Note: Descriptions are shown in the official language in which they were submitted.
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ROTARY CUTTING BIT
The present invention relates to cutting tools used for mining and
excavation purposes. The present invention has been developed principally for
use in the mining of coal and in that use, typically 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.
Various different forms of equipment and machinery can be employed for
mining and excavation operations, and typically it is the type of mining or
excavation taking place, and the type of earth being mined or excavated, that
dictates the type of equipment and machinery that is appropriate. 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 incendive sparks and thus cause fires or explosion.
Therefore, it is important that all appropriate steps be taken to minimise or
eliminate the production of sparks.
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 result in spark production between them.
Picks employed for the above purpose generally have a hard cemented
tungsten carbide tip that is fixed, usually by brazing, to a steel shank.
Picks of
this kind are disclosed in various prior art, such as U.S. Patent No.
6,113,195,
EP0274645 and DE4226976. The tip of the picks can be either of the insert or
cap style.
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The insert style is shown in DE4226976, in which a greater section of the
axial length of the tip is anchored within a bore of the shank, than extends
out of
the bore. The cap style is shown in EP0274645, in which the tip has a broader
base than the insert style tip and the base is located and brazed into a
relatively
shallow recess in the forward end of the shank. The present invention is
applicable to either of these forms of pick.
In picks of the above kind, 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.
It is an object of the present invention to provide a cutting pick which has a
reduced likelihood of producing a spark during mining or excavation
operations,
in particular underground coal mining.
According to the present invention there is provided a cutting pick which
comprises an elongate shank and a cutting tip fixed to one end of the shank to
project from that end, the cutting tip is of a material which is harder than
the
material of the shank and an annular sleeve is attached about the shank,
adjacent the cutting tip, the sleeve being of a spark resistant material which
has
a lower propensity for incendiary spark production during a cutting operation
than the material of the shank.
Also according to the present invention there is provided a cutting pick
comprising:
an elongate steel shank;
a cutting tip fixed to a cylindrical end section of the shank to project
axially
with respect to the lengthwise axis of the shank and which is of a material
that is
harder than the material of the shank; and
a composite sleeve formed of a plurality of annular sleeve portions which
are attached about the cylindrical end section and which are of a material
that is
harder than the material of the shank and which extend substantially the full
height of the end section and which have a lower propensity for incendiary
spark production during a cutting operation than the steel of the shank.
The present invention further provides a method of using a cutting pick for
mining, the cutting pick comprising: an elongate steel shank; a cutting tip
fixed
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to a cylindrical end section of the shank to project axially with respect to
the
lengthwise axis of the shank and which is of a material that is harder than
the
material of the shank; and a composite sleeve formed of a plurality of annular
sleeve portions which are attached about the cylindrical end section and which
are of a material that is harder than the material of the shank and which
extend
substantially the full height of the end section and which have a lower
propensity for incendiary spark production during a cutting operation than the
steel of the shank, the method comprising the step of mining in gas and/or
mine
dust containing environments.
By the attachment of the sleeve about the shank, the portion of the shank
in the immediate vicinity of the cutting tip, which typically is the most
likely to
contact either the earth face being cut, or the fragments of earth being
dislodged from the face, and to therefore generate an incendive spark, is
shielded against that contact by the spark resistant material. The propensity
for
spark production is therefore reduced.
In a cutting pick according to the invention, the elongate shank can take
any suitable form, such as known forms, for fixing to a rotary cutting drum.
The
shank would usually be releasably fixable to the drum so that worn cutting
picks
can be replaced as necessary and in some machinery, the shank is rotatably
mounted so that the cutting pick can freely rotate about its lengthwise axis
as it
engages an earth face. The shank usually would be manufactured from steel.
In a cutting pick according to the invention, the shank can be configured to
receive either an insert style cutting tip or a cap style cutting tip.
In a cutting pick according to the invention, the cutting tip can be
manufactured from any suitable material which is harder than the shank
material, and the preferred cutting tip material is cemented tungsten carbide.
The tip can also be diamond impregnated for increased hardness or can include
cubic boron nitride for the same purpose. The cutting tip can have any
suitable
shape, which typically is dependent on whether the tip is of the insert or cap
style. The cutting tip usually is brazed to the shank, although other
arrangements for fixing the tip, such as by chemical adhesives, can be
employed.
The sleeve which is attached about the shank adjacent the cutting tip
preferably is formed from the same material as the cutting tip and preferably
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that material is a cemented tungsten carbide. Alternatively the material could
be
or include SiC, A1203, TiN, SiC-D (silicon carbide diamond composite), cubic
boron nitride, tool steel, or other like materials. These materials can be
formed
as a composite material with other suitable materials, or they may be provided
as an outer layer or layers over a suitable base.
In a typical size of cutting pick, the axial height of the sleeve could be in
the region of about 10 mm to 15 mm, with the radial thickness of the sleeve
between inner and outer diameter, about 3 mm to 5 mm. Production of a sleeve
in these dimensions in tungsten carbide may present certain difficulties and
therefore the invention provides that the sleeve can be produced as a
composite sleeve in sleeve portions or rings of reduced height, such as about
4
mm in axial height. These portions can then be attached to the shank to form a
composite sleeve of the required height. In the preferred arrangement, three
sleeve portions are employed, although two sleeve portions, or four or more,
may be employed as required. In a preferred arrangement, each sleeve portion
has the same inside and outside diameters, and preferably the inner and outer
surfaces are parallel, although the outer surface can include a chamfered edge
or edges to reduce the likelihood of sharp edge breakage.
The envisaged difficulty with a sleeve formed of one piece relates
principally to the difference in the coefficient of expansion between the
sleeve
and the shank when the sleeve is attached to the shank. If the shank material
is
steel and the sleeve is tungsten carbide, the shank will expand as the steel
is
heated and the shank will thereafter shrink as the steel cools at a rate which
is
about twice as fast as that of the sleeve. The difference in rate of shrinking
can
introduce stresses in the sleeve, which typically will be more brittle than
the
shank and if the stresses are sufficient, the sleeve can crack. If a plurality
of
shank portions in the form of rings is employed, then the contact area between
the shank and the composite sleeve can be reduced by breaks between the
rings. This is because the medium employed to fix the rings to the shank
extends between the rings and the shank and between the rings themselves.
That medium, which is, as later described, preferably braze, can absorb some
of the induced stresses and therefore reduce the likelihood of the sleeve
failing.
This has the additional benefit that the composite sleeve can be tougher or
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stronger than a single-piece sleeve, so that the likelihood of wear or failure
under operating loads is also reduced.
In a preferred form of a cutting pick according to the invention, the shank
defines a shoulder between a generally conical section and cylindrical
section.
5 The conical section converges towards the cylindrical section, while the
cylindrical section defines a recess for receipt of a base portion of the
cutting
tip. That receipt can constitute either an insert or cap style cutting pick.
In this
arrangement, the sleeve is attached to the shank about the cylindrical section
and is supported against the shoulder. Advantageously, this arrangement
provides for accurate location of the sleeve on the shank and provides a
surface
against which the sleeve can react impact loads during a cutting operation.
To reduce the likelihood of the annular sleeve fracturing during a cutting
operation, the portion of the sleeve which is adjacent the base of the cutting
tip
can be positioned so that a cylindrical portion of the cylindrical section
remains
exposed. Preferably the extent of exposure, as measured axially, is in the
region of 1 mm to 5mm, most preferably about 3 mm. The exposed portion
therefore is relatively small and preferably also is of a diameter no greater
than
the outermost diameter of the cutting tip at the region of the base of the
cutting
tip. Because only a small portion of the cylindrical section is exposed, the
likelihood of that section engaging a cutting surface during a cutting
operation is
very low. Rather, the exposed section is likely to be within the "wear shadow"
of
the cutting tip, which is a section of the cutting pick that suffers minimal
or
negligible wear due to its close proximity to the cutting tip. Wear of the
pick is
more likely to occur at a position further away from the cutting tip. Sections
of
the pick that are more likely to wear are those sections which have
significant
contact with the cutting surface and it is those sections which are more
likely to
spark when contact occurs.
By positioning the annular sleeve further away from the cutting tip, the
sleeve is positioned in a less destructive environment during a cutting
operation
in respect of impact loads that could cause the sleeve to fracture. On the
other
hand, by positioning the sleeve to overlie areas of the pick of significant
cutting
surface contact during a cutting operation, the incidence of spark production
can be reduced, while the cylindrical section can also be protected against
wear.
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In the preferred arrangement, in which the shank is formed of steel and
the sleeve or sleeves is/are formed from tungsten carbide, the preferred form
of
attachment of the sleeve to the shank, is by brazing. In the embodiment in
which the sleeve is comprised of a plurality of sleeve portions, it is
preferred that
each portion is individually brazed to the shank and to each other.
Advantageously, the braze which is interposed between the sleeve portions and
the shank can absorb stresses that occur during heating and cooling of the
pick.
During heating and cooling, the sleeve portions and the shank expand and
shrink, but at different rates due to differences in the relative co-
efficients of
expansion. The braze can also provide a level of shock absorption during a
cutting operation. It is to be noted that the braze is intended to be present
between adjacent sleeve portions as well as between the sleeve portions and
the shank, so that stress and shock absorption between adjacent sleeve
portions also occurs.
While tungsten carbide is the preferred material for the sleeve, other
materials, such as those discussed above, may be equally appropriate.
Likewise, the material can include additives which enhance either the
resistance
to incendive spark production or which increase the wear resisting capacity of
the sleeve. In this latter respect, the sleeve for example, can be enhanced by
the addition of diamond particles. Other additives of the above discussed
kinds
may be equally appropriate. Alternatively, the material may be a composite of
a
base, which has a suitable outer layer or layers applied to it, and for this
titanium nitride is most preferred.
It will be appreciated that the above discussion principally concerns the
reduction or elimination of incendive spark production, during engagement of a
cutting pick with an earth face. While that result is the primary objective of
the
invention, a secondary aspect of the invention, is to provide the shank with a
resistance to wear. Shanks formed from steel, readily wear over time, and it
is
often the case that the steel shank wears more quickly than the harder cutting
tip, so that the cutting pick must be replaced earlier than desirable i.e.
before
the cutting pick is sufficiently worn. In other words, wear of the shank can
reduce the effective life of the cutting pick. Pick wear often occurs
principally in
the vicinity of the shank immediately adjacent the cutting tip. Accordingly,
by
suitable selection of sleeve material, the steel shank in that vicinity can be
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shielded against engagement with earth face or fragments, that would otherwise
cause it to wear and therefore the life of the cutting pick can be improved.
The
selection of a sleeve material that is the same or effectively equivalent to
the
material of the cutting tip, can provide useful wear resistance for this
purpose.
The present invention also provides a method of using a cutting pick of
any of the kinds described above, for mining in a gas and/or mine dust
environment.
Other objects, features, and characteristics of the present invention will
become apparent from the following detailed description of the preferred
embodiments and accompanying drawings, by way of non-limiting examples
only, all of which form a part of the specification, wherein like reference
numerals designate corresponding parts in the various figures.
Figure 1 is a side view of the shank of a rotary cutting pick.
Figure 2 is a side view of a tungsten carbide tip for attachment to the
shank of Figure 1.
Figure 3 is a side view of a cutting pick according to the invention.
Figure 4 is a side view of an alternative embodiment of a cutting pick
according to the invention.
Figures 1 and 2 respectively show a shank 10 of a cutting pick, and a
tungsten carbide tip 11 which is shaped for attachment to the shank 10. The
shank 10 includes a body section 12, which includes a flange 13 at one end and
a recess 14 remote from the flange 13, and whereby the flange 13 and the
recess 14 cooperate with a rotary cutting drum for fixing of the cutting pick
to
the drum. The manner with which the shank 10 is fixed to the drum will be
known to a person skilled in the art and therefore will not be further
described or
illustrated herein.
The shank 10 further defines a substantially conical section 15, a
cylindrical section 16 and a first shoulder 17. It will be appreciated that
the first
shoulder 17 is defined by a reduction in the diameter of the conical section
15
immediately adjacent the cylindrical section 16.
The cylindrical section 16 includes a recess 18 for receiving a base portion
of a cutting tip, such as of the kind shown in Figure 2. Referring to that
figure, it
will be appreciated that the cutting tip 11 is not shown to scale for
attachment to
the shank 10, but instead is shown larger to clearly show relevant detail. The
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cutting tip 11 includes a base portion 19 which extends to a maximum diameter
ring 20 and it is the base portion 19 which is received within the recess 18
of the
shank 10. The ring 20 rests against the upper edge 21 of the cylindrical
section
16, when the cutting tip 11 is fixed to the cylindrical section 16. That
fixing
typically is achieved by brazing the cutting tip 11 within the recess 18.
Figure 1
shows in broken outline, the cutting tip 11 fixed to the cylindrical section
16.
It will be appreciated from Figure 1, that when the cutting tip 11 is fixed to
the shank 10 each of the outer cylindrical surface 22, the first shoulder 17
and
the outer surface of the conical section 15 remain exposed. Thus, these
surfaces can come into contact with the earth face being cut, or with
fragments
that have been dislodged from the earth face. That engagement can result in
incendive sparks being produced, with the obvious potential hazardous
consequences. The likelihood of spark production is greatest in the sections
of
the shank 10 adjacent the cutting tip 11, while the likelihood reduces towards
the opposite end of the shank 10.
Figure 3 illustrates an embodiment of the invention, in which the likelihood
of spark production is reduced. The cutting pick 30 of Figure 3 employs the
shank 10 and cutting tip 11 of Figures 1 and 2 and therefore the same
reference
numerals as used in those figures are employed in Figure 3.
In Figure 3, a composite sleeve 31, formed of three identical sleeve
portions or rings 32, is disposed about the outer cylindrical surface 22
(Figure 1)
of the cylindrical section 16. Each of the rings 32 is formed separately from
one
another, and is fitted about the cylindrical section 16 in a snug or slightly
frictional fitting, and is brazed to the outer surface 22, and the most remote
ring
32 from the cutting tip 11 is also brazed to the first shoulder 17. As shown,
the
rings 32 provide substantially complete protection for the outer surface 22 of
the
cylindrical section 16, with only a slight cylindrical portion of the
cylindrical
section 16 visible axially beyond the most immediately adjacent ring 32 to the
cutting tip 11. That portion is identified by the reference numeral 33 and is
the
portion of the cylindrical section 16 to which the flange 20 of the cutting
tip 11 is
fixed. The cylindrical portion 33 provides some protection for the rings 32,
particularly the uppermost ring 32, against the impact of earth fragments
dislodged during a cutting operation so that the likelihood of the rings 32
fracturing is significantly reduced, particularly the uppermost ring. The
axial
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height of the exposed cylindrical portion can be in the region of 1 mm to 5
mm,
while most preferably it is about 3 mm.
The sleeve 31 is produced in separate rings, simply for ease of sleeve
production and attachment to the shank 10. Rings 32 of the dimensions shown
in Figure 3 are more easily produced from tungsten carbide, than would be a
single composite sleeve which has an axial dimension equal to the three
axially
adjacent rings. Also, by separately brazing each ring 32 in turn to the
cylindrical
section 16, a more firm attachment of the composite sleeve 31 to the shank 10
is achieved. Also, the use of rings 32 to form a composite sleeve allows the
axial height of the sleeve to be increased or decreased relative to the axial
extent of the cylindrical section 16. That is, sleeves of different axial
dimensions
need not be produced, it is simply necessary to choose the appropriate number
of rings 32 for the axial sleeve height required.
It will be seen from Figure 3, that each of the rings 32 has a chamfer
applied to the leading axial edge thereof in the direction of the cutting tip
11.
It will be further appreciated, that the axial length of the sleeve 31 could
be
extended in the direction towards the flange 13, and for this the conical
section
15 of the shank 10 can be stepped to provide a further series of shoulders, or
further sleeves could simply be attached to the outer surface of the conical
section 15. The necessity for continuing the sleeve protection towards the
flange 13 is dependent on the likelihood of incendive spark production further
behind the first shoulder 17. Present thinking indicates that a substantial
reduction in the potential for incendive spark production is achieved by a
sleeve
31 or 31' having the approximate dimensions shown in Figures 3 and 4,
respectively, relative to the remaining components of the cutting pick 30,
30'.
It will be appreciated that by proper selection of the material of the sleeve
31, that the sleeve 31 will also provide wear protection for the cylindrical
section
16 of the shank 10. While wear protection is not its primary function,
advantageously, this secondary function can significantly improve the life of
the
cutting pick. Moreover, the effect of the invention to reduce spark production
can only occur while the sleeve remains intact. That is, if the sleeve wears
away, the benefits of the invention will be lost. Accordingly, it is preferred
that
the sleeve resists wear for the anticipated life of the cutting pick.
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Referring now to Figure 4 an alternative embodiment of a cutting pick 30'
according to the invention, in which the likelihood of spark production is
reduced. The cutting pick 30' of Figure 4 employs the body section 12 and
cutting tip 11 of Figure 3 and therefore the same reference numerals as used
in
5 those figures are employed in Figure 4.
In Figure 4, a composite sleeve 31', formed of three sleeve portions or
rings 32, 32' is disposed about the outer cylindrical surfaces of first 16 and
second 16' cylindrical sections. Each of the rings 32, 32' is formed
separately
from one another, and is fitted about the cylindrical section 16, 16' in a
snug or
10 slightly frictional fitting, and is brazed to the outer surfaces. Two of
the rings 32,
the cylindrical section 16 and the first shoulder 17 are identical to the ones
previously disclosed in Fig. 3. The most remote ring of the rings 32 from the
cutting tip 11 is also brazed to the first shoulder 17. The additional third
ring 32'
is also brazed to a second shoulder 17'. The dimensions of the cylindrical
section 16', the second shoulder 17' and the ring 32' are greater than the
dimensions of the corresponding parts 16, 17 and 32. As shown, the rings 32,
32' provide substantially complete protection for the outer surfaces of the
cylindrical sections 16, 16'. Thus, the shank 10' of the above kind defines a
second shoulder 17', which is axially spaced from the first shoulder 17 in a
direction away from the cutting tip 11, and in this arrangement, a second
sleeve
32' is attached about the shank to extend between the first 17 and second 17'
shoulders. In this manner, a further portion of the shank can be protected
against contact with the earth face and so further lessen the risk of
incendive
spark production.
In the arrangement discussed above the annular sleeve could also be
supported at one axial end on the first shoulder 17, while the other axial end
extends towards but terminates prior to the first end of the cylindrical
section 16
so that a cylindrical portion of the cylindrical section remains exposed.
The arrangement discussed above in which a second shoulder is
provided, can be repeated as required, to create a third shoulder and further
shoulders as necessary. Accordingly, by this arrangement, an ever increasing
axial length of the shank can be protected.
In the arrangements discussed above, when more than a single shoulder
is provided, it is preferable that the shank portions between the respective
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shoulders are cylindrical and that each portion increases in diameter in a
direction away from the cutting tip.
The invention described herein is susceptible to variations, modifications
and/or additions other than those specifically described and it is to be
understood that the invention includes all such variations, modifications
and/or
additions which fall within the scope of the following claims.
