The tensile strength of a leaf chain derives from the number of link plates which are used in the lacing, the more plates there are, the greater the tensile strength.
For example, moving from BL634 to BL644, which is just one extra link plate, will increase the tensile strength from 75.6 kN to 97.9 kN (figures from ISO 4347) a 25% increase.
When looking at part numbers, the second number in the leaf chain part number indicates the number of load sharing links. So in BL634, there will be 3 load sharing links.
(For an explanation of leaf chain part numbers, see the leaf chain part number guide on our website).
When comparing leaf chains with equal tensile strength, selecting the one with the largest bearing area will give you the greatest durability. In the example below, we have two leaf chains with the same minimum tensile strength of 97.5kN (ISO standard) however, the BL646 (4×6 lacing) has 50% more bearing area than the BL644. The second leaf chain should, therefore, result in a longer operating life as the load is spread over a larger area.
The fatigue strength of a leaf chain is related to the number of articulating links in the leaf chain, with an increasingly uneven load dispersal occurring as more links are added. Leaf chain components, like any stamped components, have tolerances and a leaf chain with more links has longer pins which bend more under load.
A leaf chain with a 2 x 3 lacing pattern has a fatigue limit of about 20% of its tensile strength, whereas a 6 x 6 leaf chain will have a fatigue limit of about 14% of its tensile strength. So for maximum fatigue strength, select a leaf chain with the smallest number of articulating links.
Failure in Shear
A leaf chain’s ability to withstand a failure in shear is a combination of material strengths after heat treatment and the number of shear planes created by the link combination.
In a leaf chain, some links are grouped together and move as one. Shear planes only exist between two links that move differently, so the number of shear planes in leaf chains 4 x 4 and 4 x 6 are both 4 (see our example of BL644 and BL646).
The strength of material required for chain anchor bolts is also directly impacted by the number of shear planes. Picking chains with the largest number of inner or articulating links will give you the largest number of shear planes, with an 8 x 8 chain having 8 shear planes.
It is worth noting that single plate lacings i.e. 5 x 6 which are not part of international standards and have fallen out of favour, can be a solution in applications with shock loads. They also perform well in fatigue tests which is largely due to the load being more evenly distributed across the pin.
When selecting the correct leaf chain there are a number of factors that have to be considered but we would always suggest starting with 3 x 4 and 4 x 6 lacing patterns as these tend to provide the best overall benefits.
If you have any questions about leaf chain durability and strength contact our team.