Iron, nickel, cobalt and their alloys can greatly enhance the magnetic field, so they have a wide range of applications in electrical technology. Under the action of the external magnetic field, the molecular currents in ferromagnetic materials can be arranged in the direction of the magnetic field, which is much stronger than the external magnetic field, from the disorganized and magnetic field elimination distribution state. The alignment of molecular currents causes the magnetic field in a ferromagnetic material to increase dramatically, a process known as magnetization. Some of the magnetic properties of ferromagnetic materials are revealed by the process of magnetization.
Ferromagnetic materials have the following magnetic properties:
(1) The magnetic permeability is not constant and decreases with the increase of magnetic induction;
(2) The magnetic induction has a saturation value;
(3) there is remanence and hysteresis loss in repeated magnetization.
Because the above magnetic properties of ferromagnetic materials are not identical, they can be divided into two broad categories:
(1) soft magnetic materials commonly used soft magnetic materials are cast iron, cast steel and silicon steel sheet (electrical steel). This kind of material has the characteristics of high permeability and small hysteresis loss. Various specifications of silicon steel sheets with thickness ranging from 0.35 mm to 1 mm are important magnetic conducting materials for transformers, motors and AC electromagnets, with saturation values up to 18,000. Cast steel, which is used to make motor housings and parts, has a saturation value not exceeding 10,000. Iron can also be used to make motor housings with a lower saturation value than either of the above.
(2) Hard magnetic materials This type of material has a large remanence, with a value of about 10,000 high. Variety of this kind of material is various, and in constant research and improvement, in order to obtain better performance, but mainly contain different elements of aluminium, iron, nickel alloy, such as alumina 11% 2% and the rest of the ingredients are mainly iron, nickel alloy, with 7000 high remanence value, hard magnetic material can be used to manufacture a variety of USES a permanent magnet. Ferromagnetic materials are used in all kinds of electromagnets used in electrical technology. Because the electromagnet has the advantages of rapid action, sensitive, easy to control, so in the production equipment, especially automated and semi-automated equipment, often use electrical devices containing electromagnet, in order to complete a variety of control and protection. Electromagnets have two types of DC and AC, they are made of the principle of the use of a core coil to generate a current after the suction.
According to the use of different, the electromagnet can be divided into the following:
(1) lifting electromagnet. This kind of electromagnet is used for lifting and unloading all kinds of steel and iron raw materials and their parts in the crane, and its structural principle.
(2) control and protection of electromagnets in electrical appliances. It is often used in contactors and relays, control circuit on and off.
(3)electromagnetic chuck. This equipment is used to fix the steel workpiece on the working machine (such as grinder).
AC electromagnet because of the power supply is very convenient, so get a wide range of applications, but because the flow through the coil current size in constant change, resulting in unstable suction, the armature vibration, so in the AC electromagnet pole surface, embedded short circuit copper ring, using the principle of electromagnetic induction, so that the suction stability.