EP1445045A1 - Process and apparatus for continuous casting of liquid metals in particular steels - Google Patents

Abstract

Continuous casting of liquid metals, especially liquid steel, comprises partially reducing the heat transfer number alpha (W/m2>.K) during cooling in the region of the heat flow shadow of the submerged nozzle (1) so that an isotherm lying in a horizontal plane produces a uniform strand shell on the periphery (20). An independent claim is also included for a device for the continuous casting of liquid metals, especially liquid steel, comprising a mold (2) and a submerged nozzle (1) which can be adjusted below a constant casting mirror and reaches up to the funnel end between copper plates (2a).

Description

The invention relates to a method and a device for the continuous casting of liquid Metals, especially of liquid steel materials, by pouring the Pouring material into a submerged spout made of water-cooled copper plates formed and oscillating continuous casting mold down to a constant Casting level and if necessary up to a funnel end between the broadside copper plates enough and at least partially with its outer shape the inner shape of the Copper plates is approximated.

The arrangement of such a diving spout has a considerable influence on the Quality of the casting strand formed in the continuous casting mold. An associated Disadvantages are the dimensions, because of the durability for a large number of melting or its stability required in continuous operation Assume walls. These walls provide an insulator for the discharge the heat in the mold plates. In addition, the spaces are only about 25 mm between the immersion pouring wall and the mold plate. The consequence of the insulation is an uneven heat dissipation in the area of influence of the immersion nozzle compared to the area outside the immersion nozzle, so that in the middle of the broadside copper plates the strand shell grows faster, i.e. there is more energy given off in the form of solidification heat, because the overheating energy due to the isolation of the immersion spout Shows deficit. The consequences of such rapid hypothermia have so far been underestimated. In extreme cases it must be assumed that the cooling Casting strand is "cold drawn" in the heat flow shadow of the immersion nozzle. So can now be assumed that this cooling behavior leads to asymmetrical, warped, profile-distorted strands and tensions that are not uniform in thickness and thus to longitudinal cracks in the strand shell as well as internal defects leads to later disadvantages in the further processing of the material represent. Economic damage in the form of longitudinal cracks can also occur particularly sensitive types of steel are created. So are particularly peritectical Steel grades with room- or face-centered crystal grids endangered. The different After all, cooling causes such stresses in the casting strand that the resulting cracks, which are even eliminated using special flaming machines had to be.

Normally, the continuous casting molds, especially for thin and thick slabs, are designed for a constant cooling capacity in width and also in thickness, expressed in W / m ² . This can be explained by an arrangement as cooling water channels or cooling water bores across the width and constant water speed in each cooling water channel.

The method described at the outset is known from WO 02/16061 A1. This Process suggests the width of the cooling water channels depending on the pouring direction from the heat flow profile to the mold height from the mold entrance to the mold exit to reduce. This measure is a step in the right one Direction, but can still be developed further.

The invention has for its object by a more uniform cooling of the Metal melt to achieve a more uniform formation of the strand shell, the Development under the premise of the thermal treatment of continuous casting mold and diving spout must stand as a unit.

The object is achieved according to the invention in that during the cooling in the area of the heat flow shadow of the immersion nozzle, the heat transfer coefficient α [W / m ² • K] is partially reduced such that an isotherm lying in a horizontal height plane is one on the circumference uniform strand shell generated. This takes into account the effect of the immersion pouring in the continuous casting mold. Previous differences in cooling in the heat flow shadow and outside the heat flow shadow no longer occur. This results in a more uniform cooling of the casting metal over the circumference via the isotherm, so that a more uniform strand shell growth is achieved.

A further development of the concept of the invention further consists in the fact that the isotherms running in the vertically superimposed and parallel horizontal contour lines on the inner shape of the broadside copper plate each functionally on the full circumference of the inner shape by partially changing the heat transfer coefficient α [W / m ² • K] from the beginning of the immersion spout to the middle of the immersion spout and that at the same time this isotherm is supported by a partial water cover over cooling channels at different distances. The lowering of the heat transfer coefficient α takes place here in combination with the water cover and leads to the advantages mentioned.

Another possible variation is achieved in that the isotherm by reducing the amount of water and / or the water speed in the Copper plates of the continuous casting mold is produced opposite the immersion nozzle.

Another configuration as a further variation can be used in that that the isotherm is due to a section-wise change in the thickness of the copper plates and / or an applied nickel or chrome layer is generated. This Measure is both on the constructive as well as on an economical construction the continuous casting mold directed.

The design options are directed towards a variant that is alternative or additionally the isotherm by expanding a funnel with the funnel provided thin slab or thick slab continuous casting mold in the area of influence of the diving spout is generated or supported. This variant is also one under constructive or economic considerations possibility of a correspondingly higher copper use.

In terms of device technology, the device achieves the object of the invention by designing the cooling water channels or cooling water bores in the broadside copper plates over the length of the area of influence of the immersion spout for such a reduced cooling water speed by means of changed flow channel cross sections and / or for partial water coverage that the heat transfer coefficient α [ W / m ² • K] in the area of the immersion pouring shadow is smaller than in the area outside the shadow. This takes into account the effect of the immersion spout. This can compensate for the isolating effect of the immersion nozzle.

The resultant compared to the broadside copper plates and the immersion spout The area of influence in the mold plate is limited by the fact that the cooling water channels or the cooling water holes in the area of influence of the immersion spout reduced in cross-section by means of inserts or conical rods becomes.

The lateral transitions of the area of influence of the immersion spout can low and graded.

An alternative or additional measure to water speed changes is that the cooling water channels or the cooling water holes in the Area of influence of the immersion spout in the sense of a partially reduced water cover are executed. This consists of increasing the distances between the Cooling water channels or the cooling water holes and / or a reduction the flow cross-sectional areas (F).

Another alternative or additional measure is given by the fact that the Partial thickness of the broadside copper plates in the area of influence of the immersion spout is enlarged.

In order to correspond to very high copper thicknesses, this measure can still go so far be designed so that the broadside copper plates on the hot side with a Nickel or chrome layer is provided.

The heat transfer coefficient α can also be achieved by another alternative or additional measure be lowered that the broadside copper plates in the area of influence of the immersion spout with a given funnel with an expansion of the funnel are provided.

To explain the process, a drawing is attached, which the required Plant parts, devices and. The like.

Fig. 1

einen horizontalen Schnitt durch eine symmetrische Hälfte einer Stranggießkokille mit Tauchausguss als Einheit,

Fig. 2

den zu Fig. 1 gehörenden vertikalen Mittenschnitt durch die Stranggießkokille mit dem Tauchausguss,

Fig. 3A

einen Teil-Querschnitt durch die Kupferplatte mit Kühlwasserkanälen,

Fig. 3B

einen vertikalen Teilschnitt durch den Gießspiegelbereich mit den einzelnen Medien-Längen (-Dicken),

Fig. 3C

eine alternative Ausführungsform der Kühlwasserkanäle als Kühlwasserbohrungen,

Fig. 4

einen Bereich der anzupassenden Wärmeübergangszahl α als Funktion der Wassergeschwindigkeit,

Fig. 5

eine an den Strömungs-Schattenbereich des Tauchausgusses angepasste Wasserbedeckung,

Fig. 6

eine an den Schattenbereich des Tauchausgusses angepasste Kupferplattendicke,

Fig. 7

einen horizontalen Halbschnitt durch eine Trichteraufweitung in der Stranggießkokille,

Fig. 8

ein Wärme-Übergangs-Diagramm zwischen der Kupferplatte und Kühlwasser,

Fig. 9

einen senkrechten Schnitt mit Blickrichtung auf die Heißseite einer Breitseiten-Kupferplatte mit einem Horizontalschnitt des Gießstrangs im Zustand am Kokillenausgang,

Fig. 10

die Ansicht auf die Breitseiten-Kupferplatte in der Ebene der Kühlwasserkanäle oder Kühlwasserbohrungen,

Fig. 10A

einen senkrechten Schnitt durch die Breitseiten-Kupferplatte der Fig. 10 im Einflussbereich des Tauchausgusses und außerhalb,

Fig. 11

einen horizontalen Schnitt A-A durch die Breitseiten-Kupferplatte im Einflussbereich des Tauchausgusses und

Fig. 12

einen horizontalen Schnitt B-B durch die Breitseiten-Kupferplatte außerhalb des Einflussbereichs des Tauchausgusses.

Show it:

Fig. 1

a horizontal section through a symmetrical half of a continuous casting mold with immersion nozzle as a unit,

Fig. 2

1 belonging to Fig. 1 vertical center section through the continuous casting mold with the immersion spout,

Figure 3A

a partial cross section through the copper plate with cooling water channels,

Figure 3B

a vertical partial section through the casting mirror area with the individual media lengths (thicknesses),

Figure 3C

an alternative embodiment of the cooling water channels as cooling water bores,

Fig. 4

a range of the heat transfer coefficient α to be adapted as a function of the water velocity,

Fig. 5

a water cover adapted to the flow shadow area of the diving spout,

Fig. 6

a copper plate thickness adapted to the shadow area of the immersion nozzle,

Fig. 7

a horizontal half-section through a funnel widening in the continuous casting mold,

Fig. 8

a heat transition diagram between the copper plate and cooling water,

Fig. 9

a vertical section looking towards the hot side of a broadside copper plate with a horizontal section of the casting strand in the state at the mold exit,

Fig. 10

the view of the broadside copper plate in the plane of the cooling water channels or cooling water holes,

Figure 10A

10 in the area of influence of the immersion spout and outside,

Fig. 11

a horizontal section AA through the broadside copper plate in the area of influence of the immersion spout and

Fig. 12

a horizontal section BB through the broadside copper plate outside the sphere of influence of the immersion spout.

1 is an example of a continuous casting mold of any casting cross section Unit from a diving spout 1 with a thin slab casting mold 2, the consist of two broad-side copper plates 2a and two narrow-side copper plates 2b, intended. The copper plates 2a either have slot-shaped cooling water channels 3 or round cooling water holes 4. The diving spout 1 is up to immersed under a casting level 5 which is constantly regulated during the casting. In the event that the continuous casting mold 2 has a funnel 6 with a funnel end 6a, the immersion spout 1 extends to the corresponding depth. The liquid Steel material 7 flows through the lateral openings 8 in the arrow directions 9 in the side rooms 10 and around the outer shape 1 a of the immersion spout 1 also in between the outer shape 1a and the broadside copper plate 2a remaining space 11. On the mold level 5 is a by pouring mold powder Slag layer 13 formed to protect against oxidation (Fig. 2). The copper plates 2a and 2b are formed by inflow at the entrance 14a and at the exit 14b flowing cooling water formed, its direction of flow (entrance 14b and exit 14a) can also be reversed. In Fig. 3, the position of the immersion spout 1 of seen the side showing the openings 8. The copper plates 2a form the funnel 6, in which the diving spout 1 is set at an unchangeable height. The Cooling in the cooling water channels 3 causes a steadily progressing solidification of the casting material from the outside, which initially becomes a uniform thickness Strand shell 15 leads. The partial change in the heat transfer coefficient α and possibly. the changed water velocity 16 together with the partial water cover 17 by the one flowing in at the inlet 14a and the one flowing out at the outlet 14b Cooling water effect on the different contour lines 18 on the full Circumference 20 of the inner mold 2c one for the heat flow shadow of the thaw spout 1 adapted heat dissipation. The recooling of the heated cooling water, the quantities and speeds are in that receiving the copper plates 2a Water box 19 carried out or set. 3A and 3C are the cooling water channels 3 as cooling water slots and as cooling water bores 4.

In Fig. 3B the media are shown, the heat flow at different Resistance must penetrate. Here (from right to seen on the left) the liquid steel material 7 (St), the steel in the immersion spout 1 (St / C), the slag lubrication film (SL), and the copper plate 2 is taken into account.

The invention then acts in such a way that an isotherm running in the vertical contour lines 18, which are presupposed vertically one above the other and in parallel, on the inner mold 2c extends over the entire circumference 20 of the inner mold 2c due to the partial change in the heat transfer coefficient α [W / m ² • K] Beginning of the immersion pouring influence (the outer regions) up to the middle 1b is generated, at the same time this isotherm by a partial water covering 17 (see FIGS. 4 and 5) via cooling channels 3; 4 is supported.

The invention is based on an analogy to Ohm's law from electrical engineering, in which the voltage U = resistance R • the current strength J. The sum of all partial resistances in several substances with different specific conductivities λ [W / m • K] is determined metallurgically. The total resistance results in R _i = (l / λ • F), with l = length [m] and F = area [m ² ], the media resistance R _{i being} calculated using the natural conductivity values λ given in the list of reference symbols.

• Stahl (einer Dünnbramme) (St)
• der Schlacke (SL)
• dem Kupfer (Cu)
• dem Kühlwasser und andererseits mit
• Stahl im Tauchausguss (St/C)
• der Keramik (Ref)
• dem Stahl im Verfahren (St)
• der Schlacke (SL)
• dem Kupfer (Cu)
• und dem Kühlwasser.

The basic equation used equates l / λ, on the one hand, for

• Steel (a thin slab) (St)
• the slag (SL)
• the copper (Cu)
• the cooling water and on the other hand with
• Steel in the pouring spout (St / C)
• the ceramic (Ref)
• the steel in the process (St)
• the slag (SL)
• the copper (Cu)
• and the cooling water.

The isotherm calculated from this applies to a change in the heat transfer coefficient α or a water velocity to be applied, and leads, for example, to a Value α water = 1 / -1.5 = - 0.666, i.e. there is a reduction to an α of approx. 2/3 instead of 1,000 instead.

According to an alternative solution, one that runs in a height plane Additional isotherms by reducing the amount of cooling water and / or the cooling water speed 16 in the copper plates 2a of the continuous casting mold 2 in the Intermediate space 11 can be created opposite the immersion spout 1 (FIG. 4). To The heat transfer coefficient becomes the calculation method already described above α lowered to - 0.666 out of 1,000.

5 shows an additional measure, on the basis of which this isotherm by partial water cover 17 over differently spaced Cooling channels 3; 4 is supported. The water cover 17 is again arithmetically determined by equating the λ values for the immersion pouring material, the Copper plate 2, the slag SL on the one hand with the values of the immersion spout 1, the ceramic, the casting material 7, the slag SL and the copper plate Cu. In order to the water coverage by changing the cooling slots is approx. - 0.034. Consequently are (Fig. 5) in the shadow area of the immersion spout 1 fewer cooling water slots to be arranged at a greater distance.

Another alternative (Fig. 6) provides that the isotherm is separated by a section changed thickness 2d of the copper plate 2a is generated. To do this in turn the λ values for the casting material steel (St), the slag (SL) and for copper (Cu) equated to the λ values for the pouring material (St / C), the pouring ceramic (Ref), the casting material steel (St), the slag (SL) and the copper plate (Cu). From this, a theoretical copper thickness is calculated in the shadow area of the Immersion spout of - 725 mm as resistance to the strand shell in the shadow area not too hypothermic.

Another alternative for less heat dissipation in the shadow area of the Immersion spout 1 opposite areas of the copper plates 2 results from the Design according to FIG. 7. It is then provided that, alternatively or additionally, the Isotherm through a funnel expansion 21 provided with a funnel 6 Thin slab or thick slab casting mold 2 in the area of influence Dipping spout 1 generated or supported by it. The calculation is done also by the given calculation approach with the λ values for steel (St), slag (SL) and copper plate (Cu) on the one hand, which correspond to the λ values for steel in Immersion spout (St / C), the ceramic (Ref), the casting material (St), the slag (SL) and the copper plate (Cu) are equated. L = is calculated from the equation - 100 mm, so that the space 11 on both sides of the immersion spout 1 is expanded to about 50 mm.

8 shows the heat transfer from the copper plate 2a; 2b shown on the cooling water. The diagram shows that the heat transfer coefficient α [W / m ² • K] increases with increasing cooling water speed 16. The water standard WS is 46, αS = standardized as "1". With water in the center of the immersion spout shadow with αZ = 0.66 • αS, the cooling water speed is approx. 7 m / sec, which increases outside the sphere of influence of the immersion spout 1 to 12 m / sec.

According to FIG. 9, the effects of cooling without (left half) and with (right half) the lowering of the heat transfer coefficient α can be seen. In general, in the broadside copper plates 2a, the cooling capacities KW are the same with regard to the same design of the cooling water slots 3 or the cooling water bores 4. Without the cooling measures according to the invention, there is a strand surface temperature S _N1 and an identical strand surface temperature S _N2 , both of which have a value α = 1. Likewise, the strand surface temperatures T _N1 and T _{N2 are} at α = 1 outside the dip spout shadow. However, the strand shell thickness S _Z1 and the strand shell temperature T _Z1 on the left are α = 1 and the strand shell thickness S _Z2 and the strand shell temperature T _{Z2 are} α <1. Accordingly, the strand shell solidification in the area of influence of the immersion spout 1 is also uniform.

a) Die Strangoberflächentemperatur T _N1 > T _Z1 außerhalb des Tauchausguss-Schattens.

b) Die Strangschalentemperatur T _Z2 ist gleich der Strangoberflächentemperatur

c) T _N2 außerhalb des Tauchausguss-Schattens.

c) Die Strangoberflächentemperatur S _N1 (außerhalb des Tauchausguss-Einflusses) ist kleiner als Strangschalendicke S _Z1 (innerhalb des Tauchausguss-Einflusses).

d) Die Strangschalendicke S _Z2 ( innerhalb des Einflusses des Tauchausgusses ) ist gleich der Strangoberflächentemperatur S _N1 ( außerhalb des Einflusses des Tauchausgusses).

e) Die Kühlkapazität KW _N ist bei α = 1 gleich der Kühlkapazität KW _Z .

f) Die Kühlkapazität KW _Z ist bei α = 0, 66 kleiner der Kühlkapazität KW _N .

This results in the following results:

a) The strand surface temperature T _N1 > T _Z1 outside the dip pouring shadow.

b) The strand shell temperature T _Z2 is equal to the strand surface temperature

c) T _N2 outside the immersion shadow.

c) The strand surface temperature S _N1 (outside of the immersion pouring influence) is smaller than strand shell thickness S _Z1 (within the immersion pouring influence).

d) The strand shell thickness S _Z2 (within the influence of the immersion nozzle) is equal to the strand surface temperature S _N1 (outside the influence of the immersion nozzle).

e) The cooling capacity KW _N is equal to the cooling capacity KW _Z at α = 1.

f) The cooling capacity KW _Z is smaller than the cooling capacity KW _N at α = 0.66.

In Fig. 10 in conjunction with Figs. 10A, 11 and 12, the device technology Measures clearly. 10A, inserts 23 and 24 are for change the flow rate inserted into the cooling water channels 3. Appropriate conical rods 22 are located in the cooling water holes 4. In 10A are the cooling water channels located in the area of influence of the immersion spout 1 3 designed for cooling water speeds 16 with an α = 0.66.

The cooling water channels 3 that are outside the immersion spout influence with the inserts 24 (FIG. 12) or with the conical rods 22 and work with a heat transfer coefficient α = 1. The same applies to the Cooling water holes 4 with the conical rods 22nd

The essential area of the influence of the immersion spout 1 (FIG. 11) shows here a gradual increase of inserts 23 to the area outside the Dipping spout influence with the inserts 24 and with values for α = 0, 66 up to α = 1.0.

LIST OF REFERENCE NUMBERS

1

submerged nozzle

1a

external form

1b

center

2

(Thin slab) continuous casting mold

2a

Broadsides copper plate

2 B

Short-side copper plate

2c

interior shape

2d

changed thickness

3

slot-shaped cooling water channel

4

Cooling water hole

5

meniscus

6

funnel

6a

Funnel-end

7

(liquid) steel material

8th

side opening

9

(Flow or) arrow direction

10

side space

11

gap

12

Slag lubricating film

13

slag layer

14a

entrance

14b

output

15

strand shell

16

water speed

17

partial water cover

18

contour

19

cistern

20

Scope of the inner shape

21

funnel widening

1. Continuation of the list of reference symbols

22

conical rod

23

insert piece

24

insert piece

T _N1

Strand surface temperature outside the dip spout shadow at α = 1

T _N2

Strand surface temperature outside the dip spout shadow at α <1

T _Z1

Strand shell temperature in the immersion pouring shadow at α = 1

T _Z2

Strand shell temperature in the immersion pouring shadow at α <1

S _N1

Strand surface temperature outside the dip spout shadow at α = 1

S _N2

Strand surface temperature outside the dip spout shadow at α = 1

S _Z1

Strand shell thickness within the immersion pouring shadow at α = 1

S _Z2

Strand shell thickness within the immersion pouring shadow at α <1

KW

Cooling capacity [W / m ² ]

α

Heat transfer coefficient [W / m ² • K]

ws

Water Standard

αS

Heat transfer coefficient / standard = 1 (standardized)

αZ

in the center of the diving spout shadow

w Z

Water in the center of the diving spout

U

Potential difference, steel temperature and water temperature

R

Resistance in all media

R _i

Resistance in the single medium

J

Heat flow in [W / m ² ]

λ

specific thermal conductivity in [W / m • K]

l

Thickness of the specific media between the middle of the slab and the mold water cooling in [mm]

St

liquid steel material

St / C

Steel in the spout

2. Continuation of the list of reference symbols

Ref

ceramics; fireproof

SL

Slag lubricating film

Cu

Copper plate between steel material and cooling water

F

Flow area

λ _{St / C}

= 50W / m • K

λ _Ref

= 10W / m • K

λ _St

= 50W / m • K

λ _SL

= 10W / m • K

λ _Cu

= 300 W / m • K

Claims (12)

Process for the continuous casting of liquid metals, in particular liquid steel materials, by pouring the casting material into an immersion spout (1), which in a continuous casting mold (2) formed from water-cooled copper plates (2a) to below a constant casting level (5) and, if necessary. extends to a funnel end (6a) between the broad-side copper plates (2a) and its outer shape (1a) at least partially approximates the inner shape (2c) of the copper plates (2a),
characterized in that during the cooling in the area of the heat flow shadow of the immersion nozzle (1) the heat transfer coefficient α [W / m ² • K] is partially reduced in such a way that an isotherm lying in a horizontal height plane is one on the circumference (20 ) uniform strand shell (15) generated Method according to claim 1,
characterized in that the vertically superimposed and parallel horizontal contour lines (18) on the inner shape (2c) of the broadside copper plate (2) each extend over the full circumference (20) of the inner shape (2b) by partially changing the heat transfer coefficient α [W / m ² • K] is generated functionally from the beginning of the immersion spout to the middle (1b) of the immersion spout (1) and that at the same time this isotherm is achieved by partially covering the water (17) via differently spaced cooling channels (3; 4) is supported. Method according to claim 1,
characterized in that the isotherm is generated by reducing the amount of water and / or the water speed (16) in the copper plates (2a) of the continuous casting mold (2) compared to the immersion nozzle (1). Method according to claim 1,
characterized in that the isotherm is generated by a sectionally changed thickness (2d) of the copper plates (2a) and / or an applied nickel or chrome layer. Method according to claim 1,
characterized in that, alternatively or additionally, the isotherm is generated or supported by a funnel widening (21) of a thin slab or thick slab continuous casting mold (2) provided with the funnel (6) in the area of influence of the immersion spout (1). Device for the continuous casting of liquid metals, in particular steel materials, with a continuous casting mold (2) and an immersion spout (1) set under a constant casting level (5), which, if necessary, up to a funnel end (6a) between the broadside copper plates (2a) is sufficient and its outer shape (1 a) approximates the inner shape (2c) of the copper plates (2a),
characterized in that in the broadside copper plates (2a) over the length of the area of influence of the immersion spout (1) the cooling water channels (3) or cooling water bores (4) are reduced to such a reduced cooling water speed by means of variable flow channel cross sections (F) and / or to a partial water coverage are designed so that the heat transfer coefficient α [W / m ² • K] is lower in the area of the immersion pouring shadow than in the area outside the shadow. Device according to claim 6,
characterized in that the cooling water channels (3) or the cooling water bores (4) in the area of influence of the immersion spout (1) are reduced in cross-section by means of inserts (23; 24) or conical rods (22). Device according to one of claims 6 or 7,
characterized in that the inserts (23) in the area of influence of the immersion spout (1) are designed to be low and stepped. Device according to one of claims 6 to 8,
characterized in that the cooling water channels (3) or the cooling water bores (4) in the area of influence of the immersion spout (1) are designed in the sense of a partially reduced water coverage. Device according to one of claims 6 to 9,
characterized in that the thickness (2d) of the broadside copper plates (2a) in the area of influence of the immersion spout (1) is partially enlarged. Device according to one of claims 6 to 10,
characterized in that the broadside copper plates (2a) is provided with a nickel or chrome layer on the hot side. Device according to one of claims 6 to 11,
characterized in that the broadside copper plates (2a) are provided with an expansion (25) of the funnel (6) in the area of influence of the immersion spout (1) for a given funnel (6).

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