Method for controlling the non-pressed length of the tail of a bloom and method for pressing a continuous casting bloom

Abstract

The application provides a method for controlling the non-pressing length of a billet tail and a pressing method of a continuous casting billet, and belongs to the technical field of continuous casting. The method comprises the following steps: setting a tail billet non-pressing interval in the tail of the continuous casting billet; in the process of entering the tail billet, when the front end of the tail billet non-pressing interval reaches the position of the puller-straightener of the pressing section in sequence along the pulling direction, the pressing work of the corresponding puller-straightener is stopped in sequence, so that the puller-straighteners of the pressing section stop the pressing work in sequence, until the last puller-straightener of the pressing section stops the pressing work, so as to control the non-pressing length of the tail billet in the tail billet non-pressing interval. The application can solve the problem that there is no effective solution to effectively control the non-pressing length of the tail billet in the prior art, so as to reduce the cost of recycling the non-pressing continuous casting billet.

Description

Technical Field

[0001] This invention relates to the field of continuous casting technology, and more specifically, to a method for controlling the length of the billet tail that is not pressed down and a method for pressing down the continuously cast billet. Background Technology

[0002] From a technological perspective, the reduction technique has a significant effect on improving the internal quality of continuously cast billets, and it is now widely used in various billet types. However, in terms of control and execution, during the tail billet process of each continuous casting cycle, due to the reduced casting speed and capping operation, the billet at the tail is very hard. From a control perspective, when the billet tail passes through the straightener, the straightener lifts up, so it definitely cannot be reduced. At the same time, the reduced or even stopped casting speed will shorten the solidification end of the billet, shortening the reducible range, which does not meet the requirements of the reduction process. Therefore, a long section of the billet tail will not be reduced. Steel grades that must use the reduction technique to improve their internal quality are often high-grade specialty steels and special steels. The billets that are not reduced can only be recycled, resulting in billet waste and reduced yield and profit.

[0003] Near the end of a continuous casting cycle, the molten steel entering the crystallizer from the tundish stops, and the casting enters the tailing process. The casting speed will quickly decrease or even return to zero to facilitate the capping operation. This process generally takes 5-10 minutes. After the tailing temperature decreases, the casting speed is gradually increased to the normal production speed. During the tailing process, once the casting speed returns to zero, the pressing must not be stopped, otherwise it will lead to a casting accident. Furthermore, during the entire tailing process, when the casting speed is lower than the normal production speed, the solidification end will shorten due to the reduced speed, and the pressing range will decrease, even becoming smaller than the position of the first straightening machine, making it impossible to press down. Even if the casting speed recovers, due to the solidification process, the recovery of the solidification end of the billet will lag, often resulting in the entire tailing process being unable to press down. Even if the tailing process meets the pressing conditions, during execution, the pressing will stop once the first straightening machine stops pressing down, resulting in a long unpressed billet.

[0004] Extensive on-site statistics show that the length of the unpressed billet during the tailing process is related to the arrangement of the straightening machine, and can be approximately 12 to 18 meters. For large square billets, such as 250×300mm cross-section billets, this waste is quite serious. At the same time, these unpressed billets need to be remelted, increasing costs. Moreover, the larger the cross-section, the greater the impact, which can even be unacceptable.

[0005] In summary, there is currently a lack of effective solutions in the existing technology to control the length of the unpressurized billet tail, thereby reducing the cost of remelting the unpressurized billet. Summary of the Invention

[0006] In view of the above problems, the purpose of this invention is to provide a method for controlling the length of the unpressurized billet tail and a method for pressing down the continuously cast billet, so as to solve the problem in the prior art that there is no effective solution to control the length of the unpressurized billet tail and reduce the cost of remelting the unpressurized billet.

[0007] This invention provides a method for controlling the unpressed length of the billet tail, comprising the following steps:

[0008] A non-pressurized section is set at the tail of the continuously cast billet;

[0009] After the continuously cast billet enters the tail billet process, along the billet pulling direction, when the front end of the tail billet non-pressurized section reaches the position of the straightening machine in the pressing section in sequence, the pressing operation of the corresponding straightening machine is stopped in sequence, so that the straightening machine in the pressing section stops pressing operation one by one until the last straightening machine in the pressing section stops pressing operation, so as to control the non-pressurized length of the billet tail to be within the tail billet non-pressurized section.

[0010] Furthermore, in a preferred embodiment, the method further includes: preventing the casting speed of the continuous casting billet from returning to zero after the billet enters the tailing process.

[0011] Furthermore, in a preferred embodiment, the method further includes:

[0012] During the tail billet process at a lower than normal drawing speed, a low solidification end reduction process is added to the preset two-stage reduction process table so that when the front end of the non-reduced section of the tail billet passes the first tension leveler of the reduction section, the low solidification end reduction process causes the first tension leveler to perform reduction; wherein, the length of the low solidification end is less than the preset process solidification end in the two-stage reduction process table.

[0013] Furthermore, a preferred approach is to add a reduction process for the low solidification end to the pre-defined two-stage reduction process table.

[0014] The pressing process for the low solidification end is set to a single-roller pressing process.

[0015] Furthermore, in a preferred embodiment, the method further includes:

[0016] After the continuously cast billet enters the tailing process, the casting speed of the continuously cast billet is reduced to 0.25-0.35 m / min for capping, and the time from deceleration to acceleration to normal production casting speed is within 3 minutes.

[0017] Furthermore, a preferred embodiment is to reduce the casting speed of the continuously cast billet to 0.3 m / min for capping.

[0018] Furthermore, in a preferred embodiment, the method further includes:

[0019] During the process of the continuously cast billet entering the tail section and the process of the continuously cast billet being pulled down to the top speed, and then the speed of the billet being increased again, the speed of the continuously cast billet after the speed increase is greater than or equal to the normal production speed.

[0020] Furthermore, in a preferred embodiment, the method further includes:

[0021] The length of the continuously cast billet generated during the low casting speed period at the billet tail is recorded as the questionable length, and the billet with the questionable length is marked as a continuously cast billet with questionable quality.

[0022] In addition, a preferred option is that the unpressed section of the tail billet is set according to actual process requirements.

[0023] The present invention also provides a method for pressing down a continuously cast billet, wherein the unpressed length of the billet tail is controlled by the method described above during the pressing down process.

[0024] As can be seen from the above technical solution, the method for controlling the unpressurized length of the billet tail and the pressing method for continuously cast billets provided by the present invention are as follows: A non-pressurized tail section is set at the tail of the continuously cast billet; then, during the process of the continuously cast billet entering the tail section, along the casting direction, when the front end of the non-pressurized tail section reaches the position of the straightening machine in the pressing section, the pressing operation of the corresponding straightening machine is stopped sequentially, so that the straightening machines in the pressing section stop pressing operation one by one until the last straightening machine in the pressing section stops pressing operation, thereby controlling the unpressurized tail length of the billet tail to be within the non-pressurized tail section; through the above-mentioned gradual stopping of pressing, the length of the non-pressurized tail section of the billet is controlled, so as to reduce the limit of the unpressurized tail length of the billet tail during the tail section process, thereby reducing scrap billets and lowering the cost of recycling scrap billets.

[0025] To achieve the foregoing and related objectives, one or more aspects of the invention include the features that will be described in detail below. The following description and accompanying drawings illustrate certain exemplary aspects of the invention. However, these aspects indicate only a few of the various ways in which the principles of the invention can be used. Furthermore, the invention is intended to encompass all such aspects and their equivalents. Attached Figure Description

[0026] Other objects and results of the invention will become more apparent and readily understood with reference to the following description taken in conjunction with the accompanying drawings, and with a more complete understanding of the invention.

[0027] Figure 1 A flowchart of a method for controlling the unpressed length of the billet tail according to an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of the position and original calibration of the tension leveling machine according to Comparative Example 1 of the present invention;

[0029] Figure 3 This is a schematic diagram of the tail-end billet drawing speed variation according to Embodiment 1 of the present invention;

[0030] Figure 4 This is a schematic diagram illustrating the discontinuity between the low-speed casting interval and the non-pressing interval of the tail billet according to Embodiment 1 of the present invention. Detailed Implementation

[0031] In the following description, numerous specific details are set forth for illustrative purposes and to provide a thorough understanding of one or more embodiments. However, it will be apparent that these embodiments may also be implemented without these specific details.

[0032] To address the problem that the existing technologies mentioned above lack an effective solution for controlling the length of the unpressurized billet tail to reduce the cost of remelting the unpressurized billet, a method for controlling the unpressurized billet tail length and a pressing method for continuously cast billets are proposed.

[0033] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0034] To illustrate the method for controlling the non-pressing length of the billet tail provided by the present invention Figure 1 A flowchart of a method for controlling the unpressed length of the billet tail according to an embodiment of the present invention is shown; Figure 1 A flowchart of a method for controlling the unpressed length of the billet tail according to an embodiment of the present invention; Figure 2 The position and original calibration of the tension leveler according to Comparative Example 1 of the present invention are shown; Figure 3 The variation of the drawing speed during the tail billet process according to Embodiment 1 of the present invention is shown; Figure 4 The diagram illustrates the discontinuity between the low-speed casting interval and the non-pressing interval of the tail billet according to Embodiment 1 of the present invention.

[0035] like Figure 1 As shown, the method for controlling the non-pressing length of the billet tail provided by the present invention includes the following steps:

[0036] Step S1: Set a non-pressurized section at the tail of the continuously cast billet.

[0037] Specifically, a non-pressurized tail section is set at the tail of the continuously cast billet. One end of the non-pressurized tail section is the rear end of the billet tail. The non-pressurized tail section is marked on the continuously cast billet. In this invention, the tail billet or billet tail refers to the later section of the billet during the continuous casting process, and its length is determined by the actual process or steel grade.

[0038] As a preferred embodiment of the present invention, the unpressed section of the tail billet is set according to the actual process requirements.

[0039] Specifically, the unpressurized tail section in the technical solution of this invention is set according to actual process requirements and is generally set by process engineers.

[0040] Step S2: After the continuously cast billet enters the tail billet process, along the billet pulling direction, when the front end of the tail billet non-pressurized section reaches the position of the straightening machine in the pressing section in sequence, the pressing work of the corresponding straightening machine is stopped in sequence, so that the straightening machine in the pressing section stops pressing work one by one until the last straightening machine in the pressing section stops pressing work, so as to control the non-pressurized length of the billet tail to be within the non-pressurized section of the tail billet.

[0041] Specifically, based on the set non-pressurized section at the billet tail, when the non-pressurized section just reaches the first straightening machine and the first straightening machine is pressing down, only the first straightening machine stops. Obviously, at this time, the subsequent straightening machines continue pressing down. When the non-pressurized section just reaches the second straightening machine and this straightening machine is pressing down, the pressing down of this straightening machine stops. This process is repeated to gradually stop the pressing down of all straightening machines until the last straightening machine stops pressing down, thus shortening the non-pressurized length of the billet tail. Through program tracking, the position of the front end of the non-pressurized section at the billet tail reaching the straightening machine can be determined.

[0042] As a preferred embodiment of the present invention, the method for controlling the unpressurized length of the billet tail further includes:

[0043] After the continuously cast billet enters the tail billet process, the casting speed of the continuously cast billet is prevented from returning to zero.

[0044] Specifically, from an operational perspective, the pulling speed cannot be reduced to zero during the tailing process, because once the pulling speed is reduced to zero, the pressing will inevitably stop, which could lead to a pulling accident when the pulling speed is restored.

[0045] As a preferred embodiment of the present invention, the method for controlling the unpressurized length of the billet tail further includes:

[0046] During the tail billet process at a lower than normal drawing speed, a low solidification end reduction process is added to the preset two-stage reduction process table so that when the front end of the tail billet non-reduced section passes the first tension leveler in the reduction section, the low solidification end reduction process causes the first tension leveler to perform reduction; wherein, the length of the low solidification end is less than the preset process solidification end in the two-stage reduction process table.

[0047] Specifically, from a process perspective, there is a reduction in drawing speed during the tail billet process, and the natural solidification end will retract forward. If the residence time is long enough, it will not meet the normal pressing range requirements and may directly stop pressing. Therefore, by adding a pressing process corresponding to the low solidification end in the secondary pressing process table, it is possible to ensure that pressing can still be performed after the solidification of the tail billet moves forward.

[0048] As a preferred embodiment of the present invention, in the process of adding a reduction process for the low solidification end to the preset two-stage reduction process table,

[0049] The pressing process for the low solidification end is set to a single-roll pressing process.

[0050] As a preferred embodiment of the present invention, the method for controlling the unpressurized length of the billet tail further includes:

[0051] After the continuously cast billet enters the tailing process, the casting speed of the continuously cast billet is reduced to 0.25-0.35 m / min for capping, and the time from deceleration to acceleration to normal production casting speed is within 3 minutes.

[0052] Although the gradual cessation of pressing can minimize the unpressurized length during the tailing process to within a pre-defined unpressurized tailing process, it does not guarantee that the quality of the pressed billet will meet the same level as the quality at normal casting speed. Therefore, to ensure quality and identify the range of quality reduction, it is necessary to control the casting speed to be reduced to 0.25–0.35 m / min when the continuous casting billet enters the tailing process, and the time from deceleration to acceleration back to normal production casting speed should be within 3 minutes.

[0053] As a preferred embodiment of the present invention, the casting speed of the continuously cast billet is reduced to 0.3 m / min for capping.

[0054] It should be noted that reducing the casting speed of the continuous casting billet to 0.3 m / min for capping is only a preferred embodiment of the present invention.

[0055] As a preferred embodiment of the present invention, the method for controlling the unpressurized length of the billet tail further includes:

[0056] During the process of the continuously cast billet entering the tail section and the process of the continuously cast billet being pulled down to the top, the speed of the billet is increased again after the speed is increased. The speed of the continuously cast billet after the speed increase is greater than or equal to the normal production speed.

[0057] Specifically, after the tail billet is capped, the casting speed is increased. The casting speed can be higher than the normal production casting speed, so as to ensure that the solidification end is maintained at the solidification end of the normal casting speed.

[0058] As a preferred embodiment of the present invention, the method for controlling the unpressurized length of the billet tail further includes:

[0059] The length of the continuously cast billet produced during the low-speed casting period at the billet tail stage is recorded as the questionable length. Billets with this questionable length are marked as continuously cast billets with questionable quality, i.e., the low-speed casting period at the billet tail stage.

[0060] Specifically, after the solidification ends below the critical point, the continuously cast billets that have been pressed down by the straightening machine are cumulatively tracked to form a low-speed casting range at the billet tail. The quality of the billets in this range is questionable, thus achieving precise positioning of quality errors, and billet separation can be performed later.

[0061] The method for tracking and recording the length of the continuously cast billet generated during the low casting speed period at the billet tail can be achieved using the following formula:

[0062] L t =V·Δt

[0063] L = L pre +L t ,

[0064] Among them, L t V is the length of the billet within the cycle; V is the casting speed within the cycle; Δt is the cycle time; L is the length of the billet produced during the cumulative low casting speed period; L pre This represents the length of the cast billet produced during the low-speed casting period preceding the current moment. The cumulative length of the cast billet produced during the low-speed casting period can be calculated by setting a cycle time, such as 3s, 4s, or 5s.

[0065] During the tail-end casting process, as the casting speed decreases and increases, even exceeding the normal casting speed, the solidification end decreases and recovers. During this process, the solidification end may initially be lower than the critical solidification end, and then, after a period of time, exceed it. Therefore, the tracked low-speed casting range at the tail end may be discontinuous with the non-reduced casting range at the tail end. In this case, billet division can be based on the low-speed casting range at the tail end, or all continuously cast billets directly from the low-speed casting range to the non-reduced casting range at the tail end can be downgraded. The critical solidification end is related to the position of the straightening machine and the solidification end corresponding to the normal reducing process, requiring experimental verification. The low-speed casting range at the tail end is obtained through program tracking.

[0066] The continuous casting billet reduction method provided by the present invention uses the method described above for controlling the unreduced length of the billet tail to control the unreduced length of the billet tail during the continuous casting billet reduction process.

[0067] By setting a non-pressurized tail section at the tail of the continuously cast billet, and then, during the billet entry process, along the casting direction, when the front end of the non-pressurized tail section reaches the position of the straightening machine in the pressing section, the pressing operation of the corresponding straightening machine is stopped sequentially, so that the straightening machines in the pressing section stop pressing operation one by one until the last straightening machine in the pressing section stops pressing operation, thereby controlling the non-pressurized tail length of the billet within the non-pressurized tail section. Through the above-mentioned gradual stopping of pressure, the length of the non-pressurized tail section of the billet is controlled, so as to reduce the limit of the non-pressurized tail length of the billet during the billet process, thereby reducing the scrap billet and reducing the cost of recycling scrap billets.

[0068] To better illustrate the method for controlling the unreduced length of the billet tail and the reduction method for continuously cast billets provided by this invention, the following examples are given:

[0069] Comparative Example 1

[0070] Taking a 250x300mm large billet casting machine in a steel plant as an example, the main steel grade produced by this casting machine is bearing steel GCr15. It has 6 straightening machines, arranged as follows: Figure 2 As shown. In the existing original program logic, initially, due to the tailing process where the casting speed returns to zero, and the low casting speed duration of the tailing process exceeds 5 minutes, the entire tailing billet is not pressed down, resulting in at least 17m of the tailing billet not being pressed down, as shown. Figure 2 As shown, when the unpressed section of the tail billet reaches the first straightening machine and the first straightening machine performs pressing, and then stops pressing, at least 8 meters of the casting billet will not be pressed. After long-term production, this will result in a large accumulation of scrap billets, which will greatly increase costs.

[0071] Example 1

[0072] The method for controlling the length of the billet tail that is not pressed down provided by the present invention was applied to a steel plant in Comparative Example 1. Taking a large square billet casting machine of 250X300mm as an example, the main steel grade produced by the casting machine is bearing steel GCr15, and there are 6 tension leveling machines.

[0073] The unpressed section of the tail billet is set to 2m, such as Figure 2 As shown, when the unpressed section of the tail billet reaches the first tension leveling machine and this tension leveling machine performs pressing, only the pressing of the original tension leveling machine stops, and so on, gradually stopping the pressing action of the tension leveling machine.

[0074] like Figure 3 As shown, the casting speed changes during the tail billet process in this embodiment. During the tail billet process, the casting speed is quickly reduced to the capping casting speed, which is about 0.3 m / min. After the capping is completed, the casting speed is increased. The normal production casting speed is 0.8 m / min. The casting speed is increased to 0.85~0.9 m / min, which can ensure that the solidification end of the entire process is not less than 17.0 m, thereby avoiding the low casting speed casting range at the billet tail.

[0075] To ensure that the billet is pressed down throughout the entire billet tailing process, except in the non-pressurized tail section, a specific processing method is adopted. The program is set so that when the solidification end exceeds 8m, roll #1 performs a single-roller 15mm pressurization, with the critical solidification end being 17.0m. During the billet tailing process, as the casting speed decreases and increases, the solidification end decreases and recovers. However, due to the slightly longer low casting speed period and the subsequent increase to a speed greater than normal production speed, the solidification end may initially be smaller than the critical solidification end, and then larger than the critical solidification end after a period of time. Therefore, the tracked low casting speed billet tailing section may be discontinuous with the non-pressurized tail section. Figure 4 As shown, at this time, the billet division can be carried out according to the low-speed casting interval of the billet tail, or all the billets from the low-speed casting interval of the tail billet to the no-pressing interval of the tail billet can be downgraded.

[0076] It should be noted that this embodiment is merely a detailed description of the method for controlling the length of the billet tail without pressing down provided by the present invention in practical applications, and does not limit the technical solution provided by the present invention.

[0077] As can be seen from the above specific embodiments, the method for controlling the unpressurized length of the billet tail and the pressing method for continuously cast billets provided by the present invention are as follows: A non-pressurized tail section is set at the tail of the continuously cast billet; then, during the process of the continuously cast billet entering the tail section, along the casting direction, when the front end of the non-pressurized tail section reaches the position of the straightening machine in the pressing section, the pressing operation of the corresponding straightening machine is stopped sequentially, so that the straightening machines in the pressing section stop pressing operation one by one until the last straightening machine in the pressing section stops pressing operation, thereby controlling the unpressurized tail length to be within the non-pressurized tail section; through the above-mentioned gradual stopping of pressing, the length of the non-pressurized tail section is controlled, thereby reducing the limit of the unpressurized tail length during the tail section process, thus reducing scrap billets and lowering the cost of recycling scrap billets.

[0078] The method for controlling the unreduced length of the billet tail and the method for reducing the continuously cast billet according to the present invention have been described above by way of example with reference to the accompanying drawings. However, those skilled in the art should understand that various modifications can be made to the method for controlling the unreduced length of the billet tail and the method for reducing the continuously cast billet according to the present invention without departing from the scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the contents of the appended claims.

Claims

1. A method for controlling the length of the billet tail that is not pressed down, characterized in that, Includes the following steps: A non-pressurized section is set at the tail of the continuously cast billet; After the continuously cast billet enters the tail billet process, along the billet pulling direction, when the front end of the tail billet non-pressurization section reaches the position of the straightening machine in the pressing section in sequence, the pressing operation of the corresponding straightening machine is stopped in sequence, so that the straightening machine in the pressing section stops pressing operation one by one, until the last straightening machine in the pressing section stops pressing operation, so as to control the non-pressurization length of the billet tail to be within the tail billet non-pressurization section; wherein, after the continuously cast billet enters the tail billet process, the pulling speed of the continuously cast billet is not reduced to zero.

2. The method for controlling the unpressed length of the billet tail according to claim 1, characterized in that, The method further includes: During the tail billet process at a lower than normal drawing speed, a low solidification end reduction process is added to the preset two-stage reduction process table so that when the front end of the non-reduced section of the tail billet passes the first tension leveler of the reduction section, the low solidification end reduction process causes the first tension leveler to perform reduction; wherein, the length of the low solidification end is less than the preset process solidification end in the two-stage reduction process table.

3. The method for controlling the unpressed length of the billet tail according to claim 2, characterized in that, In the process of adding a reduction process for the low solidification end to the preset two-stage reduction process table, The pressing process for the low solidification end is set to a single-roller pressing process.

4. The method for controlling the unpressed length of the billet tail according to claim 1, characterized in that, The method further includes: After the continuously cast billet enters the tailing process, the casting speed of the continuously cast billet is reduced to 0.25~0.35m / min for capping, and the time from deceleration to acceleration to normal production casting speed is within 3 minutes.

5. The method for controlling the unpressed length of the billet tail according to claim 4, characterized in that, The casting speed of the continuously cast billet is reduced to 0.3 m / min for capping.

6. The method for controlling the unpressed length of the billet tail according to claim 1, characterized in that, The method further includes: During the process of the continuously cast billet entering the tail section and the process of the continuously cast billet being pulled down to the top speed, and then the speed of the billet being increased again, the speed of the continuously cast billet after the speed increase is greater than or equal to the normal production speed.

7. The method for controlling the unpressed length of the billet tail according to claim 1, characterized in that, The method further includes: The length of the continuously cast billet generated during the low casting speed period at the billet tail is recorded as the questionable length, and the billet with the questionable length is marked as a continuously cast billet with questionable quality.

8. The method for controlling the unpressed length of the billet tail according to claim 1, characterized in that, The unpressed section of the tail billet is set according to actual process requirements.

9. A method for reducing a continuously cast billet, characterized in that, During the continuous casting billet reduction process, the non-reduced length of the billet tail is controlled by the method described in any one of claims 1-8.

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