MP 25x13x8 / N38 - ring magnet

Advantages as well as disadvantages of neodymium magnets NdFeB.

Apart from their strong magnetism, neodymium magnets have these key benefits:

• They have constant strength, and over more than 10 years their attraction force decreases symbolically – ~1% (in testing),
• Their ability to resist magnetic interference from external fields is among the best,
• Thanks to the polished finish and gold coating, they have an elegant appearance,
• They have exceptional magnetic induction on the surface of the magnet,
• Thanks to their enhanced temperature resistance, they can operate (depending on the geometry) even at temperatures up to 230°C or more,
• The ability for precise shaping and customization to specific needs – neodymium magnets can be manufactured in multiple variants of geometries, which extends the scope of their use cases,
• Key role in cutting-edge sectors – they are used in hard drives, rotating machines, medical equipment or even high-tech tools,
• Relatively small size with high magnetic force – neodymium magnets offer strong power in tiny dimensions, which allows for use in small systems

Disadvantages of NdFeB magnets:

• They are prone to breaking when subjected to a sudden impact. If the magnets are exposed to physical collisions, it is suggested to place them in a protective enclosure. The steel housing, in the form of a holder, protects the magnet from breakage while also strengthens its overall durability,
• Magnets lose pulling force when exposed to temperatures exceeding 80°C. In most cases, this leads to irreversible field weakening (influenced by the magnet’s dimensions). To address this, we provide [AH] models with superior thermal resistance, able to operate even at 230°C or more,
• They rust in a humid environment – during outdoor use, we recommend using waterproof magnets, such as those made of polymer,
• Limited ability to create internal holes in the magnet – the use of a mechanical support is recommended,
• Possible threat from tiny pieces may arise, in case of ingestion, which is crucial in the family environments. Additionally, small elements from these assemblies can complicate medical imaging after being swallowed,
• High unit cost – neodymium magnets are costlier than other types of magnets (e.g., ferrite), which may limit large-scale applications

Breakaway strength of the magnet in ideal conditions – what contributes to it?

The given strength of the magnet corresponds to the optimal strength, determined in the best circumstances, specifically:

• with the use of low-carbon steel plate acting as a magnetic yoke
• of a thickness of at least 10 mm
• with a smooth surface
• with no separation
• with vertical force applied
• at room temperature

Practical aspects of lifting capacity – factors

In practice, the holding capacity of a magnet is affected by these factors, from crucial to less important:

• Air gap between the magnet and the plate, because even a very small distance (e.g. 0.5 mm) causes 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.

* Lifting capacity was determined using a steel plate with a smooth surface of optimal thickness (min. 20 mm), under perpendicular detachment force, whereas under shearing force the load capacity is reduced by as much as 5 times. Moreover, even a small distance {between} the magnet and the plate reduces the holding force.