Rolling mill and rolling method

To provide a rolling mill in which work rolls being supported horizontally by static pressure bearings wherein, even under the action of an excessive horizontal force, preventing contact between the work rolls and the static pressure bearings to ensure the production of a strip product free of flaw and superior in its surface quality. Work rolls are supported by static pressure bearings through idler rolls. The amount of offset of the work rolls are changed respectively by moving devices through static pressure bearings. Further, pushing cylinders generate a certain force through the static pressure bearings to bear the force provided from the moving devices.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a rolling mill and rolling method for 
rolling a plate. Particularly, the invention is concerned with a rolling 
mill and rolling method using work rolls of a small diameter and suitable 
for rolling a hard or ultra-thin strip. 
2. Description of the Prior Art 
Heretofore, working rolls of a small diameter have been used for rolling a 
hard or ultra-thin strip such as stainless steel strip. With a decrease in 
diameter of the work rolls, the flexural rigidity of the rolls becomes 
lower inevitably. Particularly, deflection in a horizontal plane poses a 
problem. This horizontal deflection causes a more marked disturbance in 
the shape (flatness) of the strip used. The horizontal deflection 
sometimes exceeds the correction capacity of a shape correcting device 
such as the work roll bender which has heretofore been used. If the rolls 
deflect vertically in opposite directions, the central portions of the 
upper and lower work rolls undergo forces acting in opposite directions, 
which forces promote the vertical opposite deflections in an accelerative 
manner. In this case, if the rolling load is set large, the rolls may be 
broken. In order to prevent the occurrence of such a trouble, the 
application of a large load must be avoided. 
In view of the above points, there have been developed Cluster mill type 
rolling mills, including Sendzimir mill, as well as a rolling mill having 
a horizontal deflection preventing mechanism wherein the drum portions of 
work rolls are supported horizontally with support rolls such as that 
disclosed in Japanese Patent Laid Open No.18206/85. In these rolling 
mills, however, since the support rolls are divided in the direction of 
the roll drum length, the surface properties of the plate rolled are 
deteriorated due to mark transfer by the divided support rolls. 
As a rolling mill which takes into account the prevention of such 
deterioration in the plate surface properties and which permits the use of 
work rolls of a small diameter, there has been developed such a rolling 
mill as disclosed in Japanese Patent Laid Open No.50109/93. In this 
rolling mill, horizontal support rolls are mounted outside the area 
through which the maximum width of the strip to be rolled passes, then a 
horizontal deflection of each work roll is detected and a horizontal 
bending force of the roll is controlled so that the horizontal deflection 
thereof becomes equal to zero. At the same time, the work rolls are each 
moved to a position where the horizontal force which causes the horizontal 
deflection is zero. Since a horizontal support device for the strip is not 
present in the area where the strip passes, it is possible to prevent the 
deterioration of surface properties attributable to such horizontal 
support device. 
In the rolling mill disclosed in the above unexamined publication 50109/93, 
however, a limit has so far been encountered in reducing the diameter of 
each work roll. More particularly, if the work roll diameter is set below 
a certain value, the flexural rigidity becomes extremely low, and the 
responsivity in horizontal deflection control also encounters a limit, 
resulting in that it becomes no longer possible to make the horizontal 
deflection zero. Actually, in the rolling mill of the type described in 
the above unexamined publication, it is considered that a roll diameter of 
10% or so of the maximum strip width is the limit in reducing the roll 
diameter. It has been difficult to make the roll diameter still smaller. 
For the simplification of a rolling mill and for the reduction in diameter 
of working rolls, a rolling mill having a support mechanism which prevents 
the deflection of work rolls on an incoming side of the rolls is disclosed 
in Japanese Patent Laid Open No.94509/84. The support mechanism is 
provided with a cooling means using adjustment of liquid pressure to 
prevent friction caused by the support. Each work roll is provided with a 
shifting mechanism so as to adapt itself to changes in rolling conditions 
(for example the plate to be rolled). According to such a technique, the 
deflection of work rolls can be prevented to some extent, but no 
consideration is given to diminishing the horizontal force. Besides, since 
the shifting mechanism is provided on the work roll itself, the deflection 
of the work roll is influenced by a shifting motion. It has so far been 
difficult to effect shifting while minimizing the deflection of each work 
roll. 
Further, as a rolling mill suitable for preventing the foregoing 
deterioration of the strip surface properties and for attaining a further 
reduction in diameter of work rolls, a rolling mill provided with a 
horizontal support mechanism for work rolls, using static pressure 
bearings, is disclosed in Japanese Patent Publication No.13366/96. This 
rolling mill is constructed schematically as in FIG. 17 for example. As 
shown in the same figure, work rolls 102 and 103 for rolling a strip 101 
are supported vertically by means of intermediate rolls 104,105 and back 
up rolls 106,107 and are supported horizontally by means of static 
pressure bearings 112,113,114 and 115 through idler rolls 108,109,110 and 
111. 
In the rolling mill disclosed in the Japanese patent publication 13366/96 
such as that shown as an example in FIG. 17 in which the work rolls 102 
and 103 are supported horizontally by means of static pressure bearings 
112,113,114 and 115, there have been the following points to be further 
improved. 
In the rolling mill shown in FIG. 17, the work rolls 102 and 103 are 
mounted centrally of the rolling mill. On the other hand, where the work 
roll diameter is reduced, it is impossible to drive the work rolls 
directly because a high strength of their driving shafts is to be ensured. 
It is unavoidable for the working rolls to be driven indirectly through 
back up rolls or intermediate rolls. Consequently, a tangential force 
acting in the horizontal direction is developed at the time of imparting a 
rolling torque to the work rolls through the back up rolls or the 
intermediate rolls. Under rolling conditions involving a large torque, the 
driving tangential force (horizontal force) also becomes large, so that an 
excessive force is also imposed on the static pressure bearings which bear 
the force. Therefore, if the fluid pressure fed to the static pressure 
bearings is not sufficient, it is impossible for the bearings to bear the 
horizontal force, with the result that the rolls and bearing pads of the 
static pressure bearings come into contact with each other and both are 
flawed. The flaws on the work rolls are inevitably transferred onto the 
strip being rolled, thus deteriorating the strip quality markedly. On the 
other hand, if the flaws on the bearing pads are left as they are, the 
fresh rolls after roll replacement will also be flawed. For this reason, 
it is necessary to replace the bearing pads themselves. This roll 
replacing work requires much time, thus leading to deterioration of the 
productivity. Besides, repair of the bearing pads costs much because the 
bearing pads require a high fabrication accuracy. Thus, the contact 
between the work rolls and the bearing pads of the static pressure 
bearings caused by the aforesaid excessive horizontal force results in 
great damage. 
For preventing such an inconvenience as mentioned above, it is necessary to 
take an appropriate measure, for example, let the oil pressure fed to the 
static pressure bearings have a margin. To this end, it is inevitably 
required to use a pump and a tank, resulting in an increase of the 
equipment cost and of the power cost. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a rolling mill and 
rolling method wherein work rolls are supported horizontally by means of 
static pressure bearings and which, during rolling, can prevent contact 
between the work rolls and the static pressure bearings even under the 
action of an excessive horizontal force, thereby affording a rolled 
product free of flaws and superior in the surface quality. 
According to the present invention, in order to achieve the above-mentioned 
object, there is provided a rolling mill having at least a pair of work 
rolls for rolling a strip, also having at least a pair of back up rolls 
for driving the work rolls, and further having static pressure bearings 
which support side faces of the work rolls horizontally using a fluid 
pressure over a range not smaller than the maximum width of the strip to 
be rolled, the static pressure bearings being mounted on both work roll 
incoming side and outgoing side, characterized in that moving means for 
moving the work rolls horizontally toward the incoming side and outgoing 
side are attached to the static pressure bearings. 
Thus, in the present invention, moving means are attached to the static 
pressure bearings to move the work rolls toward the incoming side and the 
outgoing side, thereby changing the amount of offset of the work rolls. By 
so doing, a component force of the rolling load, driving tangential force, 
and front and rear tensions imposed on the plate to be rolled, can be 
balanced and the total horizontal force exerted on the work rolls can be 
maintained at an allowable value (a limit value associated with contact 
between the work rolls and the bearing pads of the static pressure 
bearings) or less. Consequently, it becomes possible to prevent the work 
rolls from coming into contact with the bearing pads of the static 
pressure bearings under the action of an excessive horizontal force. 
Preferably, in the present invention, horizontal force measuring means for 
measuring a horizontal force applied to each static pressure bearing are 
attached to the static pressure bearings located on at least one of the 
incoming side and the outgoing side. 
Preferably, not only the moving means are attached to the static pressure 
bearings located on one of the incoming side and the outgoing side, but 
also pushing force generating means for generating a pushing force which 
resists the force developed by the moving means are attached to the static 
pressure bearings located on the other side. 
Preferably, there are used floating measuring means for measuring to what 
degree the rolls supported by the static pressure bearings float relative 
to the same bearings. 
Preferably, feed pressure control means are used to control the fluid 
pressure to be fed to the static pressure bearings in accordance with the 
horizontal force measured by the horizontal force measuring means. 
Preferably, static pressure bearing control means are used for moving the 
static pressure bearings to positions where the horizontal force measured 
by the horizontal force measuring means is of a predetermined value or 
smaller. 
Preferably, moving means control means are used to control the work roll 
moving means in such a manner as to move the work rolls to positions where 
the horizontal force measured by the horizontal force measuring means is 
of the predetermined value or smaller. 
According to the present invention, there is also provided a rolling method 
which comprises measuring the horizontal force applied horizontally to the 
static pressure bearings by the horizontal force measuring means and, in 
accordance with the horizontal force thus measured, controlling the force 
to be generated by the pushing force generating means. 
There is also provided a rolling method which comprises measuring the 
amount of floating of the work rolls relative to the static pressure 
bearings by the floating measuring means and, in accordance with the 
amount of floating thus measured, controlling the position of each work 
roll in the incoming and outgoing direction, or controlling the force to 
generated by the pushing force generating means, or controlling the fluid 
pressure to be fed to the static pressure bearings. 
In the above construction, for example, when the value of horizontal force 
applied to the static pressure bearings and measured by the horizontal 
force measuring means is close to the allowable value, the pushing force 
created by the pushing force generating means may be set small. For 
example, moreover, when the value of horizontal force applied to the 
static pressure bearings and measured by the horizontal force measuring 
means is close to the value allowable for the same bearings, the fluid 
pressure fed to the bearings may be increased and the allowable value 
itself increased. 
Further, instead of measuring the horizontal force, there may be adopted a 
method wherein the amount of floating of the work rolls relative to the 
static pressure bearings, i.e., the distance between the rolls and bearing 
pads, is measured by the floating measuring means, and for example when 
the amount of floating thus measured becomes a certain value or smaller, 
the position (offset) of the work rolls in the incoming and outgoing 
direction is changed, or the force developed by the pushing force 
generating means is decreased, or the fluid pressure fed to the static 
pressure bearings is increased. 
In the rolling mill described above, idler rolls are preferably disposed 
between the work rolls and the static pressure bearings. With the idler 
rollers thus disposed, even if the diameter of each work roll is changed 
by on-line grinding, it is possible to keep high the accuracy of the 
amount of roll floating and the pushing force relative to the static 
pressure bearings. Besides, the replacement of work rolls becomes easier. 
Preferably, in the static pressure bearings are formed a plurality of fluid 
feed holes in the plate width direction. The fluid feed holes are 
preferably varied in diameter in the strip width direction. By so doing, 
when the working rolls swell in the middle due to thermal expansion, the 
amount of floating at both end portions in the strip width direction can 
be increased and hence it is possible to support the rolls uniformly and 
stably. 
According to the present invention, moreover, there is provided a rolling 
method using the rolling mill described above, which method comprises 
measuring horizontal forces applied horizontally to the static pressure 
bearings on both operating side and driving side by the horizontal force 
measuring means and, in accordance with the difference between the 
horizontal force on the operating side and that on the driving side, 
controlling the difference between the fluid pressure fed to the static 
pressure bearings on the operating side and that on the driving side, or 
controlling the difference between the force generated by the pushing 
force generating means on the operating side and that on the driving side. 
Further, according to the present invention there is provided a rolling 
method using the rolling mill described above, which method comprises 
measuring the amounts of floating of the work rolls relative to the static 
pressure bearings at least two points in the strip width direction and, in 
accordance with the difference between the measured amount of floating on 
the operating side and that on the driving side, controlling the 
difference between the fluid pressure fed to the static pressure bearings 
on the operating side and that on the driving side, or controlling the 
difference between the force generated by the pushing force generating 
means on the operating side and that on the driving side. 
Thus, since the difference in the fluid pressure fed to the static pressure 
bearings between the operating side and the driving side or the difference 
in the force generated by the pushing force generating means between the 
operating side and the driving side is controlled, when an excessive 
horizontal force is applied to a certain portion in the strip width 
direction, it is possible to increase the fluid pressure in that portion 
of a large horizontal force, or the pushing force generated by the pushing 
force generating means can be diminished at that portion of a large 
horizontal force to thereby diminish the total horizontal force applied to 
the static pressure bearings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A rolling mill according to the first embodiment of the present invention 
will now be described with reference to FIGS. 1 to 6. In the rolling mill 
of this embodiment, as shown in FIG. 1, work rolls 2 and 3 for rolling a 
plate 1 are supported vertically by intermediate rolls 4,5 and back up 
rolls 6,7. The intermediate rolls 4 and 5 are connected to a motor (not 
shown), and the work rolls 2 and 3 are driven by the intermediate rolls 4 
and 5. On the other hand, the work rolls 2 and 3 are horizontally 
supported by static pressure bearings 12,13,14 and 15 through idler rolls 
8,9,10 and 11. The static pressure bearings 12 to 15 are respectively 
mounted to beams 16,17,18 and 19 of sufficient rigidity. The beams (18 and 
19 in this embodiment) located on either the incoming side or the outgoing 
side are respectively provided with moving devices (moving means) 20 and 
21 for moving the beams in the incoming and outgoing direction. The moving 
devices 20 and 21, which are secured to a housing of the rolling mill, are 
of a structure in which the beams 18 and 19 are moved in the horizontal 
direction by turning screws. With this structure, the position of the work 
rolls 2 and 3 in the incoming and outgoing direction with respect to the 
shafts of the intermediate rolls 4 and 5, i.e., offset "y", can be varied. 
Since the idler rolls 8,9,10 and 11 are provided, even in the event the 
work rolls 2 and 3 are changed in diameter by on-line grinding, the amount 
of floating of the work rolls, as well as pushing force thereof, can be 
maintained high in accuracy. Besides, the replacement of the work rolls 2 
and 3 becomes easy. 
Pushing cylinders (pushing force generating means) 22 and 23 are attached 
to the beams 16 and 17 with the moving devices 20 and 21 not connected 
thereto, whereby the work rolls 2 and 3 are pushed horizontally with a 
certain force. The forces applied horizontally to the work rolls 2 and 3 
are measured respectively by load cells (horizontal force measuring means) 
24 and 25. By setting the amount of offset y of the work rolls 2 and 3 at 
an appropriate value determined by rolling load, rolling torque, and front 
and rear tensions, the (total) amount of horizontal forces imposed on the 
work rolls 2 and 3 can be set equal to zero (or an allowable value close 
to zero or less). 
How to calculate the amount of offset, y, for setting the horizontal forces 
applied to the work rolls 2 and 3 at a value equal to zero (or an 
allowable value close to zero or less) will now be described with 
reference to FIG. 2. The horizontal force, S, applied to the work roll 2 
(or 3) is represented by the following equation: 
EQU S=FT-FP+(Tb-Tf)/2 (1) 
where Tb stands for an incoming-side tension imposed on the strip 1, Tf 
stands for an outgoing-side tension imposed on the strip, FT stands for a 
driving tangential force based on torque T of the intermediate roll 4 (or 
5), and FP stands for a horizontal component force of a rolling load P. FT 
and FP are represented as follows: 
EQU FT=T/RI (2) 
EQU FP=P.multidot.y/(RI+RW) (3) 
where RI stands for the radius of the intermediate roll 4 (or 5) and RW 
stands for the radius of the work roll 2 (or 3). 
If the horizontal force S in the above equation (1) is set at 0, the amount 
of offset, y, in this condition is given by the following equation: 
EQU y=(T/RI+(Tb-Tf)/2).multidot.(RI+RW)/P (4) 
In the above equation (4), the rolling load P, torque T, and tensions Tb 
and Tf, can be calculated if rolling conditions are determined. As to the 
roll diameters RI and RW, they are known inevitably. Therefore, before the 
start of rolling, an appropriate offset y can be obtained from the 
equation (4). 
Thus, if rolling is started after setting the work rolls 2 and 3 at 
respective positions offset by the above y to the outgoing side, it is 
possible to prevent an excessive horizontal force from being applied to 
the work rolls 2 and 3 by rolling and hence it is possible to prevent an 
excessive load from being imposed on the static pressure bearings 12 to 
15. In addition to the horizontal force S of equation (1) developed by 
rolling, a pushing force Q generated by the pushing cylinders 22 and 23 is 
also applied to the static pressure bearings 12 and 13. The pushing force 
Q is for stabilizing the working rolls 2 and 3 so as not to become 
unsteady and it is a small force lest damage should be done to the static 
pressure bearings 12 and 13. 
FIG. 3 is a top view of the static pressure bearing 12. Oil for floating, 
which is fed from an oil pressure source (not shown), passes through a 
main oiling hole 26, then through oiling holes 27 to 32 of a small 
diameter, and further flows into oil pockets 33,34 and 35, causing the 
roll (idler roll) 8 to float. The amount of floating of the roll 8 is 
measured by gap measuring devices 36,37 and 38 and the measured values are 
converted to electric signals respectively by amplifiers 39, 40 and 41. As 
shown in the figure, the gap measuring devices 36,37 and 38 are used 
respectively for floating detections on the driving side, central portion 
and operating side. 
FIG. 4 is a vertical sectional view of the oiling hole 27 and the vicinity 
thereof, and FIG. 5 is a vertical sectional view of the gap measuring 
device 36 and the vicinity thereof. The other oiling holes and gap 
measuring devices are also of almost the same constructions. A large 
diameter of the oiling holes 27 to 32 results in an increase of flow rate 
and so does the amount of floating of the roll 8, but the amount of 
displacement upon exertion of an external force on the roll 8 also becomes 
large. In other words, the spring constant of the static pressure bearings 
12 to 15 becomes smaller. Conversely, if the diameter of the oiling holes 
27 to 32 is small, the amount of floating of the roll 8 becomes small, but 
the spring constant of the static pressure bearings 12 to 15 becomes 
large. Therefore, it is necessary that the aforesaid characteristics be 
taken into account in determining the diameter of the oiling holes 27 to 
32. 
It is also possible to change the characteristics of the static pressure 
bearings 12 to 15 intentionally by making the oiling holes 27 to 32 
different in diameter according to positions in the width direction of the 
plate 1. FIG. 6 shows an example thereof, in which oiling holes 27a, 28a, 
31a and 32a formed in both end portions are larger in diameter than oiling 
holes 29a and 30a formed in the central portion. According to this 
construction, when the central portion swells due to thermal expansion of 
rolls (work rolls 2,3 and idler rolls 8 to 11), the amount of floating of 
the work rolls at both end portions in the plate width direction can be 
increased according to the swelling, whereby the working rolls can be 
supported uniformly and stably. The structures of the static pressure 
bearing 12 mentioned above in connection with FIGS. 4 to 6 are common to 
the static pressure bearings 13.about.15. 
In this embodiment, as described above, since the moving means 20 and 21 
are attached to the static pressure bearings 14 and 15 to move the work 
rolls 2 and 3 in the incoming and outgoing direction, thereby making the 
amount of offset, y, adjustable, the component force FP of the rolling 
load P, the driving tangential force FT, and the front and rear tensions 
Tf, Tb imposed on the plate 1, can be balanced, whereby the total 
horizontal force S can be maintained to 0 or at less than an allowable 
value close to 0. Therefore, it is possible to prevent the idler rolls 8 
to 11 from coming into contact with the bearing pads of the static 
pressure bearings 12 to 15 under the action of an excessive horizontal 
force. Thus, it is possible to always obtain a strip product free from 
flaws and superior in its surface quality. 
Description is now directed to a rolling mill according to the second 
embodiment of the present invention. Although only an upper half of the 
rolling mill will be described, the same is true also of a lower half of 
the rolling mill (this can be said also of the embodiments which follow). 
In FIG. 7, the same components as in the preceding figures are indicated 
by the same reference numerals as in those figures. 
In FIG. 7, a horizontal force generated in the work roll 2 in rolling is 
measured by the load cell 24. The force So detected by the load cell 24 is 
the sum of the force S of equation (1) and pushing force Q developed by 
the pushing cylinder 22. That is, the following equation is established: 
EQU S.sub.0 =S+Q (5) 
The force So detected by the load cell 24 is outputted to a calculator 42, 
which in turn subtracts the pushing force Q from the detected force in 
accordance with the above equation (5) to calculate the horizontal force S 
generated by rolling. The pushing force Q is detected by a pressure 
detector 43 and is outputted to the calculator 42. However, since the 
value of Q is usually a constant value, it may be given as a constant to 
the calculator 42 by means of a setting device provided separately. A 
controller 44 receives the value S obtained in the calculator 42 and, when 
S is a positive value, outputs to the moving device 20 a signal for 
shifting the offset y of the work roll 2 by only a very small amount 
.DELTA.y in the positive direction (rightward in the figure), while when S 
is a negative value, outputs to the moving device 20 a signal for shifting 
the offset y by .DELTA.y in the negative direction (leftward in the 
figure). In this way the change of offset using .DELTA.y is repeated until 
S becomes zero. In this case, instead of repeating the shifting until S 
becomes equal to zero, there may be provided a so-called dead band whereby 
the change of offset is stopped when the absolute value of S has reached a 
certain small value or less. 
According to this second embodiment described above, not only the same 
effect as in the first embodiment can be obtained, but also the force 
applied to the static pressure bearings 12 and 14 can be always maintained 
within an appropriate range and hence it is possible to prevent the 
occurrence of flaws in the work roll 2, idler rolls 8,10 and static 
pressure bearings 12,14. 
The third embodiment of the present invention will be described below with 
reference to FIG. 8, in which the same components as in the figures 
referred to above are indicated by the same reference numerals as in those 
figures. 
In FIG. 8, a horizontal force applied to the static pressure bearing 14 is 
measured by the load cell 24. The value of S.sub.0 detected by the load 
cell 24 is fed to a calculator 45, which in turn compares it with a limit 
pressure resistance value S.sub.max of the static pressure bearing 14. 
When S.sub.0 becomes larger than S.sub.max, the calculator 45 outputs a 
pressure increasing signal to a pressure regulator 46 disposed in an oil 
pressure system for floating. The amount of increase in pressure, 
.DELTA.p, is assumed to take the following value which is proportional to 
an amount exceeding S.sub.max : 
EQU .DELTA.p=.alpha..sub.1 (S.sub.0 -S.sub.max) (6) 
where .alpha..sub.1 is a constant. However, when .DELTA.p of equation (6) 
is negative, the reduction of pressure is not performed. On the other 
hand, to the static pressure bearing 12 on the pushing cylinder 12 side is 
fed oil held at a constant pressure by means of a pressure regulator 47. 
Alternatively, .DELTA.p may be a constant value. 
According to this third embodiment described above, not only the same 
effect as in the first embodiment is obtained, but also, when an excessive 
force is exerted on the static pressure bearing 14, an allowable load of 
the bearing 14 itself is increased by increasing the oil pressure fed, 
whereby it is possible to prevent contact and flaws of the roll 10 and the 
bearing 14. Besides, there is no fear of an excessive force being imposed 
on the static pressure bearing 12, because the bearing 12 is pushed with a 
constant force by the pushing cylinder 22. 
Now, the fourth embodiment of the present invention will be described below 
with reference to FIG. 9, in which the same components as in the figures 
referred to previously are indicated by the same reference numerals as in 
those figures. 
In FIG. 9, a horizontal force applied to the static pressure bearing 14 is 
measured by the load cell 24. The force S.sub.0 detected by the load cell 
24 is fed to a calculator 48, which in turn compares the force S.sub.0 
with a limit pressure resistance value S.sub.max of the bearing 14. When 
S.sub.0 becomes larger than S.sub.max, the calculator 48 outputs a 
pressure reducing signal to a pressure regulator 49 disposed in an oil 
pressure system for the pushing cylinder 22. The amount of reduction in 
pressure, .DELTA.q, is assumed to take the following value which is 
proportional to an amount exceeding S.sub.max : 
EQU .DELTA.q=.alpha..sub.2 (S.sub.0 -S.sub.max) (7) 
where .alpha..sub.2 is a constant. However, if the pushing force is zero, 
the rolls 2,8 and 10 become unstable positionally, so it is necessary that 
a limit be placed on .DELTA.q lest the pushing force should drop to zero 
or less due to the pressure reduction in equation (7). Alternatively, 
.DELTA.q may take a certain constant value. 
According to this fourth embodiment described above, not only the same 
effect as in the first embodiment is obtained, but also, when an excessive 
force is applied to the static pressure bearing 14, the horizontal force 
generated by the pushing cylinder 22 is decreased to diminish the total 
horizontal force exerted on the bearing 14, whereby it is possible to 
prevent contact and flaws of the roll 10 and the bearing 14. 
Next, the fifth embodiment of the present invention will be described with 
reference to FIG. 10, in which the same components as in the figures 
referred to previously are indicated by the same reference numerals as in 
those figures. 
In FIG. 10, the amount of floating, u, of the idler roll 10 in rolling is 
measured by means of a gap measuring device (floating measuring means) 50 
disposed within the static pressure bearing 14 and the measured value is 
converted to an electric signal by an amplifier 51. The value u thus 
detected is outputted to a calculator 52, which in turn calculates a 
difference .DELTA.u from the amount of floating, u.sub.0, which serves as 
a reference value, in accordance with the following equation: 
EQU .DELTA.u=u-u.sub.0 (8) 
A controller 53 receives the value .DELTA.u obtained by the calculator 52 
and, when .DELTA.u is a negative value, indicating an excessive horizontal 
force, outputs to the moving device 20 a signal for shifting the offset y 
of the working roll 2 in the positive direction (rightward in the figure) 
by only a very small amount .DELTA.y, while when .DELTA.u is a positive 
value, indicating a small horizontal force, outputs to the moving device 
20 a signal for shifting the offset y in the negative direction (leftward 
in the figure) by only .DELTA.y. In this way the change of offset using 
.DELTA.y is repeated until .DELTA.u becomes zero. Instead of repeating the 
shifting until .DELTA.u becomes zero, there may be provided a so-called 
dead band whereby the change of offset is stopped when the absolute value 
of .DELTA.u has reached a certain small value or less. 
According to this embodiment described above, not only the same effect as 
in the first embodiment is obtained, but also the amount of floating of 
the roll 10 relative to the static pressure bearing 14 can be kept to a 
value within an appropriate range and hence it is possible to prevent 
flaws of the working roll 2, idler rolls 8,10 and static pressure bearings 
12,14. 
Now, the sixth embodiment of the present invention will be described below 
with reference to FIG. 11, in which the same components as in the figures 
referred to previously are indicated by the same reference numerals as in 
those figures. 
In FIG. 11, the amount of floating, u, of the idler roller 10 in rolling is 
measured by the gap measuring device 50 disposed within the static 
pressure bearing 14 and the measured value is converted to an electric 
signal by the amplifier 51. The value u thus detected is outputted to a 
calculator 54, which in turn calculates a difference .DELTA.u from the 
amount of floating, u.sub.0, which serves as a reference value, in 
accordance with the foregoing equation (8). When .DELTA.u is a negative 
value, this indicates that the horizontal force is excessive, so the 
calculator 54 outputs a pressure increasing signal to the pressure 
regulator 46 disposed in the oil pressure system for floating. The amount 
of increase in pressure, .DELTA.p, is assumed to take the following value 
proportional to .DELTA.u: 
EQU .DELTA.p=.alpha..sub.3 .multidot..DELTA.u (9) 
where .alpha..sub.3 is a constant. Alternatively, .DELTA.p may be a certain 
constant value. However, when .DELTA.u equation (9) is a positive value, 
the reduction of pressure is not performed. On the other hand, to the 
static pressure bearing 12 on the pushing cylinder 22 side is fed oil held 
at a constant pressure by means of the pressure regulator 47. 
According to this sixth embodiment described above, not only the same 
effect as in the first embodiment is obtained, but also, when an excessive 
force is exerted on the static pressure bearing 14, the allowable load of 
the bearing 14 itself is increased by increasing the oil pressure fed, 
whereby it is possible to prevent contact and flaws of the roll 10 and the 
bearing 14. 
Next, the seventh embodiment of the present invention will be described 
below with reference to FIG. 12, in which the same components as in the 
figures referred to previously are indicated by the same reference 
numerals as in those figures. 
In FIG. 12, the amount of floating, u, of the idler roll 10 in rolling is 
measured by the gap measuring device 50 disposed within the static 
pressure bearing 14 and the measured value is converted to an electric 
signal. The value u thus detected is outputted to a calculator 55, which 
in turn calculates the difference .DELTA.u from the amount of 
floating,u.sub.0,which serves as a reference value, in accordance with the 
foregoing equation (8). When .DELTA.u is a negative value, this indicates 
that the horizontal force is excessive, so the calculator 55 outputs a 
pressure reducing signal to the pressure regulator 49 disposed in the oil 
pressure system for the pushing cylinder 22. The amount of reduction in 
pressure, .DELTA.q,is assumed to take the following value proportional to 
.DELTA.u: 
EQU .DELTA.q=.alpha..sub.4 .multidot..DELTA.u (10) 
where .alpha..sub.4 is a constant. However, when the pushing force is zero, 
the rolls 2,8 and 10 become unstable positionally, so it is necessary that 
a limit be placed on .DELTA.q lest the pushing force should drop to zero 
or less due to the pressure reduction based on equation (10). 
Alternatively, .DELTA.q may take a certain constant value. 
According to this seventh embodiment described above, not only the same 
effect as in the first embodiment is obtained, but also, when an excessive 
force is exerted on the static pressure bearing 14, the horizontal force 
generated by the pushing cylinder 22 is decreased to diminish the total 
horizontal force applied to the bearing 14, whereby it is possible to 
prevent contact and flaws of the roll 10 and the bearing 14. 
The eighth embodiment of the present invention will be described below with 
reference to FIG. 13, which is a top view of the left-hand quadrant in the 
figure of an upper half of a rolling mill according to the eighth 
embodiment. In the same figure it is assumed that the side close to the 
upper end is an operating side, while the side close to the lower end is a 
driving side. The same components as in the figures referred to previously 
are indicated by the same reference numerals as in those figures. 
In FIG. 13, a horizontal force S.sub.W applied to the operating side is 
detected by a load cell 24W disposed on the operating side, while a 
horizontal force S.sub.D applied to the driving side is detected by a load 
cell 24D disposed on the driving side. Both S.sub.W and S.sub.D are fed to 
a calculator 56, which in turn calculates a difference .DELTA.S between 
the two in accordance with the following equation: 
EQU .DELTA.S=S.sub.W -S.sub.D (11) 
The static pressure bearing 14 has three oil pockets 57,58 and 59 having 
respective independent oil pressure systems for floating. Pressure 
regulators 60, 61 and 62 are disposed respectively in those oil pressure 
systems, whereby the oil pressures in the oil pockets 57, 58 and 59 can be 
controlled each independently. A reference pressure in each system is set 
by a setting device 63. The value of .DELTA.S calculated above is 
outputted to another setting device 64, and an operating-side system 
pressure p.sub.W and a driving-side system pressure p.sub.D are determined 
in the following manner: 
When .DELTA.S is positive, p.sub.W is increased because the horizontal 
force on the operating side is large, while when .DELTA.S is negative, 
p.sub.D is increased because the horizontal force on the driving side is 
large. Although it is appropriate to set the amount of increase (decrease) 
in pressure, .DELTA. p, at a value proportional to the absolute value of 
.DELTA.S, the value of .DELTA.p may be a constant value. 
According to this eighth embodiment described above, not only the same 
effect as in the first embodiment is obtained, but also, when an excessive 
force is exerted on a certain portion in the plate width direction, the 
oil pressure fed for floating at that portion of a large horizontal force 
is increased and hence it is possible to increase the total allowable load 
imposed on the static pressure bearing 14, whereby it is possible to 
prevent contact and flaws of the roll 10 and the bearing 14. 
The ninth embodiment of the present invention will be described below with 
reference to FIG. 14, which is a top view of the left-hand quadrant in the 
figure of an upper half of a rolling mill according to the ninth 
embodiment. In the same figure it is assumed that the side close to the 
upper end is an operating side, while the side close to the lower end is a 
driving side. The same components as in the figures referred to previously 
are indicated by the same reference numerals as in those figures. 
In FIG. 14, amounts of floating, u.sub.D, u.sub.C u.sub.W of the idler roll 
10 are measured by gap detectors disposed respectively in the three oil 
pockets 57,58 and 59 of the static pressure bearing 14, and the measured 
values are converted to electric signals by means of amplifiers 68,69 and 
70. As to the amount of floating, u.sub.C, at the central portion, it is 
the same as that explained above in connection with FIGS. 10 to 12, and 
the same processing as in the fifth to seventh embodiments is performed. 
As to the amount of floating, u.sub.W on the operating side and U.sub.D on 
the driving side, they are inputted to a calculator 71, which in turn 
calculates a difference .DELTA.u.sub.L of the two in accordance with the 
following equation: 
EQU .DELTA.u.sub.L =u.sub.W -u.sub.D (12) 
Three oil pockets 57, 58 and 59 have respective independent oil pressure 
systems for floating, in which are disposed pressure regulators 60, 61 and 
62 respectively, whereby the oil pressures in the oil pockets 57,58 and 59 
can be controlled each independently. A reference pressure in each system 
is set by the setting device 63. The value of .DELTA.u.sub.L calculated 
above is outputted by another setting device 64, and both operating side 
system pressure p.sub.w and driving-side system pressure P.sub.D are 
determined as follows. 
When .DELTA.u.sub.L is positive, the amount of floating, u.sub.W, on the 
operating side is large and u.sub.D on the driving side is small, so it is 
indicated that an excessive horizontal force is exerted on the driving 
side. Therefore, the allowable load on the driving side is increased by 
increasing p.sub.D Conversely, when .DELTA.u.sub.L is negative, the amount 
of floating, u.sub.W, on the operating side is small and u.sub.D on the 
driving side is large, so it is indicated that an excessive horizontal 
force is exerted on the operating side. Therefore, the allowable load on 
the operating side is increased by increasing p.sub.w. In this case, it is 
appropriate to set the amount of increase in pressure,.DELTA.p, at a value 
proportional to the absolute value of .DELTA.u.sub.L, but the value of 
.DELTA.p may be a constant value. 
According to this ninth embodiment described above, not only the same 
effect as in the first embodiment is obtained, but also, when an excessive 
force is exerted on a certain portion in the plate width direction, the 
oil pressure fed for floating at that portion of a large horizontal force 
is increased and hence it is possible to increase the total allowable load 
imposed on the static pressure bearing 14, whereby it is possible to 
prevent contact and flaws of the roll 10 and the bearing 14. 
The tenth embodiment of the present invention will be described below with 
reference to FIG. 15, which is a top view of an upper half of a rolling 
mill according to the tenth embodiment. In the same figure it is assumed 
that the side close to the upper end is an operating side, while the side 
close to the lower end is a driving side. The same components as in the 
figures referred to above are indicated by the same reference numerals as 
in those figures. 
In FIG. 15, a horizontal force S.sub.W exerted on the operating side is 
detected by the load cell 24W disposed on the operating side, while a 
horizontal force S.sub.D exerted on the driving side is detected by the 
load cell 24D disposed on the driving side. Both S.sub.W and S.sub.D are 
fed to the calculator 56, which in turn calculates the difference .DELTA.S 
between the two in accordance with the foregoing equation (11). A 
calculator 72 receives .DELTA.S and, when .DELTA.S is positive, indicating 
that the horizontal force S.sub.W on the operating side is larger, 
provides a pressure reducing signal .DELTA.q to a pressure regulator 74 
for a pushing cylinder 22W on the operating side, while when .DELTA.S is 
negative, indicating that the horizontal force S.sub.D on the driving side 
is larger, provides the pressure reducing signal .DELTA.q to a pressure 
regulator 73 for a pushing cylinder 22D on the driving side. Although it 
is appropriate to set the amount of reduction in pressure, .DELTA.q, at a 
value proportional to the absolute value of .DELTA.S, the value of 
.DELTA.q may be a constant value. However, if the pushing force is zero, 
the rolls 2,8 and 10 become unstable positionally, so it is necessary to 
place a limit on .DELTA.q lest the pushing force should drop to zero or 
less due to the pressure reduction based on .DELTA.q. 
According to this tenth embodiment described above, not only the same 
effect as in the first embodiment is obtained, but also, upon exertion of 
an excessive force on a certain portion in the plate width direction, the 
pushing force generated by the pushing cylinder is decreased at that 
portion of a large horizontal force and hence the total horizontal force 
applied to the static pressure bearing 14 can be diminished, whereby it is 
possible to prevent contact and flaws of the roll 10 and the bearing 14. 
The eleventh embodiment of the present invention will be described below 
with reference to FIG. 16, which is a top view of an upper half of a 
rolling mill according to the eleventh embodiment. In the same figure it 
is assumed that the side close to the upper end is an operating side, 
while the side close to the lower end is a driving side. The same 
components as in the figures referred to previously are indicated by the 
same reference numerals as in those figures. 
In FIG. 16, the amounts of floating, u.sub.D, u.sub.C, u.sub.W of the idler 
roller 10 are measured by the gap detectors 65,66 and 67 disposed 
respectively in the three oil pockets 57,58 and 59 of the static pressure 
bearing 14 and the measured values are converted to electric signals by 
the amplifiers 68,69 and 70. As to the amount of floating, u.sub.C, at the 
central portion, it is the same as that explained above in connection with 
FIGS. 10 to 12, and the same processing as in the fifth to seventh 
embodiments is performed. As to the amount of floating, u.sub.W, on the 
operating side and u.sub.D on the driving side, they are inputted to the 
calculator 71, wherein the difference .DELTA.u.sub.L of the two is 
calculated in accordance with the foregoing equation (12). The value 
.DELTA.u.sub.L thus calculated is provided to a calculator 75. When 
.DELTA.u.sub.L is positive, this means that the horizontal force S.sub.D 
on the driving side is larger, so the calculator 75 provides a pressure 
reducing signal .DELTA.q to the pressure regulator 73 for the pushing 
cylinder 22D on the driving side, while when .DELTA.u.sub.L is negative, 
since this means that the horizontal force u.sub.W on the operating side 
is larger, the calculator 75 provides the pressure reducing signal 
.DELTA.q to the pressure regulator 74 for the pushing cylinder 22W. 
Although it is appropriate to set the amount of reduction in pressure, 
.DELTA.q, at a value proportional to the absolute value of .DELTA.u.sub.L 
, .DELTA.q may be a constant value. However, if the pushing force is zero, 
the rolls 2,8 and 10 become unstable positionally, so it is necessary to 
place a limit on .DELTA.q lest the pushing force should drop to zero or 
less due to the reduction of pressure based on .DELTA.q. 
According to this eleventh embodiment described above, not only the same 
effect as in the first embodiment is obtained, but also, upon exertion of 
an excessive force on a certain portion in the plate width direction, the 
pushing force generated by the pushing cylinder is decreased at that 
portion of a large horizontal force and hence the total horizontal force 
applied to the static pressure bearing 14 can be diminished, whereby it is 
possible to prevent contact and flaws of the roll 10 and the bearing 14. 
Although in FIG. 6 and FIGS. 13 to 16 referred to above the number of oil 
pockets and that of gap detectors are each three for one static pressure 
bearing, any other number (plural number) of oil pockets may be provided. 
According to the rolling mill of the present invention, as set forth 
hereinabove, when rolling is performed by the rolling mill wherein working 
rolls are supported horizontally by static pressure bearings, the working 
rolls are moved horizontally in the incoming and outgoing direction of the 
rolls by moving means attached to the static pressure bearings, so it 
becomes possible to prevent an excessive force from being exerted on the 
bearings and the rolls can be prevented from coming into contact with 
bearing pads of the static pressure bearings under the action of an 
excessive horizontal force. 
Therefore, the rolls can be prevented from being flawed, the product 
quality is no longer deteriorated, the lowering of yield can be prevented, 
and damage to the pads of the static pressure bearings can also be 
prevented. As a result, it becomes unnecessary to interrupt operation for 
a long time to replace the damaged pads with fresh pads, whereby it is 
possible to prevent the deterioration of productivity. Further, since even 
working rolls of a small diameter are employable stably in the present 
invention, it becomes possible to roll hard and thin plates efficiently.