MECANISME D'ENTRAINEMENT

DRIVER

Abrégé français

L'invention concerne un élément d'entraînement ou de serrage conçu pour transférer des forces de torsion entre un tuyau externe rotatif (10) et un trépan (1) d'un marteau fond de trou. Cet élément de serrage (7) est constitué d'une matière plus souple que les parties (3, 4) du trépan (1) qui coopèrent avec l'élément de serrage (7, 8).

Abrégé anglais

A driver or dogging element adapted to transfer torsion forces between a
rotating outer tube (10) and a drill bit (1) of a down-the-hole hammer,
wherein the dogging element (7) is made of a softer material than those parts
(3, 4) of the drill bit (1) that co-act with the dogging element (7, 8).

Revendications

1
CLAIMS
1. A dogging element adapted to transfer torsion forces be-
tween a rotating outer tube (10) and a drill bit (1) of a
down-the-hole hammer, characterised in that the drill bit (1)
comprises a shaft (3) made of steel and that the dogging
element (7) is made of a softer material than the parts (3,
4) of the drill bit (1) that co-act with the dogging element
(7, 8).
2. A dogging element according to Claim 1, characterised in
that the dogging element (7) is provided internally with
splines (8) which are intended for co-action with splines (4)
provided on the shaft (3) of the drill bit (1).
3. A dogging element according Claim 1 or 2, characterised in
that the dogging element (7) is made of a bronze alloy.
4. A dogging element according to Claim 3, characterised in
that the dogging element (7) is made of tin bronze material.
5. A dogging element according to Claim 3, characterised in
that the dogging element (7) is made of a chromium bronze
material.
6. A dogging element according to any one of the preceding
Claims, characterised in that the dogging element (7) is made
of a material that has high thermal conductivity.

Description

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Driver
The present invention relates to a driver or dogging element
for transferring torsion forces between a rotating outer tube
and the drill bit of a down-the-hole hammer.
In the case of countersink hammers, rotational forces, feed,
and percussion energy are transferred from a drilling unit to
~o a down-the-hole hammer that is lowered into the hole to be
drilled. The rotational forces are transferred with the aid
of a rotating outer tube such as to cause the drill bit to
rotate, and the percussion forces are transferred with the
aid of a piston or ram that moves reciprocatingly in the tube
~s in its longitudinal direction. The rotational force is trans-
ferred from the outer tube by means of a chuck or dogging
element screwed firmly into the outer tube. Arranged inside
the dogging element or chuck is an array of splines which co-
ast with splines arranged on the outside of the drill bit
2o shaft. The drill bit, the outer tube and the dogging element
or chuck are all made of steel.
This technique has been used with satisfaction for many
years. Because of the greater powers to which a drilling unit
25 is subjected, resulting in higher drilling speeds, the
stresses and strains to which component materials are sub-
jected have also increased. In the present case, this has
resulted in greater wear on the spline transmission which, in
turn, has led to the formation of cracks and fissures which,
so in turn, have led to breakdowns caused by fracturing of the
drill bit shaft. This can result in the loss of the drill
bit, with the drill bit remaining in the drill hole. It may

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lead to that the lost drill bit cannot be recovered and that
a new hole must be drilled from the beginning.
Accordingly, an object of the present invention is to provide
s for the transfer of torsion forces between a rotating outer
tube and a drill bit of a down-the-hole hammer a novel driver
or dogging element that overcomes the aforesaid problems.
'This object is achieved with a driver or dogging element
~o according to the present invention. The invention is
characterised in that the dogging element is made from a
material that is softer than the material from which those
parts of the drill bit that co-act with the dogging element
are made.
The invention will now be described in more detail with ref-
erence to an exemplifying embodiment and also with reference
to the accompanying drawings, in which Figure 1 is a longitu-
dinally sectioned view of a drill bit for a down-the-hole
hammer and shows those parts that are in closest connection
2o with the drill bit; and Figure 2 is a cross-sectional view of
an inventive dogging element included in the Figure 1 embodi-
ment.
Figure 1 thus shows a drill bit 1 that has rock drilling
2s buttons 2 mounted on its front end in a known manner. Typi-
cally, the drill bit 1 also includes a shaft 3 which is pro-
vided with longitudinally extending splines 4 along a part of
its length. The drill bit also has a rear end 5 against which
a percussion piston is intended to strike. The drill bit 1
so typically includes a longitudinally extending channel 6
through which compressed air is blown out from the front part
of the drill to blow the drill cuttings away from the drill
bit and out of the drill hole.

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The shaft 3 carries a driver or dogging element 7 which is
provided internally with longitudinally extending splines 8
that co-act with the splines 4. The dogging element 7 is
s generally in the form of a sleeve and is provided along at
least part of its length with an external screw thread 9 by
means of which the dogging element 7 can be screwed securely
to the front end of an outer tube 10 that surrounds at least
a part of both the dogging element 7 and the shaft 3 of the
~o drill bit 1. The outer tube 10 also surrounds the percussion
piston 11. The down-the-hole hammer can be spliced or joined
to allow the drill run to be extended to a desired length.
The drilling unit causes the outer tube 10 to rotate, where-
with the rotational movement of the tube is transmitted to
~s the dogging element 7 which, in turn, transfers the rota-
tional movement to the drill bit 1 through the medium of the
spline connection 8, 4.
According to the invention, the dogging element 7 is made of
2o a material that is significantly softer than those parts of
the drill bit 1 that co-act with the dogging element, i.e.
than the shaft 3, therewith avoiding those problems associ-
ated with the formation of cracks, fissures, and with break-
age of the shaft 3. It has been found that a bronze alloy is
25 a suitable material for the dogging element. This alloy may
be a tin bronze alloy or a chromium bronze alloy. A tin
bronze alloy produced by Applicants Atlas Copco Secoroc AB
and designated 11 9351 93 has been found to be excellent in
this respect.
When the dogging element 7 is made of this softer material,
it is this material that suffers the wear and tear rather
than the steel in the shaft 3 of the drill bit co-acting with

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the dogging element. As the dogging element 7 rotates in
response to the rotation of the outer tube 10, force is
transmitted by the splines 8 on the dogging element to the
splines 4 on the shaft 3, wherewith the splines 8 on the
dogging element, which are softer than the splines 4, will
become worn instead of the splines 4 on shaft of the drill
bit 1. There is thus obtained a controlled and observable
wear and the dogging element can be replaced when it is no-
ticed that the degree of wear on the dogging element makes
this necessary. The splines 8 on the dogging element may be
allowed to wear down to about half their original width be-
fore needing to replace the dogging element. Breakage or
fracture of the dogging element 7 will not cause any serious
damage, since it is only the dogging element that breaks
~s while the drill bit will still be held firmly by the outer
tube 10.
The preferred material is not only softer than steel, but
also has higher thermal conductivity and lower friction than
2o steel, meaning that the stresses and strains in the spline
connection will be much lower than those experienced with
known techniques using steel on steel contact.

Dessin représentatif