Millwright Certification Lubrication Systems and Practices 1 — Questions and Answers
Question 1: What does the viscosity grade of a lubricating oil describe?
- The oil's resistance to flow at a given temperature (Correct answer)
- The oil's flash point
- The additive package in the oil
- The oil's load-carrying capacity
Correct answer: The oil's resistance to flow at a given temperature
Viscosity is a measure of an oil's resistance to flow; higher viscosity oils flow more slowly and are used in higher-load, lower-speed applications.
Question 2: Which type of grease is most commonly used in electric motor bearings operating at high temperatures?
- Calcium grease
- Lithium complex grease (Correct answer)
- Sodium grease
- Bentonite clay grease
Correct answer: Lithium complex grease
Lithium complex grease has excellent high-temperature stability (dropping point above 260°C/500°F) and is the most widely specified grease for motor bearings.
Question 3: Over-greasing a rolling element bearing is dangerous because it can cause:
- Insufficient lubrication film
- Excessive heat from churning and possible seal damage (Correct answer)
- Bearing race corrosion
- Reduced bearing clearance
Correct answer: Excessive heat from churning and possible seal damage
Excess grease causes the rolling elements to churn through the grease, generating heat, which can degrade the lubricant and damage seals.
Question 4: What is the primary function of a splash lubrication system in a gearbox?
- To filter contaminants from the oil
- To use the rotation of gears to splash oil onto mating surfaces (Correct answer)
- To pressurize oil to all bearing surfaces
- To cool the gearbox through oil circulation
Correct answer: To use the rotation of gears to splash oil onto mating surfaces
Splash lubrication relies on the lower gears dipping into an oil sump and throwing oil onto gear teeth and bearing surfaces through rotation.
Question 5: What does a milky or cloudy appearance in gearbox oil indicate?
- Oxidation of the oil
- Water contamination (emulsification) (Correct answer)
- Metal particle contamination
- Additive depletion
Correct answer: Water contamination (emulsification)
Milky or cloudy oil indicates water has mixed with the oil and formed an emulsion, which severely reduces the oil's lubricating ability.
Question 6: An NLGI grade 2 grease is considered:
- Very soft, nearly fluid
- Medium consistency — the most common general-purpose grease grade (Correct answer)
- Very hard, almost solid
- A food-grade lubricant classification
Correct answer: Medium consistency — the most common general-purpose grease grade
NLGI Grade 2 is a medium-consistency grease (similar to peanut butter) and is the most widely used grade for general industrial bearing applications.
Millwright Certification Lubrication Systems and Practices 1
What does the viscosity grade of a lubricating oil describe?