Patent Publication Number: US-6220071-B1

Title: Method and apparatus for controlling strip edge relief in a cluster rolling mill

Description:
This invention relates generally to cluster rolling mills for rolling cold metal strip, and more particularly to an improved method and apparatus for adjusting the strip edge relief in the edge region of the material being rolled. 
     BACKGROUND OF THE INVENTION 
     It is known that rolls in a rolling mill flatten slightly due to rolling forces imposed on the working rolls and intermediate rolls as they are squeezed between the backing bearings and the material being rolled. Since the width of the strip material being rolled is always less than the length of the working rolls, the ends of the working rolls are not flattened by these forces and there is a transition area extending inward from the edge of the strip being rolled. This transition section causes the edges of the strip to be over-rolled at the edges. This is because the distance between the flattened work rolls in the central portion of the strip is greater than the distance between the partially flattened work rolls at the edge of the strip. A strip that is over-rolled at the edges will result in wavy or “pie crust” edges. 
     The prior art has sought to control the polarity of the rolled material in various ways, for instance by controlling the surface profile of the work rolls and intermediate rolls, by controlling the surface profile of the backup bearing rolls through hydraulic cylinders actuating eccentric shaft mounting, or by selective bending of rolls. 
     Currently, a popular method for adjusting the strip edge relief in a twenty-high cluster rolling mill is to employ a pair of intermediate rolls in contact with the upper work roll which are tapered on one end, and a pair of intermediate rolls in contact with the lower work roll, which are tapered on the other end. Then, by selectively shifting one or the other of the sets of tapered rolls in a lateral direction, using rotating couplings and linkage rods attached to hydraulic actuators, the degree of strip edge relief may be adjusted. The disadvantage of this system is that the rotating couplings must be small in diameter in order to function. Therefore lateral adjustments of the tapered rolls may only achieved under light rolling loads. 
     Although the prior art system utilizing lateral adjustments of the single-end-tapered intermediate rolls is effective for controlling over-rolling of strip edges, the lateral shifting mechanisms required are complicated and expensive. Also removal and replacement of the single-end-tapered intermediate rolls is cumbersome and time consuming. 
     Accordingly, one object of the present invention is to provide an improved method and apparatus for controlling strip edge relief in a cluster rolling mill. 
     Another object of the invention is to provide an improved method and apparatus for controlling polarity of strip material rolled in a twenty-high cluster rolling mill. 
     Still another object of the invention is to provide an improved method and apparatus for utilizing tapered intermediate rolls to adjust strip edge relief, without requiring lateral adjustment of the tapered rolls. 
     SUMMARY OF THE INVENTION 
     Briefly stated, the present invention comprises an improved apparatus and method for controlling strip edge relief in a cluster rolling mill, the cluster rolling mill comprising first and second work rolls for contacting material to be rolled, first and second pairs of intermediate rolls contacting the respective first and second work rolls, and a number of additional rolls and backing bearings providing backing support for the intermediate rolls in first and second clusters mounted in a supporting frame. 
     The improved apparatus is characterized by each roll of the first pair of intermediate rolls being double-tapered, and having a central portion contacting the first work roll, tapered portions on opposite sides of the central portion providing gradually increasing clearance with the first work roll, and having journal portions on opposite ends thereof together with means arranged to rotatably engage the opposite journal portions of the first pair of intermediate rolls and adapted to controllably exert bending forces on the first pair of intermediate rolls so as to adjust the strip edge relief on the material rolled between the first and second work rolls. 
     The improved method comprises providing a first pair of double-tapered intermediate rolls as described above, rotatably engaging the opposite journal portions and controllably exerting bending forces on the first pair of intermediate rolls so as to adjust the strip edge relief on the material being rolled between the first and second work rolls. 
    
    
     DRAWING 
     The invention will be better understood by reference to the following description, taken in connection with the accompanying drawings, in which: 
     FIG. 1 is a schematic end elevational view of a hypothetical rolling mill, illustrating the problem of “over-rolling” the edges of strip material due to work roll flattening. 
     FIG. 1 a  is a schematic partial side elevational view, in cross section, taken along lines  1   a — 1   a  of FIG. 1, 
     FIG. 1 b  is a schematic partial side elevational view, in cross section, taken along lines  1   b — 1   b  of FIG. 1, 
     FIG. 2 is a schematic end elevational view, in cross section, taken through the center line  2 — 2  of a prior art, twenty-high, cluster rolling mill, 
     FIG. 2 a  is a schematic side elevational view, in cross section, taken along lines  2   a — 2   a  of FIG. 2, 
     FIG. 3 is a schematic end elevational view, in cross section, taken through the extended vertical plane  3 — 3  shown in FIG. 6, 
     FIG. 4 is a schematic side elevational view, in cross section, taken along lines  4 — 4  of FIG. 3, looking in the direction of the arrows, 
     FIG. 5 is a schematic side elevational view, in cross section, taken alone lines  5 — 5  of FIG. 3, looking in the direction of the arrows, and 
     FIG. 6 is a schematic top plan view, in cross section, taken along lines  6 — 6  of FIG. 3, looking in the direction of the arrows. 
    
    
     Referring now to FIG. 1 of the drawings showing a prior art rolling mill having an outer supporting frame (not shown) in which are mounted upper and lower bearing enclosures  2 ,  4  and side door plates  6 ,  8 . A strip  10  of work material is shown being cold-rolled to reduce its thickness. Enclosed within bearing enclosures  2 ,  4  and side door plates  6 ,  8  are upper and lower work rolls  12 ,  14  respectively, backed up by upper and lower intermediate rolls  16 ,  18  respectively, and rolling the strip of material  10 . 
     FIG. 1 is shown only in schematic view to illustrate the problem of the prior art, and is not intended to depict any particular type of rolling mill. The intermediate rolls  16 ,  18  are backed up by other intermediate rolls  22 ,  24  which, in turn, are restrained by bearings  26 ,  28  rotatably mounted in bearing enclosures  2 ,  4 . Rolls  12 - 24  are rotatably mounted in roller thrust bearings, such as the one indicated at reference number  30  to permit vertical adjustment, as the strip material  10  is reduced in cross section. FIG. 1 a  and FIG. 1 b  are partial side elevational views, in cross section, showing the reduction of strip  10  as it passes between work rolls  12 ,  14 . 
     As is seen in FIG. 1, the center portions of work rolls  12 ,  14  are flattened slightly during the rolling process, while the ends of work rolls  12 ,  14  beyond the strip material  8  remain round. This causes a transition of each side from a thicker cross section to a thinner cross section, termed “over-rolling”. The resulting strip  10  will have wavy or “pie crust” edges. 
     Referring to FIG.  2  and FIG. 2 a , a prior art twenty-high cluster rolling mill is shown generally at  32 . The drawings are shown in schematic view only. The actual construction of a rolling mill includes the details of the supporting frame members. Details of the roller thrust bearings and slidable chocks supporting the rolls arc also omitted. The details of conventional construction in cluster rolling mills may be seen by reference to U.S. Pat. No. 2,169,711 issued Aug. 15, 1939, U.S. Pat. No. 2,479,974 issued Aug. 23, 1949, and U.S. Pat. No. 2,776,586 issued Jan. 8, 1957, all in the name of Thadeusz Sendzimir, which are incorporated herein by reference. Strip material  38  is shown being reduced in cross section between upper clusters  37  and lower clusters  39 , made up of upper and lower work rolls  40 ,  42  respectively, upper intermediate rolls  44 ,  46  in contact with upper work roll  40  and lower intermediate rolls  48 ,  50  in contact with lower work roll  42 ; an upper idler roll  52  in contact with both of the pair of intermediate rolls  44 ,  46 , a lower idler roll  54  in contact with both of the pair of lower intermediate rolls  48 ,  50 , upper drive rolls  56 ,  58  in contact with intermediate rolls  44 ,  46  respectively, lower drive rolls  60 ,  62 , in contact with lower intermediate rolls  48 ,  50  respectively, upper backing bearings  64 ,  66 ,  68 ,  70  contacting the idler roll  52  and the drive rolls  56 ,  58  as indicated in FIG. 2 a  of the drawing, and lower backing bearings  72 ,  74 ,  76 ,  78  contacting the idler roll  54 , and the drive roll  60 ,  62 , as indicated in the drawing. 
     Rolls  56 ,  58 ,  60  and  62  are designated “drive rolls” for convenience. They may be driven in some mills by suitable means, or they may not be driven at all if the material passing through the rolls supplies the driving torque on the rolls. Whether the drive rolls are driven or not is not relevant to the invention. 
     The backing bearings  64 - 78  are rotatably mounted, as indicated by the representative backing bearing  68 , on shafts, such as shaft  68   a  supported in rings  68   b,  located on both sides of each backing bearing  64 - 78 . The rings  68   b  are supported by chocks (not shown) vertically adjustable in the main supporting frame (not shown). Idler rolls  52 ,  54  are provided with roller thrust bearings  80  and are supported in slidable chocks (not shown) so as to move vertically. Work rolls  40 ,  42  being very small in diameter are free to float vertically and are restrained laterally by special bearings  82 ,  84 . Each of the bearings  82 ,  84  includes a vertical pin  82   a  serving as a journal for a roller bearing  82   b.  The ends of work rolls  40 ,  42  are free to rotate while being restrained laterally by the roller bearing  82   b.    
     Strip edge relief is accomplished in the prior art rolling mill  32  as follows. The upper intermediate rolls  44 ,  46  are provided with single tapered end sections  86 . The lower intermediate rolls  48 ,  50  are provided on the opposite end with single tapered end sections  88 . Rolling forces on the strip  38  cause the upper work roll  40  to bend toward the tapered section  86  as shown on the right hand side of FIG. 2, and cause the lower work roll  42  to bend toward the tapered section  88  on the lower intermediate roll  50  as shown in the left hand side of FIG.  2 . The degree of bending is exaggerated in the drawing to clearly illustrate the process. This relieves the strip edges on both sides of strip  38 . 
     Adjustment of the strip edge relief is provided in the prior art rolling mill  32  by lateral movement of the single tapered intermediate rolls. The upper intermediate rolls  44 ,  46  are provided with rotating couplings  90  connected by linkage  92  to double-acting hydraulic actuators  94 . The lower intermediate rolls  48 ,  50  are provided with rotating couplings  96 , connected by linkages  98  to hydraulic actuators  99 . Operation of the actuators  94 ,  99  will cause the single ended tapered intermediate rolls to slide laterally, thus controlling the degree of bending allowed to the work rolls  40 ,  42 , and thus adjusting the strip edge relief. The problem with the prior art construction of FIG. 2 is that the rotating couplings  90 ,  96  are limited in size to correspond to the diameter of the intermediate rolls and therefore are limited in strength capacity. Therefore, the lateral adjustments of the intermediate rolls can be achieved only under light rolling loads due to sliding friction between the rolls. The rotating couplings and linkages required are complicated and expensive. Removal and replacement of the intermediate rolls is cumbersome and time consuming. 
     Referring now to FIGS. 3-6, the improved method and apparatus for controlling strip edge relief is illustrated in a twenty-high, cluster type rolling mill shown generally at  100  having an upper cluster  101  and a lower cluster  102  of rolls and backing bearings. The elements which are substantially identical to those in the prior art mill  32  discussed in connection with FIG. 2 are labeled with the same reference numerals. Elements which differ in construction are side plates  104 ,  106 , upper intermediate rolls  108 ,  110 , lower intermediate rolls  112 ,  114 , and lower idler roll  116 . These elements differ from their counterparts in FIG. 2 in the following respects. Upper intermediate rolls  108 ,  110  are cylindrical, rather than tapered on one end. Lower intermediate rolls  112 ,  114  are double tapered, i.e., have a central cylindrical portion  114   a  and tapered portions  114   b,    114   c  on opposite sides of the central portion. The lower intermediate rolls also have journal portions  114   d,    114   e  extending from opposite ends. Roller thrust bearings  118 ,  120  on opposite sides of lower intermediate rolls  112 ,  114  prevent lateral movement while allowing rotation. Lastly, the lower idler roll  116  is shorter in length to allow space for hydraulic actuators. 
     In accordance with the present invention, hydraulic actuators  122 ,  124  are attached to sidewalls  104 ,  106  respectively. These include pistons  126 ,  128 , respectively, having the lower ends thereof exposed to hydraulic fluid supplied through individually controlled supply lines  130 ,  132 . Supply lines  130 ,  132  are connected to a source of high pressure hydraulic fluid having conventional controls (not shown) for admitting or discharging hydraulic fluid to increase or decrease the hydraulic pressure forcing pistons  122 ,  124  upward. External strip shape measuring devices, such as the one shown at  125  provide signals  125   a  to control means  127  to automatically control the admission and discharge of hydraulic fluid to maintain the strip edge relief at a selected setting. 
     Affixed to the top of pistons  126 ,  128  are devises  134 ,  136  carrying casters  138 ,  140  respectively mounted on roller bearings. Casters  138 ,  140  are adapted to engage the journal portions  114   d  and  114   e  of the lower intermediate rolls  112 ,  114 , as best seen in FIG. 5, when the pistons are moved upward. Further upward movement of pistons  126 ,  128 , devises  134 ,  136  and casters  138 ,  140  will controllably exert bending forces on the intermediate rolls  112 ,  114 . This is because the central portions  114   a  of the intermediate rolls are restrained by virtue of their placement with respect to the work roll and the drive rolls as seen in FIG.  5 . 
     OPERATION 
     When the pistons are in the downward position, as indicated in the right hand side of FIG.  3  and in FIG. 4, the rolling forces tend to slightly bend the end of the work roll  42  toward tapered section  114   c,  as indicated in exaggerated form on the right hand side of FIG.  3 . This gives relief on the strip edge, which would be thicker in cross section if not adjusted. 
     In accordance with the present invention, the strip edge relief is adjusted by admitting fluid through the hydraulic lines to controllably exert bending forces on the intermediate rolls. Preferably this is automatically controlled by signals from conventional strip edge thickness sensors. The central portions of intermediate rolls  112 ,  114  are restrained from moving by the central portions of the adjacent work roll  42  and drive rolls  60 ,  62 . Upward force by the caster  140  on the journal portions  112   d,    114   d  bends the intermediate rolls which tends to reduce the bend in the work rolls  42 . This is illustrated on the left hand side of FIG.  3  and in FIG. 5, where the rollers  140  have engaged the journal portions  112   d,    114   d  of the two lower intermediate rolls  112 ,  114 , and forced them upward . The left end of the work roll  42  is moved toward the material being rolled, so as to adjust the strip edge relief and achieve polarity. Ideally, there should be a very slight over-rolling of the work piece edge. 
     The foregoing adjustment is provided without lateral shifting of the intermediate rolls as in the prior art. Instead of laterally shifting single tapered intermediate rolls located in both the upper and the lower clusters, the invention is carried out by bending double tapered intermediate rolls located only in the bottom cluster. Accordingly, there are simplifications in construction, lateral size of the overall mill dimension and reduced time to remove and replace the intermediate rolls. The amount of strip edge rolling is controlled by varying the hydraulic pressure to the pistons and can be achieved under all rolling loads, because there is no sliding friction between rolls as in the prior art. Since there are no other mechanisms connected to the intermediate rolls, removal is simple and quick. The upper intermediate rolls require removal only when they are worn or marked. 
     While the invention has been described in connection with a twenty-high rolling mill, the principal may be applied to other types of rolling mills, in which there are upper and lower clusters containing a work roll, and a pair of intermediate rolls contacting the work roll, the aforesaid rolls being restrained by other surrounding rolls in various configurations. 
     While the means for engaging the opposite journal portions and exerting bending forces on a double tapered intermediate roll has been illustrated using hydraulic actuators, other types of mechanisms such as sliding wedges, rack and pinion, eccentric bearings, etc. may be substituted for the hydraulic cylinders to controllably exert bending forces on the double tapered intermediate rolls. The tapered sections may be frusto-conical or they may be contoured. Also, while the double tapered intermediate rolls and hydraulic actuators are shown in the preferred arrangement on the bottom of the rolling mill functioning in the lower cluster, they could also be located in the upper cluster located in the upper part of the rolling mill. In some cases, it may be desired to obtain additional adjustment of strip edge relief. In this case, it is feasible to utilize double tapered intermediate rolls and hydraulic actuators on the upper pair of intermediate rolls as well as on the lower pair. 
     The word “strip” as used throughout the specification and claims may sometimes be called “sheet” in rolling mills; and the use of the word strip is not intended to be limiting, as to the thickness of the material being rolled. 
     While there has been shown what is considered to be the preferred embodiment of the invention, it is desired to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.