A very simple cable is made up of a solid wire and a plastic sheath. This cable can bend and retains this bending – if you don’t do it too often, because otherwise the wire breaks. Simple cables like these are used in house installations. Once permanently installed, the cable remains in place for decades untouched. Solid wires like these aren't suitable for many other challenging applications where cables sometimes need to be extremely flexible and movable.
Find out what flexible and highly flexible cables are, how they differ, how they are constructed, what properties they have as well as when and where they are used.
What are flexible and highly flexible cables?
The absolute majority of all power, control and data cables from LAPP are flexible. However, the degree of flexibility, i.e. the mobility and bending measurement of a cable, is determined by the design and material properties. Some cables only allow occasional bending, while others can bend millions of times. Some cables are also specially optimised for axial movement stresses, known as torsions.
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How can flexible and highly flexible cables be moved and where are they used?
If cables remain in the position in which they were installed, this is referred to as fixed installation and static use. These fixed installation cables, which are typically used for building installation, are only moved for maintenance, repair or renovation. As a result, such cables are exposed to virtually no movement and, above all, no permanent flexing stress.
In an industrial environment, it is much more common for cables to be moved constantly and everywhere: on moving machine parts or processing stations on production lines, in cable chains, robots, wind turbines and oil rigs, in vehicles and motors, on cranes and commercial vehicles – even in applications where vibrations occur.
Let's take a look at the typical flexing stresses that may be faced by cables developed for flexible use or constant flexing:
Flexible cable routing
The cables are exposed to the conditions of occasional, unforced movement.
Machine tools, hand-held electrical devices, portable electrical devices, frequent reeling and unreeling of cable drums, etc.
Bending (linear movement)
The cables are permanently exposed to the stresses resulting from the bending movement.
In horizontal and vertical cable chains for automated applications – one of the most gruelling locations for a cable.
Here, power, servo and data cables are located close together and move back and forth as a machine works. Sometimes faster than five metres per second with more than five times the acceleration of gravity (5x 9.81 m/s²). The cables are laid in the cable chain in such a way that they’re bent in just one direction.
Torsion (three-dimensional movement)
The cables are permanently exposed to the stresses resulting from the torsional movement.
A gentle, slow torsion occurs in the loop between the nacelle and the tower of a wind turbine.
By contrast, many industrial robots are much more dynamic and faster. Here, the cables rotate around themselves with high torsion angles and are also exposed to high rotational speeds and intense bending. The cables are designed for 3D movements.
What exactly is torsion?
Torsion does not mean, for example, a bending of the cable, i.e. a kink or a twist, but rather a longitudinal rotation of the cable around itself at a certain angle of torsion. This torsion angle is specified in degrees per metre of cable length. A typical value is 360°/m. Such a cable can be twisted once per metre around its axis without causing any damage – and it can do so in both directions. This applies to cables without shielding; with shielding, the value is typically 180° or half a turn per metre.
The flexing stress of a torsion can either only act axially on the cable (rarely the case) or it is a combination of simultaneous bending and torsion (much more commonly the case).
In constantly flexing applications, strong forces often act on the cables. They must be equipped for high acceleration, strong deceleration and rapid changes of direction.
How are highly flexible cables constructed?
Highly flexible (data) cables are generally designed either for linear loads, as they occur in cable chains, or for torsional loads, which are predominantly caused by industrial robots. There are only a few cables that can withstand both bending and torsion over the entire service life. You can identify these at LAPP via the product name ROBOT.
Which properties are crucial for drag chain cables?
Cables must meet a number of requirements to be considered suitable for cable chains:
Which cable design dominates among robot and torsion cables?
Provided that the bending radii allow it, special robotic cables can be used in the same way as highly flexible drag chain cables in drag chain operation, where linear continuous bending movements with firmly defined parameters act on the cables. However, drag chain cables cannot be used in three-dimensional robot operation. This is due to the design and can be explained in a simplified way by taking a look at the basic structure of cable chains and robotic cables.
With drag chain cables, the principle applies: the shorter the lay length, i.e. the core stranding, the more flexible the stranding assembly. The exact opposite is the case with robotic cables, as the longer the lay length, the more gently torsion can be absorbed. This is because if the lay length is too short, the cores could break during the three-dimensional movements.
Robotic cables have sliding foils over the outer layer and, in some cases, also between the layers, so that the core assembly can move easily within the sheath in the event of torsion.
In addition, the outer sheath is usually manufactured as a hose extrusion and not as a press extrusion to make it easier to rotate the core assembly.
Which application parameters must be observed?
The aforementioned properties have a major impact on the following application parameters to be observed when selecting a cable.
Note: The cable chain must always be designed in accordance with cable/hose features and not the other way round. However, the service life of drag chain cables largely depends on the correct installation in the cable chain, the type of chain and the quality of the chain.
How flexible are fibre optic cables actually?
Fibre optic cables are the first choice for very high data transmission rates over long distances. They consist of plastic optical fibre (POF) for shorter distances of up to 70 metres, plastic cladded fibres (PCF) for distances of up to 100 metres and glass fibres for even larger distances and applications requiring the highest data transmission rates. In principle, all fibre types are suitable for flexible applications as long as the recommended bending radii are observed. Then you don’t need to be afraid that a glass fibre optic could split. However, in order to achieve the highest possible transmission performance, the bending radius in fibre optic cables should be at least 15 times greater than the diameter. While a lower bending radius will not cause them to break, it will lead to increased attenuation, meaning that light is lost in the tight curve and the signal quality will suffer. The material enveloping the fibres largely determines how well a fibre optic cable can withstand movements. Aramide fibre, i.e. synthetic fibres that give bulletproof vests or fibre-reinforced plastics their exceptional properties, are often used here. If the cable is stretched, the textile sheath absorbs the tensile force and prevents the fibre optic cable from also being stretched.
How are highly flexible data cables tested?
The decisive thing is not what is on paper, but what happens under real conditions. In the LAPP test centre, the tests are therefore carried out in such a way that the results apply to many real applications and we don't have to make false promises.
With the highly flexible cables from LAPP, you can ensure the productivity of your machines and plants.
In moving applications, and specifically where the movement ultimately takes place, it's necessary for every smallest component to be movable. Under no circumstances may the loads be permitted to cause damage. This is because only when all components last a sufficient period before maintenance becomes necessary, i.e. when they are available and deliver the required performance, can a high level of plant efficiency be achieved.
Highly flexible power and control cables from our ÖLFLEX® product brand
Electricity? – The essential power without which a machine would not function at all.
Signals? – The decision makers that determine how a machine works.
Highly flexible Ethernet data cables from our ETHERLINE® product brand
Highly resilient, highly bendable or remarkably torsionable – these are our ETHERLINE® data cables with different transmission properties (performance according to cable category "CAT"). The specific cable design (2- or 4-pair, foils over the core assembly, with or without a cross separator, many with a Fast Connect design and inner sheath, sheath material PVC or PUR) has a significant influence on the future application area.
Highly flexible fieldbus data cables from our UNITRONIC® product brand
Fieldbus systems also require the dynamic use of cables. High resistance to electromagnetic interference goes without saying. To prevent errors in signal transmission, the correct cables should always be selected. The following table provides a brief overview of highly flexible data cables for the PROFIBUS and CAN fieldbus systems.
Highly flexible fibre optic cable from our HITRONIC® product brand
If fibre optic cables are to withstand the highest bending stresses, products that are particularly elastic and mechanically resistant must be used. Plastic-sheathed fibre optic cables with a high-quality PUR outer sheath are available for this purpose. Large bending radii enable use in the cable chain without having to worry about optical losses in data transmission. Discover our top recommendations below: