The present invention relates to a threaded coupling between a female extension member and a male extension member in a drill string for percussive drilling, said female extension member being provided with an internal thread, said male extension member being provided with an external thread, said internal and external threads respectively being designed for engagement with each other. The present invention also relates to the female extension member per se, the male extension member per se and a method of maintaining a coupling between a female extension member and a male extension member for percussive drilling.

Especially for tubes for percussive drilling it is previously known to use so- i called male-female thread couplings, i.e. an externally threaded spigot, that is integral with a tube element, cooperates with an internally threaded sleeve, that is integral with an adjacent tube element. When a shock wave reaches the coupling, said shock wave is instantly affected by the dimensional variations in the coupling, e.g. change in wall thickness of the tube element. These variations give rise to reflecting waves that propagate in the tube element in the opposite direction of the shock wave. Due to the fact that both the spigot and the sleeve are integral with the adjacent tube elements, the abutting thread flanks of the spigot and the sleeve will be subjected to considerable impact when the shock wave is transmitted between the abutting thread flanks. Such an impact normally gives rise to wearing and pittings.

Also previously known are externally threaded coupling sleeves, applied internally in adjacent ends of two extension tubes. Said coupling sleeves are superior as regards the transmission of impact energy compared to the prior art male-female couplings mentioned above. Since the internal coupling sleeve is a separate detail it will only be marginally affected when the shock wave bypasses the thread coupling. Also the dimensions, i.e. the wall thickness, of

the tubes can be kept constant in the thread coupling. However, one problem with internally applied coupling sleeves is that when disconneting two tubes connected by such internally applied coupling sleeves it is impossible to control in which tube the sleeve will remain. This is a great disadvantage in connection with automatized handling of the tubes.

From SE-B-470 217 a device for yieldably locking a threaded spigot in a threaded boring is previously known, said device being a ring of urethane rubber that provides a friction action between the spigot and the boring during drilling. It has turned out that this device performs well in surface drilling, since the flushing medium normally used is air holding a certain amount of powdered cuttings. This means that the spigot/boring coupling will adopt a relatively high temperature and consequently the waxing of the rubber ring will disappear by drying. The rubber ring is almost vulcanized to the spigot.

When the device according to SE-B-470 217 is used in underground drilling the function is negatively affected, primarily due to the fact that water normally is used as flushing medium. The consequence of using water instead of air is that the temperature of the spigot/boring coupling is lower and the wax remains on the rubber ring. Thus the rubber ring exerts very little friction action upon the spigot/boring coupling. This means that there is no effective control that the internally applied sleeve will be maintained in a certain tube element by the rubber ring.

A joint for steel pipes for oil transport is previously known through US-A-4

426 105, in which a ring locks male and female parts together. If that joint was to be used for percussive drilling the ring would almost immediately, after a couple of blows, be sheared off along a path corresponding to the outer periphery of the male member. That is because the male member is more axially movable than is the ring.

One object of the present invention is to present a concept that will work both for surface drilling and underground drilling, i.e. to secure safely the internally applied coupling sleeve in one of two adjacent drilling tubes. Another object of the present invention is to present a concept wherein the internally applied coupling sleeve is permanently secured in one of two adjacent drilling tubes.

The objects of the invention are realized by a coupling, a coupling sleeve, a female extension member and a method, respectively, that has been given the characteristics of the appending claims.

Below, preferred embodiments of the invention will be described, reference being made to the accompanying drawings wherein Fig. 1 shows a partly sectioned side view of a coupling according to the present invention between two tubes for percussive drilling mounted for drilling purposes; Fig. 2 shows a detail of one end of the coupling sleeve in drilling position; Fig. 2A shows a partly sectioned side view of an alternative embodiment of a coupling according to the present invention in unscrewing position; Figs. 3a-3c show the locking ring per se; Fig. 4 shows a coupling according to the present invention between two members forming a shank adapter.

A coupling is shown in a mounted position with a non-operative position of locking means in Fig. 1. The coupling includes a first end portion 10 of a first extension drilling tube 12 and a second end portion 14 of a second extension drilling tube 16, the free ends of said end portions 10 and 14 abutting each other. The first end portion 10 is provided with a first internal cylindrical thread 18 and the second end portion 14 is provided with a second internal thread 20.

The first internal thread 18 is terminated by a first circumferential clearance 22. Adjacent to the first clearance 22, but further away from the free end of the end portion 10, an internal circumferential first groove 24 is provided, see also Fig.

2, said first groove 24 receiving a locking ring 25, preferably made out of spring steel. As can be learnt from Figs. 3a and 3b the locking ring 25 has a circumferential gap 27 of a certain width. Due to the gap 27 it is possible to reduce the diameter of the locking ring 25 when mounting said locking ring 25 in the first groove 24. Still further away from the free end of the end portion

10 a first restriction 23 is provided, said restriction 23 forming a first shoulder 29, the function of which will be described below.

The second internal cylindrical thread 20 is also terminated by a second clearance 26 that in its turn is terminated by a second restriction 28, said second restriction 28 forming a second shoulder 30, the function of which will be described below.

The coupling according to the present invention also includes an internal coupling sleeve 32 that is provided with an external cylindrical thread 34. The coupling sleeve 32 has a longitudinal, through-going, internal boring 36 to allow flushing medium to bypass the coupling. As can be seen in Fig. 1 the wall thickness of the coupling sleeve 32 continuously increases from both ends towards an intermediate portion of the coupling sleeve 32. In the intermediate portion the wall thickness of the coupling sleeve 32 is constant. At one end of the coupling sleeve 32 an external second circumferential groove 38, see Fig. 2, is provided. The free end of the coupling sleeve 32 adjacent to the second groove 38 is in the shape of a first bevelled portion 40. Between the first bevelled portion 40 and the second groove 38 a cylindrical portion 39 is provided. At the opposite end the coupling sleeve 32 also has a free end in the shape of a second bevelled portion 42.

In order to safely secure the coupling sleeve 32 in the first drilling tube 12 the end of the coupling sleeve 32 carrying the second groove 38 is threaded into the end portion 10 of the first drilling tube 12, i.e. the external thread 34 of the coupling sleeve 32 engages the first internal thread 18 of the first drilling tube

12. When the first bevelled portion 40 adjacent to the second groove 38 contacts the locking ring 25, said bevelled portion 40 forces the ring 25 against the far side wall 24a of the first groove 24, seen in the direction of displacement of the coupling sleeve 32. Further displacement inwardly of the coupling sleeve 32, i.e. to the left in Fig. 1, will expand the ring 25 due to the circumferential gap. The ring 25 will climb the bevelled portion 40 further as the coupling sleeve 32 is displaced inwardly. Eventually, the locking ring 25 reaches the cylindrical portion 39 between the bevelled portion 40 and the second groove 38. The locking ring 25 bypasses also said cylindrical portion 39 when the coupling sleeve 32 is displaced further inwardly and finally the locking ring 25 reaches the second groove 38 and is snapped into said second groove 38. The locking ring 25 is now safely secured in the second groove 38. The play between the width of the groove 38 and the width W of the ring 25, see Fig. 3c, is preferably about 10% of the width of the groove 38. Preferably, the thickness T of the locking ring 25, see Fig. 3c, is about half the width W.

The thickness T of the locking ring 25 exceeds the depth of the second groove 38, i.e. when the locking ring 25 is properly mounted in the second groove 38 the locking ring 25 extends beyond the outer periphery of the adjacent end of the coupling sleeve 32. As is evident from Fig. 1 the locking ring 25 will never abut the side walls 24a and 24b of the first groove 24 when the coupling sleeve 32 is displaced longitudinally in either direction during drilling. This means that the axial play LI between the sleeve 32 and the female parts 12 and 16 is smaller than the axial extension L2 of the groove 24. Thus, the coupling sleeve 32 is properly secured in the first end portion 10 of the first drilling tube 12.

However during unscrewing of the coupling the ring will move axially the distance L2 and contact the side wall 24b and thus stop further unscrewing of tha tparticular end of the male extension member so that further unscrewing will take place at the axially opposite end of the male extension member.

In Fig. 2 an alternative cross-section of the locking ring 25 is shown with

dotted lines. In such a case the side wall 24b should be inclined in accordance with the dotted straight line. By such an arrangement the inclined side wall will force the locking ring 25 down into the second groove 38 when contact is established between said locking ring 25 and said inclined side wall.

When the coupling sleeve 32 is properly secured in the first drilling tube 12 about half the length of the coupling sleeve 32 projects from said first drilling tube 12. To couple together the first drilling tube 12 and the second drilling tube 16, said second drilling tube 16 is threaded on the coupling sleeve 32, i.e. the internal thread 20 of the second drilling tube 16 engages the external thread 34 of the coupling sleeve 32. When the free ends of the first and second drilling tubes 12 and 16, respectively, abut each other a proper coupling is established and the percussive energy is transfered between adjacent drilling tubes 12 and 16 through the abutting free ends.

The first and second shoulders 29 and 30, respectively, constitute longitudinal stops for the ends of the internal coupling sleeve 32. These shoulders prevent the ring from being contacted by the first drilling tube 12, since the ring cannot stand many blows during drilling. Alternatively the stops could be made at another part, i.e. close to the free end of the first drilling tube 12.

Within the scope of the present invention it is possible to mount a ring of urethane rubber according to SE-B-470 217 in the clearance 22. An additional securing of the coupling sleeve 32 is thus achieved, at least for surface drilling.

Another favourable feature of the present invention is that it is possible to use different materials or materials of different heat treatment in the drilling tubes 12 and 16 on the one hand and the coupling sleeve 32 on the other hand. Such an arrangement optimizes the life of the coupling since the drilling tubes 12 and 16 are subjected to a faster wearing, i.e. both the external peripheries and the internal threads 18 and 20, respectively. Therefore, the material in the coupling

sleeve 32 should preferably be softer than the material in the drilling tubes 12 and 16.

In Fig. 2A an alternative embodiment of a concept according to the present invention is shown. A coupling is shown during unscrewing with an operative position of locking means. The threads 18' and 20' is in principle designed in a way corresponding to the threads 18 and 20, respectively, disclosed in Figs. 1 and 2 of the present application.

However in this embodiment the first internal thread 18' is not terminated in a clearance but in a mainly cylindrical surface 22', preferably essentially coinciding with the smallest diameter of the thread 18'. Adjacent to the cylindrical surface 22', but further away from the free end of the end portion of the first drilling tube 12', an internal circumferential first groove 24' is provided. The first groove 24' receives a locking ring 25', preferably made of steel such as a spring steel, designed similar to the ring 25 described in connection with Figs. 2, 3a and 3b, but with convex side walls. The ring may alternatively have a round or square cross-section and then the connected grooves should be adapted thereto. At one end of the coupling sleeve 32' an external second circumferential groove 38' is provided. The free end of the coupling sleeve 32' adjacent to the second groove 38' is in the shape of a first bevelled portion 40'. Between the first bevelled portion 40' and the second groove 38' a cylindrical portion 39' is provided. At the opposite end the coupling sleeve 32' also has a free end in the shape of a bevelled portion. The bottom of the groove 38' comprises a first portion 138' of generally smaller diameter than a second portion 238' thereof. The first portion 138' is arranged at a larger distance from the free end of the sleeve 32' than is the second portion 238'. The second portion 238' sucessively reduces the radial depth from the first portion to the cylindrical portion 39' via a wedge or radiussed shape. Alternatively the second portion may be cylindrical but with a greater radius than the first portion.

The thickness of the locking ring 25' is smaller or mainly similar to the depth of the first portion 138' of the second groove 38', i.e. when the locking ring 25' is properly mounted in the second groove 38' the locking ring 25' falls radially below or is mainly flush with the outer periphery of the adjacent cylindrical surface 139' of the coupling sleeve 32'. As is evident from Fig. 2A the locking ring 25' will abut the side walls of the first groove 24' when the coupling sleeve 32' is displaced longitudinally in either direction. Thus, the coupling sleeve 32' is properly secured in the first end portion of the first drilling tube 12'. The play between the width of the groove 24' and the width of the ring 25' is preferably about 10% of the width of the groove 24'.

Preferably, the thickness of the locking ring 25', see Fig. 3c, is about half the width. The width of the groove 38' is at least 50 % larger than the width of the ring 25'.

The thickness of the locking ring 25' exceeds the depth of the second groove portion 238', i.e. when the locking ring 25' is properly mounted in the second groove 38' the locking ring 25 extends generally beyond the outer periphery 39' and 139' of the adjacent end of the coupling sleeve 32' after having been compressed into groove portion 138'. The sleeve 32' is axially movable a distance L2' relative to the tube 12' during unscrewing of the coupling. The distance L2' is larger than the distance LI, described in connection with the former embodiment. That is to avoid blows on the locking means during drilling.

In order to safely secure the coupling sleeve 32' in the first drilling tube 12' the end of the coupling sleeve 32', carrying the second groove 38' in which the ring 24' is accomodated in the deeper first portion 138', is threaded into the end portion of the first drilling tube 12', i.e. the external thread of the coupling sleeve 32' engages the first internal thread of the first drilling tube 12'. When the radially outer periphery of the ring, in compressed state, contacts the internal thread the ring will remain in the portion 138' until it is allowed to

expand. Expansion occurs when the ring reaches the first groove 24' and further insertion of the sleeve will became impossible due to cooperation of the side wall of the groove 24', the ring 25' and a side wall 338' of the groove 38'. The ring 25' has two positions in the groove 38', that is the assembly position in radially compressed state at the portion 138' and a locking position when the ring has snapped into the groove 24'. When the ring is in the groove 24' and the sleeve is screwed axially outwardly towards the free end of the first end portion the second portion 238' will wedge up against the ring as in Fig. 2 A to prevent further outwardly directed movement of the sleeve 32'. The sleeve however, may move axially in the opposite direction a distance generally corresponding to the axial extension of the portion 138'. Once the ring has snapped into the groove 24' it will be stuck therein preferably still in a compressed state and will provide a permanent lock for the sleeve 32'. By the term "permanent" or "permanently" is meant that the ring cannot be dismounted without destroying the ring, for example by turning. The second portion 238' of the groove may instead of a being defined by a wedging conical shape or a radiussed section, be cylindrical but with a larger radius than the first portion 138'. That is to provide for just enough space for the ring between the parts 12' and 32' and to additionally secure the ring in the groove 24'. Thus, the coupling sleeve 32' is permanently secured in the first end portion of the first drilling tube 12'.

Although the embodiments according to Figs. 1, 2 and 2A refer to a threaded coupling between two tubes in a drill string the threaded coupling according to the present invention also is applicable in a threaded coupling between a tube/rod and a drill bit for percussive drilling.

In Fig. 4 a shank adapter 44 is diclosed, said shank adapter including two separate parts, i.e. a shank part 46 and a sleeve part 48. The shank part 46 is at one end provided with a boring 50 having an internal thread 51 and at the other end with a head portion carrying splines 52, said head portion being adapted to

be inserted in a top hammer rock drilling machine. The internal thread 51 is in principle designed in a way corresponding to the internal thread 18 disclosed in Figs. 1 and 2 of the present application.

The sleeve part 48 is provided with an external thread 54 adapted to be in engagement with the internal thread 51 of the boring 50 when the shank adapter 44 is in working condition. The external thread 54 extends along the entire length of the sleeve part 48 and preferably the external thread 54 has the same design along the entire length of the sleeve part 48. The sleeve part 48 is further provided with a through-going internal boring 56 that is designed in a way corresponding to the internal boring 36 of the coupling sleeve 32 of the embodiment of Figs. 1 and 2 of the present application. In the area of the end of the sleeve part 48 that is inserted into the boring 50 means are provided for axially locking the sleeve part 48 in the boring 50. Said means in principle correspond to the axially locking means of the embodiment according to Figs. 1 and 2 of the present application, i.e. said inserted end of the sleeve part 48 is provided with a locking ring 58 that is mounted in a circumferential groove 60 of the boring 50. When the inserted end of the sleeve part 48 reaches the locking ring 58 said ring will also cooperate with a circumferential groove on the sleeve part 48. In principle the axially locking of the sleeve part 48 in the boring 50 is effected in a way corresponding to the axially locking of the coupling sleeve 32 in the first end portion 10 of the first drilling tube 12 according to the embodiment shown in Figs. 1 and 2 of the present application. Therefore, in that respect reference is made to relevant portions of the description of the present application.

The external thread 54 of the end of the sleeve part 48 protruding from the shank part 46 is in working condition connected with an internal thread of a first tube/rod of a drill string for percussive drilling. Thereby the free end of the shank part 46 abuts the free end of the first tube/rod and the percussive energy is transferred via said abutting ends, i.e. the transfer of percussive

energy is effected in the same way as for the embodiment according to Figs. 1 and 2 of the present application.

Common for the above-described embodiments of the present invention is that when unscrewing the male extension member from the female extension member, the male extension member moves a limited distance relative to the female extension member until it is stopped by means 24,25,38;24',25'38' for axially locking the male extension member 32;32';48. This means that the male extension member during drilling is movable a first distance LI relative to the female extension member 12;12';46 and that the means 24,25,38;24',25'38' are operative during unscrewing when the male extension member is moved a second distance L2;L2' relative to the female extension member, wherein said first distance LI is smaller than said second distance L2;L2'.