DE102012000662A1 - Apparatus for coating a metallic strip with a coating material - Google Patents

Abstract

The invention relates to a device (1) for coating a metallic strip (2) with a coating material (3) having a coating container (4) filled with liquid coating material (3), the coated strip (2) passing through or out of the Coating container (4) vertical (V) is upwardly deflectable and wherein the liquid coating material (3) in the coating container (4) has a bath surface (O), which defines a level height of the coating material (3) in the coating container (4). In order to enable thinner layer thicknesses at high line speeds and with high product quality, the invention provides that in the coating container (4) below the bath surface (O) on both sides of the strip (2) each a baffle element (5 ', 5' ') is arranged, wherein between a belt (2) adjacent surface (6) of the baffle element (5 ', 5' ') and the belt (2), a gap (7) is present and wherein the baffle element (5', 5 '') is horizontal (H) and over the entire width (B) of the band (2).

Description

The invention relates to a device for coating a metallic strip with a coating material comprising a coating container filled with liquid coating material, wherein the coated strip is vertically upwards through the or from the coating container and wherein the liquid coating material in the coating container has a bath surface, the defines a level level of the coating material in the coating container.

Devices of this type are well known in the art. The DE 10 2008 039 244 A1 shows that, for hot dip coating, the metal strip is passed through the coating bath and discharged vertically upwards. Above the coating container, a wiping nozzle is arranged, with the excess coating material is blown off the belt surface. A similar solution is from the WO 02/14574 A1 known.

An important quality aspect of hot-dip coating, in particular in hot-dip galvanizing, is that a very thin and uniform layer of coating material is applied to the strip surface.

Since a uniform appearance of the overcoat layer of the coating material on the belt is very important, mechanical scraper systems (eg, squeeze rollers) contacting the belt surface are generally not used because of the resulting unevenness and surface markings in the layer.

Typically, therefore, for the defined adjustment of the thickness of the coating layer of zinc, aluminum, zinc or aluminum alloys (for example with magnesium or silicon) or other coating metals Abstreifdüsensysteme used, which are positioned above the Badspielgels. The tape emerging vertically upwards from the coating bath entrains excess coating material which is reduced by means of the wiper nozzle system, i. H. is blown off again. The remaining layer thickness on the metal strip results from the definition of the air or gas pressure with which the wiping nozzles work, across the width of the strip and by the distance of the wiping nozzles from the strip. The layer thickness can be adjusted over distances in this way.

However, the following problem arises when using wiping nozzles which blow off excess coating material by means of gas, in particular air:
A disadvantage is that with increasing belt speed and decreasing target layer thickness of the coating, the pressure in the stripping nozzles and thus the exit velocity of the Abblasmediums must be increased at the nozzle slot, which can be done until reaching the speed of sound of the Abblasmediums. The speed of the gas stream, which increases as a result of the speed, is excessively stripped away from the coating material entrained by the belt. When the sound velocity of the blow-off medium is reached, the adjustable layer thickness can no longer be reduced due to the self-locking of the nozzle slot with parameters held constant. As far as the exit velocity of the gas flow from the outlet nozzle with reaching the speed of sound are physically limited, the pulse on the strip surface can then no longer be increased. When reaching this limit, the belt speed is usually lowered in coating systems of the generic type in order to be able to realize even thinnest layer thicknesses. The disadvantageous consequence of this, however, is a reduction in the productivity of the plant.

Another disadvantage is that increasing blow-off pressures increase the consumption of the blow-off medium accordingly. This is particularly cost-intensive if nitrogen or other inert gas mixtures are used as the blow-off medium. Nitrogen is always used when particularly high demands are placed on the surface quality of the coating. Furthermore, at high blow-off pressures, the wear and the energy consumption of the system as well as the noise emission rise sharply. This in turn leads to an increase in production costs and lower profitability of the plant.

The invention is therefore based on the object to develop a generic coating device so that the disadvantages mentioned avoided or at least reduced. Accordingly, it should be possible, with the lowest possible blow-off pressure and thus high quality, to apply the smallest possible layer thickness of the coating material on the strip to be coated. The media consumption of blow-off should be kept as low as possible, so that the process works economically. Nevertheless, as high as possible belt conveyor speeds should be possible, so that the productivity of the system is maximum.

This object is achieved in that in the coating container below the bath surface on both sides of the band depending at least one storage element is arranged, wherein there is a gap between a surface of the baffle member adjacent the belt and the belt, and wherein the baffle member extends horizontally and across the entire width of the belt.

The two storage elements are preferably formed symmetrically with respect to the center plane of the band.

It is also possible to provide first adjustment means with which the depth of the damming element can be adjusted below the bath surface; preferably existing second adjustment means serve to adjust the distance between a surface of the baffle element adjacent to the belt and the belt. The first and second adjustment means may, for. B. include a mechanical, electrical or pneumatic positioning device.

The surface of the baffle element adjacent to the strip may be linear (straight) in a section, viewed in the direction of the center plane of the strip. However, it is also possible for the surface of the blocking element adjacent to the strip to be convex, in particular circular, in a section, as seen in the direction of the center plane of the strip.

A surface facing away from the tape surface of the storage element may be concave in a section - seen in the direction of the center plane of the belt. Said surface of the baffle element may also be formed linearly (straight), wherein the linearly formed surface is arranged at an angle to the vertical. The angle is preferably between 20 ° and 70 °.

Above the coating container, at least one stripping nozzle for stripping still liquid coating material from the strip surface is preferably arranged.

With the inventive design of a coating system, the meniscus, which forms at the outlet of the strip from the coating bath immediately above the bath level, d. H. the liquid coating metal drawn up with the band is influenced by the intended internals in the form of the stagnation elements directly below the bath level producing a stowage effect and thus retracting or reducing said meniscus. Thus, less molten metal is drawn up from the belt. Thus, the scraper nozzle must strip less melt at constant pressure, which allows a reduced layer thickness with otherwise constant setting data.

In particular, when reaching the speed of sound of the Abblasmediums so an additional stripping effect can be generated by said stowage elements, so that despite reaching the limiting speed of Abstreifmediums compared with prior art systems, a thinner layer thickness of the coating material can be set or achieved on the tape.

The internals in the form of the stowage elements may have different geometries to account for the corresponding flow situations. Furthermore, the immersed baffles are variable in vertical height and horizontal distance from the belt to achieve optimum results depending on the temperature of the coating bath and the viscosity of the coating material.

In the drawings, embodiments of the invention are shown. Show it:

1 schematically a device for coating a metal strip in a coating container, as seen in the direction of the center plane of the belt, wherein two storage elements occupy a first position below the bath surface;

2 the device after 1 as seen normal to the tape to be coated;

3 schematically the device after 1 , seen in the direction of the center plane of the belt, wherein the two storage elements occupy a second position below the bath surface;

4 schematically the device after 1 , seen in the direction of the center plane of the belt, wherein the two storage elements occupy a third position below the bath surface;

5a . 5b . 5c . 5d . 5e . 5f . 5g and 5h various cross-sectional shapes of a storage element, as seen in the direction of the center plane of the belt.

In 1 and in 2 is a device 1 for coating a metal strip 2 shown. Centerpiece of the device 1 is a coating container 4 in which liquid coating material 3 - In this case, liquid zinc - is included, which forms a bath surface O. The ribbon 2 is led out in the direction of the vertical V, ie vertically upwards from the coating bath, after it has on its surface in the coating container 4 with coating material 3 is provided.

This can be the band 2 one in the coating material 3 current diverting pulley are deflected into the vertical V. But it is also possible, a bottom open coating container 4 to use, whose bottom opening for the passage of the band 2 is closed by an electromagnetic lock.

Above the coating container 4 is a wiping nozzle 11 arranged with the excess coating material 3 is blown off the belt surface.

Leave the tape 2 the coating material 3 with a vertical exit speed, the band pulls 2 liquid coating material 3 with upward, so that directly above the bath surface O a meniscus 12 forms. The meniscus 12 represents unwanted coating material by means of the wiper 11 from the band 2 must be blown off. However, this has the limits explained above, especially when the exit velocity of the gas from the wiper nozzle reaches the speed of sound.

To the meniscus 12 to decrease and so for given performance of the wiper 11 a very thin layer of coating material 3 Despite high belt speed to reach, is below the bath surface O on both sides of the two sides of the tape 2 one stowage element each 5 ' and 5 '' arranged. The two storage elements 5 ' . 5 '' extend in the direction of the horizontal H transverse to the direction of movement of the tape 2 , Here are the two storage elements 5 ' . 5 '' at least as wide as the width B of the band 2 as it is in 2 can be seen.

The two storage elements 5 ' . 5 '' show one the band 2 adjacent surface 6 on. Here are the two storage elements 5 ' . 5 ' arranged so that between the surface 6 and the band 2 A gap 7 forms. This gap can be in the range of a few millimeters. The distance of the surface 6 from the volume is indicated with a. The distance a is thus measured in the direction perpendicular to the plane E of the strip. The depth of the baffle elements 5 ' . 5 '' below the bath surface O is indicated by t.

So that the depth t of the baffle elements 5 ' . 5 '' below the bath surface O, are first adjusting means 8th present, which are shown only very schematically. Further, second adjusting means 9 present, with which the distance a between baffle element 5 ' . 5 '' and band 2 ie the size of the gap 7 , can be adjusted.

In the synopsis of 1 . 3 and 4 can be seen as the size of the meniscus 12 changes, if on the one hand the depth t of the baffle elements 5 ' . 5 '' below the bath surface O and on the other hand, the distance a of the baffle elements 5 ' . 5 '' is changed by the strip surface.

In 4 It can be seen that in arrangement of the baffle elements 5 ' . 5 '' just below the bath surface O, z. B. in the range between 1 cm and 10 cm, and in the arrangement of the storage elements 5 ' . 5 '' close to the band, ie at a small distance a, the meniscus 12 has significantly reduced, so that given the performance of the wiper 11 a much thinner coating thickness can be achieved.

In the 5a to 5h are different embodiments of the cross-sectional area of the storage element 5 '' as seen in the direction of the horizontal H and in the direction of the plane E of the band 2 , Accordingly, the band 2 adjacent surface 6 be convex configured (s. 5a ) or linear, ie straight ( 5b to 5h ).

Also from the band 2 remote surface 10 the congestion element determines the flow conditions and thus the generated dynamic pressure, the stagnation elements 5 ' . 5 '' exercise and by means of the meniscus 12 can be downsized. As can be seen from the various embodiments, said opposite surfaces 10 be arranged concave or linear. An arrangement of linearly executed sides of the storage element at an angle α to the vertical V is possible, as it 5h shows.

LIST OF REFERENCE NUMBERS

1

Apparatus for coating a metallic strip

2

Band (steel band)

3

Coating material (zinc)

4

coating tank

5 '

retarding element

5 ''

retarding element

6

adjacent surface

7

gap

8th

first adjustment means

9

second adjustment means

10

remote surface

11

wiping

12

meniscus

V

vertical

H

horizontal

O

bath surface

B

Width of the band

e

Middle plane of the band

t

Depth of the damming element under the bath surface

a

Distance between a surface of the baffle adjacent to the belt and the belt

α

angle

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102008039244 A1 [0002]
• WO 02/14574 A1 [0002]

Claims (10)

Contraption ( 1 ) for coating a metallic strip ( 2 ) with a coating material ( 3 ), one with liquid coating material ( 3 ) filled coating container ( 4 ), wherein the coated tape ( 2 ) through or out of the coating container ( 4 ) vertically (V) is deflectable upward and wherein the liquid coating material ( 3 ) in the coating container ( 4 ) has a bath surface (O) which has a level height of the coating material ( 3 ) in the coating container ( 4 ), characterized in that in the coating container ( 4 ) below the bath surface (O) on both sides of the strip ( 2 ) at least one stowage element ( 5 ' . 5 '' ), wherein between one of the band ( 2 ) adjacent surface ( 6 ) of the storage element ( 5 ' . 5 '' ) and the band ( 2 ) A gap ( 7 ) and wherein the baffle element ( 5 ' . 5 '' ) horizontally (H) and over the entire width (B) of the strip ( 2 ). Apparatus according to claim 1, characterized in that the two storage elements ( 5 ' . 5 '' ) with respect to the middle plane (E) of the strip ( 2 ) are formed symmetrically. Apparatus according to claim 1 or 2, characterized by first adjusting means ( 8th ), with which the depth (t) of the damming element ( 5 ' . 5 '' ) is adjustable below the bath surface (O). Device according to one of claims 1 to 3, characterized by second adjusting means ( 9 ), with which the distance (a) between a band ( 2 ) adjacent surface ( 6 ) of the storage element ( 5 ' . 5 '' ) and the band ( 2 ) is adjustable. Apparatus according to claim 3 or 4, characterized in that the first and / or second adjusting means ( 8th . 9 ) comprise a mechanical, electrical or pneumatic positioning device. Device according to one of claims 1 to 5, characterized in that the tape ( 2 ) adjacent surface ( 6 ) of the storage element ( 5 ' . 5 '' ) seen in a section in the direction of the center plane (E) of the band ( 2 ) is linear. Device according to one of claims 1 to 5, characterized in that the tape ( 2 ) adjacent surface ( 6 ) of the storage element ( 5 ' . 5 '' ) seen in a section in the direction of the center plane (E) of the band ( 2 ) convex, in particular circular, is formed. Device according to one of claims 1 to 7, characterized in that one of the tape ( 2 ) facing away from the surface ( 10 ) of the storage element ( 5 ' . 5 '' ) seen in a section in the direction of the center plane (E) of the band ( 2 ) is concave. Device according to one of claims 1 to 7, characterized in that one of the tape ( 2 ) facing away from the surface ( 10 ) of the storage element ( 5 ' . 5 '' ) seen in a section in the direction of the center plane (E) of the band ( 2 ) is linear, wherein the linear surface ( 10 ) is arranged at an angle (α) to the vertical (V). Device according to one of claims 1 to 9, characterized in that above the coating container ( 4 ) at least one scraper nozzle ( 11 ) for stripping still liquid coating material ( 3 ) is arranged from the strip surface.

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