WO2010094570A1

WO2010094570A1 - Aquaculture net with cleaned metal wires

Info

Publication number: WO2010094570A1
Application number: PCT/EP2010/051329
Authority: WO
Inventors: Xavier Amils; Charles Coffin
Original assignee: Bekaert NV SA
Current assignee: Bekaert NV SA
Priority date: 2009-02-19
Filing date: 2010-02-04
Publication date: 2010-08-26
Anticipated expiration: 2011-08-19

Abstract

An aquaculture net (10) is provided comprising metal wires(12). The wire surface is cleaned to such an extent that the wires have anti-fouling properties. Sufficient cleaning means that the carbon content on the surface of the metal wires (12) is less than 20 ppm.

Description

AQUACULTURE NET WITH CLEANED METAL WIRES

Technical Field

[0001] The invention relates to an aquaculture net with metal wires.

Background Art

[0002] Aquaculture nets or fish-farming nets are used to raise aquatic life such as fish. The aquaculture net keeps the aquatic life controlled and contained and protects the aquatic life inside the net against predators such as sharks and sea wolfs.

[0003] The aquaculture nets are usually of the chain-link fence type. This is a fence of metal wires woven into a diamond pattern. The meshes have a dimension that is smaller than the dimension of the fish contained in the nets. Each metal wire is preformed by bending so that it exhibits a wavy pattern with maxima and minima. The maxima of a metal wire interlock with the minima of a neighbouring wire to form the patterns of a series of diamonds. An embodiment of an aquaculture net has been disclosed in WO-A1 -2007/031352.

[0004] Other aquaculture nets in the form of welded structures also exist.

[0005] Experience has shown, however, that aquaculture nets whether of the chain-link fence type or not also have some disadvantages. Aquaculture nets have been discovered where fouling is a big problem.

[0006] In addition, aquaculture nets have been discovered where one or more of the metal wires were broken after a limited life time. Investigation of the failing aquaculture nets revealed that particularly the upper metal wires in the aquaculture net were broken. Indeed, the ocean or the sea forms a huge challenge with respect to corrosion-resistance. In addition to this highly corroding environment, the waves and tidings subject the aquaculture net to a continuous and repeated movement. In an aquaculture net of the chain-link fence type, each metal wire must carry the weight of the rest of the net below it. The upper wire makes point contacts with the wire just below it. These point contacts are located at a point where both the upper wire and the wire just below it are subjected to both a bending and a torsion deformation. The continuous and repeated imposed movements in this aggressive environment create fretting at the point contacts and may result in breaking the wires of the net. [0007] Aquaculture nets with galvanized wires offer an acceptable resistance against bio-fouling, i.e. against fouling material that may grow on the mesh structure. Within the context of the present invention, the terms fouling material refer to fouling organisms such as barnacles, algae or molluscs, which may attach and grow to the wire material of the mesh structure. However, this fouling mechanism may be so persistent that entire openings in the meshes may be filled blocking any introduction of fresh water or nutrition into the volume inside the mesh structure, even with galvanized wires. Once fouling material can start growing on the wire surfaces, it is difficult to prevent it from further growing.

[0008] Therefore, there is a need for aquaculture nets with both better anti-fouling and anti-corrosion properties. It does not suffice to prevent fouling. In addition, the aquaculture net must have an acceptable life time.

[0009] JP-A-2004-261023 discloses a steel wire for aquaculture nets. The steel wire has a stainless steel core and a metal coating of cupronickel: a copper nickel alloy with nickel content ranging between 10 % and 30 % by weight. The metal coating can be applied either by hot dipping the stainless steel core in a copper nickel bath or by plating the stainless steel core with copper, thereafter with nickel and finally applying a thermal diffusion treatment.

Disclosure of Invention

[0010] It is an object of the present invention to avoid the drawbacks of the prior art.

[0011] It is a further object of the present invention to further improve the anti- fouling properties of aquaculture nets.

[0012] According to the present invention, there is provided an aquaculture net comprising metal wires, the surface of which is cleaned thoroughly. Indeed, it has been the experience that any remaining soap material on the surface of the wire may be a good basis for growth of fouling material, so while the soap is needed for the upstream processing of the wire the soap must be avoided on the final wire as much as possible. The amount of carbon which is part of the soap is a good indication of the amount of soap remaining on the surface of a wire. The amount of soap is to be minimized and so is the amount of carbon (as part of the soap). It has been the experience of the inventors that the cleaning must be such that the remaining C content on the surface of said metal wires is less than 20 ppm, e.g. less than 15 ppm, e.g. between 5 ppm and 10 ppm. Suitable cleaning can be done by dipping the wires in an acid or alkaline bath or by spraying acid or alkaline solutions to the wires.

[0013] In order to avoid confusion, the amount of carbon as part of the soap on the surface of the metal wires must be distinguished from carbon in the metal composition, if any.

[0014] In a particular embodiment the wires may comprise copper or a copper alloy, whereby copper oxide (CuO and / or CU2O) is present at the surface in an amount sufficient to have anti-fouling properties, i.e. to prevent or at least to delay the growth of fouling material in comparison with a surface of metallic copper. Experience and tests have shown that CuO and CU2O are very effective anti-fouling material.

[0015] The surface copper oxide layer may comprise both Cu⁺ and Cu²⁺.

Experiments have shown that sufficient amounts for anti-fouling properties mean that the surface oxide layer has a thickness varying from 10 nm to 300 nm, e.g. from 20 nm to 200 nm, e.g. between 50 nm and 150 nm.

[0016] Existing copper alloy wire surfaces may have some unavoidable traces of copper oxide at the surface before putting these wires in a marine environment. However, these traces do not provide a sufficient amount to delay fouling from the beginning. Copper oxides may start to grow when putting these wires in the ocean or the sea. However, this growth takes time. During this slow growth fouling material looks for basis on those spots of the wire surface where oxides are not yet present. As mentioned, once fouling material has found sound basis, fouling is difficult to stop.

[0017] In a preferred embodiment said copper alloy is a copper nickel alloy.

[0018] In one particular embodiment said copper alloy is CuNi_xFe_y whereby x is 9, 10 or 11 or 30 and y is 1. In another embodiment said metal coating is CuNiχSn_y whereby x is 8, 9, 10 or 11 and y is 1 , 2 or 3, or 15. Herein x and y are weight percentages. In a preferred embodiment said metal coating is CuNiioFeis or CuNigSn2 These two types of copper alloys have the advantage that they are hardening during annealing resulting in a metal wire with an increase abrasion resistance.

[0019] In a further preferable embodiment the copper nickel alloy comprises at least 80 per cent by weight copper and between 5 per cent by weight and 15 per cent by weight nickel.

[0020] In another embodiment NiO is present at the surface of the steel wire in an amount further delaying the growth of fouling material on the surface of the steel wires.

[0021] In a further embodiment an aquaculture net is provided wherein said metal wires have a steel core and a copper or copper alloy coating on and around the steel core. The steel core may be a stainless steel core or a carbon steel core.

[0022] In another embodiment an aquaculture net is provided wherein said metal wires comprise at least 10% combined Cu+ and Cu²+, preferably 15% Cu²+ and 85 % Cu and Cu+. Brief Description of Figures in the Drawings

[0023] Figure 1 shows an aquaculture net overgrown with bio-fouling material.

[0024] Figure 2 shows a cross-section of a metal wire having a steel core and a metal coating. [0025] Figure 3 shows a cross-section of a bulk metal wire.

Mode(s) for Carrying Out the Invention

[0026] Figure 1 shows an aquaculture net 10 whereby the metal wires 12 of the mesh structure are overgrown with bio-fouling organisms 13, such as barnacles, algae or molluscs that attach to the net. The fouling mechanism may be so persistent that entire openings in the meshes may be filled blocking any introduction of fresh water or nutrition into the volume inside the mesh structure.

[0027] Figure 2 shows a cross-section of a metal wire 12 according to the invention. A metal coating 16 is applied, e.g. by means of welding or by means of electroplating or by means of thermo-diffusion to a steel core 14.

[0028] Figure 3 shows show a cross-section of a bulk metal wire 18 entirely made of copper or of a copper alloy.

[0029] The aquaculture net according to the present invention is preferably manufactured from metal wires 12 where a metal coating 16 is applied to a steel core 14, e.g. a stainless steel core. The coating comprises copper or a copper alloy. Due to the higher tensile strength of stainless steel, coated stainless steel wires are much lighter in weight than e.g. bulk CuNi wires.

[0030] The metal coating may be applied either by hot dipping the stainless steel core in a copper or copper alloy bath or by plating the stainless steel core with copper or copper alloy, and/or applying a thermal diffusion treatment. Preferably, however, the metal coating is welded on or around the steel core wire. This steel core with a welded metal coating may then be further drawn to a final diameter. [0031] Preferably the steel core according to the invention is a hard drawn steel wire. Hard drawn steel increases the tensile strength and anti-corrosion properties of steel wires used in aquaculture nets.

[0032] Regarding the coating material, copper nickel coatings have proven to provide a good resistance against corrosion because of the nickel, and an acceptable resistance against fouling because of the effect of copper. CuNi is also very efficient against corrosion. The present invention, however, further increases the anti-fouling behaviour.

[0033] Example Cleaning, pre-oxidizing and continuous thermal treatment

[0034] A strip of CuNi with 10% of nickel has been clad around a hard-drawn 304 F stainless steel wire. The thus coated stainless steel wire has been hard drawn until a final diameter. The hard drawn coated stainless steel wire is then cleaned to remove soaps and / or BORAX^® (this is a natrium salt Na2B₄O7.10(HbO)), and or any drawing greases applied when drawing the wire. In one example, the amount of carbon content on the wire surface was 5,49 ppm, in another example the amount of carbon content on the wire surface as 13,62 ppm. Generally, a well cleaned wire has a carbon content on the surface which is less than 20 ppm, e.g. less than 15 ppm, e.g. between 5 ppm and 10 ppm.

Next to this cleaning or simultaneously to this cleaning, the coated wire is pre-oxidized to a certain degree.

[0035] Simultaneous cleaning and pre-oxidation can be done e.g. in a solution of NaCIO. Other suitable alkaline or acid solutions such as HsPO₄, which may content surfactants, are possible.

[0036] This pre-oxidation continues - if already started - or starts - if not already started - in a continuous thermal treatment at about 400 to 500 °C. A layer of a mixture of CU2O and CuO is forming on the surface. A minimum thickness of the layer is 20 nm.

[0037] The tensile strength of the wires was 620 MPa and the hardness of the CuNi coating was 132 HVN. [0038] The final treated wire may have a reddish surface which is due to the large amount of CU2O on the surface. [0039] The mesh resulting from the thus treated wire has good anti-fouling properties.

Claims

1. An aquaculture net comprising metal wires, said wires have a surface which has been cleaned so that the carbon content which is part of the soap remaining on the surface of the metal wires, is less than 20 ppm, e.g. less than 15 ppm, e.g. between 5 ppm and 10 ppm.

2. An aquaculture net according to claim 1 wherein said surface of said metal wires is obtainable by means of a dip in an acid or alkaline solution.

3. An aquaculture net according to any one of the preceding claims, wherein said metal wires comprise copper or a copper alloy.

4. An aquaculture net according to claim 3, where said wires have a surface oxide layer comprising Cu⁺ and Cu²⁺

5. An aquaculture net according to claim 4, wherein said surface oxide layer has a thickness varying from 20 nm to 200 nm.

6. An aquaculture net according to any one of claims 3 to 5, wherein said copper alloy is a copper nickel alloy.

7. An aquaculture net according to claim 6, wherein NiO is also present at the surface.

8. An aquaculture net according to any one of the preceding claims, wherein said metal wires have a stainless steel or carbon steel core and a copper nickel alloy coating on said core.

9. An aquaculture net according to claim any one of claims 3 to 8, wherein said metal wires comprise at least 10% combined Cu+ and Cu²+, preferably 15% Cu²+ and 85 % Cu and Cu+ at their surfaces.

10. An aquaculture net according to claim 6, wherein said copper nickel alloy comprises at least 80 per cent by weight copper and between 5 and 15 per cent by weight nickel.