MW 15x5 / N38 - cylindrical magnet

Advantages as well as disadvantages of neodymium magnets NdFeB.

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

• They do not lose their even over around ten years – the reduction of lifting capacity is only ~1% (theoretically),
• They remain magnetized despite exposure to magnetic noise,
• Because of the brilliant layer of nickel, the component looks aesthetically refined,
• The outer field strength of the magnet shows remarkable magnetic properties,
• These magnets tolerate extreme temperatures, often exceeding 230°C, when properly designed (in relation to form),
• Thanks to the freedom in shaping and the capability to adapt to specific requirements, neodymium magnets can be created in diverse shapes and sizes, which broadens their functional possibilities,
• Significant impact in cutting-edge sectors – they find application in hard drives, rotating machines, healthcare devices as well as technologically developed systems,
• Relatively small size with high magnetic force – neodymium magnets offer intense magnetic field in compact dimensions, which makes them useful in compact constructions

Disadvantages of rare earth magnets:

• They are fragile when subjected to a heavy impact. If the magnets are exposed to shocks, it is suggested to place them in a metal holder. The steel housing, in the form of a holder, protects the magnet from breakage , and at the same time enhances its overall resistance,
• High temperatures may significantly reduce the holding force of neodymium magnets. Typically, above 80°C, they experience permanent deterioration in performance (depending on shape). 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,
• Magnets exposed to humidity can oxidize. Therefore, for outdoor applications, we recommend waterproof types made of coated materials,
• The use of a protective casing or external holder is recommended, since machining multi-axis shapes in neodymium magnets is restricted,
• Health risk from tiny pieces may arise, in case of ingestion, which is notable in the context of child safety. Furthermore, small elements from these assemblies have the potential to complicate medical imaging when ingested,
• High unit cost – neodymium magnets are pricier than other types of magnets (e.g., ferrite), which can restrict large-scale applications

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

The given strength of the magnet represents the optimal strength, determined in ideal conditions, namely:

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

Lifting capacity in practice – influencing factors

In practice, the holding capacity of a magnet is affected by these factors, arranged from the most important to the least relevant:

• 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 was assessed by applying a smooth steel plate of suitable thickness (min. 20 mm), under perpendicular pulling force, whereas under parallel forces the load capacity is reduced by as much as 75%. Moreover, even a minimal clearance {between} the magnet’s surface and the plate reduces the lifting capacity.