Parylene on magnets have long been associated with medical and technology applications. They provide a durable coating that is resistant to corrosion, and are available in Parylene C, D and N. Several factors should be considered when exploring parylene coatings so let’s take a look at these factors when choosing parylene.
Process, Controls & Repeatability
Parylene coatings are generally done in three phases, Vaporize, Pyrolize, and deposition. Without going into detail of each part of the process, the main point to understand is that the process, controls and repeatability of the parylene coating process are vital to a uniform, thorough coverage. Understand how the process will be done at any parylene coating facility, and the controls within the process to ensure the coating is completely covering the magnet without voids, pits or scratches.
The controls and processes to parylene coat a magnet are usually very similar from magnet to magnet, however, request that your coating facility define and document the process once it has been finalized after testing and evaluating a lot, or several lots. This will allow the process to be the same every time and repeatability from lot to lot. Of course there are other variables within the process that can cause issues, but starting with a defined process with quality controls implemented before, during and after the coating process should reduce waste, scrap, and rejected parts.
Magnet Size & Shape
Magnet size and shape are a main factor in determining if the coating process will be done in a chamber that is continually rotating, or an environment where the magnet will be held stationary.
Smaller magnets will be done in a rotating chamber. This means the magnets are in constant motion and all sides should be equally exposed and coated evenly. However, this process will undoubtedly result in scrap magnets that don’t get complete coverage, so the quality control testing done after this process will be important. While it seems that this process should yield 100% success, the coating facility will do everything possible to reduce rejections. Our experience has been that rejection rates can run as low as 10%, and as high as 50%.
Bigger magnets are usually parylene coated in a stagnant environment so they are not tumbling against each other causing damage. These magnets are held in place with a clamp, which will cause areas where the parylene is unable to adhere. It will be important to know how the parylene coater will fill in these voids once the magnets are detached from the clamp.
Thickness of the Coating
One of the benefits of parylene is that it can be applied very thin, around 5-10 microns. However, this thickness may not be enough for some applications and a thicker coating should be considered. But, going thicker is not always better, nor is going thinner. It will depend upon your application and the environment where the magnet will perform.
Magnets that are subjected to an environment where they are banging together or hitting or grinding against other parts, may experience scratches and chips in the coating that can cause oxidation. In some applications, doubling the thickness of the coating may help, but check your tolerances to make sure the extra thickness can be used.
Environments that experience heat above 220C can have an effect on the coating. It is recommended that the coating is tested thoroughly to ensure the coating can withstand the heat. As a note, this heat test should be considered when looking at all parts of the manufacturing process to ensure the parylene coated magnet is not experiencing heat at some point. For example, one application that we worked on with a customer had a spec for the coating of 100 C. This was not an issue for the parylene coating, however, we encountered part of the manufacturing process where the parylene magnet was put into a sleeve and the sleeve was heated up to almost 250C in order to shrink the sleeve around the magnet. This heat was causing issues with the parylene.
Overall, parylene is a very solid coating for a variety of applications. Check with one of our technical sales staff to understand if this is right for you. And, please share your comments and experience with Parylene to assist others.
About SM Magnetics: SM Magnetics is privately owned company, providing assistance with permanent magnets, magnetic design & optimization, engineering support, and production. SuperMagnetMan is the online retail division of SM Magnetics offering neodymium magnets and other materials.