WCA March 2016

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Wire & Cable ASIA – March/April 2016
Introduction
Wire and cable manufacturers of automotive and control
wires as well as coax and communication cables are using
measuring and control technologies in their extrusion lines
to maintain specified cable parameters.
This is important for process optimisation and quality
assurance but is also demanded when products are
assembled automatically. In these cases, assembly failure
rates are recorded statistically, registered and assigned to
the manufacturer. For this reason, cable plants are aiming
to supply cables with reliable high quality standards.
Challenges in cable extrusion
A challenge in the cable extrusion process is maintaining
measurement values with tight tolerances of the conductor
concentricity in the insulation, the conductor diameter,
the outer diameter of the cable and the ovality of the
outer diameter. During the extrusion process deviations
of the measuring values can occur, which would remain
undetected without special equipment for visualisation.
Lumps, neckdowns, faults or bare spots in the cable
can lead to malfunctions during assembly. Early in the
assembly process, the cable or wire is cut to lengths
and stripped at the ends in order to be subsequently fitted
with plugs. The pull-off forces used for the stripping are
exactly defined. Deviations of the pull-off forces within
the conductor insulation can cause interferences during
the stripping. The use of innovative measuring and control
technology allow the cables to meet the high demand
requirements and also identify potentials for process
optimisation of the extrusion line.
Rotating/oscillating conductor
The requirements for measuring and control technologies
in cable extrusion lines are very precise where tolerances
within a few micrometres have to be maintained. While
the mean value of the diameter or the wall thickness of
the insulation is sufficient for controlling the extrusion
line, the reliable recording and visualisation of short-term
variations, especially of the eccentricity values, is
additionally necessary under the aspect of the minimum
wall thickness.
Slight oscillations of the conductor directly before the
crosshead can lead to significant deviations of the
concentricity, especially if the conductor is oscillating
in one plane or rotating. Such eccentricities cannot be
shown with a conventional graphical visualisation. A fast
rotating vector of a constant eccentricity value can only
be displayed to the operator by a visualisation beyond the
standard display.
Angle position of a conductor
During the extrusion process it is possible that a cable,
with or without guide rollers, has a slightly angled position
when running through the measuring plane. Eccentricity
measuring systems have to be able to generate accurate
measuring values even when such a position occurs (see
Picture 6).
Technique for
precise concentricity
measurement of a
conductor in the
insulation and relevant
parameters of cables
and wires
By Harald Sikora and Katja Giersch, Sikora, Germany