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Influence of shearing process on domain structure and magnetic properties of non-oriented electrical steel
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 304 (2006) e513–e515 www.elsevier.com/locate/jmmm
Influence of shearing process on domain structure and magnetic properties of non-oriented electrical steel$ Kunihiro Sendaa,, Masayoshi Ishidaa, Youichi Nakasub, Masaaki Yagib a
Steel Research Laboratory, JFE Steel Corporation, Kawasakidori 1-chome, Mizushima, Kurashiki 712-8511, Japan b Energy and Electronics Laboratory, Sojo University, Ikeda 4-22-1, Kumamoto 860-0082, Japan Available online 15 March 2006
Abstract The influence of shearing on the magnetic properties and domain structure of 0.5 mm thick non-oriented electrical steel was studied. In the region from 1 to 1.4 mm from the sheared edge, a striped domain pattern that indicated the existence of elastic strain was observed. From the degradation tendency of flux density with respect to shearing width, the width of the degraded region near the edge increased as the magnetic field decreased. These results suggested that the change in the flux density at high magnetic fields over 300 A/m were mainly dependent on the characteristics of the edge vicinity where the domain pattern was influenced by shearing. r 2006 Elsevier B.V. All rights reserved. PACS: 75.50.Bb; 75.70.Kw Keywords: Non-oriented electrical steel; Mechanical cutting; Domain structure; Magnetic properties
1. Introduction
2. Experimental
Increasing demand to improve the motor efficiency requires improvement in the prediction accuracy of core magnetic properties. Magnetic properties of electrical steel in magnetic cores are known to be influenced by manufacturing conditions such as punching, interlocking, welding, and shrink fitting. There has been growing interest in the influence of punching and shearing, especially in the width of the degraded region near the sheared edge where magnetic properties are affected [1–4]. In this paper, the influential regions on flux density and iron loss were studied from the viewpoint of magnetic domain structure and degradation tendency by shearing.
An electrical steel sheet compatible to JIS 50A400 grade (thickness: 0.5 mm, iron loss at Bm ¼ 1:5 T, f ¼ 50 Hz measured in Epstein method: 3.25 W/kg) was used. This sample was subjected to stress-relief annealing at a temperature of 750 C to eliminate initial strain. After annealing, the sheet sample was sheared into narrow pieces along the rolling direction using a mechanical shear having a clearance of 20 mm and a rake angle of 1 . The sheared pieces were taped together so that the total width was 30 mm as shown in Fig. 1. Magnetic properties in the rolling direction were measured by a SST (single sheet tester) using current method with vertical double yokes at a magnetizing frequency of 50 Hz. Strain-free magnetic properties were obtained in the samples stress-relief annealed after shearing. The density of the degraded region, which was induced by shearing near both sides of the pieces, was defined as the number of the regions per unit width of the combined specimen. Domain pattern observation using a Kerr effect microscope was carried out by the following method. The
$ This is original paper published in Journal of Electrical Engineering, ISSN 1335-3632 and with the courtesy of Editors is to serve as a template for preparing the SMM17 publications. Corresponding author. E-mail address: [email protected] (K. Senda).
0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.02.139
ARTICLE IN PRESS K. Senda et al. / Journal of Magnetism and Magnetic Materials 304 (2006) e513–e515
e514 Width of a piece × Number of pieces
Degraded region due to shearing
Number of degraded regions 2
30mm × 1 15mm × 2
4
10mm × 3
6
5mm × 6
12 180mm
Fig. 1. Schematic view of shearing.
Width of a piece (mm) 2.0
30 15 10
5
2
3
Magnetic field 50A/m 100A/m 300A/m 500A/m 1000A/m 2500A/m 5000A/m
Flux density (T)
1.8 1.6 1.4 1.2 1.0 0.8 0.6 Onset
0.4
Iron loss (W/kg)
0.2 0.0 4.5 4.0
(a) Flux density, Bm 0.5T
(b) Onset
3.5
1.0T
3.0
1.3T
2.5
1.5T
2.0 1.5 1.0 0.5 0.0 0.0
0.2
0.4
0.6
0.8
1.0
Density of degraded region (mm-1) Fig. 2. Variation of magnetic properties as a function of degraded region density: (a) flux density, (b) iron loss.
cross-section of the sheared edge was polished to 2 mm depth using abrasive paper followed by buffing with diamond paste and fine alumina particles. After polishing, a SiO layer was deposited to enhance the contrast of the domain pattern image. The domain pattern was obtained with a CCD camera having an area of 150 mm 200 mm after demagnetization. After the observation, the domain images were combined so as to consist of a wide range domain image. The domain pattern in the same plane was observed after stress-relief annealing at the temperature of 700 C to ensure a domain pattern without strain.
decreased and iron losses increased. It was noted that the flux density decreased almost linearly with the increase in the degraded region density at HX500 A=m. However, the rate of decrease in magnetic flux density declined with the increase in the degraded region density in the case of Hp300 A=m. Estimated onset points of the decline are shown in Fig. 2. On the assumption that the degradation of the magnetic properties occurred near both sides of the piece are not totally added in the middle of the piece, the decline occurs when the widths of the narrow pieces are comparable with twice the width of the degraded regions. Consequently, the widths of the degraded region at H ¼ 50, 100, and 300 A/m are estimated to be 2.5–5, 1.5–2.5 and 1–1.5 mm, respectively. Over 500 A/m, the degraded region was narrower than 1 mm. The non-linearity of iron loss with respect to the degraded region density was intensified as the flux density increased. Iron losses at low flux densities are affected by inhomogeneous flux distribution because the degraded regions have low permeability. Therefore, the influence of shearing on iron loss should be evaluated at high flux densities where the flux distribution is more homogeneous. From this viewpoint, the degraded region where iron loss was affected was estimated to be 1.5–2.5 mm considering the iron loss variation at Bm ¼ 1:5 T. Domain patterns observed by the Kerr effect near the sheared edge before and after stress-relief annealing are shown in Fig. 3. The domain patterns observed in the assheared sample were classified into three types depending on the distance from the sheared edge. In region A, a stripe patterns approximately parallel with the sheet plane were observed. Region B tends to have stripe patterns extending in the perpendicular direction with the sheet plane. Region C shows a small change in the domain patterns in the limited portions. The width of the area, including regions A–C, was 1–1.4 mm from the sheared edge, and no apparent change was observed outside of these regions except for unstable patterns after the demagnetization. The width of the region where the domain pattern changed was comparable with that of the estimated degraded region at H ¼ 300 A=m, and indicates that the magnetic properties over 300 A/m are influenced by the region where static domain pattern changes occur. The change in domain patterns was assumed to be formed by elastic strain near the sheared edge. From the data shown in Fig. 2, the degraded regions in low magnetic fields were estimated to be wider than the area where domain patterns change. From these results, it is suggested that the magnetic properties at low magnetic fields are more sensitive to strains than static domain patterns, that is, the area containing weak strains spreads wider than the area where the change in static domain pattern occurs.
3. Results and discussion 4. Conclusion The variation of flux density and iron loss with respect to the density of the degraded region are shown in Fig. 2. With increases in the degraded region density, flux densities
The width of the degraded region from shearing was studied in 50A400 electrical steel with 0.5 mm nominal
ARTICLE IN PRESS K. Senda et al. / Journal of Magnetism and Magnetic Materials 304 (2006) e513–e515
e515
Fig. 3. Change in domain pattern in the vicinity of sheared edge: (a) As-sheared, (b) after stress-relief annealing.
thickness. The degraded region where the flux density was affected increased with a decrease in the magnetic field. The width of the degraded region at HX500 A=m was estimated to be smaller than 1 mm. The degraded region where iron loss was affected was 1.5–2.5 mm. The change in domain patterns induced by the shearing was observed in the area of 1.0–1.4 mm from the sheared edge. Stripe domain patterns occurred markedly in the vicinity of the sheared edge, which implies the existence of strong elastic strain. The region where domain pattern changes occur exerts an influence on the magnetic properties of
sheared electrical steel sheets at magnetic fields higher than 300 A/m. References [1] K.H. Schmit, J. Magn. Magn. Mater. 2 (1976) 136. [2] T. Nakata, M. Nakano, K. Kawahara, IEEE Trans. Magn. Japan 7 (6) (1992) 453. [3] P. Baudouin, M. De Wulf, L. Kestens, Y. Houbaert, J. Magn. Magn. Mater. 256 (2003) 32. [4] G. Loizos, A.J. Moses, in: Soft Magnetic Materials, 16th Conference, vol. 1, 2003, pp. 317–322.
Journal of Magnetism and Magnetic Materials 304 (2006) e513–e515 www.elsevier.com/locate/jmmm
Influence of shearing process on domain structure and magnetic properties of non-oriented electrical steel$ Kunihiro Sendaa,, Masayoshi Ishidaa, Youichi Nakasub, Masaaki Yagib a
Steel Research Laboratory, JFE Steel Corporation, Kawasakidori 1-chome, Mizushima, Kurashiki 712-8511, Japan b Energy and Electronics Laboratory, Sojo University, Ikeda 4-22-1, Kumamoto 860-0082, Japan Available online 15 March 2006
Abstract The influence of shearing on the magnetic properties and domain structure of 0.5 mm thick non-oriented electrical steel was studied. In the region from 1 to 1.4 mm from the sheared edge, a striped domain pattern that indicated the existence of elastic strain was observed. From the degradation tendency of flux density with respect to shearing width, the width of the degraded region near the edge increased as the magnetic field decreased. These results suggested that the change in the flux density at high magnetic fields over 300 A/m were mainly dependent on the characteristics of the edge vicinity where the domain pattern was influenced by shearing. r 2006 Elsevier B.V. All rights reserved. PACS: 75.50.Bb; 75.70.Kw Keywords: Non-oriented electrical steel; Mechanical cutting; Domain structure; Magnetic properties
1. Introduction
2. Experimental
Increasing demand to improve the motor efficiency requires improvement in the prediction accuracy of core magnetic properties. Magnetic properties of electrical steel in magnetic cores are known to be influenced by manufacturing conditions such as punching, interlocking, welding, and shrink fitting. There has been growing interest in the influence of punching and shearing, especially in the width of the degraded region near the sheared edge where magnetic properties are affected [1–4]. In this paper, the influential regions on flux density and iron loss were studied from the viewpoint of magnetic domain structure and degradation tendency by shearing.
An electrical steel sheet compatible to JIS 50A400 grade (thickness: 0.5 mm, iron loss at Bm ¼ 1:5 T, f ¼ 50 Hz measured in Epstein method: 3.25 W/kg) was used. This sample was subjected to stress-relief annealing at a temperature of 750 C to eliminate initial strain. After annealing, the sheet sample was sheared into narrow pieces along the rolling direction using a mechanical shear having a clearance of 20 mm and a rake angle of 1 . The sheared pieces were taped together so that the total width was 30 mm as shown in Fig. 1. Magnetic properties in the rolling direction were measured by a SST (single sheet tester) using current method with vertical double yokes at a magnetizing frequency of 50 Hz. Strain-free magnetic properties were obtained in the samples stress-relief annealed after shearing. The density of the degraded region, which was induced by shearing near both sides of the pieces, was defined as the number of the regions per unit width of the combined specimen. Domain pattern observation using a Kerr effect microscope was carried out by the following method. The
$ This is original paper published in Journal of Electrical Engineering, ISSN 1335-3632 and with the courtesy of Editors is to serve as a template for preparing the SMM17 publications. Corresponding author. E-mail address: [email protected] (K. Senda).
0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.02.139
ARTICLE IN PRESS K. Senda et al. / Journal of Magnetism and Magnetic Materials 304 (2006) e513–e515
e514 Width of a piece × Number of pieces
Degraded region due to shearing
Number of degraded regions 2
30mm × 1 15mm × 2
4
10mm × 3
6
5mm × 6
12 180mm
Fig. 1. Schematic view of shearing.
Width of a piece (mm) 2.0
30 15 10
5
2
3
Magnetic field 50A/m 100A/m 300A/m 500A/m 1000A/m 2500A/m 5000A/m
Flux density (T)
1.8 1.6 1.4 1.2 1.0 0.8 0.6 Onset
0.4
Iron loss (W/kg)
0.2 0.0 4.5 4.0
(a) Flux density, Bm 0.5T
(b) Onset
3.5
1.0T
3.0
1.3T
2.5
1.5T
2.0 1.5 1.0 0.5 0.0 0.0
0.2
0.4
0.6
0.8
1.0
Density of degraded region (mm-1) Fig. 2. Variation of magnetic properties as a function of degraded region density: (a) flux density, (b) iron loss.
cross-section of the sheared edge was polished to 2 mm depth using abrasive paper followed by buffing with diamond paste and fine alumina particles. After polishing, a SiO layer was deposited to enhance the contrast of the domain pattern image. The domain pattern was obtained with a CCD camera having an area of 150 mm 200 mm after demagnetization. After the observation, the domain images were combined so as to consist of a wide range domain image. The domain pattern in the same plane was observed after stress-relief annealing at the temperature of 700 C to ensure a domain pattern without strain.
decreased and iron losses increased. It was noted that the flux density decreased almost linearly with the increase in the degraded region density at HX500 A=m. However, the rate of decrease in magnetic flux density declined with the increase in the degraded region density in the case of Hp300 A=m. Estimated onset points of the decline are shown in Fig. 2. On the assumption that the degradation of the magnetic properties occurred near both sides of the piece are not totally added in the middle of the piece, the decline occurs when the widths of the narrow pieces are comparable with twice the width of the degraded regions. Consequently, the widths of the degraded region at H ¼ 50, 100, and 300 A/m are estimated to be 2.5–5, 1.5–2.5 and 1–1.5 mm, respectively. Over 500 A/m, the degraded region was narrower than 1 mm. The non-linearity of iron loss with respect to the degraded region density was intensified as the flux density increased. Iron losses at low flux densities are affected by inhomogeneous flux distribution because the degraded regions have low permeability. Therefore, the influence of shearing on iron loss should be evaluated at high flux densities where the flux distribution is more homogeneous. From this viewpoint, the degraded region where iron loss was affected was estimated to be 1.5–2.5 mm considering the iron loss variation at Bm ¼ 1:5 T. Domain patterns observed by the Kerr effect near the sheared edge before and after stress-relief annealing are shown in Fig. 3. The domain patterns observed in the assheared sample were classified into three types depending on the distance from the sheared edge. In region A, a stripe patterns approximately parallel with the sheet plane were observed. Region B tends to have stripe patterns extending in the perpendicular direction with the sheet plane. Region C shows a small change in the domain patterns in the limited portions. The width of the area, including regions A–C, was 1–1.4 mm from the sheared edge, and no apparent change was observed outside of these regions except for unstable patterns after the demagnetization. The width of the region where the domain pattern changed was comparable with that of the estimated degraded region at H ¼ 300 A=m, and indicates that the magnetic properties over 300 A/m are influenced by the region where static domain pattern changes occur. The change in domain patterns was assumed to be formed by elastic strain near the sheared edge. From the data shown in Fig. 2, the degraded regions in low magnetic fields were estimated to be wider than the area where domain patterns change. From these results, it is suggested that the magnetic properties at low magnetic fields are more sensitive to strains than static domain patterns, that is, the area containing weak strains spreads wider than the area where the change in static domain pattern occurs.
3. Results and discussion 4. Conclusion The variation of flux density and iron loss with respect to the density of the degraded region are shown in Fig. 2. With increases in the degraded region density, flux densities
The width of the degraded region from shearing was studied in 50A400 electrical steel with 0.5 mm nominal
ARTICLE IN PRESS K. Senda et al. / Journal of Magnetism and Magnetic Materials 304 (2006) e513–e515
e515
Fig. 3. Change in domain pattern in the vicinity of sheared edge: (a) As-sheared, (b) after stress-relief annealing.
thickness. The degraded region where the flux density was affected increased with a decrease in the magnetic field. The width of the degraded region at HX500 A=m was estimated to be smaller than 1 mm. The degraded region where iron loss was affected was 1.5–2.5 mm. The change in domain patterns induced by the shearing was observed in the area of 1.0–1.4 mm from the sheared edge. Stripe domain patterns occurred markedly in the vicinity of the sheared edge, which implies the existence of strong elastic strain. The region where domain pattern changes occur exerts an influence on the magnetic properties of
sheared electrical steel sheets at magnetic fields higher than 300 A/m. References [1] K.H. Schmit, J. Magn. Magn. Mater. 2 (1976) 136. [2] T. Nakata, M. Nakano, K. Kawahara, IEEE Trans. Magn. Japan 7 (6) (1992) 453. [3] P. Baudouin, M. De Wulf, L. Kestens, Y. Houbaert, J. Magn. Magn. Mater. 256 (2003) 32. [4] G. Loizos, A.J. Moses, in: Soft Magnetic Materials, 16th Conference, vol. 1, 2003, pp. 317–322.