Views:1 Author:Site Editor Publish Time: 2020-11-27 Origin:Site
Materials with strong magnetic permeability, such as silicon steel, cast steel, permalloy, etc., are called ferromagnetic materials. Ferromagnetic materials have the following three basic characteristics. First, the permeability is not constant, but decreases with the increase of magnetic induction. The second characteristic is that the magnetic flux density has a saturation value. Third, there are remanence and hysteresis loss in repeated magnetization.
Ferromagnetic materials can be divided into the following three categories. The first category is soft magnetic materials. This type of material has the characteristics of large permeability and low hysteresis loss. Its hysteresis loop is narrow and steep, and its coercive force is small. It is easier to magnetize, but at the same time it is also easy to demagnetize, so it is suitable for repeated magnetization. Commonly used soft magnetic materials are cast steel and silicon steel sheets and so on. Silicon steel sheets of various specifications with a thickness of 0.35 to 1 mm are important magnetic materials for the manufacture of transformers, motors and AC electromagnets. The magnetic induction intensity saturation value of hot-rolled silicon steel sheets can reach 14,000 Gauss, and the magnetic induction intensity saturation value of cold-rolled silicon steel sheets Up to 18000 Gauss. Cast iron can be used to make motor casings and parts, and its saturation value does not exceed 10,000 Gauss.
The second category, hard magnetic materials. This kind of material is characterized by large remanence, large coercive force, fat and wide hysteresis loop, difficult to magnetize, and a very strong external magnetic field is required. There are many varieties of hard magnetic materials, and they are under continuous research and improvement. More widely used are alloys containing different components of aluminum, nickel, and iron, such as alloys containing 11% aluminum, 22% nickel, and the rest of iron, with a remanence value of 7000 Gauss. Using barium ferrite, strontium-calcium ferrite and other materials, a new type of hard ferrite can be made. Its coercive force is higher than that of alloy hard magnetic materials, small specific gravity, low price, but low remanence . Hard magnetic materials can be used to make permanent magnets for various purposes.
The third type of material is rectangular magnetic material. The hysteresis loop of this type of material is rectangular, and it can be magnetized and saturated under the action of a small external magnetic field. After removing the external magnetic field, its remanence is almost equal to its saturation magnetic flux density. Such materials are mainly used in digital computers, magnetic amplifiers and automatic control equipment.