Other important factors are ensuring the hardness and roughness of the shaft are correct. A shaft hardness of HRC 45 is recommended for a rubber sealing lip, with a roughness of Ra 0.4-0.8. A higher shaft hardness of HRC 60 and shaft roughness of Ra 0.1-0.4 is recommended for a PTFE lip.
Oil seals are installed beside the bearing while the flexible lip is pressed against the rotating shaft. The casing pressing into the housing holds the seal in place. The sealing lip is essentially lubricated to minimize the risk of overheating due to the generated friction.