Method of compensating forces in roll stands resulting from horizontal movements of the rolls

A method of compensating forces of force components resulting from horizontal movements of the rolls in roll stands for hot-rolling and cold-rolling of flat products, wherein the roll stands are equipped with work rolls and with one or more back-up rolls, with hydraulic adjusting units and with force measuring devices on the opposite side of the roll gap and with hydraulic devices for the horizontal displacement of the work rolls. The pressures in the two adjusting cylinders are utilized for determining the rolling forces on one side of the roll gap and the forces indicated by the force measuring devices are utilized for determining the rolling forces on the opposite side of the roll gap, and all axial forces in the stand are computed during the rolling operation by including the axial forces of the work rolls which can be determined through the pressures in the displacement cylinders of the work rolls.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method of compensating forces of force 
components resulting from horizontal movements of the rolls in roll stands 
for hot-rolling and cold-rolling of flat products, wherein the roll stands 
are equipped with work rolls and with one or more back-up rolls, with 
hydraulic adjusting units and with force measuring devices on the opposite 
side of the roll gap and with hydraulic devices for the horizontal 
displacement of the work rolls. 
2. Description of the Related Art 
When rolling flat products in hot-rolling plants and cold-rolling plants, 
there is the problem that all participating rolls are axially moved in the 
stand in different directions during the rolling process and produce axial 
forces by pressing against the respectively provided locking means. 
Together with the corresponding reaction forces, these axial forces 
produce free pairs of forces at a distance from the roll center to the 
contact with the neighboring roll. Each of these pairs of forces results 
in reaction forces in the roll bearings and, thus, in the two housing 
posts of the stand. 
FIG. 1 of the drawing illustrates the basic problem, for example, in 
connection with the upper back-up roll 1 of a four-high stand. The 
horizontally acting forces T are linearly aligned vectors, i.e., they can 
be displaced along their lines of influence. Consequently, it is of no 
significance on what side of the stand the roll is locked. Such pairs of 
forces are basically always produced by the axial force in the area of 
contact with the neighboring roll. The individual forces are superimposed 
and manifest themselves in different axial forces at all participating 
rolls and result in reaction forces in the roll housings which are 
difficult to determine. 
The reaction forces in the roll housings show extremely disadvantageous 
effects especially in reversing stands. When the direction of rotation is 
reversed, the srew-type direction of rotation of all participating rolls 
also changes. The rolls travel toward the respectively opposite sides 
which results in a reversal of the axial forces. The reaction forces in 
the roll housings change accordingly, so that the force measuring devices 
arranged in the housings indicate changes which are in no relation to the 
actual rolling process. This results in erroneous reactions of all control 
circuits which depend from the forces measured in the roll housing, such 
as, the planeness control, the automatic calibration for the parallel 
adjustment of the roll gap, the roll alignment control for compensating 
the effects of an eccentric position of the rolled product and other 
control circuits depending on the type of roll stand and rolled product. 
It is already known in the art to determine by computation or by means of 
measuring devices the vertical forces generated in the stand, such as, the 
forces from the own weights, from the roll balancing means and the roll 
bending means, and to take these vertical forces into consideration when 
measuring the forces in the two roll housings. However, such compensations 
have not been carried out for reaction forces from the above-described 
axial forces of the rolls. 
SUMMARY OF THE INVENTION 
Therefore, it is the primary object of the present invention to determine 
with sufficient certainty the reaction forces in the roll housings without 
having to establish additional measuring points in the roll stand. 
In accordance with the present invention, in a method of compensating the 
forces or force components resulting from the horizontal movements of the 
rolls in roll stands of the above-described type, the pressures in the two 
adjusting cylinders are utilized for determining the rolling forces on one 
side of the roll gap and the forces indicated by the force measuring 
devices are utilized for determining the rolling forces on the opposite 
side of the roll gap, and all axial forces in the stand are computed 
during the rolling operation by including the axial forces of the work 
rolls which can be determined through the pressures in the displacement 
cylinders of the work rolls. 
The method according to the present invention makes it possible to 
continuously determine all vagrant forces occurring in a roll stand from 
horizontal movements of the rolls and to compensate the resulting force 
components in the measured rolling forces. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of the disclosure. For a better understanding of the invention, its 
operating advantages, specific objects attained by its use, reference 
should be had to the drawing and descriptive manner in which there are 
illustrated and described preferred embodiments of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Modern roll stands for cold-rolled and hot-rolled flat products are 
equipped today almost exclusively with hydraulic adjustment means 2 as the 
adjusting members for the thickness control. The adjusting cylinders of 
the hydraulic adjustment means are located above the upper back-up roll 
chocks 3 or below the lower back-up chocks 4. 
In a preferred embodiment, force measuring devices 5 are additionally 
provided in the two roll housings on the opposite side of the stand seen 
from the roll gap, wherein the force measuring devices 5 serve the purpose 
of continuously measuring the forces occurring during the rolling process 
in the two roll housings. 
The two hydraulic cylinders of the hydraulic adjusting means provide via 
the hydraulic pressure in a preferred manner additional measurement values 
for the forces in the two roll housings, so that measuring values for the 
forces in the two roll housings above the upper back-up roll chocks and 
below the lower back-up roll chocks are available without additional 
requirements. 
Another feature of modern roll stands for hot-rolling and cold-rolling of 
flat products are displaceable work rolls 6, for example, for influencing 
the roll gap profile or for rendering the roll wear uniform. In a 
preferred embodiment, the displacement of the work rolls 6 is effected by 
means of hydraulic cylinders 7. Independently of whether the two work 
rolls are displaced during a phase of operation or are in a certain 
position, pressures are generated in the hydraulic cylinders 7 in 
dependence on the axial forces emanating from the work rolls 6. 
Consequently, the axial forces of the work rolls can be determined in a 
preferred manner without additional requirements for measuring the 
pressure in the displacement cylinders. As a result, altogether six 
measurement values are available for vertical and horizontal forces in the 
roll stand. 
FIG. 2 shows an analysis of the forces in a roll stand. Shown in FIG. 2 are 
only the forces F from the rolling process and the axial forces T of the 
rolls. The balancing forces, the bending forces and the forces resulting 
from weight are not shown because the compensation of these forces is 
known in the art. 
The statement of the equilibrium conditions for horizontal forces T, 
vertical forces F and moments M at the upper and lower sets of rolls 
results in altogether six equations. These six equations GL shown below 
represent the force equilibrium as follows: 
Top of Stand: 
Vertical Forces F: 
EQU F.sub.w -F.sub.1 -F.sub.2 =0 GL(1) 
Horizontal Forces T: 
EQU T.sub.w -T.sub.1 -T.sub.2 =0 GL(2) 
Moments M: 
EQU F.sub.w .multidot.X-F.sub.1 .multidot.a/2+F.sub.2 .multidot.a/2-T.sub.2 
(r.sub.A +r.sub.s)+T.sub.w (2r.sub.A +r.sub.s)=0 GL(3) 
Bottom of Stand: 
Vertical Forces F: 
EQU F.sub.w -F.sub.3 -F.sub.4 =0 GL(4) 
Horizontal Forces T: 
EQU T.sub.w +T.sub.3 +T.sub.4 =0 GL(5) 
Moments M: 
EQU F.sub.w .multidot.X-F.sub.3 .multidot.a/2+F.sub.4 .multidot.a/2-T.sub.3 
(r.sub.A +r.sub.s)-T.sub.w (2r.sub.A +r.sub.s)=0 GL(6) 
From these six equations, it is possible via mathematical conversions to 
determine the equations for the forces T.sub.1 and T.sub.4 emanating from 
the back-up rolls and the tangential force T.sub.w occurring in the roll 
gap. Thus, all the horizontally acting forces occurring in the stand are 
known. 
FIG. 3 is a compilation of the set of equations. 
Of particular interest for the position of the resulting rolling force in 
the roll gap is the derivation of a deviation X from the center, as seen 
in FIG. 2. This value can also be continuously determined from the six 
measurement values during the rolling operation. The equation for the 
deviation X from center is shown in FIG. 3. The value X can be utilized 
for the automatic calibration, i.e., for automatically placing the two 
work rolls in parallel positions; this is done after a roll change by 
pretensioning the stand without rolled product with rotating rolls and 
computing the eccentricity X from the six measurement values. By carrying 
out a pivoting movement by means of the hydraulic adjusting means, the 
value X is controlled so as to become zero, so that the upper and lower 
rolls are exactly in a parallel position. 
The deviation X from center can also be used for monitoring the rolling 
process, particularly in reversing stands in which the strip or sheet can 
travel from the center of the stand. The deviation X from center can be 
utilized for reporting such events and for carrying out an appropriate 
correction. 
Of course, the automatic calibration and monitoring of the rolling process 
can also be effected in such a way that, instead of the introduction of 
the deviation from center, a correction or compensation of the measured 
forces F.sub.1 through F.sub.4 is effected with the aid of the computable 
reaction forces from the axial forces. The equations for the sum of the 
reaction forces from all participating rolls required for this purpose are 
indicated with R.sub.1 through R.sub.4 in FIG. 4. After such a 
compensation, the measurement values F.sub.1 through F.sub.4 can be 
utilized in the known manner by forming the difference F.sub.1 -F.sub.2 or 
F.sub.3 -F.sub.4 for the calibration of the rolls and for monitoring the 
rolling process. 
The equations for determining the axial forces of the rolls and the 
deviation from center have the particular advantage that the measurement 
values for the axial forces in the upper or lower areas of the stand enter 
the evaluation always as differential values. This produces the result 
that the friction forces contained in the measurement values, particularly 
in the measurement values from the adjusting cylinders, do not enter into 
the evaluation as long as the friction forces are equal on both sides of 
the stand. This is true for a determination of the measurement values 
during opening movements on both sides or closing movements on both sides 
of the hydraulic adjustment means. If a pivoting movement is carried out, 
the friction forces of both stand sides would be added. Consequently, the 
operation is to be carried out in such a way that the determination of the 
measurement values is suppressed during a pivoting movement. 
It has also been found advantageous to utilize the measured and computed 
axial forces T.sub.1 through T.sub.4 and T.sub.w for monitoring the state 
of maintenance and the exactly ground contour of the rolls. Substantial 
wear of the rolls and errors in the way the rolls are ground increase the 
relative inclination of the rolls and lead to increased axial forces. 
Consequently, a display of these forces is an excellent way to 
continuously monitor the rolling mill. 
FIG. 4 of the drawing shows the set of equations for the reaction forces 
from the axial forces and for the reaction forces from the deviation from 
center of the roll force. 
FIG. 5 shows a computation example with assumed roll stand data and rolling 
data and the axial roll forces and reaction forces computed by means of 
the above-described equations. 
While specific embodiments of the invention have been shown and described 
in detail to illustrate the inventive principles, it will be understood 
that the invention may be embodied otherwise without departing from such 
principles.