Note: Descriptions are shown in the official language in which they were submitted.
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Polycrystalline Material Element with Improved Wear Resistance
And Methods of Manufacture Thereof
EACKGROUND OF THE INVENTION
1. Field of the Invention.
The invention relates to superhard polycrystalline material elements for
wear, cutting, drawing, and other applications where engineered superhard
IO surfaces are needed. The invention particularly relates to polycrystalline
diamond and polycrystalline diamond-like (collectively called PCD) elements
with greatly improved wear resistance and methods of manufacturing them.
2. Description of Related Art.
Polycrystalline diamond and polycrystalline diamond-like elements are
known, for the purposes of this specification, as PCD elements. PCD elements
are formed from carbon based materials with exceptionally short inter-atomic
distances between neighboring atoms. One type of diamond-like material
similar to PCD is known as carbonitride (CN) described in U.S Patent No.
5,776,615. In general, PCD elements are formed from a mix of materials
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processed under high-temperature and high-pressure into a polycrystalline
matrix of inter-bonded superhard carbon based crystals. A common trait of PCD
elements is the use of catalyzing materials during their formation, the
residue
from which often imposes a limit upon the maximum useful operating
temperature of the element while in service.
A well known, manufactured form of PCD element is a two-layer or multi-
layer PCD element where a facing table of polycrystalline diamond is
integrally
bonded to a substrate of less hard material, such as tungsten carbide. The PCD
element may be in the form of a circular or part-circular tablet, or may be
formed
into other shapes, suitable for applications such as hollow dies, friction
bearings,
valve surfaces, indentors, tool mandrels, etc. PCD elements of this type may
be
used in alinost any application where a hard wear and erosion resistant
material
is required. The substrate of the PCD element may be brazed to a carrier,
often
also of cemented tungsten carbide. This is a common configuration for PCDs
used as cutting elements, for example in fixed cutter or rolling cutter earth
boring bits when received in a socket of the drill bit, or when fixed to a
post in a
machine tool for machining. 'These PCD elements are typically called
polycrystalline diamond cutters (PDC).
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There are numerous variations in the methods of manufacture of these PDC
elements. For example various ranges of average diamond particle sizes may be
utilized in the manufacture to enhance wear properties as shown in U.S.
Patents
Nos, 4,861,350; 5,468,268; and 5,545,748 all herein incorporated by reference
for all they disclose. Also, methods to provide a range of wear resistance
across
or into the working surface of a PDC are shown in U.S. Patent Nos. 5,135,061
and 5,607,024 also herein incorporated by reference for all they disclose.
However, because the wear resistance is varied by changing the average size of
the diamond particles, there is an inherent trade-off between impact strength
and
wear resistance in these designs. As a consequence, the PDC elements with the
higher wear resistance will tend to have poor impact strength, which for PDC's
used in drilling applications, is often unacceptable.
Typically, higher diamond volume densities in the diamond table increases
wear resistance at the expense of impact strength. However, modem PDC
elements typically utilize often complex geometrical interFaces between the
diamond table and the substrate as well as other physical design
configurations
to improve the impact strength. Although this allows wear resistance and
impact
strength to be simultaneously maximized, the tradeoff still exists, and has
not
significantly changed for the past several years prior to the present
invention.
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PCD elements are most often formed by sintering diamond powder with a
suitable binder-catalyzing material in a high-pressure, high-temperature
press.
One particular method of forming this polycrystalline diamond is disclosed in
U.S. Patent No. 3,141,746 herein incorporated by reference for all it
discloses.
Tn one common process for manufacturing PCD elements, diamond powder is
applied to the surface of a preformed tungsten carbide substrate incorporating
cobalt. The assembly is then subjected to vezy high temperature and pressure
in
a press. During this process, cobalt migrates from the substrate into the
diamond
layer and acts as a binder-catalyzing material, causing the diamond particles
to
bond to one another with diamond-t~-diamond bonding, and also causing the
diamond layer to bond to the substrate.
After completion of the sintering process, a finishing operation is performed
which typically includes a step of machining the PCD. The machining operation
may be similar to that described in US Patent No 5,447,208 in which
progressively smaller diamond grit particles are used to produce a highly
polished working surface on the diamond material. However, the use of
progressively small grit sizes is not essential, and depending upon the
application in which the PCD is to be used, a less polished finish may be
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acceptable, in which case the machining operation may be performed with, say,
only one relatively coarse diamond grit size.
Regardless as to the finish to be produced, the action of the diamond grit on
the working surface of the PCD during the machining operation is to cause
slightly projecting parts of the PCD (at a microscopic level) to be worn or
broken away from the remainder thereof to flat a working surface of good
flatness. Where the machining operation is used to produce a highly polished
finish, then the finish working surface is of very good flatness, but will
still
include small scratches formed by the action of the diamond grit on the
working
surface. In addition to forming a surface of good flatness, the machining
operation causes the formation of very small fractures, referred to herein as
microfractures, in the diamond crystals which are exposed at the working
surface. These crystals may also be subject to other damage during the
machining operation. It is thought that, in subsequent use, cracks may
propagate
relatively easily along the microfractures, and hence that the PCD finished in
this manner is relatively weak, being of relatively low wear resistance.
Although, as described hereinbefore, cobalt is most commonly used as the
binder-catalyzing material, any group VIII element, including cobalt, nickel,
iron, and alloys thereof, may be employed.
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In an alternative form of thermally stable polycrystalline diamond, silicon is
used as the catalyzing material. The process for making polycrystalline
diamond
with a silicon catalyzing material is quite similar to that described above,
except
that at synthesis temperatures and pressures, most of the silicon is reacted
to
form silicon carbide, which is not an effective catalyzing material. The
thermal
resistance is somewhat improved, but thermal degradation still occurs due to
some residual silicon remaining, generally uniformly distributed in the
interstices of the interstitial matrix. There are mounting problems with this
type.
of PCD element because there is no bondable surface.
More recently, a further type of PCD has become available in which
carbonates, such as powdery carbonates of Mg, Ga, Sr, and Ba are used as the
binder-catalyzing material when sintering the diamond powder. PCD of this
type typically has greater wear-resistance and hardness than the previous
types
of PCD elements. However, the material is difficult to produce on a commercial
scale since much higher pressures are required for sintering than is the case
with
conventional and thermally stable polycrystalline diamond. One result of this
is
that the bodies of polycrystalline diamond produced by this method are smaller
than conventional polycrystalline diamond elements. Again, thermal degradation
may still occur due to the residual binder-catalyzing material remaining in
the
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interstices. Again, because there is no integral substrate or other bondable
surface, there are difficulties in mounting this material to a working
surface.
BRIEF SUMMA.IZY OF THE INVENTION
The present invention provides a superhard polycrystalline diamond or
diamond-like element with improved wear resistance. Collectively called PCD
elements for the purposes of this specification, these elements are formed
with a
binder-catalyzing material in a high-temperature, high-pressure (HTHP)
process.
The diamond material is formed and integrally bonded to a substrate containing
the catalyzing material during the HTHP process. The diamond body so formed
has a working surface, a plurality of crystals being exposed at the working
surface, and wherein the crystals exposed at at least a portion of the working
surface are substantially free of microfractures.
It will be appreciated that by providing a PCD element in which at least
some of the crystals at the working surface are treated to be substantially
free of
microfractures, the likelihood of cracks propagating through the crystals is
reduced, and as a consequence, the wear resistance of the element in improved
and the useful working life of the PCD is increased.
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The PCD element may be used in a wide range of applications. By way of
example only, the PCD element may fmd applications in downhole equipment,
either in cutters or for use in wear resistant bearings. The PCD element may
alternatively be used in hollow dies, friction bearings, valve surfaces,
indentors,
tool mandrels and a wide range of other applications. Additionally, the PCD
element may be used in the machining of abrasive materials, for example
abrasive wood materials, ferrous and non-ferrous materials, and hard or very
abrasive engineering materials such as stone, asphalt and the like.
In accordance with one aspect of the present invention there is provided a
PCD element comprising a body including matrix of crystals of a superhard
material, the body having a surface, a plurality of the crystals being exposed
at
the surface, wherein at least the exposed part of each of the crystals exposed
at at
least a portion of the surface is of rounded form. Crystals of this form are
substantially free of microfractures and other defects and so a PCD of this
form
is of improved wear resistance.
The PCD element conveniently comprises a substrate having a front
surface, a table of superhard material being bonded to the substrate, the
table of
superliard material comprising a matrix of crystals. The crystals of superhard
material conveniently comprise diamond crystals.
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The invention also relates to a PCD element which comprises a substrate
having a front surface, a table of superhard material being bonded to the
front
surface of the substrate, the table of superhard material comprising a matrix
of
crystals, the table having a surface at which a plurality of the crystals are
exposed, at least the exposed parts of the crystals which are exposed at at
least a
portion of the surface being substantially free of microfractures.
The exposed parts of the exposed crystals are preferably of rounded form.
In accordance with another aspect of the invention there is provided a
method of manufacturing a PCD element comprising:
sintering diamond powder with a binder-catalyst material in a high pressure,
high temperature press to form a body including a matrix of diamond crystals;
performing a machining operation on the body to form a working surface
thereon at which a plurality of diamond crystals are exposed; and
treating the body to render the crystals which are exposed at at least a
portion of the working surface substantially free of microfractures.
The step of treating the body may include performing a machining
operation on the body in the absence of a coolant material. Alternatively, the
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step of treating the body may include performing a machining operation on the
body with a restricted coolant supply. In either case, the temperature of the
diamond crystals at the exposed surface is raised, and extremely high local
temperatures and pressures are reached such that the exposed diamond surface
becomes plastic. Under these conditions, the exposed surface of the diamond
crystals can undergo limited plastic flow and thereby deform to generate a
smooth rounded surface which is substantially free of microfractures. It is
believed that the extreme localized surface temperature attained during this
treatment is in excess of 2000°C. It is well known in the art that
diamond
crystals deform in a plastic manner when subjected to high pressures and
temperatures such as during the HTHP process described briefly hereinbefore.
The deformation is normally revealed by the presence of 'deformation twinning'
within the crystals such as occurs in ductile metals at much lower
temperatures.
Prior to this invention, this plastic deformation was not known to occur
locally at
a surface as a result of a machining process, and such machining conditions
are
normally avoided.
The machining operation may be an ultra-high speed grinding operation.
Alternatively, the step of treating the body may include performing a
thermochemical treatment on the body. The thermochemical treatment may
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involve the treatment of the working surface of the body with at least one
oxidizing compound, or the treatment thereof with at least one iron group
element.
In accordance with another aspect of the invention there is provided a
method of manufacturing a PCD element comprising:
sintering diamond powder with a binder-catalyst material in a high pressure,
high temperature press to form a body including a matrix of diamond crystals;
performing a machining operation on the body to form a working surface
thereon at which a plurality of diamond crystals are exposed; and
treating the body to render at least the exposed parts of the crystals exposed
at at least a portion of the working surface of rounded form.
Crystals treated so as to be of rounded form are substantially free of
microfractures and other surface defects, and so a PCD manufactured in
accordance with the invention has the advantage that it is of improved wear
resistance as the likelihood of cracks propagating through the crystals
thereof is
reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
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The invention will further be described, by way of example only, with
reference to the accompanying drawings, in which:
Figure 1 is a typical PCD element of the present invention.
Figure 2 is a micro-structural representation of part of the PCD element.
Figure 3 is a diagrammatic representation illustrating the crystal structure
of
part of a typical PCD element close to a working surface thereof.
Figure 4 is a view similar to Figure 3 but illustrating the structure of a PCD
in accordance with an embodiment of the invention.
Figure 5 is a typical PCD of the present invention shown as a cutting
element.
Figure 6 is a perspective view of an insert used in machine tools utilizing
the PCD element of the present invention.
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Figure 7 is a perspective view of a dome shaped PCD element suitable for
use in both rolling cutter drill bits and in fixed cutter drill bits.
Figure 8 is a side view of a fixed cutter rotary drill bit using a PCD element
of the present invention.
Figure 9 is a perspective view of a rolling cutter rotary drill bit using a
PCD
element of the present invention.
F figure 10 is a section view of a wire drawing die having a PCD element of
the present invention.
Figure 11 is perspective view of a bearing having a PCD element of the
present invention.
Figures 12 and 13 are front views of the mating parts of a valve having a
PCD element of the present invention.
F baure 14 is a side view of an indentor having a PCD element of the present
invention.
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Figure 15 is a partial section view of a punch having a PCD element of the
present invention.
Figure 16 is perspective view of a measuring device having a PCD element
of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
AND THE PREFERRED EMEODIMENT
The polycrystalline diamond or diamond-like material (PCD) element 2 of
the present invention is shown in Figure 1. The PCD element 2 has a plurality
of
partially bonded superhard, diamond or diamond-like, crystals 60, (shown. in
Figure 2) a catalyzing material 64, and an interstitial matrix 68 formed by
the
interstices 62 among the crystals 60. The element 2 also has one or more
working surfaces 4 and the diamond crystals 60 and the interstices 62 form the
volume of the body 8 of the PCD element 2. Preferably, the element 2 is
integrally formed with a metallic substrate 6, typically tungsten carbide with
a
cobalt binder material. To be effective when used in an abrasive wear
application, the volume density of the diamond in the body 8 should be greater
than 85 volume %, and preferably be higher than 90%.
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The working surface 4 is any portion of the PCD body 8 which, in
operation, may contact the object to be worked. In this specification, when
the
working surface 4 is discussed, it is understood that it applies to any
portion of
the body 8 which may be exposed and/or used as a working surface.
Furthermore, any portion of any of the working surface 4 is, in and of itself,
a
working surface.
During manufacture, under conditions of high-temperature and high-
pressure (HTHP), the interstices 62 among the crystals 60 fill with the
catalyzing
material 64 followed by bonds forming among the crystals 60.
Referring now to Figure 2, it is well known that there is a random
crystallographic orientation of the diamond or diamond-like crystals 60 as
shown
by the parallel lines 61 representing the cleavage planes of each crystal 60.
As
can be seen, adjacent crystals 60 have bonded together with interstitial
spaces 62
among them. Because the cleavage planes 61 are oriented in different
directions
on adjacent crystals 60 there is generally no straight path available for
diamond
fracture. This structure allows PCD materials to perform well in extreme
loading environments where high impact loads are common.
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In the process of bonding the crystals 60 in a high-temperature, high-
pressure press, the interstitial spaces 62 among the crystals 60 become filled
with a binder-catalyzing material 64. It is this catalyzing material 64 that
allows
the bonds to be formed between adjacent diamond crystals 60 at the relatively
low pressures and temperatures present in the press.
The average diamond volume density in the body 8 of the PCD element 2 of
the present invention ranges from about 85% to about 99%. The high diamond
volume density is achieved by using diamond crystals 60 with a range of
particle
sizes, with an average particle size ranging from about 30 to about 60
microns.
Typically, the diamond mixture may comprise 20% to 60% diamond crystals 60
in the 5-15 micron range, 20% to 40% diamond crystals 60 in the 25-40 micron
range, and 20% to 40% diamond crystals 60 in the 50-80 micron diameter range,
although numerous other size ranges and percentages may be used. This mixture
of large and small diamond crystals 60 allows the diamond crystals 60 to have
relatively high percentages of their outer surface areas dedicated to diamond-
to-
diamond bonding, often approaching 95%, contributing to a relatively high
apparent abrasion resistance.
After completion of the sintering operation to form the body 8 of the PCD
element 2, and to bond the element 2 to the substrate 6, a cleaning operation
in
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performed on the element 2. The cleaning operation includes a finishing
operation of machining the working surfaces 4 of the element 2 to improve the
smoothness thereof and to remove macroscopic defects therefrom. The crystals
60 of the element 2 include a plurality of crystals 65 exposed at the working
surfaces 4. As described hereinbefore, it is thought that the machining
operation
induces the formation of microfractures 63 and other defects into the crystals
65
of the element 2 which are exposed at the working surface 4, as shown in
Figure
3. 'The formation of these defects in the crystals 65 which are exposed at the
working surface 4 may result in the element 2 being weakened as, in use,
cracks
may propagate through the crystals 65, starting at the microfractures 63, and
then
typically following the cleavage planes 61 of the crystals.
In accordance with the invention, rather than simply performing a
machining operation on the element 2, the element 2 is treated to render the
crystals 65 exposed at the working surfaces 4 thereof, or at at least a
portion of
the working surface thereof, for example around at least a part of an edge
portion
5 of the element 2, substantially free of microfractures 70 and other surface
defects. The treatment comprises performing a machining operation, for
example an ultra-high speed grinding operation, in the absence of a coolant,
or
with a'restricted coolant supply so that the machining operation is performed
at a
significantly higher surface temperature than usual. By way of example, the
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surface temperature reached may be in excess of 2000°C. The performance
of
the machining operation under such high temperature conditions is thought to
affect the way in which material is removed from the element 2 such that the
removal of the material does not result in the formation of microfractures or
other defects in the exposed parts of the exposed crystals 65. Rather, the
exposed diamond surface undergoes limited plastic deformation, the diamond
flowing to form a rounded surface which is substantially free of
microfractures.
Figure 4 is a diagrammatic view similar to Figure 3 illustrating the effect of
performing such a machining operation. As shown in Figure 4, the exposed
parts of the crystals 65 exposed at the working surfaces 4 are of rounded or
domed form, and are substantially free of stress raisers in the form of
microfractures, cracks or other surface defects. As a result, in use, the risk
of
cracks forming in the crystals 65 is reduced, and hence the wear resistance of
the
element 2 is improved.
Although as described above the step of treating the element 2 to render its
working surfaces 4 substantially free of microfractures and other surface
defects
may involve performing a machining operation in the absence of coolant or with
a restricted supply of coolant, it will be appreciated that the element 2
could be
treated in other ways to achieve the same result. For example, a
thermochemical
treatment operation could be performed on the element 2 using, for example,
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iron group elements or oxidizing compounds. Further, combinations of these
techniques may be used.
As indicated hereinbefore, a PCD element so manufactured may find
application in a wide range of uses. One particularly useful application for
the
PCD element 2 of the present invention is as cutting elements 10, 50, 52 as
shown in Figures 5, 6 and 7. The working surface of the PCD cutting elements
10, 50, 52 may be a top working surface 70 andlor a peripheral working surface
72. The PCD cutting element 10 of F Daure 5 is one that may be typically used
in
fixed cutter type rotary drill bits 12, or for gauge protection in other types
of
downhole tools. The PCD cutting element 50 shown in Figure 7 may be shaped
as a dome 39. This type of PCD cutting element 50 has an extended base 51 for
insertion into sockets in a rolling cutter drill bit 38 or in the body of both
types
of rotary drill bits, 12, 38 as will be described in detail.
The PCD cutting element 52 of Figure 6 is adapted for use in a machining
process. Although the configuration of the cutting element 52 in Figure 6 is
rectangular, it would be appreciated by those skilled in the art that this
element
could be triangular, quadrilateral or many other shapes suitable for machining
highly' abrasive products that are difficult to machine with conventional
tools.
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The PCD cutting element 10 may be a preform cutting element 10 of a fixed
cutter rotary drill bit 12 (as shown in Figure 8). The bit body 14 of the
drill bit is
formed with a plurality of blades 16 extending generally outwardly away from
the central longitudinal axis of rotation 18 of the drill bit. Spaced apart
side-by-
side along the leading face 20 of each blade is a plurality of the PCD cutting
elements 10 of the present invention.
Typically, the PCD cutting element 10 has a body in the form of a circular
tablet having a thin front facing table 30 of diamond or diamond-like (PCD)
material, bonded in a high-pressure high-temperature press to a substrate 32
of
less hard material such as cemented tungsten carbide or other metallic
material.
The cutting element 10 is preformed and then typically bonded on a generally
cylindrical carrier 34 which is also formed from cemented tungsten carbide, or
may alternatively be attached directly to the blade. The PCD cutting element
10
has working surfaces 70 and 72.
The cylindrical carrier 34 is received within a correspondingly shaped
socket or recess in the blade 16. The carrier 34 will usually be brazed or
shrink
fit in the socket. In operation the fixed cutter drill bit 12 is rotated and
weight is
applied. This forces the cutting elements 10 into the earth being drilled,
effecting a cutting and/or drilling action.
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The PCD cutting elements 10 may also be applied to the gauge region 36 of
the bit 12 to provide a gauge reaming action as well as protecting the bit 12
from
excessive wear in the gauge region 36. In order to space these cutting
elements
10 as closely as possible, it may be desirable to cut the elements into
shapes,
such as the rectangular shape shown, which more readily fit into the gauge
region 36.
In a second embodiment, the cutting element 50 (as shown in Figure 7) of
the present invention is on a rolling cutter type drill bit 38, shown in
Figure 9. A
rolling cutter drill bit 38 typically has one or more truncated rolling cone
cutters
40, 41, 42 assembled on a bearing spindle on the leg 44 of the bit body 46.
The
cutting elements 50 may be mounted as one or more of a plurality of cutting
inserts arranged in rows on rolling cutters 40, 41, 42, or alternatively the
PCD
cutting elements 50 may be arranged along the leg 44 of the bit 38. The PCD
cutting element 50 has a body in the form of a facing table 35 of diamond or
diamond like material bonded to a less hard substrate 37. The facing table 35
in
this embodiment of the present invention is in the form of a domed surface 39
and has working surfaces 70 and 72. Accordingly, there are often a number of
transitional layers between the facing table 35 and the substrate 37 to help
more
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evenly distribute the stresses generated during fabrication, as is well known
to
those skilled in the art.
In operation the rolling cutter drill bit 38 is rotated and weight is applied.
This forces the cutting inserts 50 in the rows of the rolling cone cutters 40,
41,
42 into the earth, and as the bit 36 is rotated the rolling cutters 40, 41, 42
turn,
effecting a drilling action.
In another embodiment, the PCD cutting element 52 of the present
invention is in the form of a triangular, rectangular or other shaped material
for
use as a cutting insert in machining operations. In this embodiment, the
cutting
element 52 has a body in the form of a facing table 54 of diamond or diamond
like material bonded to a less hard substrate 56 with working surfaces 70 and
72.
Typically, the cutting element 52 would then be cut into a plurality of
smaller
pieces which are subsequently attached to an insert 58 that is mounted in the
tool
holder of a machine tool. The cutting element 52 may be attached to the insert
by brazing, adhesives, welding, or clamping. It is also possible to finish
form
the cutting element 52 in the shape of the insert in a high-temperature high-
pressure manufacturing process.
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As shown in Figures 10-16, PCD elements 2, 102, 202 of the present
invention may also be used for other applications such as hollow dies, shown
for
example as a wire drawing die, 300 of Figure 10 utilizing a PCD element 302 of
the present invention.
Other applications include friction bearings 320 with a PCD bearing
element 322 shown in Figure 11 and the mating parts of a valve 340, 344 with
surfaces 342 having a PCD element 342 of the present invention as shown in
F Daures 12 and 13. In addition, indentors 360 for scribes, hardness testers,
surface roughening, etc. may have PCD elements 362 of the present invention as
shown in Figure 14. Punches 370 may have either or both dies 372, 374 made of
the PCD material of the present invention, as shown in Figure 15. Also, tool
mandrels 382 and other types of wear elements for measuring devices 380,
shown in Figure 16 may be made of PCD elements of the present inventions.
Whereas the present invention has been described in particular relation to
the drawings attached hereto, it should be understood that other and further
modifications apart from those shown or suggested herein, may be made within
the
scope and spirit of the present invention.
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