Note: Descriptions are shown in the official language in which they were submitted.
`` 11:~9$8~S8
The present invention relates to machine building and
more specifically it relates to tapered screw joints of parts
and to devices for the emergency recovery of the boring tool
from boreholes with the use of said joint.
Widely known in the previous art are tapered screw
joints with the thread profile formed by the conjugated sides
set at an angle to each other, one of the sides being a bear-
ing one.
Like in straight pipe threads, the bearing side of the
profile in the known taper threads is inclined at an angle of
0 to 75 to the plane perpendicular to the thread axis.
Such tapered screw joints can be assembled and dis-
assembled many times by rotating only one part relative to the
other one and, consequently, by applying torque, which takes
comparatively much time.
However, such joints cannot be used as quick-discon-
nect joints for instantaneous emergency disconnection of parts
for example in boreholes, pipelines and other hard-to-get-at
places because on application of axial tensile loads the bear-
ing surface of the taper thread will be destroyed (sheared andcrushed) thus rendering such a tapered screw joint unfit for
further use.
An object of the present invention resides in provid-
ing a tapered screw joint of parts and a device for the emer-
gency recovery of the boring tool from the borehole with the
use of this joint whose thread profile would ensure re~eated
disconnection of the joint under the force of axial tensile
loads.
Another object of the invention resides in providing
a device for recovering the boring tool from the borehole with
the use of th~ tapered screw joint whose thread profile would
ensure transmission by said joint of strong torques, and its
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disconnection under heavy axial loads.
This object is achieved by providing a tapered screw
joint of parts with the thread profile formed by the conjugated
sides of the thread set at an angle to each other, one of the
sides being a bearing one. According to the invention, the
bearing side of the thread profile is inclined at an angle
varying from about 86 to about 98 to a plane which is per-
pendicular to the thread axis.
Such a solution permits rapid and repeated disconnec-
tion of the tapered screw joint of parts by subjecting them toaxial tensile loads and by assembling them subsequently under
the effect of a torque.
This is achieved due to the fact that the bearing
side of the thread profile at the above-mentioned angles of
its inclination works in crushing (and not in shear as in the
known tapered screw joints) so that with sufficient surface
hardness such tapered screw joints of part~ can be used re-
peatedly for disconnecting parts by subjecting them to axial
tensile loads.
~o When the inclination angle of the bearing side of
the taper thread varies from about 90 to about 98 (i.e. ex-
ceeding the right angle), the tapered screw joint is capable of
transmitting torques similarly to the known tapered screw
joints and be disconnected under light axial loads. Therefore
such screw joints can be employed for rapid disconnection of
parts transmitting heavy torques, e.g. in emergency couplings.
When the bearing side of the profile of the taper
thread is inclined at the angles from about 86 to about 90
(i.e. smaller than the right angle) the tapered screw joint
can transmit the same torques as the known joints and be dis-
connected at heavier axial loads, therefore such screw joints
can be employed for rapid disconnection in the axial direction
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of the parts transmitting heavy torques and standing heavy
axial loads.
Such type of the tapered screw joints can be used
most effectively in the devices for emergency recovery of
boring tools from boreholes.
Known in the previous art are devices for the emer-
gency recovery of boring tools from the borehole, built into
the drilling string (see, for example, Bowen Tolls, Inc.,
General Catalog 1972-73, p. 627, Bowen Surface Jar) comprising
a hollow body which accommodates a telescopically inserted
hollow rod, both being kinematically linked with each other
with a provision for their disconnection on application of
axial tensile loads.
In these devices said kinematic linkage between the
body and the rod comprises an adjustable collet joint consist-
ing of a collet sleeve located in the conical part of the body,
and a friction piston rigidly connected with the rod.
In case of emergency, e.g. when the boring tool gets
stuck in the borehole, the device is built into the drilling
string between the driving pipe which transmits the torque
from the rotor and is located above the borehole head, and
the remaining part of the drilling string lowered into the
borehole.
In this case the rod of the device is connected by
means of an adapter bushing with the driving pipe while the
body is connected by means of another adapter bushing with the
remaining part of the drilling string.
Then internal tensile stresses are built up in the
pipes by lifting the drilling string by a system of hoists un-
til the collet joint is disconnected.
The collet sleeve goes down at a high speed so thatthe stress in the pipes of the drilling string drops to zero
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and said pipes are drawn into a vibratory process which frees
the boring tool stuck in the borehole.
One of the disadvantages of such devices for re-
covering the boring tool from the korehole lies in that the
adjustable collet joints have to be protected against the
material surrounding them in the borehole by, say, oil-filled
housings in order to prevent the particles of hard material
(drilling sludge, etc,) from getting into these joints. As a
result, the known devices are too complicated in design and
comparatively unreliable.
Another disadvantage of the known device lies in
that the adjustment of the force required for disconnecting
the collet joint is difficult since it is carried out by a
side screw located outside the borehole.
Besides, each of the known devices ca~ act on the
boring -tool stuck in the borehole in one direction only, i.e.
from top to bottom or vice versa, therefore the drilling site
has to be equipped with two devices simultaneously which is
unprofitable.
According to the invention, in the device for emer-
gency recovery of the boring tool from the borehole the end of
the rod located in the body carries a rigidly in~talled co-
axial inner conical bushing with an external taper thread
while the body accommodates an outer conical bushing which
envelops the inner bushing and has a matching internal taper
thread which, to~ether with the ~aper thread of the inner
conical bushing, froms a tapered screw joint with ~he ~hread
profile whose bearing side is inclined at an angle of from
8830' to 8940', to the plane perpendicular to the thread
axis the outer conical bushing being thin-walled and set so
as to fo~m a circular clearance between said bushing and the
body, said clearance extending throughout the length of said
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tapered screw joint.
Such an arrangement makes it possible to dispense
with the ~ea~s for protecting the unit which ensures kine-
matic linkage between the body and the rod of the device
thereby simplifying its design and stepping up its reliability.
It is practicable that the device should be built
into a drilling string by means of two adapter bushings one of
which is rigidly secured on the end of the rod protruding
from the body, while the other one is secured on the opposite
end of the body and serves for fastening the outer conical
bushing in said body, the axial hole in said bushing being
threaded and receiving an adjusting screw whose end interacts
with the end of the inner conical bushing while it is moved
relative to the outer conical bushing in order to change the
area of the matching surfaces of their tapered screw joint.
Such a solution provides for a wide range of adjust-
ments of the axial forces required for disconnecting the
tapered screw joint and thus adds to the versatility of the
device since it ensures also a wide range of adjustment of
the force and frequency of the blows dealt to the element
of the drilling string stuck in the borehole.
According to one of the embodiments of the invention,
the other adapter bushing carries a rigidly secured coaxial
damping piston which covers the circular clearance between the
outer surface of the body and the borehole walls.
This arrangement allows the device to be used for
creating a pulse-wave effect on the element of the drilling
string stuck in the borehole, since in this case the damping
piston takes the weight of the liquid contained in the upper
part of the circular clearance between the borehole walls and
the body and creates a hydrodynamic effect thereby excluding
the recoil of the hoisting devices.
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It is practicable that the outer conical bushing
should be made of a metal with a higher elasticity than that
of the metal of the inner conical bushing.
This solution ensures reliability of the outer coni-
cal bushing and of the device as a whole during its repeated
employment.
To extend the service life of the device the bearing
side of the profile of the taper thread on both conical bushings
may be surfacehardened.
In accordance with one aspect of the present inven-
tion, there .is provided a tapered screw joint comprising a
tapered externally spiral-helically grooved male member en-
gageable in a complimentary shaped female member, the grooves
forming a tapered screw joint having a thread profile whose
bearing side is inclined at an angle from 86 to 98 to the
plane which is perpendicular to the thread axis.
In accordance with a further aspect of the present
invention there is provided a device for emergency recovery of
a boring tool from a borehole, built into a drilling string
wherein a hollow body accomodates a telescopically inserted
hollow rod: and inner conical bushing with an external taper
thread is rigidly secured on the end of the rod accommodated in
the body coaxially with said rod, while an outer conical bush-
ing is secured in the body so as to form a circular clearance
between said body and bushing and to envelop said inner conical
bushing, and has a matching internal taper thread which, to-
gether with the external taper thread on the inner conical
bushing, forms a tapered screw join-t of these bushings: the
improvement consists in that the tapered screw joint of these
bushings has a thread profile whose bearing side is inclined
at an angle from 8830' to 8940' to the plane which is per-
pendicular to the thread axis which provides for repeated dis-
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connection of said body and rod under the effect of tensileloads and for subsequent connection thereof under the effect
of an applied torque.
Given below is a description of one of the possible
embodiments of the invention with reference to the accompanying
drawings in which:
Figs. 1 and 1' illustrate a fragmented schematic
general view of a device for emergency recovery of a boring
tool from a borehole with the use of a tapered screw joint of
parts in accordance with the present invention, the device as
shown is fragmented along line A-A.
Fig. 2 shows fragment "B" in Fig. 1' and designates
the geometrical elements of the tapered screw joint of parts
according to the inve~tion, enlarged,
Fig. 3 - same as in Fig. 2 with the tapered screw
joint working under load,
Fig. 4 is a ~ongitudinal section through the damping
piston.
The device for the recovery of the boring tool from
the borehole in an emergency situation ~sticking of the tool in
the borehole) comprises a hollow cylindrical body 1 (Fig. 1)
accommodating a telescopically-installed hollow rod 2 which,
according to the invention, is linked kinematically with said
body by a tapered screw joint.
The end of the rod 2 accommodated in the body 1
carries a rigidly installed coaxial inner conical bushing
with an external taper thread, said bushing made in the form of
a nipple 3 while the body 1 accommodates a rigidly secured
outer conical bushing in the form of a friction coupling 4
enveloping the nipple 3 and provided with a matching internal
taper thread which, together with the thread of the nipple 3,
forms a tapered screw joint.
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According to the invention, this joint has a thread
profile whose bearing side is inclined at an angle of from
8830' to 8940' to the plane which is perpendicular to the
thread axis.
The device for the Pmergency recovery of the boring
tool from the borehole is built into the drilling string (not
shown in the drawing) with the aid of two adapter bushings 5
and 6 one of which (5) is rigidly secured on the upper end of
the rod 2 protruding from the body whereas the other one (6)
is secured on the opposite (lower) end of the body 1 with the
aid of an intermediate bushing 7.
The lower adapter bushing 6 and the intermediate
bushing 7 also provide for fastening the conical friction
coupling 4 in the body 1.
According to the invention, the axial hole in the
lower adapter bushing 6 is threaded and receives a hollow ad-
justing screw 8 with a lock nut 9, the end of said screw 8
interacting with the end of the nipple 3 when the latter is
moved axially relative to the coupling 4 for changing the area
of the matching surfaces of the tapered screw joint between
said coupling 4 and nipple 3.
Thus, the axial tensile force for the disconnection of
the nipple 3 and coupling 4 are adjusted by turning the adjust-
ing screw 8 in or out.
The upper end of the body 1 carries a bushing 10 which
limits the travel of the rod 2 for which purpose the latter is
provided, above the nipple 3, with a rigidly secured anvil 11
interacting with the bushing 10.
The circular clearance between the body 1 and the rod
2 is sealed by cups 12 placed into the recess of the bushing
10 and held in position by a nut 13.
The device also comprises a damping piston 14 (Fig. 4)
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in the form of a threaded bushing 15 with cups 16 secured on
it. The damping piston 14 is fastened to the lower adapter
bushing 6 and covers the circular clearance between the outer
surface of the body 1 of the device and the borehole walls
(not sho~n in the dra~ing).
All the joints of the device are threaded which
facilitates its manufacture, disassembly and assembly.
The nipple 3 and the friction conical coupling 4
enveloping it form a screw pair with a pitch "S" (Fig. 2). The
thread profile of the tapered screw joint of the nipple 3 and
coupling 4 is formed by the sides "a" and "b" conjugated with
each other at rounding radiuses "r" and "rl" set at an angle
(~ + ~) to each other, the larger of these sides being a
bearing one.
According to the invention, the bearin~ side "a" of
the profile of the taper thread is inclined to the plane per-
pendicular to the thread axis "0 -0" at an angle ~ which is
selected within the range from 8830' to 8940' depending on
the pitch "S" of the taper thread, the material and the thick-
ness "d" of the friction coupling 4.
The tapered screw joint of the nipple 3 and friction
coupling 4 with such a thread profile can be used many times
for the disconnection of these parts by subjecting them to
axial tensile loads.
According to the invention, the coupling 4 is thin-
walled and there is a circular clearance "c" between said
coupling and the body 1 throughout the length of said screw
joint, the metal of the coupling 4 being at least five times
more elastic than that of the nipple 3.
It is practicable that the coupling 4 should be made
of spring steel and the nipple 3, of any harder metal.
Such a solution makes it possible to increase sub-
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stantially the reliability of the device and decrease its
overall dimensions while retaining the preset tensile charac-
teristics during repeated employment.
According to the invention, the bearing side "a" of
the taper thread profile on the nipple 3 and coupling 4 is sur-
facehardened to increase the service life of these parts.
All the characteristics, such as the average thick-
ness "d" (Fig. 2) of the coupling 4 working in the zone of
elastic deformations, pitch "S" of the taper thread, angles
and ~ determining its profile, angle of thread ~ its pitch
dîameter "D" length of engagement, rounding radiuses r and rl
are selected so as to ensure the possibility of adjusting the
axial loads P (Fig. 3) and of using repeatedly the connected
parts - nipple 3 and coupling 4, at the same time satisfying
the relation SC ~ D-f where f = coefficient of friction of
the pair: coupling 4- nipple 3.
Actually, the angle ~ is taken to be from 0 to 45
and the angle of thread ~ is selected on the basis of the
relation ~>90-~. The rounding radiuses r and rl of the taper
thread profile are practically the same, being equal to 0.05
of the taper thread pitch "S".
The sides "a" and "b" at the crest of the taper
thread of the nipple 3 and coupling 4 can be conjugated in the
zone a' (Fig. 2~ with a taper equal to the angle "~" or even in
the zone which is parallel to the thread axis, the recommended
length of this zone not exceeding 0.1 of the thread pitch "S".
The device for the emergency recovery of the boring
tool from the borehole functions as follows.
When the boring tool (drilling bit or drill pipe)
gets stuck in an oil or gas well, the free part of the drill
string is pulled out and the device couplete with the damping
piston (not shown in Fig. 1) is built into said string. For
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this purpose the adapter bushing 5 and the piStOII are con-
nected, respectively, with the upper and lower pipes of the
free part of the drilling string and the latter is again
lowered into the borehole where it is connected to the stuck
boring tool any methods and means kno~m in the drilling
technology.
The device is set to the initial position by rotating
the drilling string so as to screw the nipple 3 all the way
into the friction coupling until the lower end of the nipple
comes to bear against the end of the adjusting screw 8.
Then the drilling string is strai~ed by lifting it,
e.g. by a system of hoists, which creates internal tensile
stresses in the drilling string, said stresses being trans-
mitted to the rod 1 of the device. Under the effect of the
upward-directed axial tensile load "P" (Fig. 3) gradually
arising in the rod 1 the latter starts moving upward and
carries the nipple 3 together with it.
As a result, the following forces arise on the con-
jugated zone "L" of the bearing surfaces of the tapered screw
joint between the nipple 3 and coupling 4: force "F" which a
radial component of the axial load "P" causing internal cir-
cular stresses in the coupling 4, force "R" of reaction of
the coupling 4 directed opposite to the force "F" and force
of friction "T" between said conjugated portions "L" of the
bearing surfaces of the tapered screw joint which prevents
free movement of the nipple 3 relative to the coupling 4 over
the bearing surfaces of their tapered screw joint.
In this position the coupling 4 functions as a
spring ring and the circular stresses arising in it do not go
beyond the limit of elastic deformation while at a sufficiently
heavy axial load P which must be greater that the projection
of all the friction forces "T" on the thread axis "0 - 0",
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the coupling 4 and nipple 3 are disengaged.
~ nen the forces of frictional adhesion between the
nipple 3 and coupling 4 are exceeded, this breaks the connec-
tion between the rod 2 and the body 1 and the latter goes
down. At this moment the tensile stresses in the drilling
string drop very rapidly to zero and the string pipes are
drawn into a vibratory process which frees the tool stuck
in the borehole.
To provide for a hard (jarring) blow on the boring
tool stuck in the borehole, the device is built into the
drilling string at a point located not farther than 1/20 of
the free part of the string with the aid of ~he lower adapter
bushing 6, in which case the damping piston 14 is cancelled.
After the breaking of the frictional adhesion between the
nipple 3 and coupling 4 of the device, the rod 2 goes upward
and the anvil 11 strikes a blow on the bushing 10 which con-
veys this blow through the body 1 to the tool stuck in the
borehole thus freeing said tool.
For the second blow the rod 2 is turned together
with the upper part of the drilling string until the nipple 3
comes to bear against the adjusting screw ~ and the system is
screwed up with a torque which depends on the stiffness of
the tapered screw joint between the coupling 4 and nipple 3
after which the drilling string is again strained. Then the
above-described process is repeated over again.
In case of a wave action applied to the part of
the drilling string stuck in the borehole, the damping piston
14 takes the weight of the liquid contained in the upper part
of the circular gap in the borehole and causes a hydrodynamic
effect, thus preventing the recoil of the load-hoisting de-
vices.
Before acting on the stuck tooL the strained
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(stretched) state of the drilling string is adjusted by
means of the adjusting screw 8, the frictional adhesion of
the nipple 3 to the coupling 4 increasing with the size of
the area of the initial engagement of their tapered screw
joint.
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