Efficient chromium removal process for rolling magnetic powder

Abstract

The invention relates to the technical field of rolled magnetic powder chromium removal processes, in particular to an efficient rolled magnetic powder chromium removal process which comprises the following production steps: step 1, preparing raw materials of industrial iron oxide red and strontium carbonate according to a molecular formula of SrO.nFe2O3; 2, uniformly mixing the raw materials, and adding strontium chloride in the mixing process to obtain a mixture; 3, granulating the mixture, and then pre-sintering to obtain a pre-sintered material; 4, coarsely crushing the pre-sintered material to obtain coarse powder, wherein the particle size of the coarse powder is 3-5 microns; and 5, finely crushing the coarse powder by using a ball mill to obtain slurry. According to the efficient chromium removal process for the rolled magnetic powder, hydrochloric acid with a certain proportion is added in the washing stage, residual SrO or BaO in the magnetic powder is removed, the residual SrO or BaO is prevented from reacting with Cr2O3 in the annealing stage, and therefore generation of hexavalent chromium is inhibited in the annealing stage, and the purpose of controlling the content of hexavalent chromium is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of rolling magnetic powder chromium removal technology, and more specifically, to a rolling magnetic powder high-efficiency chromium removal technology. Background Art

[0002] M-type permanent ferrite can be divided into strontium ferrite and barium ferrite according to chemical composition, and can be divided into sintered permanent ferrite and bonded permanent ferrite according to application. Among them, bonded permanent ferrite is a composite of permanent ferrite powder and binder, which has the characteristics of high product dimensional accuracy, good mechanical properties, uniform performance of each part of the magnet, and easy radial magnetization and multi-pole magnetization.

[0003] Bonded ferrites can be divided into extrusion molded magnets, injection molded magnets, and rolling molded magnets (also called calendering molded magnets) according to different molding methods.

[0004] The manufacturing process of rolled magnets is as follows: the magnetic powder is mixed evenly with organic substances such as CPE (chlorinated polyethylene) or NBR (nitrile rubber), and the magnetic powder is oriented by mechanical force on the calender to obtain anisotropic magnets. The magnet has excellent magnetic properties and excellent flexible processing performance, and has good flexibility. It is widely used in home appliances, toys, automobiles and other fields, such as refrigerator motor magnetic strips, advertising magnetic stickers, box door seals, automobile damping plates, etc.

[0005] The manufacturing process of rolled magnetic powder is as follows: the coarse powder is put into a ball mill for fine grinding, the fine ground slurry is washed with water, the washed slurry is dried and dispersed with a high-speed crusher, the dispersed powder is annealed in a tempering kiln, then dispersed with a high-speed crusher, and sieved and packaged.

[0006] During the manufacturing process of rolled magnetic powder, the valence state of some chromium elements contained in the magnetic powder is converted from trivalent to hexavalent due to high temperature and oxidizing atmosphere during the annealing process. Since hexavalent chromium is a toxic chemical substance, long-term exposure may cause various health problems, so measures must be taken to reduce hexavalent chromium.

[0007] At present, the hexavalent chromium reduction process adopted by domestic and foreign rolling forming magnetic powder suppliers is mainly pickling after tempering, and the reduction method (adding Fe 2+ ) to reduce hexavalent chromium to trivalent chromium to achieve the purpose of reducing hexavalent chromium. However, this method requires pickling, which consumes a large amount of water, and the solution after pickling needs to be treated with water, which is not environmentally friendly and has high costs.

[0008] Therefore, we proposed a high-efficiency chromium removal process for rolled magnetic powder to solve the above problems. Summary of the invention

[0009] In order to overcome the above-mentioned defects of the prior art, an embodiment of the present invention provides a process for efficiently removing chromium from rolled magnetic powder. More specifically, a manufacturing method is provided in which a certain proportion of hydrochloric acid is added in the water washing stage to remove residual SrO or BaO in the magnetic powder, thereby suppressing the generation of hexavalent chromium in the annealing stage, so as to achieve the purpose of controlling the hexavalent chromium content, thereby solving the problems raised in the above-mentioned background technology.

[0010] To achieve the above object, the present invention provides the following technical solution: a process for efficiently removing chromium from rolled magnetic powder, comprising the following production steps:

[0011] Step 1: Use industrial grade iron oxide red and strontium carbonate as raw materials and prepare the ingredients according to the molecular formula SrO·nFe2O3;

[0012] Step 2: uniformly mixing the raw materials, adding strontium chloride during the mixing process to obtain a mixture;

[0013] Step 3: granulating the mixture, and then pre-calcining to obtain a pre-calcined material;

[0014] Step 4: coarsely crushing the pre-sintered material to obtain coarse powder with a particle size of 3-5 μm;

[0015] Step 5: grinding the coarse powder into a slurry by a ball mill;

[0016] Step 6: Add water to the slurry at a ratio of 1:3, and add a certain amount of hydrochloric acid, stir evenly, and let it stand for 30 minutes;

[0017] Step 7: Filter the slurry to remove water, add an equal amount of water, stir evenly, let stand for 30 minutes, and repeat this process twice;

[0018] Step 8: Dry the washed slurry and disperse it with a high-speed crusher to obtain dry powder;

[0019] Step nine: annealing the dried powder to obtain tempered powder;

[0020] Step 10: Disperse the tempered powder, sieve it, and obtain rolled magnetic powder.

[0021] In a preferred embodiment, in step 1, n represents the molar ratio, and satisfies n=5.4-5.8.

[0022] In a preferred embodiment, in step 1, the purity of iron oxide is 99%, and the purity of strontium carbonate is 98%.

[0023] In a preferred embodiment, in step 2, the addition ratio of strontium chloride is 3.5wt%-5.0wt%.

[0024] In a preferred embodiment, in step three, the pre-firing temperature ranges from 1050°C to 1150°C.

[0025] In a preferred embodiment, in step five, the particle size of the coarse powder after crushing is 1.0 μm-1.1 μm.

[0026] In a preferred embodiment, in step six, hydrochloric acid with a concentration of 31% is added, and the amount of hydrochloric acid added corresponds to the molar ratio.

[0027] In a preferred embodiment, in step nine, the dried powder is annealed at 920°C.

[0028] In a preferred embodiment, in step ten, the tempering powder is dispersed using a high-speed pulverizer.

[0029] Technical effects and advantages of the present invention:

[0030] 1. The present invention provides a high-efficiency chromium removal process for rolled magnetic powder. The process removes residual SrO or BaO in the magnetic powder by adding a certain proportion of hydrochloric acid in the water washing stage, thereby avoiding reaction with Cr2O3 in the annealing stage, thereby inhibiting the generation of hexavalent chromium in the annealing stage, thereby achieving the purpose of controlling the hexavalent chromium content.

[0031] 2. Different molar ratios correspond to different acid addition amounts. The amount of acid added should be sufficient to react with the excess SrO in the magnetic powder. Excessive acid will cause a decrease in the coercivity of the magnetic powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a test result diagram of Example 1 of the present invention;

[0033] Figure 2 This is a diagram of the test results of Example 2 of the present invention;

[0034] Figure 3 This is a diagram of the test results of Example 3 of the present invention. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] Reference Figure 1-3 ,

[0037] A high-efficiency chromium removal process for rolled magnetic powder, comprising the following production steps:

[0038] Step 1: Use industrial grade iron oxide red and strontium carbonate as raw materials, and prepare the ingredients according to the molecular formula SrO·nFe2O3, wherein n represents the molar ratio, and satisfies n=5.4-5.8.

[0039] Step 2: uniformly mixing the raw materials, adding 3.5%-5.0wt% strontium chloride during the mixing process to obtain a mixture;

[0040] Step 3: granulating the mixture, and then pre-calcining it at 1050° C.-1150° C. to obtain a pre-calcined material;

[0041] Step 4: coarsely crushing the pre-sintered material to obtain coarse powder with a particle size of 3 μm-5 μm;

[0042] Step 5: Grind the coarse powder with a ball mill to obtain a slurry, wherein the particle size after grinding is 1.0 μm-1.1 μm;

[0043] Step 6: Add water to the slurry at a ratio of 1:3, and add a certain concentration of 31% hydrochloric acid (the amount of hydrochloric acid added corresponds to the molar ratio), stir evenly, and let stand for 30 minutes;

[0044] Step 7: Filter the slurry to remove water, add an equal amount of water, stir evenly, and let stand for 30 minutes; repeat this process twice.

[0045] Step 8: drying the washed slurry and dispersing it with a high-speed grinder to obtain dry powder;

[0046] Step nine: annealing the dried powder at 920° C. to obtain tempered powder;

[0047] Step 10: Disperse the tempered powder using a high-speed pulverizer, and obtain rolled magnetic powder after sieving.

[0048] In summary, the present invention provides a highly efficient chromium removal process for rolled magnetic powder, and the hexavalent chromium content of the magnetic powder manufactured by the process is less than 10 ppm.

[0049] Hexavalent chromium is mainly produced in the drying and annealing processes. Due to the high temperature and oxygen environment, the following reactions are likely to occur:

[0050] 4SrO+Cr2O3+3O2=SrCrO4;

[0051] Or 4BaO+2Cr2O3+3O2=BaCrO4;

[0052] This leads to the appearance of hexavalent chromium.

[0053] The present invention proposes to remove the residual SrO or BaO in the magnetic powder by adding a certain proportion of hydrochloric acid in the water washing stage, and the amount of hydrochloric acid added corresponds to the residual SrO or BaO in the magnetic powder. The reaction formula is as follows:

[0054] SrO+2HCl=SrCl2 or BaO+2HCl=BaCl2

[0055] Since SrCl2 or BaCl2 is easily soluble in water, SrCl2 or BaCl2 can be washed away from the magnetic powder by water washing, thereby eliminating the residual SrO or BaO in the magnetic powder and avoiding the reaction with Cr2O3 to produce hexavalent chromium during the annealing stage, thereby achieving the purpose of inhibiting the production of hexavalent chromium.

[0056] Since the residual SrO or BaO content in magnetic powders with different molar ratios is different, the amount of hydrochloric acid to be added is also different.

[0057] Example 1

[0058] Step 1: weigh the raw materials of each component according to the molecular formula SrO·5.6Fe2O3, wherein the purity of iron red is 99% and the purity of strontium carbonate is 98%;

[0059] Step 2: uniformly mixing the raw materials, adding 3.5-5.0 wt % strontium chloride during the mixing process to obtain a mixture;

[0060] Step 3: granulating the mixture, and then pre-calcining it at 1150° C. to obtain a pre-calcined material;

[0061] Step 4: coarsely crushing the pre-sintered material to obtain coarse powder with a particle size of 3-5 μm;

[0062] Step 5: Weigh 650 g of the coarse powder and grind it in a ball mill for 5 hours. The particle size after grinding is 1.05 μm;

[0063] Step 6: Add water to the slurry at a ratio of 1:3, and add 10.3 ml of 31% hydrochloric acid, stir evenly, and let stand for 30 minutes;

[0064] Step 7: Filter the slurry to remove water, add an equal amount of water, stir evenly, and let stand for 30 minutes; repeat this process twice.

[0065] Step 8: drying the washed slurry and dispersing it with a high-speed grinder to obtain dry powder;

[0066] Step nine: annealing the dried powder at 920° C. to obtain tempered powder;

[0067] Step 10: Disperse the tempered powder using a high-speed pulverizer, and obtain rolled magnetic powder after sieving.

[0068] Step 11: The test results of the rolled magnetic powder hexavalent chromium are shown in Figure 1 ;

[0069] Step 12: The magnetic properties test results of the rolled magnetic powder are shown in Figure 1 :

[0070] Comparative Example 1

[0071] Step 1: weigh the raw materials of each component according to the molecular formula SrO·5.6Fe2O3, wherein the purity of iron red is 99% and the purity of strontium carbonate is 98%;

[0072] Step 2: uniformly mixing the raw materials, adding 3.5-5.0 wt % strontium chloride during the mixing process to obtain a mixture;

[0073] Step 3: granulating the mixture, and then pre-calcining it at 1150° C. to obtain a pre-calcined material;

[0074] Step 4: coarsely crushing the pre-sintered material to obtain coarse powder with a particle size of 3-5 μm;

[0075] Step 5: Grind the coarse powder with a ball mill for 5 hours, and the particle size after grinding is 1.05 μm;

[0076] Step 6: Stir the slurry evenly in a ratio of material: water = 1:3, and let it stand for 30 minutes;

[0077] Step 7: Filter the slurry to remove water, add an equal amount of water, stir evenly, and let stand for 30 minutes; repeat this process twice.

[0078] Step 8: drying the washed slurry and dispersing it with a high-speed grinder to obtain dry powder;

[0079] Step nine: annealing the dried powder at 920° C. to obtain tempered powder;

[0080] Step 10: Disperse the tempered powder using a high-speed pulverizer, and obtain rolled magnetic powder after sieving.

[0081] Step 11: The test results of the rolled magnetic powder hexavalent chromium are shown in Figure 1 ;

[0082] Step 12: The magnetic properties test results of the rolled magnetic powder are shown in Figure 1 :

[0083] Example 2

[0084] Step 1: weighing raw materials of various components according to the molecular formula SrO·5.6Fe2O3, wherein the purity of iron oxide red is 99% and the purity of strontium carbonate is 98%; Step 2: mixing the raw materials uniformly, adding 3.5-5.0wt% strontium chloride during the mixing process to obtain a mixture;

[0085] Step 3: granulating the mixture, and then pre-calcining it at 1150° C. to obtain a pre-calcined material;

[0086] Step 4: coarsely crushing the pre-sintered material to obtain coarse powder with a particle size of 3-5 μm;

[0087] Step 5: Grind the coarse powder with a ball mill for 5 hours, and the particle size after grinding is 1.05 μm;

[0088] Step 6: Add water to the slurry at a ratio of 1:3, and add 2.5 ml, 5 ml, 7.5 ml, 10.3 ml, 12.5 ml, and 15 ml of hydrochloric acid respectively, stir evenly, and let stand for 30 minutes;

[0089] Step 7: Filter the slurry to remove water, add an equal amount of water, stir evenly, and let stand for 30 minutes; repeat this process twice.

[0090] Step 8: drying the washed slurry and dispersing it with a high-speed grinder to obtain dry powder;

[0091] Step nine: annealing the dried powder at 920° C. to obtain tempered powder;

[0092] Step 10: Disperse the tempered powder using a high-speed pulverizer, and obtain rolled magnetic powder after sieving.

[0093] Step 11: The test results of the rolled magnetic powder hexavalent chromium are shown in Figure 2 ;

[0094] Step 12: The magnetic properties test results of the rolled magnetic powder are shown in Figure 2 :

[0095] Example 3

[0096] Step 1: weigh the raw materials of each component according to the molecular formula SrO·nFe2O3, wherein the purity of iron oxide red is 99% and the purity of strontium carbonate is 98%; n is 5.5, 5.6, 5.7, 5.8, 5.9, and 6.0 respectively;

[0097] Step 2: uniformly mixing the raw materials, adding 3.5-5.0 wt % strontium chloride during the mixing process to obtain a mixture;

[0098] Step 3: granulating the mixture, and then pre-calcining it at 1150° C. to obtain a pre-calcined material;

[0099] Step 4: coarsely crushing the pre-sintered material to obtain coarse powder with a particle size of 3-5 μm;

[0100] Step 5: Grind the coarse powder with a ball mill for 5 hours, and the particle size after grinding is 1.05 μm;

[0101] Step 6: Add water to the slurry at a ratio of 1:3, and add 13 ml, 10.3 ml, 7.6 ml, 5 ml, and 2.5 ml of 31% hydrochloric acid respectively, stir evenly, and let stand for 30 minutes;

[0102] Step 7: Filter the slurry to remove water, add an equal amount of water, stir evenly, and let stand for 30 minutes; repeat this process twice.

[0103] Step 8: drying the washed slurry and dispersing it with a high-speed grinder to obtain dry powder;

[0104] Step nine: annealing the dried powder at 920° C. to obtain tempered powder;

[0105] Step 10: Disperse the tempered powder using a high-speed pulverizer, and obtain rolled magnetic powder after sieving.

[0106] Step 11: The test results of the rolled magnetic powder hexavalent chromium are shown in Figure 3 ;

[0107] Step 12: The magnetic properties test results of the rolled magnetic powder are shown in Figure 3 .

[0108] Finally: The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A process for efficiently removing chromium from rolled magnetic powder, characterized in that: The production process includes the following steps: Step 1: Use industrial grade iron oxide red and strontium carbonate as raw materials and prepare the ingredients according to the molecular formula SrO·nFe2O3; Step 2: uniformly mixing the raw materials, adding strontium chloride during the mixing process to obtain a mixture; Step 3: granulating the mixture, and then pre-calcining to obtain a pre-calcined material; Step 4: coarsely crushing the pre-sintered material to obtain coarse powder with a particle size of 3-5 μm; Step 5: grinding the coarse powder into a slurry by a ball mill; Step 6: Add water to the slurry at a ratio of 1:3, and add a certain amount of hydrochloric acid, stir evenly, and let it stand for 30 minutes; Step 7: Filter the slurry to remove water, add an equal amount of water, stir evenly, let stand for 30 minutes, and repeat this process twice; Step 8: Dry the washed slurry and disperse it with a high-speed crusher to obtain dry powder; Step nine: annealing the dried powder to obtain tempered powder; Step 10: Disperse the tempered powder, sieve it, and obtain rolled magnetic powder.

2. A high-efficiency chromium removal process for rolled magnetic powder according to claim 1, characterized in that: In step 1, n represents the molar ratio, and satisfies n=5.4-5.

8.

3. A high-efficiency chromium removal process for rolled magnetic powder according to claim 1, characterized in that: In step 1, the purity of iron oxide is 99%, and the purity of strontium carbonate is 98%.

4. A high-efficiency chromium removal process for rolled magnetic powder according to claim 1, characterized in that: In step 2, the addition ratio of strontium chloride is 3.5wt%-5.0wt%.

5. A high-efficiency chromium removal process for rolled magnetic powder according to claim 1, characterized in that: In step 3, the pre-firing temperature range is: 1050℃~1150℃.

6. A high-efficiency chromium removal process for rolled magnetic powder according to claim 1, characterized in that: In step 5, the particle size of the coarse powder after crushing is 1.0 μm-1.1 μm.

7. A high-efficiency chromium removal process for rolled magnetic powder according to claim 1, characterized in that: In step six, hydrochloric acid with a concentration of 31% is added, and the amount of hydrochloric acid added corresponds to the molar ratio.

8. The high-efficiency chromium removal process of rolled magnetic powder according to claim 1, characterized in that: In step nine, the dried powder is annealed at 920°C.

9. A high-efficiency chromium removal process for rolled magnetic powder according to claim 1, characterized in that: In step ten, the tempering powder is dispersed by a high-speed pulverizer.

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