Abstract:
A device for adjusting the distance between a pair of work rollers ( 40 ) in an edger of a rolling mill comprising actuator means associable with a respective work roller ( 40 ). The actuator means comprise a roll group ( 10; 10   s ) including two cylinders ( 20, 20   s;    30, 30   s ) associated with each other so to slide inside each other and movable between a withdrawn or maximum distance position between the rollers ( 40 ) and an advanced or minimum distance position between the rollers ( 40 ).

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention regards, in general, the field of rolling plants for ferrous and non-ferrous material, in particular strips and sheets, and more specifically, a device and a method of adjusting the distance between a pair of rollers of an edging stand, below identified as edger, associable with a rolling plant. 
       BACKGROUND OF THE INVENTION 
       [0002]    As is known, a rolling mill, particularly for the rolling of strips and sheets, is composed of one or more rolling stands arranged in series to form a rolling train. Inside each rolling stand, a pair of work rolls is housed and moved through adapters by electric motors. 
         [0003]    A slab, heated to the rolling temperature in the heating furnaces, after a period of descaling, is made to pass between the work rolls of the rolling mill until it reaches the desired dimensions. The set of subsequent passages through the ports between the rolls forms the rolling path. 
         [0004]    Two rolling process series are distinguished: a roughing process, which starts from the fusion product and leads to an intermediate product, called preform, and a finishing process, which leads from the preform to the finished product. In the roughing process, the rolling is carried out at hot temperatures, while the finishing process can be conducted hot, cold or partly hot and partly cold. 
         [0005]    During the hot rolling of strips and sheets, the preform can have shape defects, which the cold finishing is unable to completely correct. These are mainly defects deriving from non-uniform deformation of the material and the establishment of voltage fields inside the material during the rolling, with consequent formation of laps on the rolled material edges. 
         [0006]    In order to minimize the formation of laps on the edges, and to maintain the width of the strip or sheet constant, one employs so-called width adjustment devices (AWC), commonly known as edging stands or edgers. 
         [0007]    An edger is composed of a pair of vertical work rollers, each controlled, by means of a respective adapter, by an electric motor and by an adjustment system of the distance between the work rollers. In use, the work rollers are in contact with the lateral edges of the slab to be subjected to rolling. 
         [0008]    It is desirable that the material exiting from the roughing train, specifically a bar or a plate, has precise width dimensions, whereby the distance between the work rollers of the edger must be able to be adjusted so to permit a control of the width of the material, in order to correct possible non-uniformities at the edges. 
         [0009]    Over the years, different systems have been developed for the adjustment of an edger. A first example consists of a system of electromechanical type comprising a screw and a nut screw, a helical wheel and a worm screw. Such kinematic chain has the disadvantage of not permitting adjustments under load, involving long reaction times and thus being not very precise. 
         [0010]    A faster and more precise adjustment system than the electromechanical system is represented by a electromechanical-hydraulic hybrid system, obtained by installing a hydraulic capsule, constituted by a cylinder and a small-stroke plunger, between auger and work roller. A system of this type, even if it permits quick corrections of the material width, is disadvantageous since it considerably complicates the structure of the edging stand and causes an increase in installation and maintenance costs. 
         [0011]    The auger-capsule hydraulic system can finally be substituted with a single cylinder having a stroke ranging from 800-1000 mm. A solution of this type, even if it is well applied to edging stands coupled with rolling trains for strips, or rather with cylinders having a stroke equal to about 900 mm, is practically unusable in edging stands coupled with sheet trains, in which a cylinder stroke is necessary ranging from 1800-2500 mm. 
         [0012]    It is known, in fact, that due to the compressibility of the hydraulic fluid therein contained, typically oil, the stiffness of the hydraulic cylinders decreases with the increase of the stroke, leading to considerable yields under load, with consequent reduction of the control accuracy of the width of the rolled material and the dynamic performances. It follows that, in the specific case of edgers coupled with sheet trains, the mechanical and electromechanical-hydraulic hybrid solutions are, up to now, the only ones applicable. 
         [0013]    The main object of the present invention is that of resolving the technical problem outlined above by providing a completely hydraulic actuation device for adjusting the distance between the work rollers of one edging stand or edger, capable of quickly and precisely completing high adjustment strokes, i.e. ranging from 1800-2500 mm, so it can be used in edgers coupled with sheet trains. 
         [0014]    Another object of the present invention is that of providing an edger equipped with an adjustment device with completely hydraulic actuation for adjusting the distance between the work rollers. 
         [0015]    Not least object of the present invention is that of providing a method for adjusting the distance between a pair of work rollers in an edger of a rolling mill. 
         [0016]    These and other objects, which will be clearer below, are attained by an adjustment device according to claim  1 , by an edging stand or edger according to claim  14 , and by an adjustment method according to claim  15 . 
         [0017]    Further advantageously aspects of the invention will be set forth in the dependent claims. 
     
    
     
       DETAILED DESCRIPTION OF THE DRAWINGS 
         [0018]    Characteristics and advantages of the present invention will be clearer from the following detailed description of its currently preferred embodiments, provided as exemplifying and non-limiting with reference to the drawing set, wherein: 
           [0019]      FIGS. 1A-1C  are side views, in section and with parts removed, of a cylinder group of an adjustment device according to the invention in different operating positions; 
           [0020]      FIG. 2  is a side and section view of an adjustment device according to the invention with the rollers of the edger in maximum mutual distance position; 
           [0021]      FIG. 3  is a section view of an adjustment device according to the present invention with the rollers in minimum mutual distance position; 
           [0022]      FIG. 4   a  is a partial view of the adjustment device of  FIGS. 2 and 3  with the cylinder groups in rest condition; 
           [0023]      FIG. 4   b  is a view similar to that of  FIG. 4   a  with the external cylinders in maximum extension position and the internal cylinders in “all in” (OFF) position; 
           [0024]      FIG. 5   a  is a view similar to that of  FIG. 2   a  with the external cylinders in rest position and the internal cylinders in “all out” (ON) position; 
           [0025]      FIG. 5   b  is a view similar to that of  FIG. 2   a  with internal cylinders in “all out” position and the external cylinders in maximum extension position; 
           [0026]      FIG. 6  shows the connection between the stroke and the movement speed of the cylinder group; 
           [0027]      FIG. 7  shows the connection between the stroke and the movement time of the cylinder groups; 
           [0028]      FIG. 8  is a hydraulic oil scheme, which illustrates the functioning of the adjustment device in the step of bringing the rollers closer to the work position; 
           [0029]      FIG. 9  is a hydraulic oil scheme, which illustrates the functioning of the adjustment device in edging step, with the rollers in a possible work position; 
           [0030]      FIG. 10  is a hydraulic oil scheme, which illustrates the functioning of the adjustment device in the step of moving the rollers away from the work position; and 
           [0031]      FIG. 11  graphically illustrates the comparison, given the same stroke carried out, between the stiffness of a single-cylinder adjustment system and a cylinder group adjustment system according to the invention. 
       
    
    
       [0032]    In the drawing set, equivalent or similar parts or and components were identified with the same reference numbers. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    With reference to  FIGS. 1A-1C , the adjustment device according to the invention comprises actuator means with completely hydraulic actuation, in particular a cylinder group  10  composed of an external cylinder  20  and an internal cylinder  30 . 
         [0034]    The external cylinder  20  is formed of a front flange  22 , a rear flange  24  and a liner  26 , which delimits, a first cylindrical chamber  28 , sealed closed by the front and rear flanges  22 ,  24 . The external cylinder also includes a hollow tubular stem  21 , which bears a piston  23 , sealingly slidable in the first cylindrical chamber  28  and adjustable so as to be able to assume a plurality of positions that can vary between a completely withdrawn position ( FIG. 1A ) and a completely advanced position ( FIG. 1B ), carrying out an overall stroke C E . For its functioning mode, the external cylinder  20  will be indicated below with the expression ‘cylinder with controlled stroke piston’ or ‘controlled cylinder. 
         [0035]    The hollow stem  21  of the controlled cylinder  20  acts as a liner  36  of the internal cylinder  30 , such liner  36  delimiting a second cylindrical chamber  38 . The internal cylinder  30  can thus slide through the front flange  22  of the controlled cylinder  20  and also comprises a front flange  32 , that seals the second cylindrical chamber  38 . The internal cylinder  30  also comprises a tubular stem  31 , which bears a piston  33 . The piston  33  sealingly slides in the second cylindrical chamber  38  and can assume only two positions, i.e. a completely withdrawn or “all in” position ( FIGS. 1A and 1B ) and a completely advanced or “all out” position ( FIG. 1C ), carrying out a fixed stroke C I . For its functioning mode, the internal cylinder  30  will be indicated below with the expression ‘cylinder with piston all in/all out’ or ‘ON/OFF or fixed stroke cylinder’. 
         [0036]    The controlled cylinder  20  and the ON/OFF cylinder can be separately moved, by carrying out the respective strokes C E  and C I , or they are moved together, so to cover a range of strokes from 0 to a value equal to the sum arm of the strokes C E  and C r . To this end, the controlled cylinder  20  advantageously has a stroke C E  that is greater than the stroke C I  of the ON/OFF cylinder  30 . 
         [0037]    According to one particularly advantageous embodiment of the invention, illustrated in  FIGS. 2 and 3 , an adjustment device of the invention comprises a pair of cylinder groups, respectively an upper. cylinder group  10   s  and a lower cylinder group  10   i.    
         [0038]    Each cylinder group  10   s,    10   i  is associated with respective mechanical equipments  11   s ,  11   i  for driving a roller  40  of an edger of a rolling mill and comprises an external or controlled cylinder  20   s,    20   i  and an internal or ON/OFF cylinder  30   s,    30   i  slidable in the external cylinder. The controlled cylinders  20   s,    20   i  and the ON/OFF cylinders  30   s,    30   i  have the same configuration as the cylinders  20 ,  30  described with reference to the  FIGS. 1A-1C . 
         [0039]    In order to maintain a correct contact between the mechanical equipments  11   s ,  11   i  and the upper and lower cylinder groups  10   s,    10   i,  balancing means are provided, for example a balancing cylinder  13 , appropriately adjusted, whose functioning is known to those skilled in the art, so that it will not be described in the present document. 
         [0040]    In  FIGS. 4   a - 5   b , different operating conditions are illustrated of a pair of cylinder groups  10   s.  It is understood that an analogous discussion holds for the cylinder group pair  10   i.    
         [0041]    Specifically, in the rest condition, illustrated in  FIG. 4   a , the controlled cylinders  20   s  as well as the ON/OFF cylinders  30   s  have respective stems  21   s  and  31   s  in totally withdrawn position. In the operative condition illustrated in  FIG. 4   b , the stems  31   s  of the ON/OFF cylinders  30   s  are in “all in” position (OFF), while the stems  21   s  of the controlled cylinders  20   s  are in maximum extension position, equal to a stroke C E ˜1150 mm. In the operating position of  FIG. 5   a , the stems  21   s  of the controlled cylinders  20   s  are in totally withdrawn position while the stems  31   s  of the ON/OFF cylinders are in “all out” (ON) position, equal to a stroke C I ˜1050 mm. Finally, in the operative condition of  FIG. 5   b , the stems  31   s  of the ON/OFF cylinders are still in “all out position” (ON), while the stems  21   s  of the control cylinders  20   s  are in totally extended position, equal to a stroke C TOT =C E +C r =2200 mm. 
         [0042]    Due to the single or combined movement of the controlled and ON/OFF cylinders, the cylinder groups can cover a variable stroke range, for example from about 1000 mm to about 2500 mm, so to permit working slabs B of width L variable from about 4800 mm to about 1100 mm. 
         [0043]    The double cylinder group has, with respect to single cylinder systems, advantages in terms of increase of the speed and consequent reduction of the times of cylinder positioning, and thus adjustment of the distance between the rollers  40 . This is clearly illustrated in the diagrams represented in  FIGS. 6 and 7 , which show the connection between the strokes C E  and C I , of controlled cylinder  20 ,  20   s,    20   i  and ON/OFF cylinder  30 ,  30   s,    30   i,  respectively, and the speed and time of positioning of the cylinder group  10 ,  10   s,    10   i.    
         [0044]    It is assumed that, as exemplifying and non-limiting, the controlled cylinder  20 ,  20   s,    20   i  completes a stroke C E =1150 mm at a speed V E =60 mm/sec and that the ON/OFF cylinder  30 ,  30   s,    30   i  completes a stroke C I =1050 mm at a speed V r =100 mm/sec. 
         [0045]    For strokes up to C I =1050 mm, only the controlled cylinder  20 ,  20   s,    20   i  is actuated, which is moved at the speed V E =60 mm/sec (section ( 1 ),  FIG. 6 ) for a time t E =17.5 sec (section ( 1 ),  FIG. 7 ). For a stroke equal to CI, only the ON/OFF cylinder  30 ,  30   s ,  30   i  is actuated, which is brought into “all out” position, completing the entire stroke CI at the speed V I =100 mm/sec (section ( 2 ),  FIG. 6 ) in a time t I =10.5 sec (section ( 2 ),  FIG. 7 ). For strokes greater than C I , the controlled cylinders  20 ,  20   s,    20   i  and ON/OFF cylinders  30 ,  30   s,    30   i  both move until the ON/OFF  30 ,  30   s,    30   i  cylinder reaches its “all out” position in the time t I =10.5 sec (section ( 3 ),  FIG. 7 ); the speed of the cylinder group  10 ,  10   s,    10   i  increases until it reaches a value V TOT =V E +V I =160 mm/sec (section ( 3 ),  FIG. 6 ). Once the time t I  has passed, the ON/OFF cylinder  30 ,  30   s,    30   i  has carried out its entire stroke C I , so that only the controlled cylinder  20 ,  20   s,    20   i  is activated, which is moved at the speed V E =60 mm/sec; the speed of the cylinder group  10 ,  10   s,    101  decreases (section ( 4 ),  FIG. 6 ) and its positioning time increases (section ( 4 ),  FIG. 7 ). 
         [0046]    With reference now to the hydraulic oil schemes illustrated in  FIGS. 8-10 , the functioning of the adjustment device of the invention with double upper  10   s  and lower  10   i  cylinder group, of  FIGS. 2 and 3  will be described in detail. For the ease of exposition, reference will be made to only one pair of cylinder groups, for example that on the motor-side, but it should be understood that the same discussion holds true for the cylinder group pair on the operator-side. 
         [0047]    In particular, two main steps are provided for: a vacuum positioning step, i.e. in absence of material, of the cylinder groups  10   s,    10   i,  schematically illustrated in  FIGS. 8 and 10 , and a working or edging step of a bar or sheet, schematically illustrated in  FIG. 9 . 
         [0048]    During the vacuum positioning step, the controlled cylinders  20   s,    20   i  and ON/OFF cylinders  30   s,    30   i  are moved, separately or together, so to cause the rollers  40  to move closer to ( FIG. 8 ) or away from ( FIG. 10 ) the work position inside the edger. 
         [0049]    With particular reference to  FIG. 8 , in which the vacuum positioning step is illustrated for bringing the rollers  40  closers, the controlled cylinders  20   s,    20   i  and the ON/OFF cylinders  30 ,  30   a  are moved together. Specifically, the controlled cylinders  20   s,    20   i  are supplied, through a high pressure line HPL, typically at 300 bars, by supply means of known type, for example a high pressure piston pump group (not shown in the drawings). The respective pistons  33   s,    33   i  therefore carry out an outgoing stroke (F arrows,  FIG. 8 ) into the respective cylindrical chambers  28   s,    28   i.  Each stroke is controlled by a position transducer  50   s,    50   i , by a pair of pressure transducers  51   s,    51   i  and  52   s,    52   i  and by a servo-valve  53   s,    53   i,  all controlled by an electronic control unit CU (not shown). 
         [0050]    In the case of long strokes, a recirculation circuit is advantageously provided, adapted to conduct the outlet flow rate from the cylindrical chamber of one of the external cylinders, for example the cylinder  20   s,  to the inside of the cylindrical chamber of the opposite cylinder  20   i.  This permits reducing the necessary flow rate of the high pressure pump in this step. 
         [0051]    In addition, in order to avoid a possible misalignment of the controlled cylinders  20   s,    20   i , typically caused by hydraulic oil leaks from the respective cylindrical chambers  28 ,  28   a,  an additional servo-valve  54  is used, also controlled by the control unit CU. 
         [0052]    More in particular, the CU executes a comparison between the positions of the cylinders and adds or subtracts flow rate to the overall flow rate exchanged between them, depending on the lower or greater speed of one of the cylinders, said slave cylinder, with respect to the other, said master cylinder. 
         [0053]    The ON/OFF cylinders  30   s,    30   i  complete their entire stroke C I  supplied, through a low pressure line LPL, typically on the order of 100 bar, by supply means of known type, for example screw pump groups with large flow rate but reduced pressure (not shown in the drawings) controlled by the electronic control unit CU. These too, like the external cylinders  20   s,    20   i,  are provided with a position transducer  60   s,    60   i,  a pair of pressure transducers  61   s,    61   i  and  62   s,    62   i  and a servo-valve  63   s,    63   i,  all controlled by the CU. 
         [0054]    The alignment between the two internal cylinders  30   s,    30   i  and the synchronisation of their movement is achieved by means of a control loop using the servo-valves  63   s,    63   i  and the position sensors  60   s,    60   i . 
         [0055]    When the ON/OFF cylinders  30   s,    30   i  reach the “all out” (ON) position illustrated in  FIG. 9 , the chambers  38   s,    38   i  on the side of the piston are pressurised, connecting them to the high pressure supply line by actuating a two-way valve  55  and the stem side chamber is connected with the discharge line RL by actuating a further two-way valve  56 . This permits obtaining a locking force of the stems  31   s,    31   i  that is greater than the maximum force resulting from the work load. Therefore, in the working step, the ON/OFF cylinders  30   s,    30   i  behave like rigid spacers. 
         [0056]    Since, during the working step, the controlled cylinders and ON/OFF cylinders  20   s,    20   i  and  30   s,    30   i  are all supplied from the high pressure line HPL, the low pressure line, with the related screw pump group supplies a hydraulic oil conditioning circuit, whose function is to maintain the temperature of the oil over values not exceeding 70-80° C. It is known, in fact, that in a hydraulic circuit there is a generation of heat, with consequent increase of the temperature and alteration of the chemical-physical characteristics of the hydraulic oil. 
         [0057]    The movement step for moving the rollers  40  away, illustrated in  FIG. 10 , is entirely analogous to that for bringing them together illustrated in  FIG. 8 , with the difference that the controlled cylinders  20   s ,  20   i  and the ON/OFF cylinders  30 ,  30   a  are moved, together or separately, by carrying out a stroke that is reverse that completed in the moving closer step (F arrows,  FIG. 10 ). 
         [0058]    In addition to the advantages in terms of speed and movement time, the double cylinder group of the invention has, with respect to a single cylinder system, advantages also in terms of stiffness. This is schematically shown in the graph of  FIG. 11 . Such graph shows a comparison between the stiffness of a double cylinder system, external or controlled and internal or ON/OFF, according to the invention (upper lines) and that of a single cylinder system with stroke equal to the sum of the strokes of the controlled cylinders and ON/OFF cylinders (lower line). 
         [0059]    As can be observed, in the case of a single cylinder, the stiffness reaches its minimum value at half the stroke (1200 mm), while the double cylinder system permits maintaining the stiffness of the controlled cylinders  20 ,  20   s,    20   i,  extending their action stroke by means of the ON/OFF cylinders  30 ,  30   s ,  30   i,  which, as said above, in extreme conditions behave like non-deformable spacers. 
         [0060]    Due to its increased stiffness characteristics, the system according to the invention has a higher frequency and consequently reduced response times while the increase of speed involves performance improvement. 
         [0061]    Although the invention was described by referring to a preferred embodiment thereof, those skilled in the art will understand that numerous modifications and variations can be made thereto, which fall within the scope defined by the accompanying claims. For example, even if in the described embodiments the external cylinder was taken as controlled cylinder and the internal cylinder as ON/OFF cylinder, the same discussion holds even if the controlled cylinder is taken as the internal cylinder and the ON/OFF cylinder as the external cylinder.