SM 25x175 [2xM8] / N52 - magnetic separator

Advantages as well as disadvantages of neodymium magnets NdFeB.

In addition to their immense pulling force, neodymium magnets offer the following advantages:

• They have unchanged lifting capacity, and over more than 10 years their performance decreases symbolically – ~1% (according to theory),
• They are highly resistant to demagnetization caused by external field interference,
• Because of the reflective layer of silver, the component looks visually appealing,
• The outer field strength of the magnet shows remarkable magnetic properties,
• These magnets tolerate elevated temperatures, often exceeding 230°C, when properly designed (in relation to profile),
• With the option for tailored forming and personalized design, these magnets can be produced in multiple shapes and sizes, greatly improving engineering flexibility,
• Key role in new technology industries – they find application in HDDs, electromechanical systems, diagnostic apparatus as well as technologically developed systems,
• Thanks to their concentrated strength, small magnets offer high magnetic performance, while occupying minimal space,

Disadvantages of neodymium magnets:

• They are fragile when subjected to a strong impact. If the magnets are exposed to physical collisions, it is advisable to use in a steel housing. The steel housing, in the form of a holder, protects the magnet from damage and additionally increases its overall strength,
• They lose power at high temperatures. Most neodymium magnets experience permanent degradation in strength when heated above 80°C (depending on the shape 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 common to use sealed magnets made of rubber for outdoor use,
• The use of a protective casing or external holder is recommended, since machining threads in neodymium magnets is risky,
• Potential hazard related to magnet particles may arise, in case of ingestion, which is notable in the context of child safety. Additionally, small elements from these devices might complicate medical imaging after being swallowed,
• Higher purchase price is an important factor to consider compared to ceramic magnets, especially in budget-sensitive applications

Magnetic strength at its maximum – what affects it?

The given holding capacity of the magnet corresponds to the highest holding force, determined in ideal 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
• in conditions of no clearance
• under perpendicular detachment force
• in normal thermal conditions

Key elements affecting lifting force

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

• Air gap between the magnet and the plate, because even a very small distance (e.g. 0.5 mm) causes 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 assessed with the use of a steel plate with a smooth surface of suitable thickness (min. 20 mm), under perpendicular pulling force, in contrast under shearing force the lifting capacity is smaller. Moreover, even a minimal clearance {between} the magnet and the plate reduces the load capacity.