Note: Descriptions are shown in the official language in which they were submitted.
CA 02688549 2009-11-27
ROUNDED CUTTER POCKET HAVING REDUCED
STRESSED CONCENTRATION
RELATED APPLICATIONS
[0001) This application claims priority to and the benefit of co-pending U.S.
Provisional
Application Ser. No. 60/946,300, filed June 26, 2007, the full disclosure of
which is hereby
incorporated by reference herein.
BACKGROUND
1. Field of Invention
[0002) The disclosure herein relates to contoured cutting teeth for use with a
drilling bit.
More specifically, the present disclosure concerns inserts having a spherical
shaped rear
portion disposed in a correspondingly formed pocket, wherein the pocket is
situated on the
cutting surface of a drag bit. The present disclosure also concerns a method
for forming the
pockets on the face of a drill bit.
2. Description of Prior Art
[0003] Earth boring bits for drilling wellbores into subterranean formations
include roller
cone bits and drag bits. The earth boring bits are typically connectable to a
drilling system
via a threaded connection disposed on the bottom portion of the bit. Drag type
bits includes
blades formed on the lower surface of the bit. The blades comprise a raised
portion of
material having a generally rectangular cross-section extending roughly from
the center
portion of the bit surface and radially outward along a side of the bit.
Cutter pockets are
formed on the upper surface of the blade, wherein the respective axes of the
pockets are
generally parallel with other pockets on the individual blade. Typically, the
pockets comprise
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CUTTER POCKET HAVING REDUCED STRESSED
CONCENTRATION
RELATED APPLICATIONS
[0001] This application claims priority to and the benefit of co-pending U.S.
Provisional
Application Ser. No. 60/946,300, filed June 26, 2007, the full disclosure of
which is hereby
incorporated by reference herein.
BACKGROUND
1. Field of Invention
[0002] The disclosure herein relates to contoured cutting teeth for use with a
drilling bit.
More specifically, the present disclosure concerns inserts having a spherical
shaped rear
portion disposed in a correspondingly formed pocket, wherein the pocket is
situated on the
cutting surface of a drag bit. The present disclosure also concerns a method
for forming the
pockets on the face of a drill bit.
2. Description of Prior Art
[0003] Earth boring bits for drilling wellbores into subterranean formations
include roller
cone bits and drag bits. The earth boring bits are typically connectable to a
drilling system
via a threaded connection disposed on the bottom portion of the bit. Drag type
bits includes
blades formed on the lower surface of the bit. The blades comprise a raised
portion of
material having a generally rectangular cross-section extending roughly from
the center
portion of the bit surface and radially outward along a side of the bit.
Cutter pockets are
formed on the upper surface of the blade, wherein the respective axes of the
pockets are
generally parallel with other pockets on the individual blade. Typically, the
pockets comprise
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a hollowed out trough portion of the upper surface of the blade, wherein the
pockets are
formed to receive a cutting element therein.
[0004] The cutting elements can be attached in any number of ways, such as
welding and
brazing or other attachment means. The cutting element has a generally
cylindrical shape
with a cutting face on one end and planar on its other end. It is well known
in the prior art to
add polycrystalline diamond compact, i.e., PDC, on the face of the cutting
element. The
cutting element body is typically formed of a relatively hard material such as
sintered
tungsten carbide. The PDC layer may be mounted directly on the mounting body
or on an
intermediate carrier also generally made from a sintered tungsten carbide.
[0005] The bit body is usually comprised of either a tungsten carbide matrix
or various
forms of steel. Drilling systems typically utilize the weight on bit to press
down into the rock
that combined with the torque crushes the rock which causes the drilling
action. Continued
turning of the drill string pushes the teeth through the rock by the combined
forces of the
weight on bit and the torque.
[0006] Known displacements have planar ends that form cutter pockets with
corresponding flat bottoms. During use of bit bodies having flat bottom cutter
pockets, the
geometry produces high stresses in the bit body adjacent the cutter pocket
bottom. The high
stresses can initiate cracking in the bit body thereby reducing bit life.
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SUMMARY OF INNENTION
[0007] Disclosed herein is a drag bit and a method for creating a drag bit. In
one
embodiment, the drag bit comprises a blade on its cutting face, with a series
of pockets on the
blade formed using displacements. In one embodiment, the displacement
comprises an insert
on one end with removable displacement material on the other. The insert end
opposite the
displacement is rounded and oriented to be at the cutter pocket bottom while
forming the bit..
The insert and displacement converge at a planar surface. After the
displacement material is
removed from the insert, a cutting element may be attached to the end of the
insert.
Optionally, the displacement may comprise only removable displacement material
with one
or more rounded ends. A method is included herein for forming the pockets on
the blade of
the drag bit. The method involves forming the cutter pocket with the
displacement having an
insert with a rounded shaped end to form a rounded cutter pocket bottom,
cleaning the
removable portion of the displacement, and adding a cutting element to the end
of the insert.
Optionally, a method is disclosed wherein a fully removable displacement is
used to form a
cutter pocket with a rounded bottom. After casting a bit body using the
displacement, the
displacement(s) can be removed and a cutting element having a rounded bottom
corresponding to the cutter pocket bottom can be affixed in the cutting
pocket.
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BRIEF DESCRIPTION OF DRAWINGS
[00081 Some of the features and benefits of the present invention having been
stated,
others will become apparent as the description proceeds when taken in
conjunction with the
accompanying drawings, in which:
[0009] Figure 1 is a bottom view of a drill bit shown during the formation
process.
[0010] Figure 2 is a side view of an example of a displacement for forming a
cutter
pocket.
[0011] Figure 3 is a side view of a displacement for forming a cutter pocket
having an
insert on one end.
[0012] Figure 4 is a partial cutaway view of a displacement forming a cutter
pocket
having an insert.
[0013] Figure 5 is a partial cutaway view of a cutting element comprising an
insert on one
end.
[0014] Figure 6 is a partial sectional view of a displacement in a bit body
having an
elliptical end.
[0015] Figure 7 is a partial sectional view of a displacement in a bit body
having an
elliptical end.
[0016] Figure 8 is a partial sectional view of a displacement in a bit body
having a frusto-
conical end.
[0017] Figure 9 is a partial sectional view of an example of a drilling system
employing a
drill bit having a cutter pocket with a rounded bottom.
[0018] Figure 10 is a partial cutaway view of a cutting element with a rounded
end in a bit
body.
[0019] While the invention will be described in connection with the preferred
embodiments, it will be understood that it is not intended to limit the
invention to that
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embodiment. On the contrary, it is intended to cover all altematives,
modifications, and
equivalents, as may be included within the spirit and scope of the invention
as defined by the
appended claims.
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DETAILED DESCRIPTION OF INVENTION
[0020] The present invention will now be described more fully hereinafter with
reference
to the accompanying drawings in which embodiments of the invention are shown.
This
invention may, however, be embodied in many different forms and should not be
construed
as limited to the illustrated embodiments set forth herein; rather, these
embodiments are
provided so that this disclosure will be through and complete, and will fully
convey the scope
of the invention to those skilled in the art. Like numbers refer to like
elements throughout.
[00211 It is to be understood that the invention is not limited to the exact
details of
construction, operation, exact materials, or embodiments shown and described,
as
modifications and equivalents will be apparent to one skilled in the art. In
the drawings and
specification, there have been disclosed illustrative embodiments of the
invention and,
although specific terms are employed, they are used in a generic and
descriptive sense only
and not for the purpose of limitation. Accordingly, the invention is therefore
to be limited
only by the scope of the appended claims.
[0022] Disclosed herein is a device and method regarding forming cutter
pockets and
cutting elements of a drag bit. In one embodiment, a cutter pocket is formed
using a
displacement comprising removable displacement material and a non-removal
insert having a
rounded end. The displacement is oriented within a bit body casting form so
when the bit
body is formed, the rounded ended of the insert is integral within the bit
body with the
removable displacement between the insert and the bit outer surface. After
removing the
displacement material from the insert a cutting element can be attached to the
insert's free
end. Another way to form a rounded cutter element to bit body interface is to
form a bit body
using a rounded end displacement, wherein the entire displacement comprises
removable
material. In one embodiment, the cutter element(s) to bit body interface
describes the contact
surface between the cutter element and the bit body. The cutter element(s)/bit
body interface
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also describes the forces and/or force distributions transferred between the
cutter element(s)
and the bit body. The interface can describe a single cutting element and bit
body, a plurality
of cutting elements and the bit body, or all cutting elements and the bit
body. After casting
the bit and then cleaning the displacement from the cutter pocket, a cutting
element with a
correspondingly rounded bottom can be affixed in the rounded bottom cutter
pocket. One of
the advantages of having a rounded cutter element to bit body interface is the
forces
experienced by the cutting element during cutting are transferred to the bit
body through the
insert (or cutter element) rounded end. A rounded interface has a greater area
than traditional
planar or flat bit body/cutting element interfaces, thus stresses imparted by
the cutting
element to the bit body are more evenly distributed throughout the bit body.
More even
stress distribution thereby minimizes stress concentrations in the bit body.
Additionally, the
improvement disclosed herein removes sharp comers in the cutter pocket rear
portion. In
contrast, some diamond fixed cutter bits have experienced primary cutter
pocket cracking,
especially for the cutters located proximate to the bit axis. These cracks
initiate from the
joint of the cutter pocket seat and propagate down towards the nozzle and/or
front blade root.
[0023] Figure 1 illustrates a bottom view of an example of a bit body 10 being
formed in
accordance with the present disclosure. In this embodiment, the bit body 10
comprises a
series of blades 12 formed on the bit face 14, wherein the blades 12 radially
extend outward
from the center towards the outer radius of the bit face 14. Cutter pockets 13
are generally
formed along the upper or outer edge of the blade for receiving cutting
elements within the
pockets. Displacements may be used in forming these cutter pockets by
positioning the
displacements inside a form as the bit body is being cast. One example of this
novel process
is provided in Figure 1 where displacements 16 were situated in a casting form
before bit
body raw materials were added. The displacements 16 were kept in place in the
casting form
during the casting process and integrated with the bit body 10. Examples of
bit body raw
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materials include a hard material, such as tungsten or tungsten carbide, and
binder
constituents. Binder constituents include copper, nickel, other soft metals,
and combinations
thereof. Processing the bit body raw materials within the casting form may
comprise heating
to soften and/or melt the binder enabling the softened binder material to
migrate within the
hard material, and when cooled will bind the hard materials together. However
the scope of
the present disclosure is not limited to a high temperature forming process,
but instead other
processing methods can be employed with the forming method described herein,
such as a
high pressure forming process, or a combination of increased pressure and
increased
temperature.
[0024] In one embodiment, the displacements 16 in Figure 1 comprise a material
that
retains its shape during the bit casting process, but are removable and can be
cleaned away
after the bit body 10 is removed from the form. Examples of materials for the
displacements
16 include generally, graphite silicon carbide, refractory materials,
compressed particulate
matter, combinations thereof, and similar substances. Sand blasting is one
example method
that can be employed for cleaning displacement material from within the cutter
pocket 13.
Accordingly the displacement(s) 16 may optionally comprise erodible materials
removable
with some applied impact, such as by particles (for example sand), water, air,
or any other
stream comprising matter directed at the displacement. In this embodiment, one
end of the
displacement 16 is shown protruding away from the cutter face. The rearward
end, or the
displacement rear portion 18 (forming the cutter pocket 13) is shown in a
dashed outline on
the blade face 12. Optionally, use of the stress minimizing cutter pockets can
be limited to
the portions of the bit face having cutters exposed to localized high
stresses.
[0025) Figure 2 provides a side view of an embodiment of a displacement 24
such as used
to form a cutter pocket 13 in the bit body 10 of Figure 1. The displacement 24
comprises a
rear section 26, a front section 28, and an indicator groove 30. A groove 30,
formed
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proximate to the front 28 circumscribes the displacement 24 outer periphery.
The
displacement 24 rear section 26 is rounded for forming a shaped cutter pocket
with a rounded
bottom. Optionally, the rear section 26 of this displacement 24 may be hemi-
spherical, oval,
or have any radial shape, with or without tapers. Examples of displacements 24
having an
end with an elliptical shape are provided in a side partial sectional view in
Figures 6 and 7.
An example of displacements 24 having an end with a frusto-conical shape is
provided in a
side partial sectional view in Figure 8. In other embodiments, the front
section 28 may be
flat, elliptical, chamfered, or have a chisel shape. The present method also
includes orienting
a displacement having a rounded end within a bit body casting form so the
rounded end is
used to shape the bottom end 15 of a cutter pocket 13. The optional groove 30
is formed to
indicate displacement position and to allow manufacturing personnel to
properly align
displacements 24 with the face of the blade 14. Optionally, the cutter can be
formed as a uni-
body assembly having a rounded rear portion, in this embodiment the cutter
would not have
an added insert.
[0026] Figure 3 provides a side view of an alternative displacement 42
embodiment. The
displacement 42 of Figure 3 comprises an insert 46 rounded on its free or
bottom end (i.e. the
end inserted into a rounded bottom cutter pocket 13). The displacement 42
further includes a
cylindrically shaped mid section 45 attached to the insert 46. A front section
44 is shown on
the mid section 45 opposite the insert 46. The mid section 45 and front
section 44 may
comprise above described displacement material such as graphite or silicon
carbide. The
insert 46 may be glued to the mid section 45 prior to being placed in the
mold. Forming a bit
body 10 with the displacement 42 of Figure 3 includes removing the front
portion 44 and mid
section 45 after the casting process. The step of removing may include the
displacement
cleaning/removal method as described above. Removing the mid section 45 leaves
the insert
46 within the cutter pocket 13. As discussed below and illustrated in Figure
5, a cutter
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element having a rounded end and a cutter face can be affixed to the insert 46
within the
cutter pocket. Typical methods of adhering cutter elements in formed pockets
exist, such as
welding, brazing and possibly gluing. Accordingly, using the insert 46 results
in cutter forces
being more evenly distributed from the cutter element to the cutter blades 12
and bit 10. The
insert 46 may comprise mild carbon steel, such as 1018 carbon steel, tungsten
carbide, alloys,
sintered tungsten carbide, low carbon alloy steels, or combinations thereof.
Cutter pockets
formed using displacements 42 that comprise an insert 46 may optionally be
described as
extending from the flat or planar surface of the insert 46 to the cutter
pocket opening on the
bit body surface. When described in this fashion, the insert 46 would not be
in the cutter
pocket and the cutter pocket would have a flat bottom defined by the insert 46
upper surface.
Optionally, the cutter pocket can be described as extending to the rounded
interface between
the insert 46 and bit body 12, thus the insert 46 would be in the bottom of
the cutter pocket.
Irrespective of how a cutter pocket is described, inserts 46 having a rounded
end provide a
rounded cutting element to bit body interface.
[0027] Figure 4 illustrates a side partial sectional view of the displacement
42 of Figure 3
disposed in a bit body 12 cutter pocket 13. This illustrates an example of a
displacement 42
combined with the bit body 12 during the casting process. The front portion 44
is removable,
such as by using the above described process, thereby leaving the insert 46
within the pocket
13. The cutter pocket bottom 15 rounded configuration with the correspondingly
contoured
insert 46 forms a rounded cutter element to bit body interface to better
distribute bit body 12
stress than the traditional flat or planar cutter element to bit body
interfaces. Unlike the bit
bodies having high stress concentrations from flat bottom cutting elements;
earth boring bit
bodies formed using the displacements (24, 42) described herein will
experience a
substantially equal cutter element to bit body stress distribution. Reducing
stress
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concentration in the bit body reduces a likelihood of crack initiation and/or
crack growth,
thereby increasing useful bit life.
[0028] After removing the front portion 44 of Figure 4, a cutting element 35
may be
secured onto the insert 46. One example is provided in Figure 5 that
illustrates a side view of
the cutting element 35 comprising a cutter body 36 secured to the insert 46
within the cutter
pocket 13. Here the cutting element 35 is attached to the insert 46 within the
cutter pocket 13
created by the mid section 45 (Figure 4) and includes a cutter tip 38 on its
outwardly facing
surface. As is known, the cutter tip 38 may be a polycrystalline diamond
compact (PDC) and
include hard or super hard materials.
[0029] With regard to the displacement 24 shown in Figure 2, after forming a
bit body 10
using a casting process, then blast removing the displacement material, a
cutting element 31
(Figure 10) having a rounded bottom 32 and a cutting tip 33 is illustrated
attached in the
rounded bottom pocket 13. Brazing or some other means of attachment can be
employed for
securing the cutting element 31 within the pocket 13.
[0030] Figure 9 illustrates an embodiment of a drilling system 50 comprising
the bit body
having a cutter pocket 13 with a rounded bottom. Here the bit body 10 is
deployed on a
drill string 52 and connected to a top drive 58 for rotating the drill string
52 and bit 10.
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