CN107745112B - Slot type ladle breathable brick - Google Patents

Abstract

The invention provides a slit type steel ladle air brick, which comprises a circular truncated cone-shaped body, wherein slit groups are arranged in the body, each slit group consists of slits which are distributed in an annular array by taking the axis of the body as the center, the number of the slits is 2-3 circles, the number of the slits in each circle of the slit group is 6-20, each slit is a through hole penetrating through the upper bottom surface and the lower bottom surface of the body, and the cross section of each slit is oval or rectangular with a chamfer angle. The slit type steel ladle air brick provided by the invention can be used for uniformly distributing the thermal stress of the air brick and reducing the phenomenon of thermal stress concentration at the slit, so that the generation and the expansion and even the fracture of cracks are reduced, the thermal mechanical property of the air brick is enhanced, and the service life of the air brick is prolonged.

Description

Slot type ladle breathable brick

technical field

The invention relates to a slit-type ladle breathable brick, which belongs to the technical field of the use of breathable bricks for refining outside a ladle furnace.

Background technique

Due to the ever-increasing requirements for steel quality due to social development, modern iron and steel enterprises have continued to conduct in-depth research on out-of-furnace refining technology for producing high-quality steel, and found that out-of-furnace refining technology plays a vital role in increasing the types of steel and improving the quality of steel. The inert gas such as argon or nitrogen is blown into the molten steel through the breathable brick installed at the bottom of the ladle, and the buoyancy of the bubbles is used to fully stir the molten steel to uniformize the molten steel temperature, remove the inclusions in the molten steel, and effectively control the element composition and alloy deviation in the molten steel. , to improve the flow of molten steel to achieve the purpose of refining outside the furnace.

Since the thermomechanical properties of the refractory material of the permeable brick have a direct impact on the steel production cycle and the quality of the molten steel, it is particularly important to improve the thermomechanical properties of the permeable brick in order to ensure the reliability and safety of the refining process outside the furnace. During the refining process outside the furnace, the refractory material lining the ladle directly contacts the molten steel and is subject to physical erosion by the shear flow of the molten steel and chemical erosion caused by the slag. In addition, the temperature of the molten steel is caused by the changes in the refining process and the boundary conditions of different processes. Changes in thermo-mechanical stress caused by a change process. The commonly used rectangular slits are distributed radially with the center of the ventilating brick as the center of the circle, and there are single ring and double ring distribution, but the thermal stress at the end of the slit is easy to concentrate; the improved arc slit ventilating brick, although considering However, ignoring the structural change of the right-angle slit at the end, it is still easy to generate thermal stress concentration at the end of the slit.

At the same time, the periodic change of axial thermo-mechanical stress or the local concentration of thermo-mechanical stress in a certain part may cause cracks in the material, and the slag resistance and erosion resistance of the material at the crack are greatly reduced, which greatly shortens the service life of the material. Therefore, in order to meet the thermo-mechanical properties of breathable bricks under severe working conditions, it is particularly important to optimize the structure to reduce the influence of stress concentration.

SUMMARY OF THE INVENTION

In order to solve the deficiencies of the prior art, the present invention provides a slot-type ladle breathable brick, which can uniformly distribute the thermal stress of the breathable brick and reduce the thermal stress concentration at the slot, thereby reducing the generation and expansion of cracks and even fractures , Enhance the thermomechanical properties of the breathable brick and prolong the service life of the breathable brick.

The technical solution adopted by the present invention to solve the technical problem is as follows: a slit-type ladle breathable brick is provided, which includes a circular truncated body, and a group of slits is arranged inside the body, and the group of slits is formed by the axis of the body as the The center is composed of slits distributed in an annular array, the number of rings of the slit group is 2 to 3, the number of slits in each circle of the slit group is 6 to 20, and each slit is penetrating the upper and lower bottom surfaces of the main body. Through hole, its cross section is oval or chamfered rectangle.

The cross section of the slit is an ellipse with a ratio of the major axis to the minor axis of 33.3-200:1.

The ratio of the short axis of the cross section of the slit to the radius of the upper bottom of the body is 1-3:625.

The slits of the slit group are arranged and distributed radiatingly with the center of the working surface of the air-permeable brick as the center of the circle.

The slits of the slit group are radially arranged and distributed with the center of the air-permeable brick working surface as the center of the circle.

The slits of adjacent circles of the slit group are arranged staggered.

The beneficial effect that the present invention has based on its technical scheme is:

(1) The slit of a slot type ladle ventilation brick of the present invention adopts an ellipsoid, or the cross-section is an ellipse or a chamfered rectangular column, and the cross-section has no sharp corners, which can effectively uniform the thermal stress and increase the Thermal stress crack propagation resistance, reducing the occurrence of slit propagation cracks;

(2) The slits in the slot-type ladle breathable brick of the present invention can be arranged and distributed in a radial manner, which can effectively reduce the thermal stress of the breathable working surface, reduce the gradient of thermal stress, and reduce the lateral peeling of the breathable brick. and fracture;

(3) The slits in the slit-type ladle permeable brick of the present invention can adopt a radial arrangement and distribution method, which is convenient to increase the number of slits, increase the ventilation area, reduce the refining time of molten steel, increase the disturbance of the molten steel flow field, and effectively Remove inclusions and reduce alloy deviation.

Description of drawings

Fig. 1 is a structural schematic diagram of a slit type ladle breathable brick of the present invention.

FIG. 2 is a schematic cross-sectional view of a slit according to an embodiment of the present invention.

FIG. 3 is a top view of the radial slit type ladle ventilation brick according to an embodiment of the present invention.

Fig. 4 is a top view of the staggered arrangement of slit ladle ventilation bricks according to an embodiment of the present invention.

Figure 5 is a schematic diagram of the description of the incision.

Figure 6 is a curve of K _t,s /K _t,E as a function of the notch parameter t/r.

Figure 7 is a fitted curve of K _t,s /K _t,E .

Figure 8 is a cross-sectional cloud diagram of the normal stress σ _x distribution in the y-axis direction of the square-hole single-hole breathable brick.

Figure 9 is a schematic diagram of the force of the thin plate.

Figure 10 is a schematic diagram of a thin plate grid with different hole types.

Figure 11 is a cloud map of the normal stress σ _x distribution of the thin plate with elliptical holes.

Figure 12 is a cloud diagram of the equivalent stress distribution of the thin plate with elliptical holes.

Figure 13 is a cloud diagram of the normal stress σ _x distribution of the square hole thin plate.

Figure 14 is a cloud diagram of the equivalent stress distribution of the square hole thin plate.

Figure 15 is a schematic diagram of the stress analysis path.

Fig. 16 shows the normal stress σ _x and its difference distribution of different hole-shaped thin plates along the path B direction.

Figure 17 is the difference distribution of the normal stress σ _x of the sheet along the path A direction of the sheet with different hole types.

Figure 18 is the difference distribution of equivalent stress along the path B direction of different hole-shaped thin plates.

Figure 19 shows the difference distribution of the equivalent stress in the direction of path A for different hole-shaped thin plates.

In the figure: 1- body, 2- slit, 3- cross section.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and embodiments.

The present invention provides a slot type ladle breathable brick, referring to FIGS. 1 , 2 and 3 , comprising a truncated cone-shaped body 1 , a group of slits is arranged inside the body 1 , and the group of slits is formed by the axis of the body as the The center is composed of slits 2 distributed in an annular array, each slit is a through hole penetrating the upper and lower bottom surfaces of the main body, and its cross section is oval or chamfered rectangle. The cross section of the slit is an ellipse with a ratio of the major axis to the minor axis of 33.3-200:1. The ratio of the short axis of the cross section of the slit to the radius of the upper bottom of the body is 1-3:625.

Taking the breathable brick shown in Figure 1 as an example, the diameter of the upper bottom is 125mm, the bottom bottom is 185mm, and the height is 350mm, then the ratio of the short axis of the cross section of the slit to the radius of the upper bottom of the body is 1:625, The transverse section 3 of the slit may be an ellipse with a ratio of the major axis and the minor axis of 100:1 as shown in FIG. 2 , and the minor axis and major axis thereof are 0.1 mm and 10 mm, respectively. The elliptical slit can effectively uniform the thermal stress, increase the thermal stress crack propagation resistance, and reduce the occurrence of slit propagation cracks.

The slits of the slit group are arranged and distributed radiatingly with the center of the working surface of the air-permeable brick as the center of the circle. The radial arrangement and distribution of the slits can effectively reduce the thermal stress on the working surface of the ventilating installation, reduce the gradient of thermal stress, and reduce the lateral peeling and fracture of the ventilating brick.

The slits of the slit group can be radially arranged and distributed with the center of the ventilation brick working surface as the center of the circle. The radial arrangement and distribution method can easily increase the number of slits, increase the ventilation area, reduce the time of molten steel refining, increase the disturbance of the molten steel flow field, and effectively remove inclusions and alloy deviations.

The number of turns of the slit group may be 2-3 turns, and the number of slits per turn of the slit group may be 6-20. Taking the two circles of slits shown in Figure 3 as an example, the inner circle of slits and the outer circle of slits are formed in a circular array with the central axis of the air-permeable brick body as the symmetry axis, and each circle of slits is arranged radially; There are 10 slits in the outer ring, 20 slits in the outer ring, the included angle between two adjacent slits in the inner ring slit is 36°, and the included angle between two adjacent slits in the outer ring slit is 18°.

The slits in the adjacent circles of the slit group may also be staggered as shown in FIG. 4 .

When single-ring slit ventilation bricks are used in ladle refining, it is often necessary to lengthen the slits in order to increase the air permeability. However, such long slits are likely to cause steel penetration or blockage during use, which affects both safe production and the effect of blowing and stirring. . The present invention can effectively reduce the occurrence of the above phenomenon by adopting multi-circle slits.

There are 10 slits in the inner ring and 20 slits in the outer ring. The determination of the number of slits in each ring is a critical value calculated according to the turbulent kinetic energy range of the turbulent flow of molten steel in the ladle and the equipment pressure limit.

During the use of the permeable bricks, there is an obvious stress concentration phenomenon between adjacent slits in the same circle, but according to the law of stress concentration phenomenon, the stress concentration phenomenon is the smallest in the middle of adjacent slits in the same circle.

To sum up, the arrangement of staggered slits in adjacent circles can increase the air permeability of the breathable brick, reduce the stress concentration phenomenon, reduce the steel penetration and blockage of the breathable brick slit, prolong the service life of the breathable brick, and increase the disturbance stirring effect. Reduce the gradient of thermal stress and avoid lateral peeling and fracture of breathable bricks.

The stress concentration factor of different incisions is studied, reducing the stress concentration of the air-permeable brick is an important theoretical basis of the present invention, and the stress concentration factor of different incisions is different. Descriptive parameters for the incision shown in Figure 5. D represents the distance from the central axis of the vented brick to the center of the slit, and a represents the distance from the center of the slit to the vertex of the slit. According to the slit depth t of the slit, the slit opening angle α of the slit, and the slit tip radius r of the slit The types of incisions are classified as shown in Table 1.

Table 1 Incision classification table

When the incision depth of the slit is t=0, it is a smooth body without incision, and there is no problem of stress concentration. For line cracks with tip radius r->0, the stress field intensity is usually described by the stress field intensity factor, and the stress concentration factor is meaningless. The following is an analysis of the stress concentration factor of oval holes, chamfered rectangles and arc chamfered cuts.

For the convenience of expressing the stress concentration factor formula, the following slit parameters are defined:

Figure 6 is based on the stress concentration factor K _t,E of the elliptical hole in the uniform infinite plate, to find the relationship between the stress concentration factor of various slit cuts and the stress concentration factor of the elliptical hole, and K _t,s /K obtained according to the experimental data The variation curve of _{t, E} with the notch parameter t/r, the fitting formula is:

In order to compare the size of the stress concentration factor of different slit cuts, the function is fitted, and the result is shown in Figure 7. It can be seen from the figure that when t>r, it belongs to an arc or ellipse cut; when t>r, it belongs to Rectangular or deep V cut. In the elliptical slit breathable brick, the stress concentration factor of the elliptical cut is obviously smaller than that of the arc cut due to t/r＞0.4; when t/r≈0.08, the stress concentration factor of the arc cut is the smallest; but when t＞ When r is a rectangular or deep V incision (right-angled rectangular incision), its stress concentration factor is significantly larger than that of an elliptical or circular arc incision.

In real life, due to the needs of actual use, when some materials must be opened, the strength at the edge of the opening will inevitably be lower than the strength of the raw material, and a large stress will inevitably be caused at the opening. This local stress suddenly The phenomenon of increase is called stress concentration.

In the refining process outside the furnace, the damage of the breathable brick is often one of the key factors that increase the smelting cost. Thermal stress caused by thermal shock from molten steel during refining is the main reason for the damage of breathable bricks. In order to further prove that the elliptical incision can reduce the stress concentration phenomenon better than other shapes of incision, the numerical analysis of the stress of the single-hole ventilation brick is carried out for different hole types, and the conclusions are as follows:

The diameter R of the breathable brick geometric model is 600mm, the height is 400mm, the rectangular hole is 100mm*10mm, the Young's modulus is 2*10 ⁹ Pa, and the Poisson's ratio is 0.3. Assuming that the cylindrical surface is under pressure of 10000Pa, the normal stress σ _x distribution of its y-axis section is shown in Figure 8. From this figure, it can be seen that the stress field at the opening of the air-permeable brick is obviously different from the stress at other positions, and the whole In terms of the stress field, both the maximum stress and the minimum stress are distributed at the opening.

In order to better analyze the stress distribution of different hole types and quantify the factors that are likely to cause damage, the stress concentration factor becomes a better choice.

The stress concentration factor refers to the ratio of the maximum stress value σ _max at the stress concentration point to the reference stress σ _n , namely:

K _t,E =σ _max /σ _n

It partly reflects the degree of stress increase somewhere. The value of the reference stress is different, and the obtained stress concentration factor is also different. Here, the stress on the section away from the hole is taken as the reference stress.

Since the reference stress cannot be taken well in the stress field of the permeable brick, the stress concentration phenomenon of different hole types cannot be better fed back. Therefore, through the differential idea, the direction of the stress gradient in the refining process other than the argon blowing stage is infinitely differentiated, and the temperature of the sheet obtained after the infinite differentiation is uniform, and it is only affected by the extrusion force on both sides during expansion. The superposition of several infinite flat plate models with different temperatures can form a ladle breathable brick model with temperature gradient. In this paper, only the single-temperature sheet stress field is simulated.

The finite element software ANSYS is used to simulate the thin plate with different hole shapes, and the stress distribution of the thin plate under different hole shapes is obtained. Referring to FIG. 9 , assuming that both ends of the sheet are loaded with 10000Pa, the sheet size is 50*30*0.2mm, the size a*b of the oval hole is 5*2.5mm, and the diagonal length of the square hole is 10*5mm. Boundary conditions: The uniform pressure q on both sides of the plate is 10000Pa. The physical parameters of the simulated material are: Young's modulus is 2*10 ⁹ Pa, and Poisson's ratio is 0.3. The mesh is automatically divided by tetrahedral mesh and refined around the hole. The obtained mesh discretization result is shown in Figure 10, in which Figure 10(1) is an elliptical hole type, and Figure 10(2) is a diamond hole type.

It can be seen from Figure 11 and Figure 12 that the maximum stress of the elliptical hole thin plate is at the edge of the long and short axes of the elliptical hole, and it gradually changes along the axis direction. Referring to Fig. 13 and Fig. 14, similar to the stress field distribution of the elliptical hole, the stress maximum value of the square hole sheet is at the sharp corner of the hole and gradually changes along the axial direction.

In order to better reflect the change of the entire stress, it is assumed that the stress analysis path is shown in Figure 15. It can be seen from Figure 16 that the normal stress σ _x along the positive direction of the x-axis of the hole gradually decreases to q ₀ , and the compressive stress increases as it is closer to the hole; at the same x , the tensile stress of the square hole sheet is significantly higher than that of the elliptical hole. The tensile stress is large, and the compressive stress rapidly becomes the tensile stress at the edge of the hole; and the closer to the hole, the greater the slope, which means the greater the stress concentration factor. It can be seen from Figure 17 that the compressive stress along the positive direction of the y-axis of the hole gradually decreases, and the compressive stress increases as it is closer to the hole, and the stress of the square hole changes more near the hole, indicating that the stress concentration factor here is is greater than the stress concentration factor of the elliptical hole; at the same y, the compressive stress of the sheet with the square hole is greater than that of the sheet with the elliptical hole; at the edge of the hole, the compressive stress of the square hole reaches the maximum value of 50297Pa, and the compressive stress of the elliptical hole is 23121Pa . As shown in Figure 18, along the x-axis direction, the equivalent stress of the elliptical hole thin plate is smaller than that of the square hole thin plate, and the equivalent stress is equal near the edge of the thin plate; at a distance of 0.006m from the origin, there are stress abrupt changes in different hole-shaped thin plates. As shown in Figure 19, along the y-axis direction, the equivalent stress of the elliptical hole thin plate is smaller than that of the square hole thin plate, and the equivalent stress is equal near the edge of the thin plate; near the hole, the stress change of the square hole thin plate is greater than that of the elliptical hole.

Stress Concentration Factor:

σ _n =σ _c =-10000Pa

From the above numerical simulation experiments and the formula K _t,E =σ _max /σ _n , it can be known that the normal stress concentration factor of the elliptical hole in the X direction is shown in the following table:

Table 2 Stress concentration factors of different hole types

From the above experimental data, the following conclusions can be drawn:

(1) When the material is under the same load condition, the stress concentration factor of the elliptical hole is smaller than that of the square hole;

(2) When there is a hole in the material, the stress field gradient near the hole is larger, and at the same position, the stress of the elliptical hole is smaller than that of the square hole;

(3) The maximum stress of the elliptical hole material is generally at the edge of the long and short axes of the elliptical hole; the maximum stress of the square hole material is at the sharp corner.

Therefore, the slit-type ladle breathable brick provided by the present invention can uniformly distribute the thermal stress of the breathable brick and reduce the thermal stress concentration phenomenon at the slit, thereby reducing the generation and expansion of cracks or even breaking, and enhancing the thermal stress of the breathable brick. Mechanical properties, prolong the service life of breathable bricks.

Claims (4)

1. A slot-type ladle breathable brick, comprising a circular truncated body, characterized in that: the body is provided with a group of slits, and the group of slits is composed of slits distributed in an annular array with the axis of the body as the center, The number of rings of the slit group is 2 to 3, the number of slits in each circle of the slit group is 6 to 20, each slit is a through hole penetrating the upper and lower bottom surfaces of the main body, and its cross-section is elliptical, The slits of the slit group are arranged and distributed radiatingly with the center of the working surface of the air-permeable brick as the center of the circle. 2 . The slot type ladle breathable brick according to claim 1 , wherein the transverse section of the slit is an ellipse with a ratio of the major axis to the minor axis of 33.3-200:1. 3 . 3 . The slot type ladle breathable brick according to claim 2 , wherein the ratio of the short axis of the cross section of the slot to the radius of the upper bottom of the body is 1-3:625. 4 . 4 . The slot type ladle ventilation brick according to claim 1 , wherein: the slits of adjacent circles of the slit group are arranged in a staggered arrangement. 5 .

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