EARTH BORING DRILL BIT WITH MATRIX DISPLACING MATERIAL

Abstract: A rotary drill bit for drilling earth formations is provided and includes a bit shank, a hard metal matrix (14) secured to a blank (10) and cutting elements (21, 22) on the exterior face thereof. The matrix includes a displacement material (D) having a different composition than the matrix material within the matrix. The displacement material is preferably less expensive than the matrix material and also has different material properties. The resulting bit may be custom-engineered for toughness, ductility, and impact resistance.

Description: This invention relates to a rotary drill bit as set forth in the pre-characterising portion of claim 1. A drill bit of the kind referred to (US-A-3757879) comprises layers of different materials such as tungsten carbide, encapsulated alumina or tungsten coated iron providing bit portions of different material characteristics. A tungsten-coated metal powder is used to provide a machinable shoulder which acts as a barrier and cover to the exterior section of the tungsten carbide portion partially coating the bit blank. The encapsulation of the particles of a displacement material will prevent metal particles from melting and percolating through the mass to attack the diamond and the tungsten carbide material. For manufacturing gradient composite cutting structures such as roller cutters or teeth advantageous for use in underground drilling tools it is known (US-A-4398952) to use first and second or more metal powder mixtures having different properties. By mixing the powders and selectively changing the composition during introduction into a mold cavity a composite structure is provided after densifying the powders into a solid member having a mechanical proporty gradients. EP-A-096591 describes an impregnated drill bit with a working face having diamond particles embedded in a matrix and the matrix including particles of a scouring agent such as alumina, boron carbide or the like. As drilling proceeds the scouring agent particles break away in time to erode the matrix to keep the bit open. Tungsten carbide or other hard metal matrix bits are brittle and can crack upon being subjected to impact forces encountered during drilling. Additionally, thermal stresses from the heat generated during fabrication of the bit or during drilling may couse cracks to form. Typically, such cracks occur where the cutter elements have been secured to the matrix body. If the cutter elements are sheared from the drill bit body, the expensive diamonds on the cutter elements are lost, and the bit may cease to drill. Additionally, tungsten carbide is very expensive. Addordingly, there is a need for an erosion resistant drill bit which has the toughness, ductility, and impact strength of steel and the hardness and erosion resistance of tungsten carbide or other hard metal on the exterior surface. The present invention meets those needs by providing a rotary drill bit as set forth in claim 1. The displacement material interspersed with the particles of hard metal matrix material imparts a greater degree of toughness, ductility and impact strength to the bit. The resulting bit may be custom-engineered to possess optimal characteristics for specific earth formations. The displacement material is preferably in the form of a plurality of particles which can vary in size. Iron and steel particles are especially preferred because it has been found that these particles impart desirable properties to the matrix while being relatively inexpensive in comparison to the cost of the tungsten carbide or other hard metal component of the matrix. Spherical or generally spherical particles are preferred because they will pack into a mold radily, although irregularly shaped particles may be employed. Other displacement materials which can be used in the practice of the present invention include other ferrous alloys such as iron-molybdenum and iron-nickel which impart increased toughness and ductility to the matrix. Other metals which may be used as displacement materials include nickel, cobalt, manganese, chromium, vanadium, and alloys and mixtures thereof. Sand, quartz, silica, ceramic materials, and plastic-coated minerals may also be utilized either in small particle sizes or agglomerated with binder to form larger particles. In practice, the displacement material may be any material which can withstand the 1000 degrees C or greater processing temperatures encountered during the bit fabrication process and which is compatible with the hard metal matrix material and binder. By withstanding the furnacing process it is meant that the displacement material may melt so long as it maintains its integrity, does not disperse in the matrix, and does not undergo excessive expansion or shrinking during the heating/cooling cycle. While the displacement material may be added in volumes as low as about 10% of total matrix volume to effect lesser changes in matrix characteristics, preferably, the displacement material is added in an amount of between about 50% to about 80% by volume of the total matrix volume. Use of different diameter spherical particles aids in obtaining optimum packing within the mold. By utilizing particles with both large and small diameters, the small diameter displacement material can pack into the interstices between the larger diameter material. With the practice of the present invention, a less expensive displacement material may be substituted for more expensive hard metals like tungsten carbide with no adverse affect on the strength properties of the finished bit. In fact, use of iron, steel, or alloys thereof as the displacement material provides a finished bit with improved toughness and ductility as well as impact strength. Furthermore, the use of such displacement materials can reduce the blank material required while maintaining desired levels of toughness, ductility, and impact strength. Further details of the present invention, will become apparent from the following detailed description, and the accompanying drawings. Fig. 1 is a view, partly in elevation and partly in section, of a rotary bit made in accordance with the present invention; Fig. 2 is a view, similar to Fig. 1 of another embodiment of the invention; Fig. 3 is a sectional view of a mold for a rotary drill bit in accordance with the present invention, with the mold containing the various materials which are used to make up the finished bit; and Fig. 4 is a stress versus strain curve for a bit body sample produced in accordance with the present invention. The invention is illustrated in the drawings with reference to a typical construction of a rotary earth boring bit. It will be recognized by those skilled in this art that the configuration of the cutting elements along the exterior face of the matrix may be varied depending upon the desired end use of the bit. Additionally, while the invention has been illustrated in conjunction with a full bore rotary matrix bit, it will be appreciated by those skilled in this art that the invention is also applicable to core head type bits for taking core samples of an earth formation. Referring now to Fig. 1, the rotary drill bit includes a tubular steel blank 10 welded to an upper pin 11 (weld line now shown) threadedly secured to a companion box 12 forming the lower end of a drill string 13. A matrix crown of hard metal matrix material 14, such as metal bonded tungsten carbide, has an upper gauge section 15 which merges into a face portion 16 extending across the tubular blank 10, which is integral with an inner portion 17 disposed within the tubular blank. Displacement material D is shown in the form of relatively large diameter spherical particles interspersed throughout the matrix. It will be understood that displacement material D can assume a variety of forms including both solid and hollow spheres, cylinders, lengths of wire, as well as irregular shapes. As is conventional, fluid pumped downwardly through the drill string and into the tubular blank can flow into the inner matrix portion 17, discharging through a plurality of nozzles or orifices 18 into the bottom of the bore hole. This fluid carries the cuttings from the drill bit in a laterally outward direction across the face of the bit and upwardly through a plurality of spaced vertical passages (not shown). Such passages are conventionally located in the gauge section and convey the cuttings and fluid into the annulus surrounding the tubular blank 10 and the drill string 13 and from there to the top of the bore hole. A number of fluid passages are of an enlarged size to function as junk slots through which upward flow of the drilling fluid and cuttings can occur more readily. Such fluid passages are conventional in the art. Diamonds 21 may be optionally embedded in the stabilizer section 15 to reduce wear on the latter section of the matrix. Cutting elements 22 are disposed in sockets 23 in matrix 14 and may be arranged in any desired conventional pattern which will be effective to perform the cutting action. Depending upon the type of diamonds utilized, sockets 23 may be preformed in the matrix during fabrication. If sockets 23 are preformed, then cutting elements 22 may be mounted therein in a separate operation after forming the bit. On the other hand, if natural diamonds or polycrystalline synthetic diamonds which can withstand the processing temperatures encountered during fabrication are utilized, the diamonds may be positioned directly in the mold and secured thereto with a conventional adhesive prior to placement of the matrix material into the mold. This latter method eliminates the need for a separate step of mounting the cutting elements after molding. The drilling fluid flows downwardly through the drilling string 13 into the inner portion 17 of the matrix bit crown 14, such fluid passing through nozzles 18 formed integrally in the matrix and discharging from the face of the bit against the bottom of the bore hole. The nozzles 18 may be circular or rectangular in cross-section. A rectangular cross-section causes the fluid discharged from each nozzle to sweep more broadly across the face of the bit and urge the cuttings toward the gauge portion 15 of the bit thereby cleaning and cooling the cutting elements 22. Referring now to Fig. 2, where like reference numerals represent like elements, there is illustrated another embodiment of the invention. In this embodiment, displacement material D is in the form of a powder which is dispersed throughout the matrix 14. Preferably, the displacement material is at least 0,00254 cm (400 mesh) in size. It has been found that very fine powdered materials (i.e., less than 0,00254 cm (0.001 inches) in diameter) such as iron may sinter and shrink during fabrication. It is undesirable for the powder to shrink substantially during heat processing. It is desirable that the binder substantially completely infiltrate the displacement material and consolidate the matrix add displacement material into a unitary solid mass. Particle sizes smaller than about 0,00254 cm (400 mesh) may be utilized in lesser amounts in admixture with larger particles; this increases the packing efficiency of the particles. Fig. 3 illustrates a preferred metallurgical process for fabricating the rotary drill bit of the present invention. A hollow mold 30 is provided in the configuration of the bit design. The mold 30 may be of any material, such as graphite, which will withstand the 1000 degrees C and greater processing temperatures. If natural diamond cutting elements or synthetic polycrystalline diamonds which can withstand the processing temperatures are utilized, they are conventionally located on the interior surface of the mold 30 prior to packing the mold. The cutting elements 21 (not shown) and 22 may be temporarily secured using conventional adhesives which vaporize during processing. During infiltration, the cutting elements will become secured in the matrix during the formation of the bit body. Alternatively, if other types of cutting elements are used, the mold is shaped to produce preformed sockets in the matrix 14 to which the cutting elements may be secured after the bit body has been formed. These elements may be then secured by any conventional means such as hard soldering or brazing. Additionally, the cutting elements may be mounted on studs which fit into the sockets, and the studs secured therein. Because of the high velocity and erosive fluids which may be typically encountered by rotary drill bits, a highly erosion resistant matrix material 14′ may optionally be placed around the face of the mold. For example, the powdered materials from which matrix material 14′ is formed by be applied to the mold as a "wet mix". This is a composition of the powdered material in a carrier such as a liquid hydrocarbon which vaporizes during high temperature processing. The wet mix may be packed along the sides and bottom of the mold and remain in place. Matrix material 14′ may be of the same hard metal material such as tungsten carbide as matrix 14. As is known in the art, the powder grain size distribution of matrix material 14′ may be varied to increase the skeletal density of the material, and thus increase its hardness and erosion resistance. After optional matrix material 14′ has been placed around the face of the mold, steel blank 10 is partially lowered into mold 30 as shown. As is conventional, elements which will form the internal fluid passages and nozzles in the finished bit are also positioned in mold 30 at this time. Then displacement material D is added. The displacement material may be any material which is different in composition than matrix material 14 and which can resist the high processing temperatures encountered. Preferably, the displacement material is less expensive than matrix material 14 and also is tougher and more ductile (less brittle) than the hard metal compounds used as matrix 14. Additionally, displacement material D should be compatible with the matrix material and binder. In a preferred embodiment, displacement material D is selected from the group consisting of iron, steel, ferrous alloys, nickel, cobalt, manganese, chromium, vanadium, and metal alloys thereof, sand, quartz, silica, ceramic materials, plastic-coated minerals, and mixtures thereof. The displacement material is preferably in the form of discrete particles, and most preferably is in the form a generally spherical particles. Such spherical particles are easier to pack into the mold. Particles sizes may vary greatly from about 0,00254 cm (400 mesh) to about 0,635 cm (0.25 inches) in diameter. Particles smaller than 0,00254 cm (400 mesh) are not preferred because they tend to sinter to themselves and shrink during heating. Particles larger than about 0,635 cm (0.25 inches) are possible, with the upper limit on particle size being that size of particles which can be efficiently packed into the mold 30. Where relatively large particle sizes of displacement material D have been used, dry powdered hard metal matrix material 14 may then be poured into the mold and around the displacement material. Where relatively small particles of displacement material have been used, it may be desirable to premix the displacement material and hard metal matrix material 14 prior to pouring the mixture into the mold 30. It is desirable to vibrate the mold gently at this point of the process to insure that the matrix material 14 and displacement material particles D are completely packed and interspersed, that all voids have been filled, and that matrix material 14 has isolated particles of the displacement material from each other. This vibration encourages the formation of good bonds between binder, matrix, and displacement particles during heating. In a preferred embodiment of the invention, the displacement material D replaces from about 50% to about 80% of the volume that the matrix material 14 would otherwise occupy. The use of different diameter displacement particles permits more efficient packing of the displacement material (the smaller particles occupy the interstices between larger particles) and a greater degree of displacement of the matrix material. In some instances, displacement material D will be less dense than the binder 34 which infiltrates it. In such cases, it is preferred that a collar 32 of a dense metal such as tungsten be positioned as shown in Fig. 3 to contain the displacement material. Collar 32 may be formed by pouring a tungsten metal powder over displacement material D and matrix material 14. Binder 34, preferably in the form of pellets or other small particles, is then poured over collar 32 and fills mold 30. The amount of binder 34 utilized should be calculated so that there is a slight excess of binder to completely fill all of the interstices between particles of displacement material and hard metal matrix material. Binder 34 is preferably a copper-based alloy as is conventional in the art. The mold 30 is then placed in a furnace which is heated to above the melting point of binder 34, typically, about 1100 degrees C. The molten binder passes through powder collar 32 and completely infiltrates displacement material D, matrix material 14, and matrix material 14′. The materials are consolidated into a solid body which is bonded to steel blank 10. After cooling, the bit body is removed from the mold, and a portion of collar 32 is machined off. Steel blank 10 is then welded or otherwise secured to an upper body or shank such as companion pin which is then threaded to box 12 of the lower most drill collar at the end of the drill string 13. Cutting elements 21 and 22, if not previously disposed in the mold, may be mounted at this time. In an alternate embodiment of the invention, displacement material D is a metal powder such as iron, steel, or alloys thereof which completely replaces matrix material 14 in mold 30. In this alternate embodiment, matrix material 14' is required to provide an erosion resistant surface for the bit. Binder 34 infiltrates both the displacement material D and matrix material 14'. The powder size is 0,00254 cm (400 mesh) or greater so that infiltration of the binder will occur without significant shrinkage of the metal powder. However, small amounts of less than 0,00254 cm (400 mesh) size powder may be used to fill in interstices between the larger particles without encountering any sintering problems. Somewhat surprisingly, it has been found that less expensive displacement material may be substituted for the more expensive hard metal matrix material and does not cause detrimental shrinkage in the mold. Additionally, when the preferred iron or steel displacement material is used, the resulting bit is tougher, less brittle, and more impact resistant than prior hard metal matrix drill bits. In order that the invention may be more readily understood, reference is made to the following examples, which are intended to illustrate the invention, but are not to be taken as limiting the scope thereof. Example 1 As a comparison of the ductility of a bit body made by the practice of the present invention to a conventional hard metal matrix bit, a sample was prepared. The sample was a 3,175 cm (1.25 inch) diameter cylinder 6,357 cm (2.5 inches) in length. The sample was prepared in a graphite mold. Steel balls having a 0,635 cm (0.25 inch) diameter were placed in the mold, and a dry powder of tungsten carbide was poured over the balls. The balls were measured to displaced approximately 66% of the volume in the mold which would otherwise have been occupied by the tungsten carbide powder. A copper allow binder, in the form of pellets, was placed in the mold over the balls and tungsten carbide. The sample was then heated in a furnace to melt the binder and cause it to infiltrate the matrix of balls and tungsten carbide. After cooling, the sample was tested on an Ingstrom testing machine. Various loads were placed on the sample to develop the stress-strain curve illustrated in Fig. 4. As shown by the graph, the modulus of elasticity of the sample was measured to be 30.4 x 10⁶. The modulus of elasticity is a measure of the stiffness of a material and is calculated from the slope of the stress-strain curve in the graph. The ultimate strength (load required to cause fracture) of the sample was measured to be 6,964-kg/cm² (9.89 x 10⁴ psi). Poisson's ratio was 0.29. By comparison, a hard metal matrix sample fabricated using the same tungsten carbide powder and same copper allow binder, but without the presence of any displacement material, has a modulus of elasticity of 15.0 x 10⁶. Thus, a sample manufactured in accordance with the present invention has approximately twice the stiffness of a tungsten carbide matrix. Example 2 Samples were prepared to evaluate the impact strength of an infiltrated matrix in accordance with the present invention as compared to a hard metal matrix. Cylindrical specimens were prepared having a 1,277 cm (0.5 inch) diameter and a length of 5,175 cm (2.25 inches). One sample was prepared using a tungsten carbide powder and a copper alloy binder. Another sample was prepared using an iron powder (50%, 0,000302 cm/0,000441 cm (48/70 mesh); 25%, 0,000441 cm (70 mesh); 25% 0,000945 cm (150 mesh)) and the same copper alloy binder. Both samples were heated in a furnace to melt the binder and permit it to infiltrate the respective metal powders. After cooling and solidification, the impact strength of each sample was tested. The tungsten carbide matrix had an impact strength 4,74J (3.5 ft-lb). while the iron matrix made in accordance with the present invention had an impact strength greater than 33,87J (25.0 ft-lb).

Claims: A rotary drill bit including a bit blank (10), a bonded matrix body secured to said bit blank (10) and cutting elements (22) mounted on the exterior (16) of said bit body, wherein said bonded matrix bit body is formed of particles of a hard metal matrix material (14) and particles of a displacement material (D) of a different composition and having different mechanical properties than said hard metal matrix material (14) both types of particles being fixed in a binder infiltrated in a liquid state into said hard metal matrix material particles (14) and displacement material particles (D) and thereafter solidified, characterized in that: said particles of displacement material (D) possess a greater degree of toughness than said hard metal matrix material (14) and are substantially interspersed with said particles of hard metal matrix material (14) prior to infiltration by said binder, said displacement material particles (D) replace at least 10% of the volume that the hard metal matrix material particles would otherwise occupy in the bit body and said displacement material particles (D) are of at least 0,00254 cm in size. The rotary drill bit of Claim 1, wherein said displacement material particles (D) are generally spherical in shape. The rotary drill bit of claim 2, wherein said displacement material particles are of a plurality of diameters. The rotary drill bit of claim 3, wherein said displacement material particles (D) have diameters in the range from about 0,00254 to about 0,635 cm. The rotary drill bit of Claim 1, wherein said displacement material particles (D) comprise steel. The rotary drill bit of Claim 1, wherein said displacement material particles (D) comprise iron, The rotary drill bit of claim 1, wherein said displacement material particles (D) are selected from the group consisting essentially of iron, steel, nickel, and alloys thereof, and mixtures thereof. The rotary drill bit of claim 1, wherein said displacement material particles are substantially uniformly distributed throughout said matrix. The rotary drill bit as claimed in one of the claims 1-8, wherein said displacement material (D) displaces about 50 percent to about 80 percent of the matrix bit body particulate volume. The rotary drill bit as claimed in one of the claims 1-9, wherein said bit blank (10) comprises steel, said hard metal matrix material (14) compromises tungsten carbide, said binder comprises a copper alloy, and said displacement material is selected from the group consisting essentially of steel powder, steel shot, iron powder, and mixtures thereof.

Inventors: HORTON, RALPH M., LOVATO, LORENZO G., TIBBITTS, GORDON A.
Applicants: EASTMAN TELECO COMPANY
Application year: 1988
Main classification: E21B10
IPC codes: E21B10, B22F7