Sliding Bearing Flashcards
What are the advantages of plane bearings?
Low cost, good for low speed and high load, smooth operation, quiet, and no rolling elements.
When are plane bearings preferred over rolling bearings?
When operating at low speeds, under high loads, where quiet operation is needed, or cost is a concern.
What is a bushing?
A lining for a hole (metal or polymer) in which a shaft revolves; can be lubricated/unlubricated, porous/non-porous.
What are some typical applications of bushings?
Joint replacements, linkages, shock absorbers, general mechanical systems where simplicity and damping are valued.
What is the formula for nominal pressure in a sliding bearing?
P = F / (L·D), where F is load, L is bearing length, and D is shaft diameter.
How is sliding speed calculated for a bearing?
V = ω·D / 2, where ω is angular speed in rad/s and D is shaft diameter.
What is the PV factor in bearing design?
Product of nominal pressure and sliding speed; used to assess bearing material suitability.
What happens if the PV limit is exceeded?
Overheating, melting, excessive wear, or seizure of the bearing.
How do you select a bearing material using PV?
Ensure material’s PV limit is at least 2× the calculated PV for safety.
What determines wear rate in sliding bearings?
Wear rate K = W / (F·V·t), where W is wear volume, F is load, V is sliding speed, and t is time.
What is the significance of wear rate constant K?
It quantifies how much material is lost per unit of force, speed, and time.
What is the basic design rule for dry sliding bearings?
Do not rely on liquid lubrication; often use PTFE or other self-lubricating materials with reinforcements.
What are common lubrication regimes?
Boundary, Mixed, and Hydrodynamic.
What defines hydrodynamic lubrication?
A full film of lubricant separates the surfaces; no contact; requires high speed and good surface finish.
What is the Stribeck Curve?
A plot showing friction coefficient vs. ηn/P, identifying lubrication regime transitions.
What is the purpose of a floating bearing?
To allow for thermal expansion and avoid axial preload.
Why must lubricant be cooled in hydrodynamic systems?
To prevent overheating due to viscous friction and maintain performance.
What is the minimum film thickness in hydrodynamic lubrication?
Typically 8–20 µm.
What is the purpose of journal bearings in engines?
They support rotating shafts with a hydrodynamic film to reduce wear and ensure longevity.
What’s the wear reduction strategy in sliding bearings?
Operate below 50% of the material’s PV limit and ensure adequate lubrication.
