EP3774626A1

EP3774626A1 - Core for coiled sheet metal, manufacturing method, and method for packaging coils

Info

Publication number: EP3774626A1
Application number: EP18718731.5A
Authority: EP
Inventors: Jordi Casas; Javier FUSTERO; Marko ILOMÄKI
Original assignee: Sonoco Alcore Oy; Sonoco Development Inc
Current assignee: Sonoco Alcore Oy; Sonoco Development Inc
Priority date: 2018-04-04
Filing date: 2018-04-04
Publication date: 2021-02-17
Also published as: US20210122562A1; WO2019192685A1

Abstract

A hollow cylindrical core (1), e.g. paperboard core, for coiled sheet metal (5), the core (1) being made from at least one ply of material wound into the shape of a tube, the core having an outer circumferential surface (2), an inner circumferential surface (3) and a cavity (4) inside the core (1) which is defined by the inner circumferential surface (3), and the core (1) being open at least at one end, wherein the core (1) is provided with a volatile corrosion inhibitor inside the cavity (4).

Description

Core for coiled sheet metal , manufacturing method , and method for packaging coils

FIELD OF THE INVENTION

The present invention relates to a core for a roll or coil of metal, such as steel, aluminum, or other metals or alloys, and to a method of manufacturing such cores.

The present invention also relates to a method for wrapping metal coils.

PRIOR ART

Steel and other metals are often made in sheets having a length many times greater than their width. The sheets are wound into coils for storage and transport. The coils of steel may be stored on pallets for ease in moving and manipulating the coils.

The metal materials are rolled into coils with or without cylindrical cores for supporting the coils. As the cores for supporting the rolls, large, thick-walled paperboard cores have been used. The paperboard core helps the wound material develop a stable roll structure and enables transportation of the manufactured material to a converting operation. The diameters of these tubes may range - depending on several factors such as tube wall thickness, weight of the metal coils to be carried thereon, purpose of application, etc. - from small inner diameters such as 15 mm to wind e.g. thin sheets of aluminum to large inner diameters such as 1000 mmm to wind e.g. thick sheets of specialty metals or alloys.

Thinner wall cores have also been known which are folded to be delivered and which are then opened up into an essentially cylindrical shape, either when putting such a core onto a winding chuck for winding material sheets thereon, or when inserting such a core into the inside of a readily wound metal coil.

In any event, once the metal coils have been formed - with or without cores -, the coils are usually wrapped in sheets of paper, such as kraft paper, or plastic material to protect them from environmental influences.

US 5,983,598 discloses a method for wrapping steel coils for storage and transport following their manufacture at steel mills. The coils are wrapped in paper or a polymeric packaging material impregnated with a volatile corrosion inhibitor, such as sodium nitrite, the layer impregnated with the volatile corrosion inhibitor being in direct contact with the metal coil.

According to GB-A-2 131 382, it has been realized that the interior surfaces of long hollow or tubular articles, such as pipes, tubes, small arms, rifles and gun barrels, may not be effectively protected merely by an external wrapping, and it is therefore suggested to additionally use an anti-corrosive packaging material for providing corrosion protection to the inside of such hollow, elongated articles. The packaging comprises an elongated core member of which at least the exposed exterior surfface is formed from a material impregnated or coated with a volatile corrosion inhibitor. Such a core member can be made to suit insertion within articles of various diameters so as to provide fully effective protection throughout the length of a hollow product. Such cores may be manufactured by conventional means utilizing known types of paper or other materials impregnated or coated in known manner with known volatile corrosion inhibitors, and serve to enhance the effectiveness of conventional sheet wrapping materials when used in relation to hollow elongated articles.

JP-A-2004/277153 discloses a paper pipe capable of preventing corrosion and deterioration of metal products, specifically electronic parts such as diodes which are provided in a lattice pattern and wound around the paper pipe for transportation and storage. A corrosion-proof functional layer is provided at least on the external surface of the paper pipe.

JP-S51-114717 discloses a process for manufacturing a paper tube in which said paper-tube is fabricated by coating or impregnating a primarily ribbon-like paper tube blank with an epoxy anti-corrosive paint, and a spiraling machine is employed to wind the thus-coated or impregnated blank into a spiral shape. The tube is finished by rapidly curing said epoxy anti-corrosive paint on the spirally wound layers.

Finally, DE-U1-298 09 872 also forms part of the prior art. The utility model discloses a winding core configured for accommodating and storing corrodible parts therein. At least a radially innermost ply of the core, which will get into contact with the corrodible part inside the core, is provided with a corrosion preventing agent. DISCLOSURE OF THE INVENTION

It is desirable to provide for a corrosion protection of metal coils, such as for shipment or storage, e.g. in view of sea transports or other extreme climate conditions.

In order to improve on the corrosion protection of metal rolls or coils, a hollow cylindrical core for coiled sheet metal as recited in claim 1 is provided. The core is made from at least one ply of material wound into the shape of a tube, and has an outer circumferential surface, an inner circumferential surface and a cavity inside the core which is defined by the inner circumferential surface. The core is open at least at one end, and it is provided with a volatile corrosion inhibitor inside the cavity.

The core of the present invention can be used for coiled sheets of metals including, but not limited to, iron, steel, copper, brass, aluminum, silver, and alloys of these metals, all of which are frequently found to be susceptible to corrosion under normal atmospheric and ambient conditions.

A volatile corrosion inhibitor (abbreviated VCI and also known as vapor corrosion inhibitor) is an organic or inorganic chemical compound that is used to protect metallic materials (including ferrous and non-ferrous metals and alloys) against corrosion, e.g. oxidation. VCI chemicals are a class of corrosion inhibiting compounds, which have sufficient vapor pressure to release molecules from the compound into the air. VCIs slowly release compounds within a sealed airspace that actively prevent surface corrosion.

The VCI on the inside of the core releases corrosion protective compounds, i.e. VCI chemicals vaporize. Since the core is open at least at one end, preferably at both its longitudinal ends, the VCI chemicals diffuse towards the outside of the core and form a mono-molecular protective layer on the metal surfaces to be protected, thereby acting to protect the exposed surface of the metal coil wound around the core from corrosion. The VCI becomes particularly effective when the metal coil is wrapped in a packaging material so that the core with the VCI is in the same air space as the metal coil: the VCI inside the core acts to protect the metal roll wound onto the core.

VCI compositions as such are known in the art, and any of the known VCI compositions can be used for the core of the present invention. For example, sodium nitrite is known as an effective volatile corrosion inhibitor when carbon dioxide and water are present in the air. Sodium nitrite, amine nitrite salts, organic amines, carboxylic acids and organic amine carboxylic acid salts have all been disclosed singularly and in combination in volatile corrosion inhibiting compositions.

The choice of a specific VCI also depends on the type of material to be protected from corrosion or oxidation, respectively. For example, if the material to be protected is aluminum, suitable VCIs are available to protect the aluminum from oxidation which in this case would become manifest in a loss of glossiness.

The hollow cylindrical core of the invention can have any inner diameter suitable for paperboard cores, e.g. within the range of 15 mm to 1000 mmm, preferably 100 to 900 mm, more preferably 200 to 800 mm. The inner diameter of the hollow cylindrical core of the invention can be within a range of about 300 mm to 600 mm, which is an exemplary diameter range for paperboard cores for the metal industry. Further possible exemplary inner diameters are within the range of 350 to 400 mm or within the range of 600 to 700 mm.

Optional features are recited in the dependent claims and the description which follows. The outer circumferential surface of the core can be left free of volatile corrosion inhibitor chemicals.

As an alternative, the volatile corrosion inhibitor can additionally be provided on the outer circumferential surface of the core. The VCI on the outer circumferential surface of the core releases corrosion protective compounds, i.e. VCI chemicals vaporize. Since the outer circumferential surface of the core is in direct contact with the innermost surface of the metallic material coil wound around the core, the corrosion protective compounds are in direct contact with the innermost surface of the material coil, thereby forming a mono-molecular protective layer on the innermost surface of the metallic material coil which is in direct contact with the outer circumferential surface of the core. Thus, the innermost surface of the metallic material coil is protected from corrosion through direct contact with the VCI chemicals. In cases where gaps between the outer circumferential surface of the core and the innermost surface of the metallic material coil exist, the VCI chemicals from the outer circumferential surface, particularly the VCI chemicals in an area close to the gap, diffuse towards and into said gap and towards the outside of the core. Providing the VCI on the outer circumferential surface can be particularly helpful in preventing corrosion of the metallic material coil when gaps between the core and the metallic material coil occur during transportation.

The volatile corrosion inhibitor can be provided as a coating on, or an impregnation into, the material forming the inner circumferential surface of the core. The core as such is thereby provided with a corrosion prevention function.

The volatile corrosion inhibitor can further be provided as a coating on, or an impregnation into, the material forming the outer circumferential surface of the core. The core as such is thereby provided with a corrosion prevention function.

Considering that the metal roll to be protected is on the outside of the core, whereas the VCI is provided at least inside - or possibly only inside - of the core, the amount of VCI inside the core must be sufficiently large so as to provide for a corrosion protection of the entire metal roll or coil. In general terms, the activity of a VCI decreases over time, i.e. the more VCI is used, the longer it remains active. In principle, VCIs can be said to provide a temporary corrosion protection.

There are several parameters which determine the amount of VCI which is needed to provide for a corrosion protection of the entire coil.

First of all, the amount of VCI needed is dependent on the chemical composition, i.e. the type of VCI and its effectiveness in terms of corrosion protection. Any type of commercially available VCI that prevents metallic materials from corroding are suitable for the purpose of this invention. The choice of a specific VCI hereby also depends on the type of metallic material (e.g. steel, aluminum or the like) to be protected.

In cases where the VCI is provided only inside of the core, the amount of VCI inside the core must be sufficiently large as to provide for a protection of the entire coil, considering that the metallic material roll to be protected is on the outside of the core. Moreover, the amount of VCI needed to provide for a corrosion protection is dependent on the type of metallic material which is wound around the core and for which corrosion protection is sought. Furthermore, the amount of VCI needed to provide for a sufficient corrosion protection is dependent on the type of material on which the VCI is impregnated into or coated onto. In addition to that, the amount of VCI which is needed to provide for a corrosion protection of the entire coil increases with increasing core size, increasing amount of metallic material and increasing duration of protection. Furthermore, the amount of VCI is dependent on the type of environment for which corrosion protection is sought, i.e. the amount of VCI which is needed to provide for a corrosion protection of the entire coil increases for harsh and/or corrosive environments which can, for example, occur during sea transport due to corrosive salt water or high-temperature environments which can, for example, occur due to direct solar radiation.

Depending on the circumstances, the inner and/or outer surface of the core can be fully or only partially covered with the volatile corrosion inhibitor.

Alternatively or in addition, the volatile corrosion inhibitor can be provided as a coating on, or an impregnation into, an additional material layer inserted into the cavity within the core. The additional material layer could be a sheet that is inserted into the inside of the core and formed into a round shape to match the shape of the inner periphery of the core. The additional material layer could also be e.g. a thin, foldable forming tube. In any case, additional material layer preferably has the volatile corrosion inhibitor coated on its surface facing the inside of the core .

The hollow cylindrical core can comprise a plurality of material plies wound into a tube. The material plies can be spirally wound into a tube. The material plies can be adhesively bonded to each other by means of glue.

At least one ply of material can be a paperboard ply. The hollow cylindrical core can be made from one or several paperboard plies. Preferably, the material ply or plies constituting the core are made from thick, soft and porous paperboard which is able to absorb, i.e. be impregnated with, a significant amount of VCI . The absorption capacity of the core can, especially in cases where the VCI is only provided in the cavity of a core, be used to compensate for the limited area inside the core where the VCI is provided, as compared to the surface area of the metal coil which is to be protected from corrosion.

The hollow cylindrical core may further comprise sheet metal wound around the outer circumference of the core so as to form a metal roll or coil.

The hollow cylindrical core can then further comprise an end header at least at one longitudinal end of the metal roll or coil, wherein the end header is preferably also provided with a volatile corrosion inhibitor. The end header can have a diameter which is larger than an outside diameter of the core. It protects the edges of the metal roll and increases the surface area which can be provided with the VCI .

The hollow cylindrical core may further include a packaging material wrapped around the metal roll or coil so as to enclose the metal roll or coil and the volatile corrosion inhibiting (VCI) composition in a substantially closed airspace .

The present invention also provides a method of manufacturing a hollow cylindrical core for coiled sheet metal (claim 12), the method comprising the steps of: winding at least one ply of material - e.g. paperboard - into the shape of a tube so as to obtain a core having an outer circumferential surface, an inner circumferential surface and a cavity inside the core which is defined by the inner circumferential surface, the core being open at least at one end; and providing a volatile corrosion inhibitor inside the cavity. The outer circumferential surface of the core can be left free of any volatile corrosion inhibitor. Alternatively, the core can be provided with a volatile corrosion inhibitor also on the outer circumferential surface thereof.

One way of providing a volatile corrosion inhibitor to the core (i.e. at least inside the cavity, and possibly also on the outer circumferential surface of the core) is to coat the volatile corrosion inhibitor onto, or impregnate it into, the material forming the inner and/or outer circumferential surface of the core.

For example, at least one ply of the material forming the core is coated or impregnated with the VCI before the ply or plies of material are wound into the shape of a tube. The material ply coated or impregnated with the VCI could then in principle correspond to a ply of conventional VCI paper.

Alternatively or in addition, the material forming the inner and/or outer circumferential surface of the core is coated or impregnated with the VCI in an in-line process while manufacturing the core, i.e. while winding the ply or plies of material into the shape of a tube.

Alternatively or in addition, the material forming the inner and/or outer circumferential surface of the core is coated or impregnated with the VCI after manufacturing the core, i.e. after winding the ply or plies of material into the shape of a tube .

The volatile corrosion inhibitor can be applied by means of a brush, a sponge, a scrape, a roll, by spraying or the like. The volatile corrosion inhibitor can be applied in one or several steps. At least one of the end surfaces of the core can be provided (e.g. coated) with VCI as well, which further increases the surface area from which the VCI is volatilized.

The at least one ply of the material coated or impregnated with the VCI is preferably dried before the ply or plies of material are wound into the shape of a tube.

Still alternatively or in addition, the volatile corrosion inhibitor is coated onto, or impregnated into, an additional material layer and the additional material layer is inserted into the cavity inside the core. In this manner, it is possible to also provide standard paperboard cores with a corrosion protecting function. The additional material layer can for example have a shape which substantially coincides with the inner circumferential surface of the core so that the additional material layer can be formed into a cylindrical shape and placed inside the cavity. The surface of the additional material layer which is coated or impregnated with the VCI should then face towards the inside of the cavity so as to achieve the desired effect.

When manufacturing the core, the material plies are preferably adhesively bonded to each other. This is done by coating or impregnating the material plies with a glue before winding .

Finally, the present invention relates to a method of packaging a coiled metal sheet for storage or transport as recited in claim 22, comprising the steps of: placing a volatile corrosion inhibitor inside the coiled metal sheet, and wrapping the coiled metal sheet in a packaging material so as to enclose the coiled metal sheet and the volatile corrosion inhibitor in a substantially closed airspace.

The method can further comprising the step of providing a core according to any one of claims 1 to 8 inside the coiled metal sheet, or winding a metal sheet about a core according to any one of claims 1 to 8.

The packaging material can also include a volatile corrosion inhibitor .

The packaging material should be wrapped around the metal coil sufficiently loosely so as to allow for a circulation of air from the inside of the core towards the metal coil surfaces to be protected from corrosion.

The plastic wrap should be sufficiently airtight and so loose that gases can move inside of the package, so as to make sure that the VCI in the inside of the core can act to protect the metal on the outside of the roll. The VCI chemicals will protect the metal even if the airspace is not totally sealed, but the best effect is achieved in a sealed airspace. It is important that air can circulate inside the package.

The packaging material can for example be a paper, e.g. kraft paper, or a plastic material, preferably a tear resistant polymeric material such as polyethylene or polypropylene; it could also be a laminate of two or more different materials, e.g. plastic and paper.

Considering that a corrosion protection is already provided by the VCI inside the core, it is not necessary for the packaging material to also have a corrosion protecting function. However, in many cases a substantially air-tight packaging of the metal coil will be required anyway, and if packaging materials - e.g. paper or plastic materials - are used to which a VCI has been added, this can suitably further enhance the corrosion protection.

An end header can be provided on at least on one of the open ends of a roll of sheet metal wound around the core within the sealed airspace of the plastic wrap, wherein the end header is preferably also provided with a volatile corrosion inhibitor .

Finally, the present invention also relates to the use of a hollow cylindrical core according to any one of claims 1 to 8, or a hollow cylindrical core manufactured in a method according to any one of claims 12 to 21, for winding sheet metal .

BRIEF DESCRIPTION OF THE DRAWINGS

In the enclosed drawings,

Figure 1 shows a paperboard core according to the present invention,

Figure 2 shows a metal roll wound on the paperboard core of Figure 1,

Figure 3 illustrates the behavior of a volatile corrosion inhibitor (VCI) used in the paperboard core of Figure 1,

Figure 4 is a schematic view of the metal roll of Figure 3 in a packaged state, and

Figures 5 and 6 illustrate two possibilities of wrapping a metal coil using the paperboard core of the present invention .

DESCRIPTION OF EMBODIMENTS

An embodiment of a paperboard core according to the present invention, a method of manufacturing the core and a method for packaging a metal coil using the core will now be described with reference to the drawings. Figure 1 shows a paperboard core 1 according to the present invention. The paperboard core 1 is a hollow cylindrical paperboard core for winding sheet metal. The core 1 is made from at least one ply of paperboard material wound, e.g. spirally, into the shape of a tube. The paperboard core can also be a convolute core, though. One possible example of the paperboard core is a Metallan® (trademark owned by Sonoco Products Company) core, which has a large inner diameter of e.g. 400 mm and is used to wind metal coils like coated aluminum.

The core 1 has an outer circumferential surface 2, an inner circumferential surface 3 and a cavity 4 inside the core 1 which is defined by the inner circumferential surface 3, and the core in this embodiment is open at both ends. Strictly speaking it would be sufficient for the core to be open at one end, but providing the core with two open ends is beneficial in view of the required circulation of air through the inside of the core which will be specified further below.

In accordance with the invention, the paperboard core 1 is provided with a volatile corrosion inhibitor inside the cavity 4. The volatile corrosion inhibitor can for example be provided as a coating on, or an impregnation into, the paperboard material forming the inner circumferential surface 3 of the core 1.

Figure 2 shows a metal roll 5 wound on the paperboard core 1 of Figure 1, and Figure 3 illustrates the behaviour of the volatile corrosion inhibitor (VCI) provided inside the paperboard core 1: The VCI in the cavity 4 inside of the core 1 releases corrosion protective compounds. Since the core 1 is open at both its longitudinal ends, the VCI diffuses towards the outside of the paperboard core 1 and acts to protect the exposed surface of the metal coil 5 wound around the paperboard core 1 from corrosion. The VCI becomes particularly effective when the metal coil 5 is wrapped in a packaging material 6, as illustrated in Figure 4, so that the paperboard core with the VCI is in the same air space as the metal coil. Air can circulate inside the package, and the VCI provided inside the core acts to protect the metal roll wound onto the core 1.

The outer circumferential surface 2 of the core 1 can be left free of any VCI chemicals, but in embodiments, the core can be provided with a volatile corrosion inhibitor also on the outer circumferential surface of the core. Provided that gaps exist between the outer circumferential surface of the core and the coiled metal sheet, air can circulate there between, and the VCI additionally provided on the outer circumferential surface 2 of the core 1 acts to additionally protect the metallic material roll 5 wound onto the core 1.

Figures 5 and 6 make it clear that there are different possible ways of packaging a metal coil supported on a paperboard core 1 of the present invention: according to Figure 5, the wrapping material is provided so as to constitute a substantially cylindrical enclosure encompassing the metal coil and the paperboard core, so that the metal coil and the paperboard core are confined within the same airspace and the VCI can diffuse towards the exposed surfaces of the metal coil. Figure 6 shows that it would as well be possible to have the packaging material extend into the cavity inside the core and along the inner circumferential surface of the core, at least about a certain distance into the core but possibly even completely through the core. Also in this case, the inner circumferential surface of the core and the exposed surfaces of the metal coil are confined within the same airspace so that the VCI on the inside of the core can protect the exposed surfaces of the metal coil.

Claims

What is claimed is:

1. A hollow cylindrical core for coiled sheet metal, the core being made from at least one ply of material wound into the shape of a tube,

the core having an outer circumferential surface, an inner circumferential surface and a cavity inside the core which is defined by the inner circumferential surface, and the core being open at least at one end, wherein the core is provided with a volatile corrosion inhibiting (VCI) composition inside the cavity .

2. The hollow cylindrical core according to claim 1, wherein the outer circumferential surface of the core is left free of any volatile corrosion inhibiting (VCI) composition .

3. The hollow cylindrical core according to claim 1, wherein the core is provided with a volatile corrosion inhibiting (VCI) composition also on the outer circumferential surface of the core.

4. The hollow cylindrical core according to any one of claims 1-3, in which the VCI composition is provided as a coating on, or an impregnation into, the material forming the inner and/or outer circumferential surface of the core.

5. The hollow cylindrical core of any one of the preceding claims, in which the VCI composition is provided as a coating on, or an impregnation into, an additional material layer inserted into the cavity within the core.

6. The hollow cylindrical core of any one of the preceding claims, comprising a plurality of material plies wound into a tube.

7. The hollow cylindrical core of claim 6, wherein the material plies are adhesively bonded to each other.

8. The hollow cylindrical core of any one of the preceding claims, in which at least one ply of material is a paperboard ply.

9. The hollow cylindrical core of any one of the preceding claims, further comprising sheet metal wound around the outer circumference of the core so as to form a metal roll or coil.

10. The hollow cylindrical core of claim 9, further including an end header at least at one longitudinal end of the metal roll or coil, wherein the end header is preferably also provided with a volatile corrosion inhibitor .

11. The hollow cylindrical core of claim 9 or 10, further including a packaging material wrapped around the metal roll or coil so as to enclose the metal roll or coil and the volatile corrosion inhibiting (VCI) composition in a substantially closed airspace.

12. A method of manufacturing a hollow cylindrical core for coiled sheet metal, the method comprising the steps of: winding at least one ply of material into the shape of a tube so as to obtain a core having an outer circumferential surface, an inner circumferential surface and a cavity inside the core which is defined by the inner circumferential surface, the core being open at least at one end, and

providing a volatile corrosion inhibiting (VCI) composition inside the cavity.

13. The method of claim 12, wherein the outer circumferential surface of the core is left free of any volatile corrosion inhibiting (VCI) composition.

14. The method of claim 12, wherein the core is provided with a volatile corrosion inhibiting (VCI) composition also on the outer circumferential surface thereof.

15. The method according to any one of claims 12 to 14, in which the VCI composition is coated onto, or impregnated into, the material forming the inner and/or outer circumferential surface of the core.

16. The method of any one of claims 12 to 15, in which at least one ply of the material is coated or impregnated with the VCI composition before the ply or plies of material are wound into the shape of a tube.

17. The method of claim any one of claims 12 to 16, in which at least one ply of the material is coated or impregnated with the VCI composition while the ply or plies of material are wound into the shape of a tube.

18. The method of any one of claims 12 to 17, in which the material forming the inner and/or outer circumferential surface of the core is coated or impregnated with the VCI composition after winding the ply or plies of material into the shape of a tube.

19. The method of any one of claims 12 to 18, in which the VCI composition is coated onto, or impregnated into, an additional material layer and the additional material layer is inserted into the cavity inside the core.

20. The method of any one of claims 12 to 19, wherein the material plies are adhesively bonded to each other.

21. The method of any one of claims 12 to 20, wherein at least one ply of material is a paperboard ply.

22. A method of packaging a coiled metal sheet for storage or transport, comprising the steps of:

placing a volatile corrosion inhibiting (VCI) composition inside the coiled metal sheet, and

wrapping the coiled metal sheet in a packaging material so as to enclose the coiled metal sheet and the volatile corrosion inhibiting (VCI) composition in a substantially closed airspace.

23. The method of claim 22, further comprising the step of providing a core according to any one of claims 1 to 8 inside the coiled metal sheet, or winding a metal sheet about a core according to any one of claims 1 to 8.

24. The method of claim 22 or 23, wherein the packaging material also includes a volatile corrosion inhibiting (VCI) composition.

25. The method of any one of claims 22 to 24, wherein the packaging material is wrapped around the metal coil sufficiently loosely so as to allow for a circulation of air from the inside of the core towards the metal coil surfaces to be protected from corrosion.

26. The method of any one of claims 22 to 25, wherein an end header is provided on at least on one of the open ends of the coiled metal sheet within the sealed airspace of the packaging material, wherein the end header is preferably also provided with a volatile corrosion inhibiting (VCI) composition.

27. Use of a hollow cylindrical core according to any one of claims 1 to 8, or a hollow cylindrical core manufactured in a method according to any one of claims 12 to 21, for winding sheet metal .