Field of the Invention:

This invention relates in general to earth-boring bits having rotating cones and in particular to a spear point or nose containing hardfacing and located on a cone having tungsten carbide cutting elements.

Background of the Invention:

In drilling bore holes in earth formations by a rotary method, one technique employs drill bits fitted with rolling cones or cutters. The bit is rotated by rotating the drill string or by a downhole motor. The cutting elements on the cones engage the earth-boring formation as each cone rotates, causing formation cuttings to be removed. Drilling fluid pumped down the drill string washes the cuttings to the surface.

One type of earth-boring bit is commonly known as a "steel-tooth" or "milled-tooth" bit. Teeth are machined in the shell of the cutter. Typically these bits are for penetration into relatively soft geological formations of the earth. The strength and fracture toughness of the steel teeth permit the use of relatively long teeth, which enable aggressive gouging and scraping actions for rapid penetration.

Another type of rolling cone drill bit employs carbide inserts, typically formed of tungsten carbide. Each insert comprises a cutting element pressed into a hole in the shell of the cone. The cutting tip portion of each insert is formed of various configurations, such as ovoid, hemispherical, chisel or conical, depending upon the type of formation to be drilled. Some of the inserts have very aggressive cutting structure designs and carbide grades to allow the bits to drill in both soft and medium formations. One of the cones of a milled tooth bit has a nose that is known as a "spear point". The spear point is integrally formed with the shell of the cone. The spear point has blades or teeth formed on its exterior. The spear point protrudes farther toward the bit axis of rotation than the other cones of the same bit. Hardfacing is applied to the spear point as well as the teeth of the milled tooth bit. The hardfacing typically consists of extremely hard particles, such as sintered, cast, or macro-crystalline tungsten carbide particles, dispersed in a steel matrix.

Hardfacing may be applied on the cones of carbide insert bits on the gage area. Tungsten carbide insert bits typically do not have any structure on the nose area that can be considered a spear point. Normally the conical portion of the shell of a carbide insert bit is not hardfaced.

Summary:

The earth-boring bit described herein has a plurality of rotatable cones. Rows of carbide cutting elements are installed within mating holes in each of the cones. A nose or spear point is symmetrically arranged on a cone axis of one of the cones. The nose has a central core with a base that may be integrally joined with supporting metal of the cone. The central core has a free end opposite the base.

A plurality of teeth extend radially outward from the core between the base and the free end. A hardfacing layer is located on the teeth. Intermediate hardfacings extend outward from the core between each of the teeth. The intermediate hardfacings protrude approximately the same distance from the core as the teeth.

In a first embodiment, each of the intermediate hardfacings comprises a lug with trailing and leading sides spaced from adjacent teeth. The lug may have a triangular shape with an outermost portion of each of the lugs defining an apex. Each of the teeth has a leading side and a trailing side with a thickness measured between the leading and trailing sides. Each of the intermediate hardfacings may have a thickness less than the thickness of the teeth.

In another embodiment, the intermediate hardfacings completely fill the spaces between the teeth. The exterior surfaces of the intermediate hardfacings may blend with the outer surfaces of the teeth, presenting a smooth, uniform exterior.

Brief Description of the Drawings:

Figure 1 is a bottom view of an earth boring bit constructed in accordance with a first embodiment.

Figure 2 is an enlarged perspective view of the nose of one of the cones of the bit of Fig.

1.

Figure 3 is an enlarged perspective view of the underlying support metal of the nose of Fig. 2, shown before applying hardfacing.

Figure 4 is an enlarged perspective view of an alternate embodiment of a nose.

Detailed Description

Referring to Fig. 1, in this embodiment, bit 11 has three cones 13, 15 and 17. Each cone 13, 15 and 17 is rotatably mounted on a bearing pin (not shown) of a bit leg of bit 11. One or more nozzles 18 is mounted to the body of bit 11 for discharging drilling fluid.

Each cone 13, 15 and 17 has a metal shell 19 that contains rows of carbide cutting elements 21. Cutting elements 21 are formed of a carbide material, normally tungsten carbide. Carbide cutting elements 21 are conventional and may have a variety of sizes and shapes.

Normally, carbide cutting elements 21 are pressed by interference fit within mating holes formed in shell 19. Each cone 13, 15 and 17 has a gage area 23 and a nose area 25. Gage area 23 defines an outer diameter of bit 1 1 for cutting the borehole sidewall. Nose area 25 is the closest portion of each cone 13, 15 and 17 to the bit axis of rotation. Nose area 25 is a frusto-conical surface that is at a different angle from the adjoining frusto-conical portion of each cone 13, 15, 17.

Nose area 25 of cone 13 has a circular perimeter 27, and in the example shown, nose area 25 of cone 13 contains a nose row of carbide elements 29 at perimeter 27. On cone 13 only, a hardfaced nose 31 is arranged symmetrically on nose area 25. Nose 31, which may also be referred to as a spear point, protrudes farther toward the bit axis of rotation than any portions of nose areas 25 of the other two cones 15 and 17. Nose areas 25 of cones 15 and 17 do not contain any hardfaced structure. Rather nose areas 25 of cones 15 and 17 may have a variety of shapes and contain a variety of carbide cutting elements 21.

Nose 31 has a central core 33, illustrated in Figure 3, that comprises supporting metal for nose 31. Core 33 protrudes from nose area 25 along cone axis 35. Core 33 is formed of the same supporting metal as shell 19 and is preferably integrally formed with the supporting metal of shell 19. Normally the supporting metal of shell 19 is a type of steel.

Core 33 has a base 37 that joins nose area 25 of cone 13. Core 33 has a free end 39 that is located opposite base 37 and which will be below base 37 when bit 11 is in operation, rather than above as shown in Figures 2 and 3. Free end 39 may be a flat surface, as shown, or it may have other shapes, including a convex shape. The particular embodiment shows free end 39 to have a perimeter that comprises an equilateral triangle. However, free end 39 could have different perimeters.

Referring also to Fig. 2, a set of blades or teeth 41 is integrally formed with core 33 and of the same material as core 33. In this embodiment, three teeth 41 are shown, but more or fewer teeth could be employed. Teeth 41 extend radially out from core 33 relative to cone axis 35. Each tooth 41 has a leading side 43, as illustrated in Figure 2, considering the direction of rotation of cone 13 illustrated by the arrow. Each tooth 41 also has a trailing side 45 facing in an opposite direction from leading side 43. In the embodiment shown, leading side 43 and trailing side 45 are substantially flat and have outer portions that are parallel to each other. Each tooth 41 has an edge or lower outer end 47 that joins free end 39 and extends toward base 37 and outward relative to cone axis 35. Each tooth 41 has an edge or upper outer end 49 that extends toward free end 39 and outward relative to cone axis 35. Outer ends 47 and 49 join each other at a rounded apex 51 that is about half-way between base 37 and free end 39. Outer ends 47, 49 and the inner portion of tooth 41 joining core 33 provide a triangular configuration for each tooth 41.

As shown in Fig. 3, a recess 53 is optionally formed in the supporting metal 57 of each tooth 41 at apex 51. Each recess 53 is a partially cylindrical surface extending from leading side 43 to trailing side 45.

Core 33 has a side surface 54 that is located between adjacent teeth 41 and extends from core base 37 to core free end 39. In the embodiment shown in Fig. 3, there are three core side surfaces 54 since three teeth 41 are shown. Core side surfaces 54 increase in distance from cone axis 35 in a direction toward base 37. Base 37 preferably has a larger diameter than the cross- sectional dimension of core 33.

As illustrated by the dotted lines in Figure 3, a hardfacing layer 55 covers the entire surface of each tooth 41 as well as recesses 53 and core side surfaces 54. Hardfacing layer 55 also defines the exterior surface of base 37, which is generally cylindrical. The cylindrical exterior of base 37 has a smaller diameter than nose area periphery 27. Hardfacing layer 55 is applied to underlying support metal 57 of core 33 to a depth that may vary. For example but not limited to, the thickness of hardfacing layer 55 may be approximately 0.60" to 0.125". The hardfacing layers 55 in recesses 53 extend outward and form each apex 51. The portions of hardfacing layer 55 at recesses 53 will thus be thicker than hardfacing layer 55 over leading side 43 and trailing side 45. Hardfacing layer 55 may optionally be applied to free end 39.

Hardfacing layer 55 may be a conventional type of hardfacing employed on earth boring bits. Preferably hardfacing layer 55 comprises hard particles, for example but not limited to tungsten carbide, located within a supporting matrix, such as steel. The carbide particles may be a variety of types, sizes and shapes, including sintered tungsten carbide, cast tungsten carbide and macro-crystalline tungsten carbide. Hardfacing layer 55 may be applied by a welding torch, which melts a steel welding tube or rod containing carbide particles, or by other heating sources.

Still referring to Figures 2 and 3, an intermediate hardfacing is bonded to each core side surface 54 between each of the teeth 41. In Figures 2 and 3, the intermediate hardfacing comprises a lug 59 that has an inner edge bonded to core 33. Because three teeth 41 are shown, three lugs 59 are also employed in this embodiment. Each lug 59 extends radially outward from cone axis 35 to approximately the same distance as apex 51 of each tooth 41. Each lug 59 has a leading side 61 that is circumferentially spaced from a trailing side 45 of an adjacent tooth 41 and faces into the direction of rotation. Each lug 59 has a trailing side 63 that is

circumferentially spaced from a leading side 43 of an adjacent tooth 41. Preferably leading side 61 and trailing side 63 have at least outer portions that are parallel to each other, defining a thickness between leading side 61 and trailing side 63. This thickness may be less than a comparable thickness between the leading and trailing sides 43, 45 of each tooth 41.

Each lug 59 in the preferred embodiment also has a triangular shape that is similar in shape to each tooth 41. Each lug 59 includes an edge or outer end 65 that extends outward from its junction with core 33 and toward base 37. Each lug 59 has an edge or outer end 67 that extends outward from its junction with core 33 and toward free end 39. Outer ends 65, 67 join each other at a rounded apex 69. The radius from cone axis 35 to each lug apex 69 is approximately the same radius as from cone axis 35 to each tooth apex 51. The apexes 51 and 69 define a maximum outer diameter of nose 31. Each lug apex 69 is located about the same midway point between base 37 and free end 39 as each tooth apex 51.

By example, but not limited to, each lug 59 is somewhat smaller in length than each tooth 41 measured along cone axis 35, however this could be changed. Each lug 59 has an end 71 that is joins one of the core side surfaces 54 and is spaced from free end 39 by a selected distance. Each lug 59 has an end 73 that joins one of the core side surfaces 54 and is spaced from base 37 by a selected distance. The distance from end 71 to end 73 is about half to three quarters the distance from free end 39 to base 37 in this embodiment. Teeth 41 are longer than lugs 59 along cone axis 35 in this example because tooth outer end 49 joins base 37 and tooth outer end 47 joins free end 39.

In the preferred embodiment, unlike teeth 41, each lug 59 is formed entirely of hardfacing material. That is, there is no underlying supporting metal for each lug 59. Rather, the operator applying hardfacing layer 55 may also form lugs 59 during that process. Lugs 59 thus may be formed of the same hardfacing material as hardfacing layer 55.

Figure 4 illustrates an alternate embodiment of a nose 75. Nose 75 has a base 79 that joins and protrudes from a cone nose area 77. A free end 81 is located opposite base 79. Nose 75 has a core 33 of underlying support metal that appears as shown in Figure 3. Nose area 75 may also have supporting metal teeth 41 as shown in Fig. 3. However, in the embodiment of Figure 4, the intermediate hardfacing completely fills the circumferential spaces between teeth 41. Preferably the intermediate hardfacings blend with outer edges of teeth 41 to define a frusto-conical surface 83 that is uniform and extends completely around nose 75. Frusto-conical surface 83 enlarges in diameter from free end 81 toward base 79. The intermediate hardfacings also mesh with outer ends of teeth 41 to define a frusto-conical surface 85 that extends outward from base 79 and enlarges in diameter toward free end 81. Frusto-conical surfaces 83, 85 join each other at an apex 87 located approximately midway between base 79 and free end 81.

Frusto-conical surfaces 83 and 85 may be machined or they may remain in an as-welded condition. The intermediate hardfacings in Figure 4 thus serve as fillers to fill the entire spaces between teeth 41 of Figure 3.

The intermediate hardfacings, whether lugs or fillers, provide additional strength for the nose to resist breakage and wear. Forming the lugs entirely from hardfacing reduces the need for machining support metal for the lugs within fairly small spaces between the teeth. Although only two embodiments are shown, it should be apparent that variations are possible.