Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
• • 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
  • C23G3/024—Apparatus for cleaning or pickling metallic material for cleaning wires, strips, filaments continuously by a combination of dipping and spraying
• • 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
  • C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
  • C23G1/08—Iron or steel
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0278—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular surface treatment
• • 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

Definitions

• the present invention relates to a method for treating a steel strip especially for a pickling treatment of the steel strip, by means of a treatment liquid in a treatment station, the treatment station comprising a treatment tank.
• the present invention relates to a system for treating a steel strip, especially for a pickling treatment of the steel strip, by means of a treatment liquid in a treatment station, the treatment station comprising a treatment tank.
• the steel strip to be treated according to the method of the present invention and in a system of the present invention is stainless steel.
• oxide scale generally refers to the chemical compounds of iron and oxygen, as well as the chemical compounds of iron alloying elements, e.g.
• chromium and oxygen formed on the surface of the steel by exposure to air while the metal is at an elevated temperature.
• Chemical compounds thus formed include iron oxides, such as FeO, Fe203 and Fe304, oxides of alloying elements such as Cr03, NiO, Si02 and complex oxide spinals like FeCr204, NiFe204, Fe2Si04 and others.
• a certain temperature 850-1 150 °C depending on steel grade
• oxide scale is formed on the surface.
• a chromium-depleted zone is formed, which is different for austenitic, ferritic and duplex stainless steel grades.
• Elements like aluminum and silicon form refractory-type oxides, which in turn lower the solubility rate of the oxide in the pickling acid.
• the thickness of the oxide scale varies considerably with practice in rolling mills. E.g. loose coiling permits greater atmospheric penetration into the wraps, with corresponding heavier oxide formation on the edge areas.
• coiling temperature affects the adherence of the oxide and determines how easy or difficult it is to remove. The lower coiling temperatures makes oxide removal easier, at higher coiling temperatures longer pickling times are required. E.g. at the coiling temperature of 750 °C, double pickling time is required compared to the coiling temperature of 570 °C.
• the stainless steel Like with carbon steel, the stainless steel also oxidizes following hot rolling and coiling.
• the oxide scale layer formed on the surface of the hot rolled stainless steel strip contains the alloying elements and is very tightly adhering on the surface, which makes the de-scaling or pickling of stainless steel very difficult as compared to the carbon steels.
• To achieve efficient and thorough surface oxide removal from a stainless steel strip more severe processing techniques must be used which substantially increase processing time and operational costs.
• chemical pickling of stainless steel strip must be preceded by mechanical de-scaling, e.g. by shot-blasting and/or scale breaking. Often nowadays additional methods of Pre-Pickling is applied to soften the oxide scale. E.g.
• hot rolled stainless steel is conventionally pre-pickled in hot sulfuric acid and the cold rolled stainless steel is pre-pickled electrolytically in neutral electrolyte of Na 2 S0 4 solution prior the main pickling in mixed acid.
• MD Mechanical de-scaling
• PP Pre-Pickling
• FP final pickling process
• the pickling process most commonly used for stainless steel involves the use of a mixture of nitric and hydrofluoric acid, the mutual concentrations of which vary according to the type of stainless steel to be pickled (austenitic, ferritic, martensitic, duplex%), its surface characteristics and its past processing history.
• various acid compositions Mat I and Mix II
• various acid mixture temperatures are required.
• the hydrofluoric acid is extremely corrosive and a harmful environmental pollutant.
• the nitric acid is the source of highly polluting nitrogen oxide (NOx) vapors which are emitted into the atmosphere and which are highly aggressive towards metals and nonmetals with which they come into contact.
• Today pickling lines are designed as shallow tank turbulence installations comprising of several consecutive pickling tanks.
• the steel strip is pulled or pushed through the treatment tanks.
• the complete pickling section is arranged as a cascade, i.e. the fresh or regenerated acid is added to the last treatment tank (i.e. the most downstream treatment tank according to the direction of movement of the steel strip) and is then processed in a countercurrent flow to the strip transport direction in order to maximize the use of the pickling acid.
• wringer rolls are installed to remove the pickling acid from the strip to the greatest possible extend in order to enhance the cascade effect.
• German patent disclosure DE 40 31 234 describes this technology.
• the pickling acid is injected on both sides of the tank creating a high turbulence between the strip surface and the pickling acid.
• the pickling acid is then overflowing from the treatment tank to a circulation tank from where it is again injected into the treatment tank by means of pumps.
• the high turbulence reduces the thickness of the liquid boundary layer on the strip surface resulting in an improved media and energy exchange and consequently reducing the required pickling time.
• Another well known pickling method is the spray pickling, wherein the pickling acid is directly sprayed onto the strip surface using several spray nozzles installed both above and below the steel strip, cf. e.g. document DE 42 28 808 A1 .
• the pickling acid is then collected in a circulation tank from where it is pumped to the spray nozzles and sprayed on to the strip surface again.
• the spray nozzles are typically operated at a pressure above 1 bar. Due to the high impulse of the pickling acid sprayed onto the strip surface, the pickling efficiency and consequently the pickling time can be further improved. However this technology has never been used commercially in strip pickling lines.
• hydrochloric acid as a pickling agent for stainless steel pickling allows the realization of pickling mechanisms of both the removal of oxide scale and the chromium- depleted zone.
• the pickling of stainless steel in hydrochloric acid is a combined process of reduction and oxidation.
• the base metal, Fe is dissolved by the oxidizing agents, mainly FeCI 3 :
• Oxidation reaction to produce the required oxidizing agent is as follows:
• a minimum proper FeCI 3 concentration is required for the pickling process of stainless steel. This is today typically reached by adding H 2 0 2 to the pickling liquid.
• chlorides of iron and chlorides of other metals are collectively referred to by the term MeCI.
• FeCI 3 can be too high (to reach 60 g/l and above), making the whole pickling process difficult to control, with a high risk of over pickling the metal strip or causing inacceptable roughness of the strip surface.
• Another drawback of the increased FeCI 3 concentration in the pickling acid is the effect on the regeneration process of the spent pickling acid. Spent pickling acid containing HCI is typically regenerated using the pyrohydrolysis process. In this process FeCI 2 and FeCI 3 are converted back to HCI and Fe 2 0 3 .
• FeCI 3 however has a much lower evaporation temperature than FeCI 2 and evaporates in the pyrohydrolysis reactor causing very fine Fe 2 0 3 particles below 1 ⁇ in size when converted to Fe 2 0 3 . These fine particles are difficult to remove from the process off-gases causing high dust emissions.
• the object of the present invention is achieved by a method for treating a steel strip, especially for a pickling treatment of the steel strip, by means of a treatment liquid in a treatment station, the treatment station comprising a treatment tank with a spray section and an immersion section, and the treatment station comprising a common collection means for the treatment liquid,
• the steel strip comprises stainless steel and is a continuous steel strip being oriented substantially horizontally, both in its longitudinal and transverse directions,
• the steel strip has a top surface and a bottom surface
• the method comprises transporting the steel strip continuously through the treatment station in a transport direction, the transport direction being parallel to the longitudinal direction of the steel strip, such that
• the treatment liquid is sprayed onto the top surface of the steel strip and onto the bottom surface of the steel strip while the steel strip being in the spray section of the treatment station,
• the steel strip is immersed in the treatment liquid while the steel strip being in the immersion section of the treatment station,
• the treatment liquid is continuously pumped out of the common collection means and through both the spray section and the immersion section of the treatment station, wherein spraying of the treatment liquid onto the top and bottom surfaces of the steel strip is provided using spray nozzles.
• the present invention is related to a process for chemical or electrochemical treatment of the surface of stainless steel, preferably strip shaped, wherein the material is treated with a pickling solution, preferably containing HCI, in one or more treatment tanks to remove an oxide scale layer which was previously formed during the hot rolling process of the metal strip (steel strip). This treatment is needed to reach a clean surface for either further processing it in a cold rolling process or for direct commercial use.
• the steel strip instead of the steel strip comprising stainless steel, it is also preferred that the steel strip consists of stainless steel.
• the process for chemical or electrochemical treatment of the surface of stainless steel is conducted using a pickling solution containing HCI as the only pickling agent, wherein the advantages of spray pickling are used to a maximum extend. Furthermore the process shall be controllable minimizing the risk of over-pickling so that the process can be realized in commercially used industrial scale pickling lines.
• the spent acid of such a process is of a quality such that it can be treated in regeneration plants without additional investment considering in particular the FeCI 3 concentration in such spent acid.
• the present invention is also directed to the possibility to revamp existing pickling lines, in particular the treatment tanks, and to use more efficient pickling technology with improved efficiency while re-using existing equipment in order to reduce installation costs, as for example acid circulation circuits etc. can be reused.
• the present invention comprising a pickling process using an HCI containing pickling solution as the only pickling acid, wherein the material to be treated (i.e. the steel strip) is processed horizontally through one or more treatment tanks which are - in case of more than one treatment tank - operated as a pickling cascade.
• each single treatment tank (of the treatment station) of the above described process comprises of one spray pickling zone and one dip pickling zone arranged as one unit using one common circulation circuit, i.e. one common circulation tank (common collection means) with several pump circuits as required. All pickling acid coming from the dip section and the spray section are collected and mixed in the common circulation tank (common collection means) and pumped back to the above mentioned two pickling sections (of the treatment tank of the treatment station).
• a guide roll underneath the strip located between the spray and pickling section might be required to better position the steel strip inside the treatment tank.
• a wringer roll unit - as it is typically installed between two pickling sections - is not required.
• the first section of the treatment tank is a spray section while the second section of the dip pickling type, preferably with high efficiency such as shallow tank turbulence technology.
• the steel strip is treated - in the treatment tank of the treatment station - by means of a treatment liquid such that the same treatment liquid is used both in the spray section and in the immersion section of the treatment tank.
• the treatment station having both the spray section and the immersion section
• the same common collection means as well as at least a part of the circulation system
• the steel strip comprises stainless steel and is a continuous steel strip being oriented substantially horizontally, both in its longitudinal and transverse directions, at least at the treatment station.
• steel strip is mostly horizontally oriented in its transverse direction but is allowed to be sagging in its longitudinal direction.
• the height variation through the treatment station of the steel strip in its longitudinal direction may reach, e.g., up to 0,5 m.
• the height variations of the steel strip in its longitudinal direction are also comprised up to 0,5 m.
• the height variation of the steel strip in its longitudinal direction is comprised between up to 0,5 m throughout the complete treatment system, that potentially (and typically) comprises a plurality of treatment stations one after the other in the transport direction of the steel strip.
• the treatment liquid is sprayed - in a first step and by means of nozzles - onto the top surface of the steel strip and onto the bottom surface of the steel strip while the steel strip is in the spray section of the treatment station.
• second step that is not necessarily subsequent to the first step but could also be preceding the first step
• the steel strip is immersed in the treatment liquid while the steel strip is in the immersion section of the treatment station.
• the treatment liquid of the treatment station is continuously pumped out of the common collection means (of that treatment station) and through both the spray section and the immersion section of the treatment tank, wherein spraying of the treatment liquid onto the top and bottom surfaces of the steel strip is provided using spray nozzles.
• two pickling technologies are directly combined in one treatment tank (i.e. in one treatment station), i.e. using physically the same pickling acids (or the same treatment liquid) in both pickling sections (i.e. in both the spray section and the immersion section of the considered treatment station), as described.
• the concentration of FeCI 3 can be kept below a critical level throughout the entire pickling process, guaranteeing a uniform pickling result without the risk of over-pickling.
• the spent acid of such process can be easily regenerated in regeneration plants without additional investment to reach the legally required emission values, especially regarding dust emissions.
• the efficiency of the treatment process is increased.
• Tests have proven that a certain increase in the FeCI 3 concentration reduces the pickling time also for the dip pickling process. Consequently the process according to the present invention uses the advantage of the high efficient spray pickling process while the efficiency of the dip pickling process is improved as well, due to the common use of the pickling acid (i.e. the same treatment liquid is used both in the spray section and the immersion section of one and the same treatment station), and the consequently increased FeCI 3 level.
• the pickling acid i.e. the same treatment liquid is used both in the spray section and the immersion section of one and the same treatment station
• the design of the treatment line or pickling line is done in such a way that it is advantageously possible that the treatment stations or treatment tanks can easily replace existing treatment tanks in case of a required revamp (or refurbishment) while the circulation circuits can be reused.
• This is mainly attributed to the fact that the spray pickling technology and the dip pickling technology (i.e. the spray section and the immersion section) are combined in one treatment tank (i.e. as part of one treatment tank).
• the design of the present invention also allows the possibility to operate the treatment tanks without an additional (external) circulation tank - or common collection means - (i.e. external or separate to the treatment tank).
• the treatment tank itself in particular the area underneath the spray section, and, if required, also underneath the dip section, is used as circulation tank (or common collection means), i.e. the circulation tank (or common collection means) is realized in a manner integrated with the treatment tank.
• circulation tank or common collection means
• the circulation tank or common collection means
• the spray section comprises an effective spray length in parallel to the longitudinal direction of the steel strip such that - during the first step - the top and bottom surfaces of the steel strip receive the treatment liquid while being located within the effective spray length
• the immersion section comprises an effective immersion length in parallel to the longitudinal direction of the steel strip such that - during the second step - the steel strip is immersed - with its top and bottom surfaces - in the treatment liquid while being located within the effective immersion length
• the effective spray length and the effective immersion length are provided having a ratio of between and including 30:70 to 70:30, especially a ratio of 50:50.
• the present invention it is thereby advantageously possible to flexibly adapt process parameters of a pickling line to fit best with the intended operative use after construction.
• the time is defined during which the treatment liquid is effectively treating the steel strip in the immersion section.
• the maximum time of spray pickling is defined in relation to the dip pickling time.
• the effective spray length and hence the ratio of the effective spray length vs. the effective immersion length is varied by activating only a part of the spray nozzles.
• the present invention it is thereby advantageously possible to vary the spray pickling time even during operational use of the pickling line, i.e. by de-activating a part of the spray nozzles.
• By selectively activating and/or de-activating groups of spray nozzles is it advantageously possible according to the present invention, that also the manner or the intensity of the spray pickling step can be varied in operational use of the pickling line, e.g. by using only every second spray nozzle such that spray pickling is less intensive in the spray section.
• the spray section is located - along the transport direction of the steel strip - upstream with respect to the immersion section. According to an alternative preferred embodiment of the present invention, the spray section is located - along the transport direction of the steel strip - downstream with respect to the immersion section.
• the present invention it is thereby advantageously possible to provide the possibility of different pickling line architectures.
• the first treatment station such that the spray section is located downstream with respect to the immersion section (i.e. the steel strip passes the immersion section first and afterwards the spray section)
• the second treatment station such that the spray section is located upstream with respect to the immersion section (i.e. the steel strip passes the spray section (of the second treatment station) first and afterwards the dip section (of the second treatment station)):
• these building blocks of two treatment stations can be either repeated or combined with other treatment stations or configurations of treatment stations.
• the method comprises using - besides using the treatment liquid in the treatment station - a further treatment liquid in a further treatment station, the further treatment station comprising a further treatment tank with a further spray section and a further immersion section, and the further treatment station comprising a further common collection means for the further treatment liquid,
• the method comprises transporting the steel strip continuously through the further treatment station in the transport direction such that
• the further treatment liquid is sprayed onto the top surface of the steel strip and onto the bottom surface of the steel strip while the steel strip being in the further spray section of the further treatment station,
• the steel strip is immersed in the further treatment liquid while the steel strip being in the further immersion section of the further treatment station,
• the further treatment liquid is continuously pumped out of the further common collection means and through both the further spray section and the further immersion section of the further treatment station , wherein spraying of the further treatment liquid onto the top and bottom surfaces of the steel strip is provided using further spray nozzles, wherein the third and fourth steps are preceding the first and second steps or are subsequent to the first and second steps.
• the two inventive treatment station are either located directly subsequent one after the other along the transport direction of the steel strip or the combination with one or a plurality of conventional treatment stations is provided such that the treatment station (or the first treatment station) is located upstream according to the transport direction of the steel strip with respect to a conventional treatment station (or with respect to a plurality of conventional treatment stations) and downstream with respect to this or these conventional treatment station(s) is located the further treatment station (or second treatment station) according to the present invention.
• the treatment liquid and/or the further treatment liquid comprises
• hydrochloric acid in a concentration ranging from and including 150 g/l to and including 250 g/l and
• FeCI 3 in a concentration ranging from and including 10 g/l to and including 35 g/l, especially in a concentration ranging from and including 15 g/l to and including 30 g/l or especially in a concentration ranging from and including 19 g/l to and including 26 g/l and,
• the present invention also relates to a system for treating a steel strip, especially for a pickling treatment of the steel strip, by means of a treatment liquid in a treatment station, the system comprising the treatment station, wherein the treatment station comprises a treatment tank with a spray section, an immersion section, and the treatment station comprising a common collection means for the treatment liquid,
• the steel strip comprises stainless steel and is a continuous steel strip being oriented substantially horizontally, both in its longitudinal and transverse directions,
• the steel strip has a top surface and a bottom surface
• system is configured to transport the steel strip continuously through the treatment station in a transport direction, the transport direction being parallel to the longitudinal direction of the steel strip, such that
• the treatment liquid is sprayed onto the top surface of the steel strip and onto the bottom surface of the steel strip while the steel strip being in the spray section of the treatment station,
• the steel strip is immersed in the treatment liquid while the steel strip being in the immersion section of the treatment station,
• system is configured such that the treatment liquid is continuously pumped out of the common collection means and through both the spray section and the immersion section of the treatment station, wherein the system comprises spray nozzles such that the treatment liquid is sprayed onto the top and bottom surfaces of the steel strip using the spray nozzles.
• the present invention it is thereby advantageously possible to provide a system (or a treatment station) that requires comparatively low installation costs as well as reduced maintenance costs. According to the present invention, it is advantageously possible to combine the advantages of spray pickling and dip pickling and to minimize the risk of over-pickling. It is furthermore advantageous that the spent acid of such a system is of a quality such that it can be treated in regeneration plants without additional investment considering in particular the FeCI 3 concentration in such spent acid.
• the steel strip instead of the steel strip comprising stainless steel, it is also preferred that the steel strip consists of stainless steel.
• the spray section comprises an effective spray length in parallel to the longitudinal direction of the steel strip such that the top and bottom surfaces of the steel strip receive the treatment liquid while being located within the effective spray length
• the immersion section comprises an effective immersion length in parallel to the longitudinal direction of the steel strip such that the steel strip is immersed - with its top and bottom surfaces - in the treatment liquid while being located within the effective immersion length
• the effective spray length and the effective immersion length are provided having a ratio of between and including 30:70 to 70:30, especially a ratio of 50:50.
• the spray section is located - along the transport direction of the steel strip - upstream with respect to the immersion section.
• the spray section is located - along the transport direction of the steel strip - downstream with respect to the immersion section.
• the common collection means for the treatment liquid of both the spray section and the immersion section is a collection means separated from the treatment tank of the treatment station.
• the present invention it is thereby advantageously possible to build the treatment tank in a very cost effective manner such that especially the volume of the treatment tank is comparably small (and hence less treatment liquid is to be used).
• the treatment liquid is pumped through the common collection means (or circulation tank) that is separated from the treatment tank.
• the common collection means for the treatment liquid of both the spray section and the immersion section is a collection means integrated with the treatment tank of the treatment station, especially integrated such that the bottom part of the treatment tank forms the common collection means.
• the system comprises - besides the treatment liquid in the treatment station - a further treatment liquid in a further treatment station, the further treatment station comprising a further treatment tank with a further spray section and a further immersion section, and the further treatment station comprising a further common collection means for the further treatment liquid,
• system is configured such that the steel strip is transported continuously through the further treatment station in the transport direction such that
• the further treatment liquid is sprayed onto the top surface of the steel strip and onto the bottom surface of the steel strip while the steel strip being in the further spray section of the further treatment station,
• the steel strip is immersed in the further treatment liquid while the steel strip being in the further immersion section of the further treatment station,
• system is configured such that the further treatment liquid is continuously pumped out of the further common collection means and through both the further spray section and the further immersion section of the further treatment station, wherein the system comprises further spray nozzles such that the further treatment liquid is sprayed onto the top and bottom surfaces of the steel strip using the further spray nozzles.
• the system comprises - besides the treatment liquid in the treatment station and the further treatment liquid in the further treatment station - a third treatment liquid in a third treatment station, the third treatment station comprising a third treatment tank with a third spray section and a third immersion section, and the third treatment station comprising a third common collection means for the third treatment liquid.
• the system comprises - besides the treatment liquid in the treatment station, the further treatment liquid in the further treatment station, and the third treatment liquid in the third treatment station - a fourth treatment liquid in a fourth treatment station, the fourth treatment station comprising a fourth treatment tank with a fourth spray section and a fourth immersion section, and the fourth treatment station comprising a fourth common collection means for the fourth treatment liquid.
• the treatment liquid and/or the further treatment liquid and/or the third treatment liquid comprises
• hydrochloric acid in a concentration ranging from and including 150 g/l to and including 250 g/l and
• FeCI 3 in a concentration ranging from and including 10 g/l to and including 35 g/l, especially in a concentration ranging from and including 15 g/l to and including 30 g/l or especially in a concentration ranging from and including 19 g/l to and including 26 g/l and,
• concentration ranging from and including 230 g/l to and including 300 g/l.
• Figure 1 schematically illustrates a treatment system comprising three different treatment stations, each one being configured according to the present invention, i.e. having a treatment tank with both a spray section and an immersion section such that a common collection means and the same treatment liquid is used for the treatment of the steel strip in both the respective spray section and the immersion section.
• Figure 2 schematically illustrates a first embodiment of a treatment station having a treatment tank and a common collection means separated from the treatment tank, the treatment tank having its spray section and its immersion section to treat the steel strip with a common treatment liquid circulating between - and within - the common collection means on the one hand, and the spray and immersion sections on the other hand.
• FIG. 3 schematically illustrates a second embodiment of a treatment station having a treatment tank and a common collection means separated from the treatment tank, the treatment tank having its spray section and its immersion section to treat the steel strip with a common treatment liquid circulating between - and within - the common collection means on the one hand, and the spray and immersion sections on the other hand.
• FIG 1 schematically illustrates a treatment system comprising three different treatment stations 3, 31 , 32 as an example of a pickling line according to the present invention.
• all three treatment stations 3, 31 , 32 represent treatment stations according to the present invention, i.e. having a treatment tank with both a spray section and an immersion section such that a common collection means and the same treatment liquid is used for the treatment of the steel strip in both the respective spray section and the immersion section.
• all three treatment stations 3, 31 , 32 are realized either according to a first embodiment of the present invention, represented in Figure 2 for the exemplary case of the treatment station being represented by reference sign 3, or according to a second embodiment of the present invention, represented in Figure 3 for the exemplary case of the treatment station being represented by reference sign 3.
• a part of the three treatment stations 3, 31 , 32 is or are realized according to the first embodiment of the present invention ( Figure 2) and another part is or are realized according to the second embodiment of the present invention ( Figure 3).
• the terms 'treatment station' and 'first treatment station' as well as 'further treatment station' and 'second treatment station' are used synonymously and only aim to differentiate the treatment stations from one another.
• the naming convention typically (but not necessarily) relates to the location of a treatment station along the transport direction of the steel strip, the transport direction being represented by reference sign 2.
• a treatment station (or first treatment station) 3 is located upstream of a further treatment station (or second treatment station) 31 .
• the further treatment station (or second treatment station) 31 is located upstream of a third treatment station 32.
• the treatment station (or first treatment station) 3 comprises a treatment tank (or first treatment tank) 4, and a common collection means (or first common collection means) 5.
• the further treatment station (or second treatment station) 31 comprises a further treatment tank (or second treatment tank) 41 , and a further common collection means (or second common collection means) 51 .
• the third treatment station 32 comprises a third treatment tank 42, and a third common collection means 52.
• all tree treatment stations 3, 31 , 32 each have a spray section and an immersion section as part of their respective treatment tank 4, 41 , 42, i.e.
• the treatment station (or first treatment station) 3 has a spray section (or first spray section) and an immersion section (or first immersion section) using a treatment liquid (or first treatment liquid)
• the further treatment station (or second treatment station) 31 has a further spray section (or second spray section) (not depicted in Figure 1 ) and a further immersion section (or second immersion section) (not depicted in Figure 1 ) using a further treatment liquid (or second treatment liquid)
• the third treatment station 32 has a third spray section (not depicted in Figure 1 ) and a third immersion section (not depicted in Figure 1 ) using a third treatment liquid.
• a first and a second embodiment of the present invention is schematically shown in Figures 2 and 3.
• FIG. 2 schematically illustrates the first embodiment of the treatment station 3 having the treatment tank 4 and the common collection means 5 separated from the treatment tank 4, the treatment tank 4 having its spray section 13 and its immersion section 14 to treat the steel strip 1 with a common treatment liquid circulating between - and within - the common collection means 5 on the one hand, and the spray and immersion sections 13, 14 on the other hand.
• Figure 3 schematically illustrates a second embodiment of a treatment station 3 having the treatment tank 4 and the common collection means 5 separated from the treatment tank 4, the treatment tank 4 having its spray section 13 and its immersion section 14 to treat the steel strip 1 with a common treatment liquid circulating between - and within - the common collection means 5 on the one hand, and the spray and immersion sections 13 on the other hand.
• Figures 1 , 2 and 3 combined illustrate the inventive treatment process and system (or treatment station) for chemical or electrochemical treatment of the surface of the steel strip 1 , the steel strip 1 being a stainless steel strip.
• the steel strip 1 is first horizontally transported through the treatment stations 3, 31 , 32 in which the steel strip 1 is treated with a treatment liquid in the form of a pickling acid, normally containing HCI.
• At least one of the treatment stations 3, 31 , 32 (or their respective treatment tanks 4, 41 , 42) comprises a spray pickling section (as represented in Figures 2 and 3 as spray section 13 of the treatment station 3) and a dip pickling section (as represented in Figures 2 and 3 as immersion section 14 of the treatment station 3) according to the present invention.
• Figure 1 shows an exemplary implementation with three treatment station 3, 31 , 32 (each having a treatment tank) as a preferred embodiment, however the number of treatment stations (and treatment tanks) is at least one and is not limited to three.
• All treatment stations 3, 31 , 32 comprise a common collection means, respectively (i.e. the respective treatment tanks 4, 41 , 42 are connected to respective common collection means (or circulation tanks) 5, 51 , 52), wherein the common collection means 5, 51 , 52 are either (i.e. potentially for each treatment station 3, 31 , 32 differently) realized as separate tanks as shown in the first embodiment represented in Figure 2 or are realized as common collection means 5, 51 , 52 integrated in the respective treatment tank 4, 41 , 42 as shown in Figure 3.
• the common collection means (or circulation tanks) 5, 51 , 52 are operated as a cascade, i.e. the fresh or regenerated acid (i.e. the treatment liquid) is added (cf. reference sign 54) to the last common collection means (or last circulation tank) 52 - i.e. being related to the most downstream treatment station 32 according to the transport direction 2 of the steel strip 1 - and is consequently transferred to the other common collection means (or circulation tanks) in counter direction to the strip transport direction 2.
• the level of free acid is the highest in the third treatment liquid (circulating in the third treatment station 32), the level of free acid is medium in the further treatment liquid (second treatment liquid) (circulating in the further (second) treatment station 31 ), and lowest in the treatment liquid (first treatment liquid) (circulating in the (first) treatment station 3.
• the spent acid is removed (reference sign 55) from the (first) common collection means (or (first) circulation tank) 5.
• the steel strip 1 is further processed in section 6 which comprises a rinse section and a dryer, if required.
• the treatment station 3 comprises the treatment tank 4 with a separate common collection means 5 (or separate circulation tank 5).
• wringer rolls 12 are installed to remove pickling acid from the strip and to guide the steel strip 1 inside the treatment tank 4.
• the wringer roll 12 in the entry section is only used when the treatment tank is the first tank in the pickling process like the treatment station 3 in Figure 1 .
• the following treatment stations (or treatment tanks), like treatment stations 31 , 32 in Figure 1 do not need such wringer roll 12.
• Figure 2 i.e.
• the first part (according to the transport direction of the steel strip 1 ) of the treatment tank 4 is a spray pickling section 13 or spray section 13, followed by a dip pickling section 14 or immersion section 14.
• spray nozzles 15 are mounted above and below the surface of the steel strip 1.
• the pickling acid (or treatment liquid) is pumped from the circulation tank 5 (or common collection means 5) by means of pumps 17, 18 to both the spray pickling section 13 and the dip pickling section 14.
• a heat exchanger 19 is installed to heat the pickling acid
• the treatment station 3 comprises the treatment tank 4 with an integrated common collection means 5.
• the other components of the treatment station 3 are analogous to the description of Figure 2.
• the pickling line is configured for a maximum width of the steel strip 1 of 1890 mm, a maximum speed of the steel strip 1 of 85 m/min.
• the distance of the spray nozzles 15 to the steel strip 1 (both from the spray nozzles to the top surface 1 ' of the steel strip 1 , and to the bottom surface 1 " of the steel strip 1 ) is 200 mm or approximately 200 mm.
• the distance of the spray nozzles 15 to each other in the lateral direction of the steel strip 1 corresponds to 200 mm or approximately 200 mm.
• the distance of the spray nozzles 15 to each other in the longitudinal direction of the steel strip 1 corresponds to 500 mm or approximately 500 mm.
• the treatment liquid is preferably pumped out of the spray nozzles having a pressure of between and including 1 bar to and including 3 bar, and the amount of treatment liquid per spray nozzle is preferably 12 l/min or approximately 12 l/min.
• the total number of spray nozzles per treatment station corresponds to 306 or approximately 306, and the amount of pumped treatment liquid per treatment station corresponds to 220 m 3 /h or approximately 220 m 3 /h.
• Test trials were carried out in a pilot plant.
• the pilot plant consisted of two treatment stations (each having a treatment tank) both arranged as described in the present invention with a first spray pickling section followed by a dip pickling section in each of the treatment tanks.
• the treatment tanks were designed so that the length of both sections was approximately the same.
• the pickling acid used was HCI with a concentration of approx. 200 g/l total acid in both tanks.
• the material treated during the test runs were different austenitic steel grades such as AISI 304 and 316.
• the concentration of HCI is in the range of between and comprising 201 g/l to and comprising 215 g/l
• the concentration of MeCI 2 is in the range of between and comprising 270 g/l to and comprising 286 g/l
• the concentration of FeCI 3 is in the range of between and comprising 23 g/l to and comprising 29 g/l.
• the temperature of the treatment liquid is in the range of between and comprising 87 °C to and comprising 89 °C.
• the concentration of HCI is in the range of between and comprising 204 g/l to and comprising 214 g/l
• the concentration of MeCI 2 is in the range of between and comprising 141 g/l to and comprising 149 g/l
• the concentration of FeCI 3 is in the range of between and comprising 19 g/l to and comprising 23 g/l.
• the temperature of the treatment liquid is in the range of between and comprising 91 °C to and comprising 93 °C.
• the concentration of HCI is in the range of between and comprising 190 g/l to and comprising 201 g/l
• the concentration of MeCI 2 is in the range of between and comprising 40 g/l to and comprising 50 g/l
• the concentration of FeCI 3 is in the range of between and comprising 20 g/l to and comprising 22 g/l.
• the temperature of the treatment liquid is in the range of between and comprising 88 °C to and comprising 91 °C.

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• 2014
  • 2014-12-02 EP EP14195952.8A patent/EP3029164B1/en active Active
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