Main Factors Affecting the Performance of Silicon Steel Sheets in Motors

Main Factors Affecting the Performance of Silicon Steel Sheets in Motors ● **Silicon content and impurities**   Silicon plays a decisive role in the properties of silicon steel sheets. Adding silicon to iron increases electrical resistivity and helps separate harmful carbon impurities. Although silicon addition slightly reduces magnetic flux density in pure iron, it **significantly lowers core loss**.

As silicon content increases, hardness and brittleness rise, creating difficulties in rolling, punching, shearing, and machining. At present, the silicon content of silicon steel sheets generally does not exceed **4.5%**; higher silicon content makes rolling and processing extremely difficult. ● **Thickness**   Eddy current loss in the core is proportional to the **square of the sheet thickness**. For the same grade of silicon steel, **thinner sheets yield lower core loss**, but increase manufacturing time and reduce stacking factor.   General motors use **0.5 mm thick** silicon steel sheets. For large steam turbine generators with strict core loss requirements, **0.35 mm thick** sheets are used. ● **Stress**   Stress generated during punching, stacking, or core winding **degrades magnetic properties** and increases core loss. A visible dark stress band forms within approximately 1 mm of the punched/sheared edge.   **Annealing** is typically used to relieve stress and restore original magnetic performance. High-performance cold-rolled silicon steel is **especially sensitive to stress**. ● **Grain orientation**   Silicon steel is a cubic polycrystalline material with three mutually perpendicular easy magnetization directions. In conventional material, grains are randomly oriented.   Through manufacturing processes, grains can be aligned such that one axis is parallel to the rolling direction and another is perpendicular to the sheet surface. This material, with **one dominant easy magnetization direction**, is called **grain-oriented silicon steel**; it has excellent magnetic properties along the rolling direction but poorer performance in other directions. **Non-oriented silicon steel** has randomly distributed grains, with similar magnetic properties in all directions.   There is also **double-oriented silicon steel**, which has two mutually perpendicular easy magnetization directions (both in the rolling plane, one parallel to rolling). Although ideal for motor cores, it involves complex processing and high cost.