Protection Against Corrosion
18 September 2019
The Galvanizer

New methods developed by using hot-dip simulators: The WAGO I/O SYSTEM functions as the central communication system.

Zinc is a particular material that shifts the expiration date of iron far in the future. It safely protects steel from corrosion, so that galvanized components do not rust. This is because zinc and iron form an inseparable elemental compound – the common ferro-zinc alloy. However, this method employs poisonous and potentially explosive gas atmospheres at high temperatures. This consequently demands a process control system that is quite sophisticated to guarantee safety. The task of constantly refining these processes falls to Surtec Research and their hot-dip simulators. The engineers from Falk Steuerungssysteme use the space-saving, easily integrated WAGO 750 I/O SYSTEM in the automation systems for the simulators.

Hot-dip galvanizing is not a new process. The earliest industrial examples extend back into the mid-1800s. However, even after more than 150 years of refinements, improvements to the process still make sense. Due to the increased strength of the steel sheets used in automotive manufacturing, in particular, they are now considerably thinner. Yet the demands placed on the corrosion protection have only increased. “Modern automobile steels are only coated under certain circumstances, due to the variety and characteristics of their alloy components,” explains Björn Beißner, Project Manager at Falk. Safely coping with these challenges on an industrial scale means prior testing of new alloys, gas atmospheres, temperature curves and processes at a laboratory scale. Surtec Research, headquartered in Düsseldorf, builds annealing and hot-dip simulators for this purpose (www.surtec-research.com), and Falk Steuerungssysteme from Stadthagen in Lower Saxony develops and programs the entire automation system. The essential challenge consists in transforming the continuous passage process, found in galvanizing systems, into a dip process, so that the lab results can be transferred into production on a one-to-one basis.

Using the WAGO I/O SYSTEM, we can collect all of the data provided by the sensors, switches, and actuators in the system.

Björn Beißner, Falk Project Manager

WAGO as Central Connection Network

Current pressure and temperature measurements at different areas of the hot-dip simulator represent just one example.

The WAGO I/O SYSTEM functions in the hot-dip simulators as a communication network, it forms both the cornerstone for the entire signal processing system, and also provides functional safety in the ATEX area – all in a very limited space. Falk uses a Siemens Failsafe PLC from the S7-1500 series as the sequence controller for drive control and other purposes, but primarily for the safety technology. A powerful, industrial PC is used as a second control unit to process all of the higher-level functions. These include test procedures and measured value administration with a sampling rate of 10 milliseconds.

The hot-dip simulator consistently functions at high temperatures during the annealing of the metal samples and also during the subsequent immersion (also known as dipping) of the workpiece in the liquid zinc alloy. The annealing phase is decisively important during galvanizing, as a precisely defined oxide coating must be formed on the steel surface.

According to Beißner, “An initial, precise pre-oxidation of the material surface is required for reliable coating.” In addition to temperature and dwell time, the composition of the gases in the hermetically-sealed annealing and coating zone is also extremely important. The use of highly explosive hydrogen or reactive and poisonous carbon monoxide emphasizes the importance of the Ex protection and safety technology incorporated into these systems. It is precisely at this point that Falk Steuerungssysteme relies on the comprehensive tool kit of solutions contained in the WAGO 750 I/O System. Operating errors must be safely avoided, due to to enormous potential risks. Malfunctions or defective components should similarly be prevented from causing accidents in the lab set up. The safety measures involved in the system are so extensive that even the screw connections between the crucible holding the liquid zinc and the induction furnace located above it are protected from unperceived access by an electronically-secured cover.

Safety and Ex as a Functional Unit

“Pressure switches monitor overpressure in the molten metal bath. This way, we ensure that no oxygen penetrates into the system,” explains Project Manager Beißner. “We run the system at a constant overpressure.” It should be obvious from this statement that the safety technology is not limited to the hot-dip simulator. Instead, the failsafe components are installed throughout the hazardous areas, as well. “Demands have risen for our customers in Ex protection – up to a completely intrinsically safe design,” states Beißner.

This is yet another advantage of WAGO technology in comparison to the control systems that Falk used in the past, which relied on the classic disconnect terminal blocks. The combined failsafe Ex i modules from WAGO save enormous amounts of space and are, according to Beißner’s experience, “… more compact than other alternatives. In addition, there is less to wire, which offers real advantages for the carriage-mounted control cabinets.” These control cabinets are subjected to a very strict height limitation. Background: There is a carriage for changing the molten metal baths in the hermetically-sealed crucibles – and they have to fit under the simulator.

... more compact than other alternatives. In addition, there is less to wire, which offers real advantages for the carriage-mounted control cabinets.

Björn Beißner, Falk Project Manager

For the most part, these are the intrinsically safe PROFIsafe input modules (750-663), which supply air in the control cabinets. The intrinsically safe module for functional safety is specifically designed to safely connect to potential-free, contact-based emergency stop switches, safety interlock switches, mode selectors, and also safety sensors located in the hazardous environments of zones 0, 1 and 2. WAGO thus unites the world of yellow safety markers with its blue Ex-protection. The intrinsically safe 750-606 Power Supply can be used in an I/O system as a direct link between the Ex and non-ex areas. The 750-375 Fieldbus Coupler is tasked with the PROFINET communication with the PLC and IPC. They form the head stations for all data, collect safety-relevant data and also Ex signals, and are responsible for forwarding this information as a bundle to the failsafe CPU or the IPC.

Intrinsically safe input modules, like the 750-663, are considered essential at Falk for realizing uninterrupted system communication with the WAGO I/O SYSTEM. The example of a plate slide valve shows why combined failsafe Ex i modules are necessary. These are used to completely seal the annealing chamber in the direction of the liquid metal and function like an airlock. They only open if both chambers are securely sealed, and the metal sample can only move into the dipping bath if they are both completely open. “This process is critical for safety,” explains Björn Beißner. If this process were not safe, then the potential for flammable, explosive, or toxic gases escaping into the room could not be excluded. Therefore, failsafe and Ex i are important. Falk developed the basic design in close collaboration with TÜV (technical inspection service). “Thanks to the secure supply valves for the reactive gases, we can be certain that no explosive or toxic gases can be fed into the system when we open it.” The valves are controlled by intrinsically safe outputs from the WAGO system.

Conclusion

What do you do if intrinsically safe technology is also demanded in the Ex areas? In particular, if the space in the control cabinet is limited, then the first query should be to find a compact, integrated solution. The WAGO 750 I/O SYSTEM offers a standardized and flexibly-combinable solution module for precisely this need. This allows even complex automation, like that in the hot-dip simulator, to be implemented in a sleek and space-saving way.