Lubrication Flashcards
What is friction?
Is the tendency to resist movement when two surfaces are in contact as they move.
List the negative effects of friction.
- increases power consumption
- causes wear
- creates heat reducing component life
Name the three types of friction?
- sliding friction
- rolling friction
- fluid friction
What type of friction exists within a lubricant?
Fluid friction.
What are the functions of a lubricant?
- stop corrosion
- reduce heat
- carry away contaminants
- help seal
- reduce friction (wear)
Describe Full Film lubrication.
Completely separates surfaces with a continuous film.
What is Sliding Friction?
When two surfaces slide over each other.
Describe Boundary Film lubrication.
A film that does not completely separate the surfaces.
How does a lubricant reduce friction?
By separating two surfaces with a film that has less friction than the moving parts.
What is Rolling Friction?
When a spherical or cylindrical body rolls over a surface.
What is the Theory of Adhesion?
Adhesive forces cause “unlike” materials to stick together.
What is the Theory of Cohesion?
Cohesive forces cause molecules of “like” materials to stick together.
Oil forms in layers of ________.
Globules.
What is Viscosity?
The resistance to flow.
What five things should be considered when choosing the right viscosity lubricant?
- speed (RPM)
- load
- temperature
- pressure
- environment
What does higher viscosity allow?
Greater loads to be carried.
What should be done to minimize power loss?
Use the lowest viscosity oil that is able to carry the load.
Name the two ways viscosity is measured?
Dynamic and Kinematic.
Dynamic viscosity is use to measure __________.
Fluid friction.
What is the most common British unit of Kinematic viscosity?
Centistoke (cSt).
Viscosity changes due to temperature are indicated by the __________.
Viscosity Index (VI).
What does a higher Viscosity Index number mean?
The smaller the change in viscosity due to temperature.
What are the three main groups Additives and Inhibitors are divided into?
- air control
- water control
- load capacity
What is Demulsibility?
The ability of petroleum to separate from water upon standing.
What is Emulsibility?
The ability of petroleum to mix with water using a special emulsifying agent.
Additives that reduce wear by polishing contacting parts are called ___________.
Anti-wear Additives.
Additives used for heavy load or shock load conditions are called __________.
Extreme Pressure Additives (EP).
How is grease usually made?
By thickening lubricating oils with “soap”.
What is the “soap” content for general use greases?
Between 7% - 18%. (Specialty grease can range from 3% - 50%).
Greases made by combining a fatty acid and a base metal are called __________.
Simple Soap Greases.
Name the five base metals used in simple soap greases.
- calcium
- sodium
- aluminum
- lithium
- barium
How is grease consistency measured?
Penetration Numbers.
What does NLGI stand for?
National Lubricating Grease Institute
What is Dropping Point when referring to grease?
Is the temperature at which a grease becomes fluid.
When in a bearing, grease “shears” into thin layers and follows rotation. This is called what?
Directional Fluidity.
Which is the best lubricant for heavy loads at low to medium speeds?
Grease
Which is the best lubricant for high to very high speeds?
Oil
When machining what is the main purpose of the lubricating cutting fluid?
To reduce friction.
Which cutting oil should only be used on ferrous metals?
Active oil.
Which cutting oil is used on both ferrous and non ferrous metals?
Inactive oil.
What are the positive effects of friction?
- provides traction
- allows a means of polishing
- used to start, accelerate and stop machines
- promotes accurate tracking in bearing raceways
What is elasto-hydrodynamic lubrication?
A lubricant film that forms under a loaded rolling element.
What is the United States kinematic unit of viscosity measured by a Saybolt Viscometer?
Saybolt Universal Seconds. (SUS or SSU)
What is Absolute Viscosity and how is it measured?
A direct measurement of the force of resistance to flow measured in centipoises.
What is Flashpoint?
The lowest temperature at which the vapor above the oil will ignite with a flame passed over it.
What type of oil was developed to solve lubricating problems that petroleum oils can’t?
Synthetic oil.
What are Additives?
Chemicals added to the base oil to enhance performance of the oil under specific operations.
What are Oxidization Inhibitors?
Additives in the oil that work to inhibit the process of oxidization.
What are Anti-wear additives?
Additives that combine chemically with the surface of the metal to form a protective coating.
What are the functions of Detergent Additives?
- keeps sludge and fine deposits off metal surfaces
- anti wear and anti scuff properties
- clean existing deposits
- rust inhibitor
- controls acid
What is the most common Solid Additive and what is its purpose?
Graphite and it is used as an anti-wear additive.
What is the purpose of Pour Point Depressants?
To make oil flow easier at lower temperatures.
What is the function of a Demulsifier?
To separate water from oil.
