Surface finishes as rough as 64 to 128 micro-inches RMS can be tolerated. However, a finish of 32 micro-inches RMS is preferred.
Surface finish (S)
- 32 for liquids
- 16 for vacuum and gases
A highly polished surface is not desirable because it will not hold lubricant. The most desirable metal surface roughness value for dynamic seal applications is from 10 to 20 micro-inches. A shot-peened or electro-polished surface is ideal, because it provides many small pockets in the metal for entrapment of lubricants. The best surfaces are honed, burnished or hard chrome plated. Softer metallic surfaces, such as aluminum or brass, should generally not be used for dynamic applications.
Shaft composition should be of a relatively hard metal and be within 0.0005″ TIR. Additionally, it is recommended that shaft surfaces be finished to 16 RMS (for smooth, non-abrasive running), with gland surfaces finished to a rougher 32 RMS (to discourage o-ring movement within the gland).