Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
A DISC CUTTER
FIELD OF THE INVENTION
This invention relates to a disc cutter and
particularly relates to a disc cutter for a rock working
machine including m~h~nec used in underground mining and
for tunnel boring.
BACKGROUND ART
Rock working m~chinec are used in underground
mines to excavate rock, or other materials such as ore,
coal and the like, and have a rotary head of about the
diameter desired for the amount of excavation required.
The rotary head has a surface on which a number of disc
cutters are located. Each disc cutter has a cutting ring
mounted to a hub, the hub being mounted to a shaft.
The rotary head is pushed hard up against the
rock face and rotated which places an enormous force onto
the disc cutters which in turn cut grooves in the rock
face. The enormous force also fractures the rock
allowing it to be excavated.
The amount of radial force on the disc cutter
varies depending on the type and hardness of the rock to
be excavated, but a typical peak force is about 100
tonnes.
The cutting rings on many conventional disc
cutters are made from steel. The steel rings blunt very
~uickly in abrasive rock and become l~neco~omical due to
the downtime of the machine during replacement of the
disc cutters.
An attempt has been to simply place a tungsten
carbide ring on a conventional steel hub. In practice it
was found that the tungsten carbide ring broke or cracked
making it unsuitable for use on a rock working machine.
The present invention is directed to a disc
cutter which can use a hardmetal, such as a tungsten
carbide ring, attached to a ferrous metal hub
characterised in that the hub contains a hardmetal
footing to support the ring.
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OBJECT OF THE INVENTION
It is an object of the invention to provide a
disc cutter which may overcome the abovementioned
disadvantages or provide the public with a useful or
5 ~ommercial choice.
In one form, the invention resides in a disc
cutter for a rock working machine, the disc cutter having
a hardmetal cutting ring attached to a hub, characterised
in that the hub has a footing portion formed of hardmetal
to support the cutting ring.
It has now been found that the incidence of
breaking or cracking of the tungsten carbide ring can be
significantly reduced if the ring is supported on a
hardmetal footing rather than supported directly on a
non-hardmetal (such as ferrous metal) hub. While not
wishing to be bound by theory, it appears that the
interface stress between the ring and the hub interface
is reduced to below a critical level by providing a
hardmetal footing.
While the entire hub can be formed of
hardmetal, it is preferred that the hub has a main body
portion formed from a non-hardmetal with only the footing
portion formed of hardmetal. The footing portion is
typically annular to support a continuous cutting ring.
There are also significant cost savings, as the
disc cutter of the invention, having the hardmetal
cutting ring, outperforms any conventional disc cutter
with a steel cutting ring, and also outperforms any disc
cutter having a tungsten carbide ring on a plain metal
hub, because of the reduction in breaking or cracking of
the ring due to the ring/hub interface stresses.
The disc cutter of the invention is cheaper and
easier to manufacture as much of the hub can be formed
from conventional ferrous metal, with only a footing
portion of the hub formed from hardmetal. Further,
should the disc cutter become worn or damaged, it is only
necessary to replace the hardmetal cutting ring.
The disc cutter can be used as a cutting tool
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on a rock working machine. The term "rock working" is
meant to include, but not be limited to, tunnel boring,
raise boring, mine shaft excavation, ore recovery in
mines, coal recovery, and surface excavation and cutting.
The term rock working is not limited to tunnelling or
mining, and the disc cutter can also be used to cut
ylooves~ channels and the like in almost any type of
solid material. Of course, in soft materials such as
coal, a normal steel cutting ring would be sufficient,
and the disc cutter according to the invention would
typically be used with a machine for excavating harder
types of rock, or a solid where hard rock portions are
likely to be encountered (for instance in tunnelling).
The term "hardmetal" is known in the art and
includes metal alloys such as carbides, and cemented
carbides such as tungsten carbides and cobalt cemented
tungsten carbides. Throughout the specification and
claims the term "hardmetal" is also meant to include non
metal materials which have the same hardness as the above
materials; and an example of such a non metal material is
a ceramic.
It is preferred that the hard metal ring has a
hardness of HV3 of 900 or more. A cemented tungsten
carbide ring formed of tungsten carbide and cobalt is
suitable. A suitable tungsten carbide ring is one having
over 80~ and preferably about 87~ of tungsten carbide in
a cobalt binder. Such a ring has a hardness HV3 of 1070,
a density of 14.2g/cm and a stiffness (Youngs Modulus) of
GPa 450.
The hub can be a more or less st~n~rd-type hub
used on conventional disc cutters. The hub is rotatably
attached to a non-rotating shaft cont~;ning roller
bearings such that the ring and the hub can be rotated
together.
The hub has a main body portion formed from
conventional material which usually comprises steel or
ferrous metal such as cast iron, and which is adapted to
be mounted to the shaft.
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The hub has a peripheral side wall and the
peripheral side wall is provided with a footing portion
which can extend about the hub and on which the cutting
ring is supported. The footing portion is formed from
hardmetal and it is found that th~s arrangement minimises
breaking or cracking of the hardmetal ring when attached
to a non-hardmetal hub.
The footing portion may be formed of a
hardmetal which is identical to or different to the
hardmetal of the cutting ring; but it is preferred that
the footing portion has a stiffness similar or greater to
that of the hardmetal ring. Thus, the footing portion
may also be formed from tungsten carbide, and while the
footing portion should be harder than the main body
portion of the hub, it is not necessary for the footing
portion to be of the same hardness as the cutting ring.
The cutting ring may have a substantially
planar inner portion and a rounded or otherwise curved
outer cutting portion. It is preferred that the inner
portion and the footing portion mate together to allow
distribution of the load. It is envisaged that if the
inner portion is not planar, it should be of a
configuration to complement the shape of the footing such
that the outer ring can mate with the footing portion.
The hub can be formed with the hardmetal
footing portion and the non-hardmetal main body portion
by a CIC process which is a known cast-in-carbide
process. In this process, the hardmetal (for instance
tungsten carbide) is metallurgically bonded to the
nodular cast iron base. Alternatively, the footing
portion can be formed separately and fitted to the main
body portion.
In order to prevent the cutting ring from
rotating relative to the hub, one or more clamp rings may
be provided. Clamp rings are known in the art and clamp
on one or both sides of the cutting ring to prevent the
cutting ring from slipping on the hub.
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BRIFF DESCRIPTION OF THE DRAWINGS
An embodiment of the invention will be
described with reference to the following drawings in
which
Figure 1 is a view of a disc cutter according
to an emboA;rent of the invention.
Figures 2A - 2G show various alternative ~h~pgc
of the hard metal cutting ring.
Figure 3 is a perspective view of the disc
cutter of Figure 1.
BEST MODE
Referring to Figure 1, there is shown a disc
cutter 10 having a hardmetal cutting ring 11 and a hub 12
which has a main body portion 13 formed from a non-
hardmetal material, and an annular peripheral footingportion 14 formed from hardmetal. Support rings 15, 16
provide side support to the hardmetal ring 11. Clamp
rings 28,29 are provided on the outside of the su~o.~
rings 15,16 to securely hold the support rings and the
hardmetal ring 11 in position.
Hub 12 has a more or less conventional design
for disc cutters and includes a bore to allow the hub to
be mounted to a shaft in the usual manner. Hub 12 has a
main body portion 13 which is formed from conventional
cast iron or steel. The main body portion has an inner
wall 17 and an outer wall 18. Inner wall 17 is made
entirely of the ~ol-ventional ferrous metal hub material
(i.e. cast iron or steel) and is not formed from
hardmetal.
In the outer wall is a radial, annular,
integrally formed footing portion 14 which is formed from
hardmetal. In Figure 1, footing portion 14 is formed
from 75% tungsten carbide and 25% cobalt binder. The
footing portion has a hardness HV3 750, a density of
13g/cm3 and a stiffness of GPa 450.
The footing portion is cast integrally with the
conventional main body portion 13 using a cast in carbide
(CIC) process which is known. The process forms the
.. . .
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composite hub having the main body portion and the
footing portion where the hard metal footing portion is
metallurgically bonded to the main body portion. A
transition zone of about 5mm extends between the two
materials, and over the transition zone, the properties
gradually change from tungsten carbide to cast iron or
steel. It is however envisaged that the footing could be
formed separately and fitted into a corresponding recess
on the main body portion.
Footing portion 14 has a first area of larger
cross-section 19 which is within the periphery of outer
wall 18 of the main body portion, and has a second
extending or proud area 20 of smaller cross-section. The
footing thereby presents a pair of upstanding shoulder
portions 21, 22.
Cutting ring 11 is formed from tungsten carbide
and the composition is 87% tungsten carbide and 13
cobalt binder. The cutting ring has a hardness HV3 1070,
a density of 14.2g/cm and a stiffness of greater than GPa
450. The cutting ring 11 has a domed upper portion 23, a
substantially straight lower edge area 24, and a flat
base portion 25.
The width of base portion 25 is substantially
the same as the width of the e~tending second area 20 of
footing portion 14.
Support rings 15, 16 function to prevent
cutting ring 11 from slipping over its footing portion
14. Support rings 15, 16 have substantially straight
clamping faces 26, 27 which are dimensioned to press
against the shoulder portions 21, 22 of footing portion
14 and also against the lower edge area 24 of cutting
ring ll.
Two clamp rings 28,29 are provided to clamp the
support rings 15,16 and the hardmetal ring 11 in place.
The clamp rings are pressed into grooves 30,31 machined
on the hub 13. The clamp rings are split rings to
facilitate attachment of the rings onto the hub.
Figures 2A - 2G illustrate some variations to
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the cross-section of the cutting ring.
The disc cutter according to the invention
allows a disc cutter to be produced which has an
extremely hard-wearing cutting ring having a reduced
tendency to break or crack under the enormous compressive
loads placed on it and on the hub. This is achieved by
supporting the hardmetal ring on a footing which is also
formed from hardmetal while the main body of the hub is
formed from conventional cast iron or steel.
While it may be possible to manufacture a hub
entirely of hardmetal to provide the same reduced
tendency for the cutting ring to break, this would be
considerably more expensive to manufacture than the hub
described above. As well, the cutting ring can be made
proportionally smaller, and particularly can have a
smaller base width without increasing the risk of
fracture of the ring under compressive loads. The
enormous loads on the smaller base width can be supported
and distributed by the footing portion. When the cutting
ring does become worn, it can be simply replaced and
there is no need to replace the hub of the disc cutter.
It should be appreciated that various other
changes and modifications may be made to the embo~ nt
described without departing from the spirit or scope of
the invention.
