Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Background of the Invention
The present invention relates in general to the art
of earth boring and more particularly to a cutting element for
an earth boring apparatus.
Earth boring apparatus having hard insert elements
mountéd in a cutter member body are utilized in the boring of
holes in the earth because of the ability of the hard insert
cutting elements to penetrate the earth formations. A problem
has been encountered with this type of apparatus, and generally
with all earth boring apparatus, in maintaining the desired
diameter or gage of the hole being bored. This is important
in the boring of raise holes and tunnels as well as being
critically important in the drilling of oil and gas wells and
the like. For example, in the drilling of a deep well wherein
more than one bit will be used in the well, the gage cutting
inserts must maintain the hole at the full diameter. Otherwise,
it would be necessary for the next bit being lowered into the
hole to ream the undersized hole out to the desired diameter
before the new bit reached drilling depth and could begin
drilling its length of ass~gned hole. Such reaming action
would reduce the useful llfetime of the second bit because by
the time the second bit reached its assigned drilling depth, a
substantial part of the lifetime of the gage cutting elements
would be exhausted.
The inserts in the gage row are exposed to the moSt
rigorous drilling. They must drill a larger area of the hole.
In addition, the formation outwardly of the gage row of inserts
is not being drilled and hence provides some degree of lateral
support for the formations being drilled by the gage row. It
will be appreciated that an improvement in the ability of an
earth boring apparatus to maintaln gage will be an improvement
of the entire earth boring apparatus and contribute significantly
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to the performance efficiency~, economy, and ].ife of the earth
boring apparatus.
Brief Descriptlon of Prior Art
In the prior art the accepted method of determining
the exact bit diameter was to gr~nd the outer or gage surface of
the gage compact. This would produce a flat on the surface of
the gage insert. The flat would contact with the ~all of the
hole. It is impractical to grind the outer or gage surface of
the existing gage inserts to the extent necessary to contact the
wall of the hole with the ma;ority of the length of their
extended surfaces. In addition, the grinding of the inserts
reduces the overall strength of the insert.
In U. S. Patent No. 3,442,342 to F. H. McElya and R. A.
Cunningham patented May 6, 1969 a specially shaped insert for
compact rock bits and rolling cutters and rock bits using such
inserts is shown. The original inserts of cemented tungsten
carbide had hemispherical cutting tips, and rock bits using such
inserts were used to drill the hardest abrasive formations, such
as taconite, bromide, and chert. This shape is not particularly
effective for the drilling of abrasive formations of medium
hardness, e.g., hard shales, dolomite, and some limestones~ and
the lnventors herein have developed inserts with more of a
chlsel or wedge shape to cut such rock. At the same time, they
avoid the pitfalls of the "roof-top" style of cutting tip, one
in which there are two flanks with flat surfaces converging to
a flat crest.
Two basic shapes of cutting tips are disclosed: (1) a
modified chisel with convex flanks converging to a crest which
is conVex along both its elongated lengths and its uniform
narrow ~idth, the flanks being normal to a common plane passing
through the axis of the inSert so that their pro;ected
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intersection is a curve normal to such axis: and (2) a wedge
shape in which the flanks are twisted or canted away from each
other so that there is no single plane through the insert axis
which is normal to both flanks and the projected intersection
is not normal to the axis, the result being that the creSt
formed normal to the axiS increases ln width from one end to the
other.
In all forms rounded intersections are provided to
avoid the sharp corners and sharp edges which cause high-stress
concentration. The inventor~s theory is that their rounding
and their convex surfaces distribute the operating load over the
cutting edge of the insert and direct such load to the center
of the insert, thus avoiding the high-stress at the edges which
they believe to be responsible for the shipplng and breaking of
roof-top inserts.
In U. S. Patent No. 2,990,025 to M. L. Talbert and
W. E. Scarborough patented June 27, 1961 an improved arrange-
ment of wear-resistant inserts to maintain the hole being drilled
at gage is shown. A first circumferential row of gage cutting
wear-resistant inserts is situated at the heel of the cutter.
A second circumferential row of wear-resistant inserts is
spaced inwardly of the first row toward the longitudinal axis
of the head with the spacing between the first and second rows
being such that the track of the second row on the bottom of
the hole being drilled overlaps the track of the first row.
The first row is sltuated at a substantially zero oversized
angle and the second row is situated at a larger oversized
angle than is the first row so that the second row affects
disintegration of the earthen formatlons closely adjacent the
wall of the hole at a level below the first row, whereby the
formation to be disintegrated by the first row is left wlthout
substantial inner lateral support thereby facilitating cutting
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the hole to gage by the first row.
In U. S. Patent No. 3,800,891 to A. D. White and A. E.
Wisler patented April 2, 1974 a hardfacing composition and gage
hardfacing on rolling cutter rock bits is shown. This patent
relates to a tooth-type bit rather than an insert bit, however,
the patent points out the importance of maintaining the proper
gage. Beginning at column 1, line 49, the importance of
maintaining gage is discussed as follows "the importance of
such gage--maintaining function in an oil well can scarcely be
exaggerated. Since all subsequent operations such as running
in casing and cementing it in place depend on having a full gage
hole, the customer demands and obtains it in one way or another.
If a bit drills an underslzed hole, the following bit must be
used to ream the hole to full gage, even if in so doing the
second bit becomes useless for further drilling. Needless to
say, the bit which drilled the undersized hole will not be
reordered if a better one is available. Thus, the gage surface
of a rolling cutter used in oil field drilling is completely
unlike many other bits used ln drilling rockj and must even be
better than the bottom--cutting structure of the same rolling
cutter on which it is employed. Wear of a gage surface cannot
be tolerated, whereas it makes little difference if the teeth
which cut the inner part of the hole gradually wear away, SO
long as they continue to penetrate effectively."
In U. S. Patent No. 2,774,570 to R. A. Cunningham
patented December 18, 1956 a roller cutter for earth drills
is shown. The rolling cutter includes an annular series of
cylindrical inserts of hard wear-resistant material having
their axis extending outwardly and substantially normal to the
surface of the body and presenting protrusions at the surface
thereof to affect disintegrating action and to maintain gage
of the well bore being drilled,
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Summary of the Invention
The present invention provides more ~urface on
the gage row insert~ for contacting the wall of the bore hole.
This decreases wear on the gage insexts and therefore increa~e~
the ability of the earth boring apparatus to maintain a full
gage hole. The insert of the presen~ invention contacts the
wall of the hole with the ma~ority of the length of its extended
surface and with the same angle as the gage angle of the earth
boring apparatus and maintains maximum hole gage retaining
ability. The earth boring apparatus includes at least one
cutter member for forming a hole in the earth. me cutter member
has an annular gage row of inserts mountea in ~ocket~ in the
cutter member body for cutting the gage of the hole~ The
in~ert~ have a shape prior to assembly in the ~ocket~ that
includes an asymmetric head with an extended gage contacting
face. The gage contacting face is planar and is ~ubstantially
- larger than any other planar face on the head. The above and
other features and advantages of the present invention will
become apparent from a consideration of the following detailea
description of the invention when taken in conjunction with
the accompanying drawings.
. In summary, therefore, the present invention may
be broadly defined as a rolling cutter for an earth boring
apparatua, comprising: a cutter body of generally conical
configuration; the cutter body having a nose and a base; and a
row of gage cutting inserts positioned proximate the base, the
inserts comprising pressed and sintered granule~ of wear-
resistant material together with a binder, the inserts having
a multiplicity of surface culminatinq in a crest with one
surface having a plane section ~ubstantially larger than any
plane sections on any other surface, the plane section facinq
generally away from the nose of the cutter body.
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Brief Description of the Drawings
Figure 1 is a cut-away perspective illu~tration
of a three-cone rolling cutter rock bit embodying the present
invention.
Figure 2 is an enlarged ~ide view illustration of
a gage row insert of the bit shown in Figure 1.
Figure 3 is an end view of the in~ert ~hown in
Figure 2 showing the gage cutting surface.
Figure 4 is a side view o~ another insert
constructed in accordance with the present invention.
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Figure 5 is an end view of the insert shown in
Figure 4.
Figure 6 is an illustration of yet another insert
constructed in accordance with the present invention.
j 5 Figure 7 is an end view of the insert shown in
Figure 6.
Detailed Description of the Invention
Referring now to the drawings and to Figure 1 in
particular, a rotary rock bit generally designated by the
reference character 10 embodying the present invention is
illustrated. The bit 10 includes a bit body adapted to be
connected at its pin end to the lower end of a rotary drill
string (not shown). The bit body includes a passage providing
communication for drilling muds or the like passing downwardly
through the drill string to allow the drilling mud to be
directed to the bottom of the well bore and pass upward in the
annulus between the wall of the well bore and the drill plpe
carrying cuttings and drilling debris therewith.
Depending from the body of the bit are three
substantially identical arms. Arms 11 and 12 are sho~n in
Figure 1. The lower end portion of each of the arms is
provided with a conventional bearing pln. Each arm rotatably
supportS a generally conical cutter member. The cutter members
being designated 13, 14, and 15 in Figure 1. The bearing pins
carrying the cutting members 13, 14, and 15 define axiS of a
rotation respectively about which the cutter members rotate.
The axis of rotation are tilted downwardly and inwardly at an
angle. The direction of rotation of drill bits is in a clock-
wise direction so that the threads making up the various joints
of the drill string are constantly tightened by the forces
exerted as the drill string rotates the bit 10.
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Each of the cutter members 13, 14, and 15 includes a
nose portion that ls oriented toward the bit axis of rotation
and a base that is positioned at the intersection between the
wall of the well bore and the bottom thereof. The cutting
action of the base defines the diameter or gage of the well bore.
Each of the cutter members 13, 14, and 15 includes
annular rows of inserts 16 for destroying the inner portion of
the hole. Each of the cutter members 13, 14, and 15 also include
annular rows of inserts 17 that are located adjacent the base
of each cutting member. The inserts 17 cut the intersection
between the well bore wall and the bottom thereof. The annular
rows of inserts 17 are generally referred to as "gage rows~' and
the inserts 17 are designated "gage inserts". The gage row
inserts are sub;ected to the most rigorous drilling action.
The present invention affords more surface for the -
gage row inserts to contact the wall of the hole. This decreases
wear on the gage inserts, therefore increasing the ability of
- the bit to ma~ntain a full gage hole. Applicant has provlded
an insert which contacts a wall of the hole with the majority
of the length of its extended surface and with the same angle
as the gage angle of the bit. This insert is believed to have
the maximum gage retaining ability.
In the prior art the accepted method of determining
the exact bit diameter was to grind the outer or gage surface
of the gage compact. This would produce a flat on the surface
of the gage insert. The flat would contact the wall of the
hole. It is impractical to grind the outer or gage surface of
the existing gage inserts to the extent necessary to contact
the wall of the hole with the majority of the length of their
30 extended surfaces. In addition, the grinding of the lnserts
reduces the overall strength of the insert.
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Referring now to ~igure 2, a side v~ew of one of the
gage inserts 17 is shown enlarged and in greater detail. The
outer or gage angle ~ of this compact before gage grind is
' within 1 30' of the gage angle of the bit. lt is not necessary
to grind the outer or gage surface excessively to bring the
insert gage angle to the bit gage angle. The inner angle ~ of
this compact is conslderably less than the outer or gage angle
a, This difference between the inner and outer angles allows
the length of the crest 19 to approximate that of conventlonal
gage inserts. The sides or flank surfaces of the gage insert
can be flat or convex surfaces, convex surfaces on the flanks
result in a larger flat area on the outer angle than do the
flat angled flanks.
Referring now to Figure 3, an end view of the insert
17 shown in Figure 2 is illustrated. The insert 17 contacts
the wall of the hole with the ma~ority of its extended surface
21 and with substantially the same angle as the gage angle of
the bit. The surface 21 is the largest plane surface on the
cutting head of the insert 17. The plane surface 21 contacts
the wall of the hole and performs the gage cutting function.
Since the surface 21 is relatively large compared to other
surfaces on the insert 17, the lifetime of the insert 17 will
be increased.
The lnsert 17 is formed by pressing granules of a
wear-resistant material such as tungsten carbide together with
granules of a binder such as cobalt. The wear-resistant material
granules and binder granules are pressed together with wax and
formed in the desired insert shape. The head of the insert
may be formed in a dle. For example, the head of the insert
ma~ be formed by a punch member ~hich molds the end of the
insert into the des~red fini~hed shape. The inserts are de-waxed
in a furnace and sintered at a higher temperature in a furnace.
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The insert is then press fit into the body of a cutter member
with the asymmetric head oriented so that the extended plane
surface of the insert is at gage. Very little, if any, gage
grinding is required.
` The foregoing should be contrasted with prior art
inserts having symmetrical heads. The prior art inserts are
pressed into the cutter member and subsequently a gage surface
is ground around the gage of a cutter producing ground flats on
the gage inserts. The inserts of the present invention are
pressed into the cutter with the pre-formed plane gage contacting
surface located at substantially the gage angle of the bit.
Referring now to Figure 4, a side view of another
embodiment of an insert 22 is shown in some detail. The insert
22 includes a cylindrical body portion 23 adapted to be mounted
in a socket in the cutter body substantially perpendicular to the
axis of rotation of the cutter body. The head of the insert 22
includes an inner surface 24 and an outer or gage surface 26.
The outer or gage surface 26 is substantially larger than the
inner surface 24. The roof top or crest 25 of the insert has
substantially the same length as that of prior art gage inserts.
Referring now to Figure 5, an end view of the insert
22 shown in Figure 4 is illustrated. The insert 22 contacts
the wall of the hole with the majority of its extended surface
26 and with substantially the same angle as the gage angle of
the bit. The surface 26 is the largest plane surface on the
cutting head of the insert 22. The plane surface 26 contacts
the wall of the hole. Since the surface 26 is relatively large
compared to the other surfaces on the insert 22, the lifetime
of the insert 22 will be increased.
Referring now to Figure 6, a side view of another
embodiment of a gage insert 27 constructed in accordance with
the present invention is illustrated. The insert 27 has a
generally spherical formation contacting head 29 and a generally
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1071184
cylindrical body portion 28. The body portion 28 ls adapted
to fit within sockets in the cutter body. The outer or gage
angle of the gage contacting surface 30 of this compact before
gage grinding is within 1 30~ of the gage angle of the bit.
It is not necessary to grlnd the outer or gage surface extensively
to bring the insert gage angle to the bit gage angle.
Referring now to Figure 7, an end view of the lnsert
27 shown in Figure 6 is illustrated. The insert 27 contacts the
wall of the hole with the majority of its extended surface 30
and with substantially the same angle as the gage angle of the
bit. The surface 30 is the largest plane surface on the cutting
head of the insert 27. The plane surface 30 contacts the wall
of the hole. Since the surface 30 is rela~ively large, compared
to other surfaces on the insert 27, the lifetime of the insert
27 will be increased.
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