The Bundling Versus Layering Technique

Flexible cables constructed in layers are significantly cheaper to produce, therefore many manufacturers offer cables with this low-cost design. However, such flexible cables are often constructed without attention to pitch length, pitch direction or center-filling material and typically have fleece wraps and binders with a tube-extruded jacket.

These types of cables may provide sufficient support in certain short-travel applications. However, in a long-travel, gliding or demanding-flex application, 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 flexible cable core is compromised and the torsional forces of the cabled conductors release and untwist in parts of the cable. This causes a 'corkscrew' effect (Figure 1).

Figure 1: 'Corkscrew' refers to the permanent deformation of flexing cables in automated applications and is caused by excessive stressing. The end result is usually core ruptures, cable failure, and machine downtime.

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

In the majority of igus®' chainflex® 'continuous-flex' cables, the conductors are bundled rather than layered to eliminate these problems (Figures 2 & 3). The wires are twisted with a special pitch length and the resulting conductors are cabled into bundles. For large cross sections, they are twisted around a strain relief element. The conductors are then bundled around a tension-proof center.

The multiple bundling of the conductors changes the inner radius and outer radius of the bent cable several times at identical intervals as it flexes. Pulling and compressive forces balance one another around the highly-tensile center cord, which provides the necessary inner stability. As a result, the cable core remains stable even under maximum bending stress.

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