GB2108554A - Improvements in drag bits - Google Patents

Abstract

Disc-type diamond compacts (60), metallurgically bonded to a tungsten carbide insert stud (52), are interference fitted into holes (58) formed in a face of a drag bit (12). To inhibit a tendency to shear the tungsten carbide stud under side loads induced by the shearing action of the drag bit as it moves through a rock bit formation, as much of the tungsten carbide stud shank as possible is supported while allowing the diamond compacts cutting surface to penetrate the formation. In order to insert the stud deeper into the face (16) of a drag bit body, a portion of the face adjacent the diamond compacts cutter is relieved (as at 70) so that the bottom edge of the cutter does not contact the face of the body of the drag bit. The means (70) to relieve the drag bit face is a circular channel in the face of the drag bit body in front of the diamond cutting disc (60), the circumference of the channel (70) being slightly larger than the diamond cutting disc (60) for inserting the stud (52) supporting the diamond cutter deeper into the drag bit body (12). <IMAGE>

Description

SPECIFICATION Improvements in drag bits This invention comprises improvements in drag bits and concerns diamond insert type drag bits.

It is known to insert diamond insert studs within the face of a drag bit body by counterboring concentrically each interference fit insert hole in the face of a drag bit to relieve an area surrounding the insert stud body to clear the bottom edge of a substantially circular diamond compact mounted to each of the stud bodies.

U.S. Patent No. 4,265,324 describes a means to relieve the face of the drag bit adjacent the diamond cutting tip of the inserts while supporting the surface of the shank opposite or behind the cutting face of the insert to support the stud during operation of the bit. Support for the insert stud is achieved by eccentrically positioning the counterbore so that the counterbore relieves only that portion of the diamond cutting face that protrudes into the drag bit face and relieves a portion of the original interference fit hole at a point opposite the cutting face of the stud, thereby providing support for the backside of the stud during operation of the bit.

U.S. Patent 4,265,324 in effect, provides a counterbored trough in front of the cutting face of the diamond inserts. During operation, the scraping and gouging action of the inserts generates considerable detritus material, some of which becomes trapped in the corners of the counterbored relief portion below the diamond cutting face of the inserts. The cuttings thus have a tendency to be impacted against the cutting face, thereby inhibiting the penetration rate of the drag bit in a borehole.

The present invention provides a diamond drag bit comprising a bit body having a multiplicity of individual diamond inserts inserted within retention holes formed in a face of the drag bit body, each of said diamond inserts having a shank portion at one end inserted into the retention hole and a diamond cutting disc mounted on the shank at the opposite cutting end and extending beyond the face of the drag bit body, said drag bit body having means for providing additional support for the cutting end of the insert along a longitudinal surface of the insert shank substantially behind the diamond cutting disc by relieving a portion of the drag bit face adjacent the retention hole in the face to clear an edge of the diamond cutting disc nearest the face of the drag bit body so that the shank may be inserted deeper into the retention hole, characterized by the relieved portion being provided by a circular channel in the face of the drag bit body in front of the diamond cutting disc, the circumference of the circular channel being slightly larger than the diamond cutting disc thereby providing relief clearance for that portion of the cutting disc that extends below the face of the drag bit body.

The circular relief channel radially extends away from the diamond compact face of the insert, the end of the channel gradually running out tangentially with the face of the drag bit. Hence, there is no counter-bored depression below the face of the drag bit to trap detritus material during bit operating modes.

The chips tend to curl into the circular trough and be directed away from the insert cutting face as they are swept up the drillstring by the drilling mud.

Experience has shown that some of the strategically positioned, inadequately supported, diamond insert studs supporting the circular diamond compacts have a tendency to fracture or shear just above the grip length of the stud shanks during operation of the drag bit in a borehole.

The present invention provides an advantage over the eccentric counterbore invention in that even more support is provided for the shank of the diamond insert. This additional support is provided by relieving only that portion that is immediately below the lower edge of the diamond cutting disc. The face of the bit body may be milled below the cutting disc at an angle that is substantially transverse of the cutting face of the disc. Thus only that circular portion of the compacts extending below the face of the drag bit is relieved, providing the rest of the material of the bit body forming the interference fit hole as additional support for the insert.

The milling operation describes a circumference slightly larger than the circumference of the diamond disc and at an angle that is substantially transverse to the axis of the disc so that the lower portion of the disc extending below the face of the steel body of the drag bit is aligned with the circumference of the milled channel in the face of the drag bit body. Thus only that portion necessary to allow the disc to extend below the surface of the face of the drag bit is relieved, leaving the rest of the area surrounding the insert stud to support the shank of the diamond insert.

A diamond drag bit is hereinafter disclosed wherein the drag bit has a multiplicity of individual diamond inserts strategically inserted within insert holes formed in a face of a drag bit body, the diamond inserts having a diamond cutting disc at a first cutting end and a shank portion at an opposite end.

A means wherein additional support is provided in the bit body face for the cutting end of the insert, along the longitudinal surface of the insert shank, located substantially behind the diamond cutting disc. The shank support means is obtained by relieving a portion of the drag bit face near the insert hole formed in the bit face to clear an edge of the disc nearest the face of the drag bit so that the shank may be inserted deeper into the insert hole. The relieved portion is provided by milling a circular slot in the face of the drag bit at an angle substantially 90 to the cutting face of the cutting disc. The circumference of the circular slot is slightly larger than the circumference of the diamond cutting disc, thereby providing relief clearance for that portion of the cutting disc that extends below the face of the drag bit.The circular slot is so positioned to provide relief clearance for an edge of the cutting disc nearest the face of the drag bit while leaving the insert shank with backup material substantially behind the cutting disc of the insert.

An advantage then over the prior art is the means in which the shank of the diamond insert is supported within the face of a diamond drag bit while relieving a portion of the face of the drag bit surrounding the insert to clear the diamond cutting face of the insert.

Yet another advantage over the prior art is the means in which detritus material is inhibited from impacting against the diamond cutting face during operation of the bit in a borehole.

A specific embodiment of the present invention will now be described by way of example and not by way of limitation with reference to the accompanying drawings in which: Figure 1 is a perspective view of a drag bit according to this invention illustrating the orientation of the diamond inserts in the face and gage row areas of the bit; Figure 2 is a partially cutaway cross section of the drag bit face portion illustrating the means in which the circular channel is formed into the drag bit face prior to insertion of the interference fit diamond inserts into the hole formed by the drag bit face;; Figure 3 is a partiai cross section of the face portion of the drag bit illustrating a diamond insert interference fitted within a hole formed by the face of the bit, the orientation of the cutter face of the insert is about 90 to the ramp angle of the circular groove in the face of the bit; and Figure 4 is a view taken through 4-4 of Fig. 3 illustrating the relationship of the cutting face of the diamond insert compacts relative to the circular channel in the drag bit face.

With reference now to the accompanying drawings and first to Fig. 1, the diamond drag bit, generally designated as 10, consists of drag bit body 12, a cutter face, generally designated as 14, mud flow dividers 20, reamer segments 28 on the sides of the bit, which also act as mud flow dividers, and pin end 24. A pair of 180 opposed slots 26 are cut in the bit nearest the pin end 24 to accommodate a spanner-type wrench to remove the bit from the drillstring. Mud flow dividers 20 radiate out from the center of the bit extending over conical face surface 18 ta the gage 21 of the bit and connect with the longitudinally extending reamer segments 28.

A series of nozzles 36 are strategically positioned within face 1 6 of the cutting end 14 of the bit body 12. Hydraulic mud is directed across the cutter face 14 containing a multiplicity of diamond inserts generally designated as 50. The mud cools and cleans each insert as well as providing a means to remove chips from a borehole during operation of the bit.

Mud is directed between the dividers 20 and the reamers 28 through mud flow channels 22 and 32.

The diamond discs 60, as well as the diamond insert stud blanks 52 that make up the diamond inserts 50, for example, are fabricated from a tungsten carbide substrate with a diamond layer sintered to a face of the substrate, the diamond layer being composed of a polycrystalline material. The synthetic, polycrystalline diamond layer is manufactured by the Specialty Material Department of General Electric Company of Worthington, Ohio.

The foregoing drill cutter blank is known by the trademark name of Stratapax drill blank.

A series of gage row inserts 38 are interference fitted within holes formed in mud flow dividers 20 and the peripheral edge 21 of the cutting face 14. The gage row inserts 38 serve to maintain gage (diameter) of a borehole. Gage reamer inserts 34 are positioned within a slot cut into reamer segments 28.

The diamond reamer inserts 34 also serve to maintain the gage of the bit as it penetrates deeper in the borehole during operation of the drag bit. Each reamer segment has a plurality of tungsten carbide wear buttons 30 inserted in holes for minimising wear at the gage of the rock bit.

With reference to all the Figures, each of the diamond inserts is interference fit within insert holes 1 7 formed in the cutting face 14 and the reamer portion 28 of bit body 12. In order to insert each insert deeper into, for example, the cutting face 14 of the bit body T2, relief must be provided near the bottom edge 64 of the diamond cutting disc 60 so that the shank of the insert body 52 can be pressed deeper in the retention hole. A circular slot or channel 70 is, for example, milled into the face 14 of the drag bit 10. The orientation of the slot 70 is dependent upon the specific rake angle of the diamond cutting disc 60 relative to the face 14 of the bit. The slope of the channel 70 is about 90' to the angle of the diamond disc 60 and a circular cross section of the channel 70 need only be slightly larger in diameter than the diameter of the diamond disc 60 (Fig. 4), thus a minimum amount of material is removed from the face 14 of bit body 12, thereby providing maxi mum support for the stud portion 52 of the diamond inserts 50.

Referring now specifically to Fig. 2, the partial cross section illustrates the method in which the channels 70 are cut into the face 16 of bit body 12. The angle "A" of the milling tool 80 (which of course sets the relief ramp angle for each insert) is dictated by the angle of the diamond cutting disc 60 affixed to stud body 52 with respect to face 1 6 of bit body 12. The ideal ramp angle 70 is 90 to the cutting face 60 of the diamond inserts 50.

Preferably the rake angle of the diamond cutting disc is between 95 and 110 with respect to the face of the drag bit body. Thus the angle "A" is from 5" to 20 .

The diameter of the milled slot need only be slightly larger than the diameter of the diamond disc 60 so that the face 62 of the diamond disc 60, at its lower portion 64, will not contact the circular channel 70 milled into face 1 6 of bit body 1 2 (Figs. 3 and 4). As can readily be realised in Fig. 2, the circular slot 70 is cut into the face 1 6 of bit body 10 before the inserts 50 are interference fitted within insert retention hole 1 7 formed in the bit body 1 2. The radial orientation of each of the circular slots or channels 70 in cutting end 1 4 again is dependent upon the rake angle of the cutting face of the inserts relative to the face of the rock bit 10.Once the rake angle is established for each insert, the slot then is aligned relative to that rake angle to properly orient the channel with the cutting disc 60 of the inserts 50.

Referring now to Figs. 3 and 4, Fig. 3 specifically illustrates the 90 orientation of the slope angle of the channel 70 with respect to the cutting face 62 of the diamond disc 60. The diamond insert 50 is inserted into the interference fit hole 1 7 in body 1 2 by applying a special tool (not shown) against top surface 54 of stud body 52 and pressing the insert into the interference hole until it bottoms in the hole by contacting end 56 with the bottom of the retention hole. Fig. 3 clearly illustrates the relationship of the insert 50 within face 16 of bit body 1 2.

If, for example, each of the diamond inserts was inserted within face 1 6 of bit body 12, without the relief channel 70, a shank portion of the inserts designated as "B" would, of course, be above the face 1 6 of the bit body and would thus be unsupported. The section designated as "C" is exposed to the hole bottom or formation and the insert would be in danger of fracturing along a line substantially even with the bottom edge 64 of diamond face 62. By milling in the circular relief slot 70, the backside 58 of shank 52 (behind cutting face 62 of diamond compact 60) is supported the additional distance designated as "C", thus providing backup for the cutting face 62 of each of the inserts and thereby greatly minimizing any tendency of the insert to fracture along a line substantially even with the face 16 of bit body 12.Of course, the degree of support for the backside 58 of stud body 52 is determined by the depth of the channel 70 in face 16. The diameter of the circular slot 70 need only be slightly larger than the diameter of the diamond disc 60.

Again, the depth of the slot determines the height at which the cutting end of the insert extends beyond face 1 6 of bit body 1 2.

The ramp angle of circular slot 70 tangets face 1 6 at point "D" where the rake angle of cutting face 62 is greater than 90 with respect to face 1 6 of bit body 1 2. The ramp 70 serves to help remove detritus material forming in front of cutting face 62 of disc 60.

The detritus material will be forced up the ramp of the channel 70 and will exit the face 1 6 without any tendency to be trapped in any sort of obstruction in front of the cutting face 62. For example, in the previously mentioned U.S. Patent Number 4,265,324, the eccentric counterbore provides a channel that could possibly trap detritus material in front of the cutting face of the diamond inserts, thereby inhibiting the cutting action of the diamond inserts as the drag bit is working in a borehole.

It would be obvious to form the circular relief ramp in the bit face by means other than the use of a mill bit. For example, the ramp could be cast in a mold and the interference fit subsequently drilled in the bit face for each of the diamond inserts.

Claims (6)

1. A diamond drag bit comprising a bit body having a multiplicity of individual diamond inserts inserted within retention holes formed in a face of the drag bit body, each of said diamond inserts having a shank portion at one end inserted into the retention hole and a diamond cutting disc mounted on the shank at the opposite cutting end and extending beyond the face of the drag bit body, said drag bit body having means for providing additional support for the cutting end of the insert along a longitudinal surface of the insert shank substantially behind the diamond cutting disc by relieving a portion of the drag bit face adjacent the retention hole in the face to clear an edge of the diamond cutting disc nearest the face of the drag bit body so that the shank may be inserted deeper into the retention hole, characterised by the relieved portion being provided by a circular channel in the face of the drag bit body in front of the diamond cutting disc, the circumference of the circular channel being slightly larger than the diamond cutting disc thereby providing relief clearance for that portion of the cutting disc that extends below the face of the drag bit body.

2. The drag bit as set forth in claim 1 wherein the circular channel in the face of the drag bit body is substantially 90 to the cutting face of the diamond cutting disc.

3. The drag bit as set forth in either of claims 1 or 2 wherein the circular channel has an axis transverse to the cutting face of the diamond disc.

4. The drag bit as set forth in any of the preceding claims wherein the angle of the cutting face of the disc, with respect to the face of the bit body, is more than 90 , and the circular channel tangets the bit body face in front of the cutting face of the diamond disc.

5. The drag bit as set forth in any of the preceding claims wherein the angle of the cutting face of the disc, with respect to the face of the bit body, is between 95 and 110'.

6. A diamond drag bit substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.