Technical Rod Breakdown Line Solutions

Power and flexible cable manufacturing process starts with a wire drawing process in a rod breakdown line. Rod breakdown line is a multi-pass drawing machine where a rod of 9,5 mm or 12,7 mm is pulled through dies with decreasing size up to the desired final diameter (usually from 1,6 mm to 4,5 mm) and collected in a reel (with a single or automatic double spooler) or a basket depending on the application (Photo 1).

Rod breakdown machines can be divided into multimotor machines and single motor machines. In a multimotor machine, each axis is driven by a motor, the kinematic ratio between each axis is variable and electronically controlled, allowing maximum flexibility and the possibility to wiredraw a wide type of alloys. In a single motor machine, the kinematic ratio between each axis is fixed because all axes are connected to a gear transmission driven by one motor. In both type of machines, the final capstan has a separate motor to allow a quick change of the final die.

In a rod breakdown machine, be it single or multimotor machine, the best solution for an efficient wiredrawing process consists in die holders and pulling rings that are fully submerged, as well as a wire path with some adjustable rollers for wire alignment and spray jet for inlet and outlet die cones.

During rod breakdown operations, net oil is used. The development of emulsions is constantly in progress and the results obtained so far in real working conditions are under evaluation.

Shaped Wire Manufacturing Process

Traditionally, power stranded conductors use round wires. Stranded conductor construction with shaped conductors was introduced on the market in the mid-1980s. The most common shapes currently used are trapezoidal (TW: Trap Wire) and Z. The benefits in using shaped conductors versus round wire conductors with equal cross section is a compact stranded conductor with less overall diameter, that allows less wind loading parameters, reduced formation of ice on the conductors, increased resistance to vibration and improved fatigue resistance.

The manufacturing process requires the use of round and shaped dies. The dies sequence generally comprises two or three round dies and 5-8 shaped dies, depending on the final shape, material and the machine. The design of die sequence and dies profile is extremely important in order to have the ideal contacting point between wire and die that will guarantee a good and progressive material deformation from round to shape. Dies can be realized in Tungsten Carbide (TC) or Polycrystalline Diamond (PCD). TC dies, less expensive than PCD dies, are used for testing production, profile optimization and low production cost. PCD dies are suggested for high production volume and wiredrawing of hard alloys (e.g. 5 xxx series). It is necessary to avoid any rotation of the die (intermediate and final) to guarantee the wire quality and the die life.

With a multimotor rod breakdown machine, the die sequence can be optimized in terms of die life, mechanical and thermal stress, slipping between wire and pulling rings. In a single motor machine, the die sequence is slave of the kinematic scheme of the machine, so it cannot be optimized and the slipping between wire and pulling rings can cause scratches and damage the wire surface.

The spooling of shaped wire can be realized with a standard dynamic spooler or with a sliding dynamic spooler. A careful spooling, in particular the absence of wire tangles, is the basic condition for an accurate unwinding process in stranding machines. Therefore the main requirements are a wire path with specialized pulleys, an accurate control of the traversing process and a straight alignment between final capstan and spooler inlet wire. In case of use of a dynamic spooler, the distance from the final capstan has to be increased to 5-8 meters. With shaped wires, double spooling is not possible.