Method for improving surface quality of rolled strip

Abstract

The invention belongs to the technical field of double-roller cast rolling, and relates to a method for improving the surface quality of a rolled strip. By means of the method, when the surface quality of the rolled belt goes wrong, online working roller replacement can be achieved. According to the method disclosed by the invention, the replacement of the working roll comprises the steps of synchronously lifting the tundish and the transition ladle, and conveying the drainage groove to the lower part of the distributed liquid outlet hole of the transition ladle through the slide rail or the guide rail so as to carry out molten steel drainage. And at the moment, under the condition that the ladle big ladle sliding plate and the tundish sliding plate are not closed and the transition ladle is not cut off, replacement of the working roller with the surface quality problem can be completed, and the surface quality of the rolled strip is improved. And after replacement, the tundish and transition ladle system is recovered to the casting working position for continuous casting, and normal rolling production is recovered in a shorter time. According to the method, the problems of low production efficiency and high cost caused by pouring stopping are solved, the production continuity is improved, and the overall production cost of double-roller cast rolling is reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of double-roller casting, and relates to a method for improving the surface quality of a cast strip. More particularly, the present application relates to an efficient production method and device for improving the surface quality of a cast strip in double-roller casting, which is suitable for efficient and low-cost production of hot-rolled steel strips of ultra-thin specifications. BACKGROUND

[0002] Double-roller casting process is a metallurgical frontier technology with the most development potential in today's steel industry. Compared with traditional continuous casting and hot-rolling processes, double-roller casting has the advantages of short production flow, few processes, low energy consumption, and green environmental protection. At present, the double-roller casting process for commercial production is to distribute molten steel through a core nozzle to a molten pool composed of a pair of counter-rotating casting rolls and a pair of side sealing plates, and directly produce a 1.7-2.5 mm strip after double-roller casting, and then roll the strip into a target thickness strip product through a single-pass rolling mill. Carbon steel, weather-resistant steel, stainless steel and other products can be produced, and the production line only has a single-pass rolling mill, and the thinnest rolling thickness is 0.6 mm.

[0003] In actual production, the cast strip comes down from the casting roll, passes through the hot box protected by inert atmosphere, and enters the rolling mill for rolling. The temperature of the cast strip is relatively high, and the rolling mill is always working under high temperature and high load, which seriously affects the service life of the rolling mill. With the pouring process, the product is prone to have quality problems such as roll marks and roughness exceeding the standard. These problems are mainly caused by the rolling mill. When the first roll mark roll or the roughness exceeds the standard roll appears, if the production continues, all the subsequent rolls will have roll marks or roughness exceeding the standard, and the produced products are unqualified products.

[0004] Therefore, when such problems occur in production, the only way to solve them is to stop pouring and start a new pouring process. Frequent pouring and stopping seriously restricts the pouring cost of double-roller casting.

[0005] Chinese patent document 201910130257.1 discloses a rolling method for improving the surface quality of a cast strip in double-roller casting. Two-pass rolling mills are installed on the double-roller casting production line. When surface problems occur in the rolling of one of the rolling mills, the other rolling mill is used instead, and the rolling mill with problems is replaced with a new rolling mill online to improve the production continuity and the product surface quality. The above-mentioned method increases the number of rolling mills and the number of rolling passes on the basis of the existing production line design, and is currently still in the theoretical research stage. This method increases the length of the production line, and there is a high risk of safety accidents when replacing the work roll under the condition that the strip is passing at high speed on the production line.

[0006] In view of the above background art, the present application aims to solve the problem that, when the surface quality of the strip cast by the existing double-roller casting is reduced due to the roller factor, the production continuity is poor because the casting is stopped and the work roller of the roller is replaced. The present application proposes a technical solution of on-line roller replacement to solve such surface quality problems, thereby realizing efficient rolling production. SUMMARY

[0007] In view of the deficiencies of the prior art, the present application aims to provide an efficient production method and device for improving the surface quality of the strip cast by the double-roller casting.

[0008] The present application overcomes the problem that, when the surface quality of the strip cast by the existing double-roller casting is reduced due to the roller factor, the corresponding surface quality problem can only be solved by replacing the hot-rolling work roller after stopping the casting.

[0009] The method of the present application, without increasing the number of rolling mills in the production line, under the condition that the single-pass hot-rolling work roller needs to be replaced, opens the molten steel flow guide groove to below the flow distribution water outlet of the transition package, catches the molten steel flowing down from the transition package and guides it to the accident package, and replaces the hot-rolling work roller on-line while keeping the tundish and the transition package continuously flowing.

[0010] After the replacement of the work roller is completed, the molten steel flow guide groove is removed, the molten steel is distributed to the core water outlet through the flow distribution water outlet of the transition package, and is distributed to each direction of the molten pool from the core water outlet, so as to form a stable molten pool for continuous casting, and to realize stable rolling of the strip steel quickly, thereby improving the production continuity, fully utilizing the single tundish and the transition package and other consumable parts, and reducing the production cost.

[0011] According to an aspect of the present application, a method for improving the surface quality of the strip is provided, which comprises the following steps:

[0012] (1) Molten steel is smelted by a converter or an electric furnace and a refining furnace, and is distributed to a molten pool through a tundish and a transition package to form a cast strip with a thickness of 1.7-2.5 mm, wherein the molten pool is composed of a pair of counter-rotating water-cooled copper casting rollers and a pair of side sealing plates;

[0013] (2) The cast strip is hot-rolled in one pass to form a rolled strip with a thickness of ≤1.65 mm; wherein: a) if the roller marks on the rolled strip cannot be eliminated, the work roller of the roller is replaced on-line; or b) if the roughness of the rolled strip exceeds the threshold value, the work roller of the roller is replaced on-line;

[0014] (3) Before replacing the work roller of the roller, the drawing speed is reduced to 10-35 m / min, and the liquid level of the tundish is adjusted to 400-600 mm;

[0015] (4) before the working roll of the rolling mill is replaced, the ladle, the tundish and the transition ladle are synchronously lifted, the lifting speed is controlled to be 3-15 mm / s, and the lifting height is controlled to be 200-400 mm;

[0016] (5) the drainage groove is sent into the distributed liquid outlet of the transition ladle to drain the liquid steel, and the sending speed is controlled to be 1-3 m / min;

[0017] (6) after the liquid is drained, the working roll of the rolling mill is replaced on line;

[0018] (7) the drainage groove is removed, and the removing speed is controlled to be 0.5-3 m / min;

[0019] (8) the ladle, the tundish and the transition ladle system are restored to the casting working position, and the drawing speed is increased to 40-80 m / min.

[0020] According to the method for improving the strip surface quality, preferably, in step (3), the drawing speed is reduced to 10-30 m / min, and the liquid level of the tundish is adjusted to 400-500 mm.

[0021] According to the method for improving the strip surface quality, preferably, in step (4), the lifting speed is controlled to be 3-8 mm / s, and the lifting height is controlled to be 200-300 mm.

[0022] According to the method for improving the strip surface quality, preferably, in step (5), the sending speed of the drainage groove is controlled to be 1-3 m / min.

[0023] According to the method for improving the strip surface quality, preferably, in step (5), the sending speed of the drainage groove is controlled to be 2-3 m / min.

[0024] According to the method for improving the strip surface quality, preferably, in step (7), the removing speed of the drainage groove is controlled to be 0.5-2 m / min.

[0025] According to the method for improving the strip surface quality, preferably, in step (7), 0-15 s after the removing of the drainage groove is started, the removing speed is controlled to be 0.5 m / min.

[0026] According to the method for improving the strip surface quality, preferably, in step (7), 15 s after the removing of the drainage groove is started, the removing speed is controlled to be 1-2 m / min.

[0027] According to the method for improving the strip surface quality, preferably, the outside of the drainage groove is a steel structure, and the inside of the drainage groove comprises a refractory material.

[0028] According to the method for improving the surface quality of the strip according to the present application, preferably, the refractory material is laid with a slope of 5-15° inside the flow guide groove.

[0029] Advantages of the present application:

[0030] 1. By the method of the present application, when facing the surface quality defects of the strip, the production stoppage caused by the necessity of closing the tundish slide gate during the replacement of the hot rolling work roll can be avoided.

[0031] 2. By the method of the present application, when facing the surface quality defects of the strip, the work roll can be replaced without stopping the continuous flow of the transition ladle, and even other abnormalities in the casting and rolling area can be handled, so as to improve the continuity of production.

[0032] 3. The method of the present application is reliable and easy to operate and realize, and compared with the existing methods for replacing the work roll on line or under development or research, the safety of the method of the present application is higher.

[0033] 4. The method of the present application saves the time and cost of stopping production to replace the tundish, the transition ladle and the accessories, fully utilizes the service life of the refractory material, and reduces the production cost.

[0034] 5. By the method of the present application, the surface quality of the strip can be ensured by replacing the work roll on line. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings described in the following description only relate to some embodiments of the present application, and are not a limitation on the present application.

[0036] Figure 1 The schematic diagram of the device for improving the surface quality of the strip according to the embodiment of the present application.

[0037] Figure 2 The schematic diagram of the transition ladle of the casting system according to the embodiment of the present application;

[0038] Figure 3 The schematic diagram of the flow guide groove according to the embodiment of the present application.

[0039] Figure 4 The schematic diagram of the improved surface quality of the strip according to the embodiment 1 of the present application.

[0040] Figure 5 The schematic diagram of the surface quality of the strip according to the comparative example. DETAILED DESCRIPTION

[0041] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the described embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without any creative effort belong to the protection scope of the present application.

[0042] Unless otherwise defined, the technical terms or scientific terms used in the present application shall have the meanings commonly understood by those of ordinary skill in the art to which the present application belongs.

[0043] Now referring to Figures 1-3 , a schematic diagram of the device used in the method for improving the surface quality of a strip according to the present application is shown. The figure shows a ladle 1, a ladle (tundish) slide plate 2, a long nozzle 3, a tundish 4, a tundish slide plate 5, a tundish nozzle 6, a transition ladle 7, a casting roll 8, a side sealing plate 9, a core nozzle 10, a molten pool 11, a strip 12, a rolling mill 13, a working roll 14, a flow guide groove 15, a slide rail (guide rail) 16.

[0044] As shown in Figure 2 , the transition ladle 7 according to the embodiments of the present application is sequentially provided with a transition ladle inlet 17 and a distributed liquid outlet hole 18.

[0045] As shown in Figure 3 , the flow guide groove 15 according to the embodiments of the present application is provided with refractory material, one end is blocked, one end is open, and the inside is laid with a slope.

[0046] Referring to Figure 1 , in the specific implementation process of the present application, the existing normal casting and rolling and off-line replacement of the working roll under normal circumstances include the following steps:

[0047] S1, normal casting process: the qualified molten steel is contained in the ladle 1 after being refined by the preliminary refining furnace and the refining furnace, the molten steel enters the transition ladle 7 through the long nozzle 3, the tundish 4 and the tundish nozzle 6, and is distributed by the distributed liquid outlet hole 18.

[0048] The molten steel is distributed to the molten pool 11 formed by a pair of counter-rotating casting rolls 8 and a pair of side sealing plates 9 through the distributed liquid outlet hole 18, and a stable molten pool liquid level is controlled and established by controlling the drawing speed and matching the opening degree of the tundish slide plate 5.

[0049] After the stable molten pool liquid level is established, the molten steel in the molten pool 11 is in rotational contact with the surface of the casting roll 8 and cools and solidifies on the surface of the casting roll 8 to form a metal shell, which is brought together at the roll gap between the two casting rolls 8 to form a strip 12 with a thickness of 1.5-2.5 mm, and the strip 12 is rolled into a target product through a pass rolling mill 13.

[0050] S2, stop pouring: under the prior art conditions, after the surface quality of the rolled product appears, the work roll needs to be replaced, and the production line is forced to stop pouring. The stop pouring operation steps include closing the ladle slide plate 2, continuing to pour the molten steel in the tundish 4, waiting for the tundish liquid level to drop to 200-300 mm to close the tundish slide plate 5, continuing to pour for 1-2 min, and executing the double-roll caster stop program to complete the stop pouring operation after the molten steel in the transition ladle 7 and the molten pool 11 is poured.

[0051] S3, replace the work roll: after the above steps are completed, a new pouring is prepared, at this time the work roll 14 on the production line needs to be pushed out of the rolling mill 13, and the new work roll 14 is hoisted and pushed into the rolling mill to complete the work roll replacement operation.

[0052] In addition, the preparation of a new pouring includes the replacement of the tundish 4, the transition ladle 7, the side sealing plate 9, the core nozzle 10, and the accessories, but the service life of the above-mentioned accessories is not fully utilized.

[0053] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined purpose of the application, the following detailed description of the specific embodiments and technical effects according to the present application is as follows.

[0054] Example 1

[0055] (1) The molten carbon steel qualified by the preliminary refining furnace and the refining furnace is cast into a cast strip by a pair of counter-rotating casting rolls, and after the start of pouring, the progressive casting is carried out to form a 1.95 mm thick cast strip at a drawing speed of 50-53 m / min.

[0056] (2) The 1.95 mm thick cast strip poured is rolled into a 1.5 mm thick rolled strip by one pass hot rolling, and then four heats are continuously poured.

[0057] (3) The work roll works for a long time under high temperature environment and high load, the surface quality of the work roll deteriorates, the rolled strip appears roll marks, and the work roll needs to be replaced or the production is forced to stop.

[0058] (4) The on-line work roll replacement operation is performed, the drawing speed is reduced to 25±0.5 m / min, the tundish and the transition ladle are lifted, the drainage groove is pushed in, the roller way is emptied, the time and space for on-line work roll replacement are created, the work roll to be replaced is pushed out and pushed in, and the on-line work roll replacement is completed.

[0059] (5) The drainage groove is removed, the front 15s is withdrawn at a speed of 0.5 m / min, the subsequent is withdrawn at a speed of 1-2 m / min, the tundish and the transition ladle are lowered to the pouring position, and the normal pouring is restored. After pouring 7 tons of molten steel, the progressive rolling is carried out to form a 1.5 mm thick rolled strip.

[0060] (6) The surface quality of the rolled strip is checked, and the surface quality is good. The specific surface quality is shown in Table 1. Figure 4

[0061] This embodiment 1 completes 6 continuous casting.

[0062] Embodiment 2

[0063] (1) The molten weathering steel qualified by the preliminary refining furnace and the refining furnace is cast and rolled into a cast strip by a pair of counter-rotating casting rolls. After starting casting, the cast strip is gradually cast and rolled into a 1.85 mm thick cast strip at a casting speed of 55-58 m / min.

[0064] (2) The 1.85 mm thick cast strip cast is hot rolled into a 1.35 mm thick rolled strip by one pass, and then 3 furnaces are continuously cast.

[0065] (3) The work roll works for a long time under high load in a high temperature environment, the surface quality of the work roll deteriorates, the roughness of the rolled strip exceeds the standard, and the work roll needs to be replaced or production is forced to stop.

[0066] (4) The online work roll replacement operation is performed, the casting speed is reduced to 25±0.5 m / min, the tundish and the transition ladle are lifted, the flow guide groove is pushed, the roller is emptied, the time and space for online work roll replacement are created, the work roll to be replaced is pushed out and pushed in, and the online work roll replacement is completed.

[0067] (5) The flow guide groove is removed, the front 15s is withdrawn at a speed of 0.5 m / min, the subsequent is withdrawn at a speed of 1-2 m / min, the tundish and the transition ladle are lowered to the casting position, the normal casting is restored, and the 10 tons of molten steel is gradually rolled into a 1.35 mm thick rolled strip.

[0068] (6) The surface quality of the rolled strip is checked, and the surface roughness of the rolled strip meets the standard requirements.

[0069] This embodiment 2 completes 5 continuous casting.

[0070] Embodiment 3

[0071] (1) The molten carbon steel qualified by the preliminary refining furnace and the refining furnace is cast and rolled into a cast strip by a pair of counter-rotating casting rolls. After starting casting, the cast strip is gradually cast and rolled into a 1.75-1.70 mm thick cast strip at a casting speed of 62-65 m / min.

[0072] (2) The 1.75-1.70 mm thick cast strip cast is hot rolled into a 0.8 mm thick rolled strip by one pass, and then 2.5 furnaces are continuously cast.

[0073] (3) The work roll works for a long time under high load in a high temperature environment, the surface quality of the work roll deteriorates, the rolled strip appears indentation, and the work roll needs to be replaced or production is forced to stop. ​

[0074] (4) Perform the online work roll replacement operation, reduce the pulling speed to 25±0.5 m / min, lift the tundish and the transition ladle, push the flow guide groove, empty the roller way, create time and space for the online work roll replacement, push out and push in the work roll to be replaced, and complete the online work roll replacement.

[0075] (5) Remove the flow guide groove, remove it at a speed of 0.5 m / min for the first 15 s, and then remove it at a speed of 1-2 m / min, lower the tundish and the transition ladle to the casting position, restore normal casting, and gradually roll into 0.8 mm strips after 20 tons of molten steel are cast.

[0076] (6) The surface quality of the strip is checked, and the surface quality of the strip is good.

[0077] Five heats of continuous casting are completed in this example 3.

[0078] Comparative example

[0079] (1) The carbon steel molten steel qualified after smelting in the preliminary smelting furnace and the refining furnace is cast and rolled into a cast strip by a pair of counter-rotating casting rolls, and after the start of casting, it is gradually cast and rolled into a 1.90 mm thick cast strip at a pulling speed of 55-57 m / min.

[0080] (2) The 1.90 mm thick cast strip is rolled into a 1.5 mm thick strip after one pass hot rolling, and then three heats of continuous casting are performed.

[0081] (3) After the fourth heat of mixed casting, the surface quality of the work roll is poor, and the strip has roll marks, as shown in Figure 5 , and the work roll has to be replaced.

[0082] (4) To maintain production continuity, continue to cast the cast strip, and return to thick production of non-order products.

[0083] (5) The entire casting casts 4 heats, of which 45 tons of steel coils have roll mark problems.

[0084] The following conclusions are obtained through the implementation of the examples and the comparative example:

[0085] Compared with the prior art, the method of the present application can improve the production continuity and the amount of molten steel per casting, thereby avoiding the situation that the intermediate ladle 4 and the transition ladle 7 and other original parts cannot be continuously used after the existing work roll replacement after casting is stopped, thereby increasing the utilization space of the entire intermediate ladle 4 and the transition ladle 7 refractory, improving the production continuity, reducing the production cost, and improving the output rate and production efficiency of the qualified strip coil.

[0086] The above merely describes the specific embodiments of the present application, and it should be pointed out that, for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the scope of the present application.

Claims

1. A method for improving the surface quality of rolled strip, characterized in that, The method includes the following steps: (1) The molten steel is smelted in a converter or electric furnace or refining furnace and then distributed to the molten pool through the tundish or transition ladle to form a casting strip with a thickness of 1.7~2.5mm. The molten pool consists of a pair of counter-rotating water-cooled copper casting rolls and a pair of side sealing plates. (2) The cast strip is hot rolled in one pass to form a strip with a thickness of ≤1.65mm; in: a) If indelible roll marks appear on the strip, replace the mill work rolls online; or b) If the roughness of the strip exceeds the threshold, replace the mill work rolls online; (3) Before replacing the mill work rolls, reduce the pulling speed to 10~35m / min and adjust the liquid level in the tundish to 400~600mm; (4) Before replacing the working rolls of the rolling mill, the ladle, tundish and transition ladle are raised synchronously. The raising speed is controlled at 3~15mm / s and the raising height is controlled at 200~400mm. (5) The molten steel is guided into the distributed outlet hole of the transition ladle by the slide rail or guide rail, and the feeding speed is controlled to be 1~3m / min; (6) After diversion, the mill work rolls are replaced online; (7) Remove the diversion channel, and control the removal speed to 0.5~3m / min; (8) Restore the ladle, tundish and transition ladle system to the casting position and increase the casting speed to 40~80m / min.

2. The method for improving the surface quality of rolled strip according to claim 1, characterized in that: In step (3), the pulling speed is reduced to 10~30m / min and the liquid level in the intermediate jar is adjusted to 400~500mm.

3. The method for improving the surface quality of rolled strip according to claim 1, characterized in that: In step (4), the lifting speed is controlled at 3~8mm / s and the lifting height is controlled at 200~300mm.

4. The method for improving the surface quality of rolled strip according to claim 1, characterized in that: In step (5), the feeding speed of the diversion channel is controlled to be 1~2m / min.

5. The method for improving the surface quality of rolled strip according to claim 1, characterized in that: In step (5), the feeding speed of the diversion channel is controlled to be 2~3m / min.

6. The method for improving the surface quality of rolled strip according to claim 1, characterized in that: In step (7), the withdrawal speed of the drainage channel is controlled to be 0.5~2m / min.

7. The method for improving the surface quality of rolled strip according to claim 6, characterized in that: In step (7), the withdrawal speed is controlled at 0.5 m / min for 0-15 seconds after the withdrawal of the drainage channel is started.

8. The method for improving the surface quality of rolled strip according to claim 7, characterized in that: In step (7), 15 seconds after the withdrawal of the drainage channel is started, the withdrawal speed is controlled to be 1~2m / min.

9. The method for improving the surface quality of rolled strip according to any one of claims 1 to 8, characterized in that: The exterior of the diversion channel is made of steel, and the interior of the diversion channel includes refractory material.

10. The method for improving the surface quality of rolled strip according to claim 9, characterized in that: Inside the drainage channel, the refractory material is laid at a slope of 5 to 15 degrees.

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