Apparatus for mounting PCD compacts

A method and apparatus for improved attachment of an ultra-hard compact, especially a two-layer disk-type PCD compact, to a tool or support surface with a mechanical connection. In general the ultra-hard compact is provided with a tool-engaging threaded end protruding from the compact. The threaded end may be facilitated by a post fitted into a blind hole in the ultra-hard compact, or may be facilitated by a threaded sleeve permanently attached to the ultra-hard compact. In any case, when the ultra-hard compact is threadably engaged into a tool or support surface, the fastening means is hidden with only the wear resistant materials of the ultra-hard compact exposed.

FIELD OF THE INVENTION
 The present invention relates to ultra hard cutting elements known as PCD
 (polycrystalline diamond) compacts, PCBN (polycrystalline cubic boron
 nitride) compacts, or compacts containing other ultra-hard material, and
 more particularly to the manner in which such compacts are mounted on
 cutting tools or other support surfaces.
 BACKGROUND OF THE INVENTION
 Ultra-hard compacts are used as small cutting or wear elements in various
 shapes, often disks, consisting of a stiff substrate with a (preferably)
 high modulus of elasticity such as cemented carbide. This preferably stiff
 substrate supports an ultra-hard cutting layer typically containing
 diamond or CBN (cubic boron nitride) and possibly other materials such as
 sintering aids, binders, and secondary abrasives. The ultra-hard layer is
 used as the cutting or wear resistant cutting surface, and is typically
 found on the cutting faces of rock drills and other industrial cutting
 tools required to cut or drill through hard, abrasive materials.
 While the above description of an ultra-hard compact is representative of
 commercially available compacts, the composition of the substrate/ultra
 hard layer compact can vary in a manner known to those skilled in the art.
 For example, a substrate may comprise something other than carbide-type
 materials when used in applications that do not demand high loading
 conditions. The ultra-hard layer may comprise multiple layers of different
 composition, or a layer which varies from one side to the other, and may
 be flat or curved or irregular. There may be non-planar interfaces between
 differing materials on the compact interior. In addition, there may be
 chip breakers or special contours on the exterior surfaces. These and
 other known variations will be apparent to those skilled in the art.
 The commercially available geometry and extreme hardness of ultra-hard
 compacts renders them difficult to attach and replace on cutting tools
 such as rock drills. Prior art methods of attachment typically involve
 brazing the substrate onto the tool face, but there are several problems
 inherent in the brazing method of attachment. The part onto which the PCD
 is being brazed needs to be heated with special equipment; brazing skill,
 like welding skill, is variable among operators; certain tools and
 environments do not tolerate the heat involved in the brazing process;
 brazing can cause thermal damage to the PCD compact itself; and, brazed
 ultra-hard compacts are difficult to replace or repair.
 There have been attempts to improve the manner in which hard cutting
 elements are attached to cutting tools. For example, U.S. Pat. No.
 4,694,918 to Hall discloses a PCD compact having a cylindrical portion
 sized for a press-fit into a drill bit or similar tool surface. The
 compacts are embedded in the bit by press-fitting or brazing them into the
 head of the bit.
 U.S. Pat. No. 4,057,884 to Suzuki discloses a tool holder in which a
 cemented carbide type cutting bit has a hole formed through it for
 attachment to a tool with a bolt mechanism. The Suzuki attachment
 structure is designed for a compact with uniform (non-ultra hard) material
 having an angular, lateral cutting edge, rather than a PCD type compact
 with an ultra-hard cutting face.
 U.S. Pat. Nos. 3,136,615 and 3,141,746 mention without explanation the use
 of "mechanical joints" to secure a cutting compact to a tool, for example:
 "mechanical joints also may be employed in the compact oriented in holder
 27 in various arrangements depending on compact configuration" (column 4,
 lines 64-66 of the '746 patent). Also: "The compact is attached to some
 support in various position by soldering or brazing, for example, a
 titanium hydride soldering process as given in U.S. Pat. No. 2,570,428,
 Kelley, or by mechanical attaching means, or by having the tool or
 adjacent metal be forced into the surface irregularities of the compact"
 (column 6, lines 17-23 of the '746 patent).
 U.S. Pat. No. 4,199,035 to Thompson discloses a threaded attachment system
 for mounting a stud- or pin-shaped PCD compact on a drill bit by way of an
 external threaded sleeve mating with a threaded bushing in the drill bit.
 The sleeve holds the compact in place in an interference-type fit as it is
 threaded down into the tool-mounted bushing over the compact. This patent
 additionally discloses a metal locating pin mounted on the tool to slide
 fit into a recess in the lower surface of the stud toward the edge of the
 stud to locate the stud at the proper rotational angle for cutting.
 The above-described prior art has not fully satisfied the need for a
 simple, efficient method for attaching PCD compacts to a tool or other
 support surface. The invention described below solves this problem.
 SUMMARY OF THE INVENTION
 The present invention is an improved mounting arrangement for a PCD
 compact, and in general takes the form of a blind bore formed in the
 relatively softer substrate of the ultra-hard compact, the blind bore
 receiving a mechanical fastening element therein to permanently secure the
 fastening element to the compact. Or the mounting arrangement may take the
 form of a modified protrusion of the substrate, also creating a
 permanently secured fastening element on the compact. The mechanical
 fastening element is designed to be easily attached to a tool or support
 surface. In a preferred form the mechanical fastener is a threaded post
 protruding from the substrate end of the ultra-hard compact to facilitate
 easy mounting and replacement of the compact on the tool face or support
 surface. When mounted, the fastening means is hidden with only the wear
 resistant materials of the ultra-hard compact exposed.
 In an alternate embodiment, the blind bore is formed with an internal
 thread to accept a mechanical fastener in threaded engagement.
 In another alternate embodiment, the external surface of the substrate is
 threaded to provide an integral threaded protrusion to facilitate a
 mechanical means of attaching the ultra-hard compact to a tool or support
 surface.
 In yet another alternate embodiment, a threaded sleeve element is
 permanently attached onto a post-like substrate protrusion, resulting in
 an integral threaded protrusion.
 The above embodiments can further be modified with an ultrahard layer
 extended down and around the substrate to fully enclose and protect the
 portion of the substrate extending above the surface of the tool on which
 it is mounted. In doing so, the mechanical fastener extending from the
 mounting face of the substrate is further protected from wear.

DETAILED DESCRIPTION OF THE DRAWINGS
 FIG. 1 illustrates a typical disk-shaped PCD compact 10 comprising a lower
 substrate layer 12 and an ultra-hard upper layer 14. In the illustrated
 embodiment the substrate layer 12 is formed from conventional cemented
 carbide material with a high modulus of elasticity to provide a very stiff
 body to support the ultra-hard layer 14. The ultra hard layer 14, in turn,
 is formed from a conventional cemented or sintered diamond or CBN
 particulate, and is significantly harder than the substrate to provide a
 durable cutting or wear surface.
 Although the PCD compact 10 in FIG. 1 is illustrated with a flat upper
 surface 15, it will be apparent to those skilled in the art that curved or
 domed-shaped upper surfaces are available, for example as illustrated in
 FIG. 9. Also, it will be apparent to those skilled in the art that
 non-planar interfaces on the interior of the compacts are available, for
 example as illustrated in FIGS. 12 and 13.
 FIG. 2 illustrates the conventional PCD compact 10 of FIG. 1, modified
 according to the present invention so that it can be easily and
 inexpensively secured to a cutting tool or other support surface without
 the need for brazing or other complicated prior art techniques. A blind
 bore 16 is formed in substrate 12 opposite ultra-hard layer 14, blind bore
 16 opening onto the lower surface 12a of the substrate. Blind bore 16
 terminates in substrate 12 at ultra-hard layer 14. In the illustrated
 embodiment blind bore 16 is a cylindrical bore, although other geometries
 such as triangular, rectangular, and tapered bores are possible. Blind
 bore 16 may also terminate in the substrate below ultrahard layer 14, i.e.
 with substrate between the end of the bore and the ultrahard layer.
 Blind bore 16 receives a mechanical fastener 18 permanently secured to the
 PCD compact under normal working conditions. In the illustrated embodiment
 the mechanical fastener 18 is a metal post with an insert end 18a secured
 in the blind bore, and a threaded tool engaging end 18b protruding from
 the PCD compact for attachment to a tool or support surface. Blind bore 16
 is preferably formed in the rotational center of the PCD compact for ease
 in threading post 18 into an aperture on a tool or support surface.
 Once secured in PCD compact 10, post 18 and PCD compact 10 form a solid,
 integral unit carrying its own mechanical fastening structure for simple,
 fast attachment to or removal from a tool. This is a significant
 improvement over the prior art brazing and mechanical attachment methods,
 since it requires no external apparatus or fastening structure; PCD
 compact 10 and post 18 can simply be threaded onto a tool as a
 self-contained unit.
 The invention is also an improvement over the prior art attachment methods
 which require drilling a hole completely through a cutting element. The
 ultra-hard layer 14 on PCD compact 10 does not lend itself to having a
 hole or bore formed therethrough, in part due to its hardness, and such a
 bore would both damage its structural integrity and leave the relatively
 soft mechanical fastener portion exposed on the upper cutting face 15,
 where it would quickly be degraded.
 The invention is also an improvement over structures such as that shown in
 the Thompson patent described above. Thompson requires separate threaded
 insert sleeves and bushings which fit over the PCD compact, suitable only
 for elongated, pin or stud-shaped PCD compacts. The exposed portions of
 Thompson's bushings would quickly erode under normal operating conditions,
 whereas the substrate-mounted fastener 18 on the tool-engaging side of the
 present inventive compact is protected. The present invention also does
 not require anti-rotation or locating structure such as that needed for
 Thompson's externally threaded sleeve fitted over the sides of the
 compact.
 Referring now to FIG. 3, an alternate embodiment of the invention is shown
 in which the fastener post is threaded at both ends 18a, 18b so that it
 can be threadably attached to the PCD compact before attaching the
 integral unit to a tool. In this embodiment blind bore 16 is provided with
 internal threads 16a to accept the threaded insert end 18a of the post 18.
 Referring now to FIG. 4, yet a further embodiment is illustrated in which
 blind bore 16 is formed with at least a portion tapered in cross-section,
 and fastener post 18 is secured to the PCD compact 10 in a swage-fit in
 which its insert end 18a is deformed to fill the tapered region 16b of
 blind bore 16 such that it cannot be removed.
 Referring now to FIG. 5, a typical compact-supporting surface, here a rock
 drill bit tool, is illustrated schematically with a plurality of
 mechanically-mounted PCD compacts according to the embodiments of the
 invention in FIGS. 2 and 3 which can be attached to its cutting surfaces.
 FIG. 5 illustrates the manner in which threaded PCD compacts 10 can be
 threaded into mating apertures 21 formed in the tool to install compacts
 10. The direction of rotation of the threaded coupling between the PCD
 compact 10 and tool 20 can be set to complement the direction of rotation
 of the drill bit or tool so that the PCD compacts are not loosened by the
 cutting action of the tool. Additionally, it is possible to supplement the
 threaded connection between compacts 10 and apertures 21 with known
 techniques such as thread-locking adhesives or washers.
 It will be understood by those skilled in the art that the blind bore 16 in
 the PCD compact substrate can be formed in situ as part of the original
 manufacturing process for the PCD compact. Alternately it can be formed
 afterwards using known methods such as ultrasonic abrasive machining,
 abrasive jet machining, grinding, electrical discharge machining, laser,
 or electrochemical machining.
 It will also be understood by those skilled in the art that the
 configuration of the blind bore 16 in substrate 12 can take forms other
 than the cylindrical bore illustrated in FIGS. 2-4. For example, it can be
 a straight bore with either a smooth or rough finish; it can be a tapered
 bore; it can have a barbed internal surface to assist in swage- or
 interference-fits; or, as described above, it may be a bore with an
 internal thread.
 Securing the mechanical fastener 18 to PCD compact 10 in blind bore 16 can
 be done mechanically, for example by the above-described threaded
 connection, or by swaging or upsetting; thermally, for example by brazing
 or welding as shown in FIG. 2; or, chemically using an adhesive (FIG. 2).
 The present invention is suitable for application in grinding, crushing,
 and milling equipment. This type of equipment is widely used by many
 industries for comminution of ores and various hard, crushable materials.
 The invention lends itself to being incorporated easily into existing
 equipment to strategically place an ultrahard wear resistant element at a
 location that is most prone to wear. The benefits of using the invention
 as described are several-fold. The useful life of equipment would be
 extended which means improved consistency and less downtime. The wear
 elements are field replaceable which reduces maintenance time. Also, the
 ultra-high modulus property of the wear elements lends itself to providing
 an energy savings for a crushing application.
 FIGS. 6 and 7 illustrate the formation of tool-receiving surfaces on PCD
 compact 10 to assist in assembling the threaded post versions of the
 invention to the desired surface. FIG. 6 illustrates wrench flats 12a
 formed on the external surface of the compact. The compact in FIG. 7 is
 provided with spanner wrench holes 12b. Other tool-receiving surfaces are
 possible to accommodate known tools.
 FIG. 8 illustrates yet a further embodiment in which mounting post 18c
 (preferably threaded) is separated from PCD compact 10 for assembly of the
 compact to a tool surface 19, inserted through hole 19a provided for that
 purpose, and subsequently reassembled to bore 16. In this manner the
 mounting post can be conveniently stored with the PCD compact in an
 assembled state, if desired.
 Through-hole mounting as shown in FIG. 8 would be most suitable for
 attaching a PCD compact according to the invention to a tool of relatively
 thin cross section, such as a cutting blade. In through-hole mounting
 applications, having the PCD compact separate from the threaded post
 provides added versatility in mounting. The tool that the PCD is mounted
 to may have a through-hole of any depth. The depth is accommodated simply
 by selecting a fastener of the proper length. In this manner, it is only
 necessary to inventory relatively inexpensive fasteners of varying shank
 length rather than PCD compacts with varying post lengths.
 FIG. 9 illustrates another embodiment which shows a PCD compact 10 with
 non-planar ultra-hard upper layer 14 and a planar upper surface substrate
 12. FIG. 9A illustrates a PCD compact 10' with a non-planar ultra-hard
 upper layer 14 and a non-planar upper surface of the substrate 12.
 FIG. 10 illustrates an embodiment of the invention where the termination
 point of the blind bore 16 and threaded post 18 is in the ultra-hard layer
 14, above the interface plane 17 between layers 12 and 14. Bore 16 extends
 up into, but not all the way through, ultra-hard layer 14. Terminating
 bore 16 in ultra-hard layer 14 provides a deeper hole and creates a
 significantly strengthened attachment of the post 18 to the compact 10.
 FIG. 11 illustrates a PCD type compact 10 where the ultra-hard layer 14
 extends down around the outer circumference of the compact 10. In this
 embodiment the blind bore 16 does not penetrate into the ultra-hard layer
 14, but the lower-most plane 17 of the ultrahard layer is again below the
 termination point of the blind bore 16 and the attachment post 18. When
 the threaded compact assembly of FIG. 11 is mounted on a flat surface,
 only ultra-hard material is exposed and the substrate and fastener are
 fully protected.
 FIGS. 12 and 13 illustrate versions of the invention with a non-planar
 interface 13 between the ultra-hard layer 14 and the substrate 12. FIG. 12
 illustrates a PCD type compact 10 according to the invention with a planar
 ultra-hard upper surface 15 and a non-planar substrate upper surface 13.
 FIG. 13 illustrates a PCD type compact 10 according to the invention with
 a non-planar ultra-hard upper surface 15 and a non-planar substrate upper
 surface. Non-planar substrate upper surfaces 13 can be used to alter the
 wear characteristics of the compact, or can be used to modify the stresses
 in a compact to improve edge impact properties, for instance. Non-planar
 ultra-hard upper surface 15 as shown in FIG. 13 can be used to provide
 certain loading conditions on the compact for a particular application, or
 for chip control of material being removed in a cutting tool application.
 It will be apparent to those skilled in the art that the term "non-planar"
 can cover a very wide range of geometries from simple curves to very
 complex combinations of compound curves, steps, grooves, and pockets.
 FIG. 14 illustrates an alternative threaded mechanical fastener on a PCD
 type compact 10. External threads 22 are formed in an integral extension
 of the material of substrate 12. It will be understood by those skilled in
 the art that the threaded section of the substrate may be formed as part
 of the original manufacturing process for the compact, or alternately may
 be formed afterwards using known methods such as grinding or electrical
 discharge machining, for example. This embodiment of the present invention
 provides a large threaded cross section while maintaining a continuous
 high modulus support under most or all of the ultra-hard layer 14. Also,
 this embodiment creates an installed compact tool with a higher aspect
 ratio. Both of these improved features result in a more robust threaded
 ultrahard tool able to perform under higher load conditions.
 FIG. 15 is another embodiment of the present invention which utilizes an
 integral protrusion 23 of the substrate material 12 onto which external
 threads 22 are secured rather than formed directly in the substrate
 material. A threaded sleeve 24 is permanently attached to the extended
 substrate post 23. The sleeve may be any material, for example steel,
 preferably a material with high tensile strength, and may be permanently
 attached by methods well known in the art such as with adhesives, shrink
 fitting, swaging, welding, or by brazing, for example. Once attached, the
 threaded sleeve 24 becomes an integral part of the compact body 10.
 Applying the threads in this manner provides improved flexibility in
 manufacturing a threaded PCD type compact. A plain post 23 is relatively
 easy to form as an extension of substrate 12, and the softer material of
 threaded sleeve 24 is easy to fabricate as well.
 FIG. 16 is yet another embodiment of the invention as it applies to a PCD
 type compact 10. The substrate 12 and threaded extension 22 are a unified
 high modulus material, preferably cemented tungsten carbide. The
 ultra-hard layer 14 extends down around the perimeter of the compact body
 10 enclosing the substrate material, so that when the compact is installed
 onto a mounting surface, only ultra-hard material 14 is exposed. In this
 embodiment with the large-diameter threaded substrate extension, the
 mounting face of the compact actually comprises ultrahard material 14, as
 indicated at 14a.
 FIG. 17 is a further embodiment illustrating a substrate 12 and threaded
 post 22 of unified material. The threaded post extends up into the
 ultra-hard layer 14. This is an example of forming an in-situ threaded
 post as an integral part of the compact 10. This model is particularly
 well suited for manufacturing ultra-hard compacts whereas the ultra-hard
 particles are molded with the aid of a binder at relatively lower pressure
 and temperature.
 The above improvements over prior art techniques for attaching compacts not
 only simplifies attachment to traditional cutting tools, but opens up
 possibilities for using compacts on non-traditional surfaces, whenever
 ultra-hard cutting elements or ultra-hard wear-resistant surfaces are
 desired.
 It will therefore be understood by those skilled in the art that the
 foregoing illustrative embodiments of my invention are exemplary in
 nature, and are not intended to limit the invention beyond the scope of
 the following claims.