Connection for percussion drilling

A connection for use in percussion drilling includes a male coupling and a female coupling. Each coupling includes a body and a respective screw thread formed on a respective inner or outer surface of the respective body. Each thread has a thread-form including a crest, a root, a contact flank and a non-contact flank. Each thread-form has a contact flank angle and a non-contact flank angle inclined relative to a respective baseline located at a respective minor or major diameter thereof. Each non-contact flank angle is greater than the respective contact flank angle. The crest of each thread-form is inclined from the respective contact flank to the respective non-contact flank such that an apex of the respective thread-form defining a respective minor or major diameter thereof is located adjacent to the respective non-contact flank.

RELATED APPLICATION DATA

This application is a § 371 National Stage Application of PCT International Application No. PCT/EP2019/054455 filed Feb. 22, 2019 claiming priority to EP 18160853.0 filed Mar. 9, 2018.

FIELD OF INVENTION

The present disclosure generally relates to a wear resistant connection for use in percussion drilling.

BACKGROUND

CN103015913 relates to the technical field of drill rods, in particular to an exploration drill rod thread structure with a 12¾-inch ultra-large caliber. The exploration drill rod thread structure includes external threads and internal threads, wherein the external threads are composed of external thread units, the internal threads are composed of internal thread units, the external thread units are composed of first roots and external thread teeth, the internal thread units are composed of second roots and internal thread teeth, the shapes of the external thread teeth and the internal thread teeth mutually correspond, and the external thread teeth and the internal thread teeth are in an abnormal asymmetric structure.

EP 0 009 398/U.S. Pat. No. 4,295,751 discloses a coupling thread structure for percussion drill elements including a rod having an external thread, and a sleeve having an internal thread with the threads, when the sleeve and rod are coupled, having abutting and non-abutting flanks and with the flanks being joined by bottom and crest portions, wherein the threads have at least two starts; the abutting flanks are substantially straight along their whole abutting contact portions and form an angle of between 10° and 25°, preferably 15° to 20°, with the drill axis; the pitch angle of the threads is in the range 9° to 20°, preferably 11° to 16°; the crest portions are substantially straight and intersect the abutting flank portions at a well-defined edge; the non-abutting flanks have a flank angle which is considerably greater than that of the abutting flanks; the flank angle of the non-abutting flanks is in the range 50° to 80°, preferably 65° to 75°, with respect to the drill axis; and the bottom portions of the threads are curved.

EP 0 253 789/U.S. Pat. No. 4,861,209 discloses a threaded coupling for a high frequency percussion drill assembly including a rod and a sleeve having external and internal threads, respectively. The threads are of the asymmetrical type and make contact along opposing shoulder portions disposed on only one side of each crown portion. The threads have a maximum diameter from 30 to 40 mm, a pitch of 7 to 11 mm, and a height from 1.2 to 1.6 mm. The parts of the root and crown portions located immediate adjacent the contacting shoulder portions have radii from 3 to 5 mm.

EP 0 324 442/U.S. Pat. No. 4,799,844 discloses a screw structure provided for male and female threads having at least one thread extending helically along a cylindrical support member in spaced thread turns. A root portion extends between adjacent thread turns and has a curvature defined by a portion of an ellipse for providing improved stress reduction during periods of severe loading.

EP 2 710 217/US 2014/0083778 discloses a device in a drill string component for percussive rock drilling including a thread for threading together with another drill string component including a complementary thread. The thread includes a thread groove formed by two thread flanks and an intermediate thread bottom. In operation one of the flanks forms a pressure flank. The thread groove has an essentially equally shaped sectional form along its axial extension. The thread bottom exhibits at least three surface portions with part-circular shape, as seen in an axial section. The surface portions with part-circular shape have increasing radiuses, as seen from each thread flank to an intermediate surface portion of the thread bottom. Also a thread joint and a drill string component.

U.S. Pat. No. 4,040,756 discloses a thread structure for use in coupling percussion drilling extension rods minimizes the torque necessary to disconnect such extension rods. This is accomplished by beveling the crest portions of the cooperating thread structures. The direction of the bevel is such that the greatest intrusion of the crest portions into the complementary portions of the cooperating thread structure occurs immediately adjacent the abutting flanks thereof. The abutting flanks then wear in such a way that wedging is substantially avoided. Additionally, the root portions are defined by a continuously curved surface that smoothly extends into a flat surface defining the thread flanks so that fatigue stresses are minimized.

The prior art generally fails to take into consideration the performance of the threads as they become worn. Accordingly, it is desirable to provide an improved drill string thread for percussion rock drilling that does not suffer from the shortcomings of the prior art.

SUMMARY OF THE INVENTION

The present disclosure generally relates to a wear resistant connection for percussion drilling. In one embodiment, a connection for percussion drilling includes a male coupling and a female coupling. Each coupling includes a body and a respective screw thread formed on a respective inner or outer surface of the respective body. Each thread has a thread-form including a crest, a root, a contact flank and a non-contact flank. Each thread-form has a contact flank angle and a non-contact flank angle inclined relative to a respective baseline located at a respective minor or major diameter thereof. Each non-contact flank angle is greater than the respective contact flank angle. The crest of each thread-form is inclined from the respective contact flank to the respective non-contact flank such that an apex of the respective thread-form defining a respective major or minor diameter thereof is located adjacent to the respective non-contact flank.

Advantageously, as compared to the prior art discussed above, due to the inclined crests of the thread-forms, the contact flanks become enlarged in response to wear of the couplings. Further, pitting formed in regions adjacent to the contact flanks may be removed as a result of the wear.

The CN'913 application does not identify the contact flanks and the non-contact flanks. The EP '398 patent discloses a main embodiment where the threads have straight crests and an alternative where the crests are declined. The EP '789 patent discloses threads with semi-circular crests. The EP '442 patent discloses threads with straight crests. The EP '217 patent discloses threads with straight crests. The US '756 patent discloses threads with declined crests and teaches away from inclined crests by emphasizing the need for the declined crests to avoid wedging of the threads in the worn condition.

In one aspect of the embodiment, each contact flank angle ranges between 15 and 50 degrees and each non-contact flank angle equals the respective contact flank angle plus 5 to 30 degrees.

In another aspect of the embodiment, the inclination of each crest is arcuate with a radius greater than 10 percent of an outer diameter of the male coupling. In another aspect of the embodiment, the inclination of each crest is linear.

In another aspect of the embodiment, a height of each crest adjacent to the respective non-contact flank is 5 to 20 percent greater than a height of the respective crest adjacent to the respective contact flank.

In another aspect of the embodiment, each root is a first arc, and each contact flank is connected to the respective root by a respective second arc. Optionally, a first radius of each first arc is greater than a second radius of the respective second arc. Optionally, each first radius is at least 50 percent greater than the respective second radius, and each second radius is greater than five percent of an outer diameter of the male coupling. None of the prior art references discussed above disclose such a dual-arc configuration.

In another aspect of the embodiment, an area of the male thread-from is at least two percent greater than an area of the female thread-form.

In another aspect of the embodiment, each non-contact flank is connected to the respective crest by a respective arc.

In another aspect of the embodiment, an outer diameter of the couplings ranges between two and 16 centimeters.

In another aspect of the embodiment, each diameter is constant.

In another aspect of the embodiment, a drill rod for percussion drilling includes: a rod body; the female coupling integrally formed with or welded to a first end of the rod body; and the male coupling integrally formed with or welded to a second end of the rod body.

In another aspect of the embodiment, a drill string comprising a drill rod.

In another aspect of the embodiment, a drill rod for percussion drilling includes: a rod body; the female coupling integrally formed in a first end of the rod body; and the male coupling integrally formed in a second end of the rod body.

DETAILED DESCRIPTION

FIGS.1A and1Billustrate a male coupling1and a female coupling2for a percussion drill string, each coupling including a wear resistant screw thread1t,2t, according to one embodiment of the present disclosure. The percussion drill string may be formed by screwing together a plurality of drill rods (FIG.4) together along with a percussion drill bit3at one end and a shank adapter (not shown) at the other end. The drill rods may be screwed together using the male1and female couplings2. The drill string may be used for percussion rock drilling with a top hammer (not shown) or downhole hammer (not shown). If a downhole hammer is used, the hammer may have each of the wear resistant screw threads1t,2tfor assembly as part of the drill string.

The male coupling1may be attached, such as welded, to an intermediate rod body so as to form a longitudinal end of a drill rod. The female coupling2may be formed integrally with the percussion drill bit3. The male coupling1may have a tubular body with an outer diameter upper portion for connection to a lower end of the rod body, a reduced diameter lower portion having the external male thread1tformed in an outer surface thereof, and a shoulder is connecting the upper and lower portions. The male thread1tmay start at a first standoff distance from the shoulder1s. The male thread1tmay end at a second standoff distance from a bottom thereof. A guide portion, such as a conical surface, may be formed in the outer surface of the lower portion of the male coupling1between the end of the male thread1tand the bottom thereof. The upper portion of the male coupling1may have a plurality of wrench flats (not shown) formed in an outer surface thereof. The male coupling1may have a flow bore formed therethrough. An outer diameter of the couplings1,2may range between two and 16 centimeters.

The female coupling2may serve as the shank of the percussion drill bit3. The percussion drill bit3may further include a head. The head may have an outermost end defining a cutting face. The cutting face may have a plurality of sockets (only one shown) formed therein for receiving crushers (not shown). Each crusher may be a pre-formed insert mounted into the respective socket by interference fit or brazing. Each cutter may be made from a cermet material, such as a cemented carbide. The sockets and cutters may be spaced about the cutting face.

FIG.2illustrates the male1and female2couplings screwed together. The female coupling2may have a tubular body. The female coupling2may have the internal female thread2tformed in an inner surface thereof adjacent to the flow bore thereof. The flow bore may be sized to receive the reduced diameter lower portion of the male coupling1. The male coupling1may be screwed into the female coupling2until the shoulder1sabuts a top2pof the female coupling, thereby creating a metal-to-metal seal for isolating the flow bore and fastening the two members together. The female thread2tmay start at a first standoff distance from the top2p. The female thread2tmay end at a second standoff distance from a bottom of the female coupling2. The flow bore of the female coupling2may be in fluid communication with flow ports formed through the head of the drill bit. Each of the male1tand female2tthreads may be single threads.

FIG.3Aillustrates a thread-form4fof the female thread2t.FIG.3Billustrates a thread-form4mof the male thread1t. Each thread-form4m,fmay start at point XBand may include a root A1. Each root A1may be a concave arc with a respective radius R1and may extend to a respective second arc A2. Each second arc A2may be concave, have a respective radius R2, and may extend from the respective first crest A1to a respective contact flank E1. Each root radius R1may be greater than the respective second radius R2, such as at least fifty percent greater than the respective second radius. Each second radius R2may be greater than five percent of the outer diameter of the male coupling1. This dual arc configuration may significantly stress in the root region of the respective thread-form4m,4f. Each contact flank E1may be a straight line inclined at a respective first flank angle α relative to a respective baseline BL. The baseline BL may be longitudinal and be located at a respective major diameter DJor minor diameter DNof the respective thread1t,2t. Each first flank angle α may range between 15 and 50 degrees. Each contact flank E1may extend from the respective second arc A2to a respective third arc A3. Each third arc A3may be convex and have a respective radius R3.

Each third arc A3may extend from the respective contact flank E1to a respective crest A4. Each crest A4may have a respective first height H1adjacent to the respective third arc A3and a respective second height H2adjacent to a respective fifth arc A5. Each height H1,H2may be measured from the respective baseline BL. Each crest A4may be inclined from the respective contact flank E1to the respective non-contact flank E2such that a respective apex XAof the respective thread-form4m,4fdefining the respective major diameter DJor minor diameter DNis located adjacent to the respective non-contact flank. Each thread-form4m,4fmay have a respective peak line PL which may be longitudinal and be located at the respective major diameter DJor minor diameter DNof the respective thread1t,2t. Each diameter DN, DJof the respective thread1t,2tmay be constant. Due to the inclination of each crest A4, the respective second height H2may be greater than the respective first height H1. Each inclination may be accomplished by the respective crest A4being a convex arc with a respective radius R4. Each crest radius R4may be greater than ten percent of the outer diameter of the male coupling1. Each crest A4may extend from the respective third arc A3to a respective fifth arc A5. Each second height H2may be 5 to 20 percent greater than the respective first height H1.

Each fifth arc A5may be convex, may have a respective radius R5, and may extend from the respective crest A4to a respective non-contact flank E2. Each non-contact flank E2may be a straight line inclined at a respective second flank angle θ relative to the respective baseline BL. Each second flank angle β may be greater than the respective first flank angle α, such as 5 to 30 degrees greater than the respective first flank angle, thereby resulting in an respective asymmetric thread-form4m,4f. Each non-contact flank E2may extend from the respective fifth arc A5to a respective sixth arc A6. Each sixth arc A6may extend from the respective non-contact flank E2to a respective end point XE. Each sixth arc A6may be concave and have a respective radius R6. Each thread-form4m,4fmay have a respective pitch P defined by a longitudinal distance between the respective start point XBand the respective end point XE. Each pitch P may be greater than the outer diameter of the male coupling1.

An area of the male thread-from4mmay be at least two percent greater or even at least five percent greater than an area of the female thread-form4f. This enlargement of the male thread-form4mmay increase the service life of the drill rods since the male thread-form is usually determinative.

FIG.4illustrates a drill rod5having a female coupling6and a male coupling9, each coupling including a respective wear resistant screw thread6t,9t, according to another embodiment of the present disclosure. The drill rod5may be made from a metal or alloy, such as steel. The drill rod5may also be case hardened, such as by carburization. Each coupling6,9may be attached, such as welded7, to an intermediate rod body8so as to form longitudinal ends of the drill rod5. The drill rod5may have a flow bore formed therethrough. The drill rod5may have a length of 6 meters. An outer diameter of the couplings6,9may range between five and 15 centimeters.

A drill string may be formed by screwing together a plurality of drill rods5together (FIG.5) along with a drill bit at one end and a shank adapter at the other end. The drill bit and shank adapter may also have either of the wear resistant screw threads6t,9t. The drill string may be used for percussion rock drilling with a top hammer (not shown) or downhole hammer (not shown). If a downhole hammer is used, the hammer may have each of the wear resistant screw threads6t,9tfor assembly as part of the drill string.

Alternatively, the drill rod5may have a pair of male couplings9and a sleeve (not shown) having a pair of female couplings6may be used to connect a pair of drill rods together. Alternatively, the drill bit may be connected to the bottom drill rod using the couplings1,2. Alternatively, each coupling6,9may be formed integrally with the rod body8instead of welded thereto.

The male coupling9may have a tubular body with an outer diameter upper portion for connection to a lower end of the rod body8, a reduced diameter lower portion having the external male thread9tformed in an outer surface thereof, and a shoulder9sconnecting the upper and lower portions. The male thread9tmay start at a first standoff distance from the shoulder9s. The male thread9tmay end at a second standoff distance from a bottom thereof. A guide portion, such as a conical surface, may be formed in the outer surface of the lower portion of the male coupling9between the end of the male thread9tand the bottom thereof. The upper portion of the male coupling9may have a plurality of wrench flats (not shown) formed in an outer surface thereof. The flow bore in the upper portion may include a nozzle and a portion of a throat. The throat may extend through the shoulder4sand the lower portion.

FIG.5illustrates the male9and female6couplings screwed together. The female coupling6may have a tubular body with a lower portion for connection to an upper end of the rod body8. The female coupling6may have the internal female thread6tformed in an inner surface thereof adjacent to the flow bore thereof. The flow bore may be sized to receive the reduced diameter lower portion of the male coupling9of another drill rod. The male coupling9may be screwed into the female coupling6until the shoulder9sabuts a top6pof the female coupling, thereby creating a metal-to-metal seal for isolating the flow bore and fastening the two drill rods together. The female thread6tmay start at a first standoff distance from the top6p. The female thread6tmay end at a second standoff distance from a bottom of the female coupling6. The flow bore of the female coupling6may include a diffuser located adjacent to a lower end of the female thread6t. Each of the female6tand male9tthreads may be double threads.

Alternatively, each of the female6tand male9tthreads may be a single thread or triple threads. Alternatively, the male coupling9may be connected to an upper end of the rod body8and the female coupling6may be connected to a lower end of the rod body. In this alternative, the nozzle of the male coupling9would be a diffuser and the diffuser of the female coupling6would be a nozzle. Alternatively, any of the threads1t,2t,6t,9tmay be used to connect non-tubular members of the drill string.

FIG.6Aillustrates the male10mand female10fthread-forms of the second couplings6,9screwed together in a new condition. Each thread-form10m,10fof the respective second couplings6,9may be similar to the respective thread-forms4m,4fincluding the root, the crest, the contact flank, the non-contact flank, and the various arcs connecting the members. Each second thread-form10m,10fmay include the inclined crest and asymmetry of the respective thread-form4m,4fwithin the parameters discussed above. The pitch of each second thread-form10m,10fmay be less than that of the respective thread-form4m,fand the height of the apex of each second thread-form10m,10fmay be greater than that of the respective thread-form4m,4f.

FIG.6Billustrates the male10mand female10fthread-forms in a worn condition. Due to the inclined crests of each second thread-form10m,10f, the contact flanks E1may become enlarged in response to wear of the second couplings6,9. Further, pitting formed in regions G adjacent to the contact flanks E1may be removed as a result of the wear. The enlarged flanks may decrease contact pressure and, in conjunction with the removed pits, may decrease risk of failure.