Electromagnetic stirring device and method for purifying aluminum by means of segregation

Abstract

The application discloses an electromagnetic stirring device and method for purifying aluminum by using a segregation method, and relates to the technical field of aluminum purification, in particular to an electromagnetic stirring device and method for purifying aluminum by using a segregation method. The electromagnetic stirring device comprises a solidification furnace main body, a traction device and a control system. The solidification furnace main body comprises a vertical furnace body, a crucible is arranged in the vertical furnace body, a heating device is arranged outside the vertical furnace body, a cooling crystallizer is arranged at the bottom of the crucible, a first electromagnetic stirrer and a second electromagnetic stirrer are further arranged outside the vertical furnace body, the first electromagnetic stirrer and the second electromagnetic stirrer are electrically connected with the control system respectively, a corresponding region of the first electromagnetic stirrer is set as a liquid zone, and a corresponding region of the second electromagnetic stirrer is set as a solid-liquid mixing zone. Low-frequency and medium-frequency electromagnetic stirring is arranged in different zones, low-frequency stirring in the liquid zone realizes melt homogenization, medium-frequency stirring in the solid-liquid mixing zone provides additional thermal kinetic energy for impurities, and the synergistic effect of the two can significantly improve the segregation purification efficiency.

Description

Technical Field

[0001] This invention belongs to the field of metal purification technology, specifically relating to an electromagnetic stirring device and method for purifying aluminum using segregation. Background Technology

[0002] High-purity aluminum (purity ≥ 99.99%) has irreplaceable application value in the electronics industry, semiconductor sputtering targets, aerospace, and integrated circuit wiring. Segregation is one of the mainstream technologies for preparing high-purity aluminum. Its principle is to utilize the difference in solubility of impurity elements in the solid and liquid phases of aluminum during directional solidification, causing impurities to be expelled into the liquid phase, thereby achieving purification.

[0003] During the directional solidification process of segregation, a solute boundary layer rich in impurities forms at the solid-liquid interface, and its thickness directly determines the purification effect. Forced stirring of the melt can effectively disrupt or thin this boundary layer, promoting solute diffusion. Electromagnetic stirring, due to its advantages of being non-contact, pollution-free, and easy to precisely control, has become an ideal stirring method in segregation purification.

[0004] However, existing segregation purification technologies mostly employ a single mode of electromagnetic stirring, failing to consider the differentiated needs of different regions within a vertical directional solidification furnace: the liquid zone requires macroscopic flow to homogenize the melt composition and temperature; the solid-liquid mixing zone requires additional thermodynamic kinetic energy to accelerate the detachment of impurity atoms from the interface and their transport into the deeper liquid phase. Electromagnetic fields of different frequencies possess different physical properties; low-frequency electromagnetic fields have a large penetration depth but impart relatively weak local thermodynamic kinetic energy to impurities, while medium-frequency electromagnetic fields can generate strong local shear flow near the solid-liquid interface. Currently, there are no known devices or methods that employ low-frequency and medium-frequency electromagnetic stirring separately for the liquid and solid-liquid mixing zones.

[0005] Therefore, developing a partitioned, frequency-matched electromagnetic stirring technology is of great significance for improving the efficiency of segregation purification. Summary of the Invention

[0006] This invention provides an electromagnetic stirring device and method for purifying aluminum using segregation, in order to solve the problems encountered in the above-mentioned background art.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: An electromagnetic stirring device for purifying aluminum using segregation includes a solidification furnace body, a traction device, and a control system. The solidification furnace body includes a vertical furnace body, a crucible is disposed inside the vertical furnace body, a heating device is disposed outside the vertical furnace body, a cooling crystallizer is disposed at the bottom of the crucible, and a first electromagnetic stirrer and a second electromagnetic stirrer are also disposed outside the vertical furnace body. The area corresponding to the first electromagnetic stirrer is set as a liquid zone, and the area corresponding to the second electromagnetic stirrer is set as a solid-liquid mixing zone.

[0008] Furthermore, the first electromagnetic stirrer and the second electromagnetic stirrer are arranged from top to bottom on the outside of the vertical furnace body.

[0009] Furthermore, the first electromagnetic stirrer and the second electromagnetic stirrer are electrically connected to the control system, respectively.

[0010] Furthermore, the heating device is an induction heating coil, which is wrapped around the outside of the vertical furnace body.

[0011] Furthermore, the crucible is made of graphite or silicon nitride.

[0012] Furthermore, the inner diameter of the cooling crystallizer is matched with the diameter of the target ingot.

[0013] A method for segregation purification of aluminum using the electromagnetic stirring device described above includes the following steps: A. Place the aluminum to be purified into a crucible, evacuate the vacuum or introduce a protective gas, and start the heating device until the aluminum is completely melted and keep it at a certain temperature for a period of time. B. Turn on the first electromagnetic stirrer to electromagnetically stir the aluminum melt in the liquid zone to achieve homogenization of the aluminum melt. C. Start the cooling crystallizer and traction device to make the aluminum melt solidify directionally from the bottom up. Use the heating device to keep the aluminum melt in the furnace at a constant temperature. At the same time, turn on the second electromagnetic stirring device to stir the aluminum melt in the solid-liquid mixing zone until solidification is complete. D. After the directional solidification reaches the preset length, stop, remove the ingot, and cut off the top and bottom.

[0014] Furthermore, in step A, the heating temperature is 720 to 780 degrees Celsius, and the holding time is 10 to 20 minutes.

[0015] Furthermore, in step B, the first electromagnetic stirrer performs electromagnetic stirring of the aluminum melt at a low frequency of 2-8 Hz and a current of 100-150 A.

[0016] Furthermore, in step C, the aluminum melt solidifies directionally from bottom to top at a speed of 2-6 cm / h, and the second electromagnetic stirrer performs electromagnetic stirring on the aluminum melt at a medium frequency of 10-40 Hz and a current of 80-150 A.

[0017] The present invention has the following beneficial effects: (1) By setting a first electromagnetic stirrer and a second electromagnetic stirrer from top to bottom on the outside of the vertical furnace body, corresponding to the liquid zone and the solid-liquid mixing zone respectively, the first electromagnetic stirrer stirs the aluminum melt at a low frequency of 2-8Hz to achieve macroscopic homogenization, and the second electromagnetic stirrer stirs the solid-liquid mixing zone at a medium frequency of 10-40Hz to provide additional thermodynamic kinetic energy for impurities. The two stirrers work together in zones, so that impurities are effectively discharged and enriched at both ends of the ingot during the solidification process, and the purity of the middle section is significantly improved.

[0018] (2) The two electromagnetic stirrers are equipped with independent frequency conversion power supplies and are electrically connected to the control system. The control system can independently adjust the frequency and current of the two stirrers, realizing differentiated stirring of the liquid zone and the solid-liquid mixing zone. The process parameters can be flexibly adjusted according to the purity of different raw materials and purification requirements, and the system is highly adaptable.

[0019] (3) By using dual anti-interference measures such as frequency staggering and time-division control, the mutual interference between induction heating and electromagnetic stirring is effectively solved, ensuring that the two work in coordination and the equipment operates stably. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the axial arrangement of the electromagnetic stirrer coil and the induction heating coil of the present invention; Figure 3 This is a process flow diagram of the method of the present invention; Figure 4 This is a schematic diagram of the impurity distribution along the axial direction of the ingot after using the method of the present invention; Figure 5 This is a schematic diagram of the structure of the cooling crystallizer of the present invention; Figure 6 This is a schematic diagram of the traction device of the present invention; In the diagram, 1-solidification furnace body, 2-traction device, 3-control system, 4-vertical furnace body, 5-crucible, 6-heating device, 7-cooling crystallizer, 8-first electromagnetic stirrer, 9-second electromagnetic stirrer, 10-inner wall, 11-outer wall, 12-annular cooling water chamber, 13-cooling water inlet, 14-cooling water outlet, 15-copper ingot head, 16-connecting shaft, 17-mounting base, 18-servo motor, 19-reducer, 20-guide rail, 21-lead screw, 22-lifting platform. Detailed Implementation

[0021] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0022] Example 1

[0023] An electromagnetic stirring device for purifying aluminum using segregation, as shown in the attached figure. Figure 1-4 As shown, the system includes a solidification furnace body 1, a traction device 2, and a control system 3. The solidification furnace body 1 includes a vertical furnace body 4, inside which a crucible 5 is installed. The crucible 5 is made of graphite or silicon nitride. A heating device 6 is installed on the outside of the vertical furnace body 4, and a cooling crystallizer 7 is installed at the bottom of the crucible 5. The inner diameter of the cooling crystallizer 7 matches the diameter of the target ingot. A first electromagnetic stirrer 8 and a second electromagnetic stirrer 9 are also installed outside the vertical furnace body 4. In this embodiment, the heating device 6 is an induction heating coil, which is wrapped around the outside of the vertical furnace body 4. The induction heating coil operates at a frequency of 4000 Hz and has a power of 60 kW. The crucible 5 has an inner diameter of φ165 mm, an effective height of 600 mm, and an aluminum loading of 18... kg, the first electromagnetic stirrer 8 and the second electromagnetic stirrer 9 are both toroidal coils, equipped with independent frequency conversion power supplies; the first electromagnetic stirrer 8 and the second electromagnetic stirrer 9 are electrically connected to the control system 3 respectively, and the control system 3 can independently adjust the frequency and current of the two stirrers. The first electromagnetic stirrer 8 and the second electromagnetic stirrer 9 are arranged from top to bottom outside the vertical furnace body 4, wherein the area corresponding to the first electromagnetic stirrer 8 is set as the liquid zone, and the area corresponding to the second electromagnetic stirrer 9 is set as the solid-liquid mixing zone. The raw material is industrial pure aluminum with a purity of 99.85%, and the main impurities are Fe 0:12% and Si 0:08%.

[0024] It should be noted that the cooling crystallizer 7 is a copper water-cooled crystallizer, located below the bottom of the crucible 5. The cooling crystallizer 7 includes an inner wall 10, an outer wall 11, and an annular cooling water cavity 12 formed between them. A cooling water inlet 13 is located at the bottom of one side of the outer wall 11, and a cooling water outlet 14 is located at the top of the other side. Cooling water enters from the bottom and flows out from the top, forming a forced water-cooling circulation from bottom to top. The inner diameter of the cooling crystallizer matches the diameter of the target ingot. The inner wall is made of thermally conductive copper, directly contacting the molten aluminum drawn from the bottom of the crucible 5. The circulating cooling water carries away the latent heat of solidification of the molten aluminum, causing the molten aluminum to solidify directionally from bottom to top within the cooling crystallizer. A copper ingot deriver 15 is located at the bottom of the cooling crystallizer. The outer diameter of the copper ingot deriver 15 is the same as the inner diameter of the cooling crystallizer, and the lower end of the copper ingot deriver 15 is connected to the connecting shaft 16 of the traction device 2. The copper ingot head 15 serves as the initial solidification base. The aluminum melt first begins to crystallize on the upper surface of the copper ingot head 15. Subsequently, driven by the traction device 2, the copper ingot head 15, together with the solidified ingot, moves downward, so that the solid-liquid interface is continuously maintained in the cooling area of ​​the cooling crystallizer, thereby achieving continuous directional solidification.

[0025] The traction device 2 is located on the cooling crystallizer 7 and includes a mounting base 17, a servo motor 18, a reducer 19, a connecting shaft 16, and a guiding mechanism. Mounting base 17 is fixed to the bottom of solidification furnace body 1. A lead screw 21 is vertically mounted on mounting base 17. A lifting platform 22 (lead screw seat) is mounted on lead screw 21. The lifting platform 22 can move up and down along lead screw 21. Servo motor 18 is connected to lead screw 21 through reducer 19. Servo motor 18 is electrically connected to control system. The control system precisely controls the speed and direction of servo motor 18. Connecting shaft 16 is a water-cooled shaft. The water-cooled shaft is a hollow shaft structure and is vertically fixed on lifting platform 22. The water-cooled shaft is filled with circulating cooling water. The upper end of the water-cooled shaft is fixedly connected to the copper ingot head 15 at the bottom of cooling crystallizer 7. The guiding mechanism includes guide rails 20 on both sides of mounting base. Lifting platform 22 slides up and down along guide rails 20 to ensure that the traction direction of copper ingot head 15 and ingot is consistent with the axis of cooling crystallizer 7, and to avoid ingot skew.

[0026] A method for segregation purification of aluminum using the electromagnetic stirring device described above includes the following steps: A. Place the aluminum to be purified into crucible 5, evacuate or introduce protective gas, and start heating device 6 until the aluminum is completely melted and kept at a certain temperature for a period of time; wherein the heating temperature is 720 to 780 degrees and the holding time is 10-20 minutes. In this embodiment, the heating temperature is 750 degrees and the holding time is 20 minutes.

[0027] B. Turn on the first electromagnetic stirrer 8 to electromagnetically stir the aluminum melt in the liquid zone to achieve homogenization of the aluminum melt; wherein the first electromagnetic stirrer 8 performs electromagnetic stirring of the aluminum melt at a low frequency of 2-8 Hz and a current of 100-150 A. In this embodiment, the first electromagnetic stirrer 8 performs electromagnetic stirring of the aluminum melt at a low frequency of 5 Hz and a current of 120 A.

[0028] C. Start the cooling crystallizer 7 and the traction device 2 to allow the aluminum melt to solidify directionally from the bottom up. Use the heating device 6 to keep the aluminum melt in the furnace at a constant temperature. At the same time, turn on the second electromagnetic stirring device to stir the aluminum melt in the solid-liquid mixing zone until solidification is complete. The aluminum melt solidifies directionally from the bottom up at a speed of 2-6 cm / h. The second electromagnetic stirrer 9 performs electromagnetic stirring of the aluminum melt at a medium frequency of 10-40 Hz and a current of 80-150 A. In this embodiment, the aluminum melt solidifies directionally from the bottom up at a speed of 4 cm / h. The second electromagnetic stirrer 9 performs electromagnetic stirring of the aluminum melt at a medium frequency of 25 Hz and a current of 100 A.

[0029] D. After the directional solidification reaches the preset length, stop and remove the ingot. The finished ingot has a diameter of 150 mm and a length of 550 mm. Impurities are mainly concentrated at both ends of the ingot, and the middle section is a high-purity area. The top and bottom are cut off. In this embodiment, 25% of the top and 5% of the bottom are cut off, and the middle section is taken to test the purity.

[0030] Results: The product purity reached 99.993%, and the ingot surface was smooth and crack-free. Axial sampling analysis showed that the Fe and Si contents were as high as 0.08% and 0.05% at the top of the ingot, respectively, and approximately 0.02% and 0.01% at the bottom, while the contents in the middle section were all below 0.005%, indicating a clear concentration of impurities at both ends. Compared with Comparative Example 1, the purification efficiency was improved by 92%; compared with Comparative Example 4, the purity was improved by an order of magnitude.

[0031] Comparative Example 1 Without turning on any electromagnetic stirrer, simply follow the basic process described above for directional solidification.

[0032] Results: The product purity was only 99.91%, the ingot surface was rough, and there were obvious macroscopic segregation striations. Impurities showed no obvious enrichment trend along the axial direction, but the impurity content was high in the middle section.

[0033] Comparative Example 2 (low-frequency stirring only in the liquid zone) Only turn on the first electromagnetic stirrer 8 (liquid zone), set the frequency to 5 Hz, and keep other parameters the same as the basic process. Do not turn on the second electromagnetic stirrer 9.

[0034] Results: The product purity was 99.96%, which was improved compared to no stirring, but local segregation still existed on the surface of the ingot. The effect of impurity enrichment towards the top was not significant, and the purity improvement in the middle section was limited.

[0035] Comparative Example 3 (medium-frequency stirring only in the solid-liquid mixing zone) Only turn on the second electromagnetic stirrer 9 (solid-liquid mixing zone), set the frequency to 25 Hz, and keep other parameters the same as the basic process. Do not turn on the first electromagnetic stirrer 8.

[0036] Results: The product purity was 99.98%, which was better than stirring only in the liquid zone, and the ingot surface was smooth. Impurities began to accumulate at the top, but due to the lack of stirring in the liquid zone, the macroscopic composition of the melt was uneven, resulting in unstable purification effects and poor repeatability.

[0037] Comparative Example 4 (Two-stage low-frequency stirring) Simultaneously turn on the first and second electromagnetic stirrers 9. The frequency of the first stirrer is 5 Hz, and the frequency of the second stirrer is also set to 5 Hz (low frequency). Other parameters are the same as the basic process.

[0038] Results: The product purity was 99.97%, which was not significantly improved compared to Comparative Example 2. This indicates that low-frequency stirring in the solid-liquid mixing zone cannot provide sufficient thermodynamic kinetic energy for impurities, cannot effectively flush the solid-liquid interface, and has a weak driving force for impurities to accumulate at both ends.

[0039] Example 2

[0040] Based on Example 1, the frequency of the first stirrer was fixed at 5 Hz, and the frequency of the second stirrer was changed to investigate the effect of the thermodynamic kinetic energy imparted by different frequencies on impurity segregation. The results are as follows: Table 1. Comparison of purification effects at different frequencies of the second stirrer The results show that within the mid-frequency range of 10–40 Hz, the thermodynamic kinetic energy provided to impurities is moderate, and the purification effect is significantly better than that of low frequency (5 Hz) or high frequency (60 Hz), with 20–30 Hz being the optimal range. This confirms the core scientific judgment of this invention that "the solid-liquid mixing zone requires mid-frequency electromagnetic stirring to impart additional thermodynamic kinetic energy to impurities."

[0041] Example 3 With the first stirrer at a constant 5 Hz and the second stirrer at 25 Hz, the traction speed was varied, and the results are as follows: Table 2 Comparison of purification effects at different traction speeds Considering both purity and production efficiency, 4 cm / h is the preferred traction speed. This embodiment demonstrates that within a traction speed range of 2-6 cm / h, the present invention can obtain high-purity products, exhibiting a wide process adaptability window.

[0042] Example 4 The raw material was changed to refined aluminum (purity 99.95%). The first stirrer had a frequency of 4 Hz and a current of 100 A, and the second stirrer had a frequency of 30 Hz and a current of 90 A. Other parameters were the same as the basic process.

[0043] Results: The product purity was 99.9992%, with impurities showing significant enrichment at both ends, meeting the requirements for high-purity aluminum sputtering targets. This example demonstrates that the method of the present invention is also applicable to the deep purification of refined aluminum into high-purity aluminum.

[0044] Example 5 To verify the effectiveness of the anti-interference measures (frequency offset, time-division multiplexing) adopted in this invention, the following comparative tests were conducted: Test A (No anti-interference measures taken): Induction heating and stirring worked simultaneously without frequency staggering or time-sharing control. Results: Temperature sensor signal fluctuated by ±5℃, stirring current output was unstable, product purity fluctuated significantly (99.95%~99.99%), and repeatability was poor.

[0045] Test B (using the anti-interference measures of this invention): frequency staggered (4000 Hz (heating device 6) vs 5 Hz / 25 Hz (first electromagnetic stirrer 8 or second electromagnetic stirrer 9)), time-division control (stirrer off during melting stage, induction heating switched to low power for heat preservation during directional solidification stage). Results: temperature sensor signal stable (±1℃), stirrer current output stable, product purity stable above 99.993%, good repeatability. When working simultaneously during directional solidification stage, melt surface flow rate change less than 5%, purity fluctuation within ±0.001%.

[0046] Table 3 Comparison of the effects of anti-electromagnetic interference measures The above results show that the dual measures of frequency staggering and time-division control adopted in this invention can effectively solve the problem of mutual interference between induction heating and electromagnetic stirring, and ensure stable operation of the equipment and consistency of purification effect.

[0047] Based on the above comparative examples and embodiments, we can conclude that: 1. Low-frequency stirring (2–8 Hz) is used in the liquid zone to achieve macroscopic homogenization, while medium-frequency stirring (10–40 Hz) is used in the solid-liquid mixing zone to provide additional thermodynamic kinetic energy to impurities. The synergistic effect of both achieves optimal segregation purification. Example 2 demonstrates that medium-frequency (25 Hz) is far superior to low-frequency (5 Hz) or high-frequency (60 Hz), verifying the scientific judgment that "different regions require different thermodynamic kinetic energies."

[0048] 2. The frequency of the liquid zone is 2-8 Hz (preferably 3-6 Hz), the frequency of the solid-liquid mixing zone is 10-40 Hz (preferably 20-30 Hz), and the traction speed is 2-6 cm / h (preferably 4 cm / h).

[0049] 3. By staggering the frequency and controlling the time, the induction heating and electromagnetic stirring can be coordinated.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An electromagnetic stirring device for purifying aluminum using segregation, characterized in that, The solidification furnace body (1), traction device (2) and control system (3) are included. The solidification furnace body (1) includes a vertical furnace body (4). A crucible (5) is provided inside the vertical furnace body (4). A heating device (6) is provided on the outside of the vertical furnace body (4). A cooling crystallizer (7) is provided at the bottom of the crucible (5). A first electromagnetic stirrer (8) and a second electromagnetic stirrer (9) are also provided on the outside of the vertical furnace body (4). The area corresponding to the first electromagnetic stirrer (8) is set as the liquid area, and the area corresponding to the second electromagnetic stirrer (9) is set as the solid-liquid mixing area.

2. The electromagnetic stirring device for purifying aluminum using segregation as described in claim 1, characterized in that, The first electromagnetic stirrer (8) and the second electromagnetic stirrer (9) are arranged from top to bottom outside the vertical furnace body (4).

3. The electromagnetic stirring device for purifying aluminum using segregation as described in claim 2, characterized in that, The first electromagnetic stirrer (8) and the second electromagnetic stirrer (9) are electrically connected to the control system (3), respectively.

4. The electromagnetic stirring device for purifying aluminum using segregation as described in claim 1, characterized in that, The heating device (6) is an induction heating coil, which is wrapped around the outside of the vertical furnace body (4).

5. The electromagnetic stirring device for purifying aluminum by segregation according to claim 4, characterized in that, The crucible (5) is made of graphite or silicon nitride.

6. The electromagnetic stirring device for purifying aluminum using segregation as described in claim 1, characterized in that, The inner diameter of the cooling crystallizer (7) matches the diameter of the target ingot.

7. A method for segregation purification of aluminum using an electromagnetic stirring device as described in any one of claims 1-6, characterized in that, Includes the following steps: A. Place the aluminum to be purified into a crucible (5), evacuate or introduce protective gas, and start the heating device (6) until the aluminum is completely melted and kept at a certain temperature for a period of time. B. Turn on the first electromagnetic stirrer (8) to perform electromagnetic stirring on the aluminum melt in the liquid zone to achieve uniformity of the aluminum melt. C. Start the cooling crystallizer (7) and the traction device (2) to make the aluminum melt solidify from the bottom up. Use the heating device (6) to keep the aluminum melt in the furnace warm. At the same time, turn on the second electromagnetic stirrer (9) to stir the aluminum melt in the solid-liquid mixing zone until solidification is complete. D. After the directional solidification reaches the preset length, stop, remove the ingot, and cut off the top and bottom.

8. The method according to claim 7, characterized in that, In step A, the heating temperature is 720 to 780 degrees Celsius, and the holding time is 10 to 20 minutes.

9. The method according to claim 7, characterized in that, In step B, the first electromagnetic stirrer (8) electromagnetically stirs the aluminum melt at a low frequency of 2-8 Hz and a current of 100-150 A.

10. The method according to claim 7, characterized in that, In step C, the aluminum melt solidifies directionally from bottom to top at a speed of 2-6 cm / h, and the second electromagnetic stirrer (9) performs electromagnetic stirring on the aluminum melt at a medium frequency of 10-40 Hz and a current of 80-150 A.

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