U.S. patent application number 11/913839 was filed with the patent office on 2008-09-18 for method and apparatus for producing strip having a variable thickness.
This patent application is currently assigned to Corus Staal BV. Invention is credited to Ralf Christian Octavie Gerardus Prevaas, Willem Cornelis Verloop.
Application Number | 20080223100 11/913839 |
Document ID | / |
Family ID | 35063079 |
Filed Date | 2008-09-18 |
United States Patent
Application |
20080223100 |
Kind Code |
A1 |
Verloop; Willem Cornelis ;
et al. |
September 18, 2008 |
Method and Apparatus for Producing Strip Having a Variable
Thickness
Abstract
Disclosed is a method for producing strip having a variable
thickness in its length direction, in particular a repetitive
thickness variation, using a stand of a rolling mill, wherein the
strip has a thickness D1 when entering the mill stand and a
thickness D2 when leaving the mill stand. The speed of the strip
when leaving the mill stand is used as an input to control the
speed of the rolls in the mill stand. Also disclosed is an
apparatus for producing strip having a variable thickness.
Inventors: |
Verloop; Willem Cornelis;
(Hoofddorp, NL) ; Prevaas; Ralf Christian Octavie
Gerardus; (Haarlem, NL) |
Correspondence
Address: |
STEVENS DAVIS LLP
1615 L STREET NW, SUITE 850
WASHINGTON
DC
20036
US
|
Assignee: |
Corus Staal BV
Ijmuiden
NL
|
Family ID: |
35063079 |
Appl. No.: |
11/913839 |
Filed: |
May 11, 2006 |
PCT Filed: |
May 11, 2006 |
PCT NO: |
PCT/EP2006/004453 |
371 Date: |
May 2, 2008 |
Current U.S.
Class: |
72/205 ;
72/161 |
Current CPC
Class: |
B21B 2275/06 20130101;
B21B 2275/04 20130101; B21B 37/26 20130101; B21B 37/50 20130101;
B21B 2265/02 20130101; B21B 37/46 20130101 |
Class at
Publication: |
72/205 ;
72/161 |
International
Class: |
B21B 39/08 20060101
B21B039/08; B21B 15/00 20060101 B21B015/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 11, 2005 |
EP |
05076114.7 |
Claims
1. Method for producing strip having a variable thickness in its
length direction, in particular a repetitive thickness variation,
using a stand of a rolling mill, wherein the strip has a thickness
D1 when entering the mill stand and a thickness D2 when leaving the
mill stand, comprising using the speed of the strip when leaving
the mill stand as an input to control the speed of the rolls in the
mill stand, and keeping the strip between the mill stand and
equipment downstream of the strip at a certain tension, the tension
of the strip being used as an input for controlling at least one
member of the group consisting of the speed of the mill stand and
the speed of the downstream equipment.
2. The method according to claim 1, wherein a decoiler supplies the
strip to the rolling mill and a coiler takes up the rolled strip,
wherein a first tension measuring device measures the tension in
the strip entering the rolling mill and a second tension measuring
device measures the tension in the strip leaving the rolling mill,
wherein a speed measuring device measures the speed of the strip
leaving the rolling mill, wherein the speed and tension measured
with the speed measuring device and the second tension measuring
device are used as input to control the rolling speed of the
rolling mill.
3. The method according to claim 2, wherein the speed and tension
measured with the speed measuring device, the first tension
measuring device and the second tension measuring device are used
as input to control the tension in the strip entering the rolling
mill using a dancer between the decoiler and the rolling mill.
4. The method according to claim 2, wherein the speed and tension
measured with the speed measuring device, the first tension
measuring device and the second tension measuring device are used
as input to control the decoiling speed of the decoiler.
5. The method according to claim 1, wherein the speed of the strip
leaving the mill stand is kept approximately constant.
6. The method according to claim 1, wherein the strip leaving the
mill stand is given a repetitive thickness variation having a
repeating profile length of at most 4 meter.
7. The method according to claim 1, wherein a program is provided
for determining the thickness D2 in the strip, the program
controlling the gap of the mill stand.
8. The method according to claim 1, wherein a program is provided
for controlling the speed of the strip when entering the mill
stand.
9. The method according to claim 1, wherein the rolling mill used
is a single stand rolling mill.
10. Apparatus for producing strip having a variable thickness in
its length direction, the apparatus comprising: a stand of a
rolling mill, upstream equipment, downstream equipment, a tension
measuring device for measuring the tension in the strip leaving the
mill stand and/or a speed measuring device for controlling the
speed of the strip leaving the mill stand, wherein a dancer or
looper has been placed between the upstream equipment and the mill
stand to accommodate changes in strip length, and wherein no dancer
or looper has been placed between the mill stand and the downstream
equipment.
11. The apparatus according to claim 10, wherein a further tension
measuring device has been provided for measuring the tension in the
strip entering the mill stand.
12. (canceled)
13. The method according to claim 1, wherein the strip's variable
thickness in its length direction comprises a repetitive thickness
variation.
Description
[0001] The invention relates to a method for producing strip having
a variable thickness in its length direction, in particular a
repetitive thickness variation, using a stand of a rolling mill,
wherein the strip has a thickness D1 when entering the mill stand
and a thickness D2 when leaving the mill stand. The invention also
relates to an apparatus for producing such strip material.
[0002] Usually when rolling a strip from a thickness D1 to a
thickness D2 the rolling speed of the rolls of the stand of the
rolling mill is the reference speed for the rolling, which stand
speed is controlled by a speed controller. The speed of the other
mill equipment, such as the coiler and decoiler, is controlled
using the stand speed as input. To keep tension in the strip
entering and leaving the stand of the rolling mill between
reference values, tension controllers measuring the tension in the
strip change the reference rotational speed of the coiler and
decoiler relative to the stand speed. The speed of the strip
entering the mill and the speed of the strip leaving the mill will
change accordingly.
[0003] However, when a strip has to be produced in which
significant thickness variations in its length direction are
present at short distance, such as a strip from which tailor rolled
blanks are made, the thickness of the strip has to be changed fast
and the change in the thickness D2 of the strip leaving the mill
stand can be up to 50%. Due to the change in thickness the speed of
the strip leaving the mill stand changes according to mass flow
preservation. As a second effect, due to the change in thickness of
the strip the motor speed of the mill stand will change temporarily
due to a change in the required rolling torque. This change in mill
speed affects the speed of both the strip entering and the speed of
the strip leaving the mill stand. For instance when the thickness
of the strip leaving the mill stand is reduced this change is felt,
since at that moment in time more energy is required for rolling
the strip. Resulting from this is a drop in the tension of the
strip entering the mill stand and of the strip leaving the mill
stand, which can only be accommodated by changing the upstream and
downstream equipment speed in an anticipatory manner, and/or by
using a dancer or looper or such-like equipment for both the strip
entering and the strip leaving the mill stand. Changing the speed
of the coiler and decoiler fast is difficult because of the high
inertia of drives and the coiled strip present on the (de)coiler,
and therefore dancers or loopers are used to maintain tension. This
however results in a costly rolling mill configuration.
[0004] It is an object of the invention to provide a method for
producing a strip having a variable thickness, which is easier to
control than with the known method.
[0005] It is another object of the invention to provide a method
for producing a strip having a variable thickness, for which the
rolling mill configuration is less complex than the present
configuration.
[0006] It is also an object of the invention to provide a rolling
mill configuration for producing strip having a variable thickness
which is simpler of construction.
[0007] According to a first aspect of the invention, at least one
of these objects is reached by executing a method for producing
strip having a variable thickness in its length direction, in
particular a repetitive thickness variation, using a stand of a
rolling mill, wherein the strip has a thickness D1 when entering
the mill stand and a thickness D2 when leaving the mill stand,
wherein the speed of the strip when leaving the mill stand is used
as an input to control the speed of the rolls in the mill
stand.
[0008] This method uses a control mechanism using the speed of the
strip leaving the mill stand to control the speed of the rolls in
the mill stand, which makes it more easy to control the rolling
mill. The change in speed of the strip leaving the mill stand when
the thickness of the strip leaving the mill is changed, is now used
to control the change in speed of the rolls in the mill stand. The
speed changes upstream of the strip leaving the rolling mill are
thus more naturally a result of the change in speed due to the
change in thickness of the strip.
[0009] Preferably the strip between the mill stand and equipment
downstream of the strip is kept at a certain tension, the tension
of the strip being used as an input for controlling the speed of
the mill stand and/or the speed of the downstream equipment. Both
the speed and the tension in the strip leaving the mill stand can
now be used to control the speed of the rolls in the mill stand,
the speed of the strip controlling the general speed of the rolls
in the mill stand, and the tension in the strip being used to
fine-tune the speed of the rolls in the mill stand. The tension in
the strip can also be used to control the speed of downstream
equipment such as a coiler.
[0010] According to a preferred embodiment the speed of the strip
leaving the mill stand is kept approximately constant. In this way
the control of the production of a strip having a variable
thickness is simpler, since now the speed of the downstream
equipment such as the coiler can be held approximately constant,
with only small variations due to the tension in the strip leaving
the roll stand. The constant speed of the strip leaving the roll
stand also provides a natural change in the speed of the rolls in
the roll stand when the thickness D2 of the strip is changed; for
instance, when the thickness D2 of the strip leaving the roll stand
is reduced and the speed of this strip is kept constant, the speed
of the strip entering the mill stand must be reduced. This means
that the rolling speed of the rolls in the mill stand must be
reduced, which is in line with the higher rolling torque required
for rolling the strip to the reduced thickness D2.
[0011] According to a preferred embodiment, the strip leaving the
mill stand is given a repetitive thickness variation having a
repeating profile length of at most 4 meter. From such a strip it
is possible to cut profiled lengths from which tailor rolled blanks
(TRBs) can be produced.
[0012] Preferably a program is provided for determining the
thickness D2 in the strip, the program controlling the gap of the
mill stand. This program thus is the input for producing the strip
having a variable thickness, and the resulting strip leaving the
mill stand provides the speed of the strip with which the speed of
the rolls in the mill stand is controlled.
[0013] Preferably another program is provided for controlling the
speed of the strip when entering the mill stand. This program can
change the speed of the strip entering the mill stand when the gap
of the mill stand is changed. Usually the speed of the upstream
equipment is changed to change the speed of the strip entering the
mill stand.
[0014] According to a preferred embodiment, a decoiler is used to
supply the strip to the rolling mill and a coiler is used to take
up the rolled strip, wherein a first tension measuring device is
present to measure the tension in the strip entering the rolling
mill and a second tension measuring device is present to measure
the tension in the strip leaving the rolling mill, wherein a speed
measuring device is present to control the speed of the strip
leaving the rolling mill, wherein the speed and tension measured
with the speed measuring device and the second tension measuring
device are used as input to control the rolling speed of the
rolling mill. In this way, the control of the rolling mill for
rolling a strip having a variable thickness is easy and
straightforward, since the control uses the speed and tension of
the strip leaving the rolling mill, and the measuring devices for
measuring this speed and tension are state of the art.
[0015] Preferably, the speed and tension measured with the speed
measuring device, the first tension measuring device and the second
tension measuring device are used as input to control the tension
in the strip entering the rolling mill using a dancer or equivalent
equipment between the decoiler and the rolling mill. In this way
the same measurements together with the measurement of the tension
using the first tension measuring device can be used to control the
entrance speed of the strip in the rolling mill.
[0016] More preferably, the speed and tension measured with the
speed measuring device, the first tension measuring device and the
second tension measuring device are used as input to control the
decoiling speed of the decoiler. All the important equipment
upstream of the produced strip is thus controlled using these
measurements.
[0017] According to a preferred embodiment the rolling mill used is
a single stand rolling mill. Using a single stand rolling mill
makes the control of the rolling mill easier, since a mill having
two or more stands requires a very accurate control of the stands
in relation to each other, or requires the use of loopers between
the stands.
[0018] According to a second aspect of the invention an apparatus
for producing strip having a variable thickness in its length
direction is provided, the apparatus comprising a stand of a
rolling mill, upstream equipment, downstream equipment, a tension
measuring device for measuring the tension in the strip leaving the
mill stand and/or a speed measuring device for controlling the
speed of the strip leaving the mill stand, wherein a dancer or
looper or equivalent equipment has been placed between the upstream
equipment and the mill stand to accommodate changes in strip
length, and wherein no dancer or looper or equivalent equipment has
been placed between the mill stand and the downstream
equipment.
[0019] With this apparatus it is possible to produce strip having a
variable thickness in a well controlled way according to the first
aspect of the invention. The apparatus is more simple than the
known apparatus for producing strip having a variable thickness,
because only one dancer or looper needs to be used.
[0020] Preferably, a further tension measuring device has been
provided for measuring the tension in the strip entering the mill
stand. The further tension measuring device can be used to control
the dancer or looper or equivalent equipment between the upstream
equipment and the mill stand and the upstream equipment, such as a
decoiler.
[0021] The invention will be elucidated hereinafter.
[0022] As an example we use a single stand mill having an available
maximum gap change speed of 20 mm/s. When the thickness D2 of the
strip has to be changed over 0.5 mm, this change will thus last at
least 0.025 seconds. Should this change in thickness be performed
over a strip length of 25 mm, the maximum rolling speed of the
rolling mill thus has to be 1 m/s. For this example, we neglect
slip.
[0023] Conventional control aims at keeping the speed of the rolls
in the rolling mill constant. However, due to slip (ration between
exit strip speed and roll speed), which we assume to change between
1% and 6%, the exit strip speed (speed of the strip leaving the
rolling mill) changes from 1.01 to 1.06 m/s. This results in a
temporary reduction of the tension in the strip between the rolling
stand and the coiler, which affects the deformation behavior in the
roll gap and thus affects the strip thickness. With conventional
tension control the coiler is controlled, such that the coiling
speed is increased to accommodate the increased strip speed. In
this way the tension is recovered to the original state, such that
the set coiling torque matches the tension torque.
[0024] However, small differences between roll gap exit strip speed
and strip coiling speed already cause big tension variations. These
variations can be compensated by anticipating what the new coiling
speed has to be and by providing extra torque to the drive of the
coiler, so as to accelerate faster. The acceleration needs to be 2
m/s.sup.2.
[0025] When we roll a steel strip of 600 mm wide, using a coiling
drive system having an inertia of 200 kgm.sup.2, the coil having a
maximum diameter of 1300 mm, the total inertia will be
approximately 1500 kgm.sup.2. In order to accelerate the drive of
the coiler and the coiled strip, an additional torque has to be
imposed to the drive of the coiler of about 4500 Nm.
[0026] Instead of accelerating the coiler, according to the
invention the coiling speed is kept constant and the driving system
of the rolling stand is decelerated, so as to keep the speed
difference in the coiler to a minimum. The driving system of the
rolling mill is usually heavier than the drive of a coiler, and the
inertia of such a driving system can be approximately 600
kgm.sup.2. The required deceleration is the same as the
acceleration of the coiler. When a work roll diameter of 300 mm is
used, the deceleration needs 8000 Nm less torque. On the other
hand, for the increased reduction in the strip leaving the rolling
mill extra torque is needed. These changes in torque will balance
each other more or less, resulting in an approximately even torque
needed for the driving system of the rolling mill when producing
strip having a variable thickness in length direction.
* * * * *