EP3797006B1 - Casting-rolling system for batch and continuous operation - Google Patents

Description

1. Field of the invention

The invention relates to a casting-rolling plant for producing a thin or ultra-thin strip, in particular hot strip, from a cast thin slab of steel in batch or continuous operation, comprising at least one casting plant for casting a thin slab, at least one continuous furnace arranged downstream of the at least one casting plant and at least seven rolling stands arranged downstream of the continuous furnace. The invention further relates to a method for producing a thin or ultra-thin strip, in particular hot strip, from a cast thin slab of steel in batch or continuous operation, preferably by means of a casting-rolling plant as mentioned at the beginning.

2. State of the art

Casting and rolling plants for producing a thin or ultra-thin strip, in particular hot strip, from a cast thin slab of steel are well known. Cast thin slabs with different formats in terms of both their thickness and width, usually with a thickness of up to 60 mm and a width of up to 2,000 mm, are cast using the continuous casting process and then hot-rolled directly in a downstream rolling mill using the casting heat to produce thin or ultra-thin strips with a thickness of at least 0.8 mm.

It is particularly important that the entire forming process up to the last rolling pass takes place above the austenite → ferrite transformation temperature in order to ensure a microstructure within the thin or ultra-thin strip that meets the requirements of hot-rolled strip.

While strip thicknesses of around 1.2 mm can be easily produced in batch operation, whereby the cast strand can be separated after leaving the strand guide and then formed in the downstream rolling mill regardless of the casting speed, rolling down to strip thicknesses of less than 1.2 mm, especially less than 1.0 mm, is associated with difficulties in process control, since strips of such a thickness tend not to be able to be safely introduced into the roll gap and can then lead to interruptions in the rolling process due to so-called cobbling.

Thin strips or ultra-thin strips with a thickness of < 1.2 mm, in particular < 1.0 mm, are therefore usually rolled in continuous operation, in which the cast strand is not separated after leaving the casting plant and before entering the rolling plant, so that the casting speed has a direct influence on the downstream rolling process, in particular the maximum rolling speed that can be achieved here. However, due to the fact that the final temperature above the austenite → ferrite transformation temperature is an essential process variable, several negative effects must be counteracted. On the one hand, the rolling speed in continuous operation, which is significantly reduced compared to batch operation, leads to lower forming speeds within the individual rolling stands and thus to a lower energy input into the formed strip. On the other hand, the thin slab/strip to be rolled stays in the casting-rolling plant longer in continuous operation than in batch operation, associated with the inevitable heat losses. In continuous operation, it has therefore been common practice to reheat the cooled steel before it enters a series of rolling stands in the rolling mill, in particular by using induction heating.

Casting and rolling plants for producing a thin or ultra-thin strip, in particular hot strip, from a pre-cast thin slab of steel are known to the person skilled in the art in a large number of ways, for example as so-called CSP or CEM plants, see for example EN 10 2008 020 412 A1 .

What all these plants have in common is that they have a casting plant in which the primary cooling of the thin slab takes place, followed by a strand guide for the cast thin slab in which the secondary cooling takes place. Behind the secondary cooling A continuous furnace must be provided to reheat the previously cast and cooled thin slab to the required rolling temperature and, in particular, to homogenize the temperature within the thin slab over its cross-section and length. Such casting and rolling plants, which can be operated in a number of operating modes, for example in batch and continuous operation, have previously required inductive or other heating of the thin strip. Casting and rolling plants of this type are therefore extremely costly and maintenance-intensive, both in terms of investment and operation.

3. Object of the invention

It was therefore an object of the invention to provide a casting-rolling plant of the type in question which is capable of rolling a wide range of steel grades into thin and ultra-thin strips, in particular hot strips, with the minimum possible final thickness and at the same time can be operated cost-effectively. This object is achieved in the sense of the invention with a casting-rolling plant comprising the features of claim 1 and with a method comprising the features of claim 12. Advantageous embodiments of the invention are set out both in the dependent claims and in the following detailed description of the invention.

4. Summary of the invention

According to a first aspect of the invention, a casting-rolling plant is provided for producing a thin or ultra-thin strip with a thickness of at least 0.8 mm to < 1.0 mm from a cast thin slab of steel in batch or continuous operation. The casting plant is intended and set up to produce thin slabs with a minimum casting thickness of > 100 mm and a maximum thickness of 150 mm, preferably from > 100 mm to 140 mm and particularly preferably from > 100 mm to 130 mm with a casting width of at least 600 mm, in particular at least 1,000 mm and a casting speed of up to 7.0 m/min. The casting systems provided for this purpose have casting molds which usually have adjustable long and/or wide sides in order to be able to cover the largest possible casting spectrum. However, it is essential for the casting molds used according to the invention that the long sides are spaced apart from one another by at least >100 mm to 150 mm, preferably >100 mm to 140 mm, particularly preferably >100 mm to 130 mm, in order to be able to cast the desired thin slab formats.

According to the invention, a casting plant can be provided upstream of one rolling mill, but it is also preferred if two parallel casting plants, each possibly provided with its own continuous furnace, are arranged upstream of a rolling mill. The reason for this is that the capacity of the rolling mill is significantly higher than the capacity of a single casting plant, since the casting speed of a single casting plant depends essentially on the casting format and the steel grade to be cast. In order to be able to make the best possible use of the capacity of the rolling mill, two casting plants are often connected in parallel and feed a rolling mill together.

As already mentioned above, a continuous furnace is arranged downstream of the casting plant, preferably downstream of each casting plant, in order to homogenize the temperature of the cast thin slab and, if necessary, to be able to heat it to the required rolling temperature. It is essential to the invention that during the entire forming process from the thin slab to the desired final thickness of the thin or ultra-thin strip, in particular hot strip, no induction heating is provided for reheating the cast thin slab and/or the rolled strip. This creates a casting-rolling plant that is able to roll cast thin slabs with a comparatively large casting thickness by means of at least seven rolling stands and rolling passes, preferably with eight rolling stands and corresponding rolling passes, without the need for inductive intermediate heating in both batch and continuous operation. The particularly high casting thickness provides a plant that can be used without the need for inductive intermediate heating. can produce a wide range of steel grades down to a thin or ultra-thin strip thickness of 0.8 mm, especially in continuous operation.

According to the invention, it is possible to produce the product mix of steels usually manufactured in casting and rolling plants, in particular LC (Low Carbon), MC (Medium Carbon), HC (High Carbon), HSLA (High Strength Low Alloy), DP (Dual Phase), other multi-phase steels, API (the commonly used American standard for pipe grades), Si grades (silicon grades such as electrical sheets), AHSS (Advanced High Strength Steel) and Corten (weatherproof structural steels) with a maximum thickness of 25.4 mm and a minimum of up to 0.8 mm safely, flexibly and cost-effectively up to an annual production capacity of 4.0 to 5.0 million tons per year (depending on the product mix).

Due to the casting thickness, the casting-rolling plant according to the invention is able to process even those steel grades that require a low casting speed, in particular this applies to the high carbon grades mentioned above, into thin or ultra-thin strips in continuous mode, since the mass flow from the casting plant, calculated as the product of casting speed (m/min.) and casting thickness (mm), is usually above a threshold value set for continuous operation.

In certain embodiments of the casting-rolling plant according to the invention, for example in a rolling plant with seven or eight consecutive rolling stands without an intermediate continuous furnace, such a threshold value is, for example, 650 mm x m/min., but can be set at, for example, 350 mm x m/min., preferably 500 mm x m/min., in a plant configuration with, for example, two roughing stands, a second continuous furnace arranged downstream of them and five, six or seven final rolling stands provided thereafter.

When determining the operating mode of the casting-rolling plant, it is essential to determine whether the final rolling temperature is above the austenite → ferrite transformation temperature so that a hot strip structure can be produced according to customer requirements. If the mass flow from the casting plant does not allow this or if there is no possibility of reheating using a continuous furnace after any roughing stands provided, rolling must be carried out in batch mode; otherwise, continuous operation can be carried out regularly, which in particular allows the reliable production of extremely thin strip thicknesses of less than 1.2 mm, in particular less than 1.0 mm.

The casting thicknesses according to the invention of >100 mm to 150 mm, preferably >100 mm to 130 mm, in particular >100 mm to 130 mm, are preferably cast into thin slabs at casting speeds of up to 7 m/min and then formed into thin strip or ultra-thin strip in a compact rolling mill. The working roll diameter of the first rolling stands, preferably the first two rolling stands of the rolling mill, is preferably more than 1,000 mm, in particular preferably 1,050 mm, whereby the first rolling stands, preferably the first two rolling stands, can apply a rolling force of a maximum of 35 mN/m at a rolling moment of a maximum of 4,000 kNm.

In a preferred embodiment of the invention, a shear for cutting off the leading strip beginning and optionally the strip end is arranged between the rolling stands, preferably after the second and before the third of the at least seven, preferably eight, rolling stands. This allows the strip beginning and optionally also the strip end, which can deform like a tongue, particularly during the first rolling passes, to be straightened, which enables a more reliable process control and a more reliable threading of the strip beginning into the further rolling stands.

According to a further preferred embodiment of the invention, the rolling stands of the rolling plants downstream of the casting plant or the casting plants can be divided into one or two roughing stands, in particular one or two roughing stands with a particularly high torque of at least 1,800 kNm, preferably at least 2,000 kNm, particularly preferably between 2,000 kNm and 3,400 kNm, and at least five, preferably six or seven, finishing stands, preferably finishing stands with a lower torque than the roughing stands. Torque of at least 100 kNm, preferably between 100 kNm and 1,400 kNm. In this context, it is particularly preferred if another continuous furnace is arranged between the roughing stands and the final stands, in which the pre-rolled strip is heated to the desired temperature and/or homogenized for the final rolling. Furthermore, inductive intermediate heating can be dispensed with entirely, since the mass flow for the production of thin or ultra-thin strips in continuous operation over a large product mix down to the smallest thicknesses is possible even for those steel grades that require a particularly low casting speed. Restrictions exist, if at all, only in the production of ultra-thin strips with a thickness < 1.2 mm for high-strength grades with a particularly low casting speed.

In a further preferred embodiment of the invention, the casting-rolling plant according to the invention has a cooling section, a shear, preferably a flying shear, and at least one reel downstream of the last rolling stand, so that the rolled hot strip can be safely cooled and wound into coils with a predefined weight.

If the casting-rolling plant according to the invention has two casting plants arranged parallel to one another in front of the rolling plant, it is preferred if a device for transferring a thin slab from the second casting plant into or behind the continuous furnace downstream of the first casting plant is provided. Such a device can be, for example, a mobile furnace segment, but it is preferred to use two stationary furnace segments both in the continuous furnace downstream of the first casting plant and in the continuous furnace downstream of the second casting plant, wherein the stationary furnace segments are designed in such a way that they have roller table segments that can be pivoted towards one another and which consist of a can be pivoted from a rest position into a transfer position in alignment with one another in order to ensure the transfer of a thin slab from the continuous furnace downstream of the second casting plant to the continuous furnace downstream of the first casting plant and, if necessary, also back.

The casting and rolling plant according to the invention is intended and set up to produce a wide range of thin slabs with different thicknesses and different widths. It is preferred if the casting molds provided in the respective casting plants have adjustable width sides, the distance between which can be at least 900 mm, preferably at least 1,000 mm to 2,000 mm, particularly preferably 1,000 mm to 1,800 mm, from one another. This creates a casting plant with particularly simple means that is able to produce the desired range of thin slab widths without the need to replace one casting mold with another.

According to the second aspect of the invention, a method is provided for producing a thin or ultra-thin strip with a thickness of at least 0.8 mm to < 1.0 mm from a cast thin slab of steel in batch or continuous operation with a casting-rolling plant, particularly preferably a casting-rolling plant according to the first aspect of the invention. The casting-rolling plant comprises at least one casting plant and at least seven, preferably eight, rolling stands arranged downstream of the casting plant. The method according to the invention comprises the steps of casting at least one thin slab with a casting thickness of 100 mm to 150 mm, preferably from 100 mm to 140 mm, particularly preferably from 100 mm to 130 mm, with a casting width of at least 600 mm, preferably at least 1,000 mm with a casting speed of up to 7.0 m/min, heating and/or homogenizing the temperature of the thin slab in a continuous furnace and rolling the heated and/or homogenized thin slab by means of at least seven, preferably eight rolling stands, to form a thin or ultra-thin strip, preferably hot strip, wherein the thin slab and/or the strip does not undergo any inductive heating during the process for producing the thin or ultra-thin strip.

The technical effects that can be achieved with the second aspect of the invention correspond to those that have already been described above with respect to the first aspect of the invention.

It is preferred if the casting-rolling plant can be switched between batch operation and continuous operation depending on the mass flow of the casting plant, calculated as the product of the casting thickness (in mm) and the casting speed (in m/min.). It is particularly preferred if continuous operation is regularly set when a threshold value for the mass flow is exceeded, with this threshold value for the mass flow being particularly preferably set at 350 mm x m/min., preferably 500 mm x m/min., when the thin slab is formed into a thin or ultra-thin strip using one or two roughing stands and five to seven final stands with an intermediate continuous furnace. However, if the forming of the cast thin slab into a thin or ultra-thin strip is carried out with at least seven, preferably eight, rolling stands without a continuous furnace arranged between them, a threshold value for the mass flow of 650 mm/m and min. is preferred in order to switch between batch operation and continuous operation.

5. Short description of the characters

The invention is explained in more detail below with reference to a table and a figure, wherein preferred embodiments of the invention are shown in the table and the figure.

Tabelle 1:

eine Beispielrechnung für den Betrieb einer erfindungsgemäßen Gieß-Walzanlage mit acht hintereinander angeordnet Walzgerüsten, und

Figur 1

eine schematische Ansicht einer erweiterten Anlagenkonfiguration gemäß der Erfindung.

It shows

Table 1:

an example calculation for the operation of a casting-rolling plant according to the invention with eight rolling stands arranged one behind the other, and

Figure 1

a schematic view of an extended plant configuration according to the invention.

6. Detailed description of the table and figure

Table 1 shows example tests for producing thin strips from different steel grades using a casting-rolling plant 1 according to the invention, here with a plant layout that has a casting plant, a downstream continuous furnace 7 and eight final rolling stands 9, 10, 14 - 19, followed by a cooling section 21 and two reels 25a, 25b. After the first two stands 9, 10, a shear 13 is arranged to cut off the strip head after it leaves the second rolling stand 10 and to straighten the strip on the head side.

A steel of grade S315MC was cast at a withdrawal speed of 7.9 m/min. or 7.2 m/min. to form a thin slab with a thickness of 100 mm or 110 mm and a width of 1,200 mm. This thin slab was rolled in continuous operation into a thin strip with a thickness of 1.0 mm and a width of 1,200 mm. In a further test, the same steel grade was cast at a casting speed of 9.1 m/min. or 8.4 m/min. to form a thin slab with a thickness of 100 mm or 110 mm and a width of 1,550 mm and also rolled in continuous operation into a thin strip with a thickness of 1.3 mm and a width of 1,550 mm. The mass flow was 700 to about 925 mm x m/min, thus above the threshold value for the use of continuous operation. The final rolling temperatures were more than 900°C, thus significantly above the austenite → ferrite transformation temperature.

In another series of tests, HDT580X steel was cast at casting speeds of 9.6 m/min. and 8.8 m/min. to form thin slabs with a thickness of 100 mm and 110 mm and a width of 1,200 mm. The continuous forming operation resulted in a thin strip with a thickness of 1.2 mm and a width of 1,200 mm. In another pair of tests, the same steel was cast at a casting speed of 11.5 m/min. and 10.7 m/min. to form a thin slab with a thickness of 100 mm and 110 mm and a width of 1,550 mm. The mass flow was 960 to 1,180 mm xm/min., thus also significantly above the threshold value for continuous operation, the final rolling temperatures for the test series with the steel grade HDT580X were above 900°C.

In another series of tests using the same plant layout, steel of grade S315MC was cast into a thin slab with a thickness of 100 mm and a width of 1,200 mm. In batch operation, a thin strip with a thickness of 2.30 mm was rolled from this. A thin slab made of steel of grade S315MC was also cast with a thickness of 100 mm and a width of 1,550 mm and finally rolled in batch operation into a thin strip with a thickness of 2.80 mm.

In another series of tests, HDT580X steel was cast into a thin slab with a thickness of 100 mm and a width of 1,200 mm or 1,550 mm and finally rolled into thin strip with a thickness of 2.75 mm or 3.50 mm in batch operation. Even in batch operation, the final rolling temperatures were above the austenite ---> ferrite transformation temperature in order to obtain a hot-rolled structure in the final rolled strip.

Figure 1 shows a casting-rolling plant 1 in a further plant layout according to the invention, wherein the casting-rolling plant 1 has two casting plants 2a, 2b with the respective casting molds 3a, 3b. After exiting the strand guide 4a, 4b, the solidified strand is cut using a pair of scissors 6a, 6b if batch operation is to be carried out on the casting-rolling plant 1 and then enters a continuous furnace 7a, 7b. Between the continuous furnaces 7a, 7b, a device 8 is provided for transferring a slab (not shown) from the continuous furnace 7b into the continuous furnace 7a. After leaving the continuous furnace 7a, the slab enters a pair of roughing stands 9, 10 and is pre-rolled in these roughing stands 9, 10 to form a strip, which then enters another continuous furnace 11 and is reheated there. After leaving the other continuous furnace 11, the pre-rolled strip can be straightened at the head end by means of a shear 13 and then enters a series of final rolling stands 14 to 20. Upon leaving the last rolling stand 20, the strip has the desired final thickness and the desired final rolling temperature, after which the rolled strip is cooled in the cooling section 21 to the temperature required for coiling. Downstream of the cooling section 21, a high-speed shear 24 is provided, which is used when thin strip is rolled in endless mode. and in this case must be cut to the reel length without interrupting the casting-rolling process. The rolled and possibly cut thin strip can then be reeled alternately onto two reels 25a, 25b in a flying change.

List of reference symbols

1

Casting-rolling plant

2a, 2b

Casting systems

3a, 3b

Casting moulds

4a, 4b

Strand guide

6a, 6b

Scissors

7a, 7b

Continuous furnace

8th

Device for transferring a slab

9

Roughing mill

10

Roughing mill

11

Continuous furnace

13

Scissors

14-20

Final rolling mills

21

Cooling section

23

Cooling section

24

High speed shear

25a, 25b

reel

Claims (20)

1. Casting and rolling plant (1) for producing a thin or ultra-thin strip with a thickness of a minimum of 0.8 mm to < 1.0 mm from a cast thin slab of steel in batch or endless operation, comprising at least one casting plant (2a, 2b) for casting a thin slab with a cast thickness of > 100 mm to 150 mm, preferably of > 100 to 140 mm, particularly preferably of > 100 mm to 130 mm, and a casting width of at least 600 mm, preferably at least 1000 mm, at least one continuous furnace (7) arranged downstream of the at least one casting plant (2a, 2b) and at least seven, preferably eight, roll stands (9, 10, 14 - 20) arranged downstream of the continuous furnace (7), wherein the at least one casting plant (2a, 2b) comprises a casting mould (3, 3b), the long sides of which have a spacing of at least > 100 mm to 150 mm, preferably > 100 mm to 140 mm, particularly preferably of > 100 mm to 130 mm, from one another and wherein the casting and rolling plant (1) does not have induction heating means for reheating the cast thin slab or induction heating means for reheating the rolled strip and wherein the casting and rolling plant is suitable for casting thin slabs at a casting rate of up to 7 m per minute.
2. Casting and rolling plant (1) according to claim 1, characterised in that shears (13) for cutting off the leading strip start and optionally the strip end are arranged between the roll stands (9, 10, 14 - 20), preferably after the second (10) and before the third (14) of the at least seven, preferably eight, roll stands (I, 10, 14 - 20).
3. Casting and rolling plant (1) according to one of the preceding claims, characterised in that the roll stands (9, 10, 14 - 20) comprise at least one roughing stand, preferably two roughing stands (9, 10), a further continuous furnace (11) arranged downstream of the roughing stand or stands (9, 10) and at least five, preferably six or seven, finishing roll stands (14 - 20) arranged downstream of the further continuous furnace (11), wherein the casting and rolling plant (1) does not have induction heating means for reheating the cast thin slab and/or the coarsely rolled strip and/or strip rolled to final state.
4. Casting and rolling plant (1) according to any one of the preceding claims, characterised in that a cooling path (21), shears (24), preferably drum shears, and at least one coiler (25a, 26b) are arranged downstream of the last roll stand (20).
5. Casting and rolling plant (1) according to any one of the preceding claims, characterised in that shears (6), preferably pendulating shears, are arranged between the at least one casting plant (2a, 2b) and the continuous furnace (7) upstream of the roll stands (9, 10, 14 - 20).
6. Casting and rolling plant (1) according to any one of the preceding claims, characterised in that two casting plants (2a, 2b) each with pendulating shears (6a, 6b) are provided.
7. Casting and rolling plant (2) according to claim 6, characterised in that an individual continuous furnace (7a, 7b) is associated with each casting plant (2a, 2b), wherein a device (8) for transfer of a thin slab from the second casting plant (2b) is provided in or behind the continuous furnace (7a) downstream of the first casting plant (2a).
8. Casting and rolling plant (1) according to claim 7, characterised in that the device (8) for transfer comprises two furnace segments adjustable relative to one another of both the continuous first furnace (7a) downstream of the first casting plant (2a) and the continuous furnace (7b) downstream of the second casting plant (2b).
9. Casting and rolling plant (1) according to any one of the preceding claims, characterised in that the wide sides of the at least one casting mould (3a, 3b) have a spacing of at least 900 mm, preferably 1000 mm to 2000 mm, particularly preferably 1000 mm to 1800 mm, from one another.
10. Casting and rolling plant (1) according to any one of claims 3 to 8, characterised in that the torque of the at least one roughing stand (9, 10) is at least 1800 kNm, preferably at least 2000 kNm, particularly preferably between 2000 kNm and 3400 kNm.
11. Casting and rolling plant (1) according to claim 10, characterised in that the torque of the at least five finishing roll stands (14 - 20) is in each instance at least 100 kNm, preferably between 100 kNm and 1400 kNm.
12. Method for producing a thin or ultra-thin strip with a thickness of a minimum of 0.8 mm to < 1.0 mm from a cast thin slab of steel in batch or endless operation with a casting and rolling plant (1), comprising at least one casting plant (2a, 2b) and at least seven, preferably eight roll stands (9, 10, 14 - 20), comprising the steps of

    casting at least one thin slab, with a cast thickness of > 100 mm to 150 mm, preferably of > 100 to 140 mm, particularly preferably of > 100 mm to 130 mm, and a cast width of at least 600 mm, preferably at least 1000 mm, and a casting rate of up to 7 m per minute, heating and/or homogenising the temperature of the thin slab in a continuous furnace (7a, 7b) and

    rolling the heated and/or homogenised thin slab by means of at least seven, preferably eight, roll stands (9, 10, 14 - 20) to form a thin or ultra-thin strip,

    wherein the thin slab and the strip do not undergo inductive heating during the method for producing the thin or ultra-thin strip.
13. Method according to claim 12, characterised in that the leading strip start and optionally the strip end are cut off between the roll stands (9, 10, 14 - 20), preferably after the second (10) and before the third (14) of the at least seven, preferably eight, roll stands (9, 10, 14 - 20).
14. Method according to claim 12 or 13, characterised in that the rolling of the thin slab to form a thin or ultra-thin strip comprises rough-rolling of the heated and/or homogenised thin slab by means of at least one roughing stand, preferably two roughing stands (9, 10), heating and/or homogenising the temperature of the rough-rolled thin slab or the strip in a further continuous furnace (11) and rolling of the rough-rolled thin slab or strip to a finished state by means of at least five, preferably six or seven, finishing roll stands (14 - 20) arranged downstream of the further continuous furnace (11).
15. Method according to any one of claims 12 to 14, characterised in that the casting and rolling plant (1) can be switched over between batch operation and endless operation in dependence on the mass flow of the casing plant (2a, 2b) as a product of cast thickness (in mm) and casting rate (in m/min.).
16. Method according to claim 15, characterised in that the casting plant (1) is operable in endless operation above a threshold value for the mass flow of 350 (mm · m) per minute, preferably 500 (mm · m) per minute.
17. Method according to any one of claims 12 to 16, characterised in that the annual production of the casting and rolling plant (1) is between 4.0 and 5.0 million tonnes.
18. Method according to any one of claims 12 to 17, characterised in that it is designed for production of thin or ultra-thin strip from LC, MC, HC, HSLA, DP, API, Si grades, AHSS and Corten steels.
19. Method according to any one of claims 12 to 18, characterised in that the finishing rolling temperature in the last roll stand (20) is set to above 820° C.
20. Method according to any one of claims 12 to 19, characterised in that it is performed by means of a casting and rolling plant (1) according to any one of claims 1 to 11.

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