A method for producing permanent ferrite products with improved yield

Abstract

This invention relates to the field of permanent magnet ferrite product preparation technology, and discloses a production method for permanent magnet ferrite products with improved yield. The method includes wet ball milling of iron oxide red, strontium carbonate, and a pre-calcination aid; pre-calcining the resulting slurry; continuously introducing oxygen-containing gas at the pre-calcination temperature, with an oxygen volume percentage ≥21%, to obtain a pre-calcined material; adding calcium gluconate to the pre-calcined material for coarse grinding to obtain coarse powder; adding a sintering aid containing sodium chloride to the coarse powder, with the sodium chloride addition amount being 0.1–0.3 wt% of the coarse powder mass; then wet ball milling to prepare a fine slurry; pressing the fine slurry into a forming magnetic field to obtain a magnetic blank; and sintering the magnetic blank to obtain the permanent magnet ferrite product. The prepared permanent magnet ferrite product has an improved yield, and its magnetic properties are largely maintained or even improved, offering advantages such as low production cost and high performance.

Description

Technical Field

[0001] This invention relates to the field of permanent magnet ferrite product preparation technology, and specifically to a method for producing permanent magnet ferrite products with improved yield. Background Technology

[0002] Since their discovery in the 1950s, permanent magnet ferrites have been widely used in products such as toroidal magnets, square magnets, and tile-shaped magnets, and have now become a core component of micromotors. Motor magnet tiles, in particular, are used as motor stators in industries such as automobiles, motorcycles, home appliances, power tools, and fitness equipment, and are the most important type of product in the permanent magnet ferrite industry.

[0003] The quality of permanent magnet ferrite products is closely related to the manufacturing process. Currently, the main manufacturing process for high-performance permanent magnet ferrite products uses high-purity iron oxide red (≥99% purity) as raw material. This is first mixed with strontium carbonate and other ingredients through continuous ball milling, followed by pre-calcination to prepare ferrite pre-fired material. This pre-fired material is then crushed, additives are added, and it is finely ground to prepare fine powder. Finally, it is molded into a green body and sintered. Each step in this manufacturing process can potentially cause defects in the product. For example, impurities in the raw materials can easily cause pinholes, and improper sintering processes can easily cause microcracks, affecting the yield of permanent magnet ferrite products.

[0004] Current research on improving the yield of permanent magnet ferrite products has been reported, but the results are not yet ideal. For example, Chinese patent application CN202010653937.4 discloses a technical solution to improve the yield of strontium permanent magnet ferrite products by introducing a dispersant composed of sorbitol and silica during the preparation of strontium permanent magnet ferrite. However, sorbitol is prone to decomposition during sintering, and the generated gas can easily cause microcracks in the product, affecting the improvement of the yield. The yield of the product obtained by this technical solution ultimately only reached 92%. Another example is Chinese patent application CN202210385629.7, entitled "An Additive for the Preparation of Permanent Magnet Strontium Ferrite Material and Its Application," which adds triethanolamine and hexadecyltrimethylammonium chloride to the pre-sintered material, grinds it, shapes it, and sinters to prepare sintered magnets. This solution can further improve the yield compared to calcium gluconate, but the overall yield is still less than 90%.

[0005] Furthermore, there are no reports on the use of low-purity iron oxide red with a purity of 97.5% to 98.5%, and how to use low-purity iron oxide red while maintaining a good yield and magnetic properties still needs further research. Summary of the Invention

[0006] The purpose of this invention is to provide a method for producing permanent magnet ferrite products with improved yield. The resulting products, such as magnetic tiles, have a high yield, reduced defects such as surface microcracks, and the performance of the magnets is maintained or even improved.

[0007] This invention provides the following technical solution:

[0008] A method for producing permanent magnet ferrite products with improved yield includes the following steps:

[0009] (1) Iron oxide red, strontium carbonate and precalcining additives are mixed and then wet ball milled. The resulting slurry is precalcined and oxygen-containing gas is continuously introduced at the precalcination temperature. The oxygen volume ratio is ≥21% to obtain the precalcined material.

[0010] (2) Add calcium gluconate to the pre-burned material and coarsely grind it to obtain coarse powder;

[0011] (3) Add a sintering aid containing sodium chloride to the coarse powder, the amount of sodium chloride added is 0.1 to 0.3 wt% of the mass of the coarse powder, and then prepare a fine slurry by wet ball milling;

[0012] (4) Press the fine slurry into a molding magnetic field to obtain a magnetic blank, and sinter the magnetic blank to obtain a permanent magnet ferrite product.

[0013] Factors affecting the yield of permanent magnet ferrite products involve all stages from raw material preparation to final product molding. The technical solution of this application focuses on controlling two aspects: pre-firing of raw materials and sintering of the magnet blank. For raw material pre-firing, a ball-milled slurry with uniform particle size is prepared using a wet process. During pre-firing, oxygen-containing gas is actively and continuously introduced to promote a full solid-phase reaction. In the sintering process, a certain amount of sodium chloride is introduced into the fine slurry. This combination of a full solid-phase reaction and the melt wettability of sodium chloride improves product performance, eliminates product defects, increases the yield of the obtained products, and significantly reduces microcracks and fractures.

[0014] As a preferred embodiment of the method of the present invention,

[0015] In step (1), iron oxide red and strontium carbonate are prepared according to SrO·nFe2O3, where n is a molar ratio of 5.9 to 6.1;

[0016] And / or the pre-calcination aid in step (1) is silicon dioxide, and the amount added is 0.15 to 0.3% of the mass of iron oxide red.

[0017] As a preferred embodiment of the method of the present invention, the particle size of the slurry in step (1) is 0.9 to 1.0 μm. The slurry can be prepared by wet ball milling for 3.5 to 5 hours using ∮6 steel balls at a material:ball:water ratio of 1:4.5:1.2.

[0018] As a preferred embodiment of the method of the present invention,

[0019] The preheating temperature in step (1) is 1200-1250℃;

[0020] And / or the oxygen-containing gas in step (1) is air, or the oxygen-containing gas is a mixture of oxygen and air or an inert gas.

[0021] As a preferred embodiment of the method of the present invention, the purity of the iron oxide red in step (1) is 97.5–98.5 wt%. Impurities in iron oxide red not only affect the performance of the product but also the yield. Therefore, high-purity iron oxide red with a purity ≥99% is currently mainly used in high-performance permanent magnet ferrite products. The production method of the present invention has been verified to be used to prepare permanent magnet ferrite products with low-purity iron oxide red of 97.5–98.5 wt%, more preferably 98–98.5 wt%.

[0022] As a preferred embodiment of the method of the present invention, step (1) further includes introducing oxygen-containing gas with an oxygen volume ratio of 30-40% when the pre-calcination temperature is raised to 900-1000°C and maintaining this temperature for 1-2 hours, and then raising the temperature to the pre-calcination temperature. For low-purity iron oxide red with a purity of 97.5-98.5 wt%, the purity of iron oxide red is low, the impurity content is high, and the pinhole phenomenon in the product is more prominent. Combining the characteristics of strontium carbonate and the like, which decompose at 800°C and begin to form ferrite crystals above 900°C, the inventors significantly advanced the ferrite crystal formation process by introducing a high content of oxygen at 900-1000°C, promoting the full formation of ferrite crystals, effectively improving product performance and yield, and reducing the adverse effects of impurities, especially suitable for low-purity iron oxide red.

[0023] As a preferred embodiment of the method of the present invention, the amount of calcium gluconate added in step (2) is 0.2 to 0.3% of the mass of the coarse powder.

[0024] As a preferred embodiment of the method of the present invention, the sintering aid in step (3) further includes 0.8-1.3% CaCO3, 0.2-0.6% SiO2, 0.2-0.4% SrCO3, 0.1-0.5% glucose, and 0.1-0.3% boric acid by weight of the coarse powder.

[0025] As a preferred embodiment of the method of the present invention, the particle size of the fine slurry obtained in step (3) is 0.7 to 0.9 μm. This slurry can be obtained by ball milling with steel balls of ∮6 and ∮8 mm in a ratio of 5.5:4.5 for 14 to 18 hours.

[0026] As a preferred embodiment of the method of the present invention,

[0027] The forming magnetic field strength in step (4) is 8000-10000 Gs;

[0028] And / or the sintering temperature in step (4) is 1220–1250 °C;

[0029] The following step (4) also includes adding a release agent to the mold before pressing.

[0030] Adding a release agent can improve the demolding efficiency of the magnetic blank and prevent surface adhesion; however, different release agents have significantly different properties. For low-purity iron oxide red raw materials, a suitable release agent is P6-16.

[0031] The beneficial effects of this invention are as follows:

[0032] The method for producing permanent magnet ferrite products of the present invention starts from the pre-firing and sintering stages. High oxygen content gas is continuously introduced for pre-firing and sodium chloride is introduced for sintering. By combining pre-firing and sintering, the yield of the prepared permanent magnet ferrite products is improved, the phenomenon of microcracks and pinholes is reduced, and the magnetic properties are maintained. The effect is particularly obvious for the preparation of permanent magnet ferrite products using low purity iron oxide red as raw material. It has the advantages of low production cost and high product performance. Detailed Implementation

[0033] The specific embodiments of the present invention will be further described below.

[0034] Unless otherwise specified, all raw materials used in this invention are commercially available or commonly used in the field. Unless otherwise specified, the methods in the following embodiments are conventional methods in the field.

[0035] Example 1

[0036] A method for preparing permanent magnet ferrite products, taking magnetic tiles as an example, includes the following steps:

[0037] (1) Weigh strontium carbonate and 98% pure iron oxide red according to SrO·nFe2O3, n is 5.95, and add SiO2, the amount of which is 0.15% of the mass of iron oxide red to obtain powder;

[0038] (2) The obtained powder is passed through a ∮6 steel ball and wet ball milled for 3.5 hours at a material:ball:water ratio of approximately 1:4.5:1.2 to obtain a slurry with an average particle size of 1.0μm. The obtained slurry is then pumped into a mixing tank and stirred.

[0039] (3) The stirred slurry is filtered by high speed and then fed into a rotary kiln. It is pre-fired at 1200℃ for 5 hours and air is actively introduced by a blower at the pre-fired temperature to obtain pre-fired material.

[0040] (4) Add 0.3wt% calcium gluconate to the pre-burned material and coarsely grind it to an average particle size of 5μm using a planetary ball mill.

[0041] (5) Add 1% CaCO3, 0.2% SiO2, 0.3% SrCO3, 0.2% glucose, 0.1% boric acid and 0.1% NaCl to the obtained coarse powder (total 2500 kg). Then, use a ball mill with steel balls of ∮6 and ∮8 mm in a ratio of 5.5:4.5 to grind for 14 hours to obtain a fine slurry with an average particle size of 0.9 μm.

[0042] (6) Use saponified oil dilution (concentration 5wt%) to wet the lower mold, then add fine slurry, and form A-type magnetic tile blanks by a press with a forming magnetic field of 8000Gs. A-type magnetic tiles are obtained by single-layer rapid sintering in a roller kiln at 1220℃.

[0043] Comparative Example 1-1

[0044] The difference from Example 1 is that the operation of actively charging air with a blower is omitted in step (3) at the pre-burning temperature.

[0045] Comparative Examples 1-2

[0046] The difference from Example 1 is that the addition of sodium chloride is omitted in step (5).

[0047] Comparative Examples 1-3

[0048] The difference from Example 1 is that the operation of actively charging air with a blower is omitted in step (3) at the pre-burning temperature, and the addition of sodium chloride is omitted in step (5).

[0049] The performance comparison of the A-type magnetic tiles obtained in Example 1 and Comparative Examples 1-1 to 1-3 is shown in Tables 1 and 2 below.

[0050] Table 1. Performance test results of the magnetic tiles prepared in the above embodiments and comparative examples (average performance of 100 qualified products).

[0051] serial number Br(Gs) Hcb(Oe) Hcj(Oe) (BH)max(MGOe) Example 1 4225 3438 3503 4.276 Comparative Example 1-1 4163 3267 3325 4.153 Comparative Examples 1-2 4189 3286 3392 4.196 Comparative Examples 1-3 4176 3251 3326 4.185

[0052] As can be seen from the table above, compared with Comparative Examples 1-3, Example 1 shows a certain degree of improvement in all magnetic properties, and the effect is better than Comparative Examples 1-1 and 1-2. This indicates that the production method of this application does not damage the magnetic properties of the product, and the magnetic properties are maintained or even improved to a certain extent. Moreover, a comparison between Comparative Examples 1-1 and 1-3 shows that for low-purity iron oxide red, adding sodium chloride alone has a slight negative impact on the magnetic properties.

[0053] Table 2. Yield of magnetic tiles prepared in the above embodiments and comparative examples (benchmark: 10,000 pieces)

[0054]

[0055] As can be seen from the table above, on the one hand, due to the lower purity of the iron oxide red used, pinhole defects account for a higher proportion of microcracks and fractures; on the other hand, the overall defect rate of the magnetic tiles prepared based on the production method of this application is reduced, manifested in a significant reduction in the microcrack rate, and a certain degree of decrease in the pinhole rate and fracture rate. Moreover, a comparison between Example 1 and Comparative Examples 1-1 and 1-2 shows that, regarding the microcrack phenomenon, the proportion of microcracks is significantly lower than that of Comparative Examples 1-1 and 1-2 when the pre-firing and sintering processes are combined, indicating that the improvements in the pre-firing and sintering processes have a synergistic effect.

[0056] Example 2

[0057] A method for preparing permanent magnet ferrite products, taking magnetic tiles as an example, includes the following steps:

[0058] (1) Weigh strontium carbonate and iron oxide red with a purity of 97.5% according to SrO·nFe2O3, where n is 6.1, and add SiO2 at a rate of 0.3% of the mass of iron oxide red to obtain powder;

[0059] (2) The obtained powder is passed through a ∮6 steel ball and wet ball milled for 5 hours at a material:ball:water ratio of approximately 1:4.5:1.2 to obtain a slurry with an average particle size of 0.9μm. The slurry is then fed into a mixing tank and stirred.

[0060] (3) The stirred slurry is filtered by high speed and then fed into a rotary kiln. It is pre-fired at 1250℃ for 3 hours and air is actively introduced by a blower at the pre-fired temperature to obtain pre-fired material.

[0061] (5) Add 0.2wt% calcium gluconate to the pre-burned material and coarsely grind it with a planetary ball mill to obtain coarse powder of 3.5μm;

[0062] (6) Add 0.8% CaCO3, 0.6% SiO2, 0.2% SrCO3, 0.1% glucose, 0.3% boric acid, and 0.2% Na2Cl by weight of the obtained coarse powder (2500kg), and then grind it for 18 hours using a ball mill with ∮6 and ∮8mm steel balls in a ratio of 5.5:4.5 to obtain a fine slurry with a particle size of 0.7μm.

[0063] (7) Use saponified oil dilution (concentration 5wt%) to wet the lower mold, then add fine slurry, and form A-type magnetic tile blanks by a press with a forming magnetic field of 8000Gs. A-type magnetic tiles are obtained by single-layer rapid sintering in a roller electric kiln with a sintering temperature of 1250℃.

[0064] The test results showed that the total defect rate of the 10,000 Type A magnetic tiles was 5.4%, and the finished product rate was 94.6%.

[0065] Example 3

[0066] A method for preparing permanent magnet ferrite products, taking magnetic tiles as an example, includes the following steps:

[0067] (1) Weigh strontium carbonate and iron oxide red with a purity of 98.5% according to SrO·nFe2O3, n is 5.9, and add SiO2, the amount of which is 0.2% of the mass of iron oxide red to obtain powder;

[0068] (2) The obtained powder is passed through a ∮6 steel ball and wet ball milled for 4 hours at a material:ball:water ratio of approximately 1:4.5:1.2 to obtain a slurry with a particle size of 0.97μm. The slurry is then fed into a mixing tank and stirred.

[0069] (3) The stirred slurry is filtered by high speed and then fed into a rotary kiln. It is pre-fired at 1230℃ for 4.5 hours and air is actively introduced by a blower at the pre-fired temperature to obtain pre-fired material.

[0070] (4) Add 0.3% calcium gluconate to the pre-burned material and coarsely grind it with a planetary ball mill to obtain coarse powder with a diameter of 4μm;

[0071] (5) Add 1.3% CaCO3, 0.3% SiO2, 0.4% SrCO3, 0.5% glucose, 0.2% boric acid, and 0.3% Na2Cl to the obtained coarse powder (2500kg). Then, use a ball mill with ∮6 and ∮8mm steel balls in a ratio of 5.5:4.5 to grind for 16 hours to obtain a fine slurry with a particle size of 0.82μm.

[0072] (6) Use saponified oil dilution (concentration 5wt%) to wet the lower mold, then add fine slurry, and form A-type magnetic tile blanks by a press with a forming magnetic field of 8000Gs. A-type magnetic tiles are obtained by single-layer rapid sintering in a roller electric kiln with a sintering temperature of 1230℃.

[0073] The test results showed that the total defect rate of the 10,000 Type A magnetic tiles was 6.2%, and the finished product rate was 93.8%.

[0074] Example 4

[0075] The difference from Example 1 is that: in the process of pre-firing and heating to the pre-firing temperature in step (3), when the temperature reaches 900°C, a mixture of air and oxygen is introduced into the rotary kiln, with the total oxygen volume accounting for 40%, and is maintained for 2 hours, and then the temperature is further increased to the pre-firing temperature, and the blower actively introduces air for pre-firing.

[0076] Comparative Example 4-1

[0077] The difference from Example 4 is that in step (3), when the temperature reaches 900°C, air is continuously introduced to replace the air and oxygen mixture and maintained for 2 hours. Then, the temperature is raised to the pre-burning temperature and the blower actively introduces air for pre-burning.

[0078] The yield of the A-grade magnetic tiles is shown in Table 3 below.

[0079] Table 3. Yield of magnetic tiles prepared in the above embodiments and comparative examples (benchmark: 10,000 pieces)

[0080]

[0081] As can be seen from the table above, the results obtained in Example 4 further improved the yield compared to Example 1, as evidenced by a significant reduction in pinholes. This indicates that significantly advancing the ferrite crystal formation temperature during pre-firing can facilitate magnet preparation, improve product performance and yield, and reduce the adverse effects of impurities. However, this requires a high-concentration oxygen atmosphere. As shown in Comparative Example 4-1, the effect of directly introducing air is not significant compared to Example 1.

[0082] Example 5

[0083] The difference from Example 1 is that: in the process of pre-firing and heating to the pre-firing temperature in step (3), when the temperature reaches 1000°C, a mixture of air and oxygen is introduced into the rotary kiln, with the total oxygen volume accounting for 30%, and is maintained for 1 hour, and then the temperature is further increased to the pre-firing temperature, and the blower actively introduces air for pre-firing.

[0084] Comparative Example 5-1

[0085] The difference from Example 5 is that in step (3), when the temperature reaches 1000°C, a mixture of air and oxygen is introduced into the rotary kiln, with the total oxygen volume accounting for 30%, and the temperature is further increased to the pre-firing temperature. Then, a blower is used to actively introduce air for pre-firing to replace the mixture of air and oxygen.

[0086] The yield of the A-grade magnetic tiles is shown in Table 4 below.

[0087] Table 4. Yield of magnetic tiles prepared in the above embodiments and comparative examples (benchmark: 10,000 pieces)

[0088]

[0089]

[0090] As can be seen from the table above, when the ferrite crystal formation temperature is brought forward, not only is sufficient oxygen required, but it must also be maintained for a certain period of time to ensure that the reaction proceeds fully. Otherwise, as shown in Comparative Example 5-1, there is no significant improvement compared to Example 1. The results are within the error range compared to Example 1, and the effectiveness is comparable.

[0091] Example 6

[0092] The difference from Example 1 is that in step (6), release agent P6-16 (Xima Petroleum Products Co., Ltd.) is used instead of saponified oil diluent. Compared with Example 1, the yield is increased by 1.8%. This shows that different release agents have different applicability. Selecting a suitable release agent according to the quality of iron oxide red or pre-fired material is also a way to improve the yield.

Claims

1. A method for producing permanent magnet ferrite products with improved yield, characterized in that, Includes the following steps: (1) After wet ball milling, iron oxide red, strontium carbonate and pre-calcination additives are prepared. The resulting slurry is pre-calcined. During the pre-calcination process, when the temperature is raised to 900-1000℃, oxygen-containing gas with an oxygen volume ratio of 30-40% is introduced and maintained for 1-2 hours. Then the temperature is raised to the pre-calcination temperature, and oxygen-containing gas is continuously introduced at the pre-calcination temperature with an oxygen volume ratio ≥21% to obtain the pre-calcined material. The purity of iron oxide red is 97.5-98.5 wt%. (2) Add calcium gluconate to the pre-calcined material and coarsely grind it to obtain coarse powder; (3) Add a sintering aid containing sodium chloride to the coarse powder, the amount of sodium chloride added is 0.1 to 0.3 wt% of the mass of the coarse powder, and then prepare fine slurry by wet ball milling; (4) Press the fine slurry into a molding magnetic field to obtain a magnetic blank, and sinter the magnetic blank to obtain a permanent magnet ferrite product.

2. The production method according to claim 1, characterized in that, In step (1), iron oxide red and strontium carbonate are prepared according to SrO·nFe2O3, where n is a molar ratio of 5.9 to 6.1; and / or the pre-calcination aid in step (1) is silicon dioxide, and the amount added is 0.15 to 0.3% of the mass of iron oxide red.

3. The production method according to claim 1, characterized in that, The particle size of the slurry in step (1) is 0.9 to 1.0 µm.

4. The production method according to claim 1, characterized in that, The preheating temperature in step (1) is 1200-1250℃.

5. The production method according to claim 1, characterized in that, In step (2), the amount of calcium gluconate added is 0.2 to 0.3% of the mass of the pre-burned material.

6. The production method according to claim 1, characterized in that, The sintering aids in step (3) also include 0.8-1.3% CaCO3, 0.2-0.6% SiO2, 0.2-0.4% SrCO3, 0.1-0.5% glucose, and 0.1-0.3% boric acid by weight of the coarse powder.

7. The production method according to claim 1 or 6, characterized in that, The particle size of the fine slurry obtained in step (3) is 0.7 to 0.9 µm.

8. The production method according to claim 1, characterized in that, The forming magnetic field strength in step (4) is 8000-10000 Gs; and / or the sintering temperature in step (4) is 1220-1250 °C; and / or step (4) further includes adding a release agent to the mold before pressing.

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