MW 25x5 / N38AH - cylindrical magnet

Advantages and disadvantages of neodymium magnets NdFeB.

In addition to their pulling strength, neodymium magnets provide the following advantages:

• They virtually do not lose strength, because even after ten years, the decline in efficiency is only ~1% (based on calculations),
• They remain magnetized despite exposure to magnetic surroundings,
• Thanks to the shiny finish and silver coating, they have an aesthetic appearance,
• They have extremely strong magnetic induction on the surface of the magnet,
• Thanks to their exceptional temperature resistance, they can operate (depending on the shape) even at temperatures up to 230°C or more,
• With the option for fine forming and personalized design, these magnets can be produced in various shapes and sizes, greatly improving design adaptation,
• Significant impact in new technology industries – they are utilized in data storage devices, electric drives, diagnostic apparatus or even sophisticated instruments,
• Relatively small size with high magnetic force – neodymium magnets offer strong power in small dimensions, which allows for use in miniature devices

Disadvantages of neodymium magnets:

• They are fragile when subjected to a sudden impact. If the magnets are exposed to external force, it is suggested to place them in a protective enclosure. The steel housing, in the form of a holder, protects the magnet from fracture and additionally strengthens its overall robustness,
• Magnets lose power when exposed to temperatures exceeding 80°C. In most cases, this leads to irreversible magnetic decay (influenced by the magnet’s form). To address this, we provide [AH] models with superior thermal resistance, able to operate even at 230°C or more,
• Magnets exposed to humidity can corrode. Therefore, for outdoor applications, we advise waterproof types made of plastic,
• The use of a protective casing or external holder is recommended, since machining fine details in neodymium magnets is risky,
• Safety concern from tiny pieces may arise, especially if swallowed, which is important in the family environments. Furthermore, tiny components from these magnets might interfere with diagnostics when ingested,
• In cases of large-volume purchasing, neodymium magnet cost may not be economically viable,

Maximum holding power of the magnet – what affects it?

The given pulling force of the magnet represents the maximum force, measured in the best circumstances, namely:

• with mild steel, serving as a magnetic flux conductor
• of a thickness of at least 10 mm
• with a polished side
• with zero air gap
• under perpendicular detachment force
• at room temperature

Practical aspects of lifting capacity – factors

Practical lifting force is determined by factors, by priority:

• 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 by applying a steel plate with a smooth surface of suitable thickness (min. 20 mm), under perpendicular detachment force, whereas under shearing force the load capacity is reduced by as much as fivefold. Moreover, even a minimal clearance {between} the magnet’s surface and the plate decreases the load capacity.