Applications in a vacuum are primarily a lubrication issue. Performance factors are often sacrificed for function in a vacuum.
Lubrication
Lubricants for vacuum applications must have a low vapour pressure of the base oil. Depending on the vacuum and temperature, there is a risk of outgassing. This reduces the performance of the grease/oil and contaminates the vacuum.
Synthetic base oils such as PAO / ester oil or PFPE with a low vapour pressure curve are predominantly used.
Solid / compound lubrication
Greases and oils can no longer be used as the temperature and negative pressure increase. Suitable solid lubricants are MoS2 and PTFE, graphite is not suitable.
If the solid lubricant is introduced into the bearing as a compound, applications with continuous temperatures of 350°C and more can be achieved in a high vacuum. Compound lubrication is a transfer lubrication, i.e. the lubricant is transferred to the raceway and rolling elements. The service life is long at high speeds.