Visco-Elastohydrodynamic (VEHD) Lubrication in Radial Lip Seals: Part 2—Fluid Film Formation

Abstract

It is shown in Part 1 of this work (Stakenborg et al., 1990) that dynamic excitation of a radial lip seal will result in nonuniform clearances, due to viscous and inertial seal material behavior. These clearances are filled with fluid. Due to entrainment effects in a converging part of the clearance, fluid pressures will develop, which are sufficiently high to overcome the radial preload. These fluid pressures are excellently described by short bearing theory. The viscous and inertial effects can lead to a type of full film lubrication which is designated visco-elastohydrodynamic (VEHD) lubrication. VEHD lubrication addresses the (apparent) parallel fluid film lubrication problem in radial lip seals. At present, it is the only macro-hydrodynamic theory that results in calculated fluid film thicknesses, friction torques and leakage rates that are in agreement with experimental data. A novel feature of VEHD lubrication is the increase of frictional torque with decreasing viscosity under conditions of full film lubrication and low viscosity values, hitherto believed to be mixed lubrication.

Stern tube seals operation: A practical approach

“…The lead of the shaft can explain the oil migration when non-pressurized. Alternatively, the loss of the nominal parallelism between the seal and the shaft 43 or the poor followability of the seal at larger velocities 40 are also plausible explanations. Reverse pumping is expected to be present under pressurized situations, that is, counteracting the natural flow direction.…”

“…During the next decades a wide range of models of various complexities were developed. The distortion of the shaft asperities, 37 the impact of operating with a non-Newtonian lubricant, 38 the direct asperity contact, 39 the viscoelasticity of the seal, 40 or the presence of a meniscus 41 were added to these deterministic models. Stern tube seals, together with the seals used for wind and water turbines, constitute one of the largest types of rotary lip seals.…”

Dynamic behaviour of rotary lip seal

“…This problem has been treated in [1,4,5,6] by assuming the viscoelastic behavior of the elastomer with Proney series and considering the excitatory effect of shaft misalignement or roundness. The effect of the shaft roughness as a source of high frequency excitation of the thin film was not analyzed.…”

Soft elastohydrodynamic analysis of rotary lip seals

“…Stakenborg and coworkers [49][50][51] developed an EHL seal model with the emphasis on viscoelastic effects. Of interest is the dynamic seal behaviour resulting from shaft eccentricity and out of roundness.…”