Iron core for low-loss low-frequency transformer and annealing process

Abstract

The invention discloses an iron core for a low-loss low-frequency transformer and an annealing process, and relates to the technical field of iron cores for transformers. According to the method, aluminum steam is prepared through heating and evaporation, silicon steel is subjected to first-time annealing in the aluminum-containing atmosphere, a layer of aluminum-containing film is deposited on the surface of the silicon steel through the aluminum steam, aluminum atoms are diffused into steel during annealing, and the interface stress of an insulating coating and a silicon steel sheet is reduced; aluminum atoms are converted into aluminum oxide, a compact protective film is formed on the surface of silicon steel, and the eddy-current loss of the iron core is reduced; after the silicon steel is subjected to secondary annealing, the internal grain boundary of the silicon steel can be diffused, and crystal grains grow up, so that the magnetic conductivity of the silicon steel is remarkably improved, the aluminum-containing film is introduced firstly, then secondary annealing is carried out, the combination path of oxygen molecules and atoms on the surface of the silicon steel is blocked through generation of aluminum oxide, and oxidation of the surface of the silicon steel is effectively inhibited. The iron core for the low-loss and low-frequency transformer and the annealing process provided by the invention have the effects of low energy consumption and corrosion resistance.

Description

Technical Field

[0002] The invention relates to the technical field of transformer iron cores, in particular to an iron core for a low-loss low-frequency transformer and an annealing process. Background Art

[0004] The iron core is the core component of devices such as transformers and reactors. Improving its performance is of great significance for achieving low-loss current conversion in transformers and high-reliability reactive power compensation in saturated reactors.

[0005] With the global emphasis on energy conservation and emission reduction, improving energy conversion efficiency has become the key. Traditional transformers will produce large iron loss and copper loss during operation, because of the hysteresis loss and eddy current loss inside, resulting in low energy conversion efficiency. Existing technology usually coats the surface of silicon steel with an insulating layer to reduce iron loss, but the coated insulating layer will inevitably fall off. In order to improve the energy efficiency of the transformer, it is necessary to develop low-loss transformer core materials and corresponding annealing processes to reduce iron loss and improve overall efficiency. Summary of the invention

[0007] The object of the present invention is to provide an iron core for a low-loss low-frequency transformer and an annealing process to solve the problems existing in the prior art.

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions: a low-loss low-frequency transformer core and an annealing process, comprising the following steps:

[0009] (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℃, annealed in an aluminum-containing atmosphere for 3~5min, and then cooled to 500℃ at a cooling rate of 5℃ / s to obtain primary annealed silicon steel. The aluminum-containing atmosphere is prepared at 17~20Pa and 1480~1670K. Aluminum vapor is introduced into the bell-type annealing furnace together with hydrogen. The total flow rate 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℃;

[0010] (2) Secondary annealing: After introducing oxygen to exhaust the gas in the system, the temperature is raised to 910~920℃, annealed in an oxygen atmosphere for 3~5min, then cooled to 450℃ at a cooling rate of 10℃ / s, and then cooled to room temperature in air to obtain secondary annealed silicon steel;

[0011] (3) The secondary annealed silicon steel is placed in the core winding equipment. The raw material is first cut into strips according to the core width requirements, and then the strips are wound into a ring-shaped core according to the mold shape.

[0012] Furthermore, 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.

[0013] Furthermore, in step (1), the hot rolling process of the silicon steel is as follows: the hot rolling is divided into rough rolling and finish rolling, and the hot rolling is followed by coiling, and the coiling temperature is 550-580°C.

[0014] Furthermore, the rough rolling temperature is 1100-1150° C., the number of rough rolling passes is 3-5 times, and the reduction is 12-15%.

[0015] Furthermore, the finishing rolling temperature is 1000-1050° C., the number of finishing rolling passes is 5-7 times, and the reduction is 10-12%.

[0016] Furthermore, the cold rolling process of the silicon steel in step (1) is as follows: the total cold rolling reduction rate is 85-90%, the number of passes is 3-5, the pass reduction is 18-20%, and the thickness of the silicon steel after cold rolling is 0.05-0.08 mm.

[0017] Furthermore, in step (2), the dew point of oxygen is ≤15°C.

[0018] Furthermore, in step (3), the width of the strip material is 45-70 mm.

[0019] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0020] The present invention provides an iron core for a low-loss low-frequency transformer and an annealing process. Silicon steel is first annealed in an aluminum-containing atmosphere for the first time, and then annealed in an oxygen atmosphere for the second time to prepare the iron core for the low-loss low-frequency transformer, so as to achieve the effects of low energy consumption and corrosion resistance.

[0021] First, aluminum vapor is prepared by heating and evaporation, and the silicon steel is annealed for the first time 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 interior of the steel, reducing the interface stress between the insulating coating and the silicon steel sheet, reducing the risk of the insulating coating falling off and cracking, and achieving a firm bond between the aluminum-containing metal layer and the silicon steel. Then, a second annealing is performed 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, thereby improving the insulation and corrosion resistance and reducing the eddy current loss of the iron core for low-loss low-frequency transformers. After the secondary annealing, the internal grain boundaries of the silicon steel will diffuse and the grains will grow, thereby significantly improving its magnetic conductivity. The aluminum-containing film is introduced first and then the secondary annealing is performed. The formation of aluminum oxide blocks the path for the oxygen molecules to combine with the atoms on the surface of the silicon steel, effectively inhibiting the oxidation of the silicon steel surface and improving the corrosion resistance of the silicon steel. DETAILED DESCRIPTION

[0023] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0024] In order to more clearly illustrate the method provided by the present invention, the following examples are used to describe in detail the various index testing methods of the low-loss low-frequency transformer core prepared in the following examples.

[0025] Core loss: The cores for low-loss low-frequency transformers prepared in the embodiment and the comparative example with the same mass were tested for loss and noise at 600 Hz using a soft magnetic measurement system and a noise meter, respectively.

[0026] Corrosion resistance: The iron cores for low-loss low-frequency transformers prepared in the embodiment and the comparative example of the same mass were immersed in a 0.1 mg / mL nitric acid solution and left to stand for 3 days, and then their corrosion degree was tested.

[0027] Example 1

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

[0029] (1) The chemical composition of the silicon steel ingot includes, by weight percentage: C: 0.05%, 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, it is coiled at a coiling temperature of 550°C, and then cold rolled. The total cold rolling reduction is 85%, with 3 passes and a reduction of 18%. The thickness of the silicon steel after cold rolling is 0.05 mm.

[0030] (2) Place the hot-rolled and cold-rolled silicon steel in a bell-type annealing furnace, heat it to 1220°C, anneal it in an aluminum-containing atmosphere for 3 minutes, and then cool it to 500°C at a cooling rate of 5°C / s to obtain a single annealed silicon steel. The aluminum-containing atmosphere is prepared at 17Pa and 1480K. Aluminum vapor is introduced into the bell-type annealing furnace together with hydrogen. The total flow rate of the aluminum-containing atmosphere is 30Nm 3 / h, the flow ratio of aluminum vapor and hydrogen is 1:10, and the dew point is ≤20℃;

[0031] (3) After oxygen is introduced to exhaust the gas in the system, the dew point of oxygen is ≤15°C, the temperature is raised to 910°C, annealed in an oxygen atmosphere for 3 minutes, then cooled to 450°C at a cooling rate of 10°C / s, and then cooled to room temperature in air to obtain secondary annealed silicon steel;

[0032] (4) Place the secondary annealed silicon steel into the core winding equipment, first cut the raw material into strips according to the core width requirements, the width of the strips is 45mm, and then wind the strips into a ring-shaped core according to the mold shape.

[0033] Example 2

[0034] The annealing process of the iron core for low-loss low-frequency transformer includes the following steps:

[0035] (1) The chemical composition of the silicon steel ingot by weight percentage includes: 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℃, with 4 passes and a reduction of 13%, and then finish rolled at 1025℃, with 6 passes and a reduction of 11%. After hot rolling, it is coiled at a coiling temperature of 560℃, and then cold rolled. The total cold rolling reduction is 87%, with 4 passes and a reduction of 19%. The thickness of the silicon steel after cold rolling is 0.07mm;

[0036] (2) The hot-rolled and cold-rolled silicon steel is placed in a bell-type annealing furnace, heated to 1300°C, annealed in an aluminum-containing atmosphere for 4 minutes, and then cooled to 500°C at a cooling rate of 5°C / s to obtain a single annealed silicon steel. The aluminum-containing atmosphere is prepared at 18 Pa and 1500 K. 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 ratio of aluminum vapor and hydrogen is 1.2:10, and the dew point is ≤20℃;

[0037] (3) After oxygen is introduced to exhaust the gas in the system, the dew point of oxygen is ≤15°C, the temperature is raised to 915°C, annealed in an oxygen atmosphere for 4 minutes, then cooled to 450°C at a cooling rate of 10°C / s, and then cooled to room temperature in air to obtain secondary annealed silicon steel;

[0038] (4) Place the secondary annealed silicon steel into the core winding equipment, first cut the raw material into strips according to the core width requirements, the width of the strips is 60 mm, and then wind the strips into a ring-shaped core according to the mold shape.

[0039] Example 3

[0040] The annealing process of the iron core for low-loss low-frequency transformer includes the following steps:

[0041] (1) The chemical composition of the silicon steel ingot includes, 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 inevitable impurities. The silicon steel ingot is first rough rolled at 1150°C, with 5 passes and a reduction of 15%, and then finish rolled at 1050°C, with 7 passes and a reduction of 12%. After hot rolling, it is coiled at a coiling temperature of 580°C, and then cold rolled. The total cold rolling reduction is 90%, with 5 passes and a reduction of 20% per pass. The thickness of the silicon steel after cold rolling is 0.08 mm.

[0042] (2) The hot-rolled and cold-rolled silicon steel is placed in a bell-type annealing furnace, heated to 1400°C, annealed for 5 min in an aluminum-containing atmosphere, and then cooled to 500°C at a cooling rate of 5°C / s to obtain a single annealed silicon steel. The aluminum-containing atmosphere is prepared at 20 Pa and 1670 K. 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 ratio of aluminum vapor and hydrogen is 1.5:10, and the dew point is ≤20℃;

[0043] (3) After oxygen is introduced to exhaust the gas in the system, the dew point of oxygen is ≤15°C, the temperature is raised to 920°C, annealed in an oxygen atmosphere for 5 minutes, then cooled to 450°C at a cooling rate of 10°C / s, and then cooled to room temperature in air to obtain secondary annealed silicon steel;

[0044] (4) Place the secondary annealed silicon steel into the core winding equipment, first cut the raw material into strips according to the core width requirements, the width of the strips is 70 mm, and then wind the strips into a ring-shaped core according to the mold shape.

[0045] Comparative Example 1

[0046] The difference between Comparative Example 1 and Example 2 is that step (2) is different. Step (2) is changed to: placing the hot-rolled and cold-rolled silicon steel in a bell-type annealing furnace, heating it to 1300°C, annealing it for 4 minutes under hydrogen protection, and then cooling it to 500°C at a cooling rate of 5°C / s to obtain a primary annealed silicon steel. The hydrogen flow rate is 35Nm 3 / h, dew point ≤20°C; the remaining steps are the same as in Example 2.

[0047] Comparative Example 2

[0048] The difference between Comparative Example 2 and Example 2 is that there is no step (3), and step (2) is changed to: placing the silicon steel after hot rolling and cold rolling in a bell-type annealing furnace, heating to 1300°C, annealing for 4 minutes in an aluminum-containing atmosphere, and then cooling to 500°C at a cooling rate of 5°C / second to obtain a once annealed silicon steel, wherein the aluminum-containing atmosphere is prepared at 18 Pa and 1500K, aluminum vapor is introduced into the bell-type annealing furnace together with oxygen, the total flow rate of the aluminum-containing atmosphere is 35 Nm3 / h, the flow ratio of aluminum vapor to oxygen is 1.2:10, and the dew point is ≤20°C; the remaining steps are the same as Example 2.

[0049] Comparative Example 3

[0050] The difference between Comparative Example 3 and Example 2 lies in step (2). Step (2) is changed to: placing the hot-rolled and cold-rolled silicon steel in a bell-type annealing furnace, heating it to 1300°C, annealing it under hydrogen protection for 4 minutes, and then cooling it to 500°C at a cooling rate of 5°C / second to obtain the primary annealed silicon steel, the hydrogen flow rate is 35Nm3 / h, and the dew point is ≤20°C; step (4) is changed to: coating the surface of the secondary annealed silicon steel with an alumina insulation layer, the insulation layer thickness is 5um, and then placing the silicon steel coated with the insulation layer into an iron core winding device, first cutting the raw material into strips according to the iron core width requirements, the width of the strips is 60mm, and then winding the strips into a ring-shaped iron core according to the mold shape; the remaining steps are the same as in Example 2.

[0051] Effect example

[0052] Table 1 below shows the performance analysis results of the iron core for low-loss low-frequency transformer using Examples 1 to 3 of the present invention and Comparative Examples 1 to 3.

[0053] Table 1

[0054] Core loss P (W / kg) Noise (dB(A)) Corrosion degree (%) Example 1 10.1 51 0 Example 2 9.8 50 0 Example 3 10.0 51 0 Comparative Example 1 20.4 76 37 Comparative Example 2 15.6 68 15 Comparative Example 3 13.2 63 21

[0055] From the comparison of the experimental data of the embodiment and the comparative example, it can be found that the present invention first heats and evaporates to prepare aluminum vapor, and then performs the first annealing on the silicon steel 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 interior of the steel, reducing the interface stress between the insulating coating and the silicon steel sheet, reducing the risk of the insulating coating falling off and cracking, and achieving a firm bond between the aluminum-containing metal layer and the silicon steel. Then, a second annealing is performed 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, thereby improving the insulation and corrosion resistance and reducing the eddy current loss of the iron core for low-loss low-frequency transformers. After the silicon steel undergoes the second annealing, its internal grain boundaries will diffuse and the grains will grow, thereby significantly improving its magnetic conductivity. The aluminum-containing film is first introduced and then the second annealing is performed. The formation of aluminum oxide blocks the path for the oxygen molecules to combine with the atoms on the surface of the silicon steel, effectively inhibiting the oxidation of the silicon steel surface and improving the corrosion resistance of the silicon steel.

[0056] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations within the meaning and scope of the equivalent elements of the claims be included in the invention. Any marking in a claim should not be considered as limiting the claim to which it relates.

Claims

1. Annealing process for iron core for low-loss low-frequency transformer, characterized in that: The following steps are involved: (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℃, annealed in an aluminum-containing atmosphere for 3~5min, and then cooled to 500℃ at a cooling rate of 5℃ / s to obtain primary annealed silicon steel. The aluminum-containing atmosphere is prepared at 17~20Pa and 1480~1670K. Aluminum vapor is introduced into the bell-type annealing furnace together with hydrogen. The total flow rate 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℃; (2) Secondary annealing: After introducing oxygen to exhaust the gas in the system, the temperature is raised to 910~920℃, annealed in an oxygen atmosphere for 3~5min, then cooled to 450℃ at a cooling rate of 10℃ / s, and then cooled to room temperature in air to obtain secondary annealed silicon steel; (3) The secondary annealed silicon steel is placed in the core winding equipment. The raw material is first cut into strips according to the core width requirements, and then the strips are wound into a ring-shaped core according to the mold shape.

2. The annealing process of the iron core for low-loss low-frequency transformer according to claim 1, characterized in that: The chemical composition of the silicon steel ingot in the 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.

3. The annealing process of the iron 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 as follows: the hot rolling is divided into rough rolling and finish rolling, and the hot rolling is followed by coiling, and the coiling temperature is 550-580°C.

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

5. The annealing process for the iron core for low-loss low-frequency transformer according to claim 3, characterized in that: The finishing rolling temperature is 1000-1050° C., the number of passes is 5-7 times, and the reduction is 10-12%.

6. The annealing process of the iron core for low-loss low-frequency transformer according to claim 1, characterized in that: The cold rolling process of the silicon steel in step (1) is as follows: the total cold rolling reduction rate is 85-90%, the number of passes is 3-5, 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 for the iron core for low-loss low-frequency transformer according to claim 1, characterized in that: The dew point of oxygen in step (2) is ≤15°C.

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