How To Improve The Glass Phase Of Fused Cast AZS Block

SiO2 and Na2O are the main components of the glass phase of fused cast AZS blocks. The content of SiO2 and Na2O is related to the amount of glass phase. Controlling the content of SiO2 and Na2O strictly is the key to ensure the performance of glass phase.
The main composition of fused cast AZS block includes baddeleyite, corundum, a small amount of mullite, glass phase and pores. In order to reduce and eliminate the residual thermal stress, the glass phase is essential for fused cast AZS to act as a buffer for the thermal stress.
However, too much glass phase will weaken the corrosion resistance. In the process of corrosion, the glass phase exudes first and be replaced with the high temperature glass melt, which will accelerate the corrosion. Accompanying the exudation of glass phase, bubbles give off, which will contaminate the glass melt.
The segregation of fused cast AZS is also caused by the glass phase. in theory, Al2O3, ZrO2 and SiO2 do not exist in the glass phase. When the alkali metal oxides(Na2O or K2O) are introduced, most SiO2 will enter the glass phase. Na2O constitutes the key components of glass phase with SiO2 and Al2O3. With the decreasing of Na2O, the glass phase decreases. But increasing the Na2O can reduce the viscosity of glass phase.
Iron, titanium, calcium, magnesium and other impurities should be avoided. The impurities can increase the glass phase but reduce the the viscosity of glass phase and pollute the glass melt.
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..

Application Of Refractories In Different Parts Of Glass Furnaces

Refractories are the main building materials for glass furnaces. It has a decisive impact on the quality of glass, energy consumption and the cost. The development of glass melting technology mainly depends on the development and quality of refractories.
Sidewall and bottom of melter predominately consist of fused cast AZS block, whereas sintered zirconia mullite brick in some cases can be applied to bottom area, where the application condition is not that demanding. Beneath the fused cast AZS lie the chamotte block at the very bottom, in between AZS ramming mix is filled. In corner area fused cast AZS with Void Free Casting is used exclusively. Fused cast AZS is so far the primary refractory brick for glass furnace.
In tin bath, alumina forming brick such as sillimanite and bottom block are used typically.
Silica brick is used also quite frequently in glass furnace. It finds its application for melter crown, front wall, breast wall and gable as well. It is the traditional choice for the crown.
α-β Fused cast alumina block is used extensively for breast wall, as well as sidewall and bottom of cooling zone. Fused cast α-βalumina block and Fused cast βalumina block are also used in the crown and superstructure.
Direct-bonded magnesia chrome brick is most suitable for upper checker, where strong alkali corrosion exist, or lower and middle checker, where sodium sulfate condenses. There are several substitute brick of chrome magnesia for checker chamber, among them are magnesia zirconia brick, magnesia forsterite brick and magnesia alumina brick. While the first two have similar thermal properties and usage as magnesia chrome brick, magnesia alumina brick is usually used for the middle checker of small regenerator. Light weight magnesia forsterite brick is used for the insulation layer of checker chamber. Sillimanite brick can be used also for checker in low temperature area (below 800°C). In principle the refractory material used for wall is in line with that of checker brick at the same height.
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..

Application Of Refractories In Glass Industry

Refractories performance affects glass manufacture in the production cost and the quality of the glass. Refractories in different areas of a glass furnace suffer different operating environment. So different types of refractory are used in the different parts of the glass furnaces.

Crown Refractories

Crown of glass furnaces are subjected to long-term thermal attack and chemical corrosion due to alkali vapor. It also need to be heavily insulated to reduce the energy loss. So it requires volume stability, low permeability, low conductivity, and high refractoriness of refractories in this area.
Silica refractories are the preferred material for crown construction due to its affordability, low stoning potential, insulating capability, resistance to creep, low thermal expansion after 600°C and compatibility with the batch material. They have been used for the construction of glass melting furnace for over a century. Although today the use of silica bricks is restricted to crown and superstructure, the steady improvement in production of silica bricks has led to greater chemical purity and stricter dimensional tolerances over a wide range of shape and sizes. To meet the demanding requirement of oxygen-fuel furnaces, fused cast alumina block is used due to its excellent resistance against acid slag, chemical corrosion and alkali vapor.

Superstructure Refractories

The superstructure of the furnace will suffer from high temperature and chemical attacks by volatile products and dust which settle on the walls and attack refractory products characterized by a progressive wear of refractory in contact with the glass. Refractories in this part are required to have a high thermal shock resistance and corrosion and erosion resistance.Fused cast AZS block, Zirconia-Mullite brick and Mullite brick with high density, low porosity, good hot strength and good sag resistance are used in this area.

Bottom and Lower Side wall Refractories

In contact with melt glass, refractories in those areas suffer high Temperature, and glass corrosion. Chemical reactions also take place between refractories and molten glass, fluxing agents, and/or volatile components. Erosion can follow; washing away refractory grains after the original bond has dissolved. With a high refractoriness, high thermal resistance, a low reaction with melt glass, a very strong glass corrosion and vapour resistance, Zirconia-Mullite bricks and Fused Cast AZS are installed on the bottom or in direct contact with sidewalls.

Regenerator Refractories

These areas of the furnaces are subject to special intense aggression in the long campaigns because of the chemical reactions between refractory material and hot gas. A higher performance of the refractory and insulating material is required in these cases in order to attain better heat efficiency. A regenerator consists of a regenerator chamber in which a checker work (or just checkers) of refractory bricks has been stacked. Due to high stability, high thermal shock resistance, low thermal expansion, high refractoriness and the high resistance to basic slags, Magnesia bricks are normally used in the regenerator including area above checker work and crown. With a high alkali resistance and creep resistance, fireclay bricks are particularly suitable for the lower parts of regenerator.
Besides refractories mentioned above, insulating refractories with low conductivity and good mechanical strength are used to reduce heat loss in areas where abrasion and wear by aggressive slag and molten metal are not severe. The insulating materials can lead to savings in fuel cost and a more rapid heat-up. After the furnaces are installed, unshaped refractories such as special ramming &patching masses are used to repair some parts of the furnaces to extend the furnace’s life until the end of the campaign.
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..

Preheating Operation Of Glass Furnaces

Preheating is one of the key factors that influence the performance and service life of glass furnaces.
Traditionally, the glass furnace is preheated by first warm-up heating and then firing at 800-850℃. Firing at 800-850℃ is because of crystal transformation of silica refractory and fireclay refractory. According to the thermal expansion coefficient and temperature range of silica refractory and fireclay refractory, the temperature curve and firing temperature range are made.
During the warm-up heating, refractory materials in all parts of glass furnaces can expand uniformly. However, after fired at 800-850℃, within 850-1200℃, the temperature fluctuates and is difficult to control. The big temperature fluctuation can cause intense changes of refractory materials. Within 950-1200℃, the crystal transformation of refractory materials occurs and is accompanied by 6% volume shrinkage. Within this temperature range, it is important to consider fused cast AZS block, because the big temperature fluctuation may cause the cracking of fused cast AZS block.
As fused refractories have high density, good abrasion resistance, good high temperature mechanical properties and good corrosion resistance to glass liquid, so the fused cast AZS block has been the most widely used refractory in the glass industry.
With the development of the preheating technology and temperature controlling technology, the temperature has been increased to 1100-1150℃. Within this temperature range, the crystal transformation of the refractory materials has been completed. Since the temperatures before and after the preheating link up well, there is no big temperature fluctuation, so the cracking of fused cast AZS can be avoided.

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..

Chemical Composition And The Quality Of Fused Cast AZS

Fused cast AZS block is the essential refractory material used in the demanding areas of glass furnaces. The quality of fused cast AZS can affect the quality and production of glass and the service life of the glass furnaces. The chemical composition of fused cast AZS is one of the key factors that determine the crystal structure and the properties.
Fused cast AZS block has many chemical and physical properties over other refractory materials, such as high temperature resistance, dense crystal structure, low porosity, high mechanical strength, good chemical stability, good corrosion resistance, good thermal stability(1200℃) and high exudation temperature of glass phase(>1400℃). Due to the features mentioned above, it is widely used in the glass industry.
It is important to select high quality raw materials and improve the purity of the raw materials. Any change of the chemical composition can change the crystal structure. Too much SiO2 can cause the formation of mullite and the decrease of glassy phase and corundum, which will destroy the crystal structure and make the structure loose. ZrO2 has the features of high temperature resistance, high mechanical strength, good corrosion resistance to glass and good chemical stability, but the drawback is its bad thermal stability at 1000-1200℃.
The corrosion resistance to glass of fused cast AZS is related to not only the content of ZrO2 but also its micro-structure. The denser its micro-structure, the better its corrosion resistance to glass. Too much ZrO2 will make its micro-structure loose and the baddeleyite will drop into the glass melt, which will cause glass defects such as stones, stripes and bubbles and reduce the service life of the glass furnaces. Therefore, its corrosion resistance to glass is not proportional to the content of ZrO2. Besides, with the increase of ZrO2, the melting temperature and viscosity of the glass melt also increases, which increases the difficulty of manufacturing and casting.
The content of Na2O and the impurities such as Fe2O3, TiO2, CaO, MgO will also affect the quality of fused cast AZS. Therefore, the stability of chemical composition is important for the quality of fused cast AZS and the service life of the glass furnaces. Sunrise offers high quality fused cast AZS block 33#, 36# and 41#.

The Reasons For The Cracks Of Fused Cast AZS Block

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.