CN116992729A - Taper optimization design method for billet continuous casting crystallizer - Google Patents
Taper optimization design method for billet continuous casting crystallizer Download PDFInfo
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- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims abstract description 149
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Abstract
The utility model provides an optimization design method for taper of a billet continuous casting crystallizer, and relates to the technical field of steelmaking continuous casting. Firstly, collecting basic parameters of an optimally designed object crystallizer, and obtaining physical parameters of steel, a crystallizer copper pipe and cooling water; then, a multi-physical field coupling simulation model of the steel casting flow-crystallizer copper pipe is established, and initial conditions, boundary conditions and solving parameters of the model are set for simulation calculation; extracting a calculation result after the simulation calculation of the multi-physical field coupling simulation model of the steel casting flow-crystallizer copper pipe is finished, and analyzing the solidification heat transfer and shrinkage behavior, the distribution of casting powder in a slag channel and the generation and expansion of an air gap of a billet shell in the billet continuous casting crystallizer; according to the distribution of the covering slag and air gaps in the slag channel, the inner cavity structure and the taper of the crystallizer are optimized and adjusted; and finally, performing geometric modeling based on the adjusted inner cavity structure and taper of the copper pipe of the crystallizer, and repeating the above processes until the air gap layer in the slag channel is completely eliminated and the slag film is uniformly distributed.
Description
Technical Field
The utility model relates to the technical field of steelmaking continuous casting, in particular to a taper optimization design method of a billet continuous casting crystallizer.
Background
The billets produced by continuous casting are main blanks of sectional materials and wire rods, and steel bars, wire rods, section steel, flat steel and the like processed by the billets are widely applied to national defense and civil fields such as building bridges, automobile manufacturing, furniture home appliances, ships and oceans and the like, and provide important support for national economic development. Because the billet drawing speed is higher, the problem of insufficient contact between the initial setting billet shell and the crystallizer copper pipe is particularly remarkable, uneven heat transfer is easy to cause, cracks on the surface and the skin of a casting blank are caused, the production quality of a downstream rolling processing link is threatened, the product degradation and even waste judgment can be caused when serious, and huge economic loss is caused for enterprises, so that the continuous casting method has become a common technical problem to be solved urgently for continuous casting high-efficiency and high-quality production of billets.
The reverse taper design of the crystallizer is a main technical means for catering to the shrinkage of the blank shell in the initial setting stage and preventing a larger air gap between the blank shell and a copper pipe of the crystallizer. In particular to continuous casting of square billets, the reverse taper of a crystallizer is usually of a nonlinear design, and whether a taper curve reasonably has an important influence on the surface quality of casting billets. In recent years, the requirements of steel enterprises on production efficiency and production quality are further improved, and the development of the traditional continuous casting technology to the high-pulling-speed direction is promoted. Under the background, the defects of the surface quality of products caused by unreasonable taper design of the billet continuous casting crystallizer are more serious. Therefore, the design of the crystallizer taper is reasonable, and the design is a key for improving the continuous casting production quality and efficiency of the billets.
At present, the method for designing and calculating the taper of the square billet continuous casting crystallizer is mainly a parabolic method, and the method comprises the following specific operations: firstly, calculating the linear shrinkage characteristic of cast steel according to an empirical formula; then, calculating the total compensation amount required from the upper opening to the lower opening of the crystallizer according to the total shrinkage of the steel grade under the target continuous casting process condition; finally, calculating the parabolic crystallizer taper curve according to the total compensation quantity. This method is simple and easy to implement, however, the shrinkage of the initially solidified shell is highly non-linear in the actual production process, and the air gap and mold flux distribution have an important influence on the shell shrinkage. Therefore, the crystallizer taper designed by the parabolic method has poor matching property in practical application, and serious casting blank surface and subcutaneous crack defects are easy to cause.
Aiming at square billet production, the utility model patent with the application number of CN201310383942.8 discloses a method for determining the taper of an inner cavity of a continuous casting crystallizer. The method aims at obtaining three-dimensional temperature distribution of a crystallizer copper pipe and a solidified blank shell through building a three-dimensional flowing heat transfer solidification model, further respectively and independently calculating deformation of the blank shell and the copper pipe, carrying out vector superposition on each point of an interface according to a calculation result to obtain blank shell-copper pipe interface gap distribution, and finally optimizing the current taper according to the gap distribution. Considering the development of high-drawing-speed continuous casting technology in recent years, the application range of the method is greatly reduced, and in order to increase the application range, the utility model patent with the application number of CN202210268630.1 discloses a method for determining the taper of the inner cavity of a super-high-drawing-speed square billet continuous casting crystallizer, which can obtain the shrinkage of a billet shell and the high-temperature deformation of a copper pipe in the crystallizer through comprehensive simulation, and calculate the three-dimensional change rule of the optimal taper along the longitudinal direction and the transverse direction under ideal working conditions. The method for determining the taper relies on independent simulation of solidification shrinkage of the shell and copper tubes of the crystallizer, and does not consider interaction between the shell and the copper tubes under the contact condition and influence of contact behavior on deformation of the shell. Thus, such methods have a lack of accuracy in calculating taper.
Considering that a continuous casting square billet is provided with round chamfers, the utility model patent with the application number of CN202210092697.4 discloses a finite element calculation method for the continuous casting solidification heat transfer of the round-corner square billet, fully considers the round-corner geometric characteristics of the square billet in actual production, adopts a triangle unit to establish a two-dimensional solidification heat transfer finite element model, calculates the temperature change of a solidified shell of the round-corner square billet in the continuous casting process (comprising a crystallizer and a secondary cooling zone), and further calculates the shrinkage of the shell along the section direction according to the solidification shrinkage characteristic of steel. The method has great progress in calculation accuracy, is more suitable for detailed description of multi-nozzle composite spraying in a secondary cooling area, and has insufficient description on comprehensive solidification heat transfer behavior in a crystallizer.
In order to control the generation of an air gap at the interface between a blank shell and a crystallizer copper pipe, the utility model patent with the application number of CN 201110209639.7 discloses a large-taper continuous casting crystallizer copper pipe based on the blank shell drawing regulation theory, and aims to improve the integral taper compensation quantity of the crystallizer. When the casting blank goes down, the crystallizer vibrates up and down in a reciprocating way, so that the blank shell forms a drawing effect in the copper pipe, the contact between the blank shell and the copper pipe is enhanced, meanwhile, the extrusion of a protective slag layer in a molten state into a slag channel in the drawing process can be promoted, and the suppression of an air gap is facilitated. However, this strategy of increasing the taper is not practical in practice because excessive taper can exacerbate copper tube wear, reducing crystallizer life. In addition, the large taper is easy to cause the surface depression of the continuous casting blank, and serious surface and subcutaneous cracks are accompanied, so that the rolled material is degraded and even judged to be wasted. In order to relieve the adverse effect caused by large taper, the utility model patent with the application number of CN201520410926.8 discloses a straight-mouth stepped curve crystallizer copper pipe with a milling groove, and the design adopts stepped curve taper, so that the friction between a blank shell at a lower mouth and the copper pipe is reduced while nonlinear taper compensation is kept, and the service life of the crystallizer is prolonged. The overall design of the method is similar to that of the parabolic method, so that the method also has the problems of insufficient compensation precision, inapplicability to high pull speed and the like.
It can be seen that in the field of taper design of small square billet continuous casting crystallizer, the existing parabolic method, independent simulation method, large taper drawing, step compensation method and the like still have great defects in design accuracy, and cannot adapt to the development trend of high-drawing-speed continuous casting technology, so that the defects of casting blank surface and subcutaneous quality are easily caused when the method is applied to actual production. In the face of the current and vigorous market competition environment and the continuously improved technical development level, an effective taper optimization and design method for the billet continuous casting crystallizer is developed, and the method has very important practical significance and economic value for improving the inner cavity structure of the crystallizer, optimizing the heat transfer uniformity, improving the product quality and the economic benefits of enterprises.
Disclosure of Invention
The utility model aims to solve the technical problem of providing an optimization design method for the taper of the billet continuous casting crystallizer to realize the optimization design of the taper of the crystallizer aiming at the defects in the prior art.
In order to solve the technical problems, the utility model adopts the following technical scheme: the method for optimizing the design of the taper of the billet continuous casting crystallizer comprises the following steps:
step 1, collecting basic parameters of an optimal design object crystallizer; the basic parameters of the crystallizer comprise the material and structure of a copper pipe of the crystallizer, the material and distribution of a coating, the composition of steel types, the pulling speed and the superheat degree, the cooling water flow of the crystallizer, the inlet and outlet water temperature, the effective working height and the water jacket structure of the crystallizer;
step 2, obtaining physical parameters of steel, a crystallizer copper pipe and cooling water according to the current production process of billet continuous casting;
step 2-1, calculating to obtain high-temperature physical parameters of steel according to steel type components; the high-temperature physical parameters of the steel comprise the evolution of the liquid phase fraction, the solidus phase temperature and the solidification phase fraction of the steel, and the change rule of density, specific heat, enthalpy value, heat conductivity, linear thermal expansion coefficient, elastic modulus and poisson ratio along with the temperature;
step 2-2, obtaining thermophysical parameters of the copper tube of the crystallizer according to the material of the copper tube of the crystallizer; the thermophysical parameters of the crystallizer copper pipe comprise the heat conductivity coefficient, specific heat and density of a copper matrix at different temperatures and the heat conductivity coefficient, specific heat and density of a coating;
step 2-3, determining physical parameters of circulating cooling water of the crystallizer according to the environmental temperature of the billet continuous casting site; physical parameters of the circulating cooling water of the crystallizer comprise density, specific heat, heat conductivity coefficient and viscosity of the water;
step 3, establishing a multi-physical field coupling simulation model of the steel casting flow-crystallizer copper pipe; considering that the continuous casting of the small square billets adopts an arc-shaped crystallizer, namely a left-right side symmetrical structure and an inner-outer arc asymmetrical structure, a 1/2 model is established, and the full-field description of the continuous casting crystallizer of the small square billets can be realized; the specific modeling process is as follows:
step 3-1, carrying out 1 on the copper pipe of the 1/2 crystallizer: 1, geometric modeling, namely establishing a geometric model of a copper pipe of the crystallizer, reserving geometric characteristics of the crystallizer, and truly reflecting the inner cavity structure of the small square billet crystallizer and nonlinear taper compensation;
step 3-2, performing grid division on the established geometric model of the copper tube of the crystallizer, and constructing a finite element model of the copper tube of the crystallizer;
step 3-3, refining grids on the inner surface of the copper pipe of the crystallizer, distinguishing grids of the copper matrix from grids of the plating layer, and adjusting the thickness distribution of the plating layer along the longitudinal direction according to the actual condition of the copper pipe of the crystallizer;
step 3-4, endowing the copper matrix grids and the coating grids with the thermal physical parameters of the copper matrix and the coating thermal physical parameters of the coating established in the step 2-2 respectively;
step 3-5, establishing a space geometric feature of the steel casting flow and establishing a 1/2 steel casting flow geometric model based on the crystallizer copper pipe geometric model established in the step 3-1 and the effective working height of the crystallizer collected in the step 1;
step 3-6, mesh division is carried out on the established geometric model of the steel casting flow, and a finite element model of the steel casting flow is constructed;
step 3-7, extending the steel casting grid along the reverse direction of the blank pulling direction, so that the length of the casting grid above the meniscus of the crystallizer reaches 3-4 times of the effective working height of the crystallizer;
step 3-8, endowing the high-temperature physical property parameters of the steel calculated in the step 2-1 with steel casting grids;
step 3-9, integrating the crystallizer copper pipe grids and the steel casting grid established in the steps 3-1 to 3-8 to obtain a steel casting flow-crystallizer copper pipe multi-physical field coupling simulation model, so that the steel casting flow surface below the meniscus is matched with the inner surface of the crystallizer;
step 4, setting initial conditions and boundary conditions of a multi-physical field coupling simulation model of the steel casting flow-crystallizer copper pipe;
step 4-1, setting a steel casting flow as a deformed body, wherein a crystallizer copper pipe is a rigid body;
step 4-2, setting initial temperatures of the steel casting flow and cooling water of the crystallizer according to the basic parameters of the crystallizer collected in the step 1, and setting the initial temperature of a copper pipe of the crystallizer to be the factory room temperature;
step 4-3, setting the space displacement of the copper pipe of the crystallizer to be 0, and simultaneously, enabling the steel casting flow to move towards the lower opening of the crystallizer at the blank pulling speed;
and 4-4, applying a load to a unit surface vertical to the surface inside the steel casting grid unit, and simulating the ferrostatic pressure born by the solidification front in the continuous casting process of the billet, wherein the concrete process is as follows:
step 4-4-1, before each incremental step of the steel casting flow-crystallizer copper pipe multi-physical field coupling simulation model begins, judging whether each steel casting flow grid unit is positioned at the solidification front according to the grid node temperature, if the grid node temperature of each steel casting flow grid unit is larger than or smaller than the solidus temperature, judging that the grid unit is a non-solidification front unit, and if part of the grid node temperature of each steel casting flow grid unit is higher than the solidus temperature and part of the grid node temperature is lower than the solidus temperature, judging that the grid unit is a solidification front unit;
step 4-4-2, extracting coordinates of a solidification front unit, calculating the depth of a molten pool where the grid unit is currently located according to the coordinates, further calculating the hydrostatic pressure of molten steel at the position, and applying the hydrostatic pressure to the corresponding grid unit surface;
step 4-4-3, for the non-solidification front unit, the load applied on the unit surface is 0;
step 4-5, calculating equivalent diameter of a water jacket drainage basin and cooling water flow rate according to the crystallizer copper pipe and water jacket structure, cooling water flow rate and inlet and outlet water temperature calculated in the step 1, and further obtaining a wall heat exchange coefficient of the crystallizer copper pipe; setting the temperature of cooling water to linearly change from an inlet to an outlet, and applying a third type of heat transfer boundary condition on a copper pipe-cooling water interface;
step 4-6, constructing a shell-crystallizer interface heat transfer model through secondary development of a multi-physical field coupling simulation model of a steel casting flow-crystallizer copper pipe, and quantitatively describing the influence of heat transfer medium distribution on shell-crystallizer interface heat transfer by coupling analysis of the distribution of liquid, solid mold flux and air gaps in a slag channel;
step 5, setting solving parameters of a multi-physical field coupling simulation model of the steel casting flow-crystallizer copper pipe to carry out simulation calculation; solving parameters including relaxation variables and termination conditions; the termination condition takes the temperature of the crystallization copper pipe as a criterion, if the temperature of the crystallizer copper pipe is not changed any more, the heat transfer in the steel casting flow-crystallizer copper pipe-cooling water system is considered to reach dynamic balance, and the calculation can be terminated at the moment;
step 6, extracting a calculation result after the simulation calculation of the multi-physical field coupling simulation model of the steel casting flow-crystallizer copper pipe is finished, and analyzing the solidification heat transfer and shrinkage behavior, the distribution of casting powder in a slag channel and the generation and expansion of an air gap of a billet shell in the billet continuous casting crystallizer;
step 7, optimizing and adjusting the inner cavity structure and the taper of the crystallizer according to the distribution of the covering slag and the air gaps in the slag channel;
and 8, performing geometric modeling based on the adjusted inner cavity structure and taper of the crystallizer copper pipe, and repeating the steps 3-7 until the air gap layer in the slag channel is completely eliminated and the slag film is uniformly distributed.
The beneficial effects of adopting above-mentioned technical scheme to produce lie in: the utility model provides a taper optimization design method of a billet continuous casting crystallizer, which is based on the description of contact, solidification, heat transfer and deformation behaviors in a crystallizer system, and based on the description, the distribution of liquid and solid slag layers in a slag channel and the formation and expansion of air gaps are analyzed in a coupling way, and on the basis, the action rule of the inner cavity structure and taper design of the billet continuous casting crystallizer on the uniformity of heat transfer and solidification growth of a billet shell is clarified, so that theoretical guidance is provided for taper optimization design. According to the analysis result, the inner cavity structure and the taper of the crystallizer are optimally designed, the heat transfer uniformity of the crystallizer and the support of the crystallizer on the shell of the primary solidification are improved, and finally the defect-free production of continuous casting billets is realized.
The method can be used for coupling analysis of the dynamic distribution of slag channel covering slag in the small square billet continuous casting crystallizer, accurately calculating the non-uniform heat transfer behavior of the billet shell and the evolution rule thereof, further obtaining the space shrinkage rule of the billet shell in the solidification process, and carrying out optimal design on the inner cavity structure of the billet crystallizer according to the space shrinkage rule, thereby improving the contact state between the billet shell and the copper pipe, homogenizing the growth of the billet shell, eliminating the defects of continuous casting billet surface and subcutaneous cracks, and comprehensively improving the product quality and the production efficiency.
Drawings
FIG. 1 is a flow chart of a method for optimizing the design of the taper of a billet continuous casting crystallizer provided by the embodiment of the utility model;
FIG. 2 is a schematic diagram of the geometry of a billet crystallizer copper tube provided by an embodiment of the utility model;
FIG. 3 is a schematic diagram of geometric modeling of a copper pipe of a billet continuous casting crystallizer provided by the embodiment of the utility model;
fig. 4 is a schematic diagram of copper tube mesh division of a billet crystallizer provided by an embodiment of the utility model;
FIG. 5 is a schematic diagram showing the thickness distribution of solid slag film between billet shell and copper pipe in the billet crystallizer provided by the embodiment of the utility model;
FIG. 6 is a schematic diagram of a shell-copper tube air gap layer distribution resulting from shell shrinkage provided by an embodiment of the present utility model;
FIG. 7 is a graph of the profile of an optimized mold corner at different heights provided by an embodiment of the present utility model.
Detailed Description
The following describes in further detail the embodiments of the present utility model with reference to the drawings and examples. The following examples are illustrative of the utility model and are not intended to limit the scope of the utility model.
In this embodiment, a taper optimization design method of a billet continuous casting crystallizer, as shown in fig. 1, includes the following steps:
step 1, collecting basic parameters of an optimal design object crystallizer; the basic parameters of the crystallizer comprise the material and structure of a copper pipe of the crystallizer, the material and distribution of a coating, the composition of steel types, the pulling speed and the superheat degree, the cooling water flow of the crystallizer, the inlet and outlet water temperature, the effective working height and the water jacket structure of the crystallizer;
in this example, 08 carbon structural steel with a casting section of 120X 120mm is taken as an example, the steel grade composition is shown in Table 1, the usual drawing speed under the common working condition is 2.6m/min, the superheat degree is 25 ℃, and the cooling water quantity of a crystallizer is 160m 3 And/h, the inlet water temperature is 29 ℃, the outlet water temperature is 34 ℃, and the inlet water temperature difference is 5 ℃. The copper pipe structure of the crystallizer is shown in figure 2, the inner surface coating of the copper pipe structure is uniformly transited from 0.5mm of the upper opening to 1.5mm of the lower opening, the taper of the crystallizer is distributed in a nonlinear manner, and the effective height is 700mm.
TABLE 1.08 carbon structural Steel Main component (wt%)
| C | Si | Mn | P | S |
| 0.09 | 0.27 | 0.5 | 0.03 | 0.03 |
Step 2, according to the existing production process of billet continuous casting, obtaining physical parameters of steel, a crystallizer copper pipe and cooling water by calculating or referring to data;
step 2-1, calculating to obtain high-temperature physical parameters of steel according to steel type components; the high-temperature physical parameters of the steel comprise the evolution of the liquid phase fraction, the solidus phase temperature and the solidification phase fraction of the steel, and the change rule of density, specific heat, enthalpy value, heat conductivity, linear thermal expansion coefficient, elastic modulus and poisson ratio along with the temperature;
in the embodiment, the high-temperature physical parameters of the steel are mainly obtained by applying professional physical parameter calculation software JMatPro.
Step 2-2, according to the material of the copper tube of the crystallizer, consulting a user manual to obtain the thermophysical parameters of the copper tube of the crystallizer; the thermophysical parameters of the crystallizer copper pipe comprise the heat conductivity coefficient, specific heat and density of a copper matrix at different temperatures and the heat conductivity coefficient, specific heat and density of a coating;
in this example, the physical parameters of the copper tube of the crystallizer are shown in Table 2 by referring to the user manual, wherein the specific heat and density of the copper matrix can be regarded as being well-known, and the thermal conductivity varies with the temperature. The plating layer on the inner surface of the copper tube can be regarded as a constant in all physical properties.
TABLE 2 physical parameters of copper tube parts of crystallizer
Step 2-3, determining physical parameters of circulating cooling water of the crystallizer according to the environmental temperature of the billet continuous casting site; physical parameters of the circulating cooling water of the crystallizer comprise density, specific heat, heat conductivity coefficient and viscosity of the water;
in this example, physical properties of the cooling water circulated in the crystallizer under the ordinary conditions were checked, and the results are shown in table 3. Since the temperature change of the cooling water flowing through the crystallizer is small, the physical property parameter thereof can be regarded as a constant.
TABLE 3 physical parameters of circulating cooling water of crystallizer
| Parameters (parameters) | Density (kg/m) 3 ) | Specific heat (J/(kg. K)) | Thermal conductivity (W/(m.K)) | Viscosity (kg/(m.s)) |
| Value taking | 998.2 | 4182 | 0.6 | 0.0006 |
Step 3, establishing a multi-physical field coupling simulation model of the steel casting flow-crystallizer copper pipe; considering that the continuous casting of the small square billets adopts an arc-shaped crystallizer, namely a left-right side symmetrical structure and an inner-outer arc asymmetrical structure, a 1/2 model is established, and the full-field description of the continuous casting crystallizer of the small square billets can be realized; the specific modeling process is as follows:
step 3-1, carrying out 1 on the copper pipe of the 1/2 crystallizer: 1, geometric modeling, namely establishing a geometric model of a copper pipe of the crystallizer, reserving geometric characteristics such as taper, inner and outer arc curvature, chamfer angle and the like of the crystallizer, and truly reflecting the inner cavity structure of the small square billet crystallizer and nonlinear taper compensation;
according to the copper pipe structure of the on-site billet continuous casting crystallizer, a 1/2 geometric model is built in the spaceclaim as shown in fig. 3, meanwhile, special attention should be paid to the taper setting of the crystallizer in the modeling process, and the inner cavity structure of the crystallizer is truly reflected;
step 3-2, performing grid division on the established geometric model of the copper tube of the crystallizer, and constructing a finite element model of the copper tube of the crystallizer;
and (3) importing the established geometric model of the crystallizer copper pipe into finite element software MSC.Marc, and performing grid division. Considering the overall structure of the copper tube of the crystallizer, the present embodiment adopts hexahedral cells for mesh division, and the result is shown in fig. 4.
Step 3-3, refining grids on the inner surface of the copper pipe of the crystallizer, distinguishing grids of the copper matrix from grids of the plating layer, and adjusting the thickness distribution of the plating layer along the longitudinal direction according to the actual condition of the copper pipe of the crystallizer;
in the embodiment, a surface layer thinning technology is applied in MSC.Marc, a coating grid with the thickness of 0.5mm is separated from the inner surface of a crystallizer copper pipe, and then the thickness distribution of the coating is changed by adjusting the nodes of the coating grid, so that the coating is gradually transited from 0.5mm of an upper opening to 1.5mm of a lower opening along the direction of drawing a blank.
Step 3-4, endowing the copper matrix grids and the coating grids with the thermal physical parameters of the copper matrix and the coating thermal physical parameters of the coating established in the step 2-2 respectively;
in this embodiment, physical parameters of the copper matrix grid and the plating layer grid are set in the finite element software msc.marc according to the data referred to in step 2-2, respectively.
Step 3-5, establishing a space geometric feature of the steel casting flow and establishing a 1/2 steel casting flow geometric model based on the crystallizer copper pipe geometric model established in the step 3-1 and the effective working height of the crystallizer collected in the step 1;
in the embodiment, a 1/2 steel casting flow geometric model is built in a space according to the inner cavity structure of the crystallizer and the effective working height.
Step 3-6, mesh division is carried out on the established geometric model of the steel casting flow, and a finite element model of the steel casting flow is constructed;
the steel casting flow geometric model is imported into finite element software MSC.Marc, and grid division is carried out on the model by adopting hexahedral units.
Step 3-7, extending the steel casting grid along the reverse direction of the blank pulling direction, so that the length of the casting grid above the meniscus of the crystallizer reaches 3-4 times of the effective working height of the crystallizer;
in this embodiment, considering that the tensile force of the solidified shell continuously moves downwards under the actual continuous casting condition, the steel casting units also need to move downwards in the corresponding finite element simulation, so that the steel casting units at the meniscus should be reversely extended along the direction of drawing the shell, and the reverse extension distance is 2000mm.
Step 3-8, endowing the high-temperature physical property parameters of the steel calculated by the JMatPro in the step 2-1 with a steel casting grid;
step 3-9, integrating the crystallizer copper pipe grids and the steel casting grid established in the steps 3-1 to 3-8 to obtain a steel casting flow-crystallizer copper pipe multi-physical field coupling simulation model, so that the steel casting flow surface below the meniscus is matched with the inner surface of the crystallizer;
in this embodiment, the finite element model of the copper tube of the crystallizer established in steps 3-1 to 3-4 is combined with the finite element model of the steel casting stream established in steps 3-5 to 3-7, and the spatial relative position of the copper tube of the crystallizer and the steel casting stream is adjusted so that the outer surface of the casting stream contacts the inner surface of the copper tube of the crystallizer, as shown in fig. 5. In addition, the spatial position of the cooling water grid in the fluent is adjusted to be matched with the outer surface of the copper pipe of the crystallizer.
Step 4, setting initial conditions and boundary conditions of a multi-physical field coupling simulation model of the steel casting flow-crystallizer copper pipe;
step 4-1, setting the steel casting flow as a deformed body in the combined steel casting flow-crystallizer copper pipe multi-physical field coupling simulation model in step 3-9, wherein the crystallizer copper pipe is a rigid body;
step 4-2, setting initial temperatures of the steel casting flow and cooling water of the crystallizer according to the basic parameters of the crystallizer collected in the step 1, and setting the initial temperature of a copper pipe of the crystallizer to be the factory room temperature;
in this example, the ladle superheat degree in billet continuous casting is 25 ℃, and the liquidus temperature of 08 carbon structural steel can be calculated to be 1523 ℃ according to the steel grade composition, so the casting temperature in MSC.Marc software should be 1548 ℃. The initial temperature of the copper tube may be set at room temperature, i.e., 25 ℃. In addition, as can be seen from step 1, the temperature of the circulating cooling water at the inlet of the crystallizer in fluent software should be set to 29 ℃.
Step 4-3, setting the space displacement of the copper pipe of the crystallizer to be 0, and simultaneously, enabling the steel casting flow to move towards the lower opening of the crystallizer at the blank pulling speed;
in this embodiment, the displacement of each node on the copper pipe grid of the crystallizer along the x, y and z directions is set to be 0. Meanwhile, the displacement speed of the steel casting flow node at the lower opening of the crystallizer along the direction of drawing the blank is set to be 2.6m/min.
And 4-4, applying a load to a unit surface vertical to the surface inside the steel casting grid unit, and simulating the ferrostatic pressure born by the solidification front in the continuous casting process of the billet, wherein the concrete process is as follows:
step 4-4-1, before each incremental step of the steel casting flow-crystallizer copper pipe multi-physical field coupling simulation model begins, judging whether each steel casting flow grid unit is positioned at the solidification front according to the grid node temperature, if the grid node temperature of each steel casting flow grid unit is larger than or smaller than the solidus temperature, judging that the grid unit is a non-solidification front unit, and if part of the grid node temperature of each steel casting flow grid unit is higher than the solidus temperature and part of the grid node temperature is lower than the solidus temperature, judging that the grid unit is a solidification front unit;
step 4-4-2, extracting coordinates of a solidification front unit, calculating the depth of a molten pool where the grid unit is currently located according to the coordinates, further calculating the hydrostatic pressure of molten steel at the position, and applying the hydrostatic pressure to the corresponding grid unit surface;
in this example, the magnitude of the required applied ferrostatic pressure is calculated according to the following formula:
P＝ρgh
where P is the applied ferrostatic pressure, ρ is the molten steel density, and h is the bath depth.
Step 4-4-3. For non-solidifying front units, the load applied on the unit face is 0, i.e. p=0;
step 4-5, calculating equivalent diameter of a water jacket drainage basin and cooling water flow rate according to the crystallizer copper pipe and water jacket structure, cooling water flow rate and inlet and outlet water temperature calculated in the step 1, and further obtaining a wall heat exchange coefficient of the crystallizer copper pipe; setting the temperature of cooling water to linearly change from an inlet to an outlet, and applying a third type of heat transfer boundary condition on a copper pipe-cooling water interface;
in the embodiment, a third type of heat transfer boundary condition is adopted to describe the convection heat exchange between the copper pipe and the cooling water, and the heat flow density can be described by the following formula;
q＝h w (T m -T w )
wherein q is the interface heat flux density, h w Is the convection heat exchange coefficient between the copper pipe and the cooling water, T m The temperature of the wall surface of the copper pipe is calculated in real time by a model, and T is w For cooling water temperature, its value varies linearly from the inlet water temperature to the outlet water temperature in the flow direction.
The heat exchange coefficient can be calculated by the following formula:
wherein ρ is w 、v w 、k w 、μ w 、c w The density, the flow rate, the heat conductivity coefficient, the dynamic viscosity and the specific heat of the cooling water of the crystallizer are respectively calculated according to the basic data in the step 1 and the step 2-3; d, d w The hydraulic diameter of the cooling water basin in the water jacket can be obtained through geometric parameters of the copper pipe and the water jacket.
Step 4-6, constructing a shell-crystallizer interface heat transfer model through secondary development of a multi-physical field coupling simulation model of a steel casting flow-crystallizer copper pipe, and quantitatively describing the influence of heat transfer medium distribution on shell-crystallizer interface heat transfer by coupling analysis of the distribution of liquid, solid mold flux and air gaps in a slag channel;
in the actual continuous casting production process of the small square billets, three heat transfer media, namely liquid slag, solid slag and air gaps, exist between a billet shell and a copper pipe of a crystallizer, wherein the liquid slag film thermal resistance can be calculated by the following formula:
wherein R is thermal resistance, superscripts c and rad respectively represent a heat conduction item and a radiation item, and subscript liq represents a liquid slag layer; d. k and E are respectively the thickness of the slag layer, the heat conductivity coefficient and the absorbance; epsilon is emissivity, and subscripts s and f respectively represent casting blanks and covering slag; t is the temperature, and the subscript cry represents the crystallization temperature of the mold flux; sigma is the Boltzmann constant, which is 5.67×10 -8 W/(m 2 ·K 4 ) The method comprises the steps of carrying out a first treatment on the surface of the r is the refractive index.
The thermal resistance of the slag fixing film can be calculated by the following formula:
wherein, the subscript sol represents a slag fixing layer; the subscript m represents a crystallizer; t (T) a 、T b All are interface temperatures, unit K.
The air gap thermal resistance is calculated by the following formula:
wherein the subscript air represents an air gap layer;
the heat exchange coefficient between the blank shell and the copper plate is determined by the following steps:
wherein h is the interface heat exchange coefficient, W/(m) 2 ·K).
The blank shell-crystallizer interface heat transfer model is embedded in a steel casting flow-crystallizer copper pipe multi-physical field coupling simulation model, so that the distribution of liquid, solid slag layers and air gaps can be solved, and an interface heat exchange coefficient can be obtained.
Step 5, setting solving parameters of a multi-physical field coupling simulation model of the steel casting flow-crystallizer copper pipe to carry out simulation calculation; solving parameters including relaxation variables and termination conditions; wherein, for general mechanical problems, the relaxation variable is 0.7, the termination condition is the temperature of the crystallization copper pipe as a criterion, if the temperature of the crystallizer copper pipe is not changed any more, the heat transfer in the steel casting flow-crystallizer copper pipe-cooling water system is considered to reach dynamic balance, and the calculation can be terminated at the moment;
in this embodiment, the relaxation variable is set to 0.5, and the calculation termination condition is whether the temperature of the copper tube of the crystallizer reaches a steady state, and if the temperature of the crystallizer is no longer significantly changed or is circularly changed in some form, the current calculation is considered to reach dynamic balance, and the calculation can be terminated. After the parameters are set, submitting the operation in MSC.
Step 6, extracting calculation results of temperature, displacement, contact state and stress-strain after the simulation calculation of the multi-physical field coupling simulation model of the steel casting flow-crystallizer copper pipe is finished, and analyzing solidification heat transfer and shrinkage behaviors of a billet shell in the billet continuous casting crystallizer, distribution of covering slag in a slag channel and generation and expansion of an air gap;
in this embodiment, after the calculation is finished, the calculation result is extracted by post-processing software msc.mentat, and the solidification heat transfer and shrinkage behavior, slag runner mold flux distribution, and air gap generation and expansion of the billet shell in the billet continuous casting crystallizer are analyzed, as shown in fig. 5 and 6;
step 7, optimizing and adjusting the inner cavity structure and the taper of the crystallizer according to the distribution of the covering slag and the air gaps in the slag channel;
in this embodiment, based on the distribution of the thickness of the mold flux film and the generation and expansion of the air gap, the taper compensation amount of the crystallizer is redesigned, the compensation for the shrinkage of the corner of the casting blank is increased, the air gap and the thick slag film are eliminated, the thickness distribution of the slag film on the surface of the casting blank is uniform, and the profile curves of the corner of the crystallizer at different heights after adjustment are shown in fig. 7.
And 8, performing geometric modeling based on the adjusted inner cavity structure and taper of the crystallizer copper pipe, and repeating the steps 3-7 until the air gap layer in the slag channel is completely eliminated and the slag film is uniformly distributed.
In this embodiment, geometric modeling is performed again based on the adjusted inner cavity structure and taper of the copper tube of the crystallizer, and the calculation, analysis and optimization design processes described in steps 3 to 7 are repeated until the air gap layer in the slag channel is completely eliminated, the thick slag film is inhibited, the whole thickness of the slag layer becomes uniform, the inner cavity structure of the crystallizer at this time is the optimum of the steel grade under the target production process condition, the heat transfer of the crystallizer and the solidification growth of the shell can be homogenized, and the surface and subcutaneous crack defects of the continuous casting blank caused by non-uniform heat transfer of the wall surface can be homogenized.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present utility model, and are not limiting; although the utility model has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced with equivalents; such modifications and substitutions do not depart from the spirit of the corresponding technical solutions, which are defined by the scope of the appended claims.
Claims (6)
1. A taper optimization design method of a billet continuous casting crystallizer is characterized by comprising the following steps of: the method comprises the following steps:
step 1, collecting basic parameters of an optimal design object crystallizer;
step 2, obtaining physical parameters of steel, a crystallizer copper pipe and cooling water according to the current production process of billet continuous casting;
step 3, establishing a multi-physical field coupling simulation model of the steel casting flow-crystallizer copper pipe;
step 4, setting initial conditions and boundary conditions of a multi-physical field coupling simulation model of the steel casting flow-crystallizer copper pipe;
step 5, setting solving parameters of a multi-physical field coupling simulation model of the steel casting flow-crystallizer copper pipe to carry out simulation calculation; solving parameters including relaxation variables and termination conditions; the termination condition takes the temperature of the crystallization copper pipe as a criterion, if the temperature of the crystallizer copper pipe is not changed any more, the heat transfer in the steel casting flow-crystallizer copper pipe-cooling water system is considered to reach dynamic balance, and the calculation can be terminated at the moment;
step 6, extracting a calculation result after the simulation calculation of the multi-physical field coupling simulation model of the steel casting flow-crystallizer copper pipe is finished, and analyzing the solidification heat transfer and shrinkage behavior, the distribution of casting powder in a slag channel and the generation and expansion of an air gap of a billet shell in the billet continuous casting crystallizer;
step 7, optimizing and adjusting the inner cavity structure and the taper of the crystallizer according to the distribution of the covering slag and the air gaps in the slag channel;
and 8, performing geometric modeling based on the adjusted inner cavity structure and taper of the crystallizer copper pipe, and repeating the steps 3-7 until the air gap layer in the slag channel is completely eliminated and the slag film is uniformly distributed.
2. The optimization design method for the taper of the billet continuous casting crystallizer is characterized by comprising the following steps of: the basic parameters of the crystallizer comprise the material and structure of a copper pipe of the crystallizer, the material and distribution of a coating, the composition of steel types, the pulling speed and the superheat degree, the cooling water flow of the crystallizer, the inlet and outlet water temperature, the effective working height and the water jacket structure of the crystallizer.
3. The optimization design method for the taper of the billet continuous casting crystallizer is characterized by comprising the following steps of: the specific method of the step 2 is as follows:
step 2-1, calculating to obtain high-temperature physical parameters of steel according to steel type components; the high-temperature physical parameters of the steel comprise the evolution of the liquid phase fraction, the solidus phase temperature and the solidification phase fraction of the steel, and the change rule of density, specific heat, enthalpy value, heat conductivity, linear thermal expansion coefficient, elastic modulus and poisson ratio along with the temperature;
step 2-2, obtaining thermophysical parameters of the copper tube of the crystallizer according to the material of the copper tube of the crystallizer; the thermophysical parameters of the crystallizer copper pipe comprise the heat conductivity coefficient, specific heat and density of a copper matrix at different temperatures and the heat conductivity coefficient, specific heat and density of a coating;
step 2-3, determining physical parameters of circulating cooling water of the crystallizer according to the environmental temperature of the billet continuous casting site; physical parameters of the circulating cooling water of the crystallizer comprise density, specific heat, heat conductivity coefficient and viscosity of the water.
4. The optimization design method for the taper of the billet continuous casting crystallizer according to claim 3, which is characterized in that: the specific method of the step 3 is as follows:
step 3-1, carrying out 1 on the copper pipe of the 1/2 crystallizer: 1, geometric modeling, namely establishing a geometric model of a copper pipe of the crystallizer, reserving geometric characteristics of the crystallizer, and truly reflecting the inner cavity structure of the small square billet crystallizer and nonlinear taper compensation;
step 3-2, performing grid division on the established geometric model of the copper tube of the crystallizer, and constructing a finite element model of the copper tube of the crystallizer;
step 3-3, refining grids on the inner surface of the copper pipe of the crystallizer, distinguishing grids of the copper matrix from grids of the plating layer, and adjusting the thickness distribution of the plating layer along the longitudinal direction according to the actual condition of the copper pipe of the crystallizer;
step 3-4, endowing the copper matrix grids and the coating grids with the thermal physical parameters of the copper matrix and the coating thermal physical parameters of the coating established in the step 2-2 respectively;
step 3-5, establishing a space geometric feature of the steel casting flow and establishing a 1/2 steel casting flow geometric model based on the crystallizer copper pipe geometric model established in the step 3-1 and the effective working height of the crystallizer collected in the step 1;
step 3-6, mesh division is carried out on the established geometric model of the steel casting flow, and a finite element model of the steel casting flow is constructed;
step 3-7, extending the steel casting grid along the reverse direction of the blank pulling direction, so that the length of the casting grid above the meniscus of the crystallizer reaches 3-4 times of the effective working height of the crystallizer;
step 3-8, endowing the high-temperature physical property parameters of the steel calculated in the step 2-1 with steel casting grids;
and 3-9, integrating the crystallizer copper pipe grids and the steel casting grid established in the steps 3-1 to 3-8 to obtain a steel casting flow-crystallizer copper pipe multi-physical field coupling simulation model, so that the steel casting flow surface below the meniscus is matched with the inner surface of the crystallizer.
5. The optimization design method for the taper of the billet continuous casting crystallizer is characterized in that: the specific method of the step 4 is as follows:
step 4-1, setting a steel casting flow as a deformed body, wherein a crystallizer copper pipe is a rigid body;
step 4-2, setting initial temperatures of the steel casting flow and cooling water of the crystallizer according to the basic parameters of the crystallizer collected in the step 1, and setting the initial temperature of a copper pipe of the crystallizer to be the factory room temperature;
step 4-3, setting the space displacement of the copper pipe of the crystallizer to be 0, and simultaneously, enabling the steel casting flow to move towards the lower opening of the crystallizer at the blank pulling speed;
step 4-4, applying load to the unit surface vertical to the surface in the steel casting grid unit, and simulating the ferrostatic pressure born by the solidification front in the continuous casting process of the billet;
step 4-5, calculating equivalent diameter of a water jacket drainage basin and cooling water flow rate according to the crystallizer copper pipe and water jacket structure, cooling water flow rate and inlet and outlet water temperature calculated in the step 1, and further obtaining a wall heat exchange coefficient of the crystallizer copper pipe; setting the temperature of cooling water to linearly change from an inlet to an outlet, and applying a third type of heat transfer boundary condition on a copper pipe-cooling water interface;
and 4-6, constructing a shell-crystallizer interface heat transfer model through secondary development of a multi-physical field coupling simulation model of the steel casting flow-crystallizer copper pipe, and quantitatively describing the influence of heat transfer medium distribution on the shell-crystallizer interface heat transfer by coupling analysis of the distribution of liquid, solid mold flux and air gaps in a slag channel.
6. The optimization design method for the taper of the billet continuous casting crystallizer is characterized by comprising the following steps of: the specific process of the step 4-4 is as follows:
step 4-4-1, before each incremental step of the steel casting flow-crystallizer copper pipe multi-physical field coupling simulation model begins, judging whether each steel casting flow grid unit is positioned at the solidification front according to the grid node temperature, if the grid node temperature of each steel casting flow grid unit is larger than or smaller than the solidus temperature, judging that the grid unit is a non-solidification front unit, and if part of the grid node temperature of each steel casting flow grid unit is higher than the solidus temperature and part of the grid node temperature is lower than the solidus temperature, judging that the grid unit is a solidification front unit;
step 4-4-2, extracting coordinates of a solidification front unit, calculating the depth of a molten pool where the grid unit is currently located according to the coordinates, further calculating the hydrostatic pressure of molten steel at the position, and applying the hydrostatic pressure to the corresponding grid unit surface;
step 4-4-3. For non-solidifying front units, the load applied on the unit face is 0.
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