SM 25x350 [2xM8] / N52 - magnetic separator

Advantages and disadvantages of neodymium magnets NdFeB.

In addition to their magnetic efficiency, neodymium magnets provide the following advantages:

• They do not lose their even during approximately ten years – the decrease of strength is only ~1% (theoretically),
• They are extremely resistant to demagnetization caused by external magnetic fields,
• The use of a polished gold surface provides a eye-catching 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 and customization to individual needs – neodymium magnets can be manufactured in many forms and dimensions, which extends the scope of their use cases,
• Wide application in new technology industries – they are used in hard drives, electric motors, diagnostic apparatus as well as other advanced devices,
• Compactness – despite their small size, they generate strong force, making them ideal for precision applications

Disadvantages of neodymium magnets:

• They can break when subjected to a strong impact. If the magnets are exposed to physical collisions, it is advisable to use in a protective enclosure. The steel housing, in the form of a holder, protects the magnet from breakage , and at the same time increases its overall robustness,
• Magnets lose field strength when exposed to temperatures exceeding 80°C. In most cases, this leads to irreversible magnetic decay (influenced by the magnet’s dimensions). To address this, we provide [AH] models with superior thermal resistance, able to operate even at 230°C or more,
• Magnets exposed to moisture can oxidize. Therefore, for outdoor applications, we suggest waterproof types made of coated materials,
• Using a cover – such as a magnetic holder – is advised due to the difficulty in manufacturing complex structures directly in the magnet,
• Potential hazard related to magnet particles may arise, especially if swallowed, which is important in the context of child safety. Furthermore, tiny components from these products might disrupt scanning once in the system,
• Due to the price of neodymium, their cost is relatively high,

Detachment force of the magnet in optimal conditions – what it depends on?

The given strength of the magnet represents the optimal strength, determined in the best circumstances, specifically:

• using a steel plate with low carbon content, acting as a magnetic circuit closure
• with a thickness of minimum 10 mm
• with a smooth surface
• with zero air gap
• in a perpendicular direction of 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, in descending order of importance:

• Air gap between the magnet and the plate, since 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 tested on a smooth steel plate of 20 mm thickness, when the force acted perpendicularly, whereas under parallel forces the lifting capacity is smaller. Additionally, even a minimal clearance {between} the magnet’s surface and the plate decreases the holding force.