Low-loss low-frequency transformer core and annealing process

Abstract

The application discloses a low-loss low-frequency transformer core and an annealing process, and relates to the technical field of transformer cores.The application first heats and evaporates to prepare aluminum vapor, and lets silicon steel perform first annealing under an aluminum-containing atmosphere; aluminum vapor will deposit an aluminum-containing film on the surface of the silicon steel; during annealing, aluminum atoms will diffuse into the steel material, reducing the interface stress between the insulating coating and the silicon steel sheet; then, second annealing is performed under an oxygen atmosphere, so that aluminum atoms are converted into aluminum oxide, and a dense protective film is formed on the surface of the silicon steel, reducing the eddy current loss of the core; after the silicon steel is subjected to the second annealing, the internal grain boundaries of the silicon steel will diffuse and the grains will grow, thereby significantly improving the magnetic conductivity of the silicon steel; the aluminum-containing film is first introduced, and then the second annealing is performed; the generation of aluminum oxide blocks the path of the combination of oxygen molecules and the atoms on the surface of the silicon steel, effectively inhibiting the oxidation of the surface of the silicon steel.The low-loss low-frequency transformer core and the annealing process have the effects of low energy consumption and corrosion resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of transformer core, in particular to a low-loss low-frequency transformer core and annealing process. BACKGROUND

[0002] The core is the core component of transformer and reactor and other devices, and its performance improvement is of great significance to realize low-loss current conversion of transformer and high-reliability reactive power compensation of saturated reactor.

[0003] With the global emphasis on energy saving and emission reduction, improving energy conversion efficiency has become a key. The traditional transformer will generate large iron loss and copper loss during operation, because of the magnetic hysteresis loss and eddy current loss inside, resulting in low energy conversion efficiency. The existing technology usually applies an insulating layer on the surface of silicon steel to reduce iron loss, but the applied insulating layer will inevitably fall off. In order to improve the energy efficiency of the transformer, it is necessary to develop a low-loss transformer core material and a corresponding annealing process to reduce iron loss and improve overall efficiency. SUMMARY

[0004] The purpose of the present application is to provide a low-loss low-frequency transformer core and annealing process to solve the problems existing in the prior art.

[0005] In order to solve the above technical problems, the present application provides the following technical scheme: a low-loss low-frequency transformer core and annealing process, comprising the following steps:

[0006] (1) primary annealing: after hot rolling and cold rolling of the silicon steel ingot, it is placed in a bell-type annealing furnace, heated to 1220-1400℃, annealed in an aluminum-containing atmosphere for 3-5min, then cooled to 500℃ at a cooling rate of 5℃ / sec to obtain primary annealed silicon steel, wherein the aluminum-containing atmosphere is prepared by preparing aluminum vapor at 17-20Pa and 1480-1670K, and introducing the aluminum vapor and hydrogen into the bell-type annealing furnace, the total flow of the aluminum-containing atmosphere is 30-40Nm 3 / h, the flow ratio of aluminum vapor and hydrogen is 1-1.5:10, and the dew point is ≤20℃;

[0007] (2) secondary annealing: after the gas in the system is exhausted by introducing oxygen, it is heated to 910-920℃, annealed in an oxygen atmosphere for 3-5min, then cooled to 450℃ at a cooling rate of 10℃ / sec, and then cooled to room temperature in air to obtain secondary annealed silicon steel;

[0008] (3) the secondary annealed silicon steel is placed in a core winding device, the raw material is cut into strips according to the core width requirement, and then the strips are wound into a ring-shaped core according to the shape of the mold.

[0009] Further, the chemical composition of the silicon steel ingot in step (1) includes, by weight percentage: C: 0.05%-0.3%, Mn: 0.2%-0.5%, Si: 2.0%-3.5%, P: 0.003%-0.006%, S: 0.006%-0.009%, Al: 2.1%-2.5%, N: 0.008%-0.010%, and the rest is Fe and other inevitable impurities.

[0010] Further, the hot rolling process of the silicon steel in step (1) is as follows: the hot rolling is divided into rough rolling and finish rolling, and the coiling temperature after hot rolling is 550-580 DEG C.

[0011] Further, the rough rolling temperature is 1100-1150 DEG C, the pass is 3-5 rough rolling passes, and the reduction is 12-15%.

[0012] Further, the finish rolling temperature is 1000-1050 DEG C, the pass is 5-7 finish rolling passes, and the reduction is 10-12%.

[0013] Further, the cold rolling process of the silicon steel in step (1) is as follows: the total reduction of cold rolling is 85-90%, the pass is 3-5 passes, the pass reduction is 18-20%, and the thickness of the silicon steel after cold rolling is 0.05-0.08 mm.

[0014] Further, the dew point of the oxygen in step (2) is ≤15 DEG C.

[0015] Further, the width of the strip in step (3) is 45-70 mm.

[0016] Compared with the prior art, the present application has the following beneficial effects:

[0017] The present application provides a kind of low-loss low-frequency transformer core and annealing process, silicon steel is first carried out first annealing under the atmosphere containing aluminum, then second annealing is carried out under oxygen atmosphere to prepare the process of low-loss low-frequency transformer core, to realize the effect of low energy consumption, corrosion resistance.

[0018] First, aluminum vapor is prepared by heating evaporation, and the silicon steel is first annealed in an aluminum-containing atmosphere. The aluminum vapor will deposit an aluminum-containing film on the surface of the silicon steel. During annealing, aluminum atoms will diffuse into the steel, reducing the interfacial stress between the insulating coating and the silicon steel sheet, reducing the risk of insulating coating peeling and cracking, and achieving firm bonding of the aluminum-containing metal layer and the silicon steel. Then, the second annealing is carried out in an oxygen atmosphere, so that the aluminum atoms are converted into aluminum oxide, and a dense protective film is formed on the surface of the silicon steel, improving the insulation and corrosion resistance, and reducing the eddy current loss of the core of the low-loss low-frequency transformer. After the silicon steel is annealed twice, the internal grain boundaries will diffuse and the grain will grow, thereby significantly improving the magnetic conductivity of the silicon steel. The aluminum-containing film is first introduced and then annealed twice, and the generation of aluminum oxide blocks the path of oxygen molecules combining with the surface atoms of the silicon steel, effectively inhibiting the oxidation of the surface of the silicon steel and improving the corrosion resistance of the silicon steel. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0020] In order to more clearly illustrate the method provided by the present application, the following examples are described in detail. In the following examples, the test methods of each index of the core of the low-loss low-frequency transformer prepared are as follows:

[0021] Core loss: The low-loss low-frequency transformer cores prepared in the examples and the comparative examples were tested for their loss and noise at 600Hz using a soft magnetic measurement system and a noise meter, respectively.

[0022] Corrosion resistance: The low-loss low-frequency transformer cores prepared in the examples and the comparative examples were immersed in a 0.1mg / mL nitric acid solution for 3d, and then tested for their corrosion degree. Example 1

[0023] The annealing process of the core of the low-loss low-frequency transformer includes the following steps:

[0024] (1) The chemical composition of the silicon steel ingot includes, by weight percentage: C: 0.05%, Mn: 0.2%, Si: 2.0%, P: 0.003%, S: 0.006%, Al: 2.1%, N: 0.008%, and the rest is Fe and other inevitable impurities. The silicon steel ingot is first rough rolled at 1100°C, with 3 passes and a reduction of 12%, and then finish rolled at 1000°C, with 5 passes and a reduction of 10%. After hot rolling, the silicon steel is coiled at a coiling temperature of 550°C, and then cold rolled, with a total reduction of 85% in 3 passes and a pass reduction of 18%. The thickness of the silicon steel after cold rolling is 0.05mm;

[0025] (2) The hot-rolled and cold-rolled silicon steel is placed in a bell-type annealing furnace, heated to 1220°C, and annealed in an aluminum-containing atmosphere for 3 minutes. Then, the silicon steel is cooled to 500°C at a cooling rate of 5°C / s to obtain a primary annealed silicon steel. The aluminum-containing atmosphere is prepared by generating aluminum vapor at 17 Pa and 1480 K, and then introducing the aluminum vapor and hydrogen into the bell-type annealing furnace. The total flow rate of the aluminum-containing atmosphere is 30 Nm 3 / h, the flow rate ratio of the aluminum vapor and the hydrogen is 1:10, and the dew point is ≤20°C.

[0026] (3) After the gas in the system is exhausted by introducing oxygen, the dew point of the oxygen is ≤15°C, the system is heated to 910°C, and then annealed in an oxygen atmosphere for 3 minutes. Then, the silicon steel is cooled to 450°C at a cooling rate of 10°C / s, and then cooled to room temperature in air to obtain a secondary annealed silicon steel.

[0027] (4) The secondary annealed silicon steel is placed in a core winding device. The raw material is first cut into a strip according to the width requirement of the core, and the width of the strip is 45mm. Then, the strip is wound into a ring-shaped core according to the shape of the mold. Example 2

[0028] The annealing process of the core for a low-loss low-frequency transformer includes the following steps:

[0029] (1) The chemical composition of the silicon steel ingot includes, by weight percentage: C: 0.2%, Mn: 0.3%, Si: 3.0%, P: 0.004%, S: 0.007%, Al: 2.3%, N: 0.009%, and the rest is Fe and other inevitable impurities. The silicon steel ingot is first rough rolled at 1130°C, with 4 passes and a reduction of 13%, and then finish rolled at 1025°C, with 6 passes and a reduction of 11%. After hot rolling, the silicon steel is coiled at a coiling temperature of 560°C, and then cold rolled, with a total reduction of 87% in 4 passes and a pass reduction of 19%. The thickness of the silicon steel after cold rolling is 0.07mm.

[0030] (2) the silicon steel after hot rolling and cold rolling is placed in a bell type annealing furnace, heated to 1300 DEG C, annealed in an aluminum containing atmosphere for 4 min, then cooled to 500 DEG C at a cooling rate of 5 DEG C / s to obtain the primary annealed silicon steel, wherein the aluminum containing atmosphere is prepared by preparing aluminum vapor at 18 Pa and 1500 K, and the aluminum vapor is introduced into the bell type annealing furnace together with hydrogen, the total flow rate of the aluminum containing atmosphere is 35 Nm 3 / h, the flow rate ratio of the aluminum vapor and the hydrogen is 1.2:10, and the dew point is less than or equal to 20 DEG C;

[0031] (3) after introducing oxygen to exhaust the gas in the system, the dew point of the oxygen is less than or equal to 15 DEG C, heated to 915 DEG C, annealed in an oxygen atmosphere for 4 min, then cooled to 450 DEG C at a cooling rate of 10 DEG C / s, and then cooled to room temperature in air to obtain the secondary annealed silicon steel;

[0032] (4) the secondary annealed silicon steel is placed into a core winding device, the raw material is first cut into a strip according to the core width requirement, the width of the strip is 60 mm, and then the strip is wound into a ring-shaped core according to the shape of the mold. Example 3

[0033] The annealing process of the core of the low-loss low-frequency transformer comprises the following steps:

[0034] (1) the chemical components of the silicon steel ingot include, by weight percentage, C: 0.3%, Mn: 0.5%, Si: 3.5%, P: 0.006%, S: 0.009%, Al: 2.5%, N: 0.010%, and the rest is Fe and other unavoidable impurities, the silicon steel ingot is first rough rolled at 1150 DEG C, the pass is 5 times, and the reduction is 15%, then finish rolled at 1050 DEG C, the pass is 7 times, and the reduction is 12%, after hot rolling, coiling is performed, the coiling temperature is 580 DEG C, then cold rolling is performed, the total reduction of cold rolling is 90%, the pass is 5 passes, and the pass reduction is 20%, the thickness of the silicon steel after cold rolling is 0.08 mm;

[0035] (2) the silicon steel after hot rolling and cold rolling is placed in a bell type annealing furnace, heated to 1400 DEG C, annealed in an aluminum containing atmosphere for 5 min, then cooled to 500 DEG C at a cooling rate of 5 DEG C / s to obtain the primary annealed silicon steel, wherein the aluminum containing atmosphere is prepared by preparing aluminum vapor at 20 Pa and 1670 K, and the aluminum vapor is introduced into the bell type annealing furnace together with hydrogen, the total flow rate of the aluminum containing atmosphere is 40 Nm 3 / h, the flow rate ratio of the aluminum vapor and the hydrogen is 1.5:10, and the dew point is less than or equal to 20 DEG C;

[0036] (3) after introducing oxygen to exhaust the gas in the system, the dew point of the oxygen is less than or equal to 15 DEG C, heated to 920 DEG C, annealed in an oxygen atmosphere for 5 min, then cooled to 450 DEG C at a cooling rate of 10 DEG C / s, and then cooled to room temperature in air to obtain the secondary annealed silicon steel;

[0037] (4) The twice annealed silicon steel is put into a core winding device, the raw material is cut into a strip according to the core width requirement, the width of the strip is 70 mm, then the strip is wound into a ring-shaped core according to the shape of the mold.

[0038] Comparative Example 1

[0039] The difference between Comparative Example 1 and Example 2 is that step (2) is changed, the step (2) is changed to: the hot-rolled and cold-rolled silicon steel is placed in a bell-type annealing furnace, heated to 1300℃, annealed for 4 min under hydrogen protection, then cooled to 500℃ at a cooling rate of 5℃ / s to obtain a primary annealed silicon steel, the flow rate of hydrogen is 35Nm3 / h, the dew point is ≤20℃; the rest of the steps are the same as Example 2. 3

[0040] Comparative Example 2

[0041] The difference between Comparative Example 2 and Example 2 is that there is no step (3), the step (2) is changed to: the hot-rolled and cold-rolled silicon steel is placed in a bell-type annealing furnace, heated to 1300℃, annealed for 4 min in an aluminum-containing atmosphere, then cooled to 500℃ at a cooling rate of 5℃ / s to obtain a primary annealed silicon steel, wherein the aluminum-containing atmosphere is prepared by passing aluminum vapor and oxygen into the bell-type annealing furnace at 18Pa and 1500K, the total flow rate of the aluminum-containing atmosphere is 35Nm3 / h, the flow rate ratio of aluminum vapor and oxygen is 1.2:10, and the dew point is ≤20℃; the rest of the steps are the same as Example 2.

[0042] Comparative Example 3

[0043] The difference between Comparative Example 3 and Example 2 is that step (2) is changed, the step (2) is changed to: the hot-rolled and cold-rolled silicon steel is placed in a bell-type annealing furnace, heated to 1300℃, annealed for 4 min under hydrogen protection, then cooled to 500℃ at a cooling rate of 5℃ / s to obtain a primary annealed silicon steel, the flow rate of hydrogen is 35Nm3 / h, the dew point is ≤20℃; the step (4) is changed to: an aluminum oxide insulation layer with a thickness of 5um is coated on the surface of the twice annealed silicon steel, then the silicon steel coated with the insulation layer is put into a core winding device, the raw material is cut into a strip according to the core width requirement, the width of the strip is 60 mm, then the strip is wound into a ring-shaped core according to the shape of the mold; the rest of the steps are the same as Example 2.

[0044] Effect Example

[0045] The performance analysis results of the cores for low-loss low-frequency transformers using Examples 1 to 3 and Comparative Examples 1 to 3 of the present application are shown in Table 1 below.

[0046] Table 1

[0047] ​

[0048] From the comparison of the experimental data of the examples and the comparative examples, it can be found that, in the present application, the aluminum vapor is prepared by first heating and evaporation, and the silicon steel is subjected to first annealing in an aluminum-containing atmosphere. The aluminum vapor will deposit an aluminum-containing film on the surface of the silicon steel. During annealing, aluminum atoms will diffuse into the steel, reducing the interfacial stress between the insulating coating and the silicon steel sheet, reducing the risk of peeling and cracking of the insulating coating, and realizing firm combination of the aluminum-containing metal layer and the silicon steel. Then, the second annealing is carried out in an oxygen atmosphere, so that the aluminum atoms are converted into aluminum oxide, and a dense protective film is formed on the surface of the silicon steel, improving the insulation and corrosion resistance, and reducing the eddy current loss of the core of the low-loss low-frequency transformer. After the silicon steel is subjected to the second annealing, the internal grain boundaries of the silicon steel will diffuse and the grain will grow, thereby significantly improving the magnetic conductivity of the silicon steel. The introduction of the aluminum-containing film before the second annealing blocks the path of the combination of oxygen molecules and the atoms on the surface of the silicon steel, effectively inhibits the oxidation of the surface of the silicon steel, and improves the corrosion resistance of the silicon steel.

[0049] It will be obvious to a person skilled in the art that the application is not limited to the details of the above-described exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or essential characteristics of the application. Therefore, the embodiments should be considered as exemplary and non-limiting, and the scope of the application is defined by the appended claims rather than the above description, and all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the application. Any mark in the claims should not be considered as limiting the involved claims.

Claims

1. Annealing process of a core for low-loss low-frequency transformers, characterized in that, The method comprises the following steps: (1) primary annealing: after hot rolling and cold rolling, the silicon steel ingot is placed in a bell-type annealing furnace, heated to 1220-1400°C, annealed in an aluminum-containing atmosphere for 3-5 min, and then cooled to 500°C at a cooling rate of 5°C / s to obtain a primary annealed silicon steel, wherein the aluminum-containing atmosphere is prepared by preparing aluminum vapor at 17-20 Pa and 1480-1670 K, and introducing the aluminum vapor into the bell-type annealing furnace together with hydrogen, the total flow rate of the aluminum-containing atmosphere is 30-40 Nm 3 / h, the flow rate ratio of the aluminum vapor and the hydrogen is 1-1.5:10, and the dew point is ≤20°C; (2) secondary annealing: after the gas in the system is exhausted by passing oxygen, the temperature is raised to 910-920 DEG C, annealed in oxygen atmosphere for 3-5 min, then cooled to 450 DEG C at a cooling rate of 10 DEG C / sec, and then cooled to room temperature in air to obtain secondary annealed silicon steel; (3) the secondary annealed silicon steel is placed in a core winding device, the raw material is cut into strips according to the core width requirement, and then the strips are wound into annular cores according to the shape of the mold.

2. The annealing process of the core for low-loss low-frequency transformers according to claim 1, characterized in that, The chemical composition of the silicon steel ingot in step (1) includes, by weight percentage: C: 0.05%-0.3%, Mn: 0.2%-0.5%, Si: 2.0%-3.5%, P: 0.003%-0.006%, S: 0.006%-0.009%, Al: 2.1%-2.5%, N: 0.008%-0.010%, and the rest is Fe and other unavoidable impurities.

3. The annealing process of the core for low-loss low-frequency transformer according to claim 1, characterized in that, The hot rolling process of the silicon steel in step (1) is: hot rolling is divided into rough rolling and finish rolling, and the coiling temperature after hot rolling is 550-580 DEG C.

4. The annealing process for the core of low-loss low-frequency transformer according to claim 3, characterized in that, The rough rolling temperature is 1100-1150 DEG C, the pass is 3-5 times of rough rolling, and the reduction is 12-15%.

5. The annealing process of the core for low-loss low-frequency transformers according to claim 3, characterized in that, The finish rolling temperature is 1000-1050 DEG C, the pass is 5-7 times of finish rolling, and the reduction is 10-12%.

6. The annealing process of the core for low-loss low-frequency transformers according to claim 1, characterized in that, The cold rolling process of the silicon steel in step (1) is: the total reduction of cold rolling is 85-90%, the pass is 3-5 passes, the pass reduction is 18-20%, and the thickness of the silicon steel after cold rolling is 0.05-0.08 mm.

7. The annealing process of the core for low-loss low-frequency transformers according to claim 1, characterized in that, The dew point of oxygen in step (2) is ≤15 DEG C.

8. The annealing process of the core for low-loss low-frequency transformers according to claim 1, characterized in that, The width of the strip in step (3) is 45-70 mm.

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