The ultimate test – Part 2: Bending tests

During the development of our cables and wires, we extensively test each product in our test laboratories. In the second part of our series we will introduce you to flexion testing.

In dynamic applications typical of mechanical engineering, installation technology, drive and automation technology, cables and wires are often exposed to mechanical bending loads. Although these loads also occur in static installations, they are much higher in dynamic applications because the force and direction of motion are constantly changing. Such situations are pure stress for the cable. The wires, core insulation, and sheath material are compressed on the inside and stretched on the outside, and the cable can tear. Degradation, up to and including cable damage, leads to malfunctions and functional failure.

To ensure that our cables and wires can reliably withstand everyday loads, we carry out the bending test in our test laboratories. This test is usually laid down in customer specifications or in standards such as those of the VDE. Our testing equipment simulates bending loads with various loads and bending radius to verify the mechanical strength of the cable. Our test methods include alternating bending tests with two rollers (according to DIN EN 50396 6.2) and three rollers (according to DIN EN 50396 6.3). Parameters such as speed, acceleration and travel path can be easily varied to create realistic test conditions for a variety of use cases.

Every cable we develop must meet strict test criteria. The copper wires, insulation material and sheathing material should show no signs of degradation after the tests. In addition, the entire wiring, including braiding and twisting, must retain its original shape. Only in this way can it be guaranteed that the cable will function reliably in daily use, even after millions of bending cycles.

In addition, we have specially designed drag chain tests for cables used in energy chains. You can read more about this in the next part of our series.

What is the minimum bend radius and what does this value tell me?

The minimum bend radius is the smallest possible radius with which the cable can be bent without damaging it. It is specified as a multiple of the cable diameter. The smaller the value, the more flexible the cable is. There are several industry standards that define the minimum bend radii for different types of cables. The values vary greatly depending on whether the cable is used in a fixed or moving application. For example, a drag chain cable of the type MULTIFLEX 512-C-PUR UL/CSA has a minimum bending radius of 4 xd in a fixed application, but only 7.5 xd in a moving application. The reason for this is that the bending load in a permanently moving cable is considerably higher because the force and direction of the bending movement are constantly changing. A suitable minimum bending radius is therefore an important criterion when choosing cables and wires. How can the flexibility of a cable be improved? There are several ways to improve this, starting with using the best materials. In most cases, copper wires consisting of fine wire conductors are sufficiently flexible. Care must be taken to ensure that the insulation and sheathing materials are also flexible. The choice of materials makes a big difference, especially in applications at extreme temperatures. PUR or TPE jackets are suitable for cold temperatures because they do not become very stiff. The diameter and construction also have a major influence on the bending properties of the cable. The shorter the laying length, or tighter twisting of the cores, the more flexible the cable is.