Vacuum diffusion furnace and diffusion method suitable for small neodymium iron boron element

Abstract

The invention belongs to the technical field of diffusion furnaces, relates to diffusion of heavy rare earth metal elements on the surface of a sintered neodymium-iron-boron permanent magnet, and particularly relates to a vacuum diffusion furnace suitable for small neodymium-iron-boron elements and a diffusion method.The vacuum diffusion furnace comprises a rotary furnace pipe (1), and the rotary furnace pipe (1) is driven by an external driving unit (2) to rotate forwards and backwards; spiral sheets (13) are arranged on the inner walls of a furnace body (11) and a neck part (12) of the rotary furnace pipe (1); a furnace body (11) of the rotary furnace pipe (1) is positioned in the heating unit; a feeding and discharging box (4) is connected outside a neck port of the rotary furnace pipe (1) in a sealed mode, and a vacuum pipeline (5) is connected to the feeding and discharging box (4). The method is reasonable in design, solves the technical problem of diffusion of heavy rare earth metal in a small sintered neodymium iron boron permanent magnet product, can directly diffuse the heavy rare earth metal to the small product, improves the working efficiency and the final product quality, and has very good practical application value.

Description

Technical Field

[0001] This invention belongs to the field of diffusion furnace technology and relates to the diffusion of heavy rare earth metal elements on the surface of sintered NdFeB permanent magnets. Specifically, it is a vacuum diffusion furnace and diffusion method suitable for small NdFeB components. Background Technology

[0002] In order to obtain sintered NdFeB permanent magnets with high remanence and high coercivity, heavy rare earth metal elements are diffused onto the surface of the sintered NdFeB permanent magnets using surface penetration and diffusion methods.

[0003] For larger sintered NdFeB permanent magnet products such as square sheets and tiles, magnetron sputtering of heavy rare earth films, screen printing of heavy rare earth metal hydrides or fluorides, and fluoride spraying are commonly used. However, for smaller products, such as small sintered NdFeB permanent magnets weighing around 1 gram, existing solutions are difficult to implement. Currently, the method involves first diffusing the larger sheet and then cutting it, which has drawbacks such as low efficiency and inconsistent diffusion depth. A more efficient solution needs to be designed. Summary of the Invention

[0004] The purpose of this invention is to provide a vacuum diffusion furnace and diffusion method for diffusing heavy rare earth metal elements into small sintered NdFeB permanent magnet products weighing less than 10 grams.

[0005] This invention is achieved using the following technical solution: First aspect: A vacuum diffusion furnace suitable for small NdFeB elements, comprising a rotating furnace chamber, the rotating furnace chamber being driven to rotate in both directions by an external drive unit, the furnace body and the inner wall of the neck of the rotating furnace chamber being provided with spiral blades; the furnace body of the rotating furnace chamber is located inside a heating unit; the neck port of the rotating furnace chamber is externally sealed to a feed and discharge box, and a vacuum pipeline is connected to the feed and discharge box.

[0006] The working principle is as follows: Magnetic devices (i.e., small NdFeB elements) and heavy rare earth metal particles (i.e., heavy rare earth metal diffusion sources) are mixed in a certain proportion and added to a rotating furnace. Under high vacuum and appropriate temperature, the surface of the heavy rare earth metal particles comes into contact with the surface of the small NdFeB workpiece, and the heavy rare earth metal diffuses and penetrates into the interior of the small NdFeB workpiece, thereby increasing the coercivity of the small NdFeB workpiece. Due to the continuous low-speed rolling, the contact probability between the heavy rare earth metal particles and the small NdFeB workpiece is equal, therefore the diffusion amount is also equal.

[0007] More preferably, the heating unit is an openable and closable electric furnace, the purpose of which is to allow the electric furnace to be opened after diffusion is completed, so as to cool the furnace body. The openable and closable electric furnace is composed of a left furnace body and a right furnace body, which are opened and closed by moving on the base frame through their respective traveling mechanisms.

[0008] In a further preferred embodiment, the neck of the rotary furnace liner is supported on a first bracket by an external first bearing, and the tail end of the rotary furnace liner is connected to a support shaft. The support shaft passes through the heating unit and is supported on a second bracket by a second bearing. This allows the rotary furnace liner to be supported on two brackets and rotate, resulting in a simple structure, low cost, and reliable performance.

[0009] In a further preferred embodiment, the rotary furnace liner is rotated via a chain drive; the neck of the rotary furnace liner is provided with a synchronously rotating first sprocket, which is connected to a second sprocket located on a first support via a chain drive; the second sprocket is driven to rotate by a drive unit mounted on the first support.

[0010] In a further preferred embodiment, the inlet and outlet are designed on the same side, with an inlet and outlet box designed and installed at the neck port via a third bearing; the third bearing is installed outside the neck port of the rotary furnace, and the neck port of the rotary furnace extends into the inlet and outlet box, with the inlet and outlet box and the outer ring of the third bearing sealed together.

[0011] A further preferred design includes a feeding structure. The feeding box has a feeding port on the side wall opposite the neck port, which is sealed by a feeding sealing end cover when not feeding. It also includes a vibrating feeder, which is located on a moving trolley that moves along a feeding guide rail. When feeding, the feeding pipe of the vibrating feeder passes through the feeding port and extends into the neck port of the rotary furnace.

[0012] Further preferably, the discharge structure is designed. The side of the inlet and outlet box is provided with a discharge port, which is sealed by a cover when not discharging; it also includes a magnetic separation and conveying mechanism, the conveying end of which is located below the neck port of the rotary furnace when discharging; the magnetic separation and conveying mechanism outputs the material to a first container for collecting heavy rare earth metal particles and a second container for collecting magnetic devices located on the outside.

[0013] A further preferred design incorporates a cooling structure. A water collection trough is located beneath the furnace body of the rotating furnace chamber, and this trough is situated on the lifting mechanism.

[0014] The second aspect: A method for diffusing heavy rare earth elements on the surface of small NdFeB elements, wherein small NdFeB elements and granular heavy rare earth metal diffusion sources are mixed in a certain proportion and added together into the rotary furnace of a vacuum diffusion furnace. Under high vacuum and a preset temperature, the rotary furnace rotates at low speed, and the granular heavy rare earth metal diffusion sources come into contact with the surface of the small NdFeB elements, so that the heavy rare earth elements diffuse and penetrate into the interior of the small NdFeB elements, thereby improving the coercivity of NdFeB.

[0015] More preferably, the diameter of the rotary furnace is 250mm-400mm; the mixing ratio of small NdFeB elements and granular heavy rare earth metal diffusion sources is 1:0.5-2; and the rotation speed of the rotary furnace is 10-25% lower than the critical rotation speed.

[0016] Further, based on the magnitude of the increase in coercivity, the heavy rare earth metal diffusion source is selected as follows: To increase coercivity by 3000-6000, a Dy, Cu, Ga, and Al alloy was selected as the dysprosium diffusion source. To improve coercivity to over 6000, a Tb, Pu, Cu, Ga, and Al alloy was selected as the terbium diffusion source.

[0017] Further preferably, the dysprosium diffusion source is an alloy of Dy, Cu, Ga, and Al; wherein Dy accounts for 50-90%, Cu 5-20%, Ga 1-5%, and Al 3-10%, with the total content of the four elements being 100%. An organic solution is dripped into the alloy during vacuum melting to obtain spherical alloys with a diameter of 1.5-6 mm. The dripping speed is controlled to ensure the formation of near-spherical shapes with a diameter of 1.5-6 mm.

[0018] The terbium diffusion source uses a Tb, Pu, Cu, Ga, and Al alloy; wherein Tb accounts for 50-90%, Pu for 10-15%, Cu for 5-20%, Ga for 1-5%, and Al for 3-10%, with the total content of Dy, Cu, Ga, and Al being 100%. An organic solution is added dropwise during vacuum melting to obtain spherical alloys of 1.5-6 mm in diameter.

[0019] During operation, magnetic components (small NdFeB elements, weighing less than 10g) and heavy rare earth metal particles are mixed and placed into the feeding hopper of the vibrating feeder. The vibrating feeder moves along the feeding guide rail via a trolley, and the feeding pipe extends from the inlet to connect with the neck port of the furnace. The drive unit is activated, the rotary furnace chamber begins to rotate, and then the vibrating feeder is started. After the material enters the neck port, it gradually enters the furnace body under the action of the spiral blades. After feeding is complete, the feeding pipe is withdrawn, and the inlet is resealed by the feeding sealing end cap. The vacuum unit is then activated to evacuate the furnace body through the vacuum pipeline. After diffusion is complete, the heating furnace is turned on, and then argon gas is introduced. The water tank rises, and the bottom of the furnace body is cooled in the water tank. The conveying end of the magnetic separation conveying mechanism extends from the discharge port into the inlet and outlet boxes, located below the neck port of the rotary furnace. Then, the rotary furnace begins to reverse, starting the magnetic separation conveying mechanism (e.g., a magnetic separation belt conveyor). Under the action of the spiral blades, small magnetic workpieces and heavy rare earth metal particles gradually flow out from the neck port and fall onto the conveyor belt with a lip. The belt rotates, moving them to the magnetic drum area. Non-magnetic particles fall into the first container due to gravity and inertia. Small magnetic workpieces are temporarily attracted when passing through the magnetic drum area, and fall into the second container due to gravity after leaving the magnetic drum area.

[0020] This invention is reasonably designed and solves the technical problem of diffusion of heavy rare earth metal elements in small sintered NdFeB permanent magnet products. It enables heavy rare earth metals to diffuse directly into small products, improving work efficiency and final product quality, and has great practical application value. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This diagram illustrates the combination of the vacuum diffusion furnace and the feeder of the present invention.

[0024] Figure 2 This diagram shows the structure of the vacuum diffusion furnace of the present invention.

[0025] Figure 3 This is a side view of the vacuum diffusion furnace of the present invention (including the vacuum unit).

[0026] Figure 4 This is a side view of the vacuum diffusion furnace of the present invention.

[0027] Figure 5 This diagram shows the heating furnace in the open state (with the water tank rising for cooling).

[0028] Figure 6 This diagram shows the electric heating furnace in the open state (water tank lowered).

[0029] In the diagram: 1-Rotating furnace chamber, 11-Furnace body, 12-Neck, 13-Spiral blade, 101-First support, 102-First bearing, 103-Second support, 104-Second bearing, 105-Support shaft, 106-First sprocket, 107-Second sprocket, 108-Third bearing; 2-Drive unit; 3-Openable and closable heating furnace, 31-Left furnace body, 32-Right furnace body, 33-Walking mechanism, 34-Base frame; 4-Inlet / Outlet 41-Feeding inlet, 42-Feeding sealing end cap, 43-Discharge outlet; 5-Vacuum pipeline, 501-Vacuum pumping unit; 6-Vibrating feeder, 61-Mobile trolley, 62-Feeding guide rail, 601-Feeding pipe, 602-Blouse; 7-Magnetic separation output mechanism, 701-First container, 702-Second container; 8-Water receiving tank, 9-Lifting mechanism, 10-Water spray pipe, 11-Heavy rare earth metal particles, 12-Magnetic device. Detailed Implementation

[0030] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0031] In this description, it should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. It should also be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joint" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0032] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0033] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0034] A vacuum diffusion furnace suitable for small NdFeB elements includes a rotary furnace chamber 1, a vibrating feeder 6, a magnetic separation and conveying mechanism 7, etc.

[0035] like Figure 1 , Figure 2 As shown, the inner walls of the furnace body 11 and neck 12 of the rotary furnace 1 are both provided with spiral blades 13. The function of the spiral blades 13 is to drive the material (heavy rare earth metal particles and small magnetic devices) to move within the rotary furnace 1. The neck 12 of the rotary furnace 1 is supported on the first bracket 101 by an external first bearing 102. The tail end of the rotary furnace 1 is connected to a support shaft 105. The support shaft 105 passes through the heating unit and is supported on the second bracket 103 by a second bearing 104.

[0036] like Figure 1 , Figure 2 As shown, the rotary furnace 1 is driven to rotate in both directions by an external drive unit 2. In this embodiment, the drive unit 2 can be a conventional combination of a motor and a reducer. The neck 12 of the rotary furnace 1 is equipped with a synchronously rotating first sprocket 106. This first sprocket 106 can be directly fixed to the outside of the neck 12, and the two rotate synchronously. In this embodiment, the first sprocket 106 is fixed to the inner ring of the first bearing 102, i.e., the first sprocket 106 and the neck 12 have a clearance fit, rather than being directly fixed to the neck 12, which reduces the pressure on the neck 12. The first sprocket 106 is connected to a second sprocket 107 located on the first support 101 via a chain drive. The drive unit 2 is mounted on the first support 101 and can achieve forward and reverse rotation. The output end of the drive unit 2 directly drives the second sprocket 107 to rotate, which reduces the transmission distance. Subsequently, the first sprocket 106 drives the rotary furnace 1 to rotate in both directions.

[0037] like Figure 2 , Figure 3 , Figure 4 As shown, since the neck port of the rotary furnace 1 extends into the feed box 4, the feed box 4 needs to be sealed to the outside of the neck port of the rotary furnace 1. In this embodiment, a third bearing 108 is installed outside the neck port of the rotary furnace 1. The third bearing 108 can be a magnetic fluid sealed bearing. The third bearing 108 is fixedly installed outside the neck port, and the feed box 4 can be sealed to the outer ring of the third bearing 108.

[0038] like Figure 3 As shown, a vacuum line 5 is connected to the inlet / outlet box 4, and the vacuum line 5 is connected to the vacuum pumping unit 501.

[0039] like Figure 2 , Figure 3 , Figure 4 As shown, the feed inlet 41 is provided on the side wall of the feed box 4 opposite the neck port. The feed inlet 41 is sealed by the feeding sealing end cover 42 when it is not feeding.

[0040] like Figure 1 As shown, the vibrating feeder 6 is located on the moving trolley 61. The vibrating feeder 6 is existing technology and will not be described in detail. The moving trolley 61 moves along the feeding guide rail 62; when feeding, the feeding pipe 601 of the vibrating feeder 6 passes through the feed port 41 and extends into the neck port of the rotary furnace 1.

[0041] like Figure 3 , Figure 4 As shown, the side of the inlet / outlet box 4 is provided with an outlet 43, which is sealed by a cover when not discharging. The inlet / outlet and the air inlet / outlet are located on the same side, and the magnetic separation belt conveyor completes the discharge and separation. In this embodiment, the magnetic separation conveying mechanism 7 is selected as a belt conveyor. The roller at the output end of the belt conveyor is magnetic. Therefore, when the material is discharging, the conveying end of the magnetic separation conveying mechanism 7 extends into the inlet / outlet box 4 through the outlet 43, located below the neck port of the rotary furnace 1. The magnetic separation conveying mechanism 7 outputs the material to the first container 701 for collecting heavy rare earth metal particles 11 and the second container 702 for collecting magnetic devices 12, which are located on the outside.

[0042] like Figure 5 , Figure 6 As shown, the furnace body 11 of the rotary furnace 1 is located within the heating unit. In this embodiment, the heating unit is selected as an openable and closable electric furnace 3, which is composed of a left furnace body 31 and a right furnace body 32. The left furnace body 31 and the right furnace body 32 are opened and closed by moving on the base frame 34 through their respective walking mechanisms 33. For example, motors and reducers are installed on the left and right furnace bodies respectively, and their respective walking mechanisms are driven by shaft transmission or other means. This is existing technology and will not be described in detail. In addition, a water receiving tank 8 is provided below the furnace body 11 of the rotary furnace 1. The water receiving tank 8 is located on the lifting mechanism 9. After the openable and closable electric furnace 3 is opened, the water receiving tank 8 rises, placing the bottom of the furnace body 11 in the water receiving tank for cooling. At the same time, a water spray pipe 10 is provided in the water receiving tank 8 to spray water onto the surface of the furnace body 11 for cooling.

[0043] The specific diffusion method works as follows: S1, a mixture of small NdFeB elements and granular heavy rare earth metal diffusion sources; S2. The material enters the furnace body through the neck of the rotating furnace chamber via a vibrating feeder; S3. Start the vacuum unit and close the openable heating furnace; S4. Drive the rotary furnace chamber to rotate, and heat up and maintain the heat for diffusion; S5. After diffusion is complete, open the switchable heating furnace, fill it with argon gas, and spray water to cool it. S6. Drive the rotary furnace to reverse and start the magnetic separation belt conveyor. The workpiece and granular material gradually flow out from the neck port of the rotary furnace and fall onto the conveyor belt with the lip. The belt rotates and moves it to the magnetic separation drum. The non-magnetic granular material falls into the first container, and the small NdFeB element falls into the second container.

[0044] In operation, the magnetic device 12 (small NdFeB element, weighing less than 10g) and heavy rare earth metal particles 11 are mixed and placed into the feeding bin 601 of the vibrating feeder 6. After the vibrating feeder 6 moves on the feeding guide rail 62 via the moving trolley 61, the feeding pipe 601 extends from the inlet 41 and connects to the neck port of the neck 12. The drive unit 2 is started, the rotating furnace 1 begins to rotate, and then the vibrating feeder 6 is started. After the material enters the neck port, it gradually enters the furnace body 11 under the action of the spiral blades 13. The material content in the furnace body 11 is 40%-75%. After feeding is completed, the feeding pipe 601 is withdrawn, and the inlet 41 is resealed by the feeding sealing end cap 42. Then the vacuum unit 501 is started to evacuate the furnace body 11 through the vacuum pipeline 5.

[0045] In this embodiment, the diameter of the rotating furnace chamber 1 is between 250mm and 400mm. If it is less than 250mm, the furnace loading capacity is too small and the processing capacity is low. If the diameter exceeds 400mm, the drop will increase during rolling, and the workpiece will be prone to chipping or breaking off.

[0046] In this embodiment, the mixing ratio of the small NdFeB element and the granular heavy rare earth metal diffusion source is 1:0.5-2. After the left furnace body 31 and the right furnace body 32 move and close, the temperature is raised to 600℃~900℃, and then held at that temperature for diffusion and penetration. Under high vacuum (0.003Pa~1Pa) and high temperature, the surface of the heavy rare earth metal particles contacts the surface of the NdFeB workpiece, and the heavy rare earth metal diffuses and penetrates into the interior of the NdFeB workpiece, thereby improving the coercivity of the NdFeB workpiece. The rotation speed of the rotary furnace is 10~25% lower than the critical rotation speed. Due to the continuous low-speed rolling, the contact probability between the heavy rare earth metal particles and the magnetic workpiece is equal, and therefore the diffusion amount is also equal. For example, for a rotary furnace with a diameter of 300mm, the critical rotation speed is 77 rpm.

[0047] In this embodiment, the heavy rare earth metal diffusion source is selected as follows, based on the magnitude of the coercivity enhancement: To increase coercivity to 3000-6000, a Dy, Cu, Ga, Al alloy is selected. If the heavy rare earth metal diffusion source is a Dy, Cu, Ga, Al alloy, with Dy at 50-90%, Cu at 5-20%, Ga at 1-5%, and Al at 3-10%, an organic solution (silicone oil or one of n-dodecane, n-trigsane, n-tetradecane, or n-pentadecane) is added dropwise during vacuum melting to obtain spherical alloy particles of 1.5-6 mm. To prevent future oxidation, the organic liquid furnace should be covered with an inert gas, such as argon. The dropwise rate should not be too fast, otherwise the oil temperature will be too high and the particles too large. The dropped metal should also pass through a 3-6 mm orifice. The organic liquid should be flowing and cooled by a heat exchanger.

[0048] To improve coercivity to over 6000, a Tb, Pu, Cu, Ga, and Al alloy is selected. If the heavy rare earth metal diffusion source is a Tb, Pu, Cu, Ga, and Al alloy, with Tb at 50-90%, Pu at 10-15%, Cu at 5-20%, Ga at 1-5%, and Al at 3-10%, an organic solution (silicone oil or one or a mixture of n-dodecane, n-trigadecane, n-tetradecane, and n-pentadecane) is added dropwise during vacuum melting to obtain spherical alloys of 1.5-6 mm.

[0049] After diffusion is complete, turn on the heating furnace (left furnace body 31 and right furnace body 32 are separated), then fill with argon gas, the water tank 8 rises, the bottom of the furnace body 11 is cooled in the water tank, and at the same time the water spray pipe 10 in the water tank 8 sprays water onto the surface of the furnace body 11 to cool it down.

[0050] The conveying end of the magnetic separation conveying mechanism 7 extends into the feed box 4 from the discharge port 43, located below the neck port of the rotary furnace 1. Then, the rotary furnace 1 begins to reverse, activating the magnetic separation conveying mechanism 7 (magnetic separation belt conveyor). Under the action of the spiral blades 13, small magnetic workpieces and heavy rare earth metal particles gradually flow out from the neck port and fall onto the lipped conveyor belt. The belt rotates, moving them to the magnetic drum area. Non-magnetic particles fall into the first container 701 due to gravity and inertia. Small magnetic workpieces are temporarily attracted when passing through the magnetic drum area and fall into the second container 702 due to gravity after leaving the magnetic drum area. The feed and discharge, as well as the air intake and exhaust, are on the same side, and the magnetic separation belt conveyor completes the discharge and separation.

[0051] Compared with existing technologies: a) Compared with vacuum sputtering, vacuum sputtering has low target utilization, generally 45-50%, and high cost; each surface of the workpiece needs to be sputtered separately, and it also needs to be sent to a vacuum furnace for vacuum diffusion treatment, resulting in low efficiency; the equipment is complex and requires large investment. b) Compared with surface coating, each workpiece needs to be sprayed, printed, and dipped individually, resulting in low efficiency; an adhesive needs to be added, and the final product is difficult to remove from the surface; the coating layer may peel off during diffusion, resulting in poor reliability. c) Compared with the embedding method, the existing embedding method keeps the workpiece and powder in contact after penetration and before cooling, which can cause surface over-penetration; because cooling occurs during contact, the rare earth-rich phase precipitated on the magnet surface adheres to the powder, resulting in waste of heavy rare earth materials and difficulty in cleaning. d) Compared with existing diffusion methods, after the magnet and diffusion source undergo primary diffusion, the diffusion source and magnet need to be separated for secondary high-temperature diffusion. e) Since this invention uses physical mixing and rotary permeation, it eliminates the need for secondary diffusion. The diffusion method of this invention optimizes process steps and parameters. By controlling the furnace diameter, the appropriate mixing ratio of the magnet and diffusion source, a suitable rotation speed, and rapid cooling, it achieves the same results as existing technologies, namely, a very small decrease in remanence and a significant increase in coercivity. Furthermore, because the workpiece can be immediately separated from the diffusion source after a single permeation step, the utilization rate of heavy rare earth materials is increased by 55-60%, saving heavy rare earth materials and labor, reducing equipment investment, and lowering overall costs.

[0052] dysprosium diffusion source

[0053] Test conditions: Diffusion temperature 650 degrees Celsius, time 6 hours. Permeation temperature 850 degrees Celsius, permeation time 12 hours.

[0054] Terbium diffusion source

[0055] Test conditions: Diffusion temperature 650 degrees Celsius, time 6 hours. Permeation temperature 850 degrees Celsius, permeation time 12 hours.

[0056] The diffusion and penetration time and temperature can be changed according to the desired increase in coercivity.

[0057] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the present invention. Although detailed descriptions have been provided with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments, and they should all be covered within the protection scope of the claims.

Claims

1. A vacuum diffusion furnace suitable for small neodymium-iron-boron elements, characterized in that: The application relates to a rotary furnace barrel (1) driven by an external driving unit (2) to rotate in opposite directions, wherein the furnace barrel (1) is provided with helical blades (13) on the inner walls of a furnace body (11) and a neck (12); the furnace body (11) of the rotary furnace barrel (1) is located in a heating unit; the neck port of the rotary furnace barrel (1) is sealingly connected with an inlet and outlet box (4) outside; and a vacuum pipeline (5) is connected to the inlet and outlet box (4).

2. A vacuum diffusion furnace suitable for small Nd-Fe-B elements according to claim 1, characterized in that: The heating unit is an openable and closable heating electric furnace (3) which is composed of a left furnace body (31) and a right furnace body (32); the left furnace body (31) and the right furnace body (32) are respectively moved on a chassis (34) through respective walking mechanisms (33) to open and close.

3. A vacuum diffusion furnace suitable for small Nd-Fe-B elements according to claim 1 or 2, characterized in that: The neck (12) of the rotary furnace barrel (1) is supported on a first support (101) through a first bearing (102); the tail end of the rotary furnace barrel (1) is connected with a supporting shaft (105); the supporting shaft (105) penetrates through the heating unit and is supported on a second support (103) through a second bearing (104); The neck (12) of the rotary furnace barrel (1) is provided with a first chain wheel (106) which rotates synchronously; the first chain wheel (106) is connected with a second chain wheel (107) located on the first support (101) through chain transmission; The second chain wheel (107) is driven to rotate by a driving unit (2); the driving unit (2) is installed on the first support (101); The first chain wheel (106) is fixedly connected with the inner ring of the first bearing (102).

4. A vacuum diffusion furnace suitable for small Nd-Fe-B elements according to claim 3, characterized in that: A third bearing (108) is installed outside the neck port of the rotary furnace barrel (1); the neck port of the rotary furnace barrel (1) extends into the inlet and outlet box (4); and the inlet and outlet box (4) is sealingly connected with the outer ring of the third bearing (108); A feeding port (41) is arranged on the side wall of the inlet and outlet box (4) opposite to the neck port; and the feeding port (41) is sealed by a feeding sealing end cover (42) in a non-feeding state; The application further comprises a vibrating feeder (6) which is located on a moving trolley (61) and moves along a feeding guide rail (62); the vibrating feeder (6) extends into the neck port of the rotary furnace barrel (1) through the feeding port (41) when feeding; A discharging port (43) is arranged on the side of the inlet and outlet box (4); and the discharging port (43) is sealed by a cover in a non-discharging state; The application further comprises a magnetic separation and material conveying mechanism (7); the material conveying end of the magnetic separation and material conveying mechanism (7) is located below the neck port of the rotary furnace barrel (1) in a discharging state; and the magnetic separation and material conveying mechanism (7) outputs materials to a first container (701) for collecting heavy rare earth metal particles (11) and a second container (702) for collecting magnetic devices (12) outside.

5. A vacuum diffusion furnace suitable for small Nd-Fe-B elements according to claim 4, characterized in that: A water collecting groove (8) is arranged below the furnace body (11) of the rotary furnace barrel (1); and the water collecting groove (8) is located on a lifting mechanism (9); The third bearing (108) is a magnetic fluid sealing bearing.

6. A method for surface diffusion of heavy rare earths to small Nd-Fe-B components, characterized in that: Mixing small Nd-Fe-B elements and granular heavy rare earth metal diffusion source in proportion, adding them into the rotating furnace tube of vacuum diffusion furnace, under high vacuum and preset temperature, the granular heavy rare earth metal diffusion source and the surface of small Nd-Fe-B elements contact in the process of low speed rotation of the rotating furnace tube, so that the heavy rare earth elements diffuse and penetrate into the small Nd-Fe-B elements, thereby improving the coercivity of Nd-Fe-B.

7. The method according to claim 6, wherein the method is applied to the surface diffusion of heavy rare earths to small Nd-Fe-B components. The diameter of the rotating furnace tube is 250-400 mm; The mixing ratio of small Nd-Fe-B elements and granular heavy rare earth metal diffusion source is 1:0.5-2; The rotation speed of the rotating furnace tube is lower than 10-25% of the critical rotation speed.

8. The method according to claim 7, wherein the method is applied to the surface diffusion of heavy rare earths to small Nd-Fe-B components. According to the size of the improved coercivity, the heavy rare earth metal diffusion source is selected as follows: For improving the coercivity of 3000-6000, Dy, Cu, Ga, Al alloy is selected as dysprosium diffusion source; For improving the coercivity of more than 6000, Tb, Pu, Cu, Ga, Al alloy is selected as terbium diffusion source.

9. The method according to claim 8, wherein the method is applied to the surface diffusion of heavy rare earths to small Nd-Fe-B components. The dysprosium diffusion source adopts Dy, Cu, Ga, Al alloy; wherein, Dy is 50-90%, Cu is 5-20%, Ga is 1-5%, and Al is 3-10%, which is dripped into organic solution after vacuum melting to obtain 1.5-6mm spherical alloy; The terbium diffusion source adopts Tb, Pu, Cu, Ga, Al alloy; wherein, Tb is 50-90%, Pu is 10-15%, Cu is 5-20%, Ga is 1-5%, and Al is 3-10%, which is dripped into organic solution after vacuum melting to obtain 1.5-6mm spherical alloy.

10. The method according to claim 9, wherein the method is applied to the surface diffusion of heavy rare earths to small Nd-Fe-B elements. The organic solution is a mixture of one or more of silicone oil or n-dodecane, n-tridecane, n-tetradecane, n-pentadecane.

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