CLS Lubrication Fundamentals & Applications 2

Question 1

Which lubrication regime is characterized by complete separation of surfaces by a full fluid film?

Accepted Answer

Hydrodynamic lubrication

Answer

Hydrodynamic lubrication occurs when a full fluid film completely separates the mating surfaces, eliminating metal-to-metal contact.

Question 2

What does the Stribeck curve illustrate?

Accepted Answer

The friction coefficient across different lubrication regimes as a function of speed and viscosity

Answer

The Stribeck curve plots friction coefficient against the ratio of viscosity × speed / load, showing transitions between boundary, mixed, and full-film lubrication regimes.

Question 3

What is the primary purpose of an EP (Extreme Pressure) additive in a lubricant?

Accepted Answer

To chemically react with metal surfaces under high pressure to prevent welding

Answer

EP additives form sacrificial chemical films on metal surfaces at high contact pressures, preventing scuffing and welding of asperities.

Question 4

Which property of a grease describes its resistance to flow and is measured by a cone penetration test?

Accepted Answer

Consistency (NLGI grade)

Answer

NLGI consistency grade, determined by cone penetration depth, classifies grease firmness from 000 (very fluid) to 6 (very hard).

Question 5

What is meant by the 'viscosity index' (VI) of a lubricant?

Accepted Answer

A measure of how much viscosity changes with temperature

Answer

Viscosity index indicates the rate of viscosity change with temperature; a higher VI means less viscosity change over a given temperature range.

(CLS) Certified Lubrication Specialist Practice Test

(CLS) Certified Lubrication Specialist Practice Test

CLS Lubrication Fundamentals & Applications 2