Preparation process of composite magnetic body and product

Abstract

The invention relates to the field of magnetic material processing, and discloses a preparation process of a composite magnetic body and a product. The preparation technology of the composite magnetic body comprises the following steps that S1, first powder is pressed, and a core body is prepared; s2, coating the core body with the second powder, performing compression, and forming a coating layer on the outer surface of the core body to obtain a composite body; s3, carrying out vacuum sintering molding on the composite body to prepare a molded composite body; s4, cutting, electroplating and magnetizing the molded composite body to obtain a composite magnetic body; the first powder is neodymium iron boron magnetic powder, and the second powder is iron powder; the iron powder is pretreated iron powder, and the pretreated iron powder is prepared from 96-98 wt% of iron powder and 2-4 wt% of an adhesive. The prepared composite magnetic body is low in cost, the coating layer has good compactness, and the prepared composite magnetic body has stable magnetic performance and good mechanical strength.

Description

Technical Field

[0001] The present application relates to the field of magnetic material processing, and more specifically, to a preparation process and product of a composite magnetic body. Background Art

[0002] NdFeB magnets are based on the intermetallic compound Nd2Fe 14 B is the basis of permanent magnetic material. NdFeB magnets are divided into sintered NdFeB and bonded NdFeB. Bonded NdFeB is magnetic in all directions and corrosion-resistant. Sintered NdFeB is easy to corrode, so the surface needs to be plated, generally with zinc, nickel, environmentally friendly zinc, environmentally friendly nickel, environmentally friendly nickel-copper-nickel, etc.

[0003] Taking sintered NdFeB magnets as an example, the components of sintered NdFeB magnets are rare metals, which makes the cost of NdFeB magnets relatively high and is not conducive to industrial large-scale production.

[0004] In order to reduce the cost of NdFeB magnets in the prior art, metal powders with magnetic properties or capable of producing magnetic effects with magnetic materials are generally added to NdFeB magnets. Although the metal powders reduce the cost of NdFeB magnets, the bonding performance between the metal powders and NdFeB magnets is poor, which reduces the magnetic properties and mechanical strength of the obtained NdFeB magnets. Summary of the invention

[0005] In order to solve the problem that the bonding performance between metal powder and NdFeB magnet in existing low-cost sintered NdFeB magnet is poor, thereby reducing the magnetic properties and mechanical strength of the obtained NdFeB magnet, the present application provides a preparation process and product of a composite magnetic body.

[0006] In a first aspect, the present application provides a process for preparing a composite magnetic body, which adopts the following technical solution: A preparation process of a composite magnetic body comprises the following steps: S1, pressing the first powder into a mold to obtain a core; S2, coating the core with the second powder and performing pressing to form a coating layer on the outer surface of the core to obtain a composite body; S3, vacuum sintering the composite body to obtain a composite body; S4, cutting, electroplating, and magnetizing the formed composite body to obtain a composite magnetic body; The first powder material is NdFeB magnetic powder, and the second powder material is iron powder; the iron powder is pretreated iron powder, and the pretreated iron powder is made of 96-98wt% iron powder and 2-4wt% adhesive. By adopting the above technical scheme, NdFeB magnetic powder is used as the first powder material, and is pressed into the required shape and size, so that the magnetic powder reaches a certain density, and the core body is obtained, so as to achieve a dense structure with high magnetic properties during sintering, while maintaining the orientation degree obtained in the magnetic field orientation process, thereby improving the magnetic properties and mechanical strength of the obtained composite magnetic body. Then, iron powder is used as the second powder material, and coated on the outer surface of the core body. After pressing, a dense and strong coating layer is formed on the surface of the core body to obtain a molded composite body. The coating layer formed by the iron powder reduces the amount of NdFeB magnetic powder used and reduces the cost of the obtained composite magnetic body. By pretreating the iron powder with a relatively high weight of adhesive to obtain pretreated iron powder, the bonding strength between the coating layer and the core can be significantly improved, and the magnetic stability and mechanical strength of the composite magnetic body obtained can be further improved. If the amount of adhesive added is too large, it is easy for the coating layer to have pores during the sintering process, which will reduce the compactness of the composite magnetic body obtained. The obtained molded composite body is then vacuum sintered. During the sintering process, the grain size of the NdFeB magnetic powder and the iron powder is reduced, the grain boundary area is increased, the compactness is enhanced, and at the same time, the bonding density between the NdFeB magnetic powder and the iron powder is enhanced, which improves the magnetic properties and mechanical strength of the composite magnetic body obtained. It is then cut, electroplated on the outer surface to form a protective layer, and finally magnetized to obtain the composite magnetic body with stable magnetic properties and mechanical strength of the present application.

[0007] Preferably, the core body is subjected to vacuum sintering before being coated with the second powder.

[0008] By adopting the above technical solution, the core body is first subjected to vacuum sintering and molding treatment before being coated with the second powder, which can effectively reduce the internal porosity of the core body, make the core body structure more compact, and thus improve the magnetic properties and mechanical strength of the composite magnetic body. At the same time, the surface of the pre-sintered core body is smoother, further improving the magnetic stability of the composite magnetic body.

[0009] Preferably, the NdFeB magnetic powder is composed of a first magnetic powder and a second magnetic powder in a weight ratio of (2-3):1, the particle size of the first magnetic powder is 15-20 μm, and the particle size of the second magnetic powder is 6-10 μm; the iron powder is composed of a first iron powder and a second iron powder in a weight ratio of (1-2):1, the particle size of the first iron powder is 10-12 μm, and the particle size of the second iron powder is 0.05-3 μm.

[0010] By adopting the above technical solution, the particle size of NdFeB magnetic powder and the particle size of iron powder are optimized, and the overall magnetic properties and mechanical strength of the composite magnetic body are further improved. The first magnetic powder with large particle size and the second magnetic powder with small particle size cooperate with each other to increase the contact area between the grains of NdFeB magnetic powder, fill the gaps, improve the density and uniformity, and thus enhance the magnetic properties and mechanical strength. The first iron powder with large particle size and the second iron powder with small particle size cooperate with each other, and the particle size of the first iron powder is between the first magnetic powder and the second magnetic powder, and the particle size of the second iron powder is smaller, so that during the sintering process, the iron powder and the core can be stably combined to form a denser structure, further improving the magnetic properties and mechanical strength of the composite magnetic body.

[0011] Preferably, the sintering temperature in step S3 is 1000-1200° C., and the sintering time is 2-4 hours.

[0012] By adopting the above technical solution and controlling the optimal sintering temperature and sintering time, the density and compactness of the composite magnetic body can be effectively improved, thereby enhancing its magnetic properties and mechanical strength. At the same time, the internal defects of the composite magnetic body can be reduced, and the consistency and stability of the composite magnetic body can be improved.

[0013] Preferably, the thickness ratio of the core and the cladding is (4-6):1.

[0014] By adopting the above technical solution, the thickness ratio of the core and the coating layer can be controlled, which can effectively improve the overall performance of the composite magnetic body, prevent the composite magnetic body from cracking and deformation, and thus improve the reliability and stability of the composite magnetic body. If the coating layer is too thick, it is easy to affect the magnetic properties of the composite magnetic body, and if the coating layer is too thin, it is easy to affect the mechanical strength of the composite magnetic body.

[0015] Preferably, the adhesive is made from the following raw materials in percentage by weight: Tackifier 5-8% Dispersant 2-5% Structural regulator 6-10% Solvent Residue.

[0016] By adopting the above technical scheme, the adhesive is composed of a thickener, a dispersant, a structure regulator and a solvent in an optimal weight ratio, and the components cooperate with each other, which effectively improves the bonding stability between the iron powder particles, so that the iron powder can be stably combined with the core body while forming a stable and dense coating layer during vacuum sintering, forming a composite magnetic body with a dense and stable structure. Under the synergistic dispersing effect of the solvent and the dispersant, the iron powder can be evenly dispersed, reducing the occurrence of agglomeration or agglomeration, and improving the uniformity and consistency of the coating layer. The thickener is dispersed into the iron powder, enhancing the adhesion between the iron powder particles and between the iron powder and the NdFeB magnetic powder, further improving the coating density and structural stability of the coating layer. During the vacuum sintering process, under the synergistic bonding effect of the thickener, the structure regulator can play a good bonding role on the iron powder and the NdFeB magnetic powder during high-temperature sintering, further improving the density of the coating layer sintering, and at the same time improving the bonding stability of the coating layer and the core body.

[0017] Preferably, the viscosity enhancer is composed of propylene glycol alginate, hydroxypropyl distarch phosphate and 3-diethylenetriaminopropyltrimethoxysilane in a weight ratio of 1:(0.2-0.4):(0.1-0.2).

[0018] By adopting the above technical scheme, propylene glycol alginate, hydroxypropyl distarch phosphate and 3-diethylenetriaminopropyltrimethoxysilane in a relatively optimal weight ratio are used as thickeners to have a good synergistic effect and form a uniform thickening system, which can significantly improve the binding force between iron powder particles and the bonding stability between iron powder and the core, thereby improving the overall structural stability and mechanical strength of the composite magnetic body.

[0019] Preferably, the dispersant is polyacrylic acid sodium salt, and the solvent is water, propylene glycol and / or ethylene glycol.

[0020] By adopting the above technical solution, sodium polyacrylate can be used as a dispersant to effectively improve the uniform dispersion performance of iron powder. Using water, propylene glycol and / or ethylene glycol as a solvent can improve the overall fluidity of the adhesive, further promote the mixing uniformity of each component, further improve the bonding stability of the adhesive, and can be evenly decomposed during the vacuum sintering process without affecting the density of the coating layer.

[0021] Preferably, the structure regulator is composed of zinc oxide and tin oxide in a weight ratio of (1-1.5):1.

[0022] By adopting the above technical scheme, using zinc oxide and tin oxide in a relatively optimal weight ratio as structural regulators, it is possible to promote grain refinement during high-temperature sintering, form an alloy structure with iron, effectively improve the internal structure of the composite magnetic body, reduce defects and porosity during the sintering process, and improve the mechanical strength and magnetic properties of the obtained composite magnetic body.

[0023] In a second aspect, the present application provides a composite magnetic body, which adopts the following technical solution: A composite magnetic body is prepared by the above preparation process.

[0024] By adopting the above technical solution, the composite magnetic body prepared in the present application has low cost and good magnetic performance stability and mechanical strength.

[0025] In summary, this application has the following beneficial effects: 1. The preparation process of the composite magnetic body of the present application improves the bonding performance of the metal powder and the NdFeB magnetic powder by coating the pretreated iron powder made of adhesive and iron powder on the outer surface of the core formed by NdFeB magnetic powder, thereby solving the problem of poor bonding between the metal powder and the NdFeB magnetic powder. The prepared composite magnetic body has stable magnetic properties and good mechanical strength while being low in cost.

[0026] 2. By optimizing the particle size of iron powder and NdFeB magnetic powder, the contact area between the grains of NdFeB magnetic powder is increased, the gaps are filled, and the density and uniformity are improved; at the same time, during the sintering process, the iron powder and the core can be stably combined to form a denser structure, further improving the magnetic properties and mechanical strength of the composite magnetic body.

[0027] 3. Using propylene glycol alginate, hydroxypropyl distarch phosphate and 3-diethylenetriaminopropyltrimethoxysilane in a preferred weight ratio as thickeners, and using zinc oxide and tin oxide in a preferred weight ratio as structure regulators, the thickeners are dispersed in the iron powder, thereby enhancing the adhesion between the iron powder particles and between the iron powder and the NdFeB magnetic powder, and further improving the coating density and structural stability of the coating layer. During the vacuum sintering process, under the synergistic bonding effect of the thickener, the structure regulator can promote grain refinement during high-temperature sintering, form an alloy structure with iron, effectively improve the internal structure of the composite magnetic body, reduce defects and porosity during the sintering process, and improve the mechanical strength and magnetic properties of the obtained composite magnetic body. DETAILED DESCRIPTION

[0028] The present application is further described in detail below with reference to the embodiments.

[0029] The following are the sources and specifications of some raw materials of this application. The raw materials used in the preparation examples and embodiments of this application can be obtained from the market, including but not limited to the raw materials of the following models and manufacturers. Raw materials with equivalent performance can be used: 1. NdFeB magnetic powder: N50 NdFeB magnetic powder; 2. Iron powder: Yinbai brand, atomized spherical iron powder; 3. Sodium polyacrylate: Dow 445N or Dow dispersant OROTAN 731A; 4. Zinc oxide: particle size 30-50nm, content 99.7%; 5. Tin oxide: particle size 30-50nm, content 99.9%.

[0030] Preparation example of adhesive Preparation Example 1 Preparation Example 1 discloses an adhesive, which is prepared by the following steps: 0.8 kg of sodium carboxymethyl cellulose as a thickener and 0.2 kg of a dispersant (composed of polyethylene glycol 400 and 445N in a weight ratio of 2:1) were added to 8.4 kg of a solvent (composed of water and propylene glycol in a weight ratio of 2:1), and after stirring and dispersing, 0.6 kg of tin oxide as a structural regulator was added and dispersed evenly to obtain an adhesive.

[0031] Preparation Example 2-3 The difference between Preparation Example 2-3 and Preparation Example 1 is that the amount of raw materials used and the preparation conditions are different, see Table 1 below for details.

[0032] Table 1 Parameters of Preparation Examples 1-3 Preparation Example 4 The difference between Preparation Example 4 and Preparation Example 1 is that the thickener is different. The thickener in Preparation Example 4 is composed of sodium carboxymethyl cellulose, hydroxypropyl distarch phosphate and vinyl trimethoxy silane in a weight ratio of 1:0.2:0.1, and the rest is the same as Preparation Example 1.

[0033] Preparation Example 5 The difference between Preparation Example 5 and Preparation Example 4 is that the thickener in Preparation Example 5 is composed of propylene glycol alginate, hydroxypropyl distarch phosphate and 3-diethylenetriaminopropyltrimethoxysilane in a weight ratio of 1:0.2:0.1, and the rest is the same as Preparation Example 4.

[0034] Preparation Example 6 The difference between Preparation Example 6 and Preparation Example 4 is that the thickener in Preparation Example 6 is composed of propylene glycol alginate, hydroxypropyl distarch phosphate and 3-diethylenetriaminopropyltrimethoxysilane in a weight ratio of 1:0.4:0.2, and the rest is the same as Preparation Example 4.

[0035] Preparation Example 7 The difference between Preparation Example 7 and Preparation Example 5 is that the dispersant in Preparation Example 7 is polyacrylic acid sodium salt, specifically sodium polyacrylate 445N, and the rest is the same as Preparation Example 5.

[0036] Preparation Example 8 The difference between Preparation Example 8 and Preparation Example 5 is that the dispersant in Preparation Example 8 is polyacrylic acid sodium salt, specifically Dow dispersant OROTAN 731A, and the rest is the same as Preparation Example 5.

[0037] Preparation Example 9 The difference between Preparation Example 9 and Preparation Example 7 is that the structure adjusting agent in Preparation Example 9 is composed of zinc oxide and tin oxide in a weight ratio of 1:1, and the rest is the same as Preparation Example 7.

[0038] Preparation Example 10 The difference between Preparation Example 10 and Preparation Example 7 is that the structure adjusting agent in Preparation Example 10 is composed of zinc oxide and tin oxide in a weight ratio of 1.5:1, and the rest is the same as Preparation Example 7. Example

[0039] Example 1 Example 1 discloses a process for preparing a composite magnetic body, comprising the following steps: S1. Using a magnetic field forming press, NdFeB magnetic powder is used as the first powder for pressing, wherein the NdFeB magnetic powder consists of a first magnetic powder and a second magnetic powder in a weight ratio of 2:1, the particle size of the first magnetic powder is 15-20um, and the particle size of the second magnetic powder is 6-10um, and a core body is obtained after pressing; S2, using the pretreated iron powder as the second powder, coating the core and continuing to use the magnetic field forming press for pressing, the pretreated iron powder is composed of 96wt% iron powder and 4wt% of the adhesive prepared in Preparation Example 1, the iron powder is composed of a first iron powder and a second iron powder in a weight ratio of 1:1, the particle size of the first iron powder is 10-12μm, and the particle size of the second iron powder is 0.05-3μm, forming a coating layer on the outer surface of the core, and controlling the thickness ratio of the core to the coating layer to be 6:1, to obtain a composite; S3, the composite body is sintered in a sintering furnace at a temperature of 1000°C for 4 h in a vacuum of 1×10 - 3 Pa, vacuum sintering is performed to obtain a composite body; S4. Cut the formed composite body, and use nickel plating liquid to electroplate it on an automatic nickel plating line to form a 10μm nickel plating layer. Then use a multi-pole magnetizer to magnetize it. The magnetizing voltage is 3000V, the capacitance is 5000μF, and the magnetizing time is 1s to obtain a composite magnetic body. The nickel plating liquid is a commercially available nickel plating liquid for magnets, and the model here is not limited.

[0040] Example 2-3 The difference between Example 2-3 and Example 1 is that the process parameters are different, see Table 2 below for details.

[0041] Table 2 Parameters of Examples 1-3 Example 4 The difference between Example 4 and Example 1 is that in step S1, the core obtained after pressing is heated to 1000°C and the vacuum degree is 1×10 -3 Pa under vacuum sintering conditions for 1 h, and then perform step S2, and the rest is the same as Example 1.

[0042] Example 5 The difference between Example 5 and Example 1 is that the second magnetic powder is replaced by the first magnetic powder in equal amount, and the rest is the same as Example 1.

[0043] Example 6 The difference between Example 6 and Example 1 is that the first iron powder is replaced by the second iron powder in equal amount, and the rest is the same as Example 1.

[0044] Embodiment 7-13 The difference between Examples 7-13 and Example 1 is that the sources of the binder in the pretreated iron powder are different, see Table 3 below for details.

[0045] Table 3 Sources of adhesives in Examples 7-13 Comparative Example Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that in step S2, iron powder is directly used as the second powder, and the iron powder is composed of a first iron powder and a second iron powder in a weight ratio of 1:1. The particle size of the first iron powder is 10-12 μm, and the particle size of the second iron powder is 0.05-3 μm. The rest is the same as Example 1.

[0046] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the amount of pretreated iron powder used is 90wt%, the amount of adhesive used is 10wt%, and the rest is the same as Example 1.

[0047] Performance testing The performance tests of the composite magnetic bodies prepared in Examples 1-13 and Comparative Examples 1-2 are performed below, with the composite magnetic bodies with a size of D20*5 mm as the test samples: 1. Residual magnetism detection: Use a permanent magnet property tester to test the remanence Br (unit: kGs) of the composite magnetic body, test and record the test results; 2. Compressive strength test: Use a pressure testing machine to apply test pressure to the composite magnetic body, record the pressure value when the composite magnetic body breaks, and record it as the compressive strength (unit: kN / mm 2), test and record the test results; The following are the performance test data of the composite magnetic bodies of Examples 1-13 and Comparative Examples 1-2, see Table 4 below for details.

[0048] Table 4 Performance data of composite magnetic bodies of Examples 1-13 and Comparative Examples 1-2 Combining Examples 1-3 and Comparative Example 1 and Table 4, it can be concluded that the composite magnetic body prepared by using the pretreated iron powder of the present application as a coating layer and vacuum sintering it with a core body has a higher remanence and better compressive strength.

[0049] Combining Examples 1-3 and Examples 7-13 with Table 4, it can be concluded that further optimizing the component ratio of the binder used in the pre-treated iron powder can further improve the magnetic properties and mechanical strength of the composite magnetic body obtained. Compared with Examples 1 and 7, Examples 8-9 further optimize the ratio and amount of the thickener in the binder, and the remanence of the composite magnetic body obtained is increased by 0.31 kGs, and the compressive strength is also significantly increased by 0.28 kN / mm 2 This may be because the thickener improves the density and adhesion of the iron powder, thereby improving the overall mechanical strength of the composite magnetic body obtained. Compared with Example 8, Examples 10-11 further optimize the type of dispersant, and the residual magnetic properties and compressive strength of the composite magnetic body obtained are also improved. Compared with Example 10, Examples 12-13 further optimize the components and proportions of the structure regulator, and the residual magnetism of the composite magnetic body obtained is significantly improved to 13.96 / kGs, and the compressive strength is also increased to 1.42kN / mm 2 , which may be because the better structure regulator improves the structural density of the coating layer under high temperature sintering conditions, thereby improving the magnetic properties and mechanical strength of the composite magnetic body. In contrast, in Comparative Example 2, the amount of binder is increased compared to Example 1, and the magnetic properties and mechanical strength of the composite magnetic body obtained are reduced, which may be because the excessive amount of viscosity enhancer causes pores and voids to form during vacuum sintering, thereby reducing the performance of the composite magnetic body obtained.

[0050] Combining Examples 1-3 and Example 4 and Table 4, it can be concluded that in Example 4, before coating the second powder, the core was sintered first, and the remanence and compressive strength of the composite magnetic body obtained were slightly reduced, but the change was not large; while in Example 5, the large-particle first magnetic powder was used for all NdFeB magnetic powders, and the remanence and compressive strength of the composite magnetic body obtained were reduced. This may be because the sintering consistency of the large-particle first magnetic powder alone was low, which reduced the bonding performance of the core and the coating layer, resulting in reduced performance of the composite magnetic body. In Example 6, the small-particle second iron powder was used for all iron powders, and the remanence and compressive strength of the composite magnetic body obtained were reduced. This may be because the small-particle second iron powder alone reduced the contact area between the iron powder particles, which reduced the density of the coating layer after sintering, thereby reducing the magnetic properties and mechanical strength of the composite magnetic body obtained.

[0051] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A process for preparing a composite magnetic body, characterized in that: The following steps are involved: S1, pressing the first powder into a mold to obtain a core; S2, coating the core with the second powder and performing pressing to form a coating layer on the outer surface of the core to obtain a composite body; S3, vacuum sintering the composite body to obtain a composite body; S4, cutting, electroplating, and magnetizing the formed composite body to obtain a composite magnetic body; The first powder material is neodymium iron boron magnetic powder, and the second powder material is iron powder; the iron powder is pretreated iron powder, and the pretreated iron powder is made of 96-98wt% iron powder and 2-4wt% adhesive.

2. A process for preparing a composite magnetic body according to claim 1, characterized in that: The core body is first subjected to vacuum sintering before being coated with the second powder.

3. A process for preparing a composite magnetic body according to claim 1 or 2, characterized in that: The NdFeB magnetic powder is composed of a first magnetic powder and a second magnetic powder in a weight ratio of (2-3):1, the particle size of the first magnetic powder is 15-20µm, and the particle size of the second magnetic powder is 6-10µm; the iron powder is composed of a first iron powder and a second iron powder in a weight ratio of (1-2):1, the particle size of the first iron powder is 10-12µm, and the particle size of the second iron powder is 0.05-3µm.

4. The process for preparing a composite magnetic body according to claim 1, characterized in that: The sintering temperature in step S3 is 1000-1200° C., and the sintering time is 2-4 hours.

5. The process for preparing a composite magnetic body according to claim 1, characterized in that: The thickness ratio of the core and the cladding layer is (4-6):

1.

6. The process for preparing a composite magnetic body according to claim 1, characterized in that: The adhesive is prepared from the following raw materials in weight percentage: Tackifier 5-8% Dispersant 2-5% Structural adjustment agent 6-10% Solvent Residue.

7. A process for preparing a composite magnetic body according to claim 6, characterized in that: The viscosity enhancer is composed of propylene glycol alginate, hydroxypropyl distarch phosphate and 3-diethylenetriaminopropyltrimethoxysilane in a weight ratio of 1:(0.2-0.4):(0.1-0.2).

8. The process for preparing a composite magnetic body according to claim 6, characterized in that: The dispersant is polyacrylic acid sodium salt, and the solvent is water, propylene glycol and / or ethylene glycol.

9. The process for preparing a composite magnetic body according to claim 6, characterized in that: The structure adjusting agent is composed of zinc oxide and tin oxide in a weight ratio of (1-1.5):

1.

10. A composite magnetic body, characterized in that: The invention is prepared by the preparation process according to any one of claims 1 to 9.

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