Claims
- 1. A process for the automatic start-up of a continuous casting plant in which molten metal is charged from a tundish via a controllable spout closure into a continuous casting mold and in which the instantaneous bath level rising therein is controlled in accordance with a predetermined start-of-casting curve so as to reach a desired bath level which is to be maintained during casting using measuring and control means, the process comprising the steps of: starting a drive means for pulling the cast bar at a predetermined instantaneous bath level; throttling the spout closure, which is initially fully open during the start of casting of the molten metal into the tundish, to a predetermined throttle position when instantaneous bath level in the mold has risen to a first signal level of a predetermined time curve; and thereafter, monitoring the further rise of the instantaneous bath level and correcting the throttle position of the closure of the spout in accordance with a second signal level of the predetermined time curve.
- 2. A process a recited in claim 1, wherein the control of the instantaneous bath level at the first and second signal levels along the predetermined time curve is changed over into a control of the desired bath level occurring within a predetermined measuring section, and wherein the changeover is carried out by further throttling of the spout closure at one predetermined signal level of the measuring section.
- 3. A process as recited in claim 2, wherein the starting of the bar removal by the drive means is set to occur at the same time as the further throttling of the spout closure.
- 4. A process as recited in claim 2, wherein the starting of the bar removal by the drive means is set to occur in a terminal range of the predetermined time curve in accordance with the speed of the bar withdrawal.
- 5. A process as recited in claim 2, wherein the throttling of the spout closure to said predetermined position occurs at a point which is 25 to 65 percent of the total level of the mold and the amount of throttling of the closure is from 5 to 30 percent of the maximum opening for billet and small bloom molds and from 15 to 50 percent of the maximum opening for large bloom and slab molds.
- 6. A process as recited in claim 3, wherein the throttling of the spout closure to said predetermined position occurs at a point which is 25 to 65 percent of the total level of the mold and the amount of throttling of the closure is from 5 to 30 percent of the maximum opening for billet and small bloom molds and from 15 to 50 percent of the maximum opening for large bloom and slab molds.
- 7. A process as recited in claim 4, wherein the throttling of the spout closure to said predetermined position occurs at a point which is 25 to 65 percent of the total level of the mold and the amount of throttling of the closure is from 5 to 30 percent of the maximum opening for billet and small bloom molds and from 15 to 50 percent of the maximum opening for large bloom and slab molds.
- 8. A process as recited in claim 1, wherein the throttling position of the spout closure occurs at a point which is 25 to 65 percent of the total level of the mold and the amount of throttling of the closure is from 5 to 30 percent of the maximum opening for billet and small bloom molds and from 15 to 50 percent of the maximum opening for large bloom and slab molds.
- 9. An apparatus for the automatic start-up of a continuous casting plant in which molten metal is charged from a tundish via a controllable spout closure into a continuous casting mode and in which the instantaneous bath level rising therein is controlled in accordance with a predetermined start-of-casting curve so as to reach a desired bath level which is to be maintained during casting using measuring and control means, the apparatus comprising:
- a means for starting a drive means for pulling a cast bar form the continuus casting mold at a predetermined instantaneous bath level;
- a means for throttling the spout closure, which is initially fully open during the start of casting of the molten metal into the tundish, to a predetermined throttle position when the instantaneous bath level in the mold has risen to a first signal level of a prdetermined time curve;
- a means for monitoring the further rise of the instantaneous bath level and correcting the throttle position of the closure of the spout in accordance with a second signal level of said predetermined time curve;
- wherein temperature sensors are provided for monitoring the bath level.
Priority Claims (1)
| Number |
Date |
Country |
Kind |
| 3509932 |
Mar 1985 |
DEX |
|
CROSS REFERENCE TO RELATED APPLICATIONS
The present application is related to copending U.S. patent application Ser. No. 772,747, filed on Sept. 4, 1985 and bearing common inventorship with the present application, and is also related to copending U.S. patent application Ser. No. 746,847, filed on June 20, 1985 and invented by a co-inventor of the present application.
The present invention relates to a process and apparatus for starting a continuous casting plant. More particularly, the present invention relates to a process and apparatus for starting a plant for casting molten steel into a permanent mold by means of a controllable spout closure mounted on a tundish, and in which, due to a constant pulling speed of the extrusion which is maintained by a measuring and controlling means, the bath level is kept at a predetermined level within a measuring section. The present invention further relates to a process and apparatus for the automatic start-up of a continuous casting plant in which molten steel is filled from a tundish over a controllable spout closure into a continuous casting mold and the instantaneous bath level rising therein is controlled along a given start-of-casting curve into a desired bath level maintained during casting by means of measuring and control devices, the drive for the withdrawal of the cast bar being triggered at a predetermined instantaneous bath level.
West German OS Patent Application No. 29 289 01 discloses a prior art process for the start of a casting plant for the continuous casting of metals, according to which the bath level in the mold, serving as a source of radiation, is monitored by an optical radiation receiver directed perpendicularly thereto; the receiver controls an actuator for the stopper rod of a tundish. In this system, it is essential that the charging of the metal into the mold and the start of the lowering of the dummy bar head or the dummy bar occur in accordance with the distance between the radiation source and the radiation receiver. However, steps for carrying out the process have not been specified and, moreover, optical measuring instruments have not proven reliable in the actual performance of the casting operation.
Basically, there are controlling means for the automatic operation of continuous casting plants using a variety of measuring instruments mostly of the radiometric or electromagnetic variety. The instruments monitor the bath level in the mold and the controlling means control the pulling of the cast strand, during which the molten steel flows to the mold through a nozzle having a constant aperture and the pulling speed of the strand is controlled. Furthermore, when the flow control is used as the preferred technology, the pulling speed of the strand remains constant and the flow of the molten steel to the mold is controlled, preferably by use of a sliding gate valve which meets control-engineering requirements more easily than, for example, a stopper rod. In the case of the control of both the pulling of the strand and of the molten steel flow, it is necessary to automatically observe a selected desired level in the mold within a measuring section monitored by a measuring instrument.
West German Patent No. 32 21 708 relates to a method and the apparatus used therefor. In this case, the empty mold is filled with molten metal in two phases over the dummy bar, namely, in an intermittent filling phase A-B and in a continuous filling phase B-D. In the A-B phase, the filling occurs in gulps by constantly opening and closing the spout closure in the tundish, while in the B-D phase, the filling occurs continuously. Both filling operations A-B and B-D are controlled along a preprogrammed start-of-casting curve (time curve) in which comparisons between desired bath levels that have been input and the particular instantaneous bath levels measured by an optical level indicator occur with proper corrections at the spout closure. The repeated full closing of the filling phase A-B, which starts with an opening procedure, is provided to quiet the steel level between the casting gulps in order to determine the particular instantaneous bath level in the mold. This is a relatively complex process that not only puts a strain on the spout closure of the tundish, particularly on its refractory wear parts, but also takes a considerable amount of time. In addition, particularly if a slide gate is employed as spout closure during the intermittent opening, which occurs with constant opening values but without completely opening the spout closure, there is greater danger of clogging of the passageway during the start of casting, despite the fact that the tundish and the spout closure are preheated. In this connection, it is pointed out that, as molten metal is charged into the tundish, the ladle lip remains closed. Moreover, optical measuring devices have not stood the test in foundry work.
In contrast, the present invention is concerned with the starting of a continuous casting plant equipped with a flow control even before the control of the desired level control has been initiated, that is to say, during the interval between the start of casting--which is equivalent to the feeding of the molten metal into the preheated tundish which charges the mold including the closure spout--and the obtaining of the desired bath level. It is an object of the invention to establish an optimum start-up process in a recurrent manner for this interval with predetermined process steps, including the turn-on of the extrusion puller. The start-up process reliably causes the proper solidification of the bar at the dummy bar head and the warming up of the sliding gate valve.
In this regard, it should also be pointed out that heretobefore, during the charging of the tundish with molten metal, the spout closure was kept shut so as to prevent molten metal from freezing in the discharge port.
The problem set forth above is solved by the present invention in which the spout closure is fully opened during the start of casting into the tundish. The actual level of the molten metal rises in the mold until, in response to the level reaching a first signal level, the spout closure is reduced to a preset throttling position in order to control the further rise of the actual level up to a predetermined level. The extrusion puller is turned on in response to the actual level reaching a second signal level. In this way, it is possible for the actual level to rise smoothly and purposefully to the desired level while providing sufficient time for the extrusion to solidify and to enable the spout closure to adapt itself sufficiently to the operating temperature as a result of the adequately flowing molten metal. Thus, damage to the extrusion due to abrasion and further cloggings in the opening of the spout closure caused by the freezing of the melt are prevented and the conditions for an optimum starting operation are satisfied.
In general, the throttling position of the sliding gate valve and of the further rise of the actual level initiated thereby, as well as the instant for starting the extrusion puller, are essentially functions of the solidification process in the mold for the extruded product and of the warming-up process in the sliding gate valve depending upon the cross section of the strand and the physical properties of the melt. Accordingly, special time constraints are developed for the process steps, whereby one considers as limiting criteria the keeping of the spout closure fully open for as long a time as possible and the avoidance of an overfill of the mold.
Another aspect of the invention is seen in the fact that, once the extrusion puller has been started, a controllable pulling speed is used to contribute to the determination of the time characteristic curve which thereby permits more extensive control options.
With respect to the throttling position of the spout closure, it has been found that this should occur at 25 to 65 percent of the total level of the mold, and the full opening of the closure should occur from 5 to 30 percent of the maximum opening for billet and small bloom molds and from 15 to 50 percent of the maximum opening for large bloom and billet molds. All current extrusion formats can be taken into account with these regions.
To carry out the process in accordance with the present invention, an arrangement has proved successful which is provided with thermocouples for detecting the signal levels and which operate in the ingot wall as discrete point measuring stations and which are located below the measuring instrument used to monitor the desired level. Such an arrangement can be arranged even in the extremely confined space conditions found in the mold environment. If, on the other hand, there is adequate space, then an arrangement is preferred with a standard measuring instrument that extends over the entire mold height.
It is the object of the present invention to simplify the start of casting and the apparatus used therefor, while improving the reliability of operation.
According to the present invention, this object is achieved in that during the start of casting of the molten metal into the tundish, the spount closure, which is fully open during the start of casting of the molten metal into the tundish, is brought from the instantaneous bath level that rises in the mold at a first signal level to a predetermined throttle position, and thereafter the further rise of the instantaneous bath level is monitored and, if necessary, corrected at a second signal level of a predetermined time curve by varying said throttle position. In this way, during the charging of the tundish, molten metal flows immediately through the spout closure into the mold from the tundish and there is no danger that the rising bath level will distort the data being measured. This bath level changes gently and purposefully to the desired bath level with only one check and is corrected with a single, simple signal level. On one hand, the new bar has enough time to solidify, while on the other hand, the spout closure is adjusted to the operating temperature by the molten metal flowing therethrough in sufficient quantity. In this manner, damage to the bar by breaking, as well as clogging in the passage opening of the spout closure caused by a freezing of the molten metal are largely prevented, so that the prerequisites for an optimum start-up are satisfied.
Basically, the throttle position of the slide gate and the further rise of the instantanous bath level triggered thereby, as well as the instant for the triggering the bar withdrawal, are functions of the bar-solidifying process in the mold and of the warming-up process in the slide gate in dependence upon cross section of the bar and the physical properties of the molten metal. Accordingly, specific time sequences or time curves for the process steps are laid down for each bar size, such that maintainig the spout closure fully open as long as possible and preventing an overfill of the mold are looked upon as the limiting criteria.
In a preferred method of the so-called open start-of-casting in accordance with the present invention, it is of advantage to proceed in such a way that the control of the instantaneous bath level by use of signal levels along the time curve changes over to a control of the desired bath level occurring within a test section and the changeover is effected by further throttling of the spout closure into the operating postition at one signal level of the test section. This combination of controls along a time curve having only one monitoring signal level with subsequent test-section control, which is triggered into the operating position within the desired-level range by further throttling of the spout closure contributes to a considerable extent to a reliable run of the start-of-casting process. In the operating position, the spout closure assumes a position in which equal allowance can be made for opening and closing commands for maintaining the desired bath level.
Other features of the present invention are seen in the fact that, particularly if bars are cast that have fairly large cross-sections, the start of the bar withdrawal occurs at the same time as the throttling of the spout closure into the operating position, while in the case of bars with rather small cross-sections, the start of the bar withdrawal occurs advantageously in the terminal range of the time curve, in the further run of which the influence of the speed on the bar withdrawal is taken into consideration. It is likewise of advantage to trigger the throttle position of the spout closure located at the start of the time curve within a range of from 25 to 65% of the entire filling height available in the mold and thereby to trigger the throttling in the case of billet molds or small cogged-ingot molds at 5 to 30% of the full approach angle, and in the case of slab molds or large cogged-ingot molds at 15 to 50%. All current bar sizes can be handled with these ranges.
To carry out the process in accordance with the present invention, it has proven advantageous to use a measuring apparatus that has thermoelements for the signal levels that act as point measuring stations underneath the measuring device in the mold wall which serves to monitor the desired bath level. Such apparatus fits nicely into the tightest places, such as are usually found in the vicinity of an ingot mold.
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| Number |
Name |
Date |
Kind |
| 4567935 |
Takeda et al. |
Feb 1986 |
|
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Patent Grant
4770230
