Refractories are used at elevated temperatures for structural purposes and they are used in many cases to contain a high temperature corrosive environment. In any process environment, refractories are potentially continuously under attack from a number of corrosive processes.
Chemical Corrosion
The corrosion envirenment usually contains materials and byproducts of the process in chemical reactions with the refractory at elevated temperatures resulting in refractory consumption or wear, potentially causing glassing or softening of the refractories. It is usually not immediately obvious, but the oxidation and reduction state of the environment can participate in and influence the chemical reactions that take place. Along with chemical reaction during corrosion, physical changes occur that may be accelerated by the corrosion process.
Erosion
Erosion is another prevalent refractory wear mechanism. Refractories can be worn away over time from the washing action of moving liquids, such as molten metals or slags. Erosion further exposes refractory to destruction by corrosive or abrasive elements.
Mechanical Abrasion
Abrasive media, including fuel, ash, and other particles, can wear away refractories over time, much like sandblasting. Refractory resistance against abrasion is a key issue for many industrial furnace applications.
Mechanical Wear
Moving parts and equipment within a process can wear against the refractory lining, jeopardizing the structural integrity of the refractory lining.
Thermal Cycling
As refractories undergo the heating and cooling cycles of a process, the refractories expands and contracts, eventually weakening and wearing down the lining. If refractories experiences a rapid change in temperature, a.k.a Thermal Shock, the refractories can experience immediate damage.
As a result of the high temperature corrosive environment, refractories will wear down over time, requiring periodic maintenance and eventual replacement. Refractory wear can be mitigated or minimized by selecting the right refractories to withstand the corrosive environments.
Sunrise Refractory offers a wide range of refractories with good wear resistance for high temperature corrosive environments in glass industry.
Sunday, May 24, 2015
Monday, May 18, 2015
Features Of High Alumina Refractories
Aluminium Oxide (Al2O3 ) or alumina is one of the most versatile of refractory ceramic oxides and finds use in a wide range of applications. High alumina refractories are alumina refractories containing more than 45% alumina.
High alumina bricks is made of high-quality bauxite chamotte as raw materials by shaping at high pressure and sintering at high temperature. Alumina is one of the most chemically stable oxides known, which offers excellent hardness, strength and spalling resistance, which imparts high alumina refractories great features.
The alumina content ranges from 45 to 100%. The refractoriness of high alumina refractories increases with increase of alumina content. So high alumina refractories have high refractoriness and excellent high temperature performance.
High alumina refractories are a kind of acid refractories. Therefore, they have good resistance to acid slags. High alumina refractories are also featured with high cold crushing strength. As the alumina content increases, the cold crushing strength also increases. This makes them to bear more load during use. The high hardness of alumina imparts high wear and abrasion resistance.
Manufacturing cost and price of these brick increase more rapidly with % alumina content, so it is essential to determine experimentally or by test installations the most economical alumina content for each service. In some areas such as the regenerators, fire clay bricks can be used as a replacement for high alumina refractories.
Due to severe service conditions prevailing in modern reheating furnaces, there is an increasing tendency to use more and more of high alumina bricks in place of conventional fireclay bricks. The applications of high alumina refractories includes the hearth and shaft of blast furnaces, ceramic kilns, cement kilns, glass tanks and crucibles for melting a wide range of metals.
Sunrise Refractory is refractory supplier from China, providing high quality high alumina refractories in various shapes at competitive prices.
High alumina bricks is made of high-quality bauxite chamotte as raw materials by shaping at high pressure and sintering at high temperature. Alumina is one of the most chemically stable oxides known, which offers excellent hardness, strength and spalling resistance, which imparts high alumina refractories great features.
The alumina content ranges from 45 to 100%. The refractoriness of high alumina refractories increases with increase of alumina content. So high alumina refractories have high refractoriness and excellent high temperature performance.
High alumina refractories are a kind of acid refractories. Therefore, they have good resistance to acid slags. High alumina refractories are also featured with high cold crushing strength. As the alumina content increases, the cold crushing strength also increases. This makes them to bear more load during use. The high hardness of alumina imparts high wear and abrasion resistance.
Manufacturing cost and price of these brick increase more rapidly with % alumina content, so it is essential to determine experimentally or by test installations the most economical alumina content for each service. In some areas such as the regenerators, fire clay bricks can be used as a replacement for high alumina refractories.
Due to severe service conditions prevailing in modern reheating furnaces, there is an increasing tendency to use more and more of high alumina bricks in place of conventional fireclay bricks. The applications of high alumina refractories includes the hearth and shaft of blast furnaces, ceramic kilns, cement kilns, glass tanks and crucibles for melting a wide range of metals.
Sunrise Refractory is refractory supplier from China, providing high quality high alumina refractories in various shapes at competitive prices.
Sunday, May 10, 2015
The Pros and Cons of Refractory Bricks and Monolithic Refractories
Refractory materials can be generally divided into two kinds: refractories bricks (shaped refractories) and monolithic refractories (unshaped refractories). Both have its pros and cons and applications in the refractory lines.
Refractories bricks are shaped refractories which have fixed shapes. The shapes of refractories bricks maybe divided into two types: standard shapes and special shapes. Standard shapes have dimensions that are conformed to by most refractory manufacturers and are generally applicable to kilns and furnaces of the same type. Special shapes are specifically made for particular kilns and furnaces. This may not be applicable to another furnaces or kiln of the same type.
Shaped Refractory bricks are almost always machine-pressed, thus, high uniformity in properties are expected. Special shapes are most often hand-molded and are expected to exhibit slight variations in properties.
Refractory bricks possess high thermal strength at elevated temperatures. Combined with chemical resistance to alkali attack, the performance is improved for areas with mechanical and chemical impact. These performance characteristics are important in where archways and belly band areas are exposed to mechanical wear and chemical attack. One advantage of refractory bricks over monolithic refractories is that the structural properties are defined during the production process.
Unshaped refractories are without definite form and are only given shape when used. It forms joint less lining and are better known as monolithic refractories. These are categorized as plastic refractories, ramming mixes, castables, gunning mixes, fettling mixes and mortars.
Monolithic refractories exhibits properties that outperform traditional refractory bricks. They have better volume stability and better mechanical resistance to vibration and impact. Another advantage over fired bricks is that shrinkage and expansion of monolithic linings can be matched to the application. In some cases shrinkage can offset the thermal expansion resulting in a significantly different thermo-mechanical behavior compared to refractory bricks.
Use of Monolithic refractories eliminates difficult brick laying tasks and joints which may be accompanied with weakness in construction. Under certain conditions, monolithic linings of the same composition as firebrick provide better insulation, lower permeability and improved resistance to the spalling effects of thermal shock. With little or no preparation, monolithic refractories can be applied to form monolithic or joint free furnace linings in new constructions or to repair existing refractory lining.
Monolithic refractories are widely used in the construction of new kilns and furnaces and in the maintenance of older ones because substantial repairs can be made with a minimum loss of time and, in some cases, even during operations, and in a variety of other applications.
Refractories bricks are shaped refractories which have fixed shapes. The shapes of refractories bricks maybe divided into two types: standard shapes and special shapes. Standard shapes have dimensions that are conformed to by most refractory manufacturers and are generally applicable to kilns and furnaces of the same type. Special shapes are specifically made for particular kilns and furnaces. This may not be applicable to another furnaces or kiln of the same type.
Shaped Refractory bricks are almost always machine-pressed, thus, high uniformity in properties are expected. Special shapes are most often hand-molded and are expected to exhibit slight variations in properties.
Refractory bricks possess high thermal strength at elevated temperatures. Combined with chemical resistance to alkali attack, the performance is improved for areas with mechanical and chemical impact. These performance characteristics are important in where archways and belly band areas are exposed to mechanical wear and chemical attack. One advantage of refractory bricks over monolithic refractories is that the structural properties are defined during the production process.
Unshaped refractories are without definite form and are only given shape when used. It forms joint less lining and are better known as monolithic refractories. These are categorized as plastic refractories, ramming mixes, castables, gunning mixes, fettling mixes and mortars.
Monolithic refractories exhibits properties that outperform traditional refractory bricks. They have better volume stability and better mechanical resistance to vibration and impact. Another advantage over fired bricks is that shrinkage and expansion of monolithic linings can be matched to the application. In some cases shrinkage can offset the thermal expansion resulting in a significantly different thermo-mechanical behavior compared to refractory bricks.
Use of Monolithic refractories eliminates difficult brick laying tasks and joints which may be accompanied with weakness in construction. Under certain conditions, monolithic linings of the same composition as firebrick provide better insulation, lower permeability and improved resistance to the spalling effects of thermal shock. With little or no preparation, monolithic refractories can be applied to form monolithic or joint free furnace linings in new constructions or to repair existing refractory lining.
Monolithic refractories are widely used in the construction of new kilns and furnaces and in the maintenance of older ones because substantial repairs can be made with a minimum loss of time and, in some cases, even during operations, and in a variety of other applications.
Monday, May 4, 2015
How To Improve The Thermal Shock Resistance Of Refractories
Thermal shock is the direct result of exposing the surface of refractory installations to rapid heating and cooling conditions which cause temperature gradients within the refractory blocks. Such gradients, in the case of uneven cooling or heating, may cause cracking. Thermal shock is one of the most important potential failure modes of refractory installations.
In many service conditions, refractories can undergo rapid temperature changes. These temperature fluctuations develop unequal thermal stresses, within the refractory, by causing either rapid expansion or contraction of a section of material. The failure occurs when the thermal stress exceeds the strength of the material in that mode of stressing. It is one of the common reasons of refractory lining damages, more dangerous, than chemical and mechanical tear and wear of the lining.
Thermal shock is a key property in refractory selection process. The most undesirable consequence of thermal shock is obviously spalling. Spalling is the loss of fragments or “spalls” from the face of a refractory brick or structure through cracking and rupture, which exposes inner portions of the refractory.
In many instances, a material properties or/and heat transfer conditions is taken to characterize thermal shock behavior of the refractories.
One of the most important parameters for thermal shock resistance is the coefficient of thermal expansion. Generally, the refractory with the lowest rate of thermal expansion (lowest coefficient of expansion) has the best thermal shock resistance. Inversely, the material with a high expansion has a low thermal shock resistance.
Aside from the thermal conductivity, another parameter which must be considered in thermal shock resistance, is the surface heat transfer coefficient.
Recommendations to improve the thermal shock resistance of refractories:
1) Use materials with a low thermal expansion coefficient, or a combination of a raw materials that would result in a low permanent linear contraction to reduce the thermally induced stresses.
2) Heat up or cool down the refractory line as slowly as possible. From an operational point of view, however, the faster heat-up or cool-down that can be achieved the less time is wasted in a furnace or vessel being not in operation and hopefully making money. These two considerations must be balanced: reducing downtime; against avoiding damaging the lining.
3) Use insulating refractories which play an insulation role and avoid too much weight and thickness.
4) Select refractories with high heat transfer coefficient.
Thermal shock resistance dictates refractory performance in many applications. The thermal shock occurs, then object temperature changes much in a short time. It can become a reason of a sudden failure of the lining at the very beginning. So it is important to take the thermal shock resistance into account when selecting and installing refractory linings.
In many service conditions, refractories can undergo rapid temperature changes. These temperature fluctuations develop unequal thermal stresses, within the refractory, by causing either rapid expansion or contraction of a section of material. The failure occurs when the thermal stress exceeds the strength of the material in that mode of stressing. It is one of the common reasons of refractory lining damages, more dangerous, than chemical and mechanical tear and wear of the lining.
Thermal shock is a key property in refractory selection process. The most undesirable consequence of thermal shock is obviously spalling. Spalling is the loss of fragments or “spalls” from the face of a refractory brick or structure through cracking and rupture, which exposes inner portions of the refractory.
In many instances, a material properties or/and heat transfer conditions is taken to characterize thermal shock behavior of the refractories.
One of the most important parameters for thermal shock resistance is the coefficient of thermal expansion. Generally, the refractory with the lowest rate of thermal expansion (lowest coefficient of expansion) has the best thermal shock resistance. Inversely, the material with a high expansion has a low thermal shock resistance.
Aside from the thermal conductivity, another parameter which must be considered in thermal shock resistance, is the surface heat transfer coefficient.
Recommendations to improve the thermal shock resistance of refractories:
1) Use materials with a low thermal expansion coefficient, or a combination of a raw materials that would result in a low permanent linear contraction to reduce the thermally induced stresses.
2) Heat up or cool down the refractory line as slowly as possible. From an operational point of view, however, the faster heat-up or cool-down that can be achieved the less time is wasted in a furnace or vessel being not in operation and hopefully making money. These two considerations must be balanced: reducing downtime; against avoiding damaging the lining.
3) Use insulating refractories which play an insulation role and avoid too much weight and thickness.
4) Select refractories with high heat transfer coefficient.
Thermal shock resistance dictates refractory performance in many applications. The thermal shock occurs, then object temperature changes much in a short time. It can become a reason of a sudden failure of the lining at the very beginning. So it is important to take the thermal shock resistance into account when selecting and installing refractory linings.
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