ROCK DRILL AND METHOD FOR MANUFACTURING SAID ROCK DRILL

Abstract: The present invention relates to a rock drill (10) for percussive drilling, preferably an integral drill rod, which has a shank (12), a collar (14) connecting to one end of the shank (12), a rod portion (16), which at its one end connects to the collar (14) while the other end surface (17) carries rock cutting means (18), a central flush channel (22) which extends from the free end of the shank (12) and in direction towards said other end (17). The invention also relates to a method for manufacturing of a rock drill (10). Known integral drill rods are not adapted to modern technique, i.e. to automatic rigs. Known integral drill rods show among other the drawbacks that they do not flush away the drill dust in a satisfactorily manner, that the penetration rate relatively seen is low, that they become too hot and that they are difficult to blast inside in connection with manufacturing. The rock drill (10) according to the present invention is characterized by that the central flush channel (22) has a substantially constant diameter (d) along essentially its entire length and in that the diameter (d) of the flushing channel (22) relates to the diameter (D) of the rod portion (16) as 0.35</=d/D</=0.43.

Description: ROCK DRILL AND METHOD FOR MANUFACTURING SAID ROCK DRILL Technical area of the invention The present invention relates to a rock drill for percussive drilling, preferably an integral drill rod, which has a shank, a collar connecting to one end-of the shank, a rod portion, which with at one end connects to the collar while the other the end surface carries rock cutting means, a central flush channel which extends from the free end of the shank and in direction towards said other end. The invention also relates to a method for manufacturing a rock drill. Prior art Integral drill rods have been available on the market for a long time and are consequently outstanding mature products. The known integral drill rods are embossed by the technique which has been developed for hand held drills where safety for the operator has been the most critical requirement. Nowadays automatic rigs are used more and more, wherein the operator sits protected in a control hut. The known integral drill rods have not been much adapted to the change in the sense of the operational technique which the introduction of automatic rigs have brought. The drawbacks with known integral drill rods are inter alia that they do not flush away the drill dust in a satisfactorily manner, they have too low penetration rate, they become too hot and they are difficult that blast inside. Through the difficulty of blasting inside many burrs remain in the flush channel, which results in poor flushing, i.e. deficient cooling of the integral drill rod, which thereby becomes too hot, which in turn may result in fatigue breakdown. At manufacturing of known integral drill rods one has started from a blank which is provided with a predrilled longitudinal center hole of a certain diameter. The blank then has been annealed, whereafter the diameter of the center hole has been reamed, limited in the longitudinal direction, from the end where the shank is formed. The reason for reaming is that the drilled center hole in function as a flushing hole shall be able to receive a flushing tube projecting from certain drill machines with such a diameter that it cannot be contained in the original 11243DE 1998-08-11 2 longitudinal center hole of the blank. When the reaming of the longitudinal center hole is completed, i.e. the flush channel has been formed forging, drilling and milling operations of the shank/collar and the drill bit end are performed. The shank of a known integral drill rod is shown partly sectioned in the enclosed Fig. 0. Furthermore US-A-3,295,613 discloses a composite drill rod wherein separate portions are welded together. Objects and features of the invention The object of the present invention is to provide a rock drill of the above defined type, which is less expensive to manufacture than known integral drill rods. An additional object of the present invention is to achieve an improved performance compared to the known integral drill rods, i.e. the integral drill rod according to the present invention has a higher penetration rate compared to known integral drill rods. Said higher penetration rate is attained by the integral drill rod according to the present invention provides an improved flushing compared to known integral drill rods. The above-indicated objects are realized by a rock drill, which has obtained the characteristics indicated in the subsequent claims. Short description of the drawings In the drawings is: Fig. 0 a partly sectioned plan view of a shank of a known integral drill rod; Fig. 1 a partly sectioned plan view of a rock drill according to the present invention; Fig. 1 a a partly sectioned plan view of the shank of the rock drill according to Fig. 1 ; Fig. 2 a front view of the part of the rock drill according to the present invention which has at least one cutting insert; Fig. 3 a side view of the rock drill according to Fig. 2; Fig. 4 an end view of the end of the rock drill according to the present invention which has at least one cutting insert; Fig. 5 a longitudinal section through the rock drill according to Fig. 2, wherein the cutting insert has been left out; Fig. 6 a section along A-A in Fig. 3; and Fig. 7 a partly sectioned exploded view of a conical rod for rock drilling. * - - Detailed description of a preferred embodiment of the invention The rock drill 10 according to the present invention shown in Fig. 1 comprises a shank 12, a collar 14, a rod portion 16 and at least one cutting insert 18 provided at the free end of the rod portion 16, i.e. at the free rock cutting end surface 1 7 of the rock drill 10. The shank 12, the collar 14 and the rod portion 16 are performed in a blank as a one-piece unit. The shank 12 has a cross section which is adapted to the internal cross section of a drill sleeve (not shown) in a drill machine. Normally, the shank 12 has a polygonal cross section and in the shown embodiment the shank has a hexagonal cross section. The shank 12 according to the present invention is however in no manner limited to have a polygonal cross section. What however must apply is to the cooperating cross sections of the shank 12 and the drill sleeve are designed such that the shank 12, i.e. the rock drill 10, is rotated when the drill sleeve rotates. Also the rod portion 16 according to the preferred the embodiment has a hexagonal cross section. In Fig. 1 a a detail of the shank 12 of the rock drill 10 is shown, wherein is evident that a central flush channel 22 extends from the free end of the shank 12 and in direction towards the free rock cutting end 1 7 of the rock drill 10, see also Fig. 1 . In Figs. 2-4 are shown details in different views of the rock cutting end portion 1 7 of the rock drill 10 which carries the cutting insert 18. The cutting insert 18 in the shown embodiment is a chisel, which in a usual manner rests in a recess 20, see Fig. 5, and secured in said recess 20, preferably by soldering. From Fig. 5 is evident how a central flush channel 22, which is rotation symmetrical with respect to a first longitudinal central line 24 of the rock drill 10, extends longitudinally and terminates at a distance from the end surface 21 of the rod portion 16 and also at a distance from of the recess 20 bottom. Said flush channel 22 extends from the one end portion of the flush channel 22 shown in Fig. 5 through the entire rod portion 16 and further past the collar 14 and through the entire shank 12 until it opens into the free end of the shank 12, see Figs. 1 and 1 a. As shown in Fig. 5 a branch channel 26 extends in the " shown " - " embodiment from the central flush channel 22 and terminates in a recess 30 in the area of the end surface 21 of the rod portion 16. The branch channel 26 is rotation symmetrical with respect to a second longitudinal central line 28. The angle α between said second central line 28 and the first central line 24 lies within the interval of 20-30° with a preferred value for α of about 25°. Such as shown in Fig. 6 the central flush channel 22 has a diameter d along essentially its entire length while the rod portion 16 has a smallest diameter which is depicted by D. According to a preferred embodiment of the present invention a drill with an external smallest diameter D of 22 mm has a diameter d of 9,0 mm at the central flushing channel. These dimensions bring a relationship d/D = 0.41 , which is the preferred value inn said relationship. Within the limits of the invention will following relationship is valid: 0.35 < d/D < 0.43. The manufacture of the above described integral drill rod 10 is different from the manufacture of known integral drill rods, which concisely has been discussed under the title "Prior art" above. Both the integral drill rod according to the present invention and known integral drill rods originate from a blank, which has a predrilled longitudinal center hole. The distinguishing for the manufacture of the integral drill rod according to the present invention is that any annealing and reaming, along a limited longitudinal direction in the area of the shank, of the predrilled longitudinal center hole in the blank is not necessary. Instead the predrilled center hole is dimensioned such that the flushing tube present in certain drill machines can be received by said predrilled longitudinal center hole, i.e. the relationship (d/D) between the diameter of the predrilled longitudinal center hole and the external diameter of the drill is bigger than at known integral drill rods. Since neither annealing nor reaming of the predrilled longitudinal center hole is necessary the manufacture of an integral drill rod according to the present invention can be start directly by forging the shank/collar and then forging the drill bit end. In this connection shall be pointed out that when the shank/drill bit end is forged a mandrel (not shown) is placed in the central flush channel 22, said mandrel having a somewhat less diameter than the flush channel 22. During the forging operation the mandrel ensures that the diameter of the central flushing channel 22 is- not - " reduced too much, however a certain reduction is done, which is depicted at 23 in Figs. 1 and 1 a. The expression "... a substantially constant diameter (d) along essentially its entire length." used in claim 1 shall in this connection be given the interpretation that therein is comprised that the central flush channel 22 can exhibit the above described diametrical reduction 23. The subsequent steps of manufacturing are in principle the same as for known integral drill rods. In this connection however shall be noted the following. According to both prior art and the present invention the branch channel 26 has a somewhat less diameter than the central flush channel 22. The reason thereto is that if at drilling of the branch channel 26 exact centering of the second central line 28 of the branch channel relative to the first central line 24 of the central flushing channel 22 is not attained the circumference of the branch channel 26 at its connection to the central flush channel 22 will still be located inside the circumference of the latter. Also if this diametrical difference is maintained the branch channel 26 can have an actual size which is bigger than in a corresponding integral drill rod according to prior art since the central flush channel 22 of the integral drill rod according to the present invention is bigger than at a corresponding known integral drill rod. This is advantageous for the fall of pressure, see below. Since both the central flush channel 22 and the branch channel 26 have bigger absolute size than at corresponding known integral drill rods also the blasting of said channels is promoted and especially the transition between said channels where known integral drill rods often have burrs which disturb the transport of flushing medium. Through the added dimensions of channels the blasting becomes more efficient since the blasting material gets better accessibility. It is understood that the improved blasting leads to an improved transport of flushing medium, which in turn promotes cooling of the drill and thereby diminishes the risk for fatigue breakdown. - Function of the drill according to the invention The integral drill rod 10 according to the present invention is used at ~ sό called percussive drilling, i.e. an impact piston impacts on the free end of the shank 12 and a shock wave propagates through the drill to the free end of the rod portion 16 where the cutting insert 18 is located. The cutting insert 18 is thrown by the impact wave against the rock surface, whereby cutting of the same occurs. Rotation of the integral drill rod 10 occurs via the above described drill sleeve. Heat is generated at percussive drilling when the impact wave propagates through the rock drill 10 as well as drill cuttings when the cutting insert 18 machines the rock surface. Flush medium, air or water, is supplied under pressure at the free end of the shank 12 via the central flush channel 22 to cool the rock drill 10 and to flush away drill cuttings. The flush medium flows in the central flush channel 22 in direction towards the free end of the rod portion 16 and is deflected into the branch channel 26 to flow out from the recess 30 at the area of the free end of the rod portion 16, more exactly beside the cutting insert 18. The flush medium will during its flow in the central flush channel 22 and in the branch channel 26 cool the rock drill 10 while the flush medium when returning from the free end of the rod portion 1 6 transports drill cuttings. Since the relationship d/D for the present rock drill 10 is bigger than for known integral drill rods, i.e. the measure d has been increased while the measure D is maintained unaltered, a less fall of pressure is attained when flush medium is brought to flow through the central flush channel, which brings an improved cooling of the rock drill 10 compared to prior art. The reduced fall of pressure in the flush medium also brings an improved flushing away of the drill dust. The cross section of the branch channel 26 is bigger in actual size than at a corresponding integral drill rod according to prior art which is likewise favorable for the fall of pressure, i.e. the pressure drop is limited. Since the angle α (about 25°) has been given a smaller value as compared to at known integral drill rods a less deflection of the flush flow occurs when it flows from the central flush channel 22 to the branch channel 26. This means that the flush medium flow is not as interrupted as in known integral drill rods where a bigger deflection is at hand. This promotes enforcement of a low fall- * of pressure for the flush medium when it passes through the integral drill rod 10. To sum up, it can be stated that despite the fact that the increase of the value of the relationship d/D has brought that material has been removed from the drill compared to a corresponding drill according to prior art, i.e. the drill according to the invention has a reduced rigidity, any added propensity for example for fatigue breakdown has not been shown. One theory is that the improved flushing/cooling which the drill according to the present invention brings more than well from strength view compensates for the reduced rigidity. Conceivable modifications of the invention The invention has been described above with reference to a so called integral drill rod. The invention is however in no manner limited to such a drill. In Fig. 7 is shown in exemplifying but not limiting purpose a rock drill in shape of an so called conical rod 10' for percussive drilling, which likewise has a shank 12', a collar 14' and a rod portion 1 6' with a cone shaped end 1 7'. Said rock drill 10' is characterized by that the rod portion 16' and a drill bit 18' (cone bit) are joined via a conical joint, i.e. the cone shaped end surface 1 7' is received in a cone shaped recess 19' of the drill bit 18'. This means that the drill bit 18' can be exchanged when it is worn-out or needs regrinding. The invention is applicable also in this type of drill rod, i.e. the central flush channel (not shown) in the rock drill 10' has a substantially constant diameter along essentially its entire length. When it comes to possible diametrical reductions in connection with forging of the shank/collar the same applies as has been said above in connection with the integral drill rod.

Claims: Claims 1. A rock drill for percussive drilling, preferably an integral drill rod, which has a shank (12; 12'), a collar (14; 14') connecting to one end of theshank (12; 12 * ), ar.cT portion (16; 16'), which at its one end connects to the collar (14; 14') while the other end surface (17; 17') carries rock cutting means (18; 18'), a central flush channel (22) which extends from the free end of the shank (12; 12') and in direction towards said other end (17; 17'), said shank (12; 12'), collar (14; 14') and rod portion (16; 16') being performed as a one-piece unit, characterized i n that the central flush channel (22) has a substantially constant diameter (d) along essentially its entire length and in that the diameter (d) of the flushing channel (22) relates to the diameter (D) of the rod portion (16;16') as 0.35 < d/D < 0.43. 2. The rock drill according to claim 1, characterized i n that the relationship d/D is in the magnitude of 0.4. 3. The rock drill according to anyone of claims 1 or 2, which comprises at least one branch channel (26) which extends from the central flush channel (22) and terminates in the area of the free end surface (21) of the rod portion (16), wherein the central line (28) of the branch channel (26) forms an angle (α) with the central line (24) of the central flushing channel (22), characterized i n that said angle (α) lies within the interval of 20 < α < 30°. 4. The rock drill according to claim 3, characterized i n that said angle (α) is in the magnitude of 25°. 5. The rock drill according to anyone of the preceding claims, characterized i n that the branch channel (26) terminates in a recess (30) in the area of the free end surface (21) of the rod portion (16). 6. A method for manufacturing of a rock drill (10; 10') for percussive drilling, preferably an integral drill rod, said manufacture starting with the production 1 of a ~ ' blank having a predrilled, longitudinal center hole, characterized i n that the predrilled, longitudinal center hole during the production of the blank is given a diameter (d) which leads to the following relationship: 0.35 < d/D < 0.43, where D is the diameter of the rod portion (16; 16') of the rock drill (10; 10'), whereafter in a known manner forging, drilling and milling operations are performed on the blank for forming the shank/collar (12,14;12',14') and drill bit end or conical end of the rock drill (10; 10'). 7. The method according to claim 6, characterized i n that the predrilled, longitudinal center hole is given a diameter (d) which makes the relationship d/D approximately the same as 0.41. 8. The method according to claim 6 or 7, characterized i n that at drilling of the branch channel (26) its center axis (28) is brought to form an angle (α), in the interval 20 < α < 30°, with the central axis (24) of a central flush channel (22), which is formed by the predrilled, longitudinal center hole of the blank. 9. The method according to claim 8, characterized i n that said angle (α) is brought to assume a value of about 25°.

Inventors: ENGSTROEM HAAKAN, HEDLUND JAN-GUNNAR, PALMBERG GOERAN, ENGSTROEM, HAAKAN, HEDLUND, JAN-GUNNAR, PALMBERG, GOERAN
Applicants: SANDVIK AB, SANDVIK AB (PUBL)
Application year: 1998
Main classification: E21B17
IPC codes: E21B17