This page talks about the steel used in electric motors.
Silicon steel is also called electrical steel, lamination steel, relay steel, or transformer steel. This is a special steel tailored to produce specific magnetic properties such as small hysteresis area resulting in low power losses, low core loss, and high permeability.
SiSteel is usually manufactured in cold rolled strips less than 2mm thickness. These sheets may be grain oriented(CRGO) or non-grain oriented(CRNGO).
These laminations may be cut to the required shapes by punch or die. In smaller quantities, they may be cut by laser, wire , or wire EDM.
The Silicon content may vary from 0 to 6.5% in typical sheets. Commercial alloys have upto 3.2% silicon. Manganese and Aluninum are added upto 0.5%. Si increases resistivity, reducing eddy currents and narrows hysteresis loop, reducing eddy currents. But the grain structure hardens and makes the material brittle. While alloying, Carbon, Sulfer, Oxygen, and Nitrogen levels must be kept low. Carbon also causes magnetic aging - increases power loss over time. CArbon levels can be lowered by annealing in decarburizing atmosphere such as hydrogen.
Resistivity for a 3% is 47.2e-8 ohm-m.
CRNGO is made without special processign to control crystal orientation has similar magnetic properties in all directions, i.e. isotropic.
for CRGO, magnetic flux density is increased by 30% in the rolling direction, magnetic saturation is reduced by 5%. Usually used for transformers.
Silicon steels are available with several types of insulation:
–C-0:
Also called bare, or oxide coated. This is a thin, tightly adherent oxide coating put on the material at the steel mill, or during the annealing process after stamping. This is the lowest cost insulation, but offers little resistance.
–C-3:
Enamel or varnish coating which offers excellent insulation, but parts so coated cannot be annealed after stamping.
–C-4:
An inorganic coating providing higher resistance than C-0, but which will withstand annealing temperatures.
–C-5:
An improved inorganic coating similar to C-4 but with significantly higher resistance. It withstands annealing well in most cases. This is probably the best choice for most performance sensitive applications. The main drawback to C-5 is an increase in tool wear due to abrasiveness.
Even though annealed at the mill, fully processed material may require further stress relief anneal after stamping. The stresses introduced during punching degrade the material properties around the edges of the lamination, and must be removed to obtain maximum performance. This is particularly true for parts with narrow sections, or where very high flux density is required. In one instance, a tachometer manufacturer was able to reduce the stack height in his product by 10% by annealing after stamping. The annealing cycle requires a temperature of 1350-1450 F in a non oxidizing, non carburizing atmosphere. Endothermic, nitrogen, and vacuum atmospheres all work well.