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How to shield magnetic during magnets shipping by air

by AOMag | post a comment

AOMAG's customers are located in 76 countries around the world. Customers who purchase strong magnets sometimes need to be transported by air to the country where the customer is located. Can powerful magnets be transported by air?
   
            The magnet can be transported by air, but it needs to be commissioned by a specialized agency (Technical Supervision Bureau) for degaussing. The so-called degaussing, in fact, the magnetic does not disappear, but the reassembly of the items in the unit package, so that the magnetic display of the unit package is up to the national regulations. The aviation safety requirements are required, and the magnetic isolation can achieve the purpose of degaussing.
    
      General requirements for the international transportation of air cargo magnets and magnets:
    
       The shipper shall comply with the IATA Packing Instruction 902. The following requirements are required. To prevent interference with aircraft instruments, especially compass instruments, the shipper shall package the magnetic materials in the following manner: instruments and devices such as magnetrons and illuminometers. The opposite poles must be placed opposite each other. The permanent magnet material must be equipped with a magnetically-loaded armature or a screen to prevent the magnetic field from causing deviation of the compass meter. Each package of magnetic material must be properly marked and labeled in accordance with the provisions of Chapter 7 of the IATA Dangerous Goods Regulations. Ensure that the magnetic field strength measured at 4.6 m (15 ft) from the surface of the package does not exceed 0.418 A/m (0.00525 gauss) before shipment.
   
       The above is the test standard for magnetic materials as dangerous goods. Domestic customers use magnetic materials as non-dangerous goods for air transportation. The shielding requirements: need to ensure that the goods are measured 2.7 meters away from the surface of the package before shipment. The magnetic field strength does not exceed 200 nT (ie equal to 2 mGs = 0.002 Gs). In order to ensure the measurement accuracy of the Gauss meter and to ensure that it is not affected by the geomagnetic field as much as possible, it is generally recommended that the customer measure at a distance of 0.5 m from the surface of the package. According to the theory, the square of the distance is inversely proportional to the strength of the magnetic field, that is, the closer the distance is measured. The greater the strength of the magnetic field. For example, the magnetic field is measured at 2.7 meters and the magnetic field is 0.002 Gs. According to the theoretical formula of 'the square of the distance is inversely proportional to the magnetic field strength', it is strictly measured at a distance of 0.5 m from the surface of the package. The size of the magnetic field should be 0.05832 Gs. . The distance is shortened by 5.4 times, that is, the magnetic field is enlarged by 29.16 times.
   
    The method generally used for magnetic isolation:
   
       Usually shielding the magnetic field, mostly refers to the steady magnetic field or low-frequency magnetic field, mainly relying on the "short circuit" mentioned above. If the box is made of high magnetic permeability material, the "magnetic line" that will be worn out of the box will concentrate on the box material. The closure is formed, and the leakage out of the box is greatly reduced.
      As a shielding effect, the higher the magnetic permeability of the material, the better; the same material, the thicker the better; the same material and thickness, the more layering the better. In addition, the magnet should be placed in the center of the shielding box to prevent the magnetic lines on one side from being more concentrated and leaking out more.
      If the high-frequency magnetic field is shielded, a method is used: using a well-conducting material such as metal, a high-frequency magnetic field is used to form an alternating eddy current, and an opposite magnetic field is formed to cancel the original magnetic field, which is essentially two magnetic fields. Superimposed, externally canceled in the shield, and a new magnetic loop is synthesized inside the shield.
  
      Regarding the second point, the material is magnetized. The magnetically permeable material is always magnetized in the magnetic field, but in addition to the hard magnetic material, once the external magnetic field is removed, the magnetic is quickly followed. Therefore, if the shielding material is made of a hard magnetic material and a new independent magnetic field is formed, it is hard to say that this is because the shielding can only use soft magnetic materials. (If you ask, the soft magnetic material will be magnetized in the magnetic field, how to complete the shielding? This is because the soft magnetic material is magnetized, and the resulting new magnetic field strength, completely independent of the external field strength. Change, and then according to the high-frequency magnetic field shielding principle mentioned above, destructively achieve "shield". "Magnetic line" is an image, the essence is the superposition of the field.)
  
      Magnetic shielding in vacuum, because the air is a paramagnetic substance, the magnetic permeability is slightly larger than the vacuum, so theoretically the magnetic shielding effect in vacuum is better than the air, but the effect on engineering is minimal. Because the ratio of the magnetic permeability of the relative vacuum of the paramagnetic substance and the diamagnetic substance (that is, the relative magnetic permeability) is almost 1, which is not more than a few thousandth; and the relative conduction of the magnetic conductive material (ferromagnetic substance) The magnetic rate is hundreds of thousands, even over 10,000 and over 100,000. In comparison, the existence of paramagnetic and diamagnetic materials in engineering is often not considered.





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