Insert attack angle for roller cone rock bits

Abstract: The inserts for a roller cone of a multiple cone rock bit are positioned or angled in the cone to attack an earthen formation normal to the formation when the inserts first encounter the formation such that the inserts are subjected to more compressive forces and the formation is subjected to more shear forces as the roller cutters roll over the bottom of the formation.

Description: This invention relates to roller cone rock bits with tungsten carbide inserts inserted within insert holes formed within the body of the roller cones. More particularly this invention relates to the attack angle of each of the tungsten carbide inserts retained within a cone. Each of the inserts has an attack angle with respect to a borehole formation that assures that the insert is primarily in a compressive mode upon initial contact with the formation, and the insert introduces more scraping and shearing to the earthen formation. Most of the roller cone prior art that teaches the use of tungsten carbide inserts pressed into roller cones has the centre line of the tungsten carbide inserts intersecting an axis of the cone. Hence the inserts are generally 90° with respect to a face of the frustoconical cone with the center line of the insert passing through the axial center line of the cone and rock bit journal. Roller cones where the center line of the inserts is offset from the axial center line of the cones are also known (GB-A-2009817). U.S. Patent No. 3,743,038 teaches an improved drill bit tooth of a milled tooth rotary cone bit having a leading tooth face, i.e. the face first contacting the formation being cut, substantially parallel with an axis of rotation of the drill bit cone. The trailing face of the milled tooth is convexly shaped to act as a fulcrum. This tooth configuration allows the tooth to get under and lift a chip from the formation being cut rather than sliding it to the side. The leading face of each of the milled teeth intersects an axial center line of the cone. The present invention orients each of the tungsten carbide inserts such that the inserts have an attack angle with respect to a formation. The center line of the insert does not intersect the axial center line of each of the cones. U.S. Patent No. 3,763,942 teaches a large mechanically driven auger or boring head designed especially for horizontal rock and earth drilling of mines or tunnels. The boring head defines a circular ring of circumferentially spaced tool bits or teeth. The cutting teeth on the ring of the body of the bit project radially outwardly from the peripheral surface of the ring and are tilted forwardly in the direction of rotation of the auger head. The cutting teeth on the body of the bit project forwardly and tilt toward the direction of rotation of the cutting head and are also tilted backwardly to present the tip end of each tooth in a straight forward direction to the surface in which it is cutting. In addition, the teeth are staggered so that successive teeth will not have the same cutting track. The present invention differs in that it is for a rotary cone rock bit wherein each of the tungsten carbide inserts are angled such that they are positioned approximately axially relative to an earthen formation at initial contact. Each of the inserts, therefore, is in a more compressive mode rather than in shear as the insert first contacts the bottom of a borehole. U.S. Patent No. 4,415,208 is yet another mining bit having individual cutters mounted to a mechanically driven ring for the tunnel cutter. This patent deals with a means of mounting the insert. The cutter bit assembly has an elongated cutter element, a bit holder, a bit block and locking means for removably affixing the bit holder to the bit block. The bit holder has a tapered locking lip and a tapered surface wherein a resulting cutting force provides a locking action against the taper. This patent, like the foregoing patent, differs from the present invention in that each of the cutters is not in a true compressive mode as the cutter attacks a formation. The present invention provides a roller cone bit wherein the cones roll on a formation bottom with a heavy weight driving the cones into the formation, each of the inserts being angled to assure that the inserts are in a compressive mode upon first contact rather than a shear mode during the cutting operation. U.S. Patent No. 4,108,260 describes roller cone rock bits with specially shaped inserts. The inserts used for cutter teeth of rock bits used in drilling soft and medium formations of the earth are generally chisel shaped with the flanks converging to a crest. However, the flanks of the inserts of the present invention are asymmetrical with respect to each other. The leading flank is scoop-shaped and the trailing flank is rounded outwardly. The center line of each of the inserts pass through an axial center line of the roller cone. As stated before, the present invention has a center line of each of the inserts that does not intersect the axial center line of the roller cone, each of the inserts being angled to insure that the insert is primarily in compression upon initial contact with the formation. The foregoing patent, while it describes a scoop-shaped insert, each of the inserts has an orientation that is primarily 90° to a surface of the roller cones, the center line of the asymmetrical inserts intersecting the axial center line of the cone. According to the invention there is provided a rotary cone rock bit, the rotary cone of said rock bit having multiple cutter inserts imbedded in insert holes formed in a body of the cone, said multiple cutter inserts generally being equidistantly spaced apart and arranged in circumferential rows along the axis of said cone, the center line of each insert and respective insert hole being angularly offset, by an attack angle α, from a radial line defined between the cone axis and the intersection of the insert center line and the outside surface of the insert, characterised in that each of the inserts is directed toward the direction of rotation of the cone and the attack angle is such that, each of the inserts is primarily in compression upon initial contact with the borehole formation. An advantage then of the present invention over the prior art is the angular orientation of inserts embedded in a rotary cone, each of the inserts having an attack angle that initially subjects each insert to compressive modes resulting in less bending and hence less breakage of the insert during initial contact of the insert with an earthen formation. The aggressive attack angle of the inserts results in more shearing, scraping and peeling of the formation during operation of a rotary cone rock bit in a borehole. The above noted objects and advantages of the present invention will be more fully understood upon a study of the following description in conjunction with the detailed drawings wherein: FIGURE 1 is a perspective view partially in phantom of a preferred embodiment of the present invention illustrating the angled inserts in a rotary cone; FIGURE 2 is a view of the prior art illustrating a typical prior art cone with tungsten carbide inserts each having their insert axis intersecting an axial center line of the cone; FIGURE 3 is a partially cutaway view illustrating a rotary cone of the present invention with the inserts having their axis not aligned with a center line of the cone. Each insert is angled with respect to an earthen formation; FIGURE 4 is a schematic illustration of a rotary cone with a single angled insert contacting a horizontal surface describing an angle α with respect to a radial plane intersecting an axis of the cone; FIGURES 5a and 5b are schematics illustrating inserts and their α angles with respect to circumferential spacing, one insert to another; FIGURE 6 is a partially broken away cross-sectional view taken through 6-6 of FIGURE 3 of a rotary cone attached to a journal in an earthen formation, the orientation of each of the inserts being relatively aligned with an axial center line of a rock bit; and FIGURE 7 is another schematic illustration showing the orientation of a single angled insert with respect to a center line of the rock bit. This view shows a β angle with respect to an axis of the cone and a horizontal surface. With reference now to FIGURE 1, the rotary cone rock bit generally designated as 10 comprises a rock bit body 12 with a pin end 11 and cutting end generally designated as 26. Each cone 28 associated with cutting end 26 is rotatably mounted on a journal bearing extending from a leg 14 that terminates in a shirttail portion 16. Each of the cones 28, for example, has a multiplicity of substantially equally spaced inserts 29 interference fitted within insert holes 27 formed in the cone body 28 (Fig. 6). A lubricant reservoir generally designated as 18 is provided in each of the legs 14 to supply lubricant to bearing surfaces formed between the rotary cones and their respective journals. Three or more nozzles 13 communicate with a chamber formed within the bit body 12 (not shown). The chamber receives drilling fluid or "mud" through the pin end 11 and the fluid is directed out through the nozzles 13 during bit operation. Turning now to the exemplary prior art of FIGURE 2, a rotary cone 34 has embedded within the cone body, a multiplicity of tungsten carbide inserts 36. The inserts 36 have, for example, conical cutting ends 39. An axis 37 of each of the inserts 36 passes through a cone axis 38. Each of the inserts is about normal to a surface 33 of the cone 34. The rotation of the cone typically is in the direction 35, however it should be noted that with the orientation of the inserts in the cone 34 normal to a surface of the cone 33 it would not matter which direction the cone was rotated. With reference now to FIGURE 3, a preferred embodiment of the invention, a cone 28 is shown in contact with an earthen formation 20. Each of the inserts 29 interference fitted within an insert retention hole 27 (Fig. 6) is illustrated with an attack angle represented as α. Angle α is defined between an axis 30 of the insert 29 and a radial line 24 defined between an axis 25 of the cone through a point at the intersection of the insert axis 30 and insert profile. This angle α may be between 0° and 45°. The cone rotation 19 subjects each of the inserts 29 oriented in the direction of rotation of the cone to a compressive load as the inserts 29 initially contact the earthen formation 20. The schematic drawing of FIGURE 4 illustrates a single angled insert 29. The α attack angle in the example shown is 30° (angle 31). The maximum angulation for α is shown by α angle 32 and is 45°. The amount of angulation for α in a particular row depends on the equidistant spacing from insert to insert in a row. FIGURES 5a and 5b illustrate schematically the preferred attack angulation from insert to insert. For example, if the insert C₁ is spaced as shown from C₁ to the insert C₃, the angle α₃ is greater than angle α₂ because of the further spacing from C₁ to C₃ as compared to C₁ to C₂. If the spacing between inserts in a single circumferential row is close then the angle α is less between each of the equidistantly spaced inserts in that particular row. In another row, if the inserts are spaced further apart around that circumferential row then the angle α is greater as illustrated by angle α₃. The attack angle is greater in α₃ than α₂ because C₃ is further from C₁ than C₂ is from C₁. With reference to FIGURE 6, the orientation of angle β is shown in four separate circumferential rows of inserts, for example, the row of inserts 29 nearest the apex 21 of the cone 28 in FIGURE 6 illustrates the insert center line 30 exactly parallel with center line 43 of the rock bit 10. The inserts 29 in the row nearest the heel 22 of the rock bit cone 28 are less parallel with center line 43 due to the material limitation of the cone. The insert retention hole 27 is angled to provide enough cone material to securely retain the insert 29 within its insert retention hole 27. The intermediate rows are at intermediate angles from the axis of the bit. With reference now to the final schematic of FIGURE 7, the inserts 29 are additionally oriented to align the center line of each of the inserts as nearly parallel to the center line 43 of the rock bit 10 as is possible. The angle β is defined between the axis 30 of the insert 29 and a line 44 parallel to the bit axis 43 through a point at the intersection of the axis 30 of the insert 29 and the insert profile. The angle β is preferably within the range of β max angles defined between the center line 25 of the cone 28 and a line 41 perpendicular to the bit axis 43. However, the angle β defined by the axis 30 of the insert 29 should be as nearly parallel with the center line 43 of the rock bit 10 as feasible; that is, the angle β should be as small as possible. By aligning each of the inserts as shown in FIGURE 7 as nearly parallel as possible to the axis 43 of the rock bit 10, the inserts are positioned so that they are subjected to compressive loads while the rock bit operates in a borehole formation. By orienting each of the inserts 29 with the attack angle α and with the orientation β as illustrated in Figs. 3 through 7, each of the inserts 29 are subjected to compressive loads rather than shear loads as the cone rotates against a borehole bottom. Moreover, by orienting the inserts as shown in Figs. 6 and 7 close to parallel with respect to a center line 43 of the rock bit 10, the journals are subjected to more out thrust loading as opposed to in thrust loading. State of the art inserts as shown in FIGURE 2 subject the journals and legs of the rock bits to severe in thrust loads which shortens bearing life leading to premature failure of the bit. By orienting the inserts through the attack angle α and the orientation β, as described, lower bending loads occur on each of the inserts, resulting in far less shearing of the inserts as they work in a borehole. By the foregoing orientation of the inserts, proper cutting action is assured which includes more shear of the material, more scraping action of each of the inserts and less insert breakage during operation of the bit in a borehole. It will be apparent that one may utilize inserts other than symmetrical frustoconical inserts. For example, chisel type or asymmetric type inserts common within the rock bit industry may be utilized

Claims: A rotary cone rock bit (10), the rotary cone (25) of said rock bit having multiple cutter inserts (29) imbedded in insert holes (27) formed in a body of the cone, said multiple cutter inserts generally being equidistantly spaced apart and arranged in circumferential rows along the axis (25) of said cone, the center line (30) of each insert and respective insert hole being angularly offset, by an attack angle α, from a radial line (24) defined between the cone axis (25) and the intersection of the insert center line and the outside surface of the insert, characterised in that each of the inserts is directed toward the direction of rotation of the cone and the attack angle is such that, each of the inserts is primarily in compression upon initial contact with the borehole formation. The rotary cone rock bit as set forth in Claim 1 wherein the attack angle α of each of said inserts is between 0° and 45° and is greater when the spacing between inserts in a circumferential row is wider apart and less where the spacing between inserts in a circumferential row is closer together. The rotary cone rock bit as set forth in any of the preceding claims wherein the center line (30) of each insert (29) when at the lowest point of its rotation is oriented to be substantially parallel to the axis (43) of said rotary cone rock bit so that weight on the bit normal to the earthen formation being bored subjects each insert to maximum compression loads and minimum shear loads during operation of the rock bit in said formation. The rotary cone rock bit as set forth in any of the preceding claims wherein an angle β between said insert center line (30) and said rock bit axis (43) is no greater than the angle β max formed between the axis (25) of the cone and a surface (41) normal to said axis (43) of said rock bit. The rotary cone rock bit as set forth in Claim 4 wherein angle α and angle β of each of said equidistantly spaced inserts in said circumferential rows are oriented to subject said insert to maximum compressive loads and minimum shear loads while said rotary cone rock bit operates in an earthen formation. The rotary cone rock bit as set forth in any of the preceding claims wherein said cutter inserts are tungsten carbide inserts. The rotary cone rock bit as set forth in any of the preceding claims wherein said tungsten carbide inserts are symmetrical frustoconical inserts. The rotary cone rock bit as set forth in any of the preceding claims wherein the inserts are chisel type inserts. The rotary cone rock bit as set forth in any of the preceding claims wherein the inserts are asymmetrical inserts.

Inventors: NGUYEN QUAN VAN, NGUYEN, QUAN VAN
Applicants: SMITH INTERNATIONAL, SMITH INTERNATIONAL, INC.
Application year: 1991
Main classification: E21B10
IPC codes: E21B10