GB2481058A

GB2481058A - Three layered web-winding core

Info

Publication number: GB2481058A
Application number: GB1009779.8A
Authority: GB
Inventors: Steven John Morgan
Original assignee: COMPOSITE CORE TECHNOLOGIES Ltd
Current assignee: COMPOSITE CORE TECHNOLOGIES Ltd
Priority date: 2010-06-11
Filing date: 2010-06-11
Publication date: 2011-12-14
Also published as: GB201009779D0; EP2616375B1; EP2616375A2; WO2011154745A3; WO2011154745A2

Abstract

A web-winding core is formed as a hollow cylindrical shell or tube, the shell being a three-layered sandwich comprising internal and external skins 12, 14, between which is a filler 16 to which the inner and outer skins 12, 14 are bonded. The filler 16 may be a lightweight natural material such as balsa or cork, a cellular material or an artificial foamed polymer. The internal and external skins 12, 14 may be reinforced composite material such as reinforcing fibres within a matrix, which may be a polymer compound including a modified polymer resin with a urethane acrylate additive. The reinforcing fibres pre-impregnated with an uncured polymer and may be natural or artificial fibres such as aramid or hemp. A ring 40 of tough, resilient material such as metal or a urethane polymer may be formed at the ends of the core to protect it from damage, which ring 40 may be chamfered 44 to facilitate insertion of handling apparatus into the core. The ring 40 may have the same inner and outer diameters as the core.

Description

Web-winding core This invention relates to a web-winding core. It has particular, but not exclusive, application to a web-winding core for use with a lightweight material, such as tissue paper.

Traditionally, webs such as paper have been wound on cores made of dense cardboard from which they are unwound, often at high speed, for subsequent processing. Since cardboard cores are essentially good for just a few uses, they are considered to be wasteful, and their disposal can be costly for their users. For that reason, alternative cores formed from metal or from composite materials have been developed that are capable of use multiple times. Metal and composite cores that have previously been proposed have been particularly intended for use with heavy webs such as newsprint. Such webs are wound with considerable tension and therefore exert substantial radial compressive forces upon the core. Therefore, the core must be made strong enough to resist crushing. They must also be made to have high beam stiffness to prevent them whirling excessively while rotating at high speed.

Much lighter webs, such as tissue paper, have also been traditionally carried on cardboard cores, and there has also been a demand to replace these with cores that can be used many times. However, those cores described above that are intended for use with newsprint have far greater strength, and are therefore heavier and more costly, than is necessary for use with a lightweight web. They are also not well-suited to production of cores with the larger diameters (150 mm or more) typically used for tissue. Excess weight of these cores mean that a core may weigh more than an equivalent cardboard core, which can cause manual handling issues..

An aim of this invention is to provide a web-winding core that is better optimised for use with a lightweight web material such as tissue paper, and which is no heavier than a cardboard core that it will replace.

To this end, from a first aspect, the invention provides a web-winding core formed as a hollow cylindrical shell, the shell being a three-layered sandwich comprising inner and outer skins, between which is a filler to which the inner and outer skins are bonded.

By careful selection of the materials from which the skins and the filler are made, the core can be sufficiently strong for use as a core for a lightweight web, and which is of a sufficiently low density that the core is not heavier than a conventional cardboard core. A cardboard core has a typical density of 0.75x103 -0.85x103 kgnt3. Embodiments of the present invention can typically save 10-15% of this. (A greater or lesser saving may be achieved while still gaining the advantage of the invention.) The inner and outer layers may be of similar construction and composition. Typically, the inner and/or the outer skin may be formed from a reinforced composite material. A preferred form of construction for the inner and outer skins comprises reinforcing fibres disposed within a matrix. The reinforcing fibres may comprise one or more of organic, inorganic or metallic materials and may be applied as preformed fabrics, short fibre fabrics or continuous orientated fibres. Fibres of aramid are particularly preferable for its resistance to cutting and abrasion. The fibres may be dry or may be pre-impregnated with an appropriate uncured polymer. The matrix is typically a thermoset or thermoplastic polymer compound. For example, it may be a modified polyester resin which has a urethane acrylate additive.

Alternatively, the inner and/or outer layer may be formed from a natural material or plant origin, such as a hemp fibre.

The filler of the tube is formed from a cellular or foam material. A high proportion of the core will be void space formed either by the use of cellular materials with entrapped air, or low density 3D woven fabrics. This achieves low overall density of the tube wall construction. Alternatively, the filler may be formed from a low-density natural material, such as balsa or cork. A wide range of alternative filler materials can be used, with an aim of achieving a density within the core of 0.3-0.6x103 kgm3. In general, the filler is bonded to the inner and outer layers so that the filler transmits stresses between the inner and the outer layers. Where the inner and/or outer layer is a composite material, the filler may be partially or wholly impregnated with the matrix of the inner and/or outer layers to form a strong bond between them, by effectively unifying the three layers of the wall.

The resin system proposed for the core tubes is a high grade modified polyester resin which has a urethane acrylate additive to impart very good impact resistant properties to the tube.

This has already been extensively trialled in the resin transfer moulding process and gives very good cycle times and product quality.

A ring of impact-resistant material, e.g., metal, such as steel, or a plastic material such as urethane polymer, may be provided at an end portion of the core to resist damage to the core, for example as might occur though impact. The ring will typically be bonded to one or both of the inner and the outer layers. Most preferably, the inner and outer diameters of the ring are substantially the same as the respective diameter of the core.

An embodiment of the invention will now be described in detail, by way of example, and with reference to the accompanying drawings, in which: Figure 1 is a side view of an end portion of a web-winding core being an embodiment of the invention; Figure 2 is a cross-section along A-A in Figure 1; Figure 3 is an end view of a mould that can be used in production of the embodiment of Figure 1; Figure 4 is a cross-section along B-B in Figure 3; and Figure 5 is a cross-section of a web-winding core being a modification of the embodiment of Figure 1.

With reference to the drawings, a core for winding a lightweight web is formed as a generally cylindrical hollow cylindrical tube that is rotationally symmetrical about a longitudinal axis X-X. For the most common applications of embodiments of the invention, the outer diameter of the cylinder is typically in the range 150-510mm, and the wall thickness of the tube is typically in the range 12-20mm. The cylindrical tube is formed with three radially-spaced layers that are disposed coaxially around the axis X-X: an inner layer 12, an outer layer 14 and a low-density reinforcing filler 16 that fills the space between the inner layer 12 and the outer layer 14. The inner and outer layers 12, 14 are bonded to the filler 16 to form a composite sandwich structure. The thicknesses of the inner and outer layers of the wall are typically in the range 1.5-4 mm, and the thickness of the filler is typically in the range 8-16 mm.

The filler 16 serves to link the inner and outer layers 12, 14 and will transmit stresses between the layers 12, 14 to provide a stable structure.

The inner and outer layers 12, 14 are formed from reinforcing fibres which are impregnated with, and embedded in, a matrix of thermoset or thermoplastic polymer compound. In this embodiment, the fibres are aramid, the matrix is a polyester resin which has a urethane acrylate additive, and the filler is an expanded hexagonal segment PET foam core.

The sandwich core portion of the tube is formed from a cellular or foam material which will be bonded between the inner and outer skins of the tube and may be partially or wholly impregnated with the polymer matrix compound. A high proportion of the core will be void space formed either by the use of cellular materials with entrapped air, or low density 3D woven fabrics. This is key to achieving low overall density of the tube wall construction The tube wall is formed in layers with internal and external skins containing a reinforcing medium, and a bonded sandwich core portion which is of low density material. The sandwich core serves to link the two skins and will transmit stresses between the skins to provide a stable structure.

The skins are formed from reinforcing fibres which are impregnated with, and embedded in, a matrix of thermoset or thermoplastic polymer compound. The reinforcing fibres may be of organic, inorganic or metallic materials and may be applied as preformed fabrics, short fibre fabrics or continuous orientated fibres. The fibres may be dry or may be pre-impregnated with an appropriate uncured polymer as described.

One method and apparatus for manufacture of a core embodying the invention, and apparatus for implementing the method, will now be described.

A one-piece metal cylindrical member 20, of external diameter equal to the internal diameter of the finished core tube 10, forms a central part of a mould tool for forming a core embodying the invention. This central cylinder 20 is mounted concentrically with an outer metal mould shell 22, with an annular space 24 between the central cylinder 20 and the outer mould shell 22 equal to the design wall-thickness of the finished core tube 10. A highly polished finish is required on this central cylinder and it is treated with a release agent to ensure that the resin will not be able to adhere to the surface.

The external mould shell 22 is split along its longitudinal centreline at 30 into two identical half shells which are precisely located relative to each other to form an accurate hollow cylindrical mould shell equal in diameter to the outside diameter of the core tube 10 to be formed. This external mould shell 22 is provided with stiffeners (not shown) to ensure good dimensional stability of the structure, to provide the close dimensional tolerances required in the finished core tube 10.

Sealing rings 32 are fitted to the central cylinder at a distance apart which is equal to the required length of the finished core tube 10. The longitudinal seams of the outer mould shell also incorporate airtight seals which are essential to the correct functioning of the mould.

A number of resin entry ports 34 and air venting points 36 are incorporated into the outer mould shell 22 to ensure that liquid resin can be introduced into the annular space 24 between the inner cylinder 20 and the outer split mould shell 22, and that air can be vented from the space 24 as the mould is filled. The air may be displaced naturally by the ingress of the resin or a small level of vacuum may be applied through the air vent ports 36 to improve the resin flow into the mould.

With the mould dismantled, the inner cylinder 20 is prepared by wrapping a layer of dry fibre fabric onto the surface between the two pre-located sealing rings 32 which determine the overall length of the core tube 10. A dry layer of the selected foam core medium is then applied to cover the inner glass fabric. This foam may be applied in sheets which are thermally preformed or may be applied as a spirally-wound or convolute-wound strip, depending upon the material selected. On top of the foam material, another layer of dry fibre fabric is applied over the entire surface.

The prepared inner cylinder 20 with the dry materials is then located within the lower half of the split external mould 22. The upper half of the external mould 22 is then accurately located onto the lower half mould trapping the internal cylinder 20 and the dry fabric and foam layers into the closed mould space.

A resin metering and pumping unit prepares a pre-determined quantity of liquid polyester resin with the appropriate curing agents added, and then pumps this mixed resin into the mould through one or more of the ingress ports 34 on the outer mould surface. Air venting or vacuum may be used to promote the resin flow through the mould and resin is pumped into the mould until all the air is displaced and resin flows from the air venting port 36.

The pumping process is stopped and the resin is allowed to cure, either at ambient temperature or at an elevated process temperature. Elevated temperature can be advantageous as it will speed up the curing reaction of the resin. Elevated temperature can readily be applied by pumping hot water or oil through the central cylindrical 20 member or by incorporating heating elements within the wall of the mould during construction.

Once the resin is cured the outer mould may be unsealed and split open and the cylindrical inner mould 20 with the laminated core tube may be removed from the assembly.

The moulded tube 10 is then drawn off the internal cylinder with a mechanical or hydraulic pulling device. The finished tube should need minimal second operation works to make it ready for despatch. The possible removal of flash lines along the mould split lines may be necessary.

Similar production techniques can be used for the construction of cores using materials other than those described in the above example.

Some applications of cores embodying the invention may favour a textured external and/or internal surface on the core tube. This may be formed directly using the mould itself Alternatively the required internal and external surface textures may be applied by wrapping peel ply or similar textured fabric onto the central cylindrical mould member prior to applying the inner structural fabric layers, and/or onto the outer surface of the external layers of structural fabrics.

There is some risk of the core tube edges spalling in the event of severe impact -typically if accidentally dropped during handling operations. A modification to the mould tooling has been incorporated within the initial design to permit a protective body 40 of tough material such as metal or urethane polymer to be bonded to an end portion of the core tube 10 to enhance the impact resistance if required, as shown in Figure 5.

The protective body 40 has a cylindrical locating portion 42 that is a close fit between the inner and the outer layers 12, 14. An end portion of each of the inner and outer layers 12, 14 projects beyond the end of the filler 16 to accommodate the locating portion 42, which is bonded to them. The protective body projects beyond the inner and outer layers 12, 14, and has an outer diameter that is substantially the same as that of the tube 10. The protective body 40 has an axial through bore that has a diameter that is substantially the same as the inner diameter of the tube 10. This arrangement ensures that the core as a whole has a substantially uniform inner and outer diameter along its length. An outer portion of the bore of the protective body, shown at 44, is chamfered to provide a lead-in to assist the insertion of handling apparatus into the bore of the core.

Claims

Claims 1. A web-winding core formed as a hollow cylindrical shell, the shell being a three-layered sandwich comprising inner and outer skins, between which is a filler to which the inner and outer skins are bonded.
2. A web-winding core according to claim 1 in which the inner and outer layers may be of similar construction and composition.
3. A web-winding core according to claim 1 or claim 2 in which the inner and/or the outer skins may be formed from a reinforced composite material.
4. A web-winding core according to claim 3 in which for the inner and/or outer skin comprises reinforcing fibres disposed within a matrix.
5. A web-winding core according to claim 4 in which the reinforcing fibres comprise one or more of organic, inorganic or metallic materials.
6. A web-winding core according to claim 4 or claim 5 in which the reinforcing fibres are in the form of a preformed fabric, a short-fibre fabric or as continuous orientated fibres.
7. A web-winding core according to any one of claims 4 to 6 in which the fibres are aramid.
8. A web-winding core according to any one of claims 4 to 6 in which the fibres are natural fibres of plant origin.
9. A web-winding core according to claim 8 in which the fibres are hemp fibres.
10. A web-winding core according to any one of claims 4 to 9 in which the fibres are pre-impregnated with an appropriate uncured polymer.
11. A web-winding core according to any one of claims 4 to 10 in which the matrix is a thermoset or thermoplastic polymer compound.
12. A web-winding core according to claim 9 in which the matrix includes a modified polyester resin which has a urethane acrylate additive.
13. A web-winding core according to any preceding claim in which the filler is formed from a cellular or a foam material.
14. A web-winding core according to any one of claims 1 to 12 in which the filler is a natural material.
15. A web-winding core according to claim 14 in which the filler is cork or balsa.
16. A web-winding core according to any preceding claim in which the filler has a density in the range 0.3 to 0.6 x 103kgm3.
17. A web-winding core according to any preceding claim in which the filler is bonded to the inner and outer layers.
18. A web-winding core according to any preceding claim in which the filler is partially or wholly impregnated with a matrix of the inner and outer layers.
19. A web-winding core according to any preceding claim further including a ring of resilient material is provided at an end portion of the core to resist damage to the core.
20. A web-winding core according to claim 19 in which the ring is a resilient polymer that is moulded on the core.
21. A web-winding core according to claim 19 in which the ring is metal.
22. A web-winding core according to any one of claims 19 to 21 in which the ring is bonded to one or both of the inner and outer layers.
23. A web-winding core according to any one of claims 19 to 22 in which the ring has an inner and outer diameter substantially the same as the respective diameter of the core.
24. A web-winding core substantially as described herein with reference to the accompanying drawings.