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

Strengths and weaknesses of rare earth magnets.

Besides their magnetic performance, neodymium magnets are valued for these benefits:

• They do not lose strength, even after approximately ten years – the drop in power is only ~1% (theoretically),
• Magnets effectively defend themselves against demagnetization caused by ambient magnetic noise,
• A magnet with a shiny nickel surface has better aesthetics,
• The surface of neodymium magnets generates a concentrated magnetic field – this is a key feature,
• Neodymium magnets are characterized by extremely high magnetic induction on the magnet surface and can work (depending on the form) even at a temperature of 230°C or more...
• Possibility of individual forming and optimizing to concrete needs,
• Huge importance in electronics industry – they are used in mass storage devices, motor assemblies, precision medical tools, also modern systems.
• Relatively small size with high pulling force – neodymium magnets offer impressive pulling force in compact dimensions, which enables their usage in compact constructions

Drawbacks and weaknesses of neodymium magnets and proposals for their use:

• At very strong impacts they can break, therefore we recommend placing them in special holders. A metal housing provides additional protection against damage, as well as increases the magnet's durability.
• Neodymium magnets decrease 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
• Due to the susceptibility of magnets to corrosion in a humid environment, we recommend using waterproof magnets made of rubber, plastic or other material stable to moisture, when using outdoors
• Limited ability of producing nuts in the magnet and complicated shapes - recommended is cover - magnetic holder.
• Health risk resulting from small fragments of magnets pose a threat, if swallowed, which is particularly important in the context of child health protection. Furthermore, small components of these products are able to disrupt the diagnostic process medical in case of swallowing.
• Higher cost of purchase is one of the disadvantages compared to ceramic magnets, especially in budget applications

Highest magnetic holding force – what affects it?

Breakaway force is the result of a measurement for ideal contact conditions, taking into account:

• with the application of a sheet made of low-carbon steel, guaranteeing full magnetic saturation
• possessing a massiveness of minimum 10 mm to avoid saturation
• with a surface cleaned and smooth
• with total lack of distance (no paint)
• during pulling in a direction vertical to the plane
• in stable room temperature

Practical lifting capacity: influencing factors

Real force is influenced by specific conditions, including (from priority):

• Air gap (betwixt the magnet and the metal), since even a tiny distance (e.g. 0.5 mm) results in a decrease in lifting capacity by up to 50% (this also applies to varnish, corrosion or dirt).
• Angle of force application – maximum parameter is obtained only during perpendicular pulling. The shear force of the magnet along the surface is standardly several times lower (approx. 1/5 of the lifting capacity).
• Plate thickness – insufficiently thick sheet does not accept the full field, causing part of the power to be lost into the air.
• Steel grade – ideal substrate is pure iron steel. Hardened steels may generate lower lifting capacity.
• Surface quality – the more even the plate, the larger the contact zone and stronger the hold. Unevenness acts like micro-gaps.
• Temperature influence – hot environment weakens pulling force. Exceeding the limit temperature can permanently demagnetize the magnet.

* Holding force was tested on the plate surface of 20 mm thickness, when the force acted perpendicularly, in contrast under shearing force the load capacity is reduced by as much as fivefold. Additionally, even a minimal clearance {between} the magnet’s surface and the plate lowers the holding force.