This article provides a brief introduction to the types of refractories (mainly refractory bricks) affected by production operations and the main damage to refractories in various areas of the kiln, as well as the use of refractories in the kiln.
Types of damage
The effects of production operations on the refractory in the kiln can be roughly divided into the following four types, but the actual effects are often caused by the simultaneous presence of several causes.
1、Spalling
(1) Thermal spalling: The sharp thermal changes such as spalling or crust adhesion off at the beginning of ignition can bring about internal thermal stress of the brick, and the resulting cracking phenomenon is called thermal spalling.
(2) Mechanical peeling: due to the influence of the kiln, the melting of the iron plate of the joint or the load of the brick and other mechanical stress and the cracking phenomenon is called mechanical peeling.
(3) Structure spalling: due to the liquid phase components of cement raw materials, alkaline components or sulfur components and other foreign components of the intrusion and the formation of metamorphic layer, because it is different in the expansion and other physical properties and the cracking phenomenon is called structure spalling.
2、Melting damage
Ignition of the initial stage or the attachment of the crust off when subjected to high heat load and cement raw material liquid phase components are formed low melting point material, thus making the refractory melt damage. Usually in the firing area of magnesium-chromium bricks or chrome-free bricks are more susceptible to melting damage, but improper production operations can also cause melting damage in the cooling area or crust adhesion off area spinel bricks and even calcined area of clay bricks.
3, Wear and tear
Refers to the loss of cement raw materials to the surface layer of the brick. It is divided into mechanical wear in the calcination area and crust adhesion off area and high temperature wear including melt damage caused by the liquid phase component of cement in the firing area or cooling area. When high alumina clay brick is used in the calcination area, it reacts with the cement raw material at a lower temperature than alkaline brick to produce low melting point products, so sometimes it also causes wear on the side of the crust adhesion off area near the higher heat load.
4、Tissue embrittlement
Refers to the embrittlement phenomenon brought about by thermal stress, mechanical stress and erosion of foreign ingredients that cause tissue damage to the brick. Thermal stress is mostly generated in the crust attachment off area and firing area, is caused by the crust attachment off frequent temperature changes brought about by; mechanical stress caused by the large kiln or crust attachment off and even brick load.
From the material, the thermal expansion rate is high in the number of alkaline brick magnesia chrome brick, impurities are particularly high, repeated heating brought about by the line change rate is also high, so the embrittlement phenomenon is particularly obvious. The spinel brick has high purity, the line change rate brought by repeated heating is low, and the embrittlement resistance is very good, so it is mostly applied to the crust adhesion off area. Compared with alkaline bricks, high alumina clay bricks have low thermal expansion rate and high bond strength, so they are not easy to produce tissue embrittlement.
The main damage to the refractory in each area of the kiln
1、Cooling area
a.High temperature wear
The production operation has an impact on the refractories in the cooling area with high-temperature wear brought by cement clinker. In the cooling area, due to the unstable adhesion of crust, it is easily worn by cement clinker after sintering, so spinel bricks with high temperature strength around 1200°C are generally used. The temperature of clinker is about 1400℃, which usually does not produce melting damage, but improper operation will cause the heat load to become larger and contribute to the formation of high temperature wear.
b.Mechanical damage
Production operations on the cooling area refractory material caused by: mechanical stress brought by large kiln (large kiln fixed core, large kiln torque, mechanical stress caused by the deformation of the barrel, etc.), the drop port part of the brick of the fixed metal parts of the deformation, brick and barrel between the friction, brick load brought about by the damage. Because of the poor stiffness of the barrel at the drop port site and the easy deformation and distortion of the barrel, the brick adjacent to the fixed metal parts of the brick is especially susceptible to the friction between the metal parts and the barrel, the barrel deformation and the deformation of the metal parts (bite into).
2、Firing area
a.Melting damage
Production operations on the firing area refractory caused by the impact of: ignition or crust adhesion off the high heat load and the liquid phase of the cement raw materials caused by the melting damage. The form of melting damage is further divided into.
① crust of part of the adhesion off to accumulate water-like melting damage.
② crust is ring-shaped melting when the high temperature wear caused by the slip-like melting damage.
b. Sulfur corrosion + spalling
Production operations on the refractory caused by the original, sulfur in the fuel to the brick caused by sulfur corrosion. In the firing area deep crust more stable area, reducing environment of sulfur corrosion will cause joints iron plate was damaged and densification, and it is different from the crust expansion rate and the stress of large kiln, will cause mechanical spalling.
3、Crust adhesion off area
a. Seam iron plate
Among the effects of production operations on refractory materials, in addition to sulfur corrosion of bricks caused by sulfur in raw and fuel, there is also the problem of mechanical peeling caused by corrosion of jointed iron plates. Although the same phenomenon occurs in the case of corrosion of the joint iron plate caused by sulfur corrosion as explained in the previous section, the brick itself is more susceptible to sulfur corrosion in a reducing environment than deep in the firing area where the crust is more stable, because the crust adheres and falls off frequently in the crust adhering and falling off area, and the heat load on the brick itself is higher.
In order to reduce the damage of the jointed iron plate, the thickness of the iron plate can be set to 0.2 mm to minimize its effect. By taking this measure, the mechanical damage caused by the melting damage of the iron plate can be greatly reduced. In addition, this reduces the thickness of the iron plate and the thickness of the bonding material so that the construction can be carried out like mortarless bricklaying, forming a compact construction whole, when the expansion allowance can be reduced to one for every 8 bricks.
b.Embrittlement peeling
In the crust attached off more frequently in this area, in addition to thermal stress and mechanical stress brought about by the tissue embrittlement, there is sulfur corrosion brought about by the tissue embrittlement, it aggravates the damage brought about by the tissue embrittlement of spinel brick.
The spinel brick is basically a combination of magnesium components, and in this combination the Ca component of the brick has an effect on the trace components. Sulfur corrosion causes a selective reaction of the Ca component in the bonding tissue, producing a complex salt of alkaline sulfate and CaSO4 or CaSO4; in addition, the movement of the resulting material within the brick causes damage to the bonding tissue and aggravates the tissue embrittlement.
In addition, in the sulfur corrosion to the brick brings the tissue destruction at the same time, the alkaline sulfate and CaSO4, MgSO4 of the complex salt and KCl deposition will form a densification layer, when its boundary parts produce cracking, the resulting peeling damage or crust adhesion off, etc. will bring the brick off.
4、Calcined area
Calcined area using high alumina brick, clay brick, will cause densification and expansion rate of the difference, and the resulting structure peeling is the main manifestation of peeling damage.
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