Nora Leuning

Effect of the Interdependence of Cold Rolling Strategies and Subsequent Punching on Magnetic Properties of NO Steel Sheets

Nowadays, optimization of non-oriented (NO) electrical steels toward lower iron-loss, improved, and isotropic magnetizability is critical to the improvement of rotating electrical machines. The whole production process chain adjusts the microstructure evolution, e.g., grain size and crystallographic texture, determining the magnetic properties. In particular, the interdependence of raw material properties and the resulting mechanical stress distribution during final assembly, e.g., punching, leading to magnetic property deterioration is crucial for the optimization of NO steel properties of rotating machines. This paper studies the effect of different cold rolling strategies, annealing treatments, and sheet metal blanking (punching) regarding microstructure evolution, magnetic properties, and deterioration.

Effect of mechanical stress on different iron loss components up to high frequencies and magnetic flux densities

Purpose The purpose of this paper is to study the variation of the specific iron loss components of electrical steel sheets when applying a tensile mechanical load below the yield strength of the material. The results provide an insight into the iron loss behaviour of the laminated core of electrical machines which are exposed to mechanical stresses of diverse origins. Design/methodology/approach The specific iron losses of electrical steel sheets are measured using a standardised single-sheet tester equipped with a hydraulic pressure cylinder which enables application of a force to the specimen under test. Based on the measured data and a semi-physical description of specific iron losses, the stress-dependency of the iron loss components can be studied. Findings The results show a dependency of iron loss components on the applied mechanical stress. Especially for the non-linear loss component and high frequencies, a large variation is observed, while the excess loss component is not as sensitive to high mechanical stresses. Besides, it is shown that the stress-dependent iron loss prediction approximates the measured specific iron losses in an adequate way. Originality/value New applications such as high-speed traction drives in electric vehicles require a suitable design of the electrical machine. These applications require particular attention to the interaction between mechanical influences and magnetic behaviour of the machine. In this regard, knowledge about the relation between mechanical stress and magnetic properties of soft magnetic material is essential for an exact estimation of the machine’s behaviour.

On the Homogeneity and Isotropy of Non-Grain-Oriented Electrical Steel Sheets for the Modeling of Basic Magnetic Properties from Microstructure and Texture

Laminations of non-grain-oriented (NO) electrical steel grades for magnetic cores of electrical machines should feature homogenous magnetic properties within the entire sheet plane. Basic empirical models have been introduced to estimate and correlate magnetic properties with microstructural material parameters. In these considerations, the steel sheets are generally considered to be homogenous, i.e., orientation dependence and variations across the sheet thickness are often disregarded. Whether or not, these simplifications are justified and how grain size and texture are described most suitable for correlations with magnetic properties is the focus of this paper discussing four industrial NO steel grades.

Impact of the interaction of material production and mechanical processing on the magnetic properties of non-oriented electrical steel

Thin laminations of non-grain oriented (NO) electrical steels form the magnetic core of rotating electrical machines. The magnetic properties of these laminations are therefore key elements for the efficiency of electric drives and need to be fully utilized. Ideally, high magnetization and low losses are realized over the entire polarization and frequency spectrum at reasonable production and processing costs. However, such an ideal material does not exist and thus, achievable magnetic properties need to be deduced from the respective application requirements. Parameters of the electrical steel such as lamination thickness, microstructure and texture affect the magnetic properties as well as their polarization and frequency dependence. These structural features represent possibilities to actively alter the magnetic properties, e.g., magnetization curve, magnetic loss or frequency dependence. This paper studies the influence of production and processing on the resulting magnetic properties of a 2.4 wt% Si ...

Loss reduction due to blanking parameter optimization for different non-grain oriented electrical steel grades

An optimized electrical machine design can improve its efficiency and power density. While magnetic and mechanical design of rotor and stator laminations for varying types of electrical machines is well understood, influence of process induced mechanical stresses on magnetic behavior of non-oriented electrical steel grades is widely unknown. Especially when looking at the blanking process, magnetic properties like iron losses and magnetizability are detrimentally altered due to cutting induced residual stresses. There have been investigations of individual electrical steel grades, which show a significant extent of magnetic property deterioration depending on the process parameters used. This paper studies influences of different blanking process parameters on magnetic properties of various non-oriented electrical steel grades. Several materials with different grain size, silicon content and thickness are investigated. Magnetic properties of processed electrical steel specimens are analyzed using a single sheet tester. The results enable a correlation between material grade, sheet thickness, blanking parameters and magnetic properties to be studied.