Do Magnet Coating Affect Magnet Strength?
Some customers ask whether the magnet coating will affect its magnetic strength from time to time? How big is the impact? Let’s talk about this topic today.
This is indeed an important factor to be considered. Although the distance of one or two millimeters between the magnet and another object does not seem to be much, each distance will reduce the overall efficiency of the magnet. In some applications, even a small distance is enough to make the original sound magnet completely useless.
Most magnets need coating because they are easy to corrode (such as neodymium magnets) and they are very brittle (such as neodymium, ferrite and samarium cobalt magnets). The coating gives the magnet additional durability, but the additional durability comes at a price.
As we said, any distance between the actual magnet and the object in front of it will reduce the strength of the magnet. This is especially true in applications where rubber or plastics are more suitable than metal coatings. Although nickel (or other metal) coatings actually help to transfer magnetic fields, rubber and plastics will not. On the contrary, they will maintain a certain distance between the magnetic field and the object being acted on.
Determine how much strength is lost?
To calculate how much strength is lost, you can use the inverse square law, which states that the force of the magnet is inversely proportional to the square of the distance from the source. Generally speaking, even in a short distance, the force of the magnet will decrease rapidly.
In an internal study, we measured the force of the magnet at 1 mm, and then measured it again at 2 mm. We found that this small increase in distance reduced the strength of the magnet by four times.
This is another way of thinking: when you touch the surface of the magnet, you will receive 100% of its force, but from only two inches away, the strength of the magnet will drop to 10%. Obviously, proximity is crucial.
What should we pay attention to in magnet coating?
When retention strength is a factor, it is best to use a metal based coating, such as nickel. However, larger magnets require multiple layers of coatings for physical protection, sometimes with a nickel layer inside, then a copper layer, and then another nickel layer outside. Because there are many layers at a distance from the magnet, the overall strength will be reduced.
If you need waterproof, non slip or color coating, it is best to use plastic or rubber. Of course, the problem is the constant distance between the magnet and the surrounding object. If you need to use a plastic or rubber coating, you may need to use a larger magnet than usual to make up for the lost strength.
Magnets without coating: Ferrite Magnets