AU2008221612A1 - Rock Bolt - Google Patents
Rock Bolt Download PDFInfo
- Publication number
- AU2008221612A1 AU2008221612A1 AU2008221612A AU2008221612A AU2008221612A1 AU 2008221612 A1 AU2008221612 A1 AU 2008221612A1 AU 2008221612 A AU2008221612 A AU 2008221612A AU 2008221612 A AU2008221612 A AU 2008221612A AU 2008221612 A1 AU2008221612 A1 AU 2008221612A1
- Authority
- AU
- Australia
- Prior art keywords
- shaft
- rock
- rock bolt
- weakened zones
- weakened
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 239000011435 rock Substances 0.000 claims description 130
- 238000005065 mining Methods 0.000 claims description 29
- 238000005553 drilling Methods 0.000 claims description 17
- 239000002184 metal Substances 0.000 claims description 6
- 238000000227 grinding Methods 0.000 claims description 4
- 238000009434 installation Methods 0.000 claims description 3
- 238000003801 milling Methods 0.000 claims description 3
- 238000009740 moulding (composite fabrication) Methods 0.000 description 8
- 239000007787 solid Substances 0.000 description 7
- 229910000831 Steel Inorganic materials 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- 239000010959 steel Substances 0.000 description 6
- 238000004873 anchoring Methods 0.000 description 5
- 239000011347 resin Substances 0.000 description 5
- 229920005989 resin Polymers 0.000 description 5
- 239000004568 cement Substances 0.000 description 4
- 239000011440 grout Substances 0.000 description 4
- 239000003245 coal Substances 0.000 description 3
- 239000012530 fluid Substances 0.000 description 3
- 238000000034 method Methods 0.000 description 3
- 238000011161 development Methods 0.000 description 2
- 230000018109 developmental process Effects 0.000 description 2
- 238000013467 fragmentation Methods 0.000 description 2
- 238000006062 fragmentation reaction Methods 0.000 description 2
- 238000003754 machining Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000006641 stabilisation Effects 0.000 description 2
- 238000007792 addition Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000035515 penetration Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000003019 stabilising effect Effects 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 230000003313 weakening effect Effects 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Classifications
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D21/00—Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection
- E21D21/0026—Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection characterised by constructional features of the bolts
Landscapes
- Engineering & Computer Science (AREA)
- Mining & Mineral Resources (AREA)
- Structural Engineering (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Geology (AREA)
- Earth Drilling (AREA)
Description
P/00/011 Regulation 3.2 00
O
0
C^
Cq
AUSTRALIA
Patents Act 1990
ORIGINAL
COMPLETE SPECIFICATION STANDARD PATENT Invention Title: ROCK BOLT Applicant: Sandvik Intellectual Property AB The following statement is a full description of this invention, including the best method of performing it known to me: 1 6067 JG 2 00 ROCK BOLT a Technical Field SThe present invention relates to a rock bolt, for the support and stabilisation of rock walls and faces, such as in tunnels. A rock bolt of the present invention is principally for use in underground mining, such as underground coal mining, in rock walls and faces that are themselves to be mined.
IND
00 Background Metal rock bolts are commonly employed in underground mining to prevent Sfailure, such as fragmentation or collapse, of tunnel walls (including the tunnel roof). In one form of rock bolt, a hole is drilled into the rock wall and thereafter the rock bolt is inserted into the hole and is secured therein, such as by a resin or a cement grout. In another form of rock bolt, a drilling tip is applied to the leading end of the bolt and the bolt itself is drilled into the rock wall. Once the bolt has been drilled to the desired depth, the bolt is secured within the hole, usually in the same manner as the first described rock bolt, i.e. with a suitable resin or cement grout.
In some forms of mining, the rock wall into which rock bolts have been inserted, is a wall which is to be subsequently mined. For example, in underground coal mining, an area to be mined and removed is formed by mining a pair of spaced apart, approximately parallel tunnels into a body of earth. The length of each tunnel can be in the order of about 1 km and the spacing between the tunnels can be in the order of about 500 m. A third tunnel is mined to join the inner ends of each tunnel. Thus, the tunnels form a boundary about an approximately rectangular body of earth.
Once the tunnels have been completed, mining and removal of the earth within the boundary of the tunnels can commence. The actual tunnel walls are mined, usually by a long wall shearer (a machine that shears rock from the tunnel wall).
W:UuieeWndrevCompetesMDGT Rock Boftdoc 3 00 O A difficulty with the above form of mining is that the tunnel walls which are Smined include rock bolts which have previously been inserted during formation e( a of the tunnels prior to mining. Removal of the rock bolts is not feasible and Stherefore during mining, the shearer is brought into engagement with the rock bolts as it shears through the tunnel walls. Rock bolts are usually made of steel. However, engagement with a steel rock bolt can damage the shearer and thus reduce operating efficiency and increase downtime and maintenance requirements. Accordingly, sometimes the rock bolts which are inserted into a
(N
0 tunnel wall which is to be mined, are made of lower strength materials, such as o plastic or resin, to reduce the likelihood of damage to the shearer. However a Sdisadvantage of those lower strength types of rock bolts is that they provide less rock support than steel bolts and are also more expensive.
Australian Patent No. 568546 discloses a roof bolt which is formed with circumferential grooves at spaced apart positions along its length, in order that the shaft of the bolt is weakened where the grooves are formed compared to the strength of the shaft between the grooves. The grooves permit mining equipment, such as long wall shearers, to break the bolt during mining, thus reducing the likelihood of damage to the mining equipment. The bolt pieces are removed with the mined material and are extracted later.
The development of Australian Patent No. 568546 was made in respect of solid bar rock bolts. Since then, significant developments have taken place in relation to rock bolt design. Applicant has developed hollow rock bolts which offer significant advantages over solid rock bolts. Such rock bolts conveniently can be post grouted, whereas solid rock bolts normally have to be grouted upon installation. Further, hollow rock bolts are more appropriate for use as self drilling rock bolts than solid rock bolts. However, such hollow steel bolts suffer from similar disadvantages as solid steel rock bolts when used for the support of tunnel walls which, for the foregoing reasons, are later to be mined.
Rodc B) doc 00 O Summary of the Invention SAccording to the present invention there is provided a rock bolt for installation e( a into a hole formed in a rock wall, the rock bolt having an elongate shaft which Sis at least partially hollow, the wall of the shaft having a plurality of weakened zones spaced apart lengthwise of the shaft, the weakened zones forming breakage positions of the shaft so that the shaft can be broken into reduced length sections during mining of a rock wall into which the rock bolt has been installed, the tensile strength of the weakened zones being about 80% of the
(N
00 tensile strength of the shaft adjacent the weakened zones.
00 SThe present invention also provides a self drilling rock bolt having an elongate shaft which is at least partially hollow, the shaft having opposite ends and having a drill tip at one end for drilling into a rock wall, the wall of the shaft having a plurality of weakened zones spaced apart lengthwise of the shaft, the weakened zones forming breakage positions of the shaft so that the shaft can be broken into reduced length sections during mining of a rock wall into which the rock bolt has been drilled, the tensile strength of the weakened zones being about 80% of the tensile strength of the shaft adjacent the weakened zones.
The requirement that the tensile strength of the weakened zones be about of the tensile strength of the shaft adjacent the weakened zones is advantageous by reducing the tensile strength in the weakened zones sufficiently to promote breakage during mining, but not sufficiently to reduce the tensile strength of the rock bolt overall below a level that will compromise the effectiveness of the rock bolt in stabilising the rock walls and faces into which the bolt is installed. The 80% requirement was arrived at following significant testing and engineering made with the object of maintaining adequate stabilisation capability, along with the ability to break under the loads applied to the rock face or wall by suitable mining equipment. The rock bolt of the invention advantageously adequately meets these criteria.
The weakened zones preferably are formed and spaced so that when a suitable force is applied to the rock bolt, either directly or indirectly by mining WMUuheMAndt(eComPletes\DGT Rock Bol dOC 00 O equipment such as by a long wall shearer, the shaft of the bolt breaks at least 0 N at two of the weakened zones, or if more than two weakened zones are formed in the shaft, at each of the weakened zones. In this form of the invention, the rock bolt is broken into manageable sections after exposure to an initial force so that further force is not required for further breakage.
Accordingly, once the rock bolt has been broken into the sections separated by the weakened zones, the wall support provided by the bolt is dramatically reduced, so that the mining equipment which mines the rock wall is not
(N
N inhibited by the existence of the rock bolt within the wall.
00 The weakened zones can be formed in any suitable manner. Roll forming is the preferred manner of forming the weakened zones, although the weakened zones could alternatively be formed by machining, for example grinding or milling, or any other material deformation or removal process.
The shaft of the rock bolt can be formed from seamless tube or it can be formed from an elongate metal section which is folded over to form an interior elongate passage. Folding of the metal section is such as to bring opposite edges thereof into abutting contact, whereafter the edges are secured together by electric resistance welding The weakened zones can be formed in any suitable shape. Preferably the weakened zones are formed to reduce the cross-sectional area of the shaft and in such an arrangement, the weakened zones can be formed to have a general V-shape, although they could alternatively be U-shaped or otherwise shaped. The extent to which the cross-sectional area of the shaft is reduced is dependent on the relative weakening that is required as compared to adjacent sections of the shaft that are not weakened. A reduction in cross-sectional area of approximately 20% could be employed, although the reduction can generally be within the range of 5% to Where the weakened zones are created by a reduction in the cross-sectional area of the shaft, the reduction can be made to a portion of the circumference of the shaft only. Thus, the cross-sectional area can be reduced at a single W:JuUe eAndreCompletes\DGT Rock Bol.doc 00 O position of the shaft circumference, or at a plurality of positions. For example, N a groove may be formed through one portion of the circumference, or at two a positions, such as diametrically opposite positions. Alternatively, the crosssectional area of the shaft can be reduced about the full circumference, i.e. the reduction can be an annular reduction. Alternatively, the weakened zones could be formed by a spiral which is roll formed into the surface of the shaft.
IND
A typical rock bolt for underground coal mining is about 1200 mm long. In
(N
N such a rock bolt, between two and eight weakened zones preferably are oO provided. Thus, upon breakage of the rock bolt during mining, the shaft of the Sbolt is broken into between two and six shaft sections of approximately 300 mm each in length. The shaft sections can be recovered from the mined material during further processing following removal of the material from within the mine. Advantageously, because rock bolts of the present invention are usually formed from steel, the shaft sections can be recovered magnetically.
Where the weakened zones are formed to have a general V-shape, the angle of the side walls can be disposed at any suitable angle to produce a profile that is between narrow and deep and wide and shallow. There is no requirement that the side walls be formed symmetrically, but rather, an asymmetrical profile if appropriate, can be adopted.
In relation to self drilling rock bolts, a hollow shaft facilitates the injection of drilling fluid into the hole being drilled to assist penetration of the rock bolt into the rock. Thus, drilling fluid can be injected through the passage of the shaft or the fluid can be returned through the passage. The passage can also be employed during the insertion of resin or cement grout to fix the rock bolt within the opening. Thus, the use of hollow rock bolts, particularly hollow self drilling rock bolts, is preferred over solid rock bolts particularly where the hollow form of rock bolt provides all the beneficial characteristics of the solid form of rock bolt and no additional disadvantages. Accordingly, by introducing the ability to break a hollow rock bolt when appropriate during mining, the attractiveness of the hollow form of rock bolt is increased.
W:UtieW\re CompIee\DGT ROaC Bol.dOC 00 O Brief Description of the Drawings N For a better understanding of the invention and to show how it may be e( a performed, embodiments thereof will now be described, by way of non-limiting Sexample only, with reference to the accompanying drawings.
C Figure 1 is a schematic perspective view of a self drilling rock bolt.
IND
Figure 2 is a sectional view of a portion of a rock bolt configured in accordance 0 with the present invention.
oO c Detailed Description of the Drawings Figure 1 illustrates a self drilling rock bolt 10 which includes an elongate, hollow shaft 11, a drilling tip 12 and a driving and tensioning nut 13. The bolt further includes an anchoring device 14 to assist anchoring of the rock bolt 10 within a self drilled hole. Threaded sections 15 and 16 are formed at each end of the shaft 11, with the nut 13 being threadably engaged with the section and the anchoring device being threadably engaged with the section 16.
The driving and tensioning nut 13 is threadably engaged with the threaded section 15 at the trailing end of the shaft 11 and is engaged by driving equipment to apply rotation and axial thrust to the rock bolt 10 for drilling the rock bolt 10 into a rock wall. Further, upon fixing of the shaft 11 within the self drilled hole, such as with resins or cement grout, the driving and tensioning nut 13 can be rotated down the shaft 11 on the threaded section 15 in the direction towards the anchoring device 14, to engage against the surface of the rock wall into which the rock bolt 10 has been drilled. The nut 13 can thus place the rock bolt 10 in tension so as to impose a compression load on the rock face to further stabilise the rock wall against fragmentation or collapse.
The operation of the rock bolt 10 is discussed in detail in Applicant's copending international application PCT/AU2006/001669, published under WO 2007/053893. Reference should be made to the specification of that international application which is incorporated herein by cross-reference, for a W:UueJAndreCometes\DGT ROd Bo.doc 00 full working description of the rock bolt 10, in particular the anchoring device c 14.
SFigure 2 shows a section 20 of a rock bolt shaft, such as the shaft 11 of the rock bolt 10 and illustrates one embodiment of the present invention. It is to be noted that the shaft 11 of the rock bolt 10 is not configured in accordance with the embodiment of Figure 2, but rather, the rock bolt 10 of Figure 1 is illustrative of one form of rock bolt to which the present invention can be
(N
0 applied.
oo N The section 20 of a rock bolt shown in Figure 2 includes a weakened zone 21 which can be one of at least two, but preferably more than two, weakened zones located in the non-threaded region 22 between the threaded sections 16 of the rock bolt 10 of Figure 1.
The weakened zone 21 is an annular groove which is generally V-shaped and which is formed by roll forming a hollow shaft. The shape of the annular groove could be other than V-shaped, such as U-shaped. It is important that the roll forming does not significantly disturb the shape of the passage 23 which extends through the section 20 and therefore the roll forming operation is such as to displace the metal in the weakened zone 21 axially and outwardly, rather than inwardly and this results in material build-up at each of the open edges 24 of the weakened zone 21. However, this build-up is insignificant and does not affect the performance of the rock bolt The side walls 25 are disposed at an angle a to each other. The angle a can vary between about 40' and 800 and, as shown, is about 40. The internal or root diameter dr of the weakened zone 21 is about 45% of the shaft diameter As indicated earlier, the preferred range of cross-sectional reduction is about 5% to As indicated above, the shape of the weakened region 21 can be selected as required and can be V-shaped, U-shaped, or otherwise shaped, while the method of production can include roll forming, machining or grinding.
W: uie AndrewCompletesDOGT Rock Bol.doc 00 O Likewise, the weakened zone 21 does not have to be annular and Figure 3 CI illustrates an alternative form of weakened zone 30, which comprises a pair of adiametrically opposite V-grooves 31, 32 formed in the section 33 of a rock bolt.
The V-grooves 31, 32 can be otherwise shaped, such as U-shaped and can be formed by grinding or milling. The Figure 3 arrangement may be more easily manufactured than the Figure 2 arrangement, although the weakness provided by the grooves 31 and 32 is directional, i.e. a greater weakness is provided through the section of the weakened zone 30 of reduced diameter d compared
(N
00 to the section of greater diameter D. Thus, mining circumstances will dictate which of the sections 20 or 33 can be employed.
However, what Figure 3 illustrates is that the weakened zone according to the invention can be provided in a number of suitable forms.
It is to be noted that grooves applied to the section 33 can be shaped, positioned or oriented so that weakened zones can be provided through more than one plane of the section 33.
The complete length of the rock bolt 10 of Figure 1 is about 1200 mm and the shaft diameter is about 20 mm. For such a rock bolt, the region 22 preferably includes about three weakened zones.
During a mining operation of a rock wall in which one or more rock bolts have previously been inserted, the rock bolt 10 is subject to attack by mining equipment, such as a long wall shearer. The weakened zones of the invention can be provided such that the rock bolt can break either with direct contact with the mining equipment or with indirect contact. Indirect breaking of the rock bolt can occur through fracture of the rock wall surrounding or adjacent the rock bolt. Regardless of whether the rock bolt is caused to fail with either direct or indirect contact, the capacity to fail according to the invention is such as to minimise or eliminate the possibility of damage to the mining equipment occurring as a result of engagement with installed rock bolts.
W:QLulAndreMCompleteslDGT Rock Bot doc 00 0 The invention described herein is susceptible to variations, modifications c and/or additions other than those specifically described and it is to be 0D understood that the invention includes all such variations, modifications and/or Sadditions which fall within the spirit and scope of the above description.
(N
00 W Uuoe\AnrevCompIeWs\DGT Rod Boh.doc
Claims (12)
1. A rock bolt for installation into a hole formed in a rock wall, the rock bolt e( a having an elongate shaft which is at least partially hollow, the wall of the shaft t' having a plurality of weakened zones spaced apart lengthwise of the shaft, the weakened zones forming breakage positions of the shaft so that the shaft can be broken into reduced length sections during mining of a rock wall into which the rock bolt has been installed, the tensile strength of the weakened zones being about 80% of the tensile strength of the shaft adjacent the weakened (N N zones. oO
2. A rock bolt according to claim 1, wherein the rock bolt is a self drilling rock bolt having a drill tip at one end of the shaft for drilling into a rock wall.
3. A rock bolt according to claim 1 or 2, wherein the elongate shaft is substantially fully hollow.
4. A rock bolt according to any one of claims 1 to 3, wherein the weakened zones weaken the shaft of the rock bolt sufficiently that the shaft breaks at the weakened zones upon fracture of the rock about the shaft. A rock bolt according to any one of claims 1 to 4, wherein the weakened zones are formed by roll forming.
6. A rock bolt according to any one of claims 1 to 4, wherein the weakened zones are formed by grinding or milling.
7. A rock bolt according to any one of claims 1 to 6, wherein the shaft is formed by folding an elongate metal section, the metal section including a profile on one side thereof such that upon folding, the weakened zones are formed.
8. A rock bolt according to any one of claims 1 to 7, wherein the weakened zones are formed to have a V-shape or a U-shape. W:Uulie1AreComlpetesDGT Roc Boft.doc 00
9. A rock bolt according to any one of claims 1 to 8, wherein the weakened c zones are formed as annular grooves. e( A rock bolt according to any one of claims 1 to 8, wherein the weakened zones are formed by a spiral groove.
11. A rock bolt according to any one of claims 1 to 9, wherein the weakened zones are formed in a portion of the circumference of the shaft. o00
12. A self drilling rock bolt having an elongate shaft which is at least partially Shollow, the shaft having opposite ends and having a drill tip at one end for drilling into a rock wall, the wall of the shaft having a plurality of weakened zones spaced apart lengthwise of the shaft, the weakened zones forming breakage positions of the shaft so that the shaft can be broken into reduced length sections during mining of a rock wall into which the rock bolt has been drilled, the tensile strength of the weakened zones being about 80% of the tensile strength of the shaft adjacent the weakened zones.
13. A rock bolt substantially as herein described with reference to the accompanying drawings.
14. A self drilling rock bolt substantially as herein described with reference to the accompanying drawings. W:UbeUdreComptesXDGT Rock Bof.doc
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AU2008221612A AU2008221612B2 (en) | 2007-09-24 | 2008-09-23 | Rock Bolt |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AU2007905206A AU2007905206A0 (en) | 2007-09-24 | Rock bolt | |
| AU2007905206 | 2007-09-24 | ||
| AU2008221612A AU2008221612B2 (en) | 2007-09-24 | 2008-09-23 | Rock Bolt |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| AU2008221612A1 true AU2008221612A1 (en) | 2009-04-09 |
| AU2008221612B2 AU2008221612B2 (en) | 2009-05-14 |
Family
ID=40516721
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| AU2008221612A Ceased AU2008221612B2 (en) | 2007-09-24 | 2008-09-23 | Rock Bolt |
Country Status (2)
| Country | Link |
|---|---|
| CN (1) | CN101397911A (en) |
| AU (1) | AU2008221612B2 (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2256292A3 (en) * | 2009-05-26 | 2015-05-20 | HILTI Aktiengesellschaft | Fastening element with a base body for use in mining and tunnel construction |
| WO2018127294A1 (en) * | 2017-01-09 | 2018-07-12 | Minova International Limited | Composite yieldable rock anchor with improved deformation range |
| WO2019217980A1 (en) * | 2018-05-11 | 2019-11-14 | Epiroc Holdings South Africa (Pty) Ltd | Method of ensuring controlled failure of rock bolt bar |
| EP3485144A4 (en) * | 2016-07-12 | 2020-01-08 | FCI Holdings Delaware, Inc. | Corrosion resistant yieldable bolt |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA948899A (en) * | 1970-02-18 | 1974-06-11 | Chester I. Williams | Rock bolt |
| AU568546B2 (en) * | 1983-07-11 | 1988-01-07 | Titan Mining & Engineering Pty. Ltd. | Roof bolt |
| BRPI0618483A2 (en) * | 2005-11-09 | 2011-08-30 | Sandvik Intellectual Property | rock self-drilling screw |
-
2008
- 2008-09-23 AU AU2008221612A patent/AU2008221612B2/en not_active Ceased
- 2008-09-24 CN CNA200810161017XA patent/CN101397911A/en active Pending
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2256292A3 (en) * | 2009-05-26 | 2015-05-20 | HILTI Aktiengesellschaft | Fastening element with a base body for use in mining and tunnel construction |
| EP3485144A4 (en) * | 2016-07-12 | 2020-01-08 | FCI Holdings Delaware, Inc. | Corrosion resistant yieldable bolt |
| US10941657B2 (en) | 2016-07-12 | 2021-03-09 | Fci Holdings Delaware, Inc. | Corrosion resistant yieldable bolt |
| WO2018127294A1 (en) * | 2017-01-09 | 2018-07-12 | Minova International Limited | Composite yieldable rock anchor with improved deformation range |
| US10697297B2 (en) | 2017-01-09 | 2020-06-30 | Minova International Limited | Composite yieldable rock anchor with improved deformation range |
| WO2019217980A1 (en) * | 2018-05-11 | 2019-11-14 | Epiroc Holdings South Africa (Pty) Ltd | Method of ensuring controlled failure of rock bolt bar |
| US11486250B2 (en) | 2018-05-11 | 2022-11-01 | Epiroc Drilling Tools Ab | Method of ensuring controlled failure of rock bolt bar |
Also Published As
| Publication number | Publication date |
|---|---|
| AU2008221612B2 (en) | 2009-05-14 |
| CN101397911A (en) | 2009-04-01 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FGA | Letters patent sealed or granted (standard patent) | ||
| MK14 | Patent ceased section 143(a) (annual fees not paid) or expired |