Reducing Power Losses by Optimizing Cooling in Final Annealing of Non-Oriented Electrical Steel

Abstract: Surahammars Bruks AB produces non-oriented electrical steel used in several types of motors and generators. Because of recent years exponentially growing market for electrical vehicles, non-oriented electrical steel used in electrical vehicle motors is becoming an increasingly important product. Magnetic properties of the steel are very important for the efficiency of the vehicle. After cold rolling, the steel coil is annealed, which is the final manufacturing step. After final annealing, the steel is cooled gently to avoid detrimental effects on the final product. Still, it is believed that residual stresses are created in the steel during cooling, which gives worse magnetic properties in the finished material. The purpose of this thesis is to investigate the detrimental effects from the non-optimized cooling of the coil and their effect on power losses. The second part of the work will focus on optimizing the cooling. Production trials were performed to test different cooling strategies. Magnetic measurements were performed and evaluated. Single strips were measured in the rolling direction (RD) and compared with Epstein measurements. Results showed possible improvement in power losses by using gentler cooling. Results also showed increased losses and changed loss pattern as an effect of cutting the material into single strips. Cutting the material into strips changed losses differently for RD losses compared to losses in the transverse direction (TD). These results showed the importance of understanding and improving power losses in both RD and TD.