What are the refractory materials commonly used in glass melting furnaces and the most important indicators to consider?
What are the refractory materials commonly used in glass melting furnaces and the most important indicators to consider?
Glass melting furnace is a thermal equipment for melting glass made of refractory materials. When choosing refractory materials for glass kiln, the type of kiln, the location of use, the mechanism of damage, the type of molten glass and the type of pigment should be considered. Refractory materials for glass kilns should be able to resist the erosion of glass melt and gaseous substances first, and should have sufficiently high load softening temperature and thermal stability.
It is generally hoped that the refractory materials in various parts of the kiln will not have local early corrosion, so as to ensure that the entire kiln has a long enough service life. However, due to the different mechanical, physical and chemical conditions of each part of the glass kiln, it is required that the performance of the refractory material used should be compatible with it, and it is required not to have adverse effects on other types of adjacent bricks.
The considerations for selecting refractory bricks for glass kilns are analyzed from various aspects.
1. Clay bricks
Low porosity fireclay brick
Clay products are acidic refractory products, and their acidity increases with the increase of SiO2 content. It has a certain corrosion resistance to acidity, but poor resistance to alkaline corrosion. There are different varieties of clay bricks, such as low porosity clay bricks, ultra-low porosity clay bricks, low creep, low porosity, low iron clay bricks and so on. Therefore, clay products are suitable for refractory materials for acid kilns. Large clay bricks for glass kilns are clay refractory bricks with a unit weight of not less than 50kg for masonry glass kilns.
The use conditions of clay bricks are different due to different molding methods and aggregates and binders of clay bricks. According to these characteristics, different clay bricks can be used in different parts of the pool furnace due to different erosion conditions. The grate bars and checker bricks in the lower part of the regenerator are relatively less eroded by batch dust and volatile matter, and the temperature is lower, and the load is heavy, so this kind of brick requires high mechanical strength. Therefore, the binder in the brick can contain an appropriate amount of SiO2 and Fe2O3, but the clay brick used in the high temperature part mainly requires high refractoriness and less impurities in the binder.
2. Silica brick
Hongtai-Silica bricks
Silica refractories are acidic materials, which have strong resistance to acid slag or solution erosion, and good high temperature performance: for example, the refractoriness is 1690-1730°C, and the load softening temperature is 1640-1680°C. The volume expansion rate is relatively large, and when the temperature is 1450 ° C, the total volume expansion is about 1, which is conducive to ensuring the structural strength and airtightness of the masonry. Therefore, silica brick is the main material of glass kiln, and it is widely used in large wall, breast wall, regenerator roof and other parts.
Precautions when baking silica bricks in the kiln: when the silica bricks are at 200-300°C and 573°C, the volume suddenly expands due to the transformation of the crystal form, so do not heat up too quickly when baking below 600°C, and when cooling to below 600°C Severe temperature changes should be avoided, and contact with alkaline substances should be avoided as much as possible.
3. Fused zirconia corundum brick
Fused Zirconia Corundum Brick-Henan Hongtai
ZA series oxidation fused zirconia corundum products are made of high-quality purified raw materials, using a special electric arc furnace, and are produced by long-arc melting and oxidation treatment. This electrofusion casting process has almost no carbon contamination from the electrodes.
Due to the adoption of this melting and casting process and the use of high-purity raw materials, ZA series oxidation fused zirconia corundum products have special, high resistance to erosion by molten glass, and minimal pollution to glass.
AZS-33 products are particularly superior in preventing contamination of the glass liquid, and it has a small tendency to cause stones, bubbles and basic glass phase precipitation in the glass. It is suitable for the upper structure of the melting pool, the pool wall brick and paving brick of the working pool, and the forehearth, etc.
AZS-36 is a standard oxidation method fused zirconia corundum brick, which has the characteristics of high resistance to glass liquid erosion and low pollution, and the performance in these two aspects is balanced. It is suitable for the parts in the glass melting furnace that directly contact the glass liquid, such as the wall bricks of the melting pool, paving bricks, feeding ports, etc.
AZS-41 is the most high-grade oxidized fused zirconia corundum brick, which has the highest corrosion resistance of molten glass and outstanding low pollution to molten glass. It is suitable for parts in glass furnaces that require particularly high corrosion resistance, such as all-electric melting furnaces, liquid flow holes, kiln ridges, bubbling, and bricks at the corners of feeding ports.
The properties and performance indicators of fused zirconia corundum bricks—the baddeleyite phase can resist the erosion of glass liquid, the glass phase can buffer the stress generated by volume change, and can keep the product in an airtight structure, but its quantity is too large, and the exudation temperature is higher The lower the brick, the worse the quality of the brick. The exudation of the glass phase will destroy the structure of the brick and affect the life. Bubbles will be released while oozing out, and there may be insoluble stones in the glass, which will seriously affect the quality of the glass. The exudation temperature is usually indicated by the foam index.
4. Fused corundum brick
α-β lip stone-Hongtai Refractory
The main crystal phase of corundum brick is corundum, which has excellent properties, such as high melting point, high hardness, and is a neutral mineral, so the product has high hardness, erosion resistance, wear resistance, and corrosion resistance. Fused-cast α-Al2O3 bricks are mainly solid fine-grained entities composed of α-type corundum. Mainly used in glass kiln. It is suitable for melting borosilicate glass and opal glass. However, its high temperature corrosion resistance is poor, and its resistance to glass liquid erosion will decrease rapidly at a high temperature of 1600 ° C, so some borosilicate glass kilns tend to use fused silica bricks. Fused-cast α-Al2O3 brick products have a bulk density of 3.15-3.30g/cm3, contain a small amount of glass phase (about 2%), and fill the intercrystalline spaces with high purity. Because it does not pollute the molten glass, and has good corrosion resistance to molten glass and excellent high-temperature wear resistance below 1350 ° C, it is an ideal refractory for the clarification part, cooling part, working pool and other parts of the glass melting furnace. Material.
β-Al2O3 A white product composed of coarse and bright crystals, containing 92%-95% of Al2O3, only less than 1% of the glass phase, and the structural strength of the product is low due to the loose crystal lattice. The Na2O contained in β-Al2O3 reacts with SiO2 to produce a large volume shrinkage, which may cause cracks and damage to the brick. Therefore, it is only applicable to the upper structure containing SiO2 fly ash, for example, the upper structure of the working pool, the breast wall near the combustion port, the small furnace nozzle and the hanging wall, etc. Because the brick does not interact with volatile alkali metal oxides, there is no need to worry about contaminating the glass with molten material dripping from the brick surface.
5. Magnesia refractories
magnesia refractories for glass kiln regenerator
(1) Magnesium material for glass kiln regenerator
Generally, the uppermost layer of the regenerator lattice body uses high-grade magnesia bricks (w (MgO) > 97 %); the upper layer uses mid-grade magnesia bricks (w (MgO) is about 95 % ~ 96 %); the middle layer uses directly bonded magnesia-chrome bricks; The lower floor uses low-porosity clay bricks. Important properties of latticework are erosion resistance and creep resistance. To improve creep resistance, it is necessary to use high-purity, low-iron, low-porosity and large-grained raw materials, and use high temperature for full sintering.
(2) Configuration of regenerator when using alternative fuel
After using petroleum coke, the refractory materials in the regenerator of the glass kiln are easily eroded, and the 95 magnesia bricks are the most severely damaged. A large amount of SiO2 and CaO invaded the brick body, destroyed the original MgO-M2S combination, and formed a continuous CMS-M2S low-melting combination phase. Petroleum coke, on the other hand, is difficult to catch fire and burns slowly. After the use of petroleum coke, the unburned components enter the regenerator and continue to burn in the regenerator, increasing the temperature of the regenerator. In this way, under the action of high temperature and erosion, the lattice body softens and then collapses. Based on the cause of the damage, the glass company expanded the amount of 97 magnesia bricks and directly bonded magnesia chrome bricks in the regenerator, and replaced the 95 magnesia bricks with poor performance. The life of the regenerator was extended from 1 year to 3 years, and the use of petroleum coke The test was initially successful. In order to meet the needs of using alternative fuels, it is also necessary to develop high-purity magnesium-aluminum spinel materials with good corrosion resistance and adaptability to changes in oxidation-reduction atmospheres. High-purity magnesia-alumina spinel bricks have good creep resistance and alkali vapor erosion resistance, and can also be used in oxy-fuel combustion glass furnaces.
6. Other refractory materials
Zircon is decomposed by heat at 1680°C, and zircon products also have good corrosion resistance. Zircon bricks have excellent properties such as high temperature resistance, good thermal shock resistance, and glass liquid erosion resistance. Aluminum-zirconium-silicon (AZS) fused cast bricks and fired bricks have good resistance to erosion by molten glass, and can be used for the walls and upper structures of glass melting tank kilns.
sintered refractories for glass furnace/kiln
7. Insulation and refractory materials
In order to save energy, more and more glass kilns have insulation structures. These insulation materials are clay-based heat-insulating refractory bricks, silicon-based heat-insulating refractory bricks, diatomite bricks, and heat-insulating ramming materials.
So when choosing and purchasing refractory materials for glass melting furnaces, what are the index performances that should be considered first?
(1) Organizational structure
Refractory materials are heterogeneous bodies composed of solid phase (including crystal and glass phase) and pores. The macroscopic structural characteristics of the product are the main factors affecting its high-temperature use properties.
① Porosity
In refractory materials, there are often many pores of different sizes and shapes. The pores that communicate with the atmosphere are called open pores (also known as apparent pores), the pores that penetrate each other are called connected pores, and the pores that do not communicate with the atmosphere are called closed pores. The porosity is usually used to reflect the compactness of refractory materials, that is, the percentage of the volume of pores in the brick to the total volume.
Porosity is the basic technical index of refractory materials, which almost affects the performance of refractory products. The smaller the porosity, the better the corrosion resistance of the refractory material and the higher the structural strength. The higher the porosity, the lower the thermal conductivity of the material.
② Bulk density
Bulk density is the mass of refractory material per unit volume (total volume including pores). It intuitively reflects the compactness of refractory products, and is an important indicator to measure the quality level of refractory materials and dense refractory products. Generally speaking, the higher the bulk density, the smaller the porosity, and the better a series of properties such as strength, high temperature and load softening temperature.
③True density
The true density refers to the ratio of the mass of the porous body material to its true volume (excluding pores). True volume refers to the volume of solid material in a porous body. Its value has nothing to do with density and porosity, but with the chemical mineral composition of refractory materials.
(2) thermal properties
①Thermal expansion
When refractory materials are heated, the property that the volume expands with the increase of temperature is called thermal expansion. It is usually expressed by the coefficient of linear expansion or the coefficient of volume expansion.
When using refractory materials, great attention must be paid to their thermal expansion. In the furnace structure, expansion joints should be reserved according to the thermal expansion characteristics of refractory materials. When firing the kiln, a reasonable heating curve should be formulated according to the thermal expansion of refractory materials. And take necessary measures such as adjusting the braces.
② Thermal conductivity
Thermal conductivity indicates the size of the thermal conductivity of the refractory material, expressed in terms of thermal conductivity. The so-called thermal conductivity refers to the rate of heat flow through a unit area of a material under a unit temperature gradient. It mainly depends on the chemical composition and organizational structure of the material.
③Heat capacity
Heat capacity, also known as specific heat capacity, refers to the heat required to heat 1 kg of refractory material to raise its temperature by 1 °C under normal pressure. It is of great significance in the design and control of furnace temperature rise and heat storage capacity.
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In helping businesses and homeowners select the correct refractory product to use for their application a few common questions kept coming around about refractory mortar their uses. Because these questions are common to so many we speak with the following article is here to address the basics about refractory cement.
Refractory Cement is a heat-resistant material designed to line fireboxes and withstand very hot environments (2,000-3,000*F) such as firebox linings, forges, kilns, ovens, incinerators, crematoriums, and other high temperature equipment. Refractory cement is commonly combined with other products like firebrick and other ceramics to further increase thermal resistance.
Keep reading to understand just how refractory cement also known as castable refractory or fire cement is used and how it differs from other similar products.
Glass melting furnace is a thermal equipment for melting glass made of refractory materials. When choosing refractory materials for glass kiln, the type of kiln, the location of use, the mechanism of damage, the type of molten glass and the type of pigment should be considered. Refractory materials for glass kilns should be able to resist the erosion of glass melt and gaseous substances first, and should have sufficiently high load softening temperature and thermal stability.
It is generally hoped that the refractory materials in various parts of the kiln will not have local early corrosion, so as to ensure that the entire kiln has a long enough service life. However, due to the different mechanical, physical and chemical conditions of each part of the glass kiln, it is required that the performance of the refractory material used should be compatible with it, and it is required not to have adverse effects on other types of adjacent bricks.
The considerations for selecting refractory bricks for glass kilns are analyzed from various aspects.
1. Clay bricks
Low porosity fireclay brick
Clay products are acidic refractory products, and their acidity increases with the increase of SiO2 content. It has a certain corrosion resistance to acidity, but poor resistance to alkaline corrosion. There are different varieties of clay bricks, such as low porosity clay bricks, ultra-low porosity clay bricks, low creep, low porosity, low iron clay bricks and so on. Therefore, clay products are suitable for refractory materials for acid kilns. Large clay bricks for glass kilns are clay refractory bricks with a unit weight of not less than 50kg for masonry glass kilns.
The use conditions of clay bricks are different due to different molding methods and aggregates and binders of clay bricks. According to these characteristics, different clay bricks can be used in different parts of the pool furnace due to different erosion conditions. The grate bars and checker bricks in the lower part of the regenerator are relatively less eroded by batch dust and volatile matter, and the temperature is lower, and the load is heavy, so this kind of brick requires high mechanical strength. Therefore, the binder in the brick can contain an appropriate amount of SiO2 and Fe2O3, but the clay brick used in the high temperature part mainly requires high refractoriness and less impurities in the binder.
2. Silica brick
Hongtai-Silica bricks
Silica refractories are acidic materials, which have strong resistance to acid slag or solution erosion, and good high temperature performance: for example, the refractoriness is 1690-1730°C, and the load softening temperature is 1640-1680°C. The volume expansion rate is relatively large, and when the temperature is 1450 ° C, the total volume expansion is about 1, which is conducive to ensuring the structural strength and airtightness of the masonry. Therefore, silica brick is the main material of glass kiln, and it is widely used in large wall, breast wall, regenerator roof and other parts.
Precautions when baking silica bricks in the kiln: when the silica bricks are at 200-300°C and 573°C, the volume suddenly expands due to the transformation of the crystal form, so do not heat up too quickly when baking below 600°C, and when cooling to below 600°C Severe temperature changes should be avoided, and contact with alkaline substances should be avoided as much as possible.
3. Fused zirconia corundum brick
Fused Zirconia Corundum Brick-Henan Hongtai
ZA series oxidation fused zirconia corundum products are made of high-quality purified raw materials, using a special electric arc furnace, and are produced by long-arc melting and oxidation treatment. This electrofusion casting process has almost no carbon contamination from the electrodes.
Due to the adoption of this melting and casting process and the use of high-purity raw materials, ZA series oxidation fused zirconia corundum products have special, high resistance to erosion by molten glass, and minimal pollution to glass.
AZS-33 products are particularly superior in preventing contamination of the glass liquid, and it has a small tendency to cause stones, bubbles and basic glass phase precipitation in the glass. It is suitable for the upper structure of the melting pool, the pool wall brick and paving brick of the working pool, and the forehearth, etc.
AZS-36 is a standard oxidation method fused zirconia corundum brick, which has the characteristics of high resistance to glass liquid erosion and low pollution, and the performance in these two aspects is balanced. It is suitable for the parts in the glass melting furnace that directly contact the glass liquid, such as the wall bricks of the melting pool, paving bricks, feeding ports, etc.
AZS-41 is the most high-grade oxidized fused zirconia corundum brick, which has the highest corrosion resistance of molten glass and outstanding low pollution to molten glass. It is suitable for parts in glass furnaces that require particularly high corrosion resistance, such as all-electric melting furnaces, liquid flow holes, kiln ridges, bubbling, and bricks at the corners of feeding ports.
The properties and performance indicators of fused zirconia corundum bricks—the baddeleyite phase can resist the erosion of glass liquid, the glass phase can buffer the stress generated by volume change, and can keep the product in an airtight structure, but its quantity is too large, and the exudation temperature is higher The lower the brick, the worse the quality of the brick. The exudation of the glass phase will destroy the structure of the brick and affect the life. Bubbles will be released while oozing out, and there may be insoluble stones in the glass, which will seriously affect the quality of the glass. The exudation temperature is usually indicated by the foam index.
4. Fused corundum brick
α-β lip stone-Hongtai Refractory
The main crystal phase of corundum brick is corundum, which has excellent properties, such as high melting point, high hardness, and is a neutral mineral, so the product has high hardness, erosion resistance, wear resistance, and corrosion resistance. Fused-cast α-Al2O3 bricks are mainly solid fine-grained entities composed of α-type corundum. Mainly used in glass kiln. It is suitable for melting borosilicate glass and opal glass. However, its high temperature corrosion resistance is poor, and its resistance to glass liquid erosion will decrease rapidly at a high temperature of 1600 ° C, so some borosilicate glass kilns tend to use fused silica bricks. Fused-cast α-Al2O3 brick products have a bulk density of 3.15-3.30g/cm3, contain a small amount of glass phase (about 2%), and fill the intercrystalline spaces with high purity. Because it does not pollute the molten glass, and has good corrosion resistance to molten glass and excellent high-temperature wear resistance below 1350 ° C, it is an ideal refractory for the clarification part, cooling part, working pool and other parts of the glass melting furnace. Material.
β-Al2O3 A white product composed of coarse and bright crystals, containing 92%-95% of Al2O3, only less than 1% of the glass phase, and the structural strength of the product is low due to the loose crystal lattice. The Na2O contained in β-Al2O3 reacts with SiO2 to produce a large volume shrinkage, which may cause cracks and damage to the brick. Therefore, it is only applicable to the upper structure containing SiO2 fly ash, for example, the upper structure of the working pool, the breast wall near the combustion port, the small furnace nozzle and the hanging wall, etc. Because the brick does not interact with volatile alkali metal oxides, there is no need to worry about contaminating the glass with molten material dripping from the brick surface.
5. Magnesia refractories
magnesia refractories for glass kiln regenerator
(1) Magnesium material for glass kiln regenerator
Generally, the uppermost layer of the regenerator lattice body uses high-grade magnesia bricks (w (MgO) > 97 %); the upper layer uses mid-grade magnesia bricks (w (MgO) is about 95 % ~ 96 %); the middle layer uses directly bonded magnesia-chrome bricks; The lower floor uses low-porosity clay bricks. Important properties of latticework are erosion resistance and creep resistance. To improve creep resistance, it is necessary to use high-purity, low-iron, low-porosity and large-grained raw materials, and use high temperature for full sintering.
(2) Configuration of regenerator when using alternative fuel
After using petroleum coke, the refractory materials in the regenerator of the glass kiln are easily eroded, and the 95 magnesia bricks are the most severely damaged. A large amount of SiO2 and CaO invaded the brick body, destroyed the original MgO-M2S combination, and formed a continuous CMS-M2S low-melting combination phase. Petroleum coke, on the other hand, is difficult to catch fire and burns slowly. After the use of petroleum coke, the unburned components enter the regenerator and continue to burn in the regenerator, increasing the temperature of the regenerator. In this way, under the action of high temperature and erosion, the lattice body softens and then collapses. Based on the cause of the damage, the glass company expanded the amount of 97 magnesia bricks and directly bonded magnesia chrome bricks in the regenerator, and replaced the 95 magnesia bricks with poor performance. The life of the regenerator was extended from 1 year to 3 years, and the use of petroleum coke The test was initially successful. In order to meet the needs of using alternative fuels, it is also necessary to develop high-purity magnesium-aluminum spinel materials with good corrosion resistance and adaptability to changes in oxidation-reduction atmospheres. High-purity magnesia-alumina spinel bricks have good creep resistance and alkali vapor erosion resistance, and can also be used in oxy-fuel combustion glass furnaces.
6. Other refractory materials
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Zircon is decomposed by heat at 1680°C, and zircon products also have good corrosion resistance. Zircon bricks have excellent properties such as high temperature resistance, good thermal shock resistance, and glass liquid erosion resistance. Aluminum-zirconium-silicon (AZS) fused cast bricks and fired bricks have good resistance to erosion by molten glass, and can be used for the walls and upper structures of glass melting tank kilns.
sintered refractories for glass furnace/kiln
7. Insulation and refractory materials
In order to save energy, more and more glass kilns have insulation structures. These insulation materials are clay-based heat-insulating refractory bricks, silicon-based heat-insulating refractory bricks, diatomite bricks, and heat-insulating ramming materials.
So when choosing and purchasing refractory materials for glass melting furnaces, what are the index performances that should be considered first?
(1) Organizational structure
Refractory materials are heterogeneous bodies composed of solid phase (including crystal and glass phase) and pores. The macroscopic structural characteristics of the product are the main factors affecting its high-temperature use properties.
① Porosity
In refractory materials, there are often many pores of different sizes and shapes. The pores that communicate with the atmosphere are called open pores (also known as apparent pores), the pores that penetrate each other are called connected pores, and the pores that do not communicate with the atmosphere are called closed pores. The porosity is usually used to reflect the compactness of refractory materials, that is, the percentage of the volume of pores in the brick to the total volume.
Porosity is the basic technical index of refractory materials, which almost affects the performance of refractory products. The smaller the porosity, the better the corrosion resistance of the refractory material and the higher the structural strength. The higher the porosity, the lower the thermal conductivity of the material.
② Bulk density
Bulk density is the mass of refractory material per unit volume (total volume including pores). It intuitively reflects the compactness of refractory products, and is an important indicator to measure the quality level of refractory materials and dense refractory products. Generally speaking, the higher the bulk density, the smaller the porosity, and the better a series of properties such as strength, high temperature and load softening temperature.
③True density
The true density refers to the ratio of the mass of the porous body material to its true volume (excluding pores). True volume refers to the volume of solid material in a porous body. Its value has nothing to do with density and porosity, but with the chemical mineral composition of refractory materials.
(2) thermal properties
①Thermal expansion
When refractory materials are heated, the property that the volume expands with the increase of temperature is called thermal expansion. It is usually expressed by the coefficient of linear expansion or the coefficient of volume expansion.
When using refractory materials, great attention must be paid to their thermal expansion. In the furnace structure, expansion joints should be reserved according to the thermal expansion characteristics of refractory materials. When firing the kiln, a reasonable heating curve should be formulated according to the thermal expansion of refractory materials. And take necessary measures such as adjusting the braces.
② Thermal conductivity
Thermal conductivity indicates the size of the thermal conductivity of the refractory material, expressed in terms of thermal conductivity. The so-called thermal conductivity refers to the rate of heat flow through a unit area of a material under a unit temperature gradient. It mainly depends on the chemical composition and organizational structure of the material.
③Heat capacity
Heat capacity, also known as specific heat capacity, refers to the heat required to heat 1 kg of refractory material to raise its temperature by 1 °C under normal pressure. It is of great significance in the design and control of furnace temperature rise and heat storage capacity.
Contact me for your requirements or questions:
WhatsApp me:
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In helping businesses and homeowners select the correct refractory product to use for their application a few common questions kept coming around about refractory mortar their uses. Because these questions are common to so many we speak with the following article is here to address the basics about refractory cement.
Refractory Cement is a heat-resistant material designed to line fireboxes and withstand very hot environments (2,000-3,000*F) such as firebox linings, forges, kilns, ovens, incinerators, crematoriums, and other high temperature equipment. Refractory cement is commonly combined with other products like firebrick and other ceramics to further increase thermal resistance.
Keep reading to understand just how refractory cement also known as castable refractory or fire cement is used and how it differs from other similar products.
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