The table below provides detailed information on the symptoms of leaf chain wear, the probable causes and the corrective measures that should be taken when regularly doing an equipment inspection.
|Worn contour||Normal wear on sheave|
Abnormal wear rubbing on guides
|Replace leaf chain when 5% worn|
Check Leaf chain alignment or increase clearance
|Worn surfaces on outer plates or pin heads||Misalignment, rubbing on side flanges||Check leaf chain alignment and correct clearance as necessary|
|Tight joints||Dirt or foreign substance packed in joints or corrosion or rust or bent pins||Clean & re-lubricate leaf chain|
Replace leaf chain
|Missing parts||Missing at original assembly||Replace leaf chain|
|Abnormal protrusion or turned pins||Excessive internal friction caused by high loading and inadequate lubrication||Replace leaf chain, improve lubrication and eliminate overload conditions|
|Cracked plates (fatigue)|
Crack from aperture towards edge of linkplate at 90º to line of pull. Note there is no linkplate distortion
|Loading beyond chain’s dynamic capacity (above fatigue endurance limit)||Replace chain with leaf chain of larger dynamic capacity or eliminate high load condition or dynamic (impulse) overloading|
|Fractured plates (tension mode)|
Note material distortion
|High overload||Replace leaf chain and correct cause of overload|
|Arc like cracked plates (stress corrosion)||Severe rusting or exposure to acidic or caustic medium, plus static pressure at press fit (between pin and pin linkplate). No cyclic stress is necessary for this phenomenon to occur.||Replace leaf chain and protect from hostile environment.|
|Enlarged holes||High overload||Replace leaf chain and correct cause of overload|
|Corrosion||Exposure to corrosive environment||Replace leaf chain and protect from hostile environment.|
|Worn leaf chain anchor bolt connecting pin||Normal wear||Replace worn leaf chain components and always when fitting new leaf chains|
Leaf chain test certificates and inspection standards
All replacement forklift truck leaf chains should be supplied with a leaf chain test certificate which indicates the leaf chain’s minimum breaking load and proof load (which shows that the leaf chain is able to support a minimum of one and a half times the safe working load).
While most forklift manufacturers and maintenance firms place a lot of emphasis on receiving these test certificates, many will file them away without looking at them.
The various different types of forklift truck leaf chain have been consolidated over the past decade with the result that, when ordering leaf chain, many firms simply ask for the generic part number from the International Leaf Chain Standard ISO4347 e.g. BL634.
However, this standard only refers to the dimensions of the leaf chain elements and the minimum tensile strength.
If you only quote the generic part number when ordering your leaf chain and do not check the breaking load of the leaf chain you purchase, you will not necessarily receive the correct product quality or consistency for your particular application.
It is important to check that the safe working load stated on the certificate exceeds the capacity of the lifting equipment. The vast majority of forklift truck manufacturers actually require leaf chain with a greater minimum tensile strength than the International Standard ISO4347.
High-quality leaf chain will be manufactured to ensure the optimum balance between strength, wear rate, fatigue life and resistance to shock loading.
It should also ideally have a consistently higher breaking load than the International Standard.
The safe working load of a leaf chain will usually be shown on a test certificate in kilonewtons (kN). If the capacity of your equipment is given in kilograms or pounds you will need to refer to the safe working load conversion table.
It is also important to ensure that the safety legislation quoted on the test certificate is reliable and up to date and that it meets the current requirements of The Machinery Directive, LOLER and PUWER.