RFID systems used in rod rolling mills have to be tough - after all, temperatures of up to +120 °C, steam, acids and dirt deposits can damage the transponders and read/write heads. One way to meet these challenges is to use all-metal systems made of stainless steel. Friedrich Kocks, a company specializing in the development of rolled blocks, opted for one of these.

Bar steel can be used as a preliminary product for axles and shafts, rotationally symmetrical tools or precision turned parts. Production is carried out by reducing a billet in several stages. For this purpose, the bloom is first heated in a heating furnace and then descaled in a descaling plant. Only then does the reducing process take place in a steel forming line consisting of a roughing and intermediate line and the finishing line, which at Kocks is a reducing and sizing block (RSB). Such an RSB consists of three to twelve stand stations, whereby a 3-roll stand is used at each stand station. The 3-roll technology enables the twist-free rolling of quality steels, special grades, superalloys, sintered materials as well as non-ferrous metals and their alloys. Each stand requires a special roll set consisting of three rolls with a specific profile, which is determined by the insertion position of the stand in the rolling block. Depending on the size range to be rolled, the stands are equipped with a different set of rolls.

To ensure that the process runs smoothly, it is crucial that each stand with the correct set of rollers is positioned in the intended place in the rolling block. If this is not the case, incorrect rolling will occur or, in the worst case, the bar will get stuck in the system. This results in long downtimes and high costs.

Process validation with RFID

Each scaffold as well as the guide that leads the rod from scaffold to scaffold is equipped with an all-metal transponder.

© Kocks

Whereas the machine operator used to check whether the rolling block was loaded correctly, today this is done by an RFID system. At Kocks, each stand and the guide that leads the bar from stand to stand and prevents it from turning during rolling is equipped with an RFID transponder. Each stand position has corresponding read/write heads. The all-metal 125 kHz system from Contrinex is used. The robust all-metal transponders are integrated flush into the roll stands and are therefore hardly noticeable. They each contain a unique ID that is assigned to a stand. The read/write head reads this ID, which is written to a database by special PC software. The database contains the current stand data, which is assigned to the stands via the ID.

Software solutions developed in-house

In order to lose as little time as possible when switching to a different dimensional range, the stands to be replaced are prepared in advance for the next task. If incorrectly assembled stands are detected during the subsequent stand change, the roller receives a message via the corresponding user interface so that he can make the appropriate corrections.

During scaffolding preparation, the scaffolding is read with a handheld reader and thus clearly identified.

© Kocks

Kocks developed a hand scanner with an integrated read/write head to identify the stands so that everything fits together during stand preparation and errors can be ruled out before insertion into the rolling block. The scanner records the data from the stand transponder and forwards it to a PC. A special user interface shows the worker whether everything has been assembled and adjusted correctly. The IT specialists at Kocks developed the necessary software components for data evaluation, user guidance and user interfaces themselves.

The read/write heads are scanned cyclically and all changes to the system are recorded and written to the database. The applications are PC-based; a TCP/IP server is used to transmit the signals via the local Ethernet network (LAN) instead of a connection and evaluation via a programmable logic controller. The transponder currently only contains the scaffolding ID; however, Kocks has kept open the possibility of being able to write information to it in the future.

In protection class IP69K

The all-metal RFID data carriers and read/write heads made of V4A stainless steel are suitable for a temperature range between -40 and +125 °C. Kocks uses transponders of type 'RTL 0262-001' with a diameter of 26 mm and protection class IP69K. The transponders can be flush-mounted in metal and can be read and written through the metal. The memory capacity of the tags is 120 words of 16 bits each. These or entire memory areas can be read and/or write-protected using a password. The number of write cycles for this type of data carrier is 100,000, the number of read cycles is unlimited.

The RFID evaluation units are optionally available with interfaces to RS485, Profibus, Devicenet and Ethernet/IP. Kocks opted for a device for connecting four read/write heads and a serial RS485 interface in combination with a separate TCP/IP interface, which transmits the data from the evaluation unit to a PC.

Equipping the rod rolling mills with RFID systems has another advantage in addition to increased process reliability: the system can be used to record all process data on a stand-specific basis. Not only is the current status of the stands known at all times, but also which stand was used when, where and in what condition, or what tonnages it has rolled in a certain period of time. This enables the rolling mill operator to plan resources better, for example when servicing and maintaining the stands or procuring rolls.

Author: Oliver Schleicher is Managing Director of Contrinex Germany in Leinfelden-Echterdingen.