Lubricants are used to reduce wear of dynamic mechanical components. Radial shaft seals keep these lubricants contained in a cavity or sump.

Referring to the Hydrodynamic Effect, a radial shaft seal rides on a film of fluid when rotating. This lubricant film is the primary reason the lip does not harden due to excessive heat. The dissipation properties of the lubricant are important and can impact the life of a radial shaft seal.

The seal lip and the lubricant must be chemically compatible to prevent elastomer degradation. With high demands being placed on the lubricants, additives are used to improve performance of lubrication. Unfortunately, these additives may have a negative affect on the sealing element. The affect of a compatibility problem is often seen when the seal lip has experienced hardening without signs of heat or the lip is excessively soft from normal use. A complete list of the additives in the lubricant are essential for a thorough analysis. Table 1 shows a list of the different types of additives that may affect material selection (See Fluid Compatibility, page). If lubricant additives are unknown, a Material Safety Data Sheet (MSDS) can be obtained, listing each additive.

Common Additives used in Lubricants:

Additives Chemical Compounds
Antifoamants Silicone Polymers
Corrosion Inhibitors Overbased Metallic Sulfonates Phenates, Fatty Amines
Detergents Amines, Phenates, Succinimides
(EP) Antiwear Additives Organic Phosphates, Chlorine, Sulfer Compounds
Friction Modifiers Amides, Phosphates, Phosphites, Acids
Metal Deactivators Metal Phenates, nitrogen
Oxidation Inhibitors Aromatic Amines, Hindered Phenols
Pour Point Depressants LMW Methacrylate Polymers
Rust Inhibitors Esters, Amines, Sulfonates

Parameters Affecting Sealing: