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        POSITION:HOME>PERFORMANCE>Knowledge of magnetism

        1, permanent magnet magnetic can include which index
        The main magnetic index of permanent magnetic material is: remanence (Jr, Br), coercive force (bHc) and intrinsic coercive force (jHc), magnetic energy product (BH) m. We usually say of permanent magnet magnetic, refers to the four. The other magnetic index of the permanent magnetic material and: Curie temperature (Tc), working temperature (Tw), the temperature coefficient of the remanence and intrinsic coercive force (Br theta, jHc theta), reply permeability (mu rec.), demagnetization curve square (Hk/jHc), high temperature can reduce magnetic and magnetic uniformity, etc.
        In addition to the magnetic, permanent magnetic material physical properties include density, conductivity, thermal conductivity, thermal expansion coefficient, etc. Mechanical properties, including the vickers hardness, compressive strength (la) strength, impact toughness, etc. In addition, the performance of the permanent magnetic material and important one, is the surface state and its corrosion resistance.

         

        2, the remanent magnetization (Jr, Br)
        Permanent magnet material in the closed circuit state after the external magnetic field to the saturation magnetization, to undo the external magnetic field, the magnetic pole of permanent magnet strength J and magnetic induction intensity B will not disappear because of the disappearance of the external magnetic field H, and will keep the size of a certain value, the value is referred to as the residual magnetic pole strength of the material Jr and residual magnetic induction intensity of Br, generally referred to as the residual magnetism.
        Remanence Jr and the units of Br and the intensity of magnetic pole and magnetic induction intensity of the same units.
        According to equation (1, 1), on the demagnetization curve of permanent magnet material, magnetic field H is 0, Jr = Br, magnetic field H is negative, J and B are not equal, then divided into J H and B - H curve. From equation (1, 1) can also see that with the increase of the reverse magnetic field H, B from the maximum Br = Jr changes to 0, the negative, for modern permanent magnet material, often as a straight line; the change rule of demagnetization curve B J is different: the change rule of demagnetization curve with the increase of the reverse magnetic field H, B value linear decreases, and as a result of B value reduction is always greater than or equal to reverse magnetic field H increased a lot, so the J in a certain area of the demagnetization curve can remain relatively flat straight, but is always less than the value of J Jr.

         

        3, coercive force (bHc) and intrinsic coercive force (jHc)
        On the permanent magnet demagnetization curve, when the reverse magnetic field H increases to a value bHc, magnets, magnetic induction intensity B is zero, called the reverse magnetic field H value is the coercive force of the material bHc; When reverse magnetic field H = bHc, magnet does not display the magnetic flux, so the coercive force bHc characterization of permanent magnetic material‘s ability to fight or other external reverse magnetic field demagnetization effect. Coercive force bHc is an important parameter in the design of magnetic circuit.
        It is worth noting: coercive force bHc on numerical value is always less than remanence Jr. Because from (1 to 1) as you can see, at H = bHc, B = 0, bHc is mu 0 = J, has shown above, any point on the J demagnetization curve of magnetic pole strength value is always less than the remanence Jr, therefore, coercive force bHc is always less than the residual magnetism on numerical Jr. For example: Jr = 12.3 kGs of magnet, its bHc may not be greater than 12.3 kOe. Remanent magnetism, in other words, Jr is coercive force on numerical bHc theoretical limit.
        When reverse magnetic field H = bHc, although the magnet of the magnetic induction intensity B is 0, magnet does not display the magnetic flux, but the interior of the magnet micro magnetic dipole moment vector and often is not 0, meaning that the magnet magnetic pole strength J in the original direction tends to remain a larger value. Therefore, bHc is not sufficient to represent the intrinsic magnetic properties of magnets; When the reverse magnetic field H jHc increases to a certain value, the internal microscopic magnets magnetic dipole moment vector and zero, called the reverse magnetic field H value is the intrinsic coercive force of the material jHc.
        Intrinsic coercive force jHc is permanent magnetic material is a very important physical parameter, for jHc far outweigh bHc magnet, when the reverse magnetic field H is greater than the bHc but less than jHc, although the magnet has been demagnetization to reverse the extent of the magnetic induction intensity B, but after the reverse magnetic field H undo, magnets, magnetic induction intensity B can still because of the internal microscopic vector and in the original direction of the magnetic dipole moment and back to the original direction. That is to say, as long as the reverse magnetic field H has not yet reached jHc, permanent magnetic material has not yet been completely demagnetization. Therefore, the intrinsic coercive force jHc is characterization of permanent magnetic material to resist external reverse magnetic field or other demagnetization effect, to maintain its original magnetization state power of one of the main indicators.
        Coercive force bHc and intrinsic coercive force jHc at the same unit with the magnetic field strength.

         

        4, magnetic energy product (BH) m
        On the permanent magnet demagnetization curve B (second quadrant), different points in different working condition, corresponds to the magnet demagnetization curve B on a point of the Bm and Hm (abscissa and ordinate) represent the magnet in the state, the magnets inside the size of the magnetic induction intensity and magnetic field, the product of the absolute value of Bm and Hm (BmHm) on behalf of the magnet in the condition of isothermal capacity, equivalent magnet magnetic energy storage, known as magnetic energy product. Br on B demagnetization curve points and bHc, magnet (BmHm) = 0, said the magnet isothermal is 0, the ability of the magnetic energy product of 0; Magnets in a certain state (BmHm) the value of the largest, said magnet foreign the ability of doing work at this time, the largest known as the maximum magnetic energy product, the magnet or magnetic energy product, remember to (BH) Max or m (BH). Therefore, people usually want the magnet in magnetic circuit can work under its maximum magnetic energy product status. Magnetic energy product unit in the system of SI for J/m3 (mj/m3), in the CGS system for MGOe (trillion high oster), 100/4 MGOe PI J/m3 = 1.

         

        5, what call Nd - Fe - B permanent magnet, it points a few categories?
        Nd - Fe - B permanent magnet is so far discovered in 1982 strongest permanent magnet magnetic materials. Its main chemical composition of Nd (Nd), Fe (iron) and B (B), and its main phase cell on the crystallography for four square structure, molecular formula for Nd2Fe14B (hereinafter referred to as 2:14:1 phase). In addition to the main phase Nd2Fe14B, Nd - Fe - B permanent magnet also contains a small amount of wealthy Nd facies, and B is equal to the other phase. The Lord and rich Nd phase is decided Nd - Fe - B magnets, permanent magnetic characteristics of the most important two phase. Today, Nd - Fe - B permanent magnet has been widely used in computer, medical equipment, communications devices, electronic devices, magnetic machinery and other fields.
        Nd - Fe - B divided into sintered and bonded magnets two kinds big. Nd - Fe - B sintered magnets are usually made of powder metallurgy method of anisotropic density magnets; And usually Nd - Fe - B bonded magnet is made of chilling method microcrystalline powder, each powder contains multiple Nd - Fe - B microcrystal grain size, with a polymer or other adhesive powder into large pieces of magnets, so usually Nd - Fe - B bonded magnet is a compact isotropic magnet. Often, therefore, Nd - Fe - B sintered magnets, magnetic can be far higher than that of Nd - Fe - B bonded magnet, but Nd - Fe - B bonded magnet has many Nd - Fe - B sintered magnets irreplaceable advantages: can be made with pressure, injection molding methods, such as small size, complicated shape, high geometric accuracy of permanent magnets, and easy to realize large-scale automated production; In addition, Nd - Fe - B bonded magnet magnetization, also facilitate any direction can easily make multi-polar and numerous high overall magnets, which for a Nd - Fe - B sintered magnets are often difficult to achieve; Because the Nd - Fe - B bonded magnet Nd2Fe14B main phase in the state of microcrystalline, therefore it also has good corrosion resistance than sintered magnet, etc.

         

        6, Nd - Fe - B the making craft of sintered magnets
        In China, Nd - Fe - B usually sintered magnets production process is:
        Melting alloy, pulverizing, orientation pressed sintering -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- tempering magnetic detection - blank finishing cutting -- -- -- -- -- -- -- -- -- - fine grinding -- -- -- -- - semi-finished products inspection - -- -- -- -- -- -- -- -- -- electroplating product packaging test -- -- -- -- -- into the Treasury.

         

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