CN1206362A - Continuous Casting Mold - Google Patents

Abstract

The invention relates to a process and a continuous-casting mold for casting thin slabs. The mold has an oblong inner cross-sectional area and cooled mold walls. The melt is poured in through at least one delivery nozzle which dips into the melt. To ensure that, during casting, markedly lower stresses and, as a consequence thereof, fewer cracks appear in the strand shell, at least at the casting level being established and at least over a part of the depth of immersion of the delivery nozzle, the ratio of the gap widths STI and SII/2 and the ratio of the cooling capacities LTI and LII of the mold wall are related by the equation: [STI/(SII/2)]/[LTI/LII]>1. STI is the width of the gap formed in the zone immediately surrounding the particular immersed delivery nozzle by the outer surface of the delivery nozzle and by the inner surface of the directly opposite mold wall, and SII/2 is half the width of the gap formed by the inner surfaces in the zones in which the inner surfaces of the mold walls are directly opposite each other. LTI and LII are the cooling capacities of the zones of the mold wall which form the respective gap or gap section.

Description

Continuous Casting Mold

The invention relates to a continuous casting mold for casting thin slabs, which has an elongated inner cross section. There is a cooled mold wall and a melt feed through at least one submerged nozzle for inserting the melt.

It is known that in the continuous casting of strands with elongated cross-sections, the inner cross-section of the continuous casting mold is designed such that a shaped strand of approximately final size is produced by the continuous casting mold. In this case, especially in profiled beams with H-shaped cross-sections and in profiled beams with a thickened cross-section at the ends of the section ("dog bone"-shaped cross-sections), the problem often arises that , profiled beams with increased and/or thickened ends compared to the web width often have cracks and stresses and/or undesired crystal structures when poured close to final dimensions. In the case of profiled beams cast not close to final dimensions, technically complex and expensive rolling processes are required after casting in order to achieve the desired final dimensions.

By DE 2034762A1 known a kind of method and the equipment of making thin strip, wherein, have the thickening along its longitudinal extension, still have liquid state core in the thickening part. This thickening is then pressed back under the crystallizer by pressing rollers.

US-PS 5082746 discloses profiled beams of special dimensions, wherein predetermined cross-sectional parameters are not allowed to be exceeded and they have a pre-specified homogeneous crystal structure in order to subsequently obtain the desired cross-sectional shape with a minimum of rolling effort . Such profiled beams can be poured empirically with one or more submerged sprues for conveying the melt. In this case it has been proven that merely limiting the cross-sectional parameters and specifying the required crystal structure is not sufficient to produce a profiled beam of near final dimensions which is free of cracks and has a uniform crystal structure along its entire cross-section. In the case of strand profiles with side walls formed at the ends, it is not sufficient even to select the web width equal to the side wall width as expressly suggested in US-PS 5082746, that is to say according to these The profiled beams produced by special regulations often have cracks and especially in the side wall area have a crystal structure that is more unfavorable than that of the web. These conditions indicate that when pouring with submerged nozzles, uniform casting conditions in any area of the cross section This is not achieved simply by observing the above-mentioned limit values for the cross-sectional parameters.

It is an object of the present invention to provide a continuous casting mold with cooling mold walls for casting a slab with an elongated inner cross-section, for example a shaped slab with an H-shaped cross-section and a predetermined web width, and In such a continuous casting mold with a melt feed through at least one submerged nozzle inserted into the melt, the stresses during the casting process are significantly reduced, with the result that fewer cracks occur in the shell of the strand. In addition, the cast strand should have a uniform crystal structure along the entire cross-section.

According to the invention, this object is achieved by the features specified in the characterizing part of patent claim 1 . The continuous casting mold can be developed in an advantageous manner by means of the characterizing features of the dependent claims 2 to 8 .

The invention provides that, at least at the level forming the metal level in the mold and at least along the insertion depth of the submerged nozzle part, the gap width S _T1 in the area immediately surrounding the submerged nozzle is directly connected to the inner surface of the mold wall. The ratio of the gap widths S _l1 /2 in adjacent areas opposite each other and the ratio of the cooling power L _T1 and L _l1 in the corresponding areas of the mold wall apply the following formula:

[S _T1 /(S _l1 /2)] / [L _T1 /L _l1 ]>1.

Here S _T1 is the gap width of the gap formed by the outer surface of the associated submerged nozzle and the inner surface of the mold wall directly adjacent to one another. S _l1 /2 is half the gap width of the gap formed by the inner surfaces, and in those regions where the inner surfaces of the mold walls are directly adjacent to each other, that is to say In the area between those inner surfaces where submerged nozzles are not installed. L _T1 and L _l1 are the cooling power of the mold wall in these respective regions. A continuous casting mold with an internal cross-section dimensioned in such a way that, even at high pouring speeds, the casting powder placed on the molten metal level in the mold is melted uniformly and discharged together with the slag, so that The section forms a layer of molten slag-casting powder of equal height. A layer of slag-foundry powder of uniform height advantageously promotes the formation of a homogeneous slag-foundry powder layer between the mold wall and the surface of the strand during the continuous casting process. This results in a very good sliding of the strand shell over the entire mold wall and during the casting process the heat of the melt or strand can be dissipated very uniformly through the mold wall, resulting in a very uniform crystal structure and Strain shell free of stress and cracks.

It is advantageous to have [S _T1 /(S _l1 /2)] / [L _T1 /L _l1 ] between 1.05 and 1.30 along the entire insertion depth of the submerged nozzle, so that especially in casting The effect of the submerged nozzle wall on the thermal conditions in the crystallizer during the period.

In the case of uniform cooling of the mold wall, the size design of the internal cross-section required by the continuous casting mold can be simplified as follows, that is, [S _T1 / (S _l1 / 2)] / > 1, preferably [S _T1 /(S _l1 /2)] between 1.05 and 1.30, so that the influence of the submerged nozzle wall on the thermal conditions in the mold during casting is still considered in particular. When the submerged nozzle is especially arranged in the web area, it is proposed according to the invention that the submerged nozzle has an elongated cross-section, so that the area of the wide side opposite the submerged nozzle only needs to have a relatively small distance outward. deformation.

Furthermore, in particular for the production of cross-sections with thickened ends (dog-bone), it is proposed according to the invention to always arrange two submerged nozzles in the region of the narrow sides. In this case it is advantageous when the submerged sprue has, for example, a substantially triangular cross-section in terms of obtaining a product close to the final size.

Cooling elements, such as cooling tubes for cooling the mold wall, are arranged distributed along the mold wall per unit area in such a way that the mold wall receives a defined cooling output in the corresponding area.

The drawings show embodiments of the invention and are described in detail below. in:

Figure 1 is a cross-section of a continuous casting mold in operation with a central submerged nozzle; and

2 shows a cross-section of a continuous casting mold in operation with two submerged nozzles arranged on the narrow side, each having a triangular cross-section.

FIG. 1 shows a cross section through a continuous casting mold with an elongated inner cross section at the height of the molten metal level in the mold formed during operation for casting a continuous casting slab. The wide-side mold walls 1, 1 and the narrow-side mold walls 2, 2 are arranged opposite each other (1-1; 2-2) to form a casting chamber, which are preferably made of copper and provided with cooling for heat dissipation. Tube 3. The cooling pipes 3 ensure uniform heat dissipation along the crystallizer walls 1, 2, which is achieved by arranging a corresponding number of cooling pipes 3 per unit area in the crystallizer walls 1, 2. When the mold shown in FIG. 1 is in operation, a submerged nozzle 4 with preferably elongated cross-section inserted into the melt is provided in the center for feeding the melt.

It can be seen from FIG. 1 that the wide-side mold walls 1, 1 are respectively bent outwards in the area directly surrounding the submerged nozzle 4. The gap 7 has a substantially constant gap width S _T1 along the entire insertion depth. The embodiment shown in FIG. 1 achieves the above-mentioned requirements in that the outer surface 6 of the submerged nozzle 4 has a contour similar to the inner surface 5 of the wide side wall 1 of the crystallizer directly facing each other. With this elongated shape of the submerged nozzle 4 , the region of the broad side 1 opposite the submerged nozzle 4 has to be deformed only slightly outwards.

In the remaining area to the left and right of the submerged nozzle 4, the inner surfaces 8 of the broad side mold walls 1 directly opposite (that is to say no submerged nozzle is arranged between them) form a gap 9, half of which The gap width S _l1 /2 is at most equal to S _T1 , in other words, the gap width of the directly opposite inner surface 8 is at most twice as large as the gap width S _T1 of the gap 7 .

FIG. 2 shows another variant of a continuous casting mold with an inner cross-section dimensioned according to the invention. The continuous casting mold shown in FIG. 2 has an enlargement of the mold cavity in the region of the narrow side walls 2 of the mold, wherein a submerged nozzle 4 is provided in each case (with a thickened end cross-section, also called the canine bone cross-section). The outer cross-section of the submerged nozzle 4 can be of almost any shape; in the exemplary embodiment according to FIG. 2 the submerged nozzle 4 has an essentially triangular outer cross-section. In this case, in the region of the submerged nozzle 4, the gap 7 formed by the outer surface 6 of the submerged nozzle 4 and the inner surface 5 directly opposite the mold wall is still dimensioned along the entire insertion depth such that The gap width S _T1 basically does not change.

In the middle of the continuous crystallizer, where the inner surfaces of the wide sidewalls of the crystallizer constituting the gap 9 are directly facing each other, the half width S _l1 /2 of the gap 9 is slightly smaller than S _T1 ; that is to say, the gap 9 itself is still at most a type The gap 7 in the region of the face ends is twice as large as the width S _T1 .

The use of a substantially constant gap width in these embodiments means that deviations from the required gap width constancy occur in smaller regions, for example at the corners of the triangular cross-section of the submerged nozzle 4; The constancy of the gap width in these regions is only approximately satisfied, but should not exceed twice the value. Similarly, the side wall (as shown in the left half of Fig. 1 ) can also be slightly deformed outward.

It is obvious that the gap width can be reduced or increased in both exemplary embodiments when the cooling power in the region of the gap 7 is reduced or increased in the corresponding region of the wide mold side wall 1 . The decisive factor is that the ratio of the gap width (S _T1 or S _l1 /2) to the cooling power (L _T1 or L _l1 ) of the corresponding area of the mold wall 1 at any position of the continuous casting mold is constant, and is preferably at 1 In the range between .05 and 1.30. In these examples this value is 1.05.

When the continuous casting mold as shown in Fig. 1 or Fig. 2 works, molten steel is continuously injected into the mold through one or more submerged nozzles 4, and the molded slab is discharged at a constant speed. In a casting process with a constant discharge rate, continuously inputting just as much molten steel as is discharged at the mold outlet, so the height of the metal liquid level in the mold formed with constant renewal of the molten steel stagnant in this area Unchanged, these molten steels also promote the melting of the casting powder supplied and placed on the molten metal surface in the mould. At the same time, the essentially constant gap width in the embodiment according to FIGS. 1 and 2 ensures a uniform upward heat flow over the entire cross-sectional area of the continuous casting mould. The casting powder is melted uniformly in the area, that is to say the same amount of casting powder is continuously melted per unit surface area of the metal level and per unit time. Furthermore, at a constant discharge speed of the cast shaped strand, due to the inventive internal cross-sectional shape, the slag-casting fines layer formed in the region of the molten metal level forms the same at all points of the internal cross-section. the height of. Correspondingly, between the mold walls 1 , 2 and the melt or strand shell, a film of slag-casting fines of constant thickness likewise forms automatically at all points on the strand surface.

Due to this special dimensioning of the mold and the resulting formation of a slag-dust film of constant thickness during casting, heat is continuously removed from the molten steel in the area of the mold wall in proportion to the area of the wall, And the molten steel is uniformly cooled to form the shell of the slab. The quantitative influence of the slag-casting powder film is directly determined by its unit thermal conductivity and the thickness of the film formed; a constant thickness beside the mold walls 1, 2 results in a transfer of heat from the melt to a given temperature difference. There is a constant thermal resistance when the body is discharged through the crystallizer walls 1, 2. The total thermal resistance is obtained from the sum of the thermal resistances of the parts in which the successive layers (mold wall-slag/casting powder-strand shell-melt-submerged sprue wall) are unit The thermal conductivities are represented by their reciprocals, respectively. The specific thermal conductivity of the slag-cast powder film is about 1 W/km and thus determines the heat dissipation and cooling of the slab, as demonstrated by experimental studies. With the invention, the constant thickness of the slag-casting fines film formed in the mold results in a homogenization of the heat conduction in the mold along the horizontal direction over the entire mold length. The temperature difference in the region of the strand shell/mold wall boundary is thus significantly reduced, so that only low stresses remain in the strand shell of the cast strand, with the result that the risk of cracks is greatly reduced. Furthermore, due to the very good uniform lubrication thus obtained, the wall wear of the continuous casting mold is reduced, so that its service life is also significantly extended.

Claims (8)

1. the continuous cast mold of thin slab is used to cast, it has microscler interior cross section, the crystallizer wall of cooled is arranged and a melt input unit by the immersed outlet of at least one insertion melt is arranged, it is characterized by: at least on the height that forms mould inner metal liquid face and at least along immersed outlet part insertion depth, gap width S _T1And S _L1/ 2 ratio and crystallizer wall (1,2) cooling power L _T1And L _L1Ratio be applicable to following formula:

(S _T1/ (S _L1/ 2))/(L _T1/ L _L1)＞1, wherein S _T1Be directly in the zone of the immersed outlet (4) that inserts by the gap width in the gap (7) of inner surface (5) formation of the outer surface (6) of immersed outlet (4) and the opposed crystallizer wall of direct neighbor (1), and S _L1The/2nd, 1/2nd gap widths in the gap (9) that in the mutual opposed zone of direct neighbor of the inner surface (8) of crystallizer wall (1), constitutes by inner surface (8), and, L _T1And L _L1It is the cooling power that constitutes crystallizer wall (1, the 2) zone of corresponding gap or gap portion.

2. according to the described continuous cast mold of claim 1, it is characterized by: for the whole insertion depth of immersed outlet, gap width S _T1And S _L1The cooling power L in/2 ratio and corresponding crystallizer wall (1,2) zone _T1And L _L1Ratio be applicable to following formula:

〔S _T1／(S _l1／2)〕／〔L _T1／L _l1〕＝1．05-1．30。

3. according to the described continuous cast mold of claim 1, it is characterized by: gap width S under the uniform situation of whole crystallizer wall (1,2) cooling power _T1And S _L1/ 2 ratio is

〔S _T1／(S _l1／2)〕＞1。

4. according to the described continuous cast mold of claim 1, it is characterized by: gap width S under the uniform situation of whole crystallizer wall (1,2) cooling power _T1And S _L1/ 2 ratio is

〔S _T1／(S _l1／2)〕=1．05-1．30。

5. according to the described continuous cast mold of one of claim 1 to 4, it is characterized by: immersed outlet (4) has microscler cross section at outlet area at least.

6. according to the described continuous cast mold of one of claim 1 to 4, it is characterized by: immersed outlet (4) has leg-of-mutton basically cross section.

7. according to the described continuous cast mold of claim 6, it is characterized by: respectively establish an immersed outlet (4) in the location of narrow side (2).

8. according to the described continuous cast mold of one of above-mentioned all claims, it is characterized by: crystallizer wall (1,2) is provided with cooling element (3), and they distribute matchingly with the cooling power of regulation.

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