Free Millwright Bearing Installation, Maintenance, and Failure Analysis Questions and Answers — Questions and Answers
Question 1: When using an induction heater to install a bearing, what is the generally recommended maximum temperature to avoid altering the bearing's metallurgy?
- 150°F (65°C)
- 250°F (121°C) (Correct answer)
- 350°F (177°C)
- 450°F (232°C)
Correct answer: 250°F (121°C)
Heating a bearing above approximately 250°F (121°C) can cause dimensional changes and alter the hardness of the steel, leading to premature failure. This temperature allows for sufficient expansion for mounting without damaging the material properties.
Question 2: A bearing raceway shows small, crater-like indentations equally spaced at the same distance as the rolling elements. What is the most likely cause of this failure?
- False brinelling
- Abrasive wear
- Electrical fluting
- True brinelling (Correct answer)
Correct answer: True brinelling
True brinelling is caused by static overload or severe impact, which presses the rolling elements into the raceway, leaving permanent indentations. False brinelling occurs from vibration while stationary and appears as polished, worn depressions without raised edges.
Question 3: When re-lubricating a bearing with grease, what is the most critical factor to consider regarding the new and existing grease?
- Thickener compatibility (Correct answer)
- Color
- Dropping point
- NLGI grade
Correct answer: Thickener compatibility
Mixing greases with incompatible thickeners (e.g., lithium complex with a polyurea) can cause the base oil to separate, leading to a loss of lubrication and rapid bearing failure. While other properties are important, thickener incompatibility is the most common and critical issue.
Question 4: A bearing is marked with a 'C3' designation. What does this indicate?
- It is a sealed bearing
- It has a greater internal clearance than standard (Correct answer)
- It is made from corrosion-resistant steel
- It has a lower load rating than standard
Correct answer: It has a greater internal clearance than standard
The 'C' designation refers to internal clearance. C3 indicates an internal clearance greater than the 'Normal' or 'CN' clearance, which is often required for applications with high temperatures or tight interference fits that reduce clearance during operation.
Question 5: When press-fitting a bearing onto a shaft, where should the installation force be applied?
- Exclusively on the outer ring
- Evenly across the entire face of the bearing
- Exclusively on the inner ring (Correct answer)
- On the cage or separator
Correct answer: Exclusively on the inner ring
The force must be applied only to the ring being fitted to prevent transmitting the force through the rolling elements. Pressing on the outer ring while fitting the inner ring to a shaft will damage the raceways and rolling elements, a phenomenon known as brinelling.
Question 6: Upon inspection, a reddish-brown or black oxide is found between the bearing bore and the shaft. This type of wear is most likely:
- Spalling
- Pitting
- Galvanic corrosion
- Fretting corrosion (Correct answer)
Correct answer: Fretting corrosion
Fretting corrosion occurs due to slight relative motion (micromovement) between two contacting surfaces, typically from a loose fit or vibration. This action breaks down surface oxides, exposing fresh metal that quickly oxidizes, creating the characteristic reddish-brown debris.
Free Millwright Bearing Installation, Maintenance, and Failure Analysis Questions and Answers
When using an induction heater to install a bearing, what is the generally recommended maximum temperature to avoid altering the bearing's metallurgy?