Magnets can be used in vacuum applications; however, some special considerations are required in the following areas:
Select a permanent magnet that is not from the bonded group. Bonded magnet materials are made by using resins to bind the powder. The resins are polymeric materials, such as thermoplastics or thermosetting resins, rubber, or elastomers, such as nylon. These materials have high TML (Total Mass Loss) and CVCM (Collected Volatile Condensable Material) values. Rare-earth magnets (Samarium Cobalt or Neodymium Iron Boron), Alnicos and Ceramics are suitable.
Magnet materials may be utilized without coating in low vacuum conditions, but under high vacuum conditions, pressures lower than 10-3 Torr, surface treatment should be considered. Metallic surface treatments are the most desirable, since polymer coatings will outgas, however, our PR1010 has been tested and found to meet standards considered very good for space applications (see outgassing characteristics on the technical data sheet for PR1010). MCE offers the following types of surface treatments that are vacuum compatible:
The pole piece or return path should be selected carefully. Consider using stainless steel CRES410, or if the material is prone to oxidation, consider Nickel plating. If you are using CRS1010, CRS1018 or other low carbon steel, or specialized steels such as Vanadium Permendur, Hiperco 50, Carpenter 50 or equivalent, Nickel plating is recommended.
Magnets can be secured in one of two ways:
If the magnet will be secured mechanically, outgassing is less of an issue. The less materials that are used that have a potential for outgassing, the better off you will be.
If the magnet is secured using bonding materials, make sure to use advanced epoxies and adhesives that have low TML and CVCM values. MCE offers a number of epoxies. Call us before deciding, and we will work with you on selecting the correct adhesive or epoxy.
Putting the parts together is very important. The parts MUST be carefully cleaned. Handling should be done by use of clean room compatible gloves. In very low pressures, even a fingerprint is a problem. We do not suggest doing this yourself. MCE has the experience necessary to put together an assembly that will be vacuum compatible. All assemblies that are manufactured for vacuum applications are done under the direct supervision of our Engineering Department.
Packaging should be done very carefully. Parts must be wrapped in a special “clean room compatible” paper. Subsequently, double bagging in a clean room semiconductor grade plastic bag is recommended. The bags should be vacuum-sealed to prevent any condensates or oils from settling on the parts during shipping. ffdas