Method and apparatus for applying liquid coating to continuously moving and downwardly traveling belt

Abstract

The invention relates to a method for coating a substrate in the form of a steel strip with a liquid, which substrate is continuously moved at least partially along a vertical line, said method comprising: using a coating (21, 22) having two vented / aerodynamic airlocks (21, 22) respectively located at the inlet and outlet of a baking unit (3); 22) at least partially isolating the baking unit (3) in order to create a dynamic pressure on the belt inside the baking unit and to prevent the coating unit (4) from being contaminated by residual vapours emanating from the baking unit (3).

Description

[0001] Subject matter of the invention

[0002] The present invention relates to the field of coating substrates such as strips with liquids, and more particularly to coating continuously moving metal strips with paint, varnish, thin organic coatings or any other surface treatment.

[0003] More particularly, the invention relates to the field of electrocoating of steel sheets with an insulating varnish (or lacquer) which subsequently makes it possible, due to its adhesive properties, to join these sheets by superposition for the production of electric cells.

[0004] Technical Background and Prior Art

[0005] It is known that application of a coating liquid to a continuously moving belt, such as a steel belt, is usually performed in an upward pass.

[0006] Figure 1 An example of an embodiment according to the prior art is shown. The steel strip 10, after degreasing / cleaning, first passes through a roller coating unit 4 so that one or two liquid formulations 41, 42 can be applied in the selected example, and then passes into an oven 3 (such as an induction oven or an infrared oven) to bake the coating, preferably after inspection and verification by a camera and wet measurement system. At the end of the baking process, the volatile organic compounds are treated in a special unit 5. When leaving the oven 3, the coated strip 12 changes direction at the deflecting top roller 2, then undergoes water cooling in a water cooling unit 6 and hot air drying in a dryer 7, before being directed towards an outlet collector 8.

[0007] Currently, the rapidly growing automotive electric / hybrid vehicle market particularly requires steel sheets which have undergone pre-coating, ie which are coated with an insulating varnish, in order to equip the electric motors being manufactured.

[0008] In electrical engineering, assemblies of soft iron laminates are used to produce magnetic circuits for coils (electromagnets, transformers, rotating machines, etc.). Such sheets are coated with an insulating varnish to limit the circulation of stray currents (eddy currents) and thus limit overheating and iron losses of the magnetic circuit which are proportional to the square of the frequency. The formulation of the insulating varnish may contain thermosetting resins in aqueous or organic phase, such as epoxides, polyesters, acrylic resins, phenolic resins, silicone resins, etc.

[0009] Regarding the production of the cores, and after cutting, the coated sheets are compressed and heated. Thus, the baking of the insulating varnish is carried out in two steps: the first time in the current line and the second time at the engine manufacturer. This means that the baking of the varnish is not complete when contacting the top deflection roller of the line, so there is an unwanted sticking or adhesion phenomenon. This phenomenon can also occur with other types of coatings and for different reasons. On the other hand, with conventional insulating varnishes, the baking is completed when the strip reaches the top roller and there are no adhesion problems.

[0010] Mechanical contact of the coating (which is not completely dry in the coating plant), more particularly contact with the top roller of the plant with the upward strands, could block this roller and damage the coating, which would therefore not meet the required standards and more particularly the minimum thickness of the adhesive layer. The adhesive layer should also not be too thick. One possibility (not shown) would be to insert a contactless additional cooling section (for example, an air cooling section) between the outlet of the induction oven 3 and the top roller 2, as already recommended in document FR 2 768 157 in the case of a galvanizing plant. After the induction oven, the strip is cooled so that the coating is not damaged when passing the top deflection roller.

[0011] However, it should be noted that there is a fundamental difference between galvanizing, which does not release solvents, and painting (varnishing), in which the solvents may be condensed by air currents. Therefore, cooling of the painted or varnished strip is carried out with water to prevent condensation of the solvents. Some of the solvents are found in water to such an extent that the water tanks must be cleaned regularly of a "creamy" precipitate from the dilution of the solvents.

[0012] It should also be noted that the use of the term "solvent" in this text is a linguistic misuse, but in fact "solvent" can also include fumes, gases or vapors that escape from the metal sheet after baking and remain, for example from the hardener and then in the form of blue irritating fumes.

[0013] Furthermore, the travel speed of the belt is very high and the air cooling rate is slow. This solution means, in the upward strand, very long drying lengths and therefore the height of the equipment must be greatly increased. Even if placing a water cooling unit at the top of the equipment is not a major technical problem, in the case of varnishing such a unit cannot be located above the oven, since it is impossible to collect the water and deflection rollers must be installed before the water cooling.

[0014] Document FR 2 640 890 A1 discloses an apparatus for depositing and drying a liquid coating on a continuous strip of metal sheet, such as a continuous painting apparatus. The sheet successively passes through a preparatory treatment station and then through at least one coating and drying station, in which the sheet moves vertically downwards. The latter station comprises, in the order of the strip's passage, a device for coating the metal sheet strip, then an induction or infrared heating tool to evaporate the solvent and polymerize the binder, and the strip then enters a cooling device, which preferably comprises a tank filled with a cooling liquid and in which are placed guide or deflection rollers that change the direction of the metal sheet strip.

[0015] Figure 2 This technique, schematically shown in Figure 1, also has difficulties that hinder its implementation. In fact, placing a solvent-based coating chamber above hot equipment is a considerable risk for personnel working in the vicinity of the coating chamber, both in terms of explosion and also in terms of health. Finally, fires due to the combustion of condensed solvents in the oven or flue system are not uncommon.

[0016] Explosions in solvent flue systems are rare but require special equipment to direct the shock wave. The damage can be significant, especially in hot air ovens which represent a large explosion volume compared to induction ovens which are much shorter and several meters shorter than hot air ovens. 2 The cross-section of the steel structure (approximately 2500mm×2500mm) is particularly small compared to the cross-section of the steel structure (approximately 2000mm×200mm).

[0017] Regarding health issues, coating chambers are generally maintained at a slightly positive pressure compared to their surroundings in order to limit the entry of dust that could contaminate the coating. These ovens are also maintained at a much lower pressure than the chambers to avoid the entry of toxic solvents into the room where the operators are located. The solvent removal fan is therefore an essential element in the overall safety system of the facility. The path of the solvent-laden air in the hot air oven is transverse to the belt, with the suction flow rate adapted to the amount of solvent produced per oven area.

[0018] On a painting line where the belt travels at more than 100 m / min, it can be seen that, without a well-designed barrier system, the flow of hot air over the coating machine is significant despite the maintenance of a negative pressure set point between the oven and the coating chamber. This effect (which can be described as "dynamic") is all the more significant because the air flow rate is high and is related to the production rate of the line and therefore to the amount of solvent to be evaporated (which can involve amounts of solvent to be discharged approaching 500 kg / hour).

[0019] In summary, the down-pass coating as in FR 2 640 890 A1 will take place in counter-current mode between the hot air and the belt. It should include a thermal system below the coating unit and end with water cooling, which has the advantage of not requiring intermediate deflection rollers which, when becoming clogged, damage the not yet completely dried coating.

[0020] However, despite the low pressure of the oven compared to the chamber, this principle currently causes serious problems of contamination of the coating chamber following the escape of large amounts of air loaded with solvent, which tends to oppose the force of gravity acting on the hot air.

[0021] Purpose of the Invention

[0022] The object of the present invention is to provide a method and an apparatus for coating a continuously moving strip with a liquid without the risk of damaging the coating by contact with deflection rollers before the strip has completely cooled down.

[0023] Main features of the invention

[0024] A first aspect of the invention relates to a method for coating a substrate in the form of a steel strip with a liquid, the steel strip moving continuously in vertically downward strand sections at a speed of more than 80 m / min, the method comprising at least the following steps:

[0025] (a) Providing steel strip after cleaning and / or stripping

[0026] (b) providing at least one liquid coating formulation

[0027] (c) applying the liquid coating formulation to the steel strip in a coating unit in order to obtain a coated strip

[0028] (d) drying or baking the coating of the coated steel strip by passing the strip through a baking unit comprising at least one oven and equipped with an environmental insulation system, the at least one oven reaching a temperature of at least 100° C. so that the coating is not completely dried or baked

[0029] (e) cooling the coated steel strip at the outlet of the oven in a liquid cooling unit;

[0030] in order to avoid mechanical contact of the coated tape after leaving the baking unit and before returning to ambient temperature in the liquid cooling unit,

[0031] The method is characterized in that the baking unit is isolated by a system having two ventilation / aerodynamic air locks, which are respectively located at the inlet and outlet of the baking unit so as to form a dynamic pressure on the strip in the baking unit and prevent the coating unit and / or the liquid cooling unit from being contaminated by residual vapor from the baking unit, and hot gas, preferably at a temperature of about 250° C., is injected into the baking unit near the outlet ventilation / aerodynamic air lock or extracted from the inlet ventilation / aerodynamic air lock, the gas flowing in the opposite direction to the coated steel strip so as to avoid condensation cold spots caused by residual vapor.

[0032] According to a preferred embodiment of the present invention, the coating method further includes at least one of the following features or a suitable combination of multiple thereof:

[0033] - the residual steam emitted by the baking unit is continuously extracted for further processing in a further processing unit;

[0034] - the hot gases extracted at the outlet ventilation / aerodynamic airlock have a temperature between 180° C. and 250° C. and are sent to the reprocessing unit;

[0035] - The coating liquid is an electrical insulating varnish or paint

[0036] The coating liquid is a thermosetting epoxy, polyester, acrylic resin, phenolic resin or silicone resin in aqueous or organic phase, or a zinc composition used for passivation or phosphating, for example

[0037] - The method further comprises the step (f) of drying the coated tape in a hot air dryer.

[0038] - The coating unit is a roller coating unit or a spray coating unit

[0039] - The steel strip is an electrical steel strip intended for use as a magnetic laminated steel sheet in the field of electrical engineering or electronics.

[0040] A second aspect of the invention relates to an apparatus for coating a substrate in the form of a steel strip with a liquid, the steel strip moving continuously and at least partially in a vertically downward strand, characterised in that the apparatus comprises, in order from top to bottom:

[0041] - coating unit;

[0042] - baking or drying unit;

[0043] - aerodynamic air lock systems, which are respectively located at the inlet and outlet of the baking or drying unit;

[0044] - in the baking unit, the inlet of the aerodynamic air lock close to the outlet is used to inject hot gases, and the outlet of the aerodynamic air lock close to the inlet is used to extract said hot gases towards a unit for continuously reprocessing the residual vapors emitted by the baking unit;

[0045] - Rapid liquid cooling unit;

[0046] - said unit for continuously reprocessing the residual vapours emitted by the baking unit;

[0047] The apparatus is configured so that the coated tape does not come into mechanical contact with any part of the apparatus between the outlet of the baking unit and the rapid liquid cooling unit before the coated tape returns to room temperature.

[0048] According to a preferred embodiment of the present invention, the coating device includes at least one of the following features or a suitable combination of multiple thereof:

[0049] - the apparatus comprises a non-contact anti-drip device located after the outlet of the coating unit;

[0050] - the rapid liquid cooling unit comprises a liquid bath in which deflection rollers are positioned and, if appropriate, said bath is preceded by liquid jets;

[0051] - Each of the aerodynamic airlocks comprises, in use, on each side of the belt, an extraction chamber extracting the gases coming from the baking unit and a reinjection chamber equipped with nozzles, the orientation of which allows reinjecting a portion of the gases extracted along the belt towards the baking unit, another portion of the extracted gases being sent to the reprocessing unit;

[0052] - The baking unit is at low pressure compared to the surrounding environment and the coating unit;

[0053] - A reinforced movable valve is placed between the inlet air locks of the coating unit and the baking unit in order to physically close the inlet air lock in case of a fire or explosion hazard. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 A device for coating a steel sheet with a liquid according to a first embodiment of the prior art is schematically shown.

[0055] Figure 2 A device for coating steel sheets with insulating varnish according to a second embodiment of the prior art is schematically shown.

[0056] Figure 3 A device for coating a steel sheet with an insulating varnish according to one embodiment of the invention is schematically represented.

[0057] Figure 4A Schematically represented is an example of an upper ventilation / aerodynamic air lock (oven inlet) in use according to the invention.

[0058] Figure 4B Schematically represented is an example of a lower ventilation / aerodynamic air lock (oven outlet) in use according to the invention. DETAILED DESCRIPTION

[0059] according to Figure 3 The embodiment shown represents the solution provided by the invention. The general idea is to move the belt continuously in a downward strand, while bypassing the difficulties encountered by implementing the basic technology according to document FR 2 640 890 A1. In this configuration, a water cooling unit 6 in a closed loop is installed after the exit of the baking unit 3 with one or more ovens, close to the lowest point of the equipment. Since the coating is already cooled by water and, in addition, the lower deflection roller 1 is in water, the quality of the coating is not affected in said configuration when the belt passes over the deflection roller, because the temperature at said location is close to the ambient temperature.

[0060] The particularity of the invention is the ability to utilize a continuous coating line for metal strips in a downward pass without damaging the coating that is not completely dried, which is necessary in certain applications, while avoiding the risks of explosion and / or fire associated with solvents as described above. The main advantages of downward pass coating, unlike upward pass coating, are that complete cooling of the metal sheet (i.e. to ambient temperature) can be carried out before the first physical / mechanical contact (which is the contact with the deflection rollers) and that no violent blowing (which condenses the solvent on the cooling device and causes significant vibrations of the strip and condensation of the fumes from the hardener on the blowing system) is used, but instead water spraying or immersion is used.

[0061] Despite the above-mentioned difficulties (explosion risk, risk to the health of operators, risk of contamination of coating units and water cooling), this principle should now be reconsidered with advantage since it makes it possible to apply viscous varnishes that allow steel sheets to be superimposed, for example for producing air gaps for electric motors.

[0062] Upward pass coating should certainly be excluded, since contact with the deflection rollers is prohibited before complete cooling (ie, approximately to ambient temperature). For a production rate of 30 tons per hour per meter width, for example, as mentioned above, this method would in fact lead to enormous cooling lengths, with the risk of belt vibrations associated with the length of the equipment and the airflow. It could also lead to condensation of residual emissions on the cold air blowing structure and to contamination of the surrounding atmosphere.

[0063] In the downward pass, only the design of an extremely efficient barrier system is suitable for limiting the concentration of the solvent to a content corresponding to natural evaporation at the ambient temperature of the chamber, more specifically the coating chamber at the top of the tower.

[0064] To this end, the inventors have developed a ventilation / aerodynamic air lock (called Aeroven) that makes it realistically possible to envision downward passage through the coating. TM ).

[0065] In practice, such a system integrates directional recovery, for example with a deflector and recirculation with an inclination of 30° relative to the horizontal, followed by a uniform blowing, which is also directional. High-speed circulation loops require fans with a capacity greater than 10000Pa. The system includes discharge or inlet ports with a flow rate controlled independently of the blowing speed for local low or overpressure and a physical barrier adjustable according to the operating conditions. The air lock is located just below or above the fresh air supply loop or the solvent-laden air recovery loop, while providing sufficient access for possible maintenance interventions.

[0066] These elements make it possible to maintain a fairly healthy environment in the coating chamber (thanks to the upper airlock) and reasonable cleanliness of the water spraying system (thanks to the lower airlock) by limiting the contamination towards the two chambers situated respectively at the top and at the bottom of the oven.

[0067] It should be noted that the pass-through device according to the present invention can be controlled by at least one operator located on the upper level (where the applicator is located) and at least one operator located on the lower level (where the oven is located), or by only one operator in a centralized manner.

[0068] Detailed examples showing implementations of the present invention are described below.

[0069] For this purpose, ventilation / aerodynamic air locks 21, 22 should be provided at the top (entrance) and bottom (exit) of the oven 3 zone, respectively.

[0070] First, according to Figure 4A The embodiment shown will provide, via the reinforced movable valve 23 , the possibility of partially or completely physically closing the inlet airlock 21 in the event of a fire or explosion hazard, which makes it possible to protect personnel from accidents of this type.

[0071] The inlet air lock 21 of the oven comprises, in sequence, on each side of the belt, chambers 25, 24 for extracting and reinjecting air, respectively (with recirculation). The extraction chamber 25 extracts both the cold air entering from the coating unit 4 and the hot air rising from the oven 3, while the chamber 24 reinjects the extracted air. The system creates an aerodynamic plug that will prevent the hot air containing solvent from the oven 3 from contaminating the coating zone 4. The hot air loaded with solvent is then finally extracted at the top of the oven towards the volatile organic compound (VOC) treatment unit 5. More particularly, the chambers 24 and / or 25 comprise nozzles whose orientation is suitable for creating an aerodynamic plug. The coating zone 4 is maintained at a slight overpressure relative to the surroundings, while the oven 3 zone is maintained at a low pressure.

[0072] Still based on Figure 4B , the outlet airlock 22 of the oven 3 further comprises, in turn, chambers 25, 24 on each side of the belt for extracting and injecting hot air (with recirculation), respectively. A high velocity of hot air (e.g. at 250° C.) is injected at the bottom of the oven zone 26. A portion of the hot air is thus extracted by the airlock and re-injected, another portion of the hot air is redirected to the VOC treatment unit 5. Most of the injected hot air flows in the opposite direction of the belt before being discharged towards the VOC treatment unit 5. The water cooling chamber 6 is maintained at a low pressure (in this case by water spraying) compared to the surrounding environment.

[0073] List of Reference Numerals

[0074] 1 Deflection bottom roller

[0075] 2 Deflection top roller

[0076] 3 Baking unit (oven)

[0077] 4-roll coating unit

[0078] 5 Volatile organic compound treatment unit

[0079] 6 Water cooling unit

[0080] 7 Hot air dryer

[0081] 8 Collector

[0082] 10 Continuously moving steel belt

[0083] 11 Stations with wet measuring instruments and cameras

[0084] 12 Coated steel strip

[0085] 20 Hot Gas Injection

[0086] 21 Upper Ventilation / Aerodynamic Air Lock

[0087] 22 Lower Ventilation / Aerodynamic Air Lock

[0088] 23 Reinforced removable valve

[0089] 24 Air injection chamber

[0090] 25 Air suction chamber

[0091] 26 High velocity hot air injection

[0092] 41, 42 Resin preparations.

Claims

1. A method for coating a substrate in the form of a steel strip with a liquid, the steel strip moving continuously in a vertically downward strand section at a speed of more than 80 m / min, the method comprising at least the following steps: (a) Providing a steel strip (10) after cleaning and / or stripping (b) providing at least one liquid coating formulation (41, 42) (c) applying the liquid coating formulation (41, 42) to the steel strip (10) in a coating unit (4) in order to obtain a coated steel strip (12) (d) drying or baking the coating of the coated steel strip (12) by passing the strip through a baking unit (3), the baking unit comprising at least one oven and equipped with an environmental insulation system (21, 22), the at least one oven reaching a temperature of at least 100° C. so that the coating is not completely dried or baked (e) cooling the coated steel strip (12) at the outlet of the oven (3) in a liquid cooling unit (6) in order to avoid mechanical contact of the coated strip (12) after leaving the baking unit (3) and before returning to ambient temperature in the liquid cooling unit (6), Characterized in that the baking unit (3) is isolated by a system having two ventilation / aerodynamic air locks (21, 22), which are respectively located at the inlet and outlet of the baking unit (3) so as to form a dynamic pressure on the belt in the baking unit and prevent the coating unit (4) and / or the liquid cooling unit (6) from being contaminated by residual vapors from the baking unit (3), and hot gas, preferably at a temperature of about 250°C, is injected into the baking unit (3) near the outlet ventilation / aerodynamic air lock (22) or is extracted from the inlet ventilation / aerodynamic air lock (21), the gas flowing in the opposite direction to the coated steel belt (12) so as to avoid condensation cold spots caused by these residual vapors.

2. The coating method according to claim 1, characterized in that: The residual steam emitted by the baking unit (3) is continuously extracted for further processing in a further processing unit (5).

3. The coating method according to claim 1, characterized in that: The hot gases extracted at the outlet ventilation / aerodynamic airlock (22) have a temperature between 180°C and 250°C and are sent to the reprocessing unit (5).

4. The coating method according to claim 1, wherein: The coating liquid is an electrical insulating varnish or paint.

5. The coating method according to claim 1, wherein: The coating liquid is a thermosetting epoxy, polyester, acrylic resin, phenolic resin or silicone resin in an aqueous or organic phase, or a zinc composition used, for example, for passivation or phosphating.

6. The coating method according to claim 1, characterized in that: The method further comprises the step (f) of drying the coated tape (12) in a hot air dryer (7).

7. The coating method according to claim 1, wherein: The coating unit (4) is a roller coating unit or a spray coating unit.

8. The coating method according to claim 1, wherein: The steel strip (10, 12) is an electrical steel strip intended for use as a magnetic laminated steel sheet in the field of electrical engineering or electronics.

9. An apparatus for coating a substrate in the form of a steel strip with a liquid, the steel strip moving continuously and at least partly in a vertically downward strand, characterized in that From top to bottom, the device consists of: - coating unit (4); - a baking or drying unit (3); - aerodynamic air lock systems (21, 22) located at the inlet and outlet of the baking or drying unit (3); - In the baking unit (3), the inlet near the outlet aerodynamic air lock (22) is used to inject hot gas, and the outlet near the inlet aerodynamic air lock (21) is used to move towards the unit (5) extracting said hot gases, the unit being used to continuously reprocess the residual vapors emitted by the baking unit; - Rapid liquid cooling unit (6); - said unit (5) for continuously reprocessing the residual vapours emitted by the baking unit (3); the device being configured so that, before the coated tape (12) returns to room temperature, the coated tape (12) does not come into mechanical contact with any part of the device between the outlet of the baking unit (3) and the rapid liquid cooling unit (6).

10. The device according to claim 9, characterized in that The apparatus comprises a non-contact anti-drip device located after the outlet of the coating unit (4).

11. The device according to claim 9, characterized in that The rapid liquid cooling unit (6) comprises a liquid bath in which a deflection roller (1) is positioned and, if appropriate, preceded by liquid jets.

12. The device according to claim 9, characterized in that Each of these aerodynamic air locks (21, 22) comprises, in use, on each side of the belt (10), a suction chamber (25) for extracting the gas from the baking unit (3) and a re-injection chamber (24) equipped with a nozzle, the orientation of which allows a portion of the gas extracted along the belt (10) to be reinjected towards the baking unit (3), another portion of the extracted gas being sent to the reprocessing unit (5).

13. The device according to claim 9, characterized in that The baking unit (3) and the rapid liquid cooling unit (6) are at low pressure relative to the surrounding environment, and the coating unit (4) is at overpressure relative to the surrounding environment.

14. The device according to claim 9, characterized in that A reinforced movable valve (23) is arranged between the coating unit (4) and the inlet air lock (21) of the baking unit (3) in order to physically close the inlet air lock (21) in case of a fire or explosion hazard.

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