CN111863367A - Method for manufacturing manganese-zinc ferrite magnetic core - Google Patents

Method for manufacturing manganese-zinc ferrite magnetic core Download PDF

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Publication number
CN111863367A
CN111863367A CN202010772214.6A CN202010772214A CN111863367A CN 111863367 A CN111863367 A CN 111863367A CN 202010772214 A CN202010772214 A CN 202010772214A CN 111863367 A CN111863367 A CN 111863367A
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sintering
magnetic core
manganese
sanding
manufacturing
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黄卫
刘云龙
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Shandong Dongtai Fangsi Electronic Co ltd
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Shandong Dongtai Fangsi Electronic Co ltd
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Abstract

A manufacturing method of a manganese-zinc ferrite magnetic core belongs to the technical field of composite ferrite. The method comprises the following steps: 1) batching, 2) wet mixing and sanding, 3) spray granulation, 4) presintering, 5) secondary batching, 6) secondary wet mixing and sanding, 7) spray granulation, 8) staling, 9) pressing green bodies and 10) sintering; step 2) and step 6), the granularity D50= 1.0-1.5 μm; step 4) presintering at 820-900 ℃ and preserving heat1.5-3 h; step 7), in granulation, the PVA content is 0.3-0.64% of the mass of the magnetic powder, the flow angle is less than or equal to 30 degrees, and 0.05-0.15% of surfactant of the mass of the magnetic powder is added after granulation; step 9) adopts bidirectional pressing, and the bearing capacity of the powder is 1.5T/cm2~1.7T/cm2. The invention can manufacture the integrally formed magnetic core with large size, and the magnetic core is not easy to crack in the forming and sintering processes, and the yield is higher.

Description

Method for manufacturing manganese-zinc ferrite magnetic core
Technical Field
A manufacturing method of a manganese-zinc ferrite magnetic core belongs to the technical field of composite ferrite.
Background
The manganese-zinc ferrite magnetic core is made of MnO-ZnO-Fe2O3Three main component groupsThe composite ferrite is formed. The material has the characteristics of high magnetic conductivity, high saturation magnetic flux density, low loss and the like, and is widely applied to the fields of household appliances, network communication, automotive electronics, aerospace and the like. The large-size magnetic core is a magnetic core with an external dimension of more than 100 mm.
The applicant found in the research that the existing manganese-zinc ferrite magnetic core has the following problems in the preparation process:
first, the problem of easy cracking in the production of the existing large-sized magnetic core is difficult to manufacture the large-sized magnetic core integrally formed. The larger the size of the magnetic core is, the larger the preparation difficulty is, and the cracking problem is more likely to occur in the preparation process. In order to overcome the problem, a plurality of small magnetic cores are spliced and bonded to form a large-size magnetic core in the prior art; for example, when a large-sized cubic magnetic core with the length of 238mm, the width of 80mm and the height of 38mm is prepared, 2-8 identical units are adopted for splicing in the prior art, and each unit is a small cuboid magnetic core. However, a new problem is brought, a seam is inevitably formed during splicing, and a part of the seam is perpendicular to the direction of magnetic force lines, so that magnetic resistance is generated, magnetic leakage of the spliced large-size magnetic core is serious, ferrite generates heat, the electromagnetic performance is reduced, and the application of downstream customers is influenced. The applicant finds that reducing the number of bonding gaps, especially the gaps perpendicular to the magnetic field lines, is important to improve the electromagnetic performance and stability of the overall device. How to produce the large-size magnetic core integrally formed becomes a problem which needs to be solved urgently.
Secondly, the magnetic core obtained by the existing preparation method has the problems of low magnetic flux density and poor dimensional consistency due to adhesion. The low magnetic flux density can reduce the direct current superposition inductance of the magnetic core, and bring adverse effects to the application of downstream customers. The magnetic cores with larger volumes are formed by splicing and bonding the magnetic cores and are commonly applied, the difficulty of batch production of the magnetic cores is high due to poor size consistency, the magnetic cores are difficult to precisely splice, and adverse effects are brought to production and application of the magnetic cores.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the method can manufacture the integrally formed large-size magnetic core, and the magnetic core is not easy to crack in the forming process and has high yield.
The technical scheme adopted by the invention for solving the technical problems is as follows: the manufacturing method of the manganese-zinc ferrite magnetic core is characterized in that: 1) batching, 2) wet mixing and sanding, 3) spray granulation, 4) presintering, 5) secondary batching, 6) secondary wet mixing and sanding, 7) spray granulation, 8) staling, 9) pressing green bodies and 10) sintering;
step 2) wet mixing and sanding and 6) secondary wet mixing and sanding, wherein the granularity of D50= 1.0-1.5 μm;
step 4), pre-sintering at 820-900 ℃ for 1.5-3 h;
step 7), adding PVA (polyvinyl alcohol) for granulation in the granulation process, wherein the content of the PVA is 0.3-0.64% of the mass of the magnetic powder, the apparent density is 1.4-1.45 g/cc, the flow angle is less than or equal to 30 degrees, and adding a surfactant after the granulation is finished, wherein the addition amount of the surfactant is 0.05-0.15% of the mass of the magnetic powder;
step 9) adopting bidirectional pressing in green pressing, wherein the bearing pressure of the powder is 1.5T/cm2~1.7T/cm2。
Preferably, the sintering in the step 10) adopts a nitrogen push plate kiln, a vacuum furnace or a bell jar furnace for sintering, the sintering temperature is 1100-1400 ℃, the heat preservation time is 3.5-6 h, the pressure is 3.5-4 KPa, and the tapping temperature is 100-200 ℃; the sintering process is protected by nitrogen, and the relationship between the equilibrium oxygen partial pressure and the sintering temperature is as follows:
log(Po2) = -A/T+B；
wherein Po2 is the partial pressure of oxygen at atmospheric pressure; A. b is a constant, the value range of A is 13000-15000, and the value range of B is 7-10; and T is the absolute temperature of product sintering.
And preferably 10), the sintering process can form composite ferrite with larger volume in the sintering process, and the material has higher magnetic permeability, higher saturation magnetic flux density and lower magnetic core loss. Further preferably, the sintering temperature in the step 10) is 1300-1380 ℃.
In the step 10), micro negative pressure sintering is adopted in the temperature rise stage in the sintering, the pressure is-0.2 KPa to-0.25 KPa, and the temperature rise speed is 100 ℃/h to 200 ℃/h. The ferrite with larger size can be realized under the optimized heating process, and the heating cracking phenomenon is reduced, so that the quality of the product is improved.
And in the cooling stage in the sintering in the step 10), micro-positive pressure sintering is adopted, the pressure is 3.5-4 KPa, and the cooling speed is 100-150 ℃/h. The crystal grain structure of the composite ferrite can be better maintained in the cooling process in the magnetic core under the optimized cooling process, and meanwhile, the phenomenon of cooling cracking is reduced, so that the quality of products is improved, and the performance of the magnetic core is more excellent.
Step 2) wet mixing sanding and 6) the granularity control D50=1.1~1.2 mu m of secondary wet mixing sanding step.
The pre-sintering temperature of the pre-sintering in the step 4) is 850-860 ℃, and the heat preservation time is 1.5-2 h.
And 7) the PVA content accounts for 0.6-0.63% of the mass of the magnetic powder.
And 7) the surfactant is acrylic resin emulsion.
And 7) adding the surfactant in the step of 0.08-0.12%.
The bearing pressure of the powder in the pressed green body in the step 9) reaches 1.6T/cm2。
The magnetic core obtained under the preferable preparation process conditions has higher overall strength, higher magnetic permeability and higher saturation magnetic flux density.
The invention is further illustrated as follows:
preferably, the step 1) of burdening comprises the following specific operations: the magnetic powder is prepared according to a formula and is made of Fe2O3、Mn3O4ZnO as raw material, Fe2O3The mol percent of MnO and ZnO is 55.5 mol%: 37.5 mol%: 7mol percent to obtain the mixture.
The polymerization degree of the PVA in the step 7) is 1700-2000, the alcoholysis degree is 88-99%, the viscosity range is 20-30cps (4% wt%, at 20 ℃), and the preferable PVA adopts BP17 and BF17 series products of Taiwan Changchun petrochemical company Limited. In order to improve the use effect of PVA, BF 17: BP17= 1: 1 to column.
Step 7), the surfactant is acrylic resin emulsion, has the solid content of 35-45 wt%, and belongs to water-based emulsion; preferably, the content of the surfactant is 0.10 percent of the mass of the magnetic powder; preferably, the acrylic resin emulsion is Water-based acrylate produced by Nippon Shukubai Co., LTD, model number PS-4621 or ACRYSETTF-300; further preferably, the model is ACRYSET TF-300.
Preferably, the bulk density of the step 7) is 1.42-1.43 g/cc.
And step 7) also comprises polyethylene glycol and glycerol, wherein the content of the polyethylene glycol is 0.05-0.2% of the mass of the magnetic powder, and the content of the glycerol is 0.01-0.05% of the mass of the magnetic powder. Preferably, the content of the polyethylene glycol is 0.09-0.12% of the mass of the magnetic powder, and the content of the glycerol is 0.02-0.03% of the mass of the magnetic powder. Further preferably, the content of the polyethylene glycol is 0.1 percent of the mass of the magnetic powder, and the content of the glycerol is 0.02 percent of the mass of the magnetic powder.
The combination of polyethylene glycol (PEG) and PVA can slow down the glue discharging speed, and avoid the magnetic core cracking caused by the rapid loss of PVA in the temperature rising process. The glycerol is used as a surface softener, can act together with PVA to enhance the binding force between particles of a formed body and reduce the phenomenon of cracking, and can improve the cracking resistance of the magnetic core in the forming and sintering processes by combining with the PEG and the PVA.
The average relative molecular weight of the polyethylene glycol is 190-450. Preferably, the polyethylene glycol is PEG200 or PEG 400. More preferably, the polyethylene glycol is PEG400, has a relative molecular weight of 380-420 and is produced by Dow in America.
Compared with the prior art, the invention has the beneficial effects that:
1. the method can manufacture the integrally formed large-size magnetic core, and the magnetic core is not easy to crack in the forming process and has high yield.
First, the amount of PVA used was controlled in the formulation and a surfactant was added. The applicant finds that in the sintering process of the large-size magnetic core, if high-proportion PVA is added, the green strength can be improved, but the problem of cracking of the magnetic core is more serious. The thickness (also referred to as height in a cube) of large-format cores is much around 30 mm; when the thickness of the magnetic core is too thick and the volume is too large, the problem of cracking of the magnetic core is easy to occur in the conventional preparation method, so that the magnetic core is unqualified. The basic reasons of the method are that the large-size magnetic core is large in area and high in height, the powder moving space is too large in the forming process, the powder moving absolute displacement of the magnetic powder is limited, the magnetic powder is difficult to uniformly fill all parts, the density distribution is widened, cracks are easy to generate at the density boundary part, and a green body is cracked due to the large expansion size in the demolding process; secondly, due to the fact that the center of the large-size magnetic core is too thick, PVA on the surface of the magnetic core is too fast in dissipation and fast in glue discharging speed in the sintering process, the center of the magnetic core is too thick, PVA discharging speed is slow, glue discharging speed difference between the center of the magnetic core and the surface is increased along with temperature rise, the temperature of the center of the magnetic core lags behind the surface temperature, and the PVA in the center of the magnetic core is finally discharged to cause product cracking.
Based on the findings, the applicant researches and determines that the PVA content of the magnetic core needs to be reduced when the large-size magnetic core is prepared; when the PVA content is 0.3-0.64% of the mass of the magnetic powder, the large-size magnetic core can be effectively prevented from cracking in the sintering process; when the addition amount of the surfactant is 0.05-0.15% of the mass of the magnetic powder, the bonding degree of the formed particles can be effectively improved, the possibility of cracking of the magnetic core is further reduced, and the yield of the magnetic core is improved.
Secondly, a specific temperature curve is designed in the step 10) of sintering, the glue discharging rate of PVA is controlled by controlling the relation among the sintering temperature, the temperature rise and the temperature reduction rate, and the phenomenon that the magnetic core is cracked due to the fact that the glue discharging rate is too fast is avoided. Through analyzing the TGA-DSC curve of the magnetic powder, the corresponding glue discharging speed is formulated, the heating process adopts step heating and heat preservation, the volatilization curve of PVA is leveled, the stability and the thoroughness of the volatilization speed of PVA are kept, and the possibility of cracking of the magnetic core is reduced.
Thirdly, the formula log (Po2) = -A/T + B of the equilibrium oxygen partial pressure and sintering temperature is designed in the step 10) sintering. By using the formula, the oxygen content at each temperature in the cooling process is calculated, so that Fe can be ensured2+And Fe3+The reasonable proportion of the ferrite core can not generate the condition of over oxidation or over reduction, and can maintain the stable ferrite crystal structure, thereby obtaining the stable and excellent magnetic core performance,
fourthly, the invention can manufacture the large-size magnetic core which is integrally formed, and solves the problem of seam existing in the large-size magnetic core. The finished product rate of the large-size magnetic core with the size of 238mm in length, 80mm in width and 38.1mm in height integrally formed by the invention can reach more than 98%. The seam does not exist in integrated into one piece's big specification magnetic core, can effectively solve the problem that seam magnetic leakage, electromagnetic properties descend that appear because of a plurality of little magnetic cores concatenation. The larger-size magnetic core directly manufactured by the invention can reduce the number of bonding gaps, can realize that the direction of magnetic lines can be horizontal to the seams, avoids the generation of the seams in the direction perpendicular to the magnetic lines in the splicing process, and greatly improves the electromagnetic performance and the stability of the whole device.
2. The large-size magnetic core obtained by the method has excellent performance, good size consistency and high stability.
First, the performance of the magnetic core is excellent. The bonding seam, especially the seam perpendicular to the direction of the magnetic force line, can seriously affect the magnetic circuit of the whole magnetic core, the magnetic leakage is serious, the phenomena of magnetic flux density reduction, rapid loss increase and the like of the magnetic core cannot be avoided, the phenomenon of integral heating of the magnetic core is serious, and the magnetic performance is reduced. The integrally formed large-sized magnetic core is large in size and free of seams, so that no seam or only one seam can be formed (the two integrally formed large-sized magnetic cores are spliced into a larger magnetic core, but the seam is parallel to the magnetic force lines and not perpendicular to the magnetic force lines), and the problems of heat generation and magnetic flux leakage in the working process of the magnetic core can be effectively avoided.
Secondly, the size consistency is good. Because the magnetic core is formed in one step, all sizes are shrunk in a consistent mode in the sintering process, bonding deviation does not exist, size difference caused by the thickness of bonding glue does not exist, and all sizes of the magnetic core have high stability.
Thirdly, the stability of the magnetic core is high. The integrally formed magnetic core has the advantages of improved stability in long-term operation, high superposed inductance value, stable operation in various complex environments such as high temperature, low temperature, oil immersion, vibration and the like, greatly reduced bonding failure, reduced noise in the working process and the like.
Detailed Description
The present invention is further illustrated by the following specific examples, of which example 1 is the most preferred;
the examples and comparative examples used the following starting materials:
PVA is BF17 from petrochemical company, Inc., Taiwan Changchun: BP17 is mixed according to the mass ratio of 1: 1, mixing, wherein the polymerization degree of PVA is 1700-2000, the alcoholysis degree is 88-99%, and the viscosity is 20-30cps (4 wt%, at 20 ℃);
the surfactant is acrylic resin emulsion produced by Japan catalyst of Kabushiki Kaisha, wherein the type of the acrylic resin emulsion used in the examples 1-4 is ACRYSET TF-300, and the type of the acrylic resin emulsion used in the examples 5-6 is PS-4621;
the polyethylene glycol is PEG400 produced by Dow in America, and the relative molecular weight is 380-420. The content of glycerol is equal to or more than 99 percent of the content of a commercial product.
Example 1
In the embodiment, a cubic large-size magnetic core with the length of 238mm, the width of 80mm and the height of 38.1mm is prepared;
1) preparing materials: the magnetic powder is prepared according to a formula and is made of Fe2O3、Mn3O4ZnO as raw material, Fe2O3The mol percent of MnO and ZnO is 55.5 mol%: 37.5 mol%: 7mol% to obtain ingredients;
then, mixing and sanding the ingredients by 2) a wet method, and 3) spraying and granulating; wherein, 2) particle size control of wet mix sanding D50=1.2 μm;
4) pre-burning: presintering in a pushed slab kiln, wherein the presintering temperature is 855 ℃, and the heat preservation time is 1.7 h;
after the pre-burning is finished, performing step 5) secondary batching, and 6) secondary wet mixing and sanding; wherein, 6) the granularity of the secondary wet mixing sanding is controlled to be D50=1.2 μm;
7) and (3) granulation: adding PVA for granulation in the granulation process, and adding a surfactant after the granulation is finished; the PVA content is 0.61 percent of the mass of the magnetic powder, the bulk density is 1.43g/cc, the flow angle is less than or equal to 30 degrees, and a surfactant is added after granulation, wherein the addition amount of the surfactant is 0.10 percent of the mass of the magnetic powder;
then ageing in the step 8), pressing the green body in the step 9), and performing bidirectional pressing by adopting a press in the step 9) to obtain powder with the bearing pressure of 1.6T/cm2Is pressed wellGreen bodies;
10) and (3) sintering: sintering the green body by adopting a full-automatic atmosphere protection bell jar furnace, wherein the heat preservation temperature of the sintering is 1320 ℃, the heat preservation time is 5.5h, and the tapping temperature is 150 ℃; the sintering process is protected by nitrogen, and the relationship between the equilibrium oxygen partial pressure and the temperature is as follows:
log(Po2) = -A/T+B；
wherein Po2 is the partial pressure of oxygen at atmospheric pressure; A. b is a constant, A is 14000, B is 8; t is the absolute temperature of product sintering; the temperature rise stage adopts micro negative pressure sintering, and the temperature rise speed is 150 ℃/h; and in the cooling stage, micro-positive pressure sintering is adopted, and the cooling speed is 125 ℃/h, so that the manganese-zinc ferrite magnetic core is obtained.
Example 2
In the embodiment, a cubic large-size magnetic core with the length of 238mm, the width of 80mm and the height of 38.1mm is prepared;
1) preparing materials: the magnetic powder is prepared according to a formula and is made of Fe2O3、Mn3O4ZnO as raw material, Fe2O3The mol percent of MnO and ZnO is 55.5 mol%: 37.5 mol%: 7mol% to obtain ingredients;
then, mixing and sanding the ingredients by 2) a wet method, and 3) spraying and granulating; wherein, 2) particle size control of wet mix sanding D50=1.1 μm;
4) pre-burning: presintering in a pushed slab kiln at the presintering temperature of 860 ℃ for 1.5 h;
after the pre-burning is finished, performing step 5) secondary batching, and 6) secondary wet mixing and sanding; wherein, 6) the granularity of the secondary wet mixing sanding is controlled to be D50=1.1 μm;
7) and (3) granulation: adding PVA for granulation in the granulation process, and adding a surfactant after the granulation is finished; the PVA content is 0.62 percent of the mass of the magnetic powder, the apparent density is 1.42g/cc, the flow angle is less than or equal to 30 degrees, and a surfactant is added after granulation, wherein the addition amount of the surfactant is 0.12 percent of the mass of the magnetic powder;
then ageing in the step 8), pressing the green body in the step 9), and performing bidirectional pressing by adopting a press in the step 9) to obtain powder with the bearing pressure of 1.6T/cm2Obtaining a pressed green body;
10) and (3) sintering: sintering the green body by adopting a full-automatic atmosphere protection bell jar furnace, wherein the sintering heat preservation temperature is 1320 ℃, the heat preservation time is 5h, and the tapping temperature is 170 ℃; the sintering process is protected by nitrogen, and the relationship between the equilibrium oxygen partial pressure and the temperature is as follows:
log(Po2) = -A/T+B；
wherein Po2 is the partial pressure of oxygen at atmospheric pressure; A. b is a constant, A takes a value of 13500, B takes a value of 9; t is the absolute temperature of product sintering; the temperature rise stage adopts micro negative pressure sintering, and the temperature rise speed is 130 ℃/h; and in the cooling stage, micro-positive pressure sintering is adopted, and the cooling speed is 135 ℃/h, so that the manganese-zinc ferrite magnetic core is obtained.
Example 3
In the embodiment, a cubic large-size magnetic core with the length of 152mm, the width of 101mm and the height of 38.1mm is prepared;
1) preparing materials: the magnetic powder is prepared according to a formula and is made of Fe2O3、Mn3O4ZnO as raw material, Fe2O3The mol percent of MnO and ZnO is 55.5 mol%: 37.5 mol%: 7mol% to obtain ingredients;
then 2) wet mixing and sanding, and 3) spray granulation are carried out; wherein, 2) particle size control of wet mix sanding D50=1.2 μm;
4) pre-burning: presintering in a pushed slab kiln, wherein the presintering temperature is 850 ℃ and the heat preservation time is 2 hours;
then carrying out secondary burdening in the step 5) and secondary wet mixing and sanding in the step 6); wherein, 6) the granularity of the secondary wet mixing sanding is controlled to be D50=1.2 μm;
7) and (3) granulation: adding PVA for granulation in the granulation process, and adding a surfactant after the granulation is finished; the PVA content is 0.63 percent of the mass of the magnetic powder, the bulk density is 1.43g/cc, the flow angle is less than or equal to 30 degrees, and a surfactant is added after granulation, wherein the addition amount of the surfactant is 0.08 percent of the mass of the magnetic powder;
then ageing in the step 8), pressing the green body in the step 9), and performing bidirectional pressing by adopting a press in the step 9) to obtain powder with the bearing pressure of 1.55T/cm2Obtaining a pressed green body;
10) and (3) sintering: sintering the green body by adopting a nitrogen pushed slab kiln, wherein the sintering temperature is 1350 ℃, the heat preservation time is 4.5h, and the tapping temperature is 130 ℃; the sintering process is protected by nitrogen, and the relationship between the equilibrium oxygen partial pressure and the temperature is as follows:
log(Po2) = -A/T+B；
wherein Po2 is the partial pressure of oxygen at atmospheric pressure; A. b is a constant, the value range of A is 14500, and the value range of B is 7.5; t is the absolute temperature of the product; the temperature rise stage adopts micro negative pressure sintering, and the temperature rise speed is 160 ℃/h; and in the cooling stage, micro-positive pressure sintering is adopted, and the cooling speed is 110 ℃/h, so that the manganese-zinc ferrite magnetic core is obtained.
Example 4
The specification, the process and the formula of the magnetic core of the embodiment are the same as those of the embodiment 1, and the differences are as follows:
7) and (3) granulation: adding PVA, PEG400 and glycerin for granulation in the granulation process, and adding a surfactant after the granulation is finished; the PVA content is 0.61 percent of the mass of the magnetic powder, the bulk density is 1.43g/cc, the flow angle is less than or equal to 30 degrees, and a surfactant is added after granulation, wherein the addition amount of the surfactant is 0.10 percent of the mass of the magnetic powder. The content of PEG400 is 0.1% of the mass of the magnetic powder, and the content of glycerin is 0.03% of the mass of the magnetic powder.
Example 5
In the embodiment, a cubic large-size magnetic core with the length of 152mm, the width of 101mm and the height of 38.1mm is prepared;
1) preparing materials: the magnetic powder is prepared according to a formula and is made of Fe2O3、Mn3O4ZnO as raw material, Fe2O3The mol percent of MnO and ZnO is 55.5 mol%: 37.5 mol%: 7mol% to obtain ingredients;
then carrying out wet mixing and sanding in the step 2) and carrying out spray granulation in the step 3); wherein, 2) particle size control of wet mix sanding D50=1.0 μm;
4) pre-burning: presintering in a pushed slab kiln, wherein the presintering temperature is 820 ℃ and the heat preservation time is 3 h;
then, carrying out secondary burdening in the step 5) and carrying out secondary wet mixing and sanding in the step 6); wherein, 6) the grain size of the secondary wet mixing sanding is controlled to be D50=1.0 μm;
7) and (3) granulation: adding PVA for granulation in the granulation process, and adding a surfactant after the granulation is finished; the PVA content is 0.6 percent of the mass of the magnetic powder, the bulk density is 1.4g/cc, the flow angle is less than or equal to 30 degrees, and a surfactant is added after granulation, wherein the addition amount of the surfactant is 0.05 percent of the mass of the magnetic powder;
then ageing in the step 8), pressing the green body in the step 9), and performing bidirectional pressing by adopting a press in the step 9) to obtain powder with the bearing pressure of 1.5T/cm2Obtaining a pressed green body;
10) and (3) sintering: sintering the green body by using a vacuum furnace, wherein the sintering temperature is 1300 ℃, the heat preservation time is 6h, and the tapping temperature is 100 ℃; the sintering process is protected by nitrogen, and the relationship between the equilibrium oxygen partial pressure and the temperature is as follows:
log(Po2) = -A/T+B；
wherein Po2 is the partial pressure of oxygen at atmospheric pressure; A. b is a constant, the value range of A is 15000, and the value range of B is 7; t is the absolute temperature of product sintering; the temperature rise stage adopts micro negative pressure sintering, and the temperature rise speed is 100 ℃/h; and in the cooling stage, micro-positive pressure sintering is adopted, and the cooling speed is 100 ℃/h, so that the manganese-zinc ferrite magnetic core is obtained.
Example 6
In the embodiment, a cubic large-size magnetic core with the length of 238mm, the width of 80mm and the height of 38.1mm is prepared;
1) preparing materials: the magnetic powder is prepared according to a formula and is made of Fe2O3、Mn3O4ZnO as raw material, Fe2O3The mol percent of MnO and ZnO is 55.5 mol%: 37.5 mol%: 7mol% to obtain ingredients;
then carrying out wet mixing and sanding in the step 2) and carrying out spray granulation in the step 3); wherein, 2) particle size control of wet mix sanding D50=1.5 μm;
4) pre-burning: presintering in a pushed slab kiln at the presintering temperature of 900 ℃ for 1.5 h;
then, carrying out secondary burdening in the step 5) and carrying out secondary wet mixing and sanding in the step 6); wherein, 6) the grain size of the secondary wet mixing sanding is controlled to be D50=1.5 μm;
7) and (3) granulation: adding PVA for granulation in the granulation process, and adding a surfactant after the granulation is finished; the PVA content is 0.64 percent of the mass of the magnetic powder, the bulk density is 1.45g/cc, the flow angle is less than or equal to 30 degrees, and a surfactant is added after granulation, wherein the addition amount of the surfactant is 0.15 percent of the mass of the magnetic powder;
then ageing in the step 8), pressing the green body in the step 9), and performing bidirectional pressing by adopting a press in the step 9) to obtain powder with the bearing pressure of 1.7T/cm2Obtaining a pressed green body;
10) and (3) sintering: sintering the green body by adopting a bell jar furnace, wherein the sintering heat preservation temperature is 1380 ℃, the heat preservation time is 3.5h, and the tapping temperature is 200 ℃; the sintering process is protected by nitrogen, and the relationship between the equilibrium oxygen partial pressure and the temperature is as follows:
log(Po2) = -A/T+B；
wherein Po2 is the partial pressure of oxygen at atmospheric pressure; A. b is a constant, the value range of A is 13000, and the value range of B is 10; t is the absolute temperature of product sintering; the temperature rise stage adopts micro negative pressure sintering, and the temperature rise speed is 120 ℃/h; and in the cooling stage, micro-positive pressure sintering is adopted, and the cooling speed is 150 ℃/h, so that the manganese-zinc ferrite magnetic core is obtained.
Comparative example 1
The magnetic core specification, process and formulation are the same as example 1 except that:
step 2) wet mixing and sanding and 6) granularity control of secondary wet mixing and sanding, wherein D50=1.8 μm;
and step 4), pre-sintering at 1000 ℃ for 1 h.
Comparative example 2
The magnetic core specification, process and formulation are the same as example 1 except that:
and 7) in the granulation process, the addition amount of PVA is 0.8 percent of the mass of the magnetic powder, and the addition amount of the surfactant is 0.3 percent of the mass of the magnetic powder.
Comparative example 3
The magnetic core specification, process and formulation are the same as example 1 except that:
step 9) the bearing pressure of the powder in the pressed green body is 0.7T/cm2。
Performance testing
And (3) carrying out performance tests on the magnetic cores obtained in the examples and the comparative examples, respectively detecting the yield, the dimensional stability and the magnetic core density, and inputting the detection results into the following table.
1. Yield: the magnetic cores of the examples and comparative examples were randomly sampled by 1 thousand, inspected, and the number of the finished magnetic cores was recorded. Yield = finished magnetic core quantity/1 thousand magnetic cores × 100%; and (4) standard of a finished magnetic core: the surface of the magnetic core is observed by human eyes by using a 40-time magnifier, and the magnetic core is crack-free and bulge-free.
2. Dimensional stability: the dimensions were measured and recorded using a digital vernier caliper according to GB 2828.1-2012 sampling standard. Dimensional deviation = actual size-standard size; the smaller the dimensional deviation, the better.
3. Number of bright crystal defects:
the visual inspection area is more than or equal to 1mm, and the number of bright crystal defects is better as the number of bright crystals is smaller.
4. And (3) superposition of inductance:
using an instrument: german ED-K DPG10-1000A direct current superposition tester. The product with the specification of 238mm, the width of 80mm and the height of 38.1mm, the number of turns of a coil of 10Ts, the superposed current of 300A, the test voltage of 300V, the test temperature of 25 ℃, and the inductance value under the condition; the specification is 152mm, the width is 101mm, the height is 38.1mm, the number of coil turns is 15Ts, the superposed current is 420A, the test voltage is 300V, the test temperature is 25 ℃, and the inductance value is tested under the condition. The higher the superposition inductance value is, the better the anti-interference performance of the magnetic core is proved to be, the more stable the working state of the magnetic core is, and the better the quality of the magnetic core is.
TABLE 1 results of performance test of examples and comparative examples
Figure 423382DEST_PATH_IMAGE001
。
As can be seen from table 1: the yield of the embodiment is obviously higher than that of the comparative example when the large-size magnetic core is manufactured, and the problem of cracking of the magnetic core is solved by the method of the embodiment when the large-size magnetic core is integrally formed.
The magnetic cores in the embodiments 1 to 3 are relatively maximum, the yield can reach more than 97.9%, the yield is high in the field, and the magnetic cores can be applied to actual production. The specification of the embodiment 4 is the same as that of the embodiments 1 to 3, and PEG400 and glycerin are additionally added in the step 7) of the embodiment 4, so that the yield of the magnetic core is further improved on the basis of the embodiments 1 to 3.
In the comparative example 1, the granularity of the step 2) wet mixing sanding and the 6) secondary wet mixing sanding is larger, the pre-sintering temperature is high and short, the finished product rate of the finally obtained magnetic core is extremely low, and the method cannot be applied to actual production.
The amount of PVA added by spray drying in step 7) of comparative example 2 is large, resulting in a decrease in yield. When the amount of the added surfactant is increased, the number of bright crystal defects is obviously increased.
Step 9) of comparative example 3 has low press bearing force, resulting in large dimensional deviation, low stacking inductance, and unsatisfactory core quality.
The foregoing is directed to preferred embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. However, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention are within the protection scope of the technical solution of the present invention.

Claims (10)

1. A method for manufacturing a manganese-zinc-ferrite core is characterized by comprising the following preparation steps:
1) batching, 2) wet mixing and sanding, 3) spray granulation, 4) presintering, 5) secondary batching, 6) secondary wet mixing and sanding, 7) spray granulation, 8) staling, 9) pressing green bodies and 10) sintering;
step 2) wet mixing and sanding and 6) secondary wet mixing and sanding, wherein the granularity of D50= 1.0-1.5 μm;
step 4), pre-sintering at 820-900 ℃ for 1.5-3 h;
step 7), adding PVA (polyvinyl alcohol) for granulation in the granulation process, wherein the content of the PVA is 0.3-0.64% of the mass of the magnetic powder, the apparent density is 1.4-1.45 g/cc, the flow angle is less than or equal to 30 degrees, and adding a surfactant after the granulation is finished, wherein the addition amount of the surfactant is 0.05-0.15% of the mass of the magnetic powder;
step 9) adopting bidirectional pressing in green pressing, wherein the bearing pressure of the powder is 1.5T/cm2~1.7T/cm2。
2. A method of manufacturing a manganese-zinc-ferrite core according to claim 1, characterized in that: step 10), sintering by adopting a nitrogen push plate kiln, a vacuum furnace or a bell jar furnace, wherein the sintering heat preservation temperature is 1100-1400 ℃, the heat preservation time is 3.5-6 h, the pressure is 3.5-4 KPa, and the discharging temperature is 100-200 ℃; the sintering process is protected by nitrogen, and the relationship between the equilibrium oxygen partial pressure and the sintering temperature is as follows:
log(Po2) = -A/T+B；
wherein Po2 is the partial pressure of oxygen at atmospheric pressure; A. b is a constant, the value range of A is 13000-15000, and the value range of B is 7-10; and T is the absolute temperature of product sintering.
3. A method of manufacturing a manganese-zinc-ferrite core according to claim 2, characterized in that: in the step 10), micro negative pressure sintering is adopted in the temperature rise stage in the sintering, the pressure is-0.2 KPa to-0.25 KPa, and the temperature rise speed is 100 ℃/h to 200 ℃/h.
4. A method of manufacturing a manganese-zinc-ferrite core according to claim 2, characterized in that: and in the cooling stage in the sintering in the step 10), micro-positive pressure sintering is adopted, the pressure is 3.5-4 KPa, and the cooling speed is 100-150 ℃/h.
5. A method of manufacturing a manganese-zinc-ferrite core according to claim 1, characterized in that: step 2) wet mixing sanding and 6) the granularity control D50=1.1~1.2 mu m of secondary wet mixing sanding step.
6. A method of manufacturing a manganese-zinc-ferrite core according to claim 1, characterized in that: the pre-sintering temperature of the pre-sintering in the step 4) is 850-860 ℃, and the heat preservation time is 1.5-2 h.
7. A method of manufacturing a manganese-zinc-ferrite core according to claim 1, characterized in that: and 7) the PVA content accounts for 0.6-0.63% of the mass of the magnetic powder.
8. A method of manufacturing a manganese-zinc-ferrite core according to claim 1, characterized in that: and 7) the surfactant is acrylic resin emulsion.
9. A method of manufacturing a manganese-zinc-ferrite core according to claim 1 or 8, characterized in that: and 7) adding the surfactant in the step of 0.08-0.12%.
10. A method of manufacturing a manganese-zinc-ferrite core according to claim 1, characterized in that: the bearing pressure of the powder in the pressed green body in the step 9) reaches 1.6T/cm2。
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