Thread coupling for percussion drilling

Abstract

 A thread coupling for drill rods for percussion rock drilling comprising a male thread (15) and a co-operating female thread (12). The threads (12, 15) are designed internally in such a way that an essentially unchanged contact surface is maintained between the contact shoulders (16) of the threads adjacent to the thread clearance of the female thread (12) or the thread outlet of the male thread (15).

Description

[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 35⁰.

[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.

Claims

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°.

Drawing