Getting chain selection right — the key to achieving maximum working life
07 March 2017
When replacing chain on industrial applications it is important to specify the new chain correctly.
Doing so will ensure that you get the best performance out of the new chain and the longest working life. Here, David Moore of Renold Chain looks at some of the key issues and offers his advice on how to overcome them.
When old chain is replaced mistakes are sometimes made in the selection of new chain that may result in premature failure. Implementing best practice in chain selection is easier today than ever before and is absolutely essential if the maximum working life is to be achieved from the new chain.
It was 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 versions, but to get the full benefit of all the recent innovations engineers need to select more carefully from all the new options.
Breaking load – the common misconception
Engineers commonly use breaking load as an absolute measure of performance, when there is actually a huge variation in working life for different chains with identical breaking loads.
Breaking load was one of the earliest chain standards so engineers became used to specifying chain by this criteria and many still do as a rule of thumb guide. But breaking load is no guide to modern chain performance, and chain strength is not the best measure of its working 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.
It is helpful 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 strength 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. It is the detail in this process that expert chain manufacturers understand and can often be the difference between the perfect solution and an inferior product.
Managing applied loads
Of great 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. Most good chain manufacturers will know the fatigue limits of their products and it is this that engineers should be taking into consideration rather than breaking load.
To help make chain selection easier and to ensure that engineers get the optimum value and working life out of chain, Renold has produced an easy-to-use chain selector program that takes the hit-and-miss out of the increasingly complex choices.
To use the Renold Chain Selector go to www.renold.com/support/chain-selector.
Renold enables peak performance
Renold Synergy chain has long been known for industrial applications. What is less well known is that the same cutting-edge chain technology platform on which Synergy was built, has recently helped the Britain Cycling team to Olympic Gold!
In 2011, British Cycling were looking for a drive chain that could meet the incredible demands of elite level competition both in the Velodrome and on the BMX track. After some discussion between British Cycling’s R&D Team and Renold Engineers it was felt that the requirements could be met using Renold’s Synergy chain technology platform. Following a great deal of collaborative work between British Cycling and Renold Chains, along with the University of Bristol, Renold engineers were able to optimise its pre-existing chain design which culminated in the chain that was used to great effect by the Great Britain Track Cycling team in both the London and Rio Olympic Games.
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