Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02639315 2008-09-04
A CUTTING ELEMENT HAVING A SELF SHARPENING TIP
BACKGROUND OF THE INVENTION
This invention relates to cutting elements or bit members
or picks and is particularly concerned with such elements having
a pointed end that makes contact with the material to be cut.
Such cutting elements are typically called a rotary cone bit of
the pick type.
A cutting element or pick or bit member according to the
present invention is a member somewhat like the cutting bit in a
machine tool and having a metal body with a hard region or a
hard insert therein at the place where the bit member engages
the work. Such bit members are well known'in many industries,
such as in the mining industry and usually comprise a steel
body, such as forged steel, with a cemented tungsten carbide tip
or insert secured thereto as by brazing. The tip usually ends
with a small radius and thus is easy to penetrate into the
material being cut. As the carbide wears, the tip rounds off or
dulls slowing penetration into the material to be cut.
Some bit members have been made with one or more layers of
polycrystalline diamond or a diamond and carbide mixture,
coating the exposed part of the bit tip. However, the diamond
coating is brittle and flakes off except under the easiest
cutting conditions.
SUMMARY OF THE INVENTION
One of the principal objects of the invention is to provide
an improved cutting element that maintains its hard tip longer
than with current cutting elements, and which tends to remain
pointed or sharp as the cutting element wears.
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The cutting element of the invention has a bit tip with a
diamond (or other material harder than the grade of carbide
making up the rest of the bit tip) core on the cylindrical axis
of the bit tip. The tougher carbide on the outside will protect
the brittle diamond from impact. The diamond exposed at the tip
will protect the carbide from excessive wear. As the diamond
and carbide wear together, they should provide a self sharpening
action.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an exploded perspective view of a bit holding
apparatus.
Figure 2 is a partial cross-sectional view of the bit shown
in Figure 1, with a hardened insert at the end of the bit
according to the present invention.
Figure 3 is a cross sectional view of an alternate
embodiment of the insert at the end of the bit shown in Figure
2.
Before one embodiment of the invention is explained in
detail, it is to be understood that the invention is not limited
in its application to the details of the construction and the
arrangements of components set forth in the following
description or illustrated in the drawings. The invention is
.capable of other embodiments and of being practiced or being
carried out in various ways. Also, it is to be understood that
the phraseology and terminology used herein is for the purpose
of description and should not be regarded as limiting. Use of
"including" and "comprising" and variations thereof as used
herein is meant to encompass the items listed thereafter and
equivalents thereof as well as additional items. Use of
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"consisting of" and variations thereof as used herein is meant
to encompass only the items listed thereafter and equivalents
thereof. Further, it is to be understood that such terms as
"forward", "rearward", "left", "right", "upward" and "downward",
etc., are words of convenience in reference to the drawings and
are not to be construed as limiting terms.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings wherein the showings are for
purposes of illustrating the present preferred embodiments of
the invention only and not for purposes of limiting same, the
Figures show a mining machine cutting drum .(not shown) which
supports a cutting bit 12 by means of a bit holder 18.
As is well known in the art, the cutting drum (not shown)
is supported by a mining machine (not shown) for rotation while
being vertically moveable and while the mining machine advances
forward. As is also well known, the cutting drum (not shown)
typically includes a plurality of cutting bits 12 arranged
thereon; however, the present description will now be directed
to a single cutting bit 12 and the structure of a single present
bit holder 18.
The bit holder 18 may be attached directly or indirectly to
the drum 10. For example, the bit holder may be welded or
clamped to the drum 10 or may be secured to a mounting block
attached to the drum 10. As described hereinafter, the bit
holder 18 receives and retains a sleeve 50 which rotatably
receives the bit 12.
The cutting element or bit 12 includes a central
cylindrical shank portion 24 and having an enlarged conical
cutting portion or nose 26 attached thereto such that a shoulder
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area 28 is formed there between. The cutting bit has a central
axis shown at 29 with a hard cutting tip 30 on one end of the
cutting bit 12. The cutting bit 12 includes on its other end a
recessed notch 32 and terminates in an end shoulder 34 such that
a retaining ring (not shown) may be received within the notch 32
to prevent the axial removal of the cutting bit 12 from a sleeve
50. In other embodiments (not shown), the shoulder area 28 can
be omitted.
The bit holder 18 has a body portion 38 and a base portion
40. The base portion 40 attaches directly to the cutting drum
(not shown) or indirectly by means of a mounting block (not
shown). The body portion 38, which is integral to the base
portion 40, includes an aperture 42 for receiving a coaxial
sleeve 50. The aperture 42 defines an inner surface 42a. The
body portion 38 includes a contact face 44 which is shown as
perpendicular to the longitudinal axis 46, which is the same as
the central axis 29 of the aperture 42, but which may also be
formed as a cone whose surface is at an angle with respect to
the longitudinal axis 46 of the aperture 42.
The sleeve 50 has an elongated body member 52 and a collar
54, the collar 54 having an inside surface 56 and an outside
surface 58. The inside surface 56 of the collar 54 abuts the
contact face 44. The collar 54 is shown as having an inside
surface 56 which is perpendicular to the longitudinal axis 46 of
the aperture 42; however, the inside surface can be conical
having a conical surface at an angle with respect to the
longitudinal axis 46 corresponding to the angle of the contact
face 44. The outside surface 58 of the collar 54 has a beveled
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surface 60 and a flat surface 62. The body member 52 of the
sleeve 50 defines an outer surface 52a.
The body member 52 of the sleeve 50 has a bore 64 which is
coaxial with the bit axis 29. The bit 12 is rotatably received
by the bore 64. The shank 24 of the bit 12 is slightly smaller
than the bore 64. The shank 24 is retained in the bore 64 by
the retaining ring and the shank may rotate about the central
axis 29 in order to avoid uneven wearing of the tip 30 of the
cutting bit 12. The shoulder area 28 of the bit 12 abuts.the
flat surface 62 to position the bit 12 axially in the bore 64
and transmit cutting forces.
More particularly, as shown in Figure 2, the conical
cutting portion 26 has a narrow end 70 and a broad end 74
connected to the shank portion 24. The conical cutting portion
narrow end 70 has an insert receiving recess 78, and the hard
cutting tip or insert 30 is secured in the insert receiving
recess 78, such as by brazing. The insert 78 has an outer layer
82 made of tungsten carbide, and an inner core 86 on the
cylindrical axis 29 (see Figure 1) of the conical cutting
portion 26. The inner core 86 is made of a material with a
greater hardness than the outer layer 82. Preferably, the
insert 30 has a cylindrical portion with the outer end 90 of the
insert 30 having a small radius so that the outer end 90 forms a
point for aiding in cutting material.
In the preferred embodiment, the inner core 86 is made of
diamond, but in less preferred embodiments, a hardened form of
tungsten carbide can be used. The diamond core 86 is a solid
diamond, not a coated structure. Further, in the preferred
embodiment, the inner core 86 is exposed at the outer end 90.
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The inner core 86 is made from a sheet of material, but in other
embodiments (not shown), the inner core 86 may be cylindrical,
or any other shape. Further, in an alternate embodiment, as
shown in Figure 3, the insert 94 can include a second layer or
core 96 with a hardness between that of the outer layer 82 and
the inner core 86, or even more layers or cores. In order to
obtain the advantage of maintaining the small radius at the
insert outer end 90, each more inner layer in the insert 30,
going from the outside of the insert 94 to the inside, should be
harder than the preceding more outer layer.
Various other features and advantages of the invention will
be apparent from the following claims.
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