SM 25x325 [2xM8] / N42 - magnetic separator

Advantages as well as disadvantages of neodymium magnets NdFeB.

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

• They have unchanged lifting capacity, and over nearly ten years their attraction force decreases symbolically – ~1% (in testing),
• They remain magnetized despite exposure to strong external fields,
• The use of a mirror-like gold surface provides a smooth finish,
• The outer field strength of the magnet shows elevated magnetic properties,
• These magnets tolerate extreme temperatures, often exceeding 230°C, when properly designed (in relation to profile),
• With the option for tailored forming and precise design, these magnets can be produced in multiple shapes and sizes, greatly improving engineering flexibility,
• Key role in advanced technical fields – they serve a purpose in data storage devices, electric motors, healthcare devices or even sophisticated instruments,
• Compactness – despite their small size, they generate strong force, making them ideal for precision applications

Disadvantages of rare earth magnets:

• They can break when subjected to a sudden impact. If the magnets are exposed to physical collisions, we recommend in a protective case. The steel housing, in the form of a holder, protects the magnet from damage and additionally strengthens its overall durability,
• Magnets lose pulling force when exposed to temperatures exceeding 80°C. In most cases, this leads to irreversible magnetic decay (influenced by the magnet’s profile). To address this, we provide [AH] models with superior thermal resistance, able to operate even at 230°C or more,
• They rust in a moist environment. If exposed to rain, we recommend using moisture-resistant magnets, such as those made of plastic,
• Using a cover – such as a magnetic holder – is advised due to the limitations in manufacturing fine shapes directly in the magnet,
• Possible threat from tiny pieces may arise, especially if swallowed, which is important in the protection of children. It should also be noted that miniature parts from these devices have the potential to interfere with diagnostics when ingested,
• In cases of tight budgets, neodymium magnet cost may be a barrier,

Maximum lifting force for a neodymium magnet – what contributes to it?

The given lifting capacity of the magnet means the maximum lifting force, calculated under optimal conditions, that is:

• with mild steel, used as a magnetic flux conductor
• of a thickness of at least 10 mm
• with a polished side
• with no separation
• in a perpendicular direction of force
• in normal thermal conditions

Impact of factors on magnetic holding capacity in practice

Practical lifting force is dependent on elements, listed from the most critical to the less significant:

• 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 measured on the plate surface of 20 mm thickness, when a perpendicular force was applied, whereas under parallel forces the holding force is lower. In addition, even a slight gap {between} the magnet and the plate lowers the holding force.