U.S. patent application number 09/915557 was filed with the patent office on 2002-01-24 for rolling mill equipped with on-line roll grinding system and grinding wheel.
This patent application is currently assigned to Hitachi Ltd.. Invention is credited to Imagawa, Yasuharu, Kondoh, Shigetoshi, Mori, Shigeru, Nishino, Tadashi, Shiraiwa, Hiroyuki, Yoshimura, Yasutsugu.
Application Number | 20020009950 09/915557 |
Document ID | / |
Family ID | 26474817 |
Filed Date | 2002-01-24 |
United States Patent
Application |
20020009950 |
Kind Code |
A1 |
Mori, Shigeru ; et
al. |
January 24, 2002 |
Rolling mill equipped with on-line roll grinding system and
grinding wheel
Abstract
A grinding head unit is constituted by a grinding wheel, a drive
device for rotating the grinding wheel, and a movement device for
moving the grinding wheel. When vibration of a mill roll is applied
to the grinding wheel, a plain wheel integral with an abrasive
layer of the grinding wheel and having an elastically deforming
function is deflected to absorb the vibration energy. The contact
force between the abrasive layer and the mill roll is measured for
determining a profile of the mill roll. The mill roll can be
thereby ground into a target profile while absorbing the vibration
transmitted from the mill roll and measuring the profile of the
mill roll, without causing any chattering marks.
Inventors: |
Mori, Shigeru; (Hitachi-shi,
JP) ; Kondoh, Shigetoshi; (Hitachi-shi, JP) ;
Nishino, Tadashi; (Hitachi-shi, JP) ; Yoshimura,
Yasutsugu; (Hitachi-shi, JP) ; Imagawa, Yasuharu;
(Hitachi-shi, JP) ; Shiraiwa, Hiroyuki;
(Hitachi-shi, JP) |
Correspondence
Address: |
CROWELL & MORING, L.L.P.
Intellectual Property Group
P.O. Box 14300
Washington
DC
20044-4300
US
|
Assignee: |
Hitachi Ltd.
|
Family ID: |
26474817 |
Appl. No.: |
09/915557 |
Filed: |
July 27, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09915557 |
Jul 27, 2001 |
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09376490 |
Aug 18, 1999 |
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6283823 |
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09376490 |
Aug 18, 1999 |
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09236570 |
Jan 26, 1999 |
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6306007 |
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09236570 |
Jan 26, 1999 |
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08590672 |
Jan 24, 1996 |
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5954565 |
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08590672 |
Jan 24, 1996 |
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08070760 |
Jun 3, 1993 |
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5562525 |
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Current U.S.
Class: |
451/8 ; 451/283;
451/49; 451/548; 451/9 |
Current CPC
Class: |
B24B 5/363 20130101;
B24B 5/167 20130101; B24D 9/08 20130101; B21B 28/04 20130101; G05B
19/4163 20130101; B21B 13/023 20130101; B24B 49/16 20130101 |
Class at
Publication: |
451/8 ; 451/9;
451/49; 451/283; 451/548 |
International
Class: |
B24B 049/00; B24B
051/00; B24B 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 3, 1992 |
JP |
4-142971 |
Aug 11, 1992 |
JP |
4-214151 |
Claims
What is claimed is:
1. A rolling mill equipped with an on-line roll grinding system
comprising a plain type grinding wheel positioned to face one of a
pair of mill rolls for grinding one said mill roll, grinding wheel
drive means for rotating said grinding wheel through a spindle,
grinding wheel movement means for pressing said grinding wheel
against said mill roll, and grinding wheel traverse means for
moving said grinding wheel in the axial direction of said mill
roll, wherein: said grinding wheel comprises a plain wheel attached
to said spindle and an abrasive layer fixed to one side of said
plain wheel, said plain wheel having an elastically deforming
function to absorb vibration transmitted from said mill roll.
2. A rolling mill equipped with an on-line roll grinding system
according to claim 1, wherein said grinding wheel is arranged such
that a contact line between said abrasive layer and said mill roll
is defined only in one side as viewed from the center of said
grinding wheel.
3. A rolling mill equipped with an on-line roll grinding system
according to claim 1, wherein said grinding wheel is arranged with
said spindle inclined by a small angle relative to the direction
perpendicular to an axis of said mill roll, so that a contact line
between said abrasive layer and said mill roll is defined only in
one side in the roll axial direction as viewed from the center of
said grinding wheel.
4. A rolling mill equipped with an on-line roll grinding system
according to claim 1, wherein said abrasive layer is annular in
shape.
5. A rolling mill equipped with an on-line roll grinding system
according to claim 1, wherein said abrasive layer contains super
abrasives.
6. A rolling mill equipped with an on-line roll grinding system
according to claim 1, wherein said abrasive layer contains cubic
boron nitride abrasives and/or diamond abrasives.
7. A rolling mill equipped with an on-line roll grinding system
according to claim 1, wherein said plain wheel has a spring
constant of 1000 Kgf/mm to 30 Kgf/mm.
8. A rolling mill equipped with an on-line roll grinding system
according to claim 1, wherein said plain wheel has a spring
constant of 500 Kgf/mm to 50 Kgf/mm.
9. A rolling mill equipped with an on-line roll grinding system
according to claim 1, wherein said abrasive layer contains cubic
boron nitride abrasives, said abrasives having a concentration of
50 to 100 and a grain size of 80 to 180, and a resin bond is used
as a binder for said abrasives.
10. A rolling mill equipped with an on-line roll grinding system
according to claim 1, wherein said on-line roll grinding system
further comprises load detecting means for measuring the contact
force between said grinding wheel and said mill roll, and control
means for controlling said grinding wheel movement means to
optionally change the contact force measured by said load detecting
means so that a grinding rate of said grinding wheel on said mill
roll is changed, for thereby grinding said mill roll into a
predetermined roll profile.
11. A rolling mill equipped with an on-line roll grinding system
according to claim 1, wherein said on-line roll grinding system
further comprises load detecting means for measuring the contact
force between said grinding wheel and said mill roll, and control
means for controlling said grinding wheel movement means so that
the contact force measured by said load detecting means is held
constant, and for simultaneously controlling said grinding wheel
traverse means to optionally change a traverse speed of said
grinding wheel in the roll axial direction so that a grinding rate
of said grinding wheel on said mill roll is changed, for thereby
grinding said mill roll into a predetermined roll profile.
12. A rolling mill equipped with an on-line roll grinding system
according to claim 1, wherein said grinding wheel movement means
comprises a rotation drive source, and a ball screw mechanism or a
gear mechanism having a small backlash and converting rotation of
said rotation drive source into axial movement of said grinding
wheel movement means for moving said grinding wheel back and forth
relative to said mill roll.
13. A rolling mill equipped with an on-line roll grinding system
according to claim 1, wherein said on-line roll grinding system
comprises at least two grinding head units for each of said mill
rolls, each of said two grinding head units including said grinding
wheel, said grinding wheel drive means, said grinding wheel
movement means and said grinding wheel traverse means, whereby said
two grinding head units can grind said mill roll independently of
each other.
14. A rolling mill equipped with an on-line roll grinding system
according to claim 13, wherein said on-line roll grinding system
further comprises control means for stopping said grinding wheel
traverse means of two said grinding head units at different
positions so that a grinding overlap zone produced when grinding
said mill roll by said two grinding head units is distributed in
the roll axial direction.
15. A rolling mill equipped with an on-line roll grinding system
according to claim 13, wherein said grinding wheels of two said
grinding head units are arranged with respective spindles inclined
by a small angle in opposite directions relative to the direction
perpendicular to an axis of said mill roll, so that respective
contact lines between said abrasive layers and said mill roll are
each defined only in one corresponding roll end side in the roll
axial direction as viewed from the center of said grinding
wheel.
16. A rolling mill equipped with an on-line roll grinding system
according to claim 1, wherein said on-line roll grinding system
further comprises displacement detector means for measuring a
stroke of said grinding wheel in the roll axial direction given by
said grinding wheel traverse means, load detecting means for
measuring the contact force between said grinding wheel and said
mill roll, and an on-line profile meter including first profile
calculating means for calculating a profile of said mill roll from
both the contact force measured by said load detecting means and
the stroke measured by said displacement detector means under a
condition of keeping a stroke of said grinding wheel movement means
constant.
17. A rolling mill equipped with an on-line roll grinding system
according to claim 1, wherein said on-line roll grinding system
further comprises first displacement detector means for measuring a
stroke of said grinding wheel movement means, second displacement
detector means for measuring a stroke of said grinding wheel in the
roll axial direction given by said grinding wheel traverse means,
load detecting means for measuring the contact force between said
grinding wheel and said mill roll, and an on-line profile meter
including second profile calculating means for calculating a
profile of said mill roll from both the stroke measured by said
first displacement detector means and the stroke measured by said
second displacement detector means under a condition of keeping the
contact force measured by said load detecting means constant.
18. A rolling mill equipped with an on-line roll grinding system
according to claim 16 or 17, wherein said on-line profile meter
further includes means for calculating a deviation of a profile of
said mill roll measured by an off-line profile meter from the
profile of said mill roll determined by said first or second
profile calculating means, determining from said deviation an error
in parallelism of the direction of movement of said grinding wheel
by said grinding wheel traverse means with respect to said mill
roll, and compensating the roll profile determined by said first or
second profile calculating means based on the determined error in
parallelism.
19. A rolling mill equipped with an on-line roll grinding system
according to claim 16 or 17, wherein said on-line profile meter
further includes means for calculating a deviation of the profile
of said mill roll determined by said first or second profile
calculating means from a preset target roll profile, and
controlling at least one of said grinding wheel movement means and
said grinding wheel traverse means based on the calculated
deviation so that a grinding rate of said grinding wheel on said
mill roll is changed, for thereby grinding said mill roll to be
identical with said target roll profile.
20. A rolling mill equipped with an on-line roll grinding system
according to claim 19, wherein said control means controls said
grinding wheel movement means so that the contact force measured by
said load detecting means is optionally changed, for thereby
changing said grinding rate.
21. A rolling mill equipped with an on-line roll grinding system
according to claim 19, wherein said control means controls said
grinding wheel movement means so that the contact force measured by
said load detecting means is held constant and, simultaneously,
controls said grinding wheel traverse means to optionally change a
traverse speed of said grinding wheel in the roll axial direction
for thereby changing said grinding rate.
22. A rolling mill equipped with an on-line roll grinding system
according to claim 16 or 17, further comprising at least one of
roll bender means for applying bender forces to said mill roll,
roll shifting means for shifting said mill roll in the axial
direction and roll crossing means for making said pair of mill
rolls crossed each other, and control means for controlling at
least one of the bender forces of said roll bender means, a shift
position set by said roll shifting means and a cross angle set by
said roll crossing means based on the profile of said mill roll
measured by said first or second profile calculating means so that
the strip crown approaches a target strip crown.
23. A rolling mill equipped with an on-line roll grinding system
according to claim 1, wherein said on-line roll grinding system
further comprises control means for measuring an inclination of the
axis of said mill roll and controlling said grinding wheel movement
means and said grinding wheel traverse means so that said grinding
wheel moves following a target roll profile in consideration of the
inclination of the axis of said mill roll.
24. A rolling mill equipped with an on-line roll grinding system
according to claim 23, wherein said on-line roll grinding system
further comprises presser means for fixing metal chocks supporting
both ends of said mill roll, and holding the inclination of the
axis of said mill roll constant during the grinding.
25. A rolling mill equipped with an on-line roll grinding system
according to claim 1, wherein said grinding wheel, said grinding
wheel drive means, said grinding wheel movement means and said
grinding wheel traverse means constitute one grinding head unit,
and said on-line roll grinding system further comprises a reference
small-diameter zone formed on at least one end of said mill roll
and having a known diameter smaller than the diameter of a roll
barrel, and a displacement meter provided on said grinding head
unit for measuring a distance from said grinding head unit to said
mill roll.
26. A rolling mill equipped with an on-line roll grinding system
according to claim 1, wherein said mill roll is a work roll, and
said grinding wheel, said grinding wheel drive means, said grinding
wheel movement means and said grinding wheel traverse means
constitute a grinding head unit for grinding said work roll.
27. A rolling mill equipped with an on-line roll grinding system
according to claim 1, wherein said mill roll is a backup roll, and
said grinding wheel, said grinding wheel drive means, said grinding
wheel movement means and said grinding wheel traverse means
constitute a grinding head unit for grinding said backup roll.
28. A rolling mill equipped with an on-line roll grinding system
according to claim 1, wherein said on-line roll grinding system
further comprises a reference small-diameter zone formed on at
least one end of said mill roll and having a known diameter smaller
than the diameter of a roll barrel, and roll diameter calculating
means for pressing said grinding wheel against said mill roll at
respective positions in said reference small-diameter zone and said
roll barrel such that the contact force between said grinding wheel
and said mill roll has the same value, determining a periphery
difference between said reference small-diameter zone and said roll
barrel from a difference in displacement of said grinding wheel at
that time, and determining a roll diameter in said roll barrel from
the determined periphery difference and the known roll diameter in
said reference small-diameter zone.
29. A grinding wheel for an on-line roll grinding system comprising
a plain wheel and an abrasive layer fixed to one side of said plain
wheel and formed of super abrasives, said plain wheel having an
elastically deforming function to absorb vibration transmitted from
a mill roll.
30. A grinding wheel for an on-line roll grinding system according
to claim 29, wherein said abrasive layer is annular in shape.
31. A grinding wheel for an on-line roll grinding system according
to claim 29, wherein said plain wheel has a spring constant of 1000
Kgf/mm to 30 Kgf/mm.
32. A grinding wheel for an on-line roll grinding system according
to claim 29, wherein said plain wheel has a spring constant of 500
Kgf/mm to 50 Kgf/mm.
33. A grinding wheel for an on-line roll grinding system according
to claim 29, wherein said abrasive layer contains cubic boron
nitride abrasives, said abrasives having a concentration of 50 to
100 and a grain size of 80 to 180, and a resin bond is used as a
binder for said abrasives.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a rolling mill equipped
with an on-line roll grinding system, and more particularly to an
on-line roll grinding system for effectively grinding mill rolls
on-line without undergoing influences of vibration of work
rolls.
[0002] Generally, when slabs are rolled by work rolls of a strip
rolling mill, there occurs a periphery difference between the
rolling zone and the unrolling zone because only the former is
abraded or worn away. This imposes such restrictions upon the
rolling operation as necessity of rolling slabs in order of wide
ones to narrow ones. To solve that problem, there have been
proposed various techniques and control methods in relation to
on-line roll grinders.
[0003] For example, "Development of On-Line Roll Grinders",
Mitsubishi Giho, Vol. 25, No. 4, 1988, discloses a technique that a
plurality of cup grinding stones are arranged along one work roll
and mounted to a one-piece frame, the frame being always moved in
its entirety over a certain range, and the cup grinding stones are
not positively driven to rotate but passively driven with the aid
of torque of the work roll, thereby grinding the entire surface of
the work roll (hereinafter referred to as first prior art).
[0004] Also, JP, U, 58-28705 discloses a technique that one roll
grinding unit is disposed for one work roll, contact rolls serving
as position sensors are held in contact with neck portions at both
ends of the work roll on the side thereof opposite to the roll
grinding unit, the position sensors detecting an offset of the work
roll, and a shifting device is controlled to move a grinding wheel
following the detected offset (hereinafter referred to as second
prior art).
[0005] Further, "On-Line Constant Pressure Grinding for Work
Rolls", Proceedings of 1992 Spring Lecture Meeting of Precision
Engineering Society of Japan, reports an experimental result of
forming an abrasive layer of a cup grinding stone using abrasives
of cubic boron nitride (CBN), arranging a spindle of the grinding
stone perpendicularly to the axis of a work roll, and grinding the
work roll (hereinafter referred to as third prior art).
[0006] In addition, JP, U, 58-28706 and JP, U, 62-95867 disclose a
technique that a cup grinding stone arranged substantially
perpendicular to a work roll is mounted to a spindle slidably in
its axial direction, and the grinding stone is axially supported at
its backside by an elastic body directly or via a boss, thereby
absorbing vibration of the work roll (hereinafter referred to as
fourth prior art).
[0007] Meanwhile, in strip rolling machines, it has been
conventionally proposed to measure the profile of a work roll and
control the crown and shape of a strip by utilizing the measured
profile. As a technique for measuring the profile of the work roll,
an on-line roll profile deter has been developed which employs a
ultrasonic profile meter. The system configuration of this profile
meter is described in "Development of On-Line Roll Grinding System
with Profile Meter", Mitsubishi Giho, Vol. 29, No. 1, 1992. In this
system, a column of water is produced between a probe with a
ultrasonic profile meter built therein and a work roll, and the
spacing from the probe to the work roll is determined based on the
time required for pulsatory ultrasonic waves emitted from the probe
to reciprocate between the probe and the surface of the work roll
(hereinafter referred to as fifth prior art).
SUMMARY OF THE INVENTION
[0008] Work rolls of a rolling mill are each held by bearings
assembled in metal chocks and rotated at a high speed. The metal
chocks each have gaps in its inner and outer circumferences for
facilitating replacement of the work roll and the bearing. During
rotation, therefore, the work roll is rotated while moving back and
forth in the gaps. In addition, since a cylindrical portion of the
work roll undergoes an offset with respect to the bearings, the
work roll is vertically moved by a screwdown device during strip
rolling. As a result of those movements combined with each other,
the work roll is rotated while vibrating at all times.
[0009] Generally, when grinding cylindrical works, the work to be
ground is supported by a tail stock rotating with high precision to
carry out the grinding under a condition that vibration of the work
is suppressed to be as small as practicable. In an attempt to grind
the work roll while rolling a strip in the rolling mill, however,
it is impossible to carry out the grinding under a condition of
very small vibration like works in the above ordinary case. During
the rolling, the work roll is rotated while vibrating usually with
an amplitude of 20 .mu.m to 60 .mu.m and an acceleration of 1 G to
2 G. An on-line roll grinding system must precisely grind the work
roll under such a condition.
[0010] With the above first to third prior arts, when they are
applied to the grinding of such a vibrating work role, there
produce irregularities on the surface of the work roll due to
chattering marks. Also, the grinding stone or wheel is remarkably
worn away with the impact force caused by chattering, and its
service life is so shortened as to require more frequent
replacement. Further, it is difficult to control the contact force
in the case of grinding the work roll into a predetermined
profile.
[0011] The above fourth prior art is designed to absorb the
vibration of the work roll by the elastic body. With this prior
art, however, since the entire grinding stone including a stone
base is supported by the elastic body and moved back and forth,
there accompanies a problem that the movable mass of the grinding
stone, i.e., the weight of a portion which is forced to move
following the vibration, is great. Even in the case of using, as
the abrasive layer of the grinding stone, abrasives of cubic boron
nitride (CBN) which has a high grinding ratio, the movable mass of
the grinding stone supported by the elastic body and moving back
and forth is at least more than 5 Kg, including the stone itself of
which diameter is assumed to be 250 mm, slide bearings and sealing
parts. Supposing that an allowable value of change in the contact
force between the work roll and the grinding stone is 4 Kgf and the
amplitude of vibration of the work roll is 30 .mu.m, the spring
constant of the elastic body must be set to 130 Kgf/mm. Under the
above conditions, the natural frequency of the movable portion
including the elastic body is calculated to be 80 c/s. The movable
portion including the elastic body, which has such a low natural
frequency, is caused to resonate with the vibration of the work
roll, thereby producing chattering marks on the roll surface and
accelerating abrasion of the grinding stone. If the stone size is
reduced to make the movable mass smaller, the grinding ability
would be lowered to a large extent.
[0012] The cup grinding stone is slidable in the axial direction of
the spindle and supported at its backside by the elastic body.
During the roll grinding, however, a coolant, grinding dust and the
like are scattered around the grinding stone, an d these foreign
matters may enter clearance between the grinding stone and the
spindle to impede smooth movement of the grinding stone. It is
therefore difficult for the elastic body to stably develop its
function for a long period of time.
[0013] The above first and second prior arts also have the
following problem. The unrolling zone of the work roll is not
subjected to abrasion by the strip and hence should be ground to a
larger extent than the rolling zone. With the above first
embodiment, however, because the circumferential speed of the cup
grinding stone is limited by the rotational speed of the work roll,
the grinding rate can be controlled only by changing the contact
force in the case of grinding the unrolling zone to a larger
extent. This imposes a limitation upon the grinding rate, making it
difficult to keep a constant roll profile for a long period of
time.
[0014] With the above second embodiment, since the spindle is
arranged perpendicularly to the work roll, the abrasive layer of
the grinding wheel contacts the work roll at two right and left
points of its annular abrasives surface and the work roll is
simultaneously ground at those two points. Therefore, if the work
roll has a periphery difference, the two grinding surfaces
interfere with each other to cause chattering marks. Also, the
contact at two points between the grinding Wheel and the work roll
leads to a difficulty in controlling the contact force
therebetween. Additionally, the position sensors have a problem of
reliability under severe environment of rolling machines. From
these reasons, the above second embodiment has not yet been put
into practice.
[0015] Measurement of a roll profile will now be considered. After
a strip is rolled by work rolls, the work rolls are each worn away
about 2 .mu.m/radius per coil of a hot rolling steel strip, for
example, in the zone where the strip is rolled. Due to this wear
and the thermal crown resulted from an increase in the roll
diameter caused by the heat of the strip, the profile of the roll
surface is changed over the entire length of a roll barrel. If the
roll profile can be correctly measured, the on-line roll grinder
provided in the rolling mill can grind the work roll into the roll
profile optimum for the rolling. Heretofore, it has been regarded
to be difficult to correctly measure the roll profile of the work
roll, which is vibrating and sprayed with a large amount of roll
coolant at all times, in the rolling mill, i.e., on-line.
[0016] As known from the above fifth prior art, there has been
developed an on-line profile meter of the type that a column of
water is produced between a probe and a work roll for determining
the spacing from the probe to the work roll based on the time
required for ultrasonic waves to reciprocate between the probe and
the surface of the work roll. However, because of measuring the
time during which ultrasonic waves reciprocate through the very
short distance, the measure time is also very short and the profile
distance is on the order of microns. There is hence a fear that
even a small error of the measured time may result in a large
profile error. Particularly, in the case of using the ultrasonic
profile meter for a long period of time, even if the state of the
column of water between the probe and the roll is so changed as to
cause an error in the measurement, it is difficult to find such an
error. Although the ultrasonic profile meter can always correctly
measure the roll profile in principles, there is a difficulty in
maintaining high precision at all times in practice when the
ultrasonic profile meter is used for a long period of time under
the severe environment as mentioned above. The presence of plural
measuring probes also makes it difficult to perform
compensation.
[0017] A first object of the present invention is to provide a
rolling mill equipped with an on-line roll grinding system and a
grinding wheel for the on-line roll grinding system in which
vibration from a work roll is absorbed to enable precise grinding
with good roughness of the roll surface without giving rise to any
chattering marks.
[0018] A second object of the present invention is to provide a
rolling mill equipped with an on-line roll grinding system and a
grinding wheel for the on-line roll grinding system in which the
profile of a work roll can be correctly measured by a roll profile
meter provided integrally with the on-line roll grinding
system.
[0019] To achieve the above first object, in accordance with the
present invention, there is provided a rolling mill equipped with
an on-line roll grinding system comprising a plain type grinding
wheel positioned to face one of a pair of mill rolls for grinding
one said mill roll, grinding wheel drive means for rotating said
grinding wheel through a spindle, grinding wheel movement means for
pressing said grinding wheel against said mill roll, and grinding
wheel traverse means for moving said grinding wheel in the axial
direction of said mill roll, wherein said grinding wheel comprises
a plain wheel attached to said spindle and an abrasive layer fixed
to one side of said plain wheel, said plain wheel having an
elastically deforming function to absorb vibration transmitted from
said mill roll.
[0020] In the above on-line roll grinding system, preferably, said
grinding wheel is arranged such that a contact line between said
abrasive layer and said mill roll is defined only in one side as
viewed from the center of said grinding wheel, and more preferably,
said grinding wheel is arranged with said spindle inclined by a
small angle relative to the direction perpendicular to an axis of
said mill roll, so that a contact line between said abrasive layer
and said mill roll is defined only in one side in the roll axial
direction as viewed from the center of said grinding wheel.
[0021] Preferably, said abrasive layer is annular in shape, and
said abrasive layer contains super abrasives, i.e., cubic boron
nitride abrasives and/or diamond abrasives.
[0022] Also, said plain wheel preferably has a spring constant of
1000 Kgf/mm to 30 Kgf/mm, and more preferably a spring constant of
500 Kgf/mm to 50 Kgf/mm.
[0023] Preferably, said abrasive layer contains cubic boron nitride
abrasives, said abrasives having a concentration of 50 to 100 and a
grain size of 80 to 180, and a resin bond is used as a binder for
said abrasives.
[0024] Preferably, said on-line roll grinding system further
comprises load detecting means for measuring the contact force
between said grinding wheel and said mill roll, and control means
for controlling said grinding wheel movement means to optionally
change the contact force measured by said load detecting means so
that a grinding rate of said grinding wheel on said mill roll is
changed, for thereby grinding said mill roll into a predetermined
roll profile.
[0025] Said on-line roll grinding system may further comprise load
detecting means for measuring the contact force between said
grinding wheel and said mill roll, and control means for
controlling said grinding wheel movement means so that the contact
force measured by said load detecting means is held constant, and
for simultaneously controlling said grinding wheel traverse means
to optionally change a traverse speed of said grinding wheel in the
roll axial direction so that a grinding rate of said grinding wheel
on said mill roll is changed, for thereby grinding said mill roll
into a predetermined roll profile.
[0026] Preferably, said grinding wheel movement means comprises a
rotation drive source, and a ball screw mechanism or a gear
mechanism having a small backlash and converting rotation of said
rotation drive source into axial movement of said grinding wheel
movement means for moving said grinding wheel back and forth
relative to said mill roll.
[0027] Preferably, said on-line roll grinding system comprises at
least two grinding head units for each of said mill rolls, each of
said two grinding head units including said grinding wheel, said
grinding wheel drive means, said grinding wheel movement means and
said grinding wheel traverse means, whereby said two grinding head
units can grind said mill roll independently of each other.
[0028] In this case, said on-line roll grinding system preferably
further comprises control means for stopping said grinding wheel
traverse means of two said grinding head units at different
positions so that a grinding overlap zone produced when grinding
said mill roll by said two grinding head units is distributed in
the roll axial direction.
[0029] Preferably, said grinding wheels of two said grinding head
units are arranged with respective spindles inclined by a small
angle in opposite directions relative to the direction
perpendicular to an axis of said mill roll, so that respective
contact lines between said abrasive layers and said mill roll are
each defined only in one corresponding roll end side in the roll
axial direction as viewed from the center of said grinding
wheel.
[0030] To achieve the above second object, in accordance with the
present invention, there is provided a rolling mill equipped with
an on-line roll grinding system, wherein said on-line roll grinding
system further comprises displacement detector means for measuring
a stroke of said grinding wheel in the roll axial direction given
by said grinding wheel traverse means, load detecting means for
measuring the contact force between said grinding wheel and said
mill roll, and an on-line profile meter including first profile
calculating means for calculating a profile of said mill roll from
both the contact force measured by said load detecting means and
the stroke measured by said displacement detector means under a
condition of keeping a stroke of said grinding wheel movement means
constant.
[0031] Also, to achieve the above second object, in accordance with
the present invention, there is provided a rolling mill equipped
with an on-line roll grinding system, wherein said on-line roll
grinding system further comprises first displacement detector means
for measuring a stroke of said grinding wheel movement means,
second displacement detector means for measuring a stroke of said
grinding wheel in the roll axial direction given by said grinding
wheel traverse means, load detecting means for measuring the
contact force between said grinding wheel and said mill roll, and
an on-line profile meter including second profile calculating means
for calculating a profile of said mill roll from both the stroke
measured by said first displacement detector means and the stroke
measured by said second displasemsent detector means under a
condition of keeping the contact force measured by said load
detecting means constant.
[0032] In the above on-line roll grinding system, said on-line
profile meter preferably further includes means for calculating a
deviation of a profile of said mill roll measured by an off-line
profile meter from the profile of said mill roll determined by said
first or second profile calculating means, determining from said
deviation an error in parallelism of the direction of movement of
said grinding wheel by said grinding wheel traverse means with
respect to said mill roll, and compensating the roll profile
determined by said first or second profile calculating means based
on the determined error in parallelism.
[0033] Preferably, said on-line profile meter further includes
means for calculating a deviation of the profile of said mill roll
determined by said first or second profile calculating means from a
preset target roll profile, and controlling at least one of said
grinding wheel movement means and said grinding wheel traverse
means based on the calculated deviation so that a grinding rate of
said grinding wheel on said mill roll is changed, for thereby
grinding said mill roll to be identical with said target roll
profile.
[0034] In this case, said control means preferably controls said
grinding wheel movement means to optionally change the contact
force measured by said load detecting means for thereby changing
said grinding rate.
[0035] Alternatively, said control means may control said grinding
wheel movement means so that the contact force measured by said
load detecting means is held constant and, simultaneously, controls
said grinding wheel traverse means to optionally change a traverse
speed of said grinding wheel in the roll axial direction for
thereby changing said grinding rate.
[0036] Also, said rolling mill preferably further comprises at
least one of roll bender means for applying bender forces to said
mill roll, roll shifting means for shifting said mill roll in the
axial direction and roll crossing means for making said pair of
mill rolls crossed each other, and control means for controlling at
least one of the bender forces of said roll bender means, a shift
position set by said roll shifting means and a cross angle set by
said roll crossing means based on the profile of said mill roll
measured by said first or second profile calculating means so that
the strip crown approaches a target strip crown.
[0037] Further, in said rolling mill, said on-line roll grinding
system preferably further comprises control means for measuring an
inclination of the axis of said mill roll and controlling said
grinding wheel movement means and said grinding wheel traverse
means so that said grinding wheel moves following a target roll
profile in consideration of the inclination of the axis of said
mill roll. In this case, preferably, said on-line roll grinding
system further comprises presser means for fixing metal chocks
supporting both ends of said mill roll, and holding the inclination
of the axis of said mill roll constant Turing the grinding.
[0038] In the above on-line roll grinding system, preferably, said
grinding wheel, said grinding wheel drive means, said grinding
wheel movement means and said grinding wheel traverse means
constitute one grinding head unit, and said on-line roll grinding
system further comprises a reference small-diameter zone formed on
at least one end of said mill roll and having a known diameter
smaller than the diameter of a roll barrel, and a displacement
meter provided on said grinding head unit for measuring a distance
from said grinding head unit to said mill roll.
[0039] In the above rolling mill, preferably, said mill roll is a
work roll, and said grinding wheel, said grinding wheel drive
means, said grinding wheel movement means and said grinding wheel
traverse means constitute a grinding head unit for grinding said
work roll. Alternatively, said mill roll is a backup roll, and said
grinding wheel, said grinding wheel drive means, said grinding
wheel movement means and said grinding wheel traverse means
constitute a grinding head unit for grinding said backup roll.
[0040] Preferably, said on-line roll grinding system further
comprises a reference small-diameter zone formed on at least one
end of said mill roll and having a known diameter smaller than the
diameter of a roll barrel, and roll diameter calculating means for
pressing said grinding wheel against said mill roll at respective
positions in said reference small-diameter zone and said roll
barrel such that the contact force between said grinding wheel and
said mill roll has the same value, determining a periphery
difference between said reference small-diameter zone and said roll
barrel from a difference in displacement of said grinding wheel at
that time, and determining a roll diameter in said roll barrel from
the determined periphery difference and the known roll diameter in
said reference small-diameter zone.
[0041] Furthermore, to achieve the above first and second objects,
in accordance with the present invention, there is provided a
grinding wheel for an on-line roll grinding system comprising a
plain wheel and an abrasive layer fixed to one side of said plain
wheel and formed of super abrasives, said plain wheel having an
elastically deforming function to absorb vibration transmitted from
a mill roll.
[0042] Operation of the present invention thus constructed is as
follows.
[0043] First, in the present invention, with an elastically
deforming function imparted to the plain wheel as a part of the
plain type grinding wheel, when the grinding wheel is pushed upon
vibration of the mill roll, the plain wheel is deflected to
momentarily absorb the vibration transmitted from the mill roll.
Accordingly, fluctuations in the contact force between the abrasive
layer and the mill roll are held down within a small range of the
elastic force fluctuating upon the deflection of the plain wheel,
thereby eliminating the occurrence of chattering marks. Further, an
elastically deforming function is imparted to the plain wheel
serving as a base for supporting the abrasive layer so that the
abrasive layer is integral with a member having the elastically
deforming function. Therefore, only both the abrasive layer and the
plain wheel provide the mass forced to move upon the vibration from
the mill roll, whereby the movable mass can be very small and the
natural frequency of the grinding wheel can be raised.
Consequently, the vibrating mill roll can be correctly ground for a
long period of time without causing any chattering marks due to
resonance.
[0044] With the grinding wheel arranged such that the contact line
between the abrasive layer and the mill roll is defined only in one
side as viewed from the center of the grinding wheel, the plain
wheel is allowed to deflect in cantilever fashion when pressed
against the mill roll, whereby the elastically deforming function
of the plain wheel is effectively developed to easily absorb the
vibration transmitted from the mill roll. Further, since the
contact line is defined in only one side of the wheel center, the
occurrence of chattering marks is prevented and contact force
control (described later) can be performed properly.
[0045] With the abrasive layers formed of super abrasive grains,
particularly, cubic boron nitride abrasives or diamond abrasives,
the grinding wheel has a grinding ratio more than 100 times that of
the grinding wheel made of aluminum oxide (Al.sub.2O.sub.2)
abrasives or silicon carbide (SiC) abrasives, resulting in that the
grinding can be continued for a long period of time with a small
weight of the grinding wheel. Consequently, the movable mass of the
grinding wheel is further reduced, which is effective in preventing
resonance during the grinding, reducing the exchange pitch of the
grinding wheel, and improving productivity of the rolling mill.
[0046] As to the spring constant of the plain wheel, if the spring
constant is too large, the chattering marks are caused, the
grinding ratio is lowered, and further the abrasive layer is soon
worn away thoroughly. Also, if the spring constant of the plain
wheel is too large, the contact force between the abrasive layer
and the mill roll is so largely fluctuated as to impose a
difficulty in controlling the grinding rate due to the contact
force. Through the studies conducted by the inventors, it has been
found that by setting the spring constant of the plain wheel to be
not larger than 1000 Kgf/mm, preferably 500 Kgf/mm, it is possible
to prevent the abrasive layer from being soon worn away thoroughly,
and use the grinding wheel continuously for not less than 5 days
once exchanged.
[0047] On the contrary, if the spring constant is small, the
contact force imposed on the grinding wheel due to the vibration of
the mill roll is less fluctuated. The grinding ratio is therefore
raised, but sensitivity of detecting the contact force is lowered
and accuracy of grinding control and roll profile measurement both
based on the contact force is degraded. Also, the smaller spring
constant of the plain wheel means that the plain wheel is thinner
and the grinding wheel is deflected to a larger extent with the
same contact force, causing cracks in the plain wheel even with the
contact force necessary for the grinding. Through the studies
conducted by the inventors, it has been found that by setting the
spring constant of the plain wheel to be not less than 30 Kgf/mm,
the plain wheel can be prevented from cracking, and by setting the
spring constant to be not less than 50 Kgf/mm, even load
fluctuations generated with a periphery difference of 10 .mu.m can
be detected.
[0048] As to compositions of the abrasive layer, in order to keep
the grinding ability constant and stabilize the grinding roughness
without dressing in on-line roll grinding, it is required for the
super abrasive grains of the abrasive layer to be spontaneously
edged at a constant rate. Proper spontaneous edging of the super
abrasive grains needs adjustment of the load imposed on one super
abrasive grain. Through the studies conducted by the inventors, it
has been found that by setting density, i.e., concentration, of the
super abrasive grains contained in the abrasive layer within the
range of 50 to 100 and using a resin bond as a binder, the super
abrasive grains are easily spontaneously edged, the service life of
the abrasive layer is not shortened, and hence continuous grinding
is enabled without dressing. It has been also found that the size
of the super abrasive grains, i.e., the grain size, is required to
be in the range of 80 to 180 for obtaining the surface roughness of
the mill roll in the range of 0. 3 to 1.5 .mu.m in average.
[0049] By continuously measuring the contact force between the mill
roll and the grinding wheel and then changing the contact force,
the grinding rate of the grinding wheel on the mill roll per unit
time is changed. Thus, by measuring the contact force at all times
and controlling the position of the grinding wheel by the grinding
wheel movement means so that the contact force is held constant,
the mill roll can be ground by the same dimension all over its
cylindrical barrel. In other words, it is possible to grind the
enter length of the mill roll while maintaining its original
profile.
[0050] Also, by controlling the contact force in such a manner as
to increased and decrease, the mill roll can be ground into an
arbitrary roll profile. Further, by optionally controlling the
traverse speed of the grinding wheel in the roll axial direction
While controlling the contact force to be kept constant, the mill
roll can also be ground into an arbitrary roll profile.
[0051] Unless the grinding wheel movement means for pressing the
grinding wheel against the mill roll is constituted by using a
mechanism having a high spring constant, there may cause chattering
marks. As grinding wheel movement means which is compact and has a
high spring constant, optimum one is a mechanism in which a
baklashless pre-loaded ball screw is driven by an electric motor.
This mechanism is also able to hold the position of the grinding
wheel constant during the grinding and to finely move the grinding
wheel back and forth.
[0052] When the grinding wheel is moved in the roll axial direction
for grinding the mill roll, it is required to grind the unrolling
zone to a larger extent than the rolling zone for eliminating a
periphery difference between the unrolling zone and the rolling
zone. The unrolling zone exists at each of both ends of the mill
roll. In view of that, a plurality of grinding head units each
including the grinding wheel, the grinding wheel drive means, the
grinding wheel movement means and the grinding wheel traverse means
are disposed to be movable independently of each other. Normally,
two units are moved to remain in the respective unrolling zones at
both roll ends for grinding them. Once per several times, the
grinding head units are moved to the rolling zone of the mill roll
for grinding a fatigue layer on the surface therein. Thus,
corresponding to wear of the rolling zone caused by rolling a
strip, the unrolling zones are ground by the grinding wheel so that
the roll profile free from a periphery difference can be
maintained.
[0053] When a plurality of grinding head units are arranged to be
movable independently of each other for grinding a mill roll, there
occurs an overlap zone on the mill roll Where the roll surfaces
ground by adjacent grinding wheels overlap with each over. The
grinding wheel traverse means are stopped at different positions so
that the overlap zone will not always produce at the same position,
thereby distributing the overlap position.
[0054] As mentioned above, by making the contact line between the
grinding wheel and the mill roll defined at one point, it is
possible to carry out satisfactory grinding under constant
conditions. In the present invention, therefore, the spindle of the
grinding wheel is inclined by a small angle relative to a line
perpendicular to the axis of the mill roll. By so arranging, in the
on-line roll grinding system having a plurality of grinding wheels,
there may occur an interference between the end of the grinding
wheel and a housing if the spindles are inclined in the same
direction at both ends of the mill roll. Such an interference in
the grinding can be avoided by arranging the spindles of the
grinding head units positioned at both ends of the mill roll to be
inclined in opposite directions. Accordingly, the grinding wheels
can be freely moved to the respective ends of the mill roll, and
there is no need of particularly considering the dimension between
the roll end and the housing.
[0055] Further, in the on-line profile meter having the first
profile calculating means of the present invention, the grinding
wheel is pressed by the grinding wheel movement means against the
rotating mill roll to deflect the plain wheel in a certain amount,
following which the grinding wheel movement means is stopped and
the contact force between the mill roll and the grinding wheel at
that time is measured by the load detecting means. Then, while
moving the grinding wheel by the grinding wheel traverse means in
the axial direction of the mill roll, the stroke (axial position)
of the grinding wheel is measured by the displacement detector
means and the contact force is measured by the load detecting
means.
[0056] Since the abrasive layer of the grinding wheel is supported
by the plain wheel having an elastically deforming function and the
plain wheel has a fixed spring constant, the larger contact force
increases a deflection of the plain wheel. Conversely, the smaller
contact force reduces a deflection of the plain wheel. On the other
hand, if the axis of the mill roll and the on-line roll grinding
system or the grinding head units are parallel to each other, the
plain wheel of the grinding wheel is deflected to a larger extent
with a larger diameter of the mill roll and to a smaller extent
with a smaller diameter of the mill roll on condition that the
grinding wheel movement means is kept fixed.
[0057] In the first profile calculating means, therefore, the
deflection of the plain wheel is determined from the value (contact
force) measured by the load detecting means and processed to be
correspondent to respective positions in the roll axial direction,
thereby obtaining a profile of the mill roll.
[0058] Moreover, in the on-line profile meter having the second
profile calculating means of the present invention, the grinding
wheel is pressed by the grinding wheel movement means against the
rotating mill roll to deflect the plain wheel in a certain amount,
and then the grinding wheel movement means is controlled so that
the deflection of the plain wheel (i.e., the contact force) is
always held constant. While measuring the stroke of the grinding
wheel in the axial direction of its spindle by the first
displacement detector means, the grinding wheel is moved in the
roll axial direction by the grinding wheel traverse means and the
stroke (axial position) of the grinding wheel is measured by the
second displacement detector means. Thus, in the second profile
calculating means, the stroke of the grinding wheel in the axial
direction of its spindle is determined from the measured value of
the first displacement detector means and processed to be
correspondent to respective positions in the roll axial direction,
thereby obtaining a profile of the mill roll.
[0059] The on-line roll grinding system is initially installed such
that the direction of traverse movement along the roll axial
direction is in parallel to the axis of the mill roll. But, there
is a fear in hot rolling mills that parallelism between them may
change for a long period of time due to the heat of strips. Unless
such a change in parallelism is compensated, the roll profile
measured as mentioned above cannot be said as a true profile. The
compensation means provided in the on-line profile meter
compensates the error in parallelism and enables the more precise
profile measurement.
[0060] More specifically, a mill roll is ground by an off-line line
roll grinder installed in a roll shop, and its roll profile after
the grinding is measured by an off-line roll profile meter. After
assembling the mill roll into the rolling mill, a profile of the
mill roll is measured by using the first or second profile
calculating means of the on-line roll profile meter. Then, a
deviation (difference) between both the profile values measured by
the off-line and on-line roll profile meters is determined and,
from this determined deviation, an error in parallelism of the
on-line roll grinding system or the grinding head units with
respect to the roll axial direction is determined. Since then, at
the time of measuring a profile of the mill roll by using the first
or second profile calculating means, the above error in parallelism
is subtracted from the measured values obtained as mentioned above,
thereby compensating the measured values to determine the correct
measured values.
[0061] In the control means for grinding the mill roll to be
identical with a target roll profile, after determining a profile
of the mill roll by the first or second profile calculating means,
a deviation of the determined profile of the mill roll from a
preset target roll profile is calculated. The grinding wheel
movement means is controlled such that the grinding wheel is
pressed against the mill roll by a stronger force in the roll
radial direction (at the roll axial position) in which the above
deviation is large, thereby controlling the grinding rate on the
mill roll so that the mill roll is ground into the target roll
profile. Alternatively, while controlling the contact force between
the mill roll and the grinding wheel to be held constant, the
traverse speed of the grinding wheel in the roll axial direction
may be changed to vary the grinding rate on the mill roll. In this
case, too, the mill roll is ground into the target roll
profile.
[0062] After determining a profile of the mill roll by the first or
second profile calculating means, the determined data is input to a
system computer for controlling the entire rolling mill and, based
on the input data, roll benders provided in the rolling mill is
operated to apply bending forces to the mill rolls, thereby
improving the profile of a hot strip. When the rolling mill has
roll shifting means for shifting the mill roll in the axial
direction or roll crossing means for making the mill rolls crossed
each other, the profile of a hot strip may be improved by
controlling such means. By so using the measured roll profile as
control data for the roll benders, the roll shifting means or the
roll crossing means, high-accurate strip crown control is
enabled.
[0063] By moving the grinding head unit in the roll axial direction
while keeping the distance between the axis of the mill roll and
the distal end surface of the abrasive layer constant, the mill
roll is ground to have the same diameter over its entire length. By
moving the grinding head unit in such a manner as to optionally
change the distance between the axis of the mill roll and the
distal end surface of the abrasive layer, the contact force between
the mill roll and the grinding wheel is increased at the position
providing the shorter distance where the mill roll is ground to a
larger extent. On the contrary, the contact force between the mill
roll and the grinding wheel is decreased at the position providing
the longer distance where the mill roll is ground to a smaller
extent. Thus, for optionally creating and maintaining a profile of
the mill roll, the grinding wheel movement means is moved to
control the distance between the axis of the mill roll and the
distal end surface of the abrasive layer such that the distal end
surface of the abrasive layer draws the same path as the target
roll profile of the mill roll.
[0064] By measuring an inclination of the axis of the mill roll and
grinding the mill roll while controlling the grinding wheel
movement means and the grinding wheel traverse means such that the
distal end surface of the abrasive layer moves along the target
roll profile of the mill roll in consideration of the inclination,
even if the axis of the mill roll is inclined, the correct roll
profile compensated for the inclination can be always
maintained.
[0065] When the work rolls is continuously ground for a long period
of time, there may occur a difference in diameter between the upper
and lower rolls, i.e., a diameter difference. If such a diameter
difference is increased, values of rolling torque necessary for the
upper and lower rolls become so different as to impose undue forces
on the spindles and so forth, which may result in a trouble. To
prevent such a trouble, the system is usually controlled so that
the diameter difference is kept within 0.2 mm/diameter.
[0066] By forming a reference small-diameter zone having a known
roll diameter in at least one end of the mill roll, and measuring a
periphery difference between the reference small-diameter zone and
the roll barrel by a displacement meter, the correct roll diameter
can be always determined. By making such measurement on the upper
and lower rolls, the diameter reference can be monitored
on-line.
[0067] Also, by measuring the roll diameter at both ends of the
mill roll, whether the mill roll is tapered or not in the roll
axial direction after the grinding (i.e., cylindricity) can be
confirmed.
[0068] Further, by pressing the grinding wheel against the mill
roll at respective positions in the reference small-diameter zone
and the roll barrel zone so that the contact force between the
grinding wheel and the mill roll has the same value, and
determining a periphery difference between the reference
small-diameter zone and the roll barrel from the difference between
two strokes of the grinding wheel measured at the respective
positions at that time, the roll diameter can be measured without
using any displacement meter.
[0069] In hot rolling mills, while work rolls are worn away due to
contact with hot strips, backup rolls supporting the work rolls
also develop a fatigue layer on their roll surfaces because the
backup rolls are contacted with the work rolls under high contact
forces. By providing the on-line roll grinding system on each of
the backup rolls as well, the fatigue layer on the backup roll
surfaces can be easily removed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0070] FIG. 1 is a side view, partially sectioned, of principal
parts of a rolling mill equipped with an on-line roll grinding
system according to a first embodiment of the present
invention.
[0071] FIG. 2 is a sectional view; partially cut away, taken along
line II-II in FIG. 1.
[0072] FIG. 3 is a transverse sectional view of a roll grinding
unit.
[0073] FIG. 4 is a vertical sectional view of the roll grinding
unit.
[0074] FIG. 5 is a representation showing arrangement and structure
of a grinding wheel and for explaining a vibration absorbing action
of the grinding wheel.
[0075] FIG. 6 is a representation showing the relationship in
arrangement between the grinding wheels of the two roll grinding
units.
[0076] FIG. 7 is a diagram for explaining a control system of the
roll grinding unit.
[0077] FIG. 8 is a representation showing scratches produced on the
surface of a work roll by chattering.
[0078] FIG. 9 is a representation showing a sectional configuration
of the work roll shown in FIG. 8.
[0079] FIG. 10 is a representation showing another example of
arrangement of the grinding wheel and for explaining a vibration
absorbing action of the grinding wheel.
[0080] FIG. 11 is a graph showing the relationship between the
spring constant of a plain wheel of the grinding wheel and a
grinding ratio.
[0081] FIG. 12 is a representation showing interference between the
grinding wheel and a stand in the case of grinding the work roll
under a condition that a spindle of the grinding wheel is inclined
relative to a line perpendicular to the roll axis.
[0082] FIG. 13 is a graph showing the relationship of a contact
force between the work roll and the grinding wheel versus a
grinding rate.
[0083] FIG. 14(A) is a representation showing an overlap zone of
the grinding occurred when using a plurality of grinding wheels,
and FIGS. 14(B) and 14(C) are representations for explaining a
control method for distributing the grinding overlap zone.
[0084] FIG. 15 is a diagram for explaining the overlap dispersion
control.
[0085] FIG. 16 is a flowchart showing procedures of the overlap
zone distributing control.
[0086] FIG. 17 is a representation for explaining the positional
relationship between the work roll, a grinding wheel movement
device, and a deflection of the grinding wheel in the case of
measuring a roll profile.
[0087] FIG. 18 is a flowchart for explaining a first roll profile
calculating function.
[0088] FIG. 19 is a flowchart for explaining a second roll profile
calculating function.
[0089] FIG. 20 is a flowchart showing procedures of compensating
the roll profile obtained by the first or second roll profile
calculating function based on roll profile data obtained
off-line.
[0090] FIG. 21 is a flowchart showing procedures of grinding the
work roll into a target profile based on the roll profile obtained
by the first of second roll profile calculating function.
[0091] FIG. 22 is a plan view, partially sectioned, of principal
parts of a rolling mill equipped with an on-line roll grinding
system according to a second embodiment of the present
invention.
[0092] FIG. 23 is a flowchart showing grinding control in the
second embodiment.
[0093] FIG. 24 is a flowchart showing rolling control according to
a third embodiment of the present invention.
[0094] FIG. 25 is a transverse sectional view of principal parts of
a rolling mill equipped with an on-line roll grinding system
according to a fourth embodiment of the present invention.
[0095] FIG. 26 is a diagram showing the relationship between the
work roll, a reference small-diameter zone, and a displacement of a
measuring rod in the fourth embodiment.
[0096] FIG. 27 is a representation for explaining a method of
measuring a periphery difference and a method of measuring
cylindricity in the fourth embodiment.
[0097] FIG. 28 is a representation for explaining a method of
measuring a wear of abrasives in the fourth embodiment.
[0098] FIG. 29 is a representation for explaining a method of
measuring roll eccentricity in the fourth embodiment.
[0099] FIG. 30 is a representation for explaining the method of
measuring a wear of abrasives in the fourth embodiment.
[0100] FIG. 31 is a representation for explaining a method of
measuring a periphery difference in a rolling mill equipped with an
on-line roll grinding system according to a fifth embodiment of the
present invention.
[0101] FIG. 32 is a flowchart showing procedures for practicing the
method of measuring a periphery difference in the fifth
embodiment.
[0102] FIG. 33 is a side view, partially sectioned, of principal
parts of a rolling mill equipped with an on-line roll grinding
system according to a sixth embodiment of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0103] Preferred embodiments of the present invention will be
described hereinafter with reference to the drawings.
First Embodiment
[0104] At the outset, a description will be given of a first
embodiment of the present invention by referring to FIGS. 1 to
21.
[0105] In FIGS. 1 and 2, a rolling mill of this embodiment is of a
4 high rolling mill comprising a pair of rolls (upper and lower
work rolls) 1a, 1a for rolling a strip S, a pair of rolls (upper
and lower backup rolls) 1b, 1b for respectively supporting the work
rolls 1a, 1a, and a pair of roll benders 30, 30 for respectively
allowing the work rolls 1a, 1a to deflect. The work rolls 1a, 1a
are supported by metal chocks 3, 3 which are assembled into
respective stands 4 on the operating and drive sides. An entry
guide 10 is disposed on the entry side of the rolling mill for
guiding the strip S to the work rolls 1a. There are also provided
coolant headers 15, 15 for cooling heat of the work rolls 1a, 1a
generated during the rolling.
[0106] Such a rolling mill is equipped with an on-line roll
grinding system of this embodiment. The on-line roll grinding
system comprises two upper grinding head units 5a, 5b (hereinafter
represented by "5" in the description common to 5a and 5b ) for the
lower work roll 1a and two lower grinding head units 6a, 6b
(hereinafter similarly represented by "6" with only one of them
being shown in FIG. 1) for the upper work roll 1a.
[0107] The upper grinding head units 5a, 5b are disposed
corresponding to the operating and drive sides of the work roll 1a,
respectively, and can be operated to grind the work roll
independently of each other. Likewise, the lower grinding head
units 6a, 6b are disposed corresponding to the operating and drive
sides of the work roll 1a, respectively, and can be operated to
grind the work roll independently of each other. These units 5a, 5b
and 6a, 6b each comprise, as shown in FIGS. 3 and 4, a plain type
grinding wheel 20 for grinding the work roll 1a, a grinding wheel
drive device 22 for rotating the grinding wheel 20 through a
spindle 21, a grinding wheel movement device 23 for pressing the
grinding wheel 20 against the work roll 1a, and a grinding wheel
traverse device 24 for moving the grinding wheel 20 in the axial
direction of the work roll 1a.
[0108] As shown in FIG. 5 in an enlarged scale, the grinding wheel
20 comprises a plain wheel 52 having a boss 52a and an annular
abrasive layer 51 fixed to the surface of the plain wheel 52 on the
side opposite to the boss 52a, the plain wheel 52 being attached to
the spindle 21. Also, the plain wheel 52 has an elastically
deforming function to absorb vibration from the work roll, and is
structured such that its deflection is changed depending on the
contact force between the work roll 1a and the abrasive layer 51.
For the purpose of developing the elastically deforming function,
the plain wheel 52 preferably has a spring constant of 1000 Kgf/mm
to 30 Kgf/mm, more preferably 500 Kgf/mm to 50 Kgf/mm. The abrasive
layer 51 is attached integrally with the plain wheel 52 by an
adhesive so that it can be stably brought into close contact with
the vibrating work roll 1a.
[0109] The abrasive layer 51 is formed of super abrasive grains
such as cubic boron nitride (generally called CBN) abrasives or
diamond abrasives. The abrasive grains have a concentration in the
range of 50 to 100 and a grain size of in the rage of 80 to 180.
The abrasive grains are aggregated together by using a resin bond
as a binder. Material of the plain wheel 52 is of aluminum or an
aluminum alloy for the purpose of easily radiating the grinding
heat from the abrasive grains of the abrasive layer 51 and reducing
movable mass of the grinding wheel 20.
[0110] As shown in FIG. 5, the grinding wheel 20 is arranged such
that an axis Gc1 of the spindle 21 is inclined by a small angle of
.alpha. relative to a line Sc perpendicular to an axis Rc of the
work roll 1a, and a contact line between the abrasive layer 51 and
the work roll 1a is defined only in one side as viewed from the
center of the grinding wheel. The angle of inclination .alpha. is
preferably on the order of 0.5.degree. to 1.0.degree.. Such an
arrangement of the grinding wheel 20 makes it possible to
effectively develop the elastically deforming function of the plain
wheel 52, and to properly control the contact force between the
grinding wheel and the work roll (as described later).
[0111] Also, the grinding wheel 20 of the grinding head unit 5a and
the grinding wheel 20 of the grinding head unit 5b are arranged, as
shown in FIG. 6, such that respective axes Gc1 of their spindles 21
are inclined by the small angle of .alpha. in opposite directions
relative to respective lines Sc perpendicular to the axis Rc of the
work roll 1a, and respective contact lines between the abrasive
layers 51 and the work roll 1a are each defined only in one
corresponding roll end side as viewed from the center of the
grinding wheel. Such an arrangement equally applies to the grinding
wheel 20 of the grinding head unit 6a and the grinding wheel 20 of
the grinding head unit 6b. This enables the grinding to be carried
out to the opposite ends of the work roll 1a without interfering
with the stands (as described later).
[0112] The grinding wheel drive device 22 comprises, as shown in
FIG. 3, a liquid motor 54 (which may be instead of an electric
motor) for driving the grinding wheel 20 to rotate at a
predetermined circumferential speed, and a pulley shaft 54b and a
belt 55 for transmitting rotation of an output shaft 54a of the
liquid motor 54 to the spindle 21, the output shaft 54a and the
pulley shaft 54b being coupled with each other through parallel
splines 54c. The pulley shaft 54b is rotatably supported by a body
59. The spindle 21 is supported in the body 59 through a pair of
slide radial bearings 21a, 21b in a rotatable and axially movable
manner. On the side of the spindle 21 opposite to the grinding
wheel 20, a load cell 53 is accommodated in the body 59 for
measuring the contact force between the grinding wheel 20 and the
work roll 1a.
[0113] The body 59 is housed in a case 25 and the liquid motor 54
is attached to the case 25. As shown in FIG. 4, the body 59 is
mounted onto the bottom of the case 25 through a slide bearing 25a
to be movable in the axial direction of the spindle 21.
[0114] The grinding wheel movement device 23 comprises, as shown in
FIG. 3, a movement motor 57 attached to the case 25, a backlashless
pre-loaded ball screw 56 for moving the body 59 upon rotation of
the movement motor 57 in the direction toward or away from the work
roll 1a to thereby shift the grinding wheel 20, the spindle 21 and
the load cell 53 together back and forth, and an encoder 57a for
detecting an angle through which the movement motor 57 is rotated.
The pre-loaded ball screw 56 may able replaced by a backlashless
gear mechanism.
[0115] The grinding wheel traverse device 24 comprises, as shown in
FIG. 4, a traverse motor 58 attached to the case 25, a pinion 58a
fitted over a rotary shaft of the traverse motor 58 and held in
mesh with a rack 14, two pairs of guide rollers 26 attached to an
upper surface of the case 25 and engaging an upper or lower
traverse rail 7, 8, and an encoder 58b for detecting the number of
revolutions of the traverse motor 58. As shown in FIGS. 1 and 2,
the traverse rails 7, 8 are extended on the entry side of the work
rolls 1a, 1a in parallel to the axes of the work rolls, and the
rack 14 is formed on the side of the traverse rail 7 or 8 opposite
to the work roll. Thus, the grinding head units 5, 6 are each
smoothly movable in the axial direction of the work roll upon
rotation of the traverse motor 58 through meshing between the
pinion 58a and the rack 14, while being supported by the traverse
rail 7, 8 via the guide rollers 26.
[0116] The grinding head units 5, 6 are each required to not
interfere with the metal chocks 3 when the corresponding work roll
1a is exchanged. Therefore, the upper traverse rail 7 is slidably
supported at its both ends on guides 9 attached to the stand 4, so
that the grinding head units 5a, 5b are moved rearwardly along with
the traverse rail 8 through a cylinder 11 and the guides 9. Also,
the lower traverse rail 8 is supported at its both ends by entry
side guides 10 so that the grinding head unit 6 is moved rearwardly
along with the corresponding entry side guide 10 upon operation of
a drive device (not shown).
[0117] In each of the grinding head units 5, 6, as shown in FIG. 7,
the movement motor 57 of the grinding wheel movement device 23, and
the traverse motor 58 of the grinding wheel traverse device 24 are
controlled by control units 13a, 13b, respectively. Also, detected
signals from the load cell 53, the encoder 57a of the grinding
wheel movement device 23, and the encoder 58b of the grinding wheel
traverse device 24 are transmitted to a computer 13c and then
processed. The computer 13c has various processing functions and
transmits signals resulted from the processing to the control units
13a, 13b for controlling the movement motor 57 and the traverse
motor 58. The processing functions of the computer 13c will be
described later.
[0118] Operation and control of the on-line roll grinding system of
this embodiment will now be described.
[0119] A description will first be given of basic operation of the
on-line roll grinding system of this embodiment
[0120] The work roll 1a is rotated while vibrating at a frequency
of 10 to 150 c/s depending on the rolling speed. When a roll
grinder having a cylindrical grinding stone, which has been
conventional in off-line grinding systems, is employed in on-line
grinding systems, the cylindrical grinding stone and the work roll
contact with each other through abrasives on the stone surface so
that the work roll is ground by mutual collision of the metal on
the roll surface and the abrasives.
[0121] Stated otherwise, the work roll is ground at the time the
abrasives come into contact with the metal on the roll surface, but
the grinding stone departs away from the work roll at a next
moment, causing the abrasives to rotate while beating the air. With
such discontinuous grinding, there occurs chattering to render the
roll surface and the roll section irregular as shown in FIGS. 8 and
9, respectively.
[0122] If a grinding wheel or stone is vibrated at the same
frequency of the work roll, no changes are caused in the contact
force between the grinding wheel and the work roll. Because of the
work roll vibrating at a high frequency of 150 c/s, however, it is
difficult to make the grinding wheel, including its entire frame,
follow the work roll, i.e., to vibrate the former in tune with the
latter. In view of the above, if the grinding wheel itself is given
with an elastically deforming function to absorb the vibration
through deflection thereof, rather than escaping the vibration
through the grinding wheel and its entire frame, the movable mass
is so reduced as to smoothly follow the vibration of the work roll,
whereby fluctuations in the contact force between the grinding
wheel and the work roll become small.
[0123] In this embodiment, such an elastically deforming function
is imparted to the grinding wheel itself by causing the plain wheel
52 as a part of the grinding wheel 20 to have an elastically
deforming function. More specifically, the grinding wheel 20 is
deflected by being pressed against the rotating work roll 1a, while
it is being rotated at a circumferential speed of 1000 m/min to
1600 m/min of the abrasive layer 51 measured at its outer
periphery. During the grinding, the work roll 1a is vibrating back
and forth, as explained above. The grinding wheel 20 is pushed by
this vibration, but at this time the plain wheel 52 is deflected,
as shown in FIG. 5, to momentarily absorb the vibration transmitted
from the work roll 1a. Accordingly, fluctuations in the contact
force between the abrasive layer 51 and the work roll 1a are held
down within a small range of the elastic force fluctuating upon the
deflection of the plain wheel 52, thereby eliminating the
occurrence of chattering marks.
[0124] In addition, for a cylindrical grinding stone, it is
difficult to give the grinding stone itself with an elastically
deforming function because the work roll and a spindle of the
grinding stone are arranged in parallel to each other. For a plain
grinding wheel, however, an elastically deforming function can be
easily imparted to the grinding wheel itself because the work roll
and the spindle of the grinding wheel are arranged in substantially
orthogonal relation. For this reason, using a plain grinding wheel
is more effective to grind the vibrating work roll.
[0125] Thus, in this embodiment, an elastically deforming function
is imparted to the plain wheel 52 as a base of the abrasive layer
51. Also, to effectively develop the elastically deforming
function, the grinding wheel 20 is arranged such that the contact
line between the abrasive layer 51 and the work roll 1a is defined
only in one side as viewed from the center of the grinding wheel,
as shown in FIG. 5. This arrangement allows the plain wheel 52 to
deflect in cantilever fashion when pressed against the work roll
1a, thereby absorbing the vibration transmitted from the work roll
1a.
[0126] For enabling the plain wheel 52 to deflect, a grinding wheel
20 A may be arranged such that its spindle 21 has an axis offset
from the axis of the work roll 1a, as shown in FIG. 10.
Furthermore, because of the abrasive layer 51 being annular in
shape, even when the grinding wheel 20 is pressed against the work
roll 1a in parallel thereto, the grinding wheel contacts the work
roll at two points of the abrasive layer 51 on both sides of the
wheel center and the plain wheel 52 can deflect. In this case,
however, since the plain wheel 52 is supported at two opposite
ends, it is less deflected. By contacting the plain wheel 52 with
the work roll at one point as with this embodiment, a larger
deflection can be obtained by using a plain wheel of the same
diameter.
[0127] A grinding wheel has an allowable range of the contact force
between the work roll and the grinding wheel depending on the
grinding ability of abrasives. In the case of imparting an
elastically deforming function to the grinding wheel itself, the
following condition must be satisfied in order that the contact
force is properly held in the allowable range and the grinding
wheel will not resonate even under vibration of the work roll.
F.gtoreq.K.times.Amax
[0128] where
[0129] F: allowable range of the contact force
[0130] Amax: one-side amplitude of vibration of work roll
[0131] K: spring constant of elastic body (plain wheel)
[0132] Thus,
K.ltoreq.F/Amax
[0133] Therefore, if an elastic body of the grinding wheel itself
has a spring constant smaller than the above spring constant K
determined from the allowable range F of the contact force between
the grinding wheel and the work roll and the one-side amplitude
Amax of vibration of the work roll, the grinding wheel can grind
the work roll while following the latter at all times.
[0134] On the other hand, if the natural frequency of the grinding
wheel coincides with the vibration frequency of the work roll, the
grinding wheel is caused to resonate and hence can no longer grind
the work roll precisely. For this reason, the natural frequency of
the grinding wheel is preferably set to be as far as possible from
the vibration frequency of the work roll.
FnFr max
[0135] where
[0136] Fn: natural frequency of the grinding wheel
[0137] Frmax: maximum number of vibration frequency of the work
roll
[0138] Meanwhile, the natural frequency of the grinding wheel is
expressed by: 1 Fn = 1 2 K / M
[0139] where
[0140] M: mass of the grinding wheel including the elastic body
(i.e., movable mass)
[0141] Accordingly, in an attempt to raise the natural frequency of
the grinding wheel, it is required to increase the spring constant
K of the elastic body, or reduce the mass M of the grinding wheel
including the elastic body. But, as mentioned above, the spring
constant K of the elastic body cannot be set larger than a certain
value (F/Amax). To raise the natural frequency of the grinding
wheel, therefore, the mass of the grinding wheel including the
elastic body must be reduced.
[0142] On condition of F=4 Kgf and Mmax=30 .mu.m, for example,
K=133 Kgf/mm is resulted: Assuming that there hold Frmax=150 c/s
and Fn=400 c/s, therefore, the movable mass M including the
grinding wheel must be held down to 0.2 Kg.
[0143] For the grinding wheel made of abrasive grains of aluminum
oxide (Al.sub.2O.sub.2) or silicon carbide (SiC) which are
generally used in grinding wheels or stones, if the movable mass is
held down to 0.2 Kg, the grinding wheel is soon worn away
thoroughly and must be exchanged may times per day. This greatly
lessens the effect of grinding the work roll in the rolling mill,
i.e., on-line.
[0144] To solve that problem, it is needed to use a grinding wheel
with a high grinding ratio (the volume of the work reduced/the
volume of the grinding Wheel reduced).
[0145] When the grinding wheel is made of abrasive grains of
aluminum oxide (Al.sub.2.sub.2O.sub.2) or silicon carbide (SiC)
which are generally used at the present, it is difficult to
increase the grinding ratio more than 3 in the case of grinding a
hard work roll. In contrast, the grinding wheel 20 of this
embodiment, which is made of super abrasive grains such as cubic
boron nitride (generally called CBN) abrasives or diamond
abrasives, has a grinding ratio above 300 even in grinding the work
roll 1a, and hence exhibits a grinding ratio more than 100 times
that of the grinding wheel made of aluminum oxide (Al.sub.2O.sub.2)
abrasives or silicon carbide (SiC) abrasives. By employing the
above super abrasive grains in; the grinding wheel of the on-line
roll grinding system so as to advantageously utilize such a high
grinding ratio of the super abrasive grains, the grinding can be
continued for a long period of time with a small weight of the
grinding wheel.
[0146] Further, in this embodiment, the abrasive layer 51 is
attached to the base in the form of the plain wheel 52, and an
elastically deforming function is imparted to the plain wheel 52,
so that the abrasive layer 51 is integral with a member having the
elastically deforming function. Therefore, only both the abrasive
layer 51 and the plain wheel 52 provide the mass forced to move
upon the vibration from the work roll 1a. Consequently, the movable
mass can be very small and the natural frequency of the grinding
wheel 20 can be raised.
[0147] As mentioned above, with this embodiment, the abrasive layer
52 is formed of super abrasive grains having a high grinding ratio
(which enable the grinding wheel to have a light weight and a long
service life) for achieving the small movable mass, and the
grinding wheel 20 made integral with the plain Wheel 52 having a
proper spring constant is pressed against work roll 1a while it is
rotating. As a result, it is possible to correctly grind the
vibrating work roll for a long period of time without causing
chattering marks due to resonance.
[0148] A proper spring constant of the plain wheel 52 will now be
described by referring to experimental data plotted in FIG. 11.
FIG. 11 shows experimental data on the relationship between a
spring constant of the plain wheel 52 and a grinding ratio. The
experimental data was obtained on condition that the
circumferential speed of the work roll 1a is vr=300 m/min, the
circumferential speed of the grinding wheel is vg=1570 m/min, the
speed of movement of the grinding wheel in the roll axial direction
(i.e., the traverse speed) is vs=10 mm/sec, the vibration frequency
of the work roll 1a is f=35 Hz, and the one-side amplitude of
vibration of the work roll 1a is a=0.01 mm.
[0149] As seen from FIG. 11, the grinding ratio lowers with the
larger spring constant, and rises with the smaller spring constant.
In other words, if the spring constant is too large, the chattering
marks are caused, the grinding ratio is lowered, and further the
abrasive layer 51 is soon worn away thoroughly. In order to
minimize the exchange pitch of the grinding wheel 20 and avoid a
reduction in productivity due to exchange of the grinding wheel,
each grinding wheel is required to permit continuous grinding for
not less than 5 days once exchanged. Meeting this exchange pitch
generally needs a grinding ratio not less than 50, preferably 250.
Since the grinding wheel 20 made of super abrasive grains is
expensive, the grinding ratio must be as high as possible for the
purpose of reducing the production cost. The reason why the
grinding ratio lowers with the larger spring constant of the plain
wheel 52 is that the contact force imposed on the grinding wheel 20
due to the vibration of the work roll 1a is fluctuated to a larger
extent and, therefore, a larger force acts on the abrasive grains
of the abrasive layer 51 correspondingly to make those abrasive
grains fall off therefrom. Also, if vibration of the work roll 1a
cannot be fully absorbed by the grinding wheel 20 and the resulting
load is transmitted to the load cell 53, which results in larger
fluctuations in the measure value of the contact force and hence a
difficulty in controlling a grinding rate based on the contact
force between the work roll 1a and the abrasive layer 51 (as
described later).
[0150] On the contrary, if the spring constant is small, the
contact force imposed on the grinding wheel 20 due to the vibration
of the work roll 1a is less fluctuated. The grinding ratio is
therefore raised, but accuracy of grinding control and roll profile
measurement (described later) both based on the contact force is
degraded. The reason why the accuracy of grinding control and roll
profile measurement is degraded is that the force acting on the
spindle 21 upon deflection of the grinding wheel 20 becomes so
small that the load cell 53 cannot detect change in the load
corresponding to small irregularities.
[0151] Assuming the spring constant of the plain wheel 52 to be 50
Kgf/mm, for example, the load difference produced by a periphery
difference of 10 .mu.m is .DELTA.F=50.times.0.01=0.5 (Kgf) which is
almost a limit of the detectable range, judging from resolution of
general load cells. Also, the smaller spring constant of the plain
wheel 52 means that the plain wheel 52 is thinner and the grinding
wheel 20 is deflected to a larger extent with the same contact
force, causing undue forces in the abrasive layer 51 due to
distortion. Thus, if the spring constant is smaller than 30 Kgf/mm,
there would occur cracks in and peel-off of the abrasive layer 51
from the plain wheel 52 even with the contact force necessary for
the grinding.
[0152] It has been found from the foregoing data that the spring
constant of the plain wheel 52 is preferably in the range of 1000
Kgf/mm to 30 Kgf/mm, more preferably 500 Kgf/mm to 50 Kgf/mm
[0153] Compositions of the abrasive layer 51 will now be described.
When the grinding wheel 20 employs the abrasive layer 51 made of
super abrasive grains, the abrasive layer 51 is usually subjected
to dressing in off-line roll grinding to keep the grinding ability
constant and stabilize the grinding roughness. In on-line roll
grinding, however, there is a difficulty in dressing the abrasive
layer 51 from the standpoints of space and so forth. In order to
keep the grinding ability constant and stabilize the grinding
roughness without dressing in on-line roll grinding, it is required
for the super abrasive grains of the abrasive layer 51 to be
spontaneously edged at a constant rate. Proper spontaneous edging
of the super abrasive grains needs adjustment of the load imposed
on one super abrasive grain. For this purpose, it is required to
set density, i.e., concentration, of the super abrasive grains
contained in the abrasive layer 51 within the range of 50 to 100,
and use a resin bond as a binder which is worn away along with the
super abrasive grains while holding them together. If the
concentration is not less than 100, the spontaneous edging of the
super abrasive grains would be hard to occur, resulting in a
decrease of the grinding ability. If the concentration is not
larger than 50, the service life of the super abrasive grains would
be shortened. Further, if a pitolifido bond or the like which is
hard to wear away is used as a binder, projection of the super
abrasive grains from the binder surface would be so small as to
require dressing. With a combination of the above range of
concentration and the binder comprising a resin bond, the super
abrasive grains can be easily spontaneously edged to enable the
continuous grinding without dressing. It has been also found that
the size of the super abrasive grains, i.e., the grain size, is
required to be in the range of 80 to 180 for obtaining the surface
roughness of the work roll 1a in the range of 0.3 to 1.5 .mu.m in
average.
[0154] Operation depending on an arrangement of the grinding wheel
20 will now be described. As mentioned above, the grinding wheel 20
is arranged such that the axis Gcl of the spindle 21 is inclined by
the small angle of .alpha. relative to the line Sc perpendicular to
the axis Rc of the work roll 1a, and the contact line between the
abrasive layer 51 and the work roll 1a is defined only in one side
as viewed from the center of the grinding wheel. With such an
arrangement of the grinding wheel 20, the plain wheel 52 can
effectively develop its elastically deforming function, also as
mentioned above. Further, because of the abrasives surface 51 being
annular, if the surface of the abrasive layer 51 is pressed against
the work roll 1a in parallel relation, there are defined contact
lines between the abrasive layer 51 and the work roll 1a at two
points on both sides of the wheel center. As a result of the two
contact lines being defined, the work roll 1a is simultaneously
ground at those two points. Therefore, if the work roll 1a has a
periphery difference, the two grinding surfaces interfere with each
other to cause chattering marks. Also, the contact at two points
between the grinding wheel and the work roll leads to a difficulty
in controlling the contact force therebetween. In this embodiment,
since the contact line between the annular abrasive layer 51 and
the work roll 1a is defined only at one point on one side of the
wheel center, the chattering is prevented to enable proper control
of the contact force (as described later).
[0155] When the spindle 21 is inclined by the small angle of
.alpha. relative to the line Sc perpendicular to the axis Rc of the
work roll 1a, there is a fear that a zone not subjected to the
grinding may occur at one end of the work roll 1a, or the grinding
wheel 20 may interfere with the stand 4 on that one end side of the
work roll 1a, as shown in FIG. 12. Therefore, the grinding wheel 20
of the grinding head unit 5a and the grinding wheel 20 of the
grinding head unit 5b are arranged, as shown in FIG. 6, such that
the respective axes Gc1 of their spindles 21 are inclined by the
small angle of .alpha. in opposite directions relative to the
respective lines Sc perpendicular to the axis Rc of the work roll
1a, and the respective contact lines between the abrasive layers 51
and the work roll 1a are each defined only in one corresponding
roll end side as viewed from the center of the grinding wheel. This
arrangement enables the work roll 1a to be ground over its entire
length without causing the above interference with the stand The
foregoing description equally applies to the grinding wheel 20 of
the grinding head unit 6a and the grinding wheel 20 of the grinding
head unit 6b.
[0156] Control of the on-line roll grinding system of this
embodiment will now be described. The on-line roll grinding system
of this embodiment has various control functions below:
[0157] (1) roll profile grinding control
[0158] (2) independent grinding control
[0159] (3) overlap zone distribution control
[0160] (4) roll profile measurement as a on-line roll profile
meter
[0161] (5) roll profile compensation
[0162] (6) combination of roll profile measurement and roll profile
grinding control
[0163] These control functions are previously stored in the form of
programs in the computer 13c.
[0164] (1) Roll Profile Grinding Control
[0165] A description will first be given of the roll profile
grinding control. FIG. 13 shows experimental data on the
relationship of a contact force F between the abrasive layer 51 of
the grinding wheel 20 and the work roll 1a versus a grinding rate Q
per unit time. The experimental data was obtained at the
circumferential speed of the work roll 1a of vr=300 m/min, 600
m/min and 900 m/min on condition that the circumferential speed of
the grinding wheel is vg=1570 m/min, the speed of movement of the
grinding wheel in the roll axial direction (i.e., the traverse
speed) is vs=10 mm/sec, the vibration frequency of the work roll 1a
is f=35 Hz, and the one-side amplitude of vibration of the work
roll 1a is a-0.01 mm. As seen from the graph of FIG. 13, the
grinding rate Q per unit time changes almost linearly depending on
the contact force F between the abrasive layer 51 and the work roll
1a. Accordingly, the grinding rate Q of the work roll 1a can be
optionally changed by controlling the contact force F between the
abrasive layer 51 and the work roll 1a by the grinding wheel
movement device 23 disposed in each of the grinding head units 5,
6.
[0166] To perform the above control, the load cell 53 is arranged
in abutment with the end of the spindle 21 on the side opposite to
the grinding wheel for more precisely detecting the contact force F
in this embodiment. Also, the relationship between the contact
force F and the grinding rate Q shown in FIG. 13 is previously
stored in the computer 13c shown in FIG. 7, and the detected
contact force F is input to the computer 13c. Then, the deflection
of the plain wheel 52 is changed by the movement motor 57 to reach
the target grinding rate, thereby controlling the 1a can be ground
to a predetermined profile.
[0167] The grinding rate is also changed by varying the speed of
movement of the abrasive layer 51 in the roll axial direction
(i.e., the traverse speed) while keeping the contact force F
between the abrasive layer 51 and the work roll 1a constant. In
other words, when the abrasive layer 51 is moved at a higher speed,
the time during which the abrasives are held in contact with the
work roll is shortened and the grinding rate is reduced.
Conversely, moving the abrasive layer 51 at a lower speed increases
the grinding rate. Accordingly, by controlling the traverse speed
of the abrasive layer 51, the grinding rate of the work roll 1a can
also be changed optionally.
[0168] Specifically, the detected contact force F is input to the
computer 13c, the traverse speed of the abrasive layer 51 is
controlled by the traverse motor 57 to reach the target grinding
rate, while controlling the deflection of the plain wheel 52b, the
movement motor 57 so that the contact force F is kept constant (see
FIG. 21). As a result, the work roll 1a can be ground to a
predetermined profile.
[0169] When controlling the contact force F between the abrasive
layer 51 and the Work roll 1a by the grinding wheel movement device
23, as mentioned above, if there exists a backlash in the axial
direction of the spindle 21, the movable mass moving back and forth
upon the vibration of the work roll 1a is abruptly increased,
whereby the contact force F between the abrasive layer 51 and the
work roll 1a is changed to a large extent. If the contact force is
changed so large, the grinding wheel movement device 23 can no
longer control the contact force. To make such a backlash as small
as possible, in this embodiment, the backlashless pre-loaded ball
screw 56 is used as the grinding wheel movement device 23, and
other slide parts are constituted by using those parts which have
small clearances. Further, the movement motor 57 for driving the
ball screw 56 comprises an electric motor. As a result, the contact
force can be easily controlled by the grinding wheel movement
device 23, making it possible to hold the position of the grinding
wheel 20 during the grinding and finely move the grinding wheel 20
back and forth.
[0170] (2) Independent grinding control
[0171] A description will now given of the independent grinding
control of the grinding head units 5a, 5b or 6a, 6b.
[0172] Because of contact with the strip, she rolling zone of the
work roll 1a is worn away about 2 .mu.m/radius after the rolling of
one coil, while the unrolling zone of the work roll is not worn
away because of no contact with the strip. Accordingly, there
occurs a periphery difference between the rolling zone and the
unrolling zone. The unrolling zone exists at both ends of the work
roll on the operating and drive sides.
[0173] In the case of mounting the grinding head units 5a, 5b or
6a, 6b together onto a single frame, when one grinding head unit 5a
or 6a is positioned in the unrolling zone on the operating side,
the other grinding head unit 5b or 6b is positioned at the center
of the work roll 1a. Therefore, in attempt to grind one unrolling
zone by one grinding head unit, the other grinding head unit is
positioned in the rolling zone and can not grind the other
unrolling zone.
[0174] Also, when the two grinding head units are mounted together
onto a single frame, the frame has a length larger than half of the
work roll 1a, causing a problem that a coolant ejected from the
coolant headers 15 during the rolling is blocked by the frame and
the work roll 1a cannot be cooled sufficiently.
[0175] In this embodiment, the two grinding head units 5a, 5b or
6a, 6b are arranged for each work roll 1a and are controlled to
perform the grinding independently of each other. Therefore, the
two grinding head units 5a, 5b or 6a, 6b are divided in their role
such that the unrolling zone on the operating side can be ground
mainly by the grinding head unit 5a or 6a and the unrolling zone on
the drive side can be ground mainly by the grinding head unit 5b or
6b. As a result, the unrolling zones subjected to no abrasion can
be ground to a larger extent so that there occurs no periphery
difference between the rolling zone and the unrolling zones. Such
control is performed by rotating the traverse motor 58 with a
command from the control unit 13b to move the grinding head unit 5
or 6 over the traverse rail 7, 8 through meshing between the pinion
58b and the rack 14, and by rotating the movement motor 57 with a
command from the control unit 13a to advance the abrasive layer 51
through movement of the ball screw 56.
[0176] The grinding head unit 5 or 6 is sometimes moved to the
center of the work roll 1a for removing the roughed roll surface in
the rolling zone or the fatigue layer on the roll surface. This
control is also performed by rotating the traverse motor 58 with a
command from the control unit 13b to move the grinding head unit 5
or 6.
[0177] In that way, it is possible to efficiently grind the
unrolling zones of the work roll 1a at its both ends and hold the
roll profile constant for a long period of time. It is to be noted
that when the work roll 1a is long as encountered in rolling mills
for slabs, the grinding head units 5, 6 may be provided three or
four such that the units are moved to respective zones to be ground
for grinding those zones independently of one another.
[0178] Further, in this embodiment, since the grinding head units
5a, 5b or 6a, 6b are separated from each other, the work roll 1a
can be cooled sufficiently by the coolant ejected from the coolant
headers 15 during the rolling.
[0179] (3) Overlap Zone Distribution Control
[0180] A description will now be given of the distribution control
for an overlap zone which occurs by using the grinding control unit
5 or 6 comprising plural units.
[0181] When the plural grinding head units 5a, 5b or 6a, 6b are
moved to the center of the work roll 1a, the grinding surfaces of
the grinding wheels 20a, 20b adjacent to each other mutually
overlap at the center of the work roll 1a, as shown in FIG. 14(A).
At this time, if the grinding surfaces always overlap at the same
position Ta, the overlap zone is ground to a larger extent than the
remaining zone, resulting in a grinding error in the overlap
zone.
[0182] If a plurality of grinding head units are mounted together
onto a single frame, a plurality of corresponding grinding wheels
are always moved in the same stroke as one-piece and, therefore,
the grinding overlap zone inevitably occurs at the same position.
Thus, an grinding error cannot be avoided in the overlap zone, with
a fear of producing a periphery difference on the roll surface.
[0183] In this embodiment, by operating the two grinding head units
5a, 5b or 6a, 6b independently of each other, the grinding overlap
zone of the grinding wheels 20a, 20b does not remain at one
location as indicated by the overlap line Ta, but can be
distributed over the range between overlap lines Tb and Tc spanning
in the roll axial direction, as shown in FIGS. 14(B) and 14(C).
Consequently, the grinding error in the overlap zone can be
reduced.
[0184] FIGS. 15 and 16 show procedures of the above control for
distributing the overlap zone. These control procedures are
previously stored in the form of programs in the computer 13c.
First, the grinding head unit 5a is operated to start grinding from
the operating side end of the work roll 1a toward the roll center
(step 100), the grinding being continued up to a position closer to
the drive side rotated to move the grinding head unit 5a in the
roll axial direction (step 301). During this movement, change in
the contact force between the work roll 1a and the abrasive layer
51 is measured by the load cell 53, and the position (stroke
position) of the grinding wheel movement device 23 is controlled by
the movement motor 57 so that the measured contact force is kept
constant (step 302). A displacement of the grinding wheel 20 is
calculated based on a signal from the encoder 57a of the movement
motor 57 (step 303). At the same time, the position of the grinding
head unit 5a in the roll axial direction is measured based on a
signal from the encoder 58b of the traverse motor 58 (step 304).
Then, a roll profile is calculated from both the roll axial
position of the grinding head unit 5a and the displacement of the
grinding wheel 20 (step 305). For the grinding head unit 5b, the
similar procedures to the above steps are executed to calculate a
roll profile (step 306). However, the grinding head unit 5b is
moved from the drive side end in the roll axial direction. The roll
profiles obtained from movement of the two grinding head units 5a,
5b are combined with each other to determine a profile over the
entire length of the work roll 1a (step 307).
[0185] In that way, the profile of the work roll can be measured
on-line by using the equipment of the on-line grinding system.
[0186] (5) Roll Profile Compensation
[0187] A description will now be given of a function of
compensating the roll profile by using the measured value of the
on-line roll profile meter.
[0188] Although the traverse rails 7, 8 of the on-line roll
grinding system are initially installed in parallel to the axis of
the work roll 1a, there is a fear in hot rolling mills that
parallelism between them may change for a long period of time due
to the heat of strips. Unless such a change in parallelism is
compensated, the work roll profile measured as mentioned above
cannot be said as a true profile. The computer 13c executes this
compensation following the procedures shown in FIG. 20.
[0189] First, the work roll 1a is ground by an off-line roll
grinder installed in a roll shop, and its roll profile after the
grinding is measured by an off-line roll profile meter in advance.
The measured roll profile is input to the computer 13c (step 400).
After assembling the work roll 1a ground by the off-line roll
grinder into the rolling mill, a profile of the work roll 1a is
measured by using the above-mentioned first or second profile
calculating function of the on-line roll profile meter (step 401).
Then, a difference between both the roll profiles measured by the
off-line and on-line roll profile meters is determined (step 402).
The determined difference is recognized as a deformation (error in
parallelism) of the traverse rail for the grinding head units and
stored in the computer 13c (step 403). Then, after grinding the
work roll 1a on-line in the subsequent rolling, a profile of the
work roll 1a is measured by using the first or second profile
calculating function (step 404). The measured roll profile values
are compensated by subtracting the above error in parallelism
therefrom (step 405), and the resulting correct measured values are
stored in the computer 13c (step 406). As a result, the precise
profile of the work roll 1a can be determined.
[0190] (6) Combination of Roll Profile Measurement and Roll Profile
Grinding Control
[0191] A description will now be given of a function of grinding
the work roll 1a into a target roll profile with the
above-explained grinding control method by using the thus-obtained
profile data of the work roll, with reference to FIG. 21. The
processing procedures shown in FIG. 21 are also previously stored
in the computer 13c.
[0192] First, a target roll profile is input in the computer 13c
beforehand (step 500). Then, a profile of the work roll 1a is
measured by using the first or second profile calculating function
(step 501). At this time, the above process for compensating the
roll profile using the measured values of the off-line roll profile
meter is executed, if necessary. After determining the correct
profile of the work roll 1a, a difference between the determined
profile of the work roll and the target roll profile is determined
(step 502). From the determined differences at respective axial
roll positions, the amounts to be ground at these respective
positions are calculated (step 503), and then grinding conditions
at the respective axial roll positions are calculated (step 504).
In the case of carrying out the grinding control while changing the
contact force, the contact force between the work roll 1a and the
abrasive layer 51 is controlled by the movement motor 57 of the
grinding wheel movement device 23 based on the relationship of the
contact force F between the work roll 1a and the abrasive layer 51
versus the grinding rate, whereby the work roll grinding rate is
changed so as to grind the work roll 1a into the target profile
(step 505). In the case of carrying out the grinding control while
changing the traverse speed, the traverse speed of the grinding
wheel 20 is controlled by the traverse motor 58 of the grinding
wheel traverse device 24, whereby the work roll grinding rate is
changed so as to grind the work roll 1a into the target profile
(step 505).
[0193] In that way, the work roll 1a is provided with a profile
identical to the target roll profile.
Second Embodiment
[0194] A second embodiment of the present invention will be
described with reference to FIGS. 22 and 23. In these figures,
those members which are identical to those in FIGS. 1 to 7 are
denoted by the same reference numerals.
[0195] During continued use of hot rolling mills, as abrasion of
the stands 4 and the metal chocks 3 progresses under an influence
of the coolant and so on, the axis Ra of the work roll 1a which has
been initially perpendicular to the strip S may incline as
indicated by Rb in FIG. 22. In this embodiment, the target roll
profile is maintained or compensated, taking into account such a
inclination of the work roll 1a.
[0196] FIG. 23 is a flowchart showing control procedures of this
embodiment. These control procedures are previously stored in the
form of programs in the computer 13c (see FIG. 7).
[0197] First, to determine an inclination of the axis of the work
roll 1a, the grinding head units 5a, 5b are respectively moved to
the roll ends on the operating and drive sides (step 600). On each
of the operating and drive sides, the movement motor 57 is rotated
to press the abrasive layer 51 of the grinding wheel 20 against the
work roll 1a (step 601). When the grinding wheel 20 is pressed
until the load cell 53 detects a predetermined load, a displacement
of the grinding wheel from the reference position at that time is
measured by the encoder 57a built in the movement motor 57 (step
602). The load at which a displacement of the grinding wheel is
measured is set to the same value on both the operating and drive
sides.
[0198] Then, a difference in displacement of the grinding wheel 20
between the operating and drive sides is calculated (step 603), and
this displacement difference is divided by the distance between
measuring points on the operating and drive sides to determine an
inclination of the axis of the work roll 1a, the determined
inclination being stored in the computer 13c (step 604).
[0199] Subsequently, a stroke position of the grinding wheel by a
distance L1 from the roll center Rm (step 101). Then, the direction
of movement of the grinding head unit 5a is reversed for grinding
the work roll 1a up to the operating side end (step 102). In
parallel, the other grinding head unit 5b is operated to start
grinding from the drive side end of the work roll 1a toward the
roll center (step 103), the grinding being continued up to the
position closer to the drive side by the distance L1 from the roll
center Rm (step 104). Then, the direction of movement of the
grinding head unit 5a is reversed for grinding the work roll 1a up
to a position closer to the operating side by a distance L2 from
the roll center Rm (step 105) and, in parallel, the direction of
movement of the grinding head unit 5b is also reversed for grinding
the work roll 1a up to the drive side end (step 106). Subsequently,
the direction of movement of the grinding head unit 5a is reversed
again for grinding the work roll 1a up to the operating side end
(step 107) and, in parallel, the direction of movement of the
grinding head unit 5b is reversed again for grinding the work roll
1a up to the position closer to the operating side by the distance
L2 from the roll center Rm (step 108). Then, after changing values
of L1, L2, the above procedures are repeated (steps 109 and 110).
In that way, the work roll 1a can be ground While distributing the
overlap zone.
[0200] (4) Roll Profile Measurement as On-Line Roll Profile
Meter
[0201] A description will now be given of operation of the on-line
roll profile meter built in the on-line roll grinding system.
[0202] In the system of this embodiment in which the plain wheel 52
of the grinding wheel 20 has an elastically deforming function and
the contact force between the work roll 1a and the abrasive layer
51 is controlled by the movement motor 57 of the grinding wheel
movement device 23, the relationship between the roll profile, the
position of the grinding wheel movement device, and the contact
force is expressed below by referring to a schematic representation
of FIG. 17.
Z(x)=S(x)-F(x)/K
[0203] where
[0204] x: coordinate in the roll axial direction
[0205] Z(x): roll profile (mm)
[0206] S(x): position of the grinding wheel movement device
(mm)
[0207] F(x): contact force between the work roll and the grinding
wheel (Kgf)
[0208] K: spring constant of the grinding wheel (Kgf/mm)
[0209] First, assuming that the grinding head unit is traversed in
the axial direction of the work roll 1a whale keeping the grinding
wheel movement device 23 fixed, since the S(x) is always constant,
change in she roll diameter is expressed by:
.DELTA.Z(x)=-.DELTA.F(x)/K
[0210] Thus, the quotient resulted by dividing the change
.DELTA.F(x) in the contact force between the work roll and the
grinding wheel by the spring constant K is a deflection of the
grinding wheel 20, i.e., the change .DELTA.Z(x) in position of the
roll surface, and the roll profile is obtained by processing that
position change to be correspondent to the roll axial coordinate.
This is a first roll profile calculating function.
[0211] FIG. 18 shows processing procedures for the first roll
profile calculating function. These processing procedures are
previously stored in the form of programs in the computer 13c.
First, the grinding wheel 20 of the grinding head unit 5a is
pressed against the operating side end of the work roll 1a and the
grinding wheel movement device 23 is fixed in place (step 200).
Then, while keeping the grinding wheel movement device 23 fixed,
the traverse motor 58 is rotated to move the grinding head unit 5a
in the roll axial direction (step 201). During this movement,
change in the contact force between the work roll 1a and the
abrasive layer 51 is measured by the load cell 53 (step 202), and
the deflection of the grinding wheel 20 is calculated from the
aforesaid relationship (step 203). At the same time, the position
of the grinding head unit 5a in the roll axial direction is
measured based on a signal from the encoder 58b of the traverse
motor 58 (step 204). Then, a roll profile is calculated from both
the roll axial position of the grinding head unit 5a and the
deflection of the grinding wheel 20 (step 205). For the grinding
head unit 5b, the similar procedures to the above steps are
executed to calculate a roll profile (step 206). However, the
grinding head unit 5b is moved from the drive side end in the roll
axial direction. The roll profiles obtained from movement of the
two grinding head units 5a, 5b are combined with each other to
determine a profile over the entire length of the work roll 1a
(step 207).
[0212] As another method of measuring the roll profile, change
.DELTA.S(x) in the position of the grinding wheel movement device
23 is detected while controlling the grinding wheel movement device
23 so that the contact force F(x) between the work roll and the
grinding wheel is always kept at a constant load in the roll axial
direction.
[0213] Since F(x)/K is constant in the roll axial direction, change
in the roll diameter is expressed by:
.DELTA.Z(x) .DELTA.S(x)
[0214] Thus, the roll profile is obtained by determining the change
.DELTA.S(x) in the position of the grinding wheel movement device
23 from the detected value of the encoder 57a of the movement motor
57, and processing that position change to be made correspondent to
the roll axial coordinate. This is a second roll profile
calculating function.
[0215] FIG. 19 shows processing procedures for the second roll
profile calculating function. These processing procedures are
previously stored in the form of programs in the computer 13c.
First, the grinding wheel 20 of the grinding head unit 5a is
pressed against the operating side end of the work roll 1a (step
300). Then, and the grinding wheel movement device 23 is fixed in
place (step 200). Then, after tentatively setting the grinding
wheel movement device 23 to a certain position, the traverse motor
58 is 20 required for obtaining the target profile is calculated by
the above-mentioned method prior to grinding the work roll 1a. The
calculated stroke position is compensated by using the above stored
inclination of the axis of the work roll 1a (step 606), and the
number of revolutions of the grinding movement motor 57 is
controlled so that the distance from the axis of the work roll 1a
to the leading end of the abrasive layer 51 is held constant (step
607).
[0216] By so performing control, even with the work roll 1a
inclined, the distance between the roll axis and the abrasive layer
51 can be held constant to enable constant position grinding. With
this constant position grinding, if there is a periphery difference
between the rolling zone and the unrolling zones as shown in FIG.
2, the deflection of the plain wheel 52 is large in the unrolling
zones and small in the rolling zone corresponding to the smaller
roll diameter. Such a deflection difference produces a difference
in the contact force between the abrasive layer 51 and the work
roll 1a, and the contact force difference in turn produces a
difference in the grinding ability. Thus, the unrolling zones is
ground to a larger extent than the rolling zone so that the
periphery difference between the rolling zone and the unrolling
zones gradually reduced and disappeared. In that way, even if the
axis of the work roll 1a is inclined, the roll profile of the same
diameter can be obtained.
[0217] In the above constant position grinding, if the axis of the
work roll 1a is displaced during the rolling, there occurs an error
in the profile grinding. To prevent such an error, as shown in FIG.
22, a chock presser 31 is mounted to a bender block 30a for each of
roll benders 30, 30 for thereby horizontally pressing the metal
chock 3 against a bender block 30a on the opposite side. The chock
presser 31 may be mounted to the metal chock 3 rather than the
bender block 30a. The chock presser 31 comprises a piston 32 and a
liquid pressure chamber 33. The piston 32 is pushed under a liquid
pressure supplied to the liquid pressure chamber 33, whereupon the
metal chock 3 is brought into abutment by a force of the piston 32
with the bender block 30a on the opposite side. By providing the
chock presser 31 on each of both the metal chocks 3, 3, the axis of
the work roll 1a is held fixed, making it possible to grind the
work roll 1a into the target profile without being affected by
abrasion of the stands 4 and the metal chocks 3, etc.
[0218] In the case of applying an arbitrary roll profile to the
work roll 1a, the work roll 1a is ground by an off-line roll
grinder into such an arbitrary roll profile and this roll profile
is previously stored as a target roll profile in the computer 13c
(see FIG. 7). After that, the number of revolutions of the grinding
wheel movement motor 57 is controlled so as to move the grinding
wheel 20 following the roll profile, thereby carrying out position
control grinding. Even though the rolling zone of the work roll la
is worn away to render the roll profile changed, the original roll
profile can be correctly maintained through compensate grinding at
all times because the grinding wheel 20 is moved following the
correct roll profile. Also in this case, an inclination of the axis
of the work roll 1a is compensated in a like manner to the above.
Specifically, an inclination of the axis of the work roll 1a is
determined from displacements of the grinding wheels 20 on the
operating and drive sides and, taking into account this
inclination, the number of revolutions of the grinding wheel
movement motor 57 is controlled so as to move the grinding wheel 20
following the target roll profile. As a result, even if the axis of
the work roll 1a is inclined, the work roll 1a can have the correct
and constant roll profile for a long period of time.
[0219] Additionally, if the inclination of the axis of the work
roll 1a determined from displacements of the grinding wheels 20 is
in excess of a certain allowable value, this may lead to a zigzag
motion or the like of the strip S. Therefore, the computer 13c may
issue an alarm in such an event.
Third Embodiment
[0220] A third embodiment of the present invention will be
described with reference to FIG. 24 This embodiment is intended to
perform strip crown control based on the measured roll profile
values.
[0221] While the work roll 1a is assembled into the stands 4 after
being ground by an off-line grinder, it produces a thermal crown by
the heat of the strip S during the rolling of the strip S.
Conventionally, such a thermal crown is calculated by a process
computer (not shown), and the roll benders 30 provided in the
rolling mill are controlled based on the calculated amount of
thermal crown for causing the work roll 1a to bend, so that the
strip crown of the strip S approaches a target value. However, the
thermal crown calculated by the process computer is often different
from the actual thermal crown depending on conditions.
[0222] To prevent such a drawback, this embodiment carries out
strip crown control according to procedures as shown in FIG. 24.
First, a roll profile is measured by using the above-mentioned
first or second roll profile calculating function (step 700). This
measurement is performed in accordance with programs previously
stored in the computer 13c (see FIG. 7), as explained before. Then,
taking into account the measured roll profile, a host computer
calculates an optimum bender force for each of the roll benders 30
from the target strip crown and the target strip shape (step 701).
The bender forces of the roll benders 30 are controlled in
accordance with the calculated result, causing the work roll 1a to
bend (step 702), followed by rolling the work roll 1a under that
state (step 703). As a result, the crown of the strip S can be
closer to the target value.
[0223] Though not shown, for a rolling mill equipped with a roll
shifting device for shifting the work roll in the axial direction,
the crown of the strip S can be still closer to the target value by
controlling not only the bender forces, but also an axial shift
position of the work roll. For a rolling mill equipped with a roll
crossing device for making the pair of work rolls 1a, 1a crossed to
each horizontally, the crown of the strip S can be ever closer to
the target value by controlling both the bender forces and the
cross angle. Of course, by inputting profile values determined by
the roll profile measurement after the grinding to the process
computer and then performing the above shape control process, the
strip crown is further improved over the entire strip length.
Fourth Embodiment
[0224] A fourth embodiment of the present invention will be
described with reference to FIGS. 25 to 30. In these figures, those
members which are identical to those in FIGS. 1 to 7 are denoted by
the same reference numerals.
[0225] When the work rolls 1a is continuously ground for a long
period of time in the on-line roll grinding system, an error in the
grinding rate may be so accumulated as to cause a difference in
roll diameter between the upper and lower work rolls, i.e., a
diameter difference. Generally, if such a diameter difference
becomes larger than 0.2 mm/diameter, a difference in rolling torque
between the upper and lower work rolls exceeds an allowable value
and, if it continues to increase, roll drive spindles and so forth
may be damaged. To prevent such a trouble, it is required to
measure diameters of the upper and lower work rolls after the
grinding at a certain time interval. In this embodiment, a system
for measuring diameters of the work rolls on-line after the
grinding is added to the above-explained on-line roll grinding
system.
[0226] In FIG. 25, the work roll 1a is formed on at least one end
thereof with a reference small-diameter zone 39a which has been
ground and measured by an off-line grinder so as to have a smaller
diameter than that of a strip passage zone (i.e., a roll barrel).
The roll diameter in the reference small-diameter zone 39a is
assumed to be D1, as shown in FIG. 26. Also, a roll periphery
difference measuring device 40 is integrally attached to the case
25 of the grinding head unit 5. The grinding head unit 6 also has
the same construction.
[0227] The roll periphery difference measuring device 40 comprises
a measuring rod 41 integral with a piston 41a, and a case 42 for
guiding both the piston 41a and the measuring rod 41. The case 42
is attached to a cover 47 in turn attached to the body 59 so that
the case 42 is movable together with the grinding wheel 20. Within
the case 42, there is defined a liquid pressure chamber 46 for
pushing both the piston 41a and the measuring rod 41 toward the
work roll 1a, and there are disposed a displacement meter 43 for
measuring a displacement of the measuring rod 41 and a spring 44
for discharging a liquid pressure out of the liquid pressure
chamber 46 and returning the measuring rod 41 back to its home
position at the time other than measurement.
[0228] A description will now be given of a method of measuring a
diameter of the work roll by the roll periphery difference
measuring device 40 with reference to FIG. 27. In FIG. 27, the
grinding head unit 5 is moved in the roll axial direction so that
the measuring rod 41 takes a position A, followed by stopping
there. Then, at the position A, a liquid pressure is introduced to
the liquid pressure chamber 46, causing the measuring rod 41 to
contact the reference small-diameter zone 39a of the work roll 1a.
The position of the measuring rod 41 at that time is measured by
the displacement meter 43. Subsequently, the grinding head unit 5
is moved to a position B, the measuring rod 41 is pressed again
into contact with the work roll 1a, and the position of the
measuring rod 41 at that time is measured by the displacement meter
43. A difference between the values measured by the displacement
meter 43 at the positions A, B is calculated by the computer 13c
(see FIG. 7), thereby determining a roll periphery difference.
Given the roll periphery difference being x, the diameter D of the
work roll 1a is expressed by D=D1+2x. More precisely, the diameter
D of the work roll 1a is measured as follows. By making a half turn
of the work roll 1a, the periphery differences are measured at
opposite sides angularly spaced 180 degrees from each other, the
measured values being assumed to be x1, x2, respectively. In this
case, the diameter D of the work roll 1a is expressed by D
=D1+x+x2. From the diameters of the upper and lower work rolls thus
obtained, there can be determined a diameter difference
therebetween.
[0229] A description will now be given of a method of measuring
cylindricity of the work roll 1a using the roll periphery
difference measuring device 40.
[0230] As shown in FIG. 27, reference small-diameter zones 39a, 39b
having been subjected to measurement are formed at both ends of the
work roll la. On the side of the reference small-diameter zone 39a,
the displacement of the measuring rod 31 is measured at each of the
positions A, B, as explained above, thereby determining a diameter
difference x between the reference small-diameter zone 39a and the
work roll 1a. On the side of the reference small-diameter zone 39b,
likewise, another grinding head unit 5 is moved to measure the
displacement of the measuring rod 31 at each of positions C, D,
thereby determining a diameter difference y between the reference
small-diameter zone 39b and the work roll 1a. From these two
diameter differences x and y, a deviation x-y therebetween is
determined. This deviation of the diameter difference is divided by
the distance between the two measuring points to obtain
cylindricity. The cylindricity thus obtained can be used for
compensating the inclination of the axis of the work roll 1a in the
above-mentioned measurement using the roll profile meter.
[0231] The roll periphery difference measuring device 40 can also
be used to measure a wear of the abrasive layer 51 for indicating
exchange information of the abrasive layer 51. A method of
measuring a wear of the abrasive layer 51 will now be described
with reference to FIG. 28.
[0232] First, after attaching a fresh grinding wheel 20 to the
rolling mill, the abrasive layer 51 is pressed by a grinding wheel
movement device 23 against the work roll la under a predetermined
force as indicated at a position F. The distance from the grinding
head unit 5 to the work roll 1a at that time is measured by the
displacement meter 43 and stored in the computer 13c (see FIG. 7).
After grinding the work roll for a certain period of time, the
measurement is performed in a like manner to the above as indicated
at a position E, thereby obtaining the measured value of the
displacement meter 43. By determining a difference s between the
previous measured value and the current measured value, the
resulting difference s provides the amount by which the grinding
wheel 20 has been worn away during the period of time between the
two measurements. Assuming that the abrasive layer 51 has a
thickness t1 of its abrasive portion, the remaining thickness t2 of
the abrasive portion is expressed by t2=t1-s. Thus, the exchange
information of the abrasive layer 51 can be indicated based on the
value of t2.
[0233] Then, after grinding the work roll 1a, whether the work roll
is eccentric or not can be measured by using the roll periphery
difference measuring device 40. This method of measuring an
eccentricity will now be described with reference to FIGS. 29 and
30.
[0234] The measuring rod 41 is pressed against the reference
small-diameter zone 39a of the work roll 1a to measure a
displacement of the work roll 1a and, at the same time, the
grinding wheel 20 is pressed against the work roll 1a to measure a
displacement of the work roll 1a. If the work roll is not
eccentric, there produces a displacement due to entire vibratory
movement of the work roll, but the reference small-diameter zone
39a and the zone which has been subjected to the grinding, i.e.,
the roll barrel, are displaced similarly, meaning that the
displacement measured by the displacement meter 43 becomes equal to
the displacement determined from the load detected by the load cell
53 and the spring constant of the grinding wheel 20. However, if
the work roll is eccentric, there produces a difference between the
two measured displacements during one rotation of the work roll.
This displacement difference can be regarded as the eccentricity of
the work roll.
Fifth Embodiment
[0235] A fifth embodiment of the present invention will be
described with reference to FIGS. 31 to 32 and FIG. 7. This
embodiment is intended to measure a diameter of the work roll 1a
without using any displacement meter.
[0236] First, as shown in FIG. 31, a reference small-diameter zone
60 is formed at one end of the work roll 1a beforehand. The
reference small-diameter zone 60 can be formed by grinding one end
of the work roll 1a by an off-line grinder so as to provide a
diameter smaller x than the roll diameter of the zone which will be
ground by the on-line grinding system (i.e., the roll barrel). The
process described so far is the same as that in the above fourth
embodiment. Then, a roll diameter D1 in the reference
small-diameter zone 60 is measured and input to the computer 13c.
The periphery difference x between the roll barrel and the
reference small-diameter zone is preferably about 1 mm, though this
value depends on an inclination of the grinding wheel 20 with
respect to the work roll la.
[0237] Then, control procedures shown in FIG. 32 are executed.
These control procedures are previously stored in the form of
programs in the computer 13c. First, rotation of the work roll 1a
and rotation of the grinding wheel 20 are both stopped to keep the
reference small-diameter zone 60 from being ground by the grinding
wheel (steps 800 and 801). The grinding wheel 20 is traversed to a
position X of the reference small-diameter zone 60 (step 802), and
then the grinding wheel 20 is moved by the grinding wheel movement
device 23 so as to contact the work roll 1a. The grinding wheel 20
is further pressed against the work roll 1a until the contact force
therebetween reaches a predetermined value (step 802). When the
load cell 53 detects that the predetermined contact force has been
reached, the movement motor 57 is stopped, following which the
position of the grinding wheel at that time is detected by the
encoder 57a and stored (step 804).
[0238] Thereafter, it is determined whether the measurement has
been made at both the position X of the reference small-diameter
zone 60 and a position Y of the roll barrel (step 805). If not,
then the grinding wheel 20 is traversed to the position Y of the
roll barrel (step 806). At the position Y, as with the case of the
reference small-diameter zone 60, the grinding wheel 20 is pressed
against the work roll 1a until the contact force therebetween
reaches a predetermined value (step 803). When the predetermined
contact force is reached, the position of the grinding wheel 20 at
that time is detected by the encoder 57a and stored (step 804).
[0239] Subsequently, a difference between the stroke positions of
the grinding wheel 20 measured at the positions A and B is
calculated (step 807). This difference provides the periphery
difference x. Finally, since the roll diameter D1 in the reference
small-diameter zone 60 is known, a roll diameter Dn of the roll
barrel is determined from the following formula (step 808).
Dn=D1+x
[0240] In that way, the diameter of the work roll 1a after the
grinding can be easily determined and used for judging the timing
of roll exchange or confirming the difference in diameter between
the upper and lower work rolls.
Sixth Embodiment
[0241] While the above description has been made in connection with
on-line grinding of the mill roll 1a, i.e., the work roll, the
rolling mill also includes the upper and lower backup rolls 1b, 1b
contacting the work rolls, the surfaces of the backup rolls being
also roughed and subjected to formation of a fatigue layer. FIG. 33
shows an embodiment in which an on-line roll grinding system is
provided on each of the upper and lower backup rolls 1b, 1b. The
on-line roll grinding system for the backup roll basically has the
same construction and functions as those of the foregoing on-line
roll grinding system for the work roll. By providing the on-line
roll grinding systems for the backup rolls so that the surfaces of
the upper and lower backup rolls 1b, 1b are ground on-line as with
the surfaces of the work rolls 1a, 1a, it is possible to prolong
the exchange pitch of the upper and lower backup rolls 1b, 1b and
improve productivity of hot rolling facilities.
Summary of Advantages
[0242] According to the present invention, as fully described
above, since the vibration of each mill roll is absorbed by an
elastically deforming function of the plain wheel of the grinding
wheel, the mill roll can be precisely ground with high surface
roughness without causing any chattering marks and resonance.
[0243] Since the abrasive layer of the grinding wheel is formed of
super abrasive grains, the movable mass of the grinding wheel can
be reduced, which is more effective in preventing resonance. Also,
the service life of the grinding wheel can be prolonged to grind
the mill roll for a longer period of time while rolling a strip or
the like. It is hence possible to greatly reduce the exchange pitch
and increase productivity of rolling facilities to a large
extent.
[0244] Since the grinding rate of the grinding wheel per unit time
is changed by varying the contact force between the mill roll and
the grinding wheel, the mill roll can be ground into an optional
roll profile.
[0245] Since the grinding wheel movement device is constituted by
using a ball screw mechanism or a gear mechanism which has a small
backlash, the spring constant of the movement device is so
increased as to prevent chattering marks caused by the backlash of
the movement device.
[0246] Since at least two grinding head units capable of grinding
independently of each other are disposed for one mill roll, the
roll profile free from a periphery difference can be maintained
over the entire length of the mill roll.
[0247] Since the grinding overlap zone produced on the mill roll by
using the plural grinding wheels is distributed, precision grinding
is enabled without grinding errors.
[0248] Since the mill roll is ground by using units corresponding
to both roll ends and having their spindles which are inclined in
opposite directions, it is possible to grind the entire length of
the mill roll without interfering with the stand.
[0249] Since the contact force between the mill roll and the
grinding w;heel is detected for calculating a profile of the mill
roll, the roll profile can be measured while grinding the mill
roll. By controlling the contact force of the grinding wheel or the
speed of movement of the grinding wheel in the roll axial direction
based on the roll profile thus measured, the mill roll can be
easily provided with a target profile.
[0250] Further, by simultaneously using an on-line roll grinding
system and an on-line roll profile meter so that the roll profile
optimum for rolling is maintained at all times, it is possible to
realize completely schedule-free rolling.
[0251] Since an error in parallelism between the direction of
traverse movement of the grinding wheel and the mill roll is
compensated, the more precise profile can be measured.
[0252] Since shape control means such as roll benders are
controlled in accordance with the roll profile determined by the
on-line roll profile meter, high-accurate strip crown control is
enabled.
[0253] Since the grinding wheel grinds the mill roll while moving
along the target roll profile, the profile of the mill roll can be
optionally created and maintained. At this time, since an
inclination of the axis of the mill roll is measured and the
grinding wheel is caused to move along the target roll profile for
the grinding in consideration of such an inclination of the roll
axis, the correct roll profile can always be maintained even if the
roll axis is inclined.
[0254] Since the grinding is carried out under a condition that the
metal chocks of the mill roll are pressed against the stands or the
bender blocks, the correct roll profile can always be maintained
without being affected by wear of the stands and the metal
chocks.
[0255] Since the reference small-diameter zone is formed at the end
of the mill roll and a periphery difference between the reference
small-diameter zone and the zone of the mill roll subjected to
grinding (i.e., the roll barrel) is measured by a displacement
meter or the grinding head unit itself, it is possible to determine
the correct roll diameter at all times and monitor a difference in
diameter between the upper and lower rolls on-line. It is also
possible to confirm cylindricity of the mill roll.
[0256] Finally, since the on-line roll grinding system is provided
on the backup roll, a fatigue layer on the surface of the backup
roll can be easily removed.
* * * * *