A preparation method of a high-performance cylindrical magnet

Abstract

The present invention discloses a preparation method of a high-performance cylindrical magnet, which relates to the technical field of sintered NdFeB magnetic materials. In order to solve the problem that it is difficult to control the uniformity of heavy rare earths during the preparation of cylindrical or circular ring magnets; the present invention includes rough machining a NdFeB blank into a cylindrical blank of required size; preparing a viscous heavy rare earth solution, in which a thickener of 10-40% of the mass of the solvent is added; soaking the blank in the solution for a period of time and then taking it out for drying to obtain an intermediate with excessive coating; grinding the intermediate with a centerless grinder to a certain size and then transferring it to a sintering furnace for heat treatment; after the heat treatment is completed, it is put into the centerless grinder again for grinding until it is completely exposed; through the excessive coating of the viscous heavy rare earth solution and the centerless grinding before heat treatment, the steps of the present invention are simple and easy to operate, without new equipment or raw materials, and can make the heavy rare earths evenly coated on the surface of the cylindrical or circular ring magnets, which can greatly save the material cost, and the magnetic properties of the products in the same batch are more stable and consistent.

Description

Technical Field

[0001] The present invention relates to the technical field of sintered neodymium iron boron magnetic materials, and particularly to a preparation method of high-performance cylindrical magnets. Background Art

[0002] Rare earth permanent magnet sintered neodymium iron boron is widely used in industrial production, daily life, etc., and the performance requirements for neodymium iron boron in various industries are also getting higher and higher. With the introduction of the grain boundary diffusion technology, the consumption of heavy rare earths in neodymium iron boron has been greatly reduced. However, for cylindrical or annular products, the difficulty of grain boundary diffusion is much greater than that of block products. One is the control of the coating amount, and the other is the subsequent processing after diffusion.

[0003] At present, the vast majority of manufacturers still adopt the traditional soaking and air-drying method in the production of grain boundary diffusion of neodymium iron boron cylinders or rings. For example, in the invention patent application with the publication number CN104681225A and the name of a processing method for improving the performance of sintered neodymium iron boron materials, it discloses that the neodymium iron boron blank is soaked in a solvent, taken out and drained, and the magnet is air-dried with hot air or dried in a drying oven, and then heat treatment and other operations are carried out. However, when this conventional method is used for the preparation of cylindrical or annular magnets, it is difficult to control the uniformity of heavy rare earths, making it difficult to reduce the production cost of diffusion. Moreover, the appearance of the cylindrical or annular magnet after grain boundary diffusion is poor, and often a large grinding amount is required. Generally, grinding 0.15 mm is required to make the outer circle completely exposed, resulting in a lot of waste. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of high-performance cylindrical magnets to solve the problem that it is difficult to control the uniformity of heavy rare earths during the preparation of cylindrical or annular magnets.

[0005] To achieve the above purpose, the present invention provides the following technical solution: A preparation method of high-performance cylindrical magnets, including the following specific steps:

[0006] S1 Rough-process the neodymium iron boron blank into a cylindrical blank of the required size;

[0007] S2 Prepare a viscous heavy rare earth solution, in which a thickener accounting for 10-40% of the mass of the solvent is added;

[0008] S3 Immerse the blank in the solution for a period of time and then take it out and dry it to obtain an intermediate with excessive coating;

[0009] S4 Grind the intermediate to a certain size with a centerless grinder and then transfer it to a sintering furnace for heat treatment;

[0010] S5 After the heat treatment is completed, put it into a centerless grinder again and grind it until it is completely exposed.

[0011] Preferably, the solvent of the heavy rare earth solution is alcohol.

[0012] Preferably, the mass of the thickener is 15-30% of the solvent.

[0013] Preferably, in step S3, the drying is by hot air blowing or drying in an oven.

[0014] Preferably, in step S4, the Tb weight gain after grinding is 0.3-1.5%.

[0015] Preferably, in step S4, the diameter after grinding is 1-3% more than the outer diameter of the blank processed in step S1.

[0016] Preferably, in step S3, the soaking time is 1-3 min.

[0017] Preferably, in the viscous heavy rare earth solution, the mass of Tb in the solute accounts for 95%

[0018] Preferably, in step S4, the ground heavy rare earth dry powder is recovered and used to re-form a viscous heavy rare earth solution.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] The preparation method of the high-performance cylindrical magnet, on the basis of the traditional heavy rare earth soaking and drying method, changes the state of the soaking solution, changing the original low-viscosity and relatively dilute state to a high-viscosity viscous state. After sufficient soaking, it is taken out and dried. After the resin is cured, the surface heavy rare earth coating amount far exceeds the required coating amount. Then, a part of the outer layer of heavy rare earth is ground off by a centerless grinder. The ground heavy rare earth dry powder can be reused to form a solution. The grinding amount and the remaining heavy rare earth film thickness can be controlled by the spacing of the centerless grinding wheel. The steps are simple and easy to operate, without new equipment or raw materials. Almost equal amounts of heavy rare earth can be attached to each blank prepared by this method. And due to centerless grinding, the heavy rare earth on the outer circle is evenly distributed. After diffusion tempering, the appearance is good. It only needs to grind off 0.03-0.05 mm to make the outer circle completely visible. Therefore, compared with the original process that needs to grind off about 0.15 mm, after adopting the method of the present invention, when making products of the same size, the blank size can be reduced on the original process, greatly saving the material cost; in addition, due to the uniform coating, the magnetic properties of the products of the same batch made by the method of the present invention are more stable and consistent. Description of the Drawings

[0021] Figure 1 It is a schematic diagram of centerless grinding for the intermediate. Detailed Embodiments

[0022] By studying the processes before and after the production of cylindrical or toroidal magnets through grain boundary diffusion, it is found that after the heavy rare earth coating, there is a large difference in the weight gain of the billets. Through theoretical analysis and speculation, it is considered that the main factors affecting the amount of heavy rare earth coating on the magnets may be the inconsistent state of the heavy rare earth solution before and after drying, resulting in unstable weight gain. During the preparation process, the distribution of heavy rare earth on the surface of the billet is mainly affected by gravity, resulting in uneven distribution. Finally, after diffusion, the surface appearance is poor, leading to an increase in the amount of external cylindrical grinding. Based on these theoretical assumptions, the researchers developed various potentially effective solutions, and through a large number of experimental practices, as well as scheme modification and optimization, the following optimal method was obtained:

[0023] A method for preparing a high-performance cylindrical magnet, comprising the following specific steps:

[0024] S1 Rough-machine the neodymium-iron-boron blank into a cylindrical billet of the required size;

[0025] S2 Prepare a viscous heavy rare earth solution, in which a thickener accounting for 10-40% of the mass of the solvent is added. More preferably, the mass of the thickener is 15-30% of the solvent. The solvent of the heavy rare earth solution is preferably alcohol, and the thickener can be phenolic resin or other common thickeners in the art. In addition, more preferably, the mass of Tb in the solute of the viscous heavy rare earth solution accounts for 95%;

[0026] S3 Immerse the billet in the solution for a period of time (such as 1-3 min), then take it out and dry it with hot air or in a drying oven to obtain an intermediate with excessive coating;

[0027] S4 Grind the intermediate with a centerless grinder to a certain size, and then transfer it to a sintering furnace for heat treatment. Considering both cost and product performance, the weight gain of Tb after grinding should be controlled within 0.3-1.5%. For reference, the diameter after grinding can be 1-3% more than the outer diameter of the billet processed in step S1. The heavy rare earth dry powder ground off can be recycled and used to re-prepare a viscous heavy rare earth solution;

[0028] S5 After the heat treatment is completed, put it back into the centerless grinder and grind it until it is completely exposed.

[0029] The toroidal product can generally be obtained by further processing the cylindrical product obtained in S5. Theoretically, it can also be prepared according to the above method, only the blank in step S1 needs to be rough-machined into a ring.

[0030] The following are the preferred embodiments of the conventional method and the method of the present invention:

[0031] Comparative example:

[0032] Select neodymium iron boron blanks of grade 48H, and cut and slice them by wire cutting and then grind them into cylindrical products with dimensions of D10mm×20mm by centerless grinding. Number the cylindrical products as A00 - A05, weigh and measure their dimensions respectively and record them. Then soak A01 - A05 in an alcohol solution containing heavy rare earth Tb (containing 3% of mixed resin by mass of alcohol, and Tb accounts for 95% of the solute). After soaking for a period of time, take them out and dry them with a hair dryer. Weigh and measure their dimensions again, and then place them neatly in a material box. Use a tube-type vacuum sintering furnace for diffusion treatment at 900°C for 10h, and adopt a tempering system of 500°C for 4h for the second tempering. After the heat treatment, observe and record their appearance, then put them into a centerless grinder and grind until they are completely polished, record their dimensions, and finally test their magnetic properties. Summarize the above data in Table 1 to obtain:

[0033] Table 1: Process and test results of the comparative example

[0034]

[0035] Example 1:

[0036] Select neodymium iron boron blanks of grade 48H, and cut and slice them by wire cutting and then grind them into cylindrical products with dimensions of D10mm×20mm by centerless grinding. Number the cylindrical products as B00 - B05, weigh and measure their dimensions respectively and record them. Then soak B01 - B05 in an alcohol solution containing heavy rare earth Tb (containing 15% of mixed resin, and Tb accounts for 95% of the solute). After soaking for a period of time, take them out and dry them with a hair dryer. Weigh and measure their dimensions again, and then place them in a special centerless grinder for grinding (as Figure 1 ) and control the dimension after grinding to be about 10.30mm. After grinding, weigh and measure their dimensions again, and then place them neatly in a material box. Use a tube-type vacuum sintering furnace for diffusion treatment at 900°C for 10h, and adopt a tempering system of 500°C for 4h for the second tempering. After the heat treatment, observe and record their appearance, then put them into a centerless grinder and grind until they are completely polished, record their dimensions, and finally test their magnetic properties. Summarize the above data in Table 2 to obtain:

[0037] Table 2: Process and test results of Example 1

[0038]

[0039] Example 2:

[0040] Select neodymium iron boron blanks of grade 48H, and cut and slice them by wire cutting and then grind them into cylindrical products with dimensions of D10mm×20mm by centerless grinding. Number the cylindrical products as C00 - C05, weigh and measure their dimensions respectively and record them. Then soak C01 - C05 in an alcohol solution containing heavy rare earth Tb (containing 30% of mixed resin, and Tb accounts for 95% of the solute). After soaking for a period of time, take them out and dry them with a hair dryer. Weigh and measure their dimensions again, and then place them in a special centerless grinder for grinding (as Figure 1) Control the size after grinding to be around 10.30 mm. After grinding, weigh and measure the size again, then place them neatly in the material box. Use a tube-type vacuum sintering furnace for diffusion treatment at 900 °C for 10 h. The second tempering adopts a system of 500 °C for 4 h. After the heat treatment, observe and record its appearance, then put it into a centerless grinder and grind until it is completely shiny, record its size, and finally test its magnetic properties. Summarize the above data in Table 3 to obtain:

[0041] Table 3: Process and test results of Example 2

[0042]

[0043] Example 3:

[0044] Select NdFeB blanks of 48H grade, and use wire cutting and slicing centerless grinding to form cylindrical products with dimensions of D10 mm × 20 mm. Number the cylindrical products D00 - D06, weigh and measure their sizes respectively and record them. Then soak D01 - D06 in an alcohol solution containing heavy rare earth Tb (containing 15% of mixed resin, and Tb accounts for 95% of the solute). After soaking for a period of time, take them out and dry them with a hair dryer. Weigh and measure the size again, and then place them in a special centerless grinder for grinding (as Figure 1 ) Control the size after grinding of D01 - D03 to be around 10.30 mm, and control the size after grinding of D04 - D06 to be around 10.33 mm. After grinding, weigh and measure the size again, then place them neatly in the material box. Use a tube-type vacuum sintering furnace for diffusion treatment at 900 °C for 10 h. The second tempering adopts a system of 500 °C for 4 h. After the heat treatment, observe and record its appearance, then put it into a centerless grinder and grind until it is completely shiny, record its size, and finally test its magnetic properties. Summarize the above data in Table 4 to obtain:

[0045] Table 4: Process and test results of Example 3

[0046]

[0047]

[0048] It can be seen from the data of the comparative example and the examples that by controlling the proportion of the thickener in the heavy rare earth alcohol mixed solution, the weight of the heavy rare earth film after drying can be changed. By adjusting the centerless grinding spacing, the thickness of the heavy rare earth film can be controlled, and the weight gain of cylindrical or ring products can be conveniently adjusted and controlled. Through the method of the present invention, it can effectively ensure uniform coating of heavy rare earth, the product performance has good uniformity, and the appearance is good after diffusion and tempering. Compared with the original process, the grinding amount can be reduced. Only 0.03 - 0.05 mm needs to be ground off when the outer circle is ground until it is completely shiny (see the sizes after seeing light in the comparative example and the examples), which can be used to reduce the amount of blank material used.

[0049] The above are only the preferred embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope defined by the claims.

[0050] Matters not described in detail in the present invention are all well-known technologies to those skilled in the art.

Claims

1. A method for preparing a high-performance cylindrical magnet, characterized in that, It includes the following specific steps: S1 Rough-machine the neodymium iron boron blank into a cylindrical blank with the required size; S2 Prepare a viscous heavy rare earth solution, in which a thickening agent accounting for 10-40% of the mass of the solvent is added; S3 Immerse the blank in the solution for 1-3 minutes and then take it out for drying to obtain an over-coated intermediate; S4 Grind the intermediate with centerless grinding until the diameter is 1-3% more than the outer diameter of the blank processed in step S1, and transfer it to a sintering furnace for heat treatment; S5 After the heat treatment is completed, put it into centerless grinding again and grind until it is completely polished.

2. The preparation method of a high-performance cylindrical magnet according to claim 1, characterized in that: The solvent of the heavy rare earth solution is alcohol.

3. The preparation method of a high-performance cylindrical magnet according to claim 1, characterized in that: The mass of the thickening agent is 15-30% of the solvent.

4. The preparation method of a high-performance cylindrical magnet according to claim 1, characterized in that: In step S3, the drying is carried out by hot air blowing or drying in an oven.

5. The preparation method of a high-performance cylindrical magnet according to claim 1, characterized in that: In step S4, the Tb weight gain is 0.3-1.5% after grinding.

6. The preparation method of a high-performance cylindrical magnet according to claim 1, characterized in that: In the viscous heavy rare earth solution, the mass of Tb in the solute accounts for 95%.

7. The preparation method of a high-performance cylindrical magnet according to claim 1, characterized in that: In step S4, the recovered heavy rare earth dry powder ground off is used to re-prepare a viscous heavy rare earth solution.

Images