Patent Application
20200215674
The present invention relates to a drill bit for the chiselling of rock. In particular, the invention relates to a drill bit in the case of which drill cuttings can be transported away via a hollow shank. The drill bit does not have or require a helical shank.
The drill bit for the chiselling of rock has an impact face at an insertion end, a hollow shank, within which a delivery passage is provided, and a drill head. The drill head has, at a front end, three or more cutting edges and one or more intake openings. Within the drill head there are intake passages that connect the intake openings to the delivery passage. In at least one of the intake passages, a first portion of the intake passage adjoining the intake opening has a first inclination with respect to the drill bit axis and a second portion of the intake passage adjoining the hollow shank has a second inclination with respect to the drill bit axis. The second inclination is greater than the first inclination. The smaller inclination of the intake passage in the upper region is advantageous as regards the break-down performance. The shock wave undergoes no or only slight radial deflections on account of the interfaces, which tend to be axially parallel.
The first inclination may be less than 5 degrees. The second inclination may be between 15 degrees and 30 degrees.
In one configuration, the second portion of the intake passage is continuously curved.
In one configuration, the drill head provides a base, in which the cutting edges are embedded, wherein the base partially surrounds the cutting edges in a circumferential direction.
In one configuration, the base consists at least partially of a sintered steel. A portion of the base that surrounds the cutting edges can be made of tungsten carbide.
In one configuration, the base consists entirely of a sintered steel.
In one configuration, a cross section of the intake passages increases from the intake opening to the delivery passage.
In one configuration, the intake openings are triangular.
The cutting edges of the drill head are preferably made of sintered tungsten carbide. The hard material is suitable particularly for the chiselling of rock. The cutting edges can have a rake face and a flank face, which both form a part of the impact face and are in contact with one another along a chisel edge. The geometry is particularly suitable for the chiselling of rock.
The following description explains the invention on the basis of exemplary embodiments and figures, in which:
Identical or functionally identical elements are indicated by the same reference signs in the figures unless specified otherwise.
The drill bit 1 is designed to break down mineral construction materials, for example concrete, brick. The insertion end 6 can be inserted into a portable power tool, for example a drilling machine or a hammer drill. An impact mechanism of the portable power tool periodically strikes the impact face 7 at the insertion end 6. The shock wave of the impact passes through the hollow shank 4 in the impact direction 9 as far as the drill head 2. The drill head 2 breaks up the mineral material. The drill bit 1 is preferably rotated in a direction of rotation 10 about its drill bit axis 11 between impacts. Consequently, the drill bit 1 strikes the material in different orientations. The resulting drill cuttings can be removed from the drilled hole directly from the front end 12 of the drill bit 1. A vacuum cleaner is attached to the sleeve 8. The air stream draws in the drill cuttings at the intake openings 3 directly at the front end 12 of the drill bit 1. The drill cuttings are transported away within the hollow shank 4.
The exemplary drill head 2 has a base 13 and a plurality of cutting edges 14 embedded in the base 13. The cutting edges 14 form the tip 15 of the drill head 2. The cutting edges 14 protrude with respect to the base 13 in the impact direction 9. The front end 12 of the drill head 2 is made up of the front faces 16, facing in the impact direction 9, of the cutting edges 14 and of the front faces 17 of the base 13. The base 13 has a cylindrical lateral surface 18. Preferably, the cutting edges 14 protrude in the radial direction with respect to the lateral surface 18. The lateral surface 18 can be circumferentially closed beneath the cutting edges 14. An underside 19 of the base 13 is arranged on the hollow shank 4. The underside 19 can be welded or soldered to the shank 4 or joined thereto in a similar materially bonded manner. In other embodiments, the drill head 2 can be connected to the shank 4 by means of a screw connection, a bayonet coupling or preferably a conical interference fit (
The cutting edges 14 are preferably made of a sintered tungsten carbide-containing material. In one configuration, a portion 20 of the base 13 that encircles the cutting edges 14 can be produced from the sintered tungsten carbide-containing material and a portion 21 forming the underside can be produced from the sintered iron-based material (
The cutting edges 14 are arranged in a star shape around the drill bit axis 11. The cutting edges 14 are monolithically cohesive, in particular joined together by welding, soldering, clamping etc. without a joint zone. The cutting edges 14 are preferably sintered from a tungsten carbide-containing material. The cutting edges 14 are preferably arranged regularly or regularly in pairs around the drill bit axis 11. For example, the four identical cutting edges 14 are arranged at spacings of 90 degrees in the direction of rotation 10. In other embodiments, the cutting edges can be formed so as to be different. For example, the drill head has main cutting edges and secondary cutting edges. The exemplary embodiment shows four cutting edges 14; in other embodiments, the drill head 2 can have three, five or six cutting edges 14.
The cutting edges 14 each have a chisel edge 22 that protrudes in the impact direction 9 and narrows in the radial direction to a tip 15 of the drill head 2. The chisel edge 22 can be straight or curved. The chisel edges 22 are preferably formed identically or identically in pairs. In the configuration illustrated, all chisel edges 22 extend as far as the tip 15; in other configurations, only chisel edges of the main cutting edges reach as far as the tip 15. The single tip 15 of the drill head 2 is located preferably on the drill bit axis 11.
The front face 16, facing in the impact direction 9, of each cutting edge 14 is formed by a rake face 23 and a flank face 24. The rake face 23 and the flank face 24 both face in the impact direction 9 and are in contact with one another along the chisel edge 22. The rake face 23 and the flank face 24 are prolonged in the radial direction. The rake face 23 and the flank face 24 extend from a location adjoining the outer peripheral face 25 as far as the drill bit axis 11 or into the vicinity of the drill bit axis 11. The rake face 23 leads the flank face 24 in the normal direction of rotation 10 of the drill head 2. Looking at the drill head 2, the normal direction of rotation 10 is counterclockwise. The rake face 23 and the flank face 24 are inclined with respect to the drill bit axis 11. The rake face 23 rises counter to the direction of rotation 10 in the impact direction 9; by contrast, the flank face 24 drops counter to the direction of rotation 10 in the impact direction 9. The rake face 23 and the flank face 24 are accordingly inclined with respect to one another. A roof angle 26 between the rake face 23 and the flank face 24 is greater than 45 degrees, for example greater than 60 degrees and less than 120 degrees. The roof angle 26 can be constant or vary in the radial direction.
A peripheral face 25, facing away from the drill bit axis 11, of the cutting edges 14 is oriented preferably parallel to the drill bit axis 11. The peripheral face 25 defines, with its radial spacing from the drill bit axis 11, the diameter 27 of the drill head 2. The peripheral face 25 forms a break-off edge 28, which bears against a drilled-hole wall during drilling. The break-off edges 28 support the formation of a circular cylindrical shape of the drilled hole by breaking off rock that protrudes radially into the drilled hole. The peripheral face 25 protrudes preferably in the radial direction with respect to the lateral surface 18 of the cylindrical base 13. The cutting edges 14 subdivide an upper portion of the lateral surface 18 into a plurality of cylindrical sectors. A lower portion, connected to the upper portion, of the lateral surface 18 is preferably circumferentially closed, i.e. fully cylindrical.
Provided at the front end 12 of the drill head 2 are a plurality of intake openings 3. The intake openings 3 can be arranged centrally between adjacent chisel edges 22. The intake openings 3 are preferably located in the front faces 17 of the base 13. The intake openings 3 are circumferentially closed, and to this end the intake openings 3 are arranged in a manner spaced apart from the lateral surface 18. A radial spacing of the intake openings 3 is for example between 5% and 20% of the diameter of the drill head 2. The intake openings 3 are arranged along the drill bit axis 11 in a manner offset from the chisel edges 22. The intake openings 3 are located lower down than the chisel edges 22 and therefore do not influence the chiselling functionality of the drill head 2, or only influence it to an insignificant extent. An axial offset 29 of the intake openings 3 with respect to the tip 15 is preferably greater than 15% of the diameter 27 of the drill bit 1.
Respective intake passages 30 connect the intake openings 3 in the front end 12 to the underside 19 of the drill head 2. The defined direction of flow 31 is from the intake openings 3 to the underside 19, i.e. counter to the impact direction 9. The intake passage 30 is closed transversely to the direction of flow along its entire length. The intake passage 30 to this end extends fully within the base 13.
The intake passage 30 approaches the drill bit axis 11 in the direction of flow 31. The approach is not in a straight line, but rather the intake passage 30 is at least partially curved. An upper portion 32 of the intake passage 30 adjoining the intake openings 3 is substantially parallel to the cutting edges 14, i.e. to the drill bit axis 11. The intake passage 30 does not approach the cutting edges 14 or only approaches them to a minor extent in the direction of flow 31. An approach of the intake passage 30 to the drill bit axis 11 in the upper portion 32 is preferably less than 5% of the diameter 27 of the drill bit 1. As a measure for determining the radial spacing, use can be made of the centroid in the cross sections perpendicular to the drill bit axis 11. The upper portion 32 extends over at least 50%, for example 75%, of the height of the cutting edges 14, preferably over at least the entire height of the cutting edges 14. The upper portion 32 can be formed in a rectilinear or curved manner. A lower portion 33 of the intake passage 30 adjoining the hollow shank 4 is inclined with respect to the cutting edges 14. The lower portion 33 increasingly approaches the drill bit axis 11 in the direction of the shank 4. The lower portion 33 of the intake passage 30 can run into the hollow shank 4 with an inclination of between 10 degrees and 30 degrees. The intake passage 30 preferably approaches the drill bit axis 11 between 5% and 30% of the diameter 27 of the drill bit 1. The exemplary lower portion 33 is continuously curved. The lower portion can also be configured in a rectilinear manner. A portion connecting the upper portion to the lower portion is suitably curved. All curved portions of the intake passage 30 have preferably a radius of curvature greater than 80% of the diameter 27 of the drill bit 1. The intake passage 30 has smooth inner walls along its entire length. The gentle curves with large radii of curvature favor friction-free transport of the drill cuttings in the intake passages 30. In particular, sticking or jamming of larger drill cutting pieces is avoided.
The intake openings 3 take up an area of 10% to 25% at the front end 12. The high percentage is advantageous for ensuring that the drill cuttings are transported away. The intake passage 30 can have a cross section that widens in the direction of flow 31. The intake passage 30 has its smallest cross section at or close to the intake opening 3. The change in cross section reduces any tendency of the intake passage 30 to become clogged. The surface area of the cross section changes change by at least 30%, preferably by more than 60%. The surface area of the cross section is determined in planes perpendicular to the drill bit axis 11. The change takes place preferably entirely or primarily within the upper portion 32, i.e. at the level of the cutting edges 14. A radially outer wall of the intake passages 30 is preferably parallel to the drill bit axis 11, while a radially inner wall of the intake passages 30 approaches the drill bit axis 11 in order to obtain the cross-sectional widening.
The exemplary intake openings 3 are noncircular. The intake openings 3 have a triangular shape. Corners of the intake openings 3 can be pointed or rounded. The sides connecting the corners can be straight or curved. In a manner typical for a triangle, a circle is able to be inscribed in the intake opening 3, said circle touching each of the three sides at precisely one point. Furthermore, in a manner typical for a triangle, a distance between the center of the inscribed circle and the sides decreases continuously from the corners to the point touched by the circle. A corner of the intake openings 3 points toward the tip 15 of the drill head 2. An internal angle 34 at the corner corresponds preferably more or less to the angular distance between the adjacent cutting edges 14, for example 90 degrees. “More or less” in this context describes a deviation of less than 20%. The surface area of the intake openings 3 is much greater than the surface area of the inscribed circle. The surface area of the intake openings 3 is at least 30% greater, for example at least 100% greater.
The hollow shank 4 has a delivery passage 35 extending along the drill bit axis 11. The delivery passage 35 has a constant cross section along the length of the shank 4. A surface area of the cross section of the delivery passage 35 is preferably equal to the sum of the cross sections of the intake passages 30. The delivery passage 35 has for example a surface area of 15% to 65% of the cross section of the shank 4. The delivery passage 35 can be arranged centrally on the drill bit axis 11. The delivery passage 35 ends beneath the drill head 2, in particular beneath the base 13. The end of the delivery passage 35 is preferably rounded in the form of a spherical cap.
The intake passages 30 in the drill head 2 open into the delivery passage 35 of the hollow shank 4. The mouth is at or close to one end of the delivery passage 35. The faces at the mouth are rounded.
Arranged at an end of the delivery passage 35 remote from the drill head 2 is the extraction port 5. The extraction port 5 contains a radial cut 36 into the delivery passage 35. The sleeve 8 surrounds the cylindrical shank, preferably in an airtight manner, in the region of the cut 36. The sleeve 8 is rotatable relative to the shank 4.
The exemplary insertion end 6 of the drill bit 1 is designed for the use of rotary chiselling portable power tools. The insertion end 6 has a substantially cylindrical shape. The insertion end 6 has two closed slots 37, in which locking elements of the portable power tool can engage radially and can slide along the drill bit axis 11. Flutes 38 oriented along the drill bit axis 11 allow torque to be introduced by the portable power tool.
The drill bit 1 is preferably manufactured from different materials. The shank 4 and the insertion end 6 are preferably made of a tough and ductile steel. The cutting edges 14 of the drill head 2 are made of very hard and abrasion-resistant sintered tungsten carbide. The tungsten carbide is present in a content of at least 70% by volume. The metallic binder contains preferably one or more of the metals: cobalt and nickel. For example, the binder can consist entirely of cobalt.
The drill head 2 can be produced in non-customary manner in a basic form, which is subsequently machined in order to form the intake passages 30. Subsequently, a production process is proposed, with which the desired intake passages 30 can be formed. The described production process can be modified in certain details without departing from the principle thereof.
A thin powder layer is produced by spraying a suspension containing tungsten carbide and the metallic binder. An adhesive is pressed onto the powder layer in a structured manner. The adhesive reproduces a cross section through the drill head 2. The deposition of a powder layer and of the adhesive is repeated as many times as necessary for a blank of the drill head 2 to be replicated. The excess powder, in particular in the intake passages 30, can be removed by water. The water penetrates between the layers not joined by adhesive and dislodges them. The resultant blank now corresponds to the shape of the drill head 2. The green body can be sintered.
The difficulty in the production of the drill head 2 is due to the high mechanical demands placed on the drill head 2, which allow only a very low level of porosity. A necessary density of the drill head 2 has to be greater than 98% of the theoretically achievable value. To this end, the green body has to have a density of at least 50% of the theoretical density before sintering. The sintering is accompanied by typical shrinkage, which sufficiently closes the pores starting from this value. Conventional processes involving compaction of the green body in a mold achieve these values. The loose joining together of the layers, in principle only by gravity, imposes new challenges here.
A promising approach is based on a powder mixture of tungsten carbide and cobalt oxide. The cobalt oxide is converted into cobalt after the formation of the green body. As liquid, the suspension contains water or alcohol, preferably isopropyl alcohol. The ratio of liquid to powder is in the range between 3 and 5 to 1. The suspension can be sprayed uniformly under pressure through a narrow nozzle. After spraying, the layer is dried at just above room temperature. The layers have a uniform thickness in the range between 20 μm and 30 μm. The adhesive is based on an aqueous solution of polyethyleneimine. Polyethyleneimine has a very high affinity for binding to the grains of the tungsten carbide. In this way, good adhesive bonding is achieved. The proportion by weight of polyethyleneimine in the solution can be in the range between 1% and 5%. After pressing, the adhesive is dried at just above room temperature. After the last layer has been applied, the adhesive is cured in a furnace at about 150 degrees Celsius (° C.). Subsequently, the excess powder is removed by water. The cobalt oxide in the green body is converted into cobalt in that the green body is kept in a hydrogen-containing atmosphere at 600° C. to 700° C. for several hours. Finally, the green body can be sintered at a temperature of between 1250° C. and 1400° C.
The iron-containing lower portion 21 of the base 13 can likewise be produced via three-dimensional shaping. For example, it is likewise possible for a green body to be pressed and subsequently sintered. Furthermore, for the production of steel bodies, processes such as laser build-up welding, selective laser melting (SLM) or selective laser sintering (SLS) are also possible.
Another embodiment of the drill head 39 is shown in
The intake passages 30 extend in a closed manner in the upper portion 41 of the base 13. The intake passages 30 are spaced apart both from the circumference of the drill head 2 and from the cutting edges 14. The course of the passages and the further properties thereof can correspond to the previous embodiment.
Another embodiment is shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 17178102.4 | Jun 2017 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/066259 | 6/19/2018 | WO | 00 |
