Patent Application
20230395300
The present invention relates to a wound core. Priority is claimed on Japanese Patent Application No. 2020-179266, filed Oct. 26, 2020, the content of which is incorporated herein by reference.
The grain-oriented electrical steel sheet is a steel sheet containing 7 mass % or less of Si and has a secondary recrystallization texture in which secondary recrystallization grains are concentrated in the {110}<001> orientation (Goss orientation). The magnetic properties of the grain-oriented electrical steel sheet greatly influence the degree of concentration in the {110}<001> orientation. In recent years, grain-oriented electrical steel sheets that have been put into practical use are controlled so that the angle between the crystal <001> direction and the rolling direction is within a range of about 5°.
Grain-oriented electrical steel sheets are laminated and used in iron cores of transformers, and as their main magnetic properties such as a high magnetic flux density and a low iron loss are required. It is known that the crystal orientation has a strong correlation with these properties, and for example, Patent Documents 1 to 3 disclose a precise orientation control technique.
In addition, the influence of the crystal grain size in the grain-oriented electrical steel sheet is well known, and Patent Documents 4 to 7 disclose a technique for improving properties by controlling the crystal grain size.
In addition, in the related art, for wound core production as described in, for example, Patent Document 8, a method of winding a steel sheet into a cylindrical shape, then pressing the cylindrical laminated body without change so that the corner portion has a constant curvature, forming it into a substantially rectangular shape, then performing annealing to remove strain, and maintaining the shape is widely known.
On the other hand, as another method of producing a wound core, techniques such as those found in Patent Documents 9 to 11 in which portions of steel sheets that become corner portions of a wound core are bent in advance so that a relatively small bent area with a radius of curvature of 3 mm or less is formed and the bent steel sheets are laminated to form a wound core are disclosed. According to this production method, a conventional large-scale pressing process is not required, the steel sheet is precisely bent to maintain the shape of the iron core, and processing strain is concentrated only in the bent portion (corner) so that it is possible to omit strain removal according to the above annealing process, and its industrial advantages are great and the applications thereof are expanding.
An object of the present invention is to provide a wound core produced by a method of bending steel sheets in advance so that a relatively small bent area having a radius of curvature of 5 mm or less is formed and laminating the bent steel sheets to form a wound core, and the wound core is improved so that deterioration of efficiency due to a combination of the shape of the iron core and the steel sheet used is minimized.
The inventors studied details of efficiency of a transformer iron core produced by a method of bending a steel sheet in advance so that a relatively small bent area having a radius of curvature of 5 mm or less is formed and laminating the bent steel sheets to form a wound core. As a result, they recognized that, even if steel sheets with substantially the same crystal orientation control and substantially the same magnetic flux density and iron loss measured with a single sheet are used as a material, there is a difference in iron core efficiency.
After investigating the cause, it was found that the difference in efficiency that is a problem is caused by the influence of the crystal grain size of the material. In addition, it was found that the degree in phenomenon (that is, the difference in iron core efficiency) also varies depending on the sizes and shapes of the iron core. In addition, when this phenomenon was studied in detail, particularly, it was speculated that the cause is the difference in the degree of iron loss deterioration due to bending.
In this regard, various steel sheet production conditions and iron core shapes were studied, and the influences on iron core efficiency were classified. As a result, the result in which steel sheets produced under specific production conditions are used as iron core materials having specific sizes and shapes, and thus the iron core efficiency can be controlled so that it becomes the optimal efficiency according to magnetic properties of the steel sheet material was obtained.
The gist of the present invention, which has been made to achieve the above object, is as follows.
A wound core according to one embodiment of the present invention is a wound core including a wound core main body obtained by laminating a plurality of polygonal annular grain-oriented electrical steel sheets in a sheet thickness direction in a side view,
Here, Dpx is the average value of Dp obtained by the following Formula (1),
In addition, the average value of Dp is the average value of Dp on the inner side and Dp on the outer side of one planar portion between two planar portions and Dp on the inner side and Dp on the outer side of the other planar portion.
Dp=√(Dc×Dl/π) (1)
In addition, a wound core according to another embodiment of the present invention is a wound core including a wound core main body obtained by laminating a plurality of polygonal annular grain-oriented electrical steel sheets in a sheet thickness direction in a side view,
In addition, the average value of Dl is the average value of Dl on the inner side and Dl on the outer side of one planar portion between two planar portions and Dl on the inner side and Dl on the outer side of the other planar portion.
In addition, still another embodiment of the present invention provides a wound core including a wound core main body obtained by laminating a plurality of polygonal annular grain-oriented electrical steel sheets in a sheet thickness direction in a side view,
Here, Dpz is the average value of Dc,
In addition, the average value of Dc is the average value of Dc on the inner side and Dc on the outer side of one planar portion between two planar portions and Dc on the inner side and Dp on the outer side of the other planar portion.
According to the present invention, in the wound core formed by laminating the bent grain-oriented electrical steel sheets, it is possible to effectively minimize deterioration of efficiency due to a combination of the shape of the iron core and the steel sheet used.
Hereinafter, a wound core according to one embodiment of the present invention will be described in detail in order. However, the present invention is not limited to only the configuration disclosed in the present embodiment, and can be variously modified without departing from the gist of the present invention. Here, lower limit values and upper limit values are included in the numerical value limiting ranges described below. Numerical values indicated by “more than” or “less than” are not included in these numerical value ranges. In addition, unless otherwise specified, “%” relating to the chemical composition means “mass %.”
In addition, terms such as “parallel,” “perpendicular,” “identical,” and “right angle” and length and angle values used in this specification to specify shapes, geometric conditions and their extents are not bound by strict meanings, and should be interpreted to include the extent to which similar functions can be expected.
In addition, in this specification, “grain-oriented electrical steel sheet” may be simply described as “steel sheet” or “electrical steel sheet” and “wound core” may be simply described as “iron core.”
A wound core according to the present embodiment is a wound core including a wound core main body obtained by laminating a plurality of polygonal annular grain-oriented electrical steel sheets in a sheet thickness direction in a side view,
Here Dpx (mm) is the average value of Dp (mm) obtained by the following Formula (1),
In addition, the average value of Dp is the average value of Dp on the inner side and Dp on the outer side of one planar portion between two planar portions and Dp on the inner side and Dp on the outer side of the other planar portion.
Dp=√(Dc×Dl/π) (1)
First, the shape of a wound core of the present embodiment will be described. The shapes themselves of the wound core and the grain-oriented electrical steel sheet described here are not particularly new. For example, they merely correspond to the shapes of known wound cores and grain-oriented electrical steel sheets introduced in Patent Document 9 to 11 in the related art.
Here, in the present embodiment, the side view is a view of the long-shaped grain-oriented electrical steel sheet constituting the wound core in the width direction (Y-axis direction in
The wound core according to the present embodiment includes a wound core main body 10 in a side view in which a plurality of polygonal annular (rectangular or polygonal) grain-oriented electrical steel sheets 1 are laminated in a sheet thickness direction. The wound core main body 10 has a polygonal laminated structure 2 in a side view in which the grain-oriented electrical steel sheets 1 are stacked in a sheet thickness direction. The wound core main body 10 may be used as a wound core without change or may include, as necessary, for example, a known fastener such as a binding band for integrally fixing the plurality of stacked grain-oriented electrical steel sheets 1.
In the present embodiment, the iron core length of the wound core main body 10 is not particularly limited. Even if the iron core length of the iron core changes, the volume of a bent portion 5 is constant so that the iron loss generated in the bent portion 5 is constant. If the iron core length is longer, the volume ratio of the bent portion 5 to the wound core main body 10 is smaller and the influence on iron loss deterioration is also small. Therefore, a longer iron core length of the wound core main body 10 is preferable. The iron core length of the wound core main body 10 is preferably 1.5 m or more and more preferably 1.7 m or more. Here, in the present embodiment, the iron core length of the wound core main body 10 is the circumferential length at the central point in the laminating direction of the wound core main body 10 in a side view.
The wound core of the present embodiment can be suitably used for any conventionally known application. Particularly, when it is applied to the iron core for a transmission transformer in which the efficiency of the iron core is a problem, significant advantages can be exhibited.
As shown in
Hereinafter, the wound core main body 10 having substantially a rectangular shape including four corner portions 3 will be described.
Each corner portion 3 of the grain-oriented electrical steel sheet 1 in a side view includes two or more bent portions 5 having a curved shape and a second planar portion 4a between the adjacent bent portions 5 and 5. Therefore, the corner portion 3 has a configuration including two or more bent portions 5 and one or more second planar portions 4a. In addition, the sum of the bent angles of two bent portions 5 and 5 present in one corner portion 3 is 90°.
In addition, as shown in
In addition, each corner portion 3 may include four or more bent portions. In this case also, the second planar portion 4a is provided between the adjacent bent portions 5 and 5, and the sum of the bent angles of four or more bent portions 5 present in one corner portion 3 is 90°. That is, the corner portions 3 according to the present embodiment are arranged between two adjacent first planar portions 4 and 4 arranged at right angles and include two or more bent portions 5 and one or more second planar portions 4a.
In addition, in the wound core main body 10 shown in
In addition, in the wound core main body 10 shown in
Here, in this specification, “first planar portion” and “second planar portion” each may be simply referred to as “planar portion.”
Each corner portion 3 of the grain-oriented electrical steel sheet 1 in a side view includes two or more bent portions 5 having a curved shape, and the sum of the bent angles of the bent portions present in one corner portion is 90°. The corner portion 3 includes the second planar portion 4a between the adjacent bent portions 5 and 5. Therefore, the corner portion 3 has configuration including two or more bent portions 5 and one or more second planar portions 4a.
The embodiment of
As shown in these examples, in the present embodiment, one corner portion can be formed with two or more bent portions, but in order to minimize the occurrence of distortion due to deformation during processing and minimize the iron loss, the bent angle φ (φ1, φ2, φ3) of the bent portion 5 is preferably 60° or less and more preferably or less.
In the embodiment of
The bent portion 5 will be described in more detail with reference to
In addition, straight lines perpendicular to the outer surface of the steel sheet extend from the point F and the point G, and intersections with the inner surface of the steel sheet are the point E and the point D. The point E and the point D are the boundaries between the planar portions 4 and 4a and the bent portion 5 on the inner surface of the steel sheet.
Here, in the present embodiment, in a side view of the grain-oriented electrical steel sheet 1, the bent portion 5 is a portion of the grain-oriented electrical steel sheet 1 surrounded by the point D, the point E, the point F, and the point G. In
In the wound core of the present embodiment, the radius of curvature r at each bent portion 5 of the grain-oriented electrical steel sheets 1 laminated in the sheet thickness direction may vary to some extent. This variation may be a variation due to molding accuracy, and it is conceivable that an unintended variation may occur due to handling during lamination. Such an unintended error can be minimized to about 0.2 mm or less in current general industrial production. If such a variation is large, a representative value can be obtained by measuring the curvature radii of a sufficiently large number of steel sheets and averaging them. In addition, it is conceivable to change it intentionally for some reason, but the present embodiment does not exclude such a form.
In addition, the method of measuring the inner radius of curvature r of the bent portion 5 is not particularly limited, and for example, the inner radius of curvature r can be measured by performing observation using a commercially available microscope (Nikon ECLIPSE LV150) at a magnification of 200. Specifically, the curvature center point A as shown in
In the present embodiment, when the inner radius of curvature r of the bent portion 5 is in a range of 1 mm or more and 5 mm or less and specific grain-oriented electrical steel sheets with a controlled crystal grain size, which will be described below, are used to form a wound core, it is possible to optimize the efficiency of the wound core according to magnetic properties. The inner radius of curvature r of the bent portion 5 is preferably 3 mm or less. In this case, the effects of the present embodiment are more significantly exhibited.
In addition, it is most preferable that all bent portions present in the iron core satisfy the inner radius of curvature r specified in the present embodiment. If there are bent portions that satisfy the inner radius of curvature r of the present embodiment and bent portions that do not satisfy the inner radius of curvature r in the wound core, it is desirable for at least half or more of the bent portions to satisfy the inner radius of curvature r specified in the present embodiment.
In the present embodiment, the entire wound core main body 10 may have a substantially rectangular laminated structure 2 in a side view. As shown in the example of
The sheet thickness of the grain-oriented electrical steel sheet 1 used in the present embodiment is not particularly limited, and may be appropriately selected according to applications and the like, but is generally within a range of 0.15 mm to 0.35 mm and preferably in a range of 0.18 mm to 0.23 mm.
Next, the configuration of the grain-oriented electrical steel sheet 1 constituting the wound core main body 10 will be described. The present embodiment has features such as the crystal grain size of the planar portions 4 and 4a adjacent to the bent portion 5 of the grain-oriented electrical steel sheets laminated adjacently and the arrangement portion of the grain-oriented electrical steel sheet with a controlled crystal grain size in the iron core.
In the grain-oriented electrical steel sheet 1 constituting the wound core of the present embodiment, in at least a part of the corner portion, the crystal grain size of the laminated steel sheets is controlled such that it becomes smaller. If the crystal grain size in the vicinity of the bent portion 5 becomes coarse, the effect of avoiding efficiency deterioration in the iron core having an iron core shape in the present embodiment is not exhibited. In other words, when crystal grain boundaries are arranged in the vicinity of the bent portion 5, this indicates that efficiency deterioration is easily minimized.
Although a mechanism by which such a phenomenon occurs is not clear, it is speculated to be as follows.
In the iron core targeted by the present embodiment, macroscopic strain (deformation) due to bending is confined within the bent portion 5 which is a very narrow region. However, when viewed as the crystal structure inside the steel sheet, it is considered that the dislocation formed at the bent portion 5 moves and spreads to the outside of the bent portion 5, that is, the planar portions 4 and 4a. In this case, it is considered that, in grain-oriented electrical steel sheets with a crystal grain size of several mm, which are assumed as a material for the iron core of the present embodiment, the crystal grain boundary acts as a strong obstacle to dislocation movement, and dislocation movement is confirmed within a single crystal grain, which can be regarded as one single crystal. That is, it is thought that dislocations are not generated in adjacent crystal grains beyond crystal grain boundaries. It is generally known that lattice defects such as dislocations significantly deteriorate iron loss. Therefore, when the crystal grain size in the vicinity of the bent portion is made fine, and the crystal grain boundary is caused to function as an obstacle (dislocation elimination site) to dislocation movement to the planar portion, it is possible to keep the region with dislocation very close to the bent portion 5. Thereby, it is thought that it is possible to minimize a decrease in iron core efficiency. Such a mechanism of operation of the present embodiment is considered to be a special phenomenon in the iron core having a specific shape targeted by the present embodiment and has so far hardly been considered, but can be interpreted according to the findings obtained by the inventors.
In the present embodiment, the crystal grain size is measured as follows.
When the steel sheet lamination thickness of the wound core main body 10 is T (corresponding to “L3” shown in
The particle size Dc (mm) in the boundary direction is, for example, as shown in a schematic view of
Dc=Lc/(Nc+1) (2)
In addition, for the particle size Dl (mm) in the boundary vertical direction (the direction perpendicular to the boundary direction), in the extension direction of the boundary line B (boundary direction), at five locations excluding the end among positions obtained by dividing Lc into six, distances from the boundary line B between one bent portion 5 and the first planar portion 4 as a starting point until the line extending perpendicular to the boundary line B in a direction of the region of the first planar portion 4 first intersect the crystal grain boundary are defined as Dl1 to Dl5 in the first planar portion 4. In addition, distances from the boundary line B between one bent portion 5 and the second planar portion (planar portion in the corner portion) 4a as a starting point until the line extending perpendicular to the boundary line B in a direction of the region of the second planar portion 4a first intersects the boundary line B between other adjacent bent portions 5 with the crystal grain boundary or the second planar portion 4a therebetween are defined as Dl1 to Dl5 in the second planar portion. For the other bent portion 5, similarly, Dl1 to Dl5 in the first planar portion 4 and the second planar portion 4a are obtained. Then, the particle size Dl in the boundary vertical direction is obtained as the average distance of Dl1 to Dl5.
In addition, the circle-equivalent crystal grain size Dp (mm) of the first planar portion 4 and the second planar portion 4a adjacent to the bent portion 5 is obtained by the following Formula (1).
Dp=√(Dc×Dl/π) (1)
In addition, as shown in the schematic view of
Here, generally, a grain-oriented electrical steel sheet has a crystal grain size having a magnitude of several mm which is very coarse compared to the sheet thickness of the steel sheet. Therefore, in many cases, a single crystal grain penetrates from one surface of the steel sheet (for example, the inner side in the present embodiment) to the other surface (for example, the outer side in the present embodiment) in a columnar shape in observation of the sheet thickness cross section. Therefore, the crystal grain sizes measured on the inner side and the outer side as described above are crystal grain sizes having substantially the same magnitude, but in reality, fine crystal grains that do not penetrate the sheet thickness may remain on the surface layer so that, in the present embodiment, the crystal grain sizes are measured on both surfaces of the steel sheet, and the average value thereof is used to define the wound core of the present embodiment.
In the present embodiment, these crystal grain sizes are defined by comparison with the width W (mm) of the bent portion 5. In the present embodiment, the width W of the bent portion 5 is the average value of the length of the inner surface of the bent portion 5 La (the length in the bending direction) (refer to
In one embodiment of the present embodiment, in at least one corner portion 3, Dpx≤2 W, where Dpx (mm) is the average value of Dp−(ii, io, oi, oo). This expression corresponds to the basic feature of the mechanism described above. When this expression is satisfied, the crystal grain boundary can function as an obstacle to movement of dislocations generated in the bent portion 5 toward the first planar portion 4 and the second planar portion 4a, and as a result, the effects of the present embodiment are exhibited. The reason why the upper limit of Dpx is two times W is that dislocations generated in the bent portion 5 move about twice the deformation region at most, and even if Dpx exceeds 2 W, it is unlikely to become an obstacle to dislocation movement. Preferably, Dpx≤W. In addition, in all of four corner portions present in the wound core main body 10, it is needless to say that it is preferable to satisfy Dpx≤2 W.
As another embodiment, in at least one corner portion 3, Dpy≤2 W, where Dpy (mm) is the average value of Dl−(ii, io, oi, oo). In consideration of the mechanism described above, this expression particularly corresponds to a feature in which crystal grain boundaries that intersect the direction toward the first planar portion 4 and the second planar portion 4a (the direction perpendicular to the boundary direction in the bent portion 5) act as obstacles to dislocation movement in the direction of each planar portion more easily than crystal grain boundaries that are parallel to the direction toward the first planar portion 4 and the second planar portion 4a (the direction perpendicular to the bent portion boundary). When this expression is satisfied, it is possible to sufficiently minimize movement of dislocations to the planar portion region. Preferably, Dpy≤W. In addition, in all of four corner portions present in the wound core main body 10, it is needless to say that it is preferable to satisfy Dpy≤2 W.
As still another embodiment, in at least one corner portion 3, Dpz≤2·W, where Dpz (mm) is the average value of Dc−(ii, io, oi, oo). This expression corresponds to a feature in which crystal grain boundaries parallel to the direction toward the first planar portion 4 and the second planar portion 4a (the direction perpendicular to the bent portion boundary) also easily act as elimination sites for dislocations that move toward the first planar portion 4 and the second planar portion 4a. When this expression is satisfied, it is possible to sufficiently minimize movement of dislocations to the planar portion region. Preferably, Dpz≤W. In addition, in all of four corner portions present in the wound core main body 10, it is needless to say that it is preferable to satisfy Dpz≤2 W.
As described above, in the grain-oriented electrical steel sheet 1 used in the present embodiment, the base steel sheet is a steel sheet in which crystal grain orientations in the base steel sheet are highly concentrated in the {110}<001> orientation and has excellent magnetic properties in the rolling direction.
A known grain-oriented electrical steel sheet can be used as the base steel sheet in the present embodiment. Hereinafter, an example of a preferable base steel sheet will be described.
The base steel sheet has a chemical composition containing, in mass %, Si: 2.0% to 6.0%, with the remainder being Fe and impurities. This chemical composition allows the crystal orientation to be controlled to the Goss texture concentrated in the {110}<001> orientation and favorable magnetic properties to be secured. Other elements are not particularly limited, but in the present embodiment, in addition to Si, Fe and impurities, elements may be contained as long as the effects of the present invention are not impaired. For example, it is allowed to contain the following elements in the following ranges in place of some Fe. The ranges of the amounts of representative selective elements are as follows.
Since these selective elements may be contained depending on the purpose, there is no need to limit the lower limit value, and it is not necessary to substantially contain them. In addition, even if these selective elements are contained as impurities, the effects of the present embodiment are not impaired. In addition, since it is difficult to make the C content 0% in a practical steel sheet in production, the C content may exceed 0%. In addition, here, impurities refer to elements that are unintentionally contained, and elements that are mixed in from raw materials such as ores, scraps, or production environments when the base steel sheet is industrially produced. The upper limit of the total content of impurities may be, for example, 5%.
The chemical component of the base steel sheet may be measured by a general analysis method for steel. For example, the chemical component of the base steel sheet may be measured using Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES). Specifically, for example, a 35 mm square test piece is acquired from the center position of the base steel sheet after the coating is removed, and it can be specified by performing measurement under conditions based on a previously created calibration curve using ICPS-8100 or the like (measurement device) (commercially available from Shimadzu Corporation). Here, C and S may be measured using a combustion-infrared absorption method, and N may be measured using an inert gas fusion-thermal conductivity method.
Here, the above chemical composition is the component of the grain-oriented electrical steel sheet 1 as a base steel sheet. When the grain-oriented electrical steel sheet 1 as a measurement sample has a primary coating made of an oxide or the like (a glass coating and an intermediate layer), an insulating coating or the like on the surface, this coating is removed by a known method and the chemical composition is then measured.
The method of producing a grain-oriented electrical steel sheet is not particularly limited, and as will be described below, when production conditions are precisely controlled, the crystal grain size of the steel sheet can be incorporated. When grain-oriented electrical steel sheets having such a desired crystal grain size are used and a wound core is produced under suitable processing conditions to be described below, it is possible to obtain a wound core that can minimize deterioration of iron core efficiency. As a preferable specific example of the production method, for example, first, a slab containing 0.04 to 0.1 mass % of C, with the remainder being the chemical composition of the grain-oriented electrical steel sheet, is heated to 1,000° C. or higher and hot-rolled and then wound at 400 to 850° C. As necessary, hot-band annealing is performed. Hot-band annealing conditions are not particularly limited, and in consideration of precipitate control, the annealing temperature may be 800 to 1,200° C., and the annealing time may be 10 to 1,000 seconds. Then, a cold-rolled steel sheet is obtained by cold-rolling once, twice or more with intermediate annealing. The cold rolling rate in this case may be 80 to 99% in consideration of control of the texture. The cold-rolled steel sheet is heated, for example, in a wet hydrogen-inert gas atmosphere at 700 to 900° C., decarburized and annealed, and as necessary, subjected to nitridation annealing. Then, after an annealing separator is applied to the steel sheet after annealing, finish annealing is performed at a maximum reaching temperature of 1,000° C. to 1,200° C. for 40 to 90 hours, and an insulating coating is formed at about 900° C. Among the above conditions, particularly, the decarburization annealing and finish annealing influence the crystal grain size of the steel sheet. Therefore, when a wound core is produced, it is preferable to use a grain-oriented electrical steel sheet produced within the above condition ranges.
In addition, generally, the effects of the present embodiment can be obtained even with a steel sheet that has been subjected to a treatment called “magnetic domain control” in the steel sheet producing process by a known method.
As above, the crystal grain size, which is a feature of the grain-oriented electrical steel sheet 1 used in the present embodiment, is preferably adjusted depending on, for example, the maximum reaching temperature and the time of finish annealing. When the average crystal grain size of the entire steel sheet is reduced in this manner and each crystal grain size is set to 2 W or less, even if the bent portion 5 is formed at an arbitrary position when a wound core is produced, the above Dpx or the like is expected to be 2 W or less. In addition, in order to produce a wound core in which grains with a small crystal grain size are arranged in the vicinity of the bent portion 5, a method of controlling the bending position of the steel sheet so that a region with a small crystal grain size is arranged in the vicinity of the bent portion 5 is also effective. In this method, a steel sheet in which, when a steel sheet is produced, the grain growth of secondary recrystallization is locally minimized according to a known method such as locally changing the annealing separator state is produced, and bending may be performed by selecting a location that becomes fine grains.
The method of producing a wound core according to the present embodiment is not particularly limited as long as the wound core according to the present embodiment can be produced, and for example, a method according to a known wound core introduced in Patent Documents 9 to 11 in the related art may be applied. In particular, it can be said that the method using a production device UNICORE (commercially available from AEM UNICORE) (https://www.aemcores.com.au/technology/Unicore/) is optimal.
In addition, in order to precisely control the above Dpx, Dpy, and Dpz, it is preferable to control the shapes of the punch and the die used during processing and the amount of increase in the steel sheet temperature due to processing heat. Specifically, when the radius of curvature of the punch used is rp (mm), and the radius of curvature of the die is rd (mm), rp/rd is preferably within a range of 2.0 to 10.0. In addition, when the amount of increase in the steel sheet temperature due to processing heat is set as ΔT, ΔT is preferably reduced to 4.8° C. or less. If ΔT is excessively large, even if a steel sheet having a crystal grain size within an appropriate range is used as a material, the crystal grain size may become coarse and the iron core efficiency of the wound core may be lowered. The cooling method is not particularly limited, but for example, the temperature of the steel sheet may be adjusted by spraying a coolant such as liquid nitrogen during processing or immediately after processing.
In addition, according to a known method, as necessary, a heat treatment may be performed. In addition, the obtained wound core main body 10 may be used as a wound core without change or a plurality of stacked grain-oriented electrical steel sheets 1 may be integrally fixed, as necessary, using a known fastener such as a binding band to form a wound core.
The present embodiment is not limited to the above embodiment. The above embodiment is an example, and any embodiment having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same operational effects is included in the technical scope of the present invention.
Hereinafter, technical details of the present invention will be additionally described with reference to examples of the present invention. The conditions in the examples shown below are examples of conditions used for confirming the feasibility and effects of the present invention, and the present invention is not limited to these condition examples. In addition, the present invention may use various conditions without departing from the gist of the present invention as long as the object of the present invention is achieved.
Using a slab having a chemical composition (mass %, the remainder other than the displayed elements is Fe) shown in Table 1 as a material, a final product (product sheet) having a chemical composition (mass %, the remainder other than the displayed elements is Fe) shown in Table 2 was produced. The width of the obtained steel sheet was 1,200 mm.
In Table 1 and Table 2, “-” means that the element was not controlled or produced with awareness of content and its content was not measured. In addition, “<0.002” and “<0.004” mean that the element was controlled and produced with awareness of content, the content was measured, but sufficient measurement values were not obtained with accuracy credibility (detection limit or less).
Here, Table 3 shows details of the steel sheet producing process and conditions.
Specifically, and hot rolling, hot-band annealing, and cold rolling were performed. In a part of the cold-rolled steel sheet after decarburization annealing, a nitridation treatment (nitridation annealing) was performed in a mixed atmosphere containing hydrogen-nitrogen-ammonia.
In addition, an annealing separator mainly composed of MgO was applied and finish annealing was performed. An insulating coating application solution containing chromium and mainly composed of phosphate and colloidal silica was applied to a primary coating formed on the surface of the finish-annealed steel sheet, and heated to form an insulating coating.
In this case, the cold rolling rate or the finish annealing time was adjusted and thus steel sheets with a controlled crystal grain size were produced. Table 3 shows details of the produced steel sheets.
The cores Nos. a to f of the iron cores having shapes shown in Table 4 and
Here, the iron core of the core No. f is conventionally used as a general wound core and is a so-called trunk core type iron core produced by a method of winding a steel sheet into a cylindrical, then pressing the cylindrical laminated body without change so that the corner portion has a constant curvature, forming it into a substantially rectangular shape, and then performing annealing, and maintaining the shape. Therefore, the radius of curvature of the bent portion varies greatly depending on the lamination position of the steel sheet. In addition, in Table 4, the radius of curvature r (mm) of the core No. f increases toward the outside, and is 6 mm at the innermost periphery part and about 85 mm at the outermost periphery part (indicated by “-” in Table 4).
The magnetic properties of the grain-oriented electrical steel sheet were measured based on a single sheet magnetic property test method (Single Sheet Tester: SST) specified in JIS C 2556: 2015.
As the magnetic properties, the magnetic flux density B8(T) of the steel sheet in the rolling direction when excited at 800 A/m and the iron loss of the steel sheet at an AC frequency of 50 Hz and an excitation magnetic flux density of 1.7 T were measured.
12 crystal grain sizes (Dcii, Dcio, Dcoi, Dcoo, Dlii, Dlio, Dloi, Dloo, Dpii, Dpio, Dpoi, and Dpoo) were determined by observing both surfaces of the steel sheet extracted from the iron core as described above.
The building factor (BF) was obtained by calculating the non-load loss for the iron core formed of each steel sheet as a material and taking a ratio with the magnetic properties of the steel sheet obtained in (1). Here, the BF is a value obtained by dividing the iron loss value of the wound core by the iron loss value of the grain-oriented electrical steel sheet which is a material of the wound core. A smaller BF indicates a lower iron loss of the wound core with respect to the material steel sheet. Here, in this example, when the BF was 1.15 or less, it was evaluated that deterioration of iron loss efficiency was minimized.
The efficiency was evaluated for various iron cores produced using various steel sheets with different magnetic domain widths. The results are shown in Table 5. Here, in Table 5, “rp/rd” represents a ratio of the radius of curvature rp (mm) of the punch and the radius of curvature rd (mm) of the die used when the iron core was processed, and “ΔT” represents the amount of increase (° C.) in the steel sheet temperature due to heat generated during processing.
It can be understood that the efficiency of the iron core could be improved by appropriately controlling the crystal grain size even if the same steel type was used.
Based on the above results, it can be clearly understood that, in the wound core of the present invention, the crystal grain sizes Dpx, Dpy and Dpz of the laminated grain-oriented electrical steel sheet each were 2 W or less so that the wound core had low iron loss properties.
According to the present invention, in the wound core formed by laminating bent steel sheets, it is possible to effectively minimize deterioration of efficiency of the iron core.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-179266 | Oct 2020 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/039560 | 10/26/2021 | WO |
