Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The inventlon relates to a drill b;t or drilling relatively deep
holes in rock in the earth's crust, the bit being of the type comprising a bit
body connectable to a pipe string and having several circumferentially spaced
bit segments UpOII which conical cutting elements are mounted for free rotation,
each cutting element having a hub or pin that forms part of the cutting ele-
ment bearing.
Such drill bits are known to the art from, for example, United States
patent 3,307,6~5. The presen~ invention is concerned with a drill bit of the
aforesaid type and in particular with the problem of cutter bearing sealing.
According to the present invention there is provided a drill bit for
drilling a hole in the earth's crust, comprising a bit body adapted to be se-
cured to a pipe string and including a plurality of circumferentially spaced -
bit segments, each having associated therewith a bearing means and a rotatable
cutting element mounted on the segment by the bearing means, said bearing means
including an annular outer race r~e~ab~ mounted on the bit segment and a hub
on the cu~ting element, projecting into the outer race9 said cutting element
having an inner surface overlying the outer surface o~ the outer race and
forming a narrow gap therebetween, the outer end of said gap being open to the
surroundings of the drill bit, and sealing means including means forming a
substantially closed inner end of the gap and first duct means for supplying
fluid to the gap such that a pressurized fluid flouing through the duct means
will flow out of the outer end of the gap.
With this arrangement, known mechanical sealing means such as pack-
ing rings can be effectively replaced by a liquid seal inasmuch as liquid
pumped through the pipe string during drilling is forced under pressure out-
wardly through the gap to be sealed so that a seal is obtained withou~ the
actual~bearing being essentially affected. A contrast to this is offered by,
~; for example the bit design described in French patent 1,~53,319, according to
which so~e otthe drilling fluid is used as a coolant ~or a journal bearing,
; 3~ ~or which purpose it is pumped via a system of ducts right up to ~he bearing.
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According to a ~referred embodiment of the present invention, duct
means includes a first duct extending through the bit segment and the outer
race and terminates in the gap, and a second duct comm~micating the first duct
with a cavity or chamber in the bit body. This enables the drilling fluid,
e.g "mud", to flow along the pipe string to which the bit is affixed, via the
chamber or cavity in ~he bit body into the abovedescribed duct system and thence
efflux along the narrow gap to the latter's open end. This effectively pre-
vents intrusion of fine cuttings from outside the bit into the bearing system
against the liquid pressure.
In order to ensure a stable mounting o a cutting element, a ball
retaining bearing, known per se to the art, may be employed. In a preferred
embodiment of ~he invention, the retaining bearing is provided by an annular
duct encircling the cutter-bearing in communication with the narrow gap and
connected with a duct of the duct means that goes through a bit segment and
the bearing outer race. The annular duct contains rolling elements. The
arrangement is such that the re~aining bearing so formed constitu~es a locking
mechanism of relatively large diameter for securing the cutting element on the
cutter bearing and at the same time forms part of the fluid seal. Moreover,
the mean diameter of the retaining bearing is preferably equal to the external
2~ diameter of the cut~er bearing's outer race. Because of this, more balls or
other rolling elements can be fitted in the annular duc~ than was previously
possible, which provides inter alia a stable fixation of ~he cutting element
on the bit segment.
Thus, the preferred embodiment of the invention provides a drill bit
which, because of the fluid seal and the improved positioning of the ball or
roller bearing lock, i.e. the retaining bearing, has a much longer service
life than prior art drill bits of the same type, inasmuch as ~he latter are
provided, just at the open end of the narrow gap, with a mechanical seal, e.g.
a packing ring which, because of the heavy wear caused in ~his zone by the
finely divided moving drilling dust, is often prematurely damaged.
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In the accompanying drawing which illustrates an exemplary embodiment
of the present invention, the single flgllre is a partial cross-sectional view
of a drill bit.
Referring to the drawing~ the drill bit 1 comprises a bit body 2 pro-
vided at the top with a screw-thread 3 by means o~ which the bit 1 can he con-
nected to a pipe string (not shown). ~ia this string fluicl ;s pumped into the
cavity or chamber 4 and some of it makes its way into the duct 5. This duct 5
is located partly in the bottom of the bit body 2 and partly in a part 6 of a
bit segment 7. In this embodiment the bit segment part 6 is substantially
wedge-shaped, as described in Netherlands patent application No. 75307355,
published June 20, 1975 in the name of the present applicant. This segment part
is detachably secured to segment 7 by a pin 8.
In the segment part 6 is a second duct 9 that communicates with duct
5. Duct 9 also extends into the outer race 13 of the cutter bearing. This
duct 9 has a diameter such as to be able to receive the balls 10 and at the
same time contain an end couyling pin 11 by means of which the balls 10 are
retained in an annular duct 12 communicating with the foremost part of duct 9.
The duct 12 is circular in cross-section and encircles the cutter bearing 14.
Part of duct 12 is formed in the cutting element 16 and its other part in the
20~ outside of ~he outer race 13.
By reason of the rolling elements or balls 10 having been inserted
into duct 12 via duct 9, a stablc retaining bearing is obtained in that the
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mean diameter of the cutter bearing is smaller than the mean diameter of the -
retaining bearing. The retaining bearing is in consequence located around as
large a diameter as possible in the cutting element 16 and in fact some dis-
tance outside the actual cutter bearing 1~. Duct 12 is in open communication
with both duct 9 and the narrow gap 17 between the outside of the outer race 13
and the opposite inside face of the cutting element.l6.
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At some distance from the retaining bearing 10, 12 is an annular ~
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~seal 18 that separates an outer part of the g~p 17 ~rom an inner part 19 of
the gap. Inner gap part l9 communicates with a space 20 forming part of a sec-
ond duct system, and accom~o-
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dating t~Yo sets of roller elements 21 and 22. In one o these sets the roller
elements 21 are tapered and in the other set the elements 22 cylindrical. The
raceways for rollers 21 and ~2 are formed in the inside of the outer race 13
and the outside of the hub or pin 15.
The second duct system is formed in this embocliment ~y the aforesaid
narrow gap 19l the space 23 at the head of the hub 15 and a chamber 24 conti-
guous to the space 23 and having a wall 25 made of :Elexible material. This
flexible wall 25 serves as a diaphragm and for this purpose communicates via a
duct 26 with the space outside the drill bit. Chamber 24 and duc~ 26 are lo-
cated in part 6 of the bit segment 7.
In operation, the drill bit 1 is screwed onto a pipe string (notshown) which can be rotated by a drive unit. The drilling aetion of the bit
into the earth's crust is brought about by a combination of rotation and pres-
sure. At the same time a pump unit (not shown) forces fluid - in most cases
muddy water - into the pipes, which fluid, or most of it, serves to flush the
drill cuttings. To this end the fluid is squirted around the rotating cutters
during drilling. Some of this fluid is also used to make a seal. For this
p~pose the drilling fluid flows via duct 5, along duct 9, then through the
annular raceway 12 into the gap 17 whence it flows to the outside of the drill
bit. This flow is ac~omplished by virtue of the pressure in the chamber 4,
the communicating duct system 5, 9, 12 and space 17 being higher than that out-
side the drill bit, at least while the pump unit is in operation.
The second duct means or system 19, 20, 23, 24 includes flexible
wall or diaphragm 25 exposed to the ambient pressure outside the drill bit
By suitably choosing or specifically shaping the flexible wall 25 one can en-
sure that it will be pressed in or displaced to an extent that is a ~unction
of the drilling depth, so that the pressure in a chamber in this second duct
s~stem which is filled with a fluid mediu~, e.g. a lubricant, will be affected
accordingly.
While the illustrated embodiment employs rollers in the cutter bear-
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ing, in other embodiments the cutter bearing can e~ually ~ell have other types
of rolling element or evcn be a journal bearing or a combination of journal
and roller or ball bearings,
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