NEIEP Generator Maintenance And Repair (440) Practice Test

Fretting corrosion happens when there is tiny relative motion between contacting surfaces, such as a shaft and the bearing bore, under load and vibration. That micro-movement breaks the protective oxide layer and allows wear and corrosion to accumulate at the interface. If the shaft and housing fit are loose, those micro-m motions can occur easily, promoting fretting damage. A tight interference fit on both the shaft and in the housing prevents this by holding the parts firmly together so the contact interface doesn’t move relative to itself, stopping the small motions that drive fretting. Pitting is a form of localized corrosion that typically stems from electrical effects or high contact stresses, not from micro-movement at a fit. Seizure results from excessive friction and heat or loss of lubrication causing surfaces to weld together; a tight fit alone doesn’t address the lubrication or heat factors that cause seizure. Bearing slippage arises when there’s too much clearance, allowing the bearing to slip on the shaft or in the housing. The scenario described targets fretting, where eliminating micro-motion with a tight fit is the preventive measure.