JP5983071B2 - Prediction method for steel slab extraction temperature - Google Patents

Description

  The present invention relates to a method for predicting a furnace extraction temperature of a steel piece subjected to hot rolling or the like.

The steel slab to be subjected to hot rolling is usually heated to a predetermined temperature in a heating furnace and then subjected to rolling. For this reason, when heating a steel slab in a heating furnace, it is necessary to heat it uniformly to the target temperature. To heat the steel slab uniformly to the target temperature, the furnace temperature of the heating furnace or the extraction of the steel slab into the furnace It is necessary to monitor the temperature from time to time.
However, if scale is generated on the surface of the steel slab extracted from the heating furnace, it is difficult to directly measure the furnace extraction temperature of the steel slab. Therefore, in Patent Document 1, the atmospheric gas components in the heating furnace are measured using a carbon dioxide gas meter and a dew point meter, the gas emissivity is obtained from the measured value, and the overall heat absorption rate is calculated from the gas emissivity. A method for predicting the furnace extraction temperature of a billet is described.

Further, in Patent Document 2, the steel slab temperature at the time of rolling is obtained based on the rolling load when the steel slab is rolled and the outer dimensions of the steel slab before and after rolling, and the steel slab reaches the rolling mill from the heating furnace. The method of calculating the furnace extraction temperature of a steel piece in consideration of the cooling up to is described.
Furthermore, in Patent Document 3, the surface of the steel slab extracted from the heating furnace is descaled with high-pressure water, and after reheating of the descaled steel slab surface is completed, the surface temperature of the steel slab is measured, A method of calculating and predicting the furnace extraction temperature of a billet based on a temperature measurement value is described.

JP-A-6-192751 Japanese Unexamined Patent Publication No. 63-26214 Japanese Patent No. 4349177

However, since the distribution of the atmospheric gas is not uniform in the heating furnace, the method described in Patent Document 1 has a very large temporal variation of atmospheric gas components, and it is extremely difficult to identify an appropriate overall heat absorption rate. There is a problem that it is difficult.
Further, it is difficult to accurately calculate the slab temperature from the rolling resistance and outer dimensions of the slab, and the cooling condition from the heating furnace to the rolling mill becomes a disturbance factor. In the method, there is a problem that the furnace extraction temperature of the billet cannot be accurately obtained.

On the other hand, in the method described in Patent Document 3, since the surface temperature of the descaled billet is measured, the surface temperature of the billet can be measured without being affected by the scale. Since the heat transfer coefficient of water is very large, and the measured temperature of the steel slab surface varies greatly depending on the boiling state of descaling water, the furnace extraction temperature of the steel slab cannot be accurately predicted.
This invention is made | formed in view of this situation, and provides the heating furnace extraction temperature prediction method of the steel slab which can estimate the heating furnace extraction temperature of the steel slab provided to hot rolling etc. correctly. It is for the purpose.

In order to achieve the above object, the present invention is a method for predicting a furnace extraction temperature of a steel slab heated in a heating furnace, wherein air is blown out onto the surface of the steel slab extracted from the heating furnace. A scale removing step of removing scale from the surface of the steel slab by spraying from a nozzle; and a temperature measuring step of measuring the surface temperature of the steel slab after completion of reheating of the steel slab surface after the scale removal process; the temperature measurements obtained by the temperature measuring step calculates the billet surface temperature at the heating furnace extraction based have a, a heating furnace extraction temperature prediction step of predicting a heating furnace extraction temperature of the steel strip, In the scale removal step, the scale is removed from the surface of the steel slab by setting an injection flow rate per nozzle of air injected from the air ejection nozzle to the surface of the steel slab at 200 to 5000 Nm ³ / h. Features .

  In the present invention, the surface temperature of the steel slab at the time of the heating furnace extraction, the surface temperature of the steel slab measured in the temperature measuring step, the air temperature around the steel slab, and the steel slab are cooled by natural air cooling. The steel slab is cooled by the heat transfer coefficient, the specific heat of the steel slab, the elapsed time from the extraction of the steel slab to the surface temperature measurement, and the air ejected from the air ejection nozzle. It is desirable to calculate based on the heat transfer coefficient and the temperature of the air sprayed from the air ejection nozzle onto the surface of the steel slab.

Moreover, it is preferable to remove the scale from the surface of the steel slab by setting the injection distance of air injected from the air ejection nozzle to the surface of the steel slab to 50 to 200 mm.
Moreover, it is preferable that the scale is removed from the surface of the steel slab by setting an injection pressure of air injected from the air ejection nozzle to the surface of the steel slab at 0.2 to 2.0 MPa .

  According to the present invention, there is no need to descal the surface of the steel slab extracted from the heating furnace with high-pressure water, and the temperature measurement value of the steel slab surface depends on the heat transfer coefficient of the descaling water and the boiling state of the descaling water. It does not fluctuate greatly. Accordingly, it is possible to accurately predict the furnace extraction temperature of a steel piece to be subjected to hot rolling or the like.

It is a figure which shows a part of continuous production line of a hot-rolled steel plate. It is a figure which shows the air ejection nozzle used when removing a scale from the surface of a steel piece. It is a figure which shows the temperature change from the time of furnace extraction of a steel piece to the time of surface temperature measurement.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
The method for predicting the extraction temperature of a steel slab according to the present invention is applied to a continuous production line for hot-rolled steel sheets, and as a continuous production line for hot-rolled steel sheets, as shown in FIG. A heating furnace 2 for heating 1, a rough rolling machine 3 for rough rolling the steel slab 1 heated in the heating furnace 2, and the like can be used.

The steel slab 1 extracted from the heating furnace 2 is conveyed to the rolling mill 3 by a number of conveying rollers 4, but before being roughly rolled by the rough rolling mill 3, the air disposed on the outlet side of the heating furnace 2. The scale 6 (see FIG. 2) is removed from the surface of the steel piece 1 by the ejection nozzles 5a and 5b.
The air ejection nozzles 5 a and 5 b are for blowing air onto the surface of the steel piece 1 to remove the scale 6 from the surface of the steel piece 1, and are arranged on the upper side and the lower side of the transport roller 4.

  Here, if the spray distance of the air sprayed from the air ejection nozzles 5a and 5b onto the surface of the steel slab 1 is less than 50 mm, the deformed steel slab collides with the air ejection nozzles 5a and 5b, resulting in an operation trouble. Moreover, if the spray distance of the air sprayed from the air ejection nozzles 5a and 5b onto the surface of the steel slab 1 exceeds 200 mm, the air ejected from the air ejection nozzles 5a and 5b is decelerated and the scale cannot be removed. Therefore, when the scale 6 is removed from the surface of the steel piece 1 by blowing air onto the surface of the steel piece 1 from the air ejection nozzles 5a and 5b, the air jetted from the air ejection nozzles 5a and 5b to the surface of the steel piece 1 It is preferable to set the spray distance to 50 to 200 mm.

  If the spray pressure of air sprayed from the air spray nozzles 5a and 5b onto the surface of the steel slab 1 is less than 0.2 MPa, the scale cannot be removed. Moreover, if the injection pressure of the air injected to the surface of the steel slab 1 from the air injection nozzles 5a and 5b exceeds 2.0 MPa, the specifications of the compressor used for air injection increase, and the running cost increases. Therefore, when the scale 6 is removed from the surface of the steel piece 1 by blowing air onto the surface of the steel piece 1 from the air ejection nozzles 5a and 5b, the air jetted from the air ejection nozzles 5a and 5b to the surface of the steel piece 1 The injection pressure is preferably set to 0.2 to 2.0 MPa.

If the spraying flow rate per nozzle of air sprayed from the air ejection nozzles 5a, 5b to the surface of the steel slab 1 is less than 200 Nm ³ / h, the scale cannot be removed. In addition, if the injection flow rate per nozzle of air injected from the air injection nozzles 5a and 5b to the surface of the steel slab 1 exceeds 5000 Nm ³ / h, the specifications of the compressor used for the air injection increase and the running cost increases. To do. Therefore, when the scale 6 is removed from the surface of the steel piece 1 by blowing air onto the surface of the steel piece 1 from the air ejection nozzles 5a and 5b, the air jetted from the air ejection nozzles 5a and 5b to the surface of the steel piece 1 It is preferable that the injection flow rate per nozzle is set to 200 to 5000 Nm ³ / h.

  The steel piece 1 from which the scale 6 has been removed by the air ejected from the air ejection nozzles 5a and 5b is located between the radiation thermometer 7a and the radiation thermometer 7b arranged opposite to each other on the upper side and the lower side of the conveying roller 4. And is conveyed to the roughing mill 3. At this time, the surface temperature of the upper surface side and the lower surface side of the steel slab 1 is measured by the radiation thermometers 7 a and 7 b, and the radiation thermometers 7 a and 7 b output signals corresponding to the surface temperature of the steel slab 1.

The signals output from the radiation thermometers 7a and 7b are supplied to the heating furnace extraction temperature prediction device 8. This heating furnace extraction temperature prediction device 8 predicts the heating furnace extraction temperature of the steel slab 1 (plate thickness direction average temperature at the time of heating furnace extraction), and is heated from the following formulas (1) and (2). The steel slab surface temperature T _A , T _A ′ at the time of furnace extraction is obtained to predict the furnace extraction temperature of the steel slab 1.
T _A = T _E + ΔT _a1 + ΔT _c −ΔT _R + ΔT _a2 (1)
T _A '= T _E ' + ΔT _a1 '+ ΔT _c ' −ΔT _R '+ ΔT _a2 ' (2)

However, T _E , T _E ′: measured values of the surface temperature of the radiation thermometers 7 a, 7 b, ΔT _a1 , ΔT _a1 ′: point A (heating furnace extraction point) to point B (air ejection nozzles 5 a, 5 b) shown in FIG. The temperature drop of the steel slab 1 until the scale removal start point by Δ, ΔT _c , ΔT _c ′: from the point B shown in FIG. 3 to the point C (end point of scale removal by the air ejection nozzles 5a, 5b) Temperature drop of steel slab 1, ΔT _R , ΔT _R ′: temperature rise of steel slab 1 from point C to point D (recovery completion point on the surface of steel slab 1) shown in FIG. _a2 , ΔT _a2 ': The temperature drop of the steel slab 1 from point D to point E (temperature measurement points by the radiation thermometers 7a, 7b) shown in FIG.

Here, the heat transfer coefficient when the steel strip 1 is cooled by natural cooling α _a, α _a ', the specific heat of the steel piece 1 c, the elapsed time from the point A shown in FIG. 3 up to point B t _a1 , T _a1 ′, and the air temperature around the steel slab is T _a , T _a ′, the temperature drop amounts ΔT _a1 , ΔT _a1 ′ in the equations (1) and (2) are expressed by the following (3) and (4 ).

Further, the heat transfer coefficients α _c and α _c ′ when the steel slab 1 is cooled by the air ejected from the air ejection nozzles 5a and 5b are c, the specific heat of the steel slab 1 is c, and the points B to C shown in FIG. , T _c , t _c ′, and temperatures of air ejected from the air ejection nozzles 5 a, 5 b are T _c , T _c ′. Temperature drop amounts ΔT _c , ΔT in the expressions (1) and (2) _c ′ is expressed by the following equations (5) and (6).

Further, the heat transfer coefficient when the steel strip 1 is cooled by natural cooling α _a, α _a ', the specific heat of the steel piece 1 c, the elapsed time from the point C shown in FIG. 3 up to point D t _R, t _R When ', the elapsed time from the point D shown in FIG. 3 up to point E t _a2, t _a2' and, (1) and (2) temperature rise of formula [Delta] t _R, [Delta] t _R 'and the amount of temperature drop [Delta] t _a2 and ΔT _a2 ′ are expressed by the following equations (7) and (8).

FIG. 3 is a diagram showing the relationship between the surface temperature of the steel slab 1 and the elapsed time from the extraction of the heating furnace. As illustrated in FIG. 3, the surface temperature of the slab 1 is about 1200 ° C. at point A in FIG. 3 immediately after being extracted from the heating furnace, but is then naturally air cooled to about 1175 ° C. at point B. Descend. And since the surface of a steel slab is forcibly air-cooled by the jet air from an air ejection nozzle from the B point to the C point, the temperature of a steel slab falls to 1165 degreeC in the C point. Thereafter, recuperation is performed on the surface of the steel slab, and the temperature of the steel slab rises to about 1170 ° C. at point D when the reheating is completed. Thereafter, the surface of the billet is naturally air-cooled, and at the point E measured by a radiation thermometer, the temperature of the billet is lowered to about 1160 ° C.
Accordingly, by solving the above equations (1) to (8), the steel slab surface temperatures T _A and T _A ′ at the time of extraction from the heating furnace can be calculated, and the steel slab surface temperatures T _A and T _A ′ are calculated. The furnace extraction temperature of the steel slab 1 can be predicted from the value.

  As described above, after the scale 6 is removed from the surface of the steel piece 1 by blowing air from the air jet nozzles 5a and 5b to the surface of the steel piece 1 extracted from the heating furnace 2, the surface temperature of the steel piece 1 is radiated. By measuring with the thermometers 7a and 7b, it is not necessary to descal the surface of the steel slab 1 extracted from the heating furnace 2 with high pressure water, and the steel depends on the heat transfer coefficient of the descaling water and the boiling state of the descaling water. The temperature measurement value on one surface does not fluctuate greatly. Moreover, since the surface temperature measurement of the steel piece 1 by the radiation thermometers 7a and 7b is performed after the reheating of the surface of the steel piece is completed, the accurate surface temperature of the steel piece 1 can be measured. Therefore, the furnace extraction temperature of the steel slab 1 used for hot rolling or the like is accurately predicted by predicting the furnace extraction temperature of the steel slab 1 based on the temperature measurement values of the radiation thermometers 7a and 7b. be able to.

Also, by comparing the heating furnace extraction temperature of the steel slab 1 predicted by the heating furnace extraction temperature prediction device 8 with the heating furnace extraction temperature of the steel slab predicted based on the temperature control model in the heating furnace, a summary of the inside of the heating furnace is obtained. It becomes possible to correct the heat absorption rate and improve the medium accuracy of the target extraction temperature.
Moreover, the steel slab 1 used for hot rolling etc. is calculated | required by calculating | requiring the steel slab surface temperature at the time of heating furnace extraction from (1) and / or (2) Formula, and predicting the heating furnace extraction temperature of the steel slab 1 The extraction temperature of the furnace can be predicted more accurately.
In one Embodiment of this invention mentioned above, the surface temperature of the upper surface side and the lower surface side of the steel piece 1 from which the scale 6 was removed is measured with the radiation thermometers 7a and 7b, and the heating furnace extraction temperature of the steel piece 1 is estimated. However, the surface temperature of one of the upper surface and the lower surface of the steel slab 1 may be measured with a radiation thermometer to predict the heating furnace extraction temperature of the steel slab 1.

(Example)
The present inventors have set the injection distance of air to be injected from the air injection nozzles 5a, 5b onto the surface of the steel piece (plate width: 1.2 m, plate thickness: 220 mm) S at 100 mm, injection pressure at 1 MPa per nozzle. The steel slab overheating temperature in the heating furnace 2 when the injection flow rate was set to 500 Nm ³ / h, the heating furnace basic unit, and the quality defect occurrence rate index due to insufficient heating were investigated. The survey results are shown in Table 1.

(Comparative example)
Also, after removing the scale from the surface of the steel slab by spraying descaling water from the spray nozzle onto the surface of the steel slab extracted from the heating furnace, the reheating of the surface of the steel slab is completed. Measured with a radiation thermometer later, calculated the furnace extraction temperature of the slab 1 based on the temperature measurement value of the radiation thermometer, and predicted the slab overheating temperature, heating furnace basic unit, heating in the heating furnace We investigated the index of quality failure rate due to the shortage. The survey results are also shown in Table 1.

Comparing the examples in Table 1 with the comparative examples, the average steel slab overheating temperature was about 30 ° C in the comparative example, whereas the average steel slab overheating temperature was less than 10 ° C in the examples. It was.
Further, when the heating furnace basic unit in the comparative example is 1.0 and the quality defect occurrence rate index due to insufficient heating is 1.0, in the example, the heating furnace basic unit is 0.9, and the quality defect occurrence rate index Was less than 0.5.

DESCRIPTION OF SYMBOLS 1 ... Steel slab 2 ... Heating furnace 3 ... Rough rolling mill 4 ... Conveying roller 5a, 5b ... Air ejection nozzle 6 ... Scale 7a, 7b ... Radiation thermometer 8 ... Heating furnace extraction temperature prediction apparatus

Claims (4)

A method for predicting a furnace extraction temperature of a steel slab heated in a heating furnace,
A scale removing step of removing scale from the surface of the steel piece by blowing air from an air jet nozzle onto the surface of the steel piece extracted from the heating furnace;
A temperature measuring step of measuring the surface temperature of the steel slab after completion of reheating of the steel slab surface after the scale removal step;
The temperature measurements obtained by the temperature measuring step calculates the billet surface temperature at the heating furnace extraction based have a, a heating furnace extraction temperature prediction step of predicting a heating furnace extraction temperature of the steel strip,
In the scale removal step, the scale is removed from the surface of the steel slab by setting an injection flow rate per nozzle of air injected from the air ejection nozzle to the surface of the steel slab at 200 to 5000 Nm ³ / h. A method for predicting the extraction temperature of a steel slab, characterized by:   The steel slab surface temperature at the time of the heating furnace extraction, the surface temperature of the steel slab measured in the temperature measuring step, the air temperature around the steel slab, and the heat when the steel slab is cooled by natural air cooling. Heat transfer when the billet is cooled by the transfer coefficient, the specific heat of the billet, the elapsed time from the extraction of the billet to the surface temperature measurement, and the air blown from the air jet nozzle The method for predicting a steel slab heating furnace extraction temperature according to claim 1, wherein the calculation is based on a coefficient and a temperature of air sprayed from the air ejection nozzle onto the surface of the steel slab.   The steel according to claim 1 or 2, wherein a scale is removed from the surface of the steel slab by setting an injection distance of air injected from the air ejection nozzle to the surface of the steel slab at 50 to 200 mm. Method for predicting the extraction temperature of a piece of heating furnace.   The scale is removed from the surface of the steel slab by setting the injection pressure of air injected from the air ejection nozzle to the surface of the steel slab at 0.2 to 2.0 MPa. The heating furnace extraction temperature prediction method of the steel slab as described in any one of these.

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