Lubrication Flashcards
Describe friction?
Friction is the resistance to movement between two surfaces.
What is lubrications main job?
Reduce friction
Why is friction bad?
Increase in power consumption
Causes wear
Causes heat
What are the three types of friction?
Sliding
Rolling
Fluid
What is viscosity?
Measurement of resistance to flow.
What is the most important property of a lubricant?
Viscosity
Higher viscosity equals?
Slower flow rate
Better sealing properties
What units are viscosity measured in?
Centistrokes
What is the viscosity index (VI)?
The amount of change of a lubricant over a temperature range. (40-100 degrees C)
Oil with very little change with temperature has a ________VI#?
High
What is the pour point of oil mean?
The lowest temperature which oil will flow
What is the flashpoint?
The lowest temperature at which the the Vapor above the oil will ignite.
What are the two SAE grade viscosity measures?
Low temp W (minus 5 to minus 30)
High temp: no letter (100 degrees C)
What does the two numbers mean in engine oil? 10w30
Flows like 10w in minus 30 degrees and still remains a film strength of 30 at 100 degrees c
How do lubricants reduce friction?
By separating moving surfaces and protect agains corrosion.
Why is full film lubrication better then elasticity-hydrodynamic film lubrication?
Offers the least friction resistance
Eliminates wear on the moving surfaces
Generates the least amount of heat
What are the 3 types of lubricant films?
Full film lubrication (thick enough to completely separate the surfaces with a continuous film)
Elasto- hydrodynamic film lubrication (similar to a full film but deformation still takes place in the loaded area)
Boundary lubrication (film does not completely separate the 2 surfaces
Describe an oil wedge?
Oil sticks to unloaded area of the shaft
As rotation begins the uncoated part of the shaft rolls up to the coated area
As the shaft hits the oil’s surface it slips back down reaping a layer of oil under it
As the shaft continues to turn it draws a wedge of oil under the loaded area slowly lifting it higher to form a full film.
How much oil do journal bearings need to avoid metal on metal?
At least 0.001”
What factor affect viscosity
Temperature
Pressure
Speed
What are the characteristics of petroleum based oil?
Oil does not wear out
Can be re-refined
Stable to 55 degrees C
Separate from water easily
Cheap
What is the characteristics of synthetic oil?
Last longer
More chemical additives for more specific conditions
Stable up to 250 degrees
Wider operating range
When are bio degradable oils used?
When there is a high chance of spills
What percent of oil can be additives?
22 percent
The oxidation rate doubles every _____degrees C at temperatures above _____ degrees C with no additives.
8
55
What do chemical inhibitors do?
Form a protective layer on the metal by reacting with it
What do foam depressants do?
Reduce the surface tension on the bubbles causing them to burst
What is the purpose of extreme pressure additives?
Protect against welding of surfaces
What are detergent additives for?
To keep sludge and deposits off metal surfaces
What does a demulsifier do
Help oils separate from water
What is the purpose of the lubrication system?
Distribute oil to the moving parts of the machines to reduce friction.
In an oil bath, how far up the lowest bearing should the oil be?
1/3 to 1/2
Any higher and excessive heat is caused
What are some different lubrication systems?
Bottle lubrication
Wick feed oilers
Drop feed lubrication
Ring or chain oilers
What are the applications for a bottle lubricator?
Low surface speeds of 250feet/min
What are the applications for a wick feeder?
Bearings with a 2” or smaller shaft that require small amounts of oil
What are the applications for a drip feed lubricator?
Shafts up to 3”
Maximum speed of 3600 RPM
Only intermittent oiling is required
What are the applications for a ring/chain oiler?
Shafts smaller then 4”
Max speed 3600rpm
Good for friction and anti friction bearings
Chain can be used on larger shafts with lower speeds
What is a pressure lubricating system?
Forces oil into engine bearings
What are the components of a pressure oil lubrication system?
Reservoir - holds oil and allows cooling
Filter - removes contamination
Pump - delivers oil
Relief valve - bypass excess oil
Distribution valve - sends oil to various lube points
Metering valve - controls amount of lube delivered to each point
Nozzles or ports
What are the applications of a pressure lubrication system?
Engine
Gas/steam turbines
Large reciprocating compressors
Medium and large vane compressors
Centrifugal compressors
What are the parts of an oil mist system?
Compressor - supplies air
Moisture trap - removes moisture
Pressure regulator - delivers right pressure of oil
Bottle of lubricant
Nozzles
What are the applications for a air activated lube system?
Small high-speed bearings
Air tools
Chain drives
Gear sets
Machine tool ways
What are air-oil lubrication systems used for?
Medium to high speed anti friction bearings
When is the block lubrication system used?
When elements are hard to access
What are the two main concerns when handling and storing oil?
Cancer
Fire
What safety precautions should be taken when dealing with oil?
Read MSDS sheet
Protect you skin
Provide proper ventilation in storage area
Avoid inhalation of lubricant fumes
Do not carry a rag covered in oil in your pocket
Report skin problems immediately
What precautions should be taken to prevent fire from lubricants?
Avoid open flame around them
Have fire watch and ABC fire extinguisher around if welding or cutting near lubricants
Do not store lubricants near heat
Post no smoking sign near lubricants
Make sure solvent drums are properly grounded
How do you protect lubrication from contamination?
Keep gloves clean when working with lubricants
Keep lubricant dispensers such as oil cans funnels and grease guns immaculate.
Store lubricant drums on their sides with the bungs at 3 and 9 o’clock
If possible use a filter cart
Keep storage area and lubricant containers very clean
Clearly identify barrels
What happens in hot weather to lubrication?
Oxidation (indicated by darkening oil)
Separation of the thickener from oil from grease
Evaporation of water from fire resistant fluid
Burst containers from expansion
What can happen to lubrication in cold weather?
Fire resistant fluids can be be damaged
Water/oil emulsion can freeze
Fluctuations above and below freezing can cause the pour point to be raised. (Pour point reversion)
What is grease?
Grease is a liquid lubrication mixed with a thickener that controls the flow of grease to the area being lubricated
How are greases classified?
By type of thickener
By a distinguishing characteristic
By its NLGI consistency #
By the Viscosity of the base oil
By its application
Proper grease selection depends on what two factors?
Temperature
Load
What grease is good for low temps?
Low consistency (NLGI 0 or 1)
Must have low base oil viscosity (about 15 centistrokes)
What grease is good for medium temps?
(Multi purpose)
Consistency should have a NLGI of 2 or 3
Base oil viscosity should be between 75-200 at 40 degrees C
What grease is good for high temperature operation?
Grease must be suitable for up to 150 degrees.
Consistency should be NLGI 3
Base oil viscosity should be 110
Centistrokes
Base oil should contain additives to improve oxidation stability
What grease additive should be used for heavy loads?
Ep additives or molybdenum disulphides
What is most important when applying grease?
The right amount of grease is being applied at the right intervals
What are some of the main methods for applying grease?
Single point methods such as:
Grease cups
Grease guns
Centralized systems:
Automatic
Manual
How do you grease a high speed bearing? Higher Than 500 rpm
House should not be more then 1/3 full
Housing should be fitted with vents to allow excess grease to flow out
On high speed applications over 3600 rpm refer to manufacturers instructions
When should you check a bearing for temp after new grease has been installed? What should the temperature of the bearing be?
After 3 hours
Should not be above 60 degrees C
For proper lubrication plain bearings need minimum of ________ “ of clearance.
.001”
To much clearance can move the shaft out of alignment
Why should EP lubricants not be used in worm wheel gear boxes with bronze in them?
EP additives tend to corrode copper and Bronze
Why should you treat maintenance of the lubrication system the same as you would for any critical component of the machine?
Improperly maintained lubrication system will cause the rest of the machine to fail
