CLS Lubrication Fundamentals & Applications 3

Question 1

What is the significance of the 'film thickness ratio' (lambda, λ) in lubrication?

Accepted Answer

It compares the minimum film thickness to the composite surface roughness

Answer

Lambda ratio (λ = minimum film thickness / composite RMS surface roughness) determines the lubrication regime: λ>3 is full-film, 1–3 is mixed, and <1 is boundary.

Question 2

Which type of wear is caused by the formation and collapse of vapor bubbles in a lubricant?

Accepted Answer

Cavitation erosion

Answer

Cavitation erosion occurs when vapor bubbles form due to local pressure drops and then implode near metal surfaces, generating intense shock waves that pit the surface.

Question 3

What is the 'pour point' of a lubricant?

Accepted Answer

The lowest temperature at which a lubricant will flow under gravity

Answer

Pour point is the lowest temperature at which a lubricant will still flow, typically 3°C above the temperature at which flow ceases.

Question 4

In elastohydrodynamic lubrication (EHL), what happens to the lubricant's viscosity under very high contact pressures?

Accepted Answer

Viscosity increases dramatically, allowing it to support high loads

Answer

In EHL contacts, pressures can reach several GPa, causing the lubricant's viscosity to increase by orders of magnitude (piezo-viscous effect), enabling it to support high loads.

Question 5

What does the term 'oil bleed' refer to in the context of grease?

Accepted Answer

Separation of base oil from the thickener during storage or use

Answer

Oil bleed (or oil separation) is the release of base oil from the thickener matrix; controlled bleed is necessary for grease to lubricate, but excessive bleed indicates an unstable product.

(CLS) Certified Lubrication Specialist Practice Test

(CLS) Certified Lubrication Specialist Practice Test

CLS Lubrication Fundamentals & Applications 3