JP4501892B2 - Method and apparatus for estimating molten metal temperature in continuous casting mold - Google Patents

Description

  The present invention relates to a technique for estimating a molten metal temperature in a mold in continuous casting of a liquid metal. In particular, the present invention relates to a technique for estimating the molten steel temperature in the mold with high estimation accuracy on the condition that the measurement can be continuously performed over time without directly immersing the probe or the like in the molten steel in the mold and there are as few consumables as possible.

  Knowing the temperature of the molten metal in the mold (mold) in continuous casting of molten metal such as molten steel is important in setting various casting conditions. For example, in the continuous casting of steel, if the molten steel temperature in the mold is too high, the solidification shell development is delayed, leading to a breakout, and the formation of equiaxed crystals is hindered, leading to deterioration of central segregation. On the other hand, if the molten steel temperature in the mold is too low, the surface of the molten metal in the mold or the poor melting of the mold powder will cause quality failure or breakout.

  Conventionally, as a widely used method, there is (1) a method of estimating a molten steel temperature in a mold by measuring a molten steel temperature in the tundish and predicting a temperature effect amount between the tundish and the mold. As a means for measuring the temperature of the molten steel in the tundish, spot measurement is generally performed with a consumable thermocouple. Further, in some cases, continuous measurement is performed with a permanent thermocouple covered with a refractory protective tube, or radiation temperature is measured by immersing a resin-coated optical fiber.

  In addition, (2) a method for directly measuring the molten steel temperature in the mold has been proposed. For example, in Patent Document 1, a temperature measuring probe embedded in a temperature measuring paper tube at a pitch of 2 to 3 mm is lifted by a lifting device. In this method, the sample is immersed for about 1 minute and measured several times during the initial, middle and final stages of casting. In Patent Document 2, a thermocouple covered with a protective tube made of cermet is continuously immersed in molten steel in a mold.

  (3) As a method for indirectly measuring the molten steel temperature in the mold, Patent Document 3 discloses a heat-resistant window glass that can measure the temperature distribution in the vicinity of the molten steel meniscus portion on the outer surface of the mold copper plate from the back of the cooling box without contact. Is provided in the cooling box, and the temperature of the molten steel is measured with a radiation thermometer through this window glass.

Japanese Patent No. 2950188 JP-A-11-123515 JP 59-225858 A

  However, in the method (1) of measuring the molten steel temperature in the tundish and estimating the molten steel temperature in the mold, an environment where there is a variation in the molten steel temperature drop between the tundish and the mold, for example, in the tundish When the thickness of the refractory lining changes significantly due to melting damage, when hot recycling of tundish is performed, or when the heat content of tundish varies due to variations in recycling time, the estimated molten steel temperature in the mold varies greatly. Occurs.

  Further, in the method (2) of immersing the probe directly in the molten steel in the mold, it is difficult to obtain continuous information on the molten steel temperature with a consumable thermocouple. In addition, even when a protective tube such as cermet is continuously immersed, the life of the protective tube is limited (1 hour to several hours) in an environment where the molten steel flow velocity is fast (about 0.1 to 0.5 m / s) as in the mold. However, the cost of the protective tube and replacement work are necessary for continuous measurement. In addition, in the method in which the probe is directly immersed in the molten steel in the mold, mold powder is entrained in the molten steel at the time of immersion, the metal bar attached around the probe is dropped into the molten steel, or the molten steel is surrounded around the immersed probe. There is a risk that flow vortices will be generated and mold powder will be entrained, and the quality of the molten steel will deteriorate.

  In addition, in the method (3) of indirectly measuring the molten steel temperature between the molds, a heat-resistant window glass is separately provided in the cooling box, so that it is necessary to improve the equipment and replace the deteriorated heat-resistant window glass.

  The present invention has been made to solve the above-mentioned conventional problems, and can continuously measure over time without directly immersing a probe or the like in molten steel in a mold, and has as few consumables as possible. It is an object of the present invention to provide a method and an apparatus for estimating the molten steel temperature in the mold with good estimation accuracy as a condition.

The present invention cools a liquid metal, forms a solidified shell, and pulls out the liquid metal slab, which is becoming a solid metal, from the mold. a step of determining the average temperature of the shell thickness direction, and determining a first enthalpy is a unit per volume enthalpy of the solid metal from the average temperature on the basis of a relationship between the temperature and the enthalpy for said solid metal, cooling the mold The step of obtaining a total heat flux in the mold corresponding to the total amount of heat flowing out of the liquid metal by the temperature difference between the inlet side and the outlet side of the water and the flow rate of the cooling water, the overall heat flux, the amount of drawn slab, From the solid shell thickness and the average density of the solidified shell at the mold outlet, the unit amount of the solid metal that is the amount of enthalpy removed from the liquid metal And determining a enthalpically amount, adding the removal enthalpy quantity in the first enthalpy, and determining a second enthalpy wherein a unit amount per enthalpy of liquid metal when it is injected into the mold, the liquid The above-mentioned problem is solved by a method for estimating the temperature of the molten metal in the continuous casting mold, which comprises the step of obtaining the temperature of the liquid metal from the second enthalpy based on the relationship between the temperature related to the metal and the enthalpy.

Further, the present invention is an apparatus for estimating a molten metal temperature in a mold in a continuous casting of a liquid metal in which the liquid metal is cooled, and a solidified shell is formed to pull out the liquid metal slab that is becoming a solid metal from the mold. Based on the relationship between the means for measuring the slab drawing amount per unit time, the means for determining the thickness of the solidified shell at the mold outlet and the average temperature in the thickness direction of the solidified shell, and the temperature and enthalpy for the solid metal Means for obtaining a first enthalpy which is an enthalpy per unit amount of the solid metal from the average temperature obtained by the means, means for obtaining a temperature difference between the inlet side and the outlet side of the cooling water of the mold and a flow rate of the cooling water, Based on the measured temperature difference between the inlet side and the outlet side of the cooling water of the mold and the flow rate of the cooling water, the total heat flux in the mold corresponding to the total amount of heat flowing out of the liquid metal is obtained. And per unit amount of the solid metal that is the amount of enthalpy extracted from the liquid metal from the overall heat flux, the slab extraction amount, the solidified shell thickness, and the average density of the solidified shell at the mold outlet Means for obtaining an extraction enthalpy amount, means for adding the removal enthalpy amount to the first enthalpy, and obtaining a second enthalpy which is an enthalpy per unit amount of the liquid metal when injected into a mold; and the liquid Means for determining the temperature of the liquid metal from the second enthalpy based on the relationship between the temperature related to the metal and the enthalpy, and solves the above problem by an apparatus for estimating the temperature of the molten metal in the continuous casting mold It is a thing.

  According to the present invention, the amount of slab drawing per unit time, the temperature difference between the inlet side and the outlet side of the cooling water in the mold, and the flow rate per hour of the cooling water are measured, and the relationship between the temperature related to metal and enthalpy By using the above, it is possible to estimate the molten steel temperature in the mold continuously with time and with high estimation accuracy without immersing the probe or the like directly in the molten steel in the mold, with as few consumables as possible.

  Therefore, the quality of the slab due to the molten steel temperature in the mold and technical calculation using the molten steel temperature in the mold as a calculation parameter, for example, the molten steel flow velocity in the mold from the copper plate temperature in the mold as described in Japanese Patent No. 3230513 The estimation can be performed with high accuracy.

  Embodiments according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic view of a cross section of a continuous casting machine (vertical bending type continuous casting machine) showing one embodiment of the present invention. In addition, the slab continuous casting of ordinary steel is shown here as an object.

  In FIG. 1, the continuous casting machine pulls out a tundish 4 that stores molten steel 2 that is a liquid metal, a mold 6 that molds the molten steel 2 while cooling, and a slab 8 in which the molten steel 2 is solidified from the mold 6. And a pinch roller 10.

  An immersion nozzle 12 for pouring the molten steel 2 into the mold 6 is provided on the tip side of the tundish 4, and the level of the molten steel surface (meniscus) 14 is set to a target value between the tundish 4 and the immersion nozzle 12. Further, a sliding nozzle 16 for adjusting the flow rate is disposed.

  A cooling water channel 18 is disposed in the mold 6, and a water supply pipe 20 is connected to the inlet side of the cooling water channel 18, and a drain pipe 22 is connected to the outlet side. A first water temperature meter 24 and a second water temperature meter 26 are provided in the water supply pipe 20 and the drain pipe 22 respectively, and an electromagnetic flow meter 28 is installed in the drain pipe 22.

  Some pinch rollers 10 are provided with a slab drawing speed meter 30 for measuring the slab drawing speed at the lower end of the mold 6.

  Cooling water is passed from the water supply pipe 20 to the copper plate of the mold 6, flows in the cooling water channel 18, the heat of the molten steel 2 is taken away, and the taken-off heat is discharged outside through the drain pipe 22.

  The first thermometer 24 measures the temperature of the cooling water in the water supply pipe 20, and the second thermometer 26 measures the temperature of the cooling water that has taken away heat flowing through the drain pipe 22, and the cooling water for the mold 6. The temperature difference between the inlet side and the outlet side of is required.

  The electromagnetic flow meter 28 measures the flow rate of the cooling water flowing through the drain pipe 22 in order to obtain the amount of heat going out from the mold 6.

  The slab drawing speed meter 30 measures a required casting speed as an independent variable or the like for obtaining an average temperature in the thickness direction of the solidified shell 32 at the outlet of the mold 6 from a regression equation (described later).

  Next, a method for estimating the temperature of the molten steel 2 in the mold 6 according to the present invention will be described.

  First, considering the physical process of solidification in the mold 6, the molten steel 2 injected into the mold 6 from the immersion nozzle 12 has a certain enthalpy (heat content) including sensible heat and latent heat of solidification.

  On the other hand, it can be considered that the mold 6 generally absorbs almost all of the heat transfer from the molten steel 2 by the cooling water flowing in the cooling water passage 18 disposed in the copper plate.

  Therefore, the amount of heat corresponding to the difference between the inlet side temperature and the outlet side temperature of the cooling water is a difference from the enthalpy of the molten steel 2 to the enthalpy at the average temperature in the thickness direction of the solidified shell 32 at the outlet of the mold 6. You can think of it as equivalent.

  Hereinafter, a procedure for obtaining the molten steel temperature in the mold 6 from the overall heat removal amount of the mold 6 obtained from the mold cooling water inlet / outlet temperature difference using the above principle is shown in the flowchart in FIG. 2 and the relationship between the temperature and enthalpy in FIG. This will be described in detail based on the graph shown.

  First, a temperature-enthalpy curve of steel is determined as a relationship between temperature and enthalpy related to a metal handled by a continuous casting machine. This is determined from generally known specific heat data and solidification latent heat data for each temperature (step S1). FIG. 3 schematically shows the relationship between temperature and enthalpy and the temperature estimation procedure.

Next, an average temperature (T1 _ave ) in the thickness direction of the solidified shell 32 at the outlet of the mold 6 is obtained (step S2). For this, heat transfer solidification calculation is used to calculate at a plurality of levels within an assumed casting speed (= slab drawing speed) Vc, and the casting speed Vc is an independent variable and the average temperature T1 _ave in the thickness direction is explained. Create a regression equation as a variable. The casting speed is measured with a slab drawing speed meter 30.

After _obtaining the average temperature T1 _ave , the first enthalpy (H ₁ ) is obtained from the average temperature T1 _ave based on the relationship between the temperature of the steel and the enthalpy (step S3).

  Next, the overall heat flux (Q), which is the overall heat removal amount in the mold per unit area, is obtained from the temperature difference between the mold cooling water input and output (step S4). The overall heat flux Q is expressed by the following equation.

here,
Q: Overall heat flux in the mold (W / m ² ),
ΔT: mold cooling water inlet / outlet temperature difference (° C),
R: Flow rate of cooling water per hour (m ³ / s),
h: distance from the meniscus of the mold to the mold outlet (m),
W: Mold width (m)
It is.

  The inlet / outlet temperature difference ΔT is obtained from water temperature gauges 24 and 26 disposed in the water supply pipe 20 and the drain pipe 22. The outflow of heat is mainly from the surface of the mold width W of the slab 8 and the distance h from the mold meniscus to the mold outlet.

  Next, from the general heat flux Q obtained by the equation (1), the removal enthalpy amount (ΔH), which is the enthalpy drop from the molten steel 2 per unit weight of the solidified shell at the outlet of the mold 6, is obtained from the following equation (2): Obtained (step S5).

here,
ρ: average density of solidified shell at the mold outlet (kg / m ³ ),
Vc: slab drawing speed at the lower end of the mold (m / s),
d: Solidified shell thickness at the lower end of the mold (m)
The solidified shell thickness d is obtained from the assumed Vc using heat transfer solidification calculation.

Next, the second enthalpy (H ₂ ) of the molten steel 2 injected into the mold 6 is obtained by the following equation (3) (step S6).

H ₂ = H ₁ + ΔH (3)

Then, the temperature of the steel H ₂ stages S1 - converted into the corresponding temperature with the enthalpy curve (step S7). Thereby, the molten steel temperature T2 in the mold 6 is obtained.

By the above procedure, T1 _ave is determined from the casting speed Vc, the overall heat flux Q is determined from the temperature difference ΔT of the mold cooling water and the flow rate R per hour of the cooling water, and the extraction enthalpy amount ΔH is determined by the slab extraction at the bottom of the mold Since the solidified shell thickness d obtained from the speed Vc and the slab drawing speed Vc can be obtained from time to time, the molten steel temperature T2 in the mold can be continuously increased over time without immersing a temperature measuring probe or the like in the molten steel. Can be estimated. In addition, since the probe or the like is not directly immersed in the molten steel, the number of consumables is minimized.

  The continuous casting machine may be of any type such as a complete vertical type and a curved type.

  Usually, the flow rate can be adjusted independently for each of the long-side copper plate and the short-side copper plate of the mold, but there is no problem even if one flow rate controller is combined with the copper plate.

  The thickness of the solidified shell and the average temperature in the thickness direction of the solidified shell are obtained from the casting speed using heat transfer solidification calculation. The thickness of the solidified shell is measured using, for example, ultrasonic waves, and the average Regarding the temperature, the surface temperature of the slab immediately below the mold may be measured, for example, with a radiation thermometer, and the average temperature may be estimated.

  Next, the Example by this invention applied to the slab continuous casting machine concretely is shown.

  In this example, the ultra low carbon steel for thin plates having the components shown in Table 1 was used.

  The outline of the apparatus configuration of the slab continuous casting machine is shown in FIG. 1 as in the embodiment of the invention described above, and was cast under casting conditions as shown in Table 2.

  FIG. 4 shows time-dependent trend data of the casting speed Vc with respect to the casting length, measured by the slab drawing speed meter 30.

  FIG. 5 shows the molten steel temperature in the tundish (spot measurement) and the molten steel temperature data in the mold measured at the same timing. The molten steel temperature data in the mold is obtained by the estimation method according to the present invention. It was measured for comparison with the value of the molten steel temperature in the mold.

  The temperature was measured by using a thermocouple covered with a transparent quartz protective tube and immersing the tip of the protective tube to 80 mm below the molten metal surface 14.

  FIG. 6 shows the trend of the overall heat flux Q in the mold obtained from the data of the temperature difference ΔT on the inlet / outlet side of the mold cooling water. This data was obtained by averaging the inlet / outlet side temperature differences ΔT on the front and rear surfaces of the long side of the mold, and calculating the overall heat flux Q for that value. The data is average value data for each slab when viewed over time.

  Hereinafter, a method for estimating the molten steel temperature T2 in the mold from the overall heat flux Q in the mold according to the procedure described in the embodiment will be described.

  i) First, the value shown in FIG. 7 was used for the temperature-enthalpy curve of steel, and linear interpolation was performed between the data (corresponding to step S1). The values are calibrated.

ii) Next, the average temperature T1 _ave of the solidified shell thickness at the mold outlet was determined by the following formula (4) by performing heat transfer solidification calculation at a plurality of casting speeds (corresponding to step S2).

T1 _ave = 28.75 × Vc + 1234.275 (4)

iii) The first enthalpy H ₁ was determined from this average temperature T1 _ave (corresponding to step S3).

  iv) Formula (1) was used to calculate the overall heat flux Q in the mold from the cooling water inlet / outlet temperature difference ΔT in the mold (corresponding to step S4). The obtained temporal trend of the overall heat flux Q in the mold is as shown in FIG.

  v) The extraction enthalpy amount ΔH was determined from the overall heat flux Q in the mold (corresponding to step S5).

vi) The second enthalpy H ₂ of the molten steel injected into the mold was determined by equation (3) (corresponding to step S6).

vii) Finally, as the molten steel temperature T2 in the mold, the second enthalpy H ₂ of the molten steel in the mold obtained in the step vi) is obtained by using the relationship data between the steel temperature and the enthalpy as shown in FIG. Obtained by converting to temperature T2 (corresponding to step S8).

  FIG. 8 shows the estimated value T2 of the molten steel temperature in the mold thus obtained. The plot line marked with “♦” is the estimated value T2 of the molten steel temperature in the mold of the present invention, and the plot marked with “●” is the spot measurement value of the molten steel temperature in the mold as shown in FIG.

  Both are in good agreement, and it can be seen that the absolute value of the molten steel temperature in the mold and the change every moment can be known from the estimated value T2 of the molten steel temperature in the mold according to the present invention.

  However, as can be seen from FIG. 8, the estimated value T2 of the molten steel temperature in the mold is abnormal in the unsteady part where the casting speed Vc is changing. In this embodiment, the casting speed Vc uses an instantaneous value every moment, while the overall heat flux Q in the mold uses the slab cutting unit data of the mold cooling water inlet / outlet temperature difference ΔT. Because.

Sectional drawing which shows the outline of the continuous casting machine of embodiment which concerns on this invention The flowchart which shows the procedure which concerns on this invention Graph that schematically shows the relationship between temperature and enthalpy In this example, a graph showing the trend of measured casting speed Graph showing measured values of molten steel temperature in tundish and mold Graph showing overall trend of heat flux in mold Graph showing the relationship between temperature and enthalpy used in the examples The graph which shows the estimated value of the molten steel temperature in a mold by a present Example

Explanation of symbols

2 ... Molten steel 6 ... Mold 8 ... Slab 32 ... Solidified shell

Claims (2)

In the continuous casting of the liquid metal, the liquid metal is cooled, the solidified shell is formed, and the slab of the liquid metal that is becoming a solid metal is drawn from the mold,
Determining the thickness of the solidified shell at the mold outlet and the average temperature in the thickness direction of the solidified shell;
And determining a first enthalpy is a unit per volume enthalpy of the solid metal from the average temperature on the basis of a relationship between the temperature and the enthalpy for said solid metal,
Obtaining the overall heat flux in the mold corresponding to the total amount of heat flowing out of the liquid metal by the temperature difference between the inlet side and the outlet side of the cooling water of the mold and the flow rate of the cooling water;
Extraction enthalpy per unit amount of the solid metal, which is the amount of enthalpy extracted from the liquid metal from the overall heat flux, the slab extraction amount, the solidified shell thickness, and the average density of the solidified shell at the mold outlet Determining the quantity;
Adding the removal enthalpy amount to the first enthalpy and obtaining a second enthalpy that is an enthalpy per unit amount of the liquid metal at the time of being injected into the mold;
And determining a temperature of the liquid metal from the second enthalpy based on the relationship between the temperature and the enthalpy for said liquid metal,
A method for estimating a molten metal temperature in a continuous casting mold, comprising: In the apparatus for estimating the molten metal temperature in the mold in the continuous casting of the liquid metal in which the liquid metal is cooled, and the slab of the liquid metal that is forming a solid metal by forming a solidified shell is pulled out of the mold,
Means for measuring the amount of slab drawing per unit time;
Means for determining the thickness of the solidified shell at the mold outlet and the average temperature in the thickness direction of the solidified shell;
Means for determining a first enthalpy is a unit per volume enthalpy of the solid metal from the average temperature determined by said means on the basis of a relationship between the temperature and the enthalpy for said solid metal,
Means for determining the temperature difference between the inlet side and the outlet side of the mold cooling water and the flow rate of the cooling water;
Means for obtaining an overall heat flux in the mold corresponding to the total amount of heat flowing out of the liquid metal from the measured temperature difference between the inlet side and the outlet side of the cooling water of the mold and the flow rate of the cooling water;
The extraction enthalpy per unit amount of the solid metal, which is the amount of enthalpy extracted from the liquid metal, from the overall heat flux, the slab extraction amount, the solidified shell thickness, and the average density of the solidified shell at the mold outlet A means of determining the quantity;
Means for adding the removal enthalpy amount to the first enthalpy and obtaining a second enthalpy which is an enthalpy per unit amount of the liquid metal at the time of being injected into the mold;
It means for determining the temperature of the liquid metal from the second enthalpy based on the relationship between the temperature and the enthalpy for said liquid metal,
An apparatus for estimating a molten metal temperature in a continuous casting mold, comprising:

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