Ex­tend­ing chain life

DEMM Engineering & Manufacturing - - HYDRAULICS & PNEUMATICS -

Power trans­mis­sion and con­veyor chain are the two com­mon chain drives found in in­dus­try, and although their pur­pose is dif­fer­ent, what is com­mon with chain drives is that they wear. The phrase “stretch” is fre­quently used when re­fer­ring to the level of elon­ga­tion of a chain.

The re­al­ity of chain elon­ga­tion is each chain link con­sists of a col­lec­tion of sur­faces which slide against each other as the chain ar­tic­u­lates, such as wrap­ping around a sprocket. Plain bear­ing sur­faces pro­vide high load car­ry­ing ca­pac­ity for small shaft di­men­sions in com­par­i­son to rolling bear­ings, but also have lower speeds due to higher fric­tion with slid­ing sur­faces rather than rolling.

On a typ­i­cal roller chain, a pair of bear­ing sur­faces can be found at ev­ery pin on both the in­ner and outer plates, and the wear of these sur­faces de­ter­mine elon­ga­tion. The al­low­able elon­ga­tion of chain de­pends on the ap­pli­ca­tion, how­ever less than 2% in­crease in length for trans­mis­sion chain is com­mon. Although this may seem in­signif­i­cant, this elon­ga­tion will cause the chain to start rid­ing up on the sprocket teeth and in more ex­treme cases can ‘jump off’. Once a chain be­gins to elon­gate, the level of wear will be­gin to ac­cel­er­ate on both the chain and sprock­ets till cat­a­strophic fail­ure or re­place­ment. Min­imis­ing chain elon­ga­tion can be achieved by the fol­low­ing: • Im­proved lu­bri­ca­tion. • Re­duc­ing chain ten­sion. • Larger sprocket sizes to re­duce the an­gle of flex. • Re­plac­ing sprock­ets when the chain is re­placed. • In­creas­ing the con­tact area be­tween pins and bush­ings

(mul­ti­ple strands, larger chain size). • In­creased hard­ness of the pins and the bush­ings.

Lim­it­ing the level of wear is one of the key main­te­nance tasks for chain in or­der to achieve bet­ter ser­vice life, and the proper lu­bri­ca­tion of the chain plays a key role in main­tain­ing a suit­ably de­signed chain drive.

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