ULTRAFAST PICKLING METHOD AND INSTALLATION THEREFOR

Abstract

A pickling installation for applying a pickling treatment to a metal strip in continuous movement, the pickling treatment using an acid solution, the pickling installation including: a plurality of cascading treatment tanks among which at least one treatment tank includes a spray/injection section for spraying/injecting the acid solution on the metal strip; and collection means for retrieving the sprayed acid solution after use and redirecting the sprayed acid solution to each spray/injection section. The at least one treatment tank has a first header in front of a first face of the metal strip and a second header in front of a second face of the metal strip. In a first treatment tank configuration, each of the first header and the second header have an internal flat surface intended to be parallel respectively to first and second faces of metal strip, and at a distance thereof.

Claims

1. A pickling installation for applying a pickling treatment to a metal strip in continuous movement, the pickling treatment using an acid solution, the pickling installation comprising: a plurality of cascading treatment tanks among which at least one treatment tank comprises a spray/injection section for spraying/injecting the acid solution on the metal strip; and collection means for retrieving the sprayed acid solution after use and redirecting the sprayed acid solution to each spray/injection section, wherein the at least one treatment tank comprises a first header in front of a first face of the metal strip and a second header in front of a second face of the metal strip, wherein, in a first treatment tank configuration, each of the first header and the second header have an internal flat surface intended to be parallel respectively to the first and second faces of metal strip, and at a distance thereof, defining a first gap and a second gap respectively, the first header and the second header each comprising a plurality of holes drilled through the internal flat surface according to a defined 2D-pattern, for spraying the acid solution to the metal strip in straight jets, under conditions suitable to create in use at the surface of the metal strip a highly turbulent liquid cushion, or alternately, wherein, in a second treatment tank configuration, each of the first header and the second header have an internal flat surface intended to be parallel respectively to the-first and second faces of the metal strip, and at a distance thereof, defining a first gap and a second gap respectively, acid solution injection means being provided at an edge injection opening of each respective gap, under conditions suitable to create at the surface of the metal strip a highly turbulent liquid zone occupying the whole respective gap volume, or alternately, wherein a third treatment tank configuration combines the first treatment tank configuration and the second treatment tank configuration, and wherein, either in the first treatment tank configuration or in the second treatment tank configuration, the internal flat surface, except at locations of the holes drilled therein in case of the first treatment tank configuration, is continuous.

2. (canceled)

3. The pickling installation according to claim 1, wherein the collection means comprise at least one storage tank and at least one pump as well as means for injecting fresh acid into the pickling tanks in counter-current in respect of a cascading direction.

4. The pickling installation according to claim 1, further comprising: at least one other treatment tank.

5. The pickling installation according to claim 3, wherein the at least one other treatment tank comprises an immersion or a rinsing treatment tank.

6. The pickling installation according to claim 1, wherein lateral side guides are provided for maintaining the liquid cushion or the highly turbulent zone in the gap, or wherein the first and the second gaps are designed to form a tunnel having a width equal to the width of the line.

7. The pickling installation according to claim 3, wherein the at least one pump comprises a material able to resist to abrasive particles present inside the acid solution, selected from a group consisting of ceramic, graphite, polyvinylidene fluoride, and polytetrafluoroethylene.

8. The pickling installation according to claim 3, wherein the at least one pump is designed so that the abrasive particles are injected by venturi effect after a pump outlet.

9. The pickling installation according to claim 1, wherein the first gap and the second gap are different.

10. The pickling installation according to claim 1, wherein the injection means are provided at an edge injection opening of the gap co-current or counter-current to the strip, in this last case to increase the relative speed between the strip and pickling flow.

11. A method for applying a pickling treatment to a metal strip in continuous movement, using the pickling installation according to claim 1, the method comprising: providing the pickling installation with the acid solution; directing the moving metal strip into the at least one treatment tank comprising athe spray/injection section for spraying/injecting the acid solution on both faces of the metal strip under high turbulence conditions; and retrieving the acid solution sprayed on the metal strip and redirecting again the acid solution to the spray/injection section using the collection means.

12. The pickling method according to claim 11, wherein the metal strip is further directed to be treated in one or more other treatment tanks.

13. The pickling method according to claim 11, wherein the metal strip comprises a steel strip selected from a group consisting of a carbon steel strip, a stainless steel strip, and an alloyed steel strip.

14. The pickling method according to claim 11, wherein the acid solution used comprises a hydrochloric acid, sulphuric acid, nitric acid, phosphoric acid, hydrofluoric acid solution or an organic, such as formic, acid solution.

15. The pickling method according to claim 11, wherein acid insoluble abrasive mineral particles insoluble in acid are added to the acid solution.

16. The pickling method according to claim 15, wherein a Mohs hardness of the acid insoluble abrasive mineral particles is between 4 and 7.

17. The pickling method according to claim 15, wherein the acid insoluble abrasive mineral particles are selected from a group consisting of corundum, glass microballs, alumina, silicate, silicon carbide, and zirconium.

18. The pickling method according to claim 11, wherein a flow rate of the sprayed/injected acid solution is selected so as to obtain in the first tank configuration a thickness of the highly turbulent liquid cushion equal to the-a thickness of the gap.

19. The pickling method according to claim 11, wherein the-a maximum temperature of the acid solution is 80° C., in case of use of polypropylene, PVDF, PTFE tanks.

20. The pickling method according to claim 11, wherein the abrasive particles are recovered at an end of the process, by filtration or decantation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. Other features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following:

[0029] FIG. 1 is a schematic view representing a metallurgical pickling line according to prior art.

[0030] FIG. 2A is a schematic cross-sectional longitudinal view representing the principle of acid pickling under high turbulence WPC conditions applied to a moving metal strip.

[0031] FIG. 2B is a schematic cross-sectional longitudinal view representing the principle of acid pickling under high turbulence HTLP conditions applied to a moving metal strip.

[0032] FIG. 2C is a schematic cross-sectional longitudinal view representing the principle of acid pickling under high turbulence respective WPC and HTLP conditions applied to a moving metal strip.

[0033] FIG. 3 is a schematic cross-sectional longitudinal view representing the principle of acid pickling under high turbulence respective WPC and HTLP conditions applied to a moving metal strip, in presence of abrasive particles in the tank solution.

[0034] FIG. 4 is a picture of the jet impacts (primary and secondary turbulence), having the form of a honeycomb, according to the first configuration of the invention.

[0035] FIG. 5 diagrammatically shows the average heat transfer coefficient in function of the average flow density for cylinder cooling installations using HTRC technology in comparison with those using high pressure flat jet sprays technology.

DETAILED DESCRIPTION

[0036] In an embodiment, the present invention provides a pickling installation and method for manufacturing metal products such as steel strips with reduced pickling time, especially in presence of hard to remove oxides such as fayalite on the steel surface.

[0037] In an embodiment, the present invention provides a pickling installation for applying a pickling treatment to a steel strip (10) in continuous movement, said pickling treatment using an acid solution, said pickling installation comprising: [0038] a plurality of cascading treatment tanks among which at least one treatment tank comprising a spray/injection section for spraying/injecting the acid solution on the metal strip, and [0039] collection means for retrieving the sprayed acid solution and redirect the same to each spray/injection section; [0040] the at least one treatment tank comprising a first header in use in front of a first face of the metal strip and a second header in use in front of a second face of the metal strip, wherein: [0041] in a first treatment tank configuration, each of the first header and the second header have an internal flat surface intended to be parallel respectively to the first and second faces of the metal strip, and at a distance thereof, defining a first gap and a second gap respectively, said first header and said second header comprising each a plurality of holes drilled through the internal flat surface according to a defined 2D-pattern, for spraying the acid solution to the metal strip in straight jets, under conditions suitable to create in use at the surface of the metal strip a highly turbulent liquid cushion, or alternately; [0042] in a second treatment tank configuration, each of the first header and the second header have an internal flat surface intended to be parallel respectively to the first and second faces of the metal strip, and at a distance thereof, defining a first gap and a second gap respectively, acid solution injection means being provided at an edge injection opening of each respective gap, under conditions suitable to create in use at the surface of the metal strip a highly turbulent liquid zone occupying the whole gap volume, or alternately; [0043] a third treatment tank configuration combines the first treatment tank configuration and the second treatment tank configuration; [0044] and wherein, either in the first treatment tank configuration (1A) or in the second treatment tank configuration (1B), said internal flat surface (6), except at the locations of the holes drilled therein in case of the first configuration (1A), is continuous.

[0045] It should be noted that a distinction is made between generally multi-jet sprays, as in the first configuration, and slot injector(s), as in the second configuration.

[0046] According to particular embodiments, the pickling installation further comprises at least one of the following characteristics or a suitable combination thereof: [0047] the collection means comprise at least one storage tank and at least one pump as well as means for injecting fresh acid into the pickling tanks in counter-current in respect of the cascading direction; [0048] the pickling installation comprises at least one other treatment tank; [0049] the at least one other treatment tank is an immersion or a rinsing treatment tank; [0050] lateral side guides are provided for maintaining the liquid cushion or the highly turbulent zone in the gap or the first and the second gaps are designed to form a tunnel having a width equal to the width of the line; [0051] the at least one pump is made of a material able to resist to abrasive particles present inside the acid solution, selected from the group consisting of ceramic, graphite, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE); [0052] the at least one pump is designed so that the abrasive particles are injected by venturi effect after a pump outlet; [0053] the first gap and the second gap are different, in particular the first gap is greater than the second gap; [0054] the injection means being provided at an edge injection opening of the gap are cocurrent or counter-current to the strip, in this last case to increase the relative speed between the strip and pickling flow.

[0055] A second aspect of the present invention relates to a method for applying a pickling treatment to a metal strip in continuous movement, using the pickling installation according to anyone of the preceding claims, wherein it comprises the steps of: [0056] providing the pickling installation with an acid solution; [0057] directing the moving metal strip into at least one treatment tank comprising a spraying/injection section for spraying/injecting the acid solution on the metal strip, and spraying/injecting the acid solution on both faces of the metal strip under high turbulence conditions; [0058] retrieving the acid solution sprayed on the metal strip and redirecting again the same to the spraying sections using the collection means.

[0059] According to particular embodiments, the pickling method further comprises at least one of the following characteristics or a suitable combination thereof: [0060] the metal strip is further directed to be treated in one or more other treatment tanks; [0061] the metal strip is a steel strip, selected from the group consisting of a carbon steel strip, a stainless steel strip, and an alloyed steel strip; [0062] the acid solution used is a hydrochloric acid, sulphuric acid, nitric acid, phosphoric acid, hydrofluoric acid solution or an organic, such as formic, acid solution; [0063] acid insoluble abrasive mineral particles are added to the acid solution; [0064] the Mohs hardness of the acid insoluble abrasive mineral particles is comprised between 4 and 7, and preferably is greater than or equal to 5; [0065] the acid insoluble abrasive mineral particles are selected from the group consisting of corundum, glass microballs, alumina, silicate, silicon carbide and zirconium; [0066] the flow rate of the sprayed/injected acid solution is selected so as to obtain in the first tank configuration a thickness of the highly turbulent liquid cushion equal to the thickness of the gap; [0067] the maximum temperature of the acid solution is about 80° C., for example in case of use of polypropylene, PVDF, PTFE tanks; [0068] the abrasive particles are recovered at the end of the process, for example by filtration or decantation.

[0069] According to a particular embodiment, the metallurgical line and thus the continuous strip movement is horizontal. In this case, the first header, the second header respectively, is an upper header, respectively a lower header. Further the first face of the strip, the second face of the strip respectively, is an upper face, a lower face respectively.

[0070] According to another embodiment, the metallurgical line and thus the continuous strip movement is vertical.

[0071] In the pickling method according to a first embodiment of the present invention, turbulence of the pickling solution is increased through the WPC and/or HTLP principles or a combination of both technologies.

[0072] Accordingly, as schematically represented in FIG. 2A, a WPC highly turbulent regime is applied to the acid solution present in one or more tanks of the pickling installation.

[0073] Let us consider the pickling process of a metal strip 10, such as a steel strip, in horizontal processing. The method could also be applicable to long products. The pickling installation comprises a number N of tanks into which the metal strip 10 moves successively on rolls (not represented). Each (or at least one) tank 1A comprises an upper header 2A in front of the upper face of the strip and a lower header 2B in front of the lower face of the strip. Each header 2A, 2B comprises holes 3 drilled in the header 2A, 2B through which injection of straight water jets 4 is performed at high flow rate so as to maintain a liquid cushion 5′ in the respective upper gap 5A and lower gap 5B between the headers 2A, 2B and the strip, with high turbulence therein. The jets are straight jets and not flared jets such as those obtained with ordinary flat nozzles. The height of the liquid cushion 5′, typically 10-100 mm, can be lower than the distance 5A, 5B separating the internal header surface 6 and the strip 10.

[0074] When using WPC, pressure will be in the range 1 to 5 bars and the specific flow rate in the range of 30 to 300 m.sup.3/h/m.sup.2 of surface.

[0075] Alternatively, as schematically represented in FIG. 2B, a HTLP highly turbulent regime is applied to the acid solution present in (a) tank(s) 1B of the pickling installation (FIG. 2C shows an embodiment with the combined use of both principles cites here above). In this case, the internal header surface 6 is located very close to the strip (typically 2-5 mm) and the electrolyte is forced to enter the gap 5A, 5B between the header plate 6 and the strip 10, through one opening 7 located at one side of the device, creating thereby a highly turbulent zone.

[0076] When HTLP is used, pressure will be in the range of 0.5 to 2 bars and the specific flow rate per side in the range of 50 to 120 m.sup.3/h/m of width.

[0077] Note that, for either WPC or HTLP, the value of the pressure obtained is linked to the specific flow rate by the design of the nozzles or slot injector, as the case may be.

[0078] According to the present invention, the use of a multi-perforated plate allows to create a more important and homogeneous turbulence by a double effect: the impact of the jets (primary turbulence) and the very important agitation of liquid between the jets following the collision of the jets coming from the nozzles (secondary turbulence). In the first configuration (WPC), honeycomb-like impacts can be observed (see FIG. 4).

[0079] The geometries according to the present invention are clearly specific and stand out from prior art of pickling units. While some create length-variable turbulence using alternating equipment geometry (such as in US 4 270 317 with turbulators or EP 1 008 676 with flat jet sprays), the present invention discloses a much simpler continuous geometry under the form of a tunnel with a flat internal surface which, with an homogeneous distribution of the perforations, especially in first and third treatment tank configurations, creates a continuous, regular and homogeneous turbulence at the surface of the strip and over the entire length of the strip. Prior art technologies are not continuous and homogeneous over the length of a unit considering their configuration of alternating equipment or sprays.

[0080] The spacing between the headers and the strip is also one parameter to be taken in consideration when comparing the present invention with prior art. FIG. 5 shows the results of back-calculation of the heat exchange coefficient in cylinder cooling using HTRC technology vs. high pressure flat jet sprays. In cylinder cooling, HTRC is a combination of a perforated plate (WPC technology) with slot injection (HTLP technology). For a gap of 45 mm or 15 mm the heat exchange is clearly more important in HTRC compared to flat sprays. By analogy, the pickling configurations of the present invention can also be considered more efficient than those of prior art.

[0081] In a second embodiment, beside the chemical action of acid and in addition of it, in order to further and efficiently assist in the removal of hard to dissolve oxides like fayalite, the inventors further assert that a mechanical action would help for strengthening removal of this kind of oxide. Such a mechanical action is intended under the form of an addition of abrasive particles 20 propelled on the strip surface in a highly turbulent tank (FIG. 3) so as to further decrease the pickling time.

[0082] Preferably, abrasive particles 20 non-soluble in acid, such as corundum, glass microballs, alumina, silicate, silicon carbide, zirconium, etc., will be used. The Mohs hardness of the acid insoluble abrasive mineral particles 20 will be comprised between 4 and 7, and preferably will be higher or equal to 5. Particles with Mohs hardness of 5 minimum have excellent resistance to HCl at all useful concentrations and temperatures.

[0083] In this case, an innovation consists in using a double action made of a chemical action and a mechanical action respectively due to acid and abrasive particles to optimize the reduction of pickling time.

[0084] So the materials used in the pickling installation will be suitably chosen so as to resist to the pickling media, acid and abrasive particles.

[0085] Advantageously, the abrasive particles will be recovered at the end of the process for example by filtration or decantation.

[0086] FIG. 3 schematically represents the principle of acid pickling under high turbulence with respective WPC and HTLP conditions, as described above, applied to a moving metal strip, but now in additional presence of abrasive particles in the tank solution.

[0087] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. Additionally, statements made herein characterizing the invention refer to an embodiment of the invention and not necessarily all embodiments.

[0088] The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C.

TABLE-US-00001 Reference symbols 1A WPC acid pickling tank 1B HTLP acid pickling tank 1C WPC and HTLP acid pickling tank 1D WPC acid pickling tank with abrasive particles 1E HTLP acid pickling tank with abrasive particles 1F WPC and HTLP acid pickling tank with abrasive particles 2A, 2B Upper header, lower header (horizontal processing) 3 Hole drilled in header (WPC) 4 Straight jet (WPC) 5A, 5B Upper gap, lower gap (horizontal processing) 5′ Liquid cushion 6 Header internal flat surface 7 Injection opening (HTLP) 8 Acid solution tank 9 Pump 10 Metal strip 11, 12, 13, .. Pickling treatment tank 18 Injection line for fresh acid 20 Abrasive mineral particle