Manufacturing method and manufacturing device for wound core

Abstract

To provide a manufacturing method and a manufacturing device with which a wound core with low iron loss can be manufactured regardless of the presence or absence of annealing.SOLUTION: One or more arbitrary bent parts 5 of directional electromagnetic steel plates 1 to be laminated are formed by compressing portions to be bent of the directional electromagnetic steel plates 1 in their thickness T direction between a concave recess part 32 in a substantially V-shape of a die 30 and a convex part 42 of a punch 40 having a shape complementary to the shape of the concave recess part 32. The convex part 42 has a circular arc part 42a having a predetermined curvature at its apex, and the concave recess part 32 has linear parts 32a, 32a extending obliquely to both sides from the apex of the V-shape. The radius of curvature rd of the circular arc part 42a satisfies the relationship of 0.2 mm≤r≤2.0 mm. The bent angle θ of the bent part 5 satisfies the relationship of 10°≤θ≤90°. The thickness T of the directional electromagnetic steel plate 1 satisfies the relationship of 0.15 mm≤T≤0.35 mm. A die width L(mm) satisfies the relationship of 2(rd+T) / sinθ≤L≤6(rd+T) / sinθ.SELECTED DRAWING: Figure 7

Description

[Technical field]

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

[0002] There are two types of transformer cores: stacked cores and wound cores. To manufacture a wound core, the rolled direction of the grain-oriented electromagnetic steel sheet, in which the axis of easy magnetization of the sheet is oriented, is generally the longitudinal direction, and the steel sheet is wound into a doughnut shape (wound shape), and the wound body is stacked in layers. After that, a rectangular parallelepiped die is inserted into the inner window side (inner hole of the doughnut shape) of the wound body, and the wound body is molded into a substantially rectangular shape by applying external pressure (in this specification, the wound core manufactured in this manner may be referred to as a trunco ​​core). At this time, the inside of the wound body is processed into a shape close to a right angle by the rectangular parallelepiped die. On the other hand, the outside of the wound body has a shape with a relatively gentle curvature. In this forming process, the entire wound body is molded as a single unit, so mechanical processing strain (plastic deformation strain) is introduced into the grain-oriented electromagnetic steel sheet that forms the wound body, and since this processing strain is a factor that greatly deteriorates the iron loss of the grain-oriented electromagnetic steel sheet, stress relief annealing is usually performed.

[0003] Meanwhile, as another method for manufacturing wound cores, techniques such as those disclosed in Patent Documents 1 to 3 have been disclosed in which the portions of the steel sheets that will become the corners of the wound core are bent in advance so that a relatively small bent region with a curvature radius of 3 mm or less is formed, and one or more bent steel sheets are then wound and stacked to form a wound core (in this specification, a wound core manufactured in this manner may be referred to as Unicore (registered trademark)). With this manufacturing method, compared to the conventional manufacturing method for Trancocore described above, no large-scale forming process or complex dies are required, the steel sheets are precisely bent to maintain the core shape, and processing distortion is concentrated only in the bent portions (corners), making it possible to omit the annealing process for removing distortion, and the industrial merits are great and the method is being increasingly applied. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-286169 A [Patent Document 2] Patent No. 6224468 [Patent Document 3] JP 2018-148036 A Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, when bending the corners of the steel sheet of the UNICORE by bending the steel sheet, the bending is usually performed by a one-side free bending method. Specifically, for example, as shown in Fig. 10, one side 100b of the grain-oriented electromagnetic steel sheet 100 placed on the die 102 is pressed by a pressing member 130, and the one side 100b is fixed and held while a punch 104 is pressed downward as shown by an arrow against the other side, that is, the one-side free end 100a of the grain-oriented electromagnetic steel sheet 100, to press the one-side free end 100a in the thickness T direction to bend the grain-oriented electromagnetic steel sheet 100. In this case, in the illustrated cross section along the thickness T direction of the grain-oriented electromagnetic steel sheet 100 (cross section along both the thickness T direction and the longitudinal direction of the grain-oriented electromagnetic steel sheet 1), the die 102 has a circular arc portion 102a at a clamping portion (outer surface of the corner portion) where the grain-oriented electromagnetic steel sheet 100 is clamped between the die 102 and the punch 104. The arc portion 102a connects a linear placement portion 102b on which the grain-oriented electromagnetic steel sheet 100 is placed and fixed, and a linear orthogonal extending portion 102c extending substantially orthogonal to the placement portion 102b. The die 102 has a similar arc portion 104a at a clamping portion (outer surface) that clamps the grain-oriented electromagnetic steel sheet 100 between the die 102 and a punch 104 that is pressed downward, specifically, the one-side free end portion 100a of the grain-oriented electromagnetic steel sheet 100 is pressed by the arc portion 104a of the punch 104 to bend the one-side free end portion 100a of the grain-oriented electromagnetic steel sheet 100 along the arc portion 102a of the die 102, thereby bending the one-side free end portion 100a of the grain-oriented electromagnetic steel sheet 100 with a predetermined curvature. The bending angle of the bent portion at this time is defined as θ(°). The fact that bending can be performed using such simple dies and processes is one of the features of Unicore, which is currently seeing a growing range of applications.

[0006] However, in bending processing by such a one-sided free bending method, even if the steel plate 100 is bent by the bending angle θ of the bending portion during processing, the bending angle θ of the bending portion becomes smaller due to "springback" caused by the residual stress in the steel plate 100. For this reason, overbending (bending the bending portion at an angle larger than θ) is performed to adjust the bending angle of the bending portion to a predetermined θ. However, since the mechanical properties of the steel plate 100 are not necessarily exactly the same at each bending portion, even if the same processing is performed, the residual stress at each bending portion is also different, and as a result, the springback may vary, and the bending angle θ of the bending portion may differ. In other words, the bending angle θ of the bending portion varies depending on the bending portion. On the other hand, it is difficult to grasp the mechanical properties and the variation of each bending portion of the steel plate 100. This phenomenon may cause a decrease in core quality. Such problems related to springback are a perspective that had not been taken into consideration at Trancore, where the bending precision itself is low and annealing after bending is assumed. However, they have become a recognized issue in the current situation where the Unicore manufacturing method, in which the effects of processing precision are more pronounced, is expanding. In addition, in the one-sided free bending method, the strain induced in the bent portion of the grain-oriented electrical steel sheet 100 is widespread over a wide area from the arc portion 102a to the bent side in Fig. 10, and therefore when the core is used without annealing (such as in the case of Unicore), there is a problem that the core core loss is inferior to that of a wound core (such as Trancocore) that is used after annealing. For this reason, it was necessary to use grain-oriented electrical steel sheets with low core loss, which are more difficult to obtain. Even when grain-oriented electrical steel sheets are used after annealing, the induced strain may not be completely released depending on the annealing conditions, and there is a risk that the core core loss will be inferior.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a manufacturing method and manufacturing apparatus for a wound core that is capable of manufacturing a wound core with low iron loss regardless of whether annealing is performed or not. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the present invention provides a wound core in the form of a unicore, that is, a wound core having a portion in which grain-oriented electromagnetic steel sheets, each having a rectangular hollow portion in the center and in which flat portions and bent portions are alternately continuous in the longitudinal direction, are stacked in the sheet thickness direction, the wound core being formed by stacking the grain-oriented electromagnetic steel sheets, each of which has been bent one by one, in layers and assembling them into a wound shape, and a plurality of grain-oriented electromagnetic steel sheets are connected to each other via at least one joint per turn, in a manufacturing method of the wound core, in which at least one of the bent portions in one or more of the stacked grain-oriented electromagnetic steel sheets is formed such that the portion to be bent of the grain-oriented electromagnetic steel sheet is bent in the thickness direction between a substantially V-shaped recessed portion of a die and a protruding portion of a punch having a shape substantially complementary to the shape of the recessed portion. the grain-oriented electrical steel sheet is formed by clamping and pressing, and in a cross section along the thickness direction of the grain-oriented electrical steel sheet, the convex portion has an arc portion having a predetermined curvature at its apex, and the concave portion has a straight portion extending obliquely to both sides from the apex of the V-shape, the radius of curvature rd (mm) of the arc portion in the convex portion of the punch satisfies the relationship of 0.20 mm≦rd≦2.00 mm, the bending angle θ (°) of the bent portion satisfies the relationship of 10°≦θ≦90°, the thickness T (mm) of the grain-oriented electrical steel sheet satisfies the relationship of 0.15 mm≦T≦0.35 mm, and a die width L (mm) which is the length of the straight line connecting at the shortest distance between extending ends of the straight portions extending on both sides from the apex of the concave portion of the die satisfies the relationship of 2(rd+T) / sinθ≦L≦6(rd+T) / sinθ.

[0009] Even in a wound core in the form of a unicore, when a bent portion is formed by the one-sided free bending method described above, the introduced strain is large and spreads over a wide area around the bent portion. Therefore, the core core core loss is inferior to that of a wound core (such as a Trancocore) that is used after annealing. Even when a grain-oriented electromagnetic steel sheet is annealed and used, if the introduced strain is not completely released, the core core core loss is inferior. In light of this situation, the inventors have focused on the fact that a wound core with low iron loss can be obtained by limiting the range of plastic strain introduced to a narrow range around the bent portion and reducing the amount of plastic strain introduced when forming a similar bent portion, and have studied how to reduce the amount of strain introduced in the bent portion and narrow the range of strain introduction. As a result, they have found that a wound core with low iron loss can be manufactured regardless of whether annealing is performed by using a V-bending method instead of the one-sided free bending method that has been widely used in the past. Furthermore, by narrowing the width of the die for bending, the strain is concentrated in a narrower range. In addition, when bending using the V-bending method, if multiple steel sheets are subjected to bending all at once, the convex portion of the inner formed body is locally pressed against the concave portion of the outer formed body by the V-bending punch, which may destroy the insulating coating of the directional electromagnetic steel sheet and cause a short circuit between the formed bodies, resulting in poor core characteristics. Therefore, it was discovered that by bending each of the steel sheets to be stacked one by one, and then stacking the processed multiple steel sheets and assembling them into a wound shape, the insulating coating is less likely to be destroyed and the formed bodies are less likely to be short-circuited, so that the core's core loss characteristics do not deteriorate.

[0010] Specifically, in such a V-bending method, at least one bent portion of one or more of the stacked grain-oriented electromagnetic steel sheets is formed by clamping the portion of the grain-oriented electromagnetic steel sheet to be bent in its thickness direction between a roughly V-shaped recess in the die and a convex portion of the punch which has a shape complementary to the shape of the recess. In this case, in a cross section along the thickness direction of the grain-oriented electrical steel sheet, the convex portion has an arc portion having a predetermined curvature at its apex, the concave portion has a straight portion extending obliquely from the apex of the V-shape to both sides, the radius of curvature rd (mm) of the arc portion at the convex portion of the punch satisfies the relationship of 0.20 mm ≦ rd ≦ 2.00 mm, the bending angle θ (°) of the bent portion satisfies the relationship of 10° ≦ θ ≦ 90°, the thickness T (mm) of the grain-oriented electrical steel sheet satisfies the relationship of 0.15 mm ≦ T ≦ 0.35 mm, and the die width L (mm), which is the length of the straight line connecting the extending ends of the straight portions extending from the apex of the concave portion of the die to both sides, satisfies the relationship of 2 (rd + T) / sin θ ≦ L ≦ 6 (rd + T) / sin θ. This reduces the distortion introduced at the bent portion, and makes it possible to manufacture a wound core with reduced core iron loss regardless of whether annealing is performed or not. Therefore, there is no need to use grain-oriented electrical steel sheets with low iron loss, which are more difficult to obtain.

[0011] In this disclosure, the bending angle of a bent portion means the angle difference generated between the straight portion on the rear side and the straight portion on the front side in the bending direction at the bent portion of the grain-oriented electrical steel sheet, and is expressed as the supplementary angle φ 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 that sandwich the bent portion 5 on the outer surface of the grain-oriented electrical steel sheet, as shown in FIG.

[0012] The present invention also provides a manufacturing device for a wound core in the form of a unicore. Specifically, the manufacturing device includes a folding unit which folds grain-oriented electromagnetic steel sheets one by one, and an assembly unit which stacks the folded grain-oriented electromagnetic steel sheets in layers and assembles them into a wound shape to form a wound core including a portion in which grain-oriented electromagnetic steel sheets, in which flat portions and bent portions are alternately continuous in the longitudinal direction, are stacked in the sheet thickness direction, the folding unit including a die having a substantially V-shaped recessed portion and a punch having a protruding portion having a shape substantially complementary to the shape of the recessed portion, and which presses a portion of the grain-oriented electromagnetic steel sheet to be bent between the recessed portion and the protruding portion in the thickness direction to form at least one of the bent portions in at least one of the grain-oriented electromagnetic steel sheets stacked. in a cross section along the thickness direction of the grain-oriented electrical steel sheet, the convex portion has an arc portion having a predetermined curvature at its apex, the concave portion has a straight portion extending obliquely to both sides from the apex of the V-shape, the radius of curvature rd (mm) of the arc portion in the convex portion of the punch satisfies the relationship of 0.20 mm≦rd≦2.00 mm, the bending angle θ (°) of the bent portion satisfies the relationship of 10°≦θ≦90°, the thickness T (mm) of the grain-oriented electrical steel sheet satisfies the relationship of 0.15 mm≦T≦0.35 mm, and a die width L (mm) which is the length of the straight line connecting at the shortest distance between extending ends of the straight portions extending on both sides from the apex of the concave portion of the die satisfies the relationship of 2(rd+T) / sinθ≦L≦6(rd+T) / sinθ.

[0013] The wound core manufacturing apparatus configured as described above can manufacture wound cores in which the distortion introduced into the bent portions is small and the core loss is reduced regardless of whether annealing is performed or not. This eliminates the need to use grain-oriented electrical steel sheets with low core loss, which are more difficult to obtain. Effect of the Invention

[0014] According to the present invention, a V-bending method is used to reduce the amount of strain introduced in the bent portion of the wound core and to narrow the range in which strain is introduced, thereby providing a manufacturing method and manufacturing apparatus for a wound core that can manufacture a wound core with low iron loss regardless of whether annealing is performed or not. [Brief description of the drawings]

[0015] [Figure 1] 1 is a perspective view showing a schematic diagram of a wound core according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a side view of the wound core shown in the embodiment of FIG. [Diagram 3] FIG. 4 is a side view showing a schematic diagram of a wound core according to another embodiment of the present invention. [Figure 4] FIG. 2 is a side view showing a schematic diagram of an example of one layer of grain-oriented electromagnetic steel sheet that constitutes a wound core. [Diagram 5] FIG. 4 is a side view showing typically another example of one layer of grain-oriented electrical steel sheet that constitutes a wound core. [Figure 6] FIG. 2 is a side view showing a schematic diagram of an example of a bent portion of a grain-oriented electrical steel sheet constituting a wound core of the present invention. [Figure 7] FIG. 1 is a cross-sectional view showing an embodiment in which a bent portion is formed by a V-bending method. [Figure 8] FIG. 2 is a block diagram illustrating a schematic configuration of a wound core manufacturing apparatus. [Figure 9] FIG. 2 is a schematic diagram showing dimensions of a wound core manufactured for characteristic evaluation. [Figure 10] FIG. 1 is a cross-sectional view showing an embodiment in which a bent portion is formed by a conventional one-sided free bending method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] A wound core according to one embodiment of the present invention will be described in detail below. However, the present invention is not limited to the configuration disclosed in this embodiment, and various modifications are possible without departing from the spirit of the present invention. The numerical ranges described below include lower and upper limits. Values ​​indicated as "greater than" or "less than" are not included in the numerical range. Furthermore, "%" in relation to chemical composition means "mass %" unless otherwise specified. In addition, terms used in this specification that specify shapes or geometric conditions and their degrees, such as "parallel," "vertical," "same," and "right angle," as well as values ​​of lengths and angles, are not to be bound by strict meanings but are to be interpreted to include a range within which similar functions can be expected. Furthermore, in this specification, a "grain-oriented electrical steel sheet" may be simply referred to as a "steel sheet" or an "electrical steel sheet", and a "wound iron core" may be simply referred to as an "iron core".

[0017] A wound core according to an embodiment of the present invention is a wound core having a wound core body that is substantially rectangular in side view. The wound core body includes a portion in which grain-oriented electromagnetic steel sheets, in which flat portions and bent portions are alternately continuous in the longitudinal direction, are stacked in the sheet thickness direction, and has a laminated structure that is substantially polygonal in side view. The inner surface side curvature radius r in side view of the bent portions in the wound core body is, for example, 0.2 mm or more and 2.0 mm or less. The grain-oriented electromagnetic steel sheets, for example, have a chemical composition that contains, by mass%, 2.0 to 7.0% Si, with the balance being Fe and impurities, and have a texture oriented in the Goss orientation.

[0018] Next, the shapes of the wound core and grain-oriented electromagnetic steel sheet according to one embodiment of the present invention will be specifically described. The shapes of the wound core and grain-oriented electromagnetic steel sheet described here are not particularly new, but merely conform to the shapes of known wound cores and grain-oriented electromagnetic steel sheets. Fig. 1 is a perspective view showing a typical embodiment of a wound core, Fig. 2 is a side view of the wound core shown in the embodiment of Fig. 1, and Fig. 3 is a side view showing a typical embodiment of the wound core. In the present invention, a side view refers to a view in the width direction (the Y-axis direction in FIG. 1) of the long grained electrical steel sheet that constitutes the wound core, and a side view is a diagram that shows the shape as seen from the side (a diagram in the Y-axis direction in FIG. 1).

[0019] A wound core according to one embodiment of the present invention includes a wound core body 10 that is substantially polygonal in side view. The wound core body 10 has grain-oriented electromagnetic steel sheets 1 stacked in the sheet thickness direction, to form a laminated structure 2 that is substantially rectangular in side view. The wound core body 10 may be used as a wound core as is, or may include a known fastener such as a cable tie in order to integrally fasten the stacked grain-oriented electromagnetic steel sheets, as necessary.

[0020] In this embodiment, there is no particular restriction on the core length of the wound core body 10, but even if the core length changes in the core, the volume of the bent portion 5 is constant, so the iron loss generated at the bent portion 5 is constant. The longer the core length, the smaller the volume ratio of the bent portion 5 to the wound core body 10, and the smaller the impact on iron loss degradation. Therefore, the longer the core length of the wound core body 10, the better. The core length of the wound core body 10 is preferably 1.5 m or more, and more preferably 1.7 m or more. In this embodiment, the core length of the wound core body 10 refers to the circumferential length at the center point of the wound core body 10 in the lamination direction when viewed from the side.

[0021] The wound core of this embodiment can be suitably used for any of the conventionally known applications.

[0022] The iron core according to this embodiment is characterized by being substantially polygonal in side view. In the following explanation using the figures, in order to simplify the illustration and explanation, a generally used substantially rectangular (quadrilateral) iron core will be described, but various shapes of iron cores can be manufactured depending on the angle and number of bends and the length of the flat portions. For example, if all bends have angles of 45° and the flat portions have the same length, the iron core will be octagonal in side view. Also, if there are six bends with angles of 60° and the flat portions have the same length, the iron core will be hexagonal in side view. As shown in FIG. 1 and FIG. 2, the wound core body 10 includes a portion in which grain-oriented electromagnetic steel sheets 1, in which flat portions 4 and bent portions 5 are alternately arranged in the longitudinal direction, are stacked in the sheet thickness direction, and has a laminated structure 2 having a substantially rectangular shape in a side view and a hollow portion 15. The corner portion 3 including the bent portions 5 has two or more bent portions 5 having a curved shape in a side view, and the sum of the bending angles of the bends 5 present in one corner portion 3 is, for example, 90°. The corner portion 3 has a flat portion 4a between adjacent bent portions 5, 5, whose length in the longitudinal direction in a side view is shorter than the length of the flat portion 4. Therefore, the corner portion 3 has two or more bent portions 5 and one or more flat portions 4a. The embodiment of FIG. 2 has two bent portions 5 in one corner portion 3, and each bent portion 5 is 45°. The embodiment of FIG. 3 has three bent portions 5 in one corner portion 3, and each bent portion 5 is 30°.

[0023] As shown in these examples, the iron core of this embodiment can be configured with bent parts having various angles, but from the viewpoint of suppressing the occurrence of distortion due to deformation during processing and suppressing iron loss, the bending angle φ (φ1, φ2, φ3) of the bent part 5 is preferably 60° or less, and more preferably 45° or less. The bending angle φ of the bent parts of one iron core can be configured arbitrarily. For example, φ1 = 60° and φ2 = 30° can be set. From the viewpoint of production efficiency, it is preferable that the bending angles (bending angles) are equal, and if the iron loss of the iron core created can be reduced by reducing the number of deformation points above a certain level, a combination of different angles may be used for processing. The design can be selected arbitrarily based on the points that are important in iron core processing.

[0024] The bend 5 will now be described in more detail with reference to FIG. Fig. 6 is a diagram showing a schematic diagram of an example of a bent portion (curved portion) 5 of a grain-oriented electrical steel sheet 1. The bending angle of the bent portion 5 means the angle difference generated between the straight portion on the rear side and the straight portion on the front side in the bending direction in the bent portion 5 of the grain-oriented electrical steel sheet 1, and is expressed as an angle φ that is a supplementary angle of an angle formed by two imaginary lines Lb-elongation1 and Lb-elongation2 obtained by extending the straight portions that are the surfaces of the flat portions 4, 4a on both sides that sandwich the bent portion 5 on the outer surface of the grain-oriented electrical steel sheet 1. In this case, the points where the extended straight lines depart from the steel sheet surface are the boundaries between the flat portions and the bent portion on the outer surface of the steel sheet, which are points F and G in Fig. 6.

[0025] Furthermore, straight lines perpendicular to the outer surface of the steel plate are extended from each of points F and G, and the intersections with the inner surface of the steel plate are points E and D. These points E and D are the boundaries between the flat portions 4, 4a and the bent portion 5 on the inner surface of the steel plate. In this embodiment, the bent portion 5 is a portion of the grain-oriented electrical steel sheet 1 that is surrounded by points D, E, F, and G in a side view of the grain-oriented electrical steel sheet 1. In Fig. 6, the steel sheet surface between points D and E, i.e., the inner surface of the bent portion 5, is shown as La, and the steel sheet surface between points F and G, i.e., the outer surface of the bent portion 5, is shown as Lb.

[0026] 6 also shows the inner surface curvature radius r (hereinafter simply referred to as the curvature radius r) of the bent portion 5 in a side view. The curvature radius r of the bent portion 5 is obtained by approximating the above La with a circular arc passing through points E and D. The smaller the curvature radius r, the sharper the curve of the curved portion of the bent portion 5, and the larger the curvature radius r, the gentler the curve of the curved portion of the bent portion 5. In the wound core of this embodiment, the radius of curvature r at each bent portion 5 of each grain-oriented electrical steel sheet 1 stacked in the sheet thickness direction may have a certain degree of variation. This variation may be due to forming accuracy, and may also occur unintentionally due to handling during stacking. In the case of current normal industrial manufacturing, such unintentional errors can be suppressed to about 0.2 mm or less. If such variation is large, a representative value can be obtained by measuring the radius of curvature for a sufficiently large number of steel sheets and averaging them. It is also possible to intentionally change the radius of curvature for some reason, but this embodiment does not exclude such a form.

[0027] There is no particular limitation on the method of measuring the radius of curvature r of the bent portion 5. For example, it can be measured by observing at 200 times using a commercially available microscope (Nikon ECLIPSE LV150). Specifically, the center of curvature A point as shown in FIG. 6 is obtained from the observation results. For example, if the intersection point A is defined as the intersection point of line segments EF and DG extended inwardly on the opposite side to point B, the magnitude of the radius of curvature r corresponds to the length of line segment AC. In this embodiment of the invention, the radius of curvature r of the bent portion 5 is not particularly limited, but may be in the range of 1 mm or more and 5 mm or less. The radius of curvature r of the bent portion 5 is preferably 3 mm or less. In this case, the effect of this embodiment of the invention is more significantly exhibited.

[0028] Figures 4 and 5 are diagrams showing typically an example of one sheet or one layer of grain-oriented electromagnetic steel sheet 1 in a wound core body 10. The grain-oriented electromagnetic steel sheet 1 used in the example of Figures 4 and 5 is folded to realize a wound core in a unicore form, and has two or more bent portions 5 and a flat portion 4, and forms a substantially polygonal ring in side view via joints (gaps) 6, which are end faces in the longitudinal direction of one or more grain-oriented electromagnetic steel sheets 1. In this embodiment, it is sufficient that the wound core body 10 has a laminated structure 2 that is generally polygonal in side view as a whole. As shown in the example of Fig. 4, one grain-oriented electromagnetic steel sheet 1 may constitute one layer of the wound core body 10 via one joint 6 (one grain-oriented electromagnetic steel sheet 1 is connected via one joint 6 for each turn), or as shown in the example of Fig. 5, one grain-oriented electromagnetic steel sheet 1 constitutes approximately half the circumference of the wound core, and two grain-oriented electromagnetic steel sheets 1 constitute one layer of the wound core body 10 via two joints 6 (two grain-oriented electromagnetic steel sheets 1 are connected to each other via two joints 6 for each turn). Naturally, a large number of joints adversely affects the characteristics of the core and increases the number of steps required to form the core, i.e., to form the wound body. For this reason, it is better to have fewer joints. On the other hand, if the size of the wound core is large, problems may arise during the winding process. Therefore, the number of joints can be determined by taking these factors into consideration.

[0029] The thickness of the grain-oriented electrical steel sheet 1 used in this embodiment is not particularly limited and may be appropriately selected depending on the application, etc., but is usually in the range of 0.15 mm to 0.35 mm, and preferably in the range of 0.18 mm to 0.27 mm.

[0030] The method for producing the grain-oriented electrical steel sheet 1 is not particularly limited, and a conventional method for producing a grain-oriented electrical steel sheet can be appropriately selected. A preferred example of the production method is a method in which a slab having 0.04 to 0.1 mass% C and the other chemical composition of the grain-oriented electrical steel sheet 1 is heated to 1000°C or higher and hot-rolled, and then annealed as necessary, and then cold-rolled once or twice or more with intermediate annealing to obtain a cold-rolled steel sheet, and the cold-rolled steel sheet is heated to 700 to 900°C in a wet hydrogen-inert gas atmosphere to be decarburized and annealed as necessary, and then nitriding annealed, and an annealing separator is applied, followed by finish annealing at about 1000°C, and an insulating coating is formed at about 900°C. Furthermore, painting or the like may be performed thereafter to adjust the friction coefficient. In addition to Si, C, Fe and impurities, the above chemical composition may contain one or more of Mn, Al, N, Cu, Nb, V, Mo, Ta and W as selective elements within a range that does not impair the effects of the present invention. The effect of this embodiment can also be obtained from steel sheets that have been subjected to a process generally known as "domain control" using distortions, grooves, or the like, in the manufacturing process of the steel sheets by a known method.

[0031] In addition, in this embodiment, the wound core composed of grain-oriented electromagnetic steel sheets 1 having the above-mentioned configuration is formed by first stacking grain-oriented electromagnetic steel sheets 1 that have been individually bent one by one in layers and assembling them into a wound shape, and then connecting one or more grain-oriented electromagnetic steel sheets 1 to each other via at least one joint 6 in each turn. Specifically, when bending each sheet one by one, at least one bent portion 5 of one or more of the laminated grain-oriented electrical steel sheets 1 is produced as follows: That is, as shown in Fig. 7, the bent portion 5 is formed by a V-bending method in which a portion of the grain-oriented electrical steel sheet 1 to be bent (a portion corresponding to the bent portion 5 of the wound core) is clamped in its thickness T direction between a substantially V-shaped recessed portion 32 of a die 30 and a protruding portion 42 of a punch 40 having a shape substantially complementary to the shape of the recessed portion 32 (in the example of Fig. 7, the punch 40 moves downward with respect to the die 30 to pressurize the grain-oriented electrical steel sheet 1, as shown by the arrow in the figure). 7 along the thickness T direction of the grain-oriented electrical steel sheet 1 (i.e., along both the thickness T direction and the longitudinal direction of the grain-oriented electrical steel sheet 1), the protrusion 42 has an arc portion 42a having a predetermined curvature on its top surface, and the recessed portion 32 of the die 30 has straight portions 32a, 32a extending obliquely on both sides from the apex P of the V. That is, the bottom surface of the recessed portion 32 has straight portions 32a, 32a extending obliquely upward on both sides from the apex P of the V, and the outer surface of the protrusion 42 has the arc portion 42a having a predetermined curvature and straight portions 42b, 42b extending from both ends of the arc portion 42a. Furthermore, the radius of curvature rd (mm) of the arc portion 42a of the protrusion 42 of the punch 40 that forms the bent portion 5 having the inner surface side radius of curvature r satisfies the relationship 0.20 mm≦rd≦2.00 mm, the bending angle θ (°) of the bent portion 5 of the grain-oriented electrical steel sheet 1 satisfies the relationship 10°≦θ≦90° (bending angle θ=90° in FIG. 7 ), and the thickness T (mm) of the grain-oriented electrical steel sheet 1 satisfies the relationship 0.15 mm≦T≦0.35 mm. And the die width L (mm), which is the length of the straight line connecting at the shortest distance between the extending ends 32aa, 32ab of the straight line portions 32a, 32a extending on both sides from the apex P of the recessed portion 32 of the die 30, satisfies the relationship 2(rd+T) / sinθ≦L≦6(rd+T) / sinθ. It is preferable that the bent portions 5 in all of the grain-oriented electrical steel sheets 1 to be laminated are formed by the above method under the above conditions.

[0032] Moreover, an apparatus that enables the manufacture of a wound core using the above-mentioned V-bending method is shown generally in a block diagram in Fig. 8. Fig. 8 generally shows a manufacturing apparatus 70 for a wound core in the form of a unicore, and this manufacturing apparatus 70 comprises a folding section 71 that folds grain-oriented electromagnetic steel sheets 1 one by one, and an assembly section 72 that stacks the folded grain-oriented electromagnetic steel sheets 1 in layers and assembles them into a wound shape to form a wound core including a portion where grain-oriented electromagnetic steel sheets 1, in which flat portions 4 and bent portions 5 are alternately continuous in the longitudinal direction, are stacked in the sheet thickness direction.

[0033] The grain-oriented electromagnetic steel sheet 1 is fed to the bending section 71 by being unwound at a predetermined conveying speed from the steel sheet supply section 50, which holds a hoop material formed by winding the grain-oriented electromagnetic steel sheet 1 in a roll shape. The grain-oriented electromagnetic steel sheet 1 thus fed is cut to an appropriate size in the bending section 71 and is folded one by one. In the grain-oriented electromagnetic steel sheet 1 thus obtained, the radius of curvature r of the bent portion 5 generated by the bending process is extremely small, ranging from 0.2 mm to 2.0 mm, so that the processing strain imparted to the grain-oriented electromagnetic steel sheet 1 by the bending process is extremely small compared to that of Trancocore (in the case of Trancocore, the radius of curvature on the outside of the core reaches several tens of mm, so that even if the radius of curvature on the inside is small, the size of the strain-imparted portion is extremely large on the outside of the core). Thus, while it is expected that the processing strain will be large, if the volume affected by the processing strain can be reduced, the annealing process can be omitted.

[0034] In addition, the bending processing section 71 comprises a die 30 having a substantially V-shaped recess 32, as described above, and a punch 40 having a protrusion 42 having a shape substantially complementary to the shape of the recess 32, and by squeezing the portion of the grain-oriented electromagnetic steel sheet 1 to be bent in the thickness T direction between the recess 32 and the protrusion 42, at least one bending portion 5 is formed in at least one or more, and preferably all, of the stacked grain-oriented electromagnetic steel sheets 1.

[0035] (Example) The technical contents of the present invention will be further explained below with reference to examples of the present invention. The conditions in the examples shown below are examples of conditions adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to these examples. In addition, various conditions can be adopted in the present invention as long as they do not deviate from the gist of the present invention and achieve the object of the present invention. In this example, the grain-oriented electrical steel sheets (steel sheets No. 1 to 8) shown in Table 1 were used to produce the iron cores shown in Table 2, and the iron core characteristics were measured. Table 3 shows the detailed manufacturing conditions and characteristics.

[0036] Specifically, Table 1 shows the chemical composition (the balance being Fe and impurities; mass %) and magnetic properties of the grain-oriented electrical steel sheets. The magnetic properties of the grain-oriented electrical steel sheets were measured based on the Single Sheet Tester (SST) method for magnetic properties specified in JIS C 2556:2015. The magnetic properties measured included the magnetic flux density B8 (T) in the rolling direction of the steel sheets when excited at 800 A / m, and the iron loss (W17 / 50 (W / kg)) at an AC frequency of 50 Hz and an excitation magnetic flux density of 1.7 T. Table 1 also shows the steel sheet thickness (mm) and the presence or absence of laser domain control for each of the steel sheets No. 1 to 8.

[0037] [Table 1]

[0038] The inventors also manufactured iron cores Nos. a to c having the shapes shown in Table 2 and Fig. 9 using each of steel sheets Nos. 1 to 8 as materials. Here, L1 is the distance between parallel grain-oriented electromagnetic steel sheets 1 at the innermost periphery of the wound core in a cross section that is parallel to the X-axis direction and includes the center CL (the distance between the inner surface flat portions), L2 is the distance between parallel grain-oriented electromagnetic steel sheets 1 at the innermost periphery of the wound core in a vertical cross section that is parallel to the Z-axis direction and includes the center CL (the distance between the inner surface flat portions), L3 is the lamination thickness (thickness in the lamination direction) of the wound core in a cross section that is parallel to the X-axis direction and includes the center CL, L4 is the laminated steel sheet width of the wound core in a cross section that is parallel to the X-axis direction and includes the center CL, and L5 is the distance between flat portions (the distance between the bent portions) that are adjacent to each other at the innermost part of the wound core and that form a right angle together. In other words, L5 is the longitudinal length of the flat portion 4a which is the shortest among the flat portions 4, 4a of the innermost circumferential grain-oriented electromagnetic steel sheet. r is the radius of curvature (mm) of the bent portion 5 on the inner surface side of the wound core, and φ is the bending angle θ (°) of the bent portion 5 of the wound core. The roughly rectangular iron cores Nos. a to c in Table 2 have an inner surface flat portion distance L1, and are divided almost in the middle of the distance L1, and have a structure in which two iron cores having a roughly U-shape are joined together. Here, the core No. c is a wound core of so-called truncated core type, which has been conventionally used as a general wound core, and is manufactured by a method in which steel sheets are wound into a cylindrical shape, and then the corners of the cylindrical laminate are pressed to have a certain curvature and formed into a substantially rectangular shape. For this reason, the radius of curvature r of the bend 5 varies greatly depending on the stacking position of the steel sheets. On the other hand, the core No. a is a wound core of unicore type having two bends 5 at one corner 3, and the core No. b is a wound core of unicore type having three bends 5 at one corner 3. The radius of curvature r of the bends in Table 2 is shown in detail in Table 3.

[0039] [Table 2]

[0040] The inventors applied the one-sided free bending method and the V-bending method as bending methods to 47 test pieces of the cores No. a to c manufactured using the steel plates No. 1 to 8 as the material, and varied the bending angle φ (°) of the bent portion 5 of the wound core, the curvature radius rd (mm) of the convex portion of the punch 40, and the die width L (mm) as shown in Table 3 to obtain the no-load loss of the cores using each steel plate as the material, and calculated the building factor (BF) by taking the ratio with the magnetic properties of the material steel plate shown in Table 1. In Table 3, (*1) in the processing adjustment indicates that in the one-sided free bending method, the stroke of the die (punch) is adjusted to φ = 45°, (*2) indicates that the stroke is adjusted to φ = 30°, and (*3) indicates that the stroke is adjusted to φ = 90°. As can be seen from Table 3, for test numbers 2, 17, 26, and 37, the die width L was small, and springback occurred in the bent portion, making it impossible to adjust φ to near the specified angle, resulting in a poor core shape (×) and making it impossible to install the windings on the core, making it impossible to measure the core characteristics. Also, for test numbers 8, 9, 23, 24, 31, 32, and 36, the die width L was large, and the steel sheet was repeatedly bent and unbent during the V-bending process, which increased the effect of processing strain imparted to the V-bend portion and its surroundings, resulting in larger core characteristics and BF. In addition, for test numbers 33 and 34, the radius of curvature rd was small, springback occurred at the bent portion, the core shape was poor (×), and the windings could not be installed on the core, so it was not possible to measure the core characteristics. In addition, for test numbers 39 and 40, the radius of curvature rd was large, and the processing distortion was large, resulting in a large BF. In addition, for test numbers 41 and 42, the radius of curvature rd was large, so the bent shape could not be frozen even by V-bending, springback occurred, and φ could not be adjusted to near the specified angle, so the core shape was poor (×) and the windings could not be installed on the core, so it was not possible to measure the core characteristics. Next, the inventors used steel plates No. 1 to 3 to create a truncated core of approximately the same size as the core No. c. Specifically, a donut-shaped winding body with an inner diameter of 180 mm and a lamination thickness of 55 mm was created using each steel plate hoop with a plate width of 150 mm. Next, a rectangular parallelepiped SKD11 die measuring 197 mm x 66 mm x 150 mm was inserted inside each winding body to transform the winding body into a roughly rectangular core, and then a SKD11 die having a recess was placed on the four outer corners of the winding body from the outside and pressed to deform and shape the core. After unloading, the die was removed, and winding was performed on the core in the same manner as above, and the no-load loss of each core was measured. As a result, as shown in test numbers No. 45 to 47, the iron loss of the wound core was large and measurement was not possible. From this, it is clear that in the method of preparing the winding body in advance and forming a wound core (so-called Trancocore), large distortion is imparted to the steel plate and core, resulting in increased iron loss, and that distortion relief annealing is essential for use as a wound core. As can be seen from the examples which satisfy the above-mentioned dimensional requirements, i.e., 0.2 mm≦rd≦2.0 mm, 10°≦θ(φ)≦90°, 0.15 mm≦T≦0.35 mm, and 2(rd+T) / sinθ≦L≦6(rd+T) / sinθ, and the comparative examples which do not satisfy the above-mentioned relationships, the building factor (BF) in the examples is kept to 1.12 or less (iron loss in the wound core is reduced).

[0041] [Table 3] [Explanation of symbols]

[0042] 1 Grain-oriented electrical steel sheet 4,4a Flat part 5 Bend 10 Wound core (wound core body) 30 Dice 32 Depression 32a Straight section 40 Punch 42 Convex 42a Arc section 71 Bending section 72 Assembly part

Claims

1. A method for manufacturing a wound core including a portion in which grain-oriented electromagnetic steel sheets, each having a rectangular hollow portion at the center and in which flat portions and curved portions alternate in the longitudinal direction, are stacked in the sheet thickness direction, the grain-oriented electromagnetic steel sheets being folded one by one and stacked in layers and assembled into a wound shape, and a plurality of grain-oriented electromagnetic steel sheets are connected to each other via at least one joint for each turn, comprising: at least one of the bent portions in one or more of the grain-oriented electrical steel sheets to be laminated is formed by clamping a portion of the grain-oriented electrical steel sheet to be bent in its thickness direction between a substantially V-shaped recessed portion of a die and a protruding portion of a punch having a shape substantially complementary to the shape of the recessed portion, In a cross section along a thickness direction of the grain-oriented electrical steel sheet, the convex portion has an arc portion having a predetermined curvature at its apex, and the concave portion has straight line portions extending obliquely on both sides from a vertex of a V shape, a radius of curvature rd (mm) of the arcuate portion of the protruding portion of the punch satisfies the relationship: 0.20 mm≦rd≦2.00 mm; The bending angle θ (°) of the bent portion satisfies the relationship of 10°≦θ≦90°, The thickness T (mm) of the grain-oriented electrical steel sheet satisfies the relationship 0.15 mm≦T≦0.35 mm, A die width L (mm), which is the length of the shortest straight line connecting the extending ends of the straight line portions extending from the apex of the concave portion of the die, satisfies the relationship 2(rd+T) / sinθ≦L≦6(rd+T) / sinθ. A method for manufacturing a wound core comprising the steps of:

2. a bending processing section for bending each grain-oriented electromagnetic steel sheet one by one; an assembly section which stacks the folded grain-oriented electromagnetic steel sheets in layers and assembles them in a wound shape to form a wound core including a portion where grain-oriented electromagnetic steel sheets, in which flat portions and bent portions are alternately continuous in the longitudinal direction, are stacked in the sheet thickness direction; Equipped with the bending processing unit includes a die having a substantially V-shaped recessed portion and a punch having a protruding portion having a shape substantially complementary to the shape of the recessed portion, and forms at least one of the bent portions of one or more of the grain-oriented electromagnetic steel sheets to be stacked by pressing a portion of the grain-oriented electromagnetic steel sheet to be bent between the recessed portion and the protruding portion in a thickness direction, In a cross section along a thickness direction of the grain-oriented electrical steel sheet, the convex portion has an arc portion having a predetermined curvature at its apex, and the concave portion has straight line portions extending obliquely on both sides from a vertex of a V shape, a radius of curvature rd (mm) of the arcuate portion of the protruding portion of the punch satisfies the relationship: 0.20 mm≦rd≦2.00 mm; The bending angle θ (°) of the bent portion satisfies the relationship of 10°≦θ≦90°, The thickness T (mm) of the grain-oriented electrical steel sheet satisfies the relationship 0.15 mm≦T≦0.35 mm, A die width L (mm), which is the length of the shortest straight line connecting the extending ends of the straight line portions extending from the apex of the concave portion of the die, satisfies the relationship 2(rd+T) / sinθ≦L≦6(rd+T) / sinθ. A wound core manufacturing apparatus comprising:

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