In line with the rapid development of iron and steel metallurgy, blast furnace smelting has gradually begun to adopt some new technologies, such as increasing iron flow, high top pressure, wind pressure and smelting intensity, large air volume, and oxygen-rich injection. Such a harsh application environment will inevitably increase the demand for the quality of iron mouth gun clay. Cannon mud not only needs to meet the requirements for the use of the taphole and facilitate construction, but also needs to be able to resist corrosion from molten slag iron, reduce environmental hazards, air pollution, and improve the operating environment.
The working conditions and damage mechanism of cannon clay mainly include the following aspects:
01Thermomechanical erosion
Before tapping the iron in the blast furnace, a drill is first used to drill the center of the taphole. After the taphole is opened, the molten slag and molten iron flow to the tap trench along the drilled taphole. At this time, the gun mud withstands the high temperature of the molten iron, which is nearly 1500°C. After the iron slag is discharged, the tap hole is blocked again by new mud. The newly driven mud will come into contact with the previous mud in the tap hole. The temperature difference between the two changes from 1500°C to about 200°C. After multiple operations, huge thermal stress can easily accumulate in the taphole mud, making arc cracks easily generated inside the taphole clay. The binder of the newly driven taphole mud is condensed and carbonized inside the taphole, and the gun The process of sintering and densification of mud will cause volume shrinkage and the formation of certain cracks. These pores and cracks provide channels for molten slag iron to penetrate into the gun mud. When the taphole is opened again, the taphole will be violently washed by the molten flow, and thermo-mechanical shedding is extremely easy to occur.
In addition, the temperature difference between the inside and outside of the taphole is very large, and there is a large temperature gradient, which will lead to inconsistent sintering rates of new gun clay inside the taphole. Thermal stress is also easily generated. The accumulation of thermal stress will form micro-cracks, which are extremely dangerous. It is easy to expand along the cracks and easily form iron breaks.
02Thermochemical attack
In China, the ore raw materials provided by blast furnaces have a high slag-to-iron ratio. For example, among the raw materials used in Shougang blast furnaces, pellets and raw ore account for 20%, sinter accounts for 80%, and the slag-to-iron ratio is 310kg/ton; the raw materials used in Angang’s blast furnaces As raw materials, pellets and raw ore account for 26%, and sinter accounts for 74%. The grade of the ore entering the furnace is low, and the slag-to-iron ratio is 343kg/ton. Slag usually contains Al2O3, SiO2, CaO, MnO, FeO, etc. The corundum and clay used in gun clay also contain 5-6 common impurities, such as some oxides containing Fe, Ca, Ti, etc. During the tapping process, molten iron and molten slag flow out from the taphole one after another. The molten slag and the gun clay are in contact with each other for a long time. The oxides of the two easily react with each other. The main products are some products with lower melting points. Phases, such as tetracalcium aluminoferrite (C4AF), fayalite (F2S), etc., thus causing the erosion of the gun clay. The main reactions are:
03Operational factors
1) Influence of slag tapping and iron tapping methods
Different blast furnaces have different designs. Some have both a slag outlet and a taphole, and some have no slag outlet. For a blast furnace with a slag taphole and a taphole, the molten slag and molten iron in the furnace are released from different channels, which can greatly reduce the workload of the taphole. However, if the taphole is also used as a channel for slag liquid to be discharged, the usage of the taphole will be greatly increased, thereby aggravating the erosion process of the gun mud. Therefore, to improve the performance of taphole clay, lengthening the tapping process under relatively stable operation should be considered. In order to avoid rapid damage to the depth and diameter of the taphole, the gun mud needs to have excellent resistance to the erosion and erosion of slag iron.
2) Influence of the number of tapping times
Appropriately reduce the number of tapping times. The more fully the sintering process of the taphole inside the taphole is carried out, the better the protection of the taphole will be. On the contrary, if the corresponding number of tapping times is increased, the time between two tappings will be shorter, and the sintering process will be less complete, and the various properties of the taphole clay will be greatly reduced, and the safe production of the blast furnace will be greatly affected. . It can be seen that correspondingly reducing the number of tapping times and obtaining a longer tapping time is beneficial to the production of large blast furnaces.
3) Influence of the way of opening the taphole
The strength of the taphole mud is too high, the taphole is too deep, iron seepage causes slag iron to be mixed in the mud core, etc., which may make it difficult to open the taphole. The difficulty in opening the opening delays the tapping time and consumes drill bits and oxygen pipes. Sometimes it is necessary to cooperate with O2 blowing, which increases the opening period of the entire taphole, greatly increases the work intensity of relevant workers, and the stability of the taphole will also decrease, and the large amount of C contained in the raw material of the gun mud is easily oxidized by O2, and the gun The oxidation resistance of the mud becomes worse and the performance is greatly reduced.