Note: Descriptions are shown in the official language in which they were submitted.
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MET~IOD AND DEVICE EOR LEVELI~ TAL STRIP TC) BE FED
INTO CONTIN~OIlS ANNE:ALING FURNACE
BACl~GROUND OF THE: INVENTION
Field of the Invention
The present invention relates generally to a
method device for leveling a series of metal strip to
subject heat treatment. such as annealing. More
specifically, the invention relates to a technic for
0 effectively performing metal strip leveling operation
with avoidance of breakage at welded joint, defect in
the series of metal strip.
Description of the Background Art
In general, a plurality of hearth rolls are
arranged in a continuous annealing furnace for defining
a zig-zag path through known heat treatment stages, such
as a heating stage, a soaking stage maintaining the
metal strip at constant heated temperature, a cooling
stage and so forth. The metal strip is wound around the
hearth rolls and runs through the zig-zag path in the
annealing furnace to be subject heat treatment.
In the practical operation of the annealing
furnace, the metal strip at the zone cross to the inlet
has relatively low temperature. At this zone in the
annealing furnace, the temperature at the transverse
edge positions of the hearth roll tends to become much
higher than that at the transverse central portion. This
temperature difference between the edge portions and the
central portion increases as increasing the line speed.
This causes substantial difference of the heat expansion
at the edge portion and the central portion to cause
reduction of the effective crown magnitude. This
redUction of the crown tends to lead unbalance of
tension to be exerted on the metal
strip in transverse direction in the case that the metal
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strip~ is in the configuration of edge wave or center
wave. Unbalance tension tends to cause meander of the
metal strip in the path.
In order to prevent this, the line speed 'co
feed the metal strip through the annealing furnace has
to be lowered in order to minimi~e temperature
difference between the edge portions and the central
portions of the hearth roll. This clearly cause
lowering efficiency of the annealing furnace. On the
0 other 'nand, possibility of the meander of the metal
strip can be reduced by providing greater magnitude of
the initial crown on the periphery of the hearth roll.
This may allow to maintain satisfactory line speed. On
the other hand, when sufficient initial crown for the
initial heating stage is provided for the hearth roll,
the crown magnitude tends to be excessive at the high
temperature zone to cause heat buckle when line speed is
lowered in some reason, such as for welding the strips.
In this view, there are various proposals for
obtaining stable operation of the annealing furnace by
controlling magnitude of crown on the peripheries of
hearth rolls. For e~ample. such proposals have been
disclosed in the Japanese Utility Model First
~unexamined) Publication (Tokkai) Showa 57-177930 and
the Japanese Utility Model First Publication (Jikkai)
Showa 58-10546. In these prior proposal, crown magnitude
have been controlled by heating and cooling the hearth
rolls. On the other hand, the ~apanese Patent First
Publication (Jikkai) Showa 55-172359 proposed to control
the crown magnitude by means of bending device.
On the other hand, the meander of the metal
strip in the annealing furnace is also caused due to
Configuration of the metal strip, such as bending,
transverse curve and so forth. If the configuration of
3~ the metal strip is not suitable for passing through the
annealing furnace to cause uneven contact with the
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hearth roll surface, meander of the metal strip is
caused even when the crown magnitude is sufficient. This
tendency increases as increasing the line speed. In
order to regulate or adjust the configuration of the
metal strip, tension leveler devices are provided.
In general, such tension leveler devices exert
substantial tension, e.g. 20 kg/mm2. Such high tension
to be exerted on the metal strip tends to cause breakage
at the welded joint between leading and trailing metal
~ coils, defects on the metal strip. On the other hand,
because of the uneveness at the welded joint, leveling
rolls in the tension leveler tends to be damaged due to
high tension. In order to prevent breakage of the metal
strip and/or damaging of the leveling rolls, it has been
taken ways to slow-down the line speed at the welded
joint or to release the roll at the welded joint.
Slow-down of the line speed necessarily causes the
lowering of the efficiency of the annealing furnace. On
the other hand, releasing of the leveling rolls
necessarily feed the metal strip with unleveled portions
to cause meander in the annealing furnace.
SUMMARY OF T~E INVENTIO~
Therefore, it is an object of the present
invention to provide a method and device for leveling
the metal strip which improves the aforementioned
drawback in the prior art.
Another object of the present invention to
pro~ide a method and device to perform tension leveling
Operation for the metal strip which successfully
eliminates the metal strip to cause meander in the
annealing furna¢e by controlling a tension to be exerted
on the metal strip so that the expansion of the metal
strip due to the exerted tension can be set in relation
to open and close positions of the leveling rolls to
release the rolls from the metal strip at the welded
joint portion in order to establish optimal
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relationship.
A further object of the invention is to
provide a level device which is suitable for
implementing quick open and quick close operation in the
leveling operation for avoiding welded joint of the
metal strip without requiring lowering of line speed.
In order to accomplish the aforementioned and
other objects, a method for leveling a metal strip
according to the present invention, performs leveling
operation by opening leveling rolls at a predetermined
position relative to the welded joint and close at a
predetermined position relative to the welded joint. A
tension to be exerted on the metal strip while the
leveling rolls are held open is set at a given value in
relation to the metal strip length where the leveling
rolls are held open. The tension to be exerted on the
metal strip while the leveling rolls is selected so that
the tension may cause a given elongation on the metal
strip and whereby levels the metal strip.
On the other hand, according to the invention,
it is also provided a leveling device according to the
present invention, which is applicable for implementing
the leveling process including quick open and quic~
Close at the welded joint of the strips. The leveling
device according to the present invention features in
that the leveling rolls as held open and thus released
from the ~etal strip is self-propelled to rotate.
According to one aspect of the invention, a
method for leveling a metal strip to be fed into an
annealing furnace, which metal strip is formed into a
series of strip by connecting coils at a joint,
comprises the steps of:
providing a leveling roll assemblies which is
Constituted of a first and second roll components
disposed between opposite sides of a path through which
the metal strip is fed;
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providing means for exerting a predetermined
magnitude of tension force to the metal strip during
leveling operation;
depressing the first and second components of
the leveling roll assembly with a predetermined pressure
for leveling the metal strip;
releasing the first component of the leveling
roller assembly from the mating surface of the metal
strip for releasing the metal strip from depressing
pressure, at a joint of the series of metal strip, and
rotatingly driving at least the released one
of the first and second component while it is released
from the metal strip.
In the method as set forth above, the rotation
speed of the first component is variable depending upon
a line speed of the metal strip. In practice, the
rotation speed of the the first component is so adjusted
as to have a given speed difference relati~Je to the line
speed so that the speed difference is reduced as
increasing the line speed.
In the practical operation, the rotation speed
of the first component is adjusted as to satisfy the
following formula:
~S < LS
where AS is speed difference: and
LS is line speed of the metal strip,
30 when the line speed is lower than or equal to 150 m/min.
and to satisfy the following formula:
~S < -a . LS+b
where ~S is speed difference;
LS is line speed of the metal strip;
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a is 0.124; and
b is 16g.6
when the line speed is higher than 150 m/min.
According to a further aspect of the
invention, a leveling device for leveling a metal strip
to be fed into an annealing furnace, which metal strip
is formed into a series of strip by connecting coils at
a join, comprises a leveling roll assembly which is
constituted of a first and second roll components
disposed between opposite sides of a path through which
the metal strip is fed, means for exerting a
predetermined magnitude of tension force to the metal
strip during leveling operation, means for depressing
the first and second components of the leveling roll
assembly with a predetermined pressure for levèling the
metal strip, means for releasing the first component of
the leveling roller assembly-from the mating surface of
the metal strip for releasing the metal strip from
depressing pressure, at a joint of the series of metal
strip, and means for rotatingly driving the first
component while it is released from the metal strip.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood more
fully from the detailed description given herebelow and
from the accompanying drawings of the preferred
embodiment of the invention~ which, however, should not
be taken to limit the invention but are for explanation
and understanding only.
In the drawings:
Fig. 1 is a fragmentary illustration of a
general construction of an inlet portion of an annealing
furnace, to which the preferred embodiment of a method
for leveling a metal strip and a leveling device
3~ therefor are applicable;
Fig. 2 is an illustration of the annealing
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furnace for performing continuous annealiny for a series
of metal strip:
Fig. 3 is an illustration of an arrangement of
leveling rollers of 'che preferred embodiment of the
leveling device according to the invention;
Fig, 4 is a graph showing steepness of the
metal strip, which steepness is defined by a ratio of
the height of a peak of the uneveness (H) versus pitch
between peak and adjacent bottom (P):
~ig. 5 is a graph showing elongation ~% of the
metal strip relative to a distance from leveling rollers
open point and/or close point to a welded joint on the
metal strip;
Fig. 6 is a chart showing axial direction
temperature distribution of the hearth roll at the
position adjacent the inlet of the annealing furnace;
Fig. 7 is a perspective view of the preferred
embodiment of a leveling roller assembly to be employed
in the preferred embodiment of the leveling device
according to the invention; and
Fig. 8 is a graph showing relationship between
a speed difference between the metal strip and the
leveling roll and a line speed.
DI~SCRIP~ION OF TEIE PREFE:RR13D EMBODIMENT
Referring now to the drawings, particularly to
Figs. 1 to 3. a annealing furnace lo to which the
preferred embodiment of a method for leveling a metal
strip 1~ and a leveling device 14 for implementing the
preferred embodiment of the leveling method according to
the invention, has an inlet side looper 16 at the
position upstream of a furnace chamber 18. The
pre~erred embodiment of rhe leveling device 14 is
provided at a position upstream of the inlet side looper
16, the leveling device 14 to be employed is a tension
leveling device.
The furnace chamber 18 is divided into a
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378~i
plurality of zones, i.e. heating zone 18a, a soaking
zone 18b, a moderate cooling zone 18c and quick cooling
zone 18d. A plurality of hearth rolls 18e are arranged
in the furnace chamber 18 to define a zig zag path for
the metal strip 12. As is well known, the hearth rolls
are separated into two groups. in which one group is
located adjacent the ceiling of the annealing furnace
and the other group of rolls are located adjacent the
floor of the furnace. Therefore, the rolls in the one
group is distanced from preceding and trailing rolls in
other group at a predetermined span L.
As shown in Fig. 3, the preferred embodiment
of the leveling device 14 comprises a plurality of
leveling roll assemblies 20. Each leveling roller
assembly comprises a work rol] 22, an intermediate rolls
24, a back-up rolls 26 and deflector rolls 28. The
deflector rolls 28 forming a deflector roll assembly 30
are oriented opposite side to the work roll 22, the
intermediate roll 24 and the back-up rolls 26 which
forms a work roll assembly 32 with respect to the metal
strip path. The leveling roll assemblies 20 are
arranged along a metal strip path in the leveling device
14 with a given interval. The leveling roll assemblies
20 are respectively associated with known mechanism for
shifting the work roll assembly 32 toward and away from
the deflector roll assembly 30 so as to release the work
rolls from the metal strip while the welding joint 34 on
the metal strip 12 passes through the leveling device
14. Bridle rolls 36 and 38 are provided at upstream end
and downstream end of the leveling device ~4 for
Controlling tension to be exerted on the metal strip 12
passing through the leveling device.
In the shown embodiment, the leveling roll
assemblies 20 is operated to be open at a point 40 o~
the metal strip x (m) ahead of the welded joint 34 and
return to closed position after x (m) from the welded
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joint at a point 42. Namely, when the point 40 of the
metal strip arrives the leveling device 14, the leveling
roll assemblies 20 are operated at the open position, in
which the work roll assembly 32 are shifted a~7ay from
the deflector roll assembly 30 to make the metal strip
free from rolling pressure. The leveling roll
assemblies 20 are operated to the closed position to
contact the work roll 22 and the deflector rolls 28 onto
the opposite sides of the metal strip when the point 42
pass the outlet of the leveling device.
On the other hand, while the leveling roll
assemblies 20 are in closed position to contact the work
rolls 22 and the deflector rolls 28 onto the surfaces of
the metal strip 12, the depression and so forth are set
so that the steepness which is the ratio of the height
of the peak H of the projecting uneveness versus the
pitch P from the peak to the bottom of the depression,
is suitable for satisfactorily high line speed in the
annealing furnace. In order to check an optimum
steepness, an experimentation has been taken place with
respect to tin plate. The result is shown in Fig. 4,
A~ seen from Fig. 4, when the steepness is less than or
equal to 1.0%, the line speed in the annealing furnace
was higher than or equal to 5~0 m/min. This is
satisfactory for obtaining high efficiency of the
annealing furnace~ In this view, the preferred
steepness is 1.0% or smallerO By repeating bending in
the leveling device with a preset depression and a given
tension force exerted on the metal strip, the steepness
can be reduced. In this leveling operation, it is also
observed elongation of the metal strip due to bending
pressure and tension.
The bridle rolls 36 and 38 are controlled to
provide a tension or the metal strip passing the
leveling device. The tension is so determined as to
provide a given elongation expansion ~ on the metal
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strip. Throughout the disclosure, the metal strip
elongation ~ (%) represents magnitude of tension force
to be exerted on the metal strip. The tension force is
determined to satisfy the following equation:
~ > o~oos2(xlsL)l 4s
The relationship between the elongation ~
and the aforementioned x(m) is shown in Fig. 5. When
0 the elongation ~(~) relative to the distance x(m) is
maintained in the hutched range. breakage of the metal
strip in the leveling device and meander of the metal
strip in the annealing furnace was not occurred~
Therefore, by setting the operating condition of the
leveling device to satisfy the foregoing equation, it
becomes unnecessary to slow-down the line speed at the
welded joint of the metal strip but can provide
satisfactorily stable and high efficiency annealing
~urnace operation.
Here, in the conventional construction, the
Work rolls 22 are idle roll rotatingly driven by the
metal strip fed at a given line speed. Therefore, the
rotation speed of the work roll was determined
corresponding to the line speed of the metal strip. In
the quick open and quick close operation for avoiding
breakage of the metal strip at the welded joints set
~orth above, substantial thrusting force may be exerted
onto the bearing section of the work roll when it is
released from the metal strip in the quick open
operation. On the other hand, while it is held at open
position, the ~ork roll stops. As a result, when the
Work roll is operated toward the metal strip in quick
Close operation, the substantial slip is created between
the metal strip and the work roll to form scratches on
the metal strip surface. In order to prevent this, the
leveling roll assembly 20 to be employed in the
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preferred embodiment of the invention, has a driving
mechanism 50 for driving the work roll 22 at least whGn
the leveling roll assembly 20 is held open position and
thus the work roll 22 is held away from the metal strip.
As shown in Fig. 7, the driving mechanism 50
comprises an electric motor 52 which drives a dri~ing
sproket 54. The driving sproket 54 is connected to a
driven sproket 56 associated with a power distributisn
mechanism s8, via a chain 60. The power distribution
0 mechanism 58 is associated with the back-up rolls 26 to
rotatingly drive the latter. Since rotation torque thus
exerted on the back-up rolls 26 are transmitted to the
Work roll 22 via the intermediate rolls 240
A clutch 62 may be provided between the driven
sproket 56 and the power distribution mechanism 58 for
establishing and releasing the power train in
synchronism with quick open and quick close operation of
the leveling roll assembly.
Fig. 8 shows a graph showing a relationship
between the line speed LS and the speed dirference ~S
(m/min) as a result of experimentation. As will be seen
from Fig. ~, when the line speed is lower than or equal
to 150 m/min, scratch was not formed even when the work
roll 22 is not driven to rotate. On the other hand,
when the line speed is higher than 150 mlmin, scratches
were made when the work roll is held stopped. As
further be observed ~rom Fig. 8, higher speed of
rotation was required t~ reduce the difference ASo
Namely, when the speed difference ~S in relation to the
line speed is held in a hutched xange, scratch will
never formed on the metal strip. Therefore, the speed
of rotatlon of the work roll is set to satisfy the
following formulae:
When LS < 150 m/min,
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~S < LS; and
When LS > 150 (m/min)
~S < -a . LS ~ b
(were a = 0~124, b = 16806)
Therefore, by driving the work roll while it
is held released from the metal strip, formation of
scratch of the metal strip can be successfull~ prevented
during leveling operation.
While the present invention has been disclosed
in terms of the preferred embodiment in order to
facilitate better understanding of the invention, it
should be appreciated that the invention can be embodied
in vario~s ways without departing from the principle of
the invention. Therefore, the invention should be
understood to include all possible embodiments and
modifications to the shown embodiments which can be
embodied without departing rom the principle of the
invention set out in the appended claims~
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