WO2009034244A1 - Equipment for coating a metal strip - Google Patents

Abstract

The invention relates to an equipment for coating a strip product (M) by passage in a liquid metal bath (31), that comprises means for controlling the running of the strip (M) between the metal bath (31) and a final quenching bath (35) along a continuous running line defined by a succession of deviation cylinders and including at least three portions, respectively a first portion (T1) at inlet of the metal bath, a second portion at the outlet of the bath (31) in an ascending direction and at least a third descending portion (T3) giving into the final quenching bath (35). According to the invention, the final quenching bath (35) is located above the metal bath (31) so that the entire running line of the strip (M) between the metal bath (31) and the final quenching bath (35) occupies an area over the ground of the same magnitude as that of the metal bath (31).

Description

 Metal coating installation Daπαe

The invention relates to an installation for coating a strip product, in particular, a metal strip, by galvanizing.

In order to improve the corrosion resistance of the metal sheets used, in particular, in certain applications such as the building, automobile or household appliances, it is common practice to deposit on the surface of these faces, a layer of zinc coating or a zinc-based alloy. The sheet being made, normally, by rolling a metal strip, it can be subjected to a galvanizing treatment performed during the running of the strip in a continuous galvanizing line. By way of example, FIG. 1 shows schematically the usual constitution of a continuous annealing and galvanizing line comprising successively, in the direction of travel of the strip, that is to say from left to right on the FIG: an inlet section 1 with one or two belt unrollers 10, 10 ', a shear 11, for example with a guillotine, a splicing welder 12 for connecting the tail of a first band from one of the unrollers 10 at the head of the next strip from the other unwinder 10 ', so as to ensure a continuous operation of the line, and a tape accumulator 13 which allows to reserve a certain length of tape so as to restore it at the line, when the flow is stopped upstream of the accumulator, to make the splice in the welder 12; a section 14 for degreasing the cold-rolled strips or acid pickling of the hot-rolled strips; - an annealing furnace 2 successively comprising a heating section 21, a retention section 22 at the annealing temperature, a rapid cooling section 23 and a section 24 for maintaining the strip at a controlled temperature, optionally for a treatment of overaging and / or to bring the band to the desired temperature before entering the molten zinc bath; a galvanizing section 3 itself, comprising a zinc bath 31 in which is immersed the strip at the outlet of the temperature holding section 24, a device 32 for spinning the liquid zinc to control the thickness of the layer coated on both sides of the strip, optionally an induction furnace 33 whose role will be indicated later, a cooling device 34 and a quenching tank 35 for the final cooling of the strip; an outlet section with, for example, a skin-pass mill 15, a passivation section 16, an outlet accumulator 17, a shear 18 and one or two winders 19.

Such an arrangement is quite conventional but, of course, may be subject to variants, depending on the processing carried out upstream or downstream of the galvanizing section itself.

FIG. 2 shows schematically, on a larger scale, the constitution of such a galvanizing section comprising means for controlling the continuous movement of the band M between a liquid zinc bath 31 and a final cooling bath. "quench tank", along a path defined by a plurality of deflection rolls and generally having a first inlet portion T1 of the band M in the metal bath 31, in a downward direction, to a first deflector roll 41 immersed in the bath 31, a second bath outlet portion 31, 31, in an upward direction, to a pair of deflector rollers 42, 42 'placed at a higher level above the bath 31 and at least a third portion T3 extending between an upper baffle roll 42 'and a lower baffle roll 43 immersed in the final cooling bath 35 and along which cooling means are placed; identification by blowing a gaseous fluid, the band M then being evacuated, passing on a deflector roll 44, towards the rest of the installation, for example a skin-pass rolling mill. Leaving the bath 31, the strip is covered on both sides with a zinc layer driven upwardly with the strip. The covered strip then passes into a wiper device 32 of known type which makes it possible to control the thicknesses of these two coating layers.

For example, French Patent No. 2,726,288 of the same company discloses such an air knife dewatering device.

In known manner, the installation may comprise, on the upstream part T2 of the path of the strip, at the outlet of the metal bath 31, a heating furnace 33 making it possible to perform a so-called alloy heat treatment which ensures the diffusion of iron from the band, to the zinc coating, to create a real iron / zinc alloy. Such a Alliation is interesting, in particular, for the automotive industry because it makes it possible to improve certain surface qualities of the coated sheets such as the adhesion of the paints or the drawing capacity.

The strip must, however, be cooled before being immersed in the quenching tank 35. The installation therefore comprises, above the alloying oven 33 and / or on the downward path T3 of the strip, a cooling device 34 comprising for example, variable speed motor-blowers blowing air on the belt and whose flow rate can be regulated by measuring the temperature. The surface quality requirements of metal sheets are becoming more severe. In particular, for automotive body panels, a visible part finish quality is required which imposes a very high level of surface quality of the strips after galvanizing.

However, metallurgical reactions occur in the zinc bath which degrade the surface of the roller 41 immersed in the zinc bath 31 quite rapidly and this results in defects which can affect the quality of the side A of the strip which is supported on the roller 41 for the change of direction, that is to say the upper face of the strip in the first part T1 entering the bath 31. That is why, usually, it is the second face A 'of the band

M, turned outward when passing on the submerged roll 41, which is reserved for parties. visible finite products, for example, a car body and it is therefore indicated to the user which of the two faces called "exposed face" has the best surface quality. However, in a conventional installation of the type shown in FIG. 2, the path of the strip at the outlet of the zinc bath 31 imposes several contacts of this exposed face A 'with deflection rollers, before sufficient cooling to prevent any degradation. the surface of the coating. For example, in the conventional arrangement shown in Figure 2, it is the upper face A of the band M that passes on the submerged roll 41 and may therefore be degraded by the defects of the roll. But in the upper part of the upward path T2, it is the second face A 'which passes over the upper deflector rollers 42, 42' before leaving the installation following the downward path T3 to the quenching bath 35 placed next to the metal bath 31. This contact of the exposed face A 'with the deflector rollers 42, 42' constitutes a risk of degradation of the surface of the coating, in particular, if an alloying treatment is carried out by passing through a oven 33 on the upward path T2 at the outlet of the bath 31. In practice it is therefore preferable to perform a first cooling of the strip before passing over the upper deflector rollers 42, 42 '. For this purpose, means 34 'of cooling by air blowing can also be placed on the upward path T2 above the alloy oven 33. This blowing cooling must, itself, be carried out with care not to degrade the quality of the zinc deposit.

However, it is necessary to have the necessary space to place the numerous apparatuses, ventilators, supply and exhaust ducts, mechanical and electrical organs, etc. In practice, two zones, respectively heating 33 and cooling 34 'are superimposed on the upward path T2, before the change of direction of the band. Such an installation must therefore be placed in a frame that can have a very high height, for example several tens of meters. Furthermore, the metal strips themselves have a large enough width, for example up to two meters and the control of their scrolling at high speed requires the use of complex and bulky equipment.

The building in which is placed such a galvanizing plant thus has a significant footprint.

However, as shown schematically in Figure 1, the galvanizing installation is only part of the production line which usually includes other sections also very cumbersome, in particular, the accumulators upstream bands 13 and downstream 17, the annealing furnace 2 which comprises a plurality of sections making it possible, on the one hand, to anneal and, on the other hand, to bring the strip to the desired temperature for galvanizing, the skin-pass rolling mill 15, the degreasing section 14 and the passivation section 16, as well as unwinding 10 and winding devices 19. The whole of such a facility is therefore an extremely important set and it is difficult, after construction, to make some sections the necessary changes while keeping the neighboring sections. It is therefore advantageous to reduce as much as possible the size of the installation, while providing opportunities for its evolution, for example by having the possibility to add, if necessary, a furnace of alliation, and / or cooling means.

The object of the invention is to solve such problems thanks to a new arrangement of the installation making it possible to reduce its footprint. On the other hand, the invention also makes it possible to delay the moment when one of the so-called "exposed face of the strip" comes into contact with a deflector roll, in order to ensure excellent quality of the coating on this exposed face. . The invention therefore applies, in a general manner, to a coating installation of a strip product by passing it into a bath of liquid metal, comprising at least three parts, respectively a first part of entering the metal bath, passing on a first deflector roll placed at a lower level, a second ascending bath outlet portion between said first lower roll and a second upper level deflector roll, above metal bath, at least a third cooling portion extending between said second upper roll and a final coolant bath, and a fourth output portion of said cooling bath.

According to the invention, the final cooling liquid bath is placed at a level higher than that of the metal bath and is shifted with respect thereto towards the inlet side, so that the fourth bath outlet portion cooling passes over the metal bath, and that the footprint of the entire coating installation does not significantly exceed that of the metal bath.

Particularly advantageously, the strip is supported, by a first face, on the first baffle roll, coming from a first inlet side in the metal bath and is supported by the same first face on the second baffle roll placed at higher level, so that the third cooling part is placed towards the same first side of the metal bath with respect to the second outlet portion of the bath.

According to another advantageous characteristic of the invention, the installation comprises a quality control station of the coating, placed on the second side of the metal bath opposite the first inlet side of the strip and in front of which passes, in the first ascending part of the metal bath outlet, the second side of the strip opposite the first bearing surface on the first and second deflection rolls, and the strip passing over a baffle roll immersed in the final cooling bath; bearing on said roll immersed by its second face, then back over the entire installation, in the fourth part of the cooling bath outlet, taking support by the same second face on two separated upper rollers and down by a last descending part of the exit of the installation by passing in front of the station of verification the same second face of the band, so that the State of the coating on this second face can be checked on the one hand to the output of the metal bath and, secondly, at the output of the installation, after final quenching.

In a preferred embodiment, the installation comprises at least one cooling means, by gas blowing, on both sides of the strip, arranged along the path thereof, or upstream of the second baffle roll in the second outlet portion of the metal bath, or downstream of said second deflector roll, at the beginning of the third cooling part. The invention also makes it possible to place a means for heating the strip in the second outlet portion of the metal bath, immediately above it, in order to perform an alloying treatment.

In a first embodiment, the third cooling portion of the web has a single strand descending from the second baffle roll to the coolant bath above the metal bath.

In another embodiment, the third cooling portion comprises, from the second baffle roll placed at a higher level, a first descending strand to a third baffle roll placed below the second roll and above the bath metallic, a second ascending strand between said third roll and a fourth baffle roll placed substantially at the second roll, and a third descending strand between said fourth roll and the coolant bath, cooling means being placed at least on the one of the two ascending and descending strands, upstream of the third deflector roll so as to allow a support of the band on said third deflector roll, by its second face opposite to the first bearing face on the first and the second deflection roll, without deterioration of the coating deposited on this second face. Advantageously, cooling means are arranged, respectively, on the upward path between the first and second baffle rolls and on the descending path between the second upper roll and the third lower roll, said cooling means being offset in height and arranged in a staggered arrangement. The invention is particularly applicable to a coating installation arranged downstream, in the direction of travel, of an annealing line placed inside a closed enclosure for maintaining a non-oxidizing atmosphere, with scrolling the strip between two sets of deflector rollers spaced apart in height, said enclosure being closed at an outlet end by a vertical wall having a height corresponding to the spacing between the deflection rollers and provided at its lower part with a closed chute outlet strip to the metal bath gulvanization. In this case, the entire coating installation can be arranged in a constricted space extending vertically along the vertical closing wall of the enclosure and horizontally over a distance corresponding to the footprint of the bath metal with the exit chute of the band.

But the invention can also be applied, advantageously, to a coating installation disposed downstream from an annealing line placed inside a closed enclosure extending horizontally between an inlet end and an end of outlet equipped with a connecting chute opening into the galvanizing metal bath.

In this case, the final cooling bath can be placed above the annealing enclosure, some distance upstream of the outlet end, and the third part of the path of the strip, along which cooling means are placed horizontally above the annealing chamber and returning upstream to the final cooling bath from which the fourth bath outlet portion extends horizontally downstream. passing over said cooling means.

The invention also covers other advantageous features which will appear in the following description of certain particular embodiments, given by way of example and shown schematically in the accompanying drawings. FIG. 1 is a general diagram of the assembly of an annealing and galvanizing line of known type;

- Figure 2 shows schematically the conventional layout of a galvanizing plant;

- Figure 3 is a diagram of a galvanizing installation according to the invention;

- Figure 4 shows a variant with staggered arrangement of the cooling means;

Figure 5 shows schematically another arrangement of a galvanizing installation according to the invention. FIG. 3 schematically shows a preferred embodiment of a galvanization plant according to the invention as indicated above, the strip M to be treated was first brought to a temperature which is desirable for galvanizing, preferably in a annealing furnace ending in a holding section 24 at a controlled temperature and having, at its outlet, a deflector roll 40 which directs the strip towards the galvanizing metal bath 31 formed in a tank

30 and wherein is immersed a first deflector roll 41. The band

M therefore follows a downward path T1 between the output roll 40 and the immersed roll 41 on which it bears by its upper face A. The strip M then leaves the bath 31 along an upward vertical path T2 to an upper roller 42 passing a wiper device 32 for controlling the thickness of the coating.

All these provisions are conventional and correspond to those described above with reference to FIG. In the invention, however, the band M is supported on the upper roll 42 by the same side A passing on the immersed roll 41.

For this, instead of being diverted out of the tray 30, the band M returns to the side by which it had entered the tray, that is to say the left side in Figure 3.

In this way, it is only at the lower end of the downward path T3 that the second face A 'of the strip M, turned downwards in the galvanizing bath 31, makes contact with a deflector roll 43. This face A 'can therefore cool successively, along the upward path T2 and the downward path T3, to a temperature enabling it to rest on the lower roller 43 without risk of degradation of the coating.

If it is desired to carry out an alloying treatment, an oven 33 is placed above the dewatering device 32 and is followed by cooling cells 6 which can be placed, not only on the upward path T2, upstream of the upper roller 42, but also on the downward path T3, above the lower roller 43. It is thus possible to achieve sufficient cooling of the strip before the contact of its side A 'with the lower roller 43. It follows from this arrangement of the path of the strip, that the tank 5 containing the quenching bath 35, in which the final cooling of the band M is achieved, is placed above the tank 30 containing the galvanizing metal bath 31 and offset by relative to it, to the inlet side of the galvanizing installation whose footprint is thus reduced compared to the conventional arrangement of Figure 2.

As indicated above and in the manner shown in FIG. 1, the galvanizing installation 3 is preceded, usually, by an annealing line 2 terminating in a section 24 in which the strip is brought to the desired temperature for galvanizing. In addition, to avoid the risk of oxidation of the band, the assembly is placed under a protective atmosphere in a closed enclosure 8 extended at its outlet end of the band M, by a chute 81 immersed in the metal bath 31 to maintain the seal.

Generally, to reduce the length of the line, the band passes on two series of deflector rollers spaced in height and the enclosure 8 is therefore closed, at its outlet end, by a vertical wall 80 of corresponding height.

According to the invention, the quench tank 35 is placed above the metal bath 31 and the outlet trough 81 and the assembly of the coating installation can therefore be arranged in a constricted space extending vertically in height, along the closing wall 80 of the annealing enclosure 8 and horizontally over a distance not exceeding the footprint of the metal bath 31 with the connecting trough 81.

Thus, the overall size, in length, of the treatment line can be decreased compared to the conventional arrangement of Figures 1 and 2.

Admittedly, such an arrangement requires the construction, above the metal bath 31, of a floor to support the quench tank 5, but this increase in height of the installation does not constitute a real disadvantage, particularly for the transformation of an existing installation. On the contrary, the transfer of the quench bath above the metal bath makes it possible to release, next to it, a space which, as will be seen below, can be used, for example, to place a station 7 of check the quality of the tape.

Similarly, the upper roller 42 may be placed at a height sufficient to have the cooling means 6 extending over the length necessary to obtain sufficient cooling of the strip before the contact of its side A 'with the lower roller 43. In this case, this roll 43 can be immersed in the quench bath 35.

However, to achieve sufficient cooling of the strip before quenching, without unduly increasing the height of the installation, after the downward path T3 and its passage on the lower roller 43, the band M can go up an ascending path T31 until to a second upper roll 44, then descend, in a descending path T32, to a deflector roll 45 immersed in the final cooling bath 35.

At the exit of this quenching bath 35, the band M follows a rising path T4 to a pair of upper deflector rollers 46, 46 'spaced apart from each other, so as to pass the band over of the whole of the galvanizing section, then down, by a downward path T5, up to a lower roll 47 to be directed towards the rest of the installation, for example a skin-pass 15 mill.

As indicated above, on the side of the galvanizing tank opposite the entrance side of the strip, that is to say to the right of the tank 30 in FIG. 3, can be placed a verification station 7, by example a control cabin for an operator.

This station 7 can thus be placed between the first ascending section T2 of the outlet of the metal bath 31 and the last descending section T5 of the outlet of the installation, deflector rollers 48 allowing, possibly, to provide the necessary location for the station 7 .

The operator placed in the control cabin thus passes, in the ascending section T2, the outer face A 'of the strip which, because of the arrangement according to the invention, comes into contact with the roll 43 after cooling along the ascending section T2 and the descending section T3. This external face A 'therefore undergoes no degradation and thus constitutes the so-called "exposed" face which will subsequently be the visible face of the sheet for example for a car body.

Thanks to the particular path of the band, shown diagrammatically in FIG. 3, it is the same exposed face A 'which passes in front of the operator in the last descending section T5, on the other side of the cabin 7.

Thus, the operator sees successively before him twice the same face. Knowing the total length of the path and the running speed of the belt which can be measured at any moment, the operator can therefore locate on the exposed face A 'of the belt, immediately above the wiper device 32, a doubtful zone and, after having allowed the time necessary for scrolling, to identify the passage of the same zone on the descending path T5 in order to check the possible presence of a defect after the final cooling and hardening of the coating. The arrangement according to the invention thus makes it possible to guarantee the best possible integrity of the exposed face of the coated strip.

Of course, the invention is not limited to the details of the embodiment which has just been described but covers all the variants using equivalent means and remaining in the same protective frame. For example, as we have seen, the arrangement according to the invention makes it possible to distribute cooling means 61, 62 not only along the upward path T2 but also along the downward path T3, so as to provide sufficient cooling from the coating to the passage of the exposed face A 'on the lower roller 43. As shown in Figure 4, cooling cells 61, 62 may advantageously be staggered on the ascending strand and descending strand. In this way, the two strands T2, T3 can be separated by a single upper roller 42, which further reduces the footprint of the assembly. In addition, such an arrangement makes it possible to distribute the cells 6 over a greater length of strip and thus to have a less violent blowing, which reduces the risk of producing a vibration of the strip which may have an impact on the quality of the coating. , in particular, the regulation of its thickness.

Furthermore, the invention is not limited to the case where, to reduce the length of the annealing line, the strip follows a zig-zag path by passing over two sets of rollers spaced apart in height. Indeed, the invention can also be applied to the case of a continuous annealing furnace in which the band scrolls horizontally over a large length.

In this case, shown diagrammatically in FIG. 5, the quenching bath 35 which, according to the invention, is offset backward with respect to the galvanizing bath 31, can be placed above the outlet end of the enclosure annealing 8 'whose height is, then, relatively reduced. The third part T3 of the path of the strip then extends horizontally while returning towards the upstream to the quenching tank 35 which is shifted back a sufficient distance to dispose the necessary means of refrofdissement 6 along said strand T3 . The fourth portion T4 of quenching bath 35 then returns horizontally downstream passing above said cooling means 6.

As before, the footprint of the coating plant 3 does not substantially exceed that of the galvanizing bath 31.

Furthermore, the invention has been described in the usual case of a coating by passing on a roll immersed in a bath of liquid metal but it could also be applied to other coating devices, for example of the type in which the metal bath of galvanization is maintained by magnetic levitation by means of induction coils arranged along the upward path of the strip after passing on the lower roller 41 which, in this case, is not immersed.

Claims

1. Apparatus for coating a strip product (M) by passing through a bath of liquid metal (31), comprising means for controlling the movement of the strip (M) between an inlet side in the metal bath liquid (31) and an outlet side of the installation, along a continuous line of scroll defined by a plurality of baffle rollers and having at least four parts, respectively a first portion (T1) of entry into the bath metallic, passing on a first deflector roll (41) at a lower level, a second upstream bath outlet portion (T2) (31), between said first lower roll (41) and a second deflection roll ( 42) placed at a higher level, above the metal bath (31), at least a third cooling portion (T3) extending between said upper roll (42) and a final cooling bath (35) and along of which means (34) are arranged cooling of the coating with a gaseous fluid, and a fourth portion (T4) of outlet of the final cooling bath (35), characterized in that the final cooling bath (35) is placed at a level higher than that of the bath metal (31) and offset from it to the inlet side, so that the footprint of the entire coating installation does not substantially exceed that of the metal bath (31) at above which passes the band (M) in the fourth part (T4) of its path between the final cooling bath (35) and the output of the installation. 2. coating installation according to claim 1, characterized in that the strip (M) is supported by a first face (A) on the first baffle roller (41), from a first inlet side in the metal bath (31) and is supported by the same first face (A) on the second baffle roll (42) placed at the upper level, so that the third cooling part (T3) is placed towards the same first side of the metal bath (31) relative to the second portion (T2) of the bath outlet. 3. Installation coating according to claim 2, characterized in that it comprises a station (7) for checking the quality of the coating, placed on the second side of the metal bath (31), opposite the first input side of the strip (M) and in front of which, in the first ascending part (T2) of exit of the metal bath, passes the second face (A ¹ ) of the strip opposite to the first face (A) of pressing on the first and second deflection rollers (41, 42), and that the band passes over a baffle roll (45) immersed in the final cooling bath (35), resting on said submerged roll (45) by its second face (A '), then, in the fourth portion (T4) of the cooling bath outlet (35), passes over the whole of the installation taking support by the same second face (A') on two upper rollers (46, 46 ') spaced apart and down by a last descending part of the output of the installation (T5) by passing in front of the verification station (7) the same second face (A') of the strip (M ), so as to verify the state of the coating on this second face, on the one hand at the exit of the metal bath (31) and, on the other hand at the end of the installation, after final cooling. 4. Installation coating according to one of the preceding claims, characterized in that it comprises at least one cooling means (6) by blowing gas on both sides (A, A ') of the strip (M) disposed along the path thereof, either upstream of the second baffle roll (42) in the second outlet portion of the metal bath (T2) or downstream of said second baffle roll (42) at the beginning of the third cooling part (T3). 5. Installation coating according to one of the preceding claims, characterized in that it comprises a heating means (32) of the strip (M) disposed in the second outlet portion (T2) of the metal bath (31) , immediately above it. 6. Installation coating according to one of the preceding claims, characterized in that the third cooling portion (T3) comprises a single strand descending from the second baffle roller (42) to the coolant bath (35). 7. Coating plant according to one of claims 1 to 5, characterized in that the third cooling part (T3) comprises, from the second baffle roller (42) placed at a higher level, a first descending strand ( T3) to a third baffle roll (43) located below the second roll (42) and above the metal bath (31), a second upstroke (T31) between said third roll (43) and a fourth baffle roll (44) substantially at the second roll (42), and a third descending run (T32) between said fourth roll (44) and the coolant bath (35), means at least on one of the two ascending and downwardly extending strands (T3), upstream of the third deflector roll (43) so as to support the web on said third deflector roll by its second face (A ') opposite to the first face (A) bearing on the first and the second baffle rollers (41, 42), without deterioration of the coating deposited on this second face (A'). 8. Installation coating according to one of the preceding claims, characterized in that cooling means (61, 62) are respectively disposed on the upward path (T2) between the first (41) and the second (42) baffle rollers as well as on the downward path (T3) between the second upper roll (42) and the third lower roll (43), said cooling means (6) being offset in height and arranged in staggered rows. 9. Installation coating according to one of the preceding claims, characterized in that it is arranged downstream in the direction of travel, a annealing line placed inside a closed chamber for the maintenance of a non-oxidizing atmosphere, with the strip running between two series of deflector rollers spaced apart in height, said enclosure being closed at an outlet end by a vertical wall having a height corresponding to the spacing between the deflection rollers and provided with at its lower part, a closed exit chute of the strip towards the galvanizing metal bath, and that the entire coating installation is arranged in a constricted space extending vertically along the vertical wall closing the enclosure and horizontally over a distance corresponding to the footprint of the metal bath with the discharge chute of the strip. 10. Installation coating according to one of claims 1 to 5, characterized in that it is arranged downstream in the direction of travel of an annealing line placed inside a closed chamber for maintaining a non-oxidizing atmosphere, said enclosure extending horizontally between an inlet end and an outlet end provided with a connecting chute opening into the metal bath of galvanizing (31), that the final cooling bath (35) is placed above the annealing enclosure, at a distance upstream of the outlet end, and that the third portion (T3) of the path of the strip, along which cooling means (6) is located extends horizontally above the annealing chamber, returning upstream to the final cooling bath (35) from which the fourth part ( T4) of the bath extends horizontally downstream passing above said cooling means (6).