Lubrication Flashcards
6 cards from real Ramsay Test practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Lubrication flashcards as text
Which type of lubricant is most appropriate for a high-speed ball bearing operating at elevated temperatures?
Answer: High-temperature bearing grease (NLGI Grade 2 or 3)
High-temperature bearing grease provides the necessary consistency to stay in place at speed and thermal stability to resist breakdown. EP gear oil and hydraulic fluid are not formulated to stay in bearings, and penetrating oil has no film strength.
NLGI grease consistency grades (000 through 6) measure which property?
Answer: The stiffness or consistency of the grease
NLGI grades classify grease from very fluid (000) to block-solid (6) based on worked penetration — essentially how stiff or soft the grease is. Base oil viscosity and dropping point are separate specifications.
A pillow-block bearing housing feels unusually hot and grease is purging out of the seals. The most likely cause is:
Answer: Over-greasing causing churning and heat buildup
Over-greasing forces excess grease through seals and causes the rolling elements to churn through the surplus, generating friction and heat. A dry bearing would show noise and rapid wear before heat; water contamination produces a milky grease appearance.
What is the primary function of Extreme Pressure (EP) additives in gear oil?
Answer: To form a protective chemical layer on gear teeth under high load and shock
Under high contact stress, EP additives chemically react with metal surfaces to form a sacrificial layer that prevents metal-to-metal welding and scoring. The other functions belong to viscosity index improvers, pour point depressants, and antioxidants respectively.
A technician finds that grease in a bearing has turned black and smells burnt. The most likely cause is:
Answer: Thermal degradation from overheating beyond the grease's service temperature
Black discoloration combined with a burnt odor is the classic signature of thermal degradation — the grease has been exposed to temperatures beyond its rated range, carbonizing the thickener and base oil. Water contamination produces a milky or whitish appearance; mixing incompatible greases causes softening or hardening.
When establishing a relubrication schedule for a bearing, which factor has the GREATEST influence on the interval?
Answer: Bearing speed (RPM) and operating temperature
Operating speed and temperature are the dominant variables in lubrication interval calculations. Higher RPM generates more heat and shears the grease faster; elevated temperature accelerates oxidation and base oil evaporation. Standard interval formulas (such as those in SKF or Dodge bearing handbooks) use these two inputs directly.