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 manufacturer, so it is important to get specific information from each manufacturer.
| Type | Reduction Ratio Against Maximum Allowable Load |
|---|---|
| Standard Connecting Link | 0~20% |
| Tap Fit Connecting Link | 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 allowable 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).
NOTE: Endless configuration: Manufacturers create connecting components that are as strong as the chain's other parts by riveting or other factory processes. The chain is assembled and delivered as an endless configuration.
The transmission-ability graph, which is sometimes called a "tent curve" because of its shape, includes the result of the three points covered above. This graph is an important tool when making chain decisions. Figure 2.19 illustrates the concept of a tent curve.
Figure 2.19 A Transmission-Ability Graph (Tent Curve)
In Figure 2.19, Line O-A is decided according to the chain's allowable tension, which includes the fatigue strength of the connecting or offset links, as well as the centrifugal force in high-speed rotation. Line B-C is decided by breakage limit of the bushing and roller. In this kind of breakage of the bushing and roller, there is no fatigue limit as there is with the link plates. Therefore, it is shown within 15,000 hours of strength-in-limited-duration. Line D-E is decided by the bearing function of the pin and the bushing.
The range defined within these three lines (O-A, B-C, and D-E) is the usable range. When the chain is used at low speeds, it is limited by line O-A, the fatigue limit. The conditions of the tent curve shown are:
- Two-shaft wrapping transmission with 100 links of chain.
- Duration of 15,000 hours work.
- Under the Additional Operating Conditions (1 through 5 shown below).
Additional Operating Conditions
- The chain operates in an indoor environment of −10°C to 60°C, and there is no abrasive dust.
- There are no effects from corrosive gas or high humidity.
- The two driving shafts are parallel with each other and adjusted properly.
- Lubrication is applied as recommended in the catalog.
- The transmission is subject to only small fluctuations in load.
