U.S. patent application number 09/839246 was filed with the patent office on 2001-11-08 for cold rolling method and installtion.
Invention is credited to Leroux, Francois, Valence, Marc.
Application Number | 20010037667 09/839246 |
Document ID | / |
Family ID | 8849516 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010037667 |
Kind Code |
A1 |
Leroux, Francois ; et
al. |
November 8, 2001 |
Cold rolling method and installtion
Abstract
The invention relates to a method for rolling a metal band in a
continuous line installation with coupling of the pickling and cold
rolling processes. According to the invention, the composition of
the pickling fluid is determined to allow the running of the band
in the bath at a minimum speed of a few meters per minute, and
similar running speeds are maintained in the pickling and rolling
sections, during the operating phases, whereas the rolling
conditions are determined in order to maintain the requested
quality of the band at a minimum rolling speed that may be as low
as 1 meter per minute.
Inventors: |
Leroux, Francois; (Senlis,
FR) ; Valence, Marc; (Courbevoie, FR) |
Correspondence
Address: |
ARENT FOX KINTNER PLOTKIN & KAHN, PLLC
Suite 600
1050 Connecticut Avenue, N.W.
Washington
DC
20036-5339
US
|
Family ID: |
8849516 |
Appl. No.: |
09/839246 |
Filed: |
April 23, 2001 |
Current U.S.
Class: |
72/39 |
Current CPC
Class: |
B21B 2001/383 20130101;
B21B 1/28 20130101; B21B 45/06 20130101; B21B 2275/06 20130101;
C23G 3/02 20130101 |
Class at
Publication: |
72/39 |
International
Class: |
B21B 045/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 21, 2000 |
FR |
00 5186 |
Claims
1. A method for continuous cold rolling of a metal band product
wound into coils by running the band through a continuous line
installation comprising successively, in the running direction of
the band: an inlet section comprising at least means for unwinding
coils after one another and a device for welding the downstream
extremity, in the running direction, of a first coil with the
upstream extremity of a following coil in order to form a
continuous band, a treatment section by running the band in contact
with a treatment fluid whose composition is set for pickling the
band, a cold rolling section with adjustment of the rolling
conditions in order to obtain a requested quality of the band, an
outlet section comprising at least one means for shearing the
rolled and means for winding the said band into a coil, at least
two means for accumulating a variable length of band, whereas both
means are interposed, respectively, one between the inlet section
and the treatment section, and the other between the treatment
section and the rolling section, to allow relative variations of
the running speeds in each of the said sections, characterised in
that the composition of the treatment fluid is determined so that
the metal of the band is not attacked during a dwelling time in the
treatment section corresponding to a minimum running speed in the
order of a few meters per minute, that the rolling conditions are
determined so that the requested speed of the band can be
maintained at minimum rolling speed that may be as low as one meter
per minute and that, during all the operating phases, the running
speed in the treatment section and the running speed in the rolling
section remain substantially similar.
2. A rolling method according to claim 1, wherein the running
speeds, respectively in the treatment section and in the rolling
section, can be reduced down to minimum speed of 1-2 m/mn while
maintaining the requested quality of the band.
3. A rolling method according to any of claims 1 and 2, wherein the
maximum running speeds, respectively in the inlet section and in
the rolling section do not exceed by more than 10% the maximum
running speed in the treatment section.
4. A rolling method according to any of claims 1 to 3,
characterised in that, during the period necessary for welding the
extremities, respectively downstream and upstream extremities of
two successive coils, the running of the band is stopped in the
inlet section and the running speed in the treatment section is
lowered to a rather small minimum value so that the length of band
running through the treatment section during the welding period
does not exceed a few ten meters.
5. A rolling method according to claim 4, characterised in that,
during the period necessary for shearing the band, the running
speed in the outlet section does not exceed 1 m/mn and the running
speed in the rolling section is lowered to a rather small minimum
value so that the length of band does not exceed a few ten
meters.
6. A rolling method according to any of the previous claims,
characterised in that, during all the operating phases, the
relative running speeds, respectively in the inlet section, the
treatment section, the rolling section and the outlet section, are
adjusted so that the speed difference between two successive
sections during an operating phase matches the running, in the
fastest section, of an additional band length not exceeding a few
ten meters.
7. A rolling method according to any of the previous claims,
characterised in that, when filling the means of accumulation, the
running speed in the section placed downstream the said means is
adjusted to a value that is smaller by approximately 10% than the
speed in the section placed upstream.
8. A rolling method according to any of the previous claims,
characterised in that an average yearly production ranging between
300,000 and one million tons can be obtained.
9. A rolling method according to any of the previous claims,
characterised in that, after cold rolling, the rolled band is
subjected to at least one finishing treatment such as lining with
continuous annealing.
10. An installation for the manufacture of a metal band comprising
successively, along the running direction of the band: an inlet
section comprising at least means for unwinding coils after one
another and a device for welding the downstream extremity, in the
running direction, of a first coil with the upstream extremity of a
following coil in order to form a continuous band, a treatment
section by running the band in contact with a treatment fluid whose
composition is set for pickling the band, a cold rolling section
with adjustment of the rolling conditions in order to obtain a
requested quality of the band, an outlet section comprising at
least one means for shearing the rolled and means for winding the
said band into a coil, at least two means for accumulating a
variable length of band, whereas both means are interposed,
respectively, one between the inlet section and the treatment
section, and the other between the treatment section and the
rolling section, to allow relative variations of the running speeds
in each of the said sections, characterised in that the
accumulation means have a capacity limited to a few ten meters,
that the rolling section comprises no more than three stands, that
the shearing device comprises fixed type shears cutting the band at
a speed not exceeding 1 m/mn and that the winding means comprise a
single reeling plant.
11. An installation according to claim 10, characterised in that
the tensioning means of the band are interposed, respectively at
the inlet and the outlet of the treatment section.
12. An installation according to claim 10, characterised in that
the accumulation means have a capacity limited to twice the
thirtieth of the maximum value of the running speed in the
treatment section.
13. An installation according to one of claims 10 to 12,
characterised in that, for the production of steel bands with
minimum thickness ranging from 0.4 to 0.5 mm, roll stands are
fitted with working rolls whose diameter ranges between 300 and 350
mm.
14. An installation according to one of claims 10 to 12,
characterised in that, for the production of steel bands with
minimum thickness ranging from 0.2 to 0.25 mm, roll stands are
fitted with working rolls whose diameter does not exceed 150
mm.
15. An installation according to one of claims 10 to 14,
characterised in that at least one roll stand is fitted with
controlled deformation back-up rolls.
16. An installation according to one of claims 10 to 15,
characterised in that at least one roll stand is of the sexto type
with lateral back-up means for the working rolls.
17. An installation according to one of claims 10 to 16,
characterised in that it comprises at least one continuous lining
facility placed on the path of the band downstream the rolling
section and followed by means for winding the band.
18. An installation according to claim 17, characterised in that
the continuous lining facility operates at a running speed similar
to the speed of the band at the outlet of the rolling section.
19. An installation according to claim 18, characterised in that
the lining facility is a galvanising facility.
20. An installation according to one of claims 18 and 19,
characterised in that it comprises a continuous annealing facility.
Description
[0001] The invention relates to a cold-rolling method and
installation for a metal band, especially suited for an average
yearly production, for example ranging between 300,000 and one
million tons.
[0002] The invention applies in particular to descaling and rolling
steel sheets and strips obtained by hot rolling or by thin
continuous casting.
[0003] It is known that generally, the manufacture of metal
products calls, first of all, for the preparation of a raw product
by ingot mould casting or continuous casting, hot transformation by
forging and/or hot rolling and cold transformation comprising
various steps that depend on the nature of the metal, for example
ferritic or austenitic steel, and on the product to be
manufactured, for instance ordinary steel, stainless steel, alloyed
steel.
[0004] Usually, the hot prepared product is subject, successively,
to a descaling treatment for descaling, to cold rolling until the
requested thickness is obtained and, possibly, to finishing
treatments that depend on the type of sheet to be produced, for
example annealed, galvanised or other surface treatment.
[0005] Cold rolling is conducted, normally, in several successive
passes, either in two opposite directions on a reversible mill, or
on several rolling stands operating in tandem.
[0006] Up to recently, the various cold treatments had always been
carried out in a discontinuous fashion in different installations,
whereas the product is wrapped into a coil at the end of each step
in order to be transferred to the next step. These non-continuous
methods therefore require several unwinding and winding operations
of coils as well as intermediate storing phases generating
significant costs, taking into account the necessary handling tools
and staff.
[0007] Moreover, in reversible rolling, a minimum band length must
remain wound on each coil and is therefore not rolled. These parts
outside tolerances cannot be marketed and must hence be
eliminated.
[0008] To remedy these shortcomings, the last few years have seen
the development of continuous line manufacturing methods that
enable doing away with coil winding at least for certain
intermediate steps. In particular, we already know methods in which
certain cold transformation operations are carried out continuously
on a single line. For example, coupling pickling with cold rolling
enables reducing, to a vast extent, the shortcomings stated
above.
[0009] A coupled line installation of this type comprises,
generally, an inlet section containing a device for unwinding, one
after the other, coils to be treated, a pickling section for
descaling, generally by immersing the band in a chemical pickling
liquid, a cold rolling section and an outlet section comprising
means for winding the rolled band into a coil.
[0010] To perform continuous running of the band, the inlet section
comprises linking means, by welding or stapling, of the downstream
extremity, in the running direction, of a first coil with the
upstream extremity of the following coil. Thus, we obtain a
continuous band running successively through the different sections
of the line.
[0011] In normal operation, a same running speed, for example 400
m/min or even more, is maintained up to the inlet of the mill and
increases then in relation to the reduction in thickness.
[0012] However, for various reasons, it is necessary to vary
considerably the speed of a section with respect to the adjacent
sections, respectively upstream and downstream.
[0013] For example, during the time necessary to the connection of
extremities of two successive coils, the inlet section is stopped,
whereas the band must still be running in the pickling section
whose stoppage might cause defects on the metal further to an
excessive dwelling in the acid used.
[0014] Similarly, it is required, in some cases, to stop or, at
least, to slow down the running in the rolling mills, for example
for maintenance operations. Indeed, the working rolls are worn
quite rapidly and must be replaced periodically with new rolls.
During the time necessary to replacement, the rolls are held away
from the band and, even if the running of the band is not stopped
completely, it should be at least slowed down in order to reduce
the length of the band that has not been rolled, which then should
be eliminated.
[0015] On the other hand, after rolling, the band is wound once
more in order to form a coil and, when the said band reaches its
maximum length, the band must be shorn to allow evacuation of the
wound coil. To avoid complete stoppage of the band during shearing,
it is advantageous to use so-called `flying` shears composed of two
blades mounted respectively on two rotating drums, but the speed
must, however be reduced.
[0016] After shearing, the band must be wound to the end and the
complete coil must be evacuated, then the shorn extremity of the
following band must be attached to the reeling plant in order to
constitute a new coil
[0017] To do so, two coilers operating alternately may be used,
with a switching system that enables, after shearing, to direct the
upstream extremity of the following band immediately to the second
coiler for winding the new coil, whereas retraction of the wound
coil on the first coiler is performed in hidden time. A so-called
carousel coiler comprising two winding mandrels operating
alternately can also be used.
[0018] These arrangements enable reducing the time necessary to
changing the coil, but the shorn band should run forward at low
enough speed to enable its extremity to engage on the chuck and to
start the winding process.
[0019] It seems therefore that even if perfected arrangements
enable to reduce the time necessary to certain operating phases
during which the running speeds in the different sections of the
line must vary independently from one another, it is necessary to
place means for accumulating the band between certain sections.
Thus, the band can be accumulated at the outlet of a section when
the running is stopped or slowed down downstream and, conversely,
when the running is stopped or slowed down in a section, it is
possible to continue running, downstream, a band length accumulated
previously.
[0020] Generally, such a coupled line must comprise at least two
means of accumulation placed, respectively, at the inlet and at the
outlet of the handling section. Thus, before reaching the end of a
coil, a certain length of the band will be accumulated, which will
continue to run in the handling section for the time necessary to
the connection with the extremity of the following coil. Similarly,
if the mill has been stopped, for example for replacing the rolls,
the band should be run further in the pickling tanks, while
accumulating the pickled length at the outlet of the treatment
section.
[0021] Obviously, other members are necessary such as tensioning
devices for traction load adjustments in the different sections or
edge shears.
[0022] All these members are obviously quite expensive and call for
high energy expenses and maintenance costs.
[0023] Indeed, to ensure the necessary high running speeds, the
control motors of the various pieces of equipment must be very
powerful.
[0024] Moreover, after usage, the inlet accumulator of the
treatment section must be emptied in order to compensate for later
speed variations.
[0025] Still, these operations must be carried out very rapidly in
order to reduce the transition periods and require therefore motors
capable of supplying the necessary accelerations.
[0026] Besides, in order to maximise the operation of the mill, the
said mill must be suited to certain types of products and the other
sections of the line, in particular pickling and finishing
sections, must be provided accordingly.
[0027] Therefore, although such installations are extremely costly,
their operating conditions must paradoxically be sufficiently rigid
to ensure profitable production with the quality requested.
[0028] Because of the investment costs, the energy expenses and the
maintenance costs, such coupled installations had been provided so
far only for high production levels, ranging for example between 1
and 2 million tons per annum, if not more. Such capacities are,
obviously, justified only for certain types of products and, in
other cases, it seems more economical to use conventional
installations in which the operations are carried out separately
and discontinuously. In particular, for average productions, cold
rolling is, normally, conducted in a reversible mill, by successive
passes in one direction and in the other.
[0029] However, as it is not possible to obtain the same advantages
as in a coupled line, such as the suppression of intermediate
stocks, diminution of staff requirements, reduction in the surface
covered or diminution of band lengths outside tolerance, such
discontinuous installations are only profitable for special
products such as stainless steels, up to 300,000 or 400,000 tons,
or in the case of mini factories producing varied sheet qualities,
but in limited quantities.
[0030] Conversely, there had not been, so far, average capacity
installations, for example between 300,000 and one million tons and
enabling economic production of sheet metals of all types.
[0031] To solve such a problem, the invention concerns a new method
for producing metal bands in a coupled line that enables to reduce
the investment and operating costs sufficiently to remain
profitable even for an average production, between 300 000 and one
million tons.
[0032] The invention applies therefore to a coupled line
installation comprising as usual, an inlet section of the treatment
band, a cold rolling section and an outlet section.
[0033] According to the invention, the composition of the treatment
fluid is determined so that the metal of the band is not attacked
during a dwelling period in the treatment section corresponding to
a minimum running speed in the order of a few meters per minute,
and the rolling conditions are determined so that the requested
qualities of the band can be maintained at minimum rolling speed
that may be as low as one meter per minute.
[0034] Thus, the running speeds, respectively in the treatment
section and in the rolling section remain substantially similar
throughout the operating phases, and it is possible to considerably
reduce the capacity of the accumulators and, consequently, the
investment and operating costs.
[0035] Indeed, as stated above, the coupled lines used until now
have a very large capacity, exceeding for example, 150,000 tons per
month and hence work at very high speed.
[0036] Moreover, the mill must be able to realise a significant
thickness reduction ratio and usually comprises four or five stands
operating in tandem. This leads to significant running speed
variations in the line.
[0037] For example, the average rolling speed of the band may range
between 500 and 1,500 m/mn at the outlet of the rolling section
whereas the running speed in the pickling section must necessarily
remain lower, for example between 100 and 400 m/mn.
[0038] Therefore, in the conventional coupled lines, the
accumulators must have a very large capacity, in the order of 400
to 600 m for compensating the necessary speed variations between
the different sections, and thus constitute extremely cumbersome
and complex installations, comprising several running levels of the
band between a series of fixed deflecting rolls and a series of
mobile rolls that may move longitudinally to vary the lengths of
the different levels.
[0039] Normally, the production capacity of an installation, at
equal width and thickness, is proportional to the running speed and
as the necessary stoppage times of the band, at the inlet and at
the outlet of the line, are the same, the capacity to confer the
accumulators is more or less proportional to the tonnage to be
realised. Consequently, for an installation producing 400,000 tons
per annum, i.e. approx. 20% of the capacity of the current coupled
lines, the capacity of the accumulators should normally be reduced
in the same proportion, which leads to a sizing from 80 m to 120 m.
Such accumulators are still very cumbersome and expensive and, for
this reason notably, it has not appeared possible so far to make a
coupled line profitable for an annual production smaller than 1
million tons.
[0040] In order to solve this problem, the inventor has deviated
from the usual operating conditions while selecting, on the
contrary, to conduct the operations so that it should be possible,
while maintaining the desired quality of the band, to use simple
and cheap equipment enabling to lower the investment, operating and
maintenance costs sufficiently so that such a coupled line is
profitable even for average capacities.
[0041] To this aim, in a particularly advantageous fashion, during
all the operating phases, the relative running speeds, respectively
in the inlet section, the treatment section, the rolling section
and the outlet section, are adjusted so that the speed difference
between two successive sections during an operating phase matches
the running, in the fastest section, of an additional band length
not exceeding a few ten meters.
[0042] Thus, whereas in conventional coupled lines, the band
accumulators are very large installations with a complex operation,
the invention enables using accumulators with reduced capacity, for
example a few ten meters, and with a far simpler constitution.
[0043] On the other hand, as can be seen in the following detailed
description, the other members of the installation can also be
simplified while preserving the qualities of the band produced.
[0044] In particular, the running speeds may be reduced
considerably, even in the rolling section, and it is therefore
possible, at the outlet of the said rolling section, to use fixed
type shears cutting the band at a speed not exceeding one meter per
minute, as well as winding means comprising a single reeling
plant.
[0045] Besides, thanks to the possibility of maintaining the
quality of the band, even at low speed, it is not necessary to
reduce the filling time of the accumulators to the maximum.
Consequently, the maximum running speeds, respectively in the inlet
section and in the rolling section need not exceed by more than 10%
the maximum running speed in the treatment section. Under these
conditions, the accelerations may be reduced. Thus, smaller and,
consequently, cheaper motors can be used.
[0046] As a result, the investment and maintenance costs of a
coupled line according to the invention are reduced considerably
with respect to those of a conventional coupled line, with very
high capacity. On the other hand, as rolling can be prolonged up to
very low speed, the yield ratio remains acceptable. It is then
possible to produce economically cold rolled coils with an average
capacity ranging between 300,000 and one million tons.
[0047] Thanks to the advantages provided by the coupling, an
installation according to the invention remains profitable even for
the production of ordinary quality sheets or strips, for instance
in low alloy steel, and will have therefore quite a varied
production range whereas, until now, the coupled lines had only
been used for certain qualities justifying a high production
capacity.
[0048] It has been noted, on the other hand, that the capacity
foreseen for an installation according to the invention
corresponded more or less to the capacity of a continuous lining or
annealing line. Consequently, it will be possible to combine an
installation according to the invention with other facilities
placed downstream the rolling section and enabling to subject the
band to various finishing treatments, according to the requested
quality. Indeed, the operation of a coupled line with average
capacity according to the invention exhibits sufficient flexibility
to enable incorporation of a lining with annealing equipment, for
example, a galvanisation line, to the same line.
[0049] Other advantageous features of the invention are covered by
sub-claims. But the invention will be understood better by the
following description of certain embodiments of a coupled line,
given for exemplification purposes and illustrated by the appended
drawings.
[0050] FIG. 1 is an assembly diagram of a coupled line installation
according to the invention.
[0051] FIG. 2 is a diagram illustrating the manufacturing capacity
of an installation according to the invention, with a roll stand
fitted with 320 mm-diameter working rolls.
[0052] FIG. 3 is a diagram representing the manufacturing capacity
of an installation according to the invention with a roll stand
fitted with 140 mm-diameter working rolls.
[0053] FIG. 4 is an assembly diagram of an installation according
to the invention associated with pieces of equipment intended for
certain finishing treatments.
[0054] FIG. 1 represents diagrammatically a coupled line according
to the invention comprising in succession, along a longitudinal
running direction of the metal bands, an inlet section 1 of the
band, a treatment section 2, a cold rolling section 3 and an outlet
section 4.
[0055] As usual, the inlet and preparation section 1 of the band M
comprises a coil unwinder 10, a device 11 for straightening and
unbending the band, cropping shears 12 and a welding device 13.
Indeed, once a coil has unwound completely, a new coil should be
placed on the unwinder 10 and the head of this new coil connected
to the tail of the preceding coil to ensure continuous treatment
over the whole line. To enable the connection of both coils, the
extremities are first cropped by the shears 12 in order to realise
two parallel edges that are welded in the welder 13. This welding
can be carried out by any appropriate means. The shears 12 and the
welding machine 13 can be grouped into a single machine.
[0056] The band then runs through a treatment section 2 that is
usually composed of several tanks 21, 22, 23 whose number and
length are determined in relation to the hourly tonnage requested
and to the running speed foreseen. Inside each tank, the band is
immersed in a chemical pickling fluid, for example hydrochloride
acid, whose composition is determined to ensure complete
elimination of the scale taking into account the dwelling time of
the band in acid, which depends on the running speed. To promote
the action of the acid, scale can be fractionated mechanically, for
example by shotblasting.
[0057] In a known fashion, the pickling section is provided at its
end with an edge shearing facility 26 for products requiring width
adjustment in this production line. Upstream the edge shears lies a
band guiding device 25 enabling good centring of the band and
adjustment of its width with minimum loss of metal.
[0058] The cold rolling section 3 comprises a mill 30 in front of
which is placed a traction device 31 to subject the band, during
rolling, to a controlled traction load. The mill 30 is composed,
normally, of several roll stands 33, 34 operating in tandem, but it
should be noted that, in the invention, the mil may comprise only
two stands 33, 34. At the inlet of the mill 30, a band guiding
device 32 enables centring the band and ensuring its correct
running between the working rolls.
[0059] The rolled band passes finally through an outlet section 4
comprising a reeling plant 42 in front of which is placed a
deflecting roll 41. The reeling plant 42 comprises a mandrel driven
into rotation round its axis and on which the extremity of the band
to be wound engages.
[0060] When the coil wound at the outlet reaches a pre-set weight,
the band must be shorn and the completed coil evacuated in order to
start winding a new coil. To this end, shears 43 are provided on
the path of the band upstream the deflecting roll 41 and the
reeling plant 42 is connected to means, not represented, for
evacuating the coils and to means for engaging the extremity of the
following coil on the mandrel of the reeling plant.
[0061] As stated above, to connect together the extremities of two
successive coils in the welding machine 13, both bands to be welded
should be stopped in the inlet section 1, but normally, the band
must continue to run in the treatment section 2 so that the
dwelling time of the band in the acid is not too long. To do so, it
is necessary to place, at the inlet of the treatment section 2 a
band accumulator 6 which is pre-loaded with a certain band length
and enables to continue the running of the band through the tanks
21, 22 during the time necessary to welding the extremities of both
coils, in the inlet section 1.
[0062] Similarly, the rolling process is stopped at least during
the time necessary to replacing the rolls in the stands 33, 34
whereas the band should still be running in the tanks 21, 22 to
avoid excessive attack by the acid. It is possible to extend the
running of the band between the working rolls that are then spaced
apart, but this produces a certain length outside the tolerances,
which must be eliminated, and thereby increases the yield ratio of
the installation. Therefore, a second band accumulator 7 should be
placed after the outlet of the treatment section 2, to enable
stopping or slowing the band down in the rolling section 3, to
allow the band to run further in the treatment section 2 while
setting aside the band length etched in that fashion, which will
then be rolled up to the thickness requested.
[0063] Obviously, other members may, in relation to the needs, be
placed on the path of the band. For example, in order to maintain
the necessary traction loads in the different sections of the line,
the said line comprises several tensioning devices, respectively,
14 at the inlet of the first accumulator 6, 24 at the outlet of the
pickling section 2 and 31 at the inlet of the rolling section 3. A
guiding device 15 is placed at the inlet of the first pickling tank
21 to compensate for the geometrical defects of the band while
maintaining the said band on the running axis, over the whole
length of the tanks 21, 22 and 23.
[0064] On the other hand, the pickling section 2 is terminated, as
usual, by an edge shearing facility 26 for products requiring width
adjustment in this production line and a band guiding device 25 is
mounted upstream the edge shears to ensure good centring of the
band and adjustment of its width with minimum loss of metal.
[0065] A tensioning device 31 is placed at the inlet of the rolling
section 3 in order to isolate the traction level of the second band
accumulator 7, which is relatively low, from the traction level of
the rolling section that must be high enough at the inlet of the
mill 30 to allow the necessary reduction ratio on the first stand.
A band guiding device 32 is also placed at the inlet of the mill 30
to ensure good running of the band up to the winding section 4.
[0066] An installation according to the invention comprises
therefore, in its different sections, the facilities that are
usually encountered in coupled lines but, as can be seen now, the
operations are conducted in order to simplify the whole
installation.
[0067] To do so, it has been observed, first of all, that the
operating conditions of the pickling installations had evolved.
Indeed, it is now possible to use addition products having an
inhibiting effect on the acid contained in the tanks so that the
said acid attacks the scale solely and remains harmless on the
metal of the band. Such products have been developed recently to
enable, in case of emergency, a rather extended stoppage of the
band in the tanks, for example, if a failure of the roll requires
the said roll to be stopped for a duration longer than the capacity
of the accumulator placed at the outlet of the treatment section.
In such a case, it was necessary, previously, to purge the acid in
order to prevent the metal from being attacked and there was a
great waste of time and of production, let alone the risks of
pollution. To avoid this purge, it is possible to add the inhibitor
in advance to the treatment bath that allows to maintain the band
in the acid for a certain time without risking any loss of
metal.
[0068] However, in any case, such inhibitors were only useful in
case of emergency.
[0069] In the invention, conversely, the inhibiting product(s)
added to the treatment bath are used in normal operating conditions
and during each coil winding cycle, to allow reduction of the
running speed in the treatment section down a speed of a few ten
meters per minute, whereas the minimum speed may even be 1 to 2
meters per minute, each time the band must be stopped or slowed
down, upstream or downstream the treatment section. The presence of
the inhibiting product(s) in the treatment bath enables, indeed,
quite a long dwelling time of the band in the pickling tanks
without risking any loss of metal, whereas only scale is
attacked.
[0070] Thus, when the band is stopped in the inlet section during
the connection phase of both bands to the welding machine 13, it is
not necessary any longer to have a great band length accumulated in
the first accumulator 6 to continue running in the treatment
section 2. Conversely, thanks to the inhibitors, it is possible to
reduce the running speed in the tanks, for example down to 5 m/mn.
If the welding time is, for example 2 mn, an accumulation capacity
in the order of 10 m of the band is then sufficient. Similarly, if
the running speed in the pickling section is reduced, according to
the invention, down to a speed in the order of 1 to 2 m/mn, a 10
m-accumulation capacity in the second accumulator 7 placed
downstream the treatment section 2 enables to stop the roll for 5
to 10 mn, for example for the evacuation of a coil from the reeling
plant 42.
[0071] But, according to another feature of the invention, the
running speed in the roll 30 can also be reduced.
[0072] It has been noted, indeed, that various improvements made
recently to the design of the rolls in order to enhance the quality
of the rolled sheet, could maintain the quality of the band down to
a very low rolling speed.
[0073] Indeed, the roll stands for example of the quarto type, can
be fitted with means for controlling the surface evenness by
cambering the working rolls and/or by using back-up rolls with a
revolving shell and with controlled deformation of the type
realised by the applicant company and known under the name `DSR`
(trademark).
[0074] We also know so-called `Z-high` sexto type roll mills, in
which lateral supports enable the use of very small diameter
working rolls.
[0075] More and more, by reasons of the increasing quality
requirements expressed by the clientele, modern mills are fitted
with such means for controlling surface evenness and it has been
discovered that the use of these means and the adaptation of the
diameter of the rolls to the features of the product to be rolled
would enable reduction of the rolling speed while preserving the
quality of the product. Still, for very low rolling speeds, the
mill load at equal reduction ratio increases, but this effect can
be compensated for by a smaller diameter of the working rolls.
Moreover, a judicious choice of the lubricant enables sufficient
lubrication while avoiding the slipping effect that could be feared
by reasons of the small diameter of the rolls.
[0076] Thus, whereas until it appeared necessary to maintain a
minimum rolling speed in the order of 100 m/mn during the cutting
process, it will be possible in the installation according to the
invention, to reduce the rolling speed down to a few meters per
minute, without losing the quality of the band and the thickness
tolerances.
[0077] To do so, the working rolls have a diameter suited to the
type of production, whereas the mill 30 is fitted with means for
changing and replacing the rolls.
[0078] In practice, installations with two diameter ranges for the
working rolls are conceivable, according to the features of the
products to be rolled:
[0079] a range in the order of 350 mm diameter to produce sheets
made of steel with low elastic limit and whose minimum thickness
would be 0.5 mm.
[0080] a range in the order of 150 mm diameter to produce sheets
made of steel with higher elastic limit, down to a minimum
thickness in the order of 0.35 mm.
[0081] Thanks to these arrangements, it will be possible to
guarantee the quality of the band over a range of very low speeds,
without increasing the production of `outside tolerance`
lengths.
[0082] Thus, in the method according to the invention, it is
possible in all the operating phases, to maintain a small
difference in the running speeds between the different sections of
the line.
[0083] During stoppage, for welding purposes, in the inlet section
1, the running speed can be reduced to a few meters per minute, not
only in the pickling section 2, but also in the rolling section 3,
without stopping the rolling process.
[0084] Similarly, during the stoppage time of the mill 30 for
shearing the band at the end of a coil and evacuating the said
coil, the running of the band in the treatment section can be
stopped or, at least, slowed down to very low speed.
[0085] Accumulators with small capacity, in the order of a few ten
meters, are therefore sufficient in all the operating phases. Such
accumulators can be realised very cheaply and are little
cumbersome. For example, as represented on FIG. 1, the accumulators
6 and 7 may be of two-belt vertical type with a vertically mobile
deflecting roll.
[0086] Such an accumulator 7 also enables to stop, for a few
minutes, the running of the band in the pickling section 2, for
example for adjusting the edge shears 26, while proceeding with the
high speed rolling.
[0087] Besides, in conventional coupled lines, the control motors
of the various facilities must be very powerful to enable very
significant speed variations with high acceleration ratios in order
to go through the transition stages as quickly as possible. Indeed,
the loss of certain quality parameters of the band produced should
be avoided and the time during which the length of the band lies
outside the tolerances should be minimised.
[0088] Conversely, in the method according to the invention, the
different sections operate permanently over a speed range between 0
and 100 meters per minute and these speeds remain in the same order
in all the different sections and in all the operating phases.
Consequently, after a slowing down phase, it is not necessary to
come back very quickly to the normal running speed since the speeds
in all the sections can be increased gradually, with an average
acceleration ratio. Therefore motors less powerful than in
conventional installations can be used and, thus, the investment
cost and the energy expenses are considerably reduced.
[0089] For example, in a conventional installation, after a
stoppage time of the inlet section for the connection of two coils,
the inlet running speed is usually increased up to two or three
times the speed in the pickling section in order to fill up the
first accumulator quickly. In an installation according to the
invention, conversely, since during the stoppage, the running speed
in the pickling section and in the rolling section was only a few
meters per minute, the mill gradually comes back to the normal
running speed, in all the sections. To fill up the accumulator that
has, anyway, a small capacity, it suffices to let the band run in
the inlet section at a speed not exceeding by more than 10% the
speed in the pickling section 2.
[0090] Thus, for a pickling speed, for example 50 m/mn, a 10% speed
increase, i.e. up to 55 m/mn, will enable to fill up the
accumulator 6 in approximately two minutes, which is quite
compatible with the unwinding time of a coil that is about 10
minutes for a 50 m/mn treatment speed and for a coil to be rolled
with a wound length of approximately 500 m.
[0091] The possibility, according to the invention, of maintaining
the rolling process down to a very low speed, but not a zero speed,
for example in the order of 1 m/mn, enables, at the outlet of the
roll mill 30, to cut the band as it is running slowly, by means of
`fixed` type shears. Such shears are, obviously, much cheaper than
flying shears of the type used normally, in high production coupled
lines, in order to shear the band without stopping the rolling
process.
[0092] Conversely, the possibility of cutting during slow running
enables doing without any stoppage of the mill, which might leave
marks on the rolled product, and of winding the coil to an end,
which can then be evacuated before the new band head formed by
cutting reaches the engaging device on the coiler 42, for the
formation of a new coil. This possibility of using a single coiler
also constitutes a very significant economy with respect to
conventional lines in which two coilers with switching devices or a
single coiler with carousel should be used, whereas such facilities
are much more expensive.
[0093] Obviously, because of the roll speed reduction and of the
limited power of the control motors, it is not intended, in a
coupled line according to the invention, to realise the same
thickness reductions as in high power lines where a four or five
stand tandem mill is used with a minimum speed of 500 m/mn. But,
precisely, certain types of products, which correspond to average
production capacities, only call for 50 to 75% thickness
reductions, which can be performed in two passes, if working rolls
with suitable diameter are used.
[0094] Consequently, a coupled line according to the invention
could be simplified further by using a mill 30 comprising,
normally, only two stands 33, 34.
[0095] The invention therefore enables reduction of the investment
and operating costs of the coupled line practically in all the
sections of the said line and thus such an installation can be
profitable even for average production capacities.
[0096] Still, the production possibilities of such a simplified
line are not the same as those of the coupled lines known until
now, but they remain sufficient, however, to justify the
profitability of an installation according to the invention.
[0097] In particular, thanks to recent technical evolutions, there
are now improved hot rolling facilities or continuous thin casting
installations that enable production of hot bands with minimum
thickness of 1.5 mm for example. From so thin incoming products, an
average reduction ratio, for example ranging from 50 to 60%, which
can be obtained in two roll passes, enables manufacture of
marketable products, for instance down to a minimum thickness of
0.5 mm.
[0098] For exemplification purposes, the diagrams of FIGS. 2 and 3
specify the production fields of a coupled line according to the
invention comprising a two stand mill, whereas both stand can be
fitted with two types of working rolls.
[0099] Each diagram indicates, in ordinate, the thicknesses that
can be obtained at the outlet of the installation for various band
widths specified in abscissa.
[0100] For a production of rolled steel with small elastic limit
and down to a minimum thickness of 0.5-0.6 mm, the mill 30 is
fitted with a working roll having a diameter in the order of 320
mm. On FIG. 2, the hatched zone indicates the production range of
such an installation per thickness and per product width, while
considering that the incoming product, delivered by a conventional
hot rolling facility or a continuous thin casting installation,
exhibits a thickness in the order of 1.5 mm. With a 50 to 64%
reduction ratio, it is possible to produce all the thicknesses
between 0.5 and 1.5 mm up to a band width of approximately 1100 mm.
However, as the power of the motors has been limited in the example
of FIG. 2, the thickness range is narrower for the widths above
1100 mm, whereas the outlet thickness ranges between 0.7 and 1.1 mm
for a maximum width of 1500 mm.
[0101] For minimum thicknesses, the lower continuous line matches
the use of shotblasted working rolls that wear rather quickly.
[0102] With smooth rolls, a 68% reduction ratio can be reached, at
least for widths smaller than 1200 mm, as shown by the lower dotted
line.
[0103] For a production of rolled steel with higher elastic limit
or in a lower thickness range, possibly as low as 0.35 mm, it is
preferable to use working rolls with a diameter in the order of 140
mm. FIG. 3 illustrates the possible production range with such an
installation and for an incoming product whose minimum thickness is
1.5 mm.
[0104] It can be seen that the production range still remains
relatively wide, whereas a 56 to 73% thickness reduction is
possible up to a width of approximately 1100 mm. With smooth rolls,
a 77% thickness reduction ratio can be reached.
[0105] Obviously, it is only for exemplification purposes that we
have described an installation according to the invention, whereas
the said invention can be subject to variations without departing
from the protection scope delineated by the claims.
[0106] For example, it is possible to use treatment or rolling
facilities of any known type, providing that they allow to obtain
the requested quality at low running speeds and with reduced
investment costs. It should be noted that, as the mill comprises no
more than three stands, the said stands may be fitted with evenness
monitoring facilities, such as controlled deformation back-up
rolls, or they may be of Z-high type. Such facilities are, indeed,
profitable even for an average production, by reasons of the
advantages brought by coupling.
[0107] Consequently, it will be possible to increase the production
of an installation according to the invention already realised by
adding an oxidebreaking device 16 enabling to increase the pickling
capacity, or a third stand 36 in the rolling section. We could also
increase the annual production of such an installation by
approximately 50% and raise the capacity from 400,000 to 600,000
tons yearly, while keeping the advantages of such a line as regards
the investment and operating costs.
[0108] On the other hand, a coupled line according to the invention
could, in a particularly advantageous fashion, be completed, before
winding the band into a coil, with one or several additional
sections enabling to realise finishing treatments, according to the
requested quality.
[0109] It has been observed, indeed, that the average capacity of
300,000 to 700,000 tons, foreseen for an installation according to
the invention, as well as the possibility of varying, in a very
flexible manner, the running speed in the different sections are
particularly compatible with the operating conditions of the lining
and/or continuous annealing lines.
[0110] FIG. 4 is therefore a diagrammatical representation of such
an improved installation comprising, as previously, an inlet
section 1, a treatment section 2 and a rolling section 3 and
completed, downstream the latter, with finishing facilities, such
as for example, a degreasing section 5, a lining section 6 possibly
connected to an annealing oven, a skin-pass roll stand 7, a temper
rolling facility 8 and a reeling plant 44. The assembly is placed
downstream the shears 43, parallel to the first reeling plant
42.
[0111] The lining section 6 may realise, for example, conventional
quenching galvanisation, electro-galvanisation or any other lining.
It is also possible to use simply a continuous annealing oven for
the production of annealed and temper-rolled or skin-passed bare
metal sheets.
[0112] Thanks to the operating flexibility of the coupled line
according to the invention and, in particular, the possibility of
slowing the band down to very low speed, it is possible, downstream
the rolling section 3, to subject the rolled band, continuously, to
these different treatments. In particular, the rolling speed can be
adapted to the speed of the galvanisation facility that is linked
to the format of the metal sheet to be lined and to the weight of
the lining requested. It is then not necessary to provide an
accumulator between the rolling section 3 and the finishing
section.
[0113] In such an installation, changing the roll can be programmed
by providing a set of coils to be lined that do not require any
rolling, in order to change the rolls during that period.
[0114] To this end, a junction enables to direct the band, either
toward the lining facility, up to the reeling plant 44, or
directly, toward the reeling plant 42.
[0115] The reference signs inserted after the technical features
mentioned in the claims solely aim at facilitating the
understanding of the said and do not limit their extent
whatsoever.
* * * * *