Optimization design method for vibration process parameters of slab continuous casting crystallizer

Abstract

The invention relates to an optimization design method for slab continuous casting crystallizer vibration process parameters, and belongs to the field of slab continuous casting. The design purpose of the invention is to improve the slab quality and smooth proceeding of the continuous casting process. According to the method, the optimization target is set through theoretical calculation, multi-parameter planning solution is executed, and the optimization value of the vibration process parameters is obtained. And the pulling speed set value is adjusted, the solving step is repeated, and the vibration process synchronous control model is formed. According to the scheme, the metallurgical process requirements and the limitation of the capacity of vibration equipment are comprehensively considered, so that the rationality and reliability of vibration parameter design are improved. By introducing more metallurgical process demand elements, the method can ensure the rationality of each key metallurgical parameter in all directions, and provides technical guarantee for high-quality continuous casting production.

Description

Technical Field

[0001] The invention belongs to the field of slab continuous casting and relates to an optimization design method for vibration process parameters of a slab continuous casting crystallizer. Background Art

[0002] In the slab continuous casting process, the crystallizer plays a vital role. As a primary cooling area, its metallurgical effect directly affects the surface quality of the slab and the smooth progress of the casting process. The crystallizer vibration technology is a key means to improve the demoulding and lubrication effect of the cast slab, and plays an irreplaceable role in ensuring the optimization of the crystallizer metallurgical effect.

[0003] In actual production, casting process parameters, especially casting speed, often fluctuate during slab continuous casting. In order to adapt to this fluctuation, the basic parameters of mold vibration, such as frequency, amplitude and waveform slope, must be adjusted accordingly. The changing relationship between these parameters, the so-called vibration process synchronization control model, is crucial to ensure the metallurgical effect of mold vibration. Therefore, the use of correct theoretical methods, such as optimization methods such as mathematical programming solution, combined with metallurgical process calculations and limiting factors of vibration devices, is a necessary means to determine the changing relationship of these parameters.

[0004] However, the traditional vibration process parameter design is often based only on the negative slip time or negative slip rate. This method only considers some influencing factors such as the consumption of mold slag and the depth of vibration marks, and is more controlled from the perspective of maintaining the stability of the vibration state. Since the target object of the optimization solution is relatively single, this method is difficult to fully take into account the various metallurgical process links closely related to the casting process and the quality of the ingot, resulting in insufficient adaptability and rationality of the design results for complex production sites.

[0005] With the continuous development of efficient continuous casting technology and the increasing attention to the quality of ingots, it is necessary to introduce more metallurgical process requirements into the design of vibration process parameters and synchronous control models. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a slab continuous casting crystallizer vibration process parameter optimization design method based on theoretical calculation, so as to improve the rationality and reliability of the crystallizer vibration parameter design, thereby ensuring the smooth progress of the continuous casting process and improving the quality of the casting.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for optimizing the vibration process parameters of a slab continuous casting crystallizer comprises the following steps:

[0009] S1 sets the optimization target based on the theoretical calculation of the liquid slag layer thickness;

[0010] S2 takes metallurgical process requirements and mold vibration equipment capabilities as reference conditions and uses multi-parameter planning and solving methods to optimize the vibration process parameters;

[0011] S3 formulates a vibration process synchronization control model.

[0012] Optionally, in S1, the thickness of the liquid slag layer above the meniscus in the crystallizer and its minimum allowable value are calculated according to the cross-sectional specifications of the ingot and the limit of the liquid level fluctuation in the crystallizer, and an optimization target is set.

[0013] Optionally, in S2, key vibration metallurgical parameters are calculated according to current vibration process parameters, and the vibration metallurgical parameters include negative slip time, positive slip time and negative slip rate.

[0014] Optionally, in S2, initial values ​​of crystallizer vibration process parameters are set according to the pulling speed conditions, including vibration stroke, frequency and waveform slope, and the solidification temperature and dynamic viscosity of the protective slag are calculated according to the component information of the protective slag.

[0015] Optionally, S2 calculates the liquid slag film thickness, the slag consumption and the vibration mark depth in combination with the protective slag performance parameters.

[0016] Optionally, S2 includes the following sub-steps:

[0017] S21 calculates the thickness of the liquid slag layer and its minimum allowable value according to the cross-sectional specifications of the ingot and the limit of the liquid level fluctuation of the crystallizer, and sets the optimization solution target;

[0018] S22 sets the value range of the vibration parameter.

[0019] Optionally, the vibration parameters include minimum mold slag consumption, maximum vibration mark depth, and reasonable vibration stroke, frequency and waveform deflection rate.

[0020] Optionally, in S3, the crystallizer vibration process parameters are optimized and designed by a multi-parameter planning solution method, and the parameters include stroke, frequency and waveform deflection rate.

[0021] Optionally, S3 includes the following sub-steps:

[0022] S31 performs multi-parameter planning and solving to obtain optimized values ​​of vibration process parameters;

[0023] S32 adjusts the drawing speed setting value and repeats the solution steps to form a vibration process synchronization control model.

[0024] The beneficial effects of the present invention are:

[0025] Improve the rationality and reliability of parameter design: This solution improves the rationality and reliability of mold vibration parameter design through theoretical calculation and multi-parameter planning solution, thereby ensuring the smooth progress of the continuous casting process and improving the quality of the ingot.

[0026] Comprehensive consideration of metallurgical process requirements: This solution comprehensively considers metallurgical process requirements and the limitations of vibration equipment capabilities during the optimization design process. By introducing more metallurgical process demand elements, the accuracy and practicality of vibration parameter design are improved.

[0027] Improve production efficiency and market competitiveness: This solution provides technical support for high-quality continuous casting production by ensuring the rationality of various key metallurgical parameters in all aspects, which helps to improve production efficiency, reduce production costs, and enhance the market competitiveness of products.

[0028] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0030] Figure 1 It is a schematic diagram of the liquid slag film in the gap between the solidified shell and the wall of the crystallizer;

[0031] Figure 2 This is a schematic diagram of the distribution of mold slag in the crystallizer;

[0032] Figure 3 Schematic diagram of vibration marks on the surface of the ingot;

[0033] Figure 4 Schematic diagram of the synchronous control model of the crystallizer vibration process.

[0034] Figure numerals: 1 crystallizer, 2 continuous casting billet, 3 liquid slag film, 4 solid slag film, 5 air gap, 6 slag ring, 7 solid slag layer, 8 sintering layer, 9 semi-molten layer, 10 liquid slag layer, 11 steel slag, 12 hook-shaped vibration mark, 13 concave vibration mark. DETAILED DESCRIPTION

[0035] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0036] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0037] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0038] Related technical terms and explanations:

[0039] Crystallizer 1: Crystallizer is a key part of slab continuous casting machine, which is used to form the initial shape of slab. The design and operation of crystallizer are crucial to the quality of slab and the smooth progress of continuous casting process.

[0040] Continuous casting ingot 2: The continuous casting ingot is a slab formed in the crystallizer, and its surface quality and internal structure are affected by the vibration parameters of the crystallizer.

[0041] Liquid slag film 3 and solid slag film 4: Liquid slag film and solid slag film are slag layers formed in the crystallizer, which are used to protect the slab surface and improve the demoulding performance of the slab.

[0042] Air gap 5: The air gap is the space formed between the crystallizer and the slab to reduce heat loss and prevent the slag layer from directly contacting the slab.

[0043] Slag ring 6: The slag ring is a part of the slag layer formed in the crystallizer, which is used to improve the demoulding performance and lubrication effect of the slab.

[0044] Solid slag layer 7, sintered layer 8 and semi-molten layer 9: The solid slag layer, sintered layer and semi-molten layer are slag layers in different states formed in the crystallizer, which are used to protect the surface of the slab and improve the demoulding performance of the slab.

[0045] Liquid slag layer 10 and steel slag 11: The liquid slag layer and steel slag are slag layers formed in the crystallizer, which are used to protect the slab surface and improve the demoulding performance of the slab.

[0046] Hook-shaped vibration marks 12 and concave-shaped vibration marks 13: Hook-shaped vibration marks and concave-shaped vibration marks are vibration marks formed on the surface of the slab, which are used to improve the demoulding performance and lubrication effect of the slab.

[0047] See also Figure 1 to Figure 4 The specific implementation method of this scheme includes the following steps:

[0048] 1) Assign initial values ​​to the vibration process parameters of the crystallizer 1, and calculate its important performance parameters according to the composition of the protective slag.

[0049] Under certain pulling speed conditions, the initial values ​​of the vibration process parameters of the crystallizer 1, including the vibration stroke, frequency and waveform deflection rate, are set according to experience, and the solidification temperature and dynamic viscosity of the mold 1 are calculated according to the composition information of the mold slag.

[0050] Mold slag solidification temperature T br The calculation method of (℃) is as follows:

[0051]

[0052] Where: X is the mass fraction of the protective slag component.

[0053] The calculation method of the dynamic viscosity η (Pa·s) of the mold slag is as follows:

[0054]

[0055] Where: M is the molar fraction of the protective slag component; T is the temperature, which can usually be taken as 1573K for calculation.

[0056] 2) Calculation of key metallurgical parameters that characterize the vibration of the crystallizer 1.

[0057] Calculate key vibration metallurgical parameters including negative slip time, positive slip time and negative slip rate based on current vibration process parameters.

[0058] Negative slip time t N (s) is defined as the time during which the downward movement speed of the crystallizer 1 exceeds the pulling speed during the vibration period. During this period, the crystallizer 1 moves downward relative to the continuous casting billet 2, and the billet shell is subjected to compressive stress. Its calculation method is as follows:

[0059]

[0060] Where: f is the vibration frequency, cpm; S is the vibration stroke, mm; α is the waveform slope, which is 0 for a sinusoidal vibration curve; v c is the pulling speed, m / min.

[0061] Positive slip time t P (s) is defined as all the time except the negative slip time in one vibration cycle, during which the mold 1 moves upward relative to the continuous casting billet 2 and the billet shell is subjected to tensile stress. It is calculated as follows:

[0062]

[0063] The negative slip rate NR is defined as the ratio of the average speed of the downward movement of the crystallizer 1 exceeding the pulling speed in one vibration cycle to the pulling speed. A larger negative slip rate is beneficial to improving the demoulding effect at the start-up stage of the casting machine and preventing steel leakage during the pouring. The calculation method is as follows:

[0064]

[0065] 3) Calculation of key parameters describing the metallurgical performance of the crystallizer 1.

[0066] Based on the current vibration process parameters and metallurgical parameters, and combined with the mold slag performance parameters, the thickness of the liquid slag film 3 in the gap between the solidified shell and the wall of the crystallizer 1, the mold slag consumption and the vibration mark depth are calculated.

[0067] The liquid protective slag flows into the gap along the channel below the meniscus of the crystallizer 1 and is cooled. The cooling intensity near the wall of the crystallizer 1 is relatively large, and a thin glassy slag film will be formed. If the protective slag stays in the crystallizer 1 for a long enough time, a crystalline slag film will be formed. The protective slag near the surface of the shell is usually kept as a liquid slag film 3 due to its relatively high temperature. It is the main factor determining the lubrication state of the crystallizer 1. The thickness of the liquid slag film d Lfilm The calculation method of (mm) is as follows:

[0068] d Lfilm =79.1512·v c -0.628 ·T br -0.866 ·S 0.341 ·f 0.076 ·t P 0.116 (6)

[0069] For metallurgical effect, mold powder has two important functions, namely, uniform heat transfer and good lubrication. Whether the lubrication of the mold 1 is good or not can be evaluated by the powder consumption, that is, the powder mass consumed per unit area of ​​the billet surface or per ton of steel, the powder consumption Q slag (Kg / m 2 ) and M slag The calculation method of (Kg / ton) is as follows:

[0070]

[0071] Where: slag is the density of protective slag, Kg / m 3 ρ steel is the density of molten steel, Kg / m 3 ; g is the acceleration due to gravity, g = 9.8 m / s 2 ; W and N are the width and thickness of the slab, m.

[0072] During the slab continuous casting production process, the periodic vibration of the crystallizer 1 will cause the pressure of the protective slag channel between the billet shell and the wall to change periodically, thereby generating evenly spaced vibration marks on the surface of the continuous casting billet 2. During the period of negative slippage during vibration, positive pressure toward the billet shell is generated in the slag channel, causing the billet shell to move away from the wall and bend and deform; during the period of positive slippage during vibration, negative pressure toward the wall is generated in the slag channel, which works together with the static pressure of the molten steel to push the billet shell toward the wall. The primary billet shell undergoes periodic movement changes relative to the wall under the alternating action of positive and negative pressures. If the strength of the primary billet shell is low, it is easily sucked onto the wall under the action of negative pressure. At this time, there is no overflow of molten steel, forming a concave vibration mark 13. Otherwise, it will combine with the overflow of molten steel that is continuously replenished to form a hook-shaped vibration mark 12. Vibration marks are usually where transverse cracks are generated, which have an important influence on the surface quality of the continuous casting billet 2. The depth of the vibration mark d osc The calculation method of (mm) is as follows:

[0073]

[0074] 4) Calculate the thickness of the liquid slag layer and its lower limit as the main optimization target object.

[0075] According to the cross-sectional specifications of the continuous casting billet 2 and the liquid level fluctuation limit of the crystallizer 1, the thickness of the liquid slag layer above the meniscus in the crystallizer and its minimum allowable value are calculated, and the optimization solution target is set.

[0076] The protective slag is evenly laid on the steel liquid surface of the crystallizer 1. The heat released by the steel liquid rapidly heats up the crystallizer to form a liquid slag layer 10, a semi-molten layer 9, a sintered layer 8 and a solid slag layer 7 from bottom to top. During the periodic vibration of the crystallizer 1, the liquid slag with good fluidity seeps in along the gap between the wall of the crystallizer 1 and the surface of the solidified shell, playing a metallurgical role in improving lubrication and controlling heat transfer. In order to prevent the unmelted solid protective slag from being drawn into the casting strand, the thickness of the liquid slag layer 10 should usually be greater than the vibration stroke of the crystallizer 1. The thickness of the liquid slag layer d L (mm) and its minimum allowable value d L,min The calculation method of (mm) is as follows:

[0077]

[0078] Where: S R The slag rate, also known as the vitrification rate, refers to the percentage of liquid slag formed by the protective slag during heating. It is a reflection of the flow and lubrication characteristics of the protective slag. Its reasonable value range is between 0.6 and 0.8. If it is too high, there will be a tendency to form a thick slag ring 6. If it is too low, it will increase the friction of the crystallizer 1 and easily cause cracks in the continuous casting billet 2. It is usually taken as 0.6 for calculation. δ is the fluctuation value of the steel liquid surface in the crystallizer 1. Under normal circumstances, δ = 1 to 3 mm, and it can be taken as 2 mm for calculation.

[0079] In principle, it is required L ≥d L,min To ensure that no entanglement occurs, the optimization goal is set to:

[0080]

[0081] 5) Reasonably set multiple restrictive conditions for optimization solution.

[0082] Restrictive conditions are set according to metallurgical process requirements and vibration equipment capabilities, including minimum protection slag consumption, maximum vibration mark depth, and reasonable vibration stroke, frequency and waveform deflection rate value ranges.

[0083] The consumption of protective slag is the main indicator for evaluating the lubrication condition of the crystallizer 1, and is proportional to the thickness of the slag film between the continuous casting billet 2 and the wall of the crystallizer 1. In order to ensure a good surface quality of the continuous casting billet 2, it is necessary to ensure sufficient consumption of protective slag; the generation of vibration marks on the continuous casting billet 2 deteriorates the surface quality of the continuous casting billet 2, reduces the local heat flux intensity, slows down the growth of the billet shell thickness, and reduces the effective force-bearing area of ​​the billet shell, which will lead to a decrease in the billet shell's ability to withstand the resistance of the billet drawing, which is equivalent to generating additional stress on the continuous casting billet 2. The depth of the vibration marks needs to be controlled as much as possible during production; in addition, the value range of the vibration parameters must take into account the capabilities of the equipment itself, otherwise it will cause an unstable vibration state, which is detrimental to production.

[0084] Based on the above process requirements and equipment capabilities, and combined with production experience, the following restrictive conditions are introduced:

[0085] 50≤f≤250 (13-1)

[0086] 2≤S≤15 (13-2)

[0087] 0≤α≤0.3 (13-3)

[0088] Q slag ≥0.3 (13-4)

[0089] d osc ≤0.5 (13-5)

[0090] 6) Perform planning and solving to obtain the optimized vibration process parameters and synchronous control model.

[0091] Perform multi-parameter planning and solving to obtain the theoretical optimization value of the vibration process parameters under the casting speed condition, then adjust the casting speed setting value, and repeat the above solving steps until the vibration process parameter optimization results within the entire casting speed range are obtained, thereby forming a vibration process synchronization control model for the crystallizer 1 that can be used for on-site production. The specific calculation example results are listed in the table below.

[0092] Slab width, mm 1500 Slab thickness, mm 230 Mold slag solidification temperature, ℃ 1030 Dynamic viscosity of mold slag, Pa·s 0.53 <![CDATA[Mould powder density, Kg / m 3 > 2500 <![CDATA[Liquid steel density, Kg / m 3 > 7400 Pulling speed, m / min 1.1 Liquid level fluctuation, mm 2 Vibration frequency, cpm 103 Vibration stroke, mm 4.8 Waveform skewness 0 Negative slip time, s 0.145 Positive slip time, s 0.44 Negative slip rate 0.496 Liquid slag film thickness, mm 0.405 <![CDATA[Consumption of mold powder, Kg / m 2 > 0.574 Consumption of mold slag, Kg / ton 0.778 Vibration mark depth, mm 0.249 Minimum liquid slag layer thickness, mm 4.85 Liquid slag layer thickness, mm 7.275

[0093] The present invention aims at the theoretical design of the vibration process parameters of the crystallizer 1 and the synchronous control model thereof, fully considers the reasonable control of important metallurgical parameters of the crystallizer 1 such as the thickness of the liquid slag film 3, the protective slag consumption, the vibration mark depth, etc., and is based on the theoretical analysis of the thickness of the liquid slag layer above the meniscus in the crystallizer. From the perspective of avoiding the slag rolling phenomenon, its target value is set and used as the optimization target object. At the same time, the capacity limitation of the crystallizer vibration device itself is fully considered, and the vibration process parameters and the synchronous control model of the crystallizer 1 are optimized by a multi-parameter planning solution method. Compared with the previous optimization method that simply considers the negative slip time or the negative slip rate, it can better reflect the comprehensiveness of its consideration of metallurgical process factors, can better reduce the probability of abnormal casting events and ensure the good quality of the continuous casting billet 2, and provide important support for the development of efficient slab continuous casting technology. It is worthy of large-scale promotion and application in the metallurgical field.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for optimizing the vibration process parameters of a slab continuous casting mold, characterized in that: The following steps are involved: S1 sets the optimization target based on the theoretical calculation of the liquid slag layer thickness; S2 takes metallurgical process requirements and mold vibration equipment capabilities as reference conditions and uses multi-parameter planning and solving methods to optimize the vibration process parameters; S3 formulates a vibration process synchronization control model.

2. The method for optimizing the vibration process parameters of a slab continuous casting mold according to claim 1, characterized in that: In S1, the thickness of the liquid slag layer above the meniscus in the crystallizer and its minimum allowable value are calculated according to the cross-sectional specifications of the ingot and the limit of the liquid level fluctuation in the crystallizer, and the optimization target is set.

3. The method for optimizing the vibration process parameters of a slab continuous casting mold according to claim 1, characterized in that: In S2, key vibration metallurgical parameters are calculated according to the current vibration process parameters. The vibration metallurgical parameters include negative slip time, positive slip time and negative slip rate.

4. The method for optimizing the vibration process parameters of a slab continuous casting mold according to claim 1, characterized in that: In S2, the initial values ​​of the crystallizer vibration process parameters, including vibration stroke, frequency and waveform slope, are set according to the casting speed conditions, and the solidification temperature and dynamic viscosity of the mold slag are calculated according to the mold slag composition information.

5. The method for optimizing the vibration process parameters of a slab continuous casting mold according to claim 1, characterized in that: In S2, the performance parameters of the protective slag are combined to calculate the liquid slag film thickness, protective slag consumption and vibration mark depth.

6. The method for optimizing the vibration process parameters of a slab continuous casting mold according to claim 1, characterized in that: S2 includes the following sub-steps: S21 calculates the thickness of the liquid slag layer and its minimum allowable value according to the cross-sectional specifications of the ingot and the limit of the liquid level fluctuation of the crystallizer, and sets the optimization solution target; S22 sets the value range of the vibration parameter.

7. The method for optimizing the vibration process parameters of a slab continuous casting mold according to claim 6, characterized in that: Vibration parameters include minimum protective slag consumption, maximum vibration mark depth, and reasonable vibration stroke, frequency and waveform deflection rate.

8. The method for optimizing the vibration process parameters of a slab continuous casting mold according to claim 1, characterized in that: In S3, the crystallizer vibration process parameters are optimized by multi-parameter planning and solving method, and the parameters include stroke, frequency and waveform deflection rate.

9. The method for optimizing the vibration process parameters of a slab continuous casting mold according to claim 1 or 8, characterized in that: S3 includes the following sub-steps: S31 performs multi-parameter planning and solving to obtain optimized values ​​of vibration process parameters; S32 adjusts the drawing speed setting value and repeats the solution steps to form a vibration process synchronization control model.

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