Preparation method of injection-molded complex-shape low-pressure sintered permanent magnetic ferrite

Abstract

The invention belongs to the technical field of sintered permanent magnetic ferrite preparation, and provides a preparation method of injection-molded complex-shape low-pressure sintered permanent magnetic ferrite, which comprises the following steps: (1) preparing a permanent magnetic ferrite master batch for injection molding; (2) performing injection molding on the master batch under the condition of applying an orientation magnetic field; and (3) putting the obtained green body into a low-pressure sintering furnace, heating to 300-600 DEG C under the condition of continuous vacuumizing, carrying out degumming treatment, stopping vacuumizing, heating to 1100-1250 DEG C, filling nitrogen or argon until the pressure in the furnace is 2-5 MPa, carrying out low-pressure sintering, and after sintering is completed, cooling to room temperature along with the furnace, thereby obtaining the high-strength silicon carbide ceramic. According to the preparation method, the problems of low magnetic performance, insufficient mechanical strength and the like of the existing bonded permanent magnetic ferrite can be solved, the problem that the existing preparation method of the sintered magnet cannot meet the design requirements of high-performance small complex special-shaped permanent magnetic ferrite products can also be solved, and the preparation of the high-magnetic-performance complex-shaped sintered permanent magnetic ferrite is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of sintered permanent ferrite preparation, and relates to a method for preparing low-pressure sintered permanent ferrite with complex shapes by injection molding. Background Art

[0002] With the continuous development and progress of industry, various mechanical and automation equipment are constantly updated and iterated. In the field of permanent ferrites, the requirements for the magnetic properties of magnet products are getting higher and higher. At the same time, there are more and more designs of magnet products with lightweight, miniaturization and complex shapes and structures. In order to solve the problem of the complicated shape and structure of the above-mentioned magnet products, the existing technology usually mixes adhesives, coupling agents and lubricants with magnetic powders evenly, and then forms them into bonded magnets. Bonded magnets have the characteristics of high dimensional accuracy, large shape freedom, and the shape and size of the product are determined by the mold. They can be prepared into free shapes such as rings, tiles, and blocks. They do not require sintering and post-machining, and can meet the requirements of miniaturization, complex and special-shaped products. However, since bonded magnets contain a large amount of non-magnetic components such as adhesives, plasticizers and stabilizers, the proportion of magnetic powder filling is not high, the magnet density is low, and bonded magnets have problems such as low magnetic properties, insufficient mechanical strength and poor thermal stability. As for bonded permanent ferrites, at present, the best magnetic properties on the market are YN12 bonded permanent ferrites, and its magnetic properties are as follows: remanence (Br) is 240-250mT, coercive force (HCB) is 1760-2010Oe, intrinsic coercive force (HCJ) is 2510-2890Oe, maximum magnetic energy product (BH (max) ) is 11.4~13.6KJ / m 3 Its magnetic properties are difficult to meet the market demand for high-performance products. The traditional method of preparing sintered permanent ferrite by dry pressing or wet pressing orientation molding followed by high-temperature sintering can produce sintered permanent ferrite with higher magnetic properties, but due to the problem of molding process, it is difficult to realize the preparation of small and complex shaped permanent ferrite devices.

[0003] The existing method of preparing bonded permanent magnet ferrites is difficult to achieve higher magnetic performance requirements while meeting the shape and structure of magnet products. The existing method of preparing sintered permanent magnet ferrites, although it can meet higher magnetic performance requirements, is difficult to achieve the design requirements of small, complex and special-shaped magnet products. This is a major problem currently faced by the preparation of small, complex and special-shaped permanent magnet ferrite products. It is urgent to develop a preparation method for sintered permanent magnet ferrites that can meet both the high magnetic performance requirements of magnet products and the complex and special-shaped shape design requirements, so as to better meet the market demand for high-performance small, complex and special-shaped permanent magnet ferrite components. Summary of the invention

[0004] In view of the problems that permanent magnet ferrites prepared by the existing bonding magnet preparation method have low magnetic properties and insufficient mechanical strength, and the problem that the existing sintered magnet preparation method cannot meet the requirements of high-performance small-sized complex and special-shaped permanent magnet ferrite product design, the present invention provides a preparation method of injection molded complex-shaped low-pressure sintered permanent magnet ferrite, so as to achieve the preparation of complex-shaped sintered permanent magnet ferrite with higher magnetic properties.

[0005] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a low-pressure sintered permanent magnetic ferrite with a complex shape by injection molding, comprising the following steps:

[0007] (1) using permanent magnet ferrite pre-sintered material magnetic powder, adhesive and auxiliary agents as raw materials, fully mixing the raw materials, drying, mixing them evenly on a mixer, and then granulating them to prepare permanent magnet ferrite masterbatch for injection molding; the auxiliary agents include silane coupling agents, lubricants and secondary additives;

[0008] (2) injection molding the permanent magnet ferrite masterbatch for injection molding, applying an oriented magnetic field during molding, and preparing a permanent magnet ferrite green body with a desired complex shape;

[0009] (3) Placing the complex-shaped permanent ferrite green body in a low-pressure sintering furnace, evacuating the low-pressure sintering furnace to a pressure of 0.1 to 20 Pa, then heating it to 300 to 600°C, and keeping it warm for 2 to 4 hours to perform debonding treatment. During the heating and keeping warm process, evacuating the furnace continuously to maintain the pressure in the furnace at 0.1 to 20 Pa. After the debonding treatment is completed, stopping evacuating the furnace, heating it to 1100 to 1250°C, and then filling the low-pressure sintering furnace with nitrogen or argon to a pressure of 2 to 5 MPa. Keeping it warm for 1 to 2 hours to perform low-pressure sintering. After the sintering is completed, cooling it to room temperature with the furnace to obtain a complex-shaped sintered permanent ferrite.

[0010] In step (1) of the technical solution of the above preparation method, the contents of the annealed permanent magnet ferrite pre-sintered magnetic powder, adhesive and additive in the masterbatch are preferably 86wt% to 92wt%, 3wt% to 10wt% and 4wt% to 8wt%, respectively.

[0011] In the technical solution of the above preparation method, the permanent magnet ferrite pre-sintered material magnetic powder is at least one of strontium ferrite magnetic powder, barium ferrite magnetic powder, and strontium-barium mixed ferrite magnetic powder.

[0012] In the technical solution of the above preparation method, the average particle size of the permanent magnet ferrite pre-sintered magnetic powder in step (1) is preferably 3 to 4 μm.

[0013] In the technical solution of the above preparation method, in the auxiliary agent, the mass ratio of the silane coupling agent, the lubricant and the secondary additive is preferably (4-8):(33-45):(3-9).

[0014] In the technical solution of the above preparation method, the adhesive includes at least one of polyethylene glycol, paraffin, camphor and nylon 6.

[0015] In the technical solution of the above preparation method, the lubricant is oxidized polyethylene wax and anhydrous ethanol.

[0016] In the technical scheme of the above preparation method, the silane coupling agent is a silane coupling agent commonly used in the art, and can be selected according to the actual application requirements with reference to the prior art. For example, feasible silane coupling agents include vinyl triethoxy silane (A151), vinyl trimethoxy silane (A171), vinyl tri (β-methoxyethoxy) silane (A172), etc.

[0017] In the technical solution of the above preparation method, the secondary additive can be selected according to the actual application requirements with reference to the prior art. For example, in order to improve the density and strength of the sintered permanent magnet ferrite, at least one of calcium carbonate, silicon dioxide, aluminum oxide and kaolin can be selected as a secondary additive. When calcium carbonate, silicon dioxide, aluminum oxide and kaolin are selected as secondary additives, the amount of calcium carbonate, silicon dioxide, aluminum oxide and kaolin should be such that the content of calcium carbonate, silicon dioxide, aluminum oxide and kaolin in all raw materials is 0.2wt% to 0.5wt%, 0.1wt% to 0.3wt%, 0wt% to 0.2wt%, and 0wt% to 0.2wt%, respectively.

[0018] In step (2) of the technical solution of the above preparation method, it is preferred to control the molding orientation magnetic field strength to at least 5000 Oe, the injection temperature to 270-300°C, the injection pressure to 150-170 MPa, and the extrusion temperature to 230-260°C.

[0019] In step (3) of the above preparation method, the heating rate is preferably controlled to be 3 to 5°C / min.

[0020] The main technical concept of the present invention is that first, the permanent magnet ferrite pre-sintered material magnetic powder, adhesive and auxiliary agent (including silane coupling agent, lubricant and secondary additive) are made into a permanent magnet ferrite masterbatch for injection molding, and then injection molding is performed into a permanent magnet ferrite green body of the required complex shape, and then degumming treatment is performed under continuous vacuum conditions to carbonize and remove the auxiliary agents of organic components such as adhesives, coupling agents and lubricants. After the degumming treatment is completed, sintering is performed under pressurized conditions (the pressure in the furnace is 2-5MPa) to increase the density of the magnet, and a complex-shaped sintered permanent magnet ferrite is obtained. On the one hand, the present invention prepares the permanent magnet ferrite green body of the required complex shape by injection molding from the permanent magnet ferrite masterbatch for injection molding, which solves the problem that the existing preparation method of sintered permanent magnet ferrite can meet the requirements of high magnetic properties, but is difficult to meet the design and use requirements of complex-shaped products such as miniaturization and special-shaped. On the other hand, the present invention subjects the obtained permanent magnet ferrite green body of complex shape to carbonization debinding and pressure sintering, thereby removing the binder and auxiliary agent of organic components, increasing the proportion of magnetic components and the density of the magnet, thereby improving the magnetic properties and mechanical properties of the permanent magnet ferrite, solving the problem that the existing preparation method of bonded permanent magnet ferrite can meet the design and use requirements of complex-shaped products but has low magnetic properties and mechanical properties, and can also solve the problem of poor thermal stability of the magnet when used under high temperature conditions caused by the presence of binders and auxiliary agents of organic components.

[0021] Compared with the prior art, the technical solution provided by the present invention produces the following beneficial technical effects:

[0022] The present invention provides a method for preparing low-pressure sintered permanent ferrite with complex shapes by injection molding. The method firstly forms a permanent ferrite masterbatch for injection molding into a permanent ferrite green body with a desired complex shape based on injection molding, and then debonds under continuous vacuum conditions and sinters under pressure conditions to obtain a permanent ferrite with a complex shape. Compared with the prior art method of preparing sintered permanent ferrite by first dry pressing or wet pressing orientation molding and then high-temperature sintering, the present invention forms the permanent ferrite masterbatch for injection molding by injection molding, realizes the free molding of the permanent ferrite green body, and can prepare a green body with a complex shape, solving the problem of the existing method for preparing sintered permanent ferrite that it is difficult to prepare small, complex and special-shaped permanent ferrite devices. Compared with the existing preparation method of bonded permanent magnet ferrite, which mixes a large amount of adhesive, plasticizer and stabilizer with magnetic powder and then forms it freely, the present invention carbonizes the green body of complex shape under continuous vacuum conditions, so that the adhesive and auxiliary agent of organic components are pyrolyzed and removed, and then sintered under pressure, which increases the proportion of magnetic components and the density of the magnet, thereby improving the magnetic properties and mechanical properties of the permanent magnet ferrite, and solves the problems of low magnetic properties and mechanical properties of existing bonded permanent magnet ferrite products, as well as poor thermal stability when used under high temperature conditions. The method of the present invention can realize the preparation of sintered permanent magnet ferrite with complex shapes and high magnetic properties, and can better meet the market demand for high-performance small-sized complex special-shaped permanent magnet ferrite components. DETAILED DESCRIPTION

[0023] The following examples further illustrate the preparation method of the low-pressure sintered permanent magnet ferrite with complex shapes by injection molding provided by the present invention. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. The technical personnel in the relevant field make some non-essential improvements and adjustments to the present invention according to the above invention content for specific implementation, which still falls within the scope of protection of the present invention.

[0024] Example 1

[0025] In this embodiment, a method for preparing a low-pressure sintered permanent magnet ferrite with a complex shape by injection molding is provided, and the steps are as follows:

[0026] (1) The barium ferrite permanent magnet powder is passed through a 60-80 mesh sieve to obtain a barium ferrite permanent magnet powder with an average particle size of 3.0 μm.

[0027] (2) Using barium ferrite permanent magnet powder with an average particle size of 3.0 μm, adhesive and auxiliary agents as raw materials, the ingredients are prepared according to the ratio of 86wt%, 8wt% and 6wt% of the barium ferrite permanent magnet powder, adhesive and auxiliary agents in all raw materials, respectively. The adhesive is paraffin, camphor and nylon 6 (PA6), and the auxiliary agents include silane coupling agent, lubricant and secondary additives. The silane coupling agent is vinyl triethoxysilane (A151), the lubricant is oxidized polyethylene wax and anhydrous ethanol, and the secondary additives are calcium carbonate, silicon dioxide, aluminum oxide and kaolin.

[0028] Weigh 860g of barium ferrite permanent magnet powder, 30g of paraffin wax, 30g of camphor, 20g of PA6, 8g of silane coupling agent A151, 3g of oxidized polyethylene wax, 40g of anhydrous ethanol, 5g of calcium carbonate, 2g of silicon dioxide, 1g of aluminum oxide, and 1g of kaolin. Stir and mix the weighed raw materials thoroughly, dry them, mix them evenly on a mixer, and then granulate them to make a permanent magnet ferrite masterbatch for injection molding.

[0029] (3) The permanent magnet ferrite masterbatch for injection molding is injection molded on an injection molding device, and an orientation magnetic field is applied during molding to produce a permanent magnet ferrite green body with the desired complex shape. The molding orientation magnetic field strength is controlled to be 6000Oe, the injection temperature to be 270°C, the injection pressure to be 150MPa, and the extrusion temperature to be 230°C.

[0030] (4) placing the permanent magnet ferrite green body in a low-pressure sintering furnace, evacuating the low-pressure sintering furnace until the pressure inside the furnace is 0.1 Pa, then heating the temperature to 600°C at a heating rate of 5°C / min, and keeping the temperature for 4 hours to perform a debonding treatment. During the heating and holding process, evacuating the green body continuously to keep the pressure inside the furnace at 0.1 Pa. After the debonding treatment is completed, stopping the evacuation, heating the temperature to 1180°C at a heating rate of 4°C / min, filling the low-pressure sintering furnace with nitrogen until the pressure inside the furnace is 3MPa, and keeping the temperature for 1.5 hours to perform low-pressure sintering. After the sintering is completed, cooling the green body to room temperature with the furnace to obtain a sintered permanent magnet ferrite with a complex shape.

[0031] The samples were taken and polished, and the magnetic properties were tested. The results showed that the remanence (Br) was 377mT, the coercive force (HCB) was 3166Oe, the intrinsic coercive force (HCJ) was 3405Oe, and the maximum magnetic energy product (BH (max) ) is 27.2KJ / m 3 .

[0032] Example 2

[0033] In this embodiment, a method for preparing a low-pressure sintered permanent magnet ferrite with a complex shape by injection molding is provided, and the steps are as follows:

[0034] (1) Strontium ferrite permanent magnet powder is passed through a 60-80 mesh sieve to obtain strontium ferrite permanent magnet powder with an average particle size of 3.2 μm.

[0035] (2) Strontium ferrite permanent magnet powder with an average particle size of 3.2 μm, adhesive and auxiliary agents are used as raw materials, and the contents of barium ferrite permanent magnet powder, adhesive and auxiliary agents in all raw materials are respectively 88 wt%, 6 wt% and 6 wt%. The adhesive is polyethylene glycol, and the auxiliary agents include a silane coupling agent, a lubricant and a secondary additive. The silane coupling agent is vinyl triethoxysilane (A151), the lubricant is oxidized polyethylene wax and anhydrous ethanol, and the secondary additives are calcium carbonate, silicon dioxide and aluminum oxide.

[0036] Weigh 880g of strontium ferrite permanent magnet powder, 60g of polyethylene glycol, 8g of silane coupling agent A151, 5g of oxidized polyethylene wax, 40g of anhydrous ethanol, 4g of calcium carbonate, 2g of silicon dioxide, and 1g of aluminum oxide. Stir and mix the weighed raw materials thoroughly, dry them, mix them evenly on a mixer, and then granulate them to make a permanent magnet ferrite masterbatch for injection molding.

[0037] (3) The permanent magnet ferrite masterbatch for injection molding is injection molded on an injection molding device, and an orientation magnetic field is applied during molding to produce a permanent magnet ferrite green body with the desired complex shape. The molding orientation magnetic field strength is controlled to be 6000Oe, the injection temperature to be 280°C, the injection pressure to be 160MPa, and the extrusion temperature to be 245°C.

[0038] (4) placing the permanent magnet ferrite green body in a low-pressure sintering furnace, evacuating the low-pressure sintering furnace until the pressure inside the furnace is 10Pa, then heating the temperature to 500°C at a heating rate of 3°C / min, and keeping the temperature for 4 hours to perform a debonding treatment. During the heating and holding process, evacuating the green body continuously to maintain the pressure inside the furnace at a level of 0.1 to 10Pa. After the debonding treatment is completed, evacuating the green body is stopped, heating the temperature to 1230°C at a heating rate of 3°C / min, filling the low-pressure sintering furnace with argon until the pressure inside the furnace is 4MPa, and keeping the temperature for 2 hours to perform low-pressure sintering. After the sintering is completed, cooling the green body to room temperature with the furnace to obtain a sintered permanent magnet ferrite with a complex shape.

[0039] The samples were taken and polished, and the magnetic properties were tested. The results showed that the remanence (Br) was 384mT, the coercive force (HCB) was 3192Oe, the intrinsic coercive force (HCJ) was 3405Oe, and the maximum magnetic energy product (BH (max) ) is 28.3KJ / m 3 .

[0040] Example 3

[0041] In this embodiment, a method for preparing a low-pressure sintered permanent magnet ferrite with a complex shape by injection molding is provided, and the steps are as follows:

[0042] (1) Strontium ferrite permanent magnet powder, barium ferrite permanent magnet powder, and strontium-barium mixed ferrite permanent magnet powder are respectively passed through a 60-80 mesh sieve, and then the sieved strontium ferrite permanent magnet powder, barium ferrite permanent magnet powder, and strontium-barium mixed ferrite permanent magnet powder are mixed in a mass ratio of 1:1:1 to obtain a permanent magnet ferrite mixed magnetic powder with an average particle size of 3.5 μm.

[0043] (2) Using permanent ferrite mixed magnetic powder with an average particle size of 3.5 μm, adhesive and auxiliary agents as raw materials, the ingredients are prepared according to the ratio of 91wt%, 5wt% and 4wt% of the contents of the permanent ferrite mixed magnetic powder, adhesive and auxiliary agents in all raw materials, respectively. The adhesive is paraffin and PA6, and the auxiliary agents include silane coupling agent, lubricant and secondary additives. The silane coupling agent is vinyl triethoxysilane (A151), the lubricant is oxidized polyethylene wax and anhydrous ethanol, and the secondary additives are calcium carbonate and silicon dioxide.

[0044] Weigh 910g of permanent ferrite mixed magnetic powder, 30g of paraffin wax, 20g of PA6, 4g of silane coupling agent A151, 3g of oxidized polyethylene wax, 30g of anhydrous ethanol, 2g of calcium carbonate, and 1g of silicon dioxide. Stir and mix the weighed raw materials thoroughly, dry them, mix them evenly on a mixer, and then granulate them to make a permanent ferrite masterbatch for injection molding.

[0045] (3) The permanent magnet ferrite masterbatch for injection molding is injection molded on an injection molding device, and an orientation magnetic field is applied during molding to produce a permanent magnet ferrite green body with the desired complex shape. The molding orientation magnetic field strength is controlled to be 8000Oe, the injection temperature to be 300°C, the injection pressure to be 170MPa, and the extrusion temperature to be 260°C.

[0046] (4) placing the permanent magnet ferrite green body in a low-pressure sintering furnace, evacuating the low-pressure sintering furnace until the pressure inside the furnace is 0.1 Pa, then heating the temperature to 600°C at a heating rate of 4°C / min, and keeping the temperature for 3 hours to perform a debonding treatment. During the heating and holding process, evacuating the green body continuously to keep the pressure inside the furnace at 0.1 Pa. After the debonding treatment is completed, evacuating the green body is stopped, heating the temperature to 1200°C at a heating rate of 4°C / min, filling the low-pressure sintering furnace with argon until the pressure inside the furnace is 3.5 MPa, and keeping the temperature for 1 hour to perform low-pressure sintering. After the sintering is completed, cooling the green body to room temperature with the furnace to obtain a sintered permanent magnet ferrite with a complex shape.

[0047] The samples were taken and polished, and the magnetic properties were tested. The results showed that the remanence (Br) was 379mT, the coercive force (HCB) was 3330Oe, the intrinsic coercive force (HCJ) was 3531Oe, and the maximum magnetic energy product (BH (max) ) is 27.4KJ / m 3 .

[0048] At present, the bonded permanent ferrite with the best magnetic properties on the market is YN12 bonded permanent ferrite. Its magnetic properties are as follows: remanence (Br) is 240-250mT, coercive force (HCB) is 1760-2010Oe, intrinsic coercive force (HCJ) is 2510-2890Oe, maximum magnetic energy product (BH (max) ) is 11.4~13.6KJ / m 3 . Combined with Examples 1 to 3, it can be seen that, compared with the YN12 bonded permanent magnet ferrite, the magnetic properties of the complex-shaped sintered permanent magnet ferrite prepared by the method of the present invention have been improved. At the same time, since the method of the present invention performs debonding and pressure sintering, the density of the magnet is further increased on the basis of removing the adhesive and auxiliary agent of the organic component. Therefore, compared with the existing bonded permanent magnet ferrite, the complex-shaped sintered permanent magnet ferrite prepared by the method of the present invention also has more advantages in mechanical properties, which can better meet the market demand for high-performance small-sized complex and special-shaped permanent magnet ferrite products.

Claims

1. A method for preparing a low-pressure sintered permanent ferrite with a complex shape by injection molding, characterized in that: The following steps are involved: (1) using permanent magnet ferrite pre-sintered material magnetic powder, adhesive and auxiliary agents as raw materials, fully mixing the raw materials, drying, mixing them evenly on a mixer, and then granulating them to prepare permanent magnet ferrite masterbatch for injection molding; the auxiliary agents include silane coupling agents, lubricants and secondary additives; (2) injection molding the permanent magnet ferrite masterbatch for injection molding, applying an oriented magnetic field during molding, and preparing a permanent magnet ferrite green body with a desired complex shape; (3) Placing the complex-shaped permanent ferrite green body in a low-pressure sintering furnace, evacuating the low-pressure sintering furnace to a pressure of 0.1 to 20 Pa, then heating it to 300 to 600°C, and keeping it warm for 2 to 4 hours to perform debonding treatment. During the heating and keeping warm process, evacuating the furnace continuously to maintain the pressure in the furnace at 0.1 to 20 Pa. After the debonding treatment is completed, stopping evacuating the furnace, heating it to 1100 to 1250°C, and then filling the low-pressure sintering furnace with nitrogen or argon to a pressure of 2 to 5 MPa. Keeping it warm for 1 to 2 hours to perform low-pressure sintering. After the sintering is completed, cooling it to room temperature with the furnace to obtain a complex-shaped sintered permanent ferrite.

2. The method for preparing a low-pressure sintered permanent ferrite with a complex shape by injection molding according to claim 1, characterized in that: In step (1), the contents of the annealed permanent magnet ferrite pre-sintered material magnetic powder, adhesive and additive in the masterbatch are 86wt% to 92wt%, 3wt% to 10wt% and 4wt% to 8wt% respectively.

3. The method for preparing a low-pressure sintered permanent ferrite with a complex shape by injection molding according to claim 1, characterized in that: The magnetic powder of the permanent ferrite pre-sintered material is at least one of strontium ferrite magnetic powder, barium ferrite magnetic powder and strontium-barium mixed ferrite magnetic powder.

4. The method for preparing a low-pressure sintered permanent ferrite with a complex shape by injection molding according to claim 1, characterized in that: In the auxiliary agent, the mass ratio of the silane coupling agent, the lubricant and the secondary additive is (4-8):(33-45):(3-9).

5. The method for preparing a low-pressure sintered permanent ferrite with a complex shape by injection molding according to claim 1, characterized in that: The adhesive includes at least one of polyethylene glycol, paraffin, camphor and nylon 6.

6. The method for preparing a low-pressure sintered permanent ferrite with a complex shape by injection molding according to claim 1, characterized in that: The lubricant is oxidized polyethylene wax and anhydrous ethanol.

7. The method for preparing low-pressure sintered permanent ferrite with complex shape by injection molding according to claim 1, characterized in that: The secondary additive includes at least one of calcium carbonate, silicon dioxide, aluminum oxide and kaolin.

8. The method for preparing a low-pressure sintered permanent ferrite having a complex shape by injection molding according to any one of claims 1 to 7, characterized in that: In step (2), the molding orientation magnetic field strength is controlled to be at least 5000 Oe, the injection temperature is controlled to be 270-300°C, the injection pressure is controlled to be 150-170 MPa, and the extrusion temperature is controlled to be 230-260°C.

9. The method for preparing a low-pressure sintered permanent ferrite having a complex shape by injection molding according to any one of claims 1 to 7, characterized in that: The heating rate during the temperature increase in step (3) is controlled to be 3 to 5°C / min.

10. The method for preparing a low-pressure sintered permanent ferrite having a complex shape by injection molding according to any one of claims 1 to 7, characterized in that: The average particle size of the permanent magnet ferrite pre-sintered magnetic powder in step (1) is 3 to 4 μm.