3.2 Lip Seals

The lip seals currently used for sealing rotary shafts have evolved from the lip seals made from leather used during the 1930s. The development was largely empirical for some 50 years or more and it was not until the 1990s that detailed mathematical analysis of the seals gave a more established basis for understanding the detail of how these seals operate.

The types of seals in common use can be divided into three broad categories:

• Elastomer lip seals, which are used for sealing of shafts against exit or ingress of liquids.

• Plastic, primarily filled PTFE, which are used as an alternative to elastomer seals where fluid resistance or lack of lubrication may be a problem.

• Bearing seals, which are really a derivative of lip seals that usually operate at lower lip loads and have exclusion of contaminants from the bearing as a prime function.

This section covers the basic operation of lip seals and then discusses the detail of the different options available.

In common with other elastomer and plastic seal types it is important to remember that this component is only part of the seal. The housing to which it is fitted and the shaft that rotates within it are equally important. With lip seals the shaft is a particularly important component of the seal as in addition to the surface texture, the machining method is also an important factor affecting seal performance. The thermal conductivity of the shaft is the primary factor affecting heat dispersion...