Frequent cable defects in moving applications

Core rupture

A core rupture is the failure of the cable's electrical conductivity due to broken copper wires. This is as a result of the mechanical loads on the individual core due to constant bending stress.
 
In most cases, a core rupture is caused by incorrect stranding wire and/or incorrect pitch direction and length. Using stranding wires which are too thin may offer more flexibility, but can lead to ruptures in the long term. igus® focuses on an optimised combination of individual strand diameter, pitch direction and length, which is the result of long-term tests in the igus® test laboratory.

Corkscrew

A corkscrew is an externally visible helical deformation of the entire cable due to broken copper strand wires. This is caused by subjecting the individual cores to mechanical loads during the bending process. A corkscrew is usually due to a faulty cable structure. Cores wound in layers with an outer jacket extruded like a hose or a missing core can cause problems here. In addition, an application outside of defined parameters (too tight a bend radius, too long travel) can lead to corkscrews.
 
To avoid corkscrews, igus® relies on cores which are wound in bundles for cables with more than 12 cores. Cores are bundled meaning all cores move through the inner and outer radius of the bent cable several times at identical spacing distances. This ensures that the tensile and compressive forces are minimised and significantly lengthens the service life of a cable.

Insulation damage

With electric cables, core insulation damage can lead to short circuits. The cause can be material fatigue under constant bending stress or material abrasion within the cable structure. Single strand wire breakage of the conductor or the shield braiding result in perforation of the insulation.
 
To avoid core insulation damage, materials such as TPE or PVC are used as they do not stick together. In the igus® test laboratory the insulation materials are tested in millions of test strokes.

Jacket damage

Jacket swelling or jacket breakage describes damage of a cable's outer jacket. The jacket becomes soft and deformed or breaks until the cores or shield can be seen. The cause can be the incorrect selection of materials with respect to the oils or other chemical substances being used. Too low an ambient temperature can also lead to jacket breakage, when the temperature is below the minimum stated in the data sheet. As soon as a jacket swelling or jacket breakage occurs, the cable needs to be changed immediately.
 
To avoid jacket breakage, it is recommended to pay special attention to the temperature range and the oil resistance of a cable. If cables are used in oil-free environments, PVC cables that are not oil-resistant are sufficient as long as the permanent ambient temperature is higher than 5°C. If cables come into contact with oils, chainflex® cables with PUR or TPE outer jacket are recommended. Cables with TPE jacket are resistant to organic oils. The oil resistance of all chainflex® cables is given according to DIN standards. These jacket materials are also suitable for temperatures of -25°C (PUR) or even -35°C (TPE) for the permanent use in the energy chain.

Shield wire breakage

A shield wire breakage occurs when the shield braiding, designed to protect a cable from EMC, breaks down. The consequences of a breakage range from reduced shielding effects up to short circuits whenever the sharp wire ends penetrate through the fleeces or foils into the cores. The cause is often an incorrect braiding angle. If after the insulation has been stripped off the shield can be easily pushed back over the jacket, it is an indication that the shield is unsuitable for use in energy supply systems.
 
To prevent shield breaks, igus® has conducted long-term tests and determined that a braiding angle that is as shallow as possible is the ideal shield braid angle for cables that are used in energy chains. This angle neutralises the tensile forces and is therefore more suitable for energy chains. The sturdy inner jacket offers additional protection, so that the shield cannot move around.