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Influence of the manufacturing process on the magnetic properties of non-oriented electrical steels
Journal of Magnetism and Magnetic Materials 215}216 (2000) 74}78
In#uence of the manufacturing process on the magnetic properties of non-oriented electrical steels A. Schoppa*, J. Schneider, C.-D. Wuppermann Department of Application, EBG Bochum, Castroper Strasse 228, 44791 Bochum, Germany
Abstract The optimal use of an appropriate material for a given application requires some considerations concerning the in#uence of the manufacturing conditions on the properties of magnetic components. The paper presents the general trends of the in#uence of manufacturing processes on the magnetic properties of non-oriented fully processed electrical steels. 2000 Elsevier Science B.V. All rights reserved. Keywords: Non-oriented electrical steel; Manufacturing process; Electric motors; Magnetic properties
1. Introduction The development of highly e$cient electric machines like pumps, fans, industrial motors may lead to give an important contribution to saving of electric energy. There is also a demand for an increase of e$ciency in other application areas like lighting engineering and white goods. Besides an improved design, the use of better material grades and broader the knowledge of the in#uence of the manufacturing process on the resulting magnetic properties may help to reach this target. Some basic aspects of the in#uence of the manufacturing process on the magnetic properties of non-oriented fully processed electrical steels have already been published [1}5].
2. Design aspects The ratio of mechanical output P and speed n of an
electrical machine determines the volume < within the stator core. The factor of proportionality between P /n and < depends on the product of the maximum
* Corresponding author. Tel.: #49-234-50851561; fax: #49234-50851042. E-mail address: [email protected] (A. Schoppa).
airgap #ux density B and the e!ective armature ampere conductors A. On the other hand, the machine will be provided for working on a network with given values of frequency and voltage. The frequency "xes the number of poles to be performed for getting the speed desired. The number of poles and the frequency determine the local distribution of magnetic induction in teeth and coreback and its dependence on time. Finally, the local variation of B with time causes magnetic losses within the core and the current necessary to excite the "eld. This current causes winding losses and, in general, with increasing the factor A and B winding losses will grow. So large values of A and B will give a small volume of the machine but bad values of the e$ciency, that means the ratio g"P /(P #P ), where the total losses P are
given as P "P #P #P (P : magnetic losses, P :
! ! winding losses, P : friction losses). Therefore, the relevant magnetic parameters for the optimum choice of nonoriented electrical steels are: frequency of the exciting current, working range of induction, extent of the appearance of higher harmonics and of rotational magnetization process. To estimate the e!ect of di!erent grades of non-oriented electrical steels on the performance of the electric machine by model calculations, one needs an appropriate model, by which the speci"c material data for the "eld and frequency dependence of the magnetic polarization J (J"B!k H) and the speci"c magnetic losses can be included in detail. Only this approach provides an appropriate evaluation of e!ects by di!erent
0304-8853/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 0 7 0 - 6
A. Schoppa et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 74}78
75
grades. To ensure an optimum utilization of the magnetic material as well as a relevant prediction by the model calculations one also needs more details about the in#uence of the di!erent manufacturing processes on the magnetic properties of the core material. These processes comprise starting from the sheet: punching or cutting by laser, conventional assembling or automatic stacking, welding, riveting or other joining techniques, pressing of magnetic cores into the frame. There hardly exists a calculation model which considers both the aspects, i.e., the speci"c magnetic parameters of the material and the in#uence of the manufacturing process on these parameters in an appropriate and complete way. The designers of electric machines use mostly &building factors', which do not give any information about the remaining magnetic properties in the magnetic core after di!erent processing steps.
3. Magnetizing behavior and in6uence of the manufacturing process The e!ect of changes in the characteristic of J versus H of the non-oriented electrical steel on the di!erent processing steps in the operating behavior of electric machines may be well described by the changes of the function ; versus I (; is the e!ective value of the input l voltage, I the magnetizing current in the important case l
Fig. 2. In#uence of the speci"c cutting length in m/kg on J versus H (high Si-alloyed grade, 50 Hz).
Fig. 3. In#uence of the speci"c cutting length in m/kg on J versus H for di!erent grades of non-oriented electrical steels (50 Hz).
Fig. 1. Changes of the function ; versus I in dependence on l the changes of J versus H [6].
of induction machines to be considered here), see Fig. 1. Furthermore, I determines the magnetic contribution l P &I to the entire winding losses P &I" ! l ! I #I"I +1#(I /I ), with I component of the l l
76
A. Schoppa et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 74}78
Fig. 4. In#uence of pressing in N/mm during stacking of toroidal laminations on J versus H (high Si-alloyed grade, 50 Hz).
Fig. 5. In#uence of welding (four welding passes) after stacking of toroidal laminations on J versus H (high Si-alloyed grade, 50 Hz).
Table 1 Importance of the change of the magnetizing by di!erent manufacturing steps Processing step
Operating range (0.5 T
Operating range 0.5}1.5 T
Operating range '1.5 T
Cutting Pressing during stacking Welding Sticking Automatic stacking, riveting Pressing into frame
# 0 # 0 0/# 0/#
### #/## ## # #/## #/##
#/0 0 0 0 #/0 #/0
current producing torque as well as the value of the power factor [6] cos u"I /I"I /(I #I) . In this l way the e!ects of using materials with a better permeability in the operating range of induction and the deterioration of the magnetic properties upon the manufacturing process of the magnetic components may be evaluated. Figs. 2}5 give some examples for the degree of deterioration by di!erent processing steps: in#uence of cutting length on J versus H (Figs. 2 and 3), in#uence of the pressure during the stacking of laminations before assembling on J versus H (Fig. 4) and in#uence of welding of the magnetic core on J versus H (Fig. 5). The measurements concerning the in#uence of cutting were
done according to Ref. [2] on strips, starting with a width of the strip of 30 mm and a length of 160 mm. The measurements concerning the in#uence of pressing and welding were done on toroidal samples (outer diameter: 100 mm, inner diameter: 60 mm, height: 10 mm). Additionally, the e!ects of the di!erent manufacturing steps were studied using stators of small industrial motors as well as universal motors [7]. Table 1 re#ects, as a summary of the above-mentioned investigations, the importance of the changes of the magnetizing behavior by di!erent manufacturing steps. For this purpose di!erent operating ranges of induction were regarded.
A. Schoppa et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 74}78
Fig. 6. In#uence of the speci"c cutting length in m/kg on P versus J (high Si-alloyed grade, 50 Hz).
77
Fig. 8. In#uence of coating upon pressing during stacking of toroidal laminations on P versus J (high Si-alloyed grade, inorganic/organic coating, respectively, bare (uncoated) surface, 50 Hz).
4. Magnetic losses and in6uence of the manufacturing process Figs. 6}9 demonstrate the in#uence of the cutting length, of pressure during stacking and of welding on the speci"c losses P versus J. Compared to the changes in the characteristic of J versus H the changes in P versus J appear over the whole range of induction. Obviously, the increase of P will be substantially higher with in creasing frequency f. For the investigated grades of nonoriented electrical steels only small di!erences of the magnetic losses between coated and bare (uncoated) material were found. Table 2 summarizes the e!ects of di!erent manufacturing steps on the speci"c losses P of non-oriented electrical steels distinguished by di!erent Si-content, including the results got by real-stator geometry for small motors [7].
5. Conclusions and outlook
Fig. 7. In#uence of pressing in N/mm during stacking of toroidal laminations on P versus J (high Si-alloyed grade, inorganic/organic coating, 50 Hz).
The obtained experimental data proved that di!erent grades of non-oriented fully processed electrical steels have di!erent sensitivities with respect to di!erent processing steps. In general, high Si-alloyed grades show
78
A. Schoppa et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 74}78
Table 2 E!ects of di!erent manufacturing steps on the speci"c losses P for electrical steel grades with a di!erent Si-content (coated with inorganic/organic coating) Processing step
Non-alloyed, low Si-alloyed
Middle Si-alloyed
High Si-alloyed
Cutting Pressing during stacking Welding Sticking Automatic stacking, riveting Pressing into frame
# 0 0/# 0 0/# #
## 0 # 0/# # #
### 0 ## # ## ##
Coated with organic adhesive coating.
observed e!ects was obtained for samples by removing the cutting burr. It should be mentioned that the e!ects of the di!erent steps of manufacturing process depend also on the conditions and quality of the equipments. Generally, the deterioration by the di!erent manufacturing steps cannot be avoided, only the e!ects of cutting may be removed using an appropriate annealing. The obtained results may be a guideline for better model calculations or even for a better design.
Acknowledgements Many thanks to Prof. G. MuK ller from the Technical University, Dresden, for useful suggestions and discussions on this paper.
References
Fig. 9. In#uence of welding (four welding phases) after stacking of toroidal laminations on P versus J (high Si-alloyed grade, inorganic/organic coating, 50 Hz).
larger deterioration of the magnetic properties. Larger grains of high Si-alloyed grades with low magnetic losses may be the origin for a higher extension of the internal stress, (see also Ref. [8]). No substantial change of the
[1] T. Nakata et al., IEEE J. Magn. Japan 7 (6) (1992) 453. [2] K.-H. Schmidt, J. Magn. Magn. Mater. 2(1}3) (1975, 1976) 136. [3] T. Belgrand, Paper for SMM13, Grenoble 1997. [4] W. Wilczynski, Paper for Gorham/Intertech, Soft Magnetic Materials 98, Barcelona 1998. [5] E. Nitsche, Verringerung der StaK ndereisenverluste, ELINZeitschrift 1985, Heft 3/4, Seite 92. [6] G. MuK ller, Konsultationen&Publikationen, Dresden, 1997, unpublished. [7] A. Schoppa, W. Wilczynski, In#uence of the manufacturing process of electric motors on the properties of laminated stators, to be published. [8] R. Rygal, A.J. Moses, N. Derebasi, J. Schneider, A. Schoppa, Paper for SMM14, BalatonfuK red.
In#uence of the manufacturing process on the magnetic properties of non-oriented electrical steels A. Schoppa*, J. Schneider, C.-D. Wuppermann Department of Application, EBG Bochum, Castroper Strasse 228, 44791 Bochum, Germany
Abstract The optimal use of an appropriate material for a given application requires some considerations concerning the in#uence of the manufacturing conditions on the properties of magnetic components. The paper presents the general trends of the in#uence of manufacturing processes on the magnetic properties of non-oriented fully processed electrical steels. 2000 Elsevier Science B.V. All rights reserved. Keywords: Non-oriented electrical steel; Manufacturing process; Electric motors; Magnetic properties
1. Introduction The development of highly e$cient electric machines like pumps, fans, industrial motors may lead to give an important contribution to saving of electric energy. There is also a demand for an increase of e$ciency in other application areas like lighting engineering and white goods. Besides an improved design, the use of better material grades and broader the knowledge of the in#uence of the manufacturing process on the resulting magnetic properties may help to reach this target. Some basic aspects of the in#uence of the manufacturing process on the magnetic properties of non-oriented fully processed electrical steels have already been published [1}5].
2. Design aspects The ratio of mechanical output P and speed n of an
electrical machine determines the volume < within the stator core. The factor of proportionality between P /n and < depends on the product of the maximum
* Corresponding author. Tel.: #49-234-50851561; fax: #49234-50851042. E-mail address: [email protected] (A. Schoppa).
airgap #ux density B and the e!ective armature ampere conductors A. On the other hand, the machine will be provided for working on a network with given values of frequency and voltage. The frequency "xes the number of poles to be performed for getting the speed desired. The number of poles and the frequency determine the local distribution of magnetic induction in teeth and coreback and its dependence on time. Finally, the local variation of B with time causes magnetic losses within the core and the current necessary to excite the "eld. This current causes winding losses and, in general, with increasing the factor A and B winding losses will grow. So large values of A and B will give a small volume of the machine but bad values of the e$ciency, that means the ratio g"P /(P #P ), where the total losses P are
given as P "P #P #P (P : magnetic losses, P :
! ! winding losses, P : friction losses). Therefore, the relevant magnetic parameters for the optimum choice of nonoriented electrical steels are: frequency of the exciting current, working range of induction, extent of the appearance of higher harmonics and of rotational magnetization process. To estimate the e!ect of di!erent grades of non-oriented electrical steels on the performance of the electric machine by model calculations, one needs an appropriate model, by which the speci"c material data for the "eld and frequency dependence of the magnetic polarization J (J"B!k H) and the speci"c magnetic losses can be included in detail. Only this approach provides an appropriate evaluation of e!ects by di!erent
0304-8853/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 0 7 0 - 6
A. Schoppa et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 74}78
75
grades. To ensure an optimum utilization of the magnetic material as well as a relevant prediction by the model calculations one also needs more details about the in#uence of the di!erent manufacturing processes on the magnetic properties of the core material. These processes comprise starting from the sheet: punching or cutting by laser, conventional assembling or automatic stacking, welding, riveting or other joining techniques, pressing of magnetic cores into the frame. There hardly exists a calculation model which considers both the aspects, i.e., the speci"c magnetic parameters of the material and the in#uence of the manufacturing process on these parameters in an appropriate and complete way. The designers of electric machines use mostly &building factors', which do not give any information about the remaining magnetic properties in the magnetic core after di!erent processing steps.
3. Magnetizing behavior and in6uence of the manufacturing process The e!ect of changes in the characteristic of J versus H of the non-oriented electrical steel on the di!erent processing steps in the operating behavior of electric machines may be well described by the changes of the function ; versus I (; is the e!ective value of the input l voltage, I the magnetizing current in the important case l
Fig. 2. In#uence of the speci"c cutting length in m/kg on J versus H (high Si-alloyed grade, 50 Hz).
Fig. 3. In#uence of the speci"c cutting length in m/kg on J versus H for di!erent grades of non-oriented electrical steels (50 Hz).
Fig. 1. Changes of the function ; versus I in dependence on l the changes of J versus H [6].
of induction machines to be considered here), see Fig. 1. Furthermore, I determines the magnetic contribution l P &I to the entire winding losses P &I" ! l ! I #I"I +1#(I /I ), with I component of the l l
76
A. Schoppa et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 74}78
Fig. 4. In#uence of pressing in N/mm during stacking of toroidal laminations on J versus H (high Si-alloyed grade, 50 Hz).
Fig. 5. In#uence of welding (four welding passes) after stacking of toroidal laminations on J versus H (high Si-alloyed grade, 50 Hz).
Table 1 Importance of the change of the magnetizing by di!erent manufacturing steps Processing step
Operating range (0.5 T
Operating range 0.5}1.5 T
Operating range '1.5 T
Cutting Pressing during stacking Welding Sticking Automatic stacking, riveting Pressing into frame
# 0 # 0 0/# 0/#
### #/## ## # #/## #/##
#/0 0 0 0 #/0 #/0
current producing torque as well as the value of the power factor [6] cos u"I /I"I /(I #I) . In this l way the e!ects of using materials with a better permeability in the operating range of induction and the deterioration of the magnetic properties upon the manufacturing process of the magnetic components may be evaluated. Figs. 2}5 give some examples for the degree of deterioration by di!erent processing steps: in#uence of cutting length on J versus H (Figs. 2 and 3), in#uence of the pressure during the stacking of laminations before assembling on J versus H (Fig. 4) and in#uence of welding of the magnetic core on J versus H (Fig. 5). The measurements concerning the in#uence of cutting were
done according to Ref. [2] on strips, starting with a width of the strip of 30 mm and a length of 160 mm. The measurements concerning the in#uence of pressing and welding were done on toroidal samples (outer diameter: 100 mm, inner diameter: 60 mm, height: 10 mm). Additionally, the e!ects of the di!erent manufacturing steps were studied using stators of small industrial motors as well as universal motors [7]. Table 1 re#ects, as a summary of the above-mentioned investigations, the importance of the changes of the magnetizing behavior by di!erent manufacturing steps. For this purpose di!erent operating ranges of induction were regarded.
A. Schoppa et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 74}78
Fig. 6. In#uence of the speci"c cutting length in m/kg on P versus J (high Si-alloyed grade, 50 Hz).
77
Fig. 8. In#uence of coating upon pressing during stacking of toroidal laminations on P versus J (high Si-alloyed grade, inorganic/organic coating, respectively, bare (uncoated) surface, 50 Hz).
4. Magnetic losses and in6uence of the manufacturing process Figs. 6}9 demonstrate the in#uence of the cutting length, of pressure during stacking and of welding on the speci"c losses P versus J. Compared to the changes in the characteristic of J versus H the changes in P versus J appear over the whole range of induction. Obviously, the increase of P will be substantially higher with in creasing frequency f. For the investigated grades of nonoriented electrical steels only small di!erences of the magnetic losses between coated and bare (uncoated) material were found. Table 2 summarizes the e!ects of di!erent manufacturing steps on the speci"c losses P of non-oriented electrical steels distinguished by di!erent Si-content, including the results got by real-stator geometry for small motors [7].
5. Conclusions and outlook
Fig. 7. In#uence of pressing in N/mm during stacking of toroidal laminations on P versus J (high Si-alloyed grade, inorganic/organic coating, 50 Hz).
The obtained experimental data proved that di!erent grades of non-oriented fully processed electrical steels have di!erent sensitivities with respect to di!erent processing steps. In general, high Si-alloyed grades show
78
A. Schoppa et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 74}78
Table 2 E!ects of di!erent manufacturing steps on the speci"c losses P for electrical steel grades with a di!erent Si-content (coated with inorganic/organic coating) Processing step
Non-alloyed, low Si-alloyed
Middle Si-alloyed
High Si-alloyed
Cutting Pressing during stacking Welding Sticking Automatic stacking, riveting Pressing into frame
# 0 0/# 0 0/# #
## 0 # 0/# # #
### 0 ## # ## ##
Coated with organic adhesive coating.
observed e!ects was obtained for samples by removing the cutting burr. It should be mentioned that the e!ects of the di!erent steps of manufacturing process depend also on the conditions and quality of the equipments. Generally, the deterioration by the di!erent manufacturing steps cannot be avoided, only the e!ects of cutting may be removed using an appropriate annealing. The obtained results may be a guideline for better model calculations or even for a better design.
Acknowledgements Many thanks to Prof. G. MuK ller from the Technical University, Dresden, for useful suggestions and discussions on this paper.
References
Fig. 9. In#uence of welding (four welding phases) after stacking of toroidal laminations on P versus J (high Si-alloyed grade, inorganic/organic coating, 50 Hz).
larger deterioration of the magnetic properties. Larger grains of high Si-alloyed grades with low magnetic losses may be the origin for a higher extension of the internal stress, (see also Ref. [8]). No substantial change of the
[1] T. Nakata et al., IEEE J. Magn. Japan 7 (6) (1992) 453. [2] K.-H. Schmidt, J. Magn. Magn. Mater. 2(1}3) (1975, 1976) 136. [3] T. Belgrand, Paper for SMM13, Grenoble 1997. [4] W. Wilczynski, Paper for Gorham/Intertech, Soft Magnetic Materials 98, Barcelona 1998. [5] E. Nitsche, Verringerung der StaK ndereisenverluste, ELINZeitschrift 1985, Heft 3/4, Seite 92. [6] G. MuK ller, Konsultationen&Publikationen, Dresden, 1997, unpublished. [7] A. Schoppa, W. Wilczynski, In#uence of the manufacturing process of electric motors on the properties of laminated stators, to be published. [8] R. Rygal, A.J. Moses, N. Derebasi, J. Schneider, A. Schoppa, Paper for SMM14, BalatonfuK red.