For over 26 years now, igus has been a cable manufacturer, and the company is associated with many different materials and products such as plastics and chain bearings. Engineering Specifier’s editor recently visited the igus headquarters in Cologne, to learn more about the company, whose chainflex cables are worth more than €100m a year.
One thing that separated the company from its competitors was the promise that even with a wide range of cables for the e-chain product, 1,381 to be exact, every one of them are always in stock.
That is because there is automation everywhere in all environments, in dirt, freezing cold temperatures, antibacterial environments, places with a small radius, oily or wet conditions and over a long distance that all require cables to withstand these different conditions. Therefore, igus provide these ranges of cables and guarantee them for a set period depending on where the cable is used.
Looking at the production industry, energy chains help protect moving machine cables and hoses from tensile and torsional forces, as well as external influences such as impact or welding sparks. Even then, the demands on the cables remain extremely high.
Justin Leonard, the-chain Director at igus, shared that, in order to ensure reliability and predictability, continuous technological advances in materials, test standards and procedures are necessary.
The energy chain is the umbilical cord of a machine – feeding it with vital energy, data and media. The degree of movement can range from simple linear strokes, such as those found on pick-and-place machines, to six-axis robotic applications. For the cables to withstand stresses millions of times (for example to not work harden), without corkscrews, core breaks or jacket ruptures after a few thousand cycles, the material and structure of the cable must be perfectly matched to each other.
Only long term tests provide predictable reliability
Experience shows that even highly flexible cables can often reach their stress limits quite rapidly when used in moving applications, especially when housed in energy chains - is their service life predictable?
The standard tests performed by VDE, IEC or UL do not 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 predict the service life reliably, igus operates the largest test lab for cables moving in energy chains in the industry (2,750 square metres). To characterise the resilience of products, they undergo continuous operation test in 58 different rigs. Since the exact reproduction of the real working conditions is crucial, numerous 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 240m is available - here products can travel at 4m/s and with a fill weight of 8kg/m for a total lifetime of 25,000km.
Simulating extreme temperatures in real conditions
Likewise, igus tests its products in temperature conditions from -40°C to 60°C using its two climatic test chambers - unlike standard cold winding tests, in which cables are wound up on a mandrel and cooled to the test temperature conditions just once - here the cables and chains are put under appropriate test temperatures and realistic motion conditions. After experiencing the chambers first hand, it is safe to say you would not want to be these types of cables.
They must withstand millions of strokes to prove they will endure the expected bending stress in a real application. A product passes the test only when no jacket ruptures occur, and proven to have the necessary cold flexibility.
The tests are not always about extreme temperatures - the most popular minimum operating temperature specified is at -5°C. igus offers cable jackets made from an oil-resistant PVC (PolyVinyl Chloride) compound, which provides high abrasion resistance over a wide temperature range. The common PVC compounds used for ‘chain-suitable’ cables do not normally meet these requirements. Another benefit is that in moderate temperature ranges, it is not 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 over a period of 25 years help steer new product developments. This has led to, among other things, the introduction of winding cores in bundles, similar to the concept used in steel cables.
In an elaborate bundle winding process, the cores are stranded in individual bundles with three, four or five wires; these are then wound with each other again into an overall bundle. For large super structures, 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 layered cable, each of the cores moves similarly in the inner and outer radius with the motion in the energy chain and thereby prevents relative stretching and compression.
In even more extreme movements, cables with a similarly complex cable structure are used. The so-called ‘robot cable’ range is primarily used in industrial robots and must follow extreme movements, bends and torsion. 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. Special shields and exterior materials also ensure an optimum durability of the cables.
With the topic of digitalisation, being hot at the moment igus explained that the basic language of Industry 4.0 is Ethernet, and the bus cable that has the transmission features, which needed to be able to transmit data at high speeds, but also sometimes low speeds.
The 32 different bus cables with Ethernet all have specific electric requirements and mechanical requirements. A spokesperson for igus said the company produce “safe cables for the industry” and that is why igus also have its own chainflex bending test.
Cables of choice
The service life of a cable used in an energy chain will depend on a variety of variables, which dictate the structure and choice of materials. This is the reason the chainflex product family currently offers 1,381 different cables. With the motto of “the cheapest cable that works”, igus also do not charge a cutting cost or have a minimum length requirement, as its main aim is to deliver the best for the customer. Cables can be provided in different way such as on the drum or come ready with the connector.
How long the cables will last in a given application is easy to find out. Using the results from two billion test cycles each year in the laboratory, the free online tool on the igus website predicts the service life of cables.