ITMC Lubrication 5 — Questions and Answers
Question 1: Which condition describes 'false brinelling' in a bearing, and what lubrication-related practice helps prevent it?
- Overloading that dents raceways; prevented by using higher-viscosity oil
- Fretting wear in stationary bearings caused by vibration; prevented by using grease with corrosion inhibitors and anti-wear additives (Correct answer)
- Electrical discharge pitting; prevented by using conductive grease
- Spalling from fatigue; prevented by more frequent oil changes
Correct answer: Fretting wear in stationary bearings caused by vibration; prevented by using grease with corrosion inhibitors and anti-wear additives
False brinelling occurs when vibration causes micro-motion between rolling elements and raceways in stationary bearings, creating wear; protective grease with corrosion inhibitors helps mitigate this.
Question 2: What is the significance of the 'total acid number' (TAN) in oil analysis?
- It measures the quantity of anti-wear additives remaining in the oil
- It indicates the level of acidic degradation products formed from oil oxidation (Correct answer)
- It quantifies the water content dissolved in the oil sample
- It measures the detergent additive concentration in engine oil
Correct answer: It indicates the level of acidic degradation products formed from oil oxidation
TAN (Total Acid Number) increases as oil oxidizes and forms acidic byproducts; a rising TAN signals oil degradation and the potential for corrosive damage to metal surfaces.
Question 3: A plant uses an ISO VG 68 hydraulic oil. In summer the system runs hot and performance suffers. Which action correctly addresses this using lubricant selection?
- Switch to ISO VG 32 to reduce heat buildup from viscous shear
- Switch to ISO VG 100 to maintain adequate film thickness at the higher operating temperature (Correct answer)
- Add a pour point depressant to the existing ISO VG 68 oil
- Blend the ISO VG 68 with grease to create a heavier lubricant
Correct answer: Switch to ISO VG 100 to maintain adequate film thickness at the higher operating temperature
At high temperatures, oil thins; switching to a higher ISO VG grade (e.g., VG 100) ensures the film remains thick enough to protect components at elevated operating temperatures.
Question 4: When taking an oil sample for analysis from a hydraulic system, which sampling method provides the most representative sample?
- Draining a sample from the bottom drain plug at shutdown
- Sampling from a live zone in the return line using a vacuum pump or minimess valve while the system is running (Correct answer)
- Removing the fill cap and collecting oil from the surface of the reservoir
- Sampling from the filter housing drain before the filter is changed
Correct answer: Sampling from a live zone in the return line using a vacuum pump or minimess valve while the system is running
Sampling from a live zone in the return line while the system is running captures a representative, well-mixed sample that accurately reflects the oil and contamination condition.
Question 5: What is the purpose of a 'base number' (BN or TBN) measurement in lubricating oil analysis?
- It measures the oil's viscosity stability over a temperature range
- It indicates the reserve alkalinity available to neutralize acids formed during operation (Correct answer)
- It measures the concentration of sulfur compounds in the oil
- It quantifies the quantity of metallic wear particles in the sample
Correct answer: It indicates the reserve alkalinity available to neutralize acids formed during operation
Total Base Number (TBN) measures the oil's remaining alkaline reserve, which neutralizes acidic combustion byproducts and oxidation products; a depleted TBN means the oil can no longer protect against acid corrosion.
Question 6: Which factor most directly determines whether a plain (journal) bearing operates in the hydrodynamic lubrication regime?
- The thermal conductivity of the bearing metal
- The shaft surface finish (roughness) alone
- The combination of shaft speed, oil viscosity, and applied load (Sommerfeld number) (Correct answer)
- The type of oil additive package used
Correct answer: The combination of shaft speed, oil viscosity, and applied load (Sommerfeld number)
Hydrodynamic film formation in journal bearings is governed by the Sommerfeld number, which combines shaft speed, oil viscosity, bearing geometry, and load to predict film thickness.
Question 7: A technician is lubricating an open gear drive exposed to the environment. Which type of lubricant is most appropriate for this application?
- Low-viscosity turbine oil for easy spray application
- Tacky, high-viscosity open gear compound that resists fling-off and protects against moisture and wear (Correct answer)
- ISO VG 32 hydraulic oil for good penetration between gear teeth
- NLGI 000 fluid grease for easy flow at low temperatures
Correct answer: Tacky, high-viscosity open gear compound that resists fling-off and protects against moisture and wear
Open gear compounds are formulated to be highly viscous, tacky, and adhesive to resist centrifugal fling-off, while providing heavy-duty EP protection and moisture resistance on exposed gear drives.
ITMC Lubrication 5
Which condition describes 'false brinelling' in a bearing, and what lubrication-related practice helps prevent it?