EP0498296A2 - Mould for continuous casting of metals, especially of steel - Google Patents

Abstract

In moulds for continuous casting of polygonal strand cross-sections, especially with quadrangular or hexagonal cross-section, the mould cavity (6) can have different geometrical shapes on the pouring-in side (4) and the strand outlet side (5). A better cooling of the crust of the strand is to be achieved by a targeted deformation of the strand cross section within the mould, in order to improve the strand quality and in addition to increase the casting speed. It is proposed for this purpose to provide, in each peripheral section of the mould cavity (6), a cross-sectional enlargement (7) in the form of a bulge (9), the extent (10) of the bulge (9) decreasing in the running direction (11) of the strand, at least along a partial length (12) of the mould cavity (6), such that the cross-sectional shape of the strand is deformed during passage through the partial length (12) of the mould cavity (6). <IMAGE>

Description

The invention relates to a mold for the continuous casting of metals according to the preamble of claim 1.

Since the beginning of continuous casting with continuous molds, experts have dealt with the problem of the formation of air gaps between the strand crust and the mold wall below the bath level. This gap formation significantly reduces the heat transfer between the mold and the strand crust and causes an uneven cooling of the strand crust, which leads to strand defects such as rhomboidity, cracks, structural defects, etc. In order to create the best possible all-round contact of the strand crust with the mold wall over the entire length of the mold and thus the best possible conditions for heat dissipation, many proposals have been proposed, such as walking beams, coolant injection into the air gap, mold cavity with different conicity, etc. .

From US Pat. No. 4,207,941, which forms the preamble, a mold for the continuous casting of steel strands with polygonal, in particular with square cross sections, is known. The cross section of the mold cavity, which is open on both sides, is a square with corner fillets on the pouring side and an irregular pentagon on the strand exit side. In the corner areas towards the corner groove the casting cone is continuously enlarged in the direction of the strand, and it is approximately twice as large in the area of the fillet over a partial length of the mold as in the central region of the mold wall. When casting with such molds, jamming of the strand inside the mold can occur, which leads to strand breaks and breakthroughs. Instead of a square, a pentagon is cast. In particular, it is difficult to dimension such molds for different casting speeds during a running casting, as are unavoidable in long sequence castings with many ladle changes.

The invention has for its object to overcome the disadvantages mentioned. In particular, deformation of the strand cross section within the mold is intended to achieve cooling of the strand crust that can be measured over the entire circumference, in order to improve the strand quality on the one hand and to increase the casting speed on the other hand. However, differences in casting speed during a running casting should also be made possible without the disadvantages mentioned, such as strand break and breakthrough.

According to the invention, this object is achieved by the entirety of the features of claim 1.

With the mold according to the invention it is possible, in the case of billets and small pre-block cross sections, to force cooling that is uniform in all circumferential sections and that can be measured in terms of its intensity within predetermined limits. This can influence the crystallization of the strand crust and improve the strand quality. Skewed edges, surface and structural defects are avoidable. Through the targeted deformation of the cross section, the uniformity of the cooling along the strand circumference can also be improved in the mold according to the invention, even at different casting speeds. The risk of strand breaks or breakthroughs can be significantly reduced at high casting speeds.

The bulges of the mold cavity in each circumferential section each represent arched vaults in the mold according to the invention, which have a higher dimensional stability compared to classic molds, in particular in the area of the bath surface that is exposed to high heat. With tube and other molds, this higher dimensional stability improves the dimensional stability of the mold cavity during the service life of the mold on the one hand and the strand quality on the other.

The bulge is usually reduced from the bath level area along the mold cavity over a partial length or over the entire length of the mold. At the mold exit, for example, a residual bulge can remain in each peripheral section. According to a further embodiment, it is additionally proposed to provide the cross section of the mold cavity on the mold exit side in a straight line on all sides between corners. At the mold exit, the mold can also be round or a preliminary profile, e.g. in the form of a double-T beam.

When dimensioning the bulge, it should be noted that even with short dwell times of the strand crust in the mold, ie at high casting speeds, the strand cannot become jammed in the border areas of two colliding peripheral sections, for example in the corners. For this purpose, the difference between the arc length at the bath level and at the mold exit or the chord length at the mold exit is determined and compared with the shrinkage of the strand crust transverse to the direction of the strand. The difference mentioned can be chosen by the degree of bulging so that it is essentially in agreement with the shrinkage mentioned. According to one exemplary embodiment, the light dimension between opposite circumferential sections of the mold cavity on the pouring side, measured in the region of the largest bulge, is approximately 5-15%, preferably at least 5% or 8%, larger than the light dimension between opposite circumferential sections can be selected on the strand exit side.

The amount of bulging along the mold can decrease degressively or possibly progressively in the casting direction and can approach zero. According to a further embodiment, the size of the bulges in the strand running direction of the following cross sections can advantageously decrease continuously. According to a further exemplary embodiment, the change in the mass of the bulge in the strand running direction can also be specified as a degree of taper. The shape and size of the bulge are generally the same in all sections. The conicity of the bulge changes in size along the circumferential section. According to one embodiment, a taper between 0 and 1% / m and at the center of the peripheral section between 10 and 35% / m can be provided at the two ends of each peripheral section.

Another possible variation is the choice of the length or partial length of the mold cavity with bulged side walls. It is fundamentally possible for the amount of bulging to be reduced over the entire length of the mold cavity. However, only partial lengths are conceivable. An advantageous embodiment provides for a partial length of at least 50% of the mold length. With today's molds of 800 mm length, the partial length is at least 400 mm.

In the case of rectangular conical molds according to the prior art, the taper in the corners or in the corner areas is greater by a factor of 2 than on the side walls. In the case of molds with a degree of taper that exceeds the usual level of 0.9-1.2% / m, this fact can lead to jams and strand breaks. Instead of the conically arranged walls of the molds known in the prior art, the The strand cross-sectional shape is deformed as it passes through the partial length of the mold cavity and the cooling capacity is controlled in the process. In the border area between two abutting circumferential sections or in the corners of the mold cavity, the design of the taper can be freely selected regardless of the size and degree of taper of the bulge. This allows molds to be built for the first time, whose taper in the corners or corner areas can be selected independently of the taper and the shape of the bulged side surfaces. For example, it is possible to make the taper in the corners positive, neutral or negative depending on the degree of the deformation of the bulge, the shrinkage of the strand crust, etc.

In one exemplary embodiment, it is proposed to provide the conicity measured over the diagonal over the partial length with bulges in the order of magnitude between 0-1% / m or between 0-0.5% / m.

For various known reasons, the corners of the mold cavity are rounded in polygonal strand cross sections. It has proven particularly advantageous if the corners of the mold cavity have fillets with a radius of 3 to 8% of the side length of the cross section.

The bulged mold walls can have different geometric shapes. According to one embodiment, it is proposed to limit the bulges by means of arcs, the radii of which increase to infinity in the direction of the strand. To simplify the manufacture of mold tubes or mold walls, it may also be advantageous to limit the bulges by means of curved and / or flat surfaces.

Regardless of the geometric shape of the bulges, it is proposed in one exemplary embodiment to connect the bulges tangentially to the radii of the fillets.

The production of molds with bulges that shrink in the direction of the strand can be accomplished by hot or cold working of copper walls. According to one embodiment, it is particularly advantageous if at least a partial length of the mold cavity is produced by explosion deformation. In the case of tubular molds, a high-precision mold with a straight or curved strand axis can be produced by pressing in a mandrel with bulges and subsequent explosion deformation.

Exemplary embodiments of the invention are explained below with reference to figures.

Fig. 1:

einen Längsschnitt durch eine Rohrkokille nach der Linie I-I von Fig. 2,

Fig. 2:

eine Draufsicht auf die Kokille gemäss Fig. 1,

Fig. 3:

eine Draufsicht auf ein Beispiel einer Ecke eines ausgebauchten Formhohlraumes mit vier Höhenkurven,

Fig. 4:

eine Draufsicht auf ein weiteres Beispiel einer Ecke eines ausgebauchten Formhohlraumes mit vier Höhenkurven,

Fig. 5:

eine Draufsicht auf ein weiteres Beispiel eines halben Formhohlraumes mit vier Höhenkurven,

Fig. 6:

eine Draufsicht auf eine runde Kokille und

Fig. 7:

eine Draufsicht auf eine Kokille, deren Formhohlraum durch Bogenlinien begrenzt ist.

Show it:

Fig. 1:

2 shows a longitudinal section through a tubular mold along the line II in FIG. 2,

Fig. 2:

2 shows a plan view of the mold according to FIG. 1,

Fig. 3:

4 shows a plan view of an example of a corner of a bulged mold cavity with four height curves,

Fig. 4:

4 shows a top view of a further example of a corner of a bulged mold cavity with four height curves,

Fig. 5:

4 shows a plan view of a further example of a half mold cavity with four height curves,

Fig. 6:

a top view of a round mold and

Fig. 7:

a plan view of a mold, the mold cavity is limited by curved lines.

1 and 2 show a mold 3 for the continuous casting of polygonal strand cross sections, in the present example of square strand cross sections. An arrow 4 points to a pouring side and an arrow 5 a strand exit side of the mold 3. The cross sections of a mold cavity 6 have different geometrical shapes on the pouring and strand exit side. As can best be seen in FIG. 2, the cross-section of the mold cavity 6 on the pouring side 4 between the corners 8 - 8 ″ ″ is provided with cross-sectional enlargements in the form of bulges 9. An arc height 10, which represents the extent of the bulge, decreases continuously in the strand running direction 11 over a partial length 12 of the mold cavity 6. The mold cavity cross sections in the planes 14 and 15 delimit a mold part 13 with a square cross section with fillets 16, as is known in the prior art.

A circumferential line 17 shows the mold cavity cross section in the plane 14 and a circumferential line 18 shows the mold cavity cross section in the plane 15. The cross section of the mold cavity 6 is straight on all sides between the corners 8 on the mold exit side. An arrow 2 denotes a peripheral section of the peripheral lines of the mold cavity 6. In this mold, 4 peripheral sections with similar cross-sectional enlargements 7 are provided. Instead of the square basic shape of the mold cavity 6, a hexagonal, rectangular etc. cross section could also serve as the basic shape.

A light dimension 20 between opposite sides of the mold cavity 6 on the pouring side 4 in the area of the largest bulge is 5 to 15% larger than a light dimension 21 between the opposite sides on the strand exit side 5. In other words, the light dimension 20 can also be at least 5% or at least 8% larger than the light dimension 22 in the plane 14 at the end of the partial length 12.

berechnet werden, wobei Bo die Breite oben in mm, Bu die Breite unten in mm, L die massgebende Länge in m und T die Konizität (oder Taper) in %/m bezeichnet. Nach dieser Formel gerechnet können Konizitäten von 10 - 35 %/m gewählt werden.The arch height 10 of the bulge 9 decreases continuously in the direction of the strand 11 with the following cross sections. The Conicity of the maximum arc height 10 along a line 24 can be according to the formula

are calculated, where Bo is the upper width in mm, Bu is the lower width in mm, L is the decisive length in m and T is the taper (or taper) in% / m. Conicities of 10 - 35% / m can be selected using this formula.

In this example, the partial length 12 is 400 mm or approximately 50% of the mold length, which measures approximately 800 mm.

In FIG. 3, height curves 30-33 show a corner of a bulged mold cavity 35. The height curve 30 represents the uppermost edge of the mold cavity 35 of the mold 34. The wall thickness of a mold tube is indicated by 36. 33 shows the height curve at the mold exit. Between the curves 30 and 33, the taper can be read out at two intermediate heights. Curves 31 and 32 show the decreasing arc heights of the bulges, which cause the strand crust to deform during casting. In the area of the fillet 38, the taper of the mold cavity 35 along a diagonal cut along the line 39 is 0-1% / m, preferably 0.1-0.5% / m. A deformation of the strand crust along line 39 is generally not provided.

FIG. 4 shows similar height curves 40-43 as in FIG. 3. The main difference lies in the design of the fillet 48 along the diagonal line 49. The fillet 48 has a negative cone in the direction of the strand. In the corner area in the strand running direction there is therefore an expansion of the mold cavity. Depending on the format of the strand, chosen arc height of the bulge, which has to be deformed back, it may be of interest to provide a negative cone at the corners 48 along the diagonal line 49 in order to eliminate any jamming of the strand in the mold. Due to the geometrical design of the corner area, the cooling in the edge area of the strand can also be controlled. A negative cone along the diagonal line 49 may also be desirable to accommodate tendon extensions when deforming strong bulges that are not compensated for by the shrinkage.

In Fig. 5 the bulges are limited by straight surface parts. Elevation curves 50 - 53 represent a steady decrease in the bulges. In order to ensure that there is no abutting edge in the middle of the bulged sides, a rounding 54 is appropriate. The straight surface portion runs tangentially to a fillet 58. In this example, no taper is provided along the groove 58 in the direction of the strand. In a section along the diagonal 59, the fillet 58 runs essentially parallel to the longitudinal central axis of the mold.

To determine the taper of the fillets 38, 48, 58 in FIGS. 3-5, calculations and / or casting tests are necessary. On the partial length of the mold, the chord associated with each circular arc lengthens on the one hand as the bulge height of the bulge decreases. On the other hand, the shrinkage of the strand crust at right angles to the strand running direction can be calculated and compared with the tendon extension. The taper in the corner area can be determined from the difference between the two values. It should be noted that at high casting speeds, ie when the strand crust remains in the mold for a short time, the shrinkage value is lower than at low casting speeds.

6 and 7 are molds whose mold cavities 60 and 70 are delimited by curved and circular surfaces. Circumferential lines 61, 71 of the mold cavity cross section are each divided into three peripheral sections 62, 72. The number of peripheral sections 62, 72 can be chosen freely, with essentially round molds, as shown in the figures, generally being divided into 2-6 peripheral sections 62, 72. Each peripheral section 62, 72 has a cross-sectional enlargement in the form of a bulge 63, 73. In these examples, the cross-sectional enlargements are represented by bulges delimited by an arc. Arrows 65, 65 ', 65' 'and 75, 75' show the size of the bulge 63, 73 on the one hand by the arrow length. This degree of bulging decreases in the direction of the arrow on the partial length of the mold cavity in such a way that the strand cross-sectional shape deforms as it passes through the partial length. The shape and the size of the bulge 63, 73 is the same in all peripheral sections 62, 72. Conicities of the bulges 63, 73 measured in the direction of the strand are different in size along the circumferential sections 62, 72. At the two ends 66, 66 ', 76, 76' of each circumferential section 62, 72 the taper is zero to 1% / m and in the middle 67, 77 of the circumferential sections a taper between 10-35% / m is generally provided .

In the case of essentially round mold cavity cross sections, it is also possible to deform the strand into two partial lengths which follow one another directly or have an intermediate zone between the partial lengths. In such molds, the peripheral sections of the successive partial lengths can be offset from one another, preferably offset by half a peripheral section.

In order to achieve long service lives of such molds, or to improve the strand surface, all measures known in the prior art for reducing friction, such as lubrication, surface treatment, coatings, choice of material for the mold etc. are used.

All figures show straight tube molds for a better overview. However, the invention is also applicable to arc molds as well as block molds, plate molds etc.

The method for producing such molds with an arcuate or straight mold cavity is, according to one embodiment, characterized by the following method steps. An extruded tube profile made of a copper alloy is bent onto a casting radius of an arc continuous caster by means of a bent mandrel according to methods known today. This step is omitted for straight molds. An expanding mandrel is then inserted or pressed into the copper pipe. The mold is expanded over its entire length or over a partial length with movable expansion parts that correspond to the intended bulges. If a hardenable copper alloy is used, the mold tube is hardened by dispersion hardening or by strain hardening, for example by shot peening. A high-precision mold cavity can be achieved with tubular molds if the mold is additionally calibrated over an entire or part of its length by explosion deformation on a mandrel.

Claims (15)

Mold for the continuous casting of metals, in particular steel, the mold (3) having a mold cavity (6, 35, 60, 70) which is open on both sides, characterized in that the circumferential line (61, 71) of the mold cavity cross section has circumferential sections (62, 72 ) and each circumferential section (62, 72) has a cross-sectional enlargement (7) in the form of a bulge (9, 63, 73) and that the dimension (10) of the bulge (9, 63, 73) in the strand running direction (11 ) reduced at least along a partial length (12) of the mold cavity (6, 35, 60, 70) in such a way that the strand cross-sectional shape deforms as it passes through the partial length (12) of the mold cavity (6, 35, 60, 70). Chill mold according to claim 1, characterized in that the shape and the mass of the bulge (9, 63, 73) are the same in all circumferential sections (62, 63) and along the conicity of the bulge (9, 63, 73) measured in the direction of run (11) the circumferential section (62, 63) are different in size, preferably at the two ends (66, 66 ', 76, 76') of each circumferential section (62, 72) a taper between 0 and 1% / m and in the middle ( 67, 77) of the peripheral section (62, 72) have such a value between 10-35% / m. Chill mold according to one of claims 1 or 2, characterized in that the mold cavity cross section on the strand exit side is polygonal, preferably quadrangular or hexagonal. Chill mold according to one of claims 1 or 2, characterized in that the mold cavity cross section on the strand exit side has arcuate boundary surfaces, preferably is essentially round. Chill mold according to one of claims 1 or 2, characterized in that the mold cavity cross section on the strand exit side has a preliminary profile, preferably in the form of a double-T beam. Chill mold according to claim 4, characterized in that an essentially round chill mold is divided into 2-6 peripheral sections (62, 72) and each section (62, 72) has a cross-sectional enlargement in the form of a substantially arcuate bulge (63, 73) . Chill mold according to claim 6, characterized in that the peripheral sections (62, 72) of a first and a second partial length (12) of the mold cavity (60, 70) are offset from one another, preferably offset by half a peripheral section (62, 72). Chill mold according to claim 3, characterized in that the light dimension (20) between opposite circumferential sections on the pouring side (4), measured in the area of the largest bulge (9), is approximately 5-15%, preferably at least 5% or 8%, larger is than the light dimension (21) between the same peripheral sections on the strand exit side (5). Chill mold according to one of claims 1-6, characterized in that the partial length (12) is at least 50% of the mold length. Chill mold according to claim 3, characterized in that in the case of a quadrangular cross-section, the conicity measured via a diagonal cut is 0-1% / m, preferably 0.1-0.5% / m. Chill mold according to claim 10, characterized in that the corners (8 - 8 '' ') of the mold cavity (6, 35) have grooves (16, 38, 48, 58) with a radius of 3 - 8% of the side length of the cross section. Chill mold according to one of claims 3 or 5, characterized in that the bulges (9) are delimited by curves and / or straight lines. Method for producing the mold according to one of claims 1-12, characterized in that an extruded tubular profile made of a hardenable copper alloy - bent by means of a bent mandrel onto a casting radius of an arc continuous caster, - The cross-sectional enlargement (7) in the form of a bulge (9, 63, 73) is expanded and expanded by means of an expanding mandrel - is hardened by dispersion hardening or work hardening by shot peening. Method for producing the mold according to one of claims 1-13, characterized in that at least a partial length (12) of the mold cavity (6, 35, 60, 70) is calibrated by explosion deformation. Method for producing the mold according to one of claims 1-14, characterized in that the taper along the partial length (12) in the border region of two colliding circumferential sections (62, 72) from the geometric calculation of the strand circumferential length and the shrinkage calculation of the strand crust transverse to the strand longitudinal axis is set.

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