DEVICE FOR SEPARATING ATMOSPHERES
The invention relates to a device for separating
atmospheres installed between two chambers of a
continuous line for heat treating metal strips, the
chambers having different types of atmospheres.
The treatment line may be, for example, an annealing
line or a galvanizing line.
The strip undergoing heat treatment moves continuously
through the successive chambers; notably heating,
holding and cooling chambers; in order to follow the
appropriate thermal path for the mechanical properties
sought.
The thermal cycle may for example comprise heating to a
temperature of 800°C, holding for 10 seconds at this
temperature, followed by quick cooling. To prevent the
strip from oxidizing, the furnace is usually kept in a
reducing atmosphere, made up of a mixture of nitrogen
and hydrogen.
The hydrogen content in the heating and slow-cooling
chambers is usually between 5% and 15%. In the rapid
convection cooling chambers, it is beneficial to have a
higher hydrogen content in order to improve cooling
performance, for example between 20% and 80% hydrogen.
Continuous metal strip annealing furnaces usually have
very high-volume chambers. The continuous atmosphere
injection rate to keep the chambers slightly
pressurized is high, for example between 100 and 300
m^/h. As hydrogen is much more costly than nitrogen, it
is beneficial to keep the hydrogen content in the
heating and holding chambers low such as to limit the
cost of the injected atmosphere. The atmospheres of the
two successive chambers of a continuous treatment
furnace for metal strips may therefore be of different
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types, in particular in terms of the hydrogen
concentration thereof.
There being no barrier between the different chambers
of the furnace, the atmospheres migrate from one
chamber to the other, changing the concentration of
each component, which may influence the results of the
heat treatment or the surface quality of the strip.
Moreover, the use of hydrogen-rich atmospheres requires
specific precautions for plant safety.
The increase in hydrogen content resulting from a
significant migration from one chamber with a high
hydrogen content to a chamber with a low content could
also require the implementation of additional
protection in the low-content chamber.
To maintain the composition of the atmosphere in each
section, it is necessary to inject additional gas
therein, which has an impact on the economic efficiency
of the equipment.
The technical problem therefore involves creating a
barrier between the different sections of the equipment
such as . to control these atmospheres, while enabling
the strip to pass through without causing it any
physical damage. This barrier must also make it
possible to limit atmosphere migrations between the two
chambers.
In the prior art, the separation of controlled
atmospheres in different sections of the equipment is
achieved by inserting a separation device comprising
two restricted zones between which either a gas is
injected to create a buffer zone, or the gases passing
between the restricted zones are suctioned.
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These restrictions are implemented for example in the
form of shutters positioned on either side of the strip
creating a passing window for the product. They
determine the relative seal of the device through the
adjustment distance of the window.
The metal strip may have different geometric defects,
such as poor flatness with curving, or creases on the
strip. These defects require an adjustment of the
restriction devices with a wider passing window to
enable the passage of the strip without damage, but
this increases the loss section and therefore reduces
the efficiency of the device.
JP 05 214450 discloses a device for separating
atmospheres placed at the inlet and at the outlet of a
bright-annealing furnace for stainless steel, in which
the hydrogen content is kept high. The plane of
movement of the strip at the outlet of the device is
the same as the plane of movement at the inlet.
To limit the loss section, the sealing devices are
sometimes modified by fitting flexible metal elements
with high temperature resistance. These elements make
it possible to reduce the loss section, but they may
scratch the strip if they come into contact with it.
This contact between the flexible elements and the
strip may occur in the event of misalignment of the
flexible elements or geometric defects in the strip.
The behavior of the flexible elements over time is also
limited if the strip' is at a high temperature, for
example 700°C.
The invention therefore relates to a device for
separating atmospheres that is installed between two
chambers of a continuous line for treating metal strips
having different types of atmospheres, making it
possible to prevent the atmosphere in the chamber
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located upstream of the device from entering the
chamber located downstream, and vice versa.
A device for separating atmospheres according to the
invention comprises:
- a first pair of motorized rollers between which the
strip moves, this first pair of rollers constituting
most of the seal between the first chamber and the
inside of the device,
- a second pair of motorized rollers between which the
strip moves, this second pair of rollers constituting
most of the seal between the second chamber and the
inside of the device,
and is characterized in that the pairs of rollers are
placed so as to cause a change in the plane of movement
of the strip between the inlet and outlet of the
device, and in that the gap between the rollers is
adjusted such that, if the strip has geometric defects,
in particular transversal curvature, the rollers reduce
the defects in the strip throughout the width thereof,
in order to limit the gas flows.
The strip undergoes no plastic deformation when passing
between the rollers of the device according to the
invention. Thus, the strip returns to the initial
profile thereof, for example curved, after passing
through the device.
According to another aspect, the device for separating
atmospheres comprises:
- an enclosure into which the outlet of the upstream
chamber and the inlet of the downstream chamber open,
- a first pair of motorized rollers at the inlet of the
enclosure, between which the strip moves, constituting
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most of the seal between the upstream chamber and the
inside of the enclosure,
- a second pair of motorized rollers at the outlet of
the enclosure, between which the strip moves,
constituting most of the seal between the downstream
chamber and the inside of the enclosure,
and is characterized in that:
the pairs of inlet and outlet rollers of the
enclosure are offset transversely in relation to the
direction of movement of the strip, such as to cause a
change in the plane of movement of the strip between
the inlet and the outlet of the enclosure, one roller
of the inlet pair bearing against a concave portion of
the strip, and one roller of the outlet pair bearing
against another concave portion of the strip located on
the opposite side to the first roller,
- and the gap between the rollers of at least one pair
is adjusted such that, if the strip has geometric
defects, in particular transversal curvature, the
rollers of this pair reduce the geometric defects of
the strip throughout the width thereof, such as to
limit the gas flows.
Preferably, the distance between the planes of movement
of the strip between the inlet and the outlet of the
device is between 30 and 100 mm.
The device may include means for drawing off the
atmosphere inside the space between the pairs of
rollers, generating gas flows from the chambers to the
inside of the device.
According to another option, the device may include
means for injecting a gas into the space between the
pairs of rollers, creating gas flows from the inside of
the device towards the chambers.
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Advantageously, at least the rollers opposite the
rollers that bear against the strip following the
change of the plane of movement can be moved in
translation to adjust the gap between the rollers, and
the distances between the rollers of each pair are
adjusted as a function of the extent of the geometric
defects in the strip.
Preferably, the rollers are borne by shafts mounted
rotatably in bearings fixed to trucks that can slide on
slideways, the trucks being moved in translation by a
driving mechanism. A flexible sealing device is
provided to provide a sealed link between the walls of
an enclosure surrounding the rollers and the fixed
housings of the bearings. The operating position of the
rollers may be obtained using adjustable stops.
Preferably, the peripheral speed of the rollers is
synchronous with the movement speed of the strip. The
loss section can then be minimized because the strip is
forced to pass between the rollers through the
"rolling" effect without consequently becoming damaged
because the circumferential speed of the rollers is
synchronous with the movement speed of the strip.
Furthermore, the surface condition of each roller is
determined such as to prevent any marking of the strip.
With an arrangement according to the invention, the
adjustment of the loss section is more precise because
the strip bears against one of the two rollers in each
pair, which provides a geometric reference position.
The fact that the strip bears against one of the two
rollers in each pair, caused by the change of the plane
of movement of the strip according to the invention,
prevents any fluttering of the strip between the pairs
of rollers. On the other hand, a device with no
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deflection of the strip between the two pairs of
rollers would result in strip fluttering liable to mark
the surface of the strip or to generate strip
fluttering upstream or downstream of the device for
separating atmospheres.
With the features of the device according to the
invention, geometric defects in the strip cease to
constitute a limit to the efficiency of atmosphere
separation.
Shaped sealing blocks may be used on either side of the
outlet of the upstream chamber and of the inlet of the
downstream chamber to close the gap between the
circumference of the rollers and the wall of the
chamber as much as possible, without hindering rotation
of the rollers.
The device according to the invention is designed to
operate with a product that may be at a high
temperature, for example 800°C, and atmospheres that
may be hot, for example 500°C. The device is also
designed to operate with a significant difference in
temperature between the atmospheres located upstream
and downstream of the device.
The device according to the invention may
advantageously be used to separate atmospheres of very
different types, for example between a strip-oxidizing
atmosphere and a reducing atmosphere, or between a damp
atmosphere and a dry atmosphere.
The invention may be implemented on a vertical or
horizontal furnace, with the strip moving in the
horizontal plane or the vertical plane at the point
where it meets the device.
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Apart from the arrangements set out above, the
invention comprises a certain number of other
arrangements, which are dealt with in greater detail
below in relation to example embodiments that are in no
way limitative. In these drawings:
- Figure 1 is a schematic vertical cross section of a
device according to the invention, the strip moving in
a vertical plane. To facilitate comprehension of the
invention, some dimensions have been deliberately taken
out of proportion.
- Figure 2 is a larger scale cross section along the
line II-II of Figure 1, showing an example profile of
the strip before it enters the device.
- Figure 3 is a partial cross section along the line
III-III of Figure 1, showing an example profile of the
strip passing between a pair of rollers of the device
according to the invention.
- Figure 4 is a larger scale end view of two rollers,
without the enclosure that normally surrounds them.
- Figure 5 is a top view of the rollers in Figure 4 in
a smaller scale according to the arrow V of Figure 4,
and
- Figure 6 is a cross section similar to the one in
Figure 1 of a device according to the invention with
gas injection in the enclosure.
Figure 1 shows a strip 1 moving vertically from an
upstream chamber Ca towards a downstream chamber Cb in
the direction of movement of the strip shown by an
arrow A. According to the example in Figure 1, the
strip . is moving downwards, but the opposite is
possible, as is movement in a direction inclined from
the vertical. The strip could also move horizontally.
A device A for separating atmospheres is placed between
the chambers Ca and Cb. The device A includes a
thermally insulated enclosure 2 providing a sealed link
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between the upstream chamber Ca and downstream chamber
Cb. In the enclosure 2, two pairs of motorized rollers
Rla/Rlb and R2a/R2b are installed respectively at the
inlet and at the outlet of the enclosure. The strip 1
moves between the rollers of each pair.
The pairs of inlet and outlet rollers Rla/Rlb, R2a/R2b
are offset transversely, by a distance D, in relation
to the direction of movement of the strip such as to
cause a change in the plane of movement between the
inlet and the outlet of the enclosure 2. The plane of
movement is designated Pa upstream and Pb downstream of
the enclosure. The pairs of rollers are positioned such
as to ensure that the strip bears cleanly against one
of the two rollers in each pair. According to Figure 1,
the strip 1 bears cleanly against the rollers Rla and
R2a, or deviation rollers. The deviation roller Rla of
the inlet pair bears against a concave portion of the
strip, and the deviation roller R2a of the outlet pair
also bears against a concave portion located on the
side of the strip opposite the first roller Rla.
The two planes Pa and Pb may be parallel or inclined in
relation to one another. The distance D between the
planes Pa and Pb is such that it enables a deflection a
of the strip sufficient to ensure that the strip bears
against the deviation rollers Rla and R2a. This
distance D is preferably between 30 and 100 mm.
The elements 3a, 3b, 3c and 3d, or shaped sealing
blocks, make it possible to reduce the loss section
between the generators of the rollers and the chambers
Ca and Cb such as to limit atmosphere consumption. The
elements 3a, 3b, 3c and 3d are made of shaped parts
attached to a wall of the chamber or enclosure, that
have a concave surface that fits the contour of the
rollers to limit the lateral losses around the rollers.
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The elements 3a, 3b, 3c and 3d are provided on either
side of the inlet and the outlet of the enclosure.
The rollers of a pair turn in opposite directions to
one another and are 'driven, by driving means that are
not shown, at a speed synchronous with the movement
speed of the strip. This makes it possible to achieve a
relative speed of zero between the faces of the strip
and the external generators of the rollers such that
the strip is not marked.
Figures 4 and 5 show the assembly of the rollers R2a,
R2b on a larger scale than Figure 1. The rollers Rla,
Rib are assembled in a similar manner and the
description of the assembly shall therefore be limited
to R2a, R2b.
The rollers R2a, R2b are borne by shafts 4a, 4b (Figure
5) mounted rotatably in bearings 5a, 5b placed on and
attached to trucks 6a, 6b. These trucks 6a, 6b slide on
horizontal slideways 7a, 7b perpendicular to the
geometric axis of the rollers R2a, R2b. The trucks 6a,
6b and the rollers R2a, R2b are moved in translation by
a pneumatic, hydraulic, mechanical or electrical
driving mechanism 8a, 8b. According to the example
embodiment in Figures 4 and 5, the driving mechanism
8a, 8b is formed by a double-acting hydraulic or
pneumatic jack 9a, 9b the axis of which is oriented
parallel to the slideways 7a, 7b. The cylinder of each
jack is fixed relative to the slideways 7a, 7b, while
the external end of the rod of each jack is attached to
a respective truck 6a, 6b.
A flexible sealing device 10a, 10b, notably comprising
an elastomer accordion-style bellows, is provided to
establish a sealed link between the walls 11 of the
enclosure 2, including openings 12 through which the
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shafts 4a, 4b pass, and the fixed housings of the
bearings 5a, 5b.
The possible translational movements of the trucks 6a,
6b are shown by the double arrows 13a, 13b.
The operating position of the rollers R2a, R2b is
obtained using adjustable stops 14a, 15a and 14b, 15b.
The position of each stop may be controlled by a
bolt/nut system, with an electric motor used to drive
the bolt in rotation. The electric motor receives
instructions from a remote command position. Contact
between a truck and a stop acts in general on an
electrical contact, which commands the driving
mechanism 8a, 8b to stop in the position reached. The
adjustable stops make it possible to adjust the roller
gap, i.e. the width of the passing window of the strip,
in consideration of the geometric features thereof
upstream of the device.
According to an example embodiment of the invention, a
member (not shown) continuously measures the geometric
features of the strip at the inlet of the device for
separating atmospheres and sends a signal to a control
system of the line. This signal is used to
automatically adjust the position of the rollers of the
device for separating atmospheres.
According to the example embodiment in Figure 1, the
supporting rollers Rla and R2a are fixed in
translation, only the rollers Rib and R2b can be moved
in translation in a direction perpendicular to the
parallel geometric axes of the rollers. According to
another example embodiment, the four rollers can be
moved in translation in the aforementioned direction.
According to the embodiment in Figure 1, the device
includes means K for drawing off the atmosphere inside
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the space between the pairs of rollers, generating gas
flows from the chambers to the inside of the device.
The atmosphere inside the enclosure 2 is suctioned and
discarded outside it by a conduit E placed between the
two pairs of rollers and connected to the drawing-off
or suction means K. This suction causes the atmospheres
inside the chambers Ca and Cb to flow towards the
inside of the enclosure. The flow F discarded outside
the device is therefore the sum of the flow Fa coming
from the chamber Ca and of the flow Fb coming from the
chamber Fb. The direction of flow of the atmospheres
from the chambers to the inside of the device A makes
it possible to prevent the atmosphere in the chamber Ca
from entering the chamber Cb and vice versa. The device
according to the invention makes it possible to achieve
a good separation of the atmospheres between the two
chambers Ca and Cb.
According to another option, shown in Figure 6, the
device includes means I for injecting a gas G into the
space between the pairs of rollers, i.e. in the
enclosure 2, generating gas flows from inside the
device to the chambers Ca, Cb, as shown by the arrows
Ga, Gb that are inverted in relation to Figure 1.
Figure 2 shows a strip 1 having a curved, i.e. arc,
profile at the inlet of the device. The extent of the
curved geometric deformation is shown by the distance X
corresponding to the bow of the arc. Figure 3 shows
that the geometric deformation of the strip is
significantly reduced to a bow value Y when the strip
passes between the pairs of rollers. The bow Y may be
reduced to the thickness of the strip if the strip is
not very deformed, or to a limited thickness.
At the outlet of the device for separating atmospheres
according to the invention, the strip can return to a
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shape similar to the shape it had before it entered the
device.
To clarify the description, without limiting it in any
way, an example of the dimensions of the device
according to the invention is given below for a strip
1500 mm wide and 2 mm thick:
- Internal length of enclosure: 2000 mm
(dimension according to the direction of movement of
the strip)
- Strip passage section: 1700 x 290 mm
(usable interior section of conduit)
- Roller diameter: 300 mm
- Center-to-center distance Z between the two pairs of
rollers: 1100 mm
- Distance D: 50 mm

CLAIMS
1. A device for separating atmospheres that is
installed between two chambers (Ca, Cb) of a continuous
line for treating metal strips, having different types
of atmospheres, in order to prevent the atmosphere of a
first chamber (Ca) located upstream of the device from
entering a second chamber (Cb) located downstream, and
vice versa, including:
- a first pair of motorized rollers (Rla, Rib) between
which the strip moves, this first pair of rollers
constituting most of the seal between the first chamber
(Ca) and the inside of the device,
- and a second pair of motorized rollers (R2a, R2b)
between which the strip moves, this second pair of
rollers constituting most of the seal between the
second chamber (Cb) and the inside of the device,
characterized in that the pairs of rollers (Rla, Rib;
R2a, R2b) are placed so as to cause a change in the
plane (Pa, Pb) of movement of the strip between the
inlet and outlet of the device, and in that the gap
between the rollers of each pair is adjusted such that,
if the strip has geometric defects, in particular
transversal curvature, the rollers reduce the defects
in the strip throughout the width thereof, in order to
limit the gas flows (Fa, Fb).
2. A device for separating atmospheres that is
installed between two chambers (Ca, Cb) of a continuous
line for treating metal strips, having different types
of atmospheres, in order to prevent the atmosphere of a
first chamber (Ca) located upstream of the device from
entering a second chamber (Cb) located downstream, and
vice versa, including:
an enclosure (2) into which the outlet of the
upstream chamber (Ca) and the inlet of the downstream
chamber (Cb) open,
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- a first pair of motorized rollers (Rla, Rib) at the
inlet of the enclosure, between which the strip moves,
constituting most of the seal between the upstream
chamber (Ca) and the inside of the enclosure,
- and a second pair of motorized rollers (R2a and R2b),
at the outlet of the enclosure, between which the strip
moves, constituting most of the seal between the
downstream chamber (Cb) and the inside of the
enclosure,
characterized in that:
- the pairs of inlet and outlet rollers (Rla, Rib; R2a,
R2b) are offset transversely in relation to the
direction of movement (A) of the strip, such as to
cause a change in the plane (Pa, Pb) of movement of the
strip between the inlet and the outlet of the
enclosure, one roller (Rla) of the inlet pair bearing
against a concave portion of the strip, and one roller
(R2a) of the outlet pair bearing against another
concave portion of the strip located on the opposite
side to the first roller (Rla) ,
- and the gap between the rollers of at least one pair
is adjusted such that, if the strip has geometric
defects, in particular transversal curvature, the
rollers of this pair reduce the geometric defects of
the strip throughout the width thereof, such as to
limit the gas flows (Fa, Fb) .
3. The device as claimed in claim 1 or 2, characterized
in that the distance (D) between the planes (Pa, Pb) of
movement of the strip between the inlet and the outlet
of the device is between 30 and 100 mm.
4. The device as claimed in any one of claims 1 to 3,
characterized in that it includes means for drawing off
the atmosphere inside the space between the pairs of
rollers, generating gas flows from the chambers to the
inside of the device.
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5. The device as claimed in any one of claims 1 to 3,
characterized in that it includes means for injecting a
gas into the space between the pairs of rollers,
generating gas flows from the inside of the device to
the chambers.
6. The device as claimed in any one of the preceding
claims, characterized in that at least the rollers
(Rib, R2b) opposite the rollers (Rla, R2a) that bear
against the strip following the change of the plane of
movement, can be moved in translation to adjust the gap
between the rollers, and in that the distances between
the rollers of each pair (Rla, Rib; R2a, R2b) are
adjusted as a function of the extent of the geometric
defects in the strip.
7. The device as claimed in any one of the preceding
claims, characterized in that the rollers (Rla, Rib;
R2a, R2b) are borne by shafts (4a, 4b) mounted
rotatably in bearings (5a, 5b) fixed to trucks (6a, 6b)
that can slide on slideways (7a, 7b), the trucks (6a,
6b) being moved in translation by a driving mechanism
(8a, 8b).
8. The device as claimed in claim 7, characterized in
that a flexible sealing device (10a, 10b) is provided
to provide a sealed link between the walls (11) of an
enclosure (2) surrounding the rollers and the fixed
housings of the bearings (5a, 5b).
9. The device as claimed in claim 7 or 8, characterized
in that the operating position of the rollers (Rla,
Rib; R2a, R2b) is obtained using adjustable stops (14a,
15a; 14b, 15b).
10. The device as claimed in any one of the preceding
claims, characterized in that the peripheral speed of
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the rollers is synchronous with the movement speed of
the strip.
11. The device as claimed in any one of the preceding
claims, characterized in that shaped sealing blocks
(3a, 3b, 3c, 3d) are used on either side of the outlet
of the upstream chamber (Ca) and of the inlet, of the
downstream chamber (Cb) to close the gap between the
circumference of the rollers and the wall of the
chamber as much as possible, without hindering rotation
of the rollers.
12. The device as claimed in claim 2, characterized in
that the enclosure (2) is thermally insulated.