1. A method for solving the problem of sintering cracking of a soft magnetic ferrite is characterized by comprising the following steps:

(1) mixing the pre-sintered soft magnetic ferrite raw material with auxiliary materials, and performing ball milling to obtain a first mixture;

or ball-milling the pre-sintered soft magnetic ferrite raw material, and then mixing the ball-milled soft magnetic ferrite raw material with auxiliary materials to obtain a first mixture;

the auxiliary materials comprise a glue, a flow aid and a plasticizer;

(2) and (2) performing spray granulation on the first mixture obtained in the step (1), and mixing the obtained granulated product with a lubricant to obtain a second mixture, wherein the second mixture is used for preparing the soft magnetic ferrite.

2. The method as claimed in claim 1, wherein the temperature of the pre-burning in step (1) is 950-1050 ℃;

preferably, the ball milling is wet ball milling;

preferably, the solvent of the ball mill comprises water.

3. The method of claim 1 or 2, wherein the average particle size of the product of the ball milling in step (1) is reduced to 1.5-2.0 μm.

4. The method of any one of claims 1-3, wherein in step (1) the auxiliary material, the adhesive comprises a polyvinyl alcohol solution;

preferably, the concentration of the solute in the polyvinyl alcohol solution is 5-10 wt%;

preferably, in the auxiliary material in the step (1), the content of the adhesive is 0.6-1.2 wt% of the mass of the soft magnetic ferrite raw material after the pre-sintering.

5. The method of any one of claims 1-4, wherein the flow aid of step (1) comprises glycerin;

preferably, in the auxiliary material in the step (1), the content of the flow aid is 0.10-0.25 wt% of the mass of the soft magnetic ferrite raw material after the pre-sintering.

6. The method of any one of claims 1-5, wherein the plasticizer of step (1) comprises polyethylene glycol;

preferably, the molecular weight of the polyethylene glycol is 200-600;

preferably, in the auxiliary material in the step (1), the content of the plasticizer is 0.05-0.1 wt% of the mass of the soft magnetic ferrite raw material after the pre-sintering.

7. The method according to any one of claims 1 to 6, wherein in step (1), the preparation method of the auxiliary material comprises: adding a fluidity auxiliary agent and a plasticizer when decocting the polyvinyl alcohol solution, and mixing the materials to obtain the auxiliary material;

preferably, the time for mixing the materials is above 2 h.

8. The process according to any one of claims 1 to 7, wherein the moisture content of the granulated product of step (2) is 0.6 to 1.0%;

preferably, the granulated product of the step (2) has a bulk specific gravity of 1.5 to 1.7g/cm³；

Preferably, the flow angle of the granulated product of step (2) is below 28 °;

preferably, in the granulated product in the step (2), the 80-160 mesh granules account for more than 85 wt%.

9. The method of any one of claims 1-8, wherein the lubricant of step (2) comprises zinc stearate;

preferably, the lubricant in the step (2) is added in an amount of 0.01-0.05 wt% of the mass of the soft magnetic ferrite raw material after the pre-sintering.

10. Method according to any of claims 1-9, characterized in that the method comprises the steps of:

(1) mixing the pre-sintered soft magnetic ferrite raw material with auxiliary materials, and performing wet ball milling to obtain a first mixture;

or performing wet ball milling on the pre-sintered soft magnetic ferrite raw material, and then mixing the soft magnetic ferrite raw material with auxiliary materials to obtain a first mixture;

the temperature of the pre-sintering is 950-1050 ℃; the auxiliary materials comprise a glue, a flow aid and a plasticizer;

in the auxiliary material, the adhesive comprises a polyvinyl alcohol solution, wherein the concentration of solute in the polyvinyl alcohol solution is 5-10 wt%, and the content of the adhesive is 0.6-1.2 wt% of the mass of the pre-sintered soft magnetic ferrite raw material;

the fluidity auxiliary agent comprises glycerol, and the content of the fluidity auxiliary agent is 0.10-0.25 wt% of the mass of the soft magnetic ferrite raw material after pre-sintering;

the plasticizer comprises polyethylene glycol, the molecular weight of the polyethylene glycol is 400, and the content of the plasticizer in the auxiliary material is 0.05-0.1 wt% of the mass of the soft magnetic ferrite raw material after pre-sintering;

the preparation method of the auxiliary material comprises the following steps: adding a fluidity auxiliary agent and a plasticizer when decocting the adhesive, and mixing the materials for more than 2 hours to obtain the auxiliary material;

(2) performing spray granulation on the first mixture obtained in the step (1), and mixing the obtained granulated product with a lubricant to obtain a second mixture, wherein the second mixture is used for preparing the soft magnetic ferrite;

the lubricant comprises zinc stearate, and the adding amount of the lubricant is 0.01-0.05 wt% of the mass of the soft magnetic ferrite raw material after pre-sintering.

Background

The production processes of the soft magnetic ferrite magnetic core are multiple, the production period is long, the product quality is closely related to the quality of each process, the quality problem of any process can cause the quality grade of subsequent products to be reduced and scrapped, the problem that the blank density of large products and thick-wall products is uneven in the forming process is a key ring, if the control is not good, the sintered products can crack for batches, and the waste loss caused by the cracking is quite remarkable.

CN104387090A slurry for ferrite powder spray granulation and a preparation method thereof. The invention discloses slurry for ferrite powder spray granulation and a preparation method thereof, and the preparation method of the slurry for ferrite powder spray granulation comprises the following steps: preparing a binder PB 72 solution and a binder PVA solution; preparing ground ferrite raw powder; and adding the binder PB 72 solution and the binder PVA solution into the ferrite raw powder for grinding to form slurry for ferrite powder spray granulation. The slurry for ferrite powder spray granulation refers to the slurry prepared according to the above preparation method. The invention adopts two components of binders, namely a large molecular weight binder PB 72 and a small molecular weight binder PVA, the glass transition temperatures of the two binders are complementary, and the combination of the two binders is beneficial to slurry granulation and dry pressing molding, so that a blank has good strength, and powder with proper granularity can be formed.

CN104387046A A ferrite powder and its spray granulation preparation method, the invention discloses a ferrite powder and its spray granulation preparation method, the ferrite powder spray granulation preparation method includes the steps: preparing a binder PB-72 solution and a binder PVA solution; preparing ground ferrite raw powder; adding the binder PB-72 solution and the binder PVA solution into the ferrite raw powder for grinding to form slurry for ferrite powder spray granulation; and (3) carrying out spray granulation on the slurry obtained by carrying out spray granulation on the ferrite powder. The ferrite powder refers to the powder prepared according to the preparation method. The invention adopts two components of binders, namely a binder PB-72 with large molecular weight and a binder PVA with small molecular weight, the glass transition temperatures of the two binders are complementary, and the combination of the two binders is beneficial to slurry granulation and dry pressing molding, so that a blank has good strength, and powder with proper granularity can be formed.

However, the above solutions can not solve the technical problem of cracks generated in the large soft magnetic ferrite product.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a method for solving the problem of sintering cracking of soft magnetic ferrite. The invention can solve the problem that the large and thick-walled soft magnetic ferrite product is easy to crack in the molding process.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention provides a method for solving the problem of sintering cracking of a soft magnetic ferrite, which comprises the following steps:

(1) mixing the pre-sintered soft magnetic ferrite raw material with auxiliary materials, and performing ball milling to obtain a first mixture;

or ball-milling the pre-sintered soft magnetic ferrite raw material, and then mixing the ball-milled soft magnetic ferrite raw material with auxiliary materials to obtain a first mixture;

the auxiliary materials comprise a glue, a flow aid and a plasticizer;

(2) and (2) performing spray granulation on the first mixture obtained in the step (1), and mixing the obtained granulated product with a lubricant to obtain a second mixture, wherein the second mixture is used for preparing the soft magnetic ferrite.

The method provided by the invention is prepared by key factors of powder parameters in the processes of pre-sintering, ball milling and spray granulation, and solves the major technical problem of cracking of large and thick-walled products after being fired by the multi-component formula combination of auxiliary materials.

In the invention, the specific types of the raw materials in the pre-sintered soft magnetic ferrite raw materials are not limited, and the soft magnetic ferrite raw materials in the prior art can be adopted.

The following is a preferred technical solution of the present invention, but not a limitation to the technical solution provided by the present invention, and the technical objects and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solution.

As a preferred embodiment of the present invention, the temperature of the pre-firing in the step (1) is 950-. In the invention, the ball milling granularity and the loose specific gravity of the spray particle materials can be effectively improved by adopting the higher pre-sintering temperature.

Preferably, the ball milling is wet ball milling.

Preferably, the solvent of the ball mill comprises water.

As a preferred embodiment of the present invention, the average particle size of the product obtained by ball milling in step (1) is reduced to 1.5-2.0. mu.m, for example, 1.5. mu.m, 1.6. mu.m, 1.7. mu.m, 1.8. mu.m, 1.9. mu.m, 2.0. mu.m, etc.

As a preferred technical scheme of the invention, in the auxiliary material in the step (1), the adhesive comprises a polyvinyl alcohol (PVA) solution.

Preferably, the concentration of solute in the polyvinyl alcohol solution is 5-10 wt%, such as 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%, etc.

Preferably, in the auxiliary material in step (1), the content of the adhesive is 0.6-1.2 wt%, such as 0.6 wt%, 0.8 wt%, 1.0 wt% or 1.2 wt% of the mass of the soft magnetic ferrite material after pre-sintering. In the invention, the lower addition amount of the PVA adhesive can effectively reduce the sintering binder removal cracking of the large-sized and thick-walled soft magnetic ferrite product.

As a preferable technical scheme of the invention, the flow aid in the step (1) comprises glycerin. In the invention, proper glycerol is added, so that the fluidity of the spray granule can be effectively improved.

Preferably, in the auxiliary material in step (1), the content of the flow aid is 0.10-0.25 wt%, such as 0.10 wt%, 0.15 wt%, 0.20 wt% or 0.25 wt% of the mass of the soft magnetic ferrite raw material after pre-sintering.

As a preferred embodiment of the present invention, the plasticizer in step (1) comprises polyethylene glycol (PEG). In the invention, the appropriate amount of PEG can enhance the plasticity of the blank during forming.

Preferably, the molecular weight of the polyethylene glycol is 200-600, such as 200, 300, 400, 500 or 600, etc., preferably 400.

Preferably, in the auxiliary material in step (1), the content of the plasticizer is 0.05-0.1 wt%, such as 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, or 0.1 wt% of the mass of the soft magnetic ferrite raw material after pre-sintering.

As a preferable technical solution of the present invention, in the step (1), the preparation method of the auxiliary material comprises: and adding a fluidity auxiliary agent and a plasticizer when decocting the polyvinyl alcohol solution, and mixing the materials to obtain the auxiliary material.

Preferably, the materials are mixed for a time of 2h or more, such as 2h, 2.5h, 3h, 3.5h, or the like. In the invention, the longer mixing and stirring time is adopted, which is beneficial to the full and uniform mixing of the glycerol, the PEG and the PVA.

In a preferred embodiment of the present invention, the granulated product in the step (2) has a water content of 0.6 to 1.0%, for example, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0%. In the invention, the higher water content is beneficial to the complete damage of the particles during the molding, enhances the uniformity of the blank density, and avoids sintering cracking caused by inconsistent shrinkage of a sintered body due to uneven density of the molded blank.

Preferably, the granulated product of the step (2) has a bulk specific gravity of 1.5 to 1.7g/cm³E.g. 1.5g/cm³、1.55g/cm³、1.6g/cm³、1.65g/cm³Or 1.7g/cm³And the like. In the invention, the higher loose specific gravity is beneficial to reducing the forming pressure of the blank, thereby reducing the risk of cracking.

Preferably, the flow angle of the granulated product of step (2) is below 28 °, such as 28 °, 27 °, 26 °, or 25 °, etc. In the invention, the granulation product with the flow angle has good fluidity and is beneficial to the consistency of the density distribution of the formed blank.

Preferably, in the granulated product in the step (2), the 80-160 mesh granules account for more than 85 wt%, such as 85 wt%, 86 wt%, 87 wt%, 88 wt% or 89 wt%. In the invention, the granules of the granulated product with the granule distribution are relatively concentrated, so that the problem of excessive fine powder is avoided, and the cracking problem generated in blank forming can be reduced.

As a preferred technical scheme of the invention, the lubricant in the step (2) comprises zinc stearate. In the invention, a proper amount of zinc stearate is added, so that an effective lubricating effect can be achieved between powder particles and between dies and particles.

Preferably, the lubricant of step (2) is added in an amount of 0.01 to 0.05 wt%, such as 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, or 0.05 wt%, etc., based on the mass of the soft magnetic ferrite material after the pre-firing.

As a further preferred technical solution of the method of the present invention, the method comprises the steps of:

(1) mixing the pre-sintered soft magnetic ferrite raw material with auxiliary materials, and performing wet ball milling to obtain a first mixture;

or performing wet ball milling on the pre-sintered soft magnetic ferrite raw material, and then mixing the soft magnetic ferrite raw material with auxiliary materials to obtain a first mixture;

the temperature of the pre-sintering is 950-1050 ℃; the auxiliary materials comprise a glue, a flow aid and a plasticizer;

in the auxiliary material, the adhesive comprises a polyvinyl alcohol solution, wherein the concentration of solute in the polyvinyl alcohol solution is 5-10 wt%, and the content of the adhesive is 0.6-1.2 wt% of the mass of the pre-sintered soft magnetic ferrite raw material;

the fluidity auxiliary agent comprises glycerol, and the content of the fluidity auxiliary agent is 0.10-0.25 wt% of the mass of the soft magnetic ferrite raw material after pre-sintering;

the plasticizer comprises polyethylene glycol, the molecular weight of the polyethylene glycol is 400, and the content of the plasticizer in the auxiliary material is 0.05-0.1 wt% of the mass of the soft magnetic ferrite raw material after pre-sintering;

the preparation method of the auxiliary material comprises the following steps: adding a fluidity auxiliary agent and a plasticizer when decocting the adhesive, and mixing the materials for more than 2 hours to obtain the auxiliary material;

(2) performing spray granulation on the first mixture obtained in the step (1), and mixing the obtained granulated product with a lubricant to obtain a second mixture, wherein the second mixture is used for preparing the soft magnetic ferrite;

the lubricant comprises zinc stearate, and the adding amount of the lubricant is 0.01-0.05 wt% of the mass of the soft magnetic ferrite raw material after pre-sintering.

Compared with the prior art, the invention has the following beneficial effects:

the method provided by the invention solves the problem that the large and thick-walled soft magnetic ferrite products are easy to crack in the forming process. The invention effectively reduces the forming cracking of the soft magnetic ferrite blank and has no adverse effect on the electromagnetic performance of the soft magnetic ferrite core. The product obtained by the method can meet the performance requirements of the soft magnetic ferrite on the material.

Detailed Description

The technical solution of the present invention is further illustrated by the following specific examples. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

Examples 1 to 5

The above examples were carried out as follows:

(1) for the soft magnetic ferrite raw material (the raw material consists of (NiZn) after presintering at 1000 DEG C_0.6Cu_0.2Zn_0.2Fe₂O₄Oxide composition of required metal elements) is subjected to wet ball milling (the solvent is water) to ball mill the average particle size to 1.8 mu m, and then the ball milling is mixed with auxiliary materials to obtain a first mixture; the auxiliary material consists of a PVA aqueous solution (with the mass concentration of 10 wt%), glycerol and PEG (with the molecular weight of 400);

the preparation method of the auxiliary material comprises the following steps: and adding glycerol and PEG during the decoction of the PVA aqueous solution, and stirring and mixing the materials for 2.5 hours to obtain the auxiliary material.

(2) Performing spray granulation on the first mixture obtained in the step (1), and mixing the obtained granulated product with a lubricant to obtain a second mixture, wherein the second mixture is used for preparing the soft magnetic ferrite; the lubricant is zinc stearate.

In the above examples, the amounts of PVA, glycerin, PEG, and zinc stearate added are shown in table 1 (mass fractions obtained by taking 100% of the soft magnetic ferrite material after the pre-firing).

The results of the performance test of the granulated product obtained by the controlled spray granulation in each of the above examples are shown in table 2.

Example 6

The present example was carried out as follows:

(1) carrying out wet ball milling (using water as a solvent) on a soft magnetic ferrite raw material (the component type and the component proportion of the raw material are the same as those in example 1) subjected to presintering at 950 ℃ to ball mill the average particle size to 1.5 mu m, and then mixing the raw material with auxiliary materials to obtain a first mixture; the auxiliary material consists of a PVA (PVA205) aqueous solution (with the mass concentration of 5 wt%), glycerol and PEG (molecular weight of 200); based on 100% of the pre-sintered soft magnetic ferrite raw material, the mass fraction of the PVA aqueous solution is 0.6 wt%, the mass fraction of the glycerol is 0.10 wt%, and the mass fraction of the PEG is 0.1 wt%.

The preparation method of the auxiliary material comprises the following steps: and adding glycerol and PEG during the decoction of the PVA aqueous solution, and stirring and mixing the materials for 2 hours to obtain the auxiliary material.

(2) Performing spray granulation on the first mixture obtained in the step (1), and mixing the obtained granulated product with a lubricant to obtain a second mixture, wherein the second mixture is used for preparing the soft magnetic ferrite; the lubricant is zinc stearate, and the mass fraction of the zinc stearate is 0.01 wt% based on 100% of the pre-sintered soft magnetic ferrite raw material. In this example, the granulated product had a water content of 0.7% and a bulk specific gravity of 1.6g/cm³The flow angle is 27 degrees, and the particle material with 80-160 meshes accounts for 86 percent.

Example 7

The present example was carried out as follows:

(1) carrying out wet ball milling (using water as a solvent) on a soft magnetic ferrite raw material (the component type and the component proportion of the raw material are the same as those in example 1) subjected to pre-sintering at 1050 ℃ to ball mill the average particle size to 2.0 mu m, and then mixing the raw material with auxiliary materials to obtain a first mixture; the auxiliary material consists of PVA (PVA205) aqueous solution (with the mass concentration of 10 wt%), glycerol and PEG (molecular weight of 200); based on 100% of the pre-sintered soft magnetic ferrite raw material, the mass fraction of the PVA aqueous solution is 1.2 wt%, the mass fraction of the glycerol is 0.25 wt%, and the mass fraction of the PEG is 0.05 wt%.

The preparation method of the auxiliary material comprises the following steps: and adding glycerol and PEG during the decoction of the PVA aqueous solution, and stirring and mixing the materials for 3 hours to obtain the auxiliary material.

(2) Performing spray granulation on the first mixture obtained in the step (1), and mixing the obtained granulated product with a lubricant to obtain a second mixture, wherein the second mixture is used for preparing the soft magnetic ferrite; the lubricant is zinc stearate, and the mass fraction of the zinc stearate is 0.05 wt% based on 100% of the pre-sintered soft magnetic ferrite raw material. In this example, the granulated product had a water content of 1.0% and a bulk specific gravity of 1.7g/cm³The flow angle is 28 degrees, and the particle material with 80-160 meshes accounts for 89 percent.

Comparative examples 1 to 5

The above comparative example was carried out as follows:

(1) carrying out wet ball milling on a soft magnetic ferrite raw material (the component type and the component proportion of the raw material are the same as those in example 1) subjected to presintering at 1000 ℃ to ball mill the average particle size to 1.1 mu m, and then mixing the raw material with an auxiliary material to obtain a first mixture; the auxiliary material only consists of PVA aqueous solution (with the mass concentration of 10 wt%);

(2) performing spray granulation on the first mixture obtained in the step (1), and mixing the obtained granulated product with a lubricant to obtain a second mixture, wherein the second mixture is used for preparing the soft magnetic ferrite; the lubricant is zinc stearate.

In the above comparative examples, the amount of PVA added is shown in table 1 (mass fraction based on 100% of the pre-sintered soft magnetic ferrite material).

The results of the performance tests of the granulated products obtained by controlled spray granulation in the above respective proportions are shown in table 2.

TABLE 1

TABLE 2

Test method

The method for preparing the soft magnetic ferrite from the second mixture provided by each example and each comparative example comprises the following steps: putting the ferrite powder with the prepared particles into a mold cavity with a certain shape, applying a certain pressure, and pressing the powder into a ferrite blank with a required shape. And (3) after certain treatment, placing the formed ferrite blank in a high-temperature furnace, heating to a sintering temperature, preserving heat at the sintering temperature, and then cooling.

And testing the density difference of each section of the blank by adopting a kerosene method. The method comprises the following specific steps:

1. turning on a power supply of the electronic balance, and starting up to preheat for 20 minutes;

2. before measuring the density, confirming the specific gravity of the kerosene, and observing the specific gravity change of the kerosene by using a hydrometer at any time;

3. the electronic balance is used after being reset to zero;

4. weighing the weight G1 of the sample to be measured;

5. placing the weighed sample in kerosene until no foaming exists, and soaking the general product in the kerosene for 3-8 minutes;

6. putting the soaked sample into kerosene, and weighing the weight G2 of the sample to be measured in the kerosene;

7. taking out the sample, absorbing kerosene on the surface of the sample by using soft paper, weighing the sample soaked in oil, and weighing the sample in the air by weight G3;

8. using the formula: and (3) calculating the density of the sample to be measured and recording the density of the sample to be measured when the density of the sample to be measured is G1 multiplied by the specific gravity of kerosene/G3-G2.

And observing whether surface cracks exist in the sintered ferrite under a magnifying glass of 30 times, so as to form the cracking proportion.

The qualified standard of the sample is that the ferrite surface has no cracks, otherwise, the sample is unqualified.

The results of the tests are given in the following table

TABLE 3

It can be seen from the above examples and comparative examples that the examples effectively reduce the cracking rate of the soft magnetic ferrite blank during the forming process, and do not have any adverse effect on the electromagnetic properties of the soft magnetic ferrite core. The reduction of the density difference of the formed blanks should be the important reason for the large reduction of the sintering cracking ratio of the materials of the examples relative to the comparative examples. The material of the present invention should be able to meet the performance requirements of soft magnetic ferrite for the material.

Comparative examples 1 to 5 have cracks at the density boundaries because the density difference at each site of the formed blank is too large, resulting in asynchronous shrinkage of the ferrite blank at each site during the high-temperature sintering.

The applicant states that the present invention is illustrated in detail by the above examples, but the present invention is not limited to the above detailed methods, i.e. it is not meant that the present invention must rely on the above detailed methods for its implementation. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.