[0001] The present invention relates to a thread coupling for drill rods for percussion
drilling comprising a male thread and a co-operating female thread. The invention
also relates to a drill rod intended to be used in such a coupling.
[0002] In conventional rock drill rods it has turned out that the thread clearance of the
female thread causes a wear in the shape of a wedge thus counter-acting a tightening
of the thread coupling resulting in an inclining of the thread coupling.
[0003] The aim of the present invention is to alter the wear configuration in such a way
that the thread clearance of the female thread not affects the male thread.
[0004] Other aims of the invention are to design the thread coupling in such a way that
the thread outlet of the male thread neither causes any bending force nor prevents
tightening of the coupling.
[0005] These and other aims have been achieved by giving the invention the characteristics
of the appending claims.
[0006] The invention is described more in detail in the following, reference being made
to the enclosed drawings disclosing an embodiment by way of example. This embodiment
is only intended to illustrate the invention that can be modified within the scope
of the claims.
[0007] In the drawings, Fig. 1 discloses a side view of a conventionally designed thread
coupling.
[0008] Fig. 2 illustrates the wear configuration of a conventional rock drill rod.
[0009] Fig. 3 illustrates the wear configuration of a section along the line III-III in
Fig. 2.
[0010] Fig. 4 illustrates the wear according to a section along the line IV-IV in Fig. 3.
[0011] Fig. 5 discloses a side view of a thread coupling according to the present invention.
[0012] Fig. 6 discloses the thread outlet of a male thread of a drill rod according to the
invention.
[0013] Fig. 7 illustrates how the thread outlet of the drill rod according to Fig. 6 can
be carried out.
[0014] Fig. 8. discloses a section along the line VIII-VIII in Fig. 7.
[0015] Fig. 9 discloses a side view of the thread outlet seen along the line IX-IX in Fig.
8.
[0016] The conventional thread coupling disclosed in Figs. 1 to 4 comprises a drill rod
100 having a sleeve-shaped end 101 with a female thread 102. The drill rod 100 is
connected to a drill rod 103, the pole-shaped end 104 of said drill rod having a male
thread 105 that is screwed into the female thread 102.
[0017] As can be seen from Fig. 2 the thread profile of a commonly used rock drill thread
has a generally seen trapezoid shape, and contact is present substantially only between
the straight contact shoulder 106 of the male thread and a corresponding straight
contact shoulder of the female thread. The wear configuration of the threads is consequently
as is illustrated by the shaded surfaces 107, 108 in Fig. 2. It has also turned out
that the thread outlet of the female thread 102 causes a wear in the shape of a wedge.
This is illustrated by the shaded surface 109 in Fig. 2. This wedge-shaped wear counter-acts
the tightening of the coupling and has turned out to provide an inclining of the coupling
and thus a bending of the drill rod.
[0018] The wedge-shaped wear surface 109 is illustrated in Fig. 3, and as can be seen from
Fig. 4 a pit 110 arises in the contact shoulder adjacent to the thread outlet, said
pit having an increasing width in the direction of the circumference.
[0019] Tn the coupling of Fig. 1 the male thread 105 extends further than the female thread
102 and thus out of the sleeve-shaped end 101. The same wear configuration and inclining
of the drill rod would happen if the female thread instead had an extension further
than the male thread.
[0020] In Figs. 5 - 9 is disclosed a preferred embodiment of a thread coupling according
to the invention. In similarity of the conventional design according to Fig. 1 - 4
the coupling comprises a drill rod 10 having a sleeve-shaped end 11 with a female
thread 12. The pole-shaped end 14 of the drill rod 13, that is connected to the drill
rod 10, comprises a male thread 15 that engages the female thread 12.
[0021] When tightening of the coupling contact arises along the contact- or pressure shoulder
16 and the corresponding contact shoulders of the female thread 12. In the preferred
embodiment the contact shoulders 16 are essentially straight. The shoulders 16 have
an inclination of 25°-40° relative the drill axis, preferably 35
0.
[0022] According to the invention the threads 12, 15 are internally designed in such a way
that an essentially unchanged contact surface between the contact shoulders 16 of
the threads 12, 15 is maintained adjacent to the thread clearance of the female thread
12 or the thread outlet of the male thread 15. This means that the contact surface
of the thread clearance and the thread outlet resp is equally large as along the rest
of the thread. In the preferred embodiment this is achieved, see Fig. 6, by maintaining
the thread profile essentially unchanged up to the thread outlet. In conventionally
designed drill rods there is a continuous decreasing of the thread profile at the
thread outlet, i e both the height and the width of the thread decrease successively
from the full profile to the transition of the thread to the unthreaded portion of
the rod. In Figs. 7 and 8 is illustrated how the maintainance of a full thread profile
can be kept up to the thread outlet on the male thread 15 by removing the shaded surfaces
17, 18. In Fig. 9 the decreasing in width and height is illustrated by the removed
portion 19 marked by chain-dotted lines.
[0023] Alternatively the same result is likely to be achieved if the male thread is designed
to extend out of the portion 11 in a full profile and that the terminating portion
of the female thread is removed, said portion having a decreasing width and height.
[0024] According to the preferred embodiment the threads 12, 15 are to be designed internally
to extend out of the portion 11 in a full profile and that at the same time the terminating
portion of the female thread is removed, said portion having a decreasing width and
height.
[0025] According to the preferred embodiment the threads 12, 15 are designed internally
in such a way that a wholly number of thread turns are in engagement in the coupling
thus guaranteeing that no bending forces appear in the coupling. This means that the
threads are designed with a wholly number of turns of a full profile.
1. Thread coupling for drill rods for percussion drilling comprising a male thread
(15) and a co-operating female thread (12),
characterized in that the threads (12,15) are designed internally in such a way that
a substantially unchanged contact surface between the contacting shoulders (16) of
the threads (12,15) is maintained adjacent to the thread clearance of the female thread
(12) or the thread outlet of the male thread (15).
2. Coupling according to claim 1,
characterized in that the threads (12,15) are so designed internally that a wholly
number of thread turns are in engagement in the coupling.
3. Coupling according to claim 1 or 2,
characterized in that the profile of the male thread (15) is maintained substantially
unchanged up to the thread outlet.
4. Coupling according to anyone of the previous claims, characterized in that the
threads (12,15) have substantially straight contact shoulders (16).
5. Coupling according to claim 4,
characterized in that the contact shoulders (16) are inclined 25°-40° relative the
drill axis, preferably in the range of 35°.
6. Drill rod having a male thread (15) and intended to be used in a thread coupling
according to claim 1, characterized in that the thread profile is maintained substantially
unchanged up to the thread outlet.
7. Drill rod according to claim 6,
characterized in that the thread (15) is designed with a wholly number of turns having
a full thread profile.
8. Drill rod according to claim 6 or 7,
characterized in that the thread (15) is designed with an essentially straight pressure
shoulder (16).
9. Drill rod according to claim 8,
characterized in that the pressure shoulder (16) has an inclination of 25°-40° relative
the drill axis, preferably in the iange of 30°.