Abstract:
A rock drill including a helical shank and a drill head. The drill head has an end face pointing in a feed direction and at least one roof-shaped carbide cutting element on the end face of the rock drill. The carbide cutting element extends transversely across the drill head and has cutting edges. The end face of the carbide cutting element has an additional chip space at least in front of the carbide cutting element and includes an encircling step to create the additional chip space in the feed direction.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a rock drill having a feed direction, a helical shank and a drill head having an end face pointing in the feed direction. 
   Rock drills with carbide cutting tips are used for producing holes in concrete, masonry, rock or the like. In this case, the drill head, at its end face, is provided with at least one carbide cutting tip which generally extends over the entire drill head diameter and which, by the rotary-percussive or rotary-hammering drilling drive, has of a type of chiseling effect on the stone material to be disintegrated. The drill hole diameter is determined by the outside diameter of the carbide cutting tip. 
   In order to reduce the surface pressure on the carbide cutting tip and thus increase the service life of the drill head, cross cutting elements in which “secondary cutting tips” are arranged transversely to a main cutting tip have been disclosed (DE 29 12 394 A1). 
   Instead of secondary cutting tips which possibly extend over the entire diameter, secondary cutting elements which extend only over part of the radius of the drill head may also be provided (DE 81 04 116 U1). 
   Furthermore, EP 0 452 255 B1 has disclosed a rock drill in which the secondary cutting elements are designed as cutting pins which are arranged in the radially outer region of the end face of the drill head. 
   The arrangement of at least one or more additional secondary cutting tips certainly has the advantage that the main cutting tip is to a certain extent relieved of load, since some of the breaking work is assumed by the secondary cutting tip or tips. A disadvantage with this arrangement is the fact that additional fastening space has to be provided here for embedding the secondary cutting tips in the drill head, so that the end face of the drill head has to be designed to be more voluminous overall. This in turn has the disadvantage that the end face of the drill head is enlarged and forms a greater resistance. This also applies in particular to the ease with which the drill can dispose of the drillings to be removed, which collect in the direction of rotation in front of the lips of the main cutting tip and the secondary cutting tips. The quantity of these drillings increases the resistance and thus reduces the drilling advance of the drilling tool. The above problems also apply in principle to drilling tools having only a main cutting tip in which the drill head is of a less slim design and material transport thereby causes problems in the region of the drill head. 
   A known drilling tool has been disclosed by U.S. Pat. No. 2,673,714. In this drilling tool, an additional chip space is provided by lateral regions of the drill head being cut off in a chord-like manner in front of and behind a cutting tip, these lateral regions exposing the carbide tip in this region. A disadvantage with this is the poor embedding of the carbide tip in this region, since the recesses extend in particular on both sides of the carbide tip. 
   SUMMARY OF THE INVENTION 
   An object of the invention is to provide improved drilling advance in a tool as first described above. 
   This and other objects are achieved by a rock drill such as that first described above and having at least one roof-shaped carbide cutting element on its end face, the carbide cutting element extending transversely across the drill head and having lateral cutting edges. An additional chip space is formed at least in front of one of the cutting edges of the carbide cutting element, and the end face of the drill head has an encircling step directly in front of each cutting edge. 
   The central idea of the invention is to improve the conveying properties of a rock drill in the region of the carbide cutting element or elements. This also applies in particular to drilling tools having a larger nominal diameter in which radially outer secondary cutting elements and in particular secondary cutting tips are provided which can perform a considerable proportion of the removal work to be applied to the rock, or to tools having a higher penetration resistance on account of a larger area of resistance of the drill head. By an enlargement of the chip space lying in front of a carbide cutting tip, in particular in the radially outer region, the drillings are disposed of more easily. In order to compensate for the disadvantage of the additional cutting elements with the associated impaired disposal of the drillings in the drill head region, the invention likewise provides an additional chip space, at least also in front of the respective secondary cutting tip or a corresponding carbide cutting element. This additional chip space is made by a step in the end face of the drill head, the stepped surface region being located, as far as possible, directly in front of a corresponding cutting tip. The enlargement of the chip space thereby provided for the disposal of drillings has a wear-reducing effect on the drill head, since the drillings form a smaller resistance and can be disposed of more easily. 
   In particular, secondary cutting tips of various designs are advantageously used, these secondary cutting tips being designed at the end face so as to be either level, that is to say at approximately a right angle to the drill longitudinal axis, or inclined. In the latter case, the lip of the secondary cutting tip, this lip lying on a lateral surface of a cone, may lie on the same lateral surface of a cone as a main cutting tip inclined in a roof shape or may be set back from this lateral surface of a cone. 
   The step-shaped, a real shoulder in front of the respective secondary cutting tip is preferably designed in such a way that a top, roughly lateral surface of a cone forms in the direction of the drill point in the radially inner region, and a type of frustoconical surface forms in the region in front of the secondary cutting tip. 
   The height of the step is selected such that it corresponds approximately to the cutting surface of the main cutting tip or of the secondary cutting element. As a result, sufficient additional chip space is provided for the disposal of the drillings in front of the corresponding cutting tip. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further details and advantages of the invention follow from the exemplary embodiments which are described below and are explained in more detail with reference to drawings. 
     In the drawings: 
       FIG. 1   a  shows a side view of a drilling tool according to the invention in the region of the drill head with conveying-helix runout, 
       FIG. 1   b  shows a side view of the drilling tool according to  FIG. 1   a,    
       FIG. 2   a  shows a further exemplary embodiment for a drilling tool according to the invention having a modified secondary cutting tip, and 
       FIG. 2   b  shows a side view of the representation according to  FIG. 2   a;    
       FIG. 3  shows an exemplary embodiment of the invention with only one carbide cutting tip. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   According to the first exemplary embodiment of the invention according to  FIG. 1   a  and  FIG. 1   b , the rock drill  1  consists of a drill head  2  and an adjoining single- or multi-start conveying helix  3 . The conveying helix  3 , with its conveying-helix flute  4 , runs out into the drill head  2 . The runout of the conveying-helix flute  4  into the drill head is designated by reference numeral  5 . 
   The drill head  2  comprises a carbide cutting tip  6  which, in side view according to  FIG. 1   a , is designed as a roof-shaped main cutting tip and encloses an angle of α≅130°. The main cutting tip passes through the entire diameter d 1  of the drill head and protrudes beyond the latter with lateral projections  7 ,  7 ′ for forming the drill nominal diameter D. The main cutting tip  6  has front-end cutting edges  10 ,  10 ′ which are arranged on both sides of a drill longitudinal axis  9  and which have, in the direction of rotation (arrow  8 ), a rake face  11 ,  11 ′ lying in front of them and a flank  12 ,  12 ′ lying behind them. The main cutting tip  6  is embedded in the drill head by means of an axial longitudinal slot  13  having a height h 1  and is firmly anchored by means of a brazed joint. 
   In addition to the main cutting tip  6 , the drilling tool according to the invention, according to  FIGS. 1   a ,  1   b , also has two secondary cutting tips  14 ,  15 , which are likewise each embedded in the drill head  2  in an axial longitudinal slot  16  by means of a brazed joint. As can be seen from the exemplary embodiment according to  FIGS. 1   a ,  1   b , the secondary cutting tips  14 ,  15  likewise have a top level cutting edge  17 , which is oriented approximately perpendicularly to the drill longitudinal axis  9 . In the direction of rotation (arrow  8 ), each secondary cutting tip again has a front rake face  18 ,  18 ′ and a rear flank  19 ,  19 ′. 
   The arrangement of main cutting tip  6  and secondary cutting tips  14 ,  15  results in a drill head having cross cutting elements, it being possible for the cross produced to assume an angle of 90° or even an obtuse angle. 
   The end face  20  of the drill head consists at least partly of a top lateral surface  21  of a cone, which is arranged on a conical surface  22  of rotation. This cone  22  of rotation lies approximately parallel to the conical surface  23  of rotation through the cutting edge  10 ,  10 ′ of the main lip  6 . 
   The radial extent of the opposite secondary cutting tips  14 ,  15  results from the inside diameter d 2  and the outside diameter d 3 . The outside diameter d 3  is greater than the diameter d 1  of the drill head  2  by a lateral projection  24 ,  24 ′. 
   According to a preferred exemplary embodiment, the end face  20  of the drill head is now provided with at least one axially extending, cylindrical shoulder  25 , which approximately has a height h 3 , the height h 3  preferably being equal to or slightly less than the lateral projection height h 4  of the rake face  18 ,  18 ′ of the secondary cutting tip  14 ,  15 . The embedding depth of the secondary cutting tip  14 ,  15  in the drill head is designated by h 2 . 
   This approximately axially oriented shoulder  25  produces an axially offset frustoconical surface  21 ′ which lies on the conical surface  26  of rotation, which is arranged in a shoulder “s” relative to the conical surface  22  of rotation. This results in an enlarged chip space  27  in front of the rake face  18 ,  18 ′ for drillings to be removed, which has a positive effect on the drilling advance. The end face  20  of the drill head  2 , by means of the shoulder  25 , is consequently designed in a step shape, having a top cone point  21 , an axial shoulder  25  and a following frustum  21 ′ of a cone, the conical surfaces  22 ,  26  of rotation running parallel to one another at a distance “s”. Such an arrangement forms an additional chip space  27 ,  27 ′, which results approximately from the thickness “s” and the diameter difference d 3 −d 2 . The radially inner edges  31  of the secondary cutting elements  14 ,  15  are consequently arranged at a distance ½ * d 2  from the drill center axis  9 . The shoulder  25  extends radially starting from the inner edge  31  of the secondary cutting elements  14 ,  15 . 
   A modified embodiment of the secondary cutting tips  28 ,  29  is selected in the exemplary embodiment according to  FIGS. 2   a ,  2   b . In this case, the front-end cutting edges  17  are likewise located on a lateral surface  30  of a cone, which is set back slightly from the conical surface  23  of rotation of the main cutting tip  6 . 
   The top part  21  of the end face  20  of the drill head  2  again lies on the conical surface  22  of rotation, which is set back slightly from the conical surface  30  of rotation of the front-end cutting edges  17  of the secondary cutting tips  28 ,  29 . 
   In a similar manner to the design of the exemplary embodiment according to  FIGS. 1   a ,  1   b , an axial shoulder  25  is also provided in the exemplary embodiment according to  FIGS. 2   a ,  2   b , this shoulder  25  being directed toward an offset, frustoconical surface section  21 ′ on the conical surface  26  of rotation. As a result, an additional chip space  27  is again formed in front of the respective rake face  18 ,  18 ′ of the secondary cutting tips  28 ,  29 , this chip space  27  serving for improved disposal of the drillings in front of these secondary cutting tip  28 ,  29 . 
   The step-shaped design of the end face  20  of the drill head  2  thus results in an increase in the chip volume, that is to say an additional chip space is formed in particular in front of the secondary cutting tips. In this case, the additional chip space extends radially outward in a frustoconical manner starting from the shoulder  25 . Here, the height h 3  of the shoulder  25  determines the additional chip space  27 . 
     FIG. 3  shows the subject matter of the present invention with only one carbide cutting tip  6 , as also shown in  FIGS. 1 and 2 . Apart from that, the same parts are provided with the same reference numerals as in  FIGS. 1 and 2 . The secondary cutting tips contained in  FIGS. 1 and 2  are omitted in  FIG. 3 , so that the additional chip space  27  serves for the disposal of the drillings which are removed by the carbide cutting tip  6 . For this purpose, the drill head  2  again has a shoulder  25  or step  25 , by means of which the axially offset lateral surfaces  22 ,  26  of the cones are formed. This corresponds to the design of the drill head in  FIG. 1  or  2 . 
   As can be seen from  FIG. 3 , the shoulder  25  or the step  25  may be formed by an axially parallel recess edge  25 ′, in which case the bottom transition to the lateral surface  26  of the cone may be rounded off, or may be of cornered design as in the exemplary embodiments according to  FIGS. 1 and 2 . The decisive factor is the additional chip space, resulting from the step, in front of the rake face  11  of the carbide cutting tip  6 . 
   The invention is not restricted to the exemplary embodiment shown and described. On the contrary, it also comprises all modifications and developments within the scope of the patent claims. In particular, the chip space enlargement formed by the shoulder  25  may also have another geometry in accordance with the head geometry of the drill head. 
   List of Designations: 
   
       
         1  Rock drill 
         2  Drill head 
         3  Conveying helix 
         4  Conveying-helix flute 
         5  Runout of 4 into 2 
         6  Carbide cutting tip 
         7  Projection 
         8  Direction of rotation 
         9  Drill longitudinal axis 
         10  Cutting edge 
         11  Rake face 
         12  Flank 
         13  Longitudinal slot 
         14  Secondary cutting tip 
         15  Secondary cutting tip 
         16  Longitudinal slot 
         17  Cutting edge 
         18  Rake face 
         19  Flank 
         20  End face 
         21  Lateral surface of a cone 
         22  Cone of rotation 
         23  Conical surface of rotation 
         24  Projection 
         25  Shoulder/step 
         26  Lateral surface of a cone 
         27  Chip space 
         28  Secondary cutting tip 
         29  Secondary cutting tip 
         30  Conical surface of rotation 
         31  Inner edge of the secondary cutting tip