Note: Descriptions are shown in the official language in which they were submitted.
835S
1 ¦ IMPROVED TOOTH DESIGN USING CYLIN~RICAL DIAMOND CUTTING ELEME~TS
3 ¦ Background of the Invention
4 1
5 i
6 ¦ 1. Field o~ the Invention
7 1
8 ¦ ~he present invention relates to the field of earth
9 1 boring tools and in particular to rotating bits incorporating
10 ¦ diamond elements.
11 I
12 ¦ 2. Description of the Prior Art
13 l
14 ¦ The use of diamonds in drilling products is well known.
15 ¦ ~ore recently synthetic diamonds both single crystal diamonds
16 ¦ (SCD) and polycrystalline diamonds (PCD~ have become commercially
17 ¦ available from various sources and have been used in such
18 1 products, with recognized advantages. For example, natural
19 ¦ diamond bits effect drilling with a plowing action in com~arison
20 ¦ to crushing in the case of a roller cone bit, whereas synthetic
21 ¦ diamonds tend to cut by a shearing action. In the case of rock
22 ¦ formations, for example, it is believed that less energy is
23 ¦ required to fail the rock in shear than in compression.
24 l
More recently, a variety of synthetic diamond products
26 has become available commercially some of which are available as
27 ¦ polycrystalline ~roducts~ Crystalline diamonds preferentially
28
page 2
ll
~ 33~5
1 fractures on (111), (110) and (100) planes whereas PCD tends to
2 be isotropic and exhibits this same cleavage but on a microscale
3 and therefore resists catastrophic large scale cleavage failure.
4 The result is a retained sharpness which appears to resist
polishing and aids in cutting. Such products are described, for
6 e~ample, in U.S. Patents 3,913,2B0; 3,745,623; 3,816,085;
7 4,104,344 and 4,224,380.
9 In general, the PCD products are fabricated from
syn~hetic and/or appropriately sized natural diamond crystals
11 under heat and pressuee and in the presence of â SOlVent/CâtalySt
12 to form the polycrystalline structure. In one form of product
13 the polycrystalline structures includes sintering aid material
14 distributed essentially in the interstices where adjacent
crystals have not bonded together.
16
17 In another form, âS described for example in U. S.
18 Patents 3,745,623; 3,816,085; 3,913,280; 4,104,223 and 4,224,380
19 the resulting diamond sintered product is porous, porosity being
achieved by dissolving out the nondiamond material or at least a
21 portion thereof, as disclosed for example, in U. S. 3,745,623;
22 4,104,344 and 4,224,380. For convenience, such a material may be
23 described as a porous PCD, as referenced in U.S. 4,224,380.
~4
Polycrystalline diamonds have been used in drilling
26 products either as individual compact elements or as relatively
2 thin PCD tables supported on a cemented tungsten carbide (WC)
page 3
ll
1 ~2
1 ¦ support backings. In one form, the PCD compact is supported on a
2 ¦ cylindrical slug about 13.3 mm in diameter and about 3 mm long,
3 ¦ with a ~CD table of about 0.5 to 0.6 mm in cross section on the
4 ¦ face of the cut~er~ In another version, a stud cutter, the PCD
5 ¦ table also is supp~rted by a cylindrical substrate of tungsten
6 ¦ carbide of about 3 mm by 13.3 mm in diameter by 26mm in overall
7 ¦ length. These cylindrical PCD table faced cutters have been used
8 ¦ in drilling products intended to be used in soft to medium-hard
9 ¦ formations.
'' 10 l
11 ¦ Individual PCD elements of various geometrical shapes
12 ¦ have been used as substitutes for natural diamonds in certain
13 applications on drilling products. However, certain problems
14 arose with PCD elements used as indiviaual pieces of a given
carat size or weight. In general, natural diamond, available in
16 a wide variety of shapes and grades, was placed in predefined
17 locations in a mola, and production of the tool was completed by
18 various conventional techniques. The result is the formation of
19 a metal carbide matrix which holds the diamond in place, this
matrix sometimes being referred to as a crown, the latter
21 attached to a steel blank by a metallurgical and mechanical bond
22 formed during the process of forming the metal matrix. Natural
23 diamond is sufficiently thermally stable to withstand the heating
24 process in metal matrix formation.
26 In this procedure above described, the natural diamond
2 could be either surface-set in a predetermined orientation, or
page 4
~Z~L8~5
1 impregnated, i.e., diamond is distributed throughout the matrix
2 in grit or fine particle form.
4 With early PCD elements, problems arose in the
produc~ion of drilling products because PCD elements especially
6 PCD tables on carbide backing tended to be thermally unstable at
7 the temperature used in the furnacing of the metal matrix bit
8 crown, resulting in catastrophic failure of the PCD elements if
9 the same procedures as were used with natural diamonds were used
with them. It was believed that the catastrophic failure was due
11 to thermal stress cracks from the expansion of residual metal or
12 metal alloy used as the sintering aid in the formation of the PCD
13 element.
14
Brazing techniques were used to fix the cylindrical PCD
1 table faced cutter into the matrix using temperature unstable PCD
17 products. Brazing materials and procedures were used to assure
1 that temperatures were not reached which would cause catastrophic
1 failure of the PCD element during the manufacture of the drilling
2 tool. The re~ult was that sometimes the PCD components separated
21 from the metal matrix, thus adversely affecting performance of
22 the drilling tool.
23
2 With the advent of thermally stable PCD elements,
2 typically porous PCD material, it was believed that such elements
2 could be surface-set into the metal matrix much in the same
2 fashion as natural diamonds, thus simplifying the manufacturing
page 5
33~
l process of the drill tOolr and providing better performance due
2 to the fact that PCD elements were believed to have advantages of
3 less tendency to polish, and lack of inherently weak cleavage
4 planes as compared to natural diamond.
6 Significantly, the current literature relating to porous
7 PCD compacts sugyests that the element be surface-set. The
8 porous PCD compacts, and those said to be temperature stable up
to about 1200C are available in a variety of shapes, e.g.,
cylindrical and triangular. The triangular material typically is
ll about 0.3 carats in weight, measures 4mm on a side and is about
12 2.6mm thick. It is suggested by the prior art that the
13 triangular porous PCD compact be surface-set on the face with a
14 minimal point exposure, i.e., less than 0.5mm above the adjacent
metal matrix face for rock drills. Larger one per carat
l6 synthetic triangular diamonds have also become available,
17 measuring 6 mm on a side and 3.7 mm thick, but no recommendation
18 has been made as to the degree of exposure for such a diamond.
ln the case of abrasive rock, it is suggested by the prior art
that the triangular element be set completely below the metal
21 matrix~ For soft nonabrasive rock, it is suggested by the prior
22 art that the triangular element be set in a radial orientation
23 with the base at about the level of the metal matrix. The degree
24 of exposure recommended thus depended on the type of rock
formation to be cut.
26
The difficulties with such placements are several~ The8
page 6
~Z~ 835~3
1 difficulties may be understood by considering the dynamics of the
~ drilling operation. In the usual drilling operation, be it
3 mining, coring, or oil well drilling, a fluid such as water, air
4 or drilling mud is pumped through the center of the tool,
radially outwardly across ~he tool face, radially around the
6 outer surface (gage~ and then back up the bore. The drilling
7 fluid clears the tool face of cuttings and ~o some extent cools
8 the cutter face. Where there is insufficient clearance between
9 the formation cut and the bit body, the cuttings may not be
cleared from the face, especially where the formation is soft or
11 brittle. Thus, if the clearance between the cutting
12 surface-formation interface and the tool body face is relatively
13 small and if no provision is made for chip clearance, there may
14 be bit clearing problems.
16 Other factors to be considered are the weight on the
17 drill bit, normally the weight of the drill string and
18 principall~ the weight of the drill collar, and the effect of the
19 fluid which tends to lift the bit off the bottom. It has been
2 reportedr for example, that the pressure beneath a diamond bit
21 may be as much as 1000 psi greater than the pressure above the
22 bit, resulting in a hydraulic lift, and in some cases the
23 hydraulic lift force exceeds 50~ of the applied load while
24 drilling.
26 One surprising observation made in drill bits having
27 surface-set thermally stable PCD elements is that even after
page 7
18355
1 sufficient ex~osure of the cutting face has been achieved, by
2 running the bit in the hole and after a fracion of the surface of
3 the metal matrix was abraded away, the rate of penetration often
4 decreases. Examination of the bit indicates unexpected polishing
of the PCD elements. ~sually ROP can be increased by adding
6 weight to the drill string or replacing the bit. Adding weight
7 to the drill string is generally objectionable because it
8 increases stress and wear on the drill rig. Further, tripping or
replacing the bit is expensive since the economics of drilling in
normal cases are expressed in cost per foot of penetration. The
11 cost calculation takes into account the bit cost plus the rig
1 cost including trip time and drilling time divided by the footage
13 drilled.
14
Clearly, it is desirable to provide a drilling tool
16 having thermally stable PCD elements and which can be
17 manufactured at reasonable costs and which will perform well in
18 terms of length of bit life and rate of penetration.
.,
2 It is also desirable to provide a drilling tool having
21 thermally stable PCD elements so located and positioned in the
22 face of the tool as to ~rovide cutting without a long run-in
23 period, and one which provides a sufficient clearance between the
24 cutting elements and the formation for effective flow of drilling
fluid and for clearance of cuttings.
22
Run-in in diamond bits is required to break off the tip
page 8
~Z~83~S
1 or point o~ the triangular cutter before efficient cutting can
2 begin. The amount of tip loss is approximately equal to the
3 I total exposure of natural diamondsO Therefore, an extremely
4 large initial exposure is required for synthetic diamonds as
compared to natural diamonds. Therefore, to accommodate expected
6 1 wearing during drilling, to allow for tip removal during run-in,
7 and to provide flow clearance necessary, substantial initial
8 ¦ clearance is needed~
9 l
10 ¦ Still another advantage is the provision of a drilling
11 ¦ tool in which thermally stable PCD elements of a defined
12 ¦ predetermined geometry are so positioned and supported in a metal
13 matrix as to be effectively locked into the matrix in order to
14 ¦ provide reasonably long life of the tooling by preventing loss of
PCD elements other than by normal wear.
16 l
17 It is also desirable to provide a drilling tool having
18 1 thermally stable PCD elements so affixed in the tool that it is
19 ¦ usable in specific formations without the necessity of
20 ¦ significantly increased drill string weight/ bit torque, or
21 ¦ significant increases in drilling fluid flow or pressure, and
22 ¦ which will drill at a higher ROP than conventional fits under the
23 ¦ same drilling conditions.
24 l
Brief Summary of the Invention
26 I
27 ¦ The present invention is an improvement in a rotating
28 l
page 9
3~S
bit having a bit face wherein the ,mprovement comprises a
plurality of teeth disposed on the bit and wherein each tooth
includes a diamond cutting element. The diamond cutting element
is particularly characterized by having the shape of a segment of
a cylinder. The segment includes at least one planar surface and
the planar surface forms, at least in part, a leading surface of
the tooth.
Thus in the broad aspect the present invention provides
a rotating bit characterized by a longitudinal axis
of rotation for use in earth boring comprising:
a matrix body member having portions forming a gage and
a face,
said face including a plurality of channels forming pad
means between at least some of the adjacent channels,
each said pad means including a plurality of spaced
synthetic polycrystalline diamond cutting elements mounted
directly in the matrix during matrix formation,
each of said cutting elements being of a predetermined
geometric shape and being temperature stable to at least about
1203 degrees C.,
the said cutting elements including a portion received
within the matrix member of said pad means and a portion which
extends above the surface of said pad means and which is adapted
to form the cutting face of said cutting elemen~,
each cutting element including a generally curved rear
face and a cutting face,
~r~
page 10 ~
g~ZgL~3~5
at least some of said cutting elements having a
longitudinal axis and being characterized in shape as a segment
of a cylinder including at least one planar surface, said planar
sur~ace forminy at least in part a leading surface of said
cutting face, said longitudinal axis of said cutting element
lying in a plane parallel to said longitudinal axis of rotation
of said bit, and
the portion of said cutting elements which forms the
cutting face of said cutting elements extending more than 0.5 mm
above the surface of the corresponding pad.
The cylindrical segment may be a split
half cylinder or a split quarter cylinder. The diamond cutting
element is characterized by having a longitudinal axis lying
along the length of the cylinder and wherein the cylindrical
shape is a half cylinder shape, the planar surface is a planar
surface lying along a diameter of the cylindrical shape. In the
case where the cylindrical segment is a quarter segment of a full
cylinder, the quarter segment includes an apical edge which lies
along the longitudinal axis of the cylinder. In each case, the
apical edge of the quarter cylinder and the planar surface of the
half cyl inder diamond cutting element serves as an exposed
leading surface of the tooth and is disposed adjacent to a fluid
channel thereby forming in whole or in part one edge or wall of
the fluid channel. As a resul~ of these improvements a cutting
tooth is proviaed using cylindrical elements characterized by
improved cutting efficiency, cleaning and cooling efficiency, and
less tendency to dull or polish than is the case with prior ar~
f ully cyl indr ical elements used in rotating bits.
page lOa
335~
1 ¦ The present invention and its various embodiments are
2 better understood by first considering the following drawings
3 wherein like elements are referenced by like numerals.
Brief ~escription of the Drawings
7 Figure l is a cross-sectional view of a tooth
8 incorporating a cylindrical diamond segment according to the
¦ ~resent invention.
10 l
11 ¦ Figure 2 is a plan view of three teeth of the type shown
12 in Figure l.
13 l
14 ¦ Figure 3 is a cross-sectional view through a rotating
15 ¦ bit sho~ing the area of a gage-to-shoulder transition
16 ¦ incorporating the teeth of Figure l.
17 I
18 ¦ Figure 4 is a plan view in reduced scale showing a
19 ¦ coring bit incorporating the teeth of Figures l and 2.
20 l
21 ¦ Figure S is a half profile view of the coring bit of
22 ¦ E'igure 4.
23 l
24 ¦ Figure 6 is a plan view of the gage-to-shoulder
transition of the coring bit in Figure 4 in conformity with the
26 teaching of Figure 3.
27
28
page ll
~ 33~5
1 Figure 7 is a cross-sectional view in enlarged scale of
2 a tooth incorporating a second embodiment of the present
3 invention.
Figure 8 is a plan view of three teeth devised according
6 to the second embodiment shown in Figure 7.
8 The present invention and its various embodiments may be
9 better understood by viewing the above figures in light of ~he
following detailed description.
11
12 Detailed Description of the Preferred Em~odiments
14 The present invention is an improvement in a tooth
design used in rotating bits, particularly rotary bits, wherein
16 the tooth includes a diamond cutting element and in particular a
diamond cutting element derived from cylindrical polycrystalline
18 synthetic diamond (PCD). Such full cylindrical elements are
19 generally commercially available but not in segment form. Such
synthetic diamond is formed in the shape of a full circular
21 cylinder having one planar end perpendicular to the longitudinal
22 axis of the cylindrical shape and an opposing domed end,
23 generally formed in the shape of a circular cone. Such elements
24 are typically available in a variety of sizes with the above
described shape.
26
227 According to the present invention, the full cylindrical
page 12
3~5
1 ¦ diamond element is segmented to form a cylindrical segment
2 ¦ wherein the segment is then axially disposed within a bit tooth.
3 ¦ Such segmented or split cylindrical elements thus provide a
4 ¦ cutting element with improved cutting efficiency with less use of
diamond material and less tendency to dull or polishG The
6 present invention and its various embodiments may be better
7 understood by now turning to Figure 1.
9 ~igure 1 is a cross-sectional view of a first embodiment
of the present invention showing a tooth, generally denoted by
11 reference numeral 10, incorporating a diamond cutting element,
12 gener~lly denoted by reference numeral 12. Element 12 is axially
13 disposed within the tungsten-carbide matrix material 14 of the
14 rotating bit. ln other words, longitudinal axis 16 of element 12
is oriented to be approximately perpendicular to bit surface 18
16 at the location of tooth 10. Bit surface 18 may be bit face of a
17 crown of a rotating bit or may be the superior sur face of a
18 raised land or pad disposed upon a bit crown. In either case,
19 bit surface 18 is taken in the present description as the basal
2 surface upon which tooth 10 is disposed.
21
2 As better seen in Figure 2, element 12 is approximately
2 a quarter section or 90 degrees of the full cylindrical shape of
2 the PCD element normally available. Element 12 is cut using a
2 conven~ional laser cutter. For example, deep cuts are made every
26 ¦ 90 degrees parallel to the longitudinal axis 16 of a full
27 ¦ cylindrical diamond element. Although the laser could be used to
28 l
page 13
Il ~L218355
1 completely cut through the diamond element, it has been found
2 ¦ possible that with deep ~coring, the diamond can then be
3 ¦ fractured with propagation of the fracture lying approximately
4 ¦ along the continuation of the plane of the laser cut. For
S ¦ example, the laser may cut a millimeter or less into and along
6 ¦ the length of the full cylindrical diamond element.
7 ¦ diametrically opposed cut of equal depth is also provided on the
8 ¦ cylinder. Thereafter, the cylinder may be split in half and then
9 ¦ later quartered on another laser cut by fracturing the diamond
10 ¦ element using an impulsive force and chisel.
11 I
12 ¦ Diamond element 12 is disposed within tooth 10 as
13 ¦ isshown in Figure 2 so that the apical edge 20 of diamond 12
14 ¦ formed by the cleavage planes or laser cuts which have formed
15 ¦ radial surfaces 22, is oriented in the leading or forward
16 ¦ direction of tooth 10 as defined by the rotation of the bit upon
17 ¦ which tooth 10 is disposed.
18 l
19 ¦ Turning again ~o Figure 1, it can be seen ~hat a portion
20 ¦ of element 12 is fully exposed above bit surface 18 and in
21 ¦ particular, that apical edge 20 forms the foremost portion of
22 ¦ diamond element 12 as the tooth moves forwardly in the plane of
23 ¦ the figure. Surfaces 22 define a dihedral angle and the
24 ¦ tangential direction of movement of tooth 10 during normal
25 ¦ cutting operation is generally along the direction of the
26 ¦ bisector of the dihedral angle. In the illustrated embodiment a
27 ¦ channel 24 is defined immediately in front of apical edge 20 to
28 l
¦ page 14
L835S
1 serve as a waterway or collector as appropriate. Thus, leading
2 ¦ 6urfaces 22 and edge 20 can be placed virtually in channel 24 or
3 ¦ immediately next thereto, forming as shown in Figure 1, one wall
4 ¦ of channel 24 or a portion thereof, whereby hydraulic fluid
5 ¦ supplied to and f lowing through channel 24 dur ing normal drilling
6 ¦ operations will serve to cool and clean the cutting face of tooth
7 ¦ 10 and in particular the leading edge and surfaces of diamond
8 ¦ element 12s
9 l
10 ¦ Further, in the illustrated embodiment, tooth 10 is
11 ¦ shown as having a trailing support 26 of matrix material
12 ¦ integrally formed with matrix material 14 of the bit and
13 I extending above bit surface 18 to the trailing surface of diamond
14 ¦ element 12. The slope of trailing support 26 is chosen so as to
substantially match the slope of the top conical surface 28 of
16 element 12 with the opposing end of element 12, which i5 a right
17 circular plane, being embedded within matrix material 14.
18 However, it must be understood that the exact shape and placement
19 of trailing support ~6 can be varied without departing from the
spirit and scope of the present invention. For example, with
21 larger dia~eter elements 12, cut from large diameter synthetic
22 cylinders, no trailing support 26 may be provi~ed at all and
23 element 12 may be totally free standing above bit surface 18 like
24 an embedded st~d. In the cases of thinner cylindrical elements
12~ trailing support 26 may be even more subs~antial than that
26 shown in Figure 1 and may assume a slope different from surface
27 28 of element 12 to thereby provide additional matrix reinforcing
28
page lS
~21~35~
1 material behind and on top of conical surface 28 and leading
2 surfaces 22.
4 Figure 2 illustrates in plan view the tooth of Figure 1
in a double row or triad configuration. In other words, a first
6 row of teeth including teeth lOa and lOb is succeeded by a
7 trailing tooth or second row of teeth including tooth lOc,
8 wherein tooth lOc is placed halfway between the spacing of teeth
: lOa and lOb. Therefore, it can be appreciated that as the teeth
lOa-c move forward during cùtting of a rock formation, the
11 diamond cutting elements incorporated within each of the teeth
12 effectively overlap and provide a uniform annular swath cut into
1 the rock formation as the bit rotates. Figure 4, which shows in
F plan view a coring bit incorporating the teeth of Figures 1 and 2
1 illustrates ~he disposition of such a double row of configured
1 teeth, collectively denoted by reference numeral 32, on pad 30.
1 Bit 34 also includes an inner gage 44 wherein the inner
and outer gage are connected by waterways 31. Each pad 30 begins
2 at or near inner gage 44 and is disposed across the bit face in a
21 generally radial direction as seen in Figure 4 and splits into
2 two pads which then extend to outer gage 36. The bifurcated pads
2 are separated by a collector 33 which communicates with a gage
24 collector 35 or junk slot 37 as may be appropriate. Clearly,
2 other types of coring bits and petroleum bits could have been
2 illustrated to show the use of the teeth of Figures 1-3 other
2 than the particular bit illustrated in Figure 4. Therefore, the
page 16
33~iS
1 inventisn is not to be limited ~o any particular bit style or in
2 fact, even to rotating bits.
4 Turning now to Figure 3, a cross-sectional view of the
shoulder-to-gage transition utilizing the teeth of Figures l and
6 2 is illustrated. The bit, generally denoted by reference
7 numeral 341 is characterized by having a vertical cylindrical
8 section or gage 36 which serves to define and maintain the
9 diameter of the bore drilled by bit 34. Below gage 36, bit 34
will slope inwardly along a designed curve toward the center of
11 the bit. In the example of coring bit of Figure 4, a half
12 profile is shown in Figure 5 and is a simple elliptical cross
13 section characterized by an outer shoulder 38, nose 40 and inner
14 shoulder 42. Inner diameter of the core is then defined by inner
gage 44. Iurning again to Figure 3, outer gage 36 is shown as
16 incorporating a half cylindrical segment 46, which is surface set
17 and embedded into gage 36 so that the rounded cylindrical surface
18 48 is exposed above bit surface 50 of gage 36 with the flat
l9 longitudinal face 52 of the half cylindrical segment embedded
2 within matrix material 54 of bit 34. Half cylindrical diamond
21 crystalline element 46 is more clearly depicted in
22 cross-sectional view in Figure 4 on gage 36.
23
24 Moving from gage 36 to outer shoulder 38, teeth 32 as
shown in Figure 4 include quarter cylindrical segments, shown in
26 rear view in Figure 3 as exemplified by diamond elements 56 and
2 58. Each element 56 is disposed within bit 34 so as to extend
page 17
~2~835~;
1 therefrom in a perpendicular direction as defined by the normal
2 to bit surface at each point where such element is located.
4 ¦In the preferred embodiment each element 56 and 58 is
5 ¦exposed by a uniform amount, n~mely, 2.7 mm (0.105n) above the
6 1 bit face. Element 56 which is the diamond element closest to
7 ¦ gage 36 is placed upon shoulder 38 at such a position nex~ to the
8 ¦ beginning of gage 36 so that its outermost radially extending
9 ¦ point, namely, apex 60, extends radially from the longitudinal
10 1 axis of rotation of bit 34 by an amount equal to the radial
11 ¦ distance from the longitudinal axis of bit 34 by the gage
12 ¦ diamonds, in particular diamond 46. ~or example, in the
13 ¦ preferred embodiment, gage diamond 46 e~tends above bit surface
14 1 50 by 0.64 mm (0.025"). While element 56 extends above bit face
15 ¦ 50 by 2.7 mm (0.105") it is placed as th~ first tooth on the bit
16 ¦ face at ~uch a distance from the gage 36 that the radially
17 I outermost exposed portion of diamond element 56 will equal the
18 ¦ radial distance of the gage diamonds 46 from the axis of rotation
21 ~ of bit 34.
I Thus, as illustrated in Figure 6, which shows a plan
22 ¦ view of the gage of the bit of Figure 4, a double row of gage
23 ¦ diamonds 46a is disposed at and slightly below gage level 62 on a
I type I gage column corresponding to a type I pad 30 shown in plan
25 ¦ view in ~igure 4. Gage diamonds 46b are thus placed adjacent to
26 ¦ a pad of type II and gage diamonds 46c placed on a gage section
27 ¦ correspondingg to a type III pad. Gage diamonds 46a-c thus form
~8 1
page 18
!1 12~L8;35S
1 a staggered pattern as best illustrated in Figure 6 which
2 effectively presents a high cutting element density as the bit
3 rotates. Above gage diamonds 46a-46b are conventional natural
4 diamonds surface set in broaches, namely~ kickers which are
typical of the order of 6 per carat in size. Whereas the double
6 row of diamonds within one gage section are offset from each
7 other by approximately half a unit spacing, a unit spacing being
8 defined as the length of a gage diamond 46, the adjacent row of
9 teeth on the next adjacent gage section begins at a quarter
spacing displaced from the corresponding row of gage diamonds on
11 the adjacent pad. In other words, while type I pad corresponds
12 to gage diamonds 46a having two rows with each row offset by half
13 a space between each other, pad II corresponds to gage diamonds
14 46b which are similarly offset with respect to each other and are
spaced down the gage one quarter of a spacing as compared to
16 gage diamonds 46a on pad type I.
17
Turning now to Figure 7, a second embodiment of the
1 present invention is illustrated wherein a tooth, generally
2 denoted by reference numeral 66, incorporates a half cylindrical
21 segment diamond element 68 extending from and embedded in matrix
22 material 14 in much the same manner as illustrated in connection
23 with the iirst embodiment of Figures l and 2. As better seen in
24 plan view of Figure 8, PCD element 68 is characterized by a half
2 cylindrical surface 70 and a planar leading surface 7~, which is
2 formed as described above by cleaving a full cylinder along the
2 diameter.
page 19
Il lZ1835~; ~
1 Turning 2gain to ~igure 7, diamond element 68 also
2 includes a conical or domed upper surface 74 forming the apical
3 point 76 of element 68. A trailing support 78 of integrally
4 formed matrix material is smoothly fared from surface 74 to bit
face 18 to provide tangential reinforcement and support for
6 diamond element 68 against the cutting forces to which element 68
7 is subjected. As better seen in plan view in Figure 8, trailing
8 supports 78 are tapered to a point 80 on bit face 18 thereby
9 forming a teardrop shaped plan outline for tooth 66.
11 As shown in Figure 7, diamond element 68 is placed
12 immediately adjacent to and forms one side of a channel 80 formed
13 into matrix material 14 which channel ao serve~ as a conventional
14 waterway or collector as may be appropriate with the same
advantages as described in connection with the first embodiment
16 of Figure 1.
17
18 As described in connection with ~igure 2, the second
19 embodiment of Figure 8 similarly consists of two rows of teeth
2 66a and 66b followed by a second row represented by tooth 66c.
21 Tooth 66c is located halfway between the spacing between tooth
22 66a and 66b ac defined with respect to the direction of
23 tangential movement durlng normal drilling operations. Ihe
24 double row of teeth are disposed on a petroleum or coring bit in
the same manner as illustrated in connection with the first
26 embodiment of the invention in Figure 4. Teeth 66 are thus
27 disposed within matrix material 14 and used on a bit in the s~me
page 20
~Z3L835~
1 manner as are teeth 10 of Figures 1 and 2. ~owever, teeth 66 as
2 shown in Figure 8, clearly provide a broader cutting surface and
3 a diamond element 68 containing twice the diamond material and
4 structural bulk as compared to diamond elements 12 of the first
embodiment. Therefore, in those applications where a larger
6 cutting bite is required or where greater structural strength is
7 needed in ~he diamond element, the half cylindrical split
8 elements 68 of the second embodiment may be more advantageously
9 used than the quarter split diamond elements of the first
embodiment.
11
12 Many alterations and modifications may be made ~o the
13 present invention without departing from its spirit and scope.
14 For example, although the split cylindrical segment has been
shown as perpendicularly embedded into the matrix material, it is
16 clearly contemplated that it may be either forwardly or
17 rearwardly raked if required by design objectives. Therefore,
18 the illustrated embodiment must be understood as presented only
19 as an example of the invention and should not be taken as
limiting the invention as set forth in the following claim.
21
22
26
27
28
page 21
