Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
  • C25F1/00—Electrolytic cleaning, degreasing, pickling or descaling
  • C25F1/02—Pickling; Descaling
  • C25F1/04—Pickling; Descaling in solution
  • C25F1/06—Iron or steel
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
  • C25F7/00—Constructional parts, or assemblies thereof, of cells for electrolytic removal of material from objects; Servicing or operating
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
  • C25F7/00—Constructional parts, or assemblies thereof, of cells for electrolytic removal of material from objects; Servicing or operating
  • C25F7/02—Regeneration of process liquids
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
  • C23G1/36—Regeneration of waste pickling liquors
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G3/00—Apparatus for cleaning or pickling metallic material
  • C23G3/02—Apparatus for cleaning or pickling metallic material for cleaning wires, strips, filaments continuously
  • C23G3/021—Apparatus for cleaning or pickling metallic material for cleaning wires, strips, filaments continuously by dipping
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G3/00—Apparatus for cleaning or pickling metallic material
  • C23G3/02—Apparatus for cleaning or pickling metallic material for cleaning wires, strips, filaments continuously
  • C23G3/027—Associated apparatus, e.g. for pretreating or after-treating

Definitions

• the present invention relates to a method permitting to improve the efficiency of a pickling line of a metallic strip. It is done by applying an alternating current to a metallic strip moved through at least a pickling bath.
• a metallic surface is, in the hot strip mill, in contact with humid air at high temperatures, from 1200°C (in the reheating furnace) to nearly 700°C (at the coiling station). These conditions favour the formation of a scale layer 1 on the metallic strip 2, as illustrated in Figure 1 .
• said scale layer is mainly composed of iron oxides, as illustrated in Figure 2 wherein a steel piece 3 is covered by a scale layer 4 composed of FeO (Wüstite), Fe 3 O 4 (Magnetite) and Fe 2 O 3 (Hematite).
• the scale thickness can vary, typically from 4 to 20 ⁇ m, depending on the hot strip mill conditions, as noted in Figure 2 by the bars.
• the scale should be removed to provide a metallic surface convenient for the following process steps such as cold rolling, annealing or hot-dip coating.
• this scale is broken by scale breakers at the pickling entry line and then removed in pickling tanks prior to the metallic strip cold-rolling and/or coating.
• the metallic strip passes through several pickling tanks (6, 6a, 6b, 6c) containing a pickling bath (7, 7a, 7b, 7c) made of at least one pickling acid or one pickling salt, as illustrated in Figure 3 .
• the successive pickling baths do not have necessarily the same process parameters nor the same composition. Moreover, their pickling liquor nature and concentration can vary.
• Patent US 5 472 579 discloses a pickling method wherein a hot-rolled steel strip is continuously fed to at least a pickling tank and an electric current pass through said steel strip.
• the purpose of this invention is to provide a solution solving the aforementioned problems.
• the invention relates to a pickling process of a metallic strip 9 comprising the steps of:
• This claimed pickling process is preferentially done downstream a hot rolling operation and even more preferentially downstream a scale breaking operation.
• the claimed pickling process is preferentially done upstream of a cold rolling operation and/or of a coating operation such as a hot-dip coating process.
• the pickling bath is contained in a pickling tank 6 as illustrated in Figure 4 .
• Said pickling tank is preferably made of at least one of the followings: raw materials bricks, granite or ebonite bricks, polypropylene, high-density polyethylene (HDPE) and/or polypropylene homopolymer (PPHP) which permits to increase its lifetime in the pickling condition.
• the tank is preferably equipped with means capable of moving the strip through the bath, such as conveying rolls 10.
• the bath can be equipped with four conveying rolls 10, a pair on the entry side 11 and another pair on the exit side 12 of the tank. In each pair, one is completely immerged in said pickling bath and one is not immerged in said pickling bath.
• the pickling line is also preferably equipped with means to add and/or regenerate the pickling solution such as acid regeneration plant (ARP), which is not represented in Figure 3 .
• ARP acid regeneration plant
• the fresh/regenerated pickling liquor is added into the last pickling tank, then it cascades from the last tank to the first tank, where the used pickling liquor is evacuated to the regeneration station (if it exists or to the storage tank).
• the acid flows are regulated by the pumps.
• the pickling bath can be any pickling bath known by the skilled in the art.
• the pickling bath comprises at least a pickling acid and/or a pickling salt at a concentration between 10 and 360 g.L -1 .
• the pickling bath 7 comprises at least a pickling acid or a pickling salt.
• the pickling acids or salts are preferentially one of the following: hydrochloric acid (HCl), sulfuric acid (H 2 SO 4 ), potassium chloride (KCl), sodium chloride (NaCl), sodium sulfate (Na 2 SO 4 ), potassium sulfate (K 2 SO 4 ) or nitric acid.
• the pickling bath can also comprise undesired materials such as dissolved metals resulting from the pickling operation (iron ions, other typical alloying elements or impurities in steel as Mn, Si, Al, Cr, Ni, Co, Ti, V, Nb, Mo, Cu, C, S, P, B, N,.9) as well as solid particles of low dissolving oxides depositing in the tanks walls or in the circuits as silica, alumina, mixed phases like fayalite (Fe 2 SiO 4 ), FeAl 2 O 4 , Mn containing spinels (Mn 2 SiO 4 , MnAl 2 O 4 ,).
• the pickling bath can also comprise an over-pickling inhibitor which protects the steel surface by limiting the steel dissolution in the pickling bath.
• Said alternating current has a current density of 10 2 to 10 5 A.m -2 of unit surface of said metallic strip. It means that a spot of the strip (and/or of the scale) will receive an alternating current, as previously defined, when it passes through the pickling bath 7 which helps the removal of the scale layer. For example, an alternating current is applied on said spot during at least 3 seconds.
• the alternating current is applied by any possible means.
• the alternating current can be of any waveform such as square, triangular, sine or complex.
• the alternating current is applied using a series of electrodes 13, forming an alternation of anode 13 a and cathode 13 b, facing the metallic strip.
• the alternation of anode and cathode is preferably made by applying either a positive or negative current to said electrodes.
• both strip faces are faced with electrodes.
• the electrodes are immerged in the pickling bath and preferably positioned at a distance between 1 and 30 cm from the moving metallic strip. Even more preferably, the electrodes are positioned at a distance between 1 and 10 cm from the moving metallic strip.
• the metallic strip in a pickling line comprising four pickling tanks (6 6a, 6b, 6c), the metallic strip can undergo a chemical pickling process in the three first tanks and the claimed pickling process in the fourth tank.
• Another possibility is to apply the claimed process in all the baths of a pickling line.
• the number of pickling tanks in the line configurations can vary from 1 to 6 and the claimed pickling process can be carried in at least one of them to all of them.
• the gain in pickling time increases with the increase of the current density and at 10 4 A.m -2 , the alternating current gives a gain in pickling time of about 40% relatively to the direct current. Consequently, the efficiency of the claimed pickling process is improved compared to an electro-assisted pickling using a direct current.
• said metallic strip is made of steel.
• said alternating current has a frequency between 0.5 and 100 Hz.
• said metallic strip is passing through the bath at a speed comprised between 10 m.min -1 and 450 m.min -1 .
• said alternating current is applied during at least 5 seconds to said metallic strip passing through said at least one pickling bath which permits to increase the scale dissolution efficiency.
• said alternating current is applied during maximum 600 seconds to said metallic strip passing through said at least one pickling bath.
• said alternating current is applied during maximum 300 seconds to said metallic strip passing through said at least one pickling bath which permits to lower the electrical consumption while achieving satisfying scale dissolution rate.
• the pickling bath 7 comprises only one pickling acid or only one pickling salt. It permits to suppress the interaction between the pickling acids and pickling salts and thus have a more stable pickling bath.
• said pickling bath comprises hydrochloric acid at a concentration between 10 and 360 g.L -1 .
• said pickling bath comprises sulfuric acid at a concentration between 10 and 360 g.L -1 .
• the brightness of the surface covered by the scale prior to its pickling, is of about 30 units and the brightness of a metallic steel without scale is typically in a range between 60 and 75 units depending on the product chemistry and surface morphology (roughness).
• the brightness increase during pickling is linked to the removal of the scale.
• said pickling bath has a temperature of at least 40°C. It improves the efficiency of the pickling compared to pickling bath temperatures lower than 39.5°C.
• the pickling time is plotted in function of the bath temperature for experiments carried out in bath having a HCl concentration of 100 g.L -1 at different temperatures and current densities.
• the oscillation frequency of AC current is of 50Hz and cathodic/anodic pulse length ratio of 1:1). It can be observed that all other parameters being equal, higher is the pickling bath temperature, smaller is the pickling time.
• said pickling bath has a pickling acid or pickling salt concentration of at least 30 g.L -1 , even more preferentially of at least 60 g.L -1 .
• a pickling acid or pickling salt concentration of at least 30 g.L -1 , even more preferentially of at least 60 g.L -1 .
• the pickling time is plotted in function of the pickling bath acid concentration at 40°C for an experimental condition carried out with AC current at a current density of 0.5x10 4 A.m -2 and 50Hz oscillation frequency with cathodic/anodic pulse length ratio of 1:1). It can be observed that all other parameters being equal, higher is the pickling acid concentration, smaller is the pickling time.
• said current density is of at least of 1x10 3 A.m -2 of unit surface of said metallic strip to said metallic strip passing through said at least one pickling bath and even more preferably of at least 1x10 4 A.m -2 . It permits to increase the pickling efficiency compared to lower current density.
• the pickling time is plotted in function of the current density applied to the metallic strip at a 50Hz frequency and a 1:1 cathodic/anodic pulse length ratio for a bath having a HCl concentration of 100 g.L -1 . It can be observed that all other parameters being equal, higher is the current density, smaller is the pickling time.
• said alternating current has a frequency of at least 15 Hz. Hence, such a lower limit permits to increase the pickling efficiency compared to lower frequency. Preferably, said alternating current has a frequency of maximum 50 Hz. Apparently, such an upper limit permits to increase the pickling efficiency compared to higher frequency.
• the pickling time is plotted in function of the current frequency applied to the metallic strip (cathodic/anodic pulse length ratio is 1:1 in these conditions) in pickling bath at 40°C having an acid concentration of 100 g.L -1 for various pickling acid and current density.
• said alternating current, having an anodic period and a cathodic period, applied on said metallic strip passing through said at least one pickling bath has a cathodic/anodic pulse length ratio of 1.5 and 2.4.
• the pickling time is plotted in function of the alternating current period ratio applied to the metallic strip for pickling bath at 40°C having an acid concentration of 100 g.L -1 and a current density of 0.5 A.cm -2 .

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrochemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)

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• 2019
  • 2019-11-25 MX MX2022006290A patent/MX2022006290A/es unknown
  • 2019-11-25 EP EP19809651.3A patent/EP4065754B1/en active Active
  • 2019-11-25 UA UAA202202150A patent/UA128807C2/uk unknown
  • 2019-11-25 US US17/778,498 patent/US20220411952A1/en active Pending
  • 2019-11-25 PL PL19809651.3T patent/PL4065754T3/pl unknown
  • 2019-11-25 WO PCT/IB2019/060108 patent/WO2021105738A1/en not_active Ceased
  • 2019-11-25 JP JP2022530240A patent/JP7454045B2/ja active Active
  • 2019-11-25 CN CN201980101585.7A patent/CN114599824B/zh active Active
  • 2019-11-25 CA CA3158225A patent/CA3158225C/en active Active
  • 2019-11-25 KR KR1020227016969A patent/KR102773151B1/ko active Active
• 2022
  • 2022-03-31 ZA ZA2022/03727A patent/ZA202203727B/en unknown

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