EP0351495A1 - Method of pouring metal, in particular steel, from a casting ladle - Google Patents

Abstract

Method of pouring a metal, in particular steel, from a casting ladle (24) into a tundish (1) or the like by means of a choking slide gate nozzle or stopper end, by which the ferrostatic height of the metal in the tundish (1) is regulated to match a set withdrawal speed of the cast strand. The regulation takes place here with a so-called tendency recognition, i.e. taking into consideration the change of the amount of metal in the tundish (1). Furthermore, with each reversal of correcting variable or motion at the casting ladle closure an error value (alpha) resulting from the system tolerances is added to the correcting variable (Y). The method is also applicable in the case of nozzle closures of tundishes (1), and to be precise in relation to the bath level in the mould (28).

Description

The present invention relates to a method for casting a metallic melt, in particular steel melt, from a ladle into an intermediate vessel by means of a throttling slide or stopper closure, by means of which the ferrostatic height of the melt is regulated in adaptation to a set withdrawal speed of the cast strand.

When casting, for example, a molten steel from a ladle into an intermediate vessel, in particular a distributor gutter, it is known to use a slide or stopper closure as a control element for the amount of melt flowing out per unit of time. The closure normally works in a variable throttling position, i.e. in a position throttled over half of the possible full flow cross-section, in order to be able to follow the opening and closing instructions or signals which, with automatic control of the flow rate from the ladle, taking into account one take-off speed of the strand which is as constant as possible is based on an electronic data evaluation device. A constant strand withdrawal speed is primarily ensured by maintaining a substantially constant ferrostatic height in the tundish. In practice, it has now been found that it is extremely difficult to keep the ferrostatic height in the tundish constant, primarily because of the relatively large mechanical tolerances of the ladle closure mechanism and the relatively slow control path of conventional control devices, all without one so-called trend detection work. When using so-called bell crank locking systems, mechanical tolerances of up to 30 mm, i.e. a dead stroke of up to 30 mm when the movement is reversed, are quite common. It is obvious that such mechanical tolerances lead to absurdity even the most accurate actual value acquisition and evaluation. Mechanical tolerances of up to 10 mm are also common for direct control of slide closures.

Maintaining a constant ferrostatic height in so-called "freewheels" is particularly problematic. H. Intermediate vessels without adjustable spout closure.

Due to the problems outlined, weight tolerances of ± 300 kg melt in the intermediate vessel and thus corresponding tolerances of the ferrostati can be achieved despite the precise actual value acquisition and corresponding activation of the ladle closures height.

Furthermore, in the known ladle slide closures, expensive displacement sensors are absolutely necessary in order to adjust to the respectively determined actual values, i. H. Level reaction in the intermediate vessel to be able to react exactly. Sensitive servo and / or proportional valves are also required. Finally, the work involved in the preparation of the hydraulic control fluid is considerable, so that the known systems, despite the relatively high tolerances, are distinguished by a considerable design and control effort.

Finally, in the known systems it is also extremely difficult, if not impossible, to react to leaks in the hydraulic system or to compensate for them.

It is also important to avoid freezing the pouring spout due to excessive and excessive throttling of the ladle closure. This is a danger with conventional systems, since they work on an optimal throttle position without touching them.

The present invention has for its object to provide a method of the type mentioned, with which the disadvantages of the conventional systems are avoided, i. H. with which the ferrostatic height in the tundish can be kept largely constant with little effort, with the result of a correspondingly constant strand withdrawal speed. Mechanical, hydraulic and / or pneumatic tolerances in the system should have no influence on keeping the ferrostatic height constant.

This object is achieved by the characterizing measures of claim 1, preferred details of the invention in the subclaims, in particular are described in claims 2 and 4. Also of particular importance are the measures according to claim 7, which can also be used independently of the proposed tendency detection in order to compensate for the system-inherent tolerances.

By the inventive method according to claim 1, at least excessive throttling of the pouring spout of the ladle and thus the risk of freezing of the pouring opening as a result thereof can be avoided, since the pouring closure literally approaches the optimal throttle position.

In combination with the measures of claim 3, the system also approaches the optimal opening position of the ladle closure. In both cases, the tendency of the level change or change in the ferrostatic level in the tundish is determined and taken into account when determining the control signal for the ladle closure. The essence of the method according to the invention thus lies in the trend detection described, which can be weight-related, ie based on the weight of the melt in the intermediate vessel, or level-related, ie based on the bath level in the intermediate vessel. Laboratory tests have shown that the weight tolerance can be reduced to ± 50 kg with the method according to the invention; the tolerance of the ferrostatic height in the tundish is reduced accordingly. In this way, the take-off speed of the strand can be kept very constant, regardless of the sometimes considerable mechanical tolerances in the ladle closure system and without complex displacement sensors and servo and / or proportional valves and without complex preparation of the hydraulic control fluid when using hydraulically controlled Pouring closures. The inertia of the control system plays no disadvantage due to the tendency detection according to the invention Roll more. In accordance with the measures according to claim 7, the system-inherent tolerances for signal or manipulated variable reversal are added up and thus compensated. Preferably, according to claim 5, a signal clock counter is also provided, by means of which it is determined how often the same actuating signal, namely either an open or closed signal, is triggered in succession, the actuating variable after a predetermined number of open or closed signals Is disproportionately reinforced with appropriate compensation of an excessive mechanical play in the slide or stopper closure and its drive. This problem occurs in particular when there are leaks or leaks in the hydraulic system. In this way, these can be determined and compensated for.

According to claim 5, amplification factors of different sizes are selected for the opposite control signals, whereby the different control volumes on the piston rod side on the one hand and piston rod-free side on the other hand of a hydraulic actuating cylinder for the pouring closure are to be taken into account.

The method according to the invention is to be described in more detail below with the aid of a correspondingly designed control device which is shown schematically in the accompanying drawing.

In this drawing, the part of a continuous casting installation of interest here with a ladle 24, an intermediate vessel 1 designed as a distribution channel and support rollers 25 for four strands 4 is shown schematically. The intermediate vessel 1 has four bottom openings 26 on which either a slide closure 3 or a plug closure 6 are assigned. Alternatively, the arrangement can be designed as a so-called "freewheeler". In this case, the bottom openings 26 of the intermediate vessel 1 are none Slider or stopper closures assigned. The ferrostatic height within the intermediate vessel 1 is primarily determined by the degree of opening of the bottom opening of the ladle 24, to which a slide closure 27 is assigned in the embodiment shown. The molten steel is introduced from the ladle into the tundish 1 in the usual way via an immersion tube 5. The parts described are conventional devices of a continuous casting plant. Below the overview of a continuous casting installation described, a so-called bell crank cylinder arrangement for the actuation of a slide closure 27 assigned to the bottom opening 39 of the ladle 24 is shown in an enlarged scale in the attached drawing, as "Alternative II". This is a construction known per se, so that a detailed description of the same is unnecessary. This construction is characterized by very large mechanical tolerances, in particular in the force deflection area, which is shown separately in the drawing by a dash-dotted circle 40. A dead stroke of up to 30 mm is not uncommon. The sum of the tolerances present within the Bell crank cylinder arrangement is shown in the attached drawing by the error size "alpha", which is taken into account in the regulation of the ferrostatic height in the intermediate vessel 1, which is still to be described.

Instead of a bell-crank cylinder arrangement, the slide closure 27 can also be directly coupled to a piston-cylinder arrangement, as shown in the attached drawing in connection with the slide closure 27 assigned to the ladle 24 as "Alternative I". Mechanical tolerances of up to 5 - 10 mm also occur in this construction. Plug closures are also characterized by large mechanical tolerances, which are also of the order of up to 30 mm. This is the reason why working in the intermediate vessel with weight tolerances of up to ± 300 kg; accordingly, the tolerances of the ferrostatic height are, and accordingly, it is difficult to maintain a constant peeling speed. This is especially true when the continuous casting system is operated as a so-called "free runner". Currently, attempts are being made to get the tolerances mentioned under control by reducing the control distances for the ladle closure; however, this has the consequence that the ladle closure is constantly in motion, which causes a not inconsiderable disturbance to the steel to be cast.

To avoid the aforementioned disadvantages of conventional methods and devices for pouring a metallic melt into an intermediate vessel and from there into a mold 28 or the like arranged below it, the intermediate vessel 1 in the present case has four weighing cells 2, namely two weighing cells 2 on each end face , assigned, the signals of which are coupled to one another in a load cell measuring circuit 7 and processed into a weight signal corresponding to the weight of the melt in the intermediate vessel 1. This is amplified in a measuring amplifier 8, the output signal of which corresponds to the so-called actual weight value "X". The actual weight value is compared in a comparator 9 with a predetermined weight target value "w", in each case at predetermined successive times. The corresponding cycle time "Tz" is specified by a time adjuster or clock generator 10. It is z. B. 5 s, ie every 5 s a comparison between the actual weight value and the desired weight value is carried out and the control deviation (Xw) <0 is determined. The value determined is entered in a so-called tendency detection 11. If the control deviation is <0 and the difference Tn between the previously measured actual weight X _old and the subsequently determined actual weight X _new > 0, the tendency detection 11 becomes a setting Signal OPEN for the ladle closure 27 issued. If the mentioned difference TN ≦ 0, it is first determined whether the actual weight difference TN> Z₁, ie greater than a predetermined lower weight trend limit value of a predetermined trend limit value bandwidth, which means that the weight increase in the intermediate vessel 1 during a Time cycle too fast. If so, a control signal CLOSED is output by the tendency detection. If Tn ≦ Z₁, it is checked whether TN <Z₂. If so, this means that the weight increase in the intermediate vessel 1 takes place too slowly during a time cycle. In this case, the tendency detection emits the control signal OPEN. If TN ≧ Z₂, no control signal is given. Rather, a new determination of the control deviation is triggered (signal 41). The mentioned values Z₂ is an upper weight trend limit of the mentioned bandwidth. Z₁ and Z₂ are entered as constant limit values beforehand, expediently in adaptation to the respective continuous casting installation.

If the control deviation ≧ 0, it is first determined whether the actual weight value difference Tn <0. If so, a control signal CLOSED is output by the tendency detection 11. If no, it is first checked whether TN> Z₁. If this is the case, a control signal OPEN is triggered, if no, it is checked whether TN <Z₂. In the event that TN <Z₂, the tendency detection gives the control signal CLOSED; if no, a new determination of the control deviation is triggered (signal 41). The control signals OPEN or CLOSE are proportionally amplified in a controller 12 (gain factor P). The corresponding manipulated variable Y _OPEN or Y _CLOSE is obtained by multiplying the difference between the actual weight value X and the desired weight value w by the gain factor "P", different amplification factors can be selected for the opposite control signals OPEN and CLOSE, e.g. B. for the reasons mentioned at the beginning. The manipulated variables Y _OPEN and A _CLOSE are processed in a so-called signal routing 13 in which the error quantity alpha mentioned above is taken into account due to mechanical or similar tolerances. The procedure is such that when entering the manipulated variable Y _OPEN or Y _{CLOSED it is} first checked whether the manipulated variable was Y _OPEN or Y _CLOSED in the preceding cycle; if yes, the manipulated variable is not changed in signal routing 13. It thus arrives unchanged at the data processing and output unit 16. If, however, it is determined in the signal routing 13 that the manipulated variable was reversed in the preceding actuating cycle, the aforementioned error variable alpha is added up. The error quantity alpha is therefore taken into account for every manipulated variable and thus movement reversal for the ladle closure.

The signal output of the signal-ranking 13 may be associated with still clock counter 15, which will determine how often carried out in succession in each case the same control signal or the same manipulated variable Y _ON or Y _ZU, wherein after a predetermined number of OPEN or CLOSE signals, the corresponding manipulated variable should be disproportionately reinforced. In the controller 12, the difference between the actual weight value and the desired weight value is then multiplied by a higher amplification factor "P". In this way, e.g. B. an excessive mechanical clearance can be overcome. Furthermore, leaks in the hydraulics for the one or more ladle closures can be compensated in this way.

The manipulated variable Y _OPEN or Y _CLOSED correspondingly with regard to their pulse width are then processed in the already mentioned output unit 16 (clock output card). In automatic mode, either the OPEN signal or the CLOSE signal is sent to them together with the corresponding pulse width signal. The signals AUTOMATIC OPEN or AUTOMATIC CLOSE are first filtered in a Schmitt trigger 17 (filtering out interference pulses). Then the signals relayed to AND gates via threshold switches 18 and timing elements 19. The pulse width signal is input to the timers 19 via an amplifier 21. The AND elements release the respective manipulated variable, provided that the AUTOMATIC signal is switched on via the control panel 14. In the AUTOMATIC ON signal line, a threshold switch 22 and signal amplifier 23 are arranged in front of the AND gates 20. Before the output signals of the AND gates 20 leave the output unit 16, these are amplified by power amplifiers 29 to a size which is sufficient to switch an electromagnetic 4/3-way valve 30 which is in the hydraulic circuit 31 for the hydraulic drive of the above ladle closure.

The pump and hydraulic tank assigned to the mentioned hydraulic circuit 31 are identified by the reference numbers 32 and 33. In this respect, it is a common arrangement.

As can be seen from the attached drawing, a purely manual operation via the control panel 14 is also possible. In this case, the AND elements 20 intended for automatic operation are deactivated. Instead, AND elements 34 connected in parallel are activated, the first input signal of which is either HAND OPEN or CLOSE HAND and the second input signal is an always activated HAND enable signal. The signals HAND OPEN and HAND CLOSE reach the mentioned AND gates 34 via threshold switches 35.

The HAND OPEN and HAND CLOSE signals then reach the 4/3-way valve 30 in the same way as described above.

In a hydraulic by-pass 36 bridging the 4/3-way valve, a manually operated 4/3-way valve 37 is also arranged which electrically connects one to the control panel 14 Has switch 38. With this switch 38, the 4/3-way valve 30 assigned to the output unit 16 can be blocked, so that the ladle closure can only be controlled via the manually operated 4/3-way valve 37. This is particularly important for emergency circuits.

In addition to the advantages of the method according to the invention and the ladle closure control according to the invention, it should also be mentioned that the tendency detection described can also prevent the ladle closure from either fully opening or closing during operation. Both should be avoided if possible.

With the system described, the weight tolerances in the intermediate vessel 1 can be reduced to ± 50 kg; Accordingly, the ferrostatic height in the intermediate vessel 1 can be kept constant, with the result that a correspondingly constant take-off speed is ensured. This is particularly important if the system works as a so-called "freewheeler". Finally, the described method can also be used for slide closures or stopper closures 3 and 5 of an intermediate vessel 1 in relation to the bath level in the associated mold 28.

All of the features disclosed in the application documents are claimed as essential to the invention, insofar as they are new compared to the prior art, individually or in combination.

Reference symbol list

• 1 intermediate vessel
• 2 load cell
• 3 slide lock
• 4 strands
• 5 dip tube
• 6 stopper closure
• 7 load cell measuring circuit
• 8 measuring amplifiers
• 9 comparators
• 10 adjusters
• 11 Trend detection
• 12 controllers
• 13 Signal routing
• 14 control panel
• 15 clock counters
• 16 data processing and output unit
• 17 Schmitt triggers
• 18 threshold switches
• 19 timer
• 20 AND gates
• 21 amplifiers
• 22 threshold switches
• 23 amplifiers
• 24 ladle
• 25 support rollers
• 26 bottom opening
• 27 slide lock
• 28 mold
• 29 power amplifiers
• 30 4/3-way valve
• 31 hydraulic circuit
• 32 pump
• 33 tank
• 34 AND gates
• 35 threshold switches
• 36 by-pass
• 37 4/3-way valve
• 38 switches
• 39 bottom opening
• 40 circle section
• 41 signal

Claims (9)

1. A method for casting a metallic melt, in particular steel melt, from a ladle (24) into an intermediate vessel (1), in particular a distribution channel or the like, by means of a throttling slide (27) or stopper closure, by means of which, in adaptation to a set take-off speed, the cast strand, the ferrostatic height of the melt in the tundish (1) is regulated,
characterized in that at successive points in time (cycle time Tz) the actual value (X) of the melt quantity in the intermediate vessel (1) in the form of the melt weight or the bath level height is determined and keyed and with the target value (w), ie the target weight or the target bath level, is compared, and that then, at least when the actual value (X) ≧ the target value (w), the tendency of the control deviation upwards or downwards is determined, when approaching or exceeding an upper (Z₂) or lower (Z₁) tendency limit value corresponding to reversed control signals (CLOSE or OPEN) to the drive of the slide or stopper closure. 2. The method according to claim 1,
characterized in that the difference (TN) between the previously determined (X _old ) and the subsequently determined (X _new ) actual value and their sign are determined for determining the actuating signal, with a negative sign, ie with TN <0 or a larger second actual value (X _new ), a signal (CLOSE) for throttling the tundish closure (3; 6) is triggered, and the determined actual value difference (TN) with the lower (Z₁) and the upper (Z₂) limit value at TN einer 0 predetermined trend limit bandwidth (Z₁, Z₂) is compared such that at
- TN> Z₁ triggered a signal (OPEN) to open the ladle closure, and
- Checked at TN ₁ Z₁ whether TN <Z₂, wherein
- At TN <Z₂ a signal (CLOSE) for throttling the ladle closure is generated, otherwise there is no closure actuation signal, preferably a new determination of the control deviation is initiated. 3. The method according to claim 2,
characterized in that even if the condition (Xw) <0 is met, the difference (TN) between the previously determined (X _old ) and the subsequently determined (X _new ) actual value and its sign are determined, with a positive Sign, ie TN> 0 or smaller second actual value (X _new ), a signal (OPEN) to open the pouring pan NEN closure triggered and at TN ≦ 0 the determined actual value difference (TN) with the lower (Z₁) and upper (Z₂) tendency limit value is compared such that
- At TN> Z₁ triggered a signal (CLOSE) for throttling the ladle closure, and
- Checked at TN ₁ Z₁ whether TN <Z₂, wherein
- At TN <Z₂ a signal (OPEN) for opening the ladle closure is generated, while otherwise there is no closure actuation signal, preferably a new determination of the control deviation is initiated. 4. The method according to any one of claims 1 to 3,
characterized in that the actuating signals (OPEN / CLOSE) are converted into a manipulated variable (pulse width Y) with amplification, in particular proportional amplification (P) of the difference between the actual value (X) and the setpoint (w). 5. The method according to claim 4,
characterized in that amplification factors of different sizes are selected for the opposite control signals, namely (OPEN) on the one hand and (CLOSE) on the other hand. 6. The method according to one or more of claims 1 to 5,
characterized in that a signal clock counter (15) is used to determine how often the same actuating signal (OPEN or CLOSED) occurs in succession, with the corresponding actuating variable (Y) after a predetermined number of (OPEN) or (CLOSED) signals is disproportionately reinforced. 7. The method, in particular according to one or more of claims 1 to 6,
characterized in that the manipulated variable (Y) with each signal or manipulated variable reversal an error quantity (alpha), which results from the mechanical, hydraulic and / or pneumatic tolerances of the ladle closure and its drive elements, is added up, whereby the final manipulated variable (pulse width) for driving the ladle closure is obtained. 8. The method according to one or more of claims 1 to 7,
characterized in that the drive of the ladle closure is additionally manually controllable while simultaneously decoupling the automatic control. 9. Application of the method according to one or more of claims 1 to 8 for the control of the pouring closure (3) of an intermediate vessel (1).

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