CPM Preventive Maintenance and Lubrication 2

Question 1

Which NLGI grease consistency grade is most commonly used for general-purpose rolling element bearings?

Accepted Answer

NLGI 2

Answer

NLGI 2 has a peanut-butter consistency that suits most plain and rolling element bearings.

Question 2

A lubricating oil's viscosity index (VI) describes what property?

Accepted Answer

How much its viscosity changes with temperature

Answer

A higher VI means the oil's viscosity changes less as temperature rises or falls.

Question 3

An oil labeled ISO VG 68 has a nominal kinematic viscosity of 68 cSt at what temperature?

Accepted Answer

40°C

Answer

ISO viscosity grades are defined by kinematic viscosity at 40°C.

Question 4

What is the most likely result of over-greasing a sealed-housing ball bearing?

Accepted Answer

Higher operating temperature from grease churning

Answer

Excess grease is churned by the rolling elements, generating friction heat and possibly blowing out seals.

Question 5

What can happen when two greases with incompatible thickeners are mixed in a bearing?

Accepted Answer

The mixture can soften, bleed oil, and lose its ability to stay in place

Answer

Incompatible thickeners can break down the grease structure, causing softening and leakage.

CPM - Certified Plant Mechanic Practice Test