Page 274 - The Tribology Handbook

Lip seals 523

Sealing lip material (rubber)

working Resistance to:
Typical trode
Qpe of rubber names temperature Relative cost of seal
range, "C Mineral oil Chemical jluids
Nitrile Hycar -40 to +IO0 Excellent Fair I
Poiysar
Acrylate Krynac -20 to +130 Excellent Fair 2
Cyanacryl
Fluoropoiymer Viton -30 to +ZOO Excellent Excellent 10
Pol ysiloxane Silastomer -70 to +200 Fair Poor 4

Nitrile synthetic rubber is the universal choice for sealing oil or grease at temperatures below IOO'C. For more extreme
temperature conditions the choice is normally one of the other materials shown in the table-with some penalty in other
directions. When in doubt consult the seal manufacturer.

Positive-action seals

Figure 23.7
(a) Section of a positive-action seal, showing the
helical ridges on the air side.

(b) View of contact band through a glass shaft,
showing one of the thread run-outs.

The 'positive-action' feature improves sealing performance and reliability. It is essential in conditions where eccentricity or
vibration is beyond the limit for a normal seal.

Storage and fitting

1. Store in a cool place in manufacturer's package. 3. Use a sleeve on the shaft to protect seal from damage by
2. Lubricate before installing. Handle carefully. sharp edges, keyways, etc.
4. Press home squarely into housing, using a proper tool.

623.3