Slab continuous casting high-temperature casting blank surface temperature on-line detection method

Abstract

The invention relates to a slab continuous casting high-temperature casting blank surface temperature on-line detection method, and belongs to the technical field of slab continuous casting, and the method comprises the following steps: S1, making a detection piece and a measuring disc based on a film temperature sensor, and installing the detection piece and the measuring disc on a corresponding secondary cooling zone fan-shaped section pinch roll according to process requirements; s2, performing local transient heat transfer conservation analysis on the temperature measurement nodes to obtain a heat balance equation considering conduction, convection and radiation heat transfer modes; s3, carrying out numerical calculation on the heat balance equation based on a single-node temperature time sequence discrete algorithm according to the temperature detection value so as to reconstruct and determine the actual temperature of the upper side of the water film on the surface of the casting blank; s4, performing theoretical analysis on a boiling heat transfer mechanism, and determining a corresponding critical characteristic temperature and a heat transfer mode; and S5, under a stable film state boiling heat transfer mechanism, according to a classical plate temperature analysis theory, reconstruction calculation is carried out again in combination with the obtained temperature of the upper side of the water film on the surface of the casting blank, and finally the real temperature value of the surface of the casting blank is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of slab continuous casting, and relates to an online detection method for the surface temperature of a high-temperature slab in slab continuous casting. Background Art

[0002] During the slab continuous casting process, the liquid cored billet enters the secondary cooling zone after leaving the crystallizer and is continuously spray cooled until solidification is completed. The cooling intensity distribution and solidification state characteristics are related to product quality and smooth production. Two metallurgical process models, dynamic secondary cooling water distribution and dynamic soft reduction, are usually used to control the cooling water volume of each secondary cooling zone and the roller gap value of each fan-shaped segment along the billet drawing direction. The key feedback information involved is the billet surface temperature. Due to the harsh casting environment and limited equipment space, there is currently no ideal online detection method for this. Either a quasi-steady-state heat transfer mathematical model is used for pure theoretical calculation (the boundary conditions are difficult to accurately and quantitatively describe), or an infrared thermometer is installed at a specific location for online remote detection ( The distance is long, there are many interference factors, the system is complex, and the maintenance is large). From the perspectives of accuracy, reliability and practicality, these two methods have major defects. It is necessary to develop a method suitable for online continuous detection of the surface temperature of the billet in the entire secondary cooling zone for the slab continuous casting, targeting the harsh environmental conditions such as high temperature, high moisture, high smoke and dust, and narrow space in the secondary cooling zone of the slab continuous casting, minimize the interference of external factors such as moisture, smoke and dust on site, make full use of the structural characteristics of the casting machine equipment to optimize the design of the shape and installation method of the sensor detection part, and consider in detail the various heat transfer modes and thermal balance relationships existing in the temperature measurement nodes and the heat transfer mechanism of the spray cooling water on the high-temperature billet surface, so as to achieve accurate online multi-point continuous temperature detection and provide technical support for high-quality continuous casting production. Summary of the invention

[0003] In view of this, an object of the present invention is to provide a method for online detection of the surface temperature of a high-temperature slab during slab continuous casting.

[0004] In order to achieve the above object, the present invention provides the following technical solutions:

[0005] A method for online detection of the surface temperature of a slab continuous casting high-temperature casting slab comprises the following steps:

[0006] S1: Make the detection parts and measuring disc based on the thin film temperature sensor, and install them on the corresponding second cooling zone fan-shaped segment roller according to the process requirements;

[0007] S2: Perform local transient heat transfer conservation analysis on the temperature measurement node to obtain the heat balance equation considering the three heat transfer modes of conduction, convection and radiation;

[0008] S3: Based on the single-node temperature time series discrete algorithm and according to the temperature detection values ​​obtained at a certain time step, the heat balance equation is numerically calculated to reconstruct and determine the actual temperature above the water film on the surface of the ingot;

[0009] S4: Theoretical analysis of boiling heat transfer mechanism is conducted on the spray water cooling state of the high-temperature ingot surface during slab continuous casting to determine its corresponding critical characteristic temperature and the heat transfer mode;

[0010] S5: Under the premise of stable film boiling heat transfer mechanism, according to the classical flat plate temperature analysis theory, combined with the obtained temperature above the water film on the surface of the ingot, reconstruction calculation is performed again to finally obtain the real temperature value of the ingot surface.

[0011] Further, step S1 specifically includes the following steps:

[0012] A radiation-type detection component is made of a nickel-chromium-nickel-aluminum-manganese-silicon K-type thin film temperature sensor, and is embedded in the bottom of a fan-shaped segment clamping roller measuring disk. The clamping roller at the entrance position of the starting fan-shaped segment and the clamping roller at the exit position of the end fan-shaped segment of each secondary cooling partition are used as the installation positions of the measuring disk. The outer surface of the radiation-type detection component is coated with a black body material, and online temperature detection is performed by close-range radiation, and the spray water volume of each partition is dynamically adjusted according to a predetermined target temperature curve.

[0013] Further, in step S2, the thermal balance equation of the temperature sensor temperature measurement node satisfies:

[0014]

[0015] Q conv =h·A conv ·(TT g ) (1-3)

[0016]

[0017] Where: m is the mass of the temperature measurement node; c is the specific heat capacity of the temperature measurement node; T is the temperature of the temperature measurement node; t is the time; Q rads It represents the radiation heat absorption from the high temperature ingot surface to the temperature measuring node; Q conv represents the convective heat loss between the temperature measurement node and the surrounding air; Q cond represents the comprehensive heat conduction loss between the temperature measurement node and other components; ε is the surface emissivity of the temperature measurement head; σ is the Stefan-Boltzmann constant; A rads A is the radiation heat transfer area between the temperature measurement node and the surface of the casting; conv is the convection heat transfer area between the temperature measurement node and the surrounding air; A condis the conduction heat transfer area between the temperature measurement node and the wire and other components; h is the convection heat transfer coefficient between the temperature measurement node and the surrounding air; λ is the comprehensive thermal conductivity between the temperature measurement node and the wire and other components; T f T is the temperature above the water film on the billet surface; g is the air temperature around the temperature measurement node; T b is the far-end temperature of the test piece; L is the heat conduction distance between the temperature measurement node and the conductor and other components.

[0018] Further, the step S3 described in which the heat balance equation is numerically calculated based on the single-node temperature time series discrete algorithm and the temperature detection values ​​obtained at a certain time step to reconstruct and determine the actual temperature of the upper side of the water film on the surface of the casting billet specifically includes the following steps:

[0019] By integrating equations (1-1) to (1-4), we can obtain:

[0020]

[0021] After moving the items, we get:

[0022]

[0023] make:

[0024]

[0025] Further rearrangement of formula (3) yields:

[0026]

[0027] make:

[0028]

[0029] The collection period of field detection is δt. For each time node in the N collection periods, the formula (5) is calculated according to the detection temperature T of the temperature measurement node, and the formula is:

[0030]

[0031] Rewrite (5) into the following simplified matrix form:

[0032]

[0033] According to the least squares method, the three coefficients in the above formula are solved, namely:

[0034]

[0035] In the solution process, the known surface temperature of the plate is set under similar conditions for testing, and the coefficients α, β and γ are calibrated;

[0036] Substituting (9) into (5) we get:

[0037]

[0038] After further sorting:

[0039]

[0040] The actual temperature T above the water film on the billet surface is reconstructed and analyzed from the currently detected temperature T f .

[0041] Further, in step S4, the minimum film boiling temperature T is constructed. LDF The analytical function relationship of is:

[0042]

[0043] Where, T LDF is the minimum film boiling temperature, ΔT sub is the subcooling degree of the spray cooling water; λ is the thermal conductivity; ρ is the density; c P is the isobaric specific heat capacity; R a is the average roughness of the solid surface; subscripts l and v represent cooling water and water vapor, respectively;

[0044] Under the premise of considering the existence of Rayleigh-Taylor instability at the gas-liquid interface, an analytical calculation formula for film boiling temperature is constructed, namely:

[0045]

[0046] Where: T sat is the saturation temperature of cooling water; L ev is the latent heat of vaporization; σ is the surface tension of cooling water; μ v is the dynamic viscosity of water vapor; g is the acceleration due to gravity;

[0047] The following dimensionless numbers are introduced:

[0048]

[0049] Where: R ref is the reference average surface roughness; Ja sub The Jacob number is the ratio of superheat to latent heat during phase change of liquid.

[0050] Rewrite (12) into a product relationship in the form of dimensionless numbers, that is:

[0051]

[0052] In the formula: a, b, c, d are all unknown coefficients;

[0053] Combining the above methods, we can obtain:

[0054]

[0055] Where: T l is the spray cooling water temperature;

[0056] For the secondary cooling scenario of conventional continuous casting slab, combined with the specific conditions of the slab and cooling water, the corresponding minimum film boiling temperature is solved by equation (16) as T LDF ; T LDF With T l The temperature gradually decreases with the increase of temperature, thereby finding the turning point between film boiling and transition boiling in the actual slab continuous casting process. When the surface temperature of the casting billet reaches or exceeds the turning point value, it is considered to be in a stable film boiling heat transfer mechanism.

[0057] Further, in step S5, for the air film layer:

[0058]

[0059] Where: t is the current moment; t-Δt is the previous moment; Δt is the time interval between two temperature detections; T w is the surface temperature of the casting billet; T v is the temperature above the air film; δ v is the thickness of the air film layer; α v is the thermal diffusion coefficient of the air film; v is the thermal conductivity of the air film; ρ v is the air film density; c P,v is the isobaric specific heat capacity of the gas film;

[0060] For the water film layer:

[0061]

[0062] Where: T f is the temperature above the water film; δ f is the thickness of the water film; α f is the thermal diffusion coefficient of the water film; f is the thermal conductivity of the water film; ρ f is the water film density; c P,f is the isobaric specific heat of water film;

[0063] Combining equation (17-1) and equation (18-1), we can deduce:

[0064]

[0065] From formula (19), we know that the surface temperature of the billet at the current moment can be approximately calculated based on the water film surface temperature obtained by online detection at the current time and the previous two moments. For the continuous casting slab moving at a certain drawing speed, the calculation is performed based on the temperature values ​​measured at the detection points spaced apart along the drawing direction at the three previous and next moments.

[0066] The beneficial effects of the present invention are as follows: the present invention makes full use of the characteristics of the thin film temperature sensor, such as small size, good protection and long service life, and combines the structural characteristics of the fan-shaped segment of the continuous casting machine to implement close-range radiation temperature measurement through the detection part embedded in the bottom of the clamping roller measuring disk, which can greatly reduce the influence of on-site interference factors such as water vapor and smoke on heat transfer, and the smaller the spatial scale of the local area, the more conducive to the reasonable determination of the heat transfer boundary conditions. In addition, based on the local transient heat transfer conservation analysis of the temperature measurement node, the single-node temperature time series discrete algorithm and the theoretical analysis of the stable film boiling heat transfer mechanism, the influence of various heat transfer modes and boiling heat transfer mechanisms on the surface of the ingot on the measured temperature is considered in detail, which can effectively overcome the problems of poor prediction / detection accuracy, limited detection position, difficult maintenance and short service life brought about by the previous reliance on heat transfer numerical theory calculation or long-distance infrared temperature measurement method, and can provide key feedback information for continuous casting metallurgical process control models such as dynamic secondary cooling water distribution and light pressure reduction, and provide important technical support for ensuring the stability of casting production and obtaining good ingot quality.

[0067] 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

[0068] 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:

[0069] Figure 1 It is a schematic diagram of a radiation type detection component;

[0070] Figure 2 This is a schematic diagram of the installation position of the test piece;

[0071] Figure 3 This is a schematic diagram of the detection working principle;

[0072] Figure 4 Schematic diagram of heat transfer conservation at the temperature measurement node;

[0073] Figure 5 Schematic diagram of boiling heat transfer mechanism;

[0074] Figure 6The effect of the surface roughness of the ingot on the minimum film boiling temperature;

[0075] Figure 7 The effect of spray cooling water temperature on the minimum film boiling temperature;

[0076] Figure 8 Schematic diagram of stable film boiling heat transfer on the surface of high-temperature ingot. DETAILED DESCRIPTION

[0077] 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.

[0078] It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and thus the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0079] In the following description, numerous details are discussed to provide a more thorough explanation of the embodiments of the present invention. However, it is obvious to those skilled in the art that the embodiments of the present invention can be implemented without these specific details. In other embodiments, well-known structures and devices are shown in the form of block diagrams rather than in detail to avoid making the embodiments of the present invention difficult to understand.

[0080] The present invention provides a method for online detection of the surface temperature of a high-temperature ingot in slab continuous casting. A sensor detection component is installed below the clamping roller of a fan-shaped segment to implement a close-range radiation temperature measurement method. Based on the local transient heat transfer conservation analysis of the temperature measurement node, the single-node temperature time series discrete algorithm and the theoretical analysis of the stable film boiling heat transfer mechanism, the surface temperature of the high-temperature ingot is reconstructed secondarylly in combination with the actual detection value of the sensor. The real tracking of the surface temperature of the ingot is achieved in the entire secondary cooling zone of the slab continuous casting, and accurate feedback information is provided for metallurgical process control models such as dynamic secondary cooling water distribution and soft reduction.

[0081] This method mainly includes the following steps:

[0082] (1) A detection component and a measuring disk are manufactured based on a thin film temperature sensor and installed on the corresponding second cooling zone fan-shaped segment nip roller according to the process requirements.

[0083] The radiation type detection part (such as Figure 1 ) and is embedded in the bottom of the measuring plate of the fan-shaped roller (such as Figure 2 ), the outer surface of the detection part is coated with black body material to improve the heat transfer efficiency, and online temperature detection is performed by close-range radiation (such as Figure 3 ).

[0084] Theoretically, measuring discs can be installed on the clamping rollers at the entrance and exit positions of all the fan-shaped segments in the entire secondary cooling zone along the direction of the billet drawing (for three-section rollers, each clamping roller can be installed one at each section position on the left and right sides). However, based on the consideration of secondary cooling water distribution control, the clamping rollers at the entrance position of the starting fan-shaped segment and the clamping rollers at the exit position of the end fan-shaped segment of each secondary cooling partition are usually selected as the installation positions of the measuring discs. The spray water volume of each partition is dynamically adjusted through real-time online temperature detection and according to the established target temperature curve.

[0085] (2) Theoretical analysis of local transient heat transfer conservation at temperature measurement nodes.

[0086] A local transient heat transfer conservation analysis is performed on the temperature measurement node to obtain the heat balance equation considering the three heat transfer modes of conduction, convection and radiation, such as Figure 4 .

[0087] Considering heat conduction, heat radiation, heat convection and the thermal inertia of the temperature measurement node itself, the thermal balance equation of the temperature sensor head (node) satisfies:

[0088]

[0089] Where: m is the mass of the temperature measurement node, Kg; c is the specific heat capacity of the temperature measurement node, J·Kg -1 ·K -1 ; T is the temperature of the temperature measurement node, K; t is the time, s; Q rads Indicates the radiation heat absorption from the high temperature ingot surface to the temperature measurement node, W; Q conv represents the convective heat loss between the temperature measurement node and the surrounding air, W; Q cond represents the comprehensive heat conduction loss between the temperature measurement node and other components such as the wire and the housing, W; ε is the surface emissivity of the temperature measurement head; σ is the Stefan-Boltzmann constant, σ=5.67×10 -8 W·m -2 ·K -4 ; A rads is the radiation heat transfer area between the temperature measurement node and the billet surface, m 2 ; Aconv is the convection heat transfer area between the temperature measurement node and the surrounding air, m 2 ; A cond is the conduction heat transfer area between the temperature measurement node and the conductor and other components, m 2 ; h is the convective heat transfer coefficient between the temperature measurement node and the surrounding air, W·m -2 ·K -1 ; λ is the comprehensive thermal conductivity between the temperature measurement node and the conductor and other components, W·m -1 ·K -1 ; T f is the temperature above the water film on the billet surface, K; T g is the air temperature around the temperature measurement node, K; T b is the far-end temperature of the test piece, K; L is the heat conduction distance between the temperature measurement node and the conductor and other components, m.

[0090] (3) Reconstruct and analyze the temperature value above the water film on the surface of the ingot.

[0091] Based on the single-node temperature time series discrete algorithm and according to the temperature detection values ​​obtained at a certain time step, the heat balance equation is numerically calculated to reconstruct and determine the actual temperature above the water film on the surface of the casting.

[0092] By integrating equations (1-1) to (1-4), we can obtain:

[0093]

[0094] After moving items, we can get:

[0095]

[0096] make:

[0097]

[0098] Further rearrangement of formula (3) yields:

[0099]

[0100] make:

[0101]

[0102] The acquisition period of field detection is δt. For each time node in the N acquisition periods, the formula (5) can be calculated according to the detection temperature T of the temperature measurement node. Let:

[0103]

[0104] Then equation (5) can be rewritten into the following simplified matrix form:

[0105]

[0106] The three coefficients in the above formula can be solved by the least squares method, namely:

[0107]

[0108] In the solution process, it is necessary to substitute T f Therefore, the known surface temperature of the plate can be set under similar conditions for testing and the coefficients α, β and γ can be calibrated.

[0109] Substituting (9) into (5) we can obtain:

[0110]

[0111] After further sorting, we can get:

[0112]

[0113] The actual temperature T above the water film on the surface of the casting billet can be reconstructed and analyzed from the currently detected temperature T f .

[0114] (4) Analysis of the heat transfer mechanism and state of water spraying on the surface of the ingot.

[0115] The boiling heat transfer mechanism is theoretically analyzed for the spray water cooling state of the high-temperature ingot surface of slab continuous casting to determine its corresponding critical characteristic temperature and the heat transfer mode, such as Figure 5 to Figure 7 .

[0116] During the slab continuous casting process, the high-temperature ingot (surface temperature after being pulled out of the crystallizer is about 1200℃) is continuously cooled by mist spray in the secondary cooling zone until it is completely pulled out of the casting machine outlet. Due to the release of latent heat in the liquid core of the ingot, the outward conduction of heat along the thickness of the solidified ingot shell, and the periodic experience of other heat transfer modes such as air cooling radiation heat transfer and roller contact heat transfer on the surface, the surface temperature of the ingot will fluctuate to a certain extent while maintaining an overall downward trend. Heat transfer theory simulation and production practice tests show that the center temperature of the ingot surface in the secondary cooling zone of the conventional slab continuous casting process is usually in the range of 850-1200℃, and for such a high-temperature solid surface, the spray cooling process is a typical boiling heat transfer mechanism.

[0117] As the surface temperature rises, the liquid undergoes a phase change of evaporation to form bubbles, and the cooling water gradually transitions to nucleate boiling heat transfer through natural convection heat transfer, and the heat flux density continues to increase until it reaches the critical heat flux density value CHF; when the surface temperature exceeds this point, a large number of bubbles are generated, forming a very high distribution density, making direct contact between the cooling water and the surface increasingly difficult, and the heat flux suddenly drops, entering the so-called transition boiling zone; as the surface temperature continues to rise, the bubbles continue to nucleate, grow and detach from the surface until they are connected to form a stable vapor film between the liquid and the solid surface. Heat transfer is mainly through conduction, convection and radiation of this layer of gas film. The vapor escapes from the film in the form of bubbles, and the thermal resistance is mainly limited to the gas film. The heat flux continues to drop to the lowest point. The corresponding temperature at this time is the so-called Leidenfrost temperature T LDF , also known as the minimum film boiling temperature; when the surface temperature exceeds T LDF Afterwards, the heat transfer through the stable gas film intensifies and the heat flux rises again, entering the so-called film boiling region.

[0118] Obviously, the minimum film boiling temperature T LDF It is the turning point between film boiling and transition boiling, the lowest temperature for maintaining a stable gas film on the solid surface, and the inflection point where the heat flux density begins to increase. Therefore, it can be said to be an important parameter for characterizing the boiling heat transfer characteristics. Its influencing factors mainly include the subcooling of the cooling water (relative to its saturation temperature), material physical properties (density, thermal conductivity and specific heat capacity), and the hydrophilicity (wetting angle) and roughness (average roughness) of the solid surface. Its accurate prediction is of great significance for evaluating and improving the boiling heat transfer cooling efficiency. It is worthwhile to construct the following analytical function relationship:

[0119]

[0120] Where: ΔT sub is the subcooling degree of the spray cooling water, K; λ is the thermal conductivity, W·m -1 ·K -1 ; ρ is density, Kg·m -3 ;c P is the isobaric specific heat capacity, J·Kg -1 ·K -1 ; R a is the average roughness of the solid surface; the subscripts l and v represent cooling water and water vapor, respectively.

[0121] In addition, considering the existence of Rayleigh-Taylor instability at the gas-liquid interface (interfacial turbulent mixing phenomenon caused by density gradient between two substances separated by an interface), the corresponding film boiling temperature analytical calculation formula can be constructed, that is:

[0122]

[0123] Where: T sat is the saturation temperature of cooling water, K; L ev is the latent heat of vaporization, J·Kg -1 ;σ is the surface tension of cooling water, N·m -1 ;μ v is the dynamic viscosity of water vapor, Pa·s; g is the acceleration due to gravity.

[0124] For the convenience of analysis, the following dimensionless numbers are introduced:

[0125]

[0126] Where: R ref is the reference average surface roughness, R ref =1μm; Ja sub The Jacob number is the ratio of superheat to latent heat during phase change of a liquid.

[0127] Considering that the effects of spray cooling water subcooling, solid surface roughness and material properties on film boiling temperature are independent of each other, equation (12) can be rewritten as a product relationship in the form of dimensionless numbers, that is,

[0128]

[0129] Wherein: a, b, c, d are all unknown coefficients. For the case of cooling water spraying flat steel plate, the approximate values ​​can be a=134.91, b=-0.0022, c=-0.181, d=0.564.

[0130] Combining the above formulas, you can get:

[0131]

[0132] Where: T l is the spray cooling water temperature, K.

[0133] For the secondary cooling scenario of conventional continuous casting slab, combined with the specific conditions of the slab and cooling water (average roughness of the slab surface R a ≈1000μm, cooling water temperature T l ≈30℃), the corresponding minimum film boiling temperature can be solved by the above formula as T LDF ≈769.8℃. Obviously, the secondary cooling zone of slab continuous casting is in a stable film boiling heat transfer mechanism, the surface of the casting is covered with air film and water film, and there is a large temperature gradient perpendicular to the direction of the casting.

[0134] T LDF With R a The increase of R aWhen the thickness increases from 100 μm to 2000 μm, T LDF It only changes from 772.7℃ to 768.9℃, and such changes can usually be ignored; T LDF With T l The cooling water subcooling ΔT sub When T decreases from 90℃ to 20℃, LDF The corresponding change is from 857.9℃ to 476.6℃, which means that film boiling turns into transition boiling later and the heat transfer effect is weakened.

[0135] In the actual slab continuous casting process, the cooling water temperature is usually in the range of 25-40°C, and considering that the surface roughness of the slab has little effect, it can be considered that T l = T at 30℃ LDF =769.8℃ is the turning point between film boiling and transition boiling. When the surface temperature of the ingot reaches or exceeds this value, it can be considered to be in a stable film boiling heat transfer mechanism.

[0136] (5) Reconstruct and analyze the actual temperature value of the ingot surface.

[0137] Under the premise of stable film boiling heat transfer mechanism, according to the classical flat plate temperature analysis theory, combined with the temperature above the water film on the surface of the ingot obtained in the previous step, the reconstruction calculation is performed again to finally obtain the actual temperature value of the ingot surface, such as Figure 8 .

[0138] The air film and water film on the surface of the ingot can be regarded as a flat layer structure with a certain thickness. The relationship between the temperatures on the upper and lower sides of each film layer can be determined by the classic flat plate temperature analytical formula, and then the relationship between the surface temperature of the ingot (i.e., the temperature below the air film) and the surface temperature of the water film (i.e., the temperature above the water film) can be found. In this way, the true surface temperature of the ingot can be reconstructed and calculated by combining the relationship between the two.

[0139] For the air film layer:

[0140]

[0141] Where: t is the current moment; t-Δt is the previous moment; Δt is the time interval between two temperature detections, s; T w is the surface temperature of the ingot (temperature below the air film), K; T v is the temperature above the air film, K; δ v is the thickness of the air film layer, m; α v is the thermal diffusion coefficient of the air film, m 2 ·s -1 ; v is the film thermal conductivity, W·m-1 ·K -1 ρ v is the air film density, Kg·m -3 ;c P,v is the isobaric specific heat capacity of the gas film, J·Kg -1 ·K -1 .

[0142] For the water film layer:

[0143]

[0144] Where: T f is the temperature above the water film (i.e. the temperature detected by the sensor), K; δ f is the thickness of the water film, m; α f is the thermal diffusion coefficient of the water film, m 2 ·s -1 ; f is the thermal conductivity of the water film, W·m -1 ·K -1 ρ f is the water film density, Kg·m -3 ;c P,f is the isobaric specific heat of water film, J·Kg -1 ·K -1 .

[0145] Combining equation (17-1) and equation (18-1), we can further deduce:

[0146]

[0147] From formula (19), we can know that the current temperature of the billet surface can be approximately calculated based on the water film surface temperature obtained by online detection at the current time and the previous two moments. Note that for a continuous casting billet moving at a certain drawing speed, this means that the calculation should be based on the temperature values ​​measured by the detection points spaced along the billet drawing direction at the previous and next three moments.

[0148] For conventional slab continuous casting with a casting speed of 1.2m / min, the temperature drop experienced by the billet at the rear end of the secondary cooling zone when it moves 100mm every 5 seconds is about 10℃. For example, the detection values ​​at three adjacent time points are 604℃, 614℃ and 624℃ respectively. Based on the actual production experience, the surface temperature of the billet at the current moment is calculated to be about 903.5℃ under the conditions of 200μm air film thickness and 2mm water film thickness. This result is consistent with the engineering experience value, which fully illustrates the rationality of the theoretical analysis.

[0149] In the above embodiments, the description's reference to "this embodiment" indicates that a particular feature, structure, or characteristic described in conjunction with the embodiment is included in at least some embodiments, but not necessarily all embodiments. Multiple occurrences of "this embodiment" do not necessarily all refer to the same embodiment.

[0150] In the above-described embodiments, although the invention has been described in conjunction with specific embodiments of the invention, many substitutions, modifications, and variations of these embodiments will be apparent to those of ordinary skill in the art based on the foregoing description. For example, other storage structures (e.g., dynamic RAM (DRAM)) may use the embodiments discussed. Embodiments of the invention are intended to encompass all such substitutions, modifications, and variations that fall within the broad scope of the appended claims.

[0151] This embodiment further provides a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, any one of the methods in this embodiment is implemented.

[0152] This embodiment also provides an electronic terminal, including: a processor and a memory;

[0153] The memory is used to store a computer program, and the processor is used to execute the computer program stored in the memory, so that the terminal executes any one of the methods in this embodiment.

[0154] The computer-readable storage medium in this embodiment can be understood by ordinary technicians in this field: all or part of the steps of implementing the above-mentioned method embodiments can be completed by hardware related to the computer program. The aforementioned computer program can be stored in a computer-readable storage medium. When the program is executed, the steps of the above-mentioned method embodiments are executed; and the aforementioned storage medium includes: ROM, RAM, magnetic disk or optical disk and other media that can store program codes.

[0155] The electronic terminal provided in this embodiment includes a processor, a memory, a transceiver and a communication interface. The memory and the communication interface are connected to the processor and the transceiver and complete communication with each other. The memory is used to store computer programs, the communication interface is used to communicate, and the processor and the transceiver are used to run computer programs so that the electronic terminal executes each step of the above method.

[0156] In this embodiment, the memory may include a random access memory (RAM), and may also include a non-volatile memory (non-volatile memory), such as at least one disk memory.

[0157] The above-mentioned processor can be a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc.; it can also be a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components.

[0158] The present invention can be used in many general or special computing system environments or configurations, such as personal computers, server computers, handheld or portable devices, tablet devices, multiprocessor systems, microprocessor-based systems, set-top boxes, programmable consumer electronic devices, network PCs, minicomputers, mainframe computers, distributed computing environments including any of the above systems or devices, and the like.

[0159] The present invention may be described in the general context of computer-executable instructions executed by a computer, such as program modules. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform specific tasks or implement specific abstract data types. The present invention may also be practiced in distributed computing environments where tasks are performed by remote processing devices connected through a communication network. In a distributed computing environment, program modules may be located in local and remote computer storage media, including storage devices.

[0160] 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 online detection of the surface temperature of a slab continuous casting high-temperature casting billet, characterized in that: The following steps are involved: S1: Make the detection parts and measuring disc based on the thin film temperature sensor, and install them on the corresponding secondary cooling zone fan-shaped segment rollers according to the process requirements; S2: Perform local transient heat transfer conservation analysis on the temperature measurement node to obtain the heat balance equation considering the three heat transfer modes of conduction, convection and radiation; S3: Based on the single-node temperature time series discrete algorithm and according to the temperature detection values ​​obtained at a certain time step, the heat balance equation is numerically calculated to reconstruct and determine the actual temperature above the water film on the surface of the ingot; S4: Theoretical analysis of boiling heat transfer mechanism is conducted on the spray water cooling state of the high-temperature ingot surface during slab continuous casting to determine its corresponding critical characteristic temperature and the heat transfer mode; S5: Under the premise of stable film boiling heat transfer mechanism, according to the classical flat plate temperature analysis theory, combined with the obtained temperature above the water film on the surface of the ingot, reconstruction calculation is performed again to finally obtain the real temperature value of the ingot surface.

2. The method for online detection of the surface temperature of a slab continuous casting high temperature casting according to claim 1, characterized in that: Step S1 specifically includes the following steps: A radiation-type detection component is made of a nickel-chromium-nickel-aluminum-manganese-silicon K-type thin film temperature sensor, and is embedded in the bottom of a fan-shaped segment clamping roller measuring disk. The clamping roller at the entrance position of the starting fan-shaped segment and the clamping roller at the exit position of the end fan-shaped segment of each secondary cooling partition are used as the installation positions of the measuring disk. The outer surface of the radiation-type detection component is coated with a black body material, and online temperature detection is performed by close-range radiation, and the spray water volume of each partition is dynamically adjusted according to a predetermined target temperature curve.

3. The method for online detection of the surface temperature of a slab continuous casting high temperature casting according to claim 1, characterized in that: In step S2, the thermal balance equation of the temperature sensor temperature measurement node satisfies: Q conv =h·A conv ·(T-T g ) (1-3) Where: m is the mass of the temperature measurement node; c is the specific heat capacity of the temperature measurement node; T is the temperature of the temperature measurement node; t is the time; Q rads It represents the radiation heat absorption from the high temperature ingot surface to the temperature measuring node; Q conv represents the convective heat loss between the temperature measurement node and the surrounding air; Q cond represents the comprehensive heat conduction loss between the temperature measurement node and other components; ε is the surface emissivity of the temperature measurement head; σ is the Stefan-Boltzmann constant; A rads A is the radiation heat transfer area between the temperature measurement node and the surface of the casting; conv is the convection heat transfer area between the temperature measurement node and the surrounding air; A cond It is the conduction heat transfer area between the temperature measurement node and the conductor and other components; is; h is the convective heat transfer coefficient between the temperature measurement node and the surrounding air; λ is the comprehensive thermal conductivity between the temperature measurement node and the wire and other components; T f T is the temperature above the water film on the billet surface; g is the air temperature around the temperature measurement node; T b is the far-end temperature of the test piece; L is the heat conduction distance between the temperature measurement node and the conductor and other components.

4. The method for online detection of the surface temperature of a slab continuous casting high temperature casting according to claim 1, characterized in that: The step S3 described in which the heat balance equation is numerically calculated based on the single-node temperature time series discrete algorithm and the temperature detection values ​​obtained at a certain time step to reconstruct and determine the actual temperature above the water film on the surface of the casting billet specifically includes the following steps: By integrating equations (1-1) to (1-4), we can obtain: After the items were moved, we got: make: Further rearrangement of formula (3) yields: make: The collection period of field detection is δt. For each time node in the N collection periods, the formula (5) is calculated according to the detection temperature T of the temperature measurement node, and the formula is: Rewrite (5) into the following simplified matrix form: According to the least squares method, the three coefficients in the above formula are solved, namely: In the solution process, the known surface temperature of the plate is set under similar conditions for testing, and the coefficients α, β and γ are calibrated; Substituting (9) into (5) we get: After further sorting: The actual temperature T above the water film on the billet surface is reconstructed and analyzed from the currently detected temperature T f .

5. The method for online detection of the surface temperature of a slab continuous casting high temperature casting according to claim 1, characterized in that: In step S4, the minimum film boiling temperature T is established. LDF The analytical function relationship of is: Where, T LDF is the minimum film boiling temperature, ΔT sub is the subcooling degree of the spray cooling water; λ is the thermal conductivity; ρ is the density; c P is the isobaric specific heat capacity; R a is the average roughness of the solid surface; subscripts l and v represent cooling water and water vapor, respectively; Under the premise of considering the existence of Rayleigh-Taylor instability at the gas-liquid interface, an analytical calculation formula for film boiling temperature is constructed, namely: Where: T sat is the saturation temperature of cooling water; L ev is the latent heat of vaporization; σ is the surface tension of cooling water; μ v is the dynamic viscosity of water vapor; g is the acceleration due to gravity; The following dimensionless numbers are introduced: Where: R ref is the reference average surface roughness; Ja sub The Jacob number is the ratio of superheat to latent heat during phase change of liquid. Rewrite (12) into a product relationship in the form of dimensionless numbers, that is: In the formula: a, b, c, d are all unknown coefficients; Combining the above methods, we can obtain: Where: T l is the spray cooling water temperature; For the secondary cooling scenario of conventional continuous casting slab, combined with the specific conditions of the slab and cooling water, the corresponding minimum film boiling temperature is solved by equation (16) as T LDF ; T LDF With T l The temperature gradually decreases with the increase of temperature, thereby finding the turning point between film boiling and transition boiling in the actual slab continuous casting process. When the surface temperature of the casting billet reaches or exceeds the turning point value, it is considered to be in a stable film boiling heat transfer mechanism.

6. The method for online detection of the surface temperature of a slab continuous casting high temperature casting according to claim 1, characterized in that: In step S5, for the air film layer: Where: t is the current moment; t-Δt is the previous moment; Δt is the time interval between two temperature detections; T w is the surface temperature of the casting billet; T v is the temperature above the air film; δ v is the thickness of the air film layer; α v is the thermal diffusion coefficient of the air film; v is the film thermal conductivity; ρ v is the air film density; c P,v is the isobaric specific heat capacity of the gas film; For the water film layer: Where: T f is the temperature above the water film; δ f is the thickness of the water film; α f is the thermal diffusion coefficient of the water film; f is the thermal conductivity of the water film; ρ f is the water film density; c P,f is the isobaric specific heat of water film; Combining equation (17-1) and equation (18-1), we can deduce: From formula (19), we know that the current billet surface temperature can be approximately calculated based on the water film surface temperature obtained by online detection at the current time and the previous two moments; For a continuous casting slab moving at a certain drawing speed, calculation is performed based on the temperature values ​​measured at detection points spaced apart along the drawing direction at three moments before and after.

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