Title of Invention

MALE PORTION, DRILL BIT AND THREADED JOINT FOR PERCUSSIVE ROCK DRILLING

Abstract According to the present invention a male portion (10) for percussive rock drilling is provided comprising sections of reduced cross-sectional areas, at least one thread (12) for percussive rock drilling provided at a portion (16) at an end of the male portion. The end of the male portion comprises an abutment surface (14) for transfer of impact waves. The length (L) of the portion (16) is defined as the length of a cylinder (C), from a plane (P) of the impact surface, that touches the external diameter (Dy) of the thread, wherein said length (L) divided by the external diameter of the cylinder lies within the interval of 1-2. The intervention further relates to a drill bit and a threaded joint.
Full Text MALE PORTION, DRILL BIT AND THREADED
JOINT FOR PERCUSSIVE ROCK DRILLING
Background of the invention
The present invention relates to a male portion, a drill bit and a threaded joint for percussive rock
drilling in accordance with the preambles of the subsequent independent claims.
Prior art
In percussive top hammer drilling in rock a drill string is intended to be fastened in a shank
adapter in a drilling machine via one end surface of a rod or a tube. The other end of the rod or the
is threaded either to another rod or to another tube or to a drill bit for percussive drilling. The rod
or the tube can also be fastened to the shank adapter or another detail by means of threaded
sleeves. A flush channel runs through the entire drill string in order to lead flush medium to the
drill bit to coil away drill cuttings.
At drilling the drill string, i. e. crowns, rods, tube, sleeves and shank adapters, is subjected to
mechanical and corrosive attack. This applies in especially at drilling below earth where water is
used as flush medium and where the environment is humid. Attacks are especially serious at the
most stressed parts, that is in thread bottoms and other reductions, that is parts with small cross-
sectional area. The drilling tool is often subjected for bending moments in connection with the
drill bit reaching a skew wall in a cavity in the rock. In combination with pulsating strain, caused
by impact waves and bending stresses, fatigue or breakage arises.
Objects of the invention
An object of the present invention is to considerably improve the resistance against fatigue in a
drill element for percussive rock drilling.
Another object of the present invention is to considerably improve the resistance against fatigue in
sections of reduced cross-sectional areas in a drill element for percussive rock drilling.
Still another object of the present invention is to considerably improve the resistance against
fatigue in thread bottoms in a threaded portion in a drill element for percussive rock drilling.
Brief description of the drawings
These and other objects have been achieved by means of a male portion, a drill bit and a threaded
joint for percussive rock drilling, which have obtained features according to characterizing
portions of the subsequent independent claims with reference to the drawings.
Fig. 1 shows a male portion of a conventional rod in a side view.
Fig. 2 shows another male portion of a conventional rod in a side view.
Fig. 3 A shows a male portion according to the present invention of a rod in a side view.
Fig. 3B shows a cross-section according to the line B-B in Fig. 3A. Fig. 3C shows a cross-section
according to line C-C in Fig. 3 A. Fig. 3D shows the male portion in a perspective.
Fig. 4 shows an axial cross-section of a drill bit according to the present invention.
Fig. 5 shows a threaded joint according to the present invention partially in cross-section.
Detailed description of the invention
Each of the rods 1,2 for percussive drilling shown in Figs. 1 and 2 is provided with a threaded
male portion 3 at its one end and an identical male portion or a female portion in the shape of an
internally threaded, sleeve-shaped portion at its other end, not shown. The male portion 3 is
connected in this case to a round rod 4, preferably by friction welding. The weakest cross-section
of the male portion is where the smallest cross-sectional area is found, see the thread clearance 5
and the last thread turn 6.
At simulated bending test with the aid of the finite element method (FEM) we have found that it is
possible to considerably lower the load at the weakest cross- section of the male portion and
thereby obtain longer life spans for the male portions.
The end of the drill rod 10 for percussive drilling shown in Figs. 3A-3D is formed with a spigot or
male portion 11 according to the present invention provided with a male thread or external thread
12. The drill rod further has a through-going flush channel 13, through which a flush medium,
generally air or water, is led. The end surface of the male portion 11 forms a ring-shaped abutment
surface 14, which at connection to a drill bit is intended to abut against a corresponding annular
abutment surface at a bottom of a central recess in the drill bit. The area of the full profile of the
thread on the male portion 11 has a smallest first cross-sectional area X, see the dashed area in
Fig. 3B. The male portion 11 comprises a last thread turn 15 or a thread exit with an increased
second cross-sectional area relative to the field of the full profile of the thread, see the dashed area
Y in Fig. 3C. The smallest cross- sectional area of the male portion is provided in the area where
the thread has full profile and the second cross-sectional area is measured within the interval of 1-
5 mm from the first cross-sectional area. The thread 12 is provided at a first portion 16 at the end
of the male portion. The length L of the portion 16 is the length from a plane P of the impact
surface 14 of an imaginary, straight circular cylinder C that touches the external periphery or
external diameter Dy of the thread, see Fig. 3D.
The external diameter Dy of the cylinder C is preferably smaller than 37 mm. The plane P is
perpendicular to the centerline CL. The length L divided by the diameter Dy of the cylinder lies
within the interval of 1-2. The interval is preferably 1,2-1, 9 and most preferably 1,3-1, 6. As an
example can be mentioned that male portions with the length L=57 mm and Dy=32,85 mm give
the approximate quota 1,7 and male portions with length L=44,3 mm and Dy=32,85 mm give the
approximate quota 1,3. The abutment surface 14 connects via a chamfer to a spigot 17 that is
cylindrical or conical. The spigot 17 lacks thread and is in certain cases intended to steer on a
recess in the drill bit when the connection has been mounted. The spigot 17 connects to the thread
12.
The drill bit 20 for percussive drilling shown in Fig. 4 comprises a drill head 21 and a shank or a
skirt 22. The drill head 21 and the skirt 22 are performed in one piece. A common longitudinal
center line CL for the drill bit 20 and the male portion 10 is drawn in the figures. The drill bit 20 is
provided with a recess 23 provided with an internal female thread 24, which will receive the
external male thread 12 of the male portion 10. The drill head 21 of the drill bit according to the
present invention is in usual manner provided with rock cutting means, in the shown embodiment
having the shape of cemented carbide inserts, of which a number of circularly positioned
peripheral inserts 25 and two front buttons 26 are shown. A number of flushing channels 27
extends axially between the recess 23 of the drill bit and the front of the drill head 21. An
abutment surface 30, a so-called bottom abutment, is provided at the bottom of said recess for the
abutment surface 14 of the male portion 10.
The thread 24 comprises a thread clearance 28 of reduced cross-sectional area. The thread 24 is
provided at a second portion 29 in the recess 23. The length L' of the portion 29 is the length from
a plane P' of the impact surface 30, that an imaginary, straight circular cylinder C' touches the
internal periphery Di of the thread.
The internal diameter Di of the cylinder C is preferably smaller than 37 mm, preferably less than
36 mm. The plane P' is perpendicular to the centerline CL. The length L' divided by the diameter
Di of the cylinder lies within the interval 1-2. The interval is preferably 1,2-1, 9 and most
preferably 1,3-1, 6. The abutment surface 30 connects via a shoulder to the thread clearance 28.
The thread clearance connects to the thread 24. As an example can be mentioned that drill bits
with the length L-39,7 mm and Di==29,5 mm give the approximate quota 1,4 and drill bits with
the length L'=52,5 mm and Di=29,5 mm give the approximate quota 1.8.
The length L, L' is calculated from the plane P, P' as long as the thread has a full profile. Stated
alternatively, a straight circular cylinder should be able to enter over the male portion 10 or to be
moved into the recess 23 with a slide fit a distance or a length L, L' from the plane P, P'until the
cylinder either clears from the thread or abuts against a thickened thread end.
In Fig. 5 a threaded joint 40 according to the present invention is shown comprising the male
portion 10 and the drill bit 20. The male portion 10 has been screwn into the drill bit 20 until the
impact surfaces 14 and 30 impacted against each other. Since the part of reduced cross-sectional
area on the male portion 10 is provided at a relatively short distance from the free end of the joint
40 the bending stress will be lower there than at conventional joints where the lever is
considerably longer. The male portion and the drill bit comprise cylindrical surfaces provided
axially beyond and radially outside of the threads for slide fit against each other during mounting.
The invention is based on that a shorter thread gives lower bending stress. The tension in the last
thread turn or the thread clearance is lowered at least 30% as compared with known joints.
Generally just a few thread turns, for example two thread turns on each part, are in engagement
with the other part as can be concluded from Figs. 3 A, 4 and 5. With a conventional threaded joint
normal tool life is about 850 m while the new male portion reached about 2050 m before the joint
was considered worn-out.
The disclosures in Swedish patent application No. 0201989-1, from which this application claims
priority are incorporated herein by reference.
1. A male portion for percussive rock drilling comprising sections of reduced cross- sectional
areas, at least one thread (12) for percussive rock drilling provided at a portion (16) at an end of
the male portion, said end of the male portion comprising an abutment surface (14) for transfer of
impact waves, said male portion having a first cross-sectional area at an area where the thread has
full profile, characterized in that the length (L) of the portion (16) is defined as the length of a
cylinder (C), from a plane (P) of the impact surface, where the diameter of the cylinder coincides
with the external diameter (Dy) of the thread, wherein said length (L) divided by the external
diameter (Dy) of the thread lies within the interval of 1 -2, said male portion having a second
cross-sectional area just beyond said area, said second cross-sectional area being greater than the
first cross-sectional area.
2. The male portion according to claim 1, characterized in that the smallest cross-sectional area of
the male portion is provided at an area where the thread has full profile and in that the second the
cross-sectional area is measured within the interval of 1-5 mm from the first cross-sectional area.
3. The male portion according to claim 1 or 2, characterized in that the interval is 1,2-1, 9, most
preferably 1,3-1, 6 and in that the external diameter (Dy) of the cylinder (C) is preferably smaller
than 37 mm.
4. The male portion according to claim 1, characterized in that it is firmly connected to an end of a
rod or a tube of steel and forms a drill rod and in that the drill rod comprises a through-going flush
channel (13).
5. A drill bit for percussive rock drilling comprising sections of reduced cross- sectional areas,
said drill bit (20) being provided with a central recess (23) comprising an internal female thread
(24) for percussive rock drilling provided at a portion (29) in the recess (23), said recess
comprising an abutment surface (30), characterized in that the length (L') of the portion (29) is
defined as the length of a straight circular cylinder (C) from a plane (P') of the impact surface (30)
where the diameter of the cylinder coincides with the internal diameter (Di) of the thread, and in
that the length (L') divided by the internal diameter (Di) of the thread lies within the interval of 1 -
2.
6. The drill bit according to claim 5, characterized in that the interval is 1,2- 1,9, most preferably
1,3-1, 6 and in that the internal diameter (Di) of the cylinder (C) is preferably smaller than 36 mm.
7. The drill bit according to claim 5 or 6, characterized in that it is firmly connected to an end of
an rod or a tube of steel and forms a drill rod (25) and in that the drill rod comprises a through-
going flush channel (20).
8. A threaded joint between a male portion and a drill bit for percussive rock drilling, said male
portion comprising sections of reduced cross-sectional areas, at least one thread (12) for
percussive rock drilling provided at a first portion (16) at an end of the male portion, said end of
the male portion comprising an abutment surface (14) for transfer of impact waves, said male
portion having a first cross-sectional area in an area where the thread has full profile, said drill bit
comprising sections of reduced cross-sectional areas, said drill bit (20) being provided with a
central recess (23) comprising an internal female thread (24) for percussive rock drilling provided
at an other portion (29) of the recess (23), said recess comprising an abutment surface (30),
characterized in that the length (L) of the first portion (16) is defined as the length of a cylinder
(C), from a plane (P) of the impact surface, where the cylinder touches the external diameter (Dy)
of the thread, wherein said length (L) divided by the external diameter (Dy) of the thread lies
within the interval of 1-2 and in that the length (L') of the second portion (29) is defined as the
length from a plane (P') of the impact surface (30) of a straight circular cylinder (C) where this
touches the internal diameter (Di) of the thread, and in that the length (L') divided by the internal
diameter (Di) of the thread lies within the interval of 1-2.
9. The threaded connection according to claim 8, characterized in that the interval is 1,2-1, 9, most
preferably 1,3-1, 6 and in that the diameter (Dy; Di) of the cylinder (C; C) is preferably smaller
than 37 mm.


According to the present invention a male portion (10) for percussive rock drilling is provided
comprising sections of reduced cross-sectional areas, at least one thread (12) for percussive rock
drilling provided at a portion (16) at an end of the male portion. The end of the male portion
comprises an abutment surface (14) for transfer of impact waves. The length (L) of the portion
(16) is defined as the length of a cylinder (C), from a plane (P) of the impact surface, that touches
the external diameter (Dy) of the thread, wherein said length (L) divided by the external diameter
of the cylinder lies within the interval of 1-2. The intervention further relates to a drill bit and a
threaded joint.

Documents:

1572-KOLNP-2004-(02-04-2012)-PETITION UNDER RULE 138.pdf

1572-KOLNP-2004-(30-04-2012)-FORM-27.pdf

1572-KOLNP-2004-ABSTRACT 1.2.pdf

1572-KOLNP-2004-ABSTRACT-1.1.pdf

1572-kolnp-2004-abstract.pdf

1572-KOLNP-2004-AMANDED CLAIMS 1.1.pdf

1572-KOLNP-2004-AMANDED CLAIMS.pdf

1572-KOLNP-2004-AMANDED PAGES OF SPECIFICATION.pdf

1572-KOLNP-2004-ASSIGNMENT.1.3.pdf

1572-kolnp-2004-assignment.pdf

1572-KOLNP-2004-CANCELLED PAGES.pdf

1572-kolnp-2004-claims.pdf

1572-KOLNP-2004-CORRESPONDENCE 1.1.pdf

1572-KOLNP-2004-CORRESPONDENCE 1.2.pdf

1572-KOLNP-2004-CORRESPONDENCE 1.3.pdf

1572-KOLNP-2004-CORRESPONDENCE 1.4.pdf

1572-KOLNP-2004-CORRESPONDENCE 1.5.pdf

1572-KOLNP-2004-CORRESPONDENCE 1.6.pdf

1572-KOLNP-2004-CORRESPONDENCE 1.7.pdf

1572-KOLNP-2004-CORRESPONDENCE.1.3.pdf

1572-kolnp-2004-correspondence.pdf

1572-KOLNP-2004-DESCRIPTION (COMPLETE) 1.2.pdf

1572-KOLNP-2004-DESCRIPTION (COMPLETE)-1.1.pdf

1572-kolnp-2004-description (complete).pdf

1572-KOLNP-2004-DRAWINGS 1.2.pdf

1572-KOLNP-2004-DRAWINGS-1.1.pdf

1572-kolnp-2004-drawings.pdf

1572-KOLNP-2004-EXAMINATION REPORT.1.3.pdf

1572-KOLNP-2004-FORM 1-1.1.pdf

1572-KOLNP-2004-FORM 1-1.2.pdf

1572-kolnp-2004-form 1.pdf

1572-KOLNP-2004-FORM 18.1.3.pdf

1572-kolnp-2004-form 18.pdf

1572-KOLNP-2004-FORM 2-1.1.pdf

1572-KOLNP-2004-FORM 2-1.2.pdf

1572-kolnp-2004-form 2.pdf

1572-KOLNP-2004-FORM 3 1.2.pdf

1572-KOLNP-2004-FORM 3-1.1.pdf

1572-KOLNP-2004-FORM 3.1.3.pdf

1572-kolnp-2004-form 3.pdf

1572-KOLNP-2004-FORM 5-1.1.pdf

1572-KOLNP-2004-FORM 5.1.3.pdf

1572-kolnp-2004-form 5.pdf

1572-KOLNP-2004-FORM 6.1.3.pdf

1572-kolnp-2004-form 6.pdf

1572-kolnp-2004-form-6-1.1.pdf

1572-KOLNP-2004-GPA.1.3.pdf

1572-KOLNP-2004-GRANTED-ABSTRACT.pdf

1572-KOLNP-2004-GRANTED-CLAIMS.pdf

1572-KOLNP-2004-GRANTED-DESCRIPTION (COMPLETE).pdf

1572-KOLNP-2004-GRANTED-DRAWINGS.pdf

1572-KOLNP-2004-GRANTED-FORM 1.pdf

1572-KOLNP-2004-GRANTED-FORM 2.pdf

1572-KOLNP-2004-GRANTED-LETTER PATENT.pdf

1572-KOLNP-2004-GRANTED-SPECIFICATION.pdf

1572-kolnp-2004-intenational publication.pdf

1572-kolnp-2004-international preliminary examinary report.pdf

1572-kolnp-2004-international search report.pdf

1572-KOLNP-2004-OTHERS 1.2.pdf

1572-KOLNP-2004-OTHERS PCT FORM.pdf

1572-KOLNP-2004-OTHERS-1.1.pdf

1572-KOLNP-2004-OTHERS.1.3.pdf

1572-KOLNP-2004-PA.1.3.pdf

1572-KOLNP-2004-PA.pdf

1572-KOLNP-2004-PETITION UNDER RULE 137.pdf

1572-KOLNP-2004-REPLY TO EXAMINATION REPORT.1.3.pdf

1572-KOLNP-2004-REPLY TO EXAMINATION REPORT.pdf

1572-kolnp-2004-specification.pdf

1572-KOLNP-2004-TRANSLATED COPY OF PRIORITY DOCUMENT.pdf


Patent Number 248848
Indian Patent Application Number 1572/KOLNP/2004
PG Journal Number 35/2011
Publication Date 02-Sep-2011
Grant Date 30-Aug-2011
Date of Filing 19-Oct-2004
Name of Patentee SANDVIK INTELLECTUAL PROPERTY AB
Applicant Address S-811 81 SANDVIKEN
Inventors:
# Inventor's Name Inventor's Address
1 LUNDBERG, CHRISTER FREDRIKSGATAN 114B, S-811 38 SANDVIKEN
2 LILJEBRAND, PER-OLOF NYGÅRDSGATAN 11, S-811 52 SANDVIKEN
3 CARLSTRÖM, BO IDROTTSVÄGEN 24C, S-811 32 SANDVIKEN
4 BRUNGS, ANDERS 6 CELTIS CRESCENT, FOURWAYS GARDEN
PCT International Classification Number E21B 17/042
PCT International Application Number PCT/SE2003/000930
PCT International Filing date 2003-06-06
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 0201989-1 2002-06-27 Sweden