AU2003201199B2 - Longwall mining method and apparatus - Google Patents

Description

WO 03/058032 PCT/AU03/00027 1 LONGWALL MINING METHOD AND APPARATUS.

Field of the Invention The present invention relates to mining and, in particular, to retreating longwall coal mining.

Background Art In such mining large blocks of coal are mined. Each block may be 200 metres wide and 2,000 metres in length and is progressively removed by a longwall mining machine.

In order to stabilize the sides (or ribs) of the block prior to the blocks removal, temporary rock bolts, termed rib bolts hereafter, are installed in the side of the block. In contrast the narrow pillars of coal between each block, and which are left in situ as mining progresses, are stabilized by permanent rock bolts, termed wall bolts hereafter.

To date the wall bolts have been solid and are fabricated from steel. The rib bolts have likewise been solid and fabricated from steel. Alternatively, the rib bolts have been solid and been fabricated from fibreglass.

The solid steel rib bolts suffer from the problem that they bend around the coal cutting teeth (shaped like picks) of the longwall mining machine. This fouls the machine and causes an expensive delay in mining whilst the machine is cleared. Also the solid steel rib bolts tend to damage the conveyor(s) which initially convey the coal from the ribs within the mine.

A major advantage of the solid steel rib bolts, however, is that they are magnetically permeable. Thus they can be removed from the downstream coal flow by passing the coal under a magnet field. The steel bolts are thus able to be easily extracted.

In order to overcome the above described problem of machine fouling, in recent years rib bolts made from solid fibreglass rods have been used. These have the advantage that the WO 03/058032 PCT/AU03/00027 2 rods are fractured by the longwall mining machine and so the machine is, in general, not repeatedly fouled.

However, the fibreglass bolts are still liable to damage the conveyor belts and, of course, cannot be magnetically removed from the coal. Also, the fibreglass tends to float in a coal washing plant flotation tank used in downstream processing. In addition, the fibreglass in the coal has various deleterious side effects and thus the miner generally receives a lower price for the coal from the customer if pieces of fibreglass are present in the coal. Some customers demand that no fibreglass be present in the coal. Thus the foregoing is a significant problem and $A500,000 (US$250,000) approximately has recently been spent on research projects in Australia, to try to overcome this problem by putting steel fibres in the fibreglass in the hope that it could then be magnetically extracted but without success.

Object of the Invention The aim of the present invention is to overcome, or at least ameliorate, the abovementioned problem by the use of magnetically permeable tubular rock bolts which are thus designed to shear into relatively small pieces when the longwall mining machine encounters same, and can, of course, be magnetically removed or sink during downstream processing.

A further problem is that the surface into which the rock bolt is embedded may be friable.

This is a particular problem with coal mining because some coals, in particular, are quite soft. The problem afflicts both rib bolts and wall bolts as referred to above. In addition, a similar problem can arise in relation to "hard rock" or metalliferous mining where the rock itself is friable or liable to crumble. This problem is that the bolt as initially installed supports the rock face by means of a support plate which compresses the rock.

Thereafter, however, the rock or coal is liable to crumble away leaving the support plate either no longer in contact with, or no longer compressing, the rock face. Since the bolt itself is immobilised in the rock or coal, it is not possible to support the rock face again other than by inserting a further rock bolt alongside the original rock bolt. This is expensive of both time and materials. A further aim of the present invention is to address 6Z-ZO-800Z OleQ Lt':9L (Lu:H) uJW! :eileJlsnv dl Aq paAiaHj tmLOOZ-SOIV :ON I1 SINOO 00 0 0 S2945CZ-AU 3 C this problem also by providing a means and method whereby the original rock bolt can effectively be re-tensioned.

Summary of the Invention O 5 In accordance with a first aspect of the present invention there is disclosed a method of C"4 C- retreating longwall coal mining, said method comprising the steps of extracting in turn 0 each of a plurality of longwall blocks between each of which a pillar of coal is left N standing, and during or immediately following creating of development headings to define the extent of a longwall block, temporarily stabilizing the ribs of the longwall block utilizing a plurality of rib bolts inserted into said ribs, characterized in that said rib bolts are formed from tubular magnetically permeable material having a strength permitting said bolts to be sheared by longwall mining machinery.

In accordance with a second aspect of the present invention there is disclosed a rib bolt for use in longwall coal mining, said bolt comprising a tubular shaft closed at its leading end and open at its trailing end, and a drive means secured to said trailing end to permit rotation of said rib bolt about its longitudinal axis, said shaft having a strength permitting same to be sheared by longwall mining machinery, and said shaft and drive means being fabricated from magnetically permeable material.

O0LSSG66O MHOS wMU a10 I3SUad 83:9T 8oo inr 63 6Z-ZO-8OO aleQ WLi:9L OUwj :B!Ijlejsnv dl Aq pAiaoa KrLOOZ-SOuV :ON r1 sIoo00 00 0 0 010 Brief Description of the Drawings Three preferred embodiments of the present invention will now be described with reference to the drawings in which: Fig 1 is a schematic perspective view of a retreating longwall coal mine in operation, Fig 2 is a truncated perspective view of a rib bolt in accordance with the preferred embodiment, Fig 3 is an exploded perspective view of the rib bolt including a load distributing plate and a support member, Fig 4 is an exploded longitudinal cross-section through an installed bolt of a second embodiment, and Fig 5 is a view similar to Fig 4 but of a still further embodiment.

Detailed Description

(N,

e¢3 Detailed Description OOL3SS6620 WHOS QWU aio0 N3SUJ 8:9T 800a inr 6a WO 03/058032 PCT/AU03/00027 As seen in Fig 1 a coal mine has a central drive 1 off which to either side extend a plurality of side drives termed development headings 2, 3, 4 and 5 (only headings to one side of the central drive 1 being illustrated). The length of each of the headings 2 5 is of the order of 2000 metres. The distance between the headings 2, 3 and 4, 5 (which defines the width of the corresponding longwall blocks 7, 8) is of the order of 200 metres.

Between the headings 3 and 4 is defined a pillar 9 of coal to be left in situ after the mining has finished. The width of the pillar 9 is of the order of 20 30 metres.

A long wall mining machine, indicated schematically at 10, attacks the face of the longwall block 7 and discharges coal onto a conveyor 12 in the development heading 2 which in turn discharges the coal onto another conveyor 13 in the central drive 1.

During, or just after, the creation of the development headings 2, 3, 4, 5 in turn, the ribs of the longwall block 7, 8 and pillar 9 need to be stabilized to prevent the ribs crumbling or collapsing. This is done by means of rib bolts 17 driven into the ribs of the longwall blocks 7, 8 and by means of wall bolts 19 driven into the ribs of the pillars 9.

The wall bolts 19 are intended to be permanent and are usually solid steel bolts each having a diameter of approximately 16mm and which are intended to be mechanically fixed or anchored, or embedded within resin in a corresponding hole of from 25 to diameter.

However, the rib bolts 17 are only temporary and are intended to be shortly devoured by the longwall mining machine 10. As explained above the rib bolts 17 have hitherto either been solid steel bolts or solid fibreglass bolts with the above described disadvantages.

In order to address these disadvantages, it is proposed to utilize a rib bolt 117 which is fabricated from a hollow steel shaft 22 which, whilst embedded in resin, is intended to shear into pieces when the longwall mining machine encounters the rib bolts 117.

WO 03/058032 PCT/AU03/00027 6 As seen in Figs 2 and 3, rib bolt 117 of the preferred embodiment has a shaft 22 which is a hollow cylinder of indefinite length. The shaft 22 is preferably fabricated from conventional steel pipe and preferably has a nominal bore of from 10-30 mm approximately. The shaft 22 has a tip 23 or leading end which is swaged closed so as to create four impellers 24 which are used to shred the resin cartridge and mix the resin or grout used to hold the shaft 22 of the rib bolt 117 in position.

At the opposite, trailing end of the shaft 22 a domed washer 25 and an hexagonal nut 26 are secured by a means of a frictional press fit, by welding, by threaded engagement, or by some other conventional such means. The interior of the nut 26 is provided with an internal thread 27 which, if desired, is able to be threadably engaged with an external thread 29 on the shank 30 of a support member 31. A typical support member 31 is fabricated from a conventional bolt to which is welded a U-shaped link 32. Such support members can be used to support temporary lights, warning signs, etc.

As best seen in Fig 2, prior to insertion of the rock bolt 1 into a hole previously drilled in the coal, the shaft 22 is passed through a support plate 37 which has a recessed collar 38 which mates with the convex face of the domed washer 25. Following installation of the rock bolt 117, a two-part epoxy resin or grout surrounds the shaft 22 and fills the space between the shaft 22 and the hole (not illustrated). This quick setting resin or grout secures the bolt in position and a hollow tubular spanner (conventional but not illustrated) is used to drive the rock bolt 117 so as to rotate it about its longitudinal axis during the installation procedure. This drives the washer 25 and nut 26 into the recessed collar 38 and ensures that the support plate 37 compresses the coal in the vicinity of the hole. The result is that the coal is stabilized.

Following installation of the rock bolt 117, if desired the support member 31 is able to be threadably engaged with the nut 26. Mine services are then supported by means, for example, of a chain and shackle or D-bolt which engages the U-link 32.

WO 03/058032 PCT/AU03/00027 7 In order to ensure adequate keying or bonding between the grout or resin and the shaft 22, the shaft 22 is preferably provided with a plurality of keying deformations 28 (only some of which are illustrated) along its length in known fashion (eg. by helically rolling). This ensures good keying between the grout and the shaft 22. The deformations 28 preferably are intermittent and have a V-shaped profile or cross-sectional shape. The deformations substantially assist in permitting the shaft 22 to break up under the action of the long wall mining machine The following table specifies a typical product range.

Nominal Bore (mm) Outside Diameter (mm) Nominal Hole Diameter (mm) 17.2 20-21 21.3 25 26 26.9 31-33 33.7 38-40 32 42.4 46 48 The largest size given in the above table represents the current practical limit to enable the nut 26 to be engaged by spanners able to be accommodated by present day bolt insertion machinery.

A particular advantage of the above described arrangements is that a wide range of tubular stock is readily available to suit urgent requests for manufactured rock bolts. The availability extends not only to size but also to the grade of material. For example, pipe with a nominal bore of 22 mm is available in a range of metal qualities which result in a typical range of ultimate tensile strengths (UTS) of from 8 to 15 tonnes.

In hard rock mining and civil engineering projects in Australia within the last 2 years or so before the priority date of the present application, it has been known to use a hollow or tubular steel rock bolt sold under the Registered Trade Mark JUMBOLT. This bolt is the subject of Australian Patent No. 712,346 (to which US Patent No. 5,123,456 WO 03/058032 PCT/AU03/00027 8 corresponds). This bolt was developed to suit the larger diameter holes (45 mm and larger typically) used in hard rock mining. The use of tubular stock to fabricate the shafts of such bolts was developed in order to save both the weight and extra material costs of conventional solid shaft rock bolts. Significant attention to the fabrication was required in order to ensure that the tubular shaft was sufficiently strong for the task. For example, keying deformations (often in the form of either continuous or discontinuous threads) were not cut into the tubular stock but were instead created by inwards deformation of the tubular stock so as not to significantly reduce the wall thickness of the tube. Such bolts have not been used to any significant extent in the coal mining industry.

Conversely, the shaft 22 of the rib bolt 117 is sufficiently weak that it can be sheared by the longwall mining machine 10. Thus conventional JUMBOLTS could not be used as rib bolts 117 without encountering the same problems as conventional solid steel rib bolts.

An alternative form of support member 131 can also be provided as illustrated in Fig. 4.

The support member 131 takes the form of a threaded shank 129 mounted within a cup 130 having a cylindrical side wall 140. A nut 126 is welded to the cap of the cup 130.

Alternatively, the shank 129 and nut 126 can also be formed as a conventional bolt which passes through the cap of the cup 130.

As also illustrated in Fig. 4, it sometimes happens that the coal face 150 in the vicinity of the bolt 117 crumbles away after the bolt has been installed. This is schematically illustrated in Fig. 4. A consequence of this change in the coal face 150 is that the support plate 37 no longer supports, or compresses, the coal face 150. Since the bolt 117 is securely embedded in resin, it is unable to be moved. So, normally in this circumstance the plate 37 lies free of the coal face 150 adjacent, but not abutting, the nut 26.

This can be remedied by engaging the shank 129 with the interior of the nut 26, (the shank 129 having an external diameter less than the internal diameter of the bolt shaft) thereby causing the cylindrical side wall 140 to pass over the nut 26 and abut the support WO 03/058032 PCT/AU03/00027 9 plate 37. Continued rotation of the nut 126 causes the side wall 140 to drive the support plate 37 into contact with the coal face 150. In this way the coal face 150 can again be supported.

The arrangement of Fig. 4 also illustrates a domed washer 125 which is slidably mounted on the bolt 117 rather than being fixed thereto, by welding for example, as illustrated in Figs. 2 and 3.

In Fig. 5, the nut 26 is provided with a hole 200 into which a breakable pin 201 is inserted by means of a friction fit. The shank 129 can then have its tip only partially threadably inserted into the nut 26 until the tip of the shank 129 abuts the pin 201. In this preassembled condition, the entire bolt 117 can be mounted in the hole in the rock or coal face 150 but with the conventional driving machinery engaging the nut 126 rather than the nut 26. In this way the support plate 37 is driven against the coal face 150 in the usual way.

If subsequently the coal face 150 should crumble away, the support plate 37 can be brought to bear against the new face 150 in the following fashion. The nut 126 is rotated thereby causing the shank 129 to rotate relative to the nut 26 which is now fixed by hardened grout. The shank 129 therefore fractures the pin 201 and progresses through the nut 26 until the front edge of the support member 131 bears against the support plate 37.

This re-engagement of the support plate 37 against the face 150 can be repeated several times, if necessary. Also the nut 126 and shank 129 can be replaced with an equivalent nut and longer shank, if necessary.

The foregoing describes only some embodiments of the present invention and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope of the present invention.

WO 03/058032 PCT/AU03/00027 The term "comprising" (and grammatical variants thereof) as used herein is used in the inclusive sense of "including" or "having" and not in the exclusive sense of "consisting only of'.

Claims (9)

1. 2. The method as claimed in claim I wherein said material is steel.
2. 3. The method as claimed in claim 1 or 2 including the step of providing at least some rib bolts with an internally threaded trailing end, and threadably engaging a threaded shank of a support member with each said internally threaded trailing end, whereby objects can be temporality supported by said support members prior to said rib bolts being sheared in said longwall coal mining.
3. 4. The method as claimed in claim 3 including the step of securing a nut at said trailing end. The method as claimed in claim 3 or 4 including the steps of: interposing a load bearing washer on the shaft of each said rib bolt between said trailing end and a face of said coal rib, engaging a threaded shank of cupped support member with said internally threaded trailing end, and rotating said support member so that it passes over said trailing end and bears on said washer, whereby said washer is moved away from said trailing end to bear, or re-bear, against said coal face.
4. 6. A rib bolt for use in longwall coal mining, said bolt comprising a tubular shaft closed at its leading end and open at its trailing end, and a drive means secured to said q -C1 OOL2SSG62O IHOS omu io N3SUNJ 8a:91 800a Inr sa 6-LO-SQOO aleo Lt:9L awIj. :el jsnV dl Aq pGA!AooaJ ILOOr-SOIV :ON CI SLAO0 00 0 0 2945CZ-AU 12 Clq trailing end to permit rotation of said rib bolt about its longitudinal axis, said shaft having a strength permitting same to be sheared by longwali mining machinery, and said shaft and drive means being fabricated from magnetically permeable material. o 7. The bolt as claimed in claim 6 wherein said drive means comprises a nut secured to said shaft trailing end. Cl 8. The bolt as claimed in claim 7 having a washer located on said shaft adjacent said shaft trailing end.
5. 9. The bolt as claimed in claim 8 wherein said washer is domed with its convex side facing away from said nut towards said leading end. The bolt as claimed in claim 8 or 9 wherein said washer is fixed to said bolt.
6. 11. The bolt as claimed in claim 10 wherein said nut is welded to said shaft.
7. 12. The bolt as claimed in claim 10 wherein said nut is threadably attached to said shaft.
8. 13. The bolt as claimed in any one of claims 9 12 wherein said washer is dimensioned to bear against the central opening of a support plate.
9. 14. A method of retreating longwall coal mining, said method being substantially as herein described with reference to the drawings. A rib bolt for use in longwall mining, said rib bolt being substantially as herein described with reference to Figs. 2-5 of the drawings. OOLaSSG66aO LHOs (mU 010 u3Su8d 82:9T 800a Int" 62 6Z-LO-9OZ (P-n-Mk ale(] k79L (wH) owij :e!Iw~snV dl Aq poAiaoaH t7ZLOQZ-SOiV :oNq ci SO 00 2945C27-AU 13 (SKIDated thi 29 1 day of July 2008 INDUSTRIAL ROLL FORMERS PTY LIMTED ON By FRASER OLD SOHN Patent Attorneys for the Applicant Z.-CI DoLaGG66ao OOL2SSG~O HOS OWU 010 MIJSUNJ 8a~9T 8OOa TnC 62