RU2536309C2 - Continuous casting and plant to this end - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, in particular, to continuous casting. This process comprises feed of liquid metal into ingot mould, drawing of ingot from the mould, flushing and bending in radius decreasing from maximum to minimum. Ingot displacement without deformation is performed in arc while ingot unbending occurs with increase in radius to maximum. Drawing of the ingot is carried out in path described by brachistochrone that meets the conditions of minimum power costs of its flushing. Ingot bending conditions are set in compliance with radius decrease algorithm and with allowance for tolerable deformation at the last point of bending. Proposed unit comprises ingot mould, section of roller guidance and draw-and-straighten devices that make a process channel with axis described by brachistochrone. The number of rollers and their pitch at bending section are set in compliance with increase in accumulated deformation in drawing path and with allowance for deformation increase constriction with admissible value at final bending section.

EFFECT: stable high quality of finished billets, longer life of guidance hardware.

6 cl, 1 dwg, 1 tbl

Description

The invention relates to metallurgy, and more particularly to steelmaking and is intended for use in the technology for the production of continuously cast billets. The most complete level of technology on the subject is described in the famous monograph of V.M. Niskovsky, S.E. Karlinsky, A.D. Berenova "Machines for continuous casting of billets." - M.: Metallurgy. 1991.272 p. The technical solutions presented here in the field of continuous casting provide a fairly complete picture of the current level of technology and allow us to establish the essence and direction of the patented item. The present invention claims patent protection for a method of continuous casting of blanks, which, according to the authors, possesses significant distinguishing features in terms of bending operations of the hardening blank in the process of pulling it along a new path and features of upgrading the technological channel of the installation that implements the method.

Information from the above source (p.20-30) allows you to clearly articulate the main features of the analogues of the present invention. An analogue of the method for continuous casting of billets includes feeding liquid metal into the mold, preparing the billet by continuously increasing the thickness of the hard shell, pulling the hardening billet from the mold along a path that provides vertical descent with simultaneous bending by reducing the radius of curvature of the path to reach its base value, moving along an arc of this radius and bending of the workpiece by increasing the radius of curvature of the path until the workpiece is completely straightened her house is in a horizontal position, while bending operations are performed in accordance with the methodology for constructing the trajectory of drawing the workpiece, providing for a constant deformation rate and limiting the magnitude of the deformation itself at a level acceptable for a particular grade of cast steel.

For the proposed method and analogue, the following distinctive features coincide. Both methods of continuous casting of billets include feeding liquid metal into the mold, preparing the billet by continuously increasing the thickness of the hard shell, pulling the hardening billet from the mold along a path that provides vertical descent with simultaneous bending by reducing the radius of curvature of the path to reach its base value, moving along an arc of this radius and bending of the workpiece, while the bending operation is performed in accordance with the methodology for constructing the trajectory of drawing preform providing compliance constant strain rate and limiting the magnitude of the deformation at the most admissible for a specific Grades pourable steels. The achievement of the expected technical result when using the known method is hindered by the fact that the workpiece is pulled in the section of its bend using a well-known technique for the bending operation, which does not imply the influence of its own weight on the course of the deformation process in conditions of insufficient strength of the hard shell and the objective presence of the gravitational field. This does not allow to obtain blanks with a consistently high quality surface and macrostructure in the bend area, where the thickness of its hard shell is much smaller and the temperature is much higher than in the bend area.

The known installation-analogue contains a mold, roller wiring sections and pulling-correct devices, which together with the section rollers form a technological channel with an axis containing vertical, bending, radial, extension and horizontal sections, while the rollers of the extension sections of the technological channel are set relative to the axis, constructed according to the method, providing for the constancy of the distances between adjacent rollers of each section and the limitation of the magnitude of bending deformations not higher than the permissible values.

In the proposed installation and analogue, such essential features coincide. Both units contain a mold, roller wiring sections and pulling-right devices, which, together with the section rollers, form a technological channel with an axis that contains vertical, bending, radial, extension and horizontal sections, while the extension sections rollers are set relative to the axis constructed according to the procedure , which provides for the constancy of the pitch of the exhibition of rollers with an acceptable value of bending strain on each of them. The achievement of the expected technical result when using the known installation is hindered by the design flaws of the technological channel at the bend in the part of the roller arrangement around its axis, the geometry of which does not meet the conditions of minimal mechanical resistance to pulling the workpiece along the trajectory of minimum energy consumption. This does not allow, especially with an increase in casting speed, to stabilize the quality of the resulting workpieces, to reduce current loads on the drives of pulling-right devices, and also to minimize wear of the roller wiring.

Closest to the proposed invention, selected as a prototype, is a method of continuous casting of steel and the apparatus used for its implementation, known from US patent No. 6155332, class. B22D 11/128 from 01/28/1999, According to the prototype, molten metal is fed into a vertically arranged flat-wall crystallizer. The resulting billet formed in this case is continuously pulled out of the mold, which is further bent during the drawing process while bending the billet radius from R _max = ∞ (corresponding to the vertical position of the initially straight billet) to a certain final minimum value R _min . Further, the bent workpiece is pulled without deformation along an arc of the minimum radius, followed by drawing through the straightening sections, where the operation of its extension is performed with increasing radius to the maximum value (Rmax = ∞), corresponding to the full straightening of the workpiece with laying it in a horizontal position. In the claimed method and prototype, the following distinctive features coincide. Both methods include feeding the molten metal into the mold, pulling the crystallized billet from the mold, lowering it and simultaneously bending it to reduce the radius from the maximum to the minimum value, moving without deformation along the arc of the minimum radius, and pulling through the rectification sections of the billet, where its expansion is performed with increasing radius from the minimum to the maximum value corresponding to the full straightening of the workpiece with laying it in a horizontal position. Obtaining the expected technical result when using the method selected as a prototype, prevents:

- the lack of an optimal algorithm for the operation of bending the workpiece with a decrease in radius, guaranteeing a given level of surface quality and macrostructure of the resulting workpieces in a wide range of their size and grade assortments;

- stretching the preform in the section of its bend (where the hard shell of the preform, due to the small intrinsic thickness and still quite high temperature, has low strength and ductility indicators) along a path taken without taking into account the influence of its own weight on the course of the deformation process. The latter does not allow to obtain blanks with a stably high quality surface and macrostructure, especially at elevated casting speeds.

In the proposed installation and prototype for US patent No. 6155332, class. B22D 11/128 of 01/28/1999, such essential features coincide. Both installations contain a crystallizer, sections of roller wiring and pulling-straightening devices, which, together with the rollers of the sections, form a technological channel with an axis containing vertical, bending, radial, extension and horizontal sections, while the rollers of the extension sections are set relative to the axis constructed according to the procedure, providing for the constancy of the installation pitch of the rollers with an acceptable value of bending deformation on each of them. Obtaining the expected technical result when using the installation selected as a prototype is hindered by the drawbacks of constructive execution of the technological channel at the bend section in terms of the arrangement of the rollers around its axis, the geometry of which does not meet the conditions of minimum mechanical resistance when pulling the workpiece. On the contrary, tough conditions are created for the interaction of the workpiece with roller wiring, which does not allow to stabilize the quality of the resulting workpieces with an increase in the casting speed, to reduce current loads on the drive, and also to minimize wear of the roller wiring.

The basis of the invention is the task of creating a method for continuous casting of workpieces and installation for its implementation, which would meet the new conditions for the implementation of techniques and operations, as well as new forms of execution and relative positions of the structural elements of the installation, allowing to obtain continuously cast billets with a consistently high quality surface and macrostructure in high-speed casting conditions. The inventive object, "Method for continuous casting of blanks and installation for its implementation", is characterized by such essential features sufficient to achieve the expected technical result.

The method includes supplying molten metal to the mold, pulling the crystallized billet from the mold, simultaneously lowering and bending it with decreasing the bending radius from the maximum to the minimum value, moving without deformation along the arc of the minimum radius, and pulling it through the straightening sections of the billet, where its expansion is performed with increasing radius from the minimum to the maximum value corresponding to the full straightening of the workpiece with laying it in a horizontal position. In the inventive method, the operation of pulling the workpiece is carried out along a new path that meets the conditions of minimum energy consumption for its descent from the mark of the maximum radius to the level mark, where the radius of the bend of the workpiece takes a minimum value, while the procedure for bending deformation is set in accordance with the algorithm to reduce the radius and taking into account the permissible value of the maximum deformation at the last bend point.

The installation contains a crystallizer, sections of roller wiring and pulling-correct devices, the rollers of which together with the rollers of the sections form a technological channel with an axis containing vertical, bending, radial, extension and horizontal sections, while the rollers of the extension sections are set relative to the axis constructed according to the method, which provides for a constant installation pitch of the rollers with an acceptable value of bending deformation on each of them. In the inventive installation, the rollers of the bending sections that form the technological channel are set relative to the axis providing the minimum mechanical resistance of the technological channel, for example, in the form of a brachistochrone, while the pitch of the rollers and their number on the bending section are set in accordance with the regulations for the increase in the accumulated bending deformation along the axis and subject to deformation limitations on the last roller of the last bend section.

In some cases, the use of the method that is claimed is characterized in that,

- drawing the workpiece is carried out along a simplified trajectory of drawing by shortening its vertical and (or) radial sections;

- pulling the workpiece is carried out with a combination of operations of bending and bending the workpiece at a point in the path that corresponds to the minimum radius of curvature,

- optimization of the trajectory of the pull with the approximation of its geometry to the geometry of the curve, which provides the minimum energy consumption for lowering the workpiece, is carried out according to the results of monitoring current loads on the drives of pulling-right devices;

- adjustment of the trajectory of the pull is carried out according to the results of wear of the rollers forming the technological channel.

When using the present invention, it is expected to achieve a technical result, which consists in improving and stabilizing the quality of continuously cast billets while increasing the casting speed, as well as in increasing the operational life of the roller wiring. Between the proposed invention and the achieved technical result, there is a causal relationship. An analysis of the solution of the well-known variational problem of finding the possible trajectory of the minimum time of descent of a material point between points spaced vertically and horizontally in a gravitational field (see G. Galilei, Selected Works, vol. 2, M., 1964, p. 298-301, note 465) shows that the conditions of minimum time for its descent are answered by the only trajectory, which was called the “brachistochrone”. The implementation of the axis of the installation of continuous casting of billets on the descent site with the simultaneous bending of the billet in the form of a brachistochron allows its own weight to be used in the gravitational field for self-centering in the technological channel and, thus, to ensure the most soft contact of the billet with roller wiring. The latter leads to a decrease in the mechanical resistance of the technological channel and the pulling force and, accordingly, to a decrease in tensile stresses in the hard shell of the crystallized billet. This is especially important when performing the bending operation, since its implementation is carried out at the initial stages of the formation of the workpiece, when the thickness of its hard shell is much less than, for example, when performing the subsequent operation of the extension. With an increase in the casting speed, the destructive conditions of the dynamic interaction of the workpiece with the roller wiring increase if the trajectory of its drawing and installation of the roller sections is not made relative to the curve of minimum energy consumption, which provides the minimum mechanical resistance of the process channel. In this case, there is a high probability of destabilizing the quality of the resulting blanks. In real operating conditions, the geometry of the axis of the technological channel can be optimized according to the results of monitoring the pulling forces or current loads on the drives of pulling-right devices, as well as adjusted according to the results of wear on the rollers. Thus, the technical result of the use of the invention is to reduce the mechanical resistance of the technological channel and the implementation of soft multipoint bending modes, which provide high quality guarantees of cast billets, as well as an increase in the operational life of the roller wiring.

The inventive method of continuous casting is implemented using the proposed installation as follows. The liquid metal from the tundish is fed to the mold of a continuous steel casting plant. As a result of contact with the working cooled surface of the mold, the liquid phase becomes solid, forming a preform, the dimensions and shape of which correspond to the parameters of the mold cavity of the mold. In the process of building up the solid phase, the hardening billet is continuously pulled out of the mold with the help of pulling-right devices, which together with the roller wiring form a technological channel. The geometry of the channel ensures the advancement of the cast billet along a predetermined trajectory, which guarantees the operation of bending the billet according to a predetermined algorithm. The bending of the workpiece in the process of drawing it out is carried out by preliminary exposure of the rollers to the sections of bending relative to the axis of the technological channel along the curve of minimum energy consumption, for example, brachistochrone:

$$y=aar\cos \left(\mathrm{one}-x/a\right)-\sqrt{\left(2ax-x^2\right)},\left(\mathrm{one}\right)$$

where a is the scale factor, and x, y are the current coordinates of the brachistochrone.

Function (1), being continuously differentiable, makes it possible to construct the axis of the technological channel under conditions of arbitrarily small deformations, which ensures casting of billets in the widest ranges of dimensional and grade assortments. Based on the results of differentiation (1), we find the first and second derivatives, the value of which we use to find the radius of curvature of the trajectory of extrusion at any point of the curve (1) and, thus, we find the algorithm for performing the operation of bending the workpiece with a continuous decrease in the radius of curvature of the trajectory of extrusion in the form of the dependence:

$$\text{R}=\text{2}\sqrt{\text{2}a\text{x}}\left(\text{2}\right)$$

Pulling the workpiece in the section of its bend x _n <x≤2 a is carried out against the x axis from the point x = 2 a , where R, in accordance with (2), acquires the maximum value R _max = 4 a to the coordinate of the last bend point x _n , where R reaches its minimum value of R _min , which provides a basis for quality assurance of the resulting workpieces. The stretching in the remaining sections of the trajectory, including the extension section with increasing radius from R _min to R _max = ∞, as well as cutting blanks to measured lengths is carried out using known methods and devices.

An example of a specific implementation of the method. It is necessary to obtain a continuously cast bloom with a size of 250 × 320 mm ² with high surface quality and macrostructure with no internal cracks. Casting speed - 1.2 m / hv. The main necessary data on the installation design: a radial-type crystallizer with a base radius R ₀ = R _max = 4 a = 16 m with a working length L _cr = 0.25 a = 1 m; the distance from the exit section of the mold to the section of the workpiece passing through the axis of the first roller, L ₀₁ = 0.05 a = 0.2 m; the number of bend points n = 7. The data showing the features of the construction of the technological channel of the installation at the site of the bending operation of the billet are shown below in table 1. These data are sufficient to build the technological channel of the installation of continuous casting of steel, which ensures the implementation of the proposed method. The data were obtained using dependences (1) and (2) provided that the scale factor a = 4000 mm was selected in the Cartesian coordinate system with the origin at the point (0; 0). Here: x / a and y / a are the relative coordinates of the current intersection of the workpiece; L is the distance from the meniscus of the liquid phase to the current section of the workpiece passing through the axis of the i-th roller; ΔL is the distance between adjacent rollers along the axis of the technological channel; Δh is the current value of the thickness of the solid shell of the ingot; R is the current value of the radius of curvature of the trajectory of the pull. The length of the trajectory within the bend area was determined by the formula

$$L=\mathrm{four}a{\left(\mathrm{one}-x/2a\right)}^{\mathrm{one}/2}\left(3\right)$$

Table 1 Roller No. 7 6 5 four 3 2 one x / a 0.50 0.75 1.00 1.25 1,50 1.75 2.00 y / a 0.1812 0.3500 0.5708 0.8553 1,2284 1.7577 3.1416 x mm 2000 3000 4000 5000 6000 7000 8000 y mm 724.7 1399.5 2283.2 3421.2 4913.5 7030.9 12566,4 L mm 15056,4 13849.1 12513.7 10998 9200 6856.9 1200 ΔL, mm 1207.3 1335.4 1515.7 1798.0 2343.1 5656.9 0.0000 Δh, mm 85.01 81.53 77.50 72.66 66.45 57.37 24.00 R mm 8000.0 9798.0 11313.7 12649.1 13856.4 14966.6 16000.0 ε, m% 1,5625 1.2758 1,1048 0.9882 0.9021 0.8352 0.7813 Δε,% 0.2867 0.1709 0.1166 0.0861 0,0669 0,0534 0.0000

The value of a was chosen taking into account the permissible overall dimensions of the installation and at the same time achieving the specified guarantees of the quality of the obtained workpieces with the minimum admissible radius R _min = 8000 mm The strain level ε (%) was determined by the well-known formula to determine its maximum value on the surface of the workpiece ε _i = δ / R _i , where δ is half its thickness. The measure of accumulated deformation Δε _i on each roller of the bend section was determined without taking into account the sign by the formula:

$$\Delta {\epsilon }_i=\delta /R_i-\delta /R_{i+\mathrm{one}}\left(\mathrm{four}\right)$$

From the data shown in table 1, it follows that, in contrast to the prototype, where the bending operation is carried out under the conditions of the same increase in the deformation measure Δε _i = ΣΔε _i / (n-1) = const <ε _cr , in the proposed method, the bending operation is carried out according to the algorithm (2) using (4), which provides a gentle mode of bending deformation of the billet with a smooth increase Δε _i in the direction of its extension. Given the above values of the technological parameters of casting and structural parameters of the installation, the total measure of accumulated deformation is ΣΔε _i = 0.78%, which for the prototype is on average equal to 0.78: 6 = 0.13% per bend point, the value of which should not exceed the critical value Δε _cr characteristic of a particular grade group of cast steel. From the distribution Δε over the bend section presented in the last row of table 1, it follows that the accumulation of deformation by the proposed method is carried out on the basis of a monotonous increase in the measure of bending deformation of the billet along the technological channel of the installation. So, at the beginning of the section, Δε is much lower than 0.13%, however, on the last two rollers (6 and 7), Δε already significantly exceeds its average value. In the framework of the proposed method, quality assurance of the workpiece is confirmed when the conditions Δε ₇ / Δε _cr are satisfied, where Δε ₇ is the strain growth on the last roller of the bend section, and ε _cr is the allowable (critical) value of the degree of deformation for the cast steel grade in the temperature zone of its reduced ductility . Thus, the given design option of the installation guarantees the quality of the obtained steel billets with ε _cr <0.28. Improving quality guarantees by reducing the local measure of deformation Δε _n on the last roller is achieved by simply increasing the number of rollers, for example, in this case, to 13 (with a decrease in the pitch of their installation along the x axis to 500 mm) or up to 25 (with a decrease in the pitch of installation x axis up to 250 mm). This design of the technological channel provides the local strain at the last bend point at the level Δε _n = 0.14 i 0.07%, respectively. Achieving such critical deformation values as low as possible allows us to solve the problem of producing continuously cast billets practically defect-free over the surface and macrostructure for the entire existing range of steel being cast. Note that in the framework of the options for choosing the number of rollers used above, there are no engineering problems associated with a decrease in the inter-roll distance and the resulting requirements for reducing the diameter of the rollers used with an increase in the number of extension points. This is due to the fact that in the proposed method, the operation of bending the billet became prevailing both in spatial (increasing the length of the bending section due to the reduction of the vertical and radial sections), and in the temporary (duration of the operation) measurements. So, in the example of the method implementation, the length of the bending section of the workpiece along the x axis was L _x = 8000-2000 = 6000 mm with a drop in its elevations ΔН = 12566.4-724.7 = 11841.7 mm. Thus, the ratio of the overall dimensions of the bend section was ΔH / L _x = 1.97. When choosing increased values of the minimum bending radius, in order to improve the quality assurance of the obtained workpieces, for example, to R _min = 10000 mm, the length of the section L _x will be reduced according to (1) and (2) to 8000-3125 = 4875 mm, and the difference in elevations ΔН = 12566.4-1497.9 = 11068.5 mm. The ratio of the overall dimensions of the bend will increase to ΔH / L _x = 2.27. In the absence of vertical and radial sections and a combination of bending and bending operations of the workpiece at x = 2000 mm, the length and height of the extension section, calculated by the known method, for example, for five point extension, will be about 8120 mm and 2419 mm, respectively. Thus, the overall dimensions of the technological channel without vertical, radial and horizontal sections provide the stretching of the workpiece with continuous deformation up to laying it in a horizontal position, amount to L _x = 6000 + 8120 = 14120 mm and H = 11069 + 2419 = 13488 mm. The last result corresponds to the ratio H / L _x = 0.955, which is very close to the small-sized version of the known design of a radial installation with single-point extension (and, accordingly, with a very low level of quality assurance of the resulting workpieces). These calculations show that the use of the invention allows to optimize the dimensions of the installation and significantly reduce capital costs for its construction. From the foregoing, it follows that, in the framework of the present invention, when considering options for its implementation in limited installation dimensions, the length of the section and the time for bending and bending operations are of paramount importance in determining the basic guarantees of the quality of the obtained blanks. The spatio-temporal characteristics of all the remaining operations and sections of the technological channel are adjusted according to the residual principle. So, in the interest of increasing the length of the bend section, the length of the radial movement section of the workpiece can be substantially reduced, up to its complete elimination with a combination of bending and bending operations at the point of the trajectory to achieve the minimum value of its radius of curvature. Thus, the presence of the scale factor a in the complex using the continuous function (1), which continuously differentiates and at the same time ensures the workpiece is descent along the trajectory of minimum energy consumption using algorithm (2) for the operation of bending the workpiece in the process of stretching it, allows optimizing the design installation parameters and, in particular, to minimize its dimensions at a given level of quality assurance of the obtained blanks.

As a result of using the invention, a technical result is achieved, which consists in improving and stabilizing the quality of the obtained workpieces with an increase in the casting speed, as well as in reducing the pulling force of the workpiece and increasing the operational life of the roller wiring.

Claims (6)

1. The method of continuous casting of billets, including the supply of molten metal to the mold, pulling the billet from the mold, lowering and bending the billet along a radius decreasing from maximum to minimum, moving without deformation along the arc of the minimum value and pulling through the rectification sections of the billet in which bending the workpiece with increasing radius from minimum to maximum value, moving the workpiece to a horizontal position while maintaining the degree of deformation below the critical value, characterized in that the descent and bending of the workpiece with a decrease in the bending radius is carried out along a path that meets the conditions of minimum energy consumption for lowering the workpiece from the level mark H_one the maximum radius to the level mark H₂on which the bending radius of the workpiece takes the minimum value described by the brachistochrone $$y=\alpha \arccos \left(\mathrm{one}-\frac{x}{a}\right)-\sqrt{2ax-x^2}$$

, where x, y are the coordinates of the workpiece moving path, a is the scale factor equal to a = (H_one- H₂) / (y_one-y₂), where y_one,y₂- ordinates of the highest and lowest points of the trajectory of movement  billets in the bending section, where the radius value takes the minimum and maximum values, respectively, while the increase in bending deformation is set in accordance with the algorithm for reducing the radius R according to the dependence R = 2√2ax, while maintaining the degree of deformation is less than the critical value at the last bending point. 2. The method according to claim 1, characterized in that the procurement of the workpiece is carried out along a simplified path by shortening its vertical and / or radial sections. 3. The method according to claim 1, characterized in that the procurement of the workpiece is carried out with the combination of bending and bending of the workpiece at a point in the path corresponding to the moment of reaching the minimum bend radius. 4. The method according to claim 1, characterized in that the optimization of the trajectory of the pull with the approximation of its geometry to the geometry of the curve, which ensures minimal energy consumption for lowering the workpiece, is carried out according to the results of monitoring current loads on drives of pulling-right devices. 5. The method according to claim 1, characterized in that the adjustment of the trajectory of the pull is carried out according to the results of wear of the rollers forming the process channel. 6. Installation for the continuous casting of billets containing a mold, sections of roller wiring and pulling-straight devices forming a technological channel with an axis consisting of a vertical section, a bending section, a radial section, an extension section and a horizontal section, characterized in that the axis of the technological channel made according to the curve described by brachistochrone $$y=\alpha \arccos \left(\mathrm{one}-\frac{x}{a}\right)-\sqrt{2ax-x^2}$$

, where x, y are the coordinates of the trajectory of movement of the workpiece, a is the scale factor equal to a = (H_one- H₂) / (y_one-y₂), where y_one,y₂- ordinates of the highest and lowest points of the trajectory of movement  the workpiece in the bending section, ensuring minimum mechanical resistance when pulling the workpiece from the maximum radius value to the level at which the bending radius takes a minimum value, while the step of the section rollers in the bending section and their number correspond to the regulation of the increase in the accumulated bending deformation along the path pulling, taking into account the restrictions on permissible deformation on the last roller of the last section of the bend.