Bearings Flashcards
Define “Tribology”
The study of friction, wear, lubrication and the design of bearings. The study of interacting surfaces in relative motion.
What are some types of bearings and what are their different functions?
> Mechanical contact
- Sliding
- Rolling
> Non-contact
What are some materials that MECHANICAL CONTACT SLIDE ROTARY bearings can be made from? (6)
> Bronze
> Brass
> Graphite
> Babbitt
> PTFE
> Sintered
What materials are used for bearings to improve lubrication?
Porous materials: They are best because it allows lubricants to flow through the material and onto the shaft reducing friction
What are the advantages and disadvantages of MECHANICAL CONTACT SLIDE ROTARY bearings?
Advantages:
> Low operational noise
> Cheap
> Small space requirement
Disadvantage
> High friction between surfaces so low energy efficient
> Susceptible to damage from impurities in lubricant
> Having stringent lubricant requirements
What are the two types of MECHANICAL CONTACT ROLLING ROTARY bearings?
> Ball bearing
> Roller bearing
What are 3 special variants for a MECHANICAL CONTACT ROLLER ROTARY bearings?
- Spherical roller thrust bearings.
> Can help with misalignment.
> Expensive to produce.
[Picture1]
- Tapered roller bearing
> Cheaper to produce than spherical bearings
> Do not facilitate misalignment
[Picture2]
- Needle radial bearing
> Low profile
> Lightweight
> Higher load capacity
> Low cost
> Used in planetary gears and universal joints
What are the advantages of MECHANICAL CONTACT LINEAR bearings?
> They can be self-lubricating and so are maintenance free
> Low friction
> Contaminated particles do not adhere to the bearing > Resistant to corrosion
> Low noise
> Light weight
> Safe in specialist environments (depending on the composites used)
> They do not have to be cylindrical
What are some examples of NON-CONTACT bearings?
> Fluid film (hydrostatic)
> Fluid film (hydrodynamic)
> Magnetic passive
> Magnetic active
What are the two types of friction and define them?
> Static friction: The friction between two surfaces when the two forces are stationary
> Kinetic friction: The friction between two surfaces when two forces are moving
What is the cause of static friction?
> Caused by micro static roughness of surfaces
> When two surfaces meet, cold welding (a molecular process) takes place. To stop this from happening a force needs to be applied.
How is static friction overcome?
When the force applied is greater than the static frictional force
What is the equation for static frictional force?
fs = μFN
> FN = force of the object on the surface
What is the cause of kinetic friction?
> Once the object is moving then the force required to overcome abrasion
> Because the object is moving, there is no time for cold welding to occur.
> As a general rule, kinetic friction is less than static friction
How is kinetic friction overcome?
F ≥ fk = μFN
What are the two ways of mounting free bearings?
> Pillow blocks [Picture 3]
> Split pillow blocks [Picture 4]
