Many things move in
industry. What is good for production is a major challenge for cables. Energy
chains are often used to 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 enormous.
An energy chain can
be described as the umbilical cord of a machine. It supplies a machine part
with energy, data and media whilst following its every movement. The degree of
movement ranges from simple linear strokes to 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.
Only long-term tests provide predictable reliability
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 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 square metres). Here, products
are tested for their resilience in continuous operation in 58 different test
rigs. Since the exact reproduction 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 km.
Simulating application at extreme temperatures in real
Likewise, temperature conditions from -40¡C to + 60¡C are tested. The specially adapted container, in which these conditions can be simulated, is
of vital importance. Unlike standard ‘cold winding’ tests, in which test 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 cold flexibility.
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 with a wide temperature bandwidth. This is unique on the market,
because the usual PVC compounds for chain-suitable cables do not normally 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
Bundle instead of layer
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 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
layer-stranded 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 cables’ are primarily 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 when 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.
1,040 different cables for application in energy chains
The service life of
a cable used in an energy chain will depend on a variety of variables that must
be considered in the structure and the choice of materials. Thus the igus chainflex
product family from Treotham currently offers 1,040 different cables. How long
the cables last in a relevant application can even be calculated by users
themselves. This is made possible by the results from the 2 billion test cycles
each year in the laboratory, which is incorporated into the igus database.
Based on this data, the free online tool on the igus website predicts the
service life of cables. For more information on the large range of chainflex
cables, speak to one of the technical engineers at Treotham Automation.
information, please visit the Treotham Automation website www.treotham.com.au
or call 1300 65 75 64.