比利时专利BE1020476A3 NOZZLE OF THICKNESS CONTROL OF THICKNESS AND COATING DISTRIBUTION WITH EXCELLENT PRESSURE UNIFORMITY

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专利摘要:

公开号:BE1020476A3
申请号:E2012/0363
申请日:2012-05-31
公开日:2013-11-05
发明作者:Michel Dubois
申请人:Cockerill Maintenance & Ingenierie Sa；
IPC主号:

专利说明:

NOZZLE OF THICKNESS CONTROL AND COATING DISTRIBUTION WITH EXCELLENT PRESSURE UNIFORMITY
Field of the invention
The present invention relates to a gas smoothing device for controlling the thickness of a film of liquid on a moving web. A typical example is a device for gas smoothing of a liquid metal on large coated sheets, such as those obtained by hot-dip coating.
General context and prior art
In hot dip coating, the uniformity of the coated sheet coating is a major problem.
When an air knife system is used, it is well known that achieving uniformity requires uniform speed of movement, constant nozzle-to-nozzle distance, and uniform gas flow at the nozzle outlet. . Any variation in these operating parameters will result in variations in coating thickness.
The devices in the context of the present invention are concerned with obtaining a uniform gas flow along a thin opening, such as a slot which has a standard length of 2.5 meters and a thickness of opening from 0.5 to 2 mm. Figure 1 is a cross-sectional view of a typical nozzle design used in the hot dip coating industry. The nozzle 1 is located at the front of the moving coated sheet 3 emerging from the coating bath containing the liquid metal. The exit of the nozzle consists of inclined lips 11 which define an extended opening or longitudinal slot 12. FIG. 2 is a corresponding front view of the strip 3 and the device of FIG. 1.
First, experience has shown that the angle between the strip 3 and the nozzle faces facing the band 3 must be large in order to reduce the vortex and recirculation created by a large flow of gas. In this regard, Figure 5 shows a typical vortex configuration development when the angle θ is small.
Thus, because of the usually small space available, the dimensions of the chamber 2, in particular its length 4 and its height 5, are quite limited (see Figure 1 and Figure 2).
The air supply 6 supplied to the device can be obtained by various known methods, for example by injection from the top (FIG. 1), from the side (FIG. 2) or from the rear. This air supply 6 must be flexible because the device is usually moved in operation according to the specific process window. A typical displacement length of the device can reach 100 mm. Therefore, the hoses used must have a special diameter-to-length ratio to accommodate this displacement without detrimental effect on their service life.
In addition, the diameter of the supply pipe 6 as well as the cross section of the chamber can not be too small because otherwise the velocity of the gas in the pipe becomes too high, which leads to a variation of the flow of gas along the opening which further provides a non-uniform coating thickness. Figure 3 shows an example of gas flow and the results obtained from an examination performed by the inventor when the design ratios are not correctly selected, actually in the case where the air is delivered through four openings 6. Figure 6 shows, in another example, the flow and outlet velocity along the nozzle in the case of a single (or asymmetric) side gas inlet.
The problems mentioned above are fairly well known in the industry and some technical solutions have already been proposed as described in US Pat.
No. 4,041,895.
This document presents a system for controlling the thickness and distribution of a coating applied to a moving substrate, comprising a pair of "air knives" that discharge a pressurized fluid onto a moving substrate as it emerges. a coating bath for trimming the excess coating of the substrate and leaving a coating deposit of a desired thickness and distribution. Each air gap has a plenum that delivers a pressurized fluid to a pair of nozzle lips that define an elongate nozzle opening. Devices influencing a fluid flow are provided between the plenum and the nozzle lips of each air knife, preferably comprising a baffle plate, a shield assembly, a shutter plate, and a set of vanes. The baffle plate and the shield assembly help to ensure that laminar flow of uniform pressure is applied to the shutter plate. The shutter plate has specially configured flow limiting apertures that cause a predetermined change in the fluid discharge pressure profile from the air knives along the length of their nozzle openings, whereby the profiles of coating are caused to vary in a predetermined manner over the width of the substrate. The blade assembly includes blades that help control the directions of fluid discharge through the nozzle openings. Pressurized fluid is applied to the airblades by a system that includes a blower, and the blower speed is controlled in response to a detected line speed of the moving substrate to ensure that a thickness of coating deposition desired remains on the substrate.
Thus, the solutions mentioned above usually consist either of deflectors installed in the chamber or, alternatively, of plates 7 (see, for example, FIG. 1) provided with a number of orifices whose object is standardize the pressure downstream of the plate by generating a fairly high pressure drop.
These solutions of the prior art, however, have two main drawbacks: they consume a large amount of energy due to the pressure drop; they are not capable of suppressing the developed vortex within the chamber since the design can not reduce fluid velocities in directions other than perpendicular to the baffle plate. Vortices are also responsible for non-uniform gas flow along the opening due to higher localized total pressure when the vortex hits them. An example of this internal vortex due to the inlet pipes is shown in FIG. 3. In addition, FIG. 4 shows the calculated velocities corresponding to the outlet along the length and the nozzle width. The different lines correspond to the speeds corresponding to the different locations along the opening thickness, the higher values thus corresponding to the center of the opening and the smaller ones to those closer to the opening walls.
Objects of the invention
The object of the present invention is to avoid the disadvantages of the prior art.
In particular, the object of the invention is to standardize the total pressure in the chamber by suppressing the internal vortex in the nozzle chamber, as well as significantly improving the uniformity of static gas pressure. Therefore, a much greater uniformity of the exit velocity must be obtained along the nozzle opening.
Another object of the invention is to limit the pressure drop in the nozzle chamber due to the presence of a perforated plate baffle.
Summary of the invention
The present invention relates to a device for controlling the thickness of a coating made by a film of liquid on a moving web, comprising a nozzle supplied with fluid under pressure in a chamber of the nozzle, said chamber ending with nozzle providing an elongated discharge opening for discharging pressurized fluid onto the moving web, said chamber also including a perforated baffle plate obstructing a section L xh of the chamber in the fluid flow, characterized in that perforated baffle has a number of orifices so that the total area of said orifices is greater than 90% of said section and has a thickness Th greater than 3 times the individual diameter of any one of said orifices and greater than 3 mm.
According to preferred embodiments, the device of the invention is further limited by a characteristic or an appropriate combination of the following characteristics: the perforated baffle plate has a honeycomb geometry, i.e. to say a geometry comprising cells with a hexagonal section; the moving band is a sheet coated with a liquid, emerging from a coating bath; the moving web is a metal foil coated with a liquid metal emerging from a hot dip coating bath; the hot dip coating bath is a galvanizing bath for sheets; the fluid under pressure is a gas under pressure; the pressurized gas comprises a mixture of oxygen and nitrogen; - The elongated discharge opening of the nozzle is a slot having a length of up to 2.5 meters and a thickness of up to 3 mm.
Brief description of the drawings
Figure 1 schematically shows a cross-section of a typical nozzle for gas smoothing of a coated sheet, provided with a perforated plate in the nozzle chamber, according to the prior art.
Figure 2 schematically shows a front view of the nozzle and the sheet of Figure 1.
Figure 3 shows the calculated gas flow for a gas-fired nozzle through four upper circular openings.
Figure 4 shows the calculated exit velocity for the simulated nozzle in Figure 3. The different lines correspond to the velocity along the height of the nozzle aperture.
Figure 5 shows the typical high vorticity obtained especially when the angle between the strip and the nozzle end is closed.
Figure 6 shows in the upper part the flow inside a nozzle chamber when it is obtained by a single lateral inlet, the lower part showing the corresponding calculated output speed.
Figure 7 schematically shows a nozzle provided with a so-called honeycomb device according to the present invention.
Figure 8 is a cross section of a typical embodiment of the invention.
Figure 9 is a perspective view of an industrial embodiment corresponding to Figure 8.
Figure 10 shows the uniform pressure profile at the outlet of the nozzle, obtained by the device of the invention, the bottom numbers referring to the position of each particular gas inlet pipe along the opening of the nozzle. the nozzle.
Detailed Description of the Invention and Preferred Embodiments
According to a first preferred embodiment, the invention relates to the implementation, within a nozzle chamber and inside a gas flow, of a particular component 8 provided with orifices, hereinafter called "honeycomb" geometry component, as shown schematically in FIG. 8. In principle, the honeycomb geometry refers to a structure! having empty cells 13 of hexagonal section. In this case, the above diameter of the cell is the diameter of the circumscribed circle of the hexagon. However, it will be within the scope of the present invention to admit d structures. orifices deviating from the "ideal" hexagonal model.
Since a perforated plate baffle is used, resulting in a pressure drop in the nozzle chamber, the invention improves the situation by seeking a void ratio, i.e. the sum of the hole sections. divided by the total cross section of the plate, close to 1.
According to the invention, this part 8 is however characterized by the following characteristics: - a plate with a large number of orifices. The total area of the orifices should be greater than 90% of the total cross section (L x h), as shown in Figure 7; a thickness (Th) of the component greater than 3 times the individual orifice diameter and greater than 3 mm.
It has been observed that the device of the invention has the property of blocking the vortex of internal gas and of directing the flow of fluid in the correct direction, that is to say the direction in which it must be at the exit of the nozzle. This is achieved with a minimum loss of energy, which means that the system does not in principle need to increase the pressure capacity of the fans usually used to produce the pressurized fluid. By using the device of the invention, the diameter of the pipes supplying the chamber can be advantageously reduced.
As a consequence of the invention, the use of a thin inner baffle plate 7, as described for example in US Pat. No. 4,041,895, is not necessary.
Example
FIG. 9 shows an exemplary industrial embodiment according to the invention.
The efficiency of the device was verified by measuring the dynamic pressure all along the nozzle by a Pitot tube. According to FIG. 10, it is possible to observe a good uniformity or a satisfactory uniformity of the pressure measured in% of the average, all along the opening in this particular device. Experiments have shown that the variations from a maximum value to a minimum value measured are less than about 1% for a nozzle that is 2 meters long and has an opening less than 2 mm.
The nozzle as described herein is generally dedicated to the smoothing of a liquid driven by a moving band. The liquid may be aqueous, or consist of a liquid metal. The band envisaged above can have a standard width of 600 to 2300 mm.
List of reference symbols 1. Nozzle 2. Chamber 3. Band 4. Chamber length 5. Chamber height 6. Air supply
DL · LMILIVOOJ
7. Perforated Plate Deflector 8. Honeycomb Component 10. Nozzle End Angle 11. Nozzle Lip 12. Nozzle Opening (or Slit) 13. Orifice

权利要求:
Claims (8)
[1]
Device for controlling the thickness of a coating made by a film of liquid on a moving web (3), comprising a nozzle (1) supplied with pressurized fluid (6) in a chamber (2) of the nozzle said chamber (2) terminating in nozzle lips (11) providing an elongated discharge opening (12) for discharging fluid under pressure to the moving web. (3), said chamber (2) also comprising a perforated deflector plate (8) obstructing a section L xh of the chamber (2) in the fluid flow, characterized in that the perforated deflector plate (8) comprises a number of orifices (13) so that the total area of said orifices (13) is greater than 90% of said section and has a thickness Th greater than 3 times the individual diameter of any one of said orifices (13) and greater than 3 mm.
[2]
2. Device according to claim 1, characterized in that the perforated deflector plate (8) has a honeycomb geometry, that is to say a geometry comprising cells (13) with a hexagonal section.
[3]
3. Device according to claim 1, characterized in that the moving strip (3) is a sheet coated with a liquid, emerging from a coating bath.
[4]
4. Device according to claim 3, characterized in that the moving strip (3) is a metal sheet coated with a liquid metal, emerging from a hot dip coating bath.
[5]
5. Device according to claim 4, characterized in that the hot dip coating bath is a galvanizing bath for sheets.
[6]
6. Device according to claim 1, characterized in that the fluid under pressure is a gas under pressure.
[7]
7. Device according to claim 6, characterized in that the pressurized gas comprises a mixture of oxygen and nitrogen.
[8]
8. Device according to claim 1, characterized in that the elongated discharge opening of the nozzle (12) is a slot having a length of up to 2.5 m and a thickness of up to 3 mm.

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法律状态:

优先权:

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