MP 30x7/3x3 / N38 - ring magnet

Advantages and disadvantages of neodymium magnets NdFeB.

Besides their high retention, neodymium magnets are valued for these benefits:

• They do not lose their magnetism, even after nearly ten years – the decrease of lifting capacity is only ~1% (based on measurements),
• They are very resistant to demagnetization caused by external field interference,
• Because of the brilliant layer of gold, the component looks high-end,
• Magnetic induction on the surface of these magnets is very strong,
• Thanks to their exceptional temperature resistance, they can operate (depending on the form) even at temperatures up to 230°C or more,
• With the option for fine forming and targeted design, these magnets can be produced in various shapes and sizes, greatly improving application potential,
• Key role in cutting-edge sectors – they serve a purpose in hard drives, electromechanical systems, healthcare devices or even technologically developed systems,
• Thanks to their concentrated strength, small magnets offer high magnetic performance, while occupying minimal space,

Disadvantages of rare earth magnets:

• They may fracture when subjected to a sudden impact. If the magnets are exposed to shocks, they should be placed in a protective case. The steel housing, in the form of a holder, protects the magnet from fracture and additionally strengthens its overall durability,
• High temperatures may significantly reduce the field efficiency of neodymium magnets. Typically, above 80°C, they experience permanent decline in performance (depending on form). To prevent this, we offer heat-resistant magnets marked [AH], capable of working up to 230°C, which makes them perfect for high-temperature use,
• Due to corrosion risk in humid conditions, it is wise to use sealed magnets made of rubber for outdoor use,
• Using a cover – such as a magnetic holder – is advised due to the limitations in manufacturing complex structures directly in the magnet,
• Possible threat from tiny pieces may arise, in case of ingestion, which is significant in the context of child safety. Furthermore, miniature parts from these assemblies have the potential to interfere with diagnostics after being swallowed,
• In cases of large-volume purchasing, neodymium magnet cost may not be economically viable,

Optimal lifting capacity of a neodymium magnet – what contributes to it?

The given holding capacity of the magnet corresponds to the highest holding force, determined in ideal conditions, specifically:

• using a steel plate with low carbon content, serving as a magnetic circuit closure
• having a thickness of no less than 10 millimeters
• with a refined outer layer
• in conditions of no clearance
• under perpendicular detachment force
• at room temperature

Lifting capacity in practice – influencing factors

The lifting capacity of a magnet is determined by in practice key elements, ordered from most important to least significant:

• Air gap between the magnet and the plate, since 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 testing was performed on plates with a smooth surface of suitable thickness, under perpendicular forces, however under parallel forces the lifting capacity is smaller. Moreover, even a minimal clearance {between} the magnet and the plate lowers the holding force.