Injection-molded ferrite magnetic powder, method for producing same, and use thereof

Abstract

The application provides an injection-molded ferrite magnetic powder and a preparation method and application thereof, and relates to the technical field of permanent magnetic materials. Specifically, the preparation method of the magnetic powder comprises the following steps: preparing iron red, strontium carbonate and strontium chloride to obtain first raw materials, balling, sintering and crushing the first raw materials in sequence to obtain coarse powder; mixing the coarse powder, fine-grained iron red, strontium carbonate, strontium chloride and bismuth oxide to obtain second raw materials, and tempering, pickling and crushing the second raw materials in sequence to obtain the ferrite magnetic powder. The injection-molded bonded ferrite magnetic powder prepared by the application has high compression density, and effectively simplifies the production process of the existing magnetic powder with bimodal or multimodal particle size distribution, improves the flowability and magnetic performance of the injection-molded magnet, exceeds the level of the same foreign products, and has a good application prospect.

Description

Technical Field

[0001] This invention relates to the field of permanent magnet materials technology, and more specifically, to a ferrite magnetic powder for injection molding, its preparation method, and its application. Background Technology

[0002] Injection-molded magnets require high melt flowability to fill the mold and be injection molded into complex magnetic materials. To ensure melt flowability, the volume ratio of magnetic powder in the magnet raw material is usually reduced to increase the volume ratio of binder and thus improve material flowability. However, this method reduces magnetic properties. Conversely, simply increasing the powder content can improve performance to some extent but reduce flowability, worsen the mechanical properties of the magnet, and even lead to molding failure.

[0003] In injection-molded bonded ferrite magnets, ferrite powder accounts for approximately 90% of the mass. The properties of the magnetic powder directly affect the magnet's flowability and magnetic properties, including intrinsic coercivity. To overcome the imbalance between flowability and magnetic properties, a higher compressibility density of the ferrite powder is required. This allows for a lower volume percentage of the same mass percentage of powder in the binder, resulting in a relatively larger volume ratio of the binder and thus improved magnet flowability. Therefore, under certain magnet formulation and molding process conditions, the flowability of the magnet is positively correlated with the compressibility density of the magnetic powder.

[0004] In conventional processes, the particle size distribution of magnetic powder follows a normal distribution, exhibiting a single peak in its waveform, and its compressive density is generally around 3.3 g / cm³. 3 The compressibility of ferrite magnetic powder produced using a mixture of coarse and fine powders can reach approximately 3.45 g / cm³. 3 At this point, the waveform of the particle size distribution will exhibit multiple peaks. This magnetic powder uses a process of mixing coarse and fine ferrite powder particles, allowing the fine magnetic powder particles to fill the pores of the coarse magnetic powder particles, thereby increasing the filling rate of the magnetic powder in the bonded magnet and thus improving the magnet's performance. Currently, there are many existing technologies in this area, but some technical problems still exist. Existing technologies all involve first manufacturing coarse and fine powders separately, and then mixing them using dry or wet methods; the powder production involves two process routes and requires a mixing step, resulting in a complex process flow; in addition, the fine powder requires a long time of fine grinding, resulting in low production efficiency and high energy consumption.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The primary objective of this invention is to provide a method for preparing ferrite magnetic powder for injection molding. This method uses a novel preparation route to obtain ferrite magnetic powder with a bimodal or multimodal particle size distribution, which can effectively improve the filling rate of magnetic powder in the magnet. At the same time, it solves the technical defects of the current process route, which involves preparing coarse powder and fine powder separately, such as complex process flow and low production efficiency.

[0007] The second objective of this invention is to provide a ferrite magnetic powder.

[0008] The third objective of this invention is to provide a method for preparing an injection-molded magnet; while achieving the technical effects of the first objective, the resulting injection-molded magnet has good magnetic and mechanical properties.

[0009] A fourth objective of this invention is to provide a magnet.

[0010] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0011] A method for preparing ferrite magnetic powder for injection molding includes the following steps:

[0012] (1) Prepare iron oxide red, strontium carbonate and strontium chloride to obtain the first raw material, and then subject the first raw material to pelletizing, sintering and crushing in sequence to obtain coarse powder;

[0013] (2) The coarse powder, fine iron oxide red, strontium carbonate, strontium chloride and bismuth oxide are mixed to obtain a second raw material. The second raw material is then subjected to tempering, pickling and crushing in sequence to obtain ferrite magnetic powder.

[0014] A ferrite magnetic powder is prepared according to the method for preparing ferrite magnetic powder for injection molding.

[0015] A method for preparing an injection-molded magnet, which is prepared using the aforementioned ferrite magnetic powder;

[0016] The preparation method of the injection-molded magnet includes the following steps: mixing the ferrite magnetic powder and the additives, extruding and granulating the mixture, and then injection molding to obtain the magnet.

[0017] A magnet is prepared using the injection molding magnet preparation method described above.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] This invention first obtains coarse powder using specific raw materials and conventional processes. Then, the coarse powder is uniformly mixed with fine-grained iron oxide, strontium carbonate, strontium chloride, and bismuth oxide, and tempered at a low temperature. The role of bismuth oxide is to prevent excessive grain growth, resulting in fine and uniform grains, making it irreplaceable. During tempering, the iron oxide, strontium carbonate, strontium chloride, and bismuth oxide undergo a certain degree of ferrite formation reaction. Due to the low tempering temperature, the iron oxide particles are small and contain a certain amount of strontium chloride and bismuth oxide adhering around the reaction grain boundaries, resulting in small grain sizes generated during tempering, theoretically less than 1.0 μm. These fine grains generated during tempering can fill the gaps between the coarse-grained ferrite magnetic powders, obtaining magnetic powder with a bimodal or multimodal particle size distribution, thereby increasing the overall compressibility density of the magnetic powder. By using magnetic powder with a higher compressibility density, the volume ratio of the binder is effectively increased while ensuring the quality and quantity of ferrite magnetic powder, thus achieving a win-win situation in both the flow and magnetic properties of the magnet. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially. In addition, the terms "first", "second", "1", and "2" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0021] The first aspect of the present invention is to provide a method for preparing ferrite magnetic powder for injection molding. (1) Iron oxide red, strontium carbonate and strontium chloride are prepared to obtain a first raw material, and the first raw material is subjected to pelletizing, sintering and crushing in sequence to obtain coarse powder; (2) The coarse powder, fine iron oxide red, strontium carbonate, strontium chloride and bismuth oxide are mixed to obtain a second raw material, and the second raw material is subjected to tempering, pickling and crushing in sequence to obtain ferrite magnetic powder.

[0022] It is worth noting that any of the raw material components involved in this invention are irreplaceable. For example, bismuth oxide can be replaced with a bismuth salt, iron oxide can be replaced with iron scale, and strontium carbonate or strontium chloride can be replaced with strontium oxide. When other substitute raw materials are used, the corresponding performance effect cannot be obtained. This is partly due to the reaction grain boundaries and grain configuration, and partly because using other substitute raw materials may introduce uncontrollable impurities that reduce performance, or increase costs due to the use of high-purity raw materials.

[0023] In a preferred embodiment, the purity of the raw materials involved in this invention is as follows: iron oxide red purity ≥ 99.8 wt%; strontium carbonate purity ≥ 99.5 wt%; strontium chloride purity ≥ 99.5 wt%; bismuth oxide purity ≥ 99.5 wt%.

[0024] In a preferred embodiment, in step (1), the mass ratio of the iron oxide red, the strontium carbonate, and the strontium chloride is (43-50):(6.6-7):(0.9-1.1); in a more preferred embodiment, the mass ratio of the iron oxide red, the strontium carbonate, and the strontium chloride is 45:6.8:1. In a more preferred embodiment, the iron oxide red and the strontium carbonate are first prepared, with a molar ratio of ferric oxide to strontium carbonate in the iron oxide red being 6:1; then 2 wt.% of strontium chloride is added to both and mixed.

[0025] In a preferred embodiment, in step (1), the granulation includes: mixing the first raw material with a small amount of water to prepare granules, and then drying the granules to complete the granulation.

[0026] In a preferred embodiment, in step (1), the particle size of the granulation is 5 mm to 10 mm.

[0027] In a preferred embodiment, in step (1), the sintering temperature is 1280℃~1300℃ and the sintering heat treatment time is 1.5h~2.5h; in a more preferred embodiment, the sintering temperature is 1290℃ and the sintering heat treatment time is 2h.

[0028] In a preferred embodiment, in step (1), the particle size of the coarse powder is 4μm to 6μm.

[0029] As a preferred embodiment, in step (1), there is no restriction on the particle size range of the iron oxide red, the strontium carbonate and the strontium chloride of the raw material components. Under normal circumstances, commercially available conventional powder-grade particle size can be selected. Similarly, in step (2), the strontium carbonate, the strontium chloride and the bismuth oxide of the raw material components are selected.

[0030] In a preferred embodiment, in step (2), the particle size of the fine-grained iron oxide is <0.7μm. There are no restrictions on the source of the fine-grained iron oxide in the art. In this invention, fine-grained iron oxide raw materials that meet the specified particle size can be purchased directly, or fine grinding can be performed on any high-purity iron oxide raw material to meet the particle size limit of the fine-grained iron oxide.

[0031] In a preferred embodiment, in step (2), the mass ratio of the coarse powder to the second raw material is 60% to 75%; in a more preferred embodiment, the mass ratio of the coarse powder to the second raw material is 70%. That is, in step (2), the mass ratio of the sum of the masses of the fine-grained iron oxide, the strontium carbonate, the strontium chloride, and the bismuth oxide to the mass of the coarse powder is (25% to 40%): (60% to 75%).

[0032] In a preferred embodiment, in step (2), the mass ratio of the fine-grained iron oxide red, the strontium carbonate, the strontium chloride, and the bismuth oxide is (170-175):(27-30):(7.7-8.5):(0.9-1.1). In a more preferred embodiment, the mass ratio of the fine-grained iron oxide red, the strontium carbonate, the strontium chloride, and the bismuth oxide is 172:28:8:1. In a more preferred embodiment, the mixture is first prepared according to a molar ratio of the fine-grained iron oxide red and the strontium carbonate of 5.5:1, and then the strontium carbonate and the bismuth oxide are added, which are 4 wt.% and 0.5 wt.% of the total mass of the iron oxide red and the strontium carbonate, respectively.

[0033] In a preferred embodiment, in step (2), the tempering temperature is 880℃~920℃, and the tempering heat treatment time is 90min~120min; the tempering step includes: reaching the required tempering temperature of the material at a heating rate of 5℃ per minute, and then performing heat treatment with heat preservation until the heat treatment time is over, and then completing the tempering; in a more preferred embodiment, the tempering temperature is 900℃ and the time is 115min.

[0034] In a preferred embodiment, in step (2), unreacted non-magnetic phase components such as strontium carbonate and strontium chloride are removed by acid washing to further enhance the magnetic properties of the magnetic powder; the acid reagent for acid washing includes hydrochloric acid with a mass concentration of 2%.

[0035] In a preferred embodiment, in step (2), the pickling includes: adding the tempered second raw material to the acid reagent, optionally stirring, until the pH of the acid reagent is 6-7, and then replacing the acid reagent.

[0036] In a preferred embodiment, in step (2), after the acid washing is completed, the solid and liquid are separated and washed and dried, and then the crushing is carried out.

[0037] In a preferred embodiment, the ferrite magnetic powder obtained by the present invention has a particle size of 1.6 μm to 1.8 μm.

[0038] In a preferred embodiment, the compressive density (CD) of the ferrite magnetic powder obtained by the present invention is ≥3.45 g / cm³. 3 .

[0039] A second aspect of the present invention is to provide a ferrite magnetic powder, which is prepared according to the method for preparing ferrite magnetic powder for injection molding.

[0040] A third aspect of the present invention provides a method for preparing an injection-molded magnet, which is prepared using the aforementioned ferrite magnetic powder. The method for preparing the injection-molded magnet includes the following steps: mixing the ferrite magnetic powder and an additive, extruding and granulating the mixture, and then injection molding the mixture to obtain the magnet.

[0041] In a preferred embodiment, the additive includes an adhesive; the additive may also include at least one of a lubricant, a stabilizer, a UV absorber, or an antioxidant.

[0042] In a preferred embodiment, the mass ratio of the ferrite magnetic powder to the additive is (90%–92%): (8%–10%).

[0043] As a preferred embodiment, the intrinsic coercivity (H) of the injection-molded magnet cj ≥218kA / m, remanent magnetic induction (B r ≥298mT, fluidity (MFR) ≥125g / 10min.

[0044] A fourth aspect of the present invention is to provide a magnet prepared by the aforementioned method for preparing injection-molded magnets.

[0045] Example 1

[0046] (1) Coarse powder manufacturing:

[0047] Iron oxide red and strontium carbonate were weighed, with a molar ratio of ferric oxide to strontium carbonate of 6:1 in the iron oxide red. 2 wt.% of strontium chloride was added to the weighed mixture, and the mixture was then granulated with water to form pellets with a diameter of 10 mm. These pellets were then dried in an oven at 120°C. The dried pellets were sintered in an electric furnace at 1290°C for 2 hours, and then crushed using a jaw crusher to obtain coarse powder with an average particle size of 5.0 μm.

[0048] (2) Magnetic powder manufacturing:

[0049] The mixture is prepared by adding 70 wt.% coarse powder and 30 wt.% other raw materials. The other raw materials are a mixture of fine-grained iron oxide red (particle size less than 0.7 micrometers), strontium carbonate, strontium chloride and bismuth oxide. The preparation of the other raw materials is as follows: first, the iron oxide red and strontium carbonate are prepared at a molar ratio of 5.5:1, and then strontium carbonate and bismuth oxide are added, which are 4 wt.% and 0.5 wt.% of the total mass of iron oxide red and strontium carbonate, respectively.

[0050] The prepared mixed powder was tempered in a 900-degree electric furnace for 115 minutes, and then allowed to cool to room temperature. It was then pickled with a 2% hydrochloric acid solution, and the tempered powder was added to the pickling solution until the pH value of the pickling solution rose to 6. Finally, it was dried and crushed to obtain the final product.

[0051] (3) Magnet manufacturing:

[0052] 91 parts by weight of mixed magnetic powder, 0.5 parts by weight of stabilizer (BASF antioxidant 1098 and UV absorber UV531, in a weight ratio of 1:1), 0.5 parts by weight of lubricant (chlorinated paraffin and TAF, in a mass ratio of 1:1) and 8.0 parts by weight of binder (nylon 6) were mixed in a mixer, and then extruded and granulated using a twin-screw extruder. The resulting granules were then injection molded on an injection molding machine to obtain the injection-molded magnet of this embodiment; the molded sample size was Φ20×10mm.

[0053] Example 2

[0054] It is basically the same as Example 1, except that in step (2): it is prepared by mixing 65 wt.% coarse powder and 35 wt.% other raw materials.

[0055] Example 3

[0056] It is basically the same as Example 1, except that in step (2): it is prepared by using 60 wt.% coarse powder and 40 wt.% other raw materials.

[0057] Example 4

[0058] It is basically the same as Example 1, except that:

[0059] In step (1): weigh iron oxide red and strontium carbonate, with the molar ratio of iron oxide to strontium carbonate in iron oxide red being 5.8:1;

[0060] In step (2): the mixture is prepared according to a molar ratio of iron oxide red and strontium carbonate of 5.3:1.

[0061] Example 5

[0062] It is basically the same as Example 1, except that:

[0063] In step (1): weigh iron oxide red and strontium carbonate, with the molar ratio of iron oxide to strontium carbonate in iron oxide red being 6.2:1;

[0064] In step (2): the mixture is prepared according to a molar ratio of iron oxide red and strontium carbonate of 5.7:1.

[0065] Example 6

[0066] It is basically the same as Example 1, except that:

[0067] In step (1): the dried pellets are sintered in an electric furnace at 1280 degrees Celsius for 2.5 hours;

[0068] In step (2): the prepared mixed powder is tempered in an electric furnace at 880 degrees Celsius for 120 minutes.

[0069] Example 7

[0070] It is basically the same as Example 1, except that:

[0071] In step (1): the dried pellets are sintered in an electric furnace at 1300 degrees Celsius for 1.5 hours;

[0072] In step (2): the prepared mixed powder is tempered in an electric furnace at 880 degrees Celsius for 120 minutes.

[0073] Comparative Example 1

[0074] It is basically the same as Example 1, except that in step (2): it is prepared by mixing 50 wt.% coarse powder and 50 wt.% other raw materials.

[0075] Comparative Example 2

[0076] It is basically the same as Example 1, except that in step (2): it is prepared by adding 80 wt.% coarse powder and 20 wt.% other raw materials.

[0077] Comparative Example 3

[0078] It is basically the same as Example 1, except that in step (2): the prepared mixed powder is tempered in an electric furnace at 800 degrees Celsius for 120 minutes.

[0079] Comparative Example 4

[0080] The process is basically the same as in Example 1, except that in step (2), the prepared mixed powder is tempered in an electric furnace at 1000 degrees Celsius for 90 minutes.

[0081] Table 1 below provides magnetic performance data for the injection-molded magnets prepared in each embodiment and comparative example.

[0082] The magnetic performance testing method includes: mixing the injection-molded magnet at 240°C to form particles with an average particle size of 3 mm; injection molding the particles into cylindrical molded products with a diameter of 20 mm and a height of 10 mm in an orientation magnetic field of 270°C and 8.0 kGS (the direction of the orientation magnetic field is parallel to the central axis of the cylinder); and then measuring its magnetic performance using a permanent magnet measuring instrument.

[0083] The flowability test method includes: mixing injection-molded magnets at 240°C to form particles with an average particle size of 3 mm; feeding the obtained particles into a melt flow index tester, measuring the extrusion weight within 10 minutes at 270°C and a load of 10 kg, and taking it as the melt flow rate (unit: g / 10 min).

[0084] The method for testing compressibility density includes: placing 15g of magnetic powder obtained in step (2) into a cylindrical mold with a diameter of 25mm, applying a forming pressure of 80kN to press it into a cylindrical blank, measuring the thickness of the blank, and calculating the compressibility density.

[0085] Table 1

[0086]

[0087]

[0088] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can 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, without departing from the spirit and scope of the present invention; 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 of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing ferrite magnetic powder for injection molding, characterized in that, The method for preparing the ferrite magnetic powder for injection molding includes the following steps: (1) Prepare iron oxide red, strontium carbonate and strontium chloride to obtain the first raw material, and then subject the first raw material to pelletizing, sintering and crushing in sequence to obtain coarse powder; (2) The coarse powder, fine-grained iron oxide red, strontium carbonate, strontium chloride and bismuth oxide are mixed to obtain a second raw material. The second raw material is then subjected to tempering, pickling and crushing in sequence to obtain ferrite magnetic powder. The particle size of the fine-grained iron oxide red is <0.7μm. The mass ratio of the coarse powder to the second raw material is 60%~75%. The tempering temperature is 880℃~920℃ and the tempering heat treatment time is 90min~120min.

2. The method for preparing ferrite magnetic powder for injection molding according to claim 1, characterized in that, In step (1), the ratio of the iron oxide red, the strontium carbonate and the strontium chloride by mass is (43~50):(6.6~7):(0.9~1.1).

3. The method for preparing ferrite magnetic powder for injection molding according to claim 1, characterized in that, In step (1), the sintering temperature is 1280℃~1300℃ and the heat treatment time for sintering is 1.5h~2.5h.

4. The method for preparing ferrite magnetic powder for injection molding according to claim 1, characterized in that, In step (2), the particle size of the ferrite magnetic powder is 1.6 μm to 1.8 μm.

5. The method for preparing ferrite magnetic powder for injection molding according to claim 1, characterized in that, In step (2), the ratio of the amount of fine-grained iron oxide red, strontium carbonate, strontium chloride and bismuth oxide by mass is (170~175):(27~30):(7.7~8.5):(0.9~1.1).

6. Ferrite magnetic powder prepared by the method for preparing ferrite magnetic powder for injection molding as described in any one of claims 1 to 5.

7. A method for preparing an injection-molded magnet, characterized in that, It was prepared using the ferrite magnetic powder as described in claim 6; The preparation method of the injection-molded magnet includes the following steps: mixing the ferrite magnetic powder and the additives, extruding and granulating the mixture, and then injection molding to obtain the magnet.

8. The method for preparing an injection-molded magnet according to claim 7, characterized in that, The additives include adhesives.

9. The method for preparing an injection-molded magnet according to claim 8, characterized in that, The additives include at least one of lubricants, stabilizers, UV absorbers, or antioxidants.

10. A magnet prepared by the method for preparing an injection-molded magnet as described in any one of claims 7 to 9.

11. The magnet according to claim 10, characterized in that, The magnet has an intrinsic coercivity ≥218kA / m, a residual magnetic induction ≥298mT, and a fluidity ≥125g / 10min.

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