Note: Descriptions are shown in the official language in which they were submitted.
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ROCK BIT TIP AND ROCK BIT
Technical Field
The present disclosure relates to tips in rock or mining bits for use in a
rock excavation apparatus.
The disclosure particularly relates to tips with hollow bases.
Background
There are several different methods used for drilling in earth formations.
Some use rotary movement and some use a combination of rotary and percussive
movement. One common aspect of these methods is that a drill bit rotates at an
end
of a drill string.
Rotary drilling is conducted by rotating a rigid string of tubular rods to
which a rock-cutting bit is attached. The rotary drill imparts two basic
actions through
the drill rod and bit into the rock, i.e. axial thrust and rotational torque.
Percussive
drills break rock predominantly by crushing and chipping rock with the
repeated
application of high-frequency, high-energy blows through a drill bit. The
impact
energy is developed by a piston that strikes the bit (down-the-hole drill) or
drill steel
(surface-mounted drill).
To improve the wear resistance and increase the lifetime of such drill
bits, cutting elements in the form of tips or inserts are attached to the
drill bit body.
These tips are often made of cemented carbide, most commonly tungsten carbide,
due to its excellent combination of high hardness and high toughness. The tips
can
also be made of polycrystalline diamond (PCD). The purpose of the tips is
mainly to
apply pressure to and fracture rock. Sometimes tips are also positioned on the
drill bit
body as protection for the surrounding steel. The tips must therefore
withstand high
compressive and transverse loads.
The tungsten carbide tips are commonly mounted in cylindrical recesses
in the outer surface of the drill bit body. The tips can be made a few
hundredths of a
mm larger than the recess and are pressed in to have a tight interference fit
to
prevent loosening during usage.
Tungsten carbide tips are also used for soft cutting conditions such as
excavation of coal. The tips are, in this application, often named caps and
are often
adhesively bonded to a pick body by, for example, brazing or welding.
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Several standard shapes are used for tungsten carbide tips, such as a
part-spherical, conical, a double cone, a ballistic and a chisel crest. Common
for
these different shapes is that the base, also called mounting portion, of the
tip is
generally cylindrical.
In many applications it is advantageous to use tips having a diameter of
about 2 cm or larger. The advantages being that fewer tips need to be used and
also
that the protrusion of the tip from the surface of the bit body can be greater
while
maintaining adequate strength to avoid transverse failure during the
excavation
operation. Having large tips concentrates the load to fewer tips and greater
rock
penetration can be obtained without engagement of the steel surface, resulting
in
improved excavation rate. Having large tips that extend a greater distance
from the
bit also increases the lifetime of the bit as the large tips can accommodate
appreciable wear before they are worn out.
One problem with large diameter tips is that they are expensive. This is
due to the high cost of the material required to manufacture a tip. The
material
quantity required increases with the square of the diameter of the tip. When
using
tungsten carbide tips it is more costly to use few tips with a diameter of
about 2 cm
than using a larger amount of small tips.
This problem is addressed in U.S. Pat. No. 4,150,728. Here tungsten
carbide tips with hollow bases are shown. Such a tip has a cavity opening to
the
inner end of the tip with a volume in the range of from about 15 to 30 % of
the volume
of the base portion of the tip.
The present inventor has surprisingly found that several prominent
problems occur at tips with hollow bases. One is that the base of the tip
tends to get
oval in shape. Another problem is that the form of the tip tends to get
conical, i.e. the
diameter of the mounting portion decreases when approaching the very bottom of
the
tip. Ovality and conicity in the mounting portion decreases the force for
pulling the tip
from the drill bit body and therefore loosening of the tip is an unfavorable
consequence.
Another problem is that the mounting portion may crack when a tip is
press fitted into a recess in the drill bit body.
These and other aspects of, and advantages with the present invention
will be apparent from the detailed description and the accompanying drawings.
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Summary
One object of the present invention is to provide a hollow tip concept,
which has better strength than known hollow tips. Another object is to provide
a
hollow tip concept which can be produced at a lower cost compared to solid
tips, thus
solving the above mentioned problems.
According to a first aspect, there is provided a rock bit tip comprising: a
mounting portion, an end portion converging from a top end of the mounting
portion
to form a work surface and at least one recess in a bottom of the mounting
portion,
the recess extending towards said end portion, wherein there are more than one
recess.
In a second aspect, there is provided a rock bit comprising a tip with
more than one recess.
Brief Description of the Drawings
In the detailed description of the present invention reference will be
made to the accompanying drawings, wherein,
Fig. 1 schematically illustrates a conventional tip or button, in a side
view, suitable for excavation of rock,
Fig. 2 schematically illustrates a tool for rotary drilling, in a side view,
Fig. 3 schematically illustrates a tool for percussive drilling, in a
perspective view from above,
Fig. 4 schematically illustrates a mining pick in a side view,
Fig. 5a schematically illustrates a first embodiment of a tip according to
the invention in a perspective view from below,
Fig. 5b schematically illustrates a first embodiment of the tip according to
the invention in an axial cross-sectional view through the tip centre axis A,
Fig. 6 schematically illustrates a second embodiment of a tip according
to the invention in a perspective view from below,
Fig. 7 schematically illustrates a third embodiment of a tip according to
the invention in a perspective view from below,
Fig. 8 schematically illustrates a fourth embodiment of a tip according to
the invention in a perspective view from below,
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Fig. 9a schematically illustrates a fifth embodiment of a tip according to
the invention in a perspective view from below,
Fig. 9b schematically illustrates the tip according to Fig. 9a in a side
view,
Fig. 9c schematically illustrates the tip according to the line IX C ¨ IX C in
Fig. 9b, and
Fig. 9d schematically illustrates the tip according to the line IX D ¨ IX D
in Fig. 9b.
Description of Embodiments
The features and advantages of the present invention are well
understood by reading the following detailed description in conjunction with
the
drawings in which like numerals indicate similar elements and in which:
FIG. 1 illustrates a tip 10 suitable for rock excavation. The tip comprises
an end portion 11 having a top 13. The end portion is intended to project from
a front
surface of a bit to form a work surface that is in contact with the rock. The
tip also
comprises a mounting portion 12 extending from the end portion 11 towards a
bottom
end 14. The mounting portion of the tip is intended to be positioned in a
recess in a
drill bit body and assures that the tip is securely fixed to the bit body. If
the tip 10 is
comprised in a mining pick, the bottom end 14 may be secured to the bit, for
example, by means of brazing or welding.
FIG. 2 illustrates a rock bit for rotary drilling 20. The bit comprises a
thread 24 whereby the rotary bit 20 is to be connected to a drill string. The
bit further
comprises legs 25 with roller cones 21 attached at one end. Tips, of the type
herein
described, can be used as protective tips 23 on the legs 25 and/or as active
tips 22
on the roller cones 21. The term "protective" means that the main purpose of
the tip
23 is to protect the steel in the drill bit from being too heavily worn. The
term "active"
means that the main purpose of the tip 22 is to apply pressure to and fracture
rock.
The technology is more closely described in US Patent Number 6,446,739.
FIG. 3 illustrates a percussive rock drill bit 30 that comprises a drill bit
head 31 and a shank 32. The drill bit head 31 may comprise tips, of the type
described below, such as peripheral tips 33 and/or front tips 34. The
technology is
more closely described in US Patent Number 7,296,641.
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FIG. 4 illustrates a mining pick 40 used in operations such as cutting soft
minerals such as, for example, coal. The mining pick 40 includes a body 41
having a
head 42 and a shank 43. The tip 44 is made according to the invention and is
the
part that actively cuts minerals. It is made of a hard material such as
cemented
carbide, diamond, SiC-D or combinations thereof. The technology is more
closely
described in US Patent Number 8,210,618.
FIGS. 5a and 5b illustrate a first embodiment of the invention. The tip
110 has a mounting portion 112. Four identical open recesses 115 extend
axially
from the bottom end 114 of the mounting portion 112. The open recesses 115
have
cross sections at the bottom end 114 that can be substantially like circle
sectors with
rounded corners for avoiding stress concentrations. The recesses 115 are
spaced
apart by a support structure 116. At least one open recess 115 has its
geometric
centre axis B separate from the longitudinal tip centre axis A.
FIG. 6 illustrates a second embodiment of the invention. The tip 120 has
a mounting portion 122. Three identical open recesses 125 extend axially from
the
bottom end 124 of the mounting portion 122. The open recesses 125 may have
cross
sections at the bottom end 124 that are substantially like truncated circle
rings. The
recesses 125 are spaced apart by a support structure 126. At least one open
recess
125 has its geometric centre axis B separate from the longitudinal tip centre
axis A.
FIG. 7 illustrates a third embodiment of the invention. The tip 130 has a
mounting portion 132. Seven identical open recesses 135 extend axially from
the
bottom end 134 of the mounting portion 132. The open recesses 135 have cross
sections at the bottom end 134 that are substantially hexagonal. The recesses
135
are spaced apart by a support structure 136. At least one open recess 135 has
its
geometric centre axis B separate from the longitudinal tip centre axis A. A
central
open recess 135 has its geometric centre axis B substantially coinciding with
the
longitudinal tip centre axis A.
FIG. 8 illustrates a fourth embodiment of the invention. The tip 140 has a
mounting portion 142. Six open recesses 145 extend axially from the bottom end
144
of the mounting portion 142. The open recesses 145 have cross sections at the
bottom end 134 that are substantially circular. The recesses 145 are spaced
apart by
a support structure 146. At least one open recess 145 has its geometric centre
axis B
separate from the longitudinal tip centre axis A.
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FIGS. 9a - 9d illustrate a fifth embodiment of the invention. The tip 150
has a mounting portion 152. One open recess 155 extends axially from the
bottom
end 154 of the mounting portion 152. Between the bottom end 154 and the end
portion, the open recess 155 is split into three identical separate recesses
157. The
recesses 157 are spaced apart by a support structure 156. At least one of the
recesses 157 has at least one cross section (IX D - IX D), parallel to the
bottom of
the mounting portion, between the bottom of the mounting portion and the end
portion, which has its geometric centre axis B separate from the longitudinal
tip
centre axis A, Fig. 9d.
The number of recesses, and their sizes, may be altered compared to
the examples described in the above-captioned embodiments. It is also possible
to
combine recesses with different sizes and shapes into a new embodiment. The
depth
of the recesses can also be varied, but the recesses are always of the blind
hole
type.
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.
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