SM 32x275 [2xM8] / N52 - magnetic separator

Advantages and disadvantages of neodymium magnets NdFeB.

Besides their stability, neodymium magnets are valued for these benefits:

• They have unchanged lifting capacity, and over nearly ten years their performance decreases symbolically – ~1% (according to theory),
• They protect against demagnetization induced by external magnetic fields effectively,
• In other words, due to the glossy silver coating, the magnet obtains an stylish appearance,
• The outer field strength of the magnet shows elevated magnetic properties,
• With the right combination of compounds, they reach significant thermal stability, enabling operation at or above 230°C (depending on the structure),
• 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 expands their usage potential,
• Wide application in new technology industries – they are utilized in data storage devices, electric drives, clinical machines or even sophisticated instruments,
• Thanks to their power density, small magnets offer high magnetic performance, while occupying minimal space,

Disadvantages of NdFeB magnets:

• They can break when subjected to a strong impact. If the magnets are exposed to physical collisions, they should be placed in a protective case. The steel housing, in the form of a holder, protects the magnet from fracture and additionally enhances its overall robustness,
• High temperatures may significantly reduce the field efficiency of neodymium magnets. Typically, above 80°C, they experience permanent decline in performance (depending on height). 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,
• Using a cover – such as a magnetic holder – is advised due to the difficulty in manufacturing holes directly in the magnet,
• Potential hazard due to small fragments may arise, if ingested accidentally, which is important in the protection of children. Additionally, miniature parts from these magnets have the potential to complicate medical imaging once in the system,
• In cases of mass production, neodymium magnet cost may be a barrier,

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

The given pulling force of the magnet represents the maximum force, measured under optimal conditions, that is:

• using a steel plate with low carbon content, serving as a magnetic circuit closure
• having a thickness of no less than 10 millimeters
• with a polished side
• with no separation
• in a perpendicular direction of force
• in normal thermal conditions

Lifting capacity in practice – influencing factors

Practical lifting force is determined by factors, listed from the most critical to the less significant:

• 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.

* Holding force was checked on a smooth steel plate of 20 mm thickness, when a perpendicular force was applied, whereas under parallel forces the load capacity is reduced by as much as 5 times. Additionally, even a minimal clearance {between} the magnet and the plate decreases the lifting capacity.