Retrofit at the weekend: a successful conversion of the logistics center of BENTELER Steel/Tube

Modernization yes, but only if the plant is ready for operation again on Monday. This was the prerequisite for the retrofit that Unitechnik implemented at BENTELER Steel/Tube at the Schloss Neuhaus site, a division of the internationally active BENTELER Group. The plant was modernized in partial steps without affecting the processes in the warehouse. With success. Thanks to the experience that Unitechnik can draw on through numerous retrofits, BENTELER has since then benefited from a highly available plant, low repair and downtimes and increased operational safety for the employees.

BENTELER Steel/Tube develops customized tube solutions for the automotive, energy and industrial sectors. As a strategic partner and reliable supplier, the company is present with seven plants in Germany, Switzerland and the USA. This enables close contact and intensive exchange with customers. Thanks to its integrated value chain - from the production of steel to the production of tubes and surface technology - the company supplies everything from a single source. The central warehouse in Paderborn, which was modernized by Unitechnik, complements the value chain by reliably handling the logistics processes.

Fully automated processes for heavy and bulky goods
The tube bundles are up to eight meters long and are temporarily stored in the 26-meter high high-bay warehouse on a floor area of 650 m². The company will accommodate 460 large tube bundles (diameter 600 mm) and 1,800 small bundles (diameter 300 mm) here. The tube bundles weigh up to 3 tons. The bundles are stored and retrieved fully automatically with the aid of storage and retrieval machines (SRMs) and bundle transport vehicles. The structure of the warehouse and the design of the storage and retrieval machines is adapted to the extraordinary goods to be transported. The tube bundles are stored on cantilever racks. Each of these racks is 24 m high and 9.5 m wide. On both sides there are 32 cantilevered compartments that can accommodate two small or one large tube bundle. 23 of these racks are placed in front of each other, so that a 1.20 m wide, 10 m long and 24 m deep shaft is created between two racks. Two overhead cranes are mounted above these racks. They lower a cross beam into the shaft between two shelves using four cables. Two load handling devices are mounted on the cross beam, which lift one large or two small tube bundles onto the cross beam. After the lifting of the cross beam, the SRM moves above the warehouse to one of two lowering positions. Here, two coil transport vehicles are waiting on the ground to transport the tube coils to the dispatch area.

The maintenance and servicing at a height of 26 m involves a great deal of effort. For BENTELER, the most trouble-free technology possible was therefore a fundamental requirement for seamless logistics processes and a future-proof alignment of the plant.

Retrofit on weekends: Conversion almost without downtime
For BENTELER, it was particularly important to modernize the drive and control technology in individual sub-steps. "For us, a conversion could only be considered if the availability of the plant was not affected for several weeks", says Manfred Gieschen, Head of Process Optimization at BENTELER Steel/Tube. "Unitechnik planned the individual work steps in such a way that the plant availability and thus the reliable product delivery to our customers was always guaranteed". During the week, Unitechnik carried out minor conversion work that did not disrupt operations. The company installed the new S7 control system parallel to the existing S5 control systems and was thus able to test the new software. The old controls were only shut down completely at weekends. The automation specialist was able to dismantle the modifications that Unitechnik initially carried out on the weekends for test purposes before the beginning of the week so that BENTELER could operate the plant as usual again. "We started in September with the first conversion step of replacing the old DC drive technology. The final conversion took place six months later. After that, there was still some remaining work to be done, extensions and assignments to dismantle old components and old cabling", Christian Neuhaus, project manager at Unitechnik Systems, explains the time schedule.

Central control technology: Turning three into one
Before the modernization by Unitechnik, there were a total of three Simatic S5 control systems in the warehouse. A central control unit was responsible for part of the plant control. Two further control units each travelled on the SRMs. To ensure future-proofing and to simplify maintenance, Unitechnik centralized the control technology of the plant to a single landside S7 control system. Decentralized peripherals are used on the SRMs, i.e. digital input and output modules that communicate with the central control system via Profibus. Signals are transmitted to the vehicles by means of Profibus data light barriers.

Millimeter accurate position detection via laser
Precise position monitoring is an important factor for the 24/7 availability of the storage and retrieval machines. Prior to the retrofit, the position was recorded via encoders driven by a gear wheel and a belt - a mechanical system that is susceptible to faults. The outdated mechanical solution has given way to a non-contact laser detection system. A laser device pointing downwards is installed on the lifting drive of the SRMs, which is located on the crane bridge. On the cross beam there is a mirror that reflects this laser beam. Over the running time of the light, a continuous measurement of the crosshead position is carried out with millimeter accuracy. Unitechnik has replaced the outdated technology on the drive system of the SRMs with a barcode positioning system. A barcode tape was applied along the entire travel path of the bridge. This is scanned by a reading head installed on the bridge using a laser beam. The position of the SRM can thus be detected with an accuracy of up to a tenth of a millimeter. These new position detection systems communicate via Profibus with the central control system.

Visualization simplifies troubleshooting
In the course of the retrofit, Unitechnik has also brought its own UniWare-VISU plant visualization system up to the latest state of the art. "BENTELER can now zoom in continuously up to the sensor level and query the plant status. At a glance it can be determined, for example, whether a sensor somewhere in the plant is sending the wrong signal. This makes troubleshooting much easier", explains Neuhaus. Unitechnik has installed a new control panel on each of the SRMs, which makes it easier for BENTELER to operate the system on site if an employee needs to enter the vehicles. Employees can use the panel to operate all the functions of the SRM by hand.

Modern components increase availability
Another challenge for BENTELER before the retrofit was the handling of the electrical components in the plant. "In the event that an electrical component in the warehouse should now fail, the modern assemblies ensure rapid availability of spare parts," explains Neuhaus. In addition, BENTELER, saves time because the new components also provide better support for troubleshooting. Error messages on the SRMs can now be read out and analyzed in real time at the central control system. Employees no longer have to climb under the hall roof to the SRMs in order to search for the error on their control system. In addition to saving time, this minimizes the risk of injury to warehouse employees.

"We value Unitechnik as a reliable partner who supported us in the construction of the warehouse as early as 1990. In the preliminary discussions on the retrofit, we were also convinced that Unitechnik had broken down the planned measures in detail and could guarantee us the necessary plant availability", explains Manfred Gieschen.