U.S. patent application number 10/546541 was filed with the patent office on 2007-01-25 for secondary cutting element for drill bit.
Invention is credited to Roy Derrick Achilles, Imraan Parker, Klaus Tank.
Application Number | 20070017710 10/546541 |
Document ID | / |
Family ID | 32928214 |
Filed Date | 2007-01-25 |
United States Patent
Application |
20070017710 |
Kind Code |
A1 |
Achilles; Roy Derrick ; et
al. |
January 25, 2007 |
Secondary cutting element for drill bit
Abstract
A rotary drag bit comprises a bit body and a plurality of blades
extending radially away from the bit body, each blade including a
cutting assembly. Each cutting assembly has a plurality of primary
cutters orientated in the direction of rotation of the drill bit
for drilling or boring into a subterranean rock formation, and a
plurality of secondary or brute cutters located behind the primary
cutters in relation to the direction of rotation of the drag bit.
The invention is concerned primarily with the secondary cutters,
which comprise a layer of superabrasive material, such as PCD, PCBN
or CVD diamond, bonded to a support substrate. The interface
between the superabrasive layer and the substrate has a stepped
region that provides the cutter with a skirt or hoop of
superabrasive extending into the substrate. The secondary cutter is
orientated in use to present a bearing surface to the rock
formation and a secondary cutting edge in the direction of rotation
of the rotary bit.
Inventors: |
Achilles; Roy Derrick;
(Bedfordview, ZA) ; Tank; Klaus; (Johannesburg,
ZA) ; Parker; Imraan; (Cape Town, ZA) |
Correspondence
Address: |
SEYFARTH SHAW LLP
131 S. DEARBORN ST., SUITE2400
CHICAGO
IL
60603-5803
US
|
Family ID: |
32928214 |
Appl. No.: |
10/546541 |
Filed: |
February 24, 2004 |
PCT Filed: |
February 24, 2004 |
PCT NO: |
PCT/IB04/00472 |
371 Date: |
October 17, 2006 |
Current U.S.
Class: |
175/432 |
Current CPC
Class: |
E21B 10/43 20130101;
E21B 10/5735 20130101 |
Class at
Publication: |
175/432 |
International
Class: |
E21B 10/46 20070101
E21B010/46 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 26, 2003 |
ZA |
2003/1571 |
Claims
1. A rotary drag bit comprising: a bit body; a plurality of blades
extending radially away from the bit body, each blade including a
cutting assembly; each cutting assembly having a plurality of
primary cutters orientated in the direction of rotation of the
drill bit for drilling or boring into a subterranean rock
formation, and a plurality of secondary cutters located behind the
primary cutters in relation to the direction of rotation of the
drag bit; and one or more of the secondary cutters comprising a
layer of superabrasive material bonded to a support substrate: the
superabrasive layer having a major bearing surface on one side
thereof and a major interface with the substrate on an opposite
side thereof, the interface defining a stepped region in the
peripheral zone of the cutter providing the cutter with a skirt or
hoop of superabrasive extending into the substrate, the or each
secondary cutter being orientated in use to present the bearing
surface to the rock formation and the secondary cutting edge in the
direction of rotation of the rotary bit.
2. A bit according to claim 1, wherein the interface has a central
table or surface which is profiled.
3. A bit according to claim 2, wherein the profile of the table or
surface is a series of concentric rings, a plurality of dimples, or
a cross-hatch structure.
4. A bit according to claim 1 wherein the table defines a periphery
and base that are each generally rounded such that the interface in
the region of the hoop or skirt is one which generally has no
discontinuities.
5. A bit according to claim 1, wherein the superabrasive material
is PCD, PCBN or CVD diamond.
6. A bit according to claim 5, wherein the superabrasive material
is PCD, the PCD comprising at least 25 percent by mass of
ultra-hard abrasive particles having an average particle size in
the range 10 to 100 microns and consisting of particles having at
least three different average particle sizes and at least 4 percent
by mass ultra-hard abrasive particles having an average particle
size of less than 10 microns.
7. A tool component in the form of a secondary cutter as defined in
claim 1 for a drill bit.
8. (canceled)
9. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] THIS invention relates to a drill bit for use in drilling or
boring into subterranean rock formations, and to a tool component
therefor.
[0002] Rotary drag bits or fixed cutter bits are well known drill
bits extensively used in subterranean rock drilling and boring
operations. They typically consist of a bit body including a first
end for connecting the body to a drill string and a second working
end having a number of blades extending radially from the bit body,
each blade carrying a cutting assembly for boring through the rock
formation. The cutting assemblies each include a number of primary
polycrystalline diamond compacts or cutting elements which provide
for boring or drilling into the subterranean rock formation upon
rotation of the drill bit.
[0003] The drill bits also include so-called secondary cutters
which are generally located behind the primary fixed cutters in
critical wear areas on the drill bit wing location. They perform
two basic functions. They protect the bit by providing a bearing
surface in the event of the loss of a primary cutter, thus
minimising the load transfer to following cutters and hence
preventing a domino effect of cutter fracture or ring out. The
secondary cutters also act as cutting elements in the event of the
loss of a primary cutter. In view of these two basic functions, the
secondary cutters are required to provide for high bearing forces
and resistance to thermal induced cracking as well as resistance to
high shear forces when acting as a cutting element. As a result of
these non-complementary functions, conventional secondary cutters
tend to be compromised in either one or both of these
requirements.
SUMMARY OF THE INVENTION
[0004] According to a first aspect of the invention, a rotary drag
bit comprises: [0005] a bit body; [0006] a plurality of blades
extending radially away from the bit body, each blade including a
cutting assembly; [0007] each cutting assembly having a plurality
of primary cutters orientated in the direction of rotation of the
drill bit for drilling or boring into a subterranean rock
formation, and a plurality of secondary cutters located behind the
primary cutters in relation to the direction of rotation of the
drag bit; and [0008] one or more of the secondary cutters
comprising a layer of superabrasive material bonded to a support
substrate: [0009] the superabrasive layer having a major bearing
surface on one side thereof and a major interface with the
substrate on an opposite side thereof, [0010] the interface
defining a stepped region in the peripheral zone of the cutter
providing the cutter with a skirt or hoop of superabrasive
extending into the substrate,
[0011] the or each secondary cutter being orientated in use to
present the bearing surface to the rock formation and the secondary
cutting edge in the direction of rotation of the rotary bit.
[0012] The interface preferably has a central table or surface
which is profiled.
[0013] The profile of the table or surface is preferably a series
of concentric rings, a plurality of dimples, or a cross-hatch
structure.
[0014] The periphery and base of the table are generally rounded
such that the interface in the region of the hoop or skirt is one
which generally has no discontinuities.
[0015] The superabrasive material may be PCD, PCBN or CVD diamond.
When the superabrasive material is PCD, it preferably comprises at
least 25 percent by mass of ultra-hard abrasive particles having an
average particle size in the range 10 to 100 microns and consisting
of particles having at least three different average particle sizes
and at least 4 percent by mass ultra-hard abrasive particles having
an average particle size of less than 10 microns.
[0016] The invention extends to a tool component as defined above
for use as a secondary cutter in a drill bit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The invention will now be described in more detail, by way
of example only, with reference to the accompanying drawings in
which:
[0018] FIG. 1 is a perspective view of a drill bit of the
invention;
[0019] FIG. 2 is a cross sectional side view of a tool component of
the invention for use in the drill bit of FIG. 1;
[0020] FIG. 3a is a perspective view of a first embodiment of a
substrate forming part of the tool component of FIG. 2;
[0021] FIG. 3b is a cross sectional side view of the substrate of
FIG. 3a;
[0022] FIG. 4a is a perspective view of a second embodiment of a
substrate forming part of the tool component of FIG. 2;
[0023] FIG. 4b is a cross sectional side view of the substrate of
FIG. 4a;
[0024] FIG. 5a is a perspective view of a third embodiment of a
substrate forming part of the tool component of FIG. 2; and
[0025] FIG. 5b is a cross sectional side view of the substrate of
FIG. 5a.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0026] Referring to FIG. 1 of the accompanying drawings, a rotary
drag bit or fixed bit cutter 10 consists of a bit body 12 having a
working end 14 including a number of blades 16 extending radially
from the central portion 18. Each blade 16 carries a row of primary
cutters 20 orientated in the direction of rotation of the drill bit
for drilling or boring into a subterranean rock formation. Each
blade 16 also includes a row of secondary cutters 22 which are
orientated generally normal to the axis of rotation of the drill
bit.
[0027] The present invention is primarily concerned with the
secondary cutters 22. Accordingly, referring to FIG. 2 of the
invention, a secondary cutter 22 of the invention consists of a
layer of superabrasive material 32 bonded to a support substrate
34. The superabrasive layer 32, which in this case is formed of
polycrystalline diamond, has a first or upper bearing surface 36
and a second or lower interface surface 38. The upper surface 36
includes a peripheral edge 40 which provides a secondary cutting
edge for the bit in use. The lower surface 38 is bonded to the
support surface 42 of the substrate 34 to form an interfacial
region 46. The superabrasive layer 32 includes a recess 48 for
receiving a complementary projection or central table 50 extending
from the substrate 34. As a consequence of the recess 48, a hoop or
skirt of polycrystalline diamond 52 surrounds the table 50. The
periphery 54 and base 56 of the table are rounded. As a result the
interface in the region of the hoop or skirt 52 has no
discontinuities. The support substrate material will typically be
of a cemented carbide, in particular tungsten carbide.
[0028] In the cutting mode of the bit 10, the secondary cutter 22
is designed to prevent failures due to high shear forces. This is
achieved by reducing the tensile axial residual stress that occurs
at the periphery of the cutter close to the PCD / substrate
interfacial region 46. As a result of the continuous uninterrupted
hoop or skirt 52, the axial stresses are also minimised over the
entire periphery of the superabrasive layer 32. Further, as a
result of the recessed PCD layer, the surface area of the support
surface 42 is increased, providing for greater load bearing
capabilities in use.
[0029] A common problem associated with primary cutters of the type
having a PCD layer bonded to a substrate is that they are prone to
interfacial failures, and much focus has been placed upon designing
primary cutters to reduce these interfacial failures. When the
secondary cutters of the invention are forced into a cutting role,
typically as a result of the failure of a primary cutter, these
interfacial failures are also of concern. In view thereof, the
preferred brute cutter of the invention provides for a so-called
textured or profiled interface between the substrate and the PCD
layer.
[0030] A number of designs for providing a greater mechanical
interlocking between the PCD layer and the substrate are shown in
FIGS. 3, 4 and 5.
[0031] Referring to FIGS. 3a and 3b, a substrate 60 has an upper
surface 62 which is checkered or cross hatched. As a result of this
profiling or texturing of the surface 62, a greater surface area is
provided than would be the case for a planar surface. When forming
the secondary cutter in a high temperature / high pressure
operation, the lower surface of the superabrasive layer (not shown)
forms a complementary interface surface. This arrangement provides
a mechanical interlocking between the superabrasive layer and the
substrate.
[0032] Referring to FIGS. 4a and 4b, the substrate 70 in this case
includes an upper surface 72 having a plurality of concentrically
grooved rings 74. Once again, in producing the compact, the
superabrasive layer forms a complementary interface to provide the
mechanical interlocking described above.
[0033] Referring to FIGS. 5a and 5b, the substrate 80 in this
embodiment has an upper surface 82 including a number of dimples 84
in a square raster formation.
[0034] As a result of the greater surface area of the substrate and
the mechanical interlocking afforded by the abovementioned designs,
greater resistance to interfacial failures is provided.
[0035] Of major concern in using a secondary cutter in a bearing
mode are thermally induced radial cracks. Accordingly, pronounced
bar like features are avoided in the substrate designs above as
these may exacerbate the hoop stress in the PCD layer as a result
of too strong a mechanical interlocking effect.
[0036] A further concern in relation to a secondary cutter of the
invention relates to the rate of recession of the bearing surface
relative to the wear of the primary cutter. Ideally, the bearing
surface must wear at the same rate or slightly faster than the
primary cutter in order not to inhibit the primary cutter function.
Balancing the rate of recession of the bearing surface with the
peak wear of the primary cutter can be achieved in two ways. This
can be achieved by balancing the wear resistance of the PCD layer
or by balancing the area of the bearing surface. In view of this
requirement, it has been found that a secondary cutter with a
Quadmodal superabrasive layer is preferred, particularly where the
primary cutter is a cutter with a multimodal (with an average
particle size of about 10 .mu.m) / Quadmodal (multimodal material
with an average particle size of about 25 .mu.m) layer, or other
multi-layer, multimodal configuration. Quadmodal superabrasives are
disclosed in SA 94/3645, which is incorporated herein by reference.
In general, a quadmodal abrasive comprises at least 25 percent by
mass of ultra-hard abrasive particles having an average particle
size in the range 10 to 100 microns and consisting of particles
having at least three different average particle sizes and at least
4 percent by mass ultra-hard abrasive particles having an average
particle size of less than 10 microns. Using a Quadmodal layer for
the secondary cutter is also advantageous due to the proven record
thereof in terms of impact resistance. However, if such a layer is
still too wear resistant, a courser multimodal material could be
used, for example a multimbdal material having an average particle
size of about 35 .mu.m to about 40 .mu.m.
* * * * *