Note: Descriptions are shown in the official language in which they were submitted.
OPPOSED BUTTON THRUST SURFACE:S FOR EARTH BORING BIT
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BACKG:ROUND OF THE INVENTION
This invention relates in general to earth boring
bits, and in particular to surfaces in a bit for absorbing
outward thrust of the cutter on the bearing pin.
Ccnventional earth boring bits have a body with thxee
depending bearing pins, each of which receives a rotatable
conical cutter. Journal or roller bearings between the
cutter and bearing pin absorb large forces imposed on the
bit during drilling. Normal downward drilling also causes
the cutter to exert an outward force on the bearing pin,
tending to push the cutter farther onto the bearing pinO
This outward thrust is handled by one or more thrust
surfaces located between the cutter and bearing pin in a
plane perpendicular to the axis of the bearing pin. Usually
these thrust surfaces ha~e inlays of hard metal to reduce
the wear on the thrust surfaces.
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One type of bit is particularly used in the mining
industry for drilling blast holes of relatively short
depth. Compressed air is pumped through -the drill bit for
cooling the blt and blowing cuttings to the surface. Some
of the air is diverted through the bearing areas for
cooling the bearinys. One of the thrust surfaces comprises
opposed shoulders on the bearing pin and in the cutter.
If these thrust shoulders wear sufficiently, the backface
of the cutter will contact the last machined surface of the
bit leg, resulting in locking and destruction of the bit.
Improving the wear resistance of the shoulders is a long
standing problem.
CROSS-REFERENCE TO RELATED APPLICATION
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This application is being filed concurrently with an
application entitled "SPACED BUTTON THRUST SURFACE FOR
EARTH BORING BIT", inventor William Leroy Shepherd, Canadian
application 421,791 filed February 17, 1983.
SUMMARY OF THE INVEWTION
In this invention, each of the thrust shoulders
contains a plurality of wear resistant buttons. These
buttons engage each other in sliding contact to absorb
outward thrust. The buttons are secured in holes with an
interference fit. The buttons in at least one of the shoulders
protrude a short distance from the shoulder to enhance cooling.
In the preferred embodiment, the buttons in one shoulder are
tungsten carbide, while the but-tons in the opposite shoulder
are of tool steel.
Accord~ng to a broad aspect of, the inven-tion relates
to an earth boring bit having a body with a depending
bearing pin having a cylindrical outer section and a cy-
lindrical inner section of lesser diameter, defining a
bearing pin shoulder at the junction of the inner and
outer sections, the bi-t having a cutter with a cavi-ty contain-
ing a cutter shoulder positioned opposite the bearing pin
shoulder, the improvmenet comprising a plurality of wear
resistant buttons secured in holes formed in each of the
shoulders, the buttons in the cutter shoulder slidingly
engaging the buttons in the bearing pin shoulder.
BRIEF DESCRIPTION OF THE DRA~INGS
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Fig. 1 is a vertical sectional view of a portion of
an earth boring bit constructed in accordance with this
invention.
Fig. 2 is an end view of the bearing pin of the bit
of Fig. 1, shown wlth the cutter remo~ed,
Fig. 3-is an end view looking inward into the cavity
of the cutter of Fig. 1, with the bearing pin not shown.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FigO 1~ earth boring bit 11 has a body
that includes three head sections 13 (only one shown). Each
head section 13 has a depending bearing pin 15 integrally
formed with it~ Bearlng pin 15 is a generally cylindrical
member~ having a cylindrical outer section 17 that joins
head section 13. An inner section 19 of smaller diameter
than the outer section 17, is formed on the free end of
bearing pin 15. The extreme end 21 of bearing pin 15 is a
flat surface perpendicular to the axis of bearing pin 15.
An annular shoulder 23 is defined by the junction of -the
inner section 19 and -the outer section 17. Shoulder 23 is
located in a plane parallel with the plane containing the
bearing pin end 21.
A plurality of spaced-apart inserts or buttons 25
are located in the shoulder 23, Each button 25 is a
cylindrical mel~er of hard, wear resistant material,
preferably sintered tungsten carbide. The cylindrical wall
surface (not shown) of each button 25 is preferably fluted
or serrated. Each button 25 is interferingly pressed into
a cylindrical hole drilled in the supporting metal of
shoulder 23. The serrated exterior helps retain the button
25 within the hole. The supporting me-tal of shoulder 23
, will be of considerably less hardness than the buttons 25.
In the preferred embodiment~ the depth of the hole for each
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button 25 is the same as the length of the button~ resulting
in the outer end of each button being flush with the surface
of shoulder 230 The vuter end of each button 25 is flat
and located in the same plane that contains the shoulder 23.
As shown in Fig. 2, buttons 25 are in a circular array,
with each button 25 spaced from adjacent buttons 25 a
distance that is equal to about one half the diameter of the
buttons.
Referring again to Fig. 1, a disk or button 27 of
considerably larger diameter than huttons 25 is located in
the bearing pin end 21. Button 27 is also formed of a
hard metal, preferably tungsten carbide. The face of button
27 contains a groove or channel 29 that extends across the
face and intersects the perimeter of button 27, Button 27
protrudes from bearing pin 21 a short distance. An axial
hole 31 extends through button 27 and intersects channel
29.
A passage 33 extends axially through bearing pin 15,
with its outlet registering with hole 31. Two passages 35
(Fig.2~ intersect bearing pin end 21 radially outward of
button 27. Passage 33 and passages 35 are in communication
with a passage 37 that extends to an axial passage (not
shown~ that is located on the axis of the bit. This axial
passage has three outlets 39, each containing a nozzle 41
for discharging drilling fluld. Other circulation passages
include two passages 43 ~Fig. 21, which extend from passage
37 to shoulder 23. The exit of each passage 43 is located
in a recessed area 45, where a shallow portion of shoulder
23 has been removed. Recesses 45 enable drilling flui~ to
circulate past the shoulder 23. As shown in Fig. 2, no
buttons 25 are located within the recessed areas 45
Each bearing pin 15 is adapted to receive a rotatable~
generally conical cutter 47. Cutter 47 has a cavity 49 that
fits over and is carried b~ bearing pin 15. Cavity 49 is
axial, and is surrounded at its entrance by a back~ace 51.
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~ackface 51 is spaced a selec-ted distance awav from the last
machined surface 50 located on the inside surface of the
head section 13. Backface 51 does not slidingly engage the
last machined surface 50 until the bit thrust surfaces have
failed after extensive use. An air exit slot 52 is located
on the inside surface of head section 13 on the upper side
of bearing pin 15. Cutter A7 is of a conventional type
having inserts or cutting elements 53 for disintegrating the
earth formation, preferably formed of tungsten carbide.
A single, large disk or button 55 is located in the
bottom of cavity 49 on the axis of ravity 49. Button 55
has a diameter equal to button 27. Button 55 is secured in
a hole in cutter 47 with its outer surface flush with the
bottom of cavity 49 in the preferred embodiment. Button 55
has a flat outer surface containing an inlay 57, as shown
in Fig. 3. Inlay 57 is a circular groove offset from the
axis of button 55 and filled with a solid lubricant such as
silver. Button 55 is formed of a hard, wear resistant
material, preferably a tool steel alloy.
Referring again to Fig. 1, cavity 49 has a small
diameter and a large diameter portion, divided by a shoulder
59. Shoulder 59 is positioned opposite bearing pin shoulder
23 and spaced a short distance away. A plurality of buttons
61 in a circular array are interferingly pressed into holes
formed in shoulder 59. Buttons 61 are o a hard, wear
resistant material, preferably tool steel alloy. Buttons 61
have a knurled cylindrical surface for assisting in retaining
the buttons within the mating holes. Buttons 61 have a
length that is greater than the depth of the holes in shoulder
59, resulting in the buttons 61 protruding a short distance
from shoulder 59. The outer ends o buttons 61 are 1at
and co-planar for slidingly engaging the outer ends of
buttons 25. As shown in Fig. 3, each outer end contains an
inlay 62 of a silver alloy. The alloy of inlay 62 is placed
in a shallow, circular groove formed eccentric to the axis
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of each button 61. The ~uttons 61 are inserted randomly
so that the inlays 62 are oriented in different ways. Inlay
62 provides lubrication.
The bit shown in Fig, 1 has bearing means that
includes a set of roller bearings 63 mounted near the
entrance to cavity 49, Roller bearings 63 are cylindrical
bearings that engage the bearing pin outer section 17 in
rolling contact. Roller bearings 63 are not intended to
absorb axial or outward thrust. The bearing means also
includes a set of roller bearings 65 of smaller diameter
than roller bearings 63. Bearings 65 are cylindrical and
positioned in a race in the inner section 19 of bearing pin
15. Bearings 65 also engage in rolling contact the cavity
39 and the bearing pin 15.
Cutter 47 is retained on bearing pin 15 by means of
a plurality of balls 67. Balls 67 lock the cutter 47 to the
bearing pin 15 after the cutter has been inserted over the
bearing pin 15. Balls 67 are placed within mating races
by means of a passage 69. A retainer 71 holds the balls 67
in place. Retainer 71 is secured by a plug weld 73.
Passage 69 is in communication with passage 37 for receiving
air being pumped through bit 11.
In operation, the bit 11 will be lowered into the
hole and rotated, causing each cutter 47 to rotate about
the axis of each bearing pin 15. The antifriction bearings
comprising rollers 63 and 65 absorb downward drilling forces
imposed on the bit 11. Outward thrust is absorbed by the
sliding contact of buttons 61 with buttons 25. Outward thrust
is also absorbed by the sliding contact of the nose buttons
27 ancl 55O Air pumped down the drill pipe will discharge
through nozzle 41 and also pass through passages 37, 35 and 33.
The air will then flow laterally through channel ~9 to flow
through the bearings 65. The air flows through bearings 65
and through the recesses 45 in the thrust shoulder 23.
Alr also is discharged through passages 43 into the recesses
^ 45 to flow through the balls 67 ar~cl bearings 63~ The air
will discharge at the backface 51 and the air exit slot 52.
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The invention has significant advantages. Locating
hard metal but-tons in the opposed thrust shoulders increases
the life of the thrust shoulders. Prolonging the life of the
thrust shoulders prolongs the life of the bit by increasing
the duration before wear finally allows the cutter to move
back into locking and sliding contact with the head section.
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 ~arious changes
without departing from the scope of the invention.
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