Patent Application
20190291176
The disclosure relates to a control method and apparatus for inhibiting slag entrapment in a steel ladle in continuous casting production, particularly to a control method and apparatus for inhibiting slag entrapment at the last phase of ladle teeming in a continuous casting process.
In continuous casting production, firstly molten steel flows into a tundish from a ladle. Subsequently, the molten steel is distributed from the tundish into a plurality of molds where the molten steel is solidified and crystallized, and then drawn into a casting billet. As the molten steel flows from the ladle into the tundish, the liquid level of the molten steel in the ladle lowers gradually as the teeming proceeds. Near the end of the teeming, the steel slag in the ladle will flow together with the molten steel into the tundish through a long nozzle to form roughing slag. Excessive steel slag will not only reduce the cleanliness of the molten steel, affect the quality of the casting billet, even lead to a breaking out accident, but also accelerate corrosion of the refractory material of the tundish, shorten its service life, increase the weight of the slag crust in the tundish, and affect the continuous casting production.
In order to reduce the adverse effects caused by the excessive steel slag flowing out of the ladle, a manual or automatic roughing slag detection means is employed in an existing continuous casting production line to judge the occurrence of steel slag. When it is detected that the steel slag exceeds a value specified for the process, a slide gate nozzle is closed in time to end the teeming. However, at this moment, there is still a large amount of clean molten steel left in the ladle. According to long-term statistics on the amount of ladle slag that is dumped after ladle teeming ends on a continuous casting production line, an average remaining casting residue (molten steel+steel slag) for a 150-ton ladle is 4 tons or more, 2 tons or more of which is clean molten steel. An average casting residue for a 300-ton ladle is 6 tons, 3 tons or more of which is clean molten steel. All of such molten steel is generally treated as steel slag, resulting in enormous waste of resources. The reason why a large amount of molten steel remains in the ladle at the end of the ladle teeming is that the molten steel induces a rotary motion in the ladle at the middle to late phases of the teeming, and finally a vortex is formed above the tap hole, so that the steel slag floating at the surface of the molten steel is dragged down by the suction force of the vortex.
As regards the problem of slag entrapment caused by vortex suction at the middle to late phases of ladle teeming during continuous casting, there are some methods that are used to inhibit the phenomenon of slag entrapment to reduce residual steel in the ladle, such as tilted-ladle teeming method in which the whole ladle is tilted to a certain angle at the late phase of ladle teeming, so that the molten steel is biased to one side, thereby increasing the height of the molten steel and allowing more molten steel to flow out; ladle slag weir technology in which some raised slag weirs are disposed at the bottom of the ladle for slowing the flow speed of the molten steel at the late phase, thereby weakening the slag entrapment phenomenon. However, the effects of these methods are not satisfactory in practical applications. Up to now, there is still no effective means for inhibiting slag entrapment and reducing residual steel in a ladle in a teeming operation of continuous casting production at home and abroad.
An object of the present disclosure is to provide a control method and apparatus for inhibiting slag entrapment at a final phase of ladle teeming in a continuous casting process, which can effectively inhibit the phenomenon of slag entrapment caused by vortex suction in the ladle at middle to late phases of the ladle teeming and realize optimal control over teeming. Therefore, the residual steel is reduced when the ladle teeming is finished, and thus the molten steel yield is increased.
To achieve the above technical object, the disclosure utilizes the following technical solution.
A control method for inhibiting slag entrapment at a final phase of steel ladle teeming in a continuous casting process, comprising the following steps:
(1) Collecting a type code of a steel being molten and teemed and a weight of a ladle itself to obtain a viscosity property of the molten steel and a dead weight of the ladle;
(2) Measuring a total weight of the ladle, subtracting the dead weight of the ladle from said total weight to obtain a net weight of the molten steel, and calculating an actual liquid level of the molten steel in the ladle based on a shape and a size of the ladle;
(3) Judging whether a slag entrapment control process should be performed based on the liquid level of the molten steel; if a condition is met, proceeding to a next step; otherwise, returning to step (2) to continue with the measurement;
(4) Measuring the molten steel for its current vortex surface size and vortex height using a device for measuring a distribution of a molten steel flow field;
(5) Measuring a nozzle opening degree using a device for measuring a slide gate nozzle opening degree of a ladle;
(6) Measuring a current steel slag content using a steel slag detecting device;
(7) Judging whether a roughing slag has been dragged in based on the steel slag content; if a condition indicating the roughing slag is met, proceeding to step (9) to perform a control process for destroying the vortex; otherwise, proceeding to step (8) to perform a control process for inhibiting the vortex;
(8) Performing the control process for inhibiting the vortex, which is an optimization control process in a period of time from start of formation of a dimple vortex at a surface of the molten steel above a tap hole to formation of a through vortex, wherein a controlling parameter is calculated using an optimization model for inhibiting vortex based on the measured vortex surface size, vortex height, nozzle opening degree and steel slag content in combination with the viscosity property of the molten steel, and an electromagnetic brake is actuated to generate a disturbing force opposite to a flow direction of the molten steel to inhibit the newly formed dimple vortex, and delay the formation of the through vortex, so that the occurrence of roughing slag is delayed, and residual molten steel in the ladle is reduced;
(9) Performing the control process for destroying the vortex, which is an optimization control process after formation of the through vortex, wherein an controlling parameter of the slide gate nozzle and an electromagnetic force are calculated using an optimization model for destroying vortex based on the measured data of vortex surface size, vortex height, nozzle opening degree in combination with the viscosity property of the molten steel, and the slide gate nozzle and the electromagnetic brake are controlled jointly to dissipate or shift the formed through vortex and weaken a suction force of the vortex, so that slag entrapment is prevented, the slag is left in the ladle, and the molten steel is allowed to flow out.
A control device for inhibiting slag entrapment at a final phase of steel ladle teeming in a continuous casting process, comprising: a ladle weight detector, a molten steel flow field distribution detector, an electromagnetic brake, a steel slag detector, a slide gate nozzle controller, a slide gate nozzle opening degree detector, a process signal interface unit, and an optimization control model calculation unit;
In the control method and apparatus for inhibiting slag entrapment at a final phase of ladle teeming in a continuous casting process according to the present disclosure, the formation processes of the vortex in the ladle at the middle to late phases of the ladle teeming in the continuous casting process are analyzed. For the two processes of vortex formation, different optimization control strategies are adopted, wherein occurrence of roughing slag is delayed by inhibiting and destroying the formation of vortex respectively, so that outflow of molten steel without slag is achieved, thereby reducing residual steel in the ladle and increasing the yield of the molten steel.
According to the disclosure, at the middle to late phases of the ladle teeming, the phenomenon of slag entrapment by vortex suction in the ladle can be inhibited effectively, and optimal control over the teeming can be realized, thereby reducing residual steel in the ladle after the teeming is finished, and the yield of the molten steel can be thus increased.
In the drawings: 1 ladle, 2 slide gate nozzle, 3 tundish, 4 ladle weight detector, 5 molten steel flow field distribution detector, 6 electromagnetic brake, 7 steel slag detector, 8 slide gate nozzle controller, 9 slide gate nozzle opening degree detector, 10 process signal interface unit, 11 optimization control model calculation unit.
The invention will be further illustrated with reference to the accompanying drawings and the specific embodiments.
Referring to
The ladle weight detector 4 is a weight measuring sensor installed on a ladle 1 turret for real-time measurement of the weight of the ladle being in teeming operation, and outputting the weight value to the optimization control model calculation unit 11.
The molten steel flow field distribution detector 5 is a measuring device which is arranged in the ladle 1 and mainly functions to measure the formation of the molten steel vortex in the ladle at the time, measure the vortex surface size and the vortex height, and transmit the measurement results to the optimization model calculation unit 11 in real time, wherein the molten steel flow field distribution detector 5 is a patented product bearing a patent number of 2014102836130.
The electromagnetic brake 6 is a device for generating an electromagnetic force, wherein it is installed near the tap hole of the ladle for generating a force opposite to the flow direction of the molten steel, and receives output control signal from the optimization control model calculation unit 11.
The steel slag detector 7 is a sensor for measuring a percentage of the steel slag, wherein it is installed above the slide gate nozzle 2 for real-time measurement of a content of the steel slag contained in the molten steel flowing over the slide gate nozzle at the time, and outputs the measurement result to the optimization control model calculation unit 11.
The slide gate nozzle controller 8 is a device that drives the slide gate nozzle into motion for controlling opening and closing actions of the slide gate nozzle, and receives output control signal from the control model calculation unit 11.
The slide gate nozzle opening degree detector 9 is a device for measuring an opening degree of the slide gate nozzle at the time, and the detected result is also transmitted to the optimization control model calculation unit 11 in real time. The meaning of the slide gate nozzle opening degree may be clarified herein. As the molten steel flows from the ladle through the slide gate nozzle to the tundish, the opening degree of the slide gate nozzle refers to a flux of the molten steel flowing therethrough.
The process signal interface unit 10 is a signal conversion device having two functions, one of which is to convert the signal information of the type of the steel currently teemed into a code, the other of which is to receive a signal of a net weight of the ladle in teeming operation at the time, and output the information to the optimization control model calculation unit 11.
The optimization control model calculation unit 11 is a computer device having functions of data acquisition, model calculation optimization and output control, which receives relevant signals and data transmitted from the ladle weight detector 4, the molten steel flow field distribution detector 5, the steel slag detector 7, the slide gate nozzle opening degree detector 9 and the process signal interface unit 10, and conducts calculation and analysis based on the optimization control model to obtain a corresponding optimization control strategy that is output to the electromagnetic brake 6 and slide gate nozzle controller 8 for inhibiting slag entrapment.
Referring to
The first process is formation of a dimple vortex above the tap hole, as shown in
The second process is a process in which a through vortex is formed ultimately as the dimple vortex gets larger and larger gradually. As shown in
The control method for inhibiting the slag entrapment at the final phase of ladle teeming in a continuous casting process according the present disclosure is implemented on the basis of the above control apparatus for inhibiting slag entrapment and the vortex forming process in teeming. The control flow is shown in
In the first step, the optimization model calculation unit 11 reads the type code of the steel being teemed and the dead weight of the ladle through the process signal interface unit 10;
In the second step, the current ladle weight is measured using the ladle weight detector 4 installed on the ladle 1 turret, and the measurement result is transmitted to the optimization model calculation unit 11 which calculates the current net weight of the molten steel in the ladle based on the existing dead weight of the ladle, and calculates the current molten steel level h in the ladle according to the shape and size of the ladle;
In the third step, the optimization model calculation unit 11 determines whether the current molten steel level meets the condition to activate control over slag entrapment, that is, whether the molten steel level h is less than H, wherein H is a constant which is a height value set according to the characteristics of a specific continuous casting production line: when the molten steel level h meets the condition to activate control over slag entrapment, proceed to the fourth step; otherwise, return to the second step;
The fourth step, the current vortex surface size and vortex height of the molten steel in the ladle are measured using the molten steel flow field distribution detector 5, and the measurement results are output to the optimization model calculation unit 11;
The fifth step, the current opening degree of the slide gate nozzle 2 is measured using the slide gate nozzle opening degree detector 9, and the measurement result is output to the optimization model calculating unit 11;
In the sixth step, the current content s of the steel slag flowing through the nozzle outlet is measured using the steel slag detector 7, and the measurement result is output to the optimization model calculation unit 11;
In the seventh step, it is determined whether the roughing slag has occurred based on the content of the steel slag, that is, whether the current content s of the steel slag is larger than S, wherein S is the roughing slag alarm value set according to the requirement of the current continuous casting production: when the content s of the steel slag meets the roughing slag condition, proceed to the ninth step to perform the control process of destroying the vortex; otherwise, proceed to the eighth step to perform the control process of inhibiting the vortex;
In the eighth step, the control process for inhibiting the vortex is performed, which is the control in the period of time from the start of the formation of the dimple vortex to the formation of the through vortex above the tap hole. This process utilizes a control method that inhibits the formation of the vortex, that is, delays the formation of the through vortex. As a result, the occurrence of the rough slag is delayed, and the residual molten steel in the ladle is reduced. The specific control process is as follows: after the data of the vortex surface size, the vortex height, the slide gate nozzle opening degree and the steel slag content are obtained, a controlling parameter is calculated using an optimization model for inhibiting vortex based on the above data in combination with the viscosity property of the molten steel, and the electromagnetic brake 6 is actuated to generate a disturbing force opposite to the flow direction of the molten steel to suppress the newly formed dimple vortex, retard it from becoming larger and stronger, and delay the formation of the through vortex. The equation for calculating the controlling parameter of the disturbing force is as follows:
In the ninth step, the control process for destroying the vortex is performed, which is the control after the formation of the through vortex, that is, after the occurrence of the roughing slag. This process utilizes a control method that destroys the vortex by dissipating or shifting the formed through vortex and weakening the suction force of the vortex, so as to prevent slag entrapment, leave the steel slag in the ladle, and allow the molten steel to flow out. After the occurrence of the roughing slag, the vortex is fully formed and goes through the ladle, and the suction force is large. The electromagnetic brake alone is unable to destroy the vortex. Therefore, it is necessary to simultaneously employ the electromagnetic brake and the opening/closing action of the slide gate nozzle to realize the control in this process. The specific control process is as follows: after the data of the vortex surface size, the vortex height, the slide gate nozzle opening degree, the viscosity property of the molten steel and the like are obtained, the controlling parameters of the slide gate nozzle and the electromagnetic force are calculated using the optimization model for destroying the vortex, and then the slide gate nozzle controller 8 is actuated to generate a rapid oscillating action, and the electromagnetic brake 6 is actuated to generate a force opposite to the flow direction of the molten steel to destroy the formed through vortex. The equation for calculating the controlling parameter of the slide gate nozzle is as follows:
The equation for calculating the controlling parameter of the electromagnetic force is as follows:
F′=N·(pDv+qHv)·hOs·rs·tμ
In the tenth step, it is judged whether the control flow should be ended. If the ending condition is satisfied, the flow is exited, and the control process is terminated. Otherwise, it is judged whether the ladle shall be replaced, as a different ladle means to start new teeming all over again. The new ladle may have a different dead weight, and thus it's necessary to acquire the dead weight value of the new ladle after the replacement. At the same time, the steel type of the new ladle may be different too, and it's necessary to collect information about the new type of steel. In this case, the control flow returns to the first step, and the above steps are repeated. If the ladle is not replaced after inspection, the control flow returns to the fourth step, and the above steps are repeated.
The above description only reveals some preferred embodiments of the disclosure, with no intention to limit the protection scope of the disclosure. Therefore, all changes, equivalents, modifications within the spirit and principles of the disclosure are included in the protection scope of the disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201610942959.6 | Oct 2016 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2017/106043 | 10/13/2017 | WO | 00 |
