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The impact of break corner on the performance of magnets

The impact of break corner on the performance of magnets

Issue Time:2021-04-26

Since the second industrial revolution and people entered the electrification era, a large number of electrical and electronic equipment have entered our lives and changed our lives. And most electrical equipment can't do without one material, that is magnet. Rare earth permanent magnets are increasingly used in various fields due to their excellent magnetic properties. Among them, NdFeB magnets are the most in demand. The sintered NdFeB industry is the top priority of the magnetic material industry. New application growth points are constantly emerging, especially the development of knowledge economy represented by the information industry, constantly bringing new uses to functional materials such as rare earth permanent magnets.

Everyone knows that sintered neodymium iron boron is prepared by powder metallurgy process, and then through mechanical processing to achieve the shape and size we need, and finally surface treatment. The process flow is long, and there are many processes that require turnover. In addition, the powder metallurgy process material is relatively brittle, and the magnet will inevitably produce some bumps during the handling and turnover process, resulting in some small chips and break corners. So will these break corners have an impact on the application, and how great is the impact?

For magnets, magnetic properties are the key functional properties of magnets. Break corners affect the size and volume of the magnet, while changes in the volume of the magnet affect the overall magnetic properties of the magnet. When the PC value is greater than 0.5 , The magnetic flux of the magnet the product of remanence*volume. Here, an ordinary magnet is used to simulate and calculate the influence of break corners on the magnetic performance. Take the magnet of NdFeB N35 as an example, the size is 20*20*20 mm, and the tolerance is all +/-0.1. We can calculate that the volume range of the upper and lower tolerance limits is 7880.6-8120.6 mm³, and the corresponding magnetic flux range is 108.458-116.956  mWb through simulation. Assuming that there are 2 break corners on the magnet, the size of each break corner is 2*2*1 mm, and the total break corner is submitted as 8 mm³, which accounts for 0.1% of the total volume. The simulation calculation results in a magnetic flux of 0.102  mWb corresponding to a volume of 8 mm³. From these data, we can find that the magnetic flux deviation of the tolerance range of the magnet itself is 8.498 mWb, and the magnetic performance loss caused by break corners accounts for 1.2% of the magnetic performance of the tolerance deviation and 0.09% of the overall magnetic performance. Therefore, the impact of the break corners on the performance is very weak, and the change in the magnetic performance is smaller than the normal tolerance range.

Most of the magnets are assembled with some metal parts, or injected into plastic parts. break corner have no effect on the appearance of the assembled and injection molded products. Some break corners have almost no effect on the performance of the magnet. Products with some small break corner can be used. In addition to break corner, there are other appearances issue, such as poor plating, cracks, pores, etc., because these poor conditions will affect the corrosion resistance and structural strength of the magnet, so this type of appearance will be directly judged as unqualified products.

Of course, for some specially application magnets, the appearance is its main function, and the appearance requirements are particularly high. When the quantity is particularly large, we will use the CCD full inspection method to make the selection, which can more efficiently meet the needs of customers.