Reliable control cables in railway technology steps at sub-zero temperatures

Profile

• What was needed: chainflex cables from the CFSPECIAL.414 series
• Requirements: Strict requirements regarding fire protection, flammability, smoke density, and toxicity properties and dripping behaviour properties during liquefaction in railway technology. A customer in Eastern Europe also wanted a permanent cable solution for extendable steps at sub-zero temperatures.
• Industry: railway technology
• Success for the customer: The control cable combined with the connectors paid off. For extending steps on trains at sub-zero temperatures, ESCHA was able to offer the entire cable set as a reliable assembly, benefiting the customer.

Figure 1: ESCHA harnesses connectors to the CFSPECIAL.414 control cable in a partially automated process.

Problem

4.6 billion people travelled with Deutsche Bahn in 2018. That is 4.6 billion people who have entrusted their lives to the trains. To ensure that passengers feel safe during their ride, hundreds of railway technology suppliers strive every day to develop safe components.
This is also true of the complex development of cable solutions for railway technology. It is subject to strict fire protection requirements: The DIN EN 45545 material test standard specifies the requirements manufacturers must meet. Numerous material properties, including flammability, smoke density, toxicity, and dripping behaviour during liquefaction, are described. But extreme cold can also be a problem: For example, a customer in Eastern Europe needed a train step cable that works reliably there even at temperatures far below zero. The cable installed to that point was a supply cable whose jacket suffered damage after just a thousand movements.
Another use case for high-quality cables in trains concerns door safety strips. The cable from the sensor is guided to the control system in an energy chain with a very small radius. This movement in a very tight installation space places enormous strain on the cable and is a very safety-relevant function for the passenger.
It is difficult to develop cables that meet these diverse requirements. Moving cables are especially challenging because standard materials are not suitable for them.
In this pioneering work, the two components of the end product – the cable and the plug-in connector – must not be considered in isolation. All materials must be harmonised.

Solution

This is where our more than 20 years of cooperation with ESCHA, a well-known manufacturer of tailor-made connection technology solutions from the Sauerland region, pays off. Cooperating with ESCHA, we created a complete solution using the special CFSPECIAL.414 cable and suitable connection technology, including overmoulded connectors.
With CFSPECIAL.414, our researchers have succeeded in combining two requirements: fire protection and movement in the energy chain. Many fire protection cables, on the other hand, approach their wear limit too quickly when they are required to move constantly. The CFSPECIAL.414 series fills this gap.
The key to its robustness is a special compound developed specifically for the outer jacket that withstands movement and meets fire protection requirements. Another special compound with a particularly low-adhesion design is used for core insulation. Cores are wound short, alternating the inner and outer radius of the curved cable several times at short intervals.
To test new developments in real applications, we operate the world's largest moving cable test laboratory in Cologne. The CFSPECIAL.414 series also demonstrated its product features here. In a long-term test of two million double strokes, the cable moved in an energy chain with a bend radius of less than 50 millimetres — a helpful complement to DIN tests.
Our cooperation with ESCHA on the CFSPECIAL.414 is as follows: The cables reach the manufacturer on drums. ESCHA assumes production of ready-to-connect cables, a process known as cable harnessing. The cables are cut to the desired length and the plug-in connectors then injection-moulded on one or both sides. Specially designed plastic composition ensures that the connection between cable and plug-in connector meets the high requirements of the IP67 and IP69 protection classes.
The collaboration has already paid off with the customer in Eastern Europe. For extending steps on trains at sub-zero temperatures, ESCHA was able to offer the entire cable set as a reliable assembly. The end customer benefited from the trusting cooperation.

Picture 2: Double moulding ensures dust and water resistance in accordance with Protection Classes IP67 and IP69.

Picture 3: The CFSPECIAL.414 was developed specifically for moving applications on rail vehicles, so its jacket material is halogen-free and flame-retardant.