WCA May 2009

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Wire & Cable ASIA – May/June 2009 36
High-throughput production machines
attain speeds of more than 30m per
second for wires of only a few
hundredths of a millimetre in diameter.
The forces applied to these wires are
of the order of a few tenths of a
Newton, and must be controlled very
precisely. The task is complicated by
the fact that the tension to be applied
must be above the elastic limit of the
wire (to give it rigidity) yet below its
breaking point (to avoid any break
leading to production shutdown).
At such speeds wire tension control
cannot be applied at the feed coil, as
its inertia is too high. The feed coil
therefore remains static, and the wire
is pulled by the tensioner and then
wound onto the receiving coil. In these
conditions the precision of tension
control during coil winding is a major
issue.
Other than technologies based on
friction brakes of various levels of
sophistication, which cannot handle
large diameter wires, the solutions
generally use motor control, but these
are also generally limited to the
finest wires for reasons of space and
budget limitations. However, future
developments are tending towards
larger wire diameters, for example in
order to meet the high demand from
China and India for power transformers,
but also for more specific applications
in the cable industry.
Altic has selected Merobel EMP
brakes, from Redex Andantex, for its
entire range of electrical and electronic
tensioners. “We can only be pleased
by the technical advantages provided
by Merobel brakes for our most
demanding applications,” states
Jean-Yves Petitgas, director of Altic.
“Their flexible, jerk-free operation, the
very low electrical power needed for
their control, the torque density and
the robustness of the brakes are
indispensable qualities for us. The
technology of Merobel’s EMP brakes
enables us to cover 100% of our
current range.”
The electromagnetic brake works on
the following principle: a change in the
magnetic field alters the viscosity of
the EMP powder, controlling the
mechanical coupling between the inner
and outer rotors. With this technique,
the torque is proportional to the current
that produces the magnetic field and is
independent of the rotation speed. The
torque/size ratio is better than for a
friction-based mechanical solution: the
torque is reliable and reproducible,
without shocks, and the response
time is rapid. Wear is also very low,
giving a long maintenance-free lifetime.
The design means that mechanical
installation is generally very simple.
Altic uses the FAS and FRAS models
(output-shaft brakes) for the smallest
sizes and the FAT and FRAT models
(through-shaft brakes) for the rest of
the range. In addition, Altic fits Merobel
PowerBlock2 power supplies in all
cases, ensuring very precise electrical
control.
Andantex Ltd – UK
Fax: +44 2476 30 4499
Email:
Redex SA – France
Fax: +33 2 38 94 42 99
Website :
For accuracy in wire tensioners