A THREAD JOINT AND A MALE PORTION

Abstract: The present invention relates to a male portion a thread joint and a male portion for percussive drilling. The threaded joint includes at least one generally cylindrical external thread (14) and one generally cylindrical internal thread (15). The external thread (14) is provided on a spigot (12) intended to constitute an integral part of a first drill string component (10A, 10B). The threads comprise thread ends (21-24) provided in connection with associated full profile threads. The threads (14, 15) comprise end areas where each thread in a longitudinal section has its smallest radius (R). The generally cylindrical external thread (14) has a first axial length (L1) and the generally cylindrical internal thread (15) has a second axial length (L2), wherein the first axial length (L1) is shorter than the second axial length (L2) such that the both end areas (23, 24) of the cylindrical internal thread (15) do not contact the cylindrical external thread (14).

Description: A THREAD JOINT AND A MALE PORTION Background of the invention The present invention relates to a thread joint and a male portion according to the preambles of the independent claims. Prior art A conventional thread joint between two components in a rock drilling equipment for percussive drilling normally uses cut male and female threads, see for example SE-B-469,602 and US-A-4,332,502. At the production of such a male thread a blank of steel is shaped, which includes an enlarged portion. The ends of the enlarged portion connect to a clearance surface or a clearance groove of smaller diameter to receive at least parts of the threading tool and to a usually conical free end. Then the enlarged portion is provided with a thread in a conventional way. Sharp edges are formed at the thread entrance and the exit due to the geometries of the clearance groove and the free end surface. Corresponding sharp edges are formed at threading of a female thread. The sharp edges make the male and female threads damage each other foremost at the respective free end during use of the joint. It is usually the male thread that limits the life span of the joint. Object of the invention One object of the present invention is to provide a thread joint of the above- mentioned type, at which a good life span is attained. Another object of the present invention is to provide a thread joint of the above-mentioned type, at which the male portion obtains a good life span. Short description of the drawings The object of the invention is realized by means of a thread joint which has obtained the characteristics of the appended claims. Below an embodiment of the invention is described with reference to the enclosed drawing wherein Fig. 1 shows a partly sectioned view of a thread joint according to the invention between two identical drill components. Fig. 2 shows a male portion according to the present invention in a perspective view. Fig. 3 shows a female portion in a cross-sectional perspective view. Fig. 4 shows a cross-section of a thread joint according to the present invention between a rock drill bit and a drill component. Detailed description of the invention A thread joint 10 according to the present invention preferably consists of two drill tubes or drill rods 10A, 10B that each includes an end with a projecting spigot or male portion 12 and an end with a sleeve or female portion 13. The spigot has a generally cylindrical external thread 14 and the sleeve has a generally cylindrical internal thread 15. Each thread 14, 15 preferably has only one entrance and one exit. When the threaded joint 10 with two drill rods 10A, 10B for percussive drilling shown in Fig. 1 is mounted the free end surface 16 of the male portion 12 will enter into the area of the free end surface or abutment surface 17 of the female portion. In most cases the rods must be rotated relative to each other while forcing them together such that the threads can engage each other. Then the rods are further rotated until the free end surface 16 of the rod abuts against a bottom 18 in the female portion and/or the abutment surface 17 abuts against an inner shoulder 19 about the inner end of the spigot 12. The threads 14 and 15 are conventionally designed such that when assembled abutment arises only at certain flank portions of the respective male and female portion. Contact between curved parties or between thread tips and thread bottoms do not occur. In US-A-4,968,068, which patent hereby is incorporated into the present description, a thread joint is shown in which the present invention can be utilized. The female portion 13 constitutes an integral part of the drill rod. Furthermore, the drill rod has a through-going flush channel 20, through which a flush medium, usually air and/or water, is transported. The male thread or the generally cylindrical external thread 14 includes at least one outer thread end 21 and at least one inner thread end 22 arranged in connection with the associated full profile thread. The female thread or the generally cylindrical internal thread 15 includes at least one outer thread end 23 and at least one inner thread end 24 arranged in connection with the associated full profile thread. Each thread end 21-24 includes a sharp edge due to clearances developed before threading, i.e. conical clearances 31 , 32 on the spigot 12 and cylindrical clearances 33, 34 on the sleeve 13. The edge defines the smallest radius R of the respective thread, in the longitudinal section according to Fig. 3. The male thread 14 and the female thread 15 has a mutual relationship as regards to the length and the position that the both thread ends or end areas 23, 24 of the female thread 15 do not contact the male thread 14 when the joint is tightened. With "do not contact" is here meant that the ends 23, 24 are provided at a distance from the male thread in a tightened joint. This has been achieved as follows: The male thread 14 has a first axial length L1 between the thread ends 21 , 22 and the female thread 15 has a second axial length L2 between the thread ends 23, 24, The length L1 is shorter than the length L2. Stated another way, the distance between the conical clearances 31 , 32 is smaller than the distance between the cylindrical clearances 33, 34. The distance L3 between the free end surface 16 of the spigot 12 and the inner thread end or end area 24 of the female thread 15 is shorter than a distance L4 between the free end surface 16 of the spigot and the outer thread end or end area 21 of the male thread when the joint is tightened. The corresponding relationship applies for the outer end of the joint. That is, the distance L5 between the shoulder 19 of the spigot 12 and the outer thread end or end area 23 of the female thread 15 is shorter than a distance L6 between the shoulder 19 of the spigot and the inner thread end or end area 22 of the male thread when the joint is tightened. The outer and inner ends of the spigot 12 includes conical guiding surfaces 25, 26 which shall cooperate axially on each side of the female thread 15 with conical guiding surfaces 27 and 28, respectively. All cone apices of the conical guiding surfaces are directed in the impact direction F. The length L1 of the male thread 14 is 50-80% of the length L of the spigot. Both end areas 21 , 22 of the male thread 14 are provided at the distances L4, L6 from the ends 16, 19 of the spigot. A trapezoidal thread is shown in the embodiment but it is understood that the invention can be used in connection with all for percussive rock drilling serviceable threads, such as rope threads for example. The female portion or the male portion may alternatively be integral with a rock drill bit instead of being integral with a drill rod or a drill tube. In Fig. 4 is shown how a rock drill bit 10C for percussive rock drilling with hard metal buttons 30 appear in a thread joint according to the present invention, with the same reference numerals as is used above. The principles of the invention can be applied also at a thread joint between a shank adapter and the drill rod as well as between two drill rods with a loose extension sleeve. Also in other respects the invention can be freely varied within the scope of the appended claims.

Claims: Claims 1. A thread joint for percussive drilling comprising at least one generally cylindrical external thread (14) and one generally cylindrical internal thread (15), said external thread (14) being provided on a spigot (12) intended to constitute an integral part of a first drill string component (10A,10B,10C), said threads comprising thread ends (21-24) provided in connection with associated full profile threads, said threads (14,15) comprising end areas where each thread in a longitudinal section has its smallest radius (R), c h a r a c t e r i z e d i n that wherein the generally cylindrical external thread (14) has a first axial length (L1) and the generally cylindrical internal thread (15) has a second axial length (L2), wherein the first axial length (L1) is shorter than the second axial length (L2) such that the both end areas (23,24) of the cylindrical internal thread (15) do not contact the cylindrical external thread (14). 2. The threaded joint according to claim 1 , wherein the inner end of the spigot (12) is provided with a shoulder (19), which has an abutment surface that faces towards the free end of the spigot (12), said internal thread (15) being provided in a sleeve, which is connected to a second drill string component, said sleeve being provided with an internal abutment surface (18). 3. The threaded joint according to claim 1 , wherein the distance (L3) between a free end surface (16) of the spigot (12) and the inner end area (24) of the internal thread (15) is shorter than a distance (L4) between the free end surface (16) of the spigot (12) and the outer end area (21) of the external thread (14) and wherein a distance (L5) between an inner end (19) of the spigot (12) and the outer end area (23) of the internal thread is shorter than a distance (L6) between the inner end of the spigot and the inner end area (22) of the external thread. 4. The threaded joint according to claim 4, wherein the outer and inner ends of the spigot (12) comprise conical guiding surfaces (25,26) for cooperation with conical guiding surfaces (27,28) axially on each side of the internal thread (15). 5. A male portion to form a part of a thread joint for percussive drilling, said male portion including at least one generally cylindrical external thread (14), said external thread (14) being provided on a spigot (12) intended to constitute an integral part of a first drill string component (10A,10B), said thread (14) including thread ends (21 ,22) provided in connection with an associated full profile thread, said thread (14) including end areas where each thread in a longitudinal section has its smallest radius (R), said spigot (12) having a length (L), c h a r a c t e r i z e d i n that the length (L1) of the generally cylindrical external thread (14) is 50-80% of the length (L) of the spigot and that the both end areas (21 ,22) of the external thread (14) are provided at a distance from the ends (16,19) of the spigot and in that the inner end of the spigot (12) is provided with a shoulder, which has an abutment surface (19) facing towards the free end of the spigot (12). 6. The male portion according to claim 5, wherein the outer and inner ends of the spigot (12) include conical guiding surfaces (25,26).

Inventors: LARSSON KENNETH, LARSSON, KENNETH
Applicants: SANDVIK AB
Application year: 2000
Main classification: E21B17
IPC codes: E21B17, F16L15