Every day, we are asked questions about the differenc […]
Every day, we are asked questions about the differences in magnetic materials. There are many options for neodymium magnets, Sa cobalt (SmCo) magnets, ceramic magnets, Alnico magnets, bonded magnets and injection molded magnets, so it is important to choose the grade that suits your application.
This article will try to simplify the naming of magnets and define the differences between magnet grades. We will focus on the strongest rare earth magnets available, neodymium magnets (NdFeB) and sa cobalt (SmCo) magnets.
When we assist customers in choosing magnets, we will undoubtedly ask questions about the application. This helps us understand the environment and requirements of magnets. Then, we will ask the following questions:
What is the temperature to which the magnet is exposed (maximum operating temperature)?
What other materials (such as steel, aluminum, plastic, etc.) are there next to the magnet?
What is the area of the magnet?
What is the required tolerance?
Does the magnet operate in the assembly or independently?
Are there specific coating requirements?
Although these are just a few questions we might ask, they may cause other questions about the operating environment and options.
The strength of the magnet can be found in the magnet specification called BHmax, which is the maximum energy density of the magnet. This is defined in Mega Gauss Oersteds or MGOe. On the magnetic demagnetization curve, this is the highest point of magnet strength, that is, the maximum energy product of the magnet.
For neodymium (NdFeB) magnets, the range of BHmax is usually 30 MGOe to 55 MGOe. Therefore, when defining magnet requirements, remember that the higher the number, the stronger the magnet. The MGOe produced by neodymium magnets is the highest among all permanent magnet materials. The most common grades of neodymium magnets are N35, N38, N40, N42, N45, N48, N50, N52 and N55.
For Sa cobalt (SmCo) magnets, BHmax ranges from 16 MGOe to 32 MGOe. Similarly, just like neodymium magnets, the larger the number, the stronger the magnet. Common grades of mar cobalt magnets are 16, 18, 20, 22, 24, 26, 28, 30 and 32. As you can see, the MGOe number of neodymium magnets is higher than that of sa cobalt magnets, which indicates that neodymium magnets are stronger than sa cobalt magnets.
First, let us define the coercivity or "Hci" of the material. When you look at the magnetic table of available materials, some grades will have different letters after them. These letters represent the ability of the magnet to withstand the demagnetizing force, which can be temperature or other magnetic forces acting on the magnet. In the world of permanent magnets, manufacturers or suppliers have two methods to define coercivity, but we will focus on the most widely used method, the engraving system. The letter system uses the following letters after the grade to define the magnet specifications that resist demagnetization: M, H, SH, UH, EH and TH.
If a letter is used after the magnet grade, it means that the particular material has greater resistance to demagnetization. For our purposes, we will use heat as the demagnetizing force because it is the most common force that affects magnets. Also, the following examples are "general rules", not "strict rules".
There is no letter after the neodymium magnet grade, that is, N38 or N45 or N52, indicating that it has the ability to work in an environment where the maximum operating temperature does not exceed 80°C. Magnets with "M" (ie N35M, N42M, etc.) usually mean that the magnet can be used in a working environment up to 100C. The maximum temperature of "H" material is 120°C, the maximum temperature of "SH" is 150C, the maximum of "UH" is 180C, the maximum of "EH" is 200C, and the maximum of "TH" is 220C. Again, these are general specifications, and other factors also play a role in coercivity decisions.