Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) can be a special steel tailored to generate specific magnetic properties: small hysteresis area leading to low power loss per cycle, low core loss, and permeability.
Electrical steel is generally produced in cold-rolled strips lower than 2 mm thick. These strips are cut to shape to make laminations which can be stacked together to form the laminated cores of transformers, as well as the stator and rotor of electric motors. Laminations can be cut for their finished shape by way of a punch and die or, in smaller quantities, can be cut with a laser, or by cut to length machine.
Silicon significantly increases the electrical resistivity of the steel, which decreases the induced eddy currents and narrows the hysteresis loop of your material, thus lowering the core loss. However, the grain structure hardens and embrittles the metal, which adversely affects the workability in the material, specially when rolling it. When alloying, the concentration amounts of carbon, sulfur, oxygen and nitrogen needs to be kept low, since these elements indicate the existence of carbides, sulfides, oxides and nitrides. These compounds, even in particles no more than one micrometer in diameter, increase hysteresis losses while also decreasing magnetic permeability. The existence of carbon carries a more detrimental effect than sulfur or oxygen. Carbon also causes magnetic aging whenever it slowly leaves the solid solution and precipitates as carbides, thus contributing to an increase in power loss as time passes. Therefore, the carbon level is kept to .005% or lower. The carbon level may be reduced by annealing the steel inside a decarburizing atmosphere, including hydrogen.
Electrical steel made without special processing to manage crystal orientation, non-oriented steel, usually features a silicon measure of 2 to 3.5% and has similar magnetic properties in all of the directions, i.e., it really is isotropic. Cold-rolled non-grain-oriented steel is often abbreviated to CRNGO.
Grain-oriented electrical steel usually has a silicon amount of 3% (Si:11Fe). It is processed in such a manner that this optimal properties are created in the rolling direction, because of a tight control (proposed by Norman P. Goss) of the crystal orientation in accordance with the sheet. The magnetic flux density is increased by 30% from the coil rolling direction, although its magnetic saturation is decreased by 5%. It is actually useful for the cores of power and distribution transformers, cold-rolled grain-oriented steel is normally abbreviated to CRGO.
CRGO is normally supplied by the producing mills in coil form and should be cut into “laminations”, which can be then used to create a transformer core, which is a fundamental element of any transformer. Grain-oriented steel can be used in large power and distribution transformers and also in certain audio output transformers.
CRNGO is cheaper than transformer core cutting machine. It is used when cost is more important than efficiency and also for applications in which the direction of magnetic flux is just not constant, as with electric motors and generators with moving parts. It can be used when there is insufficient space to orient components to leverage the directional properties of grain-oriented electrical steel.
This product can be a metallic glass prepared by pouring molten alloy steel onto a rotating cooled wheel, which cools the metal for a price of approximately one megakelvin per second, so quickly that crystals will not form. Amorphous steel is limited to foils of approximately 50 µm thickness. It offers poorer mechanical properties and also as of 2010 it costs about twice as much as conventional steel, making it cost-effective only for some distribution-type transformers.Transformers with amorphous steel cores could have core losses of merely one-third those of conventional electrical steels.
Electrical steel is usually coated to increase electrical resistance between laminations, reducing eddy currents, to provide effectiveness against corrosion or rust, and to act as a lubricant during die cutting. There are various coatings, organic and inorganic, and the coating used is dependent upon the effective use of the steel. The sort of coating selected is determined by the heat therapy for the laminations, whether or not the finished lamination will be immersed in oil, as well as the working temperature in the finished apparatus. Very early practice ended up being to insulate each lamination having a layer of paper or even a varnish coating, but this reduced the stacking factor of your core and limited the most temperature in the core.
The magnetic properties of electrical steel are determined by heat treatment, as boosting the average crystal size decreases the hysteresis loss. Hysteresis loss depends upon a regular test and, for common grades of electrical steel, may cover anything 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 might be delivered in the semi-processed state in order that, after punching the final shape, one last heat treatment does apply to create the normally required 150-micrometer grain size. Fully processed electrical steel is often delivered by having 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, and even rough handling can adversely affect electrical steel’s magnetic properties and might also increase noise as a result of magnetostriction.
The magnetic properties of electrical steel are tested while using internationally standard Epstein frame method.
Electrical steel is much more costly than mild steel-in 1981 it was actually over twice the fee by weight.
How big magnetic domains in crgo cutting machine may be reduced by scribing the top of the sheet having a laser, or mechanically. This greatly decreases the hysteresis losses inside the assembled core.