Note: Descriptions are shown in the official language in which they were submitted.
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DRILL BIT FOR PERCUSSIVE DRILLING.
For the purpose of explanation reference will be made to use of the drill bit
in top
hammer percussive drilling of rock, but it can also be used in other kinds of
percussive drilling, such as DTH.
Buttons or inserts for bits of this type generally have a cylindrical body
with opposing
ends, one of which comprises a working face for the button that is shaped so
as to
protrude from the body of the button. More particularly, this working face is
generally
hemispherical (domed) or parabolic (ballistic) in shape.
Typically, gauge buttons have a diameter which is larger than or equal to face
buttons. Examples of this can be found in US 3,519,092, US 3,997,011 and US
4,572,307 amongst others, as well as being illustrated in Figure 2 herein.
A problem with bits of the above described type is that an extent of reflected
energy
(ie. reflected from the rock face) is so great that this can damage the bit
and other
associated equipment.
In US 5,947,215 there is disclosed a drill bit having a single, centrally
positioned front
button which is of larger diameter than the gauge buttons, and wherein
forwardmost
portions of the gauge buttons and front button lie in a common plane, or the
front
button is more forwardly projecting. The object of this is to provide good bit
guidance.
It is against this background and the problems and difficulties associated
therewith
that the present invention has been developed.
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The objects and advantages of the present invention will become apparent from
the
following description, taken in connection with the accompanying drawings,
wherein,
by way of illustration and example, an embodiment of the present invention is
disclosed.
SUMMARY OF THE INVENTION
In one aspect, the invention may be said to reside in a drill bit for use in
percussive
drilling, the drill bit comprising a body having a front face, at least one
button on the
front face (hereinafter 'face button'), and a plurality of gauge buttons, each
of the
buttons having a working face, at least a portion of at least one gauge button
working
face having a curvature which deviates further from being flat (ie. is more
pronounced, pointed or sharper) than a curvature of any curved portion of at
least
one face button working face so that said portion of at least one gauge button
working face projects further than said portion of at least one face button
working
face.
In the context of the present application the term 'working face' should be
taken to
mean the part of each button which will interact with the rock during
drilling.
In one form, said portion of at least one gauge button working face projects
further
than said portion of at least one face button working face.
In one form, at least a portion of the working face of each of the face and
gauge
buttons is curved. In case said working face (10a and 20a) comprises multiple
portions, each portion may blend into adjacent portions.
In one form, the entirety of the working face of each of the face and gauge
buttons is
curved.
In one form, the curvature of the working face of at least one gauge button is
more
pronounced than the curvature of the working face of at least one face button.
In one form, the or each gauge button working face projects further than the
or each
face button working face.
In one form, a radius of curvature of the working face of at least one face
button is
greater than a radius of curvature of the working face of at least one gauge
button.
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In one form, each of the face and gauge buttons includes a substantially
cylindrical
body.
In one form, the working face of at least one gauge button is substantially
hemispherical (or domed).
In one form, the working face of at least one gauge button is substantially
parabolic
(or ballistic) in shape.
In one form, the working face of at least one face button is shaped like a
segment of
a hemisphere (or dome).
In one form, the working face of at least one face button is shaped like a
segment of
a parabola (or ballistic shape).
In one form, the cylindrical body of at least one face button has a radius
which is
different to a radius of curvature of the curved portion of the working face
thereof.
In one form, the radius of the cylindrical body of at least one face button is
less than
the radius of curvature of the curved portion of the working face thereof.
In one form, the cylindrical body of at least one gauge button has a radius
which is
substantially equal or at least similar to a radius of curvature of the curved
portion of
the working face thereof.
In one form, the drill bit comprises a plurality of face buttons.
In one form, the working face of at least one face button is or is approaching
substantially flat.
In a further aspect, the invention may be said to reside in a drill bit for
use in
percussive drilling, the drill bit comprising a body having a front face, at
least one
button on the front face (hereinafter 'face button), and a plurality of gauge
buttons,
each of the buttons having a working face, the drill bit being characterised
in that at
least a portion of at least one gauge button working face has a curvature with
a peak
that is more projecting by comparison to a peak of any curved portion of at
least one
face button working face.
In one form, the or each face button is offset with respect to the central
axis of the bit.
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A detailed description of one or more embodiments of the invention is provided
below
along with accompanying figures that illustrate by way of example the
principles of
the invention. While the invention is described in connection with such
embodiments,
it should be understood that the invention is not limited to any embodiment.
On the
contrary, the scope of the invention is limited only by the appended claims
and the
invention encompasses numerous alternatives, modifications and equivalents.
For
the purpose of example, numerous specific details are set forth in the
following
description in order to provide a thorough understanding of the present
invention.
The present invention may be practiced according to the claims without some or
all of
these specific details. For the purpose of clarity, technical material that is
known in
the technical fields related to the invention has not been described in detail
so that
the present invention is not unnecessarily obscured.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of this disclosure it will now be described with
respect to
an exemplary embodiment which shall be described herein with the assistance of
drawings wherein:
Figure 1 is a longitudinal section through the body of a drill bit; and
Figure 2 is cross-sectional view through the body of a prior art drill bit.
In the following description, like reference characters designate like or
corresponding
parts throughout the several views of the drawings.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring now to Figure 1, where there is illustrated a drill bit (1) for use
in percussive
drilling. The drill bit (1) comprises a bit body (2) of an appropriate tool
steel grade
having a front face (4) which extends generally transversely relative to a
longitudinal
axis of the bit body (2), and a rear threaded portion (6) so the drill bit (1)
can be
threadably attached to a drill rod (not illustrated) having corresponding
threads.
Located in the front face (4) is a plurality of face buttons (10) which
project and
protrude axially therefrom.
Located around the periphery of the face (4) is a plurality of gauge buttons
(20)
inclined at an angle with respect to the longitudinal axis of the bit (1). The
gauge
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buttons (20) project and protrude to such an extent that the diameter of the
drill hole
is defined by these.
The buttons (10 and 20) are either press-fit or shrink-fit into the bit body
(2), and so
are commonly and even interchangeably referred to as inserts. The buttons (10
and
5 20) are formed of a material which is harder than the material of the bit
body (2).
Each button (10 and 20) has a cylindrical body with a working face (10a) in
one case,
and (20a) in the other, the working face being the part of each button (10 and
20)
which will interact with the rock during drilling. In this embodiment, each of
these
working faces (10a and 20a) is convexly curved. The projecting distance F of
the
face button working face (10a) and the projecting distance G of the gauge
button
working face (20a) are measured from the associated body portion as shown in
Fig.
1, wherein G is greater than F.
Each gauge button (20) working face (20a) has a curvature which is more
pronounced than a curvature of at least one face button (10) working face
(10a). That
is to say, a radius of curvature (RF) of the working face (10a) of the face
buttons (10),
is significantly greater than a radius of curvature (RG) of the working face
(20a) of the
gauge buttons (20).
What is more, in the case of the face buttons (10), the radius of curvature of
the
working face (RF) is significantly greater than a radius (R') of the
cylindrical body
thereof. In contrast, for each of the gauge buttons (20), the radius of
curvature of the
working face (RG) is generally the same as a radius (R") of the cylindrical
body
thereof.
In the case of the face buttons (10) then, the radius of curvature (RF) of the
working
face (10a) may be so great that the working face approaches, or is, a
substantially
flat surface, the face button (10) working face (10a) thereby having no or
minimal
projection, and certainly less projection that the gauge button (20) working
face
(20a).
Tests which have been carried out indicate that the force required to
penetrate the
rock is less with a more pointed button such as the gauge buttons (20), than
with a
blunter one such as the face buttons (10).
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Given then, that for any rock and any drill hole therein the penetration
resistance will
be higher in a corner between an end and side of the hole than at the end of
hole
where the rock face is flat, it advantageous if, as per the present invention,
the
working face (20a) of the gauge buttons (20) is more pointed than the working
face
(10a) of the face buttons (10), as less force will be required for
penetration, resulting
in less wastage of percussive energy and less reflected energy in turn. Less
reflected
energy means less damage to drill and other associated equipment.
A further advantage of the above described drill bit (1) is higher drill speed
and
improved drilling efficiency when compared with bits of the prior art, such as
that
illustrated at Figure 2.
All gauge buttons in the drill bit may be substantially identical in shape.
All face
buttons in said or a drill bit may be substantially identical in shape.
Throughout the specification and the claims that follow, unless the context
requires
otherwise, the words "comprise" and "include" and variations such as
"comprising"
and "including" will be understood to imply the inclusion of a stated integer
or group
of integers, but not the exclusion of any other integer or group of integers.
The reference to any prior art in this specification is not, and should not be
taken as,
an acknowledgement of any form of suggestion that such prior art forms part of
the
common general knowledge.
It will be appreciated by those skilled in the art that the invention is not
restricted in its
use to the particular application described. Neither is the present invention
restricted
in its preferred embodiment with regard to the particular elements and/or
features
described or depicted herein. It will be appreciated that various
modifications can be
made without departing from the principles of the invention. Therefore, the
invention
should be understood to include all such modifications in its scope.
