THREAD COUPLING FOR DRILL STRING ELEMENTS FOR PERCUSSION DRILLING

ACCOUPLEMENT FILETE POUR TRAIN DE FORAGE A PERCUSSION

English Abstract

Thread coupling for drill string elements for percussion drilling. The thread
coupling
comprises a first drill string element (1) provided with a sleeve formed part
(2) having
an internal thread (3) and a free end (4) for cooperation with a second drill
string
element (6) provided with a stop face (10) and a spigot (7) with an external
thread
(8). The free end (4} and the stop face (10) are hardened during
manufacturing,
preferably through case-hardening, to a depth of at least 2 mm. Furthermore,
the
sleeve formed part (2) and the spigot (7) are given such dimensions during
manufacturing that a bottom play (A) of 1.1-2.0 mm, preferably 1.1-1.5 mm, is
obtained when coupling newly made drill string elements.

Claims

3
Claims:
1. Thread coupling for drill string elements for percussion drilling
comprising a first drill string element (1) provided with a sleeve formed part
(2)
having an internal thread (3), a free end (4) and a bottom surface (5) and a
second
drill string element (6) provided with a spigot (7) having an external thread
(8) and
extending between an outer end (9) and a stop face (10), characterized in
that said sleeve formed part (2) at least adjacent to its free end (4) is
hardened to a
hardening depth of at least 2 mm and that the distance between said free end
(4) and
said bottom surface (5) on the sleeve formed part (2) after manufacturing is
1.1-2.0
mm larger than the distance between said outer end (9) and said stop face (10)
on the
second drill string element (6) after manufacturing.
2. Thread coupling according to claim 1, characterized in that the
distance between said free end (4) and said bottom surface (5) on the sleeve
formed
part (2) after manufacturing is 1,1-1.5 mm larger than the distance between
said outer
end (9) and said stop face (10) on the second drill string element (6) after
manufacturing.
3. Thread coupling according to claim 1 or 2, characterized in
that said hardening is achieved through case-hardening.

Description

. . CA 02126027 2004-10-28
29312-24
1
Thread coupling for drill string elements for percussion
drilling
The present invention relates to a thread coupling
for drill string elements for percussion drilling.
In a prior art tube drilling coupling, see
US-A-4 968 068, it is ascertained that the spigot on one
drill string element is somewhat shorter, 0-1 mm, than the
distance between the free end and the bottom surface on the
sleeve formed part on the other drill string element. The
reason for arranging this play at manufacturing is that one
wishes to secure that one does not only get abutment between
the outer end of the spigot and the bottom surface of the
sleeve formed part. It is also said that the ideal
condition is to have abutment both at the free end and the
bottom surface on the sleeve formed part. This condition
cannot be achieved at the manufacturing because of
manufacturing tolerances. It is also said that the original
bottom play between the two drill string elements should be
eliminated because of wear before 20~ of the service life of
the thread coupling has been used. The aim according to
US-A-4 968 068 is thus to keep the original bottom play as
small as possible so that one quickly achieves the double
abutment between the two drill string components. This
results in the drawback that the hardening of the free end
of the sleeve formed part and of the cooperating stop face
is little used since one soon transfers the wear to the
threads of the two drill string elements.
The present invention aims at increasing the
service life of the drill elements through ascertaining that
the depth of the hardening is at least 2 mm and that the two
drill string elements at manufacturing are given such

~
CA 02126027 2004-10-28
29312-24
la
tolerances that one gets a bottom play of 1.1-2.0 mm,
preferably 1.1-1.5 mm.
A broad aspect of the invention provides thread
coupling for drill string elements for percussion drilling
comprising a first drill string element provided with a
sleeve formed part having an internal thread, a free end and
a bottom surface and a second drill string element provided
with a spigot having an external thread and extending
between an outer end and a stop face, characterized in that
said sleeve formed part at least adjacent to its free end is
hardened to a hardening depth of at least 2 mm and that the
distance between said free end and said bottom surface on
the sleeve formed part after manufacturing is l.l-2.0 mm
larger than the distance between said outer end and said
stop face on the second drill string element after
manufacturing.
An embodiment of the invention is described below
with reference to the accompanying drawing which shows a
thread coupling according to the invention, partly in
section.
The embodiment of the invention shown in the
drawing comprises a first drill string

93002.ut1
2
element 1 and a second drill string element 6. The first drill string element
1 is
provided with a sleeve formed part 2 having an internal thread 3, a free end 4
and a
bottom surface 5. The second drill string element 6 is provided with a spigot
7
extending between an outer end 9 and a stop face 10. The spigot 7 is provided
with
an external thread 8 for cooperation with the internal thread 3 on the sleeve
formed
part 2. The stop face 10 on the second drill string element 6 and the free end
4 an the
first drill string element lie in a plane perpendicular to the longitudinal
axis 11 of the
thread coupling. The stop face 10 and the free end 4 are intended for
cooperation with
each other. During manufacturing the free end 4 and the stop face 10 are
hardened,
preferably through case-hardening, to a depth of at least 2 mm from the
contact
surface. The sleeve formed part 2 and the spigot 7are at manufacturing given
such
tolerances that the distance between the free end 4 and the bottom surface 5
on the
sleeve formed part 2 is 1.1-2.0 mm, preferably 1.1-1.5 mm, larger than the
distance
between the outer end 9 and the stop face 10 on the second drill string
element 6.
This gives a bottom play A directly after manufacturing of the above mentioned
size.
By giving the parts a hardening depth of at least 2 mm and by ascertaining
that the
bottom play A when coupling newly made drill string elements is of the above
mentioned size one obtains the advantage of being able to use abutment between
the
free end 4 and the stop face 10 during substantially longer time than what has
been
possible with prior art technique. This results in substantially longer
service life of the
thread coupling than what has been possible before.

Representative Drawing