JP2005504177A - Method for molten metal immersion finishing - Google Patents

Abstract

The invention relates to, for example, a non-ferrous (NE) metal strip or a steel strip, in particular a strip, with a coating of at least one metal, at least in the process of passing through a container containing a coating material in the melt-flow state. The present invention relates to a method and an apparatus for coating the surface of a sheet-like material. The metallic strip to be coated passes through the molten metal bath of coating material in the container from top to bottom. For this purpose, suitable guiding means are provided. The container is sealed downward by a circulating permanent magnet.

Description

【Technical field】
[0001]
The present invention relates to a coating of at least one metal, for example of a non-ferrous (NE) metal strip, or of a steel strip, in particular in the form of a strip, in the course of passage through a container containing at least a melt-flowing coating material. The invention relates to a method for coating a surface. The invention likewise relates to an apparatus for carrying out this method.
[Background]
[0002]
Traditional metal strip metal plating (referred to herein as method 1) with Zn-, Zn-Al-, Al-, or Al-Si-alloy is performed in an annealing furnace in the coated region. Characterized by entering into the molten metal under air shut-off and being redirected to a vertical state and stabilized by a non-driven roller using a different device (see FIG. 1) It is attached. This applies to all the above-mentioned coated metal / coating alloys during the molten metal dip finish.
[0003]
In the case of this method 1, it is a disadvantage that the rollers and the bearing portions of these rollers are provided inside the molten metal, and that all materials are exposed to chemical erosion of the molten metal. is there. The lifetime of all built-in structures inside this molten metal is limited. Furthermore, a large molten metal volume is required with a correspondingly large molten metal container to accommodate these rollers, or the entire bath apparatus. In the case of hot dip galvanizing, zinc in a fluidized state in an amount of 200 to 400 t is common. Rapid control of this molten metal with respect to temperature and alloy composition is not possible based on this large volume. The relatively large variations in the above parameters must be accepted and in some circumstances induce quality losses. This is because alloy technical treatment and strip quality influence each other in the container.
[0004]
Yet another disadvantage is that the production rate cannot be increased in order to obtain economical equipment performance (about 180 m / min), especially for thin strips of <0, 5 mm. One reason for this is that there is a relative movement between the roller provided in the bathtub and the strip. To avoid this problem, there is a risk of strip cracking when the tension is increased. The result is scrap production and a relatively long outage.
[0005]
Yet another limitation for maximum strip travel speed of the hot dip galvanizing equipment is provided by a nozzle scraping system disposed above the zinc melt, see FIG. The coating thickness is adjusted by air or nitrogen, with the minimum embodied coating thickness increasing with increasing strip running speed. That is, thin plating cannot be formed at high strip travel speeds. However, very thin plating (<25 g / m ² , in the case of a thin metal plate hot-dip galvanized on one side) is now sought for certain demanding uses.
[0006]
As a further development method for the molten metal dip finishing of ferritic steel strips made of soft non-alloy steel, so-called vertical hot dip galvanizing is known and European Patent 630 421 ( It is described in various patents such as EP 1 630 420 (Patent Document 2) and EP 673 444 (Patent Document 3).
[0007]
In this method (referred to herein as method 2), the strip passes from below to above through a working vessel filled with a metal in a molten fluid state consisting of a zinc alloy and / or an aluminum alloy; In this case, the strip has been temperature-treated in advance, and the strip runs into the molten metal under air shut-off. This molten metal volume is basically small compared to Method 1 with the flowing zinc in an amount of about 2-5 t. Similarly, the above quality problems do not exist. This is because the alloy technical treatment is carried out in a holding container provided in parallel and the strip quality is formed separately from the alloy technical treatment in this working container. It is.
[0008]
The connection between the working vessel and the furnace chamber underneath the working vessel is approximately 800 mm high and through an airtight ceramic passage having a passage width of only a maximum of 20 mm for the strip. Done. The gap of this working vessel downwards and the avoidance of downward flow into the furnace chamber are performed inside this passage by means of inductors arranged along this passage, ie the strip, on two sides. Is called. These inductors create an electromagnetic traveling magnetic field that generates an upwardly directed force that prevents the molten metal from flowing downward. This inductive system operates like a pump, so that mutual exchange of the molten metal is also ensured in this passage.
[0009]
Method 2 can be implemented without problems in thin steel strips as well, in the range of 300 m / min, with a significantly higher strip running speed, at least in the coating region, up to the molten metal bath. The roller is also characterized by the fact that it is not provided in the coating container.
[0010]
After the strip has passed through the coating unit having a temperature of about 460 ° C., for example in the case of hot dip galvanizing, from below to above, comparable to method 1, just above the molten metal bath, by the nozzle scraping method The desired thickness of the metallic finish layer is adjusted. This is done by blowing over compressed air or nitrogen, comparable to Method 1.
[0011]
This nozzle scraping method is comparable to method 1 and also in method 2 limits the maximum possible strip running speed in the case of thin coatings. In practice, this method 2 also provides a relatively large degree of freedom for the galvanizing parameters acting on the layer thickness, ie temperature, molten metal viscosity, and alloy composition. For this reason, it is expected that the strip running speed in this method 2 can be selected higher than in method 1 when the layer thickness is the same. Compared to this method 1, this method 2 has not yet been tested on a large scale industrial technology. Traditionally, only testing with pilot equipment has been done with narrow strips. This trial was successful.
[0012]
The fact that the strip must subsequently be cooled to below 300 ° C. in the ascending articulation and before the first turning, however, hinders the increase in travel speed. If this temperature is higher, there is a risk that metallic particulates will grow on the first contact roller or turning roller in the cooling tower and form irreparable surface defects of the material. Exists.
[0013]
Cooling is usually performed using a number of air cooling sections arranged in series. This cooling action, and precisely the cooling rate, is however limited by the condition of the medium, and under the use of the cooling medium, the air is in a fixed section (eg 2 × 15 m). It cannot be increased appropriately. With increased strip travel speed or increased mass flow, these cooling sections must be extended. This, however, results in a rise of the upper turning roller in the cooling tower of the molten metal immersion finishing facility.
[0014]
In the case of equipment according to method 1, the height of the upper turning roller is usually between 30 and 60 m. For method 2, for high strip travel speeds, the cooling section must be further extended relatively, and therefore the cooling tower height is increased in the height direction to 80-90 m in some cases. The This results in higher investment costs for the building and foundation.
[0015]
Thus, the unstabilized strip section in the free-running state can be extended in the tower and the strip travel can be degraded, thus causing vibrations and adversely affecting product quality. The use of other cooling media in the ascending articulated state is problematic and has not been solved conventionally in large industrial engineering.
[0016]
Yet another problem is that, in the electromagnetic gap according to method 2, the force acting on the liquid molten metal, especially on the ferritic strip, also acts. Inconvenient contact of this strip with the magnetic path of the sealing inductor is possible only with an additional costly arrangement. Additional stabilizing coils and costly control techniques are needed for this purpose.
[Patent Document 1]
European Patent No. 630 421 [Patent Document 2]
European Patent No. 630 420 [Patent Document 3]
European Patent No. 673 444 [Disclosure of the Invention]
[Problems to be solved by the invention]
[0017]
The problem with the present invention is therefore to avoid the above drawbacks of the methods 1 and 2 and to optimize investment for better manufacturing quality, with very little possible structural engineering costs. It is to provide a high speed molten metal immersion finishing facility without cooling towers that is harmonized with cost and high equipment performance.
[Means for Solving the Problems]
[0018]
This problem is solved in the manner described in the superordinate concept of claim 1 in such a way that the container is sealed by a circulating permanent magnet. The container gap with this circulating permanent magnet is significantly more reliable than the electromagnetic solution and is less costly and for significantly less rotation than for the electromagnetic gap. It requires energy, which is advantageous especially when the current is insufficient.
【The invention's effect】
[0019]
Embodiments of the method are described in further dependent claims.
Apparatus for carrying out this method and embodiments of this apparatus are the subject of further claims.
[0020]
The invention will now be described on the basis of some schematically illustrated embodiments.
BEST MODE FOR CARRYING OUT THE INVENTION
[0021]
According to FIG. 3, the strip 1 travels downward in the vertical direction and then into the container in which the molten metal bath is provided, after the change of direction in the furnace, under air shut-off. This molten metal bath is sealed downward. For this purpose, however, a force formed with a circulating permanent magnet is required rather than in an electromagnetic manner. This gap of molten metal with a permanent magnet is known per se. There, however, it is operated with a rectangular passage. This passage shape cannot be changed in spacing and shape.
[0022]
In contrast, the present invention proposes two rotors 5, 5 ′ located in parallel with each other. These rotors are tubes 6, 6 'made of a temperature and molten metal resistant material, in particular ceramic. Inside these tubes 6, 6 ′ whose diameter can be freely selected, the rollers rotate, and permanent magnets 4 are arranged on the outer peripheral surfaces of these rollers. These rotors 5 and 5 'are pressure adjusted to the molten metal or strip. Similarly, the gap 7 can be closed when the equipment is stopped or when the equipment is started.
[0023]
Permanent magnets are basically cheaper than electromagnetic gaps with coils or inductors, and basically have less energy for rotation than for electromagnetic gaps. This is advantageous, especially in the case of current shortage.
[0024]
With a permanent magnet, a higher magnetic field strength (coefficient 3) can basically be realized as compared with an electromagnetic operation method. These high magnetic field strengths, or the relatively high forces resulting from this magnetic field strength, are required for the scraping process to adjust the desired coating thickness on the steel strip. This has to be done with an additional scraping nozzle in the case of known methods.
[0025]
An additional configuration within the range of magnetic clearance and scraping no longer has to be done in the case of the method according to the invention. This is because the narrowest passage area of the strip 1 is only a few millimeters due to the gap unit. Furthermore, this strip 1 is basically fixed in a tension state shorter and shorter than in the known methods 1 and 2. This is because, immediately below the gap unit, the strip 1 is immediately cooled and redirected in the water bath 9. The stretch length (Abspannlaenge) is advantageously only about 5000 mm in the case of the present invention, and in the case of method 1, this stretch length is higher than about 8 to 10 times, and method 2 In this case, it is even higher.
[0026]
A further advantage of the process according to the invention is that the surface of the molten, flowable metal, preferably zinc melt, is present in the coating region, preferably inside a protective gas atmosphere consisting of a nitrogen / hydrogen mixture, In addition, an oxidizing action that hinders zinc in a fluid state is not performed. In the known methods 1 and 2, this can be carried out with only additional significant effort. In addition, these known methods require that the zinc bath surface be able to be handled from the outside for a given manual operation. In the case of the present invention, access to the molten metal bath surface is not necessary for the purpose of removing oxidizing particulates.
[0027]
In the embodiment according to FIG. 3, the installation for the non-ferrous metal strip or steel strip 1 for the molten metal immersion finish is in operation in operation.
The strip 1 to be fed into and to be finished, in the furnace 2, the tension gas 17, and then the protective gas atmosphere present inside the dip finishing equipment, to the ambient atmosphere with oxygen. On the other hand, it passes through a weir 18 that is airtightly closed.
[0028]
In the subsequent galvanizing chamber 14, the strip 1 is turned to a vertical state with respect to the coating section 19 via the guide roller 13.
Upon inflow into the covering section 19, the strip 1 is a bath of molten metal 3 kept upright in the gap 7 between the rotors 5, 5 ′ in the vertical direction from top to bottom. And thus provide the desired coating.
This molten metal bath 3 is a magnetic field of a rotating permanent magnet 4 or a magnetic field of a traveling magnetic field in a gap formed between spaced apart rotors 5 and 5 'at the lower end. The force prevents it from passing down. The rotors 5 and 5 'are provided inside the pipes 6 and 6' that circumvent the rotors in a covering section 19 that is surrounded by a passage-shaped housing outwardly. The rotors 5 and 5 'are accommodated with variable intervals. These rotors are surrounded by tubes 6, 6 'made of temperature-resistant and molten metal-resistant, in particular non-magnetic material, preferably ceramic.
The permanent magnet 4 rotates inside these tubes 6 and 6 '.
[0029]
The molten metal necessary for the coating and to be continuously replenished is transferred from the receiving vessel 8 in which the molten metal is conditioned to the rotor 5 in a flow-controlled manner by a metal pump 12. Into the gap 7 between 5 '. The strip 1 coated therein passes through the gap 7 at this lower end and subsequently the device 15 for air stabilization and subsequently the device 16 for water cooling.
This strip is withdrawn from the facility for further use or processing after passing through the water bath 9 and tensioning roller 20.
[0030]
Yet another FIGS. 4 and 5 illustrate the process according to the invention.
a) in the starting state and
b) In the stop state after operation,
Show. that time,
a) Starting state:
-The strip is stationary-The rotor is rotating-The gap between these rotors is closed-Molten metal is supplied-The furnace chamber is closed, and
b) Stop state after operation:
-Molten metal reflux-The rotor is rotating-The gap is closed-The furnace chamber is open.
[Brief description of the drawings]
[0031]
FIG. 1 is a diagram of a conventional strip coating method.
FIG. 2 is a diagram of a further developed coating method according to the known art.
FIG. 3 is a diagram of a coating method according to the present invention and a correspondingly configured high speed molten metal dip finishing facility in operating condition.
4 is a diagram of the installation according to FIG. 3 in a start-up state.
5 is a diagram of the installation according to FIG. 3 in a stopped state after operation.

Claims (9)

Method for coating the surface of, for example, a non-ferrous metal strip, or a steel strip, in particular in the form of a strip, with a coating of at least one metal, in the course of passing through a container containing at least a melt-flowing coating material In
A method wherein the container is sealed by a circulating permanent magnet. The method according to claim 1, wherein the desired coating thickness on the metallic strip is adjusted simultaneously by the circulating permanent magnet. The melt-flowing coating material is introduced from the receiving container into the wedges of the two counter-rotating rotors, with the metallic strip from the top to the bottom, the molten metal bath, and spaced apart. 3. A method according to claim 1 or 2, characterized in that it is guided through these rotors provided in the manner described above. The metallic strip is guided through the molten metal bath after turning around in the preheating furnace, preferably in a protective gas atmosphere, vertically down in the protective gas atmosphere. 4. A method according to any one of claims 1 to 3, characterized in that 5. The coated strip is air-stabilized and / or water-cooled, as directly as possible, below the container gap or below the rotor. The method as described in one. 6. An apparatus for carrying out the method according to any one of claims 1 to 5, comprising at least one container for containing a coating material in the melt flow state for a metal strip product. In
In order to seal the container, there are two oppositely controlled rotors, in some cases mutually controllable, in which a rotatable roller is arranged inside these rotors. A permanent magnet is fixed on the outer peripheral surface of the roller. 7. A device according to claim 6, wherein the container containing the molten metal bath is formed by an upper central chamber between the rotors. 8. A device according to claim 6 or 7, characterized in that at least the rotor is surrounded by a housing under the maintenance of a protective gas atmosphere. The rotor housing
An upper chamber for the purpose of supplying a metallic strip from above to the rotor housing, and
A receiving container for molten metal;
And, for example, a device disposed on the underside of the rotor housing for air stabilization and water cooling of the strip, and
In some cases, another bathtub
Device according to any one of claims 6 to 8, characterized in that it is in a connected state.

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