Note: Descriptions are shown in the official language in which they were submitted.
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EARTH BORING BIT WlTH ECCENTRICALLY
MACHIN~D BEARING PIN
Technical Field
The present invention relates in general to the art
of earth boring and more particularly to a rotary rock bit
with an improved bearing system. The present invention is
especially adapted for use on that type of rotary rock bit
popularly known as a three cone bit; however, its use is not
restricted thereto and the bearing system of the present
invention can be used in other earth boring bits wherein an
improved bearing system is required.
Background of the Invention
A three cone rotary rock bit is adapted to be
connected as the lower member of a rotary drill string. As
the drill string is rotated the bit disintegrates the forma-
tions to ~orm an earth borehole. The three cone rotary rock
bit includes three individual arms that extend angularly down-
ward from the main body of the bit. The lower end of each
arm is shaped to form a bearing pin or ~ournal. A cone
cutter is mounted upon each bearing pin and adapted to rotate
thereon. The cone cutters include cutting structure on their
outer surfaces that serves to disintegrate the formations as
the bit is rotated.
A rotary rock bit must operate under very severe
environmental conditions and the size and geometry of the bit
is restricted by the operating characteristics. At the same
time, the economics of petroleum production demand a longer
lifetime and improved performance from the bit. In attempt-
ing to provide an improved bit, new and improved materials
have been developed for the cutting structure of the cone~
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cutters thereby providing a longer useful lifetime for the
cone cutters. This has resulted in the bearing systems being
generally the first to fail during the drilling operation.
Consequently, a need exists for improved bearing systems to
extend the useful lifetime of the bit.
Description of the Prior Art
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In U. S. Patent No. 3,746,405 to Russell L. Welton,
a well drilling bit lubrication system and seal is shown. A
journal bearing lubrication means and a seal cooperatively ?~
combined therewith to maintain lubrication throughout the
useful life of the roller cutter of a well drilling bit, to
the exclusion of foreign materials entering therein from the
drilling fluids and surrounding earth formations. A journal
bearing of right cylinder form is provided, characterized by
the formation of a strategically placed recess or recesses
therein and all without subtracting from the load carrying
capabilities of the bit, the assembly being retained in work-
ing condition by a single element combined with the lubrica-
tion means and assuring proper axial placement of the roller
cutter-
In U. S~ Patent No. 3,890,01~ to Robert D. Clamon,a rotary rock bit with a wiper pad lubrication system is
shown. A system is provided for circulating lubricant into
the loaded contact area between the bearing pin and the
rotating cutter of an earth boring bit. The cutter is mounted
to rotate about the bearing pin. The cutter includes a cutter
interior surface. At least one wiper pad cavity is located
in the aforementioned interior surface of the cutter. A wiper
pad is positioned in the wiper pad cavity and a resilient
member is positioned beneath the wiper pad. As the cutter
rotates, the wiper pad forces lubricant into the load area
between the bearing pin and the interior surface of the cutter.
In U. S. Patent No. 4,061,376 to Arthur A. Villalo-
boz, a rock bit bearing structure is shown. A rock bit has
a rotary cutter cone journaled on a fixed journal bearing
shaft with the radial load bei:ng taken by a cylindrical journal
bearing. The friction bearing portion of the fixed shaft has
a groove extending around the periphery of the shaft. The
groove is filled with a bearing metal over an arc on the lower
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load bearing fraction of the shaft. The remaining unfilled
portion of the groove is connected through a lubricant supply
passage in the bit body with a pressure-compensated grease
reservoir in the bit body to supply lubrication to the
journal bearing.
According to the present invention, there is provided
a roller cutter earth boring bit having a bit body with at
least one bearing pin, which has a central axis, extending
from the bit body. A rolling cone cutter is rotatably mounted
on the bearing pin. A loaded surface is provided on the
bearing pin substantially concentric with the central axis
and an unloaded surface is provided on the bearing pin
eccentric to the central axis. A seal, which may be in the
form of an O-ring, is positioned between the bearing pin and
the rolling cone cutter and is substantially evenly s~ueezed
during operation of the bit.
The present invention also resides in a method of
constructing a rotary rock bit which may have a multiplicity
of arms. In the method, there is carried out the step of
producing a cantilevered bearing pin extending from each
arm of the bit, each bearing pin having a central axis. A
load surface is formed on each bearing pin substantially
concentric to the central axis of the bearing pin, and an
unloaded surface is formed on each bearing pin eccentric to
the central axis of the bearing pin.
Reduced clearance is provided between the cutter and
the bearing pin, enabling the load to be distributed over a
greater area. In a specific em~odiment of the invention,
hard metal is applied to the load bearing surface on the
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bearing pin before machining. The unIoaded portion of the
bearing pin is provided with greater clearance to enhance
distribution of the lubricant. The unloaded portion of the ,
bearing pin includes an eccentrically machined section.
The above and other objects and advantages of the
present invention will become more apparent from a
consideration of the following detailed description of the
invention when taken in conjunction with the drawings.
Brief Description of the Drawings
_
Figure 1 illustrates one arm of a rotary rock bit
constructed in accordance with the present invention.
Figure 2 is a sectional view of the bearing pin and
a superimposed view of the rolling cone cutter of the bit
shown in Figure 1.
Detailed Description of the Invention
. .
Referring now to the drawings and to Figure 1 in
particular, illustrated therein and generally designated by
the reference number 10 is a three cone sealed bearing rotary
rock bit. The bit 10 includes a bit body 11, including an
upper threaded portion 12. The threaded portion 12 allows khe -
bit 10 to be connected to the lower end of a rotary drill
string (not shown). Depending from the bit body 11 are three
substantially identical arms with only the arm 13 being shown
in Figure 1. The lower end of each of the arms is provided
with an extended bearing pin comprising a journal portion and
the details of this journal portion will be discussed
subsequently.
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Three rotary cone cutters are rotatably positioned on the
respective three bearing pins extending from the arms. The
cutter 14 is shown in Figure 1. Each of the cutters includes
cutting structure on its outer surface adapted to disintegrate
formations as the bit 10 is rotated and moved downward. The
cutting structure is shown in the form of tungsten carbide
inserts 15. However, it is to be understood that other cutting
structures such as steel teeth may be used as a cutting struc-
ture on the cone cutters.
The bit 10 includes a central passageway extending
along the central axis of body 11 to allow drilling fluid to
enter from the upper section of the drill string (not shown)
immediately above and pass downward through jet nozzles past
the cone cutters. In use, the bit 10 is connected as the
lower member of a rotary drill string (not shown) and lowered
into the well bore until the cone cutters engage the bottom
of the well bore. Upon engagement with the bottom of the well
bore, the drill string is rotated, rotating bit 10 therewith.
Drilling fluid is forced down through the interior passage of
the rotary drill string by mud pumps located at the surface.
The drilling fluid continues through the central passageway
of bit 10, passing through the nozzles past the cutting
structure of the cutters to the bottom of the well bore, thence
upward in the annulus between the rotary drill string and the
wall of the well bore, carrying with it the cuttings and debris
from the drilling operation.
The bearing system of the bit must insure free rota-
tion of the cone cutters under the severe drilling environ-
mental conditions. The improved bearing system of the present
invention provides an earth boring bit with a long lifetime
and that will withstand the conditions encountered in drilling
a deep well. The elongated lower portion of arm 13 forms the
bearing pin 18 comprising a journal portion and the rotatable
cutter 14 is mounted upon the journal portion. Reduced
clearance is provided between the cutter and the bearing pin,
enablin~ the load to ~e distributed over a greater area. This
spreads the load from a line contact to a wider surface to
reduce unit load, resulting in reduced wear upon the journal.
The spreading of the load will reduce the heat generated by
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the bearing and reduce disintegration of grease which may be
the cause of extreme pressure in bearing and resulting
deleterious effects. The reduced clearance between the
journal and the cutter will have a cushioning, or shock
absorbing, effect between the surfaces in contact during the
rough vertical vibration of drilling. The prior art bearings
cause the journal and cutter to run eccentrically, resulting
in excessive squeezing of the rubber O-ring in the loaded
area and reduced, possibly insufficient squeeze in the unloaded
area of the journal. The present invention causes the journal
centerline and cutter centerline to coincide and produce more
evenly distributed squeeze on the O-ring seal. The unloaded
portion of the bearing pin includes an eccentrically machined
section. The unloaded portion of the bearing pin is thereby
provided with greater clearance to enhance distribution of
the lubricant.
A series of ball bearings (not shown) that bridge
between raceways 16 and 17 insure that rotatable cutter 14 is
rotatably locked on bearing pin 18. The rotatable cutter 14
is positioned upon bearing pin 18 and the series of ball
bearings inserted through a bore extending into arm 13. After
the ball bearings are in place, a plug is inserted in the bore
and welded therein. A flexible seal 9 forms a seal between
cutter 14 and bearing pin 18 to prevent loss of lubricant or
contamination of the lubricant from materials in the well bore.
The outer portion of the bearing pin 18 includes a recess on
the load side of the bearing pin 18. This recess is filled
with a hard metal bearing material. The outer portion of
bearing pin 18 cooperates with the outer bearing surface
portion 20 on the inside of cutter 14.
One of the prior art rock bit sealing problems
involves the clearance between the journal and cutter. When
the ~it is loaded on the bottom of the borehole with the
underside of the journal in contact with the cutter, all the
clearance is on the unloaded side of the bearing; thus,
increasing O-ring squeeze in the loaded area and reducing
O-ring squeeze in the unloaded area. The present invention
causes the cone cutter to run concentrically and equalizes
squeeze on the O-riny. The lower, load bearing surface of
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the journal is caused to run concentrically with the seal
gland surface (cylindrical) of the cone cutter, thus, causing
equalized squeeze on the O-ring seal at both the upper, un-
loaded and the loaded areas of the bearing.
Referring now to Figure 2, a sectional view of
bearing pin 18 is shown. The recess 21 is cut in the journal
portion of bearing pin 18. Bearing material 19 is applied in
the recess 21 and machined to coincide with the journal sur-
face on the load side of the journal. ~ space 24 for lubri-
cant is provided on the upper unloaded side of the bearing
pin 18. The central axis 22 of the load side of the bearing
pin 18 and the central axis 23 of the unloaded side of the
bearing pin 18 are offset. The load side of the journal
conforms closely with the contour of the cone bearing and
provides greater load bearing contact area for longer bearing
life. Reduced clearance provided between the cutter 14 and
journal 18 around the lower half of the journal 18 supports
the journal over an area approaching the projected diametral
area of the journal 18. The necessary clearance between the
two members is obtained by offset grinding or machining the
upper half of journal 18. This spreads the load from line
contact to a wider surface to reduce unit loading resulting
in reduced wear upon the journal. The spreading of the load
will reduce the heat generated by the bearing and reduce
disintegration of grease which may be the cause of extreme
pressure in prior art bearings. The reduced clearance between
the journal and the cutter will have a cushioning, or shock
absorbing, effect between the surfaces in contact during the
rough vertical vibration of drilling.
The structural details of an earth boring bit 10 of
the present invention having been described, the construction
of the bit 10 will now be considered with reference to Figures
1 and 2. The recess 21 is cut in the journal portion of
bearing pin 18. Bearing material 19 is applied in the recess
21. The bearing material 19 is ground or machined to coincide
with the journal surface on the load side of the journal.
The grinding or machining of the load side and unloaded side
of the journal is accomplished about axes 22 and 23 respec-
tively. This provides a radius Rl for the load side of the
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journal and a radius R2 for the unloaded side of the journal.
The radii Rl and R2 may be equal, however, it is to be noted
that the axes 22 and 23 of radii Rl and R2 respectively are
offset. The offset is substantially .005 inch providing a
.001 to .007 clearance in the space 24. The central axis of
the bearing pin 18 is located at the axis 22. The foregoing
provides reduced clearance between the cone cutter and the
loaded area of the journal, enabling the load to be distributed
over a greater area. The clearance on the load side is
substantially .001 inch. The unloaded portion of the journal
is provided with greater clearance to enhance distribution of
the lubricant and to provide necessary clearance to prevent
seizure between journal and cutter.
The present invention improves the sealing effect
of O-ring seal 9. The prior art bearings cause the journal
and cutter to run eccentrically, resulting in excessive
squeezing of the rubber O-ring in the loaded area and reduced,
possibly, insufficient squeeæe in the unloaded area of the
journal. The present invention allows the journal 18 center-
line and cutter 14 centerline to coincide and produce moreevenly distributed squeeze on the O-ring seal. The lifetime
and performance of the O-ring seal will be extended because
of the improved even loading.
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