Tabular Alumina for High Purity Corundum Brick

High purity corundum brick with Al2O3 content above 99% is studied based on tabular alumina and white fused alumina (WFA) as single aggregate and the combination of both. In comparison with Tabular alumina, WFA aggregate has relatively higher SiO2 content of above 0.10% and shows fluctuation on soda content. WFA also has a high open porosity of 8.8%, which very often exists in the form of single large pore or in the form of agglomeration of pores rather than the small closed and evenly distributed pores in tabular alumina. Refractory brick china with different ratio of tabular alumina and WFA have been tested for firing shrinkage, bulk density and apparent porosity, cold and hot strength, thermal shock resistance, and abrasion resistance. Also slag tests with a coal gasifier slag and an oil cracking slag have been conducted. The results from this evaluation conclude that high alumina brick outperforms WFA bricks and importantly gives more balanced performance.

Introduction
High purity corundum brick is widely used as refractory lining for oil cracking unit, coal gasifier, carbon black furnaces, black liquor gasification and other industrial furnaces. This is attributable to the outstanding performance of corundum brickon chemical corrosion resistance, mechanical abrasion resistance and thermomechanical properties like high temperature strength, refractoriness under load and creep resistance, even in environments with corrosive gas or liquid and with high pressure.
Synthetic alumina based aggregates like white fused alumina and tabular alumina are the two main aggregates available for high purity corundum brick. They are selected due to low impurity content (e.g. SiO2), high bulk density and thermomechanical properties, which enables corundum bricks that meet the requirements on thermal, chemical and structural attacks [1] which gasifiers and other furnaces apply in operation.

The different processes for WFA and tabular alumina production (fusion vs. sinter) certainly create differences between the aggregate, which also have an impact on the properties and performance of the corundum brick. Tabular alumina is well received and extensively used in the refractories for steelmaking such as slide gate plate, Al2O3-MgOC brick, castables and pre-cast shapes.

However, for a long period of time, WFA is very commonly used as the aggregate for high purity corundum brick to non-steel applications like gasifier and other industrial furnaces. It is often claimed that WFA aggregate has higher bulk density which consequently increases the density of fire brick China and the corrosion resistance which could enhance the overall performance. However these perceptions should be investigated by an extensive evaluation. This work is designed to evaluate in a comprehensive way the differences on performance of tabular alumina and white fused alumina in respect to aggregate itself and brick properties in order to understand these differences and provide appropriate application guideline for high purity corundum brick.

1. Refractory raw material Almatis global tabular alumina product T60/64 and a common commercial Chinese WFA grade are selected as the aggregate and fine. In the matrix, Almatis’ calcined alumina CT800FG is also used. Sulphite pulp liquor is used as temporary binder for corundum brick making.

2. China refractory brick formulation Five recipes are used in this evaluation. As per the tabular alumina content in aggregate, the formula is named as T100, T75, T50, T25 and T0 and the numbers stand for tabular alumina content in respective brick. Table 1 gives the details with bold highlighted for tabular alumina.

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The advantage and disadvantage of graphite electrode

Ultra-high power graphite electrode:
Graphite electrodes is mainly made of petroleum coke and needle coke as refractory raw materials, and coal tar pitch as a binder, which is prepared by calcining, compounding, kneading, pressing, calcining, graphitizing and machining and is released in an electric arc furnace Electrical energy on the charge heating and melting of the conductor.
Ultra-high-power graphite electrode are graphite electrodes that allow current densities greater than 25 A / cm2 and are mainly used in ultra-high-power steelmaking electric arc furnaces.
HP Graphite electrode advantages:
(1) Processing speed is faster: Under normal circumstances, graphite machining speed can be 2 to 5 times faster than copper; and discharge processing speed is 2 to 3 times faster than copper;
(2) The material is more difficult to deform: obvious advantages in the thin-walled electrode processing.
(3) lighter weight: the density of graphite is only 1/5 of copper, large electrode for electrical discharge machining, can effectively reduce the machine tool (EDM) burden; more suitable for large mold applications.
According to the use of different power and current, using different refractory raw materials and production technology, can be divided into ordinary power graphite electrodes, high power graphite electrodes, ultra-high power graphite electrodes. Graphite electrode has good electrical properties and chemical stability, high mechanical strength at high temperature, low impurity content, good vibration resistance, is a good conductor of heat and electricity.
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Graphite electrodes are widely used in steel-making electric arc furnaces, refining furnaces, ferroalloy production, industrial silicon, yellow phosphorus, corundum and other submerged arc furnaces and other arc furnaces that produce high temperatures.
HP Graphite electrode has good electrical properties and chemical stability, high mechanical strength at high temperatures, less impurities, good vibration resistance. It is a good conductor of heat and electricity.
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The features and application of graphite electrode

Graphite electrodes find application in manufacture of Steel and other non-ferrous metals through the Electric Arc Furnace and the Laddle Furnace routes. It is used as a consumable for conducting high current at low voltage which is necessary for melting and / or alloying processes.

Graphite is the unique material for Electrodes as it optimally fulfils the requirements on the following criteria :
Electric and Thermal Conductivity
Mechanical Strength
Thermal Shock Resistance
Machinability
Thermal Expansion

We are instrumental in manufacturing for our clients a commendable array of HP Graphite Electrode that are demanded for their ease of use, long time service and options for wide ranging usages. Offered range also incorporates Ultra High Power Graphite Electrodes, High Power Graphite Electrodes and Regular Power Graphite Electrodes. These offered Electrodes are prepared by using LWG Furnaces, advanced machinery and latest techniques. Backed by its excellent attributes, this offered range is extensively applauded by our patrons. Addition to this, we ensure customized product for the gratification of esteemed clients.

High power graphite electrodes refer to graphite electrodes that allow the use of current densities below 17 A / cm2. They are mainly used in electric arc furnaces, refining, ferroalloy and submerged arc furnaces.

HP Graphite electrode has advantages of high mechanical strength, low impurity content and good vibration resistance. We are amongst the leading names in the industry, offering technically advanced range of High Power Graphite Electrodes that are performance oriented and are functionally advanced in nature. They have high heating capacity and reduces the electrode consumption to the great extend. High power graphite electrodes reduces the melting cost and are offered at most affordable rates.

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Common castable for reheating furnace

1.Self leveling castable. Self leveling castable is applicable to the furnace parts which are more complex and can not be vibrated by workers.
2.Low cement castable. The low cement castable is suitable for the high temperature zone and moderate temperature zone of the heating furnace, and the service temperature is between 1400~1500 degrees centigrade.
3.Phosphate castable. Phosphate castable is suitable for heating furnace bottom and the zone where it rub with other refractory materials and erosion zone by hot wind. The service temperature is between 1000~1600 degrees.
4.Mullite castable. The mullite castable is charactorized with high thermal shock resistance, erosion resistance, good volume stability and high application temperature. So it is usually used in the key parts of the furnace wall, furnace top and depressed beam, or used to make the burner brick.
5.Light weight castable. The lightweight castable is used for the heat insulation layer of the furnace wall, furnace top, flue and other parts. High strength lightweight castable can also be used as the lining of exhaust systems and hot air pipes.
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The advantages of graphite electrode in chinafirebrick

Graphite electrode is an indispensable material used in the electric arc furnace steel making, for its excellent electrical conductivity and remarkable anti-thermal shock capability. We supply HP graphite electrode for the iron and steel sector. We specialize in providing graphite electrodes of 18 inch diameter and smaller, but larger diameters up to 28" are also available. Carbon electrode sizing ranges from 36" to 55" diameter. Our product line includes:

Advantages:
High temperature strength
Good thermal and electrical conductivity
Low thermal expansion
Appropriate machinability
These features make graphite electrode the most suitable material to melt scraps, DRI, etc.

We supply graphite electrodes for the iron and steel sector. Our main refractory product include:
Graphite and carbon sidewall blocks for aluminum smelting
Graphite electrodes for the steel and iron industry
UHP Graphite Electrodes
HP Graphite Electrode
General Power Graphite Electrode
We’re among the HP graphite electrode suppliers in the nation and can provide you with the raw materials you need at prices you can afford. We offer excellent customer service whether you order graphite electrodes and refractory fire brick.
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The details of HP Graphite Electrode

High power graphite electrodes refer to the graphite electrode that allows the use of a current density of 18 ~ 25A / cm2.
Graphite electrode has good electrical properties and chemical stability. What’s more, graphite electrode has advantages of high mechanical strength, low impurity content and good vibration resistance. Graphite electrodes are good conductors of heat and electricity. Graphite electrode is widely used in steelmaking electric furnace, refining furnaces, production of ferroalloy, industrial silicon, yellow phosphorus, corundum , submerged arc furnaces and other smelting furnaces that produce high temperatures by electric arc.
According to the different of service power and electricity , using different raw materials and production technology, graphite electrodes can be divided into ordinary power (RP) graphite electrodes, HP graphite electrodes, ultra-high power (UHP) graphite electrodes.?

Application:

High power graphite electrode is mainly used in high-power electric furnace and ladle furnace.
Changxing refractory provides refractory products, calcium silicate products, castable & mortar,?china refractory brick, ceramic fiber felt, ladle & tundish nozzle, ceramic fiber with high quality for you. Such as high alumina refractory bricks, magnesia carbon brick, clay refractory bricks and other refractory products.
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The working mode of moulding powder

Moulding powder forms ”three layers”?in the crystallizer, powder layer, sintered layer and slag layer. This working mode is the key to play the role of moulding powder.

The casting powder (1100~1200℃ melting point) on the surface of the molten steel (1500℃), heated by the molten steel and forms slag layer with 10-15mm thickness on the surface of molten steel. With the heat transfer slowed down, the moulding powder above slag layer sintered, forms sintered layer (900-600℃). And the casting powder above the sintered layer will gets fewer heat transfer, less than 500℃, so this is the powder layer. And the moulding powder covers in the molten steel surface evenly, to prevent cooling and secondary oxidation of molten steel.

During casting, the slag film between crystallizer and solidified slab shell could reduce the casting resistance and improve the heat transfer of crystallizer. As casting going , the slag layer is consumed constantly, then sintered layer becomes slag layer, powder layer becomes sintered layer, and adds more moulding powder into the crystallizer, makes the moulding powder keeps “three layers“.

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Reasons for mesh cracking of high alumina bricks

In addition, high alumina bricks on the surface of the network cracks generated in the gap between the brick brick surface. Therefore, it can be inferred that when the excess air coefficient in the kiln is small or the reducing atmosphere is generated, the CO is easy to be retained in these places due to the smaller slit, so that the Fe2O3 in the product is reduced to FeO; the surface of the channel is smooth , So it will not be affected by changes in the atmosphere, no network cracks. It is important to note that frequent changes in the nature of the combustion atmosphere should be avoided during the firing process. So that this alternating change will cause the surface to be damaged.
The chemical analysis of the surface and the central part of the products with high surface cracks in the surface of the high alumina refractory bricks shows that the Al2O3 on the brick surface is 1% -2% higher than the central part and the SiO2 is 1% -2% Center more than 10 times higher. It was found that the content of mullite was 12% lower than that of the central part, 4% -5% in corundum and 7% -8% in glass. This indicates that during the migration of Na2O, Na + volatilizes and adsorbs on the surface of high alumina brick, which will promote the decomposition of mullite, reduce the mullite on the surface of the product, and increase the corundum and glass phases. As the surface of the liquid phase increased and early appearance, so that the brick surface premature contraction, resulting in the production of reticulation.
Practice shows that in order to avoid and reduce the high aluminum brick surface network cracks, 1.2. High bauxite clinker water absorption were controlled at 4% -5% below, the tube of water absorption should also be controlled at 5.5 % Below, the excess air coefficient control between 1.1-1.2 is appropriate, so that high alumina brick firing in a stable weak atmosphere.
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How to distinguish the quality of high alumina bricks

High alumina brick is mainly used in lining of blast furnace, hot blast stove, furnace top, blast furnace, reverberatory furnace and rotary kiln. In addition, high alumina brick is also widely used as the open - hearth furnace, pouring system plug, water - mouth brick, etc.

It is featured by good quality, high refractoriness, long service life, and it is the most widely used by the industrial furnace. As the quality of it deters the service life of furnace, it’s very important to distinguish the prime and common one, the following can be referred to choose the good high alumina bricks.

Firstly, color is important for high alumina bricks, the prime one has smooth apprearance, it’s yellow white, the four sides are flat, with no broken corners and no cracks.

Secondly, it’s better to weigh, on average, the weight of the first grade is about 4.5kg and the second grade is 4.2kg, the third grade is 3.9kg.
In all, hope those is helpful to choose the prime generality high alumina brick as per your application.

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The reason of crack mesh high alumina brick

Changxing refractory shows the reasons for the high alumina refractory bricks to produce reticular cracks. It is reported that high alumina bricks often appear on the surface of the crack is the production of high alumina brick defects, the reasons for this network cracks often quite complicated. For example, the clinker content (especially R2O content), the amount of fine powder added, the critical particle size, the mixing quality of the clay, the humidity and the temperature of the green body, the shrinkage of the green body during the firing, Mulli petrochemical reaction and corundum recrystallization, etc., will lead to the surface of the refractory product produced reticulate. The sintering of high alumina brick is liquid phase sintering, the formation temperature of liquid phase and the amount of liquid phase, the firing conditions of the atmosphere is also an important factor in the surface network cracks.
The sintering degree and firing atmosphere of high alumina bricks and the volatiles present in the gas phase have a great influence on the surface crack of high aluminum products. Sintered bad clinker in the process of burning products continue to shrink, causing the product cracking and crack; at the same time sintering bad clinker, the second Mulli Petrochemical is not sufficient, in the process of burning products, clinker itself Mullerite is still continuing, which is caused by inconsistencies in the product of an internal factor, resulting in the number of products increased the number of cracks and the increase in the degree of cracking.
High-aluminum refractory products on the surface of the degree of mesh cracking with the clinker used in the water absorption is closely related. The greater the water absorption of clinker, the greater the degree of reticulation. When the clinker with the water absorption rate, the product in the firing process clinker itself to continue to complete the sintering process, products shrink larger, and uneven, and thus prone to cracking and reticulation. In addition, the firing atmosphere of the kiln is one of the causes of the network cracks in the high aluminum products. When the high aluminum products are fired, the atmosphere of the kilns is weakly oxidized and the excess air coefficient is controlled at 1.1-1.2. The practice shows that the surface cracks Excess air coefficient increases and decreases, but the excess coefficient of air fluctuations should not be too large.
Changxing refractory are mainly producing high alumina brick, high alumina refractory bricks, alkali resistant brick, castable, clay brick, insulation brick, light high alumina brick, low creep high alumina brick, high aluminum wear Brick, high aluminum lightweight insulation brick, clay insulation brick, if you have any need please contact us anytime.
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The high temperature compressive strength of the refractory fire bricks

The high temperature compressive strength of the refractory brick china (abbreviated as HCS) refers to the maximum pressure (in MPa) per unit area of the material at high temperatures above 1000-1200 °C. The compressive strength of the refractory material generally varies with increasing temperature. From the normal temperature from the temperature rise, the intensity of a straight line down. Since then, some of the material continues to decline with increasing temperature; some materials rise as the temperature rises to a certain extent and rises to a maximum temperature at a specific temperature, followed by a sharp drop. The following figure is a number of commonly used china refractory brick high temperature compressive strength with temperature changes.
The change in the high temperature compressive strength of the refractory fire brick is controlled by changes in certain components, especially those in which the matrix or its bound phase occurs at high temperatures. In general, the sintered refractory raw material, which is entirely composed of crystal, is prone to plastic deformation due to its grain and grain boundaries at high temperature, especially when its loading speed is small, so that the strength decreases with the temperature reduce. When some of the crystal phase between the melting point at high temperature or the formation of melt, such as silica brick, clay brick and high alumina brick, the matrix is mainly composed of glass phase, with the temperature rise, the strength of such multi-phase material the microstructure decreases with temperature. When the temperature is further improved, due to the viscosity of the glass phase from brittle to toughness, so that the material between the particles more firmly, so that the strength was significantly improved. Then, as the temperature increases, the melt viscosity of the material decreases sharply, and the strength of the material decreases sharply.
Changxing refractory are mainly producing high alumina brick, high alumina refractory bricks, alkali resistant brick, castable, clay brick, insulation brick, light high alumina brick, low creep high alumina brick, high aluminum wear Brick, high aluminum lightweight insulation brick, clay insulation brick, if you have any need please contact us anytime.
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Methods to masonry of boiler castable

There are several methods could be taken, to protect the boiler castable from being destroyed during masonry.
(1) The balance of refractory castable and water is important, adding not too much or too little water.
(2) Blended castable should be used within 30 minutes, and please add it to the certain depth and length at a time.
(3) Mold of it could be demolished after the castable is strong enough. The load-bearing form should be demolished when the castable reaches 70% of the strength. In order to facilitate stripping, pouring all the mold before pouring surface should be coated with a layer of oil.
(4) After the boiler masonry to have enough natural drying period, so that most of the refractory layer of water can be precipitated.
(5) Before the oven, the furnace lining material must have a certain natural strength (enough safety period) to carry out. Oven principle "should not be short, should be slow should not be fast."
Changxing refractory provides refractory products, calcium silicate products, castable & mortar, china refractory brick, ceramic fiber felt, ladle & tundish nozzle, ceramic fiber with high quality for you. Such as high alumina refractory bricks, Magnesia Carbon Brick, clay refractory bricks and other refractory products.
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