Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to diamond dxill coring
bits.
Diamond coring bits are commonly used for explor~
ation core drilling and generally fall into one o~ two
categories. In the first category, consisting of surface
set diamond bits, whole diamonds are set into a drilling
face of the bit~ So long as the diamonds are sharp, such
bits are capable of operating at a very high drill penetra-
tion rates and are extremely effective. Unfortunately, the
diamonds are relatively large and are thereEore costly.
In addition, the diamonds become dull or polished during
use so that the effectiveness of -the drill bit deteriorates
fairly rapidly during use. When the diamonds become dull,
the bit must be removed and replaced. Considerable time is
lost in this procedure, and in addition, while the diamonds
from the removed bi-t may be recovered and reset, the cost
involved in maintaining an inventory of surface set bits,
and of diamonds of various grades and sizes, is substantial.
In the second category of diamond drill bits,
numerous small diamonds are se-t in a matrix body. Commonly
the diamonds are uniformly dispersed throughout the body
of the matrix, but the diamonds can also be concentrated
in radially spaced rings, -to create a ringing pattern,
i.e. to create ribs in the material being drilled. Examp]es -
of such bits are shown in U~S. Patents Nos~ 3,106,973 and
3,127,715~ The impregnated diamond bits have the advantage
that they are consumable in use, so the bit can be used to
drill through ~ considerable footage without being removed
from the drill string. Unfortunately, the tracking ancl
flushing characteristics of such bits and their penetratlon
rates have not been as good as -those of a new surface set
bit. Therefore, surface set bits continue to be widely
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used, despite their greater cost and considerable
inconvenience.
The present invention provides an impregnated
diamond drill core bit which, in tests which have been
conducted, have been found capable of drilling at high
penetration rates, with good tracking and flushing,
through substan-tial footages before replacement is needed.
To this end the invention provides a diamond drill core
bit comprising:
(a) an annular bit body having an end,
(b) an annular crown integrally secured to said
end and having a cutting face and inner and outer
concentric side surfaces, said crown comprising:
(1) a plurality of composite segments each
extending generally radially between said
inner and outer side surfaces, said composite
segments being spaced circumferentially :Erom
each other and being elongated depthwise of ~ :
the crown and extend.ing to said cutting face
to wear with said cutting face in use,
(2) a circumferential spacer material integrally
adhered to said composite segments and extending
. circumferentially between said composite segments
to space the ~atter circumferentially apart, said .~:
circumferential spacer material also extending
- generally radially between said inner and outer
surfaces and being elongated depthwise of the
crown and extending to said cutting face to wear
wit~ said cutting face in use,
(c) each composite segment comprising a plurality
of diamond impregnated segments separated radially
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from each other by a radial spacer material, a
diamond impregnated segment being located at each
of said inner and outer side surfaces, said diamond
impregnated se~ments and said radial spacer material
therebetween all extending to said cutting face,
(d) said diamond impregnated segments having greater
abrasion resistance than that of said radial spacer
material such that said radial spacer material will
wear at a controlled rate which is greater than that
of said diamond impregnated segments but not so great
as to prematurely expose said diamond impregnated
segments,
te) said radial spacer material having greater abrasion
resistance than that of said circumferential spacer
material such that said circumferential spacer material
will wear at a controlled rate which is greater -than
that of said radial spacer material but not 50
great as to prematurely expose said composite segments,
(f) said circumferential spacer material having
substantial thermal conductivity and ductility.
Further objects and advantages of the invention
will appear from the following description, taken together
with the accompanying drawings, in which:
Fig. 1 is a perspective view, partly broken awayt
showing a bit according to the invention;
Fig. 2 is a top view of the bit of Fig. l;
Fig. 3 is a perspective view of a composite
segment which forms part of the drill bit o-f Fig. l;
FigO 4 is a diagrammatic perspective view
illustrating the manuEacture of the composite segment of
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Fig. 5 is a perspective view, partly broken
away, showing a mold used to produce the drill bit of
Fig. l;
Fig. 6 iS a per~pective view illustrating a
drill bit blank used in an alternative embocliment of the
invention;
Fig. 7 i5 a cross-sectional view taken along
lines 7-7 of Fig. 6 and showing a composite segment in
position in the blank of Fig. 7 and ready to be brazed
in position; and
Fig. 8 is a side view of a modified segment
for use in the invention.
Referenee is first made to Fig. 1, which shows
a drill bit 2 aceording to the invention. The bit 2
eomprises a shank 4 and a erown 6. The shank 4 is normally
formed of steel and is eommonly threaded as indieated at
8, for attachment to a drill string. The erown 6 has a
cutting face 10, inner ancl outer coneentrie side surfaces
12, 14 respectively, and a bottom 16 which is integrally
secured to the shank 4, e.g. by brazing or by integral
molding as will be described.
The crown 6 includes a number of eircumfer
entially spaces composite segments 18. Eaeh eomposite
segment is formed, as also shown in Fig. 2, from a number
of spaeed parallel diamoncl impregnated segments 20 separated
by a radial spacer material 22. The eomposite segments 18
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extend generally radially between the inner and outer
surfaces 12, 14 and also extend over a portion oE the depth
of the crown, from the cutting face 10 part way to the
bottom 16. A diamona impregnated segment 20 is locatecl
at each end of eaeh eomposite segment, as shown, to help
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maintain the gauge of the hold to be drilled by the bit.
Additional diamond impregnated seyments 21 are located
at the inner and ou-ter surfaces 12, 14, below eaeh composite
segment, to further help to maintain the gauge of the holeO
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The composite se~ments 18 are separated
circumferentially on the crown by a circumferential
spacer material 24 which extends the full depth and
thickness of the crown, except for conventional radial
waterways 26 which are cut to permit passage of drilling
fluid and drilling debris. The spacer material 24 is
integrally bonded to the composite segments 20, as will
be described, to hold and protect the composite segments
as will be explained. The spacer material 24 also separates
the gauge holding segments 21 both circumferentially and
radially and is integrally bonded thereto.
It is an essential feature of the invention that
the abrasion resistance of the diamond impregnated segments
20 is greater than that of the radial spacer material 22,
and that the abrasion resistance of the radial spacer
material 22 is in turn greater than that of the circumferen-
tial spacer material 240 Specifically, the abrasion resist-
ance of the radial spacer material 22 must be less than that
of the diamond impregnated segments 20, so that the radial
spacer material 22 will wear more rapidly than segments
20 and thus will cause circular ribs or rings to be formed
in the material being drilled. This effect, which is
known, assists tracking of the bit (since the ribs act
as a guide for the bit) and also improves the penetration
rate, since the ribs in the formation being drilled tend to
break off and are flushed away by the drilling fluid, without
the need for consuming diamons to abrade the rihs. However,
the abrasion resistance of the radial spacer material 22
must not be too much less than that of the diamond impregnated
segments 20J since otherwise -the diamond impregnated segments
20 will be prematurely exposed to an undue extent and will
tend to break off, shortening the life of the bit.
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The radial spacer material 22 must be of
greater abrasion resistance than that of the circumferential
spacer material 24, so that the material 2~ will in turn
wear away more rapidly than material 22~ This ensures
that the radially oriented edges of the composi-te segments
18 are adequately exposed for cutting and ensures that
the material 24 will not interfere with the cutting action.
The more rapid wear of material 2~ can also provide very
small area additional waterways between the composite
segments 18 to improve the flushing away of drilling debris,
- further reducing wear on the bit. Again, however, the
circumferential spacer material 24 must not wear too
much more rapidly than the radial spacer material 22, to i~
a~oid premature exposure of the composite segments 18.
If the composite segments 1~ are prematurely exposed, the
radial spacer material 22 will wear away too rapidly and
the diamond impregnated segments 20 will tend to break or
chip away, shortening the life of the bit. The material
24 ideally acts to buttress the composite segments 18, absorb shock
protect them against breakage, and conduct heat away from
them, particularly in the region of the cutting face 1OD
In the preferred embodiment of the invention,
the composite segments 18 are manufactured as a unit, as
indicated in Fig. 3. As diagrammatically indicated,
alternating layers of diamond impregnated material 20 and
radial spacer material 22 are placed in a mold 30. Each
layer as it is placed in position may be compressed by
rams indicated at 32, the rams then being withdrawn and
the next layer added. After -the required number of layers
has been placed in position, the resulting structure is
then hot-pressed or sintered at an appropriate temperature
~typically 1800 to 2000 F) to form a composite segment 20.
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Heating of the material can be by a torch or furnace, or, normally,
by electric induction heating. Normally a carbon plug
will be placed on the top of the mold 30 during sintering
to reduce the surface porosity of the upper face of the
composite segment 20. Typically a very large composite
segment is produced and is then cut into lengths to
produce the required composi-te segments 20. The dimensions
of the segments 20 and of the radial spacing be-tween them
may be varied depending on the nature of the ground being
drilled; in one embodiment, however, the radial thickness
of the segmen~s 20 was about .062 inches, the circumferential
dimension of the segments 20 was about .125 inches, and the
radial spacing between them was about .005 inches.
As indicated, the materials from which the
various portions of the crown are formed are impor-tant.
Firstly, the matrix in which the diamonds are embedded to
form the diamond irnpregnated segments 20 must satisfy
several requirements. The matrix must have sufficient
hardness so that the diamonds exposed at the cutting face
10 are not pushed into the matrix material under the very
high pressures used in drilling. In addition, the matrix
must have sufficient abrasion resistance so that the diamond
particles are not prematurely released. In addition, the
sintering or hot-pressing temperature for the matrix
material for segments 20 must be sufficiently low (below
about 2500~ F) that the diamonds are not graphiti~ed during
sintering or hot-pressing.
To satisfy these requirements~ the following
materials may be used for the matrix in which the diamonds
are embedded: tungsten carbide, tungsten alloys such as
tungsten/cobalt alloys, tungsten carbide or tunysten/cobalt
alloys in combination with elemental tungsten (all with an
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appropriate binder phase to facilitate bonding of particles
and diamonds), and the matrices produced by Wall Colmonoy
Corporation o~ Detroit, Michigan under its numbers 11 and
50. The number 50 material produced by Wall Colmonoy
Corporation is an iron-bronze mixture containing ~0% - 60~
iron-bronze, and the remainder a self-fluxing alloy consis-t-
ing essentially of 70% - 80% nickel and the remainder
chromium, boron, silicon and iron. The material produced
by Wall Colmonoy Corporation under its number 11 is fully
described in Canadian Patent No. 781,677 issued ~pril 2,
1968 to that company, and the disclosure of that patent
- is hereby incorporated by reference. One form o~ this
matrix contains about 26% copper, 22% tungsten, 21.7% iron, ~ :
18% nickel, 4.4% chromium, 2.5% tin, 1.7% carbon, 1~ boron,
and 1.2% silicon. In general, the hardness on the Rockwall
scale of the matrix in which the diamonds are embedded to
form the segments 20 will be at least 100B, and probably at
least lloB.The diamonds contained in the diamond impregnated
segments 20 are present in a concentration of at least 75, . .
and typically in a concentration of 100 or more. (A ..
concentration of l00 is equi~alent to 72 carats per cubic
inch).
The radial spacer material 22 must, as indicated,
wear at a greater rate than the diamond impregnated segments
20, but not at a rate so great as to prematurely expose
the diamond impregnated segments 20. In addition, since
the radial spacer material 22 is preferably hot-pressed
or sintered in the same operation as segments 20, the
. same hot-pressing and sintering temperature limits are
applicable. The radial spacer material 22 will the:refore
normally be the same material as the matrix used in the
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segments 20, but of course without the diamonds.
Alternatively, material ~4 may be a copper based material
having a dispersion o secondary abrasi~es, such as tungsten
carbide, to improve its abrasion resistance. In very
special applications, where the ground being drillecl has
very low abrasion, steel shims may if desired be used.
The circumferential spacer material 24 must as
indicated have less abrasion resis-tance than the radial
spacer material 22, so that it will wear faster, but not
so fast as to expose the composite segments 18 prematurely.
The circumferential spacer material 24 must also have
substantial thermal conductivity, so that it will act as
a heat sink for the composite segments 18 (during drilling,
the operating temperature of the crown can exceed 500 F).
In addition, the circumferential spacer material 24 should
have a hot-pressing or sintering temperature low enough
so that the diamonds in the composite segments are not
degraded during the second heating required when the crown
itself is fabricated. However, the hot-pressing or sinter-
ing temperature of material 24 should be high enough so
that the material 24 is not weakened at the operating
temperatures of about 500 F. In addition, the circumferent-
ial spacer material 24 should ha~e sufficient ductility to
absorb shocks and impacts during drilling.
It i5 found that copper based materials are
highly suitable for use as the circumferential spacer
material 2~. For example, simple bronze may be used
(85% copper, 15% tin). Nickel or aluminum based materials
may also be used, so long as the hot-pressing or sintering
temperature required is less than the melting temperature
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of any phase of materials 20 and 22 to a maximum of
2200 F to prevent deterioration o the diamonds.
Another suitable material for circum~erential spacer
material 24 is the material sold by Wall Colmonoy
Corporation under its material number 7, but with some
of the a~rasive particles removed. This material
normally consists of 50% - 60% bron~e, and the balance
iron, except for 1% - 5% chromium boride, which acts
as an abrasive. For use as the circumferential spacer
material 24, the proportion of chromium boride is held
at a maximum of abo~t 1%. Other secondary abrasives
may be used in material 24, so long as the abrasion
resistance is less than that of ma-terial 22, so that
wear of material 24 is more rapid during drilling. This
ensures that the material 24 does not interfere wi-th the
cutting action of the composite segments 18. The more
rapid wear of material 24 under some conditions also
helps provide a very small clearance between the segments
18 for passage of drilling fluid and drilling debris.
~0 In the fabrication of the complete crown, a
conventional mold 40 may be used, as shown in Fig. 5.
The mold cavity 42 is coated with a conventional release
agent, then as shown, the composite segments 18 are placed
on the mold cavlty ~2 with the desired circumferential
spacing between them. The gauge holding segments 21 (not
shown in Fig. 5) are next put in place. The circumferential
spacer material 24 in powder form is next poured into the
mold cavlty 18 to fill the spaces between the segments 18
and to cover the segments 18 to the desired depth. The top
o~ the shank 4 is then inserted into the mold cavity with
appropriate sealer blocks ~not shown) to seal the spaces
between the top o~ the shank 4 and the edges o~ the mold
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cavity, and the whole is then sintered. When material
24 is largely bronze, the sintering may be carried out
at a temperature of between 1500 F and 1700 F, which
is well below the temperature at which significant
damage to the diamonds will occur. Normally the
circumferential spacer material will have a sin-tering
or hot-pressing temperature of at least 1000 F.
An alternative embodimen-t of the invention
is illustrated in Figs. 6 and 7. In this embodiment,
the same composite segments 18 are used, but the shank
and crown of the bit are now fabricated as a single
unitary steel member 50. Slots 52 are cut in -the cut-ting
face 54 of the member 50, as shown in the blank illustrated
in Fig. 6. The composite segments 18 are then brazed in
position, as shown in Fig. 7, for example, by placing a
thin sheet of copper 56 over the exterior of the segment
18 to act as a brazing material. In this case, the
relatively high melting point of the steel member sa is
not a matter of concern, since although the composite
segments are integrally secured to the member 50, no
bulk melting of the member 50 is required. Ordinary
mild steel may be used for -the member 50.
The composite segments 1~ may be oriented
exactly radially, as shown, or -they may be disposed
slightly ~orwardly or rearedly of a radial plane.
All such orientations may be considered as being
generally radial.
The gauge holdin~ segments 21, which help preserve
the gauge of the hole being drilled until the segments 18 are
entirely consumed, are usually heavily impregnated with dia-
monds at their oute~ surfaces only. However, some of the
segments 21, at intermittent spacings circumferentially
around the crown, are fully impregnated with diamonds to
ensure that segments 18 can be ~ully consumed. The matrix
material used on segments 21 is the same as that used in
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segments 20. In the Fig. 6 version of the invention,the gauge holding segments 21 and composite seyments
20 may be formed integrally, with radial spacer material
22 located between the gauge holding segments 21,
as shown in Fig. 8.
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