Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) is really a special steel tailored to produce specific magnetic properties: small hysteresis area contributing to low power loss per cycle, low core loss, and permeability.
Electrical steel is often created in cold-rolled strips less than 2 mm thick. These strips are cut to shape to make laminations which can be stacked together to make the laminated cores of transformers, and the stator and rotor of electric motors. Laminations may be cut for their finished shape from a punch and die or, in smaller quantities, might be cut from a laser, or by cut to length machine.
Silicon significantly raises the electrical resistivity in the steel, which decreases the induced eddy currents and narrows the hysteresis loop of the material, thus decreasing the core loss. However, the grain structure hardens and embrittles the metal, which adversely affects the workability of the material, specially when rolling it. When alloying, the concentration quantities of carbon, sulfur, oxygen and nitrogen needs to be kept low, because they elements indicate the presence of carbides, sulfides, oxides and nitrides. These compounds, even in particles as small as one micrometer in diameter, increase hysteresis losses whilst decreasing magnetic permeability. The inclusion of carbon carries 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 resulting in a rise in power loss after a while. For these reasons, the carbon level is kept to .005% or lower. The carbon level can be reduced by annealing the steel in a decarburizing atmosphere, like hydrogen.
Electrical steel made without special processing to manipulate crystal orientation, non-oriented steel, usually includes a silicon amount of 2 to 3.5% and has similar magnetic properties in all directions, i.e., it is actually isotropic. Cold-rolled non-grain-oriented steel is usually abbreviated to CRNGO.
Grain-oriented electrical steel usually has a silicon measure of 3% (Si:11Fe). It is processed in such a way the optimal properties are developed in the rolling direction, as a result of tight control (proposed by Norman P. Goss) from the crystal orientation relative to the sheet. The magnetic flux density is increased by 30% within the coil rolling direction, although its magnetic saturation is decreased by 5%. It is actually utilized for the cores of power and distribution transformers, cold-rolled grain-oriented steel is frequently abbreviated to CRGO.
CRGO is generally supplied by the producing mills in coil form and needs to be cut into “laminations”, that are then used to create a transformer core, which is an integral part of any transformer. Grain-oriented steel is utilized in large power and distribution transformers and in certain audio output transformers.
CRNGO is more affordable than transformer core cutting machine. It is actually used when cost is more significant than efficiency as well as for applications where the direction of magnetic flux is not constant, like in electric motors and generators with moving parts. You can use it when there is insufficient space to orient components to benefit from the directional properties of grain-oriented electrical steel.
This product is a metallic glass prepared by pouring molten alloy steel onto a rotating cooled wheel, which cools the metal at a rate of about one megakelvin per second, so quick that crystals tend not to form. Amorphous steel is limited to foils of about 50 µm thickness. It has poorer mechanical properties so that as of 2010 it costs about double the amount as conventional steel, rendering it inexpensive only for some distribution-type transformers.Transformers with amorphous steel cores could have core losses of just one-third that of conventional electrical steels.
Electrical steel is usually coated to increase electrical resistance between laminations, reducing eddy currents, to offer potential to deal with corrosion or rust, as well as to work as a lubricant during die cutting. There are numerous coatings, organic and inorganic, and the coating used is dependent upon the use of the steel. The particular coating selected depends on the warmth therapy for the laminations, whether the finished lamination will likely be immersed in oil, along with the working temperature of the finished apparatus. Very early practice ended up being to insulate each lamination having a layer of paper or a varnish coating, but this reduced the stacking factor in the core and limited the utmost temperature in the core.
The magnetic properties of electrical steel are determined by heat treatment, as increasing the average crystal size decreases the hysteresis loss. Hysteresis loss is determined by 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 could be delivered in a semi-processed state so that, after punching the ultimate shape, one final heat treatment does apply to produce 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 fails 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 might also increase noise on account of magnetostriction.
The magnetic properties of electrical steel are tested while using internationally standard Epstein frame method.
Electrical steel is a lot more costly than mild steel-in 1981 it was actually greater than twice the cost by weight.
The actual size of magnetic domains in crgo cutting machine might be reduced by scribing the top of the sheet with a laser, or mechanically. This greatly decreases the hysteresis losses in the assembled core.