1. Technical Field
The present invention relates in general to rotary drag bits and, in particular, to an improved system, method, and apparatus for a rotary drag bit having gauge cutting elements configured at large back rake angles.
2. Description of the Related Art
Earth-boring bits of the fixed cutter variety, commonly referred to as drag bits, have no moving parts and employ an array of hard inserts to scrape and shear formation material as the bit is rotated in the borehole. Inserts on prior art fixed cutter bits are typically aligned such that the inserts scrape the material from the borehole bottom. For scraping to take place, the longitudinal axis of the insert is typically at a small acute angle (e.g., 0° to 30°) relative to the bit face. Such an alignment places the cutting face of a cylindrically-shaped insert nearly perpendicular to the borehole bottom. The contact area between the cutting element and the formation starts out very small but increases rapidly as penetration or depth of cut becomes deeper.
High impact side-loading of drill bits during operation results in non-compressive loading of the interface between the diamond and tungsten carbide components on PDC cutters. This leads to broken and/or chipped cutters in the upper shoulder and gauge areas of the bit profile. High residual stresses are inherent in this interface area as a result of varying planar and non-planar geometries and the cutter manufacturing process. An improved solution that overcomes these problems would be desirable.
Embodiments of a system, method, and apparatus for a fixed cutter rotary drill bit having gauge cutting elements at large back rake angles are disclosed. The gauge is located at the outer diameter side wall portion of the bit that extends from the cutting end. The gauge and its cutting components contact the side wall of the bore hole during drilling operations.
In accordance with the invention, the gauge cutting elements may be configured at a back rake angle in a range of about 40° to 70°. For applications where cutter damage is a concern and side-cutting aggressiveness is a low priority, a very high back rake angle helps ensure compressive cutter loading when side impact forces are higher.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings.
So that the manner in which the features and advantages of the present invention are attained and can be understood in more detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the appended drawings. However, the drawings illustrate only some embodiments of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.
Referring to
As shown in the embodiment of
Referring now to
The gauge 33 essentially defines the flat, outer diameter side wall portion of bit 11 that extends from cutting end 15 (
As shown in
Referring now to
As shown in
In a “nominal” position on the gauge 33, both the back rake angle and the side rake angle of element 17 are zero. Thus, in one embodiment of the nominal position, face 23 extends in the plane defined by axes 42, 44, such that it is perpendicular to the gauge 33 and bore sidewall, and face 23 is parallel to axes 12, 42 and 44. Rotating the face 23 about axis 42 results in a modification to the back rake angle. In the gauge area 33, a positive back rake angle inclines the cutting face 23 away from the bit axis 12 and toward the borehole 34. Rotating the face 23 about axis 44 results in a modification to the side rake angle. A positive side rake angle includes the cutting face 23 away from the drill string and toward the bottom of the bore hole.
Referring again to
For applications where cutter damage is a concern and side-cutting (e.g., cutting with the gauge 33 of the cutting profile 25) aggressiveness is a low priority, a very high back rake angle help ensures compressive cutter loading when side impact forces are higher. This is accomplished by lowering the y-component force (see, e.g.,
For example, comparing
While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.
This application claims priority to and the benefit of U.S. Provisional Patent Application No. 60/889,403, which was filed on Feb. 12, 2007, incorporated herein by reference in its entirety.
Number | Date | Country | |
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60889403 | Feb 2007 | US |