EuroWire November 2016

60 / 88

Technical article
November 2016 58
Double Twist Roll Forming Coil Pay off
Assembly into
Compact Conductor
Roll Formed Profiles
RoundWire
92 per cent fill factor is the best
compaction that can be achieved using
conventional methods. However, with the
roll forming process 96 per cent fill factor
can be achieved. This creates a potential
saving of material of around two per cent.
The productivity of the extruder relies
in part on the integrity of the strand
construction. This applies equally to low,
medium and high voltage extrusions.
Unstable strand construction not only
compromises the speed of the stranding
and extrusion processes, but can lead to
considerable losses due to scrap and down
times for both lines.
Birdcaging is often the result of unstable
strand design. A tightly wound conductor
is less likely to end up birdcaging.
The tightness of the strand is greatly
dependent on the geometry of the
elements.
For this reason, the lay of the conductor
is important. The elements of unilay/
unidirectional lay conductors are nested
and, therefore, inherently have a smaller
outer diameter than reverse concentric lay
and SZ conductors.
In addition, unilay/unidirectional lay
conductors self-tighten under tension. As a
consequence of this self-tightening feature,
the extrusion of unilay/unidirectional lay
conductors is statistically less prone to
birdcaging.
The surface of the strand is also critical.
A smooth outer layer such as one found
with a roll formed layer presents a clean
round profile to the extrusion process and,
therefore, minimises the accumulation
of conductor dust during the extrusion
process.
The process is shown in Figure 4. Round
wire is taken from large coil packs and
passes through the roll form section where
its shape is changed into various roll form
profiles that are then assembled at high
speeds by either a double twist machine
or a single twist machine, depending on
product size. This high-speed continuous
process allows for linear speeds of 200m/
min to be achieved while producing
highly compact conductors. The roll form
strander is capable of producing 40 tons of
150mm2 compact aluminium conductor in
a 24-hour cycle.
Conclusion
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 house-keeping;
and the control of high-speed double
twist stranding machines. Under the
most advantageous conditions savings
can provide quite astonishingly short
pay-back periods, but should of course be
calculated for each individual application.
The high performance of a roll form
strander coupled with the Ceeco Bartell
roll forming process will allow the cable
manufacturer to reduce costs without
compromising the 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. n
Ceeco Bartell Machinery Systems LLC
Ceeco Bartell Products
400 Applewood Crescent,
Suite 100, Vaughan,
Ontario, Canada
Tel: +1 905 761 3000
Email :
Website:
▲ ▲ Figure 4