CLS Grease Technology & Application 1 — Questions and Answers
Question 1: What is the primary function of a thickener in lubricating grease?
- To lower the oil's viscosity
- To act as a sponge-like structure that holds the base oil (Correct answer)
- To increase the flash point of the grease
- To neutralize acidic contaminants
Correct answer: To act as a sponge-like structure that holds the base oil
The thickener forms a three-dimensional matrix or sponge-like structure that holds the base oil in place and releases it under shear during lubrication.
Question 2: Which NLGI grade is most commonly used for general-purpose bearing lubrication in most industrial applications?
- NLGI 00
- NLGI 1
- NLGI 2 (Correct answer)
- NLGI 4
Correct answer: NLGI 2
NLGI Grade 2 is the most widely used grade for general-purpose bearing lubrication due to its balance of consistency and pumpability under typical operating conditions.
Question 3: What does the dropping point of a grease indicate?
- The minimum temperature at which the grease can be pumped
- The temperature at which the grease begins to bleed oil
- The temperature at which the grease loses its structure and becomes liquid (Correct answer)
- The maximum load the grease can support
Correct answer: The temperature at which the grease loses its structure and becomes liquid
The dropping point is the temperature at which the grease transitions from a semi-solid to a liquid state, indicating its upper operating temperature limit.
Question 4: Which thickener type is generally considered incompatible with most other thickener types?
- Lithium complex
- Polyurea (Correct answer)
- Calcium sulfonate
- Bentone (clay)
Correct answer: Polyurea
Polyurea-thickened greases are generally incompatible with most other grease thickener types, including lithium and calcium-based greases, and mixing can cause significant degradation.
Question 5: What is the purpose of EP (Extreme Pressure) additives in grease?
- To reduce grease bleeding at high temperatures
- To form a protective film on metal surfaces under high load and shock conditions (Correct answer)
- To increase the NLGI grade of the grease
- To improve the grease's resistance to water washout
Correct answer: To form a protective film on metal surfaces under high load and shock conditions
EP additives chemically react with metal surfaces under high pressure and temperature to form a sacrificial film that prevents metal-to-metal contact and welding.
Question 6: When is re-greasing of a bearing most appropriately performed in a continuous operation?
- Only when the bearing is cold and the equipment is shut down
- While the equipment is running so old grease can be purged (Correct answer)
- During annual scheduled shutdowns only
- Immediately after a contamination event regardless of interval
Correct answer: While the equipment is running so old grease can be purged
Re-greasing while equipment is running allows the old grease to be purged through the relief port and ensures fresh grease reaches the bearing raceways effectively.
Question 7: What property does Oil Separation (bleed) test measure in a grease?
- The tendency of base oil to separate from the thickener over time (Correct answer)
- The rate at which grease absorbs water
- The grease's resistance to shear degradation
- The evaporation rate of the base oil
Correct answer: The tendency of base oil to separate from the thickener over time
The Oil Separation test (ASTM D1742) measures the tendency of base oil to separate from the thickener matrix during storage or use, which affects shelf life and performance.
CLS Grease Technology & Application 1
What is the primary function of a thickener in lubricating grease?