MP 40x22x10 / N38 - ring magnet

Advantages and disadvantages of neodymium magnets NdFeB.

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

• They retain their full power for nearly 10 years – the drop is just ~1% (based on simulations),
• They show superior resistance to demagnetization from external field exposure,
• Thanks to the shiny finish and silver coating, they have an aesthetic appearance,
• They possess intense magnetic force measurable at the magnet’s surface,
• With the right combination of materials, they reach increased thermal stability, enabling operation at or above 230°C (depending on the form),
• With the option for customized forming and targeted design, these magnets can be produced in multiple shapes and sizes, greatly improving engineering flexibility,
• Significant impact in new technology industries – they are used in hard drives, electromechanical systems, medical equipment or even sophisticated instruments,
• Thanks to their efficiency per volume, small magnets offer high magnetic performance, in miniature format,

Disadvantages of rare earth magnets:

• They are fragile when subjected to a sudden impact. If the magnets are exposed to mechanical hits, they should be placed in a protective enclosure. The steel housing, in the form of a holder, protects the magnet from breakage and additionally strengthens its overall resistance,
• They lose power at high temperatures. Most neodymium magnets experience permanent loss 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 wet conditions can corrode. Therefore, for outdoor applications, we recommend waterproof types made of non-metallic composites,
• The use of a protective casing or external holder is recommended, since machining internal cuts in neodymium magnets is risky,
• Health risk linked to microscopic shards may arise, when consumed by mistake, which is crucial in the family environments. It should also be noted that minuscule fragments from these assemblies might disrupt scanning when ingested,
• High unit cost – neodymium magnets are pricier than other types of magnets (e.g., ferrite), which can restrict large-scale applications

Magnetic strength at its maximum – what it depends on?

The given lifting capacity of the magnet represents the maximum lifting force, assessed in the best circumstances, that is:

• using a steel plate with low carbon content, serving as a magnetic circuit closure
• of a thickness of at least 10 mm
• with a refined outer layer
• with zero air gap
• in a perpendicular direction of force
• under standard ambient temperature

Practical aspects of lifting capacity – factors

Practical lifting force is dependent on elements, by priority:

• Air gap between the magnet and the plate, as 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 tested on the plate surface of 20 mm thickness, when a perpendicular force was applied, however under parallel forces the holding force is lower. Additionally, even a slight gap {between} the magnet’s surface and the plate reduces the load capacity.