CA1064014A

CA1064014A - Rock drill bit

Info

Publication number: CA1064014A
Application number: CA275,858A
Authority: CA
Inventors: Carl E. Johansson
Original assignee: SKF Industrial Trading and Development Co BV
Current assignee: SKF Industrial Trading and Development Co BV
Priority date: 1976-04-12
Filing date: 1977-04-07
Publication date: 1979-10-09
Also published as: DE2715788A1; NL179409B; DE2715788C2; AU514631B2; IT1076714B; NL179409C; FR2348358A1; SE7703246L; AU2359777A; BR7702233A; SE433958B; ZA772203B; FR2348358B3; GB1563533A; NL7603835A; NO771246L; JPS52145302A; JPS5936076B2

Abstract

ABSTRACT OF THE DISCLOSURE

A rock drill bit is provided with a fluid seal for the cutter bear-ing. The bit has a bit segment on which an annular outer bearing race is re-movably mounted. The bearing race carries a rotary cutter with a hub project-ing into the center of the race and an inside surface overlying the outer sur-face of the race to provide a narrow gap. The gap and thus the bearing is sealed by a pressurized fluid flowing through ducts in the bit, into the gap and out of its open end to flush away any fine cuttings.

Description

1036~L4 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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~64~
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 .
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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~64~3~4 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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~964~4 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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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A drill bit for drilling a hole in the earth's crust, comprising a bit body adapted to be secured to a pipe string and including a plurality of circumferentially spaced bit segments, each having associated therewith a bear-ing means and a rotatable cutting element mounted on the segment by the bear-ing means, said bearing means including an annular outer race mounted on the bit segment and a hub on the cutting element, projecting into the outer race, said cutting element having an inner surface overlying the outer surface of 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 includ-ing 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 flowing through the duct means will flow out of the outer end of the gap.

2. A drill bit according to claim 1, including a chamber in the bit body and wherein the duct means includes a first duct extending through at least a part of the bit segment and the bearing race to terminate in the narrow gap, and a second duct providing an open communication between the first duct and the chamber in the bit body.

3. A drill bit according to claim 2, including an annular duct encircl-ing the bearing means adjacent the open end of the narrow gap and communicating with the narrow gap and the first duct.

4. A drill bit according to claim 3, where the annular duct is formed partly in the inside of the cutting element and partly in the outside of the outer race.

5. A drill bit according to claim 4, including a plurality of rolling elements retained in the annular duct such that a retaining bearing thus formed constitutes a retention mechanism between the cutting element and the bearing means and forms part of the sealing means.

6. A drill bit according to claim 5 wherein the first duct is adapted for the passage of said rolling elements into the annular duct.

7. A drill bit according to claim 5, characterized in that a second duct means is formed by a part of the narrow gap starting at a point spaced from the retaining bearing and extending to the bearing means, continuing thence via a space between the hub of that cutting element and the bit segment into a pressure equalizing chamber.

8. A drill bit according to claim 7, characterized in that the pressure equalizing chamber has a flexible wall and is located in a detachable part of the associated bit segment.

9. A drill bit according to claim 7 or 8, characterized in that the two duct means are separated from each other in the narrow gap by a sealing ring located between the retaining bearing and the bearing means.

10. A drill bit according to claim 7 or 8, characterized in that the first duct means is adapted for the passage of a drilling fluid under high pressure while the second duct means is adapted to contain a lubricant.

11. A drill bit according to claim 1, 2 or 3, characterized in that part of the first duct means is situated in a detachable part of the associated bit segment.

12. A drill bit according to claim 1, characterized in that the bearing means has two sets of rolling elements whose raceways are formed on one side by the outside surface of the hub and on the other side by the inside of the outer race.

13. A drill bit according to claim 1, characterized in that the bearing means comprises a rolling bearing and a journal bearing with respective race-ways and surfaces formed on one side in the hub and on the other side in the inside of the outer race.

14. A drill bit according to claim 5, 6, or 7, characterized in that the retaining bearing is at some distance outside the bearing means.

15. A drill bit according to claim 5, 6, or 7, characterized in that the mean diameter of the retaining bearing is substantially equal to the external diameter of the outer race.

16. A drill bit according to claim 5, 6, or 7, characterized in that the mean diameter of the bearing means is smaller than the mean diameter of the retaining bearing.