A slab continuous casting high-temperature casting blank surface temperature on-line detection method

Abstract

The present application relates to a kind of slab continuous casting high temperature casting blank surface temperature on-line detection method, belong to slab continuous casting technical field, comprising the following steps: S1: based on film temperature sensor production detection piece and measuring disc, and according to process requirement in corresponding two cooling zone sector segment clamp roll installation;S2: local transient heat conservation analysis is carried out to temperature measurement node, obtains the heat balance equation of considering conduction, convection and radiation heat transfer mode;S3: based on single node temperature time series discrete algorithm and according to temperature detection value, the heat balance equation is carried out numerical calculation, to reconstruct the actual temperature of the side above water film on slab surface is determined;S4: boiling heat transfer mechanism theory analysis is carried out, determines its corresponding critical characteristic temperature and the heat transfer mode where it is;S5: under stable film boiling heat transfer mechanism, according to classic flat plate temperature analytical theory, combined with the temperature of the side above water film on slab surface obtained again reconstruction calculation, to finally obtain the real temperature value of slab surface.

Description

Technical Field

[0001] This invention belongs to the field of slab continuous casting technology and relates to an online detection method for the surface temperature of high-temperature slabs in slab continuous casting. Background Technology

[0002] In the continuous casting process of slabs, the slab with liquid core enters the secondary cooling zone after leaving the crystallizer, where it is continuously sprayed and cooled until solidification is complete. The distribution of cooling intensity and solidification state characteristics are crucial to product quality and smooth production. Two metallurgical process models are typically used: dynamic secondary cooling water distribution and dynamic light reduction, to control the cooling water volume of each secondary cooling zone and the roll gap of each sector section along the casting direction. The key feedback information involved is the slab 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 purely theoretical calculations (where boundary conditions are difficult to describe accurately quantitatively), or an infrared thermometer is installed at a specific location for online remote detection. Due to the long distance, numerous interference factors, system complexity, and high maintenance requirements, both methods have significant drawbacks in terms of accuracy, reliability, and practicality. Therefore, it is necessary to develop a method suitable for continuous online temperature monitoring of the entire slab surface in the secondary cooling zone of slab continuous casting, addressing the harsh environmental conditions such as high temperature, high humidity, abundant dust, and confined space. This method should minimize interference from external factors like humidity and dust, fully utilize the structural characteristics of the casting machine to optimize the design of the sensor's shape and installation method, and carefully consider the various heat transfer modes and thermal balance relationships at the temperature measurement nodes, as well as the heat transfer mechanism of the spray cooling water on the high-temperature slab surface. This will enable accurate online multi-point continuous temperature monitoring, providing technical support for high-quality continuous casting production. Summary of the Invention

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

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for online detection of the surface temperature of high-temperature slabs in continuous casting includes the following steps:

[0006] S1: Fabricate a detection element and measuring plate based on a thin-film temperature sensor, and install them on the corresponding fan-shaped section of the secondary cooling zone clamping rollers according to 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 discretization algorithm and the temperature detection value obtained at a certain time step, the heat balance equation is numerically calculated to reconstruct and determine the actual temperature on the side above the water film on the surface of the billet.

[0009] S4: The boiling heat transfer mechanism of the spray water cooling state on the surface of the high-temperature slab in continuous casting is theoretically analyzed to determine its corresponding critical characteristic temperature and heat transfer mode.

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

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

[0012] A radiation-type detection element is fabricated using a nickel-chromium-nickel-aluminum-manganese-silicon K-type thin-film temperature sensor and embedded in the bottom of the fan-shaped section clamping roller measuring disk. The clamping rollers at the beginning and end of the fan-shaped section of each secondary cooling zone serve as the installation positions of the measuring disk. The outer surface of the radiation-type detection element is coated with a blackbody material, and online temperature detection is performed through close-range radiation. The spray water volume of each zone is dynamically adjusted according to a predetermined target temperature curve.

[0013] Furthermore, in step S2, the heat balance equation of the temperature sensor's 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 measuring node; c is the specific heat capacity of the temperature measuring node; T is the temperature of the temperature measuring node; t is time; Q rads This represents the radiative heat absorption from the surface of the high-temperature cast billet to the temperature measuring node; Q conv This represents the convective heat loss between the temperature measuring node and the surrounding air; Q cond This represents the total heat conduction loss between the temperature sensing node and other components; ε is the surface emissivity of the temperature sensing head; σ is the Stefan-Boltzmann constant; A rads A is the radiative heat transfer area between the temperature measuring node and the surface of the cast billet; conv A is the convective heat transfer area between the temperature measurement node and the surrounding air. condThe area of ​​heat transfer between the temperature measuring node and components such as the wires is denoted as T; h is the convective heat transfer coefficient between the temperature measuring node and the surrounding air; λ is the overall thermal conductivity between the temperature measuring node and components such as the wires; T f Temperature above the water film on the surface of the cast billet; T g The temperature of the air surrounding the temperature measurement node; T b The temperature at the far end of the sensor is denoted as L; L is the heat conduction distance between the temperature measuring node and components such as wires.

[0018] Furthermore, step S3, which involves using a single-node temperature time-series discretization algorithm and numerically calculating the heat balance equation based on temperature detection values ​​obtained at certain time steps to reconstruct and determine the actual temperature above the water film on the surface of the billet, specifically includes the following steps:

[0019] Integrating equations (1-1) to (1-4), we get:

[0020]

[0021] After rearranging the terms, we get:

[0022]

[0023] make:

[0024]

[0025] Further simplification of equation (3) yields:

[0026]

[0027] make:

[0028]

[0029] Let the acquisition period of the on-site detection be δt. For each time node within N acquisition periods, calculate equation (5) based on the detection temperature T of the temperature measurement node, and let:

[0030]

[0031] Equation (5) can be rewritten in the following simplified matrix form:

[0032]

[0033] The three coefficients in the above equation can be obtained by solving the least squares method, namely:

[0034]

[0035] During the solution process, tests were conducted using a known plate surface temperature under similar conditions to calibrate the coefficients α, β, and γ.

[0036] Substituting equation (9) into equation (5) yields:

[0037]

[0038] After further processing, the following results were obtained:

[0039]

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

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

[0042]

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

[0044] Considering the Rayleigh-Taylor instability at the gas-liquid interface, an analytical formula for calculating the film boiling temperature is constructed, namely:

[0045]

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

[0047] Introduce the following dimensionless numbers:

[0048]

[0049] In the formula: R ref For reference average surface roughness; Ja sub The Jacobian number is used to characterize the ratio of superheat to latent heat during a liquid phase transition.

[0050] Rewrite equation (12) in dimensionless form as a product relationship, i.e.:

[0051]

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

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

[0054]

[0055] In the formula: T l The temperature of the spray cooling water;

[0056] For the secondary cooling scenario of conventional continuous casting slabs, considering the specific conditions of the slab and cooling water, the corresponding minimum film boiling temperature T is obtained by solving equation (16). LDF ;T LDF With T l As the temperature increases, the temperature gradually decreases, thus finding the transition temperature point between film boiling and transition boiling in the actual slab continuous casting process. When the surface temperature of the slab reaches or exceeds the value of the transition temperature point, it is considered to be in a stable film boiling heat transfer mechanism.

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

[0058]

[0059] In the formula: t is the current time; t-Δt is the previous time; Δt is the time interval between two consecutive temperature measurements; T w T represents the surface temperature of the cast billet. v Temperature above the gas film; δ v α represents the thickness of the air film layer. v λ is the thermal diffusivity of the air film; v ρ is the thermal conductivity of the air film; v c is the air film density. P,v This refers to the isobaric specific heat capacity of the air film.

[0060] For the water film layer:

[0061]

[0062] In the formula: T f Temperature above the water film; δ f α represents the thickness of the water film layer. f λ is the thermal diffusivity of the water film. f ρ is the thermal conductivity of the water film. f c is the density of the water film. P,f The isobaric specific heat capacity of the water film;

[0063] Combining equations (17-1) and (18-1), we derive:

[0064]

[0065] As shown in equation (19), the surface temperature of the billet at the current moment can be approximately calculated based on the water film surface temperature obtained from the online detection at the current time and the previous two moments. For a continuously cast slab moving at a certain casting speed, the temperature is calculated based on the temperature values ​​measured by the detection points distributed at intervals along the casting direction at the previous three moments.

[0066] The beneficial effects of this invention are as follows: This invention fully utilizes the characteristics of thin-film temperature sensors—small size, good protection, and long lifespan—and combines them with the structural features of the fan-shaped section of the continuous casting machine. By implementing close-range radiation temperature measurement through a detection component embedded in the bottom of the clamping roll measuring plate, the influence of on-site interference factors such as water vapor and dust on heat transfer can be significantly reduced. Furthermore, the smaller the spatial scale of the local area, the more conducive it is to the reasonable determination of 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 discretization 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 billet on the measured temperature is considered in detail. This invention can effectively overcome the problems of poor prediction / detection accuracy, limited detection position, difficult maintenance, and short service life caused by relying solely on heat transfer numerical theory calculations or long-distance infrared temperature measurement methods. It can provide key feedback information for the control model of continuous casting metallurgical processes 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 billet quality.

[0067] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0068] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0069] Figure 1 This is a schematic diagram of a radiation-type detection device;

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

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

[0072] Figure 4 This is a schematic diagram of heat transfer conservation at the temperature measurement node.

[0073] Figure 5 This is a schematic diagram of the boiling heat transfer mechanism;

[0074] Figure 6The effect of billet surface roughness 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 A schematic diagram of stable film boiling heat transfer on the surface of a high-temperature cast billet. Detailed Implementation

[0077] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed 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 are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0078] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0079] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the invention. However, it will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the invention.

[0080] This invention provides an online detection method for the surface temperature of high-temperature slabs in slab continuous casting. By installing the sensor detection component below the fan-shaped section of the clamping roller to implement close-range radiation temperature measurement, based on the local transient heat transfer conservation analysis of the temperature measurement node, the single-node temperature time-series discretization algorithm, and the theoretical analysis of the stable film boiling heat transfer mechanism, the surface temperature of the high-temperature slab is reconstructed by combining the actual detection value of the sensor. This enables the accurate tracking of the slab surface temperature in the entire secondary cooling zone of slab continuous casting, providing accurate feedback information for metallurgical process control models such as dynamic secondary cooling water distribution and light pressure reduction.

[0081] This method mainly includes the following steps:

[0082] (1) Based on the thin film temperature sensor, the detection component and measuring plate are made and installed on the corresponding fan-shaped section clamping roller in the secondary cooling zone according to the process requirements.

[0083] Radiation detection devices (such as those made using nickel-chromium / nickel-aluminum-manganese-silicon K-type thin-film temperature sensors) are fabricated. Figure 1 ), and is embedded in the bottom position of the fan-shaped section clamping roller measuring plate (e.g. Figure 2 The outer surface of the test piece is coated with a blackbody material to improve heat transfer efficiency, and online temperature detection is performed through close-range radiation (e.g., Figure 3 ).

[0084] Theoretically, measuring discs can be installed on the clamping rollers at the inlet and outlet positions of all fan-shaped sections in the entire secondary cooling zone along the throwing direction (for three-section rollers, one clamping roller can be installed on each of the left and right side sections). However, based on considerations for secondary cooling water distribution control, the clamping rollers at the inlet position of the starting fan-shaped section and the outlet position of the ending fan-shaped section of each secondary cooling zone are usually selected as the installation positions of the measuring discs. The spray water volume of each zone is dynamically adjusted according to the predetermined target temperature curve by real-time online temperature detection.

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

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

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

[0088]

[0089] In the formula: m is the mass of the temperature measuring node, kg; c is the specific heat capacity of the temperature measuring node, J·kg -1 ·K -1 T represents the temperature at the temperature measurement node, in K; t represents time, in s; Q rads W and Q represent the radiative heat absorption from the surface of the high-temperature cast billet to the temperature measuring node. conv Q represents the convective heat loss between the temperature measuring node and the surrounding air, expressed in W; cond ε represents the total heat conduction loss between the temperature sensing node and other components such as wires and casing, in W; ε is the emissivity of the temperature sensing head surface; σ is the Stefan-Boltzmann constant, σ = 5.67 × 10⁻⁶. -8 W·m -2 ·K -4 A rads The radiative heat transfer area between the temperature measuring node and the surface of the cast billet is m. 2 Aconv The convective heat transfer area between the temperature measuring node and the surrounding air, in meters. 2 A cond The heat transfer area between the temperature measuring node and components such as wires, in meters (m). 2 ; h is the convective heat transfer coefficient between the temperature measuring node and the surrounding air, W·m -2 ·K -1 λ represents the combined thermal conductivity between the temperature sensing node and components such as wires, in W·m. -1 ·K -1 ;T f Temperature above the water film on the surface of the billet, K; T g The temperature of the air surrounding the temperature measurement node is measured in K and T. b The temperature at the far end of the sensor is measured in K; L is the heat conduction distance between the temperature measuring node and components such as wires, measured in m.

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

[0091] Based on a single-node temperature time-series discretization algorithm, and using 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 billet.

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

[0093]

[0094] After rearranging the terms, we can obtain:

[0095]

[0096] make:

[0097]

[0098] Further simplification of equation (3) yields:

[0099]

[0100] make:

[0101]

[0102] Let the acquisition period of the on-site detection be δt. Then, for each time node within N acquisition periods, equation (5) can be calculated based on the detection temperature T of the temperature measurement node. Let:

[0103]

[0104] Equation (5) can then be rewritten in the following simplified matrix form:

[0105]

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

[0107]

[0108] During the solution process, it is necessary to substitute T. f The values ​​are calculated, so a known plate surface temperature can be set under similar conditions for testing, and the coefficients α, β and γ can be calibrated.

[0109] Substituting equation (9) into equation (5) yields:

[0110]

[0111] Further processing yields the following:

[0112]

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

[0114] (4) Heat transfer mechanism and state analysis of water spraying on the surface of the billet.

[0115] A theoretical analysis of the boiling heat transfer mechanism was conducted on the surface of the high-temperature slab in continuous casting, specifically focusing on water spray cooling. The corresponding critical characteristic temperature and heat transfer mode were determined, such as... Figures 5-7 .

[0116] During slab continuous casting, the high-temperature slab (surface temperature approximately 1200℃ after exiting the crystallizer) is continuously cooled by air spray in the secondary cooling zone until it is completely pulled out of the casting machine. Due to the release of latent heat in the liquid core inside the slab, the outward conduction of heat along the thickness of the solidified slab shell, and the periodic heat transfer through air-cooled radiation and contact heat transfer with the clamping rollers, the surface temperature of the slab will fluctuate to some extent while maintaining an overall decreasing trend. Heat transfer theory simulation and production practice tests show that the surface center temperature of the slab in the secondary cooling zone during conventional slab continuous casting is usually in the range of 850-1200℃. For such a high-temperature solid surface, the spray cooling process belongs to a typical boiling heat transfer mechanism.

[0117] As the surface temperature rises, the liquid undergoes an evaporative phase change, forming bubbles. Cooling water gradually transitions from natural convection heat transfer to nucleation boiling heat transfer, with the heat flux density continuously increasing until it reaches the critical heat flux density value CHF. Once the surface temperature exceeds this point, a large number of bubbles are generated, forming a very high distribution density. This makes direct contact between the cooling water and the surface increasingly difficult, causing a sudden drop in heat flux and entering the so-called transition boiling zone. As the surface temperature continues to rise, bubbles continuously nucleate, grow, and detach from the surface until they coalesce to form a stable vapor film between the liquid and solid surfaces. Heat transfer mainly occurs through conduction, convection, and radiation within this vapor film. Vapor escapes from the film in the form of bubbles. Thermal resistance is primarily confined within the vapor film, and the heat flux continues to decrease to its lowest point. The temperature at this point is the so-called Leidenfrost temperature T. LDF Also known as the minimum film boiling temperature; when the surface temperature exceeds T LDF Subsequently, the heat transfer through the stable gas film intensifies, and the heat flow rises again, entering the so-called film boiling zone.

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

[0119]

[0120] Where: ΔT sub λ 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 For isobaric specific heat capacity, J·Kg -1 ·K -1 ;R a The average surface roughness of the solid is represented by the subscripts l and v, which represent cooling water and water vapor, respectively.

[0121] Furthermore, considering the Rayleigh-Taylor instability at the gas-liquid interface (the interfacial turbulent mixing phenomenon caused by the density gradient between two substances separated by an interface), a corresponding analytical formula for calculating the film boiling temperature can be constructed, namely:

[0122]

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

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

[0125]

[0126] In the formula: R ref For reference average surface roughness, R ref =1μm; Ja sub The Jacobi number is used to characterize the ratio of superheat to latent heat during a liquid phase transition.

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

[0128]

[0129] In the formula: a, b, c, and d are all undetermined coefficients. For the case of cooling water spraying on flat steel plates, the approximate values ​​can be a = 134.91, b = -0.0022, c = -0.181, and d = 0.564.

[0130] Combining the above methods, we can obtain:

[0131]

[0132] In the formula: T l The temperature of the spray cooling water is K.

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

[0134] T LDF With R a R gradually decreases as it increases, but the impact is not significant. aWhen T increases from 100 μm to 2000 μm, LDF A change of only 772.7℃ to 768.9℃ is usually negligible; T LDF With T l The effect of cooling water subcooling ΔT gradually decreases as the subcooling increases (correspondingly, the subcooling decreases), and its influence is quite significant. sub When the temperature decreases from 90℃ to 20℃, T LDF The corresponding change from 857.9℃ to 476.6℃ means that the film boiling transitions to transition boiling later, and the heat transfer effect is weakened.

[0135] In actual slab continuous casting processes, the cooling water temperature is typically in the range of 25–40℃, and considering that the surface roughness of the slab has little impact, T can be considered to be relatively stable. l =T corresponding to 30℃ LDF =769.8℃ is the transition temperature between film boiling and transition boiling. When the surface temperature of the billet 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 true temperature value of the surface of the billet.

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

[0138] The gas film and water film on the surface of the billet can be regarded as a flat plate 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 classical flat plate temperature analytical formula. Then, the relationship between the billet surface temperature (i.e., the temperature below the gas film) and the water film surface temperature (i.e., the temperature above the water film) can be found. Thus, the true billet surface temperature can be reconstructed and calculated by combining the relationship between the two.

[0139] For air film layers:

[0140]

[0141] In the formula: t is the current time; t-Δt is the previous time; Δt is the time interval between two temperature measurements, in seconds; T w The surface temperature of the cast billet (temperature below the gas film), in K; T v Temperature above the air film, K; δ v α is the thickness of the air film layer, in meters; v m is the thermal diffusivity of the air film. 2 ·s -1 ;λ v The thermal conductivity of the air film is W·m.-1 ·K -1 ;ρ v The density of the gas film is kg·m. -3 ;c P,v The isobaric specific heat capacity of the air film is expressed in J·kg. -1 ·K -1 .

[0142] For the water film layer:

[0143]

[0144] In the formula: T f The temperature above the water film (i.e., the temperature detected by the sensor), in K; δ f α is the thickness of the water film layer, in meters; f Let m be the thermal diffusivity of the water film. 2 ·s -1 ;λ f The thermal conductivity of the water film is W·m. -1 ·K -1 ;ρ f The density of the water film is kg·m. -3 ;c P,f The isobaric specific heat capacity of the water film, J·Kg -1 ·K -1 .

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

[0146]

[0147] As shown in equation (19), the surface temperature of the slab at the current moment can be approximately calculated based on the water film surface temperature obtained from the online detection at the current time and the previous two moments. Note that for a continuously cast slab moving at a certain casting speed, this means that the calculation must be based on the temperature values ​​measured at detection points distributed at intervals along the casting direction at the previous and next three moments.

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

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

[0150] In the above embodiments, although the invention has been described in conjunction with specific embodiments thereof, many substitutions, modifications, and variations of these embodiments will be apparent to those skilled in the art from the foregoing description. For example, other memory structures (e.g., dynamic RAM (DRAM)) may be used with the embodiments discussed. The embodiments of the invention are intended to cover all such substitutions, modifications, and variations falling within the broad scope of the appended claims.

[0151] This embodiment also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements any of the methods in this embodiment.

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

[0153] The memory is used to store computer programs, and the processor is used to execute the computer programs stored in the memory to cause the terminal to perform any of the methods in this embodiment.

[0154] As will be understood by those skilled in the art, the computer-readable storage medium described in this embodiment allows for the implementation of all or part of the steps in the above method embodiments by computer program-related hardware. The aforementioned computer program can be stored in a computer-readable storage medium. When executed, the program performs the steps of the above method embodiments; and the aforementioned storage medium includes various media capable of storing program code, such as ROM, RAM, magnetic disks, or optical disks.

[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 between them. The memory is used to store computer programs, the communication interface is used to perform communication, and the processor and the transceiver are used to run the computer programs, so that the electronic terminal performs the steps of the above method.

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

[0157] The processors mentioned above can be general-purpose processors, including central processing units (CPUs), network processors (NPs), etc.; they can also be digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0158] This invention can be used in a wide range of general-purpose or special-purpose computing system environments or configurations. Examples include: personal computers, server computers, handheld or portable devices, tablet devices, multiprocessor systems, microprocessor-based systems, set-top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, and distributed computing environments including any of the above systems or devices, etc.

[0159] This invention can be described in the general context of computer-executable instructions, such as program modules, that are executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, etc., that perform a specific task or implement a specific abstract data type. This invention can also be practiced in distributed computing environments where tasks are performed by remote processing devices connected via a communication network. In distributed computing environments, program modules can reside 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 solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for online detection of the surface temperature of high-temperature slabs in continuous casting of slabs, characterized in that: Includes the following steps: S1: Fabricate a detection element and measuring plate based on a thin-film temperature sensor, and install them on the corresponding fan-shaped section of the secondary cooling zone clamping rollers according to 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 discretization algorithm and the temperature detection value obtained at a certain time step, the heat balance equation is numerically calculated to reconstruct and determine the actual temperature on the side above the water film on the surface of the billet. S4: The boiling heat transfer mechanism of the spray water cooling state on the surface of the high-temperature slab in continuous casting is theoretically analyzed to determine its corresponding critical characteristic temperature and heat transfer mode. S5: Under the premise of stable film boiling heat transfer mechanism, based on the classical flat plate temperature analysis theory, and combined with the temperature above the water film on the surface of the billet, the calculation is reconstructed again to finally obtain the true temperature value of the surface of the billet. In step S5, for the air film layer: In the formula: The current moment; The previous moment; The time interval between two consecutive temperature measurements; The surface temperature of the cast billet; Temperature on the upper side of the air film; The thickness of the air film layer; is the thermal diffusivity of the air film; The thermal conductivity of the air film; This refers to the air film density; This refers to the isobaric specific heat capacity of the air film. For the water film layer: In the formula: Temperature on the upper side of the water film; The thickness of the water film layer; The thermal diffusivity of the water film; The thermal conductivity of the water film; The density of the water film; The isobaric specific heat capacity of the water film; Combining equations (17-1) and (18-1), we derive: As shown in equation (19), the surface temperature of the billet at the current moment can be approximately calculated based on the water film surface temperature obtained from the online detection at the current time and the previous two moments. For a continuously cast slab moving at a certain casting speed, the temperature is calculated based on the temperature values ​​measured by the detection points distributed at intervals along the casting direction at the previous three moments.

2. The method for online detection of surface temperature of high-temperature slabs in continuous casting according to claim 1, characterized in that: Step S1 specifically includes the following steps: A radiation-type detection element is fabricated using a nickel-chromium-nickel-aluminum-manganese-silicon K-type thin-film temperature sensor and embedded in the bottom of the fan-shaped section clamping roller measuring disk. The clamping rollers at the beginning and end of the fan-shaped section of each secondary cooling zone serve as the installation positions of the measuring disk. The outer surface of the radiation-type detection element is coated with blackbody material, and online temperature detection is performed through close-range radiation. The spray water volume of each zone is dynamically adjusted according to a predetermined target temperature curve.

3. The method for online detection of surface temperature of high-temperature slab in continuous casting according to claim 1, characterized in that: In step S2, the heat balance equation of the temperature sensor's temperature measurement node satisfies: In the formula: For the quality of temperature measurement nodes; Specific heat capacity of the temperature measurement node; For measuring the temperature of the temperature node; For time; This indicates the absorption of radiative heat from the surface of the high-temperature cast billet to the temperature measurement node; This indicates the convective heat loss between the temperature measuring node and the surrounding air; This represents the total heat transfer loss between the temperature sensing node and other components; The emissivity of the temperature sensor surface; It is the Stefan-Boltzmann constant; This refers to the radiative heat transfer area between the temperature measurement node and the surface of the billet. The convective heat transfer area between the temperature measurement node and the surrounding air; This refers to the heat transfer area between the temperature measuring node and the conductor. The convective heat transfer coefficient between the temperature measuring node and the surrounding air; The combined thermal conductivity between the temperature measuring node and the conductor; The temperature above the water film on the surface of the billet; The temperature is measured to be the air temperature around the temperature measurement node. To detect the temperature at the far end of the component; This is the heat conduction distance between the temperature measuring node and the wire.

4. The method for online detection of surface temperature of high-temperature slab in continuous casting according to claim 3, characterized in that: Step S3, which involves using a single-node temperature time-series discretization algorithm and numerically calculating the heat balance equation based on 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 billet, specifically includes the following steps: Integrating equations (1-1) to (1-4), we get: After rearranging the terms, we get: make: Further simplification of equation (3) yields: make: The collection cycle for on-site testing is as follows: ,for Each time point within a data acquisition cycle is based on the detected temperature at the temperature measurement node. Calculate equation (5) and let: Equation (5) can be rewritten in the following simplified matrix form: The three coefficients in the above equation can be obtained by solving the least squares method, namely: During the solution process, the known surface temperature of the flat plate was used for testing, and the coefficients were adjusted accordingly. , and Perform calibration; Substituting equation (9) into equation (5) yields: After further processing, the following results were obtained: Based on the currently detected temperature The actual temperature above the water film on the surface of the billet was reconstructed and analyzed. .

5. The method for online detection of surface temperature of high-temperature slabs in continuous slab casting according to claim 1, characterized in that: In step S4, the minimum film boiling temperature is established. The analytical function relation: In the formula, The lowest film boiling temperature, The subcooling degree of the spray cooling water; Thermal conductivity; Density; It is the isobaric specific heat capacity; Average surface roughness of the solid; subscript and These represent cooling water and water vapor, respectively. Considering the Rayleigh-Taylor instability at the gas-liquid interface, an analytical formula for calculating the film boiling temperature is constructed, namely: In the formula: This is the saturation temperature of the cooling water; Latent heat of vaporization; The surface tension of the cooling water; The kinetic viscosity of water vapor; It is the acceleration due to gravity; Introduce the following dimensionless numbers: In the formula: For reference average surface roughness; The Jacobian number is used to characterize the ratio of superheat to latent heat during a liquid phase transition. Rewrite equation (12) in dimensionless form as a product relationship, i.e.: In the formula: , , , All are undetermined coefficients; Combining the above methods, we can obtain: In the formula: The temperature of the spray cooling water; Based on the specific conditions of the cast billet and cooling water, the corresponding minimum film boiling temperature can be obtained by solving equation (16). ; along with As the temperature increases, the temperature gradually decreases, thus finding the transition temperature point between film boiling and transition boiling in the actual slab continuous casting process. When the surface temperature of the slab reaches or exceeds the transition temperature point value, it is considered to be in a stable film boiling heat transfer mechanism.

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