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Automation Technologies 4/2015

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Automation Technologies 4/2015

Reliable cables for

Reliable cables for industry There is continuous movement of all sorts of things in the industry. In general, when there is movement on the floor it’s good for production. But what is good for production, is a major challenge for cables. To protect moving machine cables from tensile, torsional forces and external influences such as impact or welding sparks, energy chains are used. They also reduce wear, stress on cables and hoses, prevent entanglement, and improve operator safety. An energy chain is like the umbilical cord of a machine. It supplies a machine part with energy, data and media whilst following its every movement. Energy chains are arranged to accommodate simple linear horizontal, vertical strokes, rotary strokes and even the six-axis robotic applications. For the cables to withstand stresses millions of times without core breaks or the “corkscrew” effect after a few thousand cycles, the material and structure of the cable must be perfectly matched to each other. Cross-sectional view of stranding in bundles, similar to the structure of steel ropes Only long-term tests provide predictable reliability Experience shows that even highly flexible cables in dynamic use in energy chains often quickly reach their stress limits. Can their service life be predicted? The standard tests performed by VDE, IEC or UL don’t offer a clear statement, because only a long-term test in the energy chain itself offers this. Relevant standards use other means that merely simulate the wear regardless of the chain or the chain material, again offering little accuracy for cable lifetime in energy chains. To be able to predict the service life reliably, the Cologne based company igus, as a specialist in plastics and cables in motion, operates the largest test lab for cables moving in energy chains in the industry (1,750 m 2 ). Here, products are tested for their resilience in continuous operation in 58 different test rigs. Since the exact re-production of the real working conditions is crucial, test axes are available with different travel distances and accelerations or environmental conditions. For testing large energy chain systems, such as those used in crane facilities, an outdoor test site with a travel distance of up to 240 metres is available. Here components have been successfully tested at 4 m/ s and with an additional load of 8 kg/ m for a total lifetime of 25,000 kilometers. AUTOMATION TECHNOLOGIES 4/2015

COMPONENTS AND SOFTWARE Simulating application at extreme temperatures in real conditions Testing over a range of temperature from -40 up to +60 °C is carried out. The specially adapted container, in which these conditions can be simulated, is of vital importance. Unlike standard “cold winding” tests, in which the cables are wound up on a mandrel and cooled to test in temperature conditions just once, here the cables and chains are put under appropriate test temperatures and realistic motion conditions. They must withstand millions of strokes to prove they will withstand the expected bending stress in a real application. A test is considered passed when no jacket breaks can be detected, and thus proved to have the necessary flexibility in the cold. The tests are not always about extreme temperatures. Customer requests are often about cables that must operate reliably at -5 °C. Therefore, for the last four years igus has been offering an oil-resistant PVC compound, which has a high abrasion resistance. This is unique on the market, because the usual PVC compounds for chain-suitable cables do not meet these requirements. Another benefit is that in more moderate temperatures it is not absolutely necessary to rely on expensive jacket materials such as PUR or TPR. Bundle instead of layer The findings obtained from the ongoing analysis of all tests for more than 25 years have been archived at igus and used for the development of its own, ever-growing range of cables. This has led to, among other things, the introduction of stranding in bundles, similar to the concept used in steel cables. In an elaborate bundle stranding process, the cores are stranded in individual bundles with three, four or five wires, which are then again braided with each other into an overall stranded bundle. For large stranded superstructures this is done around a strain relief element. The result is a cable that is durable in motion and suitable for chains because, in contrast to a layer-stranded cable, each of the cores moves similarly in the inner and outer radius with the motion in the energy chain and thereby prevent relative stretching and compression. Cables such as “robot cables”, with a similarly complex structure are used in industrial robots and must follow very extreme movements, bends and torsions. Special damping elements give the cores the necessary freedom of movement in the interior of the cable. Because, the more twisted the cable is approaching its load limit, the more difficult it becomes for the cable to twist further. Special shields and exterior materials also ensure an optimum durability of the cables. 1,040 different cables for application in energy chains The service life of a cable used in an energy chain depends on a variety of variables that must be considered in the structure and the choice of materials. Thus the chainflex product family from igus currently offers 1,040 different cables. Users themselves can calculate the service life of the cables in their relevant application. This is made possible by the results from the 2 billion test cycles each year, which are incorporated into the igus database. Based on this data, the free online tool on the igus website predicts the service life of cables. Photographs: igus GmbH Temperature conditions from -40 to 60°C can be simulated in the cold chamber About Company name: igus GmbH Headquarters: Cologne, Germany Turnover: € 469 million Employees: 2 700 worlwide Products: Energy chain systems, polymer plain bearings, linear bearings, low cost automation


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