Abstract:
A drill bit comprises, on its face, either only curved cutting edges or a combination consisting of at least one straight cutting edge and at least two curved cutting edges. The cutting edges on the face of the drill bit are arranged such that they start from the axis of the drill bit or end directly adjacent thereto. Three channels start from a blind hole serving to attach the drill bit to an anchor rod of an injection boring anchor, and their openings are not located in the area of the face of the drill bit but are situated in the area of the lateral surface of the same, said lateral surface conically expanding toward the cutting edges. The openings of the channels are placed in the area of concave recesses of the lateral surface of the drill bit in such a manner that they are recessed with regard to the periphery of the face of the drill bit.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a drill bit. 
   Drill bits, especially percussive or rotary percussive drill bits, with a cutting head which on its face has cutters for detaching and/or crushing the material to be worked, are known in various embodiments. 
   These drill bits are used for example on the front end of self-boring injection drill anchors which are set to protect rock against rock thrust. 
   A drill bit of the initially mentioned type is known from AT 001 513 U1. The known drill bit on its face has cutters which run in at least two different axial directions of the face. AT 001 513 U1 shows various combinations of straight and curved cutters on the face of a drill bit. 
   A drill bit with a curved cutter or with one curved and one straight cutter, or with one straight cutter or finally with two cutters which are parallel to one another is known from DE 918 741 A. 
   Similar arrangements of cutters for drill bits are known from GB 189 021 A. 
   SUMMARY OF THE INVENTION 
   The object of the invention is to develop a drill bit of the initially mentioned type such that by the shape and arrangement of the cutters better efficiency of the drill bit is achieved and a tighter stop picture is obtained when it is used in rotary-percussive drilling. 
   The arrangement of the cutters on the face of the bit as provided in the drill bit as claimed in the invention, regardless of whether they are curved or straight, yields the desired efficiency of the drill bit as claimed in the invention which is improved compared to the known drill bits. 
   Drill bits, especially percussive or rotary percussive drill bits with a cutting head which on its face bears cutters for removing or crushing the material to be worked have at least one channel which discharges in the face of the drill bit (AT 00 151 341). While drilling, a flushing medium (for example, water or air) emerges from this channel, cools the drill bit during drilling and flushes the drillings out of the drilled hole. After the drilled hole has reached the desired depth, a cementing mass (for example, mortar or concrete) is forced out of the channel and after setting fixes the injector drill anchor in the drilled hole. These known drill bits have the disadvantage that the channel from which the flushing medium is designed to emerge is often clogged by drillings, especially when drilling in soft rock, such as sandstone. 
   Furthermore the object of the invention is to develop these drill bits such that there is no danger that the channel will become clogged by drillings in the course of drilling. 
   Since in the drill bit as claimed in the invention which is intended especially for use in injection drill anchors, at least one mouth of at least one channel through which first flushing medium and then setting mass, for example bonding (cement) mortar, is forced in order to fix the injection drill anchor in the drilled hole, in the plane defined by the cutters of the drill bit in the essentially vertical side surfaces of the drill bit the channel is prevented from being clogged with drillings when using the drill bit for drilling and thus passage through at least one channel in the drill bit during flushing during the drilling process and when forcing out the binding mass is reliably not hindered. 
   In the drill bit as claimed in the invention it is preferred that the mouth of at least one channel lies in one surface of the drill bit which is set back relative to the periphery of the drill bit. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features, details and advantages of the drill bits as claimed in the invention result from the following description of drill bits as claimed in the invention. 
       FIG. 1  shows a drill bit of a first embodiment in an oblique view, 
       FIG. 2  shows the drill bit from  FIG. 1  in another oblique view, 
       FIG. 3  shows the drill bit from  FIG. 1  in a side view,  FIG. 4  shows the drill bit from  FIG. 1  in another side view, 
       FIG. 5  shows the drill bit from  FIG. 1  in a face view, 
       FIG. 6  shows a section along line VI—VI in  FIG. 3 , 
       FIG. 7  shows a section along line VII—VII in  FIG. 5 , 
       FIG. 8  shows a section along line VIII—VIII in  FIG. 4 , 
       FIG. 9  shows in an oblique view a second embodiment of a drill bit as claimed in the invention with cutters formed by hard metal inserts, 
       FIGS. 10 to 21  schematically show the arrangement and shape of cutters, each with the assigned stop picture (cutting picture) of embodiments with the drill bit as claimed in the invention, 
       FIGS. 22 ,  23 ,  24 , and  25  show in different views a drill bit with the arrangement/execution of the cutters as shown in  FIG. 10 , 
       FIG. 26  shows a section along line XXVI—XXVI in  FIG. 25 , 
       FIGS. 27 ,  28 , and  29  show another embodiment of a drill bit as claimed in the invention, 
       FIG. 30  shows a section of line XXX—XXX in  FIG. 29  and 
       FIG. 31  shows another section through the drill bit of  FIGS. 27 ,  28  and  29 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the embodiment shown in  FIGS. 1 to 8  the drill bit  1  on its face has three cutters  2  which are curved with the same radius of curvature and in the same direction, with cutting edges  3  which run toward the middle of the face and which meet one another in the middle, i.e. in the axis  4  of the drill bit  1 . 
   In the drill bit  1  there is a blind hole  5  which emerges from the end of the drill bit  1  opposite the face surface and which has an inside thread so that the drill bit  1  can be screwed onto an anchor rod which has an external thread, as is used for injection drill anchors. From the blind hole  5  in the illustrated embodiment three channels  10  emerge which are tilted to the axis  4  of the drill bit  1  at an acute angle, for example an angle of 30° (compare  FIG. 6 ). The channels  10  are aligned in the drill bit  1  such that their mouths  11  discharge on the side surface of the drill bit  1  in the area between two adjacent cutters  2 . 
   The discharges  11  of the channels  10 , as is shown for example in  FIGS. 1 to 4  and especially the section from  FIG. 6 , lie in the area of concavely curved surfaces  12  which are roughly normal to the plane which is defined by the cutting edges  3 , therefore essentially to the face of the drill bit  1 . For this reason and due to the circumstance that the outside surface  13  of the drill bit  1  is made as a cone (truncated cone) which widens toward the face and which for example has an opening angle of 10° (compare  FIGS. 3 and 6 ), the mouths  11  of the channels  10  are arranged such that the channels  10  when drilling cannot be clogged with drillings. This contrasts with the embodiment of known drill bits (compare for example AT 001 513 01) in which the channels discharge in the area of the face of the drill bit. 
   The embodiment of a drill bit  1  as claimed in the invention which is shown in  FIGS. 1 to 8  is designed for one direction of rotation in which the concave sides of the cutters  2  in the direction of rotation point to the outside. 
   In the embodiment of a drill bit as claimed in the invention which is shown in  FIG. 9 , which bit is otherwise made as has been described for the drill bit  1  of  FIGS. 1 to 8 , the cutting edges  2  are formed by hard metal inserts  20  which are attached in the drill bits  1 , for example by shrinking. In this embodiment the cutters  2  and their cutting edges  3  end with a distance from the axis  4  of the drill bit  1 . 
   The shape of the cutters  2  which is shown in the embodiments of the drill bit  1  as claimed in the invention as shown in  FIGS. 1 and 9  is shown schematically in  FIG. 11  together with the pertinent stop picture. 
   The cutters  2  of the drill bit  1  as claimed in the invention can however also be curved for certain applications such that the convex sides of the cutters  2  and the cutting edges  3 , as is shown in  FIG. 15 , point forward relative to the direction of rotation. 
   In addition to embodiments of the drill bit  1  as claimed in the invention with exclusively curved surfaces  2  which can preferably meet essentially in the center of the face of the drill bit  1 , other arrangements and combinations of cutters are also conceivable. 
   Thus for example  FIG. 10  shows (schematically) the face of a drill bit  1  in which two cutters  2  which are oppositely curved relative to the direction of rotation and which are combined with a straight cutter  2 ′ which likewise emerges from the center of the face of the drill bit  1  so that the stop picture likewise shown in  FIG. 10  results [sic]. 
   In the embodiment show in  FIG. 10  the straight cutter  2 ′ relative to the axis  4  of the drill bit  1  is opposite in the area of the face of the drill bit  1  in which the cutters  2  which are curved in opposite directions are located. 
   In the embodiment shown in  FIG. 12  a straight cutter  2 ′ is combined with two cutters  2  which are curved in the same direction. This yields the stop picture which is shown likewise in  FIG. 12 . 
   In addition to the embodiments of the drill bit  1  as claimed in the invention with three cutters  2  or  2 ′, embodiments with more than three cutters  2 ,  2 ′, for example four cutters, are also possible. Here drill bits  2  with exclusively curved cutters  2  and drill bits  1  with a combination of at least one straight cutter  2 ′ and at least one curved cutter  2  are likewise possible, as in the above described embodiments with three bits  2 ,  2 ′. 
   One example of this is shown in  FIG. 13  in which two straight cutters  2 ′ which are opposite one another relative to the axis  4  of the cutting head  1  are combined with two cutters  2  which are curved in the same direction relative to the direction of rotation and which likewise are located opposite one another with respect to the axis  4 . The stop picture of this embodiment of a drill bit as claimed in the invention is likewise shown in  FIG. 13 . 
     FIG. 14  schematically shows one embodiment in which on the face of the drill bits  1  there are exclusively curved cutters  2 , specifically four cutters  2  which all proceed essentially from the center of the face of the drill bit  1 , i.e. from its axis  4 . In the shape and arrangement of the cutters selected in  FIG. 14 , the cutters  2  are curved alternatively in opposite directions, so that two cutters  2  which are opposite one another with respect to the axis  4  of the drill bit  1  make up into a surface S. 
   In the embodiment shown in  FIG. 16 , there are four cutters  2  which are all curved in the same direction, here too similarly to the embodiment shown in  FIGS. 11 and 15  the curvature of the cutters  2  being chosen such that relative to the axis of rotation either their convex or their concave sides point forward. 
   In the embodiments of the drill bits of the invention of  FIGS. 17 and 18 , there are three curved cutters  2  which are arranged and aligned such that two of the three cutters make up into a continuous arc and the third curved cutter  2  is located from the convex side of that of the other two cutters which make up into a continuous arc. 
   In the embodiment shown in  FIG. 19 , the drill bit  1  on its face has two cutters  2  which are curved in opposite directions and two straight cutters  2 ′ which lie in the common axial plane of the drill bit  1 . 
   In the embodiment shown in  FIG. 20  the drill bit  1  has a straight cutter  2 ′ which extends to the middle (axis) of the drill bit, and two cutters  2  which are curved in opposite directions, which are located only in the outer area of the drill bit  1  and which are not diametrically opposite one another, but are located in the half of the face of the drill bit  1  which is opposite the straight cutter  2 ′. 
   The curved cutters  2  both in the embodiment shown in  FIG. 20  and also the one shown in  FIG. 21  extend as far as for example the circular depression  20  which is concentric to the axis of the drill bit  1  and which is located in the face of the drill bit. 
   In the embodiment of a drill bit  1  as claimed in the invention which is shown in  FIG. 21 , there are two diametrically opposite straight cutters  2 ′, therefore straight cutters which lie in the axial plane of the drill bit  1 , and two diametrically opposite cutters  2  which are curved in opposite directions and which extend from the outside edge of the face of the drill bit  2  as far as the depression  20 . 
   The embodiment of a drill bit as claimed in the invention which is shown in  FIGS. 22 to 26  has an arrangement of the cutters  2  and thus of the cutting edges  3  which on their face corresponds to  FIG. 10  and when used for rotary percussive drilling yields the stop picture shown likewise in  FIG. 10  (right). 
   The embodiment of the drill bit as claimed in the invention which is shown in  FIGS. 22 to 26 , proceeding from its blind hole  5 , has three channels  10  which lead from the outside peripheral surface  13  of the drill bit  1  and which in the area of the concavely curved surfaces  12  discharge in the outside surface  13  of the drill bit  1 , in a manner similar to the case in the embodiment of the drill bit which is shown in  FIGS. 1 to 8 . 
   The embodiment of the drill bit  1  shown in  FIGS. 27 to 31  likewise has a combination of curved cutters  2  with one straight cutter  1 , both the curved cutters  2  and thus their cutting edges  3  as well as the straight cutter  2 ′ and its cutting edge  3 ′ end at a distance from the axis  4  of the drill bit  1  of  FIGS. 27 to 31 . 
   In the embodiment of the drill bits as shown in  FIG. 27 , proceeding from the blind hole  5  of the drill bit  1  there are three channels  10  which are aligned, as has been described beforehand using  FIGS. 1 to 8  and  23  to  26 , specifically to the face of the drill bit  1 . The mouths  11  of the channels  10  are located off-center to the concavely curved surfaces  12  (compare  FIG. 29 ). Preferably the mouths  11  of the channels  10  in the section of the surfaces  12  which lies forward in the direction of rotation of the drill bit  1  (in  FIGS. 27 to 31  the drill bit  1  is designed for rotation clockwise) lie so to speak in the shadow of the edges between the jacket surface  13  of the drill bit  1  and the concave surfaces  12 . Thus the entry of drillings into the channels  10  is prevented even better than for the mouths  11  which are located in the middle in the surfaces  12  (compare  FIG. 22 ). Between these channels  10  there are other channels  10 ′ which discharge in the outside surface  13  of the drill bit  1  between the concavely curved surfaces  12 , as can be seen for example from  FIGS. 28 and 29 . These channels  10 ′ discharge in a concavely retracted section of the outside surface  13  of the drill bit  1 . Here the channels  10  of the drill bit  1  which is shown in  FIGS. 27 to 31 , as well as the channels  10  of the embodiments of the drill bit  1  which are shown on the one hand in  FIGS. 1 to 8  and  FIGS. 22 to 26  on the other relative to the axis  4  of the drill bit  1  are slanted pointing toward the front end (face) of the drill bit  1 . The channels  10 ′ conversely are obliquely aligned to the axis  4  of the drill bit  1  toward their end, therefore tilted away from the face of the drill bit, from which the blind hole  5  proceeds, and their mouths  11 ′ lie in a tapering section  13 ′ of the outside surface  13  of the drill bit  1 . In this alignment of the channels  10 ′ the entry of drillings into the channels  10 ′ is prevented. In addition, this alignment has the advantage that the flushing medium can enter the drilled hole without sharp deflection of its flow out of the channels  10 ′. 
   Even if  FIGS. 27 to 31  show a drill bit  1  with channels  10  and  10 ′, a drill bit as claimed in the invention can also be equipped exclusively with the channels  10  shown as in this Figure or exclusively with channels  10 ′. 
   In summary, one preferred embodiment of the drill bit as claimed in the invention can be described as follows: 
   A drill bit  1  on its face has solely curved cutters  2  or a combination of at least one straight cutter  2 ′ with at least two curved cutters  2 . The cutters  2 ,  2 ′ on the face of the drill bit  1  are arranged such that they proceed from the axis  4  of the drill bit  1  or end directly adjacent to it. Channels  10  proceed from the blind hole  5  which is used to attach the drill bit  1  to the anchor rod of an injection drill anchor. Their mouths  11  are not located in the area of the end face of the drill bit  1 , but in the area of its lateral outside surface  13  which widens conically to the cutters  2 ,  2 ′. The mouths  11  of the channels  10  in the area of the concave depressions  12  of the jacket surface  13  of the drill bit  1  are located such that they are arranged set back relative to the periphery of the face of the drill bit  1 .