Dynamic Seals Commonly Used in Mechanical Industry - Dynamic seals for rotating shaft

In mechanical engineering, sealing is said to be dynamic when it is applied between two parts in relative motion, which may be rotational and/or translational. When there is no movement between the parts, sealing is said to be static. The latter is covered in [BM 5 418] .

Dynamic sealing is considerably more involved than static sealing. A dynamic seal must seal at rest, just like a static seal. It must also be capable of performing this task in motion, taking into account frictional forces and the heating of dynamic surfaces.

Containing a gas or liquid, by its very nature, is not easy. The permissible leak rate depends on the nature of the fluid to be sealed; leakage of expensive, toxic, corrosive, explosive or flammable fluids must be kept to a minimum. Seal life and reliability are also major concerns for users, to reduce equipment and process downtime.

Seal failure can have multiple consequences, in terms of equipment availability, operation and safety. Common examples show that highly complex assemblies, such as landing gear, can experience major problems as a result of a simple leak. Good dynamic sealing reliability is not often easy to achieve.

In fact, dynamic sealing calls on many notions of physics and chemistry, in which the properties of materials and dynamic contact surfaces play an important role. In addition, the problems to be solved are varied, involving a large number of parameters that are difficult to optimize simultaneously. The best solutions for mechanical sealing in general, and dynamic sealing in particular, are almost always the result of skilful compromises.

This article is dedicated to dynamic rotary shaft seals. It describes the different technologies of dynamic seals for rotating shafts according to the different degrees of sealing: rigorous, controlled and relative. It complements [BM 5 419] , which deals with dynamic seals in translation.

At the end of the article, readers will find a glossary and a table of the notations used.