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The Applications of Refractories in Different Parts of Glass Furnaces


2021-06-03


The Applications of Refractories in Different Parts of Glass Furnaces
The maximum temperature of the melting zone in the glass furnace is 1570-1610℃. The safety limit usually depends on the glass composition and the softening point of silica brick crown. The silica bricks begin to soften and melt in 1620℃. The reason why the crown is built with silica bricks instead of other refractory materials with higher refractoriness is that they have high strength at high temperature and their ablated materials are also compatible with glass, while other refractory materials may produce insoluble stones and other inclusions.

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In the breast wall and under the liquid level, dense refractory materials with larger density than glass are used. Its corrosion resistance to molten glass is far better than other materials. Since all the materials used under the liquid level have the maximum corrosion rate, they have shorter service life and should be forced cooled in the outside. With the aging of the furnace, the weak parts are expanded and should be air cooled.

The contact surface between any brick and glass liquid is the source of defects. So, when designing the furnace, try to avoid covering any refractory material and always make sure there is a surface exposed to the air to dissipate heat.

The material is loaded into the furnace from the back end and floats and moves forward until fully melted. Usually it is completely melted in the third pair of burners. The hot spot is usually in the middle and moves forward to the third pair of burners.

Refractory materials in the first two pairs of burners are most seriously corroded. Checker bricks here are easy to be clogged. The refining tank is the lightly corroded part.

Bridge walls is used to separates two different temperature zones and also used as a skimmer. the molten glass flow through the throat.

The throat plays an important role in cooling. It can cool the molten glass from 1540-1590℃ to 1260-1310℃. The feeding channel is the channel with temperature control and connected with the discharge holes. Its role is to cool molten glass to about 1100℃ for gob forming.

The applications of refractories in different parts of glass furnaces are as the follows:

(1) Sidewall
The ideal refractory material for the sidewalls in the soda-lime-silica glass furnace and boron glass furnace is fused cast AZS block. It contains 33-41% ZrO2. In E-glass or low-alkali glass fiber furnaces, the sidewalls are built with AZS brick or dense zircon brick or fused silica brick.
(2) Bottom
The bottom bricks are required to have good wear resistance and good integrity. Now the bottom usually adopts multi-layer composite structure. The main layer of the multi-layer structure is a layer of large fire clay bricks. A protective layer and a wear resistant layer are laid on the large fire clay bricks. The protective layer is made of zircon ramming mixes or AZS ramming mass. The wear resistant layer is laid on the protective layer to protect the rammed bottom and is in direct contact with molten glass. It is usually built with AZS bricks with good corrosion resistance and wear resistance. This composite bottom structure can reduce heat loss and expand the service life of the furnace. When melting glass containing heavy elements (such as lead glass) or heavily corrosive glass (such as opal glass), in order to prevent leakage, add another protective layer and wear resistant layer on the original protective layer and wear resistant layer. The original protective layer and wear resistant layer are also the secondary paving course and can be built with sintered AZS bricks or zircon bricks.
(3) Feeding pool
The feeding pool bricks are corroded by powder and molten glass. The erosion of powder, the scouring of molten glass and the effect of flame all do harm to the bricks, so the corrosion is serious. Fused cast AZS 41# WS is used in this part and thickened and air cooled. Except the corner bricks, other parts are built with AZS 33#. The bottom the feeding pool is built with large cast kaolin bricks.
(4) Throat
The flow rate of the molten glass in the throat is the largest. And there are obvious convection phenomena. These accelerate the erosion. So, the throat cover tiles are built with AZS 41#. The sidewall bricks of the throat are built with the same materials with the cover tiles, at least WS bricks. Fused silica bricks are used when melting borosilicate glass.
(5) Cooling tank and forming tank
In the cooling tank and the forming tank is refined molten glass. It has entered the post melting process. At this time, any defects including bubbles, stripes and stones should be avoided. The cooling tank is built with AZS 33# manufactured by the oxidizing method. The exudation temperature of glass phase is high and will not produce bubbles. The forming tank should be built withα-β fused cast alumina block orα fused cast alumina block.
(6) Crown and breast wall
Refractory bricks used in the crown and breast wall are mainly corroded by erosion (mainly honeycomb erosion caused by alkaline sulfate coagulation) and burning. They are required to be stable in alkali atmosphere and have high refractoriness under load and good creep resistance. It can be silica brick, high quality silica brick or fused cast AZS 33#.
(7) Front wall and Lattice Wall
The front wall and lattice wall are the front wall and the back wall of the melting zone. They have the same erosion and burning characteristics. Furthermore, the front wall is subjected to the erosion of batch materials and the scouring of the leaked flame. It is one of the weakest points of the furnace. Currently, fused cast AZS 33# or high quality silica brick and sintered AZS bricks are used in these parts. The front wall is built with high quality silica brick and air cooled.
(8) Burner
A burner is composed of carters, burner neck and spout bricks. Refractory bricks used here should have good resistance to high temperature, corrosion and erosion and thermal shock. In furnaces fueled with producer gas (low thermal load), silica bricks and large kaolin bricks are used; in furnaces fueled with high calorific value fuel (high thermal load), carter crown bricks, carter sidewall bricks, bottom bricks, oblique crown dissection bricks, tongue bricks  and spout bricks are built with AZS 33#. The bottom bricks can also be built with dense corundum bricks.
(9) Special parts
In some special parts, such as bubble bricks, dam bricks, electrode bricks, inspection holes and measuring holes have special functions and specific damage characteristics. The bubble bricks are seriously corroded by the rapid cycling stream. The big temperature difference between the inner and outer surfaces of bubble bricks causes large mechanical stress and cracks. Dam bricks will also be damaged by the severe high temperature flow. AZS 41# WS can be used in both bubble bricks and dam bricks. Electrode bricks are seriously corroded by the recycle stream. When cooling, there will be a big temperature difference outside and inside the bricks, which will cause large mechanical stress and radial cracks around the brick holes. So, the bricks are required to have good resistance to corrosion and thermal shock and higher electric resistance. In addition to electronical properties, the conductivity of glass liquid and the arrangement of electrodes should also be taken into consideration. AZS 41# WS, fused silica bricks and sintered dense zircon bricks can be used in this part. Since the inspection holes and measuring holes are subjected to the erosion of flame in a long term, they are easily to be burned and crack. AZS 33# bricks are used in this part.

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