THREAD COUPLING

Abstract: Thread coupling for percussive drilling including at least one male thread (10), arranged on a spigot (11), and one female thread (17), arranged within a sleeve. The threads are cylindrical and include an external stop surface (20) at a free end of the sleeve, and a contact surface (14) on the spigot. Further, they include an internal stop surface (21) in the sleeve, and an end surface (16) on the free end of the spigot. Initially, there is a play ( delta ) between the end surface (16) of the spigot and the internal stop surface (21) of the sleeve, this initial play being eliminated after wearing-in of the thread coupling. By increasing the pitch angle ( alpha ) of the threads (19, 17), a less tightening coupling is achieved, that due to the shoulder-bottom stop, still has an acceptable length of life.

Description: Thread coupling The present invention relates to a thread coupling for percussive drilling including at least one male thread and one female thread, said male thread being arranged upon a spigot and said female thread being arranged within a sleeve, said male and female threads being cylindrical, an external shoulder stop at a free end of the sleeve, said shoulder stop including contact surfaces being perpendicular to a longitudinal centre axis of the thread coupling, the spigot at a free end having an end surface that is perpendicular to said longitudinal centre axis, the sleeve being provided with an internal stop surface that is perpendicular to said longitudinal centre axis, in an unused thread coupling there is an initial play between the end surface of the spigot and the internal stop surface, said initial play being eliminated after wearing-in of the thread coupling. A thread coupling of the type defined above is previously known from SE-B-469 603 (US-A-4.968,068) , said document being incorporated by reference into the present application. A problem with such a thread coupling, especially when trapezoidal threads are used, is that the coupling during use becomes so tightened that it is difficult to unscrew the coupling when one member of the coupling needs to be exchanged. The present invention has the aim to present a thread coupling of the type mentioned above, said thread coupling being less tightened than prior art thread couplings of the type defined above. The aim of the present invention is realized by a thread coupling that has been given the characteristics of the appending claims. Below embodiments of the invention will be described with reference to the enclosed drawings, where Fig.l shows a schematic, partly sectioned view of a thread coupling according to the invention; Fig.2 shows a view similar to Fig.l of an alternative embodiment of the invention; and Fig.3 shows a view similar to Fig.l of a further alternative embodiment of the invention. The thread coupling of Fig.l includes a male thread 10 that is provided on a spigot 11 which constitutes an integral part of a male extension member 12 for percussive drilling. At the inner end of the spigot 11 the male extension member 12 is provided with a shoulder 13 that has a first plane contact surface 14 directed towards the free end of the spigot 11. The first contact surface 14 has an extension perpendicular to a longitudinal centre axis 15 of the male extension member 12. The free end of the spigot 11 has the shape of a plane end surface 16 that has an extension perpendicular to the centre axis 15. The thread coupling also includes a female thread 17 that is provided in a sleeve 18 which constitutes an integral part of a female extension member 19. At the free end of the sleeve 18 a second plane contact surface 20 is provided, said second contact surface 20 having an extension perpepdicular to the longitudinal centre axis 15 of the female extension member 19, said longitudinal centre axis coinciding with the centre axis of the male extension member 12. Inside the sleeve 18 the female extension member 19 has a plane bottom surface 21 that has an extension perpendicular to the longitudinal centre axis 15. From Fig.l it is evident that in the thread coupling according to the present invention the first contact surface 14 of the male extension member 12 always contacts the second contact surface 20 of the sleeve 18, i.e. so called shoulder stop is established. It is also evident from Fig.l that between the end surface 16 of the spigot 11 and the bottom surface 21 inside the sleeve 18 there is an initial play δ that nominally is chosen to be zero (0) but with a positive manufacturing tolerance in the magnitude of one (1) mm. After a certain time of use, at the most within 20% of the length of life for the thread coupling, this play will be eliminated due to wearing-in of the thread coupling and consequently the thread coupling according to the invention will have both shoulder and bottom stop. From Fig.l it is also evident that at the right end of the thread coupling a thread clearance 22 of the male extension member 12 and a thread clearance 23 of the female extension member 19 are arranged, said clearances 22, 23 having the aim of evening out bending stresses from manufacturing inaccuracies of the contact surfaces 14, 20 or the threads. In addition the clearances 22, 23 even out torsion stresses and stresses from shock or tension waves that pass through the thread coupling. In the event that the thread coupling according to the present invention is between a drill rod and a drill bit it is favourable that the drill bit constitutes the male extension member 12 while the drill rod constitutes the female extension member 19. The reason therefore is that the region of the clearance 22 of the male thread 10 is the weakest portion of the thread coupling according to the present invention, i.e. if the coupling collapses it is likely that the fracture will occur in the region of the clearance 22. Since a drill bit is worn out up to ten times faster than a drill rod it is favourable that the fracture is located in the drill bit. As is indicated in Fig.l the male thread 11 has a pitch angle . Of course the female thread 17 has the same pitch angle . In accordance with the present invention the pitch angle o. is greater that 8.5° and less than 15° (8.5°< α < 15°) . Preferably the pitch angle a should be greater than 9.5° and less than 11.5° (9.5°< α < 11.5°) . For thread couplings without shoulder-bottom stop such pitch angles are too great and the thread coupling would be unsufficient tigthened, the consequence being that pittings occur and the length of life of the threads is unacceptable short. Due to the shoulder-bottom stop in the thread coupling according to the present invention the shock wave is transmitted simultaneously through both the spigot 11 and the sleeve 18. This means that there is very small relative motions in the axial direction between the male thread 10 of the spigot 11 and the female thread 17 of the sleeve 18. Thus, the thread coupling according to the present invention will operate properly at a lower tightening level than thread couplings without shoulder-bottom stop. Said lower tightening level is achieved by an increase of the pitch angle a . In the embodiment according to Fig.2 two drill rods 12' and 12" having two spigots 11' and 11", respectively, are coupled together by a separate coupling sleeve 18'. In case the spigot 11' is considered to belong to the male extension member then the sleeve 18' together with the drill rod 12" is considered to constitute the female extension member. Since there is a play δ between the end surfaces 16', 16" of the spigots 11' and 11" respectively the end surface 16" is considered to be the bottom surface of the female extension member. If on the other hand the spigot 11" is considered to belong to the male extension member then of course a reversed approach must be used. However, in the appending claims the spigot 11' is considered to belong to the male extension member 12'. As in Fig.l the end surfaces/bottom surfaces 16', 16'' have an extension perpendicular to the longitudinal centre axis 15. Also in the embodiment according to Fig.2 both the male threads 10', 10" and the female threads 17', 17" have the same pitch angle α. The embodiment according to Fig.3 includes a male thread 10' ''that is provided on a separate spigot 11'''. In Fig.3 the male thread 10''' is interrupted in the intermediate region of the longitudinal direction of the spigot 11' ' ' . However, within the scope of the present invention it is also possible that the male thread has a continous extension along the entire length of the spigot 11'''. Since the spigot 11''' is a separate element there are two end surfaces 16''' and 16'''' respectively. The spigot 11''' is received in two sleeves 18''' and 18'''' respectively, said sleeves 18''', 18'''' being integral with drill tubes 19''' and 19'''' respectively. The female threads 17' ' ' and 17' ' ' ' are located inside the sleeves 18' '' and 18' '' ' respectively. Both the male thread 10'' ' and the female threads 17' ' ' and 17' ' ' ' have a pitch angle a . At the free end of the sleeves 18''' and 18'''' contact surfaces 20''' and 20'''' respectively are arranged. Inside the sleeves 18''' and 18''' ' planar bottom surfaces 21' ' ' and 21' ''' respectively are arranged. The end surfaces 16''', 16'''', the contact surfaces 20'' ', 20' ' ' ' and the bottom surfaces 21''', 21'''' all have an extension perpendicular to the longitudinal centre axis 15. The embodiment of Fig.3 functions according to the principles of the present invention. First there is shoulder stop established between the contact surfaces 20' ' ' and 20' ' ' ' . Then there are two bottom stops established when after wearing in of the thread coupling the plays δ at both ends of the spigot 11' ' ' are eliminated. The invention is in no way restricted to the embodiments described above. Thus the principles of the invention can be used both for drill rods and drill tubes for percussive drilling and also in a thread coupling between a shank adapter and the first drill rod. The threads of a thread coupling according to the present invention preferably have one entry but it is also possible with two entries. The embodiments and examples should not be considered given in a restricting manner but only for examplifying purposes. Although the present invention primarily relates to trapezoidal threads, the present invention is not limited to such type of threads. Also in other respects the invention can be varied freely within the scope of the appending claims.

Claims: Claims 1. Thread coupling for percussive drilling including at least one male thread (10; 10' , 10" ;10' ' ' , 10' ' ' ' ) and one female thread (17;17' , 17" ;17' ' ' , 17' ' ' ' ) , said male thread being arranged upon a spigot (11;11' ,11";11' ' ' ,11' ' ' ' ) and said female thread being arranged within a sleeve (18 ;18' , 18" ;18' ' ' , 18' ' ' ' ) , said male and female threads being cylindrical, an external stop at a free end of the sleeve, said shoulder stop including contact surfaces (20;20' ;20' ' ' , 20' ' ' ' ) being perpendicular to a longitudinal centre axis (15) of the thread coupling, the spigot at a free end having an end surface (16,-16' ;16' ' ' ,16' ' ' ' ) that is perpendicular to said longitudinal centre axis (15) , the sleeve being provided with an internal stop surface (21;16",-21' ' ' ,21' ' ' ' ) that is perpendicular to said longitudinal centre axis (15) , in an unused thread coupling there is an initial play (δ) between the end surface (16 ;16' ;16' ' ' , 16' ' ' ' ) of the spigot and the internal stop surface, said initial play ( δ ) being eliminated after wearing-in of the thread coupling, c h a r a c t e r i z e d in that the pitch angle (o.) of the male and female threads is greater than 8.5° and less than 15° . 2. Thread coupling according to claim 1, c h a r a c t e r i z e d in that the coupling sleeve (18) constitutes an integral part of a female extension member (19) and that the internal stop surface of the thread coupling constitutes a bottom surface (21) in the transition between the coupling sleeve (18) and the rest of the female extension member (19) . 3. Thread coupling according to claim 1 or 2, c h a r a c t e r i z e d in that the initial play nominally is chosen to be zero (0) with a positive manufacturing tolerance in the magnitude of one (1) mm. 4. Thread coupling according to any one of the previous claims, c h a r a c t e r i z e d in that in the area of the inner end of the spigot (11;11') thread clearances (22, 23;22' ,23' ) are provided. 5. Thread coupling according to claim 1, c h a r a c t e r i z e d in that the coupling sleeve (18') is a detachable part of a female extension member (18',12") and a free end of a spigot (11") of the female extension member (18', 12") constitutes the internal stop surface (16") of the female extension member (18' ,12") . 6. Thread coupling according to any of the previous claims, c h a r a c t e r i z e d in that the pitch angle (α) is greater than 9.5° and less than 11.5°. 7. Thread coupling according to any of the previous claims, c h a r a c t e r i z e d in that said wearing-in is completed after at the most 20% of the length of life for the thread coupling. 8. Thread coupling according to any of claims 1, 3, 6 or 7, c h a r a c t e r i z e d in that the spigot (11' ' ' ) is a separate element having two end surfaces (16' ' ' , 16' ' ' ' ) , that the sleeves (18' ' ' , 18' ' ' ' ) are integral with extension members for percussive drilling.

Inventors: LARSSON KENNETH, LARSSON, KENNETH
Applicants: LARSSON KENNETH, SANDVIK AB, LARSSON, KENNETH
Application year: 1995
Main classification: E21B17
IPC codes: E21B17, F16L15