Bearing Installation, Maintenance, and Failure Analysis 1 Flashcards
6 cards from real Millwright Certification practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Bearing Installation, Maintenance, and Failure Analysis 1 flashcards as text
When repacking a bearing housing with grease, what is the generally recommended fill level to prevent overheating from churning?
Answer: One-third to one-half of the free space in the housing
Overfilling a bearing housing with grease causes the rolling elements to churn through excess lubricant, generating heat and ultimately degrading the grease. One-third to one-half fill allows adequate lubrication while leaving room for grease expansion and circulation.
A technician finds a reddish-brown powdery debris between a bearing outer ring and its housing bore after disassembly. This condition is most accurately identified as:
Answer: Fretting corrosion from micro-movement between mating surfaces
Fretting corrosion occurs when two clamped surfaces experience very slight oscillatory relative motion, causing micro-welding and tearing that produces the characteristic reddish-brown iron oxide powder. It is common at bearing-to-housing fits and shaft-to-ring fits.
When pressing a bearing onto a shaft using a mechanical press, to which surface should the pressing force be applied?
Answer: Only the inner ring, which is the ring receiving the interference fit
Press force must be applied only to the ring receiving the interference fit — in this case the inner ring for a shaft press-fit. Transmitting force through the rolling elements causes brinelling (indentations) on the raceways, permanently damaging the bearing.
During inspection, a millwright observes a regular corrugated or washboard pattern of shallow grooves running around the circumference of a bearing raceway. What is the most likely cause?
Answer: Electrical current passing through the bearing from a VFD or stray ground
The corrugated or fluted pattern is the signature damage of electrical current passing through a bearing. Electric discharge machining (EDM) erodes the raceway in a repeating pattern. This is increasingly common with variable frequency drives (VFDs) that produce stray currents through the motor shaft.
New bearings that will not be installed for several weeks should be stored by:
Answer: Keeping them in original manufacturer packaging, stored horizontally in a clean, dry area
Bearings should remain in their original sealed packaging until installation. The packaging protects against contamination and moisture. A clean, dry, vibration-free storage environment on flat shelving preserves the factory-applied corrosion protection and lubricant.
In the context of angular contact or tapered roller bearings, what does 'preload' mean?
Answer: A deliberate elimination of internal clearance that places the rolling elements under a compressive load
Preload removes all internal clearance and introduces a controlled compressive stress on the rolling elements and raceways. This increases bearing rigidity, reduces vibration and noise, and improves accuracy of shaft position — critical in machine tool spindles and precision gearboxes.