U.S. patent application number 16/493466 was filed with the patent office on 2020-04-30 for continuous annealing or galvanising line comprising a tensioning block between two consecutive furnaces.
The applicant listed for this patent is FIVES STEIN. Invention is credited to Michel CLIN, Stephane MEHRAIN.
Application Number | 20200131598 16/493466 |
Document ID | / |
Family ID | 58707832 |
Filed Date | 2020-04-30 |
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United States Patent
Application |
20200131598 |
Kind Code |
A1 |
CLIN; Michel ; et
al. |
April 30, 2020 |
CONTINUOUS ANNEALING OR GALVANISING LINE COMPRISING A TENSIONING
BLOCK BETWEEN TWO CONSECUTIVE FURNACES
Abstract
Continuous annealing or galvanizing line for metal strips with
at least two consecutive annealing furnaces, a tensioning unit with
at least two rollers located between the two annealing furnaces,
and a production control and optimization system for said line.
Inventors: |
CLIN; Michel;
(Maisons-Alfort, FR) ; MEHRAIN; Stephane;
(Maisons-Alfort, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FIVES STEIN |
Maisons Alfort |
|
FR |
|
|
Family ID: |
58707832 |
Appl. No.: |
16/493466 |
Filed: |
March 13, 2018 |
PCT Filed: |
March 13, 2018 |
PCT NO: |
PCT/FR2018/050594 |
371 Date: |
September 12, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C21D 9/563 20130101;
C21D 9/561 20130101; C21D 9/564 20130101 |
International
Class: |
C21D 9/56 20060101
C21D009/56 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 13, 2017 |
FR |
1752021 |
Claims
1. A continuous annealing or galvanizing line for metal strips
arranged to handle a running strip which includes at least two
consecutive annealing furnaces, and a tensioning unit comprising at
least two rollers arranged between the two annealing furnaces after
a cooling section of the first annealing furnace and before a
heating section of the second annealing furnace, in the running
direction of the strip.
2. The line according to claim 1, comprising means to control the
tensioning unit to manage tension applied on the strip by said
tensioning unit.
3. The line according to claim 1, where the tensioning unit is
placed within an atmosphere separation buffer volume of said line,
said volume placed between the upstream furnace and downstream
furnace.
4. The line according to claim 1, also including an accumulator for
a length of strip, said accumulator placed between the two
annealing furnaces.
5. The line according to claim 4, where the accumulator is placed
in a chamber with exterior walls separating the atmosphere within
said chamber from the atmosphere outside, the exterior walls also
being thermally insulated, said chamber also including the means to
heat or maintain the temperature of the strip.
6. An annealing or galvanizing process for metal strips on a line
arranged to handle a running strip which includes at least two
consecutive annealing furnaces, and a tensioning unit comprising at
least two rollers placed between the two furnaces, after a cooling
section of the first annealing furnace and before a heating section
of the second annealing furnace, in the running direction of the
strip.
7. The process according to claim 6, including applying
differentiated parameters to the line for the strip running speed
and its tension in the two furnaces, particularly to optimize
management of thermal and strip format change transitions between
the two furnaces, preferably using management of the tensioning
unit to control tension on the strip applied by said tensioning
unit.
8. A computer program product, downloadable from a communication
network and/or stored on media that can be read by a computer
and/or executed by a microprocessor, and loadable to the internal
memory of a calculating unit, characterized by the fact that it
contains programming code instructions which, when executed by the
calculating unit, initiate the stages of the process according to
claim 7.
Description
[0001] The invention relates to continuous annealing or galvanizing
lines for steel strips. By galvanizing, we intend here and below
all dip-coating, whether the coating is of zinc, aluminum, alloys
of zinc and aluminum, or any other type of coating. More
specifically, the invention relates to managing strip tension on
lines with successive furnaces.
[0002] In a continuous line, steel strips are subject to different
thermal processes in succession as they move through various
heating and cooling chambers. To ensure a good strip running
through the chambers, it must wrap correctly around the support
rollers inside the chambers. The exterior surface of the rollers is
shaped to help guide the strip through the center of the furnace.
At the same time, excessive tension must be avoided, since it risks
plasticizing the steel strip as it runs through high temperature
chambers, which in turn would create problems with wrinkling on the
surface of the strip or could even lead to stoppage of the
installation because the strip breaks. Traditionally, as
illustrated in FIG. 1 of U.S. Pat. No. 4,358,093, the level of
tension in the furnace is controlled by two tensioning unit with 2
or 3 rollers placed outside the furnace, one block upstream and the
other downstream of the furnace, with the strip tension then more
gradually and more lightly adjusted by the furnace's support
rollers according to the varying temperatures of the product in the
heating and cooling chambers. So tension can be gradually reduced
in one heating chamber then gradually increased in the cooling
chamber that comes after. Sometimes, as illustrated in FIG. 3 of
U.S. Pat. No. 4,358,093, a tensioning unit is used in the furnace
upstream of a cooling chamber to significantly increase tension
before the strip enters the latter.
[0003] EP1167553 discloses in FIG. 4 the implantation of tensioning
units on either side of a cooling chamber. The one located
downstream makes it possible to have a limited level of strip
tension in the overaging section located after the cooling chamber.
In this overaging section, the strip is reheated and maintained at
a moderate temperature, for example 300.degree. C. In the case of a
galvanizing line, a 2 or 3 roll tensioning unit is used at the end
of the furnace to significantly increase the tension of the strip
in the cooling tower.
[0004] Steel qualities are constantly evolving, particularly to
increase their mechanical strength, thereby enabling reductions in
material thickness and lighter onboard mass for lower consumption.
New grades of steel require a thermal cycle involving two
successive annealing treatments, hence the presence of two furnaces
on the same continuous annealing or galvanizing line.
[0005] In a line configuration with two annealing furnaces placed
one after the other, there is a combination of a first series of
heating chambers followed by cooling chambers for a first annealing
thermal cycle, then a second series of heating chambers followed by
cooling chambers for the second annealing thermal cycle, all
continuously in the same thermal section of the line. The annealing
temperature is related to the chemical composition of the steel,
its metallurgical state, in particular its level of hardening, as
well as the heating rate up to the annealing temperature and the
soaking time at this temperature. The annealing temperature and the
soaking time thereto depend on the austenite fraction that is
desired at the end of the soaking. Typically, the annealing
temperature is between 700.degree. C. and 1000.degree. C. At the
end of the first annealing cycle, the strip is typically cooled to
a temperature between 100.degree. C. and 300.degree. C., depending
on the desired metallurgical transformations. It is then again
brought to an annealing temperature, and then cooled, before a
possible overaging section. The problem posed by a line with two
consecutive annealing furnaces derives from the fact that the two
furnaces, and their constituent chambers, can present unusual
operating conditions when compared to lines with a single annealing
furnace. Each of the furnaces may be operating at a high or low
temperature, or even be stopped, with the strip still running
through it.
[0006] Regulating tension between the annealing furnaces and the
various chambers of both furnaces is a key element in avoiding, as
far as possible, production shutdown caused by misguiding or broken
strip. In a line with two consecutive annealing furnaces, the
length of strip in the line is significantly increased in
comparison to a traditional line with a single furnace, so there is
increased difficulty in guiding the strip all along the line.
Moreover, thermal transition and strip format transition phases
require specifically regulated tension in a two consecutive
annealing furnaces configuration, since there may at the same time
be several steel coils of different formats and with different
thermal cycles inside the thermal assembly as a whole, as
constituted by the two consecutive furnaces.
[0007] Tension management for a continuous annealing or galvanizing
line with two annealing furnaces must therefore address three core
issues: [0008] guarantee the correct alignment of the strip in the
middle of all the chambers of the two furnaces, whatever the
operating regime of each furnace. [0009] guarantee the good quality
of the product's surface by avoiding risks of plastic deformation
of a strip that is subject to various levels of temperature and
tension in the different chambers, whatever the operating regime of
each furnace. [0010] guarantee that thermal cycle and strip format
transition stages are managed with no loss of production.
[0011] Of course, these three issues are closely interlinked with
each other and with temperature control in the furnaces.
[0012] For a traditional annealing or galvanizing line, tension
management is within the state of the art. A traditional annealing
or galvanizing line is a line comprising a single furnace.
[0013] Traditionally, tension is set for low tension within heating
chambers, or to be gradually and lightly reduced between the
entrance to this chamber, which is cooler, and its exit, which is
hotter, so as to avoid plastic deformation of the strip while
ensuring its proper movement. Tension is then gradually increased
in the cooling chambers. This tension control is traditionally
achieved by torque regulation in the support rollers that are used
to move the steel strip.
[0014] The state of the art also suggests using a tensioning unit
in a furnace upstream of a cooling chamber, to maintain a low level
of tension in the furnace and increase the strip tension
significantly in the cooling chamber.
[0015] In a two annealing furnaces line, the first furnace may
comprise a heating section, for example with direct-fired burners
(NOF section) or radiant tubes (RTF section), or a combination of
the two, a soaking section, and one or several sections for cooling
by gas, by liquid, by a mist of gas and liquid, or by a combination
of several of these methods.
[0016] The second furnace may comprise, for example, a heating
section (RTF), a soaking section, and one or several sections for
cooling by gas, by liquid, by a mist of gas and liquid, or by a
combination of several of these methods Other sections may be
present, for example an overaging section after the cooling
sections
[0017] In a galvanizing line with two annealing furnaces, after the
second annealing, the steel strip is cooled down to a temperature
close to that of the zinc pot, it is then coated with zinc or
another coating by immersion in zinc pot. It is then cooled to
ambient temperature, for example with blown air.
[0018] A line with consecutive annealing furnaces creates new
difficulties for managing tension in the different sections.
[0019] The first difficulty presented by two consecutive furnaces
is how to control very different levels of tension in each of the
two furnaces in relation to the temperature levels in the various
chambers. This problem is exacerbated because the operating
temperature range of the two furnaces is considerably wider than in
current industrial practice. For one furnace operating at annealing
temperatures of the order of 700.degree. C. to 950.degree. C. in
the heating chamber, compared to operating regimes where the same
furnace or the other furnace is at a low temperature, typically
between ambient and 500.degree. C. in the heating chamber, there is
a need for a wide range of tension control. Requirements for
optimal operation of a two-furnace line dictate great flexibility
in tension control for each of the two furnaces, separately or in
combination.
[0020] A first aspect of the invention proposes a continuous
annealing or galvanizing line for running metal strips which
includes at least two consecutive annealing furnaces and a
tensioning unit comprising at least two rollers placed between the
two furnaces.
[0021] The line as per the invention may also include means to
control the tensioning unit to manage tension applied on the strip
by said tensioning unit.
[0022] One possibility is for the tensioning unit to be placed, in
strip running direction, after a cooling section of the first
furnace and before a heating section of the second furnace
[0023] The tensioning unit may be placed within an atmosphere
separation volume on said line, said volume being located between
the upstream and downstream furnaces.
[0024] The line as per the invention may also include a strip
length accumulator located between the two annealing furnaces.
[0025] The accumulator may be placed in a chamber with exterior
walls separating the atmosphere present within the chamber from the
atmosphere present outside the chamber, for example air, the
exterior walls also being thermally insulated, preferably such as
to limit thermal loss from the chamber, said chamber also possibly
including means to heat or maintain the strip temperature.
[0026] A second element of the invention proposes a process for
annealing or galvanizing metal strips on a line arranged to handle
a running strip which includes at least two consecutive annealing
furnaces and a tensioning unit comprising at least two rollers
placed between the two furnaces.
[0027] The process as per the invention may include applying
differentiated parameters to the line for the strip running speed
and/or the strip tension in the two furnaces, particularly to
optimize management of thermal and strip format transitions between
the two furnaces, preferably using management of the tensioning
unit to control the tension on the strip applied by said tensioning
unit.
[0028] Another aspect of the invention proposes a computer program
product, downloadable from a communication network and/or stored on
media that can be read by a computer and/or executed by a
microprocessor, and loadable to the internal memory of a
calculating unit, characterized by containing programming code
instructions which, when executed by the calculating unit, initiate
the stages of the process as per the invention or one or more of
its improvements.
[0029] In one possibility, on a known line, a 2- or 3-roller
tensioning unit is placed between the first and second annealing
furnace, typically between a final cooling chamber in the first
furnace and a first heating chamber in the second furnace. This
device avoids tension control for one furnace being linked to the
other furnace. It enables management of high tension in one furnace
and low tension at the same time in the other furnace. It also
enables immediate and significant increases or reductions in
tension to the strip in a strip transition phase, i.e. at the
passage of the join between two strips of a different format and/or
quality.
[0030] A first aspect of the invention may consist of a continuous
annealing or galvanizing line for metal strips which includes at
least two consecutive annealing furnaces with a tensioning unit
comprising at least two rollers placed between the two
furnaces.
[0031] In one arrangement of the invention, the tensioning unit may
be located after a cooling section of the first furnace and before
a heating section of the second furnace.
[0032] The tensioning unit may be placed in an atmosphere
separation volume between the upstream and downstream furnaces.
[0033] In another arrangement of the invention, an accumulator
enabling a length of strip to be accumulated may be placed between
the two annealing furnaces. This accumulator may be placed in a
chamber with exterior walls that can separate the atmosphere
present within said chamber from the air outside, the exterior
walls being thermally insulated so as to limit thermal loss from
the chamber, said chamber also including means to raise or maintain
the strip temperature.
[0034] The invention may also involve a production control and
optimization system for a line as per the invention, using
differentiated parameters for the strip running speed and/or the
strip tension in the two annealing furnaces, particularly to
optimize management of thermal and strip format change transitions
between the two furnaces.
[0035] Advantageously per the invention, and so as not to waste
space on the line, the unit of tensioning rollers may be placed in
a buffer volume used to manage atmosphere separation between the
two annealing furnaces. Depending on the thermal cycles and steel
strips processed, it may be necessary to manage different
atmospheres in the two furnaces.
[0036] Another difficulty for a line with two consecutive annealing
furnaces is managing the transitions between different thermal
cycles and strip formats. On a line with a single annealing
furnace, there are limitations of extent for transitions, and most
often there is only one steel coil at a time undergoing thermal
processing in the furnace. On a line with two consecutive furnaces,
several steel coils of different formats, or requiring different
thermal cycles, may be on the line at the same time.
[0037] Moreover, the heating zones, while capable of operating at
varied temperature regimes, are always active. On a double
annealing furnace line, the heating zones may be called on to work
at temperatures that are considerably lower than those of a single
furnace, around 500.degree. C., or even lower. Traditional tension
control systems using the chamber support rollers are not
sufficient for maintaining the correct levels of tension in the two
furnaces.
[0038] To resolve the problem of managing tension for transition
phases, the tensioning unit between the two furnaces can operate by
creating a tension jump, either up or down, at the appropriate
moment of transition, to manage the optimum level of tension for
each strip as it passes through each of the two furnaces.
[0039] Advantageously, the tensioning unit can also operate during
stable production phases, to adjust the correct tension levels in
the second furnace in relation to the first, enabling less use, or
even no use at all of minor tension variations applied through the
furnace's deflector rollers, which are technically more difficult
and sensitive to manage.
[0040] Finally, another challenge for managing a strip movement in
a transition phase on this type of line with two consecutive
annealing furnaces is the ability to change the strip running speed
before or during the transition, so as to optimize transition time
and improve line productivity. Traditionally, optimization systems
for level 2 control of a furnace manage strip running speed in
advance on arrival of the new strip, or while the transition takes
place in the furnace. Where there are two consecutive furnaces,
strip running speed change objectives to optimize transition may be
contradictory between the first and second furnace. At the same
time, the possibility of there being several steel coils in these
two furnaces adds to the difficulty of managing the strip running
speed and tension.
[0041] To resolve this difficulty, the invention proposes, as one
possibility, the installation of a strip accumulation area between
the two annealing furnaces, typically between the final cooling
chamber of the first furnace and the tensioning unit at the entry
of the first heating chamber in the second furnace. This device
enables the complete separation of the two consecutive furnaces in
terms of speed and tension management. It allows for the
accumulation of a certain length of strip during stable operation
phases, so that strip running speed in the first furnace can be
reduced without change to strip running speed in the second
furnace. In other cases, the intra-furnace accumulator may be empty
and enable strip running speed in the first furnace to be
accelerated while maintaining a stable strip running speed in the
second furnace. This stable strip running speed in the second
furnace is particularly important in the case of galvanizing lines,
because a stable strip running speed is required, as much as
possible, for the passage of the strip through a galvanizing bath
at the exit of the second furnace.
[0042] The invention consists, besides the arrangements described
above, of a certain number of other arrangements which will be more
explicitly addressed hereafter, with reference to assembly examples
described in relation to the attached drawings, but which are in no
way limiting. On these drawings:
[0043] FIG. 1 is a schematic view of a continuous line with two
annealing furnaces in the state of the art,
[0044] FIG. 2 is a schematic view of a continuous line with two
annealing furnaces as per a first arrangement of the invention,
[0045] FIG. 3 is a schematic view of a continuous line with two
annealing furnaces as per a second arrangement of the
invention,
[0046] FIG. 4 is a longitudinal schematic view of an example
assembly of an accumulation chamber placed between two annealing
furnaces on a continuous line, and,
[0047] FIG. 5 is a transverse schematic view of the example
assembly of an accumulation chamber placed between two annealing
furnaces from FIG. 4.
[0048] These assembly methods being in no way limiting, there may
in particular be variations of the invention that only include a
selection of the characteristics described below, as described or
generalized, or isolated from the other characteristics described,
if this selection of characteristics is sufficient to confer a
technical advantage or to differentiate the invention from the
state of the art.
[0049] The diagram in FIG. 1 of the attached drawing provides a
schematic representation of the processing sections of a continuous
galvanizing line with two annealing furnaces 30, 40, in the state
of the art. The sections of the line located up and downstream are
not shown in this diagram. The strip 1, transported by rollers 2,
first enters a preheating section 3, where it is for example
direct-fire heated to 500.degree. C. for example. It then moves
into the heating section 4, where annealing takes place at a
temperature for example of 800.degree. C. The strip then passes
into a cooling section 5 where it is cooled, for example down to
250.degree. C. It then enters a second heating section 6 where a
second annealing takes place at a temperature for example of
700.degree. C. The strip then passes into a second cooling section
7 where it is cooled, for instance down to 460.degree. C. It then
passes through a tensioning unit 9 before entering a coating
section 8 where it is dipped in a zinc bath 10. The configuration
of the line is simplified here to help in the description of the
invention. A real line would include a wider diversity of sections,
with for example chambers for heating, soaking, slow cooling, rapid
cooling, overaging, and so on.
[0050] The diagram in FIG. 2 of the attached drawings provides a
schematic representation of the processing sections of a continuous
galvanizing line with two annealing furnaces as per a first
assembly example of the invention. This figure again shows the
process sections from FIG. 1, as already described. With the aim of
separating or combining the management and control of tension in
the two furnaces 30,40, a two-roller tensioning unit 11 is placed
after the cooling section 5 of the first furnace and before the
heating section 6 of the second furnace. The tensioning unit 11 is
placed in a buffer volume 12 that manages atmosphere separation
between the two furnaces.
[0051] The diagram in FIG. 3 of the attached drawings provides a
schematic representation of the processing sections of a continuous
galvanizing line with two annealing furnaces as per a second
assembly example of the invention. This figure again shows the
process sections already described. A strip accumulation section 14
between the two furnaces is located downstream, in terms of the
strip running direction, of the cooling section 5 and upstream of
the tensioning unit placed at the entry to the heating section 6 of
the second furnace. As we have seen, this line configuration
enables the accumulation of a certain length of strip in the
accumulation section during stable operation phases, so that strip
running speed in the first furnace can be reduced without change to
strip running speed in the second furnace. It therefore enables the
complete separation of the two consecutive furnaces in terms of
strip running speed and tension management.
[0052] The diagram in FIG. 4 of the attached drawings provides a
longitudinal schematic representation of a strip accumulation
section 14 between the two annealing furnaces, as per one assembly
example of the invention. This section includes a chamber 15 into
which a strip 1 enters from the left of the figure and exits to the
right, passing through atmosphere separation seals 16. The strip is
transported by rollers 17, 18. The position of the set of seven
rollers 17 in the bottom of the chamber 15 is fixed within the
chamber. The six rollers 18, located above the set of rollers 17,
move vertically between a lower position A and a higher position B
so as to adjust the length of strip present in the chamber. The
rollers 18 are mounted on a mobile frame linked to an elevating
device, not shown in the diagram. The chamber 15 is kept under a
protective atmosphere of a mixture of nitrogen and hydrogen, for
example at 5% hydrogen. The atmosphere is, for example, injected
into the chamber from injection points 19 and leaves the chamber
through vents 20. The walls 21 of the chamber are gas-tight and
thermally insulated with refractory materials, for example ceramic
fiber, to limit the chamber's thermal losses. Heating device 22,
for example electric radiant tubes, can bring the strip to or hold
it at the desired temperature.
[0053] The diagram in FIG. 5 of the attached drawings provides a
transverse schematic representation of the chamber 15 shown in FIG.
4. The rollers 17, with their position fixed in the chamber 15, are
rotated by motors 23. The rollers 18, with their position
adjustable in the chamber, are not motorized in this assembly
example. They are rotated by the tension applied by the strip. The
rollers 18 move vertically from a level A, in the lower part of the
chamber, to a level B in the upper part of the chamber, through the
action of a lifting device 24, comprising for instance two electric
hoists (not shown) placed on each side of the chamber 15. Slots in
the chamber walls allow the movement of the shafts of the rollers
18. These are equipped with means (not shown) to limit the flow of
gas between the interior of the chamber and the volume housing the
lifting device 24, for example brushes. The lifting device is kept
under the same atmosphere as the chamber 15 with gas injection at
injection points 25 and 26, in a volume created by gas-tight walls
27. The combination of gas-tight walls 21, 27 and atmosphere
separation seals 16 help maintain the chamber under a protective
atmosphere that is non-oxidant for the strip.
[0054] The production control and optimization system for a
continuous annealing or galvanizing line for metal strips with two
annealing furnaces, as per the invention, enables differentiated
control of the strip running speed and level of tension in the two
furnaces, by acting on the tensioning unit 11 and, when present,
the accumulation section 14.
[0055] Of course, the invention is not limited to the examples
described above and numerous adjustments can be made to these
examples without moving outside the frame of the invention.
Moreover, the invention's various characteristics, forms, variants
and assembly methods can be linked to one another in different
combinations to the extent that they remain compatible and do not
exclude one another.
* * * * *