Type features on concrete sleepers defy wind and weather

In front of the concrete sleeper factory of Leonard Moll Betonwerke GmbH & Co. KG located in Biebesheim, two cranes having a span of 42 m and a load capacity of 20 tons are moving railway sleeper packages; inside the factory, equipment with a capacity of up to 1,000 liters is mixing the material for the sleepers which are cast in special molds and harden in gigantic curing chambers under defined climatic conditions. In this harsh environment, systems of the Rea Elektronik GmbH marking expert based in South Hesse apply the alphanumeric type features to the sleepers in an automated process – in an individual, flexible, reliable and above all weather-resistant manner.

Ten freshly produced railway sleepers move side by side at a transfer car to the chain conveyor of the final inspection. Five print heads of the Rea Jet DOD 2.0 large character ink jet printer are waiting on a bridge above. The front edge of every sleeper approaching is captured by light sensors, giving the print start signal to the print heads, which mark the concrete sleepers on up to three positions. Each print head gets the data for the series printing process directly from the database of the Moll factory: For this purpose, the Rea Jet control device is connected to the control system of the final production line using Ethernet. „This fully automated marking takes place in an unattended, digital process, ensuring proper marking in real time to the production; excluding manual errors,“ states Ralf Giesecke, who is responsible for control technology and automation at the factory.

Every day up to 1,400 railway sleeper leave the production line of the Biebesheim factory. These are standard sleepers as well as customized sleepers which are supplied to railway and infrastructure companies across Europe – based on framework agreements with major companies and corporate groups, but also for individual orders of small, private clients who appreciate the customized program particularly.

Five Rea Jet DOD 2.0 systems have been marking each individual sleeper since 2019. „For a larger special production lot on behalf of Deutsche Bahn Netz AG and entrusted to the Biebesheim factory, sleeper markings that exceeded the usual extent were agreed upon. In this case, for example, the crane operator should be able to recognize the type features even from a certain distance,“ Ralf Giesecke explains the beginning of the cooperation. Large characters are required that are still legible even after a longer period of outside storage. „In the past years, every now and then, there have been comparable requirements in our plants,“ Ralf Giesecke looks back on the time before the cooperation with Real Elektronik. „The marking‘s resistance to weathering and, in particular, to UV radiation was a requirement that could only be met satisfactorily together with Rea.“  

Automatic marking replaces manual work

Initially, production workers applied the data at Biesbesheim manually by means of stamps or using spray paint and stencils. However, it quickly became clear that this could not be a permanent solution – not least for reasons of health protection. The systems of Rea Jet now solve several requirements at once. They work with a special ink that is well adherent, fast drying and weather resistant. The drop-on-demand technology (DOD) of Rea does not release the ink drops through the nozzles of the print heads before they are needed for the print image. Therefore, the technology is extremely economical and ensures that the maximum workplace concentration (MAK values) of solvents is reduced to a minimum. And all of this durable and reliable even in the harsh and dusty environment of the concrete production plant.

„The fast-drying Rea ink and the cement dust in the factory are very demanding conditions,“ says Seven Kopriwa, sales representative at Rea Elektronik. „But the print heads of our DOD 2.0 large character ink jet printers are very sturdy. Moreover, our combination of ink supply and cleaning allows for easy rinsing of the entire system, improving the operational readiness of the print heads additionally.“ The Rea Jet large character technology of generation 2.0 is one of the best printing systems all over the world for harsh, dusty or humid manufacturing environments. DOD systems are excellently suited to the marking of building materials, blocks, shrink covers, insulating materials, steel sections and many other materials. This in-house technology of Rea Jet has been further developed and optimized over the years.

Connection to the company‘s database

For each sleeper package that reaches the final inspection, the Rea Jet control units get the identification data transmitted from the production database, write them into their buffer and transfer them to each of the five print heads simultaneously, which print them on each individual item of the group, and afterward they are ready for the next data packet. „Since the different markings for each sleeper type come from the subordinated control system and its database, human sources of error are excluded,“ states Ralf Giesecke referring to another decisive advantage of the Rea Jet system. The print heads used at Moll are able to apply information to up to four positions as single-line text. In addition, they are directed to the passing sleepers so that they work exactly despite the different dimensions of the various sleeper types. An especially developed, integrated collision protection prevents the print heads from damages in case sleepers are not aligned properly.

„No matter which industry is concerned, our diverse range of standard components provides us with the flexibility to configurate an individual printing solution for every customer that meets their requirements and their spatial conditions,“ says Kopriwa of Rea. In the precast concrete industry almost every company – even manufacturers of railway sleepers – work with a different technology, under different ambient conditions and with individual requirements on marking. „No matter whether for existing production lines or a new construction, with multiline lettering or logo printing, in a clean or rather dusty environment: We find the right, customized Rea solution.“

And the two partners have already thought about the next one for Biebesheim: The marking of each sleeper with a data matrix code providing for machine readability of each individual sleeper ID is intended to advance digitalization of the production and to further improve process reliability. In addition, these systems may possibly be used in other concrete plants of Moll.