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Encoder tolerates blast furnace conditions




Its use of a magnetic measuring principle means that the new GEL 235 absolute encoder is immune to ageing effects and is unaffected by wide fluctuations in temperature

Lenord + Bauer's tough new encoder, the Sensorline GEL 235, has been successfully deployed on blast furnaces manufacturing pig iron and has provided reliability and longevity in an application where frequent failure was common. The encoder is required to measure the angle of rotation of the plugging machine at the bottom of the blast furnace where the hot pig iron emerges at temperatures in the region of 1600C.

The furnaces are operated by Krupp Mannesmann (HKM) steelworks in Duisburg, Germany, and produce 5.2 million tonnes of pig iron a year. The reliable operation of machinery and equipment is essential and the plugging machines are the most critical parts of the entire plant.

Several times a day these plugging machines open tap-holes in the furnace to discharge the hot metal, ready for the next stage of its processing. To seal the hole, the tap-hole gun rotates about its attachment point to drive its stopper head to seal the previously drilled tap-hole with rapidly hardening plug material. On no account may the plugging machine apply pressure to the furnace breast, but it must travel precisely to its end position at the tap-hole in order to position the plug.

The GEL 235's exact measurement of the rotational angle enables the movement to come to a halt at precisely the right moment.

Previously, encoders performing this function have suffered frequent failures because of the extreme, fluctuating temperatures in the vicinity of the plugging machines. Optical sensors in particular regularly refused to function as a result of temperature-related material tensions between the steel encoder shaft and the optically transparent plastic or glass code discs. Absolute rotary encoders in elaborate protective housings also failed to deliver the required reliability and the temperature cycles of the environment accelerated the aging of the always susceptible LED sources.

The rugged nature of the new GEL 235 is the result of an entirely new type of contour disk made of ferromagnetic steel.

Etched into the steel disk using optical lithography and chemical etching processes are three incremental tracks with stepped numbers of ridges. The tracks are scanned magnetically using giant magneto-resistive sensor elements and the absolute position is determined by applying a Vernier scale to the readings. In such a way the new encoder is accurate to 0.1 of a degree and has an overall resolution of 28 bits (16 bit single turn and 12 bit multi-turn).

Its use of a magnetic measuring principle means that the new GEL 235 absolute encoder is immune to ageing effects and is unaffected by wide fluctuations in temperature. The ferromagnetic steel contour disk is form fixed to the encoder shaft resulting in a highly robust unit. Unlike optical systems that use transparent glass or plastic code discs it is practically impervious to dirt or vibration and is impervious to condensation.

The sensing principle and the Vernier disc of the GEL 235 are not found anywhere else in the world and offer the robustness of a magnetic system with the accuracy of an optical one.

At HKM the GEL 235 has removed the need to regularly install replacements at the tap-hole gun and since it was installed there have been no sensor related failures.

The GEL 235 encoders are available in the UK from Motor Technology, sole UK agents for Lenord + Bauer.

Watch the animated presentation on-line (low-res) or request a copy of the catalogue and accompanying CD (high-res).

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