DISC CUTTER AND A DUST REDUCTION UNIT

Field of the Invention

The present disclosure relates to a rotatable disc cutter for use in an excavation machine finding utility in mining, construction, trenching, and tunnel boring applications. In particular, it relates to a disc cutter comprising superhard cutting elements mounted in tool holders around a peripheral edge of the disc cutter.

Background

WO 2019/180164 A1 , WO 2019/180169 A1 and WO 2019/180170 A1 each disclose a cutting assembly for use in above and below ground quarries and mines. The cutting assembly is typically used to extract slabs of rock from the ground, before the slabs are taken for further processing, such as polishing.

Each cutting assembly comprises a circular disc cutter, which is moveable between horizontal and vertical cutting orientations. Referring initially to Figures 1 and 2, a cutting assembly for slicing into natural formations 2 underground is indicated generally at 10. The cutting assembly forms part of a long wall mining system 1, commonly found in underground mines. The cutting assembly is a substitute for known shearer technology, which operates on a mine floor 4, amidst a series of adjustable roof supports 6. As the shearer advances in the direction of mining, the roof supports 6 are positioned to uphold the mine roof 8 directly behind the shearer. Behind the roof supports 6, the mine roof 6 collapses in a relatively controlled manner. Typically, a gathering arm collects mined rock at the cutting face and transfers it onto a conveying system for subsequent removal from the mine.

As indicated in Figures 1 and 2, the cutting assembly 10 comprises a base unit 12, a pair of spaced apart support arms 14 extending from the base unit 12, a drive spindle 16 extending between and rotatably mounted to the pair of moveable support arms 14, and a plurality of disc cutters 18 fixed about the drive spindle 16.

In a second example, indicated in Figures 3 and 4, a single support arm 14 extends from the base unit 12. The drive spindle 16 is supported centrally by the single support arm 14, and the plurality of disc cutters 18 is mounted to the drive spindle 16, distributed either side of the single support arm 14. The base unit 12 functions as a transport system for the disc cutter 18. The base unit 12 is moveable to advance and retract the disc cutter 18 into and out of an operational position, in close proximity to the rock formation 2 to be cut. The speed at which the base unit 12 moves closer to the rock formation 2 is one of several variables determining the feed rate of the cutting assembly 10 into the rock formation 2. The base unit 12 (in concert with the roof supports 6) is also moveable sideways, from left to right and vice versa, along the long wall of the rock formation 2 to be mined.

Each support arm 14 is configured to be moveable into a first and a second cutting orientation. In the first cutting orientation, best seen in Figures 1 and 2, the drive spindle 16 is horizontal. As a result, cuts in the rock formation 2 made by the disc cutter 18 are correspondingly vertical. In the second cutting orientation, best seen in Figures 3 and 4, the drive spindle 16 is vertical. Consequently, cuts in the rock formation 2 made by the disc cutter 18 are correspondingly horizontal.

Each support arm 14 is moveable between a first operative position and a second operative position, in optionally each of the first and second cutting orientations, according to the depth of cut required. This is indicated by double end arrow A in Figure 2. For example, in the first operative position, the drive spindle 16 is lowered so as to be in close proximity to the mine floor 4 and in the second operative position, the drive spindle 16 is raised so as to be in close proximity to the mine roof 8.

In use, the disc cutter 18 is brought into contact with the rock formation 2 and rotation of the drive spindle 16, and therefore its disc cutter(s) 18, causes slicing of the rock formation 2. The cutting assembly 10 slices into the rock formation 2, for example, to create clean orthogonal cuts, the size of which depends on the size of the cutting elements 22 selected. The cut rock breakouts either under its own weight or with secondary wedge force, e.g. using a wedge- shaped tool.

A problem with the assemblies described above is that significant dust is generated by the cutting assembly during use, which leads to poor environmental conditions in which operators may work.

It is an object of the invention to provide a cutting assembly which addresses the above mentioned problem. Summary of the Invention

According to the invention, there is provided a cutting assembly comprising a disc cutter, the disc cutter comprising a cutter body having an axis of rotation, a plurality of tool holders and a plurality of cutting elements, the tool holders and cutting elements arranged in at least one set about the cutter body, each set comprising a plurality of tool holders arranged in first, second, third positions and so on, said positions being in sequential order one behind the other in the direction of rotation, each tool holder supporting one or more of the plurality of cutting elements, the cutting elements being provided in a pre-determined sequence of configurations from first position to last position, wherein in the pre-determined sequence of configurations the quantity of cutting elements and/or the lateral spacing of the cutting elements varies, the cutting assembly further comprising a dust reduction unit for reducing the transmission of dust generated by the disc cutter during use, wherein the dust reduction unit comprises a dust exhaust manifold for carrying dust away from the disc cutter, the tool holders and cutting elements successively passing through a slot in the dust exhaust manifold as the disc cutter rotates.

Optional and/or preferable features of the invention are provided in the dependent claims.

Brief Description of the Drawings

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which

Figure 1 is a schematic plan view of an underground mine incorporating an example of a prior art cutting assembly as part of a long wall mining system, and in particular shows the cutting assembly in a horizontal orientation;

Figure 2 is a schematic end view of the long wall mining system of Figure 1;

Figure 3 is a schematic plan view of an underground mine incorporating a further example of a prior art cutting assembly as part of a long wall mining system, and in particular shows the cutting assembly in a vertical orientation;

Figure 4 is schematic end view of the long wall mining system of Figure 3;

Figure 5 is a perspective view of an example disc cutter; Figure 6 is a side view of a cutter body forming part of the disc cutter of Figure 5;

Figure 7 is a front view of a set of tool holders and cutting elements forming part of the disc cutter of Figure 5;

Figure 8 is an exploded partial view of the disc cutter of Figure 5;

Figure 9 is a top view of the disc cutter of Figure 5;

Figure 10 is another top view of the disc cutter of Figure 5;

Figure 11 is a schematic front view showing the effective combined cutting face provided by the cutting elements of Figure 5;

Figure 12 is a partial view of an example of a disc cutter for use with the invention;

Figure 13 is a partial perspective view of another example of a disc cutter for use with the invention;

Figure 14 is a plan view of an embodiment of a tool holder for use in the disc cutter of Figure 12 or 13;

Figure 15 is a plan view of another embodiment of a tool holder for use in the disc cutter of Figure 12 or 13;

Figure 16 is a schematic front view showing the spatial distribution of the cutting faces provided by the cutting elements of Figure 13 when incorporating at least one tilt cutting element;

Figure 17 is a partial perspective view of another example of a disc cutter for use with the invention;

Figure 18 is a schematic front view showing the effective combined cutting face provided by the cutting elements of Figure 17; Figure 19 is a schematic perspective view showing the equivalent combined cutting face provided by the cutting elements of Figure 17;

Figure 20 is a schematic front view showing the spatial distribution of the cutting faces provided by the cutting elements of Figure 17, when incorporating at least one tilt cutting element;

Figure 21 is a side view of a tool holder and cutting element, with a 20 degree back rake angle (Figure 21a) and with a 10 degree back rake angle (Figure 21b);

Figure 22 is a line graph showing normal and cutting forces over time for a tool holder and cutting element, with a 20 degree back rake angle and with a 5 degree back rake angle;

Figure 23 is a bar chart showing averaged normal and cutting forces for a tool holder and cutting element, with a 20 degree back rake angle and with a 5 degree back rake angle;

Figure 24 is a side view of a tool holder and cutting element positioned at a first height (Figure 24a) and at a greater, second height (Figure 24b);

Figure 25 is the schematic front view showing the spatial distribution of the cutting faces provided by the cutting elements of Figure 13 when incorporating at least one tilt cutting element, and shows in particular the relative height of the tilt cutting element compared to the remaining cutting elements in the set;

Figure 26 is a front view of another example of a tool holder for use with the invention, supporting multiple cutting elements;

Figure 27 is a plan view of the tool holder of Figure 26, showing in particular two back-up cutting elements situated behind the main two cutting elements;

Figure 28 is a perspective view of the tool holder of Figure 26;

Figure 29 is a partial perspective view of the cutting assembly in accordance with the invention, showing in particular a first embodiment of a dust reduction unit;

Figure 30 is an enlarged partial perspective view of the dust exhaust manifold, part of the dust reduction unit of Figure 29; Figure 31 is a perspective view of a cutter body forming part of the dust reduction unit of Figure 29, showing in particular radial fluid conduits within the cutter body;

Figure 32 is an enlarged partial perspective view of the cutter body of Figure 31 ;

Figure 33 is a perspective view of the cutting assembly in accordance with the invention, showing in particular a second embodiment of the dust reduction unit, the dust reduction unit comprising a dust extraction manifold and a cover, and with rock shown translucently for clarity;

Figure 34 is a perspective view of the cutting assembly of Figure 33, with the dust extraction manifold omitted;

Figure 35 is a perspective view of the cutting assembly of Figure 33, with only the cover and dust extraction manifold shown translucently for clarity;

Figure 36 is a perspective view of the cutting assembly of Figure 35, with the cover, the dust extraction manifold and the rock shown translucently for clarity;

Figure 37 is a front view of the cutting assembly of Figure 35; and

Figure 38 is a front view of the cutting assembly of Figure 36.

In the drawings, similar parts have been assigned similar reference numerals and a detailed description is omitted for brevity.

Detailed Description

Figure 5 shows an example of a disc cutter 18, which comprises a generally circular body 20 and a plurality of cutting elements 22 arranged peripherally around the circular body 20. Rotation of the drive spindle 16 causes a corresponding rotation of the disc cutter 18.

The disc cutter 18 comprises a plurality of tool holders 24 for each receiving at least one cutting element 22. In this example, there is a repeating set of four tool holders 24 and seven cutting elements 22. There are forty-two cutting elements 22 in total. Each set is repeated identically about the circular body 20. In each set, there are four different spatial configurations of tool holder 24 and cutting element 22, as explained in more detail below. When arranged in sequence, one behind the other in the direction of rotation of the disc cutter 18, the required cutting force of the disc cutter 18 is significantly reduced.

Each tool holder 24 comprises a body portion 26 and a pair of spaced apart legs 28 extending from the body portion 26. The body portion 26 is generally cuboidal. The body portion 26 hosts the or each cutting element 22. Each leg 28 of the pair of legs is plate-like. The legs 28 are spaced apart by a gap 30, which enables coupling of the tool holder 24 either side of the circular body 20. A plurality of slots 32 are positioned periodically along the circumferential surface 34 of the generally circular body 20, as shown in Figure 6. Each slot 32 becomes occupied with said gap 30 when the tool holder 24 is mounted on the circular body 20. The slots 32 reduce the shear force on the bolts during use. By virtue of the circumferential surface 34 of the circular body 20 extending between neighbouring slots 32, tool holders 24 are regularly spaced apart around the circular body 20. In this example, twenty-four slots are provided for twenty-four tool holders 24.

Turning now to Figure 7, the tool holder 24 tapers inwardly from a first end 36, proximate the or each cutting element 22, towards a second end 38, proximate a free end of each leg 28.

A first variant of the tool holder 24 is shown in Figure 7a, which is configured to seat a single, (axially) centrally mounted, cutting element 22.

A second variant of the tool holder is shown in Figure 7b, which is configured to seat two adjacent cutting elements 22.

A third variant of the tool holder 24 is shown in Figure 7c, which is configured to seat two spaced apart cutting elements 22.

A fourth variant of the tool holder 24 is shown in Figure 7d, which is configured to seat two spaced apart cutting elements 22 with a central recessed channel 40 between the two cutting elements 22. The elongate channel 36 extends in the direction of intended rotation of the disc cutter 18 - see Figure 10.

Preferably, the tool holders are arranged in the following sequence: d), c), b), a) as shown in Figure 8. However, any ordering within the sequence is envisaged provided that all four tool holder configurations are used. For example, see Table 1.

Table 1

It is also feasible to use sets containing two, three or more configurations of tool holder(s) and cutting ele ent(s). The size of each cutting element 22 and the spacing between the cutting elements, if more than one cutting element is used on a particular tool holder 24, will need to be adjusted accordingly.

The cutting elements 22 in each set produce an overlapping cut, indicated generally at 42, in the rock, as shown in Figure 11. This evenly distributes the cutting force on the cutting slot. The overlapping cut in the main embodiment is 60 mm, and this is based on four tool holder and cutting element combinations within each set. If a larger overlapping cut is required, more tool holder and cutting element combinations would be used, for example, six, eight, ten, twelve etc. If a smaller overlapping cut is required, less tool holder and cutting element combinations would be required, for example two or three. Figure 12 shows one embodiment of a disc cutter at 100. The disc cutter 100 comprises a set of six tool holders 102. Cutting elements 104 mounted on the tool holders 102 are arranged in a pre-determined sequence. The total quantity of cutting elements 104 in each set is eleven. Multiple sets are mounted about the disc body. The quantity and spacing of the cutting elements depends on the position of the tool holder 102 in the set. The tool holder in first position, designated 102a leads the set. The tool holder in second position is designated 102b. The tool holder in third position is designated 102c. The tool holder in fourth position is designated 102d. The tool holder in fifth position is designated 102e. The tool holder in sixth position, designated 102f, trails the set. This is also a ‘prime’ tool holder. A prime tool holder is one that includes a tilt (or ‘gauge’) cutting element, which is explained in more detail below.

The tool holders 102 are similar to those described earlier with respect to Figure 7. There is a single cutting element on the tool holder 102a in first position. There are two adjacent cutting elements on the tool holder 102b in second position. There are two spaced apart cutting elements on the tool holder 102c in third position. In the last position of the sequence 102f, there are two spaced apart cutting elements on the tool holder, and a recessed channel extends between the two cutting elements. However, the set additionally contains two modified versions of tool holder c. In tool holder c’, the spacing between cutting elements is greater than in tool holder c. In tool holder c”, the spacing between cutting elements is greater than in tool holder c’.

The sequence is summarised in Table 2.

Table 2

Figure 13 shows another embodiment of a disc cutter 200. The disc cutter 200 comprises a set of six tool holders 202. Cutting elements 204 mounted on the tool holders 202 are again arranged in a pre-determined sequence. The total quantity of cutting elements 204 in each set is eleven. Multiple sets are mounted about the disc body. The quantity and spacing of the cutting elements 204 on each tool holder 202 depends on the position of the tool holder 202 in the set. The tool holder in first position, designated 202a leads the set. This is also a prime tool holder since it includes a tilt cutting element. The tool holder in second position is designated 202b. The tool holder in third position is designated 202c. The tool holder in fourth position is designated 202d. The tool holder in fifth position is designated 202e. The tool holder in sixth position, designated 202f, trails the set.

In this embodiment, the tool holder 202a in the first position comprises two spaced apart cutting elements. A recessed channel extends between them. The channel slopes upwardly between a leading and a trailing edge of the tool holder 202a. Tests have proved that the material between two cutting elements will gradually wear away in use. Thus, the corresponding torque and power will be higher. By removing the material between the cutting elements removed prior to first use, the unnecessary initial load is reduced and cutting occurs more smoothly. The tool holder 202b in the second position comprises two spaced apart cutting elements. There is no recessed channel extending between them. The tool holder 202c in the third position comprises two spaced apart cutting elements. These cutting elements are slightly closer together than the cutting elements on the tool holder in the second position. The tool holder 202d in the fourth position comprises two spaced apart cutting elements. These cutting elements are slightly closer together than the cutting elements on the tool holder in the third position. The tool holder 202e in the fifth position comprises two adjacent cutting elements. The tool holder 202f in the sixth position comprises a single cutting element.

The sequence is summarised in Table 3 and it is the preferred sequence.

Table 3

In brief, the sequence is a reverse of the one shown in Table 2. Possible alternative sequences are provided in Table 4.

Table 4

However, any ordering within the sequence is envisaged provided that all six tool holder configurations are used and at least one of the tool holders supports a tilt cutting element. In this embodiment, the cutting elements are polycrystalline diamond compacts (PDCs), commonly found in the Oil and Gas industry on drill bits. Each cutting element 204 is cylindrical with a planar working face that comprises polycrystalline diamond. The working surface of each cutting element 204 are all aligned in the same direction. The cutting elements 204 all face tangentially in the direction of rotation - see Figure 13. Most of the cutting elements 204 face in a direction that is parallel and in line with the disc body. At least one of the cutting elements, designated the tilt cutting element, faces in a direction that is not parallel and in line with the plane of the disc. As an example only, in Figure 14, the tilt cutting element faces in a direction that is 5 degrees from alignment with the plane of the disc body. As a further example, in Figure 15, the tilt cutting element faces in a direction that is 21 degrees from alignment with the plane of the disc body. The prime tool holder may be the tool holder disposed in any of the positions within the set, for example, first position, second position, third position and so on. Typically, the prime tool holder comprises two cutting elements, both of which will be tilt cutting elements, like the example shown in Figure 14. The two tilt cutting elements are ideally located furthest apart (like variants c” or d mentioned previously), to the extent possible along the lateral extent of the tool holder.

As the disc cutter 200 rotates, the first tool holder 202a is presented to the rock formation, then the second tool holder 202b, then the third tool holder 202c and so on. The cutting elements 204 supported by the tool holders 202 sequentially cut into the rock formation. The effect of the pre-configured sequence of cutting elements 204 results in the effective cutting pattern shown in Figure 16.

During use, the tilt cutting elements experience complex loads. It is therefore important to manage the load distribution on the cutting elements across the lateral extent of the tool holder. By doing so, the load on the tilt cutting elements can be minimised, thereby protecting the tilt cutting elements from damage. Such load distribution is achieved by varying the distance between cutting elements across the tool holder, and from first position through to the last position. Figure 16 shows the distance between the centreline of cutting elements from one side of the tool holder to the other side. The distances are non-uniform and vary, depending on the position of the cutting element across the tool holder. The greatest overlap between the cutting elements occurs proximate the outer cutting elements.

Figure 17 shows another embodiment of a disc cutter 300. The disc cutter 300 comprises a set of four tool holders 302. Cutting elements 304 mounted on the tool holders 302 are again arranged in a pre-determined sequence. The total quantity of cutting elements 304 in each set is seven. Multiple sets are mounted about the disc body. The quantity and spacing of the cutting elements 304 on each tool holder 302 depends on the position of the tool holder 302 in the set. The tool holder in first position, designated 302a leads the set. This is also a prime tool holder since it includes a tilt cutting element. The tool holder in second position is designated 302b. The tool holder in third position is designated 302c. The tool holder in fourth position, designated 302d, trails the set.

In this embodiment, the tool holder 302a in the first position comprises two spaced apart cutting elements. There is no recessed channel extending between them. The tool holder 302b in the second position comprises two spaced apart cutting elements that are closer together than the cutting elements in the first position. The tool holder 302c in the third position comprises two adjacent cutting elements. The tool holder 202d in the fourth position comprises a single cutting element.

The sequence is summarised in Table 5.

Table 5

As the disc cutter 300 rotates, the first tool holder 302a is presented to the rock formation, then the second tool holder 302b, then the third tool holder 302c and so on. The cutting elements 304 supported by the tool holders 202 sequentially cut into the rock formation. The effect of the pre-configured sequence of cutting elements 304 results in the effective cutting pattern shown in Figure 18. This effect is equivalent to using a single tool holder and a multitude of cutting elements in a side-by-side arrangement as shown in Figure 19 but with significantly reduced forces during cutting.

Figure 20 shows the distance between the centreline of cutting elements from one side of the tool holder to the other side. As with the cutting elements in Figure 16, the load distribution on the cutting elements across the lateral extent of the tool holder is managed by varying the distance between cutting elements across the tool holder, and from first position through to the last position.

In all embodiments, the back rake angle of the (PDC-type) cutting element is preferably between 5 degrees and 14 degrees. Ideally, the back rake angle is around 10 degrees. Figure

21 shows a comparison between a 20 degree back rake angle from a previous design (Figure 21a) and a 10 degree back rake angle (Figure 21b). By reducing the back rake angle from 20 degrees to 10 degrees, the cutting force is significantly reduced. This reduces the risk of damage to the cutting element(s).

As a further example, Figure 22 shows the cutting forces required for the 20 degree back rake angle compared with a 5 degree back rake angle over time. Both the normal force and cutting force are lower for the 5 degree back rake angle. Figure 23 summarises the data from Figure

22 and shows average normal and cutting forces; it is clear to see that the reduced back rake angle results in lower forces experienced by the cutting elements during cutting. The forces during cutting can also be reduced by lowering the height of the tilt cutting element in the prime tool holder. Figure 24a shows a prime tool holder in which the height of the tilt cutting element has been reduced and Figure 24b shows a prime tool holder in which the height of the tilt cutting element is unchanged. This new location manifests itself in the effective cutting pattern of Figure 25, in which the height of the tilt cutting element (indicated at X) is lower than the rest of the cutting elements in the set. In this way, the tilt cutting element may be configured to only bear the side loads, thereby protecting it from damage.

Turning now to Figures 26, 27 and 28, in an alternative embodiment of the cutting assembly, the tool holder 1000 supports multiple cutting elements. Two tilt cutting elements 1002, 1004 are disposed, spaced apart, with a channel 1006 extending between them. Each tilt cutting element 1002, 1004 is supported within a blind hole, leaving the PCD working surface 1008 exposed. An additional cutting element 1010, 1012 sits behind each of the two tilt cutting elements 1002, 1004. Each of these extra cutting elements 1010, 1012 is stored in an opening, exposing the sidewalls 1014 of the cutting element 1010, 1012. The tilt cutting elements are the ‘main’ cutting elements 1002, 1004 since they are used first, and remain in service until they have become completely worn away, or damaged. The cutting elements 1010, 1012 behind (with respect to the direction of rotation) the main cutting elements 1002, 1004 are ‘back-up’ cutting elements 1010, 1012. The back-up cutting elements 1010, 1012 come into service once the main cutting elements 1002, 1004 have reached the end of their operational life. The back-up cutting elements 1010, 1012 remain in-situ until it is their turn, at which point they are manually transferred from their storage location and inserted into the aforementioned blind holes. Having the back-up cutting elements 1010, 1012 nearby ensures that the duration of stoppages are minimised.

Turning now to Figures 29 to 38, the cutting assembly comprises a dust reduction unit for reducing the transmission of dust generated by the disc cutter during use. There are two key ways in which the dust reduction unit reduces the transmission of dust, firstly by means of dust extraction, and secondly, by means of dampening the dust generated using a fluid, preferably liquid. The dust extraction is essential whereas the dust dampening is an optional addition.

The dust reduction unit comprises a dust exhaust manifold 1100 for carrying dust away from the disc cutter. As shown in Figures 29 and 30, in a first embodiment, the dust exhaust manifold 1100 comprises an exhaust block 1102 with a slot 1104. As shown in Figure 29, as the disc cutter rotates, the tool holders pass at least partially through the slot 1104, a few at a time depending on the size of the slot 1104 (and exhaust block 1102). The exhaust block 1102 is arranged such that it effectively forms a segment with and about the cutter body. During

IB use, cutting elements in cutting mode are disposed in a minor portion of the segment and cutting elements in non-cutting mode are disposed in a major portion of the segment. In cutting mode, the cutting elements are in engagement with rock, and in non-cutting mode, the cutting elements are not in engagement with the rock.

The exhaust block 1102 comprises a primary surface 1106 surrounding the slot 1104 defined by the exhaust block 1102, a plurality of dust inlets 1108 arranged in the primary surface, and a plurality of dust outlets 1110 in a secondary surface 1112. Each dust inlet 1108 is in communication with one or more of the dust outlets 1110 by means of pipeline. The internal tubes have smooth, arcuate surfaces to minimise dust traps. The dust outlets 1110 are arranged at angle of 80 to 100 degrees to the dust inlets 1108. Preferably, the dust outlets 1110 are arranged perpendicularly to the dust inlets 1108. The dust outlets 1110 are connected to the remainder of the dust exhaust manifold, which is omitted for clarity.

As shown in Figures 31 and 32, the dust reduction unit may additionally or alternatively comprise a plurality of fluid outlets for dampening dust generated by the disc cutter. A fluid conduit is located within the disc body for transporting fluid towards the fluid outlets, and the fluid conduit is connected to the fluid outlets.

Optionally, one or more of the fluid outlets are located circumferentially between two successive tool holders. In one embodiment, the fluid outlets comprise nozzles. The nozzles are preferably configured to point towards the cutting elements. In an alternative embodiment, the fluid outlets comprise apertures 1114 in the surface of the cutter body.

In a preferred embodiment, the fluid conduit comprises a plurality of radial fluid conduits 1116, 1118, 1120 (and so on) extending radially outwardly from a central supply conduit 1122. The central supply conduit 1122 is toroidal and lies within the plane of the cutter body. The central supply conduit 1122 may be connected to a mains supply or a reservoir of liquid or gas.

The radial fluid conduits 1116, 1118, 1120 are equi-angularly spaced apart about the central supply conduit 1122. In the embodiment shown in Figures 31 and 32, the radial fluid conduits 1116, 1118, 1120 comprises interconnected first and second conduit legs 1116a, 1116b, with the first conduit leg 1116a extending from the central supply conduit, and the second conduit leg 1116b extending into the fluid outlets 1114. The second conduit leg 1116b is arranged at an angle to the first conduit leg 1116a, and this enables fluid carried within the radial fluid conduits 1116, 1118, 1120 to be directed towards a location between a pair of successive tool holders. This arrangement is preferable over nozzles as it minimises maintenance and cleaning requirements.

In Figures 33 to 38, a second embodiment of a dust exhaust manifold is indicated generally at 2000. The dust exhaust manifold 2000 comprises an exhaust chamber 2010 with conjoined first and second chamber portions 2010a, 2010b, in fluid communication with each other. The first chamber portion 2010a is cuboidal and generally enclosed (apart from the dust exhaust outlets described below) on all but one side, i.e. the side adjoining the second chamber portion 2010b. The second chamber portion 2010b comprises a pair of spaced apart walls 2012 extending away from the first chamber portion 2010a to define a slot 2014 therebetween. The walls 2012 partially overlap the cutter body in a radial direction. An entrance 2016 and an exit 2018 (Figure 36) indicate the start and the finish of the toolholders passage through the slot 2014 from one end to the other.

The slot 2014 is positioned relative to the cutter body such that the dust exhaust manifold 2000 receives cutting elements transitioning from or having immediately transitioned from cutting mode to non-cutting mode. Again, in cutting mode, the cutting elements are in engagement with rock 2019, best seen in Figure 38, and in non-cutting mode, the cutting elements are not in engagement with the rock. In use, the disc cutter rotates, the cutting elements cut into rock and generate dust, and as the cutting elements move from cutting mode into non-cutting mode, they pass through the dust exhaust manifold, at which point the dust is drawn away. The disc cutter continues to rotate and the process is repeated. As the disc cutter advances, the process leaves a channel 2021 cut in the rock.

The exhaust chamber 2010 is optimally located on the opposite side of the disc cutter to the channel 2021 , i.e. in front of the advancing disc cutter.

In this embodiment, the exhaust chamber 2010 comprises three exhaust outlets for dust extraction. Two exhaust outlets 2020, 2022 are located proximate to the entrance 2016 of the slot and one exhaust outlet 2024 is located proximate to the exit 2018 of the slot. However, two, four or more exhaust outlets in total could be used instead. The exhaust outlets are connected to exhaust ducting 2025 to direct the extracted dust away from the disc cutter as it operates.

A cover 2026 is provided to partially enclose the disc cutter. The cover 2026 is optional for both embodiments of the dust extraction unit, and though it may be omitted, it is recommended to include one as it may enable higher extraction suction to be used though the dust exhaust manifold 1100, 2000. The cover 2026 is generally hemispherical. The cover 2026 comprises a pair of spaced apart major surfaces 2028a, 2028b connected by an arcuate side wall 2030. An opening 2032 to the cover 2026 is disposed along a linear side wall of the hemisphere. For the second embodiment of the dust extraction unit, the opening 2032 extends partially into the arcuate side wall on one side, indicated in Figure 34 at 2032. It is at this location that the exhaust chamber 2010 is positioned. This extension of the cover opening 2032 is not required in the first embodiment of the dust extraction unit 1100. The ducting 2025 may be attached to the cover 2026 for added stability.

In summary, the inventors have found that by targeting the source of dust extraction, dust generated during operation of the disc cutter may be quickly and efficiently removed and directed away. This is achieved by placing dust exhaust manifolds as close as is reasonably possible to the point at which the dust is generated. In contrast with prior art solutions that effectively use powerful fans to drive the dust away, the proposed solution described herein contains the dust, thereby minimising leakage into the immediate environment. This facilitates a cleaner working environment for operators and a more compact design of cutting tool assembly. While this invention has been particularly shown and described with reference to embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.