NdFeB magnets

Many customers may have a question: do magnets of the same performance and volume have the same suction force? It is said on the Internet that the suction force of NdFeB magnets is 640 times its own weight. Is this credible?   First of all, it should be made clear that magnets only have adsorption force on ferromagnetic materials. At room temperature, there are only three types of ferromagnetic materials, they're iron, cobalt, nickel, and their alloys. They have no adsorption force on non-ferromagnetic materials.   There are also many formulas on the Internet for calculating suction. The results of these formulas may not be accurate, but the trend is correct. The strength of the magnetic suction is related to the magnetic field strength and the adsorption area. The greater the magnetic field strength, the larger the adsorption area and the greater the suction.   The next question is, if the magnets are flat, cylindrical, or elongated, will they have the same suction force? If not, which one has the greatest suction force?       First of all, it is certain that the suction force is not the same. To determine which suction force is the greatest, we need to refer to the definition of the maximum magnetic energy product. When the working point of the magnet is near the maximum magnetic energy product, the magnet has the greatest work energy. The adsorption force of the magnet is also a manifestation of work, so the corresponding suction force is also the greatest. It should be noted here that the object to be sucked needs to be large enough to completely cover the size of the magnetic pole so that the material, size, shape, and other factors of the object to be sucked can be ignored.   How to judge whether the working point of the magnet is at the point of maximum magnetic energy product? When the magnet is in a state of direct adsorption with the material being adsorbed, its adsorption force is determined by the size of the air gap magnetic field and the adsorption area.    Taking a cylindrical magnet as an example, when H/D≈0.6, its center Pc≈1, and when it is near the working point of maximum magnetic energy product, the suction force is the largest. This is also in line with the rule that magnets are usually designed to be relatively flat as adsorbents. Taking the N35 D10*6mm magnet as an example, through FEA simulation, it can be calculated that the suction force of the adsorbed iron plate is about 27N, which almost reaches the maximum value of magnets of the same volume and is 780 times its own weight.   The above is only the adsorption state of a single pole of the magnet. If it is multi-pole magnetization, the suction force will be completely different. The suction force of multi-pole magnetization will be much greater than that of single-pole magnetization (under the premise of a small distance from the adsorbed object).     Why does the suction force of a magnet of the same volume change so much after being magnetized with multiple poles? The reason is that the adsorption area S remains unchanged, while the magnetic flux density B value through the adsorbed object increases a lot. From the magnetic force line diagram below, it can be seen that the density of magnetic force lines passing through the iron sheet of a multi-pole magnetized magnet is significantly increased. Taking the N35 D10*6mm magnet as an example, it is made into a bipolar magnetization. The suction force of the FEA simulation adsorbing the iron plate is about 1100 times its own weight.     Since the magnet is made into a multi-pole magnet, each pole is equivalent to a thinner and longer magnet. The specific size is related to the multi-pole magnetization method and the number of poles.        

Air transportation has certain particularities. To ensure safety, both people and goods need to undergo security checks before boarding. If you carry magnetic materials, such as NdFeB magnets, or if customers are in a hurry to get the goods and hope that the manufacturer will ship them by air, can we bring the magnets on board?   Since weak stray magnetic fields can interfere with the aircraft's navigation system and control signals, the International Air Transport Association (IATA) has classified magnetic cargo as Class 9 dangerous goods, which must be restricted during transportation. Therefore, some air cargo with magnetic materials now needs to undergo magnetic testing to ensure the normal flight of the aircraft. Magnetic materials, audio materials, and other instruments with magnetic accessories must undergo magnetic testing.     Airlines or logistics companies that transport magnetic materials will force customers to undergo magnetic testing and issue an "Air Transport Conditions Identification Report" to ensure the normal flight of the aircraft. Air transport identification can generally only be issued by a qualified professional identification company recognized by the country's civil aviation administration, and it is generally necessary to send samples to the identification company for professional testing before issuing an identification report. If it is inconvenient to send samples, the identification company's professionals will conduct on-site testing and then issue an identification report. The validity period of the identification report is generally for the current year, and it is generally necessary to re-do it after the New Year.   During magnetic testing, customers are required to pack the goods according to air transport requirements. The testing will not damage the packaging of the goods. In principle, the goods will not be unpacked for testing, but only the stray magnetic field of the six sides of each piece of goods will be tested. If the goods fail the magnetic test, special attention should be paid. First, with the consent of the customer, the magnetic inspection staff will unpack the goods for inspection, and then make relevant reasonable suggestions based on the specific situation. If the shielding can meet the requirements of air transportation, the goods will be shielded according to the customer's entrustment, and relevant fees will be charged.  

Neodymium ndfeb materials have poor thermal stability, and their high temperature coefficient can easily cause irreversible demagnetization (also known as demagnetization) when permanent magnet motors are running.   On the one hand, the eddy current of permanent magnet motors generates heat on the surface of permanent magnets, and the heat dissipation conditions inside the motor are poor, which exceeds the working temperature of permanent magnets, causing permanent magnet demagnetization. Therefore, the temperature stability of permanent magnets is crucial to motor applications.   On the other hand, the unreasonable design of the working point of the permanent magnet motor magnetic circuit is also prone to irreversible demagnetization. When the motor encounters a large demagnetization during starting, reversing and stalling, the working point of NdFeB may drop below the inflection point of the demagnetization curve, causing irreversible demagnetization. Therefore, the working point of the permanent magnet motor magnetic circuit should be designed to be higher than the inflection point of the NdFeB material. When the motor stops running, the residual magnetic induction intensity Br of the permanent magnet material remains basically unchanged.   The design of permanent magnet motors must also understand the actual operating environment of the motor and take necessary measures in assembly to ensure that it is in a stable state without demagnetization at high temperatures. The SH grade NdFeB magnets used in motors that meet the standard requirements cannot guarantee that the motor will not lose magnetism during operation. Only by increasing the intrinsic coercive force and Curie temperature of the NdFeB magnets can the irreversible magnetic loss of the NdFeB magnets be reduced and the temperature stability of the permanent magnets be improved, thereby extending the service life of the permanent magnet motor.   

In daily life, magnets are a very common thing. From various special electronic devices to daily teaching aids and toys, magnets can often be seen.   We know that the main component of magnets is ferroferric oxide. An ordinary small magnet is made of black ferroferric oxide. However, due to the nature of ferroferric oxide itself, its attraction to iron objects is not too strong, and its magnetism will gradually weaken over time. In this case, how can we make a magnet with stronger attraction and less prone to decay? Under this premise, neodymium iron boron magnets came into being.     This kind of magnet with a shiny surface after anti-corrosion treatment is a neodymium boron magnets, and its chemical formula is Nd2Fe14B. The most commonly used neodymium iron boron magnet is made of neodymium, iron, and boron at high temperature sintering, and is the strongest artificial magnet to date. If the core element of traditional ferroferric oxide is iron, then the reason why neodymium iron boron magnets have such strong magnetism is the role of neodymium. The pieces of metal in the picture below are neodymium:     Neodymium is the fourth element of the lanthanide family of rare earth elements. Like iron, cobalt, nickel and the aforementioned gadolinium, it can also be attracted by magnets. In addition, neodymium is the most active of the lanthanide elements, so it is easily oxidized like iron, which is why there is a coating on the surface of the NdFeB magnet. If neodymium is used to enhance magnetism, then the role of boron should not be underestimated.    In the periodic table, boron is located to the left of carbon, so boron chemistry similar to carbon-centered organic chemistry has recently emerged. In NdFeB magnets, boron is the mediator between neodymium and iron. Boron greatly expands the maximum magnetism that a substance can produce while ensuring the stability of its molecular structure, making the neodymium magnetic properties of the entire magnet extremely high, and even allowing it to attract objects equivalent to 640 times its own weight.