Remarks on Modeling the Oil Film Generation of Rod Seals

• Main Authors: Oliver Feuchtmüller, Nino Dakov, Lothar Hörl, Frank Bauer
• Format: Article
• Language: English
• Published: MDPI AG 2021-09-01
• Series: Lubricants
• Subjects: hydraulic rod seal; film thickness measurement; elastohydrodynamic simulation; Reynolds equation
• Online Access: https://www.mdpi.com/2075-4442/9/9/95

The oil film generation of a U-cup rod seal and the oil film thickness on the rod after outstroke were analyzed analytically, numerically, and experimentally. The analyzed sealing system consists of an unmodified, commercially available U-cup, a polished rod, and mineral oil. The inverse theory of hydrodynamic lubrication (IHL) and an elastohydrodynamic lubrication (EHL) model—both based on the Reynolds equation for thin lubricating films—were utilized to simulate the oil film generation. In the EHL analysis, physical parameters and numerical EHL parameters were varied. Both the analytical and numerical results for the varied parameters show that the film thickness follows a square-root function (i.e., with a function exponent of 0.5) with respect to the product of dynamic viscosity and rod speed, also referred to as the duty parameter. In comparison to the analytical and numerical results, the film thickness obtained via ellipsometry measurements is a function of the duty parameter with an exponent of approximately 0.85. Possible causes for the discrepancy between theory and experiments are discussed. A potential remedy for the modeling gap is proposed.