Bar trimmers on disk bit

An earth boring drill bit comprising a milled cutter having rows of hardfacing guides on the cutter. Hardfacing is applied between adjacent hardfacing guides to form a hardfacing web that serves as a cutting element. The hardfacing web defines an interface between the hardfacing web and the hardfacing guide. The hardfacing web may extend past the crest of the hardfacing guides or end along the hardfacing guides flanks. Projecting hardfacing is provided on the interface to form trimmers.

BACKGROUND

1. Field of Invention

The disclosure herein relates in general to rolling cone earth boring bits and in particular to improving the performance of a steel tooth bit.

2. Description of Prior Art

Drilling systems having earth boring drill bits are used in the oil and gas industry for creating wells drilled into hydrocarbon bearing substrata. Drilling systems typically comprise a drilling rig (not shown) used in conjunction with a rotating drill string wherein the drill bit is disposed on the terminal end of the drill string and used for boring through the subterranean formation.

Drill bits typically are chosen from one of two types, either drag bits or roller cone bits. Rotating the bit body with the cutting elements on the outer surface of the roller cone body crushes the rock and the cuttings may be washed away with drilling fluid. One example of a roller cone bit11is provided in a side partial perspective view inFIG. 1, the bit11having a body13with a threaded attachment15on the bit11upper end for connection to a drill string (not shown). The bit11further includes legs18extending downward from the bit body13. Each bit leg18is shown having a lubricant compensator17.

The bit body13is further illustrating having a nozzle19for directing pressurized drilling fluid from within the drill string to cool and clean bit11during drilling operation. A plurality of cutters21are rotatably secured to respective bit legs18. Typically, each bit11has three cutters21, and one of the three cutters is obscured from view inFIG. 1.

Each cutter21has a shell surface including a gage surface25and a heel region indicated generally at27. Teeth29are formed in heel region27and form a heel row28of teeth. The heel teeth29depicted are of generally conventional design, each having leading and trailing flanks31which converge to a crest33. Each tooth29has an inner end (not shown) and an outer end35that joins to crest33.

Typically steel tooth bits are for penetration into relatively soft geological formations of the earth. The strength and fracture toughness of the steel teeth permits the use of relatively long teeth, which enables the aggressive gouging and scraping actions that are advantageous for rapid penetration of soft formations with low compressive strengths. However, geological formations often comprise streaks of hard, abrasive materials that a steel-tooth bit should penetrate economically without damage to the bit. Although steel teeth possess good strength, abrasion resistance is inadequate to permit continued rapid penetration of hard or abrasive streaks. Consequently, it has been common in the arts since at least the 1930s to provide a layer of wear-resistance metallurgical material called “hardfacing” over those portions of the teeth exposed to the severest wear. The hardfacing typically consists of extremely hard particles, such as sintered, cast, or macrocrystalline tungsten carbide, dispersed in a steel matrix.

Typical hardfacing deposits are welded over a steel tooth that has been machined similar to the desired final shape. Generally, the hardfacing materials do not have a tendency to heat crack during service which helps counteract the occurrence of frictional heat cracks associated with carbide inserts. The hardfacing resists wear better than the steel tooth material, therefore the hardfacing on the surface of steel teeth makes the teeth more resistant to wear.

A front view of a cutter21is illustrated inFIG. 2. Shown formed on the cutter21is an inner row36having inner row teeth37extending radially inward from the heel27(seeFIG. 1). The inner row teeth37have flanks31and crests33similar to those of the heel teeth29. An apex38is shown proximate to the cutter21center, the apex38having grooves39radially extending from the apex38midpoint to its outer periphery. A layer of hardfacing35is shown having been applied to surfaces of the heel teeth29and the inner row teeth37.

SUMMARY OF INVENTION

Disclosed herein is an earth boring drill bit comprising, a milled cutter having rows of hardfacing guides on the cutter. Hardfacing is applied between adjacent hardfacing guides to form a cutting element. The hardfacing may extend past the crest of the hardfacing guides or end along the hardfacing guides flanks. In one embodiment, an earth boring bit includes a body, a leg depending from the body, a bearing shaft extending radially inward from the leg, a cutter mounted on the bearing shaft, the cutter having a row of cutting hardfacing guides, the hardfacing guides having a base and flanks extending from the base and joining to form a crest, and hardfacing extending from a first flank onto an oppositely facing second flank, wherein the first flank and second flank are disposed on adjacently disposed hardfacing guides. An interface is formed between the hardfacing and the hardfacing guide on which additional hardfacing is provided. The additional hardfacing on the interface can project upwards from the hardfacing guide surface to form a trimmer.

DETAILED DESCRIPTION OF INVENTION

With reference now toFIG. 3Aa prior art example of a roller cone with cutter44having hardfacing is illustrated in a front view. The cutter44comprises heel teeth that serve as hardfacing guides48arranged on its outer periphery forming a heel row46. The heel hardfacing guides48are defined by flanks50on opposing sides of the hardfacing guides48. The flanks50, which comprise leading53and trailing55flanks of the teeth, are inwardly angled upward from a base49and join to form a crest52. Flanks53,55are integrally formed from the steel body of the cutter44. InFIG. 3B, a prior art example of a portion of the heel row,46is depicted in perspective view illustrating an inner side57.

Referring now toFIG. 4, hardfacing54has been added to the gap between oppositely facing flanks50of adjacently disposed hardfacing guides48. The hardfacing54is affixed to the flanks50and comprises a cutting structure for use in earth boring operations when implementing the cutter44with an earth boring bit. In one example of use, the hardfacing guides48comprise steel, which is softer than hardfacing, thus wearing quicker during boring operations. As the steel hardfacing guides48wear down, the hardfacing54remains affixed between adjacently disposed hardfacing guides48to continue providing a cutting surface. As the hardfacing54wears, the circumferential cutting contact length decreases to improve drilling. The hardfacing54upper surface can optionally form a generally sharp crest67which can have roughly the same thickness as crests52of the hardfacing guides48. Also, the hardfacing crest has a generally curved contour from one tooth hardfacing guide48to an adjacent tooth hardfacing guide48. The curved contour preferably bulges out leaving a valley66between the crests. The hardfacing54can be flush with one or both of the inner side57or outer side59. Similarly, hardfacing54can be flush or bulge outward on the inner row56sides.

The cutter44ofFIG. 3Aalso includes an inner row of hardfacing guides58forming an inner row56concentric within the heel row46. The inner row of hardfacing guides58also include flanks60angled inward to form a crest62at the outward end of the hardfacing guides58. Hardfacing54may optionally be included within the gaps existing between the oppositely facing flanks60on adjacently disposed hardfacing guides58. The cutter44also optionally includes an apex64provided on its upper surface, the apex64can have hardfacing guides65thereon forming a grooved or profiled upper surface and include hardfacing54thereon.

Embodiments exist where hardfacing54is applied only between hardfacing guides48of the heel row46or optionally only between hardfacing guides58of the inner row56or rows not shown. The amount of hardfacing54can also vary. The hardfacing54can extend outward from the gap past the crests52of adjacently disposed hardfacing guides48,58. Optionally, hardfacing54acan be added having a terminal upper surface remaining within the gap.

FIG. 3Cis a cross sectional view of a portion of an embodiment of the cutter44ofFIG. 3A. Hardfacing54is shown extending away from the trough of a heel row46with a generally planar inner surface63and an outer surface68contoured toward the front surface63so at the hardfacing crest67width is smaller than the heel row46width.

FIG. 4depicts a rearward view of an embodiment of a cutter44ahaving webs of hardfacing54spanning between adjacent heel hardfacing guides48formed on the roller cone with cutter44a. In this view the hardfacing54extends downward below the crest52of the heel hardfacing guides48and terminates at a cutter hub51. Spaces71are shown between adjacent webs54, however the hardfacing can comprise a single member over the hardfacing guides. Although hardfacing54is not shown on the gage surface in this embodiment, hardfacing54can be applied to the gauge surface.

Additional hardfacing can be included between the cutter44aand the hardfacing54. Shown in a front view inFIG. 5is an example of hardfacing80added along the interface81of the cutter44aand applied hardfacing54. As illustrated inFIG. 5, the hardfacing80spans across the interface81and is joined to the hardfacing guides48,58on the cutter44aand also to the hardfacing54. Being adhered to both the cone shell and the hardfacing54reinforces the bond between the hardfacing54and the hardfacing guides48,58. In the example ofFIG. 5, the hardfacing80projects upward from the interface81. Thus when in use, the hardfacing80can provide a trimmer function. Beads or ridges of hardfacing80can also be added to the interfaces81on the rearward sides of the rows. An example of hardfacing80along a cutter44aand hardfacing54interface81is depicted inFIG. 6. Here the hardfacing80is optionally added along the web's entire periphery, shown on both lateral sides of the web and adjacent the hub51.

FIG. 7presents a sectional view of hardfacing80on the hardfacing guide48and hardfacing54interface81. In this view the hardfacing80is semi-elliptical, but can take on any other shape, including semi-circular, rectangular, or triangular. Moreover, although shown as substantially symmetric about its mid-section, the hardfacing80can be asymmetrically shaped. In an example, the hardfacing80leading side (side in first contact boring operations) may be thicker, both upwards and laterally. Other embodiments exist having smaller sections of hardfacing80that do not span the interface's81entire length.

FIG. 8provides in perspective view an example of a cutter44bhaving hardfacing54spanning between adjacent hardfacing guides48on a cutter row. In this embodiment hardfacing80along the interface81forms a “V: shaped member that upwardly projects from the hardfacing guide48surface. The raised V shaped members shown form bar trimmers. In the embodiment ofFIG. 8, the hardfacing54is provided on alternating adjacent hardfacing guides48.

It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. For example, the scope of this disclosure includes roller cones having more than two rows of cutting elements on a roller cone land. In the drawings and specification, there have been disclosed illustrative embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the invention is therefore to be limited only by the scope of the appended claims.