Percussion drill bit with V-shaped splines
A drill bit is disclosed for use in a percussion drilling apparatus of the type for boring into the earth. Embodiments of the drill bit comprise an elongate body with a first end, a second end, and a longitudinal surface extending between the first and second ends. Embodiments further comprise a plurality of splines on the longitudinal surface of the drill bit, with at least one of the plurality of splines comprising an apex, a root, and a planar surface between the apex and root. In preferred embodiments, the planar surface is oriented at an angle between 10 and 45 degrees to a plane extending from a center of the drill bit to a midpoint of the apex.
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BACKGROUND1. Technical Field
The disclosure herein generally relates to earth boring bits used to drill a borehole for applications including the recovery of oil, gas or minerals, mining, blast holes, water wells and construction projects. More particularly, the disclosure relates to percussion hammer drill bits.
2. Description of the Related Art
In percussion hammer drilling operations, the bit impacts the earth in a cyclic fashion while simultaneously rotating. In such operations, the mechanism for penetrating the earth is of an impacting nature rather than shearing. Therefore, in order to promote efficient penetration by the bit, the cutting elements of the bit need to be “indexed” to fresh earthen formations during each impact. This need is achieved by rotating the drill string a slight amount between each impact of the bit to the earth and incorporating longitudinal splines which key the bit body to a cylindrical sleeve (commonly known as the driver sub or chuck) at the bottom of the hammer assembly. As a result, the drill string rotation is thereby transferred to the hammer bit itself. Experience has demonstrated for an eight inch hammer bit that a rotational speed of approximately 20 rpm for an impact frequency of 1600 bpm (beats per minute) typically results in efficient drilling operations. This rotational speed translates to an angular displacement of approximately 4 to 5 degrees per impact of the bit against the rock formation.
An example of a typical hammer bit connected to a rotatable drill string is described in U.S. Pat. No. 4,932,483, incorporated herein by reference. The downhole hammer comprises a top sub and a drill bit separated by a tubular housing incorporating a piston chamber therebetween. A feed tube is mounted to the top sub and extends concentrically into the piston chamber. A piston is slideably received within the housing and over the feed tube. Fluid porting is provided in the feed tube and the piston to sequentially admit fluid in a first space between the piston and top sub to drive the piston towards the drill bit support and to a second space between the piston and the drill bit support to drive the piston towards the top sub.
Rotary motion is provided to the hammer assembly and drill bit by the attached drill string powered by a rotary table typically mounted on the rig platform or top drive head mounted on the derrick. The drill bit is rotated through engagement of a series of splines on the bit and driver sub that allow axial sliding between the components but do not allow significant rotational displacement between the hammer assembly and bit.
Due to the forces transmitted between the splines, as well as the cyclic nature of the stress created, mechanical failure of the splines can force an operator to remove the drill bit from operation for repair or replacement, thereby increasing maintenance and operation costs. Typically, the mechanical failure of the splines is initiated by galling between the splines of the drill bit and the driver sub or fatigue cracking in the splines of either component.
As a result of the significant costs associated with premature failure of the drill bit, it is desirable to increase the mechanical reliability of percussion hammer drilling systems. It is also desirable to optimize the design characteristics of the percussion bit (such as the bit length and weight) to maximize the transfer of energy between the piston and the bit, thereby increasing the rate of penetration for the bit.
The embodiments described herein provide opportunities for improvement in percussion bit service life and rate of penetration. These and various other characteristics and potential advantages will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments, and by referring to the accompanying drawings.
SUMMARY OF THE PREFERRED EMBODIMENTSEmbodiments described herein comprise a drill bit for use in a percussion drilling apparatus of the type for boring into the earth. Preferred embodiments comprise an elongate body with a first end, a second end, and a longitudinal surface extending between the first and second ends. Preferred embodiments further comprise a plurality of splines on the longitudinal surface of the drill bit, with at least one of said plurality of splines comprising an apex, a root, and a planar surface between the apex and root. In certain preferred embodiments, the planar surface is oriented at an angle between 10 and 45 degrees to a plane extending from a center of the drill bit to a midpoint of the apex.
BRIEF DESCRIPTION OF THE DRAWINGSFor a more detailed description of the preferred embodiments, reference will now be made to the accompanying drawings, wherein:
Referring first to
During operation, drillsting 210 rotates, thereby rotating percussion drilling assembly 200. In addition, piston 245 travels back and forth in an axial direction so that it cyclically impacts bit 260. A series of engaged splines 265 on bit 260 and driver sub 240 allow bit 260 to slide axially relative to driver sub 240 while also allowing driver sub 240 to rotate bit 260. As described previously, this allows the cutting elements (not shown) of bit 260 to be “indexed” to fresh rock formations during each impact of bit 260, thereby improving the efficiency of the drilling operation.
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Furthermore, by increasing the number of splines 30, the overall length L of splines 30 (as shown in
While various preferred embodiments have been showed and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings herein. The embodiments herein are exemplary only, and are not limiting. Many variations and modifications of the apparatus disclosed herein are possible and within the scope of the invention. For example, the angle of the planar surfaces on each side of the spline may vary from those depicted in the embodiments shown. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims
Claims
1. A drill bit for use in a percussion drilling apparatus of the type for boring into the earth, said drill bit comprising:
- an elongate body with a first end, a second end, a central axis, and a longitudinal surface disposed about said axis and extending between said first and said second ends; and
- a plurality of splines on said longitudinal surface of said drill bit, wherein at least one of said plurality of splines comprises a base portion, an apex, a root, and a generally planar surface between said apex and said root, wherein a first plane parallel to said generally planar surface is oriented at an angle between 10 and 45 degrees to a second plane extending from said axis to a midpoint of said apex and wherein the base portion is wider than the apex.
2. The drill bit of claim 1 wherein said plurality of splines comprises a plurality of roots and each root comprises a radiused portion with a root radius that connects said planar surface from a first spline of said plurality of splines to a second planar surface from a second spline of said plurality of splines.
3. The drill bit of claim 2 further comprising a diameter inscribing said roots of said plurality of splines, wherein the ratio of said diameter to said root radius is less than 50.
4. The drill bit of claim 1 wherein said angle is between 20 and 35 degrees.
5. The drill bit of claim 1 wherein said root does not comprise a substantially flat surface.
6. The drill bit of claim 1 wherein the root comprises a curved surface that intersects a pair of planar surfaces adjacent to the root.
7. The drill bit of claim 1, wherein:
- said plurality of splines extend a distance L along said longitudinal surface;
- said elongate body has a minor diameter d; and
- a ratio of L/d is less than 0.7.
8. The drill bit of claim 7 wherein the ratio of L/D is between 0.60 and 0.40.
9. The drill bit of claim 1 wherein the root comprises a curved surface that intersects a pair of planar surfaces adjacent to the root.
10. A drill bit for use in a percussion drilling apparatus of the type for boring into the earth, said drill bit comprising:
- an elongate body with a central axis;
- a plurality of splines disposed on said elongate body, said splines disposed parallel to said central axis, wherein at least one of said plurality of splines comprises a base portion and an apex, wherein the base portion is wider than the apex and the apex is disposed between a first planar surface and a second planar surface;
- wherein a first plane parallel to said first planar surface is oriented at a first angle between 10 degrees and 45 degrees to a second plane extending from said central axis to a midpoint of said apex; and
- wherein a third plane parallel to said second planar surface is oriented at a second angle between 10 degrees and 45 degrees to said second plane.
11. The drill bit of claim 10, wherein the first angle is between 20 and 35 degrees.
12. The drill bit of claim 10, wherein the second angle is between 20 and 35 degrees.
13. The drill bit of claim 10, further comprising a root on either side of said apex, wherein said root comprises a root radius and does not comprise a flat surface.
14. The drill bit of claim 13 further comprising a diameter inscribing said roots of said plurality of splines, wherein the ratio of said diameter to said root radius is less than 50.
15. The drill bit of claim 13 wherein the root comprises a curved surface, wherein the curved surface intersects a first planar surface adjacent to the root and the curved surface intersects a second planar surface adjacent to the root.
16. A drill bit for use in a percussion drilling apparatus of the type for boring into the earth, said drill bit comprising:
- an elongate body;
- a plurality of splines disposed on said elongate body, wherein at least one of said plurality of splines comprises a first and second surface angled relative to one another and configured to form an angle therebetween of between 20 and 90 degrees.
17. The drill bit of claim 16 wherein the angle is between 40 and 70 degrees.
18. The drill bit of claim 16, further comprising a root adjacent to the first angled surface, wherein said root does not comprise a flat surface.
19. A percussion drilling assembly comprising:
- a top sub;
- a driver sub with a first plurality of V-shaped splines, wherein each spline comprises a pair of angled surfaces configured to form an angle of between 20 and 90 degrees;
- a case disposed between said top sub and said driver sub;
- a piston disposed within said case; and
- a bit with a second plurality of V-shaped splines engaged with said first plurality of V-shaped splines.
20. The percussion drilling assembly of claim 19 wherein the angle is between 40 and 70 degrees.
21. The percussion drilling assembly of claim 19 wherein the driver sub further comprises a root between a first angled surface from a first spline and a second angled surface from a second spline, wherein the root does not comprise a flat surface.
22. The percussion drilling assembly of claim 19 wherein the root comprises a curved surface that intersects the first angled surface and the second angled surface.
23. A method of drilling into the earth comprising the steps of:
- providing a drill bit with an elongate body and a first plurality of splines on said elongate body;
- providing a drive collar with a second plurality of splines that slideably engage said first plurality of splines;
- providing a piston;
- impacting said piston against said drill bit;
- impacting said drill bit against the earth; and
- rotating said drive collar and said drill bit, wherein at least one of said first plurality of splines comprises a base portion, an apex, a root, and a planar surface between said apex and said root, wherein the base portion is wider than the apex and a first plane parallel to said planar surface is oriented at an angle between 10 degrees and 45 degrees to a second plane extending from a center of said drill bit to a midpoint of said apex.
24. The method of claim 23 wherein the angle is between 20 and 35 degrees.
Type: Application
Filed: Dec 21, 2005
Publication Date: Jun 21, 2007
Applicant: Smith International, Inc. (Houston, TX)
Inventors: Alan Marshall (Lost Creek, WV), Shantanu Swadi (Cypress, TX)
Application Number: 11/313,551
International Classification: E21B 10/38 (20060101);