Helping to choose the right chain

Too many engineers are using the wrong criteria to select chain – ending up with a product that is destined to either premature wear, or even failure. This is the view of Mike Christmas, engineering director at Renold Chain, a leading UK-based manufacturer of chain. According to Christmas, who also chairs the ISO committee for transmission chain standards, many engineers use ‘breaking load’ as an absolute measure of performance when there is a huge variation in working life for different chains with identical breaking loads. “Historically, breaking load is the simplest method of selecting drive chain, but it’s really too much of a broad brush approach to selection,” he says. “It was one of the earliest chain standards, so engineers got used to specifying it that way and many of them still do. But 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.” The first chain standard -- BS 228, for steel roller chain and chain sprockets – was introduced in 1925. It initially contained only minimal requirements for chain and sprocket dimensions, but was broadened in 1934 when minimum breaking loads were included. ISO 606 is now the drive chain standard adopted globally and the ISO committee, under Christmas’ leadership, is to modify the latest version of the standard to include minimum values for fatigue performance. “Fatigue performance of chain is critical because the same load applied to a chain repetitively can cause it to crack and eventually fail. Chain should be operated below its endurance limit to ensure that wear – rather than fatigue – is the mode of failure.” Long wear life is achieved through specialist component design, consistent material specification and the correct balance of heat treatment. Heat treatment can increase wear life, but there is a balance. Prolonged heat treatment to achieve high tensile strength can leave parts brittle and with increased vulnerability to fatigue failure. “The ability to manage applied loads, and provide fatigue resistance above the application’s anticipated working loads, is of great importance for longer working life,” says Christmas. “Responsible chain manufacturers will know the fatigue limits of their products -- this is what engineers should be taking into consideration, rather than breaking loads.” To help make selection easier – and to ensure that engineers get the optimum value and working life out of chain – Renold has developed a ‘chain selector’ software programme. The software, which can be downloaded from Renold’s website, selects the most suitable chain for a given application. That is, the smallest chain available that will last a minimum of 15,000 hours – or 30,000 hours for Renold ‘Synergy’ chain – based on factors such as speed, load and the power ratings of the user’s application. The software selects the most suitable chain from 11 different product types and 400 chain variations. Using it is relatively straightforward: users should be able to make their first selections within minutes of installing it. 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. According to Christmas: “Chain products are automatically selected based on certain application parameters, including speed, torque, power and load data. Power has a direct relationship to load in the chain, while speed relates to the heat it generates.”