What is a primary cause of excessive wear in a flexible coupling?

Shaft misalignment is a primary cause of excessive wear in a flexible coupling because it creates uneven loads and stresses on the coupling components. When the shafts are not properly aligned, the flexible coupling is forced to accommodate misalignment, leading to increased friction and heat generation. This can result in accelerated wear of the coupling materials, potentially causing premature failure. Additionally, this misalignment can transmit vibrations throughout the mechanical system, exacerbating wear not just in the coupling, but in adjacent components as well.

On the other hand, over-lubrication can lead to different issues, such as increased friction if the lubricant cannot effectively handle the heat and pressure. Under-speed operation generally doesn't create the same wear patterns as misalignment; instead, it may lead to inadequate performance of the coupling. Corrosion can affect the lifespan of a coupling but is not a direct factor in causing excessive wear in the way misalignment does. Therefore, shaft misalignment stands out as the most critical factor for causing excessive wear in flexible couplings within the context of this question.