U.S. patent number 3,757,878 [Application Number 05/283,475] was granted by the patent office on 1973-09-11 for drill bits and method of producing drill bits.
This patent grant is currently assigned to Christensen Diamond Products Company. Invention is credited to Harold C. Bridwell, Arthur G. Wilder.
United States Patent |
3,757,878 |
Wilder , et al. |
September 11, 1973 |
DRILL BITS AND METHOD OF PRODUCING DRILL BITS
Abstract
Earth boring drills such as are useful in oil well drilling or
other drilling operations and methods of producing such drills in
which metal-encapsulated primary abrasive particles such as
diamonds and metal-encapsulated secondary particles are bonded
together and to a metallic shank by means of a metal matrix.
Inventors: |
Wilder; Arthur G. (Salt Lake
City, UT), Bridwell; Harold C. (Salt Lake City, UT) |
Assignee: |
Christensen Diamond Products
Company (Salt Lake City, UT)
|
Family
ID: |
23086238 |
Appl.
No.: |
05/283,475 |
Filed: |
August 24, 1972 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
219973 |
Jan 24, 1972 |
|
|
|
|
220351 |
Jan 24, 1972 |
|
|
|
|
220352 |
Jan 24, 1972 |
|
|
|
|
Current U.S.
Class: |
175/434 |
Current CPC
Class: |
B22D
19/06 (20130101); B22D 19/14 (20130101); E21B
10/46 (20130101) |
Current International
Class: |
E21B
10/46 (20060101); E21b 009/36 () |
Field of
Search: |
;175/329,330,409-411 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Brown; David H.
Parent Case Text
This application is a continuation in part of applications, Ser.
No. 219,973; 220,351; 220,352, Jan. 24, 1972.
Claims
We claim:
1. In a drill bit comprising a shank, a bore through said shank,
the improvement comprising a coating, said coating including
abrasive particles, metal matrix bonding said abrasive particles in
said coating and bonding said coating to the lower end of said
shank, said particles being encapsulated in a metal coating and
contained in said metal matrix.
2. In the drill bit of claim 1 in which the abrasive particles are
tungsten-coated alumina.
3. The drill bit of claim 1 in which the metal encapsulating said
abrasive particles is tungsten, or tantalum, or columbium (niobium)
or molybdenum or titanium.
4. In the drill bit of claim 3, said abrasive particles in said
coating are metal-encapsulated tungsten carbide, or
metal-encapsulated alumina, or metal-encapsulated silicon carbide,
or metal-encapsulated boron nitride.
5. The drill of claim 1 in which the coating extends over the crown
end of said shank and at said crown end contains a metal-bonded
mixture of diamond particles and particles of metal-encapsulated
tungsten carbide, or metal encapsulated alumina, or
metal-encapsulated silicon carbide, or metal-encapsulated boron
nitride.
6. The drill of claim 5 in which the metal-encapsulated said
particles is tungsten, or tantalum, or columbium, or molybdenum, or
titanium.
7. In the drill bit of claim 5 in which the abrasive particles are
tungsten-coated alumina.
8. The drill of claim 1 in which said coating extends over the
crown end and contains a mixture of diamond particles and tungsten
carbide particles and said coating above said crown is
substantially free of diamond particles and contains
metal-encapsulated alumina, or metal-encapsulated silicon carbide,
or metal-encapsulated boron nitride.
9. The bit of claim 8 in which said encapsulating metal is
tungsten, or tantalum, or columbium (niobium), or molybdenum, or
titanium.
10. The drill of claim 8 in which the metal-encapsulated abrasive
is tungsten-coated alumina.
11. The drill of claim 1 in which said coating extends over the
crown end and the coating at said crown end contains a mixture of
metal-encapsulated diamond particles and metal-encapsulated
tungsten carbide, or metal-encapsulated alumina, or
metal-encapsulated silicon carbide, or metal-encapsulated boron
nitride and the coating above said crown is substantially free of
diamond particles and contains metal-encapsulated tungsten carbide,
or metal-encapsulated alumina, or metal-encapsulated silicon
carbide, or metal-encapsulated boron nitride.
12. The drill of claim 11 in which said encapsulating metal is
tungsten, or tantalum, or columbium (niobium), or molybdenum, or
titanium.
13. The drill of claim 11 in which said encapsulating metal is
tungsten and the metal-encapsulated abrasive particles other than
diamonds are tungsten-encapsulated alumina.
14. The drill of claim 1 in which the coating at the crown end of
said shank includes diamond particles.
15. The drill bit of claim 14 in which the abrasive particles are
tungsten-coated alumina.
16. The drill bit of claim 14 in which the metal encapsulating said
abrasive particles is tungsten, or tantalum, or columbium
(niobium), or molybdenum, or titanium.
17. The drill bit of claim 16 in which the metal encapsulating said
abrasive particles is tungsten, or tantalum, or columbium (niobium)
or molybdenum, or titanium.
18. The drill bit of claim 17, said abrasive particles in said
coating are metal-encapsulated tungsten carbide, or
metal-encapsulated alumina, or metal-encapsulated silicon carbide,
or metal-encapsulated boron nitride.
19. The drill bit of claim 1 in which said coating extends over the
crown end of said shank and in which diamond particles are surface
set in said end in space configuration over the said end surface
forming the crown of said bit.
20. The drill bit of claim 19 in which the metal encapsulating said
abrasive particles is tungsten, or tantalum, or columbium (niobium)
or molybdenum or titanium.
21. The drill of claim 19 in which the coating at said crown end
contains metal-bonded tungsten carbide.
22. In the drill bit of claim 21 in which the coating above said
crown end contains tungsten-coated alumina.
23. The drill of claim 21 in which the coating above said crown end
contains metal-encapsulated tungsten carbide, or metal-encapsulated
alumina, or metal-encapsulated silicon carbide, or
metal-encapsulated boron nitride.
24. The drill bit of claim 23 in which the metal encapsulating said
abrasive particles is tungsten, or tantalum, or columbium (niobium)
or molybdenum or titanium.
Description
This invention is an improvement on diamond drills in which
diamonds are incorporated in the body of or positioned on the
surface of an abrader structure in the form of a drill, for
example, as may be used for earth boring.
In one form of earth-boring drill, a plurality of different
abrasive particles are employed. In addition to particles of high
hardness values, for example, diamonds which act on the primary
abrasive, there is positioned in the continuous phase of a metal
matrix binder a secondary abrasive of lower hardness value.
The purpose of this secondary abrasive particle is to wear away
preferentially thus exposing new abrasive faces of the primary
abrasive particle.
The abrader structures thus formed are deemed self-sharpening. That
is, the matrix including the secondary abrasive wears away
preferentially and uniformally exposing new primary abrasive
cutting surfaces. This, however, tends to reduce the area of the
interfacial surfaces between the bonding metal of the matrix and
the primary and secondary abrasive particles. Where the bond is
weak, the particles are torn out of the metal matrix, causing
excessive wear.
In such a structure, it is conventional to form the abrader body of
tungsten carbide to act as the secondary abrasive particle. The
diamonds and tungsten carbide are bonded by means of a metal matrix
which is formed by percolating molten metal to infiltrate the body
of discrete tungsten carbide in a suitable mold to bond the
tungsten carbide; if diamonds are also distributed throughout this
metal matrix, the mixture of diamonds and tungsten carbide form the
mass which is infiltrated by the molten metal. In another form, the
diamonds are positioned in spaced configuration on the external
grinding surface of the drill. These are termed surface set diamond
drills.
There are a number of difficulties in forming such drills arising
from the nature of the tungsten carbide and the diamonds which add
to the disadvantage of the high cost of these abrasives. Where
diamonds are employed because of their peculiar properties, this
cost must be borne.
It is a purpose of this invention to avoid the problems arising
from the chemical nature of the tungsten carbide by substituting a
different abrasive particle having suitable and improved chemical
characteristics. The substitution has also improved the economics
of the manufacture.
One of the problems arising when using tungsten carbide in such
structures is the restriction which it places on the metal which
may be used as a metal matrix bond.
The metal chosen should be fluid at the temperature at which it is
desired to employ the molten metal in forming the composite drill
structure, for example, below 2,000.degree. F. and desirably should
have, when solid, ductility as measured in the terms of
microhardness of below about 400 kg/mm.sup.2. Desirably, also, it
should have a compressive strength above about 90,000 p.s.i. and an
impact strength above about 5 foot pounds.
For this purpose, we may use copper-based alloys such as brass and
bronze alloys and copper-based alloys, for example,
TABLE 1
M.P. Sp.G. Percent Hard- .degree.C. Linear ness Coeff. kg/mm.sup.2
of Ex- Knoop* pansion Vick- .times. 10.sup.4 ers** 0.degree.-
1000.degree.F. Diamonds (Synthetic or Natural 3.5 1.5 8000*
Aluminum Oxide (A1.sub.2 O.sub.3) 2060 3.5-4 4.4 3000* Cast
Eutectic Tungsten Carbide 4800 15 Tungsten Mono Carbide (WC) 4800
15.8 2.7 Ditungsten Carbide (W.sub.2 C) 4800 17.3 1950-2400 Boron
Nitride (Cubic) >1700 3.48 .about.20 4700* Tetrachromium Carbide
(Cr.sub.4 C) 1500 6.99 3 Trichromium Dicarbide (Cr.sub.3 C.sub.2)
1910 6.68 2.4 2650 Titanium Diboride (TiB.sub.2) 2870 4.52 4.2 e.
Hafnium Diboride (HfB.sub.2) 3250 11.20 4.2 3800.degree. Zirconium
Diboride (ZrB.sub.2) 3100 6.09 4.6 2000* Calcium Hexaboride
(CaB.sub.6) 4050 2.46 3.6 2740.+-.220* Barium Hexaboride
(BaB.sub.6) 4100 4.32 3.8 3000.+-.290** Tantalum Carbide (TaC) 3.7
Silicon Carbide >1000 3.21 2.4 2200-2900*
copper-based alloys containing various amounts of nickel, cobalt,
tin, zinc, manganese, iron and silver, cast iron, iron-based
alloys, nickel-based alloys, for example,
nickel-copper-alumina-silicon alloy melting below 2,000.degree.
C.
However, tungsten carbide is attacked by iron-based or nickel-based
alloys. The W.sub.2 C tungsten carbide is attacked or dissolved in
the binder, and on freezing precipitates a new phase called Eta.
This phase is an M.sub.6 C type carbide, and in the case of nickel
binders will have the composition Ni.sub.3 W.sub.3 C. Eta phase is
more brittle than the original particle. The particle is said to be
"haloed." The "haloed" portion of particle will have a hardness
only of about 1,500 kilograms per square millimeter, compared, for
example, to 1,950 to 2,100 kilograms per square millimeter (Knoop)
for the core of the particle.
Tungsten carbide has been used in the past because among other
properties it has a high specific gravity, hardness, and high
melting point.
By encapsulating the tungsten carbide with a metal envelope, the
tungsten carbide is prevented from attack by such metals and also
obtains the additional benefit of encapsulation as described
above.
We have found that we may use alumina, silicon carbide, boron
nitride, and other abrasives as listed in Table 1 in place of
tungsten carbide. The most practical both from point of view of
economy and functional suitability are aluminum oxide, boron
nitride, and silicon carbide. However, these materials may not be
employed when a metal matrix is to be used as a bonding agent. The
particles are not sufficiently wetted by the molten metal. When the
metal solidifies, it pulls away from the abrasive particle. The
result is an excessive loss of abrasive particles as the abraded
surface exposes the loosely held particles.
We have solved this problem by encapsulating the secondary
particles with a metal envelope. The encapsulated particle is more
easily wetted by the molten metal than the non-metallic substrate.
The improved interfacial tension between the metal envelope and the
metal matrix used to bind the particles, increases the grip of the
metal matrix on the encapsulated particle and thus helps to prevent
the loss of the particle in case fragmentation of the particle does
occur.
Another problem in structure of the prior art arises from the fact
that the abrasive action places the abrasive particle in tension
and the resultant excessive fragmentation of the abrasive particles
may thereby result in loss of the particle from the matrix.
We have solved this problem referred to above by producing a novel
metal-encapsulated abrasive particle and novel abrader structures
by first encapsulating an abrasive particle with a metallic
envelope.
When metal is used as a matrix to bind the abrasive particles, both
in the case of the primary as well as in the case of the secondary
abrasive particles in the abrader structure, encapsulation of the
abrasive particles increases the grip of the metal matrix on the
abrasive particle.
In selecting the metal for the envelope when the encapsulated
particle is to be used with metal matrix acting as a bonding agent,
it is desirable that the metal in the envelope have a suitably
higher melting point than the metal matrix.
The further advantage of the encapsulated abrasive particle of our
invention when used together with a metal matrix resides in the
increased rate of heat transfer from the abrasive particle
resulting from the more intimate contact at the surfaces between
the envelope and the substrate particle and the envelope and the
metal matrix. Heat generated at the abrading surfaces, if not
readily transmitted to and absorbed in the metal matrix, acting as
a heat mass, will cause a local rise in temperature which may have
a deleterious effect upon the life of the abrasive particle.
In order to obtain the increased bond between the abrasive
particles and the metal matrix, any convenient method for deposit
of the metal envelope on the particle substrate may be employed.
Thus electrochemical or electrolytic methods which have been
previously employed in coating abrasive particles for use in
abrader structure will, when used together with a metal bonding
agent in our novel abrader structure, result in an improved bond
between the metal matrix and the coated particle due to the
improved wetting by the molten metal. In this respect, the use of
the coated particle in a composite structure employing a metal
matrix is an improvement over the use of an abrasive particle
coated by an electrochemical or electrolytic process when used with
a resin binder. It is similarly an improvement over the use of
uncoated abrasive particles with resin or metal binders acting as a
matrix for the abrasive particles.
Abrasive particles coated by such procedures result in deposits
which are contaminated by intergranular inclusions of impurities
from their aqueous environment. Furthermore, the deposits
particularly in the case of electrolytic deposits have
intergranular planes of weakness and the coating has a relatively
low tensile and bending strength. They do not improve, in any
substantial degree, the physical properties of the coated particle
as compared with the uncoated particle.
The metallic envelopes which we prefer to employ to encapsulate the
abrasive particles of our invention employed in the novel drill
structure of our invention differ from the foregoing coatings in
composition and crystalline nature.
In contrast to these deposits, the deposits of our invention are
substantially pure metal envelopes, substantially free of
intergranular inclusions.
The metallic envelope of the abrasive in the abrader structure of
our invention is composed of crystal grains which are dendrites
starting at and extending from the substrate surface, creating a
superposition of grain growth interrupted by other grain skeleton
deposit on top thereof. The grains thus deposited form a
mechanically interlocked grain structure giving to the metal sheath
high tensile strength. Such deposits are termed
"allotriomorphic."
We prefer to produce the aforesaid encapsulated abrasive of our
invention by a process of chemical vapor deposition, by subjecting
the abrasive particles to contact with a volatile metal compound at
an elevated temperature sufficient to maintain the metal compound
in vapor form and contact the vapor with a solid substrate under
metal deposition conditions.
The intermetallic bond between the metal matrix and the primary or
secondary abrasive increases the retention of the abrasive particle
until its cutting life is ended by wearing away of the particle or
breaking away of fragments thereof from the portion of the abrasive
particles which has become free of the encapsulation at the
abrading surface during the abrading action.
While the encapsulation of diamonds when used as the primary
abrasive will have the benefits described above, they may be used
unencapsulated in the structure of our invention when using
encapsulated secondary abrasive as described herein.
When employing unencapsulated diamonds or tungsten carbide as an
abrasive particle, cobalt-based, nickel-based, or iron-based alloys
are undesirable as metal-bonding agents since in their molten
condition they attack the diamonds. They may, however, be used if
the aforesaid abrasives are encapsulated in a metal sheath.
Since when using encapsulated diamonds or encapsulated tungsten
carbide or other secondary abrasive as above, the particle is
protected from attack by the metal, we may use any of the metals
referred to above as being suitable for infiltration to establish
the continuous phase forming the metal matrix of the structures of
our invention.
We prefer to use for encapsulation of the abrasive particles
tabulated in Table 1 above tungsten, tantalum, niobium (columbium)
and molybdenum, and, among the primary abrasive particles, we
prefer to employ diamonds, either the natural or synthetic forms;
and as secondary abrasive, we may use tungsten carbide but we
prefer to employ alumina, or silicon carbide with alumina most
preferred because of the inherent properties and relatively low
cost, or boron nitride and prefer to employ tungsten as the
encapsulating metal, deposited under conditions to produce pure
tungsten of the crystal form as described herein.
Where we employ the metal-encapsulated abrasive in the drill formed
by metal bonding the encapsulated abrasive in a metal continuous
phase matrix, we prefer to employ as a bonding agent a metal having
a significantly lower melting point than the metal sheath of the
abrasive substrate. When employing encapsulated or unencapsulated
diamonds as the primary abrasive particle, we prefer to limit the
melting point of the metal matrix to a temperature below about
2,800.degree. F., i.e. 1,538.degree. C., in order not to expose the
diamonds to excessive temperature which may impair the mechanical
strength of the diamonds.
Another useful property for the metal binder is a suitable
coefficient of thermal expansion of the metal matrix used as
bonding agent. Since, in general, the low melting metals and
materials have high thermal coefficients of expansion, in the
absence of an encapsulating metal which is wetted by the molten
metal, the mass of matrix on cooling would tend to pull away from
the abrasive material particularly, thus impairing the bond.
We prefer to employ for the encapsulation of the abrasive particles
the reduction of a vapor of the metal compound.
For such purpose, we prefer to select among the metals chosen
according to the aforesaid principles of our invention those which
form a compound which may be placed in the vapor state in contact
with the substrate under conditions to deposit the metal on the
substrate surface.
TABLE 2
B.P. .degree.C. at 760 m.m.* Molybdenum Pentachloride [MoCl.sub.5 ]
268 Molybdenum Hexafluoride [MoF.sub.6 ] 35 Molybdenum Carbonyl
[Mo(CO).sub.6 ] 156.4 Tungsten Pentabromide [WBr.sub.5 ] 333
Tungsten Hexabromide [WBr.sub.6 ] 17.5 Tungsten Pentachloride
[WCl.sub.5 ] 275.6 Tungsten Hexachloride [WCl.sub.6 ] 346.7
Tungsten Carbonyl [W(CO).sub.6 ] 175 at 766 m.m. Tantalum
Pentachloride [TaCl.sub.5 ] 242 Tantalum Pentafluoride [TaF.sub.5 ]
229.5 Titanium Tetraboride [TiB.sub.4 ] 230 Titanium Hexafluoride
[TiF.sub.6 ] 35.5 Titanium Tetrachloride [TiCl.sub.4 ] 136.4
Columbium Pentabromide [CbBr.sub.5 ] 361.6 Columbium Pentafluoride
[CbF.sub.5 ] 236 Columbium Pentachloride [CbCl.sub.5 ] 236 *Unless
otherwise indicated
We prefer to employ a compound which may be vaporized at a
convenient temperature either because of its relatively low boiling
point or by reduction of its partial pressure and be introduced
into the contact zone with the abrasive particle for conversion to
the metal state deposited on the substrate.
The procedure we prefer, because it produces the superior envelope
when applied to produce our novel encapsulated abrasive particle,
is the conversion of a volatile compound of the metal into the
metal deposited on the substrate and a gaseous or vaporous reaction
product which may be removed from contact with the encapsulated
metal. This leaves an envelope substantially free of included
impurities.
For this purpose, we prefer to use the halides or the carbonyls of
the metals. For convenience of operation, we prefer to employ those
compounds having a boiling point at atmospheric pressure below the
reaction temperature.
While compounds which may be placed in the liquid state and which
may be distilled by vacuum distillation or by reduction of their
partial pressure by means of a carrier gas are possible, the
compounds listed in Table 3, having reasonable boiling points, so
that their volatilization may be conveniently allowed, are
preferred by us.
In view of the above consideration, the metals whose compounds are
listed in Table 2 may be employed; however, we prefer to employ
tungsten as an encapsulating metal because of its particular
suitability in the drill of our invention. It gives under the
conditions of fabrication according to our invention a coating of
exceptionally high strength. It is readily wetted by the molten
metal matrixes described above and forms a strong metallurgical
bond with the metal matrixes employed in our invention. It is
particularly useful where the substrate is diamond or tungsten
carbide or other substrates which will react with the tungsten such
as those which form cermet with tungsten.
Our preferred primary abrasive is diamond, either unencapsulated or
encapsulated as described herein. Where encapsulated with a metal
under the preferred conditions as described herein, it will produce
a superior abrader structure of longer life. Where encapsulated
with tungsten or other suitable metals as described above, it will
after the exposed metal sheath in contact with the work has been
worn away be exposed to the work but will otherwise be gripped by
the encapsulating envelope which is in turn gripped by the metal
matrix.
In place of or in addition to the encapsulated diamond, we may use
the other abrasives as described above, preferring among them
encapsulated alumina but may also use the other secondary abrasives
as described above and as is more fully described below.
The invention will be further described by reference to the
following FIGS.
FIG. 1 is a diagrammatic flow sheet of our preferred process of
encapsulation.
FIG. 2 is a schematic vertical section through a mold for use in
the infiltrant technique of forming a bit according to our
invention.
FIG. 3 is a partial section of one form of drill bit of our
invention.
FIG. 4 is a fragmentary view partly in section of a modified
mold.
FIG. 5 is a view partly in section of a modified drill bit of our
invention .
FIG. 1 illustrates a flow sheet of our preferred process for
producing the novel encapsulated abrasive of our invention. The
particles to be coated are placed in the reactor 1, whose cap 2 has
been removed. The reactor has a perforated bottom to support the
particles of selected mesh size. With cap 2 replaced and the valves
3, 4, 5, and 13 closed, and with valve 7 open, the vacuum pump is
started to de-aerate the system. Valve 7 is closed and the system
filled with hydrogen from hydrogen storage 11, valve 5 being
open.
The reactor is heated by the furnace 9 to the reaction temperature,
for example, from about 1,000.degree. to about 1,200.degree. F.
while purging slowly with hydrogen. The hydrogen flow rate is
increased until a fluidized bed is established. Hydrogen prior to
introduction into the reactor passes through a conventional
palladium catalyst to remove any impurities, such as oxygen in the
hydrogen. Vaporized metallic compound is discharged from the
vaporizing chamber 10, which may if necessary be heated by furnace
14, together with an inert gas, for example, argon from argon
storage 6, into the reaction chamber.
Preferably we desire to employ the volatile metal halides referred
to above, although, in some cases, we may use the carbonyls listed
in Table 3. Where the halide is employed, the reaction forms
hydrogen halide, which is passed through the bubble traps and is
absorbed in the absorber. Where the volatile compound employed is a
fluoride, the produce formed is a hydrogen fluoride, and we may use
sodium fluoride for that absorption. We prefer to employ hydrogen
in stoichiometric excess.
The reaction deposits metal on the substrate and the effluent
material, being in the vapor state is discharged, leaving no
contaminants on or in the metal. The metal is formed in its pure
state.
The rate of metal deposition depends on the temperature, and flow
rate of the reactants, being the greater the higher the temperature
and the greater the flow rate of the hydrogen and volatile metals
compound.
After the deposit is formed, the valves 4 and 5 are closed and
argon is continued to pass into the reactor and the encapsulated
abrasive is allowed to cool to room temperature in the
non-oxidizing condition of the argon environment.
The conditions in the reactor, both because of the mesh size and
particle size distribution of the particles and because of the
velocity of the vapors and gases fluidizes the particles. As will
be recognized by those skilled in the art, a dense phase is
established in the lower part of the reactor in which the particles
are more or less uniformally distributed in violent agitation in
the dense phase. This results in a substantially uniform deposit
per unit of surface of the particles.
The reaction products and the carrier gases and excess hydrogen
enter the upper space termed the disengaging space where they are
separated from any entrained particles.
Where the diamond particle is smooth as for example in the case of
synthetic diamonds, we may improve the bond of the metal envelope
to the substrate diamond surface produced in the process described
above by first surface etching of the diamond. The etching of the
diamonds will also have an advantage where the metal envelope is
produced by other processes such as electrochemical or electrolytic
deposition methods. However, for the reasons previously described,
the product produced by the process of vapor deposition described
above is superior and is preferred by us.
To etch the diamonds, we immerse them in a molten bath of an alkali
metal nitrate or alkaline earth nitrate at a temperature below the
decomposition temperature, thus in using potassium nitrate,
temperature would range from 630.degree.+F. and under 750.degree.
F.; sodium nitrate, about 580.degree. F. and under about
700.degree. F.; barium nitrate, at or above 1,100.degree. F. and
below its decomposition temperature. We prefer to employ potassium
nitrate at about 630.degree. F. for about an hour. The bath is
contained in a nitrogen or other inert gas atmosphere.
At the completion of the heating process, the molten bath is cooled
and the cooled bath is then leached with water to dissolve the
salt, leaving the etched diamonds which may then be separated and
dried.
The degree of etching depends upon the immersion time and a
suitable time will be about an hour under which conditions the
particles will lose from about one-half to 1 percent of their
weight. The surface of the diamonds is roughened and pitted and
forms a desirable and improved substrate base.
For purposes of illustration, not as limitations of our invention,
the following examples are illustrative of the process of
depositing a metal sheath upon a substrate.
Diamonds, either synthetic or natural, preferably etched as above,
or the alumina, silicon carbide or other abrasive particle such as
tungsten carbide of mesh size suitable for fluidizing are
introduced into the reactor 1. The actual mesh size employed
depends upon the service to which the abrader is to be placed. For
use in oil well bits, we may use particles of size (Tyler mesh)
through a 16 and on a 400 mesh (-16 + 400). Preferably we employ 30
to 100 mesh material, for example, -30 + 60 mesh. In depositing
tungsten, we may and prefer to employ tungsten hexafluoride, which
is contained and vaporized in 10. It is volatile at atmospheric
temperatures and need not be heated. In the reactor employed after
the system has been deaerated and backfilled, hydrogen flow is
established at a low flow rate of about 100 ml/min; and as
described above, the temperatures in the reactor 1 having been
adjusted to 1,150.degree. F., as measured by the thermocouples, the
hydrogen flow is increased to about 1,250-1,350 ml/min, and the
flow of the tungsten fluoride vapor to about 150 ml/min and the
argon gas is adjusted to about 285 ml/min, all as measured by the
flow meters as indicated in FIG. 1, the hydrogen being in
stoichiometric excess over the tungsten hexafluoride.
The thickness of the coat of the tungsten on the particle depends
on the duration of the treatment and suitably for the 40 to 50 mesh
diamonds described above, the coat will be 1 mil thick in about 1
hour. Suitable thickness deposit will run from about 0.1 to about
1.5 mils thick.
In the above example, the substrate surface is completely coated,
indicating that the process of vacuum chemical vapor deposition has
great throwing power. The outer surface of the coated particles is
topographically congruent to the outer surface of the underlying
substrate and reproduces it. The interlocked structure produces a
coating of high tensile and bending strength.
Since the coating is produced at high temperature, on cooling the
contraction of some 1,100.degree. F. will be substantially in
excess of the contraction of the substrate as described and the
resultant eventual contraction will produce a compress of the
underlying abrasive particle.
The preferred embodiment of the surface set drill bit, as
illustrated in FIGS. 2-4, may be formed in a graphite mold section
18, which is formed with sockets pisitioned in the interior surface
of the mold. Diamond particles 19 are placed in the sockets
positioned on the interior surface of the crown end of the
mold.
With mold cap 24', section 18b and 18a removed and core 25 with
vent holes 26 in position, a layer 20 of particles of tungsten
carbide, such as described above, is placed in the mold 18 to cover
the protruding diamonds and vibrated in position to compact the
powder.
The threaded steel shank 15 is then placed over the mold above the
powder 20, spaced from the surface of the mold 18, and held in
position with a suitable fixture not shown.
Tungsten-coated alumina particles 17 are introduced into the
annulus spaced at the exterior and in the annulus at the interior
of the shank 15. The layer of the particles 17 in the exterior
annulus reached the level of the top of the mold section 18, but
the powder in the interior annulus may, if desired, reach a higher
level as shown.
The mold section 18a is then placed over the shank 15 and on the
mold section 18. A ring of tungsten-coated iron particles 21 is
placed in the exterior annulus over the particle section 17.
The mold section 18b is then set over the shank 15 and on the mold
section 18a; and infiltrant metal powder 22, for example, of 200
mesh size such as described above, is introduced into the annulus
on the exterior and the annulus at the interior of the shank 15
above the particles 21 and reaching into the space 23.
Where it is desired to employ iron, iron-based alloys, or other
metals which would under the conditions of the process
deleteriously attack the tungsten carbide or the diamonds, they may
be encapsulated. In such case, the iron powder in ring 21 need not
be encapsulated.
The ratio of the metal to the total void volume of the mold is
desirably such that when the infiltrant metal melts it may fill all
of the space between the secondary abrasive particles and cover the
exposed diamonds.
As previously described, in carrying out this procedure, we wish to
select a temperature of formation which will be below about
2,800.degree. F., in order not to expose the diamonds to an
excessive temperature. The binder metal will melt and percolate
through the interstices and fill all of the voids as described
above and will also wet the metallic shank. If a metallic coating
is placed upon the diamond as well as the secondary abrasive
particles, the binder metal will wet the surfaces of the
encapsulated particles, thus producing a tight bond to the
matrix.
The particle sizes of the abrasive particles are chosen to give
proper compaction and void area. A particle size through a 30 mesh
and on a 60 mesh (-30 + 60) is suitable.
The tungsten-coated iron powder 21 is used to provide a machinable
shoulder which acts as a barrier and cover to the exterior section
of the abrasive section 17. The tungsten envelope of the iron acts
to protect the iron metal from escaping because its melting point
will be below the temperature at which the mold is fired and could
if it reached the unencapsulated diamonds attack them. It also
provides for a machinable mass since the tungsten forms only a thin
coat as described above.
The section is beveled as shown at 24 in FIGS. 3 and 5. This will
assure that there is no exterior ledge which would otherwise be
formed by the tungsten-coated alumina section, or any other
secondary abrasive which is substantially unworkable to provide for
a bevel surface. In the absence of this beveled section, there
would be a danger that the drill bit could hang up on the bore wall
or be caught on a casing section in which the drill string is to
operate.
When the assembly has cooled, it is removed from the mold and the
section 21 is machined as shown in FIGS. 3 and 5, the interior box
threads can receive the connector 26 to assemble the drill.
The drill is thus composed of a tubular shank 15. Bonded to the
interior tubular surfaces and exterior tubular surface of the shank
15 and over its crown end is a coating of abrasive particles 17
bonded by a metal matrix in the form shown in FIG. 3. The crown of
said bit carried spaced diamonds embedded in said crown and
protruding externally therefrom.
The tungsten coating of the iron is also useful where tungsten
carbide or other carbides are employed with diamonds or where
diamonds are employed with other secondary abrasives.
The encapsulation of the iron with the tungsten will prevent the
iron from melting and percolating through the mass to attack the
diamond and the tungsten carbide if used.
It will be understood that the iron may be any form of the iron,
such as powdered cast iron, steel or other ferrous alloy.
The secondary abrasive used in the section 26 in the above
constructions may be a tungsten carbide instead of the alumina.
The particularly useful tungsten carbide when used in either layer
20 or 17 is one ranging from WC having 6.12 wt. % of carbon to
W.sub.2 C having a carbon content about 3.16 wt. %. A useful
material is so-called sintered tungsten carbide and consists of
microsized WC crystals and cobalt metal bonded by liquid phase
sintering at high temperature. The cobalt content varies from 3 wt.
% to over 25 wt.%. This material has a hardness of about 1,250 to
1,350 kg/mm.sup.2 (Knoop). Another form of eutectic alloy
containing about 4 percent by weight of carbon having a hardness in
the range of 1,900 to 2,000 kg/mm.sup.2 (Knoop) may also be
used.
The drill described above may also be produced by an impregnation
technique by mixing a primary abrasive, for example, diamonds with
a secondary abrasive described above, for example, tungsten
carbide, or metal-coated tungsten carbide, or metal-coated alumina,
silicon carbide or boron nitride, such as described above. We
prefer to employ the tungsten-coated alumina for the reasons
stated.
In this case, the mold section 18a does not contain pockets for
insertion of diamonds but is smooth. In all other respects, the
mold is the same as the mold shown in FIG. 2. With the shank 15 and
core 25 in position in section 18, a mixture of the metal-coated
secondary abrasive and the primary abrasive, for example, diamonds
is introduced in the same manner as is the case of 17 in FIG. 2.
This forms a layer 26 extending part way up the exterior annulus of
15 and to a higher level in the annulus in the interior side of
15.
The section 18a is then placed in position and the layer 21
introduced. The section 18b is then placed in position and the
infiltrant metal 22 is introduced into the space 23 and the cap 24'
placed in position. The same procedure is then followed as
described in connection with FIG. 2.
The mesh size of the infiltrant metal is suitably through a 200
mesh; and in both forms, the metal may be of the kind previously
described as suitable for infiltrant purposes.
The mesh size of the secondary abrasive particles employed in the
form shown in FIGS. 2 and 3 as well as in FIGS. 4 and 5 may be the
same, and the size diamond particles employed in the mixture with
the secondary abrasive used in forming the layer 26 may be equal to
that of the secondary abrasive particles. The quantity of the
diamond particles may be that of the secondary abrasive particles.
The diamond particles and the secondary abrasive are intimately
mixed to produce a uniform distribution.
Instead of natural diamonds, we may use artificial diamonds,
whether or not etched. Additionally, we may encapsulate the
diamonds as well as the secondary abrasive in the manner described
above.
Instead of employing a mixture of diamonds and secondary abrasive
to form the entire layer shown at 26, we may proceed as in the case
of the form described in connection with 2 and 5 employ an initial
crown layer formed of the mixture of diamonds and secondary
abrasive particle described for forming the layer 26 in a manner
similar to that described for forming the crown layer 20 in FIG. 2.
We may then introduce on top of the crown layer the material 17 and
the layer of tungsten-coated iron as described in connection with
FIG. 2 and complete the operation as described for the formation of
the drill in connection with FIGS. 2 and 3.
The drill shown in FIG. 3 and also 5 is composed of a threaded
shank 15 having a bore 30 to act as the conduit for mud or other
drilling fluid. The shank carries the abrasive coating 17 or 26'
welded to the shank by the bonding metal which wets the shank at
the high temperatures of the process. The abrasive coating extends
part way along the exterior and interior surface of the shank and
over the lower end of the shank away from the threaded free end
26', to form the hollow crown end 29 of the drill. In the form
shown in FIG. 3, embedded in the abrasive coating at the crown end
of the drill are a plurality of closely spaced diamonds 19 embedded
in and protruding from the crown end. This is termed a surface set
diamond drill.
Where the impregnated type of drill shown in FIG. 5 is formed, the
diamonds are not positioned in the crown end but are distributed
uniformally throughout the abrasive body carried by the shank, or
in a layer adjacent the crown end and the remainder of the abrasive
body bonded to the shank.
* * * * *