As this project has developed, I have come to the realisation that in many cases, reduced chain life is being designed into the machine. So, a quick first step to extending the chain’s life would be to select a better chain. The wear of a leaf chain is caused by friction between pins and inner plates in the leaf chain link. Experience has taught me, there is a correlation between the chain load and the elongation (wear) rate of a leaf chain. To establish some baseline data. I used a high-speed wear machine where the chain pulley is revolves 2,220 times an hour, test BL834 leaf chains under four different loads.
So, a straightforward way of increasing leaf chain life up to 6 times would be to reduce the working load to just 10% of the chain’s tensile strength.
When I started working with leaf chain more than 35 years ago, 2-ton forklift trucks were commonly fitted with two BL834 chains. Today, they are equipped with BL823 and BL634; both these chains have 50% less tensile strength than BL834. Looking through older catalogues from leading chain manufacturers they recommend a chain working between 14% and 16% of tensile strength. Other testing has shown that good quality leaf chains fatigue strength is between 15% to 18%.of their tensile strength.
There are current machinery standards, which state chains can work at a maximum of 25% of tensile strength. The main forklift and telehandler standards require a maximum load of 20% however, if the chain was designed to run at 15% of its tensile strength, it would increase its operating life by 40%. Chain history provides a significant clue that people have been aware of the connection between chain load, bearing area and working life for a long time. When leaf chain was first produced, it was made from roller chain links always laced in even patterns 2 x2 4 x4 6x 6, butin the late 1960s, a dedicated lifting chain designated BL was produced, appearing in an ANSI chain standard in 1971. Initially, only odd lacings appeared in the standard i.e. 2 x3 3×4 4×6.
Leaf chains with an odd plate combination, have a larger bearing area and therefore a greater resistance to wear. Even plate combinations give the same UTS (Ultimate Tensile Strength) and take up less space, but they will have less resistance to wear. BL 4×4 and BL 4×6 chains have the same UTS, but 4×6 lacing has a 50% greater bearing area.
BL846 working at 40 kN has a bearing pressure of 0.17 kN/mm², while BL844, with the same UTS and at the same load, would have a bearing pressure of 0.26 kN/mm² results in 25% reduction in operating life.
Based on my experience and testing, I would recommend keeping the internal bearing pressure as low as possible. We publish the bearing area for each chain in our printed catalogue but you can also work it out yourself using the following formula.
Bearing area calculation (mm2) = plate thickness (mm) x total articulating plates x pin diameter (mm)
Considering common design requirements such as space and pulley diameter, you can select a chain with the bearing pressure in the range 0.15–0.18 kN/mm2 you will have a chain which is commercially viable and will achieve optimum working life. If you’re working on a project and using leaf chain, I would be happy to share some of the other learning from my testing project.
To learn more about our Leaf Chain solutions, feel free to get in touch.
