A large-scale plant for processing heavy plates at Salzgitter Mannesmann Grobblech GmbH was due a retrofit, which was also to include modernisation of the safety architecture. The configurable control system PNOZmulti was to be used in combination with PDP67 modules. The solution from Pilz, the complete suppler for safe automation, proved to be both simple and efficient. Now the plant also meets the requirements of EN ISO 13849 up to Performance Level (PL) d.
Steel girders and gantry cranes are spread throughout the production hall and there’s a smell of metal in the air. The hall is the size of several football pitches and when the giant forming and metal cutting machines are set in motion, it’s noisy. Salzgitter Mannesmann Grobblech GmbH in Mühlheim an der Ruhr is part of Salzgitter AG and manufactures intermediary products, from which large pipes can be produced, to be used later as pipelines for example.
How plates become pipes
The “Pipes” Division comprises the following areas: plate rolling mill, pipe bending plant, test centre and energy supply. In the pipe bending plant, seamless, welded steel pipes are bent with precision and accuracy using inductive heating. This places the most stringent demands on material, manufacturing and range of sizes. The requirement is for precision prefabricated heavy plates, which may be up to 26 metres long, around 5 metres wide and between 8 and 50 millimetres thick.
Coming from the rolling mill and the subsequent cooling beds, the heavy plates reach the double side-trimming shears via a roller table. The shears trim the edges of the plates to the required size, then they are transported to the transverse shearing machine via a transverse conveyor. Once an operator has placed the parts in position, motor-driven blades cut the plates lengthwise to the customer’s specifications. The transverse shearing machine also cuts strips for ongoing processing as welding ends for pipe production, as well as test samples, which arrive at the test centre for quality assurance purposes. Finally, via the subsequent roller conveyors, the plates arrive for cold geometric measurement, during which the surface is inspected along with the lengths cut by the transverse shearing machine.
Retrofit requires a new safety concept
The heavy plate cutting machine covers an area of ten by six metres and is around five metres in height. When the time came for the plant to undergo fundamental modernisation, the agenda also included the integration of a modern safety concept. A re-assessment and evaluation of the risks was required in order to satisfy the normative requirements of the new Machinery Directive. Manual intervention in the plant for inspection, setup and maintenance purposes is essential; that includes access to the safety zone, so reliable safety solutions were required at several points in order to protect man and machine. However, these were not to restrict the plant’s productivity. Until then, safety had essentially been based on single-channel emergency stop circuits and traditional contactor technology. The customer’s future requirement was for safety to act completely independently of the control system.
The range of tasks incorporated the following points: On the fully enclosed transverse conveyor plant, a total of seven gates were to be protected against unauthorised or accidental opening; the distributed emergency stop pushbuttons were also to be monitored. The plant must be brought to a safe stop if any gate is opened without authorisation. The plate lifting equipment and the wagons for crosswise transportation of the plates were to be manoeuvrable at safely reduced speed by an enabling switch, via a mobile panel with multiple control points distributed within the safety zone for setup and maintenance mode. What’s more, the requirement manual specified that reliable management of the safety-related signal exchange with upstream and downstream plant sections was to be guaranteed. The requirements for the area with the transverse shearing machine were fairly similar: In addition to safe monitoring of 12 safety gates in the periphery and implementation of a safe plant stop, it was also to be possible to carry out setup and maintenance work in enable mode. And the situation was similar for the plant section involving cold geometric measurement, where the precision of the cutting dimensions is examined.
PNOZmulti as an efficient, easily adaptable safety solution
The configurable control system PNOZmulti is made by Pilz, the complete supplier for safe automation. Here are some of the tasks that it reliably resolves: As a centralised safety manager, PNOZmulti works in conjunction with the PDP67 modules in the periphery to monitor all safety-related signals from the emergency stop pushbuttons, safety gate systems and enabling switches. In an emergency, the configurable control system initiates safety-related actions. As there are long distances to the various gates and emergency stop pushbuttons, the PDP67 modules record the safe signals from the sensors directly on the spot, thus reducing the amount of cabling involved. The failsafe PNOZmulti base unit has 20 digital inputs, 4 digital semiconductor outputs and 2 relay outputs. It is flexible and simple to expand with up to 8 I/O modules. PNOZmulti records all the necessary sensors and switches the safe outputs directly. There’s no need for hardware that’s susceptible to wear. Free configurability using the software tool PNOZmulti Configurator and intuitive parameter setting make the intelligent safety manager simple to use. PNOZmulti stands for “Configuration rather than wiring”, because the configurable control system replaces a large number of relays and wiring connections.
Plant made safer without limiting productivity
A total of seven PNOZmulti base units and 13 PDP67 modules in the periphery guarantee safety on the heavy plate processing plant. “The plant now meets Performance Level (PL) d. Thanks to the Profibus interface on PNOZmulti, we can now also download data to the visualisation device for display. What’s more, the data can be read into a PDA system, which makes troubleshooting and fault tracking a great deal easier”, says Heiko Nickel, electrical project engineer at Salzgitter Mannesmann Grobblech GmbH, describing the benefits in a nutshell. While cooperating on the project Pilz was also able to prove itself not only as a component and system supplier but also as a competent advisor and service provider in matters relating to risk estimation and technical feasibility – from the project phase right through to technical support. “I can say with some certainty that we will work with Pilz on other retrofit projects in future”, says Heiko Nickel, summarising.
For more information
http://www.pilz.in/
