WO2002098587A2

WO2002098587A2 - Method for adjusting the dynamic soft reduction of continuous casting systems

Info

Publication number: WO2002098587A2
Application number: PCT/EP2002/005768
Authority: WO
Inventors: Udo Falkenreck
Original assignee: Sms Demag Aktiengesellschaft
Priority date: 2001-06-01
Filing date: 2002-05-25
Publication date: 2002-12-12
Also published as: ATE283742T1; WO2002098587A3; AU2002344361A1; EP1412111A2; EP1412111B1

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

Process for setting dynamic soft reduction on continuous casting machines

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

During solidification in the strand, segregating elements such as C, P, Mn and especially S are excreted at the boundary between liquid and solid due to the saturation behavior in the solid state. As a result, the remaining melt is enriched with these elements. If no countermeasures are taken, there is a clearly measurable increase in concentration in the area of residual solidification, so that failures can occur during further processing.

A suitable countermeasure is the placement of the strand guide segments below the mold at a certain rate in order to unite strand shells that are growing towards one another. This process is known as soft reduction.

According to current knowledge, a certain rate of employment of the upper segment frame must be observed. If this cannot be guaranteed, A segregations occur in the area of residual solidification if the employment rate is too high or V segregations if the employment rate is too low.

The end of a segment is determined by the position of the tangent point of the last roles of the segment; consequently, the start of the next following segment is also set directly behind this pair of roles. The inclination (taper setting) of the upper segment frame is called the taper of the continuous casting machine (CCM). This consists of two sizes: the thermal conicity based on the shrinkage of the casting strand by cooling and solidification, and the soft reduction component, which is set separately. Unless otherwise expressly requested, the latter can also take the size "0".

If, for example, the strand guide consists of 14 segments, segments 0 to 7 are clamped to a stop, taking thermal conicity into account, and segments 8 to 14 (Cyberlink) are moved to a certain pre-selected jaw width depending on the CCM mode, taking into account the max , Forces that can be introduced into the segment.

Changes in the taper setting of the CCM can only be made when the strand is moving (Vc> 0 m / min.). When the casting machine is at a standstill, the active operating states are frozen.

The new values according to the following calculations must then be traced when the strand is pulled off again.

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

In level 2, the position of the swamp tip in the strand is calculated using a thermal tracking calculation (TTSR). TTSR is a thermodynamic calculation model for determining the temperature profiles in the strand during casting, taking into account the casting parameters.

In addition, a "liquid fraction" is determined via the material data records of the TTSR. In the liquid sump of the strand, the liquid fraction denotes the proportion between liquid and already solidified crystals. The value of this key figure lies between 0 and 1, where 0 is the location of the complete Solidification (Solidus) describes and 1 the position of the liquidus temperature in the strand.

The main variables in TTSR mode are:

- the casting speed Vc, the amount of water, the type of steel, the thickness of the strand in the casting machine.

The role plan and heat output of the mold are read in.

To simplify matters, the TTSR calculation assumes that the strand shell solidifies symmetrically on the inside and outside radius. The plane of symmetry is half the strand thickness.

The level 2 functions for soft reduction can be configured in the following ways:

a dialog with the keyboard for new entries and changes, via permanently saved patterns from this dialog, which are linked to the melt.

The "Thermal Taper" for the casting machine can be configured using the same mask.

The following values must be parameterized via a dialog menu:

Soft reduction rate [mm / m],

Liquid fraction fraction before solidification. In total, six different segment positions (quotas with a liquid fraction fraction) are to be entered to influence the top of the swamp.

The TTSR value for the liquid fraction calculated from this information indicates the intersection of the liquid fraction portion with the fictitious center line of the strand. This value is measured from the mold level in the mold in the direction of the flame cutting machine. The corresponding strand segment to which the specified quota is applied can then be determined from this parameter.

Under the known boundary conditions, the possibilities for parameterization may result in more than one result for the liquid fraction calculation in a segment. This is particularly likely to happen if the borders are very close to each other.

To solve such a conflict, TTSR searches from the point of complete solidification backwards towards the mold for the first intersection with the imaginary center line and determines the segment number. The search algorithm then jumps to the next segment (solid -1) and again determines the first liquid fraction intersection there. This continues until the end. The associated segment employment rates are set in analogy.

In order to avoid - particularly in borderline cases - the segments from being unnecessarily activated in the event of minor changes in the calculated peak, a change in the peak was assigned a "default" value. If the bottom of the sump changes in the direction of the last pair of rolls of the casting machine (if necessary) the segment position is changed when the new position is advanced by> 10 cm; in the opposite case, the segment setting is activated when the calculated swamp peak has been withdrawn by> 40 cm. Both values can be parameterized.

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

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

The data from the patterns or their changes accessible to Level 2 are converted into a telegram to Level 1, in which the current quotas for the employment of the segment 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 every 5 s about the current position of the mouth width of the segment output.

At this point it should be explicitly mentioned that the dimension for the mouth width at the segment exit (in level 1) is the same as the dimension for the mouth width at the entrance of the following segment.

While TTSR creates an image for calculating the casting machine in level 2 using a "CaDesign", level 1 is based on the information of the internal width of the outlet dimension of segment 7.

The segments in the horizontal part of the casting machine can be adjusted hydraulically to a predetermined size. According to the quotas, the mouth widths are approached by changing the position of the upper frame. The pre The quotas are given by level 2 automation, while the implementation of the mouth widths is regulated by level 1.

Since the segments with the exit roller at roller position 7 must also transfer the pull-out forces to the strand or cold strand, it must be ensured that the upper frame presses on the cold or warm strand with a minimum force.

If the upper segment of the segment cannot move to a certain predetermined position, because the guided strand in the segment builds up too much resistance to deformation, an upper force limit has been introduced to prevent the rollers, bearings or trusses from being damaged.

The regulation of the segment thus works in an operating window, which is determined by the minimum and maximum force, and under all circumstances ensures that the upper frame rests with the appropriate force on the loose side of the slab.

In order to ensure the strand support by the segments for as long as possible during the switching operations, a switching logic must be ensured.

Basically, the segment that contains the (calculated) solidus point is the last (based on the casting direction) to be assigned a soft reduction rate.

1. Start of casting

As long as the cold strand is not accessible to segments 8 to 14 immediately after casting starts, the segments are in the raised position. Only when the level 1 tracking system gives the command to clamp the last role of the Cyberlink segments, is the segment in the corresponding position moved downwards with the exit rollers; the applied force is now a function of the cold strand pressure.

As soon as the tracking system in Level 1 gives the command to relieve the approaching cold strand head, the corresponding upper segment frame is raised again.

After the head has passed, the segment lowers again. The force now pending corresponds to the hot strand pressure. As soon as TTSR calculates the swamp peak in the corresponding segment, the soft reduction driving style can also be activated after level 1 has been checked for plausibility.

If the corresponding boundary conditions are met, segment 8 is gradually lowered to the predetermined soft reduction position.

As soon as the two hydraulic cylinders at the end of segment 8 move into the new mouth width settings, the two hydraulic cylinders at the entry of segment 9 are also lowered with a time delay due to the switching time. After reaching the end position, the cylinders at the outlet of segment 9 are adjusted together with the cylinders at the inlet of segment 10, taking into account the thermal taper. This process takes place again taking into account the switching cycles between segment 9 end and segment 0 input.

All of the following segments 10 to 14 are gradually moved to the new lowered position in analogy.

As soon as the top of the sump leaves segment 8 and enters segment 9, TTSR must be based on the comparison with the liquid fraction calculation. decide whether only one segment is required for the soft reduction strategy or whether a second segment is to be charged with the soft reduction rate.

Only one segment receives soft reduction (swamp tip moves to the end of the caster)

After the calculation of the bottom of the sump shows that the solidification of the strand has migrated to the following segment 9, the segment 9 is also moved to the soft reduction rate after the liquid fraction has been compared. The following segments must be adjusted in the thermal taper.

As soon as the swamp tip has penetrated into segment 9 and the defined liquid fraction part has left segment 8, the mouth widths of segment 8 exit together with segment 9 entry are moved into the new position that corresponds to the thermal taper of segment 8 - speaks; this means that segment 9 initially experiences a higher employment rate. When the transition of segments 8 and 9 is in the desired position, the soft reduction rate of segment 9 can be set to the selected value.

The following segments are to be moved in the thermal taper setting as already described.

This process is repeated analogously for the following segments.

3. Several segments receive soft reduction (swamp tip moves to the caster end or reaches steady state)

First, the segments are switched as already described in section 2 in the first paragraph.

As the swamp tip advances further, the processes are switched analogously to the second and third sections. If it becomes necessary to reduce the number of soft reduction segments as a result of the casting constraints, as the Vc increases, the transition between the segments that are closest to segment 7 is first moved into the new mouth width.

The position is then retained as a result of the TTSR calculation. This also corresponds to the steady state.

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

If the swamp tip moves back towards the mold due to changed casting parameters (such as a reduction in the Vc), the grouping of the segment position is triggered when the switching point is undershot.

Assuming first that the area of the liquid fraction retreats parallel to the swamp tip, the number of soft reduction segments in engagement must remain the same; i.e. that the sum of the segments remains the same and is shifted parallel in the mold direction.

For this purpose, the entry of segment j (old) from which the swamp tip has migrated, together with the exit of segment j (new) in which the tip is currently located, is reduced to the internal width dimension that the thermal taper of segment j ( alt) corresponds if you extrapolate the taper position from the CCM end.

The employment rate of segment j (new) is now greater than specified. To change this, the interface j (new) input and j (new) -1 output must be adapted analogously. This process is repeated until the soft reduction segments cover the entire area again. 5. Several segments receive soft reduction (swamp tip moves towards the mold, the liquid fraction area becomes smaller)

If it turns out after the end of this new employment that the number of soft reduction segments has to be reduced, the mouth width of the segment must be set to thermal taper that is closest to segment 7. The quota of the segments following towards the end of the CCM will be reset as described in Section 3.

6. Several segments receive soft reduction (swamp tip moves towards the mold,

Liquid Fraction area is below segment 8)

A similar process as described in the previous section takes place when the liquid fraction setting goes back to segment 7.

Here too, the excessive segment employment rate has to be readjusted by reversing the direction.

It goes without saying that the new strand thickness must be adapted in each case up to segment 14 in accordance with the segment positions.

7. Multiple segments receive soft reduction (Soft Reduction area grows)

When the position of the swamp tip returns to a steady state after the strand has accelerated, it often happens that the position of the area also adjusts with the liquid fraction setting. This adjustment can then be done by expanding the number of segments used for the soft reduction.

Since segment j with the swamp tip is the last soft reduction segment, a correction will be made in each case via additional soft reduction segments between segment 7 and segment j. For this purpose, the last segment (jn), which is located before the previous soft reduction section, is inserted from the thermal taper setting into the soft reduction taper (mouth width at the segment exit of the newly activated segment jn becomes smaller); at the same time, as already known, the segment (jm) next to jn in the mouth width that is closest to the swamp tip is also set.

As soon as the end position at j-m is reached, the mouth width of the segment exit j-m is adjusted according to the soft reduction taper.

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

In addition, the segments between j and the end of the caster are adapted to the new slab thickness, taking thermal tapers into account.

If a further correction is necessary, the sequence described must be repeated.

8. Multiple segments receive soft reduction

(Soft reduction area becomes smaller in steady state)

In this case, the travel scheme as described in section 5 applies.

9. Compound casting

The cases described above are used for composite casting without the use of a "separator".

If the composite casting is carried out with a "separator", TTSR first calculates the change in the bottom of the sump and leaves the segment frame as it is switch for a long time until either the sump tip has returned to segment 7 or the extractor has stopped for the flying distributor change.

According to the definition, the state now reached is frozen.

After the restart, the old swamp seats are negated (if they should be there); segments 8 to 14 are moved into the thermal taper.

As soon as the new swamp tip leaves segment 7 again, the processes described proceed as in the case of a casting start according to number 1.

10. Pouring

If the pouring end is initiated, TTSR first calculates the change in the bottom of the sump and lets the segment frames switch until either the bottom of the sump has run back into segment 7 or if the extractor is stopped for slagging. According to the definition, the state now reached is frozen.

If no standstill for slagging is practiced, the segment positions are frozen in the last position with the command "End of pouring (or discharge)".

The soft reduction driving style is switched off when the level 1 tracking system gives the command to lift the upper segment frame.

The method described above for setting the dynamic soft reduction can be used not only with conventional slabs, but also with so-called thin slabs.

Claims

claims

1.Procedure for setting the dynamic soft reduction in continuous casting plants, in particular when continuously casting slabs, characterized in that the position of the bottom tip and the proportions of solid and liquid in the casting strand are calculated and one or more segments of the strand guide are adjusted in accordance with the changes in position of the bottom tip become.

2. The method according to claim 1, characterized in that a thermodynamic computing model for determining the temperature profiles in the strand during casting is used to calculate the position of the sump tip.

3. The method according to claim 1 or 2, characterized in that in the computing model essential casting parameters such as casting speed V _c the amount of cooling water - the type of steel the thickness of the strand in the casting machine

Heat output of the mold

Role plan of the strand guide or the like

be taken into account.

4. The method according to one or more of claims 1 to 3, characterized in that when the bottom of the sump is changed in the direction of the last pair of rollers of the casting machine, the segment position is changed when the new position is advanced by> 10 cm, and in the opposite case, the segment setting is activated when the calculated swamp tip has been reduced by> 40 cm.

5. The method according to one or more of the preceding claims, characterized in that the position of the sump peak is calculated in predetermined cycles by means of the thermodynamic computing model.

6. The method according to claim 5, characterized in that the change in the position of the segments per cycle is limited to a default value.