Note: Descriptions are shown in the official language in which they were submitted.
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TRANSLATION (HM-771PCT)
Translation of WO 2006/037,456 Al (PCT/EP2005/010,078)
with Amended Pages Incorporated Therein
DEVICE FOR THE CONTINUOUS LENGTHENING OF A METAL
STRIP BY TRACTION, AND METHOD FOR OPERATING ONE SUCH DEVICE
The invention concerns a device for the continuous
stretcher leveling of metal strip, which device has at least
three bridles in the direction of strip transport, with each
bridle having at least two rolls, which are positioned in such a
way that the metal strip wraps around them over a contact roll
wrap angle of more than 1800. The invention also concerns a
method for operating a device of this type.
EP 0 393 301 B2 discloses a device for the stretcher
leveling of metal strip and a corresponding method for operating
it. The metal strip to be stretched passes through five bridles
arranged in succession, which cause the metal strip to wrap
around the rolls in the shape of an S and can cause tensile
stress to build up in the metal strip by suitable driving of the
rolls of the bridles. Plastic elongation of the metal strip
takes place during the stretching operation, and this leads to a
reduction of the strip thickness and strip width.
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During this operation, in a first stretcher leveling zone,
a tensile stress is built up which almost reaches the yield
point (QPO,2) or even exceeds it. In the event that the strip
tension remains just below the yield point, a prestretching
zone, in which the strip width is elastically reduced, forms
around the roll of the bridle in conjunction with the finite
bending radius. The actual stretching is produced in a second
stretcher leveling zone that is located downstream in the
direction of strip transport. By dividing the stretcher
leveling into two zones, the flatness result in the metal strip
after the stretcher leveling is improved.
In the solution disclosed in EP 0 393 301 B2, the strip
tension for the elastic deformation of the strip is applied
between a brake roll set and a tension roll set. The strip
tension for the plastic deformation of the strip is produced in
a pair of stretcher leveling rolls arranged between them.
EP 0 936 954 Bl discloses a stretcher leveling installation
in which the two stretching zones are formed between a brake
roll set and a centrally arranged stretcher roll and between
this stretcher roll and a downstream tension roll set.
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Furthermore, EP 1 245 301 A2 discloses an installation in
which the two stretching zones are formed between the brake roll
set and a driven roll and between this roll and the tension roll
set. It is provided that the length of the first and the second
stretching interval or stretching zone is at least 0.5 times the
maximum strip width, which is intended to improve the flatness
result of the stretching operation.
DE 21 18 051 Al discloses a stretcher leveling installation
that has bridle roll retaining stands, tensile strain adjustment
gearing, and a bridle roll tension stand. In this installation,
rolls with the same diameter are driven by a common drive motor.
Finally, DE 36 36 707 C2 describes a stretcher leveling
installation for metal strip, in which the flatness-improving
effect is achieved by stretching the strip by means of bending
in alternating directions under tension around small rollers.
Although the previously known devices for the stretcher
leveling of metal strip and the previously known methods already
make it possible to increase the degree of flatness of metal
strip, there is a need to create installations and methods that
are further improved, so that metal strip can be subjected to
stretcher leveling that is even more efficient.
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Therefore, the objective of the invention is to create a
stretcher leveling device of the aforementioned type and a
corresponding stretcher leveling method, with which the
stretcher leveling operation can be further improved.
In accordance with the invention, the solution to this
problem with respect to a device is characterized by the fact
that at least the second bridle of the stretcher leveling device
in the direction of strip transport has two rolls with different
diameters, wherein the second (following) roll in the strip
transport direction is the roll of the second bridle which has
the larger diameter, and wherein the diameter of the roll with
the larger diameter is at least 1.25 times larger than the
diameter of the roll with the smaller diameter.
It is preferred for the diameter of the bridle roll with
the larger diameter to be at least 1.5 times larger than and
especially twice as large as the diameter of the bridle roll
with the smaller diameter.
As will become apparent later, this measure results in an
improvement in the stretcher leveling operation, and this in
turn leads to improved flatness of the processed metal strip.
In accordance with a preferred embodiment, the device has
five bridles with at least two rolls each. In this connection,
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the fourth bridle in the direction of strip transport can have
two rolls with different diameters. In addition, in this case,
the roll with the smaller diameter can be the downstream roll of
the fourth bridle.
In accordance with a further refinement of the invention,
the third bridle has two rolls with diameters that are the same
as the diameters of the larger rolls of the second and fourth
bridles. Furthermore, the first and fifth bridles can each have
two rolls with diameters that are the same as the diameters of
the smaller rolls of the second and fourth bridles.
Means for measuring the tensile force present in the metal
strip can be installed after the first bridle in the direction
of strip transport. The second bridle in the direction of strip
transport can be equipped with means for measuring the tensile
force applied to the metal strip by the rolls. In addition, the
fourth bridle in the direction of strip transport can be
equipped with means for measuring the tensile force applied to
the metal strip by the rolls.
An advantageous "speedmaster" operation can be realized if
the fourth bridle in the direction of strip transport is
equipped with measuring means for measuring the speed of
conveyance of the metal strip, which means are connected with an
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open-loop or closed-loop control system, which regulates or
automatically controls the drives of at least some of the
bridles according to the determined speed of conveyance.
The method of the invention for operating the stretcher
leveling device is characterized by the fact that, in the second
bridle in the strip transport direction, a tensile stress is
built up in the metal strip which is 96% to 100% of the yield
point of the material of the metal strip. The tensile stress is
preferably 96% to 99.8% of the yield point of the material,
i.e., just below 100% of the yield point of the material.
In a device with five bridles, a tensile stress that is
greater than 100% of the yield point of the material of the
metal strip is preferably built up in the metal strip in the
third bridle in the direction of strip transport.
In addition, it can be provided that in the fourth bridle
in the strip transport direction, a tensile stress is built up
in the metal strip which is 96% to 100% of the yield point of
the material of the metal strip or again is just below the yield
point (up to 99.8% of the yield point). As an alternative to
this, a tensile stress that is greater than 100% of the yield
point of the material of the metal strip can be built up in the
metal strip in the fourth bridle in the direction of strip
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transport. Accordingly, the metal strip is further plastically
deformed.
The sole figure is a highly schematic representation of a
specific embodiment of the invention. It shows a side view of a
device for the stretcher leveling of metal strip, and basically
only the rolls that are used are illustrated in the drawing.
A metal strip 2, which can be a thin metal strip, is
processed in the stretcher leveling device 1 illustrated in the
drawing. The metal strip can consist of steel, high-grade
steel, or nonferrous metal. Typical strip thicknesses can be
0.05 to 0.5 mm.
The stretcher leveling device 1 has five bridles 3, 4, 5,
6, and 7 arranged in succession. Each bridle 3, 4, 5, 6, 7 has
two rolls 8, 9; 10, 11; 12, 13; 14, 15; and 16, 17,
respectively. The rolls are arranged in such a way that the
metal strand 2 wraps around them over a contact roll wrap angle
a of at least 180 . The contact roll wrap angle a is shown for
rolls 8 and 11 by way of example: it is about 210 . The rolls
can be driven, so that strip tension can be applied to the metal
strand 2.
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The metal strip 2 passes through the device 1 in strip
transport direction R at a conveyance speed v.
The strip tension is increased from the surrounding
installation tension level by means of the first bridle 3 on the
entry side. Means 18 for measuring the tensile force in the
metal strip 2 are installed downstream of the bridle 3. The
tensile force downstream of the bridle 3 must be known to be
able to define and then regulate or automatically control the
tension level for the further controlled tension buildup.
The following bridle 4 has the two rolls 10 and 11, which
have significantly different diameters, namely, diameters Dlo and
Dll. The roll diameter Dlo can be about 600 mm (values between
400 mm and 800 mm are typical), while the diameter D11 can be
1,200 mm (values between 1,000 mm and 1,400 mm are typical). In
this connection, the first roll 10 of the bridle 4 has the same
diameter as the rolls 8 and 9 of the first bridle 3.
The second bridle 4 also has means 19 for measuring the
tensile force in the metal strip 2 (torque measurement). The
strip tension adjusted between the rolls 10 and 11 by suitable
activation of the drives (not shown) of the rolls 10, 11 is at a
level such that theoretically no surface layer plastic
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deformation of the strip to be stretched starts to occur yet.
The following roll 11 of the bridle 4 has the significantly
larger diameter D11. This roll 11 builds up the strip tension to
a level between more than 96% of the yield point tension and
just less than 100% of the yield point tension. Since the roll
radius is finite, surface layer stretching due to bending of the
strip cannot be excluded. However, it can be reduced to an
acceptable level by the dimensioning of the diameter.
Between the roll 11 of the second bridle 4 and the
following roll 12 of the third bridle 5, there is a relatively
long unsupported length of strip, in which a nonuniform stress
distribution over the width of the strip can be equalized by the
increase in tension. In this location, stress peaks due to
areas of unflatness can be equalized by microplastic
deformation, but the actual stretching process does not yet
occur here.
With the roll 12 that comes next in the direction of strip
transport R, the strip tension is then raised to the level
necessary for the desired tensile strain. The diameter D12 of
this roll 12 is the same as the diameter D11 of roll 11. Since
the starting level of the strip tension is already very high,
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negative effects due to hindered transverse contraction on roll
12 are virtually excluded. For this reason, the stretching
interval between rolls 12 and 13 can also be very short, since
equalization of stress is not necessary.
With the next bridle 6, it is possible either to lower the
strip tension back to a level between 96% and just below 100% of
the yield point tension and thus to apply no further stretching,
or, alternatively, to impose additional tensile strain on the
metal strip 2 in a systematic way here. Since the unsupported
length of strip is again relatively long between the rolls 13
and 14, the last nonuniformities in the stress distribution can
be removed here.
The bridle 6 is again equipped with a roll 14 of large
diameter and a following roll 15 of small diameter and its
configuration is mirror-inverted relative to bridle 4 upstream
of the pair of stretcher leveling rolls 12, 13.
To allow detection of the strip tension, the bridle 6 is
also provided with means 20 for measuring the tensile force.
After the large-diameter roll 14 of the fourth bridle 6, a strip
tension level is adjusted at which plastic deformation of the
metal strip 2 is prevented as it is taken up on the small roll
15 that follows. The small roll 15 adjusts the strip tension
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. =
level to the level required for the following strip tension
measurement. The strip tension measurement is made by means 23
for measuring the tensile force.
The configuration of the last, fifth bridle 7 is again
mirror-inverted relative to the first bridle 3. Its rolls 16,
17 have the same small roll diameter as rolls 10 and 15. This
bridle 7 reduces the strip tension to the level desired or
needed for the next section of the installation.
Measuring means 21 for determining the speed of conveyance
v of the metal strip 2 are installed at the fourth bridle 6.
The measuring means 21 transmit the measured value to an open-
loop or closed-loop control system 22, which (as is shown in
only a highly schematic way) acts on the drives of the bridles
3, 4, 5, 6, 7 in such a way that a desired speed is reached.
The roll 14, at which the speed of conveyance or the strip speed
is measured in the present case, thus acts as the "speedmaster"
with a downstream speed-controlled main drive of the rolls or
the tension roll sets.
The strip tension is thus maintained at a level between 96%
of the yield point tension and just below 100% of the yield
point tension upstream of the pair of stretcher leveling rolls
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12, 13; the remaining portion of the strip tension necessary to
achieve the set amount of tensile strain is applied in the pair
of stretcher leveling rolls 12, 13. Downstream of the pair of
stretcher leveling rolls 12, 13, the strip tension is either
reduced again to between 96% and just below 100% of the yield
point tension or increased to achieve supplementary further
tensile strain.
The last roll 11 of the bridle 4 (brake bridle) before the
pair of stretcher leveling rolls 12, 13 and the first roll 14 of
the following bridle 6 (tension bridle) after the pair of
stretcher leveling rolls 12, 13 have the same diameter as the
two rolls 12, 13 of the bridle 5. As explained above, this
diameter is significantly greater than the diameter of the other
rolls 8, 9, 10, 15, 16, and 17, all of which have the same
diameter.
The strip tension in the bridle 4 upstream of the bridle 5
(stretcher leveling roll unit) and in the bridle 6 downstream of
the bridle 5 is adjusted by means of strip tension measurement
and torque measurement at the rolls in such a way that
theoretically no surface layer plastic deformation occurs at the
smaller of the two rolls 10 and 15 installed in the bridles 4
and 6, respectively.
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In the illustrated embodiment, the metal strip 2 has a
stress between the two rolls 10 and 11 of about 55-70% of the
yield point of the material. As described above, a tensile
stress between 96% of the yield point and just below 100% of the
yield point is present between the rolls 11 and 12. This region
is the prestretching zone. The first principal stretching zone
is located between the rolls 12 and 13. The second principal
stretching zone is the section between rolls 13 and 14, where a
tensile stress between 96% of the yield point and just below
100% of the yield point is generally present. Between the rolls
14 and 15, a tensile stress of 55-70% of the yield point of the
material is again present (mirroring the situation between the
two rolls 14 and 15).
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List of Reference Symbols
1 stretcher leveling device
2 metal strip
3 bridle
4 bridle
bridle
6 bridle
7 bridle
8 roll
9 roll
roll
11 roll
12 roll
13 roll
14 roll
roll
16 roll
17 roll
18 means for measuring the tensile force
19 means for measuring the tensile force
means for measuring the tensile force
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21 measuring means
22 open-loop or closed-loop control system
23 means for measuring the tensile force
R strip transport direction
a contact roll wrap angle
D8 diameter of roll 8
D9 diameter of roll 9
Dlo diameter of roll 10
D11 diameter of roll 11
D12 diameter of roll 12
D13 diameter of roll 13
D14 diameter of roll 14
D15 diameter of roll 15
D16 diameter of roll 16
D17 diameter of roll 17
v speed of conveyance
