What Is Refractory Brick

In short, refractory brick is a kind of brick that can resist combustion and high temperature. Its fire resistance is about 1700 ℃. It is usually made of refractory raw materials through batching, molding and roasting. Refractory bricks can be made for different purposes according to the raw materials used, and refractory bricks of different shapes can be made according to the parts used. Today, let's learn what fire bricks are from the following aspects.

1. Types of refractory bricks

Refractory bricks are divided into several categories. Different classification methods include five classification standards: primary chemical composition classification, scale and shape, chemical properties, manufacturing process and characteristics. According to these five classification standards, examples are briefly listed.

1.1 According to the primary chemical composition of refractory bricks, they can be divided into six categories: alumina silicate fire brick, magnesia bricks, carbon containing refractory bricks, zirconia bricks, silica fire brick, silicon carbide bricks. A kiln is not built with only one kind of kiln refractory bricks. It needs the deployment and application of different refractory bricks. The typical representatives of each material are briefly introduced below.

1.1.1 Aluminosilicate refractory bricks are typically fire clay bricks and high alumina bricks.

Fire clay bricks is composed of mullite (25% ~ 50%), glass phase (25% ~ 60%), cristobalite and quartz (up to 30%). Usually, the hard clay is used as the material, the mature material is calcined in advance, and then the soft clay is mixed and formed by semi dry method or plastic method.

The clay brick products are fired at 1300 ~ 1400 ℃, and a small amount of water glass, phosphoric acid and other binders can also be added to make superior clay firebrick. Refractory bricks are used for blast furnace, hot blast stove, heating furnace, boiler, lime kiln, rotary kiln, ceramic and red brick tunnel kiln.

The mineral composition of high alumina refractory brick is corundum, mullite and glass phase, and its content depends on the Al2O3 / SiO2 ratio and the type and quantity of impurities. The grade of refractory brick can be distinguished according to the Al2O3 content. High alumina refractory brick is divided into grade I high alumina brick, grade II high alumina brick and grade III high alumina brick. The materials of high alumina refractory bricks are natural ores such as high alumina bauxite and sillimanite.

There are also clinker mixed with corundum abrasive, sintered alumina and synthetic mullite, and clinker calcined with alumina and clay in different shares. It is mostly produced in high-temperature tunnel kiln by sintering method. High alumina refractory bricks also have unburned bricks that are not sintered in high-temperature tunnel kiln. High alumina refractory bricks are widely used in iron and steel kiln system, nonferrous metal smelting furnace system and boiler system.

1.1.2 Magnesia refractory bricks refer to refractory products with alkaline oxides such as MgO as the primary component. Typical refractory bricks include magnesia brick and magnesia chrome brick. Magnesia brick refers to the refractory brick with magnesite as the material, periclase as the main crystalline phase and MgO content of more than 60%, including general magnesia brick, magnesia aluminum brick, magnesia calcium brick, magnesia carbon brick and magnesia chromium brick.

Magnesia brick and magnesia chrome brick are the most important products in alkaline refractory brick. They have high fire resistance and have good resistance to alkaline slag and iron slag. They are an important high-grade refractory brick. They are mainly used in open hearth furnace, oxygen converter, electric furnace and non-ferrous metal smelting.

1.1.3 Carbon containing refractory brick refers to the fire bricks made of carbon or carbon compounds with different shapes of carbon as the primary component. Typical examples include carbon brick and graphite crucible products. Carbon brick is a high temperature resistant neutral refractory brick product made of carbon material as the primary material and an appropriate amount of binder. Carbon brick is widely used to build the bottom, hearth, bosh and lower part of blast furnace. It can improve the continuous operation time of blast furnace and prolong the service life.

In addition, carbon bricks are also widely used in electrochemical industry, chemical industry, petrochemical industry, electroplating industry, ferroalloy industrial furnace (or equipment lining), acid and alkali tank lining and pipeline, as well as furnace lining for smelting non-ferrous metals (such as lead, aluminum, tin, etc.). 

Graphite refractory products are made of natural graphite and clay as binder. Such products include graphite clay crucible, distillation tank, plug brick for cast steel, nozzle brick and steel barrel lining brick, among which the graphite clay crucible for steelmaking and smelting non-ferrous metals is the most produced and widely used.

1.1.4 Zirconium containing refractory brick belongs to acidic material and is a product made of natural zircon sand (ZrSiO4). Zirconium refractory brick is different from aluminum silicon refractory brick and carbon containing refractory brick. It has good slag resistance, low thermal expansion rate, thermal conductivity decreases with the increase of temperature, high load softening temperature, high wear resistance and good thermal shock resistance. Cheap fire brick has become an important material in various industrial fields.

With the development of continuous casting and vacuum degassing technology in metallurgical industry, zircon refractory bricks are more and more widely used. Typical examples include zircon brick, AZS fused brick, AZS sintered brick and zircon mullite fused brick. In the process of steelmaking, zircon brick adopts tapping degassing method, and zircon refractory material has good corrosion resistance and thermal shock resistance to slag and molten steel, and is suitable for working under reduced pressure.

It is widely used in the metallurgical industry to build the steel drum lining for degassing, as well as the stainless steel drum lining, continuous casting drum lining, mouth brick, plug brick, sleeve brick and high-temperature induction furnace lining. Zircon refractory brick has high resistance to acid slag and glass, so it is also widely used in the severely damaged parts of glass kilns melting the most vivid glass. Zircon refractory material also has the property of not being penetrated by metal aluminum, aluminum oxide and slag, so it also plays a good role in the bottom of aluminum smelting furnace.

AZS fused brick, also known as fused zirconium corundum brick, with the development of glass industry, AZS fused brick has become a key part of glass kiln, which has necessary fire-resistant data. It has strong resistance to the corrosion of liquid glass; AZS sintered brick is mainly used to build thermal equipment such as bottom, wall and heat storage lattice brick of glass tank kiln.

Zirconium mullite fused brick is characterized by fine crystal structure, high load softening temperature, good thermal shock resistance, high mechanical strength at room temperature and high temperature, good wear resistance, good thermal conductivity, and excellent ability to resist slag corrosion. This kind of fire resistant bricks has a wide range of uses. It is used in the discharge port of metallurgical heating furnace, soaking pit, calcium carbide furnace, glass furnace wall and so on.

1.1.5 Silica refractory brick refers to the refractory brick with SiO2 content of more than 90%. It is the primary type of acid refractory brick. It is mainly used for building coke ovens, as well as the vault and other load-bearing parts of various glass, ceramic, carbon calciners and refractory brick thermal kilns. It is also used in the high-temperature load-bearing parts of hot blast stove, but it should not be used in thermal equipment with temperature fluctuation below 600 ℃.

1.1.6 Silicon carbide refractory brick is the refractory material of high-grade refractory brick produced with silicon carbide abrasive(SIC). It has good wear resistance and corrosion resistance, high high temperature strength, high thermal conductivity, small linear expansion coefficient and good thermal shock resistance.

In iron and steel smelting, it can be used for steel barrel lining, nozzle, plug, blast furnace bottom and Bosh, tapping trough, converter and electric furnace tapping port, heating furnace without water-cooled slide rail and so on. In the smelting of non-ferrous metals (zinc, copper, aluminum, etc.), many are used in distillers, distillation tower trays, electrolytic cell side walls, molten metal pipes, suction pumps and molten metal crucibles.

In the silicate industry, it is often used as the shed plate and flame insulation material of various kilns, such as muffle furnace lining and sagger. In the chemical industry, it is mostly used in oil and gas generator, organic waste calciner, petroleum gasifier and desulfurization furnace. In addition, it can be used as rocket nozzle and high-temperature gas turbine blade in space technology.

1.2 According to the size and shape classification of refractory bricks, they can be divided into standard refractory bricks, ordinary special-shaped refractory bricks and special-shaped refractory bricks. The primary representative of standard brick refractory bricks is the refractory bricks with the size of 230 * 115 * 65mm.

Ordinary special-shaped refractory bricks refer to the refractory bricks whose size and shape meet certain requirements, including the ratio of long side dimension to short side dimension of refractory bricks, and the angle of refractory bricks cannot be too small.

Specific refractory brick refers to that the number of dimensions shall not be more than five, the ratio of long side dimension to short side dimension shall not be greater than 4, and the minimum angle of refractory brick shall not be less than 15 °.

1.3 According to the classification of chemical properties of refractory bricks, refractory bricks are divided into acid refractory bricks, alkaline refractory bricks and neutral refractory bricks, such as silica refractory bricks and zircon bricks. Magnesium bricks, magnesia chrome bricks and magnesia calcium bricks belong to alkaline refractory bricks, and high alumina fire bricks, clay bricks and corundum bricks belong to neutral refractory bricks.

1.4 According to the classification of refractory brick manufacturing process, refractory brick can be divided into fired brick, non fired brick, electric melting pouring brick and thermal insulation brick.

For example, high alumina brick belongs to sintered brick, phosphate wear-resistant brick belongs to non fired brick, electric melting zirconium corundum brick belongs to pouring brick, and thermal insulation brick also belongs to sintered brick. It can be reprocessed after sintering, high alumina brick does not need reprocessing, and electric melting zirconium corundum brick also needs a lot of grinding processes in the later stage. The manufacturing process is very characteristic.

1.5 According to the characteristics of refractory bricks, they are divided into high aluminum wear-resistant refractory bricks, lightweight thermal insulating fire brick and anti falling off high aluminum refractory bricks.

The typical representative of high alumina wear-resistant refractory brick is phosphate wear-resistant brick, the typical representative of lightweight thermal insulation refractory brick is high alumina thermal insulation brick (also known as high alumina poly light thermal insulation brick) and clay thermal insulation brick, and the typical representative of anti falling off high alumina brick is zirconium containing anti falling off high alumina brick. Each typical example is illustrated below.

1.5.1 the typical representative of high alumina wear-resistant refractory brick is phosphate wear-resistant brick. In order to improve the high-temperature application function of phosphate high alumina wear-resistant brick, kyanite, sillimanite, mullite, silicon carbide, zircon and zirconium corundum are usually introduced into the quality guess, which has a higher application rate in cement rotary kiln than high alumina bricks.

The wear-resistant brick is made of aluminum phosphate solution prepared from industrial phosphoric acid and industrial aluminum hydroxide as the binder, and its molar ratio is Al2O3: P2O5 = 1:3.2. The selected aggregate is the same as that of phosphate brick. In the application of bricks, the same as phosphate, a bond dominated by cristobalite aluminum orthophosphate is formed.

1.5.2 Heat insulating lightweight fire brick refers to the refractory material with high porosity, low bulk density and low thermal conductivity. Heat insulation and fire resistance data is also called light fire resistance data, and the typical representatives are high aluminum insulation brick (high aluminum poly light insulation brick), clay insulation brick and perlite fire brick; High alumina heat insulation light refractory brick is a heat insulation light refractory brick with bauxite as the primary and Al2O3 content not less than 48%.

The production process is froth method, and the burning method is also adopted. The high alumina heat insulation lightweight firebrick can be used for masonry insulation layer and the part where there is no high temperature melting material corrosion and erosion. When directly touching the flame, the surface touch temperature of general high aluminum insulating refractory bricks shall not be higher than 1350 ℃.

Mullite thermal insulation refractory brick can directly touch the flame and has the characteristics of high temperature resistance, high strength and remarkable energy saving. It is suitable for the lining of pyrolysis furnace, hot blast furnace, ceramic roller kiln, electric porcelain drawer kiln and various resistance furnaces; Clay thermal insulation lightweight refractory brick is a thermal insulation refractory brick with Al2O3 content of 30% ~ 48% made of refractory clay as the primary material.

The production process includes burning and adding method and foam method. Taking refractory clay, floating beads and refractory clay clinker as raw materials, adding binder and sawdust, the bulk density is 0.5% after batching, mixing, molding, drying and firing 0.5～1.5g / cm3 product. The output value of clay insulating brick accounts for more than half of the total output value of insulating refractory brick.

1.5.3 Anti falling off high alumina refractory brick. The typical representative of anti falling off high alumina brick is zirconium containing anti falling off high alumina brick. It takes the aggregate mixed with high-quality super grade high alumina bauxite and zircon sand containing ZrO2 as the material, and is prepared according to the established mass percentage.

The brick blank is made by high-pressure forming with an 800 ton press, and then fired at high temperature in a high-temperature tunnel kiln. The anti falling off high alumina brick has strong anti falling ability and good resistance to alkaline salt corrosion. There is significant gap peeling with the surrounding corundum and mullite.

The above structure of anti falling off high alumina brick will play the role of energy dissipation and improve thermal stability and high-temperature strength when receiving stress. Characteristics of anti falling off high alumina brick: it has excellent thermal shock stability, high load softening temperature, excellent high temperature function: high temperature strength, high temperature wear resistance, anti falling off function and low thermal conductivity. It is widely used in new dry process kilns, LIBOR kilns and wet process kilns in China.

2. Use of refractory brick

Refractory bricks are mainly used to build various industrial kilns, such as masonry iron smelting furnace, steel-making furnace, coke oven, glass furnace, cement kiln, steam boiler, various heat treatment furnaces, heating furnaces, etc., as well as the lining of other high-temperature kilns. Different varieties of refractory bricks cannot be mixed. When laying refractory bricks, refractory mud of the same variety as refractory bricks shall be used as binder.

3. Shape of refractory brick

There are many shapes of refractory bricks, but the common shapes of refractory bricks include standard bricks, special-shaped bricks and special-shaped bricks. Standard bricks are produced according to relevant standards such as industrial standards or national standards. The special-shaped brick and special-shaped brick are first provided with drawings during production, and the mold is customized according to the drawings. There are many specifications of standard bricks, which should be customized according to the needs of kiln.

4. Characteristics of refractory brick

4.1 Chemical composition: the main composition of refractory brick determines the quality and fire resistance characteristics of brick body.

4.2 Bulk density: the greater the bulk density, the better the compactness and strength of the refractory brick, and the greater the thermal conductivity may be; On the contrary, it has small compactness, low strength and good thermal insulation effect.

4.3 Apparent porosity: the apparent porosity of general high-density refractory bricks is 3% - 10%, that of ordinary dense refractory bricks is 20% - 30%, and that of light refractory bricks is 45% - 48%.

4.4 Load softening temperature: it refers to the temperature at which the refractory brick bears constant compressive load and deforms under the heating condition of a certain heating rate. It indicates the resistance of the refractory to the simultaneous action of high temperature and load. For example, the 0.2MPa load softening temperature of mullite refractory brick produced is 1650 ℃, and this mullite brick is used in the main pipe and orifice of hot air pipeline. The working environment of this part is about 1200 ℃, so mullite refractory brick is more than enough here.

4.5 Thermal shock resistance: refractory bricks can withstand extremely hot and cold temperature changes without being damaged. For example, clay bricks can be used for molten iron storage and transportation of molten iron tanks.

4.6 Compressive strength: the ultimate load that the refractory brick can bear per unit area at a certain temperature (generally under normal temperature) without being damaged.

4.7 Linear change rate of reheating: the residual shrinkage or expansion of the length of the refractory brick after heating to the specified temperature and holding for a certain time and cooling to room temperature, + indicates expansion and - indicates shrinkage. Linear change rate is an aspect of high-temperature volume stability of refractory brick. If the shrinkage is too large, the refractory brick will fall off, etc.

The characteristics of refractory brick are directly related to the content of fire brick material. The characteristics are also different with the content of fire brick material. The characteristics of refractory bricks required are also different due to the different service environment of refractory bricks.

5. Refractory brick manufacturing process

Raw material selection - powder preparation (crushing, crushing and screening) - proportioning - mixing - pi preparation and molding - drying - sintering - Inspection - packaging.

6. Refractory brick specification

According to the national standard, the specifications of general refractory bricks are divided into five types: straight brick, side thick wedge brick, vertical thick wedge brick, vertical wedge brick and arch foot brick.

According to the shape and size standard of general refractory brick, the size of straight standard refractory brick is 230mm × 114mm × 65mm. This specification is only a specification of straight brick. Since there are many specifications of refractory bricks, they will not be explained one by one. For details, please refer to the national standard of shape and size of general refractory bricks.

Presumably, through the above introduction, you have some understanding of what refractory bricks are. Refractory bricks have a wide range of uses, many types and many specifications and sizes. Therefore, if you want to buy fire brick, you should follow the requirements of the use parts and design requirements of kiln lining to avoid unnecessary losses.

Refractory brick is a common thermal lining in our life. Any high-temperature equipment needs high temperature fire brick. Different types of refractory bricks have different functions in different fields and can meet the application requirements of high-temperature furnace construction in different fields.