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BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a wear protection cap for a bit holder arrangement. 
         [0003]    2. Description of the Prior Art 
         [0004]    DE 10 2009 059 188 A1 (U.S. Pat. No. 8,746,806) discloses a bit holder arrangement. The latter encompasses a base part and a bit holder. The base part can be welded onto the outer surface of a tubular milling drum. The bit holder can then be replaceably fastened on the base part. A plurality of bit holder arrangements are secured on the surface of the tubular milling drum. They are preferably placed with respect to one another so that the base parts form a clearing and loading helix. A bit, preferably a rotatable round shank bit, can be replaceably received in the bit holder. The bit holder arrangements known from DE 10 2009 059 188 A1 are used in mining, preferably in open-cast mining. During processing use, the bits cut into the substrate that is to be removed, and detach material. The removed material flows off laterally past the bit and the bit holder and then arrives in the region of the base parts that form the clearing and loading helix. The base parts then therefore transport the removed material into the region of the center of the tubular milling drum, where it is then delivered to a loading belt. 
         [0005]    Depending on its nature, the material produces different degrees of wear as a result of abrasion processes. Whereas rather less wear occurs with softer formations, such as coal, considerable wear can take place with materials containing iron ore. The bits are subjected to particularly severe wear and must therefore be changed at regular intervals. The bit holders, on the other hand, are designed to survive over the service life of a plurality of bits. The base part, constituting the most expensive unit of the bit holder arrangement, is intended to offer a particularly long service life. In order to delay cost-intensive replacement of the base parts, it is known from the existing art to weld facing plates, in the form of steel sheets, onto particularly threatened regions of the base parts. This procedure, upon initial population of a milling drum, is time-intensive, since a plurality of delicate components must be handled, but a longer service life can thereby be obtained. It has been found, however, that the sheets are subjected to increased wear especially in the region of the weld seams. The thermal effect resulting from the welding operation causes a reduction in the strength of the steel sheet in the region adjacent to the weld seam. Greater wear accordingly occurs here as compared with the other surface regions. The facing plates accordingly detach in uncontrolled fashion from the base part after a certain service time as a result of component failures. The use of additional welding material is time- and cost-intensive and thus increases part complexity. 
         [0006]    Further wear protection systems are also known from the existing art. Hardface welds, for example, are applied directly onto bit holders or base parts of the bit holder arrangement. Effective wear protection can thereby be achieved, but the outlay for applying the welds is considerable. 
       SUMMARY OF THE INVENTION 
       [0007]    An object of the invention is to furnish a wear protection system for a bit holder arrangement with which effective and long-lasting protection of the bit holder arrangement can be achieved. 
         [0008]    This object is achieved with a wear protection cap that comprises at least two panel segments, located at an angle to one another, for covering surface regions of the bit holder arrangement, the panel segments being integrally joined to one another and the wear protection cap being configured as a primary-formed part, in particular a cast metal part, or as a reshaped part, in particular a forged metal part. Because the wear protection cap is configured as a cast metal part or forged metal part, uniform material properties can be achieved both in the region of the panel segments and in the region of the transitional regions joining the panel segments. Both the panel segments and the transitional regions between the panel segments thus offer the same material wear properties. In addition, the wear protection caps in the form of cast metal parts or forged metal parts allow for multifarious variant configurations that cannot be thus implemented with the known steel-sheet parts. For example, the panel segments can be configured in wear-optimized fashion with a different panel thickness, in particular a varying panel thickness profile. Zones of greater panel thickness can correspondingly be realized in regions in which greater wear occurs. Zones that are exposed to less abrasion, conversely, can be embodied in material-optimized fashion with a thinner cross section. Flow-optimized geometries individually matched to the utilization instance can moreover also be generated with the primary-formed or reshaped parts according to the present invention. This promotes lower-wear discharge of the removed material. 
         [0009]    According to the present invention, the transitions between two panel segments can furthermore be embodied with a greater panel thickness than at least one of the panel segments, in order to offer particular wear protection there. 
         [0010]    As mentioned previously, the wear protection cap can be configured as a forged metal part. The wear protection part can accordingly be configured as a cold-formed part or as a hot-formed part. A deep-drawn sheet part, for example, could be used as a cold-formed part. It is particularly preferred, however, to use a hot-formed part, in particular a forged part, since greater wear resistance values can thereby be achieved. In addition, more multifarious configuration possibilities, for example varying cross-sectional profiles, can be implemented with forged parts, as has been mentioned above. 
         [0011]    A maximally continuous flow of removed material is advantageous in terms of low wear. Provision can accordingly be made, according to a variant of the invention, for at least some of the panel segments to lead into one another via radius transitions. 
         [0012]    A particularly preferred variant of the invention provides that the panel segments are arranged in such a way that they are suitable for forming, during processing utilization, a positive join with the bit holder arrangement in the direction of the forces that impinge on the wear protection cap. A virtually self-securing design for the wear protection cap is thereby achieved. The wear protection cap can accordingly be fastened on the bit holder arrangement with securing means of simple configuration. In particular, these securing means can be accommodated in regions with a low risk of wear. In this context and also in connection with other variants of wear protection caps described in this patent application, welded joins, in particular linear tack welds or spot tack welds, which join the wear protection cap to the bit holder arrangement, can be used as securing means. 
         [0013]    The wear protection cap can be configured in particular for use on a base part of the bit holder arrangement. Here it offers effective protection to the comparatively most expensive component of the bit holder arrangement. 
         [0014]    For use of the wear protection cap on the base part, said cap can comprise a panel segment in the form of a top panel that transitions, via a transitional segment, into an enlargement, the enlargement transitioning, oppositely to the top panel, into a front panel constituting a further panel segment. This design protects the front region, at particularly high risk of wear, of a base part. The enlargement in the transitional region between the top panel and the panel segment provides additional wear volume in the interest of a long service life. Particularly preferably, the enlargement forms a radius transition in order to minimize abrasion processes here. 
         [0015]    Provision can furthermore be made that two side panels arranged spaced apart from one another are configured as panel segments, and lead into the top panel via transitional segments. The side panels protect the side regions of the base part and are thus ultimately associated with the transport region of the clearing and loading helix of a milling drum. The side panels additionally form a positive engagement between the wear protection cap and the bit holder arrangement with respect to forces that impinge laterally. Enlargements can also be provided in the transitional region between the side panels and the top panel. The pitch of the spiral-shaped clearing and loading helices results in creation of a pressure side, facing toward the delivery region, at which particularly severe wear occurs. Provision of an enlargement in this region of the pressure side is particularly advantageous. 
         [0016]    Provision can furthermore be made in the context of the invention that the top panel is set back in hollowed fashion by means of the transitional regions leading into the enlargements. An expansion region for the removed material being conveyed past is thereby formed, in the interest of lower abrasion. The enlargements furthermore offer a protective panel for those regions of the top panel located downstream oppositely to the motion direction, so that these regions are configured in wear-optimized fashion. In particular, a screw connection that secures a bit holder of the bit holder arrangement on the base part can, for example, then also be arranged in the hollowed region. 
         [0017]    As mentioned above, the base parts can be secured in mutually adjacent fashion on the surface of the tubular milling drum in order to form a clearing and loading helix. In order to maintain the zero-clearance association of the base parts with one another, in a wear protection cap according to the present invention a recess is configured in the transitional region between the front panel and a laterally adjacent side panel. The base parts can be set alongside one another in the region of the recess. 
         [0018]    In the context of the invention, the wear protection cap can also be configured for use on a bit holder of the bit holder arrangement. Provision can be made in particular that an aperture that is configured suitably for receiving a head of a shank bit is introduced into a panel segment configured as a front panel. The front panel protects the discharge region of the bit holder, which is configured around the head of the shank bit and is particularly at risk of wear. Particularly effective wear protection is thereby effected. 
         [0019]    According to a variant of the invention, provision can furthermore be made that a further panel segment configured as a top panel is adjacent to the front panel on the rear side in angled fashion, the top panel forming at least locally a convex discharge surface. Discharge of the milled material on both sides of the bit holder can be brought about via the convex surface region, thereby achieving optimized material flow toward the clearing and loading helix. 
         [0020]    According to a variant of the invention, provision can also be made that two side panels arranged spaced apart from one another, which are joined integrally to the top panel, are shaped onto the front panel on the rear side. The side panels protect the side region of the bit holder and moreover serve to stiffen the front panel with respect to the top panel. 
         [0021]    A wear protection cap can also be configured, according to the present invention, in such a way that the front panel exhibits, adjacently to the aperture, a bevel extending at an inclination with respect to the longitudinal center axis of the aperture. With this bevel as well, improved material flow can be achieved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The invention will be explained in more detail below with reference to exemplifying embodiments depicted in the drawings, in which: 
           [0023]      FIG. 1  is a perspective view of a bit holder arrangement having wear protection caps, 
           [0024]      FIG. 2  is a perspective exploded view of the bit holder arrangement according to  FIG. 1  having a wear protection cap, 
           [0025]      FIGS. 3 and 4  show various views of the wear protection cap according to  FIG. 2 , 
           [0026]      FIG. 5  is a perspective depiction of a bit holder of the bit holder arrangement according to  FIG. 1  together with a wear protection cap, and 
           [0027]      FIGS. 6   a  to  6   e  show various views of the wear protection cap according to  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0028]      FIG. 1  shows a bit holder arrangement that is typically utilized in a surface miner. The bit holder arrangement comprises a base part  10  and a bit holder  40 . 
         [0029]    Base part  10  will be explained in further detail below with reference to  FIG. 2 . As depicted therein, base part  10  is configured in one piece and has two side parts  11 . These are arranged spaced apart from one another. An insertion receptacle  13  is formed between side parts  11 . In the region of its underside  12 , base part  10  is provided with a concave surface. With this concave surface, base part  10  can be placed flush onto the surface of a tubular milling drum (not depicted). It can be secured there on the tubular milling drum with weld seams. Base part  10  has in the region of its front side, adjacently to side parts  11 , a frontal projection. This projection is delimited at the front by a front surface  15  and by a further front surface  16 . The two front surfaces  15  and  16  are located at an angle to one another and lead into one another via a transitional segment  15 . 1 . Transitional segment  15 . 1  is embodied as a radius transition. In the region of front surface  15 , two threaded receptacles  14 , arranged spaced apart in parallel fashion from one another, are introduced into the front-side projection of base part  10 . Threaded receptacles  14  terminate in the region of insertion receptacle  13 . As is further evident from  FIG. 2 , the outer surfaces of side parts  11  lead via radius transitions  15 . 2  into front surfaces  15  and  16 . In the region of insertion receptacle  13 , the frontal projection forms two support surfaces  13 . 1  located at an angle to one another. Support surfaces  13 . 1  can be configured as flat surfaces. At the rear, insertion receptacle  13  is likewise delimited by two support surfaces  13 . 2 . These two support surfaces  13 . 2  can likewise be of planar configuration and can extend in the direction of the longitudinal center axis of insertion receptacle  13 . Base part  10  terminates in the region of its rear side with a rearward panel that forms a rear-side terminating surface  17 . 
         [0030]    Wear protection cap  20  can be installed onto base part  10 . As is evident from  FIG. 2 , wear protection cap  20  is configured in one piece. It comprises a top panel  21  that transitions at the front, via a rising transitional region  23 , into an enlargement  24 . 1 . Enlargement  24 . 1  serves to increase the material thickness of wear protection cap  20 . Wear protection cap  20  correspondingly has, in the region of enlargement  24 . 1 , a greater panel thickness than top panel  21 . On the side, top panel  21  likewise transitions via a transitional region  23  into an enlargement  24 . 2 . Here as well, a thickened cross-sectional region is consequently formed. Top panel  21  is equipped with two arc-shaped recesses  22 . These recesses  22  transition into edge segments  22 . 1  that are set in a V-shape with respect to one another. Edge segments  22 . 1  end in further edge segments  22 . 2 . Wear protection cap  20  comprises two side panels  27  and  28  that are arranged spaced apart from one another. Wear protection cap  20  terminates at the front side in a front panel  26 . Side panels  27 ,  28  respectively transition via radius transitions  29  into the top side of wear protection cap  20 . Side panel  28  transitions via radius transition  29  directly into top panel  21 . Side panel  27  transitions via radius transition  29  into enlargement  24 . 2 . Front panel  26  furthermore transitions via radius transition  25  into enlargement  24 . 1 . 
         [0031]    It is furthermore evident from  FIG. 2  that wear protection cap  20  comprises a recess  20 . 1  in the region of front panel  26  and in the front side region of side panel  28 . 
         [0032]    For installation of wear protection cap  20 , the latter is placed over base part  10 , the two side panels  27  and  28  coming to rest against the outer sides of side parts  11 . Top panel  21  rests with its rear side on front surface  15 . Front panel  26  rests at the rear on front surface  16 . In the region of recess  20 . 1 , base part  10  stands clear at the corner transition between front surface  16  and the outer side of side part  11 . In this region, a further base part  10  that is not depicted in the drawings is set alongside in order to form the clearing and loading helix on the tubular milling drum. The two recesses  22  leave threaded receptacles  14  exposed. Welded joins are used to fasten wear protection cap  20  on base part  10 . These can be placed, for example, at locations that are favorable in terms of wear. In particular, for example, linear tack welds can be provided in the region of side panels  27 ,  28 . 
         [0033]      FIG. 5  is a perspective exploded depiction of bit holder  40  of the bit holder arrangement. As is evident from this depiction, bit holder  40  has a holding projection  44  on which an insertion projection  41  is integrally shaped. Holding projection  44  comprises a bit receptacle  45  in the form of a bore. An annular seating surface  45 . 1  is arranged around the bore entrance of bit receptacle  45 . Adjacently to seating surface  45 . 1 , holding projection  44  forms a discharge surface  46  extending at an inclination to the longitudinal center axis of bit receptacle  45 . Discharge surface  46  transitions on the top side into an enveloping surface  47  and on the side into side parts  48 . Holding projection  44  comprises, in the region of its underside, two support surfaces  43  arranged at an angle to one another. 
         [0034]    Insertion projection  41  has at the rear two bearing surfaces  41 . 1  set at an angle to one another. Insertion projection  41  is equipped in the region of the front side with two pressure surfaces  42 . Pressure surfaces  42  extend at an angle of less than 90° with respect to the longitudinal center axis of insertion projection  41 . Bit holder  40  can be installed onto base part  10 . For this, bit holder  40  is inserted with its insertion projection  41  into insertion receptacle  13  of base part  10 . In the assembled state, bit holder  40  is braced with its bearing surfaces  41 . 1  flush against support surfaces  13 . 2 , and with its two support surfaces  43  flush against support surfaces  13 . 1 . Two fastening bolts  30  (see  FIG. 2 ) are threaded into screw receptacles  14  in order to secure bit holder  40 . Pressure projections of fastening bolts  30  then act on pressure surfaces  42  of bit holder  40 , and bit holder  40  is pressed with its support surfaces  43  and with bearing surfaces  41 . 1  onto the corresponding support surfaces  13 . 1 ,  13 . 2  of base part  10 . Bit holder  40  can be installed once wear protection cap  20  is installed. 
         [0035]    As is further evident from  FIG. 5 , a wear protection cap  50  can also be installed on bit holder  40 . This wear protection cap  50  is shown in further detail in  FIGS. 6   a  to  6   e . Wear protection cap  50  accordingly comprises a front panel  54  that is penetrated by an aperture  51 . Aperture  51  is delimited by an annularly surrounding rim  52 . Adjacently to rim  52 , front panel  54  comprises a bevel  53 . Front panel  54  forms laterally protruding wing-like extensions, as are evident e.g. from  FIG. 6   b . Side panels  57  projecting rearward are shaped on integrally in the region of the free ends of the wing-shaped extensions. Side panels  57  are likewise joined integrally to a top panel  55 . Top panel  55  is also joined integrally to front panel  54 . As is evident from  FIGS. 6   b  and  6   e , front panel  54  comprises a convex elevation. A recess  56  is provided at the rear in the region of the convex elevation. 
         [0036]    It is further evident from  FIG. 5  that wear protection cap  50  is placed onto bit holder  40 . Front panel  54  sits with its rear side on discharge surface  46 . Top panel  55  is braced on enveloping surface  47 . The two side panels  57  are located opposite the outer sides of side parts  48 . Weld seams are again provided, at locations favorable in terms of wear, in order to fasten wear protection cap  50 . These seams join wear protection cap  50  to bit holder  40 . In the assembled state, aperture  51  offers wear protection cap  50  access to bit receptacle  45 . Aperture  51  is furthermore dimensioned in such a way that seating surface  45 . 1  is exposed. A round shank bit can thus be joined to bit holder  40 . The round shank bit can be held with its round shank in bit receptacle  45 , the round shank bit simultaneously being braced with its bit head on seating surface  45 . 1 . 
         [0037]    When wear protection caps  20  and  50  wear away during operational utilization, they can be replaced as necessary. This requires merely severing the joining means, for example the linear tack welds in this case. This can be effected on site using a corresponding cutting device. The worn-out wear protection caps  20  and  50  can then be replaced with new wear protection caps  20 ,  50 . The latter are then again fastened on base part  10  and on bit holder  50 . This repair action can be carried out on a short repair time scale, so that machine stoppage times are reduced. 
         [0038]    Wear protection cap  20  comprises, in the context of the invention, side panels  27 ,  28 , front panel  26 , and top panel  21  as panel segments. Wear protection panel  50  comprises, in the context of the invention, front panel  54 , top panel  55 , and side panels  57  as panel segments. The panel segments of wear protection caps  20  and  50  are joined integrally to one another; the wear protection caps can be embodied as a cast metal part or as a forged metal part.

Summary:
The invention relates to a wear protection cap for a bit holder arrangement, having at least two panel segments, located at an angle to one another, for covering surface regions of the bit holder arrangement, the panel segments being integrally joined to one another and the wear protection cap being configured as a cast metal part or as a forged metal part. With a wear protection cap of this kind, the service life of a bit holder arrangement can be substantially improved and machine stoppage time can be decreased.