A billet near-final shape continuous casting and rolling system and process

Abstract

The present invention discloses a near-net-shape continuous casting and rolling system and process for square billets, comprising a ladle, a tundish, a crystallizer, a secondary cooling zone, a straightening machine, a heat preservation cover for a cutting zone, a mechanical cutter, a conveying roller, a heat preservation cover for a conveying roller, an electromagnetic induction heating device and a rolling mill group connected in sequence, wherein a heavy pressure down and side pressure device for a continuous casting machine is added to the straightening machine, and an electromagnetic induction heating device is arranged in the heat preservation cover for the conveying roller, which can even out the temperature of the surface and core of the cast billet, and supplement heat when the temperature is insufficient. The present invention organically compresses and combines the steel mill and the rolling mill in the past, shortens the production cycle, reduces energy consumption, and thus greatly improves economic benefits.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a near-final shape continuous casting and rolling system and process for square billets. Background Art

[0002] Continuous casting technology is an advanced steel production process that directly casts molten steel into billets through a continuous casting machine, thereby replacing mold casting and initial rolling. Countries around the world use the continuous casting ratio (the proportion of continuous casting output to total steel output) to measure the degree of optimization of the steel industry production structure and the level of technology. The benefits of continuous casting are energy saving and increased metal recovery.

[0003] According to the original continuous casting and rolling process, the high-temperature ingot pulled out from the continuous casting machine is cut into fixed lengths and then cooled by water spray or stacked in the workshop to room temperature, and then quality inspection or surface finishing is carried out, and then it is sent to the heating furnace of the rolling mill to be reheated to the rolling temperature. After the ingot is cut into fixed lengths, the surface temperature of the ingot is generally 800-900℃, and about 540kJ / kg of physical heat is wasted during cooling.

[0004] Therefore, in order to help steel companies create economic and environmental benefits while meeting the requirements of carbon emission reduction, it is necessary and urgent to select appropriate processing technology and utilization methods for continuous casting and rolling. Summary of the invention

[0005] In order to overcome the above technical problems, the purpose of the present invention is to provide a near-net-shape continuous casting and rolling system and process for square billets, which organically compresses and combines the previous steelmaking mills and rolling mills, shortens the production cycle, reduces energy consumption, and thus greatly improves economic benefits.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A near-net-shape continuous casting and rolling system for square billets comprises a ladle 1, a tundish 2, a crystallizer 3, a secondary cooling zone 4, a straightening machine 6, a cutting zone insulation cover 7, a mechanical cutter 8, a transport roller 9, a transport roller insulation cover 10, an electromagnetic induction heating device 11 and a rolling mill group 12 which are connected in sequence. A continuous casting machine weight pressure and side pressure equipment are added at the straightening machine 6. The transport roller insulation cover 10 is provided with an electromagnetic induction heating device 11, which can make the surface and core temperature of the ingot 5 uniform and supplement heat when the temperature is insufficient.

[0008] The interior of the casting billet 5 is a liquid core structure, the outer side of the liquid core structure is a billet shell, and the four corners of the billet shell are the corners of the casting billet.

[0009] A preparation process of a billet near-final shape continuous casting and rolling system comprises the following steps;

[0010] 1) Rotate the ladle 1 to the casting position to perform the casting operation;

[0011] 2) The molten steel flowing out of the tundish 2 enters the crystallizer 3 for forced cooling and forming, and after forming a shell of a certain thickness, it is pulled downward by the dummy rod to form a cast billet 5;

[0012] 3) After being cooled in the secondary cooling zone 4, the ingot 5 is straightened and compressed by the puller 6 to increase the speed to match the rolling speed;

[0013] 4) The straightened ingot 5 is cut into fixed lengths by a mechanical cutting machine 8 and then transported to a rolling mill 12 by a transport roller 9 for continuous rolling and forming. During the transportation process, the ingot is evenly heated and supplemented by an electromagnetic induction heating device 11.

[0014] The first cooling section of the secondary cooling zone 4 adopts a water nozzle with a specific water volume of 1.7 to 2.1 L / kg, which can quickly thicken the billet shell and prevent steel leakage. The subsequent cooling sections until the straightening machine 6 adopt air-water spray with a specific water volume of 0.9 to 1.1 L / kg, which can make the surface temperature of the billet 5 uniform. After the straightening machine 6, the conveying roller 9 is cooled by an air-water nozzle with a specific water volume of 0.9 to 1.1 L / kg. At the same time, by controlling the ratio of the specific water volume in the middle and both sides of the surface of the billet 5 to 1.1 to 1.5:1, the shape of the liquid core can be a so-called "glasses shape" with large sides and a small middle. In this way, when the billet 5 is completely solidified, the solidification latent heat released by the liquid on both sides of the billet 5 is large, which is beneficial to the reheating of the edges of the billet 5, which not only increases the temperature of the square billet, but also makes its temperature more uniform.

[0015] The corners of the ingot 5 are rounded or chamfered to change the heat exchange state of the ingot corners, increase the temperature of the ingot corners, and reduce the temperature difference between the ingot corners and the center of the surface. The radius of the rounded corners is 10% to 15% of the ingot section.

[0016] The ingot 5 pulled out of the crystallizer 3 is pressed down by heavy pressure and squeezed by additional side rolls during the straightening process, so that the cross-section of the ingot 5 is reduced to 70-90 mm.

[0017] Beneficial effects of the present invention:

[0018] The hot charging of the ingot into the furnace shortens the distance between continuous casting and steel rolling, fully utilizes the physical heat of the ingot, reduces the heat loss in the process, and reduces the energy consumption of the steel rolling process;

[0019] Due to the elimination of flame cutting and heating furnace devices, the yield rate can be increased by 0.5% to 1.5%;

[0020] The traditional continuous casting billet cold loading furnace process has a production cycle of about 30 hours from steelmaking to steel rolling, while the continuous casting and rolling process provided by the present invention shortens the process to about 2 hours, greatly shortening the production cycle and reducing time cost;

[0021] Since near-net-shape continuous casting and rolling must use defect-free ingots, and the hot-charged ingots are squeezed and compressed during the straightening process, with less iron oxide scale, the surface quality of the steel is better than that of products produced by conventional processes, and the product quality is improved;

[0022] The near-net-shape continuous casting and rolling technology of the present invention reduces the CO2 emission of 100kg per ton of steel by shortening the steel manufacturing process. For continuous casting and rolling in steel plants, it not only saves the energy consumption of heating the cast billet, but also reduces the rolling force of the rolling mill;

[0023] The present invention only transforms the straightening area, and the crystallizer copper tube, crystallizer vibration device and secondary cooling system remain in their original state, with low investment and quick effect.

[0024] The present invention eliminates the processes of billet finishing in the traditional process, reduces the plant area for billet inventory, greatly reduces the plant construction cost and production cost, and also saves labor and reduces production cost.

[0025] The present invention is also applicable to the production requirements of similar enterprises, has obvious economic and environmental benefits, and has high practical value and promotion significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the near-final shape continuous casting and rolling system for square billets provided by the present invention.

[0027] Figure 2 This is a schematic diagram of the cross-section of the ingot at the crystallizer outlet.

[0028] Figure numerals: 1- ladle, 2- tundish, 3- crystallizer, 4- secondary cooling zone, 5- ingot, 6- straightening machine, 7- insulation cover of cutting zone, 8- mechanical cutting machine, 9- transport roller, 10- insulation cover of transport roller, 11- soaking furnace, 12- rolling mill group. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below in conjunction with embodiments.

[0030] Embodiment 1:

[0031] like Figure 1 As shown, a near-net-shape continuous casting and rolling system for square billets provided by the present invention comprises a ladle 1, a tundish 2, a crystallizer 3, a secondary cooling zone 4, a straightening machine 6, a cutting zone insulation cover 7, a mechanical cutting machine 8, a transport roller 9, a transport roller insulation cover 10, an electromagnetic induction heating device 11 and a rolling mill group 12 which are arranged in sequence, and a heavy pressure down and side pressure device for the continuous casting machine is added, and the flame cutting machine equipped on the conventional continuous casting machine and the heating furnace and rough rolling mill and other equipment equipped on the rolling mill are cancelled.

[0032] This embodiment is used to produce small square billets with a cross section of 90mm*90mm. The basic process flow includes:

[0033] 1) Rotate the ladle 1 to the casting position to perform the casting operation;

[0034] 2) The molten steel flowing out of the tundish 2 enters the crystallizer 3 for forced cooling and forming, and after forming a shell of a certain thickness, it is pulled downward by the dummy rod to form a cast billet 5;

[0035] 3) After being cooled in the secondary cooling zone 4, the ingot 5 is straightened and compressed by the puller 6 to increase the speed to match the rolling speed;

[0036] 4) The straightened ingot 5 is cut into fixed lengths by a mechanical cutting machine 8 and then transported to a rolling mill 12 by a transport roller 9 for continuous rolling and forming. During the transportation process, the ingot is evenly heated and supplemented by an electromagnetic induction heating device 11.

[0037] In the first cooling section at the bottom of the crystallizer 3, a water nozzle is used with a specific water volume of 1.86L / kg, which can quickly thicken the billet shell and prevent steel leakage. In the subsequent cooling sections until the straightening machine, air-water spray is used with a specific water volume of 1.04L / kg, which can make the surface temperature of the billet 5 uniform. After the straightening machine, the billet 5 is cooled by cooling the clamping rollers with a specific water volume of 1.04L / kg. At the same time, by controlling the specific water volume ratio between the middle and both sides of the billet 5 to be 1.25:1, the shape of the liquid phase hole can be so-called "glasses-shaped" with large sides and small middle. In this way, when the billet 5 is completely solidified, the solidification latent heat released by the liquid on both sides of the billet 5 is large, which is beneficial to the reheating of the edges of the billet, which not only increases the temperature of the billet, but also makes its temperature more uniform.

[0038] The corners of the ingot are rounded, and the radius of the rounded corners is 12% of the ingot section, which can change the heat exchange state of the ingot corners, increase the temperature of the ingot corners, and reduce the temperature difference between the ingot corners and the center of the surface.

[0039] Embodiment 2:

[0040] This embodiment is used to produce small square billets with a cross section of 250mm*250mm. The basic process flow includes:

[0041] 1 Rotate the ladle 1 to the casting position to perform the casting operation;

[0042] The molten steel flowing out of the tundish 2 enters the crystallizer 3 for forced cooling and forming, and after forming a shell of a certain thickness, it is pulled downward by the dummy rod to form a cast billet 5;

[0043] 3 After the ingot 5 is cooled in the secondary cooling zone 4, it is straightened and compressed by the puller 6 to increase the speed to match the rolling speed;

[0044] The straightened ingot 5 is cut into fixed lengths by a mechanical cutter 8 and then transported to a rolling mill 12 by a transport roller 9 for continuous rolling and forming. During the transportation process, the ingot is evenly heated and supplemented by an electromagnetic induction heating device 11.

[0045] In the first cooling section at the bottom of the crystallizer 3, a water nozzle is used with a specific water volume of 2.05L / kg, which can quickly thicken the billet shell and prevent steel leakage. In the subsequent cooling sections until the straightening machine, air-water spray is used with a specific water volume of 1.08L / kg, which can make the surface temperature of the billet 5 uniform. After the straightening machine 6, the billet 5 is cooled by cooling the clamping rollers with a specific water volume of 1.08L / kg. At the same time, by controlling the ratio of the specific water volume in the middle and both sides of the billet 5 to 1.4:1, the shape of the liquid phase hole can be so-called "glasses-shaped" with large sides and small middle. In this way, when the billet 5 is completely solidified, the solidification latent heat released by the liquid on both sides of the billet 5 is large, which is beneficial to the reheating of the edges of the billet, which not only increases the temperature of the billet, but also makes its temperature more uniform.

[0046] The corners of the ingot are rounded or chamfered, and the radius of the rounded corner is 15% of the ingot section, which can change the heat exchange state of the ingot corner, increase the temperature of the ingot corner, and reduce the temperature difference between the ingot corner and the surface center.

[0047] The near-net-shape continuous casting and rolling system and technology provided by the present invention organically compresses and combines the previous steelmaking plants and rolling mills, shortens the production cycle, reduces energy consumption, and thus greatly improves economic and environmental benefits, and has high practical value and promotion significance.

[0048] The present invention modifies the finite element mathematical and physical model by measuring the actual temperature of the ingot produced in the high-speed continuous casting industrial test. The influence of the drawing speed control, pouring superheat control, secondary water distribution, cross-sectional shape, straightening position determination, ingot cutting method, etc. on the ingot constant temperature billet discharge process is studied to optimize the high-speed continuous casting constant temperature billet discharge process. In order to discharge the billet at a constant temperature during high-speed continuous casting, the continuous casting billet is slowly cooled. In order to implement near-net shape continuous casting and rolling, the key technical problems solved by the present invention are:

[0049] Secondary cooling zone 4 compound cooling system

[0050] During the continuous casting process, a water nozzle is used in the first cooling section at the bottom of the crystallizer with a water content of 1.7 to 2.1 L / kg, which can quickly thicken the billet shell and prevent steel leakage. In the subsequent cooling sections until the straightening machine 6, air-water spray is used with a water content of 0.9 to 1.1 L / kg, which can make the surface temperature of the billet 5 uniform. After the straightening machine 6, the cooling rollers are cooled with the help of air-water nozzles with a water content of 0.9 to 1.1 L / kg. In this way, the temperature of the billet after shearing can reach 1000°C.

[0051] Controlling the shape of the liquid phase hole at the solidification endpoint

[0052] That is, by controlling the cooling intensity during continuous casting, the cooling intensity of the ingot 5 is greater in the middle and smaller on both sides, and the ratio of the cooling intensity in the middle to the two sides is 1.1-1.5:1. Before the straightening machine 6, the shape of the liquid phase hole can be made so-called "glasses-shaped" with large sides and small middle. When the ingot 5 is completely solidified, the solidification latent heat released by the liquid on both sides of the ingot 5 is large, which is beneficial to the reheating of the edges of the square billet, which not only increases the temperature of the square billet, but also makes its temperature more uniform.

[0053] Optimizing the corners of the ingot

[0054] The temperature difference between the corner and the center of the surface of the traditional right-angled billet is large, reaching 100℃ to 250℃. The present invention adopts a rounded corner or chamfer design, and the radius of the rounded corner is 10% to 15% of the billet section, which can change the heat exchange state of the billet corner, increase the billet corner temperature, and reduce the temperature difference between the billet corner and the center of the surface. The study found that: as the radius of the rounded corner of the billet increases, the corner isotherms gradually become annularly distributed, and the smaller the change in the billet surface temperature, the smaller the temperature difference between the corner and the center of the surface.

[0055] 5-weight reduction technology for casting billets

[0056] The ingot 5 is poured under heavy pressure. The ingot pulled out of the crystallizer 3 is straightened by heavy pressure and increased side roll extrusion. When the core of the ingot 5 is still in the mushy zone, the pressures of the 1#, 2# and 3# roller straightening machines are adjusted respectively. The pressure range is 18 to 22 MPa, and the ingot 51 to 60 mm of pressure is gradually applied to reduce the cross-section of the ingot 5 to 70-90 mm. The speed change brought about by the extrusion process meets the rolling needs of the rolling mill.

[0057] Insulation technology for casting 5

[0058] In order to increase the temperature of the hot-charged and directly rolled ingot 5 and prevent heat loss, the following insulation measures are adopted:

[0059] Insulation technology for casting in continuous casting machine

[0060] A heat preservation cover is installed at the rear of the continuous casting machine to keep the temperature inside the machine. The heat preservation cover is installed on both sides of the billet between the upper and lower clamping rollers. It can prevent the side of the billet from being overcooled, and increase the temperature of the edges on both sides of the billet 5 by 160℃~180℃, which is very beneficial to the uniformity of the temperature of the billet 5.

[0061] Insulation technology for ingot during transportation

[0062] In order to avoid excessive temperature drop during the transportation of the ingot 5 to the rolling mill after cutting, a closed heat-insulating cover with good thermal insulation performance and an electromagnetic induction heating device 11 are installed on the transport roller 9. The electromagnetic induction heating device can even out the surface and core temperature of the ingot 5, and supplement heat when the temperature is insufficient, so as to achieve better energy-saving effect.

Claims

1. A preparation process for a billet near-final shape continuous casting and rolling system, characterized in that: The system comprises a ladle (1), a tundish (2), a crystallizer (3), a secondary cooling zone (4), a straightening machine (6), a cutting zone heat preservation cover (7), a mechanical cutting machine (8), a transport roller (9), a transport roller heat preservation cover (10), an electromagnetic induction heating device (11) and a rolling mill group (12) which are connected in sequence. A continuous casting machine weight pressure and side pressure equipment are added to the straightening machine (6). The transport roller heat preservation cover (10) is provided with an electromagnetic induction heating device (11) which can make the surface and core temperature of the ingot (5) uniform and can supplement heat when the temperature is insufficient. The interior of the casting blank (5) is a liquid core structure, the exterior of the liquid core structure is a blank shell, and the four corners of the blank shell are corners of the casting blank; The preparation process comprises the following steps: 1) rotating the ladle (1) to a casting position to perform a casting operation; 2) The molten steel flowing out of the tundish (2) enters the crystallizer (3) and is forced to cool and form. After a shell of a certain thickness is formed, it is pulled downward by the dummy rod to form a cast billet (5); 3) After the ingot (5) is cooled in the secondary cooling zone (4), it is straightened and compressed by the puller (6) to increase the speed to match the rolling speed; 4) The straightened ingot (5) is cut into fixed lengths by a mechanical cutting machine (8), and then transported to a rolling mill group (12) by a transport roller (9) for continuous rolling and forming. During the transportation process, the ingot is evenly heated and supplemented by an electromagnetic induction heating device (11); The first cooling section of the secondary cooling zone (4) uses a water nozzle with a specific water volume of 1.7-2.1 L / kg, which can rapidly thicken the billet shell and prevent steel leakage. The subsequent cooling sections until the straightening machine (6) use air-water spray with a specific water volume of 0.9-1.1 L / kg, which can make the surface temperature of the billet (5) uniform. After the straightening machine (6), the billet (5) is cooled by cooling the conveying roller (9) with an air-water nozzle with a specific water volume of 0.9-1.1 L / kg. At the same time, by controlling the specific water volume ratio between the middle and both sides of the billet (5) surface to be 1.1-1.5:1, the liquid core can be shaped like a so-called "glasses shape" with large sides and small middle. In this way, when the billet (5) is completely solidified, the solidification latent heat released by the liquid on both sides of the billet (5) is relatively large, which is conducive to the reheating of the edges of the billet (5).

2. The preparation process of a billet near-final shape continuous casting and rolling system according to claim 1, characterized in that: The corners of the ingot (5) are rounded, which can change the heat exchange state of the ingot corners, increase the temperature of the ingot corners, and reduce the temperature difference between the ingot corners and the center of the surface.

3. The preparation process of a billet near-final shape continuous casting and rolling system according to claim 1, characterized in that: The ingot (5) pulled out of the crystallizer (3) is pressed down by heavy pressure and squeezed by additional side rollers during the straightening process, so that the cross-section of the ingot (5) is reduced to 70-90 mm.

Images