EP0223078B1 - Method of starting a multi-strand continuous-casting installation - Google Patents

Abstract

1. A method for starting up a continuous casting system comprising a plurality of castings, especially for pouring molten steel from an intermediate vessel (3) into a plurality of continuous casting moulds (A, B, C) by means of adjustable gate valves (4), with a nominal filling level (8) of the melt being within a measuring zone (9) of a filling level gauge means (9, 10, 11) associated to each mould (A, B, C) and with the resultant castings being withdrawn from a castings withdrawing aggregate (12 through 15) at the same speed, characterized in that switching on of the castings withdrawing aggregate (12 through 15) after reaching a lower signal plane (21) within the measuring zone (9) is effected through the actual filling levels (20) of all moulds (A, B, C) or through the actual filling level (20) first reaching an upper signal level (22) disposed within the measuring zone (9), with the gate valves (4) of the moulds (A, B, C) whose actual filling level is still below the lower signal level (21), in the latter instance, being closed, and that each actual filling level (20), from the lower signal level (21) along a predetermined ascending curve (40) is adjusted into the nominal filling level (8).

Description

The invention relates to a method for starting up a continuous casting plant with several strands, in particular for casting steel melt from an intermediate vessel, into several continuous casting molds by means of controllable pouring closures, with a desired fill level of the melt being within a measuring distance of a level measuring device assigned to each mold, and the resulting ones Strands are withdrawn from a strand withdrawal unit at the same speed.

It has already been proposed (DE 34 32 611 C2) that at the beginning of the pouring of the pouring closures on the intermediate vessel for pouring, the actual filling level rising in each mold above the cold strand heads at a first signal level located in the lower region of the measuring section initially the throttling of its pouring closure to equalize all the actual filling levels and then switching on the strand take-off unit, which, if the equalization has failed, is carried out at the latest at a second signal level below the target fill level by the actual fill level arriving there first. The aim of this is to improve the casting on with the same take-off speed with simple method steps, in particular with regard to operational safety.

The present invention is a further development of a casting process which is controlled within a fill level measuring section of molds by means of two signal levels via pouring closures at a constant take-off speed, known for example from EP-A-0 019 114.

The object on which the invention is based is essentially to be seen in streamlining the sprue by reducing the sprue time using simplified process steps.

To solve the problem, it is provided that the strand extraction unit is switched on after reaching a lower signal level within the measuring section through the actual filling levels of all molds or through the actual filling level first reaching an upper signal level lying within the measuring section, in the latter case the Spout closures of those molds whose actual fill level is still below the lower signal level are closed, and that each actual fill level is regulated from the lower signal level along a predetermined ascent curve into the desired fill level.

In this way, the actual fill level of each mold can be quickly and separately transferred to the normal inflow control of the target fill level, when the strand take-off unit is appropriately switched on in a filling section of the mold between the lower and the upper signal level of the measuring section, which guarantees the pull-off safety of the strands. The take-off drive of the strand take-off unit accordingly responds to what happens first when the actual fill levels rise in the molds. Either the trigger drive switches on when the lower actual level is exceeded by the last actual level or, if this is not the case, as soon as the first actual level has reached the upper signal level. After the trigger drive has been switched on, the pouring closures automatically close those molds whose actual fill level is still below the lower signal level.

For a particularly quick and yet reliable casting on, it is further proposed according to the invention to regulate the pouring closures at the lower signal level along the ascending curve in a region above the freezing limit of the melt in the pouring closures on the one hand and below the slosh limit of the melt at the mold edge during the transition to the regulation to let it take place in the target level on the other hand. With such a procedure, on the one hand, the transition from a control defined by rapid changes in the flow cross section at the pouring closures runs along the ascent. curve in a relatively sluggish regulation at the nominal level with a relatively constant mold bath level, on the other hand, freezes occurring in the pouring closures, which obstruct the pouring jet, are largely counteracted.

The latter is also used for pouring with initially only up to 50% opened spout closures, of which the spout closures that are most distant from the filling point of the intermediate vessel or belong to the outer molds are throttled less than those of the inner molds. This effectively takes into account the lower melt temperatures prevailing in the outer districts of a continuous caster or an intermediate vessel.

In addition, there is the possibility of pouring the pouring closures below the lower signal level when pouring lagging actual filling levels. H. Before the regulation along the ascent curve, briefly open fully to wash away freezing approaches.

The invention is explained below with reference to the drawing.

• Fig. 1 schematisch eine Stranggießanlage mit Kokillen in einer Angießposition sowie
• Fig. 2 und 3 mögliche Angießabläufe in graphischer Darstellung.

Show it :

• Fig. 1 shows schematically a continuous caster with molds in a pouring position and
• 2 and 3 possible sprue sequences in a graphical representation.

From a ladle 1, molten steel is fed to an intermediate vessel 3 via a controllable pouring closure 2, which in turn has three pouring closures 4 in the form of slide closures which regulate the inflow of the melt through pouring tubes 5 into continuous casting molds A, B, C. For this purpose, each pouring closure 4 is mechanically coupled to an actuator 6. the respective operating position of a position. ment meter 7 is held. The pouring tubes 5 protrude with their free ends into the molds A, B, C, whose set level 8 set for normal operation lies within a measuring path 9 of a mold level A, B, C assigned to each mold, consisting of transmitter 10 and receiver 11.

Downstream of the molds A, B, C is a secondary cooling device, which is not shown for the sake of simplicity, and a strand take-off unit common to the cold strands 18, which has drive rollers 12, a take-off drive 13, a drive controller 14 and a take-off speed meter 15. The latter transmits its measured values to the drive controller 14 and to a processor 16 which also receives and processes the measured values of the position meter 7 which controls the degree of opening of the pouring closures 4 and the receiver 11 of the level measuring devices 10, 11. The data obtained go to a control computer 17 integrated in the processor 16, the corresponding one. There are control commands to the actuators 6 of the pouring closures 4 and to the drive controller 14 of the strand extraction unit 12 to 15. There the withdrawal speed is fixed as a constant, i.e. H. the cold strands 18 retracted into the molds A, B, C are drawn off by the common strand withdrawal unit 12 to 15 at a constant speed, which means that the desired fill level 8 provided for the molds A, B, C is solely from the inflow side by means of the pouring closures 4 is regulated. For this purpose, the pouring closures 4 are kept in a normal throttling position at the desired fill level 8 in a throttle position, which enables both opening and closing.

For the casting, for which the cold strands 18 are inserted into the molds A, B, C and the trigger drive 13 is switched off, the measuring section 9 is equipped with a lower signal level 21 and an upper signal level 22 which are used to control the pouring closures 4 and the trigger drive 13 serve. The casting begins with the opening of the pouring closures 4, so that actual fill levels 20 form in the molds A, B, C above the cold strand heads 19, but these are rarely at the same level.

In detail, the pouring closures 4 are initially only partially, preferably about 35%, but not fully opened during the pouring. This results in 4 control reserves for the pouring closures both in the closing and in the opening direction, which allow each actual filling level 20 rising in the molds A, B, C (cf. FIG. 2) from the lower signal level 21 to the desired filling level 8 to let it ascend along a predetermined ascent curve 40, which is adapted to the operating conditions of the respective system by appropriate programming of the processor 16.

The criterion of the ascending curve 40, which determines the filling speed of the molds A, B, C during casting, is never to be so flat that the freezing limit of the molten steel in the pouring closures 4 has fallen below, and not to be as steep as that the upper slosh limit at the mold edge is exceeded. The regulation of each pouring closure 4 according to the ascent curve 40 begins, as mentioned, at the lower signal level 21 and is triggered by the actual fill level 20 ascending in the corresponding molds A, B, C. If the last of all the actual filling levels A20, B20 or C20 exceeds the lower signal level 21, then the control computer 17 of the processor 16 switches on the trigger drive 13 of the common trigger unit 13 to 15 for the cold strands 18. Thereafter, the actual levels A20, B20, C20 continue to rise independently of one another on the basis of the same criteria and consequently graphically parallel ascent curves 40 until they settle into the nominal level 8 set for normal casting operation If the actual fill level is 20, it would spill over the edge of the mold. If an actual filling level 20 of a mold A, B or C has already arrived at the upper signal level 22 while casting, while others are still below the lower signal level 21, 20 closing commands are issued for the pouring closures 4 of the actual filling levels remaining in the said manner.

The graph of FIG. 2 applies to the actual fill levels 20 shown in FIG. 1. After that, the actual fill level 20 of the mold C reached the lower signal level 21 in the time Ct after the simultaneous throttled opening of all pouring closures 4, the one for the Mold C responsible pouring spout 4 takes over the regulation of the melt inlet according to the designed ascent curve 40. As a result, the actual fill levels 20 of the molds B and A successively pass the signal level 21 in the times Bt and At and effect the regulation there according to the ascent curve 40. None of the actual fill levels 20 has remained significantly. The actual fill level A20 reaches the lower signal level 21 before the actual fill level C20 has caught up with the upper signal level 22, so that the start command for the trigger drive 13 originates from the actual fill level A20.

This is different in the example according to FIG. 3, where the actual fill level A20 has arrived at the upper signal level 22 and the actual fill level B20 has exceeded the lower signal level 21, but below which the actual fill level C20 lags behind. With this constellation of the actual filling levels, the trigger drive 13 is started at the upper signal level 22 from the actual filling level A20 and at the same time the pouring closure 4 of the actual filling level C20 which has not risen above the lower signal level 21 is closed.

Reference symbol list:

• 1 ladle
• 2 pouring spout
• 3 intermediate vessel
• 4 pouring closures
• 5 pouring tubes
• 6 actuators
• 7 position meters
• 8 target level
• 9 measuring section
• 10 channels? _F o _lls tandsmeßeinrichtun ^g
• 11 recipients
• 12 driving rollers I
• 13 Extraction drive, strand extraction unit
• 14 drive controller
• 15 take-off speedometer
• 16 processor
• 17 control computer
• 18 cold strands
• 19 cold strand heads
• 20 actual level
• 21 lower signal level
• 22 upper signal level
• 40 ascent curve
• A continuous casting mold
• B Continuous casting mold
• C Continuous casting mold

Claims (4)

1. A method for starting up a continuous casting system comprising a plurality of castings, especially for pouring molten steel from an intermediate vessel (3) into a plurality of continuous casting moulds (A, B, C) by means of adjustable gate valves (4), with a nominal filling level (8) of the melt being within a measuring zone (9) of a filling level gauge means (9, 10, 11) associated to each mould (A, B, C) and with the resultant castings being withdrawn from a castings withdrawing aggregate (12 through 15) at the same speed, characterized in that switching on of the castings withdrawing aggregate (12 through 15) after reaching a lower signal plane (21) within the measuring zone (9) is effected through the actual filling levels (20) of all moulds (A, B, C) or through the actual filling level (20) first reaching an upper signal level (22) disposed within the measuring zone (9), with the gate valves (4) of the moulds (A. B, C) whose actual filling level is still below the lower signal level (21), in the latter instance, being closed, and that each actual filling level (20), from the lower signal level (21) along a predetermined ascending curve (40) is adjusted into the nominal filling level (8).

2. A method according to claim 1, characterized in that the control of the gate valves (4) commencing at the lower signal level (21) is effected along the ascending curve (40) in a zone above the freezing threshold of the melt within the gate valves (4), on the one hand, and below the swash threshold of the melt on the mould rim during passing over of the control into the nominal filling level, on the other hand.

3. A method as set out in claims 1 or 2, characterized in that the gate valves (4) first are opened only up to 50 %, with the gate valves (4) belonging to the outer moulds (A and C) and to the moulds (A and C) more remote from the loading point of the intermediate vessel (3), respectively, preferably being throttled to a lower degree than the gate valves (4) belonging to the inner moulds (B) and the moulds (B), respectively, in closer relationship to the loading point of the intermediate vessel (3).

4. A method according to any one of claims 1 to 3, characterized in that the gate valves (4), during initiating the pouring process of actual filling levels (C20) lagging behind, below the lower signal level (21), i. e. before adjustment along the ascending curve (40), for a short period of time are fully opened.

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