Continuous-flex cables - a buyer's guide

Cables constructed in layers are significantly cheaper to produce than those with a bundled construction, so some manufacturers offer 'continuous-flexing cable' that is manufactured using this low-cost method. However, these cables are often constructed without attention being paid to pitch length, pitch direction or centre-filler design, and they typically have fleece wraps and binders with a sleeve-extruded jacket.

In short-travel, long-travel gliding or other demanding flex applications, layered cables tend to fatigue and their insulation and jacket compounds lose their tensile and elongation properties. This can greatly reduce service life. As these materials break down, the cable core is compromised and the torsion forces in the conductors release and cause parts of the cable to untwist, resulting in a 'corkscrew' effect (see top photo).

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

In nearly all of the Igus Chainflex cables, the conductors are bundled rather than layered to eliminate these problems (see photo right). In the example illustrated here, the single wires are twisted with a special pitch length and the resulting conductors are cabled into bundles (1). For large cross-sections, this is done around a strain relief element. The conductors are then bundled around a tension-proof centre (2). To complete the cable, a highly abrasion-resistant, gusset-filled jacket is extruded over the outside (3).

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 each other around the centre rope, which provides inner stability. As a result, the cable core remains stable even under the maximum bending stress.

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