Wound core and its manufacturing method

Abstract

The wound core 10 is formed in a wound shape by stacking folded steel plates, and in a side view of the wound shape from a direction along the surface of the steel plates, the wound core 10 has four flat portions 4 and four corner portions 3 adjacent to the flat portions 4, thereby forming a rectangular shape with a hollow portion 15 in the center, and each layer of steel plates has at least one joint 6 where the ends in the winding direction are butted together, and a gap exists between the opposing ends of the steel plates at the joint 6 of each layer of steel plates, and in a cross section perpendicular to the surface of the steel plates and along the winding direction, a tensile stress of 10 MPa or more is introduced in the thickness direction of the steel plates at one or more locations in a specified region that is defined in accordance with the positional relationship between the gap of a steel plate and the gap of a steel plate stacked adjacent to the given steel plate.

Description

[Technical field]

[0001] The present invention relates to a wound core and a method for manufacturing the same. [Background technology]

[0002] It is known that in a wound core produced by bending a steel sheet without annealing it, iron loss can be reduced by introducing closure domains at the joints (for example, Patent Document 1).

[0003] Also, a low-core-loss grain-oriented electrical steel sheet is known in which the local stress state inside the steel sheet is controlled to an appropriate condition (Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2022-78444 [Patent Document 2] JP 2008-127632 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, with the technology described in Patent Document 1, it is difficult to control the size of the extremely fine closure domains, and the size of the closure domains varies, so the effect is not complete. Also, the technology described in Patent Document 2 does not take into account the influence of the joints between the steel sheets in the wound core, so there is room for improvement.

[0006] In view of the above problems, an object of the present disclosure is to provide a wound core and a manufacturing method thereof that can appropriately control the local stress state inside the steel sheets formed in the vicinity of a joint and reduce iron loss. [Means for solving the problem]

[0007] The gist of the present disclosure is as follows.

[0008] (1) A wound core having a wound shape formed by laminating folded steel plates, The wound core has four flat portions and four corner portions adjacent to the flat portions in a side view of the wound shape seen from a direction along the surface of the steel plate, It is formed in a rectangular shape with a hollow part in the center, Each of the steel plates has at least one joint where ends in the winding direction are butted together, A gap exists between the opposing ends of the steel plates at the joint of each steel plate, In a cross section perpendicular to the surface of the steel plate and along the winding direction, At least one A wound core in which a tensile stress of 10 MPa or more is introduced in the thickness direction of a steel plate at one or more locations in a specified region defined according to the positional relationship between the gap in a steel plate and the gap in a steel plate stacked adjacent to the steel plate.

[0009] (2) A wound core as described in (1) above, in which the joints of the steel plates of each layer are arranged on the planar portion, and the joints of the steel plates of each layer are arranged with a periodic shift in the extending direction of the planar portion.

[0010] (3) A wound core according to (1) or (2) above, in which, in a wound core in which steel plates are laminated, the number of steel plates into which the tensile stress in the plate thickness direction is introduced within the specified region is defined as SM, and the total number of laminated steel plates is defined as Stot, such that SM / Stot is 1% or more.

[0011] (4) A wound core according to any one of (1) to (3) above, in which, in a wound core in which steel sheets are laminated, PM / Ptot is 0.1% or more, where PM is the area of ​​the region in which the tensile stress in the sheet thickness direction is introduced within the specified region, and Ptot is the total area of ​​the specified region.

[0012] (5) A wound core according to any one of (1) to (4) above, wherein the maximum value of the tensile stress is equal to or less than the yield stress of the steel plate.

[0013] (6) A wound core according to any one of (1) to (5) above, characterized in that in the cross section perpendicular to the surface of the steel plate and along the winding direction, the region into which the tensile stress is introduced has a width in the winding direction of one such region of 1.4 mm or less.

[0014] (7) A wound core according to any one of (1) to (6) above, characterized in that in the cross section perpendicular to the surface of the steel plate and along the winding direction, the region to which the tensile stress is introduced has a length in the plate thickness direction of one such region that is 0.2 to 1 times the plate thickness.

[0015] (8) A wound core according to any one of (1) to (7) above, wherein in the cross section perpendicular to the plane of the steel plate and along the winding direction, the distance between adjacent regions to which the tensile stress is introduced in the winding direction is 2 mm or more and 10 mm or less.

[0016] (9) A wound core according to any one of (1) to (8) above, characterized in that in the region into which the tensile stress is introduced, a point at which the tensile stress is maximum is present at a depth of more than 10 μm from the surface of the raw steel sheet.

[0017] (10) A wound core according to any one of (1) to (9) above, wherein the region into which the tensile stress is introduced extends continuously or at predetermined intervals in a direction intersecting the winding direction of the steel plate and is provided so as to traverse the winding direction.

[0018] (11) The winding direction is the {110} direction of the steel plate. <001> The wound core according to any one of (1) to (10) above, wherein the winding direction coincides with the winding direction.

[0019] (12) A wound core according to any one of (1) to (11) above, wherein the winding direction coincides with the rolling direction of the steel sheet.

[0020] (13) A wound core according to any one of (1) to (12) above, in which the tensile stress is introduced only to the predetermined region in the cross section perpendicular to the surface of the steel plate and along the winding direction.

[0021] (14) A method for manufacturing a wound core according to any one of (1) to (13) above, A step of bending the steel plate; cutting the steel plate; A step of stacking the bent and cut steel plates in layers and assembling them in a wound shape by butting ends in the winding direction together; Introducing a tensile stress in a thickness direction near the end or near a position that will become the end before cutting; A method for manufacturing a wound core comprising the steps of: Effect of the Invention

[0022] According to the present disclosure, there is provided a wound core and a manufacturing method thereof that are capable of appropriately controlling the local stress state inside the steel sheets formed in the vicinity of a joint and reducing iron loss. [Brief description of the drawings]

[0023] [Figure 1] FIG. 2 is a perspective view showing a schematic diagram of one embodiment of a wound core. [Diagram 2] FIG. 2 is a side view of the wound core shown in the embodiment of FIG. [Diagram 3] FIG. 4 is a side view showing a schematic diagram of another embodiment of a wound core. [Figure 4] FIG. 2 is a diagram showing a schematic diagram of an example of a bent portion (curved portion) of a grain-oriented electrical steel sheet. [Diagram 5] FIG. 2 is a diagram showing a schematic diagram of an example of one layer of grain-oriented electrical steel sheet in a wound core body. [Figure 6] FIG. 2 is a diagram showing a schematic diagram of an example of one layer of grain-oriented electrical steel sheet in a wound core body. [Figure 7A] 4 is a schematic diagram showing the detailed shape and arrangement of the joints in region A1 or region A2 in FIG. 2 or FIG. 3, and a region where a region where a tensile stress is introduced in the plate thickness direction is provided for a specific joint. FIG. [Figure 7B]FIG. 7B is a schematic diagram for explaining a region M where a region where a tensile stress is introduced in the plate thickness direction is provided for all the joints in FIG. 7A. [Figure 8A] FIG. 2 is a schematic diagram showing a cross section of a steel sheet, and is a diagram showing a state in which regions to which tensile stress has been introduced in the sheet thickness direction are provided periodically in the X-axis direction (winding direction). [Figure 8B] FIG. 2 is a perspective view of a steel plate, and is a diagram showing a schematic state in which a region where a tensile stress is introduced in the plate thickness direction is provided in a direction intersecting the winding direction (Y-axis direction perpendicular to the winding direction). [Figure 9A] FIG. 13 is a diagram for explaining the effect of providing a region in which tensile stress is introduced in the plate thickness direction. [Figure 9B] FIG. 13 is a diagram for explaining the effect of providing a region in which tensile stress is introduced in the plate thickness direction. [Figure 10] FIG. 1 is a schematic diagram of an apparatus for manufacturing a wound core in the form of a unicore; [Figure 11] FIG. 4 is a diagram for explaining detailed dimensions of a wound core. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, some embodiments of the present invention will be described with reference to the drawings. However, these descriptions are intended to merely exemplify preferred embodiments of the present invention, and are not intended to limit the present invention to such specific embodiments. In the following description, similar components are given the same reference numerals.

[0025] A wound core according to one embodiment of the present invention will be described in detail below. However, the present invention is not limited to the configuration disclosed in this embodiment, and various modifications are possible without departing from the spirit of the present invention. The numerical ranges described below include lower and upper limits. Values ​​indicated as "greater than" or "less than" are not included in the numerical range. Furthermore, "%" in relation to chemical composition means "mass %" unless otherwise specified.

[0026] In addition, terms used in this specification that specify shapes or geometric conditions and their degrees, such as "parallel," "vertical," "same," and "right angle," as well as values ​​of length and angle, are not to be bound by strict meanings but are to be interpreted to include a range within which similar functions can be expected.

[0027] In addition, in this specification, a "grain-oriented electrical steel sheet" may be simply referred to as a "steel sheet" or an "electrical steel sheet", and a "wound core" may be simply referred to as a "wound core body" or simply as an "iron core".

[0028] A wound core according to an embodiment of the present invention is a wound core formed by laminating folded steel sheets, and has a structure formed into a rectangular shape having a hollow portion at the center by having four flat portions and four corner portions adjacent to the flat portions in a side view of the wound shape seen from a direction along the surface of the steel sheets. Here, the flat portions refer to straight line portions other than the bent portions. The inner surface side curvature radius r in a side view of the bent portions is, for example, 1.0 mm or more and 5.0 mm or less. As an example, the grain-oriented electrical steel sheet has a chemical composition containing, by mass%, 2.0 to 7.0% Si, with the balance being Fe and impurities, and has a texture oriented in the Goss orientation. As the grain-oriented electrical steel sheet, for example, a grain-oriented electrical steel strip described in JIS C 2553:2019 can be used.

[0029] Next, the shapes of the wound core and grain-oriented electromagnetic steel sheet according to one embodiment of the present invention will be specifically described. The shapes of the wound core and grain-oriented electromagnetic steel sheet described here are not particularly new, but merely conform to the shapes of known wound cores and grain-oriented electromagnetic steel sheets.

[0030] Fig. 1 is a perspective view showing a schematic diagram of an embodiment of a wound core. Fig. 2 is a side view of the wound core shown in the embodiment of Fig. 1, showing a side view of the wound core. Fig. 3 is a side view showing a schematic diagram of another embodiment of the wound core.

[0031] Note that the side view refers to the winding shape of the wound core viewed from a direction along the surface of the steel sheet, and more specifically refers to the winding shape of the wound core viewed from the axial direction of the windings of the wound core (perpendicular to the plane of the paper in FIG. 2). In other words, the side view refers to a view in the width direction (the Y-axis direction in FIG. 1) of the long grain-oriented electrical steel sheets that make up the wound core. The side view is a diagram that shows the shape as seen from the side (a diagram in the Y-axis direction in FIG. 1).

[0032] A wound core 10 according to an embodiment of the present invention comprises a wound core body having a substantially polygonal shape in side view. The wound core body 10 has a laminated structure in which grain-oriented electromagnetic steel sheets 1 are stacked in the sheet thickness direction and have a substantially rectangular shape in side view. The wound core body 10 may be used as a wound core as is, or may be provided with a known fastener such as a cable tie in order to integrally fasten the stacked grain-oriented electromagnetic steel sheets, as necessary.

[0033] In this embodiment, there is no particular restriction on the core length of the wound core body 10. If the number of bent portions 5 is the same, even if the core length of the wound core 10 changes, the volume of the bent portions 5 is constant, so the iron loss generated at the bent portions 5 is constant. The longer the core length, the smaller the volume ratio of the bent portions 5 to the wound core body 10, and the smaller the impact on iron loss degradation. Therefore, the longer the core length of the wound core body 10, the better. The core length of the wound core body 10 is preferably 1.5 m or more, and more preferably 1.7 m or more. In the present invention, the core length of the wound core body 10 refers to the circumferential length at the center point of the wound core body 10 in the lamination direction when viewed from the side. Such a wound core can be suitably used for any of the conventionally known applications.

[0034] The iron core according to the present embodiment is characterized by being substantially polygonal in side view. In the following explanation using the figures, in order to simplify the illustration and explanation, a generally used substantially rectangular (quadrilateral) iron core will be described, but various shapes of iron cores can be manufactured depending on the angle and number of bent portions 5 and the length of the flat portions. For example, if the angle of all bent portions 5 is 45° and the length of the flat portions 4 is the same, the side view will be octagonal. Also, if there are six bent portions 5 with an angle of 60° and the length of the flat portions 4 is the same, the side view will be hexagonal.

[0035] As shown in FIG. 1 and FIG. 2, the wound core body 10 includes a portion in which grain-oriented electromagnetic steel sheets 1, in which flat portions 4, 4a and bent portions 5 are alternately arranged in the longitudinal direction, are stacked in the sheet thickness direction, and has a laminated structure 2 having a substantially rectangular shape in a side view and a hollow portion 15. The corner portion 3 including the bent portions 5 has two or more bent portions 5 having a curved shape in a side view, and the sum of the bending angles of the bent portions 5 present in one corner portion 3 is, for example, 90°. The corner portion 3 has a flat portion 4a between adjacent bent portions 5, 5 that is shorter than the flat portion 4. Therefore, the corner portion 3 has two or more bent portions 5 and one or more flat portions 4a. In the embodiment of FIG. 2, one bent portion 5 is 45°. In the embodiment of FIG. 3, one bent portion 5 is 30°.

[0036] As shown in these examples, the wound core of this embodiment can be configured with bent portions having various angles, but from the viewpoint of suppressing the occurrence of distortion due to deformation during processing and suppressing iron loss, the bending angle φ (φ1, φ2, φ3) of the bent portion 5 is preferably 60° or less, and more preferably 45° or less. The bending angle φ of the bent portions of one iron core can be configured arbitrarily. For example, φ1 = 60° and φ2 = 30° can be set. From the viewpoint of production efficiency, it is preferable that the bending angles (bending angles) are equal, and if the iron loss of the iron core created can be reduced by reducing the number of deformation points above a certain level, a combination of different angles may be used for processing. The design can be selected arbitrarily based on the points that are important in iron core processing.

[0037] The bent portion 5 will be described in more detail with reference to Fig. 4. Fig. 4 is a diagram showing a schematic example of a bent portion (curved portion) 5 of a grain-oriented electrical steel sheet 1. The bending angle of the bent portion 5 means an angle difference occurring between a straight portion on the rear side and a straight portion on the front side in the bending direction in the bent portion of the grain-oriented electrical steel sheet, and is expressed as an angle φ that is a supplementary angle of an angle formed by two imaginary lines Lb-elongation1 and Lb-elongation2 obtained by extending the straight portions that are the surfaces of the flat portions 4, 4a on both sides that sandwich the bent portion 5 on the outer surface of the grain-oriented electrical steel sheet 1. In this case, the points at which the extended straight lines depart from the steel sheet surface are the boundaries between the flat portions 4 and the bent portion 5 on the outer surface of the steel sheet, and in Fig. 4, these are points F and G.

[0038] Furthermore, straight lines perpendicular to the outer surface of the steel plate are extended from each of points F and G, and the intersections with the inner surface of the steel plate are points E and D. Points E and D are the boundaries between flat portion 4 and bent portion 5 on the inner surface of the steel plate.

[0039] In the present invention, the bent portion 5 is a portion of the grain-oriented electrical steel sheet 1 that is surrounded by the above-mentioned points D, E, F, and G in a side view of the grain-oriented electrical steel sheet 1. In Fig. 4, the steel sheet surface between points D and E, i.e., the inner surface of the bent portion 5, is shown as La, and the steel sheet surface between points F and G, i.e., the outer surface of the bent portion 5, is shown as Lb.

[0040] This figure also shows the inner surface radius of curvature r in a side view of the bent portion 5. The radius of curvature r of the bent portion 5 is obtained by approximating the above La with a circular arc passing through points E and D. The smaller the radius of curvature r, the sharper the curve of the curved portion of the bent portion 5, and the larger the radius of curvature r, the gentler the curve of the curved portion of the bent portion 5.

[0041] In the wound core of the present invention, the radius of curvature r at each bent portion 5 of each grain-oriented electrical steel sheet 1 laminated in the sheet thickness direction may have a certain degree of variation. This variation may be due to forming accuracy, and may also occur unintentionally due to handling during lamination. Such unintentional errors can be suppressed to about 0.2 mm or less in current normal industrial manufacturing. If such variation is large, a representative value can be obtained by measuring the radius of curvature for a sufficiently large number of steel sheets and averaging them. It is also possible to intentionally change the radius of curvature for some reason, but the present invention does not exclude such a form. The radius of curvature r of the bent portion 5 (the radius of curvature on the inner side in a side view of the bent portion 5) is preferably 1 mm or more and 5 mm or less. By setting the radius of curvature r to 1 mm or more and 5 mm or less, the building factor (BF) can be further suppressed.

[0042] There is no particular limitation on the method of measuring the radius of curvature r of the bent portion 5, and it can be measured, for example, by observing the bent portion 5 at 200x magnification using a commercially available microscope (Nikon ECLIPSE LV150). Specifically, the center of curvature A is determined from the observation results. For example, if the intersection point A is defined as the intersection point of line segments EF and DG extended inwardly on the opposite side to point B, the magnitude of the radius of curvature r corresponds to the length of line segment AC. Here, the intersection point C is defined as the intersection point on the circular arc DE on the inside of the bent portion of the steel plate when point A and point B are connected by a straight line.

[0043] Figures 5 and 6 are schematic diagrams showing an example of one layer of grain-oriented electromagnetic steel sheet 1 in a wound core body. The grain-oriented electromagnetic steel sheet 1 used in the example of Figures 5 and 6 is folded to realize a wound core in a unicore form, and has two or more bent parts 5 and a flat part 4, and forms a substantially polygonal ring in side view via joint parts 6 (gaps) that are end faces in the longitudinal direction of one or more grain-oriented electromagnetic steel sheets 1.

[0044] In this embodiment, it is sufficient that the wound core body 10 has a laminated structure that is generally polygonal in side view as a whole. As shown in the example of Fig. 5, one grain-oriented electromagnetic steel sheet may constitute one layer of the wound core body via one joint 6 (one grain-oriented electromagnetic steel sheet is connected via one joint 6 for each turn), or as shown in the example of Fig. 6, one grain-oriented electromagnetic steel sheet 1 constitutes approximately half the circumference of the wound core, and two grain-oriented electromagnetic steel sheets 1 constitute one layer of the wound core body via two joints 6 (two grain-oriented electromagnetic steel sheets 1 are connected to each other via two joints 6 for each turn).

[0045] The thickness of the grain-oriented electrical steel sheet 1 used in this embodiment is not particularly limited and may be appropriately selected depending on the application, etc., but is usually in the range of 0.15 mm to 0.35 mm, and preferably in the range of 0.18 mm to 0.27 mm.

[0046] In the example of Fig. 5, one joint 6 of one grain-oriented electromagnetic steel sheet that constitutes one layer of the wound core body is located in region A1 shown in Fig. 2 and Fig. 3. In the example of Fig. 6, two joints 6 of two grain-oriented electromagnetic steel sheets that constitute one layer of the wound core body are located in regions A1 and A2 shown in Fig. 2 and Fig. 3. Note that detailed shapes and arrangements of joints 6 in region A1 or region A2 are not shown in Fig. 2 and Fig. 3.

[0047] FIG. 7A is a schematic diagram for explaining the detailed shape and arrangement of the joints 6 in the region A1 or region A2 in FIG. 2 or FIG. 3, and the region where the region 12 where tensile stress is introduced in the sheet thickness direction is provided for a specific joint. FIG. 7A is a schematic diagram showing a cross section perpendicular to the surface of the steel sheet and along the winding direction. As shown in FIG. 7A, the positions of the respective joints 6 (gaps in the joints 6 are shown as 6(n-1), 6(n)..., etc. in FIG. 7A) of the grain-oriented electrical steel sheets 1 constituting each layer are shifted in the X-axis direction along which the planar portion 4 extends. In this way, the magnetic resistance in the wound core can be reduced and iron loss can be reduced compared to the case where the positions of the joints 6 of each layer are the same in the X-axis direction. FIG. 7A particularly shows a state in which the joints 6 are periodically shifted in the X-axis direction.

[0048] Furthermore, the wound core body 10 having the joints 6 is excellent in terms of productivity and ease of shape design. On the other hand, the presence of the joints 6 means that the steel sheets are cut at the joints 6, which can be a factor in increasing iron loss and noise.

[0049] The inventors have thoroughly studied the effect of the stress state inside the steel sheet on the core characteristics, and have found that controlling the tensile stress in the thickness direction of the steel sheet is particularly effective in reducing the iron loss of a wound core having a joint 6. Based on this knowledge, in this embodiment, the stress state (strain distribution) inside the steel sheet is controlled in the vicinity of the joint 6 of the wound core. Although the mechanism itself is not completely clear at this point, the inventors' thorough studies have led to the hypothesis that the tensile stress in the thickness direction makes it easier for the magnetic flux passing through the steel sheet to bend in the thickness direction. Since the steel sheet is interrupted at the joint 6 of the wound core 10, the magnetic flux needs to pass through the gap at the joint 6. In this case, if a tensile stress in the thickness direction exists near the joint, the magnetic permeability in the direction along the tensile stress direction increases, and the magnetic flux is more likely to deviate from the in-plane direction (direction along the steel sheet surface) and leak out of the steel sheet surface. Therefore, the magnetic flux, which is prevented from proceeding in the in-plane direction by the gaps in the joints 6 in the in-plane direction, can be transferred smoothly to the adjacent steel sheets that are stacked and in contact with each other. In other words, it is considered that the transfer of magnetic flux to the adjacent steel sheets occurs smoothly. And, if the transfer is smooth, it is considered that the generation of loss is suppressed more than if the magnetic flux passes through the gaps in the joints 6. In the following explanation, the mechanism of action of the tensile stress in the thickness direction near the joints in the present invention will be explained on the premise of the above phenomenon (smooth transfer of magnetic flux), but it should be noted that this is merely one hypothesis at present to theoretically support the empirical law found by the inventors as a result of their intensive research. It is expected that the academically correct mechanism will be elucidated in the future.

[0050] In this embodiment, as shown in FIG. 7A, the grain-oriented electrical steel sheet 1 is provided with a continuous region 12 (hereinafter also referred to as stress region 12) in which a tensile stress of 10 MPa or more is introduced in the sheet thickness direction. The stress value inside the sheet thickness was obtained by measuring the distortion of the crystal lattice in three directions by X-ray diffraction, and using material physical properties such as elastic modulus, the stress values ​​in the rolling direction, sheet thickness direction, and sheet width direction were obtained. The crystal distortion in these three directions can be obtained by irradiating the steel sheet with X-rays, detecting and evaluating the reflected X-rays and the transmitted X-rays. Specifically, the steel sheet (test piece) is scanned while moving, and the shift amount of the diffraction angle (2θ) of the reflected X-ray diffraction peak is evaluated by the reflection method, so that the distortion in the sheet thickness direction is obtained. In addition, the distortion in the rolling direction and sheet width direction is obtained by evaluating the shift amount of the diffraction angle of the transmitted X-ray diffraction peak by the transmission method. The conversion from distortion to stress value can be performed by a relational expression between the stress and distortion in three directions according to the material physical properties (Young's modulus, Poisson's ratio). These techniques are well known, but for example, by using the technique described in Residual Stress Distribution Measurement by Strain Scanning Method Using High-Energy Synchrotron Radiation (Reference: Transactions of the Japan Society of Mechanical Engineers (Series A), Vol. 71, No. 711, 2005, pp. 1530), it is possible to obtain the stress value within the plate thickness as described above.

[0051] Basically, the stress regions 12 are provided near the joints 6 of the steel plates, and when focusing on any one void 6, it is preferable to determine the region in which the stress regions 12 should be located, including the multiple steel plates adjacent in the stacking direction. The region in which the stress regions 12 should be located (hereinafter also referred to as the stress location region) will be described in detail below.

[0052] First, the stress distribution region is set in a region that is at least twice the thickness of the steel plate from the end of the steel plate member in the in-plane direction of the wound core. The end of the steel plate member in the in-plane direction is generally formed by shear processing, and is therefore largely plastically deformed, and is highly likely to be in an unfavorable stress state for the stress region 12 intended by the present application. For this reason, the stress distribution region excludes such end regions. One of the end regions is the surface in the Y-axis direction in the wound core of FIG. 1, that is, the region from the surface when the wound core is viewed from the side to the inside of the steel plate (Y-axis direction) up to twice the thickness of the steel plate. The other is the region from the end of the steel plate that faces the joint 6 of the wound member with a gap formed therebetween to the inside of the steel material (X-axis direction in FIG. 6) up to twice the thickness of the steel plate. In order to directly observe the stress distribution region, it is necessary to remove the end region, and one of the methods for doing so is to remove the end region by a method that is less likely to cause distortion, such as electric discharge machining or edging by pickling.

[0053] The stress distribution region provided in the vicinity of the joint 6 will be described below. FIG. 7A is a schematic diagram of a cross section of the joint 6 of the wound core 10 along the XZ plane at a distance of at least twice the plate thickness from the end of the wound core 10 in the Y-axis direction toward the inside of the steel material. Here, the "cross section at a distance of at least twice the plate thickness toward the inside of the steel material" is intended to avoid the end region. As shown in FIG. 7A, in the n-th steel plate from the innermost side in the direction from the inside to the outside of the wound core body 10 (the lamination direction of the steel plates, or the Z-axis direction), the gap between the opposing steel plate ends of the joint 6 formed by cutting the steel plate is defined as 6(n). The position that is twice the plate thickness in the positive direction of the X-axis from the end of the gap 6(n) on the positive side of the X-axis is defined as position An, and the position that is twice the plate thickness in the negative direction of the X-axis from the end of the gap 6(n) on the negative side of the X-axis is defined as position Bn.

[0054] For this void 6(n), stress distribution areas M(n) are defined on both sides of the X-axis and Z-axis. The range in the Z-axis direction of the stress distribution area M(n) based on the void 6(n) is a range of three steel plates, including the (n-1)th steel plate, the nth steel plate, and the (n+1)th steel plate from the inside. However, in a steel plate where n=1, the n-1th steel plate does not exist, and in a steel plate where n=Nmax, where the total number of stacked sheets is Nmax, the n+1th steel plate does not exist. Since the stress distribution area M(n) is meaningless in the area where no steel plates exist, the range in the Z-axis direction of the stress distribution area M based on the void 6 between the two plates where n=1 and n=Nmax is the range of two steel plates.

[0055] The range of the stress placement area on the positive side of the X-axis with respect to the void 6(n) is the range from position An to position B, which is closer to position An, either position B(n-1) or position B(n+1) located on the positive side of the X-axis than position An. Similarly, the range of the stress placement area on the negative side of the X-axis with respect to the void 6(n) is the range from position Bn to position A, which is closer to position Bn, either position A(n-1) or position A(n+1) located on the negative side of the X-axis than position Bn. Here, if neither position B(n-1) nor position B(n+1) is located on the positive side of the X-axis than position An, the range of the stress placement area on the positive side of the X-axis is the same distance from position An as the range of the stress placement area on the negative side of the X-axis. In addition, if neither position A(n-1) nor position A(n+1) exists on the negative side of the X-axis from position Bn, the range of the stress placement area on the negative side of the X-axis is set to the same distance from position Bn as the range of the stress placement area on the positive side of the X-axis. Furthermore, if neither position B(n-1) nor position B(n+1) exists on the positive side of the X-axis from position An, and neither position A(n-1) nor position A(n+1) exists on the negative side of the X-axis from position Bn, it is assumed that there is no stress placement area based on gap 6(n). In addition, if there is no region between A(n) and either B(n-1) or B(n+1) because the positions of void 6(n) and void 6(n-1) or void 6(n+1) in the X-axis direction are close to each other (the position of B(n-1) or B(n+1) is located on the negative side of the X-axis from A(n)), it is assumed that there is no stress distribution region on the positive side of the X-axis based on void 6(n) for the three target plates. Similarly, if there is no region between B(n) and either A(n-1) or A(n+1), it is assumed that there is no stress distribution region on the negative side of the X-axis based on void 6(n). In FIG. 7A, the stress distribution regions M(n), M(n+3), and M(n+7) based on voids 6(n), 6(n+3), and 6(n+7) determined according to the above definition are shown with hatching. The region from the opposing steel plate ends forming a gap at joint 6 to twice the plate thickness in the X-axis direction is the end region described above and is excluded from the stress distribution region, so is not hatched.

[0056] When stress distribution regions M are set for the individual voids 6 as described above, there may be a situation where the stress distribution regions M partially overlap each other. FIG. 7B is a schematic diagram for explaining the region M where a region in which tensile stress is introduced in the plate thickness direction is provided for all the joints 6 in FIG. 7A. For example, when the voids 6 are periodically arranged in the X-axis direction as shown in FIG. 7B, the stress distribution region M(n) based on a specific void 6 (for example, void 6(n)) has a portion where the range in the X-axis direction is the same as that of the stress distribution region M(n+1) based on the void 6 (void 6(n+1) in FIG. 7B) of the steel plate adjacent in the Z-axis direction. In FIG. 7B, the region where the stress distribution regions M partially overlap each other is shown with cross-hatching.

[0057] FIG. 8A is a schematic diagram showing a cross section of a steel plate, and schematically shows a state where a plurality of stress regions 12 are provided in the X-axis direction (winding direction). The stress regions 12 may be provided at predetermined intervals in the X-axis direction in the cross section of the steel plate, in other words, the stress regions 12 may be provided periodically. Therefore, the stress regions 12 are arranged in the stress distribution region M, but may be arranged over the entire area of the steel plate other than the stress distribution region M.

[0058] In FIG. 8A, the width D (width in the winding direction) of the stress region 12 in the X-axis direction is preferably 1.4 mm or less. The width D is preferably 0.3 to 1.1 mm, more preferably 0.7 to 1.1 mm. The length L (width in the plate thickness direction) in the Z-axis direction is preferably 0.2*t ≤ L < t, where t is the plate thickness of the steel plate. The length L is more preferably 0.4*t ≤ L ≤ 0.8*t. When the width D is 1.4 mm or more, the position of the magnetic flux passage becomes wide and varies in the X-axis direction, so the iron loss increases. Also, if the length L in the Z-axis direction is too short, the effect of the magnetic flux passage cannot be enjoyed. Therefore, it is preferable that the width D and the length L are within the above ranges.

[0059] It is desirable that the maximum stress in the stress region 12 exists at a depth of more than 10 μm from the steel sheet surface. If it exists in an area shallower than 10 μm, the bending of the magnetic flux becomes steeper when it is transferred, resulting in an increase in the thin current loss and a decrease in the iron loss reduction effect. Therefore, the maximum stress in the stress region 12 exists at a depth of more than 10 μm from the steel sheet surface, preferably at 30 to 80 μm, and more preferably at 40 to 70 μm.

[0060] When the stress regions 12 are provided periodically at a predetermined interval in the X-axis direction, the interval between the stress regions 12 in the X-axis direction affects the magnetic domain refinement due to the interaction between adjacent stress regions 12, so if the interval is too large, the effect of reducing iron loss decreases. In order to sufficiently reduce iron loss, the interval between the stress regions 12 is preferably 10.0 mm or less, and more preferably 7.0 mm or less. It is preferable that the interval between the stress regions 12 is about 5 mm, but on the other hand, the stress regions 12 are also an obstacle to the magnetic flux in the in-plane direction of the steel sheet (magnetization direction), and if the interval is too narrow, it can cause an increase in iron loss, so the interval between the stress regions 12 in the X-axis direction is preferably 2 mm or more.

[0061] FIG. 8B is a perspective view of a steel sheet, and is a diagram showing a state where the stress region 12 is provided in a direction intersecting the winding direction (Y-axis direction perpendicular to the winding direction in FIG. 8B). As shown in FIG. 8B, the stress region 12 may extend in a direction intersecting the winding direction and be provided so as to cross the winding direction. The stress region 12 may be provided continuously in the direction intersecting the winding direction, or may be provided periodically at a predetermined interval. In order to make the transfer of magnetic flux in the vicinity of the joint smoother and to further suppress the reduction of iron loss, the stress region 12 preferably extends in a direction that forms an angle of 60 to 120° with respect to the X-axis direction in a field of view along the Z axis. More preferably, the stress region 12 extends in a direction that forms an angle of 80 to 110°.

[0062] In the present invention, the stress region 12 is defined as a continuous region in which the tensile stress in the plate thickness direction is 10 MPa or more. If the tensile stress in the plate thickness direction is less than 10 MPa, the effect of the magnetic permeability is small compared to the gap in the joint 6, so that the effect of providing the region 12 in which the tensile stress is introduced cannot be fully obtained.

[0063] In addition, in the stress region 12, the maximum value of the tensile stress in the plate thickness direction is preferably equal to or less than the yield stress of the steel plate, which is the material. If the maximum value of the tensile stress becomes large, the plastic region increases, and the decrease in magnetic permeability due to plastic strain becomes significant, resulting in an increase in iron loss. In general, the point at which the stress state changes significantly from the elastic region to the plastic region can be determined by the yield stress of the material.

[0064] For the above reasons, in this embodiment, the maximum value of the tensile stress in the plate thickness direction in the stress region 12 is preferably equal to or less than the yield stress value of the material, and more preferably, the maximum value of the tensile stress is 80 to 200 MPa.

[0065] 9A and 9B are diagrams for explaining the effect of providing the stress region 12. As mentioned above, it should be noted that the explanation of Fig. 9A and Fig. 9B is one possibility regarding the mechanism of action of the present invention. In Fig. 9A, the arrows indicate the flow of magnetic flux when the stress region 12 is provided.

[0066] On the other hand, in Fig. 9B, the arrows show the flow of magnetic flux when no stress region 12 is provided. As shown in Fig. 9B, the flow of magnetic flux from one steel sheet to an adjacent steel sheet is called "magnetic flux crossing". When no stress region 12 is provided, it is more difficult for magnetic flux to cross from one steel sheet to an adjacent steel sheet, and iron loss increases, compared to when stress region 12 is provided. As shown in Fig. 9A, by providing stress region 12, it becomes easier for magnetic flux to cross from one steel sheet to an adjacent steel sheet, and iron loss decreases.

[0067] In the present invention, the stress region 12 and the stress distribution region M are defined as described above. In the present invention, the effects of the invention are achieved by the stress region 12 being present within the stress distribution region M. In this case, it is not necessary for all of one stress region 12 to be present within the stress distribution region M, and the effects of the invention are achieved as long as even a part of one stress region 12 overlaps with the stress distribution region M. In addition, the effects of the invention are achieved as long as the stress region 12 and the stress distribution region M overlap even if only a part of the stacked steel plates. The degree of overlap of the above-mentioned regions is preferably 0.1% or more, where Ptot is the total area of ​​the stress distribution region M within the observation region and PM is the total area of ​​the stress regions 12 within the stress distribution region M when observing a region that is 1 / 2 the stacking thickness in the Z-axis direction and 1 / 2 the stacking thickness in the X-axis direction. If the ratio is less than 0.1%, the effects of the invention are not sufficient. It is preferably 2% or more, more preferably 5% or more. On the other hand, since the stress regions 12 are also obstacles to magnetic flux in the in-plane direction (magnetization direction) of the steel sheet, the presence of an excessive number of stress regions 12 in the stress distribution region M can cause iron loss deterioration. For this reason, it is preferable that PM / Ptot is 40% or less, and more preferably 30% or less.

[0068] In the present invention, the degree of this overlap is defined as the ratio of the number of steel plates SM in which a stress region 12 exists within the stress distribution region M to the total number of stacked steel plates Stot. A steel plate in which a stress region 12 exists within the stress distribution region M is a steel plate in which at least one stress region 12 exists within at least one stress distribution region M. In the present invention, SM / Stot is preferably 1% or more, and more preferably 2% or more. It is preferably 5% or more, and even more preferably 10% or more. Of course, it is preferable that all steel plates have stress regions 12 within the stress distribution region M, which is 100%.

[0069] Since the stress region 12 can be an obstacle to the magnetic flux in the in-plane direction of the steel sheet and can cause iron loss deterioration, the stress region 12 is provided only within the stress distribution region M, and the stress region 12 does not have to be provided outside the stress distribution region M. In other words, a tensile stress may be introduced only in the stress distribution region M.

[0070] The winding direction of the wound core may be the rolling direction of the steel sheet. <001> 7A, 7B, 8A, 8B, 9A, and 9B, the X-axis direction may be the rolling direction of the steel sheet, and the {110} <001> It may be a direction.

[0071] The method for producing the grain-oriented electrical steel sheet is not particularly limited, and a conventionally known method for producing the grain-oriented electrical steel sheet can be appropriately selected. A preferred specific example of the production method is, for example, a method in which a slab having 0.04 to 0.1 mass% C and the other chemical composition of the grain-oriented electrical steel sheet is heated to 1000°C or higher and hot-rolled, and then annealed as necessary, and then cold-rolled once or twice or more with intermediate annealing to obtain a cold-rolled steel sheet, and the cold-rolled steel sheet is heated to 700 to 900°C in a wet hydrogen-inert gas atmosphere to be decarburized and annealed as necessary, and then further nitriding annealed, and an annealing separator is applied, followed by finish annealing at about 1000°C, and an insulating coating is formed at about 900°C.

[0072] In addition, in this embodiment, a wound core composed of grain-oriented electromagnetic steel sheets 1 having the above-mentioned configuration is formed by stacking grain-oriented electromagnetic steel sheets 1 that have been individually bent and processed in layers and assembling them into a wound shape, and multiple grain-oriented electromagnetic steel sheets 1 are connected to each other via at least one joint 6 per turn.

[0073] In this embodiment, the method of introducing tensile stress in the sheet thickness direction into the sheet thickness of the grain-oriented electrical steel sheet is, for example, a method of irradiating with a laser or an electron beam, and by irradiating in a medium in which the viscosity (mPa s) of the aqueous solution is 2 to 8, vibration of the steel sheet caused by irradiation with the laser or electron beam is reduced, making it easier to obtain the desired stress distribution. If the viscosity exceeds 8, it becomes difficult to introduce stress. A method in which the viscosity is controlled by the concentration and temperature of the aqueous solution is preferable because the conditions can be adjusted appropriately. For example, a method using an aqueous ethanol solution with a concentration of 40 to 60% at a temperature of -10°C to 20°C is a preferred example.

[0074] Regarding the timing of introducing tensile stress into the steel sheet, the tensile stress may be introduced at the stage of coiling before the steel sheet is cut in the rolling direction, or at the stage of bending.

[0075] An apparatus that enables the manufacture of a wound core involving the above-described bending of steel sheets is shown generally in a block diagram in Fig. 10. Fig. 10 generally shows a manufacturing apparatus 70 for a wound core in the form of a unicore, and this manufacturing apparatus 70 is provided with a folding processing unit 71 that individually bends grain-oriented electromagnetic steel sheets 1, and may also be provided with an assembly unit 72 that stacks the folded grain-oriented electromagnetic steel sheets 1 in layers and assembles them into a wound shape to form a wound core including a portion where grain-oriented electromagnetic steel sheets 1, in which flat portions 4 and bent portions 5 are alternately continuous in the longitudinal direction, are stacked in the sheet thickness direction.

[0076] The grain-oriented electromagnetic steel sheet 1 is fed to the bending section 71 by being unwound at a predetermined conveying speed from a steel sheet supply section 75 that holds a hoop material formed by winding the grain-oriented electromagnetic steel sheet 1 in a roll shape. The grain-oriented electromagnetic steel sheet 1 thus fed is cut to an appropriate size in the bending section 71 and is subjected to a bending process in which the grain-oriented electromagnetic steel sheet 1 is individually folded in small batches, such as one sheet at a time.

[0077] The bending processing portion 71 includes a tensile stress introduction portion 71a. The tensile stress introduction portion 71a introduces a tensile stress to the grain-oriented electrical steel sheet 1 before cutting the grain-oriented electrical steel sheet 1 or during bending processing after cutting the grain-oriented electrical steel sheet 1 by the method described above.

[0078] When introducing tensile stress only into the stress distribution region M, the stress distribution region M in each grain-oriented electromagnetic steel sheet 1 is determined in the design based on the planned position of each grain-oriented electromagnetic steel sheet 1 when the grain-oriented electromagnetic steel sheets 1, each having alternating flat portions 4 and curved portions 5, are stacked in the sheet thickness direction. For this reason, it is possible to introduce tensile stress only into the stress distribution region M by irradiating a laser, electron beam, or the like onto the planned position that will become the stress distribution region M in the design of each grain-oriented electromagnetic steel sheet 1.

[0079] In the grain-oriented electrical steel sheet 1 thus obtained, the radius of curvature of the bent portion 5 caused by the bending process is extremely small, and therefore the processing strain imparted to the grain-oriented electrical steel sheet 1 by the bending process is extremely small. Thus, while it is expected that the density of the processing strain will be large, if the volume affected by the processing strain can be reduced, the annealing step can be omitted.

[0080] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present disclosure and exhibits similar effects is included in the technical scope of the present disclosure. EXAMPLES

[0081] The present disclosure will be specifically described below by way of examples. Note that the conditions in the examples are examples adopted to confirm the feasibility and effects of the present disclosure, and the present disclosure is not limited to the conditions in the examples. The present disclosure may adopt various conditions as long as it does not deviate from the gist of the disclosure and achieves its purpose.

[0082] In this example, a laser irradiation method is used as a method for introducing tensile stress into a steel sheet. First, a laser was irradiated onto the steel sheet in ethanol at a temperature of about 3°C ​​to 15°C to introduce tensile stress into the steel sheet. In addition, a laser was irradiated onto the steel sheet in air, in water at 24°C, and in ethanol at 24°C to introduce tensile stress into the steel sheet.

[0083] At this time, the beam diameter was set to 150 μm under all conditions, the output was appropriately adjusted, and the steel plate portion corresponding to the joint 6 was irradiated with the laser in advance.

[0084] The steel plates thus obtained, A, B, C, D, D-2, E, F, G, H, I, J, K, L, M, M-2, M-3, M-4, N, O, P, Q, R, S, T, U, V, W, Z, AA, BB, CC, CC-2, CC-3, CC-4, CC-5, CC-6, DD, EE, FF, and GG, are shown in Table 1 below.

[0085] [Table 1]

[0086] A wound core was then made from the steel plates shown in Table 1. Detailed dimensions of the wound core are shown in Fig. 11 and Table 2. Note that the lap length in Table 2 indicates the distance between two adjacent joints 6 in the X-axis direction (for example, the length from the end of gap 6(n) on the positive side of the X-axis to the end of gap 6(n-1) on the negative side of the X-axis shown in Fig. 7A). The number of steps is the number of steel plates by which joints 6 are periodically shifted in the X-axis direction ("6" in Fig. 7A).

[0087] [Table 2]

[0088] The iron loss of the wound core was evaluated, and the results are shown in Table 3 below.

[0089] [Table 3]

[0090] In the evaluation in Table 3, the iron loss at 50 Hz and magnetic flux density of 1.7 T was measured by the excitation current method. The iron loss ratio was low for test No. 8 to 55 in which a tensile stress of 10 MPa or more was introduced, and the iron loss ratio was high for test No. 1 to 7 in which a tensile stress of less than 10 MPa was introduced. As shown in Tables 1 and 3, the iron loss ratio was 1.14 or less for steel sheets B, C, D, D-2, E, F, G, H, I, J, K, L, M, M-2, M-3, M-4, N, O, P, Q, R, S, T, U, V, W, Z, AA, BB, CC, CC-2, CC-3, CC-4, CC-5, CC-6, DD, EE, FF, and GG in which a tensile stress of 10 MPa or more was introduced in the sheet thickness direction. On the other hand, the iron loss ratio of steel sheet A in which a tensile stress of 10 MPa or more was not introduced in the sheet thickness direction exceeded 1.14.

[0091] Furthermore, as shown in Table 3, the examples of the invention in which SM / Stot was 2% or more had a lower iron loss ratio than the examples of the invention in which SM / Stot was less than 2%, and the iron loss ratio decreased significantly as SM / Stot increased.

[0092] Furthermore, as shown in Table 3, the examples of the invention in which PM / Ptot was 0.1% or more had a lower iron loss ratio than the examples of the invention in which PM / Ptot was less than 0.1%, and the iron loss ratio decreased significantly as PM / Ptot increased. [Explanation of symbols]

[0093] 1 Grain-oriented electrical steel sheet 2 Laminated structure 3 Corner section 4,4a Flat part 5 Bend 6 Joint 10 Wound core 12 areas 15 Hollow part 70 Manufacturing equipment 71 Processing Department 71a Tensile stress introduction section 72 Assembly part 75 Steel plate supply section

Claims

1. A wound core having a wound shape formed by laminating folded steel plates, The wound core has four flat portions and four corner portions adjacent to the flat portions in a side view of the wound shape seen from a direction along the surface of the steel plate, It is formed in a rectangular shape with a hollow part in the center, Each layer of the steel plate has at least one joint where ends in the winding direction are butted together, A gap exists between the opposing ends of the steel plates at the joint of each steel plate, A wound core, in which a tensile stress of 10 MPa or more is introduced in the thickness direction of the steel plate at one or more locations in a predetermined region defined according to the positional relationship between the gap of at least one arbitrary steel plate and the gap of a steel plate stacked adjacent to the arbitrary steel plate in a cross section perpendicular to the surface of the steel plate and along the winding direction.

2. 2. The wound core according to claim 1, wherein the joints of the steel plates of each layer are arranged on the flat portion, and the joints of the steel plates of each layer are arranged to be periodically shifted in the extending direction of the flat portion.

3. 3. The wound core according to claim 1 or 2, wherein in a wound core in which steel sheets are laminated, SM is the number of steel sheets into which tensile stress in the sheet thickness direction is introduced within the specified region, and Stot is the total number of laminated sheets, and SM / Stot is 1% or more.

4. 3. The wound core according to claim 1, wherein in a wound core in which steel sheets are laminated, when an area of ​​a region in which the tensile stress in the sheet thickness direction is introduced within the specified region is PM and a total area of ​​the specified region is Ptot, PM / Ptot is 0.1% or more.

5. 3. The wound core according to claim 1, wherein the maximum value of the tensile stress is equal to or less than a yield stress of the steel plate.

6. 3. The wound core according to claim 1, wherein in the cross section perpendicular to the surface of the steel plate and along the winding direction, the region into which the tensile stress is introduced has a width in the winding direction of 1.4 mm or less.

7. 3. The wound core according to claim 1, wherein in the cross section perpendicular to the surface of the steel plate and along the winding direction, a length in the plate thickness direction of one of the regions to which the tensile stress is introduced is 0.2 to 1 times the plate thickness.

8. 3. The wound core according to claim 1, wherein in the cross section perpendicular to the surface of the steel plate and along the winding direction, a distance between adjacent regions to which the tensile stress is introduced in the winding direction is 2 mm or more and 10 mm or less.

9. 3. A wound core according to claim 1, wherein in the region where the tensile stress is introduced, a point where the tensile stress is maximum is present at a depth of more than 10 μm from the surface of the steel sheet material.

10. 3. The wound core according to claim 1, wherein the region to which the tensile stress is introduced extends continuously or at predetermined intervals in a direction intersecting the winding direction of the steel plate and is provided so as to traverse the winding direction.

11. 3. The wound core according to claim 1, wherein the winding direction coincides with the {110}<001> direction of the steel sheets.

12. 3. The wound core according to claim 1, wherein the winding direction coincides with the rolling direction of the steel sheet.

13. 3. The wound core according to claim 1, wherein the tensile stress is introduced only in the predetermined region in the cross section perpendicular to a surface of the steel plate and along the winding direction.

14. A method for manufacturing a wound core according to claim 1 or 2, comprising the steps of: A step of bending the steel plate; cutting the steel plate; stacking the bent and cut steel plates in layers and assembling them in a wound shape by butting ends of the steel plates in the winding direction together; Introducing a tensile stress in a thickness direction near the end or near a position that will become the end before cutting; A method for manufacturing a wound core comprising the steps of:

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