MP 15x7/3.5x5 / N38 - ring magnet

Advantages as well as disadvantages of neodymium magnets NdFeB.

Apart from their notable holding force, neodymium magnets have these key benefits:

• Their strength is maintained, and after approximately 10 years, it drops only by ~1% (theoretically),
• They protect against demagnetization induced by external magnetic fields effectively,
• The use of a decorative nickel surface provides a smooth finish,
• Magnetic induction on the surface of these magnets is very strong,
• These magnets tolerate high temperatures, often exceeding 230°C, when properly designed (in relation to form),
• Thanks to the possibility in shaping and the capability to adapt to specific requirements, neodymium magnets can be created in various configurations, which expands their functional possibilities,
• Key role in advanced technical fields – they are used in hard drives, rotating machines, clinical machines along with technologically developed systems,
• Relatively small size with high magnetic force – neodymium magnets offer strong power in compact dimensions, which makes them useful in small systems

Disadvantages of magnetic elements:

• They may fracture when subjected to a heavy impact. If the magnets are exposed to shocks, we recommend in a metal holder. The steel housing, in the form of a holder, protects the magnet from cracks and additionally strengthens its overall robustness,
• They lose field intensity at elevated temperatures. Most neodymium magnets experience permanent reduction 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,
• Magnets exposed to moisture can oxidize. Therefore, for outdoor applications, it's best to use waterproof types made of plastic,
• The use of a protective casing or external holder is recommended, since machining internal cuts in neodymium magnets is not feasible,
• Health risk linked to microscopic shards may arise, especially if swallowed, which is significant in the health of young users. Moreover, small elements from these products may interfere with diagnostics if inside the body,
• In cases of mass production, neodymium magnet cost may be a barrier,

Highest magnetic holding force – what it depends on?

The given pulling force of the magnet corresponds to the maximum force, calculated in a perfect environment, namely:

• using a steel plate with low carbon content, serving as a magnetic circuit closure
• of a thickness of at least 10 mm
• with a smooth surface
• with no separation
• under perpendicular detachment force
• in normal thermal conditions

Practical lifting capacity: influencing factors

The lifting capacity of a magnet depends on 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 the force acted perpendicularly, in contrast under shearing force the lifting capacity is smaller. Moreover, even a minimal clearance {between} the magnet’s surface and the plate decreases the lifting capacity.