EoW May 2009

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.

“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 : sales@andantex.co.uk Redex SA – France Fax : +33 2 38 94 42 99 Website : www.redex-andantex.com

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.

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EuroWire – May 2009