Electromagnetic mixing device and method for mixing magnetic material powder using the same

Abstract

The application belongs to the technical field of magnetic material preparation, and relates to an electromagnetic mixing device and a method for mixing magnetic material powder by using the same. The electromagnetic mixing device comprises, from top to bottom, a feeding assembly, an electromagnetic mixing assembly and a demagnetization and screening assembly which are sequentially connected. The feeding assembly comprises a feeding inlet and a feeding pipe which are connected in a top-down manner. The electromagnetic mixing assembly comprises a stirring chamber and an electromagnetic stirrer. The demagnetization and screening assembly comprises a vibrating screen, a coarse particle outlet, a discharge outlet and a vibrating motor. The electromagnetic mixing device and the electromagnetic mixing method can realize more uniform, rapid and efficient mixing of magnetic material powder.

Description

Technical Field

[0001] This invention belongs to the field of magnetic material preparation technology, and relates to an electromagnetic mixing device and a method for mixing magnetic material powders using the same. Background Technology

[0002] The global magnetic materials market maintains steady growth, with China being the largest producer and consumer. Currently, magnetic materials are developing towards higher performance and greater consistency. Magnetic materials such as neodymium iron boron, ferrite, samarium cobalt, and AlNiCo are mostly prepared using powder metallurgy technology. The mixing process before molding in this technology modifies the powder surface, directly affecting the magnet's performance. This process places extremely high demands on the production of magnetic material powders, especially for fine-particle-size powders or those with added organic additives, regarding the uniformity of mixing, the magnetic field orientation of the pressed blank, molding efficiency, powder flowability, internal stress in the pressed blank, and mold protection.

[0003] Due to van der Waals forces, electrostatic forces, surface energy, and poor sphericity of powder particles, magnetic material powder particles exhibit strong agglomeration forces, which increase with finer particle sizes. Adding organic additives further complicates the uniform mixing of magnetic material powders. Traditional V-type mixers, double-cone mixers, or American-style three-dimensional mixers rely on mechanical tumbling, creating mixing dead zones. This results in uneven additive coating during powder mixing, failing to break up micro-agglomerates, leading to poor mixing uniformity, unstable product performance, and low yield. Ultrasonic dispersion mixing methods are energy-intensive, prone to heat generation, and difficult to scale up. Airflow mixing offers limited improvement in micron-level magnetic powder agglomeration, has complex mechanisms, high equipment costs, and suffers from mixing dead zones and powder residue issues. Some emerging mixing solutions, such as high-speed shear mixing equipment, easily introduce impurities into the magnetic material powder mixture, and the high rotation speed may damage the grain boundary structure of the magnetic powder. Furthermore, due to the relatively complex internal structure of such mixing equipment, powder residue is unavoidable.

[0004] Therefore, how to efficiently mix fine-particle magnetic material powders with added additives, break up micro-agglomerates of magnetic powders, uniformly coat the additives, improve the magnetic properties and consistency of the product, and meet the development direction of high performance and high consistency of magnetic materials has become a key technical problem that the magnetic materials industry urgently needs to solve.

[0005] Previously, electromagnetic stirring technology was mainly used in continuous casting metallurgy, targeting molten liquid metals or alloys. There was no evidence that electromagnetic stirring technology was applied to the field of solid powder mixing of magnetic materials. Summary of the Invention

[0006] The primary objective of this invention is to provide an electromagnetic mixing device that enables more uniform, rapid, and efficient mixing of magnetic material powders.

[0007] To achieve this objective, in a basic implementation, the present invention provides an electromagnetic mixing device for electromagnetic mixing of magnetic material powders. The device comprises, from top to bottom, a feeding assembly, an electromagnetic mixing assembly, and a demagnetizing sieving assembly connected sequentially. The feeding assembly includes an upper and lower connected feeding port and a feeding pipe. The electromagnetic mixing assembly includes a mixing chamber and an electromagnetic stirrer. The demagnetizing sieving assembly includes a vibrating screen, a coarse particle outlet, a discharge port, and a vibrating motor.

[0008] In the mixing chamber, magnetic material powder is fed from the feed inlet and the feed pipe, and electromagnetic mixing is carried out under the stirring of the electromagnetic stirrer.

[0009] The vibrating screen vibrates under the drive of the vibrating motor, and is used to demagnetize the magnetic material powder after electromagnetic mixing and to screen the particles of different sizes.

[0010] The coarse particle outlet is used to discharge the coarse particles obtained by the demagnetization screening of the vibrating screen.

[0011] The discharge port is used for discharging the fine particles obtained by the demagnetization screening of the vibrating screen.

[0012] The relevant principles of this invention are as follows:

[0013] The prepared magnetic material powder raw material, relying on its own gravity and further accelerated by a pneumatic vibrator, enters the mixing chamber through the feeding assembly, i.e., a continuous quantitative feeder, and undergoes electromagnetic mixing under the agitation of an electromagnetic stirrer. The electromagnetic stirrer can be configured as a single-stage or multi-stage stirrer. Multi-stage electromagnetic stirrers can be uniformly configured with the same magnetic field shape, frequency, and strength, or different magnetic field shapes, frequencies, and strengths can be set according to the characteristics of the materials to be mixed.

[0014] During mixing, an electromagnetic stirrer generates a periodically changing non-uniform magnetic field. Each magnetic material powder particle within the stirrer's space is subjected to the force of this non-uniform magnetic field, moving and colliding with each other as the magnetic field changes, thus achieving rapid and uniform mixing. Specifically, each magnetic material powder particle can be considered as a small magnetic moment. When the magnetic material powder enters a certain stage of the stirrer space, at any given moment, due to the different spatial positions of each particle, each particle will be subjected to the combined effects of a magnetic field force and gravity, both of which are not entirely identical in magnitude and direction. The electromagnetic stirrer's magnetic field rotates and changes with time and space. Under the combined influence of the changing magnetic field force, gravity, and inertia, the magnetic material powder particles move and collide with the changing magnetic field, effectively dispersing powder micro-agglomerates. If there are two or more electromagnetic stirrers, after a certain mixing step is completed, the electromagnetic stirrer of that stage is briefly powered off or the permanent magnet switch is turned off to shut off the magnetic field of the electromagnetic stirrer for a period of ≤10 minutes. This allows the magnetic material powder in the space to lose the magnetic field binding and enter the space of the next electromagnetic stirrer to continue mixing by its own gravity or other auxiliary power. At the same time, the magnetic field of the electromagnetic stirrer of that stage is activated and the feeding step is executed. This cycle is repeated to achieve the purpose of continuous, rapid and uniform mixing of magnetic material powder without dead corners.

[0015] After the final mixing step is completed, the electromagnetic stirrer of this stage is briefly powered off or the permanent magnet switch is turned off to shut off the magnetic field of the electromagnetic stirrer, so that the magnetic powder in the space loses the magnetic field binding and achieves zero residue discharge. That is, after the mixing is completed and the material is discharged, the space of the mixing chamber achieves zero residue of magnetic material powder.

[0016] Magnetic material powder particles retain a certain amount of residual magnetism after electromagnetic stirring and mixing, resulting in magnetic adhesion between the powder particles, forming magnetic chains or clusters. Mechanical methods such as mechanical stirring or airflow impact can demagnetize the weakly magnetized magnetic material powder particles, thus achieving the purpose of demagnetizing the mixed magnetic material powder. Alternatively, thermal demagnetization methods such as heating and cooling can be used to demagnetize the mixed magnetic material powder. The demagnetization step can be performed using a demagnetizing sieving component, included as a single unit within the electromagnetic mixing device, executed after the final stage of electromagnetic stirring; or it can be independent of the electromagnetic mixing device, set up as a subsequent external independent device.

[0017] In a preferred embodiment, the present invention provides an electromagnetic mixing device, wherein the feeding assembly further includes a valve disposed on the feeding pipe for controlling the entry of magnetic material powder from the feeding port into the mixing chamber.

[0018] In a preferred embodiment, the present invention provides an electromagnetic mixing device, wherein the valves, from top to bottom, include an air inlet valve, an upper flap valve, and a lower flap valve.

[0019] In a preferred embodiment, the present invention provides an electromagnetic mixing device, wherein the feeding assembly further includes a pneumatic vibrator disposed on the feeding pipe for applying vibration to the magnetic material powder feeding, thereby accelerating the magnetic material powder into the mixing chamber.

[0020] In a preferred embodiment, the present invention provides an electromagnetic mixing device, wherein the electromagnetic stirrer is divided into upper and lower groups, namely an upper electromagnetic stirrer and a lower electromagnetic stirrer.

[0021] The electromagnetic stirrer of this invention is an electromagnetic stirrer for continuous steel casting. Its principle and structural composition can be found in "Mao Bin, Zhang Guifang, and Li Aiwu, eds. Theory and Technology of Electromagnetic Stirring for Continuous Steel Casting [M]. Metallurgical Industry Press, 2012: pp. 5-20, 102". However, it should be noted that the mechanism of interaction between the magnetic field of the electromagnetic stirrer and the working fluid in continuous steel casting differs from that in this invention. In continuous steel casting, the changing magnetic field generated by the electromagnetic stirrer induces eddy currents in the molten steel, and the interaction between the magnetic field and the eddy currents causes the molten steel to move under force. In this invention, the magnetic field generated by the electromagnetic stirrer magnetizes magnetic material powder particles, and the magnetic force between the magnetic stirrer and the magnetized magnetic material powder particles causes the powder to move under force.

[0022] In a preferred embodiment, the present invention provides an electromagnetic mixing device, wherein the electromagnetic mixing assembly further includes a distributor disposed within the mixing chamber above the electromagnetic stirrer for distributing the magnetic material powder feed. The mixing chamber is a hollow elongated cylinder, and the electromagnetic stirrer is a hollow cylinder with an inner diameter slightly larger than the outer diameter of the mixing chamber, thus allowing the electromagnetic stirrer to fit snugly outside the mixing chamber. The magnetic field characteristics generated by the electromagnetic stirrer determine that its effective magnetic field range is essentially limited to the space within the mixing chamber between the upper and lower edges of the electromagnetic stirrer.

[0023] The distributor is preferably an umbrella-shaped distributor. When the magnetic material powder enters the mixing chamber through the feed pipe, the magnetic material powder can be dispersed to the edge of the mixing chamber by the help of the distributor and enter the electromagnetic stirrer space, where it is confined and mixed under electromagnetic stirring.

[0024] In a preferred embodiment, the present invention provides an electromagnetic mixing device, wherein the electromagnetic mixing device further includes a first rubber sleeve and / or a second rubber sleeve.

[0025] The first rubber sleeve is used to wrap and connect the feed pipe and the mixing chamber;

[0026] The second rubber sleeve is used to wrap and connect the mixing chamber and the vibrating screen.

[0027] The second objective of this invention is to provide a method for mixing magnetic material powder using the electromagnetic mixing device described above, so as to achieve more uniform, rapid and efficient mixing of magnetic material powder.

[0028] To achieve this objective, in a basic implementation, the present invention provides a method for mixing magnetic material powders using the electromagnetic mixing apparatus described above, the method comprising the following steps:

[0029] (1) Magnetic material powder enters the mixing chamber from the feed inlet for electromagnetic mixing;

[0030] (2) The magnetic material powder after electromagnetic mixing is demagnetized and sieved by the vibrating screen, and the coarse particles and fine particles obtained by demagnetization and sieving are collected respectively.

[0031] In a preferred embodiment, the present invention provides a method for mixing magnetic material powders using the electromagnetic mixing device described above, wherein in step (1),

[0032] The magnetic material powder is selected from one or more of the following: elemental metals of Fe, Co, and Ni; Nd-Fe-B alloys; Sm-Co alloys; Sm-Fe-N alloys; ferrites; and Al-Ni-Co alloy powders; and / or

[0033] The magnetic material powder has a particle size range of 1-100 micrometers; and / or

[0034] The magnetic material powder further contains additives selected from one or more of dipropylene glycol butyl ether, ethyl acetate, No. 120 gasoline, acetone, and sodium diisooctyl sulfosuccinate. The mass ratio of the additives to the magnetic material powder is 0.2-0.4:100; and / or

[0035] The magnetic field type within the stirring chamber is one or more of the following: rotating magnetic field, traveling wave magnetic field, spiral magnetic field, and rotating permanent magnet. See also... Figure 2 Rotating magnetic field type refers to the magnetic field generated by an electromagnetic stirrer rotating around an axis at a certain speed in space; traveling wave magnetic field type refers to the magnetic field generated by an electromagnetic stirrer moving in a straight line in one direction at a certain speed in space; spiral magnetic field type refers to the magnetic field generated by an electromagnetic stirrer moving spirally around an axis at a certain speed in space. The spiral magnetic field type is the superposition result of the rotating magnetic field type and the traveling wave magnetic field type; rotating permanent magnet type refers to the use of a permanent magnet to generate a constant magnetic field, and using mechanical methods to rotate the permanent magnet. Depending on the arrangement of the permanent magnet, a rotating magnetic field or a spiral magnetic field is generated in space. And / or

[0036] The magnetic field frequency in the stirring chamber is 10-50 Hz, and the central magnetic field strength is 50-500 Gs; and / or

[0037] The electromagnetic mixing time in the mixing chamber is 0.2-10 minutes.

[0038] In a preferred embodiment, the present invention provides a method for mixing magnetic material powder using the electromagnetic mixing device described above, wherein in step (2),

[0039] The vibrating screen has a mesh size of 40-120; and / or

[0040] The demagnetizing and screening time of the vibrating screen is 1-5 minutes; and / or

[0041] The demagnetizing method of the vibrating screen is selected from one or more of vibration mixing, airflow impact, and heating-cooling.

[0042] The beneficial effect of the present invention is that, by using the electromagnetic mixing device and electromagnetic mixing method of the present invention, more uniform, rapid and efficient mixing of magnetic material powders can be achieved.

[0043] The electromagnetic mixing device and method of this invention can stably and effectively disperse micro-agglomerates of magnetic material powders, eliminating mixing dead zones, mechanical contact contamination, and ensuring uniform, rapid, and efficient mixing. No powder residue remains after discharge, thereby comprehensively improving the performance consistency of the magnetic material mixture, ensuring uniform coating of additives, increasing the magnetic field orientation of the magnetic material compact, enhancing its fluidity, reducing internal stress, and improving the yield. Furthermore, the electromagnetic mixing device of this invention has a simple internal structure in the mixing chamber, convenient discharge, and achieves zero powder residue, facilitating processing and maintenance. Attached Figure Description

[0044] Figure 1 The following is a structural diagram of the electromagnetic mixing device for magnetic material powder of the present invention, which is an example of the present invention. It includes a feed inlet 1, an air valve 2, an upper flap valve 3, a pneumatic vibrator 4, a lower flap valve 5, a first rubber sleeve 6, a mixing chamber 7, an umbrella-shaped distributor 8, an upper electromagnetic stirrer 9, a lower electromagnetic stirrer 10, a vibrating screen 11, a coarse particle outlet 12, a discharge port 13, a vibrating motor 14, and a second rubber sleeve 15.

[0045] Figure 2 This is a schematic diagram of the magnetic field type of the electromagnetic stirrer in the electromagnetic mixing device for magnetic material powders applicable to the present invention.

[0046] Figure 3This is a spatial magnetic field distribution diagram of the stirring chamber at a certain moment during the operation of the electromagnetic mixing device for magnetic material powder of the present invention. The magnetic field type is a rotating magnetic field, the magnetic field strength is 80-500 Gs, and the magnetic field frequency is 20 Hz. The left figure is a top view and the right figure is a front view. Detailed Implementation

[0047] The exemplary composition and structure of the electromagnetic mixing device for magnetic material powder of the present invention are as follows: Figure 1 As shown, from top to bottom, the assembly includes a feeding component, a first rubber sleeve 6, an electromagnetic mixing component, a second rubber sleeve 15, and a demagnetizing screening component connected in sequence. The feeding component includes an upper and lower connected feed inlet 1, a feed pipe, and, from top to bottom, an air inlet valve 2, an upper flap valve 3, a pneumatic vibrator 4, and a lower flap valve 5 arranged sequentially on the feed pipe. The electromagnetic mixing component includes a mixing chamber 7, an umbrella-shaped distributor 8, an upper electromagnetic agitator 9, and a lower electromagnetic agitator 10. The demagnetizing screening component includes a vibrating screen 11, a coarse particle outlet 12, a discharge outlet 13, and a vibrating motor 14.

[0048] Air valve 2, upper flap valve 3, and lower flap valve 5 are used to control the entry of magnetic material powder from feed port 1 into mixing chamber 7. Pneumatic vibrator 4 is used to apply vibration to the magnetic material powder feed, accelerating the entry of magnetic material powder into mixing chamber 7.

[0049] In the mixing chamber 7, magnetic material powder is fed from the feed inlet 1 and the feed pipe, and electromagnetic mixing is performed under the agitation of the upper electromagnetic stirrer 9 and the lower electromagnetic stirrer 10. Inside the mixing chamber 7, an umbrella-shaped distributor 8 is installed above both the upper electromagnetic stirrer 9 and the lower electromagnetic stirrer 10 to distribute the magnetic material powder feed. The mixing chamber 7 is a hollow elongated cylinder, and the upper electromagnetic stirrer 9 and the lower electromagnetic stirrer 10 are hollow cylinders. Their hollow inner diameter is slightly larger than the outer diameter of the mixing chamber 7, so the upper electromagnetic stirrer 9 and the lower electromagnetic stirrer 10 can fit snugly around the mixing chamber 7.

[0050] The magnetic field characteristics generated by the upper electromagnetic stirrer 9 and the lower electromagnetic stirrer 10 determine that their effective range is basically limited to the space of the mixing chamber 7 between the upper and lower edges of the upper electromagnetic stirrer 9 and the lower electromagnetic stirrer 10. When the magnetic material powder enters the mixing chamber 7 through the feed pipe, the magnetic material powder can be dispersed to the edge of the mixing chamber 7 by the action of the umbrella-shaped distributor 8, and enter the electromagnetic stirrer space, and be bound in the electromagnetic stirrer space to complete the mixing under electromagnetic stirring. For the principle and structural composition of the electromagnetic stirrer (including the upper electromagnetic stirrer 9 and the lower electromagnetic stirrer 10), please refer to "Mao Bin, Zhang Guifang, Li Aiwu, eds. Theory and Technology of Electromagnetic Stirring for Continuous Casting Steel [M]. Metallurgical Industry Press, 2012: pp. 5-20, 102".

[0051] Vibrating screen 11 vibrates under the drive of vibrating motor 14, and is used to demagnetize and screen magnetic material powder after electromagnetic mixing.

[0052] The coarse particle outlet 12 is used to discharge the coarse particles obtained by the demagnetization screening of the vibrating screen 11.

[0053] The discharge port 13 is used to discharge the fine particles obtained by the demagnetization screening of the vibrating screen 11.

[0054] The first rubber sleeve 6 is used to wrap and connect the feed pipe and the mixing chamber 7. The second rubber sleeve 15 is used to wrap and connect the mixing chamber 7 and the vibrating screen 11.

[0055] The exemplary operation method or principle of the electromagnetic mixing device for magnetic material powder of the present invention described above is as follows.

[0056] Connect the container containing the magnetic material powder to be mixed to the inlet 1, open the air valve 2, the upper flap valve 3, and the pneumatic vibrator 4, and the powder fills the feed pipe. Close the upper flap valve 3, start the upper electromagnetic stirrer 9, and open the lower flap valve 5.

[0057] The magnetic material powder enters the mixing chamber 7 by its own gravity and the pneumatic vibrator 4, and falls to the upper electromagnetic stirrer 9 through the umbrella-shaped distributor 8. It is then bound in the magnetic field space of the upper electromagnetic stirrer 9 and begins to be stirred, while the lower flap valve 5 is closed.

[0058] When the upper electromagnetic stirrer 9 starts stirring, the next feeding process starts simultaneously, but at this time the lower flap valve 5 is in the closed state.

[0059] Before the upper electromagnetic stirrer 9 finishes stirring, the lower electromagnetic stirrer 10 is started. After the upper electromagnetic stirrer 9 finishes stirring, it is turned off for a short time (less than 5 seconds). The magnetic material powder loses the binding of the magnetic field and falls into the magnetic field space of the lower electromagnetic stirrer 10 by its own gravity through the umbrella-shaped distributor 8 and is bound and stirred.

[0060] When the current electromagnetic stirrer 10 starts stirring, the upper electromagnetic stirrer 9 is activated, the lower flap valve 5 is opened, and a new batch of magnetic material powder enters the magnetic field space of the upper electromagnetic stirrer 9 and is bound and stirred. At the same time, the next feeding process starts to be executed, but at this time the lower flap valve 5 is in the closed state.

[0061] After the lower electromagnetic stirrer 10 finishes stirring, it is turned off for a short time (less than 5 seconds). The magnetic material powder loses the binding of the magnetic field and enters the vibrating screen 11 for sorting and demagnetization by its own gravity. The coarse powder that has been sorted and demagnetized by the vibrating screen 11 is selected out by the coarse particle outlet 12, and the remaining mixed and demagnetized powder enters the packaging tank through the discharge port 13.

[0062] When the magnetic material powder enters the vibrating screen 11, the lower electromagnetic stirrer 10 is restarted. At this time, the upper electromagnetic stirrer 9 stops stirring and is turned off for a short time (less than 5 seconds). The magnetic material powder falls into the magnetic field space of the lower electromagnetic stirrer 10 by its own gravity through the umbrella-shaped distributor 8 and is bound and stirred.

[0063] After being precisely designed with time program control, the above workflow can achieve continuous operation of feeding, mixing and discharging, which greatly improves the efficiency of magnetic material powder mixing.

[0064] The method for mixing magnetic material powder using the electromagnetic mixing apparatus of the present invention, as exemplified above, includes the following steps.

[0065] Preparation step S1: Magnetic material powder or magnetic material powder with additives (the additives are selected from one or more of dipropylene glycol butyl ether, ethyl acetate, No. 120 gasoline, acetone, sodium diisooctyl sulfosuccinate, and the mass ratio of additives to powder is 0.2-0.4:100) (powder diameter in the range of 1-100 micrometers) is loaded into the raw material tank (generally, the tank should be protected by inert gas) and initial mixing is completed in a three-dimensional mixer for ≥30 minutes.

[0066] Feeding step S2: The magnetic material powder after initial mixing is fed into the mixing chamber 7 by its own gravity or in combination with other auxiliary power.

[0067] Electromagnetic stirrer parameter setting step S3: Set the same or different magnetic field type, magnetic field shape, magnetic field frequency, and magnetic field strength for the upper electromagnetic stirrer 9 and the lower electromagnetic stirrer 10. The magnetic field type can be one or more of the following: rotating magnetic field, traveling wave magnetic field, spiral magnetic field, and rotating permanent magnet. The magnetic field shape can be one or more of the following: rotating electromagnetic field, traveling wave electromagnetic field, and spiral electromagnetic field. The magnetic field frequency is in the range of 10-50Hz. The magnetic field strength refers to the magnetic field strength at the center of the electromagnetic stirrer, which is 50-500Gs.

[0068] Mixing step S4: The mixing time for both the upper electromagnetic stirrer 9 and the lower electromagnetic stirrer 10 is ≥5 seconds. After the mixing step of the upper electromagnetic stirrer 9 is completed, the magnetic field of the upper electromagnetic stirrer 9 is briefly turned off by power-off or permanent magnet switch, so that the magnetic material powder in the space of the upper electromagnetic stirrer 9 is freed from the magnetic field binding and enters the space of the lower electromagnetic stirrer 10 by its own gravity or other auxiliary power to continue mixing. At the same time, the magnetic field of the upper electromagnetic stirrer 9 is restarted and the feeding step is executed. This cycle is repeated to achieve continuous, rapid and uniform mixing of magnetic material powder without dead corners.

[0069] Demagnetization step S5: After the mixing step of the lower electromagnetic stirrer 10 is completed, the lower electromagnetic stirrer 10 is briefly powered off or the permanent magnet switch is turned off to shut off the magnetic field of the lower electromagnetic stirrer 10. This causes the magnetic powder in the space to lose its magnetic field binding, and the magnetic material powder enters the vibrating screen 11 (mesh size 40-120 mesh) by its own gravity or in combination with other auxiliary power to perform the demagnetization step. Mechanical stirring and / or airflow impact and / or heating-cooling methods are used to demagnetize the mixed magnetic material powder, and the treatment time is 1-5 minutes.

[0070] Discharge step S6: Discharge material after the demagnetization step is completed.

[0071] The implementation steps of the above mixing method are described separately. In actual operation, the process from the feeding step to the parameter setting step, mixing and demagnetizing steps, and then to the discharging step is continuous. When the upper electromagnetic stirrer 9 is working, a new batch of raw materials simultaneously enters the feeding waiting state. After the upper electromagnetic stirrer 9 completes the mixing, this batch of mixture enters the lower electromagnetic stirrer 10 and begins mixing, while a new batch of raw materials enters the upper electromagnetic stirrer 9 and begins mixing. After the lower electromagnetic stirrer 10 completes the mixing and discharges, the mixture from the upper electromagnetic stirrer 9 enters the lower electromagnetic stirrer 10 and begins mixing, while a new batch of raw materials also enters the upper electromagnetic stirrer 9 and begins mixing, thus repeating continuously.

[0072] Examples of the application of the mixing method of the present invention described above are as follows.

[0073] Example 1 and Comparative Example 1:

[0074] In this embodiment, the inner and outer diameters of the stirring chamber 7 are 250mm and 260mm, respectively, and the height is 1200mm; the heights of the upper electromagnetic stirrer 9 and the lower electromagnetic stirrer 10 are both 350mm.

[0075] (1) 1200 kg of industrially produced N52 sintered NdFeB magnetic powder with an average particle size of 2.5 ± 0.2 μm was selected. 1000 ppm of lubricant (dipropylene glycol butyl ether) and 2000 ppm of antioxidant (500 ppm of acetone + 1500 ppm of No. 120 gasoline) were added to the sintered NdFeB magnetic powder as additives.

[0076] (2) The neodymium iron boron magnetic powder with added additives was mixed using a traditional three-dimensional powder mixing equipment (ZFF-0.7m manufactured by Wenling Nanfang Powder Equipment Co., Ltd.). 3 After mixing in a nitrogen atmosphere for 30 minutes, 600 kg of the magnetic powder was taken out and used for subsequent electromagnetic mixing. The remaining 600 kg of magnetic powder was mixed for another 90 minutes using a traditional three-dimensional mixing device as a comparative example 1.

[0077] (3) 600 kg of sintered NdFeB magnetic powder, after being mixed for 30 minutes using a traditional three-dimensional mixing device, was added to the above-mentioned exemplary electromagnetic mixing device to perform a two-stage mixing process. The upper electromagnetic stirrer 9 (rotating magnetic field type) was set to a frequency of 20 Hz, a central magnetic field strength of 80 Gs, and a mixing time of 3 minutes for a single batch of 5 kg powder; the lower electromagnetic stirrer 10 (rotating magnetic field type) was set to a frequency of 30 Hz, a central magnetic field strength of 50 Gs, and a mixing time of 3 minutes for a single batch of 5 kg powder; then, the powder was demagnetized by a demagnetizing sieving assembly (120 mesh vibrating screen) through vibration mixing (demagnetizing and sieving time of 3 minutes for a single batch of 5 kg powder) before being discharged. The mixed powder is the powder of Example 1.

[0078] (4) Take a portion of magnetic powder from both Comparative Example 1 and Example 1 after mixing, and perform the same molding process on each (molding density 3.9 g / cm³). 3 Ten Φ50×40 cylinders were pressed, and then subjected to the same sintering and annealing treatment (sintering process: sintering at 1095℃ for 6 hours; annealing process: first annealing at 910℃ for 2 hours, then annealing at 580℃ for 4 hours). Finally, conventional magnetic property tests were performed (magnetic property tests were performed at 20℃ using a NIM2000 magnetic measuring instrument from the National Institute of Metrology of China).

[0079] (5) Take a portion of magnetic powder from both Comparative Example 1 and Example 1 after mixing, passivate it, and then test the additive coating degree (CD value, tested by time-of-flight secondary ion mass spectrometry (IONTOF TOF.SIMS 5), select CH3CO+ characteristic fragment ions, scan the entire particle surface, and evaluate the "coating degree" by the overlap between the distribution of fragment signals and the morphological contour of the particles) and the mixing uniformity (CV value, tested by high performance liquid chromatography (Agilent 1260 Infinity II HPLC, column: C18 column; mobile phase: phase A is water, phase B is methanol, gradient elution is used, starting from 5-10% phase B and holding for 2-3 minutes, linearly increasing to 95-100% phase B within 15-20 minutes, continuing to rinse the column for 3-5 minutes, and then rapidly recovering 5-10%). Phase B (within 1-2 minutes), equilibration column (5-10 minutes) to fully separate the components from polar (acetone) to non-polar (gasoline); column temperature: 38℃; flow rate: 0.9 mL / min; detector and wavelength: diode array detector (DAD), full-band spectrum of wavelength 190-400 nm) was used for testing. Multiple trace samples were extracted from the mixed powder, and their additive content was determined. The relative standard deviation (CV value) and angle of repose (θ value) of the content were calculated. The test method was based on the Hosokawa Powder Tester PT-X powder property tester, which used the injection method. The powder was allowed to flow freely through the funnel and formed a cone on the circular platform below. The height H of the cone and the diameter D of the base were measured, and the angle of repose θ = arctan(2H / D) was calculated.

[0080] The measurement or test results are shown in Table 1 below.

[0081]

[0082] Based on the above comparisons, the sintered NdFeB powder mixed using Example 1 of this invention exhibits significantly better performance than Comparative Example 1 in terms of additive coverage, mixing uniformity, and angle of repose. Furthermore, the magnetic properties of the magnet produced after sintering in Example 1 are also higher than those in Comparative Example 1, with the variance of the magnetic properties in Example 1 being significantly smaller than that in Comparative Example 1. This demonstrates that the electromagnetic mixing method of this invention can significantly improve the mixing efficiency of sintered NdFeB powder and enhance the magnetic properties of the sintered body.

[0083] Example 2 and Comparative Example 2:

[0084] In this embodiment, the inner and outer diameters of the stirring chamber 7 are 250 and 260 mm, respectively, and the height is 1200 mm; the heights of the upper electromagnetic stirrer 9 and the lower electromagnetic stirrer 10 are both 350 mm.

[0085] (1) 10 kg of industrially produced XGS30 samarium cobalt (2:17 type) magnetic powder with an average particle size of 4.3±0.3 μm was selected. 1500 ppm lubricant (dipropylene glycol butyl ether), 500 ppm dispersant (sodium diisooctyl sulfosuccinate) and 1200 ppm antioxidant (300 ppm acetone + 900 ppm No. 120 gasoline) were added to the samarium cobalt magnetic powder.

[0086] (2) The samarium cobalt (2:17 type) magnetic powder with additives was mixed for 20 minutes in a nitrogen atmosphere using a traditional three-dimensional mixing equipment (ZFF-0.7m3 type American-style three-dimensional motion mixer manufactured by Wenling Nanfang Powder Equipment Co., Ltd.). 5 kg was then taken out for subsequent electromagnetic mixing device mixing operation, and the remaining 5 kg of magnetic powder was mixed for 100 minutes using a traditional three-dimensional mixing equipment as comparative example 2.

[0087] (3) 5 kg of samarium cobalt (2:17 type) magnetic powder, after being mixed for 20 minutes using a traditional three-dimensional powder mixing device, was added to the above-mentioned exemplary electromagnetic mixing device to perform a two-stage powder mixing process. The upper electromagnetic stirrer 9 (rotating magnetic field type) was set to a frequency of 40 Hz, a central magnetic field strength of 100 Gs, and a mixing time of 40 seconds for a single batch of 5 kg; the lower electromagnetic stirrer 10 (rotating magnetic field type) was set to a frequency of 25 Hz, a central magnetic field strength of 60 Gs, and a mixing time of 20 seconds for a single batch of 5 kg; then, the powder was demagnetized by a demagnetizing sieving assembly (120 mesh vibrating screen) using a vibration mixing method (demagnetizing and sieving time of 3 minutes for a single batch of 5 kg powder) before being discharged. The mixed powder is the powder of Example 2.

[0088] (4) Take a portion of the magnetic powder from both Comparative Example 2 and Example 2 after mixing, and perform the same molding process on each (molding density 4.9 g / cm³). 3 Ten Φ20×30 cylinders were pressed, and then subjected to the same sintering, solution treatment and quenching, and annealing treatment (sintering process: sintering at 1215℃ for 2 hours; solution treatment and quenching process: holding at 1190℃ for 5 hours, followed by rapid cooling; annealing process: annealing at 830℃ for 10 hours). Finally, conventional magnetic property tests were performed (magnetic property tests were performed using a NIM2000 magnetic measuring instrument from the National Institute of Metrology of China at 20℃).

[0089] (5) Take a portion of magnetic powder from both Comparative Example 2 and Example 2 after mixing, passivate it, and then test the additive coating degree (CD value, tested by time-of-flight secondary ion mass spectrometry (IONTOF TOF.SIMS 5), select CH3CO+ characteristic fragment ions, scan the entire particle surface, and evaluate the "coating degree" by the overlap between the distribution of fragment signals and the morphological contour of the particles, and the mixing uniformity (CV value, tested by high performance liquid chromatography (Agilent 1260 Infinity II HPLC, column: C18 column; mobile phase: phase A is water, phase B is methanol, gradient elution is used, starting from 5-10% phase B and holding for 2-3 minutes, linearly increasing to 95-100% phase B within 15-20 minutes, continuing to rinse the column for 3-5 minutes, and then rapidly recovering 5-10%). Phase B (within 1-2 minutes), equilibration column (5-10 minutes) to fully separate the components from polar (acetone) to non-polar (gasoline); column temperature: 38℃; flow rate: 0.9 mL / min; detector and wavelength: diode array detector (DAD), full-band spectrum of wavelength 190-400 nm) for testing. Multiple trace samples were extracted from the mixed powder, and their additive content was determined. The relative standard deviation (CV value) and angle of repose (θ value) of the content were calculated. The test method was based on the Hosokawa Powder Tester PT-X and the injection method was used. The powder flowed freely through the funnel and formed a cone on the circular platform below. The height H of the cone and the diameter D of the base were measured, and the angle of repose θ = arctan(2H / D) was calculated.

[0090] The measurement or test results are shown in Table 2 below.

[0091]

[0092] Based on the above comparisons, the samarium cobalt (2:17 type) powder mixed in Example 2 of this invention exhibits significantly better performance than Comparative Example 2 in terms of additive coverage, mixing uniformity, and angle of repose. Furthermore, the magnetic properties of the magnets sintered in Example 2 are also higher than those in Comparative Example 2, with the variance of the magnetic properties in Example 2 being significantly smaller than that in Comparative Example 2. This demonstrates that the electromagnetic mixing method of this invention can significantly improve the mixing efficiency of samarium cobalt (2:17 type) powder and enhance the magnetic properties of the sintered body.

[0093] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims and their equivalents, this invention is also intended to include these modifications and variations. The above embodiments or implementations are merely illustrative examples of this invention, and it can also be implemented in other specific ways or forms without departing from its gist or essential characteristics. Therefore, the described embodiments should be considered illustrative rather than limiting in any respect. The scope of this invention should be defined by the appended claims, and any changes equivalent to the intent and scope of the claims should also be included within the scope of this invention.

Claims

1. An electromagnetic mixing device, characterized in that: The electromagnetic mixing device described herein is used for electromagnetic mixing of magnetic material powders. From top to bottom, it includes a feeding assembly, an electromagnetic mixing assembly, and a demagnetizing sieving assembly connected in sequence. The feeding assembly includes an upper and lower connected feeding port and a feeding pipe. The electromagnetic mixing assembly includes a mixing chamber and an electromagnetic stirrer. The demagnetizing sieving assembly includes a vibrating screen, a coarse particle outlet, a discharge port, and a vibrating motor. In the mixing chamber, magnetic material powder is fed from the feed inlet and the feed pipe, and electromagnetic mixing is carried out under the stirring of the electromagnetic stirrer. The electromagnetic stirrer is an electromagnetic stirrer for continuous casting steel. The magnetic field generated by the electromagnetic stirrer magnetizes the magnetic material powder particles, and then generates a magnetic field force between the magnetic material powder particles and the magnetized magnetic material powder particles, causing the powder to move under force. The vibrating screen vibrates under the drive of the vibrating motor, and is used to demagnetize the magnetic material powder after electromagnetic mixing and to screen the particles of different sizes. The coarse particle outlet is used to discharge the coarse particles obtained by the demagnetization screening of the vibrating screen. The discharge port is used for discharging the fine particles obtained by the demagnetization screening of the vibrating screen.

2. The electromagnetic mixing device according to claim 1, characterized in that: The feeding assembly also includes a valve, which is disposed on the feeding pipe and is used to control the magnetic material powder from the feeding port to enter the mixing chamber.

3. The electromagnetic mixing device according to claim 2, characterized in that: The valve, from top to bottom, includes an inflation valve, an upper flap valve, and a lower flap valve.

4. The electromagnetic mixing device according to claim 1, characterized in that: The feeding assembly also includes a pneumatic vibrator installed on the feeding pipe, used to apply vibration to the magnetic material powder feeding, thereby accelerating the magnetic material powder into the mixing chamber.

5. The electromagnetic mixing device according to claim 1, characterized in that: The electromagnetic stirrer is divided into two groups, namely the upper electromagnetic stirrer and the lower electromagnetic stirrer.

6. The electromagnetic mixing device according to claim 1, characterized in that: The electromagnetic mixing assembly also includes a distributor, which is disposed in the mixing chamber above the electromagnetic stirrer, for distributing the magnetic material powder feed.

7. The electromagnetic mixing device according to claim 1, characterized in that: The electromagnetic mixing device further includes a first rubber sleeve and / or a second rubber sleeve. The first rubber sleeve is used to wrap and connect the feed pipe and the mixing chamber; The second rubber sleeve is used to wrap and connect the mixing chamber and the vibrating screen.

8. A method for mixing magnetic material powder using the electromagnetic mixing apparatus according to any one of claims 1-7, characterized in that, The method includes the following steps: (1) Magnetic material powder enters the mixing chamber from the feed inlet for electromagnetic mixing; (2) The magnetic material powder after electromagnetic mixing is demagnetized and sieved by the vibrating screen, and the coarse particles and fine particles obtained by demagnetization and sieving are collected respectively.

9. The method according to claim 8, characterized in that: In step (2), The vibrating screen has a mesh size of 40-120; and / or The demagnetizing and screening time of the vibrating screen is 1-5 minutes; and / or The demagnetizing method of the vibrating screen is selected from one or more of vibration mixing, airflow impact, and heating-cooling.

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