Products and solutions, 2011-03-30, 05:54 PM
ThyssenKrupp Nirosta in Dillenburg: Roll management with innovative RFID technology
Five rolling mills, 2,200 rolls and bearings, 4,700 storage locations, 200 to 250 turning, grinding and polishing operations and storage movements each day: Anyone looking for a real challenge should apply for the job of roll manager in a stainless steel production plant. And yet these figures from the Dillenburg cold-rolling mill of ThyssenKrupp Nirosta give only a rough idea of how demanding the work really is. Because not all the rolls are the same. Some are suitable only for certain stainless steel grades or strip thicknesses. They come in different shapes and, even more challenging, their diameter is changing all the time.
To keep track of its rolls, ThyssenKrupp Nirosta is now using one of the most innovative and fastest-growing identification technologies around: Radio Frequency Identification, or RFID for short. With RFID, data can be read contactlessly and fully automatically over longer distances and the information can be processed for a wide variety of purposes. The technology is used in toll collection systems to identify vehicles and allocate costs, and in large libraries to collect data on loans, returns and inventory. The core components of RFID systems are transponders, readers with antennas, and interfaces to the data processing system. The Dillenburg plant uses passive transponders read by radio antennas.
At its Dillenburg plant ThyssenKrupp Nirosta, a company in the Stainless Global business area of the ThyssenKrupp Group, produces 21,000 to 24,000 metric tons per month of stainless steel cold-rolled strip with premium-quality finishes, used for example in prestigious building facades and high-end appliances. The plant features three 20-high mills and two skin pass mills, one of which operates inline. As they are subject to heavy wear in the production process, the rolls frequently have to be changed and ground. Even the slightest unevenness causes flaws in the strip surface.
“Roll management for the 20-high mills is particularly complex,” says Heinz Röther, cold-rolling mill team leader in Dillenburg. The units operate with groups of 20 rolls of different thicknesses and in some cases different shapes. The rolls support each other so as to absorb the high forces produced in the stainless steel cold rolling process. The components of the roll assembly must be selected to maintain the roll gap of just a few millimeters required for the stainless steel strip. “Because the diameters of the individual rolls are constantly changing as a result of grinding, finding the right combination is an ongoing process,” says Röther.
“With RFID roll management is largely automated,” says Herbert Schneider, head of information management and organization in Dillenburg. The new system not only knows each individual roll as if by name, it also knows where each one is, whether it is new, recently ground, polished, turned or worn, as well as details of its diameter and shape. The right roll diameters for the mills can now be assembled online, and the system also indicates the storage locations of the rolls and provides concrete suggestions for the optimum roll assembly.
Glass LF (low-frequency) transponders attached directly to the rolls in special recesses act as electronic labels. Information on the current dimensions, machining condition and period of use of each of the parts can be saved and organized in databases. UHF (ultra-high-frequency) transponders on cassettes, racks, tables and floor-level storage locations help quickly locate the rolls. RFID antennas on forklifts report cassette movements. Information on rolling, polishing and turning is entered via handheld computers. A Java-based web application ensures that employees always have access to all information via handheld computers connected to a wireless network.
It’s clear that this innovative solution can save time and money, but RFID also has a positive effect on product quality. For example, the employees in Dillenburg record details of when the rolls were installed in the mill stands and when they were removed, which helps reduce defects caused by rolls.
Because the stainless steel strip is covered in rolling oil during cold rolling, surface defects are only detected in the subsequent annealing process. Hours or even days can pass between these two production steps. Up to now it has been difficult to trace which roll was responsible for the defects because the stainless steel strip can be up to nine kilometers long and wear out as many as five work rolls. Now the team in Dillenburg has much more accurate information about which roll was being used in the mill at a particular time and which section of the strip it was used for. Team leader Röther: “We have succeeded in reducing the number of defects caused by rolls by up to 50 percent.” An impressive result, not just for customers of ThyssenKrupp Nirosta: That’s why the roll management system is now also to be used in the cold-rolling mill of the new stainless steel plant in Alabama, USA.