WO2003102374A1

WO2003102374A1 - Threaded bar & rock bolts formed therefrom

Info

Publication number: WO2003102374A1
Application number: PCT/AU2003/000671
Authority: WO
Inventors: Jeffrey Robert Fergusson
Original assignee: Industrial Roll Formers Pty Limited
Priority date: 2002-05-30
Filing date: 2003-05-30
Publication date: 2003-12-11
Also published as: AUPS266202A0

Abstract

The present invention discloses a hot rolled threaded bar (1) having a single start helical thread in which every second turn (5) of the thread is absent. In addition, the circumferential extent of each half turn of the thread approaches 50% of the bar circumference. A rock bolt (10) is able to be fabricated from the bar (1) without any further processing as a nut (13) can be received directly onto the hot rolled bar. Thus rock bolts can be assembled at a mine site from bars delivered from a rod and bar mill and nuts delivered from a rock bolt manufacturer. There is a substantial saving in processing and handling costs.

Description

THREADED BAR & ROCK BOLTS FORMED THEREFROM FIELD OF THE INVENTION

The present invention relates to threaded bar and, in particular, to a thread pattern which is particularly suited to hot rolled threaded bar. The present invention also relates to rock bolts formed from hot rolled threaded bar.

BACKGROUND ART

Threaded bar is used in a wide range of engineering applications including reinforcing bars for concrete, bars from which rock bolts can be fabricated, and the like. Such bars are intended to carry substantial tensile loads. Such loads can be applied by means of a nut threadably engaged with the bar, or by means of concrete, resin, or grout engaged with the bar in which case there is a keying inter-engagement between the concrete, etc. and the threads on the bar.

Failure can occur because the threads are insufficiently robust and the nut strips the threads from the bar. Failure can also occur because the minimum diameter of the bar caused by the depth of the threads is insufficient for the load. Failure can also occur because the height of the threads relative to the minimum diameter of the bar is insufficient for adequate keying between the concrete, etc. and the bar. Failure can also occur because the minimum spacing between threads is insufficient for the grout, etc to form a body of sufficient size to have an adequate strength. Any one of these failures can result in catastrophic consequences.

Hot rolling involves forming the thread on the bar at a rod and bar mill when the bar is hot and the bar is being formed longitudinally. The forming of the bar happens substantially perpendicular to the rolls which create the thread. The approach angle, or form, of the thread is constrained by the size of the forming rolls as there is a gear meshing action during exit of the bar from the rolls. Because the bar is formed longitudinally whilst being hot rolled, the sides of the bar cannot form a thread, instead excess material is squeezed out which forms longitudinal ribs, on the bar. If there is not an excess of material, longitudinal gaps in the thread are formed, likewise extending along the bar.

By contrast, cold rolling involves placing a cold round bar into a machine with threading rolls in an orientation which is substantially parallel to the bar. The bar is then rotated between the rolls to form the thread. Cold rolling a steel bar tends to make it brittle, especially in the case of high tensile steels.

Several threaded engineering bars are known and have various properties which result in various defects. "ALL THREAD" bar is normally cold rolled and thus tends to be brittle. "GEWI BAR" is a bar with a single start thread with a very coarse pitch. The thread is basically continuous (except for the two longitudinally extending gaps in the thread extending one along either side of the bar). Typically the thread has a coarse 10-12mm pitch for a nominal bar diameter of 20mm. This coarse thread suffers from the disadvantage that nuts tend to vibrate loose. As a consequence, GEWI BAR is not regarded as being well suited for the support of roofs in mines.

"REID BAR" has a single start, very coarse pitch, thread which is again basically a continuous thread. It suffers from similar disadvantages to the GEWI BAR, particularly in relation to the coarse threads resulting in nuts vibrating loose.

"FREYSSI BAR" is another type of bar which has a double start, very coarse pitch thread, and again basically has a continuous thread. Again, for standard bar having a nominal bar diameter of 20mm, the pitch of the FREYSSI BAR is approximately 12mm.

The REID BAR and FREYSSI BAR are pre-rolled with side grooves. This results in the bar having an oval cross-sectional shape before threading. This shape allows pushing the core back to round during the hot roll threading process thereby leaving the deformations, or height of the thread, high. In addition, any excess material is allowed to flow to a zone out of the way of the thread so there is no material from the minor diameter of the oval bar formed into the thread. This is desirable as it leads to little interference between the external thread of the bar and the internal thread of a nut which can be threadably engaged with the REID BAR and FREYSSI BARS.

Normal metric thread has a 3mm pitch which has been found to be easily fouled in the harsh mining environments in which rock bolt bars are used. For this reason, the present applicant has in the past used a rope thread with a 5mm pitch which is cold rolled onto bars, mostly after any deformations have been peeled from them by turning the portion of the bar to be threaded.

This prior art process of peeling (or effectively turning the bar in a lathe like operation) and then cold forming the threads is only one prior art method of creating suitable threads on the bar to receive the necessary nut.

Other methods of forming the thread for the nut include cold rolling the unpeeled bar as disclosed in the applicant's PCT application published under WO 00/47349. Another method is to cold roll the material of the bar deformations themselves as disclosed in the applicant's Australian patent Application No. 22994/02. It is also known to hammer the deforms until a substantially round form is produced which is then cold rolled to create the thread.

Novelty searches conducted after the priority date have disclosed International Patent Application No. PCT/AU01/00286 published under

WO 01/68287 (Gray). This specification discloses a hot rolled threaded bar having a number of quasi - semi circular or arcuate ribs. Each rib tapers at its ends so that opposite sides of the bar are entirely free of any protrusion. As seen in cross-sectional views, each rib does not extend for 180° (or 50% of the bar circumference). Given the tapered ends of each rib, each rib has an effective circumferential extent of only approximately 25% of the bar circumference in terms of the rib's ability to transfer load either from the rib to resin or grout, or from the rib to a nut threadably engaged with the ribs. The ribs are located on opposite faces of the hot rolled bar and various ones of the ribs are omitted to create a discontinuous thread effect. For example, in the embodiment of Fig. 1 every second potential rib on each side of the bar is omitted thereby effectively omitting half turns from the thread pattern.

This prior art hot rolled threaded bar has not (to the applicant's knowledge) ever been fabricated and used either in Australia or abroad. A problem in manufacturing hot rolled threaded bars is to keep the rolls aligned or synchronised so that the thread is truely helical. Often reject rates of up to 10% occur during hot roll forming of threaded bars due to the problem of roll mis-alignment or mis-synchronisation. Because the ribs of this prior art do not extend from one side of the bar to the other, it is more likely that rolls will become mal-adjusted with such short ribs than with longer thread portions which extend further circumferentially around the bar.

The result of these various prior art manufacturing methods required to create the thread for the nut is that separate organisations have evolved which have separate roles.

The first organisation is the rod and bar mill which uses as its starting material a cold billet of steel. Its end product is long lengths of hot rolled bar. Typically such lengths are approximately 12 metres which is the maximum length which can be transported by road vehicle away from the mill site. The customer of the rod and bar mill is either a steel merchant or a rock bolt manufacturer (such as the present applicant), the latter of which then carries out various manufacturing steps (generally initially cutting into more manageable lengths and then forming the desired threads, attaching the necessary support plate (or washer) and nut to the trailing end of the bolt and anchor to the leading end of the bolt).

The steel merchant customer would, for example, cut the hot rolled threaded bar to size but not otherwise process it, before on-selling the shorter lengths to either a wholesale distributor or to a rock bolt manufacturer. The wholesale distributor would, in turn, on sell to a small volume rock bolt manufacturer without carrying out any processing steps. Again the wholesale distributor may cut the hot rolled threaded bar to size.

In this connection rock bolts are traditionally fabricated in a range of sizes each increasing by 300mm steps from a minimum size of 1.2m. Thus the rock bolt sizes are 1.2m, 1.5m, 1.8m, etc up to 12m.

As a consequence of this distribution chain leading to the ultimate rock bolt manufacturer, the rock bolts themselves after their manufacture are delivered entire to the end user (be it a mine site, tunnelling site, or the like). It is sometimes known for anchors to be attached to the leading end, or tip, of rock bolts at the end user's site but the nut threadably engaged with the trailing end of the rock bolt is always so engaged by the rock bolt manufacturer before despatch of the rock bolt to the end user's store, warehouse, or site.

OBJECT OF THE INVENTION

A first object of the present invention is to create an improved threaded bar with a thread pattern which is suitable for obtaining good keying, is capable of being hot rolled and which has a pitch which is suitable for harsh conditions.

A second object of the present invention is to reduce the cost of rock bolts in two ways. Firstly, by enabling a hot rolled threaded bar to be used without further processing. Secondly, by changing the distribution and handling of the hot rolled threaded bar so that it is delivered to the end user by either the rod and bar mill or the steel merchant. Whilst only the accessories (anchor, plate, nut, resin, etc) are delivered by the rock bolt "manufacturer" to the end user. Thus the rock bolt is actually assembled by the end user on site. This stratagem is thought likely to reduce the cost of a rock bolt presently costing about A$7.00 - A$20.00 by approximately A$1.00 - A$2.00. SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention there is disclosed a thread pattern for use as a rock bolt, reinforcing bar and like engineering bars, said thread pattern comprising a single start helical thread in which every second turn of the thread is absent and the circumferential extent of each half turn of said thread approaches 50% of the circumferential extent of said bar.

In accordance with a second aspect of the present invention there is disclosed a threaded bar having the above described thread pattern.

In accordance with a third aspect of the present invention there is disclosed a rock bolt for use in mining, tunnelling and like activities, said bolt comprising a length of unprocessed hot rolled threaded bar having an exterior at least partial thread hot roll formed on said bar, and at least one accessory threadably engaged with said bar.

In accordance with a fourth aspect of the present invention there is disclosed a method of assembling a rock bolt for use in a mine site, tunnel construction site, or similar end user site, said method comprising the steps of:

(i) receiving from a first supplier a first length of unprocessed hot rolled threaded bar having an exterior at least partial thread hot roll formed on said bar,

(ii) if necessary, cutting said bar to a second, shorter, length substantially comprising the desired length of said rock bolt,

(iii) receiving from a second supplier accessories sized to be threadably engaged with said unprocessed bar, and

(iv) engaging said accessories with said threaded bar to completely assemble said rock bolt. Embodiments of the present invention will now be described with reference to the drawings in which:

Fig. 1 is a perspective view of one side of a length of the hot rolled threaded bar of the preferred embodiment, illustrating the preferred thread pattern, Fig. 2 is a perspective view of the other side of the bar of Fig. 1 ,

Fig. 3 is a plan view (also an inverted plan view) of the bar of Figs. 1 and 2,

Fig. 4 is a side elevation of the bar of Figs. 1-3 showing the side of the bar illustrated in Fig. 2,

Fig. 5 is a side elevation of the bar of Figs. 1-4 showing the side of the bar illustrated in Fig. 1 ,

Fig. 6 is a transverse cross-sectional view through the bar of Figs. 1-5,

Fig. 7 is a cross-sectional view through a single thread showing a first thread profile,

Fig. 8 is a view similar to Fig. 7 but showing an alternative thread profile, and Fig. 9 is a longitudinal view, partly in cross-section, showing a rock bolt fabricated from the threaded bar and secured by grout in a bore hole.

As seen in Figs. 1-6, the bar 1 has a thread 2 and a pair of side gaps 3. As best seen in Figs. 2 and 4, the thread is discontinuous in that every second turn of what would otherwise be a substantially continuous thread is absent.

Although the appearance of the bar 1 is that it has a relatively coarse thread, the pitch of the individual turns 5 is only preferably 5mm. That is, the spacing between the threads is coarse but the thread angle, or pitch, is fine.

In addition, it will be seen from Fig. 6 that the minimum diameter of the bar 1 is not substantially reduced but that the material of the turns 5 stands relatively proud of the minimum diameter (typically by approximately 1.5mm) for almost all of the circumferential extent of each turn. Thus the effective length of each half turn of the thread pattern as regards load transfer approaches 50% of the bar circumference. This results in good keying between the bar 1 and concrete, resin and grout etc, and good load transfer between the turns 5 and the nut 13 (referred to below). Fig. 9 illustrates a rock bolt 10 fabricated from a length of the bar 1 which is merely cut to the desired length, if necessary. Thus no peeling and threading of the bar is required to produce a rock bolt. As a consequence, the bar 1 can be used direct from the rod and bar mill without any further processing (other than being cut to length, if necessary).

The rock bolt 10 has a load plate 11 , a washer 12 and a nut 13. If desired, the leading end of the rock bolt 10 can have an expansion device 19 (illustrated in phantom in Fig. 9) threadably engaged with the rock bolt 10. The expansion device 19 is well known in the art such as that described in the applicant's Australian Patent Application No. 23309/01. Between the rock bolt 10 and the blind hole 14 into which it is inserted, a grout 15 has been installed. The grout 15 makes good keying contact with the individual turns 5 on the rock bolt 10.

In addition, the nut 13 has an interior thread 23 which has a standard 5mm pitch. As will be seen in Fig. 9, every second turn of the interior thread 23 does not mate with the rock bolt 10 at all. The alternate threads of the interior thread 23 are, however, engaged with the turns 5 of the threaded rock bolt 10. Added load transfer capability between the nut 13 and the bar 1 can be provided by making the nut 13 longer so that is engages more turns 5.

As seen in Figs. 7 and 8, various thread profiles are possible including a trapezoidal thread as illustrated in Fig. 7 or a substantially semi-circular thread as illustrated in Fig. 8. The thread can be either right handed or left handed.

The above described bar has various substantial advantages. Firstly the height of the deformations or turns 5 is high, typically 1.5mm, thereby resulting in good keying. Secondly, the circumferential extent of each turn 5 is large, thereby also resulting in good keying.

Furthermore, because the bar can be hot rolled, high tensile and extra high tensile steel can be used. Such bar fabricated from high tensile or extra high tensile steel finds particular application in coal mines where a rock bolt of high yield strength is substantially advantageous. Also the circumferential extent of the turns 5 makes for easy hot rolling.

The ability of the bar 1 to be used as a rock bolt without further manufacturing treatment or processing also provides a further very substantial advantage. That is that the bar can be shipped direct from the rod and bar mill (or steel merchant) directly to the end user (typically a mine or tunnelling site). This saves a substantial amount in transport and handling costs since the bars do not have to be unloaded and then re-packed by the rock bolt manufacturer.

Furthermore, there is an additional saving because there is no processing required to be carried out by the rock bolt manufacturer such as peeling and cold forming of threads. Thus the rock bolt manufacturer need only supply the end user with the accessories to go with the rock bolt. Such accessories include the plate 11 , domed washer 12, nut 13 and a frangible cartridge (known per se) of two part components of the grout or resin 15.

It is thought the changed manufacturing and distribution arrangements can reduce the cost of rock bolt, which typical cost from A$7.00 - A$20.00 depending on length, by approximately $A1.00 - A$2.00.

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. For example, the washer 12 can be eliminated and the nut 13 provided with a domed leading end.

The term "comprising" (and its grammatical variations) as used herein is used in the sense of "having" or "including" and not in the sense of "consisting only of.

Claims

1. A thread pattern for use as a rock bolt, reinforcing bar and like engineering bars, said thread pattern comprising a single start helical thread in which every second turn of the thread is absent and the circumferential extent of each half turn of said thread approaches 50% of the circumferential extent of said bar.

2. The thread pattern as claimed in claim 1 and hot rolled.

3. The thread pattern as claimed in claim 1 or 2 and having a pair of longitudinally extending gaps in the thread.

4. The thread pattern as claimed in any one of claims 1-3 and having a pitch of approximately 5mm.

5. The thread pattern as claimed in any one of claims 1 -4 and engageable with an interior continuous thread of a nut, said interior thread having substantially equal pitch.

6. The thread pattern as claimed in any one of claims 1-5 and being right handed.

7. The thread pattern as claimed in any one of claims 1 -5 and being left handed.

8. The thread pattern as claimed in any one of claims 1-7 wherein the thread profile is substantially trapezoidal in cross-section.

9. The thread pattern as claimed in any one of claims 1-7 wherein the thread profile is substantially semi-circular in cross-section.

10. A threaded bar having a thread pattern as claimed in any one of claims 1-10.

11. A rock bolt for use in mining, tunnelling and like activities, said bolt comprising a length of unprocessed hot rolled threaded bar having an exterior at least partial thread hot roll formed on said bar, and at least one accessory threadably engaged with said bar.

12. The bolt as claimed in claim 11 wherein said accessory comprises a nut received on a trailing end of said bolt and dimensioned to bear against an apertured plate through which the bolt passes.

13. The bolt as claimed in claim 11 or 12 wherein said accessory comprises an anchor received on a leading end of said bolt.

14. The bolt as claimed in claim 13 wherein said anchor is an expansion anchor.

15. A rock bolt as claimed in any one of claims 11-14 and fabricated from threaded bar as claimed in claim 10.

16. A method of assembling a rock bolt for use in a mine site, tunnel construction site, or similar end user site, said method comprising the steps of:

(i) receiving from a first supplier a first length of unprocessed hot rolled threaded bar having an exterior at least partial thread bar hot roll formed on said bar, (ii) if necessary, cutting said bar to a second, shorter, length substantially comprising the desired length of said rock bolt,

(iv) engaging said accessories with said threaded bar to completely assemble said rock bolt.

17. The method as claimed in claim 16 wherein said accessories are selected from the group consisting of nuts, apertured plates, and anchors including expansion anchors.

18. The method as claimed in claim 16 or 17 wherein said first supplier cuts said bar to said second length.

19. The method as claimed in any one of claims 16 to 18 wherein said first supplier is selected from the group consisting of a bar and rod mill organisation, an unprocessed steel merchant, and an unprocessed steel distributor, and said second supplier is selected from the group consisting of a steel products fabricator and a fabricated products distributor.

20. The method as claimed in any one of claims 16-19 wherein said hot rolled threaded bar is as claimed in claim 10.