Paper: Elastohydrodynamics and mechanics of rectangular elastomeric seals for reciprocating piston rods.

Author: George K. Nikas

Abstract

A numerical model was developed to study the sealing performance of rectangular elastomeric seals for reciprocating piston rods used in linear hydraulic actuators. The model takes into account a large number of parameters and has been applied in the study of seals for aircraft actuation assemblies in a broad range of temperatures (-55 to +135 °C) and sealed pressures (1-50 MPa or more). The model is used to calculate the contact pressures and film thickness maps as well as the leakage rates and friction for the dynamic or static contact between a seal and a reciprocating piston rod, aiming at the minimization of both the leakage and the wear of the seals.

Some figures from this work

The seal configuration for the model is shown in Fig. 1. The hydraulic actuator contains fluid under pressure. The piston rod reciprocates and fluid leaks under the seal and escapes to the air side of the system.

Fig. 1. Configuration for the seal model.

Figure 2 below shows a typical example of  the elastohydrodynamic (EHD) pressure at the rod-seal contact for perfectly smooth surfaces (note: the whole of the contact is mapped in the figure). The pressure resembles macroscopically a rectangular block (orthogonal parallelepiped) but with some small deviations (edge effects) at the inlet and outlet of the contact.

Fig. 2. EHD pressure at the rod-seal contact (for perfectly smooth surfaces).

Figure 3 below shows a film thickness map at a rod-seal rough contact during an outstroke. Darker blue areas indicate thicker film whereas lighter blue areas indicate thinner film and red areas indicate roughness asperities in contact (zero film thickness). Notice the film collapse as the sealed pressure is decreased.

Fig. 3. Film-thickness map at a rod-seal rough contact (red areas indicate solid contact). From left to right, sealed pressure = 4000 lb/in2, 1000 lb/in2 and 10 lb/in2. From left to right, average film thickness = 2.1, 1.0 and 0.8 microns.