How to choose right magnets for your product application?

Let's talk about the differences in magnetic materials. Neodymium(NdFeB) Magnets, Samarium Cobalt (SmCo) Magnets, Ferrite Magnets, Alnico Magnets, Bonded Magnets, Rubber coated magnets, and Injection Molded Magnets all have various options, in this case choosing the correct magnet with proper grade for your application is critical.

Go on for define the differences between magnet grades, here Our Group specifically focus on the strongest rare earth magnets - neodymium(NdFeB) magnets and samarium cobalt (Sm2Co17) magnets.

Neodymium and Samarium Cobalt Magnets are available in many grades. There are several factors and considerations that go into design, today discussed from the following aspects: magnet Strength, Magnet Coercivity and the Considerations for selection.

The application is easily ignored

When we assist customers with magnet selection we will undoubtedly discuss about their application, this helps us understand the environment and requirements of the magnet, so that we can provide customers with best solutions.

However due to confidentiality and some privacy reasons, more than 50% of our customers are not able to make known the application,If this is the situation, we will then ask such questions as:

What is the maximum operating temperature?

What other materials(rubber, steel, aluminum, plastic, etc) will the magnet be next to?

What are the special tolerances required? Our standard tolerances are +/-0.05mm.

Is the magnet used in an assembly or independently used?

Is there any specific coating requirements?

Magnet Strength

The strength of a magnet can be found in the magnet specification known as BHmax, which is the maximum energy density of a magnet. This is defined in MGOe(Mega Gauss Oersteds), On a Magnetic Demagnetization Curve this is the highest point of the magnet's strength, or the magnet's maximum energy product.

Generally Neodymium Magnets the BHmax will ranged from 30 MGOe to 55 MGOe. Neodymium magnets produce the highest MGOe of any permanent magnet material, so choose your magnet need, keep in mind that the higher the number, the stronger the magnet. The most common grades of Neodymium magnets are N35,N33H,N33AH,N33EH,N35H,N35EH,N38,N38H,N38M,N40,N40H,N40M, N42,N42H,N42M, N45,N45H,N45M, N48,N48H,N48M, N50,N50H,N50M, N52,N52M, N54 and N55.

For Samarium Cobalt (Sm2Co17) Magnet, the BHmax will ranged from 16 MGOe to 32 MGOe.the higher the number, the stronger the magnet. The common grades are 16, 18, 20, 22, 24, 26, 28, 30, and 32.

As you can see, the MGOe numbers for neodymium magnets is higher than those of samarium cobalt magnets, which indicates that NdFeB magnets are stronger than smco magnets.

Magnet Coercivity

First, let's define Coercivity(Hci) of the material. When you look at a magnet table of available materials there are different letters after some of the grades, following letters after the grade to define the magnets specification to fight demagnetization forces: M, H, SH, UH, EH, and TH. these letters represent the magnet's ability to withstand demagnetization forces, which can be temperature or other magnetic forces working against the magnet.

A Neodymium Magnet with no letter after the grade, i.e. N35,N45 or N55, would indicate that it has the ability to work in an environment that has a maximum operating temperature no greater than 80C.

A magnet with a“M” (i.e. N35M, N52M, etc) generally means that a magnet can be used in an operating environment up to 100C. “H”material is good up to 120C, “SH”up to 150C, “UH”up to 180C,“EH”up to 200C, and with a“TH”up to 220C.

Strength Considerations

why not just get the highest strength possible every time?  Simply because the highest strength isn't always the right choice.

For example, a magnet being used as a sensor magnet may be required to produce specific magnetic field at a specific distance, this field will be defined in the sensor requirements, the appropriate magnet may be a samarium cobalt 24, so if a neodymium N52 is used it could cause the sensor to work incorrectly.

Another example that a motor's windings may be good with the N48 material but may overheat with an N55. Or in a holding application a stronger magnet may be adequate while a lower grade material may not hold enough.

To define pull or holding strength, the magnetic field requirements, or the saturation point of surrounding materials will help with magnet choice.

Cost

Cost considerations are usually part of the discussion.  As a general rule, the higher the grade, the higher the price. also there are other variables, including shape and size, but for this purpose, we will use the general rule of higher grade = higher price. Similarly the higher the letter after the grade, the higher the price.

For example, N48H will cost a bit more than N48, and N48SH will cost more than N48H, and so on.

finally even a lower grade material can cost more than a higher grade material if a higher letter is selected, For example, N35SH will most likely cost more than N38 or even N40.

Application

As mentioned we understand that we may not always know the final application, but there are situations when a magnet can be combined with other materials, or even other magnets, to better influence the field, thus creating a situation where a lesser grade magnet may work fine.

Size & Shape of Magnet

In any engineering concept, there are factors that in turn influence other factors, Size & Shape of the magnet also plays its part.  For example, N45H with an operating temperature of 120C, however if the size of the magnet is extremely thin, or the shape is very tiny, it may be better to choose the N45SH material. And if the shape and size do require discussion, we can see if a solution exists to utilize other materials with the magnet to keep the coercivity intact.

Not All Grades Are Created Equal

Use of permanent magnets also means determining the tradeoffs.  As you can see from the above information, you may need to determine if strength or coercivity is more important, neodymium magnets or samarium cobalt magnets would be better.

The best situation would be to have everything you need from the magnet, but that is not always possible, there is a tradeoff between strength and coercivity. As you get stronger in a magnet grade, the coercive force in a magnet many not be available.

For example, if you need a magnet that can handle 180C temperature, the UH material will be required, However only the lower grade is available for UH material, which means that the magnet strength would need to be N40 or below.

Refering to the magnet table listed on the https://www.starunitedindustry.com/, there you can see the options between strength and coercivity.

Selection of the correct magnet is a critical step to make sure your design works correctly and as expected. We welcome you to discuss this together as well as push the limits of magnet technology and innovation. For assistance with your application, you can contact any time sales@starunitedindustry.com, or call +86 15986739311(08:00am - 23:00pm).