EP2558804B1 - Method and device for coating metal strips - Google Patents

Description

The present invention relates to heating furnaces by inducing bands in continuous scrolling.

It is applicable, for example, to pre-treatment or post-treatment coating drying ovens on the continuous treatment lines of metal strips, in particular galvanizing lines or annealing lines.

The invention is particularly applicable to drying and polymerization furnaces of the pre-lacquering lines of metal strips.

In the remainder of this document, the case of pre-lacquering lines with protective or decorative coatings using paints with organic solvents will be dealt with more particularly.

Continuous pre-lacing of metal strips involves applying a thin layer of liquid paint to the strip at the parade and drying the paint in an oven.

After baking, the coated strip is then cooled, generally with water by spraying or by immersion in a water tank.

The paints used usually contain organic solvents. Evaporated in the oven, they are sucked up and destroyed by incineration at high temperature.

The heating of the strip can be carried out in different ways. Most often it is done by convection with hot air impact.

However, other heating modes are used, in particular heating by electromagnetic induction. In this case the temperature of the sucked gases remains low and this results in condensations of solvents and resins in the furnace and in the incineration circuit.

The patent FR2734501 has proposed a method to limit these condensations, consisting of reinjecting hot air into the heating section and thermally isolating the latter. This hot air is injected and withdrawn between the inductors, in particular to limit the chimney effect caused when the tunnel is in vertical configuration.

• Il subsiste le problème des émanations diffuses de produits solvantés qui s'échappent de la bande entre le moment où celle-ci sort de la section de chauffage et où elle entre dans la section de refroidissement par eau. Ces émanations diffuses polluent l'environnement immédiat de l'installation en garnissant les planchers, garde-corps, etc., de résidus glissants et rendent l'air difficilement respirable et toxique. De plus, ces résidus sont un combustible potentiel en cas d'incendie.

However this design induces two constraints:

• There remains the problem of diffuse emanations of solvent products escaping from the web between the moment when it leaves the heating section and enters the water cooling section. These diffuse emanations pollute the immediate environment of the installation by filling the floors, railings, etc. with slippery residues and make the air difficult to breathe and toxic. In addition, these residues are a potential fuel in case of fire.

In practice, the limitation of the chimney effect in the case of a vertical heating section requires creating a back pressure by adjusting the different rates of reinjection and withdrawal along the heating section. This adjustment is difficult to implement and may require additional control of the Lower Explosive Limit in the different sections of the section. This can lead to an increase in the rate of withdrawal, and therefore the fuel consumption of the incinerator.

The document DE19633742 discloses a device for coating a metal strip according to the preamble of claim 1. The heating section and the cooler are not bound by a sheet metal continuity.

The proposed invention makes it possible to eliminate these disadvantages.

• une continuité de tôlerie est assurée entre l'entrée de la section de chauffage et la sortie du refroidisseur pour rendre l'ensemble étanche au gaz,
• un dispositif de séparation d'atmosphères est placé entre la sortie de la section de chauffage et l'entrée du refroidisseur.

According to the invention, a device for coating a metal strip in continuous displacement successively comprises, in the running direction of the strip, a coating section for depositing a coating on the strip, a heating section, for evaporating elements including solvents and drying or curing the coating and a cooler, the cooler being a water cooler, and is characterized in that:

• a sheet metal continuity is ensured between the inlet of the heating section and the outlet of the cooler to make the assembly gas-tight,
• an atmosphere separating device is placed between the outlet of the heating section and the inlet of the cooler.

Advantageously, the device for separating atmospheres comprises means for injecting a gas at a temperature above the dew point of the elements to be evaporated.

The device for separating atmospheres may comprise members making it possible to limit the passage section and therefore the gas flows.

The device for separating atmospheres may comprise an injection of hot gas placed, in the running direction of the strip, upstream of the members making it possible to limit the passage section, and a gas withdrawal placed downstream.

The furnace may comprise a vertical pass in which the band travels from bottom to top, in that a deflector roll is placed at the end of the vertical pass for returning the band to the cooling section, and in that a main injection of hot gas is located at the entrance of the furnace and a hot gas withdrawal is located at the return box.

• une continuité de tôlerie est assurée entre l'entrée du four et la sortie du refroidisseur à eau pour rendre l'ensemble étanche au gaz,
• un dispositif de séparation d'atmosphères, par injection d'un gaz à une température supérieure au point de rosée des éléments, est placé entre la sortie de la section de chauffage et l'entrée du refroidisseur à eau.

The invention also relates to a method for coating a continuously moving metal strip according to which said strip, after having received its coating, is heated in a heating section in order to evaporate elements, in particular solvents, and to ensure drying or drying. baking the coating, then is cooled with water, in a water cooler, which process is characterized in that:

• sheet metal continuity is ensured between the inlet of the furnace and the outlet of the water cooler to make the assembly gas-tight,
• an atmospheric separation device, by injecting a gas at a temperature above the dew point of the elements, is placed between the outlet of the heating section and the inlet of the water cooler.

Advantageously, an injection of a gas at a temperature above the dew point of the elements is carried out at the inlet of the furnace.

Generally, a main gas withdrawal is carried out at the outlet of the heating section. An auxiliary gas withdrawal can be carried out downstream of the atmospheric separation device, in the running direction of the strip.

The auxiliary gas withdrawal is advantageously carried out upstream of the water cooler, in the running direction of the strip.

In the preferred embodiment of the invention, the cooling of the strip is provided by a water spraying.

The continuity of the sheet metal allows a rollover of the band from its entry into the heating section to the outlet of the cooler. The diffuse emanations escaping from the band after its exit from the last inductor can thus be captured and incinerated.

To avoid condensation of solvents, it is necessary to maintain the inner surface of the cowling beyond the non-condensing temperature by thermally insulating it and sweeping this assembly by hot atmosphere, which will incinerate.

The patent FR2734501 describes a solution comprising the implantation of several withdrawal and reinjection points in the cooking zone.

The presence of the cowling according to the invention makes it possible to simplify the withdrawal and reinjection circuits. The method according to the invention leads, for example, to reinject a hot gas at a single point, located at the entrance of the baking tunnel, and to withdraw at another point, just before cooling water.

To avoid increasing the total withdrawal flow rate, that from the heating section and the one from the cooler, it will seek to limit the inflow of air, that is to say the air flow coming from from the outside of the oven and not loaded with solvents.

To do this you can use a water cooling tank in immersion mode to create a hydraulic seal to have a perfect seal.

However, this solution is not satisfactory, in particular because it imposes a vertical configuration of the water tank, more constraining in terms of implantation and more expensive. Moreover, the immersion does not make it possible not to wet one of the two faces of the strip, which may be required for hot application of some movies. In addition, this configuration promotes the pollution of cooling water by diffuse fumes.

It is therefore preferred to use a conventional cooling type sprinkler by adding a ventilation system aeraulic before the water tank, type roller lock. This separation makes it possible to cause the majority of vapors to emanate to the incineration circuit, and not to the cooling circuit.

Thus, to limit the air inlets from the cooler and not loaded with solvents, the method according to the invention comprises an atmosphere separation device placed between the outlet of the heating section and the inlet of the water cooler.

The device for separating atmospheres according to the invention comprises members making it possible to limit the passage section and therefore the gas flows.

It may for example be a roller lock, comprising at least one pair of rollers placed on either side of the band. The device may also consist of one or more support rollers on one face of the strip and flaps on the opposite face, placed opposite the rollers.

The atmospheric separation device according to the invention advantageously comprises an injection of a gas at a temperature above the dew point of the solvents.

The method according to the invention also comprises a withdrawal of the humid air from the cooler. This can be placed just downstream of the atmospheric separation device, therefore upstream of the cooler, or at the outlet of the water cooler.

The process according to the invention makes it possible to avoid diffuse fumes outside the oven. Thus all emanations are captured and incinerated. This results in a better cleanliness of the installation which makes it less dangerous by reducing the risk of spread of fire, the risk of slipping and less stale air.

This configuration according to the invention allows the absence of condensation in the solvent circulation circuit and also outside this circuit.

It also allows better control of the withdrawal rate. Ambient air at ambient temperature only comes from the inlet of the heating section. This makes it possible to better control the flow rate and the dilution of the solvents withdrawn. This results in a minimization of the fuel consumption of the incinerator and a better safety of the installation. Previous problems of balancing the flow rates in the different branches of the induction tunnel, in particular to limit the chimney effect, are thus simplified.

• La Fig.1 représente un exemple de four à induction selon l'invention, et
• La Fig. 2 représente un agrandissement du dispositif de séparation d'atmosphères 11 selon l'exemple de réalisation de la Fig. 1.

The invention consists, apart from the arrangements set out above, in a number of other arrangements which will be more explicitly discussed below with respect to an embodiment described with reference to the accompanying drawings, but which is in no way limiting. On these drawings:

• The Fig.1 represents an example of an induction furnace according to the invention, and
• The Fig. 2 represents an enlargement of the atmosphere separation device 11 according to the embodiment of the Fig. 1 .

As represented in Fig. 1 , in this embodiment, the furnace comprises two successive inductors 1a and 1b mounted on a vertical pass in which the band 2 flows from bottom to top. A deflector roll 3 placed at the end of the vertical pass enables the band to be returned to the cooling section 4.

The cooling section 4 comprises a first portion equipped with a plurality of water spray ramps 18a and 18b on the strip and a water tank 20 for collecting the water flowing from the upper part. A recovery 21 allows to supply the ramps 18a and 18b again via a closed circuit, not shown, comprising a plate heat exchanger.

From the inlet 5 of the oven to its outlet 6, the strip is held in a closed envelope consisting of the successive internal walls of the inlet box 7, the inductor 1a, the connecting box 8, the inductor 1b, connecting box 9, the return box 10, the atmosphere separation device 11 and the water cooler 4 and the water tank 20.

A main injection of hot gas 16 is located at the entrance of the furnace and a hot gas withdrawal 17 is located at the level of the return box 10.

The hot gas injected at the injection points 16 and 14 is advantageously air preheated by the incineration fumes of the solvents. Its temperature at the injection points depends on the condensation temperature of the solvents. It is typically greater than 200 ° C.

As represented in Fig. 2 in this exemplary embodiment, the device 11 for separating atmospheres comprises a support roll 12 on which the strip rests on its face 2a, and facing the opposite face, a retractable flap 13 limiting the cross section. passage of the atmosphere. It also comprises an injection of hot gas 14 placed upstream of the roller assembly 12 and flap 13 in the running direction of the strip and a gas withdrawal 15 placed downstream.

To limit the risk of marking the tape, the roller 12 can be motorized and its rotational speed regulated so that the peripheral speed of the roller is identical to that of the tape. Alternatively, the roll 12 may be positioned slightly set back from the band pass line so that it does not rest on the roll in normal operation but only punctually, for example in the case of a change in tension of band during transient phases.

An insulator 22 limits the free section for the flow of gases. A functional clearance between the roller 12 and the insulator allows rotation of the roller while limiting the flow of gas between the upstream and downstream of the roller 12.

The flap 13 is retractable to allow the introduction of the strip into the oven. The roller 12 makes it possible to control the position of the strip and thus to minimize the opening X between the end of the flap 13 and the strip. A functional clearance between the flap 13 and the insulator allows the flap to rotate while limiting the flow of gas between the upstream and downstream flap 13.

According to another embodiment not shown, the device 11 for separating atmospheres comprises two successive sets of roll 12 and flap 13. This configuration makes it possible to increase the tightness of the device by increasing the pressure drop of the gas moving.

Upstream of the roller assembly 12 and flap 13 in the running direction of the strip, the combination of the two hot gas injections 14 and 16 and the withdrawal 17 makes it possible to maintain the internal walls of the heating section from the inlet 5 to the roller assembly 12 and 13 at a sufficient temperature to avoid the condensation of solvents. It also ensures the evacuation of solvents to the incinerator.

The outlet 6 of the water cooler 4 is in the open air.

Downstream of the roller assembly 12 and flap 13 in the running direction of the strip, the combination of the draw-off point 15 and the air inlet via the outlet 6 of the cooler makes it possible to ensure the evacuation of the solvents residuals from the coating of the belt to the incinerator.

According to another embodiment not shown, the strand of tape between the deflector roll 3 and the outlet of the water cooler is horizontal.

Claims (11)

1. Device for coating a continuously moving metal strip (2), successively comprising, in the running direction of the strip, a coating section for depositing a coating on the strip (2), a heating section (1a, 1b) for evaporating elements, in particular solvents, and for drying or curing the coating, and a cooling section (4), the cooling section being a water cooler, characterised in that:

   - a continuity of sheet metal is ensured between the inlet (5) of the heating section and the outlet (6) of the cooling section (4) to make the assembly gas-tight,

   - an atmosphere-separating device (11) is placed between the outlet of the heating section and the inlet of the cooling section (4).
2. Device according to claim 1, characterised in that the atmosphere-separating device (11) comprises means (14) for injecting a gas at a temperature above the dew point of the elements to be evaporated.
3. Device according to any one of the preceding claims, characterised in that the atmosphere-separating device (11) comprises members (12, 13) which make possible to limit the flow cross section and therefore the gas flows.
4. Device according to claim 3, characterised in that the atmosphere-separating device (11) comprises a hot-gas injector (14) placed in the running direction of the strip (2) upstream of the atmosphere-separating device, and a gas extractor (15) placed downstream.
5. Device according to any one of the preceding claims, characterised in that the furnace comprises a vertical segment in which the strip (2) runs from bottom to top, in that a deflector roller (3) is placed at the end of the vertical segment allowing the strip to be redirected towards the cooling section (4), and in that a main hot-gas injector (16) is located at the inlet of the furnace and a hot-gas extractor (17) is located level with the deflector casing (10).
6. Method for coating a continuously moving metal strip, in which said strip (2), after it has been coated, is heated in a heating section (1a, 1b) for evaporating elements, in particular solvents, and for drying or curing the coating, and then cooled by water in a water-cooling section (4), characterised in that:

   - a continuity of sheet metal is ensured between the inlet (5) of the furnace and the outlet (6) of the water cooler (4) to make the assembly gas-tight,

   - an atmosphere-separating device (11), injecting a gas at a temperature above the dew point of the elements, is placed between the outlet of the heating section and the inlet of the cooling section (4).
7. Method according to claim 6, characterised in that an injector (16) for injecting gas at a temperature above the dew point of the elements is located at the inlet (5) of the furnace.
8. Method according to claim 6 or claim 7, characterised in that a main gas extractor (17) is located at the outlet of the heating section.
9. Method according to any one of claims 6 to 8, characterised in that a hot gas is reinjected at a single point located at the inlet of the curing tunnel and extracted at another point just before the water-cooling section.
10. Method according to any one of claims 6 to 9, characterised in that an auxiliary gas extractor (15) is located downstream of the atmosphere-separating device in the running direction of the strip.
11. Method according to claim 10, characterised in that the auxiliary gas extractor (15) is located upstream of the water-cooling section (4) in the running direction of the strip.

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