The harshness of the operating environment in ports or harbours, together with the requirement for long operational shifts, can place huge demands on leaf chain.
And for empty container handlers, which are often required to stack up to eight containers high (or heights of more than 20 metres), the extreme working conditions are some of the most challenging of all.
The leaf chain that is fixed to these types of heavy duty lifting machines has to cope with the effects of a highly corrosive environment. It also has to be able to handle extreme shock loads and frequent high accelerations and de-accelerations.
Many leaf chain manufacturers choose to differentiate their large leaf chain for heavy duty lifting machines from their standard leaf chain production.
In many catalogues you will find these products listed as Sky Stacker chains - large leaf chains that include some extra features to ensure they provide optimum performance.
But at FB Chain these 'extra' features all come as standard on all leaf chains that we produce that is above 1 3/4 pitch (or all our leaf chain part numbers that start BL14, LH28 and LL28.)
So what makes our big leaf chain special?
When manufacturing our link plates we use a grade of steel that is extremely ductile and that has good hardenability.
When the links are punched, the shear surfaces are very clean and smooth with very close tolerances which, once heat treated, will continue to ensure the desired end results.
All the link plates have the pin holes brought to their final dimension using a method called ballizing.
Ballizing is a metal-displacement process, in which an oversize ball is pushed through an undersized link plate hole to achieve a specified diameter.
This method expands the hole by displacing the material rather than grinding or shaving it.
It also provides the added benefits of leaving a layer of denser metal on the ID link plate hole - as well as improving surface finish by removing any tiny surface imperfections so the holes are extremely smooth.
All the pins on FB Chain's big leaf chain are induction hardened using a form of heat treatment where carbon steel part is heated by induction heating and then quenched.
When compared with standard case hardening, the compressed surface and increased depth of hardness of induction hardened parts has been proven to greatly increase wear life and fatigue resistance.
The induction hardening process also makes it possible to selectively harden only the working areas of the leaf chain pins while ensuring the core strength of the material remains soft and ductile.
The end result is a leaf chain with greater overall resistance to shock loads.
Increased press fit
Using this same method, we can also increase the amount of press fit between the outer side plates and the pins and between the inner side plates and the bushes.
When riveting our large leaf chain pins, the amount of material displaced is far greater compared to that achieved with a fully case hardened pin - offering much higher push-out values and improved resistance to pin rotation which is a common issue on empty container handlers.
Standard leaf chain is normally constructed using inner links and outer links with identical pitch lengths to the inner links. But when placed under tension, this can result in intermediate link plates not supporting the pin. In extreme applications there is also the potential for pin bending.
To increase fatigue life, our large leaf chains have compensated pitch, meaning the leaf chain is constructed using intermediate links with a shorter pitch length than that used on the outer links.
All FB Chain's big leaf chain is supplied ready to go into service with a high-quality lubricant which has been selected for its corrosion resistance and wear qualities.
The creep and penetration properties of the lubricant are especially suitable for the demands of empty container handlers as it ensures the lubrication reaches every part of the pin surface area.