Extending chain life

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.