ENERGY CHAIN SYSTEM RELIABILITY
Treotham provides a large range of high quality igus chainflex cables that can be used in energy chains for various applications.
Due to the increase in automation and industrial production, the use of energy chains is rapidly growing. The requirements for cables that supply machine parts with media, data and energy are also rising as factors such as speed and acceleration become more demanding.
Movement in the energy chain spans from horizontal or vertical for simple applications, now to multiple, complex rotations for six-axis robot applications. The system is sometimes referred to as the umbilical cord of a machine, as both the cable and the chain must perform every precise movement. Therefore the reliability and service life of moving cables could be the most important factor of the whole system.
It is also extremely important that the design and material of the cables are adapted to the energy chains so that they can withstand the mechanical loads from millions of cycles without failing and succumbing to the corkscrew effect.
Cables that are used in moving applications, especially energy chains, are subject to increased strain. Standard tests that determine the durability of the cables often neglect to take field experience into account. Field experience shows that even highly flexible cables often reach their load limits while moving in energy chains. Therefore it is evident that in conventional standard tests such as those carried out by VDE, IEC or UL, the service life cannot be predicted.
There are some well recognized test procedures from various institutes in the cable industry, however the procedures are very basic and do not include specific requirements for continuous movement in the energy chain.
The bending fatigue test as per VDE and standard wear test don’t satisfy requirements of a chain-cable combination. In the bending fatigue test the cable has a completely different movement sequence then the movement of the cable in an energy chain. Many cable designs that meet these requirements quickly fail tests conducted under real world conditions.
Standard wear tests, which use needles, sand paper or razor blades to determine the wear of a material, can only be used to make a general comparison. This test is not good when determining the durability of a jacket material in an energy chain. It is important to test the wear of the material by testing the chain and cable material together so that they can adapt to one another.
Igus thoroughly tests the jacket materials of cables by rubbing them against chain materials to determine the degree of wear. As a result they use materials such as PVC, PUR and TPE which offer minimal wear compared to standard PVC cables and provide optimal performance when used in an energy chain.
The design of cables for moving applications has also changed drastically over time, which has led to cables being braided in bundles. In a complex process, wires are braided in single bundles consisting of three, four or five wires, which are then braided with each other. For large cable designs, this is done around a strain- relief element. The result is a cable that is built for movement and ideal for use in chains. Unlike a cable with layered braiding, each of the wires in the energy chain is moved an equal amount at both the inner and outer radii. This helps prevent stretching and buckling on one side.
For more extreme movements, cables with more complex designs are used. One of the applications with the most extreme movements of bending and twisting, are industrial robots. They use damping elements to give the wires in robot cables the essential freedom of movement within the cable. The tighter the cable is wound and the closer the cable gets to its breaking point, the more difficult it becomes to twist. Special shields and outer materials also ensure optimal cable durability.
It is also important to consider environmental factors when selecting the right energy chain and cable. Depending on the application, they may be exposed to chemicals, dirt, dust, moisture, impacts or extreme temperatures at times when they are used in harsh industrial conditions. Under these conditions, field experience is extremely important for testing the resilience and service life of the cables. For this reason, igus operates a 1750 square meter test lab in which applications are run around the clock on 58 different test systems. This results in over two billion test strokes per year.
In one application, a sea container was specially modified to generate temperatures of - 40°C to 60°C and to test high temperature fluctuations. Energy chains and cables were moved millions of times in the container and the results were evaluated accordingly. This is completely different from the usual cold bending test, where a cable is wrapped once around a mandrel, cooled down to the temperature to be tested and then moved once. If the exterior mandrel shows no signs of visible damage, then the cable is considered “safe” for the respective temperature.
Therefore, the reliability of a moving cable depends on a large range of factors whose effects can ultimately only be tested and proven under real-world conditions.
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