WO2004003302A1

WO2004003302A1 - Cable covered with a xple sheath

Info

Publication number: WO2004003302A1
Application number: PCT/IB2003/002916
Authority: WO
Inventors: Francesco Ferraiolo
Original assignee: Officine Maccaferri SpA
Current assignee: Officine Maccaferri SpA
Priority date: 2002-07-01
Filing date: 2003-06-27
Publication date: 2004-01-08
Anticipated expiration: 2005-01-01
Also published as: ITBO20020420A0; AU2003244956A1; WO2004003302A8; ITBO20020420A1

Abstract

A wire covered with a sheath of protective material for use, in particular, in the construction field and in products made of double-twist wire netting which are used in the water, geotechnical, and erosion-control fields comprises a cross-linked XLPE sheath.

Description

CABLE COVERED WITH A XPLE SHEATH

The present invention relates to a wire covered with a sheath of protective material for use, in particular but in non-limiting manner, in the construction field and in products made of double-twist wire netting which are used in the water, geotechnical, and erosion-control fields. The present invention also relates to articles made of this wire.

It is known to produce plastics-coated wire that is covered with a PVC sheath in .order to protect the ferrous portion of the product from oxidation resulting from exposure to atmospheric agents. The main disadvantages of this combination of materials are due to the properties of the above-mentioned polymer which adversely affect the production process, the environmental impact, and the final characteristics of the product.

The production process is in fact greatly limited by the mechanical properties of polyvinyl chloride, otherwise known as PVC, which tends to be hard and stiff at ambient temperature unless it is supplemented with special plasticizers. However, this measure is often not sufficient to ensure adequate quality of the final product, even when it is combined with hot processing at temperatures at which the material acquires the greatest plasticity. A case in point is the production of double-twist nettings in which the sheath of the wire is greatly stressed and may undergo breakages and cuts .

PVC owes its wide use to its compatibility with a large number of additives which modify its characteristics; amongst these additives are the plasticizers already mentioned, reinforcing fillers, lubricants for facilitating moulding, and pigments and colourings of various types. All of these additional substances render the use of PVC highly environmentally disadvantageous, given the ease with which it releases pollutants, particularly in water, and toxic gases in the event of combustion.

In addition to this, the plasticizing components which are added to the polymer evaporate over time, progressively depriving the sheath of its mechanical characteristics, rendering it more fragile and subject to breakage. Moreover, the protection of the wire by the sheath is often also unsatisfactory because of the poor adhesion of the PVC to the wire; this creates spaces at the interface of the two portions into which the oxidizing agents penetrating from the breakage points can easily infiltrate. The corrosion effect is thus not restricted to the portion of wire that remains exposed but is also propagated to the portion in which the sheath is still intact .

The object of the present invention is to overcome the disadvantages of the prior art and to provide a wire covered with a sheath of polymer material which has good and enduring mechanical strength irrespective of the external temperature, which adheres strongly to the metal core of the wire, and which is self-extinguishing.

The object of the present invention is also to provide a covered wire which is easy to use, inexpensive to produce, has maximum ability to withstand production processes, and is protected against corrosion.

In order to achieve the objects indicated above, the subject of the invention is a wire of the type indicated in the introduction to this description, characterized in that the sheath comprises cross-linked XLPE. The particular plastics material which is used to solve the problems of the prior art is a cross-linked polyethylene known as XLPE which, particularly in its low-density form, is used for covering electrical cables . In this application, the polyethylene is generally filled with carbon black and supplemented with peroxides which have the purpose of permitting extrusion and preventing cross- linking, which takes place subsequently by a vulcanization process. Its principal characteristics are the ability to retain its mechanical properties over time and irrespective of the external temperature.

The extrusion process permits very good adhesion to the wire so that any damage to the sheath gives rise to purely local attack by corrosive agents .

The advantages of the use of XLPE instead of PVC lie in its mechanical, physical, and chemical properties. With regard to its mechanical properties, XLPE is flexible and tough, permitting the production of coverings which stand up well to production processes such as the manufacture of double- twist wire nettings . Owing to the paraffinic nature of the material combined with the cross-linking, at ambient temperature, the polyethylene cannot be attacked by any reagent and is insoluble in any solvent, permitting optimal isolation of the wire. Moreover, since it is an amorphous polymer, the mechanical characteristics of XLPE remain stable with variations in temperature, which is particularly advantageous for its processing at different ambient temperatures depending on the season or the country. The good adhesion between this polyethylene and metal renders the formation of spaces at the interface of the two materials unlikely, creating a condition of impermeability to oxidizing agents, the effect of which is limited purely to the exposed portion of the wire.

According to a preferred embodiment of the invention, an additive is added to the outer layer of the sheath to render it self-extinguishing in the standard environmental conditions. This additive generally reduces the mechanical characteristics of the XLPE and renders it more expensive but, by virtue of a coextrusion process, it is possible to introduce it purely into an outer layer, whilst retaining good characteristics of the sheath as a whole and limiting the costs of the product.

Further characteristics and advantages will become clear from the following detailed description with reference to the sole appended drawing which is provided purely by way of non-limiting example and in which Figure 1 is a cross- section of a wire covered with a sheath containing XLPE.

With reference to the drawing, a covered wire 10 comprises a wire 12 , made of one of the materials that are known for the production of wires for fencing or construction. In particular, but in non-limiting manner, the wire is of the type used for the production of double-twist nettings. A protective sheath 16 is applied to the outer surface 14 of the wire 12 and adheres to the outer surface 14 without leaving spaces. The protective sheath 16 is made of a plastics material comprising a type of polyethylene commonly known as XLPE, preferably but in non-limiting manner, of a variety suitable for extrusion, such as the low-density type. The protective sheath 16 also comprises one or more additives of known type amongst which, for example but in non-limiting manner, are carbon black, peroxides which assist the extrusion process, and other substances for promoting cross-linking of the material. The layer 18 of plastics material immediately beneath the outer surface 20 of the protective sheath 16 comprises an additive which renders the XLPE self-extinguishing in standard environmental conditions . The introduction of this additive is possible by virtue of the coextrusion process by which the protective sheath 16 is applied to the wire 12.

Naturally, the principle of the invention remaining the same, the forms of embodiment and details of construction may be varied widely with respect to those described and illustrated, without thereby departing from the scope of the present invention.

Claims

1. Wire covered with a sheath of protective material for use, in particular, in the construction field and in products made of double-twist wire netting which are used in the water, geotechnical, and erosion-control fields, characterized in that the sheath (16) comprises cross-linked XLPE.

2. Wire according to Claim 1, characterized in that the sheath of protective material (16) comprises, at least in an outer layer (18) , an additive which can render it self- extinguishing in standard environmental conditions.

3. Wire according to Claim 1, characterized in that the sheath (16) adheres to the wire (12) .

4. Netting produced with covered wire of the type according to Claim 1.

5. Covered wire as described and illustrated and for the purposes specified.