The extent of this area generally includes the entire superstructure of the melt pool itself, plus the small furnace neck, but does not include the regenerator or any regenerator refractory. The surface temperature in this area is slightly higher than the surface temperature of the refractory brick at the glass contact (generally 66 to 93 higher than the actual glass temperature). The change in temperature is large, and the maximum temperature is generally the hot spot in the second half of the length of the melt pool. This temperature can be as high as 1649 in soda lime glass furnaces; this temperature is higher in some borosilicate glass furnaces.
Compared with refractory bricks in contact with glass, the choice of superstructure refractory bricks is quite different, depending on whether the refractory bricks are corroded by horizontal surfaces or vertical surfaces. In general, the horizontal surface of fully exposed or partially exposed refractory bricks is subject to both vapor erosion and some degree of erosion by the batch dust or fly solid particles; while refractory bricks with only vertical exposed surfaces are usually only subject to The role of corrosive vapors.
If the refractory material has been melted, vapor erosion will cause the melt to turbulent and drip from the surface of the refractory material. This drooling and dripping can damage the underlying refractory material and cause defects in the final glazing. If the refractory material eroded by steam is not damaged (as is often the case), it is important that the surface of the refractory material is stable to the spalling reaction, the delamination reaction, the film reaction, and the splitting reaction. These reactions make it difficult to homogenize the refractory material that sinks in the glass, thus causing glass defects.
In the case of soda lime glass, the type of vapor is generally sodium oxide, sodium sulfate, and other volatile components in the batch. The main vapor species in borosilicate glass appears to be sodium tetraborate. The solids that attack the horizontal surface of the refractory are primarily alkaline earth metal oxides and silica from the batch.
The temperature fluctuations in the various regions of the superstructure are greatly increased compared to the temperature fluctuations of the melt pool itself, but they are not excessively large, except in the vicinity of the fire exit and the nozzle brick itself. The reason for this temperature cycle fluctuation is the combustion commutation of a general regenerative furnace.
Generally, near the upper structure, refractory materials having a large erosion resistance to steam and solid solution should be used, although in some places in the glass industry, silica bricks which are not very resistant to corrosion are actually used. In places such as the melting kiln wall, silica bricks are easily melted and produce silicon-containing turbulence. Even if such a silicon-containing turbulent material is present, it is easier to homogenize than a turbulent material containing alumina or zirconia.
The refractory materials used in various parts of the superstructure are not the same in terms of variety and quality. They are mainly selected according to experience and economic effects, but obviously related to the strict requirements of various production conditions, because these conditions vary with the factory and the melting. The kiln varies. The superstructure refractory may also be melted and damaged if the condensation reaction of the vapor has a chance to occur at the joint between the cooler refractory bricks in the superstructure. Insulation measures are widely used in almost all areas of the superstructure. For some refractory materials used in the superstructure, this insulation is of added benefit because they are thermally resistant to thermal fluctuations due to their relatively poor resistance to thermal fluctuations. The amplitude is reduced, thereby reducing the tendency of the refractory to peel off, crack, peel off, and the like.
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