Note: Descriptions are shown in the official language in which they were submitted.
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REVOLVING CUTT~RS FOR ROCK BITS
BACKGROUND OF T~E INVENTION
1 Field of the Invention
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This invention relates to drag type rotary drill bits.
More particularly, it relates to drag tvpe rotary drill
bits having cutters mounted to a cutting end of the drill
bit, each of the cutters being rota~ably secured to fix-
tures extending from the cutting end of the rotary drillbit.-
2. Description of the Prior Art
There are a number of issued patents that relate to
drag type rock bits as well as rock bits that are combina-
tion drag bits and rotary cone bits.
All the prior art drill bits have failed to provide
a relatively inexpensive drag bit with long lasting cutters
that is not susceptible to early failure as the result of
overheating or that prevent the balling of the cutters and
the consequent reduction in the penetration rate.
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SUMMARY OF T~IE I~VENTION
It is an object of this invention to provide a practi-
cal and inexpensive means to prolong the life of synthetic
diamond and other hard cutting faces by limiting the
cutting time of each segment against a borehole bottom.
Another object of this invention is to provide a means
to prevent "balling" of the bit (buildup of debris adjacent
the cutting face of the cutting segment).
These and other objects of the invention are accom-
plished by ske~ing the face of a rotatable cutting discinsert at an offset angle to the radii from the axis of
rotation of the rotary drill head. The cutting elements
are rotatably mounted to a saddle, or insert base. Rota-
tion of the bit will cause the cutting elements to slowly
precess as they contact the borehole formation. This
limits the exposure of the cutting discs, limiting the heat
buildup that is particularl~ damaging.
To improve heat dissipation when using diamond cutting
elements, a plurality of diamond inserts or natural diamond
particles are embedded in the cutting face of a disc, the
disc being rotatably secured within a saddle or support
structure. As the bit body is rotated by the rotary table,
downhole motor or any other prime mover connected to a
drill string and drill bit, the cutter discs are caused to
rotate due to the skewed angle of the saddle with respect
to the radii from the axis of rotation of the drill string.
Each of the multiplicity of cutter segments, eauidistantly
or randomly spaced as required around a disc, are exposed
as the cutter disc slowly rotates.
Since fluid nozzles are fixed in the bit body,
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fluid is directed toward the borehole bottom and, as thc
cutters rotate, the fluid washes and cools the synthetic or
natural diamond segments or particles adjacent the bottom
of borehole.
In order to provide a rotating cutter element sturdy
enough to withstand downhole conditions yet be capable of
slowly precessing the cutter, a cutting disc is rotated on
a journal that is supported by a pair of journal blocks.
Such a structure provides for a larger diameter cutting
10 disc causing slower rotation and consequent longer life.
This arrangement also permits selectability of the role of
the cutter disc to provide for compressive or shear cutting
forces on the formation.
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BRIEF ~)ESCRIPTION OE THE DRAWINCS
Other objects and many of the attendant advarltages of
this invention will be readily appreciated as the same
becomes better understood by reference to the following
detailed description when considered in conjunction with
the accompanying draw.ings in which like reference numerals,
designate like parts throughout the figures thereof and,
wherein:
FIGURE 1 is a perspective of a rock bit having cutters
10 structured to rotate;
FIGURE 2 is a perspective of the rear of one of the
cutter elements from the rock bit of FIGURE 1;
FIGURE 3 is a cross section along 3-3 of FIGURE 2;
FIGURE 4 is a top plan view of a cutter and its
placement on the head of the rock bit;
FIGURE 5 is a perspective of a rock bit having a
preferred embodiment of cutters structured according to the
present invention;
FIGURE 6 is a cross section of one of the cutter
20 elements shown in FIGURE 5;
FIGURE 7 is a plan frontal view of an alternate
embodiment of a cutting disc according to the present ~`
invention;
FIGURE 8 is a plan frontal view of an alternate
cutting aisc according to the present invention;
EIGURE 9 is a perspective of a rock bit showing an
alternate preferred embodiment of cutter elements according
to the present invention;
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FIGURE 10 is a top view of the drag bit head showing
placement of cutter elements according to the present
invention;
FIGURE 11 is a side perspective of the drag bit and
cutter elements shown in FIGURE 10;
FIGURE 12 is a side plan view of a cutter element that
could be used in FIGURES 9, 10 and 11;
FIGURE 13 i5 an end view of the cutter element shown
in FIGURE 12;
FIGURE 14 lS a side plan view o~ an alternate pre-
ferred embodiment showing an alternate mounting for a disc
cutter element according to the present invention;
FIGURE 15 is a perspective of a rock bit showing an
alternate preferred embodiment of cutter elements according
to the present invention;
FIGURE 16 is a side plan view of a cutter element used
in the rock bit of FIGURE 15;
FIGURE 17 is an end view of the cutter element of
FIGURE 16;
FIGURE 18 is a side plan view, partially broken away,
of another embodiment of a cutter element;
FIGURE 19 is an end view of the cutter element of
FIGURE 18; and
FIGURE 20 is a front view of the cutter element of
FIGURE 18.
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DESCRTPTION OF THE PREFERRED ~A.BODIMEMTS ANr)
BEST MODE FOR C~.RYING OUT THE :~NVENTION
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Referring first to FIGURE 1, a drag bit, generally
designated as l1, is rnodified to accommodate ~he cutter
elements of the present invention. Drag bit 11 consists
essentially of body 15 having a cukter face end 17 and a
pin end 13. The pin end 13 is the shank of the bit tha-t
connects to a drill string for rotation (not shown).
Although FIGURE 1 illustrates cutter face end 17 in an
10 upward direction from the pin end 13, it will be understood
by all those skilled in the art that the face end, when in
the hole will be in a downward direction from pin end 13.
The reader should bear this in mind as he follows through
the descriptive portion of this patent specification.
Mounted on the cutter face 17 of bit 15 is a plurality
of cutter elements, generally designated as 19, which
generally lie on radial lines eY.tending from the center of
the face 17 of the drag bit 15. Each of the cutter ele-
ments 19 are comprised of an insert base or saddle 21 and a
2Q cutter segment 22.
The insert base 21 is preferably a tungsten carbide
b]ock having an aperture 24 therethrough (FIG~RE 3). The
base of the saddle 21 is preferably keyed with a slot 27
~hich fits into an aperture and mating key formed in the
face 17 of the drill bit. The saddle ~1 may be press or
interference fitted into an aperture formed in the face or
may be fastened by brazing or some other convenient fasten-
ing means.
The cutter segment 22 is rotatably mounted within the
30 aperture 24 of the saddle 21. The structure of the cutter
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element 19 preferably comprises a suppor~ crclnk 25, which
rotates within the journal aperture 24, bearing prirnarily
against conical surface 24', formed on the end of the crank
25. The end of the crank 25 supports cutter elernent 22
mounted ~hereon. The crank 25 is contained within saddle
block 21 by a keeper sleeve 23 tapered as sho~m in YIGURE
3. The keeper is, for example, brazed onto the shaft of
crank 25 to maintain the crank and cutter in place within
the saddle.
As shown in FIGURE 3, which is cross section along 3-3
of FIGURE 2, the saddle 21 has an aperture 24 therethrough
which is a journaled bearing for the crank 25. The aper-
ture 24 is tapered at both ends (12 and 14) in a manner
which provides for both a rotary bearing and a thrust
bearing surface. Tapered end 14 may support, for example,
a conically shaped bearing sleeve 30O The sleeve may be
fabricated from, for example, aluminum bronze, copper
alloys or a spinodal alloy, all of which are suitable
bearing materials.
Moreover, all of the bearing surfaces 12, 14 and 24
may be lined with a sleeve of bearing material as set forth
above (not shown).
In a preferred embodiment, the cutter element 22
consists of a wafer of synthetic diamonds such as described
in U. S. Patent No. 4,253,533, for example. As shown in
FIGURE 3, the cutting wafer 22 is at a negative rake angle
"A" which is the result of the face 28 of saddle 21 being
slanted as shown. This negative rate angle creates a
compressive cutting force against the bottom 16 of the
- horehole which ten~s to crush more than slide away the
earth formation.
The saddle 21 of each of the cutter elements 19 is
mounted on face 17 of bit 11 along a radial line 32 (FIGURE
4). The vertical center 20 of cutting face 22 intersects
the circumferential movement arc 31 and the perpendicular
plane 29. However, the cuttiny face 22 does not lie on a
plane that is parallel to the radius 32. It is, instead,
skewed at an offset angle 33 from the radius 32. This skew
angle preferably is at a significant angle~ The amount of
s~ew is chosen on the basis of the speed at which the
cutting ~ace is to rotate. The smaller the angle of skew,
the slower the rotation of cutting element 22. Whether the
cutting element 22 turns clockwise or counterclockwise is a
matter of choice. The important limit is tha~ it is skewed
from the radius of plane 32, causing forces to be exexted
on the cutting element 22 as a result of the rotation of
the drill face 17 which rotates the crank or body 25 of the
cutter to rotate within the journal 24 in the saddle 21
IFIGURE 3)
As a result of this rotation, a continually new
diametrical portion of cutting element 22 is exposed to the
earth formation being scraped away thereby helping to keep
the cutting element 22, which is preferably synthetic
diamond, cool and relatively clear of debris. Keeping this
cutting element 22 cool prolongs the life of the cutting
wafer a substantial amount, thereby creating a more effec-
tive drag bit with a considerably extended life span. As
is well ~nown, diamond subjected to extended periods of
30 high heat concentration will cause the diamond to
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disintegra~,e -thus conti,nual movemen~, minimiY,es heat concen~
tration on the cutting edge of elernent 22.
Referxing now to FIGURE 5 which illus-trates a pre-
ferred embodiment for the cutter elements according to the
present invention, a drag bit 35 is shown having a bit face
39 at the end opposite threaded pin end 37. The cutting
elements, generally designated as 41, are as effective as
the cutting elements 19 shown in FIGURE 1. They have
cutting face 43 at one end of the journal, a saddle 42 and
a keeper 45 at the other end of the journal. Each of the
elements are mounted along a radial 1ine which extends from
the center of the face 39 of the drag bit 35 (not shown).
The face 43 is not covered with a cutting material. Only
the circumference of the face 43 has a cutting material 51
equidistantly spaced and inserted thèrein (FIGURE 6).
As can be seen in FIGURE 6, a saddle 42 has a slanting
face 47 with a journal 24 therethrough which is slanted (44
and 46) at the face and backsides to provide both thrust
and rotary bearing surfaces. The crank 49 is constructed
differently than the crank 25 of FIGURE 3 in that it is
composed of a series of parts. The first part is a shaft
50 which provides a rotary bearing surface 26, preferably '~-
of tungsten carbide material which is cast at end 48 of
shaft 50 into cutting face 43, also preferably of tungsten
carbide material. The face 43 has attached around its
perimeter a plurality of equidistantly spaced cutter
segments 51 of polvcrystalline diamond cutting elements,
for example, which are fastened directly into the matri~ of
the cutting end 43. The other end of the shaft 50 has
brazed thereon a shaft keeper element 45. The cutting
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element, as shown in FIGURE 6, provi~es for (ornp~ssiJe
cutting forces primarily due to the negative r~ke angle ~s
shown with respect to FIGURE 3.
Referring now to FIGURES 7 and 8, alternate configura-
tions for the cutting face 43 are illustrated. Primaril~
what is shown is that the particular structure for the
individual cutting segments 51, mounted along the circum-
ference of the cutting face 43, need not be cylindrical.
FIGURE 7 shows cylindrical inserts 51. PIGURE 8 shows
~0 tri~ngular prisms 52 inserted into the circumference of the
cutting face 43. Other shapes could also be used as
desired. In addition, for example, these cutting sesments
are spaced so that the entire circumference of the cutting
face is covered by the cutting segment material.
Referring now to FIGURES 9, 10 and 11, other alternate
preferred embodiments of the cutters built according to the
present invention for use in a drag bit 57 are illustrated.
Drag bit 57 has a face 61 opposite to pin end 59~ Mounted
on face 61 is a plurality of cutter elements 67 mounted for
rotation about a shaft rotatively secured to journal blocks
63 and 65. The cutting face 73 of the cutter 67 is
oriented relative to a radius extending from the
center of the face 61 of the drag bit 57, as more clearly
shown in FIGURE 10. The desired skew angle of cutting face
73 on each of the cutters 67 is skewed in the same manner
as the cutting face 22 of cutting element 19 (FIGURE 4).
FIGURE 10 also illustrates fluid nozzles 77 located in the
face 61 of drill bit 57 which causes drilling fluid to be
washed across the cutting elements 73 to cool and clean
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them as they precess during opera~ion of -the hit in a
borehole.
Referring now to FIG~RES 12 and 13, an alternate
structure for cutting elements 67 is illustrated. FIGURE
12 illustra~es the cutting face 73 of the cutter 67 which
has a plurality of circular shaped cylinders 75 embedded
around its perimeter in the manner shown. En~ 74 of
cylinders 75 serves as the cutting face for cutter 67. The
cutter 67 is mounted to a pair of bearing blocks 69 and 71
which provide both a thrust and a rotary bearing surface
Inot shown). The cutter 67 rotates around the shaft which
is held by bearing blocks 69 and 72. The shaft may either
be journaled into bearing block 69 and 71 or may be fixedly
attached into bearing block 69 and 71 with the cutter
elements 67 rotating around the fixed shaft. The latter
arrangement is preferred.
The cutter 67 comes to an apex 78 which is on the
plane passing through the geometric center of the cutter
67. The sloped surfaces 73 and 74 are part of a truncated
conical section that slopes awav from the apex 78. One end
74 of the cylinder cutting members 75 are mounted into and
exposed at the cutting face side 73 while a small portion
of the side of the cylinders 75 are exposed at the opposite
side 79. Rotation of the cutter 67 causes different
cutting cylinders 75 to come into contact with the
formation being gouged away as the drill bit head rotates.
The cutter 67 is preferably of tungsten carbide. The
cvlindrical shaped cutter elements 75 are preferably of
synthetic diamond which are held fast in the matrix of the
tungsten carbide cutter structure 67. The mounting or
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bearing block 69, 71 are also pre~erably of tunqsten
carbide or similar high streng~h material held fas~ ~co the
face 61 of drill bit 57, either by press fi-t or some other
well known technique, such as brazing for example.
Refer now to FIGURE 14. Another alternate preferred
embocliment of a cutter element according to the present
invention is illustrated. This embodiment is constructed
- to provide a positive rake angle "B" thereby providing true
shear forces for slicing away the earth formation 88. A
10 pair of bearing blocks 85 and 83 are utilized and are
fastened-to the bit face 90. Mounted for rotation with
these bearing blocks is a truncated cone shaped cutter 92
having a cutting face 94 which is the base of the cone~
The sides of the cone 91 are sloped at an angle 93 that is
less than ninety degrees. The axis of rotation 89 of the
cone cutter 92 is at an angle to the face 90 of the drill
bit, creating a positive rake angle "B" with respect to the
earth formation 88. The cone cutter 92 rota-tes about the
axis of rotation as explained above. The journal blocks 85
and 83 are shaped to provide for both thrust and rotary
bearing surfaces. The cone cutter 92 is preferahly con-
structed of a hard material such as tungsten carbide. In
the alternative, cutter elements may be located along its
circumference in the manner illustrated for the embodiments
of FIGURES 7-13.
Referring now to FIGURES 15, 16 and 17, an alternate
preferred embodiment of a drag bit with cutter elements
according to the present invention is illustrated. Drag
bit 103 has a face 101 opposite pin end 105. Mounted on
the face 101 is a plurality of disc shaped cutters,
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generally designated as 107, each mounted to ,I pair of
journal blocks 109 and 111. ~}le orientation of the cutt:in~
faces 112 of cutter elements 113 of cutters 107 is the sc~rne
as the orientation of the cut-ters shown in FT~,UR~S 9, ]0
and ll.
The cutter elements 113 mounted in the cylindrical
cutter 115 is an arcuate segment that is, for example,
three-quarters of an inch between radial sides 117 and 119.
The inlaid segments 113 are approximately five-eighths of
an inch thick. The diameter of the cylinder 115 for this
size cf cutting segment is preferably four inches. The
material variations of the cutter elements 113, the cylin-
drical cutter 115 and the mounting blocks 109 and 111 are
e~plained above. The cutting face 113 of the disc shaped
cutter 107 is preferablv mounted at a negative rake ang]e
"C" of up to forty-five degrees from the perpendicular to
the face 101 of the drag bit in certain situations.
Referring now to FIGURES 18, 19 and 20, which illus-
trate another emhodiment for the cutter elements according
to the present invention. The cutting elements, generally
designated as 241, are effective in particularly hard
formations. This particulax embodiment has a toroidally `
shaped cutting face 243 at one end of the journal generally
designated as 249. A saddle 242 is provided for journal
249 which provides a bearing surface 240 thereby. A
journal keeper 245 is provided at end 250 of journal 249.
At the opposite end of journal 249 is cutter end 243, the
peripheral ed~e of which is rounded or toroidally shaped at
periphery 252. The back side 260 of cutter end 243 is
conically shaped and provides a bearing surface which mates
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against a complementary rna~ing surface 244 in
saddle 242~ Bearing sleeves may b~ provided as set forth
relative to FIGURE 3. The conical surfaces 260 and 244
serve to take the brunt of the thrust from the rotating
cutter head 243 during operation of the cutter in a
borehole. Similar conically shaped bearing surface 246
formed in saddle 242 is provided having complementary
surfaces on the keeper 245 which retains the rotating
cutter within the saddle 242. The rounded toroid surface
252 of cutter end 248 of the shaft 249 is covered with
embedded natural or synthetic diamonds 251, the diamonds
being mechanically fixed within a matrix of, for example,
tungsten carbide applied to the end 248 of the shaft 249.
This process is well known within the art. The multi-
plicity of natural or synthetic diamonds 251 covering the
rounded peripheral edge 252 are particularly effective in
hard formations as previously indicated. The cutter
elements 241 are skewed from the radius of a plane as
previously described which causes rotational forces to be
20 exerted on the cutter elements 243.
As stated beore, a continually new diametrical
portion of the cutter element 241 is exposed to the earth '
formation being abraded away thereby helping to keep the
cutter elements 241 cool and clear of debris. The multi~
plicity of natural or synthetic diamond chips 251 are
vulnerable to heat as are the foregoing cutter elements,
hence continual rotation of the cutter head 243 within its
saddle block 242 is important to maintain the integritv of
the diamonds on cutter end 243.
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``` FIGURE 19 illustrates the rear side of the cutter
elements 241 showing the multiplicity of natural or syn-
thetic diamonds 251 completely covcring the rounded toroid
surface 252 of end 243.
FIGURE 20 lllustrates a front face view of the cutter
- element 241 showing the outer toroidally shaped .surface 252
covered with natural diamonds 251. The center portion of
the cutter end 243 is free of diamond cutter segments since
it does not significantly contact any of the formation.
The end 240 of saddle 242 is preferably interference
fitted within a hole formed in the face of a drag bit as
previously described (not shown).
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