When the shaft rotates in anticlockwise direction at slow speed in a bearing, it will
A. Have contact at the bottom most of the bearing
B. Move towards right of the bearing making no metal to metal contact
C. Move towards right of the bearing making the metal to metal contact
D. Move towards left of the bearing making metal to metal contact
Answer: Option D
Solution (By Examveda Team)
Concept: In a journal bearing, the shaft is supported on a thin film of lubricant which separates the metal surfaces during rotation.Slow speed condition: At slow speeds, the hydrodynamic pressure in the lubricant film is insufficient to fully separate the shaft from the bearing surface.
Effect of rotation direction: When the shaft rotates in an anticlockwise direction at slow speed, the load causes the shaft to shift within the bearing clearance. Due to the rotation and load combination, the shaft moves towards the left side of the bearing.
Metal-to-metal contact: In this condition, the lubricant film cannot maintain full separation, resulting in metal to metal contact between the shaft and the bearing surface on the left side.
Conclusion: At slow speed in anticlockwise rotation, the shaft moves towards the left of the bearing, causing direct metal-to-metal contact.
This Question Belongs to Mechanical Engineering >> Machine Design
Move towards right of the bearing making the metal to metal contact.
Assume:
Shaft rotates anticlockwise
View from front (shaft coming out at you)
Then:
Bottom of shaft moves left
Lubricant is dragged leftward
High-pressure wedge forms at lower left quadrant
This pushes the shaft upward and rightward
So the shaft center shifts toward the right inside the bearing
When the shaft rotates in anticlockwise direction at slow speed in a bearing, it moves toward the right of the bearing. If the speed is very low, metal-to-metal contact may occur due to insufficient film formation.