Rolling Bearing Flashcards
What are the four key advantages of rolling element bearings?
Low friction, high load capacity (radial and axial), high speed capability, and long service life.
When are plane (journal) bearings preferred over rolling bearings?
When operating at low speeds with high loads, when smooth quiet operation is needed, or when cost is a major factor.
What are the main functions of a bearing?
Reduce friction, support loads, constrain motion, locate shafts, and prevent overheating or seizure.
How many bearings are typically needed per shaft?
Usually 2; 1 for radial and 1 for axial loads. More may be used to prevent vibration or for alignment issues.
What causes friction between components in relative motion?
Microscopic surface roughness; movement requires climbing over or displacing surface asperities.
How does rolling motion reduce friction?
Rolling elements minimize sliding contact, reducing contact area and pressure, which lowers friction.
What is a typical configuration of a rolling element bearing?
It includes an inner ring, outer ring, rolling elements (balls or rollers), cage, and seals.
What are common problems with ball elements in bearings?
Load is concentrated in small contact areas causing elastic deformation or potential yielding.
Name five types of rolling elements.
Ball, cylindrical roller, spherical roller, needle roller, taper roller.
How do you estimate bearing loads using a free body diagram?
Apply superposition of forces, calculate reaction forces at supports using moments and equilibrium.
What does the static load rating (C₀) represent?
The load causing permanent deformation in the bearing equivalent to ε = 1 × 10⁻⁵.
How is static safety factor (s₀) calculated?
s₀ = C₀ / P₀, where C₀ is static load rating and P₀ is equivalent static bearing load.
What does dynamic load rating (C) represent?
The constant radial load a bearing can endure for 1 million revolutions.
What is the equation for basic rating life (L₁₀)?
L₁₀ = (C / P)ᵍ, where g = 3 for ball bearings and 10/3 for roller bearings.
How do you account for combined axial and radial loads?
Use equivalent dynamic load: P = XFr + YFa, where X and Y are from manufacturer data.
How is effective load calculated for fluctuating loads?
Use mean effective load: Fm = ³√(F₁³U₁ + F₂³U₂ + F₃³U₃ + …) / total cycles.
What factors affect bearing life adjustment (L = a₁a₂aISO·L₁₀)?
Reliability factor (a₁), material factor (a₂), and ISO factor (aISO) based on contamination and load/fatigue ratio.
What’s good practice during bearing installation?
Use interference fit on one race, provide for removal, don’t force through rolling elements, ensure alignment.
Why use a locating and floating bearing pair?
To accommodate thermal expansion and prevent unwanted axial preload.
What causes most rolling element bearing failures?
Incorrect fitting or corrosion during installation.
