Electrotechnical steel: production and use

The production of this type of steel occupies a dominant position among other magnetic materials. Electrotechnical steel is an alloy of iron with silicon, the proportion of which is from 0.5% to 5%. The wide popularity of products of this type can be explained by high electromagnetic and mechanical properties. Such steel is made from widely distributed components, where there is no shortage. This explains its low cost.

Effect of silicon

This component, in interaction with iron, forms a dense solution with a high specific resistivity, the value of which depends on the percentage of silicon in the alloy. When exposed to pure iron, it loses its magnetic properties. But when the impact on the technical, on the contrary, affects positively. Permeability of iron increases and there is an improvement in the stability of the metal. The favorable effect of silicon (Si) can be explained as follows. Under the influence of this element, there is a transition of carbon to graphite from the state of cementite, which has less magnetic properties. The element Si has an undesirable effect on reducing induction. Its influence extends to thermal conductivity and to the density of iron.

Impurities in the composition

In its composition, electrotechnical steel can contain other components: sulfur, carbon, manganese, phosphorus and others. The most harmful of them is carbon (C). It can be in the form of both cementite and graphite. This has different effects on the alloy, as well as the percentage of carbon content. To avoid undesirable inclusions of element C, steel can not be quickly cooled for the next aging and stabilization.

The following components have a negative effect on the properties of the material: oxygen, sulfur, manganese. They reduce its magnetic qualities. Technical iron in its composition necessarily has impurities. Here they have to be taken into account in the aggregate, not as for pure iron.

It is possible to improve the properties of steel by applying impurities. But this method is not always profitable for large-scale production. But with the help of cold rolling sheet electrotechnical steel forms in its structure magnetic properties. This allows you to achieve better results. But further firing is absolutely necessary.

Cold rolling

For a long time it was believed that silicon increases the brittleness of steel. Production was mainly carried out by hot rolling. The profitability of cold rolling was low.

Only after it was discovered that cold treatment along the direction increases the magnetic properties of the material, it has become widely used. Other areas showed themselves only from the worst side. Cold rolling beneficially affected the mechanical properties, as well as improving the quality of the sheet surface, increased its waviness and allowed the punching.

The distinctive properties that electrotechnical steel obtained through the application of cold working can be explained by the formation of a crystallographic texture in it. It is distinguished by several degrees. They, in turn, depend on the temperature at which the rolling takes place, also on the thickness of the required sheet and on the degree to which it is compressed.

The cost of a sheet of one thickness of hot-rolled steel is 2 times lower than that of cold-rolled steel. But this negative quality is completely compensated by low heat losses (less than about every two times), high quality and the possibility of good stamping of cold-rolled alloy. The difference in these steels is the silicon content. Its quantity ranges from 3.3% to 4.5%, respectively.

GOST

Manufacturers produce only two types of steel, which comply with GOST. The first type - 802-58 "Electrotechnical thin-sheeted". The second one is electrotechnical steel GOST 9925-61 "Cold rolled coil made of electrical steel".

Designation

It is marked with the letter "E", followed by a number, the numbers of which have a certain value:

• The first digit in the value of the marking indicates the degree of alloying of steel with silicon. From slightly alloyed to highly doped, respectively in the figures from 1 to 4. Dinamic - it is steel from the groups E1 and E2. Transformer - E3 and E4.
• The second digit of the marking has a range from 1 to 8. It shows the electromagnetic properties of the material when applied in certain operating conditions. By this marking it is possible to find out in which areas one or another steel can be used.

The zero digit followed by the second digit means that the steel is textured. If there are two zeros, then it is a little textured.

At the end of the marking, you can see the following letters:

• "A" - the specific loss of material is very low.
• "P" - a material with high strength of rolled products and high surface finish.

Scope of operation

The alloy is divided into three types of application:

• Suitable for operation in strong and medium magnetic fields (remagnetization purity of 50 Hz);
• Suitable for operation in medium fields at a frequency of up to 400 Hz;
• Steel, which is operated in medium and small magnetic fields.

Sheets of electrical steel produce the following sizes: width from 240 to 1000 mm, length can be from 720 mm to 2000 mm, thickness - in the range of 0.1 to 1 mm. Most of all, textured steel is used because they have a high value of electromagnetic properties. Sheets of such material are often used in electrical engineering.

Electrotechnical steel - properties

Properties of the alloy:

• Resistivity. The quality of the material directly depends on this indicator. Steel is used where it is necessary to hold electricity inside the conductor and deliver it to its intended use.
• Coercive force. Responsible for the ability of the internal magnetic field to demagnetize. For certain devices, this property is required to varying degrees. In transformers and electric motors, parts with a high demagnetization ability are used. In steel, this indicator has a low value. But in electromagnets, on the contrary, high coercive force is needed. To adjust the magnetic properties, the necessary percentage of silicon is added to the steel alloy.

• The width of the hysteresis loop. This indicator should be as small as possible.
• Magnetic permeability. The higher this indicator, the better the material "copes" with its tasks.
• Sheet thickness. For the manufacture of many devices and parts use materials that are less than one millimeter thick. However, if necessary, this figure is reduced to a value of 0.1 mm.

Application

From sheet materials of the first class it is possible to make different types of magnetic circuits for relays and regulators.

Electrotechnical steel of the second class can be used for starters of electric machines of DC and AC currents, rotor cores. The third class will be suitable for manufacturing magnetic cores for power transformers, as well as starters for large synchronous machines.

To make a frame for an electric machine, it is necessary to apply steel casting, in which the carbon content is not more than 1%. Products made from such material are subjected to gradual annealing. Carbon steel is used in the manufacture of machine parts subjected to welding. Of these types of materials make the main poles for DC machines.

For those parts of machines that carry the maximum load (springs, rotors, shafts of anchors), use alloys with high mechanical properties. Such material may contain nickel, chromium, molybdenum and tungsten. It is possible to manufacture magnetic cores from electrical steel. They are used for low-frequency transformers - 50Hz.

Core magnetic core

Magnetic cores they divide into armor and rod. Each species has its own characteristics.

Rod: for such a magnetic core the rod is vertical and has a stepped section inscribed in a circle. Windings of the magnetic circuit are located on them with a special cylindrical shape.

Armored

Products of this design have a rectangular shape, and their rods have a cross section, they are located horizontally. This type of magnetic core is used only in complex devices and structures. Therefore, such designs are not widely used.

So, we found out what the electrical steel is and where it is used.