Rotary Rock Bit and Method of Making Same

1. Field of the Invention

The present invention relates generally to earth boring rotary rock bits and, more particularly, to rock bits in which separate journal pins are secured to the legs during the manufacturing operation.

2. Description of the Prior Art

A rotary rock bit usually comprises a plurality of legs welded together to form a bit body having one end threaded for attachment to a drill string. The lower end of each leg extends downwardly from the bit body and includes a journal pin extending radially inwardly for rotatably supporting a cone type cutter. Each cutter is adapted to roll along the bottom of the bore and is adapted to contact and disintegrate the earth formation at the bore bottom. In rock bit legs, the journal pins are usually formed integrally with the leg from a single forging. However, the journal pin includes bearing surfaces which must be machined. Having the journal pin integral with the leg makes the machining operation lengthy and more cumbersome. Moreover, the bearing surfaces of each journal pin must necessarily be carburized while the rest of the leg surface be painted over to prevent the remaining surface from being carburized. However, carbon leakage does occur on this surface which is deleterious to subsequent operations on the legs. As a result, it is preferable to form the journal pin separately from the leg in order to have it carburized and machined prior to assembling the pins to the legs.

U.S. Pat. No. 4,043,411 shows one method of having a separate journal pin secured to a leg. However, the shortcoming found in the method of manufacture of the rock bit legs of the referenced patent is that the welding is accomplished on the interior side of the leg, i.e. the cutter receiving surface side of the leg. Such a method of manufacture severely restricts the design capabilities of the journal pin. Moreover, with such a restriction, the cone cannot be preassembled with the journal pin prior to welding the pin to the leg and may require secondary operations to clean welded areas prior to final assembly.

Referring back to present day rock bits, such bits usually include ball bearings located between the journal pin and the cutter to provide some thrust bearing support and to retain the cone on the journal pin. However, these ball bearings are not capable of absorbing axial thrust loads in either axial direction of the journal pin. Therefore, their main utility is for retention only. Other problems with utilizing ball bearings is that during operation the cone has an undesirable rocking movement and an in and out thrust movement.

Alternatives to the ball bearings have been utilized in retaining the cutter onto the journal pin. One alternative is the utilization of an annular thrust member which is retained on the journal pin and secured to the cutter. Such thrust members are shown in U.S. Pat. Nos. 959,540, 979,496, 1,010,144, 1,010,406, 1,119,163, 1,124,241, 1,484,995, 1,692,793, 1,720,401, and 3,971,600. The shortcoming with these devices is that the annular thrust members have to be threadedly secured to the cutter. Such threaded connections are not desirable because of the hostile environment the cutters are subject to. Moreover, special machines and tools are required to manufacture threads and to threadedly tighten the annular thrust members during assembly. The use of such tools is awkward and positive tightening of the various members is not always guaranteed. Also, threaded details tend to loosen when the rock bit is in use.

The present invention obviates the above-mentioned shortcomings by providing a rock bit in which each leg has a separate journal pin and a cutter retaining thrust member that is secured during assembly in one simple manufacturing operation.

In its broadest aspect, the rock bit comprises at least one leg having a bore extending through the lower end thereof. A separate journal pin is provided having one end adapted to extend into the leg bore. The other end is adapted to receive an annular thrust member. The journal pin is secured to the bore and the annular thrust member is secured to the journal pin by means of a high energy beam which welds the mating surfaces of the various parts together in a single step. The thrust member functions to be captured within an internal groove formed in the cutter in order to retain the cutter onto the journal pin. The thrust member also functions to absorb the thrust loads passing from the cutter through to the journal pin.

The advantage of the present invention is that the annular thrust member is positively secured to the journal pin and without the need for any special tools. Another advantage of the present invention is that the various interface connections described above are accomplished in a single simple assembly method.

Another advantage is that the separate journal pin permits ease of manufacturing such as surface finish on details. Still another advantage of the present invention is that the positive retention caused by the greater surface contact area of the annular thrust member greatly increases in-thrust capacity.

The features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with the further advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings.

FIG. 1 is a perspective view of a three cone rotary rock bit constructed in accordance with the present invention;

FIG. 2 is a sectional view of one leg of the rock bit of FIG. 1, showing the first embodiment of the present invention;

FIG. 3 is a fragmentary sectional view of the rock bit taken along lines 3 -- 3 of FIG. 2; and

FIG. 4 is a fragmentary sectional view of one leg of a rotary rock bit illustrating a second embodiment of the present invention.

Referring now to the drawings, FIG. 1 illustrates a three cone rotary rock bit generally indicated by arrow 10, having a bit body 11 which includes an upper threaded portion 12 for connection to the lower end of a rotary drill string (not shown). Extending from the bit body 11 are three substantially identical legs 13. The lower end of each of the legs is provided with an extended journal pin, details of which will be discussed hereinafter. Three rotary cone cutters 14 are rotatably positioned upon the three journal portions of the leg 13. Each of the cone cutters includes a cutting structure 15 on its outer face which is adapted to disintegrate the earth formations as the bit is rotated and moved downward. The cutting structure 15 is shown in the form of tungsten carbide inserts, however, it is to be understood that other cutting structures such as milled steel teeth with or without hard metal, may be formed on the cone cutters.

The bit 10 further includes a central passageway 16 extending along the center axis of body 11 to allow drilling fluid to enter from the upper section of the drill string immediately above and pass downward through three jet nozzles 17, one of which is shown in FIG. 1.

In operation, the drill bit 10 is connected as a lower member of a rotary drill string (not shown) and lowered into a well bore until the rotatable cone cutters 14 engage the bottom of the well bore. Prior to and during engagement with the bottom well bore the drill string is rotated, rotating bit 10 therewith. Drilling fluid is forced down through the interior passage of the rotary drill string and continues through the central passageway 16 of the bit 10, passing through the three nozzles 17, past the cutting structure 15 of the cutters 14 to the bottom of the well bore, and then upwardly into the annulus between the rotary drill string and the wall of the well bore carrying with it the cuttings and debris from the drilling operations.

FIG. 2 illustrates one of the legs 13 which has a cylindrical bore 19 extending through the lower extremity thereof. A journal pin 20 is provided having a cylindrical mounting surface 21 and a cylindrical bearing surface 23. The mounting surface 21 and bearing surface 23 lie in the same cylindrical plane with the mounting surface 21 extending into and engaging the bore 19 of the leg 13.

The cutter 14 is rotatably mounted about the end of the journal pin 20 which extends out of the leg 13. The cutter 14 includes an interior cavity formed by an inner end face 25, a frustro-conical face 26 and a cylindrical surface 27. The mouth of the cavity is formed by an inwardly facing flange 28 having an inner annular bearing surface which is adapted to frictionally engage an annular surface 29 formed on the leg 13. An annular compartment 31 is formed between the face of the leg 13 and the flange 28 of the cutter 14 for housing a resilient seal 32.

The inner end of the journal pin 20 includes an end face 33 which is adapted to frictionally engage the inner end face 25 of the cutter 14. A frustro-conical thrust surface 35 is also located on the end of the journal pin 20 for frictionally engaging the mating surface 26 of the cutter 14. It should be noted that these mating frustro-conical surfaces 26 and 35 are substantially parallel to the outer conical surface of the cutter 14. As a result, these mating surfaces 26 and 35 are substantially parallel to the bottom of the bore hole and function to efficiently absorb the normal loads passing from the cutter 14 to the journal pin 20.

The rock bit 10 further includes a three-piece annular thrust member 40, 40.sup.1 and 41 having an inner cylindrical surface which extends around the bearing surface 23 of the journal pin 20. The thrust members 40 and 40.sup.1 includes an outer cylindrical bearing surface 43 and a frustro-conical bearing surface 45 which are adapted to frictionally engage a portion of the frustro-conical surface 26 and the cylindrical surface 27 of the cutter 14. The bearing surface 43 functions to transmit the radial loads passing from the cutter 14 to the journal pins 20 while the bearing surface 45 functions to transmit a portion of the out-thrust load passing therethrough. The thrust members 40, 40.sup.1 and 41 also include an outer end face 46 which is adapted to engage the inner surface of the flange 28 to transmit the in-thrust load passing therethrough. It has been found that this feature functions to hold the cutter 14 onto the journal pin 20 more effectively by having eight times the in-thrust capacity of ball bearings. It should be noted that the radial extension of the thrust member 41 does not extend out to contact the cylindrical surface 27 of the cutter 14. This clearance denoted by numeral 47 forms a portion of the lubrication system which is conventional and not shown in greater detail since it does not form part of the invention.

In accordance with the present invention, the journal pin 20 is secured to the leg 13 by means of an electron beam welder, of which the gun 50 is shown. This welder 50 functions to transmit a high energy beam across the mating surfaces of the journal pin 20 and of the bore 19, in order to fuse a weld therebetween. The high energy beam extends further along the journal pin 20 in order to fuse the mating surfaces between the journal pin 20 and the inner annular surface of the thrust members 40 and 41. As a result, a single weld functions to secure the journal pin 20 to the leg 13 and to secure the thrust members 40 and 41 to the journal pin 20. Because the thrust members 40 and 41 are retained within the groove formed by the end face of the flange 28 and the frustro-conical surface 26, the cutter 14 is axially retained by the thrust members 40 and 41 onto the journal pin 20. As can be seen, this construction eliminates the need for ball bearings to retain the cutter onto the journal pin thereby greatly increasing in-thrust load capacity, and, as illustrated, a single weld step serves a double function of securing the journal pin 20 to the leg 13 and retaining the cutter 14 onto the journal pin 20.

It should be noted that the welding gun 50 moves relative to the leg 13 in a rotating motion to create the cylindrical weld. However, since the journal angle is not normal to but is at an acute angle with respect to the center axis of the main bit body 10, the weld created is of different lengths around the cylindrical surface of the journal pin 20. As illustrated in FIG. 2, the shortest extension of the weld is located on the bottom sector of the journal pin 20 whereas the longest portion of the weld is on the top sector of the journal pin. As a result, as the electron beam gun 50 is rotated relative to the leg 13, its power output must continuously vary according to the depth of the weld that is required.

FIG. 4 obviates this requirement by providing a journal pin 60 which extends partially into a cylindrical bore 61 formed in the leg 13. As can be seen, this bore 61 is coextensive around the end of the journal pin 60 and as a result the weld 64, that is created between the journal pin 60 and the cylindrical bore 61 and the thrust members 40 and 41, is also the same length completely around the journal pin 60. As a result, the welding gun does not have to change its power as it is circularly moved relative to the leg 13.

Access to the cylindrical portion 61 is provided by a larger counter bore 63. After the welding process takes place, a plug element 65 is inserted into the counter bore 63. The plug element 65 includes an end face 66 which abuts the outer end of the journal pin 60. The plug element 65 further includes an outer cylindrical surface 67 which contacts the cylindrical surface of the bore 61. After the plug element 65 is inserted into the counter bore 61, an oval weld is created at the ends of the mating faces as denoted by numeral 68. All of the rest of the elements in FIG. 4 are similar to those shown in FIG. 2 and identical numerals are utilized to denote that structure.

As can be seen, in accordance with the present invention, it is now possible to have a separate journal pin which can be carburized and finish machined separately before insertion into the leg of the bit and, as mentioned previously, a single welding step is provided which not only welds the journal pin to the leg but it also welds the thrust members to the journal pin for retaining the cutter onto the journal pin.

It should be noted that various modifications can be made to the assembly while still remaining within the purview of the following claims.