Regular leaf chain inspection, in combination with an ongoing maintenance programme, will play a crucial role in improving safety and enhancing the service life of your materials handling equipment.
In this blog post we summarise some of the key signs to look for when evaluating the condition of your leaf chain and its component parts.
What factors influence leaf chain wear?
Materials handling equipment can be required to operate in a wide variety of demanding environmental conditions - with the risk of exposure to highly corrosive atmospheres or abrasion due to sand or grit.
Excess moisture can lead to corrosive rusting, pitting and cracking which will reduce chain strength. Low temperatures, or equipment that is required to moved between extreme temperatures, can also compromise leaf chain strength as a result of embrittlement (loss of ductility) or the build up of excess moisture.
Corrosive chemicals or vapours can attach to leaf chain or chain components, causing microscopic cracking. Abrasives can lead to increased wear of the articulating elements of the chain, not all of which may be visible to the naked eye.
In addition to the effects of environmental conditions, leaf chain can also be subject to dynamic impulse/shock loads that can push the chain beyond its endurance limit.
Dynamic shock loading can occur as a result of:
- A high velocity movement followed by an abrupt stop
- "Inching" loads beyond the capacity of the handling or lifting mechanism
- The carrying of loads that are suspended over uneven surfaces or rough terrain
The areas in which materials equipment are required to operate, and the extent of exposure that they are subject to, will determine the frequency of lead chain inspection.
As a general guide, periodic inspection and lubrication is advised after every thirty-days of operation, but is likely to be required more frequently when equipment is operating in more demanding or hostile environments.
What are the signs of leaf chain wear?
When conducting a leaf chain inspection the following are all examples of leaf chain wear:
Worn contours - caused by normal wear on the sheave or abnormal wear rubbing on guides. This can be resolved by checking leaf chain alignment, increasing clearance and replacing the chain when it is 5% worn.
Worn surfaces - which can occur on either outer plates or pinheads due to misalignment or rubbing on side flanges. This issue can be solved by checking alignment and correcting the clearance.
Tight joints - as a result of rust, corrosion, bent pins, dirt or foreign substances becoming packed in the leaf chain joints. Cleaning and re-lubricating leaf chain will be required or replacement if necessary.
Missing parts - this may be due to parts having been overlooked or missed at the point of assembly. Replacement of the leaf chain will be required.
Abnormal protrusion or turned pins - which is caused by excessive internal friction as a result of high loading or inadequate lubrication. This issue can be resolved by improving lubrication, eliminating overload conditions and replacing the leaf chain if necessary.
Cracked plates - which occur when leaf chain is loaded beyond its dynamic capacity (above its fatigue endurance limit.) This can be corrected by eliminating the high load condition or replacing with leaf chain of a higher dynamic capacity.
Fractured plates - high overload can increase the chances of fracturing of the plates. This problem can be rectified by correcting cause of overload or replacing the leaf chain.
Arc-like cracked plates - as a result of stress corrosion due to severe rusting, exposure to acidic or caustic substances, or static pressure between the pin and the pin link-plate. Steps will need to be taken to protect the leaf chain from the hostile environment and to replace the leaf chain if required.
Enlarged holes - caused by high overload. The overload will need to be rectified and the chain replaced if needed.
Worn leaf chain anchor bolt connecting pin - as a result of normal wear and tear. Replace worn leaf chain components - and always replace when fitting new leaf chains.
Additional guidelines for leaf chain safety
As a general guide it is always recommended that:
- Leaf chain is constructed using only factory-assembled lengths of chain rather than lengths that have built from individual components. The joining of chain lengths, and the joining the chains sourced from different manufacturers, is never advised.
- Chains should always be replaced in their entirety, even if only one or more components that are faulty.
- Leaf chain is never heat treated once in service. In the event that a chain needs to be heated in order to necessitate its removal then it must not be reused. Likewise, welding should never be carried out on leaf chain or any of its components. All efforts must also be made to avoid welding spatter coming into contact with leaf chain.
- Regular lubrication will be required to aid satisfactory service life and prevent accelerated wear. The periodic lubrication of all chain surfaces will help to minimise joint wear, lessen internal friction, and reduce the possibility of turned pins by providing improved corrosion resistance.
The conducting of regular leaf chain inspections, and the implementing of a sound maintenance schedule, will ensure that your materials handling equipment operates safely, that leaf chain wear is minimised and that the optimum service life of your chain is achieved.