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Iron, nickel, cobalt and their alloys can greatly enhance the magnetic field, so they are widely used in electrical technology. Under the action of the external magnetic field, the molecular current in the ferromagnetic material can be arranged from a disorganized and destructive distribution state to the direction of its magnetic field and the external magnetic field, so an additional magnetic field that is far stronger than the external magnetic field is formed. Arranging molecular currents causes the magnetic field within a ferromagnetic material to increase dramatically, an effect called magnetization. Certain magnetic properties of ferromagnetic materials are revealed from the process of magnetization.
Ferromagnetic materials have the following magnetic properties:
(1) Magnetic permeability is not constant, and decreases with the increase of magnetic induction;
(2) The magnetic induction has a saturation value;
(3) There are remanence and hysteresis losses in repeated magnetization.
Since the above-mentioned magnetic properties of ferromagnetic materials are not the same, they can be divided into two categories:
(1) Soft magnetic materials commonly used soft magnetic materials include cast iron, cast steel and silicon steel sheet (electrical steel). Such materials have the characteristics of high permeability and low hysteresis loss. Silicon steel sheets of various specifications with a thickness of 0.35~1 mm are important magnetic conductive materials for the manufacture of transformers, motors and AC electromagnets, and the saturation value can reach as high as 18,000. Cast steel is used to manufacture motor casings and parts, and its saturation value is not higher than 10,000. Cast iron can also cast motor casings, and its saturation value is lower than the above two.
(2) Hard magnetic materials This type of material has a large remanence, and its value is about 10,000 high. There are many varieties of such materials, and they are constantly being researched and improved in order to obtain better performance, but the main ones are aluminum, iron-nickel alloys with different compositions, such as aluminum 11%, nickel 2% and the rest. Mainly an alloy of iron, with a high remanence value of 7,000, the hard magnetic material can be used to make permanent magnets for various purposes. All kinds of electromagnets used in electrical technology use ferromagnetic materials. Because electromagnets have the advantages of rapid action, sensitivity, and easy control, in production equipment, especially automatic and semi-automatic equipment, electrical devices containing electromagnets are often used to complete various control and protection functions. There are two types of electromagnets, DC and AC. They are all made of the principle of generating suction after the iron core coil is passed through with current.
According to different uses, electromagnets can be divided into the following types:
①Lifting electromagnet. This type of electromagnet is used for lifting and unloading various steel and iron raw materials and their parts in cranes.
②Control and protect the electromagnets in electrical appliances. It is often used in contactors and relays to control the on and off of circuits.
③Electromagnetic chuck. This equipment is used to fix steel workpieces on the mother machine (such as a grinder).
The AC electromagnet is widely used because the power supply is very convenient. However, the current flowing through the coil is constantly changing, resulting in unstable suction and vibration of the armature. Therefore, the short-circuit copper is embedded on the pole surface of the AC electromagnet. The ring, using the principle of electromagnetic induction, makes the suction stable.