Wound iron core and method for manufacturing same

Abstract

A wound iron core 10 is formed by laminating bent steel plates. The wound iron core 10, in a side view of the winding shape as seen from a direction along the surface of the steel plates, is formed of a plurality of flat portions 4 and a plurality of bent portions 5 adjacent to the flat potions 4 so as to form a rectangular shape with a hollow at the center. In a cross section orthogonal to the surface of the steel plates and along the winding direction, when the region of the bent portion 5 of an arbitrary steel plate, excluding the flat portion 4 thereof, is defined as a twin crystal designated region, the twin crystal designated region has a plurality of deformation twins extending in different directions. In at least one twin crystal designated region, a ratio obtained by dividing the number of twin intersections, at which the deformation twins extending in different directions intersect, by the total number of the deformation twins is 0.500 to 3.000 inclusive.

Description

Wound core and its manufacturing method

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

[0002] It is known that in a wound core produced by bending a steel sheet, iron loss can be reduced by controlling the shape of the bent portion (Patent Document 1).

[0003] It is also known that when grain-oriented electrical steel sheets that constitute a wound core are bent, iron loss can be reduced by suppressing the occurrence of deformation twins during bending (Patent Document 2).Also, a wound core consisting of an inner core and an outer core is known in which the grain-oriented electrical steel sheet that forms the inner core has multiple curved bends that are formed with a metal structure that includes twins and are curved in side view (Patent Document 3).

[0004] Japanese Patent No. 7239089 International Publication No. 2018 / 131613 Japanese Patent Application Laid-Open No. 2017-157806

[0005] However, in the technique described in Patent Document 1, the passage of magnetic flux is significantly hindered at the bent portion where a large amount of plastic strain is introduced, and iron loss deterioration is unavoidable, leaving room for improvement.

[0006] Furthermore, the technology described in Patent Document 2 attempts to suppress iron loss by focusing on the number of deformation twins, but does not take into account the relative positions of the deformation twins, leaving room for improvement in iron loss.The technology described in Patent Document 3 also attempts to improve iron loss characteristics by focusing on twins, but does not take into account the relative positions of the twins, leaving room for improvement in iron loss.

[0007] In view of the above problems, an object of the present disclosure is to provide a wound core capable of reducing iron loss and a manufacturing method thereof.

[0008] The gist of the present disclosure is as follows.

[0009] (1) A wound core having a wound shape formed by stacking bent steel plates, wherein the wound core has, in a side view of the wound shape seen from a direction along the surfaces of the steel plates, a plurality of flat portions and a plurality of bent portions adjacent to the flat portions, thereby forming a rectangular shape with a hollow portion at the center; in a cross section perpendicular to the surfaces of the steel plates and along the winding direction, when the region of the bent portion excluding the flat portions of any steel plate is defined as a twin-defined region, the twin-defined region has a plurality of deformation twins extending in different directions; and in at least one of the twin-defined regions, the ratio obtained by dividing the number of twin intersections where deformation twins extending in different directions intersect by the total number of deformation twins is 0.500 or more and 3.000 or less.

[0010] (2) A wound core according to (1) above, wherein in the twin-defined region where the ratio is 0.500 or more and 3.000 or less, the number of twin intersections where deformation twins extending in different directions intersect is 5 or more and 150 or less.

[0011] (3) A wound core according to (1) or (2) above, wherein, in the twin-crystal-defined region where the ratio satisfies 0.500 or more and 3.000 or less, Nout / Nin > 1.00 is satisfied, where Nout is the number of twin intersections located on the outer side of the center line at the center of the thickness of the steel sheet at the bend and Nin is the number of twin intersections located on the inner side of the center line at the center of the thickness of the steel sheet at the bend.

[0012] (4) A wound core according to (1) or (2) above, wherein, in the twin-defined region where the ratio satisfies 0.500 or more and 3.000 or less, an average value of depth positions of the twin intersection points in the sheet thickness direction of the steel sheet is present in a range of t / 50 mm to t / 2 mm in the sheet thickness direction from the outermost layer outside the twin-defined region of the steel sheet, where t is the sheet thickness of the steel sheet.

[0013] (5) A wound core according to (1) or (2) above, wherein the ratio obtained by dividing the number of twin-defined regions in which the ratio is 0.500 or more and 3.00 or less by the total number of twin-defined regions in the steel sheets constituting the wound core is 0.02 or more.

[0014] (6) A wound core according to (1) or (2) above, wherein in the twin-prescribed region where the ratio is 0.500 or more and 3.000 or less, the ratio obtained by dividing the number of twin intersections by the thickness of the steel sheet is 5 or more and 400 or less.

[0015] (7) A wound core according to (1) or (2) above, wherein in at least one of the twin-defined regions, the ratio obtained by dividing the number of twin intersections where deformation twins extending in different directions intersect by the total number of deformation twins is 0.700 or more and 2.500 or less.

[0016] (8) A wound core according to (1) or (2) above, wherein in at least one of the twin-defined regions, the ratio obtained by dividing the number of twin intersections where deformation twins extending in different directions intersect by the total number of deformation twins is 1.000 or more and 2.300 or less.

[0017] (9) A method for manufacturing a wound core according to (1) or (2) above, comprising the steps of: skin-pass rolling a steel sheet; bending the skin-pass rolled steel sheet; cutting the steel sheet; and stacking the bent and cut steel sheets in layers and assembling them in a wound shape by butting together the ends in the winding direction.

[0018] According to the present disclosure, a wound core capable of reducing iron loss and a method for manufacturing the same are provided.

[0019] FIG. 1 is a perspective view schematically showing an embodiment of a wound core. FIG. 2 is a side view of the wound core shown in the embodiment of FIG. 1. FIG. 3 is a side view schematically showing another embodiment of the wound core. FIG. 4 is a diagram schematically showing an example of a bent portion (curved portion) of a grain-oriented electromagnetic steel sheet. FIG. 5 is a diagram schematically showing an example of a grain-oriented electromagnetic steel sheet for one layer in a wound core body. FIG. 6 is a diagram schematically showing an example of a grain-oriented electromagnetic steel sheet for one layer in a wound core body. FIG. 7 is a diagram showing one steel sheet in a bent portion, and is a diagram showing deformation twins and twin intersections in a cross section perpendicular to the surface of the steel sheet and along the winding direction. FIG. 8 is a diagram for explaining how magnetic flux leakage is suppressed by the intersections of deformation twins. FIG. 9 is a diagram for explaining deformation twins in a cross section perpendicular to the surface of the steel sheet and along the winding direction. FIG. 10 is a diagram schematically showing a manufacturing apparatus for a wound core in the form of an iron core. FIG. 11 is a diagram for explaining detailed dimensions of the wound core.

[0020] Hereinafter, several 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 will be designated by the same reference numerals.

[0021] 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. Note that the numerical ranges listed below include the lower and upper limits. Numerical values ​​indicated as "greater than" or "less than" do not include the numerical range. Furthermore, "%" in relation to chemical composition means "mass %" unless otherwise specified.

[0022] Furthermore, terms used in this specification that specify shapes, geometric conditions, and their degrees, such as "parallel," "vertical," "same," and "right angle," as well as values ​​of lengths and angles, are not to be construed as being bound by strict meanings, but rather as including a range within which similar functions can be expected.

[0023] Furthermore, 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 an "iron core."

[0024] A wound core according to one embodiment of the present invention is a wound core formed by stacking folded steel sheets. When viewed from the side of the wound core from a direction along the surface of the steel sheets, the wound core has a rectangular structure with a central hollow, including four flat portions and four corner portions adjacent to the flat portions. Here, the flat portions refer to straight portions other than the bent portions. The radius of curvature r on the inner surface side of the bent portion in side view is, for example, 1.0 mm or more and 5.0 mm or less. The grain-oriented electrical steel sheet, for example, has a chemical composition containing, by mass, 2.0 to 7.0% Si, with the remainder consisting of Fe and impurities, and has a texture oriented in the Goss orientation. For example, a grain-oriented electrical steel strip as defined in JIS C 2553:2019 can be used as the grain-oriented electrical steel sheet.

[0025] Next, the shapes of the wound core and grain-oriented electrical steel sheet according to one embodiment of the present invention will be specifically described. The shapes of the wound core and grain-oriented electrical steel sheet described here are not particularly new, but merely conform to the shapes of known wound cores and grain-oriented electrical steel sheets.

[0026] Fig. 1 is a perspective view schematically showing one 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 schematically showing another embodiment of the wound core.

[0027] 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 the 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 ).

[0028] A wound core 10 according to one embodiment of the present invention comprises a wound core body that is substantially polygonal in side view. The wound core body 10 has a laminated structure in which grain-oriented electromagnetic steel sheets 1 are stacked in the thickness direction, resulting in a substantially rectangular shape in side view. The wound core body 10 may be used as a wound core as is, or may be equipped with known fasteners such as cable ties to integrally fasten the stacked grain-oriented electromagnetic steel sheets, as needed.

[0029] In this embodiment, there is no particular limit to the core length of the wound core body 10. As long as the number of bends 5 is the same, even if the core length of the wound core 10 changes, the volume of the bends 5 remains constant, and therefore the iron loss generated at the bends 5 remains constant. A longer core length reduces the volume ratio of the bends 5 to the wound core body 10, and therefore reduces the impact on iron loss degradation. Therefore, a longer core length is preferable for the wound core body 10. 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 conventionally known application.

[0030] The iron core according to this embodiment is characterized by its substantially polygonal shape in side view. In the following explanation using figures, for simplicity of illustration and explanation, a generally-shaped substantially rectangular (quadrilateral) iron core will be described. However, iron cores of various shapes can be manufactured by changing the angle and number of bent portions 5 and the length of the flat portions 4. For example, if all bent portions 5 have an angle of 45° and the flat portions 4 are the same length, the iron core will be octagonal in side view. On the other hand, if there are six bent portions 5 with an angle of 60° and the flat portions 4 are the same length, the iron core will be hexagonal in side view.

[0031] As shown in FIGS. 1 and 2 , the wound core body 10 includes grain-oriented electrical steel sheets 1, each having alternating flat portions 4, 4 a and bent portions 5 in the longitudinal direction, stacked in the sheet thickness direction. The laminated structure 2 has a generally rectangular shape in side view, with a hollow portion 15. Each corner portion 3, including the bent portions 5, has two or more bent portions 5 that are curved in side view, and the sum of the bending angles of the bent portions 5 in one corner portion 3 is, for example, 90°. The corner portion 3 has a flat portion 4 a between adjacent bent portions 5, 5, which is shorter than the flat portion 4. Therefore, the corner portion 3 has two or more bent portions 5 and one or more flat portion 4 a. In the embodiment of FIG. 2 , one bent portion 5 is 45°. In the embodiment of FIG. 3 , one bent portion 5 is 30°.

[0032] As shown in these examples, the wound core of this embodiment can be configured with bent portions having various angles. However, from the viewpoint of suppressing distortion due to deformation during processing and thereby 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°. From the viewpoint of production efficiency, it is preferable that the bending angles (bending angles) are equal. However, if the iron loss of the iron core can be reduced by reducing the number of deformation points above a certain level, a combination of different angles may be used. The design can be selected arbitrarily based on the points that are important in iron core processing.

[0033] The bent portion 5 will be described in more detail with reference to FIG. 4 . FIG. 4 is a diagram schematically illustrating an example of a bent portion (curved portion) 5 of a grain-oriented electrical steel sheet 1. The bending angle of the bent portion 5 refers to the angular difference between the straight portion on the rear side and the straight portion on the front side in the bending direction at the bent portion of the grain-oriented electrical steel sheet, and is expressed as the angle φ, which is the supplementary 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 of the bent portion 5 on the outer surface of the grain-oriented electrical steel sheet 1. In this case, the points where the extended 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.

[0034] Furthermore, 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 respectively points E and D. These points E and D are the boundaries between the flat portion 4 and the bent portion 5 on the inner surface of the steel plate.

[0035] In the present invention, the bent portion 5 is a portion of the grain-oriented electrical steel sheet 1 that is surrounded by the 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.

[0036] This figure also shows the inner surface curvature radius r of the bent portion 5 in a side view. The curvature radius r of the bent portion 5 is obtained by approximating the above La with an arc passing through points E and D. The smaller the curvature radius r, the sharper the curve of the curved portion of the bent portion 5, and the larger the curvature radius r, the gentler the curve of the curved portion of the bent portion 5.

[0037] In the wound core of the present invention, the radius of curvature r of each bent portion 5 of each grain-oriented electrical steel sheet 1 stacked in the sheet thickness direction may vary to some extent. This variation may be due to forming accuracy, or it may be due to unintended variation caused by handling during stacking. Such unintended errors can be suppressed to approximately 0.2 mm or less in current, standard industrial manufacturing. If such variation is significant, a representative value can be obtained by measuring and averaging the radius of curvature for a sufficiently large number of steel sheets. It is also possible to intentionally vary the radius of curvature for some reason, but this is not excluded by the present invention. The radius of curvature r of the bent portion 5 (the inner radius of curvature of the bent portion 5 in a side view) 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.

[0038] There are no particular limitations on the method for measuring the radius of curvature r of the bent portion 5, and it can be measured, for example, by observing 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 point of intersection between line segments EF and DG extended inward on the opposite side from point B, then the magnitude of the radius of curvature r corresponds to the length of line segment AC. Here, when points A and B are connected by a straight line, the intersection point C on the arc DE on the inside of the bent portion of the steel plate is defined as the point of intersection.

[0039] 5 and 6 are diagrams schematically showing an example of one layer of grain-oriented electrical steel sheet 1 in a wound core body. The grain-oriented electrical steel sheet 1 used in the examples of Fig. 5 and Fig. 6 is laminated by being folded and overlapped, and has two or more bent portions 5 and a flat portion 4, and forms a substantially polygonal ring in side view via joints 6 (gaps) that are the longitudinal end faces of one or more grain-oriented electrical steel sheets 1. Among these substantially polygonal rings, those that have a specific bend angle or bent portion shape are sometimes called "unicores."

[0040] 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 per turn), or as shown in the example of Fig. 6, one grain-oriented electromagnetic steel sheet 1 may constitute approximately half the circumference of the wound core, and two grain-oriented electromagnetic steel sheets 1 may 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 per turn).

[0041] The thickness of the grain-oriented electrical steel sheet 1 used in this embodiment is not particularly limited and may be selected appropriately 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.

[0042] In the example of Fig. 5, one joint 6 of one grain-oriented electrical 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 electrical 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 omitted from Fig. 2 and Fig. 3.

[0043] The present inventors have found that the magnetic permeability decreases and the iron loss increases at the bent portion 5 formed during plastic deformation when the grain-oriented electrical steel sheet 1 is bent. When a cross section of the bent portion 5 perpendicular to the surface of the grain-oriented electrical steel sheet 1 and along the winding direction is observed using an optical microscope, stripes of deformation twins are observed extending from the surface of each steel sheet toward the interior (inside of the bend). The existence of deformation twins can be confirmed by, for example, analytical evaluation using a scanning electron microscope and crystal orientation analysis software (EBSD). Deformation twins are formed by deformation such that the arrangement of atoms is symmetrical with respect to the twin plane, and the twin plane and twin direction are determined by the metal. Grain-oriented electrical steel sheets are steel sheets in which the orientation of crystal grains in the steel sheet is highly concentrated in the {110}<001> orientation (hereinafter sometimes referred to as the Goss orientation). However, the crystal orientation in the region where deformation twins occur is different from the Goss orientation, and the deformation twins are, for example, along the {112}<111> orientation. In other words, the band-like structure of the deformation twins has a different crystal orientation from the crystal orientation of the base steel sheet that has not been plastically deformed.

[0044] As described in the aforementioned Patent Document 2, as the number of deformation twins increases, the magnetic properties deteriorate. While examining the data, the inventors noticed that there were cases where differences in iron loss were observed even when the number of deformation twins was almost the same. They then concluded that the differences were influenced by the frequency of twin intersections, where deformation twins intersect with each other.

[0045] 7A is a diagram showing one steel sheet in a bent portion 5, and is a schematic diagram showing deformation twins 12 and twin intersections P in a cross section perpendicular to the surface of the steel sheet and along the winding direction. As shown in FIG. 7A , the inventors have discovered that by applying a special processing method, deformation twins 12 extending in different directions are formed, and twin intersections P are generated where deformation twins 12 extending in different directions intersect with each other. The inventors have then found that iron loss can be effectively suppressed by adjusting the number of deformation twins 12 and the number of twin intersections P in the bent portion 5.

[0046] The reason why such deformation twin morphology (frequency of intersections) affects iron loss is unclear, but the following is thought to be the case. The bend 5 has low magnetic permeability due to the large amount of strain, allowing magnetic flux to leak outside the steel sheet through the area between adjacent deformation twins. When deformation twins intersect in the area where deformation twins are concentrated, the space between the deformation twins is blocked by the deformation twins. This may ultimately suppress magnetic flux leakage outside the steel sheet, thereby suppressing iron loss degradation. However, from the perspective of suppressing iron loss degradation, reducing the number of twins that occur is more effective. Therefore, the mechanism described here should be interpreted as the effect of twin intersections on magnetic properties when the number of twins is the same, especially when the number of twins is relatively large. In the following explanation, the mechanism of action of deformation twin intersections at the bend 5 in the present invention will be explained based on the above phenomenon (suppression of magnetic flux leakage). However, this is merely a hypothesis at this time to theoretically support the empirical rule discovered by the inventors as a result of extensive research. It is hoped that the academically correct mechanism will be elucidated in the future.

[0047] 7B is a diagram showing a steel sheet 1 in a bent portion 5, showing deformation twins 12 and twin intersections P in a cross section perpendicular to the surface of the steel sheet and along the winding direction, and is a schematic diagram for explaining how magnetic flux leakage is suppressed by the twin intersections P of the deformation twins 12. In FIG. 7B, the diagram shown in the left half shows a case where, similar to FIG. 7A, there is a twin intersection P where deformation twins 12 extending in different directions intersect. On the other hand, the diagram shown in the right half of FIG. 7B shows a case where only deformation twins 12 extending in the same direction exist, and there is no twin intersection P where deformation twins 12 intersect.

[0048] As shown in the left diagram of Fig. 7B , when twin intersections P are present, the twin intersections P are generated when deformation twins 12 extend in different directions and collide with each other, causing the deformation twins 12 to cross each other and acting as a barrier to magnetic flux. This suppresses leakage of magnetic flux to the outside of the steel sheet. On the other hand, as shown in the right diagram of Fig. 7B , if there are no twin intersections P and the deformation twins 12 extend in the same direction, it is thought that magnetic flux will pass through the deformation twins 12 and leak to the outside.

[0049] Based on the above findings, the inventors have thoroughly investigated the effect of the number of deformation twins 12 and twin intersections P in the bends 5 on iron loss, and have found that controlling the number of twin intersections P relative to the number of deformation twins 12 in the bends 5 is particularly effective in reducing iron loss in wound cores.

[0050] Specifically, the wound core discovered by the inventors has the following configuration. First, if we define a twin-defined region as the region of a bent portion 5 of any steel sheet, excluding the flat portion 4, in a cross section perpendicular to the surface of the steel sheet and along the winding direction, then there are multiple twin-defined regions for each stacked steel sheet. Specifically, there are as many twin-defined regions as there are bending processes. At least one of these multiple twin-defined regions has multiple deformation twins 12 extending in different directions, and the ratio obtained by dividing the number of twin intersections P where deformation twins extending in different directions intersect by the total number of deformation twins 12 is 0.500 or more and 3.000 or less. This ratio is preferably 0.700 or more and 2.500 or less, and more preferably 1.000 or more and 2.300 or less. The bent portion 5 is a portion of the grain-oriented electrical steel sheet 1 surrounded by points D, E, F, and G shown in FIG. 4 , excluding the flat portion 4, in a cross section perpendicular to the surface of the steel sheet and along the winding direction, and the twin-defined region is defined as the region surrounded by points D, E, F, and G.

[0051] In addition, at least one of the multiple twin-defining regions has multiple deformation twins 12 extending in different directions, and the lower limit of the ratio obtained by dividing the number of twin intersections P where deformation twins extending in different directions intersect by the total number of deformation twins 12 is 0.500, and the lower limit is 0.525, 0.550, 0.575, 0.600, 0.625, 0.650, 0.675, 0.700, 0.725, 0.750, Possible values ​​are 0.775, 0.800, 0.825, 0.850, 0.875, 0.900, 0.925, 0.950, 0.975, 1.000, 1.025, 1.050, 1.075, 1.100, 1.125, 1.150, 1.175, 1.200, 1.225, 1.250, 1.275, 1.300, 1.325, 1.375, 1.400, 1.425, 1.450, 1.475, and 1.500.

[0052] In addition, at least one of the twin defining regions has a plurality of deformation twins 12 extending in different directions, and the upper limit of the ratio obtained by dividing the number of twin intersections P where deformation twins extending in different directions intersect by the total number of deformation twins 12 is 3.000, and the upper limit is 2.975, 2.950, 2.925, 2.900, 2.875, 2.850, 2.825, 2.800, 2.7 Possible values ​​are 2.75, 2.750, 2.725, 2.700, 2.675, 2.650, 2.625, 2.600, 2.575, 2.550, 2.525, 2.500, 2.475, 2.450, 2.425, 2.300, 2.275, 2.250, 2.225, 2.200, 2.175, 2.150, 2.125, 2.100, 2.075, 2.050, 2.025, and 2.000.

[0053] Here, we will explain the form of deformation twins, the evaluation method, and the preparation of samples for cross-sectional observation. In cross-sectional observation of a steel sheet, deformation twins in the present invention are basically formed in a form that extends linearly for a finite length in a specific crystal orientation of the steel sheet. In the present invention, this linear region is defined as "one (single) deformation twin." When two deformation twins extend in different directions that are not parallel and have a considerable length, the deformation twins intersect, forming a twin intersection.

[0054] (Method for Evaluating Deformation Twins) A specific method for determining the number of deformation twins 12 present in the bent portion 5 is described below. Five cross sections, perpendicular to the surface of the grain-oriented electrical steel sheet 1 of the wound core 10 (the bent body) and along the winding direction, were photographed using an optical microscope: three cross sections at the center in the Y direction (A_1) and 5 mm inward from each end face on both sides in the Y direction (A_2, A_3), as well as a cross section at a midpoint between A_1 and A_2 in the Y direction (A_4) and a cross section at a midpoint between A_1 and A_3 (A_5). For one bent portion 5, the number of deformation twins in each field of view of the twin-defined region on each cross section was counted and averaged. This average value was defined as the number of deformation twins per twin-defined region. The deformation twins were formed within the thickness of the steel sheet. Similarly, the intersections of deformation twins are evaluated in each field of view of the twin-defined region of each cross section, and the average value is taken as the number per twin-defined region. In other words, in this embodiment, the "twin-defined region" may mean "the twin-defined regions of the cross section at the above five locations of one bend portion 5."

[0055] (Preparation of Samples for Cross-Section Observation) Here, a method for preparing a sample for cross-sectional observation of the bent portion 5 will be described using the wound core 10 according to the present disclosure as an example. Similar to general cross-sectional structure observation, the sample for cross-sectional observation of the bent portion 5 was prepared by embedding the resin at the five cross sections of the bent portion 5 at the aforementioned five locations and then cutting 1 mm before the drive-in position. Rough cutting was performed using a mechanical upper-blade precision cutter (Maruto Co., Ltd., Model: MC-623EX), and a resinoid blade WA (specifications: φ150 mm, t0.3 mm, H30 mm) was used as the cutting blade. The cut sample was then polished with SiC polishing paper and diamond polishing while embedded in resin to reveal the cross section of the measurement location. The cross section was then polished to a mirror finish. Finally, to corrode the structure, the sample was immersed for just under 40 seconds in a solution of 3% nital with 2-3 drops each of picric acid and hydrochloric acid added. This resulted in the preparation of a sample for cross-sectional observation of the bent region 5.

[0056] Furthermore, in the wound core of the present invention, it is desirable that the ratio obtained by dividing the number of twin intersections P where deformation twins extending in different directions intersect in a twin-defined region by the total number of deformation twins 12 be in the range of 0.500 to 3.000 in all twin-defined regions. On the other hand, as the minimum necessary requirement for achieving the effects of the present invention, it is more preferable that the ratio obtained by dividing the number of twin-defined regions where this ratio falls within the above range by the total number of twin-defined regions in the steel sheets constituting the wound core be 0.02 or greater. In other words, if the number of all twin-defined regions is C_tot and the total number of twin-defined regions where the ratio obtained by dividing the number of twin intersections P where deformation twins extending in different directions intersect by the total number of deformation twins 12 is C_0, it is more preferable that C_0 / C_tot be 0.02 or greater. C_0 / C_tot is more preferably 0.05 or more, and even more preferably 0.10 or more.

[0057] Next, in any twin-defined region where the ratio obtained by dividing the number of twin intersections P where deformation twins extending in different directions intersect by the total number of deformation twins 12 is 0.500 or more and 3.000 or less, the iron core iron loss becomes smaller when the following relationship is satisfied for the twin intersections P. In other words, it is more preferable that the number of twin intersections P is 5 or more and 150 or less. Even more preferably, the number of twin intersections P is 5 or more and 110 or less, and even more preferably 5 or more and 70 or less.

[0058] Furthermore, in any twin-prescribed region where the ratio obtained by dividing the number of twin intersections P where deformation twins extending in different directions intersect by the total number of deformation twins 12 is 0.500 or more and 3.000 or less, the iron core iron loss becomes even smaller when the following relationship is satisfied for the twin intersections P. That is, if the number of twin intersections P located outside the center line M at the center of the steel sheet thickness is Nout and the number of twin intersections P located inside the center line M at the bend is Nin, it is more preferable that Nout / Nin > 1.00. Nout / Nin is more preferably 2.00 or more, and even more preferably 3.00 or more.

[0059] Furthermore, even in twin-defined regions where the ratio obtained by dividing the number of twin intersections P, where deformation twins extending in different directions intersect, by the total number of deformation twins 12 is 0.500 to 3.000, both iron loss and noise characteristics are improved and reduced when the following relationship is satisfied for the twin intersections P. That is, the average depth position of the twin intersections P in the thickness direction of the steel sheet is preferably within a range of t / 50 to t / 2 in the thickness direction from the outermost layer outside the twin-defined region of each steel sheet, where t is the thickness of the steel sheet 1. Here, the thickness t may be defined as the thickness of a single sheet taken from the flat portions 4, 4a of the steel sheet, excluding the bent portions 5, measured with a commercially available micrometer, in a wound core having a twin-defined region. The thickness may be measured at multiple locations, in which case the average thickness is preferably used. The average depth of the twin intersection points P in the thickness direction of the steel sheet is more preferably t / 50 to t / 3, and even more preferably t / 50 to t / 4.

[0060] Furthermore, in the twin-prescribed region where the ratio obtained by dividing the number of twin intersections P where deformation twins extending in different directions intersect by the total number of deformation twins 12 is 0.500 or more and 3.000 or less, it is more preferable that the ratio obtained by dividing the number of twin intersections P by the thickness of the steel plate is 5 or more and 400 or less. The ratio obtained by dividing the number of twin intersections P by the thickness of the steel plate is even more preferably 5 or more and 250 or less, and even more preferably 5 or more and 100 or less.

[0061] As a result of extensive investigation, the inventors have found that, as an example of a processing method for adjusting the number of deformation twins 12 and the number of twin intersections P, skin-pass rolling is performed on the grain-oriented electrical steel sheet 1 in a step immediately before the bending process for forming the bent portion 5. By performing skin-pass rolling before the bending process, strain that serves as the starting point of deformation twins 12 is introduced into the grain-oriented electrical steel sheet 1, and the subsequent bending process makes it easier for deformation twins 12 to be generated in a state where they intersect appropriately. By evaluating the generated twins and measuring the iron core iron loss while changing parameters such as the reduction amount and roll diameter of the skin-pass rolling, the inventors have found optimal ranges for parameters such as the number of deformation twins 12 and the number of twin intersections P.

[0062] 8 is a schematic diagram showing a bent portion 5 (twin-defined region) in which a deformation twin 12 is formed in a cross section of a steel sheet 1 constituting a wound core according to this embodiment, the cross section being perpendicular to the surface of the steel sheet 1 and extending along the winding direction. Note that FIG. 8 shows a state in which the steel sheet 1 is arranged so that the bent portion 5 is convex downward.

[0063] As shown in Figure 8, in the grain-oriented electrical steel sheet 1 according to this embodiment, there are two deformation twins 12a and 12b extending in different directions in the bend 5, and the deformation twins 12a and 12b intersect at a certain angle, creating a twin intersection.

[0064] The winding direction of the wound core may be the rolling direction of the steel sheet. The winding direction of the wound core may also be the {110}<001> direction of the steel sheet. Furthermore, in the explanation of Figures 1 to 6, the X-axis direction may be the rolling direction of the steel sheet or the {110}<001> direction of the steel sheet.

[0065] The method for producing the grain-oriented electrical steel sheet is not particularly limited, and any conventionally known method for producing a grain-oriented electrical steel sheet can be appropriately selected. A preferred specific example of the production method is a method in which a slab having the chemical composition of the grain-oriented electrical steel sheet, except for 0.04 to 0.1 mass %, is heated to 1000°C or higher and hot-rolled, and then annealed as needed, followed by cold-rolling once or twice or more times with intermediate annealing in between to form a cold-rolled steel sheet, which is then heated to 700 to 900°C in a wet hydrogen-inert gas atmosphere to be decarburized and annealed as needed, and further nitriding annealed as needed, and then coated with an annealing separator, followed by finish annealing at about 1000°C, and then forming an insulating coating at about 900°C.

[0066] In addition, in this embodiment, the wound core made up of grain-oriented electromagnetic steel sheets 1 having the above-described configuration is formed by stacking grain-oriented electromagnetic steel sheets 1 that have been individually bent 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.

[0067] An apparatus that enables the manufacture of a wound core involving the above-described bending of steel sheets is shown schematically in a block diagram in Figure 9. Figure 9 shows a schematic diagram of a wound core manufacturing apparatus 70 that forms the core, and this manufacturing apparatus 70 includes a bending unit 71 that individually bends grain-oriented electrical steel sheets 1, and may also include an assembly unit 72 that stacks the folded grain-oriented electrical steel sheets 1 in layers and assembles them into a wound shape, thereby forming a wound core that includes a portion where grain-oriented electrical steel sheets 1, each having a series of alternate flat portions 4 and bent portions 5 in the longitudinal direction, are stacked in the sheet thickness direction.

[0068] The grain-oriented electrical steel sheet 1 is fed to the bending processing unit 71 by being unwound at a predetermined conveying speed from a steel sheet supply unit 75 that holds a hoop material formed by winding the grain-oriented electrical steel sheet 1 into a roll. The grain-oriented electrical steel sheet 1 thus fed is cut to an appropriate size in the bending processing unit 71 and subjected to a bending process in which the grain-oriented electrical steel sheet 1 is individually bent in small batches, such as one by one. In addition, in a step prior to the bending process, the grain-oriented electrical steel sheet 1 is subjected to skin-pass rolling. The iron core of the present disclosure can be obtained by using a grain-oriented electrical steel sheet that has been pre-processed by controlling the roll diameter and tension under the skin-pass conditions and setting the reduction within an appropriate range as the iron core material.

[0069] In the grain-oriented electrical steel sheet 1 obtained in this manner, the radius of curvature of the bent portion 5 generated by the bending process is extremely small, and therefore the bending process imparts extremely small processing strain to the grain-oriented electrical steel sheet 1. While it is assumed that the density of processing strain will increase in this way, if the volume affected by the processing strain can be reduced, the annealing step can be omitted.

[0070] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiment that has substantially the same configuration as the technical idea described in the claims of the present disclosure and exhibits similar effects is included within the technical scope of the present disclosure.

[0071] The present disclosure will be specifically described below using 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. Various conditions may be adopted in the present disclosure as long as they do not deviate from the gist of the disclosure and the purpose is achieved.

[0072] The inventors produced and evaluated several wound cores using skin-pass rolled steel sheets. Detailed dimensions of the wound cores are shown in Fig. 10 and Table 1. Note that the "number of bends per corner" in Table 1 indicates the number of bends 5 present in one corner 3. A wound core with two bends per corner is the wound core shown in Fig. 2, and a wound core with three bends per corner is the wound core shown in Fig. 3. Furthermore, the "number of joints" in Table 1 indicates the number of joints in one steel sheet constituting the wound core. The wound core with one joint is the wound core made using the steel sheet shown in Fig. 5, and the wound core with two joints is the wound core made using the steel sheet shown in Fig. 6.

[0073]

[0074] The skin-pass rolling conditions are shown in Table 2. The roll rotation speed was standardized to 30 rpm. The preferred skin-pass rolling conditions were a roll diameter of 40 to 100 mm, a tension of 4 to 10 MPa, and a reduction ratio of 0.1 to 2.0%.

[0075]

[0076] The skin pass conditions, specifications (core number shown in Table 1), punch speed, and material thickness of the wound cores (Experiments No. 1 to 79) that were created, as well as the results of evaluating iron loss, are shown in Tables 3 and 4. Iron loss was measured using the excitation current method, with a magnetic flux density of 1.7 T and a frequency of 50 Hz. The cross-sectional area S of the core is the product of the steel sheet width, the core winding thickness, and the space factor (0.965).

[0077]

[0078]

[0079] Furthermore, the following values ​​for the produced wound cores (Experiments No. 1 to 79) are shown in Tables 5 and 6. Total number L of deformation twins Number M of twin intersections Ratio of the number M of twin intersections to the total number L (M / L): ratio obtained by dividing the number of twin intersections P where deformation twins extending in different directions intersect by the total number of deformation twins 12 Nout: number of twin intersections located on the outer side of the center line at the center of the thickness of the steel sheet Nin: number of twin intersections located on the inner side of the center line at the center of the thickness of the steel sheet t / 50 (μm): lower limit of the average value of the depth position D of the twin intersections P in the thickness direction of the steel sheet Average depth value of twins in the thickness direction (μm): average value of the depth position of the twin intersections in the thickness direction of the steel sheet (= D) t / 2 (μm): upper limit of the average value of the depth position D of the twin intersections P in the thickness direction of the steel sheet C_0: the number of twin-defined regions where the ratio obtained by dividing the number of twin intersections P where deformation twins extending in different directions intersect by the total number of deformation twins 12 is 0.500 or more and 3.000 or less. C_tot: the total number of twin-defined regions in the steel plate constituting the wound core. C_0 / C_tot: the ratio obtained by dividing the number of twin intersections P where deformation twins extending in different directions intersect by the total number of deformation twins 12, which satisfies the ratio of 0.500 or more and 3.000 or less, by the total number of twin-defined regions in the steel plate constituting the wound core. Ratio of the number M of twin intersections to the thickness of the steel plate (M / t): the ratio obtained by dividing the number of twin intersections by the thickness of the steel plate. It should be noted that there are multiple twin-defined regions in a wound core, and the values ​​of L, D, M, Nout, Nin, and M / t described above are values ​​obtained by extracting an unspecified location from the bend of the core and evaluating that twin-defined region.

[0080]

[0081]

[0082] As shown in Tables 3 to 6, wound cores for which the ratio obtained by dividing the number of twin intersections P where deformation twins extending in different directions intersect by the total number of deformation twins 12 is 0.500 or more and 3.000 or less have a ratio of core iron loss to material iron loss (hereinafter referred to as iron loss ratio) of 1.1 or less, and these wound cores were designated as inventive examples. On the other hand, wound cores for which the ratio obtained by dividing the number of twin intersections P where deformation twins extending in different directions intersect by the total number of deformation twins 12 does not satisfy the ratio of 0.500 or more and 3.000 or less have a ratio of core iron loss to material iron loss that exceeds 1.1, and these wound cores were designated as comparative examples.

[0083] That is, as shown in Tables 3 and 4, wound cores with M / L between 0.500 and 3.000 had an iron core iron loss ratio of 1.1 or less. When M / L exceeded 3.000, the influence of distortion became greater, and iron loss deteriorated.

[0084] Table 7 shows the results of further evaluation of magnetic flux leakage at the bends where twins were evaluated during iron loss measurements for comparative examples (Experiments Nos. 1, 21, and 24) and inventive examples (Experiments Nos. 7, 12, 17, and 50) randomly selected from the wound cores in Tables 5 and 6. In this evaluation, one turn of wire was wound around the bend where the ratio of the number of twin intersections M to the total number of twins L was evaluated, and the core was excited to a magnetic flux density of 1.7 T using an average voltage meter (a digital multimeter manufactured by Advantest Corporation, product name AD7461A). The magnetic flux densities at the bends and the flat areas adjacent to the bends were then measured, and the ratio was evaluated.

[0085]

[0086] From the ratio of the magnetic flux density of the bent portion to the magnetic flux density of the straight portion shown in Table 7 (= magnetic flux density B of the bent portion / magnetic flux density A of the straight portion), it was confirmed that the effect of reducing iron loss according to the invention example was confirmed when the ratio was 0.96 or more, and that the ratio of iron core iron loss to material iron loss (iron loss ratio (= iron core iron loss / material iron loss)) was a small value of 1.1 or less.

[0087] Therefore, according to the results in Table 7, in bent portions where the ratio (M / L) of the number M of twin intersections to the total number L is 0.500 or more and 3.000 or less, the magnetic flux densities of the bent portions and straight portions are equivalent, and the ratio of the magnetic flux density of the bent portions to the magnetic flux density of the straight portions is a sufficiently large value close to 1. As a result, it is possible to reduce the ratio of the iron core iron loss to the material iron loss.

[0088] REFERENCE SIGNS LIST 1 Grain-oriented electrical steel sheet 2 Laminated structure 3 Corner portion 4, 4a Planar portion 5 Bent portion 6 Joint portion 10 Wound core 12, 12a, 12b Deformation twin 15 Hollow portion 70 Manufacturing device 71 Processing portion 72 Assembly portion 75 Steel sheet supply portion

Claims

1. A wound core having a wound shape formed by stacking bent steel plates, wherein the wound core, in a side view of the wound shape seen from a direction along the surfaces of the steel plates, has a plurality of flat portions and bent portions adjacent to the flat portions, thereby forming a rectangular shape with a hollow portion in the center, and in a cross section perpendicular to the surfaces of the steel plates and along the winding direction, when the region of the bent portion excluding the flat portions of any steel plate is defined as a twin-defined region, the twin-defined region has a plurality of deformation twins extending in different directions, and in at least one of the twin-defined regions, the ratio obtained by dividing the number of twin intersections where deformation twins extending in different directions intersect by the total number of deformation twins is 0.500 or more and 3.000 or less.

2. A wound core according to claim 1, wherein in the twin-defined region where the ratio is 0.500 or more and 3.000 or less, the number of twin intersections where deformation twins extending in different directions intersect is 5 or more and 150 or less.

3. A wound core according to claim 1 or 2, wherein, in the twin-crystal defined region where the ratio satisfies 0.500 or more and 3.000 or less, Nout / Nin > 1.00 is satisfied, where Nout is the number of twin intersections located on the outer side of the center line at the center of the thickness of the steel sheet when bent, and Nin is the number of twin intersections located on the inner side of the center line at the center of the thickness of the steel sheet when bent.

4. A wound core according to claim 1 or 2, wherein, in the twin-defined region where the ratio is 0.500 or more and 3.000 or less, the average depth position of the twin intersection points in the sheet thickness direction of the steel sheet is in a range of t / 50 mm to t / 2 mm in the sheet thickness direction from the outermost layer outside the twin-defined region of the steel sheet, where t is the sheet thickness of the steel sheet.

5. A wound core according to claim 1 or 2, wherein the ratio obtained by dividing the number of twin-defined regions that satisfy the ratio of 0.500 to 3.000 by the total number of twin-defined regions in the steel sheets that constitute the wound core is 0.02 or greater.

6. A wound core according to claim 1 or 2, wherein in the twin-prescribed region where the ratio is 0.500 or more and 3.000 or less, the ratio obtained by dividing the number of twin intersections by the thickness of the steel sheet is 5 or more and 400 or less.

7. A wound core according to claim 1 or 2, wherein in at least one of the twin-defined regions, the ratio obtained by dividing the number of twin intersections where deformation twins extending in different directions intersect by the total number of deformation twins is 0.700 or more and 2.500 or less.

8. A wound core according to claim 1 or 2, wherein in at least one of the twin-defined regions, the ratio obtained by dividing the number of twin intersections where deformation twins extending in different directions intersect by the total number of deformation twins is 1.000 or more and 2.300 or less.

9. A method for manufacturing a wound core as claimed in claim 1 or 2, comprising the steps of: skin-pass rolling a steel sheet; bending the skin-pass rolled steel sheet; cutting the steel sheet; and stacking the bent and cut steel sheets in layers and assembling them in a wound shape by butting the ends in the winding direction together.

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