Protective mesh for civil engineering works, comprising highly resistant metal wires with a protective coating

Abstract

The protective netting for civil engineering works is made of high-strength metal wire with a protective plastic coating, and is of the double-strand or triple-strand type with a hexagonal mesh. The wire is steel wire with a tensile strength of 550 to 1350 MPa.

Description

[Technical Field]

[0001] The present invention relates to the field of civil engineering works for containment and protection, for example the construction of protective barriers against rock falls and avalanches, surface protection of rock walls to contain rock spalling, three-dimensional stabilization of soils, cliffs, river banks, embankments, tunnels and road constructions, the construction of containment walls, protection of embankments of water bodies, the construction of dams and other rock protection barriers along rivers, streams and general water works, the construction of gabions and other products made of metal mesh and other applications of commonly known civil engineering typologies.

[0002] The present invention has been developed with particular emphasis on metal mesh for protection and containment, constructed by intertwining metal wires having a protective coating. [Background technology]

[0003] Many types of metal mesh for containment and protection are known, including, for example, open mesh, electrowelded mesh, and single-, double-, or triple-strand hexagonal mesh. Single-strand mesh refers to mesh in which adjacent wires are twisted together in a helical fashion, with each wire wrapped 180°, or half a turn, around the other wire. Double-strand mesh, sometimes referred to as triple-strand mesh, refers to mesh in which adjacent wires are twisted together in a single twist direction at each node of the mesh, with at least one and a half turns, or at least one and a half turns around the other wire. Compared to single-strand mesh, double-strand (or triple-strand or higher) mesh has the advantage that if one wire breaks, the entire mesh will not open and will maintain its containment. This is due to the inherent resistance of each node of the mesh, which is due to one wire twisted 360° or more around the other in a single direction of rotation.

[0004] Each type of mesh has a specific purpose, usually depending on the technical characteristics of the metal wires that make it up and the type of arrangement of those wires. Thus, for example, electrowelded mesh usually consists of several longitudinal and transverse wires, welded together at their intersections to form a woven fabric with a square and / or rectangular mesh. Electrowelded mesh can be made of metal wires as small as 12 mm in diameter, which gives it excellent mechanical resistance to stress.

[0005] For example, in the field of enclosures, such as gardens, mesh is known, typically consisting of a single strand of metal wire protected by a plastic coating. This type of mesh does not need to support large loads, and both the wire material and the plastic coating have very low resistance, both in terms of mechanical strength and corrosion resistance. In fact, replacing rusted sections of an enclosure is often less expensive than using high-quality materials to construct the enclosure. The field addressed by this invention is entirely different, and is aimed at geological construction applications, which require completely different levels of mechanical performance, corrosion resistance, and abrasion resistance, on an order of magnitude higher. For this reason, the technology used in the field of enclosure mesh is not relevant to the present invention and will not be considered.

[0006] An example of a protective net for geological structures is a net made up of a plurality of intersecting steel wires or cables arranged at angles, preferably perpendicular, to one another. The cables may have a diameter of 10-12 mm and are secured to one another at their intersections by various types of connectors, the most common of which comprises a pair of steel wires wound very tightly around said intersections. These nets have excellent stress resistance and, at the same time, sufficient flexibility to absorb the energy of impact-bearing objects, e.g., stones, rocks, etc. An example of this type of net is shown and described in European Patent No. 0940503 by the same applicant.

[0007] Another type of metal mesh is one made up of intertwined metal wires twisted around each other multiple times. Known double-strand (sometimes called triple-strand) metal meshes belong to this category, with the wires twisted unidirectionally at each node at least 1.5 times, clockwise or counterclockwise, to form a typically hexagonal mesh. These meshes can be used as is if reinforced with stronger ropes or wires, as described in WO 2005 / 038143, WO 2011 / 030316, and WO 2018 / 146516 by the same applicant. In other cases, these meshes are used to construct protective or containment products, such as gabions made of metal mesh, or soil compaction structures, such as the product known by the trade name Terramesh® from Officine Maccaferrii Societa Per Atzioni.

[0008] As mentioned above, each known type of mesh is particularly suited for use under certain conditions. However, in some cases, using the appropriate type of mesh can be inconvenient, highly disadvantageous, and very expensive. For example, installing an electric welding protective mesh with excellent stress-resistance properties can be complicated and expensive due to transportation difficulties, very uneconomical due to the cost of the construction materials, and difficult to install due to its hardness.

[0009] WO 1999 / 043894 describes a metal mesh for preventing rock falls or consolidating soil layers, formed by twisting together corrosion-resistant wires. The wires of the mesh are twisted together in a single strand and made of high-strength steel in the range of 1000-2000 MPa (or N / mm²), of the type used for metal ropes and springs.

[0010] This type of mesh has the main drawback of being very hard and difficult to manufacture due to the high strength of the metal wires that make it up. In fact, in the protective meshes used in the field of the present invention, it is not possible to make the metal wires smaller than a certain diameter, because this would, of course, compromise the overall resistance of the mesh, which is of paramount importance in geological construction projects. Furthermore, although the metal wires are corrosion-resistant due to the inherent properties of high-resistance stainless steel, this does not prevent the wires from rusting over time as a result of the corrosive environment and atmospheric and environmental factors to which these meshes are exposed during typical on-site installations.

[0011] WO 2019 / 239220 describes a double-stranded protective metal mesh for embankments, with hexagonal meshes, each with a width-to-length ratio of less than 0.75. The metal wires are made of high-carbon steel and have a stress resistance in the range of 1500-1900 MPa. It also describes that the metal wires may have a zinc / aluminum anticorrosion coating in an amount of at least 150 g / m².

[0012] This mesh also has the above-mentioned problem of being difficult to manufacture as a result of the high-strength metal wires, which in any case need to be of sufficient diameter (not shown in WO 2019 / 239220) to give the mesh sufficient overall resistance in geological construction projects. Another problem is that the steel wires used have limited protection against corrosion, so much so that the possibility of coating the highly resistant wires with a zinc / aluminium alloy, for example of the type commercially known as Galfan®, has been described.

[0013] However, known coatings of metal wires based on zinc or zinc and aluminum are not optimal under many conditions of use for protective and containment nets, and solutions in which metal wires are coated with plastics are often preferred over these coatings, such as the polymer coating known under the trade name Polimaq® from Officine Maccaferri Société des Acciones. This type of polymer coating, and more generally plastic coatings, is certainly preferable to zinc or zinc / aluminum coatings, but to date they have only been used in the field of the present invention for wires with a low carbon content, typically with a tensile strength of 350 MPa.

[0014] WO2022 / 152697 discloses a hexagonal mesh type steel wire netting for use in civil engineering works, which is made of metal wires having high strength and a tensile strength of at least 1560 MPa, and which may have a protective plastic coating.

[0015] A technical challenge faced by applicants in using metal wires having strengths greater than 350 MPa coated with a protective polymer layer to manufacture double-stranded metal mesh is the tendency of the plastic coating to crack at the twisted joints where the metal wires are twisted over one another, creating discontinuities in the protective coating and locations where corrosion of the underlying metal wires can begin.

[0016] The behavior of the plastic coating is greatly influenced by the radius of curvature of the wire when it is twisted around another wire. For example, a 2.2 mm diameter wire with a tensile strength of 750 MPa typically has a final mechanical resistance of about 2,850 N, which is practically equivalent to a 2.7 mm diameter wire with a tensile strength of 500 MPa. The radius of curvature of a smaller diameter wire increases the mechanical stress on the wire itself during the double twisting process. This obstacle has therefore made it difficult to use thinner, more resistant wires with the same strength that are covered with a protective plastic layer.

[0017] On the other hand, if it were desired to increase the overall strength of the metal mesh using known steel wires with a lower carbon content and covered with a protective polymer layer, the diameter of the metal wires would have to be increased, which would have the adverse effect of increasing the weight per unit area of ​​the mesh and the amount of plastic material to be coated, and in any case would make the twisting of the double-stranded wires more difficult or impossible.

[0018] Therefore, there is a recognized need in the art to provide a protective mesh that has high overall strength, is relatively lightweight, is well twisted, and has wires protected by a protective plastic, particularly polymeric, layer that will not crumble, crack or fail, particularly in the area of ​​the twisting zone where the wires are twisted together. Summary of the Invention

[0019] The object of the present invention is to overcome the drawbacks and solve the problems of the prior art by providing a protective netting that has a high overall strength, is relatively light, is well twisted, and the wires are completely and reliably protected by a protective plastic, in particular polymeric, layer that does not crumble, crack or fail, especially in the area of ​​the twisting zone where the wires are twisted together.

[0020] Another object of the present invention is to provide a double-stranded protective and containment net made of wires of a metal with a high carbon content and covered with a protective plastic layer, in particular a polymer layer, that is resistant to atmospheric agents.

[0021] Another object of the present invention is to provide a protective net of the type described above by a fast, safe and economical method which can be carried out on known types of machines and installations for manufacturing double-twisted nets, without excessively costly modifications.

[0022] These and other objects are achieved by a protective and containment net and a method for its manufacture having the features set out in the following claims.

[0023] In one aspect, protective netting is described for civil engineering works, in particular for containment and protection, such as building protective barriers against rock falls and avalanches, surface protection of rock walls to contain rock spalling, three-dimensional stabilization of soils, cliffs, river banks, embankments, tunnels and road constructions, building containment walls, protecting the banks of water bodies, building dams and other rock protection barriers along rivers, streams and water facilities in general, building gabions and other products made of metal mesh, and other uses of commonly known civil engineering typologies.

[0024] Double-stranded or triple-stranded protective netting is manufactured in whole or in part by twisting together high-strength metal wires coated with a protective plastic coating. The protective plastic coating can be extruded onto the metal wires using extrusion techniques commonly known in the art. The metal wires can be steel wires with a tensile strength of 550 to 1350 MPa, more preferably 550 to 1000 MPa, and even more preferably 600 to 800 MPa.

[0025] It is particularly advantageous to define the thickness of the plastic coating in the range of 0.3 to 0.6 mm, more preferably in the range of 0.5 to 0.55 mm.

[0026] Furthermore, it is particularly advantageous to provide that the diameter of the metal wire does not exceed 4 mm, more preferably not exceed 3 mm.

[0027] The plastic coating of the metal wire can be comprised in the group consisting of PE (polyethylene), PVC (polyvinyl chloride), PA (polyamide). Preferably, the plastic coating is made of PE, in particular HDPE.

[0028] Also described is a method for manufacturing the protective netting described above, Providing a plurality of metal wires having a protective plastic coating and a tensile strength of 550-1350 MPa; - twisting the coated wires of the metal together to produce a netting comprising a mesh with single, double or triple twisted sections between the wires; Includes.

[0029] To improve the adhesion of the plastic coating to the metal wire, the following techniques can be used, alone or in combination, for example, heat treating the wire such as heating the wire before extrusion, increasing the contact surface area by knurling or other systems, controlling how the plastic material cools, increasing the pressure with which the plastic material is applied to the substrate, using various types of primers / adhesives both before and during extrusion, both hot and cold, cleaning the wire by mechanical processes, chemical processes, or lasers, etc., fusion or thermal bonding extrusion processes, and other techniques to improve adhesion.

[0030] One particularly promising approach is to coat the wire with two different polymer layers, for example, by coextrusion, either alone or in combination with one of the wire-applied methods mentioned above, such as wire heating or knurling. A particularly effective solution is to coat the wire with a high-performance first polymer layer and then with a low-cost second polymer layer. The high-performance first polymer layer can be selected to exhibit excellent adhesion properties to the wire while also providing an excellent adhesive base for the outermost second polymer layer, which confers abrasion resistance and UV resistance.

[0031] According to certain embodiments, the plastic protective coating can include an innermost first polymer layer directly coating the wire and having a first thickness. An outermost second polymer layer coats the first polymer layer and has a second thickness greater than the first thickness of the first polymer layer. The first polymer layer directly coating the wire can be polyethylene (PE) mixed with an additive to enhance adhesion of the metal to the wire. The first polymer layer coating the wire can be very thin, for example, 0.1 mm or less. The second polymer layer overlying the first polymer layer can be high-density polyethylene (HDPE), which is less expensive than the polymer forming the first layer. The second polymer layer can be thicker than the first layer, for example, 0.4 mm, resulting in a total coating polymer layer on the wire of 0.5 mm, combined with the 0.1 mm first polymer layer. Of course, the sizes shown are exemplary and can be appropriately selected by a skilled artisan based on the wire diameter required to meet the mechanical strength specifications of the wire mesh while balancing the strength properties of the wire's plastic coating and overall cost.

[0032] In fact, it has been surprisingly found that, contrary to what might seem at first sight, improving the adhesive properties of the plastic coating on the metal wire makes it possible to improve the resistance of the plastic coating in the process of twisting the plastic-coated wire when twisting between two wires occurs, especially when this twisting is multiple, for example in the case of a double-twisted hexagonal mesh. Conversely, if the plastic coating were able to slide on the plastic wire, it would be expected that the forces exerted on the plastic-coated wire during double twisting would be released mainly towards the plastic coating, which behaves like a sliding sheath, and would therefore be likely to break or crack, especially in the area of ​​twisting with the other wire.

[0033] Furthermore, it has been discovered that by improving the adhesion of the plastic coating to the metal wire, it is possible to use steel with a tensile strength of 550-1350 MPa and relatively thin metal wires with diameters of 4 mm or less, more preferably 3 mm or less, to achieve comparable mesh durability. This also allows the plastic coating to be kept in the range of 0.3-0.6 mm, more preferably 0.5-0.55 mm. This means that larger plastic-coated wires, which can be advantageously used to achieve the predetermined objectives of the present invention, can be made from metal wires with a diameter of 4 mm to which a 1.1 mm plastic coating is applied, resulting in a maximum total diameter of the plastic-coated wire of 5.1 mm, and can be processed without any special modifications on known machines for twisting meshes, particularly machines for producing double-twisted meshes with hexagonal meshes. [Brief explanation of the drawings]

[0034] Further features and advantages will be apparent from the following detailed description of preferred embodiments, given by way of non-limiting example with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 is a front view of a portion of a double-stranded mesh made of multiple metal wires covered with a protective layer of plastic material. [Figure 2] 2 is a schematic perspective view of a portion of a metal wire covered with a protective layer of plastic material and used to manufacture the mesh of FIG. 1; FIG. DETAILED DESCRIPTION OF THE INVENTION

[0035] In the following embodiments, features for implementing the present invention are described. The described features can be combined with each other in various ways and are not necessarily limited to the exact embodiments to which the drawings and related descriptions refer. In other words, by reading the following description, those skilled in the art will understand how to obtain items of information useful for knowing how to implement one or more of the described features in combination with one or more of the other described features, without any description, paragraph, term, or specific description of the drawings limiting the possibility of combining one or more of the described and illustrated features separately with any one or more of the other described and illustrated features. More specifically, in this specification, any combination of any two explicitly described features should be understood to be explicitly described, taking into account the ability and knowledge of a person skilled in the art who understands the possibility of functionally combining the features without the need for functionally applying other distinct features, even if the features are individually extracted from a specific context in which they can be juxtaposed or combined with other distinct features. Unless otherwise specified, each and every element, member, means, system, component, or object described and illustrated herein is to be understood as being described individually, autonomously variable, and separable / combinable with any and every other element, member, means, system, component, or object described and illustrated. The materials, shapes, and functions described and illustrated are not intended to limit the invention, but are presented solely to enable those skilled in the art to understand and practice the invention according to preferred, non-exclusive embodiments.

[0036] 1, there is shown a double-twist, sometimes referred to as triple-twist, protective and containment netting 10 in which one wire is twisted in one direction over the other at the nodes at least 1.5 times. The present invention is not limited to this particular type of netting, which is provided as a non-limiting example only, but it has been found that the use of this invention with this particular type of netting is particularly effective as a result of the inherent difficulties in practicing the invention using known technology. The protective mesh illustrated in Figure 1 is particularly suitable for use in civil engineering works for containment and protection, where the important properties of mechanical strength and resistance to corrosion and abrasion are required, such as the construction of protective barriers against rock falls and avalanches, the surface protection of rock walls to contain rock spalling, the three-dimensional stabilization of soils, cliffs, river banks, embankments, tunnels and road constructions, the construction of containment walls, the protection of embankments of water bodies, the construction of dams and other rock protection barriers along rivers, streams and waterworks in general, the construction of gabions and other products made of metal mesh and any other application of the commonly known civil engineering typology.

[0037] The mesh 10 is constructed wholly or partially by twisting together a plurality of plastic-coated metal wires 12, i.e., as can be seen diagrammatically in FIG. 2, each wire 12 has a metal core 16 and an integral plastic coating 18, i.e., the plastic coating 18 covers the entire wire 12, and thus the mesh 10, without any interruptions in continuity throughout the entire wire 12.

[0038] In the double-twisted network 10, each wire 12 extends in a generally longitudinal direction, perpendicular to the plane of FIG. 1. Focusing on a particular wire 12a, it can be seen that it is alternately double-twisted with two adjacent wires 12b, 12c to form a double-twisted node 14, where the wires 12a, 12b or pair of wires 12a, 12c are wound 1.5 times in a clockwise or counterclockwise direction at each node, respectively.

[0039] The metal core 16 of the plastic coated metal wire 12 is made from a high carbon content steel, typically in the range of 550-1350 MPa, preferably in the range of 550-1000 MPa, and more preferably in the range of 600-800 MPa.

[0040] To maintain sufficient flexibility of the metal wire, its diameter is preferably less than 3 mm, although the use of wires with larger diameters, for example up to 4 mm, is not excluded, as in this case the tensile strength would be close to the lower limit indicated above, about 550-600 MPa. In any case, it is also possible to exceed the upper limit indicated as 4 mm, but in this case the material savings and the environmental improvements would be less significant and less advantageous than when using wires with smaller diameters.

[0041] The metal wire is covered with a protective layer of plastic, e.g., polymeric material. Examples of coating materials include, but are not limited to, PE, PVC, or PA. PA offers excellent hardness characteristics, while PE is preferred for cost reasons. The ideal thickness of the plastic coating on the wire 12 has been found to be in the range of 0.3-0.6 mm, preferably 0.5-0.55 mm. However, it is not excluded that thinner or thicker plastic coatings than those shown may be produced naturally, even if the benefits of a thickness sufficient to ensure adequate protection and durability over time, on the one hand, and the benefits of saving on protective plastic material and environmental considerations, on the other hand, are significantly reduced.

[0042] One embodiment provides for the production of double-twisted mesh using wires plastic-coated with a PA coating. This double-twisted hexagonal mesh can provide a mesh with dimensions conventionally designated 8x10, a wire with a metal core diameter of 2.20 mm, and a tensile strength of 550 MPa. Production tests performed on such mesh have shown that the polymer coating does not break or crack when the wires are twisted in the machine.

[0043] Another example is the application of a more economical protective coating, such as that made of PE, to a double-twisted wire mesh, as shown above. In this case, it would be advantageous to improve the adhesion of the plastic coating to the metal substrate in order to improve its behavior when subjected to mechanical forces, such as those exerted by twisting the wire in a machine. Naturally, improving the adhesion of the plastic coating to the metal substrate also benefits the performance level when using a plastic coating with a better performance level, such as the PA coating mentioned above.

[0044] Another preferred embodiment is to use a protective coating formed of two or more layers of different materials, e.g., different polymers or polymers with different properties. A particular embodiment involves coating the wire with two layers of polymer, for example, by coextrusion, where the first polymer layer directly coats the wire and is a high-performance polymer, followed by a second, less expensive polymer layer that provides abrasion resistance and UV resistance to the coating. The high-performance first polymer layer can be selected to exhibit excellent adhesion properties to the wire while also providing an excellent substrate to which the outermost second polymer layer, which provides abrasion resistance and UV resistance, can adhere.

[0045] The first polymer layer, which directly coats the wire, can be polyethylene (PE) mixed with an additive to enhance adhesion to the wire. The second polymer layer, which overlaps the first polymer layer, can be, for example, high-density polyethylene (HDPE), which is less expensive than the polymer forming the first layer. For example, if a 0.5 mm thick plastic coating is desired, the first polymer layer can be relatively thin, such as up to 0.1 mm. The second polymer layer can then be thicker than the first layer, such as up to 0.4 mm, resulting in a total polymer layer coating the wire that is 0.5 mm thick. Of course, the dimensions shown are merely exemplary, and a skilled engineer can appropriately select the appropriate dimensions based on the wire diameter required to meet the mechanical strength specifications of the wire mesh while balancing the strength characteristics of the plastic coating on the wire with overall cost.

[0046] Various techniques can be used, alone or in combination, to improve the adhesion of plastic coatings to metal substrates, such as heat treating the wire, such as heating the wire before extrusion, increasing the contact surface area with knurling or other systems, controlling how the plastic material cools, increasing the pressure with which the plastic material is applied to the substrate, using various types of primers / adhesives both hot and cold, both before and during extrusion, cleaning the wire with mechanical, chemical, or laser processes, fusion or thermal bonding extrusion processes, and other techniques to improve adhesion.

[0047] If it is anticipated that the wire will be coated with two different layers of different polymers, known co-extrusion techniques can be used. Alternatively, a mixed process can be used in which a first polymer layer is deposited on the wire by melt bed or melt splicing, and a second, outermost polymer layer can be extruded to cover the first polymer layer.

[0048] These techniques improve the mechanical behavior of the wire's plastic coating, enabling the production of double-twisted mesh with strengths exceeding 550 MPa for the same wire diameter, while also achieving environmentally favorable results by reducing the amount of material used, both metal and plastic. Such mesh is also lighter due to the use of smaller diameter wire, and can therefore be more easily and cost-effectively transported to the installation site. When mesh sheets must be manually installed over large areas, for example, for surface protection or soil and embankment compaction, reduced installation force is required.

[0049] Naturally, the principles of the invention will remain the same and the details of the form and construction of the embodiments may vary widely from those described and illustrated without departing from the scope of the invention.

Claims

1. A protective net for civil engineering works, made of high-strength metal wires with a protective plastic coating, said protective net being of double-strand or triple-strand type with a hexagonal mesh, said wires being steel wires with a tensile strength of 550-1350 MPa.

2. 2. A protective net according to claim 1, wherein the tensile strength of the wires of steel is in the range of 550 to 1000 MPa, preferably in the range of 600 to 800 MPa.

3. 3. Protective netting according to claim 1 or 2, wherein the protective plastic coating has a thickness in the range of 0.3 to 0.6 mm, preferably 0.5 to 0.55 mm.

4. A protective net according to any one of claims 1 to 3, wherein the wires of metal have a diameter of less than 4 mm, preferably less than 3 mm.

5. A protective netting according to any one of claims 1 to 4, wherein the protective plastic coating is a coating selected from PE, PVC and PA.

6. A protective netting according to any one of claims 1 to 5, wherein the protective plastic coating comprises at least two polymer layers having different properties.

7. 7. The protective netting of claim 6, wherein the protective plastic coating comprises an innermost first polymer layer having a first thickness directly overlying the metal wires, and an outermost second polymer layer having a second thickness overlying the first polymer layer and greater than the first thickness of the first polymer layer.

8. A method for manufacturing a protective net according to any one of claims 1 to 6, comprising the steps of: Providing a plurality of metal wires having a protective plastic coating and a tensile strength of 550-1350 MPa; - twisting the wires of coated metal together to produce a net with a hexagonal mesh having double or triple twists between the wires; A method comprising:

9. 9. The method of claim 8, wherein the wires of metal are covered with a plastic material included in the group of PE, PVC and PA.

10. 10. The method of claim 9, wherein the wire of metal is coated with PE.

11. The method of any one of claims 8 to 10, wherein the protective plastic coating comprises at least two polymers having different properties from each other.

12. The method of claim 11 , wherein the wire is coated with at least two polymer layers using a co-extrusion process.

13. 13. The method of claim 11 or 12, wherein the innermost thinner first polymer layer is made from a PE polymer containing an additive that promotes adhesion to the wire, and the outermost thicker second polymer layer is made from an HDPE polymer.

14. 14. The method according to any of claims 8 to 13, wherein the adhesion of the plastic coating to the wire of metal is improved by a technique or combination of techniques selected from the group of: heat treatment of the wire such as heating the wire before extrusion, increasing the contact surface area by knurling or other systems, controlling how the plastic material cools, increasing the pressure with which the plastic material is applied to the support, using different types of primers / adhesives both before and during extrusion, both hot and cold, cleaning the wire, melt bonding or thermal bonding extrusion processes.

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