As a general rule, most roller chain drive applications can be considered to be worn out at a length increase of approximately 1.5%.
With regular use, some chain wear will eventually occur which will lead to an increase in chain length. If a sudden increase in elongation occurs, it will be important to check the tips of the sprocket teeth for indications of wear. Excessive elongation may be an indication that the chain and or sprockets have reached the end of their natural life and should be replaced.
It is also important that all lube free chain is regularly checked for wear.
Proper lubrication of roller chain drives is an important factor in getting the best possible performance from drive systems. No matter how well a transmission system is designed, if it is not properly lubricated its service life will be shortened. Incorrect or insufficient lubrication is one of the primary reasons for premature roller chain wear and eventual failure.
The key reason for lubricating the chain bearing surfaces is to minimise wear elongation of the chain components as a result of direct metal to metal contact resulting in increased friction. Chain elongation is primarily caused by wear between the bearing pin and bush during articulation. As well as preventing premature elongation, good lubrication also reduces noise levels and cools down the chain when running at high speed.
It is important to use the correct viscosity lubrication for roller chain. Generally heavy oils or grease are not suitable as a chain lubricant. Whilst many chain drives operate in normal ambient temperatures, some need to operate outside of these parameters often operating in higher or lower temperatures or damp conditions. In these environments it is vital that a lubricant that can operate effectively is selected.
Roller chain operates most effectively when there is a suitable amount of slack. If too much tension is applied, the oil film between the bearing surface areas (i.e. the pin and bush) can become restricted or broken, causing increased wear and damage to the bearing components.
If possible, the amount of slack should be 4% of the span (shaft centre distance between the drive and driven sprocket). In instances where the drive is vertical or close to vertical then it should be 2% maximum. A 2% ratio should also be applied for shaft centre distances exceeding 1 metre, when frequent starts are made or when sudden reverse motion takes place.
Roller chain will stretch slightly during its first few hours of service (by about 0.05%). This may result in too much slack and will require adjustment. Chain tensioners, where they can be fitted, are ideal for automatic take-up of the slack chain.