Lubrication Flashcards
What are the 3 types of friction?
Sliding friction
Rolling friction
Fluid friction
Describe sliding friction?
Sliding friction occurs when two surfaces slide over each other.
Describe rolling friction?
Rolling friction occurs when a spherical or cylindrical body rolls over a surface
Describe fluid friction?
When lubricant oil is applied to two surfaces in contact, a film of oil is formed. Filling up depressions and covering projections on both surfaces.
Because there is no metal on metal contact sliding occurs between the layers of oil.
What is lubrication?
The reduction of friction to a minimum by the replacement of dry friction with lubrication.
What is viscosity?
Viscosity is the resistance to flow. Oils with high viscosity are thicker and pour more slowly then those of lower viscosity.
What is the most important property of lubricating oil?
Viscosity
Choosing the best viscosity oil depends on what?
Speed (RPM)
Load
Temperature
Pressure
Environment
What are the two ways viscosity it measured?
Dynamic - determined by the force required to overcome fluid friction in a film of known dimensions
Kinematic - the measure of viscosity that is affected by the density of the oil.
Describe oil wedgeing?
Clearance in a bearing is taken up by oil.
As the shaft rotates oil climbs side of bearing. Moving in the opposite direction.
Eventually oil surrounds entire shaft
At full speed oil enters the area of lowest pressure
Now the shaft carries the oil in the same direction toward the area of maximum pressure.
Now an oil wedge is formed pushing the shaft up toward the centre of the bearing.
Efficiency of the oil wedge depend on what?
Load
Rubbing speed Or rpm
Operating temperature
Clearance between surfaces
Oil viscosity
Volume of lubricant
Where lubricant is introduced
Shaft surface finish
Boundary lubrication occurs when?
The film of oil fails for a short time.
What can cause hydraulic locking?
Over lubricating
Oxidation occurs because?
All petroleum and vegetable oils chemically react with oxygen.
Oxidation is increased by high temperatures, air, contaminants or water.
What are the two waste products oxidation produces?
Oil-insoluble materials such as varnish or sludge
Oil-soluble acids
Describe demulsibility?
The ability of a petroleum oil to separate from water upon standing.
It can be increased by additives
Describe Emulsibilty?
The ability of a petroleum oil to mix with water using a special emulsifying agent.
What does a rust inhibitor do?
Helps reduce the rusting of ferrous parts in the system.
What are the two types of oil lubrication systems?
A once through system
Or
Wasted oil system
Splash lubrication is most common in?
Enclosed gear systems
Worm gears and moderate speed chains are lubed by?
Running through an oil bath
High speed bearings and high velocity roller chains use a?
Oil mist system.
When doing an approximate oil quality you would check for?
Smell
Touch
Site
EP (extreme pressure) grease is used for?
Shock loaded or high local pressure areas
NLGI grades are measure by?
Numbers 00 -6. Six being the hardest.
What precautions are taken when using different grease?
Don’t mix grease from different manufactures
Don’t mix various grease grades
Don’t use extra additives
Describe the procedure for hand packing bearings?
Fill the spaces between the rings with grease after assembly
Pack the housing 1/3 full for high speeds and 1/2 full for slow speeds
Do not over pack with grease.
Open gears are lubricated with a grease or a heavy oil what conditions must you consider?
Temperature
Method of application
Environment
Gear materials
Choice of lubricant
What factors are considered for enclosed gears?
Load
Operating speed
Operating temperature
Lubrication methods
Type of gear
Environment
Oil lubrication is used in what temperatures?
Below 0 to 93 degrees C
How much oil do you use in a bearing oil bath?
Oil should cover the bottom of the outer race but does not cover the centre point of the lowest ball or roller
What are the advantages of using greased?
Good lubricant for heavy loads at low or medium speeds
Requires relatively simple seals
Provides better start up protection offer short periods of downtime
Gives better protection against rust during periods of downtime.
Tends to stay in place
What are the advantages of using oil as a lubricant?
Good for high and very high speeds
Developes less fluid friction than grease
Had a flushing action that pushes dirt and contaminants to the bottom of the housing
Can be used as a heat exchange medium
Can be removed easily from the housing
What is the purpose of cutting oil?
Cool the workpiece
Cool the cutting tool
Protect against rust
Prevent welding of metal chips with the tool
Wash away metal chips
Allow high speed cutting for better productivity and surface finish
