Abstract
Hydraulic, reciprocating, polymeric seals are met in many engineering applications and are critical components for mechanism and machine reliability in industries including the automotive, marine, and aerospace industries. A parametric and optimization study of rectangular-rounded, hydraulic, reciprocating, elastomeric rod seals at −54, +23, and +135 °C is presented, which is particularly relevant to hydraulic actuators in aircraft landing gear. Parametric optimization not only improves performance, but also helps avoid sealing failures. The calculations were based on a physically based, deterministic mathematical model of such seals, experimentally validated at the aforementioned temperatures and recently published by the author. The parameters varied were the seal axial width and corner radius, seal elastic modulus, sealed pressure, stroking velocity, operating temperature, rod surface roughness, seal radial interference, and seal swelling by fluid uptake. Their influence was established based on the following performance variables: leakage rate, frictional force, coefficient of friction, temperature rise in the sealing contact, lambda ratio (proportional to the average film thickness in the contact), and ratio of the asperity friction force to the total friction force. The parametric study greatly facilitates the selection of optimal values of the analyzed parameters to minimize leakage, friction, and wear, either concurrently as a set or individually, depending on application priorities.
Highlights
Rectangular-rounded, elastomeric, hydraulic seals (Figure 1) for reciprocating motion are used in a variety of applications such as in the automotive, aerospace, and marine industries.They constitute the simplest design of reciprocating seals together with the typical toroidal seal (O-ring).The materials they are made of obey nonlinear stress–strain laws of hyperelasticity or thermoviscoelasticity [1,2,3]
A numerical algorithm is devised to ascertain that both the average film thickness and the temperature rise in the sealing contact converge within predetermined narrow limits as indicated in the flowchart of the hydrodynamic friction force, which relates to the viscous friction of sealed fluid in areas of the sealing contact other than asperity micro-contacts; the asperity friction force, which is calculated by the statistical contact mechanics sub-model and in effect of van der Waals stresses, with various nanofilm and material strength constraints as previously explained; the deformation force, which emanates from the ploughing of rod roughness asperities through the softer asperities of the seal
It is clear that an elastic modulus of about 5 to 20 MPa gives low frictional force and low leakage rate. This is, a typical value range for elastomeric rod seals used in aircraft hydraulic actuators as in the present case [5,8,9,10,11,12,32], which gives reason to believe that this selection by the industry is purposeful and well established in practice
Summary
Rectangular-rounded, elastomeric, hydraulic seals (Figure 1) for reciprocating motion are used in a variety of applications such as in the automotive, aerospace, and marine industries. The present study is based on a recently published numerical model of the author [6] and in-house developed software ROSEAL, which analyzes rectangular-rounded, elastomeric, hydraulic rod seals in reciprocating motion. The model is almost entirely analytical and mostly based on explicit algebraic equations to deal with the solid mechanics, contact mechanics of rough surfaces, and thermoelastohydrodynamics of a rod–seal tribopair It incorporates a large number of design parameters and variables, and it is numerically optimized to compute sealing performance in terms of leakage, friction force, and a multitude of other parameters in infinitesimal time The results show that sealing performance is a complex, multivariable, nonlinear problem involving solid and contact mechanics, materials science, and lubrication, and it requires attention to detail to master Inspecting these results on the simplest of seal geometries reveals sealing principles that can be adopted to geometries other than rectangular-rounded and toroidal
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