SM 25x100 [2xM8] / N42 - magnetic separator

Advantages as well as disadvantages of neodymium magnets NdFeB.

In addition to their long-term stability, neodymium magnets provide the following advantages:

• They have constant strength, and over around 10 years their attraction force decreases symbolically – ~1% (in testing),
• They remain magnetized despite exposure to magnetic surroundings,
• In other words, due to the glossy nickel coating, the magnet obtains an stylish appearance,
• Magnetic induction on the surface of these magnets is notably high,
• Thanks to their exceptional temperature resistance, they can operate (depending on the geometry) even at temperatures up to 230°C or more,
• The ability for precise shaping and adaptation to individual needs – neodymium magnets can be manufactured in a wide range of shapes and sizes, which enhances their versatility in applications,
• Significant impact in advanced technical fields – they are used in HDDs, rotating machines, clinical machines along with sophisticated instruments,
• Thanks to their power density, small magnets offer high magnetic performance, with minimal size,

Disadvantages of rare earth magnets:

• They can break when subjected to a sudden impact. If the magnets are exposed to physical collisions, they should be placed in a steel housing. The steel housing, in the form of a holder, protects the magnet from breakage and increases its overall strength,
• They lose strength at high temperatures. Most neodymium magnets experience permanent decline in strength when heated above 80°C (depending on the geometry and height). However, we offer special variants with high temperature resistance that can operate up to 230°C or higher,
• Magnets exposed to damp air can degrade. Therefore, for outdoor applications, we suggest waterproof types made of plastic,
• Limited ability to create threads in the magnet – the use of a magnetic holder is recommended,
• Possible threat from tiny pieces may arise, especially if swallowed, which is significant in the family environments. Additionally, minuscule fragments from these devices can interfere with diagnostics after being swallowed,
• Due to a complex production process, their cost is relatively high,

Maximum magnetic pulling force – what affects it?

The given holding capacity of the magnet means the highest holding force, calculated under optimal conditions, namely:

• with the use of low-carbon steel plate acting as a magnetic yoke
• with a thickness of minimum 10 mm
• with a refined outer layer
• with no separation
• in a perpendicular direction of force
• under standard ambient temperature

Practical lifting capacity: influencing factors

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

• 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 measured on the plate surface of 20 mm thickness, when a perpendicular force was applied, however under parallel forces the holding force is lower. Additionally, even a minimal clearance {between} the magnet and the plate reduces the holding force.