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 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). Rotary 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 rotating the bit at about 250-300 rpm during drilling. The impact frequency is about six (6) blows for each one (1) revolution. Using pneumatic power, this equates to about 2100-2200 blows per minute; and a much higher impact frequency of 7000 to 8000 striking blows per minute 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 percussion drill bits are 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. This has led to drill bit redesign using more and bigger tungsten carbide 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.
In yet another aspect of the invention, an insert for a percussion drill bit comprises a cylindrical portion and a domed cutting surface. The cylindrical portion extends along an axis and has a diameter about the axis. The domed cutting surface forms an axial end of the insert and comprises polycrystalline diamond. The cutting surface has a tip radius where the axis intersects the cutting surface. The tip radius and the diameter define a tip radius-to-diameter ratio. The tip radius-to-diameter ratio being is between 0.3 and 0.4.
In another aspect of the invention, a percussion drill bit is configured and adapted to drill a hole in rock and comprises an insert. The insert has a cylindrical portion and a domed cutting surface. The cylindrical portion extends along an axis and has a diameter about the axis. The domed cutting surface forms an axial end of the insert and comprises polycrystalline diamond. The cutting surface has a tip radius where the axis intersects the cutting surface. The tip radius and the diameter define a tip radius-to-diameter ratio. The tip radius-to-diameter ratio is between 0.3 and 0.4.
In still another aspect of the invention, a percussion drill bit is configured and adapted to drill a hole in rock of a given diameter. The drill bit comprises a body having shaft and head portions. The drill bit also comprises at least one insert. The insert comprises a domed cutting surface that comprises polycrystalline diamond. The insert is rigidly attached to the head portion of the drill bit. The insert further comprises a cylindrical portion having a diameter. The diameter of the cylindrical portion is greater than the diameter of hole multiplied by 0.2.
These and other objects and advantages of the invention will become more apparent from the drawing figures and 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.
FIG. 9 is a side view of an embodiment of a PCD insert for use in percussion drill bits, with the PCD coating represented by the diamond pattern.
FIG. 10 is a top plan view of percussion drill bit that comprises the PCD insert shown in FIG. 9
FIG. 11 is cross-sectional view of the drill bit shown in FIG. 10 taken about the line 11-11 of FIG. 10.
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 press-fit 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.
An embodiment of a PCD insert in accordance with another aspect of the invention is shown in FIG. 9. This insert 200 comprises a cylindrical portion 202 and a domed cutting surface 204. The cylindrical portion 202 extends along an axis “c-c” and has a diameter “D1” about that axis. The domed cutting surface 204 forms an axial end of the insert and comprises polycrystalline diamond 206. The domed cutting surface 204 has a radius “R1” at its tip or apex (i.e. where the axis intersects the cutting surface). This tip radius and the diameter of the cylindrical portion 202 define a tip radius-to-diameter ratio. That ratio is preferably between 0.3 and 0.4, and more preferably between 0.33 and 0.35 For example, the insert 200 may have a tip radius of 0.15 inches and a diameter of 0.44 inches. Preferably the domed cutting surface 204 of the insert 200 comprises a first surface portion 208 that has a constant radius equal to the tip radius, a second surface portion 210 that has a shape defined by an arc of a constant radius “R2” revolved about the axis of the insert, and a third surface portion 212 that is frustoconical in shape. The constant radius arc that defines the shape of the second surface portion 210 preferably has a radius that is greater than the tip radius. For example, the radius of the arc may be 0.70 inches. The second surface portion 210 preferably tangentially meets the first surface portion 208 and the third surface portion 212. The third surface portion 212 extends from the cylindrical portion 202 to the second surface portion 210.
A head-on view of a percussion drill bit 214 that comprises the insert 200 shown in FIG. 9 is shown in FIGS. 10 and 11. The drill bit 214 comprises a shaft portion 216 and a head portion 218. The head portion 218 comprises a central portion 220 and a pair of wing portions 222. The wing portions 222 protrude radially from the head portion 218 in opposite directions (left and right as shown). As shown, the drill bit 214 comprises six of the PCD inserts 200, and many of the features of the other drill bit embodiments described above. Each of the wing portions 222 comprises two of the inserts 200 protruding therefrom. Those inserts 200 constitute the gauge-cutting inserts and also overlap the central portion 220 of the head portion 218 of the drill bit 214 in manner such that they also protrude from the central portion. The two remaining inserts 200 protrude axially from the head portion 218 and constitute the core-cutting inserts. These two core-cutting inserts 200 are preferably non-symmetrically spaced form the center axis. This drill bit 214 is preferably configured to cut a hole having a 2.0 inch bore diameter. The diameter of the cylindrical portion 202 of each of the gauge-cutting inserts 200 is preferably greater than the bore diameter of hole multiplied by 0.2. For example, with a 2.0 inch bore drill bit 214, the diameter of the cylindrical portion is preferably 0.44, making it 0.22 times the diameter of the gauge diameter of the hole. Preferably, the tip of each insert 200 extends approximately 0.33 inches from the head portion 218 of the drill bit 214. The drill bit 214 also preferably comprises a plurality of water holes 224 for clearing crushed rock. Some of the water holes 224 exit from the central portion 220 of the drill bit 214, and some from the flutes 226 that lie between the wing portions 222 of the drill bit.
When in use, the drill bit 214 thrust pressure is preferably kept below a maximum value depending upon the gauge diameter of the drill bit. For a bit having a gauge diameter in the range of 1.75 inches to 2.5 inches, the thrust pressure on the drill bit is preferably maintained at or below 363 psi while drilling, and more preferably at or below 290 psi. For a bit having a gauge diameter in the range of 1.375 inches to 1.625 inches, the thrust pressure on the drill bit is preferably maintained at or below 290 psi while drilling, and more preferably at or below 218 psi. Using the drill bit in this manner, the drill bit will cut on average approximately 35% faster than a new carbide drill bit operated at higher thrust pressures. Moreover, the drill bit will cut on average approximately 50% faster than a worn carbide drill bit operated in a conventional manner. Unlike conventional carbide bits, the insert of the drill wear several orders of magnitude less during use. Moreover, unlike other PCD drill bits, the drill bits of the present invention do not chip when used as described above. As such, the performance advantages achieved by the drill bits of the present invention far outweigh the higher cost of such bits as compared to conventional carbide drill bits.
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.
Patent Application
20100025114
