Note: Descriptions are shown in the official language in which they were submitted.
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. ~ACKGROUND OF TI~E INVENTTON
_
1. FIELD OF THE INUENTION
This invention relates to a method of setting a
multi-stand rolling mill train for the cold-rolling of
metal strip, more particularly the method of
calculation,from the strip data, of the process variables
employed to set the train for each strip.
2. DESCRIPTION OF THE PRIOR ART
The starting factors in the setting of the strip
velocity, the roll-gaps, the roll bending and other such
settin~ values of a multi-stand rolling-mill train are
the process variables relating to the strips and the
rolling-mill train, such as inter-stand thicknesses
~gauges), strip velocity, velocity adjustment for each
roll stand, tensi~e force between the roll stands,
tensile force exerted on the strip by the tension reel
disposed rearwardly of the roll stands, roll forces,
motor power inputs, roll gap settings and, optionally,
roll bending loads. These process variables, collectively,
determine the setting of the rolling-mill train and must
be calculated for this purpose. The actual setting based
.
on these process variables then requires to be decided
taking into account the specific factors for the installa-
tion, which are determined by the construction of the
installation.
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The reference herein to inter-stand thicknesses
is to be understood to mean the thickness of the
material being rolled between each successive pair of
roll stands.
The process variables summarised above, which require
to be known for setting the train, are calculated on the
basis of strip data for each strip, i.e. entry thickness,
desired exit thickness, strip width, desired surface
roughness and a resistance factor specific for the strip
material. The term "thickness" used here is synonymous
with ~gauge". The said resistance factor is, in this
case, a variable which is representative of the resis-
tance which the material offers against the deformation
imparted to it in the roll stands. Although usually the
tensile strength of the material is employed as a measure
of this resistance, it appears nevertheless that in
practice a more reliable setting of the rolling-mill
train can be achie~ed by employing a resistance factor
~; which is determined from the chemical analysis of the
material and the temperature at which the material is
coiled ~ubsequent to its previous rolling in a hot-strip
rolling mill.
It has appeared that the multiplicity of initial
data, the calculation variables, and the number of
setting values required for the rolling-mill train
make it impossible in practice to achieve, for each strip
to be rolled, a precise setting of the rolling-mill
train within the time available.
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U.S.A. Patent No. 3 641 325 describes a
method of computer control of a rolling mill in
,_
which a plura lity of sets of predetermined mean
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values of the proc~ess variables are employed. From
the actual entry and exit data for the strip, the
most appropriate such set of mean values of the process
variables is selected. Then, linear corrections are
~ade to the mean values of the selected set inlldependence
on the actual strip data, to arrive at the actual
process variables employed for the setting of the
rolling mill.
,
This Patent is mainly concerned with thé operation
of a hot-rolling mill in which rolling temperature
calculations are required, though there is a reference
to cold-rolling mills.
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SUMMARY OF THE I~VENTION
One ~bject of the present invention is therefore
to provide a method of setting a cold-rolling mill
whereby it is possible to achieve adequately precise
setting of the rolling mill train in practice in the
time available. Also, the aim is to achieve optimum
capacity of the rolling;mill train within the permissible
forces and other limiting factors.
~he present invention consists in that
A. in dependence on at least the follcwing three items
of strip data:
(i) the strip entry thickness into th~ train
(ii) the desired strip exit thickness from the train and
: (iii) the desired surface roughness ~f the strip on
exit from the train, the strip is classified into
one of plura lity of thickness groups, each
thickness group having a predetermined set of
standard values relating to
~i) reduction distribution among the
roll stands
. (ii) deformation work: and deformation force
per unit width of the strip,
` (iii) tensile stress between the roll stands
(iv) other influencing factors
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B. the said standard values of the class so chosen are
converted into adapted values by means of linear func-
tions in dependence on the deviations of the actual
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values of said three items of strip data for the
given strip from predetermined standard values for the
thickness group of the said three items of strip
data, the said linear functions having r as their
constants, selected val~es derived in dependence on
the rolling process for the given strip,
~. values of the said process variables are determined
from the said adapted values, and the rolling-mill
train is set for the ~iven strip in accordanc~ with the
, values of the process variables so determined.
~- The invention differs from the disclos~re of US
patent no. 3 641 325 principally in that linear corrections
are applied to standard cond~ons for the selected
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: thickness group, to produce adapted values of these
conditions which are thereafter used to calculate the process
variables. In the priorart disclosure, the corrections
are applied directly to the process variables.
The "other influencing factors" mentioned above can
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be explained as follows. For materials of different widths
and thicknesses (gauges) which may also be rolled at
different speeds, the mill frame will have differences in
deformation, in thicknesses of lubrication films, etc.
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`` 115~32g
~his ~rill affect the shapes and widths of the ~aps between
the rolls of each rollstand, so that these shapes and
widths may be different from the "theoretical" values.
Also the actual gap dimension will be affected by the
~ardually varying wear of the rollers, bearings, etc. All
these deviations between actual and theoretical conditions
should be taken into account in determ n ng the so-called
s~andard ~alues which exist for a specific thickness group.
~ he li~ear functions mentioned above have "constants"
which are in fact variables depending on such items as
gau~e distribution, actual roll diameter, etc. One of these
- ~ariables is the specific resistance factor of the sheet
material.
Furthermore, "a thicXness
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group" is to be understood to mean a table of variables
which, on the basis of an entry thickness, an exit
thickness and a desired surface roughness comprises the
following mutually dependent standard conditions:
reduction distribution, deformation work and deformation
force per width-unit and tensile stress. These stan-
dard conditions are for a material having a given re-
sistance factor which is a function of the influencin~
factors from outside the installation. They are further-
more determined for optimum operational conditions of .
production capacity within the limits permissible for
the installation. It shall be clear that the said thick-
ness groups can be determined partly by an arithmetical
manner, and partly by an empirical manner for a given
installation. In proportion as the number of thickness
groups so determined is greater, each operational
situation actually presenting itself is closer to a
known standard condition. Once the strip presented to
the rolling-mill train is classified into a thickness
group, the standard conditions applicable in the case
of this thickness group are converted to adapted
conditions for this strip before the process variables
required for the setting of the rolling-mill train can
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be computed therefrom as inter-stand thicknesses, strip
~î~ velocity, velocity setting for each roll stand, etc.
, The adapted conditions derived from the standard condi-
tions are now calculated by means of the linearized
`-; functions having the desired thickness ratios prior to
and consequent to the rolling, the actual diameters of
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the work(ing) rolls an~ the varying resistance factor
of the presented material as Yariable influencing variables.
From the literature and from practice, models are known
for the calculation of the above-mentioned setting
varia~les from the adapted standard conditions. The
adapted process variables determined in accordance
with the new method are fed to the rolling-mill train
control system. ~he rolling-mill train control system
then provides for adaptation of the setting values of the
rolling-mill train to the aata applicable ~or the strip
and relating to entry thickness, desired exit thickness,
strip width, desired surface roughness and the specific
resistance factor for the strip material. The
calculations are carried out so that with re~ard to the
required tensile forces in the strip, there is no risk
of strip rupture. However~ considerably deviating
conditions may occur during the threading-through or
tailing-out of the strip fr~m the rolling-mill train.
Thus, according to the invention it is to be recommended
that from the threading of a strip until the build-up
of the tension reel tensile force, and/or from the end
of the uncoiling of the strip supplied, until the
tailout of the strip from the last roll stand, per roll
stand a correction term is supplied to the calculated
velocity and the calculate~ gap adjustment per roll
stand, and also for the velocities of all roll stands
- simultaneously and for the gap settings whenever strip
material is present in a roll stand, the correction
terms being determined by the quotient of the average
exit tbickness in the appropriate thickness group and
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the computed actual exit thickness, both for each roll
stand, multiplied by an empirical factor determined for
each roll stand and for each thickness group. The same
considerations apply with regard to the passage of a
weld in the strip through the rolling-mill train. In
this connection, however, it is preferable that from
the time at which a weld is detected in the strip until
the weld has bee~ passed through all roll stands, per
roll stand and for all roll stands simultaneously, a
correction term is applied to the calculated velocity .
of the roll stands, which said correction term is deter-
mined in a similar manner as with respect to the
correction term during threading and/or tailing-out
of the strip. Further refinement of the method is
afforded by rolling-mill train control with the aid of
a control computer, whereas the calculation of the
adapted variables can take place with the aid o a pro-
cess computer. In a particular embodiment of the method
according to the invention, provision is made for the
occurrence of emergency situations, in which the process
computer cannot be employed. In this embodiment of
the method, the rolling-mill train control is fed
into this emergency situation by a simplified version
of the computation programme, whereby there are expected
very much diminished thic~ness groups which are classified
on the basis of only the desired exit thickness and the
desired surface rou~hness of the strip without correction
possibilities with re~ard to the standard conditions of
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reductions, deformation work and deformation force per
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width-unit, tensile stress and influence factors
outside the installation. However, an adaptation does
take place with reference to the known resistance factor
of the material. It has ~een found that, in this manner,
it is true that an optimum adjust~ent is not achieved
~ut that, in eveIy instance, operation-reliable
performance can be maintained during the period that an
emergency situation lasts.
determination
With regard to the / of the ultimate setting
values for the rolling-mill train, it is important that
the velocities are optimized within the permissible values
of the motor power and the permissible motor r.p.m. for
each of the roll stands. In this connection, it has accord-
ing to the invention been found to be useful to adiust the
velocities of the successiYe roll stands as a function of
the travel of the strip thicknesses through the rolling-
mill train, a slip coefficient which, by a linearized
dependency, is adapted to the tensile force differences
already adapted to each other over the successive roll
stands, the highest permissible values of the motor capa-
city and the permissible motor r.p.m. values for each of
the roll stands. However, since use is made of the adapted
method for emergency situations, it is to be recommended
to adjust the velocities of the successive roll stands as
a function of the travel of the strip thicknesses through
the rolling-mill train, a fixed slip coefficient, the
highest permissible values of the motor power and the
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permissible motor r.p.m. values for each of the roll
stands. In this connection, it should be pointed out
that the travel of the strip thickness through the
rolling-mill train is determined by the reduction
distribution which is determined by the choice of the
thickness group.
In addition to the adjustment of the velocity of
the successive roli stands, an important adjustment
variable of the rolling-mill train is also the roll
gap setting per roll stand. The roll gap sèttings are,
according to the new method, determined on the basis
of the exit thickness of the strip from the roll stand,
the mechanical elongation in the roll housings as a
consequence of the roll forces, velocitîes per roll
stand and the strip width, wherein the roll forces
relative to the standard roll forces for the selected
thic~ness group are adapted in linear fashion to the
resistance factor of the material, the thickness ratios,
the work-roll diameter and the non-compensated weight
of the upper rolls as well as possibly the roll bend-
ing forces. In this, the velocities per roll stand are
adjusted to the method as already discussed previously,
whereas the mechanical elongation in the roll housings,
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in consequence of the roll forces is a known datum for
~! the installation, which can be measured with respect
to a plurality of velocities of the rolls without a
steel strip being present in ~he installation.
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Naturally, also in this case, calculation of the
gap settings per roll stand must be carried out
differently, if an emergency situation occurs. Then,
this gap setting per roll stand must be determined on
the basis of the exit thickness of the strip from this
roll stand, the elongation in the roll housings as a conse-
quence of the roll forces and velocities per roll stand
and the strip width, proceeding in this case from
standard roll weights which possibly are corrected only
with reference to roll weights and bending forces.
.
Control of the rolling-mill train can, in this
manner, take place entirely on the basis of variables,
possibly calculated in a process computer, which are
functions of data characteristic for the strip concerned.
However, further enlargement of the method consists also
in that the experience of previous rollings is taken
into account. This can be effected if, per rolling
of a strip, deviations between measured roll forces and
roll forces provided by computation, motor power and gap
adjustments are determined, and for the two first-
mentioned are introduced as adapted correction relative
to deformation force and deformation work into the
appropriate thickness group of the strip, and the last-
mentioned, the gap settings ~or the purpose of an
adapted correction to the gap-setting computation for
the strip first to be rolled, subsequently. It is even
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~ advisable, as a consequence of the invention, to employ
- such corrections on the basis of comparison between
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computed roll forces and gap adjustments and establishedmeasured values also as adapted correction with reference
to the gap setting computation for the coil first to be
rolled subsequently in that this rolling must be carried
into effect in an emergency situation in which the process
computer is not avai1able
A further refinement of the method consists
consequently in that for each strip, starting from a
tensile force adapted to a resistance factor, strîp width
and inter-stand thickness, there are determined the inter-
stand tension levels which are corrected by the rolling
speeds ana are subsequently fed to an inter-stand
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tension control system. In this manner, there is obtained
a process whereby slip in the roll stands is more satisfac-
torily controllaple and strip ruptures are more satis-
factorily prevented.
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According to yet a further improvement of the
method, for each strip, starting from standard conditions
per thickness group with corrections for resistance factor
and strip width, the roll bending force per roll stand
is determined for varying speed levels of the roll
stand. Therewith, the strip form can be controlled.
.
The invention will now be further illustrated
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`- with reference to block diagrams shown in Figures 1 and 2.
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Figure l illustrates the method according
to the prior art.
Figure 2 illustrates the improved method
according to the invention.
Referring to Figure l, there is schematically
illustrated how, in general, the control of the
rolling-mill train can be effected. From data relating
to the strip process variables are determined via a
computation model. The process variables illustrate
to which process a given strip must be subjected so as to
be able to produce the desired end product. From these
process variables, according to setting values for
the rolling-mill train, it is deter~ined what setting
values are then supplied to a control of the rolling-mill
train. As a rule, the various mathematical processes
required for the determination of the process variables
and for the conversion of the process variables to the
fietting values are to be carried out with the aid of
computers. For the essential understanding of the
invention, however, this is of no importance.
As already stated hereinabove, it shall not be
possible in this manner to attain an accurate adjustment
of the rolling-mill train manipulatable in practice.
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The required m~thematical computation model must have
been expanded in non-manipulatable manner.
Figure 2 illustrates the system of the calculation
model manipulated in accordance with the invention. It
is essential in this that first the strip is classified into
thickness ~roups via a plurality of selected strip data into
a thickness group. In the calculation model, only a
predetermined plurality of thickness groups are manipula-
ted, each corresponding to only one combination of discrete
strip data. In practice, substantially no individual strip
exhibits these strip data in identical fashion, so that
a selected thickness group is only a first approximation-
to the strip which in practice is to be ~olled. For each
thickness group standard conditions of reduction distri-
bution, deformation work, deformation force, tensile stress
between the roll stands and influence factors on the strip
! from outside the installation apply. For a thickness groupthese standard conditions are decisive for the other
process variables from which the setting values for the
rolling-mill train can be derived.
Since, however, for the actual strip these stan-
dard conditions of a closely adjacent thickness group do
not exactly apply, a correction must be applied to the
~; standard conditions, and these corrections lead to adaptedc conditions. Inasmuch as the said ~dapted conditions are
predetermined, it is then possible to derive therefrom the
~ ~ actual process variables and setting values.
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To determine the a~ap~ed conditions from the standard
conditions, there is performe~, a correction on the
basis of deviations in the thickness ratios of the
strip before and after each roll stand, the diameter of
the work rolls an~ the resistance factor applicable
for these strips. With the aid of these deviations,
the standard conditions are corrected, for which purpose
as calculation process the effects of these thickness
ratios, the roll diameters and the resistance factors
to linearized functions are derived
Since~ in the first instance, use is made, for the
strip supplied~ of standard conditions resulting from
the classification into a thickness group, the correct-
ions require on~y-to be so slight (in order to achieve
the aaapted conditions) that it is justifiable to operate
with linearized functions. ~his simplifies the cal-
culation model considerably, whereby in practice improved
processing can ~e achievea.
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