Neodymium magnet production and special features of these super magnets
Apart from electromagnets, neodymium magnets are the strongest in the world. Its adhesive power is very high even in small designs and should never be underestimated. Ferrite magnets do not come close to this strength. However, what are neodymium magnets? How are these super magnets actually made? Information on this can be found in this guide.
How are neodymium magnets produced?
The production of strong neodymium magnets takes place in several consecutive steps. They consist, as the name suggests, of neodymium among others. This substance belongs to the so-called rare earths, and is assigned to the lanthanides. The metal occurs in nature only in chemical compounds - mostly together with minerals. In order to promote the substance and to separate it from the other connected substances, an extraction - for example in an electrolytic furnace - is necessary. The obtained neodymium represents one of three basic materials for neodymium magnet production.
In the next step, an alloy of neodymium, iron and boron must be produced (chemical: NdFeB). The fabrics are weighed and then placed in a vacuum induction furnace. Each magnet manufacturer swears by its own recipe and mixes the basic materials with other elements such as cobalt or copper. With these additions, the magnets can eventually take on additional properties, such as corrosion resistance. In the oven, the mixed substances are fused together. Subsequently, the resulting alloy is placed in molds. Depending on the composition, the quality of the neodymium magnets varies after production.
The resulting shapes are then directly grinded up again or embrittled and brought to a grain size of about three microns. The fine powder has been pressed and compacted several times and with different techniques. At the end of the so-called green body remains, which has only a very small magnetic and has a brittle consistency.
The last manufacturing step is sintering. In this process, the alloy is compacted 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, which 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 still do not look high quality. Two additional steps are necessary to refine the surfaces of the neodymium magnets after fabrication. First, they are sanded to remove rough spots and bumps. According to the given tolerances, you can still bring the material to the desired size. If the magnet has the correct dimensions, the surfaces must be sealed with a protective layer. For this step, the material must be thoroughly cleaned and dry. There are many different magnetic coatings for neodymium magnet production. The most commonly used coating is a Ni-Cu-Ni coating, i.e. a composition of nickel-copper-nickel. Other possible coatings are:
- Gilding (Ni-Cu-Ni-Au)
- Chromium (Ni-Cu-Ni-Cr)
- copper (Ni-Cu)
- epoxy resin (Ni-Cu-Ni-Epoxy)
- zinc (Zn)
Now only the actual magnetization is missing. This process of neodymium magnet production is implemented with a magnetic coil whose magnetic force is at least three times as high as the desired strength of the new magnets. The charge with magnets must be well fixed before the process begins because otherwise they will immediately repel each other after magnetization. The coil emits a magnetizing pulse to the raw magnets, which causes a reorientation of the crystals in their interior. 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. They are, compared to ferrite, 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). To illustrate the difference between ferrite and neodymium magnets, there is a numerical example: ferrite magnets usually have an energy density of about 30 kJ / m3. Neodymium magnets, on the other hand, have an almost 20 times higher maximum energy density, namely around 500 kJ / m3. Most of these are not used in the private sector, but are preferred in industry or similar areas of work. The reason for their enormous adhesive power lies in the chemical compound and the crystal structure. This has a large anisotropy and extremely high coercive field strengths.
How dangerous are super magnets made of neodymium?
The use of neodymium magnets should always be well thought through. Their extremely high adhesive force can lead to excessive bruising or even fractures, if handled carelessly. Often the metals have hard edges that can injure the skin if handled incorrectly. Therefore, you should wear padded gloves for all magnetic applications. When merging two magnets, you should also keep in mind that from a certain distance they might self-tighten and cause unexpected danger situations. The neodymium alloy is brittle in this state. Due to the high forces, metal chips can shatter from the magnets in an impact of the material and thus injure the skin.