Note: Descriptions are shown in the official language in which they were submitted.
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Apparatus
Field of the invention
The invention relates to cushion subs.
Background of the invention
Cushion subs are used in mining applications for dampening vibrations
transmitted
upwardly through the drill string. The cushion sub is positioned between the
top of the
drill string and the power head and serves to protect the power head from
vibrations, for
example, vibrations generated by downhole hammering operations.
US patent 4,192,155 describes a cushion sub for connecting the rotary power
head of a
drill rig to a drill string. The cushion sub includes an outer housing 24 and
a head in the
form of cap member 40 which together define a cylinder. A piston in the form
of mandrel
12 is received within the cylinder and is axially moveable therein. Guides in
the form of
axially extending splines 32 are spaced around the internal wall of the
housing 24. The
mandrel 12 includes axially extending external splines 22 which in use slide
along the
splines 32. Resilient cushion members 56 and 60 are positioned within the
cylinder-like
space defined by housing 24 and cap member 40 fore and aft of the mandrel 12.
In
operation the splines 32, 22 engage for transmitting torque, i.e. rotational
drive, and the
mandrel 12 may move axially within the housing 24 to compress the cushion
members
56, 60 at the extremes of axial motion, thus dampening axial vibration.
Some cushion subs on the market include a piston and cylinder arrangement
similar to
that of US 4,192,155 and are in use filled with a suitable fluid, such as
grease, and
configured so that the fluid is displaced by the movement of the piston within
the
cylinder to provide a dampening affect.
In operation cushion subs wear out. It is an object of the invention to
provide a cushion
sub having an improved service life, or at least provide an alternative in the
market.
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It is not admitted that any of the information in this specification is common
general
knowledge, or that the person skilled in the art could be reasonably expected
to have
ascertained, understood, regarded it as relevant or combined it in anyway at
the priority
date.
Summary of the invention
The applicant has discovered that the guides and the mounting of the guides
are areas
prone to wear. In particular the applicant has discovered that the piston
tends to wear
the guides along a region corresponding to the usual range of movement of the
piston.
This results in the formation of a raised step adjacent the limits of movement
of the
piston. This step is adverse to performance in that whenever the piston moves
beyond
its usual range of movement, e.g. when the cushion sub is experiencing greater
than
the usual vibration, the piston strikes the step causing vibration to be
transmitted. This
of course places limits on the service life of the cushion sub.
Testing has shown that the mounting of the guides within the head is another
area
where wearing is a problem. Testing of various hardened materials to mount the
guides
has been found to yield unsatisfactory results. The applicant has discovered,
surprisingly, that by using a resiliently deformable mounting the service life
of the
cushion sub can be improved. This has also been found to reduce vibration
transmission from the guides to the head.
In one aspect of the invention there is provided a cushion sub including an
input portion
for receiving drive from a drive means, and an output portion for transmitting
the drive to
a drill string;
one of the input portion and the output portion including one or more guides,
the other of
the input portion and the output portion being engaged with the one or more
guides for
transmitting the drive and arranged for relative reciprocating sliding
movement along the
one or more guides between a first and a second limit of movement;
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at least one of, and preferably each of, the one or more guides including a
shoulder
adjacent at least one of and between the first and the second limit of
movement to
minimise adverse step formation as the at least one guide wears.
The shoulder(s) could be formed by an end face of the guide, and of course may
have a
rounded profile. The shoulder(s) are preferably formed by relieved guide
portions.
The one or more guides preferably each include a shoulder adjacent each of and
between the first and the second limit of movement to minimise adverse step
formation
as the one or more guides wear.
The one or more guides may extend circumferentially about an in use uphole to
downhole axis for the cushion sub to dampen rotational vibration and transmit
axial
drive. Preferably the one or more guides extend in a direction parallel to an
axis about
which the cushion sub in use rotates for the cushion sub to dampen axial
vibration and
transmit rotational drive.
Preferably the one of the input portion and the output portion including the
one or more
guides defines a cylinder, the other of the input and the output portion
defining a piston
axially slidably housed within the cylinder.
In one embodiment the cylinder and the piston each have a complementary non-
circular
cross section, in which case internal walls of the cylinder may form the one
or more
guides. In another embodiment the cylinder includes guides in the form
inwardly
directed splines cooperable with outwardly directed splines disposed about a
periphery
of the piston.
Preferably at least one of, and more preferably each of, the one or more
guides is
formed by a pin, each pin being parallel to the axis and passing through a
respective
aperture, preferably a respective cylindrical aperture, extending through the
other of the
input and the output portion. Advantageously the pins may be cylindrical, in
which case
the relieved guide portion is preferably a cylindrical pin portion of smaller
diameter than
a main pin portion along which the other of the input portion and the output
portion
slides.
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According to preferred forms of the invention the input portion includes the
one or more
guides.
In another aspect of the invention there is provided a cushion sub including
an input
portion for receiving drive from a drive means, and an output portion for
transmitting the
drive to a drill string;
one of the input portion and the output portion defining a cylinder having a
first end wall
and a second end wall, the other of the input portion and the output portion
defining a
piston within the cylinder; and
one or more guide pins within and fixed to the cylinder; the one or more guide
pins
extending in a direction parallel to an axis about which the cushion sub in
use rotates; at
least one of, and preferably each of, the one or more guide pins passing
through a
respective aperture, preferably a respective cylindrical aperture, extending
through the
piston;
the piston being arranged for axial relative reciprocating sliding movement
along the
one or more guide pins and engaged with the guide pins for transmitting
rotational drive
from the input portion to the output portion;
each guide pin having a first end, a second end and a main pin portion along
which the
piston slides;
wherein the first end, and preferably only the first end, of at least one of,
and preferably
each of, the guide pins is press fitted into the first end wall of the
cylinder.
The pins are preferably cylindrical. The press fit preferably includes an
interference of
about 50Nm, say 50 20 pm, on diameter is preferred.
The first end of the at least one, or preferably each, guide pin is preferably
of smaller
diameter than the main pin portion. The best results are obtained when the
first end is
'straight' i.e. not tapered.
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Preferably the second end of the at least one, or preferably each, guide pin
is mounted
to the second end wall via a mounting, the mounting being formed of
resiliently
deformable material for absorbing vibrations. The mounting is preferably
fitted over and
surrounds the second end and is fltted within a respective recess in the
second end
5 wall. Preferably the mounting is press fitted to the second end. The
mounting is
preferably a tubular sleeve having open ends.
The second end of the at least one, or preferably each, guide pin is
preferably of smaller
diameter than the main pin portion. The mounting may have an outer diameter
substantially equal to the diameter of the main pin portion.
The mounting is preferably formed of urethane.
In another aspect of the invention there is provided a cushion sub including
an input
portion for receiving drive from a drive means, and an output portion for
transmitting the
drive to a drill string; and
one of the input portion and the output portion defining a cylinder having a
first endwall
and a second endwall, the other of the input portion and the output portion
defining a
piston within the cylinder;
one or more guide pins within and fixed to the cylinder; the one or more guide
pins
extending in a direction parallel to an axis about which the cushion sub in
use rotates; at
least one of, and preferably each of, the one or more guide pins passing
through a
respective aperture, preferably a respective cylindrical aperture, extending
through the
piston;
the piston being arranged for axial relative reciprocating sliding movement
along the
one or more guide pins and engaged with the guide pins for transmitting
rotational drive
from the input portion to the output portion;
each guide pin having a first end, a second end and a main pin portion along
which the
piston slides;
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wherein the second end of at least one, or preferably each, guide pin is fixed
to the
second endwall via a respective mounting, each mounting being formed of
resiliently
deformable material for absorbing vibrations.
In another aspect of the invention there is provided a cushion sub including
an input
portion for receiving drive from a drive means, and an output portion for
transmitting the
drive to a drill string;
one of the input portion and the output portion defining a cylinder having a
first endwall
and a second endwall, the other of the input portion and the output portion
defining a
piston within the cylinder;
one or more guide pins within and fixed to the cylinder, the one or more guide
pins
extending in a direction parallel to an axis about which the cushion sub in
use rotates; at
least one of, and preferably each of the one or more guide pins passing
through a
respective aperture, preferably a respective tubular aperture, within the
piston;
the piston being arranged for axial relative reciprocating sliding movement
along the
one or more guide pins and engaged with the guide pins for transmitting
rotational drive
from the input portion to the output portion;
each guide pin having a first end, a second end and a main pin portion along
which the
piston slides;
at least one of, or preferably each of, the one or more guide pins including a
lubricating
groove along its main pin portion.
The groove may be helical, and preferably extends substantially the full
length of the
main pin portion.
The various aspects of the invention are complementary; each aspect may
incorporate
the features of the other aspects of the invention.
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Brief description of the drawings
Figure 1 is a schematic axial cross-sectional view of a cushion sub according
to a
preferred form of the invention;
Figure 2 is a top end view of the piston of the cushion sub of Figure 1;
Figure 3 is an axial cross-sectional view of the piston of Figure 2;
Figure 4 is a bottom end view of the head of the cushion sub of Figure 1;
Figure 5 is an axial cross-sectional view of the head of Figure 4;
Figure 6 is a bottom end view of the cylinder of the cushion sub of Figure 1;
Figure 7 is an axial cross-sectional view of the cylinder of Figure 6;
Figure 8 is a top end view of the cylinder of Figure 6;
Figure 9 is a side view of the air nozzle of the cushion sub of Figure 1; and
Figure 10 is a side view of one of the drive pins of the cushion sub of Figure
1.
Detailed description of the embodiments
The cushion sub 10 includes two principal components: an input portion 130 and
a
piston 60. The input portion 130 includes an axially extending conical portion
270 with
external threads 80 for receiving a rotational drive from a drill rig power
head (not
shown). Piston 60 includes an internally threaded tapered section 90 for
receiving, and
thereby transmitting drive to, a drill string (not shown) and thereby forms an
output
portion. As described in more detail below a passageway, partly defined by an
air
nozzle 120, axially extends through the cushion sub 10 for conveying air
downhole.
The input portion 130 includes a cylinder body 20 and a head 50 which together
define
cylinder cavity 140. The cylinder body 20 is made up of a cylinder wall 30 and
a back
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head 40. The piston 60 is axially slideable within the cylinder cavity 140.
The input
portion 130 also includes a circular array of twelve longitudinal drive pins
70 within the
cylinder cavity 140. The drive pins 70 are equi-spaced on a concentrically
aligned pitch
circle. As described in more detail below, the drive pins 70 are connected at
end
portions 240, 320 to the back head 40 and to the head 50 respectively.
The piston 60 includes a squat cylindrical head portion 190 and an integrally
formed
tubular stem like body portion 180. A circular array of guide apertures 150
complementary to the drive pins 70 extends through the head portion 190 of the
piston
60. An interior of the body portion 180 includes threaded tapered section 90
at a
location distal to the head portion 190. Internally threaded blind bores 510
are provided
on an end face of the head portion 190 and provide attachment points to lift
and
manoeuvre the piston 60 during assembly.
The guide apertures 150 in use slidingly engage the drive pins 70. Torque
transmitted
from the power head to the input portion 130 (via the tapered thread 80) is
transmitted
to the piston 60 via the drive pins 70, and the guide apertures 150. Torque is
in turn
transmitted to the drill string via the tapered thread 90. The piston 60 is in
use free to
slide along the drive pins 70. In operation the cylinder cavity 140 is packed
with grease,
although the person skilled in the art will appreciate that other fluids may
be suitable.
The grease serves a dual role both as a lubricating fluid and as a dampening
fluid. The
grease serves to lubricate the sliding contacts between the guide pins 70 and
the
guiding apertures 150. As the cylinder 60 moves axially within the cylinder
cavity 140
the grease is displaced through small clearances between the drive pins 70 and
the
guide apertures 150 and between the cylinder 60 and the internal dimension of
the
cylinder wall 30. In this embodiment a radial clearance of about 0.25mm is
provided
about the periphery of the cylinder 60. The viscous action of the grease being
forced
through these small clearances serves to dampen axial vibration.
Resilient cushion members 100, 110 are provided within the cylinder cavity 140
at
respective ends of the piston stroke to provide further dampening. As the
piston 60
approaches either end of the cylinder cavity 140 the respective cushion member
100,
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110 compresses to provide a soft end to the piston stroke. The compressed
state of the
cushion members 100, 110 thereby defines the limits of movement of the piston
60.
Each of the cushion members 100, 110 have a circular shape corresponding to
the
interior of the cylindrical wall 30 and include circular apertures to
accommodate the
drive pins 70. Cushion member 100 includes a large central circular aperture
to
accommodate the body 180 of the piston 60. Cushion member 110 includes a
central
aperture to accommodate the air nozzle 120.
Figures 6, 7 and 8 illustrate the cylinder body 20 in more detail. In this
embodiment the
cylinder body 20 is integrally formed and includes the cylinder wall 30 and
the back
head of 40. The cylinder wall 30 has a cylindrically tubular cross section.
One end of the
cylinder wall 30 is spanned by the back head 40. The other end of the cylinder
wall 30 is
open and is in use closed by the head 50. The back head 40 is a disc-like
formation
including a large central tubular aperture 170, through which in operation the
cylinder
body 180 passes, and twelve pin mounting apertures 160 equi-spaced about a
concentric pitch circle for receiving the drive pins 70.
The aperture 170 includes seal mounting structures 200 in the form of inwardly
open
circumferential grooves. In use seals (not shown) are mounted within the seal
mounting
structures 200 to create a seal between the piston body portion 180 and the
aperture
170 to prevent grease from escaping from the cylinder cavity 140 and to
prevent dust
and debris contaminating the cylinder cavity 140. Additional sealing is
provided by
another seal (not shown) retained by the locking ring 210. The locking ring
210 has an
annular shape and includes 6 counter sunk bolting apertures 220 equi-spaced
about its
perimeter. The bolting apertures 220 in use align with complementary threaded
bores
230 (shown in Figure 6) equi-spaced about the back head 40. The locking ring
210 is in
use retained by counter-sunk bolts passing through the bolt holes 220 and
engaging
with the threaded bores 230 to compress the seal (not shown) in place. Note:
Figure 1
shows the locking ring 210 rotated from its usual position to illustrate the
bolting
apertures 220.
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The head 50 includes a disc-like portion of 250 (see Figures 4 and 5) which in
use
closes the open end of the cylinder body 20; a concentric circular boss 260
and the
conical portion 270 (which includes the external threads 80).
Twenty axially extending counter-bored bolt holes 280 are equi-spaced about
the
5 periphery of the disc-like portion 250 of the head 50. As illustrated in
Figures 6, 7 and 8
the cylindrical body 20 includes twenty threaded blind bores 290 equi-spaced
about an
end face of the cylindrical wall 30 at locations complementary to the
locations of the bolt
holes 280. The head 50 is in use retained relative to the cylinder body 20 by
bolts (not
shown) passing through the bolt holes 280 and engaging with the threaded bores
290.
10 Twelve blind bores 300 are equi-spaced on a concentric pitch circle to in-
use open into
the cylinder cavity 140. As described in more detail below the blind bores 300
are
dimensioned to receive a respective sleeve 310 and drive pin end portion 320.
Figure 10 illustrates a preferred form of drive pin 70. Drive pin 70 includes
a main pin
portion 330 which in this embodiment has a diameter of 40mm. The pin 70
includes end
portions 320 and 240 which are stepped down to smaller diameters for mounting
in the
bores 300 of head 50 and apertures 160 of back head 40 respectively. The pin
70
includes relieved portions 340, 350 intermediate the main pin portion 330 and
the end
portions 240, 320 respectively. Shoulders 500 are formed at the junctures of
the main
pin portion 330 and the portions 240, 320 respectively.
The pin mounting apertures 160 of back head 40 are straight cylindrical bores
extending
in an axial direction through the back head 40. The drive pin end portions 240
are
dimensioned for a press fit within a respective one of the apertures 160. In
this
embodiment the end portion 240 has a nominal diameter of 32 mm. The tolerances
on
the diameters of the apertures 160 and the end portions 240 are selected for
an
interference of 50 20pm. A temperature difference may be used to aid in the
assembly
of drive pins 70 and back head 40. For example, the drive pins 70 may be
cooled by
immersion in liquid nitrogen or by packing in dry ice prior to pressing into
the apertures
160.
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In this embodiment a soft mounting in the form of a sleeve 310 embraces an end
portion
320 of each respective drive pin 70. The end portion 320 and the sleeve 310
are in turn
mounted with the blind bore 300 of the head 50. The sleeve 310 is formed of
urethane,
although of course a range of other resiliently deformable materials would be
suitable,
and provides a degree of cushioning between the head 50 and the drive pin 70
which
has been found to provide an improved service life. Preferably, as
illustrated, the end
portion 320 has a lesser diameter than the main portion 330 of the pin 70.
This
advantageously allows for a relatively thick sleeve 310 to be used without
increasing the
size of the blind bore 300 (which would involve changing the layout of the
cushion sub
10, including expanding the overall diameter of the cushion sub 10).
In this embodiment the end portion 320 has a diameter of 32mm. The sleeve 310
has a
nominal internal diameter of 31 mm and an outer diameter of 40mm. The bore 300
has a
diameter of 40mm. During assembly the sleeves 310 are first fitted within the
bores 300.
The end portions 320 of drive pins 70 are then pressed into the sleeves 310.
Thus,
there is a 1 mm interference on diameter between the sleeve 310 and end
portion 320
so that the sleeve 310 is expanded and compressed in place. This mounting
arrangement has been found to locate the drive pins 70 with sufficient
accuracy, to
reduce wear, and to minimise vibration transmission from the drive pins 70 to
the head
50 and thereby minimise vibration transmission to the drill rig power head.
In this embodiment the relieved portions 340, 350 are cylindrical and have a
diameter of
38mm (the main pin portion 330 has a diameter of 40mm) so that there is a 1 mm
set
back at shoulder 500. In use the piston 60 slides along the main portion 330
of the drive
pin 70. Over time this sliding motion in conjunction with the torque being
transmitted
wears an axially extending side region of the drive pin 70. This embodiment
allows for a
full millimetre of wear on the drive pins before an adverse step starts to
form. This
greatly improves the service life of the cushion sub 10.
Another improvement directed to the problem of the main portion 330 of the pin
70
wearing is the provision of a lubricating groove in the form of helical scroll
360. In this
embodiment, the scroll 360 is a single groove helically extending the full
length of the
main portion 330. The scroll 360 is 4mm wide, 0.5mm deep and has a pitch of
48mm.
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The groove has been found to be effective at carrying lubrication to the
wearing portions
of the main portion 330.
The head 50 includes a central axial passageway 370 which is in use
communicated
with a central axial passageway 380 extending through the piston 50. These
intercommunicating passageways provide means for the drilling head to fluidly
communicate with the drill string. By way of example a charge of pressurised
air, say at
about 500 psi, can be provided from the drill rig power head to the drill
string via the
cushion sub to create an upward flow of air in the annular space downhole
about the
drill string. Dust entrained in this airflow provides information about the
rock at the lower
extent of the drill string.
Figure 9 depicts air nozzle 120 that is a cylindrical tubular structure and
towards one
end includes an outwardly extending peripheral flange 390 and between the
flange and
the end two outwardly open circumferential grooves 400.
As illustrated in Figure 1 the air nozzle 120 is in use fixed relative to the
head 50. For
this purpose the head 50 includes concentric countersunk bore portions 430,
440 and
450 of successively greater diameter (see Figure 5). As illustrated the bore
portion 430
is concentric with the head 50 and sized to receive the end portion 460 of the
air nozzle
120. Bore portion 440 is sized to receive the flange 390, and bore portion 450
is in turn
sized to receive a lock ring 410. In use the air nozzle 120 is received within
the head 50
and the lock ring 410 positioned within the bore 450 to overly the flange 390.
The lock
ring 410 has an annular form and includes six counter-bored bolt holes 470
equi-spaced
on a concentric pitch circle. The lock ring 410 is retained by flush mounted
bolts passing
through the counter-bored bolt holes 470 and engaging with the threaded blind
bores
420 (see Figures 4 and 5). In use seals are mounted within the grooves 400 and
sealingly connect the air nozzle 120 and the head 50 to prevent pressurised
air
escaping from the passageway 370.
In use the air nozzle 120 projects into the passageway 380 of the piston 50.
As shown
in Figure 3 the piston 50 includes inwardly open circumferential grooves 480
with the
passageway 380. In use seals are mounted within the grooves 480 to sealingly,
and
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slidingly, connect the air nozzle 120 and the piston 50. This arrangement
allows for the
piston 50 to slide axially along the body of the air nozzle 120 and to prevent
air leaking
from the passageway 380 into the cylinder cavity 140.
As shown in Figure 7 a radially extending threaded bore 490 passes through the
cylindrical wall 30 and provides an inlet port for supplying grease to the
cylinder cavity
140. In use a bolt (not shown) sealingly closes the bore 490.
It will be understood that the invention disclosed and defined in this
specification
extends to all alternative combinations of two or more of the individual
features
mentioned or evident from the text or drawings. All of these different
combinations
constitute various alternative aspects of the invention.
