Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2000-07-20
2003-08-19
Dixon, Merrick (Department: 1774)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S304400, C428S613000, C428S034100, C428S034900, C428S035700, C428S299700
Reexamination Certificate
active
06607798
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a fiber-reinforced composite hollow structure, and a method and an apparatus for manufacturing the same. Particularly, this invention relates to a fiber-reinforced composite hollow structure which can be suitably used as a structural member with reduced weight, increased strength, and enhanced dimensional accuracy, and especially, to a fiber-reinforced composite hollow structure which is a composite hollow structure used preferably as a scaffold board for temporary construction works, and also to a method and an apparatus for quickly manufacturing the same with a high efficiency.
BACKGROUND ART
(1) Supports, called battens, are used for installation of concrete forms in construction works or civil engineering works. In general, battens are made from steel or aluminum; however, they are heavy, and susceptible to rusting and adhesion of concrete. Because of these problems, some of battens are formed of FRP-made pipes with reduced weight, increased strength, and enhanced corrosion resistance.
Also there is a tendency to use FRP hollow members molded by pultrusion as structural members for various structures such as columns, posts, fences and scaffold boards. In such a FRP hollow member, one side or diameter in cross-section is increased over 60 mm or more. When pultruding of a FRP hollow member having such a large cross-section is implemented, if the pultruding is performed using a curing die, there may occur problems such as: the die is enlarged in size and complicated in structure; a large pultruder must be employed because of the significantly increased pultruding resistance; and the die cost becomes higher because of the need of increasing the die strength. Also, there is a problem such that the pultruding rate is as slow as 1 m/min or less.
As a FRP pipe, there is known a composite pipe, (for example, trade name “Compose”, produced by UBE-NITTO KASEI Co., LTD.) which has a three-layer integrated structure including an inner tubular layer (hereinafter, referred to as “center core”) made from thermoplastic resin, an intermediate layer made from FRP, and an outer cover layer made from thermoplastic resin. Such a composite pipe having a three-layer structure does not use any curing die and is subjected to curing with its shape kept by the center core and outer cover layer, and consequently, it has an advantage since the curing/molding rate becomes fast, and it is economical because of the significantly reduced costs of parts such as for the die. Of these composite pipes, a square-type pipe has a rectangular-like sectional shape with one side being relatively large as 50 to 60 mm; therefore, to keep the compressive strength and bending strength, the respective wall thickness of the intermediate layer and the center core is set to have large value. This not only disregards the significance of the reduction in weight, but also exhibits points to be improved in terms of resource saving and cost efficiency, with an additional inconvenience that the dimensional accuracy of the hollow portion is insufficient.
Another problem is that if the curing temperature is higher than the thermal deformation temperature of a thermoplastic resin which forms the center core, the center core is liable to be softened and deformed, leading to deformation of the cross-section of the final product.
For a composite pipe with the dimension of one side increased over 60 mm, the wall thickness of the center core and the intermediate layer is required to be increased. In this case, since there occurs a problem that the cross-section is liable to be deformed, the thickness of the center core is required to be further increased for suppressing this problem. This is because when the thickness of the intermediate layer is increased, heat generation caused by curing of FRP becomes larger, with a result that the strength of the center core is reduced and the center core is liable to be deformed. Also the contraction caused by curing becomes larger, with a result that the side portion is liable to be deformed in a convex or concave shape. That is to say, the increased thickness of the intermediate layer results in larger heat generation due to curing of FRP causing temperature rise, whereby the center core is reduced in strength and is liable to be deformed.
In addition to the above heat generation and contraction caused by curing, the following may be taken as other deformation factors. That is, when an uncured intermediate layer composed of reinforcing long fiber impregnated with a liquid-state thermosetting resin goes out of a shaping nozzle, corners of the intermediate layer are less deformed but the sides thereof are expanded in a convex-shape outward because of a repulsive force of the sides of the center core having already been cooled and solidified (the sides of the center core are deformed by the passing-resistance and pressure for squeezing the thermosetting resin upon passage thereof through the shaping nozzle, and the repulsing force is generated because of the release of the applied pressure). The larger the length of one side of a composite pipe, the stronger this tendency becomes. For a composite pipe with the length of one side in a range of about 60 mm or less, such deformation can be eliminated by preparing a shaping nozzle in which the inner surface is curved to form a concave-shape so as to compensate for the deformation.
For a composite pipe with the length of one side being much larger, since the above deformation becomes larger, it becomes difficult to compensate for the deformation. A composite pipe having a circular sectional shape is less susceptible to deformation resulting from the above reasons; however, in such a circular composite pipe with a diameter of a hollow portion being larger, the wall thickness of the intermediate layer is required to be increased over 10 mm to maintain the strength of the pipe, resulting in increased weight. For a composite pipe having a rectangular sectional shape, deformation of the longer-side becomes particularly larger. To be more specific, the larger the ratio of long-side (width)/short-side (height), particularly, this ratio being over 1.5/1, the larger the deformation becomes. Then, it is difficult to compensate for such large deformation by curving the shaping nozzle. In general, it is desired to use, as a scaffold board for construction/civil engineering works, a FRP hollow material having a thickness of about 20 to 60 mm and a width of about 200 to 300 mm in terms of light-weight, high strength, high durability, and high electric insulation. However, since the width thereof is over 60 mm, the above-described deformation becomes larger, to thereby reduce the strength of the material and to deteriorate stability in laminating these materials to each other upon storage and transportation.
When the ratio of long-side/short-side is more than 1.5/1, the compressive strength thereof is also reduced. This is because even slight deformation in the width direction tends to cause longitudinal cracks in a FRP intermediate layer because of stress concentration, and to cause concentrated overload to be particularly applied at a central portion. Such an inconvenience can be improved by also arranging reinforcing long-fibers in the width direction using a glass cloth, glass mat or the like. However, in this case, the rigidity in the longitudinal direction becomes low, and the manufacturing cost become high because of the increased number of manufacturing steps and the increased unit-weight. A composite pipe may be considered having a ladder-like sectional shape in which a plurality of FRP legs for connecting upper and lower FRP planes are arranged in the longitudinal direction in addition to outer peripheral FRP portions arranged on the upper, lower, right and left sides. In this composite pipe, however, if it is manufactured using a curing die, the die structure becomes more complicated and the pultruding resistance becomes significantly larger. In case the composite pipe is formed to have a large square cross-se
Hoshino Takayuki
Kondo Naoyuki
Matsuno Shigehiro
Nomura Hidenori
Watanabe Toru
Arter & Hadden LLP
Dixon Merrick
LandOfFree
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