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Neodymium magnets: Special features, production and uses
Neodymium magnets are the strongest permanent magnets available and can produce very strong magnetic fields in the smallest of spaces. This property allows them to be integrated into a variety of devices and applications even when space is limited.
What makes neodymium magnets so strong, what applications are available, how they are made, and what to consider when using them is discussed in this article.
What is neodymium?
Neodymium is a chemical element belonging to the group of lanthanoids. It is a rare earth metal and in its natural form is found only in chemical compounds and in the presence of other lanthanoids, especially in the minerals monacite and bastneasite. Neodymium is relatively common in the earth’s crust, but the concentration of the element is usually so low that economic mining is not possible. It is therefore often obtained as a by-product when mining more concentrated ores. With over 90% of the world’s annual production of neodymium, China is by far the most important supplier of this metal (2023).
Neodymium is a very reactive metal and oxidizes in air. By itself, it has a relatively weak magnetic force, but it obtains a very high magnetizing capacity when combined with iron and boron.
What is a neodymium magnet?
Neodymium magnets are a neodymium iron boron alloy, also abbreviated as NdFeB. These compounds are characterized by their strong magnetic force and are currently the material available with the highest magnetic force. Sometimes additional elements are added to the alloy to affect the properties of the subsequent magnet. The magnetic force of the respective neodymium magnets depends greatly on their quality and composition. MISUMI typically differentiates between strong neodymium magnets, neodymium magnets and heat-resistant neodymium magnets. For the various magnets and magnet types offered in our shop, you can find the respective magnetic surface flux density in Gauss (G) or Tesla and their magnet attraction force in N in clearly structured table form.
Production of neodymium magnets
Neodymium magnets are produced by alloying neodymium, iron and boron, while carefully controlling the exact composition. The production is for example divided into the following steps:
| Step | Description |
|---|---|
| Material selection | In the first step, the required materials boron, iron and neodymium and possibly other alloy components are melted separately and formed into round bars. |
| Alloying | The metals for the alloy are selected and liquefied in a smelting furnace. The melting process causes the atoms to mix at the atomic level. Mixing is carried out by stirring or pouring, for example. The atoms of the various metals combine to form a homogeneous alloy. Each neodymium magnet has a different composition, e.g. Nd2Fe14B. |
| Strip casting | During strip casting, the materials are placed in a large die-casting machine. In this machine, the up to 1450°C hot alloy is melted in a vacuum induction furnace, guided under pressure onto a cooling drum, and cooled extremely quickly there. The rapid cooling creates small platelets, which form the basis for further processing steps. |
| Hydrogen decrepitation (embrittlement) | The material is now subjected to a hydrogen treatment. The infusion of hydrogen leads to embrittlement and further reduction of the alloy under the influence of the hydrogen atmosphere. This makes it easier to process the material during the milling process. |
| Milling process | The mixture is then ground under a protective atmosphere into a very fine, homogeneous powder and forwarded to the pressing device. |
| Molding process | The molding process presses the powder into the rough starting form (e.g. block, cylinder). Care is taken to ensure that oxygen does not mixed in again._x000D_ In this step, a strong magnetic field is applied for the first alignment of the particles in the direction of the subsequently desired magnetic field._x000D_ In a further pressing process, the material is further compacted and the final shapes are created at a pressure of up to 1000 bar. An oil press then further compresses the shapes at up to 1600 bar._x000D_ The following pressing methods exist:_x000D_ Axial: The material is located in a tool cavity, where it is compressed by penetrating punches. The magnetic alignment field is applied prior to the compression, parallel to the compression direction. During cross-pressing, the alignment field runs perpendicular to the compression direction._x000D_ Isostatic: The alignment field is applied on a flexible container filled with powder. The container is then inserted into the isostatic press, where pressure is applied from the outside, e.g. by water. As a result, the material compacts evenly on all sides._x000D_ |
| Sintering | During sintering, the blanks are now placed into a furnace and are sintered for several hours at temperatures of 250°C - 900°C. This process can take about 20 hours for grade N35 magnets and up to 36 hours for grade N52 magnets._x000D_ Almost all magnetic force is lost during sintering, but the alignment is maintained._x000D_ Rapid cooling after sintering prevents unwanted phase formation and reduces stress in the material by tempering. |
| Molding process | After sintering, the blanks are brought into their final shape. For example, cylinders are ground down until they have the desired diameter. Blocks are brought into the correct shape on abrasive wheels and the surface is ground to a smooth finish._x000D_ The blocks are very hard and special tools are required for machining. The chips and powder must also be cooled with cooling fluid to avoid spontaneous ignition._x000D_ Magnets can be produced in a variety of variants:_x000D_ Neodymium magnet with hole_x000D_ Rubberized neodymium magnet_x000D_ Rectangular, round, cylindrical magnets_x000D_ Self-adhesive neodymium magnets_x000D_ Small and large neodymium magnets_x000D_ |
| Coating | This is followed by coating, which will protect the magnet against future oxidation. The coating can for example be made of nickel or epoxy and gives the magnet its typical appearance. |
| Magnetization | The magnet is finally magnetized in the last step. At this point, no magnetic properties remain due to the heat treatment. For magnetization, the neodymium magnet is exposed to an extremely strong and purposefully aligned magnetic field. |
After magnetization, the magnets are ready for use:
Properties of Neodymium Magnets
Neodymium magnets have a number of beneficial properties:
- High magnetic force: Neodymium magnets are extremely strong.
- Compact size: Compared to other magnets, they can be manufactured to be very lightweight and compact due to their high magnetic force.
- Miniaturization: Their small size at the same magnetic force influences the devices in which they are installed. Electronics and other devices can as a result be built much smaller.
- Efficient energy conversion: They are, for example, used in wind turbines where they increase the efficiency of electric motors due to their higher magnetic force and the ability to reduce the inertial mass, thus contributing to the production of clean energy.
- Durability: Neodymium magnets retain their magnetic properties for a long time.
However, they are also brittle, making them susceptible to fragmentation. Sintering makes them very hard and difficult to machine. Neodymium magnets are shock sensitive and are susceptible to corrosion without coating. Attention must be also paid to foreign magnetic fields when using them. Foreign, differently-oriented magnetic fields can result in partial to total loss of magnetic properties for neodymium magnets.
Instructions for use
The following precautions apply when installing magnets:
- They are very fragile, i.e. no further machining options are available.
- The magnet is shock sensitive and must be installed with care.
- Magnetic radiation can have a negative effect on the following items: electrical devices such as cell phones, PCs, watches and medical devices such as pacemakers.
- At temperatures above the maximum operating temperature, the magnetic force may decrease.
- Severe shock or changes to the magnets can reduce the magnetic force. A distance of 0.1 ~ 0.3 mm from the base body must be maintained to prevent direct shock impact on the magnets.
Neodymium magnets installation instructions
- 1 - Workpiece
- 2 - Housing
- 3 - Neodymium magnet
One should therefore carefully plan in advance what environment the neodymium magnet is used in and what groups of persons can be permitted to work near the neodymium magnet.
The following temperature ranges are considered as a reference for the various magnets:
Temperature ranges of different magnet compositions
- 1 - High-strength version - Neodymium magnet
- 2 - Neodymium magnet
- 3 - Heat resistant neodymium magnet
- 4 - Samarium-cobalt magnet
- 5 - Ferrite magnet
- 6 - AlNiCo magnet (AlNiCo)
Neodymium magnet maintenance
Maintenance and care of neodymium magnets is important to maximize their service life and to ensure that they retain their magnetic properties. The following measures extend the service life of neodymium magnets:
- Protection against shock and mechanical stress: Due to their brittle structure, neodymium magnets can break easily. Avoid subjecting them to hard impacts or dropping them.
- Corrosion protection: Corrosion can cause the performance of neodymium magnets to degrade. This can be prevented by a suitable coating. They should also be stored in a dry place.
- Protection against excessive temperatures: High temperatures can cause loss of magnetic properties. The temperature limits should therefore always be observed. They should be stored in a cool place.
- Demagnetization: Neodymium magnets can get demagnetized in proximity to other strong magnetic fields. They should therefore be used or stored outside the range of such magnetic fields.
Using Neodymium Magnets
Neodymium magnets are for example used in permanent magnet rotors (e.g. stepper and servo motors) or linear motors for positioning axes, such as in CNC applications. Some examples are explained in more detail below.
Neodymium magnets in linear motors
Neodymium magnets are for example used in linear motor rotors. They produce an extremely strong magnetic field there. Conversely, a magnetic field is generated in the stator by electrical current (coils). The rotor now moves along the line induced by the interaction between the two magnetic fields. Depending on the design of the linear motor, the permanent magnets can also be placed on the stator and the rotor can be equipped with coils. This principle is generally used in many motors or even generators. A selection of motors can also be found in our MISUMI shop.
Neodymium magnets in couplings and brakes
For example, a magnetic field transfers torque without direct mechanical contact between rotating and stationary parts. Brakes and magnetic couplings consist of a rotor and a stator. Here too, the rotor is equipped with a neodymium magnet. The magnetic interaction between the magnetic fields of the rotor and stator then leads to different reactions: in a coupling , the rotor is connected to the stator, in a brake, the rotor presses against the stator.
MISUMI allows you to choose from a wide range of neodymium magnets as well as other magnets.
