Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to drilling rigs,
and, more particularly, it relates to devices designed for
centering the drill rod throughout the drilling operation.
Known in the art are centering devices which
include rigs for centering the drill rods, made in the form
of sleeves fixed to the mast of the rig.
In some cases, these sleeves are mounted in
anti-friction bearings to reduce the friction wear and
withstand the impact loads.
A disadvantage of the above devices is their
permanent centering diameter.
There is also known a centering structure,
considered as the prior art of the present invention,mounted
on a cross-piece slidable along the mast and including two
hollow half-cylinders engaging each other to define a closed
cylindrical space directing a drill rod in the course of
drilling. One of the two half-cylinders is fixed to the
crosspiece, while the other half-cylinder is mounted on the
end of an arm attached to the same crosspiece to be retrac-
table by a hydraulic cylinder, to provide access to thedrilling axis. so that a successive drill rod can be either
installed or removed, whereafter the half-cylinder can be
returned into its initial position.
A disadvantage of this known centering device
is likewise its permanent centering diameter.
In most cases in the process of drilling the
drill rods, which are thick-wall pipes, become tapered in
the drilling direction because of the abrasion wear.
Consequently, the clearance between the center-
ing diameter of the centering device and the rod at anygiven moment of operation of the rig is a variable value and
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may acquire a considerable magnitude, particularly, at
earlier stages of the drilling cycle.
As a result, during operation, particularly in
case of inclined drilling, the drill rod might become
deflected from the required geometric axis of drilling,
which, in turn might cause relatively great bending strain
in the drill rod bearing assembly, leading to a breakdown.
It is an object of the present inventionto pro-
vide drill rod centering device for a drilling rig in which,
notwithstanding the degree of the dimensional wear of the
drill rod, the centering diameter will automatically adjust
itself corresponding to the actual rod diameter.
In accordance with the invention, there is
thus provided a drill rod centering device adapted to be
mounted on the mast of a drilling rig and comprising a
housing with a central bore provided in the bottom thereof
for the passage of a drill rod therethrough, fixed to a lower
portion of the mast, a mechanism for centering the drill rod
in the housing, a rotating mechanism connected with the drill
rod centering mechanism, and a hydraulic drive means opera-
tively connected with the rotating mechanism. The mechanism
for centering the drill rod includes at least three link
gears each mounting a roller bearing uniformly circumferen-
tially spaced within the housing. The roller bearings are
mounted on the link gears by vertical spindles adapted for
radial displacement by the action of the hydraulic drive
means by means of said rotating mechanism and the respective
link gears, and engage the drill rod by their respective
peripheral surfaces, thus defining the centering diameter;
hydraulic valves underly the roller bearings. The roller
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bearings are spring-urged along their respective axes and
mounted for axial displacement so that when the friction
between the drill rod and the roller bearings attains a pre-
determined value, the roller bearings follow the drill rod
travel in the direction of drill and actuate the hydraulic
valves, whereby the valves exert a force setting the center-
ing diameter to correspond with the drill rod diameter.
The present invention provides a centering
device wherein the constant clearance between the centering
surface of the device and a drill rod is set automatically,
notwithstanding the actual degree of the dimensional wear of
the rod.
The present invention will be further described
in connection with an embodiment thereof, with reference
being made to the accompanying drawings, wherein:
Fig. 1 shows schematically the general side
elevation of a drilling rig incorporating a drill rod center-
ing device in accordance with the invention,
Fig. 2 is a plan view of the drilling rig of
Fig. 1,
Fig. 3 is a plan view of the device in accordance
with the invention,
Fig. 4 is a sectional view taken on line IV-IV
of Fig. 3,
Fig. 5 is a sectional view taken on line V-V
of Fig. 3, and
i Fig. 6 is the hydraulic circuit diagram of the
device.
Referring now to the drawings, Figs. 1 and 2,
the drilling rig is provided with a self-propelled under-
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carriage 1 supporting two compressor units 2, a diesel-
generator unit 3, three oil pump units 4, the drilling
operator cab 5, a transformer 6, a support 7 having a mast
or derrick 8 pivotably secured thereto as well as other
auxiliary equipment and the necessary control and monitoring
gear (not shown).
The mast 8 has mounted thereon a drill string
rotating gear 9 with a hydraulic motor 10, a drill rod 11,
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and an arrangement 12 for storing drill rods and feeding
them to the drilling line, rod screw off mechanism 13, an
arrangement 14 for running in and out the drill string,
and a centering device 15.
This device 15 is shown in more detail in Figs.
3 to 5 and comprises a cup-shaped housing 16 with a central
opening for the passage of the drill rod 11 through the
bottom thereof, the housing 16 being fixed to a lower portion
of the mast 8.
10The internal cylindrical space of the housing 16
accommodates a rotation mechanism with an annular driver 17
retained against axial displacement by a flange 18.
Mounted between the bottom of the housing 16 and
the flange 18 are three axles 19 uniformly circumferentially
spaced in the housing and serving as the pivot axes of the
respective link gears 20.
The link gear 20 includes a roller bearing 21,
a fork-shaped arm 22 with a slot 23 slidably receiving a
slide block 2~ carrying a pin 25 fixed in the respective
lug of the driver 17. One end of the arm 22 has a bore
receiving the respective axle 19, while its other end has
two coaxial cylindrical bores receiving therein roller
bearings 26 in which a spindle 27 carrying the respective
roller bearing 21 is journalled. The spindle 27 with the
roller bearing 21 is mounted for limited axial displacement,
while the roller bearings 26 are fixed with lock rings 28 and
covers 29 and 30, respectively. An internal bore of the
spindle 27 receives therein a ball bearing 31 in which a
pintle 32 is journalled.
30A socket provided in the cover 30 receives a stack
of disc springs 33 urging the spindle 27 toward the opposite
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cover 29 through the pintle 32 and the ball bearing 31.
Threadedly secured in the central threaded bore of the
cover 30 is a hydraulic control valve 34 adjusted so that its
actuating stem 35 should be normally separated from the ad-
jacent end face of the pintle 32 by a design gap " ~ ".
The driver 17 is pivotally connected by means of a fork 36
with the piston rod 37 of a hydraulic cylinder 38 of which
the body 39 is likewise pivotally connected with the mast 8.
Three link gears 20 with their respective roller
bearings 21, accomodated circumferentially within the
housing 16, and the single driver 17 define a closed en-
compassing system through which the drill rod 11 passes
and is supported on the roller bearings 21.
The hydraulic circuitry of the herein disclosed
device structure includes the three positively-actuated
check valves 34, the hydraulic cylinder 38, a distributor 40,
a hydraulic lock 41 and two throttles 42 and 43. The
circuitry is supplied with oil under pressure from the cen-
tral oil pump unit 4 of the rig.
The device operates, as follows. When the hy-
draulic motor 10 of the drill rod rotation mechanism 9 is
energized, the drill rod 11 is rotated jointly with the
drilling tool 44 fixed to its lower end. Simultaneously, the
working hydraulic fluid (or oil) is fed under pressure into
the hydraulic system of the device 15. The working fluid is
supplied throughthe distributor 40 set to the position "b",
the hydraulic lock 41 and the throttle 42 into the rod-
including space of the hydraulic cylinder 38, whereas the
above-piston space of the hydraulic cylinder 38 is connected
to drain via the throttle 43, the hydraulic lock 41 and the
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distributor 40. The piston 45 with its piston rod is pulled
into the cylinder 38, whereby the driver 17 of the link
gears 20 is rotated, and the roller bearings 21 are urged
against the drill rod 11, setting the latter to the drilling
line or axis.
In operation, on account of the non-uniform
lengthwise abrasion wear, the drill rod ac~uires a noticeably
tapering shape, whereby the operation of the herein disclosed
device with a new, unabraded drill rod of a permanent diameter
differs from its operation with a dimensionally worn and,
therefore, tapering rod.
When operating with a tapering rod, the bearing
rollers 21 acted upon by the hydraulic cylinder 38 perma-
nently engaged the rod 11 and hold it strictly at the drilling
axis.
Owing to the axial feed of the drill rod and the
friction between the rod 11 and the bearings roller 21, the
latter are pulled down by the rod in the direction of the
latter's axial travel, whereby the stack of the springs 33
is compressed until the friction is compensated or by the
effort of their compression. The design gap " ~ " between
the pintle 32 and the stem 35 of each respective hydraulic
valve 34 is thus taken up, but the valves remain closed.
As the drill rod 11 is driven further into the ground, with
the drill rod 11 being encompassed by the roller bearings
21, the diameter of the tapering rod gradually increases,
building up the friction between the rod and the roller
bearings 21 whereby the stacks of the springs 33 are com-
pressed still further,until the pintles 32 actuate the
valves 34 into their open position.
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With all the three hydraulic valves 34 opening,
the hydraulic line opens to pass the working fluid under
pressure into both the under-piston and above-piston spaces
of the hydraulic cylinder 38, and since the effective area
of the piston in the above-piston space is in excess of
that in the under-piston space, the piston rod is driven
outwardly to increase the centering diameter of the drill
rod centering device.
With the centering diameter defined by the setting
of the roller bearings 21 increasing, the friction between
the rod 11 and the peripheral side surface of each roller
bearing 21 decreases, whereby the stacks of the springs 33
lift off the roller bearings 21 until a moment comes when
either one of the three hydraulic control valves 34 closes.
This is sufficient for the piston of the hydraulic cylinder
38 to be reversed, which means that the roller bearings 21
are once again urged against the rod 11.
The abovedescribed sequence is periodically
repeated until a certain drilling depth is attained, and the
centering of the drill rod is no longer necessary: conse-
quently, the distributor 40 i9 set to the position "a"
whereby the working fluid is supplied into the above-piston
spaoe of the hydraulic cylinder 38, and the piston rod 37
is driven outwardly to rotate the driver 17 and spread out
the link gears 20 with their roller bearings 21, so that
the centering function is discontinued.
Should the efforts be developed which would
be capable of driving down solely either one or two of the
rollers 21, e~g., as is often the case with inclined drilling,
either one or two hydraulic valves 34 open, respectively,
which is insufficient to increase the centering diameter of
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the drill rod centering device. Thus, only three efforts
simultaneously acting upon three roller bearings are capable
of increasing the centering diameter of the drill rod center-
ing device. In any other case the drill rod centering de-
vice maintains the preset position of the roller bearings
21 and affords an unyielding centering function.
A clearance between the rod of the minimum
diameter and the roller bearing can be preset by adjusting
the abutment collar 46 on the piston rod 37 of the hydraulic
cylinder 38.
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