Rock Bit With Powered Gauge Cutter

Abstract

A solid, button-insert-type percussion bit is disclosed having a generally cylindrical body with a forwardly facing surface provided with hardened cutter inserts and a rearward, anvil-forming portion. A diagonal chamber in the bit body reciprocably mounts a plunger having a cutter element on its forward face in such position as to be driven against the periphery of the bottom of the hole being drilled. A passage connects the chamber in back of this plunger with the forward working chamber of the percussion drill motor so that the small plunger and its cutter are driven outwardly to maintain the gauge of the hole each time the forwardly facing cutter elements are driven forwardly by axial blows applied by the hammer piston.

Description

This invention relates to percussion rock bits, particularly of the solid type, having hardened cutter inserts mounted in and projecting from the forward face and periphery thereof.

Normally, rotary-cone-type bits are used for deep hole drilling, whether of the conventional rotary type or in cooperation with a downhole type of percussion motor. This is because no fully satisfactory way has been provided for maintaining the size or gauge of the hole when solid-type bits are used for this purpose. However, rotary cone bits do not possess the strength characteristics of solid-type bits and, therefore, cannot be subjected to the full potential energy output which may be developed by modern downhole percussion tools. More particularly, with the use of solid-type bits, rapid wear on the outside diameter of the body results in unacceptable loss of hole gauge long before the face cutters of the bit are worn out. In some cases, complete failure of the peripheral cutting elements due to the pinching action of the bit makes it necessary to pull the bit early. Furthermore, reinsertion of the new or repaired bit is difficult because of the reduced size of the hole, as explained.

Accordingly, an object of the present invention is to provide a solid-type rock bit which is sufficiently rugged for use with high-pressure, percussion-type downhole tools and which will effectively maintain the desired hole gauge.

Another object is to provide such a bit having means whereby an axial percussive blow upon the bit body is accompanied by an outward cutting stroke of one or more cutting elements which will effectively maintain the original diameter or gauge of the hole.

Another object is to provide a novel, percussion-type bit which incorporates individually powered means for drilling the hole slightly larger than the diameter of the bit body so as to reduce bit wear and facilitate reinsertion of the new bit into the hole.

These objects and others are attained by means of the herein-disclosed device which comprises a solid-type rock bit body having a forward working face which is provided with hardened cutter inserts and a rear portion which forms the anvil of a percussion-type drill motor. One or more gauge cutters are provided. Each comprises a small, cylindrical chamber extending diagonally rearwardly and inwardly from an opening at or adjacent the intersection of the bit forward and side surfaces, and a plunger reciprocable in this chamber carries a hardened cutter element in its forward face. The plunger is urged rearwardly by a spring. A control passage connects the chamber in back of the plunger with the forward working chamber of the percussion motor whereby fluid pressure conditions in the mentioned forward working chamber are transmitted to the plunger for impelling the same and its cutter element diagonally against the corner of the hole being drilled, so as to chip the corner and therefore maintain the diameter of the hole slightly larger than the diameter of the bit body itself. During each upward or return movement of the hammer piston during normal operation, the pressure in the forward working chamber rises sufficiently to drive the mentioned plunger and cutter forwardly against the corner of the hole being drilled. A small, rearward boss on the plunger normally enters the mentioned control passage. This boss permits sufficient delay after commencement of the return stroke of the hammer piston so that the pressure in the control passage builds up sufficiently to cause advance of the plunger and its cutter element at a high rate of speed.

In the accompanying drawings which illustrate the invention,

FIG. 1 is a longitudinal transverse section illustrating in part a form of percussion motor which may be combined with the herein-disclosed novel rock bit.

FIG. 2 is a similar view showing the forward portion of the motor of FIG. 1 together with the novel rock bit in normal operating position.

FIG. 3 is a sectional view similar to FIG. 2, rotated somewhat from the position of FIG. 2 and showing the rock bit in the abnormally advanced position incident to suspension of the motor off bottom.

FIG. 4 is a graphical representation of various parameters during operation of the motor.

The novel percussion drill motor illustrated in FIGS. 1 and 2 is more fully disclosed and claimed in U.S. Pats. Nos. 3,229,776 and 3,105,559 assigned to the assignee of the present application. This motor comprises a ruggedly built, cylindrical casing 6 for connection at its upper end 7 with a source of fluid pressure, for instance, a conventional drill string, and having a coarse thread 8 at its lower end for reception of a split adapter nut 9 which, in turn, slidably receives the anvil 10 by means of splines 11. At the lower or forward end of anvil 10 there is provided, in this case integrally, a bit body 12 having a downward or forward face 13 provided with propitiously arranged, hardened cutting inserts 14. A chamber 15 is provided at the intersection of forward surface 13 and generally cylindrical side surface 16 of the body. The upper end of the anvil is provided with a guide enlargement 17 slidably received within casing 6. An axial duct 18, 19, 20 extends through the anvil in part, as will be explained, for conducting motor exhaust which cools and lubricates the bit cutters and carries cuttings to the surface of the hole, in the usual manner. The upper end 21 of nut 9 underlies anvil enlargement 17 to prevent the anvil from dropping out the bottom of the casing.

Reciprocably received within casing 6 is the hammer piston 24 having thickened central portions 25 and 26 which slide along the casing inner surface, and an internal annular shuttle groove 27. A control rod, generally designated 28, extends axially through the motor from its upper end, where it connects to the source of operating fluid pressure, for instance, the interior of the supporting drill stem, through an axial passage 29 in the hammer piston and into the upper portion 18 of the anvil passage. The control rod is formed of a central body portion 30 and an outer shell 31 forming between them upper longitudinal passages 32 and lower longitudinal passages 33 connecting, respectively, ports 34 and 35 leading to upper working chamber 36 and lower ports 37 and 38 leading to lower working chamber 39. A high-pressure or working fluid passage 40 extends axially through the control rod and has a choke 41 at its lower end providing a constant bypass of working fluid. Central supply ports 42 connect working fluid passage 40 with shuttle groove 27. Exhaust passages, represented by dotted lines 43, are also provided between rod core 30 and shell 31 connecting, respectively, an upper exhaust port 44 opening to upper working chamber 36 and a lower exhaust port 45 for connecting lower working chamber 39 with exhaust duct 66 in the anvil, to be described. A blowing port 46 also opens into exhaust passage 43 and, normally, is covered by the hammer piston.

As explained in the above-mentioned patents, during normal operation of the motor with the bit resting on bottom and the lower edge 9a of nut 9 resting on bit shoulder 12a, working fluid supplied through control rod passage 40 is alternately shuttled by means of groove 27 in the hammer piston 24 to lower working chamber 39 to lift the hammer piston and to upper working chamber 36 to drive the hammer piston downwardly in its power stroke. In the lowermost position of the hammer piston, upon striking the upper surface 47 of the anvil, upper exhaust port 44 will be exposed above the hammer piston so as to exhaust pressure from upper chamber 36. At the uppermost or turnaround position of the hammer piston, the lower edge 48 thereof exposes lower exhaust port 45 to exhaust lower working chamber 39. When the tool is suspended off bottom (FIG. 3), anvil 10 will drop abnormally until enlargement 17 rests upon upper end 21 of adapter nut 9. At this time, shuttle groove 27 will somewhat overlap blowing port 45 so that the high-pressure working fluid will flow directly through exhaust passages 43 into anvil exhaust duct 18, etc. As will be explained hereafter, lower working chamber 39 will be vented at the same time.

With reference to FIG. 2, a small, cylindrical chamber 50 extends diagonally inwardly and rearwardly from the intersection of forward face 13 and side face 16 of the bit and is provided with a liner 51 having a countersunk upper portion, as at 52, and slidably receiving a small, elongated plunger 53 having an upper collar 54. A coiled compression spring 55 normally urges collar 54 against a shoulder 56 at the upper end of chamber 50 and has a hardened cutter insert 57 at its lower end. Collar 54 has a central boss 58 which normally enters the countersunk lower portion 59 of a diagonal control passage 60 extending to and opening into intermediate portion 19 of the exhaust duct through the anvil.

The upper portion 18 of the anvil passage is of somewhat greater diameter than the lower extremity 28a of the control rod so as to provide an annular passage 62 between the rod and anvil. A frustoconical shell 63, in this case welded to the lower end of control rod shell 31, extends below the control rod and, normally, slidably receives the upper end portion 64a of a tubular structure 64 which is lodged in intermediate portion 19 of the anvil passage. Conical lugs 64b on structure 64 rest against incline 19a in the anvil passage while permitting free passage of fluid therepast. A sealing O-ring 64c is provided at the lower end of structure 64. The intermediate portion 64d of the tubular structure is slightly spaced from the intermediate portion 19 of the anvil passage to provide an annular passage 65 with which previously mentioned diagonal control passage 60 communicates exteriorly and, normally, independently of the exhaust duct 66 through structure 64.

FIG. 4 represents diagrammatically the pressure conditions above or behind hammer piston 24 (curve A), pressure conditions beneath (forwardly) of the hammer piston (curve B), and the position of the hammer piston (curve C). In each case, the abscissae represent time, the total time of a cycle of the hammer piston in this instance being approximately 0.060 seconds. The ordinates in the case of curves A and B represent pounds-per-square-inch absolute. The ordinates with respect to curve C represent inches. The line D represents the critical pressure beneath the hammer and in passage 60 at which boss 58 on plunger 53 advances from passage countersink 59 to expose the entire area of collar 54 to the pressure in control passage 60. Thus, lug 58 has the effect of limiting the advanced positioning of cutter 57 during which the striking blow occurs, to the time between the points 70 and 71 on the curve B during which plunger 53 drives quickly downwardly and outwardly to stroke a chipping blow against the corner portion 72 of the hole bottom. Maximum pressure in passage 60 and in forward working chamber 39 is reached at the point 73, while at the point 74, maximum pressure is reached in the upper working chamber just prior to TDC of the hammer piston. Critical pressure beneath the hammer (Curve B) is again reached at point 71 which permits spring 55 to return the plunger to its rest position, with boss 58 in passage countersink 59. The return motion of the plunger between points 71 and 75 occupies approximately 80 percent of the cycle time.

Following the guage-cutting stroke and dwell of the plunger, the hammer enters its power stroke and ultimately strikes the anvil. Just before striking of the anvil, pressure in forward working chamber 39 reaches the low point 76 (curve B). Soon this pressure begins to build up and, when line D is reached, a chipping blow of plunger 53 is again initiated.

Thus, the frequency of the gauge-cutting device is the same as that of the main hammer piston. One or more of the gauge-cutting devices may be provided, as needed, to insure drilling of the hole at a diameter slightly greater than the diameter of the bit proper. The dimensions of the percussion motor will be adjusted to accommodate the slight increase of volume which must be filled by working fluid during lifting of the hammer piston. The alternate axial and diagonal blows will continue as long as the tool is on bottom and the lower end of adapter 8 rests on shoulder 75 of the bit.

FIG. 3 shows the tool rotated so that the gauge cutter is out of the plane of the view and the tool is hanging. The upper portion 64a of the tubular structure will withdraw from conical shell 63 (FIG. 3) permitting venting of lower working chamber 39 through passage 18 and the clearance 76 between shell 63 and the tubular structure. Moreover, at this time, insufficient pressure will be developed in passage 60 to cause actuation of diagonal plunger 53. Thus, the hammer piston will remain motionless in its lowermost position, while plunger 53 will remain in its uppermost position and the full force of working fluid will "blow" through exhaust duct 66, 20.

The particular type of percussion motor shows is exemplary, but any other type may be used with the novel rock bit structure, provided a control pressure can be tapped which fluctuates so as to produce the periodical gauge-chipping action of the individual cutting plungers 53. High-pressure passaging 18, 19 leading to the gauge cutter may be otherwise formed and may communicate directly with another part of the percussion motor, for instance, top chamber 36. Moreover, in a broad sense, other types of percussive action may be utilized and distributed to provide more-or-less concurrent or sequential axial and diagonal or lateral cutting blows.

The invention may be modified in various respects as will occur to those skilled in the art and the exclusive use of all modifications as come within the scope of the appended claims as contemplated.

Claims

I claim:

1. A percussion-type rock bit comprising a solid body with forward working surface and sidewall structure and a rearward, anvil-forming part, hardened cutter inserts in said surface, a chamber extending diagonally into said body from an opening therein adjacent the intersection of said wall structures, a plunger reciprocable in said chamber along a line inclined to the axis of said body, a hardened cutter element on the forward face of said plunger, and a fluid passage extending from said chamber through said anvil-forming part for transmitting to said plunger operating fluid pressures to which said anvil-forming part is subjected.

2. In combination in a percussion drill, a differential fluid pressure motor including a working cylinder, an anvil received in the forward part thereof, a hammer piston reciprocable in said cylinder for beating upon said anvil, a rock bit on the forward part of said anvil having a body with forward and sidewall structures, hardened cutter inserts in said forward wall structure for applying blows from said piston axially to the bottom of a hole being drilled, an exhaust and cleanout fluid duct extending through said anvil and said body, a chamber extending diagonally into said body from an opening adjacent the intersection of said body forward and sidewall structures, a plunger reciprocable in said chamber, a hardened cutter element on the forward face of said plunger, and a fluid passage connecting said chamber rearwardly of said plunger to said working cylinder forwardly of said hammer piston for causing said element to apply a forward and outward blow to the periphery of the hole being drilled for maintaining the gauge of the hole.

3. The combination described in claim 2 in which said motor includes a control rod extending axially through said working cylinder and said piston and into said anvil and connecting with said exhaust duct therein, tubular means in said exhaust duct and normally connecting with said control rod for transmitting motor exhaust through said anvil and bit, said fluid passage under normal working conditions being disconnected from said exhaust duct, said anvil being forwardly movable in said working cylinder when said motor is suspended off bottom to cause disconnection of said tubular means and said control rod and direct connection of said exhaust duct and said working cylinder forward part.

4. A drilling tool as described in claim 2 further including means retarding the forward motion of said plunger to permit buildup of fluid pressure thereon sufficient to produce a sharp cutting blow of said cutting element.