Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) can be a special steel tailored to make specific magnetic properties: small hysteresis area leading to low power loss per cycle, low core loss, and high permeability.
Electrical steel is usually produced in cold-rolled strips lower than 2 mm thick. These strips are cut to shape to make laminations that are stacked together to produce the laminated cores of transformers, and the stator and rotor of electric motors. Laminations might be cut with their finished shape with a punch and die or, in smaller quantities, can be cut from a laser, or by cut to length machine.
Silicon significantly increases the electrical resistivity from the steel, which decreases the induced eddy currents and narrows the hysteresis loop from the material, thus lowering the core loss. However, the grain structure hardens and embrittles the metal, which adversely affects the workability from the material, particularly when rolling it. When alloying, the concentration degrees of carbon, sulfur, oxygen and nitrogen needs to be kept low, because these elements indicate the inclusion of carbides, sulfides, oxides and nitrides. These compounds, even during particles as small as one micrometer in diameter, increase hysteresis losses while decreasing magnetic permeability. The actual existence of carbon has a more detrimental effect than sulfur or oxygen. Carbon also causes magnetic aging when it slowly leaves the solid solution and precipitates as carbides, thus leading to a rise in power loss with time. Therefore, the carbon level is kept to .005% or lower. The carbon level might be reduced by annealing the steel in a decarburizing atmosphere, such as hydrogen.
Electrical steel made without special processing to control crystal orientation, non-oriented steel, usually has a silicon level 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 often abbreviated to CRNGO.
Grain-oriented electrical steel usually carries a silicon amount of 3% (Si:11Fe). It is actually processed in such 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% in the coil rolling direction, although its magnetic saturation is decreased by 5%. It is used for the cores of power and distribution transformers, cold-rolled grain-oriented steel is often abbreviated to CRGO.
CRGO is normally provided by the producing mills in coil form and needs to be cut into “laminations”, which can be then used to form a transformer core, which happens to be an integral part of any transformer. Grain-oriented steel can be used in large power and distribution transformers and also in certain audio output transformers.
CRNGO is more affordable than transformer core cutting machine. It can be used when pricing is more valuable than efficiency and also for applications in which the direction of magnetic flux will not be constant, like electric motors and generators with moving parts. You can use it when there is insufficient space to orient components to make use of the directional properties of grain-oriented electrical steel.
This material is 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 quickly that crystals tend not to form. Amorphous steel is restricted to foils of around 50 µm thickness. They have poorer mechanical properties so when of 2010 it costs about double the amount as conventional steel, which makes it cost-effective only for some distribution-type transformers.Transformers with amorphous steel cores can have core losses of a single-third that of conventional electrical steels.
Electrical steel is generally coated to increase electrical resistance between laminations, reducing eddy currents, to deliver effectiveness against corrosion or rust, and to serve as a lubricant during die cutting. There are numerous coatings, organic and inorganic, and the coating used depends on the use of the steel. The sort of coating selected is dependent upon the warmth treatments for the laminations, if the finished lamination will probably be immersed in oil, and the working temperature in the finished apparatus. Very early practice ended up being 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 utmost temperature of your core.
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 test and, for common grades of electrical steel, may vary from a couple of to 10 watts per kilogram (1 to 5 watts per pound) at 60 Hz and 1.5 tesla magnetic field strength.
Electrical steel could be delivered within a semi-processed state to ensure, after punching the final shape, your final heat treatment can be applied to produce the normally required 150-micrometer grain size. Fully processed electrical steel is normally delivered with an insulating coating, full heat treatment, and defined magnetic properties, for dexupky53 where punching is not going to significantly degrade the electrical steel properties. Excessive bending, incorrect heat treatment, as well as rough handling can adversely affect electrical steel’s magnetic properties and may even also increase noise because of magnetostriction.
The magnetic properties of electrical steel are tested using the internationally standard Epstein frame method.
Electrical steel is more costly than mild steel-in 1981 it was more than twice the charge by weight.
How big magnetic domains in Silicon steel cut to length may be reduced by scribing the top of the sheet by using a laser, or mechanically. This greatly lessens the hysteresis losses within the assembled core.