Unit 18 Lubrication Flashcards
Relative to lubrication, one place where wear is beneficial is
on new babbit bearing surfaces which wear smooth
Grease is not a suitable lubricant
if a large amount of cooling is desired
If an oil’s viscosity changes much with little temperature change, it will have
a low viscosity index
If you desire an oil to flow at a much lower temperature you would most likely add
pour point depressants
High capacity steam turbine oils should
fire resistant
4 properties that affect the type of lubricant that should be chosen for an application
Nature of surfaces to be lubricated
load to be carried
speed of sliding surfaces
operating temperatures
A common method of determining viscosity of an oil
A given quantity of oil is placed in a Saybolt viscosimeter at a controlled temperature. The time for the oil to pass through a standard small diameter tube is measured and this indicates viscoity in Saybolt Seconds universal
Grease is a mixture of
mineral oil and soap
3 classes of lubricants
Solid- graphite, soapstone used in extreme temps
Semi-solid - greases used where oil could leak away, where dirt and moisture is to sealed out
Liquid- mineral oils, synthetic oils and fixed oils used in service where maximum lubrication is required and heat and dirt is to be carried away from bearings
a measure of the resistance of a liquid to internal deformation and indicates a fluids ability to flow
Viscosity
temperature at which an oil will give off enough vapors to ignite momentarily
flash point
temperature at which wax in the oil begins to separate out
Floc point
Determines the amount of carbon an oil will form when subjected to a high temperature
Carbon Residue
A measure of how much an oil’s viscosity changes with temperature
Viscosity index
Define boundary lubrication
when a microscopic layer of lubricant separates the surfaces. Used when lubricant supply is intermittent
Fluid film lubrication
when the bearing is flooded with oil and a film built up that is thick enough to completely separate the surfaces
Describe the construction of shell or sleeve type bearings
bearing surface is made of white metal called babbit, which is soft enough to conform to load and debris will become embedded. Bearing housing is made of cast iron or steel. Bearings have grooves to distribute oil to the surfaces.
Describe the procedure for cooling an overheated bearing
increase oil flow to bearing to carry away heat
slacken off bearing caps if shaft is expanded, in slow moving bearings.
apply water to shaft but not directly at the bearing
Allows a wedge of oil to build up between the revolving thrust collar and the stationary pads
Tilting pads
Roller or ball type bearings are known as
antifriction bearings
A loose fitting ring hanging on the rotating shaft inside the bearing that lifts oil from the reservoir and distributes it to the bearing and shaft
Oiling ring
The ring assembly within which the balls or rollers of an antifriction bearing rotate.
Bearing Inner race
A device using a threaded spindle which is rotated to apply force on a bearing to remove it from a shaft
Bearing puller
The outer race of an anti friction bearing
Bearing shield
Indents created in the bearing race of antifriction bearings under the balls or rollers
Brinelling
4 main purposes of lubricating bearings
To protect the surfaces of the balls, rollers and raceways from corrosion; to provide a seal against dirt and other impurities into the housing; To serve as a heat transfer medium; To provide lubrication and reduce friction
Which type of thrust bearing does not utilize the oil wedge principles of lubrication
Collar
To clean a bearing
Drain old oil, remove dirt and grease from around it
fill bearing with solvent, run machine without load for a short period. Drain solvent and impurities. Continue this process until clean solvent is drained out.
Fill with a light oil and run to remove solvent.
Drain oil and fill bearing with normal lubricant
When stationary bearings are exposed to vibration causing the rollers or balls to form indentations in the bearing inner race or sleeve race
False brinelling
What to check when inspecting an antifriction bearing
pitting or flaking of balls, rollers or races
cracked ball, rollers, races shields or separators
rusting or corrosion
discoloration indicating overheating
