What causes bearing wear on startup?

The correct answer identifies the "lack of oil wedge" as the primary cause of bearing wear during startup. When machinery is powered on, there is a momentary period before lubrication reaches adequate levels. During this phase, an oil wedge—a thin film of lubricant—is not sufficiently formed to separate the moving surfaces of the bearing. This causes direct metal-to-metal contact, leading to increased friction and wear on the bearing surfaces.

In the context of bearing operation, an effective oil wedge is crucial for minimizing wear and tear. It allows for smoother operation, reduces the temperature generated by friction, and prolongs the life of the bearing. The absence of this lubrication at startup can result in substantial damage as the surfaces may grind against each other before the oil supply stabilizes.

Other factors, such as operating speed or environmental conditions, can also influence bearing performance, but they are not the primary causes of wear at the startup phase. High or low speeds may affect the load on the bearings and how they operate during normal conditions, while a hot environment can impact oil viscosity. However, it is the immediate lack of proper lubrication that predominantly contributes to initial wear during startup.