U.S. patent application number 15/532138 was filed with the patent office on 2017-09-21 for method and system of treating a stainless steel strip, especially for a pickling treatment.
The applicant listed for this patent is CMI UVK GmbH. Invention is credited to Thomas Marx, Rafael Rituper, Wolfgang Walsdorf.
Application Number | 20170268114 15/532138 |
Document ID | / |
Family ID | 51999369 |
Filed Date | 2017-09-21 |
United States Patent
Application |
20170268114 |
Kind Code |
A1 |
Marx; Thomas ; et
al. |
September 21, 2017 |
METHOD AND SYSTEM OF TREATING A STAINLESS STEEL STRIP, ESPECIALLY
FOR A PICKLING TREATMENT
Abstract
A method for treating a steel strip uses a treatment liquid in a
treatment station having at least a spray section, an immersion
section, and a common collector for the liquid, the steel. strip
including stainless steel, top surface, and a bottom surface, and
being continuous, oriented substantially horizontally, both in its
longitudinal and transverse directions, involves transporting the
steel strip continuously through the station in a transport
direction parallel to the steel strip's longitudinal direction,
first, spraying the liquid, using one or more spray nozzles, onto
the steel strip's top and bottom surfaces while in the spray
section and, second, immersing the steel strip in the liquid while
in the immersion section, wherein, while treating the steel strip,
continuous pumping the liquid out of the common collector and
through both the spray section and the immersion section.
Inventors: |
Marx; Thomas; (Siershahn,
DE) ; Walsdorf; Wolfgang; (Ettringen, DE) ;
Rituper; Rafael; (Maehren, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CMI UVK GmbH |
Montabaur |
|
DE |
|
|
Family ID: |
51999369 |
Appl. No.: |
15/532138 |
Filed: |
December 2, 2015 |
PCT Filed: |
December 2, 2015 |
PCT NO: |
PCT/EP2015/078314 |
371 Date: |
June 1, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23G 3/024 20130101;
C23G 1/08 20130101 |
International
Class: |
C23G 3/02 20060101
C23G003/02; C23G 1/08 20060101 C23G001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 2, 2014 |
EP |
14195952.8 |
Claims
1. A method for treating a steel strip, using a first treatment
liquid in a first treatment station, the treatment station
including a first treatment tank including a first spray section,
and a first immersion section, and a first common collector for the
first treatment liquid, the steel strip including stainless steel,
a top surface, and a bottom surface, and being a continuous steel
strip, oriented substantially horizontally, both in its
longitudinal and transverse directions, the method comprising:
transporting the steel strip continuously through the first
treatment station in a transport direction parallel to the
longitudinal direction of the steel strip; spraying, using spraying
nozzles, the first treatment liquid onto the top and bottom
surfaces of the steel strip while the steel strip is in the first
spray section; immersing the steel strip in the first treatment
liquid while the steel strip is in the first immersion section; and
while treating the steel strip, continuously pumping the first
treatment liquid is out of the first common collector and through
both the first spray section and the first immersion section.
2. The method of claim 1, wherein the first spray section includes
an effective spray length in parallel to the longitudinal direction
of the steel strip such that, during the spraying, the top and
bottom surfaces of the steel strip receive the first treatment
liquid while located within the effective spray length, wherein the
first immersion section includes an effective immersion length in
parallel to the longitudinal direction of the steel strip such
that, during the immersing, the steel strip is immersed, with its
top and bottom surfaces, in the first treatment liquid while
located within the effective immersion length, wherein the
effective spray length and the effective immersion length have a
ratio in a range of from 30:70 to 70:30.
3. The method of claim 2, wherein the effective spray length and
hence the ratio of the effective spray length versus the effective
immersion length is varied by activating, only a part of the spray
nozzles.
4. The method of claim 1, wherein, along the transport direction of
the steel strip, the first spray section is located upstream or
downstream of the first immersion section.
5. The method of claim 1, further comprising, using a second
treatment liquid in a second treatment station including a second
treatment tank including a second spray section, a second immersion
section, and a second common collector for the further treatment
liquid; transporting the steel strip continuously through the
second treatment station in the transport direction; spraying,
using spray nozzles, the second treatment liquid onto the top and
bottom surfaces of the steel strip while the steel strip is in the
second spray section; immersing the steel strip in the second
treatment liquid while the steel strip is in the second immersion
section of the further treatment station; and while treating the
steel strip, continuously pumping the second treatment liquid out
of the second common collector and through both the second spray
section and the second immersion section, wherein the spraying and
immersing in the second treatment liquid precede or follow the
spraying and immersing in the first treatment liquid.
6. The method of claim 5, wherein the first treatment liquid and/or
the second treatment liquid comprises hydrochloric acid in a
concentration range of from 150 g/L to 250 g/L. FeCl.sub.3 in a
concentration range of from 10 g/L to 35 g/L, MeCl.sub.2 in a
concentration range from 30 g/L to 300 g/L.
7. A system for treating a steel strip including stainless steel,
and having a top surface, and a bottom surface, and being a
continuous steel strip, oriented substantially horizontally, both
in its longitudinal and transverse directions, using a treatment
liquid in a treatment station, the system comprising: a treatment
station including a treatment tank including a spray section, an
immersion section, and a common collector for the treatment liquid:
and spray nozzles configured to spray that the treatment liquid
onto the top and bottom surfaces of the steel strip, wherein the
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 and bottom surfaces of the steel strip while the steel strip is
in the spray section, and the steel strip is immersed in the
treatment liquid while the steel strip is in the immersion section,
wherein the system is configured such that the treatment liquid is
continuously pumped out of the common collector and through both
the spray section and the immersion section of the treatment
station.
8. The system of claim 7, wherein the spray section includes 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, wherein the immersion section includes 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
located within the effective immersion length, wherein the
effective spray length and the effective immersion length have a
ratio in a range of from 30:70 to 70:30.
9. The system according to one of claim 7, wherein, along the
transport direction of the steel strip, the spray section is
located upstream or downstream of the immersion section.
10. The system of claim 7, wherein the common collector is
separated from the treatment tank of the treatment station.
11. The system of claim 7, wherein the common collector is
integrated with the treatment tank.
12. The system of claim 7, further comprising: a second treatment
liquid in a second treatment station including a second treatment
tank including a second spray section, a second immersion section,
and a second common collector for the second treatment liquid; and
second spray nozzles configured to spray the second treatment
liquid onto the top and bottom surface of the steel strip, wherein
the system is configured such that the steel strip is transported
continuously through the second treatment station in the transport
direction such that the second treatment liquid is sprayed onto the
top and bottom surfaces of the steel strip while the steel strip is
in the second spray section, and such that the steel strip is
immersed in the second treatment liquid while the steel strip is in
the second immersion section, wherein the system is configured such
that the second treatment liquid is continuously pumped out of the
second common collector and through both the second spray section
and the second immersion section.
13. The system of claim 11, further comprising: a third treatment
liquid in a third treatment station including a third treatment
tank including a third spray section, a third immersion section,
and a third common collector for the third treatment liquid.
14. The system of claim 12, wherein the treatment liquid and/or the
second treatment liquid and/or the third treatment liquid comprises
hydrochloric acid in a concentration range of from 150 g/L to 250
g/L, FeCl.sub.3 in a concentration range of from 10 g/L to 35 g/L,
and MeCl.sub.2 in a concentration range of from 30 g/L to 300 g/L.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a U.S. national stage application under
35 U.S.C. .sctn.371 of International Application No.
PCT/EP2015/078314, filed on Dec. 2, 2015, and claims benefit to
Europe Patent Application No. 14 195 952.8, filed on Dec. 2, 2014.
The International Application was published in English on Jun. 9,
2016, as WO 2016/087494 A1 under PCT Article 21(2).
FIELD
[0002] 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.
BACKGROUND
[0003] The presence of oxide scale on the surface of steel strip is
formed during high temperature processing. The term 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,
Fe.sub.2O.sub.3 and Fe.sub.3O.sub.4, oxides of alloying elements
such as CrO.sub.3, NiO, SiO.sub.2 and complex oxide spinals like
FeCr.sub.2O.sub.4, NiFe.sub.2O.sub.4, Fe.sub.2SiO.sub.4 and others.
During annealing, stainless steel grades are heated up to a certain
temperature (850-1150.degree. C. depending on steel grade) and are
kept at this temperature for some time to soften the metal in order
to release the work hardening induced by hot and cold rolling. A
uniform grain structure is obtained depending on the annealing
temperature, and oxide scale is formed on the surface. Underneath
the surface of stainless steel, a chromium-depleted zone is formed,
which is different for austenitic, ferritic and duplex stainless
steel grades.
[0004] Processes are required in the stainless steel industry to
remove that oxide scale and the chromium depleted layer to obtain
technological products, but that has to be achieved with a minimum
loss of base material. Pickling is the process of chemically
removing of oxide scale from the surface of a metal by the action
of water solution of inorganic acids. The stainless steel is widely
pickled in diluted sulfuric or hydrochloric acid. For pickling of
the stainless steel, a mixture of nitric acid and hydrofluoric acid
is widely applied. The rate of pickling is affected by numerous
variables, including the steel-based constituents and type and
adherence of oxide to be removed. Pickling solution temperature,
acid concentration, reaction product concentration, turbulence flow
conditions, immersion time and presence or absence of inhibitors
and accelerators influence the rate of acid attack. Because of
production factors including pickling speed, quality and
efficiency, as well as reduced attack of HCl on base metal,
hydrochloric acid has effectively displaced sulfuric acid as the
acid of choice in industrial large-scale pickling lines for
stainless steel. While the rate of pickling increases in direct
proportion to the concentration of the acid, the influence of
temperature is much more pronounced. On the other hand, certain
metals, such as cooper, chromium and nickel, retard the rate of
pickling when they occur in the steel base, since the scale bearing
these alloying metals inhibits acid attack. 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. In addition, 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.degree. C., double pickling time is
required compared to the coiling temperature of 570.degree. C.
[0005] 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. Frequently, to
effect complete oxide scale removal, 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.sub.2SO.sub.4
solution prior the main pickling in mixed acid. In today
state-of-the-art practice, the Mechanical de-scaling (MD) and
Pre-Pickling (PP) can remove the oxide scale layer only, the
chromiumdepleted zone and partly the base material can be only
removed by the final pickling process (FP).
[0006] 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. When processing of 300 and 400 series in the same line,
various acid compositions (Mix I and Mix II) and various acid
mixture temperatures are required. Since austenitic steel grades
are pickled at 50-65.degree. C., the most of ferritic and
martensitic stainless steel grades generate exothermal reaction
during the pickling, which require cooling facilities in the
pickling line in order to keep the acid mixture temperature in the
range of 35-40.degree. C. .Although the process enables excellent
pickling results to be obtained, it has the very serious drawback
that it creates considerable and substantial ecological problems
due to the use of these particular acids. 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. In addition, high nitrate levels exist in the rinse water
and in the spent pickling baths and create a major disposal
problem. The elimination of NOx vapors in the air by catalytic
DENOX plants and nitrates in the neutralized waste water creates
considerable plant operational problems, very high investment costs
for equipment, high maintenance demand and very high operational
costs. As a result, there has been considerable interest in
researching and developing stainless steel pickling processes and
plants which do not use either nitric acid or hydrofluoric acid and
which are ecologically safe and environmental-friendly.
[0007] 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. At the entry and exit of the
treatment tanks, 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.
[0008] Inside the treatment tank, the pickling acid is injected on
both sides of the tank creating a high turbulence between the strip
surface and the pickling acid.
[0009] 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.
[0010] 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.
[0011] The use of 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 chemical dissolution of steel in HCl is as follows:
Fe+2 HCl.fwdarw.FeCl.sub.2+H.sub.2
The base metal, Fe, is dissolved by the oxidizing agents, mainly
FeCl.sub.3:
2 FeCl.sub.3+Fe.fwdarw.3 FeCl.sub.2
Oxidation reaction to produce the required oxidizing agent is as
follows:
4 FeCl.sub.2+O.sub.2+4 HCl.fwdarw.4 FeCl.sub.3+2 H.sub.2O
A minimum proper FeCl.sub.3 concentration is required for the
pickling process of stainless steel. This is today typically
reached by adding H.sub.2O.sub.2 to the pickling liquid.
[0012] In the context of the present invention, chlorides of iron
and chlorides of other metals (especially chromium) are
collectively referred to by the term MeCl.
[0013] Laboratory tests, carried out for different steel grades,
have proven for HCl containing pickling solution, that the pickling
speed of spray-pickling is up to five times higher compared to the
shallow tank turbulence technology. In addition, the spray nozzles
used in the spray pickling technology create fine droplets with a
high surface which are in direct contact with air. The air, in
particular the oxygen contained in the air, dissolves in the
pickling acid and oxidizes the FeCl.sub.2 together with the HCl
forming FeCl.sub.3. Therefore using HCl in a spray pickling section
to treat stainless steel has the advantage, that no H.sub.2O.sub.2
is needed to create FeCl.sub.3. However, in pure spray pickling
tanks, the formation of FeCl.sub.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 FeCl.sub.3 concentration in the pickling acid is the
effect on the regeneration process of the spent pickling acid.
Spent pickling acid containing HCl is typically regenerated using
the pyrohydrolysis process. In this process FeCl.sub.2 and
FeCl.sub.3 are converted back to HCl and Fe.sub.2O.sub.3.
FeCl.sub.3 however has a much lower evaporation temperature than
FeCl.sub.2 and evaporates in the pyrohydrolysis reactor causing
very fine Fe.sub.2O.sub.3 particles below 1 .mu.m in size when
converted to Fe.sub.2O.sub.3. These fine particles are difficult to
remove from the process off-gases causing high dust emissions.
SUMMARY
[0014] An aspect of the invention provides a method for treating a
steel strip using a first treatment liquid in a first treatment
station, the treatment station including a first treatment tank
including a first spray section, and a first immersion section, and
a first common collector for the first treatment liquid, the steel
strip including stainless steel, a top surface, and a bottom
surface, and being a continuous steel strip, oriented substantially
horizontally, both in its longitudinal and transverse directions.
The method comprises: transporting the steel strip continuously
through the first treatment station in a transport direction
parallel to the longitudinal direction of the steel strip;
spraying, using one or more spraying nozzles, the first treatment
liquid onto the top and bottom surfaces of the steel strip while
the steel strip is in the first spray section; immersing the steel
strip in the first treatment liquid while the steel strip is in the
first immersion section; and, while treating the steel strip,
continuously pumping the first treatment liquid out of the first
common collector and through both the first spray section and the
first immersion section.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] 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. All features described and/or
illustrated herein can be used alone or combined in different
combinations in embodiments of the invention. The 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:
[0016] FIG. 1 schematically, 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;
[0017] FIG. 2 schematically, 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; and
[0018] FIG. 3 schematically, 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.
DETAILED DESCRIPTION
[0019] An aspect of 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. Furthermore, an
aspect of 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 an aspect of the present
invention and in a system of an aspect of the present invention is
stainless steel
[0020] It is therefore an aspect of the present invention provides
a method and a system for an improved steel strip treatment,
especially pickling, such that fixed investment as well as
maintenance costs are reduced, the treatment and pickling process
is realized comparatively quickly, with high quality, and in an
environmentally friendly manner.
[0021] An aspect of the present invention provides 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,
wherein the steel strip comprises stainless steel and is a
continuous steel strip being oriented substantially horizontally,
both in its longitudinal and transverse directions, wherein the
steel strip has a top surface and a bottom surface, wherein 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--in a first step, 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,--in a second step, the steel strip is
immersed in the treatment liquid while the steel strip being in the
immersion section of the treatment station, wherein, while treating
the steel strip, 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.
[0022] According to an aspect of the present invention, it is
thereby advantageously possible to provide a treatment station that
requires comparatively low installation costs as well as reduced
maintenance costs. An aspect of 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 HCl, 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.
[0023] According to an embodiment of the present invention, instead
of the steel strip comprising stainless steel, it is also preferred
that the steel strip consists of stainless steel.
[0024] According to an aspect of the present invention, it is
preferred that the process for chemical or electrochemical
treatment of the surface of stainless steel is conducted using a
pickling solution containing HCl 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.
[0025] This drastically shortening of the pickling time in case of
spray and turbulence pickling can be explained by a very thin
laminar boundary layer, which is much more thinner than in case of
turbulence dip process. The drive force of heat, mass and momentum
transfer across the boundary layer is faster, since the thickness
of this layer is significantly reduced.
[0026] According to an aspect of the present invention, 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 FeCl.sub.3 concentration in such spent acid.
[0027] An aspect of 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
[0028] According to an aspect of the present invention, it is
advantageously possible that such requirements can be achieved by
the present invention, comprising a pickling process using an HCl
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.
[0029] According to an aspect of the present invention, 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). Inside the single pickling tank
(treatment tank), 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. Typically, a wringer
roll unit--as it is typically installed between two pickling
sections--is not required. Preferably 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.
[0030] According to an aspect of the present invention, 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. Advantageously, it is
thereby possible to realize the treatment station (having both the
spray section and the immersion section) in a more cost effective
manner as the same common collection means (as well as at least a
part of the circulation system) can be used for both the spray
section and the immersion section, hence reducing the costs for
realizing the possibility to treat the steel strip by means of both
the spray section and the immersion section.
[0031] According to an aspect of the present invention, 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. This
means that 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. Preferably, also between the treatment station
or between the plurality of treatment stations, the height
variations of the steel strip in its longitudinal direction are
also comprised up to 0.5 m. Generally, it is preferred according to
the present invention that 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.
[0032] According to an aspect of the present invention, 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. In 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. For the treatment of the steel strip, 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.
[0033] According to an aspect of the present invention, 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. By doing so,
the concentration of FeCl.sub.3 can be kept below a critical level
throughout the entire pickling process, guaranteeing a uniform
pickling result without the risk of over-pickling. Furthermore 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.
[0034] According to an aspect of the present invention, the
efficiency of the treatment process (or pickling process) is
increased. Tests have proven that a certain increase in the
FeCl.sub.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 FeCl.sub.3 level. Of course, in (the
typical) case that more than one treatment stations are used in a
pickling line or steel strip pickling installation, this does not
mean that the same treatment liquid is used in all of such
different treatment stations. To the contrary, in case of a
plurality of treatment stations (i.e. having each a treatment tank
comprising a spray section and an immersion section), a different
treatment liquid is normally used for a different treatment
station; however within the same treatment station/treatment tank,
the same treatment liquid is used for both kinds of pickling
processes (spray and dip pickling). Thereby, it is advantageously
possible that the drawbacks of a comparatively high concentration
in FeCl.sub.3 can be avoided that would typically arise in case of
combining spray pickling and dib pickling using different treatment
liquids in the same treatment station.
[0035] According to an aspect of the present invention, 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).
[0036] The design of an aspect 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). In such
an embodiment, 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. This is
advantageous for the replacement (refurbishment) of deep bath
treatment tanks which have often been operated without circulation
circuits. In this case only the pump circuit needs to be added
while the circulation tank is incorporated (or integrated) in the
treatment tank.
[0037] According to a preferred embodiment of the present
invention, 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, wherein 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, wherein 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.
[0038] According to an aspect of 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. By means of defining the length
of the immersion section (at a given transport speed of the steel
strip through the pickling line), the time is defined during which
the treatment liquid is effectively treating the steel strip in the
immersion section. By means of defining the length of the spray
section (equally at a given transport speed of the steel strip
trough the pickling line), the maximum time of spray pickling is
defined in relation to the dip pickling time.
[0039] According to another preferred embodiment of the present
invention, 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.
[0040] According to an aspect of 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.
[0041] According to a preferred embodiment of the present
invention, 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.
[0042] According to an aspect of the present invention, it is
thereby advantageously possible to provide the possibility of
different pickling line architectures. E.g., it is advantageously
possible (in case that at least two treatment stations are used) to
provide both treatment stations such that the spray section is
located upstream with respect to the immersion section (i.e. the
steel strip passes the spray section first and afterwards the
immersion section): This results in a pickling sequence of the kind
of a spray and dip pickling (using a first treatment liquid) in the
first (or upstream) treatment station, followed by a spray and dip
pickling (using a second treatment liquid) in the second (or
downstream) treatment station. Alternatively, it is also
advantageously possible (in case that at least two treatment
stations are used) to provide 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), and to provide 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)): This results in a pickling sequence of the kind of a dip
and spray pickling (using a first treatment liquid) in the first
(or upstream) treatment station, followed by a spray and dip
pickling (using a second treatment liquid) in the second (or
downstream) treatment station. Of course, these building blocks of
two treatment stations can be either repeated or combined with
other treatment stations or configurations of treatment
stations.
[0043] According to a preferred embodiment of the present
invention, 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,
wherein the method comprises transporting the steel strip
continuously through the further treatment station in the transport
direction such that--in a third step, 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,--in a
fourth step, 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, wherein, while treating the steel
strip, 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.
[0044] According to an aspect of the present invention, it is
thereby advantageously possible to combine at least two inventive
treatment stations in a pickling line. Of course, it is also
possible and preferred according to the present invention to
combine such two inventive treatment stations with a conventional
treatment station (i.e. having solely a spray section or solely an
immersion section in a treatment tank) or with a plurality of
conventional treatment stations. In such an architecture of the
pickling line, 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.
[0045] According to another preferred embodiment of 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--FeCl.sub.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,--MeCl.sub.2 in a concentration ranging from and including 30
g/L to and including 300 g/L, especially in a concentration ranging
from and including 30 g/L to and including 60 g/L or in a
concentration ranging from and including 130 g/L to and including
180 g/L or in a concentration ranging from and including 230 g/L to
and including 300 g/L.
[0046] According to an aspect of the present invention, it is
thereby advantageously possible to combine a high efficiency of the
pickling process while retaining the possibility to comparatively
easily regenerated the used pickling acids (treatment liquids).
[0047] An aspect of 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, wherein the steel strip
comprises stainless steel and is a continuous steel strip being
oriented substantially horizontally, both in its longitudinal and
transverse directions, wherein the steel strip has a top surface
and a bottom surface, wherein the 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, wherein the 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.
[0048] According to an aspect of 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 FeCl.sub.3 concentration in such spent acid.
[0049] According to an embodiment of the present invention, instead
of the steel strip comprising stainless steel, it is also preferred
that the steel strip consists of stainless steel.
[0050] According to a preferred embodiment of the present
invention--especially regarding the inventive system--, 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, wherein 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, wherein 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.
[0051] According to a preferred embodiment of the present
invention--especially regarding the inventive system--, 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--especially regarding the inventive system--, the spray
section is located--along the transport direction of the steel
strip--downstream with respect to the immersion section.
[0052] According to an aspect of 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.
[0053] According to a preferred embodiment of the present
invention--especially regarding the inventive system--, 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.
[0054] According to an aspect of 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.
[0055] According to a preferred embodiment of the present
invention--especially regarding the inventive system--, 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.
[0056] According to an aspect of the present invention, it is
thereby advantageously possible to realize the treatment station in
a very cost effective manner as no separate common collection means
(or circulation tank) is required.
[0057] According to a preferred embodiment of the present
invention--especially regarding the inventive system--, 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, wherein the 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, wherein the
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.
[0058] According to an aspect of the present invention, it is
thereby advantageously possible to combine at least two inventive
treatment stations in a pickling line. Of course, it is also
possible and preferred according to the present invention to
combine such two inventive treatment stations with a conventional
treatment station (i.e. having solely a spray section or solely an
immersion section in a treatment tank) or with a plurality of
conventional treatment stations.
[0059] According to a preferred embodiment of the present
invention, 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.
[0060] According to an aspect of the present invention, it is
thereby advantageously possible to combine at least three inventive
treatment stations in a pickling line. Of course, it is also
possible and preferred according to the present invention to
combine such three inventive treatment stations with a conventional
treatment station (i.e. having solely a spray section or solely an
immersion section in a treatment tank) or with a plurality of
conventional treatment stations.
[0061] According to a further preferred embodiment of the present
invention, 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. According to
other embodiments, also the combination of five treatment stations
according to the present invention is possible and preferred
according to the present invention.
[0062] According to another preferred embodiment of the present
invention, 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--FeCl.sub.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,--FeCl2 in a concentration ranging
from and including 30 g/L to and including 300 g/L, especially in a
concentration ranging from and including 30 g/L to and including 60
g/L or in a concentration ranging from and including 130 g/L to and
including 180 g/L or in a concentration ranging from and including
230 g/L to and including 300 g/L.
[0063] According to an aspect of the present invention, it is
thereby advantageously possible to combine a high efficiency of the
pickling process while retaining the possibility to comparatively
easily regenerated the used pickling acids (treatment liquids).
[0064] These and other characteristics, features and advantages of
the present invention will become apparent from the following
detailed description, taken in conjunction with the accompanying
drawings, which illustrate, by way of example, the principles of
the invention. The description is given for the sake of example
only, without limiting the scope of the invention. The reference
figures quoted below refer to the attached drawings.
[0065] The present invention will be described with respect to
particular embodiments and with reference to certain drawings but
the invention is not limited thereto but only by the claims. The
drawings described are only schematic and are non-limiting. In the
drawings, the size of some of the elements may be exaggerated and
not drawn on scale for illustrative purposes.
[0066] Where an indefinite or definite article is used when
referring to a singular noun, e.g. "a", "an", "the", this includes
a plural of that noun unless something else is specifically
stated.
[0067] Furthermore, the terms first, second, third and the like in
the description and in the claims are used for distinguishing
between similar elements and not necessarily for describing a
sequential or chronological order. It is to be understood that the
terms so used are interchangeable under appropriate circumstances
and that the embodiments of the invention described herein are
capable of operation in other sequences than described of
illustrated herein.
[0068] 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. In
one possible and preferred implementation of the pickling line for
the treatment of a steel strip 1, represented in FIG. 1, 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. In this implementation or architecture
of the pickling line, all three treatment stations 3, 31, 32 are
realized either according to a first embodiment of the present
invention, represented in FIG. 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 FIG. 3 for the exemplary case of the treatment
station being represented by reference sign 3. Alternatively, a
part of the three treatment stations 3, 31, 32 is or are realized
according to the first embodiment of the present invention (FIG. 2)
and another part is or are realized according to the second
embodiment of the present invention (FIG. 3). In the context of the
present invention, 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. Typically,
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. In the implementation represented in FIG. 1, 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. In the exemplary implementation
of the pickling line represented in FIG. 1 (where all treatment
stations are configured according to the present invention), 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 FIG. 1) and a further immersion section
(or second immersion section) (not depicted in FIG. 1) using a
further treatment liquid (or second treatment liquid), and the
third treatment station 32 has a third spray section (not depicted
in FIG. 1) and a third immersion section (not depicted in FIG. 1)
using a third treatment liquid. For the exemplary case of the
treatment station 3 (first treatment station 3), a first and a
second embodiment of the present invention is schematically shown
in FIGS. 2 and 3.
[0069] 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.
[0070] FIG. 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.
[0071] FIGS. 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 HCl. 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 FIGS. 2 and 3 as spray section 13 of the treatment
station 3) and a dip pickling section (as represented in FIGS. 2
and 3 as immersion section 14 of the treatment station 3) according
to the present invention. FIG. 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.
[0072] 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 FIG. 2 or are realized as common
collection means 5, 51, 52 integrated in the respective treatment
tank 4, 41, 42 as shown in FIG. 3.
[0073] In the exemplary embodiment shown in FIG. 1, 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.
Thereby, 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.
Finally the spent acid is removed (reference sign 55) from the
(first) common collection means (or (first) circulation tank) 5.
After the pickling treatment in the three treatment stations 3, 31,
32 (in the exemplary implementation shown in FIG. 1), the steel
strip 1 is further processed in section 6 which comprises a rinse
section and a dryer, if required.
[0074] According to the first embodiment of the common collection
means (or circulation tank) 5, shown in FIG. 2, the treatment
station 3 comprises the treatment tank 4 with a separate common
collection means 5 (or separate circulation tank 5). At the entry
and exit section, 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 FIG. 1. The following
treatment stations (or treatment tanks), like treatment stations
31, 32 in FIG. 1, do not need such wringer roll 12. In the
exemplary representation of FIG. 2 (i.e. not necessarily), 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. In the spray pickling section 13, 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.
In one or more of the pump circuits, a heat exchanger 19 is
installed to heat the pickling acid (treatment liquid) to the
required temperature. If required, a guide roll 20 can be installed
between the spray pickling section 13 and the dip pickling section
14 in order to reduce the slack of the strip.
[0075] According to the second embodiment of the common collection
means (or circulation tank) 5, shown in FIG. 3, 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 FIG. 2.
[0076] While specific embodiments of the invention have been shown
and described in detail to illustrate the inventive principles, it
will be understood that the invention may be embodied otherwise
without departing from such principles.
[0077] For example, 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. Furthermore exemplarily, 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. Additionally, 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. Additionally, 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. For example, 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.sup.3/h or approximately
220 m.sup.3/h.
[0078] 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 HCl 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 test results have proven that the pickling time could be
reduced by 40-45% compared to the conventional pickling process
using dip pickling with shallow tank turbulence technology, while
the FeCl.sub.3 concentration was constantly below 30 g/L which is
considered to be uncritical as far as the acid regeneration process
is concerned. All tested materials showed uniform pickling results
without any signs of over-pickling.
[0079] In another test using the same pilot plant, the material was
treated with a reduced temperature of the pickling acid (treatment
liquid). The results showed that the temperature could be reduced
from 90.degree. C. down to 70.degree. C. while still reaching the
same pickling time as for the conventional dip pickling process
with shallow tank turbulence technology. This result is equivalent
to a 20% reduction of the energy which is needed to keep the
process temperature in the pickling process.
[0080] As an example of the operation of the system and especially
of the use of the treatment liquids as a cascade, an example is
given of the concentration values for an example of using three
treatment stations in a pickling line:
In the first treatment station 3, the concentration of HCl is in
the range of between and comprising 201 g/L to and comprising 215
g/L, the concentration of MeCl.sub.2 is in the range of between and
comprising 270 g/L to and comprising 286 g/L, the concentration of
FeCl.sub.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.degree. C. to and comprising
89.degree. C.
[0081] In the second treatment station 31, the concentration of HCl
is in the range of between and comprising 204 g/L to and comprising
214 g/L, the concentration of MeCl.sub.2 is in the range of between
and comprising 141 g/L to and comprising 149 g/L, the concentration
of FeCl.sub.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.degree. C. to and
comprising 93.degree. C.
[0082] In the third treatment station, the concentration of HCl is
in the range of between and comprising 190 g/L to and comprising
201 g/L, the concentration of MeCl.sub.2 is in the range of between
and comprising 40 g/L to and comprising 50 g/L, the concentration
of FeCl.sub.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.degree. C. to and
comprising 91.degree. C.
[0083] Various tests were made with different qualities of the hot
rolled stainless steel strips. Tests were done majority with
austenitic AISI 304 and 316 grades as well as with ferritic AISI
409 and 430 grades, but also with other steel grades. The best
results were achieved with steel that has been either shot-blasted
or the scale-broken off prior to pickling in hydrochloric acid. In
these trials some of the stainless steel grades were compared under
the same pickling conditions. In all trials combined spray pickling
and dip pickling in one treatment step using a common circulation
system gave the shortest pickling time and excellent surface
quality while the FeCl.sub.3 concentration could be kept at a level
below 30 g/L Significantly reduction of the pickling time were
achieved for heavy to pickle steel grades as this is the case of
coils coiled at higher coiling temperature e.g. >700.degree.
C.
[0084] 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.
[0085] 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.
REFERENCE SIGNS
[0086] 1 steel strip
[0087] 2 transport direction of the steel strip
[0088] 3 treatment station
[0089] 4 treatment tank (of the treatment station)
[0090] 5 common collection means (of the treatment station)
[0091] 12 wringer roll(s)
[0092] 13 spray section (of the treatment station)
[0093] 14 immersion section (of the treatment station)
[0094] 15 spray nozzles (of the treatment station)
[0095] 17, 18 pumps
[0096] 19 heat exchanger
[0097] 20 guide roll(s)
[0098] 31 further treatment station
[0099] 41 further treatment tank (of the further treatment
station)
[0100] 51 further common collection means (of the further treatment
station)
[0101] 32 third treatment station
[0102] 42 third treatment tank (of the third treatment station)
[0103] 52 third common collection means (of the third treatment
station)
[0104] 54 feeding of fresh treatment liquid
[0105] 55 removing of used treatment liquid
* * * * *