Multi-layer structure magnetic core sintering method

Abstract

The invention relates to a multi-layer structure magnetic core sintering method which comprises the following steps: laying a layer of alkali-free boroaluminosilicate glass sheets at the bottom of a setter plate, stacking a plurality of layers of structure magnetic cores in a manner of one layer of structure magnetic cores and one layer of alkali-free boroaluminosilicate glass sheets, and then feeding the setter plate into a sintering furnace, the softening starting temperature of the alkali-free boroaluminosilicate glass sheet is a DEG C, and the melting point is greater than b DEG C; the temperature in the sintering furnace is increased to c DEG C from the room temperature, and then heat preservation is conducted for t1 min; the temperature in the sintering furnace is increased from c DEG C to d DEG C, and then heat preservation is conducted for t2 min; the temperature in the sintering furnace is increased from d DEG C to e DEG C, and then heat preservation is conducted for t3 hours; carrying out gradient cooling treatment on the sintering furnace, wherein bgt; egt; gt; dgt; c; on the premise that the structure of the structural magnetic core is not changed, the multiple layers of alkali-free boroaluminosilicate glass sheets are introduced, the alkali-free boroaluminosilicate glass sheets buffer thermal strain in a mode of bonding and absorbing local stress, and the interface stability of the structural magnetic core is improved.

Description

Technical Field

[0001] This invention relates to the field of magnetic core sintering technology, and in particular to a method for sintering multilayer magnetic cores. Background Technology

[0002] Multilayer magnetic core structures are widely used in miniaturized power supply devices such as micro transformers and chip inductors. However, with the increase in the number of layers, the internal thermal stress during the sintering process of multilayer magnetic cores becomes intense, which can easily cause delamination, warping, or even cracking. In addition, due to the uneven microscopic sintering state between the layers, problems such as poor magnetic property consistency and magnetic flux leakage may occur. Referring to a magnetic core and its sintering process disclosed in Chinese Patent Publication No. CN115863012A, the magnetic core includes a core base block, side blocks symmetrically arranged on both sides of the core base block, and a column block located in the middle of a notch formed between the two side blocks. The side blocks have protrusions on both sides of their top, and a fixing part is provided on the back of the core base block. The protrusions and the fixing part are vertically aligned, and the protrusions are tangent to the fixing part. When tangent, the top of the protrusion is flush with the bottom of the fixing part. A reinforcing strip is also provided in the middle of the back of the core base block. The magnetic core sintering process includes the following steps: feeding a sintering plate carrying stacked magnetic cores into a sintering furnace; performing three-stage segmented heating treatment on the sintering furnace; performing heat preservation treatment on the sintering furnace; performing staged cooling treatment on the sintering furnace; performing cooling treatment on the semi-finished magnetic core; and performing subsequent aging treatment on the semi-finished magnetic core. This patent solves the problems of mutual adhesion and difficulty in separation between magnetic cores, as well as magnetic core cracking and scrapping, by improving the magnetic core structure itself. However, improving the magnetic core structure requires changing the mold of the magnetic core structure, and the protrusions and fixing parts of the magnetic core structure still need to be ground and cut. Although the patent also mentions injecting nitrogen into the protrusion to improve the structure of the cavity inside the protrusion, the actual production cost is too high, and there are still parts that need to be ground. Therefore, the cutting and grinding process cannot be omitted. Summary of the Invention

[0003] This invention solves the problem of severe internal thermal stress during the sintering of stacked magnetic cores, which easily leads to delamination, warping, or even cracking. It proposes a multi-layer magnetic core sintering method that introduces multiple layers of alkali-free borosilicate glass sheets without changing the structure of the magnetic core. The alkali-free borosilicate glass sheets buffer thermal strain and improve the interface stability of the magnetic core by bonding and absorbing local stress.

[0004] To achieve the above objectives, the following technical solution is proposed: A method for sintering a multilayer magnetic core includes the following steps: S1, a layer of alkali-free borosilicate glass is laid at the bottom of the sintering plate, and several layers of structural magnetic core are stacked in the manner of one layer of structural magnetic core and one layer of alkali-free borosilicate glass. Then the sintering plate is sent into the sintering furnace. The softening temperature of the alkali-free borosilicate glass is a℃ and the melting point is greater than b℃. S2, the sintering furnace is heated in one stage, the temperature inside the sintering furnace is raised from room temperature to c℃ and then held for t1 minutes. S3, the sintering furnace is heated in two stages, the temperature inside the sintering furnace is raised from c℃ to d℃ and then held for t2 minutes. S4, the sintering furnace is heated in three stages, the temperature inside the sintering furnace is raised from d℃ to e℃ and then held for t3 hours. S5, the sintering furnace is subjected to gradient cooling treatment, where: b>e>a>d>c.

[0005] This invention sets up three heating and isothermal stages, controlling the heating rate and holding time at 615±15℃ (removal of organic matter), 815±15℃ (medium-temperature pre-firing), and 965±15℃ (main sintering) to alleviate stress accumulation caused by the difference in thermal expansion between layers. An alkali-free borosilicate glass sheet is introduced as an intermediate slow-release layer: a 520μm thick alkali-free borosilicate glass sheet is added between the multilayer magnetic cores. The alkali-free borosilicate glass sheet softens at 900℃, buffering thermal strain by bonding and absorbing local stress, thereby improving the stability of the magnetic core interface.

[0006] Preferably, e = (f + 15) ± 15, where f is the sintering temperature of the structural magnetic core, d = e - 150, c = d - 200, and b = (e - 50) ± 15.

[0007] Preferably, when f = 950, the softening temperature of the alkali-free borosilicate glass sheet is between 900°C and 930°C. The alkali-free borosilicate glass sheet is made of the following materials in parts by weight: 50–70 parts SiO2, 10–20 parts Al2O3, 5–15 parts B2O3, 5–15 parts alkaline earth metal oxides and 0–5 parts ZrO2, wherein the alkaline earth metal oxides are one or a mixture of CaO, MgO or BaO.

[0008] The functions of the various components in the alkali-free borosilicate glass sheet of this invention are as follows: SiO2 (50–70%): provides framework structure, thermal stability, and chemical inertness. Al2O3 (10–20%): enhances network strength, increases softening point, and improves resistance to crystallization. B2O3 (5–15%): lowers melting temperature, but its content needs to be controlled; excessive content will reduce thermal stability. Alkaline earth metal oxides (CaO / MgO / BaO, 5–15%): replace Na2O / K2O, adjust the viscosity-temperature curve, and avoid high-temperature crystallization. Optional addition of ZrO2 / TiO2 (0–5%): further improves chemical durability and refractive index.

[0009] As a preferred embodiment, the proportions of the materials used to make the alkali-free borosilicate glass sheet by weight are as follows: SiO2:Al2O3:B2O3:CaO:MgO:ZrO2=62:16:10:6:4:2.

[0010] Preferably, the preparation process of the alkali-free borosilicate glass sheet is as follows: S11, mix the raw materials by weight evenly and pass them through a 60-mesh standard sieve to obtain a mixture; S12, place the mixture in a quartz crucible, heat it to g℃ at a rate of h℃ / min, hold it at t4 minutes to obtain glass melt; S13, pour the glass melt into a graphite mold and vacuum form it to obtain alkali-free borosilicate glass flakes. S14, polish and divide the alkali-free borosilicate glass flakes to obtain several alkali-free borosilicate glass sheets.

[0011] Preferably, in step S4, a micro-oxygen atmosphere with an oxygen content of ≤5% is used to sinter the structural magnetic core.

[0012] In the sintering process of soft magnetic ferrites (such as MnZn, NiZn, etc.), iron ions are the core component of MnZn / NiZn ferrites. During high-temperature sintering, Fe... 3+ It may be further oxidized to an unstable high-valence state such as Fe. 4+ or reduced to Fe 2+ This leads to lattice defects and deterioration of magnetic properties. The present invention uses a micro-oxygen atmosphere to improve the stability of magnetic properties by suppressing the volatilization and valence fluctuation of high-valence metal ions, especially iron ions which are prone to valence changes.

[0013] Preferably, isostatic pressing is used in S3 and S4 to ensure uniform density between the alkali-free borosilicate glass sheet and the structural magnetic core layers.

[0014] The isostatic pressing of this invention employs hot isostatic pressing (HIP) technology, which utilizes a fluid medium to uniformly transmit pressure, thereby making the material uniformly dense under high pressure. By using a gaseous medium, such as an inert gas, equal pressure (usually tens to hundreds of MPa) is applied from all directions to the alkali-free borosilicate glass sheet and the overall structure of the structural magnetic core layer, eliminating the density gradient of traditional unidirectional pressing.

[0015] Preferably, the present invention further includes: S5. Use a vibratory separator to remove the structural magnetic core from the alkali-free borosilicate glass sheet, or use a vibratory crusher to resonate and crush the alkali-free borosilicate glass sheet, and then screen out the structural magnetic core.

[0016] Preferably, the thickness of the alkali-free borosilicate glass sheet is between 500 μm and 1500 μm.

[0017] Preferably, the thickness of the alkali-free borosilicate glass sheet gradually decreases from bottom to top. This layered design aims to improve the load-bearing capacity of the alkali-free borosilicate glass sheet and prevent direct contact between the structural magnetic cores of adjacent layers due to the effects of gravity during stacking.

[0018] The beneficial effects of this invention are as follows: This invention sets three heating and isothermal stages, controlling the heating rate and holding time at 615±15℃ (removal of organic matter), 815±15℃ (medium-temperature pre-firing), and 965±15℃ (main sintering), respectively, to alleviate stress accumulation caused by the difference in thermal expansion between layers; an alkali-free borosilicate glass sheet is introduced as an intermediate slow-release layer: an alkali-free borosilicate glass sheet with a thickness of 520μm is added between the multilayer magnetic cores. The alkali-free borosilicate glass sheet softens at 900℃, buffering thermal strain by bonding and absorbing local stress, thereby improving the stability of the magnetic core interface. Attached Figure Description

[0019] Figure 1 This is an overall flowchart of the present invention; Figure 2 This is a flowchart illustrating the preparation process of the alkali-free borosilicate glass slide of the present invention. Detailed Implementation

[0020] Example 1: This embodiment proposes a method for sintering multilayer magnetic cores, including the following steps: S1, a layer of alkali-free borosilicate glass is laid at the bottom of the sintering plate, and several layers of structural magnetic core are stacked in the manner of one layer of structural magnetic core and one layer of alkali-free borosilicate glass. Then the sintering plate is sent into the sintering furnace. The softening temperature of the alkali-free borosilicate glass is a℃ and the melting point is greater than b℃. The thickness of the alkali-free borosilicate glass sheet is between 500 μm and 1500 μm. The thickness of the alkali-free borosilicate glass sheet gradually decreases from bottom to top. The purpose of this arrangement is to improve the load-bearing capacity of the alkali-free borosilicate glass sheet by layering, and to avoid direct contact between the structural magnetic cores of adjacent layers due to the effects of gravity during stacking.

[0021] S2, the sintering furnace is heated in one stage, the temperature inside the sintering furnace is raised from room temperature to c℃ and then held for t1 minutes; S3, the sintering furnace is heated in two stages, the temperature inside the sintering furnace is raised from c℃ to d℃ and then held for t2 minutes. S4 involves a three-stage heating process in the sintering furnace, where the temperature inside the furnace is raised from d℃ to e℃ and then held for t3 hours. In S4, a micro-oxygen atmosphere with an oxygen content of ≤5% is used to sinter the structural magnetic core.

[0022] In the sintering process of soft magnetic ferrites (such as MnZn, NiZn, etc.), iron ions are the core component of MnZn / NiZn ferrites. During high-temperature sintering, Fe... 3+ It may be further oxidized to an unstable high-valence state such as Fe. 4+ or reduced to Fe 2+ This leads to lattice defects and deterioration of magnetic properties. The present invention uses a micro-oxygen atmosphere to improve the stability of magnetic properties by suppressing the volatilization and valence fluctuation of high-valence metal ions, especially iron ions which are prone to valence changes.

[0023] S5, gradient cooling treatment for sintering furnace; Among them: b>e>a>d>c.

[0024] In steps S3 and S4, isostatic pressing is used to ensure uniform density between the alkali-free borosilicate glass sheet and the structural magnetic core layer. The isostatic pressing of this invention employs hot isostatic pressing (HIP) technology, utilizing a fluid medium to uniformly transmit pressure, causing the material to be uniformly densified under high pressure. A gaseous medium, such as an inert gas, applies uniform pressure (typically tens to hundreds of MPa) from all directions to the entire structure of the alkali-free borosilicate glass sheet and the structural magnetic core layer, eliminating the density gradient inherent in traditional unidirectional pressing.

[0025] In this embodiment, e = (f + 15) ± 15, where f is the sintering temperature of the structural magnetic core, d = e - 150, c = d - 200, b = (e - 50) ± 15, and f = 950. Substituting these specific parameter values, a multilayer structural magnetic core sintering method is described, see reference. Figure 1 This includes the following steps: S1, a layer of alkali-free borosilicate glass sheet is laid at the bottom of the sintering plate, and several layers of structural magnetic core are stacked in the manner of one layer of structural magnetic core and one layer of alkali-free borosilicate glass sheet. Then the sintering plate is sent into the sintering furnace. The softening temperature of the alkali-free borosilicate glass sheet is between 900°C and 930°C, and the melting point is above 1200°C. S2, the sintering furnace is heated in one stage, and the temperature inside the sintering furnace is raised from room temperature to 615±15℃ and then held for 5 to 10 minutes. S3, the sintering furnace is heated in two stages, the temperature inside the sintering furnace is raised from 615±15℃ to 815±15℃ and then held for 5 to 10 minutes. S4. The sintering furnace is heated in three stages, raising the temperature inside the sintering furnace from 815±15℃ to 965±15℃ and then holding it for 5 to 6 hours. S5 is used to perform gradient cooling treatment on the sintering furnace.

[0026] S6. Subsequently, a vibratory separator can be used to detach the structural magnetic core from the alkali-free borosilicate glass sheet, or a vibratory crusher can be used to resonate and crush the alkali-free borosilicate glass sheet, and then the structural magnetic core can be screened out. The crushed alkali-free borosilicate glass sheet can be recycled and melted for reuse. A vibratory separator is a device that uses vibration to screen, classify, or separate materials. It generates vibration through a motor-driven eccentric block, electromagnetic vibrator, or pneumatic device. Under the action of vibration, the material moves along the screen surface, and particles of different sizes or densities are stratified due to vibration. A vibratory crusher generates high-frequency vibration through a motor-driven eccentric block (vibrator), or uses hydraulic or electromagnetic vibrators. Under the action of vibration, the material collides and rubs against each other, or impacts with the liners, hammers, and other components in the crushing chamber, achieving the crushing effect.

[0027] This invention sets up three heating and isothermal stages, controlling the heating rate and holding time at 615±15℃ (removal of organic matter), 815±15℃ (medium-temperature pre-firing), and 965±15℃ (main sintering) to alleviate stress accumulation caused by the difference in thermal expansion between layers. An alkali-free borosilicate glass sheet is introduced as an intermediate slow-release layer: a 520μm thick alkali-free borosilicate glass sheet is added between the multilayer magnetic cores. The alkali-free borosilicate glass sheet softens at 900℃, buffering thermal strain by bonding and absorbing local stress, thereby improving the stability of the magnetic core interface.

[0028] Example 2: This embodiment, based on Embodiment 1, defines the fabrication of alkali-free borosilicate glass sheets and proposes a multilayer magnetic core sintering method, including the following steps: S1, a layer of alkali-free borosilicate glass is laid at the bottom of the sintering plate, and several layers of structural magnetic core are stacked in the manner of one layer of structural magnetic core and one layer of alkali-free borosilicate glass. Then the sintering plate is sent into the sintering furnace. The softening temperature of the alkali-free borosilicate glass is a℃ and the melting point is greater than b℃. The thickness of the alkali-free borosilicate glass sheet is between 500 μm and 1500 μm. The thickness of the alkali-free borosilicate glass sheet gradually decreases from bottom to top. The purpose of this arrangement is to improve the load-bearing capacity of the alkali-free borosilicate glass sheet by layering, and to avoid direct contact between the structural magnetic cores of adjacent layers due to the effects of gravity during stacking.

[0029] S2, the sintering furnace is heated in one stage, the temperature inside the sintering furnace is raised from room temperature to c℃ and then held for t1 minutes; S3, the sintering furnace is heated in two stages, the temperature inside the sintering furnace is raised from c℃ to d℃ and then held for t2 minutes. S4 involves a three-stage heating process in the sintering furnace, where the temperature inside the furnace is raised from d℃ to e℃ and then held for t3 hours. In S4, a micro-oxygen atmosphere with an oxygen content of ≤5% is used to sinter the structural magnetic core.

[0030] In the sintering process of soft magnetic ferrites (such as MnZn, NiZn, etc.), iron ions are the core component of MnZn / NiZn ferrites. During high-temperature sintering, Fe... 3+ It may be further oxidized to an unstable high-valence state such as Fe. 4+ or reduced to Fe 2+ This leads to lattice defects and deterioration of magnetic properties. The present invention uses a micro-oxygen atmosphere to improve the stability of magnetic properties by suppressing the volatilization and valence fluctuation of high-valence metal ions, especially iron ions which are prone to valence changes.

[0031] S5, gradient cooling treatment for sintering furnace; Among them: b>e>a>d>c.

[0032] In steps S3 and S4, isostatic pressing is used to ensure uniform density between the alkali-free borosilicate glass sheet and the structural magnetic core layer. The isostatic pressing of this invention employs hot isostatic pressing (HIP) technology, utilizing a fluid medium to uniformly transmit pressure, causing the material to be uniformly densified under high pressure. A gaseous medium, such as an inert gas, applies uniform pressure (typically tens to hundreds of MPa) from all directions to the entire structure of the alkali-free borosilicate glass sheet and the structural magnetic core layer, eliminating the density gradient inherent in traditional unidirectional pressing.

[0033] In this embodiment, e = (f + 15) ± 15, where f is the sintering temperature of the structural magnetic core, d = e - 150, c = d - 200, b = (e - 50) ± 15, and f = 950. Substituting these specific parameter values, a multilayer structural magnetic core sintering method is described, see reference. Figure 1 This includes the following steps: S1, a layer of alkali-free borosilicate glass sheet is laid at the bottom of the sintering plate, and several layers of structural magnetic core are stacked in the manner of one layer of structural magnetic core and one layer of alkali-free borosilicate glass sheet. Then the sintering plate is sent into the sintering furnace. The softening temperature of the alkali-free borosilicate glass sheet is between 900°C and 930°C, and the melting point is above 1200°C. When f = 950, the softening temperature of the alkali-free borosilicate glass sheet is between 900°C and 930°C. The alkali-free borosilicate glass sheet is made of the following materials in parts by weight: 50–70 parts SiO2, 10–20 parts Al2O3, 5–15 parts B2O3, 5–15 parts alkaline earth metal oxides and 0–5 parts ZrO2, wherein the alkaline earth metal oxides are one or a mixture of CaO, MgO or BaO.

[0034] The functions of the various components in the alkali-free borosilicate glass sheet of this invention are as follows: SiO2 (50–70%): provides framework structure, thermal stability, and chemical inertness. Al2O3 (10–20%): enhances network strength, increases softening point, and improves resistance to crystallization. B2O3 (5–15%): lowers melting temperature, but its content needs to be controlled; excessive content will reduce thermal stability. Alkaline earth metal oxides (CaO / MgO / BaO, 5–15%): replace Na2O / K2O, adjust the viscosity-temperature curve, and avoid high-temperature crystallization. Optional addition of ZrO2 / TiO2 (0–5%): further improves chemical durability and refractive index.

[0035] In this embodiment, the proportions of each material used to make the alkali-free borosilicate glass sheet by weight are as follows: SiO2:Al2O3:B2O3:CaO:MgO:ZrO2=62:16:10:6:4:2.

[0036] The mechanisms of action and precise proportions of each component are optimized as follows: SiO2 (50–70%) forms a [SiO4] tetrahedral network framework, which determines the basic thermal stability and chemical inertness of the glass. When the content is >65%, the softening point is significantly improved, but the melting temperature needs to be >1700℃ (energy consumption needs to be balanced). In order to balance high-temperature performance and fusibility, and to avoid excessive melt viscosity due to excessive content, the content is set at 60–65%. In this embodiment, the preferred SiO2 content is 62%.

[0037] Al2O3 (10–20%) enters the network as [AlO4] tetrahedra, synergistically enhancing structural strength with SiO2 and suppressing boron anomalies (the irreversible transformation of [BO3] to [BO4] when B2O3 is in excess). The key ratio is Al2O3 / B2O3≥1 (e.g., 15% Al2O3 with 10% B2O3) to stabilize the network. Al2O3 exceeding 20% ​​can easily lead to melt crystallization. In this embodiment, the preferred Al2O3 content is 16%.

[0038] B2O3 (5–15%) lowers the melting temperature (forming a low-melting-point borosilicate phase) and improves glass formability. When the B2O3 content is >15%, the [BO3] ratio increases, reducing high-temperature viscosity and thermal stability. The B2O3 content should be fixed at 8–12%, and its negative effects should be suppressed by Al2O3. In this embodiment, the preferred B2O3 content is 10%.

[0039] Alkaline earth metal oxides (RO = CaO / MgO / BaO, 5–15%), referring to Table 1, in this embodiment, CaO and MgO are preferred, wherein the content of CaO is 6% and the content of MgO is 4%.

[0040] Table 1. Characteristics of the effects of alkaline earth metal oxides oxides Functional characteristics Recommended ratio CaO Increasing hardness, but excessive amounts (>8%) increase the tendency for crystallization. 5–8％ MgO Reduce melt viscosity and suppress phase separation 3–5％ BaO Increasing the refractive index, but also increasing density and cost. 0–2％ Total RO control: 8–12%, to avoid excessive network structure breakage.

[0041] ZrO2 (0–5%) provides better chemical durability and thermal shock resistance. In this embodiment, the preferred ZrO2 content is 2%, which can increase the softening point by about 30–50°C. The key parameter setting for increasing the softening point to above 900°C is (SiO2+Al2O3) / B2O3>6.

[0042] Based on the melting temperature estimation formula: T melt (°C)≈1400+20×SiO2%-10×B2O3%+5×Al2O3%; The melting point is approximately 1220℃, which is greater than 1200℃, meeting the design requirements. The final softening point is 920–950℃, and the melting point is greater than 1220℃. Actual measurements require verification using differential scanning calorimetry (DSC). The coefficient of thermal expansion (CTE) is 3.8–4.2 × 10⁻⁶. -6 / ℃, suitable for packaging silicon-based devices.

[0043] refer to Figure 2 The specific preparation process of the alkali-free borosilicate glass sheet in this invention is as follows: S11, prepare raw materials by weight, mix 62 parts SiO2, 16 parts Al2O3, 10 parts B2O3, 6 parts CaO, 4 parts MgO and 2 parts ZrO2 evenly, and pass through a 60-mesh standard sieve to obtain a mixture; S12, the mixture is placed in a quartz crucible, heated to 1400℃ at a rate of 6-10℃ / min, and held for 30-60 minutes to carry out a fusion reaction to obtain glass melt; S13, pour the molten glass into a graphite mold and vacuum-form it to obtain a bubble-free, uniformly dense alkali-free borosilicate glass flake; S14, polish and divide the alkali-free borosilicate glass flakes to obtain several alkali-free borosilicate glass sheets.

[0044] S2, the sintering furnace is heated in one stage, and the temperature inside the sintering furnace is raised from room temperature to 615±15℃ and then held for 5 to 10 minutes. S3, the sintering furnace is heated in two stages, the temperature inside the sintering furnace is raised from 615±15℃ to 815±15℃ and then held for 5 to 10 minutes. S4. The sintering furnace is heated in three stages, raising the temperature inside the sintering furnace from 815±15℃ to 965±15℃ and then holding it for 5 to 6 hours. S5 is used to perform gradient cooling treatment on the sintering furnace.

[0045] S6. Subsequently, a vibratory separator can be used to detach the structural magnetic core from the alkali-free borosilicate glass sheet, or a vibratory crusher can be used to resonate and crush the alkali-free borosilicate glass sheet, and then the structural magnetic core can be screened out. The crushed alkali-free borosilicate glass sheet can be recycled and melted for reuse. A vibratory separator is a device that uses vibration to screen, classify, or separate materials. It generates vibration through a motor-driven eccentric block, electromagnetic vibrator, or pneumatic device. Under the action of vibration, the material moves along the screen surface, and particles of different sizes or densities are stratified due to vibration. A vibratory crusher generates high-frequency vibration through a motor-driven eccentric block (vibrator), or uses hydraulic or electromagnetic vibrators. Under the action of vibration, the material collides and rubs against each other, or impacts with the liners, hammers, and other components in the crushing chamber, achieving the crushing effect.

[0046] This invention sets up three heating and isothermal stages, controlling the heating rate and holding time at 615±15℃ (removal of organic matter), 815±15℃ (medium-temperature pre-firing), and 965±15℃ (main sintering) to alleviate stress accumulation caused by the difference in thermal expansion between layers. An alkali-free borosilicate glass sheet is introduced as an intermediate slow-release layer: a 520μm thick alkali-free borosilicate glass sheet is added between the multilayer magnetic cores. The alkali-free borosilicate glass sheet softens at 900℃, buffering thermal strain by bonding and absorbing local stress, thereby improving the stability of the magnetic core interface.

Claims

1. A method for sintering multilayer magnetic cores, characterized in that, Includes the following steps: S1, a layer of alkali-free borosilicate glass is laid at the bottom of the sintering plate, and several layers of structural magnetic core are stacked in the manner of one layer of structural magnetic core and one layer of alkali-free borosilicate glass. Then the sintering plate is sent into the sintering furnace. The softening temperature of the alkali-free borosilicate glass is a℃ and the melting point is greater than b℃. S2, the sintering furnace is heated in one stage, the temperature inside the sintering furnace is raised from room temperature to c℃ and then held for t1 minutes. S3, the sintering furnace is heated in two stages, the temperature inside the sintering furnace is raised from c℃ to d℃ and then held for t2 minutes. S4, the sintering furnace is heated in three stages, the temperature inside the sintering furnace is raised from d℃ to e℃ and then held for t3 hours. S5, gradient cooling treatment for sintering furnace; Among them: b>e>a>d>c.

2. The method for sintering a multilayer magnetic core according to claim 1, characterized in that, The value of e is (f+15)±15, where f is the sintering temperature of the structural magnetic core, d=e-150, c=d-200, and b=(e-50)±15.

3. The method for sintering a multilayer magnetic core according to claim 2, characterized in that, When f=950, the softening temperature of the alkali-free borosilicate glass sheet is between 900°C and 930°C. The alkali-free borosilicate glass sheet is made of the following materials in parts by weight: 50–70 parts SiO2, 10–20 parts Al2O3, 5–15 parts B2O3, 5–15 parts alkaline earth metal oxides and 0–5 parts ZrO2, wherein the alkaline earth metal oxides are one or a mixture of CaO, MgO or BaO.

4. The method for sintering a multilayer magnetic core according to claim 3, characterized in that, The proportions of each material used to make the alkali-free borosilicate glass slide by weight are as follows: SiO2:Al2O3:B2O3:CaO:MgO:ZrO2=62:16:10:6:4:

2.

5. The method for sintering a multilayer magnetic core according to claim 4, characterized in that, The preparation process of the alkali-free borosilicate glass slide is as follows: S11, mix the raw materials by weight evenly and pass them through a 60-mesh standard sieve to obtain a mixture; S12, the mixture is placed in a quartz crucible and heated to g℃ at a rate of h℃ / min, and held at that temperature for t4 minutes to obtain glass melt; S13, pour the molten glass into a graphite mold and vacuum-form it to obtain alkali-free borosilicate glass flakes; S14, polish and divide the alkali-free borosilicate glass flakes to obtain several alkali-free borosilicate glass sheets.

6. The method for sintering a multilayer magnetic core according to claim 1, characterized in that, In step S4, a micro-oxygen atmosphere with an oxygen content of ≤5% is used to sinter the structural magnetic core.

7. The method for sintering a multilayer magnetic core according to claim 1, characterized in that, In S3 and S4, isostatic pressing is used to ensure uniform density between the alkali-free borosilicate glass sheet and the structural magnetic core layers.

8. A method for sintering a multilayer magnetic core according to any one of claims 1-7, characterized in that it comprises: S6. Use a vibratory separator to remove the structural magnetic core from the alkali-free borosilicate glass sheet, or use a vibratory crusher to resonate and break the alkali-free borosilicate glass sheet, and then screen out the structural magnetic core.

9. A method for sintering a multilayer magnetic core according to any one of claims 1-7, characterized in that, The thickness of the alkali-free borosilicate glass sheet is between 500 μm and 1500 μm.

10. The method for sintering a multilayer magnetic core according to claim 9, characterized in that, The thickness of the alkali-free borosilicate glass sheet gradually decreases from bottom to top.

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