US3786856A

US3786856A - Method for controlling a continuous casting installation in the event of molten metal breakout

Info

Publication number: US3786856A
Application number: US00223674A
Authority: US
Inventors: T Nishikawa
Original assignee: Concast AG
Current assignee: SMS Concast AG
Priority date: 1971-02-22
Filing date: 1972-02-04
Publication date: 1974-01-22
Anticipated expiration: 1991-01-22
Also published as: FR2126310B2; DE2208205B2; FR2126310A2; BE779677A; DE2208205C3; ZA721074B; BR7200953D0; DE2208205A1

Abstract

A method for controlling a continuous casting installation in the event of molten metal breakout wherein during the casting operation the light intensity at the secondary cooling zone of the continuously cast strand is monitored, changes in the light intensity with predetermined threshold values are compared and upon exceeding any such predetermined threshold values electrical signals are produced by means of which it is possible to control the continuous casting operation.

Description

Nishikawa Jan. 22, 1974 [5 METHOD FOR CONTROLLING A 3,478,808 11/1969 Adams .1 16 1/4 CONTINUOUS CASTING INSTALLATION IN 3,510,057 5/1970 Werme 164/154 UX Appl. No.: 223,674

Foreign Application Priority Data Feb. 22, 1971 Japan 46-8843 U.S. Cl. 164/4, 164/82 Int. Cl B2211 11/12 Field of Search 164/4, 82, 152-154 References Cited UNITED STATES PATENTS 7/1940 Webster 164/278 X 3/1958 Jones 164/4 OTHER PUBLICATIONS Marks Mechanical Engineers Handbook," 6th Edition, McGraw-Hill, N.Y., 1958, TJ151M37 1958 C9. Pages 16-17.

Primary ExaminerR. Spencer Annear Attorney, Agent, or FirmWerner W. Kleeman 5 7 ABSTRACT A method for controlling a continuous casting installation in the event of molten metal breakout wherein during the casting operation the light intensity at the secondary cooling zone of the continuously cast strand is monitored, changes in the light intensity with predetermined threshold values are compared and upon exceeding any such predetermined threshold values electrical signals are produced by means of which it is possible to control the continuous casting operation.

7 Claims, 3 Drawing Figures METHOD FOR CONTROLLING A CONTINUOUS CASTING INSTALLATION IN THE EVENT or MOLTEN METAL BREAKOUT BACKGROUND OF THE INVENTION The present invention relates to a new and improved method of controlling a continuous casting installation in the event ofmolten metal breakout, wherein the metal flowing out of the partially solidified strand produces a breakout signal by means of which the continuous casting installation can be controlled in accordance with requirements.

Breakout of molten metal can arise during continuous casting with the liquid core or crater protruding past the end of the mold, especially during the continuous casting of steel. When this phenomenon occurs liquid metal flows out of the partially solidified strand through an opening in the thin peripheral skin or wall of the strand. There are many different causes leading to breakout, such as slag inclusions embedded in the peripheral wall of the strand, fissures, improper strand cooling, defects in the mold and so forth. Depending upon the nature of the breakout at the incipient stage thereof, as a general rule, very little metal per unit of time flows out. This stage of breakout is referred to in the art as a starting or incipient breakout. Owing to the metal which flows out, but also because of the effects of the tensional forces which prevail during strand withdrawal, the breakout opening in the wall or skin of the strand which is small at the beginning of metal breakout begins to increase in size so that eventually the outflowing quantity of metal per unit of time increases. Hence, it will be apparent that the incipient or starting breakout with time leads to a breakout having a greater outflow quantity of metal per unit of time.

Breakouts not only'cause longer standstill or downtime of the continuous casting installation or plant but they also impose expensive repair and replacement work and costs. An operator at the mold can only first ascertain a breakout when the level of the molten metal in the mold quickly sinks, so that the above-mentioned starting or incipient breakouts are not readily discernible by the operator because the level of the molten metal bath does not visibly change. By the time that the operator has finally ascertained a breakout, a considerable quantity of metal has alreadly flowed into the secondary cooling zone, resulting in interruption in the casting operation and expensive repair and replacement work. It has been found that such interruptions and repairs can be prevented if incipient breakouts can be ascertained and suitable measures initiated to cure same by freezing or solidifying the breakout opening.

The prior art has already proposed a method for controlling a continuous casting installation upon the occurrence of disturbances of the type which cause lowering of the metal bath level within the mold. According to this state-of-the-art technique components, such as thermal indicators or fusible elements, arranged at the secondary cooling zone, generate signals for controlling the continuous casting installation upon the occurrence of a breakout. With this technique, however,

it is necessary to arrange such components as near as ever, when practicing this technique it should be recognized that owing to the arrangement of the components such tend to interfere with uniform spraying of the strand surfaces with the spray water. Of course it would be possible to arrange these components externally of the spray pattern in order to prevent such disturbances. But in so doing this would render impossible early detennination of the breakout. Furthermore, when employing cooling grids in the secondary cooling zone the use of thermal indicators or fusible elements is very expensive because owing to the grid-like sub-division of the unsupported surfaces by an element only a limited surface can be monitored. Additionally this already known technique does not permit any differentiation of a breakout as a function of its size so that there can be immediately undertaken measures which are accommodated to the magnitude of such breakout.

SUMMARY OF THE INVENTION Hence, from what has been stated above, it should be apparent that the art is still in need of an improved method for controlling a continuous casting installation in the event of a breakout which is not associated with the aforementioned drawbacks and limitations of the state-of-the-art proposals. Therefore, a primary objective of the present invention is to provide a new and improved method of controlling a continuous casting installation in the event of molten metal breakout which effectively and reliably fulfills the existing need in the art and is not associated with the aforementioned drawbacks and limitations of the heretofore advanced proposals.

Still a further significant object of the present invention relates to a new and improved method for controlling a continuous casting installation in the event of a breakout and which overcomes the previously discussed drawbacks of the state-of-the-art techniques and importantly is capable of determining a breakout at the moment such arises and then in accordance with its order of magnitude and to practically eliminate or reduce the damaging effects thereof.

Now, in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the method aspects of this development propose measuring the light intensity in the secondary cooling zone during the casting operation by means of at least one photoelectric transmitter, comparing changes in such light intensity with predetermined threshold values thereof, and obtaining signals by the comparison step which are then used for control purposes.

When practicing this method of the invention it is possible to determine without delay the smallest incipient or commencing breakout at the strand and to immediately initiate those measures necessary to cure such defects. Therefore it is equally possible to prevent shutdown of a travelling cast strand and avoid prolonged downtimes for repair and replacement work at the casting installation. In the event that it is no longer possible to repair the defect at the strand which caused the breakout, even so only the smallest possible quantity of molten metal, typically steel, flows into the secondary cooling zone and thus the'damage caused by such breakout is held to a minimum. Furthermore, it is possible to monitor a relatively large region of the slab pensed with the uninterrupted monitoring of the bath level the automatic termination of an incipient or starting breakout and the initiation of the required corrective measures is of particular advantage.

The light intensity of the metal flowing out of the continuously cast strand during breakout is approximately proportional to the size or magnitude of the breakout opening at the strand skin or wall. In the case of a starting breakout the cooling chamber is only illuminated in a spark-like fashion by a number of metal or steel sprays. In order to be able to bring about freezing of the breakout opening at this stage, it is a further aspect of this invention that upon exceeding a first threshold value the metal feed is shutdown and the withdrawal of the continuously cast strand is briefly interrupted, thereafter the strand is moved further at a reduced withdrawal speed, and when the light intensity drops below the first threshold value the casting operation is resumed with throttled metal feed.

If prior to exceeding a second threshold value freezing or re-solidiflcation of the breakout opening cannot be obtained and the measured light intensity further increases, then, according to a still further feature of this development, upon exceeding the second threshold value, the low withdrawal speed is still further reduced and the quantity of infed cooling water is increased so as to promote the curing or repair of the defect. In continuous casting installations working with cooling plates or cooling grids it is particularly advantageous if by virtue of the slow strand movement the starting or incipient breakout is covered by a surface guide for the purpose of assisting freezing or re-solidification of the breakout.

In the case of breakouts of the type having large breakout openings in the peripheral skin of the strand the third threshold value is exceeded owing to the light emission of the outflowing metal jet as well as the glowing metal in the cooling compartment or chamber. The measures which are then undertaken are directed towards protecting the equipment from damage as well as those concerning safety. Hence, according to a further aspect of this invention, the withdrawal of the strand is interrupted, an alarm signal produced for informing an operator about the condition of the breakout and simultaneously the continuous casting installa' tion is switched over to manual control.

It is immaterial whether the light intensity during a breakout exceeds the first, second and third threshold values in a rapid or slow sequence. In any event, and to the extent that there is no reduction in the light intensity owing to freezing together of the breakout opening, the metal infeed into the mold is interrupted upon the occurrence of the first light beam produced by the starting or incipient breakout, so that even if there is present a breakout which cannot be repaired only the smallest quantity of metal can flow-out.

Upon repair of the breakout the light intensity again reduces so that the casting operation can be resumed. In order to protect the repaired skin or peripheral wall of the strand it is advantageous if, upon attaining the light intensity corresponding to normal operating conditions, the installation is switched back in stages, that is stepwise, to the casting parameters which were present prior to breakout.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood and objects other than those set forth above, will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawing wherein:

FIG. 1 is a vertical sectional view through a schematically illustrated continuous casting installation, depicting enough of the hardware thereof necessary for understanding the inventive method;

FIG. 2 is a block circuit diagram of equipment employed in the continuous casting installation depicted in FIG. 1; and

FIG. 3 is a graph showing the course of the light intensity curves for three different types of molten metal breakouts.

DESCRIPTION OF THE APPARATUS FOR PRACTICING TI-IE INVENTIVE METHOD Turning now to the drawing it is to be understood that there has been illustrated therein an exemplary arrangement of those components of the continuous casting installation necessary for clearly understanding the underlying concepts of the inventive method disclosed herein. Considering therefore FIG. 1 more specifically 4 it is to be understood that an intermediate vessel or container 4 is equipped with a stopper 5 which controls its outflow or discharge opening 5a. In a manner well known in the continuous casting art a partially solidifled continuous cast strand 7 is formed at the openended casting mold 6, this strand 7 being supported at the secondary cooling zone 8 by rollers or rolls 9 and cooled by spray water emanating from nozzles 10. Drive or withdrawal rolls 12 move the strand through the continuous casting installation in the normal way. Photoelectric transmitter means, such as for instance conventional photoelectric cells 14 are arranged at the secondary cooling zone 8 in such a manner that it is possible to measure a small increase in the light intensity caused by a starting or incipient breakout. Depending upon the arrangement and dimensions of the spray compartment or chamber 15 the photoelectric cells 14 could be arranged internally or externally of such spray compartment 15.

Considering now FIG. 2 there will be once again recognized the photoelectric cells 14. Depending upon the prevailing light intensity these photoelectric cells will deliver a corresponding signal or voltage to a conventional amplifier 40 which is provided at its input with a standard gain control or maximum value selector. The amplified signal or voltage is delivered to any suitable threshold value indicators 41 to 44, wherein the threshold value indicator 41 can be adjusted to a first threshold value, the threshold value indicator 42 to a second threshold value, the threshold value indicator 43 to a third threshold value and the threshold value indicator 44 to normal light intensity 22 (FIG. 3). The respective threshold values for the

threshold value indicators

41, 42 and 43 have been graphically depicted by

reference characters

1, 2 and 3 in FIG. 3. Any suitable control 49 may be provided for controlling the process steps associated with the individual threshold values 1 to 3 and the normal light intensity 22 with regard to the regulation mechanism 51 for controlling the intermediate container stopper 5, the roll withdrawal unit 12, the secondary cooling zone water control 53 and the alarm mechanism 54 which may be acoustical or visual. Sincev the hardware for regulating the various components of the continuous casting installation just discussed are conventional and appear at standardcontinuous casting plants it is unnecessary to discuss same further, particularly since the invention is not concerned with any improvements in such structure or the details thereof.

Now for the purpose of elucidating the invention there has been illustrated in FIG. 3 a graph, along the ordinate of which there is plotted the light intensity and along the abscissa 21 of which there is plotted time. As already indicated abovethe first, second and third threshold values have been plotted on this graph, 'and specifically the predetermined light intensity of the first, second and third threshold values have been respectively indicated by the horizontally extending

lines

1, 2 and 3. These light intensities can be determined most simply by simulating breakouts of different orders of magnitude during normal operation of the installation. For instance, in order to determine the location of the first threshold value 1 which, on the one hand, appears during a starting or incipient breakout, and on the other hand, to be able to distinguish such from a small breakout which is already flowing, a few drops of liquid steel are poured into the cooling compartment 15 during casting and thus the light intensity is measured. By repeating this simulation of a starting breakout a number of times it is possible to obtain very good average values of the light intensity for the light emission of a small quantity of liquid metal during the operating conditions prevailing in the cooling compartment 15. In the same way it is possible to determine the second threshold value 2 but with somewhat greater quantity of liquid metal. The third threshold value 3 can be easily determined outside of the cooling zone in that there is measured the light intensity of a quantity of metal which has flowed-out and which approximately corresponds to one-third to one-half of the mold content.

The curve 23 illustrates the course of the light intensity of a starting breakout which has frozen or resolidified. During the time period 24 the light intensity fluctuates in the cooling compartment 15 about a low value which can be designated as the normal light intensity 22. At the point in 25 there begins a small breakout which at time point 26 reaches the first threshold value 1. By means of the signal produced at the threshold value transmitter 41 the delivery or feed of metal into the mold 6 is blocked by the control 51 and the withdrawal of the strand is briefly interrupted, that is to say for about up to approximately twenty seconds, by shutting-down the withdrawal unit 12. By virtue of the thus eliminated tension force at the skin or wall of the strand 7 it is possible to cure a starting or incipient breakout caused by a crack or fissure. After this brief interruption, withdrawal of the strand at a smaller withdrawal speed continues, that is, at about one-half of the normal strand withdrawal speed. Upon falling below the first threshold value 1 at the time point 27 a throttled infeed of metal into the mold is initiated. After reaching the normal light intensity 22 at the time point 28 the casting installation switches back to normal operation in stepwise fashion until reaching the casting parameters which prevailed prior to the breakout.

Continuing, it is to be understood that reference character 30 represents a curve of the light intensity for a small breakout which can be cured or repaired. At the point in time 26 the already described measures are initiated. At the timepoint 31 the light intensity attains the value of the second threshold value 2. Consequently, the already reduced withdrawal speed is still further reduced by about 50 percent. The strand is therefore now moved only with about 25 percent of the normal withdrawal speed. Moreover at the time point 31 the quantity of cooling water is increased to about 1.5 fold. By virtue of these measures there is increased the possibility of curing or repairing small breakouts. Upon repairing the breakout the light intensity thereof reduces and the previously discussed measures for normalizing the casting operation are again automatically initiated.

Finally, the light intensity curve 33 represents a breakout which cannot be repaired or cured. At the point in time 34 the corresponding light intensity curve 33 of such breakout exceeds the third threshold value 3. At the time points 26 and 31 the already abovediscussed measures have been initiated, without however bringing about a freezing together or resolidification of the breakout. At the time point 34 there is therefore now interrupted the withdrawal of the strand, an alarm signal is triggered and the continuous casting installation is switched-over to manual operation.

While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously'embodied and practiced within the scope of the following claims. Accordingly,

I claim:

1. A method of controlling a continuous casting installation in the event of metal breakout, comprising the steps of continuously casting a strand, determining incipient metal breakout by monitoring during the casting operation the light intensity at the secondary cooling zone for the continuously cast strand at the location of such secondary cooling zone where cooling of the strand with water spray occurs, comparing changes in the light intensity with predetermined threshold values, obtaining electrical signals in response to the light intensity exceeding a threshold value owing to incipient metal breakout, and controlling the continuous casting operation to counteract against metal breakout in response to the electrical signals, said step of controlling the continuous casting operation including:

a. at least briefly interrupting the feed of molten metal to the casting mold, and

thereafter continuing the casting operation at a reduced withdrawal speed with throttled feed of the metal to the mold.

2. A method of controlling a continuous casting installation in the event of metal breakout, comprising the steps of continuously casting a strand, monitoring during the casting operation the light intensity at the secondary cooling zone for the continuously cast strand, comparing changes in the light intensity with predetermined threshold values, upon exceeding a threshold value obtaining electrical signals by means of which it is possible to control the continuous casting operation and to counteract against metal breakout, wherein said predetermined threshold values comprise a first threshold value and wherein upon exceeding said first threshold value interrupting the feed of metal to the casting mold, briefly interrupting the withdrawal of the continuously cast strand, thereafter further moving the strand at a reduced withdrawal speed, and when the light intensity falls below said first threshold value continuing the casting operation with throttled feed of metal to the mold.

3. The method as defined in claim 2, wherein said predetermined threshold values include a second threshold value, and upon exceeding said second threshold value further reducing the smaller withdrawal speed and increasing the supply of water into the secondary cooling zone.

4. The method as defined in claim 3, wherein said predetermined threshold values include a third threshold value, and upon exceeding said third threshold value completely interrupting the withdrawal of the continuously cast strand, triggering an alarm signal and switching-over the continuous casting installation to manual operation.

5. The method as defined in claim 2, further including the steps of stepwise switching-back the continuous casting installation to operate at the casting parameters which prevailed prior to the breakout upon attaining a normal light intensity for the continuous casting installation which operation corresponds to the casting operation which prevailed without the presence of molten metal breakout.

6. The method as defined in claim 1, further including the step of using photoelectric transmitter means for determining the light intensity at the secondary cooling zone during the casting operation.

7. A method of monitoring a continuous casting installation for the presence of breakout of molten metal from the continuously cast strand, comprising the steps of determining the light intensity prevailing at a predetermined zone of the continuous casting installation where cooling of the strand with water spray occurs, comparing the momentarily prevailing light intensity with at least one predetermined threshold value, producing an electrical control signal in response to the light intensity exceeding a threshold value owing to incipient metal breakout, and controlling further operation of the continuous casting installation to act against metal breakout in response to said control signal, said step of controlling the continuous casting operation including:

b. thereafter continuing the casting operation at a reduced withdrawal speed with throttled feed of the metal to the mold.

Claims

1. A method of controlling a continuous casting installation in the event of metal breakout, comprising the steps of conTinuously casting a strand, determining incipient metal breakout by monitoring during the casting operation the light intensity at the secondary cooling zone for the continuously cast strand at the location of such secondary cooling zone where cooling of the strand with water spray occurs, comparing changes in the light intensity with predetermined threshold values, obtaining electrical signals in response to the light intensity exceeding a threshold value owing to incipient metal breakout, and controlling the continuous casting operation to counteract against metal breakout in response to the electrical signals, said step of controlling the continuous casting operation including: a. at least briefly interrupting the feed of molten metal to the casting mold, and thereafter continuing the casting operation at a reduced withdrawal speed with throttled feed of the metal to the mold.

7. A method of monitoring a continuous casting installation for the presence of breakout of molten metal from the continuously cast strand, comprising the steps of determining the light intensity prevailing at a predetermined zone of the continuous casting installation where cooling of the strand with water spray occurs, comparing the momentarily prevailing light intensity with at least one predetermined threshold value, producing an electrical control signal in response to the light intensity exceeding a threshold value owing to incipient metal breakout, and controlling further operation of the continuous casting installation to act against metal breakout in response to said control signal, said step of controlling the continuous casting operation including: a. at least briefly interrupting the feed of molten metal to the casting mold, and b. thereafter continuing the casting operation at a reduced withdrawal speed with throttled feed of the metal to the mold.