Note: Descriptions are shown in the official language in which they were submitted.
10472~6
The invention relates to tandem rolling mills and
a method of operating the same whereby the utilization time
of the mill is increased.
In the past, tandem rolling mills had downtimes due
to porter bar type roll changing of 15 to 20~. The use of
rapid roll changers reduces this downtime of the mill up to
about one-half or more. However, rapid roll changers still
require a downtime of about five minutes.
The utilization time ~i.e., the time the mill is
10. actually used) could be increased another 5 to 6% by saving
the downtime it takes to perform a rapid roll changing operation.
This could bring the utilization time of a tandem cold roll
-~ mill to above the 90~ level.
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It is the general object of this invention to provide
a tandem rolling mill and a method of operating the same which
increases the utilization time of the mill by saving the
downtime resulting from a roll changing operation. This
objective is particularly advantageous in a fully continuous
rolling mill.
20. Briefly, the general object of this invention is
achieved by adding to a tandem rolling mill one more mill stand
than is required by the mill to achieve the rolling of strip in
the pass schedules for which the mill is designed. Thus, if a
! i rolling mill requires five mill stands to perform the rolling
of the design pass schedules, the tandem rolling mill of the
invention is provided with six mill stands, a prior art four
stand cold rolling mill is provided with five mill stands, and
so on. By reason of the provision of an additional mill stand,
; there is always a mill stand which can be substituted for that
30. mill stand which is to have its rolls changed. More specifically,
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the mill stands are designed so that each mill stand can achieve the rolling
action of a preceding upstream mill stand. To this end, the mill stands are
designed such that each can operate throughout most of the speed range of the
adjacent mill stand. Accordingly, a mill stand can be taken out of the roll-
ing line for roll changing without interrupting the rolling action to any
appreciable extent by adjusting the remaining operative mill stands and the
substitute mill stand to achieve the necessary rolling conditions.
The obvious objection to the concept of adding to a rolling mill
a mill stand which is unnecessary to rolling the pass schedules for which the
mill is designed is that it involves a substantial initial investment and sub-
stantially increases the cost of the mill. The additional investment for the
extra mill stand is about 12 to 15% of the total mechanical and electrical
cost of the mill. However, the economies that are produced by saving the
roll changing time more than offset this increased initial cost. With modern
high speed rolling mills it is frequently necessary to change the work rolls
several times each shift because of the changing nature of orders available,
because of steel analysis or for any variety of reasons all recognized in
the trade. Moreover, the savings are even greater in the case of fully con-
tinuous rolling mills because of the higher production involved.
; 20 In accordance with this invention, there is provided a method of
operating a tandem rolling mill having a plurality of mill stands arranged
in a rolling line for successively rolling strip to reduce the thickness
thereof to a desired thickness in a single pass through said mill stands in
accordance with a group of pass schedules for which the mill is designed,
and a mill stand added to the first group of mill stands and arranged in the
roll~ng line, each of said mill stands being independently driven and capable
of operating in most of the speed range of and at a higher maximum speed than
a mill stand immediately upstream in said rolling line, comprising the steps
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of: rolling a strip of material by the operation of only said first group
of mill stands which are set to operate at successive desired speeds and roll
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1047286
bites in accordance with a pass schedule to achieve the desired strip
reduction, adding said additional mill stand to the Tolling line and removing
one of said first group of mills from the rolling line, and operating all of
the remaining mill stands in said rolling line at the successive speed and
rol:L bite settings used during said first-mentioned strip rolling operation.
Figure 1 is a side elevation of a continuous rolling mill in
; accordance with the invention in diagrammatic form;
.. Figure 2 is a graph showing a speed cone which illustrates the
princlples of the invention; and
Figure 3 IS a chart showing a progra~ed roll changing procedure.
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10472#6
In Figure 1 there is shown a fully continuous tandem
cold roll mill illustrating the invention. The mill compTises
six mill stands l, 2, 3, 4, 5 and 6 of the conventional four-
high type. A three roll bridle unit 18 is located adjacent the
entry end of mill stand 1 and serves to control the tension of
the strip delivered thereto. Adjacent the bridle unit 18 is a
mill entry section 20 comprising a pair of payoff reels 22 and
24 and a pair of flatteners 26 and 28. Adjacent the mill entry
section 20 is a strip cutting and joining section 30 which
comprises a conventional cutting shear and welder for joining
the ends of successive coils to be rolled. From the section
30 the strip is fed to a looper section 32 comprising the usual
loop cars driven back and forth along tracks to accumulate a
predetermined length of strip to deliver strip to the mill
stands continuously while a strip joining operation is performed
in the strip cutting and joining section 30 as is conventional
in the art. From the looper section 32 the strip is fed around
a roller 34 to the bridle unit 18 from which it enters the mill -
stands.
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20. At the exit end of the mill, the strip is delivered
from the mill stand 6 to a dividing, shear and tension reel
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section 40 which comprises a pinch roll 42, a shear 44 and a
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~ pair of tension Teels 46 and 48. Adjacent section 40 is a coil
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~` delivery, inspection and strapping section 50 which comprises a
coil transfer car 52, a circumferential and eye bander 54 and a
delivery conveyor 56.
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The drive means for each of the mill stands 1, 2, 3,
: 4, 5 and 6 are indicated at 61, 62, 63, 64, 65 and 66,
respectively, and comprise motor driven speed reducers with
30. speed ranges as will be described hereafter.
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104 7286
The automatic roll changing and setting means for
each of the mill stands 1, 2, 3, 4, 5 and 6 are indicated
schematically at 71, 72, 73, 74, 75 and 76, respectively, and
may take various forms which are well known in the art. Such
means operate by computer signal to set the roll gap or bite
(gauge) and/or effect a roll changing operation.
There is provided a conventional in-line computer 80
- of a type presently in use today for controlling operation offully continuous rolling mills. The computer 80 controls the
10. entire automatic operation of the rolling mill and controls,
for example, the whole mass flow of the rolling mill, the speed~
the amount of reduction, and dynamic gauge changes. The
computer 80 is arranged to set up each stand for rolling a
desired pass schedule as is conventional in operational computers
for continuous rolling mills in use today. For the purposes of
this invention, the computer 80 is arranged to control the drive
means 61-66 and the automatic roll changing and setting means --
71-76 for the mill stands 1-6, respectively, for programmed
roll changing, as will be more fully described hereafter.
20. In the operation of the mill shown in Figure 1 as a
fully continuous rolling mill, the strip is fed from the coil
on payoff reel 22 through the strip cutting and joining section
.~ 30 and the looper 32 and around the roller 34 to the bridle unit
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18 from which it enters the mill stand 1. The strip is rolled
by fi~e of the six mill stands 1 to 6 which are set by the
computer 80 to the proper rolling condition for the pass schedule
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being rolled.
When all of the coil has passed off the reel 22, the
trailing end is joined with the beginning end of a coil on the
30. payoff reel 24. The coil on the payoff reel 24 is passed through
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10~7286
the flattener 26 to the strip cutting and joining section 30
where it is joined with the trailing end of the coil just paid
off from reel 22. During this end joining procedure, which
requires that the strip within the strip cutting and joining - -
section 30 be stopped for a short while, strip is continued
to be fed to the mill stands from the looper section 32 to
thereby maintain a continuous supply of strip for rolling. A
fully continuous rolling operation is maintained by alternately
supplying coils from the payoff reels 22 and 24 and by joining
10. in the strip cutting and joining section 30 the trailing end
of the coil beinB rolled to the beginning end of the new coil.
Conventional rolling may be performed by delivering
strip from a coil on payoff reel 24 through the flattener 28
and the bridle unit 18 directly to the mill stand. This
alternate is shown by the dashed arrow line in Pigure 1.
At the exit end of the mill, the strip is passed
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alternately to one of the tension reels 46 and 48 whereat the
strip is coiled. The rolled coil is then transferred to the
circumferential and eye bander 54 by the conveyor 56. From
the bander 54, the rolled coil continues to move along the
delivery conveyor 56 for removal as is conventional in the
art. Some coils are taken at random off conveyor 26 by the
coil car 52 for inspection.
In accordance with the invention, the utilization
time of the mill is increased by the addition of one mill stand
more than is required for rolling the pass schedules for which
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the mill is designed. This is illustrated in Pigure 2 which
'?:~ shows a speed cone type of graph as is conventionally used in
the art in designing a mill for rolling a group of random pass
30. schedules. On the left vertical side of the graph there is
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1047286
shown the speed at which the rolls are to be driven in feet
per minute. The bottom horizontal line of the graph indicates
the entry speed and the speed at each of the six mill stands
at: equally spaced locations. At the bottom of the graph there
is also listed the gear ratio and the motor horsepower for each - -
of the six mill stands. At the top of Figure 2 there is a
chart showing the essential conditions of four random pass
schedules A, B, C and D. These conditions include the entry
gauge, the delivery gauge, the total elongation, the entry
10. speed into the first mill stand, the delivery speed and the
theoretical production.
The pass schedules A to D are shown graphically by
indicating the speed at which each of the five mill stands in
the rolling line must operate to perform the strip reduction
required for that mill stand. The designer of the mill also adds
; to the graph what is known in the art as a "speed cone" which
comprises the two lines I-I, so as to be certain that each of
the mill stands in the rolling line can be operated at the speeds
required for each of the pass schedules. The lower line I of
20. the speed cone passes through the minimum or base speeds of the
mill stands 1 through 6. The upper line I of the speed cone
passes through the maximum speeds of the mill stands 1 through
6.
` It is noted that the mill stand 1 can operate in a
; speed range of between 686 and 2058 feet per minute (FPM) which
is sufficient to cover each of the speeds required by the pass
schedules A through D at the entry end. This is confirmed by
reference to Figure 2 since these speeds lie between the speed
` cone I-I. Also, mill stand 5 can operate in a speed range of
30. 2050 to 6150 FPM which is sufficient to cover the speeds required
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~047286
by the pass schedules A through D at the delivery end. This
is also confirmed by viewing Figure 2. The speed ranges for
each of the mill stands 2, 3 and 4 is also sufficient to cover
the speeds for each of the pass schedules A through D as is
apparent from Figure 2.
For example, in pass schedule A the entry speed to
mill stand 1 is 555 FPM. In accordance with the gauge setting -
to achieve the desired strip reduction, mill stand 1 is operated --
at a delivery speed of about 900 FPM. Correspondingly, mill
10. stand 2 is operated at a delivery speed of about 1600 FPM, mill
stand 3 is operated at about 2700 FPM, mill stand 4 is operated
:, at about 4175 FPM and mill stand 5 is operated at 6000 FPM. The
computer 80 is programmed to perform the gauge settings for each
mill stand 1 to 6 and control the appropriate drive means 61 to
66 to drive the mill stands 1 to 6 at the speed corresponding to
the gauge setting in accordance with pass schedule A.
It is noted that in accordance with the invention each
of the mill stands is designed to be driven in a speed range
covering most of the speed range of a preceding mill stand. This
20. is apparent from a consideration of the graph shown in Figure 2.
,~ A second speed cone comprising lines II and II is
shown in Figure Z. This speed cone represents the condition
when the mill stand 1 is out of the rolling line for a roll
change and each of the mill stands 2, 3, 4, S and 6 is shifted
to cover the speed of a preceding mill upstream thereof. This
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shifting is illustrated in Figure 2 by the horizontal arrow
lines extending from lines I-I to lines II-II. It will be noted
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; that the speed cone II-II embraces the pass schedules A through
D wherefore the design is such that all of these pass schedules
30. can be rolled by any appropriate combination of the mill stands,
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1047286
i. e. when anyone of the mill stands 1 to 6 is taken out of
the rolling line for a roll change.
It is noted that the motor speed ranges employed to
achieve the above-described flexibility of rolling is achieved
by utilizing a 3 to 1 speed range ratio. Equipment of this type
is readily available in the art.
Figure 3 illustrates a typical computer programmed
roll change schedule in accordance with the invention. This
schedule takes into account that the mill stands near the end
10. of the rolling line are changed more often than the front ones~
although any variation in the pTogram is possible. The sequence
of roll changing progresses downwardly as viewed in Figure 3.
,; Thus, in the upper row there is illustrated what occurs when
the mill stand 6 has its rolls changed. In this case mill stands
1 through 5 are active while the rolls for mill stand 6 are
changed. The mill stands 1 through 5 are, of course, set for
the speed indicated by the pass schedule such as those shown at
A through D in Figure 2.
,; The next row illustrates what occurs when the rolls
20. for mill stand 5 are changed. In this case, mill stands 1
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through 4 remain active at their previous setting while stand 6
is reset to take over the rolling action of the stand 5. This
mode of operation is illustrated in Figure 1.
The next row illustrates what occurs when mill stand
4 is changed. In this case, stands 1, 2, 3 and 5 remain active
at their previous setting and mill stand 5 is set to take over
the rolling action of mill stand 4.
; The next row illustrates the changing of mill stand
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6 again in which case mill stands 1 through 5 perform the rolling
3p. operation in accordance with the pass schedule.
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1047286
The next row illustrates what occurs when mill stand
3 is changed. In this case, stands 1 and 2 remain active at
their previous setting and mill stands 4, 5 and 6 are reset to
take over the rolling action of mill stands 3, 4 and 5,
respectively .
The next line illustrates what occurs when mill stand
5 i5 changed and this is described above.
~ The next line illustrates what occurs when mill stand
; 2 is changed. In this case, stands 1 and 6 remain active at
10. their previous setting and mill stands 3, 4 and 5 are set to
take over the rolling action of mill stands 2, 3 and 4,
respectively.
; The next line illustrates what occurs when mill stand
6 is changed and this was described above.
The last line illustrates what occurs when mill stand
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1 is changed. In this case the mill stands 2, 3, 4, 5 and 6
are reset to take over the rolling action of mill stands 1, 2,
3, 4 and 5, respectively. This corresponds with Figure 2 wherein
the entire speed cone appeaTs to be shifted to the left.
; 20. The roll changing program then continues back with a
roll change for mill stand 6 as illustrated in the top row of the
; chart shown in Figure 3 and is continuously repeated under the
control of the computer 80 in the progression indicated on this
; chart.
- The entire program is under the control of the
computer 80 which sets the drive means 61 through 66 and actuates
the roll changing and setting means 71 through 76 to achieve
the sequence of operation set in the program. In operation, the
computer 80 contrGls the bite of the stands such that while the
30. mill stand which requires roll changing is having its rolls
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withdrawn from contact with the strip, the gauge and speed of
stands downstream of the stand being changed or the stand
previously changed are set to take over the rolling action of
the stand upstream thereof. After the computer 80 has completed
the changes in roll bite (or gauge), the rolls to be changed can
be removed whenever it is convenient without affecting the
; production. During the time that the computer 80 is directing
the changes in roll bite, the strip can be moved slowly or it
can be stopped momentarily. However, this involves very little
10. or no loss of strip or reduction in the production of the mill.
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It will be apparent that by the above described
tandem rolling mill design and method of operating the mill, the
utilization time of the mill is increased, since the roll change
can take place without interrupting the rolling to any
appreciable extent. The design in accordance with the invention
,'sj~ saves the downtime it takes to perform the roll changing
operation and can thus bring the utilization time of a tandem
cold roll mill to above the 90~ level.
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