As their names imply, refractory brick is used to withstand high temperature and flame, while insulation brick is used to insulate and reduce heat loss. The insulation bricks seldom directly contact flame, while refractory bricks can directly contact flame. Both have their advantages and are used in different parts of furnaces.
Insulation bricks always have thermal conductivity between 0.2-0.4 w/m.k (350±25℃), while refractory bricks have thermal conductivity above 1.0w/m.k(350±25℃). So, insulation bricks have better insulation performance than refractory bricks. the refractoriness of insulation bricks is usually under 1400 degree, while that of refractory bricks is above 1400 degree. insulation bricks are generally lightweight materials with a density between 0.8-1.0g/cm3, while that of refractory bricks is above 2.0g/cm3.
Refractory bricks have better mechanical strength, long service life and better chemical stability. They do not react with batch materials. They have better high temperature performance and can withstand high temperature up to 1900℃.
Refractory bricks and insulation bricksa are quite different. Their applications and functions are quite different. It is important to select the right materials according to the actual conditions.
Compared to the traditional processing, modern glass making technology has undergone a qualitative change in efficiency, energy consumption and quality. Furnaces, as the core equipment of glass making, continue to be improved. The rapid development of glass making promotes the development of refractories.
Refractories used in the glass furnace are required to withstand higher temperature, sharper temperature changes, more serious chemical corrosion and severer stress damage. The common refractories used in the glass furnace are as followings:
1) Fused cast AZS and fused cast high zircon block For fused cast AZS block, it is important to improve its corrosion resistance and wear resistance. Besides the oxidizing melting method, reducing the carbon content to 0.005 and improving the exudation temperature of glass phase to 1450℃, the casting method and annealing method are also improved to improve the quality and properties of fused cast AZS. Fused cast high zircon block with more than 90% ZrO2 has excellent thermal shock resistance and low potential of pollution to glass.
2) Chrome brick Dense chrome bricks made by isostatic pressing are used in the walls, throat and other severely corroded areas in the E or C glass furnaces. Its service life can be as long as 6-7 years. Cr2O3 are added into fused cast AZS block to make fused cast AZSC block (Al2O3-ZrO2-SiO2-Cr2O3). At high temperature, Cr2O3 can from solid solution with Al2O3. Since Cr2O3 has a high melting point, it can improve the viscosity of glass phase and the exudation temperature of glass phase and improve the corrosion resistance to glass.
3) Basic brick High pure direct bond basic bricks fired at 1800℃ are widely used in the walls of regerators and crown.
4) Olivine magnesia brick Since olivine bonding phase has high corrosion resistance, increasing the olivine content in the bonding phase of magnesia can greatly improve the corrosion resistance of magnesia brick. Olivine magnesia brick is cheap and widely used in the middle part of the checker work.
5) Celsian olivine brick Olivine has good corrosion resistance but insufficient thermal shock resistance. Celsian can significantly improve the thermal shock resistance. Celsian is formed in the firing process, and exists only in the binding matrix phase. Celsian can resist the corrosion of alkali and sulphate.
6) Monolithic materials The application of monolithic materials in the glass industry can greatly reduce the joints of furnace structure and the cold repair time.
Recently, as a new refractory material, zircon refractory material has been developed. In the refractory industry, natural zircon minerals and artificial extracted or synthetic zircon oxides and composite oxides have been widely developed.
Zircon materials have been more widely used in the glass industry, metallurgical industry, cement industry, ceramics industry and refractory industry, due to high melting temperature, good chemical stability, good thermal shock, and good resistance to molten metals, slags or glass liquid.
Zircon materials are mainly used in the melting zone, superstructure, sidewall and throat. Zircon refractory materials mainly include dense zircon brick, fused cast AZS block, fused cast zircon mullite brick and rebounded AZS brick.
Zircon materials have a wide application in the metallurgical industry. According to the material, zircon materials can be divided into zircon brick, zirconite bricks, alumina zircon carbon products, zircon carbon products, zirconic acid calcium products, zirconium diboride products and zirconium oxide modified refractories.
Zirconite products have good high temperature resistance, good resistance to acid slags, low thermal expansion coefficient and good thermal shock resistance. It can be used in the ladle lining and critical parts such as the slag line and the outlet. It can also be used in the ladle nozzle, tundish nozzle and pocket block.
Semi-silica brick is an aluminosilicate refractory product containing 15-30% Al2O3. It is usually made of fire clay containing quartz, pyrophyllite (Al2O3 · 4SiO2 · H2O), refractory clay or tailings of kaolin.
According to the manufacturing method, semi-silica brick can be divided into fired brick and unfired brick. Unfired bricks are made with water glass as the binding agent. The manufacturing process of fired bricks is similar to that of fire clay brick.
Whether to add clinkers is up to the properties of raw materials and refractory bricks. Siliceous clay has small firing shrinkage and the clinker is not required. In order to improve the thermal shock resistance of semi-silica bricks, 10%-20% clinker is added.
If the raw materials contain a few fusible materials and coarse quartz grains, semi-silica bricks have low density and poor strength but good thermal shock resistance and high softening temperature under load. On the contrary, the refractory bricks have bad refractory performance and poor thermal shock resistance. Besides, according to the working conditions, fine or coarse quartz or silica clinker is added.
Under 1250℃, semi-silica brick has small volume shrinkage. At high temperature, with the increase of the liquid phase, the brick has large volume shrinkage. So, its firing temperature is higher than that of the fire clay brick, generally within 1350℃-1410℃ to obtain high density refractory bricks.
When pyrophyllite is used as the raw material of semi-silica brick, the manufacturing method is up to the chemical composition of pyrophyllite. The main chemical composition of pyrophyllite has small weight loss after dehydrated and can maintain its lattice structure. It can be directly used to manufacture bricks. In order to avoid firing expansion, it can also be calcined into clinker and added when batching.
Semi-silica brick has good volume stability at high temperature and can help to improve the integrity of the masonry and reduce the slag erosion to the masonry. When contacting hot slag, it can from a layer of glaze-like substances on the surface which can block pores, prevent the penetration of slags into the brick.
Semi-silica brick is mainly used in the ladle lining and the refractory layer of the lower steel casting system. In addition, it is also used in the roof of heating furnaces, regenerator checker bricks, the lining of Cupola furnaces, the hearth and flues of furnaces.
As we all know, alpha-beta fused cast alumina block is widely used in industrial furnaces. It is composed 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.
1) White fused alumina White fused alumina is made of industrial alumina powder as the raw material. It is melted in an arc electric furnace and crystalized by cooling. White fused alumina is white and abbreviated as WFA.
2) Dense fused alumina Dense fused alumina is made of industrial alumina powder as the raw material with the addition of additives. It is melted in an arc electric furnace and crystalized by cooling. It is gray or hoary and abbreviated as OFA.
3) Sub-white fused alumina Sub-white fused alumina is also called high alumina corundum. It is made of bauxite as the main raw material with addition of additives. It is melted in an arc electric furnace and crystalized by cooling. It is brown grey or gray and abbreviated as SFA.
4) Gray fused alumina Gray fused alumina is made of bauxite as the main raw material with addition of additives. It is melted in an arc electric furnace and crystalized by cooling. It is chocolate brown and abbreviated as BFA.
Below 1350 degree, alpha-beta fused cast alumina block has excellent corrosion resistance to glass liquid. It is widely used in the working tank of glass furnaces.
Bonded again fused cast alumina block is a type of bonded again sintered refractory brick made of fused corundum clinker as the granular material and fused corundum or sintered corundum powder as the matrix.
When using fused brown corundum or white corundum as raw materials, the frits should be smashed and then processed by removing the ferro-silicon alloy and other impurities. White corundum should be processed by removing the flaky sodium aluminate crystals and other low-melting substances. The impurities are easy to be identified since they have low density and float in the surface of corundum frits.
There are a few harmful ingredients in the corundum which will cause poor sintering or cracking, so corundum should be pre-calcined before use. The residual ferro-silicon alloy is oxidized and decomposed into Fe2O3 and SiO2 at 500-1000℃ and Ti in the minerals can be oxidized into TiO2 (rutile), which can cause large volume expansion. After pre-calcining, the stress caused by those decomposition reactions and oxidation reactions can be eliminated during the pre-calcining process and cracks caused by the volume expansion of those impurities can be avoided during the sintering process.
Fused corundum block has large volume, so it should be smashed with drop hammers and other ways and then pulverized. The pulverized fused corundum is stored by size after screened. Fused corundum is hard and difficult to grind. Therefore it is wet ground by ball mills or vibration ball mills. The grain size can be less than 40μm or even 10μm. The iron in the granular material can be removed with electromagnets and the iron in the fine powder can be washed with acids.
The batching of granular materials should be according to the principles of tightly packing, multilevel ratio, less intermediate particles and more fine powder. This can improve the density and sintering of the products. The additives include aluminum phosphate, phosphoric acid, aluminum chromium phosphate, cellulose and pulp waste solution. Among them, he most promising is active phosphate. Recently, ammonium phosphate is on the trial and achieves good results. The mud should be mixed evenly with a moisture content of 3-4%. After high pressure molding, high dense bricks are obtained.
The fused cast alumina block has high purity. It is difficult to sintere and should be sintered at 1800℃. The type of the kilns used depends on the production scale. For small batch production, high-temperature batch kiln is better. For batch stable production, the small high-temperature tunnel kiln is used.
Zhengzhou Sunrise Refractory is a refractory supplier from China. We provide various refractory materials such as fused cast AZS, fused cast alumina block, silica brick, zircon brick, etc..
There are three ways to install ceramic fiber lining: external thermal insulation, internal thermal insulation and intermediate thermal insulation. The intermediate thermal insulation, due to its drawbacks, is rarely used.
The ceramic fiber materials used to install the ceramic fiber linin include ceramic fiber board, ceramic fiber blanket and ceramic fiber module. The lining is generally 25-50mm, and 50-100mm is preferred.
1) External thermal insulation The ceramic fiber board is pasted or anchored to the cold surface of the furnace walls. This structure simply needs low temperature fiber products or lightweight bricks.
2) Internal thermal insulation Ceramic fiber board is pasted on the hot surface of the furnace walls. It has good thermal insulation performance in either batch or continuous furnaces. It can reduce the heat loss of the furnace wall and the regenerative loss.
3) Intermediate thermal insulation The ceramic fiber layer is installed in the middle of the furnace wall.
The adhesives commonly used include agents made with Silica gel and water glass or mud formulated with Portland cement and sulphate.
Now most furnaces adopt the internal thermal insulation structure, since it has high thermal efficiency, good energy-saving effect and long service life. Of course, in some cases, the structure and construction method should be chosen based on the actual situation.
Zhengzhou sunrise refractory Co., Ltd. is a refractory supplier from China, specializing in various ceramic fiber materials for glass furnaces, such as ceramic fiber board, ceramic fiber blanket, ceramic fiber module, etc.
High alumina insulating bricks are also known as high alumina heat insulating bricks. It is the ideal insulation refractory material for industrial furnaces. It is characterized with high strength, low thermal conductivity, good insulation performance and low price.
It is a new type of lightweight insulating material which contains approximately 48% alumina,mullite and glass phase or corundum. It has such advantages as high porosity, small volume density, good insulation effect, high mechanical intensity, small thermal conductivity and long service life. For various industrial kilns & furnaces, it is a kind of essential refractory for energy saving and temperature preservation.
High alumina insulation brick is made by mud pouring method. The mud contains about 50% water. By adding a small amount of gypsum, the mud will quickly be solidified. An appropriate amount of phosphoric acid is added. The ratio of the dry raw materials and the phosphoric acid is controled within 1:0.7. Chemical reactions produce CO2. The reason why use phosphoric acid instead of hydrochloric acid and sulfuric acid is that the the phosphoric acid can increase the duration time of bubbles and enhance the structural strength of semi-finished products.
Since CO2 will be produced in the mud, the embryoid bodies should be removed after two hours to ensure that embryoid bodies become strong. Embryoid bodies should be dried for three days at a temperature of 60 ℃. The final step is firing. The semi-finished products should be fired at a temperature of 1600 degrees for about 4 days.
High Alumina Insulating Brick is widely used in lining or insulating layers of various industrial furnaces, and kilns in petrochemical, machinery, ceramic industry, such as lining and insulating layer of high temperature kilns, carbon black stove, gasifier, hydrogen manufacturing furnace and shuttle kiln, etc.
Zhengzhou sunrise refractory Co., Ltd. is a refractory supplier from China, offering various insulation bricks, such as high alumina insulation brick, fire clay insulation brick, silica insulation brick and mullite insulation brick.
Ceramic fiber bulk is an excellent inorganic non-metallic material with various types and advantages of good insulation, heat resistance, corrosion resistance and high mechanical strength.
Ceramic fiber bulk is made of glass balls or waste glass by melting, drawing, winding and weaving. The diameter of the monofilament is several microns to twenty microns, equivalent of 1/20-1/5 of a single human hair. Each bundle of fiber precursor is composed of hundreds or even thousands of monofilaments.
Ceramic fiber bulk has good insulation performance. According to the physical principle, gas has low thermal conductivity, so excellent insulation materials usually have many air holes inside them. Ceramic fiber bulk has many air holes inside it and its fibers are in irregular arrangement, so it is an excellent insulation material with a low thermal conductivity of 0.03w/cm.k.
Ceramic fiber bulk has advantages of noncombustible, no distortion and no embrittlement. It can resist high temperature up to 700 degrees and has A1 level of combustion performance.
Ceramic fiber bulk has good corrosive resistance to strong acid and good recoverability. It has high tensile strength, more than 1.0kg, so it can resist any shock and vibration. It has low moisture absorption rate, close to zero.
Ceramic fiber bulk does not contain any bonding agent and has no smell and no toxic. Compared with the traditional glass wool and rock wool, it does not contain any bonding agent and will not give off any toxic, acrid smoke at high temperature.
Ceramic fiber bulk is usually used in the interior compartments and ceilings of advanced buildings and for the insulation of metal duct or the inner walls of bellows, noise absorption within the room and sweat control of metal ceilings.
Refractory selection for crowns of glass furnace regenerators must recognize both the functions of the refractories and the operating environment within the chambers.
The main function of crowns is to limit thermal losses. The main operating factors to be considered are temperature, repeated temperature cycling, airborne particulates, volatiles and load. Fuel and glass composition must also be considered when deriving the refractory specifications.
The main refractories for the crowns of glass furnace regenerators include basic refractories, silica brick, mullite brick and alumino silicates refractories. In making the choice, the resistance to creep and chemical attack must be taken into consideration.
The temperature is very important for the refractory choice. Basic refractories have limits in creep resistance. If the temperature is close to 1,500°C and the material is under a strong compression, life limiting creep will ensue. As a consequence, basic refractories can be used only if the operating temperature is lower than 1,500°C (1,460-1,480°C).
Considering only creep resistance, silica brick is the best refractory because of its lack of glassy phase and its different crystalline structure, which avoids plane slipping. Furthermore, creep starts only at temperatures close to 1700°C. Mullite brick is another quality suitable for the crowns for its excellent creep resistance.
Basic refractories have a very good chemical resistance to the alkaline gases coming from the glass furnace, but they are susceptible to carry-over enriched with silica and subsequent forsterite formation at the hot face. This chemical reaction increases volume and leads structure to a collapse.
Basic refractories can be used in the crowns temperatures lower than 1,500°C (1,460-1,480°C). Silica brick is not suggested for crowns because condensation of alkali in the colder zones of the masonry would lead to corrosion, loss of mass and also holes.
Mullite brick reacts with alkali and slags to form a series of layers which prevent alkali penetrating into the refractory and wear proceeds at a minimal rate while the thermo-mechanical properties are preserved. Mullite brick is a good choice for crowns but it must have high mullite content (95-97%).
Zhengzhou sunrise refractory Co., Ltd. is a refractory supplier from China, specializing in various refractories for glass furnaces, such as fused cast AZS block, magnesia bricks, silica brick and mullite bricks.
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