MP 40x20x5 / N38 - ring magnet

Advantages as well as disadvantages of neodymium magnets NdFeB.

In addition to their exceptional magnetic power, neodymium magnets offer the following advantages:

• Their strength is maintained, and after approximately 10 years, it drops only by ~1% (according to research),
• They are extremely resistant to demagnetization caused by external magnetic fields,
• Thanks to the shiny finish and silver coating, they have an visually attractive appearance,
• The outer field strength of the magnet shows advanced magnetic properties,
• Thanks to their exceptional temperature resistance, they can operate (depending on the form) even at temperatures up to 230°C or more,
• Thanks to the possibility in shaping and the capability to adapt to individual requirements, neodymium magnets can be created in various configurations, which increases their application range,
• Wide application in advanced technical fields – they serve a purpose in HDDs, electric motors, healthcare devices or even sophisticated instruments,
• Relatively small size with high magnetic force – neodymium magnets offer impressive pulling strength in tiny dimensions, which makes them ideal in small systems

Disadvantages of rare earth magnets:

• They can break when subjected to a sudden impact. If the magnets are exposed to physical collisions, we recommend in a metal holder. The steel housing, in the form of a holder, protects the magnet from fracture and additionally enhances its overall strength,
• They lose power at extreme temperatures. Most neodymium magnets experience permanent loss in strength when heated above 80°C (depending on the form and height). However, we offer special variants with high temperature resistance that can operate up to 230°C or higher,
• They rust in a wet environment – during outdoor use, we recommend using waterproof magnets, such as those made of non-metallic materials,
• The use of a protective casing or external holder is recommended, since machining threads in neodymium magnets is risky,
• Potential hazard linked to microscopic shards may arise, in case of ingestion, which is important in the context of child safety. Additionally, minuscule fragments from these products can interfere with diagnostics once in the system,
• Due to the price of neodymium, their cost is relatively high,

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

The given lifting capacity of the magnet corresponds to the maximum lifting force, determined in a perfect environment, 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 refined outer layer
• in conditions of no clearance
• with vertical force applied
• under standard ambient temperature

Determinants of practical lifting force of a magnet

Practical lifting force is determined by factors, 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, however under parallel forces the holding force is lower. Additionally, even a small distance {between} the magnet and the plate reduces the load capacity.