7.11 Bearings Flashcards
What are the key steps to test, clean, and inspect bearings?
- Test bearings for excessive backlash or free play
- Clean bearings using the correct manufacturer procedures
- Inspect bearings after cleaning for any defects
What types of bearings are primarily used in aircraft?
Sealed and shielded bearings
These types are designed to prevent the ingress of foreign particles.
What issues can visual examinations of bearings detect?
Surface flaws, overheating, lack of lubricant, and other defects
What is the main purpose of testing a bearing?
To check for excessive backlash or free play
What indicates a serviceable bearing?
Smooth actuation and movement
In which directions must free play be tested in bearings?
Radial and axial directions
What happens if a bearing shows any indication of a fault?
It must be removed and replaced
What is the effect of speed on bearing wear?
High-speed bearings fail quicker than low-speed bearings
What is the minimum cleaning procedure for bearings?
Clean in a solvent bath approved for bearing cleaning purposes
What is an ultrasonic bath used for?
Final cleaning method for bearings
What should be done to cleaned bearings that are not installed immediately?
Coated in rust-preventing oil, wrapped in greaseproof paper, boxed, and labelled
How should cleaned bearings be stored?
Horizontally in a clean and dry atmosphere
What are grounds for rejection or replacement of a bearing?
Any flaw or defect detected in a bearing assembly
Fill in the blank: The correct manufacturer procedure for specific bearing cleaning must be _______.
[referred to]
What is lubrication and why is it important?
Lubrication is the application of a lubricant to reduce friction between moving surfaces and is important for maintaining bearing service life.
List the lubrication requirements of bearings.
- Scheduled application of lubricant
- Thorough cleaning of lubrication equipment
- Avoiding overpacking of bearings
- Preventing contamination during lubrication
What are the different types of lubricants?
- Oil
- Grease
Explain how to perform the different methods of bearing lubrication.
Methods include oil spray, splash, mist, drip-feed, or controlled level oil bath.
What percentage of lubricants is typically base oil?
90%
What are some common base oils used in lubricants?
- Vegetable oils
- Synthetic hydrogenated esters
- Silicones
- Fluorocarbons
What are the effects of effective lubrication of rolling element bearings?
- Reduces friction and abrasion
- Reduces heat generated by friction
- Prolongs service life
- Prevents rust (corrosion)
- Keeps foreign objects away from rolling elements and raceways
True or False: Grease is suitable for high rotational speeds.
False
What is a common lubricant for low rotational speeds or oscillating functions?
Grease
What type of lubrication is often used in engines and gearboxes?
- Oil spray
- Splash
- Mist
- Drip-feed
- Controlled level oil bath
How do you prevent loss of lubricant in bearings?
Use oil retaining devices such as labyrinth seals, felt, or rubber washers.
What are shielded or sealed bearings typically packed with?
Anti-freeze grease
Fill in the blank: Grease nipples are provided for some open bearings to replenish grease at specified _______.
intervals
What is the purpose of wiping grease nipples clean before applying grease?
To prevent the entry of dirt.
What must be done when refitting wheel-hub bearings?
Repack with the correct grease.
List the four basic types of lubrication.
- Hydrodynamic lubrication
- Hydrostatic lubrication
- Boundary lubrication
- Solid Film lubrication
What is hydrodynamic lubrication?
A type of lubrication where load carrying surfaces are separated by a thick film of lubricant.
Why is viscosity important in hydrodynamic lubrication?
It reduces the mechanical friction.
What is hydrostatic lubrication?
Lubrication where air is forced into the bearing area at high pressure to separate surfaces.
What distinguishes boundary lubrication from other types?
The oil film is only a few molecules thick, and lubricity is more important than viscosity.
What are solid film lubricants?
Paint-like coatings of fine particles of lubricating pigments that create a solid film when cured.
Name two commonly used solid film lubricants.
- Graphite
- Molybdenum disulfide
What are the leading causes of bearing failure?
Bearing fatigue and contamination
Abrasive substances like sand or dust cause dents, leading to vibration and wear.
What common sources lead to contamination in bearings?
- Poor handling procedures
- Dirty hands or tools
- Foreign matter in lubricant or cleaning fluid
What are some common defects in bearings?
- Broken or cracked races
- Dented or damaged seals
- Cracked or broken separators
- Damage to the balls or rollers
- Discolouration due to overheating
What characterizes true brinelling?
Indentations in the bearing cup raceways caused by excessive impact
Indicates that the load exceeds the elastic limit of the bearing material.
What causes false brinelling?
Vibrations of the bearing while in a static state
Results in wear and corrosion patterns that resemble true brinelling.
Identify the causes of burnishing in bearings.
- Excessive loads
- Excessive impacts
- Overheating by movement
- Very loose fit
- Insufficient lubrication
What is the main cause of overheating in bearings?
Excessive operating temperatures and improper lubrication
High temperatures can lead to reduced lubricant efficiency.
What is galling in the context of bearing defects?
Metal transfer due to welding or tearing action during metal-to-metal contact
Can be caused by overspeeding, overloading, or poor lubrication.
What is spalling in bearings?
Breakdown of surfaces due to cyclic loading, resulting in irregular pitting
Progresses with the loss of large areas of metal.
What factors contribute to wear in bearings?
- Ingress of solid foreign objects
- Dirt in lubricant
- Poor lubrication
- Skewing of rollers
What is the primary cause of bearing corrosion?
Chemical attack from moisture
Evidence includes black pitting marks or reddish-brown rust.
What damages can electrical current cause in bearings?
Dark brown or greyish black fluting or craters in raceways and rollers
Damage occurs from low or high levels of electric current.
Fill in the blank: The condition characterized by indentations in the bearing raceway due to excessive impact is called _______.
True Brinelling
True or False: False brinelling results from static overload and lubricant being forced from between rollers.
True
What measures can be taken to manage true brinelling?
- Avoid unnecessary shock or high impact loads
- Isolate bearings from external vibration
What can be done to prevent overheating in bearings?
- Prevent overload
- Ensure a serviceable lubrication system
- Provide supplemental cooling
What is a key rectification for galling?
Prevention of overload
Ensuring a serviceable lubrication system is also crucial.
Identify one rectification method for spalling.
Improvement in mounting and removing procedures
What is the impact of poor lubrication in bearings?
Increases the risk of burnishing, galling, and overheating
Fill in the blank: The identification of bearing corrosion includes visible _______ marks.
black pitting
True or False: Non-rotating bearings are more resistant to electric current damage than rotating bearings.
True
