Follow us on Instagram..

Follow us on: www.Instagram.com/mehranceramics

Reasons of refractory wear. Industrial blogs by shahzaman mehar

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. 

Mehran Ceramics offers a wide range of refractories with good wear resistance for high temperature corrosive environments for industry.

Causes of refractory failure, An industrial blog by shahzaman mehar.

Refractories are heat-resistant materials that constitute the linings for high-temperature furnaces and reactors and other processing units. In addition to being resistant to thermal stress and other physical phenomena induced by heat, refractories must also withstand physical wear and corrosion by chemical agents. Any failure of refractory could result in a great loss of production time.

The refractory material failure may caused by many different factors, such as chemical reaction and corrosion, spalling, material selection, plant operations, material storage, mixing, installation, curing, and drying. Only by understanding all aspects pertaining to the design and installation of the refractory material can one find the cause of the failure and help eliminate future failures.
The most common cause for failure of refractory is chemical reaction with the environment in which it is operating and chemical corrosion from molten slag and hot gas/molten salt. Chemical corrosion of a refractory is caused by slag attack at the refractory surface. The material selected must match the chemical environment that exists.
For example, an acidic refractory should not be used in furnaces using basic fluxes, slag, etc. and vice-versa.

The porosity of refractory plays an important role in the chemical reaction. The more porous it is, the greater will be the depth to which the slag will penetrate and destroy the refractory. As the temperature increases, the rate of chemical reaction gradually increases. Sometimes, rise in temperature beyond the safe limit quickly brings about the destruction of the refractory. These chemical aspects are complementary to the engineering plant aspects and must be taken into consideration for a successful realization of the process.

Another important cause is spalling. It may be thermal, mechanical or structural. Thermal spalling may be due to unequal expansion or contraction caused by the difference in temperature at different parts. Mechanical spalling is mostly due to carelessness in loading the furnace or in the removal of materials from furnace, thereby damaging the refractory. Structural spalling takes place due to change in composition of the refractory because of reaction with slags, flux, etc. as a result its coefficient of expansion changes. Thus, different parts expand and contract to a different extent.
Improper material storage, mixing, installation, curing and drying will also cause refractory failure. Refractory material should always be stored in dry, well-ventilated conditions. Use fresh refractory materials and follow proper storage procedures to ensure that the refractory will not lose strength. Use potable water (suitable for drinking) for mixing. The use of the wrong type of water will hinder the ability of the refractory material to reach its proper strength. Using the right type of mixer, following proper mixing procedures, and staying within recommended pot life are other important installation factors. Using the wrong mixer or pneumatic gun could also affect the strength of the refractory material.

Almost all refractory materials (except those that are phosphate bonded) must be cured prior to the drying process. Failure to properly cure a cement-bonded refractory material is the number one contributor to refractory failure and lack of longevity.

Problems with the quality of the refractory material itself is also an important reason for the failure of refracoties. A selection of the right refractories for a specific application is important.

Mehran Ceramics is a leading manufacturing,service provider,and consulting company of Ceramics and Refractories in Pakistan. Our branded materials are achieving worldly appreciation in very short time. For our materials detail visit us on www.mehranceramics.com or simply type mehranceramics on Google or at any search engine.

How to avoid the thermal shock of refractories. Industrial blogs by shahzaman mehar.

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.

www.mehranceramics.com
Skype: mehranceramics
Facebook: mehranceramics
Twitter: mehranceramics
Instagram: mehranceramics

How to expand the life span of refractories. Industrial blogs by shahzaman mehar

The refractory lining plays a critical role for the total performance and reliable operation of the furnace. It can be the controlling factor in the success or failure of a furnace. The service life of the furnace depends mainly on the operating life of the refractory lining.

The following practices can be adopted while carrying out the refractory lining, in order to ensure longer operating life of the refractory lining.

Consistent quality

The quality of the refractories used in pot furnace floor needs to be consistent and assured. Blocks are to be procured from reputed manufacturers, as the quality of such blocks can be expected to be uniform.
Using larger refractory blocks
The use of larger blocks reduces the number of joints while constructing a furnace lining. However, this does not always result in improvement of performance. 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 from the procured lots should be analyzed to verify the manufacturer’s claim with the results obtained from sample analyses.
Use of anti-corrosive coating
The floor of the furnace is likely to be damaged due to the spillage of charge materials containing alkalis or due to contact with molten glass in case of pot failure. Sparking and corrosion are the main causes of wear and tear of refractories in industrial processes. The glass industry is no exception. Bricks with resistance to sparking and corrosion are preferable for using on the floor of the glass melting furnaces. Anti-corrosion coating materials particularly suitable for alkali attack could be considered. The coating should be uniform, and may be 5 mm thick.

Mortar quality

The qualities of mortar used in the furnace lining should be similar to the refractory qualities and properties. Low shrinkage (less than 1%) high-alumina mortar should be used for joining the high-alumina blocks.
Anchors
Anchors are used for almost all types of refractory applications. These are mostly metallic type. Lining failures due to inadequacies in the anchoring system are very common. Selecting the proper metallurgy, anchor dimensions, configurations, and spacing are very important to achieve the maximum service life of the lining. Where metal liners are used over the lining, the mechanical design should be sound and allow free movement of the liner on one end from its fixed positions.

Proper dimension
blocks used in furnace lining should be accurate in dimensions and warpage-free.

For more check out the website: mehranceramics.com
Skype: mehranceramics

Fused cast refractories.

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, 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 alumina and Fused cast high zirconia block.

Fused cast 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.

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.

What is the fused cast alumina blocks?

Fused cast alumina block is made of pure alumina powder(>95%) and a small amount of additions (soda sand and quartz sand). There are commercially 3 types of fused cast alumina blocks: Beta fused cast alumina block, Alpha-beta Fused cast Alumina Block and Alpha fused cast alumina block.
The manufacturing process of fused cast alumina block includes mixing the raw material, melting it in the electric furnace, casting, annealing, machining and then getting the final products.
First melt the raw materials in an electric arc furnace. When the material has become molten and its chemical and physical characteristics have been adjusted to the desired condition, pour the molten material into a mold. Then the cast product is processed with machines into the final product.

Alpha-beta Fused cast Alumina Block is formed by the compact structure of alpha alumina and beta alumina crystals in a most ideal proportion which is approximately 50% and 50% respectively,where intertwined crystals of both materials result in a very dense structure. Below 1350 ℃, it has excellent corrosion resistance against molten glass and great performance against contamination to molten glass, thus it is very suitable for paving blocks and fore-hearth channel blocks. When in contact with molten glass, it barely produces any blistering or stones. So, it may be widely used in working tank, feeder channels, superstructures and lipstone, etc.
Beta fused cast alumina block comprises of a majority of beta alumina crystals and a slight portion of alpha alumina crystals in compact structure. Moreover, the intersected texture of large beta-alumina ensures great dimensional stability and great resistance against spalling. Its property of base saturation enables 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.
Its neutrality against soda vapors makes it the best choice for the downstream part of superstructures in demanding applications.

Alpha fused cast alumina block is an ideal product for the lower temperature zones of the glass melting furnaces due to its high density, superior corrosion resistance and low blister potential. It is also an ideal material for Metallurgical Titanium Furnace because the superior thermal stability.

How to manufacture the fused cast alumina blocks ?

Fused cast alumina block is mainly composed of Al2O3 whose contents is more than 94 percent. It is produced by melting and casting high purity alumina in electric furnace at 2000℃.
The producing process of fused cast alumina block includes mixing the raw material, melting it in the electric furnace, casting, annealing, machining and then getting the final products.
In the manufacturing process of fused cast alumina blocks, first melt the raw materials in an electric arc furnace. When the material has become molten and its chemical and physical characteristics have been adjusted to the desired condition, pour the molten material into a mold. The mold is commonly made of graphite or other suitable materials. Maintain the molten material in the interior of an electric arc to accelerate and cause the solidification.
The mold is provided with a riser or header of ample size to enable complete filling of the mold without interference by material freezing in the headers. The cast material is left in its respective mold for heat treatment, or removed from the mold after the outer walls of the casting have solidified and then annealed without other than its own support. The cast parts are generally packed closer together, thereby allowing them to anneal by virtue of their own heat.
After the blocks have cooled, the cast parts are inspected and finished by diamond cutting and/or grinding. The header may be removed shortly after casting or after annealing. The amount of material in the header is often about equal to the amount of material in the desired finished refractory piece. Header material is commonly recycled, but at considerable expense.
Fused cast alumina block has excellent endurance to strong alkali. Under 1350℃, it has strong corrosion resistance and almost does not contaminate to glass melting liquid . Because it does not contain impurities such as Fe2O3 and TiO2, when it comes into contact with glass liquid, air bubbles are rarely found. Therefore, this product has the special characteristic of minimizing contamination to glass liquid.

Composition Of Fused Cast High Zirconia Block

In recent years, fused cast high zirconia block is introduced to decrease the number of glass defects and increase the corrosion resistance of refractories for high quality glasses and special glasses, due to its excellent corrosion resistance and no pollution to glass.
Fused cast high zirconia block is developed to operate in extreme condition and also require control of the making process. It is made of artificial synthesis high purity raw materials through special casting process.
The high zirconia fused cast refractory has a structure in which grain boundaries of relatively coarse baddeleyite crystals are filled with a matrix glass mainly composed of SiO2, Al2O3 and ZrO2 and contains a small amount of Na2O and/or K2O.
ZrO2 adopts a monoclinic crystal structure at room temperature and transitions to tetragonal and cubic at higher temperatures. The larger the content of the ZrO2 component in the refractory, the higher the corrosion resistance against molten glass.
However, when the content of ZrO2 is too much, it becomes difficult to obtain a fused cast refractory having no cracks by casting. When the zirconia crystals undergo reversible transformation between monoclinic crystals and tetragonal crystals, a rapid volume change will happen at a temperature from 1,000℃ to 1,150℃. as the volume expansion rate may cause cracks and a spalling phenomenon.

The Al2O3 component plays an important role in adjusting the relation between the temperature and the viscosity of the matrix glass and provides an effect of reducing the concentration of the ZrO2 component dissolved in the matrix glass. By utilizing this effect of the Al2O3 component, it is possible to prevent precipitation of zircon in the matrix glass and to prevent the change in quality of the matrix glass, whereby it is possible to avoid the chipping off phenomenon of the refractory and cracking due to an accumulation of remaining volume increase.
Na2O and/or K2O provides a function of softening glass. They are important components which influence the viscosity of the matrix glass and also have an effect of controlling the concentration of the ZrO2 component to some extent.

Fused cast high zirconia block has wide application in a wide range of super high temperature furnaces and kilns in military industry,science research, high melting point Metallurgical, laser crystal and electronic,and are used in sidewall, throat cover, throat support, electrode block, dam block parts etc.
Courtesy/AZS.Fused cast refractories.

www.mehranceramics.com

Various refractory bricks for diverse applications.

Depending on temperatures and service conditions of the applications such as boilers, furnaces, kilns, ovens etc, different types of refractories are used.
Various refractory bricks in different sizes and shapes are manufactured for diverse applications.

Fireclay refractories

Fireclay refractories are essentially hydrated aluminum silicates with 25% - 45% Al2O3 and 50% - 80% SiO2 and minor other minerals. As fireclay brick is relatively cheap and its raw materials are widespread, it is the most common type of refractory brick and used widely in most furnaces, kilns, stoves, regenerators, etc.

High alumina refractories

Alumina refractories containing more than 45% alumina are generally termed as high alumina materials. The alumina concentration ranges from 45 to 95%. Commonly used refractory are sillimanite (61%), mullite (70 –85%) and corundum (99%). The refractoriness of high alumina refractories increases with increase in alumina percentage. The applications of high alumina refractories includes the hearth and shaft of blast furnaces, lime and ceramic kilns, cement kilns, glass tanks and crucibles for melting a wide range of metals.

Silica brick

Silica brick is a refractory material containing at least 93% SiO2. The raw material is quality rocks. Silica brick has excellent mechanical strength at temperatures approaching their actual fusion point. This behavior contrasts with that of many other refractories, for example alumino-silicate materials, which begin to fuse and creep at temperatures considerably lower than their fusion points. Various grades of silica brick have found extensive use in glass making and steel industry.

Magnesite refractories

Magnesite refractories are chemically basic materials, containing at least 85% magnesium oxide. These are made from naturally occurring magnesite (MgCO3) and Silica (SiO2). The physical properties of this class of brick are generally poor, and their great value is primarily in their resistance to basic slags, particularly to lime and iron rich slags. These constitute the most important group of refractories for the basic steelmaking processes. In addition to metallurgical furnaces, basic brick are now being successfully used in glass tank checkers and in lime and cement kilns.

Chromite refractories

Chrome-magnesite material usually contain 15-35% Cr2O3 and 42-50% MgO whereas magnesite-chromite refractories contain at least 60% MgO and 8-18% Cr2O3. Chrome- magnesite refractories are used for building the critical paths of high temperature furnaces. These materials can withstand corrosive slags and gases and have high refractoriness. The magnesite-chromite products are suitable for service at the highest temperatures and in contact with the most basic slags used in steel melting. Magnesite-chromite usually has a better spalling resistance than chrome-magnesite.

Zirconia refractories

Zirconia refractories have a very high strength at room temperature which is maintained up to temperatures as high as 15000C. Its thermal conductivity is found to be much lower than that of most other refractories. Zirconia also does not react readily with liquid metals and molten glasses. They are, therefore, useful as high temperature constructional materials for metallurgical furnaces and glass furnaces.

Insulating materials

Insulating materials are high porosity refractories with low thermal conductivity used in order to reduce the heat losses. Insulating materials has a lower density and offers higher thermal resistance compared to firebricks. In all cases, thermal conductivity of the insulation increases significantly as temperature increases. A wide range of insulating refractories with wide combinations of properties are now available. It is likewise cheaper in contrast to the high duty bricks.

Monolithic refractory

Monolithic refractory, the name generally given to all unshaped refractory products, are materials installed as some form of suspension that ultimately harden to form a solid mass. Monolithic refractories are replacing the conventional type fired refractories at a much faster rate in many applications including those of industrial furnaces.

Some common types of Monolithic Refractories.

Monolithic refractory, the name generally given to all unshaped refractory products, are materials installed as some form of suspension that ultimately harden to form a solid mass.

Castable refractories

Castable refractories, also known as refractory concretes, is a dry, granular material designed to be mixed on site with water and capable of curing to a stable dimensional form through hydraulic or chemical setting. These are the materials that contain cement binder, which imparts hydraulic setting properties when mixed with water. Castable refractories have the advantage of being readily usable at the operating temperature of the equipment after hydraulic or chemical setting and removal of all moisture has taken place.
Castable refractories can be used to create the monolithic linings within all types of furnaces and kilns. Castable refractories are particularly suited to the molding of special shapes and parts at the installation site. The can be applied by pouring, pumping, troweling, funning, and shotcreting.

Plastic refractories

Plastic refractories are mixtures of refractory aggregates and cohesive clays which is prepared in stiff, unfired and formable plastic condition at the proper consistency for use without further preparation. Plastic refractories has high refractoriness and wide range of compositions, and can easily be rammed into place. They are often highly resistant to destructive spalling. Plastic refractories are used to form refractory monolithic linings in various kinds of furnaces, and are especially adaptable for making quick, economical emergency repairs.

Ramming Mixes

Ramming mixes consist essentially of ground refractory aggregates, with a semi-plastic bonding matrix which can be purchased ready-to-use or prepared by adding water in the mixer at the construction site. Ramming mixes are very similar to plastic refractories, but ramming mixes supply a denser, stronger refractory body than plastic refractories. They need some sort of form to restrain them when rammed. Ramming mixes is characterized by thermal stability, corrosion resistance and wear resistance because it contains less binders, fire clay and moisture compared to plastic refractories.
The ramming mixes are used in constructing the internal refractory lining of the stack for filling the gaps between the refractory elements and the walls or other metal elements forming the blast furnace stack. Ramming mixes are used mostly in cold applications where proper consolidation of the material is a concern.

Gunning mixes

Gunning mixes are granular refractory materials sprayed on application area using a variety of air placement guns. Gunning mixes consist of graded refractory aggregate and a bonding compound, and may contain plasticizing agent to increase their stickiness when pneumatically placed onto a furnace wall. Dense, homogeneous monolithic linings can be gunned without the use of forms to save time. More than a third of all monolithic refractories are installed by gunning.
These are heat setting and are used for patching and maintenance works for kilns and furnaces. In some industrial furnaces, turnaround time and installation costs are the major factors when choosing a refractory lining. In other cases, repairs need to be made with little or no downtime. In both circumstances, pneumatic convey-ing of material, or gunning, is often the method of choice.

Mortars

Mortars are generally neither classified under refractory brick nor monolithic refractories. These are finely ground refractory materials, which become plastic when mixed with water. Mortars must have good water retention properties and must not sediment. The composition and characteristics of the mortar materials, grain size and consistency are the important properties of the mortars.
These are used to bond the brickwork into solid unit, to provide cushion between the slightly irregular surfaces of the brick, to fill up spaces created by a deformed shell, and to make a wall gas-tight to prevent penetration of slag into the joints. Refractory mortars can be with ceramic bonding, chemical bonding or hydraulic bonding.

Patching refractories

Patching Refractories are similar to plastic refractories though have a very soft plasticity allowing them to be pounded into place. They have been widely used for steel industry, chemical furnaces, boilers, nonferrous furnaces and the other high temperature furnaces.

Coating refractories

Refractory coatings designed to protect the bricks, steel, monolithics, castables, refractory and steel shells in furnaces, kilns, boilers and various high temperature vessels usually against chemical attack. Coating refractories are normally intended to cover just the working surface of a lining. They tend to be fairly thin layers.

Fettling mixes

Fettling mixes are also granular refractory materials, with function similar to gunning mixes, but are applied by shoveling into the furnace needing patching.
Mehran Ceramics is a refractory material supplier from Pakistan, offering a wide range of refractory materials of high quality at affordable prices, including fused cast bricks, mullite brick, zircon brick, alumina bubble brick, sillimanite brick, corundum brick, low porosity fire clay brick, high alumina brick, monolithic refractories, sealing materials, building fireclay, etc..

Ceramic fiber blankets. Various features.

Ceramic fiber blanket, also called aluminum silicate fiber blanket, is a type of insulation refractory material, featuring high strength, light weight, non asbestos and organic binder, good high temperature stability and good insulation performance. It can effectively reduce the weight of high temperature equipment and heating time and save energy.

Ceramic fiber blanket is made of aluminum silicate with addition of auxiliary materials by the blowing technology. According to the production process, ceramic fiber blankets can be divided into two types: spun needle blanket and blown needle blanket. Especially the quality of products made by the double-side needle process is much better than common ceramic fiber blanket.

Ceramic fiber blanket has low thermal conductivity, good insulation and low thermal capacity, thus it can effectively improve the utilization of energy. It has light weight, good thermal shock resistance and good extension.
Ceramic fiber blanket has uniform diameter, long fiber and low shot content, which greatly improves its properties and performance. It contains no binder agent and has good reliability and stability in different environments.

Ceramic fiber blanket is white and has regular size. It is easy to be cut and install. It can maintain good tensile strength, toughness and fiber structure in neutral and oxidizing atmosphere. Its thermal and physical properties are bot affected by oil and can be restored after drying.
Due to its advantages, it is widely used in many fields such as lining for high-temperature reaction equipment and heating equipment in chemical industry, lining for industrial furnaces, high temperature filter material and fire protection and thermal insulation materials of high buildings.

Mehran Ceramics supplies various ceramic fiber products including ceramic fiber blanket, ceramic fiber board, ceramic fiber module, ceramic fiber vacuum formed shapes, calcium silicate board, ceramic millboard, etc..

Crystalline transformation of Silica bricks.

Silica brick is one of the most widely used high temperature refractory materials. Silica brick is a light yellow refractory product made from silica rock that contain at least 90 percent SiO2. It is used primarily in coke ovens and glass furnaces. It is also used in other applications, such as glass tank walls, acid practice electric furnaces, tunnel kilns, and regenerators.
Silica is the main component of silica brick. It occurs in a variety of crystalline modifications, e.g. quartz, tridymite, and cristobalite and also as an under-cooled melt called quartz glass. The crystalline modifications each have a high and low temperature forms which can transform reversibly. The crystal structure of the individual SiO2 modifications can differ widely, so that distinct density changes occur during transformation. This is of great importance during heating and cooling because of the change in the volume.
Quartz requires the smallest volume and the quartz glass the largest. During firing above approximately 900 ℃, quartz transforms into the other modifications and melt completely at 1725℃. During slow cooling , reversible volume decreases take place which are a result of the spontaneous transformation of the crystal structure from the high to the low temperature modification. The reversible and irreversible volume effects can cause considerable stress within the refractory brick structure.
Any common silica brick having large non-transformed silica content is undesirable because it exhibits extraordinary expansion so as to impair stability of industrial furnace which employs such brick as the refractory. Therefore, the extent of transformation of silica is one of very important factors which have to be considered in designing an industrial furnace in regard to selection of material and evaluation of adequateness of the use of the selected material.
Silica brick provides a high temperature resistant and non-reactive lining. It is characterized with its good resistance to spalling at high temperatures. It also retains their rigidity, are lightweight, have a good resistance to most fluxes present in coke ovens, and offer high resistance to abrasion. It has a relatively long lifespan. It is also nonreactive with the melted glass whereas other refractories, such as magnesia brick, could discolor the final product.
Silica brick is used as a refractory in building and repairing industrial furnaces, such as coke ovens, hot blast stoves and glass furnaces. Silica brick crowns have been successfully used in glass furnaces for producing container, float glass, table-ware and TV panel glass. They have the attributes of a relatively long life, excellent insulation at a low cost, and limited defects as silica is the dominant oxide.
mehranceramics.com

Select the right refractories for blast furnace trough. By shahzaman mehar

Blast furnace trough is employed to transfer the molten iron tapped from the blast furnace to torpedo cars. Appropriate refractories are applied to the respective troughs in consideration of operational conditions.
To maintain stable molten iron transfer and sufficient durability even under severe operational conditions of relatively high productivity coefficients or relatively high iron temperatures, it is important to select the proper refractories for blast furnaces operation being based on abundant field performance.
General requirements of trough refractories are:
1)Easy to install (appropriate fluidity and hardening time)
2)Good resistance to corrosion and impregnation (resistance against slag and FeO attack)
3)Abrasion resistance
4)High resistance to oxidation
5)High resistance to thermal shock and high stability
6)High residual mechanical strength, which resist mechanical abuse at wrecking
Generally in the main trough, local wear damage is observed at the slag line (the air/slag interface) and also at the metal line (the slag/metal interface). At slag line, SiC material of high silicon carbide content for excellent resistance against slag attack. At metal line, Spinel material with lower silicon carbide content for excellent resistance against FeO attack. Plotting the entire wear to be as even as possible.

Mehran Ceramics is a leading manufacturers and suppliers of refractory and industrial ceramics. mehranceramics.com

High Alumina refractories for glass furnace. By shahzaman mehar

Aluminium Oxide or alumina (Al2O3) is one of the most versatile of refractory ceramic oxides and finds use in a wide range of applications. Alumina refractories are the part of alumina- silica group of refractories. Different from fire clay refractories, high Alumina refractories normally have Al2O3 content of more than 45 %.
The raw material base for these refractories are different than the fire clay bricks. For the production of high Al2O3 refractories, both natural raw materials (such as kyanite, sillimanite, andalusite, and bauxite etc.) as well as synthetic materials (sintered mullite, fused mullite, calcined alumina, sintered corundum, and fused corundum etc,) are used.
Alumina (Al2O3) has the physical stability such as melting temperature, hardness, resistance to abrasion, and high mechanical strength. The material has the same chemical composition but have a different crystal structure which is α- Al2O3, β-Al2O3 and γ- Al2O3. The melting point, refractoriness, corrosion resistance and strength of alumina refractories increase with the increase in the Al2O3 content.
Based on the content of alumina, high alumina refractory is classified into 50%, 60%, 70%, 80%, 85%, 90% and 99%.
Refractories with 90 % and 99 % Al2O3 are among the highest strength and erosion resistant refractories. They can be used for temperatures greater than 1800℃。The most widely used alumina refractory with more than 90% Al2O3 content used in glass furnaces is Fused cast Alumina Block and Alumina Bubble block. There are three types of Fused cast Alumina Block: α Alumina, β Alumina and α-β Alumina. Fused cast Alumina Block α Alumina is an ideal product for the lower temperature zones of the glass melting furnaces due to its high density, superior corrosion resistance and low blister potential. β Alumina is the best material for molter crown, port crown, and feeder channel due to its high resistance to alkali vapor and excellent thermal shock resistance. α-β Alumina is widely used in working tank, feeder channels, superstructures and lipstone due to its excellent corrosion resistance against molten glass and no contamination to molten glass under 1350 ℃. Alumina Bubble block has low bulk density, excellent insulating properties and high hot strengths. These features make it an excellent insulating material that can withstand exceptionally high temperatures. It is always used as back-up insulation behind other refractories.
High alumina refractory with about 70% Al2O3 contains mullite as a major phase. It is made of bauxite. It can be used for temperatures greater than 1750℃. Mullite brick and high alumina brick belong to this group. Mullite brick is characterized by good high temperature resistance and good thermal shock resistance, which comes into being mullite through calcine with clay, high alumina materials and ceramics. It is mainly used in fibrous glass furnace. High alumina brick is made of high-quality bauxite clicker. It features high chemical corrosion resistance and high refractoriness. It is usually used in hot areas in glass melting tanks without glass contact.
Refractories containing 50 % and 60 % Al2O3 exhibit improved refractoriness over fireclay products. High alumina insulating brick is a new type of lightweight insulating material which contains approximately 48% alumina,mullite and glass phase or corundum. It has advantages such as high porosity, small volume density, good insulation effect, high mechanical intensity, small thermal conductivity and long service life. It is widely used in insulating layers of glass furnaces. Sillimanite brick is a kind of refractoriness which made by sillimanite and other minerals. And silimanite can be transformed to be mullite under more 1500℃ high temperature. It is mainly used in rider arches, forehearth and bushing for fiber glass furnaces.

Mehran Ceramics supplies all kinds of alumina refractories including fused cast alumina block, Alumina Bubble block, Mullite brick, High alumina brick, High alumina insulating brick, sillimanite brick, etc..
mehranceramics: Facebook | twitter | pinterest | instagram | Skype.

Asbestos as a refractory material. By shahzaman mehar

Asbestos in Refractory Products and Other Industrial Materials:

Refractories are materials that are formulated to retain their shape and tensile strength in the presence of extremely high temperatures, typically those in excess of 1000 degrees Fahrenheit. As such, these materials are used for applications such as blast furnaces and kilns, industrial incinerators and even nuclear reactors. Refractory materials are an integral part of aluminum manufacturing as well. In the home, refractory materials may be found in fire brick and around heating systems. Some types of refractory products are designed to withstand corrosive chemicals, such as various types of acid.

Today, most refractory products are made with aluminum and silicon oxide, magnesium, zirconium, silicon carbide and graphite. Throughout the late 19th and much of the 20th centuries however, the preferred material was asbestos. Asbestos had several advantages over other available refractory materials; namely, it was inexpensive, easy to obtain and easy to work with. A refractory in its finished form resembles a brick or building blocks.

Hazards Associated with Refractory Products
Workers employed in the manufacturing of refractory products suffered considerable asbestos exposure. End users were in relatively little danger as long as the refractory products were intact. However, if the surrounding material is damaged, the asbestos was likely to become friable. This means that fibers are released into the local environment where they can remain suspended in the air and inhaled by those working in the area. Asbestos refractory materials remain in many old and abandoned factories and other industrial buildings. This poses a serious safety hazard to demolition workers and renovators when such buildings are razed or remodeled. For more details contact or visit our website: mehranceramics.com