Magnetic Properties and Structure of Non-Oriented Electrical Steel Sheets after Different Shape Processing (original) (raw)
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Energies
The global drive to reduce energy consumption poses new challenges for designers of electrical machines. Losses in the core are a significant part of losses, especially for machines operating at an increased rotational speed powered by PWM inverters. One of the important problems when calculating core losses is considering the effect of material degradation due to mechanical or laser cutting. To this aim, this paper analyzes and summarizes the knowledge about the sources of material property deterioration and ways of describing this phenomenon. The cited results of material tests indicate the lack of unequivocal relationships allowing us to estimate the degree of material damage and the resulting deterioration of material properties. The main task of this article is to present the state of knowledge on the possibility of taking into account the impact of cutting the core sheets of electric motors on core losses and their impact on the efficiency of the machine. This is a significant...
2017
The use of high quality non-oriented electrical steel and of an innovative design for the magnetic cores of the electrical machines are very important, in order to minimize the value of the total energy losses. The energy losses are strongly influenced by the cutting technologies, and the producers of the electrical machines want to minimize the deterioration of the magnetic properties during the manufacturing process. The influence of the cutting density on the magnetic permeability and energy losses was analyzed and one can notice that these magnetic properties are strongly influenced by the cutting technologies. There were tested sheet samples of M400-50A and M700-50A industrial steel grades (thickness of 0.50 mm), cut through mechanical and water jet technologies. All samples have the length equal to 300 mm and the width of 30, 15, 10, 7.5 and 5 mm. The magnetic characterization was performed using a laboratory single strip tester, which can make measurements on samples with an area of 300 × 30 mm 2. In order to have the standard width of 30 mm, there were put together side by side 2, 3, 4 and 6 pieces with different widths. The magnetic properties were analyzed at 1000 mT in the frequency range 10 ÷ 400 Hz. It was observed that the processing conditions must be controlled and optimized, in order to maintain a low deterioration of the magnetic properties of the non-oriented steels. In the case of water jet technology an increase of the cutting speed will be useful for the introduction of this method in the large scale manufacturing of the electrical machines.
Journal of Magnetism and Magnetic Materials, 2015
The process of manufacturing iron cores for electric machines out of electrical steel sheets can strongly affect the magnetic properties of the material. In order to better understand the influence of cutting on the iron losses, a characterization of the magnetization behavior near the cutting edge is needed. The local magnetic properties of the material are modified by the cutting process which leads to an increase in the iron losses measured for 5 mm wide ring core samples by nearly 160% at low inductions. We present investigations on the effect of cutting by observation of the magnetic domain structure of 0.35 mm thick non-oriented electrical steel. By using the magneto-optical Kerr-effect on a ring samples the local magnetic properties of the material after processing are characterized in the form of domain wall displacements under an applied external ac-field. The influence of various cutting techniques on the magnetic properties was studied before and after stress relief annealing. This method allows a quantitative analysis of the influence of different cutting techniques on the micro-magnetic properties of nonoriented electrical steel for rotating machines.
IEEE Transactions on Magnetics, 2016
This paper provides a quantitative analysis of the degradation of the magnetic properties of nonoriented electrical steel sheets caused by laser, guillotine, and spark erosion cutting as well as the healing effect of stress relief annealing. For this purpose, the macroscopic material characteristics, such as commutation curves, dynamic hysteresis loops, and magnetic power losses, are gained by single-sheet tester measurements. The experiments are conducted on specimens composed of strips of variable width to adjust different degrees of total degradation. The origin of the observed changes of the material is elucidated by micromagnetic measurements based on the magneto-optical Kerr effect that visualizes the domain patterns and wall movements near the cutting edges. A local magnetic contrast is defined, which serves as a quantitative measure for the local degree of deterioration. The use of homogenous parameters within a numerical loss model based on the principle of loss separation is theoretically justified and experimentally proved to provide correct values of the total magnetic power loss for arbitrary magnetizations in degraded steel sheets.
Effect of Shear Cutting on Microstructure and Magnetic Properties of Non-Oriented Electrical Steel
IEEE Transactions on Magnetics, 2016
In manufacturing electrical machine cores, the electrical steel laminations are often mechanically cut, leading to residual stress and a deterioration in magnetic properties. Several cutting techniques are used in the industry, such as shear cutting, punching and laser cutting. The influence of shear cutting on the steel microstructure and magnetic properties was investigated in this paper. A single sheet tester (SST) was used for measurements of two different grades of non-oriented electrical steel at different induction levels (0.1-1.5 T) and a wide range frequency (3 Hz-1 kHz). A scanning electron microscope (SEM) was used for the characterization of the microstructure (grain size) at the cutting edges. The mechanical properties near the edge of the lamination were measured using nanoindentation. An increase in magnetic loss due to cutting was observed to be ~20% for B35AV1900 and ~9% for 35WW300, corresponding to a damaged area extending up to a distance of ~170 µm and ~140 µm, from the cut edge, respectively.
The influence of cutting technique on the magnetic properties of electrical steels
2003
Magnetic permeability and losses at 1.5 T of a 2% Si non-oriented fully processed electrical steel Epstein strip, cut by different techniques (punching, guillotine, laser and photocorrosion), have lower values at the as-cut condition, when compared to after annealing. Permeability at 1.5 T showed to be more affected by cutting than the losses. Photocorrosion is slightly less harmful, but annealing did not improve it as much as it did to samples cut with guillotine.
Identification of magnetic properties for cutting edge of electrical steel sheets
2016 XXII International Conference on Electrical Machines (ICEM), 2016
Electrical steel sheets of motors and generators are usually shaped to the final form by punching. The punching and other cutting processes generate large plastic deformations and residual stresses. These are known to deteriorate the magnetic properties of the edge region. However, the characterization of this deterioration in the form of magnetic properties is missing. The main aim of this paper is to a method to identify the magnetic properties of the edge region based on experimental results. This approach is demonstrated by using previously presented test results for magnetic properties of rectangular strips. The width of these strips is varied, and thus, the share of the edge region to the whole can be used as a variable. Based on this variation a simple model is developed and the model parameters fitted to the experimental results. The correspondence between the calculated and experimental results is good.
Magnetic Properties of Electrical Steel Sheets with Motor Control Excitation
Journal of Electronic Materials, 2018
This paper provides a quantitative analysis of the degradation of the magnetic properties of nonoriented electrical steel sheets caused by laser, guillotine, and spark erosion cutting as well as the healing effect of stress relief annealing. For this purpose, the macroscopic material characteristics, such as commutation curves, dynamic hysteresis loops, and magnetic power losses, are gained by single-sheet tester measurements. The experiments are conducted on specimens composed of strips of variable width to adjust different degrees of total degradation. The origin of the observed changes of the material is elucidated by micromagnetic measurements based on the magneto-optical Kerr effect that visualizes the domain patterns and wall movements near the cutting edges. A local magnetic contrast is defined, which serves as a quantitative measure for the local degree of deterioration. The use of homogenous parameters within a numerical loss model based on the principle of loss separation is theoretically justified and experimentally proved to provide correct values of the total magnetic power loss for arbitrary magnetizations in degraded steel sheets.
Computational Materials Science, 2008
Basic magnetic properties of non-oriented electrical steel sheets with different grain size and silicon content have different behaviour before and after cutting into strips. Cutting process causes a significant drop in flux density and deterioration of magnetic properties occurs over a region up to 10 mm from close to the cut edge. Therefore some degraded regions are formed at each side of the cut. A new mathematical model was formed for the degree of deterioration on flux distribution near the cut edge. The variation of magnetic induction in the cutting region was given as a function of four different parameters depending on the material. The model also included the variation of these parameters with the grain size and silicon content. It is observed that the change in the parameters until 2.5% Si content is not significant, while it has a remarkable variation for them after 2.5% Si content and similar effect was found to be for grain size. The mathematical model gives the degree to which the magnetic properties of the region around the edge degrade after the cutting process. The calculated results of the model showed good agreements with the experimental results.
Journal of Magnetism and Magnetic Materials, 2003
Non-oriented electrical steels have been cut with two different techniques, the laser cutting and the mechanical cutting. In order to investigate the effect of the first technique on magnetic properties, different cutting parameters have been tested. Despite this, the best magnetic properties have been obtained after mechanical cutting. The laser cutting causes a coercive field increase and a permeability drop. Due to thermal effect, internal stress seems to be the main process drawback. No correlation between the heat affected zone and the magnetic properties has been found.