Note: Descriptions are shown in the official language in which they were submitted.
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MATRIX DL~MOND DRAG BIT WITH
PCD CYLINDRICAL CUTTERS
5 Back~round
This invention relates to diamond drag bits for drilling earthen formations having
polycrystalline diamond inserts imbedded in the cutting face of the bit.
More particularly, this invention relates to matrix type diamond drag bits fabricated
by a powder metallurgy process wherein cutter pockets and relief pockets are formed in a
10 femaie mold to accept and support cylindrically shaped polycrystalline diamond inserts
subsequently brazed in place in the pre-formed pockets.
U.S. Patent No. 5,056,382 entitled MATRIX DIAMOND DRAG BIT WITH PCD
CYLINDRICAL CUTTERS provides a milled relief pocket adjacent the cutter .pocket that
is vectored at a different angle than the angle of the cutters oriented in the face of the matrix
15 bit. The relief pocket provides maximum compression support for the base of the PCD
cylindrical cutter and increased cylindrical wall support while relieving the cutter back rake
surface.
While the foregoing patent is an important advance in the state of the art it was
determined in some drilling circumstances that the wide raised support platform surrounding
20 the diamond cylindrical cutter limited insert penetration, i.e. the insert support platform
inhibited penetration of the cutter in the rock formation.
It is desirable to provide back and side support for cylindrical type diamond inserts
embedded in a matrix type drag bit yet allow the full depth of penetration of each insert as
it works in the borehole. Preferably, there is back rake clearance for each cylindrically
25 shaped PCD insert brazed in the cutting face of the matrix drag bit.
SummarY of the Invention
There is, therefor, provided a process of forming a matrix type diamond drag bitcutter head having a multiplicity of cylindrically shaped polycrystalline diamond inserts
3 0 strategica!ly positioned and metallurgically secured to a drag bit face. A female mold of heat
resistant material, such as graphite is milled with a rotary ball mill forming a multiplicity of
first~cylindrically,shaped inse~t, chlaMels, o~ pockets the diameter of which is labout the same
diameter as each of the cylindrical cutters. The pockets are formed in a direction of rotation
of the drag bit and at an angle to an earthen formation to be drilled such that a negative rake
3 5 angle is established with respect to a cutting face of the cylindrically shaped polycrystalline
diamond inserts.
A second chaMel is milled in the mold substantially aligned and superimposed over
the first chaMel, at the same or a lesser angle than the first channel. The second ball end
mill used for this chaMel is somewhat larger in diameter than the mill used to form the insert
40 pocket and is positioned substantially above the axis of the first ball end mill such that it
forms a shallow and narrow arcuate groove around the insert chaMel. The depth of the
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second cylindrically shaped channel or pocket is much less than the depth of the first
cylindrically shaped channel. This provides a small arcuate fillet of matrix material around
each of the subsequently secured inserts for ensuring the integrity of each insert without
forming a penetration limiting platform around each insert as is taught in the prior art. ~ -
The process of forming a matrix drag bit body is as follows: A heat resistant ; . ;
cylindrically shaped stud is placed into each of the first cylindrically shaped insert pockets.
The female mold is then filled with a matrix material in powder form. The mold and matrix
material is then heated in a furnace for infiltrating a binder into the matrix material, thereby
forming the diamond insert retaining cutter head.
o The heat resistant studs are removed from the first cylindrically shaped insert pockets.
The cylindrically shaped polycrystalline diamond inserts are then metallurgically bonded into
each of the first insert pockets. The inserts have additional back and side support provided :
by the matrix filled second channel surrounding each insert.
An advantage then of the present invention over the prior art is the ability to provide ~ ~
side and back support for a cylindrical PCD diasnond insert while assuring maximum r~ ~ ;
penetration of each insert as it works in a borehole. Each insert is adequately supported by
the fillet surrounding the insert to withstand compressive and shear forces under downhole
drilling conditions. Moreover, the angled double pocket mold design provides each insert ; ~. i`-
with back rake clearance as well as superior support, thereby minimizing heat bui~d up and ; - ~
2 o assuring insert integrity as the diamond matrix drag bit works in a borehole. ~ - -
Brief Description of the Drawings
FIGURE 1 is a perspective view of a matrix type diamond drag bit; ;~FIGURE 2 is a semi-schematic partial cross section of a female mold illustrating a ; ;~
milling cutter pass forming a first pocket for a cylindrically shaped diamond insert in the ~'
female mold; -i'~ i
PIGURE 3 is a semi-schematic partial cross section of a female mo1d illustrating a
second milling cutter pass at a different angle than the first milling cutter pass forming a
second pocket surrounding the first insert pocket in the female mold; , ; ~
3 0 FIGURE 4 is a semi-schematic partial cross section of a female mold with a heat i; ~ ` `
resistant insert blank positioned in the first insert pocket; i ' .
FIGUR~ 5 taken through 5-5 of Figure 4 illustrates the face of the insert blank and "!',.'~'1,, fi "~ ,",'
the surrounding second pockët;
FIGURE 6, a prior art illustration, is a partially broken away perspective view of a i~
3 5 polycrystalline diamond insert brazed into a first insert pocket, the raised surrounding matrix
material filling in a second, superimposed pocket to back up and strengthen an insert secured ,;
within the drag bit cutter head; and
FIGURE 7, an illustration of the present invention, is a partially broken away ~- .
perspective view of one of the polycrystalline diamond inserts brazed into the first insert
4 0 pocket, the raised surrounding matrix material filling in the second, superimposed pocket to ~ ~ i
back up and strengthen the multiple inserts secured within the drag bit cutter head.
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Description
FIGURE 1 is a perspective view of a matrix type diamond drag bit generally
designated as 10. Drag bit consists of a drag bit body 12 having oppositely opposed tool
grooves 13 formed therein to facilitate removal of the bit from a drill string (not shown).
5 At the upper end of body 12 is a threaded pin end 14. At the opposite end is the cutter head
generally designated as 18. The cutter head is comprised of a matrix type body or head 15
that is cast in a female mold 40 (see Figs. 2, 3, 4 and 5). The mold generally is fabricated
from, for example, a graphite material that is easily machinable and withstands extremely
high heat during the casting process.
A multiplicity of cylindrical type diamond inserts generally designated as 26 are
contained within ribs 16 which project substantially longitudinally along the head 15. Each
insert, for example, has a body 28 fabricated from, for example, tungsten carbide, a base end
29 and a cutting end 27. The cutting end 27 comprises, for example, a polycrystalline
diamond layer sintered to the tungsten carbide body. Each of the cavities surroun~ing the
inserts is formed in the female mold 40 and is an important aspect of the present invention.
One or more nozzles 11 are formed by the matrix head 15. Drilling "mud" or fluidis directed down through the pin end and out through the nozzles during operation of the bit
in a borehole. An inner cavity (not shown) is formed within the bit body 12 and is open to
both the pin end 14 and the nozzles 11.
2 o Each of the protruding ribs extending from the matrix head has a gage bearing surface
~ 20 that, for example, may be embedded with natural diamonds to help maintain the gage or
-~ diameter of the borehole as the bit is rotated in an earthen formation. ,~
Turning now to FIGURE 2 the partially cutaway illustration shows the female mold40 with a groove or pocket 42 milled within the bottom 41 of the female mold 40. A ball .
mill 43 substantially the same diameter as the insert 26, is passed into the graphite mold ; ~.
bottom at an angle 44, thereby forming the insert pocket 42. The angle may be between lS
degrees and 25 degrees. The preferred angle is 20 degrees. The angle determines the degree
of negative rake angle of the cutting face of each of the inserts with respect to a borehole
bottom. The ball mill cutter 43 passes down a 1ine at the angle 44 to the face of the mold ` ~ .
3 0 a distance sufficient to form a pocket support for an insert stud body blar,k 49 (Fig. 4).
Referring now to FIGUR~ 3, the graphite mold bottom 40 is subsequently subjectedto a second ball mill pass. The ball mill 47 is superimposed over the cavity 42 formed by the
first pass of the smaller ball mill 43. The ball mi11 47 is, for exan~ple, somewhat larger in
diameter and is directed along a different or shallower angle 48 than the angle 44 of the ~ ~ i
3 5 insert pocket cavity formed by first ball mill 43. The second ball mill may be from 25 % to
60% greater in diameter than first ball mill with the preferred size being 50% greater.
The prior art shows the second ball end mill to be about 180% greater than the first
- mill which produces a very wide cutter penetration limiting shoulder (154 in Fig. 6)
surrounding each insert 126 (Fig. 6). This formation interference drastically reduces drilling
,~ 4 0 rates in some formations. The angle 48 may be between 3 degrees and 12 degrees. The
preferred angle is S degrees. The non-parallel angulation between the insert pocket 42 and
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the surrounding pocket 46 assures adequate insert backup support while providing insert back
rake clearance 51 (see Fig. 4). The second end mill 47 is passed over the insert pocket
forming a second narrow shallower groove 46 around the cavity 42.
The second end mill pass of the second ball mill forming the insert securing fillet 56
5 is only slightly larger than the first end mill pass of the first ball end mill forming the insert
pocket to minimize the size of the fillet 56 subsequently formed, thus assuring that the fil1et
will not interfere with the depth of penetration of each of the PCD cutters as the drag bit
works in the borehole.
Again, the angles 44 and 48 differ to provide both clearance for the right angle cutting ., ~ :
l o face of the insert and adequate support for the base and sidewalls of body of the insert.
FIGURE 4 shows the completed cavities (insert pocket 42 and the insert support
pocket 46). A heat resisting substitute insert blank 49 is then secured within the i;
complementary insert pocket 42. The blank is preferably glued within the pocket. - :
There are a multiplicity of insert pockets and their attendant insert support cavities in ~ i i
15the matrix ribs protruding from the matrix body. -
The heat resisting blank is glued into position in its insert pocket prior to pouring of
the matrix powder material into the female mold, thus filling all of the voids surrounding the . - : :
stud blank prior to firing of the powdered matrix material within a furnace for a ;; .;
predetermined length of time. i
20The preferred matrix material is a powder metal such as crushed tungsten carbide i~
which may be either W2C or WC. The female mold 40 is typically formed of graphite but
may be fabricated from other suitable refractory material. The mold is vibrated to compact . ~ ;~
the tungsten carbide material around each of the insert blanks and to fill all the voids with ~ ~ i
the powdered material.
25A braze material comprised of a combination selected from the group consisting of ~ ~
copper, nickel, manganese and zinc or tin is melted and subsequently is infiltrated through .
the tungsten carbide mass to form the matrix drag bit cutter head 14. This process is well ~ i:
known in the prior art.
~IGURE S is a view looking directly into the face of the substitute insert or blank 49
30showing the sidewall cavities 46 surrounding the insert. The depth of the cavity 46
determines the amount of side support for each of the inserts. This drawing also illustrates
the narrow groove 46 around the insert thjat will subsequently be filled with matrix material
to provide side support for the insert, but will not act as a penetration limiter to inhibit i ;
drilling rates. ~ `
3 5~IGURE 6, a prior art illustration, shows one of the polycrystalline diamond inserts
126 brazed into pocket 142 formed into the completed cutter head 115 a~ter the matrix
material 122 is fired. Shown is the massive matrix shoulder 154 that is formed around the ~ ~ ~
diamond cutter insert which provides more than adequate shear and compressive strength for ~ :
the cutter, but acts as a cutter penetration inhibitor, thus drastically slowing the drilling rate ; ;~
4 0when drilling many types of rock formations. ~ "~
Finally, with respect to FIGU~ 7, a view is shown of one of the polycrystalline '- ;s
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213~1 5q
inserts brazed into the pocket in the completed cutter head after the matrix material is fired.
After the firing of the mold in a furnace following the processes just described, the
tungsten carbide cutter head is removed from the female mold. Each of the dummy inserts
49 is then removed from its cavity leaving a insert shaped cavity for insertion of a
5 cylindrically shaped polycrystalline diamond cutter into the pocket formed by the dummy
insèrt 49. The PCD inserts are then brazed into position at joint 32, thus firmly securing the ~.-
body of each of the inserts in the pockets 42 and 46 formed in the female mold through the
use of the aforementioned process of two non-parallel mill passes. The braze material used
to braze the insert bodies into the respective cavities is essentially a combination of copper,
10 silver, zinc and cadmium. The temperature of the brazing process, of course, is such that
it will not destroy the polycrystalline diamond faces of the diamond insert blanks during the
brazing process.
The result is a raised fillet S6 in the cutter head 14 that comes up the sidewall of the
tungsten carbide body and almost completely surrounds the end of the tungsten carbide body
15 of the diamond insert. The raised fillet 56 thus provides very strong resistance to
compressive forces while firmly securing the sides of the insert body during operation of the
drag bit in a borehole. As can be seen, each of the multiplicity of inserts is angled with - ~ ;`
respect to a borehole bottom such that a negative rake angle is established. This negative
rake angle of course is established by the first mill pass of ball mill 43 in the female mold. ,
~t will be apparent that any angle may be used, whether it be a negative rake angle,
zero rake angle or positive rake angle without departing from the scope of this invention.
Pluid passage grooves 17 are formed between the ribs 15 and cutter head 14 to permit
passage of detritus up tbrough the grooves in the bit to the platform of the drill rig.
Typically, after the tungsten carbide cutter head 14 is formed in the female mold, it ;~
25 then is welded to a steel body 12 completing the assembly of the rock bit 10 as shown in
PIGUR~ 1. The body is easily welded to the head after each of the tungsten carbide ~
polycrystalline faced diamond inserts are brazed into their respective insert cavities thus ~ -,
completing the construction of the matrix type drag bit.
It will of course be realized that various modifications can be made in the design and ;
3 0 operation of the present invention without departing from the spirit thereof. Thus, while the
principal preferred construction and mode of operation of the invention have been explained ;
in what is now considered to represent its best embodiments, it should be understood that
within the scope of the appended claims the invention may be practiced otherwise than as
specifically illustrated and described. i
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