Zur Schmierfilmbildung und Reibung von Stangendichtungen

Abstract

Rod seals are crucial machine elements for hydraulic and pneumatic cylinders. During the outstroke and instroke of a cylinder, the piston rod drags a thin oil film into the sealing gap forming a lubrication film. The oil film formation and tribological mechanisms in the sealing gap are of great technical interest due to their influence on friction, wear and leakage. In empirical tests with different sealing systems and operating conditions, the oil film formation and friction of rod seals were analyzed. The film thickness was measured using ellipsometry. For the friction measurements, a common test arrangement described in ISO 7986 was used. Additionally, a new measurement procedure, which combines film thickness measurements and friction measurements, is introduced. Different polyurethane U-cups and different lubricants were used for the empirical tests. Based on the results, the influence of operating conditions (rod speed, pressure, temperature) and properties of the sealing rings (hardness, surface energy, roughness) and lubricants (viscosity, surface tension) on the oil film formation and friction are discussed. It is remarkable that the analysis of the oil film formation in the nanometer range was successful, and the measured friction can be approximated by Newtonian fluid friction (speed, film thickness, viscosity, contact area). A correlation between wetting properties and the friction of the rod seals was not observed.