UMH 20x7x35 [M4] / N38 - magnetic holder with hook

Advantages and disadvantages of neodymium magnets NdFeB.

Besides their high retention, neodymium magnets are valued for these benefits:

• They have constant strength, and over around 10 years their attraction force decreases symbolically – ~1% (in testing),
• They remain magnetized despite exposure to magnetic noise,
• Thanks to the shiny finish and silver coating, they have an aesthetic appearance,
• The outer field strength of the magnet shows advanced magnetic properties,
• Thanks to their exceptional temperature resistance, they can operate (depending on the shape) even at temperatures up to 230°C or more,
• Thanks to the possibility in shaping and the capability to adapt to specific requirements, neodymium magnets can be created in different geometries, which broadens their functional possibilities,
• Key role in advanced technical fields – they find application in hard drives, electric drives, diagnostic apparatus along with high-tech tools,
• Compactness – despite their small size, they deliver powerful magnetism, making them ideal for precision applications

Disadvantages of NdFeB magnets:

• They are fragile when subjected to a strong impact. If the magnets are exposed to mechanical hits, it is advisable to use in a steel housing. The steel housing, in the form of a holder, protects the magnet from breakage while also reinforces its overall robustness,
• High temperatures may significantly reduce the magnetic power of neodymium magnets. Typically, above 80°C, they experience permanent decline in performance (depending on size). 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,
• Due to corrosion risk in humid conditions, it is wise to use sealed magnets made of rubber for outdoor use,
• The use of a protective casing or external holder is recommended, since machining internal cuts in neodymium magnets is not feasible,
• Health risk related to magnet particles may arise, in case of ingestion, which is crucial in the health of young users. Additionally, tiny components from these magnets have the potential to interfere with diagnostics when ingested,
• High unit cost – neodymium magnets are more expensive than other types of magnets (e.g., ferrite), which increases the cost of large-scale applications

Magnetic strength at its maximum – what it depends on?

The given holding capacity of the magnet means the highest holding force, measured under optimal conditions, namely:

• with mild steel, used as a magnetic flux conductor
• having a thickness of no less than 10 millimeters
• with a polished side
• in conditions of no clearance
• in a perpendicular direction of force
• in normal thermal conditions

Lifting capacity in real conditions – factors

The lifting capacity of a magnet depends on in practice key elements, 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 determined using a polished steel plate of suitable thickness (min. 20 mm), under perpendicular detachment force, however under parallel forces the lifting capacity is smaller. In addition, even a minimal clearance {between} the magnet and the plate lowers the holding force.