JPH0260954B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for repairing refractories in molten steel containers. Vacuum degassing is a method for processing molten steel.
Typical examples include the RH method and the DH method.
These vacuum degassing treatment methods for molten steel are very effective in improving the material quality of steel, and the amount of treatment is increasing dramatically. As the throughput increases, various repair methods have been applied to improve the durability of these vacuum degassing vessels. For example, in an RH type vacuum degassing tank, the inner and outer walls such as the immersion pipe, reflux pipe, tuyeres, and side walls are subject to severe abrasion and erosion by the molten steel flow and slag during processing, and the lining material of other parts is The degree of damage is large. For this reason, the immersion pipe, reflux pipe, and tuyere part become the cause of the lifespan, so the immersion pipe or lower tank is removed from the container and lined with new lining bricks, etc. There is an urgent need to establish a method for hot repair of these parts. Today, there are two methods for repairing the outer walls of dip tubes: plastic patching and spraying. The patch repair method for plastic materials uses Al ₂ O ₃
This is a method of repairing by pressing a plastic material made of high quality aggregate, Al ₂ O ₃ -SiO ₂ clay, and phosphoric acid binder onto the surface of approximately 500 kg of refractories.
It is a simple repair method that shows resistance to erosion by molten steel and slag _due to the binder's hot hardenability at 500℃, shape retention during repair, and high Al ₂ O ₃ of >80 _% . . However, the adhesion of plastic materials to the surface of refractories is based on physical and chemical bonding by clay and phosphoric acid binders, and the adhesion is weak and cannot withstand the abrasion effects of molten steel. Furthermore, it contains approximately 10% moisture from binders, etc., and it is impossible to repair refractory surfaces at temperatures higher than 500℃ due to the rapid generation of water vapor, and the porosity after evaporation of moisture is The corrosion resistance was as high as 20 to 30%, and there were problems such as limited corrosion resistance and the need for preheating time for drying to prevent explosions and peeling, making it unsatisfactory as a repair method. In addition, the spray repair method involves spraying aggregates such as MgO or Al ₂ O ₃ and binders such as phosphoric acid together with water, etc.
It is attached to the surface of refractories, and is a method that can improve efficiency and save labor by increasing the size and mechanization. However, the durability of sprayed materials is low, and since a large amount of water is used, there is a high risk of spalling of the refractory being repaired during hot repairs, and drying and preheating are required. Therefore, there were problems such as a decrease in the operating rate of the furnace, and the method was unsatisfactory. On the other hand, methods for repairing the inner walls of reflux pipes and tuyeres include spray repair methods and press-in repair methods, but the spray repair method has the same problems as those for the inner and outer walls of immersion pipes. In the press-fit repair method, a cylindrical frame is installed inside the reflux pipe and the tuyere, and a monolithic refractory is pumped into the gap between the frame and the refractory inner wall to restore the inner wall. However, due to the pressure-feeding of monolithic refractories, added moisture
15 to 20% is required, and hot repair is impossible, and the porosity after water evaporation is as high as approximately 30%.
It is not recommended as a repair method because it has limited corrosion resistance, requires drying and preheating to evaporate moisture, reduces furnace operation rate, and is complicated and requires a lot of manpower. It is sufficient. In addition, as a method for hot repairing the inner wall of a hot metal container such as a torpedo car, Japanese Patent Application Laid-Open No. 56-100173 discloses that low-melting point oxide raw material powder, refractory raw material, and coke powder are injected together with oxygen jet, and semi-molten However, for hot repair of the inner walls of molten steel containers such as ladles that handle molten steel at a higher temperature than hot metal, RH degassing tanks, and the outer walls of immersed areas, welding is not recommended. The losses would be too great to hire. As mentioned above, the present inventor focused on a thermal spraying repair method that does not require the addition of moisture in place of the conventional repair method, which has many problems, and by selecting the optimal thermal spraying repair conditions, the inventors achieved high fire resistance of the repair material. They discovered that it is possible to ensure this, and have completed the present invention. That is, the gist of the present invention is to supply refractory powder from a burner using O ₂ and LPG as fuel gas toward the surface to be repaired through a pneumatic pipe into a flame directed toward the surface to be repaired. When spraying the body, the above refractory powder has a melting point of 700°C or lower than the burner flame temperature.
Using a mixture of 5% by weight or more of a refractory powder with a low melting point within ℃ and 95% by weight or less of a refractory powder with a high melting point exceeding the burner flame temperature, this mixed refractory powder with a low melting point and a high melting point is used. Just before the outlet of the pneumatic pipe, the concentrated low-speed pneumatic supply is converted to diluted high-speed pneumatic supply and supplied into the burner flame at a rate of 50 to 200 Kg/Hr, and the distance between the tip of the burner nozzle and the surface to be repaired is reduced to 200 Kg/Hr. ~
This is a method for repairing a molten steel vessel, characterized in that the burner flame is moved at a speed of 5 cm/sec or more over the surface to be repaired. The reasons for limiting each of the above-mentioned structural conditions in the present invention will be explained below. The low melting point refractory powder in the present invention is supplied into a burner flame in a mixed state with the high melting point refractory powder, and is injected onto the surface to be repaired to form a sufficient molten phase. The refractory powder is formed on the surface to be repaired to enable strong bonding of the high melting point refractory powder and strong welding to the surface to be repaired, and its blending amount is 5% by weight or more, and its melting point The temperature shall be within 700℃ below the burner flame temperature. That is, if it is less than 5% by weight, there is a large amount of high melting point refractory powder, and the welding effect between the powders and the surface to be repaired is small, and as a result, as shown in Fig. 1, the high melting point refractory powder In this case, the strength of the welded product made of the low melting point refractory melt decreases significantly to 30 kg/cm ² or less, and the durability of the welded product decreases, and the relationship between the melting point of the low melting point material and the burner flame temperature decreases. If the difference exceeds 700℃, the second
As shown in the figure, the amount of air bubbles enclosed in the welded material is large, the apparent porosity becomes 30% or more, and the amount of erosion increases, which is undesirable.
Because it flows easily (low viscosity) during welding, it is not possible to obtain a sufficient wall thickness for the repaired product. Next, in the present invention, the feed rate of the mixed refractory powder into the burner flame is set at 50 to 200 Kg/Hr. This means that the feeding rate of the mixed refractory powder is 50 kg/
If it is smaller than Hr, the apparent porosity of the deposit on the surface of the repaired object is as small as 20% or less, as shown in Figure 3, and the strength after solidification is 50 kg/cm ² as shown in Figure 4.
As shown in Fig. 5, the amount of corrosion loss during molten steel treatment is less than 1.0 mm/CH (; 340 Ton/CH), resulting in excellent durability. However, it takes a lot of time and effort for repair work, and the work efficiency is poor.If it is larger than 200Kg/Hr, the amount of unmelted low melting point refractory powder increases, and the deposits are as shown in Figure 3. As shown, the apparent porosity is
As shown in FIG. 4, the strength after solidification decreases to 40 kg/cm ² or less, and the weldability to the surface of the repaired object also decreases. Next, in the present invention, the distance between the tip of the burner injection port and the surface to be repaired is preferably 200 to 1000 mm. As shown in Figure 6, if the length is shorter than 200 mm, there will be a large amount of air bubbles enclosed in the welded material, resulting in an apparent porosity of 30% or more, and if it is longer than 1000 mm, the low melting point refractory powder once melted in the burner flame will Body is,
This is because a large amount of the weld solidifies before reaching the surface to be repaired, resulting in the formation of a weld with poor strength and weldability, as described above. Furthermore, it is preferable that the moving speed of the burner flame on the surface to be repaired is 5 cm/sec or more. this is,
As shown in Fig. 7, if it is less than 5 cm/sec, the early solidification of the welded material will be delayed, and as a result, it will be difficult to form a welded material layer of a predetermined thickness due to the flow down on the welded surface, and there will be no flow into the welded material. This is because the amount of air bubbles enclosed is large, the apparent porosity is as high as 30% or more, and a welded product with poor strength and weldability is formed. This upper limit is not particularly determined, and may be arbitrarily set depending on the thickness of the deposit layer, economic efficiency, burner characteristics, equipment capacity, etc. Furthermore, it is preferable to apply pressure to the welded material immediately after thermal spraying on the surface to be repaired. That is, by applying pressure, the air bubbles and pores slightly generated in the welded material layer are compressed, the apparent porosity is reduced, and the fire resistance of the welded material is improved. In addition, the mixed refractory powder in the present invention prevents wear and tear on the pneumatic pipe by pneumatically delivering it at low speed in a concentrated state until just before the outlet of the pneumatic pipe, and diluting the powder by separately connecting and introducing the powder just before the outlet of the pneumatic pipe. It is accelerated with high-speed gas and fed into the flame of the burner at high speed. For example, by installing a diluter just before the burner of a burner lance with a burner at the tip,
This extends the life of the mixed refractory powder pneumatic delivery piping to the diluter, greatly reduces the frequency of replacing the lance body, and improves the operating rate of the burner lance. Next, examples of the present invention are shown in the following table along with comparative examples.

[Table] This example and comparative example are examples in which the inner wall of the immersion tube of an RH type vacuum degassing tank was hot repaired.
The inner diameter is 600mm and the outer diameter is 1200mm, the inner brick is of direct bond quality, and the surface temperature before repair is 800℃. As is clear from Examples 1 to 4, the apparent porosity of the weld on the surface to be repaired can be reduced by thermal spraying the low melting point refractory powder under conditions of 5% to 95% by weight or more.
It is extremely low at 18-26%, and the amount of erosion by molten steel in molten steel treatment after thermal spraying is 0.3-1.2mm/CH (340T/CH).
CH) and significantly extended its lifespan. In comparison, Comparative Examples 1 and 3, in which the content of low melting point refractory powder whose melting point is lower than the burner flame temperature and whose difference from the flame temperature is less than 700°C is less than 5% by weight;
Comparative Examples 2 and 4 using low melting point refractory powder with a difference from the flame temperature of 700°C or more, and the feeding rate of the mixed refractory powder into the burner flame at a rate exceeding 200 Kg/Hr Comparative example 1 or 2, 3, 4
The apparent porosity of the sprayed material is 30 to 50.
%, and the amount of subsequent erosion by molten steel was 5%.
It was unusable due to the throughput of ~10 mm/CH, which was roughly 1 to 2 channels, or due to poor welding. As is clear from the above description, the present invention provides a high melting point refractory powder having a melting point exceeding the burner flame temperature and a low melting point refractory powder having a melting point of 5% by weight or more and having a melting point within 700°C below the burner flame temperature. By using a refractory powder mixed with 95% by weight or less of It is possible to quickly and reliably weld the mixed refractory powder in a favorable molten layer formation state and in a state with low apparent porosity, and as a result, it does not peel off during molten steel treatment. It also significantly reduces the amount of corrosion damage, maintains its durability at a high and stable level, greatly extends the life of the repaired part, and makes the molten steel processing operation smooth and highly stable, contributing to industry. This is a huge amount.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the amount of low melting point refractory powder in the mixed refractory powder and the bending strength of the welded material in the molten steel container repair method of the present invention. FIG. 2 is a graph showing the relationship between the difference between the melting point of the low melting point refractory powder and the burner flame temperature and the apparent porosity of the welded material. FIG. 3 is a graph showing the relationship between the supply rate of mixed refractory powder and the apparent porosity of the deposit. FIG. 4 is a graph showing the relationship between the feeding rate of the mixed refractory powder and the bending strength of the welded material. FIG. 5 is a graph showing the relationship between the supply rate of mixed refractory powder and the erosion rate of weld deposits in molten steel processing. FIG. 6 is a graph showing the relationship between the distance between the tip of the burner injection port and the surface to be repaired and the apparent porosity of the welded material. FIG. 7 is a graph showing the relationship between the moving speed of the burner flame on the surface to be repaired and the apparent porosity of the welded material.

Claims (1)

[Claims] 1. Refractory powder is supplied from a burner using O ₂ and LPG as fuel gas into a flame directed toward the surface to be repaired through a pneumatic pipe, and the refractory powder is applied to the surface to be repaired of the molten steel container. When thermal spraying, the above refractory powder should contain at least 5% by weight of a low-melting refractory powder whose melting point is within 700°C below the burner flame temperature, and up to 95% by weight of a high-melting refractory powder that exceeds the burner flame temperature. This mixed refractory powder with low melting point and high melting point is converted from concentrated low-speed pneumatic transport to diluted high-speed pneumatic transport just before the outlet of the pneumatic pipe, and is fed into the burner flame at a rate of 50 to 200 Kg/Hr. A method for repairing a molten steel container, characterized in that the distance between the tip of the burner spout and the surface to be repaired is 200 to 1000 mm, and the moving speed of the burner flame on the surface to be repaired is 5 cm/sec or more. . 2. The method for repairing a molten steel container according to claim 1, which comprises applying pressure to the surface of the weld deposit on the surface to be repaired immediately after thermal spraying.