In rotating shaft applications, the surface topography is a known factor affecting performance of radial lip seals. There are a few specifications available today for the shaft surface geometry supposedly sufficient to allow radial shaft seals to function properly. The most widely used are ISO [1] and RMA [2] standards. If one adds here specifications used in various commercial applications, that would easily combine into more than a dozen sometimes contradicting guidelines for the shaft surface roughness, machine lead, waviness, etc. Noteworthy, these guidelines reflect practices developed by the industry in the past 30 years and are applicable to what currently is considered a "standard" sprung rubber lip seal. This type of seals has a relatively narrow contact band with the shaft, which is reflected in the current guidelines. Yet, recently, the traditional radial shaft seals are more and more being replaced with PTFE and elastomeric seals having extended contact areas with the shaft. Sometimes, these types of seals are called lay-down lip seals. The lay-down lip seals are employing a pumping mechanism different from the traditional radial shaft seals; - instead of a micro asperity pumping, they use macro mechanical pumping generated by a spiral groove imbedded into the contact surface of the seal. This shift in the nature of the pumping mechanism and the extended width of the contact band require a revision of the various shaft surface requirements to ensure robust sealing.
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