What is the inner jacket of a cable?

May 5, 2020 Max Herrmann

The structure of a cable is very complex, and like many other topics, it is not easy to explain in just a few sentences. Basically, the claim for any cable is that it operates reliably and efficiently for as long as possible. Today, we look at the inner jacket, or cable filler, which is an important part of managing the insides of a cable. To do this, we look at where the inner jacket is within a cable, what its purpose is, and how it can affect the service life of a cable.

Where is the inner jacket, or cable filler, located?

To explain the purpose of the inner jacket, we first have to take a closer look at where the inner jacket lies within the cable structure. Often, we find it in high quality cables that are designed for dynamic applications, and it is between the shield and the stranding.

Function of the inner jacket

The inner jacket separates the core stranding from the shielding. As a result, the wires are well guided while the inner jacket also serves as a secure foundation for the shield.

The inner jacket extruded under pressure

At igus®, we maximize the service life of the cables, among other things, by implementing a pressure-extruded inner jacket. A pressure-extruded jacket occurs when the jacket material is extruded at a high pressure into the spaces that are between the veins. As a result, the stranding structure lies firmly within the inner jacket.

The wires are guided in the longitudinal direction while simultaneously maintaining the required grasp in the transverse direction—like a train that runs on rails. When looking at this comparison, the train corresponds to the wires, and the inner jacket to the rails. The rails tell the train which direction it should move while keeping it on track.

Inner jacket or banding with filler

As an alternative to an inner jacket—when there are less stressed lines—a film or fleece banding with filler can be used in its place. This design is significantly simpler and more cost-effective, particularly in the manufacturing of cables. However, an inner-sheath for cables that are moving within a cable carrier guarantees a significantly longer service life since the stranding element has much better support.

Cable with taping and filler

Cable with inner jacket

Inner jacket for long travels

The pressure-extruded inner sheath clearly demonstrates its advantages, particularly under high loads—like those that occur over long travels. When compared to an inner jacket, the disadvantage of a filler is that the filling element consists of soft textile materials which offer the veins little support. Additionally, the movement creates forces within the cable that can cause the wires to come loose from the stranding, which leads to a visible, screw-like deformation of the entire line. This is known as a "corkscrew". This deformation can lead to wire breaks, and in the worst case, result in a plant shutdown.

Easy stripping despite the pressure-extruded inner jacket

By implementing the CFRIP® thread into the cable’s design, the inner jacket of chainflex® cables can be easily torn apart along the side of the entire cable length. This also ensures that none of the veins are injured if the jacket needs to be torn open. The tear thread works much like a zipper—simply pull on the tear line and open the line to the desired location. This saves engineers and electricians not only time during installation, but also from the need for additional tools. Chainflex® cables are designed so that the cord does not damage the sheath or veins even after millions of movement cycles.

Are you unsure about which cable is the right one for your application? Feel free to reach out to Don Nester, chainflex® Product Manager, by emailing him here.

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