How to Control the Casting Temperature of Fused Cast Refractories

The casting process of most fused cast refractories, especially those with multi-component, is very complex, since every component has its melting point and crystallization temperature and they can be quite different.
Before discharged, the melt of fused cast refractories should be heated. For steel, before casting, it should be heated to 100℃ higher than its melting point, so as to completely fill the model and obtain castings with exact dimensions. For fused cast AZS, the temperature should be 200℃ higher. When melting and casting multi-component materials, each component can only crystallize simultaneously at their eutectic point or invariant point.
If the temperature of the melt of multi-component fused cast refractories does not reach the temperature of the component most difficult to be melt, it relies on the excessive heating of other components to discharge the melt. But in this case, there will be unmelted components. In general, each component of refractory material has no big difference, but in the ternary system of fused cast AZS and chrome spinel, the biggest difference is about 1000℃.

The use of Fused Cast refractories in glass furnaces

AZS brick is also called fused cast AZS block. It is made by melting raw materials in an electric arc furnace, then cating the melt into a mold and cooling it into solid. It is mainly used in glass furnaces. What should pay attention to during the manufacruring process is the voids caused by the volume shrinkage.

There are four casting ways for AZS refractory bricks: PT, QX, ZWS and WS. The different cating ways of AZS bricks can meet the requirements of different pats in different glass furnaces. It has great corrosion resistance and a long service life.
Currently, there are three important driving forces of the development of AZS refractory. The first is the requirement to maintain or improve the quality of glass quality. The second is the longer service life. And the final one is the effect of the oxygen-fuel system. The three aspects determine the selection of refractory bricks.
Fused cast alumina block has been used in the crown of glass furnaces. Before the emergency of oxygen-fuel technology, only beta alumina bricks are used in the crown. Nowadays, beta or alpha-beta fused cast blocks are also used in the crown of TV glass furnaces, float glass furnaces and borosilicate glass furnaces.
Fused cast AZS bricks can be used at 1600-1650℃, while fused cast alumina bricks can be used at 1700℃. This provides a better promise for the production of high-melting glass.

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..

Features, Classifications and Applications of Fused Cast Refractories

Fused cast refractories are materials that are produced by melting the raw material of the desired composition and then casting molten refractories in molds. They are widely known for having high corrosion resistance which are entirely different in the crystalline structure and the process for their preparation from fired or unfired bonded refractories due to closed pores.
Fused cast refractories are manufactured by melting mixtures of raw materials in an electric furnace at a temperature exceeding 2000°C. Then cast the melt into molds of prescribed shapes. Finally cool and solidify them under thermal insulation in many cases. High density, small or large shapes are obtained. When appropriate, a finish work of drilling or cutting(to get different shapes) is made by grinding with diamond tools.
The dense crystalline structure provides the fused cast bricks with superb strength, corrosion and erosion resistance at very high temperatures. They are quite stable against aggressive melts such as glass and molten metal oxides, but their thermal stability is usually not very high. Fused cast refractories always have a very low and closed porosity but contains voids.
Fused cast refractories are the preferred refractories in contact with glass melts, due to the chemical stability, impermeability, and resistance to corrosion and erosion at the working temperatures in the glass melting furnaces. Therefore, used cast refractories are widely used in the glass industry as a lining for glass melting furnaces. They are also used in various other industries such as iron & steel, aluminum, petrochemistry industries.
Fusion cast refractories are normally formed from alumina usually along with zirconia and silica. Proportions of other minerals such as calcia, chromia and magnesia may be added to control the crystalline structure and physical properties of the end products. Based on the mineralogical composition, fused cast refractories can be divided into:

Fused Cast AZS Block

Fused cast AZS block is abbreviated as AZS because it contains Al2O3－ZrO2－SiO2. Based on the zirconia content which basically defines their corrosion resistance, fused cast AZS blocks can be divided into Fused Cast AZS—33# (33% ZrO2), Fused Cast AZS—36# (36% ZrO2) and Fused Cast AZS—41# (41% ZrO2). The corrosion resistance increases with growing ZrO2 content. They are the most widely used materials both in glass contact and superstructure of glass melting furnaces due to the very high glass and vapor resistance.

Fused Cast Alumina Block

Fuse cast alumina block contains over 90% Al2O3 and are a kind of pure alumina block which has excellent resistance against acid slag and chemical corrosion. Thanks to their high purity, they are perfect complements to the AZS blocks for sensitive applications. According to the crystallographic analysis, Fuse cast alumina block can be divided into alpha Fuse cast alumina block (almost 100% alpha alumina crystal), beta Fuse cast alumina block (almost 100% beta alumina crystal) and alpha-beta Fuse cast alumina block (approximately 50% alpha and 50% beta respectively). Its neutrality against alkali vapors makes it the best choice for the downstream part of superstructures in demanding applications.

Fused Cast High Zirconia Block

The Fused Cast high zirconia block contains at least 80% of ZrO2 with particularly excellent corrosion resistance against molten glass and low contamination properties. Therefore, it has been widely employed as refractory materials in contact with molten glass in a glass melting furnace.

Fused Cast Skid Rail Block

Fused cast skid rail blocks are mainly made from alumina and zirconia. They are of various types including steel discharging platform brick,skid rail block and iron discharging tank blocks. They feature great strength,good wear and fused slag corrosion resistance as well as long service life. It is mainly used in areas that require high abrasion and temperature resistance, such as gliding rail bricks in steel pusher metallurgical furnaces, the tapping platform style walking beam furnaces, and also as the interior for destructors.

Fused Cast Mullite Block

Fused Cast Mullite blocks is characterized by high resistance to acid corrosion and erosion, good high temperature resistance and good thermal shock resistance. It shows high performance on reheating furnaces' beds, skid rails, and for the linings of industrial waste incinerators. It is widely used in the metallurgical industry, glass industry, ceramic kiln, and cement industry,etc.
Sunrise is a refractory material supplier from China. The main products of Sunrise include fused cast AZS block, fused cast alumina block, mullite brick, zircon brick, alumina bubble brick, sillimanite brick, corundum brick, low porosity fireclay brick, high alumina brick, all kinds of glass furnace ramming masses, etc..

What Are Fused Cast Refractories

Fused cast refractory is named by its manufacturing method. The term Fused Cast refers to a manufacturing process in which the ceramic bonding is obtained by the solidification of a mixture which has been melted in an electric furnace and cast in liquid state into molds.
Fused cast refractories have been known and used for many years. Such refractories have presented many advantages in certain uses over the older type of refractory products. Fused cast refractories are denser and more corrosion-resistant than fired and unfired bonded refractories. Fused cast materials, especially the fused cast AZS, are the preferred grades in contact with glass melts.
Fused cast refractories usually have a lower apparent porosity (1-3%), a compression strength and a high deformation temperature. They have great corrosion resistance to melts such as glass and molten metal oxides due to compact structure and closed pores. They also offer the lowest blistering potential in many applications.
Fused cast refractories are manufactured by melting mixtures of raw material of the desired composition in an electric furnace at a temperature exceeding 2000°C, casting the melt into moulds where it solidifies and cooling the molten refractory material to form a solidified refractory. High density, small or large shapes are obtained. When appropriate, a finish is made by grinding with diamond tools.
Many different compositions for fused cast refractories have been developed, such as Fused cast AZS, Fused cast alumina and Fused cast high zirconia block.
Fused cast AZS block is the most widely used material both in glass contact and superstructure of glass melting furnaces due to its good corrosion resistance to melten glass and almost no pollution to glass liquid.
Due to good resistance to alkali vapors, fused cast alumina block is the best choice for the downstream part of superstructures of glass furnaces. the most widely used grades are alpha-beta fused cast alumina block and beta fused cast alumina block.
Fused cast high zirconia block has been frequently used for a portion of contact with molten glass of a glass melting furnace which is required to have high quality, such as substrate glass for a flat panel display.
Besides glass industry, Fused cast refractory materials are also used in many other industries such as iron & steel, aluminum, petrochemistry or wear resistant applications.