Note: Descriptions are shown in the official language in which they were submitted.
WO91/14073 PCT/SE91/00170
20~13~3
Thread~friction lockinq device
The present invention relates to a thread friction locking
device, especially adapted to be mounted in a thread
5 coupling between tubes for percussive drilling.
In EP, Bl, 0 126 740 tubes for percussive drilling of the
type referred to above is described. However, a frequent
problem in a drill tube system of this type is that the
threads, if not tightened, have a tendency to unscrew. This
happens especially when the drill string of tubes is raised
and the tubes disconnected from each other when drilling is
finlshed or the drill bit must be exchanged. In order to
loosen a tightened thread coupling the drill strin~ is
subjected to one or more strikes when the drill bit is in
raised position, i.e. not in contact with the bottom of the
drilled hole. In such a case not only the thread coupling at
the highest level but also thread couplings on lower levels
will become loose and it happens frequently that a thread
coupling in the drilled hole gets completely unscrewed and
the drill bit and one or more tubes are lost.
The aim of the present invention is to present a device for
friction locking of the thread couplings between the tubes.
Said aim is realized by a device that has been given the
characteristics of the appending claims. Below embodiments
of the invention will be described, reference being made to
the accompanying drawings, where Fig.l discloses a section
through a device according to the present invention, said
device being mounted in a thread coupling; Fig.2 discloses a
top view of a device according to the present lnvention;
Fig.3 discloses a section along III-III in Fig~2; Fig.4
discloses in enlarged scale a portion of Fig.2; and Fig.5
discloses a section through the device according to the
present invention when the nose of the male thread enters
said device, said Figure also being provided with
dimensional definitions.
WO91/14073 PCT/SE91/00170
In Fig.l a device lO according to the invention is shown
mounted in a thread coupling between a first tube 11 and a
second tube 12. The device lO is in the shape of an annular
ring and will be described more in detail further down.
The first tube 11 has a spigot 13 that is-provided wlth a
male thread 14 and the second tube 12 has a boring 15 that
is provided with a female thread 16. ~oth tubes ll and 12
have central flushing holes 17 that align with each other
when the tubes 11, 12 are assembled by the thread coupling.
The spigot 13 is also provided with a nose 18 at its free
end, said nose 18 having a smaller diameter than the rest of
the spigot 13.
At its bottom the boring 15 is provided with a thread
clearance l9. The thread friction locking device 10
according to the present invention is mounted in said thread
clearance l9 and when the first and second tubes ll, 12 are
assembled by the thread coupling the nose 18 will enter the
internal periphery of the device lo and compress the cross-
section of said device 10 in radial direction in its
position in the thread clearance 19.
2s An embodiment of the thread friction locking device 10
according to the present invention is disclosed in Figs.2-4.
As mentioned above the device lO is in the shape of an
annular ring that has a certain extension in axial
direction. The outer periphery of the device 10 is smooth
but the inner periphery is provided with a number of axially
extending grooves 20 that will allow flushing medium,
preferably water or air, to enter between the end of the
nose 18 and the bottom of the boring 15 and then pass
between the device 10 and the nose 18 and further on to the
thread coupling, said flushing medium having a cooling
effect upon the thread coupling. In the disclosed embodiment
the grooves 20 are spaced apart equally around the
circumference by an angle ~ that is 30. The angle ~ can of
WO91/14073 PCT/SE91/00170
3 2081363
course also have other values within the scope of the
invention.
In Fig.4 one groove 20 is shown more in detail and it can be
learnt that on one side of the groove 20 there is a bevel
21 that will reduce friction between the inner perlphery of
the device lO and the nose 18 when the first tube ll is
rotated in a direction to tighten the thread coupling.
As is shown in the cross-sectional view of Fig. 3 the o~lter
periphery is rounded at the lower end in Fig.3, i.e. the end
that is directed towards the bottom of the boring 15 in
mounted position of the device lO, while the upper end in
Fig.3, i.e. the end that is directed from the bottom of the
boring 15 in mounted position of the device lO, is bevelled
at both its outer and inner periphery. The bevel 2~ on the
outer periphery makes the device lO fit into the thread
clearance l9 while the bevel 23 on the inner periphery helps
the nose l~ to enter the device lO. The bevel 22 is defined
by the angle B in Fig.3, B preferably being about 25~. The
bevel 23 is defined by the angle ~ in Fig.3, ~ preferably
being about 30. Instead of the bevel 22 the device lO can
be provided with a radiused portion.
Although the e~bodiment according to Figs.2-4 discloses
axial grooves 20 on the inner periphery of the device lO the
invention is in no way restricted to such an embodiment. The
axial grooves can also or instead be provided on the outer
periphery o~ the device lO. It is also possible to have
axial channels thr~ugh the device lO. A further possible
embodiment is to have helical grooves on the inner and/or
outer periphery of the device. The requirement is that
flushing medium can pass axially from one end of the device
lO to the other end of the device lO.
In Fig.5 the dimensions of the device lO, the nose 18 and
the thread clearance l9 are defined.
WO~1/14073 PCT/5E91/00170
20~1363 4
- The axial length of the thread friction locking device lO is
marked by l. The cross-sectional thickness is marked by t.
The following relationship between t and l must be valid:
0,l < t/l ~ 0,6.
The diameter of the thread clearance l9 is marked by Di. The
external diameter of the nose 18 is marked by dy. The
internal diameter of the thread friction locking device l0
is marked by di. The external diameter of the thread
friction locking device lO is marked by Dy. The following
relationship between Di, dy, di and Dy must be valid:
0,55 ~ (Dy - Di)/(dy - di) ' O,95.
The thread friction locking device lO according to the
present invention is preferably made out of urethane
rubber. The material that has been used in our field tests
is marketed under the trade mark TREKOLLAN, types 4020 and
40l3.
The material should have a hardness within the interval
80 - 105 IHR.
The tensile stress of the material at 300 % extension in
room temperature should be in the interval lO - 25 MPa.
The tensile strength of the material in room temperature
should be in the interval 20 - 55 MPa.
The ultimate elongation of the material in room temperature
should be in the interval 400 - 850 %.
Also after aging tests according to SIS l~2205 the above
listed characteristics of the material must be in the given
intervals.
The function of the thread friction locking device according
to the present invention is best understood when studying
Figs.l and 5. In Fig.s the nose 18 of the spigot 13 enters
WO9l/14073 PCT/SE91/00l70
2081363
the internal periphery of the device 10. Due to the
dimensional relationship defined above a certain compres~ion
in radial direction of the cross-section of the device 10
will take place. The bevel 23, see Fig.3, makes the entering
of the nose 18 easier and avoids a compression of the device
lo in axial direction. In Fig.1 the nose 18 contacts the
bottom of the boring 15 and the device 10 is in its
operative position. It is at once understood that said
compressed device lo exerts friction forces against an
unscrewing relative rotation between the male and the female
threads 14 and 16, rasp.. In this connection reference is
made to the bevel 21, see Fig.4. Said design decreases the
friction between the device 10 and the nose 18 when the
thread coupling is tightened and increases the friction when
the thread coupling is unscrewed.
The invention is in no way restricted to the embodiments
described above but can be freely varied within the scope of
the appending claims.
