Note: Descriptions are shown in the official language in which they were submitted.
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Down-the-Hole Drill Hammer
The present invention relates to an arrangement pertaining to
down-the-hole hammers.
In the case of down-the-hole hammers, rotational forces,
feed, and percussion energy are transferred from a drilling
unit to a down-the-hole hammer, which is lowered into the
~o hole to be drilled. The rotational forces are transmitted
with the aid of a rotating outer tube, causing the drill bit
to rotate, and the percussion forces are transmitted with the
aid of a piston or ram that moves reciprocatingly in the tube
in its longitudinal direction. The rotational force is trans-
ferred from the outer tube by means of a chuck or driver
screwed firmly into the outer tube. Arranged inside the
driver or chuck is an array of splines which co-act with
splines arranged on the outside of the bit shaft. The
driver/chuck is thus seated in the connection between the
2o drill bit and the outer tube and the end of the driver/chuck
facing towards the head of the drill bit has an outer diame-
ter that corresponds roughly to the outer diameter of the
outer tube and forms a direct extension thereof. The drilling
bit, the outer tube and the driver or chuck are all made of
2s steel.
In an attempt to solve problems arising from the formation of
cracks or fissures that can cause the shaft of the bit to
break at the spline connection to the driver, it has been
so proposed to replace the steel in the driver with a softer
material, for instance with a bronze alloy. Unfortunately,
this replacement has resulted in external wear and tear on
the driver due to the backflow of cuttings along the outer
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surfaces of the drill bit, the driver and the outer tube.
Although such wear can be observed from without and a change
to a new driver can be made when it is seen that said element
has worn down to an extent that makes such a change neces-
sary, the new driver will normally have a larger diameter
than the worn outer tube, therewith resulting in greater
turbulence around the new driver and accelerated wear on the
outer tube.
~o Accordingly, an object of the invention is to provide a novel
arrangement that enables these problems to be avoided.
This object is achieved with an arrangement pertaining to
down-the-hole hammers in which a driver is adapted to trans-
mit torsion forces between a rotating outer tube and a drill
bit belonging to the down-the-hole hammer, wherein the outer
tube is arranged to fully surround the outside of the driver,
in accordance with the invention.
2o Total enclosure of the driver by the outer tube enables the
driver to be made of a softer material without being sub-
jected to external abrasion that would result in premature
wear on the driver. Such external wear would only affect the
outer tube, the material of which is considerably harder and
2s much more wear resistant than that from which the driver is
made. Moreover, the outer tube can be given a surface coating
which will make abrasive wear on the outer tube lower never-
theless.
so 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
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hammer and shows those parts that are in closest connection
with the drill bit in accordance with known technology and
Figure 2 is a corresponding longitudinally sectioned view of
a drill bit for a down-the-hole hammer, showing those parts
s that are in closest connection with the drill bit in accor-
dance with the present invention.
Figure 1 thus shows a drill bit 1 that has rock drilling
buttons 2 mounted on its front end in a known manner. Typi-
~o tally, 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
typically includes a longitudinally extending channel 6
15 through which compressed air is blown out from the front part
of the drill to blow the drill cuttings away from the bit and
out of the drill hole.
The shaft 3 carries a driver 7 which is provided internally
2o with longitudinally extending splines 8 that co-act with the
splines 4. The driver 7 is 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 driver 7 can be
screwed securely to the front end of an outer tube 10 that
25 surrounds at least a part of both the driver 7 and the shaft
3 of the drill bit 1. The outer tube 10 also surrounds the
percussion piston 11. The drill 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,
so wherewith the rotational movement of the tube is transmitted
to the driver 7 which, in turn, transfers the rotational
movement to the drill bit 1 through the medium of the spline
connection 8, 4.
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As will be seen from Figure 1, the end part 12 of the driver
7 facing towards the head 13 of the drill bit 1 has an outer
diameter which corresponds essentially to the outer diameter
s of the outer tube 10 and constitutes an extension thereof.
Thus, it is this end part 12 of the driver 7 and the outer
tube 10 that are strongly abraded by the externally flowing
cuttings.
~o Figure 2 illustrate the inventive arrangement, in which the
driver 7 is generally in the form of a cylindrical sleeve
which is totally enclosed externally by the outer tube 10, so
that in this case said tube will reach all the way to the bit
head 13. The driver 7 is thus fully protected from the exter-
~s nal affect of drill cuttings flowing back along the outside
of the bit head and the outer tube. This allows the driver to
be made of a much softer material than the material from
which the drill bit 1 and its shaft 3 is made.
2o The driver will suitably be made of a material based on an
alloy other than iron. The alloy will conveniently have a
frictional coefficient of -< 0.25 in respect of a non-
lubricated surface against steel, and a coefficient of ther-
mal conductivity of >- 320 W/m K. Examples of alloys that ful-
2s fil these requirements are alloys of bronze and copper.
As mentioned before, the outer tube 10 is preferably made of
steel and may be provided with a harder outer coating to
further reduce abrasive wear by the drill cuttings.
