What Will Make the Demagnetization of Neodymium Bar Magnets?

Powerful magnets generally refer to neodymium bar magnets, which are tetragonal crystals formed by neodymium, iron, and boron (Nd2Fe14B). At present, this material is widely used in the market, but strong magnets often encounter the situation of weakening or disappearing of the magnetic force of the neodymium bar magnet during the use process.

1. Factors affecting the demagnetization of neodymium bar magnets

(1) The magnet is demagnetized or demagnetized after injection. The minimum temperature resistance of the NdFeB N series is 80°C, and sometimes the injection molding is basically above 120°C, so a short injection of 2 to 3 seconds may cause some Demagnetization phenomenon.

(2) The magnet is demagnetized after hot pressing, and glass fiberboard hot pressing is often used at a temperature above 150°C.

(3) The magnet is demagnetized after baking in the oven.

(4) neodymium bar magnet material contains too many impurities, resulting in a weak magnetic field. This is the result of most buyers seeking small bargains because choosing the manufacturer with the lowest quotation in the quotations. The customer requires the N35 brand but the defective manufacturers with ultra-low quotation use n28 and N33 materials. The customer can't expect to detect it. If the quantity reaches 30K, can it be measured slowly with a fluxmeter? (Demagnetization occurs in as short as 6 months and as fast as two months also occurs). So it is really important to have a reliable and stable supplier.

(5) The impact causes the resultant demagnetization of the neodymium bar magnet, such as high-frequency impact, etc., so be careful in the process of transportation.

(6) The material contains metal lanthanum, which causes the magnet to become powdered.

(7) The high magnetic field environment causes the magnet force of the magnet to disappear or the N/S pole change.

From the above, we can summarize that four reasons for most of the demagnetization: high-temperature demagnetization, demagnetization due to material problems, high-frequency impact demagnetization, and high magnetic field demagnetization.

2. The method of shielding the magnetic field of neodymium bar magnets

(1) For magnets with a magnetic field strength of ordinary neodymium bar magnets, we only need to use ordinary iron plates to shield the magnetic field. Magnetic field shielding requires materials with high magnetic permeability. Most of the materials that meet this requirement are iron-nickel alloys, which have very high magnetic permeability.

(2) When the magnetic field that needs to be shielded is very strong, it is difficult to meet the shielding requirements with only a single layer of shielding material, and the magnetic field will leak.

(3) At this time, one method is to increase the thickness of the magnetic isolation material. But a more effective method is to use a combined shield, place one shield in the other, leaving some air gaps between them.

(4) The air gap can be filled with any non-permeable material for support, such as aluminum. The shielding effectiveness of the combined shield is much higher than that of a single shield, so the combined shield can attenuate the magnetic field of the neodymium bar magnet to a very low degree.