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The invention relates to a chain guide for a driving chain of a mining machine, in particular for a plow chain for moving a winning plow, comprising driving and/or return stations which are provided on or can be arranged on end regions of the mining machine and have driving or return sprockets for the driving chain, and comprising at least one chain guide element which is arranged in spatial proximity to the sprockets at the driving and/or return station and can be adjusted, or is engaged in operational use, transversely to the direction of movement of the chain against its load strand and/or return strand. 
     BACKGROUND OF THE INVENTION 
     A chain guide arrangement on a mining machine is known (DE 20 2004 000 924 U) in which a chain guide element is formed by a hold-down device which has a pressure surface and can be inserted into an accommodating pocket in the region of the chain guide in such a way that it can be put, with a pin receptacle open on one side, onto a hinge pin arranged in the region of the accommodating pocket and is then pivoted about said hinge pin into the pocket until its bottom pressure surface presses against the driving chain and it can be locked in this position by a locking arrangement. It is possible to quickly exchange the hold-down device together with the pressure surface formed thereon for a new chain guide element of corresponding design, whereby downtimes in the event of wear of the pressure surface of the hold-down device can be minimized. At the same time, the known chain guide elements, past which the driving chain is moved with a considerable pressure force and at a considerable speed, is subjected to high wear, and therefore it is necessary to exchange it within relatively short time intervals in order to ensure the proper operation of the mining machine. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to avoid these disadvantages and provide a chain guide of the type mentioned at the beginning with which the wear in the region of the chain guide element is markedly reduced. 
     This object is achieved by the invention in that the chain guide element has at least one pressure roller which is adjusted or can be adjusted against the chain links of the driving chain. 
     Through the use of a pressure roller on the chain guide element, sliding contact between said chain guide element and the driving chain is at least largely prevented, for the peripheral speed at which the pressure roller rotates is the same as the passage speed of the chain, against which it presses in order to guide it. Even if coal dust or other material, possibly also abrasive material, gets between chain and pressure roller, the wear caused by this on the pressure roller track, which in a preferred configuration of the invention can be adapted to the envelope curve defined by the chain links, is only slight, for which reason it is not necessary to exchange the chain guide element substantially formed by the pressure roller until after a period of use considerably longer than was the case with the chain guide elements used hitherto. 
     The pressure roller is preferably rotatably mounted on a roller axle and can be exchanged together with the latter. The roller axle, in a construction unit with the pressure roller which is rotatably mounted thereon, is then removed and exchanged for a corresponding new part, wherein the downtimes of the mining machine are reduced to a minimum. The pressure roller can then be arranged or mounted in an especially advantageous manner on an attachment which can be interchangeably inserted or is interchangeably inserted in the entry region of the driving and/or return station. In this especially advantageous design, the pressure roller is therefore arranged on an attachment which can be interchangeably inserted in an accommodating pocket and which can then also contain still further components of the chain guide, such as, for example, a catch, known per se, for the chain, said catch being used when the driving or return sprockets of the driving or return stations are exchanged in order to keep the chain tensioned during such maintenance work. 
     According to an advantageous configuration, the roller axle of the pressure roller can be supported on one or more bearing blocks which are preferably interchangeably fitted in an accommodating pocket. In this case, a bottom bearing block and a top bearing block can preferably be provided on both sides of the roller. In this configuration, the bearing blocks can more preferably be secured against release in the accommodating pocket by means of a preferably hinged lid. Alternatively, the bearing blocks can be secured against release in the accommodating pocket by means of at least one sliding bolt. In this configuration, it is especially advantageous if a top bearing block is provided with sliding guides for sliding bolts. The sliding guides can consist in particular of hook-like strips which vertically fix and at the same time guide in a horizontally movable manner the one sliding bolt or preferably the two sliding bolts displaceable relative to one another. In this case, retaining blocks having locking pockets which face one another are more preferably fitted above the accommodating pocket, and/or the sliding bolts have locking lugs which engage in the locking pockets in the locking state in order to secure the top bearing block against release in the locking state of the locking bolts. 
     In an especially preferred configuration having form-fitting bolt securing for the bearing blocks, a pair of sliding bolts are provided, wherein each sliding bolt has a U-shaped base having three legs, of which one marginal leg and an intermediate leg are provided, on outer sides facing away from one another, with guide strips for form-fitting engagement in sliding guides, and of which the second marginal leg has a through-hole for a securing screw. A bottom axle receptacle for the roller axle can be arranged directly at the bottom of the recess and can preferably be fixedly formed on or fastened to the attachment. 
     In particular if it is necessary to guide and keep under tension especially long and/or heavy chains using a chain guide element according to the invention, a design which has a plurality of pressure rollers which are arranged one behind the other in the passage direction of the chain and are adjusted against the chain can be advantageous, as a result of which the requisite, high pressure force can be distributed over a plurality of rollers and the surface pressures between chain and running surface of the pressure rollers can be kept low or reduced. The pressure roller can be adjusted against the chain under the effect of at least one spring element and/or of at least one shock absorber, thereby making it possible for the chain to yield in a direction transversely to its passage direction, for example if shock-like loads occur, but without the pressure roller lifting from the chain, not even temporarily, and thereby no longer being able to perform its guide function, even if only briefly. 
     These and other objects, aspects, features, developments, embodiments and advantages of the invention of this application will become apparent to those skilled in the art upon a reading of the Detailed Description of Embodiments set forth below taken together with the drawings which will be described in the next section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail and illustrated in the accompanying drawings which form a part hereof and wherein: 
         FIG. 1  shows a chain guide for a driving chain of a coal plow in longitudinal section; 
         FIG. 2  shows a chain guide according to  FIG. 1  in an oblique perspective illustration from above, partly in section; 
         FIG. 3  shows the pressure roller used in the chain guide according to  FIGS. 1 and 2 , in section; 
         FIG. 4  shows an attachment which can be inserted in the chain guide according to  FIGS. 1 and 2  and has a pressure roller accommodated therein, in a perspective illustration, according to a first embodiment variant; 
         FIG. 5  shows an attachment which can be inserted in the chain guide according to  FIGS. 1 and 2  and has a pressure roller accommodated therein, in a perspective exploded illustration, according to a second embodiment variant; 
         FIG. 6  shows a longitudinal section through the attachment according to  FIG. 5  in the fitted state of the pressure roller; and 
         FIG. 7  shows a perspective detailed view of the sliding bolt pair. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Referring now to the drawings wherein the showings are for the purpose of illustrating preferred and alternative embodiments of the invention only and not for the purpose of limiting the same,  FIGS. 1 and 2  show a scraper chain conveyor at one of its end regions, said scraper chain conveyor being provided, in a manner known per se, with a plow guide for a coal-winning plow. The plow (not shown) is driven by means of a driving chain  11  which is accommodated in a chain box  10  lying below the conveying plane. 
     To this end, the arrangement has a first chain passage  13  for the load strand  14  of the driving to chain and a second chain passage  15  through which the return strand  16  of the driving chain runs. Located at the end regions of the chain passages  13 ,  15  is a driving station  17  having a driving sprocket  18 , around which the driving chain  11  is looped and with which the chain is pulled through the chain passages in a known manner. Arranged in the transition region  19  between the second chain passage  15  and the driving station  17  is a chain guide  20  having a chain guide element  21  which pushes the return strand of the chain downward and thereby deflects said return strand out of the chain passage for the return strand toward the driving sprocket  18  and which has a pressure roller  22 , or consists substantially of such a pressure roller, which presses from above with its track  23  against the driving chain  11  and thereby deflects the chain toward the driving sprocket and keeps the chain under tension. 
     The chain guide  20 , which consists of an attachment  25  interchangeably fitted into a gap  24  above the chain passage  15  at the transition region  19  of the mining machine, is shown in more detail in a first embodiment in  FIGS. 3 and 4 . It can be seen that the attachment  25  consists of a housing having two side walls  26  and a rear end wall  27 , wherein the two side walls  26  are provided with upwardly open recesses as accommodating pockets  40  for bearing blocks  28 ,  28 A which accommodate a roller axle  29  for the pressure roller  22  in a rotationally fixed manner. The accommodating pocket  40  is defined at the rear by the end wall  27  and at the bottom and at the front by the respective side wall  26 . Both bearing blocks  28 ,  28 A are formed congruently with the circumferential wall of the accommodating pocket  40  and are accommodated in the latter in a form-fitting manner. The bottom bearing block  28 , if need be, may also be fixedly anchored in the accommodating pocket and, for example, welded in place for this purpose. The top bearing block  28 A, once the nuts  41  have been released from the two vertically disposed threaded rods  42  anchored in the bottom bearing block  28  or in the side wall  26 , can be removed upward, as a result of which the roller axle  29  is exposed and can then also be removed together with the pressure roller  22  from the bottom bearing block  28  and exchanged for another pressure roller  22  plus roller axle  29 . 
     The pressure roller  22  is rotatably mounted on the roller axle  29  with two tapered roller bearings  30  in back-to-back arrangement and is provided with lateral sealing covers  31  to prevent the ingress of coal dust or other contaminants. It can be seen in particular in  FIG. 3  that the track  23  of the pressure roller  22  has a concave shape adapted to the envelope curve  34  defined by the chain links  33 , such that the pressure roller, when it acts on the chain, not only keeps said chain under tension and deflects it, but at the same time also prevents lateral running of the chain. 
     During operation, the pressure roller  22  accommodated in the attachment  25  or in the accommodating pocket  24  is covered at the top by a hinged lid  35  which prevents, to the greatest possible extent, coal dust or rock fragments from reaching the roller but, after it has been opened, allows easy access to the pressure roller  22  and thus enables dust or other contaminants which have nonetheless settled in the region of the pressure roller and/or in the accommodating pocket to be removed again with simple means. If it should transpire during such an inspection that the functioning of the roller is no longer reliably ensured due to wear, said roller can be exchanged quickly and simply by the lid  35  mounted on one side on the hinge spindle  45  being swung open and then, as described above, by the bearing blocks  28 ,  28 A being opened and by the pressure roller  22  together with its roller axle  29  being lifted out and exchanged for a new roller with roller axle. If both the bottom bearing block  28  and the top bearing block  28 A sit loosely in the accommodating pocket  40 , i.e. in such a way as to be removable upward here, the lid  35  can at the same time form the securing element which presses the bearing blocks  28 ,  28 A downward into the accommodating pocket  40  and secures them against release. However, the lid  35  can also hold only the top bearing block  28 A in the closed position. 
       FIGS. 5 and 6  show an alternative configuration of a chain guide  120  according to the invention, which again consists substantially of an attachment  125  which, via the side wall  126 , here the rear side wall  126 , designed as a bearing plate having strip-shaped edges, can be fastened to a spill plate, designed for accommodating the bearing plate, of a driving station of a plow installation. In the exemplary embodiment of the attachment  125  shown, the front side wall  126 , only shown in  FIG. 6 , can be fastened to a spar or a side spill plate of the driving station via a tilting hinge  160 , as a result of which, provided the retaining hooks for the rear side wall  126  are released, the entire attachment  125  can be pivoted in order to be able to carry out, for example, repair work on a scraper chain conveyor laid parallel to the plow installation. As in the previous exemplary embodiment, a catch  161  is also pivotably linked between the two chain walls  126  in the case of the attachment  125  in order to be able to secure the chain strand of the plow chain for repairs when the closing lid  162  is removed or swung up. An accommodating pocket  140  is again formed in the left-hand half of the attachment  125 , in which accommodating pocket  140  a pressure roller  122  rotatably mounted on a bearing axle  129  and forming the actual chain guide element  121  can be interchangeably fastened, wherein the pressure roller  122  can be pressed in an adjustable manner, or with its track, as already described further above, against a plow chain (not shown in  FIGS. 5 and 6 ). In the operating state, the plow chain passes through a passage opening  151  in the end wall  127 , here the front end wall  127 , and a passage opening  152  in the end wall  127 A, here the rear end wall  127 A. In the fitted state of the attachment  125  at the driving station, the top chain guide passage for the plow chain adjoins the front passage opening  151 , whereas the plow chain behind the rear passage opening  152  enters the driving or return sprocket for the plow chain. With the pressure roller  122 , the plow chain can be preloaded downward between both passage openings  151 ,  152 , thereby enabling the top chain strand of the plow chain to enter the plow chain sprocket (not shown) with low wear in an optimum manner without the plow chain coming into contact with, for example, the edges of the rear passage opening  152 . As in the previous exemplary embodiment, here, too, the pressure roller  122  and roller axle  129  are designed as a construction unit, for which reason the entire pressure roller  122  can be exchanged for another pressure roller without any problems and quickly if wear has occurred at the envelope curve of the pressure roller  122  or the mounting thereof. 
     In order to enable the pressure roller  122  together with roller axle  129  to be exchanged as simply as possible and at the same time achieve stable and reliable locking of the roller axle  129  even in the event of disproportionately high vertical forces on the pressure roller  122 , the roller axle  129 , with its two axle journals  129 A which project laterally beyond the pressure roller  122 , is inserted in axle receptacles  155  in a rotationally fixed manner, wherein the bottom axle receptacle  155  is formed directly on a wall section  126 A of the side wall  126 , here the front side wall  126 , and the rear bottom axle receptacle is formed on a rear wall section in the rear side wall  126 . In this case, the axle receptacle  155  can either consist of a correspondingly integrally formed recess in the wall section  126 A or, as shown in  FIG. 5 , can be formed inside a ring segment  156  which is welded to the wall section  126 A and could also be exchanged in the event of repair if the axle receptacle  155  is worn. The axle receptacle  155  together with ring segment  156  therefore forms a bottom bearing block in the attachment  125  of the chain guide  120 , this bearing block being formed fixedly and in one piece on the attachment  125 , whereas only a top bearing block designated overall by reference numeral  128  can be removed. The top bearing block  128  at the same time forms the lid for the pressure roller  122 , and the bearing block  128  has two side webs  171  which in this case have a rectangular cross section and can be inserted in an accurately form-fitting manner into the correspondingly congruently designed accommodating pockets  140  in the wall sections  126 A. Both side webs  171  are provided at their bottom edge with further ring segments  176 , which, like the bottom ring segments  156  on the wall sections  126 A, each form one half of the axle receptacle, here therefore the top half of the axle receptacle  155 , and, in the fitted state, accommodate the axle journal  129 A in a rotationally fixed manner between both ring segments  156 ,  176 , said axle journal  129 A having a noncircular, preferably approximately oval cross section in the exemplary embodiment shown. 
     The bearing block  128  designed as a lid is provided with a cover web  172  which connects the two side webs  171  and above which two lateral, approximately L-shaped hook strips  173  are welded on, which form, with their undercut sections, sliding guides for two sliding bolts  190  of identical design, with which the locking position of the top bearing block  128  can be secured in order to prevent unintentional release of the bearing block  128  and in this respect also the displacement of the roller axle  129  of the pressure roller  122 . 
     Reference will now first be made to  FIG. 7 , in which the two sliding bolts  190  of identical design, which are used as a pair of sliding bolts  190 , are shown. Each sliding bolt  190  has a substantially U-shaped basic body  191  having a short marginal leg  192 , a longer marginal leg  193  and an intermediate leg  194  which runs perpendicularly to both marginal legs  192 ,  193 . Both the intermediate leg  194  and the end face of the longer marginal leg  193  are each provided at the margin with a step, as a result of which guide strips  195  and  196  are formed on the marginal leg  193  and intermediate leg  194 , respectively, with which the sliding bolts  190  can each be secured in a form-fitting manner to the strips ( 173 ,  FIG. 5 ), forming the sliding guide, in such a way as to be guided in a vertically fixed and horizontally movable manner. The shorter marginal leg  192  in each case is dimensioned in such a way that, in the fitted state, the guide strip  196  on the intermediate leg  194  and the substantially shorter guide strip  195  on the end face of the marginal leg  193  lie such as to be plane-parallel relative to one another. Due to the U-shaped configuration, the respectively shorter marginal leg  192  plunges into the intermediate space  197  between the two marginal legs  192 ,  193 , and the distance between the two longer marginal legs  193  can be reduced by pushing apart the two shorter marginal legs  192 . Only in this position, which is not shown in the figure, can the top bearing block ( 128 ,  FIG. 5 ) be fitted or removed in the accommodating pocket in order to open or close the mounting for the roller axle ( 129 ,  FIG. 5 ). To lock the bearing block by a form fit, the longer marginal legs  193  are provided on the outside with locking lugs  198 , the top sides of which taper in a wedge shape toward the free ends and which, for locking the bearing block  128 , as shown in  FIG. 6 , to engage in locking pockets  165  which are formed on retaining blocks  166 , which in turn are fitted on the top surfaces of the two end walls  127 ,  127 A with locking pockets  165  facing one another. 
     In order to prevent the sliding bolts  190  from being released from one another and from the locking position, even during vibrations, and at the same time in order to be able to apply as high a clamping force as possible, in each case the shorter marginal leg  192  is provided with a through-hole  199 , through which a clamping screw  180  passes. The distance between the two shorter marginal legs  192  can be reduced via the clamping screw  180 , as a result of which the distance between the two outer, longer marginal legs  193  increases and the locking lugs  198  engage correspondingly deeper in the locking pockets  165 . 
     The invention is not restricted to the exemplary embodiments shown and described, but rather various modifications and additions are conceivable without departing from the scope of the invention. It is thus possible, for example, to provide a plurality of pressure rollers arranged one behind the other in the passage direction of the chain in order to provide a guide for the chain over a longer distance, said guide working largely free of wear. It is also possible to adjust the pressure roller against the chain under the effect of a spring element and/or of a shock absorber, whereby reliable contact between roller and chain is always ensured, even during shock-like loads on the driving chain. The chain guide according to the invention can alternatively or additionally act on the load strand of the driving chain and is of course suitable not only for a plow chain but also, for example, for driving chains of scraper chain conveyors. The bearing blocks can also be inserted in accommodating pockets which are formed directly on the side cheeks of the driving or return stations. 
     Further, while considerable emphasis has been placed on the preferred embodiments of the invention illustrated and described herein, it will be appreciated that other embodiments, and equivalences thereof, can be made and that many changes can be made in the preferred embodiments without departing from the principles of the invention. Furthermore, the embodiments described above can be combined to form yet other embodiments of the invention of this application. Accordingly, it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

Summary:
A chain guide for a driving chain of a winning plow or the like, the chain guide being provided with a chain guide element which is arranged in spatial proximity to the sprockets at a driving or return station and is against the chain transversely to the direction of movement of the latter, provision is made according to the invention for the chain guide element to have at least one pressure roller which can be adjusted against the chain links of the driving chain, as a result of which the wear on the chain guide element is considerably reduced.