Why does some leaf chain measure under pitch?
All leaf chains are manufactured to International Standard ISO 4347:2004, 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 depends on the manufacturer.
So that it interacts consistently and meshes with the sprockets, short pitch transmission roller chain must be manufactured with the highest possible degree of accuracy. To ensure that this is the case, the outer and centre link plate components are typically made slightly short of nominal pitch.
The roller chain components that are used to manufacture ‘LL’ (EL) series forklift truck leaf chains are the outer link plates and the centre (intermediate) link plates used for multi-strand roller chains. As these parts are manufactured short of pitch, the actual pitch of the leaf chain will always be shorter than the given nominal pitch.
When measuring forklift truck chains for wear that have been produced from roller chain elements, it must, therefore, be taken into account that this type will be 0.75% more worn than those constructed from specific leaf chain elements. This is especially important as the chain reaches the end of its life. For example, a leaf chain constructed from roller chain components will only appear to be 3% worn when compared with nominal pitch but it will actually be 3.75% worn. This discrepancy will affect both chain wear gauge and manually calculated readings.
If when measuring a forklift truck chain for wear, there are doubts as to the original pitch of the chain, the actual pitch of the chain must first be determined so that allowances can be made when gauging the true amount of wear. The actual pitch can be determined by measuring the leaf chain across an outer link close to the leaf chain anchor bolt. This section typically experiences little or no chain wear. This section should then be compared with the section of the chain that usually experiences the most wear, namely the part where the leaf chain passes over the pulley.
To avoid this issue, all FB forklift truck leaf chain (including ‘LL’ series) have been purposely designed and manufactured from leaf chain components only. The actual pitch of all FB leaf chain will, therefore, be the same as the given nominal pitch.
By only using components specifically designed for leaf chain, FB are able to ensure that the leaf chain link plate is correctly seated onto the rivet pin, which both increases the breaking and fatigue strength of the chain and improves all of the various leaf chain elements.