Laminated iron core and its manufacturing method

Abstract

To provide a laminated core capable of sufficiently suppressing generation of red rust inside.SOLUTION: A laminated core 10 includes a laminate 10A of a magnetic steel sheet W, and a granular oxide containing magnetite, for covering the side face 20 of the laminate 10A; in which a contact angle of a water droplet is 80° or more until 20 minutes pass from dropping the water droplet onto the side face 20 covered with the granular oxide. In the laminated core 10, assuming that the height of each peak is H1 and H2 respectively, when 2θ is detected in the range of 41-42° and 38-39° in XRD measurement of the side face 20 covered with the granular oxide, H1 / (H1+H2) is 0.8 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a laminated core and a method for manufacturing the same. [Background technology]

[0002] There are known techniques for forming an oxide film on the surface of an iron-based laminated product in a bluing furnace. For example, Patent Document 1 proposes a technique for forming an oxide film by bluing the inner surface of a housing or the outer surface of a stator core in air at 500 to 550°C. Patent Document 2 proposes forming an oxide film on the workpiece by charging a dry inert gas with a higher oxygen concentration than inert gas into a bluing furnace whose temperature gradually decreases from the inlet side to the outlet side. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-42015 [Patent Document 2] Special Publication No. 7-42508 Summary of the Invention [Problem to be solved by the invention]

[0004] Laminated cores are used in a variety of environments. Red rust forms on laminated cores when they come into contact with water and air (oxygen). Red rust formed inside a laminated core can cause a decrease in performance of the laminated core. Therefore, the present disclosure provides a laminated core that can sufficiently suppress the formation of red rust inside the core, and a method for manufacturing such a laminated core. [Means for solving the problem]

[0005] A laminated core according to one aspect of the present disclosure is a laminated core comprising a laminate of electromagnetic steel sheets and a granular oxide containing magnetite that covers the side surfaces of the laminate, wherein the contact angle of a water droplet is 80° or greater for 20 minutes after the water droplet is dropped onto the granular oxide covering the side surfaces.

[0006] The side surfaces of the laminated magnetic steel sheets in the laminated core are covered with granular oxides containing magnetite. Because they are covered with granular oxides containing magnetite, the occurrence of red rust on the side surfaces can be sufficiently suppressed. Furthermore, the contact angle of a water droplet dropped on the granular oxide covering the side surfaces is 80° or more for 20 minutes after the droplet is dropped on the granular oxide, demonstrating high water repellency. Because the side surfaces have high water repellency, water can be prevented from penetrating into the gaps between adjacent magnetic steel sheets in the lamination direction. Therefore, the occurrence of red rust can be sufficiently suppressed not only on the side surfaces of the laminated magnetic steel core but also inside the core.

[0007] A laminated core according to one aspect of the present disclosure is a laminated core comprising a laminate of electromagnetic steel sheets and a granular oxide containing crystalline magnetite and covering the side surface of the laminate, wherein when the heights of the peaks detected in an XRD measurement of the side surface covered with the granular oxide are H1 and H2, respectively, within the 2θ ranges of 41 to 42° and 38 to 39°, H1 / (H1+H2) is 0.8 or greater.

[0008] The side surfaces of the laminated magnetic steel sheets in the laminated core are covered with granular oxides containing crystalline magnetite. Because the side surfaces are covered with granular oxides containing crystalline magnetite, the occurrence of red rust on the side surfaces can be sufficiently suppressed. Furthermore, when XRD analysis of the side surfaces covered with the granular oxides is performed, H1 / (H1+H2) is 0.8 or greater. Here, peaks detected between 2θ of 41 and 42 degrees include diffraction peaks attributable to both crystalline magnetite and crystalline hematite. Meanwhile, peaks detected between 2θ of 38 and 39 degrees include diffraction peaks attributable to crystalline hematite, but do not include diffraction peaks attributable to crystalline magnetite. Therefore, when H1 / (H1+H2) is 0.8 or greater, the ratio of crystalline magnetite to crystalline hematite in the granular oxides is sufficiently high. Side surfaces covered with oxides containing a sufficiently high ratio of crystalline magnetite exhibit high water repellency. This prevents water from penetrating into the gaps between adjacent magnetic steel sheets in the lamination direction, thereby sufficiently preventing the occurrence of red rust not only on the side surfaces of the laminated core but also inside the core.

[0009] A method for manufacturing a laminated core according to one aspect of the present disclosure includes heating a laminate of electrical steel sheets in an oxygen-containing atmosphere while introducing water vapor, thereby oxidizing the side surfaces of the laminate. In the brewing furnace, the laminate is heated under conditions of an oxygen concentration of less than 500 ppm and a heating temperature of 400 to 600°C, thereby generating granular oxides containing magnetite on the side surfaces of the laminate.

[0010] According to the above manufacturing method, the side surfaces of the laminate of magnetic steel sheets can be covered with oxides having a high proportion of magnetite. Therefore, the occurrence of red rust on the side surfaces can be sufficiently suppressed. Furthermore, the side surfaces covered with oxides having a sufficiently high proportion of magnetite have high water repellency. Therefore, the infiltration of water into the gaps between adjacent magnetic steel sheets in the stacking direction can be suppressed. Therefore, the occurrence of red rust can be sufficiently suppressed not only on the side surfaces of the laminated core but also inside the laminated core. [Effects of the Invention]

[0011] It is possible to provide a laminated core that can sufficiently suppress the occurrence of red rust inside, and a method for manufacturing such a laminated core. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a perspective view showing an example of a laminated core. [Figure 2] 2 is a cross-sectional view schematically showing a cross-sectional structure when a laminated core is cut along the lamination direction. FIG. [Figure 3] FIG. 10 is a diagram schematically showing the contact angle of a water droplet dropped onto the side surface of a laminate. [Figure 4] 10A and 10B are diagrams showing examples of XRD measurement results of a side surface covered with granular oxide. [Figure 5] 1A to 1C are diagrams illustrating an example of a method for manufacturing a laminated core. [Figure 6] FIG. 1 is a graph showing the change over time in the contact angle y of a water droplet in Examples 1 to 4. [Figure 7] FIG. 1 is a graph showing the change over time in the contact angle y of a water droplet in Examples 5 and 6 and Comparative Examples 1 to 3. [Figure 8] FIG. 10 is a graph showing the change over time in the contact angle y of a water droplet in Examples 7 and 8. [Figure 9] 10 is a photograph of the side surface of a laminate in the laminated core of Examples 2 to 6. [Figure 10] 10 is a photograph of the side and cross section of the laminated body in the laminated cores of Examples 2, 3, and 4. [Figure 11] 10 is a photograph of the side and cross section of the laminated body in the laminated cores of Examples 5 and 7. [Figure 12] 10 is a photograph of the side and cross section of a laminate in the laminated cores of Comparative Examples 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings as needed. However, the following embodiments are merely examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content. In the description, the same elements or elements having the same functions will be designated by the same reference numerals, and redundant explanations will be omitted where appropriate. Furthermore, unless otherwise specified, positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios of each element are not limited to those shown in the drawings.

[0014] A laminated core according to one embodiment includes a laminate of magnetic steel sheets and a granular oxide containing magnetite that covers the side surfaces of the laminate. The contact angle y of a water droplet is 80° or more for 20 minutes after the water droplet is dropped on the side surfaces covered with the granular oxide. From the viewpoint of further improving water repellency, the contact angle y for 20 minutes after the water droplet is dropped may be 100° or more. The upper limit of the contact angle y for 20 minutes after the water droplet is dropped may be, for example, 140°. In other words, an example of the contact angle y for 20 minutes after the water droplet is dropped is 80 to 140°. The contact angle y can be adjusted by changing the conditions of the bluing process. For example, the contact angle y can be increased by increasing the heating time or the heating temperature while controlling the oxygen concentration within a predetermined range. Increasing the water repellency in this manner can prevent water from penetrating into the gaps between adjacent magnetic steel sheets in the stacking direction of the laminate. This makes it possible to sufficiently suppress the occurrence of red rust inside the laminated core.

[0015] From the viewpoint of further improving water repellency, the contact angle y of a water droplet may be 80° or more, or may be 85° or more, until 40 minutes have elapsed since the water droplet is dropped onto the side surface of the laminate covered with the granular oxide. The upper limit of the contact angle y of a water droplet may be, for example, 140°. That is, an example of the contact angle y of a water droplet until 40 minutes have elapsed since the water droplet is dropped is 80 to 140°.

[0016] At least a portion of the magnetite may be crystalline. This sufficiently increases water repellency and sufficiently suppresses the occurrence of red rust inside the laminated core. All of the magnetite contained in the oxide may be crystalline, or the magnetite contained in the oxide may include both crystalline and amorphous magnetite.

[0017] When the heights of the peaks detected within the 2θ ranges of 41 to 42° and 38 to 39° in an XRD measurement of the side surface of the laminate covered with the granular oxide are H1 and H2, respectively, the ratio H1 / (H1+H2) may be 0.8 or more. Within the 2θ range of 41 to 42°, the highest diffraction peak of crystalline magnetite (Fe3O4) and the second highest diffraction peak of hematite (Fe2O3) are detected. Meanwhile, within the 2θ range of 38 to 39°, the highest diffraction peak of crystalline hematite is detected. Therefore, the larger the value of H1 / (H1+H2), the higher the ratio of magnetite to the total of crystalline hematite and crystalline magnetite. Thus, the side surface covered with an oxide containing a sufficiently high proportion of crystalline magnetite has high water repellency. By increasing the water repellency, water penetration into the gaps between adjacent electrical steel sheets in the stacking direction of the laminate can be suppressed.

[0018] From the viewpoint of further increasing the water repellency, H1 / (H1+H2) may be 0.9 or more, 0.95 or more, or even 0.98 or more. The value of H1 / (H1+H2) can be adjusted by changing the conditions of the bluing process. For example, the value of H1 / (H1+H2) can be increased by extending the heating time, increasing the heating temperature, or increasing the dew point. For the XRD (X-ray diffraction) measurement in this specification, a commercially available X-ray diffraction measurement device using CuKα radiation (for example, D8 DISCOVER (trade name) manufactured by BRUKER) can be used.

[0019] Another embodiment of the laminated core includes a laminate of magnetic steel sheets and granular oxides containing crystalline magnetite that cover the side surfaces of the laminate. When the heights of the peaks detected within the 2θ ranges of 41-42° and 38-39° in an XRD measurement of the side surfaces covered with the granular oxides are H1 and H2, respectively, the ratio H1 / (H1+H2) is 0.8 or greater. The side surfaces of such a laminate are covered with granular oxides that contain a high proportion of magnetite relative to the total of crystalline hematite and crystalline magnetite. The side surfaces of such a laminate have high water repellency. This high water repellency can prevent water from penetrating into the gaps between adjacent magnetic steel sheets in the stacking direction of the laminate. Therefore, the formation of red rust inside the magnetic steel sheets can be sufficiently suppressed.

[0020] In each of the above embodiments, the granular oxide covering the side surface of the laminate may include particles having a particle diameter of 0.3 μm or more. Such oxide particles have high crystallinity, which can further improve the water repellency of the side surface. From the viewpoint of further improving water repellency, the particle diameter may be 0.4 μm or more, or 0.5 μm or more. From the viewpoint of increasing the adhesive strength to the side surface, the upper limit of the particle diameter may be 3 μm or 2 μm. The particle diameter of the oxide particles can be measured as the distance between the two most distant points on the outer edge of one particle in an SEM image showing an enlarged view of the side surface of the laminate.

[0021] In each of the above embodiments, the side surfaces of the laminate may be covered with an oxide film containing granular oxides. This can further suppress the occurrence of red rust on the side surfaces and inside the laminate. The thickness of the oxide film containing granular oxides may be 0.1 to 2 μm. This thickness can be measured by photographing a cross section obtained by cutting the laminate along the stacking direction with a scanning electron microscope (SEM) and measuring the length in the SEM photograph in a direction perpendicular to the side surfaces. The lower limit of the thickness of the oxide film may be 0.1 μm, 0.2 μm, or 0.3 μm. This can sufficiently increase the corrosion resistance of the side surfaces of the laminate. On the other hand, the upper limit of the thickness of the oxide film may be 2 μm or 1 μm. This can sufficiently suppress peeling of the oxide film. From the viewpoint of suppressing peeling of the oxide film, it is preferable that the oxide film does not have cavities.

[0022] In each of the above embodiments, the granular oxide covering the side surface of the laminate may not contain crystalline hematite. This allows the side surface of the laminate to have sufficiently high water repellency. The presence or absence of hematite can be determined by the presence or absence of a diffraction peak in the above-mentioned XRD measurement. The granular oxide may be granular iron oxide. The granular oxide covering the side surface of the laminate may not contain crystalline or amorphous hematite. In other words, it may not contain hematite at all.

[0023] In each of the above embodiments, the electromagnetic steel sheets constituting the laminate may include punched steel sheets. The side surfaces of the punched steel sheets have a disordered atomic arrangement due to shearing. Therefore, the bluing process can smoothly form granular oxides on the side surfaces of the laminate. This can improve the corrosion resistance of the laminated core.

[0024] In each of the above embodiments, the punched steel plates may be fastened to each other by caulking. A gap is more likely to occur between a pair of punched steel plates fastened to each other by caulking than between a pair of punched steel plates bonded with an adhesive. This makes it easier for water to penetrate and red rust to form inside the laminate. In this embodiment, the water repellency of the side surfaces of the laminate is sufficiently high, so that even when fastened by caulking, water penetration can be sufficiently reduced and red rust formation can be sufficiently suppressed inside.

[0025] A manufacturing method of a laminated iron core according to one embodiment includes heating a laminate of magnetic steel sheets in a bluing furnace having an oxygen-containing atmosphere while introducing water vapor to oxidize the side surfaces of the laminate, and in the bluing furnace, heating the laminate under conditions (bluing treatment conditions) of an oxygen concentration of less than 500 ppm, a heating temperature of 400 to 600°C, and a heating time at the heating temperature of 10 minutes or more, thereby generating granular oxides containing magnetite on the side surfaces of the laminate.

[0026] From the viewpoint of promoting the formation of crystalline magnetite and suppressing the formation of hematite, the oxygen concentration under the above bluing treatment conditions may be 200 ppm or less, 50 ppm or less, or 30 ppm or less. The oxygen concentration in this specification is measured using a commercially available oxygen concentration meter under standard conditions (temperature: 298.15 K, pressure: 10 5 The lower limit of the oxygen concentration in the above bluing treatment conditions may be 5 ppm, from the viewpoint of promoting the generation of granular oxides.

[0027] From the viewpoint of promoting the generation of crystalline magnetite and reducing damage to the insulating coating provided on the surface of the laminate, the upper limit of the heating temperature in the bluing treatment conditions may be 580° C. From the viewpoint of shortening the time required for the bluing step, the lower limit of the heating temperature in the bluing treatment conditions may be 450° C. or 500° C.

[0028] From the viewpoint of reducing damage to the insulating coating provided on the surface of the laminate and from the viewpoint of shortening the time for the bluing step, the heating time at the heating temperature may be 10 hours or less, or may be 5 hours or less. From the viewpoint of promoting the generation of crystalline magnetite, the heating time at the heating temperature may be 30 minutes or more, or may be 1 hour or more.

[0029] The dew point of the bluing furnace (bluing treatment conditions) may be 10°C or higher. This dew point can be adjusted by changing the flow rate of water vapor introduced into the bluing furnace. By adding water vapor to increase the dew point, it is possible to promote the formation of oxides (oxide films) on the side surfaces of the laminated body and suppress the occurrence of red rust on the side surfaces. The dew point may be 20°C or higher, or 40°C or higher, from the viewpoint of promoting the formation of oxides (oxide films) on the side surfaces of the laminated body in the laminated core and sufficiently suppressing the occurrence of red rust. From the same viewpoint, the upper limit of the dew point may be 100°C or 80°C.

[0030] FIG. 1 shows an example of a laminated core according to each of the above embodiments. The laminated core 10 is a stator laminated core and has a cylindrical shape. A through-hole 10a extending along the central axis Ax is provided in the center of the laminated core 10. A rotor core (not shown) can be placed inside the through-hole 10a. The laminated core 10 may form an electric motor together with the rotor core.

[0031] The laminated core 10 includes a laminate 10A in which a plurality of electromagnetic steel sheets W having the same shape are stacked. The yoke portion 12 and the teeth portion 13 are provided with crimped portions 12a and 13a, respectively. The crimped portions 12a and 13a fasten two adjacent electromagnetic steel sheets W among the plurality of electromagnetic steel sheets W to each other. The laminate 10A has an annular yoke portion 12 and teeth portions 13 inside the yoke portion 12.

[0032] The yoke portion 12 has an annular shape and extends to surround the central axis Ax. The radial width, inner diameter, outer diameter, and thickness of the yoke portion 12 may each be set to various sizes depending on the application and performance of the motor. The teeth portions 13 extend along the radial direction of the yoke portion 12 from the inner edge of the yoke portion 12 toward the central axis Ax. In the laminate 10A, twelve teeth portions 13 are formed integrally with the yoke portion 12. The teeth portions 13 are arranged at equal intervals in the circumferential direction of the yoke portion 12. Slots 14, which are spaces for arranging windings (not shown), are defined between adjacent teeth portions 13.

[0033] The laminate 10A has side surfaces 20 consisting of an outer surface 21 (outer peripheral surface) and an inner surface. The inner surface has inner wall surfaces 23 that define the slots 14 and opposing surfaces 22 that face the rotor core at the tips of the teeth portions 13. Both the outer surface 21 and the inner surface (opposing surfaces 22, inner wall surfaces 23) are covered with granular oxides containing crystalline magnetite. The end surfaces 15 and the opposing surfaces of adjacent electromagnetic steel sheets W may be covered with an insulating coating containing organic and inorganic substances.

[0034] FIG. 2 is a cross-sectional view schematically illustrating the cross-sectional structure of the laminate 10A cut along the lamination direction. In FIG. 2, the side surface 20 faces upward, as indicated by the direction of the reference numerals. The laminate 10A is composed of n stacked electromagnetic steel sheets W1, W2, ... Wn. Adjacent electromagnetic steel sheets W1, W2 are fastened to each other by crimping portions 12a, 13a shown in FIG. 1. The side surface 20 of the laminate 10A is covered with an oxide film 30 composed of an oxide containing crystalline magnetite. The highly water-repellent oxide film 30 reduces the contact area of ​​water on the side surface 20. Furthermore, water is prevented from penetrating the oxide film 30 and infiltrating between adjacent electromagnetic steel sheets. The oxide film 30 may contain oxide particles 31 having a particle size of 300 nm or more. The oxide particles 31 may be iron oxide particles.

[0035] The thickness of the oxide film 30 is measured along the direction X perpendicular to the lamination direction of the electrical steel sheet W in an SEM photograph showing a cross section as shown in Fig. 2. The range of the thickness (film thickness) of the oxide film 30 measured along the direction X is as described above. The contact angle y can be measured by dropping a water droplet 50 onto the oxide particle 31 covering the side surface 20, as shown in Fig. 2.

[0036] FIG. 3 is a diagram showing the contact angle y of a water droplet 50 dropped onto the side surface 20 of the laminate. The range of the contact angle y is as described above. The contact angle y is measured as follows. The measurement environment and water temperature are set to 25°C. 50 μl of water is collected using a syringe. The laminated core is fixed so that the side surface 20 faces upward, and a water droplet is dropped onto the side surface 20 from the syringe. At this time, the height of the tip of the syringe from the side surface 20 is set to 10 mm. The change over time in the contact angle of the water droplet dropped onto the surface of the oxide film 30 on the side surface 20 is measured. A microscope (for example, a digital microscope VHX-5000 (device name) manufactured by Keyence Corporation) can be used for the measurement.

[0037] FIG. 4 shows an example of the results of X-ray diffraction (XRD) measurement of the side surface 20 covered with granular oxide. In both charts (A) in FIG. 4, peak P1 is shown in the 2θ range of 41 to 42° and peak P2 is shown in the 2θ range of 38 to 39°. The height H1 of peak P1 is determined as the maximum height when multiple peaks are included in the 41 to 42° range. The height H2 of peak P2 is also determined as the maximum height when multiple peaks are included in the 38 to 39° range. Comparing charts (A) and (B) in FIG. 4, the height H1 of peak P1 relative to the height H2 of peak P2 is larger in chart (A). Therefore, the granular oxide covering the side surface in chart (A) has a higher proportion of crystalline magnetite. Note that heights H1 and H2 are both measured relative to the baseline.

[0038] FIG. 5 shows an example of a manufacturing method for the laminated core 10. In the manufacturing method for the laminated core 10, first, a laminate 10A of electromagnetic steel sheets (core pieces) is prepared. The laminate 10A can be manufactured by a known method. For example, a base material of the electromagnetic steel sheets is punched out with a press to obtain a plurality of electromagnetic steel sheets (core pieces). These are then stacked, and adjacent electromagnetic steel sheets (core pieces) are fastened together by caulking or the like.

[0039] A plurality of laminates 10A are arranged on a transport jig 75 and transported into annealing equipment 70. In the annealing equipment 70, a deoiling furnace 71 for performing the burn-off process, an annealing furnace 72 for performing the annealing process, and a bluing furnace 73 for performing the bluing process are arranged in this order from upstream to downstream. In the burn-off process, the laminate 10A is heated in an inert gas atmosphere such as nitrogen to volatilize the punching oil adhering to the electromagnetic steel sheets. In the annealing process, the laminate 10A is heated and annealed in an inert gas atmosphere such as nitrogen. This allows iron loss to be recovered.

[0040] In the bluing process, the annealed laminate 10A is heated in an atmosphere containing oxygen and water. The operating conditions (bluiing conditions) of the bluing furnace 73 are as described above. In the bluing process, oxide particles 31 containing crystalline magnetite are formed on the side surfaces 20 of the laminate 10A. In this way, the side surfaces 20 are covered with granular oxides. This makes it possible to obtain a laminated core 10 in which the contact angle y of a water droplet is 80° or greater 20 minutes after the water droplet is dropped. Furthermore, when XRD is measured on the side surfaces 20 covered with granular oxides, a laminated core 10 can be obtained in which, where H1 is the height of the peak detected within a 2θ range of 41 to 42° and H2 is the height of the peak detected within a 2θ range of 38 to 39°, H1 / (H1 + H2) is 0.8 or greater. In such a laminated core 10, the formation of red rust is sufficiently suppressed not only on the side surfaces but also inside the laminated core 10.

[0041] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments. For example, the shape and structure of the laminated core are not limited to those shown in FIG. 1. That is, the structure and shape of the laminate 10A, yoke portion 12, and teeth portion 13 are merely examples. The laminate may be formed, for example, by connecting components each having one yoke and one tooth along the circumferential direction. Also, only one of the yoke portion 12 and the teeth portion 13 may have a crimped portion. [Example]

[0042] The present disclosure will be described in more detail with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0043] [Laminated core manufacturing] Example 1 A laminate consisting of approximately 50 stacked electromagnetic steel sheets (punched steel sheets: thickness: 0.25 mm) was prepared. In this laminate, adjacent electromagnetic steel sheets were fastened to each other by caulking. This laminate was introduced into an annealing facility as shown in FIG. 5, and the burn-off process, annealing process, and bluing process were carried out in that order. In the bluing process, water vapor and air were introduced along with an inert gas to achieve a predetermined oxygen concentration and dew point. The bluing process was carried out while monitoring the heating temperature, oxygen concentration, and dew point in the bluing furnace with a thermometer, an oxygen concentration meter, and a dew point meter, respectively. The processing conditions for the bluing process (heating temperature, heating time, oxygen concentration in the atmosphere, and dew point) were as shown in Table 2. In this manner, a stator laminated core was manufactured.

[0044] Examples 2 to 4 A stator laminated core was manufactured in the same manner as in Example 1, except that the heating time in the bluing step was changed as shown in Table 2.

[0045] Example 5 A stator laminated core was manufactured in the same manner as in Example 2, except that the heating temperature in the bluing step was changed as shown in Table 3.

[0046] (Example 6) A stator laminated core was manufactured in the same procedure as in Example 3, except that the heating temperature in the annealing process was changed as shown in Table 3.

[0047] (Comparative Example 1) A stator laminated core was manufactured in the same procedure as in Example 5, except that the heating time and oxygen concentration in the annealing process were changed as shown in Table 3.

[0048] (Comparative Example 2) A stator laminated core was manufactured in the same procedure as in Example 1, except that the annealing process was not performed.

[0049] (Example 7) A stator laminated core was manufactured in the same procedure as in Example 1, except that the dew point in the annealing process was changed as shown in Table 4. The adjustment of the dew point was performed by changing the amount of water vapor introduced into the annealing furnace.

[0050] (Example 8) A stator laminated core was manufactured in the same procedure as in Example 2, except that the dew point in the annealing process was changed as shown in Table 4. The adjustment of the dew point was performed by changing the amount of water vapor introduced into the annealing furnace.

[0051] (Comparative Example 3) A stator laminated core was manufactured in the same procedure as in Example 1, except that heating was not performed with annealing equipment.

[0052] [Evaluation of Laminated Core] <XRD Measurement> XRD measurement was performed on the side surface of the laminated cores manufactured in each example and each comparative example. For the XRD measurement, an X-ray diffractometer (manufactured by BRUKER, model name: D8 DISCOVER, CuKα) was used. The measurement conditions were as follows. Measurement range (2θ): 22° to 47° Measurement time: 600 seconds Tube target: Co tube target Measuring diameter: φ0.5mm

[0053] The height H1 of peak P1 detected within the 2θ range of 41 to 42° and the height H2 of peak P2 detected within the 2θ range of 38 to 39° were determined. When peak P2 was buried in noise near the baseline and could not be detected, H2 was set to 0. The value of H1 / (H1+H2) was calculated from the determined heights H1 and H2. The results are shown in Table 1.

[0054] As shown in Table 1, it was confirmed that in all of Examples 1 to 8, oxides containing crystalline magnetite were produced on the side surfaces of the laminate. On the other hand, in Comparative Example 1, where the oxygen concentration in the atmosphere was high, it was confirmed that crystalline hematite was produced in addition to crystalline magnetite. In Comparative Example 2, no clear peaks indicating the presence of crystalline magnetite and crystalline hematite were detected, and both H1 and H2 were 0. It is believed that, like Comparative Example 2, no crystalline magnetite or crystalline hematite was present in Comparative Example 3, where heating in the annealing equipment was not performed.

[0055] [Table 1]

[0056] <Contact angle measurement> The laminated cores manufactured in each example and comparative example were clamped so that a portion of the side surface of the laminate faced upward. In a 25°C environment, 50 μl of water (25°C) was dropped onto the upward-facing portion of the side surface of the laminate using a syringe. At this time, the height of the syringe tip from the side surface was 10 mm. The change over time in the contact angle y (Figure 3) of the water droplet dropped onto the side surface was measured. A microscope (Keyence Corporation's VHX-5000 digital microscope) was used for the measurement. The data on the contact angle and the elapsed time after the water droplet was dropped are shown in Tables 2, 3, and 4. The relationship between the elapsed time and the contact angle y is also shown in Figures 6, 7, and 8.

[0057] As shown in Tables 2, 3, and 4, as well as FIGS. 6, 7, and 8, the side surfaces of the laminates in the laminated cores of each example had a larger contact angle y and exhibited higher water repellency than the comparative examples. The higher the heating temperature in the bluing process, the larger the contact angle y and the higher the water repellency tended to be. On the other hand, comparative example 1, which had a high oxygen concentration, had a smaller contact angle y and lower water repellency than the examples. One possible reason for this low water repellency is the formation of hematite.

[0058] <Accelerated rust test> The stator laminated cores of each example and comparative example were cut along the lamination direction to obtain samples. These samples were placed in a thermo-hygrostat (temperature: 50°C, humidity: 90% RH). Because the temperature of the samples before being placed in the thermo-hygrostat was 25°C, condensation occurred when the samples were placed in the thermo-hygrostat, making them prone to rust. 24 hours after being placed in the thermo-hygrostat, the samples were removed from the thermo-hygrostat and the side surfaces of the laminates were visually inspected.

[0059] Fig. 9 shows microscope photographs of the side surfaces of Examples 2 to 6. As shown in Fig. 9, it was confirmed that red rust occurring on the side surfaces can be reduced at 550°C compared to 450°C. It was also confirmed that a longer heating time can reduce the area where red rust occurs on the side surfaces.

[0060] The amount of red rust generated on the side surfaces and inside of the samples (laminates) of each Example and Comparative Example was evaluated according to the following criteria: The inside of the laminate was evaluated by disassembling the laminate and sampling one of the electrical steel sheets contained inside the laminate, and the amount of red rust generated on its surface (main surface) was evaluated.

[0061] A: There was almost no red rust. B: The area where red rust occurred was smaller than in Example 2, and a small amount of red rust occurred. C: The area where red rust occurred was equivalent to that of Example 2, and the area where red rust occurred was clearly smaller than that of Comparative Example 2. D: The area where red rust occurred was larger than that of Example 2 and smaller than that of Comparative Example 2. E: The area where red rust occurred was equivalent to that of Comparative Example 2.

[0062] As shown in Tables 2, 3, and 4, the area where red rust occurred on the side surfaces of the laminates of Examples 1 to 8 was smaller than that of Comparative Examples 2 and 3. Furthermore, the area where red rust occurred inside the laminates of Examples 1 to 8, i.e., on the main surfaces of the electromagnetic steel sheets, was also smaller than that of Comparative Examples 2 and 3, just like the side surfaces. Although almost no red rust occurred on the side surfaces of the laminate of Comparative Example 1, a lot of red rust occurred inside the laminate. This is thought to be because the oxides covering the side surfaces contained hematite and had low water repellency, allowing a large amount of moisture to penetrate into the interior of the laminated core.

[0063] Thus, it was confirmed that in Examples 1 to 8, the occurrence of red rust inside the laminations of the laminated core could be suppressed more than in Comparative Examples 1 to 3. Furthermore, as shown in Table 4, it was confirmed that the occurrence of red rust on the side surfaces and inside could be suppressed even if the dew point was increased. When comparing Examples 1 and 7, and Examples 2 and 8, which were the same conditions except for the dew point, there was not much difference in the contact angle y.

[0064] <SEM observation of side and cross section> SEM observations were performed on the side and cross sections of the laminated stator cores of Examples 1 to 8 and Comparative Examples 1 and 2. Note that, for some Examples and Comparative Examples, SEM observations were performed only on the cross sections. The cross sections were observed near the outer circumferential surface of the cut samples after cutting the laminated cores along the lamination direction. Fig. 10 shows SEM photographs (20,000 magnification) of the side and SEM photographs (30,000 magnification) of Examples 2, 3, and 4, respectively. Figs. 11 and 12 show SEM photographs of Examples 5 and 7, and Fig. 12 shows SEM photographs of Comparative Examples 1 and 2, respectively. Figs. 10, 11, and 12 also show microscope photographs of the side.

[0065] The particle size of the oxide particles adhering to the side surfaces of each example and comparative example was measured based on SEM photographs of the side surfaces. The particle size of the largest oxide particle in the SEM photographs was as shown in Tables 2, 3, and 4. The particle size tended to increase with increasing heating temperature and increasing heating time. In each table, "-" indicates that no measurement was performed.

[0066] Based on SEM photographs of the cross section of the side surface of each example and comparative example, it was determined whether or not an oxide film had formed on the side surface of the laminated core laminations. If a film was formed, i.e., if an oxide film had been formed, its thickness (film thickness) was measured based on the SEM photograph. For examples and comparative examples in which the film thickness was measured, the measurement results are shown in Tables 2, 3, and 4. For examples in which no measurement was performed, the column was left blank. If oxide particles were scattered on the side surface and the oxide was not formed in a film shape, the oxide film was evaluated as "absent."

[0067] The results are shown at the bottom of Tables 2, 3, and 4. As shown in Tables 2, 3, and 4, in Examples 1 to 8, the entire side surfaces of the laminates were covered with an oxide film. The evaluation results for the "interior" of these accelerated rusting tests were "A," "B," or "C," and the occurrence of red rust was sufficiently suppressed on the main surfaces of the electromagnetic steel sheets that make up the laminated core. This indicates that the oxide film containing magnetite effectively acted to suppress the occurrence of red rust inside. Although the entire side surfaces of the laminate in Comparative Example 1 were also covered with an oxide film, there were some cavities in the oxide film. The evaluation result for the "interior" of the accelerated rusting test was "D."

[0068] [Table 2]

[0069] [Table 3]

[0070] [Table 4] [Industrial Applicability]

[0071] A laminated core capable of sufficiently suppressing the occurrence of red rust and a method for manufacturing the same are provided. [Explanation of symbols]

[0072] 10... laminated core, 10A... laminate, 10a... through hole, 12... yoke portion, 13... teeth portion, 12a, 13a... crimped portion, 14... slot, 15... end face, 20... side face, 21... outer surface, 22... opposing surface, 23... inner wall surface, 30... oxide film, 31... oxide particle, 50... water droplet, 70... annealing equipment, 71... deoiling furnace, 72... annealing furnace, 73... bluing furnace, 75... conveying jig, Ax... central axis, W... electromagnetic steel sheet.

Claims

1. A laminate of electromagnetic steel sheets and a granular oxide containing magnetite covering a side surface of the laminate, A laminated core, wherein the contact angle of a water droplet is 81° or more for 25 minutes after the water droplet is dropped onto the side surface covered with the granular oxide.

2. The laminated core of claim 1 , wherein at least a portion of the magnetite is crystalline.

3. A laminated core comprising a laminate of electromagnetic steel sheets and a granular oxide containing crystalline magnetite and covering a side surface of the laminate, A laminated iron core, wherein when the heights of peaks detected within the 2θ ranges of 41 to 42° and 38 to 39° in an XRD measurement of the side surface covered with the granular oxide are H1 and H2, respectively, H1 / (H1+H2) is 0.98 or more.

4. The laminated core according to any one of claims 1 to 3, wherein the granular oxide includes particles having a particle size of 300 nm or more.

5. 5. The laminated core according to claim 1, wherein the side surfaces of the laminates are covered with an oxide film containing the granular oxide.

6. 6. The laminated core according to claim 1, wherein the granular oxide does not contain crystalline hematite.

7. the electromagnetic steel sheet includes a stamped steel sheet, 7. The laminated core according to claim 1, wherein the punched steel plates adjacent to each other in the lamination direction are fastened to each other by caulking.

8. A laminated iron core described in any one of claims 1 to 7, wherein the contact angle of a water droplet is 95° or more for 28 minutes after the water droplet is dropped onto the side surface covered with the granular oxide.

9. The method includes heating a laminate of electrical steel sheets while introducing water vapor in a bluing furnace having an oxygen-containing atmosphere to oxidize the side surfaces of the laminate, In the bluing furnace, the laminate is heated for 30 minutes or more under conditions of an oxygen concentration of 15 ppm or less, a heating temperature of 450 to 600°C, and a dew point of 30°C or more, thereby generating granular oxides containing magnetite on the side surfaces of the laminate.

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