Patent Publication Number: US-9421595-B2

Title: Integrated bending and shifting system under load for large opening stands between the working rolls

Description:
FIELD OF THE INVENTION 
     The present invention relates to a combined system which allows the working rolls under load to be shifted while the bending load is simultaneously applied to the chocks of the working rolls also if a large opening is to be ensured between the working rolls in a rolling stand. 
     STATE OF THE ART 
     In rolling stands, in particular in those requiring large openings between the working rolls for rolling large product thicknesses, high reaction forces are unloaded onto the structure of the rolling stands, caused by the high rolling forces which are to be applied to the material being rolled. It is common art that bending devices for the rolls are also provided in such stands to compensate for the normal deformation of the rolls themselves, which bend under the load during the rolling operation and cause a lenticular shape to be taken by the rolling gap. If corrective or compensation measures are not implemented, such a deformation of the working rolls causes poor rolling close to the side edges of the material to be rolled, which would deform more in such areas, and the cross section thereof would take a convex, lenticular shape. Moreover, as the cooling of the rolling product is greater in the area of the side edges, the surface of the rolls faces a greater resistance precisely in such an area, resulting in greater wear of the rolls and tendency of the working rolls to wear more in such areas, thus negatively affecting the quality of the rolled product. 
     In order to minimize such a wear and the causes leading to the rise of grooves or of other surface defects and hence to extend the life of the rolling rolls, related bending and shifting devices are provided of the rolls in the rolling stands. These devices apply a load to the chocks of the working rolls so that the chocks of the lower working roll are neared to the respective chocks of the upper working rolls, thus taking advantage of the reaction to the deformation which the working rolls receive from the back up rolls. Thereby, the working rolls tend to take a shape such as to oppose the natural deformation thereof under the rolling load, therefore limiting or cancelling the lenticular shape of the rolled product exiting the stand. 
     Various kinds of bending devices for rolling rolls are disclosed in patent documents U.S. Pat. Nos. 4,770,021, 5,752,404, 6,112,569. In essence, these are bending devices implemented on rolling stands suitable for rolling thin material which however have certain limitations if a large rolling gap is required to be ensured between the rolls when rolling larger thicknesses and applying the reciprocal shifting of the working rolls is required. Shifting devices are provided in certain types of rolling stands for moving, during the rolling operation, the rolling rolls in a direction transversal to the rolling axis, so that the surface section of the rolls which works in contact with the areas of the side edges of the rolling material is not always the same, rather changes. This contrivance allows the wear to be reduced and the working life of the rolls to be extended. 
     WO2005/011885 discloses a rolling stand provided with a bending and shifting system under load. The upper working roll is provided with two pressure pistons on each side of the axis surrounded by an intermediate pressure-transmitting element, which can slide vertically and resist tilting against axial shifting forces. An axial shifting device is provided on either side of the center of the upper work roll. These devices are rigidly mounted with one of their axial ends on the rolling stand. The work roll chock has two arms which extend symmetrically from the axis of the work roll. In the locked position, the ends of the arms are held in the axial shifting device in a receiving slot, which extends vertically and offers the possibility that the work roll chock and thus the work roll can be vertically positioned and secured at the height in the rolling stand that corresponds to the required roll gap. The receiving slot is bounded on one side by a linear guide, which has the work roll locking mechanism, and it is bounded on the other side by a lock. Such a vertical positioning system of the work roll has however the disadvantage that it is complicated and not adaptative enough to the work conditions and it can cause the danger that during rolling the axial force acting on the work roll may not remain coaxial and could induce bending moments on the axial shifting device. Also, the presence of the intermediate-transmitting element, which can slide vertically introduces another element to be maintained because of wear; also due to the wear the system can vertically slide but in the meantime could move in horizontal direction jeopardizing the precision of the gap between rolls. 
     Therefore, the need is felt to provide a rolling stand having a bending device combined with a shifting device for the rolling rolls, which allows to overcome the aforesaid drawbacks. 
     SUMMARY OF THE INVENTION 
     The main object of the present invention is to provide a rolling stand with a bending device for rolling rolls which also has shifting devices, which has an improved running when activated during an operation, particularly when the gap between the rolling rolls is large in value. 
     The object of the invention is thus achieved by a rolling stand having bending and shifting devices for rolling rolls, which defines a rolling axis comprising, in accordance with claim  1 , two housings each arranged at a respective axial end of the rolling rolls, two or more upper rolling rolls, one roll of which is the upper working roll with its own longitudinal axis, and two or more lower rolling rolls, one roll of which is the lower working roll with its own longitudinal axis, in which at a first of said two housings, there are provided two lower blocks, two upper blocks, an upper chock and a lower chock, a shifting device for the upper working roll connected to the upper chock to generate a first shifting movement of the upper roll in a parallel direction to the axis thereof by means of a first sliding coupling, a shifting device for the lower working roll connected to the lower chock to generate a second shifting movement of the lower roll in a parallel direction to the axis thereof by means of a second sliding coupling, at least one upper bearing inserted into the upper chock to allow the upper working roll to rotate about the longitudinal axis thereof, at least one lower bearing inserted into the lower chock to allow the lower working roll to rotate about the longitudinal axis thereof, in which the two lower blocks are integrally fixed to the first housing, in which the lower chock is coupled with the lower blocks by means of a third sliding coupling which allows a third shifting movement of the lower chock in the vertical direction to allow a bending load to be transmitted to the lower working roll by means of actuators reacting against the two fixed lower blocks, in which the two upper blocks are connected to the first housing by means of a fourth sliding coupling which allows a fourth vertical shifting movement of the upper blocks with respect to the first housing, to allow a bending load to be transmitted to the upper working roll by means of actuators reacting against the two fixed lower blocks, in which the first shifting movement of the upper roll is obtained by means of a sliding coupling between the upper chock and the two upper blocks and said first and second shifting movements may be carried out under load while the rolling operation occurs. 
     Due to this arrangement of the elements forming the bending device, to provide the bending in the lower working roll, the two actuators directly act with their rods on the chocks of the lower working roll, while the bending actuators of the upper working roll act not with the cylinder rods against the upper chocks, but by shifting the upper bending blocks which directly press against the tabs of the chocks of the upper working roll. In this way, also the pressure force transmission between top bending block and top work roll chock are optimized because a larger surface of contact can be designed. This ensures that the chocks arranged at both the ends of the upper working roll are always in contact and accurately guided by the bending blocks during the movement of the chocks in the vertical direction, and moreover, that the chocks remain in a firm position during the rolling since this device also ensures a good sliding surface between the upper bending blocks and the chocks of the upper working roll. Indeed, all the forces which are generated during the rolling operations and having directions parallel to the axis of the rolls are unloaded onto the fixed guides arranged between blocks and housings, and do not load the rods of the upper actuators, generally of the hydraulic type, in a direction transversal to the axis. 
     The solution of the invention allows a series of advantages to be achieved, among which we mention that the shifting may be performed under load without risks of damaging neither the actuating rolls for bending the rolls nor the blocks on which they act. In fact the shifting blocks of the working roll, due to the fact that they are rigidly fixed to the bending blocks which in turn are joined to the housing in a sliding manner in the vertical direction and not directly rigidly fixed to the housing, allow for a vertical displacement sufficient to compensate the necessary vertical displacement of the working roll, thus ensuring a parallelism of the axial forces applied by the shifting blocks to the working roll axis for every gap width. Undesired bending forces are thus avoided which could overstress the shifting system and could rapidly jeopardize the behaviour of any devices, i.e. bearings, but not only. Also, the absence of these undesidered bending forces, allows a better control of the complete rolling stand by the automatic control means. 
     Moreover, the solution of the invention may be applied to rolling stands equipped with rolling roll shifting devices, or in the absence of such shifting devices, and also in those stands where the rolling gap is very large. 
     During the application of the bending force to the rolling rolls, the chocks of the upper working roll are properly guided without creating an abnormal movement in a direction parallel to the rolling direction, with consequential decrease of the hysteresis of the rolling stand. 
     Another advantage of the solution of the invention is that it may be used in rolling stands which include shifting blocks for the upper and lower working rolls, which may be operated when rolling products having large thickness and which therefore require a large rolling gap between the rolls. 
     Moreover in this configuration, the upper and lower bending blocks remain close to the vertical axis of the housing of the rolling stand, thus avoiding the large tensions in the tabs of the chocks generated in the bending moment when the bending load is applied to the rolling rolls. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the invention will be more apparent in the light of the detailed description of preferred, but not exclusive, embodiments of a rolling stand having a bending and shifting device for rolling rolls, shown by way of non-limiting example, with the aid of the accompanying drawings, in which: 
         FIG. 1  depicts a section along axis A-A of the rolling stand of the invention; 
         FIG. 2  depicts a section along axis B-B of the rolling stand of the invention; 
         FIG. 3  depicts an enlarged detail of  FIG. 1 ; 
         FIG. 4  depicts an enlarged detail of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
     With particular reference to the figures, part of a rolling stand  1  is depicted from the direction perpendicular to the rolling axis, denoted by Z. 
     Commonly, bending devices are always provided both on the operator side and on the control side, while shifting devices may be arranged either on the operator side or on the control side, but they are not normally arranged on both sides in the rolling systems where they are provided. 
     In this preferred variant of the invention, the operator side of rolling stand  1  is shown, but the structure of the bending and shifting devices is substantially the same even if it is located on the motor side of stand  1 . 
     The motorized rolls in hot rolling systems usually are the working rolls, however in the case of cold stands or process lines, the back up ones may be motorized. In the embodiment illustrated and described herein, motors activate the working rolls  10  and  11 . Rolling stand  1  may be of the fourth type with the two upper  10  and lower  11  working rolls, while the two back up rolls  8 ,  9 , which have a larger diameter than the working rolls  10 ,  11 , are partially drawn. Depending on the type of rolling stand considered, the back up rolls may be more than two both below and above the rolling product. The upper working roll  10  defines its longitudinal axis X′, while the lower working roll  11  defines its longitudinal axis X″, which is parallel to axis X′. 
     Rolling stand  1  defines the rolling axis Z of the rolling product (not shown in the figures) and a vertical direction Y which is orthogonal to axis Z and the roll axes X′ and X″. The rolling product may be either a tape or a product of larger thickness such as a slab, for example. Stand  1  includes two housings, each housing being arranged at a respective axial end of the rolling rolls and only housing  2  on the operator side is shown in the figures, while the housing on the motor side is not shown, as its structure is similar to that of the former. 
     Stand  1  includes both a bending device for the rolling rolls  10 ,  11  and a shifting device for the rolls themselves, described in greater detail below. 
     The two lower bending blocks  12 ,  13  are integrally fixed to housing  2 , e.g. by means of screws or nuts or another suitable fasteners. The two axial ends of the lower rolling roll  11  are each carried by two bearings  19 ,  19 ′ inserted into the two lower chocks, chock  17  of which is only shown in the figures. Bearings  19 ,  19 ′ allow working roll  11  to rotate about its longitudinal axis to perform the rolling operation. Bearings  19 ,  19 ′ may be equal to (in this case, the axial bearing is missing) or more than 1. 
     One or more hydraulic actuator rolls  20  are incorporated into the lower bending block  12  and one or more hydraulic actuator rolls  21  are incorporated into the lower bending block  13 . Hydraulic actuators  20  and  21  transmit the load to two tabs  39  and  40  of the lower chock  17 , respectively, thus unloading the reaction loads onto the other side on the lower bending blocks  12  and  13 . Chock  17  is coupled with the lower blocks  12 ,  13  by means of a sliding coupling at least comprising the two surfaces  37  and  38 . This coupling allows the lower chock  17  to perform a shifting movement in the vertical direction and chock  17  to be kept centered in relation to the direction of the longitudinal axis Z without obstructing it following the rolling efforts. By generating loads by means of the actuators  20 ,  21  which unload the reactions onto the two lower blocks  12 , 13 , a bending load is applied to the lower working roll  10 , which deviates roll  10  by a small value considering the rigidities involved, thus compensating for the bending induced by the load acting on roll  10  when rolling. As noted above, such a load is also defined as a positive bending load. 
     Obtained or fixed on housing  2  are two guide tracks  41 ,  42  which along with two complementarily shaped guides  43  and  44  form a sliding coupling which allows the two upper bending blocks  14 ,  15  to make a vertical shifting movement with respect to housing  2 . In the embodiment shown in the figures, guides  43  and  44  are of the T-shaped type and, with particular reference to  FIG. 4 , the two guide elements  44 ′ and  44 ″ obtained in a single piece form, along with track  42 , the sliding coupling having one single level of freedom corresponding to the vertical shifting in direction Y, while it longitudinally holds chock  16  according to direction Z, thus allowing the sliding thereof in a direction parallel to axis X′. In this vertical upward or downward shifting movement in a direction of Y, which is a widening of rolling gap G or a narrowing of gap G, blocks  14  and  15  are loaded by the forces generated by the hydraulic actuator rolls  23  and  22 , which unload the reactions against the two lower blocks  12 ,  13  integrally fixed to housing  2 . Blocks  14  and  15  transmit a bending load to tabs  45  and  46  of chock  16 , and obviously to the symmetrical one arranged at the other axial end of the upper working roll  10 . The load applied by the hydraulic actuators  22  and  23  deforms the upper roll  10  just enough, thus compensating for the deflection induced by the load acting on roll  10  when rolling. 
     The two bearings  18 ,  18 ′ are inserted into the upper chock  16  and allow the upper working roll  10  to rotate about its longitudinal axis X′, which rotation is required to roll the product. The arrangement and operation of bearings  18  and  18 ′ in relation to the lower working roll  11  is similar. 
     The same constructional elements included in the above-described bending and shifting devices are also present in the part of the bending and shifting devices arranged at the second axial end of the rolling rolls  10 ,  11 , on the opposite side to rolling stand  1  (not shown in the figures). The bending and shifting movements of the rolls are also complementarily performed on the side of stand  1  which cannot be seen, whereby they are not shown in the figures and are not further described. Four shifting blocks  30 ,  31  are provided on the operator side of rolling axis Z or on the motor side with respect to rolling axis Z. 
     Of these four blocks, two upper shifting blocks—of which only block  30  is shown in the figures—are respectively fixed to the two bending blocks  14 ,  15  of the upper chock  16  of the upper working roll  10  so as to be able to exert on the upper chock  16  a force parallel to upper roll axis X′. 
     The other two shifting blocks—of which only block  30  is shown in the figures—are fixed to housing  2  or to another structure integral with rolling stand  1 , and are able to exert on the lower chock  17  of the lower working roll  11  a force parallel to lower roll axis X″. 
     The shifting block  30  is made integral with the upper chock  16  by means of the plates  53 ′,  53 ″ which are fixed to an extremity of the chock  16  and by means of rigid structural elements  51 ,  55  is rigidly fixed to the upper bending block  14 . As the upper bending block  14  is slidingly connected to housing  2 , also the shifting block  30  can move along a vertical path, sliding with block  14 . The shifting block  30  thus follows exactly the translation of the bending block  14  during the closing or opening operation of the two working rolls  10 ,  11  necessary to modify the amplitude of the gap G. 
     In this manner no undesired bending forces are introduced into the structure comprised of the chock  16  and plates  53 ′,  53 ″,  51 ,  55  and the shifting forces acting on the working roll  10  remain always parallel to the axis X′, unlike other solutions of the state of the art. 
     In the apparatus according to the invention the axial force F A  exerted by the working roll  10  on the chock  16  will produce a reaction on the housing  2 , not directly on the body of the housing, but over the block  14  and the guide track  42  with a better distribution of loads on the structure. 
     When pushing or pulling chock  16 , the shifting block  30  allows a shifting movement of the upper roll  10  to be generated in a direction parallel to its axis X′ due to the presence of the sliding coupling consisting of the sliding surfaces  47  and  49  on the side of block  14  and of the sliding surfaces  48  and  50  on the side of block  15 . Since the shifting performed by working roll  10  in the direction of axis X′ occurs due to the presence of the coupling consisting of the surfaces  47 ,  49  and  48 ,  50 , respectively, arranged at the two sides of chock  16 , the two hydraulic actuator  22  and  23  are not subjected to loads which cause the piston rod to bend, which is thus compression loaded only. 
     As the two hydraulic actuators  22  and  23  are configured in such a manner that the piston rods are positioned below the pistons  60 ,  61 , so that the blocks  14  and  15  constitute the housing for the pistons  60 ,  61  the sliding surfaces  47 ,  49  and  48 ,  50  are designed with a larger area thus improving the slidability of the chock  16 . Thanks to this configuration the piston rods of actuators  22  and  23  may also be made longer, which allows a larger rolling gap to be obtained. 
     Shifting block  31  of the lower working roll  11  is integrally fixed to the lower chock  17  and can generate a shifting movement of the lower working roll  11  in a direction parallel to its axis X″ by means of the sliding coupling which comprises the contact surfaces  35  and  37  arranged on the side of block  12  and the contact surfaces  36  and  38  arranged on the side of block  13 . The piston rods of actuators  20  and  21  may be made shorter since the lower chock, and therefore the working roll  11 , should provide a lesser travel as the height of rolling gap G is mainly determined by the travel of the upper working roll. The bending force which is to be applied by the upper actuators  22  and  23  when the rolling gap is large implies a greater extension of the rod of the upper actuators  22  and  23  with respect to the lower ones  20 ,  21 . The rolling stand also has control devices  25   a - d  (see  FIG. 1 ) of the height of the rolling gap G, which set the gap value at the required value. 
     The shifting movements of the rolls controlled by the shifting blocks  31  may be performed under load during the rolling operation, because even if the rods of the upper actuators  22  and  23  are longer, they are not subjected to transversal loads to their axis and do not risk bending, while the rods of the lower actuators  20  and  21 , which instead slide along surfaces  35  and  36  with respect to tabs  39  and  40 , are squat and may oppose the side loads generated during the sliding movement caused by shifting, thus not risking bending. Alternatively to the configuration described, the hydraulic actuators  23  and  22  may be arranged upside down by 180°, hence acting upwards on the tabs  46  and  45  of chock  16  (which solution has been already commonly used). In this case, for large travels of the actuators  22  and  23 , therefore for large values of the rolling gap G, the diameter of the rods should be sized larger to prevent maximum load problems from arising. 
     In all the above-described sliding couplings which allow sliding movements between the surfaces forming the couplings themselves even in the presence of large loads due to the high forces involved during the rolling operation, a coating is advantageously provided on the surfaces, with metals having a low friction coefficient, e.g. by arranging brasses, which also allows a quick replacement when the sliding surfaces are worn by the sliding movements which occur under load. 
     The hydraulic actuator rolls  20 ,  21 ,  22 ,  23  arranged at each chock  16  and  17  of the upper and lower rolls are advantageously two, i.e. they are advantageously arranged in pair on each side of each chock as particularly shown in  figures 2 and 4 . Such a paired arrangement of the actuators allows the bending load applied to the chocks of the rolls to be redistributed along the axial length of each bearing  18 ,  19 . Indeed, when a single actuator is placed on each side of the bearing, the force of compensating for the bending generated by the actuator overloads a limited axial area of the bearing, thus generating an increased wear of the bearing in such an area. Arranging two actuators results in an almost uniform distribution of the load acting on the bearing over its length, and in practice, the resultant of the bending load always acts at the axis of the bearing, thus differently loading the two actuators which form the pair.