Ramsay Test Lubrication — Questions and Answers
Question 1: Which type of lubricant is most appropriate for a high-speed ball bearing operating at elevated temperatures?
- EP (Extreme Pressure) gear oil
- High-temperature bearing grease (NLGI Grade 2 or 3) (Correct answer)
- Penetrating oil
- Hydraulic fluid
Correct 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.
Question 2: NLGI grease consistency grades (000 through 6) measure which property?
- The viscosity of the base oil in the grease
- The dropping point temperature of the grease
- The stiffness or consistency of the grease (Correct answer)
- The percentage of thickener by weight
Correct 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.
Question 3: A pillow-block bearing housing feels unusually hot and grease is purging out of the seals. The most likely cause is:
- Insufficient lubrication — the bearing is running dry
- Water contamination in the grease
- Over-greasing causing churning and heat buildup (Correct answer)
- The wrong NLGI grade — grease is too thin
Correct 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.
Question 4: What is the primary function of Extreme Pressure (EP) additives in gear oil?
- To raise the viscosity index so the oil thins less with temperature
- To form a protective chemical layer on gear teeth under high load and shock (Correct answer)
- To lower the pour point for cold-weather startup
- To prevent oxidation of the oil during storage
Correct 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.
Question 5: A technician finds that grease in a bearing has turned black and smells burnt. The most likely cause is:
- Normal darkening from extended service intervals
- Thermal degradation from overheating beyond the grease's service temperature (Correct answer)
- Water contamination from washdown operations
- Mixing of incompatible grease types
Correct 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.
Question 6: When establishing a relubrication schedule for a bearing, which factor has the GREATEST influence on the interval?
- The color of the existing grease
- Bearing speed (RPM) and operating temperature (Correct answer)
- The brand of grease being used
- The diameter of the grease fitting (zerk)
Correct 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.
Ramsay Test Lubrication
Which type of lubricant is most appropriate for a high-speed ball bearing operating at elevated temperatures?