U.S. patent application number 13/813250 was filed with the patent office on 2013-08-15 for metal matrix composite mining pick and method of making.
This patent application is currently assigned to SANDVIK INTELLECTUAL PROPERTY AB. The applicant listed for this patent is Andy Bell. Invention is credited to Andy Bell.
Application Number | 20130207445 13/813250 |
Document ID | / |
Family ID | 45442305 |
Filed Date | 2013-08-15 |
United States Patent
Application |
20130207445 |
Kind Code |
A1 |
Bell; Andy |
August 15, 2013 |
Metal Matrix Composite Mining Pick and Method of Making
Abstract
A mining pick is disclosed. The pick has 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 body,
and a shank extending from the body. The at least part of the body
formed of the metal matrix composite is configured to provide a
barrier during an excavation operation.
Inventors: |
Bell; Andy; (Groventry,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bell; Andy |
Groventry |
|
GB |
|
|
Assignee: |
SANDVIK INTELLECTUAL PROPERTY
AB
Sandviken
SE
|
Family ID: |
45442305 |
Appl. No.: |
13/813250 |
Filed: |
May 2, 2011 |
PCT Filed: |
May 2, 2011 |
PCT NO: |
PCT/SE2011/050547 |
371 Date: |
April 11, 2013 |
Current U.S.
Class: |
299/105 ; 419/1;
419/18 |
Current CPC
Class: |
E21C 35/1835 20200501;
E21C 35/183 20130101; E21C 35/18 20130101 |
Class at
Publication: |
299/105 ; 419/18;
419/1 |
International
Class: |
E21C 35/183 20060101
E21C035/183 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 30, 2010 |
AU |
2010206065 |
Claims
1. 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; and a
shank extending from the body, wherein the at least part of the
body formed of the metal matrix composite is configured to provide
a barrier during an excavation operation.
2. A mining pick defined by claim 1 wherein 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.
3. A mining pick defined by claim 1, wherein the at least part of
the body formed of the metal matrix composite forms an exterior
surface of the body adjacent the cutting element.
4. A mining pick defined by claim 3 wherein the exterior surface
encircles the cutting element.
5. A mining pick defined by claim 1, wherein the metal matrix
composite has less propensity to cause ignition of a flammable
substance adjacent the body during the excavation operation than at
least one of cemented carbide, a material of the shank, and a
material of the cutting element.
6. A mining pick defined by claim 1, wherein the at least part of
the body formed of the metal matrix composite is configured to
provide a barrier after the cutting element fails.
7. A mining pick defined by claim 1, wherein the particles have a
hardness greater than 1000 Hardness Vickers and a modulus greater
than around 200 Gigapascals.
8. A mining pick defined by claim 1, wherein the metal has a
hardness and a modulus less than the particles, and a thermal
conductivity greater than around 100 W/m/C).
9. A mining pick defined by claim 1, wherein the particles
constitute between 20% and 90% by volume of the metal matrix
composite.
10. A mining pick defined by claim 1, wherein the metal constitutes
between 10% and 80% by volume of the metal matrix composite.
11. A mining pick defined by claim 1, wherein the particles are
tungsten carbide and constitute around 60% by volume of the metal
matrix composite.
12. A mining pick defined by claim 1, wherein the particles
comprise steel.
13. A mining pick defined by claim 1, wherein the metal comprises
65% to 75% by volume copper, 5% to 15% by volume silver and 15% to
25% by volume zinc.
14. A mining pick defined by claim 1, wherein the metal is
copper.
15. A mining pick defined by claim 1, wherein the metal matrix
composite constitutes the body and the shank has an end embedded in
the metal matrix composite.
16. A mining pick defined by claim 1, wherein the cutting element
is mechanically attached to the metal matrix composite.
17. A mining pick defined by claim 1, wherein at least one
transverse dimension of at least some of the portion embedded in
the metal matrix composite increases in a direction inward of the
body.
18. A mining pick defined by claim 1, wherein the cutting element
is metallurgically attached to the metal matrix composite.
19. A mining pick defined by claim 1, wherein the cutting element
is attached to the metal matrix composite by a metallurgical high
temperature braze.
20. A mining pick defined by claim 1, wherein the cutting element
is attached to the metal matrix composite by a sintered bond.
21. A mining pick defined by claim 1, wherein a portion of the
cutting element is embedded in the metal matrix composite.
22. A mining pick defined by claim 1, wherein the cutting element
comprises thermally stable silicon carbide diamond composite
(SCDC), the cutting element has a surface bonded to a product of a
reaction of a metal with the SCDC, and the product is bonded to the
metal matrix composite.
23. A mining pick defined by claim 1, wherein the body comprises a
plurality of monoliths.
24. A mining pick defined by claim 23, wherein the plurality of
monoliths comprise at least one of diamond, cermet, ceramic, and
cemented carbide.
25. A mining pick defined by claim 23 wherein the plurality of
monoliths are embedded in a plurality of carbide containing pellets
which are imbedded in the metal matrix compound.
26. A mining pick defined by claim 23, wherein the plurality of
monoliths are disposed adjacent a surface of the body.
27. A mining pick defined by claim 1, wherein 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.
28. A mining pick defined by claim 27 wherein one of the portions
is disposed at a distal end of the body, and another of the
portions is disposed at a proximal end of the body.
29. A mining pick defined by claim 27 wherein one of the portions
is disposed in a pocket formed in another of the portions.
30. A mining pick defined by any claim 1, wherein the body
comprises a ring of material encircling the cutting element, the
ring having an equal or lesser hardness than that of the cutting
element and greater than the metal matrix composite.
31. A mining pick defined by claim 1, wherein 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.
32. 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; and 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.
Description
FIELD OF THE INVENTION
[0001] 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
[0002] 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.
[0003] 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.
[0004] Prior 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
[0005] 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.
[0006] According to a first aspect of the invention there is
provided a mining pick, the pick comprising:
[0007] a body;
[0008] at least part of the body being formed of a metal matrix
composite comprising particles dispersed in a metal;
[0009] a cutting element mounted to the body;
[0010] a shank extending from the body;
[0011] the at least part of the body formed of the metal matrix
composite being configured to provide a barrier during an
excavation operation.
[0012] 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.
[0013] In an embodiment, the at least part of the body formed of
the metal matrix composite is configured to provide a barrier after
the cutting element fails.
[0014] 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.
[0015] 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
[0016] 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.
[0017] 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.
[0018] 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).
[0019] 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).
[0020] In an embodiment, the particles constitute between 20% and
90% by volume of the metal matrix composite.
[0021] In an embodiment, the metal constitutes between 10% and 80%
by volume of the metal matrix composite.
[0022] In 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.
[0023] In an embodiment, the particles comprise steel.
[0024] 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.
[0025] In an embodiment, the metal is copper.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] In an embodiment, the cutting element is metallurgically
attached to the metal matrix composite. The cutting element may be
attached to the metal matrix composite by a metallurgical high
temperature braze.
[0030] In an embodiment, the cutting element is attached to the
metal matrix composite by a sintered bond.
[0031] In an embodiment, a portion of the cutting element is
embedded in the metal matrix composite.
[0032] In an embodiment, the cutting element comprises thermally
stable silicon carbide diamond composite (SCDC).
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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 element and greater than that of
the metal matrix composite.
[0037] 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.
[0038] In an embodiment, the mining pick is configured as a point
attack pick.
[0039] In an embodiment, the mining pick is configured as a radial
attack pick.
[0040] 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.
[0041] According to a second aspect of the invention there is
provided a method of making a mining pick, the method comprising
the steps of:
[0042] 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;
[0043] 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
[0044] Features and advantages of the present invention will become
apparent from the following description of embodiments thereof, by
way of example only, with reference to the accompanying drawings,
in which:
[0045] FIG. 1 shows a side elevation view of an embodiment of a
mining pick in accordance to an aspect of the invention;
[0046] FIG. 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;
[0047] FIG. 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;
[0048] FIG. 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;
[0049] FIG. 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;
[0050] FIG. 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;
[0051] FIG. 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;
[0052] FIG. 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
[0053] FIG. 9 is a graph showing probability curves of two
embodiments of a mining pick having respective metal 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
[0054] FIG. 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.
[0055] 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.
[0056] 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 indicated 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 FIG. 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.
[0057] 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.
[0058] In the embodiment of FIG. 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.
TABLE-US-00001 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) 5 60-95 35-5 (<10)
(<10)
[0059] 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.
[0060] 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.
[0061] 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.
[0062] 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.
[0063] 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 FIG. 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.
[0064] 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 FIG. 1 instead of a prior art pick may greatly reduce
the incidence of friction induced ignition during excavation which
is very dangerous in a mine, for example.
[0065] 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.
[0066] 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.
[0067] It will be appreciated that in an embodiment, the shank and
body may both be formed of a metal matrix composite.
[0068] 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 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.
[0069] Various techniques may be employed to mount a cutting
element such as 14 to a body such as 20. In the embodiment of FIG.
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.
[0070] 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 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.
[0071] 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.
[0072] 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
oxidation during processing. FIG. 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
[0073] FIG. 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 materials such as a steel.
[0074] FIG. 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.
[0075] 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 FIG. 4. These
diamond and/or ceramic particles can be also incorporated within a
carbide containing pellet.
[0076] FIG. 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 FIG. 5,
however, provides better wear resistance than the pick embodiment
of FIG. 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.
[0077] FIG. 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.
[0078] FIG. 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.
[0079] FIG. 8 shows a side elevation view of another embodiment of
a mining pick 100. In this embodiment, the 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.
[0080] FIG. 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.
[0081] 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 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.
[0082] While in FIG. 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.
[0083] 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.
[0084] 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 of the common general knowledge
in the art, in Australia or any other country.
[0085] 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.
[0086] 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.
* * * * *