EoW May 2009

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EuroWire – May 2009 49
Materials handling & equipment
For accuracy in wire tensioners
Today’s high-throughput production machines routinely 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.
Various braking technologies can be considered to control the
torque applied to the shaft of the capstan pulley around which the
wire is wound (without slippage) to generate the winding tension.
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. In this context,
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. Altic is the inventor of the modern wire tensioner and
manufactures the only closed loop force control solutions available
on the market. Based in southern France, Altic now exports almost
80% of its production.
Andantex Ltd – UK
Fax: +44 2476 30 4499
Email:
Redex SA – France
Fax: +33 2 38 94 42 99
Website :