Roller Chain Tension Initial tension for roller chain power transmission is not as critical as for belt transmission. Generally, roller chain is used with adequate slack. Slack on the lower side is most desirable. If the chain is excessively tight, chain damage or rapid use of lubricant may result. If the chain is too loose, damage due to vibration or chain winding may result.
Figure 8-6: Improper Chain Tension
Slack (S S') should be adjusted to four percent of the chain span (AB). For example, if the chain span is 800 mm (31.5 in.), slack should be: 800 mm (31.5 in.) • 0.04 = 32 mm (1.26 in.)
Figure 8-7: Measuring Chain Slack
Slack should be adjusted to approximately two percent in the following situations. 1) Vertical power transmission (idler is required) 2) Distance between the shafts is more than 1 m (3.3 ft.) 3) Heavy loads and frequent starting 4) Sudden backward rotation The chain will elongate slightly from the beginning of initial operation from 0.05 to 0.1 percent of the full length. As this causes extra slack, adjustment is required. A tensioner can be used to take up the slack or the shaft can be adjusted to minimize chain elongation. Trial Run A trial run should be performed before regular operation to check for the following: 1. Proper fit of the connecting link plate (and spring clip or cotter pin) 2. Adequate chain slack 3. Sufficient lubrication 4. No contact between chain and its case 5. No abnormal noise 6. No excessive vibration 7. Chain does not wind around the sprocket 8. No kinks or stiff chain parts If any problems are discovered, re-install the chain and sprocket, referring to the checkpoints on pages 16 and 17.
RS R OLLER C HAIN I NSTALLATION AND L AYOUT 15
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