Engineers often select chain according to the wrong criteria and risk ending up with a product that is destined to suffer from either premature wear, or even failure, as a result.
Renold Chain report that a lot of engineers are using breaking load as an absolute measure of performance when there is a huge variation in working life for different chains with identical breaking loads.
In explaining the origin of the problem Renold report that in the past, breaking load was one of the earliest chain standards so engineers got used to specifying it that way and many of them still do.
Break the Breaking Load Performance Guide
Engineers should be aware that breaking load is no guide to chain performance, and that chain strength is not the best measure of chain life. In fact, high tensile strength can lead to a shortened working life if component strength has been achieved by making parts hard but brittle.
Back in 1925 when the first chain standard was introduced: BS 228 for Steel Roller Chain and Chain sprockets. BS 228 initially contained only minimal requirements for chain and sprocket dimensions but it was broadened in 1934 when minimum breaking loads were included.
Chain design and manufacture has come a long way since then and a correctly selected modern chain will now last years on applications that back in the mid-twentieth century might have worn out in a matter of months. Modern chain is a much more reliable, high-tech product than its earlier form, but to get the full benefit of recent innovations, engineers need to select more carefully from current options.
Acheiving Longer Working LIfe
The first thing is to put considerations of breaking load to one side.
Chain should be operated well below any load at which it could break. In fact, permanent damage will occur if the load on a chain is more than the elastic limit of the steel parts. Chain should be operated below its endurance limit to ensure that wear is the mode of failure, rather than fatigue, or even complete failure because of overload.
In order to achieve long wear life it is essential to have specialist component design, consistent material specification and the correct balance of heat treatment. Heat treatment not only refines the mechanical strengths of components, it will also, in part, increase their wear life. But it’s a fine balance. Prolonged heat treatment to achieve high tensile strength can leave parts brittle and with increased vulnerability to fatigue failure.
Also of importance for longer working life, is the overall ability of the selected chain to manage the applied loads and provide fatigue resistance well above the application’s anticipated working loads. Good chain manufacturers should know the fatigue limits of their products and it is this that engineers should be taking into consideration rather than breaking loads.
To help make chain selection easier and to ensure that engineers get the optimum value and working life out of chain, Renold has a Chain Selector that takes all the hit-and-miss out of the increasingly complex choices. The Renold Chain Selector can be found at www.renold.com/support/chain-selector.
The detailed search results can be printed out and show the optimum chain to meet all criteria including corrosion resistance, resistance to abrasive debris, lack of lubrication or the need for high performance.
For further help and assistance contact your local ERIKS Service Centre on 0845 006 6000.