CN113305277A - Method for judging slag coiling in plate blank crystallizer casting powder shearing - Google Patents
Method for judging slag coiling in plate blank crystallizer casting powder shearing Download PDFInfo
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- 239000002893 slag Substances 0.000 title claims abstract description 198
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- 229910000831 Steel Inorganic materials 0.000 claims abstract description 79
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- 239000007788 liquid Substances 0.000 claims abstract description 44
- 238000009749 continuous casting Methods 0.000 claims abstract description 31
- 238000005520 cutting process Methods 0.000 claims abstract description 23
- 238000004519 manufacturing process Methods 0.000 claims abstract description 21
- 230000008569 process Effects 0.000 claims abstract description 20
- 238000005096 rolling process Methods 0.000 claims description 26
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- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 6
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- 238000013461 design Methods 0.000 description 4
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- 229910052786 argon Inorganic materials 0.000 description 3
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- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
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Abstract
The invention discloses a method for judging cutting slag entrapment of plate blank crystallizer covering slag, which comprises the following steps: collecting crystallizer liquid level fluctuation value H detected by continuous casting machinebA value; obtaining a viscosity value mu and an interfacial tension value sigma of the casting powder according to the physicochemical properties of the casting powder provided by a casting powder supplier; obtaining the maximum critical liquid level fluctuation value H for judging the cutting slag coiling behavior of the covering slag in the crystallizer under the specific process environmentb，Hb＝0.4(606+474σ)0 . 5+4.6 μ, i.e. when the level fluctuation in the crystallizer does not exceed HbIn the process, the phenomenon of slag entrapment of the casting powder caused by the impact flow reflowing near the narrow edge can be avoided. The invention can effectively improve the phenomenon that the covering slag in the crystallizer is sucked into the molten steel due to the shearing impact action of the narrow edge, thereby improving the cleanness of the molten steelThe method reduces the content of impurities in the steel, reduces the slag inclusion rate of the continuous casting billet, reduces the production cost and improves the productivity.
Description
Technical Field
The invention belongs to the technical field of shearing slag entrapment application, and particularly relates to a method for judging the shearing slag entrapment of plate blank crystallizer covering slag.
Background
The slag entrapment during the cutting of the continuous casting crystallizer is a slag entrapment phenomenon that the covering slag is dragged into molten steel under the cutting action of a molten steel stream on the surface of a convolution area on the crystallizer. Shear slag entrapment is one of the most common forms of slag entrapment and is the most studied form of slag entrapment. The degree of cutting slag entrapment is directly related to the flow velocity of the surface of the molten steel, so that a great deal of research also takes the velocity of the molten steel flow at the critical slag entrapment as a judgment criterion for cutting slag entrapment. The influencing factors of the cutting slag inclusion include almost all the factors influencing the flow rate of molten steel, including a water gap structure, the size of a middle hole, the insertion depth of a water gap, the pulling speed, the argon blowing amount, the section size of a crystallizer and the like. In addition, the physical properties of the mold flux and the thickness of the slag layer also affect the possibility of occurrence of shear slag entrapment. In the process of electromagnetic braking, the influence of braking on a flow field can also have certain influence on cutting slag entrapment, and the possibility of slag entrapment can be reduced by weakening the flow in the upper convolution area under reasonable electromagnetic braking. However, the electromagnetic stirring applied near the steel slag interface promotes the flow of the molten steel and at the same time, slag entrapment is likely to occur.
The shearing slag entrapment is the slag entrapment type which is most easily generated under the condition that the crystallizer does not blow argon or blows argon weakly, a large amount of researches are also carried out on the mechanism of the shearing slag entrapment generation by a plurality of researchers, and judgment formulas of a plurality of quantitative semi-quantitative critical slag entrapment conditions are obtained.
Therefore, it is necessary to provide a method for judging the cutting slag entrapment of the slab mold covering slag.
Disclosure of Invention
In view of the above, the present invention provides a method for determining cutting slag entrapment of slab mold covering slag, which is provided by the invention, under the given characteristic parameters of covering slag or mold nozzle, by using the critical slag entrapment method provided by the invention, other control parameters in a continuous casting mold are reasonably adjusted, and the covering slag absorbing behavior formed by impact of cutting stream in the mold is effectively inhibited.
In order to solve the technical problem, the invention discloses a method for judging the cutting slag entrapment of plate blank crystallizer covering slag, which comprises the following steps:
step 3, obtaining the maximum critical liquid level fluctuation value H for judging the cutting slag coiling behavior of the covering slag in the crystallizer under the specific process environmentb，Hb＝0.4(606+474σ)0.5+4.6 μ, i.e. when the level fluctuation in the crystallizer does not exceed HbIn the process, the phenomenon of slag entrapment of the casting powder caused by the impact flow reflowing near the narrow edge can be avoided.
Optionally, the step 1 collects a crystallizer liquid level fluctuation value H detected by the continuous casting machinebThe values are specifically: a sensor of a continuous casting crystallizer liquid level detection system is arranged at the narrow side 1/4 of the crystallizer and is used for detecting the liquid level fluctuation condition at the narrow side 1/4, and the liquid level fluctuation numerical value Ha at the position near the narrow side of the crystallizer 1/4 is directly read from the liquid level detection system of the continuous casting machine.
Optionally, the value of μ in the step 2 is in the range of 0.0001 to 0.5Pa.s, and the value of σ is in the range of 0.1 to 1.2) N/m.
Optionally, the maximum critical liquid level fluctuation value H for judging the cutting slag coiling behavior of the mold flux in the crystallizer in the step 3 is obtainedb，Hb＝0.4(606+474σ)0.5+4.6 μ, i.e. when the level fluctuation in the crystallizer does not exceed HbDuring the time, the covering slag can not produce the covering slag and roll up the sediment phenomenon because of the near impact stream of narrow limit backward flow, specifically do:
f number is the reaction of the submerged nozzle structure and the geometric shape of the crystallizer to the liquid level condition of the crystallizer, and can be expressed as:
wherein F is the F number (N/m), rhoSteelIs the density of molten steel, QSteelIs the steel passing amount (m)3/s)，VcollIs the impact velocity (m/s) of the molten steel at the narrow side, thetacollIs the angle of inclination of the jet, hcollIs the depth of impact; the slag entrapment frequency Enf is configured as F number and the critical slag entrapment speed vcDefining the Ds number related to the crystallizer process parameters, and analyzing the dimensions to obtain the unit of kg.m-1·s-1Or Pa s, [ MT ]-1L-1]：
Wherein F is the F number (N/m), vcCritical slag entrapment velocity (m/s);
wherein the light phase velocity is v1Light phase density is rho1The dynamic viscosity of light phase is mu1The thickness of the light phase is h1(ii) a Heavy phase velocity v2Density of heavy phase is rho2The dynamic viscosity of the heavy phase is mu2The heavy phase thickness is h2The pressure on the upper side of the wave crest of the interfacial wave is p1Lower side pressure of p2K is the wave number; the slag entrapment frequency is expressed as:
Enf＝f(Ds) (4)
ds number equal to 0.67 Pa.s is taken as the critical condition for shear coil formation in the crystallizer under airless conditions, due to the dimension [ MT ] of Ds number-1L-1]According to a similar principle, the physical model has the following relation with the Ds number in the actual crystallizer:
wherein, CDsSimilarity ratio of model to Ds number in prototype, CmMass similarity ratio of model to prototype, CρDensity similarity ratio between model and prototype, CtFor time similarity ratio in model and prototype, Clλ is the geometric similarity ratio of the model to the prototype; the density ratio C of the molten steel in the model and the prototypeρComprises the following steps:
where ρ isWater (W)Is the density of water, pMolten steelThe density of the molten steel is; the relationship between the model and the number of Ds in the prototype is:
taking the critical slag rolling speed of a steel slag interface as 0.46m/s and the Ds number as 13.4Pa · s, obtaining the F number of the crystallizer in the critical slag rolling state as 6.2N/m according to the equation (2), and if the influence of viscosity and interface tension reduction on the steel slag interface is considered, and the lowest critical slag rolling speed in the actual crystallizer is 0.26m/s, ensuring that the F number of the crystallizer is not higher than 3.5N/m at the moment; the optimal F number range of the surface quality of the casting blank in the conventional continuous casting is 3-5N/m;
modifying equation (3) to obtain:
Hb＝3Ds·Vc (7)
wherein Ds is the critical slag entrapment number, and Vc is the critical slag entrapment speed; taking the casting powder with the density of 2600, the molten steel density of 7000, the interfacial wave k number of 300, the gravity acceleration of 9.8, the impact inclination angle theta of a shearing stream of 30, the cothkh1 of 1 and the interfacial tension introducing active factor of 0.3, simplifying the formula (3) used in the actual continuous casting crystallizer production process into the following steps:
Vc＝0.01(606+474σ)0.5+0.115μ (8)
the value of Ds and formula (8) can be substituted for formula (7):
Hb＝0.4(606+474σ70.5+4.6μ (9)
wherein HbThe critical liquid level fluctuation number under the conditions of a specific crystallizer production process and the casting powder is shown as the sigma, the steel slag interfacial tension and the mu, the casting powder viscosity.
Compared with the prior art, the invention can obtain the following technical effects:
the invention develops a critical judgment method for cutting and rolling up slag in consideration of the viscosity, density and interfacial tension physicochemical property of the protective slag in the actual production process of a slab continuous casting crystallizer, aiming at the protective slag with different physicochemical properties used in the slab crystallizer, the influence of the different protective slag used on the cutting and rolling up slag of the crystallizer under specific process conditions can be quantitatively analyzed through the critical judgment criterion, and the phenomenon that the protective slag in the crystallizer is sucked and rolled into molten steel due to the narrow-edge cutting impact effect can be effectively improved, so that the cleanliness of the molten steel is improved, the inclusion content in the steel is reduced, the slag inclusion rate of a continuous casting billet is reduced, the production cost is reduced, and the production efficiency is improved.
Of course, it is not necessary for any one product in which the invention is practiced to achieve all of the above-described technical effects simultaneously.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 is a drawing of an interface profile of crystallizer steel slag with a physical simulation of a pulling-down speed of 1.2 and a liquid level fluctuation value of 1.2m/min of 13.7 according to the present invention;
FIG. 2 is the profile of the interface of the steel slag in the crystallizer with a liquid level fluctuation value of 19.5 and a physical simulation pull-down speed of 1.2 and 1.6 m/min;
FIG. 3 is the relationship between the slag entrapment frequency and the Ds number under the non-blowing condition of the present invention;
Detailed Description
The following embodiments are described in detail with reference to the accompanying drawings, so that how to implement the technical features of the present invention to solve the technical problems and achieve the technical effects can be fully understood and implemented.
The invention discloses a method for judging cutting slag entrapment of plate blank crystallizer covering slag, which comprises the following steps:
step 3, obtaining the maximum critical liquid level fluctuation value H for judging the cutting and slag rolling behavior of the covering slag in the crystallizerb，Hb＝0.4(606+474σ)0.5+4.6 μ, i.e. when the level fluctuation in the crystallizer does not exceed HbDuring the time, the covering slag can not produce the covering slag and roll up the sediment phenomenon because of the near impact stream of narrow limit backward flow, specifically do:
under the condition of no air blowing, the slag coiling type of a steel slag interface in the crystallizer is mainly shear slag coiling, and the influence of process parameters on the slag coiling behavior of the steel slag interface is mainly divided into two main types: firstly, the shearing speed of molten steel is influenced; ② the ability of the mold flux to resist shear impact is affected. The influence of most process parameters on the shearing and slag rolling behaviors of the steel slag interface belongs to the first category, such as: the pulling speed, the insertion depth, the water gap structure, the cross section of the crystallizer and the like. The influence on the steel slag interface is mainly shown as follows: under the same property of the covering slag, the interface profile of the steel slag, particularly the interface characteristic of the bulge position, is influenced by enhancing or weakening the shearing speed of the molten steel, and a large number of physical simulation researches show that the activity degree of the bulge of the steel slag interface in the crystallizer has the most direct relation with the formation of the shearing slag coil. The second kind of process parameters are mainly the physical parameters of the mold flux, such as: the viscosity, the density, the steel slag interface tension and the like, and the slag rolling behavior of the steel slag interface is influenced mainly by changing the shearing resistance of the covering slag to molten steel.
Because the process factors influencing the slag rolling behavior of the interface shearing of the steel slag are more, in order to evaluate the influence of different process factors on the slag rolling behavior, the influence weight of each process parameter on the slag rolling is often analyzed by taking the slag rolling frequency, the critical slag rolling speed or the F number and the like of the interface of the steel slag in a physical model, and the specific significance is as follows:
slag rolling frequency. The influence of the flow field of the crystallizer and the physical property condition of the covering slag on slag entrapment can be intuitively reflected;
② the critical slag rolling speed. The critical slag rolling speed obtained by calculating the two-phase physical property condition is an important index for judging the shearing impact of the molten steel against the protective slag with certain physical property;
and F is the reaction of the submerged nozzle structure and the geometric shape of the crystallizer to the liquid level condition of the crystallizer. The F number can be expressed as:
wherein F is the F number (N/m), rhoSteelIs the density of molten steel, QSteelIs the steel passing amount (m)3/s)，VcollIs the impact velocity (m/s) of the molten steel at the narrow side, thetacollIs the angle of inclination of the jet, hcollIs the depth of impact. FIGS. 1-2 are the interface profiles (corresponding to the pulling speed of the crystallizer of 1.2-1.6 m/s) at different water flows in the water model experiment, the surface flow velocity of the crystallizer is small at low flow, the shearing action of the flow is weak, the interface bulge is not obvious, and the fluidity of the casting powder is poor; after the flow is increased, the surface flow velocity is increased, a relatively obvious bulge phenomenon is gradually formed near the narrow edge under the shearing action of the strand, and the slag entrapment phenomenon occurs on the steel slag interface; when the pulling speed is further increased, the bulge is severely fluctuated under the action of strong stream shearing, and a frequent slag entrapment phenomenon is formed.
Through equation (3) and statistics of flow parameters in the crystallizer in the water model experiment, the characteristic parameters of interface slag entrapment under different crystallizer water flows (corresponding to the crystallizer pulling speed of 1.2-1.6 m/s) in the water model experiment can be calculated and are shown in table 1. It can be seen that when the two-phase physical property parameters are stable, the critical slag coiling speed is unchanged, the shear deformation capability of the casting powder against the stream is unchanged, and the increase of the water flow leads to the increase of the F number. Because the flowing scale is far smaller than the flowing of the molten steel in the actual crystallizer, the F number in the water model experiment is also far lower than that obtained in the actual crystallizer, but no matter for the steel slag interface in the model or prototype, the overlarge F number reflects stronger fluctuation of the steel slag interface and larger shearing action of the molten steel on the protective slag.
TABLE 1 interface characteristic parameters at different water flows in water model
In a water model experiment, under different water gap insertion depths (corresponding to 100-160 mm of a prototype), characteristic parameters of slag entrapment at a steel slag interface are shown in table 2, along with the reduction of the insertion depth, the space of an upper convolution area is reduced, the F number is increased to some extent, the impact strength on the steel slag interface is increased, but the influence degree on the steel slag interface is relatively weak, and the generation of interface shearing slag entrapment behavior is not caused.
TABLE 2 characteristic parameters of the lower interface for different water gap insertion depths in water molds
In a water model experiment, characteristic parameters of interface slag entrapment under different mixed oil viscosities (corresponding to the viscosity of the casting powder being 0.098-0.192 Pa · s) and interface tensions (corresponding to the interface tension of the steel slag being 290-900 mN/m) are shown in Table 3, the F value is relatively stable under a specific water gap structure and a specific section pulling speed of a crystallizer, the critical slag entrapment speed is reduced along with the reduction of the viscosity of the casting powder and the interface tension of the steel slag, the capability of the casting powder for resisting the shearing of molten steel is weakened, and the slag entrapment times are increased.
TABLE 3 interfacial characteristic parameters for different mixed oil viscosities in water model
TABLE 4 characteristic parameters of the interface at different interfacial tensions in the water model
As can be seen from the combination of tables 1 to 4, the slag entrapment frequency representing the severity of slag entrapment is influenced by the critical slag entrapment speed and the F number, the slag entrapment frequency is approximately in inverse proportion to the first power of the critical slag entrapment speed and approximately in direct proportion to the first power of the F number, and the influence of the F number and the critical slag entrapment speed on the slag entrapment frequency is in the same order of magnitude, so that the slag entrapment frequency Enf can be constructed into the F number and the critical slag entrapment speed vcDefining the Ds number (the analytical dimension can be given in kg.m) related to the crystallizer process parameters-1·s-1Or Pa s, [ MT ]-1L-1])：
Wherein F is the F number (N/m), vcThe critical slag entrapment velocity (m/s) is obtained. The vc calculation formula is as follows (verification process is already published in]L.Zhang,Y.Li,Q.Wang and C.Yan:Predictionmodel for steel/slag interfacial instability in continuous casting process.Ironmaking&Steelmaking,2015,42(2):705–713.)。
Wherein the light phase velocity is v1Light phase density is rho1The dynamic viscosity of light phase is mu1The thickness of the light phase is h1(ii) a Heavy phase velocity v2Density of heavy phase is rho2The dynamic viscosity of the heavy phase is mu2The heavy phase thickness is h2The pressure on the upper side of the wave crest of the interfacial wave is p1Lower side pressure of p2And k is the wave number. The slag entrapment frequency can be expressed as:
Enf＝f(Ds) (4)
and fitting the data of tables 1-3 to obtain a graph 3, wherein the relation between the slag entrapment frequency and the Ds number has a relatively obvious linear relation, when the Ds number is less than 0.67Pa & s, the slag entrapment behavior of the steel slag interface does not occur, and when the Ds number is more than 0.67Pa & s, the slag entrapment frequency is rapidly increased along with the increase of the Ds number. Therefore, a Ds number equal to 0.67 Pa.s can be taken as a critical condition for the formation of shear coils in the crystallizer under airless conditions, due to the presence of a dimension [ MT ] of the Ds number-1L-1]According to a similar principle, the physical model has the following relation with the Ds number in the actual crystallizer:
wherein, CDsSimilarity ratio of model to Ds number in prototype, CmMass similarity ratio of model to prototype, CρDensity similarity ratio between model and prototype, CtFor time similarity ratio in model and prototype, Clλ is the geometric similarity ratio in the model and prototype. The density ratio C of the molten steel in the model and the prototypeρComprises the following steps:
where ρ isWater (W)Is the density of water, pMolten steelIs the molten steel density. The relationship between the model and the number of Ds in the prototype is:
therefore, if the critical condition Ds for slag entrapment in the mold is equal to 0.67Pa · s, the critical Ds number of occurrence of shear slag entrapment in the actual mold is 13.4Pa · s, and when the critical condition Ds for slag entrapment in the actual mold is greater than this value, there is a possibility that shear slag entrapment will occur. When the physical property condition of the protective slag and the steel slag is good, the critical slag rolling speed of a steel slag interface can reach more than 0.46m/s, so the critical slag rolling speed of the steel slag interface is 0.46m/s, and the Ds number is 13.4 Pa.s, the F number of the crystallizer in the critical slag rolling state can be obtained to be 6.2N/m according to the equation (2), and if the influence of the reduction of the viscosity and the interfacial tension on the steel slag interface is considered, when the lowest critical slag rolling speed in the actual crystallizer is 0.26m/s, the F number of the crystallizer is ensured to be not higher than 3.5N/m at the moment. The optimal F number range of the surface quality of the casting blank in the conventional continuous casting is 3-5N/m.
In order to provide a more direct and simple design guidance for the production process, and the formula (3) involves too many physical variables, it is very inconvenient to use in the actual production process, and in addition, it is difficult to determine the F number of the crystallizer flow field in the production process, so the formula (3) is modified to obtain:
Hb＝3Ds·Vc (7)
wherein Ds is the critical slag entrapment number, and Vc is the critical slag entrapment speed. In the actual production process, most of the physical variables for designing Vc can be constant, so that Vc is simplified, because the production conditions of parts in the continuous casting crystallizer are relatively fixed. Taking the density of the casting powder as 2600, the density of the molten steel as 7000, the k number of interfacial waves as 300, the gravity acceleration as 9.8, the impact inclination angle theta of a shearing stream as 30 and the cothkh1 as 1, and considering the influence of the active elements of the interface of the actual steel slag, introducing an active factor of 0.3 into the interfacial tension, the formula (3) used in the production process of the actual continuous casting crystallizer can be simplified as follows:
Vc＝0.01(606+474σ)0.5+0.115μ (8)
the value of Ds (known from the above discussion as 13.4Pa · s) and formula (8) can be substituted for formula (7):
Hb＝0.4(606+474σ70.5+4.6μ (9)
wherein HbIs a special crystallizer production process and under the condition of protective slagThe critical liquid level fluctuation number, sigma, steel slag interfacial tension and mu, covering slag viscosity. Therefore, aiming at the covering slag with different physical and chemical properties used in the slab crystallizer, the influence of the different used covering slag on the shearing and slag rolling of the crystallizer under specific process conditions can be quantitatively analyzed through the critical judgment criterion, so that a direct and concise design basis is provided for technical managers or technicians of an enterprise to the design of a production process.
Example 1
In the casting process of the slab continuous casting crystallizer, the method can be adopted to adjust the technological parameters of the crystallizer, so that the pulling speed is improved as much as possible under the condition of not generating shearing slag entrapment, and the production rate is increased.
(1) Firstly, the viscosity and the interfacial tension value of the casting powder used for production are obtained according to the physicochemical properties of the casting powder provided by a casting powder supplier, and are substituted into the critical judgment formula provided by the invention to calculate and obtain the critical Hb value.
(2) The enterprise starts production according to the production task of the day, carries out parameter design on the crystallizer and starts production, and reads the liquid level fluctuation numerical value Ha detected by the continuous casting machine after casting is stable.
(3) Comparing the value H of the fluctuation of the liquid level obtained by the continuous casting machine with the calculated critical value HbThe magnitude of the value, if critical HbIf the value is less than the liquid level fluctuation value, shearing slag entrapment is possibly generated in the casting process, the pulling speed is gradually reduced according to each grade of 0.05m/min, the insertion depth is gradually increased according to a grade of 0.1m, if the pulling speed or the insertion depth is the designed limit value, the type of a water gap is replaced, and the liquid level activity is reduced; otherwise, the liquid level activity degree in the surface casting process is reasonable, and the situation of cutting and slag rolling is avoided; if the value of the liquid level fluctuation is far less than the critical value HbThe value can be gradually increased by 0.05m/min until the liquid level fluctuation value approaches the critical value HbThereby improving the liquid level activeness, leading the protective slag to have better fluidity and improving the productivity.
After the technology is used, the phenomenon of slag entrapment of the covering slag caused by the fact that the shearing action of a narrow-edge impact stream of the continuous casting crystallizer is too strong can be effectively controlled, and therefore the surface slag inclusion rate of the continuous casting billet is reduced. Continuous casting machineWhen the casting speed of the crystallizer with the surface of 1550mm multiplied by 250mm is 1.22m/min, the insertion depth is 160mm, the interfacial tension of the steel slag is 900mN/m, the viscosity of the covering slag is 0.192Pa s, and the critical liquid level fluctuation H obtained by calculation of the method is adoptedbThe value is about 13.7, and the surface fluctuation of the crystallizer is more active at the moment, but the phenomenon of slag entrapment due to shearing is generated; when the pulling speed is 1.6m/min, the liquid level fluctuation of the crystallizer becomes strong, the liquid level fluctuation value is increased and is larger than the liquid level fluctuation H which generates critical slag entrapmentbValue, a more severe slag entrapment was produced with a slag entrapment frequency of 5 times/min. The interface profile of the crystallizer steel slag at the pulling speeds of 1.2m/min and 1.6m/min under physical simulation is shown in figures 1 and 2.
While the foregoing description shows and describes several preferred embodiments of the invention, it is to be understood, as noted above, that the invention is not limited to the forms disclosed herein, but is not to be construed as excluding other embodiments and is capable of use in various other combinations, modifications, and environments and is capable of changes within the scope of the inventive concept as expressed herein, commensurate with the above teachings, or the skill or knowledge of the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (4)
1. A method for judging slag coiling in cutting of plate blank crystallizer casting powder is characterized by comprising the following steps:
step 1, collecting crystallizer liquid level fluctuation numerical value H detected by a continuous casting machinebA value;
step 2, obtaining a viscosity value mu and an interfacial tension value sigma of the obtained casting powder;
step 3, obtaining the maximum critical liquid level fluctuation value H for judging the cutting slag coiling behavior of the covering slag in the crystallizer under the specific process environmentb，Hb＝0.4(606+474σ)0.5+4.6 μ, i.e. when the level fluctuation in the crystallizer does not exceed HbIn the process, the phenomenon of slag entrapment of the casting powder caused by the impact flow reflowing near the narrow edge can be avoided.
2. Judging slab crystallizer mold flux shear of claim 1The slag rolling method is characterized in that the step 1 is used for collecting the crystallizer liquid level fluctuation value H detected by the continuous casting machinebThe values are specifically: a sensor of a continuous casting crystallizer liquid level detection system is arranged at the narrow side 1/4 of the crystallizer and is used for detecting the liquid level fluctuation condition at the narrow side 1/4, and the liquid level fluctuation numerical value Ha at the position near the narrow side of the crystallizer 1/4 is directly read from the liquid level detection system of the continuous casting machine.
3. The method for judging the cutting slag entrapment of the slab crystallizer covering slag according to claim 1, wherein the μ value in the step 2 is in a range of 0.0001 to 0.5Pa.s, and the σ value is in a range of 0.1 to 1.2) N/m.
4. The method for judging the shearing slag entrapment of the slab mold covering slag according to claim 1, wherein the maximum critical liquid level fluctuation value H for judging the shearing slag entrapment of the covering slag in the mold in the step 3 is obtainedb，Hb＝0.4(606+474σ)0.5+4.6 μ, i.e. when the level fluctuation in the crystallizer does not exceed HbDuring the time, the covering slag can not produce the covering slag and roll up the sediment phenomenon because of the near impact stream of narrow limit backward flow, specifically do:
f number is the reaction of the submerged nozzle structure and the geometric shape of the crystallizer to the liquid level condition of the crystallizer, and can be expressed as:
wherein F is the F number (N/m), rhoSteelIs the density of molten steel, QSteelIs the steel passing amount (m)3/s)，VcollIs the impact velocity (m/s) of the molten steel at the narrow side, thetacollIs the angle of inclination of the jet, hcollIs the depth of impact; the slag entrapment frequency Enf is configured as F number and the critical slag entrapment speed vcDefining the Ds number related to the crystallizer process parameters, and analyzing the dimensions to obtain the unit of kg.m-1·s-1Or Pa s, [ MT ]- 1L-1]：
Wherein F is the F number (N/m), vcCritical slag entrapment velocity (m/s);
wherein the light phase velocity is v1Light phase density is rho1The dynamic viscosity of light phase is mu1The thickness of the light phase is h1(ii) a Heavy phase velocity v2Density of heavy phase is rho2The dynamic viscosity of the heavy phase is mu2The heavy phase thickness is h2The pressure on the upper side of the wave crest of the interfacial wave is p1Lower side pressure of p2K is the wave number; the slag entrapment frequency is expressed as:
Enf＝f(Ds) (4)
ds number equal to 0.67 Pa.s is taken as the critical condition for shear coil formation in the crystallizer under airless conditions, due to the dimension [ MT ] of Ds number-1L-1]According to a similar principle, the physical model has the following relation with the Ds number in the actual crystallizer:
wherein, CDsSimilarity ratio of model to Ds number in prototype, CmMass similarity ratio of model to prototype, CρDensity similarity ratio between model and prototype, CtFor time similarity ratio in model and prototype, Clλ is the geometric similarity ratio of the model to the prototype; the density ratio C of the molten steel in the model and the prototypeρComprises the following steps:
where ρ isWater (W)Is the density of water, pMolten steelThe density of the molten steel is; the relationship between the model and the number of Ds in the prototype is:
taking the critical slag rolling speed of a steel slag interface as 0.46m/s and the Ds number as 13.4Pa · s, obtaining the F number of the crystallizer in the critical slag rolling state as 6.2N/m according to the equation (2), and if the influence of viscosity and interface tension reduction on the steel slag interface is considered, and the lowest critical slag rolling speed in the actual crystallizer is 0.26m/s, ensuring that the F number of the crystallizer is not higher than 3.5N/m at the moment; the optimal F number range of the surface quality of the casting blank in the conventional continuous casting is 3-5N/m;
modifying equation (3) to obtain:
Hb＝3Ds·Vc (7)
wherein Ds is the critical slag entrapment number, and Vc is the critical slag entrapment speed; taking the casting powder with the density of 2600, the molten steel density of 7000, the interfacial wave k number of 300, the gravity acceleration of 9.8, the impact inclination angle theta of a shearing stream of 30, the cothkh1 of 1 and the interfacial tension introducing active factor of 0.3, simplifying the formula (3) used in the actual continuous casting crystallizer production process into the following steps:
Vc＝0.01(606+474σ)0.5+0.115μ (8)
the value of Ds and formula (8) can be substituted for formula (7):
Hb＝0.4(606+474σ70.5+4.6μ (9)
wherein HbThe critical liquid level fluctuation number under the conditions of a specific crystallizer production process and the casting powder is shown as the sigma, the steel slag interfacial tension and the mu, the casting powder viscosity.
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