Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED DRILL BIT
FIELD OF THE INVENTION
The present invention relates to a drill bit for
drilling into earth formations, and more particularly
to a drill bit having means for providing a controlled
flow of lubricant or combining liquid lubricant with
gaseous drilling fluid to ~upply a lubricant and
ga~eous fluid mixture to the cutting cones for
lubrication and cooling of the cutting cone bearings.
DESCRIPTION OF THE PRIOR ART
Typical drill bits are used in combination with,
for example, a rotary drill pipe system, for drilling
deep holes into underground formations, such as into
rock, coal, or the like. In a drilling system of this
type, a drill string is formed by connecting a number
of hollow extension pipes through which a drilling
fluid, which may be either a drilling mud or a gaseous
drilling fluid such as air, is supplied by way of the
extensions to the drill bit to be exhausted at the
surface being drilled. The drill bit contains suitable
openings, such as nozzles, for discharging the
drilling fluid from the drill bit onto the surface
being drilled to clear dust and cuttings and scavenge
them away from the area of the cutting cones. The
drill bit of the present invention is for use in
connection with drilling systems using a gaseous
drilling fluid.
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In the above-de~cribed ~y~tem, a 3ubas~emb1y may
be located on the drill string between the drill bit
and the extension pipe line. A ~ubassembly structure
i~ known in the art and generally includes a central
conduit, or plenum chamber, which extends from the
rotary drill extension pipe to the vicinity of the
drill bit. Pressurized air or other gasous drilling
fluid from the rotary drill flows through the plenum
chamber and is discharged downwardly through the
drill bit, either through a central opening, or through
nozzles positioned between the cutting cones.
A source of major concern in the drilling art is
protection of the cutting cones from excess wear and
heat. It is desirable to lubricate or cool the cutting
cone bearings and shafts which increases the useful
life of the cutting cones and avoids the necessity of
frequent drill bit replacement during a drilling
operation. In the prior art, various systems have been
employed to supply lubricant to the cutting cone
bearings for lubrication during operation. In these
systems, lubricant may be supplied from a storage means
which i9 located either in the subassembly structure or
in the drill bit itself. For example, in U.S. Patent
No. 3,029,881, a system is disclosed wherein a
lubricant storage means is provided in the subassembly.
The pressure of the gaseous fluid in the subassembly
plenum chamber acts upon an expandable liner to force
lubricant from the storage means, and into a lubricant
supply conduit provided in the subassembly. The
subas~embly conduit communicates with a drill bit
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conduit to supply lubricant to the bearings. A majoc
disadvantage which may arise in this system is that
lubricant accumulates in the area of the bearing~, and
may brea~ down due to the heat of the cutting cones.
S It iR desirable, therefore, to provide means to
continually flush lubricant from the bearings hefore
such breakdown occurs.
Another approach in the prior art has been to
u~e the ga~eous drilling fluid it~elf to cool the
utting cone bearings. For example, in U.S. Patent No.
4,080,091, a drill bit is disclosed which provides a
conduit communicating between the hollow interior of
the drill bit and the cutting cone bearings, to allow
passage of drilling air to the bearings. In this
lS arrangement, relatively cool drilling air is intro-
duced to cool the cutting cone bearings and shafts,
as they become heated during the drilling operation.
U. S. Patent No. 3,125,175 also discloses a structure
which provides a conduit communicating between the
hollow interior of the drill bit and the cutting cone
bearings. In this structure, a ring member is provided
in the drill bit, which reduces the quantity of air
which enters the conduit, as compared to the quantity
of air which exits in the vicinity of the cutting
cones. Both of these systems suffer from the
disadvantage that, although the bearings are cooled,
they are not lubricated.
U. S. Patent No. 2, 814,464 discloses a drill
bit structure provide a conduit between the drill bit
interior and the cutting cone bearings, and sugge3ts
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that the drilling fluid may consist of an air stream
containing a fine ~pray of lubricant such a~ oil, to
lubricate the cutting cone bearings. Of course, when
oil is injected into the drilling air, oil is also
contained in the air which exits at the drilling
surface in the vicinity of the cutting cones. This is
unde3irable since it results in oiling the drilling
surface and oiling of the dust and cuttings arising
from the drilling operation.
Another gaseous fluid drilling system employing
lubricant entrained in the gaseous drilling fluid is
diqclosed in U. S. Patent No. 3,924,695. The drill bit
structure disclosed includes a separator assembly,
which acts to remove lubricant from the gaseous
drilling fluid beore it is discharged onto the
drilling surface. The lubricant, removed from the
gaseous stream i3 then directed to the cutting cone
bearings by way of a conduit provided in the drill
bit.
A drill bit ~tructure providing for an internal
storage source of liquid lubricant is di~closed in U.S.
Patent No. 4,375,242. In the drill bit, an air conduit
i~ provided between the drill bit interior and a
sealing o-ring, which supports the cutting cone on
the bit. The pre~sure from the air conduit also acts
to urge lubricant from the internal storage ~ource, and
supply the lubricant by way of a separate conduit to
the cutting cone bearings for lubrication.
With the foregoing in mind, it is an object of
the present invention to provide for an improved drill
lZ~
bit ~tructure which enables lubricant, which ~ay be
supplied, for example, from a storage means in a drill
subassembly, to be combined with gaseou~ drilling fluid
in a conduit means which communicate~ between the
interior of the drill bit and the cutting cone
bearing~. A ga~eous fluid and lubricant mixture or at
the normal operating pressure, lubricant is supplied
through the conduit means at a controlled rate to the
cutting cone bearings to provide both cooling and
lubrication.
SUMMARY OF THE INVENTION
The present invention provides for a drill bit
for use in a rotary drill system utilizing a source of
gaseou~ fluid under pressure. The drill bi~ is
lS provided with at least one rotary cutting cone for
drilling into an earth formation, such as rock or coal.
The bit is provided with a first conduit means, in the
form of an air passage which extends from the hollow
interior of the drill bit to the cutting cone bearings.
A second conduit means i~ provided in the drill bit for
receiving lubricant from an external storage source,
which may be contained in a drilling subassembly. The
second conduit means is in the form of a lubricant
passage which intersects with and provides lubricant to
the first conduit means, whereby a lubricant and
gaseous fluid mixture may be formed beyond the
intersection. The resulting mixture or lubricant flow
is directed, through the first conduit means, to the
cutting cone~ for cooling and lubrication of the
cutting cone shafts and bearings. Additionally, the
second conduit means may contain replaceable orifice
elements which regulate the amount of lubricant
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entering the second conduit mean~ for combining with
the ga3eous fluid in the fir~t conduit mean~.
DESCRIPTION OF THE DRAWINGS
Figure 1 is a cut-away perspective view of a
drill bit of the pre3ent invention:
Figure 2 i9 cro~s-sectional view taken acro~
line 2-2 in Figure l; and
Figure 3 iY a cross-~ectional view of a drill
bit of the present invention attached to a subassembly
having an internal storage supply of lubricant.
DE.SCRIPTION OF Tl~E INVENTION
The drill bit of the present invention i3
intended to be attached to a drill string or drilling
subassembly, the drill string or ~uba3sembly having a
lubricant 3torage means and means for supplying the
lubricant to the drill bit.
The drill bit of the present invention comprise~
a main body portion 10 as shown in Figure 1. An upper
nipple 11 attaches the drill bit to a drilling
subassembly, or to the extension pipe~ forming a drill
string. The nipple of the drill bit i9 threaded, 80 as
to threadedly engage the tapered socket of a
subas~embly and form a firm connection therebetween.
One or more leg portions 12 extend downwardly from the
body portion 10 of the drill bit at circumferencially
spaced intervals. Mounted for rotation in each leg
portion 12 is a rotary cutter 13. It is generally
preferred in the industry to use a drill bit having
three cutting cone~. Cutting cones 13 are rotatably
mounted to the leg portion of the drill bit by bearings
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14 and bearing ~haft~ 15.
Th~ dcill bit contain~ a hollow interior portion
16 forming a chamber for receiving ga~eous drilling
fluid from the ~uba3~embly plenum chamber. The gaseou3
drilling fluid from chamber 16 i~ exhausted from the
drill bit into the area of the cutting cone~ to pick up
and remove the dust and cuttings which result from the
drilling operation. l'he gaseous drilling fluid may be
ejected through nozzles 17 located between the cutting
cone~. Alternatively, the nozzle~ may be omitted
and the gaaeou~ f1uid ejected through a central orifice
located between the cutting cones, as i~ known in the
art. In the present ca~e, the orifice must have
sufficient restriction to provide an elevated pre3qure
lS within the chamber 16.
Communicating between chamber 16 and the cutting
cone bearings 14 and bearing shaft~ 15, i9 firqt
conduit means 18 forming passage for the ga~eou~
drilling fluid. First conduit means 18 allows gaseous
drilling fluid, ~uch as air, to pa~s from the hollow
interior of the drill bit through the fir~t conduit
mean~ to cool the cutting cone bearings 14 and bearing
shafts 15.
The drill bit of the preqent invention is also
provided with a circumferential groove 20 surrounding
the drill bit, to form a reservoir for lubricant which
is located in the qurface of the drill bit surrounding
the nipple 11. The circumferential groove, which
preferably is approximately 3/16" wide by 3/i6~ deep,
receives lubricant from, for example, a supply conduit
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34 in a drilling subassembly, a~ described hereinafter
in connection with Fig. 3. Second conduit means or
bore 19 connect~ circumferential groove 20 with fi~st
conduit means 18, and supplie~ lubricant from the
groove 20 to the gaseous drilling fluid pa~sing through
the fir~t conduit means 18 to the bearings. The
precise point where second conduit means 19 intersects
with first conduit means 18 i~ a choice of design.
In one mode of operation, the lubricant supplied
by second conduit means or bore 19 i9 picked up and
combined with the gaseous drilling fluid in fir~t
conduit means 18, and is supplied to the cutting cone
bearings 14. In this manner, a mixture of lubricant
and gaseous drilling fluid is supplied to the bearing~
to achieve both a lubricating and a cooling effect.
Also, lubricant build-up and heat breakdown at the
bearings i9 avoided due to the continuous supply of
fresh mixture provided to the bearings, the air in the
mixture acting to flush out lubricant before it
~0 accumulates.
Means is provided to regulate the amount of
lubricant supplied to the bearings. To this end,
second conduit means 19 may be fitted with replaceable
orifices, in the present instance annular rings 21.
Z5 The diameter of the orifice in annular rings 21 may be
varied to regulate the flow of lubricant supplied to
the bearings. The annular rings 21 may be formed of
metal, plastic, or any suitable material. The annular
rings 21 are inserted into second conduit means 19 in
~0 the vicinity of circumferential groove 20, for e~ample
in a counter bore 22 at the mouth of the bore 19. When
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it i8 de~ired to modify the rate at which lubricant i~
~upplied to the bearingR, the user simply remove~ the
drill bit from the ~uba~sembly, and replace~ annular
ring 21 with an annular ring having a different ~ized
orifice, to provide the de~ired lubricant flow.
Referring to Figure 3, the drill bit of the
pre~ent invention i9 ~hown attached to a drilling
~uba~sembly. The drill bit of the pre~ent invention i~
de~igned to work in combination with a ~uba~embly
having a supply of lubricant contained therein.
, ..........
-- - - A ~ubas~embly having
lubricant ~torage i~ ~hown in U. S. Patent No.
3,029,881.
A repre~entative subassembly comprise~ a
housing 30 and a hollow plenum chamber 31. Ga~eou~
drilling fluid from the drill line is ~upplied to
plenum chamber 31, and then to drill bit interior
chamber 16. The ~uba~embly ~tructure additionally
contains lubricant ~torage mean~ in the form of, for
example, annular chamber 32 surrounding the tlou~ing.
The flow of lubricant from the storage means may be
effected in various way~. For example, a passageway 35
may be provided to allow communication between the
pressurized gaseou3 fluid in the plenum chamber and the
lubricant ~torage area, to act as a pressure ~ource
forcing lubricant downward and into lubricant ~upply
conduits 34, at spaced intervals around the
circumference of the subassembly. A piston (not shown)
may be provided in the annular chamber 32 to force
lubricant from the chamber. It should be
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:IZ~318
apparent that other types of pres3ure means are equally
suitable to force lubricant from the 3torage mean3, for
example, an expandable liner.
The lubricant forced through supply conduit 34
accumulate~ in the circumferential groove 20 on the
drill bit. In the preferred embodiment, illu~trated in
Figure 2, the circumEerential groove extends entirely
around the drill bit. This obviates the need to align
supply conduit(s) 34 on the subassembly with individual
bores or second conduit means 19 in the drill bit in
order to supply lubricant to the second conduit means.
It ha~ been found beneficial to the operation of
the present invention for an orifice ring 36 to be
placed in the plenum chamber of the ~ubassembly in
order to somewhat reduce the flow of gaseous fluid.
The orifice should be located downstream from the
pressure means acting on the lubricant storage in the
suba~embly, and upstream of the entrance to first
conduit means 18 in the hollow interior chamber 16 of
the drill bit. By varying the pressure as controlled
by orific ring 36, the flow of lubricant to the
bearings can be varied or controlled. In this manner,
a greater pre~sure of gaseous fluid is acting upon the
lubricant storage means, while a ~omewhat reduced
pressure acts upon the first conduit means 18.
Sufficient force to achieve continuous lubricant flow
from the chamber 32 is thereby maintained. One
expedient arrangement is to place an orifice ring
directly at the connection between the subassembly and
the drill string below passageway 35. This allows the
orifice ring to be removed or replaced ~imply by
removing the suba~embly from the drill string.
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Instead of receiving lubricant from a supply
conduit in a subas~embly, the drill bit of the present
invention may receive lubricant that is supplied by a
conduit in the drill string from a surface-mounted
supply, as sl)own in u.S. Patent No. 4,508,183. In this
arrangement, the drill bit may be attached directly to
the extension pipe, and the circumferential groove 20
may receive lubricant directly from the drill string
conduit.
In actual operation of the aforesaid structure,
it has been found that, at the operating pressures for
the gaseous drilling fluid commonly employed in the
drill string, the flow to the bearings through first
conduit 18 is substantially entirely lubricant. The
1~ flow of lubricant to the bearings and the exclusion of
any significant amount of gaseous fluid i3 believed to
result from the generally higher pressure in pa~ageway
35 delivering the lubricant to conduit 18, than the
flow of gaseous fluid after it has passed through
orifice ring 36. As noted previou~ly, orifice ring 36
increases the back pressure above the orifice ring 36
and reduces the quantity of flow of ga3eous fluid in
plenum chamber 31. ~lence, a greater pressure iq
exerted upon the lubricant storage means 32 by way of
~upply conduit 35, than is present in the plenum
chamber 31 and hollow bit interior 16 after the gaseous
fluid has passed through orifice ring 36, which results
in a lesser pressure gaseous fluid flow inside plenum
chamber 31 and in hollow drill bit interior 16.
Accordingly, at the intersection between first conduit
18 and second conduit 19 in the drill bit, the gaseous
fluid from the bit interior portion 16 is substantially
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- excluded from the lower portion oE conduit 18 at the
intersection of conduit 19. ~lence, the flow reaching
the cutting cone bearings, through the lower portion of
first conduit mean~ 18, i9 substantially entirely
lubricant received at a higher pres~ure from conduit
19, with the general re~ult that no subatantial amount
of gaseous fluid reache~ the bearings during normal
operation. It has been found most beneficial to have
the pressurized lubricant metered to the bearings in a
controlled manner. ~9 noted earlier, the pressure for
the lubricant flow can be controlled by varying the
size of the orifice ring 36. In the preferred
operation of the system, a limited quantity of
lubricant i9 provided for packing the bearing~, without
having an excess lubricant flow from the bearing3 into
the drill hole which may permit cuttings to float back
to the bearing holders and bearings.
It should also be appreciated that, in the
preferred operation of the system, when the flow of
lubricant of the present system is depleted, the flow
of gaseous fluid acting on conduit means 18 will be
such that a flow of gaseous fluid is provided to the
bearings. Accordingly, in the event the supply of
lubricant in ~torage means 32 is exhausted or
interrupted, the bearings are nonetheless given some
degree of protection by the cooling effect of gaseous
fluid supplied to the bearings by first conduit means
18 until such time as the lubricant supply is
replenished or reestablished.
In a preferred embodiment of the present
invention, a perforated member 40 in the form of a
slotted tube is fitted into the mouth of the first
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conduit 18 and act~ to filter dirt, ~tone, or other
heavy material which may be pre3ent in the gaqeous
drilling fluid from entering the fir~t conduit means
18.
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