An immersion type inner cooling device for semi-continuous casting of rare earth magnesium alloy and an application method thereof

Abstract

This invention discloses an immersion-type internal cooling device and its application method for semi-continuous casting of rare earth magnesium alloys, belonging to the field of non-ferrous metal semi-continuous casting technology. The device includes a guide pipe, a crystallizer, a distribution plate, and an immersion-type internal cooling body. The internal cooling body extends into the high-temperature zone of the liquid cavity along the central axis of the crystallizer. Its head has a semi-circular streamlined structure, employing a three-layer composite structure: a core flow channel layer, a pressure-bearing sealing layer, and an outer protective layer. An internal spiral cooling channel is provided, and the outer layer is coated with a ceramic coating resistant to magnesium melt erosion and equipped with an inert gas sealing interlayer. The outer diameter of the semi-circular head of the internal cooling body is matched to the inner diameter of the crystallizer according to a dimensional ratio coefficient k (0.32≤k≤0.45). In application, pressurized circulating deionized water is used as the cooling medium, constructing an internal and external cooling synergistic control system. The cooling intensity and immersion depth are differentiated and adjusted in three stages: casting start-up, steady state, and final stage. The liquid cavity depth and ingot temperature field can be quantitatively controlled, ensuring the solidification front flatness is ≤15°. This invention can reduce the radial temperature difference of ingots, achieve synchronous solidification of the center and the edge, and suppress rare earth segregation, shrinkage cavities, porosity and hot cracking defects. It is suitable for semi-continuous casting production of large-diameter rare earth magnesium alloy ingots.

Description

Technical Field

[0001] This invention belongs to the field of solidification control technology for semi-continuous casting of rare earth magnesium alloys. Specifically, it relates to an immersion internal cooling device and casting method that addresses the problems of high hot cracking sensitivity, easy segregation of rare earth elements, and coarse and uneven microstructure of large-diameter rare earth magnesium alloy ingots. This is achieved by setting up an immersion internal cooling device, anti-pollution and anti-shell protection, and a special adapter design for rare earth magnesium alloys, thereby realizing coordinated control of internal and external cooling and uniform ingot microstructure. Background Technology

[0002] Large-diameter rare-earth magnesium alloy ingots are key basic raw materials for aerospace equipment manufacturing. Existing semi-continuous casting processes generally suffer from prominent problems such as insufficient central cooling, large radial temperature gradient, and uneven solidification when preparing large-diameter ingots. These problems easily lead to typical defects in the ingots, such as high susceptibility to hot cracking, rare-earth element segregation, coarse and uneven microstructure, and low internal density, making it difficult to meet the quality requirements of high-end applications.

[0003] The current industrial production of large-diameter rare earth magnesium alloy ingots mainly reduces the internal and external temperature difference by lowering the cooling intensity and slowing down the casting speed. Although this can alleviate the tendency of hot cracking and segregation to a certain extent, it will significantly reduce production efficiency, increase the uncertainty and process risk of the casting process, and make it difficult to balance ingot quality and production stability. Patents CN201110386386.0 and CN200610031524.2 disclose bidirectional cooling or internal cooling strengthening devices for semi-continuous casting of light alloys, which mainly improve the cooling capacity of the ingot center by adding internal cooling components; patents CN202411146710.5, CN201210524673.8, and CN201510472954.7 target rare earth magnesium alloy ingots, and adopt methods such as optimizing flow channels, electromagnetic composite fields, and controlling cooling processes to suppress compositional segregation, reduce the tendency of hot cracking, and improve the uniformity of microstructure; patents CN200810010647.7 and CN201110236278.5 disclose semi-continuous casting technology with electromagnetic field assistance and optimized cooling structure, which is mostly used to improve the surface quality and internal density of ingots. Although the aforementioned existing technologies have made some progress in cooling enhancement and defect control, they generally suffer from shortcomings such as simple internal cooling structure design, lack of quantitative collaborative control mechanism with external cooling, lack of specialized anti-pollution and anti-shell protection for rare earth magnesium alloy melt characteristics, and difficulty in achieving uniform and precise control of solidification throughout the entire process of large-diameter ingots. They still cannot fundamentally balance the quality stability and production efficiency of large-diameter rare earth magnesium alloy ingots.

[0004] Accordingly, for semi-continuous casting of large-size rare earth magnesium alloy ingots, if a uniform and precisely controllable directional cooling path can be constructed in the high-temperature zone at the center of the liquid cavity, and the synergistic coupling and control of central internal cooling and peripheral cooling can be achieved, the radial temperature gradient can be effectively weakened, the depth of the liquid cavity can be reduced, and the non-uniform solidification state can be improved from the perspective of the temperature field formation mechanism. This will reduce the thermal stress level of the ingot and provide key technical support and feasible solutions for simultaneously suppressing the tendency of hot cracking, reducing the segregation of rare earth elements, and obtaining a uniform and refined as-cast microstructure. Summary of the Invention

[0005] To address the problems of insufficient central cooling, excessive liquid cavity depth, large radial temperature difference within the ingot, easy segregation of rare earth elements, shrinkage porosity, and obvious tendency to hot cracking in the existing semi-continuous casting process of rare earth magnesium alloys, this invention provides an immersion-type internal cooling device and its application method for semi-continuous casting of rare earth magnesium alloys. This invention overcomes the technical shortcomings of traditional semi-continuous casting internal cooling devices, such as lack of coordinated control between internal and external cooling, easy reaction between the device and the melt causing contamination and crust formation, and lack of specialization for the characteristics of rare earth magnesium alloys. Through immersion cooling body structural design, coordinated control of internal and external cooling, anti-contamination and anti-crust protection, and specialization for rare earth magnesium alloys, it achieves precise and enhanced cooling of the high-temperature zone at the center of the liquid cavity, improves the temperature field and solidification behavior of the ingot, enhances the uniformity of the ingot structure and internal quality, and ensures the safety and stability of the casting process.

[0006] To solve the above problems, the technical solution adopted by the present invention is as follows, wherein the application method is implemented in sequence according to the following steps: Step 1: Equipment Pre-treatment and Installation / Commissioning An immersion-type internal cooling device is assembled. This device comprises a three-layer composite structure: a core flow channel layer, a pressure-bearing sealing layer, and an outer protective layer. The head features a streamlined, semi-circular, refined structure with an internal spiral cooling channel. A condensate inlet and outlet are located at either end of the flow channel. A boron nitride or rare earth oxide anti-pollution and anti-scabbing coating is applied to the surface of the outer protective layer, followed by curing. The guide pipe, crystallizer, and distribution plate are then assembled sequentially with the internal cooling device, ensuring concentric arrangement along the crystallizer's central axis. The inner wall of the guide pipe is pre-coated with a 0.8-1.0 mm thick high-temperature resistant ceramic coating to reduce melt erosion loss and alloy contamination risks. Nitrogen or argon gas is introduced into the inert gas sealing jacket of the internal cooling device to check its sealing performance and ensure no leakage.

[0007] Step 2: Size matching and gap adjustment Based on the production requirements of large-size rare earth magnesium alloy ingots, the matching relationship between the inner diameter D of the crystallizer and the outer diameter d of the semi-circular head of the internal cooling device is determined to satisfy d=kD, where 0.32≤k≤0.45; the position of the internal cooling device is adjusted to form a constant flow and stable flow single-sided gap δ=(Dd) / 2 between the semi-circular head and the inner wall of the crystallizer, ensuring that the gap width is uniform and constant, ensuring smooth melt flow and stable flow rate, and avoiding eddies, slag entrapment and liquid surface fluctuations.

[0008] Step 3: Cooling medium and parameter settings Pressurized circulating deionized water is introduced into the spiral cooling channel of the internal cooling device as the cooling medium. The operating parameters of the cooling medium are set as follows: operating pressure is 0.2~0.6MPa, and inlet water temperature is controlled at 25~35℃. The cooling medium circulation system is debugged to ensure stable flow and normal heat exchange. The heat exchange capacity Q per unit time of the internal cooling device (i.e., Q_internal_cooling) is calculated according to the formula Q=ρqc(T1-T2), where ρ is the density of deionized water, q is the volumetric flow rate, c is the specific heat capacity at constant pressure, T1 is the cooling water outlet temperature, and T2 is the cooling water inlet temperature. When only considering the heat exchange on the outer arc surface of the semi-circular head, the effective heat exchange area A=πd 2 / 2 (d is the outer diameter of the semi-circular head of the internal cooling device); at the same time, the heat exchange per unit time of the external cooling system is defined as Q external cooling, and the coordination control coefficient λ is defined as λ=Q internal cooling / Q external cooling, and its value range is controlled to be 0.3~0.6, so as to ensure that the ratio of internal cooling heat exchange to external cooling heat exchange is reasonable, and to provide a quantitative basis for the coordinated regulation of internal and external cooling.

[0009] Step 4: Construction of an internal and external cooling coordinated control system The internal cooling device is immersed in the high-temperature zone of the ingot molten metal cavity along the central axis of the crystallizer. A double-layer inert gas seal provides continuous ventilation, preventing direct contact between the internal cooling device and the rare-earth magnesium alloy melt, which could lead to contamination or crust formation. A synergistic control system is constructed, with internal cooling as the core and external cooling as an auxiliary. The synergistic control coefficient λ = Q_internal_cooling / Q_external_cooling is defined, with a value strictly controlled within the range of 0.3 to 0.6, ensuring that the internal cooling heat exchange is 30% to 60% of the external cooling heat exchange. Simultaneously, an effective utilization coefficient η for the internal cooling device is defined, with a value ranging from 0.80 to 0.90, used to characterize the ratio of the actual heat exchange efficiency to the theoretical heat exchange efficiency of the internal cooling device. This is combined with the effective heat exchange area of ​​the internal cooling device, A = πd. 2 / 2 (d is the outer diameter of the semi-circular head of the internal cooling device), establish the formula H=H0 / (1+λη) for the liquid cavity depth (where H0 is the liquid cavity depth when the internal cooling device is not installed), and ensure that the flatness of the solidification front of the ingot is ≤15° by precisely controlling the values ​​of λ and η, and the corresponding liquid cavity depth reduction ΔH=H0·λη / (1+λη).

[0010] Step 5: Coordinated Cooling Control at Different Casting Stages According to the process characteristics of different casting stages, a synergistic cooling control process is adopted to carry out semi-continuous casting: (1) Casting start-up stage: The internal cooling device is shallowly immersed in the liquid cavity, and a weak cooling intensity is adopted. Combined with weak external cooling spray, the initial solidified shell is stabilized and the thermal stress is too great, which leads to damage; (2) Steady-state casting stage: The internal cooling device is inserted into the maximum depth of the liquid cavity to enhance the cooling intensity. The matching degree of internal and external cooling is controlled by the synergistic coefficient λ to achieve synchronous solidification of the center and edge of the ingot and weaken the radial temperature difference; (3) Casting end stage: The height of the internal cooling device is gradually increased to reduce the cooling intensity. The external cooling system is coordinated to reduce the flow, suppress the shrinkage cavity at the top of the ingot and the looseness in the center, and ensure the quality of the ingot end.

[0011] Step 6: Precise Control and Quality Assurance Throughout the Entire Process Throughout the casting process, the immersion depth of the internal cooling device, the flow rate of cooling water, and the billet pulling speed are continuously and precisely adjusted. The depth of the liquid cavity, the inlet and outlet temperatures of the cooling water, and the changes in the ingot temperature field are monitored in real time. The collaborative control coefficient λ and the effective utilization coefficient of internal cooling η are finely adjusted to ensure that the cooling intensity is precisely matched with the solidification characteristics of rare earth magnesium alloy, suppress the segregation of rare earth elements, reduce the risk of hot cracking, and finally obtain a high-quality ingot with uniform structure and no pollution.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The internal cooling device adopts a three-layer composite structure and an inert gas sealing jacket for double protection. The cooling medium adopts closed-loop deionized water, which eliminates the risk of contact reaction between cooling water and magnesium melt from both structural and medium aspects, and is compatible with the safety casting requirements of high-temperature melt of rare earth magnesium alloy; (2) The internal cooling device acts directly on the high-temperature zone at the center of the liquid cavity. With the help of the spiral flow channel to enhance heat exchange, combined with the size quantitative matching model, the depth of the liquid cavity can be reduced, the radial temperature difference can be reduced, and the center and edge can be solidified synchronously, solving the industry problem of insufficient cooling at the center of large-diameter ingots; (3) Through the uniform temperature field and solidification front, the segregation of rare earth elements at the center can be effectively suppressed, shrinkage and porosity defects can be reduced, thermal stress and residual stress can be reduced, the ingot structure can be refined and uniform, and the internal defect rate can be reduced; (4) The internal cooling device has a simple structure and adjustable parameters. The cooling medium is compatible with the existing semi-continuous casting water cooling system. The synergistic cooling process of different casting stages can be directly applied to the existing vertical semi-continuous casting equipment without major modification, and has good industrial application prospects. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1: Cross-sectional view of the overall structure of the immersion internal cooling device of the present invention; Figure 2 : A partially enlarged cross-sectional view of the immersion-type internal cooling device of the present invention; Figure 3 : Overall assembly diagram of the internal cooling device and crystallizer of this invention; Figure 4 Flowchart of the application method of the device of the present invention; Figure 5 Macroscopic view of the cross-section of the Φ500mm Mg-Zn-Y-Zr alloy ingot prepared by this invention.

[0015] Explanation of reference numerals in the attached drawings: 1-Internal cooling device, 2-Core flow channel layer, 3-Pressure-bearing sealing layer, 4-Outer protective layer, 5-Streamlined semi-circular head, 6-Spiral cooling channel, 7-Condensate inlet, 8-Condensate outlet, 9-Special coating for preventing pollution and crust formation, 10-Inert gas sealing jacket, 11-Crystallizer, 12-Single-sided gap δ, 13-Guide pipe, 14-Ingot liquid cavity, 15-Solidification front, 16-Ingot, 17-Cross-section of the ingot of this invention. Detailed Implementation

[0016] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. These embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention. The values ​​of each key parameter are determined in combination with the casting characteristics of rare earth magnesium alloys, the performance of the equipment, and the actual needs of industrial production. The specific values ​​are based on the following.

[0017] Example 1: Structure of Immersion Internal Cooling Device This embodiment provides an immersion-type internal cooling device adapted for semi-continuous casting of Φ500mm Mg-Zn-Y-Zr rare earth magnesium alloy, such as... Figure 1 , Figure 2 As shown, the internal cooling device 1 adopts a three-layer composite structure, consisting of a core flow channel layer 2, a pressure-bearing sealing layer 3, and an outer protective layer 4 from the inside out. The three-layer structure is fixed by high-temperature welding, so that the device meets the requirements for pressure bearing and sealing, and is suitable for casting conditions with melt temperature of 660~730℃.

[0018] The internal cooling device 1 has a streamlined semi-circular head 5, which reduces melt resistance and prevents eddy currents and slag entrapment. An internal spiral cooling channel 6 is provided, with condensate inlets 7 and outlets 8 at both ends, enabling circulating heat exchange of the cooling medium. The outer protective layer 4 is coated with a boron nitride anti-pollution and anti-shelling coating 9, with a thickness of 0.1~0.2mm, a curing temperature of 200~220℃, and a curing time of 2 hours, which isolates the device from direct contact with the melt.

[0019] An annular inert gas sealing interlayer 10 is provided between the outer protective layer 4 and the pressure-bearing sealing layer 3. Nitrogen gas with a purity of ≥99.9% is introduced, and the gas pressure is 0.1~0.15MPa, forming a double protection with the coating.

[0020] like Figure 3 As shown, the inner diameter of crystallizer 11 is D=500mm, and the outer diameter of the semi-circular head of the internal cooling device is d=180mm, satisfying d=kD (k=0.36, 0.32≤k≤0.45); the single-sided gap δ=(Dd) / 2=160mm, the gap is uniform and constant, ensuring smooth flow of the melt.

[0021] Example 2: Application method of immersion internal cooling device This embodiment uses the apparatus described in Embodiment 1, applied to the semi-continuous casting of Φ500mm Mg-Zn-Y-Zr rare earth magnesium alloy. The casting process parameters of temperature, speed, and water volume are set according to actual production. The specific steps are as follows: (1) Equipment pretreatment and installation and commissioning After completing the coating curing of the internal cooling device, the guide pipe 13, crystallizer 11, and distribution plate are concentrically assembled with the internal cooling device 1; the inner wall of the guide pipe 13 is coated with a 0.9mm high-temperature resistant ceramic coating; nitrogen is introduced into the inert gas sealing jacket 10, and the seal is checked for leaks.

[0022] (2) Size matching and gap adjustment Complete the size matching with D=500mm and d=180mm (k=0.36), and adjust the position of the internal cooling device to make the single-sided gap δ=160mm uniform and constant.

[0023] (3) Cooling medium and parameter settings Pressurized circulating deionized water is introduced into the spiral cooling channel 6 at a working pressure of 0.4 MPa and an inlet water temperature of 30°C; the external cooling system cooling water flow rate is 10~11 m³ / h. 3 / h; Define the collaborative control coefficient λ=Q_internal_cooling / Q_external_cooling=0.45 (steady-state optimal value), and the effective utilization coefficient of internal cooling η=0.85; without internal cooling, the liquid cavity depth H0=380mm, substituting into the formula, we get: liquid cavity depth H=H0 / (1+λη)=380 / (1+0.45×0.85)≈275mm, and the liquid cavity reduction ΔH=H0・λη / (1+λη)=105mm.

[0024] (4) Construction of internal and external cold coordinated control system The internal cooling device is immersed in the high-temperature zone of the liquid cavity along the central axis of the crystallizer, with an immersion depth of 60% to 70% of the liquid cavity depth; the inert gas sealing jacket provides continuous ventilation protection, and the three-layer composite structure and gas medium ensure efficient heat transfer to the cooling channel; the flatness of the ingot solidification front is controlled to ≤15°, and the flatness is the maximum angle between the solidification front and the vertical ideal plane, which is measured by the temperature field detection method.

[0025] (5) Phased coordinated cooling regulation Casting start-up stage: After slowly laying the bottom layer by layer, start the machine at a speed of 6~7mm / min; the internal cooling device is shallowly immersed in 30% of the liquid cavity depth, with a weak cooling intensity of λ=0.3~0.4, to ensure the stability of the initial solidified shell; Casting speed-up stage: The casting speed is gradually increased to 30mm / min, and the internal cooling intensity is increased simultaneously, with λ gradually adjusted to 0.45; Steady-state casting stage: The casting speed is stable at 35 mm / min, the internal cooling device is immersed in 70% of the liquid cavity depth, strong cooling intensity, λ=0.45, to achieve synchronous solidification of the center and the edge, and the radial temperature difference is ≤35℃; In the final stage of casting: the immersion depth of the internal cooling device is reduced to 20% of the depth of the liquid cavity, reducing the cooling intensity to λ=0.5~0.6, which, together with the external cooling to reduce flow, suppresses shrinkage cavities and porosity at the top.

[0026] (6) Precise control and quality assurance throughout the entire process Throughout the process, the melt temperature (720~730℃ inside the furnace, 660~680℃ at the outlet of the guide pipe), the inlet and outlet temperatures of the cooling water, the depth of the liquid cavity, and the flatness of the solidification front are monitored; λ (0.3~0.6), η (0.80~0.90), the immersion depth of the internal cooler, and the flow rate of the cooling water are finely adjusted to ensure that the flatness of the solidification front is ≤15°, thereby suppressing rare earth element segregation, shrinkage cavities, porosity, and hot cracking defects.

[0027] The depth of the liquid cavity decreased from 380 mm without internal cooling to 275 mm, a reduction of 105 mm. This shortened the solidification time in the central region and reduced the temperature difference between the ingot surface and the central region, which helps to reduce internal thermal stress and the tendency for hot cracking. Figure 5 As shown, the cross-section 17 of the ingot prepared by the present invention is dense and uniform, without obvious porosity, shrinkage cavities and hot cracks, and the cross-sectional quality meets the technical requirements for large-size rare earth magnesium alloy ingots.

[0028] The above embodiments are merely preferred embodiments of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the core technical features of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An immersion-type internal cooling device for semi-continuous casting of rare earth magnesium alloys, characterized in that, The system includes a guide pipe, a crystallizer, a distribution plate, and an immersion-type internal cooling body. The immersion-type internal cooling body extends into the high-temperature zone of the ingot liquid cavity along the central axis of the crystallizer, and its head has a semi-circular streamlined structure. The internal cooling body has a three-layer composite structure from the inside out, consisting of a core flow channel layer, a pressure-bearing sealing layer, and an outer protective layer. A spiral cooling channel is provided inside, with a cooling water inlet and a cooling water outlet at each end of the spiral cooling channel. The outer protective layer is coated with a pollution-resistant and anti-shelling ceramic coating that resists magnesium melt erosion. An inert gas sealing interlayer is provided between the outer protective layer and the pressure-bearing sealing layer. The outer diameter d of the semi-circular head of the internal cooling body and the inner diameter D of the crystallizer satisfy a matching relationship: d=kD, where 0.32≤k≤0.45, and a uniform one-sided gap δ=(Dd) / 2 is formed between the semi-circular head and the inner wall of the crystallizer.

2. The immersion internal cooling device according to claim 1, characterized in that, The anti-pollution and anti-crust ceramic coating is a boron nitride coating or a rare earth oxide coating, with a coating thickness of 0.1~0.2mm.

3. The immersion-type internal cooling device according to claim 1, characterized in that, The inert gas sealing interlayer is purged with nitrogen or argon gas with a purity of ≥99.9% at a pressure of 0.1~0.15MPa.

4. The immersion internal cooling device according to claim 1, characterized in that, The cooling medium of the spiral cooling channel is pressurized circulating deionized water, with a working pressure of 0.2~0.6MPa and an inlet water temperature of 20~35℃.

5. The immersion-type internal cooling device according to claim 1, characterized in that, The inner wall of the guide tube is coated with a high-temperature resistant ceramic coating with a thickness of 0.8~1.0mm.

6. A method for applying an immersion-type internal cooling device in semi-continuous casting of rare earth magnesium alloys, characterized in that, The immersion internal cooling device according to any one of claims 1 to 5 includes the following steps: (1) Pretreatment and installation and commissioning of the device: After the coating of the internal cooling body is cured, the guide pipe, crystallizer, and flow distribution plate are concentrically assembled with the internal cooling body. Inert gas is introduced into the inert gas sealing jacket and the sealing performance is checked. (2) Size matching and gap adjustment: Determine the size of the internal cooling body and the crystallizer according to d=kD (0.32≤k≤0.45), and adjust the gap δ on one side to be uniform and constant; (3) Cooling medium and parameter setting: Pressurized circulating deionized water is introduced into the spiral cooling channel, and the working parameters of the cooling medium are set; (4) Construction of internal and external cooling coordinated control system: The internal cooling body is immersed in the high temperature zone of the liquid cavity, and the coordinated control coefficient λ=Q internal cooling / Q external cooling=0.3~0.6 and the internal cooling effective utilization coefficient η=0.80~0.90 are defined. The cooling intensity is adjusted by the liquid cavity depth formula H=H0 / (1+λη). (5) Phased coordinated cooling control: Adjust the internal cooling immersion depth and cooling intensity according to the three stages of casting start-up, steady state and end; (6) Precise control throughout the entire process: real-time monitoring of cooling parameters and ingot temperature field to ensure that the flatness of the ingot solidification front is ≤15°.

7. The application method according to claim 6, characterized in that, In step (3), the working pressure of the cooling medium is 0.2~0.6MPa and the inlet water temperature is 25~35℃.

8. The application method according to claim 6, characterized in that, In step (4), the immersion depth of the internal cooling body is 60% to 70% of the depth of the liquid cavity; the formula for the reduction in liquid cavity depth is ΔH=H0・λη / (1+λη), where H0 is the depth of the liquid cavity when the internal cooling device is not installed.

9. The application method according to claim 6, characterized in that, In step (5), during the casting start-up stage, the internal cooling body is shallowly immersed to 30% of the depth of the liquid cavity, and a weak cooling intensity is adopted, with λ maintained at 0.3~0.

4.

10. The application method according to claim 6, characterized in that, In step (5), during the steady-state casting stage, the internal cooling body is immersed to 70% of the depth of the liquid cavity, and strong cooling intensity is adopted, with λ maintained at 0.4~0.5.

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