CA1232266A

CA1232266A - Rolling cutters for drill bits, and processes to produce same

Info

Publication number: CA1232266A
Application number: CA000485466A
Authority: CA
Inventors: Gunes M. Ecer
Original assignee: CDP Ltd
Current assignee: CDP Ltd
Priority date: 1984-07-23
Filing date: 1985-06-27
Publication date: 1988-02-02
Also published as: DE3570104D1; EP0169717B1; US4562892A; JPS6160987A; EP0169717A3; JPH0321716B2; EP0169717A2; SG106491G; ATE42990T1

Abstract

ROLLING CUTTERS FOR DRILL BITS, AND PROCESSES TO PRODUCE SAME

ABSTRACT OF THE DISCLOSURE

A roller bit cutter comprises:
a) a tough, metallic, generally conical and fracture resistant core having a hollow interior, the core defining an axis, b) an annular, metallic, radial bearing layer carried by said core at the interior thereof to support the core for rotation, said bearing layer extending about said axis, c) a wear resistant outer metallic layer on the exterior of the core, d) metallic teeth integral with the core and protruding outwardly therefrom, at least some of said teeth spaced about said axis, e) and an impact and wear resistant layer on each tooth to provide hard cutting edges as the bit cutter is rotated about said axis.

Description

I

BACKGROUND OF TAO INVENTION

This invention relates generally to conical cutters utilized in roller bits employed in -the oil~well-drilling industry and in mining and, more particularly concerns unique 5 combinations including materials, that make up the composite cone and a unique manufacturing process by which the said composite cones are formed. The description of the invention that follows relates to three-cone rolling cutter bits manufac-lured or the oil and gas industry; however, the invention is 10 applicable to other types of bits utilizing conical rolling cutters, such as tycoon rolling cutter bits, geothermal and mining bits of primary importance from bit manufacturing and design punts of view is the assurance that the bit will exhibit the desired cutting action, that it will leave no rings 15 of uncut formation on the hole bottom, that it will be capable of drilling at an economically acceptable rate of penetration (into the rock formation), and that the bearing and cutting structures are sufficiently durable so that the bit can achieve maximum drilling footage at its maximum rate of penetration.
20 Among these, rate of penetration and structural durability to achieve drilling depths are the most important factors from the user' 5 point ox view and are related to the subject matter of this invention.
The invention is primarily concerned with the cutting 25 elements which are integral with -the cone structure, as opposed to carbide cutting elements which are pitted into holes drilled in-to -the cone, as is the practice presently. As the bit is rotated, the cones roll around the bottom of the hole, each - - Q
r 1~2~

tooth intermittently penetrating into the rock, crushing, whipping and caging it The cones are designed so that the teeth intermesh, to facilitate cleaning. In soft rock formations, long, widel~-spaced steel teeth are used which easily penetrate the formation.
queue present state-of~the-art manufacturing methods usually involve forging, then machining, of the cone followed by hard facing of the steel teeth HardEacing is applied in a way to provide Noah only a hard-wear resistant layer to reduce the raze at Welch the cutting elements (teeth) are worn off, buy to provide a sharp cutting edge as the tooth wears. This .
manufacturing scheme, however, it heavily labor dependent, and imprecise in that hard facing deposit thickness, as well as its . .. I-'chemical composition, is not normally uniEoxm. This is a consequence of several factors which the conventional manufacturing methods cannot, in a practical and commercially-viable sense, control.
Consider first how the hardEacincJ operation lo performed.
A foal of -the hard-wear resistant alloy is fed into a jet of hot welding arc or flame. Heat causes the rod to melt and deposit onto the steel tooth which also becomes hot and partially molten Then, the deposit is allowed to solidify. Even if one assumes that the hard-acincJ alloy is introduced uniformly and the heat is applied uniformly, both of which are usually not achieved, the natural phenomena that determine the way the molten deposit freezes, are not controlled. For example, the rate of removal of heat from the molten puddle is not uniform, because the steel tooth shape is not uniform Consequently, tooth tips remain ho-t longer due -to insouciant chilling action of the tooth section there, while at the root of the -tooth, the massive steel cone body extracts heat quickly and solidification occurs rapidly.

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This can easily produce a deposit that is non-uniforlrl in thickness and nonuniform in chemistry in a micro-structural sense Addition-ally, gravity surface tensional forces and environmental reaction, such as oxidation, play complicated roles ion preventing the formation of a uniform structurally sound hard-:Eaced deposit.
One objective of the present invention it to provide a uniform and structurally sound hard-wear resistant layer or layers at the desired locations on the cone, thus improving the cutting action of the conical cutters and allowing longer drilling times at maximum rates of penetration Another objective of the invention is to reduce the labor con-cent of the drill. boil cone by utilizing a high--temperacure/
short-cycle consolidation process by which a compositely structured . . -: --cone can be produced from its powders or powder plus solid cornpo-newts combinations..
A 'further objective is to increase the freedom of material selection o'er the various components of the cone as a direct result of the use of a short-time/high-tempera-ture . consolidation process which does not affect the usual properties-of the cone and its components Thus, materials and material combinations heretofore not used in conical cutters of steel tooth design, may be used without fear of detrimental side effects associated with long-time/high tem~Qrat.ure processing operations.

PRIOR PROCESSES
Methods of manufacturing employed by different bit manufacturers are similar in their major operations. Typically, steel bars are cut to size, heated and forged to a prewarm which is later machined to form the outer cutting structure and inner-bearing bore. After further grinding to finalize the shape, cutter teeth are hard faced my using any one of several fusion welding tweakers, and -the cone is carhurized at likelihood Sirius areas lo The inner radial bearing is, then either weld deposited or force fitted. Finally, the cutter is heat treated and bearinc3s are finished motioned The milled-tooth cone body normally requires surface hardening to withstand the erosive/abrasive effects of rock drilling. This may be accomplished by any of the widely used surface hardening techniques, such as transformation hardening, carburizing, nitrlding, or hard metal coating.
In addition, interior surfaces of the cone are required to in certain areas to be hard, wear and impact resistant to accommodate loading from both the thrust and the radial directions (with respect to the journal pin axial direction). Consequently, these surfaces are also hardened by a surface hardening process.

-On the journal side, the pin surfaces likely to contact "thrust bearing'/ surfaces are usually hard faced and run against a hardened cone or a hardened nose button insert in the cone or a carburizecd . -tool steel bushing. In most roller cones, a row of uncapped balls .
Hun in races between the nose pin and the roller or journal bearing.
These balls may carry some thrust loading, but their primary function is to retain the cone on the journal pin when not pressing against the bottom owe the hole The major load is the radial load and is carried substantially either by a full complement of cylindrical rollers, or a sealed journal bearing, mostly used in oil-field drilling.
The journal bearings are sometimes operated with crease lubrication and employ additional support to prolong bearing life; ire , sel:Elubricating porous floating rings(1),beryllium-copper alloy bearing coated with a soft metal lubricating film '3), a bearing with inlays of soft metal to provide lubrication and heat -transfer), or an aluminum bronze inlay ( yin the cone as -the soft, lubricating member of the journal-cone bearing couple.
The main body of the cone is usually a forging that is milled to create protruding, sharp, wide chisel-shaped Titan, as the cutting elernentsO
Most recently, certain powder metallurgy produced conical cutters have been proposed. Eric Drake) suggests cutting elements and conical cutters to be produced by powder metal mixing of two or more phases, and consolidation techniques where the composition could be changed gradually from surface to center. Such composite structures are stated to have a substantially continuous mechanical property gradient. Neder-~een and Verburgh , on the other hand, suggest a drill bit cone having a solid-core member comprising the bearing surrounded by a powder-consolidated, partially-dense cone body onto which a hard metal is applied by -thermal spraying. The composite cone . .
! is then hot isostatically pressed. The three layers are said to be solidly bonded providing a drill bit of superior mechanical properties, including high resistance to wear and chipping.

:
D FICIENCIES OF THE PRIOR ART_ As described above, milled-tooth cutters are machined from a single piece of a hard enable metal, yet various portions of the cone require differing properties which are difficult to achieve in an optimized manner using the same material and allowing it to respond to heat treatments. The additional materials are, therefore, sometimes applied through welding which results in layers of non-uniform thickness and chemistry Thus, the existing milled tooth cone manufacturing art provides a compromised set of engineering properties.

it further difficulty with the existing art is its large labor content, since all of the exterior and interior shapes, including cutting elements and bearings, are developed by milling and grindlny from a single forging. These milling and grinding operations, and the associated quality inspections, lengthen the manufacturing operations, thus adding substantially to the final manufacturing cost.
Cone surfaces may be treated to impart the desired localized properties; however, these treatments are usually long or inadequate, or have side effects what compromise overall properties of the cone.
On addition, hard facing of the milled teeth, as - . ;
discussed earlier, results in a non-uni~ormed do, omit thus compromL~:ing the self-sharpening effect (expected only when one side of the tooth is hardEaced), and occasionally creates ! notch lie treasons of the deposited alloy into the forged cone body, thus weakening it.
-I The recently-provided powder metallurgy methods to produce conical cutters suffer from several disadvantages as well. The co~positlonal gradient, to produce a properties gradient suggested by Drake (7), is no-t only complicated and time consuming to produce, but could, in fact, produce the opposite effect, namely create a region of inferior properties within the gradient zone. The compositional gradient, after all, is a continual dilution of the alloys present at the extremities. "Dilution," as is well known my those who are familiar with the metallurgical arts, is a major problem where a high-hardness, high-carbide content alloy is fusion-welded onto an alloy of differing, yet purer, composition The "diluted"
30 region is the region between -the two alloys and is formed by

2~6 mixing of the two Allis, thus creating a layer of high brittleness and low strength. Such is -the danger associated with the conical cones provided by Drake.
As contrasted with such prior techniques, the present invention deliberately avoids alloy gradients, in view of the problem referred to. This is accomplished -through applications of discrete layers of differing materials and by use of the short-time hot-pressing technique where atomic diffusion is limited only Jo the interface to form a strong metallurgical bond, but not to cause excessive mixing (dilution).
Nederveen and Verburyh's(6)powder metallurgy cutters utilize high temperature spraying techniques to apply powders to form surface lyres This approach roost readily incorporates oxides into the alloy layer and the alloy layer/cone-body interface, which weakly the structure. The present invention, on the other hand, accomplishes the cladding (applying a layer of one metal on the other) by room-te~lperature painting, spraying or dipping in a slurry of the powder metal, and thus provides a means to produce conical cutters owe superior quality.
Additionally, Nederveen and Verburgh(6) refer to the use of a single, solid interior metal member to be used as -the bearings portion of the cone. This expectably creates a compromise in properties needed for the radial bearing where the alloy is to be soft and malleable as against the alloy layer for the thrust and ball bearings where the surface needs to be more rigid to prevent slackening of the clearance between the cone and -the journal pin. A tight maintenance of the tolerances is a must, especially if the bearings are protected by a sealed-in lubricant.
An increase in hue "clearance" or the "tolerances" in service can shorten the seal life. The present inventor on the other I

hand, provides different materials for the different bearing surfaces in the interior ox the cone.

SUMMARY OF THE INVENTION

It is a major object of the invention to provide manufacturing methods thaw. eliminate separate surface hardening or modification treatments for different cone surfaces and replace them with simple, low temperature painting, or slurry dipping or spraying, or inserting operations. desired localized properties are obtained by applications of selected powders or lo shaped inserts rather than by thermal treatments, thus providing a wider selection of property variation for a more precise means of meeting external wear, impact or simple loading requirement is .
The subject processes involve near isos-ta-tic ho-t pressing owe cold-formed powders. See US. Patents 3,356,496 and 3,689,259. The basic process, isostatically hot presses near net-shape parts in a matter of a few minutes, producing properties similar. to those produced by the conventional Hot Isostatic Pressing IMP process without the lengthy thermal cycle required by Whopping The resultant roller bit cutter basically comprises:
- a) a tough, metallic, generally conical and fracture resistant core having a hollow interior, the core defining an axis, b) an annular, metallic, radial bearing layer carried by said core at the interior thereof to support the core for rotation, said bearing layer extending about said axis, c) a wear resistant outer metallic layer on the exterior of the core.

1~3~
d) metallic teeth irlte~ral with the core and protruding outwardly therefrom, at least some of said teeth spaced about said ayes, en and an impact and wear resistant layer on each tooth to provide hard cutting edges as the bit cutter is rotated about said axis Further, and as will be seen, an impact and wear resistant metallic inner layer may he employed on the core a-t the interior thereof, to provide an axial thrust bearing; the outer layer on the core preferably covers the core between the teeth; the layer on each tooth may consist of tungsten carbide;
and at least one and preferably all the layers consist of consolidated powder metal.
In addition, the core typically consists essentially of steel alloyed with elements that include carbon, manganese, 1 silicon, nickel, chromium, molybdenum, and vanadium, or the core . . may consist of cast alloy steel, or of ultra high strength steel. The outer layer may consist of a composite mixture of refractory particles in a binder motel such particles typically having micro hardness in excess of 1,OOOkg/mm2, and : melting point in excess of 1,600C. Also, the refractory particles are typically selected from the group consisting of Tip W, Al, V, Or, Or, Mow Tax by Hi, and carbides, oxides, nitrides and brides thereof. us, an alternative, the outer layer may consist of tool steel initially in powder form, or of a hardfacin~ alloy, as will be seen, or of wear resistant, : inter metallic Loves phase materials, as will appear.
These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following specification and drawings in which:

1.0 -DRAWING DESCRIPTION

Fig. 1 is an elevation, in section, showing a t~70-cone rotary drill bit, with inter meshing teeth to facilitate cleaning Fig. 2 is an elevation, in section, showing a milled tooth conical cutter;
Fig. pa is a cross section taken -through a tooth insert;
Fig. 3 is a flow diagram showing steps of a manufacturing process for the composite conical drill bit cutter;
Figs. I and I are perspective views of a conical cutter tooth according to the invention, respectively before and after Donnelly service use; and Pigs. I and I are perspective views of a prior design hardEaced tooth, respectively before and after Donnelly service;
Figs. Audi are elevations, in section, showing various bearing inserts employed to form interior surfaces of proposal conical cutters; and Fig. 6 is an elevation, in section, showing use of of powdered metal bonding layer between a bearing insert and the core piece, and Figs. 7 and 8 show process steps ;' ' , ' .
DETAILED DESCRIPTION
.

In Fig. 1, the illustrated improved roller bit cutter 10 incorporating the invention includes a tough, metallic, generally conical and fracture resistant core 11. The core has a hollow interior Andy defines a central axis 13 of rotation.
The bottom of the core is tapered at 14, and the interior includes multiple successive zones aye, 12_, 12c and 12_ concentric I

to axis 13, as shown. An annular metallic radial (sleeve type) bearing layer 15 is carried by -the core at interior zone aye to support the core for rotation. Layer 15 is attached to annular surface ha of -the core, and extends about axis 13. I consists of a bearing alloy, as will appear.
An impact and wear resistant metallic inner layer 15 is attached to the core at its interior zones blue, to provide an axial -thrust bearing; as at end surface aye. A
plurality of hard metallic teeth 17 are carried by -the core, as for example integral therewith at the root ends aye of the teeth. The teeth also have portions 17b -thaw p otcude outwardly, as shown, with one snide of each tooth carrying an impact and wear resistant layer 17c to provide a hard cutting edge 17d as the bit cutter rotates about axis 13. At least some of the teeth'extend'about axis 13 r and layers 17c face in the same rotary direction. One tooth 17' ma be located at the extreme outer end of the core, at axis 13. The teeth are spaced apart.
Finally, a wear resistant outer metallic skin or layer 19 lo on and attached to the core exterior surface, to extend completely over that-sur~ace and between the teeth 17.
In accordance with an important aspect of the invention, at least one or two layers 15, 16 and 19 consists essentially of consolidated powder metal, and preferably all three layers consist of such consolidated powder metal. A variety of US manufacturing schemes are possible using the herein disclosed hot pressing technique and the alternative means of applying the surface layers indicated in Fig. 2. It is seen from the previous discussion that surface layers 15, 16 and Lo are to have quite different engineering properties than the interior core section 11. Similarly, layers 16 and 19 should be different than 15~ and even 16 should differ from 19. Each of these layers and the core piece 11 may, therefore, be manuractu~ed separately or applied in place as powder mutters prior to cold pressing.' Thus, there may be a number of possible processing schemes as S indicated by arrows in Fig. 3. the encircled numbers in this figures refer to the possible processing steps (or operations) listed in below Table 1. Each continuous path in the figure, starting prom Step No 1 and ending at Step No. 15, defines separate processing schemes which, when followed, are capable of producing integral consolidated composite conical cutters.

A list of major processlny steps which may be included in the processing:
1. Blend powders 2. Cold press powder to preform green interior core ; piece 11 (see Figure 2 err location), which includes teeth 17.

3. Cold press and shier or hot press powder to preform, less -than fully dense, core piece 11.
Sinteriny or hot pressing can usually be done at a preferred temperature range 1800F to 1~50F.
If sistered, typical sistering times may be, OWE -to 4 hours depending on temperature I Forge or cast fully dense core piece 11.
I Apply powdered hard metal compound skin 19;
i.e., by painting, slurry dipping or cold spraying a hard metal powder mixed with a fugitive organic binder and a volatile seventy.
6. Place tungsten cribbed inserts 17c on teeth Essays I apply thrust-beariny alloy powder layer 16; i.e., by painting, slurry dipping or cold spraying an alloy binder mixture as in Step 5 above.
8. Apply powdered radial bearing alloy 15 in the core piece; lieu by painting, slurry dipping or cold spraying an alloy-binder mixture as in Step 5 above.
JO Apply powdered radial blaring alloy 15 in -the cold piece, i.e., by painting slurry dipping or cold lo spraying an alloy-binder mixture as in Step 5 above.
10. Place wrought, cast or sistered powder metal radial bearinc3 alloy 15 in the core pie-e 11.
11. Bake or dry to remove binder from powder layers 15, 16 and/or 19. Drying may be accomplished at room temperature overnight. If slurry applied layers are thick the preform may be baked in non oxidizing atmosphere at 70-300F for several nouns to assure complete volatilization of the volatile portion of the birder.
12. Hot press to consolidate the composite in-to a fully dense (99+ of theoretical density) conical - cutter. Typically, hot pressing temperature range of 1900-2300F and pressures of 20 to 50 tons per square inch may be required.
I 13. Weld deposit radial-bearing alloy 15 in the densified cone.
14. final finish; i.e. ! grind or machine ID profile, finish grind beatings, finish machine seal seat, inspect, etc.

The processing outlined incluc1e only the major steps involved in the flow of processing operations. Other secondary operations that are routinely used in most processing schemes for similarly rnanu~actured products, are not included for sake of simplicity. These may be cleaning, manual patchwork to repair small defects, grit blasting to remove loose particles or oxide scale, dimensional or structural inspections, etc.
All of the processing steps are unique, as may easily be recognized by those who are familiar with the metallurgical Lo arts in the powder metals processing filed. Each scheme provides a number of benefits from the processing point of view, and some of which are lusted as follows:
(1) Aye assembly operations; it painting, spraying, placing, etc., in preparing -the composite cutter structure for the hot-pressing operation (Step No. 12 in Table 1) are performed at or near room temperature. Thus, problems associated with thermal property differences or low strength, unconsolidated -Lowe-r .
I
state of the composite cone prior to hot densifica~
lion, are avoided. Repair work, geometrical or dimensional control, and in-process handling are greatly simplified.
(2) Application of powdered metal or alloy or metal compound surface layers, using volatile binders, such as cellulose acetate, corn starch and various distilled products, provide sturdy powder layers strongly held together by the binding agent, thus adding to the green strength of the total ` unconsolidated cone structure. This makes it Jo easy to control surface layer thickness, handling of the assembly in processing and provides mechanical I- support for the carbide inserts.
15 , , (3) Low-temperature application of aforementioned ' surface layers avoids pitfalls associated with high-temperature spraying of powders.

(4) The proposed schemes in every case produce a near-net-shape product, greatly reducing the labor-intensive machining operations required in the conventional conical cutter production.

PROPOSED CONE MATERIALS

Various sections of the cone c~oss,section, have been identified in Figure 2, each requiring different engineering US properties to best function in service. Consequently, materials for each section should be selected separately.
Interior core piece 11 should be made ox an alloy possessing high strength and toughness, and preferably require thermal treatments below 1700F (to reduce damage due to cooling stresses) to impart its desired mechanical properties Such restrictions can be met by the following classes of materials:
(1) Hardening grades of low-alloy steels (ferrous base) with carbon contents ranging norninall~
between 0.1 and 0.65%, manganese 0.25 to 2.0%, S silicon 0.15 to 2.2%, nickel to 3.75%, chromium to 1.2%, molybdenum to 0.40%, vanadium to 0!3%
and remainder substantially iron, total of all .. other elements to be less than 1.0% by weigh-t.
- . (2) Cartable alloy steels having less than 8% total I: 10 alloying element content; most typically STYMIE grades.
(3) Ultrahigh strength steels most specifically known in the industry as: DOW, H~11, Nikko, Noah . managing, 300-M, 4130, 4330 V, 4340. These steels ! . nominally have the same levels of C, My, and So as do the low-alloy steels described in (l) above.
; However, they have higher contents of other alloyingelements: chromium up to 5.0%, nickel to 19.0%, molybdenum to 5D0%/ vanadium to 1.0%, cobalt to guy/ with remaining substantially iron, and all . other elements totaling less than 1.0%.
. . .
(4) (Ferrous) powder metal steels with nominal chemistries falling within: 79 to 98% iron, 0-20% copper, 0.4 to 1.0 carbon, and 0.4.0% nickel.

(5) Age hard enable and mar-tensitic stainless steels whose compositions fall into the limits descried in (3) above, except that they may have chromium up to 20%, aluminum up to owe titanium up to 1.5%, copper up to 4.0%, and columbium plus tantalum up to owe.

I

In all cases, the core piece mechanical properties should exceed the following:
130 ski ultimate tensile strength 80 ski yield strength 5% tensile elongation 15% reduction in area 10 ft-lb (issued impact strength Wear resistant exterior skin 19, which may have a thickness within 0.01 -to 0.20 inch range, need not be uniform in thickness. Materials suitable for the cone exterior include:
(1) A composite mixture of particles of refractory herd compounds in a binding metal or alloy where -the refractory hard compounds have a micro-hardness . of higher than l,OOOkg/mm (50-100 g testing load), and a melting point of 1600C or higher in their commercially pure forms, and where the binding metal or alloy may be those based on iron, nickel, cobalt or copper. Examples of such refractory hard compounds include carbides, oxides, nitrides and brides (or their soluble mixtures of the Tip I Alp TV Or, Or, Mow Tax Nub and Hf.
(2) Specialty tool steels, readily available in powder form, having large amounts ox strong carbide former such as Tip V, Nub, Mow W and Or, and a carbon content higher than 2.0~ by weight.
(3) Hard facing alloys based on transition elements Fe, Nix or Co, with the following general chemistry ranges:

-17~

I

Cobalt Nickel - Iron Base Base Base Chromium 25-30~(*) 10-30% 0-27%
Carbon 0.1--3.5% 0.4-3.0% 0.1-4.0%
Tungsten ~-13% 0-5.0% -- -Molybdenum 0-56 0--17.0% 0-11%
Boron 0-2.5% 0~5 0% --Iron 0-3.Q~ 329~ Balance Nickel 0-3.0% Balance 0-1~75%
Cobalt Balance 0-12% --Silicon 0-2.0% 0-4.5% 0-1.5%
Manganese 0-1~0% . 0-1.0% 0-1.0%
(*) percentage by weight (4) Wear resistant inter metallic slaves phase) materials based on cobalt or niclcel as the primary constituent .
and havincJ molybdenum (25---35%), chromium ~8-18%), silicon (2-4%) and carbon 0.08% maximum.
Thrust bearing 16 may be made of any metal or alloy having a hardness above 35 Arc. They may, in such cases, have a composite structure where part of the structure is a lubricating material such as molybdenum disulfide, tin, copper, silver, lead or their alloys or graphite.
Cobalt-cemented tungsten carbide inserts 17c cutter teeth 17 in Figure 2, are to be readily available cohalt--tungst2n carbide compositions whose cobalt content usually is within the 5-18% range.
Bearing alloy 15 r if incorporated into the cone as a separately-manufactured insert, may either be a hardened or carburized or nitride or bonded steel or any one of a number owe readily available commercial non-ferrous bearing alloys, ~3Z~

such as bronzes, If the bearing is weld deposited, the material may still be a bronze. If, however, the bearing is integrally ho-t pressed in place from a previously applied powder, or it the insert is produced by any of the known powder metallurgy -techniques, then it may also have a composite structure having dispersed within it a phase providing lubricating properties to the bearing.

Examples ' " ' ' ', .
on example for the processing of roller cutters includes the steps 1, 3, 5, 6, 7, 10, 11, 12 and 14 provided in Table 1.
A low alloy steel composition was blended to produce the final chemical analysis: 0.22% manganese, 0.23% molybdenum 1,84 nickel, 0.27~ carbon and remainder substantially iron. The powder was mixed with a very small amount of zinc Stewart, for ; 15 lubricity, and cold pressed to the shape of the core piece 11 (Figure 2) under a 85 Sue pressure. The preform was then sistered For one hour at 2050F to increase its strength.
A slurry was prepared of Satellite No. 1 alloy powder and 3% by weight cellulose acetate and acetone in amounts adequate -to provide the desired viscosity to the mixture. The Stilt No. 1 nominal chemistry is as follows: 30% chromium by weight), 2.5% carton, 1% silicon, 12.5% tungsten, 1% maximum - .
each of iron and nickel with remainder being substantially cobalt.
The slurry was applied over -the exterior surfaces of the core piece using a painter's spatula, excepting those teeth surfaces where in service abrasive wear is desired in order to create self-sharpeniny effect. Only one side of the teeth was thereby covered with the slurry and before the slurry could dry -to harden, 0.08" thick. cobalt cemented I cobalt) tungsten carbide ~2t~fi~

inserts (Figure 4, a) were pressed in-to -the slurry. Recess slurry at the carbide insert eyes were removed and interfaces smoothed out using the spatula.
A thin layer of an alloy steel powder was similarly applied, in a slurry state, on thrust bearing surfaces identified as 16 in Figure 2. The thrust bearing alloy steel was identical in composition to the steel used to make the core piece, except the carbon content was 0.8% by weight. Thus, when given a hardening and tempering heat treatment the thrust bearing :
surfaces would harden more than the core piece and provide the : :
needed wear resistance.
:
on ASSAY 1055 carbon steel tube having 0 1" wall thickness was fitted into the radial bearing portion ox the core . - .
piece by placing it on a thin layer of slurry applied alloy steel powder used for the core piece.
. -: :
The preform assembly, thus prepared, was dried in an oven at 10~0F for overnight driving away all volatile constituents of the slurries used. It was then induction heated to-about I, 2250F within four minutes and immersed in ho ceramic grain, which was also at 2250F, within a cylindrical die. A pressure of 40 -tons per square inch was applied to the grain by way of an hydraulic preys. The pressurized grain transmitted the pressure to the preform in all directions. The peak pressure was reached within 4-5 seconds, and the peak pressure was maintained for less than two seconds and released. The die content was emptied separating the grain from -the now consolidated roller bit cutter. Before the part had a chancy two cool below 1600F, it was transferred to a furnace operating at 1565F, kept there for one hour and oil quenched. To prevent oxidation the furnace atmosphere consisted of non-o~idizing cracked ammonia I

The hardened part was then tempered for one hour at 1000F
and air cooled to assure toughness in the core.
A similarly processed tensile test bar when tensile tested exhibited 152 ski ultimate tensile strength, 1~1 ski yield strength, 126 elongation and 39% reduction of area.
Another -test bar which was processed in the same manner as above, except tempered at 450F, exhibited 215 ski ultirna-t~
tensile strength, 185 ski yield strength, I elongation and 21% reduction of area. Thus, it is apparent that one may easily develop a desired set of mechanical properties in the consolidated core piece by tempering at a selected temperature.
In another example, powder slurry for the wear resistant exterior skin and the thrust bearing surface was prepared using a 1.5~ by weight mixture of cellulose acetate with Satellite alloy No. 1 powder. This preform was dried at 100~F for overnight instead of 250~F for two hours, and the remaining processing steps were identical to the above example.
No visible diE~erences were detected between the two parts produced by the two experiments.
In yet another example, radial bearing alloy was affixed on the interior wall of the core through the use of a nickel powder slurry similarly prepared as above Once again the bond between the radial bearing alloy and the core piece-was extremely strong as determined by separately conducted bonding experiments.

OUTWORE PERTINENT INFOR~!LZ\rrION

The term "composite" is used both in the micro-structural sense or from an engineering sense, whichever is more -~322~

appropriate. Thus, a material made up of discrete wine phase(s) dispersed within another phase is considered a composite of phases, while a structure made up of discrete, relatively large regions joined or assembled by some means, together is also considered a "composite." An alloy composed of a mixture OX
carbide particles in cobalt, would micro-structurally be a composite layer, while a cone cutter composed of various distinct layers, carbide or other inserts, would be a composite part.
The term "green" in Table l, line 2, reveres to a : : :: -lo state where the powder metal part is not yo-yo fully densifiéd buy has suEf1c1ent strength to be handled without chipping or breakage.

Sistering (the same table, line 3) is a process by which powdered (or otherwise) material is put in intimate contact and heated to :
` cause a metallurgical bond between them.
This invention introduces, for the firs-t time, the i following novel features to a drill bit cone: -.
(l) A "high-temperature - short-heating cycle" means ox consolidation of a composite cone into a ;: :
nearly finished product, saving substantial labor .
time.

:

I;:; : I: \ ' I
' .

and allowing the use of multiple }materials tailored to meet localized demands on their properties.
(2) Application of material layers at or near room temperature, which eliminates thermally-induced structural damage if a thermally-activated process were to be used.
.
(3) A "high-temperature - high-pressure - short-time"
processing scheme, as outlined in Figure 3, err time-temperature dependent diffusion reactions are substantially reduced.
(4) A rock bit conical cutter having a hard, wear-resistant exterior skin and an iIlterior profile which may consist of a layer bearing alloy or -two :
different alloys, one for each radial and thrust bearings; all of which substantially surround a high strength tough core piece having protruding -; teeth.
,:
(5) A conical cutter same as in Item (4), but having teeth partially coveted on one side with an insert, ;20 preferably a cobalt cemented -tungsten carbide insert, which is bonded onto -the interior core piece 11 by a thin layer of a carbide-rich hard alloy similax~-to those used for the exterior skin 19. This~ls illustrated in Figs. I and I, 25~ and is intended to provide a uniform, hard-cutting edge to the cutting teeth as they wear in Donnelly service i.e., self-sharpeniny of teeth (see Fig.
I. This is to be contracted with problems of .
degradation of the cutting edge encountered in .

~.~3Z2~6 hard aced teeth (see Figs. I and I) A conical cutter, as in Item (5), but having interior bearing surfaces provided by preform and shaped inserts prior Jo hot consolidation of the composite cone. These inserts may be one or more pieces, at least one of which is the radial-bearing piece Thrust bearing may be provided in the form of a single insert, or two : :
or more inserts, depending on the cone interior design. These variations are illustrated in Figs Audi Fig. I shows one insert 30; Ego. I shows a second insert 31 covering - all interior surfaces, except for insert 30;

Fig. So shows a third insert 32 combined with insert and a modified second insert 31'; and ., : .
Fig. So shows modified second and third inserts :
31" and 32".
(7) A conical cutter, as in Item (6), but having interior bearing inserts 33 and 34 bonded onto ; the interior core piece 11 by a thin layer or layers aye and aye ox a ductile alloy, as : . _ illustrated in Figure 6.
8) A conical cutter same as in (5), but interior bearings surface is provided by a powder metallurgically applied layer of a bearing alloy.
Fig. 1 shows a bit body 40, threaded at aye, with conical cutters 41 mounted to journal pins 42, with ball bearings 43 and thrust bearings 44.

.

I

Step 3 of the process as listed in Table is for example shown in Fig. 7, the arrows 100 and 101 indicating isosta-tic pressurization of both interior and exterior surfaces of ye core piece 11. Note that the teeth 17 are integral with the core-piece and are also pressurized Pressure application is ejected or example by the use of rubber molds or ceramic : Jo granules packed about the core and teeth, and pressurized. Step : 12 of the process as listed in Table 1 is for example shown in Pig 8. The part as shown in Fig. 2 is embedded in hot : ceramic grain or particulate 102, contained within a die 103 : I: having bottom and side walls 104 and 105. A plunger 106 fits within the cylindrical bore aye and presses downwardly on the hot grain 102 in which consolidating force is transmitted to the part, generally indicated at 106. Accordingly the core : 15 11 all components and layers attached thereto as referred to j above are simultaneously consolidated and bonded together.

.

:' :
,: ' : -. .

:: :: :
::

. :

-aye-REFERENCES
. _ . . . _ _ .

.
1. I K. Sorensen and A. T. Rallies, "Journal and Pilot Bearings with Alternating Surface Areas of Wear-P~esistant and Anti-Galling Materials, "US. Pat. No. 3,984,158 I Out 5, 1976) I Howe Murdoch, "Drill Bit," US. Pat. No. 4,074,922 phoebe. 21, 197$) 3. To H. Mayo, "Drill Bit Bearings US. Pat. No. 3,721,307 : ` :
Myra 20, 1971) I ~.~ I Hanger, journal Bearing with Alternating Surface , Areas of Wear Resistant and Anti-Galling Materials, "US.
Pat. No. 3j235,316 (Feud 15, 1966) 5. JD~R.~Qulnlan, "aluminum Bronze Bearing," US. Pat. No 3,~9g~5,017 (Dec. ?, 1976)

6. Hans B. Van Nederveen, Bosch en Dun and Martin B. Verburgh, "Drill Bit," US. Pat. No. 4,365,679 (Dec. 28, 1982)

7. Eric Fox Drake "Metal Cutting Tools Utilizing Gradient Composites," US. Pat. No. 4,368,788 (Jan. 18, 1983)

8. Eric F. Drake "Cutting Teeth or Rolling Cutter Drip Bit," US. Pat. No. 4,372,404 (Feb. 3, 1~83) : : . , :-: : . , : : -:

I:

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A roller bit cutter, comprising, in combination:
(a) a tough, metallic, generally conical and fracture resistant core having a hollow interior, the core defining an axis, (b) an annular, metallic, radial bearing layer carried said core at the interior thereof to support the core for rotation, said bearing layer extending about said axis, (c) a wear resistant outer metallic layer on the exterior of the core, (d) metallic teeth integral with the core and protruding outwardly therefrom, at least some of said teeth spaced about said axis, (e) and an impact and wear resistant layer on each tooth to provide hard cutting edges as the bit cutter is rotated about said axis, (f) said core consisting essentially of steel alloyed with elements that include carbon, manganese, silicon, nickel, chromium, molybdenum, and vanadium, said elements having the following weight percents:

carbon 0.1 to 0.65 manganese 0.25 to 2.0 silicon 0.15 to 2.2 nickel 0.01 to 3.75 chromium 0.01 to 1.2 molybdenum 0.01 to 0.40 vanadium 0 to 0.3

2. The combination of claim 1 including a) an impact and wear resistant metallic inner layer on the core at the interior thereof, to provide an axial thrust bearing.

3. The combination of claim 1 wherein said outer layer covers the core between said teeth.

4. The combination of claim 1 wherein said layer on each tooth consists essentially of tungsten carbide.

5. The combination of claim 1 wherein at least one of said layers consists essentially of consolidated powder metal.

6. The combination of claim 1 wherein at least two of said layers consist essentially of consolidated powder metal.

7. The combination of claim 1 wherein at least three of said layers consist essentially of consolidated powder metal.

8. The combination of claim 1 wherein said core consists essentially of cast alloy steel.

9. The combination of claim 1 wherein said core consists of ultra high strength steel.

10. The combination of claim 1 wherein at least one tooth is proximate the conical core tip.

11. The combination of claim 1 wherein said outer layer consists of tool steel initially in powder form.

12. The combination of claim 11 wherein said steel is selected from the group consisting of D-6A, H-11, 9Ni-4Co, 18-Ni maraging, 300-M, 4134, 4330V and 4340.

13. The combination of claim 1 wherein said inner layer consists of tool steel initially in powder form.

14. The combination of claim 1 including mounting structure on which said core and bearing layer are carried for rotation in a drilling operation.

15. The combination of claim 1 wherein said layer carried by the core at the interior thereof consists essentially of alloy having a composition selected from one of the following three columnar groups:

16. The combination of claim 1 wherein said layer carried by the core at the interior thereof consists essentially of wear resistant, intermetallic Laves phase, materials based on a primary constituent selected from the group consisting essentially of cobalt and nickel, and having the following alloying elements, with indicated weight percents:

molybdenum 25 to 35%
chromium 8 to 18%
silicon 2 to 4%
carbon 0 to 0.08%

17. A roller bit cutter, comprising, in combination:
(a) a tough, metallic, generally conical and fracture resistant core having a hollow interior, the core defining an axis, (b) an annular, metallic, radial bearing layer carried by said core at the interior thereof to support the core for rotation, said bearing layer extending about said axis, (c) a wear resistant outer metallic layer on the exterior of the core, (d) metallic teeth integral with the core and protruding outwardly therefrom, at least some of said teeth spaced about said axis, (e) and an impact and wear resistant layer on each tooth to provide hard cutting edges as the bit cutter is rotated about said axis, (f) said core consisting of consolidated ferrous powder metal steel having the following composition, indicated percentages being by weight:

iron 79 to 98%
copper to 20%
Caribbean to 1.0%
nickel to 4.0%

18. A roller bit cutter, comprising in combination:
(a) a tough, metallic, generally conical and fracture resistant core having a hollow interior, the core defining an axis, (b) an annular, metallic, radial bearing layer carried by said core at the. interior thereof to support the core for rotation, said bearing layer extending about said axis, (c) a wear resistant outer metallic layer on the exterior of the core, (d) metallic teeth integral with the core and protruding outwardly therefrom, at least some of said teeth spaced about said axis, (e) and an impact and wear resistant layer on each tooth to provide hard cutting edges as the bit cutter is rotated about said axis, (f) said outer layer consisting of a composite mixture of refractory particles in a binder metal.

19. The combination of claim 18 wherein all of said layers consist essentially of consolidated powder metal.

20. The combination of any one of claims 3, 7 and 19 wherein the core has mechanical properties in excess of the following lower limits:
130 ksi ultimate tensile strength 80 ksi yields strength 5% tensile elongation 15% reduction in area 10 ft-lb (izod) impact strength.

21. The combination of claim 18 wherein said refractory particles have micro hardness in excess of 1,000 kg/mm2, and a melting point in excess of 1,600° C.

22. The combination of claim 18 wherein said refractory particles are selected from the group consisting of Ti, W, Al, V, Zr, Cr, Mo Ta, Nb, Hf, and carbides, oxides, nitrides, and borides thereof.

23. A roller bit cutter, comprising, in combination:
(a) a tough, metallic, generally conical and fracture resistant core having a hollow interior, the core defining an axis, (b) an annular, metallic, radial bearing layer carried by said core at the interior thereof to support the core for rotation, said bearing layer extending about said axis, (c) a wear resistant outer metallic layer on the exterior of the core, (d) metallic teeth integral with the core and protruding outwardly therefrom, at least some of said teeth spaced about said axis.
(e) and an impact and wear resistant layer on each tooth to provide hard cutting edges as the bit cutter is rotated about said axis, (f) said outer layer consisting of a hardfacing alloy having a composition selected from one of the following three columnar groups:

24. A roller bit cutter, comprising, in combination.
(a) a tough, metallic, generally conical and fracture resistant core having a hollow interior, the core defining an axis, (b) an annular, metallic, radial bearing layer carried by said core at the interior thereof to support the core for rotation, said bearing layer extending about said axis, (c) a wear resistant outer metallic layer on the exterior of the core, (d) metallic teeth integral with the core and protruding outwardly therefrom, at least some of said teeth spaced about said axis, (e) and an impact and wear resistant layer on each tooth to provide hard cutting edges as the bit cutter is rotated about said axis, (f) said outer layer consisting of wear resistant, intermetallic Laves phase, materials based on a primary constituent selected from the group consisting of cobalt and nickel, and having the following alloying elements, with indicated weight percents:
molybdenum 25 to 35%
chromium 8 to 18%
silicon 2 to 4%
carbon 0 to 0.08%

25. The combination of one of claims 2, 3 or 4 wherein at least one of said layers consists essentially of consolidated powder metal.

26. The combination of one of claims 2, 3 or 4 wherein at least two of said layers consist essentially of consolidated powder metals.

27. The combination of one of claims 2, 3 or 4 wherein at least three of said layers consist essentially of consolidated powder metal.

28. The combination of claim 7 including:
(a) an impact and wear resistant metallic inner layer on the core at the interior thereof to provide an axial thrust bearing;
(b) wherein the layer on each tooth consists essentially of tungsten carbide; and (c) wherein the core has mechanical properties in excess of the following lower limits:
130 ksi ultimate tensile strength 80 ksi yields strength 5% tensile elongation 15% reduction in area 10 ft-lb (izod) impact strength.