Diamond drag bit

Abstract: A diamond drag bit (10) has a multiplicity of diamond cutter inserts (20) secured within strategically positioned insert holes (26) formed by a cutter face (18) of the drag bit body (12). Means are provided for supporting the portion of the cutting end of each of the extended cutter inserts (20) protruding above the bit face. Preferably the support for each insert is provided by a support stud (28) in a hole at the back side of the cutter insert (20). Such a stud (28) has a concave face (29) bonded to the surface of the insert through an angle of 120° and for substantially the full length of the insert above the face of the drag bit (10).

Description: The present invention relates to a diamond drag bit of the type as indicated in the precharacterizing portion of claim 1. Such a diamond drag is known from US-A-4505342, which discloses a drag type well drilling bit including a bit body comprised of a generally non-frangible metallic material. Ribs are provided in the face of the bit body, each of said ribs having a respective leading edge surface with respect to the intended direction of rotation of the bit. The innermost end of these ribs are located at various distances from the center line of the bit body and each of said ribs is extending generally outwardly from its respective inner end in a direction which has a substantial radial component with respect to an end face of the bit body. A number of prior art patents reflect the state of the art relative to the use of diamond insert studs in diamond drag bits. U.S. Patent Number 4,265,324 teaches the use of insert studs that are counterbored in the face of a drag bit. The counterbore relieves the upper portion of the bored hole formed in the face of the bit body. The hole is formed to receive the shank of the cutter insert. The counterbore serves to clear the bottom edge of the diamond cutting face of the insert. The shank portion behind the cutting face of the insert is then supported by the bit face depending upon the depth of the counterbore. While this means to support the cutter insert is fairly satisfactory, the counterbore causes turbulent flow of the cooling and cleaning fluid passing by each of the diamond inserts during operation of the bit in a borehole. The use of a counterbore to add strength to the cutter insert also substantially reduces the extension of the cutter insert below the bit body face, thereby reducing the depth of cut or the plastic deformation of the rock reducing the drill rate. U.S. Patent Number 4,505,342 also has added support for the shank of a cutter insert. That support is in the form of rigs extending radially on the bit body. In a sense it corresponds to the counterbore by having a recessed area in front of the ribs for exposing the face of the diamond cutter disc. U.S. Patent Numbers 4,244,432 and 4,351,401 are examples of other diamond drag bits that utilize stud type diamond inserts pressed into insert holes formed in the face of the drag bit. In the foregoing patents the cutting end of the inserts are unsupported and are vulnerable to fracturing just above the face of the bit. It is an object of the present invention to provide an improved diamond drag bit which allows an increased elevation of the cutter insert above the face of the bit for better bit penetration while still supporting the insert. That is, the improved diamond drag bit according to the invention should allow for a maximum cutter exposure or extension, thereby permitting a significantly greater depth of cut for use in highly plastic rock, while preventing shear or breakage of the diamond cutter insert. The above object is achieved by the subject matter of claim 1. Preferred embodiments and further improvements are indicated in the depending subclaims. The diamond drag of the invention bit has a multiplicity of individual diamond inserts inserted within insert holes formed in a face of a drag bit body. The diamond inserts each have a cylindrical shank and a diamond cutting disc at a first cutting end protruding from the bit body for cutting rock formation. Additional support for the cutting end of the insert is provided along a longitudinal surface of the insert shank 180° from the cutting disc, in the form of an adjacent mass extending substantially the full length of the cutter insert shank that is exposed beyond the face of the drag bit body. The support has the same width as the cutter insert when viewed transverse to a bit radius through the cutting disc. Preferably, the means for supporting the insert shank is a second cylindrical stud body inserted in an insert hole formed in the face immediately adjacent to or overlapping the cutter insert hole. A concave cylindrical surface of the stud body supports the back side of the cylindrical diamond cutter insert. Preferably, the second cylindrical stud body is metallurgically bonded to the shank of the diamond insert. An alternative embodiment comprises a portion of the bit body having a curved concave surface formed therein that conforms to an supports a 120° portion of the back side of the cylindrical shank of the diamond insert. BRIEF DESCRIPTION OF THE DRAWINGS The above noted 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 of a diamond rock bit with cutter inserts secured within insert holes formed in a face of a rock bit body; FIGURE 2 is an end view of the cutting end of the drag bit; FIGURE 3 is a side elevational view of a cutter insert with a backup stud supporting the cutter insert; FIGURE 4 is a view taken through 4-4 of FIGURE 3 illustrating the backup stud connected to the cutter insert; FIGURE 5 is a view taken through 5-5 of FIGURE 3; FIGURE 6 is a diagrammatic illustration of a cutter insert and backup stud and their inter-relationship; FIGURE 7 is an alternative embodiment wherein the backup insert support is provided by a matrix material formed from the body of the drag bit; FIGURE 8 is a top view taken through 8-8 of FIGURE 7; and FIGURE 9 is an end front view of the diamond cutter face exposed above the face of the bit body. DESCRIPTION FIGURE 1 depicts a diamond drag rock bit generally designated as 10. Drag bit consists of a bit body 12 having a threaded pin end 14 and a cutting end generally designated as 16. A pair of conventional tool groove slots 13 on opposite sides of the bit body 12 provide a means to remove the bit from a drill string. The cutting face 18 includes one or more fluid passages 22. Typically, cooling fluid or "mud" is pumped down a drill string into the pin end 14 and out through the fluid passages 22 in which nozzles 24 are secured (Fig. 2). The drill string that connects to the threaded pin end is not shown. The cutting end of the drag bit comprises a multiplicity of diamond inserts 20 imbedded in strategic locations in insert holes 26 formed in the cutting face 18 of the bit body. Each insert 20 comprises a cylindrical base end or shank 21 formed of cemented tungsten carbide, a cutting end having a cemented tungsten carbide disc 23 including a polycrystalline diamond cutting surface layer 25 sintered to the face of the disc. The insert, for example, is backed up by a buttress-like steel support stud 28 that is retained within a stud insert hole 30 drilled adjacent to or overlapping the insert hole 26. The support stud is located on the back side of the cutter insert, that is, 180° from the diamond layer. A suitable insert with a 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 Stratapax drill blank. FIGURES 3, 4 and 5 illustrate a preferred embodiment wherein the support stud 28 is crescent shaped when viewed from the end. A concave surface 29 on the support stud is, for example, the same radius as and tightly interfitted with the back surface of the cutter shank 21. The length of the support stud matches the length of the cutter so that the outer end of the support stud is in line with the end of the cutter insert. Thus, the support stud provides support along substantially the full longitudinal length of the back side of the cutter. The shank 21 of the cutter insert and the steel backing support stud 28 are of the same width transverse to the cutting direction, that is, the same width when viewed transverse to a bit radius through the cutting disc. The insert shank and support stud are rigidly fixed together at a junction 30 by, for example, brazing or other metallurgical connection means. The insert shank and the support stud are the same width so that there is no increase in resistance to rotation of the bit because of the support stud. There is no reason to make the stud narrower than the insert, and if it were made wider, the support stud would simply wear away to the same width as the insert. The bending strength of this assembly increases approximately by the square of the distance between the axis 32 of the support stud and the axis 34 of shank of the cutter insert. Therefore, the backing support 28 is significantly useful in increasing the bending strength of the cutter 20. FIGURE 6 depicts a specific example wherein a three quarter inch (19 mm.) diameter cylindrical diamond cutter insert may be offset from its backing support stud any distance from 3/16 inch (4.8 mm.) to 3/4 inch (19 mm.). In the illustrated embodiment, the insert is offset by 9/16 inch (14.3 mm.), or 75% of the insert diameter. This means that the sud is supporting the back of the insert through an angle of about 120°. This large an engagement with the back of the cutter provides ample support to a large area of the back of the insert and a large increase in the bending strength. This cutter insert-support stud assembly as described is a significant improvement and greatly resists bending and shear forces as heretofore described. The backup support stud 28 is preferably fabricated from steel, the steel support being brazed to the cutter shank 21. The foregoing assembly has five times the shear resistance of a non-supported cutter. Another embodiment has the combination of a supported cutter in a matrix bit body; the support stud 28 and cutter 20 being, for example, brazed into preformed pockets strategically located in the cutting face 18 of the bit body 12. A matrix bit body refers to one having a body made from cemented tungsten carbide, for example, where a mass of carbide is infiltrated with a binder metal for forming at least a portion the bit body adjacent to the cutting face. FIGURES 7, 8 and 9 illustrate an alternative embodiment wherein the drag bit generally designated as 200 comprises a cutting end generally designated as 116 that is fabricated from a matrix material. Cutter insert pockets 126 are formed in the cutting face 118 of the bit body. The backup support 128 is formed in the female drag bit mold (not shown) in which the carbide material is infiltrated. The support 128 extends along the back side of the insert 200 in the same manner as that shown in Figures 1 through 5, but is formed of matrix material integral with the matrix body of the drag bit. While the steel support 28 is superior in toughness to the matrix backup support 128, the combination of the insert with matrix backup is still stronger than a free standing insert 20 without support. It will also be recognized that the back side of the insert may be supported in a steel body having a buttress-like mass behind the insert which is the same width as the insert shank when viewed transverse to a bit radius. This embodiment resembles the matrix bit embodiment illustrated in FIGURES 7 to 9, but is made of steel instead of cemented tungsten carbide. Also, in such an embodiment, the inserts may be press fitted into the bit body instead of being brazed in place. It will of course be realized that various modifications can be made in the design and operation of the present invention. Thus, while the principal preferred construction and mode of operation of the invention have been explained in what is now considered to represent its best embodiments, which have been illustrated and described, it should be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

Claims: A diamond drag bit (10;200) having a multiplicity of individual diamond inserts (20) inserted within insert holes (26;126) formed in a face (18,118) of a drag bit body (12), the diamond inserts each having a cylindrical shank (21) and a diamond cutting disc (23) at a first cutting end protruding from the bit body for cutting rock formation, and means (28,128) for providing support for the cutting end of each insert along a longitudinal surface of the insert shank 180° from the cutting disc, characterized by the means (28,128) for providing support being an adjacent mass extending substantially the full length of the cutter insert shank that is exposed beyond the face of the drag bit body (12), the support having the same width as the cutter insert (26) when viewed transverse to a bit radius through the cutting disc (23). The drag bit as set forth in claim 1, wherein the means (28,128) for supporting comprises a curved concave surface (29) that conforms to and parallels a portion of the cylindrical shank portion (21) of the diamond cutter insert. The drag bit as set forth in either of claims 1 or 2, wherein the means (28,128) for supporting contacts the cylindrical shank (21) of the diamond insert (20) through about 120° of the surface of the shank of the cutter. The drag bit as set forth in any of the preceding claims, wherein the means (28,128) for supporting each insert shank (21) comprises a cylindrical stud body inserted in an insert hole formed in the face adjacent to the cutter insert holes, a surface (29) of the cylindrical stud body being adjacent to the surface of the cylindrical shank (21) of the diamond cutter insert (20). A diamond drag bit as set forth in claim 4, wherein the cylindrical stud body (28,128) comprises a crescent face interfitted with a back side of the cutter insert. The drag bit as set forth in either of claims 4 or 5, wherein the cylindrical stud body (28,128) is fabricated from steel. The drag bit as set forth in any of claims 1, 2 or 3, wherein the means for supporting the insert shank (21) comprises a portion of the body which extends beyond the face of the drag bit adjacent to the exposed shank of the cutter insert. The drag bit as set forth in any of the preceding claims, wherein the means (28,128) for supporting is metallurgically bonded to the diamond cutter insert. The drag bit as set forth in claim 8, wherein the metallurgical bond is a braze.

Inventors: CLENCH MARK NMI, IZAGUIRRE SAUL N, CLENCH, MARK (NMI), IZAGUIRRE, SAUL N.
Applicants: SMITH INTERNATIONAL, SMITH INTERNATIONAL, INC.
Application year: 1992
Main classification: E21B10
IPC codes: E21B10