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Это просто Вьюи блог

Дата регистрации: 13 апреля 2015 года

Персональный блог REFRACTORY — Это просто Вьюи блог

Cracks are the defect of fused cast AZS block which will seriously affect the quality of fused cast AZS and economic benefits. There are different kinds of cracks that are caused by different reasons.

According to the depth of the cracks, the cracks of fused cast AZS can be divided into surface cracks and deep cracks (or internal cracks). The surface cracks include longitudinal cracks, transverse cracks, electrical cracks and corner cracks. The deep cracks are mainly micro-cracks caused by the crystal phase transformation of baddeleyite. According to the thermal state of the melt, the cracks can also be divided into high temperature cracks and normal temperature cracks.

The cracks generally start from the corners and mainly in the edge and seldom in the center. The larger the size, the more possible to form cracks. The more complex the shape, the easier to miss angles and edges. The darker the block, the more the cracks. The cracks of fused cast AZS block are also related to its micro-structure. The denser the micro-structure, the less the cracks.

The reasons that cause the cracks are as follows:
1) During the cooling process, the temperature in the surface drops faster than in the inside, which causes a big temperature difference between the inner and outer layer. The temperature difference causes inconsistent shrinkage between the inner and outer layer, which causes the thermal stress. The thermal stress may broke the surface and cause cracks. The thermal stress is generally proportional to the temperature difference.
2) During the casting process, due to the gas, impurities or the uneven surface of the mold, the solidified shell grows unevenly in the early stage. The thermal stress concentrates in the thin parts and may cause cracks. Although the cracks can be filled with the residue, the crystals formed in those parts are vulnerable. Shrinkage of the melt when solidifying may cause cracks again.
3) The crystal phase transformation of baddeleyite can cause volume change. At 1050℃~950℃, baddeleyite is transformed from the tetragonal crystals to monoclinic crystals, which cause 9% volume expansion. The volume change and the temperature difference between the inner and outer layer produce a stress, which is the main reason of deep cracks.

Since cracks can seriously affect the quality of fused cast AZS, cracks must be avoided. Careful operation and oxidizing production can effectively reduce or avoid cracks. Sunrise offers high quality fused cast AZS block 33#, 36#, 41# for glass furnace. High purity raw material, scientific formula, advanced technology and professional guide all contribute to high quality fused cast AZS production.

The production of refractory materials for glass furnaces is quite different from the production of refractory materials for other types of furnaces. The quality of the refractory materials not only influence the quality of the glass but also the service life of the glass furnaces.

Most refractory materials for glass furnaces are large in size, which makes the manufacturing technology more complicated. The refractory materials must meet the particular requirement of the glass industry.

The glass melt can corrode the refractory materials. The refractory fragments may drop into the glass melt and cause stripes or stones in the glass. In many cases, when the refractory materials are corroded, bubbles may be formed in the glass melt near the wall. Since the viscosity of the glass melt is high and the density of the glass melt and the refractory materials is similar, the bubbles and the refractory fragments are remained in the glass melt.

The refractory materials for glass furnaces, especially the fused cast AZS, should meet the requirements as follows:
1) Sufficient mechanical strength
2) At the operating temperature, have good resistance to mechanical load
3) Have good corrosion resistance to the components of the batch materials and glass.
4) Have low potential of causing stones, stripes, bubbles and coloring.
5) Have good thermal shock resistance.
6) Have low thermal expansion at the operating temperature.
7) Have accurate shape and size and meet the technical criteria.

Sunrise is a refractory material supplier for glass furnaces from China. We provide various refractory materials for glass furnaces, including fused cast AZS, fused cast alumina block, silica brick, zirconia brick, high alumina brick, silicate brick, etc..

Fused cast AZS is made of pure alumina powder and zircon sand(65% ZirO2, 34% SiO2). Its main crystal phase consists of corundum, baddeleyite and glass phase. The use of fused cast AZS expands the life of glass furnaces.

The life of glass furnaces can be expanded from 11-15 months to 3-4years, even longer. The melting temperature of the glass can be increased from 1450 ℃ to 1550 ℃, even up to 1600 ℃. The glass defects are reduced and the quality of glass is improved. The production capacity of the glass furnace can be increased by 20-30%.

The damage of fused cast AZS is mainly caused by chemical attack and thermal stress. The quality and property of fused cast AZS plays a remarkable influence on the life of glass furnaces and quality of glass. The use of poor quality bricks will not only result in frequent shutdown and repair, limiting melting temperature and reducing the furnace production, but also shorten the life of furnaces, cause glass defects (stripes, stones, etc.) and reduce the quality of the glass.

When selecting the size of fused cast AZS, the furnace design principles and the producing conditions of fused cast AZS must be taken into account. When the dimension is too big, it tends to crack and will increase the difficulty of packaging, transport and masonry. For the shaped brick, the feasibility of each production procedure and the specialty of the casting method should be taken into account.

The corner brick, dam block, bubble brick and doghouse always employ the fused cat AZS block 41#. The gaps between bricks should be less than 0.5mm. The bottom of the brick should not have voids. The brick should not contains too many impurities. If the color of the brick is blue, there may be too much C in the brick. The cutting will directly determine the degree of convergence during masonry. The smaller the gaps are, the longer the life of the glass furnace is.

Sunrise offers different types of fused cast AZS block, including AZS 33#, AZS 36# and AZS 41#. Our fused cast AZS block is made of high quality raw materials and advanced technology. It has been widely used in the glass furnaces and improves the life of glass furnaces effectively.

The fused cast AZS block is widely used in the sidewall in the glass furnaces. The service life of the fused cast AZS sidewall block determines the campaign life of the glass furnaces. So, it is important to prolong the service life of fused cast AZS sidewall block.

How to decrease the corrosion rate of sidewall blocks and improve the corrosion resistance is the key to prolong the service life of sidewall blocks. It is well-known that controlling the operation temperature is one of the effective approaches to prolong the service life of refractory blocks. In different areas and different periods, different cooling methods should be adopted to achieve the desired the results.

In the top parts of the sidewall where are not insulated. In horseshoe flame glass furnaces, as the flame is heating in the surface of glass melt, the temperature of the upper parts of the glass melt is higher than that of the lower parts. Silicate is formed and the refining of glass melt produces a lot of bubbles. Heat convection is very severe here. As a result, the corrosion rate of is bigger there. To solve this problem, it is necessary to select and design the cooling fan reasonably. The cooling should be started slowly at first and then increases gradually to reduce or avoid the thermal stress caused by temperature gradient.

The service life of fused cast AZS block lasts about 3-5 years. During the preheating of the glass furnaces, cracks may be formed. After 2-year operation, there will be holes in the body of the brick. Glass melt may exude though the holes and cracks. To solve these problems, a single-point, focused and forced air cooling method can be adopted, which can crease the viscosity and reduce the temperature of the bricks.

Some special parts of the melting zone is corroded at the fastest rate and not easy to repair. Due to strong mechanical erosion, the glass furnace can just be used for 2.5 years before cold repair. Air and spray mixed cooling method can be adopted here. It is easy, stable and effective. It avoids the problems caused by the water cooling method.

Shower cooling method is mainly used in the middle and upper parts in the later period of the glass furnace campaign. 3 years after the cold repair, the problem of glass melt exudation may occur in these areas. As there are layers of insulating materials here, forced air cooling and water cooling method can not be used here. Compared to other methods, shower cooling method is more suitable for this parts.

Sunrise offers various high quality refractory materials for glass furnaces, including fused cast AZS, fused cast alumina block, zirconia block, mullite block, silica block, magnesia block, etc..

Fused cast AZS block is the most widely used refractory material in the demanding areas. It is thought as the leading cause of knot and cord defects. Fused cast AZS exudation in glass contact is the main cause of impaired performance of AZS under particular working conditions.

The main crystal phase of Fused cast AZS consists of corundum, baddeleyite and glass phase. The glass phase can reduce the expansion or shrinkage of ZrO2 within the above temperature range and prevent cracking. However, the glass phase is easy to be corroded and cause corrosion of the fused cast AZS and glass defects.

Fused cast AZS exudation exhibits a shiny "wet looking" appearance at the surface of blocks during heat-up process and beginning of a furnace campaign. This situation tends to stabilize all along the campaign life, with a generally moderate dripping of a viscous glassy phase into the smelted glass.

Fused cast AZS exudation at high temperatures, can lead to the formation of defects in the glass, especially during furnace start-up. It is only a short-term cause of glass defects. Fused cast AZS exudation from a glass contact surface is not very visible than that in the superstructure.

In the glass furnaces, a portion of the glass phase of fused cast AZS block exudes onto the superstructure surface during furnace heat-up, until the furnace has achieved stable temperature profile. The exuded glass, often containing small zirconia crystals, tends to run down into the glass bath. This is a major concern to glass producers since this glassy phase often causes defects, such as viscous knots and stones.

To solve this problem, low exudation fused cast AZS has been developed. With modification of chemical compositions and glass phase, it offers low exudation level and maintains all other positive characteristics of fused cast AZS.

Sunrise offers various refractory materials for glass furnaces including fused cast AZS, silica brick, fireclay brick, high alumina brick, silimanite brick, mullite brick, etc..

Fused cast alumina block is made of pure alumina powder(>95%) and a small amount of additions (soda sand and quartz sand). There are commercially 3 types of fused cast alumina blocks: Beta fused cast alumina block, Alpha-beta Fused cast Alumina Block and Alpha fused cast alumina block.

The manufacturing process of fused cast alumina block includes mixing the raw material, melting it in the electric furnace, casting, annealing, machining and then getting the final products. First melt the raw materials in an electric arc furnace. When the material has become molten and its chemical and physical characteristics have been adjusted to the desired condition, pour the molten material into a mold. Then the cast product is processed with machines into the final product.

Alpha-beta Fused cast Alumina Block is formed by the compact structure of alpha alumina and beta alumina crystals in a most ideal proportion which is approximately 50% and 50% respectively, where intertwined crystals of both materials result in a very dense structure. Below 1350 ℃, it has excellent corrosion resistance against molten glass and great performance against contamination to molten glass, thus it is very suitable for paving blocks and fore-hearth channel blocks. When in contact with molten glass, it barely produces any blistering or stones. So, it may be widely used in working tank, feeder channels, superstructures and lipstone, etc. In soda-lime container furnaces, it is installed in the Alcove and channel areas, as alternative to fused cast AZS for Alcoves and as alternative to fused cast AZS, zirmul, sinter-alumina and other sinter refractories for channels.

Beta fused cast alumina block comprises of a majority of beta alumina crystals and a slight portion of alpha alumina crystals in compact structure. Moreover, the intersected texture of large beta-alumina ensures great dimensional stability and great resistance against spalling. Its property of base saturation enables 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. Its neutrality against soda vapors makes it the best choice for the downstream part of superstructures in demanding applications.

Alpha fused cast alumina block is an ideal product for the lower temperature zones of the glass melting furnaces due to its high density, superior corrosion resistance and low blister potential. It is also an ideal material for Metallurgical Titanium Furnace because the superior thermal stability.

Sunrise provides high quality fused cast alumina block at a competitive price. It can be widely used in glass furnaces and improve the service life of glass furnaces effectively.

The interaction of glass melts and refractories in glass furnaces has a large impact on the resulting glass quality. The mostly applied type of refractory in the glass industry, in direct contact with the glass melt, is fused cast AZS. Due to the interaction of the glass melt with fused cast AZS, glass defects like stones, knots and bubbles can be generated.

Fused cast AZS block exudation is thought as the leading cause of knot and cord defects. Fused cast AZS exudation is only a short-term source of glass defects. Fused cast AZS corrosion is a more potent and long-term source of defects. Glass melt contact refractory corrosion can lessen with time due to boundary layer formation and the effect of external cooling at the metal line.

Fused cast AZS block has no open porosity but there are some closed voids and pores which arise from the manufacturing process. These pores are filled with gases. The gases in these pores have an air like composition, with nitrogen and oxygen as main components and some carbon dioxide. When fused cast AZS is in contact with glass, it reacts with the glass melt and slowly dissolves in this melt. The closed pores will be opened and then release their gas content, forming bubbles.

Impurities, which can oxidize, are for example elemental carbon originating from graphite electrodes of the fused casting operation, sulfur or zirconium carbide originating from raw materials of the AZS. The dissociation and oxidation of nitrides, oxynitrides, produced by reactions with the graphite electrodes during melting of the AZS, could give nitrogen gas.

When fused cast AZS block is brought into contact with a glass melt, an electrical potential is generated between the refractory and the glass melt because generally no thermodynamic equilibrium exists between these materials. The electromotive force (emf) generated between glass melt and refractory interior can cause the formation of oxygen bubbles.

The generation of a knot is due to one or more forces, which drive the fused cast AZS glass phase towards the refractory surface and into the bulk of the glass melt. Those forces can be caused by gravity, thermal expansion of zirconia and gas formation.

Glass defects are typically unavoidable, but their occurrence must be minimized during the production of high-quality glasses. Some alternatives, such as fused cast AZS with modified chemistry and glassy phase and alpha-beta fused cast alumina block are used to replace fused cast AZS to reduce the glass defects and improve the glass quality.

Modern glass furnace refractories requirements for increasingly harsh, long life, low emission glass liquid in the glass melting furnace refractories amount is growing. Different parts of the furnaces may require different refractories.

The crown of glass furnace is always operated at 1600℃. It is exposed to the conditions of high temperature, erosion of high temperature alkali vapor and batch dusts, and load. In this part, silica brick is typically used as they provide good resistance to creep and good mechanical strength at the operating temperature. In the Oxy-fuel glass furnaces, fused cast alumina block is also used as it has higher corrosion resistance to alkali vapor.

Since Zircon exhibits very low thermal losses and does not react readily with glass liquid, fused cast AZS block is probably the most used refractory in contact with the melted glass. In the working tank, the temperature is low and mild but refractories influence the quality of glass. Fused cast AZS block is preferred since they possess higher corrosion resistance to glass liquid.

The throat being the narrow path connecting the melter and the working tank, where the temperature is high and witnesses a rapid glass stream, it is subject to severe erosion. Here fused cast AZS block 41# is used.

For the glass contact parts of the sidewall, fused cast AZS block and fused cast alumina block are used. Both have good corrosion resistance to glass liquid and cause almost no pollution to glass liquid. As fused cast alumina block is not stable at high temperature and has better corrosion resistance under 1350℃, it is always used in the sidewall of cooling zone.

In the breast wall where is not in direct contact with glass liquid and exposed to alkali vapor and batch dusts, corundum block and silica brick are used.

The Magnesia bricks are mainly used as checker bricks of the regenerator. The checker bricks are working in conditions of air and coal gas, oxidation and revivification reaction, high temperature changes and condensation of alkali smoke. So the checker brick which is made of alkali refractory materials is the best choice to work for such atmosphere. High alumina bricks and fireclay bricks are also used in this parts in some cases.

Sunrise Refractory offers all kinds of refractories for glass furnaces including fused cast AZS, fused cast alumina block, silica brick, magnesia brick, etc..

Alumina is available in many crystal phases (α, β, etc.). According to the crystal phases of fused cast alumina block, it can be divided into α-β fused cast alumina block, α fused cast alumina block and β fused cast alumina block.

Fused cast alumina block is made of pure alumina powder(>95%) and a small amount of additions (soda sand and quartz sand). The mixed materials are melt in the three-phase industrial arc furnace at 2300℃. Thereafter the melt liquid is cast into the mold. After cooling and annealing, the cast product is cut is processed into the final product.

α-β fused cast alumina block is formed by the compact structure of α alumina and β alumina crystals in a most ideal proportion which is approximately 50% and 50% respectively, where intertwined crystals of both materials result in a very dense structure. Below 1350 ℃, it has excellent corrosion resistance against molten glass and great performance against contamination to molten glass. When in contact with molten glass, it barely produces any blistering or stones. It also presents good corrosion resistance to alkali vapor. α-β fused cast alumina block may be widely used in working tank, feeder channels, superstructures and lipstone, etc.

α fused cast alumina block comprises of a majority of α alumina crystals and a slight portion of β alumina crystals in compact structure. It has good corrosion resistance to molten glass and good wear resistance, but it is sensitive to thermal shock. It is an ideal product for the lower temperature zones of the glass melting furnaces due to its high density, superior corrosion resistance and low blister potential. It is also an ideal material for Metallurgical Titanium Furnace because the superior thermal stability.

β fused cast alumina block comprises of a majority of β alumina crystals and a slight portion of α alumina crystals in compact structure. Moreover, the intersected texture of large β-alumina ensures great dimensional stability and great resistance against spalling. Its property of base saturation enables a higher resistance to alkali vapor, thus it has excellent thermal shock resistance and does not form molten droplets. However, it is easy to form Nepheline(Na2O·Al2O3·2SiO2) with SiO2. It can be transformed into α alumina under reducing atmosphere and is easy to crack due to volume expansion. It has better corrosion resistance to molten glass than α fused cast alumina block under oxidizing atmosphere. It is the best material for molter crown, port crown, feeder channel, ect.

Sunrise offers high quality α-β fused cast alumina block, α fused cast alumina block and β fused cast alumina block available in different shapes and sizes.

Aluminium Oxide or alumina (Al2O3) is one of the most versatile of refractory ceramic oxides and finds use in a wide range of applications. Alumina refractories are the part of alumina- silica group of refractories. Different from fire clay refractories, high Alumina refractories normally have Al2O3 content of more than 45%.

The raw material base for these refractories are different than the fire clay bricks. For the production of high Al2O3 refractories, both natural raw materials (such as kyanite, sillimanite, andalusite, and bauxite etc.) as well as synthetic materials (sintered mullite, fused mullite, calcined alumina, sintered corundum, and fused corundum etc,) are used.

Alumina (Al2O3) has the physical stability such as melting temperature, hardness, resistance to abrasion, and high mechanical strength. The material has the same chemical composition but have a different crystal structure which is α- Al2O3, β-Al2O3 and γ- Al2O3. The melting point, refractoriness, corrosion resistance and strength of alumina refractories increase with the increase in the Al2O3 content.

Based on the content of alumina, high alumina refractory is classified into 50%, 60%, 70%, 80%, 85%, 90% and 99%.

Refractories with 90 % and 99 % Al2O3 are among the highest strength and erosion resistant refractories. They can be used for temperatures greater than 1800℃。The most widely used alumina refractory with more than 90% Al2O3 content used in glass furnaces is Fused cast Alumina Block and Alumina Bubble block. There are three types of Fused cast Alumina Block: α Alumina, β Alumina and α-β Alumina. Fused cast Alumina Block α Alumina is an ideal product for the lower temperature zones of the glass melting furnaces due to its high density, superior corrosion resistance and low blister potential. β Alumina is the best material for molter crown, port crown, and feeder channel due to its high resistance to alkali vapor and excellent thermal shock resistance. α-β Alumina is widely used in working tank, feeder channels, superstructures and lipstone due to its excellent corrosion resistance against molten glass and no contamination to molten glass under 1350 ℃. Alumina Bubble block has low bulk density, excellent insulating properties and high hot strengths. These features make it an excellent insulating material that can withstand exceptionally high temperatures. It is always used as back-up insulation behind other refractories.

High alumina refractory with about 70% Al2O3 contains mullite as a major phase. It is made of bauxite. It can be used for temperatures greater than 1750℃. Mullite brick and high alumina brick belong to this group. Mullite brick is characterized by good high temperature resistance and good thermal shock resistance, which comes into being mullite through calcine with clay, high alumina materials and ceramics. It is mainly used in fibrous glass furnace. High alumina brick is made of high-quality bauxite clicker. It features high chemical corrosion resistance and high refractoriness. It is usually used in hot areas in glass melting tanks without glass contact.

Refractories containing 50 % and 60 % Al2O3 exhibit improved refractoriness over fireclay products. High alumina insulating brick is a new type of lightweight insulating material which contains approximately 48% alumina, mullite and glass phase or corundum. It has advantages such as high porosity, small volume density, good insulation effect, high mechanical intensity, small thermal conductivity and long service life. It is widely used in insulating layers of glass furnaces. Sillimanite brick is a kind of refractoriness which made by sillimanite and other minerals. And silimanite can be transformed to be mullite under more 1500℃ high temperature. It is mainly used in rider arches, forehearth and bushing for fiber glass furnaces.

Sunrise supplies all kinds of alumina refractories including fused cast alumina block, Alumina Bubble block, Mullite brick, High alumina brick, High alumina insulating brick, sillimanite brick, etc..

In recent years, fused cast high zirconia block is introduced to decrease the number of glass defects and increase the corrosion resistance of refractories for high quality glasses and special glasses, due to its excellent corrosion resistance and no pollution to glass.

Fused cast high zirconia block is developed to operate in extreme condition and also require control of the making process. It is made of artificial synthesis high purity raw materials through special casting process.

The high zirconia fused cast refractory has a structure in which grain boundaries of relatively coarse baddeleyite crystals are filled with a matrix glass mainly composed of SiO2, Al2O3 and ZrO2 and contains a small amount of Na2O and/or K2O.

ZrO2 adopts a monoclinic crystal structure at room temperature and transitions to tetragonal and cubic at higher temperatures. The larger the content of the ZrO2 component in the refractory, the higher the corrosion resistance against molten glass.

However, when the content of ZrO2 is too much, it becomes difficult to obtain a fused cast refractory having no cracks by casting. When the zirconia crystals undergo reversible transformation between monoclinic crystals and tetragonal crystals, a rapid volume change will happen at a temperature from 1,000℃ to 1,150℃. As a result, fused cast high zirconia block is more difficult than fused cast AZS, as the volume expansion rate may cause cracks and a spalling phenomenon. The stress caused by the volume change can be absorbed by glass phase. So the SiO2 component is an essential component to avoid cracking.

The Al2O3 component plays an important role in adjusting the relation between the temperature and the viscosity of the matrix glass and provides an effect of reducing the concentration of the ZrO2 component dissolved in the matrix glass. By utilizing this effect of the Al2O3 component, it is possible to prevent precipitation of zircon in the matrix glass and to prevent the change in quality of the matrix glass, whereby it is possible to avoid the chipping off phenomenon of the refractory and cracking due to an accumulation of remaining volume increase.

Na2O and/or K2O provides a function of softening glass. They are important components which influence the viscosity of the matrix glass and also have an effect of controlling the concentration of the ZrO2 component to some extent.

Fused cast high zirconia block 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. Sunrise Refractory offers fused cast high zirconia block TY-Z88-WS and TY-Z95-WS, and are used in sidewall, throat cover, throat support, electrode block, dam block parts.

Float glass furnaces are used to make flat toughened glass which is widely used in the fields of architecture, decoration, furniture, electronic apparatus, vehicles, ships, aviation, and more. Float glass furnaces consist of three main parts, the melter, refiner and regenerators or checkers.

The Melter is a rectangular basin in which the actual melting and fining (seed removal) takes place. In a side-fired furnace, the batch is charged into the furnace through the doghouse, which is an extension of the melter, protruding from the back wall. Along each side of the melter, above glass level, are three to seven ports, which contain the natural gas burners and direct the combustion air and exhaust gases.

In the melter zone, due to its high temperature and severe corrosion, fused cast AZS block 41# and 36# are used in the sidewall, electrode block, bubbling block and other glass contact areas. Fused cast alumina block and fused cast high zirconia block are also use in the glass contact areas for special glass furnaces.

The melter basin is separated from the refiner by the bridge wall (throat end wall). Glass passes from the melter to the refiner through the throat, which is a water-cooled tunnel that extends through the bridge wall. The throat is always subjected to strong attack and severe corrosion, so fused cast AZS block 41# and 36# are used here.

The Refiner acts as a holding basin where the glass is allowed to cool to a uniform temperature before entering the forehearths. The melter and refiner are covered by crowns to contain the heat. In the refiner zone, the temperature is lower and the wear and corrosion is not so severe, so fused cast AZS block 33# is used here.

The regenerators consist of two chambers, each of which is filled with a network of refractories, referred to as the packing. Regenerator chambers are normally vertical constructions in which the waste gases pass downwards, whilst the combustion air travels upwards. There are various forms of regenerator packing, but only two are now widely used. Both designs utilise specially shaped blocks, cross-shapes for the cruciform system, and square section tube shapes for the chimney block system.

The top courses of regenerator checkerwork are subjected to high temperature and severe attack and magnesia block is employed here. In the middle courses, as the temperature is lower, magnesia block with lower content of MgO is used here. In the lower courses, as the atmosphere is not quite severe, fireclay brick is always used here as an economic choice.

Sunrise Refractory is a refractory supplier from China, specializing in all types of refractory materials used in glass making. The main products are as follows: fused cast AZS, mullite brick, zircon brick, alumina bubble brick, sillimanite brick, corundum brick, fireclay brick, high alumina brick, ramming masses, insulating materials, etc.

In the past, wear of superstructure refractories, primarily silica crowns, is probably the most serious concern. Fused cast AZS block has been suggested as an alternative to the traditional silica crown as it has good corrosion against and can slow the wear of superstructure and improve the life of the furnaces.

Superstructure and crown refractories are subjected to corrosive reactions with the vapor species of the batch components and batch carryover. In the melting of soda-lime glasses, the vapor species are primarily soda and sodium sulfates. For borosilicate glasses, Na-tetraborate and B2O3 predominate. Direct attack occurs by condensation of the hot face of the refractory. The chemical changes in this reaction zone result in mechanical stresses and flaking, peeling or spalling of the hot face. Vapor penetration into joints with subsequent condensation and corrosion lowers the mechanical integrity of the superstructure or crown.

Corrosion phenomenon in superstructure have environmental and intrinsic causes. Heavy metals from fossil fuels, volatile component of the glass can reach the refractory surface as vapors, but the most severe attack can be caused by silica, reaching the surface as dust. Silica reacts easily with the corundum crystals of the fused cast AZS and, with the contribution of refractory's soda, produce sodium-alumina-silicates, pealing off the external layer of refractory, exposing deeper layers to corrosion and so forth.

Fused cast AZS block is not exposed to peculiar environmental attack. In some case, due to recurrent thermal cycling and subsequent multiple exudation, the refractory is losing very significant amounts of glassy phase, extruded with a gas-driven mechanism, replacing it with increasing amounts of closed porosity. When this happens, in relatively deep zone under the hot face there is formation of mullite by reaction of silica of the glassy phase and corundum crystals; while minor amounts of alkaline glassy phase are extruded, the increasingly acidic refractory structure undergo progressive mullitization. Volumetric changes and depletion of the liquid phase necessary to absorb the thermal dilatation of crystalline components are concurrent causes of possible cracking and deep spalling of surface, as a consequence of intrinsic corrosion subsequent to exudation.

At temperatures above 1475 ℃, the bond strength between the embedded ZrO2 crystals and the alumina is reduced, attributed to the variation in the thermal expansion characteristics of A12O3 and ZrO2.

While the wear of fused cast AZS block in the superstructure has been a potent and long-term source of glass defects, it is proved a longer service life as superstructure refractories in glass melting furnaces and other similar applications, it still encounters wear in the superstructure.

Fused cast alumina block is mainly composed of Al2O3 whose contents is more than 94 percent. It is produced by melting and casting high purity alumina in electric furnace at 2000℃.

The producing process of fused cast alumina block includes mixing the raw material, melting it in the electric furnace, casting, annealing, machining and then getting the final products.

In the manufacturing process of fused cast alumina blocks, first melt the raw materials in an electric arc furnace. When the material has become molten and its chemical and physical characteristics have been adjusted to the desired condition, pour the molten material into a mold.

The mold is commonly made of graphite or other suitable materials. The mold is provided with a riser or header of ample size to enable complete filling of the mold without interference by material freezing in the headers. The cast material is left in its respective mold for heat treatment, or removed from the mold after the outer walls of the casting have solidified and then annealed without other than its own support. The cast parts are generally packed closer together, thereby allowing them to anneal by virtue of their own heat.

After the blocks have cooled, similar to fused cast AZS block, the cast parts are inspected and finished by diamond cutting and/or grinding. The header may be removed shortly after casting or after annealing. The amount of material in the header is often about equal to the amount of material in the desired finished refractory piece. Header material is commonly recycled, but at considerable expense.

Fused cast alumina block has excellent endurance to strong alkali. Under 1350℃, it has strong corrosion resistance and almost does not contaminate to glass melting liquid. Because it does not contain impurities such as Fe2O3 and TiO2, when it comes into contact with glass liquid, air bubbles are rarely found. Therefore, this product has the special characteristic of minimizing contamination to glass liquid.

Sunrise Refractory offers high quality fused cast alumina block including fused cast alpha alumina block, fused cast beta alumina block and fused cast alpha-beta alumina block at competitive prices.

The crown of an oxygen fuel glass furnace is exposed to the conditions of erosion of high temperature alkali vapor and batch dusts, and load. A better high temperature creep resistance is key for the crown blocks of the Oxy-fuel glass furnaces. Fused cast alumina block has been now used as crown refractories in oxy-fuel furnaces for several years.

Oxy-fuel technology involves the replacement of the combustion air with oxygen (>90 % purity). The technique can be used with either natural gas or oil as the fuel, although the use of gas is more common. In the glass industry, oxy-fuel technology offers advantages including increased productivity, noise reduction, reduced melting times, and glass quality improvements. However, it may increase refractory wear, which may affect the product quality by increasing silica corrosion at the crown of the furnace, and decrease furnace life, oxygen production costs, and potential problems related to conversions from regenerative furnaces.

Fused cast alumina block for crown application in glass industry is commercially available in two types, alpha-beta and beta alumina. Fused cast alumina blocks have high refractoriness, spall resistance, and low levels of porosity and possess low levels of glassy phase in their structure, making them less susceptible to deformation by the mechanisms of creep.

Due to their high thermal conductivity, heat flow through a furnace crown composed of fused cast alumina is higher than through traditional silica crowns, affecting back-up insulation designs and cooling methods employed on the exterior of the furnace.

In conventional(air-fuel-fired) furnaces, alpha-beta alumina has been used primarily in glass contact applications in applied exclusively in superstructure application. In oxy-fuel furnaces both types of refractories have been used for crown and superstructure applications. The alpha-beta alumina blocks have been exposed to a much wider range of temperature, stress(span), atmospheric chemistry, and length of campaign than beta alumina blocks. Fused cast Alpha-beta alumina block has been used for oxy-fuel furnaces crowns in specialty, float and container glass furnaces.

Sunrise Refractory offers different type of fused cast Alumina blocks which are made with high-purity raw materials and advanced technology. They are ideal refractory materials for different types of glass furnaces including oxy-fuel glass furnaces.

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