Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Flat and Bevel Chipbreaker Insert
BACKGROUND OF THE INVENTION
Field of the Invention - This invention is in the field of tools used
downhole,
in oil or gas wells, to mill or otherwise cut metal objects in the borehole.
Background Art - In the drilling, completion, or re-work of an oil or gas
well,
it often becomes necessary to cut into or through a metal object which is
located
downhole in the well bore. This can be required, for instance, in cutting
through the
wall of a well casing, removing a packer, or milling away some other metal
obstruction which may be present in the borehole. This type of cutting or
milling
operation is very different from the type of metal cutting operations
typically found in
a machine shop environment. The downhole metal cutting operation involves the
rotation of a very large tool by a very heavy workstring, by comparison with
the
typical machine shop operation. The downhole cutting operation itself involves
a
great deal of vibration and even severe impact, between the cutting tool and
the metal
object being cut. In fact, much of the force of any such impact or vibration
is typically
brought to bear directly on the cutting insert or inserts which are mounted on
the-
cutting face of the downhole cutting tool. These cutting inserts are
essentially the
"teeth" of the cutting tool. They are typically made of a very hard material,
such as
tungsten carbide.
The operator can not closely observe the downhole cutting operation and
monitor the condition of the cutting insert or inserts. By contrast, the
machine shop
operator can closely observe the cutting operation as it progresses, and he
can change
the cutting insert regularly as its cutting surfaces degrade. Stopping the
operation in
the machine shop is typically significantly cheaper than pulling a downhole
tool from
the well bore and checking or changing the tool out. This means that the
typical
machine shop operation is always done with a basically fresh cutting insert in
good
condition.
The downhole operator, on the other hand, must simply rotate the workstring
and rely upon fairly remote indicators of the performance of the tool, such as
vibration
and rate of penetration, to judge the progress of the cutting operation. As a
result, as
the cutting operation continues, the cutting insert on the face of the cutting
tool
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usually wears away and disintegrates. It is common, in fact, to have multiple
cutting
inserts on a downhole cutting tool, with the inserts being arranged
progressively
across the cutting face of the tool. This is done so that, as each cutting
insert wears
away and disintegrates or falls off the tool, another adjacent cutting insert
establishes
contact with the work piece, thereby continuing the cutting action. This
alleviates the
need to pull the work string and replace the tool, or at least delays the
necessity of
replacing the tool.
An unfortunate aspect of this situation is that each cutting insert must
remain
effective in spite of having its original cutting geometry drastically changed
as the
cutting operation progresses; that is, the insert will not retain its original
cutting edge
for very long. If the cutting insert wears to such an extent that the cutting
edge is
gone, the portion of the insert contacting the work piece can act as a bearing
surface.
If the cutting insert can not cut effectively after having its original
cutting edge worn
away, the insert will not be an effective part of the tool, arid it can even
impede the
action of nearby cutting inserts, by acting as a bearing surface, rather than
as a cutting
surface.
It is also known to provide a chip breaking feature on the forward face of a
cutting insert for use in the downhole environment, which causes the insert to
break
off metal chips from the work piece at short lengths, allowing the chips to be
more
easily removed from the well bore by the flow of drilling fluid. So, as wear
progresses across the insert face, through the chip breaking feature, the
insert might
cease to break off short chips and begin to produce long, thin metal turnings.
The
long thin turnings are not easily removed from the well bore by the flow of
fluid, so
this type of insert wear can lead to the clogging of the area around the
cutting tool,
preventing further penetration of the work piece. Further, if the chip
breaking feature
contributes in any way to the fragility of the insert body, it can cause the
insert to
disintegrate prematurely and fall off the cutting tool, resulting in. a
complete loss of
the ability to cut, until the tool body wears sufficiently to allow the
adjacent cutting
insert to come into play.
It is desirable to have, therefore, a cutting insert which is sufficiently
robust to
.withstand the impacts experienced in the downhole environment, and which is
designed to break off short metal chips from the work piece, and to continue
to
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present an effective cutting geometry to the work piece, even as the original
cutting
geometry of the insert gradually wears away.
BRIEF SUMMARY OF THE INVENTION
The present invention, in summary, is a downhole cutting insert which has one
or more lands on its cutting face, interspersed with one or more beveled
surfaces,
creating a robust cutting face on the insert. The juxtaposition of bevels with
lands
causes the insert to break off metal chips from the work piece at short
lengths,
allowing the chips to be more easily removed from the well bore by the flow of
drilling fluid. Use of alternating multiple bevels and lands allows the
insert, to
continue to effectively form short metal chips, even as the forward face and
the edge
of the insert gradually degrade.
The novel features of this invention, as well as the invention itself, will be
best
understood from the attached drawings, taken along with the following
description, in
which similar reference characters refer to similar parts, and in which:
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
Figure 1 is an elevation view of a downhole cutting tool which can incorporate
a cutting insert according to the present invention;
Figure 2 is a top or front elevation view of a first embodiment of a cutting
insert according to the present invention;
Figure 3 is a top or front elevation view of a second embodiment of a cutting
insert according to the present invention;
Figure 4 is a partial axial section view of a third embodiment of a cutting
insert according to the present invention;
Figure 5 is a partial axial section view of a.fourth embodiment of a cutting
insert according to the present invention;
Figure 6 is a partial axial section view of the cutting insert shown in Figure
2
or Figure 3; and
Figure 7 is a partial axial section view of a fifth embodiment of a cutting
insert
according to the present invention.
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DETAILED DESCRIPTION OF THE INVENTION
As illustrated in Figure 1, a cutting insert according to the present
invention
can be mounted on a cutting tool 10 designed for use in cutting metal objects
downhole, in an oil or gas well. The cutting tool 10 can be a pilot mill, junk
mill,
casing cutter, window mill, or any other type of downhole cutting tool. The
cutting
tool 10 has a tool body 12, which is adapted to mount to a work string WS. The
tool
body 12 has at least one cutting feature, such as the blades 14, attached
thereto or
formed thereon. Each cutting feature or blade 14 has at least one cutting
insert 20
mounted on a cutting face 16 thereof, and oriented to face in the direction 18
in which
the blades 14 and the cutting inserts 20 will advance when the cutting tool 10
is
rotated. Advancement in the direction 18 will cause the cutting inserts 20 to
advance
toward and into the downhole metal object or work piece (not shown).
The cutting inserts 20 can take various shapes, some of which will be
designated as 20, 2,0A and 20B in the Figures discussed below. Other shapes
can also
be used without departing from the spirit of the present invention, as long as
they
exhibit the features described below. Figure 2 shows the forward or front
elevation of
a round or cylindrical cutting insert 20A, oriented in the drawing the same as
the
orientation of the cutting inserts 20 on the right hand blade 14 in Figure 1.
Where a
round or cylindrical insert is discussed herein, it should be understood that
a half
round or otherwise pa~.-tially round insert can also be intended, where the
context
allows. The cutting insert 20A has at least one land 22A and at least one
bevel or
beveled surface 24A, with a first land 22A being located immediately next to
the
original leading edge 28A of the cutting insert 20A. Where present, successive
lands
22A and bevels 24A are alternatingly arranged from the leading edge 28A toward
the
axis A of the cutting insert 20A. The cutting insert 20A is shown with three
lands
22A and. three bevels 24A, but it can have any number of each. The cutting
insert
20A can also have a surface 26A substantially orthogonal to the axis A, on the
front
face of the insert 20A.
As illustrated in Figure 3, the cutting insert 20 can also have a rectilinear
shaped body, such as the insert 20B. The cutting insert 20B is shown oriented
in the
drawing the same as the orientation of the cutting inserts 20 on the right
hand blade 14
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in Figure 1. Where a rectilinear insert is discussed herein, it should be
understood that
a square or otherwise rectangular insert can be intended. The cutting insert
20B has at
least one land 22B and at least one bevel or beveled surface 24B, with a first
land 22B
being located immediately next to the original leading edge 28B of the cutting
insert
20B. Where present, successive lands 22B and bevels 24B are alternatingly
arranged
from the leading edge 28B toward the axis of the cutting insert 20B. The
cutting
insert 20B is shown with three lands 22B and three bevels 24B, but it can have
any
number of each. The cutting insert 20B can also have a surface 26B
substantially
orthogonal to the axis, on the front face of the insert 20B.
Figure 4 shows the most basic illustration of the features of the lands 22 and
bevels 24 on the inserts 20 shown in Figures 2 and 3, or on any insert 20
according to
the present invention. The insert 20 has a solid body. Each land 22 is a
substantially
flat surface which is substantially orthogonal to the axis of the cutting
insert 20. Each
land can be, more specifically, angled between approximately 75 degrees and
approximately 90 degrees relative to the insert axis. It can be seen that, on
the round
insert 20A shown in Figure 2, the land 22A would be a substantially planar,
annular,
surface, substantially or nearly orthogonal to the axis of the cutting insert
20A. It can
further be seen that, on the rectilinear insert 20B shown in Figure 3, the
land 22B
would be a substantially planar, rectangular or otherwise rectilinear,
surface,
substantially or nearly orthogonal to the axis of the cutting insert 20B.
Each bevel 24 is angled forward, or in the direction 18 of rotation, above or
forward of the outwardly adjacent land 22 by a distance 32, at an angle 34
from a
plane orthogonal to the axis of the cutting insert 20. The angle 34 can be
between
approximately 20 degrees and approximately 70 degrees, with a preferred angle
of
approximately 45 degrees. Put another way, the bevel 24 is also angled
relative to the
axis of the cutting insert 20, by an angle between approximately 20 degrees
and
approximately 70 degrees, with a preferred angle of approximately 45 degrees.
A
representative raised distance 32 could be on the order of approximately 0.015
inch. It
can be seen that, on the round insert 20A shown in Figure 2, the bevel 24A
would be a
substantially frusto-conical surface, angled relative to the axis of the
cutting insert
20A. It can further be seen that, on the rectilinear insert 20B shown in
Figure 3, the
bevel 24B would be a substantially planar, rectangular or otherwise
rectilinear,
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surface, angled relative to the axis of the cutting insert 20B. The cutting
insert 20 can
also have a relief angle 36 between approximately 3 degrees and approximately
9
degrees, which promotes the cutting action of the edge 28 into the work piece.
A rear
face 40 is provided for mounting the cutting insert 20 on the cutting feature
or blade
14 of the cutting tool 10.
The distance 32 by which each bevel 24 rises above its outwardly adjacent
land 22 terminates the bevel 24 either in the surface 26 or in an inwardly
adjacent land
22, as shown in Figure 5, in which the cutting insert 20 has two lands 22 and
two
bevels 24. This embodiment has been found to be somewhat more robust in
resisting
impact than the single land, single bevel embodiment shown in Figure 4. As
shown in
Figure 6, the cutting insert 20 can have three sets of lands 22 and bevels 24,
or even
more. Each land can be relatively narrow, for example, in the range of
approximately
0.004 inch to approximately 0.060 inch. As shown in Figure 7, the cutting
insert 20
can also have other features on its leading face 26, such as a depression 38.
While the particular invention as herein shown and disclosed in detail is
fully
capable of obtaining the objects and providing the advantages hereinbefore
stated, it is
to be understood that this disclosure is merely illustrative of the presently
preferred
embodiments of the invention and that no limitations are intended other than
as
described in the appended claims.
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