11:00 am
Impact of curing temperatures and drying under hydrothermal conditions on phase composition and microstructure of cement bonded castables
Andreas Koehler | Almatis GmbH | Germany
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Authors:
Andreas Koehler | Almatis GmbH | Germany
Dr. Sebastian Klaus | Almatis GmbH | Germany
Dr. Stefan Kuiper | Almatis BV | Netherlands
Jerry Dutton | United Kingdom
Prof. Dr. Friedlinde Goetz-Neunhoeffer | Friedrich-Alexander-Universität Erlangen-Nürnberg | Germany
During drying of modern highly dispersed cement bonded castables, hydrothermal conditions appear because the water cannot evaporate fast enough from the bulk of the dense castable body. Under such high-pressure conditions, problems such as explosive spalling can arise. Different curing temperatures lead to the formation of different hydrate phases and accordingly, different microstructures can develop in the hardened material. Under hydrothermal conditions, original hydrate phases can transform into new hydrate phases, yet still leaving a footprint of the initial microstructure behind. This study presents the changes in porosity and in the mineralogical composition of a refractory castable model system under hydrothermal conditions depending on the curing temperature (5, 23, and 40 °C).
Quantitative X-ray diffraction (QXRD) measurements show that different hydrate phases are formed during curing, while C3AH6 and boehmite are formed in the same quantities after hydrothermal treatment in an autoclave at ~11 bar/180 °C. Although the mineralogical composition after autoclaving is not different, the three samples differ in their microstructure. Mercury intrusion porosimetry measurements reveal that although the total porosity after autoclaving is the same, the 40 °C samples have a higher proportion of large pores. SEM images also show that the appearance of C3AH6 in the 40 °C autoclaved samples varies, which originates from the starting phase composition and microstructure after curing.
11:20 am
CO2-footprint reduction in dry tundish wear lining installation with respect to refractory material and electrical equipment (eMould) technology
Emine Sari | Weerulin GmbH | Germany
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Authors:
Emine Sari | Weerulin GmbH | Germany
Thorsten Bierkämper | Bierkämper GmbH Stahl- Anlagenbau | Germany
Sven Karrasch | Thyssenkrupp Steel Europe AG | Germany
Manuel Schmitz | Thyssenkrupp Steel Europe AG | Germany
M. Goedecke | Sievering GmbH &Co.KG | Germany
Malte Kreuels | Weerulin GmbH | Germany
In general two different lining concepts exist for the wear lining of modern continuous casting tundishes: wet gunning and dry mix. Both concepts have specific advantages and disadvantages.
The dry mix technology has been standard in thyssenkrupp plants Beeckerwerth and Bruckhausen for more than 20 years. The reduction of energy consumption and the reduction of CO2 emissions could be achieved in part by switching from wet spray to dry mix. The last continous caster changed to dry mix at thyssenkrupp Steel in 2015. The thin slab caster changed after some years of parallel wet spray usage. In the second step, the heavy 90 DBM was successfully replaced by the light magnesia to reduce the consumption quantities per tundish. The light magnesia product has been used and established in both plants since 2012. The aim of this work is to prove that it is possible to cast the same grades and sequences with a new European olivine-based formulation, which has a much lower carbon footprint than magnesia (and light magnesia) in production and transport. The objectives are to first optimize the dry mix product for thyssenkrupp and then implement field trials to change the technology of baking the dry mix with today`s hot air mould to eMould, an electrical heating solution, to save even more CO2 emissions, time and energy in the future.
11:40 am
Investigation of the Drying Behavior of Low Cement Castables
Uwe Klippel | Calderys Deutschland GmbH | Germany
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Authors:
Uwe Klippel | Calderys Deutschland GmbH | Germany
Patrick Malkmus | Calderys Deutschland GmbH | Germany
Dr.-Ing. habil. Steffen Möhmel | IMERYS Villach GmbH | Austria
Monolithic refractory castables still comprise a hydraulic bond in the vast majority of the cases despite of many new developments for chemical or non-cement castable (NCC) binders in the last decade, respectively. In particular deflocculated dense castables of the Low Cement Castable (LCC) range can be considered as the workhorse in this field. The first heat up or drying of such monolithic deflocculated dense refractory linings maintained to be a challenge while complying with constantly increasing market demands for simpler procedures and quicker drying regimes, respectively. Quite a few publications have been released on this topic for the last ten years, indeed. However, mostly either the product is altered in regard to its bond nature or worst-case scenario spalling tests were investigated to qualify new product types. This paper, however, introduces a simple laboratory scale test setup to study and iteratively improve the drying schedule of a given castable lining, e.g. ramp and hold, to deliver both, enhancing the drying effectiveness in avoiding spalling as well as the drying efficiency in releasing physical as well as chemical bonded water as quick as possible. The influence of the matrix and the bond is showcased by an experimental design comprising self-compacting and vibrocasting Low Cement Castables (LCC), with and without silica fume or drying fibres, respectively.
12:00 pm
A novel type of anti-spalling natural straw fibers for refractory castables
Minghua Zhang | Höganäs Borgestad AB | Sweden
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Authors:
Minghua Zhang | Höganäs Borgestad AB | Sweden
Micael Larsson | Sweden
Edina Alibasic | Sweden
Ronald Robles | Sweden
With the coaction of internal pressure created by water vapor and thermal stress triggered by temperature gradient, cement based castables are prone to structural damage and even explosive spalling during dry-out process; thus to cut down the service life of refractory linings and cause economic loss. Here we introduce a novel type of natural straw fibers in terms of castables’ anti-spalling property. The permeability of conventional castables and ultra-low cement castables are tested and presented in combination of the novel fibers and polypropylene (PP) fibers. The results demonstrate those natural straw fibers are functional with enhanced properties and lower risk of cracking. Furthermore, industrial practices have confirmed that those fibers make cement based castables no cracking during optimum quick dry-out.