CLS Grease Technology & Application 2 — Questions and Answers
Question 1: Which thickener type provides the highest dropping point among common grease thickeners?
- Lithium 12-hydroxystearate
- Calcium soap
- Polyurea
- Bentone (clay) (Correct answer)
Correct answer: Bentone (clay)
Bentone (clay or anhydrous calcium silicate) greases have no true dropping point as they do not melt; they degrade thermally rather than becoming liquid, giving them the highest effective upper temperature limits.
Question 2: What does the worked penetration test (ASTM D217) measure in grease?
- The viscosity of the base oil after separation
- The depth a standard cone penetrates the grease after 60 strokes of a worker (Correct answer)
- The temperature at which grease hardens under pressure
- The water resistance of grease at elevated temperatures
Correct answer: The depth a standard cone penetrates the grease after 60 strokes of a worker
Worked penetration (ASTM D217) measures how far a standardized cone penetrates the grease after 60 double strokes in a grease worker, which determines the NLGI consistency grade.
Question 3: What is the main advantage of calcium sulfonate complex grease over conventional lithium complex grease?
- Lower cost of manufacture
- Inherent EP and rust protection without requiring additives (Correct answer)
- Better low-temperature performance below -40°F
- Superior compatibility with all other grease types
Correct answer: Inherent EP and rust protection without requiring additives
Calcium sulfonate complex grease provides inherent extreme pressure (EP) and anti-rust properties due to its unique thickener chemistry, without requiring separate EP and rust-inhibitor additives.
Question 4: In a centralized automatic grease lubrication system, what is a primary advantage over manual re-greasing?
- Ability to use higher NLGI grade greases
- Delivery of smaller, more frequent grease quantities while equipment is running (Correct answer)
- Elimination of the need for grease nipples (zerk fittings)
- Reduced need for grease compatibility verification
Correct answer: Delivery of smaller, more frequent grease quantities while equipment is running
Centralized automatic systems deliver precise, small quantities of grease at frequent intervals while equipment is running, which maintains optimal lubricant film thickness and reduces waste and over-greasing.
Question 5: What is 'channeling' behavior in grease and why can it be beneficial?
- Channeling means grease flows to the bottom of the housing, which prevents over-lubrication
- Channeling is when grease forms a channel allowing the bearing to run through the grease without churning it, reducing heat generation (Correct answer)
- Channeling refers to grease migrating through seals, which helps prevent seal wear
- Channeling occurs when grease hardens into channels, improving its load-carrying capacity
Correct answer: Channeling is when grease forms a channel allowing the bearing to run through the grease without churning it, reducing heat generation
Channeling occurs when a bearing clears a path through the grease, allowing it to operate with minimal grease churning, which reduces energy losses and heat generation in high-speed applications.
Question 6: Which test method is commonly used to evaluate the water washout resistance of grease for wet environments?
- ASTM D2266 (Four-Ball Wear)
- ASTM D1264 (Water Washout Characteristics) (Correct answer)
- ASTM D217 (Cone Penetration)
- ASTM D2596 (Four-Ball EP)
Correct answer: ASTM D1264 (Water Washout Characteristics)
ASTM D1264 measures the water washout resistance of grease by exposing a greased bearing to a water spray at controlled temperatures and measuring the percentage of grease lost.
Question 7: What is the recommended practice when mixing two different grease types in a bearing housing?
- It is always acceptable as long as both greases have the same NLGI grade
- Mixing greases should be avoided; perform a compatibility test or completely purge old grease before switching (Correct answer)
- Mix only if both greases use the same base oil viscosity
- Mixing is acceptable for soap-thickened greases but not for clay-thickened greases
Correct answer: Mixing greases should be avoided; perform a compatibility test or completely purge old grease before switching
Mixing incompatible greases can cause softening, hardening, oil separation, or loss of structure, so compatibility should be verified or old grease completely purged before introducing a new type.
CLS Grease Technology & Application 2
Which thickener type provides the highest dropping point among common grease thickeners?