BACKGROUND OF THE INVENTION

The invention relates to winding cores for web materials such as paper. Web converters such as printers or the like continually strive to increase productivity of converting processes by increasing the total amount of web throughput per unit time. To this end, there has been a continual push toward wider webs and higher web speeds, which lead to longer winding cores that must rotate at higher rotational speeds and must support heavier rolls of the wider web material. For instance, rotogravure printer designers are currently developing 4.32 meter wide printing presses for high-speed printing. Paper supply rolls for such presses would weigh in excess of 7 tons. Applications such as this place extreme demands on the stability of current winding cores. A chief difficulty with conventional paperboard winding cores is that in the increased 4.32 meter length, the core generally is not stiff enough to avoid the core encountering its natural frequency when the unwinding roll reaches the end of the paper and the rotational speed of the core is at a maximum. This can lead to extreme vibration and catastrophic failure of the core. A potential solution to the problem is to increase core stiffness by increasing core diameter, but this would be undesirable if it meant that the cores would not be compatible with existing winding and unwinding machinery, as would be the case if the inside diameter of the core were increased. During a winding or unwinding operation, a core is typically mounted on a rotating expandable chuck that is inserted into each end of the core and expanded to grip the inside of the core so that the core does not slip relative to the chuck as torque is applied therebetween. Typically, the rotation of the core is achieved by means of a drive coupled to one or both of the chucks, and the core is rotated to achieve web speeds of, for example, 15 to 16 m/s. The rolls of material are often subjected to substantial circumferential acceleration and deceleration by the winding machines. This, in turn, subjects the engaged ends of the paperboard roll

to substantial torque forces. This often leads to some slippage of the chuck on the inside of the core. In an extreme situation, the slippage can lead to "chew-out" wherein the core is essentially destroyed by the chuck.

Thus, for extreme applications such as 4.32 meter wide gravure presses, there is a need for a core with a high stiffness and adequate resistance to chew-out, but it is desired to maintain standard core diameters for compatibility with existing winding and unwinding equipment.

BRIEF SUMMARY OF THE INVENTION

The invention addresses the above needs and achieves other advantages, by providing a winding core that has high stiffness by virtue of being formed predominantly of fiber-reinforced plastic (FRP) such as fiber glass material or the like. In particular, the winding core comprises a tubular shell of FRP, which is substantially stiffer than a paperboard tube of the same dimensions. However, expandable chucks cannot readily "dig into" and grip the FRP shell because of its hardness. Accordingly, the winding core also includes a pair of generally tubular end fittings bonded to the inner surface of the shell at the opposite ends, the end fittings comprising a material having a durometer hardness substantially lower than that of the shell and being positioned to be engaged by winding or unwinding chucks. Each end fitting has an axial length that is a relatively small fraction of the length of the shell. The winding core in one embodiment has a length sufficient to accommodate 4.32-meter wide paper as required in the new rotogravure printing presses.

In one embodiment of the invention, the end fittings comprise a coating of the material having a relatively low durometer hardness in comparison with the FRP shell. The material can comprise a rubbery or elastomeric material such a polyurethane or the like. The coating can be provided by depositing the material in fluid form onto the inner surface of the shell while the shell is rotated about its axis so that the material is slung radially outward by centrifugal force and therefore flows to form a coating of substantially uniform thickness about the circumference of the shell. Alternatively, the end fittings could be separately manufactured as tubular articles and inserted into the shell and bonded thereto in suitable fashion.

Winding cores in accordance with the invention can have nominal inside diameters ranging from about 76 mm (3 inches) to about 560 mm (22 inches), and wall thicknesses ranging from about 9 mm (0.34 inch) to about 18 mm (0.710 inch). The winding cores can have lengths exceeding 1 meter, up to a length sufficient to accommodate 4.32-meter wide paper used in the new rotogravure printing presses. The end fittings can each have an axial length of about 50 to 300 mm and a radial thickness of about 1 to 6 mm.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

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:

FIG. 1 is a perspective view of a winding core in accordance with one embodiment of the invention, with a chuck to be inserted into the core;

FIG. 2 is a cross-sectional view along line 2-2 in FIG. 1, after insertion of the chuck; and FIG. 3 is a cross-sectional view along line 3-3 in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION 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.

FIGS. 1-3 illustrate a tubular article or winding core 10 in accordance with one embodiment of the invention. The winding core 10 comprises a tubular shell 12 of fiber-reinforced plastic (FRP), which can be formed, for example, by a pultrusion process in which resin-impregnated fiber tows are pulled linearly through an annular die about a center cylindrical mandrel or support. The particular manner in which the shell 12 is formed is not critical to the invention, and other processes for forming the shell can be used if desired. The FRP material can comprise various fiber materials and resin matrix materials. The fibers can be,

for example, glass, carbon, aramid, polyester, and the like. The resin matrix can comprise any known suitable materials such as epoxy, polyester, nylon, vinyl ester, and the like.

The winding core also includes a pair of tubular end fittings 14 (only one shown) respectively mounted within the opposite ends of the shell 12 and bonded to the inner surface of the shell. Each end fitting has an axial length substantially less than the length of the shell 12, and need be only long enough to be engaged by the chucks 20 (only one shown) that are inserted into the ends of the core to grip and support the core during winding or unwinding of a roll of material wound about the core. Thus, in preferred embodiments of the invention, each end fitting has an axial length ranging from about 100 mm to about 300 mm, whereas the winding core's length generally exceeds 1 meter and may be up to about 4.3 meters.

The end fittings 14 are constructed to have a durometer hardness substantially lower than that of the FRP shell 12. In general, the FRP shell has a hardness too great to enable the chucks to grip the shell with enough frictional resistance to prevent slippage between the core and the chucks during certain operations when there is acceleration or deceleration of the core or chucks. The end fittings provide a surface that the chucks can more readily "dig into" and frictionally grip so that slippage is prevented. Toward this end, the end fittings are preferably constructed of a deformable material such as an elastomeric or rubbery type of material. Polyurethane is a particularly suitable material for the end fittings, but other materials can be used instead, including paperboard or other relatively soft material. The end fittings 14 can be formed and bonded to the shell 12 in various ways. An in situ method of forming the end fittings comprises rotating the shell 12 about its axis and applying the end fitting material in fluid form to the inner surface of the shell at its opposite ends. Centrifugal force slings the material outwardly and causes it to flow along the inner surface of the shell so that a coating of substantially uniform thickness is formed on the inner surface at the ends of the shell. The material then cures to form a coating at each end of the shell. Alternatively, the end fittings could be formed separately and then bonded to the

shell with a suitable adhesive. For instance, the end fittings could be formed as thin-walled paperboard tubes and then adhered to the inner surface of the shell.

The end fittings 14 provide their intended function in part by being deformed in the radial direction by the inserted chucks, which in some cases have leaves or lugs that are expandable radially outwardly to engage the inner surface of a core. Accordingly, the end fittings desirably should have a radial thickness sufficient to allow some degree of radial deformation. Advantageously, the radial thickness can be about 1 mm to 6 mm.

The durometer hardness of the end fittings 14 preferably should be less than about 20 Rockwell C.

Winding cores in accordance with the invention can be formed in a wide range of sizes. Winding cores tend to be somewhat standardized in terms of their inside diameters, but multiple standards exists. For example, commonly used cores have nominal inside diameters of about 76 mm (3 inches), 127 mm (5 inches), 152 mm (6 inches), 203 mm (8 inches), 254 mm (10 inches), 305 mm (12 inches), 406 mm (16 inches), and 559 mm (22 inches). There are several commonly used wall thicknesses for cores, including 8.6 mm (0.34 inch), 12.7 mm (0.5 inch), 13.7 mm (0.54 inch), 15 mm (0.59 inch), 15.2 mm (0.60 inch), and 18 mm (0.71 inch). Of course, while the invention can be applied to cores having these dimensions, the invention is not limited to any particular inside diameter and wall thickness dimensions.

In terms of length, the winding cores in accordance with the invention generally exceed 1 meter in length, and can be long enough to accommodate 4.32- meter wide paper used in the new rotogravure printing presses that have recently been developed. The high stiffness provided by the FRP shell 12 of the winding core leads to an increase in the natural frequency of the core relative to a conventional paperboard core, so that the core can be rotated at a higher speed before encountering its first natural frequency. By suitable design of the core (i.e., material selection, wall thickness, etc.), it can be assured that the natural frequency is higher than the highest rotational speed expected to be encountered by the core during use.

The invention enables the advantages of high-stiffness FRP material to be enjoyed in winding cores, while still retaining sufficient frictional gripping of the cores by winding/unwinding chucks.

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.