JP4373796B2 - Steel strip casting - Google Patents

Description

  The present invention relates to continuous casting of steel strip in a strip casting machine, in particular a twin roll casting machine.

  In a twin-roll caster, molten metal is introduced between a pair of horizontally-rotating horizontal casting rolls that are cooled inside, thereby solidifying the metal shell on the moving roll surface, and the roll gap between the roll surfaces. The metal shells are united to produce a solidified strip product and fed downward from the roll gap. In this specification, the term “roll gap” (nip) is used to indicate the entire region where casting rolls are closest to each other. Molten metal is poured from the ladle into a small container, flows from there to a metal supply nozzle located above the roll gap, is supported by the roll casting surface immediately above the roll gap, and extends in the length direction of the roll gap. Form a casting sump. This casting reservoir is usually limited between side plates or side weirs that are slidably engaged and held on the end face of the casting roll so as to block overflow from both ends of the casting reservoir. Means have also been proposed.

  When casting steel strips in a twin roll caster, the strips can exit the roll gap at ultra-high temperatures in the 1400 ° C range and undergo very rapid scale formation due to oxidation at such high temperatures. Such scale formation can be a significant loss of steel products. For example, 3% of a 1.55 mm thick strip (typical scale thickness is 23 microns) may be lost due to oxidation during cooling of the strip. In addition, such scale formation requires that the strip be descaled by pickling to avoid surface quality problems such as rolled-in scale before further processing. Cause significant complexity, cost and environmental problems. The hot strip material can be passed directly through a rolling mill in the same line as the strip casting machine, then transferred to a run-out table, cooled to the winding temperature on the run-out table, and then wound up. The scale formation of the hot strip material proceeds so rapidly that it may be necessary to install a descaling device and descal the material just before the strip enters the in-line mill. Even when the strip is cooled to the coiling temperature without hot rolling, it is generally necessary to descal the strip prior to winding or at a post-treatment stage.

  In order to address the problem of rapidly scaling the strip coming out of the twin roll caster, the newly formed strip is surrounded by a sealed enclosure or a series of such enclosures to oxidize the cast strip. It has been proposed to maintain a controlled atmosphere to prevent this. A controlled atmosphere can be created by filling the seal enclosure or series of enclosures with non-oxidizing gas. Such gas can be an inert gas such as nitrogen or argon or an exhaust gas from a fuel burner.

US Pat. No. 5,762,126 US Pat. No. 5,816,311 International Patent Application PCT / AU00 / 01478

  U.S. Pat. No. 5,762,126 discloses a relatively inexpensive and energy efficient alternative to limiting exposure of hot strips to oxygen. The strip is passed through the enclosure where oxygen is extracted from the atmosphere by scale formation. The enclosure is sufficiently sealed to control oxygen penetration into the enclosure atmosphere and to control the extent of scale formation. With this method of operation, a steady state can be reached quickly and scale formation is at a low level without the need to supply non-oxidizing or reducing gas to the enclosure.

  U.S. Pat. No. 5,816,311 discloses a method for controlling the degree of scale formation by providing a chamber downstream and spraying a quench medium onto the strip by a group of nozzles there. The quenching medium was methyl alcohol, water, or a mixture of methyl alcohol and other quenching medium (liquid at room temperature). Since water contains dissolved oxygen and water (steam) decomposes into oxygen and hydrogen, further oxidation is expected, and it was expected that spraying with water in a nitrogen atmosphere would result in an unacceptable level of oxidation. However, as disclosed in U.S. Pat. No. 5,816,311 it was surprisingly surprising that it was found that the oxide thickness on the strip could be limited to less than 0.5 microns. Even more surprisingly, it has been found that these oxide levels can withstand cold rolling without pickling and metallizing the strip. However, it has been found that such rapid cooling of the steel strip results in non-uniform cooling of the steel strip, resulting in defects such as stress in the strip.

  International patent application PCT / AU00 / 01478, the basis of US patent application Ser. No. 10 / 121,567, generates steam by introducing water in a fine mist spray into a downstream enclosure through which a high temperature cast steel strip passes. Thus, it is disclosed how an essentially non-oxidizing atmosphere can be created inexpensively and effectively. When steam is generated, the gas volume in the enclosure increases, creating a positive pressure in the enclosure and essentially preventing air from entering. This also increases the hydrogen gas level in the enclosure, greatly reducing the oxygen level in the enclosure and slowing down the oxidation rate of the strip. In the international patent application PCT / AU00 / 01478, it is considered necessary to isolate the enclosure where steam is generated from the enclosure where the casting roll is exposed so that the risk of exposing the casting pool to water or steam is avoided. It was done. Surprisingly, we introduced water in a fine mist spray this time, making water-to-steam conversion and hydrogen gas production very effective. Increasing the hydrogen gas level in the enclosure to which the casting roll is exposed by flowing gas between the downstream enclosure to be introduced and / or performing fine mist spray directly in the enclosure to which the casting roll is exposed. I found out that I can make it. It is also possible to dispense with a separate downstream envelope by directly introducing a fine mist spray into the envelope to which the casting roll is exposed.

The present invention
(a) forming a molten steel casting pool on the cooling casting surface of a pair of horizontally arranged casting rolls forming a roll gap between them ;
(b) mutually rotating the casting rolls to produce a casting strip downward from the roll gap ,
(c) atmospheric is sealed so as to prevent entry of feeding a strip surrounding portion that extends to the roll gap directly from the nip, the transfer path away from the nip through the enclosure street strip,
; (d) surrounded by increasing the hydrogen gas levels within enclosure by introducing the water in the form of a fine mist to the portion, together with the strip exiting the nip is to be exposed to the hydrogen gas, liquid water Steel Prevent contact with the casting surface of the strip and casting roll
A steel strip continuous casting method is provided.

  In this specification, “fine mist” generally refers to a water spray that reaches the surface of the strip after water is evaporated and converted into vapor. This may still cause extra water droplets to adhere to the strip, but the purpose is to prevent liquid water from coming into contact with the strip. Too much liquid water in the strip can cause the strip to cool unevenly. The exact size and size range of the water droplets contained in the fine mist depends on the temperature of the strip in the enclosure spraying the fine mist, the position of the spray nozzle in the enclosure and the distance from the strip to the spray nozzle. In particular, when the fine mist is sprayed in the first enclosure to prevent liquid water from coming into contact with the casting surface of the casting roll, the position of the spray nozzle with respect to the size and range of the water droplets is delicate. The size and range of the water droplets in the fine mist can be generated according to the embodiment that gives the work flexibility in the embodiment, and can generate hydrogen gas while preventing the liquid water from coming into contact with the strip or the casting surface. Should be selected.

  The step of introducing water in the form of fine mist to generate steam also generates a positive pressure at the introduction surrounding part, ie, the first surrounding part or the second surrounding part. However, if the fine water mist is sprayed into the second enclosure and not into the first enclosure, the first and second enclosures can be directly interconnected or separated from each other in one or more chambers. A passage is provided between them, and gas can flow from the second surrounding portion to the first surrounding portion through the passage. This passage may be the same as or different from the passage through which the cast strip moves from the first enclosure to the second enclosure. In any case, it is not necessary to completely seal the first and / or second enclosure, and a positive pressure atmosphere is provided in the first enclosure and, if provided with the second enclosure, in the second enclosure. It is sufficient to reduce the oxygen level relative to the outside air and increase the hydrogen gas level.

  In an embodiment in which fine mist is sprayed into the second enclosure to produce hydrogen gas and flows through the communication passage to the first enclosure, water is further introduced into the first enclosure in the form of fine mist to generate steam. The hydrogen gas level can be increased while trying to prevent liquid water from coming into contact with the steel strip or the cooling casting surface of the casting roll.

  In an alternative embodiment, the first enclosure and the second enclosure are sealed separately so that the atmosphere does not enter, and water is introduced into the first enclosure in the form of fine mist, and the liquid water is applied to the steel strip or casting. The hydrogen gas level can be increased while trying to prevent contact with the cold cast surface of the roll. The water thus introduced as fine mist also generates steam in the first surrounding part to generate a positive pressure, thereby preventing air from entering the first surrounding part. In this embodiment, water is further introduced into the second enclosure in the form of a fine mist to increase the hydrogen gas level and / or generate steam while preventing liquid water from coming into contact with the steel strip. Thus, a positive pressure can be generated.

  In either embodiment, the cast strip passes through the first enclosure and is guided on the transfer path to the second enclosure via the communication passage. Alternatively, the strip may be guided along the transfer path from the first enclosure to the second enclosure and through a second passage and / or a connection chamber separate from the first passage through which the gas flows.

The present invention
(a) a pair of substantially horizontal casting rolls forming a roll gap between them;
(b) a metal feeding system that feeds molten steel above the roll gap between the casting rolls to form a casting pool of molten steel supported on the casting roll;
(c) a cooling system for cooling the inside of the casting roll;
(d) a drive system for mutually rotating the casting rolls in opposite directions;
(e) producing a cast strip fed downward from the roll gap, the casting roll having a cooled casting surface;
(f) Sealing so that the atmosphere does not enter, and being arranged so as to extend to the roll gap between the casting rolls, directly receiving the casting strip that exits the roll gap, and the surrounding portion through which the strip passes through the transfer path away from the roll gap;
(g) at least operable to prevent liquid water from contacting the steel strip and the casting surface of the casting roll while spraying water on the enclosure in the form of fine mist to increase the hydrogen gas level in the enclosure; Further provided is a steel strip casting apparatus comprising one water sprayer.

  The fine mist water spray can further generate steam in either or both of the first and second surrounding portions.

  The steel strip casting apparatus may also include a strip guide that guides the strip fed downward from the roll gap through the transfer path of the first surrounding part and the transfer path of the second surrounding part.

  The first enclosure part and the second enclosure part can be interconnected by a connecting passage so that gas flows between them, and the water sprayer prevents the liquid water from coming into contact with the steel strip while preventing the water from coming into contact with the steel strip. Hydrogen gas in both enclosures comprising one or more water spray nozzles attached to the second enclosure, operable to spray fine mist in the second enclosure adjacent to the strip, and generating steam The level can be increased.

  In the above method, the cast steel strip can be fed to a hot rolling mill and hot-rolled as it is manufactured. The strip can exit the second enclosure and enter the rolling mill, which in this embodiment is comprised of a pair of rolling rolls, between which the strip can exit the second enclosure. However, the strip can remain in the second enclosure as it enters the mill, or the mill can be positioned between the first and second enclosures. Such positioning of the rolling mill can be achieved by sealing the second surrounding portion to the rolling roll or housing of the rolling mill.

  In order that the invention may be more fully described, specific embodiments are described in detail with reference to the accompanying drawings.

  The casting / rolling equipment shown in FIGS. 1 to 7 is composed of a twin roll casting machine indicated by 11 as a whole, which produces a cast steel strip 12 that reaches the pinch roll stand 14 through the guide table 13 in the transfer path 10. Is done. After exiting the pinch roll stand 14, the strip reaches the hot rolling mill 16, where it is hot rolled to reduce the plate thickness. The rolled strip exits the rolling mill, passes through the run-out table 17, and is forcedly cooled on the table by fine mist from the water jet 18 before reaching the coiler 19.

  The twin roll casting machine 11 is composed of a main machine frame 21 that supports a pair of parallel casting rolls 22 having a casting surface 22A. During the casting operation, the molten metal is fed from the ladle 23 through the refractory ladle outlet shroud 24 to the tundish 25 and further to the metal feed nozzle 26 above the roll gap 27 between the casting rolls 22. The molten metal thus fed forms a casting pool 30 that is supported on the casting surface 22A of the casting roll 22. The casting pool 30 is confined at the roll end by a pair of side enclosure weirs or side enclosure plates 28, and the enclosure weir or enclosure plate is composed of a pair of fluid pressure cylinder units 32 connected to the side plate holder 28A. The thruster 31 is attached to the stepped end of the roll. The upper surface of the casting pool 30 (generally called “meniscus level”) may be raised above the lower end of the feeding nozzle 26, and the lower end of the feeding nozzle may be immersed in the casting pool.

  Since the inside of the casting roll 22 is water-cooled, the metal shell is solidified on the casting surface of the moving casting roll and is joined at the roll gap 27 between the rolls to produce the cast strip 12, and is sent downward from the roll gap between the rolls. Be paid.

  At the beginning of the casting operation, a short incomplete strip is produced as the casting situation stabilizes. Once continuous casting is established, the casting rolls are moved a little apart and then recombined so that the front end of the strip is broken as described in Australian Patent Application No. 27036/92 to form the clean front end of the next cast strip To do. The incomplete material falls into a scrap box 33 located below the caster 11, where an apron 34, usually hanging from the pivot to one side of the caster exit, swivels across the swivel caster exit. Thus, the clean end of the cast strip is guided to the guide table 13 from where the strip is fed to the pinch roll stand 14. The apron 34 is then returned to the suspended position so that the strip 12 can loop in a loop down the caster, and then the strip reaches the guide table 13 and engages a series of guide rollers 36.

  The twin roll caster is of the type described and disclosed in some detail in permitted Australian Patents 631,728 and 633548 and US Pat. Nos. 5,184,668 and 5,277,243. Reference may be made to these patents for appropriate structural details that do not form part of the present invention.

  Between the casting roll and the pinch roll stand 14, the newly formed steel strip is within a first enclosure indicated generally at 37 that defines a sealing space or atmosphere 38 adjacent to the casting surface 22 A of the casting roll 22. Surrounded. A plurality of separate wall portions 41 form the first surrounding portion 37, and the wall portions are combined at various seal connecting portions to form a continuous surrounding wall. The surrounding portion 37 is formed in a twin roll casting machine to surround the casting roll, and the surrounding portion wall portion 42 extends below the wall portion 41 and engages with the upper end of the scrap box 33 in the operating position. Consists of. The scrap box and the surrounding wall portion 42 can be connected by a seal 43, and a ceramic fiber rope forming the seal is fitted into a groove at the upper end of the scrap box, and a flat sealing gasket 44 attached to the lower end of the surrounding wall portion 42; Engage. The scrap box 33 can be attached to a carriage 45 with wheels 46 running on rails 47 so that the scrap box can be moved to a scrap discharge position after the casting operation. The screw jack unit 40 can be operated so that the scrap box is pressed against the surrounding wall portion 42 by compressing the seal 43 by lifting the scrap box in the operating position from the carriage 45. After the casting operation, the scrap box can be lowered onto the carriage 45 by moving the jack unit 40 and moved to the scrap discharge position.

  The first surrounding portion 37 is further configured by a wall portion 48 that is disposed around the guide table 13 and connected to the frame 49 of the pinch roll stand 14. The pinch roll stand includes a pair of pinch rolls 50, and the surrounding portion 37 is sealed by a sliding seal 60 against them. Accordingly, the strip passes between the pair of pinch rolls 50 to exit the first surrounding portion 37, reaches the second surrounding portion generally indicated by 61, and enters the hot rolling mill 16 through the second surrounding portion. Most of the first enclosure wall can be lined with refractory brick and the scrap box 33 can be lined with refractory brick or castable refractory lining. Or you may form all or one part of a 1st surrounding part wall part with an internal water-cooled metal panel. A side plate 51 having a notch 52 is formed on the surrounding wall 41 surrounding the casting roll, and the notch receives the side plate holder 28A when the side dam plate 28 is pressed against the roll end by the cylinder unit 32. It has a shape. The interface between the side plate holder 28 </ b> A and the enclosure side wall 51 is sealed by the sliding seal 53 to maintain the seal of the first enclosure 37. The seal 53 can be formed of a ceramic fiber rope.

  The cylinder unit 32 extends outside through the surrounding portion 41, and a seal plate 54 that seals the first surrounding portion 37 at these positions is fitted into the cylinder unit, and the side plate is pressed against the roll end by the operation of the cylinder unit. The enclosure portion wall portion 41 is engaged with each other. The thruster 31 also moves the fireproof slide 55, which is moved by the operation of the cylinder unit 32 and closes the long hole 56 at the top of the first surrounding portion 37. The slot is for inserting a side plate for application to the roll, initially into the enclosure and into the holder 28A. When the side dam plate is applied to the roll by the operation of the cylinder unit, the top of the first surrounding portion 37 is closed by the tundish, the side plate holder 28 </ b> A and the slide 55. In this way, the entire enclosure 37 is sealed prior to the casting operation, establishing a sealed space 38 adjacent to the casting surface 22A of the casting roll 22.

  The second surrounding part 61 can be separated from the first surrounding part 37, in which case the strip can be held in a separate atmosphere of the second surrounding part 61 until reaching the hot rolling mill 16. The rolling mill 16 includes a series of pass line rollers 62 to guide the strip horizontally through the second enclosure 61 to a work roll 63 of the rolling mill 16 disposed between two large backup rollers 64. One end of the second surrounding portion 61 is sealed with respect to the pinch roll 50 by the sliding seal 65, and the other end is sealed with respect to the work roll 63 of the rolling mill 16 by the sliding seal 66. The sliding seals 65 and 66 can be replaced with running parts in the vicinity of the pinch roll and the reduction roll, that is, a rotary seal roll for the strip.

  A pair of water spray nozzles 67 and 68 that can be operated to spray fine water droplet mist adjacent to the surface of the steel strip passing through the second surrounding portion are attached to the second surrounding portion 61, respectively. Steam is generated in the second enclosure while trying to prevent contact with the steel strip. The spray nozzle 67 is attached to the roof of the surrounding portion 61 on the downstream side of the pinch roll stand 14. The nozzle 68 is disposed at the other end of the surrounding portion 61 in front of the rolling mill 16. The nozzles 67, 68 may be standard commercially available mist spray nozzles that can be operated with high pressure gas to produce fine water mist. In the method illustrated in the present invention, the high pressure gas may be an inert gas such as nitrogen. In a typical installation, the nozzle is operated with nitrogen at a pressure of about 400 kPa. Water is supplied at about 100-500 kPa, but the water pressure is not critical. The nozzle is set to produce a fine mist spray in the strip width direction, and generates steam in the second surrounding portion 61.

  In the operation of the illustrated casting machine, both the first surrounding portion 37 and the second surrounding portion 61 can be first purified with nitrogen gas before the start of casting. Since the water spray is activated before casting, as soon as the hot strip enters the second enclosure 61, steam is generated in the enclosure to create a positive pressure and prevent air from entering. The supply of nitrogen may be terminated after the start of casting. Initially, the cast strip absorbs all oxygen from the first enclosure 37 to form a thick scale on the strip. However, since the space 38 of the first surrounding portion 37 is sealed, the invasion of the atmosphere containing oxygen is controlled so that a considerable amount of oxygen is less than or equal to the amount absorbed by the steel strip. Thus, after the initial ramp-up period, the oxygen content in the first enclosure 37 is still exhausted, limiting the use of oxygen for strip oxidation. In this way, scale formation on the cast strip is controlled without having to maintain a nitrogen supply to the space 38 of the first enclosure 37.

As already described, the pinch roll 14 includes the sliding seals 60 and 65 and slides on the pinch roll 50 at the boundary between the first surrounding portion 38 and the second surrounding portion 61. While the pinch roll and seal are effective in preventing liquid water from flowing back from the second enclosure 61, the pinch roll stand 14 provides a passage for the gas to flow near both ends of the pinch roll 50, thereby allowing the gas to flow second. It can flow from the surrounding portion 61 to the first surrounding portion 37 . During the operation of this device, the interconnection between the two enclosures via this interconnecting passage is sufficient to increase the hydrogen level and thereby flow from the second enclosure 61 to the first enclosure 37. It turned out to be. This is shown by the following results obtained from the operation of the twin roll casting and rolling facility as shown in the drawing and the experiments with and without working fine mist water sprays 67,68. Gas sampling of the atmosphere in both the first enclosure 37 and the second enclosure 61 was performed at locations A, B, and C shown in FIG. 1, and the following gas analysis was reported in Table 1 below. . The gas residue of the analyzed atmosphere is nitrogen gas (N ₂ ).

  Although the hydrogen level in the 1st surrounding part 37 is lower than the hydrogen level in the 2nd surrounding part 61, it turns out that the operation | work of the fine mist water spray in the 2nd surrounding part 61 has increased considerably. An increase in the hydrogen level in both the first enclosure 37 and the second enclosure 61 is associated with a significant decrease in oxygen content and drastically reduces scale formation. Further, it can be seen that there is an increase in the humidity level in both the first and second enclosures, indicating that steam is being generated, and that both enclosures are under positive pressure due to the presence of steam. The increase in the hydrogen level can be explained by the fact that the water molecules of the fine mist catalyze to form hydrogen gas under the high temperature condition surrounding the steel strip in the second enclosure. Oxygen gas simultaneously formed from water molecules is absorbed by the oxidation of the strip when the strip first passes through the second enclosure, generating a significant amount of hydrogen gas. Subsequent oxidation of the strip is suppressed by the positive pressure in the second enclosure that limits the ingress of hydrogen gas and air, but maintains the hydrogen content in the second enclosure and creates a very thin scale layer on the strip. It has been found that this scale layer is desirable to prevent sticking in roll biting during hot rolling. Also, the very thin scale layer made in the extremely wet atmosphere in the second enclosure 61 provides a strong adhesive lubricant that minimizes roll friction and operational problems in the rolling mill. It has been found. At the same time, since the fine mist spray is converted into vapor in the second enclosure, it is easy to prevent liquid water from coming into contact with the steel strip, which is considerably reduced if not eliminated that the strip may be cooled unevenly. .

  FIG. 8 shows a modification of the casting / rolling equipment. Additional water spray nozzles 71 and 72 are provided to generate fine water mist spray in the first surrounding portion 37. Except for these additional spray nozzles, the installation shown in FIG. 8 is the same as already disclosed. Accordingly, the other parts of FIG. 8 are denoted by the same reference numerals as in FIG. Spray nozzles 71 and 72 are similar to nozzles 67 and 68 and operate in a similar manner and under the same conditions to adjoin the surface of strip 12 while attempting to prevent liquid water from contacting the strip. Fine water mist can be sprayed. Further, the spray nozzles 71, 72 are arranged on the outlet end side of the surrounding portion 37 to minimize the possibility that the liquid water comes into contact with the casting surface 22 </ b> A of the casting roll 22. In order to further suppress this risk, a curtain gate seal may be installed at a position indicated by 73 between the spray nozzles 71 and 72 and the casting roll.

  The operation of increasing the hydrogen gas level in the first surrounding portion 37 can be achieved by fine mist spraying from the nozzles 71 and 72 without the operation of the nozzles 67 and 68 in the second surrounding portion 61, and the second surrounding portion. The fact that it can be achieved without 61 is also shown in FIG.

1 is a vertical cross-sectional view of a steel strip casting and rolling facility constructed and operated in accordance with the present invention. The main part of the twin roll casting machine incorporated in the facility and including the first high temperature strip enclosure is shown. It is a vertical sectional view of a twin roll casting machine. It is sectional drawing of the edge part of a casting machine. FIG. 5 is a sectional view taken along line 5-5 of FIG. FIG. 6 is a sectional view taken along line 6-6 of FIG. It is sectional drawing of the installation downstream of a casting machine containing a 2nd strip surrounding part and an in-line rolling mill. Figure 5 is a modified embodiment incorporating an additional water mist sprayer.

Claims (2)

(a) forming a molten steel casting pool on the cooling casting surface of a pair of horizontally arranged casting rolls forming a roll gap between them ;
(b) mutually rotating the casting rolls to produce a casting strip downward from the roll gap ,
(c) atmospheric is sealed so as to prevent entry of feeding a strip surrounding portion that extends to the roll gap directly from the nip, the transfer path away from the nip through the enclosure street strip,
; (d) surrounded by increasing the hydrogen gas levels within enclosure by introducing water in the form of a fine mist to the portion, together with the strip exiting the nip is to be exposed to the hydrogen gas, liquid water Steel Prevent contact with the casting surface of the strip and casting roll
A steel strip casting method comprising: (a) a pair of substantially horizontal casting rolls forming a roll gap between them;
(b) a metal feeding system that feeds molten steel above the roll gap between the casting rolls to form a casting pool of molten steel supported on the casting roll;
(c) a cooling system for cooling the inside of the casting roll;
(d) a drive system for mutually rotating the casting rolls in opposite directions;
(e) producing a cast strip fed downward from the roll gap, the casting roll having a cooled casting surface;
(f) Sealing so that the atmosphere does not enter, and being arranged so as to extend to the roll gap between the casting rolls, directly receiving the casting strip that exits the roll gap, and the surrounding portion through which the strip passes through the transfer path away from the roll gap;
(g) at least operable to prevent liquid water from contacting the steel strip and the casting surface of the casting roll while spraying water on the enclosure in the form of fine mist to increase the hydrogen gas level in the enclosure; Steel strip casting equipment consisting of one water sprayer.

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