Abstract
Typically, film formation in a rotary lip seal is explained by microscopic effects, but here it will be explained from a macroscopic point of view. When the nominal parallelism between the shaft and the seal is lost, the contact area is distorted leading to a skewed sealing profile. The resultant slanted gap between the shaft and the seal presents a macroscopic wedge profile in the direction of rotation, hence constituting a source of hydrodynamics. An elastohydrodynamic model is developed predicting the implications of operating a rotary lip seal under misalignment. It is concluded that the non-concentric operation of rotary lip seals leads to a bidirectional fluid migration from the back to the spring side of the seal and vice versa.
Highlights
In the 1950s a degree of hydrodynamic action was observed carrying some or all of the radial load of rotary lip seals [1]
Since the success or failure of a rotary lip seal was shown to be tightly coupled to the surface roughness of the contact, researchers relied on microscopic-scale hy drodynamics to explain the operation of rotary lip seals
The hydrodynamic model described above predicts the pressure distribution and the flow rates on a misaligned seal-shaft gap profile. The model makes it possible to study the individual contribution of the shaft radial offset ε, the seal angles α and β, the shaft liner velocity vshaft and the lubricant dynamic viscosity η to the operation of a rotary lip seal under radial misalignment
Summary
In the 1950s a degree of hydrodynamic action was observed carrying some or all of the radial load of rotary lip seals [1]. The nowadays widely accepted theory is based on the micro-hydrodynamic pressure bumps generated between the seal and the asperities on the shaft. This allows the load to be carried, wholly or partially, in the seal-shaft con tact [2]. The seal asperities deform in micro-ridges or vanes resembling a screw pump, a visco-seal or a herring-bone bearing, with the ability of pumping fluid towards one of the sides of the seal [4]. This approach assumes perfect concentricity between the seal and the shaft. Under real operating conditions nominal parallelism is hardly ever achieved [5]
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