Method and apparatus for monitoring a continuous steel casting process

Abstract

A method, an apparatus and a computer readable-medium for monitoring a continuous steel casting process where molten steel is poured from a ladle into a tundish to be transferred through an exit nozzle into a mold. The method includes obtaining a critical superheat temperature value for the molten steel; measuring temperature values of the molten steel over a time period; determining superheat temperature values corresponding to the measured temperature values by comparing the measured temperature values with a liquidus temperature of the molten steel; and predicting a forecast time instance when the critical superheat temperature value is reached.

Claims

1. A method for monitoring a continuous steel casting process where molten steel is poured from a ladle into a tundish to be transferred through an exit nozzle into a mold, the method comprising: obtaining a critical superheat temperature value for the molten steel; measuring temperature values of the molten steel over a time period; determining superheat temperature values corresponding to the measured temperature values by comparing the measured temperature values with a liquidus temperature of the molten steel; predicting a forecast time instance (t.sub.Forecast) when the critical superheat temperature value is reached, wherein
t.sub.Forecast=(T.sub.SH−T.sub.SH Critical)/((T.sub.SH−T.sub.SH Predicted)/(t.sub.End Predicted−t.sub.Actual)) where T.sub.SH represents the determined superheat temperature, T.sub.SH Critical represents the critical superheat temperature, T.sub.SH Predicted represents the predicted superheat temperature, t.sub.End Predicted represents the remaining time span and t.sub.Actual represents the time instance when the forecast time instance t.sub.Forecast is calculated, wherein predicting the superheat temperature is performed by determining the actual slope of the superheat versus time slope; obtaining a remaining time span for casting which is the predicted time until the molten steel is transferred from the ladle into the tundish; and determining whether the forecast time instance is within the remaining time span.

2. The method of claim 1, wherein obtaining the remaining time span comprises: determining the remaining time span based on a current casting flow, and/or an amount of molten steel in the ladle, and/or obtaining empirically determined time values for the remaining time span.

3. The method of claim 2, wherein the amount of molten steel in the ladle is determined by determining the weight of the molten steel in the ladle.

4. The method of claim 1, wherein the predicting the forecast time instance when the critical superheat temperature value is reached is based on the determined superheat temperature values, and on predicted superheat temperature values corresponding to an expected superheat value at an end time of the remaining time span.

5. The method of claim 4, wherein predicting the superheat temperature values corresponding to the expected superheat value at a predicted end time of the remaining time span comprises: predicting as a linear function of the determined superheat values.

6. The method of claim 4, wherein predicting the superheat temperature values corresponding to the expected superheat value at a predicted end time of the remaining time span comprises predicting as a quadratic evolution of the determined superheat values.

7. The method of claim 1, wherein the critical superheat value is an empirically determined value.

8. The method of claim 1, wherein determining superheat temperature values corresponding to the measured temperature values starts (i) after a minimum of 20% of the initial amount of molten steel was transferred from the ladle in the tundish; and/or (ii) after a maximum temperature in the measured temperature values was detected.

9. The method of claim 1, wherein measuring temperature values comprises measuring at least three temperatures at different time instances to generate a function of temperature over time.

10. The method of claim 9, further comprising applying a smoothing function to the function of temperature over time.

11. The method of claim 1, wherein the liquidus temperature is determined based on an analysis of a steel composition of the molten steel, and/or based on a general grade composition and/or based on an in situ measurement, and/or based on an analysis of a steel composition from a previous steel treatment process.

12. The method of claim 1, wherein measuring the temperature values of the molten steel comprises measuring the temperature of the molten steel by means of a temperature measuring device mounted through a side-wall or bottom portion of the tundish.

13. The method of claim 1, wherein the time period is a time period of at least 5 minutes.

14. The method of claim 1, wherein the predicting of the forecast time instance is performed after: (i) a new temperature value of the molten steel was measured, and/or (ii) acquiring a new critical superheat temperature of the molten steel, and/or (iii) determining the remaining time span.

15. The method of claim 1, wherein the method steps are performed in real-time.

16. The method of claim 1, wherein determining superheat temperature values corresponding to the measured temperature values starts (i) after at least 30% of the initial amount of molten steel was transferred from the ladle in the tundish; and/or (ii) after a maximum temperature in the measured temperature values was detected.

17. The method of claim 1, wherein measuring temperature values comprises measuring continuously to generate a function of temperature over time.

18. A computer-readable medium comprising a computer program comprising instructions for influencing a processor to carry out a method according to claim 1.

19. An apparatus for monitoring a continuous steel casting process where molten steel is poured from a ladle into a tundish to be transferred through an exit nozzle into a mold, the apparatus comprising: means for obtaining a critical superheat temperature value for the molten steel; means for measuring temperature values of the molten steel over a time period; means for determining superheat temperature values corresponding to the measured temperature values by comparing the measured temperature values with a liquidus temperature of the molten steel; and means for predicting a forecast time instance (t.sub.Forecast) when the critical superheat temperature value is reached, wherein
t.sub.Forecast=(T.sub.SH−T.sub.SH Critical)/((T.sub.SH−T.sub.SH Predicted)/(t.sub.End Predicted−t.sub.Actual)) where T.sub.SH represents the determined superheat temperature, T.sub.SH Critical represents the critical superheat temperature, T.sub.SH Predicted represents the predicted superheat temperature, t.sub.End Predicted represents the remaining time span and t.sub.Actual represents to the time instance when the forecast time instance t.sub.Forecast is calculated, wherein predicting the superheat temperature to obtain T.sub.SH Predicted is performed by determining the actual slope of the superheat versus time slope; means for obtaining a remaining time span for casting which is the predicted time until the molten steel is transferred from the ladle into the tundish; and means for determining whether the forecast time instance is within the remaining time span.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The following schematic drawings show aspects of the invention for improving the understanding of the invention in connection with some exemplary illustrations, wherein

(2) FIG. 1 shows an evolution of a tundish temperature over a casting process where several ladles of molten steel are subsequently poured into the tundish;

(3) FIG. 2 shows a detailed view of the tundish temperature where a single ladle of molten steel is poured into the tundish;

(4) FIG. 3 shows the determined superheat temperature values corresponding to measured temperature values according to an embodiment of the invention;

(5) FIG. 4 shows the evolution of a predicted superheat temperature over time according to an embodiment of the invention;

(6) FIG. 5 shows the predicting of a forecast time instance according to an embodiment of the invention;

(7) FIG. 6 shows the method steps of the method according to an embodiment of the invention; and

(8) FIG. 7 shows a schematic view of an apparatus according to an embodiment of the invention.

DETAILED DESCRIPTION

(9) FIG. 1 shows an evolution of a tundish temperature over a casting process where several ladles of molten steel are subsequently poured into the tundish. In total, six ladle changes are exemplarily shown in FIG. 1. It can be seen that the evolution of the temperature and the time to cast can vary from ladle to ladle. In addition, it can be seen that towards the end of the ladle, a steep drop in temperature takes place. In the shown example, a liquidus temperature of 1529° C. was calculated. As it can be seen from FIG. 1, the measured temperature of the molten steel almost dropped to the level of the liquidus temperature during the first and fourth ladle change. Therefore, determining superheat values and predicting based on the determined temperature values a forecast time instance when the critical superheat temperature is reached can be very beneficial for monitoring a continuous steel casting process.

(10) FIG. 2 shows a detailed view of the tundish temperature where a single ladle of molten steel is poured into the tundish. FIG. 2 can be a detailed view of the evolution of the tundish temperature which corresponds to the measured temperature T.sub.Meas over one ladle of the casting process which is shown in FIG. 1. In the shown example, the ladle-to-ladle time is 59 minutes. However, the skilled person would know that the ladle-to-ladle time could be shorter or longer depending on the process.

(11) In general, the evolution of the tundish temperature does not follow a linear pattern, since the temperature has a tendency to drop after a short and steep increase almost linearly towards the end of a predicted ladle change time. The figure shows that after a short time, i.e. when a minimum of 20% to 30% of the molten steel was transferred from the ladle into the tundish, the temperature evolution starts to show a more linear behavior. Therefore, it is meaningful to determine superheat temperature values corresponding to the measured temperature values after a minimum of 20% of the initial amount of molten steel was transferred from the ladle into the tundish, and/or after a maximum temperature in the measured temperature values was detected.

(12) FIG. 3 shows the determined superheat temperature values T.sub.SH corresponding to measured temperature values T.sub.Meas according to an embodiment of the invention. The measured temperature values T.sub.Meas of the molten steel that are shown using circles can be those of FIG. 2. In the shown embodiment one new temperature value is obtained per minute. Also, in the shown embodiment for determining the superheat temperature values T.sub.SH a smoothing function (which is not shown in FIG. 3) is applied to the function of temperature over time. However, in other embodiments no smoothing function might be applied, and the sampling time might be faster or slower than one temperature value per minute.

(13) As discussed above, the step of comparing the measured temperature values T.sub.Meas with a liquidus temperature of the molten steel to determine superheat temperature values T.sub.SH corresponding to the measured temperature values T.sub.Meas starts when a minimum of 20% to 30% of the molten steel was transferred from the ladle into the tundish. The determined superheat temperature values T.sub.SH corresponding to the measured temperature values T.sub.Meas are shown using squares. For the purpose of the present discussion, the critical superheat temperature value T.sub.SH Critical was set to be 25° C. and is shown using crosses.

(14) In the shown embodiment, the critical superheat temperature value T.sub.SH Critical was determined only once for the process. However, in other embodiments the critical superheat temperature can be updated regularly or irregularly during the process.

(15) FIG. 4 shows the evolution of a predicted superheat temperature T.sub.SH Predicted over time according to an embodiment of the invention. The determined superheat temperature values T.sub.SH and measured temperature values T.sub.Meas can be those which are shown in FIG. 3. Hence, FIG. 4 and FIG. 3 can relate to the same embodiment.

(16) In the shown embodiment, the predicted superheat temperature values T.sub.SH Predicted are calculated as a quadratic evolution of the determined superheat temperature values T.sub.SH. The predicted superheat temperature values T.sub.SH Predicted correspond to an expected superheat value at the predicted end time t.sub.End Predicted of the process or to the time instance of the next ladle-change.

(17) FIG. 5 shows the predicting of a forecast time instance t.sub.Forecast according to an embodiment of the invention. The determined superheat temperature values T.sub.SH, predicted superheat temperature values T.sub.SH Predicted, and measured temperature values T.sub.Meas can be those of the embodiment of FIGS. 3 and 4. Hence, FIGS. 3, 4 and 5 can all relate to the same embodiment.

(18) In FIG. 5 the forecast time instance t.sub.Forecast is predicted dynamically every minute following the determination of a new superheat temperature value T.sub.SH. The forecast time instances t.sub.Forecast are shown as lines and refer to the remaining time for casting, i.e. to the predicted time when the critical superheat temperature value T.sub.SH Critical is reached.

(19) The forecast time instance t.sub.Forecast can be calculated by the equation:
t.sub.Forecast=(T.sub.SH−T.sub.SH Critical)/((T.sub.SH−T.sub.SH Predicted)/(t.sub.End Predicted−t.sub.Actual))

(20) The remaining time span t.sub.End Predicted is a prediction of the time when the process ends or the next ladle change occurs. The actual time t.sub.Actual corresponds to the time instance when the forecast time instance t.sub.Forecast is calculated.

(21) FIG. 6 shows the method steps of the method 1000 for monitoring a continuous steel casting process where molten steel is poured from a ladle into a tundish to be transferred through an exit nozzle into a mold according to an embodiment of the invention. The method 1000 comprises the steps:

(22) obtaining 1010 a critical superheat temperature value for the molten steel;

(23) measuring 1020 temperature values of the molten steel over a time period;

(24) determining 1030 superheat temperature values corresponding to the measured temperature values by comparing the measured temperature values with a liquidus temperature of the molten steel; and

(25) predicting 1040 a forecast time instance when the critical superheat temperature value is reached.

(26) Optionally, the method 1000 can comprise the steps:

(27) obtaining 1050 a remaining time span for casting; and

(28) determining 1060 whether the forecast time instance is within the remaining time span.

(29) FIG. 7 shows a schematic view of an apparatus 100 for monitoring a continuous steel casting process where molten steel is poured from a ladle into a tundish to be transferred through an exit nozzle into a mold according to an embodiment of the invention. The apparatus 100 comprises:

(30) means for obtaining 110 a critical superheat temperature value for the molten steel;

(31) means for measuring 120 temperature values of the molten steel over a time period;

(32) means for determining 130 superheat temperature values corresponding to the measured temperature values by comparing the measured temperature values with a liquidus temperature of the molten steel; and

(33) means for predicting 140 a forecast time instance when the critical superheat temperature value is reached.

(34) Optionally, the apparatus 100 can also comprise:

(35) means for obtaining 150 a remaining time span for casting; and

(36) means for determining 160 whether the forecast time instance is within the remaining time span.

(37) The features disclosed in the claims, the specification, and the drawings may be essential for different embodiments of the claimed invention, both separately or in any combination with each other.

REFERENCE SIGNS

(38) 100 Apparatus for Monitoring 110 Means for Determining a Critical Superheat Temperature Value 120 Means for Measuring Temperature Values 130 Means for Determining Superheat Temperature Values 140 Means for Predicting 150 Means for Obtaining a Remaining Time Span 160 Means for Determining whether the Forecast Time Instance is within the Remaining Time Span 1000 Method for Monitoring 1010 Determining a Critical Superheat Temperature Value 1020 Measuring Temperature Values 1030 Determining Superheat Temperature Values 1040 Predicting 1050 Obtaining a Remaining Time Span 1060 Determining whether the Forecast Time Instance is within the Remaining Time Span T.sub.SH Determined Superheat Temperature Values T.sub.SH Predicted Predicted Superheat Temperature Values T.sub.Meas Measured Temperature Values T.sub.SH Critical Critical Superheat Temperature Value t.sub.Actual Actual Time t.sub.End Predicted Predicted End Time t.sub.Forecast Forecast Time Instance