2.2.3.2 Effect of Normal Chain Wear on Fatigue Strength

When a chain is operating, the outer surface of the pin and inner surface of the bushing rub against one another, wearing little by little. (Proper lubrication reduces the amount of wear but does not eliminate it.)

The problem is the wear of the pin. As the surface of the pin is reduced, the rigidity of the pin decreases and eventually fatigue failure may result. The question is how much wear is acceptable and at what point should you be concerned.

Testing shows that when wear elongation is less than or equal to 1.5 percent for transmission chain, or less than or equal to 2 percent for conveyor chain, there is almost no risk of fatigue failure.

NOTE: This replacement limit applies to situations in which every pin and bushing wears equally. If one part is subject to greater wear, the system should be examined and repaired. Chains should be replaced at the same time.

In practical terms, the most important consequence of deterioration is a decrease in the fatigue strength by environmental factors. This problem will be discussed in Basics Section 5.4.