Lubrication Flashcards
Purposes of lubrication
- Reduce friction
- Reduce wear and abrasive wear
- Dampen shock
- Provide cooling
- Reduce corrosion
- Minimize intrusion of contaminates
Define Friction
A force that acts between 2 surfaces to resist their sliding or rolling across each other
What is Static or Surface Friction
Static friction exists between a body at rest and the surface upon which it rests.
Static friction must be overcome to start a body in motion and keep it in motion.
What is kinetic friction
Friction that exists between moving bodies or between one moving body and a stationary surface. Kinetic friction must be overcome to keep a body in motion.
3 types
Sliding friction
Rolling friction
Fluid friction
Development of oil wedge
Depends on cohesion, adhesion and viscosity
At rest, shaft and bearing make contact through boundary film layers. As shaft begins to turn (roll uphill)a oil wedge begins to form at the edge of the crescent between shaft and bearing. As oil is forced into small wedge its viscosity increases, causing opposing fluid pressure to build and separate shaft and bearing surfaces. As shaft speed increases, adhesive and cohesive properties drag additional film layers into wedge from top of crescent. Full film is established when shaft turning at full speed towards center of bearing
General classifications of lubricants
Liquid
Semisolid
Solid
Gas
Major properties of oil
Viscosity- tendency of fluid to resist flow due to internal friction of molecules
Flash point- temp at which oil is vaporized enough to momentarily ignite when a flame or spark applied
Auto ignition point-temp at which the flammable vapors is an oil will burn without spark or flame
Neutralization number- acid content of oil
Demulsibility- ability of oil and water to separate
Precipitation- amount of carbon or asphalt residue
Major properties of grease
Oil- basic lubricant. Higher viscosity for high temp or slow speed. Lower viscosity for more modest temps and high speeds
Thickener- supplies body. Most common is soap
Additives-enhance properties. Can improve characteristics such as oxidation stability, load carrying capability and consistency. Fillers can also be added to further extend properties. Graphite, molybdenum and zinc oxide are typical
Hardness, dropping point, stability, water resistance and pumpability are additional properties.
Considerations for designing lubrication systems
Regulation-control of flow
Adaptability- can it be adjusted
Uniform rate-supplies lubricant at set rate for long periods
Continuity-must reach desired destination
Reliability- reliable
Methods and Systems for lubrication
Manual-oil cans, grease guns
Gravity or Drip Feed-oil drips thru needle valve
oilers- rings, gears or scoops pick up oil from reservoir and deposit oil on moving parts
Pressure lubrication-pump or pneumatics
- Wet sump- sump is integral
- dry sump- sump is external
Air line lubricator- air flows thru a Venturi, creates a low pressure area, to draw in oil. Oil enters air line and is broken down into a mist, which goes on to lubricate equipment
Methods of oil purification
Gravity settling-simplest and slowest
Centrifuge- centrifugal force moves water and particulate outward as the oil flows upward thru discs
Turbo Toc-uses filters to remove water and particulates
Symptoms of improper lubrication
High temperature
Vibration
Varnish and lacquer deposits
Foaming
Proper methods for lubricant storage
Proper storage is important for following reasons:
- can cause safety and fire hazard
- reduces possibility of obtaining wrong type of lubricant
- use older lubricants first and store new stock in back
Inside- stored in paint locker or separate room of fireproof construction. Should have automatic fire suppression and portable fire extinguishers. All lubricants positioned so they are easily accessible and so ID markings are visible
Outside- 55 gallon drums should be placed on their sides and covered to protect them from weather. Placing on side prevents water from collecting on top and corroding drum. Ensure drums are raised off ground to prevent corrosion of bottom.
Safety precautions for handling lubricants
Smoking prohibited
Provide adequate ventilation
Wear gloves and long sleeved shirt
Wear safety glasses or goggles
Environmental hazards
Oil spill-
Small- soak up and dispose
Large- wear respirator and protective clothing. Dike and contain. Remove with vacuum or pump to storage vessel. Get help from Environmental Department. Surface Soil/Groundwater contamination. Air Pollution.
Lube oil reservoir has a mist eliminator to meet Maricopa County Pollution regulations.
