Patent Grant
6851643
The invention relates to tubes made by spirally winding a plurality of paperboard plies about a forming mandrel and adhering the plies together.
Spirally wound tubes are used in a variety of applications in which radially inward compressive forces are imposed on the outside diameter of the tubes. For example, continuous materials such as paper, plastic film, metal sheet, and textiles are commonly wound about winding cores formed of spirally wound paperboard tubes. The winding tension required for winding a stable roll of such materials results in substantial compressive forces being exerted by the wound material on the tube in the radially inward direction. Such forces are in a direction to tend to force the inner diameter of the tube to shrink in size. This phenomenon has been referred to as “ID comedown.”
The degree to which a given paperboard tube resists such inner diameter reduction under a given load is referred to herein as the ID stiffness of the tube. The ID stiffness may be expressed as the amount of radially inward uniform compressive pressure on the tube OD that the tube can withstand for a given amount of inner diameter reduction; thus, for instance, the ID stiffness may have units of psi per inch of inner diameter reduction.
In web winding applications, it is desirable to have a high ID stiffness so that the tube can readily be removed from a winding apparatus after a roll of web material is wound onto the tube. A winding apparatus typically includes some type of chuck or mandrel that is inserted into the tube and is radially expanded to grip the core from the inside. If the tube inner diameter shrinks too much as a result of the forces imposed by the wound material, it can be difficult or impossible to remove the tube from the winding apparatus without destroying the tube.
The assignee of the present application has previously discovered that the tendency of a winding core to experience ID comedown can be reduced by forming the core wall to have a radially central region whose compliance in the radial direction is increased relative to that of the core wall regions lying radially inward and radially outward of the central region. See, for example, U.S. Pat. No. 5,505,395, incorporated herein by reference. In the '395 patent, this increased compliance was achieved by using paperboard plies of lower density and strength in the central region of the wall relative to the density and strength of the plies lying radially inward and outward of the central region.
While the approach represented by the '395 patent is effective in enhancing the ID stiffness of tubes, it would be desirable to be able to achieve even greater gains in ID stiffness, and to do so in a cost-effective manner.
The present invention addresses the above needs and achieves other advantages, by intentionally introducing wide ply gaps into one or more plies in a radially intermediate zone of the tube wall between the innermost and outermost plies of the tube. Each ply having wide ply gaps is narrower than the width that would ordinarily be employed at a given spiral winding angle to achieve a butt joint between adjacent edges of consecutive turns of the ply, and the ply is wound at that given spiral winding angle in such a manner that gaps are defined between the adjacent edges of the consecutive turns of the ply. The wide ply gaps have the effect of increasing the compliance of the intermediate zone of the tube wall in the radial direction. Such increased radial compliance has been found to improve the ID stiffness of the tube relative to a tube constructed of the same materials but having no ply gaps in the intermediate zone. The invention thus gives the tube designer another parameter that can be manipulated to achieve the desired ID stiffness for a particular application. The invention runs completely contrary to the ordinary convention used in winding tubes, wherein the plies all have substantially the same width or become wider by small increments from the inside diameter to the outside diameter of the tube to attempt to achieve a butt joint in each ply.
The intermediate zone of the tube wall can include more than one ply having wide ply gaps. The plies having gaps can be contiguous with one another; alternatively, plies having gaps and plies having no gaps can be alternated in the radial direction. Where there are a plurality of plies having gaps, the gaps of the various plies preferably are axially staggered relative to one another.
The gaps between adjacent edges of consecutive turns of a ply preferably have a width from about 6.5 percent to about 50 percent of the width of a normal “full-width” ply (i.e., the width that would produce a butt joint when the full-width ply is wound at the same spiral wind angle as the actual ply), and more preferably about 10 to 40 percent of the full ply width. Thus, for example, for a full-width ply that is 4 inches wide, the gaps preferably are from about 0.26 inch to about 2.0 inches wide, and more preferably about 0.4 to 1.6 inches wide.
If desired, each ply having gaps can be made of a material have greater compliance than that of other plies of the tube not having gaps. In this way, the effective compliance of the ply in the radial direction of the tube can be increased still further. For instance, the plies in the radially inwardly located and radially outwardly located zones of the tube wall can be selected to have a relatively high modulus while plies in the radially intermediate zone can be selected to have a relatively lower modulus, and one or more of the intermediate plies can have ply gaps.
In preferred embodiments of the invention, all of the plies of the tube are wound at substantially the same spiral wind angle α. Thus, based on the geometry of spiral winding, to achieve a perfect butt joint in a ply wound at the spiral wind angle α (measured from the axis of the tube), the width of the ply Wi must be equal to
Wi=πDi cos α,
where Di is the diameter at which the ply is wound. In accordance with the invention, however, in the intermediate zone of the tube wall (i.e., somewhere between a radially outermost and a radially innermost ply of the tube) there is at least one ply whose width is given by
W=ki·πDi cos α,
where ki is a scalar having a value from about 0.5 to about 0.935, and more preferably from about 0.6 to 0.9. Thus, gaps exist between adjacent edges of consecutive turns of the intermediate ply, the intermediate ply having an increased compliance in the radial direction of the tube by virtue of the gaps. Where there are two or more plies having gaps, those plies can have different scalars ki and hence different gap widths, or the scalars and gap widths can be the same.
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.
In contrast, for the intermediate ply 14, a relatively wide gap 18 is intentionally created between the adjacent edges of consecutive turns of the ply. The gap 18 extends helically along the tube at the spiral wind angle α at which the ply 14 is wound. The ply gap 18 is created in preferred embodiments of the invention by winding the ply 14 at the same spiral wind angle α at which the other plies 12, 16 are wound, but selecting the width of the ply 14 to be narrower than that of the plies 12, 16.
More particularly, it is known from geometrical considerations applicable to spiral winding that to achieve a perfect butt joint, the width of an individual ply, Wi, is related to the spiral wind angle α and the diameter Di at which the ply is wound by the equation
Wi=πDi cos α.
Thus, based on the known diameters at which the inner ply 12 and outer ply 16 are to be wound, and the known spiral wind angle α, the ply widths of the inner and outer plies can be determined that will yield perfect butt joints under idealized winding conditions. In practice, plies may be available only in certain selected widths, and hence the spiral wind angle may have to be adjusted somewhat to satisfy the above equation with the available ply widths, and/or an available ply whose width approximates the theoretically optimum width according to the above equation can be used and a small gap or small overlap can be tolerated between the edges of the ply. Such small gaps that result not from the tube designer's intent but rather from the limitations and constraints on ply material availability and/or from inaccuracies in controlling the ply width and/or winding angle are referred to herein as “inadvertent” ply gaps. Such inadvertent gaps are usually relatively small (e.g., less than 0.25 inch) under good quality control conditions. Thus, the inner and outer plies 12 and 16 have either no gaps or at most relatively small inadvertent gaps between their ply edges.
The intermediate ply 14 is intentionally provided with gaps by selecting the width of the ply to be less than the width that would ordinarily be used to produce a butt joint as dictated by the above equation. Expressed in equation form, the width of the ply having intentional ply gaps is given by
W=kiπDi cos α,
where ki is a scalar ranging in value from about 0.5 to about 0.935, and more preferably from about 0.6 to about 0.9. In other words, the ply width is from 50 to 93.5 percent (more preferably from 60 to 90 percent) of the width that would ordinarily be used to achieve a perfect butt joint (i.e., zero gap). As a result, the gap produced between the edges of the ply is about 6.5 to 50 percent of the normal width of the ply, and more preferably about 10 to 40 percent of the normal ply width.
As shown, the intermediate ply 14 is narrower than the inner and outer plies. Consequently, a gap 18 is produced between the adjacent edges of consecutive turns of the ply 14, as best seen in FIG. 1A.
To maintain the narrower ply 14 in the proper axial position as it is wound onto the mandrel so that the gap 18 is generally uniform along the tube, the apparatus preferably includes a ply positioning arrangement. The ply positioning arrangement can comprise an edge stop 26 or the like along which an edge of the ply is guided. The edge stop 26 can be adjusted in axial position to properly position the ply so that it is wound in such a manner that the desired gap is produced between the ply edges. Instead of an edge stop, other ply positioning mechanisms can be used. It is also possible to adhere the narrower ply 14 to one of the wide (i.e., normal-width) plies of the tube prior to winding to form a two-ply laminate structure, and to then wind the two-ply laminate onto the mandrel in essentially the same manner that the other wide plies are wound.
The invention is applicable to tubes having various numbers of plies and various types of plies. For instance,
The invention is applicable to multi-grade paperboard tubes having plies of various grades of paperboard within the same tube wall. For instance, since one objective of introducing wide ply gaps into the intermediate zone of the tube wall is to increase the compressibility or compliance of the zone in the radial direction, it may be advantageous to form the intermediate zone at least in part from paperboard having a greater compliance than that used in the radially inwardly and radially outwardly located zones of the tube wall. As an example, in the tube 30 of
Four different configurations of paperboard tubes were constructed and tested to determine their ID stiffness. All tubes had 14 or 15 plies making up a wall thickness of 0.300 inch in each case. The tubes had an inner diameter of 3.701 inches (94 mm) and an outer diameter of 4.301 inches (109 mm), and all plies were wound at a spiral wind angle of 70°. A first configuration had 15 plies of a relatively high-density paperboard (referred to herein as Board A) of nominally 4 inch width and caliper of 0.020 inch, with no gaps in any of the plies. A second configuration had 5 inner plies and 4 outer plies of the same high-density Board A of nominally 4 inch width, and 5 intermediate plies of approximately 4-inch wide low-density paperboard (referred to herein as Board B) of 0.024 inch caliper; again, none of the plies had gaps. A third configuration was similar to the second, but the 5 intermediate plies of Board B were approximately 3 inches wide, thus producing approximately 1-inch wide gaps in these plies. A fourth configuration was similar to the second and third, but the 5 intermediate plies of Board B were approximately 2.5 inches wide, thus producing approximately 1.5-inch wide gaps in these plies. A plurality of tubes of each configuration were tested for ID stiffness and the results were averaged for each configuration. The results are shown in the following table:
The results show that increasing the compliance of the intermediate zone of the tube wall by simply using a more-compliant paperboard (Board B) produced a modest gain in ID stiffness of about 16 percent compared to an all-Board A tube; however, introducing 1-inch gaps in the Board B plies resulted in a 77 percent gain in ID stiffness compared to the all-Board A tube, and the 1.5-inch gaps more than doubled the all-Board A ID stiffness. Comparing the A/B/A tubes to one another, it can be seen that the tubes with 1-inch ply gaps had an ID stiffness about 52 percent greater than those with no ply gaps; the tubes with 1.5-inch gaps had an ID stiffness about 81 percent greater than those with no gaps. Thus, it is apparent that the ply gaps have a dramatic beneficial effect on ID stiffness.
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.
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| Number | Date | Country | |
|---|---|---|---|
| 20040144885 A1 | Jul 2004 | US |
