KR102512125B1 - A continuous annealing or galvanizing line comprising a tensile block between two consecutive furnaces - Google Patents

Abstract

Continuous annealing or galvanizing line with a tensioning unit between two consecutive furnaces
Continuous annealing or galvanizing line for metal strips with at least two consecutive annealing furnaces, a tensioning unit having at least two rollers located between the two annealing furnaces, and a production control and optimization system for the line. .

Description

A continuous annealing or galvanizing line comprising a tensile block between two consecutive furnaces

The present invention relates to continuous annealing or galvanizing lines for steel strips. By galvanizing, whether the coating is zinc, aluminum, an alloy of zinc and aluminum, or any other type of coating, all herein intended as dip-coating. More specifically, the present invention relates to managing strip tension on lines with continuous furnaces.

In a continuous line, the steel strips are successively subjected to different heat treatments as they travel through the various heating and cooling chambers. To ensure good strip progression through the chambers, it is necessary to wrap them precisely around the support rollers inside the chambers. The outer surfaces of the rollers are shaped to help guide the strip through the center of the furnace. At the same time, excessive tension must be avoided, since there is a risk of plasticizing the steel strip as it progresses through the hot chambers, thereby causing wrinkles on the surface of the strip or breaking the strip, which may interrupt the installation. . Traditionally, as shown in Figure 1 of US4358093, the tension level in the furnace is controlled by two tensioning units with two or three rollers located outside the furnace, one block of which is Upstream of the furnace and another downstream of the furnace, the strip tension is adjusted more gradually and lightly by the support rollers of the furnace according to the changing temperatures of the product in the heating and cooling chambers. Thus the tension is progressively reduced in one heating chamber and gradually increased in the subsequent cooling chamber. Sometimes, as shown in Figure 3 of US4358093, a tensioning unit is used in the furnace upstream of the cooling chamber before the strip enters the cooling chamber.

EP1167553 discloses the implantation of tension units on both sides of the cooling chamber in FIG. 4 . Being located downstream allows for a limited level of strip tension in the overaging section located after the cooling chamber. In this overaging section, the strip is reheated and maintained at a suitable temperature, for example 300°C. In the case of galvanizing lines, two or three roll tensioning units are used at the end of the furnace to greatly increase the tension of the strip in the cooling tower.

Steel quality is constantly evolving, in particular to increase the mechanical strength of steel, thereby making it possible to reduce material thickness and lower consumption through weight reduction. New grades of steel require a thermal cycle with two consecutive annealing treatments, which is why there are two furnaces in the same consecutive annealing or galvanizing line.

In a line configuration in which two annealing furnaces are arranged in sequence, a first series of heating chambers followed by cooling chambers for a first annealing thermal cycle and a second series of heating chambers followed by cooling chambers for a second annealing thermal cycle There are combinations of series, all consecutive in the same column section of the line. The annealing temperature is related to the chemical composition of the steel, its metallurgical state, in particular the level of hardening, and the heating rate to the annealing temperature and the immersion time at this temperature. The annealing temperature and, therefore, the immersion time depend on the austenite fraction required at the end of immersion. Typically, the annealing temperature is between 700 °C and 1000 °C. At the end of the first annealing cycle, the strip is typically cooled to a temperature of 100 °C to 300 °C depending on the desired metallurgical transformations. The annealing temperature is then reached again and then cooled before a possible overaging section. The problem posed by a line with two consecutive annealing furnaces stems from the fact that the two furnaces and their constituent chambers may exhibit abnormal operating conditions compared to a line with a single annealing furnace. Each furnace can be operated at high or low temperatures, or it can be stopped while the strip is still running through the furnace.

Controlling the tension between the annealing furnaces and the various chambers of both furnaces is an important factor in avoiding, as far as possible, production stoppages caused by misleading or breaking the strip. In a line with two consecutive annealing furnaces, the strip length in the line is significantly increased compared to a conventional line with a single furnace, making it more difficult to guide the strip along all the lines. Moreover, the thermal transfer and strip format transfer steps require clearly controlled tension in the configuration of two successive annealing furnaces, which at the same time constitute different thermal assemblies as a whole. This is because there can be several steel coils of different formats with thermal cycles.

Thus, tension management for a continuous annealing or galvanizing line with two annealing furnaces must address three key issues:

. Ensures exact alignment of the strip in the center of all chambers of the two furnaces, regardless of how each furnace operates.

. Regardless of how each furnace is operated, good product surface quality is ensured by avoiding the risk of plastic deformation of the strip subjected to different levels of temperature and tension in different chambers.

. Ensuring that thermal cycles and strip format transition steps are managed without loss of production.

Of course, these three problems are closely linked to each other and to the temperature control of the furnaces.

For existing annealing or galvanizing lines, tension management is within the state of the art. Existing annealing or galvanizing lines are lines comprising a single furnace.

Traditionally, the tension is set to a low tension within the heating chamber, or to gradually decrease slightly between the cooler inlet of this chamber and its hotter outlet, to avoid plastic deformation of the strip while ensuring its proper movement. . Tension is gradually increased in the cooling chambers. This tension control is traditionally achieved by torque regulation of the support rollers used to move the steel strip.

The state of the art also suggests using a tensioning unit in the furnace upstream of the cooling chamber to maintain a low level of tension in the furnace and significantly increase the strip tension in the cooling chamber.

In a line of two annealing furnaces, the first furnace has, for example, a heating section with direct combustion burners (NOF section) or radiant tubes (RTF section), or a combination of the two, an immersion section, and a gas cooling by cooling, by liquid, by mist of gas and liquid, or by a combination of some of these methods.

The second furnace includes, for example, a heating section (RTF), an immersion section, and one or several sections for cooling by gas, by liquid, by mist of gas and liquid, or by a combination of some of these methods. Other sections may exist, for example an overaging section after cooling sections.

In a galvanizing line with two annealing furnaces, after the second annealing, the steel strip is cooled to a temperature close to that of a zinc pot and then coated with zinc or another coating by being immersed in a zinc pot. It is then cooled to ambient temperature, for example by blowing air.

Lines with consecutive annealing furnaces create new difficulties in managing tension in different sections.

The first difficulty posed by two series of furnaces is how to control the very different tension levels in each of the two furnaces in relation to the temperature levels in the various chambers. This problem is exacerbated by the fact that the operating temperature range of the two furnaces is considerably wider than current industry practice. For one furnace operating at an annealing temperature of the order of 700 °C to 950 °C in the heating chamber, compared to modes of operation where the same furnace or other furnaces in the heating chamber are at lower temperatures, typically between ambient and 500 °C, a wide range There is a need for tension control. The requirements for optimal operation of the two furnace lines impose great flexibility in the tension control individually or in combination for each of the two furnaces.

A first aspect of the present invention is a method for advancing metal strips comprising at least two successive annealing furnaces and a tensioning unit comprising at least two rollers disposed between the two furnaces. A continuous annealing or galvanizing line is suggested.

A line according to the invention may also comprise means for controlling the tensioning unit to manage the tension applied to the strip by the tensioning unit.

One possibility is that, in the direction of strip travel, the tensioning unit is arranged after the cooling section of the first furnace and before the heating section of the second furnace.

The tensioning unit may be disposed within an atmosphere separation volume on the line, the volume being located between upstream and downstream furnaces.

The line according to the invention may also include a strip length accumulator located between the two annealing furnaces.

The accumulator may be disposed in a chamber having outer walls that separate an atmosphere present within the chamber from an atmosphere present outside the chamber, eg air, the outer walls also preferably removing heat from the chamber. Being thermally insulated, such as to limit losses, the chamber may also include means for heating or maintaining the strip temperature.

A second element of the invention is a metal in line arranged to steer a running strip, comprising a tensioning unit comprising at least two successive annealing furnaces and at least two rollers disposed between the two furnaces. We propose processes for annealing or galvanizing the strips.

The process according to the invention, in particular to optimize the management of thermal and strip format transitions between two nodes, preferably using the management of the tensioning unit to control the tension on the strip applied by the tensioning unit, and applying differentiated parameters to the line for strip running speed and/or strip tension at the two nodes.

Another aspect of the invention is a computer program product downloadable from a communication network and/or stored on a computer readable medium and/or executable by a microprocessor and loadable into an internal memory of a computing unit. , characterized in that it comprises programming code instructions which, when executed by said calculating unit, initiate one or more of the steps of the process according to the invention or improvements thereof.

One possibility, on a known line, is that a two-roller or three-roller tensioning unit is placed between the first and second annealing furnaces, typically between the final cooling chamber of the first furnace and the first heating chamber of the second furnace. is placed on This device avoids tension control where one furnace is connected to another furnace. This allows the management of high tension in one furnace and simultaneously low tension in the other furnace. This also allows for an immediate and significant increase or decrease in the tension on the strip in the strip transfer step, ie when the junction between two strips of different format and/or quality is passed.

A first aspect of the invention consists of a continuous annealing or galvanizing line for metal strip comprising at least two consecutive annealing furnaces with a tensioning unit comprising at least two rollers disposed between the two furnaces. can

In one configuration of the invention, the tensioning unit may be located after the cooling section of the first furnace and before the heating section of the second furnace.

The tensioning unit may be disposed in an atmosphere separation volume between upstream and downstream furnaces.

In another configuration of the invention, an accumulator allowing the length of the strip to be accumulated may be disposed between the two annealing furnaces. Such an accumulator may be disposed in a chamber having outer walls capable of isolating the atmosphere present in the chamber from outside air, the outer walls being insulated to limit heat loss from the chamber, the chamber also having the strip temperature It may include means for heating or maintaining.

The present invention also relates to the use of differentiated parameters for strip advance speed and/or strip tension in the two annealing furnaces to optimize the management of thermal and strip format change transitions between the two annealing furnaces. It may include a production control and optimization system for the line.

Advantageously, according to the invention, in order not to waste space on the line, a tensioning unit of rollers can be arranged in the buffer volume used to manage the atmospheric separation between the two annealing furnaces. Depending on the steel strips processed and the thermal cycles, there may be a need to manage different atmospheres in the two furnaces.

Another difficulty in a line with two consecutive annealing furnaces is managing transitions between different thermal cycles and strip formats. In a line with a single annealing furnace, the range for transitions is limited, and in most cases there is only one steel coil at a time when performing heat treatment in the furnace. In a line with two consecutive furnaces, several steel coils requiring different thermal cycles or of different formats may be on the line at the same time.

In addition, heating zones that can operate in various temperature situations are always active. In a double annealing furnace line, heating zones may be required to operate at temperatures well below that of a single furnace, about 500° C. or even lower. Existing tension control systems using chamber support rollers are not sufficient to maintain correct levels of tension in the two furnaces.

To solve the problem of managing the tension of the transition stages, a tensioning unit between the two nodes is placed at the appropriate transition moment to manage the optimum level of tension for each strip as it passes through the two nodes. It can work by creating a downward tension jump.

Advantageously, the tensioning unit can also operate during stable production stages to adjust the exact tension levels in the second furnace relative to the first furnace, via the deflector rollers of the furnaces which are technically more difficult and sensitive to maintenance. It is possible to use little or no use of the slight tension fluctuations applied.

Finally, another challenge for managing the strip motion in the transition stage in this type of line with two consecutive annealing furnaces is to change the strip advance speed before or during transition to optimize transition time and improve line productivity. is the ability to Traditionally, an optimization system for level 2 control of a furnace manages strip running speed prior to the arrival of a new strip or during transition in the furnace. If there are two furnaces in series, the target for changing the strip travel speed to optimize the transition may be reversed between the first and second furnaces. At the same time, the possibility of multiple steel coils within these two furnaces adds to the difficulty of managing strip running speed and tension.

To solve this difficulty, the present invention provides, as one possibility, a strip between the two annealing furnaces, typically between the final cooling chamber of the first furnace and the tensioning unit at the inlet of the first heating chamber in the second furnace. We propose the installation of an accumulation area. This device allows complete separation of the two successive furnaces in terms of speed and tension management. This allows the accumulation of a certain length of strip during stable operating phases, so that the strip running speed in the first furnace can be reduced without change to the strip running speed in the second furnace. In other cases, the accumulator in the furnace can be emptied and allow the strip running speed in the first furnace to accelerate while maintaining a stable strip running speed in the second furnace. This stable strip running speed in the second furnace is particularly important in the case of a galvanizing line, since in order to pass the strip through the galvanizing bath at the outlet of the second furnace, as stable a strip running speed as possible is required. Because it is necessary.

In addition to the foregoing configuration, the present invention consists of, but is by no means limited to, a specific number of other configurations which will be more clearly mentioned below with reference to assembly examples described in conjunction with the accompanying drawings.

Figure 1 is a schematic diagram of a continuous line with two annealing furnaces in the state of the art.
Figure 2 is a schematic diagram of a continuous line with two annealing furnaces according to a first configuration of the present invention.
3 is a schematic diagram of a continuous line with two annealing furnaces according to a second configuration of the present invention.
4 is a longitudinal schematic view of an exemplary assembly of accumulation chambers disposed between two annealing furnaces on a continuous line.
FIG. 5 is a cross-sectional schematic view of an exemplary assembly of accumulation chambers disposed between two annealing furnaces of FIG. 4;

These methods of assembly are in no way limiting, and in particular there may be variations of the present invention comprising only a selection of the features described below, either described, generalized, or separated from other described features, such that these selections of features are state of the art. This is the case if it is sufficient to differentiate the present invention from the state of the art or to provide a technical advantage.

The diagram in FIG. 1 of the accompanying drawings provides a schematic diagram of processing sections of a continuous galvanizing line with two annealing furnaces 30, 40 in the state of the art. Sections of the line located upstream and downstream are not shown in this diagram. The strip 1 conveyed by the rollers 2 first enters the preheating section 3 and is heated by direct-fire, for example to 500°C. It then goes to the heating section 4, where annealing takes place at a temperature of eg 800 °C. The strip then passes to a cooling section 5 where it is cooled, for example to 250 °C. The strip then enters a second heating section 6, where a second annealing takes place, for example at a temperature of 700°C. The strip then passes to a second cooling section 7 where it is cooled, for example to 460 °C. The strip is then passed through a tensioning unit (9) and immersed in a zinc bath (10) before entering the coating section (8). The configuration of the lines here is simplified to help explain the invention. An actual line will include various sections with chambers for heating, immersion, slow cooling, fast cooling, overaging, etc., for example.

The diagram in Figure 2 of the accompanying drawings provides a schematic view of processing sections of a continuous galvanizing line having two annealing furnaces according to a first assembly example of the present invention. This figure again shows the processing sections from FIG. 1 as already described. For the purpose of separating or combining the management and control of tension in the two furnaces (30, 40), a two-roller tensioning unit (11) is placed behind the cooling section (5) of the first furnace and the heating section of the second furnace. (6) is placed in front. A tensioning unit 11 is placed in a buffer volume 12 which manages the atmosphere separation between the two furnaces.

The diagram of FIG. 3 of the accompanying drawings provides a schematic view of processing sections of a continuous galvanizing line having two annealing furnaces according to a second assembly example of the present invention. This figure again shows the processing sections already described. The strip accumulating section 14 between the two furnaces is located downstream of the cooling section 5 in the direction of strip travel and upstream of the tensioning unit arranged at the inlet of the heating section 6 of the second furnace. As we have seen, this line configuration allows the accumulation of a certain length of strip in the accumulating section during stable operating phases, such that the strip running speed in the first furnace is reduced without change to the strip running speed in the second furnace. It can be. Thus, this allows complete separation of the two successive furnaces in terms of strip travel speed and tension management.

The diagram of FIG. 4 of the accompanying drawings provides a longitudinal schematic view of a strip accumulation section 14 between two annealing furnaces according to one assembly example of the present invention. This section includes a chamber 15 in which the strip 1 enters from the left side of the figure and exits on the right side and passes through atmosphere separation seals 16 . The strip is conveyed by rollers 17 and 18. The position of the set 17 of seven rollers at the bottom of the chamber 15 is fixed within the chamber. Six rollers 18 positioned above the set of rollers 17 move vertically between a lower position (A) and an upper position (B) to adjust the length of the strip present in the chamber. The rollers 18 are mounted on a moving frame connected to an elevating device not shown in the drawings. Chamber 15 is maintained under a protective atmosphere of a mixture of nitrogen and hydrogen, for example 5% hydrogen. The atmosphere is injected into the chamber from, for example, injection points 19 and leaves the chamber via exhaust ports 20 . The walls 21 of the chamber are airtight and insulated with a heat-resistant material, for example ceramic fibers, to limit heat loss of the chamber. Heating devices 22, for example electric radiant tubes, can bring or maintain the strip to a desired temperature.

The diagram of FIG. 5 of the accompanying drawings provides a transverse schematic view of the chamber 15 shown in FIG. 4 . Rollers 17 having a fixed position in the chamber 15 are rotated by motors 23 . The rollers 18, whose position is adjustable within the chamber, are not powered in this assembly example. They are rotated by the tension applied by the strip. The rollers 18 are lifted to the level of the lower part of the chamber 15 through the operation of a lifting device 24 comprising, for example, two electric hoists (not shown) disposed on each side of the chamber 15. It moves vertically from A) to level B at the top of the chamber. Slots in the chamber walls allow movement of the shafts of the rollers 18 . They are equipped with means (not shown) for restricting the flow of gas between the interior of the chamber and the volume housing the lifting device 24, for example brushes. The lifting device is maintained under the same atmosphere as the chamber 15 with gas injection at injection points 25 and 26 within the volume created by gas-tight walls 27 . The combination of airtight walls 21 and 27 and atmosphere isolating seals 16 help maintain the chamber under a protective atmosphere that is non-oxidizing to the strip.

A production control and optimization system for a continuous annealing or galvanizing line for metal strips with two annealing furnaces according to the invention is operated on a tensioning unit (11) and, if present, by an accumulating section (14). , enabling differentiated control of the strip advancing speed and tension level at the two nodes.

Of course, the present invention is not limited to the examples described above, and numerous adjustments can be made to these examples without departing outside the framework of the present invention. Moreover, the various features, forms, modifications, and assembly methods of the present invention may be interconnected in different combinations to the extent that they remain interchangeable and do not exclude one another.

Claims (8)

In a continuous annealing or galvanizing line for metal strips arranged to steer a running strip,
at least two consecutive annealing furnaces (30, 40) including a first annealing furnace (30) and a second annealing furnace (40); and
Between the at least two consecutive annealing furnaces (30, 40) after the cooling section (5) of the first annealing furnace (30) and before the heating section (6) of the second annealing furnace (40) in the direction of travel of the strip. a tensioning unit (11) comprising at least two rollers arranged on
the line comprises means for controlling the tensioning unit to manage the tension applied to the strip by the tensioning unit;
use management of the tensioning unit to control the tension applied to the strip by the tensioning unit to optimize management of thermal and strip format change transitions between the at least two consecutive annealing furnaces (30, 40); Thus, a continuous annealing or galvanizing line, wherein parameters varying depending on the speed of the strip running in the at least two consecutive annealing furnaces (30, 40) and the tension thereof are applied to the line. delete 2. The method according to claim 1, wherein the tensioning unit (11) is disposed within an atmosphere separation buffer volume (12) of the line, said volume being the first annealing furnace (30) and the second annealing furnace (40), a continuous annealing or galvanizing line. 2. The continuous annealing or galvanizing line according to claim 1, further comprising an accumulator (14) for the strip length, said accumulator being disposed between said at least two consecutive annealing furnaces (30, 40). 5. The accumulator (14) is arranged in the chamber (15) having external walls (21) separating the atmosphere within the chamber from the external atmosphere, the external walls (21) being also insulated, The chamber also comprises means (22) for heating or maintaining the temperature of the strip. An annealing or galvanizing process for metal strips on an annealing or galvanizing line, arranged to steer a running strip, comprising:
The line comprises at least two consecutive annealing furnaces (30, 40) including a first annealing furnace (30) and a second annealing furnace (40); and
Between the at least two consecutive annealing furnaces (30, 40) after the cooling section (5) of the first annealing furnace (30) and before the heating section (6) of the second annealing furnace (40) in the direction of travel of the strip. a tensioning unit (11) comprising at least two rollers disposed on
In the process, wherein the line includes means for controlling the tensioning unit to manage the tension applied to the strip by the tensioning unit.
The process includes the use of the tensioning unit to control the tension applied to the strip by the tensioning unit to optimize the management of thermal and strip format change transitions between the at least two consecutive annealing furnaces (30, 40). using management, applying parameters to the line that depend on the speed of strip progression in the at least two successive annealing furnaces (30, 40) and its tension. delete A computer readable recording medium having stored thereon a computer program comprising program code instructions which, when executed by a processor, initiate steps of a process according to claim 6 .

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