What Kinds of Permanent Magnets
Permanent magnets have become indispensable in today’s technology-focused world. The many different magnetic materials and their manifold characteristics have firmly established permanent magnets as important elements in countless application fields. In addition to the proven materials ferrite and AlNiCo, modern magnets are also made from rare earth materials such as neodymium-iron-boron and samarium-cobalt. Even small magnets made from these materials offer strong magnetic force and thereby cater to the growing demand for smaller and stronger magnets.
Permanent magnets also play a key role in the growing field of automation technology, where it is essential to continue the development of drives, actuators and sensors. A particular leap in the direction of future technologies was the discovery of the new materials samarium-cobalt and neodymium-iron-boron. Some of the particularly suitable applications are products that can only function with permanent magnets, including e-bikes, electric drives in the automotive sector and hybrid cars. The generation of green energy from wind and hydropower as well as other types of modern generators also depends on the use of permanent magnets.
Another important area that uses permanent magnets is sensor technology. Permanent magnets are in demand wherever measurements must be transmitted indirectly. Under difficult environmental conditions (dust, temperature, humidity etc.), they are frequently the only possible way of recording measurement data.
Hard ferrite magnets
Hard ferrites are the least expensive and globally most commonly available of all magnetic materials. They are ceramic materials, and thus very hard and brittle.
Compared to other metallic materials, the magnetic properties of hard ferrite permanent magnets are fairly weak. Their benefits include lower costs as well as a higher resistance against corrosion and chemicals. They are also easy to magnetize and suitable for many different applications.
Permanent magnets made from AlNiCo are frequently used in applications that require a resistance to high temperatures of up to 500 °C (930 °F). They are metallic permanent magnets on the basis of an aluminum-nickel-cobalt alloy. Additional metals such as iron, copper or titanium are sometimes added to the alloy.
The great magnetic stability when exposed to temperatures, the temperature coefficient and a high remanence make this easily magnetizable material an interesting option for different applications.
However, one has to take into account that the low coercive field strength of AlNiCo magnets makes them easily demagnetizable.
SmCo magnets consist of samarium (Sm) and cobalt (Co). With respect to the two possible alloy compositions, a distinction is made between Sm1Co5 and Sm2Co17, also referred to as 1/5 alloy and 2/17 alloy. These materials are part of the group of rare earth materials, and permanent magnets made from them offer a high temperature stability and corrosion resistance, a low temperature coefficient and a very high coercive field strength.
This makes samarium-cobalt (SmCo) an extremely versatile but expensive all-round material. Magnets made from samarium-cobalt alloys are used in applications that require very strong magnetic fields in extreme temperatures.
Neodymium-iron-boron (NdFeB) is a material that is composed of the rare earth metal neodymium (Nd), iron (Fe) and boron (B). Magnets made from neodymium-iron-boron are often just called neodymium magnets; they boast the highest energy density of all magnetic materials and are used in applications that require extreme forces in the smallest possible space.
Permanent magnets made from neodymium can often be worked to conform with the desired geometry, which allows for the production of small quantities at reasonable prices.
When used in open spaces, it is recommended to apply metallic or non-metallic coatings to the NdFeB magnets in order to prevent corrosion and use them at higher temperatures of up to 200 °C (392 °F).
Plastic-bonded hard ferrite magnets
Plastic-bonded hard ferrite magnets are composite materials that consist of permanent magnetic powder made from hard ferrite and embedded in thermoplastic materials. Using injection molding, this material can be used to inexpensively produce complex or filigree shapes with different magnetic and mechanic properties. It is also possible to integrate axles, shafts and bearing bushes. Another advantage of plastic-bonded magnets is their high resistance against corrosion and breakage, although, of course, the magnetic performance of sintered magnets without plastic additives cannot be matched by plastic-bonded magnets.
Plastic-bonded neodymium-iron-boron magnets
Plastic-bonded neodymium-iron-boron magnets (NdFeB-p) are composite materials that consist of permanent magnetic powder made from NdFeB and embedded in plastic materials. Depending on the manufacturing technique, they can be either injection molded or pressed plastic-bonded magnets.
Compared to sintered NdFeB magnets, these plastic-bonded permanent magnets are particularly suitable for high-precision parts. It is also possible to integrate axles, shafts and bearing bushes.
Injection molding can be used to inexpensively produce complex or filigree shapes with different magnetic and mechanic properties. Another advantage of plastic-bonded magnets is their high resistance against corrosion and breakage. The highest magnetic performance within the product group of bonded magnets can be achieved by performing the injection within the magnetic field. However, due to the low fill quantity of magnetic powder, the performance of plastic-bonded neodymium-iron-boron magnets is still significantly lower than the performance of sintered magnets.