refractory

The micro-structure of fused cast AZS block has a big effect on the properties and performance of fused cast AZS block. The main crystal phase of fused cast AZS consists of corundum, baddeleyite and glass phase.

Generally, corundum and baddeleyite exist in eutectic crystals, which contribute greatly to the stable structure of fused cast AZS block. Some products may contain mullite which has bad effect on the performance of AZS. With the presence of mullite in the boundary of ZrO2 crystals, glass phase cannot fully absorb the stress caused by the volume expansion due to crystalline transformation, which may result in cracks.

After the fused cast AZS molten is cast into the mold, it must be subjected to thermal annealing to make the molten crystallized slowly. Since the sidewall and the central region are cooling at different speed, the surface is cooling faster and first forms a layer with uniform fine grain structure, which is called dense layer. The chemical composition of the dense layer is substantially the chemical composition of the original design and the main crystal phase is C+Z.

Along the sidewall to the center of the mold, the cooling speed gradually slows and forms the slow cooling layer. Baddeleyite first separates out in the form of primary crystals and is precipitated and enriched by gravity to form the zirconia-rich layer. Finally as the residual liquid phase of the melt is concentrated, it separates out as stacked and oriented eutectic crystals. Thus, along the solidification temperature gradient, different layers have different chemical composition and phase composition, resulting in segregation of the main phase. The higher the ZrO2 content, the larger the size, the more remarkable the segregation.

Although the chemical compositions of fused cast AZS from different manufacturers are similar, the micro-structure can be quite different. The differences between the micro-structures of AZS are mainly owed to the cooling and annealing rate. Lower cooling and annealing rate will cause the enrichment or separation of minerals in some regions and the decrease of corundum and baddeleyite eutectic crystals. Therefore, an appropriate increase in cooling and annealing rate is the key to obtain fused cast AZS blocks with even component distribution, reasonable crystal size and excellent performance.

In the fused cast AZS, ZrO2 has the best corrosion resistance. The increase of ZrO2 content can improve the corrosion resistance. However, the increase of the corrosion resistance is not proportional to the content of ZrO2, as it will increase the difficulty of manufacturing and has a bad effect on the performance of fused cast AZS.

Zhengzhou Sunrise is a refractory material supplier from China, offering high quality refractory materials for glass fuaces, 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 fuace ramming masses, etc..

Refractories are the main materials used in the glass fuaces and have big influence on the service life of glass fuaces, 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 fuaces. The larger the scale of glass fuaces is, the bigger the production capacity is. The quality and accuracy of refractories has direct influence on the scale of glass fuaces. 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 fuaces, the quality of glass required and the production capacity, different refractories are selected. So far, refractories for the glass industry, especially the float glass fuaces, 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 fuaces 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 fuaces, Electronic glass fuaces, household glass fuaces, and pharmaceutical glass fuaces. 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 fuaces, especially in the crown and superstructure. The quality of glass fuaces will affect the normal operation and service life of glass fuaces.

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.

Zhengzhou Sunrise is a refractory material supplier from China, offering high quality refractory materials for glass fuaces, 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 fuace ramming masses, etc..

Fused cast refractory is a special type of refractory made by melting the raw materials in the electric arc fuace, 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 fuace.

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 fuaces. 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 fuaces, 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 fuace 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 coer, throat, etc..

Fused cast high zirconia block is specially designed refractory for glass fuace 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 fuaces, 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 fuace ramming masses, etc..

The popular type of fuace used for the production of E glass is the unit fuace. More than 10 kinds of refractories are used to build to the fuace.

Fused cast AZS block

Fused cast AZS 33# is mainly used in the buer block of the melting zone and the feeder block.

Dense chromium oxide brick

Dense chromium oxide brick has the best resistance to the corrosion by E glass. It almost causes no pollution to the glass liquid. It is ideal for the E glass fuace. It is made by isostatic pressing. It has a very dense structure. It contains more than 94% Cr2O3 and less than 15% pores and its bulk density is 4.24g/cm3. Its erosion loss is only 1/10 of that of the dense zircon brick. It is mainly used in the high temperature glass-contact areas, such as the sidewall and the tank bottom of the melting zone and the sidewall of the main channel and transition channel.

Dense zircon brick

The resistance of Dense zircon brick to high temperature and E glass is not as good as dense chromium oxide brick. It is made by isostatic pressing too. It contains more than 65% ZrO2 and less than 2.0% pores and its bulk density is 4.25g/cm3. If the operating temperature exceeds 1370℃, it will be eroded. It is mainly used as the bottom block in the lower temperature parts of the melting zone and the forming channel and transition channel, flow block and back-up block.

Zircon brick

Zircon brick contains 66% ZrO2 and its bulk density is 3.7g/cm3. It has good thermal stability and good creep resistance. Its is the sidewall and breast wall of the feeder port where the erosion of batches is severe, peep hole and the breast wall, crown and buer of the flame space of the channel.

Sintered mullite brick

Sintered mullite brick contains more than 74% Al2O3;2.2% SiO2 and its bulk density is 2.5g/cm3. It is generally used as the back-up brick of the zircon brick, the breast wall and front wall of the melting zone, the lining brick of the flue of the channel, the foot parts of the crown and the outside layer of the discharging port

There is another type of mullite brick which is made by melting the raw materials first to form mullite crystals and then sintering it. It has better resistance to creep and thermal shock than mullite brick. It can be used in the crown and the breast wall of the flame space.

Fused cast mullite brick

Fused cast mullite brick is made of the bauxite, high quality alumina powder and clay by the fused cast method. It is mainly used in the flue.

Fused chrome corundum brick

Fused chrome corundum brick contains 28.3% Cr2O3, 58.3% Al2O3, and 5.2% MgO and Fe2O3. Its bulk density is 3.4g/cm3. It is used as the flue interface brick of the heat exchanger.

Besides the refractories mentioned above, difference types of fireclay brick and insulation brick are used in the outside layer of the fuace.

The need of the glass manufacturers to maintain and improve the quality of glass and expand the service life of the glass fuace and the impact and influence of the oxygen-fuel combustion technology, promote the improvement of refractories and development of the new refractories.

Fused cast alumina block has been widely used in the crown of the oxygen-fuel fuace, especially when manufacturing high quality glass. Before the application of the oxygen-fuel combustion technology, only β alumina block is used in the superstructure of the melting fuace. Now both β fused cast alumina block and α-β fused cast alumina block can be used in the crown of the oxygen-fuel fuace for producing TV glass, float glass and borosilicate glass.

Fused cast AZS block has been successfully used in the crown for many years. It can be used at 1600℃ or 1650℃ and can withstand the cycle of cooling and heating well. Compared to fused cast AZS, fused cast alumina block can be used at 1700℃ and has better mechanical strength and thermal stability.

In the past, high chromium brick was mainly used for the production of reinforced glass and sometimes in the insulation glass fuace. Now it is increasingly used in some soda-lime glass fuaces. It has much better corrosion resistance to glass and can prolong the service life of throat. Besides the throat, it is also used in the end wall, the angle brick of the feeder port. However, the chromium may color the glass liquid, thus it can not be used in the white glass fuace. It was primarily used in the colored glass fuace, but now it has been successfully used in the transparent container glass fuace.

Low glass phase fused cast AZS block has been successfully used in the superstructure. The development of the oxygen-fuel combustion technology makes it find wider application in the superstructure. Since it contains a low amount of glass phase, it has better creep resistance and the amount of exuded glass phase has been reduced to a very low level.

Fused cast high zirconia block is a new type of refractory, mainly used in the glass contact areas in high quality glass fuace. It has a low potential of causing stones, knots and bubbles and can effectively reduce glass defects. It is also in some low alkali glass or hard borosilicate glass fuaces.

Zhengzhou Sunrise is a refractory material supplier from China, offering high quality refractory materials for glass fuaces, 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 fuace ramming masses, etc..

The quality of fused cast AZS block is related to many factors such as the chemical composition of raw materials, the melting process, the casting process and the annealing process. One of the main quality problems of the fused cast AZS block is cracking.

Fused cast AZS block is mainly composed of baddeleyite, corundum, and a small amount of mullite, glass phase and pores. When the Al2O3 content of the raw materials exceeds 30%, the raw materials is difficult to melt and the cracking rate will increase. So before feeding the raw materials into the fuaces, the Al2O3 content must be measured to ensure it does not exceed 30%.

The way of feeding will directly affect the melting. Once feeding all the raw materials may cause incomplete melting and the products will be easy to crack. Feeding small quantities repeatedly is better.

If the melting temperature is too high or low, the cracking rate will increase too. Melting the raw materials at the melting temperature and then increasing the temperature can reduce the cracking rate.

In order to reduce the residual thermal stress and avoid crack, there should be a certain amount of glass phase in the fused cast AZS to absorb the thermal stress. However, the glass phase is the weak point for the corrosion resistance of fused cast AZS. During the corrosion process, the glass phase is exuded first and replaced with the high temperature molten glass. Bubbles are released accompanying the exudation of the glass phase and pollute the glass. Fused cast AZS block (33#, 36# and 41#) contains 14-20% glass phase, thus the glass phase content has a big effect on its quality.

During the casting process, if the casting temperature is too high, the shrinkage rate and the temperature difference between the inside and outside increase and the products are easy to crack. Before casting, stop heating for 3-5 minutes to cool the molten glass to the casting temperature and then cast, which can greatly reduce the cracking rate.

During the annealing and cooling process, the casting products should be put in the insulating box. The initial temperature should not be too low. Then cool the products slowly. The crack rate can be reduced.

Zhengzhou Sunrise is a refractory material supplier from China, offering high quality refractory materials for glass fuaces, 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 fuace ramming masses, etc..

Alumina (Al2O3) refractories are the part of alumina- silica group of refractories. They differs from fireclay refractories in term of Al2O3 content and normally have Al2O3 content of more than 45 %. The raw material base for these refractories are different than the fire clay bricks.

As the Al2O3 content is increased, the melting point of the refractory increases to a maximum of 2054℃ which is the melting point of pure corundum. Refractoriness increases with the increase in the Al2O3 content. The only stable compound in the system is mullite, which has a defective space lattice and decomposes into corundum and liquid phase at around 1840℃.

According to the Al2O3 content, alumina refractories can be divided into:

Al2O3 less than 50%

Fireclay belongs to this group. Its main crystal phases are mullite and glass. It can contain free SiO2. Normally it is made from 100% fireclay. High quality fireclay is used at about 1600℃,  Usually it contain 38 % to 42 % Al2O3 and are based on fireclay minerals.

Al2O3 50% or 60%

The main crystal phases of these refractories are mullite as major phase and glass as minor phase. They can contain free SiO2. These refractories cannot be made from 100 % clay since Al2O3 content of clay are lower. They are made from minerals containing 60% Al2O3 and contains some fireclay. They can be made with bauxite and clay and can be used for temperatures greater than 1700℃.

Al2O3 70%

The major phase of these refractories is mullite. They contain corundum, mullite and glass. They are made either from bauxitic clay or calcined bauxite and clay. They can be used for temperatures greater than 1750℃.

Al2O3 80% and 85%

These refractories are made from calcined bauxite. The main phases of these refractories are corundum as the major phase along with minor quantity of mullite and glass.

Al2O3 90%

These refractories consist of corundum as the major phase with a minor amount of mullite and glass. Fused cast alumina block belongs to this group. It is used in contact with liquid steel or glass due to its enhanced abrasion resistance and corrosion resistance. When in contact with molten glass, it barely produces any blistering or stones. so it is ideal for the high quality glass fuace and special glass fuace.

Zhengzhou Sunrise is a refractory material supplier from China, offering high quality refractory materials for glass fuaces, 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 fuace ramming masses, etc..

The service life of the glass fuace, energy efficiency and the quality of glass is mainly up to refractory materials. The following practices can be performed in order to select the right refractory materials and ensure longer operating life of the glass fuace.

Consistent quality

The quality of the refractories needs to be consistent and assured. Refractories should be bought from reliable manufacturers. Normally, reliable manufacturers can develop the correct physical properties of the refractories such as high temperature strength and correct mineral structure. Once these desired properties are achieved, the performance of the refractories will be predictable and better.

Using larger refractory blocks

The use of larger refractory blocks reduces the number of joints while constructing a fuace. Recently, large sidewall blocks made up of fused cast AZS are used in the glass fuace to reduce the joints and the corrosion of refractories. The manufacturing of large blocks requires a high-capacity press for developing uniform property characteristics. Hence, it is necessary to consider the dimensions of the block and its properties to ensure its suitability for a particular application. Further, random samples should be analyzed to make sure that its properties can meet the requirement of the operating environment.

Mortar and ramming mix

The quality of the mortar and ramming mix used in the glass fuace should be similar to the quality and properties of the refractories. AZS ramming mix is used to join the fused cast AZS blocks, while low shrinkage high alumina mortar is used for joining the high alumina blocks.

Proper dimension

The dimensions of the refractories should be accurate and warpage-free.

Use of anti-corrosion refractory materials

The the refractories is likely to be damaged due to contact with molten glass and slags. In general, sparking and corrosion are the main causes of the wear and tear of refractories in the glass fuaces. Refractories with good resistance to sparking and corrosion are preferable for the glass melting fuace. Anti-corrosion refractory materials particularly suitable for alkali attack can be considered. The coating should be uniform.

Right refractory for different parts

Since the operating environment of different parts are different, it is necessary to select the right refractory materials. Silica bricks are preferred in the crown and the fused cast AZS block is ideal for the sidewall and tank bottom.

Zhengzhou Sunrise is a refractory material supplier from China, offering high quality refractory materials for glass fuaces, 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 fuace ramming masses, etc..