Patent Publication Number: US-2009218435-A1

Title: Web-Winding Core

Description:
This invention relates to a web-winding core. 
     In the conventional manufacture of a product such as paper in the form of a web, the web is mechanically wound onto a rotating core member. There exists a requirement for a stiff, lightweight core member. New machinery, which runs at higher speeds with heavier loadings and increased spans, is being introduced in the paper manufacturing industry and most of the present materials used for web-winding cores are unsuited to the increased duty cycle. 
     The web is wound on to the core at constant linear speed. The maximum rotational speed of the core is therefore seen at the start of the process when the core is bare. When layers of the web have been wound on, the rotational speed is reduced proportionally to the increased circumference of the roll, so that constant web velocity is maintained. 
     Premature failure of high-speed rotating shafts frequently arises—often under low-stress conditions—as a result of “whirling” of the shaft which induces buckling. All rotating shafts are subject to a critical whirling frequency that may be influenced by the design of the shaft. 
     WO-A-02/00539 discloses a reel shaft upon which a paper web can be rolled made of a composite material. A reel shaft effectively replaces a conventional core that has an inner support. Such cores have a relatively large outer diameter, and this is reflected in the diameter of the shaft disclosed in WO-A-02/00539, which is in the range 310-800 mm. At these large diameters, the shaft can easily be made with sufficient inherent stiffness that whirling can be avoided at the maximum operating speed. 
     It is also known to make cores out of aluminium, and an example is disclosed in FR-A-2848272. The stiffness of aluminium minimises the problem of whirling. However, aluminium is heavier than composite materials, and is prone to damage by impact or during cutting the remnants of fee web from the core using a knife. 
     An aim of this invention is to provide an improved web-winding core that can replace conventional cardboard cores with a durable, lightweight and re-usable alternative. 
     The invention provides a web-winding core comprising a tubular wall and longitudinal ribs extending radially inward from said wall, the core being formed from a fibre reinforced polymeric composite material. 
     The longitudinal ribs add substantial stiffness in the particular direction that adds to the whirling resistance of the core yet with minimal additional weight, so increasing its critical whirling speed. 
     Most preferably, the ribs extend the length of the core. Their cross-section may be substantially constant throughout the length of the core. A rectangular profile has been found to be particularly effective. This may be modified by providing a radiused region where the ribs extend from the wall to reduce the possible occurrence of stress risers. 
     Because reinforced composite material is anisotropic, unlike metals such as steel and aluminium which are isotropic (the properties of the metal are not directionally dependent), a more economic structure can be produced giving the required strengths in specific directions by design orientation of the reinforcing fibres. 
     Thus, tire fibres may be disposed so as to influence the stiffness properties of the core and increase its load bearing capability and whirling performance. In particular, the core may include reinforcing fibres disposed substantially parallel to the longitudinal axis of the core. At least some of these fibres may he disposed within the longitudinal ribs. 
     The core may include reinforcing fibres disposed substantially perpendicular to the longitudinal axis of the core. 
     Finally, the core may include reinforcing fibres disposed at at least one angle other than 90° to the longitudinal axis of the core. 
     An outer layer of the tubular wall may comprise more fibres than an inner layer thereof. 
     The fibres may comprise glass, carbon, aromatic polyamide such as Aramid, other polymeric, natural (of vegetable origin) and/or metallic fibres. The tubular wall may comprise layers including respective different types of fibre. 
     The core may include a radio frequency identification device (RFID). Compared to steel and aluminium cores, the composite core possesses a high degree of transparency to radio frequency (RF) radiation. Since tracking and data logging may be used to locate and monitor the cores whilst in service, the RF transparency of the composite improves the signal reception. 
     The RFID device may be attached to the inner wall of the core or at least one of the longitudinal ribs or to an insert. 
     The core may further include end adaptors fitted to facilitate engagement of a drive system. The insert may include a head portion and a tail portion, the tail portion being disposed coaxially with the core body. The tail portion typically has an outer diameter that is substantially the same as the inner diameter of the core body to form a smooth outer surface therewith. The tail portion may have a plurality of axial grooves. In such embodiments, typically the diameter of the tail portion and the size and position of the grooves are such that the tail portion is a close sliding fit within the core body, with each rib entering a corresponding groove. 
     The tail portion of the insert may advantageously include re-enforcing material to resist transmission of radial forces from a chuck to tire core body. 
     The invention is particularly advantageous when applied to the construction of cores having an outer diameter of less than 300 mm. It will find particular application in the construction of cores having an outer diameter in the range of 80 mm to 250 mm. The low inherent beam stiffness (absent the provisions of the present invention) and the high rotational speeds encountered by cores having diameters in this range make them particularly susceptible to whirling failure. 
    
    
     
       Particular embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  shows a transverse cross section through a core according to the invention; 
         FIG. 2  is a cut-away perspective view of the core of  FIG. 1 ; 
         FIG. 3  is a perspective view of an insert being a component of the embodiment of  FIG. 1 ; 
         FIG. 4  is an end view of the insert of  FIG. 3 ; and 
         FIG. 5  is cross-sectional view of the insert of  FIGS. 3 and 4  in place in the core of  FIGS. 1 and 2 . 
     
    
    
     The core shown in the drawings comprises a rigid hollow web-winding core formed from a fibre reinforced polymeric composite material. The fibres may comprise glass, carbon, aromatic polyamide such as Aramid, other polymeric, natural (of vegetable origin) and/or metallic fibres. 
     The core comprises a core body being formed from a cylindrical wall  1  and a plurality of longitudinal ribs  2  extending radially inwardly from the inside of fire wall  1 . In this example there are eight ribs  2 . 
     The core of the embodiment is formed by a known production method. The fibres can be individual fibres or fibres formed into a fabric either before or during the manufacture of the core. 
     In its specific application as a high speed rotating tubular core, the core of the invention performs better than a core of isotropic material. 
     The key criteria affecting whirling are: (i) rigidity of the core end fixing imparted by the core chucks, (ii) core length; (iii) elastic modulus in the axial direction; (iv) core mass; (v) moment of inertia; (vi) initial straightness; (vii) external load and (viii) rotational speed. 
     In any given situation the geometry of the installation, the loading conditions and the required rotational speeds are fixed, so that the only criteria under the control of the designer are numbers (iii) (iv) and (v) above. The mass of the core can be altered by changing the density of the material, and the moment of inertia can be altered by changing the cross-sectional geometry of tire core. 
     In the invention, the modulus of elasticity is enhanced by selective orientation of the reinforcing fibres. Hybrid fibre laminates including more than one type of fibre are beneficial to performance. The fibres are located and orientated in the most structurally effective areas of the core, on the outer skin and in the ribs  2 . This control cannot be exercised when an isotropic material is used for the core. 
     By careful selection of polymer matrix and reinforcing fibres, composite laminates of controlled density can be produced. The density range of the materials used in the invention is typically between 1300 and 1900 kgm −3 . By contrast, aluminium has a density of about 2700 kgm −3  and steel has a density of about 8800 kgm −3 . The reduced weight of the core according to the invention not only improves whirling performance, but also has a safety advantage in the manual handling of the core. 
     The moment of inertia of the core can be controlled and optimised to give maximum resistance to bending with the lowest weight of material. In particular, localised variations in the core wall thickness, (for example, the ribs) can be controlled. Additionally, localised variations in the density of tire wall  1  can be controlled by incorporating sandwich structures. 
     The core of the invention is much more resistant to impact damage, denting and permanent deformation than most non-reinforced plastics or aluminium cores. 
     At the end of the unwinding process, when the web material may be cut off the core with a knife. On an aluminium surface the edges of the resulting knife scores may became razor-sharp and cause danger to the operatives is handling these cores. The core of the invention has a better cut resistance and does not develop these sharp-edged score lines on its surface, thus improving operator safety in handling. 
     The core of composite material has no realisable value as scrap, unlike the aluminium core, so that pilferage of the tubes is no longer an issue. 
     In a particular embodiment, the core includes a radio frequency identification tag. Compared to steel and aluminium cores, the composite core possesses a high degree of transparency to radio frequency (RF) radiation. Since RF tracking and data logging may be used to locate and monitor the cores whilst in service, the RF transparency of the composite improves the signal transmission to at a RF transponder in the vicinity of the core, and eliminates the need for a special antenna which has to be used with metallic cores. 
     The core of the invention is optionally provided with engaging means at its ends for engaging driving machinery, which rotates the core about its axis at high speed. One such engagement means is an end adapter in the form of a pair of inserts  12 , one of these being shown in  FIG. 3 . 
     The inserts  12  are disposed at opposite ends of the core body  1 . The insert  12  is formed as a rotationally symmetrical body. In this embodiment, the body is formed of self-healing polymeric material. The insert has a head portion  16  and a tail portion  18  disposed coaxially with the core body  1 . The head portion  16  has a cylindrical outer surface that is substantially the same diameter as the outer surface of the core body  1 . The tail portion  18  has an outer diameter that is substantially the same as the inner diameter of the core body  1 , and has a plurality of axial grooves  20 . The diameter of the tail portion  18  and the size and position of the grooves  20  are such that the tail portion  18  is a close sliding fit within the core body  1 , with each rib  2  entering a corresponding groove  20 . Additional grooves are provided in some embodiments to accommodate other items, such as RFID antennas or other items. Thus, the core body  10  and insert  12  are constrained to rotate together, torque being passed between the ribs and grooves. A fastener or fasteners (not shown) may be passed radially through the core body  1  to enter the material of the insert  12  to secure the insert axially in place. Alternatively or additionally, the insert  12  may he secured by adhesive. 
     The head portion  16 , being of substantially the same diameter as the core body  1 , has an outer surface that forms a substantially continuous surface with the outer surface of the core body  1 , as can be seen in  FIG. 5 . This ensures compatibility of the core with existing apparatus that is intended for use with a conventional core of continuous diameter. Since the head portion  16  abuts an end surface of the core body  10 , it serves to protect that end surface. The end surface of the core as a whole is formed by an end surface  22  of the head portion  16 , which can be moulded or machined to a suitable shape and finish. 
     Optional re-enforcement may be provided within the insert to resist transmission of radial forces from a chuck to the core body  1 . One manner in which the required reinforcement in the insert can be achieved is through introduction of local reinforcement into an insert formed primarily from soft polymeric material that is suitable to be gripped by the chuck. For example, as shown in  FIGS. 4 and 5 , a sleeve  30  of high-modulus material is introduced into the insert during manufacture. The sleeve is coaxial with the bore of the insert  12 . The bore can be formed to have substantially the same diameter as that of a conventional core, and the jaws of the chuck can penetrate into the material to provide the required grip. Material radially inwardly of the sleeve can be deflected by the chuck as required to achieve adequate Motional coupling between the sleeve  12  and the chuck. However, the sleeve  30  substantially prevents deflection of material radially outwardly of the sleeve  30 , so that radial loads are substantially prevented from being transmitted to the core  10 . 
     The sleeve  30  can be formed in a variety of ways. For example, it may be a simple metal tube moulded into the insert  12 . This is a low-cost approach, but can, under conditions, cause weakness within the moulding of the insert  12 . This disadvantage can be mitigated by use of a perforated sleeve  30 , which allows the material of the insert  12  to flow through the perforations during moulding so promoting the integrity of the moulding as a whole. Likewise, this could be achieved by use of several coaxial, axially-spaced rings. Alternatively, the reinforcement may be formed from many high modulus materials, such as reinforcement using inorganic, organic or metallic fibres or high-modulus polymers. The reinforcement could be either integrally inserted within the insert profile during manufacture or subsequently fitted externally to the insert  12 , for example, as a baud surrounding it. 
     The insert can be formed by one or more of machining and moulding, including co-moulding or two-shot moulding, as required. 
     All forms of the verb “to comprise” in this specification and the appended claims should be understood as forms of the verbs “to consist of” and/or “to include”. 
     Aramid is a registered trade mark of E.I. du Pont de Nemours and Company.