RU2220812C2 - Method for continuous casting of billets and apparatus for performing the same - Google Patents

Abstract

FIELD: metallurgy, namely metal continuous casting processes and equipment. SUBSTANCE: method for continuous casting of billets in vertical and curvilinear metal continuous casting plants comprises steps of feeding metal to mold; drawing billet out of mold; holding and guiding billet in secondary cooling zone; reducing billet in roller sections along its thickness; calibrating billet for final dimension by means of rollers of drawing stand; terminating reduction of billet outside roller sections in drawing stand; realizing calibration of billet by means of last pair of rollers of stand. In plant for billet continuous casting drawing stand is provided with hydraulic distributor having control system and pickups for detecting gap position of rollers of stand. Said pickups are placed on hydraulic cylinders for forcing each pair of rollers to billet. EFFECT: increased rate of casting without deterioration of ingot structure. 2 cl, 6 dwg, 3 ex

Description

 The invention relates to metallurgy, and more particularly to continuous casting of metals.

 A known method of profiling an ingot on a continuous casting machine according to the application of Japan 6049217 B4 (publ. 29.06.94), which is the closest to the proposed method for continuous casting of billets.

 The method consists in the fact that the preform is cast in a mold, sent to a secondary cooling zone, subjected to compression in the roller section in an incompletely hardened state, then profiled to a final rectangular profile in the pulling stand.

 This method is carried out in a continuous casting device known from the same application, comprising a mold, a secondary cooling zone, a roller section providing soft compression of the ingot and a pulling stand located at some distance from the roller section.

 A disadvantage of the known method and device for its implementation is the limitation of the casting speed from the condition of positioning the top of the liquid well relative to the roller sections of the soft reduction zone: the solid phase content in the central section of the workpiece at the exit from the section of the conical solution of the roller sections should reach 90 ... 95% for low-carbon steels and up to 70% for high carbon. A further increase in casting speed leads to the effect of suction of segregated steel as a result of buckling of the workpiece outside the roller sections and, as a consequence, to axial friability and central segregation.

 Closest to the proposed invention relating to a device for continuous casting of blanks is the installation of SMS Schlomaim-Siemag of the reconstructed slab UNRS at the Dillinger Huttenwerke metallurgical plant (railway "Ferrous metals", December 1999, p.24-25).

 This known installation includes a crystallizer, a secondary cooling zone, a replaceable roller section with a hard gauge, roller sections 2 and 3, hydraulically adjustable for a specific solution, roller sections 4 ... 8, which provide compression of the workpiece with an uncured core in thickness, and a multi-roller pulling stand with individual hydraulic clamping of each pair of rollers to the already hardened workpiece. The metallurgical installation length is 15.0 m and corresponds to the length of the roller wiring.

 The pulling stand rollers of this unit operate in pressure mode. In this case, it is impossible to profile the solution of the rollers of the pulling stand and, as a result, the compression modes of the continuously cast billet, as well as the calibration of the cross section in height, are excluded.

 The proposed invention solves the problem of increasing the casting speed without deterioration of the structure of the ingot.

 To obtain such a technical result in the proposed method for continuous casting of billets, including supplying metal to the mold, drawing it out of the mold, maintaining and guiding the workpiece in the secondary cooling zone, compressing the workpiece with an uncured core in thickness in the roller sections, subsequent calibration to the final size in the pulling stand , the compression of the workpiece is completed outside the roller section in the pulling multi-roll stand at a certain distance from the meniscus of the metal in the mold, and calibration is performed by at least the last pair of rollers of this stand.

 Distinctive features of the proposed method are the end of the compression of the workpiece outside the roller section in the pulling multi-roller stand at a certain distance from the meniscus of the metal in the mold and calibration of the workpiece with at least the last pair of rollers of this stand.

 The presence of these signs allows you to increase the casting speed and get the workpiece without axial friability and central segregation, as well as to give the workpiece the correct shape. Giving the correct shape increases the efficiency of ultrasonic inspection of the internal structure of the workpiece, solves the problems of hot posad.

 To achieve the named technical result, a device is proposed that, like the one closest to it, known from the journal "Ferrous metals", 12-1999, contains a mold, a secondary cooling zone, roller sections with hydraulic adjustment of the solution of rollers, providing compression of the workpiece with uncured core in thickness, and multi-roll pulling stand with individual hydraulic clamping of each pair of rollers to the workpiece. The pulling stand is equipped with a control valve with a roller control system and position sensors installed on the pressure cylinders, the position sensors being interconnected with the control valve.

 The described design of the device allows, depending on the position of the apex of the liquid well, to set the channel profile not only along the rollers of the soft reduction sections, but also on the pulling stand. The configuration of a liquid well is calculated in real time using a mathematical model of solidification of a continuously cast billet depending on the grade of cast steel, a diagram of the casting speed and cooling conditions.

 The signals from the position sensors installed on the hydraulic cylinders are used as feedback in the control system, tracking the reproduction of the optimal design profile of the foundry channel.

The invention is illustrated by drawings, which depict:
in FIG. 1 is a diagram of a vertical continuous casting machine for implementing the proposed method (example 1);
in FIG. 2 is a diagram of the roller sections and the pulling stand (enlarged);
in FIG. 3 is a diagram of a radial continuous casting machine for implementing the proposed method (example 2);
in FIG. 4 - the same (example 3);
in FIG. 5 - kinetics of solidification of a slab 200 mm thick of mild steel with a casting speed of 0.7 m / min;
in FIG. 6 - kinetics of solidification of bloom 300 • 450 mm from high-carbon steel with a casting speed of 0.68 m / min.

 The following are embodiments of the inventions that do not exclude other variations within the scope of the claims.

 The proposed method is as follows.

 Example 1

 In the process of continuous casting of a slab 200 • 1550 from St 3sp (Fig. 1), liquid steel is fed into the mold 1 and the billet is pulled out of it at a variable speed. In the secondary cooling zone 2, the workpiece 3 is supported and guided by means of split rollers of the four roller sections 4, and also cooled by the water-air mixture supplied by the collectors installed on these sections. The metallurgical length of the continuous casting machine is limited to the last fourth section and is 9.32 m.

 After the fourth section, the workpiece is pulled and squeezed by the rollers of the pulling stand 5, set in the profile channel by hydraulic cylinders 6 with position sensors 7 by the control system through the valve.

 The last roller 8 of the pulling stand is separated from the metal meniscus in the mold at a distance of 11.4 m.

In accordance with the kinetic solidification diagram (Fig. 5) for a slab with a cross section of 200 from mild steel, τ _0.2 = 9.1 min; τ _0.25 = 10 min; τ _0.3 = 10.7 min; τ _0.9 = 15.1 min; τ _0.95 = 15.3 min; τ _1.0 = 15.4 min.

Here τ _0.2 ; τ _0.25 ; τ _0.3 ; τ _0.9 ; τ _0,95 , τ _1,0 - the time after which the cross section of the workpiece in the center is characterized by a solid content of 20, respectively; 25; ... 100%.

Протяженность зоны мягкого обжатия, обеспечивающая обжатие в максимальное число проходов, составит

что соответствует суммарной протяженности двух последних роликовых секций с гидравлическим поджатием, которые в этом случае образуют профильный канал обжатия.Casting using a known method is limited to a maximum speed:

The length of the soft reduction zone, providing compression in the maximum number of passes, will be

which corresponds to the total length of the last two roller sections with hydraulic preload, which in this case form a profile compression channel.

 The increase in casting speed in the known method over 0.6 m / min will lead to the exit of the liquid wells beyond the roller sections. Uncured blank in the rollers of the pulling stand will have significant reductions, accompanied by internal cracks.

 The value of the total compression and the final size of the billet thickness in this case depends on the temperature-speed mode of casting and has a significant scatter.

При этом последняя пара валков работает по уже затвердевшей заготовке и выполняет необходимую степень обжатия, обеспечивая калибровку сечения.The application of the proposed method with the installation of position sensors on the rollers of the pulling stand and control of the latter through the control valve allows to increase the casting speed to

In this case, the last pair of rolls works on the already hardened workpiece and performs the necessary degree of compression, providing calibration of the cross section.

 At casting speeds of not more than 0.6 m / min, calibration is performed by all the rollers of the pulling stand.

 The application of the proposed method improves the central porosity, provides a high-quality macrostructure of the ingot and increases the productivity of the installation from 6 to 23%, providing a tolerance on the thickness of the workpiece ± 0.5 mm.

 Example 2

 In the process of continuous casting of bloom 300 • 450 from cordova steel grade on a radial caster with a base radius of 12 m and differentiated extension over a length of 7.5 m (Fig. 3), molten steel is fed into the mold 1 and the billet is pulled out of it at a variable speed. In the secondary cooling zone 2, the workpiece 3 is supported and guided using idle roller sections at a length of 15.1 from the meniscus of the metal in the mold.

 A soft compression roller section 4 is installed at the extension section, directly adjacent to which is the pulling stand 5, structurally made by three separate blocks on a common frame with individual hydraulic clamps 6 of the upper rollers.

In accordance with the kinetic diagram of solidification of the continuously cast billet 300 • 450 of high-carbon steel, we have τ _0.2 = 26 min; τ _0.4 = 30.8 min; τ _0.7 = 35.0 min; τ _1.0 = 36.6 min.

 The last roller of the roller section of the soft reduction is separated by a distance of 21.4 m from the meniscus of the metal.

Протяженность зоны мягкого обжатия, обеспечивающей обжатие в максимальное число проходов, составляет
L_sr = (τ_0,7-τ_0,2)•0,6 = (35-26)•0,6 = 5,4 м, что соответствует длине секций мягкого обжатия.Casting using the technology of the known method is limited to a maximum speed

The length of the soft reduction zone, providing compression in the maximum number of passes, is
L _sr = (τ _0.7 -τ _0.2 ) • 0.6 = (35-26) • 0.6 = 5.4 m, which corresponds to the length of the soft reduction sections.

Калибровка при этом выполняется последней парой роликов 8 тянущей клети.The application of the proposed method involves the direct adjoining of the pulling stands to the roller section of the soft reduction. The distance from the meniscus to the rollers of the pulling stands in this case is 22.6, respectively; 23.8 and 25 m. Maximum speed in soft reduction mode increases

Calibration is performed by the last pair of rollers 8 of the pulling stand.

 The application of the proposed method increases the productivity of the installation by 15%, improves the central porosity, provides a high-quality macrostructure of the ingot and a minimum thickness tolerance.

 Example 3

 Casting is similar to the method described in example 2, but with the additional possibility of crimping the workpiece in the roller section 4 to bend the workpiece (Fig. 4).

 In this case, the high quality of the macrostructure of the workpiece from hardly deformable steel grades such as ШХ15, ШХ15СГ is ensured.

 The application of the proposed method and device for its implementation allows to increase the casting productivity by 15-23% without compromising the quality of the workpiece, to reduce the tolerance on the thickness of the workpiece, in order to increase the efficiency of ultrasonic inspection of the internal structure of the workpiece and solve the problems of hot planting.

Claims (2)

1. The method of continuous casting of billets, including feeding metal into the mold, drawing from the mold, maintaining and directing the billet in the secondary cooling zone, compressing the billet with an uncured core in thickness in the roller sections and its subsequent calibration to the final size by the rollers of the pulling stand, characterized in that the compression of the workpiece with a non-hardened core is completed outside the roller sections in the pulling multi-roll stand at a certain distance from the meniscus of the metal in the mold, and the calibration of the workpiece is performed by at least the last pair of rollers of this stand. 2. A device for continuous casting of billets, containing a mold, a secondary cooling zone, roller sections with hydraulic adjustment of the roller solution, providing compression of the billet with a non-hardened core in thickness, and a multi-roll pull stand with individual hydraulic clamping of each pair of rollers to the workpiece, characterized in that the pull stand equipped with a control valve with a control system and position sensors of the stand rollers solution mounted on the clamp hydraulic cylinders, moreover, position sensors interrelated with control valve control system.

Images