Patent Publication Number: US-2023149994-A1

Title: Rolling mill, rolling mill control method, and thrust force supporting method in rolling mill

Description:
TECHNICAL FIELD 
     The present invention relates to a rolling mill, a rolling mill control method, and a thrust force supporting method in the rolling mill. 
     BACKGROUND ART 
     As an example of a rolling mill having a work roll shift function, which is capable of rolling a high-quality rolled material without a transfer flaw on a surface thereof by suppressing the occurrence of abrasion flaws on work rolls, which are caused by both end portions in the width direction of the rolled material, when controlling an edge drop of the rolled material by shifting the work rolls in the axial direction of the work rolls, the work rolls having one end formed in a tapered shape, Patent Document 1 describes a reversing rolling mill including: a pair of upper and lower work rolls that have, at one ends of roll barrel portions, tapered portions having a roll diameter gradually decreased toward a roll end, and sandwich the rolled material such that the tapered portions are located on opposite sides from each other in the axial direction; and roll shift devices that shift the work rolls in the axial direction, the surfaces of the roll barrel portions in the work rolls being formed of a ceramic material or a cemented carbide material. 
     Prior Art Document 
     Patent Document 
     Patent Document 1: JP-2011-25299-A 
     SUMMARY OF THE INVENTION 
     Problem to Be Solved by the Invention 
     Studies for reducing the diameter of the work rolls have been progressing. However, since bearings of the work rolls also become smaller with a reduction in diameter of the work rolls, parts receiving thrust forces of the work rolls also become smaller, and thus a capability of supporting the thrust forces becomes insufficient. 
     For example, Patent Document 1 discloses a structure in which shift driving units are provided on both a drive side and an operation side of the work rolls, and the work rolls sandwiched by both the shift driving units are shifted in the axial direction. 
     However, in the structure of Patent Document 1 described above, the shift driving unit on the operation side only pushes the work rolls to the drive side, and the shift driving unit on the drive side only pushes the work rolls to the operation side, so that only one shift driving unit contributes when supporting a thrust force. Therefore, studies by the present inventor et al. have clarified that there is room for improvement in sufficiently supporting the thrust force in work rolls of a small diameter, in particular. 
     The present invention provides a rolling mill, a rolling mill control method, and a thrust force supporting method in the rolling mill that can improve the capability of supporting the thrust force. 
     Means for Solving the Problems 
     The present invention includes a plurality of means for solving the above-described problems. To cite an example of the means, there is provided a rolling mill including: a work roll; bearings that are provided on an operation side and a drive side of the work roll, and support the work roll; an operation side thrust force supporting device that is provided on the operation side of the work roll, and applies forces in both directions of the operation side and the drive side to the bearing on the operation side; and a drive side thrust force supporting device that is provided on the drive side of the work roll, and applies forces in both directions of the operation side and the drive side to the bearing on the drive side; the operation side thrust force supporting device and the drive side thrust force supporting device each applying a force in a same direction to the bearing when the work roll is not shifted in an axial direction at least during rolling. 
     Advantages of the Invention 
     According to the present invention, the capability of supporting the thrust force can be improved. Problems, configurations, and effects other than those described above will be made apparent by description of the following embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram showing an outline of rolling equipment including rolling mills according to a first embodiment of the present invention. 
         FIG.  2    is a front view of assistance in explaining an outline of a rolling mill according to the first embodiment. 
         FIG.  3    is a view taken in the direction of arrows along a line A-A′ in  FIG.  2   . 
         FIG.  4    is a diagram showing relation between a rolling load and a thrust resistance force. 
         FIG.  5    is a diagram showing relation between an outside diameter of a thrust bearing, a thrust dynamic load rating of the thrust bearing, and a life of the thrust bearing. 
         FIG.  6    is a plan view of assistance in explaining details of an upper work roll part in the rolling mill according to the first embodiment. 
         FIG.  7    is a plan view of assistance in explaining a part taken in the direction of arrows along the line A-A′ in  FIG.  2    in a rolling mill according to a first modification of the first embodiment. 
         FIG.  8    is a plan view of assistance in explaining a part taken in the direction of arrows along the line A-A′ in  FIG.  2    in a rolling mill according to a second modification of the first embodiment. 
         FIG.  9    is a plan view of assistance in explaining a part taken in the direction of arrows along the line A-A′ in  FIG.  2    in a rolling mill according to a third modification of the first embodiment. 
         FIG.  10    is a plan view of assistance in explaining details of an upper work roll part in a rolling mill according to a second embodiment of the present invention. 
         FIG.  11    is a plan view of assistance in explaining details of an upper work roll part in a rolling mill according to a modification of the second embodiment. 
         FIG.  12    is a plan view of assistance in explaining details of an upper work roll part in a rolling mill according to a third embodiment of the present invention. 
         FIG.  13    is a flowchart showing a flow of roll axis direction positional adjustment in the rolling mill according to the third embodiment. 
         FIG.  14    is a flowchart showing a flow of shift force adjustment in the rolling mill according to the third embodiment. 
         FIG.  15    is a plan view of assistance in explaining details of an upper work roll part in a rolling mill according to a modification of the third embodiment. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     Embodiments of a rolling mill, a rolling mill control method, and a thrust force supporting method in the rolling mill according to the present invention will hereinafter be described with reference to the drawings. 
     In the following, same or corresponding constituent elements in the drawings used in the present specification are identified by the same or similar reference numerals, and repeated description of these constituent elements may be omitted. 
     In addition, in the drawings, a work side may be denoted as “WS (Work Side),” and a drive side may be denoted as “DS (Drive Side).” 
     Further, a thrust resistance force is a force in a roll axis direction, which acts on each roll of the rolling mill and a bearing housing thereof during rolling or when a shift is performed during rolling, and which means a force acting on devices supporting the force, and has the same meaning as a thrust force. A thrust reaction force is a force occurring from the devices supporting the thrust resistance force, and means a force having an opposite direction from that of the thrust resistance force and having a same magnitude as that of the thrust resistance force. 
     First Embodiment 
     A first embodiment of the rolling mill, the rolling mill control method, and the thrust force supporting method in the rolling mill according to the present invention will be described with reference to  FIGS.  1  to  6   .  FIG.  1    is a diagram showing an outline of rolling equipment including rolling mills according to the present first embodiment.  FIG.  2    is a front view of assistance in explaining an outline of a rolling mill according to a first embodiment.  FIG.  3    is a view taken in the direction of arrows along a line A-A′ in  FIG.  2   .  FIG.  4    is a diagram showing relation between a rolling load and a thrust resistance force.  FIG.  5    is a diagram showing relation between an outside diameter of a thrust bearing and a thrust dynamic load rating of the thrust bearing.  FIG.  6    is a plan view of assistance in explaining details of an upper work roll part. 
     An outline of rolling equipment including rolling mills according to the present embodiment will first be described with reference to  FIG.  1   . 
     As shown in  FIG.  1   , the rolling equipment  1  includes a plurality of rolling mills that hot roll a rolled material  5  into a strip, and the rolling equipment  1  includes a control device  80  and five stands, which are, from an entry side of the rolled material  5 , a first stand  30 , a second stand  40 , a third stand  50 , a fourth stand  60 , and a fifth stand  70 . 
     Of these, each of the first stand  30 , the second stand  40 , the third stand  50 , the fourth stand  60 , and the fifth stand  70  and a part that controls each stand in the control device  80  correspond to a rolling mill as referred to in the present invention. 
     Incidentally, the rolling equipment  1  is not limited to the five stands as shown in  FIG.  1   , but can be constituted of a minimum of two stands or more. 
     A part of an outline of the rolling mill according to the present invention will next be described with reference to  FIG.  2   . It is to be noted that while description will be made by taking the fifth stand  70  shown in  FIG.  1    as an example in  FIG.  2   , the rolling mill according to the present invention can be applied to any of the first stand  30 , the second stand  40 , the third stand  50 , and the fourth stand  60  shown in  FIG.  1   . 
     In  FIG.  2   , the fifth stand  70  as a rolling mill according to the present embodiment is a six-high rolling mill that rolls the rolled material  5 , and the fifth stand  70  includes a housing  700 , the control device  80 , and a hydraulic device  90 . 
     The housing  700  includes an upper work roll  710  and a lower work roll  711  as well as an upper intermediate roll  720  and a lower intermediate roll  721  that support the upper work roll  710  and the lower work roll  711  by being in contact with the upper work roll  710  and the lower work roll  711 , respectively. The housing  700  further includes an upper back-up roll  730  and a lower back-up roll  731  that support the upper intermediate roll  720  and the lower intermediate roll  721  by being in contact with the upper intermediate roll  720  and the lower intermediate roll  721 , respectively. 
     A radial bearing  790 A and a thrust bearing  792  (see  FIG.  6    for both) that shift together with the upper work roll  710  in the axial direction of the roll and receive a load from the roll are provided on the operation side of end portions in the axial direction of the upper work roll  710  among these rolls. The radial bearing  790 A and the thrust bearing  792  are supported by an upper work side bearing housing  712 A. Similarly, a radial bearing  790 B (see  FIG.  6   ) that shifts together with the upper work roll  710  in the axial direction of the roll and receives a load from the roll is provided on the drive side. This radial bearing  790 B is supported by an upper drive side bearing housing  712 B. 
     The lower work roll  711  is also similarly provided with bearings (omitted for the convenience of illustration) at end portions thereof in the axial direction on each of the drive side and the operation side. These bearings are supported by a lower work roll bearing housing  713  (a bearing housing  713 A on the operation side and a bearing housing  713 B on the drive side). 
     In the present embodiment, the upper work roll  710  is configured to be shiftable in the roll axis direction by a shift cylinder  715  as shown in  FIG.  3    via the upper work side bearing housing  712 A on the operation side. Similarly, the lower work roll  711  is also configured to be shiftable in the roll axis direction by a shift cylinder  717  as shown in  FIG.  3    via the lower work roll bearing housing  713 A on the operation side. 
     In addition, as shown in  FIG.  3   , a tapered portion is provided to end portions on the operation side in the upper work roll  710  and the lower intermediate roll  721  and end portions on the drive side in the lower work roll  711  and the upper intermediate roll  720 . The upper work roll  710  and the lower work roll  711  are vertically point-symmetric to each other, and the upper intermediate roll  720  and the lower intermediate roll  721  are vertically point-symmetric to each other. 
     Returning to  FIG.  2   , an entry side fixed member  702  is fixed to the housing  700  on the entry side of the rolled material  5 . An exit side fixed member  703  is fixed to the housing  700  on an exit side of the rolled material  5  so as to face the entry side fixed member  702 . 
     In the fifth stand  70 , as shown in  FIG.  2    and  FIG.  6   , on each of the operation side and the drive side, the upper work roll bearing housing  712  is supported by upper work roll bending cylinders  740  and  742  provided in twos in the axial direction of the roll to the entry side fixed member  702  and upper work roll bending cylinders  741  and  743  provided in twos in the axial direction of the roll to the exit side fixed member  703 . 
     A bending force is applied in a vertical direction to the bearings of the upper work roll  710  by driving these cylinders as appropriate. 
     Similarly, on each of the operation side and the drive side, the lower work roll bearing housing  713  is supported by lower work roll bending cylinders  744  and  746  provided to the entry side fixed member  702  and lower work roll bending cylinders  745  and  747  provided to the exit side fixed member  703 . A bending force is applied in the vertical direction to the bearings of the lower work roll  711  by driving these cylinders as appropriate. 
     Of these cylinders, the upper work roll bending cylinders  740  and  741  are arranged so as to apply a bending force on a vertical direction increase side (in a direction opposite from a rolled material side) to the bearings of the upper work roll  710  in contact with the rolled material  5 . In addition, the upper work roll bending cylinders  742  and  743  are arranged so as to apply, to the bearings, a bending force on a vertical direction decrease side (in a rolled material side direction) as an opposite direction from that of the upper work roll bending cylinders  740  and  741 . 
     Similarly, the lower work roll bending cylinders  744  and  745  are arranged so as to apply a bending force on the vertical direction increase side to the bearings of the lower work roll  711  in contact with the rolled material  5 . In addition, the lower work roll bending cylinders  746  and  747  are arranged so as to apply, to the bearings, a bending force on the decrease side as an opposite direction from that of the lower work roll bending cylinders  744  and  745 . 
     Further, as shown in  FIG.  2    and  FIG.  6   , with an objective of removing backlash, the entry side fixed member  702  on the entry side of the rolled material  5  is provided with two upper work roll bearing housing backlash removing cylinders  760  in the axial direction of the roll to apply a force in a horizontal direction, specifically a pressing force in a rolling direction to the upper work roll  710  via a liner (not shown) of the upper work roll bearing housing  712 . 
     Similarly, the entry side fixed member  702  is provided with two lower work roll bearing housing backlash removing cylinders  762  to apply a pressing force in the rolling direction to the lower work roll  711  via a liner of the lower work roll bearing housing  713 . 
     These cylinders enable desired forces to be applied to the upper work roll  710  and the like in directions orthogonal to the roll axis direction. 
     Returning to  FIG.  2   , bearings (not shown) are provided to end portions in the axial direction of the upper intermediate roll  720  on each of the drive side and the operation side. These bearings are supported by an upper intermediate roll bearing housing  722 . The lower intermediate roll  721  is also similarly provided with bearings (not shown) at end portions thereof in the axial direction on each of the drive side and the operation side. These bearings are supported by a lower intermediate roll bearing housing  723 . 
     The upper intermediate roll  720  has the upper intermediate roll bearing housing  722  supported on each of the operation side and the drive side by upper intermediate roll bending cylinders  750  provided to the entry side fixed member  702  and upper intermediate roll bending cylinders  751  provided to the exit side fixed member  703 . A bending force is applied on the vertical direction increase side to the bearings by driving these cylinders as appropriate. 
     The lower intermediate roll  721  also has the lower intermediate roll bearing housing  723  supported on each of the operation side and the drive side by lower intermediate roll bending cylinders  752  provided to the entry side fixed member  702  and lower intermediate roll bending cylinders  753  provided to the exit side fixed member  703 . A bending force is applied on the vertical direction increase side to the bearings by driving these cylinders as appropriate. 
     In addition, as shown in  FIG.  2   , the housing  700  on the exit side is provided with an upper intermediate roll bearing housing backlash removing cylinder  771  to apply a force in the horizontal direction to the upper intermediate roll  720  via the upper intermediate roll bearing housing  722 . Similarly, the housing  700  on the exit side is provided with a lower intermediate roll bearing housing backlash removing cylinder  773  to apply a force in the horizontal direction to the lower intermediate roll  721  via the lower intermediate roll bearing housing  723 . 
      Further, bearings (not shown) are provided to end portions in the axial direction of the upper back-up roll  730  on each of the drive side and the operation side. These bearings are supported by an upper back-up roll bearing housing  732 . The lower back-up roll  731  is also similarly provided with bearings (not shown) at end portions thereof in the axial direction on each of the drive side and the operation side. These bearings are supported by a lower back-up roll bearing housing  733 . 
     In addition, as shown in  FIG.  2   , the housing  700  on the entry side is provided with an upper back-up roll bearing housing backlash removing cylinder  780  to apply a force in the horizontal direction to the upper back-up roll  730  via the upper back-up roll bearing housing  732 . Similarly, the housing  700  on the entry side is provided with a lower back-up roll bearing housing backlash removing cylinder  782  to apply a force in the horizontal direction to the lower back-up roll  731  via the lower back-up roll bearing housing  733 . 
     A hydraulic device  90  is connected to hydraulic cylinders such as the bending cylinders and the backlash removing cylinders described above, the shift cylinders  715  and  717 , rolling cylinders (not shown) that apply a rolling force for rolling the rolled material  5  to the upper work roll  710  and the lower work roll  711 , or the like. This hydraulic device  90  is connected to the control device  80 . 
     The control device  80  supplies and discharges hydraulic fluid to and from the above-described bending cylinders or the like by performing operation control on the hydraulic device  90 . The control device  80  thereby performs driving control on each of these cylinders. 
     Characteristic parts of the rolling mill, the control method thereof, and the thrust force supporting method in the present invention will next be described with reference to  FIG.  6    by taking as an example a configuration related to the upper work roll  710  among the rolls of the fifth stand  70 . Incidentally, the lower work roll  711  can adopt a configuration and a method similar to those of the upper work roll  710  and has substantially the same detailed configuration as the upper work roll  710 , and therefore description thereof will be omitted. 
     A background that led to introduction of a configuration shown in  FIG.  6    will first be described with reference to  FIG.  4    and  FIG.  5   . 
     First, in the present invention, it can be assumed that letting D w  be the diameter of the upper work roll  710  and the lower work roll  711 , and letting L B  be a maximum rolling strip width of the rolled material, the upper work roll  710  and the lower work roll  711  satisfy a condition that D w/ L B  is 0.28 or less. 
     When the work rolls of such a relatively small diameter are used, the size of the radial bearings and the thrust bearings is limited because of limitations in the vertical direction on the work roll bearing housings, and large bearings cannot be used. In addition, spaces in the vertical direction for the shift cylinders are also reduced, and the shift cylinders cannot be formed as large devices. The bearings themselves become small and decrease in strength in the first place. Therefore, even when devices related to shifts can be made large, the life of the bearings presents a major problem. 
       FIG.  4    is a diagram showing relation between a rolling load and a thrust resistance force. An axis of abscissas indicates the rolling load [MN]. An axis of ordinates indicates the thrust resistance force [MN]. “-” on the axis of ordinates indicates a drive side direction. “+” on the axis of ordinates indicates a work side direction. 
     As shown in  FIG.  4   , a straight line  202  indicating a work side direction maximum value of the thrust resistance force when no shift is performed during rolling is substantially equal to Rolling Load × 0.02. In addition, a straight line  204  indicating a drive side direction maximum value of the thrust resistance force when no shift is performed during rolling is substantially equal to minus Rolling Load × 0.02. A thrust resistance force  203  when no shift is performed during rolling is larger than minus Rolling Load × 0.02, and is smaller than Rolling Load × 0.02. 
     This thrust load occurs due to a fact that the axes of the upper work roll  710  and the upper intermediate roll  720  slightly cross each other between the rolls and a fact that the axis of the upper work roll  710  slightly crosses the width direction (direction at a right angle to a travelling direction) of the rolled material  5 . The direction of the thrust load may be the drive side direction, or may be the work side direction. 
     On the other hand, when a shift is performed during rolling, slip resistance between the rolls, which changes according to a ratio between a shift speed and a rolling speed, frictional resistance in a shift direction of forces acting on the bearing housings, extension or contraction resistance of driving spindles (frictional resistance of tangential forces acting on splines due to driving torque), and the like further act as the thrust resistance force. The forces acting on the bearing housings are bending forces and backlash removing cylinder forces as well as an offset component force of the rolling load due to a pass direction offset between the rolls and the like. 
     Therefore, a straight line  201  indicating a work side direction maximum value of the thrust resistance force when a shift is performed during rolling is located on a positive side of the straight line  202 , and a straight line  205  indicating a drive side direction maximum value of the thrust resistance force when a shift is performed during rolling is located on a negative side of the straight line  204 . 
     Incidentally, the straight lines  201  and  205  shown in  FIG.  4   , which indicate the maximum values of the thrust resistance force when a shift is performed during rolling, are represented by solid lines by linear approximation. This linear approximation is not accurate because rolling torque and the rolling load are not in linear relation, but is used as one approximation for facilitating the description. 
     In addition, the bending forces and the backlash removing cylinder forces are set in a manner not too closely related to the rolling load. Thus, there is a thrust resistance force even when the rolling load is 0 [MN]. 
     As shown in  FIG.  4   , when the rolling load exceeds 20 [MN], a thrust resistance force equal to or more than twice the thrust force at a time of a rolling load of 40 [MN] in a case where no shift is performed during rolling acts in a case where a shift is performed during rolling. 
      In addition, in a case where a shift is performed during rolling, a thrust resistance force close to a maximum value of the thrust resistance force at a time of a rolling load of 40 [MN] in a case where no shift is performed during rolling acts on an average even when the rolling load is small at 20 [MN] or less. 
     Further, in a rolling mill with a rolling load max of 40 [MN], a thrust resistance force 3.0 times that in a case where no shift is performed during rolling acts on an average when a shift is performed during rolling. 
       FIG.  5    is a diagram showing relation between an outside diameter Do [mm] of a thrust bearing, a thrust dynamic load rating Ca [MN] of the thrust bearing, and a life Lh [h] of the thrust bearing. 
     Here, a case is assumed in which when the rolling load max is 40 [MN] and the thrust resistance force max is 2.0 [MN], 75% of the thrust resistance force max is an average thrust load. In this case, an average thrust load Fa is about 2.0 × 0.75 = 1.5 [MN]. 
     Incidentally, even when equipment specifications of the rolling mill represent equipment with a rolling load of 40 [MN], the rolling load of 40 [MN] does not always act. The rolling load is determined by a rolling schedule including a strip width, a rolling reduction, and the like, and it is obvious that the average thrust load Fa differs in different equipment. 
     As shown in  FIG.  5   , the thrust dynamic load rating Ca when the outside diameter Do is 470 [mm] is 2.0 [MN], and the thrust dynamic load rating Ca when Do is 340 [mm] is 1.2 [MN]. The thrust dynamic load rating Ca is thus decreased to 60%. 
     As for a lifetime number of revolutions Lhr of a bearing, a relation Lhr∝(Ca/Fa) 10/3  is known. In a case where the outside diameter Do becomes 340 [mm], the lifetime number of revolutions is decreased to 1/5.5 as compared with a case where the outside diameter Do is 470 [mm] even when the average thrust load Fa is the same. 
     When the diameter D w  of the work roll is reduced, the outside diameter Do of the thrust bearing becomes small. For example, it is assumed that Do is about 470 [mm] when D w  = 520 [mm], and that Do is about 340 [mm] when D w  = 380 [mm]. 
     In this case, it is understood that the lifetime number of revolutions of the bearing is decreased to 1/5.5 = 18% when D w  is reduced to 73%, and that a significant decrease in the life of the bearing is unavoidable. 
     For example, supposing that the maximum rolling strip width L B  of the rolled material is 1600 [mm], the life Lh [h] of the thrust bearing at a rolling speed of 900 [m/min] and a rolling load of 40 [MN] is as follows. 
     When Do = 470 [mm], D w  = 520 [mm], and D w/ L B  = 0.33, Ca = 2.0 [MN], Fa = 1.5 [MN], and Lh = 79 [h]. When Do = 400 [mm], D w  = 445 [mm], and D w/ L B  = 0.28, Ca = 1.5 [MN], Fa = 1.5 [MN], and Lh = 26 [h]. When Do = 340 [mm], D w  = 380 [mm], and D w/ L B  = 0.24, Ca = 1.2 [MN], Fa = 1.5 [MN], and Lh = 11 [h]. 
     When D w  becomes a smaller diameter while the rolling speed is the same, the number of revolutions is increased, and therefore the life is shortened more than a decrease in the lifetime number of revolutions. Here, in a case where D w/ L B  = 0.28, there is a condition of Ca = Fa, and the life Lh of the thrust bearing in this case is 26 [h]. In actual operation, the work roll is replaced a few times a day. However, it is obvious that the life of the bearing is reached in a very short time. Even when operation is performed while a few sets of bearings are retained, the bearing reaches a life in one week at most. Thus, the thrust bearing can be said to have a limit in actual equipment from both viewpoints of operation and equipment maintenance. When D w/ L B  = 0.24, Lh = 11 [h]. Then, it is uncertain when damage is caused during operation, and the thrust bearing can be said to be inapplicable in actual equipment. 
     In such a rolling mill in which a work roll of a small diameter is used and, in particular, a shift is performed during rolling, the life of the bearing with respect to the thrust load on the work roll becomes a problem. In a conventional system in which only either the work side or the drive side is provided with a shift device, a problem of a short life occurs in the case of a work roll of a small diameter even though the life of the bearing is not a problem in the case of a conventional work roll of a relatively large diameter. Further, even when rolling is continued without a shift being performed during rolling, a thrust load always acts during rolling. Thus, the life of the bearing with respect to the thrust load presents a problem of a short life in the case of a work roll of a small diameter. 
     The present inventor et al. accordingly have conceived decreasing the average thrust load Fa. Conventionally, the shift device is disposed only on either the work side or the drive side. However, this shift device is provided also to the drive side or the work side, and the thrust resistance force is supported by the shift devices on both the work side and the drive side also when no shift is performed during rolling. Consequently, the average thrust load Fa can be basically halved by supporting the thrust resistance force on the work side and the drive side. When Fa can be halved, the lifetime number of revolutions can be extended by 10 times because the lifetime number of revolutions Lhr has the relation Lhr∝(Ca/Fa) 10/3 . Incidentally, load allocation between the work side and the drive side can be selected, and is not particularly limited. 
     The present invention has been made on the basis of such findings. 
     Characteristic configurations and control of the present invention will next be described. 
     As shown in  FIG.  6   , the entry side fixed member  702  on the operation side is provided with a shift cylinder  715 A that applies forces in both directions of the work side and the drive side to the upper work roll  710  via a connecting member  714 A connected to the upper work side bearing housing  712 A that supports the radial bearing  790 A and the thrust bearing  792  on the work side. 
     In addition, the exit side fixed member  703  on the operation side is provided with a shift cylinder  715 B that applies forces in both directions of the work side and the drive side to the upper work roll  710  via a connecting member  714 B connected to the upper work side bearing housing  712 A that supports the radial bearing  790 A and the thrust bearing  792  on the work side. 
     The part of this shift cylinder  715 B is provided with a position sensor  716  that senses the position in the roll axis direction of the upper work roll  710 . Incidentally, the position at which the position sensor  716  is provided is not limited to this, but may be the position of another shift cylinder  715 A,  715 C, or  715 D. In addition, the position sensor does not need to be one position sensor, but two or more position sensors can be provided. 
     Similarly, the entry side fixed member  702  on the drive side is provided with a shift cylinder  715 D that applies forces in both directions of the work side and the drive side to the upper work roll  710  via a connecting member  714 D connected to the upper drive side bearing housing  712 B that supports the radial bearing  790 B on the drive side. 
     In addition, the exit side fixed member  703  on the drive side is provided with a shift cylinder  715 C that applies forces in both directions of the work side and the drive side to the upper work roll  710  via a connecting member  714 C connected to the upper drive side bearing housing  712 B that supports the radial bearing  790 B on the drive side. 
     A force in the axial direction, which acts on the upper work roll  710 , acts on the thrust bearing  792  provided only to the work side, and is ultimately supported by the shift cylinders  715 A and  715 B on the work side. Similarly, the force in the axial direction, which acts on the upper work roll  710 , acts on the radial bearing  790 B on the drive side, and the force is supported by the shift cylinders  715 C and  715 D on the drive side. 
     The force in the axial direction, which acts on the upper work roll  710 , may be the work side direction, or may be the drive side direction. Thus, both of the shift cylinders  715 A and  715 B on the work side and the shift cylinders  715 C and  715 D on the drive side can support the force in each of the work side direction and the drive side direction. 
     Hence, in both a case where a shift is performed during rolling and a case where no shift is performed during rolling, the force in the axial direction, which acts on the upper work roll  710 , can be supported by a total of the work side and the drive side. 
     These shift cylinders  715 A,  715 B,  715 C, and  715 D have a cylinder slid by an inflow or an outflow of oil into or from each of a head side space and a rod side space. The rod side space of each of the shift cylinders  715 A and  715 B on the work side and the shift cylinders  715 C and  715 D on the drive side is disposed on a side close to the rolled material  5 . 
     Here, the thrust reaction force is a sum of one force on a head side, which is a side pushing the upper work roll  710 , and another force on a rod side, which is a side pulling the upper work roll  710 . 
     In addition, the upper work roll  710  has a high load capability against being pushed. On the other hand, a thrust force transmitting member  794  is fitted to a part that transmits a pulling force to the upper work roll  710 . However, the diameter of the upper work roll  710  side at the part provided with the thrust force transmitting member  794  is narrowed. The load capability of the upper work roll  710  against the pulling force therefore depends on the strength of the part of the narrow diameter. Thus, the load capability against the pulling force is lower than the load capability against being pushed. 
     In the shift cylinders  715 A,  715 B,  715 C, and  715 D, output power on the head side is higher than on the rod side. Thus, as shown in  FIG.  6   , the pushing side is set as the head side, and the pulling side is set as the rod side, so that the force of pushing the upper work roll  710  can be made larger than the force of pulling the upper work roll  710 . 
     The thrust bearing  792  and the radial bearing  790 A are disposed in the upper work side bearing housing  712 A. The radial bearing  790 B is disposed in the upper drive side bearing housing  712 B. 
     Forces of the upper work roll bending cylinders  740  and  741  and the upper work roll bearing housing backlash removing cylinders  760  act on the radial bearings  790 A and  790 B among these bearings. These radial bearings  790 A and  790 B support these forces in the perpendicular directions, which act on the roll shaft, while the radial bearings  790 A and  790 B rotate. 
     The radial bearing  790 B on the drive side also supports the force in the axial direction, which acts on the upper drive side bearing housing  712 B. Thus, a four-row tapered roller bearing is generally used as the radial bearing  790 B. In addition, bearings of the same specifications are used as the radial bearing  790 B on the drive side and the radial bearing  790 A on the work side, so that complication of maintenance work can be avoided. 
     On the other hand, a double-row tapered roller bearing or the like is generally used as the thrust bearing  792  provided only to the work side. Reasons for providing the thrust bearing  792  only to the work side are as follows. 
     A shaft end on the drive side of the upper work roll  710  is coupled to a driving spindle (not shown). A driving torque acts on a roll shaft end portion, and therefore a torsion acts on the roll. There is thus a desire to increase the shaft diameter as much as possible. Here, when a configuration in which a thrust bearing is disposed also on the drive side is adopted, the shaft diameter is decreased, and the driving torque that can be transmitted is limited. 
     Therefore, the drive side is not provided with a thrust bearing, but is provided with only the radial bearing  790 B, so that the shaft diameter of the drive side shaft end portion of the upper work roll  710  is increased. Accordingly, the radial bearing  790 B on the drive side receives both the roll bending force and the thrust reaction force. Then, as for a method of receiving the forces on the work side and the drive side, the forces can be increased on the work side, for example. 
     A driving system of the shift cylinders  715 A,  715 B,  715 C, and  715 D is provided with a solenoid selector valve  810  that regulates inflow/outflow amounts of oil on the exit sides of a pressure line  801  branched from a pressure line  800  through which the hydraulic fluid delivered from a pump (not shown) of the hydraulic device  90  flows and a tank line  802  branched from a tank line  850  connected to a tank (not shown) that stores the hydraulic fluid. 
     When the solenoid selector valve  810  is a-energized, the rod sides of the shift cylinders  715 A and  715 B on the work side are connected to the pressure line  800 , so that a force in the work side direction acts on the thrust bearing  792 , and the head sides of the shift cylinders  715 C and  715 D on the drive side are connected to the pressure line  800 , so that a force in the work side direction acts on the radial bearing  790 B. Then, the head sides of the shift cylinders  715 A and  715 B on the work side and the rod sides of the shift cylinders  715 C and  715 D on the drive side are connected to the tank line  850 . The shift cylinders  715 A,  715 B,  715 C, and  715 D on each of the work side and the drive side thereby produce a shift force in the work side direction. 
     In addition, when the solenoid selector valve  810  is b-energized, the head sides of the shift cylinders  715 A and  715 B on the work side are connected to the pressure line  800 , so that a force in the drive side direction acts on the thrust bearing  792 , and the rod sides of the shift cylinders  715 C and  715 D on the drive side are connected to the pressure line  800 , so that a force in the drive side direction acts on the radial bearing  790 B. Then, the rod sides of the shift cylinders  715 A and  715 B on the work side and the head sides of the shift cylinders  715 C and  715 D on the drive side are connected to the tank line  850 . The shift cylinders  715 A,  715 B,  715 C, and  715 D on each of the work side and the drive side thereby produce a shift force in the drive side direction. 
     With the configuration of the solenoid selector valve  810  and the energization control of the control device  80 , the shift cylinders  715 C and  715 D apply a force of pulling to the drive side to the radial bearing  790 B when the shift cylinders  715 A and  715 B apply a force of pushing to the drive side to the thrust bearing  792 , and the shift cylinders  715 A and  715 B apply a force of pulling to the work side to the thrust bearing  792  when the shift cylinders  715 C and  715 D apply a force of pushing to the work side to the radial bearing  790 B. 
     Here, the head sides of the shift cylinders  715 A,  715 B,  715 C, and  715 D have higher output power than the rod sides thereof, and therefore the pushing force of each cylinder is larger than the pulling force thereof. When the upper work roll  710  is shifted in the drive side direction, load assignments received by the rod sides of the shift cylinders  715 C and  715 D on the drive side are made smaller than those of the head sides of the shift cylinders  715 A and  715 B on the work side. When the upper work roll  710  is shifted in the work side direction, load assignments received by the rod sides of the shift cylinders  715 A and  715 B on the work side are made smaller than those of the head sides of the shift cylinders  715 C and  715 D on the drive side. The pushing forces applied by the shift cylinders  715 A and  715 B or the shift cylinders  715 C and  715 D can be thereby made larger than the pulling forces. 
     Consequently, on the drive side, a resultant force of torsional stress caused by the driving torque and tension caused by a shift can be reduced. In particular, the thrust bearing  792  is present on the work side, and therefore a shaft end of the roll is particularly thin. Thus, the life of the shaft end of the roll can be lengthened by reducing the tension caused by a shift, which acts on the shaft end of the roll. 
     A pilot check valve  822  is provided to the pressure line  801  on the downstream side of the solenoid selector valve  810 . A pilot check valve  821  is provided to a pressure line  803  on the downstream side of the solenoid selector valve  810 . The hydraulic fluid is prevented from flowing to both the rod sides and the head sides of the shift cylinders  715 A,  715 B,  715 C, and  715 D when the solenoid selector valve  810  becomes neutral. Consequently, even when the shifting of the upper work roll  710  is stopped, the upper work roll  710  is supported by the shift cylinders  715 A and  715 B on the work side and the shift cylinders  715 C and  715 D on the drive side so as not to move in the axial direction. 
     On the downstream side of the pilot check valve  822  in the pressure line  801 , the pressure line  801  is branched into a drive side head side pressure line  804  connected to the head sides of the shift cylinders  715 C and  715 D on the drive side and a work side rod side pressure line  805  connected to the rod sides of the shift cylinders  715 A and  715 B on the work side. 
     Similarly, on the downstream side of the pilot check valve  821  in the pressure line  803 , the pressure line  803  is branched into a drive side rod side pressure line  806  connected to the rod sides of the shift cylinders  715 C and  715 D on the drive side and a work side head side pressure line  807  connected to the head sides of the shift cylinders  715 A and  715 B on the work side. 
     In such a hydraulic circuit, the control device  80  drives the hydraulic device  90  such that the shift cylinders  715 A,  715 B,  715 C, and  715 D each apply a force in a same direction to the radial bearing  790 B and the thrust bearing  792  so as to support a thrust force when the upper work roll  710  is not shifted in the axial direction at least during rolling. 
     The control device  80  regulates the solenoid selector valve  810  on the basis of the position of the upper work roll  710 , which is measured by the position sensor  716 . 
     Further, preferably, the control device  80  makes shifts of the upper work roll  710  performed in one direction during rolling, and makes the moving directions of the two facing rolls opposite from each other. Consequently, the life of the rolls and the bearings can be lengthened even in a case of a severe load condition where rolling is continued for a long time, and slight shifts continue to occur one after another during the rolling. 
     Incidentally, the hydraulic system of  FIG.  6    represents only parts for describing the present invention, and relief valves, flow control valves, check valves, and the like are added as appropriate when desired. For example, for a reason of elongation of the work roll due to thermal expansion, a change in the direction of the thrust force acting on the roll set, or the like, an excessive pressure may occur within coupled pipes of the head sides on the work side and the rod sides on the drive side or within coupled pipes of the rod sides on the work side and the head sides on the drive side. In order to deal with an excessive load at the time, relief valves are provided between the pilot check valves  821  and  822  and the shift cylinders  715 A,  715 B,  715 C, and  715 D, and a pressure increase within the pipes is thereby held to an allowable pressure of the machine. 
     Effects of the present embodiment will next be described. 
     In the rolling mill according to the foregoing first embodiment of the present invention, the shift cylinders  715 A,  715 B,  715 C, and  715 D each apply a force in a same direction to the radial bearing  790 B and the thrust bearing  792  when the upper work roll  710  is not shifted in the axial direction at least during rolling. The shift cylinders  715 A,  715 B,  715 C, and  715 D on both sides can thereby receive a thrust force from the upper work roll  710  in a distributed manner even in a case where no shift is performed during rolling. Thus, a large thrust force can be supported even in a case where a work roll of a relatively small diameter is used. 
     In addition, also when the upper work roll  710  is shifted, the force can be distributed to the shift cylinders  715 A,  715 B,  715 C, and  715 D on both the operation side and the drive side. In particular, the present embodiment can counteract the load of the thrust force, exposure thereto continuing for a long time, during normal operation, and is suitable for improving the life of the radial bearing  790 B, the thrust bearing  792 , and the like. 
     In addition, the shift cylinders  715 A,  715 B,  715 C, and  715 D are controlled such that the shift cylinders  715 C and  715 D apply a force of pulling to the drive side to the radial bearing  790 B when the shift cylinders  715 A and  715 B apply a force of pushing to the drive side to the thrust bearing  792 , and the shift cylinders  715 A and  715 B apply a force of pulling to the work side to the thrust bearing  792  when the shift cylinders  715 C and  715 D apply a force of pushing to the work side to the radial bearing  790 B. Thus, operation timings in which the shift cylinders  715 A,  715 B,  715 C, and  715 D on the work side and the drive side push and pull can be synchronized. The thrust force can therefore be distributed with high accuracy. 
     Further, the pushing forces applied by the shift cylinders  715 A and  715 B or the shift cylinders  715 C and  715 D are made larger than the pulling forces. Thus, even when a problem of a reduced diameter occurs at a shaft end part of the upper work roll  710 , the roll life can be lengthened by distributing the forces such that the pushing forces are made larger than the pulling forces. 
     In addition, the shift cylinders  715 A,  715 B,  715 C, and  715 D have a cylinder slid by an inflow or an outflow of oil into or from each of the head side space and the rod side space. The following are further provided: the pressure lines  801  and  803  into or from which the oil flows; the tank line  850 ; the drive side head side pressure line  804 ; the work side rod side pressure line  805 ; the drive side rod side pressure line  806 ; the work side head side pressure line  807 ; the position sensor  716  that senses the position of the upper work roll  710 ; and the solenoid selector valve  810  that is provided to the pressure lines  801  and  803 , and regulates the inflow/outflow amount of the oil. The control device  80  is further provided which regulates the solenoid selector valve  810  on the basis of the position of the upper work roll  710 , which is measured by the position sensor  716 . Thus, the upper work roll  710  can be shifted while the force is distributed to the shift cylinders  715 A,  715 B,  715 C, and  715 D on both the operation side and the drive side. 
     Further, the rod side space of each of the shift cylinders  715 A and  715 B on the work side and the shift cylinders  715 C and  715 D on the drive side is disposed on a side close to the rolled material. Thus, for the upper work roll  710  having a higher load capability against being pushed than a load capability against a pulling force, the pushing side providing high output power can be disposed on the head side, and the pulling side can be disposed on the rod side providing lower output power than the head side. A more reasonable arrangement relation can therefore be set. 
     In addition, letting D w  be the diameter of the upper work roll  710 , and letting L B  be a maximum rolling strip width of the rolled material, the upper work roll  710  satisfies a condition that D w/ L B  is 0.28 or less. Consequently, a steel strip harder than conventional can be rolled with a conventional work roll diameter or less, and more complex shape control can be performed. 
     It is to be noted that the configuration of the rolling mill according to the present embodiment is not limited to the form shown in  FIG.  2    and the like. Other forms will be described in the following with reference to  FIGS.  7  to  9   .  FIGS.  7  to  9    are plan views of assistance in explaining the part taken in the direction of arrows along the line A-A′ in  FIG.  2    in rolling mills according to modifications of the first embodiment. 
     In the rolling mill shown in  FIG.  7   , the shift cylinders  715  of the upper work roll  710  and the shift cylinders  717  of the lower work roll  711  are provided, and a shift cylinder  718  of the upper intermediate roll  720  and a shift cylinder  719  of the lower intermediate roll  721  are provided. 
     In the rolling mill shown in  FIG.  8   , the shift cylinders  715  of the upper work roll  710  and the shift cylinders  717  of the lower work roll  711  are provided, and only the upper intermediate roll  720  is provided. Incidentally, a form can be adopted in which only the lower intermediate roll  721  is provided in place of the form shown in  FIG.  8   . 
     In the rolling mill shown in  FIG.  9   , a form is adopted in which the upper intermediate roll  720  and the lower intermediate roll  721  are not provided, but the upper back-up roll  730  directly supports the upper work roll  710 , and the lower back-up roll  731  directly supports the lower work roll  711 . These correspond to the first stand  30 , the second stand  40 , and the third stand  50  shown in  FIG.  1   . 
     In addition, the above-described rolling mills can adopt a configuration in which at least the upper work roll  710  and the lower work roll  711  can cross each other during rolling. In particular, in the rolling mill in which the upper work roll  710  and the lower work roll  711  cross each other during rolling, the thrust force acting on the upper work roll  710  and the lower work roll  711  is increased. Even when the upper work roll  710  and the lower work roll  711  are shifted in such a rolling mill, the provision of the shift cylinders  715  and  717  on both the work side and the drive side can reduce shift forces on at least one side, and lengthen the life of various kinds of constituent members constituting the rolling mill, such as the bearings, the rolls, and the like. In addition, a configuration can be adopted in which the upper intermediate roll  720  and the lower intermediate roll  721  can cross each other. 
     Second Embodiment 
     A rolling mill, a rolling mill control method, and a thrust force supporting method in the rolling mill according to a second embodiment of the present invention will be described with reference to  FIG.  10    and  FIG.  11   .  FIG.  10    is a plan view of assistance in explaining details of a work roll part in the rolling mill according to the present second embodiment.  FIG.  11    is a plan view of assistance in explaining details of a work roll part in a rolling mill according to a modification of the second embodiment. 
     As shown in  FIG.  10   , on the work side of the driving system of the shift cylinders  715 A,  715 B,  715 C, and  715 D in the rolling mill according to the present embodiment, a work side solenoid selector valve  910  that regulates inflow/outflow amounts of oil is provided to the exit sides of a pressure line  901  branched from the pressure line  800  and a tank line  902  branched from the tank line  850 . 
     On the drive side, a drive side solenoid selector valve  915  that regulates inflow/outflow amounts of oil is provided to the exit sides of a pressure line  951  branched from the pressure line  800  and a tank line  952  branched from the tank line  850 . 
     The work side solenoid selector valve  910  and the drive side solenoid selector valve  915  have the same configuration as the solenoid selector valve  810  in the first embodiment. 
     In the present embodiment, as for operation of the work side solenoid selector valve  910  and the drive side solenoid selector valve  915 , as shown in the following Table 1, preferably, both the work side solenoid selector valve  910  and the drive side solenoid selector valve  915  are a-energized when the shift direction of the upper work roll  710  is the work side, both the work side solenoid selector valve  910  and the drive side solenoid selector valve  915  are b-energized when the shift direction is the drive side, and the work side solenoid selector valve  910  and the drive side solenoid selector valve  915  are set to N as a neutral state when a shift is stopped. 
     In addition, when switching is performed, the work side solenoid selector valve  910  and the drive side solenoid selector valve  915  are preferably switched to a-energization, b-energization, or the neutral state at the same time. When a-energization and b-energization are reversed between the work side and the drive side, forces in opposite directions occur, thus decreasing the effect of the original function of reducing the thrust resistance force. It is therefore preferable to perform the same a-energization or b-energization simultaneously. The shift cylinders  715 A and  715 B on the work side and the shift cylinders  715 C and  715 D on the drive side can thereby receive a force necessary for a shift in a distributed manner at least at a time of a work side direction shift or at a time of a drive side direction shift. 
     Incidentally, these conditions are set for a case where the work side solenoid selector valve  910  and the drive side solenoid selector valve  915  are of the same specifications. In a case where the work side solenoid selector valve  910  and the drive side solenoid selector valve  915  have port configurations opposite from each other, a-energization and b-energization are preferably reversed between the work side and the drive side.  
     
       
         
          TABLE  1 

           
               
               
               
             
               
                 Shift direction 
                 WS solenoid selector valve 
                 DS solenoid selector valve 
               
             
            
               
                 WS 
                 a 
                 a 
               
               
                 DS 
                 b 
                 b 
               
               
                 Stop 
                 N 
                 N 
               
            
           
         
       
     
     In the present embodiment, when the work side solenoid selector valve  910  and the drive side solenoid selector valve  915  are a-energized, the rod sides of the shift cylinders  715 A and  715 B on the work side are connected to the pressure line  800  via a work side rod side pressure line  903  and the pressure line  901 , so that a force in the work side direction acts on the thrust bearing  792 , and the head sides of the shift cylinders  715 C and  715 D on the drive side are connected to the pressure line  800  via a drive side head side pressure line  953  and the pressure line  951 , so that a force in the work side direction acts on the radial bearing  790 B. 
     Then, the head sides of the shift cylinders  715 A and  715 B on the work side are connected to the tank line  850  via a work side head side pressure line  904  and the tank line  902 , and the rod sides of the shift cylinders  715 C and  715 D on the drive side are connected to the tank line  850  via a drive side rod side pressure line  954  and the tank line  952 . A shift force in the work side direction thereby occurs. 
     In addition, when the solenoid selector valve  810  is b-energized, the head sides of the shift cylinders  715 A and  715 B on the work side are connected to the pressure line  800  via the work side head side pressure line  904  and the pressure line  901 , so that a force in the drive side direction acts on the thrust bearing  792 , and the rod sides of the shift cylinders  715 C and  715 D on the drive side are connected to the pressure line  800  via the drive side rod side pressure line  954  and the pressure line  951 , so that a force in the drive side direction acts on the radial bearing  790 B. 
     Then, the rod sides of the shift cylinders  715 A and  715 B on the work side are connected to the tank line  850  via the work side rod side pressure line  903  and the tank line  902 , and the head sides of the shift cylinders  715 C and  715 D on the drive side are connected to the tank line  850  via the drive side head side pressure line  953  and the tank line  952 . A shift force in the drive side direction thereby occurs. 
     A pilot check valve  922  is provided to the work side rod side pressure line  903  on the downstream side of the work side solenoid selector valve  910 , and a pilot check valve  921  is provided to the work side head side pressure line  904  on the downstream side of the work side solenoid selector valve  910 . 
     Similarly, a pilot check valve  923  is provided to the drive side rod side pressure line  954  on the downstream side of the drive side solenoid selector valve  915 , and a pilot check valve  924  is provided to the drive side head side pressure line  953  on the downstream side of the drive side solenoid selector valve  915 . 
     Further, the work side rod side pressure line  903  is provided with a work side rod side pressure measuring device  932  that measures the pressures of the rod side spaces of the shift cylinders  715 A and  715 B, and the work side head side pressure line  904  is provided with a work side head side pressure measuring device  931  that measures the pressures of the head side spaces of the shift cylinders  715 A and  715 B. Similarly, the drive side rod side pressure line  954  is provided with a drive side rod side pressure measuring device  934  that measures the pressures of the rod side spaces of the shift cylinders  715 C and  715 D, and the drive side head side pressure line  953  is provided with a drive side head side pressure measuring device  933  that measures the pressures of the head side spaces of the shift cylinders  715 C and  715 D. 
     In such a hydraulic circuit, the control device  80  regulates the work side solenoid selector valve  910  and the drive side solenoid selector valve  915  on the basis of the respective pressures measured by the work side head side pressure measuring device  931 , the work side rod side pressure measuring device  932 , the drive side head side pressure measuring device  933 , and the drive side rod side pressure measuring device  934 . 
     In addition, the control device  80  regulates the work side solenoid selector valve  910  and the drive side solenoid selector valve  915  on the basis of the position of the upper work roll  710 , which is measured by the position sensor  716 . 
     Details of control thereof can, for example, be similar to those of control in a third embodiment to be described later. 
     Incidentally, in the circuit shown in  FIG.  10   , when a shift is performed and thereafter stopped during rolling, the upper work side bearing housing  712 A is supported by the shift cylinders  715 A and  715 B on the work side, the upper drive side bearing housing  712 B is supported by the shift cylinders  715 C and  715 D on the drive side, and the oil is sealed by the pilot check valves  921 ,  922 ,  923 , and  924 . Therefore, for a reason of elongation of the upper work roll  710  due to thermal expansion, a change in the direction of the thrust force acting on the roll set, or the like, only either the shift cylinders  715 A and  715 B on the work side or the shift cylinders  715 C and  715 D on the drive side may support the thrust reaction force. 
     In order to deal with an excessive load at the time, it is preferable to provide relief valves onto the work side rod side pressure line  903  and the work side head side pressure line  904  between the pilot check valves  921  and  922  and the shift cylinders  715 A and  715 B and onto the drive side rod side pressure line  954  and the drive side head side pressure line  953  between the pilot check valves  923  and  924  and the shift cylinders  715 C and  715 D, and thereby hold a pressure increase within the pipes to an allowable pressure of the pipes. 
     Other configurations and operations are substantially the same configurations and operations as those of the rolling mill, the rolling mill control method, and the thrust force supporting method in the rolling mill according to the foregoing first embodiment, and therefore details thereof will be omitted. 
     The rolling mill, the rolling mill control method, and the thrust force supporting method in the rolling mill according to the second embodiment of the present invention also provide effects substantially similar to those of the rolling mill, the rolling mill control method, and the thrust force supporting method in the rolling mill according to the foregoing first embodiment. 
     In addition, a balance between the pushing and pulling of the hydraulic cylinders on the operation side and the drive side, that is, load allocation can be adjusted by regulating the work side solenoid selector valve  910  and the drive side solenoid selector valve  915  on the basis of the respective pressures measured by the work side head side pressure measuring device  931 , the work side rod side pressure measuring device  932 , the drive side head side pressure measuring device  933 , and the drive side rod side pressure measuring device  934 . In a case where an allowable load differs because the bearings being used are different, for example, an effect is obtained in that a large thrust force can be supported on both the work side and the drive side without exceeding the allowable load of the bearings. 
     Further, the work side solenoid selector valve  910  and the drive side solenoid selector valve  915  are regulated also on the basis of the position of the upper work roll  710 , which is measured by the position sensor  716 . It is therefore possible to shift the upper work roll  710  while distributing the force to the shift cylinders  715 A,  715 B,  715 C, and  715 D on both the operation side and the drive side, and further easily set the position of the upper work roll  710  during a shift or after stopping the shift. 
     Incidentally, the form of the rolling mill according to the present embodiment is not limited to the form shown in  FIG.  10   . As shown in  FIG.  11   , it is possible to dispose a pressure control valve  930  on the entry side of the drive side solenoid selector valve  915  on the pressure line  951  on the drive side where the position sensor  716  is not disposed, and perform, by the pressure control valve  930 , control equivalent to aa adjustment using a drive side servo valve  1070  in flowcharts shown in  FIG.  13    and  FIG.  14    according to a third embodiment to be described later. This also enables the adjustment of load allocation. 
     In addition, the adjustment of load allocation is enabled also by installing a servo valve in place of the drive side solenoid selector valve  915  and the pressure control valve  930  in the configuration shown in  FIG.  11   , and perform adjustment equivalent to aa adjustment using the drive side servo valve  1070  in the flowcharts shown in  FIG.  13    and  FIG.  14   . 
     Further, the configuration according to the present embodiment can be applied to the modifications of the first embodiment, which are shown in  FIGS.  7  to  9   . 
     Third Embodiment 
     A rolling mill, a rolling mill control method, and a thrust force supporting method in the rolling mill according to a third embodiment of the present invention will be described with reference to  FIGS.  12  to  15   .  FIG.  12    is a plan view of assistance in explaining details of an upper work roll part in the rolling mill according to the present third embodiment.  FIG.  13    is a flowchart showing a flow of roll axis direction positional adjustment in the rolling mill according to the third embodiment.  FIG.  14    is a flowchart showing a flow of shift force adjustment in the rolling mill according to the third embodiment.  FIG.  15    is a plan view of assistance in explaining details of an upper work roll part in a rolling mill according to a modification of the third embodiment. 
     As shown in  FIG.  12   , on the work side of the driving system of the shift cylinders  715 A,  715 B,  715 C, and  715 D in the rolling mill according to the present embodiment, a first work side solenoid selector valve  1010  that regulates inflow/outflow amounts of oil is provided to the exit sides of a pressure line  1001  branched from the pressure line  800  and a tank line  1051  branched from the tank line  850 . 
     In addition, a work side servo valve  1030  that regulates inflow/outflow amounts of oil is provided to the exit side of a pressure line  1002  branched from the pressure line  800  and a tank line  1052  branched from the tank line  850 . 
     Further, a second work side solenoid selector valve  1040  that performs on/off regulation of a pilot check valve  1023  and a pilot check valve  1024  via a pilot line  1017  is provided to the exit sides of a pressure line  1003  branched from the pressure line  800  and a tank line  1053  branched from the tank line  850 . 
     On the drive side, a first drive side solenoid selector valve  1060  that regulates inflow/outflow amounts of oil is provided to the exit sides of a pressure line  1004  branched from the pressure line  800  and a tank line  1054  branched from the tank line  850 . 
     In addition, a drive side servo valve  1070  that regulates inflow/outflow amounts of oil is provided to the exit sides of a pressure line  1005  branched from the pressure line  800  and a tank line  1055  branched from the tank line  850 . 
     Similarly, a second drive side solenoid selector valve  1080  that performs on/off regulation of a pilot check valve  1027  and a pilot check valve  1028  via a pilot line  1018  is provided to the exit sides of a pressure line  1006  branched from the pressure line  800  and a tank line  1056  branched from the tank line  850 . 
     A pilot check valve  1021  is provided to a work side rod side pressure line  1015  on the downstream side of the first work side solenoid selector valve  1010 , and a pilot check valve  1022  is provided to a work side head side pressure line  1016  on the downstream side of the first work side solenoid selector valve  1010 . 
     Similarly, a pilot check valve  1025  is provided to a drive side head side pressure line  1066  on the downstream side of the first drive side solenoid selector valve  1060 , and a pilot check valve  1026  is provided to a drive side rod side pressure line  1065  on the downstream side of the first drive side solenoid selector valve  1060 . 
     Further, the work side rod side pressure line  1015  is provided with a work side rod side pressure measuring device  1032  that measures the pressures of the rod side spaces of the shift cylinders  715 A and  715 B, and the work side head side pressure line  1016  is provided with a work side head side pressure measuring device  1031  that measures the pressures of the head side spaces of the shift cylinders  715 A and  715 B. 
     Similarly, the drive side rod side pressure line  1065  is provided with a drive side rod side pressure measuring device  1034  that measures the pressures of the rod side spaces of the shift cylinders  715 C and  715 D, and the drive side head side pressure line  1066  is provided with a drive side head side pressure measuring device  1033  that measures the pressures of the head side spaces of the shift cylinders  715 C and  715 D. 
     In the present embodiment, operations of the first work side solenoid selector valve  1010 , the work side servo valve  1030 , the second work side solenoid selector valve  1040 , the first drive side solenoid selector valve  1060 , the drive side servo valve  1070 , and the second drive side solenoid selector valve  1080  are as shown in the following Table 2.  
     
       
         
          TABLE  2 

           
               
               
               
               
               
               
               
               
               
             
               
                 Shift direction 
                 Shift speed 
                 State 
                 WS first solenoid selector valve 
                 WS second solenoid selector valve 
                 WS servo valve 
                 DS first solenoid selector valve 
                 DS second solenoid selector valve 
                 DS servo valve 
               
             
            
               
                 WS 
                 High speed 
                 Not during rolling 
                 a 
                 N 
                 N 
                 a 
                 N 
                 N 
               
               
                 Low speed 
                 During rolling 
                 N 
                 a 
                 on 
                 N 
                 a 
                 on 
               
               
                 DS 
                 High speed 
                 Not during rolling 
                 b 
                 N 
                 N 
                 b 
                 N 
                 N 
               
               
                 Low speed 
                 During rolling 
                 N 
                 a 
                 on 
                 N 
                 a 
                 on 
               
               
                 Stop 
                 Not during rolling 
                 N 
                 N 
                 N 
                 N 
                 N 
                 N 
               
               
                 During rolling 1 
                 N 
                 a 
                 on 
                 N 
                 a 
                 on 
               
               
                 During rolling 2 
                 N 
                 N 
                 N 
                 N 
                 N 
                 N 
               
            
           
         
       
     
     A high shift speed at which only the first work side solenoid selector valve  1010  and the first drive side solenoid selector valve  1060  are a-energized or b-energized is used not during rolling. For example, the high shift speed is used when the upper work roll  710  is desired to be shifted at high speed, for example when the upper work roll  710  is moved in the axial direction within the rolling mill for roll rearrangement. The high shift speed is set at about 20 [mm/s], for example. 
     A low shift speed at which the work side servo valve  1030 , the second work side solenoid selector valve  1040 , the drive side servo valve  1070 , and the second drive side solenoid selector valve  1080  are used is used when the upper work roll  710  is shifted during rolling. In this timing, a rolling load acts, and therefore shift resistances between the upper work roll  710  and the rolled material  5  and between the upper work roll  710  and the upper intermediate roll  720  are increased as the shift speed becomes faster. Therefore, a shift is performed at a low speed during rolling. The low shift speed is set at 2.0 [mm/s] or lower, for example. 
     Shifts during rolling are performed on the upper and lower sides at the same time; for example, the upper work roll  710  is shifted in the work side direction and the lower work roll  711  is shifted in the drive side direction at the same time. The shift speeds are made to be substantially the same, and the upper work roll  710  and the lower work roll  711  are shifted such that the upper work roll  710  and the lower work roll  711  are in a point-symmetric state with respect to the center of the rolled material  5  (or the pass center of the rolling mill) also during shift operation. When the point-symmetric state is disturbed during rolling, leveling changes, one side in the width direction of the rolled material  5  is rolled more than another side, thus forming a wedge shape, and consequently off-center tends to be caused. The upper work roll  710  and the lower work roll  711  are moved in the point-symmetric state in order to avoid such unstable rolling. 
     Both when the shift direction of the upper work roll  710  is the work side and when the shift direction of the upper work roll  710  is the drive side, the second work side solenoid selector valve  1040  and the second drive side solenoid selector valve  1080  are each a-energized. 
     The work side servo valve  1030  and the drive side servo valve  1070  are each driven to be ON. At this time, the position sensor  716  senses the position of the upper work roll  710 , and the position and a moving speed are determined from a result of the position sensing, and are regulated to be a target position and a target moving speed. 
     That is, the control device  80  in the present embodiment regulates the work side servo valve  1030 , the second work side solenoid selector valve  1040 , the drive side servo valve  1070 , and the second drive side solenoid selector valve  1080  on the basis of the respective pressures measured by the work side head side pressure measuring device  1031 , the work side rod side pressure measuring device  1032 , the drive side head side pressure measuring device  1033 , and the drive side rod side pressure measuring device  1034 . 
     In addition, the control device  80  regulates the work side servo valve  1030 , the second work side solenoid selector valve  1040 , the drive side servo valve  1070 , and the second drive side solenoid selector valve  1080  also on the basis of the position of the upper work roll  710 , which is measured by the position sensor  716 . 
     More specifically, a shift force on the work side is obtained from measured values of the work side head side pressure measuring device  1031  provided to the work side head side pressure line  1016  shown in  FIG.  12    and the work side rod side pressure measuring device  1032  provided to the work side rod side pressure line  1015 . A shift force Fw on the work side is obtained from (rod side pressure PTwr of the shift cylinders  715 A and  715 B on the work side) × (rod side area Awr of the shift cylinders  715 A and  715 B on the work side) – (head side pressure PTwh of the shift cylinders  715 A and  715 B on the work side) × (head side area Awh of the shift cylinders  715 A and  715 B on the work side). 
      In addition, on the drive side, a shift force on the drive side is obtained from measured values of the drive side head side pressure measuring device  1033  provided to the drive side head side pressure line  1066  and the drive side rod side pressure measuring device  1034  provided to the drive side rod side pressure line  1065 . A shift force Fd on the drive side is obtained from (head side pressure PTdh of the shift cylinders  715 C and  715 D on the drive side) × (head side area Adh of the shift cylinders  715 C and  715 D on the drive side) – (rod side pressure PTdr of the shift cylinders  715 C and  715 D on the drive side) × (rod side area Adr of the shift cylinders  715 C and  715 D on the drive side). 
     Thereafter, the drive side servo valve  1070  performs adjustment such that the obtained shift force on the work side and the obtained shift force on the drive side each have a same force magnitude and a same force direction. Here, it is also possible to change the shift forces optionally while the shift forces on the work side and the drive side have the same direction. 
     Thus, the work side servo valve  1030  is used for positioning, and the drive side servo valve  1070  is used for shift load allocation adjustment. 
     A flow of roll axis direction positional adjustment will next be described with reference to  FIG.  13   . 
      First, the control device  80  receives an input of a command value xr of a roll axis direction movement amount (step S 701 ), and receives an input of a shift movement amount (that is, a measured value of the position sensor  716 ) xa of the shift cylinders  715 A,  715 B,  715 C, and  715 D at a present point in time (step S 702 ). The command value xr of the roll axis direction movement amount is specified according to wear in the roll or in order to make the position of a roll tapered portion with respect to a strip width end portion a desired position. 
     Next, the control device  80  determines whether or not an absolute value |xr - xa| of a difference between the command value xr input in step S 701  and the shift movement amount xa input in step S 702  is equal to or more than a predetermined difference value Δx (step S 703 ). When the control device  80  determines that the absolute value |xr -xa| is equal to or more than the difference value ΔX, the control device  80  advances the processing to step S 704 , adjusts the shift movement amount xa by the work side servo valve  1030  (step S 704 ), and then returns the processing to step S 703 . When the control device  80  determines that the absolute value |xr - xa| is smaller than the difference value Δx, on the other hand, the control device  80  ends the processing. 
     This positioning adjustment is performed such that xa is automatically adjusted by the work side servo valve  1030   when |xr - xa| ≥ Δx at a time of a shift during rolling as shown in Table 2 or “During rolling 1” as shown in Table 2 even at a time of a stop. Incidentally, a value of ±5 [mm] or the like, for example, is set as Δx. 
     Incidentally, the roll axis direction position can be adjusted also by using the work side solenoid selector valve  910  on the side where the position sensor  716  is present in  FIG.  10   , and performing control equivalent to the adjustment of the shift movement amount xa by the work side servo valve  1030  in the flowchart shown in  FIG.  13    through the switching of the work side solenoid selector valve  910 . 
     A flow of shift force adjustment will next be described with reference to  FIG.  14   . 
     First, the control device  80  receives an input of a command value ar of a ratio between the shift forces on the work side and the drive side as a command value of shift load allocation itself in Table 2 (step S 711 ), and obtains a measured value aa of the ratio between the shift forces on the work side and the drive side, which is obtained from (ratio aw (= Fw/Ftt) of the shift force on the work side)/(ratio ad (= Fd/Ftt) of the shift force on the drive side), where a sum of the shift force Fw on the work side and the shift force Fd on the drive side is Ftt (step S 712 ). 
     Next, the control device  80  determines whether or not an absolute value |αr - αa| of a difference between the command value ar input in step S 711  and the measured value aa obtained in step S 712  is equal to or more than a difference Δα (for example, a setting is made such that Δα = 0.1 × aa or the like) between the command value and the measured value of the ratio between the shift forces on the work side and the drive side (step S 713 ). When the control device  80  determines that the absolute value |αr - αa| is equal to or more than the difference Δα, the control device  80  advances the processing to step S 714 , makes an adjustment by the drive side servo valve  1070  such that the measured value aa is decreased (step S 714 ), and then returns the processing to step S 713 . When the control device  80  determines that the absolute value |αr - αa| is smaller than the difference Δα, on the other hand, the control device  80  ends the processing. 
     This shift force adjustment is performed at a time of a shift during rolling as shown in Table 2 or “During rolling 1” as shown in Table 2 even at a time of a stop. Load allocation is thus adjusted. 
     In addition, the lower work roll  711  opposite in the vertical direction from the upper work roll  710  shown in  FIG.  12    is shifted in a manner point-symmetric to the upper work roll  710 . Also in the case of the lower work roll  711 , as in  FIG.  12   , the servo valve on the work side is used for positioning, and the servo valve on the drive side is used for shift load allocation adjustment. In addition, it suffices for one of the servo valves on the work side or the drive side to be for positioning, and it suffices for the other servo valve to be for shift load allocation adjustment. Either of the work side and the drive side may be for positioning or for shift load allocation adjustment. 
     During a stop, one of various kinds of states in three rows in a lower part of Table 2 can be assumed. N as a neutral state is assumed when rolling is not being performed. “During rolling 1” in Table 2, a servo valve is used to retain the position, so that the servo valve for positioning performs position retention, and the servo valve for shift load allocation adjustment performs shift load allocation. “During rolling 2” in Table 2, the pressures of the shift cylinders  715 A,  715 B,  715 C, and  715 D are simply set in a sealed state without the use of the work side servo valve  1030  and the drive side servo valve  1070 . 
     Other configurations and operations are substantially the same configurations and operations as those of the rolling mill, the rolling mill control method, and the thrust force supporting method in the rolling mill according to the foregoing first embodiment, and therefore details thereof will be omitted. 
     The rolling mill, the rolling mill control method, and the thrust force supporting method in the rolling mill according to the third embodiment of the present invention also provide effects substantially similar to those of the rolling mill, the rolling mill control method, and the thrust force supporting method in the rolling mill according to the foregoing first embodiment. 
     In addition, in the first embodiment, there is an advantage of being able to provide a simple hydraulic system in which switching between the work side and the drive side can be performed by one solenoid selector valve  810 . On the other hand, although a certain load allocation is performed, it is not possible to adjust the measured value aa of the ratio between the shift forces on the work side and the drive side as in the flowcharts as shown in  FIG.  13    and  FIG.  14   . 
     In a case where the bearings on the work side and the drive side are the same and thus the bearings have a same load resistance life, for example, the thrust reaction forces on both sides may be made to be substantially the same. In addition, even in a case where the bearings on the work side and the drive side are different, and have different load resistance lives, setting a bearing ratio between one thrust reaction force and the other thrust reaction force such that both lives become substantially the same is also one method. In the present embodiment, a configuration can be adopted in which consideration is given also to the load resistance lives of such bearings. 
     Incidentally, as shown in  FIG.  15   , it is possible to exclude the thrust bearing  792  on the work side shown in  FIG.  12   , make also a radial bearing  790 A 1  on the work side a four-row tapered bearing, and thereby adopt the same structure as the radial bearing  790 B on the drive side. 
     According to this, it is possible to reduce the thrust reaction force on the work side by sharing the thrust reaction forces, and resist the thrust reaction force by the same bearing structure as that on the drive side. Thus, the kinds of bearings can be reduced, and a maintenance load can be reduced. 
     Further, load allocation can be adjusted also by arranging a solenoid selector valve and a pressure control valve in place of the drive side servo valve  1070  in  FIG.  12   , and performing, by the pressure control valve, adjustment equivalent to the adjustment of the measured value aa of the ratio between the shift forces on the work side and the drive side by the drive side servo valve  1070  in the flowchart shown in  FIG.  14   . 
     In addition, the side on which shift load allocation adjustment is performed may not be the side of the drive side servo valve  1070 , but another method can also be adopted. For example, there is a method of reducing the shift force on the positioning side by enabling a certain shift force to be supplied when the shift force on the positioning side exceeds a certain value. 
     Further, in Table 2, the first work side solenoid selector valve  1010  and the first drive side solenoid selector valve  1060  are used when the shift speed is a high speed. However, the work side servo valve  1030  and the drive side servo valve  1070  can be used at all times including times when the shift speed is a high speed, and the first work side solenoid selector valve  1010  and the first drive side solenoid selector valve  1060  can be set as backups in case of the occurrence of an abnormality in the work side servo valve  1030  and the drive side servo valve  1070 . 
     In addition, the configuration of the present embodiment can be applied to the modifications of the first embodiment, which are shown in  FIGS.  7  to  9   . 
     Others 
     It is to be noted that the present invention is not limited to the foregoing embodiments, but includes various modifications. The foregoing embodiments have been described in detail in order to describe the present invention in an easily understandable manner, and are not necessarily limited to embodiments including all of the described configurations. 
      In addition, a part of a configuration of a certain embodiment can be replaced with a configuration of another embodiment, and a configuration of another embodiment can be added to a configuration of a certain embodiment. In addition, for a part of a configuration of each embodiment, another configuration can be added, deleted, or substituted. 
     DESCRIPTION OF REFERENCE CHARACTERS 
     
         
           1 : Rolling equipment 
           5 : Rolled material 
           30 : First stand (rolling mill) 
           40 : Second stand (rolling mill) 
           50 : Third stand (rolling mill) 
           60 : Fourth stand (rolling mill) 
           70 : Fifth stand (rolling mill) 
           80 : Control device 
           90 : Hydraulic device 
           201 : Straight line 
           202 : Straight line 
           203 : Thrust resistance force 
           204 : Straight line 
           205 : Straight line 
           700 : Housing 
           702 : Entry side fixed member 
           703 : Exit side fixed member 
           710 : Upper work roll (work roll) 
           711 : Lower work roll (work roll) 
           712 : Upper work roll bearing housing 
           712 A: Upper work side bearing housing 
           712 B: Upper drive side bearing housing 
           713 : Lower work roll bearing housing 
           713 A: Bearing housing 
           713 B: Bearing housing 
           714 A,  714 B,  714 C,  714 D: Connecting member 
           715 : Shift cylinder (work side and drive side thrust force supporting devices) 
           715 A,  715 B: Shift cylinder (operation side thrust force supporting device) 
           715 C,  715 D: Shift cylinder (drive side thrust force supporting device) 
           716 : Position sensor 
           717 : Shift cylinder (work side and drive side thrust force supporting devices) 
           718 ,  719 : Shift cylinder 
           720 : Upper intermediate roll 
           721 : Lower intermediate roll 
           722 : Upper intermediate roll bearing housing 
           723 : Lower intermediate roll bearing housing 
           730 : Upper back-up roll 
           731 : Lower back-up roll 
           732 : Upper back-up roll bearing housing 
           733 : Lower back-up roll bearing housing 
           740 ,  741 ,  742 ,  743 : Upper work roll bending cylinder 
           744 ,  745 ,  746 ,  747 : Lower work roll bending cylinder 
           750 ,  751 : Upper intermediate roll bending cylinder 
           752 ,  753 : Lower intermediate roll bending cylinder 
           760 : Upper work roll bearing housing backlash removing cylinder 
           762 : Lower work roll bearing housing backlash removing cylinder 
           771 : Upper intermediate roll bearing housing backlash removing cylinder 
           773 : Lower intermediate roll bearing housing backlash removing cylinder 
           780 : Upper back-up roll bearing housing backlash removing cylinder 
           782 : Lower back-up roll bearing housing backlash removing cylinder 
           790 A,  790 A 1 ,  790 B: Radial bearing 
           792 : Thrust bearing 
           794 : Thrust force transmitting member 
           800 ,  801 ,  803 ,  901 ,  951 ,  1001 ,  1002 ,  1003 ,  1004 ,  1005 ,  1006 : Pressure line (pipe) 
           802 ,  850 ,  902 ,  952 ,  1051 ,  1052 ,  1053 ,  1054 ,  1055 ,  1056 : Tank line 
           804 ,  953 ,  1066 : Drive side head side pressure line (pipe) 
           805 ,  903 ,  1015 : Work side rod side pressure line (pipe) 
           806 ,  954 ,  1065 : Drive side rod side pressure line (pipe) 
           807 ,  904 ,  1016 : Work side head side pressure line (pipe) 
           810 : Solenoid selector valve (inflow/outflow oil amount adjusting unit) 
           821 ,  822 ,  921 ,  922 ,  923 ,  924 ,  1021 ,  1022 ,  1023 ,  1024 ,  1025 ,  1026 ,  1027 ,  1028 : Pilot check valve 
           910 : Work side solenoid selector valve (inflow/outflow oil amount adjusting unit) 
           915 : Drive side solenoid selector valve (inflow/outflow oil amount adjusting unit) 
           930 : Pressure control valve 
           931 ,  1031 : Work side head side pressure measuring device 
           932 ,  1032 : Work side rod side pressure measuring device 
           933 ,  1033 : Drive side head side pressure measuring device 
           934 ,  1034 : Drive side rod side pressure measuring device 
           1010 : First work side solenoid selector valve (inflow/outflow oil amount adjusting unit) 
           1017 ,  1018 : Pilot line 
           1030 : Work side servo valve (inflow/outflow oil amount adjusting unit) 
           1040 : Second work side solenoid selector valve (inflow/outflow oil amount adjusting unit) 
           1060 : First drive side solenoid selector valve (inflow/outflow oil amount adjusting unit) 
           1070 : Drive side servo valve (inflow/outflow oil amount adjusting unit) 
           1080 : Second drive side solenoid selector valve (inflow/outflow oil amount adjusting unit)