EP2188403B1 - Process and hot-dip coating system for stabilizing a strip guided between stripping dies of the hot-dip coating system and provided with a coating - Google Patents

Abstract

The invention relates to a process for stabilizing a strip guided between stripping dies of a hot-dip coating system and provided with a coating, and also to a corresponding hot-dip coating system. In this context, stabilizing forces are exerted on the strip on the basis of the detected strip position by means of spools which are arranged downstream of the stripping dies in the strip running direction and act electromagnetically and in a contactless fashion on the steel strip running through. In order to improve the stabilization of the strip in the region of the stripping die, the invention proposes that the distance between the line of action of the strip-stabilizing device and the stripping dies be adjusted to a value ≤ a distance threshold value which is determined as a function of the strip width taking into account a factor Phi, wherein the factor Phi is calculated as a function of the strip thickness and the strip tension.

Description

The invention relates to a method for stabilizing the strip of a tape provided with a coating between stripping nozzles of a hot-dip coating plant and a corresponding hot-dip coating installation. In this case, by acting in the strip running direction downstream of the stripping nozzles electromagnetically contactless acting on the continuous steel strip coils stabilizing forces in accordance with the detected tape position on the tape.

Electromagnetic band stabilizers are based on the principle of induction, in order to generate attractive forces perpendicular to the ferromagnetic steel strip by means of defined magnetic fields. Thus, the position of the steel strip between two opposite electromagnetic inductors (electromagnets) can be changed without contact. Such systems are known in different types. They are used, for example, in hot-dip coating plants in the coating area above the so-called wiping nozzles. Different regulation. and control concepts are known (e.g. DE 10 2005 060 058 A1 . WO 2006/006911 A1 . WO 02/14572 A1 ).

Wiping nozzles are used in hot-dip coating plants for steel strip to obtain a defined amount of coating medium on the strip surface. The quality of the coating (uniformity of application, layer thickness accuracy, homogeneous surface gloss) depends to a large extent on the uniformity of the wiping medium (eg air or nitrogen) as well as on the band movement in the nozzle area. The belt movements are caused by non-circularity of roles or eg by pulse effect of the air in the cooling tower area of hot dip finishing plants.

As the strip movement in the stripper nozzle increases, the coating quality or uniformity of the coating of the continuous steel strip is reduced.

The use of belt stabilization systems connected downstream in the belt running direction can damp or reduce a belt movement occurring within the scraping nozzle, so that an improvement in the coating accuracy and coating uniformity of the liquid metal on the steel belt is achieved. This can z. B. electromagnetically acting actuators exercise the non-contact attractive forces on the continuous steel band and thus change the band position.

In the known systems, due to the type in the strip running direction of the stripper downstream band stabilization results in a reduced effect of the regulation on the band movement in the scraper. The settling of the vibrations takes place above the wiping nozzle within the band stabilization by means of the band stabilization coils with high efficiency. In the area of the nozzle, however, the effect is clearly limited with increasing distance between it and the stabilization unit. The position of the strip stabilization is determined according to the structural conditions, without describing the physical dependencies.

Therefore, the goal of all applications is to position the belt stabilization as close as possible to the wiper nozzle, ignoring the relationship between distance and effect.

The object of the invention is therefore to improve the strip stabilization in the region of the wiper.

This object is achieved according to the invention with the method according to claim 1. This is characterized in that the distance (the effect) of the band stabilization of the wiping nozzles is set to a value equal to a distance threshold value, which as a function of Bandwidth is determined taking into account a factor Phi, wherein the factor Phi is calculated as a function of the strip thickness and the strip tension.

In the context of the present description, the measured quantity strip position represents the temporal and / or local change of the distance of the strip with respect to a straight reference line transversely to the strip running direction; that is, the tape position represents the tape profile and / or its vibration behavior as a function of time.

The term strip stabilization encompasses two essential aspects in the context of the present description: On the one hand, strip stabilization means smoothing of a wave-shaped strip profile, and on the other hand, this term means damping of vibrations of the strip. Both aspects of band stabilization can be implemented independently or in combination or simultaneously with the aid of suitable control circuits.

The essential advantage of the claimed limitation of the distance can be seen in the fact that when the distance is set to a value below the distance threshold value that can be calculated according to the invention, a significantly better effect is achieved for both aspects of the desired band stabilization. In contrast, the effect of band stabilization at intervals above the distance threshold decreases significantly or the band is despite stabilization even more unstable than without control (opposite effect).

Ideal would be a distance of zero, that is, if the band stabilization at the level of the scrapers would be arranged, because then the band stabilization would act directly at the level of the stripping and the tape would then held optimally stable during a measurement process. However, this arrangement is structurally not feasible due to lack of space in the rule. Therefore, the distance should be as small as possible, but maximally set to the value of the distance threshold value which can be calculated according to the invention.

The electromagnetic forces are applied by on each band side in pairs opposing coil assemblies whose distance from the wiping nozzles is changeable.

In the method according to the invention, the band position within the coil arrangement is preferably measured, specifically in the spatial vicinity of the coil arrangement.

In addition, the tape position above and below the coil assembly can be measured.

According to one embodiment of the invention, a plurality of coils are arranged on each band side, wherein the respective outer coils are arranged to be adjustable on the continuous band edges parallel to the plane of the band. This arrangement advantageously allows an optimum effect in the smoothing of the strip profile.

The distance of the belt stabilization device, hereinafter also abbreviated to belt stabilization, of the wiping nozzles should not exceed their bandwidth for wider belts (B> 1400 mm). For narrower bands (B <1400 mm), a margin of up to 1.75 times the bandwidth can be allowed. This distance results from the principle of Staint-Venant, which states that with increasing distance of an attacking force on z. B. a clamped steel strip whose effect on the overall state decreases.

The basis for the solution according to the invention is the positioning of the strip stabilizer to the wiping nozzle or the wiping nozzles, taking into account the stress mechanism.

The effect of a punctual load attack in a given load system results according to the principle of Saint Venant only in a small area around the load intervention point. The force distributions, which are locally irregular due to the introduction of forces, are very rapid. This principle is used as standard in strength calculations for component dimensioning and is applied here to the strip stabilization effect in the stripping nozzle area.

mit $$\mathrm{Phi}=\mathrm{Funktion}\left(\mathrm{Banddicke},\mathrm{Bandzug}\right)$$

In order to achieve a sufficient effect in the scraper on the strip profile and the belt movement (vibration) to significantly alter or dampen them, must be selected in accordance with the principle of Saint-Venant, the distance between the stabilizing effect and the scraper in a specified range or shall not exceed a maximum value in the form of a distance threshold value, the distance, ie the length of steel strip, in which an effect due to strip stabilization is to be expected shall be chosen in accordance with the following rule: $$\mathrm{distance}\le \mathrm{Distance\; threshold}=\mathrm{Phi}*\mathrm{characteristic\; length}$$

With $$\mathrm{Phi}=\mathrm{function}\left(\mathrm{strip\; thickness},\mathrm{Bandzug}\right)$$

The above object is further achieved by the claimed hot dip coating equipment. This is characterized in that the distance (effect) of the strip stabilization from the wiping nozzles is set to a value less than or equal to a distance threshold determined as a function of the bandwidth taking into account a factor Phi as a function of strip thickness and strip tension.

The advantages of this system correspond to the advantages mentioned above with reference to the claimed method.

Further advantageous embodiments of the invention are the subject of the dependent claims, in particular of claims 5-8 and 14th

The solution according to the invention will be explained in more detail below - also with reference to the drawings.

Fig. 1

schematisch die Anordnung der Bandstabilisierungsspulen,

Fig. 2

die Profilierungen des Bandes,

Fig. 3

schematisch die Anordnung der Düsenbalken,

Fig. 4

das Bandstabilisierungssystem,

Fig.5

die Abhängigkeit des Faktors Phi von der Bandbreite und

Fig.6

den Zusammenhang zwischen Bandschwingungen und dem Abstand der Bandstabilisierung von der Abstreifdüse.

Showing:

Fig. 1

schematically the arrangement of the band stabilizing coils,

Fig. 2

the profiles of the band,

Fig. 3

schematically the arrangement of the nozzle bars,

Fig. 4

the belt stabilization system,

Figure 5

the dependence of the factor phi on the bandwidth and

Figure 6

the relationship between belt vibrations and the distance of belt stabilization from the wiper.

The arrangement of the belt stabilization and the wiper nozzle is in principle from the FIG. 4 seen.

The distance threshold results according to the principle of Venant for continuous wide steel bands to about the bandwidth and for narrower bands to max. 1.75 times the bandwidth (see FIG. 5 ). At a greater distance is the effect of the band stabilization with respect to a smoothing of the band profile (transverse arc, S-shape, see Fig. 2 ) very limited or no longer recognizable at long distances.

The force application point of the band stabilization is then too far away from the nozzle lip to a sufficient effect on the band deformations such. B. exercise reduction of the transverse bow.

Furthermore it could be proven by measurements and simulations that the vibration influence (damping of the amplitude of the band vibration) In the nozzle gap also depends on the distance of the point of application of force to Wirkstelle nozzle gap.

This results in the following relationship: $$\mathrm{distance}\le \mathrm{Phi}\left(\mathrm{strip\; thickness},\mathrm{Bandzug}\right)*\mathrm{bandwidth}=\mathrm{Distance\; threshold}\mathrm{,}$$

Depending on the strip tension and the strip thickness, the factor Phi was investigated and determined both analytically by means of FEM simulations and empirically on strip processing lines. In Fig. 5 the connection is shown. As the bandwidth decreases, the potential gap between the belt stabilizer and the scraper nozzle increases (see FIG. 4 ), because due to the reduced bandwidth, an asymmetrical stress distribution or a non-optimal wavy band profile has less adverse effect on the band stabilization. Due to differences in tension over the strip thickness, elastic deformations result. The stress over the sheet thickness has an effect above a limit value in the form of strip transverse deformation (transverse arc).

Local changes in the stress distribution over the sheet thickness due to the external force influence of the belt stabilization are seen, depending on the functional curve shown, up to a distance of 0.75 to 1.75 times the belt width direction.

If vibrations of the steel strip due to z. B. out of round run of the stabilizing roll in the zinc vessel, then achieved with a control for band stabilization, a reduction of the band oscillation against a situation without band stabilization control, if the distance of the band stabilization of the scraper typically max. 1.5 m from the nozzle gap. How out FIG. 5 can be seen, the distance threshold of about 1.5 m results for many different typical bandwidths. If the belt stabilization is farther away from the wiper nozzle than this distance threshold value, then the vibrations in the area of the wiper nozzle no longer occur attenuated, but can even be excited, which, despite vibration damping in the area of strip stabilization, leads to an increase in strip movement within the stripper nozzle and thus to a reduction in coating quality ( Fig. 6 ).

The same applies to the stabilization / smoothing of the strip profile. At distances below the distance threshold, a good smoothing is achieved, beyond which smoothing becomes difficult or no longer possible.

Furthermore, the following device is provided for combining the strip stabilization with the wiping nozzle, in which the strip stabilizing coils always act towards the centered strip layer:

Compared to the known systems, the stabilization must be respectively aligned to the band position and the actual position must be determined. The alignment is done by means of specially mounted alignment aids.

Due to the special frame construction of the wiper nozzle, the stabilization is mounted on this frame and is thus mechanically fixed and reproducibly adjustable ( Fig. 3 ). The centering on the band position or band center is therefore always identical between stabilization and the scraper nozzle.

This is followed by a possible rotation of the tape during production and it is not necessary to redetermine the zero position or the desired position of the tape layer. Wiping nozzles and stabilizing coils are mechanically synchronized and aligned!

1. 1. Festlegung des maximal zulässigen Abstands zwischen Stabilisierungswirkung und Abstreifdüse aufgrund der physikalischen Zusammenhänge (Prinzip nach Saint Venant) zu Abstand ≤ Phi * Bandbreite.
2. 2. Der Korrekturfaktor Phi ergibt sich aus Simulationen und Betriebsversuchen als Funktion von der Bandbreite zwischen 1,75 und 0,75. Die Verformungen des Bands in Querrichtung ergeben sich aus der Instabilität aufgrund der geringen Banddicke. Mit verringerter Bandbreite wirken sich diese nicht so stark aus, was in einer Vergrößerung des möglichen Abstandes der Bandstabilisierung von der Abstreifdüse resultiert.
3. 3. Integration der Bandstabilisierungsspulen innerhalb der Abstreifdüsenkonstruktion zur Erhöhung der Ausrichtgenauigkeit aufgrund einer mechanischen Kopplung der Düse mit den Stabilisierungsspulen.
4. 4. Die Bandstabilisierungsspulen sind über die Kopplung an die Abstreifdüse immer identisch ausgerichtet, auch bei Schräglagen oder Bandverwindungen.

In summary:

1. 1. Determination of the maximum permissible distance between stabilizing effect and wiper nozzle due to the physical relationships (Saint Venant principle) to distance ≤ Phi * bandwidth.
2. 2. The correction factor Phi results from simulations and operational tests as a function of the bandwidth between 1.75 and 0.75. The deformations of the strip in the transverse direction result from the instability due to the small strip thickness. With reduced bandwidth, these do not affect as much, resulting in an increase in the possible distance of the belt stabilization of the wiper.
3. 3. Integration of the belt stabilizing coils within the stripping nozzle design to increase alignment accuracy due to mechanical coupling of the nozzle to the stabilizing coils.
4. 4. The band stabilization coils are always aligned identically via the coupling to the wiper nozzle, even with skewed or band distortions.

Claims (14)

1. Method for strip stabilisation of a strip which is guided between stripper nozzles of a hot-dip finishing plant and provided with a coating, wherein the strip position is detected and stabilising forces are exerted on the strip depending on the detected strip position by coils arranged downstream of the stripper nozzles in strip running direction and acting electromagnetically and contactlessly on the strip running through, characterised in that the distance (of action) of the strip stabilisation means from the stripper nozzles is set to a value smaller than or equal to a distance threshold value determined as a function of the strip width with consideration of a factor Phi, wherein the factor Phi is calculated as a function of the strip thickness and the strip tension, and that the spacing is 1.75 to 0.75 times the strip width depending on the instantaneous strip width.
2. Method according to claim 1, characterised in that the strip position is measured within the coil arrangement.
3. Method according to one of the preceding claims, characterised in that the strip position is measured in physical proximity to the coil arrangement.
4. Method according to any one of the preceding claims, characterised in that the strip position is additionally measured above or below the coil arrangement.
5. Method according to any one of the preceding claims, characterised in that the strip position is detected as a local distribution of the distance of the strip relative to a straight reference line over the strip width and to that extent represents, as actual measurement value, the actual strip profile.
6. Method according to claim 5, characterised in that the stabilising forces act on the strip transversely to the transport direction depending on the detected actual strip profile so as to assimilate the detected actual strip profile to a predetermined optimum target strip profile in the form of a smooth, wave-free strip profile transversely to the strip direction.
7. Method according to any one of claims 1 to 4, characterised in that the strip position is detected as a change over time of the distance of the strip relative to a straight reference line and to that extent represents, as actual measurement value, the actual oscillation behaviour of the strip in dependence on time.
8. Method according to claim 6, characterised in that the stabilising forces act on the strip, preferably perpendicularly to the transport direction, in dependence on the detected actual oscillation behaviour of the strip so as to suitably damp the detected actual oscillation behaviour of the strip if required.
9. Method according to any one of claims 5 to 8, characterised in that the measured strip position represents, as a change - which is distributed over time and locally over the strip width - of the spacing of the strip relative to the straight reference line, the oscillation behaviour of the strip profile as a function of time and that the stabilising forces are suitable for acting on the strip in such a manner that the strip profile is, to the extent required, smoothed and at the same time this oscillation behaviour suitably damped.
10. Hot-dip finishing plant for coating a strip with a coating, comprising:

    at least one stripper nozzle for removing excess coating from the strip;

    a measuring device for detecting the strip position; and

    a strip stabilisation means with electromagnetic coils, which are arranged downstream of the stripper nozzle in strip running direction, for generating stabilising forces, which contactlessly act on the steel strip, in dependence on the detected strip position;

    characterised in that

    the distance (of action) of the strip stabilisation means from the stripper nozzles is set to a value smaller than or equal to a distance threshold value which is determined as a function of the strip width with consideration of a factor Phi, wherein the factor Phi is calculated as a function of strip thickness and strip tension; and

    the spacing is 1.75 to 0.75 times the strip width depending on the respective instantaneous strip width.
11. Hot-dip finishing plant according to claim 10, characterised in that the coils are arranged in pairs opposite one another on the upper side and lower side of the strip and the spacing thereof from the stripper nozzles is variable.
12. Hot-dip finishing plant according to claim 10 or 11, characterised in that the measuring device is arranged at the level of the coils or in the vicinity thereof and detects the strip position there.
13. Hot-dip finishing plant according to claim 10, 11 or 12, characterised in that several coils are arranged in distribution over the width of the strip respectively on the upper side and/or lower side of the strip and that the respective outwardly disposed coils are arranged to be settable to the transiting strip edges parallel to the plane of the strip.
14. Hot-dip finishing plant according to any one of claims 11 to 13, characterised in that the strip stabilisation means and the measuring device are fixedly mechanically coupled to one another at a spacing.

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