Note: Descriptions are shown in the official language in which they were submitted.
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Metal matrix composite mining pick and method of making
Field of the Invention
The present invention relates to mining picks used
for mining and excavation purposes, and particularly but
not exclusively to a mining pick that has a relatively low
propensity to ignite a flammable substance adjacent the
pick when used.
Background of the Invention
Various different forms of equipment and machinery
can be employed for mining and excavation operations, such
as long wall miners. The present invention is principally
concerned with underground coal mining and one of the
major safety difficulties in that type of mining relates
to fires or explosions within the mine. These can occur
due to the generation during mining of methane gas and
coal dust (commonly known as mine dust), which can be
trapped within the mine and is readily ignitable.
Disadvantageously, the equipment used in coal mining can
generate heat and/or incendive sparks that may initiate a
fire or explosion, especially from frictional contact with
coarse grained quartz containing lithologies. Therefore,
it is important that all appropriate steps be taken to
minimize or eliminate the risk of ignition.
Equipment used to mine or excavate in hard earth can
include rotary cutters, in which a rotating drum that
carries a plurality of projecting cutting bits or picks,
is brought into engagement with an earth face. The picks
bite into the earth face as they rotate with the drum, to
impact against and to dislodge or fragment earth from the
face. This highly aggressive engagement between the picks
and the earth face can generate heat and/or sparks.
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Pr i or art picks employed for the above purpose
generally have a hard cemented tungsten carbide tip that
is fixed, usually by brazing, to a steel shank. Sparks
can be produced between the tungsten carbide tip and the
earth face and also between the steel shank and the earth
face, although there typically is greater likelihood of
spark production between the shank and the earth face.
Summary of Invention
Some embodiments of the present invention may be used
in underground coal mining. It will therefore be
convenient to describe the invention in relation to that
use although it will be readily appreciated that the
invention could be employed for any mining or excavation
operation to which its function is suitable.
According to a first aspect of the invention there is
provided a mining pick, the pick comprising:
a body;
at least part of the body being formed of a metal
matrix composite comprising particles dispersed in a
metal;
a cutting element mounted to the body;
a shank extending from the body;
the at least part of the body formed of the metal
matrix composite being configured to provide a barrier
during an excavation operation.
In an embodiment, the at least part of the body
formed of the metal matrix composite is configured to
provide a barrier disposed adjacent to a distal end of the
body, the barrier protecting at least a portion of the
mining pick disposed between the barrier and a proximal
end of the shank. The barrier may protect the shank.
In an embodiment, the at least part of the body
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f ormed of the metal matrix composite is configured to
provide a barrier after the cutting element fails.
In an embodiment, the at least part of the body
formed of the metal matrix composite forms an exterior
surface of the body adjacent the cutting element. The
exterior surface may encircle the cutting element.
In an embodiment, the metal matrix composite has a
lower propensity to cause ignition of a flammable
substance adjacent the body during excavation than a
material of the shank. The material of the shank may
comprise a steel, or any other suitable material
In an embodiment, the metal matrix composite has less
propensity to cause ignition of a flammable substance
adjacent the body during excavation than a material of the
cutting element.
In an embodiment, the metal matrix composite has less
propensity to cause ignition of a flammable substance
adjacent the body during excavation than cemented carbide.
In an embodiment, the particles have a hardness
greater than 1000 Hardness Vickers and a modulus greater
than around 200 Gigapascals. The particles may have a
thermal conductivity lower than around 100 W/m/C).
In an embodiment, the metal has a hardness and a
modulus less than the particles. The metal may have a
thermal conductivity greater than around 100 W/m/C).
In an embodiment, the particles constitute between
20% and 90% by volume of the metal matrix composite.
In an embodiment, the metal constitutes between 10%
and 80% by volume of the metal matrix composite.
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I n an embodiment, the particles in the metal matrix
composite are tungsten carbide. The tungsten carbide
particles may constitute around 60% by volume of the metal
matrix composite.
In an embodiment, the particles comprise steel.
In an embodiment, the metal comprises copper, silver
and zinc. The metal may comprise 65% to 75% by volume
copper, 5% to 15% by volume silver and 15% to 25% by
volume zinc.
In an embodiment, the metal is copper.
In an embodiment, the metal matrix composite
comprises at least one of tungsten carbide, vanadium,
chromium, silicon, boron, a carbide forming element, a
metal carbide, copper, zinc, manganese, tin, iron, and
silver.
In an embodiment, the metal matrix composite
constitutes the body. The shank may have an end embedded
in the metal matrix composite. Alternatively, the metal
matrix composite constitutes both the body and the shank.
The shank may be integral with the body.
In an embodiment, the cutting element is mechanically
attached to the metal matrix composite. At least one
transverse dimension of at least some of the cutting
element may increase in a direction inward of the body.
The at least some of the cutting element may be embedded
in the metal matrix composite.
In an embodiment, the cutting element is
metallurgically attached to the metal matrix composite.
The cutting element may be attached to the metal matrix
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c omp osite by a metallurgical high temperature braze.
In an embodiment, the cutting element is attached to
the metal matrix composite by a sintered bond.
In an embodiment, a portion of the cutting element is
embedded in the metal matrix composite.
In an embodiment, the cutting element comprises
thermally stable silicon carbide diamond composite (SCDC).
The cutting element may have a surface bonded to a product
of a reaction of a metal with the SCDC. The product may
be bonded to the metal matrix composite.
In an embodiment, the body comprises a plurality of
monoliths. The monoliths may comprise at least one of
diamond, cermet, ceramic, and cemented carbide. The
plurality of monoliths may be embedded in a plurality of
carbide containing pellets which are imbedded in the metal
matrix compound. The plurality of monoliths may be
disposed adjacent the exterior surface of the body near
the cutting element.
In an embodiment, the body comprises at least two
portions, each portion having a respective metal matrix
composite, one of the metal matrix composites having a
composition that is different to that of the other metal
matrix composite. One of the portions may be disposed at
a distal end of the body. Another of the at least two
portions may be disposed at a proximal end of the body.
One of the portions may be disposed is a pocket formed in
another of the at least two portions. The pocket may have
the cutting element disposed therein.
In an embodiment, the body comprises a ring of
material encircling the cutting element, the ring having
an equal or lesser hardness than that of the cutting
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e 1 ement and greater than that of the metal matrix
composite.
In an embodiment, the body has a portion disposed at
a distal end comprising a metal matrix composite and
another portion disposed at a proximal end comprising a
steel. The portion comprising a steel may be integral
with the shank.
In an embodiment, the mining pick is configured as a
point attack pick.
In an embodiment, the mining pick is configured as a
radial attack pick.
In an embodiment, the mining pick is configured to
couple to a mining apparatus by a pair of cooperating
elements that engage when the mining pick and the mining
apparatus are so coupled, each of the pair of elements
being disposed on one of the shank and apparatus
respectively.
According to a second aspect of the invention there
is provided a method of making a mining pick, the method
comprising the steps of:
disposing a powder used in the manufacture of a metal
matrix composite in a mould of complementary shape to at
least a portion of a body of a mining pick;
heating the powder to a temperature for a period of
time to form the metal matrix composite that has the shape
of the at least the portion of the body.
Brief description of the Figures
Features and advantages of the present invention will
become apparent from the following description of
embodiments thereof, by way of example only, with
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reference to the accompanying drawings, in which:
Figure 1 shows a side elevation view of an embodiment
of a mining pick in accordance to an aspect of the
invention;
Figure 2 shows a cross section through a cutting
element bonded to a metal matrix composite body via a
product of a reaction, in accordance with an embodiment of
an aspect of the invention;
Figure 3 shows a cross section through an example of
a cutting element that is mechanically attached to a
respective body in accordance with an embodiment of an
aspect of the invention;
Figure 4 shows a cross section through a cutting
element and respective body wherein the body comprises a
plurality of very hard monoliths in accordance with an
embodiment of an aspect of the invention;
Figure 5 shows a cross section through a cutting
element and a respective body having a continuous ring of
very hard material, such as cemented carbide, encircling
the cutting element in accordance with an embodiment of an
aspect of the invention;
Figure 6 shows a side elevation view of an embodiment
of a mining pick having a body comprising first and second
portions, each portion having a respective metal matrix
composite in accordance with an embodiment of an aspect of
the invention;
Figure 7 shows a side elevation view of an another
embodiment of a mining pick having a body comprising first
and second portions, each portion having a respective
metal matrix composite in accordance with an embodiment of
an aspect of the invention;
Figure 8 shows a side elevation view of another
embodiment of a mining pick have a body comprising steel
and metal matrix composite in accordance with an aspect of
the invention; and
Figure 9 is a graph showing probability curves of two
embodiments of a mining pick having respective metal
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matrix body portions causing ignition in comparison to a
prior art mining pick, over the respective lives of the
picks.
Detailed Description of embodiments of the invention
Figure 1 shows a side elevation view of an embodiment
of a mining pick generally indicated by the numeral 10.
This embodiment is symmetric around a central axis. The
pick has a body 12. In this embodiment the body 12 is
formed of a metal matrix composite comprising particles
dispersed in a metal. In some other embodiments, however,
only a part of the body is formed of the metal matrix
composite.
The pick 10 of this embodiment has at a distal end
thereof 22 a cutting element 14 configured to cut,
fracture, wear, plough or otherwise remove material from a
formation in use. Examples of formations include
geological formations such as a body of coal, and man made
structures. The cutting element 14 is in the form of an
insert or tip having a ballistic shape. It will be
appreciated that any suitable cutting element may be used.
In this embodiment, a portion of the insert is disposed in
a pocket 22 formed at a distal end 15 of the pick body 12.
The pocket is indicated by dashing. The insert 14 is
attached to the side and/or bottom walls of the pocket.
The pick has at a proximal end 13 a shank 16
extending from a proximal end 26 of the body 12. The shank
is one of by a pair of cooperating elements that engage
when the pick and the rotary drum of the mining machine
are coupled. The other of the pair of elements is disposed
on the rotary drum. The shank includes a recess 18. A
clip engages the shoulders of the recess to retain the
pick at the drum. A portion of the shank is embedded in
the metal matrix composite body and this portion is
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i nd i cat ed by dashing. In this embodiment the shank
comprises an air hardening steel and is joined to the
metal matrix composite by a high temperature braze,
although the shank may be formed of any suitable material.
In another embodiment, the metal matrix composite
constitutes both the body and the shank, and the shank is
integral with the body (as would be represented by figure
1 if the dashed triangle with a round apex, in that
figure, was deleted). A pick embodiment having a body and
a shank made from a contiguous metal matrix composite may
have less steps during its manufacture than that of a pick
embodiment having a body and shank separately formed and
subsequently joined.
The mining pick 10 is configured as a point attack
mining pick, however it will be appreciated that
alternative embodiments may be configured as a radial
attack mining pick.
In the embodiment of Figure 1, the cutting element 14
is formed of a cemented carbide comprising tungsten
carbide particles dispersed in metallic cobalt
(alternatively metallic nickel or metallic iron, for
example), and the body 12 is formed from a metal matrix
composite comprising around 60% by volume tungsten carbide
particles dispersed in a metal. The metal of this
embodiment comprises around 70% by volume copper, 10% by
volume silver and 20% by volume zinc. Five other examples
of compositions of a metal for use in forming a matrix
composite are listed in Table 1, although it will be
appreciated that there are many other compositions not
listed in the table.
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Table 1. Some alternative metal compositions by volume %.
Cu Zn Mn Ni Ag Sn Pb
1 60-95 40-5 (<10) (<10)
2 60-95 40-5 (<10) (<10)
3 60-95 30-5 10-0 (<10) (<10)
4 60-95 20-5 10-0 10-0 (<10) (<10)
60-95 35-5 (<10) (<10)
5 The applicant has unexpectedly found that the body
12, comprising the metal matrix composite, did not produce
a spark on contact with a workshop grinder wheel rotating
at high speed. The wheel comprises resin bonded ceramic.
The wheel simulates an environment that is more severe
than that typically experienced by the pick 10 during
excavation. Contact between the cemented carbide cutting
tip 14 and the wheel, however, produced sparks. Contact
between the steel shank 16 with the wheel produced a
proliferation of sparks. The applicant has also found
that a metal matrix composite body comprising steel
particles dispersed in cooper also has a low propensity to
spark. This was very much unexpected especially in light
of the fact that steel generally has a propensity to
spark.
The reason for the particularly low propensity of the
metal matrix composite body to produce a spark is not
known by the applicant definitively, however the applicant
is of the opinion that the metal within the metal matrix
composite may act as a contiguous path for the flow of
heat away from the point of contact and so prevent the
build up of heat and sparking.
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In use, the tip 14 engages the formation. Fragments
cut from the formation may contact the metal matrix
composite exterior surface 20 disposed at a distal end 15
of the body adjacent the cutting element 14. The exterior
surface 20 encircles the cutting element 14. The metal
matrix composite surface 20 acts as a barrier against the
fragments, protecting at least a portion of the mining
pick disposed between the barrier 20 and a proximal end 17
of the shank 16. Even if some of the surface 20 is worn
away a barrier is still provided by the exposed metal
matrix composite. If the cutting element penetrates the
formation deeply and the body is dragged across the
formation the surface 20 will provide a barrier against
the formation.
As described, the metal matrix composite barrier has
a relatively lower propensity to spark and contact of the
fragments with the exterior surface 20 is unlikely to
produce a spark. Typically the barrier 20 greatly reduces
the chance of a fragment striking the shank 16, or any
other component of the pick that may present an ignition
risk, for example.
The distal end 26 of the body is wider than the shank
16, and thus the barrier provides a region protected from
fragments that encompass more than the shank. In the
embodiment of Figure 1 the protected region is around 1.3
times the width of the shank. Other embodiments have a
protected area width of 3 times the width of the shank.
By way of contrast, prior art mining picks,
particularly those having a body formed of steel, may heat
up and/or spark during excavation. Hot and/or sparking
picks have been known to ignite methane and/or coal dust
in mines. Thus, use of the pick embodiment of figure 1
instead of a prior art pick may greatly reduce the
incidence of friction induced ignition during excavation
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which is very dangerous in a mine, for example.
It is not uncommon during excavation for a cutting
element to fail. For example, the element 14 may shear
off adjacent the surface 20 or become dislodged from the
pocket 22. In this case, the surface 20, which now may
extend to include the surface of the pocket 22, provides a
wear resistant barrier with a low propensity to ignite a
flammable material. Even if the body is subsequently
dragged across the formation it is unlikely that this
would cause ignition.
In prior art devices, the fragments may wear the body
or shank so that the pick becomes unusable before the tip
wears out. The barrier, being much harder than steel, for
example, may protect the shank and/or other parts of the
pick 10 from fragments which may otherwise cause the pick
to reach the end of its working life prematurely. In
contrast, the use of a super or ultra hard insert within a
metal matrix body provides extended tool life and
productivity.
It will be appreciated that in an embodiment, the
shank and body may both be formed of a metal matrix
composite.
Some properties of metal matrix composites that may
form at least part of a pick having a low propensity to
cause ignition will now be described. The particles may
have hardness greater than 1000 Hardness Vickers and a
modulus greater than around 200 Gigapascals. The thermal
conductivity of the particles may be less than 100 W/m/C.
The metal may have a hardness and a modulus less than the
particles. In some but not all embodiments, the thermal
conductivity of the metal may be greater than 100 W/m/C,
although metals having a higher thermal conductivity such
as cooper (around 400 W/m/C) may be preferable in some
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circumstances, especially if heat needs to leave the point
of contact more rapidly because of aggressive excavation.
The metal matrix composite may comprise at least one of
tungsten carbide, vanadium, chromium, silicon, boron, a
carbide forming element, a metal carbide, copper, zinc,
manganese, tin, iron, and silver. The particles may
constitute between 20% and 90% by volume of the metal
matrix composite, and the metal constitutes between 10%
and 80% by volume of the metal matrix composite.
Various techniques may be employed to mount a cutting
element such as 14 to a body such as 20. In the
embodiment of figure 1, the cemented carbide cutting
element 14 is attached to the metal matrix composite 12 by
a metallurgical high temperature braze. In making the pick
10, a powder containing the particles to be included in
the metal matrix composite is disposed in a mould of
complementary shape to at least a portion of a body, and
the cutting part is disposed in the mould and in contact
with the powder. A metal, such as copper, typically in the
form of pellets, is disposed over the powder.
Subsequently heating the mould in a furnace for a period
of time causes the metal to melt and infiltrated and bind
the powder to form the metal matrix composite which
permanently adopts the shape of the body on cooling, and
simultaneously forms the braze. The temperature of the
furnace is typically in the range of 900 to 1200 degrees
centigrade, and the mould is typically in the furnace for
between 5 and 90 minutes. In the case of the manufacture
of a metal matrix composite made using silver-zinc-copper
metal together with a tungsten carbide powder, the furnace
temperature is around 1050 centigrade and the mould is
typically in the furnace for 45 minutes.
Alternatively, a cutting element may be attached to
the metal matrix composite by a sintered bond. In making
picks of this embodiment, the powder and cutting element
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are disposed in a mould, and mechanical pressure is
applied to the powder while being heated in a furnace and
a low pressure atmosphere. The powder may comprise at
least one of cobalt, iron and carbides. A metal may be
optionally disposed in the mould during heating to form a
metal binder.
In an embodiment, the cutting element comprises
polycrystalline diamond compact (PDC) which degrades in
air at temperatures above around 750 degrees centigrade.
In this case, during the making of the pick at least one
pocket forming element may be disposed in a mould and the
powder disposed around the at least one element. The at
least one element may be removed after the powder is
caused to adopt the shape of at least a portion of the
body providing a pocket in the body into which the PDC
cutting element may be disposed. The PDC cutting element
may then be brazed using conventional silver soldering
techniques, for example. The pocket forming element may
comprise, for example, graphite or sand.
An embodiment of a mining pick has a cutting element
comprising thermally stable silicon carbide diamond
composite (SCDC). The cutting element has a surface
coated by a product of a reaction of a metal with the
SCDC, and the product is bonded to both the metal matrix
composite and the cutting element. In this case, during
the making of the pick, elements that form carbides and/or
take carbon into solution may be disposed in the mould.
The SCDC cutting element is prior coated with a metal such
as titanium, silicon, and tungsten using, for example,
deposited using a chemical or physical vapour deposition
process. During heating the chemical bond between the
SCDC, metal coating, and metal matrix composite is formed.
In some circumstances a plating (another coating) may be
applied to the metal coating, such as a nickel, iron or
copper plating. The additional plating may prevent
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oxidation during processing. Figure 2 shows a cross
section through an example of a SCDC cutting element 30
bonded to a metal matrix composite body 32 via a product
of the reaction, which in this case is a metal carbide 34.
Other methods of chemical retention of the SCDC insert
include the addition of carbide and/or solution forming
elements of diamond/carbon. Such elements include but are
not restricted to chromium, titanium and tungsten. During
the making of the pick, these elements may be dispersed in
the powder, or more desirably locally around the SCDC
insert. During liquid metal infiltration transport of
these elements bond to the diamond through the formation
of carbides and/or by taking the diamond surface into
solution. Other approaches include the use of a high
manganese containing binder or the local insertion of
active braze metals at or around the SCDC prior to
infiltration
Figure 3 shows a cross section through an example of
a cutting element 40 that is mechanically attached to a
respective body 42. At least one transverse dimension of
at least some of the portion embedded in the metal matrix
composite increases in a direction 44 inward of the body
42. The portion embedded in the metal matrix composite
mechanically interferes with a complementarily shaped
pocket providing resistance to separation of the cutting
element 40 from the body 42. Generally, any tapered, cap,
or dove tail geometry may be used. The bottom of the
cutting element 40, which is embedded in the metal matrix
composite, gently transitions to the side rather than
having an abrupt transition marked by a corner, for
example. Avoiding corners reduces stress concentration
which assists in reducing the probability of fracture of
the metal matrix composite during excavation, especially
in the case of the end of the cutting element being
embedded in t a metal matrix composite which may have a
relatively low fracture toughness compared with other
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materials such as a steel.
Figure 4 shows a cross section through an example of
a cutting element 50 and respective body 52 wherein the
body comprises a plurality of very hard monoliths such as
54. This may improve wear resistance of the body. Each
monolith may comprise, for example, diamond 56, a cermet
58, a ceramic 60, and a cemented carbide 62. The plurality
of monoliths 54 to 62, in this but not necessarily all
embodiments, are embedded in a plurality of carbide
containing pellets which are in turn imbedded in the metal
matrix composite 52. The plurality of monoliths are
disposed adjacent a surface of the body. The monolith may
be arranged in a ring around the cutting element.
In another embodiment, diamond or other ceramic
particles can be dispersed throughout the metal matrix
composite or added to the surface locations occupied by
monoliths shown in Figure 4. These diamond and/or ceramic
particles can be also incorporated within a carbide
containing pellet.
Figure 5 shows a cross section through an example of
a cutting element 70 and a respective body 72 having a
continuous ring 74 of very hard material, such as cemented
carbide, encircling the cutting element. The ring 74 may
be bonded to the metal matrix composite 76 by a high
temperature braze. The ring 74 would typically have an
equal or lesser hardness than that of the cutting element
and greater than the metal matrix composite 76. Benefits
of the ring include intimate and improved wear resistance
compared with a metal matrix composite without additions.
The maximum width D1 of the cutting part is greater than
an inner circumference D2 of the ring 74. While it may be
advantageous in view of wear resistance to form the entire
pick from cemented carbide, this is typically
prohibitively expensive. The pick embodiment of Figure 5,
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however, provides better wear resistance than the pick
embodiment of Figure 1 and may still be economical. When
a SCDC cutting element is used there may not by a bond
between the cutting element and the metal matrix
composite. Mechanical retention is thus assisted by the
ring 74, which has an inner circumference D2 less than the
maximum outer circumference D1 of the cutting element.
Figure 6 shows a side elevation view of an embodiment
of a mining pick 80 having a body 82 comprising first 84
and second 86 portions, each portion having a respective
metal matrix composite. The first portion 84 is adjacent
a proximal end of the body and may comprise a material
that is softer, cheaper and/or easier to make, than that
of the second portion 86. The second portion 86 is
located adjacent a distal end of the body and adjacent to
the tip 88 and so is more wear resistant than the first
portion 84. This approach may reduce the cost of the pick
80 compared with a pick having the entire body comprising
a hard metal matrix composite.
Figure 7 shows a side elevation view of an another
embodiment of a mining pick 90 having a body 92 comprising
first 94 and second 96 portions, each portion having a
respective metal matrix composite. The metal matrix 96 is
more ductile than 94, to increase toughness and fracture
resistance adjacent the cutting element 98 which may
reduce the likelihood of cracking and failure of the metal
matrix composite adjacent the cutting element. This may
be achieved by including iron, steel, copper, tungsten, or
molybdenum, for example, in portion 96. Metal matrix
composite 94 may be harder than metal matrix composite 96
providing improved wear resistance and protection of metal
matrix composite 96.
Figure 8 shows a side elevation view of another
embodiment of a mining pick 100. In this embodiment, the
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proximal end 101 of the body has a portion 102 comprising,
for example, a steel and another portion 104 at a distal
end 106 comprising a metal matrix composite 104. The
metal matrix composite portion 104 may be sufficient
protection and reduce the propensity of the pick to cause
ignition when used. The steel portion 102 and the metal
matrix composite portion 104 may be joined by, for
example, a pair of cooperating elements such as a thread
on each of the portions 102 and 104, shrink fitting,
chemical or metallurgical bonding etc. Alternatively, the
shank and the steel portion of the body may be formed of
the one piece of steel. Some of the relatively expensive
metal matrix composite has been substituted in this
embodiment for relatively inexpensive steel reducing
costs. Also, the configuration of the distal end 106 of
the pick may be kept constant across a range of
embodiments while the proximal end 108 is adapted to
engage machines having various pick coupling
configurations.
Figure 9 is a graph showing, for two embodiments
120,130 of a mining pick having respective metal matrix
body portions, the probability of causing ignition in
comparison to a prior art mining pick 110 over their
respective lives. One embodiment 120 has a cemented
carbide cutting element, and the other 130 has a silicon
carbide diamond (SCDC) cutting element. Both embodiments
120, 130 have at least a portion of the body comprising
metal matrix composite at a distal end. The probability of
ignition when using the embodiments 120,130 is lower than
that when using the prior art pick 110.
Prior art pick 110 has a body comprising only steel
and a cemented carbide cutting element (insert). Region A
corresponds to the period of usage wherein the cutting
element is not significantly worn. Region B corresponds
to the period of usage where the cutting element exhibits
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significant wear. The probability of ignition increases
as the cemented carbide blunts and creates more fine
particles during cutting. Region C corresponds to a
period after the cutting element fails. The cutting
element may be lost or broken, for example, or worn down
to or near the level of the body and the steel body is
exposed. Sparking is very likely and the risk of
frictional ignition very high.
While in Figure 9 Region B is shown to correspond to
periods of identical length in the case of the prior art
device 110 and the embodiment 120, in some embodiments the
wear resistant metal matrix composite may in fact extend
Region B so that it is longer than the corresponding
Region B for the prior art device 110.
A SCDC cutting element such as that of embodiment 130
stays sharp for a significantly longer period than an
equivalent cemented carbide cutting element and shows no
significant propensity for sparking. In the case pick
embodiment 130, Region A is about 10 to 100 times longer
than that for prior art pick 110. The probability of
ignition in Region A is low. If and when the SCDC insert
is lost (Region C) and the matrix directly contacts the
formation the probability of ignition is significantly
lower than that of either the prior art pick or the
embodiment of the pick having a metal matrix body portion
with the cemented carbide cutting element in place. Thus,
it may be desirable to use in some circumstances a pick
embodiment having a SCDC cutting element and a body with
at least a portion comprising a metal matrix composite, in
view of the prolonged tool life and productivity and the
low probability of ignition.
It is to be understood that, if any prior art
publication is referred to herein, such reference does not
constitute an admission that the publication forms a part
WO 2012/015348 CA 02805376 2013-01-14PCT/SE2011/050547
¨ 20 ¨
of the common general knowledge in the art, in Australia
or any other country.
In the claims which follow and in the preceding
description of the invention, except where the context
requires otherwise due to express language or necessary
implication, the word "comprise" or variations such as
"comprises" or "comprising" is used in an inclusive sense,
i.e. to specify the presence of the stated features but
not to preclude the presence or addition of further
features in various embodiments of the invention.
It will be understood to persons skilled in the art
of the invention that many modifications may be made
without departing from the spirit and scope of the
invention. For example, the cutting element may comprise
a rotary cutter.
