Abstract:
A steel bodied PCD drag bit is disclosed having a plurality of blades integrally formed thereon, each blade having a bottom surface that includes an angular front section and rear section intersecting to form an apex, the front section having a plurality of sockets formed thereon to receive a plurality of cylindrical cutters elements, the rear section being substantially parallel to the cylindrical cutting.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of 35 U.S.C. 111(b) provisional application Ser. No. 60/019,386 filed Jun. 5, 1996 and entitled A Drill Bit. Having Trapezium-Shaped Blades. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to drag-type drill bits and, more particularly, to the type of drag bit in which a plurality of cutters are mounted in a body. 
     2. Description of the Prior Art 
     Drag bits, of the type described, usually include a bit body having a cutting face with the cutters mounted thereon. The cutters usually comprise a carbide stud having an angled face for having a polycrystalline diamond (hereinmatter called PCD) compact affixed thereto, or a cylindrical piece of carbide having an end face for having the PCD compact mounted thereon. The stud cutters are usually brazed or force fitted into cylindrical holes formed in the cutting face, whereas the cylindrical cutters are usually placed on their sides into channels formed in the cutting face and are brazed thereto. 
     Conventionally there are two types of bit bodies utilized. One type is a steel body bit which normally had the cylindrical holes bored into the cutting face for receiving stud cutters. The other type is where the bit body is formed from a matrix material. The matrix body is formed in a mold and channels are normally formed on the cutting face to accept cylindrical cutters although initially stud cutters were also utilized on matrix bits. Normally cylindrical cutters were not used on steel body bits because the steel material would erode from around the cutters and the cylindrical cutters would fall out. 
     Early on in the development of these types of bits, the steel body bits had a relatively flat continuous cutting face, with the stud cutters extending outwardly therefrom. The original matrix bits also had similar face constructions. 
     Later on, bit bodies were formed with a plurality of blades extending downwardly to accept the cutters mounted thereon. Channels were formed between the blades to form fluid passages. The blades were either straight, radial blades or they were curved in a spiral fashion. 
     Initially the blades on steel body bits were formed with a bottom flat face that was parallel to the formation. The cylindrical cutters were mounted on the face with the cutting surfaces facing the direction of rotation. The problem with this construction is that the flat surfaces on the blade behind the cutting elements functioned as penetration limiters and also inhibited hydraulic flow passing by the cutting elements. 
     The matrix bits evolved to where matrix material was added to the surface of the blade directly behind the cylindrical cutters and along the sides thereof in order to add support to the cutting elements. These projections were easily formed on matrix bits by forming additional indentions of the mold surface forming the blades. These indentations accommodated the space for the cutters and for the additional supporting matrix material. 
     This type of construction can not be easily produced on a steel body bit, because machining such projections on the blade surface would be quite difficult. As a result steel body bits normally have not been able to utilize cylindrical cutters on the blades because of erosion problems and machining limitations. 
     U.S. patents illustrating the state of the art is given as follows: U.S. Pat. Nos. 4,073,354; 4,491,188; 4,558,753; 4,883 132; 4,898,252; 4,949,598; 4,995,887; 5,332,051; and 5,383,527. 
     SUMMARY OF THE INVENTION 
     The steel body drag bit made in accordance with the present invention obviates the above mentioned shortcomings by providing a blade construction that maximizes the cylindrical cutter exposure while minimizing the structure that inhibits hydraulic flow and limits penetration of the cutters. 
     The steel body drag bit of the present invention includes blades having a portion of the bottom surface extending across the blade that is substantially parallel to the bottom side of the cylindrical cutter. In the preferred embodiment, this surface is preferable at a steeper angle than parallel in order to remove material from the blade that contacts the formation to limit penetration and inhibit the hydraulic flow over the blade. This continuous surface could also have a wave form for providing support behind the cylindrical cutters and removing more material between the cutters for enhanced hydraulic flow. 
     The channels formed in the blades to receive the cutters are constructed in such a manner that substantially the entire front faces of the cutting elements are exposed, while substantially the entire back faces of the cylindrical cutters are embedded therein. In this manner, preferably more than half of each cutter is embedded and constrained by the channel to form a mechanical lock on the cutter. 
     The front face of each blade also includes an angled portion below the cutters to enhance the hydraulic flow over the blade. 
     As a result, the cross sectional shape of each blade for the steel body bit is in the form of a modified trapezium. Such blade structure has not been utilized before on drag bits of the type described. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the head portion of the drill bit made in accordance to the present invention; 
     FIG. 2 is a bottom elevational view of the drill bit of FIG. 1; 
     FIG. 3 is an enlarged fragmentary view of the drill bit of the present invention illustrating a section of a blade having cutters mounted thereon; 
     FIG. 4 is another enlarged fragmentary view of the drill bit of the present invention, showing the blade cutter construction from a more forward perspective; and 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 illustrate a drag-type drill bit, generally indicated by arrow 10, having a head portion 11 formed on the lower end thereof. A threaded pin portion (not shown) is integrally formed with the bit head 11, on the upper end of the drill bit 10. The pin portion is conventional in construction and is adapted to be threadedly connected to the bottom of a drill string. 
     The head portion 11, along with the pin portion, is preferably made of a unitary steel construction and substantially cylindrical side portion 12, and an end face portion 13. A plurality of blades 15 and 17 are integrally formed on the head portion 11. The blades 15 and 17 extend from the bottom surface of the head portion 11 and extend downwardly along the sides 12 thereof. The blades 15 and 17 then extend radially inwardly along the end face 13 with the blades 15 extending further inward to the center of the bit face 13, while the blades 17 are shorter and extend only a portion of the radial distance inwardly. 
     The lower portion of each blade 15 and 17 includes a plurality of buttons 19 embedded therein. The buttons 19 are preferably cylindrical tungsten carbide inserts extending into the blades 15 and 17 with the end faces extending slightly beyond the surface of the blades. The end faces of the buttons 19 are preferably coated with a layer of synthetic polycrystalline diamond. The portions of the blades 15 and 17 extending along the sides 11 of the bit extend to the gage of the bore hole being drilled, and function to stabilize the bit during drilling. The diamond coated buttons 19 function to maintain the gage of the bore-hole that has been formed and to protect the steel body construction of the blades. 
     Each blade 15 and 17 also includes a plurality of cylindrical cutters 20 mounted on the bottom side 21 thereof. The inserts 20 are conventional in construction and each includes a cylindrical body 23 preferably made of tungsten carbide and a front face 24 having a surface formed of synthetic polycrystalline diamond. The bottom side 21 of each blade is oriented to be at an angle with respect to the bottom and side-wall of the bore-hole facing the direction of rotation. Each cutter 20 is mounted within a socket 25 which is completely cylindrical at the rear end thereof and transitions to a semi-cylindrical groove at the forward end. The transition from a cylindrical hole completely enveloping the rear end of the cutter 20 to the semi-cylindrical groove supporting the bottom front end of the insert is accomplished in such a manner that the rear half of the insert is contacted by the socket over greater than half of its periphery to enable the cutter to be mechanically locked by the socket. 
     In manufacture, the cutter are bonded within the sockets by conventional braze material. 
     It should be noted that the cutter are oriented to have a negative rake with respect to the bore hole bottom and side walls. Although a side-rake is not being utilized, it would be within the realm of the present invention to orient the cutter 20 to achieve a side-rake. 
     As more clearly shown in FIG. 3, the back end of each blade 15 and 17 includes an angled surface 30 which is substantially parallel with bottom edge 31 of each cutter 20. The bottom side 21 and angled surface 30 meet at an apex 32 to form the bottom face of the blade. In this preferred embodiment, the angled surface 30 falls away at a slightly greater angle than parallel. In rotation, this surface 30 falls away from the bore hole bottom and side walls to enable fluid flow to efficiently pass over the blades. 
     The rear of each blade 15 and 17 includes an additional surface 35 that is falling away from parallel at a faster rate for these same hydraulic purposes. 
     As more clearly shown in FIG. 4, the front side of each blade 15 and 17 includes a front face 37 and an angled surface 39 located at the base of the inserts. The angled surface 39, which also extends the length of the blade like the rear surfaces 30 and 35. The angled surface 39 functions to allow the drilling fluid to pass over the top of each blade in a proficient manner. 
     Referring back to all of the FIGS., the drill bit 10 also includes a plurality of channels 40 formed between the blades 15 and 17. A plurality of nozzles 45 are located on the face of the head portion 11. These nozzles 45 communicate with the interior of the bit to enable drilling fluid to pass therethrough. In operation, the drilling fluid would pass over the blades 15 and 17 as the bit rotates on the bore hole bottom. After cleaning and cooling the cutters 20, the drilling fluid, with the formation cuttings would pass up the side of the bit through a plurality of junk slots 50 formed between the longitudinal sectional of the blades 15 and 17. The drilling fluid would then pass up the annulus formed by the bore hole and the exterior of the drill string. 
     In this preferred embodiment, the entire outer surface of the steel body 11 is coated by a hard material to prevent erosion during operation. The preferred coating is described in U.S. Pat. No. 5,535,838, and is incorporated herein. 
     While a preferred embodiment of the invention has been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit of the invention.