The Thermal Expansion Performance of Electric Fused Bricks and the Influence of Glass Kilns
2023年04月24日
The ignition and baking process of a glass furnace is based on the physical and chemical properties of the refractory material used in the furnace, which is the thermal expansion performance of the refractory material. After heating and baking, the refractory material completes the internal crystal transformation and volume change, in order to achieve normal use at high temperatures.
In the past, AZS bricks were expensive. Therefore, kilns do not require or only use a small amount in key areas. In the past two decades, with the development of high-efficiency and energy-saving technologies in kilns, AZS bricks have been widely used, not only in contact with the pool walls of glass liquid, but also in flame spaces. Due to the influence of traditional inertia thinking, most glass factories still only consider the thermal expansion of silicon bricks when baking, and do not pay attention to the thermal expansion of AZS bricks. Therefore, the fracture of AZS bricks often occurs before and after the kiln is put into operation, which directly affects the lifespan of the kiln.
1. Thermal expansion characteristics of AZS bricks
AZS bricks contain a certain amount of ZrO2, which belongs to homogeneous polycrystalline materials with the same chemical composition. Due to different temperature conditions,
Three different structures and properties of crystals can be formed. They are monoclinic crystal system ZrO2, tetragonal ZrO2 and cubic ZrO2.
≈1200℃ ≈2370℃
Monoclinic crystal system ZrO2 -- -- → tetragonal system ZrO2 -- -- → cubic system ZrO2
Changes in crystals are often accompanied by changes in volume. Taking 33 # AZS as an example, it was found through experiments that when the temperature range is between 0-1100 ℃, the bricks gradually expand as the temperature increases; When the temperature range is 1100-1200 ℃, the brick shrinks violently with the temperature rising, and the linear expansion rate decreases from about 0.8% to about 0.6%, which causes the abnormal expansion phenomenon that is usually said, because the ZrO2 monoclinic crystal system is transformed into ZrO2 tetragonal system; When the temperature exceeds 1200 ℃, the bricks start to expand again as the temperature increases.
From laboratory testing data, it can be seen that the overall expansion is not significant below 1600 ℃, with an average expansion coefficient of about 70 * 10-7/℃.
2. Precautions during kiln baking
There is a fire amplification link in the baking kiln. The hot air baking kiln usually fires at 900-1000 ℃. Practice has proved that the fracture of AZS bricks mostly occurs after the fire amplification. The reason is that the heating rate is too fast during the 1100-1200 ℃ transition from monoclinic crystal system ZrO2 to tetragonal ZrO2. So, the general requirement is that the speed should not exceed 15 ℃/hour, and many manufacturers control it at 5 ℃/hour. In other temperature ranges, the speed should not exceed 15 ℃/hour, so that AZS bricks have sufficient time for crystal transformation and can avoid fracture.
There is a temperature difference of several degrees between the contact flame surface and the non-contact flame surface during the baking process. To ensure that the outer side of the brick can safely undergo crystal transformation, it is necessary to maintain a lower heating rate within a larger temperature range. Therefore, the temperature range inside the kiln is usually expanded from the theoretical range of 1100-1200 ℃ to around 1100-1350 ℃.
The upper part of the pool wall brick is 300-400 millimeters away from insulation during normal production and requires cooling. In order to reduce the temperature difference between the inner and outer sides during kiln baking, temporary insulation materials such as aluminum silicate fibers should be used to prevent the brick from breaking. When the temperature reaches 1500 ℃ or above, the insulation fibers can be removed.
When cooling the pool wall bricks, the cooling air inlet should be gradually opened, usually in 5 times, and can be opened by 20% every hour.
3. Conclusion
The quality of baking kiln work is related to the lifespan of the kiln. Therefore, it is extremely important to correctly grasp the expansion performance of fused zirconia corundum bricks, standardize and conscientiously implement them in the heating curve of the baking kiln. Our company's relevant personnel should communicate more with users on this issue, serve as good advisors, and promote the common development of both supply and demand sides
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Electric fusion bricks and clay bricks are both refractory materials and have a wide range of uses in building materials. Today, Yuhua Electric Fusion Technology will introduce their differences to everyone:
Refractory bricks are abbreviated as firebricks. Refractory materials made by firing refractory clay or other refractory materials. Light yellow or brownish in color. Mainly used for building smelting furnaces, capable of withstanding high temperatures ranging from 1580 ℃ to 1770 ℃. Also known as firebricks. Refractory materials with a certain shape and size. According to the preparation process, it can be divided into fired bricks, unburned bricks, electric fused bricks (fused cast bricks), and fire-resistant and insulated bricks; According to shape and size, it can be divided into standard bricks, ordinary bricks, special bricks, etc. It can be used as high-temperature building materials and structural materials for building kilns and various thermal equipment, and can withstand various physical and chemical changes and mechanical effects at high temperatures. For example, refractory clay bricks, high alumina bricks, silica bricks, magnesium bricks, etc.
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