JPWO2014024746A1 - Method for producing non-oriented electrical steel sheet and method for producing stator core of electric motor - Google Patents

Abstract

In electrical steel sheets used in an environment where compressive stress acts, at least one surface of the area where compressive stress acts to affect at least iron loss characteristics is machined such as blasting or surface grinding with a grinding wheel The surface processing influence layer based on the lattice distortion is provided.

Description

  The present invention relates to an electrical steel sheet used in a state in which compressive stress acts as an iron core material for electrical equipment.

  In order to increase the efficiency of various electric devices, magnetic steel sheets used as iron cores for electric motors and the like are required to have excellent magnetic properties such as low iron loss and high magnetic flux density.

  By the way, when using an electromagnetic steel sheet as an iron core of an electric motor or the like, generally, a plurality of non-oriented electromagnetic steel sheets are laminated, and bolting, caulking, or the like is performed on the laminated body. Further, from the viewpoint of rationalization of the manufacturing process, shrink fitting is often employed as a method for fixing the iron core of the stator portion composed of this laminate to the motor housing. In such a state of bolting, caulking, or shrink fitting, a compressive stress is generated in the iron core, and in particular near the outer peripheral portion of the stator portion due to shrink fitting, a compressive stress parallel to the plate surface of the electromagnetic steel sheet. Works.

  It is known that when magnetic steel sheets are distorted, the magnetic properties change, and when compressive stress is applied, the iron loss increases, that is, the iron loss properties deteriorate.

  Therefore, JP2010-252463A discloses a structure control technique for making an electromagnetic steel sheet an in-plane isotropic texture in which magnetic moments can be distributed in the same direction in order to suppress deterioration of iron loss characteristics under compressive stress. .

  According to JP2010-252463A, reduction of iron loss under compressive stress has been proposed by surface processing of an electromagnetic steel sheet. In any case, it is an essential requirement to provide grooves by surface processing. And, by providing the groove, it is expected to reduce the so-called classical eddy current loss caused by the induced current, but in actuality, the stress increases not only the eddy current but also the hysteresis loss. In some cases, the increase in iron loss may not be sufficiently suppressed.

  Therefore, an object of the present invention is to provide an electrical steel sheet in which an increase in iron loss is suppressed even under compressive stress.

FIG. 1 is a configuration diagram of a yoke type iron loss evaluation apparatus. FIG. 2A is a plan view of the test piece. FIG. 2B is an enlarged view of a portion A surrounded by a broken line in FIG. 2A. FIG. 3A is a cross-sectional view of a test piece subjected to MRF processing. FIG. 3B is a cross-sectional view of a test piece subjected to grinding. FIG. 3C is a cross-sectional view of the test piece subjected to etching. FIG. 4 is a table summarizing the results of the iron loss evaluation test. FIG. 5 is a diagram showing the relationship between the processing-affected layer depth and the iron loss. FIG. 6 is a diagram illustrating a part of a cross section of the electric motor perpendicular to the rotation axis.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  In carrying out the present invention, the inventors evaluated the iron loss under compressive stress for the electromagnetic steel sheets subjected to various surface treatments.

  FIG. 1 is a diagram showing a yoke type iron loss evaluation apparatus 10 used for the iron loss evaluation of the present embodiment.

  A stage 11 for fixing the test piece 1 is disposed in the exciting coil 12, and a yoke 13 is disposed so as to connect both ends of the exciting coil 12 in the axial direction. Further, a fixed clamp 15 and a movable clamp 16 for fixing the test piece 1 are arranged on the outer side of the connection portion of the yoke 13 with the exciting coil 12. A load cell 17 is connected to the movable clamp 16. The axial length of the exciting coil 12 is shorter than the longitudinal length of the test piece 1.

  A buckling prevention plate 14 is disposed in the exciting coil 12 so as to face the stage 11. The buckling prevention plate 14 is moved in the direction of the stage 11 by the pneumatic cylinders 18 disposed at both ends of the exciting coil 12 and presses the test piece 1 against the stage 11. This can prevent the test piece 1 from buckling when a compressive load is applied to the test piece 1. Although pressing was 200 kgf, it was confirmed that the presence or absence of pressing did not affect the iron loss.

  FIG. 2A and FIG. 2B are diagrams illustrating an example of the test piece 1.

  As the test piece 1, a single plate of a rectangular electromagnetic steel plate was used. Specifically, an electrical steel sheet equivalent to JIS35A300 having a thickness of 0.35 [mm] is cut into 180 [mm] × 30 [mm] with the rolling direction as the longitudinal direction, and surface processing is performed on one side of the cut steel sheet. The iron loss was evaluated. The processing conditions will be described later.

  The iron loss evaluation method by the yoke type iron loss evaluation apparatus 10 of the above structure is demonstrated.

  The test piece 1 is set on the stage 11 so that both ends protrude from the exciting coil 12, and one end of the test piece 1 is fixed by a fixed clamp 15 and the other end is fixed by a movable clamp 16. Further, the test piece 1 is pressed toward the stage 11 by the buckling prevention plate 14.

  Then, in a state where compressive stress is generated in the test piece 1 by applying a compressive load by the load cell 17, an alternating current is passed through the exciting coil 12 to measure the magnetization characteristics of the test piece 1. Here, in a state where a compressive stress of 30 [MPa] was applied in the longitudinal direction of the test piece 1, measurement was performed by alternating magnetization at a magnetic flux density of 1.0 [T] and a frequency of 1.0 [kHz].

  Next, processing conditions for surface processing applied to the test piece 1 will be described.

  In the surface processing, when a groove shape is given, as shown in FIGS. 2 (A) and 2 (B), a groove perpendicular to the magnetization direction is given to the entire surface at a pitch of 0.5 [mm].

  The processing method is as follows. Blasting and grinding have been adopted as processing classified as “no groove, with influence layer” where the cross section after processing is flat, has no grooves or irregularities, and the surface processing influence layer described later is formed. . Press processing, cutting processing, micro roll forming (MRF) processing is adopted as processing classified as “grooved, with affected layer” where the processed cross-section has grooves and irregularities and a surface processing affected layer is formed did. Etching and laser processing were adopted as the processing classified as “having a groove and no influence layer” in which a groove is formed in the cross section after processing but a surface processing influence layer is not formed.

  For blasting, microblasting using alumina beads was employed. The blasting device is MB2-ML-300 type manufactured by Shinto Kogyo Co., Ltd., and the alumina beads are white fused alumina WA grit NO. The test piece was processed using a nozzle diameter of 150 [μm], a nozzle feed rate of 2.0 [mm / s], a projection pressure of 0.4 [MPa], and a projection distance of 50 [mm].

  The depth of the processing-affected layer is determined by observing the processing cross-sectional structure with an electron probe surface imaging microscope (EP-SIM), and introducing lattice strain from the bottom of the groove in the observation image shown in FIG. 3 to be described later. The depth of the range that is being measured was measured as a processing-affected layer. The EP-SIM used was ULTRA55 manufactured by Carl Zeiss.

  FIG. 3 shows an example of an observation image by EP-SIM. 3A to 3C show cross sections when MRF processing, grinding processing, and etching are performed, respectively. In the case of MRF processing, not only grooves are formed on the surface, but also lattice strain is confirmed in the structure around the grooves. That is, a processing influence layer based on lattice distortion is confirmed in addition to the groove. In addition, when grinding is performed, no groove is formed on the surface, but a processing-affected layer based on lattice distortion is confirmed. On the other hand, when etching is performed, grooves are formed on the surface, but a processing-affected layer based on lattice distortion is not confirmed.

  Grinding was performed using a surface grinder. The grinding wheel was CBN80N100B, the grinding wheel rotation speed was 2850 [rpm], the grinding wheel peripheral speed was 1834 [rpm], and the grinding amount was 20 [μm].

  In the press working, a single-edged blade-shaped jig having a 30 ° inclination is made of cemented carbide, and grooves 21 are formed at a pitch of 0.5 [mm] using a press with a stage capable of controlling the indentation depth and feed. . The correlation between the indentation depth and the groove cross-sectional depth was investigated in advance, and the indentation depth was controlled with a target groove depth of 10 [μm]. In addition, the groove cross-sectional depth for correlation investigation was measured with the three-dimensional shape measuring instrument.

  Cutting was performed at a cutting depth of 10 [μm] and a cutting speed of 100 [mm / min].

  For MRF machining, a cemented carbide tool capable of machining 10 grooves with a pitch of 0.5 [mm] is manufactured, and each time one pass machining is performed using this tool, the workpiece is shifted by 10 [mm] in the lateral direction. Groove processing was applied to the entire surface. As in the case of press working, the correlation between the load and the groove cross-sectional depth was investigated, and the load was set so that the indentation depth could be controlled with a groove depth of 10 [μm] as a target. The groove cross-sectional depth for the correlation investigation was measured with a three-dimensional shape measuring instrument.

  Table 1 shows the test results. The value of the iron loss evaluation is shown as a relative value where 1 is the case without processing.

  “Surface effect layer including irregularities” in Table 1 is the depth and plate thickness ratio of “groove + work effect layer” in FIG. 3 (A), and the depth and plate thickness of the process effect layer in FIG. 3 (B). In FIG. 3C, the thickness ratio of the groove depth.

  According to the above results, it can be seen that iron loss is reduced under compressive stress even if blasting or grinding without grooves or irregularities occurs if the surface processing affected layer reaches 1% or more of the plate thickness. .

  Table 2 shows the test results for the test piece 1 obtained by performing the MRF processing while changing the load and the number of passes and having different depths of the processing-affected layer based on the groove depth and the lattice strain.

  According to the above results, it can be seen that if the depth of influence of processing including irregularities is 50% or less of the plate thickness ratio, the iron loss is reduced under compressive stress.

  Table 3 shows the test results for the test piece 1 subjected to the groove processing by etching processing and laser processing performed for comparison. Both etching processing and laser processing are performed by a processing manufacturer, and grooves perpendicular to the magnetization direction are formed on the entire surface at a pitch of 0.5 [mm]. The groove depth was set to 15, 20, and 30 [μm] as target values.

  Note that, as described above, both the etching process and the laser processing are processing methods in which a processing influence layer does not occur, and therefore, the numerical values in the column “surface processing influence layer including irregularities” in Table 3 are the groove depth and the plate thickness. Is the ratio.

  According to the above results, it can be seen that even if the groove is deep, the effect of reducing the iron loss is hardly obtained when there is no work-affected layer based on lattice distortion.

  FIG. 4 summarizes the relationship between the processing methods in Tables 1 and 3 and the iron loss reduction effect. FIG. 5 summarizes the relationship between the depth of the processing-affected layer including the irregularities in Tables 1 and 2 and the iron loss reduction effect.

  As shown in FIG. 4, regardless of whether or not grooves are provided by surface processing, if there is a working influence layer, that is, if there is a working influence layer due to lattice distortion, the effect of reducing iron loss Is obtained. On the other hand, even when the groove is provided, the effect of reducing the iron loss cannot be obtained if there is no processing-affected layer.

  As shown in FIG. 5, when the depth of the processing-affected layer including the depth of the groove exceeds 50 [%] of the plate thickness, the iron loss reduction effect cannot be obtained. This is considered to be because although the increase in iron loss due to compressive stress can be suppressed by providing a work-affected layer, the effect of the increase in iron loss due to work increases as the degree of work increases.

  In addition, although the clear principle is unknown about the iron loss reduction effect by providing a process influence layer, it can be considered as follows.

  Under the influence of compressive stress, the domain structure changes so that the magnetic domain orthogonal to the stress direction is enlarged due to the inverse effect (biliary effect) of magnetostriction, and the domain wall becomes difficult to move. If a certain degree of processing-affected layer is provided in this state, the magnetic domain structure changes and a large number of magnetic domains having an orientation close to the stress direction are generated. For this reason, it is particularly advantageous in the rotation of the magnetization direction and the motion of the domain wall in the region where the magnetization is small, and the effect of reducing the iron loss can be obtained.

  Next, the electrical steel sheet of the present embodiment determined based on the above-described experimental results and considerations will be described.

  The electrical steel sheet according to this embodiment is an electrical steel sheet used in an environment where compressive stress acts, and at least one surface of a region where compressive stress that affects iron loss acts acts on lattice distortion. Has a processing impact layer based. By having the processing-affected layer, the iron loss reduction effect can be obtained as described above.

  In particular, the electromagnetic steel sheet is a non-oriented electrical steel sheet that is used as a stator core of a motor. When shrink fitting is performed in the manufacturing process, the effect of compressive stress is inevitable, so the iron loss reduction effect according to this embodiment is effective. It is.

  In the electrical steel sheet of the present embodiment, the depth of the surface processing-affected layer including irregularities by machining is 1 [%] or more and 50 [%] or less of the plate thickness. If it is greater than 50 [%], the effect of increasing iron loss due to processing becomes larger than the effect of reducing iron loss due to the provision of a work-affected layer, so that it is difficult to obtain the effect of reducing iron loss under compressive stress. is there. In addition, if it is less than 1 [%], there is a problem that the effect of reducing the iron loss may not be obtained due to variations in the depth of the processing-affected layer.

  The electrical steel sheet of the present embodiment may be a flat electrical steel sheet provided with only a processing-influenced layer without providing grooves by blasting or grinding. Even if the surface is flat, there is variation in the surface shape after processing, but the size of the variation is much smaller than the variation in shape caused by groove processing. Accordingly, the space factor can be improved when the core is formed by laminating the electromagnetic steel sheets provided with the surface processing-affected layer in the range of 1 [%] to 50 [%] of the plate thickness. Further, when the groove is provided, the groove portion becomes a gap, but since no gap is generated by not providing the groove, the magnetic flux density can be improved. Furthermore, since no grooving is involved, an increase in iron loss due to excessive deepening of the work-affected layer cannot occur. In addition, since processing becomes easy, it is particularly advantageous when processing a large area.

  The “flat steel plate” preferably has a 10-point average roughness Rz of 30 [μm] or less, a reference length of 25 [mm], and an evaluation length of 40 [mm] or more. Rz is preferably 20 [μm] or less, more preferably 10 [μm] or less.

  Moreover, the electrical steel sheet of this embodiment can be used for an electric motor.

  FIG. 6 shows a part of a cross section orthogonal to the rotation axis of the electric motor 30 using the non-oriented electrical steel sheet of the present embodiment described above as a stator core. The electric motor 30 includes an annular back yoke 32, a stator core 34 having a plurality of teeth 33 protruding from the back yoke 32 toward the inner peripheral side, and a rotor 36 disposed coaxially within the stator core 34. . A slot 35 is formed between adjacent teeth 33, and a coil wound around the teeth 33 is stored therein.

  In this electric motor 30, the stator core 34 is fitted with the stator core 34 in a state where the case 31 is expanded by heating, so-called shrink fitting, or is fitted in the case 31 with the stator core 34 contracted by cooling, so-called cold fitting. To fix.

  By the way, the iron loss reduction effect under compressive stress by surface processing tends to be large when the magnetic flux density is low. Therefore, by providing a work-affected layer on the back yoke 32 of the stator core 34 fixed by shrink fitting, an increase in iron loss due to shrink fitting can be suppressed, and a small and highly efficient electric motor 30 can be obtained. Further, the increase in iron loss can be similarly suppressed by using the non-oriented electrical steel sheet of the present embodiment for the stator core 34 to be placed under compressive stress by being fitted by cold fitting.

  In the above description, the case where machining or the like is performed on one side of the test piece 1 has been described, but when the machining is performed on both sides, the effect of reducing the iron loss by the surface processing affected layer can be obtained similarly.

  The embodiment of the present invention has been described above. However, the above embodiment only shows a part of application examples of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiment. Absent.

  This application claims the priority based on Japanese Patent Application No. 2012-17395 for which it applied to the Japan Patent Office on August 6, 2012, and all the content of this application is integrated in this specification by reference.

Claims (7)

In electrical steel sheets used in environments where compressive stress acts,
An electrical steel sheet having a surface processing affecting layer based on lattice strain on at least one surface of a region where a compressive stress that affects at least iron loss characteristics acts.   The electrical steel sheet according to claim 1, wherein the electrical steel sheet is non-directional. In the electrical steel sheet according to claim 1 or 2,
The surface processing affecting layer is provided by machining,
The depth of the surface processing-affected layer is a magnetic steel sheet that is 1% or more and 50% or less of the plate thickness including the depth of unevenness formed on the surface by machining. In the electrical steel sheet according to claim 3,
An electrical steel sheet provided with the surface processing-affected layer on the surface by finishing a machined surface flat by the machining. In the electrical steel sheet according to claim 4,
A magnetic steel sheet in which the depth from the surface of the surface processing-affected layer is 1% to 50% of the plate thickness. In the electrical steel sheet according to any one of claims 1 to 5,
An electromagnetic steel sheet used as a stator of an electric motor and having a portion having the surface processing influence layer as a back yoke portion.   The stator core of the electric motor which consists of a laminated body of the electromagnetic steel plate in any one of Claim 1 to 6.

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