EP0444297A2 - Method for starting up automatically a continuous casting installation - Google Patents

Abstract

In a method for starting up automatically a continuous casting installation, molten metal (11) is poured out of a vessel (10) in a controlled manner by means of a plug (15) provided in the said vessel and a continuous casting mould (20) closed off at the bottom by a dummy bar head is filled with the molten metal (11). During filling, the plug (15) is opened and closed several times at programme-controlled time intervals and with different opening and closing travels (s1 to sn) assigned to these time intervals. During the first or the first few opening(s) (s2), the plug (15) is preferably moved approximately into the fully open position (P1) and its opening travels (s3,s4,s5) are consequently reduced as the filling level (h) increases. With this very precise automatic start-up method, starting up can be performed with an extremely high degree of reliability and operational safety. <IMAGE>

Description

The invention relates to a method for the automatic casting of a continuous casting system, in which metal melt is poured out of a vessel in a controlled manner by means of a stopper closure provided therein and a continuous casting mold closed at the bottom by a start-up head is filled with the melt, the stopper opening and closing several times according to program-controlled time intervals is moved.

When casting a strand, it must always be ensured that the mold is continuously filled with molten steel over a certain dwell time, so that the said melt can solidify and connect to the start-up head.

If the dwell time is observed based on experience, the start-up head is extended without having to expect that the melt is still liquid and this would cause a breakthrough.

In a method of the type described at the outset (control engineering practice and process computer technology, number 2, 1969, p.68), automatic casting is achieved by actuating the stopper by a control device according to a predetermined time program “open” and “close”. As soon as the level reaches the beginning of the measuring range of a level measuring device located in the upper area of the mold, a limit indicator switches off the open / close control and the melt flow rate is regulated to achieve a constant set level in the mold. In practice it has been shown that automatic casting with a stopper as an actuator is extremely difficult to accomplish because of its control characteristics. The quantity regulation of the outflowing melt cannot be finely adjusted for the stopper, since the stopper only describes a relatively short stroke from the closing to the full opening position.

The object of the present invention is therefore to improve the automatic casting with a stopper closure in such a way that great reliability and thus reliable casting can be achieved under the given conditions.

The object is achieved according to the invention in that the stopper which is moved open / closed several times during casting is actuated with different opening and closing paths assigned to the program-controlled time intervals.

With this very precise procedure, a stopper closure can automatically be cast on without any problems, even under the most varied of conditions and arrangements of continuous casting plants.

In a preferred method variant, the stopper is brought approximately into the full opening position in the first or in the few first opening (s), and consequently its opening paths are reduced with increasing fill level.

As soon as the rising fill level approaches the target fill level, the stopper is advantageously controlled with opening paths that correspond to the average opening position during a regulated pouring that follows the target fill level. This results in a continuous transition from controlled to regulated pouring.

The opening / closing movements of the stopper are to be understood in the sense that these movements open or close the closure fully or throttled, or bring them back into the throttled position.

The effective closing position of the stopper is different on the one hand before each pouring start because of the insertion of the pouring sleeve (or pouring tube) into the fire-resistant vessel lining, and on the other hand, experience has shown after the first opening of the stopper when pouring on that when the stopper is closed again, its position changes by a certain amount. In the present invention, the effective measured closing position is adopted adaptively for each opening, which in turn brings about a more precise definition of the casting process.

The invention can also be applied equally well to stopper-like closures.

Fig.1

eine schematische Darstellung der Stranggiessanlage mit einem Blockschema seiner Steuerung,

Fig.2

einen erfindungsgemässen Angiessvorgang in Form eines Weg/Zeit-Diagrammes,

Fig.3

eine Sollangiesskurve mit dem Füllstandverlauf in Funktion der Zeit und

Fig.4

eine weitere Variante eines Angiessvorganges in einem Weg/Zeit-Diagramm.

Further advantages and exemplary embodiments are explained in more detail with reference to the drawing. It shows:

Fig. 1

a schematic representation of the continuous casting plant with a block diagram of its control,

Fig. 2

a casting process according to the invention in the form of a path / time diagram,

Fig. 3

a target angle curve with the level curve as a function of time and

Fig. 4

another variant of a casting process in a path / time diagram.

In a continuous casting installation according to FIG. 1, molten metal 11 flows from a vessel 10 through a refractory pouring tube 12 arranged at its pouring opening into a mold 20. The vessel 10 is usually an intermediate container which consists of a refractory lining and a steel jacket. The amount of melt can be poured on in a controlled manner by a stopper closure 15 in the vessel 10 and subsequently poured off in a regulated manner. The refractory stopper 15 is fastened to a support arm 16 and can be adjusted by means of an articulated lever 18 on a linkage 13, especially in an emergency, by hand or by a drive element 17 in the vertical direction. A transmitter 21, which normally works on a radioactive basis, in the upper region of the mold 20 measures the fill level h of the melt and delivers a corresponding signal to a fill level measuring device 31, which in turn forwards a processed signal to a computer 30. The strand 23 formed by the solidified melt is pulled out by a take-off drive 24 at a take-off speed v. In one command, the computer 30 can start the trigger drive 24 via a switch 32.

In the present exemplary embodiment, a weight measuring device 33 is also shown, with which the bath level in the vessel 10 can be determined indirectly. A commercially available pressure cell 33 'serves as a signal transmitter for the device 33.

The automatic casting according to the invention is started after the melt 11 has been poured into the vessel 10, either by manually operating a switch or automatically via the signal supplied by the weight measuring device 33 to the computer 30 as soon as it corresponds to the desired level.

According to FIGS. 2 and 3, the program-controlled casting process begins by briefly fully opening the stopper 15 into a position P2, and thus the first melt flowing into the mold 20. Before a time interval t 2 has elapsed, there is a first closing movement into a closing position P2 ', in which it has been shown in practice that this sets itself apart from the closing position P1 by a certain amount. This stroke position P2 'is determined by the computer 30 and the stopper 15 is stored in the following opening paths by one stroke s each, which is adaptively based on this effective closed position P2'. The program-controlled casting process then continues with time intervals t₂ ', t₃, t₃', t₄, t₄ ', t₅ and t₅' and the associated opening paths s₃ to s₅ with the positions P3 to P5. The paths s₃, s₄ and s₅ of the controlled open / close movements are reduced until they approach the average opening path s₇ during the subsequent regulated pouring, the path s₇ being stored in the computer 30 as an experience or calculated value. A larger position P6 is then again provided for the opening path s₆ with the corresponding time interval t₆, after which the stopper is opened by the path s₇ during the time interval t₇. As soon as the fill level h of the melt in the mold 20 now reaches the measuring range of the sensor 21, the program-controlled casting process is ended by the computer 30; the latter transfers to an automatic fill level control, in which a target fill level is adjusted, for example, to 80% of the measuring range by means of a PID controller integrated in the computer 30. Since the measuring range usually only covers the upper part of the mold 20, this takes place Transition from automatic pouring to regulated pouring as soon as the fill level of the melt reaches the measuring range 21. In the event of deviations from the desired fill level h _s , the controller controls the stopper 15 accordingly via the control 36 and the drive 17, after which more or less amount of melt is poured into the mold 20. The drive 17 is, for example, a piston / cylinder unit. A position transmitter 19 and a measured value unit 37 deliver the actual value of the drive position to the computer 30 in a feedback signal. A subordinate position controller in the computer 30 ensures the desired position of the drive 17 and thus of the plug 15.

The opening and closing paths s₂ to sn as well as the opening and closing times t₂ to tn are entered into the software 30 as parameters in the computer. These parameters are specifically designed for the respective continuous caster.

In the casting process according to FIG. 2, such a number of open / close movements are also programmed in the computer 30 that if after the sixth movement the actual fill level would not yet be within the measuring range, further program-controlled open / close movements would take place until the fill level reaches the measuring range and the controller can thus adjust it to the target level.

In Figure 3, the start of the starting head 26 is indicated with a speed curve v₁. In the exemplary embodiment, the starting time takes place approximately when the desired fill level h _{s is reached} . Further, the mold 20 filled in the casting-in accordance with the actual course shown h _is on.

As an alternative to the described end of the automatic pouring process, the stopper can be opened into position P7 - provided the filling level has been reached in the measuring range - according to the dashed line according to Fig. 2, again brought under program control into the closed position. After a time interval t₇ ', the starting head 26 is pulled out according to a withdrawal speed curve v₂. As soon as the fill level h _x now drops below 20% of the measuring range, the stopper is opened in several partial steps around the opening path s₇ and then the fill level controller in the computer 30 takes over the fill level to the desired level h _s . With this deliberate delay in pulling the starting head 26 out, the solidification of the melt in the mold can be ensured as an additional measure.

FIG. 4 again shows a casting process according to the invention in a path / time diagram. At the start of the sprue, the stopper 15 is moved to the full open position P2 and then moved to the closed path s₂ 'in a throttled position P2'. Even after the openings in the positions P3 and P4 with reduced opening paths, the stopper is brought into throttled and not completely closed positions S₃ 'or S₄'. Corresponding time intervals t₂, t₂ ', t₃, t₃', t₄, t₄ 'are assigned to these open / close movements. Only after opening in the position P5 is the stopper brought into the closed position P5 ', this during a time interval t₅'. When reopening, the controller in the computer 30 takes over the casting process and brings the fill level of the melt in the mold to the desired level hs. The process for automatic casting according to FIG. 4 makes it clear that the procedure according to the invention can very well take account of the plant-specific requirements and that a wide variety of filling processes can be achieved.

The invention is of course not limited to the casting process shown in the exemplary embodiments, but, as already mentioned, can be variably adapted for continuous casting plants with different requirements or for casting different types of steel by changing the parameters.

The invention is also not limited to a conventional stopper closure, but rather can be applied for known stopper-like systems, as is known, for example, in the published patent application (WO 88/04209). In this flow control device, the stopper has a cylindrical pin at its lower end, which projects into the pouring opening of the vessel and seals laterally together with the pouring sleeve. The pin has at least one radial inlet opening on its circumference and one longitudinal opening extending from this. As an additional seal, the stopper has a truncated cone-shaped shut-off surface above the pin, which forms an additional seal together with the end face of the pouring sleeve when the closure is closed. The closure is opened and closed again by adjusting the height of the stopper.

Claims (7)

Process for the automatic casting of a continuous caster, in which molten metal is poured from a vessel in a controlled manner using a stopper closure provided therein and a continuous casting mold closed at the bottom by a start-up head is filled with the melt, the stopper being opened and closed several times during filling according to program-controlled time intervals , characterized in that the stopper (15) which is moved up and down during casting is actuated with different opening and closing paths (s₂ to s _n ) assigned to the program-controlled time intervals (t₁ to t _n ). A method according to claim 1, characterized in that the stopper (15) in the first or the few first opening / s (s₂) is brought approximately into the full opening position (P2), and that its opening paths (s₃, s₄, s₅) consequently , can be reduced with increasing fill level (h) of the melt in the mold (20). A method according to claim 2, characterized in that the stopper (15) immediately before reaching the target level (h _s ) with one or more opening path ( _s ) corresponding to a stored average opening position (P7) during a pouring controlled at the set level (h _s ). Method according to one of the preceding claims, characterized in that the stopper (15) in the open movements in full or in throttled opening positions (P2 to Pn) while in the closing movements in the closed or throttled position (s) (P2 'to Pn') is controlled. Method according to one of the preceding claims, characterized in that the respective closing position (P1, P2 ') of the stopper (15) is measured and the subsequent opening paths (s₂, s₃) each adaptively start from the measured, effective closing position of the stopper. Method according to one of the preceding claims, characterized in that when the fill level (h) of the melt in the measuring range of the plug (15) is reached, the stopper (15) is closed again, that the starting head (26) after a time interval (t₇ ') starting from this closing of the plug ) is pulled out and that after the fill level has dropped to a stored fill level (h _x ) the stopper is opened again. Method according to one of the preceding claims, characterized in that, instead of a conventional stopper, one is used which has a laterally sealing cylindrical spigot projecting into the pouring opening of the vessel and having at least one radial opening on its circumference and one longitudinal opening extending therefrom.

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