ITMC Lubrication 2 — Questions and Answers
Question 1: What does the viscosity index (VI) of an oil indicate?
- The oil's resistance to oxidation at high temperatures
- How much the oil's viscosity changes with temperature (Correct answer)
- The oil's ability to resist foaming
- The oil's flash point temperature
Correct answer: How much the oil's viscosity changes with temperature
Viscosity index measures how much an oil's viscosity changes with temperature — a higher VI means the viscosity stays more stable across temperature ranges.
Question 2: Which lubrication method continuously delivers oil to a bearing by using a wick or felt pad submerged in an oil reservoir?
- Splash lubrication
- Mist lubrication
- Wick-feed lubrication (Correct answer)
- Pressure-feed lubrication
Correct answer: Wick-feed lubrication
Wick-feed lubrication uses capillary action through a wick or felt pad to draw oil from a reservoir and deliver it continuously to a bearing surface.
Question 3: What is the primary purpose of an EP (extreme pressure) additive in a lubricant?
- To lower the pour point of the lubricant
- To prevent metal-to-metal contact under high load conditions (Correct answer)
- To increase the oil's viscosity at operating temperature
- To neutralize acids formed during oxidation
Correct answer: To prevent metal-to-metal contact under high load conditions
EP additives react chemically with metal surfaces under high pressure and temperature to form a sacrificial film that prevents metal-to-metal contact and welding.
Question 4: A grease with an NLGI grade of 2 is compared to one with an NLGI grade of 0. Which statement is correct?
- Grade 0 is stiffer and better for high-speed bearings
- Grade 2 is stiffer and more commonly used in general bearing applications (Correct answer)
- Grade 2 flows more freely and is used in centralized systems
- Both grades have identical consistency
Correct answer: Grade 2 is stiffer and more commonly used in general bearing applications
Higher NLGI numbers indicate stiffer grease; NLGI 2 is a medium-firm grease used widely in general-purpose bearing lubrication.
Question 5: During a routine oil analysis, the report shows a high level of silicon in the oil sample. What does this most likely indicate?
- Bearing wear is occurring inside the gearbox
- Dirt or dust is entering the system through a failed seal or breather (Correct answer)
- The oil has become oxidized
- Copper alloy components are degrading
Correct answer: Dirt or dust is entering the system through a failed seal or breather
Silicon is a primary indicator of dirt or dust ingression, which typically occurs through failed seals, damaged breathers, or contaminated fill equipment.
Question 6: What is the function of a labyrinth seal on a lubricated bearing housing?
- To pressurize the bearing housing to keep lubricant in
- To create a tortuous path that prevents contaminants from entering without contact friction (Correct answer)
- To meter the exact amount of grease delivered to the bearing
- To act as a pressure relief when grease is over-applied
Correct answer: To create a tortuous path that prevents contaminants from entering without contact friction
Labyrinth seals use a series of grooves and channels to create a non-contact barrier that makes it difficult for contaminants to enter the bearing housing.
Question 7: Which property of a lubricant describes its ability to spread over and adhere to metal surfaces even under pressure?
- Viscosity
- Demulsibility
- Film strength (oiliness) (Correct answer)
- Pour point
Correct answer: Film strength (oiliness)
Film strength or oiliness refers to a lubricant's ability to maintain an adsorbed film on metal surfaces and resist being squeezed out under load.
ITMC Lubrication 2
What does the viscosity index (VI) of an oil indicate?