FIELD 0F THE INYENTION
[0001] The present invention relates to a drill bit for drilling into earth formations,
and more particularly to a driIl bit having means for providing a controlled flow
of lubricant or combining liquid lubricant with gaseous driIling fluid to supply a
lubricant and gaseous fluid mixture to the cutting cones for lubrication and cooling
of the cutting cone bearings.
DESCRIPTION OF THE PRIOR ART
[0002] 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.
[0003] ln the above-described system, a subassembly may be located on the dri)l string between
the drill bit and the extension pipe line. A subassembly structure is 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.
[0004] 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 is located either in the subassembly structure or in the drill bit itself. For
example, in U.S. Patent No. 3,029,88l, 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 subassembly conduit
communicates with a drill bit conduit to supply lubricant to the bearings. A major
disadvantage which may arise in this system is that lubricant accumulates in the area
of the bearings, and may break down due to the heat of the cutting cones. It is desirable,
therefore, to provide means to continually flush lubricant from the bearings before
such breakdown occurs.
[0005] Another approach in the prior art has been to use the gaseous drilling fluid itself
to cool the cutting cone bearings. For example, in U.S. Patent No. 4,080,09l, 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 arrangement, relatively cool drilling air is introduced to
cool the cutting cone bearings and shafts, as they become heated during the drilling
operation. U. S. Patent No. 3,l25,l75 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.
[0006] U. S. Patent No. 2, 8l4,464 discloses a drill bit structure provide a conduit between
the drill bit interior and the cutting cone bearings, and suggests that the drilling
fluid may consist of an air stream containing a fine spray of lubricant such as 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 undesirable since it results in oiling the drilling
surface and oiling of the dust and cuttings arising from the drilling operation.
[0007] Another gaseous fluid drilling system employing lubricant entrained in the gaseous
drilling fluid is disclosed 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 before it is discharged onto the drilling surface. The lubricant, removed
from the gaseous stream is then directed to the cutting cone bearings by way of a
conduit provided in the drill bit.
[0008] A drill bit structure providing for an internal storage source of liquid lubricant
is disclosed in U.S. Patent No. 4,375,242. In the drill bit, an air conduit is provided
between the drill bit interior and a sealing o-ring, which supports the cutting cone
on the bit. The pressure from the air conduit also acts to urge lubricant from the
internal storage source, and supply the lubricant by way of a separate conduit to
the cutting cone bearings for lubrication.
[0009] With the foregoing in mind, it is an object of the present invention to provide for
an improved drill bit structure which enables lubricant, which may be supplied, for
example, from a storage means in a drill subassembly, to be combined with gaseous
drilling fluid in a conduit means which communicates between the interior of the drill
bit and the cutting cone bearings. A gaseous 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
[0010] The present invention provides for a drill bit for use in a rotary drill system utilizing
a source of gaseous fluid under pressure. The drill bit is 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 is 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 cones 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 entering
the second conduit means for combining with the gaseous fluid in the first conduit
means.
DESCRIPTION OF THE DRAWINGS
[0011]
Figure l is a cut-away perspective view of a drill bit of the present invention;
Figure 2 is cross-sectional view taken across line 2-2 in Figure l; and
Figure 3 is a cross-sectional view of a drill bit of the present invention attached
to a subassembly having an internal storage supply of lubricant.
DESCRIPTION OF THE INVENTION
[0012] The drill bit of the present invention is intended to be attached to a drill string
or drilling subassembly, the drill string or subassembly having a lubricant storage
means and means for supplying the lubricant to the drill bit.
[0013] The drill bit of the present invention comprises a main body portion l0 as shown
in Figure l. An upper nipple ll attaches the drill bit to a drilling subassembly,
or to the extension pipes forming a drill string. The nipple of the drill bit is threaded,
so as to threadedly engage the tapered socket of a subassembly and form a firm connection
therebetween. One or more leg portions l2 extend downwardly from the body portion
l0 of the drill bit at circumferencially spaced intervals. Mounted for rotation in
each leg portion l2 is a rotary cutter l3. It is generally preferred in the industry
to use a drill bit having three cutting cones. Cutting cones l3 are rotatably mounted
to the leg portion of the drill bit by bearings l4 and bearing shafts l5.
[0014] The drill bit contains a hollow interior portion l6 forming a chamber for receiving
gaseous drilling fluid from the subassembly plenum chamber. The gaseous drilling fluid
from chamber l6 is exhausted from the drill bit into the area of the cutting cones
to pick up and remove the dust and cuttings which result from the drilling operation.
The gaseous drilling fluid may be ejected through nozzles l7 located between the cutting
l0cones. Alternatively, the nozzles may be omitted and the gaseous fluid ejected through
a central orifice located between the cutting cones, as is known in the art. In the
present case, the orifice must have sufficient restriction to provide an elevated
pressure within the chamber l6.
[0015] Communicating between chamber l6 and the cutting cone bearings l4 and bearing shafts
l5, is first conduit means l8 forming passage for the gaseous drilling fluid. First
conduit means l8 allows gaseous drilling fluid, such as air, to pass from the hollow
interior of the drill bit through the first conduit means to cool the cutting cone
bearings l4 and bearing shafts l5.
[0016] The drill bit of the present invention is also provided with a circumferential groove
20 surrounding the drill bit, to form a reservoir for lubricant which is located in
the surface of the drill bit surrounding the nipple ll. The circumferential groove,
which preferably in both width and depth measures approximately 5 mm (3/l6"), receives
lubricant from, for example, a supply conduit 34 in a drilling subassembly, as described
hereinafter in connection with Fig. 3. Second conduit means or bore l9 connects circumferential
groove 20 with first conduit means l8, and supplies lubricant from the groove 20 to
the gaseous drilling fluid passing through the first conduit means l8 to the bearings.
The precise point where second conduit means l9 intersects with first conduit means
l8 is a choice of design.
[0017] In one mode of operation, the lubricant supplied by second conduit means or bore
l9 is picked up and combined with the gaseous drilling fluid in first conduit means
l8, and is supplied to the cutting cone bearings l4. In this manner, a mixture of
lubricant and gaseous drilling fluid is supplied to the bearings to achieve both a
lubricating and a cooling effect. Also, lubricant build-up and heat breakdown at the
bearings is 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 accumulates.
[0018] Means is provided to regulate the amount of lubricant supplied to the bearings. To
this end, second conduit means l9 may be fitted with replaceable orifices, in the
present instance annular rings 2l. The diameter of the orifice in annular rings 2l
may be varied to regulate the flow of lubricant supplied to the bearings. The annular
rings 2l may be formed of metal, plastic, or any suitable material. The annular rings
2l are inserted into second conduit means l9 in the vicinity of circumferential groove
20, for example in a counter bore 22 at the mouth of the bore l9. When it is desired
to modify the rate at which lubricant is supplied to the bearings, the user simply
removes the drill bit from the subassembly, and replaces each annular ring 2l with
an annular ring having a different sized orifice, to provide the desired lubricant
flow.
[0019] Referring to Figure 3, the drill bit of the present invention is shown attached to
a drilling subassembly. The drill bit of the present invention is designed to work
in combination with a subassembly having a supply of lubricant contained therein.
A subassembly of this type is shown, for example, in applicant's co-pending European
Patent Application 0106700, filed October 18, 1982. Another subassembly having lubricant
storage is shown in U. S. Patent No. 3,029,88l.
[0020] A representative subassembly comprises a housing 30 and a hollow plenum chamber 3l.
Gaseous drilling fluid from the drill line is supplied to plenum chamber 3l, and then
to drill bit interior chamber l6. The subassembly structure additionally contains
lubricant storage means in the form of, for example, annular chamber 32 surrounding
the housing. The flow of lubricant from the storage means may be effected in various
ways. For example, a passageway 35 may be provided to allow communication between
the pressurized gaseous fluid in the plenum chamber and the lubricant storage area,
to act as a pressure source forcing lubricant downward and into lubricant supply 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 apparent that other types of pressure means are equally suitable to force
lubricant from the storage means, for example, an expandable liner.
[0021] The lubricant forced through supply conduit 34 accumulates in the circumferential
groove 20 on the drill bit. In the preferred embodiment, illustrated in Figure 2,
the circumferential 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 l9 in the drill bit in order to supply lubricant to the second conduit
means.
[0022] It has been found beneficial to the operation of the present invention for an orifice
ring 36 to be placed in the plenum chamber of the subassembly 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 subassembly, and upstream of
the entrance to first conduit means l8 in the hollow interior chamber l6 of the drill
bit. By varying the pressure as controlled by orifice ring 36, the flow of lubricant
to the bearings can be varied or controlled. In this manner, a greater pressure of
gaseous fluid is acting upon the lubricant storage means, while a somewhat reduced
fIow acts upon the first conduit means l8. 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 simply by removing the subassembly from the drill string.
[0023] Instead of receiving lubricant from a supply conduit in a subassembly, 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 shown in U.S. Patent No. 4,508,l83.
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.
[0024] 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 l8 is substantially entirely lubricant.
The flow of lubricant to the bearings and the exclusion of any significant amount
of gaseous fluid is believed to result from the generally higher pressure in passageway
35 delivering the lubricant to conduit l8, than the flow of gaseous fluid after it
has passed through orifice ring 36. As noted previously, orifice ring 36 increases
the back pressure above the orifice ring 36 and reduces the quantity of flow of gaseous
fluid in plenum chamber 3l. Hence, a greater pressure is exerted upon the lubricant
storage means 32 by way of supply conduit 35, than is present in the plenum chamber
3l and hollow bit interior l6 after the gaseous fluid has passed through orifice ring
36, which results in a lesser pressure gaseous fluid flow inside plenum chamber 3l
and in hollow drill bit interior l6.
[0025] Accordingly, at the intersection between first conduit l8 and second conduit l9 in
the drill bit, the gaseous fluid from the bit interior portion l6 is substantially
excluded from the lower portion of conduit l8 at the intersection of conduit l9. Hence,
the flow reaching the cutting cone bearings, through the lower portion of first conduit
means l8, is substantially entirely lubricant received at a higher pressure from conduit
l9, with the general result that no substantial amount of gaseous fluid reaches the
bearings during normal operation. It has been found most beneficial to have the pressurized
lubricant metered to the bearings in a controlled manner. As 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 is provided
for packing the bearings, without having an excess lubricant flow from the bearings
into the drill hole which may permit cuttings to float back to the bearing holders
and bearings.
[0026] 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 l8 will be such that a flow of gaseous fluid is provided to
the bearings. Accordingly, in the event the supply of lubricant in storage 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
l8 until such time as the lubricant supply is replenished or reestablished.
[0027] 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 conduit l8 and acts to
filter dirt, stone, or other heavy material which may be present in the gaseous drilling
fluid from entering the first conduit means l8.
1. An earth boring drill bit for use, in a gaseous fluid drilling system, in combination
with a drill string having means for supplying lubricant to the drill bit, the drill
bit comprising:
a) a body portion (10) having a hollow interior (16);
b) a shank portion (11) extending from said body portion for attachment of the drill
bit to a drill string;
c) at least one leg portion (12) extending from said body portion;
d) one or more cutting cones (13) supported on said leg portion by bearings (14);
e) one or more discharge openings (17) communicating with said hollow interior (16)
for exhausting gaseous fluid from the hollow interior onto the surface being drilled;
f) one or more first conduit means (18) providing gaseous passage means communicating
between said hollow interior (16) and said cutting cone bearings (14);
g) supply reservoir means (20) between the top of said body portion and said shank
portion, for receiving lubricant; and
h) second conduit means (19) providing lubricant passage means communicating between
said supply reservoir means (20) and said first conduit means (18);
whereby lubricant from said second conduit means (19) is combined with gaseous fluid
in said first conduit means (18) to provide a mixture of lubricant and gaseous fluid
to the cutting cone bearings.
2. The drill bit set forth in claim 1 comprising three leg portions (12), three cutting
cones (13) supported thereon, three first conduit means (18), and three second conduit
means (19).
3. The drill bit set forth in claim 1 or claim 2 wherein said one or more discharge
openings consist of nozzles (17) connected to said hollow interior (16) and opening
between adjacent cutting cones (13).
4. The drill bit set forth in any preceding claim wherein said reservoir supply means
consists of a circumferential groove (20) surrounding said body portion.
5. The drill bit set forth in claim 4 wherein said circumferential groove (20) is
provided with orifice rings (21) at the point of communication with said second conduit
means (19) to control the amount of lubricant supplied to said second conduit means
(19).
6. The drill bit set forth in any preceding claim wherein the first conduit means
(18) contain a perforated member (40) at the point of communication with the hollow
interior (16).