WO2015088420A1

WO2015088420A1 - Threaded drill string device, threaded joint and method of manufacturing a threaded male portion for percussive drilling

Info

Publication number: WO2015088420A1
Application number: PCT/SE2014/051408
Authority: WO
Inventors: Alexander Beronius; Jing James Yao
Original assignee: Atlas Copco Secoroc Ab
Priority date: 2013-12-13
Filing date: 2014-11-26
Publication date: 2015-06-18
Also published as: SE538948C2; SE1351494A1

Abstract

A threaded drill string component (2) for percussive drilling, said drill string component (2) having a central axis (A) and a threaded male portion (4) exhibiting: a proximal end portion (4'), a distal end portion (4'') having an axially directed, substantially planar impact surface (7), a thread ridge (5) and a thread bottom (6). The distal end portion (4'') is formed such that at least a part of a peripheral wall thereof, which is adjoining to the impact surface (7), is located at a first distance (R1) from the central axis exceeding a second distance (R2) between the central axis and an innermost portion of a wall of the thread bottom, such that an enlarged impact surface is created. The invention also relates to a thread joint and a method of manufacture.

Description

THREADED DRILL STRING DEVICE, THREADED JOINT AND METHOD OF MANUFACTURING A THREADED MALE PORTION FOR PERCUSSIVE DRILLING

FIELD OF THE INVENTION

The invention relates to a threaded drill string component for percussive drilling, said drill string component having a threaded male portion for joining to a threaded female portion of another drill string component. The invention also relates to a thread joint and a method of manufacturing.

BACKGROUND OF THE INVENTION

In a percussive rock drilling process, a shank adapter, a number of drill rods and a drill bit are joined together through thread joints to form a drill string. Percussive energy is transferred as impact/shock waves from the rock drilling machine to the rock through, the drill string components. The shock wave is transferred from component to component through contacting impact surfaces that are normally positioned at each end region of each component .

When the components are joined together, the thread joints are subjected to a torque whereby the impact surfaces are pressed together because of the normal forces occurring between the pressure flanks of the threads.

Percussive rock drilling has to be performed during conditions that sometimes result in that the drilled holes deviate from a straight line. Hereby the drilling components are subjected to bending moments during operation. These bending moments have to be counteracted by the threads and by the impact surfaces .

Further, these bending moments are. alternating during the drilling process because, of the rotation of the drill string. In particular the last thread turn of the male thread is subjected to high stress and wear as a result of these

alternating bending moments. The counteraction by the threads and by the impact surfaces results in a force balance such that a bending moment on the thread joint will be balanced on the one hand at the impact surface by normal forces on the side of the impact surface being compressed by the bending moment. On the other hand, there will also be a balancing contribution from increased normal forces on the pressure flanks at an outside of the threaded parts,, as seen in the bending direction.

As an example of the background art US 6,767,156 Bl could be mentioned. This document describes a thread, joint wherein the male and female threaded components have mating conical guiding surfaces that will contact one another during any relative bending .

AIM AND MOST IMPORTANT FEATURE OF THE INVENTION

It is an aim of the present invention to address the above mentioned problem and provide a solution which at least reduces said problem in respect of a threaded drill string component for percussive drilling, said drill string component having a central axis arid an axially extending threaded male portion for joining to a threaded female portion of another drill string component, wherein the threaded male portion exhibits: a proximal end portion, a distal end portion having an axially directed, substantially planar impact surface for abutting a surface of another drill string component, and a substantially helically extending thread ridge and a substantially helically extending thread bottom.

The above aim is obtained in that the distal end portion is formed such that at least a part of a peripheral wall thereof, which is adjoining to the impact surface (in the axial

direction) , is located at a first distance from the central axis exceeding a second distance between the central axis and an innermost portion of a wall of the thread bottom, such that an enlarged impact surface is created.

In other words, at least a part of said peripheral wall, which is facing substantially radially out from the central axis, is situated at a distance from the central axis which is greater than the distance from the thread bottom to the central axis.

Hereby it is been made possible to obtain a larger impact surface compared to the background art, given that the

peripheral wall adjoins in the same manner to the impact surface as is the case according to the background art. This results in that the bending moment occurring during bending of a thread joint will be more effectively counteracted by the normal forces occurring at the impact surface, since a greater moment arm is allowed to be formed. This in turn also reduces the magnitude of the normal forces acting on the pressure flanks of the thread ridges. It also reduces amplitudes of the stress change in the thread occurring when rotating a bent coupling during operation, leading to a lower degree of pulsating load on the threads.

Altogether the reduced stress results in that a longer working life can be expected for drill string components according to the invent ion .

As a further explanation, when a bending moment is applied, it is balanced at the impact, surface, by normal forces that are increased on the side of the impact surface which is put under compression by the bending moment. These normal forces will be higher for a given bending moment the. smaller the diameter of the impact surface is, because they will have a shorter moment arm. On the opposite side of the bent coupling, on the other hand, the normal forces on the impact surface are reduced. Further on, also the normal forces acting on the. pressure flanks of the thread being at the "outside" of the bend will be increased during bending and will contribute to the balancing of the bending forces.

Hereby it is understood that the provision of a larger impact surface, according to the invention, results in that the normal forces acting on said impact surface are reduced and also that the normal forces acting on the pressure flanks of the thread parts being at the outside of the bend will be reduced. In other words, a larger impact surface, having greater outer dimensions, causes a smaller amount of deformation in the threaded coupling when it is subjected to a bending moment and thereby reduced stress amplitude in the thread.

The external dimensions of the distal portion are limited by inside dimensions of a threaded female portion of another drill string component to be joined to threaded male portion. These inside dimensions correspond to the inside free diameter described by the innermost parts, being thread tops, of thread turns of a female thread ridge being inside sa.id threaded female portion.

Normally, a certain play is provided between the female thread tops and the. male thread bottoms to avoid unwanted contact therebetween during operation. It has been found, that in practice the dimensions of the distal portion can be allowed to exceed an imagined diameter described by the innermost portion of a wall of the thread bottom. A part of this play can thus be exploited by increasing the dimensions of the distal end portion without jeopardizing entering of the male thread into the mating female thread.

An intermediate edge zone, where the peripheral wall adjoins to the impact surface, is preferably radiused or beveled so as to create a suitable transition between the peripheral wall and the impact surface. This is preferred even if a theoretical effect of the invention is higher when said at least a part of the peripheral wall is allowed to adjoin to the impact surface, in the axial direction, more or less directly. Having a sharp or almost sharp edge between the peripheral wall and the impact surface, however, results in difficulties in entering the threads into one another and also to result in increased tendencies of unwanted edge chipping in use during the

percussive action. For that reason, it is useful to provide the intermediate edge zone with a radius or a bevel.

When, according to a first preferred aspect, the peripheral wall of the distal end portion forms a circular cylinder which in particular has an axis being said central axis, the benefits of the invention is afforded, evenly over the periphery of the distal portion and thereby evenly during rotation of the drill string.

In a preferred second aspect of the invention, the thread ridge is allowed to extend all the way to the section of the impact surface in order to form a surface contribution for increased surface area of the impact surface.

The first and second aspects can be combined, such that an enlarged circular cylindrical distal portion can also exhibit a thread ridge, or a part thereof, extending over its axial length .

Having 100% of the thread ridge extending all the way so as to form said surface area contribution would contribute to highest degree of balance and normal force reduction in one axial section of the male threaded portion. Such a construction would, however, be likely to cause negative implications in certain embodiments resulting in difficulties in threading together a male portion according to the invention with a female portion, since the mating has to be initiated very carefully. For that reason most often, only a part of a thread ridge is brought, to extend along the distal end portion so as to provide impact surface area contribution.

In particular the thread ridge is reduced in height and/or reduced at its sides at the impact surface section so as to provide possibilities of smooth entering of the male thread into a female thread, It is preferred that said at least a part of the thread ridge contributes to the impact surface with 15 - 100% of the total sectional area of the thread ridge, as seen in a section perpendicular to said central axis.

The surface area of the impact surface exceeds advantageously by 4 - 40% a surface area based on an imagined circular surface of the distal portion having a distance from the central axis to the thread bottom as its radius. All in all this results in possibilities of considerable stress reductions to the elements involved event at the low part of the range. The edge of the impact surface is rounded or beveled along its periphery. Rounding of the edge for providing a radiused edge or beveling for providing a chamfer surrounding the impact surface also is preferred on the one hand for increasing entry of threaded parts into each other and for avoiding edge

chipping during operation.

The component is suitably any one selected from the group consisting of a drill rod, a shank adapter, a rod adapter and a dril 1 bit .

According to a preferred embodiment of the invention:

i) said central axis, ii) a radial line in the impact surface being a central symmetry line of the section of the part of the thread ridge at the impact surface, and

iii) a radial line through a thread start engagement region of the male thread ridge in a mating female thread ridge at the proximal portion of the male portion, are included in a radial plane such that the radial line through said thread start engagement region is offset about 180° in respect of said radial line in the impact surface.

Hereby the part of the male thread ridge which is most

subjected to stress and wear will be protected by the increased balancing forces from the thread ridge surface contribution being carefully brought to act together with the normal forces from the most sensitive part of the male thread ridge, which part will hereby be subjected to normal forces of lower amplitude .

It is further advantageous that a radial flushing groove is formed in the impact surface, said radial flushing groove essentially coinciding with a radial line in the impact surface being said central symmetry line.

The invention also concerns a thread joint for threaded drill string components for percussive drilling, said thread joint including a threaded male portion and a mating threaded female portion, wherein the threaded male portion exhibits: a proximal end portion, a distal end portion having an axially directed, substantially planar impact surface for abutting a surface of another drill string component, and a substantially helically extending thread ridge and a substantially helically extending thread bottom. The distal end portion is formed such that at least a part of a peripheral wall thereof, 'which is adjoining to the impact surface, is located at a first distance from the central axis exceeding a second distance between the central axis and an innermost portion of a wail of the thread bottom, such that an enlarged impact surface is created.

Corresponding advantages as above, are achieved through the inventive thread joint,

Features that are subordinate to the inventive drill string component are also applicable in respect of the inventive, thread j oint .

In an inventive method of manufacturing a threaded male portion of a drill string component for percussive drilling, said drill string component having a central axis and an axially extending threaded male portion for joining to a threaded female portion of another drill string component, wherein the threaded male portion is provided with: a proximal end portion, a distal end portion having an axially directed, substantially planar impact surface for abutting a surface of another drill string

component, a substantially helically extending thread ridge and a substantially helically extending thread bottom. The distal end portion is formed such that at least a part of a peripheral wall thereof is brought to adjoin to the impact surface, and is brought to be located at a first distance from the central axis exceeding a second distance between the central axis and an innermost portion of a -wall of the thread bottom, such that an enlarged impact surface is created.

It is preferred that the peripheral wall is brought to adjoin to the impact surface over an intermediate radiused or beveled edge zone.

It is suitable, according to one aspect of the invention, that the peripheral wall of the distal end portion is formed into a circular cylinder. It is suitable, according to another aspect of the invention, that at least a part of the thread ridge is brought to extend over the distal end portion and adjoin to the impact surface.

Said at least a part of the thread ridge is suitably formed to contribute to the impact surface with 15 - 100% of the total sectional ctx"ea of the thread ridge, as seen in a section perpendicular to said central axis.

Advantages explained in respect of the main and subordinate features related to the inventive component are correspondingly obtained in respect of the inventive joint and the inventive method .

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be described in greater detail by way of embodiments with reference to the annexed drawings, wherein:

Fig. 1 is an axial section through a thread joint according to the invention,

Figs. 2a, b and c show different views of a threaded male portion according to the invention,

Fig. 3 shows a blank of a threaded male portion according to the invention prior to thread cutting,

Fig. 4 shows a corresponding blank of a thread male part according to background art before thread cutting, and

Fig. 5 shows a simplified block diagram of a method sequence according to the invention.

Fig. 6a shows a shank adapter. Fig. 6b shows a drill bit and Fig. 6c shows a rod adapter according to the invention. Fig. 7 shows, for comparison, longitudinal sections of parts of treaded male portions according to the invention and according to background art .

Fig. 8 illustrates a thread ridge of an inventive component. DETAILED DESCRIPTION OF EMBODIMENTS

The thread joint 1 in Fig. 1 relates to parts of a first 2 and a second 3 drill string component comprising drill rods to be positioned between a percussive rock drilling machine and a drill bit .

The first drill string component 2 is provided with a threaded male portion 4 having a proximal portion 4' and a distal portion 4" being a free end portion of the component. The threaded male portion 4 is thread- j oined into a sleeve-shaped female portion 40 having a mating thread. The threaded male portion 4 is provided with a helical thread ridge 5 which in this case is trapezoid-shaped having substantially straight lines defining its flanks as seen in the axial section. Between each turn of the thread ridge 5 there are thread bottoms 6.

At the end of the male portion its free, distal portion 4" has a substantially planar impact surface 7 which is intended to transfer impact shock waves emanating from the percussive rock drilling machine (not shown) to the next drill string component 3 which in turn has a mating impact surface. 8. 9 indicates a flushing channel extending through the entire drill string in order to allow transfer of flushing medium such as air or water for flushing purposes to a drill bit.

A indicates a central symmetry axis of the components and in particular of the threaded male portion 4. 10 and 11 indicate first and second rod joints between shaped end parts of the respective first and second drill string components 2 and 3. 1

These end parts can be joined to first and second rod portions 12 and 13 respectively through friction welding in a per se known manner or by any other suitable method. It is also possible to form the drill string component including one or both end parts through conventional machining methods from one single rod blank.

When the thread joint 1 is subjected to a bending moment M, as shown in Fig. 1, this bending moment, will be resisted and balanced by normal forces Νχ between the lower parts of the impact surfaces 7 and 8 and by normal forces n acting between the pressure flanks at the upper parts of the thread ridge 5. From this it should be understood that increased moment arm for the normal force N_:, results in reduced magnitude of the normal forces n. For simplicity of explanation, with N_:. and n is meant only the normal force components depending on the bending moment M. Indeed the thread joint is also subject to normal force components existing because of the ordinary threading together of the drill string components. All the existing normal forces contribute to affecting the. thread joint. Figs. 2a, 2b and 2c illustrate the invention in greater detail. Here the entire thread ridge 5 has been allowed to extend all the way to the impact surface 7 of the threaded male portion 4. This results in that the impact surface is considerably

increased and in particular that a surface area 7' has been added to the impact surface since also the thread ridge

material is contributing to the impact surface.

R2 illustrates a distance from the central symmetry axis A to the lowest part of the thread bottom 6 whereas Rl illustrates the distance from the central symmetry axis A to the thread ridge top of the thread. Potential surface area from the thread ridge that could potentially contribute to the impact surface area is thus the sectional area of the thread ridge outside a circle defined with R2 as radius.

In order to fully have the benefits of the invention, according to one important aspect, the surface area contribution from the thread ridge is positioned such in respect of a thread start engagement region 14, wherein the load during bending of the thread joint can be expected to be highest according to the following ,

The bending moment occurring in the rotational position in a section illustrated through the plane P is thus most resisted by the surface area being contributed by the thread ridge when the thread ridge contribution to the impact surface is in the compressed state, which in an advantageous manner reduces the tension on the most sensitive part of the thread when there is a 180^u separation between the centre of the contributed surface of the thread ridge and the thread start , Hereby the part of the. male thread ridge which is most subjected to stress and wear will be protected as is described above.

In Fig. 2b, 16 indicates with interrupted lines a radial flush groove which is known per se and is often included in a

threaded male portion. This radial flush groove is suitably positioned so that said plane P passes through it in order to have as little as possible impact on the integrity of the impact surface. The aim of the radial flush groove 16 is to allow part of flushing fluid through the flushing channel 9 to find its way out in the thread joint between the thread ridges for cooling purposes.

It should be noted that the embodiment in Figs. 2a. 2b and 2c is shown for illustration of the full potential of the

invention. Normally, the edge 15 of the impact surface is beveled or radiused in order to allow smooth entering of the threads into one another. Normally, also the top of the thread ridge is reduced in the region of the impact surface.

The blank shown in Fig. 3 is made such that at the free, distal portion 4'' of the male portion 4 there is a dimensional reduction 17 having a radius seen from the central axis being between the radius of the thread ridge top and the thread ridge bottom of the completed thread. Thread cutting of the blank in Fig. 3 therefore results in that a part of the thread ridge extends over the distal portion 4^'"' such that, compared to a threaded male portion according to the background art, which is illustrated in Fig. 4, there will be an increased area of the impact surface 7.

In Fig. 4, the distal portion 4'^' of the blank of the male portion 4 is given a surface reduction 17 to the radius of the thread bottom.

Altogether, the result is an increased surface area of the impact surface for the inventive embodiment of Fig. 3 compared to the resulting threaded male portion according to the

background art as illustrated in Fig. 4.

The axial length 1 of the distal portion 4" in Fig. 3 is advantageously 5 - 15 mm and more preferred 8 - 12 mm for a drill string component according to the invention.

Fig. 5 illustrates a method sequence wherein:

Position 20 indicates the start of the sequence.

Position 21 indicates providing a blank for a male threaded. portion for a drill string component.

Position 22 indicates cutting a substantially helically

extending thread ridge, and a substantially helically extending thread bottom

Position 23 indicates bringing at least a part of the thread ridge to extend along the distal end portion so as to thereby provide a thread ridge surface area contribution for increased surface area of the impact surface .

Position 24 indicates rounding or beveling the intermediate edge zone of the impact surface along its periphery.

Position 25 indicates joining the part including the threaded male portion with a. rod by friction welding to form a complete drill string component.

Position 26 indicates the end of the sequence. Figs . 6a, 6b and 6c illustrate other examples of drill string components according to the invention, i.e. a shank adapter 30, a drill bit 31, and a rod adapter 39 having two opposite threaded male portions.

Fig. 7 shows, for comparison, a section of a part of a first treaded male portion 32 according to the invention and a part of a second treaded male portion 33 according to background art . It should be noted that the heights of the tread ridges are exaggerated for sake of illustration.

From Fig. 7 it is apparent that a surface area (with diameter Dimp ) of an impact surface 36 of the distal portion 34 of the first threaded portion 32 exceeds a surface area of an impact surface 37 of the distal portion 35 of the second threaded portion 33.

The diameter defined by a diameter related to an innermost region of a thread groove bottom is indicated with D_B, The play between a ridge top 38 of the female thread ridge (indicated with interrupted lines at a diameter D_RF) and the innermost region of the male thread groove bottom is ¾(D_RF - D_B) = P.

By increasing the diameter D_DP of the distal portion it has been made possible to reach the area increase of the impact surface compared to an impact surface area (with diameter d_imp) since the intermediate edge zone E_:l has been provided with the same preferred radius r as the intermediate edge zone E₂ of the second, background art, threaded male portion 33. The distal portion 35 of the second threaded male portion 33 has the same diameter, D_B, as the one being related to an innermost region of a thread groove bottom -which is thus also D_B,

Fig. 8 shows a thread ridge 41 of an inventive component wherein the thread is a trapezoidal thread and wherein is illustrated an angle β of inclination of a pressure flank of the thread ridge. The angle β of inclination is suitably less than 45°, more preferably 25° - 45º and most preferred 30º - 40° .

The invention can be modified within the scope of the annexed claims. The threaded male portion can have a cylindrical extension as well as conical extension wherein a cone angle of between 2 degrees and 10 degrees is suitable. When used in respect of a conical thread, the extra surface area can normally be allowed to be relatively greater because of the inherent simpler entry of the male portion into a mating femal portion for such thread joints. R2 (compare with Fig. 2b) is here, for the conical thread, measured at a position being adjacent to the distal end portion since this is the position of an innermost part of the thread groove bottom in this case.

It should be noted that also when the resulting impact surface is in practice reduced after beveling or radiusing of the edge of the impact surface to the extent that the planar impact surface is smaller than a potential impact surface having a radius (R2) being the distance from the central symmetry axis (A) , will indeed exist an enlargement of the impact surface compared to what would have resulted in a correspondingly beveled or radiused impact surface made according to a

background art, since according to the invention, it has been made possible to have the radius and bevel of the edge of the impact surface at a greater distance from said central symmetry axis .

The thread of the male and female portions are shown and described as helical with trapezoid-shaped ridge section, It is also within the scope of the invention to use other thread shapes having curved lines defining its flanks such as so called rope threads.

EXAMPLE ;

As an example of the invention, an inventive threaded male part was produced from the blank shown in Fig. 3. The machining operation for producing the thread ridge and the thread bottom was in this case not performed over the distal portion, leaving the distal portion intact with a circular cylindrical

peripheral surface having a diameter of 52.5 mm which adjoins to the impact surface with the intermediate of an edge zone with a radius of 3 mm. The diameter 52.5 leaves a sufficient play in respect of an inner diameter of a mating threaded female part for swift entering of the threads into one another.

As comparison, the background art threaded part was produced from the blank shown in Fig.4. The distal portion also in this case has a circular cylindrical peripheral surface having a diameter of 49.5 mm, corresponding to the diameter described by the thread groove bottom. The circular cylindrical peripheral surface also in this case adjoins to the impact surface with the intermediate of an edge zone with a radius of 3 mm.

Claims

PATENT CLAIMS

1. Threaded drill string component (2) for percussive drilling, said drill string component (2) having a central axis (A) and an axially extending threaded male portion (4) for joining to a threaded female portion (40) of another drill string component, wherein the threaded male portion (4) exhibits:

- a proximal end portion (4") ,

- a distal end portion (4 ") having an axially directed, substantially planar impact surface (7) for abutting a surface of another drill string component, and

- a substantially helically extending thread ridge. (5) and a substantially helically extending thread bottom (6) ,

characterized in

- that the distal end portion (4" ) is formed such that at least a part of a peripheral wall thereof, which is adjoining to the impact surface (7) , is located at a first distance (Rl) from the central axis exceeding a second distance (R2) between the central axis and an innermost portion of a wall of the thread bottom, such that an enlarged impact surface is created.

2. Component (2) according to claim 1, characterized in that the peripheral wall adjoins to the impact surface over an intermediate radiused or beveled edge zone.

3. Component (2) according to claim 1 or 2, characterized in that the peripheral wall of the distal end portion forms a circular cylinder.

4. Component (2) according to claim 1, 2 or 3, characterized in

- that at least a part of the thread ridge (5) extends over the distal end portion (4'') and adjoins to the impact surface (7) .

5. Component (2) according to claim 4, characterized in that said at least a part of the thread ridge (5) contributes to the impact surface (7) with 15 - 100% of the total sectional area of the thread ridge, as seen in a section perpendicular to said central axis.

6. Component (2) according to claim 4 or 5, characterized in that :

i) said central axis (A) ,

ii) a radial line in the impact surface (7) being a central symmetry line of the section of the part (7") of the thread ridge (5) at the impact surface (7) , and

iii) a radial line through a thread start engagement region (14) of the male thread ridge (5) in a mating female thread ridge at the proximal portion of the male portion,

are included in a radial plane. (P) such that the radial line through said thread start engagement region (14) is offset about 180° in respect of said radial line in the impact surface (7) .

7. Component (2) according to any one of the previous claims. characterized in that the surface area of the impact surface

(7) exceeds by 4 - 40% a surface area based on an imagined circular surface of the distal portion (4^''') having a distance from the central axis to the thread bottom as its radius (r) .

8. Component according to any one of the previous claims, characterized in

- that the component is any one selected from the group

consisting of a drill rod (2,3) , a shank adapter (30) , a rod adapter (39) and a drill bit (31) .

9. Component according to any one of the previous claims, characterized in - that a radial flushing groove is formed in the impact

surface .

10. Thread joint for threaded drill string components (2,3) for percussive drilling, said thread joint including a threaded male portion (4) and a mating threaded female portion (40) , wherein the threaded male portion (4) exhibits:

- a proximal end portion (4") ,

- a distal end portion (4") ) having an axially directed, substantially planar impact surface (7) for abutting a surface of another drill string component, and

- a substantially helically extending thread ridge (5) and a substantially helically extending thread bottom (6) ,

characterized in

- that the distal end portion (4'' ) is formed such that at least a part of a peripheral wall thereof, which is adjoining to the impact surface (7) , is located at a first distance (Rl) from the central axis exceeding a second distance (R2) between the central axis and an innermost portion of a wall of the thread bottom, such that an enlarged impact surface is created.

11. Joint according to claim 10, characterized in that the peripheral wall adjoins to the impact surface over an

intermediate radiused or beveled edge. zone.

12. Joint according to claim 10 or 11, characterized in that the peripheral wall of the distal end portion forms a circular cylinder.

13. Joint according to claim 10, 11 or 12, characterised in

- that at least a part of the thread ridge (5) extends over the distal end portion (4" ) and. adjoins to the impact surface (7) ,

14. Joint according to claim 13, characterized in that said at least a part of the thread ridge (5) contributes to the impact surface (7) with 15 - 100% of the total sectional area of the thread ridge, as seen in a section perpendicular to said central axis.

15. Joint according to claim 13 or 14. characterized in that:

i) said central axis (A) ,

ii) a radial line in the impact surface (7) being a central symmetry line of the section of the. part (7') of the thread ridge (5) at the impact surface (7) , and

are included in a radial plane (P) such that the radial line through said thread start engagement region (14) is offset about 180º in respect of said radial line in the impact

surface .

16. Joint according to any one of claims 10 - 15, characterized in that the surface area of the impact surface (7) exceeds by 4

- 40·% a surface area based on an imagined circular surface of the distal portion (4'') having a distance from the central axis to the thread bottom as its radius (r) .

17. Method of manufacturing a threaded male portion (4) of a drill string component (2) for percussive drilling, said drill string component (2) having a central axis (A) and an axialiy extending threaded male portion (4) for joining to a threaded female portion (40) of another drill string component, wherein the threaded male portion (4) is provided with:

- a proximal end portion (4") ,

- a distal end portion (4" ) having an axialiy directed, substantially planar impact surface (7) for abutting a surface of another drill string component, and - a substantially helically extending thread ridge (5) and a substantially helically extending thread bottom (6) ,

characterized in

- that the distal end portion (4^") is formed such that at least a part of a peripheral wall thereof is brought to adjoin to the impact surface (7) , and is brought to be located at a first distance (Rl) from the central axis exceeding a second distance (R2) between the central axis and an innermost portion of a wall of the thread bottom, such that an enlarged impact surface is created.

18. Method according to claim 17, characterized in that the peripheral wall is brought to adjoin to the impact surface over an intermediate radiused or beveled edge zone.

19. Method according to claim 17 or 18, characterized in that the peripheral wall of the distal end portion is formed into a circular cylinder.

20. Method according to claim 17, 18 or 19, characterized in

- that at least a part of the thread ridge (5) is brought to extend over the distal end portion (4^"") and adjoin to the impact surface (7) .

21. Method according to claim 20, characterized in that said at least a part of the thread ridge (5) is formed to contribute to the impact surface (7) with 15 - 100% of the total sectional area of the thread ridge, as seen in a section perpendicular to said central axis.