All Bearings before reaching the users have been 100% cleaned. During manufacturing, Bearings will be cleaned by specialized machines to clean dust smaller than 5mc (20 times smaller than which can be observed).
During long term use, Bearings will be contaminated for many reasons. Then, the most common and effective remedy is to change grease/ oil for them. However, if you do not know how to clean before changing grease/ oil, Bearings will even dirtier. Contamination of Bearings causes it’s life shortening.
How to clean Bearings properly?
Before changing grease/ oil, we should use hot oil to wash Bearings to remove dirt. For large size Bearings, you can use a strong alkaline solution to rinse while the shaft is rotating for greater efficiency.
Fluorine can be used for cleaning
Using Hydrocarbon for lubrication is good for the movement of Bearings
Use oilfree solvent for cleaning to not damage the Bearings.
Caution: If apply these methods for Bearings with plastic (polyamide fibers) seals, premature damage may result.