Note: Descriptions are shown in the official language in which they were submitted.
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Background of the Invention
- The present invention relates to the art of earth boring
and, more particularly, to an earth boring cutter unit with
improved means for sealing the bearings of the cutter unit from
materials in the borehole and retaining lubricant within the
bearing area. The present invention is especially adapted for
use with cutter units in that type of bit popularly known as a
three-cone rotary rock bit; however, its use is not restricted
thereto, and the present invention can be used in other types of
rock drilling cutter units.
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A three-cone rotary rock bit consists of a main bit
body adapted to be connected to a rotary drill string. The bit
includes three individual rotatable cone cutters mounted on three
~; individual bearing pins extending from the main bit body. Bearing
systems are provided between the cone cutters and the bearing pins
to promote rotation of the cutters and means are provided on the
outer surface of the cone cutters for disintegrating the earth
formations as the bit and the cutters rotate. A sufficient supply
of uncontaminated lubricant must be maintained proximate the
bearing systems throughout the lifetime of the bit. Various forms
of seals have been provided between the cone cutters and the
bearing pins upon which they are mounted to retain lubricant and
prevent contamination; however, the need for new sealing systems
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is as acute today as any time in the history of rock drilling.
A three-cone rotary rock bit must operate under very
` severe 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 attempting to provide
an improved bit, new and improved materials have been developed
for the cutting structure of the cone cutters. They have provided
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a longer useful lifetime for the cone cutters. This has resulted
in the bearing systems of the bit being often the first to fail
during the drilling operation. Consequently, a need exists for
new and improved bearing systems to extend the useful lifetime of
the bit and to allow development of other elements that interact
with the sealing and bearing systems. In attempting to improve
the bearing systems, various seal systems have been provided to
maintain the bearing area free of harmful materials and retain
lubricant. In attempting to provide new sealing systems, great
care must be taken that the overall capacity of the bearing systems
is not reduced.
Description of Prior Art
In U. S. Patent No. 3,765,495 to Henry W. Murdoch and
- Percy W. Schumaucher, Jr. patented October 16, 1973, a drill bit
seal is shown. An earth boring drill employing roller cutters is
. provided with a new and improved seal to inhibit ingress of
detritus into the cutter bearing area and egress of lubricant
therefrom. The parts may be so arranged that when assembled, the
seal is placed in hoop compression. The shape of the seal is such
that its cross section is not overly compressed or displaced when
- in operating position; this prevents undue compression set, wear
and heating of the seal. Also, the seal has a greater radial cross
sectional extent than axial extent by a ratio of at least one-and- ~ ~-
one-half-to-one to conserve bearing space and to provide the
necessary flexibility to accommodate the various movements of the
cutter relative to the shaft upon which it is rotatably mounted.
In U. S. Patent No. 3,397,928 to E. M. Galle patented
August 20, 1968, a seal means for drill bit bearings is shown.
The seal means includes a shaft rigidly secured to a drill bit
body with a bearing surface formed thereon. A cutter element
is rotatably mounted to said shaft and includes a bearing surface
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thereon that opposes and engages the bearing surface on the
shaft. A resilient packing ring is positioned in a groove
in one of the surfaces. The packing ring, the groove and
- an opposing surface are sized such that upon assembly of
the cutter element upon the shaft the cross sectional
thickness of the packing ring is compressed by not less
than substantially 10% of this thickness prior to assembly
of the cutter element upon the shaft.
Summary of the Invention
';~
r' 10 The present invention provides a sealing system
for an earth boring cutter unit that acts as a barrier to
the drilling fluid, pulverized cuttings and other materials
in the borehole to prevent the materials from entering the
bearing area of the cutter unit and retains lubricant
within said bearing area.
According to the present invention there is
provided an earth boring bit having a bit body, a bearing
shaft extending from the bit body and a rotatable cutter
, adapted to be rotatably mounted on the bearing shaft. A
shallow annular groove is provided in the rotatable cutter
and a one piece seal element is positioned around the bearing
shaft between the rotatable cutter and the bearing shaft.
The seal element is positioned in the annular groove and
has a cross-section with a radial extent that is greater
than its axial extent but less than one-and-one-half times
its axial extent with a substantial portion of the seal
element extending out of the shallow annular groove. The ~`
seal element is compressed less than substantially 10%
when compressed between the rotatable cut-ter and the bearing
shaft.
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The unique seal of the present invention can be
shown to have a number of important features not existing
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in the prior art described above. It is; however, to be
understood that the scope of the present invention is
: defined by the claims at the end of this specification
and a general description of the prior art and distinctions
thereover is not to be interpreted as limiting the coverage
~ of the present invention. The Murdoch and
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Schumaucher seal shown in U. S. Patent No. 3,765,495 would have
a greater tendency to fall over than the seal element of the
present invention because it tends to be taller than the seal
element of the present invention. The seal element of the present
invention takes up less of the critical bearing space than the
" Murdoch and Schumaucher seal or the Galle seal shown in U. S.
Patent No. 3,397,928. The seal element of the present invention
provides a greater surface area in uniform contact with the
rolling cutter than any of the seal elements shown in the prior
art. The above and other features and advantages of the present
invention will become apparent upon consideration of the following
detailed description of the invention when taken in conjunction
with the accompanying drawings.
Brief Description of the Drawings
Figure 1 is an illustration of an earth boring bit
constructed in accordance with the present invention.
Figure 2 is an enlarged view of a portion of the bit
shown in Figure 1.
Figure 3 shows a side view of the seal element shown
in Figures 1 and 2.
Figure 4 is a cross sectional view of the seal element
shown in Figure 3 taken along lines 4-4.
Detailed Description of the Invention
Referring now to Figure 1, a sectional view of one arm
18 of a three-cone rotary rock bit 10 is shown. It is to be
understood that the structure of the other two arms are substantially
identical to the arm 18. A cutter 14 is rotatably positioned on
the journal portion or bearing pin 17 of the arm 18 and adapted to
disintegrate the earth formations as the bit 10 is rotated. The
bearing pin 17 projects from the cutter receiving surface 35 of
the arm 18. The cutting structure 15 on the surface of cutter 14
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contacts and disintegrates the formations in a manner that is well
known in the art. The cutting structure 15 is shown in the form
of tungsten carbide inserts. However, it is to be understood that
other cutting structures such as steel teeth may be used as the
cutting structure on the cone cutter 14.
The body 13 of the bit 10 includes an upper threaded
portion 12 that allows the bit 10 to be connected to the lower
end of a rotary drill string (not shown). The bit 10 also includes
a central passageway 16 extending along the central axis of the
bit to allow drilling fluid to enter from the upper section of the
drill string (not shown) immediately above and pass downward to
the bottom of the well bore to flush cuttings and drilling debris ~-
from the well bore.
A plurality of bearing systems are located in the bearing
area between the cutter 14 and the bearing pin 17. The bearing
systems in the bearing area include an outer friction bearing 19,
a series of ball bearings 20, an inner friction bearing 21, and a
thrust button 22. A seal unit 11 is positioned between the cutter
14 and the bearing pin 17. The seal unit 11 retains lubricant in
the bearing area around the bearing systems and prevents any
materials in the well bore from entering the bearing area.
Passageways 23 and 24 are provided to allow lubricant to be
transmitted to the bearing systems. The passageway 24, as shown,
also allows the balls that make up the ball bearing system 20 to
; 25 be inserted into position after the cone cutter 14 is placed on
the bearing pin 18. The series of ball bearings 20 serves to lock
` the cone cutter 14 on bearing pin 18. After the balls are in place,
a plug 25 is inserted into the passageway 24 and welded therein by
weld 26. Plug 25 has a reduced diameter throughout the major
portion of its length to allow lubricant to be transmitted to the
bearing area. The additional passageways 23 extend from passage-
way 24 to the bearing area to insure a sufficient supply of
lubricant to bearings 19, 20, 21 and 22.
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A bore 30 extends into the body 13 from the surface
` of the bit body. A passage 31 extends from the bore 30 to the
passageway 24. A lubricant reservoir 32 is located in the bore
30. The lubricant reservoir 32 is located between a flexible
diaphragm 28 and a reservoir cap 34. An O-ring seal prevents
borehole fluid from by-passing the upper portion of the reservoir
cap 34 and lubricant within the lubricant reservoir 32 from
escaping into the borehole. A retaining ring 33 holds reservoir
cap 34 in position in bore 30. The flexible diaphragm 28 prevents
lubricant in the lubricant reservoir 32 from escaping into the
; bore 30 and fluid in the borehole that has entered bore 30 through
passage 27 from entering the lubricant reservoir 32. Lubricant
within the lubricant reservoir 32 is channeled into the passage 31
through opening 29 and is directed to the bearings.
Referring now to Figure 2, an enlarged view of a portion
' of the arm 18, the cone 14 and seal unit 11 is shown. The seal
unit 11 is positioned between a surface 36 on the bearing pin 17
~ and a groove 38 in the cone cutter 14. The groove 38 includes
:` radii 39 and 40 to avoid sharp corners that would concentrate
stress. The seal unit 11 is also positioned between the cutter
- receiving surface 35 and a surface 37 on the bearing element 19.
- The pressure of fluid outside the bit 10 will tend to force the
seal 11 toward the surface 37 on the bearing element 19 and the
surface 36 on the bearing pin 17, thereby establishing a barrier
to fluid and materials in the borehole. Internal pressure of
, lubricant within the bit will tend to force the seal 11 outward
toward the cutter receiving surface 35 and the surface 38 on the
, cone cutter 14, thereby blocking flow of lubricant from the bit.
In both situations the integrity of the seal will be maintained.
Referring now to Figures 3 and 4, the seal unit 11 is
shown in greater detail. The cross section of the seal unit 11
is elongated in the radial direction. As shown in Figure 4, the
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radial dimension R of the seal unit 11 is greater than the axial
dimension A. It is however to be understood that the radial
dimension R of the seal 11 is less than one-and-one-half times
the axial dimension A. When the cutter 14 is assembled upon the
bearing pin 17, the seal 11 is compressed. The seal 11 is generally
compressed 10~ or less of the radial dimension R. It is to be
understood that because of tolerance variations the compression
on the seal in some circumstances might be greater than 10%.
The structural details of an earth boring bit 10
constructed in accordance with the present invention having been
described, the operation of the bit 10 will now be considered with
reference to Figures 1-4. The lubrication system of the bit 10 is
filled with a suitable lubricant. The area within the flexible
diaphragm 28 provides a reservoir of lubricant. The flexible
diaphragm 28 seals the lower end of the lubricant reservoir and
is held in place by the cap 34. The bit 10 will be lowered into
a well bore until the cutter 14 contacts the earth formations at
the bottom of the borehole. The hydrostatic pressure of fluid in
the well bore is substantial. The lubrication system of the bit
10 allows the pressure of fluid in the well bore to be transmitted
to the lubricant reservoir through passage 27 to the lubricant
through diaphragm 28. This allows the pressure of lubricant inside
the bit and fluid in the borehole to beequalized as the bit 10 is
moved through the borehole. Lubricant from the lubricant reservoir
can migrate through passages 3Ii 24 and 23 and be transmitted to
the bearing systems.
The bit 10 is rotated and thrust downward, thrusting the
cutter 14 against the earth formations. Continued rotation
with the weight of the drill string applying a thrust force to
the bit 10 causes the cutters to disintegrate the formations and
form the desired borehole. The present invention provides a
seal unit 11 in the cone mouth of the bit which will act as a
barrier to the pulverized cuttings, the borehole fluid and any
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other materials in the borehole. The seal unit 11 acts to
prevent these materials from entering the bearing area through
the cone mouth opening, thus providing an uncontaminated environ-
;` ment for the metal bearing elements and eliminating the abrasive
wearing action of foreign materials in the bearing area. The
~` lubricant is retained within the bit 10 by the seal unit 11 to
assure a long lifetime for the bearing systems.
External pressure of fluid outside the bit 10 will movethe seal 11 against the surface 36 on the bearing pin 17 and the
surface 37 on the bearing element 19 providing a positive seal.
Internal pressure within the lubricant inside the bit 10 will move
the seal 11 outward against sidewall 41 of the groove 38, tending - -
to support the seal and promote rotation of the seal 11 with the
cutter 14 with minimal rotational contact with the cutter receiving
surface 35.
The desired closure of the area between the cutter 14 -
and the bearing pin 17 is maintained from groove 38 to seal unit
11 to bearing pin 17 due to the radial squeeze of 10% or less of
the relaxed dimension R of the seal unit 11. The ratio of R-to-A -
of more than one-to-one provides a sufficiently large R dimension
of seal unit 11 to reduce the required squeeze to 10% or less
while maintaining sufficient interference on the seal to keep the
seal unit 11 in contact with the bearing pin 17 and cutter 14 at
all times and providing the necessary clearance in the bearing
elements to permit free rotation of the cutter 14. The ratio of
R-to-A of less than one-and-one-half-to-one keeps the proportions
- of the seal sufficiently stable to avoid tilting of the seal to a
diagonal position which could relax some of the radial squeeze on
the seal element 11. A ratio of R-to-A of more than one-and-one-
30 half-to-one would require additional guide means to prevent
undesirable misalignment of the radial cross section of the seal.
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The seal element of the present invention takes up
less of the critical bearing space for bearing element 19 than
the Murdoch and Schumaucher seal shown in U. S. Patent No.
3,765,495. The seal element of the present invention provides
i 5 a greater surface area in uniform contact with the rolling cutter
than any of the seal elements shown in the prior art. The seal
element 11 may be installed in the groove 38 in hoop compression
with the flat outer surface of seal unit in intimate contact
with groove 38~ The seal element will rotate with the cutter
14 and provide a dynamic seal to maintain the integrity of the
lubrication system of the bit 10.
The seal element of the present invention provides
equal squeeze to the Galle seal shown in U. S. Patent No.
3,397,928 but as a lower percentage of the squeezed seal cross
section dimension. The lower percentage squeeze while maintaining
sealing contact results in a lower contact pressure between the
seal 11 and the metal surface, resulting in a reduced wear rate.
A rock boring cutter as for example for a large diameter
earth boring head can be similarly sealed on a supporting bearing
shaft.
A rock contacting roller as for example on a drill
string stabilizer or reamer can be similarly sealed on a supporting
bearing shaft.
