EP3688284A1

EP3688284A1 - Cutting drum for borer miner

Info

Publication number: EP3688284A1
Application number: EP17784883.5A
Authority: EP
Inventors: Ralf Grief; Friedrich Pucher; Karl IRREGGER
Original assignee: Sandvik Intellectual Property AB
Current assignee: Sandvik Intellectual Property AB
Priority date: 2017-09-29
Filing date: 2017-09-29
Publication date: 2020-08-05
Anticipated expiration: 2037-09-29
Also published as: CA3075427A1; CN111148886B; WO2019063088A1; CN111148886A; ES2893534T3; EP3688284B1; PL3688284T3; RU2742930C1

Abstract

A cutting drum for a borer-type continuous miner and in particular, although not exclusively, to a bottom cutting drum mountable immediately behind forwardmost primary cutting rotors. The cutting drum comprises a plurality of material transport blades extending lengthwise along the drum between the pick holders and positioned side-by-side in a circumferential direction around the drum to cover an outward facing drum face. The blades are effective to provide transport of cut material to minimise power consumption of the cutting head and accelerated wear of cutting picks.

Description

Cutting Drum for Borer Miner

Field of invention

The present invention relates to a cutting drum for a borer miner and in particular, although not exclusively, to a bottom cutting drum configured to work cooperatively with forwardmost primary cutting rotors of a borer miner to both cut and facilitate rearward transport of cut material.

Background art

Continuous mining machines have been developed to provide uninterrupted continuous mining. Typically, the continuous miner has a mining head to abrade material at the mine face which is gathered and deposited onto a rearward extending conveyor projecting from a forward to a rearward region of the mining machine.

Borer miners may be crawler mounter full-face continuous miners, capable of powerful and rapid forward advancement into rock and being either manually driven or remote control operated. Typically, a borer miner is used to drive entries and headings, mine rooms and extract pillars as fast as haulage equipment can remove the material from the region of the miner. Usually, a borer miner includes a cutting head having one or more pairs of forwardmost primary cutting rotors with rotational axes aligned generally parallel with a main length of the machine. Top and bottom cutting drums are positioned in the lengthwise direction of the machine immediately behind and respectively at the upper and lower regions of the primary rotors. These cutting drums provide a dual operation to cut or abrade rock at the mine face that is untouched by the rotors in addition to providing further cutting of material fragments already cut by the rotors.

However, conventional borer miners whilst being effective for rapid forward cutting, are typically energy inefficient, in part, due to the operation of the bottom cutting drum. In particular, existing bottom drums are not adapted to gather and clear material at the lowest most regions of the miner resulting in an accumulated mass of cut material at the forward and lower regions of the machine. This material is periodically reengaged by the lower cutting drum and primary rotors and re ground. Accordingly, additional and unnecessary energy is consumed by this regrinding and the forward pushing of the already cut material at the mine floor. Additionally, and as will be appreciated, accelerated wear of the working parts of the rotors and drums is a common problem. Accordingly, what is required is a borer miner and a cutting drum for a borer miner that at least in part addresses these problems.

Summary of the Invention It is an objective of the present invention to provide a borer miner cutting drum and a borer miner offering enhanced gathering and rearward transport of cut material from the forwardmost cutting head of the machine. It is a specific objective to provide a borer miner cutting drum to reduce motor power demand and to increase productivity of the mining machine. It is a further specific objective to reduce secondary crushing of the borer miner and the maximised gathering and rearward transport of cut material at the mine face. The objectives are achieved via a cutting drum for a borer miner mountable immediately behind and at the lower region of forwardmost primary cutting rotors having a plurality of material transport blades extending between cutting pick holders (and cutting picks). The blades are adapted specifically to provide multiple modes of operation and function. In a first mode of operation, the blades collate and temporarily hold material cut primarily by the lower drum and then transport and discharge this material directly to the rearward transport conveyor of the miner. In a second mode or function the blades are adapted to gather, transport and propel material already cut by the primary rotors (or even the cutting drums) into the path of the primary rotors for indirect supply to the rearward conveyor. Additionally, the present bottom drum via the material transport blades is adapted to gather cut material at the very lowermost regions of the mine being specifically the region immediately underneath the prime rotors at the mine floor. The plates are adapted specifically to both gather cut material and then to transport the material (in the rotational direction of the drum around the drum longitudinal axis) such that cut material is transported (by rotation) upwardly and then ejected from the drum either into the path of the primary rotors or directly onto the miner conveyor. Advantageously, the blades are orientated at the drum so as to release the cut material from rotation about the drum into the path of the primary rotors or onto the conveyor such that the material does not accumulate at the drum and/or is ejected from the drum back at an undesirable position i.e., towards the mine floor or other regions of the mine or borer miner.

According to a first aspect of the present invention there is provided a cutting drum for a borer miner having a longitudinal axis to extend transverse or perpendicular to rotational axes of forwardmost primary cutting rotors of the borer miner, the drum comprising: a main body centred on the longitudinal axis and having an external facing drum face; a plurality of cutting pick holders projecting outwardly from the drum face to mount respective cutting picks at the main body; characterised by: a plurality of material transport blades each having a respective outward facing blade face being raised radially from the drum face, each of the blades extending generally lengthwise along the drum between the pick holders and positioned side-by-side in a circumferential direction around the drum to cover the drum face. Optionally, each blade face may be generally planar. Optionally, each blade face comprises a generally rectangular shape profile in which a main length of the blade extends lengthwise along the drum and generally parallel to the longitudinal axis of the drum. Preferably, in a cross sectional plane perpendicular to the longitudinal axis, each blade face is declined in a circumferential (rotational) direction of the drum such that a first lengthwise side is positioned radially beyond an opposite second lengthwise side i.e., at a greater radial separation from the drum axis. Such a configuration is advantageous to gather and capture cut material for partial rotational transfer around the longitudinal axis of the drum. The angle of the decline is configured specifically to provide a desired and a predetermined distance of angular transport as the material is cut and/or gathered by the drum, rotated and then ejected either into the path of the primary rotors (involving a generally upward and possibly forward material transfer) or onto the rearwardly extending conveyor (involving upward and rearward transport of the material around and from the drum) relative to the drum longitudinal axis and a main length of the miner. Optionally, an angle by which each blade face is declined relative to the radius of the drum is in a range 35 to 85°, 40 to 80°, 45 to 75° or 50 to 70°. This angled orientation of the blade face (relative to the radial spokes of the drum) provides the desired capture, retention and release characteristics of the drum and specifically avoids cut material accumulating around the drum which would otherwise be continuously rotated and accordingly increase power consumption.

Preferably, the blades extend over a majority of the surface area of the drum face between the cutting pick holders (and the picks). This majority may be greater than 50%, 60%, 70%, 80%, 90% or 95% of the surface area of the drum face being the outward facing generally cylindrical drum face extending at a central region of the drum axially between a pair of arms that mount the drum at the miner cutting head. In particular, and preferably, the blade faces cover a majority of the drum face in both an axial and a circumferential direction between the pick holders. The surface area of uncovered and exposed drum face is therefore minimised to avoid accumulating cut material that is not otherwise transported into the primary rotors or to the conveyor. Preferably, the drum further comprises a plurality of cutting picks mounted at the pick holders, each of the picks having a cutting tip, the blades positioned at the main body such that a radial separation distance between the cutting tips and a radially outermost part of the blades is in a range 20 to 80 mm, 25 to 75 mm, 30 to 70 mm or 35 to 65 mm. This separation distance between the cutting tips and outermost portions of the blades provides an optimised compromise between forward penetration rate of the borer miner and power consumption. That is, the separation distance provides a sufficient length of the pick cutting tips extend in a radial direction of the drum to be capable of penetrating and abrading the rock whilst avoiding or minimising direct contact between the blades and rock. The present drum therefore is configured both for effective rock cutting/abrading and also to gather and transport cut material either into the path of the primary rotors or directly onto the rearward conveyor.

Preferably, the blades are arranged into sets in which each set comprises a plurality of blades positioned side-by-side in the circumferential direction, each of the sets being separated axially by a plurality of pick holders. Distributing the blades into sets is advantageous to maximise surface area coverage at the drum between the pick holders projecting radially outward from the drum face. Optionally, the drum comprises in a range 4 to 16, 4 to 14, 4 to 12 or 8 to 12 of the sets. Optionally, at least some of the sets extend over an angular distance in the range 60 to 120°, 70 to 110° or 80 to 100°. Optionally, a length of each blade or at least some of the blades within each set are different.

Optionally, a length of the blades within each set is the same. Preferably, the drum comprises blades of different lengths to fit appropriately between the pick holders both in the longitudinal and circumferential directions at the drum face. Optionally, where the drum comprises sets of material transport blades, each blade may be individually mounted within each set. Optionally, the blades within each set may be integrally formed such that each set may be independently changeable at the drum with respect to other sets.

Optionally, the number of blades within at least some of the sets is different.

Preferably, the drum, at least at selected axial sections of the drum, comprises pick holders arranged along a single helical path. Optionally, the pick holders may extend over the drum face following two or multiple helical paths. A single helical path is preferred to maximise the arrangement and distribution of the plates so as to reduce drive power consumption as cut material is effectively and efficiently gathered and transported rearward from the mine face to eliminate or minimise undesirable regrinding. Optionally, the drum may be divided axially to comprise a central section and a first and a second end section, wherein the blades are mounted at the central section. Preferably, the first and second end sections comprise respective material conveyor fins projected radially outward from the drum face and extending helically over the drum face around the axis. Preferably, the end sections are devoid of the material transport blades. Such a configuration is advantageous to optimise the effectiveness of the material conveyor fins at the drum end sections to transport axially cut material towards the drum central section, for subsequent transport and transfer into the path of the primary rotors and/or to the miner conveyor. Optionally, the material transport blades are removably mounted at the drum to represent wear parts capable of convenient interchange at or between servicing intervals of the borer miner. Optionally, regions of the material transport blades including preferably radially outer regions comprise welded seams, coatings or reinforcement to protect against accelerated frictional wear or rock abrasion damage.

According to a second aspect of the present invention that is provided a borer miner comprising: a plurality of primary cutting rotors positioned axially forwardmost at the miner and having respective rotational axes aligned generally in a lengthwise direction of the miner; and a cutting drum as claimed herein positioned such that the longitudinal axis of the drum extends widthwise across the miner, the drum mounted in a lengthwise direction of the miner behind and at a lower region of the cutting rotors.

Preferably, the miner further comprises a top cutting drum having a longitudinal axis and mounted at the miner such that said longitudinal axis extends widthwise across the miner, the top cutting drum mounted in a lengthwise direction of the miner immediately behind and at an upper region of the cutting rotors. Preferably, the borer miner is a crawler mounted full-face continuous miner configured for use in demanding environments. Optionally, the miner is configured for manual or remote control in which the cutting drum is capable of manual or automatic powered control.

Brief description of drawings

A specific implementation of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

Figure 1 is a perspective view of a crawler mounted boring-type continuous miner having a top and bottom cutting drum positioned immediately behind a pair of forwardmost primary cutting rotors according to a specific implementation of the present invention;

Figure 2 is a perspective view of the bottom cutting drum of the borer miner of figure 1 ; Figure 3 is a lengthwise side view of the cutting drum of figure 2;

Figure 4 is a cross sectional view through A- A of figure 3;

Figure 5 illustrates a section of the drum of figures 2 and 3 in a plane perpendicular to the drum longitudinal axis according to a specific implementation of the present invention.

Detailed description of preferred embodiment of the invention

Referring to figure 1, a crawler mounted boring type full-face continuous miner 10 comprises a main frame and chassis 12 mounting crawler tracks 13 and a rearward transport conveyor 14 extending lengthwise along the miner 10 from a forward to a rearward position. A cutting head 11 is positioned at forward end of miner 10 and comprises a pair of primary cutting rotors 15a, 15b having respective rotational axes 33a, 33b aligned parallel with a main length of miner 10 and conveyor 14. A pair of elongate cutting drums 16, 17 are positioned immediately behind rotors 15a, 15b (in a lengthwise direction) with the first (bottom) drum 16 mounted at a lower region of miner 10 and second (top) drum 17 mounted at an upper region of miner 10. Each drum 16, 17 comprises a respective longitudinal axis 18a, 18b aligned perpendicular to the respective rotational axes 33a, 33b of primary rotors 15a, 15b. Accordingly, cutting drum 16, 17 extend widthwise across miner 10 at head 11 so as to define a maximum cutting width of head 11. As will be appreciated, miner 10 is effective via the cutting head 11 to abrade rock continuously as miner 10 is advanced forward via tracks 13. Primary rotors 15a, 15b provide an initial and primary cutting of the rock and the drums 16, 17 provide a secondary and supplementary cutting action. Miner 10 is typically configured for creating drive entries, headings, mine rooms and to extract pillars continuously for rapid advancement rates. Efficient forward cutting is achieved via the direct rearward transport of cut material from cutting head 11 to a stock pile at the rearward lengthwise end of machine 10 via material transport conveyor 14. In particular, as primary rotors 15a, 15b are rotated about axes 33a, 33b in respective rotational directions Ri and R₂, material is cut and driven into the axial centre of head 11. The forwardmost end of conveyor 14 emerges at the axial centre of head 11 immediately behind rotors 15a, 15b. Further cutting and transport of cut material into the axial centre of head 11 is achieved via the respective bottom and top drums 16, 17 rotating respectively about axes 18a, 18b in respective rotational directions R₃ and R₄. In particular, bottom cutting drum 16 is specifically adapted according to the present invention to greatly facilitate collation and transport of cut material into the axial centre of the head 11 and to the forwardmost end of conveyor 14 for efficient rearward transport and to avoid specifically regrinding of the cut material by the rotors 15a, 15b and drums 16, 17 as described below.

Referring to figures 2 and 3 bottom cutting drum 16 comprises a generally elongate configuration centred on axis 18a. An outward facing drum face 21 is generally cylindrical about axis 18a. Drum 16 is mounted at cutting head 11 via a pair of gear box arm mountings 27 (only one is shown in figure 2 and 3) so as to maintain the drum 16 in rotational mounted position at the lower region of miner 10 and immediately behind the lower region of rotors 15a, 15b. Drum 16 is divided in this lengthwise direction to comprise a pair of first and second axial end sections 19 separated by an axial central section 20, with the sections 19, 20 separated axially by gear box arms 27. A plurality of cutting pick holders 22 are distributed at the end 19 and central 20 sections to mount respective cutting picks 23, with each pick having a respective cutting tip 24 configured to abrade the rock for forward advanced cutting of the continuous miner 10 as drum 16 is rotated about axis 18a in direction R₃. According to the specific implementation, pick holders 22 are mounted and project from drum face 21 to follow helical paths around axis 18a. In particular, pick holders 22 and picks 23 at the drum end sections 19 are arranged to follow two separate helical paths and at central section 20 to follow a single helical path around axis 18a (from a first end to a second end of central section 20) between the pair of gear box arms 27.

A pair of elongate conveyor fins 26 (alternatively termed blades) project radially from drum face 21 at each end section 19. The conveyor fins 26 are arranged to follow respective helical paths approximately aligned with the helically distributed pick holders and picks 22, 23 at the respective end sections 19. Conveyor fins 26 are adapted to facilitate axial transport of cut material towards the axial centre of drum 16 and in particular the central section 20. This axial transport is achieved via the helical path of fins 26 at drum face 21.

Drum central section 20 further comprises a plurality of material transport blades 25 that cover substantially the drum face 21 (at central section 20). Each of the blades 25, according to the specific implementation, comprise a respective radially outward facing blade face 28, with each face 28 being elongate in the axial direction of drum 16. In particular, each blade face 28 comprises a main length aligned with the drum axis 18a and a corresponding width extending in the circumferential direction around axis 18.

Accordingly, each blade face 28 is defined by respective first and second lengthwise ends 29c, 29d with each end 29c, 29d positioned approximately at respective axially separated pick holders 22. Each blade face 28 is further defined by a pair of opposite lengthwise sides 29a, 29b that are separated in the circumferential direction around drum 16 within central section 20. The blades 25 are mounted at drum 16 in a side-by-side arrangement with the respective lengthwise sides 29a, 29b of neighbouring blades 25 being generally parallel with one another and in touching or near touching contact. Accordingly, the outward facing drum face 21 is substantially and generally covered by the pick holders 22 and the blades 25, with the blades 25 positioned axially and in a circumferential direction between the helically extending pick holders 22 (and picks 23). Referring to figure 4 in combination with figures 2 and 3, the blades 25 may be considered to be divided into a plurality of sets 32a, 32b at drum central section 20 with the sets 32a, 32b being defined by their different respective positions at the drum face 21 relative to the pick holders 22, the axial ends of the central section 21 and the pair of gearbox arms 27. Each set indicated generally be reference 32a, 32b may be defined as comprising a plurality of blades 25 with each of the blade lengthwise sides 29a, 29b positioned side-by- side with a respective neighbouring blade 25 (of the same set) so that the blades within each set extend substantially continuously in a circumferential direction around axis 18a to effectively fill the gap at the external facing side of the drum 16 between the pick holders 22. The number of blade 25 within each of the sets 32a, 32b may be different depending upon the position of each respective set 32a, 32b at drum central section 20 as indicated above. For example, set 32a is axially closest to gear box arms 27 and comprises three blades 25, with each blade comprising a respective blade face 28 defined by lengthwise ends 29c, 29d and lengthwise sides 29a, 29b.

Each blade set 32a, 32b extends over an angular distance Θ. According to the specific implementation, the axially outer sets 32a (positioned immediately inboard of the gear box arms 27) extends over an angular distance Θ being 80 to 100°. The axially inner set 32b comprising more blades than sets 32a may extend over an angular distance Θ in a range 140 to 190°. Optionally, the axially outer sets 32a may comprise three blades and the axially inner set 32b may comprise four, five, six, seven, eight or more blades 25.

Each blade 25 at drum 16, according to the specific implementation, comprises a respective rib 30 having a main length extending axially over drum face 21 and a width extending radially at drum 16 being aligned on a respective drum radius. Accordingly, each rib 30 comprises a width that protects radially outward from drum face 21 and a length that extends axially between respective pick holders 22 within the single helical path at drum face 21. Each blade 25 further comprises a blade plate 29 having a respective blade face 28 defined by lengthwise sides 29a, 29b and lengthwise ends 29c, 29d. Each blade plate 29 is mounted at and extends in a circumferential direction between adjacent blade ribs 30 via the plate lengthwise sides 29a, 29b. According to the specific implementation, blades 25 are rigidly mounted at neighbouring ribs 30 (in the

circumferential direction) via welded seams 31. Seams 31 are further advantageous to reinforce and provide frictional wear resistance to the blades 25 against abrasion induced wear. According to the specific implementation, each blade plate 29 is mounted at an angled or declined orientation in a circumferential direction around axis 18a relative to drum face 21. In particular, a first lengthwise side 29a is separated from axis 18a by a first radial separation distance R' which is greater than a corresponding radial distance R'" of a second respective lengthwise side 29b. As illustrated in figure 4, each blade plate 28 is declined relative to each blade rib 30 at a declined angle a. According to the specific implementation a is in a range 50 to 70°. Accordingly, a radial separation distance between the first and second lengthwise sides 29a, 29b of each blade plate 28 may be in a range 35 to 65 mm (corresponding to the difference between R' and R'").

Referring to figure 5, blades 25 are mounted at drum 16 such that they are positioned in a radial direction entirely inboard of cutting tips 24 and the cutting picks 23, or at least a majority of a radial length of each pick 23. Such a configuration is required to achieve the desired penetration of picks 23 into the rock and to avoid rock fouling of the blades 25 as drum 16 is rotated in direction R₃. Accordingly, each pick tip 24 is positioned at a radial distance R" which is greater than the radial distance R'. In particular, the radial separation difference h between R" and R' according to the specific implementation is in a range 35 to 65 mm. Such a configuration is advantageous to achieve a desired maximum forward penetration rate of miner 10 whilst avoiding fouling and accelerated frictional wear of blades 25. In use, as drum 16 is rotated in direction R₃ different sections along the length of drum 16 are required to provide different cutting and transport functions as determined by their different respective axial positions at drum 16 relative to the forwardmost primary rotors 15a, 15b. That is, drum end sections 19 generally project outward beyond the radial cutting paths of rotors 15a, 15b and in turn make a significant contribution to the cutting of fresh rock as miner 10 is advanced. Material cut by picks 23 at end sections 19 is transported axially along drum 16 to the central section 20 via helical conveyor fins 26. The axially outermost sets 32a of blades 25 may be considered to be positioned immediately behind the radial cutting path of rotors 15a, 15b so as to encounter already cut material. The blades 25 at these axial positions (immediately axially inboard of gear box arms 27) are effective to transport cut material in a rotational direction R₃ around axis 18a and then to eject the material upwardly into the radial cutting path of rotors 15a, 15b. The material ejected from blade sets 32a is then transported by rotors 15a, 15b into the axial centre of head 11 and onto the forward end of conveyor 14. The blades 25 at and towards the axial centre of drum 16 (represented, in part, by blade set 32b) are positioned outside the radial cutting path of rotors 15a, 15b and accordingly encounter a wall of uncut rock. The material cut primarily by bottom drum 16 at the axial central region of drum section 20 is gathered and transported by blades 25 (within sets 32b) in the rotation direction R₃ so as to be transported upwardly and then to be ejected rearwardly into the axial centre of head 11 and onto the forward end of conveyor 14 (without being delivered to the cutting path of rotors 15a, 15b). Accordingly, the blades 25 at the different axial positions of drum 16 provide a different respective function for material cutting, gathering and rotational transport depending upon their respective axial positions relative, for example, to the rotational cutting paths of primary rotors 15 a, 15b. Accordingly, the declined angle a by which each blade plate 28 is aligned to extend in a circumferential direction relative to blade ribs 30 is configured to retain cut material for a sufficient time period as it is transported in rotational direction R₃ so as to be capable of being ejected both into the rotational paths of rotors 15a, 15b and also in the rearward direction from axis 18a onto the forward end of conveyor 14. Blades 25 being configured to substantially completely cover drum face 21 are effective to deliver cut material into the cutting paths of rotors 15a, 15b and onto conveyor 14 and specifically to minimise or avoid unnecessary re grinding of material in addition to greatly facilitating rearward transport of cut material via conveyor 14.

Again referring to figure 4, the present arrangement of blades 25 is further advantageous to minimise a separation distance S between the blades 25 and the mine floor 34. Effectively, the free volume below the bottom drum 16 is reduced by a radial volume of the blades 25 that are arranged at drum 16 to occupy a majority of otherwise free volume between the picks 23 in both the axial and circumferential directions. The blades 25 occupying this free volume are effective to gather and collate cut material at the mine floor 35 to avoid material accumulating at the lower region of the cutting head 11. Material accumulated at this lower region is undesirable as it reduces material cutting efficiency and significantly increases power demand of the miner 10. That is, with conventional borer miners, material collected at the lower region of the cutting head 11 is effectively carried forward with the forward advancement of the miner 10 and periodically introduced into the cutting path of the rotors 15a, 15b and drum 16 where it is reground. Blades 25 minimise and preferably eliminate material stock piling below drum 16 that reduces power consumption of cutting head 11 and increases service lifetimes of the active components of the cutting head 11 including picks 23, pick holders 22 as well as gear box components 27. The respective radial separation distance h between R' and R" accordingly represents a compromise between forward penetration rates and power consumption with the present arrangement of blades 25 representing an appropriate compromise with a specific focus on minimising power consumption.

Claims

1. A cutting drum (16) for a borer miner (10) having a longitudinal axis (18a) to extend transverse or perpendicular to rotational axes (33a, 33b) of forwardmost primary cutting rotors (15a, 15b) of the borer miner (10), the drum (16) comprising:

a main body centred on the longitudinal axis (18a) and having an external facing drum face (21);

a plurality of cutting pick holders (22) projecting outwardly from the drum face (21) to mount respective cutting picks (23) at the main body;

characterised by:

a plurality of material transport blades (25) each having a respective outward facing blade face (28) being raised radially from the drum face (21), each of the blades (25) extending generally lengthwise along the drum (16) between the pick holders (22) and positioned side-by-side in a circumferential direction around the drum (16) to cover the drum face (21).

2. The drum as claimed in claim 1 wherein each blade face (28) is generally planar.

3. The drum as claimed in claim 2 wherein in a cross sectional plane perpendicular to the longitudinal axis (18a), each blade face (28) is declined in a circumferential direction around the drum (16) such that a first lengthwise side (29a) is positioned radially beyond an opposite second lengthwise side (29b).

4. The drum as claimed in claim 3 wherein an angle (a) by which each blade face (28) is declined relative to the radius of the drum (16) is in a range 35 to 85°, 40 to 80°, 45 to 75° or 50 to 70°.

5. The drum as claimed in any preceding claim wherein the blade faces (28) cover a majority of the drum face (21) in both an axial and circumferential direction between the pick holders (22).

6. The drum as claimed in any preceding claim comprising a plurality of cutting picks (23) mounted at the pick holders (22), each of the picks (23) having a cutting tip (24), the blades (25) positioned at the main body such that a radial separation distance (h) between the cutting tips (24) and a radially outermost part of the blades (25) is in a range 20 to 80 mm, 25 to 75 mm, 30 to 70 mm or 35 to 65 mm.

7. The drum as claimed in any preceding claim wherein the blades (25) are arranged into sets (32a, 32b) in which each set (32a, 32b) comprises a plurality of blades (25) positioned side-by-side in a circumferential direction around the drum, each of the sets (32a, 32b) being separated axially by a plurality of pick holders (22).

8. The drum as claimed in claim 7 comprising in a range 4 to 16, 4 to 14, 4 to 12 or 8 to 12 of the sets (32a, 32b).

9. The drum as claimed in claims 7 or 8 wherein at least some of the sets (32a, 32b) extend over an angular distance (Θ) in the range 60 to 120°, 70 to 110° or 80 to 100°.

10. The drum as claimed in any preceding claim wherein the pick holders (22) are distributed at the drum (16) face to follow a generally helical path around the longitudinal axis (18a) from a first to a second lengthwise end of the drum (16).

11. The drum as claimed in claim 10 wherein the pick holders (22) are arranged along a single helical path.

12. The drum as claimed in any preceding claim divided axially to comprise a central section (20) and a first and a second end section (19), the blades mounted at the central section (20).

13. The drum as claimed in claim 12 wherein the first and second end sections (19) comprise respective material conveyor fins (26) projected radially outward from the drum face (21) and extending helically over the drum (16) face around the axis (18a).

14. The drum as claimed in claims 12 or 13 wherein the end sections (19) are devoid of the material transport blades (25).

15. A borer miner (10) comprising:

a plurality of primary cutting rotors (15a, 15b) positioned axially forwardmost at the miner (10) and having respective rotational axes (33a, 33b) aligned generally in a lengthwise direction of the miner (10); and

a cutting drum (16) as claimed in any preceding claim positioned such that the longitudinal axis (18a) of the drum (16) extends widthwise across the miner (10), the drum (16) mounted in a lengthwise direction of the miner (10) behind and at a lower region of the cutting rotors (15a, 15b).

16. The miner as claimed in claim 15 comprising a top cutting drum (17) having a longitudinal axis (18b) and mounted at the miner (10) such that said longitudinal axis (18b) extends widthwise across the miner (10), the top cutting drum (17) mounted in a lengthwise direction of the miner (10) behind and at an upper region of the cutting rotors (15a, 15b).