Alnico Magnets FAQs
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owner of the online magnet store, www.Custom-Magnets.com. Custom-Magnets has been supplying
magnetic material and custom fridge magnets since 1999.
What are alnico magnets?
Developed in the 1940s, alnico magnets are magnets made from an alloy of ALuminium, NIckle and CObalt. They may include other elements such as Titanium and Copper. The percentage of the components can be varied to manufacture magnets that suit a wide variety of purposes based on their composition.
How are alnico magnets manufactured?
Mainly two processes are used to manufacture alnico magnets:
What is the difference between anisotropic and isotropic magnets?
Alnico magnets are heat-treated as part of the manufacturing process. When the magnets are treated in a magnetic field they take on the properties of that field and are known as anisotropic magnets. Magnets treated outside of a magnetic field are known as isotropic magnets.
What is magnetizing?
Magnetizing is done after the magnet has been machined to correct tolerances. Because alnico magnets are hard and brittle they chip off and break easily. Regular machines cannot be used to process alnico magnets. Specialized machines are required to grind alnico magnets to their proper size.
For the most efficient use of Alnico magnets they must be magnetized after the magnet has been assembled with its pole pieces into the final circuit. Shipping the non-magnetized product would also eliminate the need for specialized packaging as well as prevent contamination from stray clips etc.
Magnetic saturation at the end-use location requires the application of a magnetizing force 4 to 5 times greater than the coercive force of the material. For Alnico 5, a magnetizing force of 3000 oersteds (240 KA/m) is recommended. For Alnico 8, the magnetizing force should be at least 7000 oersteds (560 KA/m). The magnetizing force need be applied only momentarily. Thus, impulse magnetizers employing a capacitor discharge are commonly used. Direct current magnetizers are also effective.
What is the proper method of storing alnico methods?
Alnico magnets have a low resistance to demagnetization and loose power quickly if stored improperly. Never store alnico magnets with the unlike poles repelling each other. For best results, alnico magnets must be stored with the like poles attracting each other. A steel keeper may also be used.
What are the design considerations one faces with alnico magnets?
Alnico magnets cannot be conventionally drilled or machined because they are coarse-grained, hard and brittle. These mechanical properties of alnico magnets makes them a bad choice as structural members. Instead of holes, slots are used. Cross sections of less than 3.18 mm are avoided.
Finished surfaces if the need arises, can be produced by grinding. However, the industry has found that for most applications the cast alnico magnet or sintered alnico magnet is satisfactory as it is and the cost is significantly lower.
What about stability and temperature effects on alnico magnets?
Alnico magnets offer exceptional stability with temperature changes. Heating may sometimes produce an irreversible loss of magnet strength but the loss is less than 5% and can be recovered by remagnetization. At temperatures exceeding 10000C, a metallurgical change takes place which causes magnetic strength to reduce rapidly. This change will not be recovered by remagnetization.
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