Causes of abnormal state of silica bricks in melting furnace
1. Changes in the holding force of the kiln wall
During the use of the furnace, some special conditions may be encountered: such as coal quality or operational reasons, resulting in insufficient fuel, or out of control of the secondary air equipment, failure of the control instrument, and serious dust accumulation in the flue, etc., which will cause the kiln The flame temperature drops. If the flame temperature in the kiln drops too much, and the time is longer, the temperature of the molten glass will drop significantly, and the temperature of the furnace cover will be greatly reduced at this time (the heat transfer between the molten glass, the flame and the furnace cover is a dynamic balance). If the furnace maintenance personnel do not adjust the top wire of the dome foot in time, the dome brick will shrink due to the decrease in temperature, the original volume of the furnace cover will decrease, and the dome brick will sink under the action of gravity, and the entire dome will rise and fall. , Resulting in cracks in the lower mouth of the bricks.
Due to the small contact area of ??the bricks in "line" contact, the frictional force becomes smaller, the clamping force becomes smaller, and the weight of the
silica brick does not change; in addition, the thickness of the bricks is not exactly the same, and the bricks with smaller heads are easy to fall down, resulting in Part of the furnace cover is broken or "skewed". When the furnace cover is "opened", there is a difference of a few millimeters between the size and thickness of the bricks. When the bricks are "skewed" and fall down, they are easily caught by the surrounding bricks (unless the bricks are very small). Will cause fatal effects on the furnace cover. The "under-opening" is different. Once a block of brick is "skewed", the brick will easily fall into the kiln, and the dropped brick will form a "cantilever beam" structure because there is no force support point. This is very dangerous, and this is the reason why the large-brick brick requires staggered joint masonry and does not allow ring masonry. Once the bricks are dropped from the large slab, the weight of the ring slabs is transferred to the adjacent bricks. Because the adjacent bricks' stress surface is reduced, and the stress is uneven, and it is in line contact, the above-mentioned parts are likely to fall again. Once the brick is dropped again, it will form a "domino effect", causing the furnace cover to collapse in a larger area.
2. Crystal transformation of siliceous materials
Silica brick products are mainly composed of tridymite, cristobalite, residual quartz and a small amount of silicate liquid phase. When silicon bricks are in use, the transformation of various crystal forms is still in progress. With the increase of temperature, it gradually transforms into α-cristobalite, but a considerable part of α-tridymite exists.
The temperature is above 1470℃ (the temperature in the furnace far exceeds this temperature, but it cannot reach the melting temperature of cristobalite of 1 723℃), the internal crystal form of the silicon brick is transformed from α-tridymite to α-cristobalite, forming about 50 mm Α-cristobalite crystal phase protective layer. However, due to the large temperature difference between the inner and outer surfaces of the aquarium, it cannot be completely converted into α-cristobalite; if the temperature in the kiln is reduced to about 1 200°C or lower due to changes in conditions, α-cristobalite will change to α-tridymite and β-cristobalite. Quartz transformation. Theoretically, the volume shrinkage of α-cristobalite to α-tridymite is 4.7%, and that of α-cristobalite to β-cristobalite is 2.8%. In a certain period of time, due to the large temperature difference between the inside and outside of the dome brick, the outer surface of the dome brick is also undergoing crystalline transformation, the volume is also decreasing, and the position of the dome brick and the dome brick are also changing, thereby destroying the stability of the silica brick itself. Belt" (α-cristobalite crystal phase layer).
In the actual production process, the temperature in the kiln decreases, and the height of the rise of the large slabs decreases, which is caused by the transformation of the crystal form inside the silica bricks and the volume shrinkage. After several or more temperature changes, continuous heating and cooling, continuous changes in crystal form and reorganization, the positions of the dome bricks and dome bricks continue to change, which will seriously affect the corrosion resistance and service life of the dome.
