US3125175A - figure - Google Patents

Description

March 17, 1964 J. D. MEDLOCK ETAL ROCK BIT WITH REPLACEABLE AIR COURSE 4 Sheets-Sheet 1 Filed May 22, 1961 52 JAMES D. MEDLOCK EDWARD M. GALLE Fig. 5

INVENTORS GERALD O. ATKINSON March 17, 1964 J. D. MEDLOCK ETAL 3,125,175

ROCK BIT WITH REPLACEABLE AIR COURSE 4 Sheets-Sheet 2 Filed May 22, 1961 lllIiIlI JAMES D. MEDLOCK EDWARD M. GALLE GERALD O. ATKINSON INVENTOR- TORNEY March 17, 1964 Filed May 22, 1961 J. D. MEDLOCK ETAL 3,125,175

ROCK BIT WITH REPLACEABLE AIR COURSE 4 Sheets-Sheet 3 Fig. 14

Fig. 15

Fig. 16

JAMES D. MEDLOCK EDWARD M. GALLE GERALD O. ATKINSON INVENT0R ATTORNEY March 17, 1964 J. D. MEDLOCK ETAL ROCK BIT WITH REPLACEABLE AIR COURSE Filed May 22, 1961 IIIIIIIILCQ? 4 Sheets-Sheet 4 JAMES D. MEDLOCK EDWARD M. GALLE GERLD O. ATKINSON 0R BYflZ WM) ATTORNEY United States Patent 3,125,175 ROCK BIT WITH REPLACEABLE AIR COURSE Jamaal). Medlock, Edward M. Gallo, and Gerald O. Atkinson, all of Houston, Tex., assignors to Hughes Tool Company, Houston, Tex., a corporation of Delaware Filed May 22, 1961, Ser. No. 111,518 12 Claims. (Q1. 175-337) The present application is a continuation-in-part of copending application 88,160 of the same inventors, filed February ,9, 1961, and the benefit of such filing date is claimed for all disclosure therein which is common to the present application.

The present invention deals with rock bits of the rolling cutter type, and more particularly with those rock bits utilizing air or another gas, frequently laden with water or another liquid, as the flushing and cleaning medium. Such a bit is attached to a hollow drill string member through which the gas is pumped to the bit and thereafter through a number of passages in the bit to the bottom of the hole. Some of these passages divert part of the gas to the bearing spaces between the rolling cutters and their associated shafts to cool these elements and to keep such spaces cleared of foreign matter and abrasion products, the balance of the gas being passed directly through other passages in the bottom of the bit head to impinge either on the exterior of the cutters or directly on the formation being drilled, or a combination of both.

In the prior art, it has been customary to provide one or more such passages at or near the bit axis for the direct air flow, such passages being commonly known in the art as drilled air courses. When an air stream passes through such air courses at the flow rate necessary to carry away the cuttings produced by the action of the bit, there is frequently severe erosion of the cutter cutting structure.

Since a typical modern bit has three cones interfitting so closely as to leave no gaps except toward the bit periphery, such erosion could not be avoided by reorienting the centrally disposed air courses. Other expedients were adopted, e.g., moving the air courses to locations near the bit periphery in the gaps between the cutters, thus converting the structure to what is now commonly called a jet bit. Jet bits do not present the same erosion problems, but they are more difiicult to manufacture and consequently are more expensive than drilled air course bits.

It is the primary purpose of the present invention to provide a rock bit of the rolling cutter type in which a gas may be passed axially and generally centrally from the cavity in the hollow bit head to the bottom of a formation borehole with little or no erosion of the rolling cutters mounted below the head of such bit, but with adequate clean-up of the formation cuttings.

Another purpose is to provide such a bit in which portions of the gas stream are diverted into the bearing spaces between the rolling cutters and their shafts, such gas thereby flushing and cooling the bearing surfaces, and in which means are provided to prevent the introduction of particulate material with the gas passing into the bearings.

Another difficulty with the prior art drilled air courses relates to changeovers in such air courses dictated by changes in drilling conditions and available equipment. When such changes require a reduction in orifice size, a sleeve must be inserted in each hole, a simple but nevertheless somewhat time-consuming procedure. On the other hand, when the orifice size must be increased, it is generally necessary to ship the bit to a machine shop for re-working, i.e., reaming out the original air course to a larger diameter.

It is a further object of the present invention to provide a bit having the previously mentioned advantages and also having the advantage of replaceability of that part of the bit defining the air course. Stated in diiferent words, that part of the bit through which air or other gas flows may be removed and replaced with a different but similar member to change one or both of the flow rate of the gas and the pressure drop through the bit.

In arriving at the present invention, it was first determined that the cutter erosion characterizing prior art bits did not result from the introduction of abrasive particles with the air entering the bit from the drill string, but rather was the result of turbulence in the air after its passage through the bit. Such air leaves the bit and strikes the rolling cutters and the bottom of the borehole with considerable velocity. Cuttings and rock dust are picked up by this violent air and recirculated with various turbulent trajectories in the spaces between the cutters, bit head and borehole bottom before such air and its load pass into the annulus around the bit and upwardly through the annulus surrounding the drill string. When such turbulent air collides with the high velocity air emerging from the drilled air courses of the bit, in the space between the bottom of the bit head and the cutters, the recirculating rock cuttings and rock dust are violently projected downward on the top surfaces of the cutters. The action is similar to sand blasting, and the result is an accelerated wearing of the cutting structure, particularly toward the center. The elfect is most pronounced with the more abrasive formations.

Although prior art air bits were designed with the tacit assumption that extremely high velocity air was required at the bottom of the borehole, the theory underlying the present invention discards such assumption and substitutes the idea that efiicient entrainment and asportation of cuttings can be accomplished with lower velocity air. In comparing the behavior of the bits of the present invention with that of prior art bits which satisfactorily accomplish the bottom flushing and cleaning function, the important criterion is to maintain about the same mass flow rate.

Continuing such comparison, it seemed apparent that air bits of the present invention could be developed from the older drilled air course bits simply by providing a single large air course at the axis, larger than either a single prior art air course or the combined multiple air courses in cross-sectional area. This would virtually eliminate any pressure drop through the bit and would make it possible to use a pump of reduced pressure capacity while maintaining the same mass flow rate.

While a bit thus modified would be practicable with a sealed bearing bit, it could not be used to furnish the air for air-cleaned and lubricated bearings such as those employed with bits of the present invention. Experience with such air-cleaned and lubricated bearings indicates that a minimum pressure drop over the bit of 15 psi. is required, and that 20 to 30 psi. or higher is preferable. To provide such a pressure drop through the bearing structure, it is of course necessary to provide the same drop in the passageways used to supply air directly to the bottom of the hole.

It thus became apparent that the bits of the present invention should have about the same pressure drop through the bit as those of the prior art, and should deliver volumes of air at about the same rate, but with lower linear velocities of the emerging gas stream at the axial positions where such streams contact the cutter surfaces. It was determined that this must be accomplished by causing rapid divergence of the central airstream at some point downstream from the high pressure area where a portion is diverted to the bearing ports, and it is accordingly an object of the present invention to provide a bit which will cause a rapid divergence of the central airstream. Such divergence must be large compared with the substantially non-divergent emergent airstreams of prior art bits to avoid the abrasive wearing characteristic of prior art bits. Stated in other words, an object of the present invention is to provide a rock bit with one or more central air flushing passageways in which there is considerably less abrasion of the cutting structure than with comparable prior art bits under the same conditions.

The explanation below of the manner of accomplishing this object and those mentioned above will be apparent to those skilled in the art from a consideration of the drawings attached hereto, in which:

FIGURE 1 is a partially sectioned elevation of a rock bit of the present invention complete with one cone, it being understood that there maybe two, three or more similar cones, and that other types of rolling cutters including reamers may be used,

FIGURE 2 is a partial cross section on lines 2-2 of FIGURE 1, showing a detail of the ball loading bore and ball plug therein to illustrate the air passage therebetween,

FIGURE 3 is a partial section, similar to that of FIG- URE 1, of an alternate embodiment which includes an alternate optional structure for avoiding the introduction of particulate material into the bearing ports,

FIGURE 4 is another partial section like that of FIG- URE 3 showing another optional alternate structure for keeping particles out of the bearings, and also an alternate nozzle shape,

FIGURE 5 is a partial section showing still another alternate screen structure, together with alternate nozzle structures,

FIGURE 6 is a partial section of a bit head showing a means for retaining a nozzle in an unstepped head passage way, and also showing a modified form of exit orifice,

FIGURE 7 is a partial top view of the FIGURE 6 embodiment,

FIGURE 8 is similar to FIGURE 7 but with an axial groove cut into the bit pin rather than the nozzle,

FIGURE 9 is a partial section similar to FIGURE 6 but with a downstream orifice formed in'the bit head,

FIGURE 10 illustrates a bit head with two orifices formed in a bit head,

FIGURE 11 illustrates a modified form of the invention utilizing three separate openings to define an upstream orifice,

FIGURES 12 and 13 show various forms of alternate exit orifices,

FIGURE 14 illustrates one way of shaping an upstream orifice,

FIGURES 15 and 16 show an alternative embodiment illustrating that the upstream orifice may not only be divided but also that it may be slanted with respect to the bit axis, FIGURE 15 being a top view of the orifice and FIGURE 16 a section on lines 1616 thereof,

FIGURES 17 and 18 show an alternative embodiment in which the member defining the orifice is curved, FIG- URE 17 being a longitudinal section on lines 17-17 of FIGURE 18,

FIGURES 19 and 20 show two alternative means for disposing an upstream orifice plate in the bit head, and

FIGURE 21 illustrates an embodiment of the present invention in which not only is a ditferent means provided for supplying and screening high pressure air to the bearing ports, but also a novel means is provided for securing a replaceable nozzle member in the bit.

Turning to FIGURE 1, the rock bit indicated generally at 1 includes a head 2 having an upwardly extend ing tapered pin or shank 3 for attachment to the corresponding box in the lower end of a drill stem member such as a drill pipe, drill collar or sub (not shown).

Depending from head 2 are one or more downwardly extending legs 4, from each of which a shaft or hearing pin 5 extends generally inwardly. Such bearing pin 5 is cylindrical and stepped to. provide a pilot pin 6, the surfaces of which are especially treated to obtain wear resistant surfaces.

Surroundingpilot pin 6 is a bushing 7 of wear resistant material, and a thrust button 8 of similar material is disposed at the lower end of the pilot pin. Each of the members 7 and 8 is f'orcefitted into the indicated recesses in the cutter 13. A. roller bearing is provided by rollers 9 mounted in registering annular grooves 10 and 11 in bearing pin 5 and cutter 13, respectively, and a ballbearing is provided by balls 15 mounted in similar registering annular grooves. All of such recesses and grooves may be considered as enlarged parts of the hearing gap 14. The cutter is originally mounted with rollers 9 in place, after which balls 15 are loaded through ball loading opening 16 to lock the cutter in place. The escape of balls 15 is avoided by inserting'ball plug 17 in opening 16 until the contoured end 19 is flush with the corresponding groove in bearing pin 5, after which the position of ball plug 17 is secured by welding it to leg 4 with weld metal 18;

It should be noted that a flow passage is provided between balls 15 and the portion of ball plug 17 underlying the downward terminus of fluid passageway 25 extending from the main opening 2%) in pin 3. Such flow passage is provided by the annular gap 28 surrounding reduced diameter portion 26 of ball plug 17 and the axially contiguous spaces 29 between ball loading bore 16 and the wedge shaped portion 27 of ball plug 17 (see FIG. 2). An alternate passageway which may be substituted or used in addition is indicated by the dashed passageway 30. Many other alternate passageways may be used to furnish air for the bearings. It is not necessary to utilize opening 16, but the latter is conveniently available.

It should also be noted that the various bearings mentioned above and the various members defining such bearings are so proportioned as to define gaps appropriate for the pressure drops mentioned above. This is entirely a matter of engineering experience, and is mentioned here largely as a reminder to those of ordinary skill in the art seeking-to learn how the present invention may be constructed and used. In general such bearing gap widths and lengths are calculated for satisfactory cleaning and cooling at a minimum pressure drop of 15-30 p.s.i., and it is apparent that higher pressure drops are beneficial to such cleaning and cooling.

No cutting structure has been shownon the surface of cutter 13 because the present invention is not concerned with or limited to any particular cutting structure. It is to be understood that some such structure is provided and that it may take many forms, e.g., integral teeth or inserted wear resistant compacts of the type introduced to the trade in rock bits now known by the Hughes Tool Company trademark Hugheset.

The number and shape of the cutters may vary, but typically there are three conical cutters, as in the three cone bits sold to and known in the trade under the Hughes Tool Company trademark Tri-Cone. Such conical cutters are disposed uniformly around the bit axis and define a space 12 lying above cutters 13 and below the bottom of bit head 2. It is into this space that the major flow of air is discharged from the main opening 20 of hollow pin 3.

Returning to FIGURE 1, itcan be seen that the bottom of bit head- 2 has been machined out as a large center borewall 33, into which is inserted the air course nozzle generally indicated as 40. This nozzle includes as major parts the cylindrical wall 41, upper orifice plate or transverse member 42 defining orifice 43, and flared bearing port screen or skirt 44v provided with axial slots 45 to allow air to pass into gap 46 between the bore 21 of the pin and nozzle 40, and thence through ports 24 of fluid passageways 25. Slots 45 are sufiiciently narrow to prevent all but very small particles from entering ports 24, e.g., A3 inch.

While the flared bearing port screen 44 is not indispensable, it does protect against the introduction of trash through bearing ports 24 in the event that water or some other formation fluid rises through the nozzle, carrying with it cuttings or other comminuted material, as is particularly likely to happen when the air supply is shut off.

When screen 44 is used, it need not necessarily be provided with slots 45 around the complete periphery of the nozzle, as shown, but may be limited to one or more slots in the vicinity of each bearing port. The number of slots is somewhat arbitrary, so long as a suflicient number are provided to insure essentially a zero pressure drop from above the nozzle to gap 46, but the preferable construction is to space slots 45 uniformly and frequently about the entire periphery of the upper edge of the nozzle. This construction makes it possible to use a nozzle having a greater outside diameter in its uninstalled position than the inside diameter of the bore 21 at the height of contact, thereby providing a small force normal to such borewall which resists upward movement of the nozzle, normally not likely because it is held down by the downwardly flowing air. For the same reasons, it is preferable to spring the webs of material between gaps 45 in inserting the nozzle rather than making the maximum flare slightly less than the diameter of borewall 21 to provide a filtering gap therebetween.

Nozzle 40 is secured against downward movement by a step or shoulder 47 abutting against the corresponding corner of borewall 21. At and just above such point, the nozzle wall 41 must be thick enough to withstand substantially the full pressure drop across the nozzle, from gap 46 to the main opening 48 of the nozzle.

Near the bottom of bit head 2 a second transverse member is formed as nozzle wall 41 converges at surface 49, extends over a short straight portion 50 defining a Wide orifice 52 of only slightly smaller diameter than that of the main opening 48, and finally diverges at surface 51. The relatively wide orifice converging-diverging nozzle thus formed is not essential, and the nozzle may take the alternate form 40 indicated in FIGURE 4, in which the main opening 48 does not change in cross- .sectional area at the lower end of the nozzle, or the alternate form 40 of FIGURE 12, in which the main opening 48 flares divergingly at its lower end 52 at angle X. FIGURE 13 is similar to FIGURE 12 in defining an exit 52 of main passage 48 diverging at angle X, but utilizes the construction of FIGURE 5 in that exit orifice 52 is defined by the bit head rather than the nozzle, the bit passage 33 also being shouldered at 53 to prevent downward axial movement of the nozzle.

FIGURE 3 illustrates an embodiment of the present invention in which the nozzle 40 does not include a flared bearing port screen similar to element 44 of FIG- URE 1, but is similar in other respects. In this embodiment, particulate materials may be prevented from en- .tering ports 24- by as screen 35 secured in place by tack welding at 36 and 37. Screen 35 may be in short circumferential sectors, each covering a single bearing port 24,

but is more conveniently a single cylindrical piece.

Although the structure of FIGURE 3 does not provide against upward movement of nozzle 40 it is ap parent that such movement may be prevented in many ways. The nozzle may be cemented in by adhesives, but

preferably is held by means permitting ready replaceability, e.g., a split retaining ring engaging matching circumferential grooves in borewall 33 and the outside of nozzle wall 41.

FIGURE 4 is similar to FIGURE 3 except as mentioned above and except that in FIGURE 4 a flat screen 38 is disposed on top of orifice plate 42, and is secured in place by any suitable means such as tack welding 39 securing it to borewall 21. Screen 38 may either com- 6 pletely fill the cross-section of opening 20, as indicated, or may be annular, overlying only gap 46.

In the drawings, the cross hatching for nozzle 40 and its variants indicates a synthetic plastic, and a wide range of thermosetting and thermoplastic resins may be used in forming the nozzle. Plastic pieces are preferred because they can be produced relatively inexpensively, but there is no physical requirement barring the use of metals such as steel and aluminum, or other appropriate materials. The nozzle need only be able to retain its shape with pressures up to a maximum of the order of p.s.i.g. and with a modest temperature rise, e.g., to 300 F.

It is believed to be apparent that the nozzles described above are easily removeable through main opening 20 in pin 3. The FIGURE 4 embodiment is somewhat of an exception when screen 38 is tack welded at 39, but the use of such screen is not mandatory. Furthermore, such screen when used need not necessarily be secured to borewall 21, but may be secured instead to the nozzle. Such removability is to be preferred to a structure in which the nozzle is more permanently secured in place, as by welding, because it is frequently necessary to make field changeovers.

Many modifications of the nozzle structure shown are possible without departing from the basic innovation of disposing a flow restricting orifice plate at a considerable distance upstream from a relatively wide discharge passage at the bottom of the bit head. The removable nozzle may be terminated at some distance above the latter position, as indicated in FIGURE 5, a shoulder 53 being provided in the bit head passage by making such passage step to a smaller bore 54, at the same time providing for a flush fit between the bore of the removable piece and the bore of the bit head. When the discharge orifice is to be slightly restricted, it may be so machined as a part of the bit head when the large pas sageway is formed, as indicated by the dashed outline 55 thereof in FIGURE 5.

FIGURE 5 also illustrates an older form of bearing port screen 56 which may be used when desired. Screen 56 is essentially a tube having its outer end closed and pierced with a number of flow holes 57.

In laboratory tests with the nozzle 40 exhausting into the atmosphere, the bore of main opening 48 was 2 orifice plate 42 was /8 inch thick, upper orifice 43 was 1 7 in diameter at an axial distance of 3%" from the lower end of the nozzle. At the lower orifice 52 cross sectional angles with the axis of the nozzle were 45 for converging surface 49 and 30 for diverging surface 51. The axial distances of these surfaces were 4 for surface 49, /s" for surface 50 and l" for surface 51.

The diameter of lower orifice 52 was 2 inches.

The nozzle as thus constructed was tested with air at 30 p.s.i.g., the air containing suflicient water to render the discharge stream visible. The flow rate measured at the higher pressure was 815 cubic feet per minute (c.f.m.), and the included plane angle between the divergent extremities of the discharge was 26". Decreasing the distance between the lower end of the nozzle and upstream orifice 43 to 2 /8" (slightly less than the bore of passage 48) caused the discharge stream to narrow to an essentially straight, high velocity stream.

Such results were contrasted with those obtaining from prior art devices by delivering the same type of air through a single drilled air course through the bottom of the bit, i.e., by removing nozzle 40 from bit 1 of FIGURE 1 and using a diameter of 1 for the entire length of borewall 33, approximately 2 inches. With the same 30 p.s.i.g. pressure drop over the bit, the upstream flow rate was 900 c.f.m. and the included plane angle of the discharge was only 7". The high velocity of the discharge was not significantly reduced up to 6 inches from the discharge exit by modifying the straight through bore to provide a converging entrance, a diverging exit, or both.

Field tests were also run with the FIGURE 1 embodiment and with the prior art drilled air course bits, both drilling through the same levels of the same medium hard iron ore formation and both otherwise identical 9-inch (gage) bits which are sold and known to the trade as the Hughes Tool Companys W7R bits, as listed and described in its current catalogue 23. Both bits were used with a pressure drop of 32-35 p.s.i.

In the FIGURE 1 embodiment, the replaceable nozzle was of synthetic plastic, had an upper orifice 43 of diameter, inch axial length, located 3 above the bottom of the bit head, and a lower orifice 52 of 1 inch diameter, A: inch axial length, located of an inch above the bottom of the bit head. The diameter of the main opening 48 was 1 This bit drilled 1834 feet at 55 ft./hr., 6090 rpm. and 2040,000 lb. weight on bit, before dulling to the point of unprofitable drilling. Examination of the dull bit disclosed even wear over the cutting structure of each of the three cones.

The standard prior art bit (W7R) had three /2 diameter holes of uniform section drilled centrally through the bottom of the bit head on a %1" diameter bolt circle. This bit drilled only 557 feet at 53 ft./hr., at the same weight and rotary speed, before dulling to the point of unprofitable drilling. Examination disclosed that the teeth of the heel rows on each cutter were still capable of further drilling but that the cutting structures toward the center of all three cutters, including the entire spearpoint of the No. l cutter, had been completely eroded away by blast effect. Similar comparative runs with the FIGURE 1 embodiment resulted in runs of 2333 feet and 2903 feet while the nearest competitive bit of other manufacturers made only 1215 feet.

In using the replaceable nozzle of the present invention, it may become necessary to provide for changes in flow rate, pressure or both. This is most easily ac complished by replacing the entire nozzle with one in which the only important difference is the size of the upstream orifice. As an example, assume that a particular bit equipped with a nozzle provided for a 32 p.s.i.

pressure drop and an air flow of 800 c.f.m. has been cleaning bottom satisfactorily in a particular formation.

Witha change in formation, assume further that it becomes necessary or desirable to increase the flow rate with the same pressure drop. This is provided for by changing to a nozzle having a larger upstream orifice. If, on the other hand, the change is to be to a higher pressure at the same flow rate (all flows being in volume under standard atmospheric conditions), the area of the upstream orifice must be decreased. When both the flow rate and pressure drop are to be increased or decreased together, a change may or may not be necessary, depending on the relative extent of the changes.

A number of generalizations have been deduced as a result of further experiments with the FIGURE 1 embodiment and various modifications thereof. The upstream orifice plate 42 should be located as far above exit orifice 52 as possible, at least as much as and preferably two or more times the diameter of main opening 48. The bore of main opening 48 should also be maximized. Apparently the initial gas stream emerging from the restricted upstream orifice 43 has a higher internal pressure than the pressure of the gas in the main opening, and thus starts to expand. When it can ex pand sufficiently to contact the borewall of the main opening, the area of contact progresses rapidly backward until the discharge stream essentially fills the tube. Thus the greater the length of the main opening, the greater is the probability that the discharge stream will expand to make the initial contact.

While the diameter of the main opening 48 must be small enough to insure such initial contact, a large value is desirable because there is little further divergence of the gas stream below the exit end or orifice of the main opening. The gas stream pressure at that point is about equal to the pressure of the surrounding gas, and there is no divergence except by the frictional edge effect. The diverging exits of FIGURES 12 and 13 capitalize on this effect, using values of angle X in the region of /230 degrees, 15 apparently being better than either extreme.

As one example of the extent to which diffusion of the airstream can be accomplished with a nozzle of the FIG- URE 1 type modified as in FIGURE 12 with angle X equal to 15 and with a large length of main opening, such a nozzle had such length of 4%.", a main opening diameter of 1% and an upstream orifice diameter of 4;. With air delivered at a flow rate of cu. ft. per minute at standard conditions and a pressure. drop of 20 psi. over the nozzle, the included plane angle of divergence of the emergent air stream was 41.6". The nozzle thus described fits a rock bit having a 4 /2-inch regular shank.

The further experiments mentioned above also verify that various other embodiments utilizing variants of the single axial orifice are the full equivalents thereof. Thus in FIGURE 11, showing a top. view of a nozzle similar to that in FIGURE 7, three openings 43 of 0.577" dia. were provided in a A" thick orifice plate 42, equally spaced on a 4" bolt circle. Tests therewith yielded the same results as with a single orifice of the same area (1 dia.).

The thickness of orifice plate 42 is immaterial insofar as eifects on divergence of the airstream are concerned. Like results were obtained on plates of from to 1 /2" thick. Of course, too thick a plate can result in having the upstream orifice too close to the exit end of the main opening, and will thus lose the advantage of an upstream location.

Shaping of the upstream orifice has no observable effect on the divergence of the airstream leaving the nozzle, but it does increase the airflow over the unshaped orifice for the same pressure drop. Thus the entrance of the orifice 43 of the FIGURE 14 orifice plate 42 was rounded with a radius half the thickness of the plate, and such eifects were observed. Itseems apparent that other shapes would cause like effects, e.g., the traditional elliptical design.

The orifice or orifices need not be coaxial with the bit axis, and there is actually some increase in exit stream divergence observed therewith. Thus orifice plates similar to the orifice plate 42 of FIGURES 15 and 16 contained three equally spaced /2" dia. openings 43 (in some cases dia.) inclined to the vertical but tangent to the bolt circle containing their centers. The direction of slant was away from the direction of rotation, and angle Y was 20, 25 and 45 for different nozzles. Some increase in divergence was noted in each case over the divergence for the equivalent straight through orifice. At thesame. time, little or no improvement was noted through the use of openings connecting gap 46 with main opening 48 below the upper orifice plate, whether such openings were radial or inclined to the radial in either the same cross section, axially, or both.

FIGURES 6 through 9 illustrate alternate means for securing the replaceable nozzles 40 and 40 against axial movement. Some such means is necessary in the FIGURE 6 embodiment because there is but one straight through opening 20 of bore 21 in'bit head 2, and pin 3, but it is apparent that the retaining means of FIGURES 6-8 can be used with the embodiments of FIGURES 1-5 previously described. In FIGURE 6 the upper part of the nozzle is necked down to wall 59 to provide gap 46' around bearing ports 24, wall 5% extending above plate 42. A groove 60 is provided in this upwardly extending part of wall 59, registering with a similar groove 61 in borewall 21 of pin 3. A flexible split ring fastener 62 is seated in grooves 60 and 61 to prevent axial movement in either direction.

An axial groove 63 is providedin the periphery of wall 59, extending from the top surface to radial groove 60,

. 9 to permit the insertion of a compressive tool in assembly and disassembly. Such a tool has points fitting into the indicated holes in nibs 68 of the split ring (see FIG. 7), and is used to compress the ring and withdraw it from engagement in groove 61, the nozzle then being removable with the ring.

FIGURE 8 illustrates an alternate means for insertion of the compressive tool, through an axial slot 65 in the borewall 21 of pin 3, extending into radial slot or groove 61.

It is apparent that the nozzle 46 of FIGURE 6 may have an alternate upward termination which eliminates groove 60, as indicated by the dashed line 64 in FIGURE 6. With such construction, ring 62 prevents only upward movement of the nozzle, and some means must be provided to prevent downward movement, e.g., the construction of FIGURE 9. The construction of FIGURE 9 is the same as that of FIGURE 6 except that the lower orifice 52 is formed in a thin plate 58 extending from bit head 2. It is apparent that the restraint against downward movement of the nozzle provided by plate 58 can be retained when the lower orifice 52 is not restricted by simply increasing bore 50 to a diameter less than that of bore 33 but equal to or greater than that of the main opening 48 of the nozzle.

In the embodiments of FIGURES 6-9, air at the upstream pressure is supplied to the bearing ports 24 through a multiplicity of passages 66 through wall 59. These passages are sufficiently spaced and sufficiently numerous that they may be of relatively small size, e.g., inch diameter, and thus serve as the screen to prevent particulate material from entering gap 46 and bearing ports 24.

FIGURE 10 has been included simply to demonstrate that the upstream orifice plate 42 as well as the exit orifice plate 58 may be integral with bit head 2. While such construction sacrifices the ready replaceability of the earlier described embodiments, it does embody the broadest inventive concept, that of a thin plate upstream orifice over which essentially the full pressure drop takes place. In this embodiment, screen of the bearing air may be accomplished through inserted screens 56, as described in connection with FIGURE 5, or equivalents.

FIGURES 17 and 18 depict a modification 40 of the nozzle 40 of FIGURE 1 to illustrate that the orifice plate 42 may be curved and that orifices 43 may be slanted at different angles spaced at various distances from the axis of the nozzle. Thus in FIGURE 18 the openings 43 aligned with the vertical edges of the drawing are closer to the nozzle axis than those aligned with the horizontal edges. FIGURE 18 shows that such openings may be normal to the curved surface of plate 42 FIGURE 19 illustrates a simplified form of orifice plate 42 which may be used to obtain the use of the maximum axial length of the bit. In this embodiment the entire nozzle is reduced to such orifice plate 42 containing orifice 43, the same being retained in borewall 21 of pin 3 by the threaded engagement illustrated or by equivalent means such as the split retaining ring of FIGURES 6-9. In this embodiment air to the bearings flows through a multiplicity of passages 25 passing through the wall of pin 3 to the top thereof. This is possible because there is actually a gap between the top of pin 3 and the lowermost surface of the drill string member into which hit 1 is threaded. A multiplicity of bearing air passages 25 converging in the lower portions of bit head are provided to avoid weakening of bit head 2 that would occur with a single, large bore air passage for each cutter. Such passages 25 are sufficiently small that no further filtering is necessary.

FIGURE 20 is a modification of FIGURE 19 illustrating an embodiment which avoids the likelihood of plugging the bearing air passages by the collection of grease and dust. In FIGURE 20 the orifice plate 42 is set further into borewall 21 of pin 3, and an enlarged bore 22 may be provided at the top of opening 20. A multiplicity of passages 25 are provided opening through borewall 22 rather than through the top 7 surface of pin 3, such passages 25 being similar to passages 25 in number and diameter. Where necessary, they are jointed, or double drilled, as indicated.

FIGURE 21 illustrates still another embodiment of the invention, utilizing a nozzle 46 in which the orifice plate 4'2 and orifice 43 are disposed at the maximum axial length above the discharge opening 52 at the bottom of the bit head and the nozzle is retained in the bit by yet another means. In this embodiment nozzle 40 is shaped to define gap 46 communicating with bearing ports 24, wall 41 being of smaller outside diameter than the outer diameters of orifice plate 42 and bottom flange 23, the latter being essentially equal to that of borewall 21 of pin 3. Gap 46 extends upwardly to orifice plate 42, the air passage through the plate is provided by a multiplicity of passages 45 of sufficiently small bore as to be self filtering. Alternately, passages 45 may be omitted and gap 46 may be connected to the air supply by passages 25 through the pin 3, or a combination of both may be used.

Nozzle 40 is held in position within pin 3 by a pair of radially extending retaining pins 32 extending through appropriate registering openings in bit head 3 and nozzle 42.. It is apparent, of course, that other means such as the split retaining ring of FIGURES 6-9 may be used. The FIGURE 21 embodiment has the virtue that the replaceable nozzle need not extend to the bottom of the bit head.

It will be apparent from the above that the upstream orifice need not be exactly coaxial with the bit, but on the other hand may depart considerably from such condition. Broadly the invention comprises providing a main longitudinal opening of considerable diameter through the head of a rock bit and generally at the center thereof, and disposing a member defining a relatively small orifice in such main opening as far above the downstream terminus of the latter as possible. The upstream orifice-defining member should be so disposed as to allow access of the upstream gas to the bearing ports of the bit at essentially its maximum pressure, and the orifice of such member should have a maximum cross-sectional area such that the pressure drop through the orifice is equal to or greater than the minimum pressure required to cool and clean the bearings.

What is claimed is:

1. A rolling cutter rock bit suitable for use with gaseous fiushing media comprising a head section with an upstandmg shank suitable for connection to a drill string, said head and shank having an axially extending and coextensive central passageway therethrough, at least one leg extending downwardly from said head, a bearing pin thereon extending generally inwardly beneath said passageway, a rolling cutter rotatably mounted on said hearing pin to define therewith a hearing gap, passage means in said head, leg and bearing pin extending from said bearmg gap to a bearing port in said central passageway, and a member extending transverse said passagewy upstream from the exit end thereof, said member having at least one restricted orifice therethrough and being supported from the wall of said passageway to divide the passageway into a high pressure zone and a low pressure zone, said low pressure zone lying downstream from said member and above the exit end of the passageway, said member being secured to said wall against at least downward movement with respect thereto and to prevent the flow of flushing fluid into said low pressure zone except through said orifice, said bearing port being in communication with said high pressure zone, said passageway over the axial extent of said low pressure zone having a clear transverse cross-section generally at least as large as such cross-section immediately below said transverse member.

2. The rolling cutter rock bit of claim 1 in which said clear transverse cross-section diverges axially downwardly at the exit end of said passageway.

1 1 3. The rolling cutter rock bit of claim 2 in which said. clear transverse cross-section diverges axially downwardly at the exit of said central passageway at an angle of from 7 /2 to 30 degrees with the axis of the bit.

4. The rolling cutter rock bit of claim 3 in which said angle is about 15 degrees.

5. The rolling cutter rock bit of claim 1 in which said transverse member is a part of a removable nozzle slidably and sealingly inserted into said central passageway, said nozzle comprising a tubular wall and said transverse member secured thereto to block the flow of flushing fluid except through the orifice of the member, and said passageway wall is stepped inwardly to a smaller crosssection near its exit end to define an upwardly facing shoulder, the lower end of said nozzle butting against such shoulder in essentially flush relationship.

6. The rolling cutter rock bit of claim 5 in which the exit end of said passageway diverges outwardly and downwardly.

7. The rolling cutter rock bit of claim 1 in which said transverse member is a part of a removable nozzle slidably and sealingly inserted-into said central passageway, said nozzle comprising a tubular wall and said transverse member secured thereto to block the flow of flushing fluid except through the orifice of the member, said tubular wall extending substantially to the exit end of the passageway and terminating in a downwardly and outwardly diverging opening.

8'. The rolling cutter rock bit' of claim 7 in which said nozzle wall terminates downwardly with an opening diverging at an angle of from 7%. to 30 degrees with the axis of the bit.

9. The rolling cutter rock bit of claim 8 in which said angle is about 15 degrees.

10. The rolling cutter rock bit of claim 1 in which said transverse member is arcuate.

' serted in said central passageway from the top thereof and secured to the wall thereof, said nozzle comprising a tubular wall and said transverse member, said wall being externally recessed to define upper and lower outside flanges slidably and sealingly engaging the wall of the passageway and a gap intermediate said flanges in communication with said bearing port, said transverse member being secured to said wall at about said upper flange to block the flow of flushing fluid through the opening in the wall except through the orifice of the member, said upper flange having a multiplicity of self-filtering small passages communicating between said gap and the space above said shank.

References Cited in the file of this patent UNITED STATES PATENTS 1,816,203 Behnke July 28, 1931 2,329,745 Crook Sept. 21, 1943 2,661,932 Woods Dec. 8, 1953 2,719,026 V Boice Sept. 27, 1955 2,751,196 Smith- June 19, 1956 2,814,464 Pike et a1 Nov. 26, 1957 2,815,936 Peter et a1 Dec. 10, 1957 2,880,970 SWart Apr. 7, 1959 FOREIGN PATENTS 763,676 Great Britain Dec. 12, 1956 1,196,450 France May 25, 1959

Claims (1)

1. A ROLLING CUTTER ROCK BIT SUITABLE FOR USE WITH GASEOUS FLUSHING MEDIA COMPRISING A HEAD SECTION WITH AN UPSTANDING SHANK SUITABLE FOR CONNECTION TO A DRILL STRING, SAID HEAD AND SHANK HAVING AN AXIALLY EXTENDING AND COEXTENSIVE CENTRAL PASSAGEWAY THERETHROUGH, AT LEAST ONE LEG EXTENDING DOWNWARDLY FROM SAID HEAD, A BEARING PIN THEREON EXTENDING GENERALLY INWARDLY BENEATH SAID PASSAGEWAY, A ROLLING CUTTER ROTATABLY MOUNTED ON SAID BEARING PIN TO DEFINE THEREWITH A BEARING GAP, PASSAGE MEANS IN SAID HEAD, LEG AND BEARING PIN EXTENDING FROM SAID BEARING GAP TO A BEARING PORT IN SAID CENTRAL PASSAGEWAY, AND A MEMBER EXTENDING TRANSVERSE SAID PASSAGEWAY UPSTREAM FROM THE EXIT END THEREOF, SAID MEMBER HAVING AT LEAST ONE RESTRICTED ORIFICE THERETHROUGH AND BEING SUPPORTED FROM THE WALL OF SAID PASSAGEWAY TO DIVIDE THE PASSAGEWAY INTO A HIGH PRESSURE ZONE AND A LOW PRESSURE ZONE, SAID LOW PRESSURE ZONE LYING DOWNSTREAM FROM SAID MEMBER AND ABOVE THE EXIT END OF THE PASSAGEWAY, SAID MEMBER BEING SECURED TO SAID WALL AGAINST AT LEAST DOWNWARD MOVEMENT WITH RESPECT THERETO AND TO PREVENT THE FLOW OF FLUSHING FLUID INTO SAID LOW PRESSURE ZONE EXCEPT THROUGH SAID ORIFICE, SAID BEARING PORT BEING IN COMMUNICATION WITH SAID HIGH PRESSURE ZONE, SAID PASSAGEWAY OVER THE AXIAL EXTENT OF SAID LOW PRESSURE ZONE HAVING A CLEAR TRANSVERSE CROSS-SECTION GENERALLY AT LEAST AS LARGE AS SUCH CROSS-SECTION IMMEDIATELY BELOW SAID TRANSVERSE MEMBER.

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