Basics
Figure 2.8 Back Tension on a Toothed Belt
2. Chain wear and jumping sprocket teeth The key factor causing chain to jump sprocket teeth is chain wear elongation (see Basics Section 2.2.4). Because of wear elongation, the chain creeps up on the sprocket teeth until it starts jumping sprocket teeth and can no longer engage with the sprocket. Figure 2.9 shows sprocket tooth shape and posi- tions of engagement. Figure 2.10 shows the engagement of a sprocket with an elongated chain. In Figure 2.9 there are three sections on the sprocket tooth face: a: Bottom curve of tooth, where the roller falls into place; b: Working curve, where the roller and the sprocket are working together; c: Where the tooth can guide the roller but can’t transmit tension. If the roller, which should transmit tension, only engages with C, it causes jumped sprocket teeth. The chain’s wear elongation limit varies according to the number of sprocket teeth and their shape, as shown in Figure 2.11. Upon calculation, we see that sprockets with large numbers of teeth are very limited in stretch percentage. Smaller sprockets are limited by other harmful effects, such as high vibration and decreasing strength; therefore, in the case of less than 60 teeth, the stretch limit ratio is limited to 1.5 percent (in transmission chain).
Figure 2.10 The Engagement Between a Sprocket and an Elongated Chain
Figure 2.9 Sprocket Tooth Shape and Positions of Engagement
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