Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02757795 2011-11-15
PATENT
Attorney Docket No. 047317-501 9-P 1-U S
POLYGON-SHAPED CARBIDE TOOL PICK
FIELD
[0001] The present disclosure relates to a tool pick having an overall
polygonal
shaped that is formed entirely from a hard material such as cemented carbide
("carbide"), and in particular to a carbide tool pick having a polygonal shape
along its
entire length that can be mounted in a wheel used for microtrenching.
BACKGROUND
[0002] In the discussion of the background that follows, reference is made to
certain
structures and/or methods. However, the following references should not be
construed
as an admission that these structures and/or methods constitute prior art.
Applicant
expressly reserves the right to demonstrate that such structures and/or
methods do not
qualify as prior art.
[0003] Tool picks known in the art typically employ a cemented carbide tip
that is
brazed to a steel shank having an enlarged tail at an end of the shank
opposite the tip.
In part, this construction is used because it would be excessively expensive
to produce
and entire tool pick out of cemented carbide, without commensurate benefits in
performance. The pick is commonly retained in a cylindrical bore of a holder
using a
cylindrical spring retainer positioned around the shank. When installed in the
bore, the
spring retainer presses against the inner wall of the bore, creating a
frictional force that
resists movement of the retainer with respect to the bore. The shank has an
outer
diameter slightly smaller than the inner diameter of the spring retainer so
that the pick
can rotate freely within the retainer, while spring retainer has an inside
diameter smaller
than that of the tail to prevent axial movement of the pick out of the bore.
Therefore,
the enlarged tail is essential to maintaining the pick within the holder, such
that if the tail
is worn away, the pick may be lost.
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[0004] Microtrenching is a low-impact method of burying conduit by digging a
narrow
slot-cut trench in the ground typically between about 19 mm and about 25 mm
wide and
less than about one foot deep, laying the conduit in the trench, and
backfilling the
trench. Microtrenching machines commonly employ a vertical rotating wheel on
which
are mounted a plurality of tool picks. As the wheel rotates, a tip of each
pick cuts into
the ground. Commonly, diamond-tipped saw blades are used for microtrenching.
[0005] Because of the narrow trench width and relatively shallow depth in
microtrenching applications, tool picks for mounting on a microtrenching wheel
require a
short shank length, as well a small shank diameter of typically less than
about 10 mm.
When mounted with lean and skew angles required for microtrenching, the tail
of the
pick shank is exposed at the opposite end of the holder from the pick cutting
tip,
causing the tail to be worn away significantly by microtrenching debris. The
wear on the
tail causes the tail to become sufficiently small that it no longer is larger
than the
retainer. As a result, the retainer is no longer confined such that the pick
may fall out of
the holder.
[0006] The cost to manufacture a small carbide tip and narrow steel shank for
microtrenching is actually higher than that to produce similar larger picks
due to
difficulties with the small scale. Additionally, because of the small size of
the carbide tip
and the small diameter of the steel shank, brazing the carbide tips to the
steel shanks is
difficult, in part because the slimness of the steel shank makes it especially
susceptible
to overheating during brazing.
SUMMARY
[0007] An exemplary embodiment of a polygonal tool pick is formed entirely of
a
single hard material. The tool pick includes a head, a shoulder extending
rearwardly
from the head and having an outer dimension at least as large as a largest
outer
dimension of the head, a shank extending rearwardly from the shoulder and
having an
outer dimension smaller than the outside dimension of the shoulder, and a tail
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extending rearwardly from the shank and having an outer dimension larger than
the
outer dimension of the shank. The head, the shoulder, the shank, and the tail
each
have a plurality of faces with at least one pair of opposed faces being
parallel to each
other. In one embodiment, the head includes a pyramidal cutting tip
terminating in a
frontward tip end and a truncated pyramidal base supporting the cutting tip
and
disposed rearwardly with respect to the cutting tip, the pyramidal cutting tip
having a
steeper slope than the truncated pyramidal base with respect to an axis of the
tool pick.
[0008] Another exemplary embodiment of a polygonal tool pick is formed
entirely of
cemented carbide. The tool pick includes a pyramidal cutting tip terminating
in a
frontward tip end, the cutting tip having an even number of equally sized
faces, and a
truncated pyramidal base supporting the cutting tip and disposed rearwardly
with
respect to the cutting tip, the truncated pyramidal base having a shallower
slope than
the pyramidal cutting tip with respect to an axis of the tool pick, the base
having an
even number of equally sized faces aligned with the faces of the cutting tip.
A shoulder
extends rearwardly from the head and has an outer dimension at least as large
as a
largest outer dimension of the base, the shoulder having an even number of
equally
sized faces aligned with the faces of the base. A shank extends rearwardly
from the
shoulder and has an outer dimension smaller than the outside dimension of the
shoulder, the shank having an even number of equally sized faces aligned with
the
faces of the shoulder. A tapered frontward seat is located between the
shoulder and
the shank, the seat being tapered from a smaller outer dimension at a junction
with the
shank to a larger outer dimension at a junction with the shoulder, the
frontward seat
having an even number of equally sized faces aligned with the faces of the
shank. A
tail extends rearwardly from the shank and has an outer dimension larger than
the outer
dimension of the shank, the tail having an even number of equally sized faces
aligned
with the faces of the shank. A tapered rearward seat is located between the
tail and the
shank, the seat being tapered from a smaller outer dimension at a junction
with the
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shank to a larger outer dimension at a junction with the tail, the rearward
seat having an
even number of equally sized faces aligned with the faces of the shank.
[0009] An exemplary embodiment of a pick assembly includes a holder having a
cylindrical bore, a polygonal tool pick, and a compressible cylindrical
retainer for holding
the tool pick within the cylindrical bore of the holder. The polygonal tool
pick is formed
entirely of cemented carbide. The tool pick includes a pyramidal cutting tip
terminating
in a frontward tip end, a truncated pyramidal base supporting the cutting tip
and
disposed rearwardly with respect to the cutting tip, the truncated pyramidal
base having
a shallower slope than the pyramidal cutting tip with respect to an axis of
the tool pick, a
shoulder extending rearwardly from the base and having an outer dimension at
least as
large as a largest outer dimension of the base, a shank extending rearwardly
from the
shoulder and having an outer dimension smaller than the outer dimension of the
shoulder, and a tail extending rearwardly from the shank and having an outer
dimension
larger than the outer dimension of the shank. The cutting tip, the base, the
shoulder,
the shank, and the tail each have an even number of faces with at least one
pair of
opposed faces parallel to each other, the faces of each of the cutting tip,
the base, the
shoulder, the shank, and the tail being aligned. When the retainer is
compressed, the
retainer is located between the shank and the cylindrical bore, and the inner
diameter of
the compressed retainer is less than the outer dimension of the tail and the
outer
dimension of the shoulder.
[0010] An exemplary embodiment of a microtrenching wheel has a disk and a
plurality of pick assemblies mounted around the circumference of the disk.
Each pick
assembly includes a holder having a cylindrical bore, a polygonal tool pick,
and a
compressible cylindrical retainer for holding the tool pick within the
cylindrical bore of
the holder. The polygonal tool pick is formed entirely of cemented carbide.
The tool
pick includes a pyramidal cutting tip terminating in a frontward tip end, a
truncated
pyramidal base supporting the cutting tip and disposed rearwardly with respect
to the
cutting tip, the truncated pyramidal base having a shallower slope than the
pyramidal
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cutting tip with respect to an axis of the tool pick, a shoulder extending
rearwardly from
the base and having an outer dimension at least as large as a largest outer
dimension
of the base, a shank extending rearwardly from the shoulder and having an
outer
dimension smaller than the outer dimension of the shoulder, and a tail
extending
rearwardly from the shank and having an outer dimension larger than the outer
dimension of the shank. The cutting tip, the base, the shoulder, the shank,
and the tail
each have an even number of faces with at least one pair of opposed faces
being
parallel to each other, the faces of each of the cutting tip, the base, the
shoulder, the
shank, and the tail being aligned. When the retainer is compressed, the
retainer is
located between the shank and the cylindrical bore, and the inner diameter of
the
compressed retainer is less than the outer dimension of the tail and the outer
dimension
of the shoulder.
[0011] It is to be understood that both the foregoing general description and
the
following detailed description are exemplary and explanatory and are intended
to
provide further explanation of the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWING
[0012] The following detailed description can be read in connection with the
accompanying drawings in which like numerals designate like elements and in
which:
[0013] FIG. 1 is a side perspective view of an exemplary polygon-shaped
carbide
tool pick.
[0014] FIG. 2 is a side view of the tool pick of FIG. 1 showing a parting line
from
pressing.
[0015] FIG. 3 is a top end view of the tool pick of FIG. 1.
[0016] FIG. 4 is a bottom end view of the tool pick of FIG. 1 inserted in a
holder
having a cylindrical bore.
[0017] FIG. 5 is a side view of a microtrenching wheel supporting a plurality
of tool
picks as in FIG. 1.
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DETAILED DESCRIPTION
[0018] FIGS. 1-4 illustrate an embodiment of a polygonal tool pick 10. The
pick 10
has a front end 16 and a rear end 18. Through its entire length, the pick 10
has a
polygonal shape. Because the entire cross-section of the pick is polygonal
shaped with
alternating faces and edges, the cross-sectional size of the pick at various
points is
described here with reference to an "outer dimension" rather than a
"diameter." When
comparing the relative sizes of various portions of the pick 10, the outer
dimension may
be obtained by measuring the width of the pick between opposed edges on
opposite
sides of the pick (i.e., a maximum outer dimension), or alternatively by
measuring the
width of the pick between opposed faces on opposite sides of the pick.
[0019] The pick 10 includes a head 12 having a base 30 supporting a cutting
tip 20
that projects frontwardly from the base 30. The base 30 and the cutting tip 20
are
joined at a junction 26. A shoulder 40 is disposed rearwardly adjacent to the
head 12
and joins with the head 12 at a junction 36. A shank 60 projects rearwardly
with respect
to the shoulder 40. As depicted, a tapered frontward seat 50 provides a
transition from
the shoulder 40 to the shank 60. The seat 50 is joined to the shoulder 40 at a
junction
46 and to the shank 60 at a junction 56. Extending rearwardly from the shank
60 is an
enlarged tail 80. As depicted, a tapered rearward seat 70 provides a
transition from the
shank 60 to the tail 80. The seat 70 is joined to the shank 60 at a junction
66 and to the
tail 80 at a junction 76.
[0020] The cutting tip 20, as the frontwardmost portion of the tool pick 10,
provides a
primary cutting surface during use of the pick 10. The cutting tip 20 has a
plurality of
faces 22, with each pair of adjacent faces 22 being joined at an edge 24. The
cutting
tip 20 has a pyramidal shape, tapering frontwardly from a largest outer
dimension at the
junction 26 to a smallest outer dimension at a tip end 14. The taper of the
cutting tip 20
is relatively sharp, and is preferably angled at about 20 to about 60 with
respect to an
axis of the pick 10. More preferably, the pyramidal faces 22 and the edges 24
of the
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cutting tip 20 are angled at about 300 to about 50 with respect to the axis
of the pick
10, and most preferably at about 35 with respect to the axis of the pick 10.
The tip end
14 may be pointed, blunt, or rounded, depending on the desired application. In
the
depicted embodiment, the tip end 14 of the cutting tip 20 is blunted.
[0021] The base 30 of the head portion 12 has a truncated pyramidal shape that
supports the cutting tip 20. The base 30 has a plurality of faces 32, with
each pair of
adjacent faces 32 being joined at an edge 34. The faces 32 and the edges 34 of
the
base 30 are aligned with the faces 22 and the edges 24, respectively, of the
cutting tip
20. The base 30 tapers frontwardly from a largest outer dimension at the
junction 36 to
a smallest outer dimension, matching the largest outer dimension of the
cutting tip 20,
at the junction 26. The taper of the base 30 is shallower than that of the
cutting tip 20,
and is preferably angled at about 5 to about 30 with respect to the axis of
the pick 10.
More preferably, the pyramidal faces 32 and the edges 34 of the base 30 are
angled at
between about 10 to about 20 with respect to the axis of the pick 10, and
most
preferably at about 15 with respect to the axis of the pick 10.
[0022] The shoulder 40 has a polygonal disk shape defined by a plurality of
faces
42, with each pair of adjacent faces 42 being joined at an edge 44. The faces
42 and
the edges 44 are aligned with the faces 22, 32 and the edges 24, 34,
respectively, of
the cutting tip 20 and the base 30. The shoulder 40 has an outer dimension at
least as
large as the largest outer dimension of the base 30. In the depicted
embodiment, the
outer dimension of the shoulder 40 is larger than the largest outer dimension
of the
base 30 such that a radially outer portion of a forward face 38 of the
shoulder 40 is
exposed adjacent to the junction 36.
[0023] The shank 60 has an elongated polygonal shape defined by a plurality of
faces 62, with each pair of adjacent faces 62 being joined at an edge 64. The
faces 62
and the edges 64 are aligned with the faces 22, 32, 42 and the edges 24, 34,
42
respectively, of the cutting tip 20, the base 30, and the shoulder 40. The
shank 60 is
sized to be received into a sleeve retainer within a cylindrical bore 102 of a
holder 100
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when the pick 10 is in use. The shank 60 has an outer dimension smaller than
the
outer dimension of the shoulder 40, such that when the pick 10 is installed in
the bore
102 of a holder 100, the shoulder 40 is adjacent to a front face of the holder
100 but
does not fit within the bore 102.
[0024] The frontward seat 50 provides a transition between the larger outer
dimension of the shoulder 40 and the smaller outer dimension of the shank 60,
eliminating a stress concentration that might otherwise exist should the
shoulder 40 and
the shank 60 be joined at a perpendicular junction. The seat 50 has a
truncated
pyramidal shape and has a plurality of faces 52, with each pair of adjacent
faces 52
being joined at an edge 54. The faces 52 and the edges 54 of the seat 50 are
aligned
with the faces 22, 32, 42, 62 and the edges 24, 34, 44, 64, respectively, of
the cutting
tip 20, the base 30, the shoulder 40, and the shank 60. The seat 50 tapers
rearwardly
from a largest outer dimension at the junction 46 to a smallest outer
dimension,
matching the outer dimension of the shank 60, at the junction 56. In the
depicted
embodiment, the outer dimension of the shoulder 40 is larger than the outer
dimension
of the seat 50 such that a radially outer portion of a rearward face 48 of the
shoulder 40
is exposed adjacent to the junction 46. The taper of the seat 50 is preferably
angled at
about 30 to about 60 with respect to the axis of the pick 10. More
preferably, the
pyramidal faces 52 and the edges 54 of the seat 50 are angled at about 40 to
about
50 with respect to the axis of the pick 10, and most preferably at about 45
with
respect to the axis of the pick 10.
[0025] The tail 80 has a polygonal disk shape defined by a plurality of faces
82, with
each pair of adjacent faces 82 being joined at an edge 84. The faces 82 and
the edges
84 are aligned with the faces 22, 32, 42, 52, 62 and the edges 24, 34, 44, 54,
64
respectively, of the cutting tip 20, the base 30, the shoulder 40, the seat
50, and the
shank 60. The tail 80 has an outer dimension greater than largest outer
dimension of
the shank 60, but equal to or slightly smaller than the inner diameter of the
bore 102 so
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that the edges 84 are circumscribed by the bore 102 when the pick 10 is
installed in the
holder 100.
[0026] The rearward seat 70 provides a transition between the larger outer
dimension of the tail 80 and the smaller outer dimension of the shank 60,
eliminating a
stress concentration that might otherwise exist should the tail 80 and the
shank 60 be
joined at a perpendicular junction. The seat 70 has a truncated pyramidal
shape and
has a plurality of faces 72, with each pair of adjacent faces 72 being joined
at an edge
74. The faces 72 and the edges 74 of the rearward seat 70 are aligned with the
faces
22, 32, 42, 52, 62, 82 and the edges 24, 34, 44, 52, 64, 82, respectively, of
the cutting
tip 20, the base 30, the shoulder 40, the frontward face 50, the shank 60, and
the tail
80. The seat 70 tapers frontwardly from a largest outer dimension at the
junction 76 to
a smallest outer dimension, matching the outer dimension of the shank 60, at
the
junction 66. In the depicted embodiment, the outer dimension of the tail 80 is
larger
than the outer dimension of the shank 60 such that a radially outer portion of
a forward
face 78 of the tail 80 is exposed adjacent to the junction 76. The taper of
the seat 70 is
preferably angled at about 30 to about 60 with respect to the axis of the
pick 10.
More preferably, the pyramidal faces 72 and the edges 74 of the seat 70 are
angled at
about 40 to about 50 with respect to the axis of the pick 10, and most
preferably at
about 45 with respect to the axis of the pick 10.
[0027] The pick 10 can be of any polygonal shape having at least one pair of
opposite sides that are parallel to each other, to enable the pick 10 to be
pressed into
shape. In particular, the tool pick 10 is preferably formed from cemented
carbide or
other hard material, and more preferably from cemented tungsten carbide. The
hardness of the tool pick material is preferably at least about 1200 as
measured on the
Vickers scale. The tool pick 10 is preferably formed by pressing, which is
facilitated by
having a parallel portion or flat on both sides of the pick 10 where the top
and bottom
pressing dies meet. FIG. 2 shows a side view of the tool pick 10 having a
parting line
on the parallel portion wherein the top and bottom dies met during pressing.
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[0028] Typically, but not necessarily, a polygon having at least one pair of
opposite
sides that are parallel will have an even number of sides. In the depicted
embodiment
of FIGS. 1-4, the pick 10 has a regular octagonal shape, i.e., it has eight
approximately
equal sides. Alternatively, the pick 10 can have any even number of sides
greater than
or equal to four. For example, the pick 10 can have a number of sides
including, but
not limited to, four, six, ten, or twelve. It is also understood that the
sides need not
necessarily be equal. For example, an embodiment of a tool pick may have eight
sides
that are alternately longer and shorter. It is also understood that should the
number of
sides become large, the pick will have an approximately circular cross
section.
[0029] Manufacturing the entire pick 10 from a hard material such as cemented
carbide provides a tail 80 that is more resistant to wear, which prolongs the
operating
life of the tool by keeping the retainer groove intact. In addition, a pick 10
made entirely
from carbide also does not suffer from steel wash on the head 12 of the pick
10, and
thus avoids the lost productivity and cost of wash-out. In contrast, in
conventional picks
having a steel shank with a carbide tip, the steel shank is prone to wear more
rapidly
than the carbide tip due to abrasion from cutting debris, and often enough
steel is
eroded that the steel shank can no longer support the carbide tip, causing the
tip to fall
off the steel shank prematurely. Further, in conventional picks, the steel
shank typically
includes a relatively deep socket or receptacle for holding the carbide tip,
so that only a
small portion of the cutting tip is available for cutting. Therefore, when the
socket wears
away prematurely, a large portion of the cutting tip remains unused when the
carbide tip
"washes out" or becomes detached from the steel shank. A washed-out tool
results in
lost productivity, due to the less effective cutting capability of a tool
after the cutting tip
has become detached, as well as the downtime required to replace the washed-
out
tool. But these problems do not occur with a tool pick 10 as disclosed herein,
in which
the entire pick 10 is made from carbide or other hard material.
[0030] As disclosed herein, the tool pick 10 preferably has a weight in the
range of
about 10 grams to about 60 grams, depending on the overall size of the pick 10
and the
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grade of carbide used. Tool picks 10 larger than 60 grams can readily be made
as well;
however, based on current material and manufacturing costs, a tool pick 10
weighing
equal to or less than about 60 grams is economically competitive with a
conventional
tool pick of similar size having a steel shank and a carbide tip. It is
believed that a tool
pick weight less than about 10 grams would probably have insufficient mass to
be
effective at cutting and would be relatively more prone to fracture on impact.
In one
embodiment, the tool pick 10 weighs about 40 to about 42 grams.
[0031] As shown in FIG. 5, a microtrenching machine includes a mounting wheel
110 with a disk 112 having a plurality of holders 100, each holder 100 holding
a
rotatable tool pick 10 that rotates about its own axis during operation. Each
holder 100
can be oriented so that its respectively tool pick 10 extends radially outward
from the
disk 112 or is canted at an angle to one side or the other. As the cutting tip
20 of the
pick 10 contacts the surface of the ground that is to be cut, the frictional
forces of
cutting can cause wear of the cutting tip 20 and the base 30. To maximize the
working
life of the cutting tip 20, and thus of the pick 10, continuous rotational
movement of the
pick 10 is essential. Rotation enables the cutting tip 20 to be exposed to the
ground
from all angles and thus to wear substantially uniformly around its outer
surfaces.
[0032] The polygonal faces 22 of the cutting tip 20, along with the polygonal
faces
32 of the base 30, enhance rotation of the pick 10. During operation, debris,
such as
fines, dust, grit, pebbles, dirt, and the like, is produced and pushes against
the faces
22, 32, causing the pick 10 to constantly be caused to rotate about its axis
on one
direction or another.
[0033] The polygonal shape of the shank 60 and the tail 80 also provides
advantages that cannot be obtained with a pick having a cylindrical shank.
When
mounted, the polygonal shank 60 is circumscribed within the cylindrical
retainer (not
shown) and the tail 80 is circumscribed within the cylindrical bore 102 of a
holder 100,
such that the distance between opposite edges 64 of the shank 60 is at least
slightly
less than the internal diameter of the retainer and the distance between
opposite edges
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84 of the tail is at least slightly less than the internal diameter of the
bore 102. Due to
the polygonal shape of the shank 60 and the tail 80, a clearance gap exists
between
the faces 62 of the shank 60 and the retainer and between the faces 82 of the
tail and
the bore 102, which enables fines to move freely through the bore 102 without
binding
rotation of the tool pick 10.
[0034] Although described in connection with preferred embodiments thereof, it
will
be appreciated by those skilled in the art that additions, deletions,
modifications, and
substitutions not specifically described may be made without department from
the spirit
and scope of the invention as defined in the appended claims.
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