What are neodymium magnets

The neodymium magnet production and special features of these super magnets

Apart from electromagnets, neodymium magnets are the strongest in the world. Their adhesive force is very high even with small versions and should never be underestimated. Ferrite magnets do not come close to this strength. But what are neodymium magnets and how are these super magnets actually made? You can find information on this in this guide.

How are neodymium magnets made?

The production of strong magnets from neodymium takes place in several successive steps. As the name suggests, they consist of neodymium, among other things. This substance belongs to the so-called rare earths and is assigned to the lanthanoids. The metal occurs naturally only in chemical compounds - mostly together with minerals. In order to convey the substance and to separate it from the other connected substances, an extraction - for example in an electrolysis furnace - is necessary. The neodymium obtained is one of three basic materials for the manufacture of neodymium magnets.

In the next step an alloy of neodymium, iron and boron has to be produced (chemically: NdFeB). The substances are weighed and then placed in a vacuum induction furnace. Every magnet manufacturer swears by its own recipe and adds other elements such as cobalt or copper to the basic materials. With these additions, the magnets can ultimately take on additional properties, such as corrosion resistance. The mixed substances are fused together in the furnace. The resulting alloy is then put into molds. Depending on the composition, the quality of the neodymium magnets varies after manufacture.

The resulting shapes are then directly ground or embrittled again and brought to a grain size of approx. Three micrometers. The fine powder has then already been pressed and compacted several times using various techniques. In the end, what is left is what is known as the green compact, which has only a very low magnetic effect and a brittle consistency.

The last manufacturing step is sintering. In this process, the alloy is compressed and fired both under high pressure and at high temperatures. This creates the final shape of the magnets. After this process, the blanks are finally cooled down slowly. Various chemical reactions ensure that the magnet consists of a special crystal structure that is particularly beneficial for later magnetization.

The surface treatment turns a blank into a magnet

The cooled magnets are technically finished after sintering, but they don't really look high quality. Two further steps are necessary to refine the surfaces of the neodymium magnets after manufacture. First, they are sanded to remove rough spots and bumps. According to the given tolerances, the material can still be brought to the desired size.

If the magnet has the right dimensions, the surfaces must be sealed with a protective layer. For this work step, the material must be thoroughly cleaned and dry. There are many different magnetic coatings for the production of neodymium magnets. The most frequently used coating is a Ni-Cu-Ni coating, i.e. a composition of nickel-copper-nickel. Other possible coatings are:

  • Gold plating (Ni-Cu-Ni-Au)
  • Chromium (Ni-Cu-Ni-Cr)
  • Copper (Ni-Cu)
  • Epoxy resin (Ni-Cu-Ni-epoxy)
  • Zinc (Zn)

Now the only thing missing is the actual magnetization. This process of neodymium magnet production is implemented with a magnetic coil, the magnetic force of which is at least three times as high as the desired strength of the new magnets. The batch with magnets must be firmly fixed before the process begins, because otherwise they will immediately repel or attract each other after magnetization. The coil emits a magnetization pulse to the raw magnets, which realigns the crystals inside. From this point on, the blanks are permanently magnetized.

Why are neodymium magnets so strong?

Neodymium magnets are also often referred to as super magnets. Compared to ferrite magnets, they are much more attractive. Some of them hold six hundred times their own weight. The energy density is given in kilojoules per cubic meter (kJ / m3). A numerical example can be used to illustrate the difference between ferrite and neodymium magnets: Ferrite magnets normally have an energy density of approx. 30 kJ / m3. Neodymium magnets, on the other hand, have a maximum energy density that is almost twenty times as high, namely approx. 500 kJ / m3.

Magnet type
 ferriteNeodymium
Energy density30 kJ / m³500 kJ / m³
scope of application


Private sector, household


Industry

 

 

These are mostly not used in the private sector, but preferably in industry or similar work areas. The reason for their enormous adhesive force is due to the chemical connection and the crystal structure. This has a large anisotropy and extremely high coercive field strengths.

How dangerous are neodymium super magnets?

The use of neodymium magnets should always be well thought out. Their extremely high adhesive strength can lead to severe bruises, bruises or even broken bones if handled carelessly. The metals often have hard edges that can damage the skin if handled incorrectly. Therefore, you should wear padded gloves with all magnet applications.

When bringing two magnets together, you should also bear in mind that from a certain distance they will attract themselves and this can lead to unexpected dangerous situations. The neodymium alloy is brittle in this state. Due to the high forces, metal chips can splinter off the magnets in the event of a material impact and thus also injure the skin.