2. Chain Dynamics
If you follow the JIS definition of P max as maximum allowable load and you choose a chain on the higher limits of the scale, the chain might not stand up to those strength requirements. In some situations a fatigue failure might occur even though it met the JIS requirement for maximum allowable load. This is the reason that some manufacturers, such as Tsubaki, use 2P a as the maximum allowable load; or some manufacturers calculate 2P a under the situation of P min = 0 and show this in their catalog. In the latter method, the 2P a' value is larger than the value of the former method. The maximum allowable load value of the JIS method is 10 percent greater than the former method of 2P a . In addition, some manufacturers, including Tsubaki, establish a fatigue limit for strength at 10 7 cycles. JIS sets a fatigue strength at 5 3 10 6 cycles. Including the JIS scale, there are more than three ways of expressing the same information in manufacturers’ catalogs. Therefore, you should not make a final determination about a chain’s functions simply by depending on infor- mation found in different catalogs. Consider a manufacturer’s reliability by checking whether they have their own fatigue-testing equipment. Ask if they show fatigue limit data in their catalogs. The quality guarantee system of ISO 9000 series is checked by third parties (instead of users) to gauge whether or not their system of quality guarantee is adequate. It would be safe to choose manufacturers who are ISO-9000-series certified. 2.2.3 Transmission Capability of Drive Chains We have derived fatigue limits by testing. But just as you can’t judge a per- son by examination alone, so we must also check whether the results of our tests can be put to practical use. Some questions remain: 1. The chain’s fatigue limit (see Basics Section 2.2.2) is tested in a linear configuration (Figure 2.1). But in wrapping transmission, the chain is engaging with the sprocket. Is there any difference between these two? 2. A new roller chain is used. Is there any decrease in the strength of a used chain? 3. Do connecting links or offset links have the same strength? To answer these questions, a number of experiments and investigations were done. The following are the findings. 2.2.3.1 Difference Between Linear Tension and Wrapping When the chain engages the sprocket, the chain collides with the sprocket tooth surfaces. The transmission capability is limited by the roller or bushing breakage during collision.
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