JPH0435530B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for extending the useful life of refractory-coated lances used in molten metal stirring and refining processes. Generally, a refractory-coated lance (hereinafter simply referred to as a lance), which is a metal tube coated with a refractory on the outside, is called a stirring lance and is used in the refining process. FIG. 1 is an explanatory diagram for performing a refining process using a stirring lance in a refining vessel, and FIG. 2 is an explanatory diagram of the structure of the stirring lance. In Figures 1 and 2, numeral 1 is a ladle, 2
3 is a ladle lid, 3 is a stirring lance, 4 is molten iron, 5 is slag floating on the molten iron 4, and 6 is a diagram showing bubbling when gas is blown from the stirring lance 3. Further, 7 is a metal tube of the stirring lance 3, 7' is a gas passage hole of the metal tube 7, 8 is a coated refractory coated on the outside thereof, and 9 is a flange. The stirring lance 3 having the structure shown in FIG.
A ladle or the like shown in the figure is immersed in the molten metal in the refining vessel 1, and stirring gas or refining gas and flux are blown into the stirring lance 3 to stir and refine the molten metal. used for. Further, Table 1 shows the usage conditions of the lance during general refining treatment. Conventionally, under the usage conditions shown in Table 1,
If no measures are taken to extend the service life of the lance, as shown in Table 2 below, the life of the lance is short, with an average of 27.5 cycles when hot metal is processed and an average of 2.8 cycles when molten steel is processed. It was. As a result, there is a problem of increased costs, and improvements have been desired to extend the life of the lance. In order to clarify the mechanism of the wear and tear of the coated refractory as the cause of the short service life of this lance, the present inventors investigated temperature changes within the refractory and the depth from the surface of the lance coated refractory. When refining the thermally expanded intestines in the directions (30 mm and 5 mm) using a lance,
Each was investigated when not treated. The result is the third
As shown in the figure. In FIG. 3, the vertical axis shows the temperature, and the horizontal axis shows the elapsed time of the refining process.

[Table] Furthermore, the coefficient of thermal expansion of the coated refractory of the lance is constant and does not change with temperature, and the thermal expansion coefficient is proportional to the temperature difference as shown in the following equation. △L=α(T-T ₀ ) L ₀ where △L: Thermal expansion (length at T) α: Coefficient of thermal expansion (constant with temperature) T: Temperature at that time T ₀ : Room temperature (20℃ ) L ₀ : Initial length Therefore, Figure 3 can be seen as a diagram of changes in thermal expansion over time. By the way, when a lance is immersed in molten metal in a container for refining treatment, the outer surface of the lance immediately receives heat from the molten metal and its temperature rises, as shown in FIG. In that case, the temperature inside the refractory increases later than the outside surface. At this time, thermal expansion is larger on the outer surface than on the inside, and compressive stress is applied to the surface of the coated refractory, but since the compressive strength of refractories is generally sufficiently high and does not pose a problem, preheating of the lance is not particularly necessary. found. However, after the smelting process, when the lance that has been immersed in the molten metal is pulled out into the atmosphere, it is rapidly cooled by the atmosphere. Therefore, as shown in FIG. 3, the temperature on the surface of the refractory is lower than the temperature inside the refractory. Specifically, in Figure 3, at the beginning of the refining process after 120 minutes of refining process elapsed, the refractory temperature at the surface 5 mm from the lance outer surface (solid line)
is higher than the temperature of the internal refractory at a position 30 mm from the outer surface of the lance (dashed line), but after that, the temperature of the refractory on the surface shown by the solid line is lower than the temperature of the internal refractory shown by the chain line. The initial temperature gradient per 25 mm in the thickness direction (temperature difference t between the temperature at the 30 mm position and the temperature at the 5 mm position) is approximately -200°C, and similarly, the temperature of the refractory on the surface shown by the solid line and the dashed line When the internal refractory temperature shown in each case is cooled to approximately 800℃, the temperature gradient in the thickness direction is approximately 350℃.
It shows large temperature. When the temperature gradient in the thickness direction is large like this,
Tensile stress acts on the surface of the refractory material as it attempts to contract, but the refractory material is weak against tension and cracks C occur on the surface as shown in FIG. It has been found that this crack is further enlarged during the next treatment, and that the crack is subject to slag erosion, damaging the refractory. An object of the present invention is to extend the service life of the refractory coating of a molten metal stirring lance used in molten metal stirring and refining processes, and to reduce costs. Based on the above findings, the present inventors have developed a method for preventing cracks and peeling of coated refractories and the resulting slag erosion into the cracks by lowering the lance surface temperature, which is the cause of cracks. prevent,
Furthermore, the present invention was achieved by focusing on reducing the temperature gradient in the thickness direction from the surface layer between the inside and outside of the refractory. That is, the present invention involves blowing gas and/or flux into the molten metal in a refining container such as a ladle using a molten metal stirring lance made of a metal tube having gas passage holes and a refractory material surrounding the outer periphery. When stirring, a heat insulating container made of an iron shell and a heat insulating material, which has a heating burner port at the bottom and a lid that can be opened or closed at the lower end, is installed directly above the refining container, and after the refining process is completed, the heat insulating container is The molten metal stirring lance is pulled up and housed inside the lance, and the lance is kept warm and heated so that the temperature gradient per 25mm in the thickness direction is 100℃ or less while the temperature within 30mm of the refractory surface layer of the lance is cooled to approximately 800℃. Alternatively, there is a method for extending the life of a molten metal stirring lance, which is characterized by cooling the lance metal pipe portion after heat retention and heating. The method of the present invention can be applied to any structure of the stirring lance, but as an example, the method of keeping warm or heating when using the stirring lance shown in Fig. 2 is shown in the figure. I will explain based on this. FIGS. 5a, b, c, and d are explanatory diagrams showing an example of a heat-insulating container for keeping the stirring lance 3 warm, respectively;
FIG. 6 is an explanatory diagram showing a state in which the heat insulating container is installed directly above the ladle 1. In the figure, 10 is a heat insulating container, 11 is an iron shell, 1
2 is a heat insulating material, 13 is a heat insulating lid, 14 is a hinge, 15
is a burner. This heat insulating container 10 includes an iron skin 1 including a heat insulating lid 13.
1 and a heat insulating material 12. From the standpoint of heat retention and workability, it is preferable to install this heat insulating container 10 directly above the ladle 1, as shown in FIG. . The lower end of the heat-insulating container 10 may be left open as shown in FIG. 5a, but in order to enhance the heat-insulating effect, a hinge 14 may be used as shown in FIG. It is preferable to make it openable and closable by using a sliding mechanism in the direction of the arrow as shown in FIG. If you need to heat it again,
Fuel is fed and heated by the burner 15 shown in FIG. 5d. In the method of the present invention, the stirring lance 3 after the refining process is insulated or heated to reduce thermal expansion based on the above-mentioned equation regarding the thermal expansion of the lance-coated refractory, and within 30 mm from the surface layer of the refractory. While the temperature of the refractory is being cooled to approximately 800℃, the temperature gradient per 25mm in the thickness direction of the refractory is maintained at 100℃ or less. Gas (air, _N2 ,
The lance metal tube 7 is cooled by blowing Ar, etc.), and the thermal expansion of the metal tube 7 is suppressed to eliminate the physical distortion that conventionally occurs between the metal tube 7 and the coated refractory 8. , prevents cracks and peeling that occur on the outer surface of refractories. As a result, the service life of the stirring lance 3 can be extended. Table 2 below shows examples in which the refining treatment conditions and the structure of the heat-insulating container were variously changed. In addition, as a comparative example, an example in which no heat retention or heating was performed was given as a conventional method. Further, FIG. 7 shows the temperature change in the thickness direction within the refractory in Example No. 8 shown in Table 2, with respect to the elapsed time of the refining treatment during treatment and in non-treatment.

【table】

[Table] As shown in Figure 7, at the beginning after the elapsed time of 120 minutes of refining treatment, as in Figure 3 for the conventional method,
The temperature of the refractory at a depth of 5 mm from the outer surface of the lance (solid line) is higher than the temperature of the refractory at a depth of 30 mm from the outer surface of the lance (dashed line), but after that, the temperature of the refractory at the surface (solid line) is higher. Internal refractory temperature (dashed line)
After the refining process with an elapsed time of 180 minutes, the surface refractory temperature (solid line) is higher than the internal refractory temperature (dashed line), unlike in FIG. Also, the temperature gradient per 25 mm in the thickness direction (temperature difference t between the temperature at the 30 mm position and the temperature at the 5 mm position) is maintained at 100°C while the surface temperature is cooled to 800°C.
The temperature is kept as below, so it is the third method of conventional method.
Compared to the figure, the temperature gradient in the thickness direction is reduced to 1/3, and the drop in the lance outer surface temperature is suppressed, resulting in cooling down to approximately 800°C, reducing fluctuations in thermal expansion, and increasing the life of the lance. 7.6 times. In this example, only heat insulation was performed, but in the case of Example No. 10, in which heat insulation was performed using the heat insulation container shown in FIG. 5d, the life was further extended to 8.0 times. According to the method of the present invention, as shown in Table 2, the life of the lance is longer than that of the conventional method when processing hot metal.
It is 1.2 to 1.5 times longer, and 1.9 to 2.9 times longer in the case of molten steel processing, and when the conventional method of molten steel processing is set as standard 1, the cost has become dramatically lower to 0.13 to 0.5 as shown. In the method of the present invention, the stirring lance after the refining process is placed directly above the refining container, and a heat-insulating container made of an iron skin and a heat insulating material is provided, so that the workability of heating and heat-retaining is good.
While the temperature within 30mm from the surface of the refractory is cooled to approximately 800℃, the temperature gradient per 25mm in the thickness direction of the refractory is maintained at 100℃ or less by keeping it warm, heating it, or keeping it warm, and cooling it as necessary after heating. By blowing gas into the stirring lance, it is cooled, preventing cracks and peeling that occur on the outer surface of the refractory, and as a result, the service life of the stirring lance is extended and costs are reduced.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of refining using a stirring lance in a refining vessel, Fig. 2 is an explanatory diagram of the structure of the stirring lance, and Fig. 3 is an explanatory diagram of the refining process using a stirring lance in the conventional method. An explanatory diagram showing the temperature change during non-treatment, Fig. 4 is an explanatory diagram showing cracks on the refractory surface of the stirring lance, and Figs. 5 a, b, c, and d are examples of heat-insulating containers used in the examples. Fig. 6 is an explanatory drawing showing a heat insulating container installed directly above the ladle in an example of the present invention, and Fig. 7 shows temperature changes of refractories when treated and not treated by the method of the present invention. It is an explanatory diagram. In the figure, 1... ladle, 2... ladle lid, 3...
... Stirring lance, 4... Molten iron, 5... Slag, 6...
...Bubbling, 7...Metal tube, 7'...Gas passage hole, 8...Coated refractory, 9...Flange, 10...
...Thermal insulation container, 11...Iron shell, 12...Insulation material, 1
3...Thermal lid, 14...Hinge, 15...Burner.

Claims (1)

[Scope of Claims] 1 A method for blowing gas and/or flux into molten metal in a refining container such as a ladle using a molten metal stirring lance made of a metal tube with gas passage holes and a refractory material surrounding the outer periphery. When stirring, a heat insulating container made of an iron shell and a heat insulating material, which has a heating burner port at the bottom and a lid that can be opened or closed at the lower end, is installed directly above the refining container, and after the refining process is completed, the The molten metal stirring lance is pulled up and housed in a heat insulating container, and the lance is kept warm, heated or kept warm, and after heating, the lance metal pipe section is cooled to remove water from the refractory surface layer.
A method for extending the life of a molten metal stirring lance, characterized by controlling the temperature gradient per 25 mm in the thickness direction of the refractory to 100°C or less while the temperature within 30mm is cooled to approximately 800°C.