Coating section of a continuous line

Abstract

The invention relates to a method for cooling a metal strip (2) in a coating section (1) of a continuous line for treating strips, the strip being coated beforehand with a coating comprising dry extracts and a diluent before being dried in a heating section (300) and then cooled in a cooling section (600), characterised in that the cooling is carried out successively in a primary cooler (400) and then in a secondary cooler (500), wherein the strip is cooled in the primary cooler by convection by means of a gas blown onto the strip, the temperature of which is chosen so as to maintain, in the primary cooler, a temperature higher than the condensation temperature of the diluent.

Description

SECTION OF COATING OF A CONTINUOUS LINE Designation of the technical field concerned

[0001] The invention relates to continuous lines for processing metal strips and more particularly to painting or varnishing sections, whether these are vertical or horizontal, that is to say that the strip circulates vertically or horizontally in said sections.

[0002] It particularly concerns the coating sections of carbon steel, silicon steel or aluminum strips.

[0003] From now on, we will use the term "coating" to refer to any type of coating, whether it is paint, varnish, or any other type of coating. Technical problems addressed by the invention

[0004] A coating section consists of: an area for applying the coating to the strip, a coating drying / polymerization area, and a strip cooling area.

[0005] In the coating application area, the coating is applied to the strip using a roll coating process.

[0006] A coating thickness is deposited in a calibrated manner on the strip.

[0007] The coating is generally composed of: dry extracts (pigment, binder, etc.), one or more diluents (solvent, water, or solvent + water).

[0008] Once the coating has been applied to the strip, it must be dried, i.e. all the diluents contained in the coating must be evaporated so that only the dry extracts remain on the strip.

[0009] Subsequently, we will consider that the coating comprises only one diluent without this limiting the scope of the patent to this single case, the invention being able to be applied indifferently with a coating comprising one or more diluents.

[0010] The temperature that the strip must reach in the heating section is called PMT (Peak Metal Temperature). It varies depending on the nature of the coating, but is usually between 200°C and 300°C.

[0011] Heating of the strip in a heating section is achieved by convection, radiation (infrared) or induction.

[0012] The ambient temperature in the heating section must be maintained at a temperature higher than the condensation temperature of the diluent present in the coating in order to prevent the diluent, once evaporated from the substrate, from recondensing on the walls of the heating section in contact with cold surfaces. The evaporation temperatures of diluents are approximately 100 °C for water and between 150 °C and 250 °C for solvents.

[0013] A heating section can consist of heating zones alone or a combination of heating zones and a temperature maintenance zone.

[0014] The drying or holding areas are maintained under negative pressure by air extraction to evacuate the evaporated solvents. This extraction is sent either directly outside the building if the diluent is water, or to a treatment system, if the diluent is a solvent, before releasing the treated air into the atmosphere.

[0015] After drying, the strip is cooled in a cooling section.

[0016] In most cases, water spray cooling is used immediately after exiting the heating section.

[0017] In some cases, due to process reasons, the strip cannot be cooled directly with water. In this case, cooling is carried out completely or partially with air. This involves blowing cold air onto the sheet metal to cool it.

[0018] We find this air cooling configuration for example: in certain sections of aluminum strip coating for which water cooling is too violent and generates flatness defects on the strip, on sections of steel strip painting with application of a plastic film after painting, on sections of silicon sheet varnishing.

[0019] In a coating section, when the cooling of the strip is not carried out by water jet spraying, but by blowing cold air, certain problems appear.

[0020] In fact, water cooling allows the strip to be cooled quickly and almost instantly stops the fumes coming from the substrate.

[0021] When air cooling, cooling is slower and the strip continues to emit fumes. The fumes are mainly solvents and resins.

[0022] These fumes (diffuse discharge) pollute the cooling zone, causing environmental problems. These discharges are usually captured, at best, and very rarely treated. They are generally simply released into the atmosphere.

[0023] Also, since these emissions occur in a cold zone, this generates problems of condensation of solvents / resins in the cooling zone as well as in the collection ducts, posing safety problems because these condensates are highly flammable.

[0024] The object of the invention is to overcome these problems.

[0025] According to a first aspect of the invention, there is provided a method for cooling a metal strip in a coating section of a continuous strip processing line, the strip being previously coated with a coating comprising dry extracts and a diluent before being dried in a heating section and then cooled in a cooling section, characterized in that the cooling is carried out successively in a primary cooler and then in a secondary cooler, in which the strip is cooled in the primary cooler by convection using a gas blown onto the strip, the temperature of which is chosen so as to maintain in the primary cooler a temperature higher than the condensation temperature of the diluent.

[0026] The gas blown onto the strip has a temperature lower than that of the strip, which allows it to be cooled, but higher than the condensation temperature of the diluent in the cooler. The convection exchange with the strip causes the gas to heat up, which nevertheless remains at a temperature lower than that of the strip. After exchange with the strip, the gas spreads into the primary cooler before being recirculated or extracted by suction for incineration. The gas in the primary cooler is always at a temperature higher than the condensation temperature of the diluent in the cooler.

[0027] The condensation temperature of the diluent in the primary cooler depends in particular on the nature of the diluent and the diluent load in the gas present in the primary cooler (kg of diluent per m3 of gas).

[0028] For a given diluent, its condensation temperature depending on the diluent load can be determined by tests easily carried out on a test facility. For example, by placing a small volume of hot gas (whose temperature is higher than the condensation temperature), whose diluent load is known, in a glass enclosure where it is cooled while its temperature is monitored. The condensation temperature is the temperature at which droplets appear on the internal surface of the glass enclosure.

[0029] According to the invention, the strip is cooled in the secondary cooler by means of a fluid having a temperature lower than the temperature of the gas blown onto the strip in the primary cooler.

[0030] The fluid used in the secondary cooler can be a gas, for example air, or a liquid, for example water. Its temperature can be lower than the condensation temperature of the diluent, to achieve efficient cooling, because there is no significant diluent emission in the secondary cooler and therefore no risk of condensation.

[0031] Advantageously according to the invention, the strip is cooled in the primary cooler to a temperature between 130°C and 170°C. Below this temperature, the diluent emissions become negligible. The end of the cooling can then be carried out in a secondary cooler according to the state of the art, i.e. without withdrawal and incineration and using a fluid whose temperature is below the condensation temperature of the diluent.

[0032] According to the invention, air preheated to a temperature higher than the condensation temperature of the diluent in the primary cooler is injected into the primary cooler via an injection line and a gas comprising the injected air and vapors of the diluent is extracted from the primary cooler via a withdrawal line.

[0033] Injecting preheated air into the primary cooler helps maintain the cooler walls at a temperature above the diluent condensation temperature, for example at a wall temperature between 100°C and 150°C. This prevents diluent from depositing on the walls and the associated fire risks if the diluent is organic.

[0034] Extraction allows the fumes from the diluent to be captured and sent to an incinerator to be neutralized.

[0035] According to one embodiment of the invention, the gas present in the primary cooler is extracted via the heating section by the withdrawal line connected to the heating section. Thus, the primary cooler is connected to the oven.

[0036] This configuration avoids the risk of diluent vapors escaping into the building through a free space between the oven and the primary cooler.

[0037] Advantageously according to the invention, the gas blown onto the strip in the primary cooler is extracted from the primary cooler and recirculated via a recirculation circuit, the temperature of said gas blown onto the strip being adjusted by injecting, via an air inlet, a controlled flow of fresh air into the recirculation circuit.

[0038] This recirculation of the gas present in the cooler provides hot gas, preheated by its convection exchange with the strip.

[0039] The entry of a controlled flow of fresh air into the recirculation circuit makes it possible to adjust the temperature of the gas blown onto the strip to a temperature which allows the desired strip cooling efficiency to be obtained while being at a temperature higher than the condensation temperature of the diluent in the primary cooler.

[0040] According to a second aspect of the invention, there is provided a coating section of a continuous line for processing metal strips comprising a section for coating the strip with a coating comprising dry extracts and a diluent, a heating section for drying the coating and a cooling section, characterized in that the cooling section comprises a primary cooler in which the strip is cooled by convection by means of a gas blown onto the strip, the temperature of which is chosen so as to maintain in the primary cooler a temperature higher than the condensation temperature of the diluent followed by a secondary cooler in which the strip is cooled by means of a fluid having a temperature lower than the temperature of the gas blown onto the strip in the first cooler.

[0041] The primary cooler comprises blowing boxes arranged opposite the strip and supplied with cooling gas by a recirculation circuit of the gas present in said primary cooler, said primary cooler being connected to a controlled injection line of a flow of preheated air into said primary cooler.

[0042] Advantageously according to the invention, the recirculation circuit comprises an air inlet allowing injection of a controlled flow of fresh air into said recirculation circuit to adjust the temperature of the gas supplying the blowing boxes.

[0043] According to an exemplary embodiment of the invention, the primary cooler is connected to the heating section, the coating section further comprising a withdrawal pipe connected to the heating section capable of extracting the gas from said primary cooler via the heating section.

[0044] In this embodiment, the withdrawal capacity of the oven must therefore be sufficient to extract the gas present in the oven and that of the primary cooler.

[0045] According to an exemplary embodiment of the invention, the coating section further comprises an airlock arranged at the inlet of the heating section.

[0046] An airlock is advantageous when the quantity of solvent is low and, consequently, a low extraction flow rate is sufficient. This is particularly the case in the varnishing sections. By having an airlock that limits the entry of air through the oven inlet, a reduced extraction flow rate is maintained. The capacity of the incinerator and the equipment located on the extraction circuit and the injection circuits can thus be limited, which reduces the investment cost and the operating cost.

[0047] Note that for paint lines, the quantity of solvent being significant, the airlock is not strictly necessary due to the air inlets required to dilute the solvents.

[0048] According to another embodiment of the invention, the coating section comprises a withdrawal pipe connected to the primary cooler for extracting the gas present in said primary cooler.

[0049] Adding a cooler draw may be necessary for a large capacity installation where it is difficult to draw gas from the cooler via the oven draw circuit.

[0050] Adding a draw in the cooler can also be advantageous to have less draw in the heating section and thus limit the inflow of fresh air into the oven. Brief description of the figures

[0051] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which reference will be made to the appended drawings in which: is a schematic and partial representation of a section of coating according to a first exemplary embodiment of the invention, and is a schematic and partial representation of a section of coating according to a second exemplary embodiment of the invention. Detailed description of the invention

[0052] The embodiments described below being in no way limiting, it will be possible in particular to consider variants of the invention comprising only a selection of the characteristics described, subsequently isolated from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art. This selection comprises at least one characteristic, preferably functional without structural details, or with only a part of the structural details if this part only is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art.

[0053] In the remainder of the description, elements having an identical structure or similar functions will be designated by the same references.

[0054] Illustrates schematically and partially the principle of the invention, according to a first example of embodiment for a vertical covering section.

[0055] A strip 2 circulates vertically from bottom to top in the coating section, which successively comprises, in the direction of travel of the strip, a coating section 100, an isolation airlock 200, a baking oven 300, a cooling section 600 comprising a primary cooler 400 and a secondary cooler 500.

[0056] The coating section 100 includes two roller coating machines 101 to be able to quickly switch between two types of coatings.

[0057] Hoods 103 are arranged above the coating machines in order to capture the solvent vapors present at the coating machines. They are connected via a suction line 102 to an exhauster 221. The suction line comprises members 104 for adjusting the suction of the hoods.

[0058] The 200 isolation airlock located at the entrance to the oven prevents a chimney effect that would lead to the entry of a large quantity of air into the oven. It allows an air barrier to be created by combining air injection and controlled extraction.

[0059] It includes a line 210 for injecting air and a line 220 for extracting the atmosphere present in the airlock.

[0060] The air injection line 210 comprises a fan 211 controlled by a speed variator, a member 212 for measuring the pressure at the fan discharge and a member 213 for measuring the flow rate of the fan 211.

[0061] The withdrawal line 220 is connected to the same exhauster 221 as the hoods above the coating machines. It comprises a member 222 for measuring the pressure at the airlock suction, a member 223 for measuring the withdrawal flow rate in the airlock and a member 224 for regulating the withdrawal flow rate.

[0062] The speed variator of the exhauster 221 makes it possible to adjust the overall withdrawal flow rate, the members 104 and 224 making it possible to adjust the proportion of flow drawn from the airlock and the hoods above the coating machines.

[0063] The 300 cooking oven is hermetically connected to the 200 isolation airlock in its lower part and to the 400 primary cooling section in its upper part.

[0064] The oven 300 comprises a heating zone 310 equipped with two inductors 311 to bring the strip to the target PMT temperature for drying and / or polymerization of the coating, for example 250°C, followed by a temperature maintenance zone 320.

[0065] The oven comprises an effluent withdrawal line 330 connected to the holding zone for withdrawing the solvents released during the curing of the coating. This withdrawal line comprises, from its connection to the oven, a fire damper 331, a member 332 for measuring the temperature of the effluents, a member 333 for measuring the flow rate of the effluents, a member 334 for regulating the flow rate of the effluents, a by-pass valve 336 preceding an incinerator 337 intended to incinerate the solvents present in the effluents, a member 338 for measuring the temperature of the effluents at the outlet of the incinerator, an exchanger 339, a member 340 for measuring the temperature of the effluents at the outlet of the exchanger and an exhauster 341 discharging the incinerated and cooled effluents into a chimney 342.

[0066] The bypass valve 336 allows the incinerator 337 to be bypassed by means of a bypass pipe 345.

[0067] The exchanger 339 makes it possible to preheat fresh air before it is injected into the oven and the primary cooler. With the aid of a fan 346, it supplies four ducts 350, 360, 370, 380 for injecting preheated fresh air into the oven 300 and a duct 410 for injecting preheated fresh air into the primary cooling section 400.

[0068] A pipe 390 makes it possible to send excess flow passing through the exchanger to the chimney 342. It comprises a member 391 making it possible to control the temperature of the air preheated by the exchanger 339 by acting on the flow of air passing through the exchanger.

[0069] The preheated fresh air injection line 350 is connected to the oven between the airlock 200 and the first inductor 311. It allows hot air to be injected at the inlet of the oven in order to maintain a hot ambient temperature in the first inductor. It comprises a member 351 for controlling the injected flow rate and a member 352 for measuring the injected flow rate.

[0070] The preheated fresh air injection line 360 ​​is connected to the oven between the two inductors 311. It allows a warm ambient temperature to be maintained in the second inductor. It comprises a member 361 for controlling the injected flow rate and a member 362 for measuring the injected flow rate.

[0071] The preheated fresh air injection line 370 is connected to the oven at the outlet of the second inductor, in the direction of travel of the strip. It contributes to the flow of effluents into the holding zone 320 and ensures the temperature level thereof. It comprises a member 371 for controlling the injected flow rate and a member 372 for measuring the injected flow rate.

[0072] The preheated fresh air injection line 380 is connected to the oven outlet, in the direction of travel of the strip, near the connection between the primary cooler and the oven. The air injected through line 380 raises the temperature of the gases coming from the primary cooler to maintain an ambient temperature of 200-220 °C in the oven. It also contributes to the flow of effluents into the holding zone 320 and to the temperature level thereof.

[0073] The pipe 380 comprises a member 381 for controlling the injected flow rate and a member 382 for measuring the injected flow rate.

[0074] The withdrawal in the holding zone and the injections of preheated fresh air into the oven lead, in the lower part of the oven, to a flow of effluents from bottom to top from the oven inlet to the withdrawal point in the holding zone and, in the upper part of the oven, to a flow of effluents from top to bottom from the oven outlet to the effluent withdrawal point in the holding zone.

[0075] The primary cooling section 400 consists of a sealed enclosure physically connected to the heating oven.

[0076] It comprises blowing ducts 401 supplied by a fan 402 via a recirculation circuit 403 comprising an isolation valve 404. The fan is equipped with a frequency converter to control its flow rate.

[0077] The return temperature of the recirculation circuit 403 is, for example, 120°C to 140°C.

[0078] The strip is thus cooled in the primary cooling section with gas taken from it.

[0079] The temperature of the air blown into the primary cooler, measured with the temperature probe 413, is adjusted by means of a controlled air inlet 405 upstream of the recirculation fan 402, by means of a member 406 for controlling the flow of fresh air entering the recirculation circuit.

[0080] The controlled air inlet 405 upstream of the recirculation fan 402 may result from a simple suction of ambient air, at room temperature, due to the primary cooler being under vacuum.

[0081] The characteristics of the controlled air inlet 405 are such that the ambient temperature throughout the primary cooler 400 does not cause recondensation of the solvents emanating in this section.

[0082] The air blown onto the belt is, for example, 100°C to 120°C.

[0083] The length of the primary cooler is sized to cool the strip to approximately 150°C. At this strip temperature, solvent and resin emissions are low enough to complete cooling in a conventionally designed 500 secondary cooling section.

[0084] The primary cooling section also includes a hot air injection pipe 410 from the exchanger 339, arranged at the outlet of the cooler in the direction of travel of the strip. This injection of preheated fresh air makes it possible to condition the temperature of the primary cooler when the installation is started. It also contributes to controlling the temperature of the gas recirculated in the primary cooler. The pipe includes a valve 411 for regulating the flow of injected hot air and a member 412 for measuring the flow of injected hot air.

[0085] Locating the hot air injection at the top of the primary cooler limits the entry of fresh air into the cooler through its upper end.

[0086] Controlling the flow of hot air injected through line 410 into the primary cooler and controlling the flow of fresh air injected into the recirculation circuit 403 make it possible to adjust the temperature of the gas blown onto the strip in the primary cooler.

[0087] Controlling the flow rate blown onto the strip, via the fan speed variator 402, allows the strip temperature at the outlet of the primary cooling section to be finely adjusted.

[0088] The primary cooling section 400 is hermetically connected to the upper part of the oven. The withdrawal carried out in the holding zone of the oven and the injection of hot air at the outlet of the cooler, via line 410, leads to a top-down flow of gases in the cooler, towards the oven.

[0089] The flow rate drawn from the primary cooler is at least equal to the sum of the flow rate of preheated air injected via line 410 and the flow rate of fresh air introduced into the recirculation circuit 403.

[0090] Thus the solvents / resins released in the primary cooler are captured via the extraction line 330 of the oven and incinerated.

[0091] The pressure in the primary cooler is controlled by means of a member 414 so as to maintain the cooler in slight depression by adjusting the withdrawal flow rate via line 330 and the preheated air injection flow rate, via line 410.

[0092] Alternatively, additional extraction is carried out directly in the primary cooler 400 when the extraction carried out in the oven via the pipe 330 is not sufficient to extract all the gases from the primary cooler, or when the amount of extraction carried out in the oven via the pipe 330 would be such as to cause too much air to enter the oven via the airlock 200 arranged at the entrance to the oven.

[0093] The secondary cooling section 500 comprises two cooling units 501, each having ducts 502 supplied with fresh air by a fan 503 via a duct 504. A speed variator makes it possible to control the flow of air blown onto the strip and thus the temperature of the strip at the outlet of each cooling unit 501.

[0094] The line also includes a 700 system for controlling and monitoring the installation. Depending on the nature of the strip, in particular its width, the speed of the strip, the nature and thickness of the paint on each side of the strip, the PMT temperature for baking the paint, the control and command system determines the operating conditions of the line and controls the various components to obtain them.

[0095] The 500 secondary cooling section allows the strip to be cooled to the desired temperature. The technology of this secondary cooling section is a conventional design.

[0096] Schematically illustrates a second example of embodiment of the invention represented here for a horizontal covering section, knowing that the technical solution also applies to vertical sections.

[0097] In addition to the removal of the airlock at the oven inlet, it differs from the first embodiment mainly in that the primary cooler 400 is not connected to the oven 300.

[0098] At the inlet of the latter, in the direction of circulation of the strip, is connected a pipe 416 for withdrawing the atmosphere present in the primary cooler connected to the suction pipe 330 of the oven, upstream of the by-pass member 336 of the incinerator 337.

[0099] This withdrawal at the primary cooler inlet combined with the injection of hot air carried out at the cooler outlet via line 410, means that the effluents emitted by the strip in the primary cooler are captured and incinerated.

[0100] The pressure in the primary cooler is controlled by means of a member 414 so as to maintain the cooler under slight depression by adjusting the withdrawal flow rate, via line 416, and the preheated air injection flow rate, via line 410.

Claims

Method for cooling a metal strip (2) in a coating section (1) of a continuous strip processing line, the strip being previously coated with a coating comprising dry extracts and a diluent before being dried in a heating section (300) and then cooled in a cooling section (600), characterized in that the cooling is carried out successively in a primary cooler (400) then in a secondary cooler (500), in which the strip is cooled in the primary cooler by convection using a gas blown onto the strip, the temperature of which is chosen so as to maintain in the primary cooler a temperature higher than the condensation temperature of the diluent. Method according to the preceding claim, in which the strip is cooled in the secondary cooler (500) by means of a fluid having a temperature lower than the temperature of the gas blown onto the strip in the primary cooler (400). Method according to the preceding claim, in which the strip is cooled in the primary cooler (400) to a temperature between 130°C and 170°C. Method according to one of the preceding claims, in which air preheated to a temperature higher than the condensation temperature of the diluent in the primary cooler is injected into the primary cooler (400) via an injection line (410) and a gas comprising the injected air and vapors of the diluent is extracted from the primary cooler via a withdrawal line (416, 330). Method according to the preceding claim, wherein the gas present in the primary cooler (400) is extracted via the heating section (300) by the withdrawal pipe (330) connected to the heating section. Method according to one of claims 4 or 5, in which the gas blown onto the strip in the primary cooler (400) is extracted from the primary cooler (400) and recirculated via a recirculation circuit (403), the temperature of said gas blown onto the strip being adjusted by injecting via an air inlet (405) a controlled flow of fresh air into the recirculation circuit (403). Coating section (1) of a continuous line for processing a metal strip (2) comprising a section (100) for coating the strip with a coating comprising dry extracts and a diluent, a heating section (300) for drying the coating and a cooling section (600), characterized in that the cooling section comprises a primary cooler (400) in which the strip is cooled by convection by means of a gas blown onto the strip, the temperature of which is chosen so as to maintain in the primary cooler a temperature higher than the condensation temperature of the diluent followed by a secondary cooler (500) in which the strip is cooled by means of a fluid having a temperature lower than the temperature of the gas blown onto the strip in the first cooler. Coating section (1) according to the preceding claim, in which the primary cooler (400) comprises blowing boxes (401) arranged opposite the strip and supplied with cooling gas by a circuit (403) for recirculating the gas present in said primary cooler (400), said primary cooler being connected to a controlled injection line (410) of a flow of preheated air into said primary cooler. Coating section (1) according to one of claims 7 or 8, in which the recirculation circuit (403) comprises an air inlet (405) allowing injection of a controlled flow of fresh air into said recirculation circuit to adjust the temperature of the gas supplying the blowing boxes (401). Coating section (1) according to one of claims 7 to 9, wherein the primary cooler (400) is connected to the heating section (300), the coating section further comprising a withdrawal pipe (330) connected to the heating section (300) capable of extracting the gas from said primary cooler (400) via the heating section (300). Coating section (1) according to one of claims 7 to 10, further comprising an airlock (200) arranged at the inlet of the heating section (300). Coating section (1) according to one of claims 7 to 11, further comprising a withdrawal line (416) connected to the primary cooler (400) for extracting the gas present in said primary cooler.

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