WO2001076853A2

WO2001076853A2 - Fiber reinforced threaded rod

Info

Publication number: WO2001076853A2
Application number: PCT/CA2001/000479
Authority: WO
Inventors: Randel Brandstrom
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-04-06
Filing date: 2001-04-06
Publication date: 2001-10-18
Anticipated expiration: 2002-10-06
Also published as: AU2001250196A1; WO2001076853A3

Abstract

A fully threaded composite reinforcing rod (85) formed by providing a reinforcing material supply of fiber strands rovings (16); a resin supply bath (30), and a puller (80) for pulling the resin-impregnated reinforcing material through the resin bath. A hot compression (or autoclave) apparatus includes two half autoclave molds (50), which can be arranged in a reciprocating die autoclave (60) or a tractor die autoclave (70) process. A mandrel or plastics tubing core is used to form a hollow shape of the composite materials to get an external threaded composite tubing. The two autoclave molds (51, 53) have an internal thread and clamp to form the threaded section in the outer of the resin-impregnated reinforcing material (43). The molds press and squeeze the resin out of the impregnated fibers to the mold internal surfaces, and push the outer fibers which may be the basic longitudinal roving fibers or may include a wrapped mat and/or helically wrapped fibers toward the crest of the thread of the molds so that the thread when formed is reinforced by fibers extending into the core of the rod.

Description

FIBER REINFORCED THREADED ROD

The present invention relates a method for manufacture of fiber reinforced threaded rod.

The term "rod" as used herein is intended to include bars and rods which are hollow, that is tubing. The outside surface is preferably but not necessarily of circular cross- section. The rods can be of any length including elements which are relatively short so that they are sometimes referred to as "bolts".

The use of fiber reinforced plastics (FRP) rods in construction, marine, mining and others has been increasing for years. This is because FRP has many benefits, such as non-(chemical or saltwater) corroding, non-metallic (or non-magnetic) and non- conductive, about twice to three times tensile strength and 1/4 weight of steel reinforcing rod, a coefficient of thermal expansion more compatible with concrete or rock than steel rod. Most of the bars are often produced by pultrusion process and have a linear or uniform profile. Conventional pultrusion process involves drawing a bundle of reinforcing material (e.g., fibers or fiber filaments) from a source thereof, wetting the fibers and impregnating them (preferably with a thermosettable polymer resin) by passing the reinforcing material through a resin bath in an open tank, pulling the resin-wetted and impregnated bundle through a shaping die to align the fiber bundle and to manipulate it into the proper cross- sectional configuration, and curing the resin in a mold while maintaining tension on the filaments. Because the fibers progress completely through the pultrusion process without being cut or chopped, the resulting products generally have exceptionally high tensile strength in the longitudinal direction (i.e., in the direction the fiber filaments are pulled). Exemplary pultrusion techniques are described in U.S. Patent No. 3,793,108 to Goldsworthy; 4,394,338 to Fuwa; 4,445,957 to Harvey; and 5,174,844 to Tong.

FRP uniform profile or linear rods offer several advantages in many industrial applications. The rods are corrosion resistant, and have high tensile strength and weight reduction. In the past, threaded steel rods or bolts had been widely used in engineering practice. However, long-term observations in Sweden of steel bolts grouted with mortar have shown that the quality of the grouting material was insufficient in 50% of the objects and more bolts have suffered from severe corrosion (see reference Hans K.Helfrich). In contrast with the steel bolts, the FRP bolts are corrosion resistant and can be simultaneously used in the temporary support and the final lining, and the construction costs of single lining tunnels with FRP rock bolts are 33% to 50% lower than of tunnels with traditional in-site concrete (see reference Amberg Ingenieurburo AG, Zurich). This FRP rock bolting system is durable and as a part of the final lining supports a structure during its whole life span. Furthermore, due to their seawater corrosion resistance, the FRP bolts and anchors are also proven as good solutions in waterfront (e.g., on-shore or off-shore seawalls) to reinforce the concrete structures. In general the fibreglass rod/bolt is already an important niche, and will be a more important product to the mining and construction industries. The critical needs of these industries are for structural reinforcements that provide long-term reliability that is of cost-effective. The savings in repair and maintenance to these industries will be significant, as the composite rebar will last almost indefinitely.

The mining industry requires composite rods for mining shafts or tunnel roof bolts. These rods are usually carried by hand and installed overhead in mining tunnel, so there is a benefit that the fibreglass rod is 1/4 the weight and twice the strength of steel rebar which are widely used currently. Fibreglass rod also does not damage the mining equipment. In construction industries, such as bridges, roads, seawall and building structures, reinforcements of the steel rebar have been widely used and the most of steel rebars have been corroded after a few years of service life. Typically, the structures with the steel rebars are often torn down after a period of time. Therefore, the use of the corrosion resistant composite rebars have been increased for construction industries in recent years.

Non-uniform profile or non linear threaded rods are also required in many industrial applications. For example, threaded FRP rods and associated nuts have been used as rock bolting system in mining industries (e.g., for tunnel roof bolts), as threaded reinforcing rebar structures in construction industries (e.g., in bridge construction), as well as seawall bolting system in marine structures.

The structures of the threaded composite rods from existing manufacturing technology consist of two styles:

(1) Pultruded rod with machined threads in outside surface, and

(2) Pultruded rod has a core of fiber ravings with plastic materials molded outside the core to form threads.

In style (1 ), the problem of machining composite rebar surface after it is fully cured is that the fibers in a depth of surface are cut into segments. The benefit of high tensile strength of the fibers are lost when they are cut into short lengths. The strength of the threads now rely on the shear strength of the cured resin which is much less than that of the fibers. Thus, the rebar could not be used under tension since the threads of the rebar will shear away from the core. The rebar uses a specially designed nut that compresses against the rebar to give it holding strength when a load is placed on the rebar. The nut of threaded onto the rebar has just enough resistance to take up any slack between the nut and the thread surface. Therefore the nut is used without pre-tension.

In style (2), the rebar has a core of fiberglass ravings and a plastics molded threads surface. This rebar is only capable of withstanding a small amount of longitudinal loads. This is because the threads formed by the molded plastics lack the fiberglass reinforcements for having the longitudinal strength. Other rebars, such as those shown in a brochure by Marshall Industries Composites Inc C-BAR 1996, are a combination of a fiber- reinforced polyester core and a urethane-modified vinyl ester outer skin, which do not include the thread features in rebar surface.

There is therefore a need in mining, construction and other industries for composite rod and nut fastening system that the rod and nut have a fully threaded feature without the disadvantages of the style (1) and (2) described in the paragraph above.

In view of the foregoing, it is an object of the present invention to provide a fully threaded glass-fiber reinforced composite rod, and associated mechanical fastening system.

It is an additional object of the present invention to provide a composite material suitable for the compression-pull into the fully threaded composite rod component.

It is also an object of the present invention to provide a method for pressing and squeezing the resin out of the impregnated fibers to the mold internal surfaces, and pushing the outer fibers which may include wrapped fibers and the axial direction oriented fibers toward the crest of the internal thread of the moulds.

According to a first aspect of the invention there is provided a method for forming a threaded rod comprising: providing a longitudinally continuous fibrous structure formed of a plurality of fibers; impregnating the fibrous structure with a settable resin; providing a die having a plurality of parts which can be opened to receive the fibrous structure and clamped together to form a hollow die interior defining a generally cylindrical shape with a helical thread therealong; engaging the parts onto a portion of the length of the impregnated fibrous structure while the resin remains in an un-set condition so as cause the portion of the fibrous structure to conform to the shape of the hollow interior and thus to mold on the fibrous structure a thread having a helical thread root having a minimum diameter at a core of the fibrous and a helical thread crest having a maximum diameter; and compressing the fibrous structure within the hollow interior so as to cause some of the fibers of the fibrous structure to be distorted such that a portion of the distorted fibers lies inwardly of the root and a portion extends into the thread toward the crest such that the thread is reinforced by fibers which extend from the thread into the core.

The thread may extend along the full length of the rod or thread portions may be separated each from the next by a short length where the rod is not threaded or smooth. Such smooth portions are provided between each molded section and the next to avoid misalignment of the threads formed by the molds which could cause damage to the molds. Molding techniques which avoid this alignment problem as described hereinafter can provide a method for generating a continuous thread.

If it is required that the rod be hollow, there is provided a mandrel inside the die to form a hollow interior of the rod or there is provided a tubing core inside the rod.

Preferably the fibrous structure includes a plurality of longitudinally continuous rovings and a mat surrounding the rovings, at least some of the distorted fibers being formed by fibers in the mat.

Preferably the fibrous structure includes a plurality of longitudinally continuous rovings and a plurality of helically wrapped fibers surrounding the rovings, at least some of the distorted fibers being formed by helically wrapped fibers.

Preferably the die parts act to press and squeeze the resin out of the impregnated fibers to the mold internal surfaces and to push the fibers toward the crest of the internal thread of the die parts.

Preferably the die parts comprise two half molds forming an autoclave in which the two half molds are heated.

Preferably the impregnated fibers are pulled into the space between the die parts, the die parts are clamped to autoclave the resin-impregnated fiber reinforcing material for forming a length of the threaded rod and the die parts are released to get threaded composite rod.

Preferably the die parts are moved longitudinally of the fibrous structure to form a further length of the threaded rod in a further cycle.

Preferably there is provided two pairs of die parts which are operated alternately and move longitudinally to form adjacent lengths of the threaded rod.

Preferably one pair of die parts move in a first plane and the other pair of die parts move in a plane at right angles to the first plane. Preferably there is provided two rows of die parts each of which moves in a continuous loop to form a tractor die station where the die parts meet to form adjacent lengths of the threaded rod in a continuous process.

Preferably the die parts of each loop slide along a heated platen.

Preferably clamping process is repeated along the fibrous structure such that the rod is threaded along its full length.

According to a second aspect of the invention there is provided an apparatus for forming a threaded rod comprising: a supply for providing a longitudinally continuous fibrous structure formed of a plurality of fibers; a resin system for impregnating the fibrous structure with a settable resin; a die having a plurality of parts which can be opened to receive the fibrous structure and clamped together to form a hollow die interior defining a generally cylindrical shape with a helical thread therealong; and a pulling system for pulling the fibrous structure into the die parts for compression therein.

Preferably the die parts comprise two half molds forming an autoclave in which the two half molds are heated and wherein the die parts are moved longitudinally of the fibrous structure to form a further length of the threaded rod in a further cycle.

Preferably one pair of die parts move in a first plane and the other pair of die parts move in a plane at right angles to the first plane.

Preferably there is provided two rows of die parts each of which moves in a continuous loop to form a tractor die station where the die parts meet to form adjacent lengths of the threaded rod in a continuous process.

Preferably the die parts of each loop slide along a heated platen.

The present invention thus provides a fully threaded FRP rod for use with a mechanical fastening systems, a forming process of the threaded composite bars, and the apparatus for making such the threaded rods. The threaded rods can operate with a nut or coupling to be screwed onto the ends of the rod. The rods can be tensioned with the nut or jointed together with 45 , 90 , etc., elbow couplings to allow the rod to make turns or bends. The threaded rod can also be fastened together to make various patterns for reinforced concrete. The threaded rod can also be jointed together with FRP or plastic nut connectors to extend to any length of the rod in sites to avoid transportation problems. The threads on the rod are not only used for screwing on nuts and adapters, but they also provide an excellent anchoring system when the rod is glued or grouted into rock or concrete. The threads make it very difficult for the rod to be pulled out of the rock or concrete cement.

Embodiments of the invention will now be described in conjunction with the accompanying drawings in which:

Figure 1 is a schematic representation of the fully threaded composite rod- forming apparatus of the present invention.

Figure 2A is a schematic illustration of a method of two halves die autoclave to form the fully threaded composite rod indicated in Figure 1.

Figure 2B is a schematic representation of an apparatus of the reciprocated die autoclave for producing the fully threaded composite rod indicated in Figure 1.

Figure 2C is a schematic illustration of a method of the tractor die autoclave to form the fully threaded composite rod indicated in Figure 1.

Figure 2D is a scrap view of one element of the embodiment of Figure 2C.

Figures 3A and 3B are side elevational and end elevational views respectively of a rod formed by the method of the present invention.

Figures 4A and 4B are side elevational and end elevational views respectively of a tube formed by the method of the present invention.

Figure 5A is a cross sectional views of the fiber structure of the rod of figure 3A showing the provision of a fixed stationary mandrel within the die.

Figure 5B is a cross sectional views of a portion of the fiber structure of the rod of figure 5A showing the distortion of fibers from the mat within the die.

Figure 5C is a cross sectional views of a portion of the fiber structure of the rod of figure 5A showing the distortion of helically wound fibers within the die.

The present invention will now be described more particularly hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. The invention can, however, be embodied in many different forms and should not be limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in this art.

Referring now to the drawings, the apparatus for forming the threaded rod of the present invention is illustrated in Figure 1. The apparatus comprises a reinforcing material supply station 10, a creel guide 20, a resin bath 30, a circumferential winder 40, a two halves die autoclave station 50 (Figure 2A), or a reciprocating die autoclave station 60 (Figure 2B), or a tractor die autoclave station 70 (Figure 2C), a tension puller 80 and a cutting station 90. The reinforcing material supply 10 comprises a plurality of reinforcing material 11 on a plurality of spools 12 mounted on a storage rack, such as the bookshelf style creel 14 shown in Figure 1. The reinforcing material 11 comprises fibers selected from the group consisting of fibers of glass, carbon, metal, aromatic polyamides, polybenzimidazoles, aromatic polyimides, polyethylene, nylon, and blends and hybrids thereof. These fibers are supplied in the form of a roving, mat, veil, fabric or the like. Typically, the reinforcing material is glass fibers in the form of a roving. The creel 14 can include virtually any number of spools 12; creels including 100 or more spools are common. Preferably, the reinforcing material 16 is drawn from the spools 12 through a series of ceramic bushings (not shown) positioned at the front of the creel 14 to maintain alignment and reduce breakage of the reinforcing material 16.

The suitable reinforcing fibers 11 are carbon, glass, metal, high modulus organic fibers (e.g., aromatic polyamides, polybenzimidazoles, and aromatic polyimides), and other organic fibers (e.g., polyethylene, liquid crystal and nylon). Blends and hybrids of the various fibers can also be used. Higher tensile strengths can be accomplished with different kinds of fibers having a higher tensile strength. These can be treated to provide other properties such as corrosion resistance.

Turning to Figure 1, from the creel 14, the reinforcing material 16 is guided via a creel guide to the bath 30 (shown in Figure 1 ) of an unsaturated polyester resin or other thermosetting resin 31 such as vinyl ester resins, polyurethanes, epoxies, and phenolics. The organizer card 21 controls alignment to prevent twisting, knotting or any other damage to the reinforcing material 16. The reinforcing material 16 is directed to the bath 30, wherein the reinforcing material 16 is immersed in and thereby impregnated with a pool of resin 31. Other techniques for impregnating the reinforcing material with resin, such as direct injection, sleeve immersion, and the like, are also suitable for use with the present invention.

The resin material is preferably a thermosetting resin. The term "thermosetting" as used herein refers to resins which irreversibly solidify or "set" when completely cured. Suitable thermosetting resins include unsaturated polyester, phenolic resins, vinyl ester resins, polyurethanes, and the like, and mixtures and blends thereof. Additionally, the thermosetting resins useful in the present invention may be mixed or supplemented with other thermosetting or thermoplastic resins. Exemplary supplementary thermosetting resins include epoxies. Exemplary thermoplastic resins include polyvinylacetate, styrene-butadiene copolymers, polymethylmethacrylate, polystyrene, cellulose acetatebutyrate, saturated polyesters, urethane-extended saturated polyesters, methacrylate copolymers, polyethylene terephthalate (PET), and the like in a manner known to one skilled in the art.

Thickening or partial curing is achieved in a variety of ways. For example, the thermosetting resin may be thickened by the inclusion of a thickening agent. Suitable thickening agents are commonly known to those skilled in the art and include crystalline unsaturated polyester, polyurethanes, alkali earth metal oxides and hydroxides, and polyureas. The amount of thickening agent added to the thermosetting resin will vary depending upon the particular thermosetting resin employed. The resin material also may include an initiator system, which cooperates with the conditions of the hot compression molding to thicken the resin material by curing the resin material. The initiator system may be present in addition to any of the foregoing thickening agents, or as an alternative thereto. A catalyst such as organic peroxide initiator is employed to facilitate curing of the chemical thickening composition. Such catalysts are described in U.S. Patent No. 4,062,826, 4,073,828; and 4,232,133, the disclosures of which are incorporated by reference herein.

Turning again to Figure 1 , the reinforcing fibers 32, which are impregnated with the resin 31, can comprise of the order of 60 to 90 percent fibers by weight. Additionally the reinforcing fibers 32 may be circumferentially wound with additional reinforcing fibers or mats to provide additional strength thereto and to enhance the mechanical bonding of the core to the surface threads. After impregnation, the impregnated reinforcing material 32 can then travel through the circumferential winder 40 positioned prior to the two halves die station 50 of the hot compression molding process. The circumferential winder 40 mainly comprises a rotating plate and several rolls of fiber filament or mat rovings. The winder 40 wraps one or more fiber layers around a bunch core of the reinforcing material 32. The fibers layers are typically oriented in an inclined direction rather than in the longitudinal direction of core of the reinforcing material 32. Preferably, two fiber layers are added: one that is placed on the core so that its fibers are oriented at 20 ~ 60 degree angle to the core fibers, and another that is placed on the core so that its fibers are wrapped in reverse direction and oriented to be perpendicular to the first wrap and 20 ~ 60 degree relative to the core fibers. The wrap angles can be controlled by the number of rotational rolls of the reinforcing material rovings 41 added and the speed of the winding and pulling. The fiber layers, if used, add torsional strength to the core, particularly in non- longitudinal directions. In addition, because the fiber layers are added to the core as a fibrous surface, the fibers contained therein remain on the surface of the core 32 as it travels to the molding stations as shown in Figure 2A to Figure 2C, and the resin therein should be sufficiently viscous to be easily molded by the mold stations 50 to 70.

As shown in Figure 5A, 5B and 5C, the outermost fibers of the fibrous structure are distorted by the compression on the fibrous structure and resin as the resin is squeezed so that the outermost fibers extend from the core of the rod inside the root of the threads into the area under the crest of the threads. In the arrangement where mat is applied on the outside, the distorted fibers are mainly mat fibers so that they can include some transverse fibers not just longitudinal fibers as shown. In the arrangement where the helical fibers are applied, the distorted fibers will be mainly helical fibers. In both cases, the use of mat and/or helical fibers may assist in distorting the fibers since they tend to be under less tension than the longitudinal fibers themselves. However, the construction can be formed wholly using longitudinal continuous rovings where the roving fibers pass from the core into the threads and back to the core. This provides the best strength since the fibers in the threads are continuous and therefore must be broken before stripping of the thread occurs.

If a threaded FRP tubing 87 shown in Figure 4A or 5A is required to be produced rather than a solid threaded rod 86 shown in Figure 3A, the winding must use a stationary mandrel as shown in figure 5A or a tubing core which may be of metal or plastics as shown in figure 4A placed along the center of the longitudinal oriented fibers to make a hollow shape.

The wound and impregnated material 43 then proceeds to the two halves die autoclave station 50, or to the reciprocating die autoclave station 60, or to the tractor die autoclave station 70 for producing the fully threaded composite rod (Figure 3). The threads are formed at the outside of the materials and the materials are compressed and squeezed to expel excess resin out during the autoclave process. If the threaded tubing is required, a removable or tubing core mandrel must be placed along the center of the longitudinal oriented fibers to make a hollow shape.

The two halves die autoclave process is illustrated schematically in Figure 2A, the reciprocating die autoclave is illustrated schematically in Figure 2B and the tractor die autoclave process is illustrated schematically in Figure 2C. Each of the process is described separately hereinbelow. The two halves die station 50 (Figure 2A) mainly includes an upper mold 51 with few upper heating elements 52, a lower mold 53 with few lower heating elements 54, and two hydraulic cylinders for clamping the two molds. The upper mold 53 is operated by the hydraulic cylinder 55. Heat is applied to the upper and lower molds 51 and 53 to initiate the thermosetting reaction of the resin. A few heater cartridges that employ electrical resistance are positioned along the longitudinal at desired locations inside both the molds. Thermocouples are also placed inside the molds to control the level of heating applied. Multiple individually-controlled zones can be configured in this manner. After the wound and impregnated material 43 is pulled along the longitudinal direction and seated on the lower mold 53, the upper mold 51 presses the material 43 down to the lower mold 53. Since the upper and lower molds have an internal surface with the threaded features, the materials 43 takes a threaded shape corresponding to the internal profile of the molds. Also, as the material 43 is placed between the mold 51 and mold 53, the thermosetting resin reacts under the heat and pressure and partially cures. Under a certain amount of molding pressure, some resin is squeezed out of the impregnated fibers into the mold internal surface, and acts to push the outer fibers or mats, which may include the wrapped fibers or mats and the longitudinal oriented fibers towards the outer circumference of the internal thread of the molds (Figure 4). The lower mold 53 is fastened in a stationary frame.

After the material is cured and formed threaded surface, the upper mold 51 is released and the material is pulled a length of the mold 51 (or mold 53) and then the autoclave process starts another cycle. If a threaded FRP tubing 87 shown in Figure 4A is required to be produced rather than a solid threaded rod 86 shown in Figure 3A, the autoclave process uses a stationary mandrel placed along the center of the longitudinal oriented fibers to make a hollow shape of the product, and after curing, the mandrel is removed from the product, or the autoclave process can use a tubing core to make a hollow shape of the product to get a threaded tubing product.

The reciprocating die autoclave station 60 (Figure 2B) comprises a pair of vertical mold halve 62, and a pair of vertical mold support rails 61, and a pair of horizontal mold halves 64, and a pair of horizontal mold support rails.63, and several cylinders 65 for clamping the molds, and two pairs of gear 66 and rack 67 for reciprocating the molds. The operation principle of the reciprocating dies substantially as previously described. This process acts alike a pair of the two halves die which works in a same time with a matched sequence. For example, after the material 43 is pulled into the space between the pairs of the reciprocating dies, the pair of vertical mold halves 62 clamps and holds the materials to form the threaded profile, while it travels backwards driven by the gear-rack 66 and 67 along the vertical support rails 61. While the vertical mold halves capture the impregnated material and go backwards, the material is gradually cured and a fully threaded profile of a rod is formed as shown in Figure 2B. At the same time, the pair of the horizontal mold halves 64 opens and travels towards the front of the station along the horizontal support rails 63. As soon as the horizontal mold halves 64 arrive the front end of the horizontal support rails 63 and the vertical mold halves 62 reach the back end of the vertical support rails 61 , the horizontal mold halves start to clamp for forming another segment of threaded profile as shown in Figure 2B. After the threaded profile segment is formed by the vertical mold halves, the vertical mold halves release and then go to the front. At the same time, the clamped horizontal mold halves move backward along the horizontal support rails. After the clamped horizontal mold halves arrive the back end of the horizontal rails and another threaded segment is formed, and then the horizontal mold halves start to releasing, the vertical mold halves start clamping, in this way, the process is repeated. Therefore, the two pairs of mold halves reciprocate to produce a length of the threaded features along the production line.

If a threaded FRP tubing 87 shown in Figure 4A or 5A is required to be produced rather than a solid threaded rod 86 shown in Figure 3A, the autoclave process uses a stationary mandrel placed along the center of the longitudinal oriented fibers to make a hollow shape of the product, and after curing, the mandrel is removed from the product, or the autoclave process can use a tubing core to make a hollow shape of the product to get a threaded tubing product.

The above arrangements provide a rod which has the threaded sections equal in length to the molds and separated each from the next by a short smooth section.

The tractor die station 70 (Figure 2C) mainly includes a pair of endless series 72 of mold halves 76, and two sets of sprockets 71 , and a pair of heating platens 73 and several hydraulic rams 74. The several small die sections 76, one of which is shown in figure 2D, link together via an interlocking chain mechanism. There are two mating halves on these interlocking chained die sections opposing each other. Each half of the die section has a cavity with a threaded interval. The chained die sections are linked together and extend two to three feet in length and wrapped around a set of sprockets to form a continuous chain. The inside cavity of the die section faces an identical chain of die cavities directly across from them. The two opposing die chain cavities face each other and rotate around their respective sprockets. When the die cavities come in contact with the resin- impregnated fiber the die captures the resin-impregnated fiber and also pulls the fibers along the longitudinal direction from left to right, shown in Figure 2C.

The backside of the die cavities rides on a heating platen 73 that transfers heat to the chained die sections. This causes the resin-impregnated fiber material to cure and solidify while the material is being pulled by the two halves of the tractor die cavities. As the die cavities capture the material, the die cavities are squeezed together by a hydraulic clamping system 74. This causes the material to take on the impression of the threaded profile inside the die cavities. While the die sections travel backwards (or to the right shown in Figure 2C), the resin gradually cures and a complete fully threaded product is formed. Once the cured product escapes from the rear of the tractor die, a pulling mechanism (as described as a pulling station as follows) is to be required to maintain the straightness of the product.

This arrangement produces a threaded rod where the thread is continuous without smooth sections since each die section can be co-ordinated with the previous so that the thread continues through the die intersection. The die sections are arranged to allow the excess resin squeezed from the rod to escape between the die sections. The die sections can include areas, preferably between the die sections, which are cooled so as to maintain the escaping resin in a cooled condition separate from the heating zone so that the escaping resin does not set to require messy clean-up and can be re-used.

If a threaded FRP tubing 87 shown in Figure 4A is required to be produced rather than a solid threaded rod 86 shown in Figure 3A, the autoclave process uses a stationary mandrel placed along the center of the longitudinal oriented fibers to make a hollow shape of the product, and after curing, the mandrel is removed from the product, or the autoclave process can use a tubing core to make a hollow shape of the product to get a threaded tubing product.

Turning again in Figure 1 , the pulling force in the production line is provided by a pulling station 80, which mainly comprises few pairs of friction rollers 81 and 82. This kind of puller can be adjusted very easily. After the material 85 (Figure 1 ) exits the pulling station 80, the threaded products are produced. The threaded product can be sent to a cutting station 90 to cut. As a final step, a cut-off saw 91 operable coupled with a computer cuts the product 86 to a desired predetermined length. The programmable computer and a sensor or other control means monitors the lengths of rod 86 produced during the process. The individual rods 86 are then conveyed to an off-loading station for packing.

The foregoing discussion demonstrates that the apparatuses of the present invention can be used to produce threaded reinforced composite threaded rods or tubing using as desired methods. The manufacture of the threaded composite rod product enables the manufacture to choose whichever autoclave process is desired as the need arises without investing in multiple autoclave lines, thereby reducing the cost of production.

One important end use for the threaded rod is that of ground anchors where the rod is hollow and is used with a disposable drill bit at the lower end for drilling into the ground. Such arrangements are previously known and the details are known to one skilled in the art. Examples are manufactured by Ischerbeck under the trade mark "Titan" and by MAI International in Austria. In theses devices, the hollow interior is used to carry a slurry of a lubricating and transport fluid for carrying the particles from the drill bit along the outside of the rod to the surface. When drilled to the required depth, the fluid is caused so set by use of a cementitious binder to form a rigid concrete material inside and outside the rod to locate it in place. A holding nut is then threaded to the upper end to attach to an element to be located on the ground.

Claims

1. A method for forming a threaded rod comprising: providing a longitudinally continuous fibrous structure formed of a plurality of fibers; impregnating the fibrous structure with a settable resin; providing a die having a plurality of parts which can be opened to receive the fibrous structure and clamped together to form a hollow die interior defining a generally cylindrical shape with a helical thread therealong; engaging the parts onto a portion of the length of the impregnated fibrous structure while the resin remains in an un-set condition so as cause the portion of the fibrous structure to conform to the shape of the hollow interior and thus to mold on the fibrous structure a thread having a helical thread root having a minimum diameter at a core of the fibrous and a helical thread crest having a maximum diameter; and compressing the fibrous structure within the hollow interior so as to cause some of the fibers of the fibrous structure to be distorted such that a portion of the distorted fibers lies inwardly of the root and a portion extends into the thread toward the crest such that the thread is reinforced by fibers which extend from the thread into the core.

2. The method according to Claim 1 wherein there is provided a mandrel inside the die to form a hollow interior of the rod.

3. The method according to Claim 1 wherein there is provided a tubing core inside the rod.

4. The method according to Claim 1 , 2 or 3 wherein the fibrous structure includes a plurality of longitudinally continuous rovings and a mat surrounding the rovings, at least some of the distorted fibers being formed by fibers in the mat.

5. The method according to Claim 1 , 2 or 3 wherein the fibrous structure includes a plurality of longitudinally continuous rovings and a plurality of helically wrapped fibers surrounding the rovings, at least some of the distorted fibers being formed by helically wrapped fibers.

6. The method according to any preceding Claim wherein the die parts act to press and squeeze the resin out of the impregnated fibers to the mold internal surfaces and to push the fibers toward the crest of the internal thread of the die parts.

7. The method according to any preceding Claim wherein the die parts comprise two half molds forming an autoclave in which the two half molds are heated.

8. The method according to any preceding Claim wherein the impregnated fibers are pulled into the space between the die parts, the die parts are clamped to autoclave the resin-impregnated fiber reinforcing material for forming a length of the threaded rod and the die parts are released to get threaded composite rod.

9. The method according to Claim 8 wherein the die parts are moved longitudinally of the fibrous structure to form a further length of the threaded rod in a further cycle.

10. The method according to Claim 9 wherein there is provided two pairs of die parts which are operated alternately and move longitudinally to form adjacent lengths of the threaded rod.

11. The method according to Claim 10 wherein one pair of die parts move in a first plane and the other pair of die parts move in a plane at right angles to the first plane.

12. The method according to Claim 9 wherein there is provided two rows of die parts each of which moves in a continuous loop to form a tractor die station where the die parts meet to form adjacent lengths of the threaded rod in a continuous process.

13. The method according to Claim 12 wherein the die parts of each loop slide along a heated platen.

14. The method according to Claim 1 wherein clamping process is repeated along the fibrous structure such that the rod is threaded along its full length.

15. An apparatus for forming a threaded rod comprising: a supply for providing a longitudinally continuous fibrous structure formed of a plurality of fibers; a resin system for impregnating the fibrous structure with a settable resin; a die having a plurality of parts which can be opened to receive the fibrous structure and clamped together to form a hollow die interior defining a generally cylindrical shape with a helical thread therealong; and a pulling system for pulling the fibrous structure into the die parts for compression therein.

16. The apparatus according to Claim 15 wherein the die parts comprise two half molds forming an autoclave in which the two half molds are heated and wherein the die parts are moved longitudinally of the fibrous structure to form a further length of the threaded rod in a further cycle.

17. The apparatus according to Claim 16 wherein there is provided two pairs of die parts which are operated alternately and move longitudinally to form adjacent lengths of the threaded rod.

18. The apparatus according to Claim 17 wherein one pair of die parts move in a first plane and the other pair of die parts move in a plane at right angles to the first plane.

19. The apparatus according to Claim 18 wherein there is provided two rows of die parts each of which moves in a continuous loop to form a tractor die station where the die parts meet to form adjacent lengths of the threaded rod in a continuous process.

20. The apparatus according to Claim 19 wherein the die parts of each loop slide along a heated platen.