KR20020063886A - Production of thin steel strip - Google Patents

Abstract

The twin roll caster 11 manufactures a steel strip 12 passing through the conveying passage 10 across the guide table 13 at the pinch roll stand 14. After exiting the pinch roll stand 14, the strip passes through a rolling mill 15 having two roll stands 16 which are hot rolled to reduce their thickness. The rolled strip passes through the run out table 17, which can be forcedly cooled by the water jet 18. The already rolled strip is then descaled in a descaling device 19 with top and bottom water jet nozzles 61 and 62 which remove scale from both the top and bottom of the strip.

Description

Method and apparatus for manufacturing thin steel strips {PRODUCTION OF THIN STEEL STRIP}

Steel strips produced by continuous thin slab casting or twin roll strip casting may be hot rolled in series to reduce the strip to final volume.

In a twin roll caster, molten metal is a pair of inverses where the metal shell is cooled to solidify the moving roll surface and to collect in the nip between the surfaces to produce a solidified strip product that is transferred downward from the nip between the rolls. Guided between rotating horizontal casting rolls. Here, the term "nip" is used to refer to the general area where the rolls are closest to each other. The melt can be poured from a ladle into a small vessel flowing through a metal transfer nozzle located above the nip to face the melt in the nip between the rolls, thus forming a casting pool of melt supported on the casting surface of the roll directly above the nip. , Extend along the length of the nip. The casting pool is formed between a side plate or a dam that is slidably engaged with the end face of the roll to prevent both ends of the casting pool against outflow, but alternative means such as electromagnetic barriers are also provided. It is also proposed.

When casting steel strips in twin roll casters, the strip leaves the nip at a high temperature of 1400 ° C. and when exposed to the atmosphere, undergoes very rapid scaling due to oxidation at high temperatures. Therefore, it has already been proposed to install descaling equipment for descaling strips just before entering the tandem rolling mill. On the other hand, the new casting strips are wrapped in an enclosure containing a non-oxidising atmosphere by the time it enters the tandem rolling mill to reduce scaling before hot rolling and to avoid removing the scale. Is proposed. This proposal is described in US Pat. No. 5,762,126, through which the casting strip passes through a sealed enclosure from which oxygen is extracted by the initial oxidation of the strip, after which the oxygen content in the sealed enclosure is released from the enclosure. It is kept less than the ambient atmosphere by the continuous oxidation of the strip through it to adjust the thickness of the scale of the strip. By this means, the strip exits the enclosure and can only be present in the hot rolling mill with a scale thickness of 10 μm.

In accordance with the aforementioned U.S. Patent No. 5,762,126, the strip leaving the hot rolling mill is wound after being water cooled. By this process, the strip eventually needs to be descaled or pickled before finishing. If scaling of the hot rolled strip is removed at a temperature in the range of 900 ° C. to 600 ° C. prior to winding, it is determined that the scale reoccurrence rate is very low. The strip can be wound on very small scales with a thickness of only 1 μm to 2 μm. The coil thus can be sent directly to the end user for various applications such as the manufacture of drums and any paint strip products. In other applications, the coil may allow for faster pickling than the unscaled material just before winding.

The present invention relates to a method and apparatus for producing thin steel strips. In particular, it relates to a method and apparatus for producing steel strips of final volume or final thickness by continuous casting and tandem hot rolling of the strips.

1 is a vertical sectional view of a steel strip casting and rolling plant constructed and operated in accordance with the present invention.

2 shows the essential elements of a twin roll caster coupled to the installation.

3 is a vertical sectional view of a twin roll caster.

4 is a cross-sectional view of the end of the caster.

FIG. 5 is a cross-sectional view taken along line 5-5 of FIG. 4.

FIG. 6 is a view of lines 6-6 of FIG. 4.

7 is a view of a modified installation constructed and operated in accordance with the present invention.

According to the present invention, a continuous casting of a steel strip, guiding the strip through an enclosure comprising an atmosphere that inhibits oxidation of the strip surface and thus the formation of scale, a rolling mill that is rolled as the strip is manufactured Supplying the strip through the step of passing the rolled strip through a descaling device to remove scale from exiting the rolling mill, and passing the rolled and descaled strip through a coiler. Provided is a method for producing a steel strip, the method comprising:

The strip may exit the enclosure before passing through the rolling mill.

Optionally, the rolling mill may be arranged in the enclosure to pass through the rolling mill before the strip exits the enclosure.

Preferably, the strip is continuously cast as it supports a casting pool of molten steel on a pair of cold cast rolls forming a nip therebetween, and solidifies as the rolls rotate in opposite directions to move the solidified strip downward from the nip. Strips are manufactured.

The atmosphere in the enclosure is formed of an inert gas or a reducing gas, and may contain a lower level of oxygen than the atmosphere around the enclosure.

Preferably, the atmosphere in the enclosure is formed by sealing the enclosure to limit the entry of an atmosphere containing oxygen, which causes oxidation of the strip in the enclosure during the initial stages of casting, thereby releasing oxygen from the sealed enclosure , After causing the enclosure to have a sparse amount of oxygen than the ambient atmosphere, and subsequently maintaining the amount of oxygen in the hermetically sealed enclosure less than the amount of oxygen in the ambient atmosphere by continuous oxidation of the strip through the sealed enclosure, thereby scaling on the strip accordingly. To control the thickness.

Preferably, the rolling mill hot rolls the strip at a temperature range of 750 ° C to 1250 ° C.

The present invention provides a continuous caster for continuous casting of steel strips, strip guiding means for guiding the strip through a transfer passage away from the caster, and oxidation inhibiting formation of a strip over the transfer passage to control the formation of scale on the strip. An enclosure, a rolling mill capable of rolling the strip as the strip is manufactured, a descaling device capable of descaling the strip as the strip exits the rolling mill, and receiving the rolled and descaled strip Further provided is a steel strip manufacturing apparatus having a coiler.

Preferably, the continuous caster comprises a pair of general horizontal casting rolls forming a nip therebetween, metal transfer means for transferring molten steel to the nip between the casting rolls forming a casting pool of molten steel supported on the roll, Means for chilling the casting roll, and means for rotating the casting rolls in opposite directions to cast the strip and to transfer the strip downward from a nip.

The depicted casting and rolling equipment has a twin roll caster, designated 11, for producing a cast steel strip 12 that has passed through a conveying passage 10 across a guide table 13 at a pinch roll stand 14. Immediately after exiting the pinch roll stand 14, the strip passes through a hot rolling mill 15 having a roll stand 16 which is hot rolled to reduce its thickness. Thus, the rolled strip exits the mill and passes through a run out table 17, which can be forcibly cooled by the water jet 18. According to the invention, the strip then passes through the descaling device 19 before passing through the coiler 50 between the pinch rolls 20A of the pinch roll stand 20.

The twin roll caster 11 has a main machine frame 21 for supporting a pair of parallel casting rolls 22 having a casting surface 22A. Melt through metal transfer nozzle 26 into nip 27 between casting rolls 22 during casting operation from ladle 23 to tundish 25 via refractory ladle outlet shroud 24. Is supplied. Thus, the metal transferred to the nip 27 forms a pool 30 over the nip, which is a pair of thrusters 31 having a hydraulic cylinder unit 32 connected to the side plate holder 28A. It is formed at the end of the roll by a plate 28 or a pair of side closure dams applied to the step ends of the roll. The upper surface of the pool 30 (generally referred to as the “meniscus” level) may raise the lower end of the delivery nozzle so that the lower end of the delivery nozzle falls into this pool.

The casting roll 22 is water cooled such that the shell solidifies at the moving roller surface and contacts the nip 27 therebetween to make the solidified strip 12 transferred downward from the nip between the rollers.

At the start of the casting operation, a short length of incomplete strip is produced as the casting conditions stabilize. After the continuous casting has been established, the casting roll is finely separated and then caused to cut this tip of the strip in the manner described in Australian Patent No. 27036/92 to form the clean head end of the subsequent casting strip. Contact again. The incomplete material falls into the scrap box 33 located below the caster 11, wherein the swinging aprons 34, apron, which are generally suspended downward from one side of the caster outlet from the pivot 35, are pinch roll stands. It swings across the caster outlet to guide the clean end of the casting strip on the guide table 13 which feeds the cast strip to 14. The apron 34 is then retracted to a hanging position that allows the strip 12 to hang in a loop below the caster before passing through the guide table 13 which engages the series of guide rollers 36.

The twin roll casters may be one of those described and illustrated in Australian Patents 631728 and 637548 and U.S. Patents 5,184,668 and 5,277,243, for their proper structural description that do not form any part of the present invention. See patents.

In the entry nip 39 of the pinch roll stand 14 forms a large single scale enclosure, indicated 37, which forms a sealed space 38 in the steel strip 12 formed from the nip between the casting rolls over the transfer passageway. The equipment for making is manufactured and assembled.

Enclosure 37 is formed by a number of separate wall portions that are secured together with various sealing connections to form a continuous enclosure wall. This is because the wall part 41 formed in the twin roll caster closing the casting roll and the wall part 41 engaging the upper edge of the scrap box 33 when the strap box is in the operating position such that the scrap box is part of the enclosure. It has a wall portion 42 extending below. The scrap box and enclosure wall portion 42 are connected by a seal 43 formed by a ceramic fiber rope that fits into the groove of the upper edge of the scrap box and a flat sealing gasket that fits into the lower end of the wall portion 42. 44). The scrap box 33 can be mounted on a carriage 45 that fits on the wheel 46 moving on the rail 47, whereby the scrap box can be moved to the scrap outlet after the casting operation. When the cylinder unit 40 is in an operating position to push upward to press the seal 43 against the enclosure wall portion 42, it can be operated to lift the scrap box from the carriage 45. After the casting operation, the lower scrap box on the carriage 45 is released so that the cylinder unit 40 can move to the scrap discharge portion.

The enclosure 37 is arranged with respect to the guide table 13, and the enclosure is connected to the frame of the pinch roll stand 14 comprising a pair of pinch rolls 14A opposed to being sealed by the sliding seal 60. It further has a wall portion 48 to be formed. Thus, the strip passes between the pair of pinch rolls 14A, exits the enclosure 38 and immediately passes through the hot rolling mill 15. The space between the pinch rolls 14 and the mill inlet should be as small as possible to control the shape of the scale before entering the mill.

Most enclosure wall sections are lined with fire bricks, and scrap boxes 33 can be lined by either fire bricks or castable fire linings.

When the side dam plate 28 is pressed against the end of the roll by the cylinder unit 32, the enclosure wall portion 41 surrounding the casting roll is shaped to comfortably receive the side dam plate holder 28A. It is formed in the side plate 51 provided in the notch 52. The boundary between the side plate holder 28A and the enclosure side wall portion 51 is sealed by the sliding seal 53 to maintain the sealing of the enclosure. The seal 53 may be formed of a ceramic fiber rope.

The cylinder unit 32 extends upwardly through the enclosure wall portion 41, in which the enclosure is enclosed in the enclosure wall portion 41 when the cylinder unit is operated to press the side plate against the end of the roll. Is sealed by a sealing plate 54 which fits into the cylinder unit. The thruster 31 is also driven by the drive of the cylinder unit 32 for closing the slot 56 at the top of the enclosure via the side plate which is initially inserted into the enclosure and inserted into the holder 28A for application to the roll. The fireproof slide 55 to be moved is moved. When the cylinder unit is driven to be applied to the side dam plates opposite the rolls, the top of the enclosure is closed by the tundish, side plate holder 28A and the slide 55. In this way, the complete enclosure 37 is sealed before the casting operation so that the sealing space 38 is established, thereby limiting the supply of oxygen from the casting roll to the strip 12 passing through the pinch roll stand 14. do. Initially, the strip absorbs all the oxygen from the enclosure space 38 to form a large amount of scale on the strip. However, the sealing of the enclosure space 38 controls the entry of oxygen containing the atmosphere below the amount of oxygen absorbed by the strip. Thus, after the initial drive cycle, the amount of oxygen in the enclosure space 38 will remain empty to limit the usefulness of oxygen for oxidation of the strip. In this way, the shape of the scale is controlled such that there is no need to continuously supply reducing gas or non-oxidizing gas into the enclosure space 38. In order to avoid large amounts of scaling during the initial drive cycle, the enclosure space reduces the initial oxygen level in the enclosure, allowing time to meet the level of oxygen established as a result of the interaction of oxygen from the scaled enclosure due to oxidation of the strip passing through it. Can be purified immediately prior to the start of casting to reduce. The enclosure is easily purged by nitrogen gas. Reduction of the initial amount of oxygen between 5% and 10% limits the scaling of the strip exiting the enclosure to about 10 μm to 17 μm even during the initial run phase.

In a typical caster installation, the temperature of the strip passing through the caster is 1400 ° C and the temperature of the strip present in the rolling mill is about 1200 ° C. The strip has a width in the range from 0.9 m to 2.0 m and a thickness in the range from 0.7 mm to 2.0 mm. The speed of the strip is 1.0 m / s. Strips produced under these conditions allow air to escape from the enclosure space 38 and limit the growth of scale on the strip to a thickness of less than 5 μm, estimated to be 2% of the average oxygen level in the enclosure space. Leakage can be controlled. The volume of the enclosure space 38 is not particularly important because all the oxygen can be quickly absorbed by the strip during the initial drive phase of the casting operation, and the subsequent shape of the scale is determined by the rate of leakage of the atmosphere in the enclosure space through the seal. Determined alone. It is desirable to control the leak rate so that the thickness of the scale at the inlet of the mill is in the range of 1 μm to 5 μm. Experiments have shown that it is necessary to prevent multiple scales from sticking and sticking to the surface of the strip during hot rolling. In particular, this work suggests a minimum thickness of 0.5 μm to 1 μm to ensure satisfactory rolling. An upper limit of about 8 μm and preferred 5 μm is preferred to prevent the “rolling scale” defect of the strip surface after rolling and to ensure that the scale thickness of the final product is not larger than conventional hot rolled strips.

After exiting the hot rolling mill, the strip passes through a run out table 17 which is forcibly cooled by the water jet 18. According to the invention, thereafter, it passes through the descaling device 19 before being wound on the coiler 20. The descaling device 19 can have a conventional structure. This is generally the upper and lower sides where water is supplied from the pressure pump through each water jet manifold 63, 64 to produce water jets 65, 66 opposite the upper and lower sides of the strip to remove the scale on both sides. Water jet nozzles 61 and 62 are provided.

In a general installation for producing steel strips 1300 mm to 1700 mm wide, there is an upper nozzle 61 of arrows 15-20 and a lower nozzle 62 of similar arrows 15-20 in the space across the strip. In general, the nozzles each have a spray angle of 50 ° to 55 ° and are spaced apart to make fan-shaped jets overlapping about 10 mm. The nozzles are stand off at intervals of 60 mm to 70 mm and are operated to generate a nozzle flow rate of about 60 L / min at a pressure of 7 MPa to 10 MPa.

The water jet of the descaling device further reduces the temperature of the strip prior to cooling. Generally, the strip is descaled at 750 ° C. and wound at about 600 ° C. In this situation, the strip in the coil generally has a scale of only 1 μm to 2 μm thick and no scaling is more sensitive as it cools the strip at ambient temperature. This is an important advance, and as a result, in commercially valuable products, such as drum making or the manufacture of painted products, cleanly scaled strips can be used directly as a feed without further processing, and thus strips formed in conventional processes This eliminates the cost of pickling or pretreatment that is normally required for an application. In applications that require greater effort, cleanly scaled strips can be pickled much faster than strips not descaled immediately before cooling.

FIG. 7 shows a variant of the enclosure 37 which is extended to surround the rolling mill 15 so that the strip is rolled before exiting the enclosure space 38. In this case, the strip exits the enclosure through the end of the mill stand 16 in a roll that performs the sealing of the enclosure so that no separate sealing pinch roll is required.

To prevent excessive scale formation, the strip should exit the enclosure 37 preferably at least 925 ° C. Thus, with the arrangement shown in FIGS. 1 to 6, the strips are hot rolled in a temperature range of 750 ° C. to 925 ° C., while in a facility arranged as shown in FIG. Hot rolled at

Although a preferred embodiment of the present invention employs a twin roll strip caster, this is not the whole point of the present invention, the twin roll caster initially produces an initial slab or strip having a thickness of 120 mm to 50 mm, and then 16.0 mm. It can be replaced with a prior art continuous thin slab caster that can be rolled under a hot rolling mill to a final thickness of from 0.7 mm.

Strips scaled according to the invention can be used directly as feedstock without further processing, thus eliminating the pickling or pretreatment costs normally required for strips formed in conventional processes. In addition, the strips can be pickled much faster than strips not descaled immediately before cooling.

Claims (14)

Continuous casting of steel strips, Directing the strip through an enclosure comprising an atmosphere that inhibits oxidation of the strip surface and thus formation of scale, Feeding the strip through a rolling mill that is rolled as the strip is manufactured, Passing the rolled strip through a descaling device to remove scale from exiting the mill, and Passing the rolled and descaled strip to a coiler. The method of claim 1, The rolling mill is a steel strip manufacturing method, characterized in that for hot rolling the strip in the temperature range of 750 ℃ to 1250 ℃. The method according to claim 1 or 2, Wherein said strip is discharged out of said enclosure before passing through said rolling mill. The method according to claim 1 or 2, And the rolling mill is disposed in the enclosure such that the strip passes through the rolling mill before exiting the enclosure. The method according to any one of claims 1 to 4, The strip is continuously cast as it supports a casting pool of molten steel on a pair of cold cast rolls forming a nip therebetween, and is produced by rotating the rolls in opposite directions to move the solidified strip downward from the nip. Characterized in that the steel strip manufacturing method. The method according to any one of claims 1 to 5, The atmosphere in the enclosure is a steel strip manufacturing method, characterized in that formed of inert gas or reducing gas. The method according to any one of claims 1 to 5, Wherein the atmosphere in the enclosure is an atmosphere containing a lower level of oxygen than the atmosphere around the enclosure. The method of claim 7, wherein The atmosphere in the enclosure is formed by sealing the enclosure to limit the entry of an atmosphere containing oxygen, which causes oxidation of the strip within the enclosure during the initial stages of casting, thereby releasing oxygen from the sealed enclosure, thereby After causing the enclosure to have a sparse amount of oxygen than the atmosphere, the continuous oxidation of the strip through the sealed enclosure maintains the amount of oxygen in the hermetically sealed enclosure less than the amount of oxygen in the ambient atmosphere, thereby reducing the thickness of the scale accordingly on the strip. Controlling the steel strip. The method according to any one of claims 1 to 8, And wherein said strip exits said enclosure at a temperature below 925 ° C. The method according to any one of claims 1 to 9, Wherein said strip is generally passed horizontally through a descaling device, the scale being removed by water jets opposed to the top and bottom of the strip to remove the scale on both sides. Continuous caster for continuous casting of steel strip, Strip guiding means for guiding the strip through a transport passage away from the caster, An oxidation inhibiting enclosure that forms a strip over the transfer passage to control the formation of a scale on the strip, A rolling mill capable of rolling the strip as the strip is manufactured, A descaling device capable of removing the scale of the strip as the strip exits the rolling mill, and And a coiler for receiving the rolled and descaled strip. The method of claim 11, And the rolling mill is positioned outside of the enclosure to receive the strip after the strip exits the enclosure. The method of claim 12, The rolling mill is positioned in the enclosure for rolling the strip after the strip exits the enclosure. The method according to any one of claims 11 to 13, A pair of plain horizontal casting rolls, forming a nip between Metal delivery means for transferring molten steel to the nip between casting rolls forming a casting pool of molten steel supported on the roll, Means for cooling the casting roll, and And a continuous caster comprising means for rotating the casting rolls in mutually opposite directions to cast the strip and to deliver the strip downward from a nip.