WCA January 2011

The single input wire method can save between 15% and 20% on wire drawing costs, including the elimination of re-strings for size changes, lower die inventory and reduced in-process wire. Double twist stranding has always been among the most productive methods of producing strand. Its incorporation into the roll form strander, with the application of the individual shaping of the wire, has further extended its performance range. In Figure 4 its performance can clearly be seen. Each machine type works the wire differently, and this impacts on the strand design that can be used for that process. Figure 4 highlights some of the advantages and disadvantages of each machine type as they relate to product capability and relative

Line speed comparison aluminium

Line speed (metre per minute)

Conductor size (mm 2 )

RC double twist

Ceeco Bartell

Single twist

Figure 5 ❍ ❍ : Line speed comparisons

cost. It is important to recognise that if the roll formed or die shaped wire is used in the strand construction a ‘rigid’ machine, or a machine that puts a twist in the wire for each lay length, is a prerequisite for manufacture. Capital cost per twist Determining the range of equipment to cover the strand designs is an important consideration in achieving the lowest conversion cost. For example, the double twist machine offers the lowest cost per twist but is the most limiting in terms of the construction possibilities. By its incorporation into the roll form strander this range of construction possibilities has been greatly expanded. The planetary machine, at the other end of the spectrum, has the highest cost per twist but the greatest construction possibilities, which is why it is used for special purpose products. Material limitations Each machine type works the wire differently. For this reason alone it is necessary to identify the differences to be able to use the same drawn wire size for the multitude of stranding possibilities. This applies not only to the principle of the machine but also to the area reduction that can be expected from different machine types. Keep in mind that in most cases the area reduction through the machine varies at different speeds and, to some extent, all machines used to manufacture strand require that the stress in the wire during the stranding point exceed the yield point of that material. For example, the double twist, single twist and rigid strander put a twist into each input wire along the axis of the wire for each lay length; the tubular and planetary machines are more forgiving and put almost no twist into each wire, which is important when stranding steel wire. Lay and layer limitations Both the double twist and single twist machines currently can manufacture up to four layers (typically a 37-wire

Ceeco Bartell believes its roll form strander is the only process to fully utilise the advantages of single input wire (SIW) diameter. SIW represents a strand and design mentality, with a manufacturing methodology that effectively reduces the conversion cost from rod to strand without compromising conductor performance. This concept replaces the traditional stranding of wires using different wire diameters with the stranding of wires using the same wire diameter for a wide range of cross sections. SIW diameter meets major conductor standards such as IEC 60228, HD 383 and the ASTM standards. By incorporating a single input wire diameter program into the strand design, significant savings can be achieved in wire drawing, stranding and the insulation processes. Traditionally a finished stranded conductor requires its own drawn wire diameter. Each wire diameter typically requires a new string-up in the wire drawing machine. Some conductor designs require more than one drawn wire size. The set up time taken on the drawing, combined with inventory levels that are necessary to manage the number of wire diameters, represent unnecessary activities that add to the cost of conversion from rod to strand. The SIW approach, using the same input wire diameter to finish a range of stranded conductors, eliminates much of the unnecessary activity associated with the traditional set up. This leads to increased efficiency in the wire drawing process. Instead of having to produce a large number of different wire sizes only one or two are required using the SIW system. The improvements can be seen in the following areas: Higher productivity in wire drawing • Lower drawn wire scrap • Quicker set-up • Reduced work in process • Shorter cycle times •

Smaller input wire storage area • Reduced drawing die inventories •

65

Wire & Cable ASIA – September/October 2007 Wire & Cable ASIA – January/February 11