THREAD JOINT FOR PERCUSSIVE DRILLING, MALE AND FEMALE PORTION FOR FORMING PART OF THE JOINT AND METHOD OF MANUFACTURING A PRODUCT HAVING THREAD FOR FORMING PART OF A THREAD JOINT FOR PERCUSSIVE DRILLING

Abstract: The present invention relates to a thread joint, a male portion, a female portion and a method for manufacturing a product for percussive drilling. The threaded connection comprises at least one substantially cylindrical external thread and a substantially cylindrical internal thread. The external thread is provided on a spigot (13) of a drill string component. The thread comprises thread ends (30) provided in connection with an associated full profile thread (14A). Said thread comprises thread flanks (30A, 30B, 14B, 14C). At least one of the substantially cylindrical threads comprises at least one thread end (30) the shape of which differs from the shape of the full profile thread (14A). Each thread flank (30A, 30B) of the thread end (30) has a profile, which differs from the profile of the associated flanks (14B, 14C) of the full profile thread (14A).

Description: THREAD JOINT FORPERCUSSIVE DRILLING, MALE AND FEMALE PORTION FOR FORMING PART OF THE JOINT AND METHOD OF MANUFACTURING A PRODUCT HAVING THREAD FORFORMING PART OF A THREAD JOINT FORPERCUSSIVE DRILLING Background of the invention The present invention relates to a thread joint, a male portion, a female portion and a method for manufacturing a product according to the preambles of the independent claims. Prior art In a conventional thread joint between two components in a rock drilling equipment for percussive drilling one normally uses cut male and female threads, see for example SE-B-469,602. At manufacturing of such a male thread a blank of steel is formed, which comprises a thick part which ends connect to a clearance surface or a clearance groove with less diameter for to receive at least portions of the threading tool and to a often conical free end. Subsequently, the tool's lateral and longitudinal feed are coordinated with the rotational movement of the thick portion such as to generate the thread in a conventional manner during at least one pass. Sharp edges are formed at the entrance and exit of the thread due to the geometry's of the clearance groove and the free end surface. Corresponding sharp edges are formed at threading of a female thread. The sharp edges makes the male and female threads damaging each other foremost at the free end of the respective drilling element during mounting and dismounting of the joint. In addition, the threads are case hardened and the sharp edges become hardened too much such that the sharp edges define the area for the deepest case depth of the thread. Results from the hardening show cracking and fatigue in these areas during drilling, and therefore the lifespan of the joint becomes relatively short. Another conventional thread joint between two components in a rock drilling equipment for percussive drilling and experience cracking is shown in EP-A2-220 147 wherein the thread end is cut away to maintain a full thread profile to the end of the thread. Objects of the invention One object of the present invention is to provide a thread joint of the above- indicated type in which a good tool life is attained. Another object of the present invention is to provide a thread joint including entrances and exits with substantially the same case depth as in the rest of the thread joint. Still another object of the present invention is to provide a thread joint the parts of which do not damage each other during mounting and dismounting. Still another object of the present invention is to provide strong male and female portions. Still another object of the present invention is to provide a method for manufacturing rock drilling products that have strong thread starts. Short description of the drawings The objects of the invention are realized by a thread joint, a male portion, a female portion and a method for manufacturing a product that have the features indicated in the subsequent claims. Below, one embodiment of the invention will be described with reference to the enclosed drawings wherein, Fig. 1 shows a cross-section of an end of a female portion according to the present invention; Figs. 2A and 2B show an end of a male portion according to the present invention in a side view. Fig. 3 shows a partly sectioned view of a thread joint according to the invention. Fig. 4 shows an end view of the male portion. Figs. 5A-5D show various cross-sections of a thread entrance. Detailed description of the invention The drill rod 10 for percussive drilling shown in Figs. 1 , 2A and 2B is provided with a sleeve-shaped part or a female portion 11 according to the present invention at one end having a female thread or internal thread 12. The female portion 11 constitutes an integral part of the drill rod 10. At the other end the drill rod 10 is formed with a spigot or male portion 13 according to the present invention equipped with a male thread or external thread 14. The drill rod further has a through-going flush channel 15, through which a flush medium, generally air or water, is conducted. The female portion 11 bottom forms a ring- shaped abutment surface 16, which at mounting of two drill rods 10 is intended to abut against a corresponding annular abutment surface 17 at the free end of the shank 13 of the other drill rod. In Figs. 4 and 5A-5D are shown an end view of the male portion and different cross-sections l-IV of an entrance thread 30 and a finished full profile thread in shape of a trapezoidal thread 14A. The thread end 30 has a more rounded cross-section than the full profile thread 14A. The cross-sections l-IV are taken with 90°:s partition and towards the center axis CL of the male portion. At the section I according to Fig. 5A, here taken as reference at 0°, the threading tool does not reach the envelope surface of the thick part of the steel body and the entrance thread still has not started to be cut but instead is provided an end surface 18 only, which is defined by a straight line in the section I. The end surface 18 is usually conical. The entrance thread 30 describes at the section II according to Fig. 5B, at 90°:s difference from the section I counter-clockwise, a path which resembles a bell curve or the cross section of a symmetrical ridge has a smallest radius R1 which is bigger than 0.2 mm and a height h The entrance thread 30 comprises substantially identical flanks 30A and 30B. In the section according to Fig. 5C, at 90°:s difference from the section II counterclockwise, the cross-sectional area has grown further, whereby the ridge and the flanks have a smallest radius R2 which is bigger than 0.2 mm and a height h2. In Fig. 5D according to the section I, i.e. 360° from the above-described section I the entrance thread has entirely surpassed into a full profile thread or finished trapezoidal thread 14A with a smallest radius R3 that is bigger than 0.2 mm and a height h3. The full profile thread 14A has substantially identical flanks 14B and 14C. It can be seen from Figs. 5A-5D that both the cross- sectional area and the height of the entrance thread 30 increase from the start between the sections I and II circumferentially to the finished thread 14A while the smallest radius R1-R3 is not less than 0.2 mm. In case the finished thread is a trapezoidal thread 14A then the smallest radius R2 of the entrance thread 30 in the section III is greater than the smallest radius R3 of the trapezoidal thread 14A. Since sharp edges do not exist at entrances and exits 30 of the thread 14 the hardening depth at heat-treatment, for example case hardening, becomes essentially constant along the entire thread, and therefor cracks and fatigue is avoided in these areas. At conventional cut threads one of the thread flanks at the thread end always has the same profile as the full profile thread except for being somewhat lower while both thread flanks 30A, 30B of the current thread end 30 have profiles which differ from the profile of the connected flanks 14B and 14C, respectively, of the full profile thread 14A, see Figs. 5B and 5D. Preferably there are provided two entrances and two exits at the thread ends. A corresponding soft profile is attained at the entrances and exits of the female thread 12. When the threaded connection, Fig. 3, of two drill rods 10 according to the present invention is mounted, the free end of the male portion 13 will enter at the area of the free end of the female portion. In most cases the rods must be rotated relative to each other during insertion such that the threads can come into engagement with each other. Before threading starts the soft thread ends prevent that the rods damage each other. Subsequently, the rods can be rotated until the front surface 17 of the rod abuts against the bottom 16. The full profile threads 12 and 14 are designed in a conventional manner such that when they have been mounted abutment arises only at the straight flank portions 14B and the corresponding flanks at the female portion. Consequently, contact between curved parties or between peaks and bottoms do not occur. At tests the thread joint according to the present invention has exhibited at least doubled tool life compared to conventional thread joints. Turning of the thread 12 or 14 is made in the following manner. In a conventional manner the lateral and longitudinal feed and cutting depth of the tool is co-ordinated with the rotational movement of the thick portion such that a thread is generated during at least one passage. This is attained by a thread master or via a threading program in a lathe. Having the threading tool deciding the thread profile substantially without being influenced by connecting clearances thereby attains soft entrances and exits at the thread ends. Subsequently at least the cut thread is heat treated for example through case hardening. Conceivable modifications of the invention Alternatively, the rod is provided in the shape of a drill tube and can also comprise shoulder abutment of the type that is illustrated in US-A-4,968,068 which hereby is incorporated into the description. In the shown embodiment a trapezoidal thread is shown but it is implicit that the invention can be utilized for all rock drilling threads, such as for example rope threads. The female portion or the male portion may alternatively be integrated with a rock drill bit instead of with a drill rod or a drill rod. The principles of the invention can be applied also at a thread joint between a shank adapter and the drill rod and between two drill rods with a loose threaded 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 including at least one substantially cylindrical external thread (14) and a substantially cylindrical internal thread (12), said external thread (14) being provided on a spigot (13) intended to constitute an integral part of a first drill string component (10), said threads comprising thread ends (30) provided in connection with an associated full profile thread (14A), said threads (12,14) comprising thread flanks (30A,30B,14B,14C), c h a r a c t e r i z e d in that at least one of the substantially cylindrical threads (12,14) comprises at least one thread end (30) the shape of which differing from the full profile thread (14A) shape and that both thread flanks (30A,30B) of the thread end (30) have a profile which differs from the profile of the connected flanks (14B.14C) of the full profile thread (14A). 2. The thread joint according to claim 1 , wherein the thread end (30) has a more rounded cross-section than the full profile thread (14A) and wherein both the cross-sectional area and the height of the thread end (30) increase from the start of the thread end in direction circumferentially towards the associated full profile thread (14A) and in that the flanks (30A.30B) of the thread end (30) are substantially identical. 3. Thread joint according to claim 1 or 2, wherein the smallest radius (R1 ,R2) of the thread end (30) is at least as large as the smallest radius (R3) of the full profile thread (14A). 4. Thread joint according to claim 1 , 2 or 3, wherein the smallest radius (R1 ,R2) of the thread end (30) is bigger than 0.2 mm. 5. Male portion for forming a part of a thread joint for percussive drilling, wherein the male portion (13) includes at least one substantially cylindrical external thread (14), said external thread (14) being provided on a spigot (13) intended to constitute an integral part of a first drill string component (10), said thread (14) comprising thread ends (30) provided in connection to an associated full profile thread (14A), said external thread (14) comprising thread flanks (30A,30B,14B,14C), c h a r a c t e r i z e d in that the substantially cylindrical thread (14) comprises at least one thread end (30) the shape of which differs from the full profile thread (14A) shape and that both thread flanks (30A.30B) of the thread end (30) have a profile which differ from the profile of the associated flanks (14B.14C) of the full profile thread (14A). 6. Male portion according to claim 5, wherein both the cross-sectional area and the height of the thread end (30) increases from the beginning of the thread ends circumferentially in direction towards the associated full profile thread (14A) and that the smallest radius (R1 ,R2) of the thread end (30) is bigger than 0.2 mm and that the smallest radius (R1 ,R2) of the thread end (30) is at least as large as the smallest radius (R3) of the full profile thread (14A). 7. Female portion for forming a part of a thread joint for percussive drilling, wherein the female portion (11) includes at least one substantially cylindrical internal thread (12), said internal thread (12) being provided in an end intended to constitute an integral part of a first drill string component (10), said thread comprising thread ends (30) provided in connection with an associated full profile thread (14A), said internal thread (12) comprising thread flanks (30A,30B,14B,14C), c h a r a c t e r i z e d in that the substantially cylindrical thread (12) comprises at least one thread end (30) the shape of which differs from the full profile thread (14A) shape and that both thread flanks (30A,30B) of the thread end (30) have a profile which differs from the profile of the connected flanks (14B.14C) of the full profile thread (14A). 8. Female portion according to claim 7, wherein both the cross-sectional area and the height of the thread end (30) increases from the thread end start 8 circumferentially in direction towards the associated full profile thread (14A) and that the smallest radius (R1 ,R2) of the thread end (30) is bigger than 0.2 mm and of that the smallest radius (R1 ,R2) of the thread end (30) is at least as large as the smallest radius (R3) of the full profile thread (14A). 9. Method for manufacturing a product having a thread for forming a part of a thread joint for percussive drilling, wherein the thread includes at least one thread end (30) having flanks (30A,30B) and a full profile thread (14A) having flanks (14B.14C), wherein the method comprises the following steps: a) provide a blank of metal in a machine for metallic machining, b) provide a threading tool in the machine, c) co-ordinate longitudinal and lateral feed of the tool with rotational movement of the blank about an axis of rotation (CL) such that the thread is generated on the blank, c h a r a c t e r i z e d in that step c) further comprises the step of adjusting the threading tool to profile the thread end (30) such that each thread flank (30A,30B) of the thread end (30) obtains a profile which differs from the profile of the associated flanks (14B,14C) of the full profile thread (14). 10. Method according to claim 9, wherein the method further comprises the step of: d) heat-treating at least the cut thread.

Inventors: LILJEBRAND PER-OLOF, OLSSON URBAN, LILJEBRAND, PER-OLOF, OLSSON, URBAN
Applicants: SANDVIK AB
Application year: 1999
Main classification: E21B17
IPC codes: E21B17