Abstract:
A roller press for the pressure treatment or compaction of granular material, having at least two rolls formed as freely rotating rolls, in each case rotatably mounted in a machine frame by a shaft, driven in opposite directions and separated from one another by a roll gap. The shafts of the rolls are accommodated in bearing housings movably mounted in the machine frame and in each case two bearing housings arranged on one side of the rolls and belonging to different rolls are connected to each other via at least one pressure cylinder. The connection between the bearing housings in each case has at least one torque balance. In this way, the structure of a roller press having roller centering is simplified and can be produced more cost-effectively.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a roller press for the pressure treatment or compaction of granular material, having at least two rolls, configured as freely rotating rolls, which are respectively rotatably mounted in a machine frame via a shaft, are driven in counter rotation and are separated from one another by a roll gap, wherein the shafts of the rolls are accommodated in bearing housings movably disposed in the machine frame, and wherein in each case two bearing housings disposed on one side of the rolls and belonging to different rolls are connected to each other via at least one pressure cylinder. 
     For the centering of the roll gap in roller presses for the pressure treatment or compaction of granular material, the rolls of the roller press are generally held by large-sized hydraulic drives in their desired position in order that, on the one hand, the pressure in the roll gap between the rolls is maintained and, on the other hand, as a result of the centering, the parallelism of the boundary of the roll gap is maintained by the surface of the rolls. In this centering operation, the hydraulic drives operate with high force, both to maintain the parallelism of the roll gap and to maintain the pressure in the roll gap. To this end, in the simplest case a first roll is mounted as a fixed roll immovably in the machine frame in bearings, which for their part are fastened to brackets by bearing housings in a machine frame. In contrast, a second roll is mounted as a movable roll in bearings which are disposed in bearing housings arranged movably between two brackets of the machine frame. The hydraulic drives, for the relative positioning of the movable roll in relation to the fixed roll and for the maintenance of the pressure in the roll gap, apply high forces to the machine frame as a counter bearing, so that it is necessary to design the machine frame in appropriately stable construction. 
     In roller presses having rolls with a weight of up to 50 metric tons, an appropriately large dimensioning of the machine frame is necessary, so that, in a necessary and scheduled roll change, the logistics and handling of the machine frame are complex and possible only with appropriately large-sized cranes and disassembly aids. 
     In order to reduce the scale of the necessary dimensioning of the machine frame, it is proposed in DE 102005006090 A1 to configure both rolls of the roller press as a movable roll, wherein these two movable rolls are connected to each other via the bearings and the bearing housings and via hydraulic drives. The rolls, the bearings, the bearing housings and the hydraulic drives here form a closed system of forces which relieves the machine frame of load and which machine frame can thus be dimensioned smaller. This arrangement has proved itself in practice. Since in this roller press the closed system of forces is configured displaceably in relation to the machine frame, it is necessary to center the closed system of forces during operation in order that the roll gap does not drift during operation of the press. This centering is achieved by the use of an appropriately dimensioned hydraulic system. It is here necessary to control by control circuits the hydraulics, which, counter to the forces of the moving system of rolls, hydraulics and bearings, such as bearing housings, center the roll gap. 
     In a refinement of this roller press, in DE 102007059072 it is proposed to use a hydraulic double cylinder which is fastened to the machine frame. In this hydraulic double cylinder, two adjacent hydraulic chambers operate and are supported one against the other. Despite the forces which operate on the hydraulic system, that force of the hydraulic cylinder which acts upon the roll gap is not transmitted to the machine frame. For the centering of the roll gap, it is necessary however to provide by a multi-quadrant operation the hydraulic pressures necessary to generate the pressure in the roll gap. 
     SUMMARY OF THE INVENTION 
     The object of the invention is therefore to refine the roller presses such that the centering is designed such that it can be produced more easily and more cost-effectively, while maintaining the system of forces which is self-contained and is largely separate from the machine frame. 
     The object of the invention is achieved by virtue of the fact that the connection between the bearing housings respectively has at least one torque balance. Further advantageous embodiments of the invention are described herein. The method-related object of the invention is achieved by the use of the torque balance between the bearing housings. 
     By a torque balance is understood a rocker-like or pendulum-like suspension mounting, which is acted upon by first and second hydraulic cylinders, which work one against the other in pairs, on opposite-situated arms of the torque balance. These mutually counteracting hydraulic cylinders in each case individually produce the tilting of the torque balance in the direction of the related hydraulic cylinder. This change in position of the torque balance has on the side lying opposite the related first hydraulic cylinder the effect that the opposite-situated second hydraulic cylinder is more strongly loaded and therefore the control circuit of the now more strongly loaded second hydraulic cylinder builds up a higher pressure and acts counter to the first hydraulic cylinder until the torque balance is positioned back in its equilibrium setting. In the inventive roller press, the first and the second hydraulic cylinder have a clutch which is designed to be rotationally movable, so that the first and the second hydraulic cylinder can also act at an angle upon the arms of the torque balance. As a result of this rotationally movable clutch, it is possible that the rolls of the roller press can also assume settings which are not parallel to one another, which is always the case whenever a larger grain outside the middle of the roll gap passes through the roll gap or whenever the roll gap is unevenly charged with grinding stock. The effect of the torque balance is that, via a simple, movably mounted, mechanical element, a roll centering is enforced, insofar as the hydraulic cylinders working to generate the pressure in the roll gap counteract each other. As a result of the torque balance, it is also possible, where necessary, to equalize the force of two non-balanced and mutually counteracting hydraulic cylinders. Hydraulic regulating systems for operating the various cylinders in multi-quadrant operation are not necessary in this case, because the equalization happens automatically. 
     The torque balance can be of non-symmetrical or symmetrical construction. In the case of nonsymmetrical construction, the symmetry of the torque balance, specifically the unequal length of the arms of the torque balance, reflects the different size and nominal load capacity of the mutually opposing hydraulic cylinders. However, a symmetrical embodiment of the torque balance, which is disposed roughly midway between the bearing housings, is referred. The equal length arms of the torque balance are in this case acted upon by two identical hydraulic cylinders or, at least, two hydraulic cylinders having the same nominal load capacity and the same characteristic curve. 
     The torque balance is mounted in a preferred manner rotatably about a vertical rotation shaft which lies in a plane spanned by the centerline of the roll gap and the vertical. As a result of the vertical rotation axis, the torque balance rotates in a horizontal plane and thus allows a misalignment of the rolls relative to one another, wherein the torque balance has a compensating effect, so that the rolls, in the event of misalignment, are subjected to a force which, following the return of the roller press into the equilibrium setting, causes the rolls of the roller press to stand parallel to one another again. 
     In a preferred embodiment of the invention, the torque balance has a rocker having two arms, via which the two bearing housings of the roller press are connected to each other, and the torque balance has a rotatably mounted pendulum, via which the two-armed rocker is mounted pivotably about the rotation shaft. As a result of the pendulum, the two-armed rocker of the torque balance rotates about a center of rotation outside the force line between the two hydraulic cylinders, which pull on the opposite-situated arms of the torque balance. The effect of this is that only a small part of the force of the hydraulic cylinders is transmitted to the rotation shaft, since the torque balance, if the force of two mutually counteracting hydraulic cylinders is uneven, tilts toward the one or other side, so that the force of the hydraulic cylinders, which have a changed direction as a result of the misalignment, is always transmitted in a straight line one to another and not to the machine frame. 
     Although the system of forces consisting of rolls, shafts, bearings, bearing housings, hydraulic cylinders and torque balance is closed and therefore does not transmit the force for generating the pressure in the roll gap to the machine frame, or only transmits said force to the machine frame to the extent of a small directional component, the rotation shaft is nevertheless fixedly connected to the machine frame. Even though the torque balance is supported on the rotation shaft, the high forces of the hydraulic cylinders, which act upon the torque balance respectively in pairs and in mutually opposing arrangement, are diverted by the torque balance, so that the force, or at least the greatest share thereof, acts always in the direction of the hydraulic cylinders. 
     In the inventive roller press, the hydraulic cylinders are subjected only to tensile load. The torque balance hence has the effect that the distance apart of the hydraulic cylinders is minimized and the torque balance thereby aligns itself. This produces the centering effect on the roll gap. 
     In a preferred embodiment of the invention, two bearings of two different rolls on one side of the roller press are configured as fixed bearings, and two bearings on the opposite side of the roller press are configured as loose bearings. The loose bearings enable an axial movement of the shaft in the bearing, so that the temperature-induced change in the length of the roll is compensated and also the distance apart of the bearings when the rolls are tilted. Irrespective of the degrees of freedom provided by the loose bearings, the bearing housings of all bearings are mounted on a slide rail in the machine frame. Thus the bearings can travel in a direction perpendicular to the centerline of the roll gap and the loose bearings provide a degree of freedom in the axial direction, i. e. parallel to the centerline of the roll gap. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in greater detail with reference to the following figures, wherein: 
         FIG. 1  shows a diagrammatized view of an inventive roller press in the state of equilibrium from above, with partially blanked-out machine frame parts, 
         FIG. 2  shows the same arrangement as in  FIG. 2 , but in the deflected state, 
         FIG. 3  shows a perspective view of selected elements of an inventive roller press. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIG. 1 , an inventive roller press  100  is depicted in a view from above (parts of a machine frame are blanked out for better representation of the individual parts). In this roller press  100 , a first roll  110  is rotatably mounted in the roller press  100  with the aid of shafts - 111  and  112 . A second, adjacent roll  120 , which for its part is rotatably mounted via shafts  121  and  122  in the roller press, is disposed in the roller press  100 , with the formation of a roll gap  115  to be centered. During operation of the roller press  100 , the two rolls  110  and  120  are driven in counter rotation, so that the grinding stock delivered from above to the roll gap  115  is drawn into the roll gap  115 . 
     The mounting of the rolls  110  and  120  in the roller press  100  is realized via fixed bearings disposed in the fixed bearing housings  130  and  140  and via loose bearings disposed in the loose bearing housings  150  and  160 , which in the roller press  100  lie opposite the fixed bearing housings  130  and  140  in the axial direction of the rolls  110  and  120 . These bearing housings  130 ,  140 ,  150  and  160  are, for their part, disposed on slide rails  170  and  180 , on which the bearing housings  130 ,  140 ,  150  and  160 , together with the therein accommodated bearings and the, in turn, therein accommodated shafts  111 ,  112 ,  121  and  122 , can perform in the machine frame  171 , which is here represented only fragmentally and in part, horizontal compensating motions perpendicular to the axis of the rolls  110  and  120 . The bearing housings  130 ,  140 ,  150  and  160  can also in small measure execute rotary motions about a vertical axis of the bearing housings  130 ,  140 ,  150  and  160 . 
     Fixed bearing housings  130  and  140  and loose bearing housings  150  and  160  respectively form on an axial side of the rolls  110  and  120 , together with the respectively upper torque balance  250  or torque balance  260  (visible in this view), the lower torque balances  250 ′ and  260 ′ (non-visible in this view), and the respectively associated, tensile loaded, top-situated hydraulic cylinders  210 ,  220 ,  230  and  240 , as well as non-visible, bottom-situated hydraulic cylinders  210 ′,  220 ′,  230 ′ and  240 ′, a closed system of forces. In this system of forces, the respectively upper torque balances  250  and  260 , as well as the lower torque balances  250 ′,  260 ′ (non-visible in this view), are fastened in a rotationally movable manner to the machine frame  171  via pivots  310  and  320 . 
     During the operation of the roller press  100 , it happens that the rolls  110  and/or  120  must perform compensating motions for the passage of, where necessary, non-reducible particles, such as, for instance, pieces of metal which have inadvertently made their way into the grinding stock, or for the passage of grinding stock which is unevenly distributed over the length of the roll gap  115 . During this compensating motion, the roller press is temporarily in a state of disequilibrium. This state is represented in the following figure,  FIG. 2 . 
       FIG. 2  shows the roller press  100  during a moment of a compensating motion, which motion is shown in exaggerated representation. Both the roll  110  and the roll  120  have a slight rotary motion about a vertical axis, whereby the roll gap,  115  has a trapezoidal profile, having an opening of the roll gap  115  which in  FIG. 2  is larger on the bottom side. This compensating motion is only possible if the bearing housings  130 ,  140 ,  150  and  160  on the slide rail  170  and  180  can deviate in the horizontal direction and if the loose bearings in the loose bearing housings  150  and  160  permit an axial motion of the shafts  112  and  122 . 
     As a result of the tilt of the rolls  110  and  120 , the bearings, together with the bearing housings  130 ,  140 ,  150  and  160 , are also moved forcibly out of their position of equilibrium. Since the bearing housings  130  and  140 , and  150  and  160 , are connected in pairs via the torque balances  250  and  260 , and since the torque balances  250  and  260 , by pivots  310  and  320 , are mounted via the pendulums  290  and  300  rotatably about a vertical axis in the machine frame  171 , the force is transmitted by the compensating motion of a roll  110 ,  120  to the respectively other roll  120 ,  110 . The, in  FIG. 2 , upper torque balance  260  is skewed in the clockwise direction, while in that state of the roller press  100  which is represented here the lower torque balance  250  is skewed slightly in the counterclockwise direction. In this state of the roller press  100 , the distance apart of the bearing housings  130  and  140  and/or bearing housings  150  and  160 , which are grouped in pairs, is greater than in the state of equilibrium depicted in  FIG. 1 . As a result of the tensile force of the two hydraulic cylinders  210  and  220  and/or of the hydraulic cylinders  230  and  240 , the roller press  100  is inclined to revert to the state of equilibrium represented in  FIG. 1 , whereupon the trapezoidal roll gap represented in  FIG. 2  reassumes a rectangular profile and is aligned centered in the machine frame  171 . For the centering of the roll gap  115 , the pivots  310  and  320  do not have to absorb the forces of the tensile loaded hydraulic cylinders  210 ,  220 ,  230  and  240 , yet the rotationally movable suspension mounting of the torque balance  250  and/or  260  means that an aligned equilibrium setting of the rolls  110  and  120  is possible only in a horizontal position, whereby the roll gap  115  is centered. 
     One advantage in the use of the torque balance is a simplification of the hydraulic control, which in extremis can take place on an individual basis without mutual compensation, because the torque balance is capable of compensating slight deviations in the control characteristic of the hydraulic systems one to another. In addition, the use of multi-chamber hydraulic cylinders is able to be dispensed with. The here presented roller press  100  is robust, offers automatic centering and, as a result of the closed system of forces, can be equipped with a light machine frame. 
     Finally, a perspective view of an inventive roller press  100 , in which selected elements are blanked out in order to clarify the invention, is represented in  FIG. 3 . It can be seen from the perspective view that a roll  120  is accommodated via a shaft  122  in a loose bearing housing  160 . At this site, the shaft  122  projects from the loose bearing housing  160  and the drive side of the shaft  122  is found there. This loose bearing housing  160  is accommodated, like the loose bearing housing  150  of the second roll  110  (here blanked-out), within a frame made up of several elements, which frame, in this embodiment of the roller press  100 , consists of four tensile loaded hydraulic cylinders  230 ,  230 ′,  240  and  240 ′, the blocks  155  and  165 , embracing the loose bearing housings  150  and  160 , and the torque balances  260  and  260 ′, wherein this frame forms a closed system of forces which is designed to absorb the force resulting from the pressure in the roll gap  115 . Apart from the accommodation in the frame made up of various elements, the here non-blanked-out loose bearing housings  150  and  160  rest on a slide rail  180 , which is not part of the above-described frame made up of several elements, but is instead part of a machine frame  171  (not shown here). The slide rail  180  thus absorbs only the weight of the rolls  110  and  120 , together with their shafts  111 ,  112 ,  121  and  122  and the loose bearing housings  150 ,  160 . The torque balances  260  and  260 ′ consist of two powerful rockers  280 ,  280 ′, in which the hydraulic cylinders  230 ,  230 ′,  240  and  240 ′ engage. Between the two rockers  280 ,  280 ′ is accommodated a pendulum  300 ,  300 ′, via which the torque balance  260 ,  260 ′ can rotate about a journal in the form of the pivot  320 . This journal is fixedly  15  mounted on a part of the machine frame  171  and absorbs, in comparison to the tensile force of the hydraulic cylinders  230 ,  230 ′,  240  and  240 ′, lowly dimensioned forces. 
     As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art. 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 REFERENCE SYMBOL LIST 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 100 
                 roller press 
               
               
                   
                 110 
                 roll 
               
               
                   
                 111 
                 shaft 
               
               
                   
                 112 
                 shaft 
               
               
                   
                 115 
                 roll gap 
               
               
                   
                 120 
                 roll 
               
               
                   
                 121 
                 shaft 
               
               
                   
                 122 
                 shaft 
               
               
                   
                 130 
                 fixed bearing housing 
               
               
                   
                 140 
                 fixed bearing housing 
               
               
                   
                 150 
                 loose bearing housing 
               
               
                   
                 155 
                 block 
               
               
                   
                 160 
                 loose bearing housing 
               
               
                   
                 165 
                 block 
               
               
                   
                 170 
                 slide rail 
               
               
                   
                 171 
                 machine frame 
               
               
                   
                 180 
                 slide frame 
               
               
                   
                 210 
                 hydraulic cylinder 
               
               
                   
                 210′ 
                 hydraulic cylinder 
               
               
                   
                 220 
                 hydraulic cylinder 
               
               
                   
                 220′ 
                 hydraulic cylinder 
               
               
                   
                 230 
                 hydraulic cylinder 
               
               
                   
                 230′ 
                 hydraulic cylinder 
               
               
                   
                 240 
                 hydraulic cylinder 
               
               
                   
                 240′ 
                 hydraulic cylinder 
               
               
                   
                 250 
                 torque balance 
               
               
                   
                 250′ 
                 torque balance 
               
               
                   
                 260 
                 torque balance 
               
               
                   
                 270 
                 rocker 
               
               
                   
                 270′ 
                 rocker 
               
               
                   
                 280 
                 rocker 
               
               
                   
                 280′ 
                 rocker 
               
               
                   
                 290 
                 pendulum 
               
               
                   
                 290′ 
                 pendulum 
               
               
                   
                 300 
                 pendulum 
               
               
                   
                 300′ 
                 pendulum 
               
               
                   
                 310 
                 pivot 
               
               
                   
                 320 
                 pivot