Electrical Sheet

a soft-magnetic sheet steel used for the magnetic flux bars (cores) of electrical equipment, such as transformers, generators, electric motors, reactors, stabilizers, and relays. It contains silicon in various amounts depending on the required level of the steel’s magnetic properties.

Electrical sheet is classified according to the production technology used as cold-rolled (isotropic or anisotropic; up to 3.3 percent Si) and hot-rolled (isotropic; up to 4.5 percent Si); it may contain up to 0.5 percent Al as an alloying admixture. Electrical sheet is sometimes conventionally subdivided into dynamo steel (0.8–2.5 percent Si) and transformer steel (3–4.5 percent Si). It is manufactured in the form of sheets (often in rolls) and narrow strips from 0.05 to 1 mm thick. Electrical sheet also includes pure iron in the form of sheets or strips from 0.1 to 8 mm thick and in the form of rolled circular or rectilinear sections of various sizes.

The quality of electrical sheet is determined by its electromagnetic properties (core loss, coercive force, and magnetic induction), isotropism of the magnetic properties (differences in the values of magnetic properties of the metal with and across the direction of rolling), dimensions and quality of the sheets and strips, mechanical properties, and the parameters of the material’s coating of insulation. A reduction in core loss reduces the energy loss in magnetic flux bars; an increase in magnetic induction permits a reduction in the size of magnetic flux bars; and a decrease in anisotropy improves the characteristics of equipment with rotating magnetic flux bars.

Electrical sheet is usually delivered in an annealed state. Extensive use is being made of high-quality, cold-rolled electrical sheet having a ribbed texture with lower core loss (less than 1 watt per kg with an induction of 1.5 teslas at a frequency of 50 hertz for sheets 0.35 mm thick). In order to relieve mechanical stresses that arise during the fabrication of parts of magnetic flux bars, the items are annealed a second time for a short period at 800°–850°C. Some electrical sheet is delivered in an unannealed state; articles manufactured from such material must be heat-treated after fabrication in order to achieve the same level of magnetic properties.