Abstract
To investigate the tribological interaction and wear mechanisms of polytetrafluoroethylene-lined radial lip oil seals in service, a sleeve, seal and lubricant sample taken off a rotating rig are studied. The test was terminated at 72 h, after severe leakage in the final 15 h of the test. All three components are studied using a coherence scanning interferometer and environmental scanning electron microscopy to investigate wear after testing. Results show a wear band on the aerospace grade case-hardened sleeve, appearing as a ‘polished in’ area by the seal. A study of the filler content of the polytetrafluoroethylene coating uncover glass fibres, calcium carbonate, carbon and graphite layers present, assumed responsible for the wear to the sleeve. The polytetrafluoroethylene coating is a 300 μm coating, distinct from the bulk elastomer. This finding is confirmed after observing this layer on both, the tested and new seal lip. Wear of the seal lip is measured and facilitated by comparison to the identical new seal. Lastly, debris from the seal and sleeve wear are found in the lubricant sample.
Highlights
The primary purpose of an oil seal is to prevent loss of oil from any given system
The measured surface topography covers an area of 1.56 mm × 11 mm across the sleeve surface (Figure 9(a))
This paper investigates the tribological behaviour of a sleeve, seal and lubricant sample from a high-speed rotating test rig
Summary
The primary purpose of an oil seal is to prevent loss of oil from any given system. A seal prevents debris from entering into the system. Zero-leakage seal is an ideal situation, but all seals leak to some extent. In some cases, this leakage is referred to as ‘emission’ because it is almost negligible.[1] In the aerospace industry, oil seals are used in both aero-engines and helicopter gearboxes to prevent leakage of oil. The industry standard for an ‘acceptable’ leakage level for such applications is known to be 1–2 ml/h, and any excess is undesirable.[2] Leakage of oil from the bearing chamber can be detrimental to the overall safety of the aircraft, making it important to enhance seal performance and prolong the life expectancy of seals.[3,4,5]
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