CLS Grease Technology & Application 3

Question 1

For a high-speed electric motor bearing (ndm > 300,000), which NLGI grade and base oil viscosity combination is most appropriate?

Accepted Answer

NLGI 2, ISO VG 32 base oil

Answer

NLGI 3, ISO VG 220 base oil

Answer

NLGI 0, ISO VG 460 base oil

Answer

NLGI 4, ISO VG 100 base oil

Question 2

What is the primary mechanism by which antioxidant additives in grease extend its service life?

Accepted Answer

They interrupt oxidation chain reactions by donating hydrogen atoms to free radicals

Answer

They neutralize acidic contaminants formed during oxidation

Answer

They increase the dropping point of the grease base

Answer

They coat metal surfaces to prevent catalytic oxidation

Question 3

Which factor most significantly increases the re-lubrication interval for a grease-lubricated bearing?

Accepted Answer

Reducing operating temperature and speed

Answer

Using a higher NLGI grade grease

Answer

Increasing the shaft diameter

Answer

Using a grease with a lower dropping point

Question 4

What condition is indicated when a grease sample taken from a bearing housing shows a significant decrease in worked penetration (hardening) compared to fresh grease?

Accepted Answer

Churning and working hardening or evaporation of lighter base oil fractions

Answer

Oxidation and thickener degradation producing soft, fluid grease

Answer

Mechanical shear breakdown reducing consistency

Answer

Excessive water contamination washing out the thickener

Question 5

What is the purpose of the 'purge and replace' method when switching to a new incompatible grease type?

Accepted Answer

To completely remove the old grease and prevent incompatible mixing that could cause degradation

Answer

To increase the NLGI grade of the new grease by blending in the old

Answer

To reduce the quantity of new grease needed for first fill

Answer

To flush out wear debris before introducing clean lubricant

Question 6

In evaluating grease for a food-grade application, which certification or standard is most relevant?

Accepted Answer

NSF H1 registration for incidental food contact

Answer

ISO 4406 cleanliness standard

Answer

NLGI GC-LB certification for automotive chassis

Answer

ASTM D2596 for EP performance

Question 7

What does the Four-Ball Weld Load test (ASTM D2596) specifically evaluate in a grease?

Accepted Answer

The maximum load at which the lubricant film fails and metal-to-metal welding occurs

Answer

The grease's ability to reduce wear under moderate load conditions

Answer

The viscosity of the base oil after separation from the thickener

Answer

The grease's resistance to oxidation at elevated temperatures