EP1412111B1 - Method for adjusting the dynamic soft reduction of continuous casting systems - Google Patents

Abstract

The invention relates to a method for adjusting the dynamic soft reduction of continuous casting systems, in particular when casting slabs. The method consists in calculating the position of the edge of the crater, in addition to the proportion of solids and liquids in the casting roller and in adjusting one or several guiding segments of the casting roller according to the positional change of the edge of the crater.

Description

The invention relates to a method for adjusting the dynamic soft reduction on continuous casting plants, in particular in the continuous casting of slabs.

During the solidification in the strand are at the border between liquid and Fixed because of the saturation behavior in the solid state seigemde elements such as C, P, Mn and in particular S excreted. This enriches the remaining Residual melt with these elements. Will not be countermeasures In the area of the Resterstarrung there is a clearly measurable Concentration increase, so that it fails during further processing can come.

A probate countermeasure is the employment of strand guide segments below the mold at a certain rate to grow on each other Unite strand bowls together. This procedure designates one as a soft reduction.

According to current knowledge, it must be a certain Anstellrate the Segment upper frame are maintained. Can not be guaranteed thus in the area of the Resterstarrung A segregations arise, if the Anstellrate too large or V segregations if the pitch is too small.

The end of a segment is determined by the position of the tangent point of the determined last roles of the segment; consequently, it is immediately behind this Roll pair also the beginning of the next segment scheduled.

The skewing (tap adjustment) of the segment upper frame is called conicity the continuous casting machine (CCM). This consists of two Sizes together: the thermal conicity based on the shrinkage of the Casting by cooling and solidification, as well as the Soft Reduction Share, which is set separately. The latter may, if not expressly otherwise required, also take the size "0".

If, for example, the strand guide consists of 14 segments, the segments are 0 to 7, taking into account the thermal taper clamped on a stop and the segments 8 to 14 (Cyberlink) become the CCM depending on the mode driven to a certain preselected distance, taking into account the Max. Forces that can be initiated in the segment.

Changes in the tap setting of the CCM can only take place when the strand moves (Vc> 0 m / min.). At stoppages of the casting machine the active operating states are frozen.

The new values according to the following calculations must then be reconstructed when the strand is withdrawn again.

The adjustment strategy for setting up the new boundary conditions is in the the following sections.

In Level 2, a thermal tracking calculation (TTSR) will determine the location of the Calculated marsh tip in strand. TTSR is a thermodynamic model for determining the temperature profiles in the strand during casting taking into account the casting parameters.

In addition, a "Liquid Fraction" is generated via the material data records of the TTSR. certainly. The Liquid Fraction designates in the liquid swamp of the strand the proportion between liquid and already solidified crystals. The value of this Metric is between 0 and 1, where 0 is the location of the full Solidus describes and 1 the position of the liquidus temperature in the Strand.

• die Gießgeschwindigkeit Vc,
• die Wassermenge,
• die Stahlsorte,
• die Dicke des Stranges in der Gießmaschine.

The main variables in TTSR mode are:

• the casting speed Vc,
• the amount of water
• the steel grade,
• the thickness of the strand in the casting machine.

Roller plan and heat output of the mold are read.

For the TTSR calculation, it is assumed for simplicity that the strand shell on the inner and outer radius symmetrically solidified. The symmetry plane is half the strand thickness.

• ein Dialog mit Hilfe vom Keyboard zur Neueingabe und Änderung, über fest gespeicherte Pattem aus diesem Dialog, die an die Schmelze gekoppelt sind.

The Level 2 features for Soft Reduction can be configured in the following ways:

• a dialogue with the help of the keyboard to re-enter and change, via fixed Pattem from this dialogue, which are coupled to the melt.

The "Thermal Taper" for the casting machine can be over the same mask configure.

• Soft Reduction Quote [mm/m],
• Liquid Fraction Anteil vor der Durcherstarrung.

The following values must be parameterized via a dialog menu:

• Soft Reduction Quote [mm / m],
• Liquid fraction before solidification.

Overall, the input is from six different segment positions (Quotas with liquid fraction fraction) are provided to influence the sump tip.

The TTSR value for the Liquid Fraction calculated from this information the intersection of the liquid fraction with the notional midline of the strand. This value is measured from the pouring level in the mold in Direction to the cutting machine. From this parameter can then the corresponding strand segment can be determined that with the given Quota is charged.

With the possibilities for the parameterization it can under the known boundary conditions In addition, in a segment more than one result for the Liquid Fraction calculation is. This is especially likely when the borders are very close together.

In order to solve such a conflict, TTSR seeks from the point of complete Solidification from backwards towards the mold after the first intersection with the imaginary centerline and determines the segment number. Then the search algorithm jumps to the next segment (Solidus -1) and again determines the first there Liquid Fraction Intersection. This continues until the end. The associated segment employment rates are set in analogy.

To avoid that - especially in borderline cases - the segments at minor Changes in the calculated sump tip unnecessarily controlled If the change in the sump tip was assigned a "default" value. If the sump tip changes in the direction of the last pair of rollers the casting machine is then changed (if necessary) the segment position, when the new position is advanced ≥10 cm; in reverse In this case, the segment setting is activated when the calculated sump peak has been withdrawn by ≥40 cm. Both values can be parameterized.

The TTSR calculation is triggered in a short rhythm of, for example, 10 s, so that then the current calculation is output again.

In this way it is ensured that changes in the casting process such as changes in the Vc, splash water changes or strand thickness changes be detected accordingly.

The Level 2 accessible data from the Pattem or from their changes are converted to a telegram to the level 1, in which the current Quotas for employment of segmental frames are reported.

The maximum permissible change in the quota per cycle was limited to 0.2 mm / m.

In return for this telegram, Level 1 informs you about the current one every 5 seconds Position of the jaw width of the segment output.

It should be mentioned again at this point that the measure of the Jaw width at the segment exit (in level 1) equal to the measure for the jaw width at the entrance of the subsequent segment.

While TTSR in level 2 a "CaDesign" an image for the calculation of Casting machine created, sets level 1 on the information of the mouth width of the exit dimension of the segment 7.

The segments in the horizontal part of the casting machine are hydraulically to a predetermined Measure adjustable. After setting the quotas, the mouth widths approached by changing the position of the upper frame. The default the odds are made by the Level 2 Automation, while the repositioning the mouth width is regulated by Level 1.

Since the segments with the exit role at role position 7 also the pull-out must be transferred to the strand or cold strand, must be ensured be that the upper frame with a minimum force on the cold or press warm strand.

Can the segment upper frame not approach a certain predetermined position? because the guided strand in the segment too much deformation resistance an upper limit of force is introduced, which is supposed to prevent that rolls, bearings or trusses suffer damage.

The control of the segment thus operates in an operating window, the is determined by the minimum and maximum force, and takes care of all Circumstances that the upper frame with the appropriate force on the Losseite the slab rests.

To the strand support through the segments even during the switching operations To ensure the longest possible period, must be a switching logic be ensured.

Basically, the segment containing the (calculated) solidus point last (in terms of casting direction) with a soft reduction Quote is occupied.

1st casting start

As long as the cold strand immediately after casting start not yet in the access of Segments 8 to 14, the segments are in the raised position.

Only when the Level 1 Tracking System commands to clamp the last Role of the cyberlink segments, will be in the appropriate position Segment with the exit rollers moved down; the upcoming one Force is now a function of cold extrusion pressure.

Once the tracking system in level 1 because of the approaching cold strand head Giving the command for relief, the corresponding segment upper frame raised again.

After the head has passed, the segment lowers again. The upcoming one Force corresponds to the hot rod pressure. Once TTSR the sump tip Calculated in the appropriate segment, can also be the Soft Reduction driving style be activated after checking the plausibility by level 1.

If the corresponding boundary conditions are met, the segment 8 becomes Gradually lowered to the specified soft reduction position.

In this case, as soon as the two hydraulic cylinders at the end of the segment 8 into the new jaw settings, the two hydraulic cylinders at the entrance of the segment 9 with a time delay by the switching time lowered with. After reaching the end position, the cylinders at the exit of the segment 9 together with the cylinders at the entrance of the Segmentes 10, taking into account the thermal tapers set. Also this process takes place again taking into account the switching cycles between Segment 9 end and segment 10 input.

All the following segments 10 through 14 will be used gradually in analogy to the traced new lowered position.

As soon as the sump tip leaves the segment 8 and enters the segment 9, TTSR must decide on the basis of the comparison with the Liquid Fraction calculation, whether only one segment is needed for the soft reduction strategy, or a second is charged to the Soft Reduction Quote.

2. Only one segment receives soft reduction (Swamp tip moves to the caster end)

After the calculation of the sump tip shows that the solidification of the strand has migrated to the following segment 9, after reconciliation of Liquid Fraction also moved segment 9 into the soft reduction quota. The following segments must be adjusted in the Thermal Taper.

Once the sump tip has advanced further into the segment 9 and the defined Liquid Fraction part has left the segment 8, first the Gap widths of segment 8 output together with segment 9 inlet moved to the new position corresponding to the segment 8 thermal taper; As a result, the segment 9 first experiences a greater employment rate. When the transition of segments 8 and 9 is in the desired position, can the soft reduction rate of segment 9 to the selected value be set.

The following segments are in the Thermal Taper setting as before described procedure.

This process is repeated analogously in the subsequent segments.

3. Multiple segments receive Soft Reduction moves to the caster end or reaches steady state)

First, the circuit of the segments is made as in paragraph 2 in the first Paragraph already described.

As the sump tip continues to advance, the processes are analogous to the second and third section switched.

Will it be necessary as a result of the technical casting conditions the number shrinking the soft reduction segments, initially with rising Vc the transition between the segments closest to segment 7 are, drove into the new mouth width.

Thereafter, the position is retained as a result of the TTSR calculation. This then also corresponds to the stationary state.

4. Several segments receive soft reduction (Swamp tip moves towards the mold)

Moves through changed casting parameters (such as a reduction in the Vc) the sump tip back towards the mold, is falling below the switching point the regrouping of the segment adjustment triggered.

Assuming first that the area of the liquid fraction parallel to Sumpfspitz withdraws, the number of engaged Soft Reduction Segments remain the same; i.e. that the sum of the segments is the same remains and is moved parallel in the mold direction.

For this purpose, the entry of the segment j (old), out of which the bottom tip migrated is, together with the exit of the segment j (new), in which the tip is currently located, lowered to the Maulweitenmaß, the thermal Taper of segment j (old) corresponds to the Taper position of CCM end extrapolated.

Now the start rate of segment j (new) is greater than specified. To this The interface must be j (new) input and j (new) -1 output analog be adjusted. This process is repeated until the Soft Reduction Segments cover the entire area again.

5. Several segments receive soft reduction (sump tip moved towards the mold, area Liquid Fraction becomes smaller)

If after the end of this new employment it turns out that the number of soft Reduction segments must be reduced, the jaw output of the Segmented on thermal taper, the segment 7 am next stands. The rate of succession towards the end of the CCM Segments are reset as described in section 3.

6. Several segments receive soft reduction (sump tip moves towards the mold, Liquid Fraction area is below segment 8)

A similar procedure as described in the previous section then expires, when the Liquid Fraction setting goes back to Segment 7.

Again, the excessive segment employment rate must be reversed the direction are readjusted.

It goes without saying that the new strand thickness corresponds to the segment settings must be adjusted by segment 14 respectively.

7. Several segments receive soft reduction (Soft Reduction area gets bigger)

If the location of the sump tip after the acceleration of the strand again gets into a stationary state, it happens more often that the situation of the area with the Liquid Fraction setting also adapts. This adaptation can then be done by expanding the number of segments that for the soft reduction is used.

Since the segment j with the sump tip. the last soft reduction segment is, There will be a correction each over additional soft reduction segments between Segment 7 and segment j.

This will be the last segment (j-n) before the previous soft reduction section is located, from the thermal taper setting in the soft reduction Taper set (jaw width at the segment exit of the newly activated segment j-n gets smaller); At the same time, as already known, this becomes the bottom of the pool next segment (j-m) next to j-n in the jaw width with.

As soon as the end position at j-m is reached, the jaw width of the segment exit becomes j-m adapted according to the Soft Reduction Taper.

This process continues until all segments between j-n and j have reached the new mouth width.

In addition, those between j and the caster end are also Segments on the new slab thickness taking into account the thermal Adapted to Tapers.

If further post-correction is required, the sequence described is to repeat.

8. Several segments receive soft reduction (Range Soft Reduction becomes smaller when stationary)

In this case, the procedure is as described under point 5.

9. composite casting

When compound casting without the use of a "separator" come before described cases for use.

If composite casting is carried out with a "separator", TTSR calculates first the change in the sump tip and leaves the segment frame so switch long until either the sump tip has run back into the segment 7 is or the Ausziehmaschine stopped for the flying distributor change Has.

After definition, the state that has now been reached is frozen.

After the restart, (if it should be) the old swamp seats will be negated; the Segments 8 to 14 are driven into the Thermal Taper.

As soon as the new sump tip again leaves the segment 7 run the described Procedures as in the case of a casting start according to paragraph 1.

10th pouring

When the pouring end is initiated, TTSR first calculates the change in the sump tip and keeps the segment frames shifting until either the sump tip has returned to segment 7 or if the extraction machine is stopped for slagging.
After definition, the state that has now been reached is frozen.

If no standstill is to be practiced for slagging, the segment positions with the command "Gießende (or Ausfördem)" in the last one Frozen position.

The Soft Reduction driving style is then turned off when the Level 1 system is on gives the command to raise the segment upper frame.

The above-described method for setting the dynamic soft reduction is not only applicable to conventional slabs, but also to so-called thin slabs.

Claims (6)

1. A method for adjusting the dynamic soft reduction of continuous casting systems, particularly during the continuous casting of slabs,
   characterized in that the position of the crater edge as well as the proportion of solids and liquids in the billet being cast are calculated and one or more segments of the billet guide are adjusted in accordance with the positional changes of the crater edge.
2. The method according to Claim 1,
   characterized in that the position of the crater edge is calculated with a thermodynamic computing model for determining the temperature profiles in the billet during the casting process.
3. The method according to Claim 1 or 2,
   characterized in that essential casting parameters such as

   the casting speed V_c

   the cooling water quantity

   the steel type

   the thickness of the billet in the casting machine

   the thermal output of the mould

   the roll layout of the billet guide or the like

   are taken into account in the computing model.
4. The method according to at least one of Claims 1-3,
   characterized in that the segment adjustment is changed during a positional change of the crater edge in the direction of the last pair of rolls when the new position is shifted forward by □ 10 cm, and in that the segment adjustment is activated, vice versa, when the calculated crater edge has been shifted backward by □ 40 cm.
5. The method according to at least one of the preceding claims,
   characterized in that the position of the crater edge is calculated with the aid of the thermodynamic computing model in predetermined cycles.
6. The method according to Claim 5,
   characterized in that the change of the adjustment of the segments per cycle is limited to a default value.