We have been asked many times about the shelf life of […]
We have been asked many times about the shelf life of permanent magnets and the service life of neodymium magnets. The simple answer is, no, there is no shelf life; however, everything has magnets, and things are not that simple.
The shelf life indicates when a product can no longer perform its intended function, or becomes unhealthy or dangerous. In order for the permanent magnet to no longer perform its intended function, it needs to partially or completely lose its ability to generate a net external field. The extent of this loss will determine the performance of the magnet.
Therefore, if the magnet is placed alone on a shelf that is not affected by the outside, only "magnetic creep" may cause the magnet's magnetic field to weaken. When the magnet begins to yield to the self-demagnetizing force, "magnetic creep" occurs. Generally, for a well-designed magnet that is not subject to any other pressure, even small changes can take a long time to achieve. What is long time? From a few years to several decades, it depends on the magnetic alloy.
However, in the real world, we must store, handle, pack, count and other magnets, and they may encounter other negative factors. What factors will a magnet encounter in storage will negatively affect its ability to generate a net field?
Volume loss, external demagnetizing field and heat
Volume loss is the most prominent factor, which may be due to corrosion or impact that caused actual debris or part of the magnet to be removed. If the magnet is smaller, the magnetic field it can generate is lower. Since it is important to protect the magnet in its intended application, it must also be protected during storage.
To prevent corrosion, always store the magnet in a clean, dry environment. It is best to keep them in the packaging of the magnet supplier. Usually, magnets attracted in rows are provided, sometimes with spacers. The magnet should also be kept in the configuration provided by this supplier to eliminate the possibility of volume loss due to disposal where debris may occur.
The permanent magnet is magnetized by a very strong magnetic field. Sometimes, magnets may encounter magnetic fields from other magnets, which may cause damage. This is especially true when magnets with multiple different part numbers are stored in the same area. Larger, stronger magnets can generate a magnetic field, which partially demagnetizes smaller magnets. Some magnet alloys are more susceptible to this effect. Certain grades of Alnico (aluminum nickel cobalt) and ceramics (strontium ferrite) are the most sensitive alloys.
Steps to reduce the influence of external magnetic field:
Put the magnet in the packaging provided by the supplier
Keep the magnet continuously attracted, and the position of the attracting line
Separate packages and pads of different magnets
The following table shows the general tolerances of common commercial magnet alloys to corrosion, shock and external magnetic fields.
Heat always affects permanent magnets, but most storage and transportation methods will never reach a sufficient temperature, resulting in irreversible loss of magnets. However, high temperature will accelerate corrosion and negative effects of demagnetization. It is a good practice to store magnets in an environment where humans feel comfortable.
If you have older magnets, or magnets with suspicious storage history, you can take steps to assess inventory.