At present, increasing prices for iron and steel are again markedly enlivening the economic situation for steel manufacturers, such as the depicted Krupp Mannesmann (HKM) steelworks in Duisburg, Germany. HKM is a blast furnace operator and specialist steel manufacturer that operates pig-iron production including blast furnaces, coking plant and sintering plant plus pig iron production for the manufacture of continuous cast slabs and rod stock.

HKM is a company that continually reexamines and optimizes its work processes both technically and financially in relation to working conditions and environment protection. And it is currently setting standards for the global steel market in both of these areas, production and the environment, employing the very latest equipment to ensure the economic production of high-quality iron and steel.

HKM operates two pig iron blast furnaces that manufacture 5.2 million tonnes of pig iron annually for the highly competitive world market. Smooth operation of the equipment is thus absolutely vital for the company to be able to produce economically.

Several times a day, plugging machines open tapholes in the ca. 1600°C blast furnaces to discharge the hot metal ready for the next stage of its processing. Since these machines are among the most safety-critical parts of the entire plant, manufacturers have always placed a high value on their reliability and robustness.

Previously, industrialists spend a great deal of money installing an assortment of absolute rotary encoders enclosed in elaborate protective housings. But the extreme requirements of widely fluctuating temperatures regularly caused these devices to fail. Optical sensors in particular regularly refused to function: temperature-related material tensions between the steel encoder shaft and the optically transparent plastic or glass code discs, the material expansion itself and various other effects all combined to cause the failures. Added to which the temperature cycles accelerated the aging of the always susceptible LED sources.

The convincing performance of the new Lenord + Bauer Sensorline GEL 235 is thanks to its innovative magnetic scanning of an extremely robust steel code disc that does away with the need for regular replacements.

A new type of ferromagnetic measuring scale was developed for this absolute rotary encoder. It has three incremental tracks with staggered numbers of ridges that are scanned using giant magnetoresistance (GMR) elements. The numbers of ridges and their geometry are chosen in such a way that their relative positions are always unique, permitting application of the vernier principle. When the three tracks are magnetically scanned by the GMR sensors the ridge positions are mapped onto three sinusoidal signals with correspondingly unique phase relationships, from which a vernier algorithm determines the absolute position.

A self-centering process pressure-bonds this new type of vernier disc to the steel encoder shaft. This robust unit – which also possesses a uniform temperature coefficient – not only makes the GEL 235 eminently suitable for the most rugged of tasks but also offers the same high precision as an optical code disc manufactured using conventional exposure and etching technology. Even when things get hot!

This sensing principle and the vernier disc of the GEL 235 are not found anywhere else in the world, and are clearly superior to other absolute rotary encoders because they make it possible to combine the robustness of a magnetic system with the accuracy of an optical one. The permissible temperature range of the GEL 235 is from -40°C to 105°C, making it suitable for extreme operating conditions. And thanks to its accuracy – plus the fact that it is a readily obtainable and economical series product – it is equally suitable for standard applications.

At HKM the GEL 235 has removed the need to regularly install replacements at the taphole gun: since it was installed there have not been any sensor-related failures. Undoubtedly, markedly longer and safer plant operation are positive results contributing to improvements in this country’s iron and steel production.

Lenord + Bauer offers its GEL 235 absolute rotary encoder as singleturn and multiturn units with SSI / BISS interfaces and an additional 1 VPP sin/cos difference signal. The fieldbus profiles PROFIBUS DP and CANopen can be used via a plug-on bus cover. The flange measures 58 mm and the housings of both singleturn and multiturn variants both measure only 46.5 mm (without the bus cover), giving the GEL 235 the most compact mounting depth of any device on the market. The GEL 235 is available with clamping or synchronous flanges or a semi hollow shaft, and with cable or plug outlets.