Breaking Load: No Longer a Guide to Drive Chain Performance

Too many engineers are selecting chain according to the wrong criteria and are ending up with a product that is destined to either premature wear, or even failure, as a result. That is according to a recent report on Renold Chain’s website as the company launches a series of initiatives to try to educate engineers that chain will last longer if it is specified correctly.

According to the company, many 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.

Explaining the origin of the problem, Renold Chain’s marketing manager, David Turner, said: “You can’t blame engineers for using breaking load as a criteria for selecting chain. Breaking load was one of the earliest chain standards, so engineers got used to specifying it that way and many of them still do. What we have to do now is to re-educate engineers 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.”

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 cousins, but to get the full benefit of all the recent innovations, engineers need to select more carefully from all the new options.

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.

Heat treatment

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.

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 loads.

This article was prepared by Renold Chain. For more information, visit www.renoldcanada.com.

Free chain selection software

To help make chain selection easier and to ensure that engineers get the optimum value and working life out of chain, Renold has produced a sophisticated chain selector program that takes the hit-and-miss out of the increasingly complex choices.

The program can be downloaded free from the company’s website and will select the best chain for any given application. That is, the smallest chain available that will last a minimum of 15,000 hours (or 30,000 hours for Renold Synergy) based on factors such as speed, load and the power ratings of the user’s application.

The program selects the best chain from 11 different product types and 400 chain variations. Using the program is easy and users will be able to make their first selections within minutes of installation.

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.

To download Renold’s new Chain Selector software program, visit www.renoldchain.com and select the Chain icon.