Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Percussive Rock Drill Bit
Field of invention
The present invention relates to a percussive rock drill bit and in
particular, although not
exclusively, to a drill bit formed with a cutting head mounting a plurality of
peripheral
gauge buttons and front buttons configured to cut material via a guiding cone
action to
optimize the rock breaking and cutting operation.
Background art
Percussion drill bits are widely used both for drilling relatively shallow
bores in hard rock
and for creating deep boreholes. For the latter application, drill strings are
typically used
in which a plurality of rods are added to the string via coupling sleeves as
the depth of the
hole increases. A terrestrial machine is operative to transfer a combined
impact and rotary
drive motion to an upper end of the drill string whilst a drill bit positioned
at the lower end
is operative to crush the rock and form the boreholes. Fluid is typically
flushed through
the drill string and exits at the base of the borehole via apertures in the
drill head to flush
the drill cuttings from the boring region to be conveyed backward and up
through the bore
around the outside of the drill string. It is a typical requirement that the
borehole should be
as straight as possible particularly where the drilling is directed to a
predetermined target
deep below the earth surface. This commonly involves the drill bit passing
through many
different types of rock formation. Example percussive drill bits are disclosed
in US
3,388,756; US 3,357,507, US 2008/0087473; and WO 2009/067073.
The drill bit typically comprises a drill head that mounts a plurality of hard
cutting inserts,
typically referred to as buttons. Such buttons comprise a carbide based
material to enhance
the lifetime of the drill bit. In particular, WO 2006/033606 discloses a rock
drill bit having
a head with a plurality of peripheral gauge buttons distributed
circumferentially at an outer
perimeter of the drill head. The gauge buttons are configured to engage
material to be
crushed and to determine the diameter of the borehole. The head also mounts a
plurality of
front buttons provided at a recessed front face of the drill head for engaging
material to be
crushed at the axial region immediately in front of the drill head.
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However, conventional drill bits are susceptible to deflection and non-uniform
bore
creation due for example to anomalies in the rock structure such as cracks,
fissures and
sudden changes in the rock structure and type. There is therefore a need for
an improved
percussive drill bit that addresses these problems.
Summary of the Invention
It is an objective of the present invention to provide a percussive rock drill
bit configured
to aggressively break through subterranean materials including in particular
rock and
minerals via a combined impact and rotary motion. In particular, it is a
specific objective
to provide a drill bit that impacts through fault and cracks in the rock via a
cutting action in
which the drill bit is self-stabilising via a shape profile created in the
rock during rotation.
The objectives are achieved by providing a drill bit head having a plurality
of cutting
inserts aligned and positioned at different regions of a cutting head to
perform different
functions and in particular to stabilise the drill head as it is rotated and
advanced through
the subterranean material. In particular, the inventors have identified
advantages with
providing a head having outer peripheral gauge buttons that are tilted
outwardly from a
central longitudinal axis of the drill bit and are positioned axially
forwardmost of any other
component of the drill head. Additionally, the drill head, at a forward facing
region,
comprises a rearwardly projecting cavity or recess within which are mounted
front facing
buttons, (positioned at the lowest region of the cavity) and side buttons
(positioned at the
circumferential cavity sides and radially inside the gauge buttons). The front
and side
buttons of the cavity are effective to create a 'cone' shaped projection in
the rock as the
drill bit is rotated and advanced. This cone formation is provided by the
relative size and
orientation of the front and side buttons. In particular, the side buttons are
tilted radially
inward towards the axis such that a tip (or a leading cutting edge) of the
buttons is
positioned closer to the axis than a base of the buttons embedded in the drill
head.
Additionally, the peripheral gauge buttons are advantageously tilted radially
outward such
that their tip (or leading cutting edge) is positioned radially furthest from
the axis than a
base region of the buttons embedded in the drill head.
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It is a further advantage of the subject invention that the outer peripheral
gauge buttons are
effective to create an annular groove in the rock during rotation with this
annular groove
surrounding the guiding cone. The inventors have identified that this annular
groove is
effective to further stabilise the drill head during rotation and advancement.
This is
achieved, in part, via the relative axial positioning of the gauge buttons
being axially
forwardmost of the side and front buttons.
According to a first aspect of the present invention there is provided a
percussive rock drill
bit comprising: a head coupled to a rearwardly projecting skirt, a
longitudinal axis
extending through the head and the skirt; the head having a front face and an
outer collar
being raised and projecting axially forward of the front face, the collar
having an inner
sloping surface being inclined relative to the axis and being radially inward
facing such
that the front face and the sloping surface define a rearwardly projecting
cavity in a
forward region of the bit; a plurality of gauge buttons distributed over the
collar and
mounted at the head to tilt radially outward from the axis; a plurality of
front buttons
distributed over the front face; characterised by: a plurality of side buttons
distributed over
the inner sloping surface of the collar wherein at least a portion of each
gauge button is
positioned axially forwardmost of each side button.
Preferably, each side button is mounted at the head to tilt radially inward
towards the axis.
Reference within the specification to 'buttons' encompasses inserts adapted
specifically to
be harder than the main body of the drill (being typically steel) including
the drill head.
The cutting inserts may typically comprise a carbide based material such as
cemented
carbide or tungsten carbide for example.
Optionally, a diameter or width of the gauge buttons is greater than a
diameter or width of
the side buttons. Optionally, a diameter or width of the gauge buttons is
greater than a
diameter or width of the front buttons.
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Optionally, the gauge buttons are tilted radially outward from the axis at an
angle in the
range 30 to 50 , 30 to 45 , 35 to 45 . Optionally, the side buttons are tilted
radially towards
from the axis at an angle in the range 30 to 500, 30 to 45 , 35 to 45 .
Preferably, the gauge
buttons are tilted radially outward from the axis at an angle of substantially
40 and the
side buttons are tilted radially towards the axis at an angle of substantially
40 .
Preferably, the collar comprises a peripheral surface extending around the
inner sloping
surface and orientated to be declined relative to the axis to be radially
outward facing, the
gauge buttons projecting from the gauge surface.
Preferably, the drill bit further comprises axially projecting channels
extending from a
peripheral region of the cutting head and along the length of the skirt.
Optionally, the drill
head further comprises radially extending grooves formed in the peripheral
collar.
Preferably, the drill bit further comprises an annular flange provided at an
axially rearward
end, the flange comprising a plurality of rearward facing teeth with a cutting
region to
provide a cutting action when the drill bit is rotated for extraction from the
borehole.
Preferably, the drill bit further comprises at least one fluid supply conduit
formed
internally within the drill bit and extending axially rearward from the
cutting head and in
particular the front face. Preferably, the drill bit further comprises an
axially inner bore
extending lengthwise within the main body of drill bit to mount the drill bits
on a shaft of
the terrestrial machine to impart the impact and rotary motion.
Optionally, the gauge, front and/or side buttons comprise any one or a
combination of the
following: a domed shape configuration; a rounded shape configuration; a
conical shape
configuration; a ballistic shape configuration; a semi-spherical shape
configuration; a flat
end configuration. Preferably, the buttons (optionally turned hardened
inserts) are
embedded into the cutting head via conventional manufacturing methods known to
those
skilled in the art.
Optionally, the drill bit comprises eight gauge buttons. Optionally, the drill
bit comprises
six side buttons. Optionally, the drill bit comprises four front buttons.
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Preferably, the collar comprises at least one groove extending axially between
an end
peripheral surface and the front face. Optionally, collar comprises at least
one channel
extending from an end peripheral surface axially towards the front face.
Brief description of drawings
A specific implementation of the present invention will now be described, by
way of
example only, and with reference to the accompanying drawings in which:
Figure 1 is an upper perspective view of the percussive rock drill bit having
a skirt and a
drill head mounting a plurality of cutting inserts (buttons) according to a
specific
implementation of the present invention;
Figure 2 is a lower perspective view of the drill bit of figure 1;
Figure 3 is a plan view of the head region of the drill bit of figure 2;
Figure 4 is an external side elevation view of the drill bit of figure 2;
Figure 5 is a cross sectional side view through A¨A of figure 4;
Figure 6 is a magnified view of the inserts mounted at the bit head of figure
5.
Detailed description of preferred embodiment of the invention
Referring to figures 1 to 4 a drill bit 100 comprises a drill head 101 formed
at one end of a
generally elongate shaft 108. An opposite end of shaft 108 is flared radially
outward to
provide an annular flange 109. Shaft 108 and flange 109 collectively define a
skirt 102
that represents a trailing region of drill bit 100 as it is advanced through
the rock or
subterranean material via the leading drill head 101. A plurality of axially
extending
channels 111 are recessed into the outer surface of skirt 101 and extends
almost the entire
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axial length of drill bit 100. Channels 111 terminate at head region 101 to
create
depressions 114 that extend radially inward towards a central longitudinal
axis 119
(extending through drill bit 100) from a radially outermost peripheral edge
120 of head
101. The circumferentially spaced apart channels 111 define intermediate
axially
extending ridges 110 that are also provided over the substantially entire
axial length of drill
bit 100.
A plurality of cutting teeth 112 are provided at an axially rearward region
121 of skirt 102
and in particular annular flange 109. Teeth 112 comprise an axially rearward
facing
cutting surface 200 configured to facilitate extraction of the drill bit 100
backwards
through the borehole created by the advancing head 101. Teeth 112 are formed
at the end
regions of each ridge 110.
Head 101 is flared radially outward relative to shaft 108 and comprises a
maximum
diameter being approximately equal to a diameter of flange 109 to form a
raised outer
collar represented generally by reference 107. Collar 107 forms a perimeter of
a cavity
103 that projects axially rearward from a forwardmost annular rim 122 of
collar 107.
Cavity 103 is also defined, in part, by a sloping side surface 105 that is
tilted radially
outward from axis 119. The inclined side surface 105 is terminated at an upper
end by
annular rim 122 and at a lower end by a front facing surface 106. Front
surface 106 is
aligned substantially perpendicular to axis 119 and comprises a generally
circular
configuration.
Collar 107 is further defined, in part, by a peripheral surface 104 that
extends
circumferentially and radially outward beyond rim 122. Peripheral surface 104
is
terminated by radially outermost edge 120. Surface 104 is tilted radially
outward from
axis 119 so as to be generally outward facing whilst cavity side surface 105
is orientated to
be generally inward facing towards axis 119. A head trailing surface 123
extends axially
rearward of peripheral surface 104 and is also orientated transverse to axis
119 so as to
decrease the diameter of collar 107 towards a diameter of shaft 108. According
to the
shape profile and configuration of head 101 and in particular the peripheral
raised collar
107, cavity region 103 comprises a generally bowl or dish-shaped configuration
in which
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the sides of the bowl are defined by sloping surface 105 and the base of the
bowl is defined
by front surface 106. A pair of diametrically opposed grooves 113 are formed
within
collar 107 from axially forwardmost rim 122 to an axial depth aligned with
front surface
106. Each groove 113 comprises a generally V-shaped configuration in which a
width of
the groove at its lower region (corresponding to front face 106) is smaller
than a
corresponding width at an upper region (corresponding to rim 122). Some
channels 111
terminate at head 101 to form depressions 114 recessed axially and extending
radially
through the forwardmost region of collar 107 from rim 122. Depressions 114 and
grooves
113 allow debris material to pass radially outward from cavity 103 to a region
outside of
drill bit 100. Additionally some channels 111 terminate at head 101 to form
indents 124 in
the radially outermost region 120 of collar 107, where such indents 124 do not
extend
radially through the collar wall to emerge at cavity 103.
Drill head 101 comprises three types of hardened cutting inserts (referred to
herein as
buttons). A first set of buttons 115 are positioned at peripheral surface 104
and are
configured as gauge buttons to determine and maintain a predetermined diameter
of the
borehole formation. Gauge buttons 115 are tilted radially outward so as to be
generally
inclined and outward facing from axis 119 consistent with peripheral surface
104. Gauge
buttons 115 are embedded within and distributed circumferentially around the
perimeter
region of collar 107 to project axially forward of rim 122 and to represent
collectively an
axially forwardmost cutting edge of drill bit 100. A second set of buttons 117
are
embedded in front facing surface 106 at the cavity base region 103. Buttons
117 are
aligned generally with axis 119. A third set of buttons 116 are embedded in
the collar side
wall at the inward facing sloping surface 105. Buttons 116 are positioned at a
region
radially intermediate the outer peripheral gauge buttons 115 and radially
inner front facing
buttons 117. Side buttons 116 are mounted at the collar wall region to tilt
radially inward
towards axis 119 having an opposite angle of inclination to gauge buttons 115.
Side
buttons 116 are provided at different axial heights at sloping surface 105
such that at least
one button is provided at an axially lower position (towards front surface
106); at least one
button 116 is positioned axially higher (towards peripheral rim 122) and at
least one button
116 is positioned axially between these two upper and lower buttons 116.
Accordingly, the
relative position of buttons 116 over surface 105 ensures a continuous cutting
edge is
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formed over the entire axial length of surface 105 between rim 122 and front
surface 106.
Additionally and referring to figure 3, each gauge button 115 comprises a
region 300 that
extends radially outward beyond the outermost edge 120 of collar 107.
Referring to figures 5 and 6 each of the three types of cutting button 115,
116, 117
comprises a generally dome-shaped cutting surface provided at one end of a
generally
elongate main body. The main body of each button 115, 116, 117 is embedded
within drill
head 101 such that only the domed surface protrudes to represent semi
spherical cutting
surfaces. Outer gauge buttons 115 comprise a domed end portion having a
diameter
greater than that of side and front buttons 116, 117. Side buttons 116, 117
comprise
approximately equal diameter domed head portions. The elongate main body of
gauge
buttons 115 are tilted radially outward as illustrated by reference 502
relative to
longitudinal axis 119. The inclined angle a is typically between 30 to 45 and
is
substantially 40 . Accordingly, the domed head surface 115 projects generally
radially
outward from axis 119. Additionally, each elongate main body of side buttons
116 is
mounted at head 101 so as to tilt towards axis 119 to be generally inward
facing. An angle
of inclination ia of side buttons 116 is represented by reference 503 and is
typically
between 30 to 45 and is substantially 40 relative to axis 119. As
illustrated in figure 5,
the front buttons 117 comprise a main body that is aligned substantially
parallel with axis
119 as indicated by reference 504.
Drill bit 100 comprises an elongate central bore 200 extending from the
axially rearward
region 121 to head 101. An opening 501 of bore 200 is flared radially outward
and a
corresponding innermost region 500 of bore 200 is also flared radially outward
to engage
and mate with a driving tool coupled to the terrestrial machine to impart the
hammer-like
impacting force and a rotary motion to bit 100. A plurality of fluid conduits
118 extend
from bore 200 to emerge from front facing surface 106 to provide a fluid flow
pathway.
Accordingly, a fluid may be provided to drill bit 100 to flow through bore 200
and
conduits 118 to the cavity region 103. Cutting debris is then flushed from
head 101 via
grooves 113 and depressions 114 to be carried rearwardly through channels 111.
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Referring to figure 6, each gauge button 115 comprises a region 500 of the
domed cutting
surface that is positioned axially forward from a corresponding region 501 of
the domed
cutting surface of each side button 116. Accordingly, the axially forwardmost
region 500
of gauge button 115 is positioned axially proud of the axially forwardmost
region 501 of
side button 116 by a distance d. According to the specific implementation,
distance d is
substantially 0.3 to 1.5 mm and is in particular 0.5 or 0.7 mm.
In use, drill bit 100 is configured to rotate about axis 119. As the gauge
buttons 115 are
positioned axially forwardmost and radially outermost, these cutting
components 115
provide the principal cutting action through the rock. In particular, the
radially outward
tilting orientation of gauge buttons 115 provides that cutting head 101
creates an annular
groove in the rock at the leading end region of drill bit 100. This as-formed
groove is
effective to stabilise bit 100 and inhibit undesirable lateral deflection from
axis 119 during
advancement. Additionally, the relative orientation and configuration of side
buttons 116
and front facing buttons 117 (mounted within recess 103) are affective to
create a 'guide
cone' in the rock as drill bit 100 advances. This guide cone projects
rearwardly into cavity
103 from rim 122 and is surrounded by the as-formed annular groove created by
gauge
buttons 115. The formation of the guide cone is optimised by the tilting
angular alignment
of side buttons 116 to be inward facing towards axis 119. The relative axial
positioning of
gauge regions 115 relative to side button regions 116 ensures the leading
groove is
continually formed circumferentially around the guide cone to provide a
combined means
of anchorage of the drill bit 100 within the borehole. The present
configuration of the
three types of cutting insert 115, 116, 117 provide that the drill bit 100 is
effective to
aggressively break through fault and cracks in the rock.
The present invention is not limited to the above described embodiments.
Different
alternatives, modifications and equivalents might be used. The above mentioned
embodiments should therefore, not be considered limiting to the scope of the
invention,
which is defined by the patent claims.
