DEVICE TO ABSORB THE AXIAL LOADS GENERATED ON THE ROLLS IN A ROLLING STAND

Abstract: Device to absorb the axial loads generated on the rolls in a rolling stand (11) having a pair of working rolls (12a, 12b), a corresponding pair of back-up rolls (15a, 15b) and at least an intermediate roll (14) located between a working roll (12a) and a corresponding back-up roll (15a), in said device holding means (16, 40, 41) are provided to support the axial loads on the back-up rolls (15a, 15b) and/or the working rolls (12a, 12b) caused by the crossing of said at least one intermediate roll (14), so that the axial loads are discharged onto elements with very low rolling friction, totally or almost totally annulling the hysteresis relating to the vertical movements of the back-up rolls (15a, 15b) and working rolls (12a, 12b) and the relative chocks (26).

Description: "DEVICE TO ABSORB THE AXIAL LOADS GENERATED ON THE ROLLS IN A ROLLING STAND" • k - -k • ic FIELD OF THE INVENTION The invention refers to a device to absorb the axial loads generated on the rolls in a rolling stand, and in particular on the working rolls and the back-up rolls in a six-high stand. BACKGROUND OF THE INVENTION It is well-known that two counter-rotating rolls thrust against each with a determined force S and subjected to reciprocal crossing by a determined angle ot (Fig. 1) , even limited to a few tenths of a degree, with respect to the vertical plane passing through the median rolling axis, are also subject to axial thrusts. In the zone of contact between the working rolls in a rolling stand, because of the sliding speeds Vs=V'-V (vectorial difference of the peripheral speeds of the rolls) , where V is the peripheral speed of the upper roll and V is the peripheral speed of the lower roll, and because of the contact friction due to the force S, axial forces T are produced on the upper roll and T' on the lower roll, which can even be of strong intensity, if the force S is high. Therefore, a rolling stand equipped with a system to cross the rolls such as to generate an angle α between two rolls in contact generates a thrust T, which changes sign when the rotation of the rolls is reversed, and which is discharged onto the respective thrust bearings A and B. In the case of a six-high rolling stand, the two intermediate rolls (IR) , pressed with the force of separation S by the corresponding back-up rolls (BUR) and working rolls (WR) on opposite generatrixes, if they are inclined, that is crossed, by the same angle antisymmetrically, induce axial forces of the opposite sign on the back-up rolls and the working rolls. The thrusts which can occur are transmitted by means of the thrust bearings to the respective chocks, which discharge them on the bilateral axial holding elements (called chock gates) which discharge the forces onto the housings of the stand. It should be noted that the intermediate rolls are, in theory, exempt from axial thrust, since each is loaded, on the two opposite generatrixes, with equal axial forces of the opposite sign, if the friction coefficients on the two contacts are equal . Consequently, it is necessary to adopt low-friction holding elements (chock gates) , both for the working rolls and for the back-up rolls, in order to contain the vertical friction forces which generate hysteresis which impedes the small vertical movements of the roll pack during rolling. The axial forces are discharged onto the chock, which transmits the load to the chock gates which clamp the chock axially. To regulate the thickness of the rolled product, it must be easy to position the rolling rolls vertically. The reaction of the chock gates, multiplied by the coefficient of friction between the chock and the chock gate, generates a vertical force which opposes the movement of vertical positioning of the rolls . Thus a hysteresis is created which has a harmful effect on the correct control of the thickness of the rolled product. SUMMARY OF THE INVENTION The device to absorb axial loads generated on the rolls in a rolling stand according to the invention is set forth and characterized in the main claim, while the dependent claims describe other innovative features of the invention. One purpose of the invention is to achieve a device which will allow both the working rolls and the back-up rolls to be contained axially so that the vertical force generated by friction can be restrained to very low levels, to limit as much as possible the hysteresis which impedes the small vertical movements of the roll pack during rolling, which are needed to adequately control the thickness . In accordance with this purpose, the device according to the invention comprises holding means to support the axial loads on the back-up rolls and the working rolls caused by the crossing of the intermediate rolls, so that the axial loads are discharged onto very low friction means, of the rolling type, totally or almost totally annulling the hysteresis relating to the vertical movements of the rolls and of the relative chocks . To be more exact, the holding means comprise at least a rolling element which, in the case of back-up rolls, consists advantageously of a rolling bearing whereas, in the case of the working rolls, consists of a barrel-shaped element . BRIEF DESCRIPTION OF THE DRAWINGS These and other characteristics of the invention will become clear from the following description of a preferred form of embodiment, given as a non-restrictive example with reference to the attached drawings wherein: Fig. 1 is a diagram illustrating the forces which develop between two counter-rotating rolls; Fig. 2 is a schematic view of a six-high rolling stand on which a device according to the invention is assembled; Fig. 3 is a partly sectioned view of a device according to the invention associated with a back-up roll of the stand shown in Fig. 1; Fig. 4 is a part and sectioned front view of the rolling stand in Fig. 3 ; Fig. 5 is an enlarged detail of Fig. 4; Fig. 6 is a section from A to A of Fig. 5. DETAILED DESCRIPTION OF A PREFERENTIAL EMBODIMENT With reference to Fig. 2, a device lOa-lOb according to the invention is shown assembled in a six-high rolling stand 11, which comprises a pair of working rolls 12a, 12b, between which the plane product 13 to be rolled, consisting for example of steel strip, is able to pass. Associated with the two working rolls 12a, 12b there are two corresponding intermediate rolls 14a, 14b, and two backup rolls 15a, 15b which are able to contrast the thrusts due to the rolling of the product 13 and to prevent an excessive bending of the working rolls 12a, 12b and that of the intermediate rolls 14a, 14b. The device according to the invention comprises two assemblies 10a associated with the back-up rolls 15a and 15b and two assemblies 10b associated with the working rolls 12a and 12b, to support them adequately with respect to the housings 23 of the stand 11. Each device 10a (Fig. 3) associated with the back-up rolls 15a and 15b comprises a holding element 16 provided with a rolling bearing 17, which is inserted in a mating groove 18, made in a chock 26, associated with the roll to be supported, which in the example shown here is the upper back-up roll 15a. The bearing 17 is mounted cantilevered on the end 19a of a tube 19 with a polygonal cross section, which is guided prismatically partly on the housing 23 and partly on a fixed frame 42, which is attached to the housing 23. A double effect hydraulic cylinder 43 is able to selectively command the insertion and removal of the bearing 17 into/from the groove 18 of the chock 26, to arrange the back-up roll 15a in a working position and respectively an inactive position or roll change position. The bearing 17 allows the chock 26 to move freely in a vertical direction, practically without friction or with friction reduced to a minimum. Every device 10a also comprises a load cell 44 able to measure the constraint reactions at point b of the tube 19, which rests at points a and b, in order to determine the value of the force T. When the rolling stand 11 is of the reversible type, there are two load cells 44 provided, arranged on opposite sides of the tube 19. Each device 10b associated with the working rolls 12a and 12b comprises a pair of cylindrical actuators 20 (Fig. 4) which can be activated simultaneously. It must be pointed out that, to simplify the drawing, in Fig. 4 only the device 10b associated with the upper working roll 12a is shown, while the other device 10b, that is, the one associated with the lower working roll 12b, is the same as the one shown. The actuators 20 are arranged on the same motor side (on the left in Fig. 4) and are assembled on a supportimg frame 22, attached to a housing 23 of the rolling stand 11. The actuators 20 are able to shift, simultaneously and parallel to the axis Xa of the working roll 12a, a pair of movable blocks 24 which are assembled each on a housing 23 of the rolling stand 11 and are connected together by a connection rod 30. The movable blocks 24 are guided on prismatic guides 25 attached in the housings 23. The motor side chock 26 (on the left in Fig. 4) is provided with shoulders 31, arranged transverse to the axis Xa; the corresponding movable block 24 is able to cooperate with the sides thereof, in order to shift the working roll 12a axially. To be more exact, the axial shifting of the working roll 12a towards the operator side (on the right in Fig. 4) is performed by a direct thrust of the movable block 24 on the left-hand sides of the shoulders 31. To transform the sliding friction into rolling friction, a first rolling element 40, substantially barrel-shaped, is assembled on the movable block 24, in correspondence with each shoulder 31; in the working position said element 40 is in contact with the corresponding left side of the shoulder 31. On the contrary, the axial shifting of the working roll 12a towards the motor side (on the left in Fig. 4) is performed by a pair of hook-type levers 28, each of which pivots on a pin 29 of the movable block 24 and oscillates between an inactive position (un-hooked from the corresponding shoulder 31) and a working position (hooked onto the shoulder 31) , shown by a line of dashes in Fig. 5. Each lever 28, in correspondence with its terminal hook 27, is provided with a second rolling element 41, also barrel-shaped, which is able to cooperate with the corresponding right-hand side of the shoulder 31 of the chock 26, when the lever 28 is in the working position. The lever 28 is rotated by means of a pair of hydraulic cylinders 32 assembled on the movable block 24 and able to be activated simultaneously. To be more exact, the levers 28 are closed when the hydraulic cylinders 32 are in the contracted position, while with the hydraulic cylinders 32 in the extended position the levers 28 are opened. The hydraulic cylinders 32 also act on two holding elements 33 (Figs. 10 and 11) able to slide axially on the movable block 24 and guided on horizontal platelets 35. The holding elements 33, in the extended position of the hydraulic cylinders 32, are able to support a spindle- support element (called "coupling ring") 36, arranged on the command side of the relative spindle 37 which connects the working roll 12a to the motor assembly, which is not shown in the drawings . Therefore, the hydraulic cylinders 32, in the extended position, are able both to open the hook-type lever .28 and also, at the same time, to support the element 36 (change position of the working roll 12a) , while in the contracted position, they are able to close the hook-type lever 28 on the chock 26 and to simultaneously release the element 36 (working position) . According to a variant, not shown in the drawings, the holding elements 33 consist of a saddle, for example formed by the platelets 35, which is able to move with respect to the movable block 24 to selectively arrange itself below the element 36, on the command of the hydraulic cylinders 32. The contemporary movements, obtained simply by driving the hydraulic cylinders 32, of the closing/opening of the hook- type levers 28 and the opening/closing of the spindle- support elements 36, not only simplify the mechanical solution but also shorten the sequence of the roll change, and make it more reliable. The function of the rolling elements 40 and 41 is to transform the sliding friction into rolling friction when the chock 26 is displaced in a vertical direction. The rolling element 40 (Figs. 5 and 6) is mounted rotatable on two coaxial pins 47a and 47b of the movable block 24, while the rolling element 41 is mounted rotatable on two coaxial pins 48a and 48b supported by the lever 28. The rolling elements 40 and 41 are kept in a horizontal position by two packs of cup-type springs 45 and respectively 46, so that they can transmit the forces (actions and reactions) between the movable block 24 and the chock 26 in both directions. Therefore, when one rolling element is compressed (for example the element 40) , the other is released (for example the element 41) . Each rolling element 40 and 41 is thus able to pivot horizontally to follow the small movements of the chock 26 during rolling. If the force transmitted by each rolling element 40, 41, multiplied by the coefficient of friction, is less than the return forces of the corresponding cup-type springs 45 and 46, the rolling element 40, 41 is repositioned horizontally by said cup-type springs. This certainly happens at the end of rolling of a strip 13 , when the axial forces between the working rolls 12a, 12b - intermediate rolls 14a, 14b - backup rolls 15a, 15b, generated by possible relative axial movements between the working/intermediate/back-up rolls and between the working rolls 12a, 12b and the strip 13 descend to practically zero values, since the vertical rolling force stops . In conditions when the axial force is greater than a value such that μF is greater than the force F of the cup-type springs 45, 46, one of the two rolling elements 40 or 41, the compressed one, will rotate, transforming the sliding friction into rolling friction. In this way, the vertical hysteresis on the chocks 26 is reduced to a value which practically does not depend on the axial load of the shifting on the rolling rolls. The axial thrust on the working rolls 12a and 12b is monitored by means of transducers 49 (Fig. 2) . In the device 10 as described heretofore, the movable blocks 24 (Fig. 4) have the same shifting movements as the chocks 26 of the corresponding working roll 12a, 12b; therefore the hydraulic jacks 50, which are assembled on the movable blocks 24 and are included to bend the rolls, always act on the same point of the chock 26. It is obvious that modifications or additions may be made to the device 10 as described heretofore, without departing from the spirit and scope of the invention. It is also obvious that, although the invention has been described with reference to a specific example, a skilled person shall certainly be able to achieve many other equivalent variants, all of which shall come within the field and scope of this invention.

Claims: CLAIMS 1 - Device to absorb the axial loads generated on the rolls of a rolling stand (11) having a pair of working rolls (12a, 12b) , a corresponding pair of back-up rolls (15a, 15b) and at least an intermediate roll (14) located between one of said working rolls (12a) and a corresponding back-up roll (15a) , the device being characterized in that holding means (16, 40, 41) are provided to support the axial loads on said back-up rolls (15a, 15b) and/or said working rolls (12a, 12b) caused by the crossing of said at least one intermediate roll (14) , so that said axial loads are discharged onto elements with very low friction, of the rolling type, totally or almost totally annulling the hysteresis relating to the vertical movements of said back- up rolls (15a, 15b) and working rolls (12a, 12b) and the relative chocks (26) . 2 - Device as in claim 1, characterized in that said holding means comprise at least a rolling element (16, 40, 41) associated with each of said chocks (26) . 3 - Device as in claim 2, characterized in that said rolling element, in the case of said back-up rolls (15a, 15b) , comprises a rolling bearing (17) . 4 - Device as in claim 3, characterized in that said rolling bearing (17) is able to be selectively inserted into a mating groove (18) made in the corresponding chock (26) associated with the roll (15a, 15b) to be supported. 5 - Device as in claim 3, characterized in that said rolling bearing (17) is cantilevered mounted at the end (19a) of an element (19) with a polygonal cross section, which is guided prismatically partly on a housing (23) of said rolling stand (11) and partly on a fixed frame (42) attached to said housing (23) . 6 - Device as in claim 4 or 5, characterized in that a hydraulic cylinder (43) is able to selectively command the insertion and removal of said rolling bearing (17) into/from said groove (18) , to arrange the corresponding back-up roll (15a, 15b) in a working position and respectively an inactive or roll change position. 7 - Device as in claim 5, characterized in that at least a load cell (44) is associated with said element (19) with a polygonal cross section to determine the value of said axial load. 8 - Device as in claim 7, characterized in that, in the case where said rolling stand (11) is of the reversible type, at least two load cells (44) are provided, arranged opposite with respect to said element (19) with a polygonal cross section. 9 - Device as in claim 2, characterized in that said rolling element, in the case of said working rolls (12a, 12b) , comprises a barrel-shaped element (40, 41) . 10 - Device as in claim 9, characterized in that said barrel-shaped element (40, 41) is located between a corresponding chock (26) of a working roll (12a, 12b) and a movable block (24) associated therewith. 11 - Device as in claim 9, characterized in that a pair of axial pins (47a, 47b and 48a, 48b), elastically pre-loaded by elastic means (45, 46) , are associated with said barrel- shaped element (40, 41) to keep it in a horizontally pivoting position, so as to allow said barrel-shaped element (40, 41) to follow the movements of said chock (26) during the rolling step, transforming the friction from sliding friction to rolling friction. 12 - Device as in claim 11, characterized in that said elastic means comprise cup-type springs (45, 46) arranged coaxial to said pins (47a, 47b and 48a, 48b) . 13 - Device as in claim 1, characterized in that said holding means comprise a first rolling element (40) , substantially barrel-shaped, assembled on a movable block (24) able to slide transversely on a corresponding housing (23) of said rolling stand (11) , said first rolling element (40) , in the working position, being in contact with a shoulder (31) of a corresponding chock (26) , to transform any possible sliding friction into rolling friction. 14 - Device as in claim 13, characterized in that at least a hook-type lever (28) pivots on said movable block (24) to shift axially a corresponding working roll (12a, 12b) in a determined direction, said hook-type lever (28) being able to oscillate between a working position wherein it is hooked onto said shoulder (31) and an inactive position wherein it is released from said shoulder (31) . 15 - Device as in claim 14, characterized in that said lever (28) , in correspondence with its terminal hook (27) , is provided with a second rolling element (41) , substantially barrel-shaped, which is able to cooperate with said shoulder (31) when said lever (28) is in the working position. 16 - Device as in claim 15, characterized in that said first rolling element (40) is assembled rotatable on two first coaxial pins (47a, 47b) of said movable block (24) , and that said second rolling element (41) is assembled rotatable on two second coaxial pins (48a, 48b) supported by said hook- type lever (28) . 17 - Device as in claim 16, characterized in that said rolling elements (40, 41) are kept in the horizontal position by two packs of cup-type springs (45, 46), so that they can transmit the forces (actions and reactions) between said movable block (24) and said chock (26) in the two directions . 18 - Device as in claim 1, characterized in that transducer means ( 60 ) are provided to monitor the axial thrusts on said working rolls (12a, 12b) .

Inventors: DRIGANI FAUSTO, PAWLOWSKI STANISLAW, VENTULINI ENRICO, DRIGANI, FAUSTO, PAWLOWSKI, STANISLAW, VENTULINI, ENRICO
Applicants: DANIELI OFF MECC, DRIGANI FAUSTO, PAWLOWSKI STANISLAW, VENTULINI ENRICO, DANIELI & C. OFFICINE MECCANICHE SPA, DRIGANI, FAUSTO, PAWLOWSKI, STANISLAW, VENTULINI, ENRICO
Application year: 2001
Main classification: B21B13
IPC codes: B21B13, B21B31