DRILL STRING ROD WITH GUIDANCE SHOULDER

Abstract

A drill string rod and a drill string assembly includes a drill rod and a drill bit. The rod includes a threaded male end and a female end. An axially extending shoulder is provided at the male end and has an axial length greater than an outside diameter of the shoulder to provide a shoulder driven rod exhibiting enhanced guidance to achieve straighter holes and better collaring.

Claims

1. A drill string rod to form part of a drill string, the rod comprising: a hollow elongate main length section extending axially between a male end and a female end, the male end including a spigot having a threaded section projecting axially from a shoulder that axially separates the spigot and the main length section, the shoulder having an outside diameter that is greater than an outside diameter of the main length section, wherein an axial length of the shoulder over which the greater outside diameter of the shoulder extends is greater than the outside diameter of the shoulder.

2. The rod as claimed in claim 1, wherein the outside diameter the shoulder is a maximum outside diameter of the rod.

3. The rod as claimed in claim 2, wherein the maximum outside diameter of the rod at the shoulder is uniform or approximately uniform over the axial length of the shoulder.

4. The rod as claimed in claim 1, wherein the female end includes a sleeve portion having an internal threaded section to cooperate with the threaded section of the spigot of a further drill rod of the drill string, an outside diameter of the sleeve portion being greater than the outside diameter of the main length section.

5. The rod as claimed in claim 4, wherein the outside diameter of the shoulder is equal to or approximately equal to the outside diameter of the sleeve portion.

6. The rod as claimed in claim 1, wherein the spigot extends axially from an annular end surface of the shoulder, an axial length of the spigot being configured such that the annular end surface of the shoulder is arranged to abut an annular end surface of the female end of a neighbouring rod of the drill string.

7. The rod as claimed in claim 1, wherein an axial length of the spigot is less than or equal to the axial length of the shoulder.

8. The rod as claimed in claim 1, wherein an outside diameter of the spigot is equal to or less than the outside diameter of the main length section along a full axial length of the spigot.

9. The rod as claimed in claim 1, further comprising an internal bore extending axially through the main length section and the spigot, the internal bore being of uniform internal diameter along a full axial length of the main length section and the spigot.

10. The rod as claimed in claim 1, wherein the threaded section includes at least one axially extending helical ridge and trough, wherein the outside diameter along the threaded section at radial positions of the ridge and trough is uniform over a full axial length of the threaded section.

11. The rod as claimed in claim 1, further comprising a transition section positioned axially at a junction of the main length section and the shoulder, wherein an outside diameter at the transition section changes according to at least one radius of curvature.

12. The rod as claimed in claim 11, wherein the outside diameter at the transition section decreases radially according to a first radius of curvature from the main length section to an intermediate section and the outside diameter increases radially according to a second radius of curvature from the intermediate section to the shoulder.

13. A drill rod assembly to form part of a drill string, the assembly comprising: a drill rod including a hollow elongate main length section extending axially between a male end and a female end, the male end including a spigot having a threaded section projecting axially from a shoulder that axially separates the spigot and the main length section, the shoulder having an outside diameter that is greater than an outside diameter of the main length section, wherein an axial length of the shoulder over which the greater outside diameter of the shoulder extends is greater than the outside diameter of the shoulder; and a drill bit releasably attachable to the male end of the drill rod; the drill bit having an axially forward cutting head and an axially rearward mounting sleeve to attach to the male end of the drill rod, wherein an outside diameter of the mounting sleeve is equal to or approximately equal to the outside diameter of the shoulder.

14. The assembly as claimed in claim 13, wherein the outside diameter of the mounting sleeve is uniform or approximately uniform over an axial length of the mounting sleeve being defined between a rearwardmost end of the drill bit and an axially forwardmost end of the mounting sleeve at which region the outside diameter of the mounting sleeve increases to form a junction with the cutting head.

15. The assembly as claimed in claim 14 wherein the axial length of the shoulder is approximately equal to or less than an axial length of the mounting sleeve.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0023] A specific implementation of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

[0024] FIG. 1 is an external perspective view of a drill string rod coupled to a percussion drill bit according to a specific implementation of the present invention;

[0025] FIG. 2 is a cross sectional view through the drill rod and bit assembly of FIG. 1;

[0026] FIG. 3 is a perspective view of a male end of the drill rod of FIG. 2;

[0027] FIG. 4 is a further perspective view of the male end of the drill rod of FIG. 2;

[0028] FIG. 5 is a perspective view of the male of the drill rod of FIG. 2 coupled to the drill bit of FIGS. 1 and 2;

[0029] FIG. 6 is a cross section through the male end and drill bit of FIG. 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION

[0030] Referring to FIGS. 1 and 2, a percussion drill rod 100 comprises an axially extending main length section 101 that is terminated at a first end by a male end indicated generally by reference 103 and at a second opposite end by a female end indicated generally by reference 102. Rod 100 is capable of being coupled end-to-end with adjacent rods to form a drill string. Male end 103 comprises a shoulder 110 that projects radially outward relative to main length section 101 and is formed as a cylindrical section extending over an axial distance being a fraction of the length of main length section 101. Similarly, female end 102 comprises a cylindrical sleeve section 111 having a length approximately equal to the axial length of shoulder 110. According to the specific implementation, an outside diameter of shoulder 110 and female sleeve 111 are approximately equal. A respective transition section 107 extends axially between main length section 101 and the respective shoulder 110 and female sleeve 111. Each transition section 107 comprises an axial length being slightly less than the axial length of shoulder 110 and female sleeve 111. Additionally, an outside diameter of each transition section 107 is less than the outside diameter of main length section 101 as described in further detail referring to FIG. 4.

[0031] FIG. 1 illustrates drill rod 100 releasably coupled to a drill bit indicated generally by reference 112 of conventional configuration. Drill bit 112 comprises an axially forwardmost drill head 105 that mounts a plurality of wear resistant cutting buttons 106 projecting axially forward from head 105. A mounting sleeve 104 extends axially rearward from head 105 and comprises an internal threaded cavity to receive a male part of male end 103. In particular, and referring to FIG. 2, male end 103 comprises a spigot 204 that projects axially forward from shoulder 110 and in particular an annular abutment surface 108 that represents a forwardmost end of shoulder 110. Abutment surface 108 is positioned in contact with an annular endmost contact surface 109 of drill bit sleeve 104. According to the specific configuration, an axial length of spigot 204 is less than a corresponding axial length or depth of a cavity within bit sleeve 104 such that the present drill rod 100 is configured as a shoulder contact or shoulder driven rod. Accordingly, the shockwave generated by the surface piston is translated through mated surfaces 108, 109 from rod 101 into drill bit 112. In particular and referring to FIGS. 3 and 6, an annular endmost surface 303 of spigot 204 is separated axially from the innermost end 600 of the internal cavity within bit sleeve 104 to provide the shoulder contact configuration. As detailed in FIG. 6, releasable mating of rod 100 and bit 112 is achieved by cooperating screw threads 301, 302 projecting radially at spigot 204 and threads 601 projecting radially within the internal facing surface of the bit sleeve cavity.

[0032] Referring to FIG. 2, the female end 102 of rod 100 comprises an internal cavity 200 extending axially within sleeve 111 from an axially rearward end surface 202. End surface 202 of a first rod is configured to contact the shoulder abutment surface 108 of the male end 103 of a second rod when multiple drill rods 100 are coupled together end-to-end to form the drill string. Screw threads 201 are provided at the internal facing surface of sleeve cavity 200 and are configured to cooperate with the spigot threads 301, 302 of a neighbouring rod 100. An internal bore 203 extends axially through rod 100 and in particular axially from female cavity 200 to the annular end surface 303 of spigot 204. According to the specific implementation, bore 203 comprises an internal diameter that is substantially uniform over its entire axial length between the male 103 and female 102 ends.

[0033] Referring to FIG. 3 spigot 204 projects axially from the annular abutment surface 108 that extends substantially perpendicular to the cylindrical external surface at shoulder 110. Spigot 204 may be considered to be divided axially into threaded section 301, 302 and a non-threaded shank 300 that is positioned axially intermediate threaded section 301, 302 and shoulder 110. Shank 300 is flared radially outward relative to a longitudinal axis 305 of rod 100 at the junction 304 with annular abutment surface 108 such that the external surface of the shank 300 at the shoulder junction 304 increases according to a radius of curvature.

[0034] The threaded section of spigot 204 comprises a pair of helical ridges 302 that define axially intermediate troughs 301 extending between shank 300 and the annular spigot end surface 303. Referring to FIG. 4, an axial length L.sub.B of spigot 204 including shank 300 and threaded section 301, 302 is less than an axial length L.sub.A of shoulder 110. Shoulder length L.sub.A is defined axially between annular abutment surface 108 (aligned perpendicular to axis 305) and an axially rearwardmost part of shoulder 110 at which the outside diameter of rod 100 decreases and is no longer uniform in the axially rearward direction from annular abutment surface 108. In particular, the rearward end of shoulder 110 is terminated by transition section 107. According to specific implementations, the axial length L.sub.B may be in the range 60 to 100% or 75 to 85% of the axial length L.sub.A.

[0035] Section 107 may be considered to be divided into three axial regions including a first region 401 bordering main length section 101, a second region 402 bordering the rearward end of shoulder 110 and an intermediate region 400 positioned axially intermediate the first and second regions 401, 402. An outside diameter of rod 100 at the first transition region 401 decreases radially according to a first radius of curvature (relative to main length section 101). The outside diameter of rod 100 is substantially uniform over intermediate region 400 and then increases radially according to a second radius of curvature at second region 402. Accordingly, the outside diameter of rod 100 at transition section 107 is formed as an axially broad groove or slight depression positioned axially between main length section 101 and shoulder 110. The radially curved transition 304 minimises stress concentrations at the junction of spigot 204 and shoulder 110. Additionally, the radius of curvature at second transition region 402 minimises stress concentrations at the axially rearward end of the shoulder 110 and the junction with main length section 101.

[0036] Shoulder 110 comprises an outside or external diameter D.sub.A being approximately equal to the outside diameter of female sleeve 111 at female end 102. Outside diameter D.sub.A represents the largest outside diameter section of rod 100 along its entire axial length. A corresponding outside diameter of spigot 204 at the threaded section corresponding to a radial position at the peak of each helical ridge 302 is represented by D.sub.C when D.sub.C is less than D.sub.A. In particular, and according to specific implementations, D.sub.C may be in the range 60 to 100% or 75 to 85% of D.sub.A. Additionally, an external diameter D.sub.B of main length section 101 is less than the outside diameter D.sub.A of shoulder 110 and according to specific implementations D.sub.B is 70 to 100% or 85 to 99% of D.sub.A.

[0037] The enhanced drilling guidance and the capability of drilling straighter holes at increased rate is provided by the axial length of shoulder L.sub.A being greater than the outside diameter of shoulder D.sub.A. When rod 100 is coupled to the drill bit 112 as illustrated in FIGS. 1 and 2, shoulder 110 effectively provides an axial extension of bit sleeve 104. In particular, and referring to FIG. 5, an outside diameter D.sub.E of bit sleeve 104 is substantially equal to the outside diameter D.sub.A of shoulder 110 such that the two cylindrical sections 104, 110 collectively define a single cylinder extending between bit head 105 and transition section 107 having a uniform diameter D.sub.A, D.sub.E over its entire axial length being the combination of L.sub.A and the axial length of the bit sleeve L.sub.C. It follows therefore that the shoulder axial length L.sub.A is greater than the outside diameter D.sub.E of bit sleeve 104.

[0038] Shoulder 110 effectively provides a linear extension of bit sleeve 104 that reduces the possible deviation angle of the bit 112 and male end 103 of rod 100 as it is both inserted and extracted from the hole. That is, any bending or lateral deviation, perpendicular to axis 305 within the bore at the region of bit 112 is reduced and is effectively restricted by the axial length L.sub.A of shoulder 110 and in particular the axially rearward end of shoulder 110 contacting the internal surface of the bore. According to the specific implementation, an axial length L.sub.C of bit sleeve 104 is defined between the annular contact surface 109 (at the axially rearward end of bit 112) and the axially forwardmost sleeve end 500 at which the outside diameter D.sub.E increases to form the radially enlarged drill head 105. According to specific implementations, bit sleeve axial length L.sub.C may be in the range 60 to 100% or 75 to 95% of the shoulder axial length L.sub.A.