RU2241573C1 - Mold for continuous casting of slabs - Google Patents

Abstract

FIELD: metallurgy, namely designs of molds for continuous casting of slabs.

SUBSTANCE: mold includes narrow and wide cooled walls. Narrow walls have two portions with length l1, l2 respectively. In first upper portion working surface of wall is rectilinear, it is made according to expression y = (a - ω) x. In lower portion there is curvilinear working surface made according to expression

where y - difference between thickness values of wall in upper portion of mold and in portion spaced by distance x from mold top, mm; x - spacing from mold top, mm; a, b - coefficients depending upon kind of cast steel, modes and conditions of casting process, size of billet cross section; ω - coefficient of turning working surface. All other terms of expression are determined according to condition of gradual transition of rectilinear working surface to curvilinear one.

EFFECT: improved design, enhanced heat exchange between narrow faces of slab and narrow walls of mold, increased strength of mold walls.

3 dwg

Description

The invention relates to metallurgy, and more particularly to the design of molds, and is intended for the production of continuously cast slabs.

The closest in technical essence is a cooled mold (mold), made with tapering in at least one section, presented in the method of continuous casting of peritectic steels (see patent RU No. 2142861 C1, CL 6 B 22 D 11/04) . The mold has wide walls and narrow side walls, which can be made movable, and includes a through central filling chamber for introducing the exhaust nozzle. The initial mold segment has a taper of 2 to 6% per 1 m. Analytically, the shape taper is understood to mean [(l _a -L _B ) / (L _B · h _i )] · 100, in which h _i is the height of the mold segment, whose taper is to be determined, l _a is the effective width at the inlet of a segment having a height h _i taking into account the resulting expansion determined by any casting chamber, and l _b is the width at the outlet of a segment having a height h _i taking into account the expansion determined by a casting chamber.

A disadvantage of the known mold (including double and triple taper) is the formation of a gap near the middle of the straight section due to the mismatch of the straightness of the curved shrinkage of the workpiece, especially in the upper part of the mold. The resulting gap in the mold reduced the heat sink and led to the heating of the slab crust. In this regard, there was a problem of the possibility of a freeze or breakthrough. The clearance was reduced by increasing the taper, and thus increasing the contact pressure between the surfaces of the workpiece and the working walls at the contact points. The increase in pressure led to increased wear in these areas.

The working surface of the prototype in the i-th plot can be mathematically described as follows:

where x is the distance from the top of the mold;

y is the difference between the wall thickness at the top of the mold and at a distance x from the top of the mold;

l _j is the length of the j-th section;

and _i is the coefficient characterizing the slope of the i-th section.

The desired technical result of the claimed device is to increase the resistance of the narrow walls of the mold (reducing wear in the lower part of the mold) and improving heat transfer between them and the narrow faces of the slab.

The specified technical result is achieved by creating a mold for continuous casting of slabs containing wide and narrow walls, in which the narrow walls contain two sections: the upper I with a rectilinear working surface and the lower II with a curved working surface, and the rectilinear working surface smoothly passes into a curvilinear, respectively l ₁ and l ₂ (see figure 2).

In section I, the working surface of the narrow wall is made rectilinear according to the following relationship:

and the curved section of the working surface is made according to

where x is the distance from the top of the mold, mm;

y is the difference between the thickness of the narrow wall at the top of the mold and at a distance x from the top of the mold, mm;

a, b - coefficients depending on the steel grade, casting conditions and conditions, size of the workpiece section;

ω is the dimensionless coefficient of rotation of the working surface.

The remaining terms of dependence (2) were determined from the condition of a smooth transition of the linear part to the curvilinear.

The metal entering the crystallizer crystallizes around the perimeter. In the region of the linear portion, the formed crust departs from the walls of the mold. Due to this, the temperature of copper does not exceed the critical value at which softening occurs. Intensive growth of the crust occurs in this area. Just above the middle of the mold, the growth rate of the crust decreases significantly. But the crust has already acquired sufficient thickness for strength. Next, there is already a tight contact between the surface of the workpiece and the working surface of the mold.

The proposed mold provides the necessary gaps and contact density between the narrow working walls and the workpiece along the entire length of the mold. An increase in the resistance of narrow walls (reduced wear) is provided by a decrease in the contact pressure between the surfaces of the working walls and the workpiece due to an increase in the contact area and the absence of the need to use an additional increase in taper.

The essence of the device is illustrated by drawings, where:

figure 1 is a section of the mold, where 1 is a wide wall of the mold; 2 - crystallizer housing; 3 - channels;

figure 2. - side view from the working surface of the narrow wall of the mold. Type I - the shape of the working surface of the narrow wall of the mold.

The coefficient a is dimensionless, and the coefficient b has the dimension mm. Coefficients a and b vary widely. But the ranges of variation of these coefficients are limited by various conditions. For a> 0.025, with a slight change in the meniscus level, the gap between the workpiece and the walls of the mold changes significantly. Therefore, for these values of a, it becomes necessary to precisely maintain the metal level at a given level. The minimum possible value of coefficient a is limited by the maximum possible casting speed and the maximum slab cross-sectional size used at metallurgical plants (with a casting speed of 2 m / min and a slab cross-section width of 1000 mm a not less than 0.0005). Thus, the range of variation of a is 0.0005 ... 0.025.

The minimum value b of the coefficient tends to zero. The maximum value of the coefficient is determined by the casting speeds used and the dimensions of the slab cross section at metallurgical plants and cannot currently exceed 1000 mm.

The choice of the coefficient ω is based on various conditions: equality of wall thickness at the top and bottom of the mold; reduction of copper costs during gouging, etc. The value of ω can be any (even negative), but it makes sense to use walls with a range of changes in the value of this coefficient from 0 to 0.025.

Since the temperature of the crust in the upper part of the mold is close to the solidus temperature, and its thickness is still quite small, tight contact of the mold walls with the workpiece can lead to significant crust deformation. In order to avoid this, it is necessary to provide a “safe” gap in the upper part of the mold (see FIG. 3). The size of this gap is limited from above by the condition of the required heat sink. This gap in the claimed device is provided by a straight taper. The length of the straight section is determined by the grade of steel and the casting mode. For steel grades with strong creep at high casting speeds, the curved section can begin with the meniscus (0.05L, where L is the length of the mold).

In the lower part of the mold, the crust acquires sufficient strength to withstand close contact with the walls of the mold. The length of the curved section is determined by the grade of steel and the casting mode. In order to obtain the effect, it is advisable to use a curved section with a length not less than the length of the contact area of the ingot with the walls of the mold in the prototype (according to experimental data, it is at least 0.3L). The lengths of the sections can be determined experimentally by the nature of the wear of narrow walls with a rectilinear working surface.

Thus, the length of the straight section I is l ₁ = 0.05 ... 0.7 · L, and the length of the curved section II, respectively, l ₂ = 0.3 ... 0.95 · L.

In the converter shop of OJSC Severstal at UNRS No. 2 and No. 3, the curved crystallizer was tested with the following parameters: a = 0.00675; b = 89 mm; ω = 0; l ₁ = 400 mm. For comparison, we used neighboring streams on which crystallizers stood with rectilinear narrow walls. During the test, slabs were poured from various steel grades (17G1SU, 17GS, 17GSU, 08PS, 1PS, 2PS, 10SP, 20SP, DZYU, 2DZU, Ch09SF, 08Yu, DKh51D, 08E, 20YUU, 20YuA, S1006, S1008, S235, SPSSD1 SPCC1D, DS01, W400-50A, SPHC, SPHT1, SPHT2, SGCC, SPCC, ST12) with a cross section of 1070 × 250 mm, the casting speed varied from 0.6 to 1.0 m / min. Under the conditions of the converter shop, when casting a slab with a cross section of 1070 × 250 mm, the narrow walls of the mold are removed due to wear on average after 156 melts. The maximum observed resistance of narrow rectilinear walls was 222 heats. Experienced curved narrow walls defended 308 heats. Thus, the resistance of the walls increased due to the use of a curved surface by at least 40%.

Claims (1)

A mold for continuous casting of slabs containing cooled wide and narrow copper walls, characterized in that the narrow walls contain two sections - the upper with a rectilinear working surface and the lower with a curved working surface, and the rectilinear working surface smoothly transforms into a curved, while the rectilinear portion of the working the surface of the narrow wall is made according to the following relationship: y = (a-ω) and the curved section of the working surface is made according to:

where y is the difference between the thickness of the narrow wall in the upper part of the mold and at a distance x from the top of the mold, mm; x is the distance from the top of the mold, mm; a is a dimensionless coefficient depending on the properties of the cast steel grade, casting conditions and conditions, the size of the billet cross section and equal to 0.0005 ... 0.025; ω is the dimensionless coefficient of rotation of the working surface, equal to 0 ... 0,025; b is a coefficient depending on the properties of the cast steel grade, casting mode, the size of the cross section of the workpiece and equal to 0 ... 1000 mm; l ₁ - the length of the rectilinear section of the narrow wall, mm, the length l _{1 of the} rectilinear section is 0.05 ... 0.7 of the length of the mold, and the length l _{2 of the} section with a curved surface is 0.3 ... 0.95 of the length of the mold.

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