KR20030036719A - Chilled continuous casting mould for casting metal - Google Patents

Abstract

The invention relates to cooling for casting slab-shaped metal, in particular steel, in particular having a mold wall of plates 7 and 7.1 with coolant channels for cooling, in particular 40 to 400 mm in thickness and 200 to 3,500 mm in width. It relates to a formula continuous casting mold. In order to improve such continuous casting molds so that the thermal stress over the mold height, ie, the heat profile over the mold height, can be lowered to lower the mold skin film temperature at the casting liquid level, the width 26.1 of the coolant channel 29 is Depending on the heat flow profile 2.1 over the height 13 it is reduced from the mold inlet 13.1 to the mold outlet 13.2 in the casting direction.

Description

Cooling Continuous Casting Mold for Metal Casting {CHILLED CONTINUOUS CASTING MOULD FOR CASTING METAL}

Based on FIG. 1, the relationship known at the time of continuous casting of metal is demonstrated. Continuous casting of metals, in particular steel, by vibrating molds (1), as well as by moving molds formed as twin rolls with fixed roll cores and rotating tube cases, results in a heat flow J according to the potential drop U (3). 2) a mold coolant 9 through a billet shell 5 formed from a mold center or billet center 4, a slag film 6 which is normally present in a mold plate 7.1 of a given copper plate thickness 8; To the side. Here, reference numeral 8 indicates the copper plate thickness between the course of the slag and the mold cooling water or between the "hot face" and "cold face". The mold coolant 9 is, for example, a controlled speed expressed in m / s, a predetermined pressure 11 in bar measured at the mold coolant inlet, and a controlled coolant inlet temperature T-0 measured at the mold coolant inlet. 12) flows in the continuous casting direction 14 or the opposite direction to absorb and carry out the above-described heat flow J (2). The total heat flow J (2) carried out by the mold coolant 9 is transferred to the individual medium 16 with its own individual resistance Ri 17, in particular to the medium between the billet center 4 and the mold coolant 9. Is determined by the total resistance R-total (15). Such individual resistance 17 is determined by its length l (18), its specific thermal conductivity λ (19), and its conduit cross section F (20), and the potential drop U (3) and heat flow J Together with (2) form a mass flow equation (20.1). The equation substitutes the resistance of the individual medium between the mold center 4 and the path of the mold cooling water, such as the resistance of the mold plate made of liquid steel, billet shells, slag, refractory coating, and in particular copper.

The heat flow that reaches the phase boundary 21 (also referred to as a "cold face") between the copper plate 7 and the course of the coolant 9 causes the interface resistance between the copper of the mold plate to the coolant 22 ), So that between the phase boundary 21.1 and the phase boundary 21, referred to as the "hot face" or phase boundary between the copper plate 7 and the slag film 6 or billet shell 5, Epidermal film temperature or temperature gradient 25 is created. Such a temperature gradient depends on the strength of the heat flow across the mold height 13 and on the interface resistance 22 at the phase boundary 21 between the copper plate / coolant. It is also known that the heat flow is reduced correspondingly to the profile 2.1 (referred to as a "heat beam") from the casting liquid level 30 to the mold outlet 13.2.

The interface resistance 22 is determined by the size of the cooling channel 13 extending parallel across the mold height 13, which cooling channel 13 is here width 26.1, depth 26, 2. , And thus the flow cross section Q and a cooling slit having a length 26.4 approximately coincident with the mold height 13 except for the boundary layer (layer of Nernst) which is a function of the flow velocity 10 (FIG. 3E). See). In addition, the resistance 17 is defined as the difference of the mold width that is not directly cooled from the maximum cooled mold width divided by the cooled mold width or in the first approximation the cooling channel / cooling channel spacing except for the bridge width 27.1. (27) is determined by the coolant covering percentage 27.2 for the mold width, defined as divided by cooling channel / cooling channel spacing (see FIG. 3E). Such a relative coolant covering 27.2 corresponds to the conduit cross section F 20 in terms of the mass flow equation U = ΣRi × J. In addition, the resistance 17 depends on the copper plate thickness I (8) and the specific thermal conductivity λ (19), and the resistance of the water pressure (26.6) at the inlet of the mold cooling water and the flow resistance (26.5) or pressure loss at the mold Depends on the coolant velocity 10 as a function. Relative coolant covering 27, 2 may be regarded as conduit cross section F (20) in terms of the mass flow equation U = ΣRi × J, which conduit cross section F (20) is known as mold height 13 in known molds. Constant across. That is, the mold channels extend parallel to each other.

In the conventional mold structure, such interface resistance 22 is constant over the mold height 13. Formation of the mold channel is provided with a cooling hole 28 (not shown) or a cooling water baffle plate 27.6 having a constant diameter, with or without a drain 28.1 and a constant cross-sectional Q 26.3. It can be implemented by cooling slit 26 (FIGS. 3D and 3E).

Summarizing the prior art of any mold type (slab equipment, bloom equipment, billet equipment, profile equipment, and strip equipment, etc.) in the present situation, the percentage of cooling water covering over the mold height 13 as well as the mold width ( 27.2) is geometrically identical regardless of whether the cooling holes 28 or cooling slits 26 are used, and thus the same in the cooling operation of the methodology.

The isotropic or homogeneous structure of the mold cooling over such mold height is due to the billet shell being in close contact with the casting liquid surface 30 directly below and to the subsequent shrinkage process of the billet shell 5 over the mold height 13. This increases heat flow and at the same time generates a high "hot face" temperature of the mold plate 23. Such a high copper plate skin film temperature 23 introduces the risk of excessive re-crystallization temperature T-Cu-Re 31 of the re-rolled copper (see FIG. 3C).

As such, the risk of exceeding the mold plate recrystallization temperature (T-Cu-Re) is greater as the casting speed is increased. That is, FIG. 2 shows in table a summary of the structural features of the thin slab and standard slab mold and the technical features of the method.

From the tabulated drawing of such characterized mold data, a greater 60 to 40% coolant covering percentage (27.2), higher than 12 to 8 m / s for thin slab 32 compared to standard slab 33 Heat flow 2 or thermal stress of the mold, even with a coolant speed 10 of 10, a thinner 25 to 15 mm cold plate thickness 18.1, and a higher 12 to 8 bar mold cooling water pressure 26.6. It can be seen that the elevated thermal stress of the mold is indicated by a stress of 2.2 / 3.2 MW / m2 characterizing. The elevated thermal stress or elevated heat flow of such a mold is lower than 0.4 in 0.2 mm slag film thickness 18.2 in the case of thin slab 32, higher casting speed 14 of thin slab 32, And thinner slab thickness 34/32 or 34.1. At the same time, it can be seen that the mold skin film temperature 23 on the side facing the steel is 300 ° C. to 400 ° C., depending on the casting speed, so that the spacing for the recrystallization temperature 31 of cold rolled copper is smaller than that of the standard slab. have. The recrystallization temperature of the cold rolled copper sheet is 350 ° C. (Cu-Ag) to 700 ° C. (CU-CrZr) or 500 ° C. (softening temperature) depending on the copper quality.

Further reduction of the Cu plate thickness 18.1 is due to the high water pressure (at the mold coolant inlet) 26.6 in the hole 28 or cooling slit 26 and thus the copper plate surface facing the steel, ie “ It is difficult because the "hot face" may be mechanically convex.

FIG. 3 shows a known water cooling device for slab molds or thin slab molds with cooling slits 26 and a coolant baffle plate 26.7. 3a shows a billet with half of the wide side 7 of the slab mold with a narrow side 7.1 and an immersion injection trough 35 and with a billet shell 5 at the river flow 36 and the mold outlet. 37). From such a figure, it can be seen that the cooling slit 26 extends uniformly and parallel over the mold height 13 and the position of the casting liquid surface 30.

FIG. 3B shows in cross section a mold wide side 7 having a coolant tank 38. 1 as well as a coolant tank 38 for coolant reflux or a coolant tank inlet 38.2. Reference numerals "38.1.1" or "38.2.1" indicate that the cooling water is transferred from the cooling water tank 38.1 to the cooling slit 26 or the cooling holes 28 (not shown).

In addition, the tension bolt 39 for coupling the copper plate 40 with the cooling slits to the cooling water tank 38 or the copper plate 40.1 without the cooling slits to the cooling water tank 38 from FIG. 3B. The multi-part mold can be clearly seen, but in the latter case, the intermediate plate 41 with the cooling slit 26.3 is interposed therebetween (see FIG. 3D for details). The intermediate plate 41 may directly form the wall 41.1 (FIG. 4) of the coolant tank.

3C shows the profile of the mold skin film temperature (“hot face”) 23, the heat flow J (2), and the recrystallization temperature T-Cu-Re 21 over the mold height 13 as prior art. have.

From FIG. 3C, both the profiles 23.1 (epidermal film temperature profile) and 2.1 (heat flow profile) are functionally similar, and the thermal stress 23 has a recrystallization temperature 31 especially when the casting speed 41 is high. It can be seen that the copper plate exhibits a relatively short endurance life in the region of the casting liquid level 30 accordingly.

3d shows a horizontal cross-sectional view of the mold, in which the cooling slits 26 with the cooling water baffle plate 26.7 are arranged in parallel, the cooling water from the cooling water flow 38.1 to the cooling slit 26, and cooling It can be seen that the slit transitions to the coolant reflux 38.2 through the mold coolant transition 38.2.1, respectively.

In FIG. 3E, parallel cooling slits 26 are shown in a horizontal sectional view. From that figure, the cooling water covering percentage (27.2), cooling channel cross section (26.3), cooling water baffle plate (26.7), cooling given by the slit width (26.1), ratio of cooling channel width to cooling channel / cooling channel spacing (27) The channel / cooling channel spacing 27, and the copper plate thickness 8 can be seen. Structural features are shown in cross sections A-A'-A "and B-B'-B" over the mold height, where the mold coolant is constant with Nernst's upper zone (flow velocity = 0) decreasing as the flow rate rises. Due to the flow profile of (9) a constant conduit cross section F 20 and a constant interface resistance 22 over the mold height are shown.

4 shows a possible known structure of the mold wide side 7 consisting of a copper plate and a coolant tank 38. The mold may consist of a copper plate 40 with cooling slits and a coolant tank 38 (part 4a), a copper plate without cooling slits 40.1, or an intermediate plate 41.1 with cooling slits (sandwich ) And a coolant tank 38 (part 4b), or at the same time a cooler slitless copper plate 40.1 assembled on an intermediate plate 41.1 forming the wall of the coolant tank (part 4b). 4c). FIG. 4D shows again the profile of the heat flow J (2.1) and the thermal stress over the mold height and the recrystallization temperature 31 of the cold rolled copper plate 31.

The invention provides a cooled continuous casting mold for casting a slab-shaped metal, in particular steel, having a mold wall of plate and a cooling coolant channel, in particular here 40 to 400 mm thick and 200 to 3,500 mm wide. It is about.

Hereinafter, the present invention will be described by way of example with reference to the prior art on the basis of Figures 5 and 6. Among the accompanying drawings,

1 to 4 each show a prior art,

5 and 6 illustrate the present invention by way of example, respectively.

The prior art has already been described in detail. 5 and 6, reference numerals corresponding to the same parts as the molds shown in FIGS.

-Explanation of reference numerals-

1 vibration mold 2 heat flow J

2.1 Heat flow density or heat flow profile 3 potential drop U

4 mold center or billet center 5 billet shell

6 slag 7 copper plate

7.1 mold plate 9 mold coolant

8 Copper plate thickness between the slag and the path of the mold coolant or between the "hot face" and "cold face"

10 Coolant speed, m / s13 mold height

Pre-determined pressure in bar measured at 11 mold coolant inlet

Controlled coolant inlet temperature measured at 12-week coolant inlet, T-0

13.1 Mold inlet 13.2 Mold outlet

14 Casting speeds (up to 15 m / min) 15 Total resistance R-total

16 individual media 17 individual resistors Ri

18Length l (m) 18.1Cu plate thickness, cooling plate thickness (mm)

18.2 Slag film thickness (mm) 19 Specific thermal conductivity, λ (W / K × m)

"Hot face" temperature of copper plate F23.2.

20.1 Mass Flow Equation U = ΣRi × J; ΣRi = (l / λ × F) i

Phase boundary between the copper plate (7), the course of the coolant (9), cold face

21.1 Phase boundary, hot face between copper plate (7), slag membrane (6) or billet shell (5)

Interface resistance between copper of 22 mold plate

23 Epidermal membrane temperature (hot face) 23.1 Epidermal membrane temperature profile

23.2.1 Temperature of copper plate 25 Copper plate temperature

24 Cuticle Temperature Copper / Water ("Cold Face")

24.1Copper / Water Temperature Profile ("Cold Face")

26 Cooling slit 26.1 Width of cooling channel

26.2 Depth of cooling channel 26.3 Cross section, Q

26.4 Length approximately equal to mold height

26.5 Flow resistance 26.6 Water pressure at the mold coolant inlet

26.7 Chilled water baffle plate 27 Cooling channel / cooling channel spacing

27.1 bridge width 28 cooling holes

27.2 Percentage of coolant covering for mold width, defined as the cooling channel / cooling channel spacing 27 divided by the cooling channel / cooling channel spacing, excluding the bridge width (27.1), also in the first approximation.

28.1 Drainage 29.1 Baffle Plate

29 cooling slit, its boundaries do not extend parallel

30 casting liquid level, casting liquid level

31Recrystallization Temperature of Rolled Copper T-Cu-Re

3240-150 mm thick slab 33400-150 mm thick slab

34 Slab thickness 34.1150-40 mm slab

34.2400-150 mm slab 35 Immersion inlet trough, SEN

35.1 Casting Sand 35.2 Casting Clinker

36 Flow 37 Billet

38 Chilled water tank 38.1 Chilled water pure water, coolant tank

38.1.1 the cooling water being transferred from the cooling water tank (38.1) to the cooling slits (26, 29)

38.2 Chilled water pure water, Chilled water tank 39 Tension bolt

38.2.1 the transfer of cooling water from the cooling slits (26, 29) to the cooling water tank (38.2)

40 Copper plate with cooling slit 40.1 Copper plate without cooling slit

41 middle plate with cooling slit (sandwich)

41.1 Intermediate plates forming the wall of the coolant tank

It is an object of the present invention to provide a continuous casting mold capable of lowering the mold skin film temperature at the casting liquid level by evening the thermal stress over the mold height, ie the thermal profile over the mold height.

Such an object is achieved by a continuous casting mold with the features of claim 1. Preferred embodiments are disclosed in the dependent claims.

In accordance with the present invention, measures are taken to improve the continuous casting mold of the predicate type such that the width of the coolant channel is reduced from the mold inlet to the mold outlet in the casting direction depending on the heat flow profile over the mold height.

The width refers to the extension size of the channel wall extending along (approximately) the hot plate inner wall side. In that case, the cross section of the cooling channel is preferably rectangular. Elliptic forms can also be considered.

According to the invention, the phase interface between the mold plate wall and the mold cooling water is reduced from the mold inlet to the mold outlet.

According to the first embodiment, the width of the coolant channel in the first approximation is reduced in the casting direction between the mold inlet and the mold outlet as a function of the heat flow profile over the mold height, or the boundary line of the coolant channel or adjacent coolant channel or The interface extends out of parallel.

According to the second embodiment, the width of the coolant channels in the first approximation is reduced linearly in the casting direction, but extends at an acute angle from each other such that the boundary lines or boundary surfaces of the coolant channels or adjacent coolant channels are not parallel.

It is linearly reduced in width of each of the cooling channels across the mold height, with the interface of adjacent channels having a rectangular cross section at an angle or a line of adjacent channels having an elliptical cross section parallel to the surface of the cooling plate. This means that they form a constant angle to each other when viewed from a cross section that crosses the common center of the.

According to a very preferred embodiment, the mold channel is formed such that the depth of the cooling channel over the mold height is increased from the mold inlet to the mold outlet in the casting direction.

Depth refers to the size of the cooling channel required to calculate the area in conjunction with the width.

In such a case, according to a very preferred embodiment, the increase in depth is correspondingly changed depending on the decrease in width so that the size of each cross-sectional area of the cooling channel remains constant from the mold inlet to the mold outlet, and thus the coolant channel The flow rate of the coolant in the chamber is made constant between the mold inlet and the mold outlet.

Based on the constant resistance of the cooling channel between the mold coolant inlet and the mold coolant outlet, the flow rate of the coolant remains unchanged.

The cooling water tank preferably serves to feed water to the cooling channel provided in the mold wall plate. In that case, the coolant tank outlet is arranged at the height of the mold inlet, and the coolant tank inlet is arranged at the height of the mold outlet, respectively. Cooling water flow is located above the casting liquid at the mold inlet and cooling water reflux at the mold outlet, respectively, so that the maximum cooling capacity or maximum spacing to the vaporization point of the water is below the zone of the casting liquid where the highest thermal stresses develop. It is preferred to allow the low temperature coolant with no heat load to operate at a pressure of 1 to 25 bar.

Another preferred feature is contained in claims 7-12.

The cooling channel may be cooling slits or holes. Cooling slits are provided on the plate from the sides of the plate inside and outside the mold or on separate intermediate plates. To set the desired cross-sectional area, the cooling slits are closed with correspondingly formed coolant baffle plates over the mold height, the width of the coolant baffle plates over the mold height being dependent on the change in width of the cooling channel path from the coolant inlet to the coolant outlet. It is desirable that the thickness is adjusted, ie reduced, and the thickness over the mold height is likewise reduced while being tightly fitted to the sides of the mold inner and outer plates.

5A shows the present invention, in which the adjacent cooling slit 29 or its boundary lines do not extend in parallel, but from the mold inlet 13.1 or the casting liquid surface 30 to the mold outlet 13.2. The width is reduced, so that the channel cross section or interface F 20 behaves as a function of the heat flow density or heat flow profile 2.1. At the same time, by correspondingly increasing the depth 26.2 of the cooling channel (FIG. 5B), the flow cross section Q 26.3 for the cooling water and thus the flow rate of the cooling water 26.5 in the first approximation remains constant. It becomes possible. The interface of the cooling channels in the form of cooling slits 29 no longer extends in parallel, but forms an acute angle 29.2 with each other. Thus, the cooling water covering percentage 27.2, or even the conduit cross section 20, will be at most 100%, for example, at the casting liquid level 30 when casting thin slabs, and at least 30% at the mold outlet.

In FIG. 5C the thermal stress 23.2 of the mold plate according to the mold height 13 thus smoothed is shown in contrast to the heat flow profile 2.1 and the recrystallization temperature 31. From that figure, it can be seen that the "hot face" temperature 23.2 of the copper plate 7 is lower and evenly extended, while at the same time the durability life of the copper plate is longer.

Part 5d shows the mold inlet (13.1) for a cooling plate 40 with non-parallel cooling slits, as well as for a mold plate with a sandwich plate, ie an intermediate plate 41 with non-parallel cooling slits according to the invention. And cross sections A-A'-A "and B-B'-B" of the wide side 7 of the mold outlet 13.2.

Such a figure shows that the flow cross section Q 26.3 remains constant from the mold inlet to the mold outlet by means of a corresponding increase in cooling channel depth over the mold height, even though the cooling water covering in the casting liquid zone 30 is larger. Due to this, the flow velocity is kept constant, and is exemplarily shown.

FIG. 5C shows the cooling channel 29 at the mold inlet 13.1 and the mold outlet 13.2 with the baffle plate 29.1 varying in width and depth.

Figure 6 illustrates a solution according to the invention (partial figure 6b) facing the prior art (partial figure 6a). Basically, the proposed scheme can be dedicated to molds with cooling holes (not shown) in connection with the cooling slit 29 with baffle plate 29.1, in which case the hole cross section over the mold length It can be altered by the use of conical drainage (not shown).

Claims (14)

Cooled continuous casting mold for casting slab-shaped metal, in particular steel, with a mold wall of plates 7 and 7.1 and a coolant channel for cooling, in particular 40 to 400 mm thick and 200 to 3,500 mm wide To The width 26.1 of the coolant channel 29 is reduced from the mold inlet 13.1 to the mold outlet 13.2 in the casting direction depending on the heat flow profile 2.1 over the mold height 13. Cooled continuous casting molds. 2. The width 26.1 of the coolant channel in the first approximation is reduced in the casting direction between the mold inlet 13.1 and the mold outlet 13.2 as a function of the heat flow profile across the mold height 13. Cooled continuous casting mold characterized by. The coolant channel width 26.1 in the first approximation is reduced linearly in the casting direction, with the acute angles 29.2 of each other so that the boundary lines or boundary surfaces of the coolant channels or adjacent coolant channels are not parallel. Cooled continuous casting mold, characterized in that extending. 4. The method according to claim 1, 2 or 3, characterized in that the depth 26.2 of the cooling channel across the mold height 13 is increased from the mold inlet 13.1 to the mold outlet 13.2 in the casting direction. Cooled continuous casting mold. 5. The method according to claim 4, wherein the increase in depth 26.2 over the mold height 13 is correspondingly changed depending on the width reduction so that the size of each cross-sectional area 26.3 of the cooling channel is from the mold inlet 13.1. Cooled continuous casting mold, characterized in that the flow rate of the coolant in the coolant channel is kept constant between the mold inlet (13.1) and the mold outlet (13.2) by keeping it constant until the outlet (13.2). The coolant tank (38) of any one of the preceding claims, wherein the coolant tank (38) feeding the cooling channel is connected to the plates (7, 7.1), in particular a copper plate, of the mold wall, the coolant tank outlet (38.1) of the mold. Cooled continuous casting mold, characterized in that at the height of the inlet (13.1), and the coolant tank inlet (38.2) are respectively disposed at the height of the mold outlet (13.2). The coolant covering percentage, in particular the coolant covering percentage (27.2), defined by the ratio of the difference between the maximum cooled mold width and the non-cooled mold width, is determined by the mold inlet. Cooled continuous casting mold, characterized in (13.1), in particular at most 100%, in particular 100%, at the height of the casting liquid level 30, and at least 30%, in particular at least 10%, at the mold outlet 13.2. 8. The cooled continuous casting mold according to any one of claims 1 to 7, wherein the coolant is coolant having a flow rate of 25 to 2 m / s over the channel length. 9. The cooled continuous casting mold according to any one of claims 1 to 8, wherein the thickness of the copper plates (7, 7.1) between the melt and the coolant path is at least 5 mm. 10. The cooled continuous casting mold according to any one of claims 1 to 9, wherein the mold coolant pressure at the coolant tank inlet (38.1) is 2 to 25 bar. Cooled continuous casting mold according to any of the preceding claims, characterized in that the continuous casting speed V _G (11) is 1 to 15 m / min. 12. The method according to any one of claims 1 to 11, wherein the steel melt is introduced by the immersion injection trough (SEN) 35 to apply the molding sand 35.1, and the vibration stand mold 1 is used. Cooled continuous casting Note 1 type. The cooling slit 29 according to any one of the preceding claims, wherein the cooling channel is a cooling slit 29 provided in the plate from the sides of the mold inner and outer plates 7, 7.1, and the cooling slit 29 is a mold. The coolant baffle plate 29.1 correspondingly formed to set the desired cross sectional area over the height 13 is closed and the width of the coolant baffle plate 29.1 over the mold height 13 is from the coolant inlet 13.1. Cooled continuous casting mold, characterized in that it is adapted to the width change of the cooling channel path to the outlet (13.2). 13. The cooling continuous casting mold according to any one of claims 1 to 12, wherein the cooling channel is a cooling hole provided with a conical drainage therein.