Leaf chain system design - Six steps

Leaf chain system design – 6 things to consider

A leaf chain system design for safety-critical materials handling equipment like forklift trucks or telehandler booms must ensure functionality, compliance, and longevity without compromise.

In this post we explore six features to consider in leaf chain system design:

Components of leaf chain system design

1. Leaf Chain Tensile load

Firstly, to determine the tensile load, you must decide whether to use international chain standards or the manufacturer’s catalogue figures.

The standard requires all chains to meet minimum tensile requirements, but each manufacturer’s data may differ significantly. Most manufacturers will exceed any international standard by 20%.

We highly recommend using the chain standards as a dimensional reference, especially for chain anchor bolts slots, to ensure interchangeability when replacing the chain throughout its working life.

2. Bearing pressure

While meeting the minimum requirements of the machinery standard receives significant focus, it can occasionally result in suboptimal choices.

When comparing chains with equal tensile strength, choose the one with the largest bearing area, calculated by multiplying plate thickness, total articulating plates, and pin diameter.

Let’s consider the differences between the BL646 and the BL644 leaf chains, for example. Both chains have a minimum tensile strength of 127kN so are well above the ISO standard of 97.5kN, however the 4×6 lacing of the BL646 has a 50% greater bearing area than the BL644. 

As the width and number of links increases, the fatigue limit will also reduce, which will require the need for more frequent replacement of chain.

3. Fatigue

The number of articulating links directly affects the fatigue strength of a leaf chain, increasing the likelihood of an uneven dispersal of load as more links are added.

Like any stamped components, chain components have tolerances and a leaf chain with more links and longer pins will be more susceptible to bending under load.

Higher quality chains will have close tolerances on the chain pitch and high precision bores in the link plates. The application of a high pre-load to a leaf chain at the end the manufacturing process can also bed-in the components and increase fatigue strength.

While the general process for leaf chain is the same for most manufacturers, each will have their own opinions as to what they believe offers the best performance. They should also be able to supply you with fatigue data for each size of leaf chain that they produce.

4. Pulley design 

When designing a leaf chain pulley it is important to consider the ISO4347 international standards.

To achieve normal wear life rates, for example, it is recommended that the minimum running diameter of a pulley is equal to five times the nominal pitch of the chain.

The minimum width between the flanges should also be 1.05 times the pin length (or pin width if using riveted bearing pins.) The minimum outside diameter (or flange diameter) can be calculated by combining the running diameter with the link plate height.

5. Leaf chain termination

You can achieve the strongest possible connection by combining the maximum number of sheer faces with the greatest tensile strength. Therefore, the ideal chain termination occurs when the leaf chain ends on inner links and fits internally to the chain anchor.

If space is restricted then it is also possible to connect the chain anchor on the outer links – but with the chain rivet pin being the widest part and the chain being joined to the anchor with a riveting or cotter pin unit.

When the termination or last links of the chain are both on the inner links or outer links the chain length must be an odd number of pitches i.e 137 and can only be adjusted by x 2 the chain pitch. If the ends are odd (i.e one inner and one outer) the chain length can be moved by x 1 chain pitch.

6. Leaf chain anchor thread length

Over time, chain will gradually increase in length as a direct result of articulation around the chain sheave or pulley. When designing a leaf chain chain system it’s important to consider adjustment due to wear – and that the chain is no longer used once its elongation limit has been reached.

It is recommended that the amount of adjustment be set to allow no more than 3% of the chain length which articulates the pulley.

In the case of a 5000mm chain, for example, where 3800mm wraps round the pulley, there should be no more than 114mm of adjustment.

What’s also important that the tensile strength of the thread is greater than the strength of the chain that’s been selected.

It’s best to calculate the strength of the thread in the shear and the tensile of the head and in the tensile strength of the threads. Chain anchors should also be either constructed or heat-treated, to achieve a strength of 850Kn mm².

If you would like to discuss an idea for your leaf chain system design contact us below:

View all articles