MP 40x20x5 / N38 - ring magnet

Advantages and disadvantages of neodymium magnets NdFeB.

Besides their durability, neodymium magnets are valued for these benefits:

• They have stable power, and over around ten years their attraction force decreases symbolically – ~1% (in testing),
• They show exceptional resistance to demagnetization from external field exposure,
• By applying a bright layer of gold, the element gains a modern look,
• They exhibit elevated levels of magnetic induction near the outer area 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 accurate shaping or customization to specific needs – neodymium magnets can be manufactured in a wide range of shapes and sizes, which enhances their versatility in applications,
• Key role in modern technologies – they are used in hard drives, rotating machines, clinical machines as well as high-tech tools,
• Thanks to their power density, small magnets offer high magnetic performance, while occupying minimal space,

Disadvantages of rare earth magnets:

• They can break when subjected to a powerful 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 and reinforces its overall strength,
• They lose strength at extreme temperatures. Most neodymium magnets experience permanent loss in strength when heated above 80°C (depending on the dimensions and height). However, we offer special variants with high temperature resistance that can operate up to 230°C or higher,
• Due to corrosion risk in humid conditions, it is wise to use sealed magnets made of synthetic coating for outdoor use,
• Using a cover – such as a magnetic holder – is advised due to the difficulty in manufacturing threads directly in the magnet,
• Possible threat due to small fragments may arise, especially if swallowed, which is crucial in the protection of children. It should also be noted that miniature parts from these assemblies might complicate medical imaging after being swallowed,
• In cases of large-volume purchasing, neodymium magnet cost may be a barrier,

Maximum lifting force for a neodymium magnet – what contributes to it?

The given lifting capacity of the magnet corresponds to the maximum lifting force, determined in the best circumstances, that is:

• using a steel plate with low carbon content, acting as a magnetic circuit closure
• with a thickness of minimum 10 mm
• with a smooth surface
• with zero air gap
• under perpendicular detachment force
• at room temperature

Determinants of practical lifting force of a magnet

The lifting capacity of a magnet is influenced by in practice the following factors, from primary to secondary:

• 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.

* Holding force was checked on a smooth steel plate of 20 mm thickness, when a perpendicular force was applied, however under parallel forces the load capacity is reduced by as much as 75%. Additionally, even a slight gap {between} the magnet’s surface and the plate reduces the lifting capacity.