Patent Application
20060214049
The invention relates to tubular articles in general, and relates particularly to winding cores for materials such as paper, plastic film, foil, sheet metal, and the like.
A spirally wound tube usually is formed by winding one or more strips or plies of flexible material such as paperboard about a circular cylindrical mandrel that is stationary. In the case of a single-ply tube, the edges of the ply are overlapped and adhered together with a suitable adhesive; in the case of a multi-ply tube, the edges of adjacent plies are axially staggered relative to one another and the plies are adhered together. A winding belt engages the tube formed on the mandrel and advances the tube along the mandrel in screw fashion.
Spirally wound tubes are used in a variety of applications, and particularly are used as winding cores. Winding cores made by the spiral winding process are constrained to be circular in cross-section because the core is advanced along the mandrel in screw fashion, which would be impossible if the mandrel were non-circular.
Advantages could be attained if a winding core could be made to have a non-circular cross-sectional shape at its outer surface. At the same time, the inner surface desirably is circular because winding and unwinding equipment in common use is designed for conventional circular cores. Therefore, the sought-after winding core with non-circular outer surface cannot be provided by forming the core about a non-circular mandrel, as is sometimes done in the manufacture of non-round container bodies using a convolute wrapping process, because then the inner surface of the core would be non-circular. Additionally, convolute wrapping is much slower than spiral winding.
Tubular articles can be extruded from plastic materials in many different cross-sectional shapes. In the case of a winding core, which generally has a relatively thick wall (e.g., 0.3 to 0.7 inch or more) and can range from 3 to 22 inches in inside diameter, a considerable amount of plastic material would be necessary to make an all-plastic core. For the types of high-strength plastics that would be needed for a winding core, which are relatively expensive, the all-plastic construction would not be able to effectively compete with paperboard cores on a cost basis.
The invention addresses the above needs and achieves other advantages by providing a tubular article that is formed of a spirally wound tube of paperboard. The paperboard tube has a circular cross-section at both its inner and outer surfaces. A shell of resin is pultruded onto the outer surface of the tube. Various resins can be used, including polyesters, vinyl esters, thermosetting epoxy resins, and others. The shell can optionally include reinforcing fibers, which can be short fibers or substantially continuous fibers oriented in various orientations relative to the paperboard tube. The reinforcing fibers can be in the form of rovings or fiber mats or woven fabrics. The shell's inner surface conforms to the circular outer surface of the tube and is intimately bonded thereto. The outer surface of the shell is defined by the pultrusion die to be non-circular in cross-section. Various non-circular shapes can be provided at the outer surface of the shell.
For instance, in one embodiment of the invention comprising a winding core, the outer surface of the shell defines at least one longitudinally extending groove. As an example, a single groove can extend the length of the core for receiving the end of a web material to be wound about the core. As a result, the end of the web material does not form a bump that normally would propagate out to other layers of the wound material and possibly leave undesirable marks in the material.
In another embodiment, the outer surface of the shell defines a plurality of longitudinally extending grooves that are circumferentially spaced apart. The grooves, for example, could provide a surface for anchoring devices, could contain chemicals for performance enhancement, or could be useful in transporting moisture away from the wound product.
A further embodiment of the invention comprises a tubular article wherein the outer surface of the shell is polygonal in cross-section, or generally oval in cross-section. These types of shapes can provide enhanced strength to the tubular article.
In some embodiments of the invention, the resin shell has a smaller radial thickness, on an average basis about the circumference of the tubular article, than that of the paperboard tube. Preferably, the shell at its minimum thickness location(s) is only thick enough to cover the paperboard tube surface and maintain continuity of the resin material about the circumference.
In other embodiments, the average thickness of the shell can be substantially equal to or greater than that of the paperboard tube.
Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
The present inventions now will be described more fully hereinafter with reference to the accompanying drawings, in which some but not all embodiments of the invention are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.
An apparatus and a process for making tubular articles in accordance with the invention are illustrated in
The pultrusion device 20 is depicted in schematic fashion, but generally includes an infeed hopper or inlet 22 that receives plasticized polymer matrix material and feeds the material into an annular chamber 24 that surrounds the paperboard tube 10 as the tube is advanced axially through the chamber. A cylindrical center plug or mandrel 25 optionally can be included as a guide for the tube, the mandrel 25 having an outer diameter slightly smaller than the inside diameter of the tube 10. A die 26 surrounds the tube 10 and receives the plasticized matrix material along with the tube. The die is shaped to impart a non-circular profile to the shell 30 of matrix material that covers and is bonded to the outer surface of the tube 10. The pultrusion apparatus also includes a cooling chamber or the like (not shown) for cooling and curing the resin shell. The resulting non-circular tube 12 exits the pultrusion apparatus with the aid of rollers (not shown) or the like, which frictionally engage the tube 12 and pull the tube linearly in the direction of the tube's longitudinal axis. A cutting device (not shown) cuts the tube into desired lengths.
Various matrix materials or resins can be used for the shell 30, including but not limited to polyesters, vinyl esters, or thermosetting epoxy resins. These resins could be further modified by the use of pigments, UV stabilizers, and other chemicals to enhance the resin's characteristics for a particular application, such as resistance to chemical attack.
It will be appreciated that the radially inner surface 32 of the resin shell 30 is circular in cross-section, since it conforms to the circular outer surface of the paperboard tube 10. However, the outer surface 34 of the shell is non-circular in cross-section. Various non-circular cross-sectional shapes can be provided by suitably configuring the die 26 of the pultrusion apparatus. In
A further advantage of a polygonal tube over an equivalent circular tube (i.e., a tube whose wall has the same total volume) is that a plurality of the polygonal tubes can be packed in a denser array than can the circular tubes.
As noted, other cross-sectional shapes can be provided to achieve other objectives. For example, the tube 12′ of
In other cases, it may be desirable to have a plurality of grooves in the outer surface of a winding core.
Another aspect of the invention, as depicted in
Yet another embodiment of a pultruded tube in accordance with the invention is shown in
As already noted, the resin shell of a tube in accordance with the invention can be reinforced with fibers. Various fibers can be used, including glass, aramid (e.g., KEVLAR®), carbon, natural fibers, and others. The fibers can be incorporated in various ways and in various forms. In some cases, short chopped fibers can be included in the resin matrix material. In other cases, much longer fibers can be incorporated into the resin shell.
To incorporate reinforcing fibers in the shell, the apparatus includes one or more creels 306 of fiber material in continuous form. The creels can hold fiber roving, fiber mat, woven fabric, or the like. The fiber material 308 is drawn from the creels and pulled, along with the paperboard tube 10, through the chamber 300. The fiber material is impregnated or coated with the fluid resin material as it passes through the chamber. The fiber material then is pulled through the pultrusion die, which shapes the fiber-reinforced resin shell. After the shell is cooled and at least partially cured, the resulting tube 312 exits the chamber, being advanced by friction rollers 314 or the like. A cutting device (not shown) cuts the tube into desired lengths.
The fiber material 308 in
Tubular articles in accordance with the invention can be put to various uses, including use as winding cores, use as construction forms (e.g., forms for poured concrete), and use as structural members. The paperboard tube portion of the article can have a wall thickness ranging from about 0.075 inch to about 1.5 inches. In the case of winding cores, the inside diameter of the paperboard tube can range from about 1 inch to about 22 inches.
The outer shell can have a radial thickness ranging from as little as about 0.005 inch at the minimum thickness locations, up to as much as approximately 0.5 inch at the maximum thickness locations. In many applications, it will be advantageous for the circumferentially-averaged thickness of the shell to be less than the wall thickness of the paperboard tube, such that the paperboard tube comprises the majority of the total volume of the tubular article. For instance, the paperboard tube may constitute the primary structural member of the tubular article, and the outer shell may be provided mainly for the purpose of imparting a non-circular shape to the article. In other cases, the shell may constitute the majority of the total volume of the tubular article and may be the primary structural member, while the paperboard tube may function mainly as the substrate onto which the shell is pultruded; the paperboard tube may also be useful in providing a relatively soft, deformable surface at the inside of the tubular article (e.g., so that a winding chuck can readily grip the inside of the article, in the case of a winding core).
Other effects can be achieved in accordance with the invention. For example, by suitable selection of the resin composition, various surface textures and aesthetic effects can be created on the outer surface of the tubular articles of the invention.
Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
