Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) is a special steel tailored to generate specific magnetic properties: small hysteresis area leading to low power loss per cycle, low core loss, and high permeability.
Electrical steel is generally manufactured in cold-rolled strips under 2 mm thick. These strips are cut to contour around make laminations that happen to be stacked together to produce the laminated cores of transformers, as well as the stator and rotor of electric motors. Laminations might be cut on their finished shape by way of a punch and die or, in smaller quantities, may be cut with a laser, or by Core cutting machine.
Silicon significantly increases the electrical resistivity in 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 of the material, particularly when rolling it. When alloying, the concentration degrees of carbon, sulfur, oxygen and nitrogen should be kept low, because these elements indicate the inclusion of carbides, sulfides, oxides and nitrides. These compounds, even just in particles as small as one micrometer in diameter, increase hysteresis losses as well as decreasing magnetic permeability. The actual existence of carbon includes 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 leading to a rise in power loss after a while. Because of this, the carbon level is kept to .005% or lower. The carbon level might be reduced by annealing the steel inside a decarburizing atmosphere, like hydrogen.
Electrical steel made without special processing to regulate crystal orientation, non-oriented steel, usually has a silicon measure of 2 to 3.5% and possesses similar magnetic properties in all directions, i.e., it is actually isotropic. Cold-rolled non-grain-oriented steel is often abbreviated to CRNGO.
Grain-oriented electrical steel usually features a silicon amount of 3% (Si:11Fe). It is actually processed in such a way that this optimal properties are created in the rolling direction, because of 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 can be useful for the cores of power and distribution transformers, cold-rolled grain-oriented steel is usually abbreviated to CRGO.
CRGO is normally provided by the producing mills in coil form and has to be cut into “laminations”, that are then used produce a transformer core, which happens to be 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 core cutting machine. It is used when price is more significant than efficiency and for applications in which the direction of magnetic flux is just not constant, like 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.
This material is really a metallic glass prepared by pouring molten alloy steel onto a rotating cooled wheel, which cools the metal for a price of about one megakelvin per second, so quick that crystals will not form. Amorphous steel is restricted to foils around 50 µm thickness. They have poorer mechanical properties so that as of 2010 it costs about twice as much as conventional steel, which makes it inexpensive just for some distribution-type transformers.Transformers with amorphous steel cores could have core losses of just one-third those of conventional electrical steels.
Electrical steel is usually coated to boost electrical resistance between laminations, reducing eddy currents, to offer effectiveness against corrosion or rust, as well as behave as a lubricant during die cutting. There are many coatings, organic and inorganic, along with the coating used depends on the application of the steel. The kind of coating selected is dependent upon the temperature management of the laminations, regardless of if the finished lamination will probably be immersed in oil, and the working temperature of your finished apparatus. Very early practice ended up being to insulate each lamination with a layer of paper or perhaps a varnish coating, but this reduced the stacking factor in the core and limited the most temperature in the core.
The magnetic properties of electrical steel are dependent on heat treatment, as enhancing the average crystal size decreases the hysteresis loss. Hysteresis loss depends on a typical test and, for common grades of electrical steel, may range 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 might be delivered in a semi-processed state so that, after punching the final shape, one last heat treatment does apply to produce 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, and even rough handling can adversely affect electrical steel’s magnetic properties and may 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 more than twice the fee by weight.
How big magnetic domains in crgo cutting machine might be reduced by scribing the top of the sheet by using a laser, or mechanically. This greatly decreases the hysteresis losses inside the assembled core.