Module 7.11 Flashcards
slow rotation of bearings highlights what?
roughness due to damage, corrosion or wear
bearing tests are usually restricted to rotational checks for excessive backlash or free play, what direction is freeplay in?
axial or radial
if a bearing shows a fault or defect, what must be done?
remove or replace
how is preservation oil removed?
solvent bath
how is heavy grease, carbon or oil removed ?
in a soak bath
what is the final cleaning method?
ultrasonic bath
what must be done to the bearing if it is not going to be used immediately?
coated with rust preventing oil
what is likely to be grounds for any replacement of a bearing?
any flaw of defect
what properties must a lubricant have?
-reduces friction and abrasion
-reduces heat from friction
-prolongs life
-prevents rust
-keep foreign objects away from rollers
what lubricant is a better choice than grease for high rotational speeds?
oil is for high RPM. grease gets very hot at high RPM
how is loss of lubricant stopped?
retaining device
-labrynth seals
-felt
-rubber washers
most bearings are shielded or sealed, what must be done if evident lubricant has been washed out or lost?
replaced
grease nipples are provided for some bearings, what must be done before applying through the nipple?
wiped clean to prevent dirt ingress
what type of bearing is on a wheel hub? how is this regreased?
tapered roller bearing, usually regreased by hand
what is hydrodynamic lubrication?
load carrying surfaces separated by a thick film of lubrication to reduce friction
what is hydrostatic lubrication? and what does it not require?
high pressure oil or air to separate surfaces. Doesn’t require relative motion
what is boundary lubrication and why is it important?
thin layer of lubrication between mating parts. Viscosity is not important, however lubricity is
what is solid film lubrication? how is it applied and what are the benefits?
paint like coatings are applied by spraying, dipping or brush. film repels water, reduces friction and increases wear life.
what is true brinelling?
regularly spaced indents with a vibraion increase
cause of true brinelling?
-loads from incorrect mounting
-debris
- excessive static overload or impact loads
rectification of true brinelling?
avoid unnecessary shock or impact loads
what is false brinelling?
hollow spots on the raceway that resemble true brinelling
what is the cause of false brinelling?
vibration in a static state, which causes metal to metal contact. poor luibrication
how is false brinelling rectified?
reduce vibration by preloading,
use proper lubrication
what is burnishing?
splits or cracks in rolling elements or bearing rings
what causes burnishing?
-insuffcient lube
- excessive loads and impacts
- overheating by movement and rapid cooling
- very loose fits
what does overheating look like?
discolouration of elements from gold to blue
how is burnishing rectified?
- prevent movement
- correction of fit
- correct lube
what causes overheating?
poor lube, heavy electrical loads and insufficient cooling
how do you rectify overheating?
prevent overload, serviceable lubricant system, supplemental cooling.
what does galling look like? and caused by?
metal to metal contact, metal transfer. looks like skidding due to overspeed
what is the rectification of galling?
prevent overload and have a serviceable lubing system
what is spalling?
breakdown of surface due to cyclic loading
what is wear caused by?
worn surface and dimensions are reduced component to other portions, caused by FOD, poor lube ect.
what bearings are more suceptible to damage?
moving bearings
what is one way to rectify electric damage?
prevent current from passing through
how does electric damage appear?
dark brown, greyish black corrugating or craters on raceway, balls have dark discolouring only.
what does corrosion on bearings look like and what is it caused by?
black pitting marks or reddish brown marks, caused by moisture and contamination.
