PCD PERCUSSION DRILL BIT

Abstract

The invention is embodied in a percussion drill bit which comprises a steel body with a working front head portion having a front central zone and plural wing zones radiating from the central zone and being spaced at the outer circumferential edges thereof; first gauge-cutting PCD inserts are secured in the wing zones to extend forwardly at an angle relative to the axis of the bit, and of at least one second core-cutting PCD insert is non-axially secured to extend forwardly from the central zone.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a non-provisional of U.S. application Ser. No. 61/022,614, filed Jan. 22, 2008, the entire disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to rock drill bits, and more particularly to rotary percussion drill bits having PCD inserts constructed and arranged for improved performance and duration of the drill bit in rock crushing and boring operations.

As used in the following disclosure and claims, the term “polycrystalline diamond” and/or its abbreviation “PCD” refers to a material formed of diamond crystals fused or sintered under high pressure and temperature into a predetermined layer or shape. The PCD material is permanently bonded to a substrate of tungsten carbide (WC) in a cobalt binder or like carbide matrix, also known in the art as “precemented carbide” to form a PCD insert. Also, as used herein, the term “high density ceramic” or its abbreviation “HCD” refers to a mining tool having an abrasive working insert embodying a PCD layer.

2. Description of the Prior Art

The three basic ways of drilling bores in rock and earthen formations are rotary, percussion (or impact) and rotary percussion (or rotary impact). Percussion drilling is typically carried out by driving the drill bit into the rock work surface in a reciprocating manner at a striking or impact force of about 300-500 ft/lbs and also rotated at about 250-300 rpm during drilling. The impact frequency is about six (6) blows for each one (1) degree of rotation. Using pneumatic power this will equate to about 2100-2200 blows per minute; and a much higher impact frequency of 7000 to 8000 striking blows if using hydraulic power. Thus, rotary percussion drilling is carried out by reciprocatingly driving the drill bit to crack and crush the rock and rotating the bit to cut away and remove the crushed rock from the developing bore hole.

A principal problem encountered in using prior art percussion drill bits (as in rotary cutting tools), is the rapid wear and high cost of continual replacement along with machine down-time for changeover or replacement of these inefficient bits coupled with the hazardous safety risks involved in hammering off the worn bits for replacement with new ones. Typically prior art tools have only been made with tungsten carbide inserts because it is a cheap and easily worked material, but such tools result in rapid failure due to wear and breakage—particularly in percussion drilling. This has led to drill bit redesign using more and bigger WC inserts, which in turn generally generates higher dust levels and other health problems.

SUMMARY OF THE INVENTION

One aspect of the invention is embodied in a percussion drill bit for drilling bore holes in hard rock (minerals) which comprises a steel body having a working front head portion and a rearward shank portion for connection to an impact driving force, the head portion having a front facing central zone and plural side wing zones extending radially from the central zone and spaced apart at the outer circumferential edges thereof by grooves in the outer wall of the front head portion, first gauge-cutting PCD inserts are secured in at least two of said side wing zones of the steel body and are constructed and arranged to extend forwardly and outwardly at an angle to the axis of the bit and be operable for forming the bore hole, at least one second PCD insert is non-axially secured in the central zone and projects forwardly of the first PCD inserts and is operable for impact at the core area of the bore hole to pilot the boring effort of the first PCD inserts.

In another aspect of the invention the head portion of the steel body is armored with a hard cladding material tougher than the steel body to thereby reduce outer body wear at the side wing zones and to thereby prolong the PCD insert integrity and provide a substantially longer drill bit life.

These and other objects and advantages of the invention will become more apparent from the following description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings which form a part of the specification and wherein like numerals refer to like parts wherever they occur:

FIG. 1 is a perspective view of a first embodiment of a percussion drill bit according to the invention;

FIG. 2 is a side elevational view of the first embodiment, partly broken away to show a PCD insert socket;

FIG. 3 is another side elevational view, as rotated 90° from the FIG. 2 position, and broken away to show flushing fluid distribution;

FIG. 4 is a top plan view of the first embodiment;

FIG. 5 is a cross-sectional view taken substantially along line 5-5 of FIG. 4;

FIG. 6 is a greatly enlarged diagrammatic and fragmentary view illustrating the geometry of the working head portion of the first embodiment;

FIG. 7 is a side elevational view of a second embodiment of the invention with portions broken away to show side wall cladding; and

FIG. 8 is a section similar to FIG. 5 and showing a metal cladding of the head portion front face.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-6 show a first embodiment of a percussion rock drill bit of the present invention, generally designated 10. The drill bit includes a steel body 12 having a working head portion 14 and a rearward shank portion 16 with a common central axis “a-a” (FIG. 6). The shank portion 16 has a central bore 20 with an internal rope thread 21 for threaded connection to a hammer driven drill string apparatus (not shown). The central bore 20 connects to three flushing channels 22 constructed and arranged to direct flushing and cooling fluid through the head portion 14 and around the front facing surface 23 thereof. The front surface is generally perpendicular to the central axis “a-a” (as shown by reference line “b-b” in FIG. 6).

The circumference of the front facing head portion area is larger than the circumference of the shank portion 16 whereby the outer side wall 24 of the head portion 14 tapers inwardly from the front circumference down to the shank portion 16 about 8° (as shown in FIG. 6). It will be understood that the taper may be other than 8° within the scope of the present invention. The head portion 14 is provided with three vertical and elongate grooves or channels 25 that are symmetrically spaced around the circumference and extend vertically toward the shank portion 16 and which define therebetween three symmetrically spaced wing zones 27. It will be clear that these wedge-shaped grooves 25 are constructed to receive the flushing fluid ported from the passageways 22 and channel it toward the working front face (23) of the head portion 14 as well as providing a flow path for removing the rock chippings (not shown) as the bore hole is being formed.

The head portion 14 is provided with three first or primary gauge-cutting PCD inserts 30 symmetrically spaced from each other and secured in primary sockets 38 into the wing zones 27. The head portion 14 also is provided with second or secondary PCD inserts 31 constructed and arranged as core-cutters in a central zone 33 of the front face (23). Three such second PCD inserts are shown in the preferred embodiment of FIGS. 1-6, and these are asymmetrically and non-axially arranged in secondary sockets 45 in the central zone 33 at the front of the head portion 14. The circumferential area 35 of the front face of the tool extending radially outwardly from around the central zone 33 is sloped axially rearwardly (or downwardly in the drawings) at an angle of about 15° to 35°, and preferably about 22° to 26° (see “h” in FIG. 6). The head portion 14 is provided with the three primary sockets 37 formed in each of the wing zones 27 and extending into the steel body 12 on axes substantially perpendicular to the slope of the wing zone surface 35, and these sockets 37 are slightly smaller (i.e., about 0.002 inch) than the base diameter of the first PCD inserts 30 whereby the pressfit of the inserts under about 5 tons of force provides a secure seating of the inserts 30 in the sockets 37 through it will be noted that the first gauge-cutting PCD inserts 30 in the first embodiment are larger than the second core-breaking PCD inserts 31. The first PCD inserts 30 will typically have a main body of tungsten carbide with a cylindrical base section 42 and a domed working end 39 capped with a parabolic or bullet-shaped domed crown 40 of PCD material (see FIG. 5). When assembled the base section 42 is deeply seated in the socket 37 of each wing zone 35 and the cylindrical wall extends beyond the sloping head portion surface about 1/16 inch (at 41) so that the gauge-cutting PCD crown caps 40 are precisely set at a predetermined position (see “e-e” of FIG. 6) in front of the front face “b-b” of the head portion 14.

The secondary core-cutting PCD inserts 31 have essentially the same configuration as the first PCD inserts 30, although they have a smaller diameter in the preferred first embodiment. The coring PCD inserts 31 are set in sockets 45 formed in the central zone 33 of the front face (23) and are non-symmetrically and non-axially arranged to impact against different adjacent core areas as the bore hole is being formed. The secondary PCD inserts 31 are also set to extend forwardly of the front face (23), but in an axial direction and to a precise spaced distance (plane “d-d” in FIG. 6) that is beyond the plane “e-e” of the gauge-cutting PCD inserts 30. As shown in FIGS. 1-3, the central zone 33 may be formed as an elevated or raised platform having a side wall 43. Thus, in operation, it will be clear that the core-cutting PCD inserts 31 initiate or pilot the bore hole formation by breaking a smaller central core area thereof followed by the gauge-cutting action of the first PCD inserts 30 to complete the full bore hole drilling. Clearly the flushing fluid carries away the loose chippings as the hole is formed as well as cools the diamond inserts 30, 31 to prevent overheating thereof. It will be understood that a wide variance of non-symmetrical coring insert arrangements can be made, and that having a side wall 43 larger diameter inserts 31 may be used on larger sized boring tools 10.

The geometry of the PCD inserts 30 and 31 in their sockets 37 and 45 can best be seen in FIGS. 5 and 6. This geometry contributes to the integrity of the drill-bit, 110 and prolongs its useful life; and includes the angular relationship between the primary sockets 37 and the secondary sockets 45 and the depth thereof in the head portion 14 of the drill bit. As shown, the primary sockets 37 extend deepest (at 38) into the tool body 12. The primary PCD inserts 30, extend outwardly at an angle to the axis of the drill bit but are arranged to produce a reaction force vector in an axial direction to push these primary inserts 30 more firmly into these sockets 37. The secondary sockets 47 for the core-cutting PCD inserts 31 extend in an axial direction, but the bottoms 46 thereof are above the deeper primary sockets 37 and have no negative influence thereon. It may also be noted that the spherical cutting face of the respective PCD inserts distribute impact forces through the insert bodies, and further that the PCD layer itself does not wear out.

As shown best in FIGS. 1 and 4, the central zone 33 is shown as a circular area that is axially centered and is also shown as a raised platform having a side wall 43 of a minor dimension. The distance that the contact point of the core-breaking inserts extends forwardly of the crown of the gauge-cutting inserts is at least as large as the platform elevation. It will be understood that the central zone 33 of the front face 23 may be a different shape such as a triangle, trapezoid or pentagon that will help to define selected non-asymmetrical locations for orientation of multiple cone-cutting inserts 31 without interference with the seating sites (primary sockets 37) for the gauge-cutting inserts 30. In other words, the raised platform 43 facilitates the location of secondary sockets in an axial direction away from the angularly related sockets 37 for the outer PCD inserts but without direct interference or compromising their structural integrity or the press-fit strength thereof.

Referring to a second form of the invention shown in FIGS. 7 and 8, the steel body 112 at the head portion 114 of the drill bit 110 can be strengthened to better obviate erosion and wear of the head portion surface areas if reinforced by a harder metal cladding 150. It will be appreciated that parts of the drill bit 110 corresponding to drill bit 10 will are given the same reference numeral, plus “100.” The use of exotic steels alloyed with chromium carbide or vanadium carbide would provide the toughest steel bodies for percussion tools, but at great expense. The present invention contemplates bonding a chromium or chromium alloy jacket 150 over the entire head portion 114 of the tool 110. This chromium cladding layer 150 would have a thickness in the range of 0.005 to 0.010 inches and be tempered to a Rockwell hardness of at least 60 Rc and preferably 65-68 Rc. In manufacturing the drill tool 110, the sockets 137 and 145 for the first and second PCD inserts 130 and 131 will be formed after cladding process is completed.

Although the present invention has been described with reference to the preferred embodiments, it will be apparent to those skilled in the art that changes and modifications not specifically disclosed can be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A percussion drill bit for drilling bore holes in hard rock and mineral, comprising:

(a) a steel body having a working front head portion and a rearward shank portion for connection to an impact driving force;

(b) said head portion having a front facing central zone and plural wing zones extending radially from the central zone and being spaced apart at the outer circumferential edges thereof by grooves in the outer wall of the front head portion;

(c) a first gauge-cutting PCD insert secured in the steel head portion of at least two wing zones and being constructed and arranged to extend at a predetermined angle to the axis and have a gauge-cutting PCD surface operable for forming the bore hole dimension; and

(d) at least one second PCD insert non-axially secured in the central zone to project forwardly of the first PCD inserts and being operable for impact at the core area of the bore hole to pilot the boring hole effort of the first PCD inserts.

2. The drill bit of claim 1 in which the head portion has an outer side wall that tapers inwardly from the circumferential edges of the wing zones to the shank portion of the steel body.

3. The drill bit of claim 1 wherein there are three side wing zones each having a first gauge-cutting PCD insert secured therein.

4. The drill bit of claim 3, in which there are plural second core-cutting PCD inserts projecting forwardly from the central zone and being asymmetrically and non-axially disposed.

5. The drill bit of claim 4, in which the wing zones have front faces sloping at a predetermined angle rearwardly from the front facing central zone to the outer circumferential edge of the head portion, and a primary socket extending into each sloping front face and being recessed normal thereto for seating said first gauge-cutting PCD insert therein.

6. The drill bit of claim 5, wherein the sloping surfaces of the side wing zones are formed at an angle in the range of 15° to 35° relative to a plane perpendicular to the axis of the drill bit.

7. The drill bit according to claim 6 wherein the gauge cutting inserts have cylindrical body sections and parabolic head sections, the cylindrical body sections being press-fit into said first sockets to a depth of about 0.250 to 0.390 inches.

8. The drill bit according to claim 7 in which the cylindrical body sections extend outwardly from the sloping surface of each side wing zone to space the domed head sections of these inserts forwardly of the plane of the front facing central zone.

9. The drill bit according to claim 8, wherein there are at least two second PCD inserts non-axially secured in the front facing central zone and extending forwardly from the plane thereof.

10. The drill bit of claim 9, wherein the central zone lies on a plane perpendicular to the axis of the drill bit, and second socket means formed in the central zone for seating the second PCD inserts therein.

11. The drill bit according to claim 10 wherein the first and second socket means are formed in said head portion to open outwardly at the wing zones and front-facing central zone on different radius lines from the axis of the drill bit.

12. The drill bit according to claim 11 wherein said first and second socket means are formed to extend into said head portion and have bottoms that are offset axially from each with the bottoms of the first socket means being below the bottoms of the second socket means.

13. The drill bit according to claim 10 in which the second PCD inserts are constructed and arranged as core-cutters for the bore hole being formed, the second PCD inserts having parabolic working surfaces extending forwardly beyond the parabolic head sections of the first PCD inserts.

14. The drill bit of claim 3 in which said head portion of said steel body is armored with a hard cladding material tougher than the steel body to thereby reduce outer body wear at the side wing zones and thereby prolong the PCD insert integrity with a substantially longer drill bit life.

15. The drill bit of claim 14, in which the hard cladding material covers the front face of the head portion around the first and second PCD inserts and circumscribes the outer side wall of the head portion.

16. The drill bit of claim 15 in which the hard cladding material includes chromium (CR) and is plated to a hardness of at least 60 Rc and a thickness in the range of 0.001 to 0.030.

17. The drill bit of claim 16 in which the plated chromium material has a Rockwell hardness of 65 to 68 and a thickness in the range of 0.005 to 0.015.

18. A percussion drill bit comprising:

(a) a head portion having a front-facing central zone and multiple wing zones radiating symmetrically therefrom and being spaced apart at the outer circumferential edges thereof;

(b) first gauge-cutting PCD inserts secured in at least two of said wing zones and being constructed and arranged to extend angularly relative to the axis of the drill bit and being operable for forming the fore hole dimension; and

(c) at least one second PCD insert non-axially secured in the central zone to project forwardly of the first PCD inserts and being operable for piloting the bore hole formation.

19. The drill bit of claim 18, in which said first and second PCD inserts are seated in primary and secondary angularly related socket means extending into the head portion, said primary socket means being deeper than said secondary socket means.

20. The drill bit of claim 18 wherein the first PCD inserts are relatively large and sized to do the principle drilling work while the smaller second PCD insert initiate the bore-hole and then work in conjunction with the first PCD inserts.

21. The method of making an armored percussion bit with PCD inserts

(a) forming a steel bit body having a shank portion and a working head portion with a central zone and plural spaced wing zones extending radially from the central zone and being separated circumferentially by spaced grooves in the outer head portion wall;

(b) bonding a hard cladding material to cover the exposed surface areas of the head portion;

(c) boring the shank portion axially to provide a threaded means for connecting the drill bit to an impact driving force, and providing axial passageways for flushing fluid;

(d) boring the head portion to provide flushing fluid passages from the axial passageway to each of the spaced grooves in the outer head portion wall

(e) forming sockets through the hard cladding material into the central zone and wing zones of the head portion to accommodate PCD inserts; and

(f) press fitting the PCD inserts into the sockets.

22. The method according to claim 21, in which the cladding material comprises chromium.

23. The method according to claim 21 including the step of constructing and arranging the PCD inserts so that the central zone PCD inserts project forwardly of the wing PCD inserts whereby to initiate and pilot the bore hole drilling operation.