Product Code Database
Electrical steel ( E-steel, lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) is speciality steel used in the cores of electromagnetic devices such as Engine, generators, and Transformer because it reduces power loss. It is an iron alloy with silicon as the main additive element (instead of carbon).
Silicon increases the electrical resistivity of iron by a factor of about 5; this change decreases the induced and narrows the hysteresis loop of the material, thus lowering the core loss by about three times compared to conventional steel.Buschowl, K.H.J. et al. ed. (2001) Encyclopedia of Materials:Science and Technology. Elsevier. pp. 4807–4808. However, the grain structure hardens and embrittles the metal; this change adversely affects the workability of the material, especially when rolling. When alloying, contamination must be kept low, as , , and , even in particles as small as one micrometer in diameter, increase while also decreasing magnetic permeability. The presence of carbon has a more detrimental effect than sulfur or oxygen. Carbon also causes magnetism aging when it slowly leaves the solid solution and precipitates as carbides, thus resulting in an increase in power loss over time. For these reasons, the carbon level is kept to 0.005% or lower. The carbon level can be reduced by annealing the alloy in a decarburizing atmosphere, such as hydrogen.
| Silicon Core Iron "A" |
| Silicon Core Iron "A-FM" |
| Silicon Core Iron "B" |
| Silicon Core Iron "B-FM" |
| Silicon Core Iron "C" |
Grain-oriented electrical steel usually has a silicon level of 3% (Si:11Fe). It is processed in such a way that the optimal properties are developed in the rolling direction, due to a tight control (proposed by Norman P. Goss) of the crystal orientation relative to the sheet. The magnetic flux density is increased by 30% in the coil rolling direction, although its magnetic saturation is decreased by 5%. It is used for the cores of power and distribution , cold-rolled grain-oriented steel is often abbreviated to CRGO.
CRGO is usually supplied by the producing mills in coil form and has to be cut into "laminations", which are then used to form a transformer core, which is an integral part of any transformer. Grain-oriented steel is used in large power and distribution transformers and in certain audio output transformers.
CRNGO is less expensive than CRGO. It is used when cost is more important than efficiency and for applications where the direction of magnetic flux is not constant, as in electric motors and generators with moving parts. It can be used when there is insufficient space to orient components to take advantage of the directional properties of grain-oriented electrical steel.
Electrical steel is usually coated to increase electrical resistance between laminations, reducing eddy currents, to provide resistance to corrosion or rust, and to act as a lubricant during die cutting. There are various coatings, organic molecule and inorganic, and the coating used depends on the application of the steel.Fink, Donald G. and Beatty, H. Wayne (1978) Standard Handbook for Electrical Engineers 11th ed. McGraw-Hill. pp. 4–111. The type of coating selected depends on the heat treatment of the laminations, whether the finished lamination will be immersed in oil, and the working temperature of the finished apparatus. Very early practice was to insulate each lamination with a layer of paper or a varnish coating, but this reduced the stacking factor of the core and limited the maximum temperature of the core.
ASTM A976-03 classifies different types of coating for electrical steel.
| No |
| No |
| No |
| No |
| No |
| No |
| Yes |
| No |
| No |
| Yes |
| Yes |
table 5.2 for the 38000
The magnetic properties of electrical steel are dependent on heat treatment, as increasing the average crystal size decreases the hysteresis loss. Hysteresis loss is determined by a standard Epstein frame and, for common grades of electrical steel, may range from about 2 to 10 watts per kilogram (1 to 5 watts per pound) at 60 Hz and 1.5 tesla magnetic field strength.
Electrical steel can be delivered in a semi-processed state so that, after punching the final shape, a final heat treatment can be applied to form the normally required 150-micrometer grain size. Fully processed electrical steel is usually delivered with an insulating coating, full heat treatment, and defined magnetic properties, for applications where punching does not significantly degrade the electrical steel properties. Excessive bending, incorrect heat treatment, or even rough handling can adversely affect electrical steel's magnetic properties and may also increase noise due to magnetostriction.Jump, Les (March 1981) Transformer Steel and Cores, Federal Pioneer BAT
The magnetic properties of electrical steel are tested using the internationally standard Epstein frame method. IEC 60404-2
The size of magnetic domains in sheet electrical steel can be reduced by scribing the surface of the sheet with a laser, or mechanically. This greatly reduces the hysteresis losses in the assembled core.de Lhorbe, Richard (June/July 1981), Steel No Lasers Here, Federal Pioneer BAT
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