Abstract:
A drill with a drill flute ( 12 ) includes symmetrical fluted lands ( 20 ) helically extend around a core, wherein grooves ( 18 ) remain between the fluted lands, said grooves having a width ( 72 ) that exceeds the spine thickness or width ( 24 ) of the fluted lands ( 20 ), and wherein the grooves ( 18 ) comprise a convex core reinforcement ( 22 ) at the groove bottom thereof. The width ( 24 ) of the fluted lands ( 20 ) at the drill head side end ( 16 ) is smaller than at the shank side end ( 14 ) of the drill helix ( 12 ), and at least increases in certain areas. The core reinforcement ( 22 ) at the drill head side end ( 16 ) is more convex than at the shank side end ( 14 ), thus has larger radii ( 40, 42 ).

Description:
The instant application should be granted the priority date of Sep. 6, 2013, the filing date of the corresponding German patent application DE 10 2013 109 796. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a drill, in particular to a rock drill with a drill head equipped with a hard metal insert. 
     A drill of this kind is known from DE 197 27 070 C2. This drill with a core reinforcement in practice has turned out to be particularly efficient and durable. 
     This type of drill is still used today as a so-called four-flute cutter and offers the possibility to combine a good stability and a relatively large drill dust removal groove. The core reinforcement makes it possible to work with a quite thin core resulting in a correspondingly large drill dust removal groove, but nevertheless on the other hand makes it possible to reduce the tendency to break due to the effected reinforcement of the core. 
     By core reinforcement a convexity in the direction of the drill longitudinal axis is understood, that is to say a convex structure of the drill core within each drill dust removal groove if viewed at a longitudinal section of the drill. 
     On the other hand, the invention is based on the object of providing a drill, whose long-term stability and resistance to breakage are still further enhanced. 
     SUMMARY OF THE INVENTION 
     According to the invention a drill with a core reinforcement is provided whose spinal width of the fluted land at the drill head side end is smaller than at the shank side end of the fluted lands or the drill helix. Hereby, the tendency of the drills to break at the transition between the cylindrical part of the drill at the shank side end thereof and the drill helix, is eliminated by surprisingly simple means. Due to the increase of the spine thickness or width at this position or due the broadening of the spinal fluted lands the notch effect at this position is significantly reduced. 
     At the same time the drill at this position becomes more rigid and thus the transfer of the impact energy to the drill tip is improved. 
     The drill tip in a manner known per se is provided with a drill head comprising a hard metal insert. The inventive drill is thus especially suitable for rock, etc. 
     According to the invention, it is provided to configure the core reinforcement at the shank side end to be more slender, i.e. less convex. The rigidity and stability of the core hereby are not influenced at all or only to a very small extent because the absolute depth of the drill dust removal groove at the tip of the core reinforcement remains unchanged. However, more space for the drill dust removal is created due to the more slender configuration by still increasing the volume of the drill dust removal groove to the side of the center of the core reinforcement. This compensates by far the reduction of volume or free space per axial length section of the drill in the area of the shank side end of the helix that is available for the drill dust removal. 
     At the drill head side end of the helix, the spine width of the fluted lands is correspondingly smaller than at the shank side end. Hereby, the drill itself is less rigid at this position. Due to the more convex configuration of the core reinforcement, that is to say a configuration with larger radii of convexity if viewed in the longitudinal section of the drill, however, a higher mass helix section is available that correspondingly better transfers the impact energy introduced. 
     In this respect, the core reinforcement is inventively configured to be more rigid at the position at which the drill is weakened by a weaker helix, and less rigid at the position at which the drill is more rigid due to a more rigid helix comprising a broader spine. 
     Thus, it is possible in a surprisingly simple manner to compensate for the tendency of breakage of the drills used so far, in particular of the drills without a core reinforcement, at those positions at which the drill tends to break, namely in particular at the transition between the shank and the drill helix. 
     A further advantage arises from the reduction of the spine width in the front region of the drill. Due to the narrower spinal fluted lands there is a smaller contact surface between the drill hole and the drill. Less friction is produced resulting in an increase of the drilling progress, especially also during the production of a drill hole. The front part of the drill is in contact with the drill hole already at the beginning of the drilling process, and the friction thereof significantly determines the drilling performance. 
     Due to the groove space that has been enlarged in the rear area, a larger volume is available for the reception of drill dust. Hereby, the tendency for deflagrations at a nearly finished drill hole is reduced. 
     It is particularly advantageous that due to the steeper helix angles of the drill helix, the shock wave introduced into the drill from the shank end, can be better introduced into the drill helix, thus introducing more impact energy into the drill head which increases the drill performance. 
     In an advantageous embodiment, the change of shape of the core reinforcement is symmetrical, that is to say in mirror image relative to one another on both faces of the core reinforcement. In this manner the maximum possible volume enlargement is achieved that at the same time prevents a weakening of the core reinforcement. 
     In a further advantageous embodiment, the core thickness of the drill, measured against the tip or center of the core reinforcement, is constant along the contour of the helix. Hereby, a weakening of the drill and a reduction of the rigidity due to a possible reduction of the core diameter is avoided. 
     According to the invention a particularly advantageous combination of a variable core reinforcement is combined with a drill helix that is variable as to the form of the variable spine thickness or width of the fluted land. 
     According to the invention the shape of the core reinforcement changes along the contour of the drill. The area of the core reinforcement in a favorable configuration is reduced towards the shank side end of the helix. 
     Due to the change of the fluted land width along the contour of the drill helix, the fluted land has a different mass if viewed along the contour of the drill helix. This surprisingly results in the avoidance of vibrancy due to the introduced longitudinal pulses of the impact energy. 
     In a further advantageous embodiment of the invention it is provided to increase the width of the fluted lands at the drill head side end and to configure the core reinforcement at this position more slender and thus narrower than at the shank side end. This design has the particular advantage that at the position at which the wear of the fluted land is biggest, the largest fluted land mass is available. Said position, that is to say the drill head side end of the transport helix is most frequently in contact with the drill hole surrounding the drill and is thus subjected to the heaviest wear. In this respect, in this configuration a particularly favorable wear compensation is present. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages, details and features of the invention emerge from the subsequent description of two embodiments of the invention based on the drawing in which: 
         FIG. 1  is a side view of a substantial part of an embodiment of an inventive drill; 
         FIG. 2  is an enlarged longitudinal sectional view of a detail of the drill according to  FIG. 1  in the rear or shank side end region of the drill; 
         FIG. 3  illustrates a sectional view similar to  FIG. 2 , however of a drill head side end region or front end region of the drill according to  FIG. 1 ; and 
         FIG. 4  illustrates a view of a further embodiment of an inventive drill in a representation according to  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The drill  10  illustrated in  FIG. 1  comprises a drill helix  12  that extends from a shank end  14 , also referred to as a rear end, to a front end or drill head end  16 . 
     The drill  10  comprises in a manner known per se a drill dust removal groove  18  in the area of the helix, said drill dust removal groove  18  being configured in a helically circulating manner. In a manner known per se as well, a spine fluted land  20  is also configured in a helically circulating manner in the same direction, which spine fluted land  20  is inventively configured in a special manner as described in the following. 
     The drill dust removal groove  18  comprises a core reinforcement  22 . The core reinforcement  22  is designed more convex in the area of the drill head end  16  and more acute or slenderer in the sense of a reduced cross-section of the core reinforcement in the area of the shank end  14 . As far as the individual shape of the core reinforcement  22  is concerned, it is referred to  FIGS. 2 and 3 . 
     According to the invention the width  24  of the fluted land  20  in the area of the drill head  16  is relatively narrow and the width  26  of the fluted land  20  in the area of the shank end  24  is large. In the illustrated exemplary embodiment that shows a drill with a nominal diameter of 14 mm, the width  24  at the drill head end  16  amounts to 2 mm and the width  26  at the shank end  14  amounts to 5 mm. 
     It is to be understood that the ratio of the spine widths  24  to  26  may be adapted to the requirements in many areas. For example the width ratio may amount to 1 to 1.2 or 1 to 6. It is preferred that the ratio of the spine fluted lands widths amounts to between 1 to 1.5 and 1 to 3.5, particularly preferred to between 1 to 2 and 1 to 3. 
     According to the invention it is further provided that the core reinforcement  22  in its design changes in the opposite direction compared to the change of the width  24  or  26 , respectively. The core reinforcement  22  is thus broader in the area of the drill head end  16 , i.e. at the position at which the width  24  of the fluted land  20  is narrower, and in the area of the shank end  14 , at which position the width  26  of the fluted land  20  is broader, it is narrower. The result is the desired compensation of the relatively narrower drill dust removal groove  18  in the area of the shank end  14  due to the larger width  24 , and thus a relative enlargement of the drill dust removal groove  18  despite an increased rigidity is provided. 
       FIG. 2  illustrates in which manner the drill dust removal groove  18  and the fluted land  20  are designed at this position, i.e. in the area  14  of the shank end, and how the groove changes along the contour thereof. 
     As it can be seen in  FIG. 2 , two turns of the helix are illustrated. The shank end side fluted land width  26   a  is larger than the fluted land width  26   b  facing towards the drill head. 
     The drill dust removal groove  18  comprises symmetrical exit angles  30  and  32 . The term exit angle refers to the final angles of the drill dust removal groove  18  relative to the fluted land  20 , i.e. at the transition between the drill dust removal groove  18  and the fluted land  20 . 
     The exit angle  30  at the drill head side end of the fluted land  20  correspondingly is exactly as large as the exit angle  32  at the shank side end of the fluted land  20 . 
     In the illustrated exemplary embodiment, said angle amounts to 72°, however, it can be adapted to the requirements in large areas. In order to limit the wear and in order to prevent the drill from getting stuck, the angle in any case should amount to significantly less than 85° if possible, preferably less than 80°. 
     The drill dust removal groove  18  is designed with the core reinforcement  22  in a particular manner. In the area  14  of the drill the core reinforcement  22  is quite slender. Its central radius  40 , i.e. the radius of convexity in the view according to  FIG. 2  in the immediate neighborhood to the center of the core reinforcement  22 , is quite small. In the illustrated exemplary embodiment the radius amounts to significantly less than the nominal diameter of the drill, that is to say to approximately half the nominal diameter. Said radius is detected via the central 20° of the convex core reinforcement  22 . 
     On the other hand, the side radius  42  is significantly larger. In the illustrated exemplary embodiment it amounts to somewhat less than the nominal diameter of the drill that is somewhat larger than the diameter of the drill in the area of the fluted land  20  due to the hard metal tip that protrudes in a manner known per se. The radius, however, can also be somewhat larger than the nominal diameter and may be preferably detected as an angle of about 35° via the central convexity of the core reinforcement  22 . 
     Due to this design the side faces of the core reinforcement  22 , that is to say the front face  46  facing the drill head and the rear side face  48 , are straight sloping and flat. The tilt angle towards the drill axis amounts to between 5 and 18 degrees and in the illustrated exemplary embodiment approximately to 10 degrees. 
     Due to this design with flat side faces, the core reinforcement  22  becomes more acute and narrower. 
     This benefits the volume  50  of the drill dust removal groove  18  that is thus enlarged in the area of the lateral chamfers  52  and  54  of the drill dust removal groove  18 . 
     When viewed from the exit angle  30  or  32 , respectively, the drill dust removal groove  18  comprises an involute-like structure in the area of the chamfers  52  and  54 , in fact nearly to the point at which it merges into the center  60  of the core reinforcement. 
     Contrary thereto, a different drill dust removal groove  18  can be seen in  FIG. 3 ;  FIG. 3  illustrates the design of the drill dust removal groove  18  and of the core reinforcement  22  in the area of the drill head side end of the helix. In this view according to  FIG. 3 , i.e. viewed in the longitudinal section through the drill, the core reinforcement  22  is significantly more convex. The result is that the central radius  40  and the side radius  42  coincide and in total are significantly larger than the respective radii according to  FIG. 2 . In the illustrated exemplary embodiment, both radii are approximately as big as twice the nominal diameter of the drill  10 . 
     The contour of the chamfers  52  and  54  is such that they quite fast merge into the convexity of the core reinforcement  22  when viewed from the exit angles  30  or  32 , respectively. In this design, the concave area of the chamfers  52  and  54  is immediately followed by the convex area of the core reinforcement  22 . The area of convexity of the core reinforcement  22  in this design has a convexity width  70  that is significantly enlarged as compared to the the convexity width  70  according to  FIG. 2 . The width amounts to significantly more than half the width  72  of the drill dust removal groove  18 . The width ratio at the drill head side end according to  FIG. 3  amounts to approximately 0.8 to 1, whereas it amounts to approximately 0.2 to 1 at the shank side end. 
     It is to be understood that the ratio of the convexity width  70  to the drill dust removal groove width  72  may be adapted to the requirements in large areas and that in case of a relatively larger convexity width, a more convex design of the core reinforcement is contemplated. 
     Whereas with the drills illustrated here, a spiral having two flutes is provided which spiral is typically used with so-called two-flute cutters, it is to be understood that instead the same effects may be achieved with four-flute spirals or drill helices, as they are typical with four-flute cutters. A correspondingly designed drill helix  12  becomes apparent from  FIG. 4 . 
     Here, as well as in the remaining figures, same reference numerals refer to the same parts and do not require further reference thereto. The width ratio of the widths  24  and  26  of the fluted lands  20  here amounts to 1 to 2, and the core reinforcement  22  changes as described before in the opposite direction as compared to the width change of the fluted lands  20 . 
     The same applies analogously to three-flute cutters and other multi-flute cutters. 
     As it becomes apparent from  FIG. 4 , the rearward third  80  is equipped with a larger fluted land width  26 , and the two front thirds  82  of the drill  10  comprise a smaller fluted land width  24 . In between a continuous transition extends. 
     The result is that the change of shape of the core reinforcement  22  and the change of the fluted land widths  24  or  26 , respectively, has not to take place continuously and steadily along the contour of the drill  10 , but that a change section by section is also sufficient should the occasion arise. 
     The specification incorporates by reference the disclosure of German patent application DE 10 2013 109 796, filed Sep. 6, 2013. 
     The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.