Method for recycling old neodymium-iron-boron magnet and sintered neodymium-iron-boron magnet

Abstract

The invention discloses a method for recycling an old material of a neodymium-iron-boron magnet and a sintered neodymium-iron-boron magnet. The method for recycling the old neodymium-iron-boron magnet material comprises the following steps that (1) burdening is conducted according to a set formula, smelting is conducted, and a neodymium-iron-boron rapid hardening sheet is obtained; 2) mixing the neodymium-iron-boron rapid hardening sheet with the pretreated neodymium-iron-boron magnet old material to obtain a mixture; performing hydrogen decrepitation on the mixture through hydrogen absorption and dehydrogenation processes to obtain neodymium iron boron coarse powder; wherein the mass ratio of the pretreated neodymium iron boron magnet old material to the neodymium iron boron rapid hardening sheet is (5-40): 100; 3) performing jet milling on the neodymium iron boron coarse powder to obtain magnetic powder; and 4) pressing and sintering the magnetic powder to obtain the sintered neodymium-iron-boron magnet. By the adoption of the method, the neodymium-iron-boron magnet old material can be recycled, and the obtained sintered neodymium-iron-boron magnet is high in residual magnetism, coercive force and squareness.

Description

Technical Field

[0001] The present invention relates to a method for recycling waste neodymium-iron-boron magnets and a sintered neodymium-iron-boron magnet. Background Art

[0002] Sintered neodymium-iron-boron permanent magnetic materials are a kind of rare earth permanent magnetic materials with relatively wide applications. Since waste materials will inevitably be generated during the production of sintered neodymium-iron-boron products, and finished products such as neodymium-iron-boron motors are scrapped, the quantity of waste sintered neodymium-iron-boron magnets is increasing day by day. Therefore, how to recycle waste sintered neodymium-iron-boron permanent magnets has increasingly become a problem that people pay more and more attention to.

[0003] CN104575904A discloses a method for preparing a neodymium-iron-boron magnet sintered from neodymium-iron-boron recycled waste, which includes the following steps: S1. Weigh raw materials according to the components and their mass percentages in the neodymium-iron-boron preparation material, and then vacuum melt to make a neodymium-iron-boron preparation material flake; Clean the neodymium-iron-boron recycled waste to obtain a neodymium-iron-boron recycled waste with a certain composition, and then perform hydrogen crushing on the neodymium-iron-boron preparation material flake and the neodymium-iron-boron recycled waste respectively to obtain a neodymium-iron-boron preparation material coarse powder and a neodymium-iron-boron recycled waste coarse powder; S2. Grind the neodymium-iron-boron recycled waste coarse powder by a jet mill to make a neodymium-iron-boron recycled waste fine powder with an average particle size of 20-100 μm, and mix the neodymium-iron-boron recycled waste fine powder with the neodymium-iron-boron preparation material coarse powder to obtain a neodymium-iron-boron mixture; S3. Perform secondary jet milling on the above neodymium-iron-boron mixture to obtain a neodymium-iron-boron fine powder with an average particle size of 2-4 μm; S4. Press the above-prepared neodymium-iron-boron fine powder into a green body under the protection of an inert gas, put the green body into an isostatic press to apply pressure, and keep the pressure to obtain a billet; S5. Place the above billet in a vacuum sintering furnace to dehydrogenate first, evacuate and then sinter, and perform aging treatment after sintering is completed to obtain a neodymium-iron-boron magnet. Although this method has relatively high remanence and coercivity, the squareness is relatively low. Moreover, this method is a bit cumbersome.

[0004] CN109192495A discloses a method for preparing a recycled sintered neodymium-iron-boron permanent magnet, including: (1) first, performing surface pretreatment on waste sintered neodymium-iron-boron permanent magnets, and then crushing them into magnetic powders with an average particle size of 2.0 - 4.0 μm; (2) mixing and heat-treating the magnetic powders and heavy rare earth-rich powders at a mass ratio of 98:2 - 99.5:0.5, so that heavy rare earth atoms diffuse into the surface layer of the magnetic powders to obtain modified magnetic powders; (3) mixing the high-abundance rare earth-rich powders and the modified magnetic powders at a mass ratio of 1:100 - 5:100 to obtain mixed magnetic powders; (4) placing the mixed magnetic powders in a magnetic field with a magnetic field strength of more than 1.5 T and subjecting them to orientation pressing to form a green compact; (5) subjecting the green compact to high-temperature sintering and tempering treatments to prepare a recycled sintered neodymium-iron-boron permanent magnet. The heavy rare earth in the heavy rare earth-rich powders is at least one of Dy and Tb, and the high-abundance rare earth in the high-abundance rare earth-rich powders is at least one of La and Ce. The squareness of the recycled magnet obtained in this patent document is relatively low.

[0005] CN113724992A discloses a neodymium-iron-boron rare earth permanent magnet waste recycled magnet and a preparation method thereof. This patent document makes extensive use of Ce-containing waste, solving the problem of the backlog of a large amount of existing Ce-containing waste. The preparation method includes: mixing rare earth waste powders and R-M alloy powders to obtain mixed fine powders, and sequentially subjecting the mixed fine powders to forming, sintering, and heat treatment to obtain a neodymium-iron-boron rare earth permanent magnet waste recycled magnet. The coercivity of the recycled magnet prepared by this method is unstable in magnitude, has slightly poor repeatability, and has a relatively low squareness. Summary of the Invention

[0006] In view of this, an object of the present invention is to provide a method for recycling used neodymium-iron-boron magnets. This method can utilize used neodymium-iron-boron magnets, and the remanence, coercivity, and squareness of the sintered neodymium-iron-boron magnets obtained by this method are all relatively high. Further, this method has good repeatability. Another object of the present invention is to provide a sintered neodymium-iron-boron magnet obtained according to the method described above.

[0007] The present invention provides a method for recycling used neodymium-iron-boron magnets, including the following steps:

[0008] 1) Mixing and melting according to a set formula to obtain a neodymium-iron-boron rapid solidification sheet;

[0009] 2) Mixing the neodymium-iron-boron rapid solidification sheet with pretreated used neodymium-iron-boron magnets to obtain a mixture; subjecting the mixture to hydrogen crushing through a hydrogen absorption and dehydrogenation process to obtain neodymium-iron-boron coarse powders; wherein, the mass ratio of the pretreated used neodymium-iron-boron magnets to the neodymium-iron-boron rapid solidification sheet is 5 - 40:100;

[0010] 3) Obtaining magnetic powders by passing the neodymium-iron-boron coarse powders through a jet mill;

[0011] 4) Press the magnetic powder and sinter it to obtain a sintered NdFeB magnet.

[0012] According to the method of the present invention, preferably, the mass ratio of the pretreated NdFeB magnet scrap to the NdFeB rapid solidification sheet is 15-30:100.

[0013] According to the method of the present invention, preferably, the NdFeB magnet scrap before pretreatment includes finished product scrap with a coating, blank scrap, black sheets, and material skins.

[0014] According to the method of the present invention, preferably, the pretreated NdFeB magnet scrap is obtained by the following steps:

[0015] (1) Remove the surface dirt or coating of the NdFeB magnet scrap before pretreatment completely to obtain clean NdFeB magnet scrap;

[0016] (2) Coarsely crush the clean NdFeB magnet scrap to obtain the pretreated NdFeB magnet scrap with a particle size of 1-30 mm.

[0017] According to the method of the present invention, preferably, in step (1), clean NdFeB magnet scrap is obtained by any of the following methods:

[0018] (I). Use a sandblasting machine to remove the surface dirt or coating of the NdFeB magnet scrap before pretreatment completely;

[0019] (II). Use silicon carbide or brown fused alumina to remove the surface dirt or coating of the NdFeB magnet scrap before pretreatment completely;

[0020] (III). Sequentially perform pickling, water washing, and drying to remove the surface dirt of the NdFeB magnet scrap before pretreatment completely.

[0021] According to the method of the present invention, preferably, in step (1), sequentially perform pickling, water washing, and drying to remove the surface dirt of the NdFeB magnet scrap before pretreatment completely.

[0022] According to the method of the present invention, preferably, in step (2), use a jaw crusher to coarsely crush the clean NdFeB magnet scrap.

[0023] According to the method of the present invention, preferably:

[0024] In step 2), the hydrogen absorption pressure is 0.05-0.15 MPa, and the time is 2-4 h; the dehydrogenation temperature is 400-600 °C, and the time is 5-12 h; the particle size of the NdFeB coarse powder is 10-300 μm;

[0025] In step 3), the rotational speed of the sorting wheel of the jet mill is 2,600 - 2,900 rpm; the D of the magnetic powder 50 is 3 - 5 μm.

[0026] According to the method of the present invention, preferably, in step 4), the sintering includes primary sintering and secondary sintering. The temperature of the primary sintering is 900 - 1,100 °C, and the time is 4 - 10 h; the temperature of the secondary sintering is 450 - 550 °C, and the time is 4 - 9 h.

[0027] On the other hand, the present invention also provides a sintered neodymium iron boron magnet obtained according to the method as described above, and its squareness is greater than 98%.

[0028] The method for recycling waste neodymium iron boron magnets of the present invention can recycle waste neodymium iron boron magnets, and the remanence, coercivity and squareness of the obtained sintered neodymium iron boron magnets are all relatively high. According to the preferred technical solution of the present invention, the neodymium iron boron rapid solidification sheet obtained from normal raw materials is combined with the pretreated waste neodymium iron boron materials and then hydrogenated under specific conditions, and then through a jet mill, pressing and sintering, a sintered neodymium iron boron magnet is obtained. The squareness of the sintered neodymium iron boron magnet obtained by the present invention is greater than 98%. Detailed Embodiments

[0029] The following further illustrates the present invention with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0030] The "remanence" described in the present invention refers to the value of the magnetic induction intensity corresponding to the zero magnetic field strength on the saturation hysteresis loop, usually denoted as Br, and the unit is tesla (T) or gauss (Gs). 1 Gs = 0.0001 T.

[0031] The "coercivity" described in the present invention, also known as the intrinsic coercivity, refers to the magnetic field strength when the magnetic field is monotonically reduced to zero and then increased in the reverse direction from the saturated magnetization state of the magnet, so that the magnetization intensity is reduced to zero along the saturated hysteresis loop, usually denoted as Hcj, and the unit is oersted (Oe) or ampere per meter (A / m). 1 Oe = 79.6 A / m.

[0032] Remanence, intrinsic coercivity and squareness are important indicators for characterizing the performance of sintered rare earth permanent magnets. A magnet with high remanence and intrinsic coercivity can only exhibit a high magnetic energy product on the premise of having good squareness. While the remanence and intrinsic coercivity are the same, a good squareness means good demagnetization resistance, and a poor squareness means easy demagnetization. Generally, it is desired that the sintered rare earth permanent magnet has relatively high remanence, coercivity and squareness. However, in many cases, when the coercivity is increased, the remanence and squareness both decrease.

[0033] The method for recycling waste NdFeB magnets of the present invention, while utilizing waste NdFeB magnets, results in sintered NdFeB magnets having relatively high remanence and coercivity, and also relatively high squareness.

[0034] Through a large amount of research and experiments, the present invention has found that the pretreated waste NdFeB magnets can be hydrogenated and crushed after being combined with normal NdFeB melt-spun flakes during the hydrogenation and crushing stage, and then subjected to jet milling, compacting, and sintering, so as to obtain sintered NdFeB magnets with relatively high remanence, coercivity, and squareness. Moreover, the method of the present invention has stable process and good repeatability.

[0035] A method for recycling waste NdFeB magnets provided by the present invention includes the following steps: 1) batching and melting step; 2) mixing the waste with melt-spun flakes and hydrogenation and crushing step; 3) jet milling step; 4) compacting and sintering step. Optionally, it further includes: a step of pretreating the waste NdFeB magnets. The following is a detailed description.

[0036] In the present invention, the waste NdFeB magnets refer to the waste NdFeB magnets before pretreatment, which include coated finished product waste, blank waste, black pieces, and scraps.

[0037] Among them, the coated finished product waste refers to the magnets after electroplating. Generally, the surface treatment of NdFeB is not for improving its magnetic properties, and the surface coating of NdFeB mainly plays a protective role. NdFeB permanent magnets without surface coating are very easy to react with oxygen in the air and oxidize rapidly. Therefore, in order to prevent this situation, electroplating treatment is usually carried out. Common coatings (i.e., plating layers) include nickel plating, zinc plating, etc.

[0038] Among them, the blank waste refers to the waste NdFeB magnets after the first sintering or multiple aging treatments, excluding diffusion magnets and without coatings.

[0039] Among them, the black pieces refer to the sheet-shaped, cylindrical or other shaped magnets with non-conforming dimensions or appearance that appear during the machining of the blank to specified dimensions.

[0040] Among them, the scraps refer to the thin sheet-shaped magnets cut from the surface of the blank during machining. In the present invention, the element composition and content in the waste NdFeB magnets are not particularly limited.

[0041] <Step of pretreating the waste NdFeB magnets>

[0042] In the present invention, the pre-treated waste NdFeB magnets are obtained by the following steps: (1) removing the surface dirt or coating of the waste NdFeB magnets before pretreatment completely to obtain clean waste NdFeB magnets; (2) coarsely crushing the clean waste NdFeB magnets to obtain the pre-treated waste NdFeB magnets. This is conducive to better utilization of the waste NdFeB magnets to improve the magnetic properties of the obtained sintered NdFeB magnets.

[0043] Among them, the types and sources of the waste NdFeB magnets before pretreatment are as described above.

[0044] In the present invention, the surface of the waste NdFeB magnets before pretreatment generally has oil stains, and the surface without oil stains is considered to be cleaned. Specifically, the standard for cleaning is that there are no obvious oil stains or rust stains on the surface of the waste materials.

[0045] In step (1), the clean waste NdFeB magnets are obtained by any of the following methods:

[0046] (1) Using a sandblasting machine to remove the surface dirt or coating of the waste NdFeB magnets before pretreatment completely;

[0047] (2) Using silicon carbide or brown fused alumina as abrasives to remove the surface dirt or coating of the waste NdFeB magnets before pretreatment completely;

[0048] (3) Sequentially using pickling, water washing, and drying to remove the surface dirt of the waste NdFeB magnets before pretreatment completely.

[0049] In method (1), that is, using a sandblasting machine to obtain clean waste NdFeB magnets through sandblasting. The sandblasting treatment generally uses compressed air as the power to form a high-speed jet beam to spray the abrasive (such as quartz sand, emery) onto the surface of the waste NdFeB magnets before pretreatment at a high speed to remove the surface dirt or coating completely.

[0050] In method (2), silicon carbide or brown fused alumina is used as the abrasive.

[0051] Preferably, method (3) is adopted, that is, sequentially using pickling, water washing, and drying to remove the surface dirt of the waste NdFeB magnets before pretreatment completely to obtain clean waste NdFeB magnets.

[0052] Among them, pickling refers to placing the waste NdFeB magnets before pretreatment in an acid solution for ultrasonic washing. The concentration of the acid solution is less than 10 wt%, preferably less than or equal to 6 wt%. More preferably, first wash with an acid solution with a concentration of 4 - 6 wt% for 30 - 90 s, preferably 30 - 60 s; then wash with a 2 - 4% acid solution for 2 - 5 min, preferably 2 - 4 min, and more preferably 2 - 3 min. The acid solution can be selected from sulfuric acid solution, hydrochloric acid solution or nitric acid solution, preferably nitric acid solution.

[0053] Water washing refers to placing the pickled waste NdFeB magnets in water for ultrasonic washing. After water washing, drying is carried out, and the drying temperature can be 70 - 110 °C.

[0054] In step (2), a jaw crusher is used to coarsely crush the cleaned waste NdFeB magnets. The particle size of the pretreated waste NdFeB magnets obtained by coarse crushing is less than or equal to 30 mm, for example, it can be 1 - 30 mm, preferably 1 - 20 mm, and more preferably 1 - 10 mm.

[0055] <Ingredient mixing and melting steps>

[0056] Ingredient mixing is carried out according to a set formula and then melting is carried out to obtain NdFeB rapid solidification flakes.

[0057] In the present invention, the set formula refers to a magnet whose elemental composition can form an R - Fe - B - based magnet and has Nd2Fe 14 B as the main phase.

[0058] In some embodiments, based on the weight of the NdFeB rapid solidification flakes, the elemental composition is as follows: Nd 10 - 30.5%, Pr 0.05 - 8.5%, B 0.8 - 1.1%, Al 0.1 - 1.5%, Co 0.13 - 7%, Cu 0.1 - 0.5%, Dy 0.1 - 8.2%, Ga 0.1 - 0.4%, Gd 0.1 - 11%, Tb 0 - 1.5%, Zr 0 - 0.25%, Ce 0 - 13.5%, La 0 - 3.5%, and the balance is Fe.

[0059] In some other embodiments, based on the weight of the NdFeB rapid solidification flakes, the elemental composition is as follows: Nd 10 - 30.5%, Pr 0.05 - 8.5%, B 0.8 - 1.1%, Al 0.1 - 1.5%, Co 0.13 - 7%, Cu 0.1 - 0.5%, Dy 0.1 - 8.2%, Ga 0.1 - 0.4%, Gd 0.1 - 11%, Ho 0.1 - 7.5%, Tb 0 - 1.5%, Zr 0 - 0.25%, Ce 0 - 13.5%, La 0 - 3.5%, and the balance is Fe.

[0060] In certain specific embodiments, based on the weight of the NdFeB rapid solidification sheet, the elemental composition is as follows: Nd 12.0 - 25.5%, Pr 1.0 - 8.5%, B 0.8 - 1.1%, Al 0.1 - 1.2%, Co 0.25 - 5.2%, Cu 0.1 - 0.5%, Dy 0.1 - 5.4%, Ga 0.1 - 0.4%, Gd 0.1 - 5.5%, Zr 0.05 - 0.25%, Ce 0.5 - 13.5%, La 0 - 3.5%, and the balance is Fe.

[0061] In some other specific embodiments, based on the weight of the NdFeB rapid solidification sheet, the elemental composition is as follows: Nd 14.5 - 16.5%, Pr 4.7 - 6.5%, B 0.8 - 1.0%, Al 0.22 - 0.36%, Co 0.95 - 1.5%, Cu 0.20 - 0.32%, Dy 0.27 - 0.35%, Ga 0.16 - 0.25%, Gd 0.55 - 0.75%, Zr 0.14 - 0.23%, Ce 6.8 - 9.3%, and the balance is Fe.

[0062] According to a specific embodiment of the present invention, based on the weight of the NdFeB rapid solidification sheet, the elemental composition is as follows: Nd 15.9 - 16.3%, Pr 5.3 - 5.7%, B 0.9 - 1.0%, Al 0.29 - 0.33%, Co 0.9 - 1.1%, Cu 0.24 - 0.26%, Dy 0.28 - 0.30%, Ga 0.17 - 0.20%, Gd 0.57 - 0.65%, Zr 0.18 - 0.21%, Ce 7.8 - 8.1%, and the balance is Fe.

[0063] In the present invention, melting can be carried out using a vacuum rapid solidification furnace to melt normal raw materials to obtain the NdFeB rapid solidification sheet. Among them, normal raw materials refer to non-recycled old materials. In some other embodiments, normal raw materials may include praseodymium-neodymium, lanthanum-cerium, boron, pure iron, etc., and may also include cobalt, copper, zirconium, gadolinium, etc.

[0064] According to an embodiment of the present invention, the required raw materials are put into a vacuum rapid solidification furnace, evacuated to less than 1 Pa, and then argon (Ar) is filled. Under the protection of argon, heating and melting are carried out to form an alloy liquid, and then the alloy liquid is poured onto a rotating cooling copper roll to prepare an NdFeB rapid solidification sheet with a thickness of 0.2 - 0.5 mm. Among them, the temperature of the alloy liquid is controlled between 1400 - 1500 °C. The thickness of the NdFeB rapid solidification sheet is preferably 0.25 - 0.45 mm, and the thickness is the average thickness.

[0065] <Mixing the old materials with the rapid solidification sheet and hydrogenation and crushing steps>

[0066] Mix the NdFeB rapid solidification flakes with the pretreated waste NdFeB magnets to obtain a mixture; subject the mixture to hydrogen pulverization through a hydrogen absorption and dehydrogenation process to obtain NdFeB coarse powder. The remanence, coercivity, and squareness of the sintered NdFeB magnets obtained in this way are all relatively high.

[0067] The composition of the waste NdFeB magnets can be close to that of the NdFeB rapid solidification flakes. In the present invention, the waste NdFeB magnets can be waste materials of a single formulation or a mixture of waste materials of multiple formulations.

[0068] In some embodiments, based on the weight of the waste NdFeB magnets, the elemental composition is as follows: Nd 10 - 30.5%, Pr 0.05 - 8.5%, B 0.8 - 1.1%, Al 0 - 1.5%, Co 0.13 - 7%, Cu 0 - 0.5%, Dy 0 - 8.2%, Ga 0 - 0.4%, Gd 0.1 - 11%, Tb 0 - 1.5%, Zr 0 - 0.25%, Ce 0 - 13.5%, La 0 - 3.5%, and the balance is Fe.

[0069] In other embodiments, based on the weight of the waste NdFeB magnets, the elemental composition is as follows: Nd 10 - 30.5%, Pr 0.05 - 8.5%, B 0.8 - 1.1%, Al 0 - 1.5%, Co 0.13 - 7%, Cu 0 - 0.5%, Dy 0 - 8.2%, Ga 0 - 0.4%, Gd 0.1 - 11%, Ho 0.1 - 7.5%, Tb 0 - 1.5%, Zr 0 - 0.25%, Ce 0 - 13.5%, La 0 - 3.5%, and the balance is Fe.

[0070] In some specific embodiments, based on the weight of the waste NdFeB magnets, the elemental composition is as follows: Nd 14.5 - 30%, Pr 0.05 - 8%, B 0.8 - 1.1%, Al 0 - 1.5%, Co 0.5 - 2%, Cu 0 - 0.5%, Dy 0 - 2.3%, Ga 0 - 0.4%, Gd 0 - 11%, Tb 0 - 1.4%, Zr 0 - 0.2%, and the balance is Fe.

[0071] In yet some other specific embodiments, based on the weight of the waste NdFeB magnets, the elemental composition is as follows: PrNd 29 - 33% (weight ratio of Pr to Nd is 1:3), B 0.88 - 1.0%, Al 0.2 - 1.5%, Co 0.95 - 1.95%, Cu 0.1 - 0.25%, Dy 0 - 0.65%, Ga 0.08 - 0.28%, Gd 0 - 0.35%, Zr 0.08 - 0.2%, and the balance is Fe.

[0072] In some more specific embodiments, the recycled neodymium iron boron magnet materials are obtained by mixing the recycled materials of five formulations, and the five formulations are mixed according to a weight ratio of 1:1:1:1:1. The five formulations are Formulation A, Formulation B, Formulation C, Formulation D, and Formulation E respectively. The specific composition of Formulation A is as follows: based on the weight of the recycled material of Formulation A, PrNd is 29.7-30.3%, B is 0.89-0.91%, Ga is 0.19-0.23%, Co is 0.97-1.13%, Zr is 0.15-0.19%, Cu is 0.10-0.14%, Dy is 0.51-0.56%, Al is 0.27-0.31%, and the balance is Fe. The specific composition of Formulation B is as follows: based on the weight of the recycled material of Formulation B, PrNd is 30.0-31.3%, B is 0.91-0.95%, Ga is 0.19-0.22%, Co is 1.15-1.45%, Zr is 0.15-0.19%, Cu is 0.17-0.23%, Al is 0.55-0.72%, and the balance is Fe. The specific composition of Formulation C is as follows: based on the weight of the recycled material of Formulation C, PrNd is 30.0-31.3%, B is 0.92-0.95%, Ga is 0.08-0.15%, Co is 1.15-1.45%, Zr is 0.08-0.15%, Cu is 0.17-0.23%, Dy is 0.38-0.47%, Al is 0.57-0.71%, and the balance is Fe. The specific composition of Formulation D is as follows: based on the weight of the recycled material of Formulation D, PrNd is 31.0-33.0%, B is 0.91-0.95%, Ga is 0.10-0.15%, Co is 1.23-1.46%, Zr is 0.16-0.23%, Cu is 0.17-0.22%, Al is 1.22-1.45%, Gd is 0.21-0.27%, and the balance is Fe. The specific composition of Formulation E is as follows: based on the weight of the recycled material of Formulation E, PrNd is 30.0-31.5%, B is 0.93-0.97%, Ga is 0.08-0.15%, Co is 1.56-1.71%, Zr is 0.15-0.19%, Cu is 0.17-0.22%, Dy is 0.33-0.42%, Al is 0.72-0.95%, and the balance is Fe. In these five formulations, the weight ratio of Pr to Nd is 1:3.

[0073] Among them, the mass ratio of the pretreated recycled neodymium iron boron magnet materials to the neodymium iron boron rapid solidification flakes can be 5-40:100, preferably 15-35:100, and more preferably 20-30:100.

[0074] During the hydrogen absorption process, the hydrogen absorption pressure can be 0.05 - 0.15 MPa, preferably 0.08 - 0.12 MPa, more preferably 0.1 - 0.12 MPa. The hydrogen absorption time can be 2 - 4 h, preferably 2.5 - 3.5 h, more preferably 3 - 3.5 h. During the dehydrogenation process, the dehydrogenation temperature can be 400 - 600 °C, preferably 450 - 550 °C, more preferably 500 - 550 °C. The dehydrogenation time can be 6 - 12 h, preferably 8 - 12 h, more preferably 10 - 11 h.

[0075] After the hydrogen absorption process and the dehydrogenation process are completed, water cooling is carried out for 3 - 6 h to obtain NdFeB coarse powder. The water cooling time is preferably 4 - 6 h, more preferably 4 - 5 h. The particle size of the NdFeB coarse powder can be 10 - 300 μm, preferably 20 - 300 μm, more preferably 30 - 300 μm.

[0076] According to an embodiment of the present invention, the hydrogen crushing process of the present invention is preferably carried out in a hydrogen crushing furnace.

[0077] <Jet mill step>

[0078] The NdFeB coarse powder is passed through a jet mill to obtain magnetic powder.

[0079] In order to prevent the alloy flakes and the coarse powder obtained by crushing them from being oxidized, the powder making of the present invention is carried out in a vacuum or an inert atmosphere. The inert atmosphere can be an atmosphere formed by an inert gas, for example, it can be an atmosphere formed by argon or helium. The powder making is carried out in a vacuum, that is, under the condition of having a certain vacuum degree, for example, the vacuum degree can be less than 50 Pa.

[0080] The rotation speed of the sorting wheel of the jet mill is 2600 - 2900 rpm, preferably 2700 - 2900 rpm, more preferably 2800 - 2850 rpm. The D 50 of the magnetic powder is 3 - 5 μm.

[0081] <Pressing and sintering step>

[0082] The magnetic powder is pressed and sintered to obtain a sintered NdFeB magnet. Specifically, the magnetic powder is placed in a magnetic field for pressing, and then isostatically pressed to obtain a green body; the green body is sintered to obtain a sintered NdFeB magnet.

[0083] In order to prevent the magnetic powder from being oxidized, the pressing and isostatic pressing are carried out in a vacuum or an inert atmosphere. The pressing process preferably adopts a die pressing process. The direction of the orientation magnetic field and the direction of the magnetic powder pressing are oriented parallel or perpendicular to each other. In order to obtain a higher remanence, a certain strength of the orientation magnetic field is required, and the magnetic field strength is greater than 1.0 T, preferably greater than 1.5 T, more preferably greater than 1.7 T.

[0084] In some embodiments, the green compact formed by die pressing is taken out and vacuum packaged, and then placed in an isostatic press for pressurization at 150 - 250 MPa. After pressure holding, the green body is taken out.

[0085] The density of the green compact can be 2.5 - 4.0 g / cm 3 , preferably 2.8 - 3.5 g / cm 3 , more preferably 3.0 - 3.5 g / cm 3 . For example, it can be 3.16 g / cm 3 . The density of the green body can be 3.5 - 5.5 g / cm 3 , preferably 3.8 - 5.0 g / cm 3 , more preferably 4.3 - 5.0 g / cm 3 . For example, it can be 4.81 g / cm 3 . This is beneficial for the sintered NdFeB magnet to maintain a high remanence.

[0086] The green body is subjected to vacuum sintering to obtain a sintered NdFeB magnet. The vacuum degree during vacuum sintering is less than or equal to 0.5 Pa, preferably less than or equal to 0.3 Pa, more preferably less than or equal to 0.1 Pa, and still more preferably less than or equal to 0.01 Pa. The sintering includes primary sintering and secondary sintering. The temperature of the primary sintering can be 900 - 1100 °C, preferably 1000 - 1100 °C, more preferably 1000 - 1055 °C. The time of the primary sintering can be 4 - 10 h, preferably 5 - 9 h, more preferably 6 - 8 h. The temperature of the secondary sintering can be 450 - 550 °C, preferably 465 - 500 °C, more preferably 485 - 500 °C. The time of the secondary sintering can be 4 - 9 h, preferably 5 - 8 h, more preferably 5 - 6 h.

[0087] The remanence, coercivity, and squareness of the sintered NdFeB magnet obtained by the method of the present invention are all relatively high, and can be equivalent to, or slightly higher than, the remanence, coercivity, and squareness of the sintered NdFeB magnet obtained from normal materials (i.e., materials without recycled materials). Moreover, the oxygen content, carbon content, nitrogen content, and sulfur content are all relatively low. The method of the present invention has good process stability and repeatability.

[0088] The test methods used in the following examples and comparative examples are described as follows:

[0089] Magnetic property test: Use a B - H magnetometer to measure the magnetic properties of the sintered NdFeB magnet at room temperature to obtain the room - temperature remanence Br, room - temperature coercivity Hcj, and squareness Hk / Hcj.

[0090] Oxygen content, carbon content, nitrogen content, sulfur content: Tested using an ONH analyzer (ONH-2000, OH-3000) and a high-frequency infrared carbon-sulfur analyzer.

[0091] Example 1

[0092] Batching: Batch according to the chemical composition shown below. Based on the weight of the obtained NdFeB rapid solidification sheet, Nd 15.9%, Pr 5.3%, B 0.9%, Al 0.29%, Co 1.1%, Cu 0.26%, Dy 0.3%, Ga 0.2%, Gd 0.65%, Zr 0.18%, Ce 8.1%, and the balance is Fe.

[0093] Smelting: Use a vacuum rapid solidification furnace to form NdFeB rapid solidification sheets from raw materials. The average thickness of the NdFeB rapid solidification sheet is 0.25 - 0.45 mm.

[0094] Hydrogen crushing: Mix 100 parts by weight of the above NdFeB rapid solidification sheet with 20 parts by weight of pretreated NdFeB magnet scrap. Absorb hydrogen at 0.1 MPa for 3 h and dehydrogenate at 550 °C for 10 h, then cool with water for 4 h to obtain NdFeB coarse powder. The particle size D 50 of the NdFeB coarse powder is 200 μm.

[0095] The composition of the NdFeB magnet waste material is as follows: based on the weight of the NdFeB magnet waste material, Nd 14.5-30%, Pr 0.05-8%, B 0.8-1.1%, Al 0-1.5%, Co0.5-2%, Cu 0-0.5%, Dy 0-2.3%, Ga 0-0.4%, Gd 0-11%, Tb0-1.4%, Zr 0-0.2%, Fe balance. The NdFeB magnet waste material is obtained by mixing waste materials of multiple formulas. Specifically, the waste materials of formula A, formula B, formula C, formula D, and formula E are mixed in a weight ratio of 1:1:1:1:1. The specific composition of formula A is: based on the weight of the old material of formula A, PrNd 30.09%, B 0.908%, Ga 0.21%, Co 1.08%, Zr 0.17%, Cu 0.12%, Dy 0.54%, Al 0.29%, Fe balance. The specific composition of formula B is: based on the weight of the old material of formula B, PrNd 31.08%, B 0.938%, Ga 0.21%, Co 1.34%, Zr 0.17%, Cu 0.19%, Al 0.62%, Fe balance. The specific composition of formula C is: based on the weight of the old material of formula C, PrNd 31.09%, B 0.940%, Ga 0.10%, Co 1.34%, Zr 0.11%, Cu 0.19%, Dy 0.42%, Al 0.61%, Fe balance. The specific composition of formula D is: based on the weight of the old material of formula D, PrNd 32.03%, B 0.930%, Ga 0.13%, Co1.35%, Zr0.20%, Cu 0.19%, Al 1.32%, Gd 0.24%, Fe balance. The specific composition of formula E is: based on the weight of the old material of formula E, PrNd 31.23%, B 0.954%, Ga0.10%, Co 1.61%, Zr 0.17%, Cu 0.19%, Dy 0.39%, Al 0.82%, Fe balance. The weight ratio of Pr to Nd in each formula is 1:3.

[0096] The pretreated NdFeB magnet waste material is prepared by the following steps: firstly pickling with a nitric acid solution with a concentration of 6wt% for 30 seconds, then pickling with a nitric acid solution with a concentration of 2wt% for 3 minutes, then washing with water and drying to obtain clean NdFeB magnet waste material; using a jaw crusher to coarsely crush the clean NdFeB magnet waste material to obtain pretreated NdFeB magnet waste material with a particle size of 1 to 30mm. The jaw crusher is only used as a coarse crushing tool, and the particle size and shape after crushing are uneven, generally not exceeding 30mm.

[0097] Airflow mill: NdFeB coarse powder is jet milled at a separation wheel speed of 2800r / min to obtain NdFeB fine powder.50 is 4.25μm.

[0098] Pressing: NdFeB fine powder is formed into a density of 3.16g / cm 3 The green body is isostatically pressed to form a green body with a density of 4.81 g / cm 3 The blank.

[0099] Sintering: The green body is sintered at 1055℃ for 6h, and then sintered at 485℃ for 5h to obtain a sintered NdFeB magnet. The remanence of the sintered NdFeB magnet is 12.88kGs, the coercive force is 13.65kOe, and the squareness is 98.8%. The oxygen content of the sintered NdFeB magnet is 1005ppm, the carbon content is 495ppm, the nitrogen content is 348ppm, the sulfur content is 26.5ppm, and the density of the sintered NdFeB magnet is 7.572g / cm 3 .

[0100] Example 2

[0101] The only difference from Example 1 is that, in the hydrogen crushing step, 100 parts by weight of NdFeB quick-setting sheets are mixed with 30 parts by weight of pre-treated NdFeB magnet waste material. The other steps and parameters are the same as those in Example 1.

[0102] The magnetic properties and other impurity contents of the obtained sintered NdFeB magnets are shown in Table 1.

[0103] Comparative Example 1

[0104] The only difference from Example 1 is that in the hydrogen crushing step, the NdFeB quick-setting sheets and the pre-treated NdFeB magnet waste material are hydrogen crushed to obtain two coarse powders. Then, the two coarse powders are mixed (100 parts by weight of the coarse powder obtained from the NdFeB quick-setting sheets and 20 parts by weight of the coarse powder from the NdFeB magnet waste material) and then jet milled. The other steps and parameters are the same as those in Example 1.

[0105] The magnetic properties and other impurity contents of the obtained sintered NdFeB magnets are shown in Table 1.

[0106] Comparative Example 2

[0107] The only difference from Example 1 is that in the hydrogen crushing step, no pre-treated NdFeB magnet waste material is added. That is, the sintered NdFeB magnet is produced only from normal raw materials. The other steps and parameters are the same as those in Example 1.

[0108] The magnetic properties and other impurity contents of the obtained sintered NdFeB magnets are shown in Table 1.

[0109] Table 1

[0110]

[0111] Example 1 was repeated 10 times, and the resulting sintered NdFeB magnet had a remanence of 12.84-12.91 kGs, a coercive force of 13.61-13.67 kOe, and a squareness of 98.2-98.8%.

[0112] Thus, the remanence, coercive force and squareness of the sintered NdFeB magnet obtained by the method of the present invention are all high, and the repeatability is good. The performance of the sintered NdFeB magnet obtained by the method of the present invention is equivalent to or slightly higher than that of the sintered NdFeB magnet obtained without adding old materials (i.e., produced only by normal raw materials). Comparative Example 1 is different from the process of adding old NdFeB magnets of the present invention. Although the remanence and coercive force of the sintered NdFeB magnet obtained by Comparative Example 1 are equivalent to those of the present invention, its squareness is obviously lower.

[0113] The present invention is not limited to the above-mentioned embodiments. Without departing from the essential content of the present invention, any deformation, improvement and substitution that can be conceived by those skilled in the art shall fall within the scope of the present invention.

Claims

1. A method for recycling old NdFeB magnets, characterized in that: The steps include: 1) Prepare the ingredients according to the set formula and smelt to obtain NdFeB quick-setting sheets; 2) Mixing the NdFeB quick-setting sheet with the pretreated NdFeB magnet waste material to obtain a mixture; hydrogen crushing the mixture through hydrogen absorption and dehydrogenation processes to obtain NdFeB coarse powder; wherein the mass ratio of the pretreated NdFeB magnet waste material to the NdFeB quick-setting sheet is 5 to 40:100; 3) Grinding the NdFeB coarse powder by jet milling to obtain magnetic powder; 4) Pressing and sintering the magnetic powder to obtain a sintered NdFeB magnet.

2. The method according to claim 1, characterized in that The mass ratio of the pretreated NdFeB magnet waste material to the NdFeB quick-setting sheet is 15-30:

100.

3. The method according to claim 1, characterized in that The old NdFeB magnet materials before pretreatment include old finished materials with coating, old blank materials, black sheets and material skins.

4. The method according to claim 3, characterized in that The pretreated NdFeB magnet waste material is obtained by the following steps: (1) removing dirt or coating from the surface of the old NdFeB magnet material before pretreatment to obtain clean old NdFeB magnet material; (2) The clean NdFeB magnet waste material is coarsely crushed to obtain pretreated NdFeB magnet waste material with a particle size of 1 to 30 mm.

5. The method according to claim 4, characterized in that In step (1), clean NdFeB magnet waste material is obtained by any of the following methods: (1) Use a sandblasting machine to remove the dirt or coating on the surface of the old NdFeB magnet before pretreatment; (ii) Use silicon carbide or brown corundum as abrasive to remove dirt or coating on the surface of old NdFeB magnets before pretreatment; (3) Use pickling, water washing and drying in sequence to remove the dirt on the surface of the old NdFeB magnets before pretreatment.

6. The method according to claim 4, characterized in that In step (1), pickling, water washing and drying are sequentially adopted to remove dirt on the surface of the old NdFeB magnet material before pretreatment.

7. The method according to claim 4, characterized in that In step (2), a jaw crusher is used to coarsely crush the old clean NdFeB magnet material.

8. The method according to claim 1, characterized in that: In step 2), the hydrogen absorption pressure is 0.05-0.15 MPa, and the time is 2-4 h; the dehydrogenation temperature is 400-600° C., and the time is 5-12 h; the particle size of the NdFeB coarse powder is 10-300 μm; In step 3), the speed of the classifying wheel of the jet mill is 2600-2900 rpm; the D 50 3~5μm.

9. The method according to claim 1, characterized in that: In step 4), the sintering includes primary sintering and secondary sintering. The primary sintering temperature is 900-1100° C. and the time is 4-10 hours; the secondary sintering temperature is 450-550° C. and the time is 4-9 hours.

10. A sintered NdFeB magnet obtained by the method according to claim 1, characterized in that: Its squareness is greater than 98%.

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