Lubrication Fundamentals & Applications Flashcards
7 cards from real CLS practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Lubrication Fundamentals & Applications flashcards as text
What is the effect of increasing lubricant viscosity on bearing operating temperature, assuming all other conditions remain constant?
Answer: Temperature increases because higher viscosity generates more churning and shear heat
Higher viscosity increases internal fluid friction (churning losses), generating more heat; selecting the minimum adequate viscosity balances film thickness against power loss and heat generation.
What is the purpose of a 'base number' (BN or TBN) in engine lubricants?
Answer: To quantify the oil's alkaline reserve available to neutralize acidic combustion products
Total Base Number (TBN, ASTM D2896) measures the alkaline reserve (mg KOH/g) that neutralizes sulfuric and other acids formed during combustion, protecting engine components.
What is 'oxidative thickening' of a lubricant and why is it a concern?
Answer: Viscosity increase caused by oxidation-driven polymerization and varnish formation in aged oil
Oxidative thickening occurs when heat and oxygen cause base oil molecules to polymerize, forming high-molecular-weight products and varnish that increase viscosity and restrict flow.
Which ASTM test method is commonly used to determine the oxidation stability of turbine and hydraulic oils?
Answer: ASTM D943 (TOST – Turbine Oil Stability Test)
ASTM D943 (TOST) measures the time in hours for turbine or hydraulic oil to reach a specified acid number under heat, oxygen, water, and metal catalyst conditions.
What is the function of a 'metal deactivator' additive in a lubricant?
Answer: To form a passive film on metal surfaces that inhibits catalytic oxidation of the oil
Metal deactivators (e.g., benzotriazole derivatives) chelate or coat catalytically active metal surfaces (especially copper), suppressing their ability to accelerate lubricant oxidation.
When selecting a lubricant for a worm gear drive, which property is most critical due to the high sliding contact between the worm and wheel?
Answer: Good film strength and anti-wear/EP properties to handle high sliding losses
Worm gears have predominantly sliding (not rolling) contact and low mechanical efficiency, requiring lubricants with excellent film strength, anti-wear/EP additives, and thermal stability.
What is 'micro-pitting' on gear teeth surfaces and what lubrication factor primarily influences it?
Answer: Shallow surface fatigue damage caused by asperity contact in the mixed lubrication regime
Micro-pitting is sub-surface fatigue damage creating tiny pits on gear flanks, driven by insufficient lambda ratio (thin film relative to surface roughness) in the mixed lubrication regime.