SM 18x225 [2xM5] / N42 - magnetic separator

Advantages and disadvantages of neodymium magnets NdFeB.

In addition to their immense pulling force, neodymium magnets offer the following advantages:

• Their strength is maintained, and after approximately ten years, it drops only by ~1% (according to research),
• They are extremely resistant to demagnetization caused by external field interference,
• The use of a polished silver surface provides a refined finish,
• They have very high magnetic induction on the surface of the magnet,
• With the right combination of compounds, they reach excellent thermal stability, enabling operation at or above 230°C (depending on the design),
• The ability for accurate shaping or customization to specific needs – neodymium magnets can be manufactured in multiple variants of geometries, which extends the scope of their use cases,
• Significant impact in modern technologies – they are used in computer drives, electromechanical systems, diagnostic apparatus or even sophisticated instruments,
• Relatively small size with high magnetic force – neodymium magnets offer strong power in compact dimensions, which makes them ideal in small systems

Disadvantages of neodymium magnets:

• They are prone to breaking when subjected to a sudden impact. If the magnets are exposed to external force, they should be placed in a metal holder. The steel housing, in the form of a holder, protects the magnet from cracks while also strengthens its overall resistance,
• High temperatures may significantly reduce the holding force of neodymium magnets. Typically, above 80°C, they experience permanent loss 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,
• They rust in a wet environment, especially when used outside, 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 fine details in neodymium magnets is difficult,
• Possible threat related to magnet particles may arise, especially if swallowed, which is notable in the family environments. Moreover, small elements from these devices may hinder health screening when ingested,
• High unit cost – neodymium magnets are pricier than other types of magnets (e.g., ferrite), which may limit large-scale applications

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

The given lifting capacity of the magnet corresponds to the maximum lifting force, measured in ideal conditions, that is:

• with mild steel, serving as a magnetic flux conductor
• having a thickness of no less than 10 millimeters
• with a polished side
• with zero air gap
• under perpendicular detachment force
• under standard ambient temperature

Determinants of lifting force in real conditions

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

• 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 was determined by applying a steel plate with a smooth surface of suitable thickness (min. 20 mm), under vertically applied force, however under attempts to slide the magnet the load capacity is reduced by as much as 75%. Moreover, even a small distance {between} the magnet and the plate decreases the holding force.