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Spinel bricks for highly stressed roofs in glass melting furnaces
New challenges are raised to the refractory materials in the crown and superstructure of oxy-fuel fired glass melting furnaces in comparison to air-fuel fired glass melting furnaces. In glass melting furnaces which are oxy-fuel fired the water steam partial pressure above the melt increases very strongly. In the case of soda-lime-silica glass melts together with the water steam partial pressure the alkaline hydroxide partial pressure increases with a factor of three in comparison to an air-fuel firing system. This leads to an aggressive action on the refractory lining in the crown and superstructure. After extensive thermodynamic calculations and laboratory tests a pure spinel refractory material (MgO ∙ AI2O3) was developed for the application in the crown and superstructure of oxy-fuel fired glass melting furnaces. The chemical and physical properties as well as the results of corrosion tests under oxy-fuel conditions of this direct-bonded fused spinel material will be discussed. Because of the high corrosion resistance to alkaline attack and the excellent behaviour of the creeping under load even at a temperature of 1650 °C, this spinel material can be proposed for the successful application as crown and superstructure refractory for oxy-fuel fired glass melting furnaces.
Non-destructive testing of ceramically bonded refractories - Application of ultrasound and microwaves
Quality control on refractory bricks is either mostly destructive or methods are used which require samples with a certain geometry. In a joint project between the University of Erlangen and industry the applicability of non-destructive testing methods for sintered refractory bricks was tested. Various materials with artificial flaws were measured in transmission with ultrasound (500 kc/s) as well as with microwaves (24 to 40 Gc/s) and the results were compared. Despite of good results, the testing with ultrasound proved to be unsuitable for the measurements of greater lots, because the open-pore blocks have to be coupled in water. An excellent alternative is the transmission measurement with microwaves. With both methods structural inhomogeneities as well as density differences or inclusions can be detected.
Chromic oxide blocks for use in the container glass industry
Large parts of the tank superstructure of soda - lime - silica glass melters for the production of Hat and container glass are mostly lined with fused-cast AZS blocks today These linings are standind about 8 to 10 years. However, from pracdcal experience it is well-known that certain furnace areas such as doghouse corners, weirs, throat assemblies etc. are prone to progressive corrosion. In order to eliminate these shortcomings by providing cost-effective Solutions, isostatically pressed and sintered chromic oxide blocks were tested successfully for use in soda - lime - silica glass furnaces. Questions concerning the corrosion behaviour, the colouradon of the glass and the formation of Chromate are discussed.
Silica wrecking material as a substitute for glassmaking sand in a container ware batch
Industrial high-temperature processes like steel making, glass melting, cement production etc. need sintered or fused-cast refractory materials. During the operating time the reactions of the fused product and the bricks of the furnaces lead to contaminated refractory materials, which should no longer be disposed of and, therefore, have to be recycled, that means converted to raw materials for different industrial processes. Regarding these conditions the authors have tried to introduce silica bricks from the crown of glass melting furnaces and from the walls of coke ovens into the batch, replacing the glassmaking sand. First in laboratory-scale tests the melting behaviour and the optimum grain size distribution of ground silica bricks were studied. After a successful termination of these laboratory tests the results were transferred to an industrial furnace for melting container ware, replacing step by step the glass making sand without observing any stones or cords in the melted glass.
Feuerfeste Werkstoffe für den Betrieb von Glasschmelzöfen : Stand der Technik und Ausblick
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