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

TITLE WOUND CORE AND METHOD OF PRODUCTION OF SAME FIELD

[0001] The present invention relates to a wound core and a method of production of the same. BACKGROUND

[0002] Known in the art is a wound core fabricated by bending a steel sheet wherein the shapes of the bent parts are controlled to reduce the core loss (PTL 1).

[0003] Further, it is known to reduce the core loss by suppressing the occurrence of deformation twin crystals when bending the grain-oriented electrical steel sheet forming the wound core (PTL 2). Further known in the art is a wound core comprised of an inside core and an outside core in which the inside core is formed by a grain-oriented electrical steel sheet having a plurality of bent parts formed by a metallostructure including twin crystals and having curved shapes when seen from the side (PTL 3). [CITATION LIST] [PATENT LITERATURE]

[0004] [PTL 1] Japanese Patent No. 7239089 [PTL 2] WO2018 / 131613 [PTL 3] Japanese Unexamined Patent Publication No. 2017-157806 SUMMARY [TECHNICAL PROBLEM]

[0005] However, in the art described in the above PTL 1, passage of magnetic flux at the bent parts where large amounts of plastic strain had been introduced was greatly obstructed. Deterioration of the core loss was unavoidable. There was therefore room for improvement.

[0006] Further, in the art described in the above PTL 2, the number of deformation twin crystals was focused on so as to try to suppress core loss, but the positional relationship of the deformation twin crystals with each other was not considered. There was room for improvement in core loss. In the art described in the above PTL 3 as well, twin crystals were focused on so as to try to improve the core loss property, but the positional relationship of twin crystals with each other was not considered. There was room for improvement in core loss.

[0007] In view of the above problem, an object of the present disclosure is to provide a wound core able to reduce core loss and a method of production of the same. [SOLUTION TO PROBLEM]

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

[0009] (1) A wound core of a wound shape comprised of stacked layers of a bent steel sheet, in which wound core, the wound core having pluralities of plane parts and bent parts adjoining the plane parts in a side view looking at the wound shape from a direction running along a surface of the steel sheet and thereby formed into a rectangular shape having a hollow part at its center, in a cross-section perpendicular to the surface of the steel sheet and running along the winding direction, when defining regions of bent parts other than plane parts of any steel sheet as prescribed twin crystal regions, the prescribed twin crystal regions having pluralities of deformation twin crystals extending in different directions, in at least one of the prescribed twin crystal regions, a ratio obtained by dividing a number of twin crystal intersections where deformation twin crystals extending in different directions cross by a total number of deformation twin crystals being 0.500 or more and 3.000 or less.

[0010] (2) The wound core according to the above (1), wherein, in a prescribed twin crystal region where the ratio satisfies being 0.500 or more and 3.000 or less, a number of twin crystal intersections where deformation twin crystals extending in different directions cross is 5 or more and 150 or less.

[0011] (3) The wound core according to the above (1) or (2), wherein, in a prescribed twin crystal region where the ratio satisfies being 0.500 or more and 3.000 or less, if a number of twin crystal intersections present at an outside of a bend from a center line of a sheet thickness center of the steel sheet is Nout and a number of twin crystal intersections present at an inside of a bend from the center line of the sheet thickness center of the steel sheet is Nin, Nout / Nin>1.00 is satisfied.

[0012] (4) The wound core according to the above (1) or (2), wherein, in a prescribed twin crystal region where the ratio satisfies being 0.500 or more and 3.000 or less, the average value of depth positions of the twin crystal intersections 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 at the outside of the prescribed twin crystal region of the steel sheet, where “t” is the sheet thickness of the steel sheet.

[0013] (5) The wound core according to the above (1) or (2), wherein a ratio obtained by dividing a number of prescribed twin crystal regions where the above ratio satisfies 0.500 or more and 3.000 or less by a total number of prescribed twin crystal regions of the steel sheet forming the wound core is 0.02 or more.

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

[0015] (7) The wound core according to the above (1) or (2), wherein, in at least one of the prescribed twin crystal regions, a ratio obtained by dividing a number of twin crystal intersections where deformation twin crystals extending in different directions cross by a total number of deformation twin crystals is 0.700 or more and 2.500 or less.

[0016] (8) The wound core according to the above (1) or (2), wherein, in at least one of the prescribed twin crystal regions, a ratio obtained by dividing a number of twin crystal intersections where deformation twin crystals extending in different directions cross by a total number of deformation twin crystals is 1.000 or more and 2.300 or less.

[0017] (9) A method of production of the wound core according to the above (1) or (2), the method of production of the wound core comprising a step of skin pass rolling a steel sheet, a step of bending the skin pass rolled steel sheet, a step of cutting the steel sheet, and a step of stacking the bent and cut steel sheet in layers and making end parts in the winding direction abut against each other to assemble a wound shape. [ADVANTAGEOUS EFFECTS OF INVENTION]

[0018] According to the present disclosure, a wound core able to reduce core loss and a method of production of the same are provided. BRIEF DESCRIPTION OF DRAWINGS

[0019] FIG. 1 is a perspective view schematically showing an embodiment of a wound core. FIG. 2 is a side view of a wound core shown in the embodiment of FIG. 1. FIG. 3 is a side view schematically showing another embodiment of a wound core. FIG. 4 is a view schematically showing one example of a bent part (curved part) of a grain-oriented electrical steel sheet. FIG. 5 is a view schematically showing one example of one layer’s worth of a grain-oriented electrical steel sheet in a wound core body. FIG. 6 is a view schematically showing one example of one layer’s worth of a grain-oriented electrical steel sheet in a wound core body. FIG. 7A is a schematic view showing one steel sheet at a bent part and showing deformation twin crystals and twin crystal intersections in a cross-section perpendicular to the surface of the steel sheet and running along the winding direction. FIG. 7B is a schematic view for explaining the state of suppression of leakage of magnetic flux by cross points of deformation twin crystals. FIG. 8 is a schematic view of deformation twin crystals in a cross-section perpendicular to the surface of the steel sheet and running along the winding direction. FIG. 9 is a view schematically showing an apparatus for production of a wound core forming an example of a core. FIG. 10 is a view for explaining detailed dimensions of a wound core. DESCRIPTION OF EMBODIMENTS

[0020] Below, several embodiments according to the present invention will be explained while referring to the drawings. However, these explanations are intended to simply illustrate the preferred embodiments of the present invention and are not intended to limit the present invention to such specific embodiments. Note that, in the following explanation, similar component elements are assigned the same reference numerals.

[0021] Below, wound cores according to embodiments of the present invention will be explained in detail in order. However, the present invention is not limited to only the constitutions disclosed in the present embodiment and can be changed in various ways within a scope not departing from the gist of the present invention. Note that the ranges of numerical values explained above include the lower limit values and upper limit values in their ranges. Numerical values shown with “more than” or “less than” are not included in the ranges of numerical values. Further, the “%” relating to the chemical compositions mean “mass%” unless otherwise particularly indicated.

[0022] Further, the, for example, “parallel”, “vertical”, “same”, “perpendicular”, and other terms specifying the shapes and geometric conditions and their extents used in this Description and the values of the lengths and angles etc. shall be interpreted without being bound by their strict meanings and including ranges of an extent enabling similar functions to be expected.

[0023] Further, in this Description, a “grain-oriented electrical steel sheet” will sometimes be simply referred to as a “steel sheet” or “electrical steel sheet” and a “wound core” will sometimes be simply referred to as a “wound core body” or “core”.

[0024] The wound core according to an embodiment of the present invention is a wound core of a wound shape comprised of a stacked layers of a bent steel sheet, in which wound core, the wound core having respectively four plane parts and corner parts adjoining the plane parts in a side view looking at the wound shape from a direction running along a surface of the steel sheet. Thereby the wound core has a configuration formed into a rectangular shape having a hollow part at its center. Here, the “plane parts” mean straight parts other than the bent parts. The radius of curvature “r” of the inside in the side view of a bent part is, for example, 1.0 mm or more and 5.0 mm or less. The grain-oriented electrical steel sheet, as one example, has a chemical composition containing, by mass%, Si: 2.0 to 7.0% and having a balance of Fe and impurities and has a texture aligned to a Goss orientation. As the grain-oriented electrical steel sheet, for example, it is possible to employ the grain-oriented electrical steel strip described in JIS C 2553:2019.

[0025] Next, the shapes of the wound core according to an embodiment of the present invention and the grain-oriented electrical steel sheet will be specifically explained. The shapes themselves of the wound core and grain-oriented electrical steel sheet explained here are not particularly novel and are only ones based on the shapes of known wound cores and grain-oriented electrical steel sheets.

[0026] 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 and shows what is viewed from the side of the wound core. Further, FIG. 3 is a side view schematically showing another embodiment of a wound core.

[0027] Note that, “viewed from the side” means the case of viewing the wound shape of the wound core from a direction along the surface of the steel sheet, more specifically means the case of viewing the wound core from an axial direction of winding of the wound core (direction vertical to paper surface in FIG. 2). In other words, “viewed from the side” means viewed in a width direction of a long shape grain-oriented electrical steel sheet forming the wound core (Y-axial direction in FIG. 1). A “side view” is a view showing the shape seen when viewed from the side (figure of Y-axial direction of FIG. 1).

[0028] The wound core 10 according to one embodiment of the present invention is provided with a wound core body of a substantially polygonal shape viewed from the side. That wound core body 10 is comprised of a stack of layers of a grain-oriented electrical steel sheet 1 in the sheet thickness direction and has a stacked layer structure of a substantially wound shape viewed from the side. That wound core body 10 may be used as is as a wound core. To integrally fasten a plurality of grain-oriented electrical steel sheets stacked in layers in accordance with need, bundling bands or other known fasteners etc. may be provided.

[0029] In the present embodiment, the core length of the wound core body 10 is not particularly limited. If the numbers of bent parts 5 are the same, even if the core length in the wound core 10 changes, the volume of the bent parts 5 is fixed, therefore the core loss generated at the bent parts 5 is fixed. The longer the core length, the smaller the volume ratio of the bent parts 5 to the wound core body 10 becomes, therefore the smaller the effect on deterioration of core loss. Accordingly, a longer wound core body 10 is preferable. The core length of the wound core body 10 is preferably 1.5 m or more, more preferably 1.7 m or more. Note that, in the present invention, the “core length of the wound core body 10” means the circumferential length at the center point of the stacking direction of the wound core body 10 viewed from the side. Such a wound core can be suitably used for any conventionally known application.

[0030] The core according to the present embodiment is characterized by being a substantially polygonal shape viewed from the side. In the following explanation using the following drawings, to simplify the illustrations and explanations, the explanation is given of a core of a substantially rectangular shape (square shape), which is also the general shape, but cores of various shapes can be produced depending on the angles and number of the bent parts 5 and the lengths of the plane parts. For example, if the angles of all of the bent parts 5 are made 45° and the lengths of the plane parts 4 are made equal, the shape viewed from the side becomes octagonal. Further, if having six bent parts 5 with angles of 60° and having lengths of the plane parts 4 which are equal, the shape viewed from the side becomes hexagonal.

[0031] As shown in FIG. 1 and FIG. 2, the wound core body 10 has a substantially rectangular shaped stacked structure 2 including parts where grain-oriented electrical steel sheets 1 comprised of plane parts 4, 4a and bent parts 5 alternately continuing in the longitudinal direction are stacked in the sheet thickness direction and having a hollow part 15 viewed from the side. A corner part 3 including bent parts 5 has two or more bent parts 5 having curved shapes viewed from the side. The total of the bending angles of the bent parts 5 present at one corner part 3 becomes for example 90°. A corner part 3 has a plane part 4a shorter than a plane part 4 between adjoining bent parts 5, 5. Therefore, the corner part 3 becomes a shape having two or more bent parts 5 and one or more plane parts 4a. Note that, the embodiment of FIG. 2 has one bent part 5 of 45°. In the embodiment of FIG. 3, there is a single bent part 5 of 30°.

[0032] As shown in these examples, the wound core of the present embodiment can be formed by bent parts having various angles. But from the viewpoint of suppressing the generation of strain due to deformation at the time of working to suppress core loss, the bending angles 9 (91, 92, 93) of the bent parts are preferably 60° or less, more preferably 45° or less. The bending angles 9 of the bent parts of the core can be formed to any angle. For example, it is possible to make 91=60° and 92=30°. From the viewpoint of the production efficiency, the bending angles (bend angles) are preferably equal. If possible to reduce the core loss of the core prepared from the core loss of the steel sheet used by reducing the deformed locations by a certain extent or more, a combination of different angles may be worked. The design can be freely selected from the points emphasized in working the core.

[0033] Referring to FIG. 4, the bent parts 5 will be explained in more detail. FIG. 4 is a view schematically showing one example of a bent part (curved part) 5 of the grain-oriented electrical steel sheet 1. A “bending angle of a bent part 5” means the difference in angle between the rear side straight part and the front side straight part at the grain-oriented electrical steel sheet bent part. The “bending angle of a bent part 5” is expressed as the angle 9 of the supplementary of the angle formed by the two imaginary lines Lb-elongation 1 and Lb-elongation 2 obtained by extending the straight parts of the surfaces of the plane parts 4, 4a at the two sides straddling the bent part 5 at the outside surface of the grain-oriented electrical steel sheet 1. At this time, the points where the extended lines depart from the steel sheet surface are at the boundaries of the plane parts 4 and bent parts 5 at the surface at the outside of the steel sheet. In FIG. 4, they are the point F and point G.

[0034] Furthermore, lines vertical to the steel sheet outside surface are extended from the point F and point G. The cross points of these with the surface of the inside of the steel sheet are respectively designated as the “point E” and “point D”. The point E and point D form the boundaries of plane parts 5 and bent parts 5 at the surface at the inside of the steel sheet.

[0035] Further, in the present invention, a “bent part 5” is a portion of the grain-oriented electrical steel sheet 1 surrounded by the point D, point E, point F, and point G viewed from the side of the grain-oriented electrical steel sheet 1. In FIG. 4, the steel sheet surface between the point D and the point E, that is, the inside surface of the bent part 5, is shown as “La” while the steel sheet surface between the point F and point G, that is, the outside surface of the bent part 5, is shown as “Lb”.

[0036] Further, in this drawing, the radius of curvature “r” of the inside viewed from the side of the bent part 5 is shown. The La is approximated by the arc passing through the point E and point D to obtain the radius of curvature “r” of the bent part 5. The smaller the radius of curvature “r”, the sharper the curve of the curved part of the bent part 5, while the larger the radius of curvature “r”, the gentler the curve of the curved part of the bent part 5.

[0037] In the wound core of the present invention, the radii of curvature “r” at the bent parts 5 of the grain-oriented electrical steel sheet 1 stacked in the sheet thickness direction may vary to a certain extent. This variation is also variation due to the shaping precision. It may be that unintended variation occurs due to handling at the time of stacking etc. Such unintended error can be suppressed to 0.2 mm or so or less if according to current usual industrial production. If such variation is large, it is possible to measure the radii of curvature of a sufficiently large number of steel sheets and obtain their average so as to obtain a representative value. Further, the radius may be intentionally changed for some sort of reason. The present invention does not exclude this. The radii of curvature “r” of the bent parts 5 (inside radii of curvature of bent parts 5 viewed from side) are preferably made 1 mm or more and 5 mm or less. By making the radii of curvature “r” 1 mm or more and 5 mm or less, it is possible to further suppress the building factor (BF).

[0038] Note that the method of measurement of the radii of curvature “r” of the bent parts 5 is also not particularly limited, but for example a commercially available microscope (Nikon ECLIPSE LV150) can be used to examine the parts by 200X to measure the radii. Specifically, the curvature center A point is found from the results of examination. As the method of finding it, for example if defining the cross point A where the line segment EF and the line segment DG are made to extend to the inside at the side opposite to the point B as “A”, the magnitude of a radius of curvature “r” corresponds to the length of the line segment AC. Here, when connecting the point A and the point B by a straight line, the cross point on the arc DE at the inside of the steel sheet bent part is C.

[0039] FIG. 5 and FIG. 6 are views schematically showing examples of one layer’s worth of the 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 one which is bent and stacked superposed and has two or more bent parts 5 and plane parts 4. The grain-oriented electrical steel sheets 1 form a substantially polygonal shaped ring viewed from the side via joint parts 6 (gaps) which is the end faces of one or more of grain-oriented electrical steel sheets 1 in the longitudinal direction. Among such substantially polygonal shaped rings, ones having specific bending angles or bent part shapes are sometimes called “unicores”.

[0040] In the present embodiment, the wound core body 10 need only overall have a stacked structure of a substantially polygonal shape viewed from the side. As shown in the example of FIG. 5, one grain-oriented electrical steel sheet may form one layer’s worth of the wound core body through one joint part 6 (one grain-oriented electrical steel sheet connected through a joint part 6 at one location for each turn). Or, as shown in the example of FIG. 6, one grain-oriented electrical steel sheet 1 may form about half a circumference’s worth of the wound core and two grain-oriented electrical steel sheets 1 may form one layer’s worth of the wound core body through two joint parts 6 (two grain-oriented electrical steel sheets 1 connected with each other through joint parts 6 at two locations for each turn).

[0041] The sheet thickness of the grain-oriented electrical steel sheet 1 used in the present embodiment is not particularly limited and may be suitably selected in accordance with the application etc., but usually is a range of 0.15 mm to 0.35 mm, preferably a range of 0.18 mm to 0.27 mm.

[0042] In the case of the example of FIG. 5, one joint part 6 of one grain-oriented electrical steel sheet forming one layer’s worth of the wound core body is positioned in the region A1 shown in FIG. 2 and FIG. 3. Further, in the case of the example of FIG. 6, the two joint parts 6 of the two grain-oriented electrical steel sheets forming one layer’s worth of the wound core body are positioned at the region A1 and region A2 shown in FIG. 2 and FIG. 3. Note that, in FIG. 2 and FIG. 3, illustration of the detailed shape and arrangement of the joint part 6 in the region A1 or the region A2 is omitted.

[0043] The inventors found that at a bent part 5 formed at the time of plastic deformation when bending a grain-oriented electrical steel sheet 1, the permeability falls and the core loss increases. In the bent part 5, if using an optical microscope to examine the cross-section perpendicular to the surface of the grain-oriented electrical steel sheet 1 and running along the winding direction, streak like deformation twin crystals are observed running from the steel sheet surface toward the inside (inside of bend). Note that deformation twin crystals can be confirmed by analysis and evaluation using, for example, a scan electron microscope and crystal orientation analysis software (EBSD). In deformation twin crystals, the arrangements of atoms become symmetric about the twinning crystal plane. The twinning crystal plane and the twinning crystal directions are determined by the metal. A grain-oriented electrical steel sheet is a steel sheet with orientations of crystal grains in the steel sheet concentrated in the {110}<001> orientation (below, sometimes referred to as the “Goss orientation”) to a high degree, but parts where deformation twin crystals occur differ in crystal orientation from Goss orientations. Deformation twin crystals for example run along the {112}<111> orientation. That is, the band shaped structures of deformation twin crystals have orientations different from the crystal orientations of the base steel sheet not plastically deformed.

[0044] As described in the above-mentioned PTL 2, if the number of deformation twin crystals formed becomes greater, the magnetic properties end up deteriorating. The inventors studied the data and during that noticed that despite the number of deformation twin crystals formed being almost the same, sometimes a difference is seen in the core loss. Further, they concluded that this difference is affected by the frequency of formation of twin crystal intersections where deformation twin crystals cross.

[0045] FIG. 7A is a schematic view showing one steel sheet at a bent part 5 and showing deformation twin crystals 12 and twin crystal intersections P in a cross-section perpendicular to the surface of the steel sheet and running along the winding direction. As shown in FIG. 7A, the inventors discovered that by applying a special working method, deformation twin crystals 12 extending in different directions are formed and twin crystal intersections P where deformation twin crystals 12 extending in different directions cross occur. Further, the inventors discovered that by adjusting the number of deformation twin crystals 12 and the number of deformation twin crystal intersections P at the bent parts 5, it is possible to effectively suppress core loss.

[0046] The reason why the form of deformation twin crystals (frequency of occurrence of cross points) affects the core loss is not clear, but it may be the following: bent parts 5 are subjected to large amounts of strain, therefore become low in permeability. The magnetic flux passes through the regions between adjoining deformation twin crystals and end up leaking to outside the steel sheet. If deformation twin crystals cross in a region where such deformation twin crystals concentrate, the spaces between the deformation twin crystals will be blocked by the deformation twin crystals. Due to this, as a result, it may be that the effect arises of leakage of magnetic flux to outside the steel sheet being suppressed and deterioration of core loss being suppressed. However, from the viewpoint of suppressing deterioration of the core loss, there is a large effect due to reducing the occurrence of such twin crystals themselves. The mechanism explained here should be interpreted as one of the state of crossing of twin crystals affecting the magnetic properties in the case where the numbers of twin crystals formed are the same, in particular the case where the numbers formed are relatively large. In the following explanation, the mechanism of action of crossing of deformation twin crystals at the bent parts 5 in the present invention will be explained predicated on the above phenomenon (suppression of magnetic flux density). But it should be added that in the final analysis this is one hypothesis at the current point of time for theoretically explaining the empirical principle which the inventors found as a result of intensive studies. It is expected that the scientifically correct mechanism will be elucidated in the future.

[0047] FIG. 7B is a view showing one steel sheet at a bent part 5 and showing deformation twin crystals 12 and twin crystal intersections P in a cross-section perpendicular to the surface of the steel sheet and running along the winding direction and is a schematic view for explaining the state of suppression of leakage of magnetic flux by the twin crystal intersections P of the deformation twin crystals 12. In FIG. 7B, the drawing shown at the left side, in the same way as FIG. 7A, shows the case where there are twin crystal intersections P where deformation twin crystals 12 extending in different directions cross present. On the other hand, the drawing shown at the right half of FIG. 7B shows the case where there are only deformation twin crystals 12 extending in the same direction present and there are no twin crystal intersections P where deformation twin crystals 12 cross present.

[0048] As shown at the left drawing of FIG. 7B, if there are twin crystal intersections P present, the twin crystal intersections P are formed by deformation twin crystals 12 extending in different directions and striking each other, therefore a state is formed where deformation twin crystals 12 cross and the deformation twin crystals 12 become barriers to magnetic flux. Due to this, leakage of magnetic flux to outside the steel sheet is suppressed. On the other hand, as shown by the right drawing in FIG. 7B, if there are no twin crystal intersections P present and deformation twin crystals 12 extend in the same directions as each other, it may be that magnetic flux ends up passing between the deformation twin crystals 12 and leaking to the outside.

[0049] Based on the above findings, the inventors intensively studied the effects of the numbers of deformation twin crystals 12 and twin crystal intersections P at bent parts 5 on the core loss and discovered that, in particular, controlling the number of twin crystal intersections P with respect to the number of deformation twin crystals 12 at bent parts 5 is effective for reducing the core loss of a wound core.

[0050] Specifically, the configuration of the wound core discovered by the inventors is as follows: First, if defining a region of bent part 5 other than a plane part 4 of any steel sheet in a crosssection perpendicular to the surface of the steel sheet and running along the winding direction as a “prescribed twin crystal region”, there are a plurality of prescribed twin crystal regions present in each stacked steel sheet 1. Specifically, there are the same number of prescribed twin crystal regions present as the times of bending. But at least at one location of the plurality of prescribed twin crystal regions present, there are a plurality of deformation twin crystals 12 extending in different directions and the ratio obtained by dividing the number of twin crystal intersections P where deformation twin crystals extending in different directions cross by the total number of deformation twin crystals 12 is 0.500 or more and 3.000 or less. This ratio is preferably 0.700 or more and 2.500 or less, more preferably 1.000 or more and 2.300 or less. Note that, a “bent part 5” is a portion of the grain-oriented electrical steel sheet 1 surrounded by a point D, point E, point F, and point G other than a plane part 4 at a cross-section perpendicular to the surface of the steel sheet and running along the winding direction, while a “prescribed twin crystal region” is defined as a region surrounded by the point D, point E, point F, and point G.

[0051] Further, at least at one location of the plurality of prescribed twin crystal regions present, there are a plurality of deformation twin crystals 12 extending in different directions. The lower limit value of the ratio obtained by dividing the number of twin crystal intersections P where deformation twin crystals extending in different directions cross by the total number of deformation twin crystals 12 is 0.500. The lower limit value may also be a value of 0.525, 0.550, 0.575, 0.600, 0.625, 0.650, 0.675, 0.700, 0.725, 0.750, 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] Further, at least at one location of the plurality of prescribed twin crystal regions present, there are a plurality of deformation twin crystals 12 extending in different directions. The upper limit value of the ratio obtained by dividing the number of twin crystal intersections P where deformation twin crystals extending in different directions cross by the total number of deformation twin crystals 12 is 3.000. The upper limit value may also be a value of 2.975, 2.950, 2.925, 2.900, 2.875, 2.850, 2.825, 2.800, 2.775, 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, the form and method of evaluation of deformation twin crystals and the preparation of samples for examination of the cross-section will be explained. The deformation twin crystals in the present embodiment are formed basically in shapes extending straight by finite lengths at specific orientations of the steel sheet crystals in examination of the cross-section of the steel sheet. In the present invention, this straight shaped region is defined as “a single (one) deformation twin crystal”. Further, two deformation twin crystals extend not parallel in different directions. In states having considerable lengths, the deformation twin crystals cross to form a twin crystal intersection.

[0054] (Method of Evaluation of Deformation Twin Crystals) The specific method of finding the number of deformation twin crystals 12 present in a bent part 5 will be explained below. On a cross-section of a wound core 10 constituting a bent body perpendicular to the surface of the grain-oriented electrical steel sheet 1 and running along the winding direction, cross-sections at the cross-sections of the three locations of the center in the Y-direction (A_1) and 5 mm inside from the end faces at the two sides in the Y-direction (A_2, A_3) plus the cross-sections of the median point (A_4) of A_1 and A_2 and median point (A_5) of A_1 and A_3 in the Y-direction, that is, cross-sections of a total of five locations, are photographed using an optical microscope. At one bent part 5, the numbers of deformation twin crystals of the different fields when viewing the prescribed twin crystal regions of the different cross-sections are counted up and the average taken. This average value defines the number of deformation twin crystals per location of prescribed twin crystal region. The deformation twin crystals are formed inside the sheet thickness of the steel sheet. The cross points of deformation twin crystals as well, in the same way, are evaluated in the different fields when viewing the prescribed twin crystal regions of the different the cross-sections and the averages taken. These are made the numbers per location of prescribed twin crystal region. In other words, in the present embodiment, a “prescribed twin crystal region” may mean a “prescribed twin crystal region of the cross-section of the above five locations of the one bent part 5”.

[0055] (Preparation of Samples for Examination of Cross-Section) Here, the method of preparation of samples for examination of the cross-sections of a bent part 5 will be explained with reference to the example of the wound core 10 according to the present disclosure. The samples for examination of the cross-sections of a bent part 5, like for general examination of a cross-sectional structure, are prepared by embedding the part in a resin, then cutting it 1 mm in front of the push positions at the afore-mentioned five locations of crosssections of the bent part 5. The cutting is rough cutting using a mechanical upper blade precision cutting machine (made by Maruto, model: MC-623EX). For the cutting blade, a resinoid blade WA (specifications: ¢150 mm-t0.3 mm-H30 mm) is used. The cut out samples are ground using SiC polishing paper and diamond polishing in the state embedded in the resin to bring out the cross-sections of the measurement locations. Further, the cross-sections are finished to a mirror surface. Finally, to corrode the structure, the samples are dipped for just under 40 seconds in a solution of 3% Nital in which two to three drops of picric acid and hydrochloric acid are respectively added to thereby corrode the structure. Due to this, samples for examination of the cross-sections of a bent region 5 are prepared.

[0056] Further, in the wound core of the present embodiment, the ratio obtained by dividing the number of twin crystal intersections P where deformation twin crystals extending in different directions cross by the total number of deformation twin crystals 12 being in the range of 0.500 or more and 3.000 or less is preferably satisfied in all of the prescribed twin crystal regions. On the other hand, as the necessary lowest limit for obtaining the effect in the present embodiment, the ratio obtained by dividing the number of prescribed twin crystal regions with this ratio in the above range by the total number of prescribed twin crystal regions of the steel sheets forming the wound core is more preferably 0.02 or more. That is, if the number of all of the prescribed twin crystal regions is C_tot and the total number of prescribed twin crystal regions with a ratio obtained by dividing the number of twin crystal intersections P where deformation twin crystals extending in different directions cross by the total number of deformation twin crystals 12 of a range of 0.500 or more and 3.000 or less is C_0, more preferably C_0 / C_tot satisfies 0.02 or more.C_0 / C_tot is still more preferably 0.05 or more, even more preferably 0.10 or more.

[0057] Next, when the twin crystal intersections P satisfy the following relationship in any prescribed twin crystal region with a ratio obtained by dividing the number of twin crystal intersections P where deformation twin crystals extending in different directions cross by the total number of deformation twin crystals 12 satisfying 0.500 or more and 3.000 or less, the wound core loss becomes smaller. That is, the number of twin crystal intersections P more preferably becomes 5 or more and 150 or less. Still more preferably the number of twin crystal intersections P becomes 5 or more and 110 or less, even more preferably 5 or more and 70 or less.

[0058] Furthermore, when the twin crystal intersections P satisfy the following relationship in any prescribed twin crystal region with a ratio obtained by dividing the number of twin crystal intersections P where deformation twin crystals extending in different directions cross by the total number of deformation twin crystals 12 satisfying 0.500 or more and 3.000 or less, the wound core loss becomes further smaller. That is, if the number of twin crystal intersections P present at the bend outside from the center line M is Nout and the number of twin crystal intersections P present at the bend inside from the center line M is Nin, Nout / Nin>1.00 is more preferably satisfied. Nout / Nin is still more preferably 2.00 or more, even more preferably is 3.00 or more.

[0059] Furthermore, when the twin crystal intersections P satisfy the following relationship even in a prescribed twin crystal region with a ratio obtained by dividing a number of twin crystal intersections P where deformation twin crystals extending in different directions cross by the total number of deformation twin crystals satisfies 0.500 or more and 3.000 or less, along with the core loss, the noise property is also improved and becomes smaller. That is, the average value of the depth positions of the twin crystal intersections P in the sheet thickness direction of the steel sheet is preferably in the range of t / 50 to t / 2 in the sheet thickness direction from the outermost layer at the outside of the prescribed twin crystal region of the individual steel sheets when the sheet thickness of the steel sheet 1 is “t”. Here, the sheet thickness “t” may be defined as the thickness when measuring by a commercially available micrometer a single sheet taken from plane parts 4, 4a other than bent parts 5 of the steel sheet at a wound core having prescribed twin crystal regions. The sheet thickness may be measured at several locations. In that case the sheet thickness is preferably made the average value. The average value of the depth positions of the twin crystal intersections P in the sheet thickness direction of the steel sheet is more preferably t / 50 to t / 3, still more preferably t / 50 to t / 4.

[0060] Further, in a prescribed twin crystal region where the ratio obtained by dividing the number of twin crystal intersections P where deformation twin crystals extending in different directions cross by the total number of deformation twin crystals 12 satisfies 0.500 or more and 3.000 or less, the ratio obtained by dividing the number of twin crystal intersections P by the sheet thickness of the steel sheet is more preferably 5 or more and 400 or less. The ratio obtained by dividing the number of twin crystal intersections P by the sheet thickness of the steel sheet is still more preferably 5 or more and 250 or less or even more preferably 5 or more and 100 or less.

[0061] The inventors discovered skin pass rolling the grain-oriented electrical steel sheet 1 in the step right before bending to form the bent part 5 as a result of intensive study as one example of the method of working the sheet for adjusting the number of the deformation twin crystals 12 and the number of twin crystal intersections P. By performing skin pass rolling before bending, strain becoming starting points of deformation twin crystals 12 is introduced to the grain-oriented electrical steel sheet 1 and subsequent bending causes deformation twin crystals 12 to easily form in a suitably crossed state. They evaluated the twin crystals formed and measured the wound core loss while changing the rolling reduction, roll diameter, and other parameters of the skin pass rolling and discovered the optimum ranges of the number of deformation twin crystals 12, number of twin crystal intersections P, and other parameters.

[0062] FIG. 8 is a schematic view showing a bent part 5 (prescribed twin crystal region) where deformation twin crystals are formed in a cross-section perpendicular to the surface of the steel sheet 1 and running along the winding direction in the steel sheet 1 forming the wound core according to the present embodiment. Note that, in FIG. 8, the state is shown of arranging the steel sheet 1 in a state with the bent part 5 projecting out downward.

[0063] As shown in FIG. 8, in the grain-oriented electrical steel sheet 1 according to the present embodiment, there are two deformation twin crystals 12a, 12b differing in direction of extension in the bent part 5. The deformation twin crystal 12a and the deformation twin crystal 12b cross at a fixed angle and form a twin crystal intersection.

[0064] Note that, the winding direction of the wound core may also be the rolling direction of the steel sheet. Further, the winding direction of the wound core may also be the {110}<001>direction of the steel sheet. Furthermore, in the explanation of FIG. 1 to FIG. 6, the X-axial direction may also be the rolling direction of the steel sheet and may also be the {110}<001>direction of the steel sheet.

[0065] The method of production of the grain-oriented electrical steel sheet is not particularly limited. A conventionally known method of production of a grain-oriented electrical steel sheet can be suitably selected. As a preferable specific example of the method of production, for example, the method may be mentioned of heating a slab containing C in 0.04 to 0.1 mass% and otherwise having the chemical composition of the above grain-oriented electrical steel sheet to 1000°C or more and hot rolling it, then annealing the hot rolled sheet in accordance with need, then cold rolling it one time or two times or more interspaced with intermediate annealing to obtain a cold rolled steel sheet and heating that cold rolled steel sheet in for example a wet hydrogen-inert gas atmosphere to 700 to 900°C to anneal it for decarburization, then if necessary further annealing it for nitriding then coating an annealing separator, then annealing it for finishing at 1000°C or so and forming an insulating coating at 900°C or so.

[0066] Further, in the present embodiment, the wound core comprised of a grain-oriented electrical steel sheet 1 provided with such a form is formed by stacking in layers individually bent grain-oriented electrical steel sheets 1 to assemble a wound shape. A plurality of grain-oriented electrical steel sheets 1 are connected with each other through at least one joint part 6 for each turn.

[0067] An apparatus enabling production of a wound core accompanied with the above such bending of steel sheets is schematically shown in the block diagram in FIG. 9. FIG. 9 schematically shows an apparatus 70 for production of a wound core forming the form of the core. This production apparatus 70 is provided with a bending part 71 for individually bending the grain-oriented electrical steel sheets 1. Further, it may also be provided with an assembling part 72 for stacking the bent grain-oriented electrical steel sheets 1 in layers to assemble them into a wound shape to thereby form a wound core of a wound shape including parts where grain-oriented electrical steel sheets 1 comprised of plane parts 4 and bent parts 5 alternately continuing in the longitudinal direction are stacked in the sheet thickness direction.

[0068] At the bending part 71, the grain-oriented electrical steel sheet 1 is supplied by being fed out by a predetermined conveyance speed from a steel sheet supply part 75 holding a hoop material formed by winding the grain-oriented electrical steel sheet 1 in a roll shape. The grain-oriented electrical steel sheet 1 supplied in this way is bent at the bending part 71 where it is cut to a suitable appropriate size and individually bent in small numbers such as one sheet at a time. Further, in the steps before the bending, the grain-oriented electrical steel sheet 1 is skin pass rolled. By controlling the roll diameter and tension of the skin pass conditions and using a grain-oriented electrical steel sheet processed in advance with a suitable range of rolling reduction as the core material, it is possible to obtain the core of the present disclosure.

[0069] In a thus obtained grain-oriented electrical steel sheet 1, the radius of curvature of the bent parts 5 formed by the bending becomes extremely small, therefore the working strain imparted to the grain-oriented electrical steel sheet 1 by the bending becomes extremely small. In this way, if it is assumed that the density of working strain will become greater and the volume effective for working strain can be reduced, it is possible to eliminate the annealing step.

[0070] The present disclosure is not limited to the above embodiments. The above embodiments are illustrative. Anything have substantially the same configuration as the technical idea described in the claims of the present disclosure and exhibiting similar actions and effects is encompassed in the technical scope of the present disclosure. EXAMPLES

[0071] Below, examples will be illustrated to specifically explain the present disclosure. Note that the conditions of the examples are illustrations employed for confirming the workability and effects of the present disclosure. The present disclosure is not limited to the conditions of the examples. The present disclosure can employ various conditions so long as not departing from its gist and achieving its object.

[0072] The inventors prepared and evaluated a plurality of wound cores using skin pass rolled steel sheets. Detailed dimensions of the wound core are shown in FIG. 10 and Table 1. Note that, the “no. of bent parts of 1 corner” of Table 1 shows the number of bent parts 5 present in one corner part 3, a wound core with a number of bent parts of one corner of “2” is a wound core shown in FIG. 2, and a wound core with a number of bent parts of one corner of “3” is a wound core shown in FIG. 3. Further, the “no. of joint parts” of Table 1 shows the number of joint parts of one steel sheet forming the wound core, a wound core with a number of joint parts of “1” is a wound core prepared using the steel sheet shown in FIG. 5, and a wound core with a number of joint parts of “2” is a wound core prepared using the steel sheet shown in FIG. 6.

[0073] [Table 1]_____________________________________________________________________________________________ Core no. Core shape LI L2 L3 L4 L5 9 r No. of bent parts of 1 corner No. of joint parts mm mm mm mm mm ° mm A-1 197 66 47 152.4 4 45 1.3 2 1 A-2 197 66 47 152.4 4 45 3.5 2 2 B-l 197 66 47 152.4 4 30 4.3 3 1 B-2 197 66 47 152.4 4 30 5.0 3 2

[0074] Table 2 shows the conditions of skin pass rolling. Note that the roll rotational speed was standardized at 30 rpm. The conditions of skin pass rolling were preferably a roll diameter of 40 to 100 mm, a tension of 4 to 10 MPa, and a rolling reduction of 0.1 to 2.0%.

[0075] [Table 2] Skin pass conditions Roll diameter (mm) Tension (MPa) Rolling reduction (%) a 1 0 0.05 b 40 4 0.1 c 45 4 0.1 d 50 4 0.2 e 55 4 0.1 f 200 0 0.08 g 20 3 4 h 35 3 5 i 40 5 0.3 .j 50 5 0.3 k 60 5 0.3 1 300 3 4 m 1 3 0.08 n 60 6 0.4 o 70 6 0.4 p 80 7 0.8 q 90 7 1 r 300 11 3.3 s 35 2 0.05 t 95 5 1.2 u 100 7 1.2 v 100 9 2 w 100 10 2 z 300 10 2.2 aa 1 25 2.5 ab 5 25 4.4 ac 15 25 5.2 ad 30 25 7.3 ae 100 10 1.6 af 600 25 9.3 5      

[0076] The skin pass conditions, specifications (core no. shown in Table 1), punch speed, and material sheet thickness of the prepared wound cores (Experiment Nos. 1 to 79) and the results of evaluation of the core loss are shown in Table 3 and Table 4. Note that, the core loss is measured by the excitation current method. The magnetic flux density is 1.7T and the frequency 10     is 50 Hz. The cross-sectional area S of the core is made the product of the sheet width of the steel sheet, the wound thickness of the core, and the space factor (0.965).

[0077] [Table 3] Experiment no. Skin pass conditions Core spec. Punch speed (mm / sec) Material sheet thickness “t” (mm) Material core loss (W / kg) Wound core loss (W / kg) Wound core loss / Material core loss Remarks 1 - A-1 40 0.23 0.72 0.821 1.14 Comp. ex. 2 a A-1 10 0.23 0.72 0.835 1.16 Comp. ex. 3 a A-1 40 0.23 0.72 0.835 1.16 Comp. ex. 4 f A-1 100 0.23 0.72 0.835 1.16 Comp. ex. 5 g A-1 200 0.23 0.72 0.850 1.18 Comp. ex. 6 h A-1 700 0.23 0.72 0.871 1.21 Comp. ex. 7 b A-1 10 0.23 0.72 0.778 1.08 Inv. ex. 8 c A-1 40 0.23 0.72 0.763 1.06 Inv. ex. 9 d A-1 100 0.23 0.72 0.742 1.03 Inv. ex. 10 e A-1 500 0.23 0.72 0.742 1.03 Inv. ex. 11 i A-l 1000 0.23 0.72 0.734 1.02 Inv. ex. 12 k A-1 20 0.23 0.72 0.742 1.03 Inv. ex. 13 1 B-1 1000 0.23 0.72 0.871 1.21 Comp. ex. 14 . j B-1 1000 0.23 0.72 0.778 1.08 Inv. ex. 15 n B-1 2000 0.23 0.72 0.756 1.05 Inv. ex. 16 o B-1 700 0.23 0.72 0.778 1.08 Inv. ex. 17 p B-1 500 0.23 0.72 0.770 1.07 Inv. ex. 18 q B-1 300 0.23 0.72 0.763 1.06 Inv. ex. 19 t B-1 1 0.23 0.72 0.742 1.03 Inv. ex. 20 u B-1 1 0.23 0.72 0.749 1.04 Inv. ex. 21 v B-1 1 0.23 0.72 0.756 1.05 Inv. ex. 22 w A-2 1 0.23 0.72 0.734 1.02 Inv. ex. 23 z A-2 1000 0.23 0.72 0.871 1.21 Comp. ex. 24 aa B-2 1000 0.23 0.72 0.806 1.12 Comp. ex. 25 ad B-2 1000 0.23 0.72 0.821 1.14 Comp. ex. 26 - A-1 500 0.20 0.68 0.823 1.21 Comp. ex. 27 b A-1 300 0.20 0.68 0.775 1.14 Comp. ex. 28 d A-1 300 0.20 0.68 0.700 1.03 Inv. ex. 29 e A-1 600 0.20 0.68 0.714 1.05 Inv. ex. 30 i A-1 1000 0.20 0.68 0.741 1.09 Inv. ex. 31 .j A-1 2000 0.20 0.68 0.748 1.1 Inv. ex. 32 k A-1 3000 0.20 0.68 0.694 1.02 Inv. ex. 33 n A-1 2000 0.20 0.68 0.714 1.05 Inv. ex. 34 o A-1 1000 0.20 0.68 0.700 1.03 Inv. ex. 35 p A-1 1000 0.20 0.68 0.700 1.03 Inv. ex. 36 r B-1 300 0.20 0.68 0.823 1.21 Comp. ex. 37 z B-1 2000 0.20 0.68 0.823 1.21 Comp. ex. 38 b B-1 20 0.20 0.68 0.748 1.1 Inv. ex. 39 c B-1 20 0.20 0.68 0.700 1.03 Inv. ex. 40 d B-1 20 0.20 0.68 0.700 1.03 Inv. ex.

[0078] Table 4] Experiment no. Skin pass conditions Core spec. Punch speed (mm / sec) Material sheet thickness “t” (mm) Material core loss (W / kg) Wound core loss (W / kg) Wound core loss / Material core loss Remarks 41 e B-1 20 0.20 0.68 0.694 1.02 Inv. ex. 42 e B-1 20 0.20 0.68 0.694 1.02 Inv. ex. 43 n B-1 20 0.20 0.68 0.694 1.02 Inv. ex. 44 m B-1 20 0.20 0.68 0.762 1.12 Comp. 45 af B-2 20 0.20 0.68 0.823 1.21 Comp. 46 s A-1 20 0.18 0.58 0.702 1.21 Comp. 47 t A-1 100 0.18 0.58 0.661 1.14 Comp. 48 u A-1 100 0.18 0.58 0.626 1.08 Inv. ex. 49 b A-2 100 0.18 0.58 0.661 1.14 Comp. 50 d A-1 100 0.18 0.58 0.597 1.03 Inv. ex. 51 e A-1 100 0.18 0.58 0.592 1.02 Inv. ex. 52 i A-2 100 0.18 0.58 0.603 1.04 Inv. ex. 53 j A-1 100 0.18 0.58 0.609 1.05 Inv. ex. 54 aa B-1 100 0.18 0.58 0.702 1.21 Comp. 55 ab B-1 100 0.18 0.58 0.702 1.21 Comp. 56 k B-1 1000 0.18 0.58 0.621 1.07 Inv. ex. 57 b B-2 1000 0.18 0.58 0.615 1.06 Inv. ex. 58 d B-1 1 0.18 0.58 0.597 1.03 Inv. ex. 59 e B-2 1 0.18 0.58 0.586 1.01 Inv. ex. 60 r B-1 1000 0.18 0.58 0.702 1.21 Comp. 61 j B-1 3000 0.18 0.58 0.632 1.09 Inv. ex. 62 k A-2 3000 0.18 0.58 0.597 1.03 Inv. ex. 63 b A-1 3000 0.15 0.53 0.572 1.08 Inv. ex. 64 c A-1 3000 0.15 0.53 0.583 1.1 Inv. ex. 65 d A-2 3000 0.15 0.53 0.546 1.03 Inv. ex. 66 e A-1 1000 0.15 0.53 0.546 1.03 Inv. ex. 67 h A-1 1000 0.15 0.53 0.599 1.13 Comp. 68 j A-1 1000 0.15 0.53 0.551 1.04 Inv. ex. 69 k A-1 1000 0.15 0.53 0.557 1.05 Inv. ex. 70 n A-2 1 0.15 0.53 0.583 1.1 Inv. ex. 71 o A-1 1 0.15 0.53 0.578 1.09 Inv. ex. 72 t B-1 1 0.15 0.53 0.578 1.09 Inv. ex. 73 u B-1 1 0.15 0.53 0.578 1.09 Inv. ex. 74 w B-2 40 0.15 0.53 0.551 1.04 Inv. ex. 75 ae B-1 40 0.15 0.53 0.562 1.06 Inv. ex. 76 b B-1 40 0.15 0.53 0.557 1.05 Inv. ex. 77 c B-2 3000 0.15 0.53 0.546 1.03 Inv. ex. 78 d B-1 3000 0.15 0.53 0.541 1.02 Inv. ex. 79 e A-2 3000 0.15 0.53 0.525 0.99 Inv. ex.

[0079] 5          Further, the following values of the prepared wound cores (Experiment Nos. 1 to 79) are shown in Table 5 and Table 6: • Total number L of deformation twin crystals • Number M of twin crystal intersections • Ratio (M / L) of number M of twin crystal intersections to total number L: ratio obtained by dividing number of twin crystal intersections P where deformation twin crystals extending in different directions cross by total number of deformation twin crystals 12 • Nout: number of twin crystal intersections present outside of bend from center line of sheet thickness center of steel sheet • Nin: number of twin crystal intersections present inside of bend from center line of sheet thickness center of steel sheet •    t / 50 (pm): lower limit value of average value of depth positions D in sheet thickness direction of steel sheet of twin crystal intersections P • Average value of depth in sheet thickness direction of twin crystals (pm): average value (=D) of depth positions in sheet thickness direction of steel sheet of twin crystal intersections •    t / 2 (pm): upper limit value of average value of depth positions D in sheet thickness direction of steel sheet of twin crystal intersections P •    C_0: number of prescribed twin crystal regions where ratio obtained by dividing number of twin crystal intersections P where deformation twin crystals present in different directions cross by total number of deformation twin crystals 12 satisfies 0.500 or more and 3.000 or less • C_tot: total number of prescribed twin crystal regions of steel sheet forming wound core • C_0 / C_tot: ratio obtained by dividing number of prescribed twin crystal regions where ratio obtained by dividing number of twin crystal intersections P where deformation twin crystals present in different directions cross by total number of deformation twin crystals 12 satisfies 0.500 or more and 3.000 or less by total number of prescribed twin crystal regions of steel sheet forming wound core • Ratio (M / t) of number M of twin crystal intersections to sheet thickness of steel sheet: ratio obtained by dividing number of twin crystal intersections by sheet thickness of steel sheet Note that, there are a plurality of prescribed twin crystal regions at the wound core, but the values of the above L, D, M, Nout, Nin, and M / t are values obtained by extracting nonspecific locations from among the bent parts of the core and evaluating the prescribed twin crystal regions.

[0080] Exper. no. No. L of twin crystals ‘( / mm) No. M of cross points M / L Nout (point) Nin (point) t / 50 (Pm) Average value of depth in sheet thickness direction (p m) t / 2 (Pm) C_0 (region) C_tot (region) C_0 / C_tot M / t Remarks 1 11 0 0.00 0 0 4.6 153 115 0 1635 0.000 0.00 Comp. ex. 2 20 0 0.00 0 0 4.6 173 115 0 1635 0.000 0.00 Comp. ex. 3 20 0 0.00 0 0 4.6 173 115 0 1635 0.000 0.00 Comp. ex. 4 30 0 0.00 0 0 4.6 173 115 0 1635 0.000 0.00 Comp. ex. 5 50 0 0.00 0 0 4.6 153 115 0 1635 0.000 0.00 Comp. ex. 6 55 0 0.00 0 0 4.6 173 115 0 1635 0.000 0.00 Comp. ex. 7 40 20 0.50 0 20 4.6 5 115 14 1635 0.009 86.96 Inv. ex. 8 24 17 0.71 8 9 4.6 65 115 20 1635 0.012 73.91 Inv. ex. 9 10 5 0.50 4 1 4.6 80 115 33 1635 0.020 21.74 Inv. ex. 10 4 6 1.50 4 2 4.6 70 115 120 1635 0.073 26.09 Inv. ex. 11 38 70 1.84 55 15 4.6 86 115 300 1635 0.184 304.35 Inv. ex. 12 40 90 2.25 50 40 4.6 80 115 500 1635 0.306 391.30 Inv. ex. 13 49 300 6.12 30 270 4.6 90 115 0 2452 0.000 1304.35 Comp. ex. 14 40 120 3.00 32 88 4.6 115 115 1200 2452 0.489 521.74 Inv. ex. 15 39 110 2.82 63 47 4.6 110 115 1000 2452 0.408 478.26 Inv. ex. 16 46 120 2.61 29 91 4.6 130 115 1600 2452 0.652 521.74 Inv. ex. 17 20 60 3.00 11 49 4.6 120 115 1700 2452 0.693 260.87 Inv. ex. 18 10 30 3.00 6 24 4.6 110 115 1600 2452 0.652 130.43 Inv. ex. 19 15 12 0.80 3 9 4.6 100 115 2424 2452 0.989 52.17 Inv. ex. 20 9 5 0.56 2 3 4.6 5 115 1800 2452 0.734 21.74 Inv. ex. 21 10 5 0.50 2 3 4.6 5 115 2000 2452 0.816 21.74 Inv. ex. 22 10 5 0.50 1 4 4.6 5 115 1633 1635 0.999 21.74 Inv. ex. 23 49 200 4.08 34 166 4.6 20 115 0 1635 0.000 869.57 Comp. ex. 24 50 151 3.02 40 111 4.6 50 115 46 2452 0.019 656.52 Comp. ex. 25 40 5 0.13 0 5 4.6 100 115 2000 2452 0.816 21.74 Comp. ex. 26 26 0 0.00 0 0 4 95 100 0 1880 0.000 0.00 Comp. ex. 27 6 1 0.17 1 0 4 5 100 12 1880 0.006 5.00 Comp. ex. 28 6 3 0.50 1 2 4 5 100 20 1880 0.011 15.00 Inv. ex. 29 24 72 3.00 36 36 4 40 100 30 1880 0.016 360.00 Inv. ex. 30 40 120 3.00 35 85 4 115 100 56 1880 0.030 600.00 Inv. ex. 31 40 120 3.00 11 109 4 130 100 72 1880 0.038 600.00 Inv. ex. 32 2 1 0.50 1 0 4 115 100 1213 1880 0.645 5.00 Inv. ex. 33 40 20 0.50 0 20 4 5 100 42 1880 0.022 100.00 Inv. ex. 34 40 20 0.50 1 19 4 5 100 1863 1880 0.991 100.00 Inv. ex. 35 40 20 0.50 3 17 4 60 100 1800 1880 0.957 100.00 Inv. ex. 36 10 35 3.50 3 32 4 50 100 0 2820 0.000 175.00 Comp. ex. 37 64 400 6.25 5 395 4 100 100 0 2820 0.000 2000.00 Comp. ex. 38 40 120 3.00 22 98 4 140 100 57 2820 0.020 600.00 Inv. ex. 39 37 100 2.70 92 8 4 115 100 2721 2820 0.965 500.00 Inv. ex. 40 28 80 2.86 58 22 4 100 100 680 2820 0.241 400.00 Inv. ex.

[0081] Exper. no. No. L of twin crystals ‘( / mm) No. M of cross points M / L Nout (point) Nin (point) t / 50 (Pm) Average value of depth in sheet thickness direction (y m) t / 2 (Pm) C_0 (region) C_tot (region) C_0 / C_tot M / t Remarks 41 19 57 3.00 54 3 4 20 100 2800 2820 0.993 285.00 Inv. ex. 42 16 8 0.50 5 3 4 5 100 2810 2820 0.996 40.00 Inv. ex. 43 13 7 0.54 1 6 4 8 100 2790 2820 0.989 35.00 Inv. ex. 44 8 3 0.38 1 2 4 5 100 2200 2820 0.780 15.00 Comp. ex. 45 40 300 7.50 22 278 4 110 100 0 2820 0.000 1500.00 Comp. ex. 46 25 280 11.20 200 80 3.6 79 90 0 2089 0.000 1555.56 Comp. ex. 47 8 26 3.25 0 26 3.6 140 90 41 2089 0.020 144.44 Comp. ex. 48 8 24 3.00 0 24 3.6 115 90 42 2089 0.020 133.33 Inv. ex. 49 8 3 0.38 0 3 3.6 28 90 360 2089 0.172 16.67 Comp. ex. 50 36 58 1.61 49 9 3.6 120 90 890 2089 0.426 322.22 Inv. ex. 51 38 90 2.37 88 2 3.6 115 90 2056 2089 0.984 500.00 Inv. ex. 52 40 120 3.00 112 8 3.6 115 90 400 2089 0.191 666.67 Inv. ex. 53 49 25 0.51 10 15 3.6 100 90 60 2089 0.029 138.89 Inv. ex. 54 34 0 0.00 0 0 3.6 120 90 0 3133 0.000 0.00 Comp. ex. 55 15 0 0.00 0 0 3.6 110 90 0 3133 0.000 0.00 Comp. ex. 56 7 18 2.57 0 18 3.6 5 90 66 3133 0.021 100.00 Inv. ex. 57 40 20 0.50 0 20 3.6 5 90 64 3133 0.020 111.11 Inv. ex. 58 12 7 0.58 5 2 3.6 115 90 500 3133 0.160 38.89 Inv. ex. 59 6 14 2.33 14 0 3.6 96 90 2027 3133 0.647 77.78 Inv. ex. 60 40 130 3.25 34 96 3.6 120 90 200 3133 0.064 722.22 Comp. ex. 61 40 120 3.00 12 108 3.6 115 90 3128 3133 0.998 666.67 Inv. ex. 62 5 10 2.00 7 3 3.6 50 90 1000 2089 0.479 55.56 Inv. ex. 63 40 110 2.75 40 70 3 115 75 2500 2507 0.997 733.33 Inv. ex. 64 40 60 1.50 0 60 3 130 75 1700 2507 0.678 400.00 Inv. ex. 65 12 6 0.50 1 5 3 30 75 1056 2507 0.421 40.00 Inv. ex. 66 6 3 0.50 2 1 3 20 75 920 2507 0.367 20.00 Inv. ex. 67 40 1 0.03 1 0 3 5 75 830 2507 0.331 6.67 Comp. ex. 68 27 34 1.26 26 8 3 10 75 300 2507 0.120 226.67 Inv. ex. 69 6 4 0.67 1 3 3 100 75 100 2507 0.040 26.67 Inv. ex. 70 40 120 3.00 0 120 3 115 75 70 2507 0.028 800.00 Inv. ex. 71 40 116 2.90 35 81 3 130 75 12 2507 0.005 773.33 Inv. ex. 72 40 120 3.00 40 80 3 115 75 40 3760 0.011 800.00 Inv. ex. 73 40 120 3.00 40 80 3 115 75 76 3760 0.020 800.00 Inv. ex. 74 5 8 1.60 1 7 3 50 75 1200 3760 0.319 53.33 Inv. ex. 75 6 3 0.50 0 3 3 5 75 2600 3760 0.691 20.00 Inv. ex. 76 40 20 0.50 0 20 3 5 75 3520 3760 0.936 133.33 Inv. ex. 77 35 18 0.51 1 17 3 20 75 2300 3760 0.612 120.00 Inv. ex. 78 17 9 0.53 2 7 3 40 75 3754 3760 0.998 60.00 Inv. ex. 79 11 8 0.73 6 2 3 75 75 1346 2507 0.537 53.33 Inv. ex.

[0082] As shown in Table 3 to Table 6, wound cores with a ratio obtained by dividing the number 5      of twin crystal intersections P where deformation twin crystals extending in different directions cross by the total number of deformation twin crystals 12 satisfy 0.500 or more and 3.000 or less had a ratio of wound core loss to the material core loss (below, referred to as the “core loss ratio”) of 1.1 or less. These wound cores were designated as invention examples. On the other hand, wound cores with a ratio obtained by dividing the number of twin crystal intersections P where deformation twin crystals extending in different directions cross by the total number of deformation twin crystals 12 not satisfying 0.500 or more and 3.000 or less had a ratio of wound core loss to the material core loss of more than 1.1. These wound cores were designated as comparative examples.

[0083] That is, as shown in Table 3 and Table 4, a wound core with an M / L of 0.500 or more and 3.000 or less had a wound core loss ratio of 1.1 or less. If the M / L becomes greater than 3.000, this time the effect of strain became greater and the core loss deteriorated.

[0084] Table 7 shows the results of further evaluation of leakage of magnetic flux in bent parts evaluated for twin crystals at the time of measurement of the core loss in the comparative examples (Experiment No. 1, No. 21, and No. 24) and inventive examples (Experiment No. 7, No. 12, No. 17, and No. 50) freely selected from the wound cores in Table 5 and Table 6. In this evaluation, a winding wire was wound one turn about a bent part evaluated for ratio of number M of twin crystal intersections to the total number L of twin crystals and an average voltmeter (digital multimeter, product name AD7461A made by Advantest Corporation) was used to excite the magnetic flux density of the core to 1.7T. Further, the magnetic flux density of the bent parts at that time and the magnetic flux density of the plane parts adjoining the bent parts were measured and the ratio was evaluated.

[0085] [Table 7]________________________________________________________________________________________ Experiment no. M / L Set magnetic flux density (T) A: straight part magnetic flux density (T) B: core bent part magnetic flux density B (T) B / A Remarks 1 0.00 1.70 1.70 1.57 0.92 Comp. ex. 7 0.50 1.70 1.70 1.65 0.97 Inv. ex. 12 2.25 1.70 1.70 1.68 0.99 Inv. ex. 17 3.00 1.70 1.70 1.64 0.96 Inv. ex. 23 4.08 1.70 1.70 1.54 0.91 Comp. ex. 44 0.38 1.70 1.70 1.56 0.92 Comp. ex. 50 1.61 1.70 1.70 1.69 0.99 Inv. ex.

[0086] From the ratio of magnetic flux density of the bent parts to the magnetic flux density of the straight parts shown in Table 7 (=magnetic flux density of bent parts B / magnetic flux density of straight parts A), the effect of reduction of core loss by invention examples with a ratio of 0.96 or more was confirmed and the ratio of the wound core loss to the material core loss (core loss ratio (=wound core loss / material core loss)) becoming a small value of 1.1 or less was confirmed.

[0087] Therefore, according to the results of Table 7, at bent parts with a ratio (M / L) of the number M of twin crystal intersections to the total number L satisfying 0.500 or more and 3.000 or less, the bent parts and straight parts become substantially equal in magnetic flux density and the ratio of the magnetic flux density of the bent parts to the magnetic flux density of the straight parts becomes a sufficiently large value close to 1. As a result, the ratio of the wound core loss to the material core loss can be reduced. [REFERENCE SIGNS LIST]

[0088] 1 grain-oriented electrical steel sheet 2 stacked structure 3 corner part 4, 4a plane parts 5 bent part 6 joint part 10 wound core 12, 12a, 12b deformation twin crystals 15 hollow part 70 production apparatus 71 worked part 72 assembled part 75 steel sheet supply part

Claims

1. A wound core of a wound shape comprised of stacked layers of a bent steel sheet, in which wound core,the wound core having pluralities of plane parts and bent parts adjoining the plane parts in a side view looking at the wound shape from a direction running along a surface of the steel sheet and thereby formed into a rectangular shape having a hollow part at its center,in a cross-section perpendicular to the surface of the steel sheet and running along the winding direction, when defining regions of bent parts other than plane parts of any steel sheet as prescribed twin crystal regions, the prescribed twin crystal regions having pluralities of deformation twin crystals extending in different directions,in at least one of the prescribed twin crystal regions, a ratio obtained by dividing a number of twin crystal intersections where deformation twin crystals extending in different directions cross by a total number of deformation twin crystals being 0.500 or more and 3.000 or less.

2. The wound core according to claim 1, wherein, in a prescribed twin crystal region where the ratio satisfies being 0.500 or more and 3.000 or less, a number of twin crystal intersections where deformation twin crystals extending in different directions cross is 5 or more and 150 or less.

3. The wound core according to claim 1 or 2, wherein, in a prescribed twin crystal region where the ratio satisfies being 0.500 or more and 3.000 or less, if a number of twin crystal intersections present at an outside of a bend from a center line of a sheet thickness center of the steel sheet is Nout and a number of twin crystal intersections present at an inside of a bend from the center line of the sheet thickness center of the steel sheet is Nin, Nout / Nin>1.00 is satisfied.

4. The wound core according to claim 1 or 2, wherein, in a prescribed twin crystal region where the ratio satisfies being 0.500 or more and 3.000 or less, the average value of depth positions of the twin crystal intersections 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 at the outside of the prescribed twin crystal region of the steel sheet, where “t” is the sheet thickness of the steel sheet.

5. The wound core according to claim 1 or 2, wherein a ratio obtained by dividing a number of prescribed twin crystal regions where the above ratio satisfies 0.500 or more and 3.000 or less by a total number of prescribed twin crystal regions of the steel sheet forming the wound core is 0.02 or more.

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

7. The wound core according to claim 1 or 2, wherein, in at least one of the prescribed twin crystal regions, a ratio obtained by dividing a number of twin crystal intersections where deformation twin crystals extending in different directions cross by a total number of deformation twin crystals is 0.700 or more and 2.500 or less.

8. The wound core according to claim 1 or 2, wherein, in at least one of the prescribed twin crystal regions, a ratio obtained by dividing a number of twin crystal intersections where deformation twin crystals extending in different directions cross by a total number of deformation twin crystals is 1.000 or more and 2.300 or less.

9. A method of production of the wound core according to claim 1 or 2,the method of production of the wound core comprisinga step of skin pass rolling a steel sheet,a step of bending the skin pass rolled steel sheet,a step of cutting the steel sheet, anda step of stacking the bent and cut steel sheet in layers and making end parts in the winding direction abut against each other to assemble a wound shape.

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