EP0351465A1 - Rock bolt - Google Patents
Rock bolt Download PDFInfo
- Publication number
- EP0351465A1 EP0351465A1 EP88306706A EP88306706A EP0351465A1 EP 0351465 A1 EP0351465 A1 EP 0351465A1 EP 88306706 A EP88306706 A EP 88306706A EP 88306706 A EP88306706 A EP 88306706A EP 0351465 A1 EP0351465 A1 EP 0351465A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- bar
- rolls
- rock bolt
- thread
- metal
- 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 title claims abstract description 67
- 239000002184 metal Substances 0.000 claims abstract description 25
- 238000004519 manufacturing process Methods 0.000 claims abstract description 10
- 230000015572 biosynthetic process Effects 0.000 claims description 25
- 238000005755 formation reaction Methods 0.000 claims description 25
- 238000000034 method Methods 0.000 claims description 17
- 239000000463 material Substances 0.000 description 16
- 229910000831 Steel Inorganic materials 0.000 description 4
- 239000010959 steel Substances 0.000 description 4
- 239000003054 catalyst Substances 0.000 description 3
- 238000003754 machining Methods 0.000 description 3
- 238000004873 anchoring Methods 0.000 description 2
- 239000011159 matrix material Substances 0.000 description 2
- 239000012260 resinous material Substances 0.000 description 2
- 239000002775 capsule Substances 0.000 description 1
- 238000005097 cold rolling Methods 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000011440 grout Substances 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 238000005065 mining Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 230000003014 reinforcing effect Effects 0.000 description 1
Images
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/16—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling wire rods, bars, merchant bars, rounds wire or material of like small cross-section
- B21B1/163—Rolling or cold-forming of concrete reinforcement bars or wire ; Rolls therefor
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21H—MAKING PARTICULAR METAL OBJECTS BY ROLLING, e.g. SCREWS, WHEELS, RINGS, BARRELS, BALLS
- B21H3/00—Making helical bodies or bodies having parts of helical shape
- B21H3/02—Making helical bodies or bodies having parts of helical shape external screw-threads ; Making dies for thread rolling
-
- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
- E04C5/00—Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
- E04C5/08—Members specially adapted to be used in prestressed constructions
- E04C5/12—Anchoring devices
- E04C5/125—Anchoring devices the tensile members are profiled to ensure the anchorage, e.g. when provided with screw-thread, bulges, corrugations
-
- 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
- E21D21/008—Anchoring or tensioning means
Definitions
- This invention relates to a rock bolt and more particularly, but not exclusively, to a rock bolt for use in underground mining operations.
- rock bolts are used to secure rock strata underground.
- One kind comprises a length of reinforcing bar having ribs along its length.
- the ribs enhance the anchoring ability of the bolt.
- the bolt is usually rotated in the hole to mix the settable material and the ribs also serve the purpose of assisting the mixing of the settable material.
- known ribbed formations on rock bolts do not provide good mixing characteristics.
- the end of the bolt which is intended to project from the rock face has a rolled thread thereon which receives a nut used to tension the bolt.
- the bar from which such a prior art rock bolt is made is manufactured in a steel mill and is supplied with the ribs formed on the whole length of the bar.
- the bolt has to be machined to remove the ribs on a section thereof and to ensure that such section has a circular cross-section. Such a machining operation adds to the cost of the prior art rock bolt.
- pitch diameter in relation to a straight thread, means the diameter of an imaginary co-axial cylinder, the surface of which passes through the thread profiles at such points as to make the width of the groove equal to one half of the basic pitch of the thread. On a perfect thread this occurs at the point where the width of the thread and groove are equal.
- bar when used in this specification includes a pipe and a bar with an axial bore.
- a method of making a rock bolt with a thread on a section thereof comprises the steps of providing a metal bar of circular or near circular cross-section having a diameter which is substantially equal to the pitch diameter of the thread to be provided thereon, forming a series of protrusions on a selected section of the bar, straightening the bar, and, forming a thread with the said pitch diameter on a further selected section of the bar.
- This method obviates the need for machining the bar before forming the thread thereon. As will become evident in the subsequent description, the method also results in a saving of material without reducing the yield or tensile load-carrying ability of the rock bolt.
- the metal bar is first cut to a discrete length, is then advanced through means forming the series of protrusions on the selected section of the bar, and is thereafter advanced through straightening means to straighten it, whereafter thread is formed on the further selected section of the bar.
- a continuous length of the metal bar is first advanced through means forming the series of protrusions on selected sections of the bar, the continuous length is thereafter advanced through straightening means to straighten it, whereafter the bar is cut to required lengths and thread is formed on a selected section of each length.
- the protrusions may be formed in the metal bar in a single pass through a pair of rolls in the cold condition of the bar.
- the protrusions may be formed on the bar by pinching the metal of the bar at intervals along the length of the selected section of the bar.
- the protrusions which are thus formed may be in the form of flat lobes provided in staggered formation along opposite sides of the bar.
- the sides of each lobe nearest and furthest the axis of the bar may be arcuate so that each lobe has a generally elliptical outline.
- the protrusions may be formed on substantially the entire length of the bar, save for the selected section on which the thread is formed.
- the thread formed on the further selected section of the bar may be formed by cold rolling.
- a method of making a rock bolt from a metal bar comprising the steps of providing a pair of rolls defining a nip between them and having formations provided at selected positions along their peripheries, rotating the rolls in opposite directions so that a formation on one roll coincides periodically with a formation on the other roll in the nip of the rolls, and, feeding the bar lengthwise through the nip of the rolls so that the formations pinch the metal of the bar at selected positions along its length.
- the metal bar may be straightened in two planes, preferably by passing it sequentially through two sets of opposed, staggered rollers.
- the invention also provides apparatus for making a rock bolt from a metal bar comprising a pair of rolls, means for driving the rolls about their axes in opposite directions, each roll having a channel formed in its surface facing the other roll, the channels defining a passage for receiving the bar in lengthwise fashion, each roll having formations provided along its periphery which align periodically with similar formations on the other roll in the nip of the rolls when they are rotated in opposite directions.
- the apparatus may include means for straightening the bar after it has been passed between the rolls.
- the means for straightening the bar may comprise two sets of opposed staggered rollers through which the bar is passed, the rollers of one set being located at right angles to those of the other set.
- the formations on the rolls may be in the form of pegs mounted on the rolls.
- a rock bolt comprising a metal bar having a circular or near circular cross-section of a selected uniform diameter, the bar having a thread with a selected pitch diameter formed on a selected section thereof located at at least one end of the bar, the pitch diameter of the thread on the bar being substantially equal to the diameter of the bar, and a series of protrusions pinched from the bar formed on a further selected section of the bar.
- the rock bolt of the invention can be of any required length and the selected section carrying the protrusions will normally be longer than 1 metre.
- the invention also extends to a rock bolt when made according to the method of the invention described above.
- a prior art steel bar (a) is provided, and is cut to the required length.
- the bar (a) carries a series of diametrically opposed inclined ribs (b) separated by a pair of longitudinal ribs (c) of which only one is shown.
- the ribs (b), (c) are formed conventionally by hot rolling during manufacture of the bar (a) in a steel mill.
- the next step in making the prior art rock bolt is to machine or shave the bar (a) as shown in Figure B along a section (d) of its length to remove the ribs (b), (c) and to provide the section (d) with a circular cross-section of diamater (e).
- a rock bolt according to the invention is formed from a steel bar 1 of circular or near circular cross-section.
- the first step in making a rock bolt from the bar 1 is to form a series of protrusions in the form of flat lobes 2 in the bar by a method which will be more fully described hereunder.
- a section 3 of the bar which is to be threaded is left free of lobes 2.
- a thread 4 is cold rolled on to the section 3 of the bar.
- the pitch diameter of the thread 4 is indicated by numeral 5 and is substantially equal to the diameter of the bar.
- the lobes 2 are arranged in staggered formation along the length of the bar 1.
- the sides 2a, 2b of each lobe respectively nearest and furthest the axis of the bar are arcuate so that each lobe has a generally elliptical outline in plan view.
- the thread 4 may first be rolled onto the section 3 of the bar after which the lobes 2 may be formed on the remainder of the bar. Thereafter the bar may be straightened.
- the apparatus indicated generally by numeral 6, comprises a frame 7 having a pair of rolls 8, 9 mounted thereon for rotation about horizontal axes.
- An electric motor 10 is provided to drive the rolls about their respective axes in opposite directions.
- the drive is effected through a pulley 11 and a suitable gear train (not shown).
- the rolls 8, 9 are mounted in such a manner that they can selectively be displaced towards and away from one another. This may conveniently be effected by hydraulic means (not shown).
- the rolls 8, 9 have grooves 12, 13 formed respectively in their edges facing one another, which grooves define a passage for receiving the bar 1 in lengthwise fashion (Figure 3a).
- Each roll has a plurality of pegs 14 mounted thereon along its periphery.
- the pegs 14 are arranged in such a manner that corresponding pegs on the rolls periodically align in the nip of the rolls when they are rotated.
- the pegs 14 are preferably of cirular cross-section but they may be of any required cross-section depending on the shape of the lobes 2 required on the bar 1.
- the bar 1 is cut to a discrete length and is fed through a pair of guide rollers 21 into the nip of the rolls 8, 9 while the rolls are driven in opposite directions.
- the pegs 9 periodically pinch the metal of the bar 1 to form the lobes 2 therein. This is achieved in a single pass of the bar 1 through the rolls 8, 9 in the cold condition of the bar.
- the lobes 2 are not shown on the bar 1 in Figures 2a and 2b. They are, however, shown in Figures 3a and 3d.
- the rolls 8, 9 are controlled to ensure that the lobes 2 are formed only on a selected section of the bar. In this embodiment of the invention this is achieved by means of a pair of sensing devices 22, 23 mounted ahead of and behind the rolls 8, 9.
- the sensing device 23 mounted behind the rolls 8, 9 comprises a support 24 carrying a retractable stop member 25 and a sensor 26 ( Figure 3b).
- the support 24 also carries two pairs of dependent guides 27, 28 through which the bar 1 moves.
- the sensing device 22 mounted ahead of the rolls 8, 9 may be the same as the sensing device 2, 3 but the retractable stop member 25 may be omitted.
- the bar 1 With the rolls 8, 9 in an open position, the bar 1 is advanced freely therebetween. As the leading end of the bar enters the sensing device 23 located behind the rolls 8, 9 the sensor 26 of the device 23 causes the stop member 25 to retract and causes the rolls 8, 9 to close and to commence rotating. The bar 1 advances further through the rolls 8, 9 as the lobes 2 are formed thereon and as the trailing end of the bar leaves the sensing device 22, the rolls 8, 9 are caused by the sensor of the device 22 to open and to cease rotation.
- the sensing devices 22, 23 are adjustable in the direction of the path of the bar 1 and hence the sections of the bar which are free of lobes 2 and which carry lobes 2 can be selected by forward and rearward adjustment of the sensing devices 22, 23.
- the driven rollers 15, 17 and 19 serve to advance the bar 1 along its path through the apparatus 6.
- pneumatic heads 29 are provided which carry the upper rollers in the sets.
- Each head 29 has a dependant rod 30 which connects to a mounting 31 which carries the associated roller 16 and which is slidable in a guide 32 ( Figure 3c).
- rollers 16 As the bar passes between the straightening rollers 16 it is straightened in a vertical plane and as it passes between the straightening rollers 18 it is straightened in a horizontal plane.
- the rollers 18 have central channels 33 formed therein to accommodate the lobes 2 on the bar as it passes between the rollers ( Figure 3d).
- each of the straightening rollers 16, 18 is adjustable towards and away from its opposing rollers to enable its effect on the bar 1 to be varied.
- each straightening roller 16, 18 is mounted on a slide 34 which is slidable in a guide 35 and is adjustable by means of a setting bolt 36 ( Figure 3e).
- the slide 34 is secured by lock nuts 37, 38.
- the rollers, 16, 18 will be so adjusted that a flexing of the bar 1 takes place as it passes between the rollers.
- the thread 4 is rolled onto a selected section of the bar in conventional manner.
- a chute 39 is positioned beneath the rolls 8, 9 to collect scale generated by the action of the rolls on the bar 1.
- the manner of forming the lobes 2 on the bar 1 described above is relatively simple and inexpensive and the apparatus 7 can maintain speeds of the bar 1 passing therethrough of at least 35m/min.
- the lobes 2 are formed in a single plane but if desired they can be formed in two or more planes.
- a continuous length of the bar 1 may be fed through the apparatus shown in Figures 2a to 2b.
- the rolls 8, 9 are periodically displaced away from and towards one another to ensure that the lobes 2 are formed only on consecutive selected sections of the bar.
- FIGs 4a and 4b two rock bolts made according to the invention are shown.
- the rock bolt 40 shown in Figure 4a is intended for embedding in a settable resinous material mixed with a catalyst. It has thread 4 formed at one end thereof to receive a nut (not shown). At its other end it has a chamfered point 41 which is used to rupture a capsule of the settable material (not shown) located in the hole in the rock matrix in which the bolt is to be embedded.
- the rock bolt 42 shown in Figure 4b is similar to the one shown in Figure 4a but instead of the point 41 it has a thread 43.
- the thread 43 is used to connect the rock bolt to a conventional mechanical anchor (not shown) which expands when the rock bolt is tensioned to anchor it in a hole.
- a mechanical anchor not shown
- settable resinous material or concrete can be used to grout the rock bolt 42 in the hole.
- a rock bolt made according to the invention is to be embedded in a settable material mixed with a catalyst
- the rock bolt will, in use, be rotated about its axis to assist in mixing of the settable material.
- the lobes 2 on the bolt will in such a case assist considerably in mixing the settable material by causing lateral displacement of the settable material during rotation of the bolt.
- any particle situated adjacent the bolt between two lobes 2 will be displaced by the lobe on the opposite side of the bolt when it is rotated.
- the improved mixing ability of the bolt arises from the fact that with the use of the lobes 2, the diameter of the bolt at the apices of opposed lobes can be as much as 1,5 times the diameter of the bolt.
- the rock bolt described above provides a continuously changing perimeter along its length and this in itself enhances its mixing ability in use.
- the lobes 2 will also assist in the anchoring of the bolt in settable material.
- the rock bolt of the invention provides a continuously changing perimeter along its length
- the provision of the lobes 2 thereon does not materially alter its cross-section along its length. This means that the provision of the lobes does not result in a sacrifice of cross-section and hence does not affect the tensile strength of the rock bolt.
- the machining or shaving step in the prior art method described above is dispensed with.
- a substantial saving of material can be obtained with a rock bolt made according to the invention, when regard is had to the following.
- the diameter of the ribbed section of the prior art rock bolt is larger than the diameter (e) thereof. Yet this larger diameter does not increase the tensile strength of the prior art bolt, since the tensile strength is determined by the minimum diameter of the thread (f).
- the prior art rock bolt therefore carries excess material over the length of its ribbed section. In the rock bolt made according to the invention, such excess material is limited since the diameter of the bar 1 is in the first place chosen to equal the pitch diameter of the thread 4. In this way a saving of material of up to 25% can be achieved compared with a prior art rock bolt, which results in a less expensive rock bolt when made according to the method of the invention.
- the load capacity of the anchorage provided by a rock bolt embedded in a settable material such as concrete is proportional to the perimeter of the bolt.
- the perimeter of the bar 1 may be increased before, during or after the operation in which the lobes 2 are formed in the bar. This may be done, for example, by changing the cross-section of the bar in the lobe forming operation from a circular to an elliptical shape.
- the rock bolt of the invention formed in this way from a bar of smaller cross-section than that of a conventional rock bolt, can provide the same anchorage capacity as the conventional rock bolt.
- the rock bolt of the invention can also be made from pipe or metal bar with an axial bore, for use in applications where settable material is injected through the rock bolt itself. Also, any part of the rock bolt of the invention may be left free of lobes 2, if required.
- the invention has particular application to rock bolts which are provided in lengths in which the lobed section is longer than 1 metre.
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- Engineering & Computer Science (AREA)
- Structural Engineering (AREA)
- Mining & Mineral Resources (AREA)
- Mechanical Engineering (AREA)
- Architecture (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Geology (AREA)
- Civil Engineering (AREA)
- Forging (AREA)
Abstract
Description
- This invention relates to a rock bolt and more particularly, but not exclusively, to a rock bolt for use in underground mining operations.
- Many different kinds of rock bolts are used to secure rock strata underground. One kind comprises a length of reinforcing bar having ribs along its length. The ribs enhance the anchoring ability of the bolt. In the case where a settable material with a catalyst is used to secure the bolt in a hole in the rock matrix, the bolt is usually rotated in the hole to mix the settable material and the ribs also serve the purpose of assisting the mixing of the settable material. However, known ribbed formations on rock bolts do not provide good mixing characteristics.
- The end of the bolt which is intended to project from the rock face has a rolled thread thereon which receives a nut used to tension the bolt. The bar from which such a prior art rock bolt is made is manufactured in a steel mill and is supplied with the ribs formed on the whole length of the bar. Thus, in order to provide the rolled thread on the bolt, the bolt has to be machined to remove the ribs on a section thereof and to ensure that such section has a circular cross-section. Such a machining operation adds to the cost of the prior art rock bolt.
- It is an object of the invention to lessen the problems associated with prior art rock bolts.
- In this specification, the term "pitch diameter", in relation to a straight thread, means the diameter of an imaginary co-axial cylinder, the surface of which passes through the thread profiles at such points as to make the width of the groove equal to one half of the basic pitch of the thread. On a perfect thread this occurs at the point where the width of the thread and groove are equal.
- The term "bar" when used in this specification includes a pipe and a bar with an axial bore.
- According to the invention, a method of making a rock bolt with a thread on a section thereof, comprises the steps of providing a metal bar of circular or near circular cross-section having a diameter which is substantially equal to the pitch diameter of the thread to be provided thereon, forming a series of protrusions on a selected section of the bar, straightening the bar, and, forming a thread with the said pitch diameter on a further selected section of the bar.
- This method obviates the need for machining the bar before forming the thread thereon. As will become evident in the subsequent description, the method also results in a saving of material without reducing the yield or tensile load-carrying ability of the rock bolt.
- In one form the metal bar is first cut to a discrete length, is then advanced through means forming the series of protrusions on the selected section of the bar, and is thereafter advanced through straightening means to straighten it, whereafter thread is formed on the further selected section of the bar.
- In another form a continuous length of the metal bar is first advanced through means forming the series of protrusions on selected sections of the bar, the continuous length is thereafter advanced through straightening means to straighten it, whereafter the bar is cut to required lengths and thread is formed on a selected section of each length.
- The protrusions may be formed in the metal bar in a single pass through a pair of rolls in the cold condition of the bar.
- The protrusions may be formed on the bar by pinching the metal of the bar at intervals along the length of the selected section of the bar. The protrusions which are thus formed may be in the form of flat lobes provided in staggered formation along opposite sides of the bar. The sides of each lobe nearest and furthest the axis of the bar may be arcuate so that each lobe has a generally elliptical outline.
- The protrusions may be formed on substantially the entire length of the bar, save for the selected section on which the thread is formed.
- The thread formed on the further selected section of the bar may be formed by cold rolling.
- According to a further aspect of the invention there is provided a method of making a rock bolt from a metal bar comprising the steps of providing a pair of rolls defining a nip between them and having formations provided at selected positions along their peripheries, rotating the rolls in opposite directions so that a formation on one roll coincides periodically with a formation on the other roll in the nip of the rolls, and, feeding the bar lengthwise through the nip of the rolls so that the formations pinch the metal of the bar at selected positions along its length.
- The metal bar may be straightened in two planes, preferably by passing it sequentially through two sets of opposed, staggered rollers.
- The invention also provides apparatus for making a rock bolt from a metal bar comprising a pair of rolls, means for driving the rolls about their axes in opposite directions, each roll having a channel formed in its surface facing the other roll, the channels defining a passage for receiving the bar in lengthwise fashion, each roll having formations provided along its periphery which align periodically with similar formations on the other roll in the nip of the rolls when they are rotated in opposite directions.
- The apparatus may include means for straightening the bar after it has been passed between the rolls.
- The means for straightening the bar may comprise two sets of opposed staggered rollers through which the bar is passed, the rollers of one set being located at right angles to those of the other set.
- The formations on the rolls may be in the form of pegs mounted on the rolls.
- According to a further aspect of the invention there is provided a rock bolt comprising a metal bar having a circular or near circular cross-section of a selected uniform diameter, the bar having a thread with a selected pitch diameter formed on a selected section thereof located at at least one end of the bar, the pitch diameter of the thread on the bar being substantially equal to the diameter of the bar, and a series of protrusions pinched from the bar formed on a further selected section of the bar.
- The rock bolt of the invention can be of any required length and the selected section carrying the protrusions will normally be longer than 1 metre.
- The invention also extends to a rock bolt when made according to the method of the invention described above.
- A preferred embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which;
- Figures A to C illustrate a prior art method of making a rock bolt;
- Figures 1a to 1c illustrate steps in making a rock bolt according to the method of the invention;
- Figures 2a and 2b are a schematic elevation and plan view respectively of apparatus used to carry out the method of the invention;
- Figures 3a to 3e are enlarged views of parts of the apparatus of Figures 2a and 2b; and
- Figures 4a and 4b show two different kinds of rock bolts made according to the invention;
- With reference to Figure A, a prior art steel bar (a) is provided, and is cut to the required length. The bar (a) carries a series of diametrically opposed inclined ribs (b) separated by a pair of longitudinal ribs (c) of which only one is shown. The ribs (b), (c) are formed conventionally by hot rolling during manufacture of the bar (a) in a steel mill. The next step in making the prior art rock bolt is to machine or shave the bar (a) as shown in Figure B along a section (d) of its length to remove the ribs (b), (c) and to provide the section (d) with a circular cross-section of diamater (e). Thereafter a thread (f) is rolled onto the section (d) of the bar as shown in Figure C to complete the rock bolt. It will be appreciated that the tensile strength of the bolt is determined by the minimum diameter of the thread (f) of the bolt, since that is its smallest diameter.
- With reference to Figures 1a to 1c, a rock bolt according to the invention is formed from a
steel bar 1 of circular or near circular cross-section. The first step in making a rock bolt from thebar 1 is to form a series of protrusions in the form offlat lobes 2 in the bar by a method which will be more fully described hereunder. Asection 3 of the bar which is to be threaded is left free oflobes 2. After thelobes 2 have been formed in the bar and after the bar has been passed through a straightening station to straighten it, athread 4 is cold rolled on to thesection 3 of the bar. The pitch diameter of thethread 4 is indicated by numeral 5 and is substantially equal to the diameter of the bar. - In this embodiment of the invention, as most clearly shown in Figures 1b and 1c, the
lobes 2 are arranged in staggered formation along the length of thebar 1. Thesides 2a, 2b of each lobe respectively nearest and furthest the axis of the bar are arcuate so that each lobe has a generally elliptical outline in plan view. - In an alternative method the
thread 4 may first be rolled onto thesection 3 of the bar after which thelobes 2 may be formed on the remainder of the bar. Thereafter the bar may be straightened. - The manner of forming the
lobes 2 on the bar and the apparatus used for this purpose is illustrated in Figures 2 and 3. The apparatus, indicated generally bynumeral 6, comprises aframe 7 having a pair ofrolls electric motor 10 is provided to drive the rolls about their respective axes in opposite directions. The drive is effected through a pulley 11 and a suitable gear train (not shown). - The
rolls - The
rolls grooves bar 1 in lengthwise fashion (Figure 3a). Each roll has a plurality ofpegs 14 mounted thereon along its periphery. Thepegs 14 are arranged in such a manner that corresponding pegs on the rolls periodically align in the nip of the rolls when they are rotated. Thepegs 14 are preferably of cirular cross-section but they may be of any required cross-section depending on the shape of thelobes 2 required on thebar 1. - Alongside the
rolls rollers 15 followed by a set of straighteningrollers 16 which are arranged in opposed, staggered formation (Figures 2a, 2b). Alongside the straighteningrollers 16 there is a further set of drivenrollers 17. The sets ofrollers rollers 17 there is a further set of straighteningrollers 18 arranged in opposed, staggered formation and mounted for rotation about vertical axes. Finally, alongside the straighteningrollers 18 there is a set of drivenrollers 19 mounted for rotation about horizontal axes. The sets of drivenrollers electric motor 20. - In use, the
bar 1 is cut to a discrete length and is fed through a pair of guide rollers 21 into the nip of therolls bar 1 passes through the nip of the rolls thepegs 9 periodically pinch the metal of thebar 1 to form thelobes 2 therein. This is achieved in a single pass of thebar 1 through therolls lobes 2 are not shown on thebar 1 in Figures 2a and 2b. They are, however, shown in Figures 3a and 3d.) - The
rolls lobes 2 are formed only on a selected section of the bar. In this embodiment of the invention this is achieved by means of a pair ofsensing devices rolls - The
sensing device 23 mounted behind therolls support 24 carrying aretractable stop member 25 and a sensor 26 (Figure 3b). Thesupport 24 also carries two pairs ofdependent guides bar 1 moves. Thesensing device 22 mounted ahead of therolls sensing device retractable stop member 25 may be omitted. - With the
rolls bar 1 is advanced freely therebetween. As the leading end of the bar enters thesensing device 23 located behind therolls sensor 26 of thedevice 23 causes thestop member 25 to retract and causes therolls bar 1 advances further through therolls lobes 2 are formed thereon and as the trailing end of the bar leaves thesensing device 22, therolls device 22 to open and to cease rotation. Thesensing devices bar 1 and hence the sections of the bar which are free oflobes 2 and which carrylobes 2 can be selected by forward and rearward adjustment of thesensing devices - The driven
rollers bar 1 along its path through theapparatus 6. To maintain pressure between opposing sets of drivenrollers head 29 has adependant rod 30 which connects to a mounting 31 which carries the associatedroller 16 and which is slidable in a guide 32 (Figure 3c). - As the bar passes between the straightening
rollers 16 it is straightened in a vertical plane and as it passes between the straighteningrollers 18 it is straightened in a horizontal plane. Therollers 18 havecentral channels 33 formed therein to accommodate thelobes 2 on the bar as it passes between the rollers (Figure 3d). - Each of the straightening
rollers bar 1 to be varied. For this purpose each straighteningroller slide 34 which is slidable in aguide 35 and is adjustable by means of a setting bolt 36 (Figure 3e). Theslide 34 is secured bylock nuts bar 1 takes place as it passes between the rollers. - Once the
bar 1 has passed through theapparatus 7, thethread 4 is rolled onto a selected section of the bar in conventional manner. - A
chute 39 is positioned beneath therolls bar 1. - The manner of forming the
lobes 2 on thebar 1 described above is relatively simple and inexpensive and theapparatus 7 can maintain speeds of thebar 1 passing therethrough of at least 35m/min. - In this embodiment of the invention the
lobes 2 are formed in a single plane but if desired they can be formed in two or more planes. - In an alternative form, a continuous length of the
bar 1 may be fed through the apparatus shown in Figures 2a to 2b. In such a case therolls lobes 2 are formed only on consecutive selected sections of the bar. Once the bar has passed through the apparatus, it is cut into the required lengths and threads are rolled onto the individual lengths in conventional manner. - In Figures 4a and 4b two rock bolts made according to the invention are shown. The
rock bolt 40 shown in Figure 4a is intended for embedding in a settable resinous material mixed with a catalyst. It hasthread 4 formed at one end thereof to receive a nut (not shown). At its other end it has a chamferedpoint 41 which is used to rupture a capsule of the settable material (not shown) located in the hole in the rock matrix in which the bolt is to be embedded. - The
rock bolt 42 shown in Figure 4b is similar to the one shown in Figure 4a but instead of thepoint 41 it has athread 43. Thethread 43 is used to connect the rock bolt to a conventional mechanical anchor (not shown) which expands when the rock bolt is tensioned to anchor it in a hole. In addition to the mechanical anchor, settable resinous material or concrete can be used to grout therock bolt 42 in the hole. - Where a rock bolt made according to the invention is to be embedded in a settable material mixed with a catalyst, the rock bolt will, in use, be rotated about its axis to assist in mixing of the settable material. The
lobes 2 on the bolt will in such a case assist considerably in mixing the settable material by causing lateral displacement of the settable material during rotation of the bolt. In this regard, any particle situated adjacent the bolt between twolobes 2 will be displaced by the lobe on the opposite side of the bolt when it is rotated. The improved mixing ability of the bolt arises from the fact that with the use of thelobes 2, the diameter of the bolt at the apices of opposed lobes can be as much as 1,5 times the diameter of the bolt. It will also be appreciated that the rock bolt described above provides a continuously changing perimeter along its length and this in itself enhances its mixing ability in use. Thelobes 2 will also assist in the anchoring of the bolt in settable material. - Whilst the rock bolt of the invention provides a continuously changing perimeter along its length, the provision of the
lobes 2 thereon does not materially alter its cross-section along its length. This means that the provision of the lobes does not result in a sacrifice of cross-section and hence does not affect the tensile strength of the rock bolt. - With the method of making a rock bolt in accordance with the invention the machining or shaving step in the prior art method described above, is dispensed with. In addition, a substantial saving of material can be obtained with a rock bolt made according to the invention, when regard is had to the following. The diameter of the ribbed section of the prior art rock bolt is larger than the diameter (e) thereof. Yet this larger diameter does not increase the tensile strength of the prior art bolt, since the tensile strength is determined by the minimum diameter of the thread (f). The prior art rock bolt therefore carries excess material over the length of its ribbed section. In the rock bolt made according to the invention, such excess material is limited since the diameter of the
bar 1 is in the first place chosen to equal the pitch diameter of thethread 4. In this way a saving of material of up to 25% can be achieved compared with a prior art rock bolt, which results in a less expensive rock bolt when made according to the method of the invention. - It is well known that the load capacity of the anchorage provided by a rock bolt embedded in a settable material such as concrete is proportional to the perimeter of the bolt. To ensure that a rock bolt according to the invention does not have a lesser anchorage capacity compared with a conventional rock bolt, the perimeter of the
bar 1 may be increased before, during or after the operation in which thelobes 2 are formed in the bar. This may be done, for example, by changing the cross-section of the bar in the lobe forming operation from a circular to an elliptical shape. - Thus, the rock bolt of the invention formed in this way from a bar of smaller cross-section than that of a conventional rock bolt, can provide the same anchorage capacity as the conventional rock bolt.
- The rock bolt of the invention can also be made from pipe or metal bar with an axial bore, for use in applications where settable material is injected through the rock bolt itself. Also, any part of the rock bolt of the invention may be left free of
lobes 2, if required. - The invention has particular application to rock bolts which are provided in lengths in which the lobed section is longer than 1 metre.
- Other embodiments of the invention may be made without departing from the scope of the invention as defined in the appended claims.
Claims (22)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE19883887326 DE3887326T2 (en) | 1988-07-21 | 1988-07-21 | Anchor bolt. |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
ZA868649 | 1986-11-14 | ||
ZA878529A ZA878529B (en) | 1986-11-14 | 1987-11-13 | Rock bolt |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0351465A1 true EP0351465A1 (en) | 1990-01-24 |
EP0351465B1 EP0351465B1 (en) | 1994-01-19 |
Family
ID=27137658
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP88306706A Expired - Lifetime EP0351465B1 (en) | 1986-11-14 | 1988-07-21 | Rock bolt |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP0351465B1 (en) |
AU (1) | AU604948B2 (en) |
ZA (1) | ZA878529B (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO1993010362A1 (en) * | 1991-11-12 | 1993-05-27 | Heinrich Liebig | Roof boolt for imbedding in plastic mortar |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5054146A (en) * | 1988-12-08 | 1991-10-08 | Videx-Wire Products (Pty.) Limited | Anchor bolt |
Citations (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2347904A (en) * | 1941-07-26 | 1944-05-02 | Gerald G Greulich | Method of cold-working metallic bars |
US2911865A (en) * | 1957-01-17 | 1959-11-10 | United States Steel Corp | Apparatus for making formed wire |
US3742747A (en) * | 1971-11-30 | 1973-07-03 | Nippon Concrete Ind Co Ltd | Method for shaping indented steel wire and apparatus therefor |
US4064729A (en) * | 1977-03-02 | 1977-12-27 | Alex Homery | Metal forming device |
CH604951A5 (en) * | 1976-08-11 | 1978-09-15 | Belloli Ferriere & Co | Concrete reinforcing anchorage rod with threaded ends |
GB2045836A (en) * | 1979-03-28 | 1980-11-05 | Peabody Coal Co | Rock bolting |
AU523376B3 (en) * | 1980-08-22 | 1982-06-24 | Titan Manufacturing Co. Pty. Ltd., The | Production of a rolled thread onto a deformed bar |
US4649729A (en) * | 1985-01-14 | 1987-03-17 | Florida Steel Corporation | Method for manufacturing steel bar with intermittent smooth surface and patterned relief segments, and mine roof bolt product |
-
1987
- 1987-11-13 ZA ZA878529A patent/ZA878529B/en unknown
-
1988
- 1988-07-21 EP EP88306706A patent/EP0351465B1/en not_active Expired - Lifetime
- 1988-08-01 AU AU20227/88A patent/AU604948B2/en not_active Expired
Patent Citations (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2347904A (en) * | 1941-07-26 | 1944-05-02 | Gerald G Greulich | Method of cold-working metallic bars |
US2911865A (en) * | 1957-01-17 | 1959-11-10 | United States Steel Corp | Apparatus for making formed wire |
US3742747A (en) * | 1971-11-30 | 1973-07-03 | Nippon Concrete Ind Co Ltd | Method for shaping indented steel wire and apparatus therefor |
CH604951A5 (en) * | 1976-08-11 | 1978-09-15 | Belloli Ferriere & Co | Concrete reinforcing anchorage rod with threaded ends |
US4064729A (en) * | 1977-03-02 | 1977-12-27 | Alex Homery | Metal forming device |
GB2045836A (en) * | 1979-03-28 | 1980-11-05 | Peabody Coal Co | Rock bolting |
AU523376B3 (en) * | 1980-08-22 | 1982-06-24 | Titan Manufacturing Co. Pty. Ltd., The | Production of a rolled thread onto a deformed bar |
US4649729A (en) * | 1985-01-14 | 1987-03-17 | Florida Steel Corporation | Method for manufacturing steel bar with intermittent smooth surface and patterned relief segments, and mine roof bolt product |
Non-Patent Citations (1)
Title |
---|
PATENT ABSTRACTS OF JAPAN, vol. 8, no. 234 (M-334)[1671], 26th October 1984; & JP-A-59 113 948 (NIHON BIYOURATEI SEISAKUSHO K.K.) 30-06-1984 * |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO1993010362A1 (en) * | 1991-11-12 | 1993-05-27 | Heinrich Liebig | Roof boolt for imbedding in plastic mortar |
Also Published As
Publication number | Publication date |
---|---|
EP0351465B1 (en) | 1994-01-19 |
AU2022788A (en) | 1990-02-01 |
ZA878529B (en) | 1989-06-28 |
AU604948B2 (en) | 1991-01-03 |
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