Yusof, Nurul Farhana Mohd
(2012)
Surface Degradation Analysis Of Roller Bearing.
Masters thesis, Universiti Sains Malaysia.
Abstract
Surface degradation analysis and defects detection of roller bearing are crucial for
the prediction of the impending failure in machineries. In this work, two conditions
of grease lubrication and unlubricated condition are investigated. The analysis is
focused on the surface degradation of the inner race and the rolling element since
these surfaces suffer from the higher contact stress level. The natural surface
degradation of the roller bearing is monitored from the beginning of the experiment
until damage. The lubrication film thickness is determined by the Hamrock-Dowson
equation which showed that the grease lubricated bearing operated under the elastrohydrodynamic
lubrication, with the ratio of lubrication film thickness to the surface
roughness of λ in the range of 0.9 to 3.65. The unlubricated bearing was damaged
after 20 minutes whereas the grease lubricated bearing continued to operate for 6600
minutes. The observation under microscope showed that the surface underwent
smoothening process where the surface roughness decreases during the running-in
state with the λ = 3.65 to 2.3 followed by roughening at the steady state where the
surface roughness increases, with λ = 2.3 to 0.9. At damage, the value of λ = 0.9 can
be associated with the high level of the bearing vibration. The increase of vibration
level becomes rapid at the critical value of λ = 1.6. As such the overall vibration
level of the bearing can be related to the surface degradation. For unlubricated
condition, these processes took place faster. Both waviness and roundness
measurement showed higher form change of the inner race. Envelope analysis at the
end of experiment showed that the bearing damaged can be traced at the inner race
with the clear peak of the inner race bearing defect frequency.
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