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Zürich, October 09, 2019

A revolutionary sensor for the casting process

Improving product quality by measuring the mold level and the flux powder level

With CONGAUGE LB 6755, the initial shell forming can be controlled more effectively because now the actual liquid steel level in the mold is known. This information allows  to set up a closed control loop for the automation of the powder feeding system. This makes CONGAUGE LB 6755 a compact Industrie 4.0-application capable of ensuring a constant flux powder level throughout the casting campaign. As a result, the new sensor helps to significantly improve the metallurgical properties of the final product.

In order to achieve a uniform casting behavior in the mold and optimal product quality, both the level of the liquid steel in the mold and the thickness of the flux powder covering the steel must be controlled with greatest accuracy in continuous casting plants. The inflow of steel into the mold is controlled via measurement of the liquid steel level (meniscus). For a stable continuous casting process it is essential that this measurement is reliable, correct and that it provides the results instantly. The flux powder serves many purposes: It protects the liquid steel against oxidation and, in the form of molten slag, it serves as lubricant between the solidified steel shell and the mold, provides thermal insulation of the meniscus and makes for uniform heat exchange between the steel and the mold. Care has to be taken that the flux powder melts appropriately and in sufficient amount. Otherwise the consequences may be severe casting defects or even the need to abort the casting process.

Conventional sensors used so far in mold level gauges have only been able to measure either the level of the liquid steel in the mold or a mixed signal as a combination of the steel and the powder levels in the mold. Measuring both levels separately used to require two independent measuring techniques working on different physical principles. The solutions involving two separate devices, however, entail high costs, increase the maintenance effort and make the evaluation of the measured results a rather cumbersome procedure. The newly developed CONGAUGE LB 6755 sensor solves exactly this problem as it combines both level measurements within one unit. In addition to new plants, the sensor can just as well be retrofitted to existing casting plants. Particularly producers of high-grade steels will benefit from this new development.

Improved control of the casting process

While the new radiometric multi-tasking sensor is based on the commonly used, fast and reliable radiometric mold level measurement principle, it is yet capable of simultaneously measuring the steel level and the thickness of the covering layer of flux powder in the mold. The availability of both measurements at the same time provides a clearer picture of the situation in the mold, allows for better control of the casting process and, as a result, increases the quality of the cast product. The new CONGAUGE LB 6755 sensor has been developed in close cooperation between SMS Concast and Berthold Technologies, based on a proof of concept devised by SMS Concast, and taken to industrial maturity by the two companies. The performance capability of the new sensor has been proved in successful trials on continuous casting machines at the German steelmakers Saarstahl AG and Lech-Stahlwerke.

The system sends out three different signals. The first signal provides the classical radiometric measurement of the mold level. The second and the third signals allow to differentiate between the actual steel level and the actual thickness of the covering flux powder in the mold. Thus operators of continuous casting plants can benefit from a compact gauge with a sensor that allows - in addition to a closed control loop for the meniscus measurement - the setup of a closed loop for the control of customary flux powder feeding systems. The latter are still commonly controlled by open-loop systems as the changing powder level as a result of the powder feeding makes the measurement quite difficult. However, with CONGAUGE LB 6755 it is now possible to establish a reliable, automated powder feeding system that makes for more precise control of the flux powder layer in the mold.

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Principle of radiometric measurement
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The enhanced radiometric measurement provided by the CONGAUGE LB 6755 multi-crystalline sensor.
Summary

To summarize, it can be said that with CONGAUGE LB 6755 initial shell forming can be controlled more effectively because now the actual liquid steel level in the mold is known. Moreover, the newly available information allows the operator to set up a closed control loop for the automation of the powder feeding system. This makes CONGAUGE LB 6755 a compact Industrie-4.0 application capable of ensuring a constant flux powder level throughout the casting campaign. As a result, CONGAUGE LB 6755 helps to significantly improve the metallurgical properties of the final product.