Note: Descriptions are shown in the official language in which they were submitted.
104332~
Background of the Invention
1. Field of the Invention: This invention re-
lates in general to earth boring drill blts and in particu-
lar to improved means ~or their lubrication.
2. Description of the Prior Art: Earth
drill bit commonly utilize bearing lubrication systems.
The successful lubrication of drill bit bearings depends upon
an effective seal such as that disclosed in U. S. Patent No.
3,397,928 issued to Edward M. Galle. The lubrication system
10- typically includes a compensator that equalizes the pressure
differential across the seal, as described in U. S. Patents
to Cunningham, Nos. 3,007,750 and 3,137,508. Further, it is
advantageous to include a pressure relief valve to limit the
internal lubrication system pressure to a selected magnitude
above the pressure in the well bore, as disclosed in U. S.
Patent No. 3,476,195 issued to Edward M. Galle.
Though previously known lubrication systems for
drill bits have been successful, certain problems persist.
The prior art rubber diaphram compensators sometimes be-
come damaged. Their manufacture and assembly requires care-
ful attention. The prior art compensators have numerous
areasthat require sealing to avoid lubricant loss or en-
trance of ambient drilling fluids. In general, the prior
art compensator systems have a degree Or complexity that
should be avoided to improve reliability.
-3- ~
_ .
iO433Z8
Summary of the Invention
It is therefore the general object of this inven-
tion to provide a drill bit having a simplified lubrication
system that achieves pressure control of the lubricant with
a reduced number of components. This object is accomplished
in general by eliminating complex pressure compensation struc-
tures. The system is filled with a lubricant essentially
free of all air and gas. The lubricant experiences thermal
expansion with increasing hole depth. Lubrication pressure
control is achieved with a pressure relief means and seal
displacement. The system comprises a closed cavity isolated
from external pressures except for displacement of the seal.
The walls of the cavity are rigid except for the seal, which
with the pressure relief means and thermal expansion of the
lubricant accomplishes lubricant pressure control. Additional
objects, features, and advantages of the invention will become
apparent in the following description.
~ _4_
r
104332B
In accordance with one broad aspect, the invention
relates to an earth boring drill bit having a rotatable cutter
retained on a bearing shaft, a lubrication system, and seal
means between the cutter and shaft, the improvement comprising:
lubricant in a closed and rigid cavity of a lubrication system
isolated from external pressure except for displacement of the
seal means; pressure relief means in the lubricant system to
discharge lubricant responsive to thermally induced expansion;
said lubrication system pressure being controlled by the
pressure relief means.
10433Z8
Brief Description of the Drawings
Fig. 1 is a perspective view, partially in sec-
tions, of an earth boring drill bit having a lubrication
system in accordance with the principles of the invention.
Fig. 2 is a view in longitudinal and fragmentary
section of a portion Or the drill bit shown in Fi~. 1.
Flg. 3 is a longitudinal sectional view of a pres-
sure relief valve.
Fig. 4 is a cross-sectional view as seen looking
along the lines IV-IV of Fig. 2.
Fig. 5 is a cross-sectional view as seen looking
along the lines V-V of Fig. 2.
Fig. 6 is schematic representation of apparatus
used to lubricate the bit shown in Fig. 1.
Fig. 7 is a graph in which one curve shows the
correlation of lubricant pressure in a bit versus hole depth
in the earth for a geothermal gradient of 1F. per 100 feet.
The other three curves show hydrostatic pressure of the
fluid surrounding the bit versus depth when the fluid is
respectively water, drilling mud with a density of ten
pounds per gallon and drilling mud with a density of six-
teen pounds per gallon.
~ _ _ __ _ _
,
-:
1043328
Description of the ~ref'erred ~mbodimerlt
_ _ _ _
In a copending application filed of even date
herewith E~ward ~l. Galle discloses an invention entitled
"Fully Lubricated Earth Boring Drill Bit" that utilizes
vacuum filling and degassed lubricant to eliminate substan-
tially all air and gas in the lubrication system of a drill
bit to improve lubrication. The present invention involves
the recognition it is possible to eliminate the compensator
and utilize only a pressure relief valve and displacement
of the seal between cutter and shaft to control lubricant
pressure. This invention is practicable since lubricant
pressure increases with depth faster than does hydrostatic
pressure at the bottom of a well bore when using drilling
mud of typical density.
Fig. 7 is a graph which plots increases in lubri-
cant pressure versus hole depth as indicated by the curve 11.
This increase in bearing pressure is caused by the increas-
ing temperature of the lubricant as it is warmed geothermally
with increasing depth. For the graph of Fig. 7, a geothermal
gradient of 1F. per 100 feet is assumed, although the geo-
thermal gradient varies geographically. Also included in
Flg. 7 are curves 13, 15 and 17, showing respectively how
the hydrostatic pressure of a drilling fluid in a well bore
lncreases with depth with drllling muds of densities respec-
tlvely of sixteen pounds per gallon, ten pounds per gallon
and with water (8.3 pounds per gallon). Thus Fig. 7 shows
that typically the pressure of the lubricant inside the bear-
ing rises with depth faster than does the hydrostatic pres-
--6--
r
. . :
10433Z8
sure of the fluid surrounding the bit. Thus a success-
ful drill bit can be achieved, as described below, through
utilization of a lubrication system that relieves increas-
ing internal pressure. Therefore, additional compensation
such as that described in the above mentioned copending
application of Edward M. Galle is unnecessary, and indeed
has disadvantages, as contrasted with the system described
below.
The numeral 19 in Fig. 1 of the drawing designates
10 - a lubricated, rotatable cutter type earth boring drill bit
having a body formed with three head sections 21, each sup-
porting a rotatable cutter 23 having earth disintegrating
teeth 25. A filler hole 27 has an enlarged upper region 29,
threaded at 31 to receive a pressure relief valve 33 and a
retaining plug 34, as seen generally in Fig. 2 and in greater
detail in Fig. 3. The central relief portion 35 of the re-
lief valve has the same general construction as disclosed
in U. ~. Patent No. 3,476,195 issued to Edward M. Galle.
It is retained by a threaded cap 37 to a cylindrical housing
39 which has one or more radial ports 41 covered by an elas-
tomeric sleeve 43 in an annular groove 45. The sleeve func-
tions as a secondary pressure relief means and has as a
primary purpose protection of the central, spring-type re-
lief portion. An O-ring 46 is included in a groove 49 of
the housing 39 to seal against the enlarged upper portion
29 of the filler hole 27. When the pressure of the lubri-
cant inside the filler hole 27 exceeds the relief pressure
of the relief valve 33, the resilient pad 51 lifts from
r
10433~:8
the end of tube 53, enabling discharge of lubricant into
the axial passage 55, through radial ports 57 and outward
beneath the elastomeric sleeve 43 and from the bit through
hole 58 in the associated head section. By this means,
the pressure of the lubricant inside the lubrication sys-
tem is limited to a selected value above the ambient drill-
ing fluid pressure.
A bearing shaft or pin 59 extends inwardly in
cantilever fashion from each head section 21 and terminates
in a pilot pin 61 extending rrOm a thrust face 63. A ball
bearing raceway 65 is formed on the shaft, as is a friction
bearing surface 67. The end 69 of the pilot pin may include
a deposit of bearing material such as one of the cobalt base
alloys, as may be surface 71 of the pilot pin and surface 72
f the friction bearing surface 67.
The cutter 23 has a thrust button 73 to engage the
end of the pilot pin, a bushing 75 to engage its cylindrical
surface 71, a ball race 77 and a seal ring groove 79, gen-
erally L-shaped. A plug 81 is welded at 83 to the leg 21
to fill a mating hole through which the balls 85 are fed to
fill the matching raceways 65, 77 to retain the cutter on
the bearing shaft. The 0-ring 87 is capable of displace-
ment by distortion and also by movement a selected amount
on the bearing shaft and in the L-shaped groove 79 of the
cutter.
As seen in the cross-sectional view of Fig. 4 and
to some extent in Fig. 1, the bearing shaft is flattened as
indicated by the numerals 89 and 91 and is slotted as indi-
cated by the numerals 93 and 95 to form pockets and passages
--8--
r
. . .
~0433:~8
for lubricant reserve. While lubricant loss is minimized
with the disclosed sealing system, some leakage may be ex-
pected. The pocket type lubricant reserve permits a pre-
determined amount of loss without detriment. A drilled
hole 97 extends between the filler hole 27 and a slot 99
(see Fig. 5) formed in the thrust face 63 and across a
portion of the pilot pin 61 to form a flat 101 thereon
for the improved flow of lubricant.
The lubricant system is preferably filled wlth a
degassed lubricant by a method that eliminates essentially
all air and gas in the system by means of apparatus shown
schematically in Fig. 6 of the drawing. A vacuum pump P
is connected by a pipe or conduit 103 and through a valve
Vl with a sump 105, there also being a vacuum gage 107 con-
nected with conduit 103 intermediate valve Vl and the sump
105.
"T" connection 107 connects a valve V3 and an air
supply P2 through conduit 109 with conduit 103, which extends
to valve V4, another "T" connection 111, valve V5, pressure
gage 113, and ultimately to a chamber 115 that contains a
piston 117 sealed with 0-ring 119 against the interior side
wall of the chamber. Screw 121 engage mating threads 123
in a lower region of the chamber and when rotated with han-
dle 125, selectively enlarges or decreases a sealed volume
127 in the chamber.
From "T" connection 111 a conduit 129 leads to a
manifold 131 connected to three separate conduits 133, 135,
137 respectively through valves V6, V8, V7 to nipples 137,
141, 143, each having a sealing 0-ring 145.
~ , , . _,
. .
10433Z8
The lubricant used to fill the bit should be sub-
stantially free of air and gas. Otherwise, the increase
in lubricant pressure, as shown by curve 11 in Fig. 7, will
be substantially less than shown. If enough air or gas is
trapped in the bearing, the hydrostatic pressure may be
greater than the lubricant pressure. Air and gas removal
may be accomplished with the apparatus shown in Fig. 6 by
opening valves Vl, V2, V4 and V5 while closing valves V3,
V6, V7 and V8. Pump Pl is energized to pull a vacuum of
preferably substantially equal to atmospheric pressure.
The lubricant in sealed volume 127 of chamber 115 is sub-
~ected to this vacuum for a period of about twenty-four
hours. This has been found sufficient to rid a lubricant
with a viscosity of 1200 Seconds Saybolt Universal at 100F.
of substantially all air and gas.
The lubricating passages and spaces of the drill
bit are also evacuated of air and gas, but not necessarily
simultaneously with the degassing of the lubricant. Each
nipple 139, 141, 143 is connected to an enlarged region or
recess 29 of each of the three filler holes 27 of a three
cone bit, the O-rings 145 forming a fluid tight seal. The
previously described passages and spaces are then evacuated
by opening valves V6, V7, V8 to the vacuum pump Pl. Valve
V5 may remain open or may be closed.
After both the lubricant and the passages and
spaces are substantially free of air and gas, valve Vl is
closed and the system checked for leaks by observlng gage
107. If no gage variation is detected, valve V4 is closed
to block the lubricant, valve V5 opened and lubricant forced
--10--
1043328
into the passages and spaces of the drill bit by turning
screw handle 125 to move piston 117 inwardly. The desired
pressure, which for the disclosed viscosity is about 500 psi
tpounds per square inch), will be indicated by gage 113.
After filling, valve V5 is closed, the nipples
139, 141, 143 are removed from the bit, and a pressure re-
llef valve 33 and retaining plug 34 inserted into each
enlarged upper region 29 of each filler hole 27. If any
appreciable amount of bleed-back of lubricant occurs when
nipples 93, 95, 97 are removed from the bit, this indi-
cates that either the lubricant was not properly degassed
or that the passages and spaces were not properly evacuated.
To prepare for the next drill bit which must be
evacuated prior to being filled with lubricant, the lubri-
cant within conduits 129, 133, 135, 137 and conduit 103
between valve V4 and "T" 111 must be removed. This is ac-
complished by opening valve v3 to the air supply P2, while
closing valves V2 and v5 and two of the valves V6, v7, v8-
The air forces the remaining lubricant from the conduit
associated with the open valve V6, v7 or V8. Each conduit
133, 135, 137 should be purged of lubricant in this manner.
When the conduits 129, 133, 135, 137 have been
purged, valve V3 is closed and the nipples 139, 141, 143
connected to the filler holes of a second bit for evacuation
and lubrication as previously described. Should any lubri-
cant remain in the conduits and be drawn towards the vacuum,
it will be collected in sump 105. If there is sufficient
lubricant remaining in chamber 115 from the prior filling,
then the degassing of the lubricant step may be eliminated.
When necessary to replenish the lubricant, chamber 115 may
--11--
r
~0433'~8
be detached from conduit 103, plston 117 withdrawn to en-
large the sealed volume 127, and fresh lubricant introduced.
The fresh lubricant should be degassed as previously dis-
cussed.
In operation and during drilling with a bit of the
preferred embodiment filled with lubricant by the apparatus
and method described, the volumetric expansion of the lubri-
cant, due to geothermal temperature increase as illustrated
in Fig. 7 and due to bearing friction, causes the pressure
of the lubricant in the closed cavity to increase more rapidly
than does the hydrostatic pressure of the drilling fluid in
the well bore surrounding the bit. If the lubricant pressure
exceeds the pressure required to open the relief valve, some
lubricant is expelled to maintain pressure below a selected
value. Further, the O-ring is capable of axial movement and
will therefore compensate for some pressure differences to
help maintain the pressure across the seal in a selected
range of values. The lubrication system is isolated from the
external pressures except for displacement of the seal in the
preferred embodiment.
It should be apparent from the foregoing that an
invention having significant advantages has been provided.
The invention eliminates the need for additional compensa-
tors of the type described in the copending application of
Edward M. Galle, "Fully Lubricated Earth Boring Drill Bit".
All necessary compensation is achieved by utilizing the
thermal exp~nsion of the lubricant, the pressure relief
valve and to a limited extent the volume displacement of
the seal between the cutter and its supporting shaft. The
elimination of additional components simplifies manufacture
and assembly and leads to greater reliability by minimizing:
the total possible number of manufacturing and assembly errors;
-12-
10433Z8
the number of sealing areas in the bit; and the number of
components that could possibly fail during operation.
While the invention has been shown in only one of
its forms, it should be apparent to those skilled in the
art that it is not so limited, but is susceptible to various
changes and.modifications without departing from the spirit
thereof. The principles of the invention may be achieved
with structures and geometries other than the preferred
embodiment.
r - ~
.
