Flex your grey matter

Choosing the right cable from the many thousands of options out there may be all that stands between you and equipment failure. Alpha Wire’s EMEA director, Harry Quinn, warns against making assumptions Specifying the best fit, best price, cable for any application can be daunting, simply because there is so much choice. When it comes to industrial applications such as manufacturing or materials handling, however, where cables can be under constant stress, purchasers also have to consider the risk of equipment failure, brought about by inappropriate cable choice.
To make matters even more confusing, many flexible cables are not actually suited to environments that subject them to constant bending and flexing cycles. In fact, there are notable differences between a flexible cable and one that is designed for constant flexing. Making the assumption that a flexible cable will perform in an extreme flexing application could be a costly mistake, resulting in unscheduled downtime or even equipment failure.
So what can reasonably be expected of flexible cable? Flexibility allows for easier installation where cable follows a pre-determined path in order to create a tidy installation. It also simplifies troubleshooting in the cabinet and/or cable tray.
A round-geometry cable provides greater reliability as it does not incline itself to preferential axis bending. With this in mind, routing requires a cable with the correct level of ‘bend-ability,’ assuming that once installed, the cable will be static during the life span of its service. If this is the case, a standard cable with a good degree of ‘bend-ability’ would suffice.
In many manufacturing and material handling applications however, cables are exposed to constant flexing during operation. The ability to withstand millions of flex cycles is more complex than simple flexibility and comes with its own set of considerations.

Flexing facts
So, how do you specify the correct flexing cable? First consider the type of flexing likely to be encountered by the cable since each requires a specific set of cable attributes. There are four common types of flexing movements to consider: rolling flex; bending flex or ‘tic-toc’; torsional flex; and variable/random motion flex.
Different cable construction methods and materials are used depending on the cable flexing movement. In applications where cables will be subject to torsional or variable flexing, such as in robotics, it is essential to specify cables capable of twisting and random robotic flexing operation of ±360 deg per meter. Torsional cables, for example, will have a different lay length and cabling method from a rolling flex cable.
Another application which requires serious thought is ‘C’ track installations, in which cables experience continuous flexing linear motion. One of the key factors in cable failure is the breakdown of jacket materials, particularly the shielding, which is exposed to the differences in bend radiuses on the inner and outer surfaces.
The performance of a cable is evaluated using physical test data and statistical analysis to produce a ‘flex life’ and overall system reliability. As there were no flex test machines that could quantify cable performance under accelerated conditions of continuous flexing linear motion, Alpha Wire developed its own testing machine. This provides accelerated cable track motion for a protracted period of time using a test protocol thought to be more severe than most real-world ‘C’ track installations today.
Perhaps the best way to illustrate the importance of correct cable specification is to use a real-life application as an example. Alpha Wire has been working with an automobile assembly plant that had purchased a number of paint-robots to automate the paint spraying process. Unfortunately, the robots were failing during the engineering performance and validation run due to repeated cabling failures. At this stage, Alpha Wire was called in to look at the installation.
Engineers analysed the failures, reviewed the robots’ movements and consulted with plant personnel. By far the most problematic issue was the use of a cable actually recommended by the robot manufacturer. This basic flexible cable did a fine job of contouring around corners but was not able to continually flex in any plane, meaning that it failed after a short while. Alpha recommended a different cable and the robots have now been running for nearly two and a half years with no cable replacements.
Specifying the correct cable from the outset reduces the risk of cable failure and ensures that productivity and performance are protected. With this in mind, the question ‘to flex or not to flex’ becomes a critical decision.

www.alphawire.com