SM 25x200 [2xM8] / N42 - magnetic separator

Advantages as well as disadvantages of neodymium magnets NdFeB.

In addition to their pulling strength, neodymium magnets provide the following advantages:

• Their power is durable, and after around 10 years, it drops only by ~1% (according to research),
• Their ability to resist magnetic interference from external fields is notable,
• Because of the reflective layer of silver, the component looks aesthetically refined,
• They have extremely strong magnetic induction on the surface of the magnet,
• These magnets tolerate high temperatures, often exceeding 230°C, when properly designed (in relation to build),
• Thanks to the flexibility in shaping and the capability to adapt to specific requirements, neodymium magnets can be created in various configurations, which broadens their usage potential,
• Wide application in advanced technical fields – they serve a purpose in hard drives, electromechanical systems, clinical machines along with technologically developed systems,
• Thanks to their power density, small magnets offer high magnetic performance, in miniature format,

Disadvantages of rare earth magnets:

• They are fragile when subjected to a strong impact. If the magnets are exposed to mechanical hits, they should be placed in a metal holder. The steel housing, in the form of a holder, protects the magnet from cracks , and at the same time strengthens its overall durability,
• Magnets lose pulling force when exposed to temperatures exceeding 80°C. In most cases, this leads to irreversible power drop (influenced by the magnet’s structure). To address this, we provide [AH] models with superior thermal resistance, able to operate even at 230°C or more,
• They rust in a humid environment. If exposed to rain, we recommend using moisture-resistant 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 risky,
• Health risk related to magnet particles may arise, in case of ingestion, which is important in the family environments. Furthermore, tiny components from these products have the potential to disrupt scanning when ingested,
• High unit cost – neodymium magnets are more expensive than other types of magnets (e.g., ferrite), which may limit large-scale applications

Detachment force of the magnet in optimal conditions – what contributes to it?

The given lifting capacity of the magnet corresponds to the maximum lifting force, measured in the best circumstances, namely:

• with the use of low-carbon steel plate acting 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

In practice, the holding capacity of a magnet is conditioned 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) 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.

* Holding force was checked on a smooth steel plate of 20 mm thickness, when a perpendicular force was applied, however under shearing force the load capacity is reduced by as much as 75%. Moreover, even a minimal clearance {between} the magnet’s surface and the plate decreases the lifting capacity.