Fermat spiral gradient round hole type vent plug for bottom blowing process and preparation method of Fermat spiral gradient round hole type vent plug

Abstract

The invention discloses a Fermat spiral gradual change round hole type vent plug for a bottom blowing process and a preparation method thereof.The preparation method of the Fermat spiral gradual change round hole type vent plug for the bottom blowing process comprises the following steps that 1, a geometric model of the vent plug is constructed, and a blowing hole of the vent plug is set to be in a Fermat spiral curve shape; 2, a vent plug template is manufactured through the 3D printing technology according to the geometric model; and 3, pouring vent plug slurry into the vent plug template for molding, and carrying out maintenance, drying and cooling processes to obtain the Fermat spiral gradual change round hole type vent plug. The Fermat spiral structure is fused in the channel of the vent plug, the spiral path slows down the gas flow rate and strengthens fluid-solid heat exchange, optimization of stress distribution of the vent plug is achieved, meanwhile, generated spiral bubbles form strong rotational flow in a steel ladle, and the uniform mixing efficiency and the inclusion removing effect of molten steel are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of air plugs, and in particular relates to a Fermat spiral gradient circular hole air plug for a bottom blowing process and a preparation method thereof. Background Art

[0002] In the modern steelmaking process system, the refining process outside the furnace is crucial to improving the quality of steel. As a key component of the process, the service life of the gas plug directly affects the downtime and use efficiency of the entire ladle. At present, the mainstream hole channel structure of the gas plug in the actual production process mainly includes slit type and round hole type. The slit type gas plug is the first choice for gas bricks for the ladle due to its advantages of good stirring effect and high repeated blowing rate. However, there is stress concentration in the four corners of the rectangular hole. The slit is easily penetrated by molten steel to form steel clamps, which makes it difficult to blow argon in the later stage. The uneven gap may induce the generation of large-volume bubbles, resulting in a low removal rate of tiny impurities and it is difficult to achieve the effect of pure molten steel. Compared with slit type gas bricks, round hole type gas bricks have a long service life, can significantly reduce the thermal stress concentration phenomenon around the hole, blow out bubbles of controllable size, which is conducive to optimizing the metallurgical effect, but the repeated blowing rate is low, and foreign particles will repeatedly block the channel, resulting in poor argon blowing effect. Therefore, the existing gas plugs cannot extend the service life while taking into account good metallurgical effects.

[0003] Traditional methods for preparing air plugs mainly include buried pipe type, joint type and slit type. The buried pipe type is to pre-embed several stainless steel pipes with a diameter of 1-3mm in the brick, and then cast the brick body into shape, which has the function of ventilation; the joint type is to divide the brick into multiple parts for assembly, and adjust the gaps between each part to control the number and size of the air permeable gaps. This method provides greater flexibility and can adjust the air permeability according to actual needs; the slit type is to pre-cast dozens of straight slits in the brick body, and the preparation process is relatively simple. However, this traditional preparation method has poor integrity, low production efficiency, easy deformation during casting, and it is difficult to achieve precise control of structural parameters, which limits the structural optimization of the air plug. Summary of the invention

[0004] In order to solve the above technical problems, one of the purposes of the present invention is to provide a method for preparing a Fermat spiral gradient circular hole air plug for a bottom blowing process, wherein the prepared air plug has the characteristics of high air permeability efficiency and good durability.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows: a method for preparing a Fermat spiral gradient round hole type vent plug for bottom blowing process, the preparation method is as follows:

[0006] Step 1: constructing a geometric model of a vent plug, wherein the blowing hole of the vent plug is set to be in the shape of a Fermat spiral curve;

[0007] Step 2: Use 3D printing technology to produce a breathable plug template according to the geometric model;

[0008] Step 3: Pour the breathable plug slurry into the breathable plug template for molding, and obtain a Fermat spiral gradient round-hole type breathable plug after curing, drying and cooling processes;

[0009] Among them, the Fermat spiral curve is designed by the Fermat spiral formula, and the parametric equations are as follows:

[0010] t = θ (t≥0);

[0011]

[0012] In the formula, x is the abscissa value, y is the ordinate value; a is a constant, and its value is 20 - 50 (it can be any value among 20, 25, 30, 35, 40, 45, and 50 or the corresponding range between any two values); θ is the polar angle, and its value is 0 - 180° (it can be any value among 0°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, 90°, 100°, 110°, 120°, 130°, 140°, 150°, 160°, 170° and 180° or the corresponding range between any two values).

[0013] In the above technical solution, the parameters of the breathable plug in Step 1 are as follows:

[0014] The overall height H of the breathable plug = 320 - 400 mm (it can be any value among 320 mm, 330 mm, 340 mm, 350 mm, 360 mm, 370 mm, 380 mm, 390 mm and 400 mm or the corresponding range between any two values);

[0015] The aperture r1 of the bottom air blowing section = 0.4 - 1.0 mm (it can be any value among 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm and 1.0 mm or the corresponding range between any two values);

[0016] The aperture r2 of the top air blowing section = 0.2 - 0.6 mm (it can be any value among 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm and 0.6 mm or the corresponding range between any two values);

[0017] The number of hole circles z of the breathable plug = 4 - 6 (it can be 4, 5 or 6);

[0018] The number of holes n in the z-th circle z = 2n;

[0019] The hole inclination angle α = 0 - 8° (which can be any value among 0°, 1°, 2°, 3°, 4°, 5°, 6°, 7° and 8° or the corresponding range between any two values);

[0020] The hole spacing d per turn = 16 - 20 mm (which can be any value among 16 mm, 17 mm, 18 mm, 19 mm and 20 mm or the corresponding range between any two values);

[0021] When performing parametric calculations, the pressure difference P between the upper and lower end faces is selected df as the optimization goal. At the same time, the aperture r1 of the bottom blowing section, r2 of the top blowing section, and the hole inclination angle α are determined as the input variables P1, P2, P3. Considering that the maximum temperature P4, the maximum equivalent stress P5, and the maximum plastic deformation P6 are all key factors determining the thermo-mechanical properties and metallurgical properties of the porous plug, P4 - P6 are regarded as constraint conditions. The mathematical model is as follows:

[0022]

[0023] In the formula: T max , σ, s are respectively the maximum temperature, the maximum equivalent stress, and the maximum plastic deformation of the porous plug structure; P L , P U are respectively the upper limit value and the lower limit value of the design variable.

[0024] The preparation method of the porous plug slurry in the above technical solution is: mixing sintered CMA aggregate, C12A7 aggregate, tabular corundum aggregate, tabular corundum fine powder, alumina fine powder and pure aluminate cement to obtain a mixture, adding polycarboxylate to the mixture, and stirring evenly after mixing with water to obtain the porous plug slurry.

[0025] When preparing the porous plug slurry in the above technical solution, it meets at least one of the following conditions A1 - N1:

[0026] A1: The sum of the contents of the sintered CMA aggregate and the C12A7 aggregate in the mixture is 0 - 8 wt% (which can be any value among 0 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt% and 8 wt% or the corresponding range between any two values);

[0027] B1: The content of the tabular corundum aggregate in the mixture is 62 - 70 wt% (which can be any value among 62 wt%, 63 wt%, 64 wt%, 65 wt%, 66 wt%, 67 wt%, 68 wt%, 69 wt% and 70 wt% or the corresponding range between any two values);

[0028] C1: The content of tabular corundum fine powder in the mixture is 15 - 19 wt% (which can be any value among 15 wt%, 16 wt%, 17 wt%, 18 wt%, and 19 wt% or the corresponding range between any two values);

[0029] D1: The content of alumina fine powder in the mixture is 6 - 10 wt% (which can be any value among 6 wt%, 7 wt%, 8 wt%, 9 wt%, and 10 wt% or the corresponding range between any two values);

[0030] E1: The content of pure aluminate cement in the mixture is 1 - 10 wt% (which can be any value among 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, and 10 wt% or the corresponding range between any two values);

[0031] F1: The addition amount of polycarboxylate is 0.05 - 1% of the total weight of the mixture (which can be any value among 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, and 1 wt% or the corresponding range between any two values);

[0032] G1: The addition amount of water is 4 - 6% of the total weight of the mixture (which can be any value among 4 wt%, 5 wt%, and 6 wt% or the corresponding range between any two values);

[0033] H1: The particle size of the tabular corundum aggregate is 0.5 - 6 mm (which can be any value among 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, and 6 mm or the corresponding range between any two values);

[0034] I1: The Al₂O₃ content in the tabular corundum fine powder is ≥ 98 wt%;

[0035] J1: The particle size of the tabular corundum fine powder is 0.1 - 0.5 mm (which can be any value among 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, and 0.5 mm or the corresponding range between any two values);

[0036] K1: The Al₂O₃ content in the alumina fine powder is ≥ 99 wt%;

[0037] L1: The particle size of the alumina fine powder is ≤ 6 μm;

[0038] M1: The content of Al2O3 in the calcium aluminate cement is 70 - 80 wt% (which can be any value among 70 wt%, 71 wt%, 72 wt%, 73 wt%, 74 wt%, 75 wt%, 76 wt%, 77 wt%, 78 wt%, 79 wt% and 80 wt% or the corresponding range between any two values).

[0039] N1: The particle size of the calcium aluminate cement is ≤ 50 μm.

[0040] In the above technical solution, the slurry for 3D printing in step 2 is one of photosensitive resin, polyurethane and polyvinyl alcohol.

[0041] In the above technical solution, the specific operation of step 3 is to pour the breathable plug slurry into the breathable plug template, cure it for 20 - 28 h under the conditions of an ambient temperature of 20 - 30 °C and a humidity of 70 - 85%; then dry it for 20 - 28 h under the condition of 100 - 120 °C; then under the condition of 1 - 100 Pa, heat it up to 650 - 750 °C at a rate of 0.5 - 3 °C / min, keep it warm for 1 - 3 h, after the heat preservation ends, heat it up to 900 - 1500 °C at a rate of 3 - 5 °C / min, keep it warm for 3 - 5 h, and then cool it to room temperature with the furnace, thus obtaining the Fermat spiral gradient round-hole type breathable plug.

[0042] In the above technical solution, the geometric model is parametrically calculated by using MOGA combined with the fluid-structure direct coupling technology.

[0043] The second object of the present invention is to provide a Fermat spiral gradient round-hole type breathable plug for bottom blowing process with high breathable efficiency and good durability.

[0044] In order to achieve the above object, another technical solution of the present invention is as follows: A Fermat spiral gradient round-hole type breathable plug for bottom blowing process is prepared by using the preparation method as described above.

[0045] In the above technical solution, the breathable plug is frustum-shaped, and there are evenly spaced blow holes penetrating through both ends thereof, and the blow holes are Fermat spiral gradient circular holes with a smaller upper aperture and a larger lower aperture.

[0046] In the above technical solution, the aperture of the upper end of the blow hole is 0.2 - 0.6 mm (which can be any value among 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm and 0.6 mm or the corresponding range between any two values), and the aperture of the lower end of the blow hole is 0.4 - 1.0 mm (which can be any value among 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 mm or the corresponding range between any two values).

[0047] The beneficial effects of the present invention are as follows: In the present invention, the Fermat spiral structure is incorporated into the channel of the gas permeable plug. The spiral path slows down the gas flow rate, enhances the fluid-solid heat transfer, realizes the optimization of the stress distribution of the gas permeable plug, and at the same time, the generated spiral bubbles form a strong swirl in the ladle, improving the mixing efficiency of the molten steel and the inclusion removal effect (the existing slit-type gas permeable plug and round-hole type gas permeable plug have the disadvantages of fast longitudinal heat exchange, large and few blown bubbles, easy steel leakage, and heat stress concentration at the hole corners).

[0048] The present invention adopts 3D printing technology and uses a method of layer-by-layer stacking to photocure and form the gas permeable plug template. The gas permeable plug template will burn out and leave a porous structure during firing, and will not affect the green body structure due to the formation of the pore structure. Therefore, the prepared gas permeable plug has good integrity, and at the same time can shorten the research and development cycle, and has the advantages of low production cost, high material utilization rate and high precision.

[0049] The present invention adopts the integral casting method and uses CMA aggregate, tabular corundum aggregate and calcium aluminate cement as raw material components, improving the overall strength of the Fermat spiral gradient round-hole type gas permeable plug.

[0050] The Fermat spiral round-hole type gas permeable plug prepared by the present invention is detected: the gas permeability is increased by 20% compared with the gas permeable plug disclosed in CN118635491A "A Y-type Gradient Oblique-through Round-hole Type Gas Permeable Plug for Bottom Blowing Process and Its Preparation Method", and is increased by 45% compared with the round-hole straight-through type gas permeable plug.

[0051] The present invention uses the finite element simulation software ANSYS to simulate the thermo-mechanical properties of the designed Fermat spiral gradient round-hole type gas permeable plug: compared with the Y-type gradient round-hole type gas permeable plug, the central axis temperature of the Fermat spiral gradient round-hole type gas permeable plug is lower, and the maximum temperature difference between the two reaches 278.33 °C.

[0052] The gas permeable plug prepared by the present invention has the advantages of large gas permeability and not easy to clamp steel. During service, the temperature distribution inside the gas permeable plug is uniform, relieving the heat stress concentration phenomenon, extending the service life of the gas permeable plug, and the angled spiral structure strengthens the swirl effect and has a better inclusion removal effect. Description of the Drawings

[0053] Figure 1 It is a three-dimensional schematic diagram of the gas permeable plug described in the embodiment of the present invention;

[0054] Figure 2 It is a structural schematic diagram of a single row of blow holes of the gas permeable plug described in the embodiment of the present invention;

[0055] Figure 3 It is a schematic diagram of the spiral of the blow holes in the top view state of the gas permeable plug described in the embodiment of the present invention;

[0056] Figure 4The line graph showing the temperature comparison of the central axis of the air vent plug described in the embodiments of the present invention and the Y-shaped gradually changing round-hole air vent plug in the prior art;

[0057] Figure 5 The line graph showing the pressure comparison of the central axis of the air vent plug described in the embodiments of the present invention and the Y-shaped gradually changing round-hole air vent plug in the prior art.

[0058] In the figure: 1. Air vent plug; 2. Blowing hole. Specific embodiments

[0059] The principles and features of the present invention will be described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not intended to limit the scope of the present invention. In the following paragraphs, the present invention will be described more specifically by way of example with reference to the accompanying drawings. The advantages and features of the present invention will be clearer according to the following description and the claims. It should be noted that the drawings are all in a very simplified form and use non-precise scales, only for the purpose of conveniently and clearly assisting in explaining the embodiments of the present invention.

[0060] Embodiment 1

[0061] As Figures 1 - 3 shown, this embodiment provides a Fermat spiral gradually changing round-hole air vent plug for bottom blowing process, and its preparation method is as follows:

[0062] Construct a three-dimensional geometric model of the air vent plug. The parameters in this embodiment are as follows:

[0063] The overall height H of the air vent plug = 320 mm;

[0064] The aperture r1 of the bottom blowing section = 0.5 - 0.6 mm;

[0065] The aperture r2 of the top blowing section = 0.2 - 0.3 mm;

[0066] The number of hole circles z of the air vent plug = 4 circles;

[0067] The number of holes n in the z-th circle z = 2n;

[0068] The interval d between each circle of holes = 16 mm;

[0069] The hole inclination angle α = 0 - 2°;

[0070] The constant a = 26;

[0071] The polar angle θ of the Fermat spiral = 0°;

[0072] Among them, the Fermat spiral is designed through the Fermat spiral formula, and the parametric equations are as follows:

[0073] t = θ (t ≥ 0);

[0074]

[0075] Where x is the abscissa value and y is the ordinate value.

[0076] Parametric calculations are carried out by using MOGA (i.e., multi-objective genetic algorithm) combined with the direct fluid-structure coupling technology. When carrying out the parametric calculations, the pressure difference P between the upper and lower end faces is selected df as the optimization objective. At the same time, the aperture r1 (0.5 - 0.6 mm) of the bottom blowing section, the aperture r2 (0.2 - 0.3 mm) of the top blowing section, and the hole inclination angle α (0 - 2°) are determined as the input variables P1, P2, and P3. Considering that the maximum temperature P4, the maximum equivalent stress P5, and the maximum plastic deformation P6 are all key factors determining the thermo-mechanical properties and metallurgical properties of the porous plug, P4 - P6 are regarded as the constraint conditions. The mathematical model constructed therefrom is as follows:

[0077]

[0078] Where: T max , σ, and s are respectively the maximum temperature, the maximum equivalent stress, and the maximum plastic deformation of the porous plug structure; P L , P U are respectively the upper limit value and the lower limit value of the design variable.

[0079] The geometric model is imported into a 3D printer and printed with a 3D printing slurry to obtain a porous plug template.

[0080] The porous plug slurry is poured into the porous plug template and cured for 24 h under the conditions of an environmental temperature of 20 - 30 °C and a humidity of 70 - 85%, and dried for 24 h at 110 °C; then under the condition of 1 - 100 Pa, it is heated to 650 - 750 °C at a rate of 0.5 - 3 °C / min, held for 1 - 3 h, and after the holding is completed, it is heated to 900 - 1500 °C at a rate of 3 - 5 °C / min and held for 3 - 5 h, and then cooled to room temperature with the furnace to obtain a Fermat spiral gradually changing round hole type porous plug;

[0081] Mix the sintered CMA aggregate, C12A7 aggregate, tabular corundum aggregate, tabular corundum fine powder, alumina fine powder and calcium aluminate cement to obtain a mixture. Add polycarboxylate to the mixture, stir for 3 - 5 min, then add water and stir again for 10 - 30 min to obtain the breathable plug slurry. Among them, the sum of the contents of the sintered CMA aggregate and C12A7 aggregate in the mixture is 0 - 8 wt%; the content of the tabular corundum aggregate in the mixture is 62 - 70 wt%; the content of the tabular corundum fine powder in the mixture is 15 - 19 wt%; the content of the alumina fine powder in the mixture is 6 - 10 wt%; the content of the calcium aluminate cement in the mixture is 1 - 10 wt%; the addition amount of the polycarboxylate is 0.05 - 1% of the total weight of the mixture; the addition amount of water is 4 - 6% of the total weight of the mixture; the particle size of the tabular corundum aggregate is 0.5 - 6 mm; the Al2O3 content in the tabular corundum fine powder is ≥98 wt%; the particle size of the tabular corundum fine powder is 0.1 - 0.5 mm; the Al2O3 content in the alumina fine powder is ≥99 wt%; the particle size of the alumina fine powder is ≤6 μm; the Al2O3 content in the calcium aluminate cement is 70 - 80 wt%; the particle size of the calcium aluminate cement is ≤50 μm.

[0082] The breathable plug (referred to as "Fermat spiral type") prepared in this example was tested: the air permeability was increased by 16% compared with the breathable plug (referred to as "gradual round hole type") disclosed in the patent document with the document number CN118635491A, "A Y-shaped Gradual Inclined Through Round Hole Type Breathable Plug for Bottom Blowing Process and Its Preparation Method" (as Figure 4 and Figure 5 shown).

[0083] Example 2

[0084] Same as Example 1, the difference is that:

[0085] The overall height H of the breathable plug is 340 mm;

[0086] The aperture r1 of the bottom blowing section is 0.6 - 0.7 mm;

[0087] The aperture r2 of the top blowing section is 0.2 - 0.3 mm;

[0088] The number of hole circles z of the breathable plug is 4 circles;

[0089] The number of holes nz in the z-th circle z = 2n;

[0090] The hole inclination angle α is 2 - 4°;

[0091] The hole interval d of each circle is 17 mm;

[0092] The constant a is 32;

[0093] The polar angle θ of the Fermat spiral is 60°.

[0094] The air permeable plug prepared in this embodiment is detected: due to the spiral structure of the Fermat curve, the pore volume is greatly increased, the air permeability is increased by 17%, and the heat exchange effect is enhanced.

[0095] Example 3

[0096] Same as Example 1, the difference is:

[0097] The overall height H of the air permeable plug is 360 mm;

[0098] The pore diameter r1 of the bottom air blowing section is 0.7 - 0.8 mm;

[0099] The pore diameter r2 of the top air blowing section is 0.3 - 0.4 mm;

[0100] The number of pore circles z of the air permeable plug is 5 circles;

[0101] The number of pores n in the z-th circle z = 2n;

[0102] The pore inclination angle α is 4 - 6°;

[0103] The pore interval d of each circle is 18 mm;

[0104] The constant a is 36;

[0105] The polar angle θ of the Fermat spiral curve is 90°;

[0106] The air permeable plug prepared in this embodiment is detected: due to the spiral structure of the Fermat curve, the pore volume is greatly increased, the air permeability is increased by 18%, and the heat exchange effect is enhanced.

[0107] Example 4

[0108] Same as Example 1, the difference is:

[0109] The overall height H of the air permeable plug is 380 mm;

[0110] The pore diameter r1 of the bottom air blowing section is 0.8 - 0.9 mm;

[0111] The pore diameter r2 of the top air blowing section is 0.4 - 0.5 mm;

[0112] The number of pore circles z of the air permeable plug is 5 circles;

[0113] The number of pores n in the z-th circle z = 2n;

[0114] The pore inclination angle α is 2 - 4°;

[0115] The pore interval d of each circle is 19 mm;

[0116] The constant a = 42;

[0117] The polar angle θ of the Fermat spiral curve = 120°.

[0118] The air-permeable plug prepared in this embodiment is detected: Due to the spiral structure of the Fermat curve, the pore volume is greatly increased, the air permeability is increased by 19%, and the heat exchange effect is enhanced.

[0119] Example 5

[0120] Same as Example 1, the difference is:

[0121] The overall height H of the air-permeable plug = 400 mm;

[0122] The pore diameter r1 of the bottom air-blowing section = 0.9 - 1.0 mm;

[0123] The pore diameter r2 of the top air-blowing section = 0.5 - 0.6 mm;

[0124] The number of pore circles z of the air-permeable plug = 6 circles;

[0125] The number of pores n in the z-th circle z = 2n;

[0126] The pore inclination angle α = 4 - 6°;

[0127] The interval d between each circle of pores = 20 mm;

[0128] The constant a = 50;

[0129] The polar angle θ of the Fermat spiral curve = 150°.

[0130] The air-permeable plug prepared in this embodiment is detected: Due to the spiral structure of the Fermat curve, the pore volume is greatly increased, the air permeability is increased by 20%, and the heat exchange effect is enhanced.

[0131] The above is only a preferred embodiment of the present invention, and it does not impose any form of limitation on the present invention; any ordinary technical personnel in the industry can smoothly implement the present invention according to the illustrations in the specification and the above description; however, any minor changes, modifications, and equivalent variations made by those skilled in the art within the scope of the technical solution of the present invention using the technical content disclosed above are equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications, and variations made to the above embodiments based on the essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a Fermat spiral gradient round hole type vent plug for bottom blowing process, characterized in that: The preparation method is as follows: Step 1: constructing a geometric model of the vent plug, wherein the blowing hole of the vent plug is set to be in the shape of a Fermat spiral curve; Step 2: Using 3D printing technology to make a vent plug template according to the geometric model; Step 3: pouring the vent plug slurry into the vent plug template for forming, and obtaining a Fermat spiral gradient circular hole vent plug after curing, firing and cooling processes; Among them, the Fermat spiral curve is designed by the Fermat spiral formula, and the parameter equation is as follows: t=θ(t≥0); Wherein, x is the horizontal coordinate value, y is the vertical coordinate value; a is a constant, and its value is 20-50; θ is the polar angle, and its value is 0-180°.

2. The method for preparing the Fermat spiral gradient round hole type vent plug for bottom blowing process according to claim 1, characterized in that: The parameters of the vent plug in step 1 are as follows: The overall height of the vent plug is H = 320-400mm; Bottom blowing section aperture r1 = 0.4-1.0mm; The aperture of the top blowing section r2 = 0.2-0.6mm; The number of holes of the vent plug is z = 4-6; Number of holes in the zth circle n z =2n; Hole inclination angle α = 0-8°; The interval between each circle of holes is d = 16-20 mm; When performing parametric calculation, select the upper and lower end pressure difference P df It is set as the optimization target, and the bottom blowing section aperture r1, the top blowing section aperture r2, and the hole inclination angle α are determined as input variables P1, P2, and P3. Considering that the maximum temperature P4, the maximum equivalent stress P5, and the maximum plastic deformation P6 are the key factors that determine the thermomechanical properties and metallurgical properties of the breathable plug, P4-P6 are taken as constraints, and the mathematical model is as follows: Where: T max , σ, and s are the maximum temperature, maximum equivalent stress, and maximum plastic deformation of the vent plug structure, respectively; P L , P U are the upper and lower limits of the design variable respectively.

3. The method for preparing the Fermat spiral gradient round hole type vent plug for bottom blowing process according to claim 1, characterized in that: The preparation method of the air plug slurry is: sintered CMA aggregate, C12A7 aggregate, plate-shaped corundum aggregate, plate-shaped corundum fine powder, alumina fine powder and pure aluminate cement are mixed to obtain a mixture, polycarboxylate is added to the mixture, and water is added to mix well to obtain the air plug slurry.

4. The method for preparing the Fermat spiral gradient round hole type vent plug for bottom blowing process according to claim 3, characterized in that: The preparation of the gas plug slurry meets at least one of the following conditions A1-N1: A1: The sum of the contents of sintered CMA aggregate and C12A7 aggregate in the mixture is 0-8wt%; B1: The content of plate-shaped corundum aggregate in the mixture is 62-70wt%; C1: The content of plate-like corundum fine powder in the mixture is 15-19wt%; D1: The content of alumina powder in the mixture is 6-10wt%; E1: The content of pure aluminate cement in the mixture is 1-10wt%; F1: The amount of the polycarboxylate added is 0.05-1% of the total weight of the mixture; G1: The amount of water added is 4-6% of the total weight of the mixture; H1: The particle size of the plate-shaped corundum aggregate is 0.5-6 mm; I 1: The Al2O3 content in the plate-like corundum fine powder is ≥ 98wt%; J1: The particle size of the plate-like corundum fine powder is 0.1-0.5 mm; K1: The Al2O3 content of the alumina powder is ≥ 99wt%; L1: The particle size of the alumina powder is ≤6 μm; M1: The Al2O3 content in the pure calcium aluminate cement is 70-80wt%; N1: The particle size of the pure calcium aluminate cement is ≤50 μm.

5. The method for preparing the Fermat spiral gradient round hole type vent plug for bottom blowing process according to claim 1, characterized in that: The slurry for 3D printing in step 2 is one of photosensitive resin, polyurethane and polyvinyl alcohol.

6. The method for preparing the Fermat spiral gradient round hole type vent plug for bottom blowing process according to claim 1, characterized in that: The specific operation of step 3 is to pour the air plug slurry into the air plug template, and cure it for 20-28 hours under the conditions of ambient temperature of 20-30°C and humidity of 70-85%; then dry it at 100-120°C for 20-28 hours; then heat it to 650-750°C at a rate of 0.5-3°C / min under the conditions of 1-100Pa, keep it warm for 1-3 hours, and then heat it to 900-1500°C at a rate of 3-5°C / min after the insulation, keep it warm for 3-5 hours, and then cool it to room temperature with the furnace to obtain the Fermat spiral gradient round hole air plug.

7. The method for preparing the Fermat spiral gradient round hole type vent plug for bottom blowing process according to claim 1, characterized in that: The geometric model is parameterized by MOGA combined with fluid-solid direct coupling technology.

8. A Fermat spiral gradient round hole type vent plug for bottom blowing process, characterized in that: The method is prepared according to any one of claims 1 to 7.

9. The Fermat spiral gradient round hole type vent plug for bottom blowing process according to claim 8, characterized in that: The air-permeable plug is in the shape of a truncated cone, and has air blowing holes evenly spaced therein and running through both ends thereof. The air blowing holes are circular holes of a Fermat spiral gradient type with a small aperture at the upper end and a large aperture at the lower end.

10. The Fermat spiral gradient round hole type vent plug for bottom blowing process according to claim 8, characterized in that: The diameter of the upper end of the blowing hole is 0.2-0.6 mm, and the diameter of the lower end of the blowing hole is 0.4-1.0 mm.

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