Cables for fixed installation in wire channels or long walls or long sealings of rooms need to be bendable. Cores for moveable electric devices and units need to be flexible. The required processability is achieved by using stranded conductors inside the cable which are produced on stranding machines.

Stranding is the process where a particular number of stranding elements are joined together while winding them round a common axis.

Stranding is a result of rotating and forward movement. The rotation creates winding of the stranding elements around an axis or a center element. The forward movement is made using a capstan.

The most common and simplest stranding system is the 6-wire system. This system has a center element and 6 wires are helically laid around this center element. All additional layers on top of this one have 6 wires more than the layer before. For example 1+6+12+18+24 etc.

When using the 6-wire system all wires in all layers have exactly the same diameter. Such a design is called concentric design.

Lay-length -The lay-length is the measurement parallel along the axis that every individual stranding element needs for one complete winding around the axis.

Stranding direction -The stranding direction can be indicated when looking on the rope in the roll axis. When looking on a right-stranded rope the stranding elements are going from front left to down right. For this direction the character “Z” is indicated. The character “S“ is symbolic for left stranding. The assignment of “S” or “Z” is related to the center of the character which either goes right to left or left to right.

The cross lay stranding has an opposite direction of each layer to the one before.

When designing the cable with mono lay all layers have the same stranding direction.

Single Twist Bunching

The advantage of the single twist bunching machine is a spinning of the take-up reel around its centre axis.

The production speeds to be achieved are in comparison to a drum twister much higher. The single twist buncher is limiting the bending radius of the ingoing individual products. In case the min. achievable bending radius of the single conductor is bigger than the bending radius inside the single twist machine another way of production has to be selected for example drum twister Thanks to modern control technology the single twist machines can perform good stranding results for the entire production length.

Double Twist Bunching

The double twist bunching machine is making two twists in turn of the bow. In the double twist bunching machine the take-up bobbin or reel is installed and a bow is rotating around the pay-off. The pay-offs for the individual products are outside of the machine. The machine usually has a housing. In addition to bobbins barrels can be used as pay-off for the individual wires. The individual elements are outside the machine housing and are going to the lay-plate in front of the machine. From the lay-plate they are going through the bow where the two twists are added before going onto the spool or drum.

Compacting can also been done in Double Twist Bunching Machines.

Compacting

Round conductors -When compacting a round conductor this is usually made using the stranding nipple and/or compacting rollers. Both ways of compacting are reducing the cross section of the individual wires until the strand has the requested diameter. The geometric shape of the cross section regarding the single wire is unevenly changed.

Sector conductors -To reduce the cross section of stranded conductors, especially for energy cable, sector shaped conductors are replacing round conductors. Multi wire sector conductors are always compacted.

Depending on cable design there are 60°, 90°, 100° and 120° sectors. The sum of the angle of the individual conductors has to be 360°.

Compacting and production of sector shaped conductors is usually made using compacting rollers.