Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) is actually a special steel tailored to make specific magnetic properties: small hysteresis area causing low power loss per cycle, low core loss, and high permeability.
Electrical steel is generally created in cold-rolled strips lower than 2 mm thick. These strips are cut to contour around make laminations which are stacked together to make the laminated cores of transformers, as well as the stator and rotor of electric motors. Laminations can be cut to their finished shape with a punch and die or, in smaller quantities, may be cut by a laser, or by Core cutting machine.
Silicon significantly raises the electrical resistivity of the steel, which decreases the induced eddy currents and narrows the hysteresis loop from the material, thus reducing the core loss. However, the grain structure hardens and embrittles the metal, which adversely affects the workability of your material, especially when rolling it. When alloying, the concentration degrees of carbon, sulfur, oxygen and nitrogen must be kept low, since these elements indicate the actual existence of carbides, sulfides, oxides and nitrides. These compounds, even just in particles no more than one micrometer in diameter, increase hysteresis losses whilst decreasing magnetic permeability. The inclusion of carbon has a more detrimental effect than sulfur or oxygen. Carbon also causes magnetic aging if it slowly leaves the solid solution and precipitates as carbides, thus causing a rise in power loss as time passes. For these reasons, the carbon level is kept to .005% or lower. The carbon level could be reduced by annealing the steel in a decarburizing atmosphere, for example hydrogen.
Electrical steel made without special processing to manage crystal orientation, non-oriented steel, usually includes a silicon degree of 2 to 3.5% and it has similar magnetic properties in all of the directions, i.e., it is actually isotropic. Cold-rolled non-grain-oriented steel is frequently abbreviated to CRNGO.
Grain-oriented electrical steel usually carries a silicon level of 3% (Si:11Fe). It is actually processed in a way how the optimal properties are created in the rolling direction, because of a tight control (proposed by Norman P. Goss) from the crystal orientation in accordance with the sheet. The magnetic flux density is increased by 30% inside the coil rolling direction, although its magnetic saturation is decreased by 5%. It can be employed for the cores of power and distribution transformers, cold-rolled grain-oriented steel is frequently abbreviated to CRGO.
CRGO is often supplied by the producing mills in coil form and should be cut into “laminations”, that are then used to form a transformer core, which can be an integral part of any transformer. Grain-oriented steel is used in large power and distribution transformers and also in certain audio output transformers.
CRNGO is less expensive than transformer core cutting machine. It is used when price is more significant than efficiency as well as for applications the location where the direction of magnetic flux is just not constant, as in electric motors and generators with moving parts. It can be used if you have insufficient space to orient components to take advantage of the directional properties of grain-oriented electrical steel.
This material can be a metallic glass prepared by pouring molten alloy steel onto a rotating cooled wheel, which cools the metal at a rate around one megakelvin per second, so fast that crystals usually do not form. Amorphous steel is restricted to foils around 50 µm thickness. It has poorer mechanical properties and as of 2010 it costs about double the amount as conventional steel, making it inexpensive just for some distribution-type transformers.Transformers with amorphous steel cores may have core losses of merely one-third that from conventional electrical steels.
Electrical steel is normally coated to enhance electrical resistance between laminations, reducing eddy currents, to deliver effectiveness against corrosion or rust, as well as to work as a lubricant during die cutting. There are many coatings, organic and inorganic, as well as the coating used depends on the use of the steel. The kind of coating selected is dependent upon the heat therapy for the laminations, regardless of if the finished lamination will be immersed in oil, and also the working temperature in the finished apparatus. Very early practice was to insulate each lamination by using a layer of paper or a varnish coating, but this reduced the stacking factor of the core and limited the maximum temperature from the core.
The magnetic properties of electrical steel are influenced by heat treatment, as increasing the average crystal size decreases the hysteresis loss. Hysteresis loss depends upon an ordinary test and, for common grades of electrical steel, may range between 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 might be delivered in a semi-processed state to ensure that, after punching the ultimate shape, one last heat treatment can be applied to form the normally required 150-micrometer grain size. Fully processed electrical steel is normally delivered with the insulating coating, full heat treatment, and defined magnetic properties, for dexupky53 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 even also increase noise on account of magnetostriction.
The magnetic properties of electrical steel are tested utilizing the internationally standard Epstein frame method.
Electrical steel is a lot more costly than mild steel-in 1981 it absolutely was a lot more than twice the cost by weight.
The size of magnetic domains in Silicon steel cut to length may be reduced by scribing the top of the sheet having a laser, or mechanically. This greatly cuts down on the hysteresis losses in the assembled core.