AM szekla [M10] - magnetic accessories

Advantages and disadvantages of neodymium magnets NdFeB.

In addition to their long-term stability, neodymium magnets provide the following advantages:

• They do not lose their strength approximately ten years – the loss of lifting capacity is only ~1% (theoretically),
• Their ability to resist magnetic interference from external fields is among the best,
• In other words, due to the metallic silver coating, the magnet obtains an aesthetic appearance,
• Magnetic induction on the surface of these magnets is very strong,
• These magnets tolerate extreme temperatures, often exceeding 230°C, when properly designed (in relation to build),
• Thanks to the possibility in shaping and the capability to adapt to individual requirements, neodymium magnets can be created in diverse shapes and sizes, which expands their usage potential,
• Key role in cutting-edge sectors – they find application in hard drives, electromechanical systems, clinical machines and sophisticated instruments,
• Compactness – despite their small size, they generate strong force, making them ideal for precision applications

Disadvantages of rare earth magnets:

• They are prone to breaking when subjected to a heavy impact. If the magnets are exposed to physical collisions, we recommend in a protective enclosure. The steel housing, in the form of a holder, protects the magnet from cracks while also strengthens its overall durability,
• They lose strength at high temperatures. Most neodymium magnets experience permanent loss in strength when heated above 80°C (depending on the geometry and height). However, we offer special variants with high temperature resistance that can operate up to 230°C or higher,
• Magnets exposed to damp air can corrode. Therefore, for outdoor applications, we advise 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 risky,
• Health risk due to small fragments may arise, if ingested accidentally, which is significant in the protection of children. It should also be noted that tiny components from these devices might interfere with diagnostics if inside the body,
• Higher purchase price is one of the drawbacks compared to ceramic magnets, especially in budget-sensitive applications

Maximum holding power of the magnet – what contributes to it?

The given pulling force of the magnet means the maximum force, calculated in ideal conditions, that is:

• with the use of low-carbon steel plate serving as a magnetic yoke
• with a thickness of minimum 10 mm
• with a smooth surface
• with no separation
• with vertical force applied
• under standard ambient temperature

Lifting capacity in practice – influencing factors

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

• Air gap between the magnet and the plate, because even a very small distance (e.g. 0.5 mm) can cause 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 measured by applying a smooth steel plate of suitable thickness (min. 20 mm), under perpendicular pulling force, however under shearing force the load capacity is reduced by as much as 75%. In addition, even a small distance {between} the magnet’s surface and the plate reduces the load capacity.