Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F27/00—Details of transformers or inductances, in general
  • H01F27/24—Magnetic cores
  • H01F27/245—Magnetic cores made from sheets, e.g. grain-oriented
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
  • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets

Definitions

• the present invention relates to a wound core and a manufacturing method thereof.
• Patent Document 1 It is known that in wound cores made by bending steel sheets, iron loss can be reduced by controlling the shape of the bent parts.
• Patent Document 2 It is also known that when bending grain-oriented electromagnetic steel sheets that make up a wound core, iron loss can be reduced by suppressing the occurrence of deformation twins during the bending process (Patent Document 2). Also known is a wound core consisting of an inner core and an outer core, in which the grain-oriented electromagnetic steel sheet that makes up 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).
• Patent No. 7239089 International Publication No. 2018/131613 Japanese Patent Application Laid-Open No. 2017-157806
• Patent Document 1 the passage of magnetic flux at the bent portion where a large amount of plastic strain has been introduced is significantly hindered, and iron loss degradation is unavoidable, leaving room for improvement.
• 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.
• the purpose of this disclosure is to provide a wound core that can reduce iron loss and a method for manufacturing the same.
• the gist of this disclosure is as follows:
• a wound core having a wound shape formed by laminating folded steel plates the wound core is formed into a rectangular shape having a hollow portion at the center by having a plurality of flat portions and a plurality of bent portions adjacent to the flat portions, in a side view of the wound shape seen from a direction along the surface of the steel plate,
• a region of the bent portion excluding the flat portion of any steel plate is defined as a twin-defined region in a cross section perpendicular to the surface of the steel plate and along the winding direction
• the twin-defined region has a plurality of deformation twins extending in different directions
• a wound core, 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 0.500 or more and 3.000 or less.
• a wound core according to (1) or (2) above in which 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.
• a method for manufacturing a wound core comprising:
• This disclosure provides a wound core capable of reducing iron loss and a method for manufacturing the same.
• FIG. 1 is a perspective view schematically illustrating an embodiment of a wound core.
• FIG. 2 is a side view of the wound core shown in the embodiment of FIG. 1;
• FIG. 10 is a side view schematically showing another embodiment of a wound core.
• FIG. 2 is a diagram schematically illustrating an example of a bent portion (curved portion) of a grain-oriented electrical steel sheet.
• FIG. 2 is a diagram schematically illustrating an example of one layer of grain-oriented electromagnetic steel sheets in a wound core body.
• FIG. 2 is a diagram schematically illustrating an example of one layer of grain-oriented electromagnetic steel sheets in a wound core body.
• FIG. 1 is a diagram showing one steel sheet at a bent portion, and is a schematic 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. 10 is a schematic diagram for explaining how magnetic flux leakage is suppressed by the intersection of deformation twins.
• FIG. 1 is a schematic diagram of deformation twins in a cross section perpendicular to the surface of the steel sheet and along the winding direction.
• 1 is a diagram showing a schematic diagram of a manufacturing apparatus for a wound core in the form of an iron core;
• FIG. 4 is a diagram for explaining detailed dimensions of a wound core.
• gray-oriented electromagnetic steel sheet may be referred to simply as “steel sheet” or “electromagnetic steel sheet”
• wound core may be referred to as “wound core body” or simply as “core.”
• a wound core according to one embodiment of the present invention is a wound core formed by stacking folded steel sheets.
• the wound core When viewed from the side of the wound core in a direction along the surface of the steel sheets, the wound core has a rectangular structure with a central hollow, consisting of four flat portions and four corner portions adjacent to the flat portions.
• the flat portions refer to the straight portions other than the bent portions.
• the inner surface curvature radius r of the bent portions 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 direction.
• a grain-oriented electrical steel strip as defined in JIS C 2553:2019 can be used as the grain-oriented electrical steel sheet.
• the shapes of the wound core and grain-oriented electromagnetic steel sheet described here are not particularly new, but merely conform to the shapes of known wound cores and grain-oriented electromagnetic steel sheets.
• Fig. 1 is a perspective view showing a schematic representation of 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 showing a schematic representation of another embodiment of a wound core.
• a 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 (perpendicular to the plane of the paper in Figure 2).
• a side view refers to a view in the width direction (the Y-axis direction in Figure 1) of the long grain-oriented electrical steel sheets that make up the wound core.
• a side view is a diagram that shows the shape as seen from the side (a diagram in the Y-axis direction in Figure 1).
• a wound core 10 comprises a wound core body that is approximately 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 an approximately rectangular shape in side view.
• the wound core body 10 may be used as a wound core as is, or, if necessary, may be equipped with known fasteners such as cable ties to secure the stacked grain-oriented electromagnetic steel sheets together.
• the core length of the wound core body 10 there are no particular restrictions on the core length of the wound core body 10. If 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. The longer the core length, the smaller the volume ratio of the bends 5 to the wound core body 10, and therefore the smaller 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.
• 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 stacking direction when viewed from the side. Such a wound core can be suitably used for any of the conventionally known applications.
• the iron core of this embodiment is characterized by its approximately polygonal shape when viewed from the side.
• an iron core with a generally approximately rectangular (quadrilateral) shape will be described; however, iron cores of various shapes can be manufactured by changing the angle and number of bends 5 and the length of the flat surfaces. For example, if all bends 5 have an angle of 45° and the flat surfaces 4 are of equal length, the iron core will be octagonal when viewed from the side. Alternatively, if there are six bends 5 with an angle of 60° and the flat surfaces 4 are of equal length, the iron core will be hexagonal when viewed from the side.
• the wound core body 10 includes grain-oriented electromagnetic steel sheets 1, each having alternating flat portions 4, 4a and bent portions 5 in the longitudinal direction, stacked in the thickness direction, and has a generally rectangular laminated structure 2 with a hollow portion 15 in side view.
• Each corner portion 3, including the bent portion 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 4a that is shorter than the flat portion 4. Therefore, the corner portion 3 has two or more bent portions 5 and one or more flat portion 4a.
• one bent portion 5 is 45°.
• one bent portion 5 is 30°.
• the wound core of this embodiment can be constructed with bent portions having various angles, but from the standpoint of suppressing distortion due to deformation during processing and thereby suppressing iron loss, the bending angle ⁇ ( ⁇ 1, ⁇ 2, ⁇ 3) of bent portion 5 is preferably 60° or less, and more preferably 45° or less.
• the design can be selected as desired based on the points that are most important in core processing.
• FIG 4 is a schematic diagram showing an example of a bend (curved portion) 5 of a grain-oriented electrical steel sheet 1.
• the bending angle of the bend 5 refers to the angular difference between the straight portion on the rear side of the bending direction and the straight portion on the front side of the bending portion of the grain-oriented electrical steel sheet. It is expressed as the supplementary angle ⁇ of the 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 bend 5 on the outer surface of the grain-oriented electrical steel sheet 1.
• the points where the extended lines depart from the steel sheet surface are the boundaries between the flat portion 4 and the bend 5 on the outer surface of the steel sheet, and in Figure 4, these are points F and G.
• 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.
• the bent portion 5 is the portion of the grain-oriented electrical steel sheet 1 that is surrounded by the above-mentioned points D, E, F, and G when viewed from the side of the grain-oriented electrical steel sheet 1.
• the steel sheet surface between points D and E, i.e., the inner surface of the bent portion 5, is shown as La
• the steel sheet surface between points F and G, i.e., the outer surface of the bent portion 5 is shown as Lb.
• This diagram also shows the inner radius of curvature r of bend 5 when viewed from the side.
• the radius of curvature r of bend 5 is obtained by approximating La above with an arc passing through points E and D. The smaller the radius of curvature r, the sharper the curve of the curved portion of bend 5, and the larger the radius of curvature r, the gentler the curve of the curved portion of bend 5.
• the radius of curvature r at each bend 5 of each grain-oriented electrical steel sheet 1 stacked in the sheet thickness direction may vary to a certain extent. This variation may be due to forming accuracy, or it may be due to unintended variation caused by handling during stacking. With current, standard industrial manufacturing, such unintended errors can be kept to approximately 0.2 mm or less. If such variation is significant, a representative value can be obtained by measuring the radius of curvature for a sufficiently large number of steel sheets and averaging them. It is also possible to intentionally vary the radius of curvature for some reason, and this is not excluded by the present invention.
• the radius of curvature r of the bend 5 (the inner radius of curvature of the bend 5 when viewed from the side) 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 reduced.
• the method for measuring the radius of curvature r of the bent portion 5 can be measured, for example, by observing at 200x magnification using a commercially available microscope (Nikon ECLIPSE LV150).
• the center of curvature, point A is determined from the observation results.
• the magnitude of the radius of curvature r corresponds to the length of line segment AC.
• the intersection point on arc DE on the inside of the bent portion of the steel plate is defined as C.
• Figures 5 and 6 are schematic diagrams showing an example of one layer of grain-oriented electromagnetic steel sheet 1 in a wound core body.
• the grain-oriented electromagnetic steel sheet 1 used in the examples of Figures 5 and 6 is folded, overlapped, and laminated, and has two or more bent portions 5 and a flat portion 4, and forms a roughly polygonal ring in side view via joints 6 (gaps) that are the longitudinal end faces of one or more grain-oriented electromagnetic steel sheets 1.
• joints 6 (gaps) that are the longitudinal end faces of one or more grain-oriented electromagnetic steel sheets 1.
• these roughly polygonal rings those with a specific bend angle or bent portion shape are sometimes called "unicores.”
• the wound core body 10 may have a laminated structure that is approximately polygonal in side view overall.
• 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 Figure 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).
• 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 typically in the range of 0.15 mm to 0.35 mm, and preferably in the range of 0.18 mm to 0.27 mm.
• one joint 6 of one grain-oriented electromagnetic steel sheet that constitutes one layer of the wound core body is located in area A1 shown in Figures 2 and 3.
• two joints 6 of two grain-oriented electromagnetic steel sheets that constitute one layer of the wound core body are located in areas A1 and A2 shown in Figures 2 and 3. Note that detailed shapes and arrangements of joints 6 in area A1 or area A2 are omitted from Figures 2 and 3.
• the inventors have discovered that magnetic permeability decreases and iron loss increases at the bent portions 5 formed during plastic deformation when grain-oriented electrical steel sheet 1 is bent.
• a cross section of bent portion 5 perpendicular to the surface of grain-oriented electrical steel sheet 1 and along the winding direction is observed using an optical microscope, stripes of deformation twins can be observed extending from the surface of each steel sheet toward the interior (inside the bend).
• the existence of deformation twins can be confirmed by analytical evaluation using, for example, a scanning electron microscope and crystal orientation analysis software (EBSD).
• EBSD crystal orientation analysis software
• 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 sheet is a steel sheet in which the orientation of the crystal grains in the steel sheet is highly concentrated in the ⁇ 110 ⁇ 001> orientation (hereinafter sometimes referred to as the Goss orientation), but the crystal orientation in the areas where deformation twins occur is different from the Goss orientation, with deformation twins, for example, oriented along the ⁇ 112 ⁇ 111> orientation.
• the band-like structure of the deformation twins has a different orientation from the crystal orientation of the base steel sheet that has not been plastically deformed.
• Figure 7A is a diagram showing steel sheet 1 in 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.
• the inventors have discovered that by using 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. The inventors have then discovered that iron loss can be effectively suppressed by adjusting the number of deformation twins 12 and the number of twin intersections P in bent portion 5.
• the mechanism described here should be interpreted as the effect of the intersection of twins on magnetic properties when the number of twins is the same, particularly when the number is relatively large.
• the mechanism of action of deformation twin intersections at the bend 5 in this invention will be explained based on the above phenomenon (suppression of magnetic flux leakage).
• this is merely a hypothesis at this time to theoretically support the empirical rule discovered by the inventors after extensive research. We hope that the academically correct mechanism will be elucidated in the future.
• Figure 7B is a diagram showing steel sheet 1 at 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.
• the diagram shown in the left half shows a case where, like Figure 7A, there is a twin intersection P where deformation twins 12 extending in different directions intersect.
• the diagram shown in the right half of Figure 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.
• twin intersections P when twin intersections P exist, 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 prevents magnetic flux from leaking to the outside of the steel sheet.
• twin intersections P do not exist and the deformation twins 12 extend in the same direction, it is believed that magnetic flux will pass through the deformation twins 12 and leak to the outside.
• the inventors conducted extensive research into the effect that the number of deformation twins 12 and twin intersections P in the bends 5 have on iron loss, and discovered 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.
• the wound core discovered by the inventors has the following configuration. First, if the region of the bent portion 5 of any steel plate, excluding the flat portion 4, in a cross section perpendicular to the surface of the steel plate and along the winding direction is defined as a twin-defined region, then there are multiple twin-defined regions for each laminated steel plate. Specifically, there will be as many twin-defined regions as there are bending processes, and 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.
• the bent portion 5 is the portion of the grain-oriented electrical steel sheet 1 surrounded by points D, E, F, and G shown in Figure 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.
• At least one of the multiple twin-defined 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 values are 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.
• At least one of the multiple twin-defined regions has multiple 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 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.
• deformation twins are basically formed in a form that extends linearly for a finite length in a specific orientation of the steel sheet crystal when observed across the steel sheet. In the present invention, this linear region is defined as "one (single) deformation twin.” When two deformation twins extend in different, non-parallel directions and have a considerable length, they intersect, forming a twin intersection.
• a specific method for determining the number of deformation twins 12 present in the bent portion 5 is described below.
• 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 is defined as the number of deformation twins per twin-defined region. Deformation twins are formed within the thickness of the steel sheet. Similarly, the intersections of deformation twins and deformation twins were evaluated in each field of view of the twin-defined region on each cross section, and the average value was calculated to define the number per twin-defined region.
• the "twin-defining region” may mean "the twin-defining region of the cross section at the above five locations of one bent portion 5.”
• 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 cut-off machine (Maruto Co., Ltd., Model: MC-623EX), with a resinoid blade WA (specifications: ⁇ 150 mm, t0.3 mm, H30 mm) as the cutting blade.
• a mechanical upper-blade precision cut-off machine Maruto Co., Ltd., Model: MC-623EX
• 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.
• 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. This resulted in the preparation of a sample for cross-sectional observation of the bent region 5.
• 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 or more and 3.000 or less in all twin-defined regions.
• 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 plates constituting the wound core be 0.02 or more.
• C_0/C_tot is more preferable that C_0/C_tot be 0.02 or more.
• C_0/C_tot is more preferably 0.05 or greater, and even more preferably 0.10 or greater.
• the number of twin intersections P is between 5 and 150. Even more preferably, the number of twin intersections P is between 5 and 110, and even more preferably between 5 and 70.
• the number of twin intersections P located outside the bend of the center line M at the center of the steel plate thickness is Nout
• the number of twin intersections P located inside the bend of the center line M is Nin
• Nout/Nin is more preferably 2.00 or greater, and even more preferably 3.00 or greater.
• the average depth position of twin intersections P in the thickness direction of the steel sheet be 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.
• the thickness t can be defined as the thickness measured with a commercially available micrometer of a single sheet taken from the flat portions 4, 4a of the steel sheet excluding the bent portions 5 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 position of the twin intersection points P in the thickness direction of the steel plate is more preferably t/50 to t/3, and even more preferably t/50 to t/4.
• 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.
• one example of a processing method for adjusting the number of deformation twins 12 and the number of twin intersections P is to perform skin-pass rolling on the grain-oriented electrical steel sheet 1 in the process immediately prior to the bending process that forms the bent portion 5.
• strain that serves as the starting point for deformation twins 12 is introduced into the grain-oriented electrical steel sheet 1, making it easier for deformation twins 12 to be generated in an appropriately intersecting state during the subsequent bending process.
• the optimal ranges for parameters such as the number of deformation twins 12 and the number of twin intersections P were discovered.
• Figure 8 is a schematic diagram showing a bent portion 5 (twin-defined region) in which deformation twins 12 are formed in a cross section perpendicular to the surface of the steel sheet 1 constituting the wound core according to this embodiment and along the winding direction. Note that Figure 8 shows the steel sheet 1 positioned so that the bent portion 5 is convex downward.
• two deformation twins 12a and 12b extending in different directions are present in the bend 5, and the deformation twins 12a and 12b intersect at a certain angle, creating a twin intersection.
• 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.
• the X-axis direction may be the rolling direction of the steel sheet or the ⁇ 110 ⁇ 001> direction of the steel sheet.
• the method for manufacturing grain-oriented electrical steel sheet is not particularly limited, and any conventionally known method for manufacturing grain-oriented electrical steel sheet can be appropriately selected.
• a preferred example of a manufacturing method is to heat a slab containing 0.04 to 0.1 mass% C and otherwise having the chemical composition of the grain-oriented electrical steel sheet to 1000°C or higher and hot-roll it, followed by hot-rolling annealing as needed, followed by cold-rolling once or twice or more times with intermediate annealing between them to form a cold-rolled steel sheet.
• This cold-rolled steel sheet is then heated to 700 to 900°C in a wet hydrogen-inert gas atmosphere for decarburization annealing, further nitriding annealing as needed, coated with an annealing separator, and then finish-annealed at around 1000°C, followed by forming an insulating coating at around 900°C.
• a wound core composed 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 and assembling them into a wound shape, with multiple grain-oriented electromagnetic steel sheets 1 connected to each other via at least one joint 6 per turn.
• FIG. 9 shows a schematic diagram of a wound core manufacturing apparatus 70 that forms the core.
• This manufacturing apparatus 70 includes a bending unit 71 that individually bends grain-oriented electromagnetic steel sheets 1, and may also include an assembly unit 72 that stacks the bent grain-oriented electromagnetic steel sheets 1 in layers and assembles them into a wound shape, thereby forming a wound core that includes a portion where grain-oriented electromagnetic steel sheets 1, each with alternating flat portions 4 and bent portions 5 in the longitudinal direction, are stacked in the thickness direction.
• Grain-oriented electromagnetic steel sheet 1 is supplied to bending section 71 by being unwound at a predetermined transport speed from steel sheet supply section 75, which holds hoop material formed by winding grain-oriented electromagnetic steel sheet 1 into a roll.
• the grain-oriented electromagnetic steel sheet 1 supplied in this manner is cut to an appropriate size in bending section 71 and then individually bent in small batches, such as one by one.
• grain-oriented electromagnetic steel sheet 1 is subjected to skin-pass rolling.
• the iron core of the present disclosure can be obtained by using pre-processed grain-oriented electromagnetic steel sheet as the iron core material, controlling the roll diameter and tension under the skin-pass conditions and keeping the reduction within an appropriate range.
• the radius of curvature of the bent portion 5 created by the bending process is extremely small, and therefore the processing strain imparted to the grain-oriented electrical steel sheet 1 by the bending process is extremely small. While it is expected that the density of processing strain will be large, if the volume affected by the processing strain can be reduced, the annealing process can be omitted.
• Table 2 shows the skin-pass rolling conditions.
• the roll rotation speed was standardized to 30 rpm.
• the optimal 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%.
• Tables 3 and 4 show 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. 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 calculated as the product of the steel sheet width, the core winding thickness, and the space factor (0.965).
• C_0 The number of twin-defined regions for which the ratio obtained by dividing the number of twin intersection points 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 intersection points P where deformation twins extending in different directions intersect by the total number of deformation twins 12, the ratio being 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 intersection points to the thickness of the steel plate (M/t) The ratio obtained by dividing the number of twin intersection points 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.
• 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 between 0.500 and 3.000 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 examples of the invention.
• 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 between 0.500 and 3.000 have a ratio of core iron loss to material iron loss that exceeds 1.1, and these wound cores were designated as comparative examples.
• wound cores with M/L between 0.500 and 3.000 had an iron core iron loss ratio of 1.1 or less.
• M/L exceeded 3.000, the effect of distortion became greater, and iron loss deteriorated.
• Table 7 shows the results of further evaluation of magnetic flux leakage at the bends where twins were evaluated during iron loss measurement for comparative examples (Experiments No. 1, No. 21, No. 24) and invention examples (Experiments No. 7, No. 12, No. 17, No. 50) randomly selected from the wound cores in Tables 5 and 6.
• 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 voltmeter (digital multimeter manufactured by Advantest Corporation, product name AD7461A). The magnetic flux density at the bend and the magnetic flux density at the flat area adjacent to the bend were then measured, and the ratio was evaluated.

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