What are the pros and cons of fixing leaf chain using outer links
Leaf chain anchor bolts (also known as leaf chain clevises) play a safety-critical role in forklift truck operations.
Depending upon the application, they can be manufactured to a wide variety of sizes and designs.
It is widely accepted that the strongest possible connection is achieved when the leaf chain ends on the inner links and fits internally to the leaf chain anchor, as it is a manufacturing method that ensures the maximum number of sheer faces and the greatest tensile strength.
But, as forklift manufacturers in Japan have discovered, there are also a number of advantages in fixing leaf chain to the outer links of an anchor bolt.
The pros – fewer materials means lower cost
If we take the case of a BL834 leaf chain for example, it is possible to reduce the amount of material required from 1.95kg (when the leaf chain ends on the inner links) to a finished weight of 1.10kg when the leaf chain ends on the outer links.
That’s a materials saving of 77%.
Removing less material also means there’s less machining and as the part takes less time to make, it is more cost effective to produce.
The cons – servicing leaf chain in the field
With so many Japanese forklift trucks now in use in the UK, there can be some challenges for technicians when it comes time to replace worn leaf chain in the field.
In a factory environment it is easy as long as you have the right equipment as you can simply join the leaf chain using a rivet link.
When companies cut the leaf chain from bulk, they normally push the pins with a press, to break the press fit.
As the rivet head passes through the leaf chain links this can then damage the outer link – but as these links are normally thrown away when leaf chain ends on the inner links, this needn’t cause a problem.
Ending on the outer link, however, means you’re leaving a damaged component on the leaf chain which can create a weak point for a stress or fatigue failure to start.
It is almost impossible to push an anchor pin into the hole of the outer plate of a leaf chain, as it is an interference fit or press fit – which means that the hole is slightly smaller than the pin diameter.
Even if you are able to force the pin through both outer plates, the complete load of the leaf chain will be held by just the outer links as the pin will not be touching the inner link holes.
Some companies may choose to use a smaller diameter pin which will pass through the outer links – but this will then not touch the inner links at all which could mean that only three of the seven links are taking the load on 3 x 4 leaf chains.
It is also possible to ensure all links take the load, by using a special last link, which has the same hole diameter on the last hole as the inner links. These will however need to be made to length in a leaf chain factory. If the leaf chain lengths need adjusting then this can create other challenges.
If it is necessary to carry out a replacement in the field, then the recommended fix is to cut the leaf chain two pitches shorter (i.e 71 inner to inner) and to then use a cotter connecting link to join the leaf chain to the leaf chain anchors. Using this method you’ll only have a slight reduction in tensile strength when compared with riveting the links.
It is important to bear in mind that you should never attempt to rivet or join leaf chain yourself.
If you’re in doubt, then the best course of action will be to seek advice from your industrial leaf chain manufacturer.