ITMC Lubrication 4 — Questions and Answers
Question 1: What is the primary reason synthetic lubricants are preferred over mineral oils in extreme cold temperature applications?
- Synthetic oils have higher flash points, making them safer at low temperatures
- Synthetic oils maintain lower viscosity at cold temperatures and have lower pour points (Correct answer)
- Synthetic oils contain more EP additives suitable for cold environments
- Synthetic oils are thicker at low temperatures, providing better film protection
Correct answer: Synthetic oils maintain lower viscosity at cold temperatures and have lower pour points
Synthetic lubricants are engineered to flow at much lower temperatures than mineral oils, ensuring proper lubrication during cold starts.
Question 2: In a centralized automatic lubrication system, what is the role of the injector or metering valve?
- To pressurize the main reservoir to push lubricant to all points
- To deliver a precise, measured amount of lubricant to each lubrication point per cycle (Correct answer)
- To filter contamination from the lubricant before distribution
- To detect when a lubrication point has received too much grease and shut off flow
Correct answer: To deliver a precise, measured amount of lubricant to each lubrication point per cycle
Injectors or metering valves in centralized systems dispense a fixed, pre-set volume of lubricant to each point during each pressurization cycle.
Question 3: What is 'oxidation stability' in the context of lubricating oils?
- The oil's ability to resist chemical breakdown when exposed to oxygen over time (Correct answer)
- The oil's resistance to changes in viscosity under load
- The oil's ability to prevent corrosion on ferrous metals
- The oil's capacity to suspend and carry away wear particles
Correct answer: The oil's ability to resist chemical breakdown when exposed to oxygen over time
Oxidation stability measures how well an oil resists reacting with oxygen, which causes thickening, varnish, sludge, and acid formation that shorten oil and equipment life.
Question 4: A ball bearing has a recommended relubrication interval of 2,000 hours. The bearing is operating at twice the rated speed. How should the relubrication interval be adjusted?
- Keep the interval the same since speed does not affect grease life
- Extend the interval because higher speed generates heat that keeps grease fluid
- Shorten the interval because higher speed degrades grease more rapidly (Correct answer)
- Double the grease quantity per interval instead of changing the interval
Correct answer: Shorten the interval because higher speed degrades grease more rapidly
Higher operating speeds increase heat generation and mechanical working of the grease, accelerating degradation and requiring more frequent relubrication.
Question 5: What is the correct procedure when switching a system from a mineral oil to a synthetic lubricant?
- Add the synthetic directly on top of the mineral oil to allow gradual blending
- Drain the mineral oil, flush the system thoroughly, then fill with synthetic (Correct answer)
- Mix equal parts mineral and synthetic to create a transition blend
- Increase the quantity of synthetic used to displace the residual mineral oil
Correct answer: Drain the mineral oil, flush the system thoroughly, then fill with synthetic
Most synthetic lubricants are incompatible with mineral oils; the system must be fully drained and flushed to prevent the mixture from degrading both lubricants' performance.
Question 6: Which bearing failure mode is directly associated with lubricant film breakdown due to metal-to-metal contact?
- Fretting corrosion
- Fatigue spalling
- Adhesive wear (scuffing/scoring) (Correct answer)
- Electrical erosion fluting
Correct answer: Adhesive wear (scuffing/scoring)
Adhesive wear (scuffing or scoring) occurs when the lubricant film fails and opposing metal surfaces weld and tear apart microscopically due to direct contact.
Question 7: What does the 'four-ball wear test' evaluate in a lubricant?
- The lubricant's resistance to oxidation at elevated temperatures
- The lubricant's ability to prevent wear and its load-carrying capacity (Correct answer)
- The lubricant's pour point under refrigerated conditions
- The lubricant's foaming tendency under agitation
Correct answer: The lubricant's ability to prevent wear and its load-carrying capacity
The four-ball wear test uses three stationary balls and one rotating ball under load to measure the lubricant's wear scar diameter and load-carrying (EP) performance.
ITMC Lubrication 4
What is the primary reason synthetic lubricants are preferred over mineral oils in extreme cold temperature applications?