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Statement (I): The journal while rotating inside a bearing automatically shifts its centre to one side and thus the journal is eccentric inside the bearing. Statement (II): The wedge shape of oil film gives rise to thin-film lubrication, which is considered as stable lubrication.

Statement (I): The journal while rotating inside a bearing automatically shifts its centre to one side and thus the journal is eccentric inside the bearing. Statement (II): The wedge shape of oil film gives rise to thin-film lubrication, which is considered as stable lubrication. Correct Answer Statement (I) is true, but Statement (II) is false

Explanation:

Statement 1

  • The pressure in the oil film is not distributed uniformly over the bearing surface. The distribution has a peak close to the location of minimum oil film thickness.
  • So, the journal while rotating inside a bearing automatically shifts its centre to one side and thus the journal is eccentric inside the bearing.
  • The value of the peak is dependent on the average load applied to the bearing, the journal rotation speed, the lubricant viscosity, and the value of journal eccentricity ‘e’ relative to the bearing.
  • The more the journal centre has shifted from the bearing centre, the higher the hydrodynamic force generated by the rotating journal.
  • Thus, eccentricity ‘e’ is a fundamental parameter of a journal bearing.

Statement 2:

  • The wedge shape of oil film gives rise to thick film lubrication, so statement II is incorrect.​

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