Patent Publication Number: US-2011061435-A1

Title: Plant for the reversible rolling of steel strip

Description:
The invention relates to a rolling installation of the type comprising a two-stand reversing mill. 
     Steel strips may be rolled using different types of rolling installation. “Reversing” rolling installations make it possible to roll a strip, moving in a rolling direction, alternately in one direction and then the other. The strip is rolled by passing it through a mill comprising, between two coiling/uncoiling devices, one stand or two stands arranged successively in the rolling direction. 
     Two-stand reversing installations have a production capacity of 300,000 to 1,000,000 metric tons per year compared to a production capacity of 200,000 to 600,000 metric tons per year for “single stand” reversing installations. Two-stand reversing installations also have the advantage of reducing the number of rolling passes in one direction and then the other. Patent EP 0 618 018 B1 describes such a two-stand reversing rolling installation for cold rolling. 
     In the case of reversing rolling performed in more than three passes, the head and tail ends of the strip remain clamped to the mandrels of the coiling/uncoiling devices located on either side of the two stands. A service length between, firstly, the head or tail end of the strip and, secondly, the roll gaps in the stand located near to the coiling/uncoiling device to which is attached the head or tail end in question, is not rolled to the desired thickness. 
     Furthermore, at the end of the pass, an inter-stand length between the roll gaps of the two stands is not rolled to the required thickness. In fact, this inter-stand length has only been rolled by passing through one of the two stands, i.e. the stand located close to the coiling/uncoiling device to which is attached the head or tail end in question. 
     Thus, at each end of the strip, an end length corresponding to the sum of a service length and an inter-stand length has a thickness outside the tolerances. The two end lengths have to be removed after rolling, creating offcuts. Offcuts affect the performance of two-stand reversing installations. 
     For example, for a rolling mill using three passes to roll a steel coil with a width of up to 1600 mm, an initial thickness of 3 mm and a length of 700 m, to obtain a steel strip with a target thickness of 1 mm, a two-stand reversing rolling installation in which each stand has a rolling capacity of around 2,400 metric tons is required. To achieve this, each stand is for example fitted with backup rolls with a diameter of 1,250 mm and work rolls with a diameter of 450 mm. To withstand the corresponding stresses, each stand typically has uprights 9,000 mm tall and 4,000 mm wide. The center-to-center distance separating the planes of symmetry of the two stands, vertical planes in which the roll axes rest, is 6,000 mm. 
     In such installations the quantity of strip lost on the service lengths is 2% of the original coil. With a center-to-center distance between the two stands of 6,000 mm, the offcut corresponding to the two inter-stand lengths is 1% of the original coil. Consequently, the resulting total loss is greater than 3% of the original coil. This should be compared to the habitual loss of a single-stand mill which is around 2% and that of a continuous tandem mill which is negligible. 
     It should be noted that the center-to-center distance is necessarily greater than a minimum resulting from the geometry of the stands and their installation constraints on the building structure. In particular, according to the prior art, the uprights of the stands of the two-stand reversing mills include lugs in the building structure. A lug on an upright forms a protuberance, in the rolling direction, beyond the vertical plane of the face of the upright bearing the lug. In particular, the side face of an upright of the first stand, perpendicular to the rolling direction and oriented towards the second stand, has a lug projecting towards the second stand. Symmetrically, the side face of an upright of the second stand, perpendicular to the rolling direction and oriented towards the first stand, has a lug projecting towards the first stand. The lugs result in a center-to-center distance of 6,000 mm, or an inter-stand distance of 2,000 mm, the inter-stand distance corresponding to the distance separating the two external lateral faces located on each of the uprights of the first and second stands and facing one another. 
     The lugs have throughbores to accommodate elements to attach the uprights to the building structure. Moreover, the lower face of these lugs constitutes the support surface for the upright on the building structure. With regard to this, the lower face of the upright drops below the level of the lower faces of the lugs, and is situated above a pit created in the building structure, beneath the stand, to collect used lubricating oils. 
     We have attempted to reduce offcuts in two-stand reversing mills. 
     For example, the patent JP 03-138004 describes the use of extensions welded onto each end of the strip to be rolled, and a particular sequence for opening and closing the stands and the clamp to roll the entire strip to the required thickness. 
     Apart from the fact that this method takes a long time to implement, there is a risk of breaking around the junction between the extensions and the strip, in particular during rolling under traction. 
     The invention is therefore intended to reduce the length of the strip cut off during operation of a two-stand reversing rolling installation. 
     To achieve this the invention relates to a rolling installation of the type comprising a reversing mill with two stands, adjacent in a rolling direction, each stand having two roll supporting uprights, each upright resting on a support structure by means of a support surface and being fixed to the support structure by means of at least one shank attached to the support structure and cooperating with the upright by means of detachable fixing means. The support surface of each upright is provided on the lower face of the upright, without extending beyond the lateral faces of the uprights oriented in the rolling direction and includes at least one hole opening into a hollow seat provided for in the upright and having an aperture opening onto a lateral face of the upright. The shank attached to the support structure extends through the hole and projects into the seat, and the detachable fixing means is placed inside the seat. 
     According to the specific embodiments of the invention, the rolling installation has one or more of the following characteristics, separately or in any of the technically feasible combinations:
         the hollow seat is a cell, the cell having an aperture opening onto a lateral face of the upright, perpendicular to a direction transversal to the rolling direction and oriented towards the outside of the stand.   the hollow seat is a slot, the slot having an aperture opening onto a lateral face of the upright, perpendicular to a direction transversal to the rolling direction and oriented towards the outside of the stand.   the detachable fixing means is a nut, the shank is a pin and the support structure is solid concrete, the pin being anchored in the solid concrete and inserted into the hole passing through the upright of the stand and the nut being screwed to the pin.   the installation also includes means for driving the rolls comprising a reduction gear including an input shaft intended to be connected to a motor, first and second output shafts intended to be connected to the rolls to be driven and at least one intermediate shaft coupling the input shaft to the first and second output shafts, and at least the axes of the output and intermediate shafts are vertically superposed such as to reduce the footprint in the rolling direction.   the installation also includes means to change rolls, including a carriage shared by the first and second stands that can be moved, in a direction perpendicular to the rolling direction, between a service position near to the first and second stands and a waiting position away from the first and second stands, the carriage having at least two racks able to carry a train of rolls and arranged side by side in the rolling direction, and roll loading/unloading means enabling worn rolls to be unloaded from a stand onto an empty rack and for new rolls to be loaded from a rack into a stand.   the carriage includes a mobile deck that can be moved in parallel to the rolling direction, and said at least two racks are placed on the mobile deck.   the carriage includes four racks and the mobile deck can be moved between the first and second positions, such that, in the first position of the mobile deck, the racks of a first pair of racks are respectively placed in the vertical plane of the rolls of the first stand and the second stand, and, in the second position of the mobile deck, the racks of a second pair of racks are respectively placed in the vertical plane of the rolls of the first stand and the second stand, the carriage having first loading/unloading means to serve the first rack and second loading/unloading means ( 324 ) to serve the second stand, it being possible to load and/or unload the first and second stands simultaneously or separately.   the installation is able to roll strips with an entry thickness of up to 10 mm and up to 1,600 mm wide, and the distance between the lateral face of an upright of the first stand, perpendicular to the rolling direction and oriented towards the second stand, and the lateral face of an upright of the second stand, perpendicular to the rolling direction and oriented towards the first stand, is less than 1,500 mm.   the distance between the lateral face of an upright of the first stand, perpendicular to the rolling direction and oriented towards the second stand, and the lateral face of an upright of the second stand, perpendicular to the rolling direction and oriented towards the first stand, is greater than the space strictly necessary to enable an operator to pass through for exceptional interventions, a space of at least 700 mm.       

    
    
     
       The invention and its advantages can be better understood from the description below, given purely by way of example, and drafted with reference to the attached drawings, in which: 
         FIG. 1  is a schematic representation of a two-stand reversing rolling installation; 
         FIG. 2  is a side view of a two-stand reversing rolling installation according to one embodiment of the invention; 
         FIG. 3  is a top view of the installation in  FIG. 2 ; 
         FIG. 4  is a partial perspective view of the fixing means on the support structure of a stand of the installation in  FIGS. 2 and 3 ; 
         FIG. 5  is a partial perspective view of an alternative embodiment of the fixing means of a stand on the support structure; 
         FIG. 6  is a front view of the reduction gears of the drive means of the rolls of the installation in  FIGS. 2 and 3 ; and, 
         FIG. 7  is a front view of an alternative embodiment of the reduction gears of the drive means of the rolls. 
     
    
    
       FIG. 1  is a schematic representation of a two-stand reversing rolling installation  1  for rolling a metal strip M moving in a horizontal plane in a rolling direction A. The strip M is driven to move alternately in a positive direction (from left to right in  FIG. 1 ) and in a negative direction (from right to left in  FIG. 1 ). The rolling installation  1  includes, placed successively along the rolling direction A, a first stand  2  and a second stand  4 . The first and second stands  2  and  4  are of the six-high type. Each stand  2 ,  4  is fitted with a pair of work rolls  6  and  7 , a pair of intermediate rolls  8  and  9  and a pair of backup rolls  10  and  11 . The axes of the different rolls of a stand rest in a single vertical plane P of symmetry of the stand. 
     The rolling installation  1  also includes, upstream of the first and second stands  2  and  4 , a strip uncoiler  12 , a first coiling/uncoiling device  14 , a clamping device  16 . The rolling installation  1  includes, downstream of the first and second stands  2  and  4 , a deflector roll  18  and a second coiling/uncoiling device  20 . The first and second coiling/uncoiling devices  14  and  20  are respectively provided with mandrels to apply traction to the strip M during rolling such as to increase the thickness reduction rate of the strip M. 
     The rolling installation  1  includes other elements, not shown but known to the person skilled in the art, such as a preparation device for the head end of the strip M, thickness measurement means, etc. 
       FIGS. 2 and 3  show the rolling installation  1  according to the invention in greater detail, in which the stand uprights are adapted to minimize the center-to-center distance between the two stands, the distance separating the planes of symmetry P of the first and second stands  2  and  4 . 
     The first stand  2  includes two lateral uprights  22  arranged on either side of the rolling axis A in a transversal direction Y. The two lateral uprights  22  of the stand  2  are linked to each other in particular by upper crosspieces  24 . 
     An upright  22  has an external shape contained within a rectangular parallelepiped. It has a rear face  26 , perpendicular to the rolling direction A and oriented towards the second stand  4 ; a front face  27 , perpendicular to the rolling direction A and oriented the opposite way to the rear face  26 ; a lower face  28 , perpendicular to the vertical direction Z and oriented downwards; and an external lateral face  30 , perpendicular to the transversal direction Y and oriented towards the outside of the stand. The upright  22  rests on a support structure  25 , preferably made of concrete, by means of its lower face  28  comprising a flat support surface. The upright  22  is provided with an oblong window  32  in the vertical direction Z. The upright  22  is consequently ring-shaped. The window  32  is intended to receive the support means of the roll chocks  6  to  11 . 
     The second stand  4  includes a pair of uprights  42  arranged on either side of the rolling direction A and connected to each other by upper crosspieces  44 . 
     An upright  42  has a front face  46 , perpendicular to the rolling direction A and oriented towards the first stand  2 ; a rear face  47 , perpendicular to the rolling direction A and oriented the opposite way to the front face  46 ; a lower face  48 , perpendicular to the vertical direction Z and oriented downwards, forming a support surface of the second upright  42  on the support structure  25 ; and it has an external lateral face  50  perpendicular to the transversal direction Y and oriented towards the outside of the second stand  4 . One upright  42  is ring shaped, and defines internally a window  52  for the support means of the roll chocks  6  to  11 . 
     Thus, the rear face  26  of the first stand  2  and the front face  46  of the second stand  4  are arranged opposite one another. The distance separating the front and rear faces  26  and  46  is the inter-stand distance D. 
     According to the invention, the inter-stand distance D is minimized by bringing the first and second stands  2  and  4  closer to one another in the rolling direction A. To enable this, the rear and front faces  26  and  46  do not have any projections, in the rolling direction A, forming a protuberance towards the other stand. The rear and front faces  26  and  46  are flat. As shown in detail in  FIG. 2 , an upright  22 ,  42  includes hollow seats intended to receive means for fixing the upright to the support structure  25 . 
     In a first embodiment shown in  FIG. 4 , the upright  22  includes, in its lower part, a hollow seat forming a cell  62 . This leads to the rear face  26  of the upright  22  and the external lateral face  30  of the upright  22 . The upright  22  also has a throughbore  64 , with a vertical axis opening, at one end, onto the lower face  28  of the upright  22  and, at the other end, onto the lower surface  66  of the cell  62 . 
     The throughbore  64  enables the passage of a shank  80  of a pin, of which one end is anchored to the support structure  25  and the other end, threaded and free, protrudes out of the throughbore  64 , inside the cell  62 , above its lower surface  66 . A nut  82  is screwed to the shank  80  and tightened against the lower surface  66  of the cell  62  to attach the upright  22  to the support structure  25 . Thus, the cell  62  forms a seat to receive the nut  82 . 
     The upright  22  also has a second cell  63  along the edge between its front face  27  and its external lateral face  30 . A throughbore  65  leads to a cell  63  and enables the passage of a pin  80 . A nut  82 , seated in the cell  63 , is screwed to the threaded end of the shank of the pin  80  and enables the fixing means of the upright  22  to be tightened to the support structure  25  at a second fixing point. 
     Similarly, an upright  42  of the second stand  4  has a first cell  72  opening onto the front face  46  and onto the external lateral face  50  of the upright  42 , and a second cell  73  opening onto the rear face  47  and onto the external lateral face  50  of the upright  42 . The throughbores  74  and  75  are arranged between the lower face  48  and the first and second cells  72  and  75  to enable the passage of pins  80 . Nuts  82  are screwed to the threaded ends of the shanks  80  to attach the upright  42  to the support structure  25 . 
     Thus, according to the invention, the fixing means of an upright to the support structure are within the footprint of the upright in the rolling direction A. 
       FIG. 5  shows a second embodiment of the hollow seats. The hollow seats of the lower part of an upright  122  is realized such as to form a horizontal slot  162  on the external lateral face  130  of the upright  122 . The slot  162  extends from the front face  127  to the rear face  126  of the upright  122 . A lower surface  166  of the slot  162  has three throughbores  163 ,  164  and  165  that lead to the lower surface  128  of the upright  122 . They permit the passage of shanks with one end anchored to the support structure  25  and the other, threaded, end entering the slot  162 . Nuts screwed to the threaded ends of the shanks are inserted into the slot  162 . They enable, by tightening onto the lower face  166  of the slot  162 , to fix the upright  122  to the support structure  25  at different fixing points. 
     To withstand the stresses applied to them, the person skilled in the art will be able to determine the geometry of the uprights as a function, among other things, of the shape of the cells, the position of the anchor points on the support structure, and the surface of the support face of the support structure actually making contact. 
     Although it is beneficial to minimize the inter-stand distance D to reduce the corresponding inter-stand length lost, a minimum space must be left between the rear and front faces  26  and  46  of the stands  22  and  24 . Indeed, this space must be sufficient to enable the insertion and removal of tools such as the C-clamp of an X-ray thickness gauge used to measure the thickness of the strip in order to provide adjustment data to the control system of the rolling installation. Furthermore, albeit exceptionally, the possibility of a strip engagement problem in one of the stands or a breakage of the strip in the gap between the two stands occurring cannot be discounted. It is therefore necessary to retain an inter-stand distance to enable an operator to pass through. To assess the minimum dimension of the inter-stand distance, reference may be made to machine safety standards, and in particular standard EN 547 which proposes leaving a minimum space of 700 mm between two machines to enable access on all fours while enabling the body to move. 
     By way of example, and returning to the numerical data given in the introduction, the first and second six-high stands  2  and  4  have a rolling capacity of around 2,400 metric tons each. The backup rolls  10  and  11  have a diameter of 1,250 mm, the intermediate rolls  8  and  9 , a diameter of 550 mm, and the work rolls  6  and  7 , a diameter of 450 mm. Each stand  2 ,  4  typically has uprights  22 ,  24  9,000 mm tall and 4,000 mm wide. According to the invention the inter-stand distance D is reduced to 700 mm. Consequently, the center-to-center distance is reduced by 1,300 mm and the inter-stand length of the strip M is 4,700 mm. For a production of 1,000,000 metric tons per year, the annual gain realized by implementing this invention could reach 1,000 metric tons of strip. 
     In the installation according to the invention, the drive means of the work, intermediate or backup rolls, depending on the installation type, have a reduced footprint in the rolling direction A. 
     As shown in  FIG. 3  and  FIG. 6 , in a first embodiment, the drive means of the rolling installation have two reduction gears  200  arranged one after the other, parallel to the rolling direction A, on the drive side of the first and second stands  2  and  4 . 
     The reduction gear  200  includes: an input shaft  212 , coupled to a drive motor  214 , and two output shafts  216  and  218 , coupled respectively to each of the rolls to be driven. Where appropriate, a pair of extensions  220  couples the output shafts  116  and  118  and the rolls to be driven. The reduction gear  200  also includes, between the input shaft  212  and the output shafts  216  and  218 , at least one intermediate shaft  222  bearing a set of cogs meshed with cogs either on the output shafts  216  and  218 , or the input shaft  212 . 
     In this first embodiment, the axes of the output shafts  216  and  218  and intermediate shaft  222  are arranged horizontally one above the other in a vertical plane, while the axis of the input shaft  212  is arranged laterally in relation to the axis of the intermediate shaft  222 . The reduction gear  200  has an “L” layout. 
     A second embodiment of the reduction gear in the installation according to the invention is shown schematically in  FIG. 7 . According to this second embodiment, all of the axes of the shafts of the reduction gear  210  are arranged horizontally one above the other, in a vertical plane. The reduction gear  210  is vertical and has a reduced footprint in the rolling direction A. 
     In the installation according to the invention, the roll change system has a single carriage  300  as shown in  FIGS. 2 and 3 . The carriage  300  is fitted with wheels  302  and can be moved along the rails  304 , arranged in the transversal direction Y. The carriage  300  is moved by actuating the movement means  306  between a waiting position away from the first and second stands  2  and  4 , and a service position near to the first and second stands  2  and  4 .  FIG. 3  shows the carriage  300  in its waiting position away from the first and second stands  2  and  4 . 
     The carriage  300  has a mobile deck  310  fitted with a row of four racks  312   a - d  arranged side by side in the rolling direction A. The racks  312   a  and  312   b  serve the first stand  2  and the racks  312   c  serve the second stand  4 . Each rack  312   a - d  is able to carry a train of rolls comprising the work rolls  6  and  7  and the backup rolls  8  and  9 . At the beginning of the roll change method, the two racks  312   a  and  312   c  carry a train of new rolls, fitted with their chocks, while the other two racks  312   b  and  312   d  are empty, waiting to load the used rolls removed from each of the first and second stands  2  and  4 . 
     The mobile deck  310  is moveable by translation in the rolling direction A, along the rails  316  provided on the carriage  300 . The mobile deck  310  is moved in relation to the carriage  300  by actuating means such as a rack (not shown) on the carriage  300 . 
     In the first position of the deck  310 , the vertical plane of symmetry of the racks  312   b  and  312   d  coincides with the plane of symmetry respectively of the first and second stands  2  and  4 . The first and second push/pull devices  322  and  324 , provided on the carriage  300 , can pull the used rolls from the first and second stand  2  and  4  to place them on the racks  312   b  and  312   d.    
     In the second position of the mobile deck  310 , the vertical planes of symmetry of the racks  312   a  and  312   c  coincide with the planes of symmetry respectively of the first and second stands  2  and  4 . The first and second push/pull devices  322  and  324  can then be actuated to push the new rolls, waiting in racks  312   a  and  312   c , into each of the first and second stands  2  and  4 . 
     Once the rolls have been replaced, the carriage  300  is moved to its waiting position away from the mill. 
     In a synchronous roll-change method, the first and second push/pull devices  322  and  324  are actuated simultaneously to pull out the used rolls and push in the new rolls. This ensures a quick roll change. 
     Alternatively, an asynchronous roll-change method is possible in which the push/pull devices  322  and  324  are actuated separately in order to enable the rolls of one of the stands of the mill to be changed. 
     The person skilled in the art will be able to modify the installation described above to implement other roll replacement methods. Thus, in certain types of installation, the drive is provided via the backup or intermediate rolls. The work rolls are then driven by friction on the intermediate rolls. In this type of installation the drive side of the mill is relatively unencumbered. A roll loading/unloading carriage may therefore be provided on the drive side of the mill. Furthermore, although a push/pull roll change system has been described, alternatively, the roll change system may be push-through only or pull-through only.