Laminated iron core, manufacturing method of laminated iron core, and transformer

Abstract

To provide a laminated core that reduces noise of a transformer while suppressing an increase in iron loss of the transformer.SOLUTION: A laminated core 1 is formed by stacking a plurality of steel plates 10, and includes a yoke portion 2 and a leg portion 3. The steel plates 10 include first steel plate members 11, 12 included in the yoke portion 2, and second steel plate members 13, 14, 15 included in the leg portion 3. The ratio of the maximum peak height Rp of the surfaces of the second steel plate members 13 to 15 to the maximum peak height Rp of the surfaces of the first steel plate members 11, 12 exceeds 1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a laminated core, a method for manufacturing a laminated core, and a transformer. [Background technology]

[0002] There are various requirements for the cores used in transformers. Among these, there is a strong demand for reducing the noise of transformers. Therefore, a method for reducing the noise of transformers using laminated cores is known (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-077747 Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 1, the noise of a transformer is reduced by applying an adhesive such as resin to the lamination end surfaces of a laminated core. However, applying an adhesive such as resin to the lamination end surfaces may reduce the space factor of the laminated core. A reduction in the space factor of the laminated core may increase the iron loss of the transformer.

[0005] In view of the above, an object of the present disclosure is to provide a laminated core, a manufacturing method for a laminated core, and a transformer that reduce noise of a transformer while suppressing an increase in iron loss of the transformer. [Means for solving the problem]

[0006] (1) A laminated core according to one embodiment of the present disclosure includes: A laminated core in which a plurality of steel plates are laminated, the core having a yoke portion and a leg portion, The steel plate includes a first steel plate member included in the yoke portion and a second steel plate member included in the leg portion, The ratio of the maximum peak height Rp on the surface of the second steel plate member to the maximum peak height Rp on the surface of the first steel plate member exceeds 1.

[0007] (2) In the laminated core of (1) above, A ratio of a maximum peak height Rp on a surface of the second steel plate member to a maximum peak height Rp on a surface of the first steel plate member may be 1.15 or more.

[0008] (3) In the laminated core of (1) or (2) above, A ratio of a maximum peak height Rp on a surface of the second steel plate member to a maximum peak height Rp on a surface of the first steel plate member may be 1.15 or more and 1.45 or less.

[0009] (4) A method for manufacturing a laminated core according to one embodiment of the present disclosure includes: In the manufacturing method of any one of the laminated cores (1) to (3) above, chemical polishing, shot blasting, or emery polishing is performed on the second steel plate member or on the steel plate before forming the second steel plate member.

[0010] (5) A transformer according to one embodiment of the present disclosure includes: The motor includes a laminated core of any one of (1) to (3) above. [Effects of the Invention]

[0011] According to an embodiment of the present disclosure, it is possible to provide a laminated core, a manufacturing method for a laminated core, and a transformer that reduce noise of a transformer while suppressing an increase in iron loss of the transformer. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram showing a schematic configuration of a laminated core according to an embodiment of the present disclosure. FIG. [Figure 2] FIG. 2 is a diagram showing the steel plate shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The drawings are schematic and may differ from the actual product.

[0014] (Laminated core configuration) The transformer according to this embodiment includes a laminated core 1 as shown in Fig. 1. The laminated core 1 can be used in a three-phase, three-limbed transformer. The laminated core 1 includes yoke portions 2A and 2B and leg portions 3A, 3B, and 3C.

[0015] Hereinafter, when there is no particular distinction between yoke portions 2A and 2B, they will also be simply referred to as "yoke portion 2." When there is no particular distinction between leg portions 3A, 3B, and 3C, they will also be simply referred to as "leg portion 3."

[0016] The laminated core 1 according to this embodiment has three legs 3. However, the number of legs 3 provided in the laminated core 1 is not limited to three. The laminated core 1 may have any number of legs 3 depending on the type and configuration of the transformer in which the laminated core 1 is used. As another example, when the laminated core 1 is used in a three-phase five-limbed transformer, the laminated core 1 may have five legs 3. As yet another example, when the laminated core 1 is used in a single-phase transformer, the laminated core 1 may have two legs 3.

[0017] A coil is wound around leg 3. Yoke 2A connects one ends of legs 3A to 3C together, and yoke 2B connects the other ends of legs 3A to 3C together.

[0018] The laminated core 1 includes a plurality of stacked steel plates 10. Fig. 1 shows an example in which the laminated core 1 includes five stacked steel plates 10. However, the laminated core 1 may include any number of steel plates 10 depending on the application of the transformer in which the laminated core 1 is used, etc.

[0019] The material of the steel sheet 10 is, for example, a grain-oriented electromagnetic steel sheet. <001> The steel sheet 10 has a crystalline structure whose orientation is highly aligned in the rolling direction of the steel sheet. However, the material of the steel sheet 10 may be any material. As another example, the material of the steel sheet 10 may be an electrical steel sheet that exhibits a given magnetic flux density B8 when excited at a magnetic field strength of 800 [A / m], or a steel sheet that exhibits a given iron loss when excited. The magnetic field strength of 800 [A / m] is an index for measuring the degree of orientation of crystal grains in the electrical steel sheet. As yet another example, the material of the steel sheet 10 may be a steel sheet that has undergone a magnetic domain refinement process. The magnetic domain refinement process is, for example, a process of forming grooves on the steel sheet surface by electrolytic etching, gear rolling, laser etching, or the like. As yet another example, the material of the steel sheet 10 may be a non-heat-resistant magnetic domain refinement material that has undergone thermal distortion using a laser, electron beam, plasma jet, or the like before or after a surface treatment to increase the maximum peak height Rp described below.

[0020] The steel plate 10 has a rectangular outer shape. As shown in FIG. 2 , the steel plate 10 has first steel plate members 11 and 12 and second steel plate members 13, 14, and 15. Hereinafter, when the first steel plate members 11 and 12 are not particularly distinguished, they are also simply referred to as "first steel plate members." Hereinafter, when the second steel plate members 13 to 15 are not particularly distinguished, they are also simply referred to as "second steel plate members."

[0021] The first steel plate member 11 is included in the yoke portion 2A of the laminated core 1. The extending direction of the first steel plate member 11 corresponds to the magnetization direction in the yoke portion 2A. The first steel plate member 11 is made of grain-oriented electromagnetic steel plate. <001> The orientation is formed to correspond to the extension direction of the first steel plate member 11. The first steel plate member 11 includes joints 11A, 11B, and 11E. The joint 11A has an inclined shape that is inclined with respect to the extension direction of the first steel plate member 11. The inclined shape of the joint 11A and the inclined shape of the joint 11B are line-symmetric. The joint 11E has a V-shape.

[0022] The first steel plate member 12 is included in the yoke portion 2B of the laminated core 1. The extending direction of the first steel plate member 12 corresponds to the magnetization direction in the yoke portion 2B. The first steel plate member 12 is made of grain-oriented electromagnetic steel plate. <001> The orientation is formed to correspond to the extension direction of the first steel plate member 12. The first steel plate member 12 includes joints 12C, 12D, and 12F. The joint 12C has an inclined shape that is inclined with respect to the extension direction of the first steel plate member 12. The inclined shape of the joint 12C and the inclined shape of the joint 12D are line-symmetric. The joint 12F has a V-shape.

[0023] The second steel plate member 13 is included in the leg portion 3A of the laminated core 1. The extending direction of the second steel plate member 13 corresponds to the magnetization direction of the leg portion 3A. The second steel plate member 13 is made of grain-oriented electromagnetic steel plate. <001> The orientation is formed to correspond to the extension direction of the second steel plate member 13. The second steel plate member 13 includes joints 13A and 13D. The joint 13A has an inclined shape that is inclined with respect to the extension direction of the second steel plate member 13. The inclined shape of the joint 13A and the inclined shape of the joint 13D are line-symmetrical.

[0024] The second steel plate member 14 is included in the leg portion 3B of the laminated core 1. The extending direction of the second steel plate member 14 corresponds to the magnetization direction in the leg portion 3B. The second steel plate member 14 is made of a grain-oriented electromagnetic steel plate. <001> The orientation is formed to correspond to the extension direction of the second steel plate member 14. The second steel plate member 14 includes joints 14E, 14F. The joints 14E, 14F have a V-shape. The shape of the joint 14E and the shape of the joint 11E are substantially the same shape. The shape of the joint 14F and the shape of the joint 12F are substantially the same shape.

[0025] The second steel plate member 15 is included in the leg portion 3C of the laminated core 1. The extending direction of the second steel plate member 15 corresponds to the magnetization direction in the leg portion 3C. The second steel plate member 15 is made of grain-oriented electromagnetic steel plate. <001> The orientation is formed to correspond to the extension direction of the second steel plate member 15. The second steel plate member 15 includes joints 15B and 15C. Joint 15B has an inclined shape that is inclined with respect to the extension direction of the second steel plate member 15. Joint 15C has an inclined shape that is inclined with respect to the extension direction of the second steel plate member 15. The inclined shape of joint 15B and the inclined shape of joint 15C are line-symmetrical.

[0026] When assembling the steel plates 10, the joints 11A and 13A are butted together, the joints 11B and 15B are butted together, the joints 15C and 12C are butted together, and the joints 12D and 13D are butted together. Furthermore, when assembling the steel plates 10, the joints 11E and 14E are butted together, and the joints 12F and 14F are butted together. The joints 11A, 13A, etc. may be butted together without an adhesive or the like. By butting the joints 11A, 13A, etc. together without an adhesive or the like, the space factor of the steel plates 10 in the laminated core 1 can be increased compared to when the joints 11A, 13A, etc. are butted together using an adhesive or the like.

[0027] The plurality of steel plates 10 are stacked without the use of adhesive or the like. By stacking the plurality of steel plates 10 without the use of adhesive or the like, the space factor of the steel plates 10 in the laminated core 1 can be made higher than when the plurality of steel plates 10 are stacked with the use of adhesive or the like. The plurality of steel plates 10 may be stacked in any manner. For example, the plurality of steel plates 10 may be stacked in a step-lap manner at butt joints 11A, 13A, etc.

[0028] In the laminated core 1 according to this embodiment, the ratio of the maximum peak height Rp on the surface of the second steel plate member to the maximum peak height Rp on the surface of the first steel plate member exceeds 1. The maximum peak height Rp is one index of surface roughness. In this embodiment, the maximum peak height Rp is the highest peak on the profile curve within the reference length. A peak is a portion that is higher than the average line. In this embodiment, the maximum peak height Rp refers to the maximum peak height Rp specified in JIS B0601:2001 (ISO 4287:1997). The minimum value of the maximum peak height Rp on the surface of the second steel plate member is preferably 14.0 μm, as shown in Table 6 below.

[0029] In this manner, in the laminated core 1 according to this embodiment, the ratio of the maximum peak height Rp of the surface of the second steel plate member to the maximum peak height Rp of the surface of the first steel plate member exceeds 1, so that the surface of the second steel plate member is rougher than the surface of the first steel plate member. By roughening the surface of the second steel plate member included in the leg portion 3 in this manner, the frictional force between the multiple second steel plate members in the laminated core 1 can be increased. By increasing the frictional force between the multiple second steel plate members in the laminated core 1, the multiple steel plates 10 are less likely to slide sideways in the laminated core 1, even when the multiple steel plates 10 are stacked without an adhesive or the like. By reducing the resistance of the multiple steel plates 10 to sliding sideways in the laminated core 1, the rigidity of the laminated core 1 can be increased. Increasing the rigidity of the laminated core 1 reduces the natural vibration of the laminated core 1. The natural vibration of the laminated core 1 refers to the vibration of the laminated core 1 at a specific frequency as a single structure. Therefore, in this embodiment, by reducing the natural vibration of the laminated core 1, the noise of a transformer including the laminated core 1 can be reduced. Furthermore, in the laminated core 1 according to this embodiment, the plurality of steel plates 10 are laminated without the use of adhesive or the like, thereby making it possible to increase the space factor of the steel plates 10 in the laminated core 1. Increasing the space factor of the steel plates 10 in the laminated core 1 makes it possible to suppress an increase in iron loss in a transformer including the laminated core 1.

[0030] Furthermore, in a transformer including the laminated core 1 according to this embodiment, coils are wound around the legs 3. Therefore, the legs 3 are not fastened by components or the like. In contrast, the yoke 2 is fastened by components such as clamps or brackets. Fastening the yoke 2 in this manner makes it difficult for the steel plates 10 in the laminated core 1 to slide sideways, even without increasing the maximum peak height Rp of the first steel plate member. In this embodiment, by not making the maximum peak height Rp of the surface of the first steel plate member larger than the maximum peak height Rp of the surface of the second steel plate member, an increase in iron loss in the transformer can be suppressed. In other words, in this embodiment, by making the ratio of the maximum peak height Rp of the surface of the second steel plate member to the maximum peak height Rp of the surface of the first steel plate member greater than 1, an increase in iron loss in the transformer can be suppressed.

[0031] Therefore, in the laminated core 1 according to this embodiment, the ratio of the maximum peak height Rp on the surface of the second steel plate member to the maximum peak height Rp on the surface of the first steel plate member exceeds 1, thereby suppressing an increase in iron loss in a transformer including the laminated core 1 and reducing noise of the transformer. See also the results of Experiment 2 for this effect.

[0032] (Experiment 1: Skidding) An experiment was conducted to examine the relationship between the maximum peak height Rp of a steel sheet, which is used as an iron core material, and lateral slippage. Grain-oriented electrical steel sheets with a phosphorus hydrochloride-based insulating coating were used as the iron core material. These grain-oriented electrical steel sheets were manufactured using a known method. The grain-oriented electrical steel sheets were divided into rectangular steel sheet members. These rectangular steel sheet members measured 30 mm in width, 280 mm in length, and 0.23 mm in thickness. Some of the divided steel sheet members were subjected to a surface treatment to roughen the surface. The surface treatment involved immersing the steel sheet members in a 1 mol / L sodium hydroxide aqueous solution for 2 minutes. This resulted in the preparation of surface-treated steel sheet members and untreated steel sheet members.

[0033] Surface-treated and untreated steel plate members were stacked to prepare two laminates: one with surface-treated steel plate members and the other with untreated steel plate members. Each of these two laminates had 70 layers. The ease of sliding was measured for these two laminates. The measurement method employed was to place the laminate on a horizontal table, tilt the table in 1-degree increments from the horizontal up to a maximum of 90 degrees, and measure the angle at which the steel plate members in the laminate began to move. In this measurement method, the closer the table angle was to 90 degrees when the steel plate members in the laminate began to move, the less likely the laminate was to slide. In the experiment, a stopper half the height of the laminate was installed on the table to prevent the laminate from behaving as a single rigid body and moving without sliding.

[0034] Table 1 shows the results of Experiment 1. The maximum peak height Rp of the surface of the steel plate member was measured by surface roughness measurement using a laser microscope VK-X100 manufactured by Keyence Corporation.

[0035] [Table 1]

[0036] As shown in Table 1, the maximum peak height Rp of the untreated steel plate member was 12.2 μm. The angle at which the steel plate member in the stack of untreated steel plate members began to move was 35 degrees. The maximum peak height Rp of the surface-treated steel plate member was 16.5 μm. The angle at which the steel plate member in the stack of surface-treated steel plate members began to move was 48 degrees.

[0037] From the results of Experiment 1 above, the inventors have found that a stack made of steel plate members whose surfaces have been roughened by surface treatment is less prone to skidding than a stack made of steel plate members whose surfaces have not been treated.

[0038] (Experiment 2: Transformer noise and iron loss) In Experiment 2, the noise and iron loss of a transformer equipped with a laminated core were measured. First, a laminated core was assembled using steel plate members under conditions 1 to 4 shown in Table 2. These steel plate members included a first steel plate member included in the yoke section and a second steel plate member included in the legs. As in Experiment 1, the surface treatment involved immersion in a 1 mol / L sodium hydroxide aqueous solution for two minutes. To assemble the laminated core, 70 layers of steel plate members under conditions 1 to 4 were stacked in a five-layer step-lap format consisting of pairs of sheets with a lap length of 2 mm.

[0039] [Table 2]

[0040] In Condition 1, no surface treatment was performed on any of the steel plate members, i.e., the first steel plate member and the second steel plate member. In other words, all of the steel plate members were surface untreated.

[0041] In condition 2, the surface treatment was carried out on all the steel plate members, that is, the first steel plate members and the second steel plate members.

[0042] In condition 3, the first steel plate member included in the yoke portion was subjected to surface treatment, but the second steel plate member included in the leg portion was not subjected to surface treatment.

[0043] In condition 4, the second steel plate member included in the leg portion was subjected to surface treatment, but the first steel plate member included in the yoke portion was not subjected to surface treatment.

[0044] The sizes of the steel plate members under conditions 1 to 4 were as shown in Table 3. Height a is the height of the laminated core, as shown in Figure 2. Width b is the width of the laminated core, as shown in Figure 2. Length c is the height of the gap between the two legs, as shown in Figure 2. Spacing d is the spacing between the two legs, as shown in Figure 2. Length e is the length of the second steel plate member at the center. Angle f is the angle at which the joint is inclined with respect to the extension direction of the first steel plate member. Thickness is the thickness of the steel plate. In other words, for the steel plate members under conditions 1 to 4, height a was 500 mm, width b was 500 mm, length c was 300 mm, spacing d was 100 mm, length e was 400 mm, angle f was 45 degrees, and thickness was 0.23 mm.

[0045] [Table 3]

[0046] After assembling the laminated core, backing plates were placed on the front and back of the yoke, and clamps were used to apply a uniform pressure of 0.2 [MPa] from above. The legs were fixed in place by wrapping glass tape around them so as not to interfere with winding the coil around them. A 50-turn primary coil and a secondary coil were wound around each of the three legs, creating a laminated core for a three-phase, three-limbed transformer. Three-phase excitation was performed on this laminated core at a frequency of 50 [Hz] and a maximum excitation magnetic flux density of 1.7 [T], and the noise and iron loss of the transformer were measured.

[0047] The noise of the transformer was measured at eight equally spaced locations surrounding the laminated core. These eight locations were located at half the height of the laminated core and 30 cm from the surface of the laminated core. The average value of these eight locations was taken as the noise of the transformer.

[0048] In measuring the iron loss of a transformer, the primary current and secondary voltage during three-phase excitation were measured with a wattmeter to calculate the no-load loss.The no-load loss was then divided by the weight of the laminated iron core to calculate (measure) the iron loss of the transformer.

[0049] Table 4 shows the results of Experiment 2. As in Experiment 1, the maximum peak height Rp of the surface of the steel plate member was measured by surface roughness measurement using a laser microscope VK-X100 manufactured by Keyence Corporation.

[0050] [Table 4]

[0051] Under condition 1, the maximum peak height Rp of the surface of the first copper plate member was 12.4 μm. The maximum peak height Rp of the surface of the second steel plate member was 12.2 μm. The noise of the transformer was 62.2 dBA. The iron loss of the transformer was 1.02 W / kg.

[0052] Under condition 2, the maximum peak height Rp of the surface of the first steel plate member was 16.7 μm. The maximum peak height Rp of the surface of the second steel plate member was 16.5 μm. The noise of the transformer was 57.3 dBA. The iron loss of the transformer was 1.10 W / kg.

[0053] Under condition 3, the maximum peak height Rp of the surface of the first steel plate member was 16.5 μm. The maximum peak height Rp of the surface of the second steel plate member was 12.2 μm. The noise of the transformer was 62.0 dBA. The iron loss of the transformer was 1.11 W / kg.

[0054] Under condition 4, the maximum peak height Rp of the surface of the first steel plate member was 12.3 μm. The maximum peak height Rp of the surface of the second steel plate member was 16.8 μm. The noise of the transformer was 57.5 dBA. The iron loss of the transformer was 1.01 W / kg.

[0055] Under conditions 2 to 4, the noise of the transformer was reduced more than under condition 1. This result shows that it is possible to reduce the noise of the transformer by increasing the maximum peak height Rp of the surface of the steel plate member. However, under condition 3, the degree of reduction in the noise of the transformer was smaller than under condition 1. The reason for this is that, by tightening the yoke portion, the multiple steel plates in the laminated core are less likely to slip sideways, even if the maximum peak height Rp of the first steel plate member included in the yoke portion is not increased.

[0056] Under conditions 2 and 3, the iron loss of the transformer was greater than under condition 1. From this result, it can be seen that from the viewpoint of iron loss of the transformer, it is better not to increase the maximum peak height Rp of the first steel plate member included in the yoke portion.

[0057] From the results of Experiment 2 above, the inventors have discovered that when the ratio of the maximum peak height Rp on the surface of the second steel plate member to the maximum peak height Rp on the surface of the first steel plate member exceeds 1, it is possible to reduce the noise of the transformer while suppressing an increase in iron loss in the transformer.

[0058] (Experiment 3: Transformer noise and iron loss) In Experiment 3, the optimum ratio of the maximum peak height Rp of the second steel plate member to the maximum peak height Rp of the first steel plate member was evaluated. In Experiment 3, the noise and iron loss of the transformer were measured while varying the maximum peak heights Rp of the first and second steel plate members. The dimensions of the steel plate members used in the laminated core were as shown in Table 5. Specifically, the height a was 700 mm, the width b was 700 mm, the length c was 420 mm, the spacing d was 140 mm, the length e was 560 mm, the angle f was 45 degrees, and the thickness was 0.23 mm. The laminated core was assembled using 70 layers of steel plate members with the dimensions shown in Table 5, stacked in a 10-layer step-lap format with a lap length of 2 mm, consisting of two pairs of sheets. After assembly, a 50-turn primary coil and a secondary coil were wound around each of the three legs to form a laminated core for a three-phase, three-limbed transformer. This laminated core was subjected to three-phase excitation at a frequency of 50 [Hz] and a maximum excitation magnetic flux density of 1.7 [T], and the noise and iron loss of the transformer were measured.

[0059] [Table 5]

[0060] Table 6 shows the results of Experiment 3. As in Experiment 1, the maximum peak heights Rp of the surfaces of the first steel plate member and the second steel plate member were measured by surface roughness measurement using a laser microscope VK-X100 manufactured by Keyence Corporation.

[0061] [Table 6]

[0062] In Nos. 1 to 15, the maximum peak height Rp of the surface of the first steel plate member was 12.2 μm. Of Nos. 1 to 15, No. 1 is a comparative example, and Nos. 2 to 15 are working examples. In Nos. 2 to 4 (working examples), the change in the ratio of the maximum peak height Rp was small compared to No. 1 (comparative example). Therefore, in this experiment, Nos. 2 to 4 (working examples) did not show any significant improvement in suppressing the increase in iron loss and reducing noise in the transformer. However, in Nos. 5 to 15 (working examples), in which the ratio of the maximum peak height Rp of the surface of the second steel plate member to the maximum peak height Rp of the surface of the first steel plate member was 1.15 or more, significant improvement in suppressing the increase in iron loss and reducing noise in the transformer was seen compared to No. 1 (comparative example). In particular, good results were obtained in Nos. 5 to 11 (Examples), where the ratio of the maximum peak height Rp on the surface of the second steel plate member to the maximum peak height Rp on the surface of the first steel plate member was 1.15 or more and 1.45 or less. The reason why the results of Nos. 12 to 15, where the ratio of the maximum peak height Rp was 1.45 or more, were worse than the results of Nos. 5 to 11 is thought to be because the surface of the second steel plate member was roughened by the surface treatment. In other words, in Nos. 12 to 15, the surface of the second steel plate member was roughened by the surface treatment, which is thought to have reduced the contact area between the second steel plate members rather than increasing the friction force between them.

[0063] In Nos. 16 to 34, the maximum peak height Rp of the surface of the first steel plate member was 13.8 μm. Among Nos. 16 to 34, Nos. 16 to 19 are comparative examples, and Nos. 20 to 34 are working examples. In Nos. 20 to 23 (working examples), the change in the ratio of the maximum peak height Rp was small compared to No. 16 (comparative example). Therefore, in Experiment 3, Nos. 20 to 23 (working examples) did not show any significant improvement in suppressing the increase in iron loss and reducing noise in the transformer. However, in Nos. 24 to 34 (working examples), in which the ratio of the maximum peak height Rp of the surface of the second steel plate member to the maximum peak height Rp of the surface of the first steel plate member was 1.15 or more, significant improvement in suppressing the increase in iron loss and reducing noise in the transformer was seen compared to No. 16 and other comparative examples. In particular, good results were obtained in Nos. 24 to 32 (Examples), in which the ratio of the maximum peak height Rp of the surface of the second steel plate member to the maximum peak height Rp of the surface of the first steel plate member was 1.15 or more and 1.45 or less. The reason why the results of Nos. 33 to 34, in which the ratio of the maximum peak height Rp was 1.45 or more, were worse than the results of Nos. 24 to 32 is thought to be because, as described above, the surface of the second steel plate member was roughened by the surface treatment.

[0064] In Nos. 35 to 45, the maximum peak heights Rp of the first steel plate member and the second steel plate member were increased while maintaining the ratio of the maximum peak height Rp of the surface of the second steel plate member to the maximum peak height Rp of the surface of the first steel plate member at approximately 1. Among Nos. 35 to 45, Nos. 36 to 45 are comparative examples, and No. 35 is an example. The results of Nos. 35 to 45 show that when the ratio is approximately 1, no significant improvement is seen in suppressing the increase in iron loss of the transformer and reducing noise.

[0065] (Laminated core manufacturing method) A method for manufacturing a laminated iron core will be described. First, a grain-oriented electrical steel sheet to which an insulating coating has been applied after finish annealing is prepared. Next, a first steel sheet member and a second steel sheet member are formed from the grain-oriented electrical steel sheet to which an insulating coating has been applied after finish annealing. After the second steel sheet member is formed, a surface treatment is performed on the second steel sheet member. The surface treatment is a process for increasing the maximum peak height Rp of the second steel sheet member. Examples of surface treatments include chemical polishing, shot blasting, and emery polishing. On the other hand, the first steel sheet member is not surface-treated. For example, the second steel sheet member may be surface-treated so that the ratio of the maximum peak height Rp of the second steel sheet member to the maximum peak height Rp of the surface of the first steel sheet member is 1.15 or more and 1.45 or less. By performing the surface treatment on the second steel sheet member without performing the surface treatment on the first steel sheet member, the manufacturing cost of the laminated iron core can be reduced. However, the grain-oriented electrical steel sheet may be surface-treated before being formed into the second steel sheet member.

[0066] Other processes included in the manufacturing method of the laminated core may be known processes.

[0067] Although the embodiments according to the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications or alterations based on the present disclosure, and therefore, it should be noted that these modifications and alterations are included within the scope of the present disclosure. [Explanation of symbols]

[0068] 1 Laminated core 10 steel plate 11, 12 First steel plate member 11A, 11B, 11E, 12C, 12D, 12F joint 13, 14, 15 Second steel plate member 13A,13D,14E,14F,15B,15C joint 2, 2A, 2B Yoke section 3,3A,3B,3C Legs

Claims

1. A laminated core in which a plurality of steel plates are laminated without adhesive, the laminated core comprising a yoke portion and a leg portion, The steel plate includes a first steel plate member included in the yoke portion and a second steel plate member included in the leg portion, and the first steel plate member and the second steel plate member are butted together without an adhesive, A laminated core, wherein the ratio of the maximum peak height Rp of the surface of the second steel plate member to the maximum peak height Rp of the surface of the first steel plate member exceeds 1.

2. 2. The laminated core according to claim 1, wherein a ratio of a maximum peak height Rp of the surface of the second steel plate member to a maximum peak height Rp of the surface of the first steel plate member is 1.15 or more.

3. 2. The laminated core according to claim 1, wherein a ratio of the maximum peak height Rp of the surface of the second steel plate member to the maximum peak height Rp of the surface of the first steel plate member is 1.15 or more and 1.45 or less.

4. A method for manufacturing a laminated iron core according to any one of claims 1 to 3, wherein chemical polishing, shot blasting or emery polishing is performed on the second steel plate member or only on the steel plate before forming the second steel plate member, in order to obtain the maximum peak height Rp on the surface of the second steel plate member.

5. A transformer comprising the laminated core according to any one of claims 1 to 3.

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