SM 32x325 [2xM8] / N42 - magnetic separator

Strengths as well as weaknesses of neodymium magnets.

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

• They virtually do not lose power, because even after ten years the decline in efficiency is only ~1% (based on calculations),
• Magnets perfectly protect themselves against demagnetization caused by external fields,
• In other words, due to the shiny finish of gold, the element is aesthetically pleasing,
• They feature high magnetic induction at the operating surface, making them more effective,
• Neodymium magnets are characterized by very high magnetic induction on the magnet surface and are able to act (depending on the shape) even at a temperature of 230°C or more...
• Possibility of accurate forming as well as adapting to specific conditions,
• Versatile presence in modern industrial fields – they serve a role in mass storage devices, brushless drives, precision medical tools, also technologically advanced constructions.
• Thanks to efficiency per cm³, small magnets offer high operating force, in miniature format,

What to avoid - cons of neodymium magnets and proposals for their use:

• Brittleness is one of their disadvantages. Upon intense impact they can fracture. We advise keeping them in a special holder, which not only protects them against impacts but also increases their durability
• Neodymium magnets lose their strength under the influence of heating. As soon as 80°C is exceeded, many of them start losing their force. Therefore, we recommend our special magnets marked [AH], which maintain stability even at temperatures up to 230°C
• When exposed to humidity, magnets usually rust. To use them in conditions outside, it is recommended to use protective magnets, such as those in rubber or plastics, which secure oxidation and corrosion.
• Limited possibility of producing threads in the magnet and complicated forms - recommended is a housing - mounting mechanism.
• Health risk to health – tiny shards of magnets are risky, when accidentally swallowed, which becomes key in the context of child health protection. Furthermore, small elements of these devices can be problematic in diagnostics medical after entering the body.
• With budget limitations the cost of neodymium magnets can be a barrier,

Maximum lifting force for a neodymium magnet – what it depends on?

The load parameter shown concerns the limit force, measured under laboratory conditions, namely:

• on a block made of mild steel, perfectly concentrating the magnetic flux
• possessing a thickness of min. 10 mm to ensure full flux closure
• characterized by lack of roughness
• without any air gap between the magnet and steel
• under perpendicular application of breakaway force (90-degree angle)
• at temperature approx. 20 degrees Celsius

Impact of factors on magnetic holding capacity in practice

In real-world applications, the actual holding force is determined by a number of factors, ranked from crucial:

• Clearance – the presence of foreign body (paint, tape, gap) acts as an insulator, which reduces power steeply (even by 50% at 0.5 mm).
• Direction of force – highest force is obtained only during perpendicular pulling. The force required to slide of the magnet along the plate is standardly several times smaller (approx. 1/5 of the lifting capacity).
• Substrate thickness – for full efficiency, the steel must be sufficiently thick. Thin sheet restricts the lifting capacity (the magnet "punches through" it).
• Chemical composition of the base – low-carbon steel attracts best. Alloy admixtures reduce magnetic properties and lifting capacity.
• Smoothness – ideal contact is obtained only on polished steel. Rough texture create air cushions, reducing force.
• Heat – NdFeB sinters have a negative temperature coefficient. At higher temperatures they are weaker, and at low temperatures they can be stronger (up to a certain limit).

* Holding force was tested on the plate surface of 20 mm thickness, when a perpendicular force was applied, in contrast under attempts to slide the magnet the lifting capacity is smaller. Additionally, even a small distance {between} the magnet’s surface and the plate lowers the holding force.