Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR PROVIDING AT LEAST ONE WORK ROLL
FOR ROLLING ROLLING STOCK
The invention concerns a method for preparing at least
one work roll for the rolling of preferably strip-shaped
rolling stock, wherein the work roll is provided to interact
with a second roll, especially an intermediate roll or backup
roll, and to be supported by this roll, and wherein the axial
end regions of the second roll have a setback.
In particular, when very wide plate is being rolled
(e.g., width greater than 3,000 mm), undesired profile shapes
sometimes develop in the strip, especially W-shaped profiles
and ridge formation near the edges and flatness defects
(quarter waves) in the final product.
This can be attributed, among other things, to the fact
that during the rolling of wide strips or plates it happens
that the outer regions of the rolling stock are located in the
area of the setback of the backup rolls or intermediate rolls
or, in the case of extended work rolls, actually lie outside
the edges of the barrels of the backup rolls or intermediate
rolls. The work roll bends back in these regions, and as a
result of this, a nonparabolic profile shape can develop in
the roll gap, namely, e.g., the aforementioned ridge
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formation. High rolling forces and work roll bending forces
can intensify this effect.
The rolling stock profile is the distribution of the
thickness of the rolling stock over its width. Rolling stock
profiles that deviates greatly from the parabolic form are
generally undesirable, since they can lead to nonflatness in
the rolling process or in the downstream processes. In
addition, the accuracy to gage of the product can be adversely
affected.
The application of roll cuts to work rolls for
systematically affecting the roll gap profile is already
known. For example, EP 0 294 544 B1 provides that the work
roll is provided with a profile that is described by a
polynomial. EP 1 307 302 B1 proposes a similar solution, in
which a so-called CVC profile is provided. Other similar and
different solutions are disclosed in EP 1 703 999 B1, EP 0 937
515 B1, JP 3032412 A, JP 9253726 A, DE 39 19 285 Al, JP
8332509 A, JP 6015322 A, and JP 2179308 A. The profiles
applied on the work roll are thus parabolic contours or
contours described by polynomials. In the latter case, when
an axial work roll shifter is present and shifting is used as
a profile correcting element, the S-shaped contours described
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by the aforesaid polynomials are applied to the roll (CVC
cut).
The application of special contours to reduce edge drop
or to reduce ridge formation is also well known. The goal
here is to influence the rolling stock profile contour in the
immediate edge region in order to compensate effects of work
roll flattening in the roll gap or of thermal expansion of the
work roll on the roll gap profile.
The prior art cited above does not provide practical
advice on how good rolling results can be achieved despite
furnishing backup rolls or intermediate rolls with a setback.
But this is precisely why the aforementioned problems occur,
especially in the case of very wide strips.
Therefore, the objective of the invention is to propose a
method for preparing a work roll of the type described at the
beginning, with which it is possible, even when there is a
corresponding setback of the backup roll or intermediate roll,
to achieve optimum rolling, i.e., to roll a strip that is
characterized by high quality and the desired shape.
Accordingly, undesirable nonparabolic effects of the backup
roll or intermediate roll setback on the roll gap profile
shape are to be largely compensated. The provision of the
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work rolls with a special cut (e.g., CVC cut) should not be
compromised.
The solution to this problem by the invention is
characterized in that the method for preparing at least one
work roll for the rolling of preferably strip-shaped rolling
stock has the following steps:
(a) computation of the roll gap profile that is formed
between two interacting work rolls, where a defined width of
the rolling stock is assumed, which extends at least partially
into the region of the setback of the second roll;
(b) definition of a desired rolling stock contour that is
to be produced by the rolling process during passage through
the work rolls;
(c) computation of a compensation cut for the work roll
by subtraction of the rolling stock contour defined according
to step (b) from the roll gap profile according to step (a)
and multiplication of the computed difference by a damping
factor;
(d) at least proportional application of the compensation
cut computed according to step (c) to at least one work roll.
The compensation cut according to step (c) can be
superimposed on another profiling of the work roll. This
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other profiling of the work roll is preferably a parabolic
profiling or an S-shaped profiling (so-called CVC profiling).
The damping factor for the computation according to step
(c) is preferably 0.3-0.9 and more preferably 0.4-0.8. A
value of 0.6 has been found to be especially effective. The
factor is chosen in such a way that for the broad strips or
products, ridge-shaped profile forms no longer arise or the
ridges are greatly reduced, and for narrower dimensions of the
strip, no disturbing effects or only slightly disturbing
effects arise.
In accordance with a preferred embodiment, the
computation according to step (a) is based on the maximum
width provided for the rolling stock that is to be rolled with
the work rolls.
The computation according to step (a) is preferably based
on a well-defined rolling force and a well-defined work roll
bending force. The definition according to step (b) is
preferably based on the same parameters as in step (a).
It is advantageous for the profile that is to be defined
in accordance with step (b) to be based on a roll gap profile
computed offline. In this case, it can be provided that the
roll gap profile computed offline is based on an extended
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backup roll barrel, so that the edges of the rolling stock are
not located in the region of the setback of the second rolls.
Accordingly, the proposed method provides a work roll cut
to compensate the bending behavior of the work roll in the
region of the backup roll setback. A possibly desired special
roll cut (e.g., a CVC cut) is superimposed on the compensation
cut provided in accordance with the invention.
An essential feature of the proposed cut is that the
effect of the setback compensation is almost independent of
the axial shift position of the work rolls to each other, so
that in the case of shiftability of the work rolls, this
effect is effective over the entire shift range.
The compensation cut can be used both on work rolls that
can be axially shifted and on work rolls that cannot be
shifted.
It can be proportionally applied to only one work roll or
to the upper and the lower work roll.
The compensation cut can be combined with any desired
roll cut, i.e., it can be superimposed on it. The height of
the cut can be varied according to the current work roll
diameter. The height can also be adapted to the current
backup roll contour or intermediate roll contour (with respect
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to wear).
The cut can be described, for example, by a sequence of
points or by a mathematical function (e.g., by a polynomial
function).
The drawings illustrate a specific embodiment of the
invention.
-- Figure 1 is a schematic drawing of the work rolls and
backup rolls of a four-high rolling stand during the rolling
of strip-shaped rolling stock, viewed in the direction of
rolling.
-- Figure 2 shows the variation of the roll gap, i.e.,
the height of the roll gap over the width less the height in
the center, between two work rolls over the width of the
rolling stock during the rolling of the rolling stock without
the use of the method of the invention.
-- Figure 3 shows the variation of the roll gap between
two work rolls over the width of the rolling stock as a target
contour (ideal profile shape).
-- Figure 4 shows the variation of the roll gap between
the work rolls over the width of the rolling stock as the
difference contour between the target contour according to
Figure 3 and the variation according to Figure 2.
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-- Figure 5 shows the variation of a compensation cut for
the work rolls over the width of the rolling stock.
-- Figure 6 shows the effect of the compensation cut
(supplementary cut) over the width of the rolling stock for
different axial shift positions on the unloaded roll gap.
-- Figure 7 shows the variation of the roll gap between
two work rolls over the width of the rolling stock with the
use of the compensation cut according to Figure 5.
Figure 1 shows two work rolls 1, 2, which are part of a
four-high rolling stand (which itself is not shown). The work
rolls 1, 2 are supported in a well-known way by backup rolls
4, 5. The rolling stock 3 that is to be rolled, which in the
present case is a strip with a width B of 3,100 mm, is located
between the work rolls 1, 2.
In their lateral regions, i.e., their axial end regions,
the backup rolls 4, 5 have a setback 6, i.e., the profile is
set back compared to a pure cylinder. In Figure 1 this is
shown with strong exaggeration.
Accordingly, for the embodiment illustrated here, this
has the following consequence: Full support of the work rolls
1, 2 by the backup rolls 4, 5 is provided only in the middle
region over a distance of 2,050 mm, since each setback 6 in
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the two lateral regions extends over a distance of 500 mm.
The work rolls, which have a length of 3,450 mm, extend beyond
the width B of the rolling stock 3 of 3,100 mm.
The work rolls 1, 2 are acted upon not only by the
support forces of the backup rolls 4, 5 but also by work roll
bending forces FB and the rolling forces themselves, so that
the work rolls experience reverse bending, which is indicated
by the arrows 7.
The reverse bending of the work rolls in the area of the
setback 6 of the backup rolls thus depends on the rolled width
of the rolling stock 3, the rolling force that is applied, and
the work roll bending force FB that is set. Therefore, the
choice of a frequently rolled large width of the rolling stock
and of a mean rolling force that is customary for the last
passes of a pass program and a bending force (balancing force)
at a low level are advantageous for the cut configuration. In
this regard, we can initially proceed from average roll
diameters. The roll cambers are chosen in each case in such a
way that the computed roll gap profiles fall within the usual
range (about 0.000 mm to 0.200 mm).
In a first step of the work roll configuration or
preparation, the roll gap profile to be expected is computed
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for the rolling stand to be considered under the aforesaid
boundary conditions for the maximum width to be rolled. An
example of the result of such a computation is shown in Figure
2. Here we see the shape of the roll gap profile for a
rolling stock width of 3,100 mm without compensation of the
reverse bending effect. It is clearly seen that the profile
takes an undesired course in the lateral region of the strip
due to the reverse bending of the work rolls.
After this profile has been determined, an ideal rolling
stock contour is defined for the same case. This can be, for
example, a roll gap profile computed offline under the
assumption of an extended backup roll barrel, so that the
edges of the rolling stock are not located in the area of the
setback 6 of the backup rolls. This ideal profile shape is
shown in Figure 3 as an example of a target contour, again for
a strip with a width of 3,100 mm.
In the next step, the undesired profile component
produced by the reverse bending effect is determined by
subtracting the target contour (according to Figure 3) from
the roll gap shape without compensation cut (according to
Figure 2). This is illustrated in Figure 4. Sketched here is
thus the difference contour between the target contour and the
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roll gap shape without compensation, again for a strip with a
width of 3,100 mm. The solid curve is the roll gap shape
without compensation cut, while the dot-dash curve indicates
the target contour. Accordingly, the broken curve represents
the difference contour that is needed to compensate the
reverse bending effect.
The compensation cut for the work roll is obtained by the
difference contour according to Figure 4, where the difference
that is determined is multiplied by a damping factor K of,
e.g., 0.7. This factor is chosen in such a way that in the
case of broad strips, ridge-shaped profile forms do not arise,
while in the case of narrower dimensions of the strip, no
disturbing effects or only slightly disturbing effects arise.
The compensation cut for application to both work rolls
1, 2 is shown in Figure 5. The graph shows the radius
deviation (ar) over the barrel length.
If the compensation cut is to be applied to only one work
roll, its height is doubled accordingly.
In the region near the rolling stock towards the edges of
the barrel, the contour should run out harmonically, as is
indicated in Figure 5 with reference number 8.
The effect of the supplementary cut on the unloaded roll
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gap is illustrated in Figure 6 for different axial shift
positions. The solid line indicates the curve that is
obtained with work rolls 1, 2 that have not been axially
shifted. On the other hand, the broken line shows the curve
that is obtained when the upper and lower work rolls are
shifted relative to each other by 150 mm. Figure 6 thus shows
the effect on the unloaded roll gap as a function of the axial
shift position. It is apparent that even in the case of a
relatively large axial shift of the rolls, the desired effect
remains largely constant.
Finally, Figure 7 shows the resultant roll gap shape
obtained with the use of the compensation cut. The
improvement that is realized in the profile shape is apparent
from a comparison of this contour with the original contour
without compensation cut according to Figure 2.
When a six-high rolling stand is used instead of the
four-high rolling stand illustrated here, similar results are
obtained, but in this case the backup roll is replaced by the
intermediate roll.
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List of Reference Numbers and Letters
1 work roll
2 work roll
3 rolling stock
4 second roll (intermediate roll, backup roll)
second roll (intermediate roll, backup roll)
6 setback
7 bending direction (reverse bending of work roll)
8 harmonic runout
B width of the rolling stock
K damping factor
FB work roll bending force
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