Abstract:
A tool bit for a chisel or a hammer drill, in particular, a insertable chisel or insertable drill for power-driven drill and chisel hammers, has an insertion end, with a chisel shank or drill shank, and a chisel head or drill shank located opposite the insertion end. The diameter of the shank increases in the direction of the chisel head at least once from a first, small diameter to a second, large diameter and decreases again from this to a small diameter or forms at least one bead.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of German Patent Application No. 101 32 292.5 filed Jul. 6, 2001 and German Patent Application No. 102 08 628.1 filed on Feb. 28, 2002, the disclosures of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     This invention relates to an insertable hammer drill, or an insertable chisel, for power-driven drill or chisel hammers. The drill, or chisel, has an insertion end, a shank attached to the insertion end, and a drill or chisel head attached to the shank and located opposite the insertion end 
     In addition, for example, to the configuration of the cutting edge and to the material used, the shape of the shank of a chisel is also critical for the effectiveness of the latter. DE 40 24 650 A1 discloses, for example, a chisel in which the diameter of the chisel shank narrows in steps from the insertion end toward the chisel tip, and, in this case, a contraction may also be provided. Furthermore, DE-UM 92 09 647 discloses a chisel which is produced as a forged part and the shank of which narrows conically toward the working end and may likewise have a contraction. DE 199 14 522 A1 discloses a chisel with a hexagonal insertion end which has a collar between the insertion end and the shank. This collar has purely the function and action of an abutment. The disadvantage of the two known chisels mentioned first is that the diameter of the shank narrows toward the chisel cutting edge and the stability of the chisel shank decreases continuously or in steps toward the working end. A shaping of this kind is critical, in particular, in the case of chisels with a medium and smaller initial diameter of the chisel shank and in the case of chisels with long chisel shanks, since, as a result of the narrowing, a chisel shank diameter is quickly reached which, because of the minimum mechanical requirements to be met by the chisel shank, is within a critical range and counteracts unintended vibrations to only a slight extent. These considerations also apply similarly to hammer drills as regards their hammering or chiseling property. In the field of drills, what may be referred to as collar drills are known (see, for example, DE 43 22 588 A1, FIG. 3), which have a thickening in the shank region or spiral region. This thickening is co-ordinated in its position with the drilling depth provided. The size and shape of this thickening are aimed at taking as great a care as possible of the workpiece to be machined when the desired drilling depth is reached. 
     SUMMARY OF THE INVENTION 
     The object on which the invention is based is to develop a chisel or hammer drill of the type initially described, the shank of which has a shape which has a beneficial action on the effectiveness and the vibrational behavior of the chisel or hammer drill, but does not lead to a mechanically critical narrowing of the diameter of the shank. 
     This object is achieved, according to the invention, by having a drill or chisel shank wherein the diameter of the shank increases in the direction of the head at least once from a first small diameter, or a first small cross sectional area, to a large diameter, or a large cross sectional area, and then decreases again to a second small diameter or a second small cross-sectional area. 
     The chisel or hammer drill according to the invention has a shank with at least one thickening or upset which is formed by an increase in the cross-sectional area of the shank and a subsequent decrease in the cross-sectional area of the shank in the direction of a longitudinal axis. By the shape of the shank being changed in regions in this way, a concentration of the percussion or impact energy, which is introduced into the chisel or hammer drill by the power-driven drill or chisel hammer, is brought about and a damping of vibrations is achieved. That region of the beadlike thickening which narrows toward the working end exerts virtually a comparable action to the chisels which narrow continuously or in portions, this action being achieved in the chisel or hammer drill according to the invention, without a reduction in the initial cross-sectional area or in the initial diameter of the shank taking place. By thickenings according to the invention being lined up directly and/or distributed regularly and/or irregularly over the length of the shank, it is possible to utilize, and consequently accumulate, the positive influence of narrowings over the entire length of the shank. 
     An advantageous design of the subject of the invention provides for making the first, small diameter or the first, small cross-sectional area approximately identical to the third, small diameter or the third, small cross-sectional area. This ensures that a minimum diameter of the shank is maintained. 
     Furthermore, the invention provides for making the third, small diameter or the third, small cross-sectional area of a first bead approximately just as large as the first, small diameter or the first, small cross-sectional area of a second bead. By virtue of dimensional ratios of this kind, a transitional region between two beads acquires a shape of constant cross section. 
     The chisel or the hammer drill acquires advantageous properties, in particular, when the first and the third, small diameters have a ratio of about 1:1.6 to the second, large diameter. It is also advantageous if the third and the first, small diameters have a ratio of about 1:1.2 to the second, large diameter. 
     By the use of the circular and/or oval and/or elliptic and/or polygonal cross section of the shank, the latter can be optimized particularly in terms of the working end. For example, in the case of a wide flat chisel, it is advantageous to use an elliptic cross section of the shank, in which a large semiaxis of the ellipse has the same orientation as the chisel cutting edge. 
     It is particularly advantageous if the increase in diameter or increase in cross section and the decrease in diameter or decrease in cross section of the shank takes place over length portions of approximately equal length. Increases and decreases which are in a ratio of about 1:10 or 10:1 are also considered advantageous. Beads which are designed within these limits have a damping of the vibrations and a quicker chiseling or drilling/chiseling advance than conventional chisels or hammer drills. 
     The invention provides, furthermore, for arranging at least two beads in an identical orientation one behind the other. This gives rise to a kind of series connection, in which the positive properties of the individual beads supplement one another. 
     Finally, there is provision for arranging beads mirror-symmetrically to a plane perpendicularly intersecting the longitudinal axis of the shank and, in particular, for causing said beads to merge directly one into the other. The positive influences of the beads likewise interact as a result. 
     Moreover, the invention provides for placing the position of the bead on the hammer drill or on the chisel as a function of the length of a beater working in the power-driven drill hammer or in the chisel hammer. It is thereby possible to design the hammer drill and chisel for a special power-driven drill hammer or chisel hammer or to optimize them for an entire construction series of power-driven drill hammers or chisel hammers. It is optimum if the bead is at a distance from the rear end of the hammer drill or chisel which corresponds approximately to 2 to 4 times the length of the beater. There is also provision for adapting the hammer drill or the chisel to the power-driven drill hammer or chisel hammer in terms of the weight of the bead which likewise decisively co-determines its mode of action. An optimum action of the bead can thereby be achieved. This optimum action is afforded when the mass of said bead is co-ordinated with the weight of the beater in the power-driven drill hammer or chisel hammer and is approximately 0.2 to 0.7 times the beater mass. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details of the invention are described, with reference to diagrammatically illustrated exemplary embodiments, in the drawing in which: 
         FIG. 1  shows a side view of a chisel, 
         FIG. 2  shows a side view of a chisel shank, 
         FIG. 3  shows a top view of the chisel shank illustrated in  FIG. 2 , 
         FIG. 4  shows a side view of a further chisel shank, 
         FIG. 5  shows a top view of the chisel shank illustrated in  FIG. 4 , 
         FIG. 6  shows a side view of a third chisel shank, 
         FIG. 7  shows a top view of the chisel shank illustrated in  FIG. 6 , 
         FIG. 8  shows a side view of a fourth chisel shank, 
         FIG. 9  shows a top view of the chisel shank illustrated in  FIG. 8 , 
         FIGS. 10   a  to  10   f  show side views and top views of three hammer drills with beads thickening in the effective direction of the hammer drills, 
         FIGS. 11   a  to  11   d  show side views and top views of two hammer drills with beads narrowing in the effective direction, 
         FIGS. 12   a  to  12   d  show side views and top views of two hammer drills with approximately spherical beads, 
         FIGS. 13   a  to  13   f  show side views and top views of three hammer drills with approximately rectangular beads, and 
         FIGS. 14   a  to  14   d  show side views and top views of two hammer drills with beads approximately in the form of a mushroom head. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  illustrates a side view of a chisel  1 . The chisel  1  is composed of an insertion end  2 , of a chisel shank  3  and of a working end  4  with a cutting edge  5 . The insertion end  2  extends over an insertion region a, the chisel shank  3  extends over a shank region b and the working end  4  extends over a working region c. The chisel shank  3  has toward the insertion end  2  and toward the working end  4  an initial diameter d 0 . Two beads or thickenings or upsets  8  are formed on the chisel shank  3  between an upper chisel shank portion  6  and a lower chisel shank portion  7 . The thickenings  8  are composed in each case of two cone frustums  9 ,  10  of circular cross section. Between the thickenings  8 , the chisel shank  3  has a middle chisel shank portion  11  which corresponds in cross section to the upper and the lower chisel shank portion  6 ,  7 . 
       FIG. 2  shows a chisel shank  3  of a chisel  1 , the illustration of an insertion end and of a working end having been dispensed with for the sake of simplification. The chisel shank  3 , like the chisel shank illustrated in  FIG. 1 , has a thickening  8  which is formed by two cone frustums  9 ,  10 . Above the thickening  8 , the chisel shank  3  merges into an upper chisel shank portion  6 . Below the thickening  8 , the chisel shank  3  merges into a lower chisel shank portion  7 . The chisel shank portions  6 ,  7  have identical initial diameters d 0 . The thickening  8  grows in the percussion direction p from a first, small diameter d 1 , which corresponds to the initial diameter d 0 , to a second, large diameter d 2  and subsequently decreases, in the region of the cone frustum  10 , to a third, small diameter d 3 , which again corresponds to the initial diameter d 0 . In the region of the cone frustum  10 , percussion waves  12  acting on the chisel  1  or the chisel shank  3  from a power-driven drill or chisel hammer, not illustrated, are concentrated toward a longitudinal mid-axis x of the chisel  1  and thus ensure an effective transmission of the energy introduced. The thickening  8  extends over a length l 0 , the cone frustums  9 ,  10  extending over the lengths l 1  and l 2 . The lengths l 1  and l 2  are approximately identical. 
       FIG. 3  shows a top view of the chisel shank illustrated in  FIG. 2 . The upper chisel shank portion  6  and the thickening  8  have circular cross sections A, B. According to the change in diameter, the cross section A of the chisel shank portion  6  increases over the length l 1  to the maximum cross section B of the thickening  8  and then decreases again to a cross section C (see  FIG. 2 ) of the lower chisel shank portion  7 . 
       FIG. 4  shows a further chisel  1 , of which only a chisel shank  3  is illustrated for the sake of simplification. Between an upper chisel shank portion  6  and a lower chisel shank portion  7  is arranged a thickening  8  which is composed of a cone frustum  10  and of a body of revolution  13 . The body of revolution  13  has a curved generatrix  14  which runs in an approximately S-shaped manner. In the region of the thickening  8 , the diameter of the chisel shank  3  rises from a first, small diameter d 1  to a second, large diameter d 2  and then falls again back to a third, small diameter d 3 . In this case, the diameters d 1 , d 3  correspond to diameters d 0  of the chisel shanks  6 ,  7 . The increase in diameter and the decrease in diameter of the thickening  8  take place over length portions l 3  and l 4  which are in a ratio of about 1:5. That is to say, the increase in diameter takes place more quickly than the decrease in diameter. A slow concentration of percussion waves  12  onto the lower chisel shank portion  7 , which merges into a working end, not illustrated, is thereby possible. 
       FIG. 5  shows a top view of the chisel shank  3  illustrated in  FIG. 4 . The upper chisel shank portion  6  and the body of revolution  13  have circular cross sections A, B. This also applies to the cone frustum  10  and to the lower chisel shank portion  7 . 
       FIG. 6  shows a further chisel  1 , of which only a chisel shank  3  is illustrated for the sake of simplification. The chisel shank  3  has, between an upper chisel shank portion  6  and a lower chisel shank portion  7 , two thickenings  8  which butt directly onto one another or merge directly one into the other. The two thickenings  8  are formed mirror-symmetrically to a mirror plane E, through which a chisel longitudinal axis x runs perpendicularly. The upper thickening  8  increases from a diameter d 1  to a diameter d 2  and then decreases again to a diameter d 3 . The diameter d 3  of the upper thickening  8  corresponds to the first, small diameter d 4  of the lower thickening  8  which increases from the diameter d 4  to a diameter d 5  and then decreases again to a diameter d 6 . The initial diameter d 1  and the final diameter d 6  of a double bead  15  formed by the two thickenings  8  corresponds to initial diameters d 0  of the chisel shank portions  6 ,  7 . The double bead  15  possesses, in particular, also vibration-damping properties which assist in avoiding unintended vibrations of the chisel  1 . 
       FIG. 7  shows a top view of the chisel shank  3  illustrated in  FIG. 6 . The upper chisel shank portion  6  and a body of revolution  13  of the upper thickening  8  have circular cross sections A, B. The chisel shank  3  is of rotationally symmetric design in its entire region and therefore has circular cross sections perpendicularly to the longitudinal mid-axis x. 
       FIG. 8  shows a further chisel  1 , of which only a chisel shank  3  is illustrated for the sake of simplification. The chisel shank  3  has, in a similar way to the chisel shank illustrated in  FIG. 6 , a double bead  15  consisting of two thickenings  8  which are arranged mirror-symmetrically to a plane E, to which a longitudinal mid-axis x of the chisel shank  3  is perpendicular. The thickenings each consist of a body of revolution  13  and of a cone frustum  10  and extend over length portions l 3 , l 4 , which are in the ratio of about 1:6. The upper thickening  8  first increases from a cross section A to a cross section B and then decreases again to a cross section C. The latter corresponds to a small cross section D of the lower thickening  8  which increases to a cross section E and subsequently decreases again to a cross section F. The cross sections A, C, D and F correspond to a cross section G of chisel shank portions  6 ,  7 . 
       FIG. 9  shows a top view of the chisel shank  3  illustrated in  FIG. 8 . This shows a circular cross section A of a chisel shank portion  6  and a circular cross section B of the body of revolution  13  partially forming the upper thickening  8 . 
       FIG. 10   a  shows a side view of a hammer drill  16 . This has a drill shank  3  which consists of an insertion end  2 , of an upper drill shank portion  6 , of a thickening  8  adjoining the latter, of an lower drill shank portion  7 , of a helix  17  and of a drill head  4 . Starting from an initial diameter d 0  of the upper drill shank portion  6 , the bead  8  increases from a first diameter d 1 , corresponding to the initial diameter d 0 , virtually abruptly and then slowly to a second, large diameter d 2  and thereafter narrows on a short portion to a third, smaller diameter d 3  which corresponds to the first diameter d 1 . The lower drill shank portion  7  decreases in an effective direction p, via a shoulder  18 , from a diameter d 0  or d 3  to a spine diameter d R  of the helix  17 . 
       FIG. 10   b  shows a top view of the hammer drill  16  illustrated in  FIG. 10   a . The rotationally symmetric design of the thickening  8  can be seen in the top view. A cutting plate  19 , to which two auxiliary cutting edges  20  are assigned, can be seen in the drill head  4 . 
       FIG. 10   c  illustrates a further hammer drill  16  which, in principle, has the same construction as the hammer drill illustrated in  FIG. 10   a . In contrast to this, the hammer drill  16  illustrated in  FIG. 10   c  has a spine diameter d R  which is larger than an initial diameter d 0  of the drill shank  3 . A bead  8  of the hammer drill  16  is at a distance g from an insertion end  2  of a hammer drill  16 . The distance g is, in practice, about 140 to 150 mm and is calculated from a length of a beater arranged in a drill hammer, multiplied by a factor of 2 to 4. For example, the beater of a drill hammer of the 5-kg class has a length of 30 to 40 mm. In the case of the drill hammer of the 7-kg class, the beater length is about 50-60 mm. A rock drill hammer of the 10-11 kg class possesses a beater with a length greater than 60 mm. Conventional hammer drills  16  have an overall length of about 520 mm, the drill head  4  and the helix  17  occupying approximately 340 mm. The shank length is then about 180 mm. 
       FIG. 10   d  shows, in a similar way to  FIG. 10   b , a top view of the hammer drill illustrated in  FIG. 10   c.    
       FIGS. 10   e  and  10   f  illustrate a further variant of a hammer drill  16 . This has a bead  8  of trapezoidal cross section. 
       FIGS. 11   a  to  11   g  show two further hammer drills  16  in side view and top view. The hammer drills  16  have beads  8  which are designed and arranged as cone frustums  21  oriented in an effective direction p. 
       FIGS. 12   a  to  12   d  illustrate two design variants of a hammer drill  16  having beads  8  which are formed as a spherical thickening. As compared with a hammer drill without a bead, the mass of the hammer drill with the bead  8  is increased by a differential mass m. The additional mass m brought about by the bead  8  is, for example, about 80 g and amounts approximately to 0.2 to 0.7 times a mass of a beater of a drill hammer. For example, the beater mass of what is known as a 5-kg drill hammer is about 125 g, in the case of a 7-kg drill hammer the beater weighs about 205 g and, in the case of a 10- or 11-kg drill hammer, the weight of the beater is in the region of about 440 g. 
       FIGS. 13   a  to  13   f  illustrate three further hammer drills  16 . The characteristic of these hammer drills is that the diameter of a shank  3  increases from a small diameter d 1  abruptly to a large diameter d 2 , remains constant or approximately constant at the large diameter d 2  over a portion  12  and thereafter decreases abruptly to a third, smaller diameter d 3 . 
       FIGS. 14   a  to  14   d  illustrate two further hammer drills  16 . These have beads  8  which are approximately in the form of a mushroom head  22 . In this case, the mushroom heads  22  of the hammer drills  16  illustrated in  FIGS. 14   a ,  14   b  and  14   c ,  14   d  are oriented differently in an impact direction p. 
     The beads illustrated in  FIGS. 1 to 9  for chisels may likewise be used in hammer drills. The beads illustrated in  FIGS. 10   a  to  14   d  for hammer drills may advantageously also be used in chisels. The statements made on  FIGS. 10   a  to  14   d  with regard to the position of the thickening or with regard to the mass of the thickening also apply in a similar way to chisels. 
     The bead can be arranged in that half of the shank which faces the insertion end. 
     The invention is not restricted to exemplary embodiments illustrated or described. On the contrary, it embraces developments of the invention within the scope of the patent claims. In particular, the invention also provides for arranging a plurality of thickenings spaced apart from one another in the region of a shank. Furthermore, there is also provision for causing differently designed thickenings to merge one into the other. A further design variant of the invention provides for rotating the shank about the longitudinal axis, a rotation of the thickening, in particular of a thickening which is not rotationally symmetric, also selectively being provided.