Batch production method of bonded neodymium-iron-boron magnet

Abstract

The invention provides a batch production method for bonded neodymium-iron-boron magnets, and belongs to the technical field of permanent magnet materials, and the method specifically comprises the following steps: dissolving epoxy resin in an alcohol acetone solvent to prepare a glue solution, kneading the glue solution with neodymium-iron-boron magnetic powder which is subjected to forward and reverse rotation in a kneading machine, and screening and crushing to obtain mixed glue powder; adding the mixed rubber powder into a pressing mold, and carrying out compression molding to obtain a blank; the blanks are placed on a carrying disc to be cured in batches; the blank is placed on a numerical control vehicle for magnet end face, inner hole and chamfer machining, and a negative pressure dust suction device and a wet dust removal device are arranged; fixing the workpiece on a frame type cleaning tool for ultrasonic cleaning; performing double-layer electrostatic spraying on the surface of the workpiece to form a composite coating of which the bottom layer is epoxy resin coating and the surface layer is polyurethane coating; and assembling and magnetizing. According to the invention, the product consistency, economical efficiency and production efficiency in batch production are improved.

Description

Technical Field

[0001] This application relates to the field of permanent magnet materials technology, and in particular to a method for batch production of bonded NdFeB magnets. Background Technology

[0002] With the development of third-generation permanent magnet materials, neodymium iron boron (NdFeB) magnets have been widely used. Different application environments impose varying performance requirements on them. One application requires a magnet with high consistency, demanding that mass-produced products have a density fluctuation range of ≤±0.5% and a dimensional fluctuation range of ≤±0.2%. The product surface must undergo anti-corrosion treatment, eliminating weak points such as traditional spray coating adhesion points. A 500-hour neutral salt spray test must not reveal any surface quality issues such as rust. After magnetization, the magnetic eccentricity (the deviation between the magnet's geometric axis and the magnetic center) must be extremely high, ≤0.15mm. The resulting magnet components must exhibit high consistency in magnetic properties, with a magnetic pull range of ±0.2N for specific components. The magnets must demonstrate good magnetic stability, with a magnetic pull loss of ≤0.6% after 200 hours of treatment at 60℃. Furthermore, this magnet requires high-efficiency, mass production to ensure good quality in terms of geometric dimensions, density, appearance, and magnetic properties, resulting in a high product qualification rate and good consistency.

[0003] Therefore, it is necessary to study a batch production process for bonded NdFeB magnets that can produce large-size bonded NdFeB magnets with excellent performance and stable and reliable quality, while ensuring product consistency, economy and production efficiency in batch production. Summary of the Invention

[0004] In view of this, embodiments of this application provide a batch production method for bonded NdFeB magnets, which at least partially solves the problems of poor product consistency, low production efficiency, and difficulty in meeting stringent performance requirements in the batch production process of bonded NdFeB magnets in the prior art.

[0005] This application provides a method for batch production of bonded NdFeB magnets, including:

[0006] Mixing: Epoxy resin is dissolved in alcohol and acetone to prepare a glue solution. The glue solution is then kneaded with neodymium iron boron magnetic powder that has been rotated in both directions in a kneader. The mixture is then sieved and crushed to obtain mixed glue powder. Compression molding: The mixed powder is added to the cavity of the compression mold and molded to obtain a blank; Curing: The blanks are placed on a carrier plate with evenly distributed holes for batch curing; Shaping: The cured blank is placed on a CNC lathe to process the end face, inner hole and chamfer of the magnet to obtain the workpiece. The CNC lathe is equipped with a negative pressure dust collection device and a wet dust removal device. Ultrasonic cleaning: The workpiece is fixed on a frame-type cleaning fixture for ultrasonic cleaning; Electrostatic spraying: Double-layer electrostatic spraying is performed on the surface of the cleaned workpiece to form a composite coating with an epoxy resin coating as the bottom layer and a polyurethane coating as the top layer. Assembly and magnetization: The electrostatically sprayed workpiece is assembled and magnetized.

[0007] According to a specific implementation of this application, the volume ratio of alcohol to acetone in the alcohol-acetone solvent is 1:1 to 1:1.2, and the mass ratio of epoxy resin to alcohol-acetone solvent is 1:1.5 to 1:2.

[0008] According to a specific implementation of an embodiment of this application, the kneading of the adhesive liquid with neodymium iron boron magnetic powder that has undergone forward and reverse rotation in a kneader includes: Add neodymium iron boron magnetic powder into the kneader and repeat the reverse, stop, and forward rotation process three times. Then, the neodymium iron boron magnetic powder and the adhesive liquid are mixed thoroughly in a kneader by first reversing the rotation and then rotating it forward. When the powder increases in volume and foams, reverse the kneading process. Once the powder is semi-dry, alternate between forward and reverse rotation until the solvent has completely evaporated. Throughout the kneading process, the kneading machine cavity is kept at a temperature below 40°C for heating and drying. The volatilized alcohol and acetone gases are collected and recovered by a condenser at a temperature of -50°C to -40°C using a sealed negative pressure method. The recovery pressure is 0.1MPa to 0.3MPa.

[0009] According to a specific implementation of an embodiment of this application, the sequential screening and crushing includes: Screening is performed using a gyratory screen with 50 mesh upper and 500 mesh lower screens. The crushing process is carried out using a cylindrical vibratory mill.

[0010] According to one specific implementation of this application, the compression molding adopts an automatic weighing and feeding method and an automatic floating die pressing method. The pressing die of the automatic floating middle die pressing method includes a mandrel, a middle die and a punch. The mandrel and the middle die are made of tungsten steel with a hardness greater than 89HRC, and the punch is made of alloy steel with a hardness of 62~68HRC. The single-sided gap between the punch and the middle die mandrel is 0.01mm, and an clearance zone is set below the effective section of the punch. The automatic weighing and feeding system adopts a dual-channel spiral feeding method with large and small channels. The servo motor first controls the large channel to weigh the powder to 92%~98% of the target value, then stops and switches to the small channel to continue weighing with high precision to the target value, with a weighing accuracy of ±0.2%. The feeding system uses a double-splitting conical hopper with a middle partition. After the bottom cover is opened, the powder leaks into the mold cavity formed by the middle mold and the mandrel.

[0011] According to a specific implementation of an embodiment of this application, the negative pressure dust collection device and the wet dust removal device are connected by a pipe. The negative pressure dust collection device includes a negative pressure fan and a suction nozzle. The negative pressure fan is installed on the pipe, and the suction nozzle is installed at one end of the pipe. The suction nozzle is fixed by a fixing clamp and has an inclined dust collection port. The wet dust removal device includes a water tank and a cover plate installed on the upper side of the water tank. The cover plate has an exhaust hole and a pipe inlet, and the other end of the pipe is connected to the pipe inlet.

[0012] According to a specific implementation of an embodiment of this application, the ultrasonic cleaning includes sequentially performing rinsing, cleaning, rinsing and drying. The rinsing process employs a multi-nozzle, multi-angle high-pressure rinsing method. A negative pressure condensation pipe is installed above the rinsing tank, through which the volatile cleaning agent enters the return tank. The cleaning process involves immersing the workpiece in a hydrocarbon-based cleaning agent for vortex-type turbulent cleaning, followed by ultrasonic cleaning, with a cleaning time of 1-2 minutes.

[0013] According to a specific implementation of this application, the epoxy resin coating in the electrostatic spraying has a macromolecular resin content of 30%~45%, a resistivity of 5MΩ·cm~20MΩ·cm, and a curing temperature of 210℃±5℃; the curing temperature of the polyurethane coating is 230℃±5℃.

[0014] According to a specific implementation of the embodiments of this application, during the electrostatic spraying process, the bottom of the tooling is designed to have a copper plate in contact with the conveyor roller, the conveyor roller is connected to the copper frame through a wire, and the copper frame is buried below the ground surface. The electrostatic spraying coating uses a fully automatic feeding method. A conical hopper with a vibrator is used at the top, and a pneumatic butterfly valve is installed at the mouth of the conical hopper. A weighing sensor is installed at the bottom of the feeding box. When the quality of the coating in the feeding box is lower than the preset lower limit, the pneumatic butterfly valve is opened to feed the coating. When the quality of the coating in the feeding box reaches the preset upper limit, the pneumatic butterfly valve is closed.

[0015] According to a specific implementation of an embodiment of this application, the step of placing the blank on a carrier disk with evenly distributed holes for batch curing includes: Multiple blanks are placed on multiple carriers with evenly distributed holes; Multiple trays are placed on a movable multi-layer frame, with a spacing of more than 150mm between adjacent trays; The multi-layer frame is moved to an electric heating drying oven for curing. The curing temperature is 195~205℃ and the curing time is 2~4h. The compressive strength of the cured blank is greater than or equal to 300MPa.

[0016] Beneficial effects: The batch production method for bonded NdFeB magnets in this application includes seven core steps: mixing, pressing, curing, shaping, ultrasonic cleaning, electrostatic spraying, and assembly magnetization, forming a complete batch production process. In the mixing stage, forward and reverse kneading ensures uniform mixing of magnetic powder and adhesive, while sieving and crushing processes guarantee consistent particle size of the mixed powder, laying a good foundation for subsequent pressing. During pressing, the precise design of the mold cavity effectively controls the dimensional accuracy of the blank. During curing, the evenly distributed perforated carrier plate ensures uniform heating of the blank, improving curing quality and efficiency. The shaping stage employs CNC machining technology, combined with negative pressure dust collection and wet dust removal devices, ensuring processing accuracy while reducing dust pollution. Ultrasonic cleaning thoroughly removes oil and impurities from the workpiece surface, providing a clean surface for electrostatic spraying. The double-layer electrostatic spraying process gives the coating good adhesion and corrosion resistance; the bottom epoxy resin ensures bonding strength with the workpiece, while the top polyurethane layer enhances the coating's wear resistance and weather resistance. The entire production method has closely integrated processes and controllable process parameters, making it suitable for large-scale mass production of bonded NdFeB magnets. It can stably manufacture magnet products with excellent performance and high dimensional accuracy. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A flowchart illustrating a batch production method for bonded NdFeB magnets according to an embodiment of the present invention; Figure 2 A microscopic view of the structure of the mixed powder according to an embodiment of the present invention; Figure 3 This is a schematic diagram of a pressing mold according to an embodiment of the present invention; Figure 4 This is a schematic diagram of a carrier disk according to an embodiment of the present invention; Figure 5 A perspective view of a multi-layer vehicle frame according to an embodiment of the present invention; Figure 6 A front view of a multi-layer vehicle frame according to an embodiment of the present invention; Figure 7 A side view of a multi-layer vehicle frame according to an embodiment of the present invention; Figure 8 This is a schematic diagram of a negative pressure dust collection device and a wet dust removal device according to an embodiment of the present invention; Figure 9 This is a schematic diagram of a cleaning device according to an embodiment of the present invention; Figure 10 This is a microscopic cross-sectional view of a double-layer composite coating according to an embodiment of the present invention.

[0019] In the diagram: 1. Dust; 2. Sloping dust inlet; 3. Nozzle; 4. Fixing clamp; 5. Pipeline; 6. Negative pressure fan; 7. Water tank; 8. Water; 9. Cover plate; 10. Exhaust vent; 11. Pipe inlet; 12. Vibrating plate; 13. Workpiece; 14. Hanger; 20. Powder; 21. Mandrel; 22. Mold; 23. Punch; 24. Air gap. Detailed Implementation

[0020] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0021] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this application, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0023] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application. The illustrations only show the components related to this application and are not drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0024] Furthermore, specific details are provided in the following description to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that the described aspects can be practiced without these specific details.

[0025] This application provides a method for batch production of bonded NdFeB magnets, as described below. Figures 1 to 10 Provide a detailed description.

[0026] In one embodiment, refer to Figure 1 A method for batch production of bonded NdFeB magnets includes the following steps: Step S101, Mixing: Dissolve epoxy resin in alcohol and acetone to prepare a glue solution. Mix the glue solution with neodymium iron boron magnetic powder that has been rotated in both directions in a kneader. Then, sieve and crush the mixture to obtain mixed glue powder. Step S102, Compression Molding: Add the mixed powder into the cavity of the compression mold for compression molding to obtain a blank; Step S103, Curing: Place the blanks on a carrier plate with evenly distributed holes for batch curing; Step S104, Shaping: Place the cured blank on a CNC lathe to process the magnet end face, inner hole and chamfer to obtain workpiece 13. The CNC lathe is equipped with a negative pressure dust collection device and a wet dust removal device. Step S105, Ultrasonic cleaning: Fix the workpiece 13 on the frame-type cleaning fixture for ultrasonic cleaning; Step S106, electrostatic spraying: Double-layer electrostatic spraying is performed on the surface of the cleaned workpiece 13 to form a composite coating with an epoxy resin coating as the bottom layer and a polyurethane coating as the top layer. Step S107, Assembly and Magnetization: Assemble and magnetize the electrostatically sprayed workpiece.

[0027] This embodiment includes seven core steps: mixing, pressing, curing, shaping, ultrasonic cleaning, electrostatic spraying, and assembly magnetization, forming a complete mass production process. In the mixing stage, forward and reverse kneading ensures uniform mixing of magnetic powder and adhesive, while sieving and crushing processes guarantee consistent particle size of the mixed powder, laying a good foundation for subsequent pressing. During pressing, the precise design of the mold cavity effectively controls the dimensional accuracy of the blank. During curing, the evenly distributed perforated carrier plate ensures uniform heating of the blank, improving curing quality and efficiency. The shaping stage employs CNC machining technology, combined with negative pressure dust collection and wet dust removal devices, ensuring processing accuracy while reducing dust pollution. Ultrasonic cleaning thoroughly removes oil and impurities from the surface of workpiece 13, providing a clean surface for electrostatic spraying. The double-layer electrostatic spraying process gives the coating excellent adhesion and corrosion resistance; the bottom epoxy resin ensures bonding strength with workpiece 13, while the top polyurethane layer enhances the coating's wear resistance and weather resistance. The entire production method has closely integrated processes and controllable process parameters, making it suitable for large-scale mass production of bonded NdFeB magnets. It can stably manufacture magnet products with excellent performance and high dimensional accuracy.

[0028] Furthermore, the volume ratio of alcohol to acetone in the alcohol-acetone solvent is 1:1 to 1:1.2, and the mass ratio of epoxy resin to alcohol-acetone solvent is 1:1.5 to 1:2.

[0029] In this embodiment, a mixed solvent of alcohol and acetone is used to dissolve the epoxy resin. On the one hand, the mixed solvent has a 100% solubility for the epoxy resin powder. On the other hand, it can significantly reduce the amount of acetone, a controlled material, used, and reduce production costs.

[0030] Furthermore, the kneading of the adhesive with neodymium iron boron magnetic powder that has undergone forward and reverse rotation in a kneader includes: Add neodymium iron boron magnetic powder into the kneader and repeat the reverse, stop, and forward rotation process three times. Then, the neodymium iron boron magnetic powder and the adhesive liquid are mixed thoroughly in a kneader by first reversing the rotation and then rotating it forward. When powder 20 shows signs of increasing volume and foaming, reverse the kneading process. After the powder is half dry, alternate between forward and reverse rotation until the solvent has completely evaporated. Throughout the kneading process, the kneading machine cavity is kept at a temperature below 40°C for heating and drying. The volatilized alcohol and acetone gases are collected and recovered by a condenser at a temperature of -50°C to -40°C using a sealed negative pressure method. The recovery pressure is 0.1MPa to 0.3MPa.

[0031] Furthermore, the sequential screening and crushing process includes: Screening is performed using a gyratory screen with 50 mesh upper and 500 mesh lower screens. The crushing process is carried out using a cylindrical vibratory mill.

[0032] In specific implementation, neodymium iron boron magnetic powder is first added to a kneader and reversed for 5 minutes, stopped for 10 minutes, and then forward for 1 minute, repeated 3 times. Then, the magnetic powder is thoroughly mixed with the adhesive solution prepared in step S101 in the kneader, reversed for 5 minutes, then forward for 60 minutes. When powder 20 shows signs of volume increase and foaming, reverse kneading is performed. After powder 20 is semi-dry, forward and reverse kneading is alternated for 5 minutes, then stopped for 30 minutes until the solvent has completely evaporated. Throughout the process, a negative pressure suction device is needed to maintain negative pressure, promptly sucking away the evaporated alcohol and acetone for collection and recovery. The recovery pressure is 0.1MPa~0.3MPa. The alcohol and acetone gas is condensed in a (-50~-40)℃ condenser, ensuring a safe and environmentally friendly production process. The recovered alcohol and acetone can be reused after treatment, reducing production costs. The kneader chamber is kept at a low temperature (below 40℃) for heating and drying.

[0033] In this embodiment, the magnetic powder itself is rotated forward and backward before the adhesive is added. This forces the polygonal NdFeB powder particles generated by rapid quenching to rub, collide, and grind against each other, blunting and rounding the sharp edges and corners. This improves the flowability of the powder and reduces the bridging effect caused by powder accumulation, thereby increasing the powder's bulk density and flowability. This can reduce the powder pressing force by more than 15%, significantly reducing the pressing force and extending the life of the pressing mold.

[0034] Furthermore, during the sieving process, the dried powder is sieved through a vibrating screen, and the feeding process is carried out in a suitable and uniform manner, selecting powder 20 with a particle size between 50 and 500 mesh for later use. In this embodiment, powder 20 with a suitable particle size distribution is selected for pressing and molding. On the one hand, this avoids excessive large particles in powder 20, which may cause segregation, and on the other hand, it removes ultrafine powder below 500 mesh. Experiments and analysis have shown that ultrafine powder contains a large number of colloidal particles, which leak into the mold gaps during the pressing process, easily causing ultrafine powder to stick to the mold wall, thereby scratching the mold.

[0035] The crushing process involves placing large, unsieving powder particles 20 into a cylindrical vibratory mill for crushing, followed by re-sieving until all large powder particles 20 have passed through the sieve. The cylindrical vibratory mill is ideal for wet-mixing bonded NdFeB magnetic powder, as it can break up large agglomerates and significantly reduce the sharp angles of the powder particles 20, improving their pressing performance.

[0036] The mixed powder formed by the above mixing process has a uniform colloid coating on the surface of the magnetic powder, such as... Figure 2 As shown. Loose bulk density > 2.5 g / cm³ 3 It has a flowability of <50s / 25g and excellent pressing performance.

[0037] Therefore, the powder 20 formed by the processes of steps S101 and S102 has excellent pressing performance, low pressing force, uniform magnet density, and uniform magnetic properties.

[0038] Furthermore, the compression molding process employs an automatic weighing and feeding system and an automatic floating die pressing method. The pressing die of the automatic floating middle die pressing method includes a mandrel 21, a middle die 22 and a punch 23. The mandrel 21 and the middle die 22 are made of tungsten steel with a hardness greater than 89HRC, and the punch 23 is made of alloy steel with a hardness of 62~68HRC. The single-sided gap between the punch 23 and the middle die 22 and the mandrel 21 is 0.01mm. An clearance zone is set below the effective section of the punch 23. The automatic weighing and feeding system adopts a dual-channel spiral feeding method with large and small channels. The servo motor first controls the large channel to weigh the powder to 92%~98% of the target value, then stops and switches to the small channel to continue weighing with high precision to the target value, with a weighing accuracy of ±0.2%. The feeding system uses a double-splitting conical hopper with a middle partition. After the bottom cover is opened, the powder falls into the mold cavity formed by the middle mold 22 and the core rod 21. Then, a rake-shaped brush head is used to rotate and level the powder, ensuring the parallelism of the product.

[0039] In this embodiment, the pressing process is a compression molding method. The weighing accuracy is not less than ±0.2%. After the powder 20 is added to the mold cavity, it is pressed using a semi-automatic floating middle mold pressing method. The press adopts a servo closed-loop control system, and the pressing pressure fluctuation range is ±2%. During the pressing process, the blank first undergoes top pressing, then bottom pressing to ensure uniform blank density. After holding the pressure for 5-8 seconds, it is automatically demolded. The pressing mold material: the mandrel 21 and the middle mold 22 are made of tungsten steel with a hardness >89HRC, and the punch 23 is made of alloy steel with a hardness of 62-68HRC, forming a hardness gradient. The structure of the pressing mold is as follows: Figure 3 As shown, the single-sided gap between the punch 23 and the mandrel 21 of the die 22 is 0.01mm (as shown). Figure 3 An air gap 24 is provided in the middle, and an air-avoiding zone is set below the effective section of the punch 23 to facilitate the discharge of ultrafine powder.

[0040] In this embodiment, the automatic weighing and feeding system adopts a dual-channel feeding device. The large channel diameter can be selected as 30mm, which is used for rapid feeding to reach the set value. The small channel feeding diameter can be selected as 5mm~6mm, which is used for final precise control. The control accuracy can reach ±0.1g. This design ensures both feeding efficiency and feeding accuracy.

[0041] Furthermore, the step of placing the blank on a carrier disk with evenly distributed holes for batch curing includes: Multiple blanks are placed on multiple carriers with evenly distributed holes; Multiple trays are placed on a movable multi-layer frame, with a spacing of more than 150mm between adjacent trays; The multi-layer frame is moved to an electric heating drying oven for curing. The curing temperature is 195~205℃ and the curing time is 2~4h. The compressive strength of the cured blank is greater than or equal to 300MPa.

[0042] In practice, the curing process uses an electrically heated forced-air drying oven. The curing temperature is selected based on the adhesive, at 200℃±5℃, and the curing time is 2~4 hours, forming a compact with a compressive strength ≥300MPa. During the curing process, the compact is placed on a carrier plate with evenly distributed holes. The structure of the carrier plate is as follows... Figure 4 As shown, the carrier tray is placed on a multi-layer frame, with a spacing of more than 150mm between layers. This multi-layer arrangement improves production capacity while ensuring good hot air circulation. The structure of the multi-layer frame is as follows: Figures 5 to 7 As shown.

[0043] Furthermore, refer to Figure 8 The negative pressure dust collection device and the wet dust removal device are connected by a pipe. The negative pressure dust collection device includes a negative pressure fan 6 and a suction nozzle 3. The negative pressure fan 6 is installed on the pipe 5, and the suction nozzle 3 is installed at one end of the pipe 5. The suction nozzle 3 is fixed by a fixing clamp 4 and has an inclined dust collection port 2. The wet dust removal device includes a water tank 7 and a cover plate 9 installed on the upper side of the water tank 7. The cover plate 9 has an exhaust hole 10 and a pipe inlet 11. The other end of the pipe 5 is connected to the pipe inlet 11.

[0044] In practice, the shaping process employs CNC machining to process the magnet end face, inner hole, and chamfer to ensure consistent product dimensional accuracy. The shaping uses SCMT09T304-C25 NC3120 inserts with a depth of cut ≤0.2mm, a spindle speed of 180m / min, and a feed rate of 0.2mm / r. A negative pressure dust collection device is used to prevent sparks during machining. The entire negative pressure dust collection pipe 5 is made of fireproof metal tubing, with a negative pressure exceeding 4MPa to ensure timely removal of metal powder. Pipe 5 connects to a wet dust collection device, where powder enters a water tank to prevent further combustion from sparks.

[0045] Since the bonding process of NdFeB is prone to generating sparks or even open flames, this embodiment uses a metal pipe negative pressure device and a wet dust removal device to solve the fire problem during the process in a simple and efficient way.

[0046] Furthermore, the ultrasonic cleaning includes sequential rinsing, cleaning, rinsing, and drying; The rinsing process employs a multi-nozzle, multi-angle high-pressure rinsing method. A negative pressure condensation pipe is installed above the rinsing tank, through which the volatile cleaning agent enters the return tank. During the cleaning process, workpiece 13 is immersed in a hydrocarbon-based cleaning agent and first undergoes vortex-type turbulent cleaning, followed by ultrasonic cleaning. The cleaning time is 1-2 minutes.

[0047] In practice, during the ultrasonic cleaning step, workpiece 13 is fixed on a special cleaning tool, the structure of which is as follows: Figure 9 Specifically, the fixture includes a vibrating plate 12, on which a hanger 14 is mounted. The hanger 14 has a frame structure, and the workpiece 13 is inclinedly positioned within each cell of the hanger 14. The hanger 14 includes parallel transverse support rods supporting the outer circular surface of the workpiece 13 and longitudinal support rods on both sides of the workpiece 13. The longitudinal support rods on both sides are respectively provided with an upwardly inclined upper limit protrusion and a downwardly inclined lower limit protrusion supporting the upper and lower ends of the workpiece 13. The workpiece 13 forms a four-point inclined positioning in the hanger 14. The four-point inclined positioning of the workpiece 13 is a spatial four-point inclined positioning, including a support point with the two transverse support rods, a support point with the upper limit protrusion, and a support point with the lower limit protrusion. These support points are located on different horizontal planes. The hanger 14 is welded from stainless steel steel bars with a diameter of 6-10mm, has a simple structure, produces less liquid residue, and has little impact on the workpiece 13.

[0048] The cleaning process mainly includes rinsing, cleaning, rinsing, and drying. Rinsing employs a multi-nozzle, multi-angle high-pressure rinsing method. A negative pressure condensation pipe is installed above the rinsing tank, and the volatile cleaning agent is condensed and enters the return tank for recycling. Rinsing removes large dust particles, followed by immersion in a hydrocarbon-based cleaning agent at an ultrasonic frequency of 28kHz. Cleaning is performed first, followed by rinsing, with a cleaning time of 1-2 minutes, to remove fine dust impurities from the microstructure. Finally, the product is dried using an air knife and removed.

[0049] Furthermore, the epoxy resin coating in the electrostatic spraying process has a macromolecular resin content of 30% to 45%, a resistivity of 5 MΩ·cm to 20 MΩ·cm, and a curing temperature of 210℃ ± 5℃; the polyurethane coating has a curing temperature of 230℃ ± 5℃, and the curing temperature difference between the two layers is 20℃.

[0050] In practice, electrostatic spraying employs a double-layer electrostatic spraying technology, using a composite coating formed by a base layer of epoxy resin coating and a top layer of polyurethane coating. A microscopic cross-sectional view of the composite coating is shown below. Figure 10As shown, epoxy powder coatings, when used as a primer, provide an ideal substrate and a pore-sealing effect. Following this, a polyurethane topcoat is applied, resulting in excellent adhesion and complete film coverage. Controlling the temperature difference between the top and bottom layers allows the primer to soften better and bond more firmly during topcoat curing. It also ensures the complete release of additives during polyurethane curing, improving coating surface quality. A double-layer electrostatic spraying process, combining primer and topcoat application, eliminates any weak points or adhesion points on workpiece 13, resulting in excellent corrosion resistance. The epoxy resin coating's properties have been adjusted; the high-molecular-weight resin content (30%~45%) in the raw material, after curing, results in a coating with moderate hardness, exhibiting good adhesion to both the substrate and topcoat. Furthermore, it does not stick to tooling during high-temperature secondary curing on the reverse side, demonstrating excellent performance.

[0051] The electrostatic spraying process employs a roller electrostatic spraying line, a tunnel curing line, a tunnel cooling line, a return line, an automatic flipping device, and an automatic centering device. The entire process is combined with a depalletizing and palletizing system to achieve full automation, making it suitable for batch processing and reducing manual labor.

[0052] Furthermore, during the electrostatic spraying process, the bottom of the tooling is designed to have a copper plate in contact with the conveyor roller. The conveyor roller is connected to a copper frame with a length × width of 1m × 1m via a wire. The copper frame is buried 1.5m below the ground surface to ensure good conductivity of the workpiece. The electrostatic spray coating uses a fully automatic feeding method. The upper part uses a conical hopper with a vibrator. A pneumatic butterfly valve is installed at the mouth of the conical hopper. A weighing sensor is installed at the bottom of the feeding box, with upper and lower limits set. When the mass of the feeding box is lower than the preset lower limit, the pneumatic butterfly valve is opened to feed the material. When the mass of the feeding box reaches the preset upper limit, the pneumatic butterfly valve is closed.

[0053] In one embodiment, a more specific method for batch production of bonded NdFeB magnets is provided, comprising the following steps: (1) Weigh 3% of the epoxy resin adhesive according to the mass of powder 20, dissolve the epoxy resin in alcohol and acetone solvent to form an adhesive solution, the volume ratio of alcohol to acetone is 1:1~1:1.2, and the mass ratio of epoxy resin to solvent is 1:1.5-1:2; (2) The adhesive and magnetic powder are thoroughly mixed in the kneader, reverse for 5 minutes, then forward for 60 minutes. When the powder 20 shows an increase in volume and foaming state, reverse kneading is performed. After the powder 20 is half dry, forward and reverse kneading is performed alternately for 5 minutes, and then stopped for 30 minutes until the solvent evaporates completely. The entire process requires a negative pressure suction device to maintain negative pressure and promptly remove the evaporated alcohol and acetone. The kneader cavity is kept at a low temperature (below 40°C) for heating and drying. (3) After drying, sieve in a gyratory screen. During the feeding process, the amount of material should be appropriate and uniform. Select 20g of powder with a mesh size of 50-500 for later use. (4) Put the large particles 20 that cannot be sieved into the vibrating mill for crushing, and then sieve them again until all the large particles 20 are sieved. (5) Weigh 2000g of powder using an automatic weighing device with a weighing accuracy of ±0.2%; (6) Set the press parameters to semi-automatic floating pressing, pressing speed 5mm / s, holding time 5~8s, and air pressure protection demolding; (7) After the workpiece 13 is formed, take it out and place it in a multi-layer tooling tray. After the tray is full, push it into the drying oven for curing. Set the temperature to 200℃±5℃ and the time to 2-4h. After curing, push it out and let it cool naturally in an environment with humidity ≤60%RH. (8) The workpiece 13 is machined on a CNC lathe, with the end face, inner hole and chamfer being machined. The entire process is vacuumed to avoid sparks. SCMT09T304-C25 NC3120 inserts are used, with a depth of cut ≤0.2mm, a rotation speed of 180m / min and a feed rate of 0.2mm / r. (9) After machining, place the workpiece 13 in a special cleaning tool and clean the workpiece 13 according to the process of rinsing-cleaning-rinsing-drying; (10) The workpiece 13 is placed in a special spraying fixture for double-layer electrostatic spraying. After curing at 180°C for 15 minutes and cooling for 15 minutes, an anti-corrosion film layer is formed; two coats of primer and two coats of topcoat are applied, for a total of four coats. (11) After electrostatic spraying, the parts are assembled and magnetized to obtain the required workpiece 13.

[0054] The batch production method for bonded NdFeB magnets disclosed in this application can guarantee a magnet production capacity of 500,000 pieces / year, with a batch production density fluctuation range of ≤±0.5%, a dimensional fluctuation range of ≤±0.2%, good product surface quality, a neutral salt spray test of 500h, a surface quality of grade 0 or 1, extremely high magnet uniformity, and a magnetic eccentricity (the deviation between the geometric axis of the magnet and the magnetic center) of ≤0.15mm.

[0055] The embodiments provided by this invention include a process comprising seven core steps: mixing, pressing, curing, shaping, ultrasonic cleaning, electrostatic spraying, and assembly magnetization. This process offers the following advantages: 1. The wet mixing, screening, crushing and screening process ensures that powder 20 is fully mixed with colloid. After mixing, powder 20 has good bulk density and flowability, and the pass rate is ≥99.5%. 2. The molding process adopts a precise weighing compression molding process. The floating pressing method ensures the uniformity of product density in batch production. The mold is specially designed to ensure product size while greatly increasing mold life, making the molding process economical. 3. The curing process adopts a multi-layer stacked forced-air drying method, which can process pressed blanks in large quantities. The process is stable, energy-saving and efficient, and suitable for batch processing. 4. The shaping process, employing negative pressure dust extraction and wet dust removal, effectively solves the problem of sparks generated during NdFeB machining and the unsuitability of using coolant, thus ensuring the safety of the machining process. Shaping further improves the geometric accuracy and consistency of the product, laying the foundation for ensuring stable and consistent product performance. 5. Ultrasonic cleaning uses hydrocarbon cleaning agents, which will not corrode neodymium iron boron and will not react with epoxy resin. The active bonds in the cleaning agent can efficiently remove dust particles, achieving efficient cleaning. The frame-type cleaning tool solves the positioning and support problem of workpiece 13, which does not affect the micro-vibration effect of workpiece 13 under ultrasonic action and also solves the problem of difficult drying of liquid and dust accumulation on the surface of workpiece 13. 6. Electrostatic spraying process: For the first time, a double-layer, non-hanging treatment process is adopted for NdFeB corrosion protection. The use of epoxy resin + polyurethane double coating gives the workpiece 13 coating good adhesion and corrosion and weather resistance.

[0056] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for batch production of bonded NdFeB magnets, characterized in that, include: Mixing: Epoxy resin is dissolved in alcohol and acetone to prepare a glue solution. The glue solution is then kneaded with neodymium iron boron magnetic powder that has been rotated in both directions in a kneader. The mixture is then sieved and crushed to obtain mixed glue powder. Compression molding: The mixed powder is added to the cavity of the compression mold and molded to obtain a blank; Curing: The blanks are placed on a carrier plate with evenly distributed holes for batch curing; Shaping: The cured blank is placed on a CNC lathe to process the end face, inner hole and chamfer of the magnet to obtain the workpiece. The CNC lathe is equipped with a negative pressure dust collection device and a wet dust removal device. Ultrasonic cleaning: The workpiece is fixed on a frame-type cleaning fixture for ultrasonic cleaning; Electrostatic spraying: Double-layer electrostatic spraying is performed on the surface of the cleaned workpiece to form a composite coating with an epoxy resin coating as the bottom layer and a polyurethane coating as the top layer. Assembly and magnetization: The electrostatically sprayed workpiece is assembled and magnetized.

2. The batch production method of bonded NdFeB magnets according to claim 1, characterized in that, The volume ratio of alcohol to acetone in the alcohol-acetone solvent is 1:1 to 1:1.2, and the mass ratio of epoxy resin to alcohol-acetone solvent is 1:1.5 to 1:

2.

3. The batch production method of bonded NdFeB magnets according to claim 1, characterized in that, The process of kneading the adhesive with neodymium iron boron magnetic powder that has undergone forward and reverse rotation in a kneader includes: Add neodymium iron boron magnetic powder into the kneader and repeat the reverse, stop, and forward rotation process three times. Then, the neodymium iron boron magnetic powder and the adhesive liquid are mixed thoroughly in a kneader by first reversing the rotation and then rotating it forward. When the powder increases in volume and foams, reverse the kneading process. Once the powder is semi-dry, alternate between forward and reverse rotation until the solvent has completely evaporated. Throughout the kneading process, the kneading machine cavity is kept at a temperature below 40°C for heating and drying. The volatilized alcohol and acetone gases are collected and recovered by a condenser at a temperature of -50°C to -40°C using a sealed negative pressure method. The recovery pressure is 0.1MPa to 0.3MPa.

4. The batch production method of bonded NdFeB magnets according to claim 1, characterized in that, The sequential screening and crushing process includes: Screening is performed using a gyratory screen with 50 mesh upper and 500 mesh lower screens. The crushing process is carried out using a cylindrical vibratory mill.

5. The batch production method of bonded NdFeB magnets according to claim 1, characterized in that, The compression molding process employs automatic weighing and feeding, as well as an automatic floating die pressing method. The pressing die of the automatic floating middle die pressing method includes a mandrel, a middle die and a punch. The mandrel and the middle die are made of tungsten steel with a hardness greater than 89HRC, and the punch is made of alloy steel with a hardness of 62~68HRC. The single-sided gap between the punch and the middle die mandrel is 0.01mm, and an clearance zone is set below the effective section of the punch. The automatic weighing and feeding system adopts a dual-channel spiral feeding method with large and small channels. The servo motor first controls the large channel to weigh the powder to 92%~98% of the target value, then stops and switches to the small channel to continue weighing with high precision to the target value, with a weighing accuracy of ±0.2%. The feeding system uses a double-splitting conical hopper with a middle partition. After the bottom cover is opened, the powder leaks into the mold cavity formed by the middle mold and the mandrel.

6. The batch production method of bonded NdFeB magnets according to claim 1, characterized in that, The negative pressure dust collection device and the wet dust removal device are connected by a pipe. The negative pressure dust collection device includes a negative pressure fan and a suction nozzle. The negative pressure fan is installed on the pipe, and the suction nozzle is installed at one end of the pipe. The suction nozzle is fixed by a fixing clamp and has an inclined dust suction port. The wet dust removal device includes a water tank and a cover plate installed on the upper side of the water tank. The cover plate has an exhaust hole and a pipe inlet. The other end of the pipe is connected to the pipe inlet.

7. The batch production method of bonded NdFeB magnets according to claim 1, characterized in that, The ultrasonic cleaning process includes rinsing, cleaning, rinsing and drying in sequence; The rinsing process employs a multi-nozzle, multi-angle high-pressure rinsing method. A negative pressure condensation pipe is installed above the rinsing tank, through which the volatile cleaning agent enters the return tank. The cleaning process involves immersing the workpiece in a hydrocarbon-based cleaning agent for vortex-type turbulent cleaning, followed by ultrasonic cleaning, with a cleaning time of 1-2 minutes.

8. The batch production method of bonded NdFeB magnets according to claim 1, characterized in that, The epoxy resin coating used in the electrostatic spraying process has a macromolecular resin content of 30% to 45%, a resistivity of 5 MΩ·cm to 20 MΩ·cm, and a curing temperature of 210℃ ± 5℃; the polyurethane coating has a curing temperature of 230℃ ± 5℃.

9. The batch production method of bonded NdFeB magnets according to claim 1, characterized in that, During the electrostatic spraying process, the bottom of the tooling is designed to have a copper plate in contact with the conveyor roller. The conveyor roller is connected to the copper frame through a wire, and the copper frame is buried below the ground surface. The electrostatic spraying coating uses a fully automatic feeding method. A conical hopper with a vibrator is used at the top, and a pneumatic butterfly valve is installed at the mouth of the conical hopper. A weighing sensor is installed at the bottom of the feeding box. When the quality of the coating in the feeding box is lower than the preset lower limit, the pneumatic butterfly valve is opened to feed the coating. When the quality of the coating in the feeding box reaches the preset upper limit, the pneumatic butterfly valve is closed.

10. The batch production method of bonded NdFeB magnets according to claim 1, characterized in that, The step of placing the blank on a carrier plate with evenly distributed holes for batch curing includes: Multiple blanks are placed on multiple carriers with evenly distributed holes; Multiple trays are placed on a movable multi-layer frame, with a spacing of more than 150mm between adjacent trays; The multi-layer frame is moved to an electric heating drying oven for curing. The curing temperature is 195~205℃ and the curing time is 2~4h. The compressive strength of the cured blank is greater than or equal to 300MPa.

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