EP0325931B1 - Method and apparatus for the oscillation of a continuous-casting mould - Google Patents

Description

The invention relates to a method and a device for oscillating a continuous steel casting mold according to the preambles of claims 1 and 9.

In continuous casting, in particular in the continuous casting of steel, continuous molds are oscillated in order to introduce lubricant between the strand crust and the mold wall, as a result of which sticking of the strand crust is to be avoided or reduced.

Various oscillation devices and oscillation methods have been proposed for continuous steel casting. Mechanical oscillation drives with sinusoidal motion characteristics have found wide application. The sinusoidal oscillation movement has proven itself well at low and medium casting speeds. From DE-AS 2'002'366 it is known with an adaptation of sinusoidal oscillatory movements to high speeds to increase the lifting height in proportion to the line withdrawal speed. However, other literature also suggests increasing the frequency as a function of the line withdrawal speed. If the movement ratios between a sinusoidal mold movement and a moving strand crust are transmitted proportionally at high strand withdrawal speeds, for example between 2 and 6 m / min, either a correspondingly long stroke or a correspondingly high frequency or a combination of an enlargement of both design parameters can be selected. With this type of strand oscillation, it was not possible to achieve satisfactory results, particularly in the case of strand qualities which are difficult to cast, so-called adhesive grades.

In addition to the sinusoidal oscillation movement, other oscillation movements have also become known, for example, in JP-OS 61-162 256. These non-sinusoidal oscillatory movements usually have an uneven time ratio between the down and up stroke, e.g. 1: 3. In the path-time diagram, such oscillations have a sawtooth-shaped movement line. The drive can take place via hydraulic or equivalent power devices. Such non-sinusoidal oscillation drives are easily adjustable in terms of stroke and frequency. Nevertheless, the quality of the strand surface with regard to oscillation marks, strand breakthroughs in the mold at high casting speeds, in particular in the case of steel qualities known as adhesive grades, is still unsatisfactory.

The invention is therefore based on the object of providing an oscillation method for continuous steel casting which on the one hand improves the strand surface with respect to oscillation marks or reduces surface defects and at the same time permits great variability in the strand pull-out speed during casting and while a casting is in progress. In addition, it should also be possible to produce adhesive grades with an improved strand surface and, with a high level of breakthrough security, casting speeds adapted to the casting cycle. Furthermore, casting speeds should be made possible which go beyond the state of the art, e.g. 2 - 6 m / min for slabs or 4 - 10 m / min for billets and thin slabs.

This task is accomplished with the features of claim 1 or of claim 9 solved.

The oscillation method according to the invention or the Oszil Lation device enable continuous casting with an improved strand surface, in particular if the strand pull-out speed has to be varied for procedural reasons or, for example, by predetermined cycle times in connection with the steel production. The formation of oscillation marks is reduced. Steel grades known as glue grades tend to reduce the tendency to crack in the oscillation marks in combination with appropriate lubricants. Starting breakthroughs (bleedings) within the mold or breakthroughs outside the mold can be reduced. The extrusion speeds known as casting speeds can be increased far beyond the conventional range with this method.

gewählt und n < 0,5, K = 100 - 200 cpm eingesetzt wird. Die Oszillationsfrequenz kann dabei im ersten Bereich unter Beibehaltung der Hubhöhe hochgefahren werden.The oscillation frequency can be gradually increased in the first area with the increasing strand withdrawal speed. According to a further process example, the oscillation frequency of approximately 60-120 strokes per minute can be increased proportionally to 120-200 strokes per minute in the first area, with a proportionality f = K · V $\genfrac{}{}{0ex}{}{\text{n}}{\text{c}}$

selected and n <0.5, K = 100 - 200 cpm is used. The oscillation frequency can be raised in the first area while maintaining the lifting height.

An essential feature of the non-sinusoidal oscillation is the widely variable speed of the mold up and down movement within an oscillation cycle or within a certain stroke height. In the sense of a further process example, it is recommended to increase the oscillation frequency in the first area while maintaining the lifting height between 2 mm and 5 mm and in the second area to increase the lifting height between 2 and 12 mm in proportion to the line withdrawal speed.

As an additional limitation, a negative strip time t _N = 0.1-0.2 t _{c is} proposed in the first area, where t _{c represents} the time for an oscillation cycle.

vorgeschlagen und die Negativstripzeit t_N nach folgender Gleichung eingestellt: $${\text{t}}_{\text{N}}{\text{= 0,2 - 0,33 t}}_{\text{c}}$$

wobei t_c die Zeit für einen Oszillationszyklus beträgt.In the second area, the frequency ratio is kept at a constant frequency in the sense of additional process examples $$\frac{\text{Mold downward speed}}{\text{Strand withdrawal speed}}\text{=}\frac{{\text{V}}_{\text{N}}}{{\text{V}}_{\text{c}}}\text{= 1.02 - 1.10}$$

proposed and the negative strip time t _{N set} according to the following equation: $${\text{t}}_{\text{N}}{\text{= 0.2 - 0.33 t}}_{\text{c}}$$

where t _{c is} the time for an oscillation cycle.

• Fig. 1 ein Weg-Zeit-Diagramm einer sägezahnartigen Oszillationsbewegung,
• Fig. 2 ein Geschwindigkeits-Zeit-Diagramm gemäss der Oszillationsbewegung von Fig. 1,
• Fig. 3 ein Frequenz-Strangabzugsgeschwindigkeits-Diagramm,
• Fig. 4 ein Hubhöhe-Strangabzugsgeschwindigkeits-Diagramm
• Fig. 5 eine schematische Darstellung einer Oszillationseinrichtung.

In the following, the invention is to be further explained using diagrams and process examples. Show it:

• 1 is a path-time diagram of a sawtooth-like oscillation movement,
• 2 shows a speed-time diagram according to the oscillation movement of FIG. 1,
• 3 is a frequency-strand withdrawal speed diagram,
• Fig. 4 is a lifting height-strand withdrawal speed diagram
• Fig. 5 is a schematic representation of an oscillation device.

To explain a sawtooth-like oscillation movement of a continuous casting mold, an oscillation cycle t _{c is} shown in FIG. 1 in the path-time diagram. H is the lifting height and t is the time. In Fig. 2 is dash-dotted with V _{c on} the same time scale Line withdrawal speed, with V _N the mold downward speed, which is substantially greater than V _c during the entire downward stroke, and with V _P the mold upward speed, ie during the upward stroke. A time period t _N represents the negative strip time and a time period t _P the positive strip time. During the time period t _N , the solidifying strand crust is subjected to a compressive stress and during the time period t _{P to} a tensile stress. In FIG. 3, a frequency range f in cpm (cycles per minute) is shown in a hatched field as a function of different line pull-out speeds. This frequency range includes the frequencies according to the invention for different steel qualities. Along the boundary line marked x, the frequencies for steel grades with strong adhesive properties, or in other words, with a weak strand shell lie in the area of the bathroom mirror. These steel grades are also referred to as "adhesive grades".

Along the boundary line denoted by y in Fig. 3 are the frequencies for steel grades with pronounced indentation and oscillation mark formation, i.e. these steels already form a strong strand shell in the area of the bathroom mirror, and thereby receive deep oscillation marks or depressions.

A steel from the group of adhesive grades is oscillated in the area 1 (indicated by the dimensional arrow) along the boundary line x, ie up to a strand withdrawal speed between 0.1 and approximately 1.2 m / min between 60 and 120 strokes per minute (cpm). In area 2, ie at a line withdrawal speed from approximately 0.8-1.2 m / min, the oscillation frequency f remains constant at approximately 120 strokes per minute. As can be seen from FIG. 4, in region 2 the lifting height h is, for example, proportional to the strand withdrawal speed between 2 and 20 mm, preferably between 4 and 10 mm increased at constant oscillation frequency. The negative strip time t _N is approximately 0.1 seconds in areas 1 and 2.

In the case of a steel quality with pronounced oscillation mark formation, the frequency is increased in the area 1 along the boundary line y in the area 1 from 0.1 m / min to approximately 1.2 m / min from 120 to approximately 200 strokes per minute. In area 2, ie at line withdrawal speeds above approximately 1.2 m / min, the frequency f remains constant at approximately 200 strokes per minute. As can be seen from FIG. 4, the lifting height in area 2 is increased, for example, in proportion to the strand withdrawal speed between 2 and 10 mm, preferably between 2 and 8 mm at a constant oscillation frequency. The negative strip time t _N is in the order of 0.1 seconds in the areas 1 and 2. The negative strip time t _N is further set in the first area to values between 0.1 and 0.2 t _c , where t _{c is} the time for represents an oscillation cycle. In area 2 with strand pulling speeds above approximately 1.2 m / min, the negative strip time t _N = 0.2-0.33 t _c .

5, a mold is suspended from two short levers 6 and 7 at 5 and guided in its oscillating movement according to arrow 8. 10 shows a raised foundation or a corresponding steel structure. The short lever 7 is connected at its extension 9 to a hydraulic oscillation drive 11, only shown schematically. A controller 12 ensures that the oscillation frequency f and the lifting height h of the oscillation drive 11 are set according to the program during the casting operation according to the stored programs in the computer 14. From the hydraulic control 12 is feedback 21 about the lau The measured oscillation force determined the friction in the mold 5 and compared it with a predetermined friction value 22 in the discriminator 15. Using the comparison signal 23 obtained, the setting of the negative strip time t _N and the ratio t _N to t _c , the lifting height, the frequency etc. can be continuously optimized in the predetermined frame. The friction can also be measured directly on the mold or on the lever arms of the oscillation drive using known devices, such as accelerometers, pressure gauges and / or strain gauges, and a combination of these measuring devices.

In the sense of an additional alternative, the mold 5 can be provided with a known breakthrough warning device 25. A signal 26 of the breakthrough warning 25 can directly influence the strand pull-off speed via a controller 18 and thereby prevent a strand breakthrough.

Claims (10)

1. Process for oscillating a continuous steel casting mould by means of an oscillation device, with the stroke length being adjusted in dependence upon the strand withdrawal speed, characterised in that during a saw-tooth oscillating movement the mould outruns the strand during substantially the entire downward movement and in a first region (1) at low strand withdrawal speeds up to around 0.8 - 1.2 m/min the oscillation frequency is raised from about 60 - 120 strokes per minute at the start to 120 - 200 strokes per minute while retaining a negative strip time t_N of around 0.1 s, and that upon a further increase in the strand withdrawal speed above 0.8 - 1.2 m/min in a second region (2) the oscillation frequency is held constant and the stroke length is increased in dependence upon the strand withdrawal speed while retaining the negative strip time t_N of around 0.1 s.

2. Process according to claim 1, characterised in that in the first region the oscillation frequency f is raised from around 60 - 120 strokes per minute at the start in proportion to the strand withdrawal speed to 120 - 200 strokes per minute, with the proportionality f = K . V $\genfrac{}{}{0ex}{}{\text{n}}{\text{c}}$

with n < 0.5 being selected.

3. Process according to claim 1 or 2, characterised in that in the first region the oscillation frequency is raised while retaining the stroke length.

4. Process according to one of claims 1 to 3, characterised in that in the first region the oscillation frequency is raised while retaining the stroke length between 2 mm and 5 mm.

5. Process according to one of claims 1 to 4, characterised in that in the first region the negative strip time t_N = 0.1 - 0.2 t_c, in which t_c is the duration of one oscillation cycle.

6. Process according to one of claims 1 to 5, characterised in that in the second region the stroke length is increased in proportion to the strand withdrawal speed between 2 and 12 mm.

7. Process according to one of claims 1 to 6, characterised in that in the second region the casting speed ratio is $$\frac{\text{mould downward speed}}{\text{strand withdrawal speed}}\text{=}\frac{{\text{V}}_{\text{N}}}{{\text{V}}_{\text{c}}}\text{= 1,02 - 1,10}$$

8. Process according to one of claims 1 to 7, characterised in that in the second region the negative strip time t_N is $${\text{t}}_{\text{N}}{\text{= 0.2 - 0.33 t}}_{\text{c}}$$

in which t_c represents the duration of one oscillation cycle.

9. Apparatus for effecting the process according to one of claims 1 to 8, with an oscillation device for a continuous steel casting mould (5) being provided with frequency and amplitude adjusting devices and having a drive (11) for a saw-tooth oscillation characteristic and a guide device for the oscillating movement, characterised in that the oscillation device is connected to a computer control unit (12) and the computer has oscillation programs for a first and second region stored for different steel grades, casting speeds, and that a differential connection compares the actual value of friction measured between strand and mould with the stored setpoint value of friction and continuously checks the oscillation programs with a view to minimising the actual friction value.

10. Apparatus according to claim 9, characterised in that the guide device for the oscillating movement comprises two short levers (6, 7), of which one lever (7) is connected to a hydraulic oscillation drive.

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