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

Advantages and disadvantages of neodymium magnets NdFeB.

Besides their magnetic performance, neodymium magnets are valued for these benefits:

• They virtually do not lose power, because even after ten years, the performance loss is only ~1% (based on calculations),
• They show superior resistance to demagnetization from external field exposure,
• Thanks to the polished finish and silver coating, they have an aesthetic appearance,
• They possess significant magnetic force measurable at the magnet’s surface,
• They are suitable for high-temperature applications, operating effectively at 230°C+ due to advanced heat resistance and form-specific properties,
• The ability for precise shaping and adjustment to custom needs – neodymium magnets can be manufactured in many forms and dimensions, which extends the scope of their use cases,
• Important function in modern technologies – they find application in computer drives, electromechanical systems, clinical machines along with other advanced devices,
• 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 sudden impact. If the magnets are exposed to physical collisions, it is suggested to place them in a protective case. The steel housing, in the form of a holder, protects the magnet from fracture and additionally increases 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 form). 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,
• They rust in a moist environment. If exposed to rain, we recommend using encapsulated magnets, such as those made of polymer,
• The use of a protective casing or external holder is recommended, since machining multi-axis shapes in neodymium magnets is restricted,
• Potential hazard from tiny pieces may arise, if ingested accidentally, which is crucial in the protection of children. Moreover, miniature parts from these products may interfere with diagnostics if inside the body,
• High unit cost – neodymium magnets are costlier than other types of magnets (e.g., ferrite), which increases the cost of large-scale applications

Maximum holding power of the magnet – what it depends on?

The given strength of the magnet corresponds to the optimal strength, assessed under optimal conditions, specifically:

• using a steel plate with low carbon content, serving as a magnetic circuit closure
• of a thickness of at least 10 mm
• with a polished side
• in conditions of no clearance
• with vertical force applied
• at room temperature

Impact of factors on magnetic holding capacity in practice

In practice, the holding capacity of a magnet is conditioned by these factors, from crucial to less important:

• Air gap between the magnet and the plate, as 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 testing was conducted on plates with a smooth surface of suitable thickness, under a perpendicular pulling force, however under parallel forces the lifting capacity is smaller. Moreover, even a small distance {between} the magnet’s surface and the plate reduces the lifting capacity.