Magnetic Component Engineering

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Surface Treatment of Magnet/Steel Assemblies


Magnets are typically used with steel structures. To retard corrosion, it is desirable to use some type of surface treatment on the magnets and on the steel structures, especially low carbon steels. This article covers aspects of surface treatment to the magnet/steel structure as one assembly.

The following factors should be considered:

  1. Materials
  2. Bonding Materials
  3. Magnetizing

Materials

Typically, the plating process for rare earth magnets is different from the plating processes for metals. For example, our neodymium iron boron (NdFeB) can only be plated by some of our proprietary processes which are all electrolytic based. Steel structures can be plated per Military or Federal Specifications, and these can be electroless or electrolytic. The pretreatment process of Neodymium Iron Boron is different from the pretreatment process of metal components. Therefore, using a pretreatment that is compatible with one material will be incompatible with the other material, and will lead to failure of the plating on either the magnet or the metal. Similar problems can occur with samarium cobalt magnets. MCE does not plate rare-earth magnets in metal structures and does not recommend that customers plate our magnets in magnet/steel structures and assemblies.

Surface treatment using polymer coatings, such as our PR1010, can be successfully achieved as long as magnetic demagnetization due to elevated temperature cure is taken into account.

Alnico magnets are typically plated using standard plating processes that would be used for metals. Magnets can be assembled onto a steel structure and then plated; however, before proceeding with a large batch, small test runs are recommended.

Ceramics are non-conductive. Typically, metallic platings will not adhere to them. Specialized processes for "metalizing" ceramics are known, but are costly and are not offered as standard surface treatments at MCE. Ceramics can be coated with the polymer coatings PR1010. Bonded Neodymium Iron Boron and Bonded Samarium Cobalt fall in the same category.

Bonding Materials

Select the appropriate bonding materials before plating or coating a magnet assembly. For example, our PR1010 coating is cured at elevated temperatures. The adhesives or epoxies used to bond the magnet to the structure must be able to withstand the coating cure temperatures.

Magnetizing

Occasionally, magnets may need to be magnetized prior to assembly. Surface treatment of magnetized structures may be expensive or not possible. For example, if the magnet material has a low "maximum operating temperature" such as N5064, and you select PR1010 as the post assembly coating, the magnet assembly will lose its field strength during the coating cure cycle. Post assembly magnetizing should be explored.