15 concepts related to magnetic materials explained-2

8.SI system and CGS system

 That is, the International System of Units and the Gaussian System of Units are like the difference between "meter" and "mile" in the unit of length. There is a complicated conversion relationship between the International System of Units and the Gaussian System of Units.

9. Curie temperature

 It is the temperature at which a magnetic material changes between a ferromagnetic body and a paramagnetic body. When the temperature is lower than the Curie temperature, the material becomes a ferromagnetic body. At this time, the magnetic field related to the material is difficult to change. When the temperature is higher than the Curie temperature, the substance becomes a paramagnetic body, and the magnetic field of the magnet easily changes with the surrounding magnetic field.

 The Curie temperature represents the theoretical working temperature limit of magnetic materials. The Curie temperature of neodymium iron boron is about 320-380 degrees Celsius. The level of the Curie point is related to the crystal structure formed by the sintering of the magnet. If the temperature reaches the Curie temperature, the molecules inside the magnet move violently and demagnetize, and it is irreversible; after the magnet is demagnetized, it can be magnetized again, but the magnetic force will drop significantly, only reaching about 50% of the original.

10. Working temperature

 The maximum working temperature of sintered NdFeB is much lower than its Curie temperature. The magnetic force will decrease when the temperature rises within the working temperature, but most of the magnetic force will recover after cooling.

The relationship between working temperature and Curie temperature: Curie temperature is about high, the working temperature of the magnetic material is relatively higher, and the temperature stability is better. The addition of cobalt, terbium, dysprosium and other elements to the sintered NdFeB raw material can increase its Curie temperature, so high coercivity products (H, SH,...) generally contain dysprosium.

 The maximum use temperature of sintered NdFeB depends on its own magnetic properties and the selection of operating points. For the same sintered NdFeB magnet, the closer the working magnetic circuit is, the higher the maximum use temperature of the magnet and the more stable the performance of the magnet. Therefore, the maximum operating temperature of the magnet is not a certain value, but changes with the degree of closure of the magnetic circuit.

11. Magnetic field orientation

 Magnetic materials are divided into two types: isotropic magnets and anisotropic magnets. Isotropic magnets have the same magnetic properties in any direction and can be attracted together at will; anisotropic magnets have different magnetic properties in different directions. The direction in which it can obtain the best magnetic properties is called the orientation direction of the magnet.

For a square sintered NdFeB magnet, only the orientation direction has the highest magnetic field strength, and the other two directions have much lower magnetic field strength. If the magnetic material has an orientation process during the production process, it is an anisotropic magnet. Sintered NdFeB is generally molded and pressed by magnetic field orientation, so it is anisotropic. Therefore, it is necessary to determine the orientation direction before production, the upcoming magnetization direction . Powder magnetic field orientation is one of the key technologies for manufacturing high-performance NdFeB. (The bonding of NdFeB is isotropic and anisotropic)

12. Magnetic

 It refers to the magnetic induction intensity of a certain point on the surface of the magnet (the surface magnetism of the center and the edge of the magnet are not the same). It is the value measured by the Gauss meter contacting a certain surface of the magnet, not the overall magnetic performance of the magnet.

13. Magnetic flux

 Suppose that in a uniform magnetic field with a magnetic induction intensity of B, there is a plane with an area S and perpendicular to the direction of the magnetic field. The product of the magnetic induction intensity B and the area S is called the magnetic flux passing through this plane, referred to as the magnetic flux, and the symbol "Φ" , The unit is Weber (Wb). Magnetic flux is a physical quantity that represents the distribution of the magnetic field. It is a scalar, but it has positive and negative values, which only represent its direction. Φ=B·S, when there is an angle θ between the vertical plane of S and B, Φ=B·S·cosθ.

14. Electroplating

 The sintered neodymium iron boron permanent magnet material is produced by powder metallurgy technology. It is a kind of powder material with very strong chemical activity. There are tiny pores and cavities inside, which are easily corroded and oxidized in the air. Therefore, strict surface treatment must be carried out before use. Electroplating is widely used as a mature metal surface treatment method.

 The most commonly used coatings for NdFeB magnets are galvanized and nickel-plated. They have obvious differences in appearance, corrosion resistance, service life, and price:

 Polishing difference: nickel plating is superior to zinc plating in polishing, and the appearance is brighter. Those with high requirements for product appearance generally choose nickel plating, while some magnets are not exposed, and the general zinc plating is relatively low for product appearance requirements.

 Difference in corrosion resistance: Zinc is an active metal and can react with acid, so it has poor corrosion resistance; after nickel-plated surface treatment, its corrosion resistance is higher.

 Service life difference: due to the different corrosion resistance, the service life of zinc plating is lower than that of nickel plating, which is mainly manifested in that the surface coating is easy to fall off after a long time of use, causing the magnet to oxidize, thereby affecting the magnetic performance.

 Difference in hardness: Nickel plating is higher than zinc plating. During use, collisions can be avoided to a great extent, causing the neodymium iron boron strong magnet to appear corners and chipping.

Price difference: galvanizing is very advantageous in this regard, and the prices are arranged from low to high as galvanizing, nickel plating, epoxy resin, etc.

15.Single-sided magnet

 Magnets have two poles, but in some working positions, single-sided magnets are needed. Therefore, one side of the magnet needs to be covered with iron sheets so that the side covered by the iron sheets is magnetically shielded. Such magnets are collectively called single-sided magnets. Or single-sided magnet. There is no real single-sided magnet.