EP0274516B1 - Process for controlling a multi-line casting plant - Google Patents

Abstract

In the continuous casting plant described, a melt which is poured from a distribution channel (10) with several discharge nozzles (11, 12, 13, 14) solidifies in a corresponding number of chill moulds and is withdrawn in the form of cast bars (15, 16, 17, 18), which after being subjected or not to forming, are cut to the desired bar length in a parting installation (19). After initiation of ''end of casting'', all of the discharge nozzles (11, 12, 13, 14) should first be left open until the height of the melt in the distribution channel (10) has dropped to a predetermined threshold value, upon which first one (for example 11) of the two outer nozzles is closed. Thereafter a new threshold value is determined for the remaining nozzles still open (12, 13, 14). After this new value has been reached, the other two (14) outer nozzles are closed. This process is continued until progressively from the outside inwards all of the nozzles have been closed. The closing times of the nozzles (11, 12, 13, 14) are so selected that the length of the residual bar still to be extracted corresponds to a multiple of the predetermined bar cutting length plus a predetermined final bar length. The final bar length is obtained from the sum of the bar cutting length and a predetermined stub length. In this way, an optimum distribution of the remaining melt is achieved on the discharge nozzles in such a way that only in the case of the last open discharge nozzle is a final bar length set, which deviates from the preset final bar length.

Description

The invention relates to a method for controlling a multi-core continuous casting installation according to the preamble of claim 1. Such a method is known from FR-A-2055 806.

Multi-core continuous casting machines are operated in such a way that the molten metal in a ladle is poured into several water-cooled molds by means of a tundish or tundish provided with several spouts and is continuously drawn off in the form of partially solidified casting strands by means of driven guide rollers. Using so-called flying separators, the strands are then cut to a predetermined length and placed on a cooling bed. After the pouring ladle has been emptied or closed, there is still residual melt in the tundish, which is distributed to the individual strands until it is completely empty. The subdivision of the strands into predetermined strand cut lengths generally results in a strand remnant for all strands at the end of the continuous casting, the length of which minus one cropping end or stump is greater than zero but less than the predetermined strand cut length.

In order to avoid such remaining lengths in multi-strand systems, it is proposed in DE-OS 24 40 414 that a timer with an adjustable resistance combination for adjusting the profile length is provided for each strand, the input of which is connected to a tachometer generator coupled to a guide roller set for generation a control voltage proportional to the line withdrawal speed and a pulse generator controlled by the separating device for generating a start pulse is connected, and that to the output of the timing element a switching amplifier with latching for generating a periodic control signal sequence which determines the possible closing times of each floor spout connected. In this way, a control signal with a defined time interval can be generated starting with each cut, at which point the strand length cast in each case is an integral multiple of the profile length. Each line is controlled separately, ie independently of the other lines. The known system cannot control the strands as a function of the constantly changing amount of melt located in the distribution channel.

This object is achieved by the characterizing measures according to claim 1, preferred details of the method according to the invention being described in the subclaims.

According to the invention, the floor spouts of the distribution channel and thus the strand withdrawal when the pouring end is initiated are controlled in a predetermined order, namely from the outside inwards, in each case as a function of the constantly changing amount of melt in the distribution channel, in such a way that after a floor spout is closed, the assigned mold can still pull a strand with an overall length that corresponds to a multiple of the predetermined strand cut length and a predetermined butt length. The closing signal for a floor spout is preferably triggered after the weight of the melt located in the distribution channel has decreased to a newly set threshold value, the threshold value depending on the number of floor spouts still open.

The strand length still to be subtracted after a floor spout has been closed can preferably be derived from the (variable) strand withdrawal speed, predetermined strand cutting length, butt length and machine length which is constant in the system.

The weight threshold mentioned depends, among other things, on a predetermined weight of the distribution channel remaining slag.

Instead of a weight threshold, it is also possible to work with a volume threshold or fill level threshold, since the latter threshold values can always be converted into a weight threshold value if the specific weight of the melt to be cast and the dimensions of the distribution channel are known.

The method according to the invention is described in more detail below with the aid of an example of a program sequence, as is shown schematically in the attached drawing.

The exemplary embodiment shown is about the control of a four-wire continuous casting installation, in which molten metal cast from a distribution channel 10 with four bottom outlets 11, 12, 13 and 14 solidifies a corresponding number of molds, not shown, and in the form of casting strands 15, 16, 17 and 18 is withdrawn, which are then cut unmolded or deformed by means of a flying separating device 19 to the desired strand cut length STR _SL . A ladle 20 is arranged above the tundish 10, the bottom spout of which is controlled by a ladle slide 21. The ladle slide 21 is shown only symbolically in the drawing; likewise the drive 22 for this. The ladle 20 can also be equipped with a slag sensor 23 in the bottom area. Then, taking into account the ladle residual slag, the minimum ladle weight "X", with which the actual ladle weight "Y" is constantly compared, can be specified by means of a comparator 24. The actual ladle weight "Y" drops to the minimum ladle weight " X ", the drive 22 of the ladle slide 21 is given the command to close the ladle slide 21. The signals from the slag sensor 23 are read into the comparator 24 via a signal converter 25.

The distribution channel 10 are also assigned weighing cells 26, by means of which the total net channel weight VR _{G is} determined. The total gutter net weight VR _G comprises the gutter residual slag weight VR _GS as well as the weight of the melt still located in the distributor gutter 10. The read total net gutter weight VR _G is compared in a comparator 27 with the predetermined gutter residual slag weight VR _GS . If the total gutter net weight reaches the size of the gutter residual slag weight, the comparator 27 gives the command to close all the gutter slides 28, 29, 30 and 31 or their drives assigned to the floor spouts 11, 12, 13 and 14. This reliably prevents residual slag from getting into one of the strands 15, 16, 17 or 18. The corresponding command signal from the comparator 27 to the drives of the distributor channel slides is identified in the drawing by the reference number 32 or 32a, 32b, 32c, 32d.

Is now using a z. B. manually operated switch 32, the pouring end is initiated after the ladle slide 21 has been brought into its closed position, on the other hand, an end length optimization, as will be described in more detail below, is triggered. The pouring end can of course also be initiated by the comparator 24 which is assigned to the last ladle in the sequence. That is, when the actual ladle weight "Y" of this ladle has dropped to the minimum ladle weight "X". If the pouring end has been initiated, a weight threshold is determined in a computing unit 33, upon reaching or falling below which the distribution channel slide 28 of the one outer floor spout 11 of the distribution channel 10 is activated such that it follows a predetermined Program closes. The weight threshold results from the difference between the total net gutter weight and the remaining gutter slag weight divided by the product of the final strand length weight and the number of still open strands or floor spouts. The weight _threshold VR _{GRL is} shown in the schematic longitudinal sectional view of the distributor channel 10 filled with melt. If the melt located in the distribution channel 10 drops below this weight threshold, the mentioned closing program is triggered for a predetermined floor pouring. This signal is supplied by a comparator 34 arranged downstream of the computing unit 33.

wobei die Bruchzahl "O, X" erhalten wird aus den %
$$\frac{\text{ML}}{{\text{STR}}_{\text{SL}}}\text{= X, X}$$

unter Unterdrückung der Zahl links vom Komma.In the example shown, after reaching or falling below the weight threshold, the distributor channel slide 28 assigned to the bottom spout 11 is to be actuated in such a way that it closes according to a predetermined program. The bottom spout 14 could just as well be provided first for closing. The closing control signal supplied by the comparator 34 is identified in the drawing by the reference number 35, 35a. The signal 35a arrives in a second computing unit 36, the output of which is coupled to the drive of the distributor trough slide 28 (signal 37). In the arithmetic unit 36, after receiving the control signal 35a and starting at the starting point Ta of the strand separating device 19, individual path sections Δ S, which are determined from the strand speed v _ETR , are continuously added up until the required remaining strand length STR _Rest or length still to be cast until the specified final strand length STR _ELG is reached. Then the signal 37 is emitted to the drive of the distributor channel slide 28 so that it is brought into the closed position. The required remaining strand length is as follows:
$${\text{STR}}_{\text{rest}}{\text{= STR}}_{\text{EL}}{\text{\_ (STR}}_{\text{SL}}\text{· O, X)}$$

where the fraction "O, X" is obtained from the%
$$\frac{\text{ML}}{{\text{STR}}_{\text{SL}}}\text{= X, X}$$

while suppressing the number to the left of the comma.

• STR_Rest erforderliche Reststranglänge bzw. noch zu vergießende Länge bis zur Erreichung der Strang-Endlänge;
  
• STR_EL Strang-Endlänge = Strang-Schnittlänge STR_SL + Stumpflänge.
  

In the above calculation operation:

• STR _rest required remaining strand length or length still to be cast until the end strand length is reached;
  
• STR _EL final strand length = strand cutting length STR _SL + butt length.
  

The line speed v _{STR of} the lines 15, 16, 17 and 18 is determined by means of these separately assigned measuring rollers MR1, MR2, MR3 and MR4.

As soon as the first outer floor spout 11 is closed, the signal is sent to the first computing unit 33 that only three floor spouts, namely the floor spouts 12, 13 and 14, are open. A new weight threshold is calculated accordingly. If this new weight threshold is reached or fallen below, the comparator 34 arranged downstream of the arithmetic unit 33 supplies a signal 35, 35b to a second arithmetic unit 38, which is assigned to the distributor trough slider 31, which is used to control the other outer floor spout 14 of the distributor trough 10. The closing signal supplied to the computing unit 38 is identified by the reference number 39. The computing units 36 and 38 work in the same way. They each contain an adding unit and a comparator.

As soon as the floor spout is closed, a corresponding signal is fed back to the computing unit 33. A new weight threshold is then calculated taking into account the two still open floor spouts 12 and 13. If this falls below again, the comparator gives 34 a control signal 35, 35c or 35, 35d to the computing units 40 or 41, which are assigned to the distributor channel slider 29, 30 of the two internal floor spouts 12, 13. The computing units 40, 41, like the computing units 36, 38, each include an adding unit and a comparator. The closing signals supplied by the computing units 40, 41 are identified with the reference numbers 42, 43. The control signals 35, 35c and 35, 35d only reach the computing units 40 and 41 when the two outer floor spouts 11, 14 are already closed. For this purpose, the control signals 35, 35c and 35, 35d each have to pass through an AND gate 44 and 45, which is arranged upstream of the computing units 40, 41. Is z. B. first activated the computing unit 40 and the associated trough slide 29 brought into the closed position, the computing unit 33 is informed that only one floor spout, namely the floor spout 13 is open. A weight threshold corresponding to this state is calculated again and after falling below the same, the process described for the remaining distributor trough slider 30 is repeated until the latter is also in the closed position.

• Verteilerrinnen-Restschlackengewicht VR_GS
• Strang-Endlänge STR_EL = Strang-Schnittlänge STR_SL +  Stumpflänge
• Strangformat (Querschnitt)
• spezifisches Gewicht der zu vergießenden Metallschmelze
• zur Errechnung des Gewichtes der Strang-Endlänge STR_ELG.

The computing unit 33 is entered as fixed data:

• Distribution channel residual slag weight VR _GS
• End strand length STR _EL = strand section length STR _SL + butt length
• Strand format (cross section)
• specific weight of the molten metal to be cast
• to calculate the weight of the final strand length STR _ELG .

• Maschinenlänge ML
• Strang-Schnittlänge STR_SL
• Strang-Endlänge STR_EL,
• so daß aus diesen Größen die erforderliche Reststranglänge STR_Rest errechnet werden kann. Wie oben dargelegt, werden die Schließsignale 37, 39, 42 bzw. 43 immer dann ausgelöst, wenn durch fortlaufende Addierung von Einzelwegstrekken, die aus der Stranggeschwindigkeit ermittelt werden, die erforderliche Reststranglänge bzw. die noch zu vergießende Länge bis zur Erreichung der Strang-Endlänge erhalten ist.

The second computing units 36, 38, 40, 41 are entered as fixed data:

• Machine length ML
• Strand cutting length STR _SL
• End strand length STR _EL ,
• so that the required remaining strand length STR _Rest can be calculated from these quantities. As stated above, the closing signals 37, 39, 42 and 43 are always triggered when the required remaining strand length or the length still to be shed is reached by continuously adding individual path sections, which are determined from the strand speed, until the end strand length is reached is preserved.

The counters (adding units) respectively assigned to the computing units 36, 38, 40, 41 are each assigned from the starting point TS _{a of} the flying separating device, e.g. B. separator, 19 started. TSe means the time of the cut end.

At this point it should also be mentioned that it is metallurgically extremely advantageous if the outer floor spouts are closed first so that the path of the residual melt to the still open floor spouts is minimal. Otherwise, excessive heat losses would occur on the way to the outer floor outlets at the end of the casting process, with the result that there would be a risk of freezing them.

Claims (5)

1. Method of controlling a multistrand continuous casting installation in which a metal melt poured from a distributing launder (10) having a plurality of bottom nozzles (11, 12, 13, 14) is solidified in a corresponding number of moulds and is withdrawn in the form of cast strands (15, 16, 17, 18) which are subsequently cut, undeformed or deformed, by means of a cutting device (19) to the desired strand cut length (STR_SL), in which method

a) after initiation of the "end of the pour", all of the bottom nozzles (11, 12, 13, 14) remain open until the melt in the distributing launder (10) reaches a predetermined threshhold value, in particular a predetermined weight threshhold (VR_GRL),

b) after reaching this threshhold value, firstly one bottom nozzle is closed,

c) subsequently the threshhold value for the remaining bottom nozzles (12, 13, 14) which are still open is re-determined,

d) after reaching this new threshhold value, a further bottom nozzle (14) is closed, and in which method

e) this process is continued until all of the bottom nozzles are progressively closed, characterised in that

f) firstly one (11) of the two outer bottom nozzles is closed, then the other (14) of the two bottom nozzles is closed and, correspondingly, as this process progresses all of the bottom nozzles are closed progressively from the outside inwards, and in that

g) the closing times of the bottom nozzles (11, 12, 13, 14) are chosen in each case so that the length of the residual strands still to be withdrawn _ except possibly in the case of the bottom nozzle (12 or 13) open last _ in each case corresponds to a multiple of the preset strand cut length (STR_SL) plus a preset strand final length (STR_EL), which is equal to the strand cut length (STR_SL) plus preset stump length.

2. Method according to Claim 1, characterised in that the weight threshhold which triggers the closure of a bottom nozzle (11, 12, 13 or 14) is determined as follows:
$$\frac{{\text{VR}}_{\text{G}}{\text{\_ VR}}_{\text{GS}}}{{\text{STR}}_{\text{ELG}}\text{×α}}\text{≦ 1}$$

where

VR_G = total net weight of the distributing launder (kg),

VR_GS = residual slag weight of the distributing launder (kg),

STR_ELG = weight of the strand final length (kg), and

α = number of open bottom nozzles or running strands _ sliding gates open.

3. Method according to Claim 1 or 2, characterised in that the total net weight of the distributing launder (VR_G) is constantly measured by means of a weight sensor (weighing cells 26) and read into a comparator (27) and compared therein with the predetermined residual slag weight of the distributing launder (VR_GS), in which method, if
$${\text{VR}}_{\text{G}}{\text{= VR}}_{\text{GS}}$$

all of the bottom nozzles (11, 12, 13, 14) are simultaneously closed.

4. Method according to one or more of Claims 1 to 3, characterised in that a bottom nozzle (e.g. 11) intended for closure is closed only when, after the closure, one more strand can be withdrawn with a length which corresponds to the sum of machine length (ML) and a residual strand length (STR_rest) which is required to obtain the strand final length (STR_EL), in which method, given a preset strand final length (STR_EL), the residual strand length STR_rest is determined as follows:
$${\text{STR}}_{\text{rest}}{\text{= STR}}_{\text{EL}}{\text{\_ (STR}}_{\text{SL}}\text{· O, X),}$$

and the expression (STR_SL · O, X) denotes the difference between the machine length (ML) and an integral multiple, contained in the machine length (ML), of the predetermined strand cut length (STR_SL).

5. Method according to Claim 4, characterised in that, before the closure of a bottom nozzle (e.g. 11), the distance covered by the strand is determined from the strand speed (v_STR), starting from the starting time of the cutting device (19) associated with the respective strand (e.g. 15), and is constantly compared with the required residual strand length (STR_rest), and to be precise until the distance covered by the strand corresponds to the required residual strand length, in order then to trigger the closing signal for the sliding gate (e.g. 28) of the distributing launder associated with the bottom nozzle (e.g. 11).

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