SM 32x200 [2xM8] / N42 - magnetic separator

Advantages as well as disadvantages of neodymium magnets NdFeB.

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

• They retain their magnetic properties for nearly ten years – the loss is just ~1% (based on simulations),
• They are extremely resistant to demagnetization caused by external magnetic sources,
• Thanks to the shiny finish and gold coating, they have an visually attractive appearance,
• They possess significant magnetic force measurable at the magnet’s surface,
• Thanks to their high temperature resistance, they can operate (depending on the shape) even at temperatures up to 230°C or more,
• The ability for precise shaping and adjustment to custom needs – neodymium magnets can be manufactured in many forms and dimensions, which extends the scope of their use cases,
• Wide application in cutting-edge sectors – they serve a purpose in computer drives, electric motors, healthcare devices as well as high-tech tools,
• Compactness – despite their small size, they generate strong force, making them ideal for precision applications

Disadvantages of NdFeB magnets:

• They are fragile when subjected to a powerful impact. If the magnets are exposed to shocks, we recommend in a protective case. The steel housing, in the form of a holder, protects the magnet from damage while also increases its overall robustness,
• They lose magnetic force at elevated temperatures. Most neodymium magnets experience permanent degradation in strength when heated above 80°C (depending on the dimensions and height). However, we offer special variants with high temperature resistance that can operate up to 230°C or higher,
• Due to corrosion risk in humid conditions, it is advisable to use sealed magnets made of synthetic coating for outdoor use,
• The use of a protective casing or external holder is recommended, since machining fine details in neodymium magnets is difficult,
• Health risk from tiny pieces may arise, in case of ingestion, which is important in the family environments. It should also be noted that small elements from these magnets can hinder health screening when ingested,
• High unit cost – neodymium magnets are more expensive than other types of magnets (e.g., ferrite), which may limit large-scale applications

Detachment force of the magnet in optimal conditions – what contributes to it?

The given pulling force of the magnet corresponds to the maximum force, measured under optimal conditions, namely:

• using a steel plate with low carbon content, serving as a magnetic circuit closure
• of a thickness of at least 10 mm
• with a smooth surface
• in conditions of no clearance
• with vertical force applied
• in normal thermal conditions

Impact of factors on magnetic holding capacity in practice

In practice, the holding capacity of a magnet is affected by these factors, from crucial to less important:

• Air gap between the magnet and the plate, because 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.

* Lifting capacity was determined with the use of a smooth steel plate of suitable thickness (min. 20 mm), under vertically applied force, in contrast under shearing force the holding force is lower. Additionally, even a slight gap {between} the magnet and the plate decreases the lifting capacity.