Cores wound in bundles or in layers?

Jan Arnoldy | 7. April 2020

Stranding means wrapping the cores of multi-core cables around a centre element. During cable design, stranding plays a decisive role with respect to movement. There is a fundamental distinction between cores wound in bundles and cores wound in layers. We will examine both of them more closely below.

What are cores wound in layers?

When cores are wound in layers, several layers are wound around the centre. The stranding is more or less tight, and strands are relatively long.

Cores wound in layers are usually easier to manufacture than cores wound in bundles, which can be found in chainflex cables. Cores wound in layers can therefore be found on the market at low prices also in cables with more than seven cores. These are usually “chain friendly” cables.

Cable with cores wound in layers
Cable with cores wound in layers

Disadvantages of cores wound in layers

At first glance, low costs are very tempting. But, with more than seven cores, this can quickly prove to be an expensive error. A bending compresses the cores in the inner radius during movement. At the same time, the cores in the outer radius are elongated.

This behaviour shifts the cores in the cable’s interior. They are no longer in their original position. Over long periods, core shifting can lead to core rupture and the corkscrew effect.  

What are cores wound in bundles?

Both defects occur frequently in multi-core energy chain cables with cores wound in layers. These problems are eliminated when cores are wound in bundles thanks to their very painstaking interior arrangement. There, multiple cores are wound in bundles. These individual bundles are wound together around a high tensile strength centre element. The result is called overall braiding.

This multiple stranding of the cores makes all cores change the inner radius and the outer radius of the bent cable repeatedly at identical intervals. Push and pull forces cancel each other. Stranding remains strong even when the cable is subjected to great bending stress.

Cable with cores wound in bundles
Cable with cores wound in bundles

Conclusion

Cores wound in bundles or in layers? For cable use in an e-chain, cores wound in bundles are better suited to cables with more than 12 cores than cores wound in layers. This type of stranding avoids core rupture and corkscrews caused by stranding of bundles with short pitch lengths. This extends the cable’s service life.

Avoiding corkscrews
Cores wound in bundles prevent corkscrews

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