Iron core manufacturing method and manufacturing device

Abstract

To provide a manufacturing method for an iron core that can improve productivity, while preventing a deterioration in characteristics.SOLUTION: A manufacturing method for an iron core includes a molding step of superimposing a plurality of directional electromagnetic steel plates and executing bending processing on the directional electromagnetic steel plates in a superimposed state to mold a bent processed body, and a lamination step of laminating the bent processed bodies in a plate thickness direction. The plate thickness of the directional electromagnetic steel plate is 0.23 mm or less. The coefficient of friction between layers of the directional electromagnetic steel plates in the superimposed state at the time of the bending processing is controlled to be 0.60 or less.SELECTED DRAWING: Figure 7

Description

[Technical Field]

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

[0002] Wound cores are widely used as magnetic cores for transformers, reactors, noise filters, and the like.

[0003] A widely known method for manufacturing wound cores is to roll up steel sheets into a cylindrical shape, press the cylindrical laminate to form a roughly rectangular shape so that the corners have a certain curvature, and then anneal the laminate to remove distortion and maintain the shape (see, for example, Patent Document 1).

[0004] Another known method for manufacturing wound cores involves pre-bending the steel sheet portions that will become the corners of the wound core so as to form relatively small bent regions with a curvature radius of 3 mm or less, and then stacking these bent steel sheets to obtain the wound core (see, for example, Patent Documents 2 to 4). This manufacturing method does not require a large-scale press process, and the steel sheets are precisely bent to maintain the core shape. Furthermore, because processing strain is concentrated only in the bent portions (corners), it is possible to omit the need for strain removal by annealing (annealing process). Due to these significant industrial advantages, this manufacturing method is increasingly being adopted.

[0005] Furthermore, as described above, it is known that controlling the processing strain is important for iron cores that concentrate processing strain only in the bent portions (corners) and make it possible to omit the annealing process for strain removal (see, for example, Patent Document 5). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-286169 [Patent Document 2] Patent No. 6224468 [Patent Document 3] Japanese Patent Application Publication No. 2018-148036 [Patent Document 4] AU2012337260A1 [Patent Document 5] WO2018 / 131613 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a method and apparatus for manufacturing an iron core that can improve the productivity of wound cores while suppressing deterioration of the characteristics of the wound core. [Means for solving the problem]

[0008] In a manufacturing method in which electromagnetic steel sheets are bent in advance and then the bent electromagnetic steel sheets (referred to as bent bodies) are stacked to obtain a wound core, productivity is improved by bending a plurality of electromagnetic steel sheets in a stacked state rather than bending the electromagnetic steel sheets one by one. The inventors of the present application have found that when bending multiple overlapping electromagnetic steel sheets, unless the bending conditions are appropriately controlled, the characteristics of the wound core deteriorate compared to when bending each sheet individually. Specifically, if the interlayer friction coefficient (sliding condition) of the overlapping electromagnetic steel sheets is not appropriate, problems such as the generation of numerous twins in the bent portion and deterioration of bending accuracy occur, resulting in an increase in core iron loss in the wound core.

[0009] The inventors of the present application have found that even when a method of bending multiple stacked electromagnetic steel sheets is used, by appropriately controlling the bending conditions, it is possible to achieve wound cores manufactured by stacking bent bodies obtained by this method that have properties equal to or better than those of wound cores manufactured by stacking bent bodies obtained by bending electromagnetic steel sheets one by one. This makes it possible to improve the productivity of wound cores while suppressing deterioration in the properties of the wound cores.

[0010] In order to achieve the above object, the present invention provides a method for manufacturing an iron core, comprising the steps of: a forming step of stacking a plurality of grain-oriented electromagnetic steel sheets and bending the stacked grain-oriented electromagnetic steel sheets to form a bent body; and a stacking step of stacking the bent bodies in a sheet thickness direction, The thickness of the grain-oriented electromagnetic steel sheet is 0.23 mm or less, The interlayer friction coefficient of the overlapping grain-oriented electrical steel sheets at the time of the bending process is controlled to be 0.60 or less.

[0011] The method for manufacturing an iron core of the present invention further comprises the steps of: the grain-oriented electromagnetic steel sheet located on the outer side of the bent body is referred to as an outer steel sheet, the grain-oriented electromagnetic steel sheet located on the inner side of the bent body is referred to as an inner steel sheet, a feed amount of the outer steel plate to the bending device is set to a first feed amount; a feed amount of the inner steel plate to the bending device is set to a second feed amount; an increment of the first feed amount relative to the second feed amount is defined as a first increment; In the bent body, a length of the bent portion of the outer steel plate determined based on a geometric shape is defined as a first length, In the bent body, a length of the bent portion of the inner steel plate determined based on a geometric shape is defined as a second length, If the increment of the first length relative to the second length is a second increment, The control is characterized in that the value obtained by dividing the first increment by the second increment is controlled to be 1.70 or less.

[0012] The present invention also provides an iron core manufacturing apparatus including a processing device that performs bending processing on grain-oriented electrical steel sheets to form a bent body, the processing device stacks a plurality of the grain-oriented electromagnetic steel sheets together, and performs bending on the grain-oriented electromagnetic steel sheets in the stacked state; The thickness of the grain-oriented electromagnetic steel sheet is 0.23 mm or less, The method is characterized in that immediately before the bending process, the interlayer friction coefficient of the grain-oriented electrical steel sheets in the overlapped state is 0.60 or less.

[0013] The iron core manufacturing apparatus of the present invention also includes: a supply control device that controls the supply of the plurality of grain-oriented electrical steel sheets to the processing device; the grain-oriented electromagnetic steel sheet located on the outer side of the bent body is referred to as an outer steel sheet, the grain-oriented electromagnetic steel sheet located on the inner side of the bent body is referred to as an inner steel sheet, a feed amount of the outer steel plate to the bending device is set to a first feed amount; a feed amount of the inner steel plate to the bending device is set to a second feed amount; an increment of the first feed amount relative to the second feed amount is defined as a first increment; In the bent body, a length of the bent portion of the outer steel plate determined based on a geometric shape is defined as a first length, In the bent body, a length of the bent portion of the inner steel plate determined based on a geometric shape is defined as a second length, If the increment of the first length relative to the second length is a second increment, The supply control device controls the first increment divided by the second increment so that the value is 1.70 or less. [Effects of the Invention]

[0014] According to the present invention, it is possible to improve the productivity of wound cores while suppressing deterioration of the characteristics of the wound cores. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 2 is a perspective view schematically showing an example of a wound core. [Figure 2] FIG. 2 is a side view of the wound core shown in FIG. [Figure 3] FIG. 10 is a side view schematically showing another example of a wound core. [Figure 4]FIG. 2 is a side view schematically showing an example of a bent body. [Figure 5] FIG. 10 is a side view schematically showing another example of a bent body. [Figure 6] FIG. 2 is a side view schematically showing an example of a bent portion of a bent body. [Figure 7] FIG. 1 is a schematic view showing an example of a manufacturing apparatus used in a manufacturing method according to the present invention. [Figure 8] 1 is a diagram schematically illustrating an example of a bent body manufactured by a manufacturing method according to the present invention. [Figure 9] 1A and 1B are schematic diagrams showing an example of bending using a manufacturing apparatus according to the present invention, in which (a) shows the state before bending, (b) shows the state during bending, and (c) shows the state after bending in which the grain-oriented electrical steel sheet has been cut. [Figure 10] FIG. 2 is a schematic diagram showing dimensions of a wound core manufactured in an example (comparative example). DETAILED DESCRIPTION OF THE INVENTION

[0016] The iron core manufacturing method and manufacturing apparatus according to 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 listed below include the lower and upper limits. Numerical values ​​indicated as "more than" or "less than" are not included in the numerical range. Furthermore, "%" in chemical composition refers to "mass %" unless otherwise specified. Furthermore, terms used in this specification that specify shape and geometric conditions and their degrees, such as "parallel," "perpendicular," "identical," and "right angle," as well as values ​​of length and angle, are not limited to their strict meanings but are interpreted to include a range within which similar functions can be expected. Furthermore, in this specification, "grain-oriented electrical steel sheet" may be simply referred to as "steel sheet" or "electrical steel sheet," and "wound iron core" may be simply referred to as "iron core."

[0017] First, a wound core manufactured using the core manufacturing method according to the present invention will be described. <Wound core> FIG. 1 is a perspective view that schematically shows one embodiment of a wound core. FIG. 2 is a side view of the wound core shown in FIG. 1. FIG. 3 is a side view that schematically shows another embodiment of the wound core. In the present invention, "side view" refers to a view in the width direction (the Y-axis direction in FIG. 1) of the long grain-oriented electrical steel sheets that make up the wound core, and "side view" refers to a diagram that shows the shape as seen from the side (a diagram in the Y-axis direction in FIG. 1). Furthermore, "sheet thickness direction" refers to the thickness direction of the grain-oriented electrical steel sheets, and means the direction perpendicular to the peripheral surface of the wound core when the sheet is formed into a rectangular wound core.

[0018] Wound core 10 has a laminated structure in which bent bodies 1 formed from grain-oriented electromagnetic steel sheets are stacked in the sheet thickness direction and have a generally rectangular shape in side view. Wound core 10 may be used as a wound core as is, or, if necessary, may be provided with known fasteners such as cable ties to integrally fasten a plurality of stacked bent bodies 1.

[0019] The core length of wound core 10 is preferably 0.6 m or more, and more preferably 0.7 m or more. The core length of wound core 10 refers to the circumferential length at the center point of wound core 10 in the lamination direction when viewed from the side. Even if the core length changes, the volume of the bent portions remains constant, so the iron loss generated in the bent portions remains constant. However, as the core length increases, the volume fraction of the bent portions decreases, reducing the impact on iron loss degradation.

[0020] The thickness of the steel sheets of the wound core 10 is not particularly limited and is, for example, 45 mm. The thickness of the steel sheets of the wound core 10 refers to the maximum thickness in the lamination direction of the flat portion of the wound core 10 when viewed from the side.

[0021] As shown in FIGS. 1 and 2 , wound core 10 has a laminated structure 2 that is generally rectangular in side view. The laminated structure 2 includes bent bodies 1 stacked in the thickness direction, with flat portions 4 and corner portions 3 alternately arranged in the longitudinal direction. Each bent body 1 has two or more curved bends 5 in side view, and the total bending angle of the bends 5 in one corner 3 is 90°. Each corner 3 has a flat portion 4a between adjacent bends 5. Each corner 3 has two or more bends 5 and one or more flat portions 4a. FIG. 2 shows a case where one corner 3 has two bends 5, while FIG. 3 shows a case where one corner 3 has three bends 5. Although not shown, one corner 3 may have only one bend 5.

[0022] When one corner portion 3 is configured to have two or more bent portions 5, 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 portions 5 is preferably 60° or less, and more preferably 45° or less. In the case where one corner portion 3 has two bent portions 5 as shown in FIG. 2, it is preferable that φ1 = 60° and φ2 = 30°, or that φ1 = 45° and φ2 = 45°, for example. In the case where one corner portion 3 has three bent portions 5 as shown in FIG. 3, it is preferable that φ1 = 30°, φ2 = 30°, and φ3 = 30°, for example. Furthermore, from the viewpoint of improving production efficiency, it is preferable that the bending angles are equal. Therefore, in the case where one corner portion 3 shown in FIG. 2 has two bent portions 5, it is preferable that φ1=45° and φ2=45°, and in the case where one corner portion 3 shown in FIG. 3 has three bent portions 5, it is preferable that, for example, φ1=30°, φ2=30° and φ3=30°.

[0023] The bent portion 5 will be described in detail using FIG. 6. FIG. 6 is a diagram schematically illustrating an example of the bent portion 5 (curved portion) of the bent body 1. The bending angle of the bent portion 5 refers to the angle difference 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 bent body 1, 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 flat portions 4, 4a sandwiching the bent portion 5, the flat portions 4a, 4a sandwiching the bent portion 5, or the surfaces of the flat portions 4, 4 sandwiching the bent portion 5 on the outer surface of the bent body 1. In this case, the points where the extended lines depart from the steel sheet surface are the boundaries between the flat portions 4 and the bent portion 5 on the outer surface of the steel sheet, and in FIG. 6, these are points F and G.

[0024] Furthermore, lines perpendicular to the outer surface of the steel sheet are extended from each of points F and G, and the points at which they intersect with the inner surface of the steel sheet are designated points E and D, respectively. Points E and D are the boundaries between flat portion 4 or flat portion 4a on the inner surface of the steel sheet and bent portion 5. Bent portion 5 is the portion of the grain-oriented electrical steel sheet surrounded by points D, E, F, and G in a side view of the bent body 1. In FIG. 6, the steel sheet surface between points D and E, i.e., the inner surface of bent portion 5, is designated La, and the steel sheet surface between points F and G, i.e., the outer surface of bent portion 5, is designated Lb.

[0025] This figure also shows the inner surface curvature radius r of the bent portion 5 in a side view. The curvature radius r of the bent portion 5 is obtained by approximating the above La with an arc that passes 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 the present invention, the radius of curvature r at each bent portion 5 of each bent body 1 stacked in the sheet thickness direction may vary to some extent. This variation may be due to forming accuracy, or it may be due to unintended variation caused by handling during stacking. In current, normal industrial manufacturing, such unintended error can be suppressed to approximately 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 vary the radius of curvature for some reason, and this is not excluded by the present invention. There are no particular limitations on the method for measuring the radius of curvature r of the bent portion 5, and it can be measured, for example, by observing at 200x magnification using a commercially available microscope (Nikon ECLIPSE LV150). Specifically, the center of curvature, point A, is determined from the observation results. For example, if the intersection point A is defined as the point at which line segments EF and DG are extended inward on the opposite side from point B, then the magnitude of the radius of curvature r corresponds to the length of line segment AC.

[0026] The radius of curvature r of the bent portion 5 in a side view is, for example, in the range of more than 1 mm and not more than 3 mm.

[0027] Fig. 4 is a diagram schematically showing an example of a bent body 1. The bent body 1 shown in Fig. 4 is a single grain-oriented electromagnetic steel sheet that has a substantially rectangular ring shape in side view, and has four corner portions 3 and four flat portions 4. Fig. 4 shows a case where one bent body 1 constitutes one layer of a wound core 10. In the bent body 1 shown in Fig. 4, one flat portion 4 has a joint (gap) 6 that is an end face in the longitudinal direction, and the other three flat portions 4 do not have a joint 6.

[0028] FIG. 5 is a schematic diagram showing another example of a bent body 1. The bent body 1 shown in FIG. 5 is made of a single grain-oriented electromagnetic steel sheet that is roughly U-shaped in side view and has two corner portions 3 and three flat portions 4. FIG. 5 shows a case in which one bent body 1 constitutes approximately half the circumference of a wound core 10, and two bent bodies 1 constitute one layer of the wound core 10 via two joints 6. In other words, FIG. 5 shows a case in which two grain-oriented electromagnetic steel sheets form a roughly rectangular ring shape in side view and constitute one layer of the wound core 10. When two bent bodies 1 constitute one layer of the wound core 10, a joint (gap) 6 is formed where the end faces of the bent bodies 1 face each other. Note that one bent body 1 shown in FIG. 5 may constitute one layer of the core 10. In this case, stacking the bent bodies 1 results in an iron core 10 that is roughly U-shaped in side view.

[0029] Although not shown in the drawings, the bent body 1 may be a single grain-oriented electromagnetic steel sheet that is approximately L-shaped in side view and has one corner portion 3 and two flat portions 4. In this case, when the bent bodies 1 are stacked, an iron core 10 that is approximately L-shaped in side view is obtained.

[0030] <Iron core manufacturing method> Next, a method for manufacturing an iron core according to the present invention will be described. The method for manufacturing an iron core according to the present invention includes (1) a preparation step, (2) a pretreatment step, (3) a molding step, and (4) a lamination step.

[0031] (1) Preparation process The preparation process is a process for preparing (manufacturing) a general grain-oriented electrical steel sheet in which a coating is formed on the surface of a base steel sheet whose composition / crystal orientation is controlled. (2) Pretreatment process This is a pretreatment process to control the friction coefficient (interlaminar friction coefficient, which will be described later) of the grain-oriented electrical steel sheet. (3) Molding process This is a process in which a plurality of grain-oriented electromagnetic steel sheets are stacked together and then bent to form a bent body. Hereinafter, the operation of stacking a plurality of grain-oriented electromagnetic steel sheets before bending may be referred to as the first lamination. (4)Lamination process This is a step of stacking bent bodies to form a laminate. Hereinafter, the operation of stacking bent bodies may be referred to as second stacking.

[0032] (1) Preparation process (base steel plate) The base steel sheet can be appropriately selected from known grain-oriented electrical steel sheets. <001> It is a steel sheet that is highly concentrated in the orientation and has excellent magnetic properties in the rolling direction. An example of a preferable base steel sheet will be described below, but the present invention is not limited to the following.

[0033] The chemical composition of the base steel sheet is, by mass%, 2.0% to 7.0% Si, with the balance being Fe and impurities. This chemical composition has a crystal orientation of {110} <001> This is to control the Goss texture, which is concentrated in the Goss orientation, and ensure good magnetic properties. There are no particular restrictions on the other elements, and known elements may be included within known ranges in place of Fe. Typical content ranges for the most common elements are as follows: C: 0~0.0050%, Mn: 0 to 1.0% S: 0 to 0.0150%, Se: 0 to 0.0150%, Al: 0 to 0.0650%, N: 0 to 0.0050%, Cu: 0-0.40% Bi: 0 to 0.010% B: 0~0.080%, P: 0~0.50%, Ti: 0 to 0.0150%, Sn: 0 to 0.10% Sb: 0 to 0.10% Cr: 0~0.30%, Ni: 0 to 1.0% Nb: 0 to 0.030% V: 0~0.030%, Mo: 0 to 0.030% Ta: 0 to 0.030%, W: 0~0.030%, These optional elements may be contained according to their purpose, so there is no need to set a lower limit, and they may not be contained substantially. Furthermore, these optional elements may be contained as impurities. The term "impurities" refers to elements that are unintentionally contained, and refers to elements that are mixed in from raw materials such as ore and scrap, or the manufacturing environment, during industrial production of base steel sheets.

[0034] The chemical composition of the base steel sheet may be measured by a general steel analysis method. For example, the chemical composition of the base steel sheet may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Specifically, for example, a 35 mm square test piece is obtained from the center of the base steel sheet, and the components are measured using a measuring device such as Shimadzu's ICPS-8100 under conditions based on a pre-prepared calibration curve. C and S may be measured using the combustion-infrared absorption method, and N may be measured using the inert gas fusion-thermal conductivity method.

[0035] The above chemical composition is that of the base steel sheet. If the grain-oriented electrical steel sheet to be measured has a primary coating (glass coating, intermediate layer) made of oxides or the like on its surface, or an insulating coating, these are removed by a known method before measuring the chemical composition.

[0036] (Manufacturing method) The method for producing grain-oriented electrical steel sheets is not particularly limited, and conventionally known methods for producing grain-oriented electrical steel sheets can be appropriately selected. A preferred example of the production method involves, for example, heating a slab containing 0.04 to 0.1 mass% C and otherwise having the above-mentioned chemical composition to 1000°C or higher and hot-rolling it, followed by annealing the hot-rolled sheet as needed, followed by cold-rolling once or twice or more times with intermediate annealing to produce a cold-rolled steel sheet. The cold-rolled steel sheet is then heated to 700 to 900°C in a wet hydrogen-inert gas atmosphere for decarburization annealing, optionally followed by nitriding annealing as needed, coated with an annealing separator, and finally annealed at approximately 1000 to 1200°C, followed by forming an insulating coating at approximately 900°C. Further, painting or other processes for adjusting the friction coefficient may be performed. Furthermore, the steel sheet may be subjected to a process commonly known as "magnetic domain control" during the steel sheet production process.

[0037] (plate thickness) It is well known that a thinner sheet thickness is advantageous for reducing the iron loss of the grain-oriented electrical steel sheet itself and the iron loss of the iron core manufactured therefrom. Another object of the present invention is to eliminate the need for an increased number of laminations, i.e., an increased number of bending processes, when manufacturing an iron core using thin steel sheets. For this reason, the present invention is particularly useful in manufacturing methods using thin grain-oriented electrical steel sheets with a thickness of 0.23 mm or less. In the present invention, if the bending radius of the bending die is r and the number of laminations in the first lamination is two, and the thickness of the steel sheets to be laminated and bent is t, the steel sheets located on the outer side of the bent body will be bent using a die with a bending radius of r + t. This would defeat the purpose of the processing method of the present invention, which benefits from the localization of the bending strain region by reducing the bending radius. From this perspective, the grain-oriented electrical steel sheets used in the present invention preferably have a thickness of 0.23 mm or less. While there is no particular need to set a lower limit for the sheet thickness, considering the manufacturing efficiency of the steel sheet itself, the lower limit for the sheet thickness of the grain-oriented electrical steel sheet in question is preferably 0.05 mm, more preferably 0.09 mm, and even more preferably 0.12 mm. Furthermore, when the number of sheets stacked in the first lamination is three or more, taking into consideration the production efficiency of the bending process and an increase in the effective bending radius of the steel sheets located on the outer side of the bent body, the sheet thickness of the grain-oriented electrical steel sheet to be stacked is preferably less than 0.23 mm. For example, when the number of sheets stacked in the first lamination is three, the sheet thickness is preferably 0.20 mm or less, and when the number of sheets stacked in the first lamination is four, the sheet thickness is preferably 0.15 mm or less.

[0038] In this embodiment, a strip-shaped grain-oriented electrical steel sheet is wound into a coil to form a hoop material (coil material).

[0039] (2) Pretreatment process The friction coefficient (interlaminar friction coefficient) of the grain-oriented electrical steel sheet manufactured in the preparation process is controlled. Pretreatment is carried out using a pretreatment device. Pretreatment includes applying a lubricant (lubricating substance) using a spray or roll coater. Another pretreatment is to change the surface roughness by lightly rolling using a rolling roll.

[0040] (Measurement of interlayer friction coefficient) After pretreatment and before bending, a grain-oriented electrical steel sheet (sample) is taken out and the interlayer friction coefficient is measured. The interlayer friction coefficient is the friction coefficient between the steel sheet surfaces of the grain-oriented electrical steel sheets laminated in the first lamination. When pretreatment and bending are separate processes (separate lines), a specific grain-oriented electrical steel sheet (sample) is taken out after pretreatment but before bending, and the interlayer friction coefficient is measured. Note that, as will be described in detail later, a pretreatment device for pretreatment may be provided immediately before the bending die that performs bending in the processing device, and a bent body may be produced by performing pretreatment and bending consecutively. In other words, the pretreatment process and the bending process may be performed on the same line. In this case, a grain-oriented electrical steel sheet sample that has only been pretreated is produced on a separate line, and the interlayer friction coefficient is measured using this sample.

[0041] The interlaminar friction coefficient of grain-oriented electrical steel sheets is measured, for example, for a total of 10 sets, each set consisting of three grain-oriented electrical steel sheets (first stack). The interlaminar friction coefficient of grain-oriented electrical steel sheets is determined for each set by applying a uniform load in the stacking direction to the central steel sheet and pulling it from the relationship between the load and tensile force. Specifically, the interlaminar friction coefficient of the grain-oriented electrical steel sheets is determined by dividing the maximum tensile force by the load. The interlaminar friction coefficient of the grain-oriented electrical steel sheets is then determined as the average of the 10 sets of measurements. The interlaminar friction coefficient obtained by the above-mentioned procedure is generally the static friction coefficient, but it does not necessarily have to be the static friction coefficient; it may also be the dynamic friction coefficient. In the present invention, the maximum interlaminar friction coefficient in the above measurement is defined as 0.60 or less. The interlaminar friction coefficient of grain-oriented electrical steel sheets is preferably 0.03 to 0.50, more preferably 0.05 to 0.40.

[0042] Instead of providing a separate pretreatment process, the pretreatment process, i.e., the control of the interlaminar friction coefficient, may be performed during the preparation process. The interlaminar friction coefficient is controlled based on the type of coating and the surface condition, such as surface roughness. The method is not particularly limited, and any known method may be used as appropriate. For example, the roughness of the base steel sheet can be controlled by appropriately controlling the roll roughness of the hot-rolled steel sheet and / or cold-rolled steel sheet, grinding the surface of the base steel sheet, or chemical etching such as pickling. Another method involves increasing the baking temperature or time of the coating to promote surface smoothing of the glassy coating, reducing the roughness, and increasing the contact area between the steel sheets, thereby increasing the static friction coefficient. In practice, it may be necessary to observe the surface condition of an actual prototype steel sheet to ultimately achieve the desired friction coefficient. However, this is not difficult for those skilled in the art who routinely adjust the surface condition of products through rolling and surface treatment. When pretreatment is performed during the preparation process, a pretreated hoop material is prepared.

[0043] As described above, the pretreatment process may not be provided as an independent process, but may be performed immediately before bending in the forming process described below. That is, a pretreatment device (pretreatment device) may be provided before the processing device that performs bending, and the pretreatment may be performed in the pretreatment device, followed by bending in the processing device. In the following, the present embodiment will be described with reference to a case where the pretreatment is performed immediately before bending, i.e., a case where the pretreatment and bending are performed consecutively. Note that the pretreatment device may be provided integrally with the processing device. In this embodiment, the pretreatment device controls the interlayer friction coefficient of the overlapping grain-oriented electrical steel sheets to be 0.60 or less at the time of bending. In other words, the pretreatment device controls the interlayer friction coefficient of the overlapping grain-oriented electrical steel sheets to be 0.60 or less immediately before bending.

[0044] (3) Molding process A bent body is formed from pretreated grain-oriented electrical steel sheets. In this embodiment, two grain-oriented electrical steel sheets are stacked (first stacking) as the plurality of grain-oriented electrical steel sheets, and then bending is performed. Three or more grain-oriented electrical steel sheets may be stacked and then bent. There is no particular upper limit to the number of sheets stacked in the first stacking. However, the greater the number of sheets stacked, the larger the bending radius of the outermost steel sheets. This may result in a loss of the advantage of the iron core manufactured according to the present invention, which is characterized by processing with a small bending radius. Furthermore, considering the complexity of controlling the feed rate of the steel sheets depending on the stacking position within the iron core, as described below, it is practically preferable to keep the number of stacked sheets to four or less, although this depends on the thickness of the steel sheets to be stacked. In the following description, the control of the feed rate will be described assuming that the number of stacked sheets is two.

[0045] Figure 7 is a schematic diagram showing an example of a manufacturing apparatus 100 used to manufacture wound iron cores. The manufacturing apparatus 100 includes a supply control device (feeder) 20, a pre-processing device 40, and a processing device 30. The hoop materials 10a and 10b shown in Figure 7 are manufactured in a preparation process and are placed (set) at a position a predetermined distance away from the processing device 30. In the manufacturing apparatus 100, the line for carrying out pre-processing and the line for carrying out bending are the same line.

[0046] Of the two hoop materials 10a, 10b, the grain-oriented electromagnetic steel sheet 8A is supplied from the upper hoop material 10a, and the grain-oriented electromagnetic steel sheet 8B is supplied from the lower hoop material 10b.

[0047] The supply control device 20 is provided between the hoop materials 10a, 10b and the processing device 30, and intermittently transports the strip-shaped grain-oriented electromagnetic steel sheets (grain-oriented electromagnetic steel sheets 8A and 8B in this example) along the longitudinal direction of the grain-oriented electromagnetic steel sheets toward the processing device 30. It can be said that the supply control device 20 controls the supply of the grain-oriented electromagnetic steel sheets toward the processing device 30. As shown in FIG. 7 , the direction from the hoop materials 10a, 10b toward the processing device 30 is defined as the conveying direction X. The supply control device 20 feeds out a predetermined length of the grain-oriented electromagnetic steel sheet per predetermined time in the conveying direction X. Here, the predetermined length of the grain-oriented electromagnetic steel sheet fed by the supply control device 20 per predetermined time is defined as the feed amount (supply amount). The supply control device 20 preferably controls the feed rate of the grain-oriented electrical steel sheet 8A located on the outside in the stacking direction of the bent body (stacking direction of the second stack) so that it is greater than the feed rate of the grain-oriented electrical steel sheet 8B located on the inside. The stacking direction of the bent body is the direction from the center (inside) of the bent body 1 to the outside when substantially rectangular annular bent bodies 1 are stacked facing outward, and the direction from the recess side (inside) of the bent body 1 to the outside when substantially U-shaped bent bodies 1 are stacked facing outward. Furthermore, the direction is the direction from the inside of the L shape of the bent body 1 to the outside of the L shape when substantially L-shaped bent bodies 1 are stacked facing outward.

[0048] If the feed amount of the grain-oriented electromagnetic steel sheet 8A (hereinafter simply referred to as the outer steel sheet 8A) were not larger than that of the grain-oriented electromagnetic steel sheet 8B (hereinafter simply referred to as the inner steel sheet 8B) located on the inside, and both sheets were fed by the same amount, a problem would occur in that the ends of the outer steel sheet 8A and the inner steel sheet 8B in the feed direction would not be aligned when the bent body 1 was formed. That is, the length of the outer steel sheet 8A would be shorter than that of the inner steel sheet 8B. In other words, the end of the inner steel sheet 8B would protrude beyond the end of the outer steel sheet 8A. This occurs because the length of the outer steel sheet 8A is insufficient due to the bending radius of the outer steel sheet 8A being larger than that of the inner steel sheet 8B during bending (the extension distance is longer on the outer periphery, and the extension distance of the outer steel sheet 8A is longer than that of the inner steel sheet 8B). Note that the "extension distance" refers to the length along the longitudinal direction of the steel sheets for laminated steel sheets that are stacked at different positions within the core. In the core, the steel sheets located closer to the outside have a geometrically longer perimeter (extension distance) (larger diameter). The more outer the steel sheet, the greater the geometric perimeter. However, by increasing the feed amount of the outer steel sheets by an amount corresponding to the increased perimeter (increased length of the bent portion), it is possible to prevent the above-mentioned uneven edges from occurring.

[0049] Assume that two stacked steel plates with a thickness of t [mm] are bent at a bending angle φ [°] using a die with a radius of curvature r [mm]. In this case, the inner extension distance of the bent portion of the inner steel plate 8B is 2πr × φ / 360. Meanwhile, the inner extension distance of the bent portion of the outer steel plate 8A is 2π(r + t) × φ / 360. Therefore, when bending the stacked inner and outer steel plates 8B and 8A to form a single bent portion, in order to align the edges of the inner and outer steel plates 8B and 8A, the outer steel plate 8A must be longer than the inner steel plate 8B by a predetermined length (2πt × φ / 360). This predetermined length is calculated based on the increment in the length (perimeter) of the bent portion of the laminated steel plate that forms the iron core. It should be noted that this calculation is not based on the increment in the total perimeter of the laminated steel plate that forms the iron core, but is an amount unrelated to the length of the flat portion (flat portion 4 in Figure 2). The absolute value of this predetermined length is determined by the steel plate thickness t and the bending angle φ. Alternatively, it can be expressed as a ratio (relative value) to the extension distance (2πr×φ / 360) of the inner side of the bent portion of the inner steel plate 8B as a "reference." In other words, (2πt×φ / 360) / (2πr×φ / 360)=t / r, and it can also be expressed as the ratio of the steel plate thickness t to the curvature radius r. In the present invention, this increment, i.e., the increment of the extension distance of the outer steel plate 8A (first length of the bent portion of the outer steel plate 8A) relative to the extension distance of the inner steel plate 8B (second length of the bent portion of the inner steel plate 8B), which is determined based on the geometric shape, is called the "increment determined based on the geometric shape" (second increment), and is defined using this ratio. Above, the "increment determined based on the geometric shape" was explained in relation to the case where two steel plates are bent together. However, a generalized formula for calculating the "increment determined based on the geometric shape" that also applies to the case where three or more steel plates are bent together is shown below. That is, the "increment determined based on the geometric shape" for the nth steel plate (n is 2 or more, counting from the inside) can be calculated using the following formula: t×(n-1) / r

[0050] Here, regarding the steel sheet feed rate controlled by the supply control device 20, the increment of the feed rate of the outer steel sheet 8A (first feed rate) relative to the feed rate of the inner steel sheet 8B (second feed rate) is referred to as the "feed rate increment" (first increment). This first increment is the increment per bend. If the feed rate during processing is inappropriate, the edges of the bent body will not be aligned as described above, resulting in gaps at the joints when assembled into an iron core, degrading the iron loss characteristics. Furthermore, in addition to these geometrical adverse effects, the influence of the friction coefficient between the overlapping steel sheets will also result in inadvertent forces acting during bending, degrading the magnetic properties of the bent body itself and, ultimately, the magnetic properties of the iron core assembled from them. In this embodiment, to ensure good jointing of the ends and prevent the application of inadvertent forces during bending, it is preferable that the ratio of the "increment in the feed rate" to the "increment determined based on the geometric shape" (second increment), i.e., "increment in the feed rate" / "increment determined based on the geometric shape" (value obtained by dividing the first increment by the second increment), be 1.70 or less. That is, the supply control device 20 preferably controls the feed rate of the steel plate so that the value obtained by dividing the first increment by the second increment is 1.70 or less. If the value obtained by dividing the first increment by the second increment exceeds 1.70, the feed rate of the outer steel plate 8A becomes excessive, which can lead to uneven edges and the generation of inadvertent forces during bending. While there is no particular lower limit, if this value is less than 0.30, the effect of correcting the difference in the geometric extension distance between the outer steel plate 8A and the inner steel plate 8B is reduced. Therefore, the value obtained by dividing the first increment by the second increment is preferably 0.60 to 1.40, and the closer to 1.00 the value is, the more preferable. Note that when the value obtained by dividing the first increment by the second increment is 0, the first increment is 0, in other words, when the feed amount of the inner steel plate 8B and the feed amount of the outer steel plate 8A are the same. Furthermore, when multiple bends are provided in one bent body, the value obtained by dividing the first increment by the second increment may be the value obtained by dividing the sum of the first increments (the value obtained by multiplying the first increment by the number of bends) by the sum of the second increments (the value obtained by multiplying the second increment by the number of bends). Furthermore, when bending three or more stacked steel plates, the effect of the invention can be obtained as long as at least one of the steel plates (excluding the innermost steel plate) satisfies the above condition (first increment / second increment ≦ 1.70).

[0051] Although FIG. 7 shows that the supply control device 20 and the processing device 30 are provided separately, the supply control device 20 may be configured integrally with the processing device 30.

[0052] The pre-treatment device 40 is provided between the supply control device 20 and the processing device 30, and performs pre-treatment on the grain-oriented electrical steel sheets 8A and 8B. This controls the interlayer friction coefficient between the grain-oriented electrical steel sheets 8A and 8B. Note that the pre-treatment device 40 may be provided separately from the processing device 30, or may be provided integrally with the processing device 30.

[0053] The processing device 30 is equipped with roll members. The processing device 30 sandwiches the grain-oriented electromagnetic steel sheet 8A and the grain-oriented electromagnetic steel sheet 8B between the roll members from above and below to form a stacked state (first stacked state). The stacked grain-oriented electromagnetic steel sheets 8A and 8B are then bent to form a bent body.

[0054] FIG. 8 is a diagram schematically illustrating an example of a bent body 1 manufactured by a processing apparatus 30. The bent body 1 has flat portions 4 and corner portions 3 that are alternately connected, and at least one bent portion 5 is provided in each corner portion 3. The bent body 1 shown in FIG. 8(a) has a generally rectangular ring shape in side view, has four corner portions 3, and has two bent portions 5 in each corner portion 3. The bent body 1 shown in FIG. 8(b) has a generally U-shape in side view, has two corner portions 3, and has two bent portions 5 in each corner portion 3.

[0055] An example of a bending method will now be described. FIG. 9 is a schematic diagram showing an example of the bending method. As shown in FIG. 9(a), a processing apparatus 30 is provided with a bending die 31 that performs bending. The bending die 31 is provided with a die (lower die) 31b and a punch (upper die) 31a for press working. Also, as shown in FIG. 9(b), the processing apparatus 30 according to this embodiment is provided with a press die 32 that presses (sandwiches) the overlapping grain-oriented electrical steel sheets 8A, 8B when performing bending. Note that, although FIG. 9(b) shows the press die 32 provided on the front side (steel sheet supply side) of the bending die 31, the press die 32 may also be provided on the rear side (steel sheet delivery side) of the bending die 31.

[0056] Hereinafter, in the conveying direction X, the front side of the grain-oriented electromagnetic steel sheet in the traveling direction will be referred to as the front side (leading end side) of the grain-oriented electromagnetic steel sheet, and the side opposite to the traveling direction will be referred to as the rear side (rear end side) of the grain-oriented electromagnetic steel sheet.

[0057] The grain-oriented electrical steel sheets 8A, 8B are conveyed along the conveying direction X and stopped at a predetermined position. Because the supply control device 20 feeds out more of the outer steel sheet 8A than the inner steel sheet 8B, the leading edge of the outer steel sheet 8A protrudes beyond the leading edge of the inner steel sheet 8B, as shown in FIG. 9(b). The rear sides of the outer steel sheet 8A and the inner steel sheet 8B are clamped and fixed by a presser die 32. Then, bending is performed as shown in FIG. 9(c).

[0058] As a result of the bending process, the outer steel plate 8A shifts rearward relative to the inner steel plate 8B (toward the side opposite the die 31b in the vertical direction), so that the amount of protrusion of the outer steel plate 8A at the tip becomes zero, and the tips of the outer steel plate 8A and the inner steel plate 8B are aligned when the bending process is completed.

[0059] When the rear side (rear end side) of the outer steel plate 8A and the inner steel plate 8B is fixed in this manner, there is no need to move the pressure die 32 during the bending process (bending process), as is the case when the front side is fixed as described below, which makes it easier to configure and control the device.

[0060] The processing device 30 also includes a cutting unit (not shown). After bending the outer steel plate 8A and the inner steel plate 8B, the processing device 30 cuts the outer steel plate 8A and the inner steel plate 8B to a predetermined length behind the bent portion. This causes the rear ends of the outer steel plate 8A and the inner steel plate 8B to be aligned. As a result, a substantially L-shaped bent body 1 with one bent portion 5 formed therein is sent out from the processing device 30.

[0061] In this embodiment, the rear sides of the outer steel plate 8A and the inner steel plate 8B are fixed with a pressure die 32 to prevent them from shifting, but instead of being fixed with the pressure die 32, the rear sides may be fixed by coils (hoop material 10a and hoop material 10b) and controlled to prevent the outer steel plate 8A and the inner steel plate 8B from shifting.

[0062] During bending, the outer steel plate 8A and the inner steel plate 8B are pressed by the punch 31a with a predetermined force (pressure). This forms a bent portion 5 with a bend angle φ in the outer steel plate 8A and the inner steel plate 8B. There are no particular limitations on the method for adjusting the radius of curvature r of the bent portion 5 to a range of more than 1 mm and not more than 3 mm. However, the radius of curvature r of the bent portion 5 can typically be adjusted to the above-mentioned specific range by changing the distance between the die 31b and the punch 31a or the shapes of the die 31b and the punch 31a. The bent portions 5 of the bent bodies 1 stacked in the thickness direction are processed so that their radii of curvature r are consistent. However, errors may occur in the radius of curvature of the processed steel plates due to the roughness and shape of the steel plate surfaces. If an error occurs, it is preferable that the error be 0.1 mm or less. The error here refers to the error when comparing the outer steel plates 8A and the error when comparing the inner steel plates 8B of the bent body 1. The inner steel plate 8B is bent with a curvature r, and the outer steel plate 8A is bent with a curvature (r+t), so there is a difference between the two plates by the amount of plate thickness.

[0063] Here, another example of bending will be described. First, the leading ends of the outer steel plate 8A and the inner steel plate 8B are aligned by butting or the like. Next, the leading ends of the outer steel plate 8A and the inner steel plate 8B are clamped and fixed by a pressure die 32 that prevents misalignment. Next, bending is performed. In this case, during bending, the pressure die 32 needs to be moved appropriately in synchronization with the bending die 31 (punch 31a). When the pressure die 32 is moved, the outer steel plate 8A is automatically pulled in as the bending process progresses, increasing the feed amount of the outer steel plate 8A.

[0064] After being bent, the outer steel plate 8A and the inner steel plate 8B are cut to a predetermined length behind the bent portion, so that the rear ends of the outer steel plate 8A and the inner steel plate 8B are also aligned.

[0065] In this example, after the leading ends of the outer steel plate 8A and the inner steel plate 8B are aligned, the leading ends of the outer steel plate 8A and the inner steel plate 8B may not be clamped by the pressing die 32. In this case, simultaneously with the bending process, that is, as the bending process progresses, the supply control device 20 simultaneously feeds out only the outer steel plate 8A as the extension distance of the outer steel plate 8A increases. In other words, as the extension distance of the outer steel plate 8A increases, the supply control device 20 increases the feed amount of the outer steel plate 8A in accordance with the increase in the length of the bent portion so that the leading ends do not shift.

[0066] (multiple bending processes) Next, an example will be described in which the outer steel plate 8A and the inner steel plate 8B are bent multiple times and then cut. First, in the first bending (first stage), the leading edge of the outer steel plate 8A is made to protrude beyond the leading edge of the inner steel plate 8B, and the rear side is fixed with a presser die 32, and bending is performed. As a result, a bent portion 5 is formed in one location, and the leading edges of the outer steel plate 8A and the inner steel plate 8B are aligned. When the bent portion 5 is formed in one location in this way, the front side (leading edge side) is restrained so that the steel plates do not shift. In other words, this is essentially the same as when the front sides of the grain-oriented electromagnetic steel plates 8A, 8B are fixed. This can also be said to be a natural restraint of the front side by the bent portion 5 (bent portion).

[0067] In the second (second stage) and subsequent bending processes, bending is performed without pressing the rear sides of the outer steel plate 8A and the inner steel plate 8B with the pressing die 32, and the amount of steel plate supplied from the rear side is adjusted. That is, as bending is performed, more outer steel plate 8A is supplied than inner steel plate 8B in accordance with the increase in the length of the bent portion.

[0068] After the outer steel plate 8A and the inner steel plate 8B have been bent a predetermined number of times, they are cut to a predetermined length (for example, a length equivalent to about half the circumference of the wound core) behind the bent portion. This causes the rear ends of the outer steel plate 8A and the inner steel plate 8B to be aligned. Then, the bent body 1 is sent out from the processing device 30.

[0069] (Bending after cutting) In this embodiment, the outer steel plate 8A and the inner steel plate 8B are cut after bending, but cutting may be performed first and then bending may be performed after cutting. First, the outer steel plate 8A and the inner steel plate 8B are each cut to a predetermined length on the front side of the bending die 31. At this time, the cut length of the outer steel plate 8A is made longer than that of the inner steel plate 8B by the amount that the extension distance becomes longer during bending. The processing device 30 includes, for example, a first cutting unit for cutting the outer steel plate 8A and a second cutting unit for cutting the inner steel plate 8B.

[0070] Next, the processing device 30 overlaps the outer steel plate 8A and the inner steel plate 8B. The processing device 30 overlaps the outer steel plate 8A with the inner steel plate 8B on the bottom, for example. One way of overlapping at this time is a first overlapping method in which the rear ends of the outer steel plate 8A and the inner steel plate 8B are aligned and fixed at their rear ends, with the front end of the outer steel plate 8A protruding forward beyond the inner steel plate 8B. In the first overlapping method, for example, when a single bending process is performed using the bending die 31, the outer steel plate 8A moves relative to the inner steel plate 8B as the bending process is performed, and the front ends also become aligned after the bending process.

[0071] Alternatively, a second overlapping method may be used in which the leading edge of the outer steel plate 8A and the leading edge of the inner steel plate 8B are aligned and fixed at the front side, with the rear edge of the outer steel plate 8A protruding rearward. As described above, the second overlapping method requires that the presser die 32 be moved appropriately in synchronization with the bending die 31 (punch 31a). When the second overlapping method is used and, for example, one bending operation is performed using the bending die 31, the outer steel plate 8A moves relative to the inner steel plate 8B as the bending operation proceeds, and the rear edges of the outer steel plate 8A and the inner steel plate 8B are aligned after the bending operation.

[0072] Alternatively, a third stacking method may be employed, in which the outer steel plate 8A is placed on the bottom and the inner steel plate 8B is placed on the top, with the protruding length (protruding amount) of the outer steel plate 8A relative to the inner steel plate 8B being approximately equal (half each) at the front and rear ends. The third stacking method does not require clamping (fixing) at the front or rear ends. For example, using a die with a V-groove and a punch with a V-shaped tip, the central portion of the stacked steel plates is pressed downward from above with the punch, causing the outer steel plate 8A to shift equally in the front-to-rear direction (inward) relative to the inner steel plate 8B around the bent portion. As a result, after bending, the front ends of the outer steel plate 8A and the inner steel plate 8B are aligned, and the rear ends of the outer steel plate 8A and the inner steel plate 8B are aligned.

[0073] Alternatively, grain-oriented electrical steel sheets that have been cut to a predetermined length and stacked may be subjected to multiple bending processes. For example, the outer steel sheet 8A is placed on top and the inner steel sheet 8B is placed on the bottom, with the outer steel sheet 8A protruding further than the inner steel sheet 8B at both the front and rear ends. Here, the amount of protrusion of the front end of the outer steel sheet 8A relative to the front end of the inner steel sheet 8B is denoted as S, and the amount of protrusion of the rear end of the outer steel sheet 8A relative to the rear end of the inner steel sheet 8B is denoted as T. The first bending process is performed while the rear side is held down by the presser die 32. After the first bending process, the protrusion amount S becomes zero, and the front ends are aligned, and the steel sheets are restrained at the front end to prevent slippage. Then, from the second bending process onward, the rear side is not held down. After the predetermined number of bending processes, the protrusion amount T becomes zero, and the rear ends are also aligned.

[0074] (Sheet pressure when bending) As described above, during bending, the presser die 32 may press down on the front or rear side of the overlapping steel plates with a predetermined force (predetermined pressure). This predetermined force is called the plate pressing pressure. The presser die 32 applies the predetermined plate pressing pressure in the thickness direction of the steel plates. In this embodiment, the predetermined plate pressing pressure is 0.10 MPa or more and 1.0 MPa or less. By pressing the outer steel plate 8A and the inner steel plate 8B, i.e., by applying plate pressing pressure to the outer steel plate 8A and the inner steel plate 8B, unintended misalignment of the steel plates due to differences in the extension lengths (extension distances) between the inner and outer steel plates during bending can be avoided, and the leading or trailing ends can be aligned.

[0075] (4)Lamination process In the stacking process, multiple bent bodies 1 are stacked in the plate thickness direction (second stacking). That is, the bent bodies 1 are stacked by aligning the corner portions 3 and overlapping them in the plate thickness direction to form a stack. When bent bodies 1 having a substantially rectangular ring shape in side view are stacked in the plate thickness direction, a wound core 10 having a substantially rectangular ring shape in side view can be obtained. When bent bodies 1 having a substantially U-shape in side view are stacked in the plate thickness direction, a wound core 10 having a substantially U-shape in side view can be obtained. Note that by using two cores 10 having a substantially U-shape in side view, a wound core 10 having a substantially rectangular ring shape in side view can be obtained. Note that by stacking bent bodies 1 having a substantially L-shape in side view in the plate thickness direction, a wound core 10 having a substantially L-shape in side view can be obtained. Note that by using four cores 10 having a substantially L-shape in side view, a wound core 10 having a substantially rectangular ring shape in side view can be obtained.

[0076] (Bending conditions) When the interlaminar friction coefficient of multiple overlapping grain-oriented electrical steel sheets exceeds 0.60, the deformation of the grain-oriented electrical steel sheet located on the outer side of the bent portion 5 (outer steel sheet 8A in this example) is constrained, resulting in a situation in which strong shear stress acts on the surface layer of the steel sheet on the lamination surface side, causing noticeable twinning in the bent portion 5. Twinning is formed in stripes from the surface of the steel sheet toward the inside. When such noticeable twinning occurs, the properties of the iron core deteriorate. Specifically, the core iron loss of the iron core increases.

[0077] Furthermore, if the interlayer friction coefficient of multiple overlapping grain-oriented electrical steel sheets is less than 0.05, the steel sheets will slip during bending, reducing the bending accuracy. This reduction in bending accuracy will cause the core shape to deteriorate, resulting in a deterioration in the core's properties. Specifically, the core's iron loss will increase.

[0078] Furthermore, it is preferable that the interlayer friction coefficient μ and the tensile strength TS (MPa) of the steel sheet satisfy the following formula. Interlayer friction coefficient μ × tensile strength TS≦300

[0079] The interlayer friction coefficient μ roughly functions as the friction between the flat parts, which contributes greatly to the relative and macroscopic slippage between the outer steel plate and the inner steel plate during the bending process, and the friction at the bent part, which acts on the surface of the contact surface between the outer steel plate and the inner steel plate at the bent part 5 during the bending process and contributes to the shear stress that causes the generation of deformation twins.

[0080] The above formula is particularly relevant to the latter, and is thought to relate to the fact that the load with which the outer steel plate is pressed against the inner steel plate at the bent part during bending deformation is proportional to the deformation resistance of the steel plate, i.e., the tensile strength TS, and that the above shear stress acts with a magnitude proportional to the product of this deformation resistance and the friction coefficient.

[0081] If the value of μ×TS exceeds 300, deformation twins may occur significantly on the surface layers of the contact surfaces of the laminated steel sheets. The value of μ×TS (the value obtained by multiplying the interlaminar friction coefficient and the tensile strength of the grain-oriented electrical steel sheet) is preferably 300 or less, more preferably 250 or less, and even more preferably 200 or less. The smaller the value of μ×TS, the more the occurrence of deformation twins is suppressed. However, if μ is too small, as mentioned above, the bending accuracy will decrease significantly.

[0082] In the method for manufacturing an iron core according to this embodiment, the thickness of the grain-oriented electromagnetic steel sheets is 0.23 mm or less, and the interlayer friction coefficient of the grain-oriented electromagnetic steel sheets 8A, 8B in the overlapping state is controlled to 0.60 or less. As a result, (1) the outer grain-oriented electromagnetic steel sheet 8A in the bending portion 5 does not undergo tensile deformation, and the occurrence of twin crystals in the bending portion 5 can be suppressed. This suppresses an increase in core iron loss of the iron core. (2) Furthermore, no shifting of the steel sheets occurs during bending, and good bending accuracy can be achieved. This suppresses an increase in core iron loss of the iron core. (3) Furthermore, since a bent body is formed by overlapping multiple grain-oriented electromagnetic steel sheets and bending the overlapping grain-oriented electromagnetic steel sheets, productivity can be improved compared to when bending grain-oriented electromagnetic steel sheets one by one to form a bent body.

[0083] (Variation) In this embodiment, the processing device 30 performs the first lamination of grain-oriented electrical steel sheets in the forming process. However, pretreatment (control of the interlayer friction coefficient) and the first lamination may be performed in the preparation process, followed by winding into a coil. That is, for example, a two-ply coil (two-ply coil material) may be manufactured in the preparation process. When a two-ply coil is manufactured and then bent while unwinding the two-ply coil in the forming process, bending the steel sheets stacked on the outer periphery of the coil to be the outer periphery of the bent body reduces unevenness at the edges of the bent body. Using a two-ply coil in this way has the advantages of reducing the number of coils to be set and simplifying the device by eliminating the need for the supply control device 20. However, from the perspective of aligning the edges of the bent body, it is preferable to provide two coils (hoop materials 10a, 10b) as in this embodiment, and have the supply control device 20 control the feed rate of each grain-oriented electrical steel sheet.

[0084] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included within the technical scope of the present invention. [Example]

[0085] The technical content 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 adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to these examples. Furthermore, various conditions can be adopted in the present invention as long as they do not deviate from the gist of the present invention and the object of the present invention is achieved.

[0086] FIG. 10 is a diagram showing the size of the wound core manufactured in the example (comparative example). A wound core is used in which two bent portions 5 are formed at one corner portion 3, forming a roughly rectangular ring with an octagonal shape in side view. The steel plates of the wound core are designated steel plate a, steel plate b, steel plate c, and steel plate d from the inside to the outside. Although not shown, the wound core shown in Figure 10 is divided into two at roughly the center of the flat portion that constitutes the distance L1 between the flat portions on the inner surface, and has a structure in which two roughly U-shaped bent bodies are joined together. The distance L1 between the flat portions on the inner surface is 173 mm. The distance L2 between the flat portions on the inner surface is 93 mm. The layer thickness L3 is 45 mm. The laminate thickness width L4 is 160 mm. The innermost flat distance L5 is 16 mm. The bending angle φ is 45°.

[0087] The following Tables 1 and 2 summarize the configurations and manufacturing conditions of the examples (comparative examples). The grain-oriented electrical steel sheet conforms to JIS C 2553 and has a chemical composition of Si: 2.8%-3.5%, C: 0.001%, Mn: 0.007-0.010%, S<0.002%, Al<0.004%, N<0.002%, and P: 0-0.2%. The strength was adjusted primarily by the Si and P contents. The friction coefficient was adjusted by controlling the surface roughness of the base steel sheet through transfer using a rolling mill roll with adjusted surface roughness, as well as by controlling the baking temperature and time of the insulating coating. For samples A0 to A19, the thickness of the grain-oriented magnetic steel sheets was 0.23 mm. For samples B0 to B6, the thickness of the grain-oriented magnetic steel sheets was 0.18 mm. For samples A0 and B0, a bent body was produced by bending one grain-oriented magnetic steel sheet, and the bent body was then stacked to form 192 layers to obtain a wound core. For samples A1 to A19, a bent body was produced by bending two grain-oriented magnetic steel sheets in a stacked state, and the bent body was then stacked to form 192 layers to obtain a wound core. For samples B1 to B6, a bent body was produced by bending three grain-oriented magnetic steel sheets in a stacked state, and the bent body was then stacked to form 192 layers to obtain a wound core. The control of the feed amount is a value obtained by dividing the "increment of the feed amount (first increment)" by the "increment determined based on the geometric shape (second increment)." When the value obtained by dividing the first increment by the second increment is 0, the first increment is 0; in other words, when the feed amount of the inner steel plate 8B and the feed amount of the outer steel plate 8A are the same. In addition, in Table 2, two values ​​are listed in the upper and lower rows for the control of the feed amount. The upper row is the value obtained by dividing the first increment for the third steel plate from the inside by the second increment, and the lower row is the value obtained by dividing the first increment for the second steel plate from the inside by the second increment. [Table 1] [Table 2] The following Table 3 shows the evaluation results of the Examples and Comparative Examples (Reference Examples). [Table 3]

[0088] <Evaluation> (1) Bending accuracy (Evaluation method) The actual bending angles were measured at n arbitrary locations (n ​​is 24, for example) in the bent body constituting the wound core, relative to a target bending angle of 45°, and the standard deviation was calculated and used as an evaluation index for processing accuracy. (Judgment criteria) A test piece having a standard deviation (variation) of 0.5° or less in the measurement results at n locations (n ​​is, for example, 24) was deemed to be acceptable. (2) Number of twins (Evaluation method) Samples were taken from the corners 3 of the bent bodies that make up the wound core, and the number of twins was measured using a known method. (Judgment criteria) Those with fewer than 5 twins were considered to be acceptable. (3) Core iron loss (Evaluation method) A primary coil (30 turns) and a secondary coil (30 turns) were wound around the straight section of the core excluding the four corners, and a 50 Hz sinusoidal voltage was applied to the primary coil. The effective voltage U2 of the secondary coil was calculated from the required value of magnetic flux density using the following formula. U2=4.44×f×N2×A×J In the above formula, f: excitation frequency is 50Hz, N2: number of turns in the secondary coil is 30 turns, and A: core cross-sectional area is 45mm x 160mm = 0.0072m 2 If J is the peak value of the magnetic flux density and 1.5T, then U2 = 71.9V. The iron loss value was measured by connecting the current in the primary circuit and the voltage in the secondary circuit to a wattmeter. (Judgment criteria) For samples A1 to A19, the iron loss value of A0 was normalized to 100, and samples with a value of 105 or less were deemed acceptable. For samples B1 to B6, the iron loss value of B0 was normalized to 100, and samples with a value of 105 or less were deemed acceptable. If the iron loss value exceeds 100, the core iron loss will be inferior to that of cores made using the conventional method, in which each core is bent one by one. However, in this invention, productivity is also taken into consideration when determining whether the invention is acceptable, so a value up to 105 is deemed acceptable. In other words, considering the benefit of improving productivity by nearly 100% by bending two or more cores simultaneously, a deterioration in core iron loss of about 5% is acceptable, and the invention is deemed acceptable. (4) Productivity The method of manufacturing a bent body by bending a single grain-oriented electromagnetic steel sheet has low productivity (NG), while the method of manufacturing a bent body by bending multiple (two or more) grain-oriented electromagnetic steel sheets in a stacked state has high productivity (Good, Very Good).

[0089] [Sample No. A0 and Sample No. B0] To obtain one iron core, the number of bending processes required in the forming process is large, and the number of times that bent bodies are stacked (second stacks) in the stacking process is large, which results in low productivity. [Sample No. A1 to A4] When bending two sheets at a time, using steel sheets with an appropriately controlled interlayer friction coefficient can ensure acceptable bending accuracy, twin count, and core iron loss, while also achieving high productivity. If the interlayer friction coefficient is optimal, the occurrence of twins is suppressed, and improvements in core iron loss can be expected compared to when processing each sheet individually. [Sample No. A5] It can be seen that the interlayer friction coefficient was not properly controlled and exceeded 0.60, and results within the acceptable range were not obtained. [Sample No. A6~A8] Compared to samples A1 to A4, by more optimally controlling the feed rate, the combination of the ends is improved, processing precision is improved, and the occurrence of twins is suppressed, ensuring even better core iron loss than samples A1 to A4. [Sample No. A9] It can be seen that the interlayer friction coefficient was not properly controlled and exceeded 0.60, and results within the acceptable range were not obtained. [Sample No. A10] Compared with sample No. A8, it can be confirmed that by more optimally controlling μ×TS, processing precision is improved and the occurrence of twins is suppressed, making it possible to improve core iron loss. [Sample No. A11] Compared with sample No. A10, it can be seen that μ×TS is not optimal, that is, μ×TS exceeds 300, but a result within the acceptable range is obtained. [Sample No. A12~A19] It can be confirmed that samples A12 to A18 obtained results within the acceptable range, while sample A19 did not. From the evaluation results of samples A12 to A19, it can be confirmed that an optimal range for controlling the feed amount is found, and that an insufficient outer feed amount has a small adverse effect, while an excessive outer feed amount has a large adverse effect. [Sample No. B1 to B5] Even when bending three stacked sheets, by using steel sheets with an appropriately controlled interlayer friction coefficient, it is possible to ensure bending accuracy, the number of twins, and core iron loss within the acceptable range, while also achieving high productivity. If the interlayer friction coefficient is optimal, the occurrence of twins is suppressed, and it is expected that core iron loss will also be improved compared to when processing each sheet individually. [Sample No. B6] It can be seen that the interlayer friction coefficient was not properly controlled and exceeded 0.60, and results within the acceptable range were not obtained. [Explanation of symbols]

[0090] 1 Bent body 10 Wound core (iron core) 30 Processing equipment (equipment for bending)

Claims

1. A method for manufacturing an iron core, comprising: a forming step of stacking a plurality of grain-oriented electromagnetic steel sheets and bending the stacked grain-oriented electromagnetic steel sheets to form a bent body; and a stacking step of stacking the bent bodies in a sheet thickness direction, The thickness of the grain-oriented electromagnetic steel sheet is 0.23 mm or less, the coefficient of static friction between the layers of the grain-oriented electrical steel sheets in the overlapping state at the time of the bending process is controlled to be 0.60 or less; In the bending process, the radius of curvature of the inner surface side of the grain-oriented electromagnetic steel sheet, which is the inner side of the bent body, is set to 3 mm or less, the grain-oriented electromagnetic steel sheet located on the outer side of the bent body is referred to as an outer steel sheet, the grain-oriented electromagnetic steel sheet located on the inner side of the bent body is referred to as an inner steel sheet, a feed amount of the outer steel plate to the bending device is set to a first feed amount; a feed amount of the inner steel plate to the bending device is set to a second feed amount; an increment of the first feed amount relative to the second feed amount is defined as a first increment; In the bent body, a length of the bent portion of the outer steel plate determined based on a geometric shape is defined as a first length, In the bent body, a length of the bent portion of the inner steel plate determined based on a geometric shape is defined as a second length, If the increment of the first length relative to the second length is a second increment, The value obtained by dividing the first increment by the second increment is controlled to be 1.70 or less. A method for manufacturing an iron core.

2. An iron core manufacturing apparatus including a processing device that performs bending processing on grain-oriented electromagnetic steel sheets to form a bent body, the processing device stacks a plurality of the grain-oriented electromagnetic steel sheets and performs the bending process on the grain-oriented electromagnetic steel sheets in the stacked state; The thickness of the grain-oriented electromagnetic steel sheet is 0.23 mm or less, immediately before the bending process, the coefficient of static friction between the layers of the grain-oriented electrical steel sheets in a stacked state is 0.60 or less, In the bending process, the radius of curvature of the inner surface side of the grain-oriented electromagnetic steel sheet, which is the inner side of the bent body, is set to 3 mm or less, a supply control device that controls the supply of the plurality of grain-oriented electrical steel sheets to the processing device; the grain-oriented electromagnetic steel sheet located on the outer side of the bent body is referred to as an outer steel sheet, the grain-oriented electromagnetic steel sheet located on the inner side of the bent body is referred to as an inner steel sheet, a feed amount of the outer steel plate to the bending device is set to a first feed amount; a feed amount of the inner steel plate to the bending device is set to a second feed amount; an increment of the first feed amount relative to the second feed amount is defined as a first increment; In the bent body, a length of the bent portion of the outer steel plate determined based on a geometric shape is defined as a first length, In the bent body, a length of the bent portion of the inner steel plate determined based on a geometric shape is defined as a second length, If the increment of the first length relative to the second length is a second increment, The supply control device controls the first increment divided by the second increment to be 1.70 or less. An iron core manufacturing apparatus characterized by:

3. A method for manufacturing an iron core, comprising: a forming step of stacking a plurality of grain-oriented electromagnetic steel sheets and bending the stacked grain-oriented electromagnetic steel sheets to form a bent body; a pretreatment step of treating the grain-oriented electrical steel sheets in a superposed state so that the coefficient of static friction between the layers at the time of the bending process becomes a predetermined value; a lamination step of laminating the bent body in the plate thickness direction, The thickness of the grain-oriented electromagnetic steel sheet is 0.23 mm or less, The predetermined value is 0.60 or less, In the bending process, the radius of curvature of the inner surface side of the grain-oriented electromagnetic steel sheet, which is the inner side of the bent body, is set to 3 mm or less, the grain-oriented electromagnetic steel sheet located on the outer side of the bent body is referred to as an outer steel sheet, the grain-oriented electromagnetic steel sheet located on the inner side of the bent body is referred to as an inner steel sheet, a feed amount of the outer steel plate to the bending device is set to a first feed amount; a feed amount of the inner steel plate to the bending device is set to a second feed amount; an increment of the first feed amount relative to the second feed amount is defined as a first increment; In the bent body, a length of the bent portion of the outer steel plate determined based on a geometric shape is defined as a first length, In the bent body, a length of the bent portion of the inner steel plate determined based on a geometric shape is defined as a second length, If the increment of the first length relative to the second length is a second increment, The value obtained by dividing the first increment by the second increment is controlled to be 1.70 or less. A method for manufacturing an iron core.

4. An iron core manufacturing apparatus including a processing device that performs bending processing on grain-oriented electromagnetic steel sheets to form a bent body, the processing device stacks a plurality of the grain-oriented electromagnetic steel sheets and performs the bending process on the grain-oriented electromagnetic steel sheets in the stacked state; a pretreatment device that performs a treatment so that the coefficient of static friction between the layers of the grain-oriented electrical steel sheets in the overlapping state at the time of the bending process becomes a predetermined value, The thickness of the grain-oriented electromagnetic steel sheet is 0.23 mm or less, The predetermined value is 0.60 or less, In the bending process, the radius of curvature of the inner surface side of the grain-oriented electromagnetic steel sheet, which is the inner side of the bent body, is set to 3 mm or less, a supply control device that controls the supply of the plurality of grain-oriented electrical steel sheets to the processing device; the grain-oriented electromagnetic steel sheet located on the outer side of the bent body is referred to as an outer steel sheet, the grain-oriented electromagnetic steel sheet located on the inner side of the bent body is referred to as an inner steel sheet, a feed amount of the outer steel plate to the bending device is set to a first feed amount; a feed amount of the inner steel plate to the bending device is set to a second feed amount; an increment of the first feed amount relative to the second feed amount is defined as a first increment; In the bent body, a length of the bent portion of the outer steel plate determined based on a geometric shape is defined as a first length, In the bent body, a length of the bent portion of the inner steel plate determined based on a geometric shape is defined as a second length, If the increment of the first length relative to the second length is a second increment, The supply control device controls the first increment divided by the second increment to be 1.70 or less. An iron core manufacturing apparatus characterized by:

Images