A North Devon-based manufacturer of flat pack furniture uses moving cables guided by cable chains on its sawmill and packing machinery, but it was suffering cable failures every six months. Following a chance meeting at an exhibition, an igus sales engineer paid a visit and discovered that the problem was related to sag on the installed cable carriers. It also emerged that cable breakage within the plant was occurring on a regular basis, mainly involving so-called 'super-flexible' data and control cables. The key problem was that some of the chain radii were too small for the cables, so the inner cores were failing. Typical performance life was just six to eight months.
igus recommended that the manufacturer replace its existing cables with Chainflex CF5 and CF211. The latter agreed to test them, but was not convinced by guarantees that they would outperform those previously used by some three to four times. A sample of the CF5 cable wasduly installed on a machine and tested. This same cable is still running with no failures and no sign of corkscrews two years on. So, having fulfilled the original guarantee, igus now believes that its cable will do even better. Impressed by this performance, the furniture manufacturer now uses both igus E-Chain and Chainflex.
According to igus, it is difficult for users to get a proper perspective on the cable market. Competition between cable suppliers is intensifying and manufacturers are trying to outshine one another in promises to guarantee cable service life in guided applications. Stranding in layers is significantly easier to produce and cables are therefore offered on the market as so-called 'chain suitable' at low cost. However, what appears to be tempting at first can quickly turn into an expensive mistake when a corkscrew immobilises the system that relies upon these cables.
A corkscrew happens because the cable cores are usually stranded relatively tightly in several layers around the centre and enclosed by a jacket extruded in the form of a tube. Shielded cable cores are wrapped up with fleece or foils. When these layered cables are bent, the core compresses in the inner radius of the cable and stretches in the outer radius. Initially, this works quite well, because the elasticity of the material is still sufficient. Very soon, however, material fatigue causes permanent deformations: the cores deviate from their intended path and make their own compressing and stretching zones. A corkscrew is created and is usually quickly followed by core ruptures (examples of a 'corkscrew' and subsequent rupture is shown on this page).
Chainflex cables are stranded in bundles. This eliminates any problems due to their sophisticated, multiply stranded, internal structure. The litz wires are stranded with a special pitch length first, and the resulting cores are then stranded into single core bundles. For large cross sections, these are braided around a strain relief element, and the core bundle stranded around a tension-proof centre. Due to this multiple stranding, pulling and compressive forces balance one another around the highly tensile central core, giving the stranded structure its necessary inner stability and it endures even under maximum bending stress.