A method for manufacturing a high magnetic field gradient M-type ferrite rectangular magnet

Abstract

The invention discloses a method for manufacturing a high magnetic field gradient M-type ferrite rectangular magnet, which belongs to the technical field of magnetic materials. The molecular formula of the M-type ferrite rectangular magnet is SrFe 12 O 19 The magnetic properties of the material are the same as the industry standard of permanent ferrite. It is made of ceramic technology. The molding orientation lower mold in the molding process meets the following requirements. The lower mold is divided into a magnetic conductive material A area and a non-magnetic conductive material B area. The size of the A and B areas is related to the green billet length L. The A area adopts a narrow upper and wide lower structure design. The heights of the A and B areas are the same as the thickness H of the lower mold. It can be realized by surfacing welding and then machining. After saturation magnetization, it has a high magnetic field gradient value (H 梯 ≥80Gs / cm), the magnetic field gradient value is that the magnetic field strength at the center of the magnet is higher than the magnetic field strength around the surface of the magnet. The magnetic field strength in the middle of the rectangular magnet designed by the present invention is higher than that around it, and has a higher magnetic field gradient value.

Description

Technical Field

[0001] The invention belongs to the technical field of magnetic materials, and in particular relates to a method for manufacturing a high magnetic field gradient M-type ferrite rectangular magnet. Background Art

[0002] High magnetic field gradient magnetic separator is a new type of magnetic separator developed on the basis of strong magnetic separator. Compared with ordinary magnetic separator, its magnetic field gradient is increased by 10~100 times, so that fine particles and weak magnetic mineral particles can be effectively recovered. High magnetic field gradient magnetic separator can be used for weak magnetic mineral separation, non-metallic mineral iron removal and water treatment.

[0003] High magnetic field gradient magnetic separator uses M-type ferrite rectangular magnet with high magnetic field gradient as the magnetic field source of the ore dressing machine. Its magnetic field strength is large, and the minimum limit of the recovered particle size can reach 1 micron. It can collect concentrate from poor, weak, fine, mixed and difficult ore bodies, and the collection rate is increased from 25% of conventional magnetic separators to 40%.

[0004] After the M-type ferrite magnet is magnetized to saturation, a magnetic field will be generated in the space of the magnetized surface. According to the distribution of magnetic field strength, there are uniform magnetic field and non-uniform magnetic field. The so-called uniform magnetic field means that the magnetic field strength at each point in the magnetic field is basically the same, otherwise it is a non-uniform magnetic field. The degree of non-uniformity of the magnetic field can be measured by the magnetic field gradient. The so-called magnetic field gradient is the change in the magnetic field strength per unit distance. Suppose the magnetic field strength at the distance X1 from the N pole of a certain magnet surface is H1, and the magnetic field strength at the distance X2 is H2, then the magnetic field gradient H 梯 The values ​​are: Rectangular magnets with magnetic field gradient distribution are mainly used in mine concentrate magnetic separators. The magnetic field gradient is a necessary condition to ensure the selection of concentrates, otherwise the magnetic ore particles cannot be attracted to the magnetic poles, and magnetic separation is impossible. Therefore, it is very important to increase the magnetic field gradient value of the magnet. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a method for manufacturing a high magnetic field gradient M-type ferrite rectangular magnet, wherein the magnet has a high magnetic field gradient value.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for manufacturing a high magnetic field gradient M-type ferrite rectangular magnet, wherein the molecular formula of the M-type ferrite rectangular magnet is SrFe 12 O 19The magnetic properties of the material are the same as the industry standard of permanent magnet ferrite. Pre-sintered materials are added with CaCO3, La2O3, Co2O3, SiO2, H3BO3 and other additives, and wet ball milling is performed to a particle size of 0.75-9.0μm. After discharging, the water content of the slurry is controlled at about 25% by a dehydrator. The green body is oriented and formed with a magnetic field strength of more than 800KA / m. The green body is sintered at 1200-1240℃ for about 2 hours to obtain a cooked body. The cooked body is processed to the size requirements and the product is obtained after passing the test. The molding orientation lower mold in the molding process meets the following requirements. The lower mold is divided into a magnetic conductive material A area and a non-magnetic conductive material B area. The size of the A and B areas is related to the length L of the green body. The A area adopts a narrow upper and wide lower structural design. The height of the A and B areas is the same as the thickness H of the lower mold. It can be achieved by surfacing welding and machining. After saturation magnetization, it has a high magnetic field gradient value (H 梯 ≥80Gs / cm), the magnetic field gradient value is that the magnetic field intensity at the center of the magnet is higher than the magnetic field intensity value around the surface of the magnet, wherein the cross section of the magnetic conductive material A area is a triangular structure, and its vertex angle is designed to be 90°.

[0007] If the rectangular magnet molding process uses a magnetic field to orient the molding material for magnetic moment, when both the upper mold and the lower mold are fully magnetic conductive materials, the surface magnetic field strength of the magnet after magnetic field orientation molding is a uniform magnetic field distribution, which will appropriately reflect that the magnetic field strength at the center of the magnet is relatively low, and the magnetic field strength on the surrounding surface is relatively high.

[0008] The center part of the lower mold of the mold designed for the orientation magnetic field of the present invention is the magnetic conductive material A area, and the rest is the non-magnetic conductive material B area. The pressed green sheet is arranged between the upper mold and the lower mold, and the mold base is arranged at the bottom of the lower mold. The mold base adopts the magnetic conductive material. The cavity is arranged around the lower mold. The cavity adopts the non-magnetic conductive material, and the coil is arranged outside the cavity. When the magnetic lines of force of the orientation magnetic field generated by the coil are formed, most of them pass through the magnetic conductive material A area in the lower mold, and a few pass through the non-magnetic conductive material B area, so that the green material is fully magnetized in the center of the magnetic blank, and the surrounding is not fully magnetized. After the blank is sintered and magnetized, the surface magnetic field strength is high in the middle and low around, that is, the magnetic field gradient is different with the magnetic conductive and non-magnetic conductive designs of the lower mold, so as to meet the different magnetic field gradient requirements of users.

[0009] Compared with the prior art, the present invention has the following advantages and effects: the surface magnetic field of the existing rectangular magnet is generally a uniform magnetic field or the surrounding magnetic field strength is slightly higher than the middle magnetic field strength, and the magnetic field gradient value is low. The present invention is designed through optimization and improvement, and the middle magnetic field strength of the rectangular magnet is higher than that of the surroundings, and has a higher magnetic field gradient value. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic diagram of the structure of the magnet in the present invention.

[0011] Figure 2It is a relationship diagram between the lower mold size and the green body size in the present invention.

[0012] In the figure: upper die 1, coil 2, pressed blank 3, cavity 4, lower die 5, die base 6. DETAILED DESCRIPTION

[0013] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. All other embodiments obtained by ordinary technicians in this field without making creative work based on the embodiments of the present invention shall fall within the scope of protection of the present invention.

[0014] See also Figure 1 and Figure 2 In this embodiment, a technical solution is provided: a method for manufacturing a high magnetic field gradient M-type ferrite rectangular magnet, the molecular formula of which is SrFe 12 O 19 The magnetic properties of the material are the same as the industry standards of permanent magnet ferrites. Pre-burned materials purchased on the market are used, and CaCO3, La2O3, Co2O3, SiO2, H3BO3 and other additives are added to wet ball milling to a particle size of 0.75-9.0μm. After discharging, a dehydrator is used to control the water content of the slurry to about 25%. The green body is obtained by orientation molding with a magnetic field intensity of more than 800KA / m. The green body is sintered at 1200-1240℃ for about 2 hours to obtain a cooked body. The cooked body is processed to the size requirements and the product is obtained after passing the inspection. The molding orientation lower mold 5 in the molding process meets the following requirements. The lower mold 5 is divided into a magnetic conductive material A area (A3 steel, low carbon steel, No. 10 steel, etc.) and a non-magnetic conductive material B area (non-magnetic stainless steel). Figure 2 As shown in the figure, the dimensions of the A and B regions are related to the green billet length L. The top angle of the A region is designed to be 90°. The heights of the A and B regions are the same as the thickness H of the lower die 5. They can be realized by surfacing welding and then machining. After saturation magnetization, they have a high magnetic field gradient value (H 梯 ≥80Gs / cm), the magnetic field gradient value is that the magnetic field intensity at the center of the magnet is higher than the magnetic field intensity around the magnet surface.

[0015] If the rectangular magnet forming process uses a magnetic field to orient the magnetic moment of the molding material, when the upper mold 1 and the lower mold 5 are both fully magnetic conductive materials, the surface magnetic field strength of the magnet after magnetic field orientation forming is a uniform magnetic field distribution, which will appropriately reflect that the magnetic field strength at the center of the magnet is relatively low, and the magnetic field strength on the surrounding surface is relatively high.

[0016] In this embodiment, the center area of ​​the lower mold 5 of the mold for designing the orientation magnetic field is the magnetic conductive material A area, and the rest is the non-magnetic conductive material B area. The pressed green sheet 3 is arranged between the upper mold 1 and the lower mold 5, and the mold base 6 is arranged at the bottom of the lower mold 5. The mold base 6 is made of magnetic conductive material. The cavity 4 is arranged around the lower mold 5. The cavity 4 is made of non-magnetic conductive material, and the coil 2 is arranged outside the cavity 4. When forming, the magnetic lines of force of the orientation magnetic field generated by the coil 2 mostly pass through the magnetic conductive material A area in the lower mold 5, and a few pass through the non-magnetic conductive material B area, forming a green green sheet with sufficient magnetic moment magnetization in the center of the magnetic green sheet and insufficient magnetization around it. After sintering and magnetization, the surface magnetic field of the green sheet is high in the middle and low around it, that is, the magnetic field gradient is different with the magnetic conductive and non-magnetic conductive designs of the lower mold 5, meeting the different magnetic field gradient requirements of users.

[0017] In this embodiment, the manufacture of high magnetic field gradient M-type ferrite rectangular magnets uses domestic advanced M-type ferrite rectangular magnet pre-sintering materials (Y41H in SJ / T10410-2016 permanent magnet ferrite materials) to form molding materials through ball milling and precipitation, and uses a 150×100×25mm rectangular magnet mold. The lower mold is calculated according to the molding shrinkage, and the length and width of the lower mold are 175mm and 116mm respectively. The height of the lower mold is 50mm, and the magnetic conductive material A area in the center of the lower mold is made of magnetic conductive material A3 steel, and its size is: length×width×height=58×38×48mm. The remaining non-magnetic conductive material B area of ​​the lower mold is welded with stainless steel electrodes and processed to the size of the lower mold. After the material is oriented and formed, it is sintered in a natural gas oxygen atmosphere sintering furnace, and then surface grinding and polishing are performed, and the magnet is saturated magnetized in a direction parallel to the pressed magnetization direction. The surface strength of the magnet is measured using a Tesla meter. The magnetic field strength at the center surface is 138mT (1380Gs), and the magnetic field strength at 7.5cm from the center is 60mT (600Gs). The magnetic field gradient is calculated as follows: =104Gs / cm.

[0018] The difference between this embodiment and the above-mentioned embodiment 2 is that (Y32H-2 in SJ / T10410-2016 permanent magnet ferrite material) brand pre-sintered material is used, and the other processes and molds remain unchanged. The magnetic field intensity on the center surface of the magnet obtained is 120mT (1200Gs), and the magnetic field intensity at 7.5cm from the center is 50mT (500Gs). The calculated magnetic field gradient is 93Gs / cm.

[0019] The difference between this embodiment and the above-mentioned embodiment 3 is that the magnetic field strength during molding is greater than 1000KA / m, and the selection of other pre-sintered materials, processes, and molds remain unchanged. The magnetic field strength on the center surface of the obtained magnet is 148mT (1480Gs), and the magnetic field strength at 7.5cm from the center is 61mT (610Gs). The calculated magnetic field gradient is 116Gs / cm.

[0020] The difference between this embodiment and the above-mentioned embodiment 3 is that the ball mill particle size is controlled at 0.75-0.77 μm, the sintering temperature is 1240°C and maintained for 2.5 hours, and the selection of other pre-sintered materials, processes, and molds remain unchanged. The magnetic field intensity on the center surface of the obtained magnet is 151 mT (1510 Gs), and the magnetic field intensity at 7.5 cm from the center is 58 mT (580 Gs). The calculated magnetic field gradient is 124 Gs / cm.

[0021] The difference between this embodiment and the above-mentioned embodiment 5 is that the ball mill particle size is controlled at 0.88-0.9 μm, the sintering temperature is 1220°C for 2 hours, CaCO3 and SiO2 are used as additives, and the water content of the slurry is controlled at 24% by a dehydrator. The selection of other pre-sintered materials, processes, and molds remain unchanged. The magnetic field intensity on the center surface of the obtained magnet is 121.5 mT (1215 Gs), the magnetic field intensity at 7.5 cm from the center is 60 mT (600 Gs), and the magnetic field gradient is calculated to be 82 Gs / cm.

[0022] The difference between this embodiment and the above-mentioned embodiment 5 is that the sintering temperature is 1200°C for 2.2 hours, Co2O3 is used as the additive, and the water content of the slurry is controlled at 26% by a dehydrator. The selection of other pre-sintered materials, processes, and molds remain unchanged. The magnetic field intensity on the center surface of the obtained magnet is 147.5mT (1475Gs), the magnetic field intensity at 7.5cm from the center is 50mT (500Gs), and the calculated magnetic field gradient is 130Gs / cm.

[0023] Although embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and concepts of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for manufacturing a high magnetic field gradient M-type ferrite rectangular magnet, characterized in that the process The method is as follows: adding additives to the pre-burned material and wet ball milling, treating the material with a dehydrator after discharge, orienting and forming the green body, and sintering the green body to obtain a cooked body; The molecular formula of the M-type ferrite rectangular magnet is SrFe 12 O 19 The magnetic properties of its materials are the same as the industry standards for permanent ferrites; The additives include CaCO3, La2O3, Co2O3, SiO2 and H3BO3; In the molding process, the center area of ​​the lower mold (5) of the mold for designing the orientation magnetic field is the magnetic conductive material A area, and the remaining area is the non-magnetic conductive material B area. The magnetic conductive material A area adopts a structural design of being narrow at the top and wide at the bottom. The heights of the magnetic conductive material A area and the non-magnetic conductive material B area are both the same as the thickness H of the lower mold (5); a pressed blank (3) is arranged between the upper mold (1) and the lower mold (5); a mold base (6) is arranged at the bottom of the lower mold (5), and the mold base (6) is made of magnetic conductive material. A cavity (4) is arranged around the lower mold (5), and the cavity (4) is made of non-magnetic conductive material. A coil (2) is arranged outside the cavity (4); during molding, the magnetic lines of force of the orientation magnetic field generated by the coil (2) mostly pass through the magnetic conductive material A area, and a few pass through the non-magnetic conductive material B area, so that the green blank has a fully magnetized magnetic moment at the center of the magnetic blank and an insufficiently magnetized surrounding area. After sintering and magnetization, the surface magnetic field of the blank has a high intensity in the middle and a low intensity around it, and the magnetic field gradient value H 梯 Satisfy H 梯 ≥80Gs / cm, the magnetic field gradient value is the magnetic field intensity at the center of the magnet is higher than the magnetic field intensity around the magnet surface.

2. The method for manufacturing a high magnetic field gradient M-type ferrite rectangular magnet according to claim 1, characterized in that: After discharging, a dewatering machine is used to control the moisture content of the slurry at 22-26%.

3. The method for manufacturing a high magnetic field gradient M-type ferrite rectangular magnet according to claim 2, characterized in that: After discharging, a dewatering machine is used to control the moisture content of the slurry at 25%.

4. The method for manufacturing a high magnetic field gradient M-type ferrite rectangular magnet according to claim 1, characterized in that: The cross section of the magnetic conductive material A region is a triangular structure, and the top angle thereof is designed to be 90°.

5. The method for manufacturing a high magnetic field gradient M-type ferrite rectangular magnet according to claim 1, characterized in that: The magnetic conductive material A region and the non-magnetic conductive material B region are formed by surfacing welding and then machining.

6. The method for manufacturing a high magnetic field gradient M-type ferrite rectangular magnet according to claim 1, characterized in that: The pre-sintered material is ball-milled to a particle size of 0.75 to 9.0 μm.

7. The method for manufacturing a high magnetic field gradient M-type ferrite rectangular magnet according to claim 1, characterized in that: The green body is obtained by orientation molding with a magnetic field strength of more than 800KA / m.

8. The method for manufacturing a high magnetic field gradient M-type ferrite rectangular magnet according to claim 1, characterized in that: The green body is sintered at 1200-1240°C for 2-2.5 hours to obtain a cooked body; the cooked body is processed to a size that meets the requirements, and the product is obtained after being tested and qualified.

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