Book chapter: Research on the tribology of hydraulic reciprocating seals. (46 pages, 147 references.)
Author: George K. Nikas
Published in: chapter 1 (pp. 11-56) in the book "Tribology Research Trends" (Ed.: T. Hasegawa). Nova Science Publishers, New York, USA, 2009. ISBN: 978-1-60456-912-4.
Download a PDF copy of this chapter (8.9 MB)
Hydraulic seals are found in industrial applications involving linear or rotary motion, as for example in hydraulic actuators. They are usually made of a polymeric material (for example, elastomer or “rubber”) or a combination of materials (composite seals, for example, elastomer and PTFE with glass fibres). Their shape varies from the typical rectangular cross-section with chamfered or rounded corners and the typical O-ring to hundreds of less conventional designs with complex geometries, although they all have the same basic function, which is the sealing of fluids, normally under relatively high pressure (typically up to 80 MPa) and with operating temperature ranging from subzero values (typically as low as –65 °C) to relatively high values of up to 200 °C, depending on application. Low-pressure applications are also met when seals are used as wipers, as for example in tandem seal arrangements.
Theoretical research on sealing involves concepts and methods from elastohydrodynamics, contact mechanics, thermoviscoelasticity, adhesion and surface topography, in order to achieve good agreement with experimental results and industrial experience, yet this is still quite difficult to achieve because of the mathematical and numerical complexity of the problem. Proof of such difficulty is the fact that after more than 60 years of research in this field, fundamental aspects of the problem are still being tackled, for example, elastohydrodynamics with surface roughness effects, whilst making simplifying assumption about others, for example, treating seal mechanics in the frame of linear elasticity and ignoring frictionally induced, thermal effects.
The present chapter explores the progress and research trends in computational and experimental tribology of hydraulic, reciprocating, rod and piston seals. Topics include the solution of the elastohydrodynamic and contact mechanics problem of flexible polymeric and composite seals, the modelling of seal extrusion and anti-extrusion rings, seal elasticity and its effect on sealing performance, the modelling of tandem seals, rotary vane seals, transient effects in lubrication, as well as performance evaluation in terms of leakage, friction, extrusion and wear, followed by optimization. Experimental studies are also briefly discussed, together with a presentation of the difficulties in validating existing models and in producing realistic, reliable and consistent results. The review covers the period from the 1940s to 2008 and serves as a reference source for further study and development in this challenging field, from the original basic experimental rigs and archaic computers of mid 20th century to the sophisticated numerical methods and expensive experimental devices of the recent era.