Chemistry And Physical Properties Of Fused Cast AZS Block

Fused cast AZS block is made from pure alumina powder and Zircon sand (composed of 65% zirconia and 34% SiO2). Fused cast AZS block is abbreviated as AZS because it contains Al2O3－ZrO2－SiO2.
The main chemical composition of fused cast AZS includes Al2O3(45%-50%), ZrO2(33%-41%), SiO2(13%-16%) and alkali metal oxides(Na2O+K2O, 1.3%-1.4%). According to the different content of ZrO2 from 33%-41%, fused cast AZS block can be divided into three types AZS—33#,AZS—36# and AZS—41#.
ZrO2 is preferably contained in a large amount with a view to improving the corrosion resistance. Al2O3 is an important component like ZrO2. Al2O3 constitutes corundum crystals. The corundum crystals exhibit strong corrosion resistance and have a characteristic that they show no abnormal expansion or shrinkage due to a temperature change. SiO2 is the main component for forming the network of the matrix glass. Na2O constitutes a structure for modifying the network of the matrix glass and exhibits an action to control the viscosity of the matrix glass and an action to inhibit formation of mullite. K2O is not an essential component, but shows the same action as Na2O. For cost reasons, the alkali metal oxide is preferably Na2O.
The crystal phase of fused cast AZS block consists of corundum, baddeleyite, eutectic phase of corundum and baddeleyite, glass phase and a small amount of mullite. Corundum has a high melting point. It is the stablest crystal phase of Al2O3. It presents a shape of rhombohedral cylindrical skeleton in AZS. Baddeleyite has a high melting point and stable chemical property. It is a kind of particulate mineral in the AZS. It presents a shape from ovate to droplet and is often clustered into a chain, herringbone, etc. A small amount of baddeleyite is dissolved in glass phase. It has the strongest corrosion resistance to glass melt. The glass phase has a low softening point. At a high temperature, it becomes liquid and exudes to the surface of the brick and leaves pores in the brick. The glass melt diffuses into the brick through the pores and aggravate the corrosion of brick. The mullite should be avoided as it will reduce the amount of corundum and baddeleyite.
Fused cast AZS block has a dense structure with a high bulk density (about 4.00g/cm3) and low apparent Porosity(1.0%-1.2%). It has high cold crushing strength(300 Mpa), high exudation temperature of glass phase (1400℃) and high refractoriness(1700℃). Its bubble separation ratio（1300℃×10h）is 1.0-1.2. It has strong corrosion resistance to glass melt and its anti-corrosion rate of glass liquid under 1500℃X36h（mm/24h）is 1.2%-1.4%.
Due to its strong glass corrosion resistance and high thermal shock stability, fused cast AZS block is widely used in the glass contact area and superstructure of glass furnaces.
Zhengzhou Sunrise is a refractory material supplier from China, offering high quality refractory materials for glass furnaces, including fused cast AZS block, fused cast alumina block, fused cast high zirconia block, mullite brick, zircon brick, alumina bubble brick, magnesia brick, sillimanite brick, corundum brick, low porosity fireclay brick, high alumina brick, all kinds of glass furnace ramming masses, etc..

The Application Of Refractories In The Glass Industry

Refractories are the main materials used in the glass furnaces and have big influence on the service life of glass furnaces, the quality of glass, the energy consumption and the cost. The development of the manufacturing technology of glass greatly depends on the the development of refractory technology and improvement of the quality of refractories.
Glass is melt at more than 1600℃, so the refractories will suffer from corrosion during the manufacturing process. The corrosion resistance performance and corrosion rate of refractories determines the service life of glass furnaces. The larger the scale of glass furnaces is, the bigger the production capacity is. The quality and accuracy of refractories has direct influence on the scale of glass furnaces. The application of the oxygen-fuel technology and reduced pressure technology depends on the performance of refractories, since those technologies increase the concentration of alkali vapor and water vapor, make the refractories more serious and have more demanding performance on the performance of refractories. Since the corrosion of refractories can also cause glass defects such as stones, bubbles and stripes, the corrosion resistance performance has a big influence on the quality of glass.
According to the types of glass produced, the size and structure of furnaces, the quality of glass required and the production capacity, different refractories are selected. So far, refractories for the glass industry, especially the float glass furnaces, include fused cast refractories, silica bricks and magnesia refractories.

Fused Cast Refractories

Fused cast refractories are refractories made by melting the raw materials and then casting the melt into a mold. Fused cast refractories for glass furnaces mainly include fused cast AZS, fused cast alumina block and fused cast high zirconia block. Fused cast AZS and fused cast alumina block are the main refractories used in float glass furnaces, Electronic glass furnaces, household glass furnaces, and pharmaceutical glass furnaces. Besides glass contact areas, they are also used in demanding areas such as the beast wall and the crown.

Silica brick

Silica brick is a traditional refractory used in glass furnaces, especially in the crown and superstructure. The quality of glass furnaces will affect the normal operation and service life of glass furnaces.

Magnesia refractories

Magnesia refractories are alkali refractories, including fused cast magnesia brick, high pure magnesia brick, direct bonded magnesia chrome brick and magnesia zircon brick. Magnesia refractories are mainly used in the regenerator.

Key Factors For The Casting Process Of Fused Cast AZS

Casting is an important step of the manufacturing process that has great influence on the quality of the fused cast AZS block. Key factors that affect the casting process of fused cast AZS include the casting temperature, casting speed, the casting time and back pour.
The casting temperature is the temperature of the melt when it is poured into the mold. The casting temperature of fused cast AZS can be as high as 1820-1840℃. The viscosity of the melt is up to the chemical composition and temperature of the melt. The chemical composition is up to the formulation. The casting temperature is crucial since the higher the temperature, the lower the viscosity, the better the flow-ability. However, if the temperature is too high, the temperature difference between the casting and the mold is small, which will increase the shrinkage stress and cause cracks.
The casting speed determines the casting time. Every casting products has its best casting time. Improper casting time will cause many defects. If the casting speed is too fast, the stream will be coarse and the flowing speed will be too fast, which will produce big impact force on the mold. The force may destroy or melt the mold and cause protrusions. Additionally, gas will be brought into the mold and produce a thin shell filled with gas and bubbles in the casting. Besides gas, raw materials in the furnace mouth may be brought into the melt and cause defects. Conversely, if the casting speed is too slow, it will produce defects such as loose corners, knots, sand and pouring shortage.
Back pour refers to the process of repouring some melt into the shrinkage cavities after the casting is completed. Generally, small bricks are solidified quickly and do not require back pour. Medium bricks can be repoured. Large bricks require back pour and it takes a long time. Back pour is one of the effective ways to reduce the shrinkage cavities and improve the bulk density.
Zhengzhou Sunrise is a refractory material supplier from China, offering high quality refractory materials for glass furnaces, including fused cast AZS block, fused cast alumina block, fused cast high zirconia block, mullite brick, zircon brick, alumina bubble brick, magnesia brick, sillimanite brick, corundum brick, low porosity fireclay brick, high alumina brick, all kinds of glass furnace ramming masses, etc..

Fused Cast Refractories And Float Glass Furnaces

Fused cast refractory is a special type of refractory made by melting the raw materials in the electric arc furnace, pouring the melt into a mold and cooling the melt to solidify. It features dense structure, good corrosion resistance, low pollution to glass and long service life. Its quality and development has great influence on the service life of the float glass furnace.
Fused cast alumina block includes alpha alumina block, beta alumina block and alpha-beta alumina block. Alpha-beta alumina block mainly consists of intertwined crystals of alpha alumina and beta alumina with just a small amount of glass phase. It has excellent corrosion resistance to glass liquid under 1350℃ and produces almost no pollution to the glass liquid, so it is widely used in working tank, feeder channels, superstructures and lipstone of the high quality glass and special glass furnaces. Beta alumina block has a higher resistance to alkali vapor, thus it has excellent thermal shock resistance and does not form molten droplets. It is the best material for molter crown, port crown,feeder channel,ect.. After the oxygen-fuel technology is applied in the glass furnaces, beta alumina block replace the silica brick to be used in the crown.
Fused cast AZS block is the most widely used fused cast refractory used in the float glass furnace due to its good corrosion resistance to glass liquid and good high temperature performance. According to the content of ZrO2, fused cast AZS block can be divided into AZS 33#, 36# and 41#. According to the casting method, fused cast AZS can be categorized into PT AZS, QX AZS, ZWS AZS and WS AZS.
The crystal structure of AZS mainly consists of the eutectic crystal of Al2O3 and ZrO2, scattered baddeleyite crystal and a small amount of glass phase and pores. Its micro-structure determines its performance, while its micro-structure is up to the chemical composition, melting method and annealing method.
AZS 33# is generally used in the sidewall, the bottom paving block and the superstructure. In order to eliminate the horizontal mortar joints, large sidewall block made of QX AZS 33# is used. Due to its higher ZrO2 content and better corrosion resistance, AZS 41#, especially WS AZS 41#, is always used in the demanding areas such as the feeder corner, throat, etc..
Fused cast high zirconia block is specially designed refractory for glass furnace application. It is made of artificial synthesis high purity raw materials through special casting process. The crystalline texture consists of baddeleyite and with the characteristics of excellent high temperature and corrosion resistance, low blister and stoning potential. These advantages can prevent liquid glass from pollution effectively. It is used in sidewall, throat cover, throat support, electrode block, and dam block parts.
Zhengzhou Sunrise is a refractory material supplier from China, offering high quality refractory materials for glass furnaces, including fused cast AZS block, fused cast alumina block, fused cast high zirconia block, mullite brick, zircon brick, alumina bubble brick, magnesia brick, sillimanite brick, corundum brick, low porosity fireclay brick, high alumina brick, all kinds of glass furnace ramming masses, etc..

Compositions and Features of The Silica Brick

Silica brick belongs to acid refractories, mainly consisting of tridymite, cristobalite and a small amount of residual quartz and glass phase. It has good resistance to acid slags.
The raw material for silica brick production is silica. The silica has a high content of SiO2 and high refractoriness. The most harmful impurities are Al2O3, K2O, Na2O, etc. They can seriously reduce the refractoriness of the silica brick. Silica brick is made of silica containing more than 96% SiO2 , with addition of mineralizing agent (such as iron scales, lime) and binder (such as molasses, sulfite pulp waste), by kneading, shaping, drying and calcining.
Silica brick has a high softening temperature under load up to 1640 ~ 1670 ℃ and good volume stability in long term use. The mineralogical composition of silica brick mainly consists of tridymite and cristobalite, as well as a small amount of quartz and glass phase.
Tridymite, cristobalite and residual quartz has a big volume change due to crystal transformation at low temperatures. Therefore, the thermal stability of silica brick is poor at low temperatures. During the use, the silica brick should be heated and cooled slowly in order to avoid cracks. It should not be used in the furnaces that have rapid temperature change below 800℃.
The property and process of the silica brick is closely related to the crystal transformation of SiO2. Therefore, the true specific gravity is an important quality indicator of silica brick. Generally it should be under 2.38. For the high quality silica brick, it should be under 2.35. The low true specific gravity means the quantity of tridymite and cristobalite is high and the amount of residual quartz is small. Therefore, the residual linear expansion is small and the strength decreases.
SiO2 has seven crystalline variants and a amorphous variant. These variants can be divided into two categories. the first category include quartz, tridymite and cristobalite. Their crystal structure is very different and the transformation between them is very slow. The second category are subspecies of the variants above, α,β and γ. They have similar structures and can be transformed to each other quickly.
Zhengzhou Sunrise is a refractory material supplier from China, offering high quality refractory materials for glass furnaces, including fused cast AZS block, fused cast alumina block, fused cast high zirconia block, mullite brick, zircon brick, alumina bubble brick, magnesia brick, sillimanite brick, corundum brick, low porosity fireclay brick, high alumina brick, all kinds of glass furnace ramming masses, etc..

Refractory Selection for the Container Glass Furnace

Container glass is a type of glass for the production of glass containers, such as bottles, jars, drinkware, and bowls. With the increasing of the demand for the container glass, the quality requirement for the container glass is higher too. Refractory is one of the most important factors that affect the quality of the container glass.
Container glass is made by melting silica sand, soda ash and limestone. Various secondary ingredients are added to control color, provide ultra-violet protection and enhance the working properties of the molten glass. Container glass has a lower MgO and Na2O content than flat glass, and a higher SiO2, CaO, and Al2O3 content. Its melting temperature is up to 1580～1600℃.
The raw materials is continuously fed to a furnace where it is melted to molten glass. Molten glass is continuously withdrawn through a submerged throat where it proceeds to the refiner area of the furnace and cooled. Then the molten glass is delivered to the individual bottle-making machines via the forehearths and fed into the molds of the bottle-making machine.
Generally, container glass furnaces employ silica brick in the crown, due to its good mechanical properties at high temperature and good creep resistance. Sometimes, fused cast AZS 33# is also used in the superstructure. The drawback is the exudation of the glass phase, which will cause glass defects such as stones and stripes. Reducing the glass phase can effectively reduce the exudation of the glass phase. Fused cast AZS with a lower glass phase is developed for the use of superstructure. Fused cast alumina block is also used in the crown of the glass furnace, especially the oxygen-fuel furnace, due to its good resistance to glass liquid corrosion and alkali vapor and low blistering and stoning potential.
In the glass contact areas, fused cast AZS is used. The higher the content of ZrO2, the better the corrosion resistance. Fused cast AZS 41# is widely used in the demanding areas such as sidewalls, doghouses, throat, bottom budding, dam blocks, and electric block corners.
Fused cast AZS , alpha-beta fused cast alumina block and sintered brick are used in the channel of the container glass. Fused cast AZS has good corrosion at high temperature, but the drawback is the potential of glass defects. when the requirement of the glass is higher, alpha-beta fused cast alumina block is used. However, under 1350℃, it is recommended to use fused cast AZS.
In the regenerator, the chamber work mainly uses sintered tubular block and fused cast cross block. Basic sintered tubular block is used more widely due to stable mechanical structure and low possibility of clogging. Low porosity fireclay brick is used in the lower parts, direct-bonded magnesia brick in the middle part, 95 magnesia brick in the upper part and 97 magnesia brick or sintered AZS brick in the top part.
Zhengzhou Sunrise is a refractory material supplier from China, offering high quality refractory materials for glass furnaces, including fused cast AZS block, fused cast alumina block, fused cast high zirconia block, mullite brick, zircon brick, alumina bubble brick, magnesia brick, sillimanite brick, corundum brick, low porosity fireclay brick, high alumina brick, all kinds of glass furnace ramming masses, etc..

Refractory Selection Of The Regenerator Of The Glass Furnace

The regenerator is an important part of the glass furnace, not only deciding the lifelong of the furnace but also directly affecting the production process. The refractory selection of the regenerator are of great importance. It must be proper for both the functions of the refractories and the operating environment.
The regenerators comprise a succession of chambers forming a stack and recovering and restoring the heat in cycles. Checkers and internal separation walls function as heat exchangers, while crowns and external walls limit thermal losses. The main operating factors to be considered are temperature, repeated temperature cycling, airborne particulates, volatiles and load. Fuel and glass composition must also be taken into consideration when choosing the refractories.
A regenerator chamber is composed of a checker composed of an upper, middle and lower zone. As heat exchangers, checkers must have high thermal conductivity and good thermal shock resistance. Basic materials and fused cast refractories are the best choices. However, the operating conditions will be very different at different position within the chamber.
Fused cast refractories have no surface porosity thus they are resistant to the corrosive effects of waste gases and carryover and can be used in all the checker zones. Compared to sintered refractories they are more resistant to abrasion due to their dense and homogeneous structure.
In the upper zone of the checker, high temperature combined with batch carry over results in chemical attack and gradual degradation of the basic checkers. The atmosphere in the top zone is laden with alkali vapors. The refractories in this area must have low iron. The best choice is 97 magnesia brick, with well developed periclase crystals and a direct bonded structure. Fused cast alumina is also used for its very limited glassy phase.
The middle zone is protected by the upper checker area and temperature level is lower. The atmosphere is rich in alkali vapors, and some deposition of condensates occurs. Thus magnesia brick 96 is used. Fused cast AZS 33# can also be used. However, in term of costs, magnesia brick is a better choice.
In the lower zone, the temperature is lower, but the temperature cycles may be wide where cold incoming air enters the checker, under higher load and temperature fluctuations, with sulphuric salt erosion. Low porosity fireclay bricks or high alumina bricks can be used in non severe working conditions and 90-92 magnesia brick is recommended when firing by natural gas. Fused cast AZS 33# is also used in this zone.
The rider arches is subjected to high temperature chemical attacks by high temperature glass material dust, fuel impurities and alkaline steam. Refractories used here should have good resistance to erosion and high temperature. Traditionally high quality silica brick is used, but silica bricks have poor resistance to alkaline erosion. Sillimanite and mullite bricks are recommended. Fused AZS bricks can also be used.
Considering only creep resistance, silica brick is ideal because of its lack of glassy phase but condensation of alkali in the colder zones of the masonry would lead to corrosion, loss of mass and also holes of silica bricks. Mullite brick is also suitable for the crowns for its excellent creep resistance. Mullite bricks react with alkali and carryover to form a series of layers which prevent alkali penetrating into the bulk of the refractory and wear proceeds at a minimal rate.
The refractories used in the sidewalls and floor are usually selected from fireclay brick, high alumina brick, and silica brick.

Crystal Structure Of Fused Cast High Zirconia Block

Fused cast high zirconia block is a new type of fused cast refractory. It is specially designed refractory for glass furnace application. It features excellent corrosion resistance to molten glass due to its dense microstructure.

Fused cast refractory materials are widely used in glass furnaces to resist corrosion by the molten glass. Such a quality is especially due to the low apparent porosity of these materials. First generations of these products is fused cast AZS, which is widely applied to soda-lime furnaces. Then fused cast high zirconia block containing 90% or more of ZrO2 was developed to answer to special needs for the manufacturing of special technical glasses (LCD screens, lead crystal) and very corrosive glasses (boron-silicate glasses).

Fused cast high zirconia block is designed to operate in extreme condition and also require control of the making process. Elaborated by a fused cast process followed by a controlled cooling step, these materials exhibit specific thermal and mechanical properties.

Fused cast high zirconia bricks are made of artificial synthesis high purity raw materials through special casting process. The crystalline texture consists of baddeleyite and with the characteristics of excellent high temperature & corrosion resistance, low blister and stoning potential. These advantages can prevent liquid glass from pollution effectively.

In high zirconia fused cast refractories, the majority of the refractory crystalline structure are composed of baddeleyite crystals (ZrO2). During the cooling process, zirconia transforms successively through cubic, tetragonal and monoclinic form, with tetragonal and monoclinic forms exhibiting anisotropy in thermal expansion along their crystallographic axes. The resulting complex microstructure is made of numerous different crystallographic domains called variants. Finally, the shift from the tetragonal to the monoclinic structure is responsible for a large volume expansion which causes cracks. The manufacturing process must be rigorously controlled, in particular the cooling rate after fusion, in order to limit mechanical stresses induced by important thermal gradients and the martensitic tetragonal–monoclinic transformation of zirconia.

When heated, fused cast high zircnoia block undergoes a volume shrinkage at about 1150℃，due to the crystal transformation from monoclinic crystals to tetragonal crystals in accordance with the crystal transformation specific to baddeleyite crystals. When cooled, it undergoes a volume expansion at about 950℃ due to the crystal transformation from tetragonal crystals to monoclinic crystals. The volume expansion may cause cracking, and in an extreme case, the refractory undergoes a spalling phenomenon due to many cracks.

The transformation of the baddeleyite crystals is absorbed by a matrix glass. SiO2 is essential for forming the matrix glass. However, if the SiO2 content is too high, the corrosion resistance tends to deteriorate. The Al2O3 component plays an important role in adjusting the relation between the temperature and the viscosity of the matrix glass, and reduces the concentration of the ZrO2 component in the matrix glass.

Fused cast high zirconia brick has wide application in a wide range of super high temperature furnaces and kilns, especially special glass and high quality glass furnaces.

Special Glass Manufacturing and Fused Cast Zirconia Block

The term special glass refers to a wide range of technical glasses with highly different chemical compositions and functions which are designed for special applications. Special glass features high cost, special functions, production complexity and diversity, and technological progress.
Special glasses use highly different furnaces and manufacturing procedures. Many methods have been applied into the manufacturing process of special glass, including electric heating, high frequency induction heating, multi-crucible melting, high pressure vacuum melting, solar furnace melting, plasma flame to melt and laser melting.
New technology is the key to competitiveness and originality. The glass manufacturers require technological progress in order to stay ahead. In addition, however, to improved control over production techniques, the glass manufacturers also seeks longer furnace life and increased pull in order to lower the cost. The refractory materials are the key factor that affects the furnace life and the cost.
The manufacturing of special glass has higher requirement for refractories materials. The main refractory materials for the manufacturing of special glass are zirconia refractories. One of the zirconia refractories is fused cast high zirconia block. It is a kind of novel refractory specially developed for the glass furnaces.
Fused cast high zirconia bricks are made of artificial synthesis high purity raw materials through special casting process. The crystalline texture consists of baddeleyite and with the characteristics of excellent high temperature and corrosion resistance, and low blister and stoning potential. These advantages can prevent liquid glass from pollution effectively and reduce or avoid many glass defects caused by fused cast AZS block.
Fused cast high zirconia brick has wide application in a wide range of super high temperature furnaces and kilns in military industry, science research, high melting point Metallurgical, laser crystal and electronic,etc. It is ideal for high quality and special glass furnaces such as TV glass, Borosilicate glass, Alumina silicate glass, Halogen lighting glass, Opal glass and Fiber glass. It is usually used in sidewall, throat cover, throat support, electrode block, dam block parts of the glass furnaces.
Sunrise is a refractory material supplier from Zhengzhou, China, supplying high quality fused cast high zirconia block. Sunrise will be present at Vitrum 2015 in Milan, Italy from October 6, 2015 to October 9, 2015. Visit us at Booth U13, Hall 22.