6.8 Flashcards
What are plain bearings made from?
Hard wearing materials
When are plain bearings used?
Where loads are relatively light and motion is relatively continuous
Why are bearings used?
To support the journals of shafts and axles
What are bearings called that accept forces at right-angles to the drilling axis?
Journal or roller bearings
What are bearings called that accept forces in a longitudinal direction?
Pivot or axial bearings
Why is bearing play necessary?
To allow for continuous lubrication
What is the main disadvantage of a sliding bearing?
It’s high starting resistance
What are the two types of loads a bearing has to deal with?
Radial and thrust
Describe how thrust load works on a bearing?
When the force is coming against rotation (through the eye-end)
Describe how radial load works on a bearing?
When the force is in the same direction as the rotation (like a cog)
What are the five types of anti-friction bearings?
- tapered
- needle
- ball
- spherical
- cylindrical
Why is the roller element very important in a anti-friction bearing?
Because it replaces the high friction sliding with low friction rolling
What are the components of anti-friction bearing?
- outer raceway
- inner raceway
- rolling element
- rolling element cage
Why is a rolling element cage used?
To keep the rolling elements evenly spaced
What are the raceways and rolling elements manufactured from?
Chromium steel
What are the rolling element cages made from?
Steel or brass plate
Why are ball bearings used?
Low starting resistance and are suitable for high rotation speeds
If ball bearings are so efficient why are roller bearings sometimes used instead?
Because roller bearings are better at spreading stressful loads due to weight distribution
Why are spherical roller bearings used?
Because they self-align for minor angular displacement
What is special about the tapered roller bearings?
They can handle radial and thrust loads
If a bearing is missing lubrication, what will happen?
It will start to break own the bearing
Why are synthetic bearings often lubricated with water?
Because water wont react with the synthetic material and they tend to retain heat
How do air bearings provide a ‘zero friction’ load bearing interface?
They utilise a thin film of pressurised air
When are air bearings used?
When rotational speeds are extremely high
Why is maintenance so easy on air bearings?
They have no friction, wear, and lubricant
