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Common causes and solutions to the damage of refractory cast

Date:2019-06-24 15:15     writer:cement editor     Views:

1. Use position of casting material in cement kiln


The refractory castable has the advantages of low production cost, convenient construction and wide application in the cement industry. At present, it is mainly used in the pre-heater, the blanking pipe, the front and the rear kiln mouth, the third air pipe and the cooling machine, etc., and the normal service life is generally over one year.

2. Common abnormal damage in use


The castable on the top of grate cooler falls off abnormally, if it falls off after several hours of production, and then the steel plate is burned red;The service life of the castable at the kiln mouth is short, for example, the concrete plant of ShandongTai'an No. 1 has started to be damaged in less than three months. First, the end surface falls off, the main body has a slight crack and a small amount of falling off, and the large crack and obvious block fall off in the short term. These results in shutdown maintenance, which affects production.

3. Cause analysis of abnormal damage

3.1 shedding of castable due to shedding of anchor parts


During the application of castable, the anchor plays the role of tight attachment to the wall of the container, maintaining the integrity of the castable and increasing the bending resistance of the castable. In the part where the castable shedding, it is found that the anchor joint root falls off in many places, and only some solder joint imprinting is left in the smooth place, which is obviously due to the fact that the open welding of the pickpocket nail at the solder point results in the sheet shedding of the castable.

3.2 the rapid damage of castable caused by repeated and drastic changes in temperature


The thermal shock stability of castable is poor, and it is easy to be damaged by severe temperature change. Take the cooling belt of rotary kiln (especially at the mouth of kiln) as an example, which is not only subjected to continuous erosion of clinker, but also constantly subjected to secondary air and high temperature clinker in kiln. Every turn, kiln lining material is sometimes buried under high temperature material and sometimes exposed to flame, resulting in simultaneous change of lining surface temperature with the rotation of kiln, the temperature difference is above 200 ℃, and the influence depth is 15 × 20mm. According to the kiln speed 3.5r/min calculation, the periodic temperature rise and fall repeatedly leads to thermal fatigue in the surface layer of castable. If the cold kiln, this kind of temperature changes more violently. They are all the causes of castable damage. When overhaul and elimination, it can be found that the residual castable surface 20~50mm depth range is mostly peeling off, falling block phenomenon, which is mainly caused by thermal fatigue damage.

3.3 causes of construction


Refractory castable has a set of strict construction requirements, which must be operated according to this requirement in order to ensure the good physical properties of castable. For example, a company decided to replace the top castable in the high temperature area of the grate cooler. In order to ensure the ignition and commissioning according to the scheduled plan, the construction team adopted integral pouring and did not reserve expansion joints according to regulations. At the same time, in order to facilitate the construction, the water consumption is obviously larger than the required use. What is more serious is that as soon as the construction is over, the ignition heats up immediately and the material is fed as scheduled. Because of the rapid temperature rise, the temperature of castable rises sharply, and a large amount of internal moisture evaporates rapidly, resulting in large expansion stress, which makes the castable burst, spalling and leading. A large-area drop-off accident.

The above operation obviously violates the construction requirements of the refractory castable. First, there is no control of the amount of water and water, and the effect of the amount of water on the strength of the casting material is very large; secondly, no expansion joint is reserved (the expansion joints shall be reserved at intervals of about 1.5m), and it is necessary to generate a large expansion force at the time of heating.

3.4 Abnormal operation of the kiln


In other abnormal production conditions such as ignition or kiln shutdown and kiln skin falling off, there is often a rapid change in temperature, resulting in great internal stress of the castable and damage due to thermal fatigue. At the position where the air gun is installed, the service life of the castable is reduced due to frequent start-up and shutdown of the air gun. In addition, the large mechanical(shear)stress caused by the excessive deformation of the cylinder during the operation of rotary kiln causes the kiln lining to be subjected to periodic pressure and looseness, resulting in the damage of the whole refractory castable.

4 Solutions


4.1 Correct selection of the material of the anchor and the material of the welding rod, so as to prevent the anchor from falling off.


Due to the different materials of steel plate, anchor rod and electrode in kiln equipment, the thermal expansion of each part is inconsistent when heated, resulting in huge thermal stress, which can easily lead to solder joint cracking, resulting in anchor parts falling off with castable. Therefore, when choosing anchor and electrode, we should pay attention to the same material as the steel plate of kiln equipment to avoid the cracking of solder joint due to different expansion. In addition, try to use a single anchor with more solder joints or increase the length of solder joints to improve welding firmness. If the "Y" anchor firmware can be replaced with the "L" shape, or even the "L" shape can be crossed into the "X" shape welding, the anchor can also be fixed when the castable is very thin. Ability to prevent falling off.

4.2 Increase the thermal shock resistance of the castable or use the castable with better thermal shock stability


The castable with corundum as aggregate has good high temperature wear resistance and liquid corrosion resistance, but there are no microcracks and large internal pores in corundum castable, and the thermal shock resistance of corundum castable is relatively poor compared with other aggregates. After the refractory castable of corundum-mullite composite aggregate is adopted in an enterprise, the thermal shock resistance of the castable body is obviously improved.

4.3 improve the quality of castable, increase thermal capacity and reduce the change of temperature fluctuation


the internal thermal stress of the pouring material is caused by the great change of the heat of the pouring body, and the change of the heat Q of the casting body is influenced, The relation Q = m · Cp · T. T. The change of the heat change of the casting material under the same heat transfer condition can be controlled by the difference in the quality and heat capacity or the temperature difference in the use, and the damage of thermal stress can be greatly reduced. The use temperature of the position of the casting material is determined by the firing system, and does not change greatly during the whole use process; in the same way, the heat capacity belongs to the property of the casting material, and the heat capacity value of the same casting material is the phase The heat capacity of the castable with similar properties and similar properties is also different; therefore, the most effective way is to increase the total mass of the casting body by improving the quality of the casting body, so as to realize the purpose of reducing the temperature fluctuation. And the mechanical strength of the whole casting material can be improved by improving the mass and the volume of the pouring body, so that the mechanical stress damage caused by the deformation of certain casting materials in the running process is reduced. For example, in December of 2007, the Zhonglian Taishan Cement Group Co., Ltd. made a technical transformation for a 5000t/ d production line rotary kiln mouth casting material, which greatly increased the axial casting length of the kiln mouth, which was made up of the original 60 And the actual mass ratio of the casting material is increased by 50% compared with that of the original casting material. After the transformation, the service life of the castable of the kiln mouth is up to 1 year or more by the original average of less than 5 months and sometimes even less than 3 months.

4.4 Improvement of construction quality


Before construction of the casting material, the working area and the surrounding environment must be enclosed and kept clean to prevent the material from polluting the refractory material, and the construction tools and equipment shall be kept clean. If the higher hydraulic fire-resistant pouring material is adopted, the corresponding fluidity is poor under the water addition amount satisfying the strength, and the construction has a certain effect. On this basis, the strength of the castable can be reduced by any increase in the amount of water. Therefore, in order to facilitate the construction, the operator can increase the amount of water at will, resulting in a decrease in the performance of the casting body. In addition to the addition of water, the flow of the casting material is affected, and the stirring time is also improved. Some people[1] have been refractory to a certain water content. The relationship between the fluidity of the injection material and the mixing time was calculated.

In addition, curing and baking are also important factors affecting the performance of castable. Curing is to give the binder in castable a solidification and hardening time to obtain enough initial strength. The key to control the curing period is the humidity of castable (should be kept moist), the curing temperature (should be 15 ≤ 35 ℃) and the time. Baking is to evaporate the remaining water after the castable harden, promote the sintering process at high temperature, and further improve the physical properties of the castable. The heating rate is mainly controlled in the baking process, which is generally 15 °35 ℃ per hour. Once heating begins, the heating process cannot be interrupted or stopped until Heating ends. Otherwise, very careful should be taken to cool the lining, and when the temperature is re-heated, the specified steps must be followed. If a company[2]temporarily decides to replace the castable at the top of high temperature zone of grate cooler. In order to ensure the feeding according to the scheduled plan, the construction team adopts the integral pouring, and the expansion joint is not reserved as required;At the same time, the water consumption is significantly larger than the required amount for the convenience of construction. It is more serious that the ignition shall be heated immediately after the construction is completed, and the materials shall be fed as scheduled. Due to the rapid rise of temperature, the temperature of the castable rises sharply, and the large amount of internal moisture evaporates rapidly, producing a large expansion force, which causes the castable to burst and peel, causing large area. A fall-off accident. This is typical of the lack of maintenance and baking, resulting in serious consequences.

5 concluding remarks


In the actual production process, the causes of refractory castable damage and the solutions taken may not only mention the above, and they are often related to each other, so we should analyze and deal with it flexibly according to the specific situation, so as to give full play to the unique properties of refractory castable and achieve the best use effect.

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