CA2182492C - Inhibiting resin expulsion during molding of elongate fiber reinforced products - Google Patents

Abstract

Elongate products are moulded in a die (27, 28 47) from fibre reinforced plastics by drawing a bundle of tows (23) through a bath (16) of resin (17) and between two portions of an open die (27, 28, 47), which is closed under high pressure are heated to cure the resin. The die is opened, and the product is then partly withdrawn lengthwise, to draw further wetted tows (23) between the die portions, and the die is again closed, clamping the tail end of the already cured product which still projects into the die space, or clamping blocks (41) at its downstream end. Cold clamping blocks (24) also clamp the tows (23) at the die upstream end. The products are subsequently severed externally of the die by cutter wheels (44).

Description

2~ 82~92 ~ WO 96116792 PCI/AU94/00749 rNHlBITING RESrN EXPULSION DURING
MOLDING OF ELONGATE FIBER RE}NFORCED PRODUCTS
This ~l ~e~ iric~ relates to an extension oF Australian Application 28899/92 (PCTIAU92/00585) the "later" ~pe~iiricdliù, ,. The invention relates toa further extension of an earlier Australian Patent Application 56990/90 (PatentNo 631881 ) entitled "High strength fibre reinforced polymeric fasteners having threads for example a nut and bolt", (the 'original' :,I,e~ .;rl ~liol~) both said patents being applied for by the Applicant herein.
BACKGROUND OF THE INVENTION
The original Patent 631881 was directed primarily to a means for and a method of forming a rock bolt of fibreglass reinforced plastics material ~particularly a polyester formulation), but did not disclose any means for or method of rendering a rock bolt electrically conductive. The later ~l ~e~ ir~ iodiscloses a method of rendering a rock bolt ele~,l, i 'Iy conductive, and disclosed a method of production of such a rock bolt. The method disclosed in that s~e~;iriwliu,, indicated the need to supply sufficient pressure to wetted tows to cause flow of resin into contact with bolt thread forming surfaces, and further disclosed applying chopped strand reinforced fluid but settable plasticsmix to the weffed tows at the locdlity of a thread forming surface, before closure of dies. Further, the method disclosed forming a bolt with a shank longer than the shank forming surface of the dies by firstly forming a bolt with a shank equal to the length of the shank forming surface, and withdrawing the threaded end outwardly from between the dies so as to form further wetted tows of a bundle between the shank forming cdvities of the die and again closing the die to clamp portion of the shank and applying pressure to the wetted tows while the resin sets. Pressure was also indicated to be required to force resin to flow into close contact with thread forming surfaces, and protuberance recesses.
In both the original ~,ueciri~,d~io,1 and in the later ~I e iri~ some pressure was indicated as being desirable during the moulding of a rock bolt, inorder to cause a flow of resin through the fibres into cavities defined by the die surfaces, but nevertheless with the relatively small pressures which were r~on~" ~,uldl~d at the time that ~l ~el .;r ~l i. .., was prepared, a cu, I:~ial~ :l IL torsional strength was difficult to obtain. However, it has been found that by i".,, ~asi"g the pressures to pressures greater than 2ûû psi (14ûû kPa) for low viscosity resin, below 5ûû centipoise, the air inclusion which frequently occurs in products made from wetted tows, is ~lil "i, Idldd, or greatly reduced, and what would otherwise be unwet fibres are fully wetted, so that there is no discontinuity of resin at that point, which otherwise occurs if very low pressures WO 96/16792 ~ 1 ~ 2 ~ 9 ~ PCIIAU94/00749 are used. Desirably the pressures exceed 500 psi (3500 kPa) for viscosities up to 2000 centipoise, and 700 psi (5000 kPa) for viscosities above 5000 centipoise, or for densely packed fibres. Efforts have been made by the inventors to get even hi3her pressures. It is beliaved that under those pressures the air actually dissolves in the resin, but does not appear to have any deleterious effect on the shear strength of the resin which is relevant to the torsional stren3th of the product.
A problem which is encountered if hi3h pressure is used in moulding a hbre reinforced product is that the resin tends to be extruded from the ends of a die through which the product extQnds. If that extrusion takes place at the upstream end of a hot die, a bulbous knob of set resin will form which needs to be removed, and that operation is not viable for production of continuous uniform len3th products.
The main object of this invention is inhibition of extrusion of resin through die ends and preventin3 a bulbous knob from forming at the entry end of the die, in an ~"ll~o~i",a"1 of this invention, use is made of clamping meanscomprised in the die, and having a cold surface at the upstream end of the die, the clamping means preferably being separate blocks appended to the die ends, while obviously they can be cu" ' ~' ' by portion of the heated die itselfat the upstream end, if it is kept water cooled.
In many dur l;cdlio,~s of fibreglass reinforced plastics (FRP) although the tensile strength may be adequate because it is imparted by the ~" ,iui,~iu, Idl fibres, the torsional strength is ir~A~eq~ lZltf!, and it is an object of this invention to provide a method of production of an elongate fibre reinforced product which has a more reliable torsional strength than products presently produced by known cùlllul~5a;0l~ methods. In an aspect of this invention, entrained air is SULJ~Ldl l~;.. 'y removed from the product.
The later ~,u~-.iri~,dLiul, disclosed (in Fig 6) drawin3 a bundle of resin wetted fibres throu3h an open die as a trailing extension of a premoulded product, and se,ud, dlil ,~ the moulded prûducts externally of the die.
This invention relates to the abov, .,. "t~ iUI ,ed method, and to further e, 1l Idl IC~ of the production method disclosed in the later al~euiriwliul ,. In particular, there is a requirement which is frequently met of producin3 an elon3ate product of a length which is within a tolerance specified by a customer, and further, quite often there is a requirement for a fibre reinforcedplastics product which is suitable for use as a, t:i"ru, ~:" ,~ bar for, ~i"rul ,i"~
of concrete. This is particularly desirable (when ~ all ~ased) because of the J
WO 96/16792 2 ~ 2 ~ ~ 2 PCilAU94/00749 much lower Youngs modulus of FRP compared with steel which is otherwise used, and the second favourable .1 Idl duL~I ialiu of FRP is that of having a very high yield point, yield taking place close to the ultimate tensile strength of the product if in tension. Still further when embodied in concrete, the corrosion problem which is encountered by steel is not encountered by plastics. This in turn simplifies the structure of a concrete beam, for example, because there is not the need for a thick overlay of concrete to nearly such an extent as occurs with metal, to avoid "concrete cancer", that is, corrosion of steel within the concrete, with increase of volume causing further cracking and corrosion.
In an aspect of this invention, ~;LI ~ ..v~' of a precured product from an open die is only partial, the moulded tail end functioning as a "plug" at the do.~"aL,~d", end of the die so as to enable high die pressures to be used. The degree of withdrawal can be varied, so that products can be moulded to varying lengths which are greater than the die length and in the case of concrete rul Uil l9 bar, to a tolerance of one pitch of the protuberances on its outer surface.
The invention can be extended to other products, which are not nec~ad, ily of constant cross-sectional shape throughout their lengths. In those instances, wherein part of the product length has a constant cross-section, products can be made to a very small length tolerance.
In most ~" ' " la of fibre reinforced ~ sioni"3 members, bolts and rul Uil Ig bar, tensile strensth is the most desirable feature, and the tensile strength is largely a function of the amount of, ~i, If O~ ,i"~ fibre which exists in a given cross-sectional area in a product. For that reason, it is an object of this invention to provide improvements whereby the ratio of fibres to resin may be much higher than what has been c~l "" 1~, ui~'!y produced previously, achieved by using the abov~l "el ,Lio,~ed higher pressures.
BRIEF SUMMARY OF THE INVENTION
In this invention, production of elongate moulded products of settable resin reinforced with fibres cu" ,,u, iaes the steps of drawing a bundle of fibres through a bath of fluid but settable resin mix and between cavities of die portions of an open die, closing the open die under pressure to form the shape of the required product, applying heat and " ,a;, lldil lil)9 pressure to cure the resin and form a product, and clamping the wetted tows between unheated surfaces at the upstream end of the die so as to prevent expulsion of resin fromthe die cavities. The invention can further comprise partly wi:l ~dl ;. ~ the product from the die l~r,ytl ,~ so as to introduce further tows and entrained ~ ~2~g2 wo 96116792 2_ 4 - PCT/AU94100749 resin between the cavities of the open die, producing subsequent products successively each by repetition of those steps, and severing the moulded products From one another externally of the die. The cured product may be clamped by a spring loaded clamping block where it projects at the cluJ~";,1, ~dl11 end of the die, and the wetted tows adjacent the upstream end of the die clamped between cold surfaces with sufficient force to inhibit resin expulsion from the die.
In this invention, the cold surfaces are used at the upstream end so that, not~ dl Idi~ I~J restrition against expulsion, if any resin is expelled through the upstream end, that resin is not heated as the resin within the dies is heated, and therefore remains in a fluid state in the tows as they are drawn through thedies to produce a subsequent product. In a further ~ O~illlt:rl~ of the invention, the cold clamping surfaces at the upstream end are surfaces of a pair of water cooled metal clamping blocks which come together upon closure of the dies, and are separated from the hot portions of the die ends by means of a heat insulating separator pad. There is no need to water cool the clamping blocks at the do.~ ,L, '3dl11 end of the dies, since the clamping blocks (which form portions of the die portions) only engage cured material, or in extreme conditions, are themselves sufficiently hot to cure the resin.
In many other products which are likely to be produced, including both rock bolts and, ~i"rul ~,i"g bars, there is frequently a need for threaded ends. In a still further ~ u~ of the invention, at the downstream end of the die, there is provided a three part die portion for dehning thread forming surfaces, two of the portions se~d, dlil ,9 out laterally when the die is opened and the third portion being lifted away, and the length of the thread forming portion equals the combined lengths of two threads one at each end of a product, the first saidproduct being separated from the second said product and so on by dividing the thread into two equal parts externally of the die.
By partial v.;~ ' only of a product after it has been cured in the dies, products can be made longer than the die length, as said above. No loss of strength has been found to exist due to curing of a shank portion to a trailing end of a previously cured shank portion. It becomes inconvenient if fibres wet with uncured resin extends beyond the die (including dc,... Iall l::dll I clamps), and it is impor~ant that v~ . ' of cured resin should be partial only, so that cured resin lies at least between the ~u~,la~,~dl,, clamps, (which are herein defined as being portions of the die) and preferably extends into the cavity of the die. However, if the die cavity at the d~ sll tldl 11 end includes thread WO 96/16792 2 1 ~ 2 ~ 9 ~ PCIIAU94100749 forming cu, If ul " IdLiUI 1:~, the cured resin should not extend into the cavity for the length of the thread when forming a thread, since moulding of uncured resin over cured resin may fail to achieve full adhesion, when a thread forming mix isinjected.
PRIOR ART
The US Patent No 3,96û,629 in the name of William Brandt GOLDSWORTHY disclosed a cu",,uosil~ strand of Ille""~s~Ii"g synthetic plastic resin reinforced with fibres and produced by a pultrusion machine and process. This constitutes the relevant prior art, but neither the end clamping of the product, nor the die forming method of the Applicant's is disclosed therein,nor is it disclosed elsewhere within the context of forming elongate moulded products under pressure and heat by producing the products successively and j)dl d~il 19 them subsequent to curing.
Other relevant prior art includes:
Australian patents 5797û3 (52431/86) W2;~ 11dllll 586930 (76314157) DuPont 487898 (74319/74) Titan A very large amount of literature exists on the ~ , ' " , of fibreglass reinforced plastics as l l,;. ,ru, ui"g bars for ~" ,L,e,ldi"g in conuete. Reference is made herein to "I~ ,. l IdLiOlldl Encyclopedia of Col, Ir ~ , Volume 6, pages 173 to 186, which summarises usage of FRP r~i"ru, ~i, ,9 bars, and also provides an extensive list of It:r~ lllCe5~ (ISBNO-89573-736-1; VCR Publishers, New York, USA).
BRIEF SUMMARY OF THE DRAWINGS
An ~"~L~di"~"~ of the invention is described hereunder in some detail with reference to and is illustrated in the acc~",,ud"ying drawings in which:
Fig 1 shows the steps of drawing a bundle of fibres through a bath of fluid but settable resin mix;
Fig 2A shows the steps of closing die portions of a die to fomm a product, with the upstream end of the die closed by a water cooled clamping block and the ~o~ dl11 end of the relevant part of the die closed by the tail end of the previously moulded product;
Fig 2B is a continuation of Fig 2A and illustrates the severing of previously moulded products externally of the die;
Fig 3 is a section taken on plane 3-3 of Fig 2A, showing the three part die at the thread forming locality at the dU.\'I'l::-Ll~dlll end of the die, drawn to a larger scale;

WO96/16792 ~1~2~ PCT/AU94100749 Fig 4 illustrates the thread fommation and the flbre formation at the locality of threads;
Fig 5 is a view similar to Figs 2A and 2B, but showing rock bolts being formed two at a time with the thread fomming portion of the die central between its upstream and ,~ dl11 ends;
Fig 6 shows to a larger scale the detail of the coid blocks which are otherwise illustrated in Figs 2A and 5;
Fig 7 is a rldyl~ dly "e)~plod~d" view of the do~ bll~dlll end clamping blocks;
Fig 8 shows a joining of continuously threaded, ~:i"rul ~i"~ bars by means of a turnbuckle nut;
Fig 9 shows a threaded end which could be useful in retaining the ends of a ,t,i"r",~i"~ bar in concrete;
Fig 10 shows one form of hook dl I dl 19el 111311~ again using a turnbuckle nut, for posi~ior,i"~ upper and lower, ~ rul~;il ,g bars; and Fig 11 shows an altemative dl I dl~9t~ wherein a length of threaded ,~i"ru,~i"9 bar ~ "i, Id~tlS at its ends in upper and lower hooks.
DESCRIPTION OF l'Kt~t~RED EMBODIMENTS
Referring first to Fig 1, a series of reels 14 carry fibreglass or other fibre strands 15 (carbon, or aramid "Kevlar") which pass through a bath 16 containing fluid but settable polyester resin 17, and pass over the three curveddeflectors 19, 20 and 21 and into nozle 22 to emerge as a bundle of tows 23.
From the nozle 22, the bundle of tows 23 passes first through a pair of metal clamping blocks 24 cooled by waterway 26 as shown in Fig 2A, then through a heat insulating separator pad 25 which in this ~",uuui",t:"~ is of PTFE ("Teflon") to which the resin is non adhesive. The bundle 23 is drawn through the then open die portions 27 and 28, the die portions being heated by ~"liJedd~d ~ ,l"o~ i.,ally controlled heating elements 29, and being closable by means of hydraulic rams 30 which are arranged to apply a projected area pressure of more than 2û0 psi (140û kPa), but in this e",i~odi"~t:"~, the pressure is in the order of 1000 psi (7 mPa).
As shown in Fig 2A, adjacent the ~o .. . Iall t~dl 11 end of the die there is a thread forming formation 31 which, as shown in Fig 3, is constituted by an upper part 32, and two lower parts 33 and 34, and the lower parts are separable laterally to open the die while the upper part moves upwardly. The three part die portion is required because of the retum surfaces of a thread when moulded. If a fully threaded rod is required, the entire length of the die wo96/16792 ` " ~ 8 2 4 9 2 PCT/AU94/00749 needs to be three part. Altematively, the circular shape shown in Fig 2 may have parallel sides as shown in the later ~,ueuiriudliul 1.
The thread forming portion 31 and its die parts extend for double the Iength of a required thread 37 (Fig 2B), and an accurately d~'~, ",i,~ed amount of thread fomming resin is injected by an ~jl lc~hle injection ram 38. In order to provide a strong thread, not only is the pitch diameter made greater than the outside diameter of the shank 39 of a, t.i, If u, ui"g bar, but the thread mix is of stronger material. Use can, for example, be made of chopped hbreglass strand embodied in a high strength resin (in this t." ,bodi" ,~nl, using 20 parts of chopped strand glass fibres to 100 parts of resin). In this t."l~udi,"t."~, the resin used in the shank was a relatively i, ,a~,ua~ l3;~/e resin (eg, an iau,ul l~l l " resin having only 1% to 2% elol~gdliùl~). However, the thread resin is a Dow Chemical 'Derakene 411 vinyl ester' having a 4% to 5% elu,~gdliù,~.
The use of cr~ntinuous bulked roving still further increases the thread strength. Bulked roving is a texturized product which i".,u"uu, ~ . transverse filaments in addition to axis-oriented filaments, and is produced by PPG
Industries Inc., Fiber Glass Products, One PPG Place, Pittsburgh, Pennsylvania, USA.
The I ~.i, I~u~ ,i"g bar which is shown to be produced in Figs 2A and 2B is an elongate bar, and the length is d~rlt.l l,,i, ,ed by the number of portions which are moulded in s~lcc~scion within the shank forming part of the die. The bundle of tows is drawn through the separated die portions 27 and 28, and the die is closed, the upstream and du.."al~:d"~ projecting ends of the tows being clamped to avoid excessive resin expulsion. Thread cu,,,,uusilioll is injected to form a thread adjacent the ~' ... ,al,~d,n clamping blocks 41, the clamping blocks 41 enabling high pressure to be used to produce a hrst moulding, as well as all successive mouldings. The die portions are separated and the three part die of Fig 3 is also opened and the cured product is withdrawn from the dieportions by the puller 42, until the cured end of shank 39 is located slightly upstream of the thread forming formation 31, and this then functions as a plug to prevent extrusion of resin from the ' A.lallt:dlll end. Fommed protuberances ~2 (if any) must register in the die recesses. The shank length is then extendedby closing the die portions and setting the resin entrained by the tows in the bundle 23 upstream of the set portion of the shank 39, without forming further threads. The distance the set portion of shank 39 p~r,~', d~as the die cavity upstream of the thread forming formation 31 will determine the final length of WO 96/16792 218 2 4 9 2 PCIIAU94100749 ~

the ~ ful Uil lg bar. This is controlled by cu"l" " ,~ the distance of the set portion of shank 39.
During curing of the resin, there is a small change in volume, and therefore the upper die portion 27 will move aowl~il l.Jly in a vertical direction, I l Idil ILd;l lil 1!3 pressure on the product during the curing period. The du .~. IS~ dl 11 clamping blocks 41 are required to clamp the previously cured tail end of a fommerly moulded product to inhibit resin extrusion, and therefore is spring loaded d~ i. dly by Bellville springs 43.
Assuming that one more closure of the dies is required for the compiete bar which may be much longer than the die, the third closure occurs when the shank has been withdrawn further by the puller 42, and for the third closure thread forming mix is agarn injected by the injection ram 38.
The product is a3ain withdrawn from the dies after the die portions have been separated, and successive products are made in much the same way.
The thread 37 is separated in halves by the cutting wheel 44 as shown in Fig 2B, leaving the left hand end of shank 39 remaining in the die space, and the process is repeated for successive products.
As best seen in Fig 3, the lower die portion 28 has a 'U' shaped cross-section slot, the side walls GUl ILdil lil l~ fibres against sepd, dliUn when pressing.
This in turn enables a larger content of, ~i, Iru~ 1il l~ fibre, and for example, the Applicant has been .cl Irr~e.scfl ll in producing a bar with glass fibres contributing more than 8û% of the weight, and resin less than 20%. Such densely packed tows require low viscosity resin, and require high pressure to be imparted to cause resin flow between the fibres, and intû die recesses. Use of filler is at least reduced, if not ~`;.llilldltd in such instances.
Results are enhanced if some of the outer tows are of bulked rovings.
Fig 4 illustrates to a larger scale the thread 37 with its higher elongation, higher strength resin content and its chopped strand fibre surrounding the bundle of tows 23. Since the thread is of larger pitch diameter and since it wlllp'~t~l,t surrounds the bundle of tows 23, which otherwise set to form shank 39, if the composite plastic I t~ rul ~ 9 bar is to be pl t::,t, ~s~ed, the thread strength will be at least 45% of the ultimate tensile strength of the shank, since pl~LI~si"g to 4û% of the ultimate tensile stress is ,~wl",~ ded.
Furthermore, because of the relatively high degree of elol-udlion available within the workable range of tensile forces, use can be made of elongate nuts as described below to Ll ll ~add~ engage a greater number of threads and the load will be much more evenly spread than in the case of, say, a steel thread ~O 96/16792 ~ 9 2 PCT/AU94/00749 where most of the load is taken by one or two threads. The small d~ru, Illdliùl~s of the outer axial fibres 40, shown in Fig 4, has a significant effect on threadstrength.
R,,~. ~nce is now made to Fig 5 which is otherwise illustrated in the parent ~l~e~ , and Fig 5 differs from the ~Illbodi~ l of Figs 2A, 2B and 3, in that the thread forming formation 46 is located centrally of the die assembly 47, and two rock bolts 48 may be moulded simultaneously, subsequently seYered by wheels 44. The threads 49 and the shanks 50 are otherwise similar to what is shown in Figs 2A and 2B. Use is made of the cold clamping blocks 24 at the upstream end of the die assembly 47, and at the downstream end clamping blocks 41 are spring loaded by Bellville springs 43 as in the first described ~",uo~i",t:"l.
In both e",L,o~i",~"l~, no attempt is made or is necessary to be made in most instances for the thread strength to equal the tensile strength of the shank, although the thread must be capable of p, ~all ~SSil l9 a, ~i, If ul ~,i"g bar to 40% of its ultimate tensile strength. The, ~i"ru, ,i"g bar which is illustrated in Figs 2A and 2B is proYided with a plurality of protuberances 52, and these protuberances may be spaced for example 20 mm apart. In that instance, it is necessary for the length to be d~l~l "~i"ed within a 2û mm pitch tolerance, but when the bar is embodied in concrete, protuberances ~i2 lock the bar for the entire length of the concrete. Thus it is desirable that some ~ ssi"g be imparted. Once the concrete has set, the load on the nuts is not excessively increased upon loading of the concrete because of the locking effect of the protuberances 52.
However, in the case of a rock bolt with point anchor, the thread may be required to support a heavier load, and this can be imparted simply by i"~ asi"9 pitch diameter, i".,, I:d:/il 19 bulked roving content or both.
Fig 6 is a larger scale ,~ st~, Itd~ of the upstream clamping blocks 24 and the insulating pad 25, and Figs 2a and 7 in addition show spring 43 at the downstream end, which retains high pressure l~utv~ ldl l~il ,g expansion or COl Illd~,liUI~ of the bundle of tows 23, upon heating and ~ Ihseql ~nt cooling. Sometimes there is a requirement for a use of a turnbuckle on a , ~i, If ul .,i"g bar, for example, of continuous threaded rod, and Fig 8 shows a tumbuckle nut 55 engaging a right hand thread 56 at the right hand side and the leff hand thread 57 at the left hand side of respective moulded continuously threaded rods 58.

WO96/16792 ~ 8249Z PCI/AU94100749 When a composite thermoset It:i"rul~;i"g bar is used in concrete, it is not feasible to bend the ends, as in the case of steel, and use may be made of the moulded flanged end member 60 which is illustrated in Fig 9, which is provided with retention hooks 61.
In many i" " ,s of concrete, there is need for both upper and lower I t~il Irul Uil lua, and these are usually retained in their separate locations by means of wired in stirrups. Fig 10 illustrates a turnbuckle sleeve 62 v,/hich threadably engages right and left hand threads of respective hooks 63 for engaging upper and lower, t:i"ru, ,i"g rods 64 and 65.
Fig 11 illustrates an alternative dlldl l~",e"I wherein a length of continuously threaded, t,i, If ul 1il ,g bar 68 is cut to length and engages female threads in the hooks 69 for the same pur,oose.
The following tests confirm the effectiveness of bulked roving vis a vis single ended ("nommal") roving:
The following results were obtained by replacing the "normal" 4800 tex fibreglass with two 24ûû tex bulked rovings in the bolt, ie one 48ûû tex fibreglass tow was taken out and replaced with two 24ûû tex bulk rovings.
Tex is the weight of 1 kilometre of fibreglass, eg 480û tex fibreglass weights 4.8 UIllS/",~ , so that the l~ldC~ did not change the quantity of fibreglass in the bolt.
TECHNIQUE: -Torque - The bolt was placed in a custom built torque tester, which requires clamping the bolt by the flat sides at one end, the other end which clamped the bolt on the flat sides was free to rotate in ball bearings and Ul ~JOI d~d a fixture to which a torque wrench is attached. The bolt was then twisted about the longitudinal axis until failure occurs.
Results - A normal bolt with no bulked rovings withstood 5û-56 ft/lb torque.
Replac~",~"l of outside 3 strands of the normal 48ûû tex fibreglass with 6 strand of 24ûû tex bulked roving achieved an average torque , ~aiaId"ce of:
6 strands of 2400 tex bulked rovings 67 ft/lb 12 strands of 2400 tex bulked rovings 7û fttlb 18 strands of 2400 tex bulked rovings 73 ft/lb The bulked roving increase the torque I ~aialdl ,~,e by 3 fVlbs per 6 strands of 2400 tex placed on the periphery of the bolt where it has the best effect.

WO 96/16792 1~ 9 2 PC17AU94/00749 Each of the bolts prior to being subjected to the torque test was subjected to a tensile load where a nut was placed on the threaded section and placed in a universal tensile tester.
- Two types of failure occurred: the thread stripped off the bolt (thread had insufficient shear strength) or the nut split (nut had insufficient hoop strength).
The normal nuVthread strength is 45-50 kN.
6 strands bulked roving ,t:place",e"L normal fibreglass -Average tensile NuVthread 50.7 kN - 2 nut failures out of 6 12 strands bulked roving ,~plac~",e"~ normal fibreglass -Average tensile NuVthread 54.2 kN - 2 nut failures out of 6 18 strands bulked roving, ~,lac~" ,t:"l normal fibreglass -Average tensile NuVthread 58 kN - 6 nut failures out of 6 That is bulked roving increased the thread strength which is shown by increase in the ultimate tension load that the thread/nut will withstand. The numerical increase in nut failure d~l,lor,DI, _~,3 the i"~ r~D;"g shear strength of the thread caused by the use of the bulked roving.
It is also il ll~l ~Di;l l~ to note the almost perfect linearity of the results.TORQUE - 6-12 tows bulk roving 3 fVlbs increase 12-18 tows bulk roving 3 ft/lbs increase TENSILE - 6-12 tows bulk roving 3 5 kN increase 12-18 tows bulk roving 3.8 kN increase A . ~"~ide, c,Lio,~ of the above factors will also indicate the invention makes possible for the first time known to the Applicant a production method forproducing resilient strong rock bolts which meet all criteria presently known tothe Applicant and which can be produced for relatively low cost since the bolt shanks can embody large quantities of i, ~ IJel ,siv~ filler. The invention is further ~ , - to products of fibre reinforced plastics other than rock bolts and I t:i"ru, 1il ,9 bars wherein polymer products are required R~i"r.,, ~i"~ bars and other elongate products can be produced in continuous lengths with or without threads and with ~, ,i.li, ~ Liunal fibres. This can be achieved with short fixed length dies.

Claims

CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:
1. A method of forming a plurality of elongate moulded products of settable resin reinforced with fibres, comprising the steps:
(a) drawing a bundle of tows of fibres through a bath of fluid resin mix and between cavities of die portions of an open die, (b) applying pressure to close the die portions to conform the envelope shape of said tows and said resin entrained and wetted thereby to the shapes of surfaces which define said cavities, retaining pressure on said tows and applying heat to said die portions to accelerate curing of said resin there between, (c) clamping said bundle of tows between unheated surfaces at the upstream end of said die with sufficient force to inhibit expulsion of resin from said die cavities at said upstream end when said die portions close.
(d) opening said die portions and partly withdrawing a moulded product lengthwise therefrom, thereby drawing a further bundle of tows wetted with said resin between said die cavities, the further bundle of wetted tows being a trailing extension of said moulded product, (e) repeating said steps (b) and (c) to form successive identical moulded products, and (f) separating said moulded products externally of the die.
2. A method according to claim 1 wherein said unheated surfaces are surfaces of metal clamping blocks comprised in the upstream ends of respective said die portions, and further comprising water cooling said clamping blocks.
3. A method according to any either claim 1 or claim 2 further comprising clamping portion of a partly withdrawn moulded product the resin of which has already been at least partly cured during step (b) of claim 1, betweensurfaces at the downstream end of said dies with sufficient pressure to inhibit expulsion of uncured resin from said die cavities at said downstream end when said die portions close.
4. A method according to claim 3 wherein said downstream end clamping surfaces are surfaces of metal clamping blocks comprised in downstream ends of respective said die portions, and further comprising applying said clamping pressure by spring loading one at least of said blocks toretain said clamping pressure during the curing of resin in step (b) of claim 1. 5. A method according to claim 3 or claim 4 further comprising repeating said partial withdrawal of said moulded product from said dies, said clamping at the downstream end, and steps (a) and (b) of claim 1, to produce said moulded products to be of length exceeding said die length.
6. A method according to claim 1 further comprising extending step (d) thereof by retaining between said die portions, a portion of a partly withdrawn moulded product the resin of which has already been at least partly cured during step (b) of claim 1, and closing said die portions over saidretained moulded product portion to thereby form a plug and inhibit expulsion ofuncured resin from said die cavities at the downstream end of said die.
7. A method according to claim 1 wherein said products are fibre reinforced plastics concrete reinforcing rods, further comprising forming said products in accordance with step (b) of claim 1 to have protuberances spaced along their length, and partly withdrawing said product in accordance with step (d) of claim 1, repeating steps (b) and (d) of claim 1 to form a rod of indefinite length, and subsequently separating rods externally of the die into lengths by severing the rods.
8. A method according to claim 1 wherein said products are fibre reinforced plastics concrete reinforcing plastics concrete reinforcing rods, and wherein said cavity surfaces include relatively small diameter shank forming surfaces extending inwardly from said upstream end and relatively large diameter thread forming surfaces extending inwardly from the die downstream end, further comprising forming said products by moulding a reinforcing rod in accordance with step (b) of claim 1, in the entire length of said die, to have athread at the downstream end of said shank, at least once partly withdrawing said product in accordance with step (d) of claim 1 but terminating said withdrawal with a cured portion of said resin still between said shank forming surfaces, moulding said wetted tows in said die in accordance with step (b) to extend shank length, at least partly withdrawing the moulded product from said die in accordance with a cured portion of said resin only at a downstream end of said die, again moulding said wetted tows in said die in accordance with step (b) and simultaneously injecting a thread forming resin mix into space surrounding a downstream end of said wetted tows and defined by said thread forming surfaces, repeating the method herein to remove the product from the die in accordance with step (d), and severing said moulded products in accordance with step (f) by cutting through the threads, such that each reinforcing rod has a shank with a thread at each end.
9. A method according to claim 1 wherein said products are fibre reinforced plastics rock bolts, further comprising moulding two rock bolts end-to-end simultaneously in a die in accordance with step (b) to have shanks extending both upstream and downstream from a central threaded portion, partly withdrawing in accordance with step (d), and separating from each other in accordance with step (f) by severing shanks and threads.