N2 Fitting and Machining Theory|Hands-On! 163
• Correct mounting of the chain Wrap the chain around the sprockets and bring both ends together on the same sprocket to connect them with a connecting (cotter or spring) link. Te tension in the chain must now be checked and corrected if necessary.
• Chain tension Chains should never run with both sides tight. To check tension, turn one sprocket to tighten the lower span on the chain. Ten measure the sag on the top strand of the chain which should be about 2% to 3% of the tangent to the sprocket. In an inclined drive, the sag should be less. In vertical drives a chain tightener (jockey or idler) must be provided.
straight edge
sprocket slack side chain sprocket Figure 13.28 Determining chain slack Figure 13.29 Measuring chain slack ruler
Exercise 13.1
1. Name three advantages of chain drives compared to gear drives. 2. Give two reasons for the need to eliminate excessive sag on chain drives.
3. State four advantages and two disadvantages of chain drives in comparison with V-belt drives.
4. Name three different types of sprockets associated with chain drives.
5. State four safety precautions to be considered when working on or around chain drives.
6. Explain in your own words, the following chain-drive terms: 6.1. chain pitch 6.2 drive sprocket 6.3 idler sprockets 6.4 driven sprocket.
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