Bearings Flashcards
Purpose of a bearing
Device used to enable rotational or linear movement, while reducing friction and handling stress
How does a bearing work
Make use of relatively small simple ball structure, with internal and external smooth surfaces to aid in rolling. not all loads put force on the bearing in the same way.
2 kinds of bearing loading
- Radial Load = puts weight on the bearing in a anner that causes bearing to roll/rotate as a result of tension
- Thrust Load = Put a tire on its side and its a thrust load, same with a bar stool, the bearing is being thrusted and compressed.
- Bearings can be subject to both thrust and radial loads, EG a car tyre going straight is radial but when it hits a corner its a thrusting force.
what loads do roller bearing face
- Axial or thrust loading
- Radial loadings (shaft sideward loads)
- Compound loads (Both directions)
Benefits of A roller bearing
- Excellent capabilities in handling radial loads
- larger load carrying capacity
- longer life and endurance for heavy loads and shock loads
Benefits of a ball bearings
- Lower frictional resistance
- Lower face-run out in rotation
- More suitable for high speed applications
Plain bearings
Plain piece of durable metal or plastic that when in motion uses an oil layer to create a gap between the 2 metal surfaces reducing the contact. when not in motion the oil layer is broken creating contact between the 2 faces. used when loads are light and motions are continuous. when its first started the oil isnt spread creating contact, increasing friction and causing wear/damage. extreme care for no FOD to be in the bearing and regular maintenance is required.
What are plain bearings made of?
- cast iron
- Phosphor bronze
- Beryillium-copper
- white metal (babbit)
Spherical bearings
- Used in Push pull rod applications and other a/c linkages/. serve primarily as a force transporter and angular movement.
- not intended for rotation
- spherical design allows for more/less angular movement/correction.
- rod end can be installed with a grease nipple facilitating easy maintenance.
- Low maintenance
- sliding contact may be of several designs
spherical bearings contact surface designs
- steel on steel
- Steel/sinter bronze composite
- Teflon (PTFE) fabric.
air bearings
use a thin film of pressurise air that provide extremely low friction between surfaces.
2 surfaces are contact free and they avoid the traditional faults with normal bearings.
Advantages of air bearings
Distinct advantage in precision positions, such as lacking backlash and static friction
- can be used in high speed applications.
Air pocket in air bearings
-air is constantly escaping but there is always enough pressure to keep them working.
Difference between aerodynamic bearings and aerostatic bearings
- Aerodynamic bearings create air pocket during movement
- Aerostatic bearings have the air externally inserted.
Types of roller element bearing
Ball bearings- use steel ball bearings which rotate in grooved raceways
-accept both radial and axial loads
Roller bearings- use more cylindrical type bearings that operate on suitable raceways.
-may only accept radial loads
Difference between caged and uncaged bearings
- Caged are using in engines and gearboxes where rotational speeds are no more that 100rev/min
- uncaged are used in aircraft engines, intended for oscillating or slow rotation conditions
12 types of internal bearings
- Deep groove ball bearings
- Angular contact ball bearings
- Self aligning ball bearings
- Cylindrical ball bearings
- Needle roller bearings
- Taper roller bearings
- spherical roller bearings
- Toroidal (Crowned) roller bearings
- Thrust ball bearings
- Cylindrical roller thrust bearings
- Needle roller thrust bearings
- Spherical roller thrust bearings
Ball bearings
- Inner and outer race separated by steel balls. uses the balls to reduce friction between 2 spaces..
- constructed using either single or double row of balls, each row controlled by bronze of brass cage. Cage doesnt always need to be used.
- rigid or self aligning.
- designed for thrust and radial loads.
- Low maintenance, can handle operational conditions. suitable for high and very high speeds
Angular Contact Bearings
- Have orbital paths that are mutually offset in the direction of the bearing axis.
- retain large axial forces.
- paired and installed in opposite direction to resist against axial forces in multiple directions
- Lower load rating than tapered but used at higher speeds.
- Rigid types and perfect alignment dont allow for any swinging
Roller bearings
- inner and outer race seperated by hardened steel rollers instead of balls.
- normally support radial loads but can be made to compensate linear expansion
- Location and controll is achieved by a groove cut inside the races.
- this allows the rollers to take lateral expansion by sliding across the surface during rotation
3 types of roller bearings
- Cylindrical roller bearings
- Spherical roller bearings
- Tapered roller bearings
Spherical roller bearings
- have 2 rows of spherical rollers with a common spherical path on outer ring. allows mutual tilting of springs
- have high load rating, retention of raidal and also axial forces.
- suitable for high loads with misaligned seating.
- non dismountable
Tapered roller bearing
- Coned shapes inner, cup shaped outer.
- rollers are hardedend steel
- only support radial loads in one direction
- pair up and put in opposite directions so they can support from all directions
- caple of accepting radial and axial loads
Torodial (Crowned) bearings
- single row bearings with long spherical roller bearings , parts outside are symmetrical and run along the bearing centre
- Design combines tilting ability with radial balancing
- reduce vibrations in seating, axial vibrations are not transferred to the body, load rating is higher than bearings with cages.
Needle roller bearings
- uses long thin cylindrical rollers, like needles.
- needle bearing rollers are 4x longer than the diameter.
- greater surface area which increase the load limit,
- thinner and require less clearance between axle and the surrounding
- used in rocker arm pivots, pumps, compressors and transmissions. used where reciprocal movements are.
- used whenspace saving is a factor, physically smaller but can support the same loads as other bearings
Thrust bearings
- designed for axial forces, radial cant be contained, can be paired to cover axial forces in both directions
- not suitable for high speeds, must not work unloaded to prevent slipping of the balls.
- dismountable bearings, simple shapes and designs.
Instrument precision bearings
Roller bearings that are precise to a high accuracy and finish, found in both instrument and communication equiptment.
Self alignment bearings.
two rows of balls that allow mutual tilting of the rings. suitable for seating where the shaft shows deflections or misalignment
Load limit is smaller than single row bearings
Single and double row bearings
Double row are suitable where the load carrying of a single is not enough, higher load carrying capacity but slightly larger in size.
Sealed bearings
seal put on the side of the bearing during manufacture, appropriate lubrication is applied in manufacture sealing it off. no FOD can get in..
Cant be maintained other than wiping down exterior and checking for damage.
Purposes of a CAGE
- Keep elements at an appropriate distance, keeps friction and heat generation at a min
- keeps rolling elements evenly distribute, improve rolling conditions
- guide rolling elements in the unloaded zone
- retain rolling elements where there is a separable design
3 Cage classifications
- pressed
- solid
- pin type
Linear bearings
consist of a raceway with a cage to guide balls in sets around the systems. Recirculating balls provide unlimited stroke and low friction movement.
Prove axial movement along a shaft with minimal friction. seeing in a/c push pull flight controls.
Bearing appliations
Roller bearings are used in a/c gas turbine engines. axial forces are high because of the shaft loadings and radial forces are high because of the sideward forces in rotation
Cleaning Bearings
- Remove from seating, immersion in a tank of white spirit.
- Wash tank should be fitted with a small jet, place bearing on a metal mesh so that the bearing is submerged enough for FOD to fall.
- using a jet of white spirit clean the bearing of grease and fod whilest moving it around slowly. until all is gone.
Bearing examination
If the measurement and condition of track surfaces are satisfactory.
Use feeler gauges to measure the diametrical clearance
Bearing outer race and bore of inner race against the tolerance in AMM
Houses should be measured for bore, ovality and width
Hand rotation test
manually rotate the bearing to see if it works correctly.. any bad balls will show and other faults.
Hand rotation test points
- Diametrical slackness measure against a new bearing to see wear
- check for catches, indicates raceway faults
- check for irregular catching as it could sign faulty ball or defective surface
- Any roughness will suggest FOD is present, or the ball is worn
Visual examination
Visually check for:
- General flaking
- pitting
- Corrosion
- heat discoloration
- cracking
Common causes of premature failure
- FOD present
- brinelling (ball bearing crate dents in raceway after sudden impacts)
- False brinelling (the balls overtime deform raceway)
- Misalignment
- thrust in the wrong direction
- Pre-loading
Lubrication
Appropriatly lube the bearing so that no errors can occur. bad lube means more friction, which leads to faster wear.
