CN113963932A - Preparation method of small-size R-T-B rare earth permanent magnet - Google Patents
Preparation method of small-size R-T-B rare earth permanent magnet Download PDFInfo
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
- H01F41/0293—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets diffusion of rare earth elements, e.g. Tb, Dy or Ho, into permanent magnets
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Manufacturing Cores, Coils, And Magnets (AREA)
- Hard Magnetic Materials (AREA)
Abstract
The invention discloses a preparation method of a small-size R-T-B rare earth permanent magnet, relates to the technical field of magnetic materials, and aims to solve the problem that a small-size product is difficult to produce in a large scale by a grain boundary diffusion process; the invention includes R-T-B system sintered magnet after surface activation treatment with any shape and any size, the sintered magnet is put into a roller-shaped rotating device, rotary surface attached slurry is attached while rotating, the attachment mode is spraying to the rotating sintered magnet, or the lower part of the rotating device where the sintered magnet is stacked is soaked in the slurry to dip the slurry into the sintered magnet; the invention realizes the batch production of conventional and special-shaped products with smaller specifications, has high production efficiency and good product performance consistency, greatly reduces the use amount of heavy rare earth for the products, greatly improves the coercive force of the permanent magnet after heat treatment, and has good thermal demagnetization performance and good product appearance.
Description
Technical Field
The invention relates to the technical field of magnetic materials, in particular to a preparation method of a small-size R-T-B rare earth permanent magnet.
Background
The R-T-B series rare earth permanent magnet material is an important basic functional material for supporting the modern society, has ultrahigh energy density and better high-temperature service performance, can efficiently realize the interconversion between energy and information, and is widely applied to a plurality of fields such as transportation, medical treatment, computers, household appliances, energy sources, aerospace and the like due to the excellent magnetic performance, goes deep into the aspects of national economy and is closely related to the life of people.
The R-T-B rare earth permanent magnetic material mainly consists of Nd2Fe14The coercive force machine is made of a reverse magnetization domain nucleation theory and a grain boundary demagnetization coupling exchange mechanism, which determine the important influence of a main phase grain anisotropy field and a grain boundary phase microstructure on the coercive force. In general, the method for improving the coercive force mainly comprises the steps of refining grains and optimizing a grain boundary phase structure, or adding Tb, Dy, Ho and other elements with higher anisotropic fields in the smelting process, but Dy, Tb, Ho and Fe are in antiferromagnetic coupling, so that the saturation magnetization and remanence of the magnet are greatly reduced, and meanwhile, heavy rare earth elements enter a main phase, so that the expensive heavy rare earth resources are greatly wasted, the ultrahigh-performance magnet cannot be produced, and the product cost is remarkably increased. The grain boundary diffusion technology attaches a simple substance, an alloy or a compound which takes heavy rare earth elements as main components to the surface of the magnet, the heavy rare earth elements are diffused into the magnet in a mode of taking crystal edge as main components and crystal penetration as auxiliary components through heat treatment, a shell layer with a high anisotropy field is formed on the surface of a main phase crystal grain, and the effect of greatly improving the coercive force of the magnet by using a small amount of heavy rare earth is achieved.
At present, the types of grain boundary diffusion process methods are various, and spraying, physical vapor deposition, silk-screen printing, dipping and the like are mainly used in mass production in enterprises. The conventional spraying, physical vapor deposition, silk-screen printing and dipping methods are difficult to carry out elemental substance and composite alloy film diffusion on the magnet with smaller size, and the problems of low production efficiency, poor product consistency and low performance exist in the actual production process.
In patent CN102473515A mentions putting into the frock with heavy rare earth metal or alloy diffusion source and tombarthite permanent magnet, make it carry out heat treatment under the state that can relative movement and fully be close or direct contact, greatly reduced the coating by vaporization temperature, improved the diffusion source utilization ratio, improved magnet performance uniformity. However, the target material and the rare earth permanent magnet are easy to adhere in a contact state, and because the vapor pressure of each element of the alloy is inconsistent, the components of the alloy are continuously segregated in the continuous evaporation process of the alloy diffusion source, so that the components of the diffusion source are continuously changed, the service life of the diffusion source is greatly reduced, and the production consistency of the rare earth permanent magnet is uncontrollable.
The diffusion process usually needs alloy elements, and the low-melting-point alloy diffusion source enters a grain boundary phase in the heat treatment process to reduce the melting point of the rare earth-rich liquid phase, so that the rare earth elements can be diffused quickly, the rare earth elements can be diffused to a position deeper than the surface, the diffusion efficiency of the rare earth elements is improved, and the consumption of the diffused rare earth elements is greatly reduced.
In patent CN101331566B, the diffusion source is dispersed after being gasified in a mode that the diffusion source and the rare earth permanent magnet are separated and are relatively static, the utilization rate of the diffusion source is very low, the consistency of a deposited film layer of the rare earth permanent magnet is poor, and marks exist between the rare earth permanent magnet and an isolation net, so that the product quality is seriously influenced.
It is worth to be noted that since the PVD evaporation process concept was first proposed by the independent administrative law scientific and technological joy organization in 6 months and 6 months in 2004, from 3 months in 2006, a great deal of evaporation processes for products with smaller specifications were continuously applied by the japanese metal and department of love, and a great deal of research and development work was also performed on the evaporation processes by institutes of public health, research institutes and neodymium iron boron enterprises in domestic and foreign countries.
At present, the technological lines of the mass production of products with larger specifications, such as magnetron sputtering, multi-arc ion plating, spraying, silk-screen printing and the like which are well known in the neodymium iron boron industry, are very mature, but aiming at the problems that the conventional grain boundary diffusion processes such as magnetron sputtering, multi-arc ion plating, spraying and the like of magnets with smaller specifications can not realize mass production well, the swing and turnover are difficult, the production efficiency is very low, the labor cost is very high, the operation is very inconvenient, and the quality of products is high, therefore, part of the neodymium iron boron enterprises propose a method of adopting grain boundary diffusion of a larger magnet, which needs to diffuse more heavy rare earth, and after diffusion, small pieces and wafers need to be cut and processed, so that the processing cost is increased, heavy rare earth waste is caused, the machining damage effect of small piece products is prominent, thick products need to be diffused, a large performance gradient exists in the diffusion direction, and the use of the products is influenced to a certain extent. Enterprises try to carry out impregnation diffusion treatment on products with smaller sizes in an impregnation mode, the product prepared by the process is poor in performance consistency, low in performance improvement amplitude and low in automation degree, and a plurality of problems exist in production.
In addition, the products with special shapes such as cylinders, complex tiles, rings and the like and special orientations such as radial and multipolar products have the defects that the orientation direction is not easy to find due to the fact that the diffusion surface is not plane, the surface magnetic requirements usually exist, and the products with special requirements cannot be produced by the conventional grain boundary diffusion process. The products with smaller sizes are usually added in a heavy rare earth element adding mode in a smelting process, most heavy rare earth elements enter main phase crystal grains, and the utilization rate of the heavy rare earth elements is low. In the process of processing the sintered blank into a product with a smaller specification, the outturn rate is extremely low and is usually less than 40%, most of blanks rich in heavy rare earth elements are processed into a stub bar and magnetic mud, and great waste of the heavy rare earth elements is caused.
Therefore, a method for preparing a small-sized R-T-B rare earth permanent magnet is needed to solve the problem.
Disclosure of Invention
The invention aims to provide a preparation method of a small-size R-T-B rare earth permanent magnet, which aims to solve the problem that the grain boundary diffusion process of a small-size product is difficult to produce in a large scale.
In order to achieve the purpose, the invention provides the following technical scheme: a process for preparing small-size R-T-B rare-earth permanent magnet includes such steps as activating the surface of R-T-B sintered magnet, putting it in a drum-type rotary unit, and rotary surface adhering slurry while rotating.
In a preferred embodiment, the rotating device is a cylindrical rotating cage, the surface of the rotating cage is net-shaped, the center line of the rotating device is horizontal, and the rotating device rotates in one direction by taking the center line as a rotating shaft.
Optionally in the scheme, one spray gun or a plurality of spray guns which are distributed along the central line at equal intervals are fixedly arranged at the central line inside the rotating device; the rotating device is provided with a pumping and air-supplying system for preheating and air-drying the sintered magnet.
In this alternative, preferably, when the rotating device rotates, the central angle corresponding to the arc surface range occupied by the sintered magnet inside the rotating device is β 1, the actual injection angle of the spray gun is β 2, β 1 is 2 β 2, and the injection range of the spray gun includes the tail end of the sintered magnet in the rotating direction.
Optionally in the above scheme, the rotating device is installed in the solution tank, and the solution tank is provided with a material inlet and a material outlet for supplying and discharging the slurry and adjusting the height of the slurry in the solution tank; the solution tank is also provided with a pumping and air-supplying system for preheating and air-drying the sintered magnet; the bottom of the solution tank is also provided with an ultrasonic system to ensure that the solution tank is uniformly and compactly attached.
In this alternative, the central angle corresponding to the portion of the rotating device immersed in the slurry is θ 1, the central angle corresponding to the arc surface range occupied by the sintered magnet inside the rotating device when the rotating device rotates is θ 2, and the front ends of the arcs corresponding to the two central angles coincide or are close to each other in the rotating direction.
Preferably, in any of the above embodiments, the sintered magnet is placed in the rotating device at the same time as placing a suitable amount of auxiliary balls, including but not limited to zirconia balls.
In any of the above embodiments, preferably, the sintered magnet is first machined to a size close to that of the finished product and subjected to chamfering treatment while reserving a proper amount of positive tolerance before being placed in the rotating device.
In any of the above schemes, preferably, the sintered magnet is in a block shape, a cylinder shape, a tile shape, a ring shape, a sheet shape or an irregular shape, and the volume of the sintered magnet is less than 15cm3。
Preferably, in any of the above embodiments, the slurry includes at least one of rare earth metal powder, rare earth fluoride, rare earth oxide, rare earth hydride, or an alloy of a rare earth element and another element;
in any of the above embodiments, preferably, the sintered magnet is an R-Fe-B-M sintered magnet, wherein R is one or more rare earth elements selected from La, Ce, Pr, Nd, Dy, Tb, Gd, Ho, and the total amount of which is 26.5 wt% to 34 wt%, M is one or more metal elements selected from Ga, Al, Cu, Co, Ti, Zr, Nb, and W, and the total amount of which is 0 to 6 wt%, the total amount of B is 0.55 wt% to 1.5 wt%, and the remaining elements are Fe;
preferably, in any of the above embodiments, the surface activation treatment comprises degreasing, cleaning, pickling, and blasting;
in any of the above schemes, preferably, after the slurry is attached to the rotary surface, the sintered magnet is subjected to heat treatment in a vacuum sintering furnace to diffuse the rare earth elements in the slurry into the sintered magnet, the heat treatment comprises two stages, the temperature range of the first stage heat treatment is 750-960 ℃, the heat treatment time is 2-72 h, the temperature range of the second stage heat treatment is 430-580 ℃, the heat treatment time is 2-8 h, and the vacuum degree of the sintering furnace is controlled to be 10-1-10-4Pa。
Compared with the prior art, the invention has the beneficial effects that:
1. the preparation method of the small-size R-T-B rare earth permanent magnet solves the problem that the conventional process can not adopt low cost to directly carry out mass production on products with smaller specifications by diffusion, and solves the problem that the conventional process of special-shaped products can not carry out diffusion.
2. According to the preparation method of the small-size R-T-B rare earth permanent magnet, the special design of a rotary wet dipping/dry spraying process is adopted, the batch production of small-specification conventional and special-shaped products is realized, the production efficiency is high, the product performance consistency is good, meanwhile, the efficient utilization of ultralow loss of raw materials is ensured, the heavy rare earth consumption is greatly reduced, the coercive force of the permanent magnet is greatly improved after heat treatment, the thermal demagnetization performance is good, and the product appearance is good.
Drawings
FIG. 1 is a side view of one embodiment of a rotational surface attachment of the present invention;
FIG. 2 is a schematic view of one embodiment of the preheating mode of dry spraying according to the present invention, wherein Q1 and Q2 indicate two sides of a central angle β 1 of a range in which a product is located during rotation;
FIG. 3 is a schematic view of one embodiment of the spray coating step of the embodiment of FIG. 2, where β 2 is the actual spray gun launch angle;
FIG. 4 is a schematic perspective view of the embodiment shown in FIG. 3, with the product omitted;
FIG. 5 is a schematic view of an embodiment of air drying before wet impregnation according to the present invention;
fig. 6 is a schematic view of an embodiment of wet impregnation according to the present invention, in which N1 and N2 indicate both sides of a central angle θ 2 of a range in which a product is located during rotation, and M1 and M2 indicate both sides of a central angle θ 1 corresponding to a portion in a liquid.
Detailed Description
A method for preparing small-size R-T-B rare earth permanent magnet comprises the steps of carrying out surface activation treatment on R-T-B system sintered magnet with any shape and any size, wherein the sintered magnet is R-Fe-B-M sintered magnet, is prepared by a conventional known method and can be directly purchased from the market, in an optional embodiment, R is selected from one or more of La, Ce, Pr, Nd, Dy, Tb, Gd and Ho rare earth elements, the total amount of the rare earth elements is 26.5-34 wt%, M is selected from Ga, Al, Cu, Co, Ti, Zr and Nb,one or more of W metal elements, the total amount of which is 0-6 wt%, B is 0.55-1.5 wt%, and the rest elements are Fe, and the surface activation treatment comprises oil removal, cleaning, acid cleaning, sand blasting and the like; the sintered magnet which can be processed by the method comprises a block-shaped magnet, a cylindrical magnet, a tile-shaped magnet, a ring-shaped magnet, a sheet-shaped magnet or an irregular magnet, and the like, especially a magnet with a smaller specification or an irregular shape, such as a cuboid with the length, width and thickness of the applicable specification of less than 30, 30 and 15mm or a cylindrical magnet with the diameter of less than 30mm and the thickness of less than 15mm or a hollow ring with the smaller specification of less than tile-shaped magnet; the further typical applicable specification is a cuboid with the dimensions of the length, the width and the thickness of less than 15, 15 and 5mm respectively or a cylindrical magnet with the diameter of less than 15mm and the thickness of less than 5mm or a hollow ring with smaller specification, a tile-shaped magnet and other special-shaped magnets; furthermore, the magnet is more advantageous for special-shaped magnets with the specifications of length, width and thickness of less than 12, 12 and 1.0mm cuboids or with the diameters of less than 12mm and less than 3mm specifications of cylindrical magnets or hollow rings, tile shapes, radial orientation, non-conventional orientation and the like, and the volume of the preferred sintered magnet is less than 15cm3；
In the adhering step, the sintered magnet is placed in a roller-shaped rotating device, and the rotary surface adhered with slurry is rotated while adhering, wherein the adhering mode is that the sintered magnet is sprayed on the rotating sintered magnet, or the lower part of the rotating device where the sintered magnet is stacked is soaked in the slurry to ensure that the slurry is soaked in the sintered magnet; the slurry comprises at least one of rare earth metal powder, rare earth fluoride, rare earth oxide, rare earth hydride or rare earth element and other element alloy, wherein the rare earth comprises elements such as Dy, Tb, Ho, Pr, Nd and the like, the rare earth element and other element alloy comprises elements such as Al, Ga, Cu, Zr, Nb, Ti, Ni and the like besides the rare earth elements, preferably rare earth alloy or compound, and substances such as alcohols, surface modifiers and the like can be added into the slurry;
after the rotary surface is adhered with the slurry, the sintered magnet is subjected to heat treatment in a vacuum sintering furnace to ensure that the rare earth elements in the slurry are diffused into the sintered magnet, the heat treatment comprises two stages, the temperature range of the first-stage heat treatment is 750-960 ℃, the time of the first-stage heat treatment is 2-72 h, and the second-stage heat treatment comprises two stagesThe heat treatment temperature range is 430-580 ℃, the heat treatment time is 2-8 h, and the vacuum degree of a sintering furnace is controlled to be 10-1-10-4Pa。
The rotating means are preferably cylindrical cages, see fig. 1 to 6, and preferably have a reticular surface, to ensure a substantially uniform contact between the product and the slurry; in a preferred embodiment, the central line of the rotating device is kept horizontal, and the rotating device keeps rotating in one direction by taking the central line as a rotating shaft; for example, circular plates are fixedly arranged on two sides of the rotating device, and a rotating shaft is fixed in the middle of one side plate and is driven by a motor.
The invention has two embodiments, dry method and wet method, when adopting the dry method process, can adopt the following structure, refer to fig. 2 to 4, the centre line of the inside of the rotating device is fixedly equipped with a spray gun or a plurality of spray guns distributed equidistantly along the centre line; further, when the rotating device rotates, the central angle corresponding to the arc surface range occupied by the sintered magnet in the rotating device is beta 1, the actual injection angle of the spray gun is beta 2, beta 1 is 2 beta 2, and the injection range of the spray gun comprises the tail end of the sintered magnet along the rotating direction, so that the one-time effective receiving rate is improved as much as possible; in addition, the rotating device is provided with an air pumping and supplying system for preheating and air-drying the sintered magnet, the specific position can be determined according to the actual use requirement, the arrow directions of heating and air pumping in the reference figures 2 and 3 can be shown, namely the arrow directions are mainly towards the sintered magnet, and the air supplying system can be used for supplying a proper amount of hot air so as to ensure the temperature and humidity of the spraying chamber; the product can be preheated and air-dried before or after spraying, and can also be subjected to single or multiple cyclic operations of preheating-spraying-preheating-spraying according to performance requirements or process requirements for different film thicknesses of the product, so that the spraying uniformity of the product and the spraying effect of a thicker film layer are fully ensured.
When the wet process is adopted, the following structure can be adopted, referring to fig. 5 to 6, wherein the rotating device is arranged in the solution tank, and the solution tank is provided with a material inlet and a material outlet for supplying and discharging the slurry and adjusting the height of the slurry in the solution tank; the solution tank is also provided with a pumping and air-supplying system for preheating and air-drying the sintered magnet, specifically, the pumping and air-supplying system can be positioned above the solution tank, the rotating device can be moved to the position of the pumping and air-supplying system from the solution tank when preheating and air-drying are needed, the product can be subjected to preheating and air-drying treatment before or after impregnation, and single or multiple cyclic operations of impregnation, hot air-drying, impregnation and hot air-drying can be carried out according to the process requirements of different film thicknesses of the product according to the performance requirements, so that the impregnation uniformity of the product and the impregnation effect of a thicker film layer can be fully ensured; as shown in fig. 6, the bottom of the solution tank may be further provided with an ultrasonic system to ensure uniform and dense adhesion of the powder on the product; further, the central angle of the portion of the rotating device immersed in the slurry is θ 1, the central angle of the arc surface occupied by the sintered magnet inside the rotating device when the rotating device rotates is θ 2, and the front end positions of the arcs corresponding to the two central angles in the rotating direction, i.e., M1 and N1 in fig. 6, should be as close as possible.
In order to reduce the proportion of the product colliding with the unfilled corner, the sintered magnet is placed into the rotating device, and simultaneously, a proper amount of auxiliary spheres are placed into the rotating device, so that the appearance quality of the product is improved, and the auxiliary spheres include but are not limited to zirconia balls.
In addition, before the sintered magnet is placed into the rotating device, under the condition of reserving a proper amount of positive tolerance, the sintered magnet can be firstly processed to be close to the size of a finished product, and more preferably, chamfering treatment can be carried out.
Example 1:
R-Fe-B-M sintered magnets were prepared by methods well known to those skilled in the art and tested in the examples below using an N52 matrix, where R includes Pr and Nd in a total amount of 30.5 wt%, M includes Al, Cu, Ga, Co, Zr, Nb, Ti in a total amount of 2.1 wt%, B in a total amount of 0.96 wt%, and the remainder is Fe, and matrix properties are Br 14.44-14.51KGs and Hcj 13.0-13.6 KOe.
The formula is adopted to prepare the N52 matrix, the specification of a product to be diffused is 8.3x5.1x1.12mm, a dry spraying process is adopted, and the spraying powder is Tb alloy. 42Kg of product is weighed and poured into a rotary drum, 3.5Kg of zirconia balls with the diameter of 3mm are added, the product collision is inhibited, the separation degree of the product in the rotary process is increased, and the film deposition effect is improved. And carrying out rotary preheating treatment on the magnet in the roller, wherein the preheating temperature is 120 ℃, the rotating speed of the roller is 3r/min, and the preheating time is 7-15 min. After preheating, spraying treatment is carried out, the spraying rotation speed is 3r/min, and the spraying time is 18-25 min. And after the spraying is finished, moving the roller to a heating and air-drying station, carrying out air-drying at the temperature of 120 ℃, and spraying air for 5-10min while rotating until the volatile solvent substrate on the surface of the product volatilizes. And weighing the weight of the product with the film layer, and calculating the weight gain percentage of pure Tb in the product to be 0.36%. Putting the processed product into a composite graphite box with a molybdenum plate lining, performing heat treatment in a vacuum sintering furnace at 900 ℃ x5h and 500 ℃ x4h without putting the product in order, and controlling the vacuum degree of the sintering furnace to be 10-2-10-4Pa, noting that two-stage tempering is carried out by opening a diffusion pump and pumping high vacuum, and surface oxidation of small-size products is reduced as much as possible.
The product after heat treatment is randomly sampled and subjected to performance and magnetic flux tests, and the product tested by the Metis has the magnetic performance of 14.26-14.33KGs Br and 21.3-21.9KOe Hcj. The magnetic moment and attenuation data of the product tested with 0.5mm thick iron plate at 100 ℃ x2h are shown in the following table, and 30 groups of data were randomly tested.
The data show that the magnetic moment and the attenuation of the product prepared by the rotary dipping method show better consistency. By adopting the process for production, the process that the product needs to be orderly stacked in the traditional process is avoided, the product after heat treatment has good appearance and no adhesion phenomenon, the production efficiency is greatly improved, the labor cost is reduced, in addition, the production efficiency is higher, the period for producing a barrel of product is only 35min, and the process is very suitable for the mass production of the product of the type.
Example 2:
R-Fe-B-M sintered magnets were prepared using methods well known to those skilled in the art and tested in the examples below using an N42 matrix, where R includes Pr, Nd, Gd, Ho, Ce in a total amount of 31.50 wt%, where Ce is 6.8 wt%, M includes Al, Cu, Ga, Co, Zr, Ti, Nb in a total amount of 0.95 wt%, B in a total amount of 0.97 wt%, and the remaining elements are Fe, the matrix properties are Br 13.16KGs, Hcj 3512.11-12.59 KOe.
The N45 matrix is prepared by the formula, and the specification of the product to be diffused is phi 16x3.8mm, which is calledWeighing 39kg of product, placing 3kg of zirconia balls with the diameter of 5mm in a roller, placing the bottom of the roller in prepared Dy alloy liquid, starting a bottom ultrasonic system, rotating the roller at a speed of 3r/min, soaking for 10min, removing the roller from a liquid tank to a heating and air-drying station, drying at a temperature of 100 ℃, and spraying air for 3-8min while rotating; and putting the roller into the liquid tank again for rotary dipping for 7min, and spraying hot air for 8-15min until the volatile solvent substrate on the surface of the product volatilizes. And weighing the weight of the product with the film layer, and calculating the weight gain percentage of pure Dy in the product to be 0.46%. Putting the processed product into a composite graphite box with a molybdenum plate lining, performing heat treatment in a vacuum sintering furnace at 900 ℃ x8h and 500 ℃ x4h without putting the product in order, and controlling the vacuum degree of the sintering furnace to be 10-2-10-4Pa, noting that two-stage tempering is carried out by opening a diffusion pump and pumping high vacuum, and surface oxidation of small-size products is reduced as much as possible.
And randomly sampling the product after heat treatment, and performing performance and magnetic flux tests, wherein the magnetic performance of the product is tested to be Br of 12.95-13.08KGs and Hcj of 17.84-18.38KOe by adopting Metis. The magnetic moment and attenuation data of the 120 ℃ x2h half-open circuit test product are shown in the table below, and 20 groups of data were randomly tested.
The data show that the magnetic moment and the attenuation of the product prepared by the rotary dipping method show better consistency. By adopting the process for production, the process that the product needs to be orderly stacked in the traditional process is avoided, the product after heat treatment has better appearance and no adhesion phenomenon, the production efficiency is greatly improved, the labor cost is reduced, in addition, the production efficiency is higher, the period for producing a barrel of product is only 33min, and the process is suitable for the mass production of the product. In addition, by adopting the process route, the matrix magnet contains more Ce and Gd elements with low cost, Dy elements with relatively low price are adopted for diffusion, and the material cost is greatly reduced on the premise of obtaining higher performance.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are also included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope defined by the claims.
The present invention is not described in detail, but is known to those skilled in the art.
Claims (10)
1. A preparation method of a small-size R-T-B rare earth permanent magnet is characterized by comprising the following steps: the method comprises the steps of putting the R-T-B sintered magnet subjected to surface activation treatment in any shape and any size into a roller-shaped rotating device, and carrying out rotary surface adhesion slurry which adheres while rotating, wherein the adhesion mode is that the slurry is sprayed to the rotating sintered magnet, or the lower part of the rotating device where the sintered magnet is stacked is soaked in the slurry to dip the slurry into the sintered magnet.
2. The method for preparing R-T-B rare earth permanent magnet with small size according to claim 1, wherein the method comprises the following steps: the rotating device is a cylindrical rotating cage, the surface of the rotating device is net-shaped, the central line of the rotating device is horizontal, and the rotating device rotates in one direction by taking the central line as a rotating shaft.
3. The method for preparing R-T-B rare earth permanent magnet with small size according to claim 2, wherein the method comprises the following steps: one or more spray guns which are distributed at equal intervals along the central line are fixedly arranged at the central line in the rotating device; the rotating device is provided with a pumping and air-supplying system for preheating and air-drying the sintered magnet.
4. The method for preparing R-T-B rare earth permanent magnet with small size according to claim 3, wherein the method comprises the following steps: when the rotating device rotates, the central angle corresponding to the arc surface range occupied by the sintered magnet in the rotating device is beta 1, the actual injection angle of the spray gun is beta 2, beta 1 is 2 beta 2, and the injection range of the spray gun comprises the tail end of the sintered magnet along the rotating direction.
5. The method for preparing R-T-B rare earth permanent magnet with small size according to claim 2, wherein the method comprises the following steps: the rotating device is arranged in the solution tank, and the solution tank is provided with a material inlet and a material outlet for supplying and discharging the slurry and adjusting the height of the slurry in the solution tank; the solution tank is also provided with a pumping and air-supplying system for preheating and air-drying the sintered magnet; the bottom of the solution tank is also provided with an ultrasonic system to ensure that the solution tank is uniformly and compactly attached.
6. The method for preparing R-T-B rare earth permanent magnet with small size according to claim 5, wherein the method comprises the following steps: the central angle corresponding to the part of the rotating device soaked in the slurry is theta 1, when the rotating device rotates, the central angle corresponding to the arc surface range occupied by the sintered magnet in the rotating device is theta 2, and the front ends of the arcs corresponding to the two central angles along the rotating direction are overlapped or close.
7. The method for producing a rare earth permanent magnet of small size R-T-B according to any one of claims 1 to 6, wherein: the sintered magnet is placed into the rotating device and simultaneously placed with a proper amount of auxiliary spheres, wherein the auxiliary spheres include but are not limited to zirconia balls.
8. The method for producing a rare earth permanent magnet of small size R-T-B according to any one of claims 1 to 6, wherein: before the sintered magnet is placed into a rotating device, under the condition of reserving a proper amount of positive tolerance, the sintered magnet is firstly processed to be close to the size of a finished product, and chamfering treatment is carried out.
9. The method for producing a rare earth permanent magnet of small size R-T-B according to any one of claims 1 to 6, wherein: the sintered magnet is in a block shape, a cylinder shape, a tile shape, a ring shape, a sheet shape or an irregular shape, and the volume of the sintered magnet is less than 15cm3。
10. The method for producing a rare earth permanent magnet of small size R-T-B according to any one of claims 1 to 6, wherein:
the slurry comprises at least one of rare earth metal powder, rare earth fluoride, rare earth oxide, rare earth hydride or alloy of rare earth element and other elements;
the sintered magnet is an R-Fe-B-M sintered magnet, wherein R is selected from one or more of La, Ce, Pr, Nd, Dy, Tb, Gd and Ho rare earth elements, the total amount of the R is 26.5-34 wt%, M is selected from one or more of Ga, Al, Cu, Co, Ti, Zr, Nb and W metal elements, the total amount of the M is 0-6 wt%, the total amount of B is 0.55-1.5 wt%, and the rest elements are Fe;
the surface activation treatment comprises oil removal, cleaning, acid pickling and sand blasting;
after the slurry is attached to the rotary surface, the sintered magnet is subjected to heat treatment in a vacuum sintering furnace, so that rare earth elements in the slurry are diffused and enter the sintered magnet, the heat treatment comprises two stages, the temperature range of the first-stage heat treatment is 750-960 ℃, the heat treatment time is 2-72 h, the temperature range of the second-stage heat treatment is 430-580 ℃, the heat treatment time is 2-8 h, the vacuum degree of the sintering furnace is controlled to be 10-1-10-4Pa。
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114823118A (en) * | 2022-06-27 | 2022-07-29 | 宁波科宁达工业有限公司 | Rare earth permanent magnet and preparation method thereof |
Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20050233068A1 (en) * | 2002-11-29 | 2005-10-20 | Kohshi Yoshimura | Method for producing corrosion-resistant rare earth based permanent magnet, corrosion-resistant rare earth based permanent magnet, dip spin coating method for work piece, and method for forming coating film on work piece |
| CN1898757A (en) * | 2004-10-19 | 2007-01-17 | 信越化学工业株式会社 | Method for producing rare earth permanent magnet material |
| CN101110289A (en) * | 2005-07-22 | 2008-01-23 | 信越化学工业株式会社 | Rare earth permanent magnet, its manufacturing method, and permanent magnet rotary machine |
| CN101908397A (en) * | 2010-07-30 | 2010-12-08 | 北京工业大学 | Rare earth hydride surface coating treating agent, application thereof and method for forming rare earth hydride surface coating |
| CN103258633A (en) * | 2013-05-30 | 2013-08-21 | 烟台正海磁性材料股份有限公司 | Method for preparing R-Fe-B series sintered magnets |
| CN107533913A (en) * | 2015-04-28 | 2018-01-02 | 信越化学工业株式会社 | The manufacture method of rare earth element magnet and the apparatus for coating of rare-earth compounds |
| EP3291261A1 (en) * | 2015-04-28 | 2018-03-07 | Shin-Etsu Chemical Co., Ltd. | Method for producing rare-earth magnets, and slurry application device |
| CN109695015A (en) * | 2019-01-16 | 2019-04-30 | 东北大学 | Masking liquid and its preparation method and application is seeped in Fe-B rare-earth permanent magnet heavy rare earth thermal expansion |
-
2021
- 2021-10-21 CN CN202111225615.0A patent/CN113963932A/en active Pending
Patent Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20050233068A1 (en) * | 2002-11-29 | 2005-10-20 | Kohshi Yoshimura | Method for producing corrosion-resistant rare earth based permanent magnet, corrosion-resistant rare earth based permanent magnet, dip spin coating method for work piece, and method for forming coating film on work piece |
| CN1898757A (en) * | 2004-10-19 | 2007-01-17 | 信越化学工业株式会社 | Method for producing rare earth permanent magnet material |
| CN101110289A (en) * | 2005-07-22 | 2008-01-23 | 信越化学工业株式会社 | Rare earth permanent magnet, its manufacturing method, and permanent magnet rotary machine |
| CN101908397A (en) * | 2010-07-30 | 2010-12-08 | 北京工业大学 | Rare earth hydride surface coating treating agent, application thereof and method for forming rare earth hydride surface coating |
| CN103258633A (en) * | 2013-05-30 | 2013-08-21 | 烟台正海磁性材料股份有限公司 | Method for preparing R-Fe-B series sintered magnets |
| CN107533913A (en) * | 2015-04-28 | 2018-01-02 | 信越化学工业株式会社 | The manufacture method of rare earth element magnet and the apparatus for coating of rare-earth compounds |
| EP3291261A1 (en) * | 2015-04-28 | 2018-03-07 | Shin-Etsu Chemical Co., Ltd. | Method for producing rare-earth magnets, and slurry application device |
| CN109695015A (en) * | 2019-01-16 | 2019-04-30 | 东北大学 | Masking liquid and its preparation method and application is seeped in Fe-B rare-earth permanent magnet heavy rare earth thermal expansion |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114823118A (en) * | 2022-06-27 | 2022-07-29 | 宁波科宁达工业有限公司 | Rare earth permanent magnet and preparation method thereof |
| CN114823118B (en) * | 2022-06-27 | 2022-10-25 | 宁波科宁达工业有限公司 | Rare earth permanent magnet and preparation method thereof |
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