Visco-Elastohydrodynamic (VEHD) Lubrication in Radial Lip Seals: Part 1—Steady-State Dynamic Viscoelastic Seal Behavior

Abstract

In general, most analyses of radial lip seal behavior assume a static deformation state in the seal lip. Nevertheless, a dynamic excitation of the seal lip always occurs in practice, due to unroundness of the shaft or motions of the shaft center. In this first part of a two part paper the influence of dynamic excitation on the occurrence of clearances in a dry seal-shaft contact is studied, taking into account viscoelasticity and inertia of the seal material. The ultimate goal is to determine whether viscoelastic seal behavior can result in a continuous fluid film or not. First, attention is paid to the mechanical behavior of synthetic rubber under an oscillating load. The seal elastomer shows a glass transition, resulting in a strong increase in stiffness with frequency. Next, a FEM analysis of the seal-shaft contact under dynamic conditions is presented. The steady-state response of the seal is represented by a transfer function approach. It is shown that clearances develop due to viscous and inertial seal material behavior. In practice, these clearances are filled with fluid. Due to entrainment and squeeze effects a fluid film is generated. This phenomenon is designated visco-elastohydrodynamic (VEHD) lubrication, and is subject of Part 2.

Dynamic behaviour of rotary lip seal

“…In order to validate the analytic model, the result was compared to simulations made in [1]. By adopting the same mechanical characteristics of the lip and lubricant, the minimum and maximum film thickness of each approach give a good concordance with a marginal gap about 2% and 15% as shown in Figure 6.…”

“…In this section, we focus on the dynamic of the lip seal in lubricated rough contact with shaft surface. Note that in [1] it was assumed the roundness and misalignment of smooth shaft. Practically, the lashing effect is about 100Hz as excitation frequency instead of 10GHz for roughness effect.…”

“…In order to characterize the viscoelastic law of the rotary lip seal, we propose to simulate the dynamic behavior by adopting "Proney" Series as described in [1], using FEA (Figure 1). Figure.1.…”

“…Figure.1. Finite Element Analysis with "Abaqus" According to Stakenborg model [1], the parameters used in FEA simulation are chosen as follow: ȡ (elastomer density) = 1,46.10 3 Kg/m 3 , Moony Rivlin" model (long term) C 1 =-2.746MPa, C 2 =4.597MPa, and Proney series (instantaneous) g 1 =0.999 and IJ 1 =0.003s. Shaft radius is Rs=35mm, seal radius Rj=34.9mm, the contact width b=0.07mm and the maximum contact pressure ps=4.7MPa.…”

“…In addition to the elasticity of the elastomer, the dissipative characteristic (viscoelastic) of the material was considered. An original study that addresses the dynamic of the lip seal was proposed in [1], showing a high correlation between the viscoelastic behavior of the material and the creation of the thin film. This approach is based on resolving Reynolds equation, coupled with lip mechanical behavior, by using Finite Element Analysis (FEA).…”