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Это просто Вьюи блог

Дата регистрации: 13 апреля 2015 года

Персональный блог REFRACTORY — Это просто Вьюи блог

Fire clay brick accounts for an important position in the refractory industry. The most important feature of fire clay brick is that the raw materials can be obtainded locally.

Fire clay brick is cheap and durable. It can be used for fire protection, thermal insulation, sound insulation and moisture absorption. Therefore, it is widely used in industrial production. The scrap bricks can be reused as aggregate.

When purchasing fire clay bricks, some professional knowledge is needed and some principles should be followed.

1) Take your need into account, such as specifications and materials.

2) Select appropriate manufacturers. Shop around and capare the price before you buy. Also pay attention to the credibility of manufacturers, after sales service, product quality and service attitude.

3) After selecting a manufaturer, give a visit to the factory to understand the strength of manufacturers, scale, production qualification, production capacity and evaluation on the product from other customers.

4) Pay attention to the proper use of fire clay brick in the production and the implementation of safety measures so as to make full use of fire clay brick, reduce unnecessary losses, extend the service life ansd reduce the cost.

Recently, with the development of furnace technology, more and more fused cast AZS block is used in the glass furnace. So, how to select fused cast AZS block?

1) fused cast AZS 33# block is used in the sidewall in contact with glass liquid. In the upper part of the sidewall, WS AZS 44# block is the best choice.

2) PT fused cast AZS is enough in the upper part of the glass furnace.

3) In the insulated bottom, fused cast AZS WS 33# is suitable as the paving block and can be used with AZS ramming mass during the construction.

4) PT AZS 33# block made by the reducing method is used in the sidewall, flat arch and oblique arch of the small furnace.

5) PT α—β fused cast alumina block is generally used in the sidewall of the refining zone, while WSα—β fused cast alumina block is used in the bottom. However, fused cast alumina block is expensive, so 33# AZS block is used as an alternative.

Hot stove fire clay brick is made of refractory clay as the raw material. It is used in the hot stove, regenerator and partition walls. It is required to have good thermal shock resistance, high softening temperature and low creep rate.

China Metallurgical standard (YB / T 5107-1993) classifies the hot stove fire clay brick into RN-42、RN-40 and RN-36 3 according to the physical and chemical parameters.

There are the following provisions for the physical and chemical parameters and the allowable size deviation.

1) If the width is not more than 0.25mm, no limit to the length;

2) If the width is between 0.26-0.5mm, length should be no more than 30mm;

3) If the width is more than 0.5mm, not allowed.

Since the silica brick has low price, high purity, high softening temperature under load, no pollution to glass liquid and good resistance to R2O gases and aicd gases, it is widely used in the crown of the glass furnace, the upper part of the suspended wall, the back wall and the front wall.

The SiO2 content in the silica brick used in the glass furnaces should be controlled. And it should be mainly composed of cristobalite. For large glass furnaces and oxy-fuel glass furnaces, refractory materials with high purity, good creep resistance and good corrosion resistance are used.

Since the advent of brick, there are three types of brick. The first is the common silica brick. the second is high quality silica brick. the third category is improved high quality silica brick.

With the development of glass mleting technology, silica bricks with better performance are required.

The checker work of glass furnaces is subjected to more serious corrosion than the crown and sidewall since all checker bricks are subjected to high temperature, duct and alkali vapor. The plugging and collapsing are the main reasons for the shutdown and cold repair of glass furnaces. Therefore, the refractory materials of the checker work should have high mechanical strength, low creep and good resistance to the changes in temperature and atmosphere and alkali corrosion and does not adsorb dust.

In the top part of the checker work, the temperature is high, which can reach up to 1400-1500℃. It is subjected to the most severe erosion by alkali vapor and dust. Rebonded fused magnesia brick is used here. Since rebonded fused magnesia brick contains less silicate phase, periclase crystals are fully developed and are directly bonded, which delays and deters the growing speed of the periclase crystals under the effect of alkali vapor and cracking and pulverizing of bricks.

In the upper part of the checker work, the temperature is 1100-1400℃. Rebonded magnesia brick 95 is used.

In the middle part of the checker work, the temperature is 800-1100℃, within which alkali metal sulfate is condensed and magnesium and calcium checker work severely eroded by Na2O and SO3. It is accompanied with large expansion of bricks and badly damaged. Therefore, the site should not use magnesia brick but direct bonded magnesia chrome brick, magnesia zirconia brick, synthetic magnesia olivine brick and magnesia alumina spinel brick.

In the lower part of the checker work, the temperature is low here and the corrosion is not quite severe. However, it is close to the flue and directly affected by cold air, so it should have good thermal shock resistance and low prices. low porosity fire clay brick is used here.

Fire clay brick plays a versatile role in the many industries.

Fire clay brick can be used in the metallurgical industry. Fire clay materials including shaped refractory materials and unshaped refractory materials acount for about 70% of the total refractory materials. Hard clay is used to produce refractory materials for theblast frunace, hot stove, ladle lining brick and plug brick.

High-alumina clay is used to produce alumina bricks for electric furnaces and blast furnaces, high aluminum lining brick and high alumina refractory mud. Hard clay and high alumina clay are often calcined into clinker at high temperature (1400 - 1800℃).

Refractory clay also has important roles in the grinding industry, chemical industry and ceramics industry. High-alumina clay can be made into abrasive materials by melting in an electric arc furnace. Fused corundum abrasive material is currently the most widely used an abrasive material. It acounts for 2/3 of the total abrasive materials.

High alumina clay can be used to produce a variety of aluminum compounds such as aluminum sulfate, aluminum hydroxide, aluminum chloride, aluminum potassium sulfate and other chemical products. In the ceramic industry, hard clay and semi-hard clay can be used to manufacture household porcelain, construction porcelain and industrial porcelain.

In the construction materials industry, refractory clay can be used to produce high alumina bricks, phosphate high alumina refractory bricks and high alumina fused cast bricks. High-alumina clay can be made into aluminum-containing cement by calcining and then mixing with limestone. This quick-setting cement has strogn heat and corrosion resistance.

Magnesia brick is a basic refractory product with periclase as its main mineral phase. It contains not less than 91% MgO and not less than 3.0% CaO.

Magnesia brick is composed of 80-90% periclase and 8%-20% other mineral phase including magnesium ferrite (MgO·Fe2O3), forsterite (2MgO · SiO2) and Calcium and magnesium olive stone (CaO·MgO·SiO2). Silicate glass contains about 3-5% magnesium, calcium and iron. These silicates may contain tricalcium silicate (3CaO · SiO2), magnesium rhodonite (3CaO · MgO · 2SiO2), calcium and magnesium olivine and forsterite, dicalcium silicate (2CaO · SiO2).

Magnesia brick has good thermal conductivity, good thermal expansion, good corrosion resistance to alkali molten slags and bad corrosion resistance to acid molten slags. Due to the low-melting silicate cements surrounded periclase, the beginning point of the softening temperature under load is not too high, but the collapse temperature is close to the beginning point. Its refractoriness is over 2000℃, but it does not make sense in the actual use. Bad thermal shock stability is one of the main reasons for the destruction.

In the storage and transport, special attention should be paid to moisture-proof to avoid burst after affected with damp.

Zircon is chemically inert with good erosion resistance to high temperature molten glass and slag solution. High dense zircon brick made of zircon powder as the main raw material has good high temperature strength and strong resistance to glass liquid, so it is widely used as the bottom paving block and back lining structure in the glass furnaces and the lining of the glass furnaces for producing glass fiber.

During the use, some parts of the glass furnace are required to have good thermal shock resistance. Since the thermal shock stability of the dense zircon brick is bad, it reduces the service life of glass furnaces and increases the repair cost of glass furnaces.

Zircon can improve the properties of dense zircon brick. The dense zircon brick is made of zircon powder by adding high pure industrial zirconia, fused stabilized zirconia and desilicated zirconia. After Formulating according to the amount of the added zirconia, wet-mixing, spray granulation, isostatic pressing and sintering at 1530 ℃ and 12h insulation, 69% dense zircon brick is made.

Research about these three different samples of zirconia on the apparent porosity, bulk density, firing shrinkage and thermal shock stability and a scanning electron microscope (SEM) on the microstructure and fracture surface samples are carried out.

The results showed that: compared to 65 dense zircon brick without ZrO2 added, the samples with ZrO2 added have higher apparent porosity, bulk density, firing shrinkage and thermal shock stability.

Fire clay brick is the refractory brick containing 30-46% SiO2. It is made of clinkers calcined from refractory clays as the oxidant and bond clay as a binder agent.

The main raw material is refractory clay. Clay is an earthy mineral. It can form plastic mud pie when mixed with water and maintain the shape after drying. It has rock-like hardness after fired at high temperature.

Additionally, the clay contains a certain amount of impurities such as quartz, mica, pyrite, feldspar and organic substances. The impurities, especially iron, can reduce the quality of clay and are harmful to the fire clay bricks.

Alkalis such as Na2O and K2O exist as mica. It can improve the sintering properties of clay and form dense products after sintered. It should be fewer than 2%.

The content of CaO is generally under 11.5% and distributed evenly. So, it will not affect the refractory properties of raw materials.

There is a certain amount of TiO2 in the bond clay. It exists as diamond. When it is less than 1%, it has no big effect on the quality of bond clay. In the chemical analysis, its content is not tested alone but counted in the content of A1203 + TiO2.

When the impurities in the clay exceed 6%, the refractoriness of clay will decease and cannot be used as the raw materials. The content of organic substances in the clay is fluctuated greatly, up to 5%.

Fused cast AZS block is the most widely used fused cast refractory brick. According to the ZrO2 content, it can be divided into 33#, 36# and 41#AZS.

Fused cast AZS containing 33% ZrO2 is called 33# fused cast AZS; fused cast AZS containing 36% ZrO2 is called 36# fused cast AZS; fused cast AZS containing 41% ZrO2 is called 41# fused cast AZS.

Fused cast AZS is mainly composed of baddeleyite and corundum and their eutectic crystals. High viscosity glass phase is filled in the gaps of crystals. The crystals is directly precipitated from the molten liquid and well developed. So, it has large crystal particles and stable crystal phase. Except the voids, it has compact structure and better density than the common sintered bricks. The pores are mainly closed pores and the crystals are intertwined each other, so it has good mechanical properties and wear resistance. The impurities are difficult to invade the bricks. Therefore, this refractory brick has good corrosion resistance. besides, the transformation of ZrO2 at 900~1150℃ when heating or cooling may cause irregular deformation.

Fused cast AZS block can be used in areas in direct contact with molten metals and molten slags. It is the essential material used in the key areas that suffer from severe corrosion.

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.

The use of insulation bricks in the thermal equipment can greatly reduce the heat loss and the weight of furnaces and improve the thermal efficiency and labor productivity.

For most thermal equipment, in order to save energy and improve the working conditions, insulation is necessary. However, for some equipment, insulation is not necessary, given the pros and cons of insulation. Therefore, the actual conditions and the properties of insulation bricks should be taken into consideration when selecting the right insulation bricks.

The insulation bricks can be divided into the following types:
1) Fire clay insulation brick GB/T 3994-2005
2) High alumina insulation brick
3) Mulite insulation brick

The principles for selecting insulation bricks include:
1) It should not affect the service life of the entire refractory masonry;
2) For continuously working high temperature furnaces, generally large area insulation is reasonable and can reduce the heat loss. However, for some special areas such as the open hearth roof, insulation may reduce the service life. For periodically working furnaces, regenerative heat loss is the main factor of heat loss. Insulation may increase the temperature of masonry and increase regenerative heat loss. So, whether periodically working furnaces should be insulated is determined after calculating the heat storage and heat loss.
3) Since the insulation bricks have high porosity, they cannot withstand too much load and should not directly contact the molten metals, molten slags and high-temperature dust.
4) Insulation bricks have low strength. The brick joints and expansion joints should be properly disposed avoid the damage caused by volume expansion. Insulating firebrick should not be subjected to intense mechanical vibration, shock and friction;
5) Since insulation bricks have big reheating linear shrinkage, the maximum working temperature should be 100℃ less than the firing temperature.

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.

Insulation materials are always used as the insulation layer and lining of heating furnaces. It can reduce heat loss and save energy. There are a variety of insulation materials, including lightweight refractory products, insulation monolithic materials and refractory fiber products.

The roofs of the heating zone and soaking zone are constructed with high alumina hanging brick, with a layer of insulation board laid over it. The wall is successively constructed with high alumina brick, fire clay brick, fire clay insulation brick and insulation board. The bottom of heating zone is constructed with magnesia chrome brick, magnesia brick, fire clay brick, fire clay insulation brick and insulation board. The lining of the preheating zone is constructed with fire clay brick. Recently, more and more refractory castables are used in the heating furnace. High alumina cement, refractory castables, clay bonding refractory castables and lightweight casting materials is used in the lining.

Lightweight refractory products mainly include silica insulation brick, fire clay insulation brick, high alumina insulating brick and alumina bubble brick. The bulk density of lightweight refractory products is generally 0.6-1.2g/cm3. Its service temperature is 900-1350℃. alumina bubble brick can be used below 1800℃ for a long time.

Refractory fiber is a type of new efficient fibrous refractory insulation material. The main manufacturing methods include Melting-blowing method, high-speed centrifugation method and colloidal method.

Refractory fiber products mainly include ceramic fiber, zirconia ceramic fiber, high-purity high alumina ceramic fiber, polycrystalline mullite fiber, alumina fiber and zirconia fiber. Besides, materials for low temperature insulation include slag wool and glass fiber.

Refractory fiber products have low bulk density, low thermal conductivity, good thermal stability and mechanical shock resistance. It is soft and easy to cut and construct. Using refractory fiber as the lining can effectively reduce heat loss, save energy and rise the temperature.

REFRACTORY

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