Note: Descriptions are shown in the official language in which they were submitted.
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ROCK DRILL BIT
Background of the invention
The present invention relates to a rock drill bit for percussive drilling,
comprising a head and a shank. The shank has a central boring in which a
thread is provided, said thread being provided to cooperate with a
corresponding thread in a drill string driven by a top hammer. The boring
is connected to at least one fluid passage, which emerges in or in the
vicinity of a front face of the head. The fluid passage connects to a first
groove, which connects to a second groove. At least three second grooves
are provided and form between them axially forward lands, each of which
carries a gauge insert.
Previously known drill bits of the above-mentioned type have a number of
disadvantages. The chipways constitute only a small part of the total front
face area of the head such that the average diameter of the cuttings have to
be small. This means that the hitherto known bits are not particularly suited
for excavation purposes. Furthermore their gauge inserts are many in
number relative to the diameter of the bit, which means that the chipways
must be relatively small. Many gauge inserts also means costly and time-
consuming regrinding. In addition the relatively poor flushing resulting
from the narrow or small chipways makes it possible for cuttings to build
up on the center of the front face. This built-up process impairs transfer of
energy to the solid rock material in the bore which also impairs the threads
in the drill string.
Objects of the invention
An object of the present invention is to provide a rock drill bit with
asymmetrically positioned gauge inserts for enhancing the average diameter
of the cuttings.
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Another object of the present invention is to provide a rock drill bit with a
limited number of big gauge inserts in comparison with the rock drill bit
diameter, partly to increase diametrical wear and partly to facilitate the
regrinding process.
Still another object of the present invention is to provide a rock drill bit
which improves the transfer of energy to the solid rock material in the bore
and which also spares the threads in the drill string.
Brief description of the drawings
Fig. 1 shows a rock drill bit according to the present invention; Fig. 2
shows the rock drill bit in a cross section along the line II-II in Fig. 1;
Fig. 3
shows the rock drill bit in a bottom view; Fig. 5 shows the rock drill bit in
a cross section along the line V-V in Fig. 4.
Detailed description of the invention
A rock drill bit 10 for percussive drilling according to the present invention
is shown in Figs. 1 and 2. The rock drill bit 10 comprises a drill head 11
and a shank 12 and has a center axis 13. The shank has a central bore
provided with a thread 14. The thread 14 is provided to cooperate with a
corresponding thread in a drill string driven by a top hammer, not shown.
The bore connects to three flushing channels 15 emerging in or in the
vicinity of a front face 16 of the head 11. Preferably the front face 16 is
perpendicular to the center axis 13. Each channel 15 connects to a first
groove 17 which has radially outwardly increasing width and depth and
which connects to a second groove or chipway 18. Each chipway 18 is
substantially V-shaped and has substantially constant width and depth
axially rearwards. The chipway 18 intersects the front face 16 in a frusto-
conical bevel 19. The number of chipways 18 is larger than the number of
the first grooves 17. Axially Forward lands 20 protrude between the
chipways 18. Each land 20 carries a gauge insert 21 which is inclined
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about 35° relative to the center axis 13. The number of lands 20 is 4
to 10
pieces and preferably 4 to 6 pieces, depending on the size of the drill bit.
' The outer diameter of the drill bit is determined by the gauge inserts 21.
The drill bit has three symmetry lines N1 perpendicular to the center axis
13. The gauge inserts are asymmetrically positioned on the drill bit but are
symmetrically positioned on each land. With the line II-II as a reference
line, see 0° in Fig. 1, the inserts 21 are placed anti-clockwise as
follows:
65°; 117.5°; 182.5°; 237.5°; 302.5° and
357.5°. This means that every
other chipway 18 has an available space proportional to 65° and that
each
of the rest of the chipways 18 has an available space proportional to
55°
An insert 21 is positioned such that it forms a first angle a with the center
axis 13 and a first adjacent insert 21 A. That insert 21 forms a second angle
f~ with the center axis 13 and a second adjacent insert 21 B. The first angle
a is always different from the second angle f3. The advantage with such a
geometry is the possibility to manufacture some large chipways on the drill
bit. The insert 21 projects a distance P1 perpendicularly from the bevel 19.
Furthermore three front inserts 22 are provided in the front face 16 and
each front insert projects a distance P2. The distance P1 is preferably
somewhat larger than the distance P2, about 1 mm. Each gauge insert 21
has a diameter d measured at the grip portion of the insert. The diameter d
is as large as 10 - 30 %, preferably 14 - 30 °/°, of the
diameter of the rock
drill bit diameter D. When comparing said available space or bow length
for the chipway 18 and the gauge insert 21 diameter d the space is 1.2 to
1.6 times the gauge insert 21 diameter. The front inserts 22 and the
flushing channels 15 form a crown of equal spacing about the center axis
13. Each chipway 18 has a radial extension L1 from the envelope surface
of the lands 20 to the bottom of the V-shape that is 10 - 30 % of the drill
bit diameter D and preferably 14 - 30 %. Stated another way the chipway
18 extend radially inwards to or beyond an imaginary circle C touching the
radially innermost points of the inserts 21 in the plane of the front surface.
The number of gauge insert 21 can be 4 to 10 pieces. The first groove 17
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extends radially inwardly beyond the flushing channel 15 towards the
center axis 13 of the drill bit and terminates in the vicinity of a central
insert 23. The drill bit is provided with 6 axially rearwards lands 24 which
have equal spacing of 60°, see Fig. 3. The rearward lands 24 are
provided
to guide the drill bit in case of deflection. The envelope surface of the
rearward lands 24 is on a diameter which is less than the diameter of the
envelope surface of the forward lands 20.
Figs. 4 and 5 shows an alternative embodiment of a drill bit 10' according
to the present invention constructed for drilling of smaller holes. Like
reference numerals define like details as disclosed in connection with Figs.
1 - 3. In this embodiment the drill bit is provided with one central insert
23' in the front face 16' and four gauge inserts 21'. No front inserts are
present. The chipway 18' is substantially V-shaped and its width increases
but its depth decreases axially rearwardly. The drill bit has only one
symmetry line N 1 perpendicular to the center axis 13'. The drill bit has no
rearward lands. Also in this drill bit the gauge insert 21' are asymmetrically
positioned but centrally on each land 20'. With the line V - V taken as a
reference, see 0° in Fig. 5, the inserts 21' are spaced as follows in
the anti
clock-wise direction: 96°; 185° and 272°. This means that
an insert 21' is
positioned such that it forms a first angle a' with the center axis 13' and a
first adjacent insert 21 A' and a second angle f~' with the center axis 13'
and
a second adjacent insert 21 B'. The first angle a' is always different from
the
second angle f~'.
Thus a drill bit with asymmetrically positioned gauge insert 21, 21' has
been disclosed, having chipways occupying a relatively large part of the
total area of the drill head in order to increase the average diameter of the
cuttings to increase penetration rate and to facilitate geological sampling
during ordinary drilling. The drill bit 10, 10' has a relatively small number
of large gauge insert 21, 21' compared to the diameter of the drill head to
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resist diametrical wear and to facilitate regrinding. The drill bit improves
power transfer to the hole bottom thereby increasing penetration rate while
sparing the threads in the drill string from blow reflexions.
