MP 24x16x2 / N38 - ring magnet

Advantages as well as disadvantages of neodymium magnets NdFeB.

In addition to their pulling strength, neodymium magnets provide the following advantages:

• They do not lose their even over nearly ten years – the decrease of power is only ~1% (theoretically),
• They protect against demagnetization induced by surrounding magnetic fields very well,
• In other words, due to the shiny silver coating, the magnet obtains an aesthetic appearance,
• They possess significant magnetic force measurable at the magnet’s surface,
• Neodymium magnets are known for strong magnetic induction and the ability to work at temperatures up to 230°C or higher (depending on the magnetic form),
• Thanks to the possibility in shaping and the capability to adapt to individual requirements, neodymium magnets can be created in different geometries, which broadens their functional possibilities,
• Key role in new technology industries – they are utilized in hard drives, electric drives, healthcare devices or even high-tech tools,
• Thanks to their efficiency per volume, small magnets offer high magnetic performance, with minimal size,

Disadvantages of rare earth magnets:

• They are fragile when subjected to a strong impact. If the magnets are exposed to physical collisions, they should be placed in a protective enclosure. The steel housing, in the form of a holder, protects the magnet from fracture and additionally increases its overall robustness,
• They lose field intensity at increased temperatures. Most neodymium magnets experience permanent decline in strength when heated above 80°C (depending on the shape and height). However, we offer special variants with high temperature resistance that can operate up to 230°C or higher,
• Magnets exposed to damp air can degrade. Therefore, for outdoor applications, it's best to use waterproof types made of plastic,
• Limited ability to create internal holes in the magnet – the use of a mechanical support is recommended,
• Safety concern from tiny pieces may arise, in case of ingestion, which is important in the context of child safety. It should also be noted that small elements from these devices can complicate medical imaging after being swallowed,
• Higher purchase price is an important factor to consider compared to ceramic magnets, especially in budget-sensitive applications

Best holding force of the magnet in ideal parameters – what it depends on?

The given holding capacity of the magnet represents the highest holding force, assessed under optimal conditions, namely:

• with the use of low-carbon steel plate acting as a magnetic yoke
• having a thickness of no less than 10 millimeters
• with a refined outer layer
• with no separation
• with vertical force applied
• in normal thermal conditions

Impact of factors on magnetic holding capacity in practice

In practice, the holding capacity of a magnet is affected by the following aspects, in descending order of importance:

• Air gap between the magnet and the plate, as even a very small distance (e.g. 0.5 mm) can cause a drop in lifting force of up to 50%.
• Direction of applied force, because the maximum lifting capacity is achieved under perpendicular application. The force required to slide the magnet along the plate is usually several times lower.
• Thickness of the plate, as a plate that is too thin causes part of the magnetic flux not to be used and to remain wasted in the air.
• Material of the plate, because higher carbon content lowers holding force, while higher iron content increases it. The best choice is steel with high magnetic permeability and high saturation induction.
• Surface of the plate, because the more smooth and polished it is, the better the contact and consequently the greater the magnetic saturation.
• Operating temperature, since all permanent magnets have a negative temperature coefficient. This means that at high temperatures they are weaker, while at sub-zero temperatures they become slightly stronger.

* Holding force was measured on the plate surface of 20 mm thickness, when the force acted perpendicularly, however under parallel forces the lifting capacity is smaller. Additionally, even a small distance {between} the magnet’s surface and the plate reduces the holding force.