DE10141128A1 - Adjusting the dynamic soft reduction in continuous casting plants comprises calculating the position of the tip of the liquid phase and components in the casting strand, and adjusting segments of the strand guide accordingly - Google Patents

Abstract

Adjusting the dynamic soft reduction in continuous casting plants comprises calculating the position of the tip of the liquid phase and the solid and liquid components in the casting strand; and adjusting one or more segments of the strand guide according to the position changes of the tip of the liquid phase. Preferred Features: A thermodynamic arithmetic model for determining the position of the tip of the liquid phase in the strand during casting is used to calculate the position of the tip of the liquid phase.

Description

The invention relates to a method for setting the dynamic soft reduc tion on continuous casting plants, especially when continuously casting slabs.

During the solidification in the strand on the border between liquid and Fixed elements such as C, due to the saturation behavior in the solid state, P, Mn and especially S excreted. This enriches the remaining one Residual melt with these elements. No countermeasures are taken fen, there is a clearly measurable concentrate in the area of residual solidification on increase so that failures can occur during further processing.

An effective countermeasure is the employment of the strand guide segments below the mold at a certain rate to grow together To combine strand shells with each other. This process is known as Soft reduction.

According to current knowledge, a certain employment rate of the Upper segment frame are observed. If this cannot be guaranteed, then A segregations occur in the area of residual solidification if the employment rate increases is large 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 determined roles of the segment; consequently is immediately behind this The beginning of the next segment.

The slant (taper setting) of the segment upper frame is called taper the continuous casting machine (CCM). This consists of two sizes together: the thermal conicity based on the shrinkage of the casting strand through cooling and solidification, as well as the soft reduction portion is set separately. The latter can, if not expressly different is required to 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 if the strand is moving (Vc <0 m / min.). When the casting machine stops, who which the currently active operating states are frozen.

The new values after the following calculations must then be understood when the strand is pulled off again.

The adjustment strategy for setting up the new boundary conditions is described in the fol mentioned 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 computing 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, whereby 0 describes the position of the complete solidification (Solidus) 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 the calculation of the TTSR, it is assumed that the strand shell solidifies symmetrically on inner and outer 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 using the keyboard for new entries and changes, via fixed saved patterns from this dialog, which are coupled to the melt are.

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

The following values must be parameterized via a dialog menu:

• - soft reduction rate [mm / m],
• - Liquid fraction fraction before solidification.

In total, the entry of six different segment positions (Quotas with a liquid fraction fraction) to influence the bottom of the swamp hen.

The TTSR value calculated from this information for the liquid fraction denotes net 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 towards on the flame cutting machine. This can then correspond to this parameter appropriate strand segment can be determined, be with the specified quota is opened.

With the possibilities for parameterization it can be under the well-known Randbe conditions that there is more than one result for the Liquid fraction calculation lies. This is particularly likely to happen when the borders are very close to each other.

To resolve such a conflict, TTSR searches from the point of the complete Solidification from backwards towards the mold after the first Intersection with the imaginary center line and determines the segment number. because after the search algorithm jumps to the next segment (Solidus -1) and be again agrees with the first Liquid Fraction intersection there. This sets  progressed to the end. The associated segment employment rates are in analog set.

To avoid - especially in borderline cases - the segments at low Subsequent changes in the calculated swamp peak unnecessarily driven who , the change in the bottom of the sump was assigned a "default" value. at a change in the top of the swamp towards the last pair of rollers Casting machine (if necessary) the segment setting is changed when the new position is advanced by ≧ 10 cm; in the opposite case Segment setting activated when the calculated swamp peak turns ≧ 40 cm has been withdrawn. Both values can be parameterized.

The TTSR calculation is initiated in a short rhythm of, for example, 10 s ß, 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 be 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 rate per cycle was limited to 0.2 mm / m advantage.

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 information about 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 level. According to the quotas, the mouth widths are approached by changing the position of the upper frame. The quotas are specified 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 also have to transfer the pull-out forces to the strand or cold strand, it must be ensured that the upper frame presses with a minimum force on the cold or warm strand.

Can the segment upper frame not start a certain predetermined position ren because the guided strand in the segment has too great a deformation resistance builds up, an upper force limit is introduced, which is to prevent Rol oil, bearings or trusses are damaged.

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

To the strand support through the segments even during the switching operations To ensure the longest possible period of time, a switching logic si be made.

Basically, the segment that contains the (calculated) solidus point last, with respect to the casting direction, with a soft reduction rate is occupied.

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 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 10 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 decide on the basis of the comparison with the liquid fraction calculation whether only one segment is required for the soft reduction strategy or whether a second is applied with the soft reduction rate ,

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

After the calculation of the sump peak shows that the solidification of the strand has migrated to the following segment 9 , 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 are first moved into the new position, which is the thermal taper of segment 8 corresponds; 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 in the thermal taper setting as before described procedure.

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 in section 2 in the first Paragraph already described.

As the swamp tip advances, the processes become analogous to the two th and third section switched.

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 then corresponds to the steady state.

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

Moves through changed casting parameters (such as a decrease in Vc) the bottom of the swamp back towards the mold, will fall below the Switching point triggered the regrouping of the segment position.  

First assume that the area of the liquid fraction is parallel to the Withdrawing the swamp tip, the number of Soft Reducs in the tion segments remain the same; d. H. that the sum of the segments remains the same and is moved parallel in the mold direction.

For this, the entry of segment j (old), from which the bottom of the swamp emerges migrates, together with the exit of segment j (new), in which the Tip is currently located, reduced to the internal width that the Thermal Ta corresponds to the segment j (old) if you move the taper from the CCM end extrapolated.

The employment rate of segment j (new) is now greater than specified. To do this the interface j (new) input and j (new) -1 output analog be adjusted. This process is repeated until the soft reduction Cover the entire area again.

5. Multiple 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, the 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 .

Again, the excessive segment employment rate must be reversed Direction can be adjusted again.

It goes without saying that the new strand thickness must be adjusted according to the segment positions up to segment 14 .

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

If the position of the swamp tip in after the acceleration of the strand reaches a steady state, it happens more often that the location of the Area with the Liquid Fraction setting. This adjustment can then be done by expanding the number of segments required for Soft Re duction is used.

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, the last segment (y-n), which was before the previous Soft Reduction Ab from the Thermal Taper setting in the Soft Reduction Ta hired by (mouth width at the segment exit of the newly activated segment y-n gets smaller); at the same time, as already known, the nearest to the swamp tip segment (j-m) next to j-n in the mouth width.

As soon as the end position at j-m is reached, the mouth width of the seg ment exit j-m adjusted according to the Soft Reduction Taper.  

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

In addition, those between j and the caster end Segments to the new slab thickness taking into account the thermal Ta customized.

If a further correction is necessary, the sequence described is closed to repeat.

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

In composite casting without the use of a "separator" they come before written cases for application.

If the composite casting is carried out with a "separator", 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 returned to segment 7 or the pulling machine for the flying distributor change has stopped.

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 described processes run 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 pull-out machine is stopped for slagging.

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

If there is no standstill for slagging, the segments positions with the command "pouring (or conveying)" in the last position frozen.

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

The procedure described above for setting the dynamic soft reduc tion is not only applicable to conventional slabs, but also to such called thin slabs.

Claims (6)

1.Procedure for setting the dynamic soft reduction in continuous casting plants, in particular in the continuous casting of 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 in accordance with the changes in position of the bottom tip be adjusted. 2. The method according to claim 1, characterized, that to calculate the position of the swamp tip a thermodynamic Calculation model for determining the temperature profiles in the line during of casting is used. 3. The method according to claim 1 or 2, characterized in that in the computing model essential casting parameters such
Casting speed Vc
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, that if the bottom of the swamp changes in the direction of the last roller pair of the casting machine then changed the segment setting when the new layer is advanced by ≧ 10 cm, and vice versa If the segment setting is activated when the calculated Swamp tip has been withdrawn by ≧ 40 cm. 5. The method according to one or more of the preceding claims, characterized, that by means of the thermodynamic calculation model the position of the swamp peak is calculated in predetermined cycles. 6. The method according to claim 5, characterized, that changing the position of the segments per cycle to a default Value is limited.