SM 25x250 [2xM8] / N42 - magnetic separator

Advantages as well as disadvantages of neodymium magnets NdFeB.

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

• Their magnetic field remains stable, and after around ten years, it drops only by ~1% (theoretically),
• They show strong resistance to demagnetization from external magnetic fields,
• Because of the brilliant layer of silver, the component looks aesthetically refined,
• Magnetic induction on the surface of these magnets is impressively powerful,
• With the right combination of compounds, they reach significant thermal stability, enabling operation at or above 230°C (depending on the form),
• 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 usage potential,
• Significant impact in modern technologies – they find application in hard drives, rotating machines, healthcare devices as well as high-tech tools,
• Relatively small size with high magnetic force – neodymium magnets offer impressive pulling strength in small dimensions, which allows for use in small systems

Disadvantages of rare earth magnets:

• They may fracture when subjected to a sudden impact. If the magnets are exposed to mechanical hits, they should be placed in a steel housing. The steel housing, in the form of a holder, protects the magnet from cracks , and at the same time reinforces its overall durability,
• High temperatures may significantly reduce the field efficiency of neodymium magnets. Typically, above 80°C, they experience permanent decline 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,
• Due to corrosion risk in humid conditions, it is advisable to use sealed magnets made of plastic for outdoor use,
• The use of a protective casing or external holder is recommended, since machining multi-axis shapes in neodymium magnets is restricted,
• Possible threat linked to microscopic shards may arise, if ingested accidentally, which is significant in the health of young users. Moreover, small elements from these devices may complicate medical imaging if inside the body,
• Higher purchase price is one of the drawbacks compared to ceramic magnets, especially in budget-sensitive applications

Best holding force of the magnet in ideal parameters – what contributes to it?

The given strength of the magnet corresponds to the optimal strength, determined in the best circumstances, namely:

• with the use of low-carbon steel plate acting as a magnetic yoke
• of a thickness of at least 10 mm
• with a refined outer layer
• in conditions of no clearance
• with vertical force applied
• under standard ambient temperature

Determinants of practical lifting force of a magnet

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, 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.

* Lifting capacity testing was carried out on a smooth plate of optimal thickness, under a perpendicular pulling force, in contrast under attempts to slide the magnet the load capacity is reduced by as much as 75%. Additionally, even a minimal clearance {between} the magnet and the plate lowers the lifting capacity.