The silicon steel sheet production process can effectively reduce iron loss and enhance the efficiency and performance of equipment such as motors by optimizing processes such as stacking, grain orientation, and surface treatment. This is also the main topic of this article.
Definition of Iron Loss
Iron Loss refers to the energy losses that occur in ferromagnetic materials (such as silicon steel sheets and amorphous alloys) when they are repeatedly magnetized in an alternating magnetic field. This loss primarily manifests as heat, leading to increased core temperatures, which reduces the efficiency of electrical devices (such as transformers and motors) and may cause overheating failures. Iron loss is mainly composed of the following three parts:
| Hysteresis Loss: Ferromagnetic materials consist of many tiny “magnetic domains.” When an external magnetic field changes, the domains must overcome internal frictional resistance to change direction, aligning with the external magnetic field. This process is similar to mechanical friction, consumes energy, and converts it into heat. The size of the area enclosed by the hysteresis loop is proportional to the hysteresis loss; the wider the loop, the greater the loss.
| Eddy Current Loss: According to the principle of electromagnetic induction, the alternating magnetic field induces an electromotive force in the core (acting as a conductor), which forms closed swirling currents (i.e., eddy currents). These eddy currents flow through the resistance of the core, generating Joule heat and resulting in energy loss.
| Residual Loss: This refers to other losses excluding hysteresis and eddy current losses, including domain wall relaxation losses, magnetic aftereffect losses, and local eddy current losses. This part of the loss is usually small under low-frequency weak magnetic fields.
Impact of Silicon Steel Sheet Production Processes on Iron Loss
| Punching Process of Silicon Steel Sheets: The production and processing of cores can damage the grain orientation near the punching edges of silicon steel sheets, leading to increased iron loss under the same magnetic field; for frequency-variable motors, additional iron losses due to harmonics must also be considered. This should be a comprehensive factor considered during the design stage.
| Stacking Process of Silicon Steel Sheets: Issues may occur during the stacking of the cores. Excessive pressure during stacking can damage the insulation layers between silicon steel sheets, or welding processes may also damage the insulation, increasing eddy current loss. Insufficient compression between the sheets can lead to a core weight deficit, directly causing excessive current and exceeding iron loss thresholds.
| Annealing Process of Silicon Steel Sheets: The influencing conditions of iron loss primarily exist in silicon steel sheets, where mechanical and thermal stresses can affect the sheets’ actual properties. Excess mechanical stress may cause variations in iron loss. Additionally, the continuous rise in internal motor temperatures can exacerbate iron loss issues. Implementing effective annealing measures to remove extra mechanical stress can positively impact reducing iron loss within the motor.
| Post-processing of Silicon Steel Sheets: If the burrs after stamping are too large, removing them through grinding may severely damage the surface insulation layer of the punched sheets. Additionally, if the core is uneven after stacking or if machining is necessary due to misalignment of the stator’s inner bore and the housing, these methods can damage insulation, leading to short circuits between silicon steel sheets.
| Insulation Treatment of Silicon Steel Sheets: If silicon steel sheets have not undergone insulation treatment or are inadequately treated, this issue can be detected during the inspection process. However, not all motor manufacturers conduct such inspections, making it difficult to identify this problem effectively. Another reason is that if the insulation layer of the silicon steel sheet is too thick, leading to magnetic circuit saturation, severely bending the relationship curve between no-load current and voltage. This is a critical element in the silicon steel sheet production process.
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