A basic guide to continuous-flex cables - the bundling versus layering technique

Cables constructed in layers are significantly cheaper to produce, therefore some  manufacturers offer 'continuous-flexing cable' with this low-cost approach. However, these cables are often constructed without attention to pitch length, pitch direction or centre-filler design and typically have fleece wraps and binders with a sleeve-extruded jacket.

In a short travel, long-travel gliding or other demanding flex applications, they tend to fatigue and their insulation and jacket compounds lose their tensile and elongation properties. This greatly reduces service life. As these materials break down, the cable core is compromised and the torsion forces of the cabled conductors release and untwist in parts of the cable. This causes a 'corkscrew' effect.

The risk of such problems is increased with cables that have multiple layers (usually more than 12 conductors).

In nearly all igus' Chainflex cables, the conductors are bundled rather than layered to eliminate these problems (see photo above). The wires are twisted with a special pitch length and the resulting conductors are cabled into bundles. For large cross sections, this is done around a strain relief element. The conductors are then bundled around a tension-proof centre.

The multiple bundling of the conductors changes the inner radius and the outer radius of the bent cable several times at identical intervals. Tensile and compressive forces balance one another around the centre rope, which provides inner stability. As a result, the cable core remains stable even under maximum bending stress.

Photo caption: Wire and core structures of a Chainflex cable:  1. Single wire bundles with short pitch lengths. 2. Tension-proof centre element.  3. Highly abrasion-resistant, gusset-filling extruded jacket.

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