Basic Knowledge of Silicon Steel

Commonly used transformer cores are generally made of silicon steel. Silicon steel is used as the core of a transformer because it is a magnetic material with high permeability and can produce a large magnetic induction in an energized coil.

Silicon steel is a steel containing silicon, a soft magnetic material widely used in the electrical field. Electrical silicon steel is often rolled into large sheets or strips of standard size for use, commonly known as silicon steel sheets, and is widely used in electric motors, generators, transformers, electromagnetic mechanisms, relay electronics and measuring instruments.

Silicon is a good deoxidizer for steel, which combines with oxygen to transform oxygen into stable SiO2 that is not reduced for carbon, avoiding lattice distortion of iron due to oxygen atom doping. Silicon becomes solid solution in alpha iron to increase the resistivity, while helping to separate out the harmful impurities carbon. Therefore, the addition of silicon to iron containing impurities in general can increase the magnetic permeability, reduce the coercivity and iron loss. However, the increase in silicon content will make the material hard and brittle, thermal conductivity and toughness, heat dissipation and mechanical processing is not conducive, so the general silicon steel sheet silicon content does not exceed 4.5%.

According to the manufacturing process and use of electrical steel is divided into three categories: hot-rolled silicon steel, cold-rolled electrical steel and special-purpose silicon steel.

The main quality characteristics of silicon steel sheets are iron loss value, magnetic flux density, hardness, flatness, thickness uniformity, coating type and flushing properties, etc.

1. Iron Loss Value

Low iron loss is the most important indicator of the quality of silicon steel sheets. Countries are divided into grades according to the iron loss value, the lower the iron loss, the higher the grade.

2. Magnetic flux density

Magnetic flux density is another important electromagnetic characteristic of silicon steel sheet, which indicates the difficulty of silicon steel sheet being magnetized. In a particular frequency of magnetic field strength, the magnetic flux per unit area is called magnetic flux density. The flux density of a silicon steel sheet is usually measured at a frequency of 50 or 60 Hz and an applied magnetic field of 5000 A/m, called B50, and is measured in Tesla.

The magnetic flux density is related to the collective organization of the silicon steel sheet, impurities, internal stresses and other factors. Flux density directly affects the energy efficiency of motors, transformers and other motor equipment. The higher the flux density, the greater the flux per unit area, the better the energy efficiency, therefore, the higher the flux density of silicon steel sheet, the better, usually, the specification only requires the minimum value of flux density.

3. Hardness

Hardness is one of the quality characteristics of silicon steel sheet. When modern automatic punching machines are used to punch the sheet, the requirements for hardness are more stringent.

In order to meet the above requirements, the hardness of the silicon steel sheet must be higher than a certain hardness value.

4. Flatness

Flatness is an important quality characteristic of silicon steel wafers. Good flatness facilitates sheet punching and assembly work. Flatness is directly and closely related to rolling and annealing technology.

5. Thickness uniformity

Thickness uniformity is a very important quality characteristic of silicon steel sheets. If the thickness uniformity is not good, the thickness difference between the center and the edge of the sheet is too large, or the variation of the sheet thickness in the length of the sheet is too large, it will affect the thickness of the assembled core. Different core thickness, the variation of its magnetic conductivity is also large, which directly affects the characteristics of motors and transformers, therefore, the smaller the variation of the thickness of silicon steel sheet, the better. The thickness uniformity of the steel sheet is closely related to the hot rolling and cold rolling technology and process, so that the thickness variation of the steel sheet can be reduced by improving the rolling technology.

6. Coating film

Coating is a very important quality item for silicon steel sheets. The surface of the silicon steel sheet is chemically coated and a thin film is attached to it, which provides insulation, rust prevention and lubrication.

7. Punch ability

Punch ability is one of the most important quality characteristics of silicon steel sheet. Good punch ability increases the life of the die and reduces the burr of the punch. Punch ability is directly related to the coating type and hardness of the silicon steel sheet. The newer coating types have been developed to improve the punch ability of silicon steel sheets.

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