Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) is really a special steel tailored to generate specific magnetic properties: small hysteresis area resulting in low power loss per cycle, low core loss, and high permeability.
Electrical steel is normally created in cold-rolled strips below 2 mm thick. These strips are cut to shape to make laminations that happen to be stacked together to form the laminated cores of transformers, and the stator and rotor of electric motors. Laminations may be cut with their finished shape from a punch and die or, in smaller quantities, could be cut with a laser, or by Core cutting machine.
Silicon significantly increases the electrical resistivity of your steel, which decreases the induced eddy currents and narrows the hysteresis loop of your 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 degrees of carbon, sulfur, oxygen and nitrogen needs to be kept low, because they elements indicate the actual existence of carbides, sulfides, oxides and nitrides. These compounds, in particles no more than one micrometer in diameter, increase hysteresis losses while decreasing magnetic permeability. The actual existence of carbon features 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 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 could be reduced by annealing the steel within a decarburizing atmosphere, such as hydrogen.
Electrical steel made without special processing to manage crystal orientation, non-oriented steel, usually carries a silicon level of 2 to 3.5% and it has similar magnetic properties in most directions, i.e., it can be isotropic. Cold-rolled non-grain-oriented steel is often abbreviated to CRNGO.
Grain-oriented electrical steel usually carries a silicon level of 3% (Si:11Fe). It is processed in such a manner that this optimal properties are developed in the rolling direction, as a result of tight control (proposed by Norman P. Goss) of 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 can be useful for the cores of power and distribution transformers, cold-rolled grain-oriented steel is normally abbreviated to CRGO.
CRGO is generally provided by the producing mills in coil form and needs to be cut into “laminations”, which are then used produce a transformer core, which is a fundamental part of any transformer. Grain-oriented steel is commonly used in large power and distribution transformers and then in certain audio output transformers.
CRNGO is cheaper than transformer core cutting machine. It can be used when pricing is more valuable than efficiency and for applications where the direction of magnetic flux is not constant, like in 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 can be a metallic glass prepared by pouring molten alloy steel onto a rotating cooled wheel, which cools the metal for a price of around one megakelvin per second, so quickly that crystals will not form. Amorphous steel has limitations 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, making it cost-effective only for some distribution-type transformers.Transformers with amorphous steel cores may 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 supply resistance to corrosion or rust, and to serve as a lubricant during die cutting. There are many coatings, organic and inorganic, and the coating used is dependent upon the effective use of the steel. The type of coating selected is determined by the high temperature treatment of the laminations, whether the finished lamination will probably be immersed in oil, along with the working temperature in the finished apparatus. Very early practice was to insulate each lamination by using a layer of paper or perhaps a varnish coating, but this reduced the stacking factor of your core and limited the utmost temperature of your core.
The magnetic properties of electrical steel are influenced by heat treatment, as boosting the average crystal size decreases the hysteresis loss. Hysteresis loss is dependent upon a regular 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 inside a semi-processed state in order that, after punching the ultimate shape, your final heat treatment does apply to form the normally required 150-micrometer grain size. Fully processed electrical steel is usually 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, or even rough handling can adversely affect electrical steel’s magnetic properties and may even 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 absolutely was over twice the cost by weight.
The dimensions of magnetic domains in crgo cutting machine might be reduced by scribing the top of the sheet using a laser, or mechanically. This greatly lessens the hysteresis losses within the assembled core.