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MINING MACHINE WITH RELEASABLE GUIDE PIECE AND THE GUIDE PIECE FOR IT 
   The invention relates to a mining machine for underground mining, more specifically to a winning or coal plough, which mining machine is guided along a machine guide that includes a guide rail. The invention also relates to a guide piece that slides on or along the guide rail. 
   A generic mining machine, configured as an extraction plough, is known from DE 37 11 105 A1. The plough described therein has an upper guide pawl that engages the guide rail from above. A guide piece, provided between the guide pawl of the plough and the guide rail, is attached to the guide pawl and slides on or against the fixed guide rail when the plough is being operated. Since the guide piece is exposed to extreme strain it is subjected to a high rate of wear. It is therefore detachably attached to the guide pawl so that it can be exchanged regularly. The U-shaped guide piece is configured with two limbs, set apart from one another. The guide piece on one base and on a transverse web that connects the limbs thereof is provided with bores through which bolts engage via which the exchangeable guide piece can be attached to the guide pawl of the plough body. If, in the course of an exchange, a new guide piece is to be attached to the guide pawl, the guide piece must be held in a corresponding position until the joint with the guide pawl has been effected. Only then does the guide pawl hold the weight of the guide piece via the bolts. 
   In the practice of underground mining, the exchange of the guide piece with the bolts guided through its base has proven to be awkward and requires a great deal of effort. Therefore the purpose of the invention is to provide a mining machine of the type mentioned above in which replacement of the guide piece is easier to achieve. 
   SUMMARY OF THE INVENTION 
   This object according to the invention is achieved in that the guide pawl that serves to receive the exchangeable guide piece has, or forms, at least one support on or against which the guide piece can support itself, and that a locking mechanism is provided with which the guide piece is fixed in its installation position against the guide pawl in the longitudinal direction of the guide rail, i.e. parallel to the direction of movement of the plough. 
   With the mining machine according to the invention, the weight of the guide piece is no longer held on the guide pawl by a bolt connection that is to be established, but rather by said support or more specifically by a plurality of positive locking supports. The support or the plurality of supports, and the guide piece they support, are preferably made so that the guide piece can be pushed or moved parallel to the direction of movement of the mining machine into a corresponding mounting at the guide pawl, wherein the guide piece then comes into positive locking contact with the projections on the guide pawl that form the support. The guide piece, the weight of which is now held by the positive or form-locking connection, is only fixed by the locking mechanism transverse to the positive direction of the weight, especially in the longitudinal direction of the guide piece or in the longitudinal direction of the guide rail. 
   For downward support, the guide piece can additionally have at least one lug to create or effect a further support, which lug engages in a correspondingly formed recess on the guide pawl, especially an open-rim recess. It is also possible for the guide pawl to have a lug or a projection that co acts with a corresponding recess on the guide piece. Lugs, projections and/or corresponding recesses, for example groove-shaped recesses, can also extend over the entire length of the guide piece, wherein the guide piece advantageously can be pushed into the holding fixture of the guide pawl like a drawer and can be supported therein. In the preferred embodiment, a support is provided on the guide pawl at both respective sides of the guide piece. 
   In a preferred embodiment, a bolt can be provided as a locking mechanism that engages through at least one bore in the side walls of the guide pawl and against which the guide piece abuts in the lateral direction or in the longitudinal direction of the guide rail. A securing device can be provided to ensure that the bolt does not release itself from its locking position. For example, the bolt can be provided with a thread at one end to receive a nut. 
   In its position of use, the guide piece, according to the invention, for a mining machine with the aforementioned features engages around the guide rail from above and is configured in a U-shape with two limbs that are at a distance from one another. It characterises in that projections and/or recesses are provided on the outer sides of the limbs, with which the guide piece can support itself with positive (form-) locking on the guide pawl in the vertical direction. 
   In a preferred embodiment, an edge is formed on the first front end that projects with regard to the outer sides of the limbs and with regard to an outer side of a transverse web that connects the limbs. From this projection, a rear side of the edge results that serves as an abutment of the guide piece on a front surface of the guide pawl. It is also preferred that a projection or lug is formed on the respective outer sides of the limbs which projection or lug extends from the edge in the longitudinal direction of the guide piece. It is also preferred that on a second front end of the guide piece a recess is provided on one limb each which recess is preferably open in the direction of the second front end. The recess is preferably disposed on the outer side of a limb but it can also involve the entire wall thickness of the limb. It is preferred that the recess is defined as a semi-circle. In order to facilitate the insertion of a round lug or the like into the recess, wherein the lug and the recess engage with positive locking, the front-side opening of the recess can be opened out further by means of a chamfer or an inclination. The inclination can be disposed at an upper end of the recess so that it slightly lifts the guide piece when it abuts the lug on insertion into the holding fixture of the guide pawl. 
   It is also preferred that at least one groove, extending from limb to limb, is formed on the outer side of the transverse web that connects the two opposed limbs. Preferably, the groove can be semi-circular in cross-section and, at least in part, can receive a bolt or the like in its longitudinal direction. If the guide piece is fixed in its position of use both in the upward direction by the abutment of the guide pawl that engages around the guide piece from above and that is open to the bottom, and in the downward direction by the holding fixture of the guide pawl, the guide piece can be locked in the lateral direction, that is, in the direction of movement of the extraction machine, by the bolt that engages in the groove and is rigidly connected to the guide pawl. 
   The guide piece preferably forms a wearing part that is easy to replace. To this end, an area with increased resistance to wear or a wearing plate can especially be provided on an inner side of at least one limb. The increased resistance to wear can especially be attained by inductive hardening. It is also possible to provide recesses on the inner sides to receive wear inlays, preferably made of hard metal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be explained in greater detail with reference to an example shown in the drawings. It shows: 
       FIG. 1  a schematic view of a section of a plough guide with a plough including a guide piece guided along the plough guide; 
       FIG. 2  a front elevation of the guide pawl of the plough according to  FIG. 1  without the guide piece; 
       FIG. 3  a sectional view along line III—III in  FIG. 1 ; 
       FIG. 4  a sectional view along the line IV—IV in  FIG. 3 ; 
       FIG. 5  an individual view of the guide piece of the plough according to  FIG. 1  in an increased scale; 
       FIG. 6  a side elevation of the guide piece; 
       FIG. 7  a top view of the guide piece; and 
       FIG. 8  a perspective view of the guide piece. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  indicates a face conveyor  1  laid out before a coal head (not illustrated), of which conveyor only a face cutting-side profile  2  and a conveyor base  3  are shown. A plough guide  4  is attached to the side profile  2  of the face conveyor  1  on the face-cutting side, here shown schematically only in outline. The plough guide  4 , like a track of conveyor pans of the face conveyor, comprises individual sections that can be angled slightly with respect to each other in the horizontal and vertical plane. 
   The plough guide  4  comprises a rail  6  angled at an acute angle to the floor  5 , on which a plough  7  is supported on its two front-side ends by means of a sliding runner  8  each, of which only one sliding runner  8  is shown in  FIG. 1 . Above the rail  6 , the plough guide has a lower chain channel  9  and an upper chain channel  10 , through which the runs of an endless plough chain  11  extend to drive the plough  7  along the plough guide  4 . A bearing journal  12  is formed on the plough body of the plough  7  for a pivotable mounting of a cutting bar, not illustrated, on which tools are disposed to dislodge, for example, coal. 
   The plough guide  4  has an upwardly-directed guide rail  13  at its apex. An upper guide pawl  14  engages over the guide rail  13  at both face-side ends of the plough  7  like a hook. Between the guide pawl  14  and the guide rail  13  a U-shaped guide piece  15  is provided that can be detached from the guide pawl and replaced because it is exposed to increased wear and is therefore a wearing item. Here, the guide piece  15  sits in a similarly U-shaped holding fixture of the guide pawl  14  that is open to the bottom. Crane eyelets  16  are disposed on an upper side of the plough  7 , with which the plough  7  can be lifted with suitable lifting means. 
     FIG. 2  shows a front view of one the guide pawls  14  of the plough with the guide piece removed. The holding fixture  40  of the guide pawl that is open to the bottom and to the rear is limited by two lateral side walls  41 ,  42  and an upper wall  43  that connects these. The three walls  41 ,  42 ,  43  being arranged in a U-form are provided with a continuous step  44  on their inner sides so that the walls  41 ,  42 ,  43  form a U-shaped rear stop face  45  for the guide piece within the holding fixture, whilst the face sides  41 ′,  42 ′ and  43 ′ of the walls  41 ,  42 ,  43  form a front stop for the guide piece. 
     FIG. 3  and  FIG. 4  show, by means of a horizontal longitudinal section, the installation position of the guide piece  15  in the guide pawl  14 . It can easily be seen that the rear stop face  45  is disposed at the rear end of the holding fixture  40 . It can also be seen from  FIG. 2  and  FIG. 3  that on the one hand, a rectangular recess  46 ,  47  is formed in the face side  41 ′,  42 ′ of both side walls  41 ,  42  which recesses are open to the inner sides and that on the other hand, two lug stumps  48 ,  49  project over the inner sides of the side walls  41 ,  42  directly before the stop wall  47  which lug stumps particularly can be formed by the ends of two bolt lugs  53 ,  54  immovably mounted in transverse bores  51 ,  52  in the side walls  41 ,  42 . The projecting ends of the bolt lugs  53 ,  54 , configured as lug stumps  48 ,  49 , form a first support, designated in its entirety with  55 , on which the guide piece  15  is supported in a positive form-locking manner against the guide pawl  14  in its installation position, and the recesses  46 ,  47  in the front sides  41 ′,  42 ′ form a second support, designated in its entirety with  56 , for the guide piece  15  against the guide pawl  14 , as will be explained below. 
   Firstly, the structure of the guide piece  15 , shown in detail in  FIGS. 5 to 8 , will now be explained. Here,  FIG. 5  shows an enlarged detail view of the guide piece  15  that is recognisable in front elevation in  FIG. 1 .  FIG. 6  shows the guide piece from the side, whilst  FIG. 7  shows a top view of one half of the guide piece  15 . Two limbs  17 ,  18  of the guide piece  15 , set apart from one another, are connected by a perpendicularly-set base or transverse web  19 . The guide piece  15  has an edge  21  on a first front end  20  that projects with regard to the outwardly-directed sides (outer sides  22 ,  23 ) of the limbs  17 ,  18  and over the outer side  24  of the transverse web  19 . A rear side  25  of the edge  21  results from this projection that faces away from the first front side of the guide piece  15  and in the installation position of the guide piece  15  abuts on the front side ( 43 ′,  FIG. 2 ) of the upper wall ( 43 ,  FIG. 2 ) of the guide pawl ( 14 ,  FIG. 2 ). The corners of the edge  21  are rounded and their edges are chamfered. 
   On a second front end  26  the guide piece  15  has semi-circular recesses  27 ,  28  that are open to the front side  26  on its limbs  17 ,  18 , into which, in the installation position of the guide piece  15 , as especially shown in  FIG. 2  to  FIG. 4 , the lug-shaped stumps  48  and  49 , that are round in cross-section and that project into the holding fixture  40  within the guide pawl  14 , engage in a positive form-locking manner to provide the first support  55  for the guide piece  15 . The guide piece  15  is therefore supported in a positive locking manner by these stumps in the downward direction on the second front end  26 . Both recesses  27 ,  28  have a rounded portion  29  on their upper, front-side end that facilitates engagement of the lug stumps ( 49 ,  FIG. 4 ) in the recesses  27 ,  28  when the guide piece  15  is inserted into the holding fixture ( 40 ,  FIG. 4 ) of the guide pawl. 
   Furthermore, in each case a lug-like projection  30 ,  31  is formed onto the two outer sides  22 ,  23  of the guide piece  15 , extending in the direction of the second front end  26 . The projection  30 ,  31  has a cross-section that is basically rectangular. Both, the longitudinal edges  32  that extend in the longitudinal direction and the front edges  33  that extend perpendicular thereto of the projection  30 ,  31 , are chamfered. The chamfered edges  32 ,  33  of the projections  30 ,  31  and the rounded portions  29  of the recesses  27 ,  28  facilitate their engagement in the associated, open-rim recesses ( 46 ,  47 ,  FIG. 2 ), that are formed within the holding fixture of the guide pawl in a corresponding position, as explained above. In this way, the guide piece  15  is also supported, positive locking, on the second front end  20  by the guide pawl in the downward direction, therefore in the vertical direction, on both sides by a further support ( 56 ,  FIG. 4 ), wherein the guide piece  15  is held in position without detachable attachment means. It can easily be seen from  FIG. 4  that in each case a lug stump  49  on the guide pawl  14  forms a first support  55  with the associated recess  27  in the guide piece  15  and in each case a projection  30  on the guide piece  15  forms a further support  56  with the associated recess  47  in the guide pawl  14 , wherein the guide piece  15  supports itself on both sides of the guide pawl  14  on this total of four supports  55 ,  56 . 
   As can especially be seen in  FIG. 6  and  FIG. 7 , two semicircular grooves  34 ,  35  extend between the limbs  17 ,  18  on the outside  24  of the transverse web  19 . The grooves extend perpendicular to the longitudinal direction of the guide piece  15  and therefore also, in the installation position of the guide piece, perpendicular to the guide rail ( 13 ,  FIG. 1 ). The groove  34  is set adjacent to the first front end, whilst the groove  35  is formed adjacent to the second front end. As can especially be seen from  FIG. 4 , the grooves  34  and  35  together with correspondingly-configured grooves  60  open in the downward direction, in the side walls of the guide pawl  14 , each form a channel with a round cross-section that serves for insertion of a locking bolt  61  or  62 . Since the bolts  61 ,  62  on both sides of the guide piece penetrate closed-rim bores  64  in the side walls  42  of the guide pawl  14 , at least at their ends, the position of the guide piece  15  in the holding fixture  40  of the guide pawl  14  is fixed by the bolts  61 ,  62  as a locking mechanism. 
     FIG. 8  shows the guide piece in a perspective view. Even the longitudinal edges  36 , on which the outer sides  22 ,  23  of the limbs  17 ,  18  abut on the outer side  24  of the transverse web  19  are chamfered, wherein the guide piece  15  has no projecting edges that could be easily damaged. The inner sides  37 ,  38  of the limbs  17 ,  18  are inductively hardened to obtain a hardened, wear-resistant surface at those points where the guide piece comes into contact with the guide rail  13 . Preferably, the hardened surface exceeds a hardness of 52 HRC.

Summary:
A mining machine for underground mining is disclosed, particularly an extraction or coal plough. When in use, the mining machine is guided along a machine guide, said machine guide including a guide rail and a guide pawl. The guide pawl engaging around said guide rail from above wherein a guide piece is disposed between said guide pawl and said guide rail. The guide piece is releasably attached or attachable to said guide pawl and is sliding along said guide rail. According to the invention, said guide pawl has at least one support means whereassaid guide piece in its installation position is supported on said support means. Further, the guide piece with said guide pawl is fixed by means of a locking mechanism in the longitudinal direction of said guide rail.