Preparation method for improving size consistency of sintered neodymium iron boron

Abstract

The invention discloses a preparation method for improving the size consistency of sintered neodymium iron boron, and belongs to the technical field of neodymium iron boron magnet preparation, and the preparation method comprises the steps that neodymium iron boron alloy is cast into a throwing sheet with the thickness of 0.2-0.35 mm in a vacuum environment, and the casting temperature is 1450 DEG C; introducing hydrogen into a vacuum environment to carry out coarse crushing, and carrying out dehydrogenation treatment in an environment of 560 DEG C after crushing to obtain coarse powder; putting the coarse powder into a material tank, and carrying out jet milling to obtain powder with the particle size of 3.0 microns; magnetizing and pressing the powder through a pressing machine to obtain a blank; and the blank is subjected to cold isostatic pressing for 30 s under the pressure of 200 Mpa and then placed in a sintering furnace to be sintered. According to the method, the consistency of the powder is improved through control over agent adding and powder mixing in the powder preparing stage, and then the size consistency of the product is improved through change of powder distribution, control over the forming process and control over the sintering process in the forming process.

Description

Technical Field

[0001] The invention belongs to the technical field of NdFeB magnet preparation, and in particular relates to a preparation method for improving the dimensional consistency of sintered NdFeB. Background Art

[0002] Sintered NdFeB permanent magnet materials are widely used in electronics, electromechanics, communications, instruments, medical and military fields due to their excellent comprehensive magnetic properties. However, in the preparation process of traditional sintered NdFeB permanent magnet materials, due to the limitations of the blank deformation and oxide layer, a large amount of excess needs to be removed during the subsequent processing, resulting in a low yield rate. This increases material consumption and processing costs.

[0003] In the prior art, a Chinese patent with the announcement number CN103506624B discloses a sintering method for NdFeB magnets, which reduces the oxidation of NdFeB green billets before entering the furnace, thereby reducing the deformation during sintering and reducing the reserved processing allowance of the NdFeB green billets. However, the above method often has problems such as uneven powder distribution and poor dimensional consistency during the molding process, which affects the quality and performance of the product.

[0004] Therefore, it is necessary to propose a preparation method for improving the dimensional consistency of sintered NdFeB to solve the above problems. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a preparation method for improving the size consistency of sintered NdFeB, and to achieve uniform distribution of powder and precise control of magnet size by optimizing the powder making, molding and sintering processes. The present invention first improves the consistency of powder by controlling the additives and powder mixing in the powder making stage, then improves the size consistency of the product by changing the powder distribution and controlling the molding process in the molding process, and finally by controlling the sintering process.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a preparation method for improving the dimensional consistency of sintered NdFeB, comprising the following steps:

[0008] S1: Casting stage: The NdFeB alloy is cast into a sheet with a thickness of 0.2-0.35 mm in a vacuum environment at a casting temperature of 1450°C and a casting time of 20 minutes;

[0009] S2: Coarse powder preparation stage: hydrogen is introduced into the vacuum environment for coarse crushing, and after crushing, dehydrogenation treatment is performed at 560°C to obtain coarse powder;

[0010] S3: fine powder making stage: the coarse powder is placed in a material tank and subjected to airflow grinding to obtain a powder with a particle size of 3.0 um. A stirring assembly is provided in the material tank. During the airflow grinding process, the material tank is rotated by a rotating mechanism so that the stirring assembly stirs the powder.

[0011] S4: magnetization and pressing stage: the powder body is magnetized and pressed by a press to obtain a blank, wherein the magnetization position is in the middle of the press;

[0012] S5: Sintering stage: The blank is cold isostatically pressed at 200 MPa for 30 seconds and then placed in a sintering furnace for sintering.

[0013] Furthermore, the stirring assembly includes a plurality of vibration motors installed on the material tank, the output end of the vibration motor is fixedly connected to a stirring member, and the stirring member is movably arranged in the material tank away from the end of the vibration motor.

[0014] Furthermore, the stirring member is a 80-mesh screen.

[0015] Furthermore, during the sintering stage, the blanks are placed in graphite boxes arranged in an array in a sintering furnace, gaps are provided between adjacent graphite boxes in a horizontal direction, and through holes are provided on two opposite side walls of the graphite boxes.

[0016] Furthermore, 0.8 g / kg and 1 g / kg of lubricant are added in the coarse powder making stage and the fine powder making stage respectively, and the lubricant consists of zinc stearate and petroleum ether in a ratio of 1:1.

[0017] The beneficial effects of the present invention are:

[0018] The invention significantly improves the uniformity of powder particles by introducing an active stirring device, a magnetizing position, screen filtering and gap ventilation.

[0019] Other advantages, objectives and features of the present invention will be described in the following description and will be apparent to those skilled in the art to some extent, or those skilled in the art may be taught from the practice of the present invention. The objectives and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to make the purpose, technical solution and beneficial effects of the present invention clearer, the present invention provides the following drawings for illustration:

[0021] Figure 1 is a flow chart of the preparation method of an embodiment of the present invention;

[0022] Figure 2 This is a schematic diagram of the installation of a stirring assembly according to an embodiment of the present invention;

[0023] Figure 3 A schematic diagram of placing a graphite box according to an embodiment of the present invention;

[0024] Figure 4 FIG. 4 is a diagram showing the magnetic field distribution of a press according to an embodiment of the present invention.

[0025] The markings in the accompanying drawings are as follows: material tank 1, vibration motor 2, stirring element 3, graphite box 4, through hole 5. DETAILED DESCRIPTION

[0026] like Figures 1 to 4 As shown, the present invention provides a preparation method for improving the dimensional consistency of sintered NdFeB, comprising the following steps:

[0027] S1: Casting stage: The NdFeB alloy is cast into a 0.25 thick sheet in a vacuum environment at a casting temperature of 1450°C and a casting time of 20 minutes;

[0028] S2: Coarse powder preparation stage: hydrogen is introduced into the vacuum environment for coarse crushing, and after crushing, dehydrogenation treatment is performed at 560°C to obtain coarse powder;

[0029] S3: fine powder making stage: the coarse powder is placed in the material tank 1 and subjected to airflow grinding to obtain a powder with a particle size of 3.0 um, wherein a stirring assembly is provided in the material tank 1. During the airflow grinding process, the material tank 1 is rotated by a rotating mechanism so that the stirring assembly stirs the powder;

[0030] Among them, the additive in the coarse powder stage is 0.8g / kg, and the additive in the fine powder stage is 1g / kg; the additive is a lubricant, which is composed of zinc stearate and petroleum ether in a ratio of 1:1.

[0031] S4: magnetization and pressing stage: the powder body is magnetized and pressed by a press to obtain a blank, wherein the magnetization position is in the middle of the press;

[0032] S5: Sintering stage: The blank is cold isostatically pressed at 200 MPa for 30 seconds and then placed in a sintering furnace for sintering.

[0033] This solution significantly improves the uniformity of powder particles by introducing an active stirring device and consistent control of the magnetizing position, and achieves a size consistency of 85.3%. The magnetizing position is set in the middle of the press, making the magnetic field the strongest and most uniform, the orientation degree the highest, and the blank shrinkage more uniform.

[0034] In one embodiment of the present invention, the stirring assembly includes a plurality of vibration motors 2 mounted on the material tank 1, the output end of the vibration motor 2 is fixedly connected to a stirring member 3, and the stirring member 3 is movably arranged in the material tank 1 away from the end of the vibration motor 2.

[0035] In this solution, during the fine powder making stage, the material tank 1 is driven to rotate by the rotating mechanism, so that the stirring element 3 rotates with the material tank 1 to stir the coarse powder in the material tank 1, and at the same time, the vibration motor 2 is started to drive the stirring element 3 to vibrate to improve the stirring effect.

[0036] In one embodiment of the present invention, the stirring member 3 is a 80-mesh screen, so that the agglomerated particles are dispersed again during the stirring process, making the powder more uniform, reducing agglomeration, and improving the molding effect; and the size consistency is further improved to 97.5%.

[0037] In one embodiment of the present invention, during the sintering stage, the blank obtained by magnetization pressing is placed in a graphite box 4, and a plurality of graphite boxes 4 are arrayed in a sintering furnace, with gaps provided between adjacent graphite boxes 4 in the horizontal direction, and a plurality of graphite boxes 4 are overlapped in the vertical direction, and the graphite boxes 4 are provided with through holes 5 on both side walls opposite to each other in the width direction.

[0038] In the conventional graphite box process, the graphite boxes are stacked in a closed manner, which will make the graphite boxes highly airtight, and the internal gas will not be able to be completely discharged or discharged in time, which will make it impossible to reduce the carbon content of the blank, and the sintering atmosphere of the blank is inconsistent, resulting in inconsistent shrinkage and dimensional consistency problems. The sintered graphite box 4 adopts a two-side opening method and a gap arrangement method. The graphite box 4 is 300mm long, 280mm wide, and 80mm high. The two sides opposite to the width direction of the graphite box 4 have a through hole 5 with a diameter of 10mm. The through hole 5 is located in the middle of the 300*80 surface and is 10mm away from the top surface. Different graphite boxes 4 can be stacked together in the vertical direction. At the same time, during the placement of the graphite boxes, between adjacent graphite boxes 4 in the horizontal direction The invention has a gap; the advantage is that the modification to the graphite box 4 is relatively small, which reduces the modification cost; the method of use is simple and practical; and the sintering process does not need to be changed to achieve the effect of exhaust and improving the dimensional consistency; since a hole is opened in the middle, during the vacuuming stage of the sintering process, the gas released from the inside of the blank during the vacuuming and exhausting stages is smoothly discharged through the holes, thereby making the sintering atmosphere of the blanks between different layers in the sintering furnace body more consistent, reducing the difference in dimensional consistency and improving dimensional consistency; at the same time, the additives released in the blank are discharged in the form of gas, which is conducive to faster vacuuming of the graphite box 4 during the vacuuming stage and reducing the pollution of the blank by the surrounding atmosphere; and the dimensional consistency is further improved to 100%.

[0039] As shown in the following table, in the following embodiments, based on the addition of 0.8 g / kg in the coarse powder stage and 1 g / kg in the fine powder stage, Example 5 adopts active stirring as the stirring method, wherein normal stirring is that no stirring component is provided in the material tank 1, and stirring is performed only by the rotation of the material tank; active stirring is that a stirring component is provided in the material tank 1, and active stirring is performed by rotating the material tank 1 in conjunction with the stirring component; in the molding powder method, the normal method is that no screen is provided, and the screen filtration method is that the stirring member 3 is set to a screen of 80 mesh; the magnetization position is as follows Figure 4 In the sintering method, the normal method is to use a graphite box 4 without a through hole 5, and there is no gap between adjacent graphite boxes 4 in the horizontal direction. The gap vent valve is to use a graphite box 4 with a through hole 5, and there is a gap between adjacent graphite boxes 4 in the horizontal direction. After setting the parameters as shown in the table below, the parameters used in Example 5 can further improve the dimensional consistency to 100%, thereby maximizing the quality and performance of the product.

[0040]

[0041] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A preparation method for improving the dimensional consistency of sintered NdFeB, characterized in that: The following steps are involved: S1: Casting stage: The NdFeB alloy is cast into a sheet with a thickness of 0.2-0.35 mm in a vacuum environment at a casting temperature of 1450°C and a casting time of 20 minutes; S2: Coarse powder preparation stage: hydrogen is introduced into the vacuum environment for coarse crushing, and after crushing, dehydrogenation treatment is performed at 560°C to obtain coarse powder; S3: fine powder making stage: the coarse powder is placed in a material tank and subjected to airflow grinding to obtain a powder with a particle size of 3.0 um. A stirring assembly is provided in the material tank. During the airflow grinding process, the material tank is rotated by a rotating mechanism so that the stirring assembly stirs the powder. S4: magnetization and pressing stage: the powder body is magnetized and pressed by a press to obtain a blank, wherein the magnetization position is in the middle of the press; S5: Sintering stage: The blank is cold isostatically pressed at 200 MPa for 30 seconds and then placed in a sintering furnace for sintering.

2. The method for preparing sintered NdFeB with improved dimensional consistency according to claim 1, characterized in that: The stirring assembly comprises a plurality of vibration motors mounted on the material tank, wherein the output end of the vibration motor is fixedly connected with a stirring member, and the stirring member is movably arranged in the material tank away from the end of the vibration motor.

3. The method for preparing sintered NdFeB with improved dimensional consistency according to claim 2, characterized in that: The stirring member is a 80-mesh screen.

4. The method for preparing sintered NdFeB with improved dimensional consistency according to claim 1, characterized in that: During the sintering stage, the blanks are placed in graphite boxes arranged in an array in a sintering furnace, gaps are provided between adjacent graphite boxes in a horizontal direction, and through holes are provided on two opposite side walls of the graphite boxes.

5. The method for preparing sintered NdFeB with improved dimensional consistency according to claim 1, characterized in that: 0.8 g / kg and 1 g / kg of lubricant are added in the coarse powder making stage and the fine powder making stage respectively. The lubricant consists of zinc stearate and petroleum ether in a ratio of 1:1.

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