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  • INFORMATION

    1. Background and History

    Permanent magnets are a vital part of modern life. They are found in or used to produce almost every modern convenience today. The first permanent magnets were produced from naturally occurring rocks called lodestones. These stones were first studied over 2500 years ago by the Chinese and subsequently by the Greeks, who obtained the stone from the province of Magnetes, from which the material got its name. Since then, the properties of magnetic materials have been profoundly improved and today’s permanent magnet materials are many hundreds of times stronger than the magnets of antiquity. The term permanent magnet comes from the ability of the magnet to hold an induced magnetic charge after it is removed from the magnetizing device. Such devices may be other strongly magnetized permanent magnets, electro-magnets or coils of wire that are briefly charged with electricity. Their ability to hold a magnetic charge makes them useful for holding objects in place, converting electricity to motive power and vice versa (motors and generators), or affecting other objects brought near them.

    2. Design

    Superior magnetic performance is a function of better magnetic engineering. For customers who require design assistance or complex circuit designs, GREAT WELL's team of experienced application engineers and knowledgeable field sales engineers is at your service. GREAT WELL engineers work with customers to improve or validate existing designs as well as develop novel designs that produce special magnetic effects. GREAT WELL has developed patented magnetic designs that deliver extremely strong, uniform or specially shaped magnetic fields that often replace bulky and inefficient electro-magnet and permanent magnet designs. Customers are confident when hey bring a complex concept or new idea that GREAT WELL will meet that challenge by drawing from 10 years of proven magnetic expertise. GREAT WELL has the people, products and technology that put magnets to work.

    3. Magnet Selection

    Magnet selection for all applications must consider the entire magnetic circuit and the environment. Where Alnico is appropriate, magnet size can be minimized if it can be magnetizing after assembly into the magnetic circuit. If used independent of other circuit components, as in security applications, the effective length to diameter ratio (related to the permeance coefficient) must be great enough to cause the magnet to work above the knee in its second quadrant demagnetization curve. For critical applications, Alnico magnets may be calibrated to an established reference flux density value. A by-product of low coercivity is sensitivity to demagnetizing effects due to external magnetic fields, shock, and application temperatures. For critical applications, Alnico magnets can be temperature stabilized to minimize these effects there are four classes of modern commercialized magnets, each based on their material composition. Within each class is a family of grades with their own magnetic properties. These general classes are:

      Neodymium Iron Boron

      Samarium Cobalt

      Ceramic

      Alnico

    NdFeB and SmCo are collectively known as Rare Earth magnets because they are both composed of materials from the Rare Earth group of elements.

    Neodymium Iron Boron (general composition Nd2Fe14B, often abbreviated to NdFeB) is the most recent commercial addition to the family of modern magnet materials. At room temperatures, NdFeB magnets exhibit the highest properties of all magnet materials. Samarium Cobalt is manufactured in two compositions:

    Sm1Co5 and Sm2Co17 - often referred to as the SmCo 1:5 or SmCo 2:17 types. 2:17 types, with higher Hci values, offer greater inherent stability than the 1:5 types

    Ceramic, also known as Ferrite, magnets (general composition BaFe2O3 or SrFe2O3) have been commercialized since the 1950s and continue to be extensively used today due to their low cost. A special form of Ceramic magnet is "Flexible" material, made by bonding Ceramic powder in a flexible binder. Alnico magnets (general composition Al-Ni-Co) were commercialized in the 1930s and are still extensively used today.

    These materials span a range of properties that accommodate a wide variety of application requirements. The following is intended to give a broad but practical overview of factors that must be considered in selecting the proper material, grade, shape, and size of magnet for a specific application. The chart below shows typical values of the key characteristics for selected grades of various materials for comparison. These values will be discussed in detail in the following sections. 
     

    Magnet Material Comparisons

    Material

    Grade

    Br

    Hc

    Hci

    BH max

    T max (Deg C)*

    NdFeB

    39H

    12,800

    12,300

    21,000

    40

    150

    SmCo

    26

    10,500

    9,200

    10,000

    26

    300

    NdFeB

    B10N

    6,800

    5,780

    10,300

    10

    150

    Alnico

    5

    12,500

    640

    640

    5.5

    540

    Ceramic

    8

    3,900

    3,200

    3,250

    3.5

    300

    Flexible

    1

    1,600

    1,370

    1,380

    0.6

    100

    * T max (maximum practical operating temperature) is for reference only. The maximum practical operating temperature of any magnet is dependent on the circuit the magnet is operating in.

    4. Surface Treatment

    Magnets may need to be coated depending on the application for which they are intended. Coating magnets improves appearance, corrosion resistance, protection from wear and may be appropriate for applications in clean room conditions.

    Samarium Cobalt, Alnico materials are corrosion resistant, and do not require to be coated against corrosion. Alnico is easily plated for cosmetic qualities. NdFeB magnets are particularly susceptible to corrosion and are often protected in this way. There are a variety of coatings suitable for permanent magnets, not all types of coating will be suitable for every material or magnet geometry, and the final choice will depend on the application and environment. An additional option is to house the magnet in an external casing to prevent corrosion and damage.

     

    Available Coatings:

    Surface

    Coating

    Thickness (Microns)

    Color

    Resistance

    Passivation

    1

    Silver Grey

    Temporary Protection

    Nickel

    Ni+Ni

    10-20

    Bright Silver

    Excellent against Humidity

    Ni+Cu+Ni

    Zinc

    Zn

    8-20

    Bright Blue

    Good Against Salt Spray

    C-Zn

    Shinny Color

    Excellent Against Salt Spray

    Tin

    Ni+Cu+Sn

    15-20

    Silver

    Superior Against Humidity

    Gold

    Ni+Cu+Au

    10-20

    Gold

    Superior Against Humidity

    Copper

    Ni+Cu

    10-20

    Gold

    Temporary Protection

    Epoxy

    Epoxy

    15-25

    Black, Red, Grey

    Excellent Against Humidity
    & Salt Spray

    Ni+Cu+Epoxy

    Zn+Epoxy

    Chemical

    Ni

    10-20

    Silver Grey

    Excellent Against Humidity

    Parylene

    Parylene

    5-20

    Grey

    Excellent Against Humidity, Salt Spray. Superior Against Solvents, Gases, Fungi and Bacteria.
    FDA Approved.

       

    5.Dimension Range, Size and tolerance

    except for the dimension in the direction of magnetization, the maximum dimension of the permanent magnet is not exceed 50mm, which is limited by the orientation field and sintering equipment. The dimension in the unmagnetization direction is up to 100mm.

    The tolerance is usually +/-0.05 -- +/-0.10mm.  

     

    Ring

    Outer Diameter

    Inner Diameter

    Thickness

    Maximum

    100.00mm

    95.00mm

    50.00mm

    Minimum

    3.80mm

    1.20mm

    0.50mm

    Disc

    Diameter

    Thickness

    Maximum

    100.00mm

    50.00mm

    Minimum

    1.20mm

    0.50mm

    Block

    Length

    Width

    Thickness

    Maximum

    100.00mm

    95.00mm

    50.00mm

    Minimum

    3.80mm

    1.20mm

    0.50mm

    Arc-segment

    Outer Radius

    Inner Radius

    Thickness

    Degree

    Maximum

    75mm

    65mm

    50mm

    150

    Minimum

    1.9mm

    0.6mm

    0.5mm

    5

     

     

     

     

     


     

     

     

     

     

     

     

     

     

     

    Remark: Other shapes can be manufactured according to customer's sample or blue print

     

    6. Safety principle for manual operation

    1. The magnetized permanent magnets with strong magnetic field attract the iron and other magnetic matters around them greatly. Under common condition, the manual operator should be very careful to avoid any damage. Due to the strong magnetic force, the big magnet close to them takes the risk of damage. People always process these magnets separately or by clamps. In this case, we should ware the protection gloves in operation.

    2. In this circumstance of strong magnetic field, any sensible electronic component and test meter may be altered or damaged. Please see to it that the computer, display and magnetic media , for example the magnetic disc ,magnetic cassette tape and video record tape etc., are far from the magnetized components, say farther than 2m.

    3. The collision of the attracting forces between two permanent magnets will bring enormous sparkles. Therefore, the flammable or explosive matters should not be placed around them.

    4. When the magnet is exposed to hydrogen, it is prohibited to use permanent magnets without protection coating. The reason is that the sorption of hydrogen will destroy the microstructure of the magnet and lead to the deconstruction of the magnetic properties. The only way to protect the magnet effectively is to enclose the magnet in a case and seal it.

     

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