A method for preparing NdFeB magnets using NdFeB waste powder

Abstract

The present invention provides a method for preparing NdFeB magnets using NdFeB waste powder, and relates to the technical field of NdFeB magnetic materials. Specifically, the method comprises the following steps: collecting the waste powder generated in the hydrogen crushing process of the NdFeB magnet production process according to the performance grade, dehydrogenating, adding antioxidant to mix, air flow grinding into fine powder, pressing and sintering, and then the NdFeB magnets can be prepared. The preparation process of the present invention is simple to operate, has low energy consumption, and is easy to control the production process. The waste in the production and processing is used as raw materials, and is recycled and reused to prepare NdFeB magnets with performance equivalent to that prepared by traditional processes, which can greatly reduce production costs and reduce waste emissions, and has the beneficial effects of energy saving, environmental protection, and green recycling.

Description

Technical Field

[0001] The invention belongs to the technical field of NdFeB magnetic materials, and in particular relates to a method for preparing a NdFeB magnet by utilizing NdFeB waste powder. Background Art

[0002] NdFeB permanent magnets are the most widely used rare earth magnets in the world due to their excellent magnetic properties. They are known as the "King of Magnets". They are used in electric vehicles and wind power generation motors to improve the efficiency of motors and drives.

[0003] However, in the production process of NdFeB permanent magnets, some waste will inevitably be produced. Among them, hydrogen crushing is a key process in the NdFeB magnetic material manufacturing industry. This process is to hydrogen crush the NdFeB casting into powder particles of a certain size. There are two main links in hydrogen crushing, one is hydrogen absorption and the other is dehydrogenation. During dehydrogenation, the excess hydrogen will be pumped away with the help of a vacuum system. Since it is inevitable that powder with too fine particle size will appear in the hydrogen crushing process, a part of the fine powder will move into the filter with the hydrogen gas flow in the dehydrogenation link and be separated from the hydrogen gas flow by the filter. We call this part of fine powder waste powder. When the dehydrogenation is completed, it will be found that the filter will intercept a small amount of waste powder. At the same time, because the filter cannot provide enough temperature, the waste powder is not completely dehydrogenated. How to deal with the large amount of waste powder generated has become a common problem faced by manufacturers.

[0004] At present, most manufacturers collect waste powder, burn it spontaneously and then sell it. This method of dealing with waste powder will make the production cost relatively high, the processing process will generate a lot of energy consumption, and the economic benefits are low.

[0005] In summary, how to develop a green and environmentally friendly method for treating NdFeB waste powder is an urgent problem to be solved by technicians in this field. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing NdFeB magnets using NdFeB waste powder. The waste powder generated during the hydrogen crushing process of the NdFeB magnet production process is collected and classified according to performance grades, dehydrogenated, mixed with antioxidants, air-milled into fine powder, pressed and sintered, so as to prepare NdFeB magnets.

[0007] Using waste materials from production and processing as raw materials and recycling them to prepare NdFeB magnets with performance equivalent to those prepared by traditional processes can greatly reduce production costs, reduce waste emissions, and have the beneficial effects of energy conservation, environmental protection, and green recycling.

[0008] To achieve the above object, the present invention provides a method for preparing NdFeB magnets using NdFeB waste powder, which specifically comprises the following steps:

[0009] S1 Collection and classification: Classify NdFeB waste powder according to performance grades, and seal different grades of NdFeB waste powder separately and place them in an oxygen-free environment protected by inert gas;

[0010] S2 dehydrogenation: vacuum the NdFeB waste powder after S1 classification in advance, then heat it to a certain temperature, keep it warm for dehydrogenation, and introduce argon gas after dehydrogenation to cool the material;

[0011] S3 mixing: mixing the NdFeB waste powder after dehydrogenation in S2 with the antioxidant;

[0012] S4 grinding: adding tributyl borate to the NdFeB waste powder after mixing in S3, mixing thoroughly and grinding;

[0013] S5 pressing: the fine NdFeB powder after S4 grinding is oriented in a magnetic field and cold isostatically pressed;

[0014] S6 sintering: The S5 pressed green sheet is sintered and tempered twice to prepare NdFeB magnets.

[0015] In a preferred embodiment, in step S1, the inert gas is nitrogen or argon.

[0016] In a preferred embodiment, in step S2, the pre-vacuum treatment is to reduce the vacuum degree of the reaction tank to below 5Pa; the certain temperature is 600-620°C, and the insulation time is 3-5h; the condition for the end of dehydrogenation is: insulation at 600-620°C for more than 3h and the vacuum degree of the reaction tank is below 10Pa.

[0017] In a preferred embodiment, in step S2, the argon pressure ranges from 0.01 to 0.03 MPa, and the next step can be started when the material temperature after cooling is below 60°C.

[0018] In a preferred embodiment, in step S3, the antioxidant is 5# NdFeB special antioxidant, and the weight ratio of the antioxidant to NdFeB waste powder is (0.03%-0.06%):1.

[0019] In a preferred embodiment, in step S4, the grinding is to grind the NdFeB waste powder into fine powder with an average particle size of 2.7-3 μm using a jet mill.

[0020] In a preferred embodiment, in step S4, the weight ratio of tributyl borate to NdFeB waste powder is (0.03%-0.06%):1.

[0021] In a preferred embodiment, in step S5, the magnetic field strength is above 1.3 T, the cold isostatic pressing pressure ranges from 160 to 450 MPa, and the holding time is 180 seconds.

[0022] In a preferred embodiment, in step S6, the sintering temperature is 1080-1120°C, and the sintering holding time is 240-390min; the primary tempering temperature is 940°C, and the time is 210-240min; the secondary tempering temperature is 580-640°C, and the time is 420-540min; and the vacuum is less than 0.5Pa during the entire sintering process.

[0023] Compared with the prior art, the method of preparing NdFeB magnets by using NdFeB waste powder of the present invention has the following advantages:

[0024] 1. In the present invention, the recycling of NdFeB waste powder can be completed only through the steps of collection by performance grade, dehydrogenation, adding antioxidant to mix, air flow grinding into fine powder, pressing and sintering, which can greatly reduce production costs, reduce waste emissions, and has the beneficial effects of energy saving, environmental protection and green recycling.

[0025] 2. According to statistics from actual applications, in the process of preparing NdFeB magnets in the prior art, the yield rate is 99.83%, and 0.17% is waste powder. The present invention provides a recycling method that can convert 0.17% of waste powder into qualified powder for use, and the overall yield rate reaches 100%. Moreover, the performance of the NdFeB magnets prepared by the present invention is consistent with that of the NdFeB magnets prepared without waste powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] These and / or other aspects and advantages of the present invention will become more clear and easier to understand from the following detailed description of the embodiments of the present invention in conjunction with the accompanying drawings, in which:

[0027] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0028] The present invention provides a method for preparing a NdFeB magnet by using NdFeB waste powder, which specifically comprises the following steps:

[0029] S1 Collection and classification: Classify NdFeB waste powder according to performance grades, and seal different grades of NdFeB waste powder separately and place them in an oxygen-free environment protected by inert gas;

[0030] In a preferred embodiment, the NdFeB waste powder comes from the fine powder retained by the filter in the dehydrogenation process, which is classified and collected according to the performance grade standard in GB / T13560-2000.

[0031] In a preferred embodiment, in step S1, the inert gas is nitrogen or argon. The inert gas protection can prevent the NdFeB waste powder from being oxidized and affecting the dehydrogenation effect. The seal can provide an oxygen-free space for the NdFeB waste powder. There are no special requirements for the sealing materials and devices, which can be selected by conventional methods by technicians in this field.

[0032] S2 dehydrogenation: vacuumize the NdFeB waste powder after S1 classification in advance, then heat it to a certain temperature, keep it warm for dehydrogenation, and introduce argon gas after dehydrogenation to cool the material;

[0033] In a preferred embodiment, the S1 classified NdFeB waste powder is placed in a reaction tank, the vacuum degree of the reaction tank is controlled below 5Pa in advance, and then the reaction tank is heated to 600-620°C and kept warm for 3-5h. After being kept warm at 600-620°C for more than 3h and the vacuum degree of the reaction tank is below 10Pa, the dehydrogenation can be stopped, and argon gas is introduced into the reaction tank. The pressure range of argon gas is 0.01-0.03MPa. The next step can be started when the material temperature in the reaction tank is below 60°C.

[0034] In this step, there is no special requirement for the vacuum pumping device, which can be selected conventionally by a person skilled in the art; preferably, a Roots vacuum pump can be selected.

[0035] Keeping the temperature at 600-620℃ for 3h can remove the hydrogen content in the waste powder and reduce the energy waste caused by long-term treatment. Controlling the argon pressure range can help cool the powder without other refrigeration operations by only introducing argon. Controlling the temperature of the reaction tank material below 60℃ can prevent the powder from oxidizing and burning during discharge, increasing the safety of operation.

[0036] In this step, there is no special requirement for the material cooling method, which can be selected by the technicians in this field. Preferably, after filling with argon, the furnace door is opened for self-cooling for 60 minutes. After the self-cooling is completed, the reaction tank can be water-cooled again. During the cooling process, ensure that the pressure in the tank is ≥0.02MPa.

[0037] S3 mixing: mixing the NdFeB waste powder after dehydrogenation in S2 with the antioxidant;

[0038] In a preferred embodiment, the antioxidant is a 5# NdFeB special antioxidant, and the weight ratio of the antioxidant to the NdFeB waste powder is (0.03%-0.06%): 1. There are no special requirements for the mixing device and method, and the mixing method can be selected by a technician in this field. Preferably, a special mixing rack can be selected to mix for 1-2 hours until the NdFeB waste powder and the antioxidant are fully mixed.

[0039] S4 grinding: adding tributyl borate to the NdFeB waste powder after mixing in S3, mixing thoroughly and grinding;

[0040] In a preferred embodiment, the grinding is to grind the NdFeB waste powder into fine powder with an average particle size of 2.7-3.0 μm by using a jet mill, add tributyl borate to the waste powder, and the weight ratio of tributyl borate to NdFeB waste powder is (0.03%-0.06%): 1, and mix the tributyl borate and NdFeB waste powder by any method known to those skilled in the art; preferably, a special mixing rack can be selected to mix for 6-8 hours, until the NdFeB waste powder and tributyl borate are fully mixed.

[0041] Adding antioxidants is to protect the powder from oxidation during canning, airflow grinding and molding. If oxidation occurs, the performance of the NdFeB product will be unqualified; adding tributyl borate can increase the fluidity of the powder and facilitate molding; adding too much tributyl borate will affect molding and size, and adding too little will not increase the fluidity of the powder; and the particle size distribution of the powder will affect the consistency of product performance and the sintering phase. Research has found that after sintering, fine powder with a particle size distribution of 2.7-3.0μm has the best product performance consistency and improves the magnetic properties of NdFeB products.

[0042] S5 pressing: the fine NdFeB powder after S4 grinding is oriented in a magnetic field and cold isostatically pressed;

[0043] In a preferred embodiment, the magnetic field strength is above 1.3 T, the cold isostatic pressing pressure ranges from 160 to 450 MPa, and the holding time is 180 seconds.

[0044] S6 sintering: The S5 pressed green sheet is sintered and tempered twice to prepare NdFeB magnets.

[0045] In a preferred embodiment, the formed green compact is sequentially sintered at 1080-1120°C with a holding time of 240-390 min; after sintering, a primary tempering treatment is performed at 940°C for 210-240 min and a secondary tempering treatment is performed at 580-640°C for 420-540 min.

[0046] Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art, and the raw materials used are all commercially available products.

[0047] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0048] In the embodiments of the present invention, the antioxidant used is 5# antioxidant purchased from Tianjin Yuesheng New Materials Research Institute; the tributyl borate used is purchased from Suqian Nanxiang Chemical Manufacturing Co., Ltd.

[0049] Example 1

[0050] Raw materials: 40H performance neodymium ferromagnetic waste powder;

[0051] Preparation method:

[0052] S1 collects the 40H waste powder produced during the hydrogen crushing process and stores it in an argon environment. When the weight of the waste powder reaches 600 kg, it is loaded into the reaction tank.

[0053] S2 pre-controls the vacuum degree of the reaction tank below 5Pa, then heats the reaction tank to 610℃, starts the Roots pump to keep it warm for dehydrogenation. When the reaction tank is kept warm at 610℃ for more than 3 hours and the vacuum degree is below 10Pa, dehydrogenation can be stopped. Introduce argon into the reaction tank, keep the argon pressure range at 0.01-0.03Mpa, and after filling with argon, open the furnace door for self-cooling for 60 minutes. After self-cooling, water-cool the reaction tank, and ensure that the pressure in the tank is ≥0.02MPa during the cooling process.

[0054] When the material temperature in the S3 reaction tank is below 60°C, the dehydrogenated waste powder is placed in a powder transfer container, and an antioxidant is added at 0.03% of the mass of the waste powder, that is, 0.18 kg of antioxidant is added, and the waste powder and antioxidant are fully mixed for 2 hours.

[0055] S4: Add 0.04% tributyl borate based on the mass of the waste powder, i.e. 0.24 kg tributyl borate, to the mixed waste powder, mix thoroughly, place in a jet mill device for powder making, grind to fine powder with an average particle size of 2.9 μm, and continue mixing for 8 hours after the jet milling is completed.

[0056] S5 places the mixed waste powder in a magnetic field for orientation and isostatic pressing, the magnetic field strength is 1.3T, the isostatic pressing pressure is 190MPa, and the isostatic pressing time is 35 seconds to form a compact.

[0057] S6: The formed green compact is subjected to sintering at 1120°C, holding for 240 min, primary tempering at 940°C for 210 min, and secondary tempering at 620°C for 420 min under a vacuum degree of 0.4 Pa, thereby obtaining a NdFeB magnet.

[0058] The performance indicators of the prepared NdFeB magnets are as follows:

[0059] The residual magnetic induction intensity (Br) of the magnet is 1.23-1.245T, the intrinsic coercive force (Hcj) is 15.2-15.8KOe, and the HK is 14.0-15.0KOe.

[0060] Example 2

[0061] Raw materials: N40 neodymium ferromagnetic waste powder;

[0062] Preparation method:

[0063] S4: Add 0.035% tributyl borate of the mass of the waste powder, i.e. 0.21 kg tributyl borate, to the mixed waste powder, mix thoroughly, place in a jet mill device for powder making, grind to fine powder with an average particle size of 2.9 μm, and continue mixing for 8 hours after the jet milling is completed.

[0064] In S6, the formed green compact is subjected to sintering at 1080°C, holding time of 390 min, primary tempering treatment at 940°C for 210 min, and secondary tempering treatment at 620°C for 420 min under vacuum condition of 0.3 Pa, thereby obtaining a NdFeB magnet.

[0065] The performance indicators of the prepared NdFeB magnets are as follows:

[0066] The residual magnetic induction intensity (Br) of the magnet is ≥1.29T, the intrinsic coercive force (Hcj) is ≥12.00KOe, and HK is ≥10.50KOe.

[0067] Comparative Example 1

[0068] Raw materials: 40H performance neodymium ferromagnetic raw materials;

[0069] Preparation method:

[0070] S1 puts 600Kg of smelted raw materials, 40H performance neodymium ferromagnetic flakes, into the reaction tank.

[0071] S2 pre-controls the vacuum degree of the reaction tank below 5Pa, then heats the reaction tank to 350℃ and keeps it warm for ≥2 hours. After preheating, start hydrogen filling. When the pressure of the reaction tank rises to positive pressure, keep the hydrogen pressure range at 0.04-0.05MPa. The time from start to finish of hydrogen filling is 3.5 hours. After hydrogen filling, prepare for dehydrogenation, vacuumize and start the heating system at the same time, heat the reaction tank to 610℃, start the Roots pump when the temperature rises to 610℃ and keep it below 10Pa for 4 hours. After dehydrogenation, turn on the argon button to fill the reaction tank with argon, keep the argon pressure range at 0.01-0.03MPa, and open the furnace door for self-cooling for 60 minutes. After self-cooling, water-cool the reaction tank, and ensure that the pressure in the tank is ≥0.02Mpa during the cooling process.

[0072] S3 When the material temperature in the reaction tank is below 60°C, the hydrogen-decomposed powder is placed in a powder transfer container, and an antioxidant is added at 0.03% of the weight of the powder, that is, 0.18 kg of antioxidant is added, and the materials are fully mixed for 2 hours.

[0073] S4: The mixed powder is placed in a jet mill to grind into fine powder with an average particle size of 2.9 μm. After the jet milling is completed, 0.045% of tributyl borate by weight of the powder, i.e., 0.27 kg of tributyl borate, is added to the powder tank and mixed thoroughly for 8 hours.

[0074] S5: Orient the mixed powder in a magnetic field and perform isostatic pressing. The magnetic field strength is 1.3 T, the isostatic pressing pressure is 190 MPa, and the isostatic pressing time is 35 seconds to form a compact.

[0075] S6 makes the formed compacts undergo vacuum degree of 0.4Pa, sintering at 1120°C, holding time of 390min, primary tempering at 940°C for 210min, and secondary tempering at 630°C for 240min, to obtain NdFeB magnets.

[0076] The performance indicators of the prepared NdFeB magnets are as follows:

[0077] The residual magnetic induction intensity (Br) of the magnet is ≥1.24T, the intrinsic coercive force (Hcj) is 15.5-16.5KOe, HK14.5-15.5KOe.

[0078] The foregoing description of specific exemplary embodiments of the present invention is for the purpose of illustration and demonstration. These descriptions are not intended to limit the present invention to the precise form disclosed, and it is clear that many changes and variations can be made based on the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical application, so that those skilled in the art can realize and utilize various different exemplary embodiments of the present invention and various different selections and changes. The scope of the present invention is intended to be limited by the claims and their equivalents.

Claims

1. A method for preparing NdFeB magnets using NdFeB waste powder, characterized in that: The specific steps include: S1 Collection and classification: Classify NdFeB waste powder according to performance grades, and seal different grades of NdFeB waste powder separately and place them in an oxygen-free environment protected by inert gas; S2 dehydrogenation: vacuumize the NdFeB waste powder after S1 classification in advance, then heat it to a certain temperature, keep it warm for dehydrogenation, and introduce argon gas after dehydrogenation to cool the material; S3 mixing: mixing the NdFeB waste powder after dehydrogenation in S2 with the antioxidant; S4 grinding: adding tributyl borate to the NdFeB waste powder after mixing in S3, mixing thoroughly and grinding; S5 pressing: the fine NdFeB powder after S4 grinding is oriented in a magnetic field and cold isostatically pressed; S6 sintering: Sintering and twice tempering the green compact after S5 pressing to prepare NdFeB magnets; Among them, in step S2, the pre-vacuum treatment is that the vacuum degree of the reaction tank is below 5Pa; the certain temperature is 600-620°C, and the insulation time is 3-5h; the condition for the end of the dehydrogenation is: the temperature is kept at 600-620°C for more than 3h and the vacuum degree of the reaction tank is below 10Pa; In step S2, the argon pressure range is 0.01-0.03 MPa, and the material temperature after cooling is below 60° C. to start the next step; In step S4, the grinding is to grind the NdFeB waste powder into fine powder with an average particle size of 2.7-3 μm by using a jet mill; In step S5, the magnetic field strength is above 1.3 T, the cold isostatic pressing pressure ranges from 160 to 450 MPa, and the holding time is 180 seconds; In step S6, the sintering temperature is 1080-1120°C, and the sintering holding time is 240-390min; the primary tempering temperature is 940°C, and the time is 210-240min; the secondary tempering temperature is 580-640°C, and the time is 420-540min; and the vacuum is less than 0.5Pa during the entire sintering process.

2. The method for preparing NdFeB magnets using NdFeB waste powder as claimed in claim 1, characterized in that: In step S1, the inert gas is nitrogen or argon.

3. The method for preparing NdFeB magnets using NdFeB waste powder as claimed in claim 1, characterized in that: In step S3, the antioxidant is 5# NdFeB special antioxidant, and the weight ratio of the antioxidant to NdFeB waste powder is (0.03%-0.06%):

1.

4. The method for preparing NdFeB magnets using NdFeB waste powder as claimed in claim 1, characterized in that: In step S4, the weight ratio of tributyl borate to NdFeB waste powder is (0.03%-0.06%):1.

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