Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2001-12-06
2004-10-05
Aftergut, Jeff H. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S180000, C156S242000, C156S245000, C156S433000, C156S441000
Reexamination Certificate
active
06800164
ABSTRACT:
The present invention relates a method for manufacture of fiber reinforced 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”.
BACKGROUND OF THE INVENTION
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 ¼ 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. Pat. No. 3,793,108 to Goldsworthy; U.S. Pat. No. 4,394,338 to Fuwa; U.S. Pat. No. 4,445,957 to Harvey; and U.S. Pat. No. 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 ¼ 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 rovings 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 rovings 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.
SUMMARY OF THE INVENTION
In view of the foregoing, it is one object of the present invention to provide a fully threaded glass-fiber reinforced composite rod, and associated mechanical fastening system.
It is also an object of the present invention to provide a method for manufacturing a molded rod by pressing and squeezing the resin out of the impregnated fibers to the mold internal surfaces.
According to 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;
the fibrous structure including longitudinally extending continuous fibers;
impregnating the fibrous structure with a settable resin;
collating the impregnated fibrous structure including the longitudinally extending continuous fibers into an elongate continuous rod in which the resin throughout the rod is an un-set condition;
providing a generally cylindrical die having a plurality of die parts for surrounding a portion of the rod and for extending along a part of the length of the rod, which die parts can be opened in a direction transverse to the length of the rod to receive the rod and clamped together to form a hollow die interior defining a generally cylindrical shape with a continuous helical thread therealong;
in a compression step, closing the die parts into a closed position onto the portion of the length of the impregnated fibrous structure while the resin remains in the un-set c
Aftergut Jeff H.
Battison Adrian D.
Dupuis Ryan W.
Williams Michael R.
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