It doesn't always have to be copper

MS Spaichingen GmbH is active in various business areas for the automotive industry. The welding technology division specialises in the construction of individual ultrasonic welding systems for joining plastic parts. However, there are also limits to ultrasonic welding. If, e.g., metal and plastic are to be joined, heated contact riveting is used as an alternative. In this process developed by MS Spaichingen, only temperature is applied to the material and a gap-free riveted joint is produced. The process also involves measuring the temperature at the riveting points. Every riveting die used in the MS Spaichingen systems is therefore equipped with a thermocouple that measures the temperature.

Initially, a cable from the heating manufacturer was used for the energy and signal supply. However, after around 100,000 double strokes, which corresponds to a system operating time of one year, the cable began to break and move up and down with each cycle.
The search for an alternative cable was not easy, as special materials had to be used. The process requires the cable to have the same alloy as the thermocouple rather than the usual copper conductor. This means that cables made of alloys such as a nickel/chromium-nickel compound are required - and in large quantities. A flexible and dynamic cable was also required.

The igus developers first had to do the groundwork by looking for ways to process the comparatively hard and brittle alloys into wires. In addition to the sensor signal, the cables also had to transmit energy to the sensor head. A combination of copper cables and thermocouple cables had to be selected, whereby the comparatively soft copper cores had to be combined with the hard cores of the thermal alloys in such a way that a long service life was achieved even under dynamic stress.

According to these specifications, igus first developed a flexible cable with thermocouples only, which is now available in the product range as chainflex CFTHERMO.K.001, as well as a cable with three copper cores and a thermocouple (CFTHERMO.K.002). The cable type K.002 was tested at igus and MS Spaichingen, and the MS designers gave their approval after 300,000 double strokes. The CF thermal cables have now been in use for several years and the experience has been positive all round. Joachim Wein, responsible for electronics development in the welding technology division at MS Spaichingen: "We use the cables with and without an energy chain and have not yet had a single failure."

igus has expanded the CFTHERMO product range and added further alloys, which are used for measuring higher temperatures, for example. In addition, readycable, i.e. ready harnessed cables for thermocouples, have also been available since last year. The connectors are made from the same material as the cables. The dynamic tests that igus carried out with the first chainflex thermocouple cables are still ongoing. They started in January 2011 and have now reached over 100 million double strokes, and the resistance measurements still show no irregularities. In the meantime, igus has also come across other applications for such cables - even in-house, more precisely in the injection moulding shop, where several hundred injection moulding machines produce plain bearings, energy chains and other igus products. In these machines, the temperature of the process must also be monitored, and this task is performed by thermocouples. But moving cables that have the specifications of a thermocouple and are also extremely reliable are also increasingly being used in other areas.