Why does some leaf chain measure under pitch?
All leaf chains are manufactured to International Standard ISO 4347:2015, which allows for ‘LL’ (EL) series leaf chains to be produced from link plates that can also be used to construct short pitch transmission roller chain.
Whether the actual pitch of the leaf chain is the same as its nominal pitch, however, depends on the manufacturer.
In this blog post we explain how to allow for the discrepancy between the nominal and actual pitch of leaf chain – and the alternatives that can solve the problem altogether.
It’s all in the detail
Short pitch transmission roller chain must be manufactured with the highest possible degree of accuracy so that it interacts consistently and meshes with the sprockets.
To ensure that this is the case, the outer and centre link plate components are typically made slightly short of nominal pitch.
Some chain companies take roller chain outer link plates and the centre (intermediate) link plates used for multi-strand roller chains and use them to manufacture ‘LL’ (EL) series forklift truck leaf chains.
Again, as these parts are manufactured short of pitch, the actual pitch of the leaf chain will always be shorter than the given nominal pitch (known as under pitching).
Spot the difference
The difference between a chain manufactured using leaf chain specific components and one that has been manufactured using short pitch transmission roller chain components is 0.75%.
So, when measuring the wear of forklift truck chains that have been produced from roller chain elements, it’s important to take into account that this type of chain will typically be 0.75% more worn than a chain that has been constructed from specific leaf chain elements.
While it might seem insignificant, it’s a key difference that will become especially important as the chain reaches the end of its life.
A leaf chain constructed from roller chain components, for example, will only appear to be 3% worn when compared with nominal pitch – where as in reality it is 3.75% worn.
Crucially too, the discrepancy will affect both chain wear gauge and manually calculated readings.
Calculating actual pitch
If you are measuring a forklift truck chain for wear, and you have any doubts as to the original pitch of the chain, it will be helpful to firstly calculate the actual pitch of the chain so that any allowances can be made.
A simple way to determine the actual pitch is to measure a section of the leaf chain that typically experiences little or no chain wear – for example, an area across an outer link and close to the leaf chain anchor bolt.
It’s then simply a case of comparing this relatively unworn section with the section of the chain that typically experiences the most wear – for example, the part where the leaf chain passes over the pulley.
The advantage of leaf chain components
If you’d prefer to avoid any risk of discrepancies then the best option is to select a forklift truck leaf chain that has been designed and manufactured from leaf chain components only – so that the actual pitch of the leaf chain is the same as the given nominal pitch.
By only using components specifically designed for leaf chain, you can then ensure that the leaf chain link plate is correctly seated onto the rivet pin, which in turn will increase the breaking and fatigue strength of the chain and ensure improved performance of all the various leaf chain elements.