MP 25x7x9 / N38 - ring magnet

Advantages and disadvantages of neodymium magnets NdFeB.

Besides their stability, neodymium magnets are valued for these benefits:

• They do not lose their magnetism, even after nearly 10 years – the loss of power is only ~1% (according to tests),
• They protect against demagnetization induced by surrounding magnetic fields effectively,
• By applying a bright layer of nickel, the element gains a sleek look,
• The outer field strength of the magnet shows advanced magnetic properties,
• These magnets tolerate extreme temperatures, often exceeding 230°C, when properly designed (in relation to form),
• With the option for customized forming and targeted design, these magnets can be produced in multiple shapes and sizes, greatly improving engineering flexibility,
• Important function in new technology industries – they are used in HDDs, electric motors, healthcare devices and sophisticated instruments,
• Compactness – despite their small size, they provide high effectiveness, making them ideal for precision applications

Disadvantages of NdFeB magnets:

• They may fracture when subjected to a heavy impact. If the magnets are exposed to physical collisions, we recommend in a protective enclosure. The steel housing, in the form of a holder, protects the magnet from cracks while also increases its overall strength,
• Magnets lose magnetic efficiency when exposed to temperatures exceeding 80°C. In most cases, this leads to irreversible magnetic decay (influenced by the magnet’s profile). To address this, we provide [AH] models with superior thermal resistance, able to operate even at 230°C or more,
• Due to corrosion risk in humid conditions, it is wise 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 restricted,
• Possible threat from tiny pieces may arise, especially if swallowed, which is important in the family environments. It should also be noted that miniature parts from these products have the potential to interfere with diagnostics once in the system,
• Higher purchase price is one of the drawbacks compared to ceramic magnets, especially in budget-sensitive applications

Maximum magnetic pulling force – what contributes to it?

The given pulling force of the magnet represents the maximum force, calculated 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 smooth surface
• with no separation
• in a perpendicular direction of force
• under standard ambient temperature

Key elements affecting lifting force

The lifting capacity of a magnet is determined by in practice the following factors, ordered from most important to least 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.

* Holding force was checked on the plate surface of 20 mm thickness, when the force acted perpendicularly, whereas under attempts to slide the magnet the lifting capacity is smaller. Additionally, even a slight gap {between} the magnet and the plate decreases the load capacity.