CLS Lubricant Selection & Management 2 — Questions and Answers
Question 1: A high-speed spindle bearing operates at 25,000 RPM with a light radial load. Which grease consistency grade is most appropriate?
- NLGI 2
- NLGI 0 (Correct answer)
- NLGI 4
- NLGI 6
Correct answer: NLGI 0
Lighter NLGI grades (0 or 1) are preferred for high-speed applications because they offer lower churning resistance and better flow to the bearing.
Question 2: Which base oil property most directly determines the suitability of a lubricant for low-temperature start-up conditions?
- Viscosity Index
- Pour Point (Correct answer)
- Flash Point
- Acid Number
Correct answer: Pour Point
Pour point is the lowest temperature at which an oil flows, making it the key indicator for cold-start lubricant selection.
Question 3: A food-processing facility requires a lubricant for incidental food contact. Which lubricant designation is required by USDA/NSF?
- H2
- H1 (Correct answer)
- 3H
- HX-1
Correct answer: H1
NSF H1 lubricants are approved for incidental food contact and are required wherever accidental contact with food is possible.
Question 4: When selecting a compressor oil for a reciprocating air compressor, which property is critical to prevent deposit formation and fire risk?
- High Viscosity Index
- Low Flash Point
- Low Carbon Residue (Correct answer)
- High Pour Point
Correct answer: Low Carbon Residue
Low carbon residue (Conradson or Ramsbottom test) minimizes deposit buildup in hot discharge zones, reducing fire and explosion risk.
Question 5: A lubricant's 'R&O' designation indicates it contains which additive package?
- Rust inhibitors and oxidation inhibitors only (Correct answer)
- Rust inhibitors and oiliness agents
- Oxidation inhibitors and EP additives
- Rust inhibitors and detergents
Correct answer: Rust inhibitors and oxidation inhibitors only
R&O oils contain rust inhibitors and oxidation inhibitors, making them suitable for circulating systems and turbines without EP additives.
Question 6: Which lubrication regime is characterized by the lubricant film completely separating the mating surfaces with no asperity contact?
- Boundary lubrication
- Mixed lubrication
- Hydrodynamic lubrication (Correct answer)
- Elastohydrodynamic lubrication
Correct answer: Hydrodynamic lubrication
In full hydrodynamic lubrication, a continuous pressurized film separates surfaces entirely, resulting in very low friction and wear.
Question 7: An engineer selects a gear oil with an ISO VG 320 viscosity grade. At 40°C, the kinematic viscosity will be closest to:
- 100 cSt
- 220 cSt
- 320 cSt (Correct answer)
- 460 cSt
Correct answer: 320 cSt
ISO VG grades define the nominal kinematic viscosity in cSt at 40°C, so ISO VG 320 oil has approximately 320 cSt at 40°C.
CLS Lubricant Selection & Management 2
A high-speed spindle bearing operates at 25,000 RPM with a light radial load.
Which grease consistency grade is most appropriate?