Drill bit cutting element and method for mounting a cutting element on a drill bit

Abstract: A full cutting element including a substantially cylindrical backing and cutter mounted thereon is cut generally along the length thereof to produce a pair of semicylindrical partial cutting elements. In the case of an unused cutting element, each partial cutting element is mounted on a different semicylindrical tungsten carbide base to produce a substantially cylindrical unit which is mounted on a bit using a low temperature braze. In the case of a used full cutting element, the cutting element is cut to separate the worn portion from the remainder of the bit and only the unused portion is used to form a cylindrical unit with a corresponding semicylindrical tungsten carbide base. In another aspect, a partial cutting element is received in a pocket formed on a bit body. The pocket includes a pair of opposed side surfaces which substantially flushly abut the curved surfaces of the backing on the partial cutter.

Description: The present invention relates to a cutting element according to the pre-characterizing portion of claim 1, a stud cutter according to the pre-characterizing portion of claim 11, and a stud cutter according to the pre-characterizing portion of claim 16. A generic cutting element as described in the pre-characterizing portion of claim 1 is known from US 4,498,549. Various other cutting devices for an earth boring drill bit are known from the state of the art. According to US 4,373,593 a rotary boring bit for boreholes comprises a body provided on its outer periphery with cutting members consisting of a cutting portion and a supporting portion. Each cutting member is formed as a segment of a sintered body having a core of cutting material encased by a shell. A cutting element for a rotary drill bit according to EP 0 336 697 A2 comprises a layer of polycrystalline diamond material having a front face and a rear face, a backing layer of less hard material bonded to the rear face of the diamond layer, and a front layer of less hard material bonded to the front base of the diamond layer and extending across at least the major part thereof. The front layer is thinner than the backing layer, at least in the vicinity of the cutting edge of the cutting element. The closest prior art is seen in US-A-4,767,050. US 4,767,050 discloses an improved brazed implement comprising a composite compact having an abrasive particle layer bonded to a support and a substrate bonded to the support by a brazing filler metal. Said implement is intended for use in drill bits for oil and gas exploration and in mining applications. The composite compact comprises a sectioned cylindrical composite compact having a lower support surface opposite the support surface bonded to the abrasive particle layer. The composite compact has also a mating surface. The substrate about its upper end has a pocket which comprises an interior face complementary in shape with the compact lower support surface and a land complementary in shape with the compact mating surface. The compact is brazed to the substrate. The abrasive particle layer is spaced-apart from contact with the substrate a distance adequate to minimize thermal damage thereto during the brazing of the compact to the substrate. The land is of sufficient depth, however, to provide support for the compact. A generic stud cutter is known from US 4,705,122. A conventional cutting element for an earth boring drill bit typically comprises a substantially cylindrical backing made from a cemented metal carbide such as tungsten carbide. One end of the backing has a cutting blank, referred to herein as a cutter, bonded thereto. The cutter typically comprises a disk of cemented carbide having a polycrystalline compact diamond (PCD) layer formed on one end thereof which defines a cutting surface. The PCD layer may be of the type having metals leached therefrom to enable the cutting element to withstand higher temperatures. In such cases the PCD layer may comprise a mosaic of smaller PCD elements mounted on the end of the substrate. Such cutting elements are typically mounted on a drill bit body by brazing. The drill bit body is formed with recesses therein for receiving a substantial portion of the cutting element in a manner which presents the PCD layer at an appropriate angle and direction for cutting in accordance with the drill bit design. In such cases, a brazing compound is applied to the surface of the backing and in the recess on the bit body in which the cutting element is received. The cutting elements are installed in their respective recesses in the bit body and heat is applied to each cutting element via a torch to raise the temperature to a point which is high enough to braze the cutting elements to the bit body but not so high as to damage the PCD layer. During drilling, the cutting elements are urged against a formation. As drilling proceeds, the cutter and portions of the backing adjacent thereto tend to wear away from one side. By the time wear extends to the middle of the PCD layer, the cutting element is substantially spent and must be removed and replaced or, in some cases, the entire bit must be replaced. Prior art half cutting elements are usually semicylindrical in shape. In the case of such a cutting element, each half cutting element includes a backing having a substantially flat side surface and a semicircular cross section. A half cutler including a PCD layer is mounted on one end of the backing. While half cutting elements are desirable because they provide all the PCD cutting surface normally used during drilling (with less PCD material), the reduced surface area of the semicylindrical backing provides less surface area for brazing the cutting element to the drill bit body. As a result, half cutting elements are relatively easier than a full cutting element to break away from the bit body. Although prior art high temperature brazes exist which provide high strength bonds, the heat required to effect the bond is high enough to damage the PCD cutting layer. Such brazes cannot be used in the process described above in which a torch is used to braze the cutting elements thereto because the cutters will be damaged. It would be desirable to provide a half cutting element which could be mounted on a drill bit body as securely as a conventional full cutting element. It is an object of the present invention to provide a cutting element for an earth boring drill bit, which cutting element is less expensive than prior art cutting elements, which element further provides a secure bond between the cutting element and the bit body, and which cutting element may be constructed from a partially worn prior art full cutting element. Furthermore it is an object of the invention to provide a stud cutter comprising the same advantages as the cutting element mentioned in the preceding sentence. According to the invention this object is achieved by a cutting element according to claim 1, a stud cutter according to claim 11, and a stud cutter according to claim 16. Advantageous and preferred embodiments of the cutting element according to the invention are subject matter of claims 2 to 10. Advantageous and preferred embodiments of the stud cutter according to claim 11 are subject matter of claims 12 to 15. Advantageous and preferred embodiments of the stud cutter according to claim 16 are subject matter of claims 17 and 18. Preferred embodiments of the cutting element according to the invention as well as of the stud cutters according to the invention will now be described with respect to the accompanying drawings in which: FIG. 1 is a perspective view of a first embodiment of a cutting element constructed in accordance with the present invention. FIG. 2 is a perspective view of a second embodiment of a cutting element. FIG. 3 is a perspective view of a third embodiment of a cutting element comprising a partial cutting element and a base and showing a substantially planar boundary between the two. FIG. 4 is a sectional view illustrating a portion of another embodiment of the cutting element of FIG. 3 and depicting a slightly different boundary than the planar boundary along line 4-4 in FIG. 3. FIG. 5 is a view similar to the view of FIG. 4 illustrating another embodiment of the cutting element of FIG. 3 and depicting a slightly different structure at the boundary. FIG. 6 is another embodiment of the cutting element of the present invention illustrating a boundary having complementary geometric features between a partial cutter and a base. FIGS. 7-10 are embodiments similar to FIG. 6 showing different complementary geometric features. FIG. 11 is an exploded perspective view of a prior art drill bit illustrating the manner in which a cutting element is received in a matrix pocket of the bit. FIG. 12 is a cutting element and pocket constructed in accordance with the present . invention. FIG. 13 is a perspective view of a stud cutter constructed in accordance with the present invention. FIG. 14 is a perspective view of another embodiment of a stud cutter constructed in accordance with the present invention. FIG. 15 is a perspective view of another embodiment of a stud cutter constructed in accordance with the present invention. Indicated generally at 10 in FIG. 1 is a first embodiment of a cutting element constructed in accordance with the present invention. Cutting element 10 includes a partial cutting element 12 and a base 14. Base 14 is preferably formed of tungsten carbide or of a metallic or other bondable material. In the embodiment of FIG. 1, both partial cutting element 12 and base 14 comprise substantially semicylindrical bodies bonded together, in a manner which will hereinafter more fully described, to form a substantially cylindrical unit. It should be appreciated that the present invention can be practiced with other geometries, e.g., a body having triangular or other geometrical cross section such as one half of a hexagon. Moreover, the base might comprise one geometry, e.g., semicylindrical, and the partial cutting element another, e.g., triangular or other geometrical cross section. In the embodiment of Fig. 1, partial cutting element 12 includes a backing 16, which in the present embodiment is formed from a cemented metal carbide such as tungsten carbide. A cutter 18 is bonded to one end of backing 16 in a manner which will be more fully described hereinafter. Cutter 18 is conventional and may comprise a substrate of cemented carbide having a polycrystalline compact diamond (PCD) formed on one end to define a cutting surface 20. Cutter 18 may, e.g., alternately comprise a synthetic diamond mosaic cutter. Consideration will now be given to the manner in which culling element 10 is manufactured. Partial cutting element 12 is obtained by cutting a prior art full cutting element, such as the one indicated generally at 22 in FIG. 11, into two halves generally along a plane containing the longitudinal axis of the cutting element. A full cutting element, like cutting element 22, can be cut immediately after it is manufactured to provide two semicylindrical partial cutting elements, like partial cutting element 12, for making two cutting elements, like cutting element 10. Alternatively, a prior art full cutting element like cutting element 22 can be installed on a bit as illustrated in FIG. 11 and used until the cutting edge is substantially worn. The worn cutting element is then removed from the bit and cut generally along a plane containing the longitudinal axis of the cutting element with the plane being oriented so that substantially all of the worn portion of the full cutting element is on one side of the plane, thereby creating a first partial cutting element which is worn and a second partial cutting element which is substantially unworn, like partial cutting element 12 in FIG. 1. Continuing description of the manufacture of cutting element 10, partial cutting element 12 is thereafter bonded to semicylindrical base 14. The bond so formed is a high strength bond which is heated in a small furnace, such as one that might be used for bonding synthetic diamond to an appropriate substrate as opposed to a furnace capable of receiving an entire matrix bit. The furnace is conventional and those skilled in the art can use it, along with a suitable bonding material, to form a high strength bond between the planar surfaces of partial cutting element 12 and base 14. In part, this is accomplished by heating the base and partial cutting element in a manner which would damage cutter 18 except that conventional cooling equipment is used for cooling the cutter during the high strength bonding process. The high strength bond is thus formed between partial cutting element 12 and base 14 by heating both bodies to a level which would damage the cutler if the same heat was applied thereto during a conventional brazing process in which each of the cutters are heated with a torch. After cutting element 10 is manufactured as described above, it is installed in a known manner on a bit crown. The technique for installing cutting element 10 includes utilizing a conventional brazing material between both backing 16 and base 14 and the surfaces of a pocket, like pocket 28 formed in an earth-boring drill bit body 30 in FIG. 11. As used herein, the term conventional brazing refers to brazing accomplished with low to moderate temperatures which are not high enough to damage the PDC layer in the cutter. Such conventional brazing can produce bonds in the range of 35,000 to 140,000 p.s.i. shear strength. The term high temperature brazing refers to brazing accomplished with a temperature which is high enough to damage the PDC layer in the cutter in the absence of cooling during brazing. Such high temperature brazing can produce bonds having even higher shear strength than conventional brazing and are known in the art. With continued reference to FIG. 11, cutting element 10 is oriented to present cutter 18 at an appropriate angle so that a curved edge thereof is presented to an earth formation during drilling. After the cutting elements are set into the pockets with a suitable brazing material, each cutting element is heated , typically with a torch, to produce a low to moderate temperature bond between the cutting elements and the bit body. Because cutting element 10 includes substantially more surface area than a partial culling element, the low temperature bond is sufficient to retain the cutting element in its pocket during drilling. Although there is a relatively small surface area between base 14 and backing 16, the high temperature bonding process described above produces a high strength bond which maintains its integrity during drilling. It should be noted that the brazing step required to join cutting element 12 and base 14, in FIG. 1, could be accomplished with a moderate temperature conventional braze and the brazing required to install cutting element 10 into the bit crown pockets could be accomplished with a low temperature conventional braze as described above. It is important that the braze used to join cutting element 12 and base 14 have a higher brazing temperature than that used to install cutting element 10 into a bit crown pocket to prevent debrazing of the bond in cutting element 10 when it is brazed into its associated bit crown pocket. Turning now to FIG. 2, a second cutting element 24 which is constructed in accordance with the present invention is illustrated. The numbers used in FIG. 2 and previously appearing in FIG. 1 correspond generally to the previously identified structure. In the embodiment of FIG. 2, backing 16 is shorter than cutting element 10. Another substantially semicylindrical body portion 26 is received against one end of backing 16 and is likewise abutted against base 14 as shown. Brazing is provided as described above between the surfaces of backing 16 and cutting element 26 which are abutted against base 14 as well as the surfaces of backing 16 and body portion 26 which are directly abutted together. Cutting element 24 may be used in substantially the same manner as cutting element 10. Turning now to FIG. 3, indicated generally at 32 is another cutting element constructed in accordance with the present invention. In the embodiment of FIG. 3, which is manufactured and used substantially as described above, neither partial cutting element 12 nor base 14 is substantially semicylindrical. Each does, however, include a complimentary substantially planar brazing surface, the boundary of which is shown partially in dashed lines and partially in a solid line, so that when the two are bonded together, a substantially cylindrical unit, as in the cutting elements of FIGS. 1 and 2, is formed. Turning now to FIG. 4, shown therein is an enlarged view of the boundary between a partial cutting element and body, like partial cutting element 12 and body 14 in FIG. 3, in a modified version of the cutter of FIG. 3. As can be seen, partial cutting element 12 and body 14 include complementary geometric features which interface with one another to resist shear forces applied to partial cutting element 12 during drilling which tend to break the bond between the partial cutting element and the base. FIG. 5 illustrates another modified version of the boundary between the partial cutting element and the base also including complementary geometric features which resist shear forces. Such features may be incorporated into an embodiment in which the partial cutting element is not cut from a full cutting element along a cutting plane containing the longitudinal axis of the full cutting element, as in FIG. 3, or may be incorporated into cutting elements like those shown in FIGS. 6-9 and in FIG. 10 where only a partial cutting element 12 is shown to illustrate an interfacing feature 33 formed thereon. A complementary recess is formed in a semicylindrical base (not shown) to engage the feature 33 so as to resist shear forces during drilling. Turning now to FIG. 11, full cutting element 22 includes a substantially cylindrical backing 16 and a cutter 18. Cutting element 22 may be cut as described above to form partial cutters utilized in the present invention. Also as described above, prior art full cutting element 22 is brazed into corresponding pocket 28 formed in bit body 30 utilizing conventional brazing techniques which involve placing a suitable conventional braze and a full cutting element, like full cutting element 22 in each pocket. Thereafter, brazing is accomplished by heating the cutter, the surrounding pocket and the braze with a torch. In another aspect of the invention depicted in FIG. 12, a partial cutter 35 may be received into a pocket, indicated generally at 36, formed on a drill bit body 38. Partial cutter 35 is formed in the same manner as the previously described partial cutters, namely by cutting a full cutting element generally along the length thereof. In the embodiment of FIG. 12, a lower substantially planar surface, not visible, is formed during the cutting process which is substantially parallel to the longitudinal axis of the full culling element. Pocket 36 includes a substantially planar rear surface 40, a curved surface 42 and a substantial planar surface 44 which flushly abuts the cut surface of partial cutter 35 when the same is received in pocket 36. A surface (not visible) symmetrical with and opposite to surface 44 comprises a portion of pocket 36. As with the prior art technique described in connection with FIG. 11, a suitable conventional bonding material is placed in pocket 36, on the rear planar surface of backing 16, on the lower planar surface of backing 16 and on the curved lower side surfaces, like surface 42, of the backing. Thus, when partial cutter 35 is received in pocket 36, bonding material is disposed between substantially all of the abutting surfaces of the pocket and partial cutter 35. Thereafter, the cutters surrounding the pockets and braze are heated with a torch to braze the cutters into the pockets. Because the partial cutter and pocket depicted in FIG. 12 provide increased area of contact between the pocket and cutter over prior art techniques for mounting half cutters on bits, and because curved surface 42 and the opposing symmetrical surface tend to retain the partial cutter in the pocket, the bond between the partial cutter and the pocket is able to withstand the forces applied during drilling. The cutter of FIG. 10 may be received into a pocket, like pocket 36 in FIG. 12, having a recess complementary to feature 33 formed on surface 44 in order to provide increased mechanical resistance to shear forces. Turning now to FIG. 13, indicated generally at 46 is a stud cutter constructed in accordance with the present invention. Included therein is a cutting element 48 similar to cutting element 10 in FIG. 1. The cutting element is mounted on a stud 50, which may be formed from tungsten carbide or may be metallic or other suitable material. Preferably cutting element 48 is mounted on the stud utilizing high temperature brazing. The cutting element may be mounted on the stud using any of the brazing or bonding techniques referred to above or with another suitable technique for securely mounting the cutting element on the stud. Stud cutter 46 is mounted, along with other similar stud cutlers, on the bit body to create a stud cutter bit. FIGS. 14 and 15 illustrate different embodiments of stud cutters in which a half cutter, formed by cutting a new or worn cutter as described above, is brazed to the upper surface of a stud preferably using high temperature brazing. Having illustrated and described the principles of our invention in a preferred embodiment thereof, it should be readily apparent to those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. We claim all modifications coming within the spirit and scope of the accompanying claims.

Claims: A cutting element (10, 24, 32) for an earth boring drill bit comprising a backing (16) formed from a cemented metal carbide, a base (14) mounted on the backing (16), and a cutter (18) mounted on the backing (16), characterized in that the backing (16) has a substantially semicylindrical shape which includes a generally longitudinal substantially planar surface, the base (14) has a substantially semicylindrical shape which includes a generally longitudinal substantially planar surface, said base (14) being mounted on the backing (16) by a bonding layer formed between said substantially planar surfaces, and the cutter (18) is mounted on one end of the backing (16) and comprises a substrate having a polycrystalline compact diamond layer formed thereon. The cutting element (10, 24) of claim 1, characterized in that said base (14) is substantially in the shape of a half cylinder and is bonded to said backing (16) so as to form a cutting element (10, 24) having a generally cylindrical shape. The cutting element (32) according to any of the preceding claims, characterized in that said backing (16) and said base (14) include complementary geometric features which interlock with one another. The cutting element (10, 24, 32) of claim 1, characterized in that said bonding layer extends substantially to at least one of a front surface of said cutting element (10, 24, 32). The cutting element (10, 24, 32) of claim 1, characterized in that said bonding layer comprises a high strength bond. The cutting element (10, 24, 32) of claim 5, characterized in that said high strength bond comprises a high temperature braze. The cutting element (10, 24, 32) of claim 6, characterized in that said cutting element (10, 24, 32) is mounted on a drill bit body (30) in a generally cylindrical pocket (28) by a bonding layer comprising a conventional braze. The cutting element (10, 24, 32) of claim 7, characterized in that said cutting element (10, 24, 32) is generally cylindrical and includes a substantially planar rear surface which flushly abuts a corresponding surface in a drill bit pocket (28) when said cutting element (10, 24, 32) is mounted on a drill bit body (30). The cutting element (10, 24, 32) of claim 4, characterized in that said bonding layer extends substantially to both said front and rear surfaces of said cutting element. The cutting element (10, 24, 32) of claim 1, characterized in that said cutter (18) is substantially coextensive with said one end of the backing (16) on which the cutter (18) is mounted. A stud cutter for an earth boring drill bit comprising a stud (50), a backing mounted on the stud (50), which backing is formed from a cemented metal carbide, and a cutter mounted on the backing, characterized in that the backing has a substantially semicylindrical shape which includes a generally longitudinal substantially planar surface, a bonding layer is formed between said substantially planar surface and said stud (50) and bonding the two together, and the cutter is mounted on one end of the backing and comprises a substrate having a polycrystalline compact diamond layer formed thereon. The stud cutter of claim 11, characterized in that said bonding layer comprises a high strength bond. The stud cutter of claim 12, characterized in that said high strength bond comprises a high temperature braze. The stud cutter of claim 13, characterized in that said bonding layer extends to a front surface of said stud cutter and to a rear surface of said stud cutter. The stud cutter of claim 14, characterized in that said cutter is substantially coextensive with said one end of the backing on which the cutter is mounted. A stud cutter (46) for an earth boring drill bit, comprising a stud (50), characterized by a cutting element according to any of claims 1 to 10, and a further bonding layer formed between said stud (50) and said cutting element and bonding the two together. The stud cutter (48) according to claim 16, characterized in that said further bonding layer comprises a high strength bond. The stud cutter (48) according to claim 17, characterized in that said high strength bond comprises a high temperature braze.

Inventors: TIBBITTS GORDON A, TIBBITTS, GORDON A.
Applicants: BAKER HUGHES INC, BAKER HUGHES INCORPORATED
Application year: 1995
Main classification: E21B10
IPC codes: E21B10