Casting method of vertical double-roller thin-strip continuous casting system for steel

Abstract

The invention belongs to the technical field of continuous casting, and relates to a casting method of a vertical double-roller thin-strip continuous casting system for steel. According to the casting method, vertical type double-roller thin strip casting of steel is carried out, a molten pool can be rapidly established to achieve the balance casting state and accurately keep the stability of the casting balance state, then a crystallization roller molten pool which is reasonable and stable in height is obtained within the least time, balance of the whole casting process is established, and loss is minimized. And in the casting process, intelligent online adjustment is achieved to stabilize the operation condition, continuous and efficient casting is achieved, the cast strip quality is high, and strip breakage is not likely to happen.

Description

Technical Field

[0001] This invention relates to continuous casting technology, and particularly to a casting method for a vertical twin-roll thin strip continuous casting system for steel. Background Technology

[0002] Twin-roll strip casting is an advanced short-process metallurgical technology. As a prime example of near-net-shape technology, it can directly produce metal strips with a thickness of 1.0~3.0 mm by sub-rapid solidification of molten metal injected into a twin-roll molten pool, followed by online hot rolling, cooling, and coiling. The cooling rate can reach 10... 2 ~10 4 K / s. Compared with traditional production processes and thin slab continuous casting, thin strip continuous casting is more compact and has a shorter process flow. Thin strip casting and rolling technology has wide applications in the non-ferrous metallurgical field. The application research of twin-roll thin strip continuous casting technology in the steel industry is very extensive, and the commercial production of ordinary carbon steel has been achieved. Furthermore, the mechanical properties of strip steel prepared by the short-process technology of thin strip casting and rolling are comparable to those of strip steel obtained by conventional complex processes, indicating that the unique sub-rapid solidification characteristics of thin strip continuous casting have a natural advantage in producing advanced special steel products that are difficult to roll in thin dimensions. Its specific casting process is as follows: Figure 1As shown, the steel sample is added to an induction furnace with a protective atmosphere. The heating system is started, and the steel sample is completely melted into molten steel. Temperature is measured, and the casting process begins when the target superheat is reached. After passing through the distributor, the molten steel enters the crystallizing roll space and forms a molten pool together with the side sealing plate. After exiting the rolls, the molten steel solidifies into a thin strip and enters the cooling zone along the guide rail. Finally, it is coiled and sent to the resistance furnace for heat treatment. Because vertical twin-roll thin strip continuous casting of steel strip is characterized by high speed and short process, the rapid establishment of the molten pool to achieve a balanced casting state is crucial during the casting process. At the same time, it is also important to accurately maintain the stability of the casting balance. Existing methods for establishing the molten pool mainly involve pre-setting a small roll gap and a large casting speed, and then gradually increasing the roll gap and adjusting the casting speed to obtain a molten pool of a certain height. This process takes a long time for laboratory casting systems, resulting in some metal waste and potentially affecting the establishment of subsequent casting balance. Therefore, a method is needed to quickly establish the molten pool and achieve a balanced casting state. In the balanced casting state, both the distributor and the molten pool should have a certain liquid level height. A properly leveled liquid in the distributor acts as a buffer, reducing the impact of molten steel poured from the induction furnace and minimizing fluctuations in the molten steel flowing into the lower molten pool. A reasonable and stable molten pool height on the crystallizing roll serves several purposes: first, it ensures sufficient cooling time and intensity for the molten steel to form a stable casting strip upon exiting the roll; second, it guarantees that the solidification endpoint of the molten steel is at a reasonable position (approximately near the meshing point of the two rolls); and third, it prevents the molten steel from exceeding the height of the side sealing plates or the crystallizing roll, which could pose a danger. During subsequent steady-state casting, factors such as changes in molten metal temperature, roll surface temperature, and slight widening of the roll gap may affect the balance. Therefore, maintaining the molten pool level and the stability of the casting force are crucial for preserving this balance. This, in turn, ensures the smooth and continuous vertical twin-roll thin strip casting process.

[0003] Several patents exist concerning twin-roll thin strip casting of steel. For example, patent CN1282512C mentions the production process of twin-roll thin strip casting for high-speed steel, and patent CN1208155C mentions a thin strip casting method and apparatus. While these patents describe the specific process of vertical thin strip casting, they do not provide a good explanation of the establishment and maintenance of the molten pool on the crystallizing roll. Therefore, there may be unreasonable or unstable molten pool heights, which are detrimental to the smoothness and continuity of casting. There are also patents concerning the control of casting process parameters / casting models for thin strip continuous casting machines. For example, patent CN 112475254B mentions a method and apparatus for controlling the casting speed and strip thickness of a thin strip continuous casting machine. Although it performs detailed calculations of the parameters of each stage under steady-state conditions and establishes the corresponding relationship between casting speed and strip thickness, it does not explain how to achieve steady state, how to achieve it quickly, or how to maintain steady state.

[0004] Therefore, considering the continuous vertical twin-roll thin strip casting of steel, if a new casting method can be adopted, including the rapid establishment of the molten pool to achieve a balanced casting state and the precise maintenance of the stable casting balance, a reasonably high and stable crystallizing roll molten pool can be obtained in the shortest time, thereby establishing the balance of the entire casting process and minimizing losses. Furthermore, intelligent online adjustment during the casting process ensures stable operation, achieving continuous and efficient casting with high-quality strip and reduced breakage. Summary of the Invention

[0005] Based on the above background technology, the purpose of this invention is to provide a casting method for a vertical twin-roll thin strip continuous casting system for steel, which is applicable to the production of various types of thin strip steel by vertical twin-roll thin strip continuous casting.

[0006] Specifically, the technical solution adopted in this invention is as follows:

[0007] According to one aspect of the present invention, a casting method for a vertical twin-roll thin strip continuous casting system for steel is provided, the casting method comprising the following steps:

[0008] (1) The steel sample is added to an induction furnace with a protective atmosphere, the heating system is started, and the steel sample is completely melted into molten steel. The temperature of the molten steel is measured. When the molten steel reaches the target superheat, the casting process begins. The induction furnace discharges steel at a balanced flow rate, which is equal to the steel flow rate at equilibrium. The formula for the balanced flow rate is as follows:

[0009] ,

[0010] in, To balance the casting speed, m / s; Density of molten steel, kg / m³ 3 ; The width of the casting strip is in meters (m). The thickness of the cast strip is in meters (m).

[0011] (2) After passing through the distributor, the molten steel enters the crystallization rollers and forms a molten pool together with the side sealing plate. After exiting the rollers, the molten steel solidifies into a thin strip and enters the cooling area along the guide rail. Finally, it is rolled and sent to the resistance furnace for heat treatment.

[0012] In step (2), establishing equilibrium involves two steps:

[0013] (a) The liquid level in the distributor is established and reaches the first equilibrium;

[0014] (b) The molten pool of the crystallizing roller is established and reaches a second equilibrium.

[0015] According to the casting method of the vertical twin-roll thin strip continuous casting system of steel according to the present invention, preferably, in step (a), the liquid level of the distributor will be established naturally after the steel pouring begins, and the outlet flow rate of the distributor increases from 0 to the equilibrium flow rate.

[0016] According to the casting method of the vertical twin-roll thin strip continuous casting system of the present invention, preferably, the flow difference between the tapping flow rate of the induction furnace and the outlet flow rate of the distributor is the mass of molten steel in the distributor, and the height of molten steel in the distributor is calculated using the following formula.

[0017] ,

[0018] in The pressure at a certain point; This represents the velocity of the molten steel at that point. Density of molten steel; It is the acceleration due to gravity; The height of that point. It is a constant.

[0019] According to the casting method of the vertical twin-roll thin strip continuous casting system of steel of the present invention, preferably, in step (b), in the initial stage of casting, the crystallizing roll runs at a casting speed lower than the equilibrium casting speed, the casting speed is uniformly increased when the first equilibrium is reached, and the casting speed also reaches the equilibrium casting speed when the liquid level of the molten pool reaches the target height, and then casting is carried out at the equilibrium casting speed.

[0020] According to the casting method of the vertical twin-roll thin strip continuous casting system of steel of the present invention, preferably, in step (b), before the second equilibrium is reached, the difference between the outlet flow rate of the distributor and the flow rate of the steel passing through the crystallizing roll is the mass of the molten steel in the molten pool.

[0021] According to the casting method of the vertical twin-roll thin strip continuous casting system of the present invention, preferably, after the entire process is rapidly balanced, the casting speed is finely adjusted in real time by means of a casting and rolling force control model to ensure that the casting and rolling force is kept constant at an optimal level to obtain the best strip forming effect.

[0022] According to the casting method of the vertical twin-roll thin strip continuous casting system of steel of the present invention, preferably, the gap between the two rolls is automatically corrected to prevent overflow based on the real-time monitoring of the specific height of the molten pool.

[0023] In the casting method of the vertical twin-roll strip casting system for steel according to the present invention, preferably, the included angle of the molten pool is 45°.

[0024] Beneficial technical effects

[0025] This casting method for vertical twin-roll thin strip steel casting allows for rapid establishment of a molten pool to achieve a balanced casting state and precisely maintain its stability. This results in a reasonably high and stable crystallizing roll molten pool in the shortest possible time, thus establishing balance throughout the casting process and minimizing losses. Furthermore, intelligent online adjustments ensure stable operation, enabling continuous and efficient casting with high-quality strip and reduced breakage. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below. Obviously, the drawings described below only relate to some embodiments of the present invention and are not intended to limit the present invention.

[0027] Figure 1 This is a schematic diagram of the vertical thin strip continuous casting process for steel.

[0028] Figure 2 A schematic diagram illustrating the process of establishing the liquid level in the distributor and the molten pool in the crystallizing roller.

[0029] Figure 3 This is a diagram showing the included angle of the molten pool and the molten pool itself.

[0030] Figure 4 This is a comparison chart of casting using the new casting model and the old model. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0032] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0033] The purpose of this invention is to provide a casting method for a vertical twin-roll thin strip continuous casting system, which is applicable to the production of various types of thin strip steel by vertical twin-roll thin strip continuous casting.

[0034] To achieve the above objectives, the technical solution of the present invention is as follows:

[0035] First, calculate the balanced flow rate using the following formula: .in, The casting speed is expressed in m / s. Density of molten steel, kg / m³ 3 ; The width of the casting strip is in meters (m). Let be the thickness of the casting strip, in meters (m). The flow rate calculated here is the theoretical equilibrium flow rate of the entire system at a specific casting speed and a specific casting strip thickness.

[0036] Furthermore, the induction furnace flow rate is calculated based on the equilibrium flow rate value, while simultaneously calculating the entire process of establishing equilibrium. The induction furnace rotates at a real-time varying angular velocity to ensure a consistent steel output per unit time, i.e., a constant flow rate. The induction furnace outputs steel at a constant flow rate, equal to the steel throughput at equilibrium. Equilibrium is then established in two steps. The first step is the establishment and equilibration of the liquid level in the distributor, and the second step is the establishment and equilibration of the molten pool in the crystallizing roll. After the second step is completed, the entire system is in equilibrium and continues to operate in this balanced state until casting is finished. Specifically, the liquid level will naturally establish itself after steel pouring begins, i.e., the distributor outlet flow rate increases from 0 to the equilibrium flow rate. During this period, the flow difference between the induction furnace output flow rate and the distributor outlet flow rate represents the mass of molten steel in the distributor. Based on this, the time to reach equilibrium and the height of the molten steel level in the distributor can be calculated. The height of the molten steel in the distributor is calculated using Bernoulli's equation. .in The pressure at a certain point; This represents the velocity of the molten steel at that point. Density of molten steel; It is the acceleration due to gravity; The height of that point. It is a constant. The second step is the establishment and equilibrium of the molten pool in the crystallizing roller. Specifically, in the initial stage of casting, the crystallizing roller runs at a speed lower than the equilibrium casting speed. When the first equilibrium is reached, the casting speed is increased uniformly. After a period of time, the liquid level in the molten pool reaches the target height, at which point the casting speed also reaches the equilibrium casting speed. Casting is then carried out at the equilibrium casting speed. The difference between the flow rate at the distributor outlet and the flow rate of steel exiting the crystallizing roller during the period before equilibrium is reached is the mass of molten steel in the molten pool. The time to finally reach equilibrium can be calculated based on this. The overall schematic diagram is as follows: Figure 2 As shown. The induction furnace flow rate is Q1, the distributor flow rate is Q2, the crystallizing roller flow rate is Q3, and the molten pool height is h. r The liquid level height of the distributor is h, the initial casting speed is V1, the equilibrium casting speed is V2, and the molten pool volume is V. 熔池 The volume of molten steel in the distributor is V 布流器 The time for the flow rate of the distributor and the flow rate of the induction furnace to reach equilibrium is t1, and the time for the flow rates of all three to reach equilibrium together is t2.

[0037] Existing methods for establishing the molten pool primarily involve pre-setting a small roll gap and a high casting speed, then gradually increasing the roll gap and adjusting the casting speed to achieve a molten pool of a certain height. This process is time-consuming and may cause several problems. Firstly, during the initial balancing phase, insufficient solidification strength may result in softer cast strips sticking to the casting rolls, rotating with them and hindering the casting process, potentially leading to accidents. This is because before the molten pool is established, the cooling area of ​​the molten metal is small, resulting in insufficient solidification and an inability to support its smooth descent from below. Secondly, prolonged periods without establishing the molten pool lead to intermittent casting strips, resulting in molten metal waste and potentially affecting the stability of subsequent casting balance. Furthermore, if significant time is spent establishing the molten pool level, the strip length at equilibrium will be greatly reduced, hindering the subsequent coiling process. The main advantage of this method for establishing the molten pool level and achieving a balanced casting state is that it allows for rapid establishment of the crystallizing roll molten pool with minimal losses, mitigating most risks and facilitating the subsequent coiling process.

[0038] Furthermore, after the entire process quickly reaches equilibrium, an adaptive model is used to regulate parameters and maintain balance. This adaptive model for casting process parameters primarily aims to improve the error tolerance of the casting process. If deviations occur in the aforementioned balance during operation (due to factors such as changes in molten metal temperature, changes in the surface temperature of the casting rolls, or slight widening of the roll gap), the casting force control model can be used to fine-tune the casting speed in real time, ensuring that the casting force remains constant at an optimal level to achieve the best strip formation effect. Simultaneously, based on real-time monitoring of the specific height of the molten pool, the gap between the two rolls (cast strip width) can also be automatically corrected to prevent overflow. In other words, real-time adjustment and dynamic balance can be achieved for casting speed, casting strip width, and casting force.

[0039] Furthermore, the casting force control model first needs to determine the optimal casting force for a specific type of steel material through preliminary experiments. Different steel materials have different physical and chemical properties, including strength, hardness, viscosity, solid-liquid phase temperature, and latent heat, etc. The optimal casting force F for casting needs to be determined through preliminary experiments. After determination, the specific value is input into the control system, and an appropriate fluctuation range (±20%) is selected to obtain an optimal casting force range (0.8F~1.2F). During the casting process, based on this range, the casting roll speed is increased or decreased to ensure that the casting force is within this range. In the specific experimental process, after the balance is established, the casting force of the casting machine is monitored in real time. The casting force is ensured to fluctuate within the above range through a pre-set program. If the measured casting force exceeds the pre-set range, the casting roll speed will be increased or decreased accordingly to stabilize the fluctuation of the casting force and keep it constant at the optimal level, thereby ensuring that the solidification endpoint is near the meshing point of the two rolls and that continuous strip formation is achieved.

[0040] Furthermore, the automatic roll gap correction model to prevent overflow first calculates the total length of contact between the molten steel and the casting rolls based on the heat transfer requirements for complete solidification of the steel strip and the cooling intensity of the casting rolls, thus determining the optimal liquid level. During the casting process, the gap between the two casting rolls can be adjusted in real time based on the liquid level gauge and real-time observation feedback. If the liquid level is higher than the pre-calculated ideal level, the roll gap will be slightly widened to lower the liquid level, and vice versa. Through real-time adjustment of the liquid level and roll gap, good interfacial heat transfer of the molten steel, a reasonable solidification endpoint, and no risks such as overflow can be generated, ensuring smooth casting.

[0041] The following are embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention. All other embodiments that can be obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0042] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0043] Example

[0044] Using the vertical strip casting method for steel mentioned in this invention, low-carbon steel strips were cast on a laboratory twin-roll strip casting machine to verify the reliability of the casting model.

[0045] The first step is the preliminary model calculation, which involves parameters such as induction furnace flow rate Q1, flow distributor flow rate Q2, crystallizer roll flow rate Q3, and molten pool height h. r The liquid level height h of the distributor, the initial casting speed V1, the equilibrium casting speed V2, and the molten pool volume V 熔池 The volume of molten steel in the distributor is V 布流器 The flow rates of the distributor and the induction furnace reach equilibrium in time t1, and the combined flow rates of all three reach equilibrium in time t2. The main idea is to rapidly establish the molten pool level under conditions of balancing the casting strip thickness and a casting roll speed slightly below the balancing casting speed. The flow rate difference is used to establish the flow level of the distributor and the molten pool of the crystallizing roll, respectively. The molten pool level of the crystallizing roll is kept constant by adjusting the induction furnace flow rate to ensure castability. The calculation process mainly involves first determining the equilibrium flow rate based on the casting speed and dimensional parameters, then using Bernoulli's equation to calculate the molten level height of the distributor and the mass of molten steel in the distributor, and finally converting the mass of molten steel in the distributor into volume to calculate the time it takes for the distributor flow rate to reach equilibrium. When the molten pool angle is 45° (e.g., ...), ... Figure 3As shown in the figure, the molten pool height is reasonable, and the cooling intensity is appropriate. The volume of the molten pool and the mass of the molten steel in the pool are calculated. Then, given an initial casting speed, the time for the molten pool to reach equilibrium and all parameters for casting can be calculated. The casting speed is set to 30 m / min, the casting strip thickness is 2 mm, the equilibrium flow rate is 0.72 kg / s, the initial casting speed is set to 40% of the casting speed, and the total time to reach equilibrium is 11 s.

[0046] For the casting force control model, several preliminary tests revealed that the optimal casting force for low-carbon steel strip is approximately 10-15 kN. By setting the casting force fluctuation range to ±20%, i.e., 10-14 kN, the casting roll speed is automatically adjusted to achieve stable casting force and a suitable solidification endpoint. The method for automatic roll gap correction to prevent overflow involves pre-calculating the ideal molten pool height, as described above. Figure 3 As shown, due to the existence of liquid level fluctuations, a liquid level height range of 42-47° is considered a reasonable value. Once the liquid level exceeds this range, the roller gap will be increased or decreased accordingly to ensure that the liquid level fluctuates slightly within the optimal range.

[0047] The model was implanted into a laboratory twin-roll thin strip continuous casting machine, and low-carbon steel was cast according to the model. The results were also compared with those obtained by experiments not using this casting model. Figure 4 The experiment, conducted using low-carbon steel and employing a casting model, demonstrated good casting continuity for the thin strip. It reached casting equilibrium relatively quickly (approximately 14 seconds), closely matching the theoretical calculation time, with minimal losses, high strip quality, and effective model control. The casting and rolling force fluctuated within a small range, resulting in strong casting stability and a high tolerance for errors. This indicates that using this method for vertical twin-roll thin strip casting can achieve a reasonably high and stable crystallizing roll molten pool, ensuring stable and continuous casting with high casting stability, high strip quality, and reduced risk of breakage. In contrast, experiments without the new casting model encountered numerous problems, such as strip sticking to the rolls and prolonged strip breakage. Furthermore, the time to reach equilibrium was generally higher than 20 seconds, and in several instances, equilibrium was not reached at all.

[0048] The above description is merely a specific embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A casting method for a vertical twin-roll thin strip continuous casting system for steel, characterized in that, The casting method includes the following steps: (1) The steel sample is added to an induction furnace with a protective atmosphere, the heating system is started, and the steel sample is completely melted into molten steel. The temperature of the molten steel is measured. When the molten steel reaches the target superheat, the casting process begins. The induction furnace discharges steel at a balanced flow rate, which is equal to the steel flow rate at equilibrium. The formula for the balanced flow rate is as follows: ， in, To balance the casting speed, m / s; Density of molten steel, kg / m³ 3 ; The width of the casting strip is in meters (m). The thickness of the cast strip is in meters (m). (2) After passing through the distributor, the molten steel enters the crystallization rollers and forms a molten pool together with the side sealing plate. After exiting the rollers, the molten steel solidifies into a thin strip and enters the cooling area along the guide rail. Finally, it is rolled and sent to the resistance furnace for heat treatment. In step (2), establishing equilibrium involves two steps: (a) The liquid level in the distributor is established and reaches the first equilibrium; (b) The molten pool of the crystallizing roller is established and reaches a second equilibrium.

2. The casting method of the vertical twin-roll thin strip continuous casting system for steel according to claim 1, characterized in that: In step (a), the liquid level of the distributor will be established naturally after the steel pouring begins, and the outlet flow rate of the distributor will increase from 0 to the equilibrium flow rate.

3. The casting method of the vertical twin-roll thin strip continuous casting system for steel according to claim 2, characterized in that: The difference between the tapping flow rate of the induction furnace and the outlet flow rate of the distributor represents the mass of molten steel inside the distributor. The height of the molten steel inside the distributor is calculated using the following formula. ， in The pressure at a certain point; This represents the velocity of the molten steel at that point. Density of molten steel; It is the acceleration due to gravity; The height of that point. It is a constant.

4. The casting method of the vertical twin-roll thin strip continuous casting system for steel according to claim 1, characterized in that: In step (b), during the initial stage of casting, the crystallizing roller operates at a casting speed lower than the equilibrium casting speed. When the first equilibrium is reached, the casting speed is increased uniformly. When the liquid level of the molten pool reaches the target height, the casting speed also reaches the equilibrium casting speed, and then casting is performed at the equilibrium casting speed.

5. The casting method of the vertical twin-roll thin strip continuous casting system for steel according to claim 4, characterized in that: In step (b), before the second equilibrium is reached, the difference between the outlet flow rate of the distributor and the flow rate of the steel passing through the crystallizing roll is the mass of molten steel in the molten pool.

6. The casting method of the vertical twin-roll thin strip continuous casting system for steel according to claim 1, characterized in that: After the entire process quickly reaches equilibrium, the casting speed is finely adjusted in real time using a casting and rolling force control model to ensure that the casting and rolling force remains constant at an optimal level to achieve the best strip formation effect.

7. The casting method of the vertical twin-roll thin strip continuous casting system for steel according to claim 1, characterized in that: Based on real-time monitoring of the specific height of the molten pool, the gap between the two rollers is automatically corrected to prevent overflow.

8. The casting method of the vertical twin-roll thin strip continuous casting system for steel according to claim 1, characterized in that: The included angle of the molten pool is 45°.

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