Double Twist Buncher

The combination of a pre-twister with a double twist buncher machine brings out the most robust and most flexible cables and ropes.

A double twist machine has a vital role in the wire and cable industry. It is a machine with many advantages that can operate for 24 hours. It also gives improved production within a short time due to its superior twisting technique. It is an excellent option for stranding copper, aluminium, alloys and multi-wire cables. It can be used to produce sector shape cable by laying up insulated wires with or without taping.

Why Use A Double Twist Machine?
High flexibility and current-carrying capacity are mandatory in locomotive cables, mining cables, geophysical cables, welding cables and automotive battery cables. Thus, these cables cannot have single solid metal in concentric or unilay configuration. They should have various layers of multi-wires or bunched wires.

The cross-section, as well as flexibility, are maintained by using more number of wires with a smaller diameter. Traditional planetary cabler wires posed challenges like low production speed, short production length and long changeover time. These issues can be avoided by using double twist buncher.

Issues Cropping With a Double Twist Buncher
In the double twist bunching process, the final lay length is half the lay length at the external closing die. The double twist machine pulls the respective heights of each member wire corresponding to its position for each layer.

The outer wires have tension while the inner cables are compressed. The relative movement between layers and compression of inner layers adds to the extra length. When the product reaches the take-up reel or inside capstan, the buncher reduces the lay length.

Because of this, the accumulated length of the wires in the inner layer comes out or pops-out as knots in the main cable. These knots are produced at regular intervals.

How is The Problem Solved?
A pre-twister resolves this challenge. Using a pre-twister in line with a double twister has become popular in making steel ropes. The idler pulleys in the pre-twister rotor have rotating speed same as twist per minute (TPM) of the double twist buncher.

The idler pulleys guide the wires, also called ‘members from pay-offs’, through the closing die to the pre-twister. As the lay length approaches its finality, the pre-twister pulls members of an appropriate range from the payoffs. The rightly adjusted speed of the pre-twister will ensure reduced compression. It eliminates ‘pop-outs’ or knots and gives a smooth finish to the product.

Where is a Pre-twister Used?
Elastic ropes with multi-wire strands of 19 or more need a pre-twister. Less number of wires bunched together may not need one.

Cables of insulated conductors have low-elastic yarns inside them. Without the use of a pre-twister, these yarns will not maintain their position and will get pulled into inner layers.

Reverse concentric products such as AAAC and ACSR conductors as well as two-layer cables with insulated cores use pre-twisters.

Other areas where it can be used are: for producing straight sector-shaped conductors using copper and aluminium wires, and pre-spiralled sector-shaped conductors.

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