive to electrode melting. However, this process utilizes induction heating to compensate for this deficiency. The components of the slag system matched to this process, by mass percentage, are: CaF2 65%–80%, Al2O3 15%–30%, and NaCl 5%–10%. Because the melting rate of the droplets is faster than conventional methods, to ensure sufficient contact between the falling droplets and the liquid slag, the amount of slag added is increased by 1–3 times compared to conventional methods, ensuring that the depth of the liquid slag pool is controlled at 100–300 mm.

[0015] 5) After the slag is fed into the crystallizer, adjust the position of the induction heating coil, maintaining the distance between the bottom surface of the induction heating coil and the slag surface within the range of 20-50mm. Start the induction heating coil to provide auxiliary heating to the electrodes. Adjust the power to control the heating temperature of the electrodes by the induction heating coil to be 20-50℃ below the solidus temperature of the electrode steel. Select the frequency of the induction heating coil according to the size of the heating electrode. The heated electrode gradually melts in the slag and falls into the molten metal pool in the form of droplets. Under the water cooling effect of the crystallizer and the bottom water tank, the molten steel in the molten metal pool is gradually cooled and solidified to form electroslag steel ingots.

[0016] 6) After the electrode has completely melted, turn off the induction heating coil and move the induction heating coil out of the working position to complete the electroslag remelting operation.

[0017] An apparatus used in a method to improve the production capacity of electroslag remelting includes a crystallizer, an induction heating coil, and a bottom water tank. The crystallizer is placed above the bottom water tank, and the induction heating coil is above the crystallizer and on the same axis as the center of the crystallizer. During production, the electrode is inserted into the crystallizer from the top of the induction heating coil.

[0018] The induction heating coil is a single-turn solenoid structure, and its overall shape is circular or square.

[0019] Considering that the electrode melting rate during remelting is typically 20–50 mm / h, while induction heating can reach the target heating temperature per minute, using a multi-turn induction heating coil would inevitably result in some high-temperature areas of the electrode being exposed for extended periods before entering the high-temperature slag melting process. This would lead to oxidation of the electrode surface in these high-temperature areas, reducing the cleanliness of the final steel ingot. Simultaneously, this high-temperature area continuously loses heat through radiation, significantly increasing electricity costs. For example, a 10-turn coil consumes approximately 15% more electricity during electroslag remelting compared to without induction heating. To address these issues, the induction heating coil is designed as a single-turn solenoid structure. This ensures that only a narrow area of ​​the electrode surface is heated during induction heating, minimizing surface oxidation caused by induction heating. For steel grades with extremely high cleanliness requirements, an alumina powder coating can be applied to the electrode surface to prevent oxidation at high temperatures. Using a single-turn coil helps reduce heat loss. At the same time, in order to reduce heat loss and oxidation, the distance between the coil and the liquid slag surface is controlled within a small range of 20-50mm, so that the coil can enter the liquid slag pool in the shortest time after heating the electrode.

[0020] The specific shape of the induction heating coil is determined by the cross-sectional shape of the electrode being heated. The coil solenoid has a rectangular cross-section, the induction heating coil height is h, and the induction heating coil diameter is D. If the coil is rectangular, the diameter D is calculated based on the diameter of the lower circle of equivalent area, and the height-to-diameter ratio h / D ranges from 0.05 to 0.1. To prevent contact between the electrode and the coil, the gap between the inner wall of the coil and the electrode surface must be controlled between 10 and 50 mm. The height-to-diameter ratio h / D of the electrode's equivalent cross-sectional diameter can be designed within the following ranges: when the equivalent cross-sectional diameter of the electrode is ≤100 mm, the height-to-diameter ratio h / D is 0.09 to 0.1; when 100 mm < equivalent cross-sectional diameter of the electrode is ≤360 mm, the height-to-diameter ratio h / D is 0.07 to 0.09; when the equivalent cross-sectional diameter of the electrode is >360 mm, the height-to-diameter ratio h / D is 0.05 to 0.07. To achieve good heating effects on electrodes of different sizes while ensuring they do not melt, the heating power of the induction heating coil is set to a range of 10–300 kW. During induction heating, the coil frequency significantly affects the heating effect. High-frequency heating, due to the skin effect, concentrates the induced current on the electrode surface, resulting in slow internal heating of the electrode. This is unsatisfactory for large electrodes. However, for smaller electrodes, high-frequency heating can quickly heat them, improving the heating effect. Therefore, a suitable heating frequency should be selected based on the size of the electrode being heated. In this invention, the coil frequency range is 50–1000 Hz. When the equivalent diameter of the electrode (2) is ≤100 mm, the induction heating frequency is 800–1000 Hz; when 100 mm < equivalent diameter of the electrode (2) is ≤360 mm, the induction heating frequency is 200–800 Hz; when the equivalent diameter of the electrode (2) is >360 mm, the induction heating frequency is 50–200 Hz.

[0021] This invention, through a novel design of the electroslag remelting process, incorporates electromagnetic induction heating as an auxiliary function. Combined with the use of specialized slag materials, this invention offers significant advantages over existing electroslag remelting processes, as detailed below:

[0022] 1) It significantly reduced the power consumption per ton of steel during the electroslag remelting process, decreasing it from 1500-2000 KW.h / t steel to 1200-1400 KW.h / t steel;

[0023] 2) The effective utilization rate of electrical energy has increased from an average of 75% to an average of 85%, reducing production costs;

[0024] 3) This method can increase the electroslag remelting production capacity from 0.3-0.8 t / h to 0.6-1.5 t / h. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of an induction heating electroslag remelting device.

[0026] Figure 2 This is a schematic diagram of the appearance of an induction heating coil.

[0027] Figure 3 This is a schematic diagram of the cross-section of an induction heating coil.

[0028] In the diagram: 1-Induction heating coil drive mechanism; 2-Electrode; 3-Crystallizer; 4-Induction heating coil; 5-Liquid slag; 6-Metal liquid pool; 7-Electroslag ingot; 8-Bottom water tank. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the specific implementation methods of this invention will be further described below in conjunction with the embodiments. The following embodiments are used to specifically illustrate the content of this invention. These embodiments are only general descriptions of the content of this invention and do not limit the content of this invention.

[0030] This invention uses induction heating to assist in heating the electrodes, thereby reducing the power consumption of the entire system, increasing the electrode melting rate, and improving the electroslag remelting production capacity.

[0031] This invention utilizes an electroslag remelting device with electrode induction heating to perform the remelting and smelting of electrodes, thereby increasing the melting rate of the electrodes in the liquid slag and achieving a metallurgical effect that improves production capacity. The following is a description of the device with reference to a schematic diagram:

[0032] like Figure 1 As shown, the device for improving the production capacity of electroslag remelting used in the embodiment of the present invention includes a crystallizer 3, an induction heating coil 4, and a bottom water tank 8. The crystallizer 3 is placed on the bottom water tank 8, and the induction heating coil 4 is above the crystallizer 3 and on the same axis as the center of the crystallizer 3. During production, the electrode 2 is inserted into the crystallizer 3 from the upper part of the induction heating coil 4.

[0033] The induction heating coil 4 is driven by the induction heating coil holding mechanism 1 to complete the up, down, left, and right adjustment actions, which meet the adjustment of the position of the induction heating coil in production.

[0034] The induction heating coil 4 is a single-turn solenoid structure. For example... Figure 3 As shown, the cross-section of the coil solenoid is rectangular, and its height-to-diameter ratio h / D ranges from 0.05 to 0.1, where h is the height of the induction heating coil 4 and D is the diameter of the induction heating coil 4.

[0035] The process of this invention embodiment is as follows:

[0036] Example 1:

[0037] Electroslag remelting of H13 mold steel, electrode 2 is 300mm in diameter, and electroslag ingot 7 is 400mm in diameter. The specific process operation method is as follows:

[0038] Based on the process requirement that the gap distance between the inner wall of the induction heating coil 4 and the surface of the electrode 2 be controlled at 10-50mm, and that when 100mm < equivalent diameter of the electrode cross-section ≤ 360mm, the height-to-diameter ratio h / D of the induction heating coil 4 be 0.07-0.09, the diameter D of the induction heating coil 4 is adopted as a 360mm circular coil (e.g., Figure 2 As shown in the figure, the height of the coil solenoid is 27mm, and the induction heating frequency is 500Hz.

[0039] The specific process is as follows:

[0040] 1) Install the crystallizer 3 onto the bottom water tank 8 and complete the routine process operation;

[0041] 2) Place the induction heating coil 4 above the crystallizer 3, and make the induction heating coil 4 and the center of the crystallizer 3 on the same axis;

[0042] 3) Insert electrode 2 through the upper part of induction heating coil 4 and make the gap between induction heating coil 4 and electrode 2 uniform;

[0043] 4) Sprinkle ignition slag onto the bottom water tank 8. Move the electrode downwards to contact the ignition slag, and then apply electricity to ignite the arc. After the ignition slag has completely melted and the current and voltage have stabilized, add the CaF2-Al2O3-NaCl ternary slag material into the crystallizer 3. The mass percentages of CaF2-Al2O3-NaCl in the slag material are 75%, 19%, and 6%, respectively, and the depth of the liquid slag 5 is controlled at 150 mm.

[0044] 5) After the slag is fed into the crystallizer 3, adjust the position of the induction heating coil 4 so that the distance between the bottom surface of the induction heating coil 4 and the surface of the liquid slag 5 is kept within 50mm. Start the induction heating coil 4 to assist in heating the electrode 2. Adjust the power to control the heating temperature of the electrode 2 to 40℃ below the solidus temperature of the electrode steel.

[0045] 6) After electrode 2 has completely melted, turn off induction heating coil 4, move induction heating coil out of the working position, and complete the electroslag remelting operation.

[0046] Example 2:

[0047] Electroslag remelting of Invar steel, electrode 2 has a rectangular cross-section of 300*1500mm, and electroslag ingot 7 has a cross-section of 450*1000mm. The specific process operation method is as follows:

[0048] Based on the shape and size of electrode 2, a rectangular induction heating coil 4 is selected. The cross-section of electrode 2 is rectangular, 300*1500mm, with an equivalent area circle diameter of 379mm. According to the process requirement that the gap distance from the inner wall of the induction coil to the surface of electrode 2 be controlled between 10 and 50mm, and that when the equivalent diameter of the electrode cross-section is >360mm, the height-to-diameter ratio h / D of the induction heating coil 4 should be between 0.05 and 0.07, a rectangular coil of 320*1520mm is used for the induction heating coil 4, with a coil solenoid height of 25mm, and an induction heating frequency of 150Hz. The specific process method is as follows:

[0049] 1) Install the crystallizer 3 onto the bottom water tank 8 and complete the routine process operation;

[0050] 2) Place the induction heating coil 4 above the crystallizer 3, and make the induction heating coil 4 and the center of the crystallizer 3 on the same axis;

[0051] 3) Insert electrode 2 through the upper part of induction heating coil 4 and make the gap between induction heating coil 4 and electrode 2 uniform;

[0052] 4) Sprinkle ignition slag onto the bottom water tank 8. Move electrode 2 downwards to contact the ignition slag, then apply current to ignite the arc. After the ignition slag has completely melted and the current and voltage have stabilized, add CaF2-Al2O3-NaCl ternary slag material into the crystallizer 3. The mass percentages of CaF2-Al2O3-NaCl in the slag material are 77%, 18%, and 5%, respectively, and the depth of the liquid slag 5 is controlled at 200 mm.

[0053] 5) After the slag is fed into the crystallizer 3, adjust the position of the induction heating coil 4 so that the distance between the bottom end of the induction heating coil 4 and the surface of the liquid slag 5 is kept within 45mm. Start the induction heating coil 4 to assist in heating the electrode 2. The heating temperature of the electrode 2 by the induction heating coil 4 is controlled at 30℃ below the solidus temperature of the electrode steel.

[0054] 6) After the electrode 2 has completely melted, turn off the induction heating coil 4 and move the induction heating coil 4 out of the working position to complete the electroslag remelting operation.

[0055] Example 3:

[0056] Electroslag remelting of 9Cr18 bearing steel, electrode 2 has a square cross-section of 85*85mm, and electroslag ingot 7 is 100*100mm. The specific process operation method is as follows:

[0057] Based on the shape and size of electrode 2, a square induction heating coil 4 is selected. The cross-section of electrode 2 is 85*85mm, and the diameter of the equivalent area circle is 96mm. According to the process requirements that the gap distance from the inner wall of the induction coil to the surface of electrode 2 should be controlled between 10 and 50mm, and the equivalent diameter of the electrode cross-section should be ≤100mm, the height-to-diameter ratio h / D should be between 0.09 and 0.1. Therefore, the induction heating coil 4 is a 100*100mm square coil with a coil solenoid height of 11mm, and the induction heating frequency is 900Hz.

[0058] The specific process is as follows:

[0059] 1) Install the crystallizer 3 onto the bottom water tank 8 and complete the routine process operation;

[0060] 2) Place the induction heating coil 4 above the crystallizer 3, and make the induction heating coil 4 and the center of the crystallizer 3 on the same axis;

[0061] 3) Insert electrode 2 through the upper part of induction heating coil 4 and make the gap between induction heating coil 4 and electrode 2 uniform;

[0062] 4) Sprinkle ignition slag onto the bottom water tank 8. Move electrode 2 downwards to contact the ignition slag, then apply electricity to ignite the arc. After the ignition slag has completely melted and the current and voltage have stabilized, add CaF2-Al2O3-NaCl ternary slag material into the crystallizer 3. The mass percentages of CaF2-Al2O3-NaCl in the slag material are 72%, 21%, and 7%, respectively, and the depth of the liquid slag 5 is controlled at 240 mm.

[0063] 5) After the slag is fed into the crystallizer 3, adjust the position of the induction heating coil 4 so that the distance between the bottom surface of the induction heating coil 4 and the surface of the liquid slag 5 is 50mm. Start the induction heating coil 4 to assist in heating the electrode 2. Adjust the power to control the heating temperature of the electrode 2 by the induction heating coil 4 to be 25℃ below the solidus temperature of the electrode steel.

[0064] 6) After the electrode 2 has completely melted, turn off the induction heating coil 4 and move the induction heating coil 4 out of the working position to complete the electroslag remelting operation.

Claims

1. A method for improving the production capacity of electroslag remelting, characterized in that, This method involves using an induction heating coil to assist heating of the electrode during electrode remelting and smelting operations, thereby increasing the melting rate of the electrode in the slag. Specific methods include: 1) Install the crystallizer on the bottom water tank and complete the routine process operations; 2) Position the induction heating coil above the crystallizer, ensuring that the induction heating coil and the center of the crystallizer are on the same axis; 3) Insert the electrodes into the crystallizer from the top of the induction heating coil; 4) Sprinkle ignition slag on the bottom water tank, move the electrode downwards to contact the ignition slag, and then ignite the arc by applying electricity. After the ignition slag has completely melted and the current and voltage have stabilized, feed the slag material into the crystallizer. 5) Adjust the position of the induction heating coil, keeping the distance between the bottom surface of the induction heating coil and the liquid slag surface within the range of 20-50mm. Start the induction heating coil to provide auxiliary heating to the electrode. The heating temperature of the electrode by the induction heating coil should be controlled at 20-50℃ below the solidus temperature of the electrode steel. 6) After the electrodes have completely melted, turn off the induction heating coil to complete the electroslag remelting operation; The slag material is selected from the CaF2-Al2O3-NaCl ternary slag system, and the amount of slag added is sufficient to ensure that the depth of the liquid slag pool is controlled at 100-300mm. The CaF2-Al2O3-NaCl ternary slag system, by mass percentage, is: CaF2 65%–80%, Al2O3 15%–30%, NaCl 5%–10%; The heating power of the induction heating coil can be adjusted from 10 to 300 kW. When the equivalent diameter of the electrode cross-section is ≤100 mm, the heating frequency of the induction heating coil is 800 to 1000 Hz. When 100 mm < equivalent diameter of the electrode cross-section is ≤360 mm, the heating frequency of the induction heating coil is 200 to 800 Hz. When the equivalent diameter of the electrode cross-section is >360 mm, the heating frequency of the induction heating coil is 50 to 200 Hz. The gap distance between the inner wall of the induction heating coil and the electrode surface is 10-50 mm.

2. The method for improving electroslag remelting production capacity according to claim 1, characterized in that, The induction heating coil is a single-turn solenoid structure, and its overall shape is circular or square.

3. The method for improving electroslag remelting production capacity according to claim 2, characterized in that, The cross-section of the induction heating coil is rectangular, and its height-to-diameter ratio h / D ranges from 0.05 to 0.1, where h is the height of the induction heating coil and D is the diameter of the induction heating coil.

4. The method for improving electroslag remelting production capacity according to claim 3, characterized in that, The ratio h / D of the equivalent diameter of the electrode cross-section to the height of the induction heating coil is designed within the following ranges: when the equivalent diameter of the electrode cross-section is ≤100mm, the ratio h / D is 0.09~0.1; when 100mm < equivalent diameter of the electrode cross-section is ≤360mm, the ratio h / D is 0.07~0.09; when the equivalent diameter of the electrode cross-section is >360mm, the ratio h / D is 0.05~0.07.

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