Basics
As it wraps on the sprocket and rotates, the chain receives centrifugal force. The faster the speed of rotation, the larger the centrifugal force becomes. Additionally, the pin and the bushing are also subject to tension. There is a limit to their bearing function. 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 replacment 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.
2.2.3.3 Strength Differences Between Chain and the Connecting Links and Offset Links
The individual connecting links and offset links have lower fatigue strength than the chain itself. Therefore, you have to consider the strength-decrease ratio shown in Table 2.1. The strength-decrease ratio differs from manufacturer to manufactur- er, so it is important to get specific information from each manufacturer.
Table 2.1 Strength Reduction of Connecting Links and Offset Links
Reduction Ratio
Type
Against Maximum Allowable Load
Standard Connecting Link Tap Fit Connecting Link
0~20%
No reduction
Offset Link
35%
Two-Pitch Offset Link
0 ~ 25%
If you use chain with loads that are almost the same as the maximum allow- able load, you should avoid using offset links. Use tap fit connecting links, which are stronger than standard connecting links. In some cases, you can order chains in an endless configuration (see NOTE on next page).
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