Unlike traditional magnets, which are magnetized longitudinally or radially, diametrically magnetized cylinder magnets are simply magnetized through their diameter. They are mounted at the end of a shaft and are used to generate rotation. This forms unique magnetic field arrangements that lead to various industrial uses.
Cylindrical magnets are considered one of the most common shapes for this type of magnetization. For all the owners and suppliers who purchase magnetic products, it is important to get to know how neodymium cylinder magnets are manufactured and selected. This article will certainly help you make the right buying decision.
What Does “Diametrically Magnetized” Mean?
Of course, magnets will always naturally have their poles at both magnetic ends. However, when we speak of diametrically magnetized magnets, what we mean is that they have their poles across the diameter of the magnet, 180° apart. The north pole is found at one of the curved surfaces, while the south pole is found at the other curved surface.
The field rotates with the cylinder. This special configuration allows for rotational movements since there will always be a force applied to the shafts where they are mounted.
How Are Diametric Cylinder Magnets Made?
High-performing diametric cylinder magnets are made from a sintered neodymium iron boron alloy to ensure the performance consistency of finished products. The key steps are listed below.
1. Initial Alloy-Making
After selecting the premium rare earth metals, the alloy is melted, rapidly cooled, and crushed into a fine magnetic powder. A correct proportion of elements ensures stable magnetic performance.
2. Pressing in a Transverse Field
The powder is then pressed in a mold under a transverse magnetic field to align the crystal axes across the diameter. It is compacted into a dense cylindrical blank with structural uniformity.
3. Sintering
These pressed blocks are sintered at around 1000–1100 °C to tighten the internal material structure by fusing the particles. It lays the foundation for magnetic shaping.
4. Magnetic Machining
Manufacturers use precise tools for fixed-length grinding and cutting of sintered blocks to correct the deformation and smooth the surfaces. The custom cylindrical magnets meet the dimensional tolerance requirements through mechanical processing.
5. Magnetizing
These fully formed blanks are then placed between the poles of a strong electromagnet inside a specialized fixture or coil. As the sintering locks in the crystallographic texture, the material prefers to be magnetized diametrically.
6. Coating
Surface protective coating is necessary to prevent corrosion, as neodymium magnets are prone to oxidation. The coating options can be customized and include nickel-copper-nickel, zinc, or epoxy plating.
7. Quality Control
Every batch undergoes magnetic strength testing to detect the Gauss value, magnetic flux, and grade of each finished cylinder magnet. Dimensional accuracy and safe shipping are also prioritized before delivery.
At BMAG, quality control and standard testing at each stage are done to guarantee a long service life.
Why Do Industries Need 3x3mm Cylindrical Magnets?
Industries need 3x3mm diametric cylindrical magnets for efficient rotation applications. As they create a transverse magnetic field, they are used in miniaturized sensors, motors, encoders, couplings, latching systems, and flow meters for rotary motion and non-contact sensing.
Rotary Encoders (Hall Effect Sensing)
The angles can be measured accurately using only one diametrically oriented magnet located near a semiconductor chip. The changing magnetic field is read by sensors and used for motion tracking in automation devices.
High-Performance DC Motors
Brushless DC motors and linear actuators employ diametric magnets in the rotor to enable the controller to monitor the shaft’s position.
Magnetic Couplings
Placing two diametric magnets on different shafts causes them to rotate in sync through a barrier. It can be used in fluid or pump systems to avoid the risk of leaks due to mechanical contact.
Directional Latching
The transverse pull allows the snap to align together at a very specific orientation in magnetic switch locking and closures.
Scientific Instruments
Instruments such as NMR and flow meters, which record revolutions of a turbine carries a diametric magnet.
How Diametric Magnetization Is Different From Axial Magnetization?
The flat ends and the rounded side wall surface make these cylindrical magnets versatile, enabling both axial and diametrical magnetizations.
As opposed to axially magnetized cylinder magnets, diametrical magnets have their poles not at the end faces, but on the lateral side of the cylinder.
When put together, axially magnetized ones tend to stick together end to end, and diametrically magnetized magnets cling together at the sides.
To tell the difference, here is a table for simpler understanding.
| Feature | Axial (Standard) | Diametric |
| Pole location | Flat ends | Curved surface |
| Common use | Holding, sensing | Rotating, encoding |
| Manufacturing complexity | Standard | Higher |
| Cost | Lower | Slightly higher |
| Available grades | All | Most (confirm with manufacturer) |
Such a distinction results in a variation of the magnetic field configuration, and it generally impacts the positioning of the magnet within the assembly.
Technical Specs of Diametric Cylinder Magnets To Consider
Neodymium magnets’ service life can also be shortened due to factors including heat, corrosion, and physical damage. Hence, technical specifications should be considered when using neodymium cylinder magnets.
1. Dimension Requirements
Dimensions and the grade of the magnet go hand in hand. The dimension of a diametrically magnetized cylindrical magnet is determined by its length-to-diameter ratio (L/D). The ideal L/D ratio of 1 produces maximum field strength, while going for a thinner design (L/D >2) reduces the transverse surface field. Longer cylinders are also hard to manufacture and tend to crack.
The recommended ratios according to applications include
- Rotary Encoders and Sensors: 0.4 to 0.6 for good linearity and accurate angle detection
- Motors, couplings, and actuators: 0.8 to 1.2 for mechanical rigidity against demagnetization forces within
A small-sized magnet of high grade is preferable compared to a bigger-sized magnet of low grade. If high-coercivity materials such as Neodymium (NdFeB) are used, then flat designs can be used.
2. Magnetization angle
Tilted, single, or multi-pole magnetization angle is a choice made before ordering. Multi-poles add complexity and require the Hall sensors to be capable of handling multi-pole inputs. True diametric magnets give full rotation and require pressing with a transverse field during sintering. Single-pole cylinders are suitable for rotary encoders and sensors, while multi-pole cylinders are used for high-speed motors.
3. Tolerance and concentricity
Dimensional tolerances for diametrical magnets are critical in determining the size and positioning of the poles. For tighter tolerances, cylindrical grinding after sintering is required. If the cylinder is off-center, rotating it will produce a field that “wobbles” — leading to angular position errors in certain applications.
4. Coating Selection
NdFeB rusts easily if not coated and can ruin the magnet internally. Depending on your specific installation needs, select the coating material. For example, epoxy coating for highly humid and nickel triple layer coating for dry applications.
- Ni-Cu-Ni coating is the most common choice for a bright silver finish, but it is not suitable for salt environments.
- Epoxy resin provides chemical resistance and is best suited for motors and industrial sensors.
- Nickel-Gold coating can be used in medical settings where direct contact with tissues is required.
- Zinc offers cheap coating resistance, but it is not recommended for precision encoder magnets.
Also, consider the effect of coating thickness when doing bore calculations.
5. Grade selection
For diameter cylinder magnets, the N42–N45 range is practically optimal. The higher the grade, the stronger the magnet. Thus, the N52 neodymium diametric magnet has the highest magnetic pull.
The grade selection depends on the temperature suffix (M, H, SH, UH, EH) that defines the coercivity. Hence, N52SH shows better resistance to demagnetization at elevated temperatures than simple N52, which would demagnetize over time.
Why Choose BMAG?
As an industry leader in the magnetics industry, BMAG magnets are made with long-term performance and reliability in mind. Its newly developed HRE-Free NdFeB magnets provide excellent performance.
In addition, our team works closely with you to customize magnetic assemblies according to your specific requirements throughout the process. BMAG supports custom grade, angle, and size selection to cater to a wide range of OEMs and distributors.
Conclusion
In diametrically magnetized cylinders, the North and South poles exist on the curved surfaces instead of the flat ends. A great diametric magnet is made of high-grade neodymium material and nickel coating with minimum tolerance errors. They are used mainly in rotational applications like angular sensors and rotary encoders.
Contact our team to get the superior diametric cylindrical magnets at a competitive price.
