Millwright Certification Lubrication Systems and Practices 2 — Questions and Answers
Question 1: What is the purpose of a bearing isolator (labyrinth seal) used at bearing housings?
- To retain grease inside the bearing and exclude contamination without contact friction (Correct answer)
- To measure bearing temperature continuously
- To provide emergency lubrication on seal failure
- To align the bearing during installation
Correct answer: To retain grease inside the bearing and exclude contamination without contact friction
Bearing isolators use a non-contact labyrinth design to keep lubricant in and contaminants out without the wear associated with lip seals.
Question 2: In a forced (pressure) lubrication system, the oil pump is typically driven by:
- A separate electric motor only
- The main machine shaft, an electric motor, or a hydraulic motor (Correct answer)
- Gravity feed from an overhead tank
- Compressed air
Correct answer: The main machine shaft, an electric motor, or a hydraulic motor
Forced lubrication system pumps can be shaft-driven, motor-driven, or hydraulically driven depending on the machine design.
Question 3: What does ISO VG 68 indicate about a lubricating oil?
- The oil has a kinematic viscosity of approximately 68 cSt at 40°C (Correct answer)
- The oil meets ISO standard grade 68 for cleanliness
- The oil has a flash point of 68°C
- The oil is suitable for use up to 68°C
Correct answer: The oil has a kinematic viscosity of approximately 68 cSt at 40°C
ISO VG (Viscosity Grade) 68 specifies a midpoint kinematic viscosity of 68 cSt at 40°C, with a tolerance band of ±10%.
Question 4: Which condition indicates that lubricating oil should be changed immediately?
- Oil temperature is above ambient
- Oil appears dark or has a strong burnt smell and high acid number (Correct answer)
- Oil viscosity is slightly higher than new oil
- Oil has minor air bubbles after pump startup
Correct answer: Oil appears dark or has a strong burnt smell and high acid number
Dark color, burnt odor, and elevated acid number (TAN) indicate oxidation and thermal degradation, meaning the oil has lost its protective properties.
Question 5: A centralized automatic grease system is most beneficial for:
- Bearings that only require annual lubrication
- Multiple lubrication points that are difficult to access or require frequent greasing (Correct answer)
- High-speed spindle bearings requiring oil mist lubrication
- Sealed-for-life bearings
Correct answer: Multiple lubrication points that are difficult to access or require frequent greasing
Centralized systems deliver precise grease quantities automatically to many points simultaneously, improving reliability and safety where manual access is difficult or frequent.
Question 6: When lubricating an open gear drive (such as a kiln or mill pinion), the lubricant of choice is typically:
- Light machine oil (ISO VG 32)
- Heavy open gear compound with tackifiers and anti-wear additives (Correct answer)
- Food-grade white grease
- Engine motor oil SAE 30
Correct answer: Heavy open gear compound with tackifiers and anti-wear additives
Open gear compounds are high-viscosity, adhesive lubricants with tackifiers that cling to teeth under heavy loads and low speeds, protecting against wear and scuffing.
Millwright Certification Lubrication Systems and Practices 2
What is the purpose of a bearing isolator (labyrinth seal) used at bearing housings?