Note: Descriptions are shown in the official language in which they were submitted.
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PICK TOOL AND METHOD FOR MAKING SAME
Background
Embodiments of the invention relate generally to pick tools comprising a
superhard tip, particularly but not exclusively degrading hard or abrasive
bodies, such as rock, asphalt, coal or concrete, for example, and to a method
for making same.
Pick tools may be used for breaking, boring into or otherwise degrading
structures or bodies, such as rock, asphalt, coal or concrete and may be used
in applications such as mining, construction and road reconditioning. For
example, in road reconditioning operations, a plurality of pick tools may be
mounted on a rotatable drum and caused to break up road asphalt as the
drum is rotated. A similar approach may be used to break up rock formations
such as in coal mining. Some pick tools may comprise a working tip
comprising synthetic diamond material, which is likely to have better abrasion
resistance than working tips formed of cemented tungsten carbide material.
However, synthetic and natural diamond material tends to be more brittle and
less resistant to fracture than cemented carbide material and this tends to
reduce its potential usefulness in pick operations. There is a need to provide
a pick tool having longer working life.
United States patent application publication number 2008/0035383 discloses
a high impact resistant tool having a superhard material bonded to a
cemented metal carbide substrate, the cemented metal carbide substrate
being bonded to a front end of a cemented metal carbide segment, which has
a stem formed in the base end, the stem being press fit into a bore of a steel
holder. The steel holder is rotationally fixed to a drum adapted to rotate
about
an axis.
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Summary
Viewed from a first aspect, there can be provided a pick tool (also referred
to
as a superhard pick tool) comprising an insert (also referred to as a pick
insert) mounted in a steel holder, the insert comprising a superhard tip
joined
to a cemented carbide support body at an end of the support body, the
support body comprising an insertion shank (also referred to simply as a
shank); the steel holder having a bore configured to accommodate the
insertion shank and comprising a shaft configured for mounting the steel
holder onto a tool carrier; such as a pick driver apparatus; the volume of the
cemented carbide support body being at least 6 cm3, at least 10 cm3 or at
least 15 cm3. The insertion shank may be shrink-fitted within the bore. The
cemented carbide may comprise cemented carbide material having a fracture
toughness of 8 to 17 MPa.m%, in which an inserted portion of the insertion
shank is secured in the bore, the inserted portion having an axial length of 4
to
8.5 cm, and a mean diameter of 2 to 3.5 cm.
Viewed from another aspect there can be provided a kit of components for the
present pick tool, the kit being in an unassembled or partly assembled state.
Viewed from a second aspect, there can be provided a method for making a
pick tool, the method including providing an insert and a steel holder for the
insert, the insert comprising a superhard tip joined to a cemented carbide
support body having an insertion shank; the steel holder comprising a shaft
for
connection to a tool carrier, and provided with a bore for receiving the
insertion shank; the insertion shank having a volume of at least 10 cm3; and
shrink fitting the insertion shank into the bore of the steel holder. The
cemented carbide support body may have a volume of at least 15 cm3 and
comprise cemented carbide material having a fracture toughness of 8 to 17
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MPa.m1/2, in which an inserted portion of the insertion shank is secured in
the
bore, the inserted portion having an axial length of 4 to 8.5 cm, and a mean
diameter of 2 to 3.5 cm.
Viewed from a third aspect, there can be provided a method of disassembling
a pick tool, the method including heating the steel holder to expand the bore
and withdrawing the insertion shank from the bore.
Brief introduction to the drawings
Non-limiting example arrangements to illustrate the present disclosure are
described hereafter with reference to the accompanying drawings, of which:
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FIG 1A shows a schematic partially cut-away side view of an example of a
pick tool.
FIG 1B shows a schematic side view of the pick insert of the example pick tool
shown in FIG 1A.
FIG 10 shows a partially cut-away perspective view of the steel holder of the
example pick tool shown in FIG 1A.
FIG 2 shows a schematic partially cut-away side view of an example of a pick
tool.
FIG 3 shows a schematic partially cut-away side view of an example of a pick
tool.
FIG 4 shows a schematic partially cut-away side view of an example of a pick
tool, in which dimensions are in millimetres.
FIG 5 shows a schematic partially cut-away side view of an example of a pick
tool, in which dimensions are in millimetres.
FIG 6 shows a schematic partially cut-away side view of an example of a pick
tool, in which dimensions are in millimetres.
FIG 7 shows a schematic longitudinal cross section view of the example of a
superhard tip and part of the support body of any one of the example pick
tools shown in FIG 1A to FIG 6.
FIG 8 shows a schematic side view of an example of a superhard tip and part
of the support body of any one of the example pick tools shown in FIG 1A to
FIG 6, in which dimensions are in millimetres and angles are in degrees.
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FIG 9 shows a schematic partially cut-away side view of an example of a pick
tool mounted to a carrier body, in which only a portion of the pick tool is
shown.
FIG 10 shows a schematic side view an example of a pick tool for a different
carrier than that illustrated in FIG 9.
FIG 11 shows a schematic partially cut-away side view of an example of a
pick tool, with a section of the steel holder in a worn-away condition.
The same reference numbers refer to the same general features in all
drawings.
Detailed description
As used herein, "superhard" means a Vickers hardness of at least 25 GPa,
and a superhard tool, insert or component means a tool, insert or component
comprising a superhard material.
Synthetic and natural diamond, polycrystalline diamond (POD), cubic boron
nitride (cBN) and polycrystalline cBN (PCBN) material are examples of
superhard materials. As used herein, synthetic diamond, which is also called
man-made diamond, is diamond material that has been manufactured. As
used herein, polycrystalline diamond (POD) material comprises a mass (an
aggregation of a plurality) of diamond grains, a substantial portion of which
are directly inter-bonded with each other and in which the content of diamond
is at least about 80 volume percent of the material. Interstices between the
diamond grains may be at least partly filled with a binder material comprising
a catalyst material for synthetic diamond, or they may be substantially empty.
As used herein, a catalyst material for synthetic diamond is capable of
promoting the growth of synthetic diamond grains and or the direct inter-
growth of synthetic or natural diamond grains at a temperature and pressure
at which synthetic or natural diamond is thermodynamically stable. Examples
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of catalyst materials for diamond are Fe, Ni, Co and Mn, and certain alloys
including these. Bodies comprising POD material may comprise at least a
region from which catalyst material has been removed from the interstices,
leaving interstitial voids between the diamond grains. As used herein, PCBN
5 material comprises grains of cubic boron nitride (cBN) dispersed within a
matrix comprising metal or ceramic material.
Other examples of superhard materials include certain composite materials
comprising diamond or cBN grains held together by a matrix comprising
ceramic material, such as silicon carbide (SiC), or cemented carbide material,
such as Co-bonded WC material (for example, as described in United States
patents numbers 5,453,105 or 6,919,040). For example, certain SiC-bonded
diamond materials may comprise at least about 30 volume percent diamond
grains dispersed in a SiC matrix (which may contain a minor amount of Si in a
form other than SiC). Examples of SiC-bonded diamond materials are
described in United States patents numbers 7,008,672; 6,709,747; 6,179,886;
6,447,852; and International Application publication number W02009/013713).
Example arrangements of pick tools for degrading hard or abrasive bodies or
structures are described with reference to FIG 1A to FIG 6.
Examples of pick tools 100 comprise an insert 110 and a steel holder 120 for
the insert 110. The insert 110 comprises a superhard tip 112 joined to a
cemented carbide support body 114 comprising an insertion shank 118. In
these examples, the insertion shanks 118 are generally cylindrical in shape
and have a mean diameter D, the superhard tips 112 comprise respective
POD structures 111 bonded to cemented carbide substrates 113, which are
joined to respective support bodies 114 at respective interfaces 115 by means
of braze material, and the support bodies 114 have generally frusto-conical
portions 116 to which the superhard tips 112 are brazed. The steel holders
120 comprise shafts 122 for connection to a pick drum device (not shown),
and a bores 126 are configured for shrink-fitting the insertion shanks 118.
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The steel holders 120 may be provided with respective insert receiver
members 124 in which the bores 126 are formed.
At least a portion of the insertion shank 118 may be secured within the bore
126 by means of a shrink fit. As used herein, a shrink fit is a kind of
interference fit between components achieved by a relative size change in at
least one of the components (the shape may also change somewhat). This is
usually achieved by heating or cooling one component before assembly and
allowing it to return to the ambient temperature after assembly. Shrink-
fitting
is understood to be contrasted with press-fitting, in which a component is
forced into a bore or recess within another component, which may involve
generating substantial frictional stress between the components.
Shrink-fitting is likely to result in a region (not indicated) of the steel
holder 120
adjacent the bore 126 being in a static state of circumferential tensile
stress.
In some examples of pick tools, a region within the steel holder adjacent the
bore may be in a state of circumferential (or hoop) static tensile stress of
at
least about 300 MPa or at least about 350 MPa, and in some pick tools, the
circumferential static tensile stress may be at most about 450 MPa or at most
about 500 MPa. As used herein, the static stress state of a tool or element
refers to the stress state of the tool or element under static conditions,
such as
may exist when the tool or element is not in use.
In some example pick tools, a portion 119 of the support body 114, including
the frusto-conical portion 116, may protrude from the steel holder 120 and
extend beyond a mouth 128 of the bore 126. In some examples, the diameter
of the protruding portion 119 along the entire length of the protruding
portion
may be at most about 5% greater, or substantially no greater than the mean
diameter D of the bore 126. In the examples illustrated in FIG 1A to FIG 6,
the diameter of the protruding portion 119 does not substantially exceed that
of the bore 126.
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In one embodiment, a collar encloses at least part of a protruding portion of
the cemented carbide support body, and in one embodiment the collar may be
shrink-fitted onto the protruding portion. In one embodiment, the collar has
lower hardness and abrasive wear resistance than cemented carbide, and in
one embodiment the collar comprises steel. In one example, the collar is
joined to the steel holder by means of brazing. The collar may provide
support or protection for the cemented carbide support body.
With reference to the example pick tool variants shown in FIG 2 and FIG 4, a
collar 130 encloses part of the protruding portion 119 of the support body
114.
The collar 130 may enclose at least part of the protruding portion 119, and in
one example the collar 130 may be shrink-fitted onto the protruding portion.
The collar 130 may have lower hardness and abrasive wear resistance than
cemented carbide and may comprise steel. In one embodiment, the collar
130 is joined to the steel holder 120 by means of brazing. The collar 130 may
provide support or protection for the cemented carbide support body 114. The
collar 130 may have various shapes, such as generally conical or generally
rounded, and it may be substantially symmetrical or non-symmetrical. At least
part of the outer surface of the collar 130 may be protected by means of a
wear protective hard facing (not shown), for example a layer or sleeve
comprising tungsten carbide. In particular, at least a part 127 of the outer
surface of the steel holder 120 adjacent the mouth 128 of the bore 126, for
example a surface region of the insert receiver member 124 extending up to
20 mm from the mouth 127, may be protected by means of a wear protective
means (not shown). Examples of such means may be a layer or sleeve
comprising tungsten carbide and / or grains of superhard material such as
diamond or cBN. In one example embodiment, the collar 130 may have a
protective hard facing disposed mainly or only on a side that would be
exposed to greater wear in use.
With reference to FIG 3, a major portion of the insertion shank 118 is secured
within the bore 126 of the steel holder 120 by means of a shrink fit. In this
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example, the insert receiver member 124 is provided with a seat 129 against
which the insertion shank 118 of the support body 114 may be positioned.
The seat 129 may be provided with a through-hole 1291 for facilitating
extraction of the insert 112 or brazing the end of if the insertion shank 118
to
the seat 129. For example, the through-hole 1291 of the seat 129 may have a
diameter S of at least about 0.6 cm and at most about 2 cm. The insert
receiver member 124 may have an outer dimension W, which may be about
4.8 cm. In general, the greater the diameter D of the insertion shank 118 of
the support body 114, the thinner the wall of the insert receiver member 124
defining the bore 126 may need to be, since the external dimensions of the
steel holder 120 may be constrained by the design of the pick apparatus (not
shown) or the requirements of the pick operation. For example, the thicker
the wall of the insert receiver member, the more robust the pick tool is
likely to
be in general, but as a trade-off, the energy requirement of the operation and
wear of the steel are likely to be higher.
In the examples illustrated in FIG 1A, FIG 2 and FIG 4, the bore 126 may
extend through the holder 120, providing a through-hole having a pair of
opposite open ends (or mouths) 128. In these examples, least a portion of the
insertion shank 118 may extend substantially through the insert receiver
member 124.
In some examples of pick tools, the ratio of the volume of the cemented
carbide support body to the volume of the superhard structure is at least
about
30, at least about 40 or at least about 50. In some embodiments, the ratio of
the volume of the cemented carbide support body to the volume of the
superhard structure is at most about 300, at most about 200 or at most about
150. In some embodiments, the volume of the superhard structure is at least
about 200 mm3 or at least about 300 mm3. In some embodiments, the volume
of the superhard structure is at most about 500 mm3 or at most about 400
3
mm.
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In some variants of pick holders, the length of the bore may be at least equal
to its diameter. In one example, the diameter of the insertion shank and the
bore may be about 2.5 cm and the length of the bore and the inserted portion
of the insertion shank may be about 6 cm; and therefore the volume of the
bore and the inserted portion of the insertion shank may be about 29 cm3 and
the area of contact between the internal peripheral surface of the bore and
the
insertion shank may be about 47 cm2. In another example, the diameter of
the insertion shank and the bore may be about 2 cm and the length of the
bore and the inserted portion of the insertion shank may be about 8.3 cm; and
therefore the volume of the bore and the inserted portion of the insertion
shank may be about 26 cm3 and the area of contact between the internal
peripheral surface of the bore and the insertion shank may about 52 cm2. In
yet another example, the diameter of the insertion shank and the bore may be
about 3.5 cm and the length of the bore and the inserted portion of the
insertion shank may be about 6.9 cm; therefore the volume of the bore and
the inserted portion of the insertion shank may be about 66 cm3 and the area
of contact between the internal peripheral surface of the bore and the
insertion
shank may be about 76 cm2.
In some examples of pick tools, the insertion shank may not be substantially
cylindrical and may exhibit any of various shapes when viewed in transverse
cross section. For example, insertion shank may be generally elliptical, egg-
shaped, wedge-shaped, square, rectangular, polygonal or semi-circular in
shape; or the cross-sectional shape of the insertion shank may vary along its
length.
In some examples, the shank may have a substantially cylindrical form and
may have a diameter of at least about 15 mm, at least about 20 mm, at least
about 25 mm or even at least 30 mm. In some embodiments, the shank has a
diameter of at most about 20 mm, at most about 25 mm, at most about 30 mm,
at most about 35 mm, or even at most about 40 mm. In some embodiments,
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the diameter of the shank varies by less than about 5 mm along its entire
length, or the diameter is substantially invariant along its entire length.
The table below summarises certain example combinations of approximate
5 dimensions that may be used with variants of pick tools disclosed herein.
The
dimensions relate to the length of the bore and the length of the inserted
portion of the insertion shank, the mean diameter of the bore and of the
inserted portion of the insertion shank, the minimum volume of the bore and
the volume of the inserted portion of the insertion shank; and the area of
10 contact between the peripheral internal wall of the bore and the
corresponding
surface of the inserted portion of the insertion shank.
a b c d e f g
Bore length / depth
L of insertion of 7.0 7.7 4.9 6.5 6 6.5 6.7
shaft, cm
Bore / insertion
shank diameter D, 2.0 2.0 2.5 2.5 2.5 3.0 3.5
cm
Volume of bore /
inserted portion of 22 24 24 32 29 46 64
shaft, cm3
Area of contact of
bore and insertion 44 48 38 51 47 61 73
shank, cm2
In some embodiments, the support body comprises a cemented carbide
material having fracture toughness of at most about 17 MPa.m1/2, at most
about 13 MPa.m1/2, at most about 11 MPa.m1/2 or even at most about 10
mpa.m1/2. In some embodiments, the support body comprises a cemented
carbide material having fracture toughness of at least about 8 MPa.m1/2 or at
least about 9 MPa.m1/2. In some embodiments, the support body comprises a
cemented carbide material having transverse rupture strength of at least
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about 2,100 MPa, at least about 2,300 MPa, at least about 2,700 MPa or even
at least about 3,000 MPa.
In some embodiments, the support body comprises a cemented carbide
material comprising grains of metal carbide having a mean size of at most
about 8 microns or at most about 3 microns. In one embodiment, the support
body comprises a cemented carbide material comprising grains of metal
carbide having a mean size of at least about 0.1 microns.
In some embodiments, the support body comprises a cemented carbide
material comprising at most about 13 weight percent, at most about 10 weight
percent, at most about 7 weight percent, at most about 6 weight percent or
even at most about 3 weight percent of metal binder material, such as cobalt
(Co). In some embodiments, the support body comprises a cemented carbide
material comprising at least about 1 weight percent, at least about 3 weight
percent or at least about 6 weight percent of metal binder.
In some examples, the support body may consist essentially of, or consist of
cemented carbide material.
In some examples of pick tools, the shrink-fitting of the components may be
reversible and the steel holder and / or the insertion shank may be detached
and reused, which may in effect reduce the cost of the pick tool and permit
extended use of the steel holder. This could be achieved by heating the steel
holder in the vicinity of the bore to cause it to expand relative to the
cemented
carbide insertion shank, permitting the insertion shank to be removed from the
bore.
A method for making a pick tool is provided, the method including providing a
pick insert comprising a superhard tip joined to a cemented carbide support
body at an end of the support body, the support body comprising a shank
(insertion shank); providing a steel holder having a bore configured to
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accommodate the shank and comprising a shaft suitable for mounting the
holder onto a tool carrier; and shrink-fitting the shank into the bore of the
steel
holder. The insertion shank may be shrink-fitted into the bore of the steel
holder by heating at least the part of the steel holder including the bore to
a
temperature of about 350 degrees centigrade, inserting the shank into the
bore of the heated holder and allowing the bore of the steel holder to cool
and
shrink, thereby holding the insertion shank in compression. In examples
where the steel holder comprises a seat, the insertion shank may be inserted
all the way into the bore so that the inserted end abuts the seat.
The interference between the insertion shank and the bore of the holder is the
difference in size between them, which may be expressed as a percentage of
the size. For example, in embodiments where the insertion shank (and the
bore) has a generally circular cross section, the interference may be
expressed as the difference in diameter as a percentage of the diameter. The
dimension between the insertion shank and the bore would be expected to be
selected depending at least on the diameter of the insertion shank, and may
be at least about 0.002 percent of the diameter of the insertion shank. In one
example, the diameter of the insertion shank is about 2.5 cm and the
interference between the insertion shank and the bore is about 0.08 percent
of the diameter of the insertion shank. The interference between the insertion
shank and the bore may be at most about 0.3 percent of the diameter of the
diameter of the insertion shank. If the interference is too great, the elastic
limit
of the steel material of the holder may be exceeded when the steel holder is
shrink-fitted onto the onto the insertion shank, resulting in some plastic
deformation of the steel adjacent the bore. If the interference is not high
enough, then the shrink fit may not be sufficient for the insert to be held
robustly by the holder in use.
In some versions of the method, the precise dimensions of the insertion shank
and the bore may be selected such that after shrink-fitting the insertion
shank
into the bore, a region within the steel holder adjacent the bore is in a
state of
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circumferential (or hoop) static tensile stress of at least about 300 MPa or
at
least about 350 MPa. In some embodiments, a region within the steel holder
adjacent the bore is in a state of circumferential (or hoop) static tensile
stress
of at most about 450 MPa or at most about 500 MPa.
As a non-limiting example, a pick tool as disclosed may comprise a superhard
tip as described in United States patent application publication numbers
2009/0051211; 2010/0065338; 2010/0065339 or 2010/0071964. With
reference to FIG 7, an example of an insert for an embodiment of a pick tool
as disclosed herein comprises a superhard tip 112 comprising a superhard
structure 111 in the general form of a cap bonded to a cemented carbide
substrate 113. The superhard tip 112 is joined to a frusto-conical portion 116
of a support body 114. The major part of the superhard structure 111 has a
spherically blunted conical outer shape, having a rounded apex 1111 with a
radius of curvature in a longitudinal plane, and a cone angle x between an
axis parallel to the longitudinal axis AL and conical portion 1112 of the
outer
surface of the superhard structure 111. The
superhard structure 111
comprises a nose region 1113 and a skirt region 1114, which depends
longitudinally and laterally away from the nose region 1113. In some versions
of the example, the minimum longitudinal thickness of the skirt region 1114
may be at least about 1.3 mm or at least about 1.5 mm. In some versions of
the example, the longitudinal thickness of the superhard cap 111 at the apex
1111 is at least about 4 mm or at least about 5 mm and at most about 7 mm
or at most about 6 mm. In one version of the example, the longitudinal
thickness of the superhard structure 111 at the apex 1111 is in the range from
about 5.5 mm to 6 mm. In some versions of the example, the radius of
curvature of the rounded apex 1111 is at least about 2 mm and at most about
3 mm. In some embodiments, the cone angle x is at most 80 degrees or at
most 70 degrees. In some versions of the example, the cone angle x is at
least 45 degrees or at least 50 degrees.
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With reference to FIG 8, an example of an insert for an embodiment of a pick
tool as disclosed comprises a superhard tip 112 comprising a superhard
structure 111 bonded to a cemented carbide substrate 113. The superhard tip
112 is joined to a frusto-conical portion 116 of a support body 114. The
radius
of curvature R of the spherically blunted cone nose 1111 is about 2.25 mm
and the cone angle x is about 42 degrees.
With reference to FIG 9, a part of an example of a steel holder 120 for a pick
tool as disclosed is attached to a base block 200 (carrier body) by means of
an interlocking fastener mechanism 210 in which the shaft 122 of the steel
holder 120 is locked within a bore formed within the carrier body 200. Part of
the insertion shank 118 of an example pick tool is also shown. The shaft 122
may be releasibly connectable to the base block 200 welded or otherwise
joined to the drum. The base block 200 and holder 120, more specifically the
shaft 122, may be configured to permit releasable inter-engagement of the
steel holder 120 and base block. The shaft 122 may be configured to inter-
engage non-rotationally with a base block, and may be suitable for use with
tool carriers disclosed in German patents numbers DE 101 61 713 B4 and DE
10 2004 057 302 Al, for example. The tool carrier, such as a base block,
may be welded onto a component of a drive apparatus, such as a drum, for
driving the superhard pick tool. FIG 10 shows a side view of a pick tool 100
for a different tool carrier than the example illustrated in FIG 9, the shaft
122
of the steel holder 120 being configured differently. The pick tool 100
comprises an insert 110 with a superhard tip 112 joined to a portion 116 of a
support body.
A method is provided for attaching a superhard pick tool to a tool carrier
joined
to a component for a drive apparatus, the method including joining a pick
insert to a steel holder to form a pick tool, the steel holder comprising a
shaft
configured operable to attach the steel holder onto the tool carrier, the tool
carrier comprising an engagement means configured to receive the shaft of
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the steel holder; and then attaching the superhard pick tool to the tool
carrier.
In one embodiment of the method, the tool carrier is welded onto a component
of a drive apparatus, such as a drum, for driving the superhard pick tool.
5 In
operation, the pick tool may be driven forward by a drive apparatus on
which it is mounted, against a structure to be degraded and with the
superhard tip at the leading end. For example, a plurality of pick tools may
be
mounted on a drum for asphalt degradation, as may be used to break up a
road for resurfacing. The drum is connected to a vehicle and caused to rotate.
10 As the
drum is brought into proximity of the road surface, the pick tools are
repeatedly impacted into the road as the drum rotates and the leading
superhard tips thus break up the asphalt. A similar approach may be used to
break up coal formations in coal mining.
15 With
reference to FIG 11, the example pick tool illustrated in FIG 5 is shown
schematically in a worn condition, in which a part 1201 of the steel holder
120
has been worn away in use to expose part of the surface of the insertion shaft
118 to which that part 1201 had been adjacent.
Although the example pick tool illustrated in FIG 11 is shown in a worn
condition, some example pick tools may be provided with a cut-away portion
1201 prior to use. In this configuration, the insertion shank 118 is only
partially surrounded by the bore 126 at a range of axial positions R along the
length L of the insertion shank 118 (i.e. within the range R of axial
positions,
the insertion shank 118 is not entirely surrounded or enclosed by the steel
holder 120).
When designing pick tools for highly abrasive operations such as asphalt, coal
or potash degradation, it would be desirable to achieve a balance between the
cost of the tool and its resistance to abrasive wear and fracture in use.
Superhard materials such as synthetic diamond tend to be much more
abrasion resistant but also much more costly than cemented carbide materials,
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which in turn tend to be much more abrasion resistant but much more costly
than steel materials. One approach may be to minimise the amounts of
diamond-containing and cemented carbide materials in the tool according to
their relative costs and to configure components comprising these materials
so as to achieve an acceptable tool life.
A cemented carbide support body having a relatively large volume of at least
about 6 cm3, at least about 10 cm3 or at least about 15 cm3 arranged behind
the POD tip in the direction of movement in use and extending relatively
deeply into the steel holder seems to improve the working life of the tool to
a
surprising degree that is likely to justify additional cost of the carbide
material.
While wishing not to be bound by a particular theory, the high density and
relatively high mass of the carbide insertion shank, as well as its high
stiffness
may provide substantially improved support for the POD tip by tending to
resist deformation or bending of the tip when it is thrust against the
structure
being broken. The carbide insertion shank may be viewed as forming a spine-
like structure extending relatively deeply into the steel holder. The elongate
carbide insertion shank may also function as a stiffening spine extending into
the steel holder and making it more robust.
It has been found that a superhard-tipped pick tool having the combination of
a relatively large insertion shank and a shrink-fit connection of the
insertion
shank within the steel holder exhibits a extended working life in an asphalt
degradation operation. If the volume of the inserted portion of the insertion
shank is less than about 6 cm3, less than about 15 cm3, or even less than
about 15 cm3, there may be insufficient support for the superhard tip in
operation; and if the interface area between the insertion shank and the bore
is less than about 20 cm2, the carbide support body may not be sufficiently
robustly gripped by the steel holder into which it is shrink-fitted. If the
diameter of the insertion shank is less than about 2 cm, it may not provide
adequate support and robustness for the tool, which may break in particularly
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harsh operations, and / or the steel holder may wear excessively. If the
length
of the support body is less than about 4 cm, it may not provide sufficient
support for the steel holder and / or the POD tip, which may fracture
prematurely.
In pick tools disclosed herein, in which the volume of the insertion shank and
the bore as well as the area of contact between them are relatively high,
shrink-fitting the insertion shank into the steel holder may have benefits
over
press-fitting. Considerably less force would be required to shrink fit the
relatively large insertion shank than would be needed to press it into the
bore.
This may have the aspect that the insert can be held securely enough within
the bore of the steel holder without the elastic limit of the steel material
being
substantially exceeded, thereby reducing plastic deformation of the steel
holder. While wishing not to be bound by a particular theory, this may have
the aspect that a region of the steel holder adjacent the bore may suffer less
deformation and axial stress arising from the pressing force and friction
between the insertion shank and the bore surface. The insertion shank may
also have reduced residual stress components, which may result in greater
resistance to fracture in use. As a trade-off, shrink-fitting may require
somewhat more sophisticated equipment and procedure.
Shrink-fitting may permit reduced reliance on brazing to join the insert to
the
steel holder. This may be particularly useful where the superhard tip
comprises synthetic or natural diamond, for example polycrystalline diamond,
because of reduced thermal degradation of the tip as a result of brazing,
which requires the use of high temperature (diamond, particularly in POD form,
tends to have a relatively low thermal stability and to convert into graphite
at
high temperatures). Additionally, brazing may need to be carried out in a
special furnace and a special atmosphere, which may not be required for
shrink fitting.
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Example pick tools are provided. The following clauses are offered as further
descriptions of the disclosed pick tools.
1. A superhard pick tool (for brevity, also referred to as a pick tool)
comprising an insert and a steel holder for the insert, the insert comprising
a superhard tip joined to a cemented carbide support body having an
insertion shank; the steel holder comprising a shaft for connection to a tool
carrier and the steel holder provided with a bore configured for receiving
the insertion shank; the volume of the cemented carbide support body
being at least 6 cm3, at least 10 cm3 or at least 15 cm3.
2. A pick tool comprising an insert and a steel holder for the insert, the
insert
comprising a superhard tip joined to a cemented carbide support body
having an insertion shank; the steel holder comprising a shaft for
connection to a tool carrier and the steel holder provided with a bore
configured for receiving the insertion shank; an inserted portion of the
insertion shank being secured in the bore; the inserted portion having an
axial length and a mean diameter; the axial length being no less than the
mean diameter.
3. The pick tool of clause 2, in which the axial length of the inserted
portion is
at least about 4 cm and at most about 8.5 cm.
4. The pick tool of clause 2 or clause 3, in which the mean diameter of the
inserted portion is at least about 2 cm and at most about 3.5 cm.
5. A pick tool comprising an insert and a steel holder for the insert, the
insert
comprising a superhard tip joined to a cemented carbide support body
having an insertion shank; the steel holder comprising a shaft for
connection to a tool carrier and the steel holder comprising an insert
receiver member provided with a bore configured for receiving the
insertion shank; an inserted portion of the insertion shank being secured in
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the bore and abutting a surface area of the bore; the magnitude of the
abutted surface area being greater than the magnitude of the volume of
the inserted portion.
6. The pick tool of clause 5, in which the magnitude of the abutted surface
area is at least about 20 cm2 and the volume of the inserted portion is at
least about 15 cm3.
7. The pick tool of any one of the preceding clauses, in which the insertion
shank is shrink-fitted within the bore.
8. A superhard pick tool (for brevity, also referred to herein simply as "pick
tool") comprising a pick insert mounted to a steel holder, the pick insert
(for brevity, also referred to herein simply as "insert") comprising a
superhard tip joined to a cemented carbide support body at an end of the
support body, the support body comprising a shank (also referred to herein
as "insertion shank"); the steel holder having a bore configured to
accommodate the insertion shank and comprising a shaft configured for
mounting the holder onto a tool carrier; the shank being shrink fitted within
the bore of the steel holder.
9. The pick tool of any one of the preceding clauses, in which the insertion
shank (shank) has a volume of at least 15 cm3.
10.The pick tool of any one of the preceding clauses, in which a surface area
of the insertion shank abuts a corresponding inner peripheral (side)
surface area of the bore, the surface area being at least 20 cm2.
11 .The pick tool of any one of the preceding clauses, in which the insertion
shank has a diameter (or a mean diameter) of at least 1.5 cm or at least 2
cm and at most 4.0 cm or at most 3.5 cm.
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12.The pick tool of any one of the preceding clauses, in which the lengths of
the insertion shank and the bore are each at least about 4 cm.
13.The pick tool of any one of the preceding clauses, in which the ratio of
the
5 volume of the cemented carbide support body to the volume of the
superhard tip is at least 30 and at most 300, and the volume of the
superhard tip is at least 200 mm3 and at most 500 mm3.
14.The pick tool of any one of the preceding clauses, in which the volume of
10 the superhard structure is least 0.2 cm3.
15.The pick tool of any one of the preceding clauses, in which at least a
portion of the insertion shank is substantially cylindrical in shape.
15 16.The pick tool of any one of the preceding clauses, in which the bore
has a
length that is at least equal to its diameter.
17.The pick tool of any one of the preceding clauses, in which the
interference
between the insertion shank and the bore is at least about 0.002 percent
20 of the diameter of the insertion shank and at most about 0.3 percent of
the
diameter of the diameter of the insertion shank.
18.The pick tool of any one of the preceding clauses, in which a region of the
steel holder adjacent the bore is in a state of circumferential (or hoop)
static tensile stress of at least about 300 MPa and at most about 500 MPa.
19.The pick tool of any one of the preceding clauses, in which the diameter of
the insertion shank varies by less than about 5 mm along its entire length,
or the diameter, and is substantially invariant along its entire length.
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20.The pick tool of any one of the preceding clauses, in which a portion of
the
insertion shank is only partly surrounded by the bore of the steel holder (at
a range of axial positions along the length of the insertion shaft).
21 .The pick tool of any one of the preceding clauses, in which the steel
holder
is provided with a seat for supporting an end of the cemented carbide
support body. The bore may communicate with the outside of the steel
holder through a passage or aperture provided through or adjacent the
seat.
22.The pick tool of any one of the preceding clauses, in which the bore
extends through the holder, providing a through-hole having a pair of open
ends.
23.The pick tool of any one of clauses 1 to 21, in which the bore is
substantially closed at one end.
24.The pick tool of any one of the preceding clauses, in which a portion of
the
cemented carbide support body protrudes from the steel holder and
extends beyond a mouth of the bore.
25.The pick tool of clause 24, in which the diameter of the protruding portion
of the cemented carbide support body along the entire length of the
protruding portion is at most 5% greater than the diameter of the mouth of
the bore from which it protrudes.
26.The pick tool of clause 24, comprising a collar enclosing or surrounding at
least part of the protruding portion.
27.The pick tool of any one of the preceding clauses, in which the insertion
shank has a diameter of at least about 15 mm, at least about 20 mm, at
least about 25 mm or even at least 30 mm (in some embodiments, the
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insertion shank may have a diameter of at most about 20 mm, at most
about 25 mm, at most about 30 mm, at most about 35 mm, or even at
most about 40 mm).
28. The pick tool of any one of the preceding clauses, in which the superhard
tip comprises natural or synthetic diamond material or cBN material.
29. The pick tool of any one of the preceding clauses, in which the superhard
tip comprises a polycrystalline diamond structure bonded to a cemented
carbide substrate.
30. The pick tool of any one of the preceding clauses, in which the superhard
tip comprises diamond grains dispersed in a matrix comprising SiC
material, or diamond grains dispersed in a matrix comprising cemented
carbide material.
31. The pick tool of any one of the preceding clauses, in which the cemented
carbide support body comprises cemented carbide material having fracture
toughness of at least 8 MPa.m1/2 and at most 17 MPa.m1/2.
32. The pick tool of any one of the preceding clauses, in which the cemented
carbide support body comprises cemented carbide material comprising at
most 13 weight percent and at least 1 weight percent metal binder material.
33. The pick tool of any one of the preceding clauses in which the support
body comprises superhard material (for example, the support body may
comprise diamond or cBN grains dispersed within a cemented carbide
matrix).
34. The pick tool of any one of the preceding clauses, for pavement or road
degradation, or for coal or potash mining.
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35. The pick tool of any one of the preceding clauses, in which the tool
carrier
is welded or weldable onto a component of a drive apparatus, such as a
drum, for driving the superhard pick tool.
36. The pick tool of any one of the preceding clauses, in which the tool
carrier
comprises or is connectable to a drive or drivable apparatus.
37.A method for making a pick tool of any one of the preceding clauses, the
method including providing an insert and a steel holder for the insert, the
insert comprising a superhard tip joined to a cemented carbide support
body having an insertion shank; the steel holder comprising a shaft for
connection to a tool carrier and the steel holder provided with a bore for
receiving the insertion shank; the insertion shank having a volume of at
least 6 cm3, at least 10 cm3 or at least 15 cm3; and shrink fitting the
insertion shank into the bore of the steel holder.
38. The method of clause 37, including selecting the interference between the
insertion shaft and the bore such that after shrink-fitting the insertion
shaft
into the bore, a region within the steel holder adjacent the bore is in a
state
of circumferential static tensile stress of at least about 300 MPa and at
most about 500 MPa, or substantially below the elastic limit of the steel
material comprised in the steel holder.
A non-limiting example of a pick tool is described in more detail below.
A superhard tip comprising POD integrally attached to a cobalt-cemented
tungsten carbide (Co-WC) substrate as illustrated in FIG 8 was brazed to a
support body. The POD structure had a volume of about 382 mm3. The
support body was formed of Co-WC comprising about 13 weight percent Co
and having a fracture toughness of about 16.3 MPa.m1/2 and transverse
rupture strength (TRS) of about 2,200 MPa. In another example, the support
body was formed of Co-WC comprising about 8 weight percent Co and having
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a fracture toughness of about 14.6 MPa.m1/2 and transverse rupture strength
(TRS) of at about 2,800 MPa. The support body comprised a substantially
cylindrical insertion shank and a frusto-conical end portion to which the POD
tip was brazed. The insertion shank had a surface finish in the range from
about 0.04 microns Ra to about 0.5 microns Ra. The diameter of the insertion
shank was 2.5 cm and its length was 6.7 cm.
A steel holder formed of 420r-Mo4 grade of steel and comprising an insertion
receiver member with a bore was provided, the diameter of the bore being
about 2.5 cm and its length being about 6.7 cm. An annular seat was
provided at the bottom end of the bore. The insertion shank was shrink-fitted
into the bore of the steel holder by heating the insertion receiver member of
the steel holder in air to a temperature of about 350 degrees centigrade,
inserting the shaft into the bore of the heated holder and allowing the
insertion
receiver member to shrink onto the insertion shank, thereby holding it in
compression. The insertion shank was inserted all the way into the bore so
that the inserted end abutted the annular seat. The volume of the inserted
portion of the insertion shank was therefore about 33 cm3 and the interface
area between the insertion shank and the peripheral internal wall of the bore
was about 53 cm2. The interference between the insertion shank and the
bore was about 0.02 mm and the static tensile hoop stress of the region of the
steel holder adjacent the bore was estimated to be in the range from about
300 MPa to about 500 MPa.
Pick tools according to the present example have been tested in road
reconditioning operations, in which they were mounted onto drums and used
to degrade road asphalt. These were still in working condition after degrading
at least about 20 km of road.
Various example embodiments of pick tools and methods for assembling and
connecting them have been described above. Those skilled in the art will
CA 02787541 2014-01-16
understand that changes and modifications may be made to those examples
without departing from the scope of the claimed invention.
