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Wire & Cable ASIA – September/October 2007 67 Wire & Cable ASIA – January/February 11
Comparing unilay and reverse concentric strands of the
same round element input diameter, the unilay strand will
inherently have a smaller conductor diameter (4.86d versus
5d) and thus a higher fill factor (80.3% versus 76%).
Note: the fill factor represents the ratio of conductor area
to the total circular area enclosing the elements.
The amount of extrusion material necessary is defined by
the strand design; the smaller the outer diameter of the
bare conductor, the less extrusion material is necessary.
Figure 6 shows how a unilay/unidirectional lay conductor is
inherently smaller in diameter than a reverse concentric lay
conductor. The more compact the conductor, the smaller
the outer diameter.
The surface of the outer diameter is critical. A smooth
outer layer, such as one found on a solid conductor or a
roll formed layer, has fewer interstices and, therefore,
fewer gaps that need to be filled with insulation. This can
be clearly seen when comparing a compressed conductor
with a compacted conductor, as seen in Figure 7.
As the conductor is compacted the diameter of the
conductor and the interstices are reduced in size, leading
to a reduction of used extrusion material. The extrusion
process is most economical and productive when using a
stable, tight conductor with the minimum outer diameter
and smoothest possible surface.
Conventional stranders can only achieve a maximum fill
factor of 92%, whereas the roll form strander can achieve
fill factors of 96% and above. The effective saving in
insulation costs between the two processes is around 2%.
Case studies have been carried out from wire drawing
to final insulation of the conductor, taking all downtime
parameters into consideration. The comparison was
between a conventional 19-wire rigid strander and a
roll form strander, each producing 3,000km of 150mm2
compact aluminium per year. The predicted annual savings
were demonstrated to be in the region of €430,000.
It should be remembered that savings in production costs
depend on many factors such as existing manufacturing
facilities, whether the strand is currently manufactured
in-house or purchased, the care and control exercised over
input copper and aluminium wire, general housekeeping
and the control of high-speed roll form stranding machines.
Under the most advantageous conditions savings can
provide extremely short payback periods, but should of
course be calculated for each individual application.
The high performance of roll form stranders coupled
with the Ceeco Bartell patented roll forming process will
allow the cable manufacturer to reduce costs without
compromising finished conductor performance.
An awareness of this and other new technologies,
combined with enlightened specifications, will further
enhance the development of strand design and the
potential to optimise further the manufacture of stranded
conductors.
Sean Harrington was awarded the HW Bennett Non-Ferrous
Trophy 2010 for this paper, which was presented at Istanbul
Cable & Wire ’09. It is reproduced here by kind permission
of the conference organiser the IWMA.
Sean Harrington
Ceeco Bartell Products,
Bartell Machinery Systems LLC
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