Abstract
Interfacial surface roughness can result in fluid leakage of seals, and in the design of seals it is standard to give an upper limit for the surface root-mean-square (rms) roughness amplitude h_text{rms}. However, h_text{rms} is determined mainly by the long-wavelength roughness, which is (nearly) irrelevant for the sealing. I discuss the parameters which determine the leakage of seals, and present results for static rubber seals with circular cross-section (like rubber O-rings). I also study the influence of the fluid pressure on the interfacial surface separation and the leakrate.Graphical
Highlights
Leakage of fluids through interfaces formed between rough surfaces squeezed together is a topic of great practical importance and its neglect can lead to huge economic losses andIn the design of seals limits on the surface roughness is usually specified
I will show that if ∕R is fixed and if the fluid pressure is negligible compared to the rubber-countersurface pressure, the fluid leakage rate does not depend on the elastic modulus of the rubber seal
In the former case the nominal contact pressure is below the percolation pressure everywhere in the nominal contact region, while in the second case the contact area percolate in a rectangular strip −b < x < b at the center of the contact area
Summary
For complete sealing (no fluid leakage) the area of real contact must percolate. For surfaces with random roughness this occur when the relative contact area [5] A∕A0 ≈ 0.42. I will show that if ∕R is fixed and if the fluid pressure is negligible compared to the rubber-countersurface pressure, the fluid leakage rate does not depend on the elastic modulus of the rubber seal. This fundamental result differs from what is stated in the literature. In this paper I will consider the dependency of the leakage rate as the fluid pressure approach the rubber-countersurface contact pressure, resulting in “lift-off” and a strong increase in the fluid leakrate [6]
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