EP2803751A1 - Method for applying an anti-corrosion coating - Google Patents

Abstract

The present invention relates to a method for applying an anti-corrosion coating to components using an aluminum-zinc coating as an anti-corrosion coating, and wherein the anti-corrosion coating is applied by thermal spraying using an inert carrier gas with a reducing gas component for thermal spraying.

Description

The invention relates to a method for applying an anti-corrosion coating to components, wherein the anti-corrosion coating is at least partially formed as an aluminum-zinc coating; a use of a reducing gas-containing gas mixture for applying an anti-corrosion coating to components, and a use of an aluminum-zinc coating as part of an anti-corrosion coating for components.

State of the art

In a method of thermal spraying, spray particles are directed onto a workpiece by means of a carrier gas. On the workpiece, the spray particles form a coating. The spray particles adhere to the surface of the workpiece and to one another due to the kinetic energy and heat that they have on impacting the workpiece. Active corrosion protection by means of anti-corrosion coating of aluminum and / or zinc is the largest. Scope of thermal spraying. Of these materials, with increasing tendency, about 20,000 tons of wire are processed annually. For example, in the commercial offshore sector, the spray application of both materials, even in combination, is partly standard. In the field of offshore wind turbines, there is a special requirement to keep maintenance intervals as long as possible, which u.a. can be realized by the use of durable surface coatings. In the past, spray metallizations have been used on offshore wind turbines essentially on components which are subject to high mechanical stress, such as flanges, ribs, rivet holes, bolt holes and attachment surfaces, etc.

From the EP 1 674 590 A1 the use of a gas mixture for thermal spraying is known. In the process, spray material is melted in the course of arc spraying in an arc and atomized into spray particles in a carrier gas. In this case, a gas mixture is used as a carrier gas containing hydrogen. For example, the gas mixture contains 1 to 30% by volume of hydrogen. For this invention, hydrogen is used as a pure carrier gas to bind atmospheric oxygen.

The EP 2 186 593 A1 discloses a gas mixture comprising a mixture of argon, helium, nitrogen, carbon dioxide or hydrogen or mixtures thereof with a gaseous hydrocarbon under normal conditions. The gas mixture is used inter alia for thermal spraying and / or surface treatment by means of an arc. In this invention, the mixtures are each used as a pure carrier gas.

One problem of thermal spraying, however, is the influence of oxygen on the spray material. Due to high temperatures, the spray material is oxidized to a high degree in the presence of oxygen. Oxygen can reach the spray material either through the carrier gas, for which compressed air is often used, or through the ambient air swirling with the carrier gas. Depending on the energy present, the molten and atomized spray particles burn completely or the metal particles oxidize to metal oxides. The completely burned spray particles are no longer available for the coating, it is called burning. The burnup thus reduces the efficiency for the application of the spray material to the workpiece. The efficiency is defined as the ratio between the spray material forming the coating to the total molten spray material. In contrast, the metal oxides, together with the metallic spray particles, reach the workpiece and become part of the coating there.

However, with anti-corrosion coatings, these metal oxides result in degradation of the coating's durability in the presence of corrosive environmental conditions. To avoid this deterioration of the quality of the anti-corrosion coating, nitrogen can be used as a carrier gas. Nitrogen reduces the oxidation of the spray particles. However, oxidation is insufficiently suppressed by the use of nitrogen, and the coatings often do not meet the quality requirements.

The invention has for its object to apply an anti-corrosion coating on workpieces or components, with the highest possible efficiency for the application of the anti-corrosion coating is to be made possible and oxidation of the anti-corrosion coating by the process of applying the anti-corrosion coating should be prevented.

Disclosure of the invention

This object is achieved by a method for applying an anti-corrosion coating to components, a use of a gas mixture containing a reducing gas for applying an anti-corrosion coating to components, and a use of an aluminum-zinc coating as part of an anti-corrosion coating for components according to the independent claims. Advantageous embodiments will become apparent from the dependent claims and the description below.

For an inventive method, an aluminum-zinc coating is used at least as part of an anti-corrosion coating. This component of the anti-corrosion coating is applied by thermal spraying on the components, wherein for thermal spraying an inert carrier gas is used with a reducing gas component. This coating is also referred to below as "spray-metallized coating".

The term "components" are to be understood as meaning both individual components as components of larger systems or machines, as well as workpieces that are not (yet) installed in plants or machines and coated according to the invention in the course of their manufacturing process.

Advantages of the invention

In the context of the invention, the corrosion protection effect of various anti-corrosion coatings which were applied to components by different methods was investigated. In each case, aluminum-zinc coatings and aluminum coatings in different layer thicknesses and characteristics were applied to components using different methods and sealed on a case-by-case basis and provided with a multilayer organic coating system. The main objective was to produce an oxide-free anticorrosive coating that is superior in its effect to the layers oxidized by the process.

In the course of the invention, significant advantages of an aluminum-zinc coating were discovered as part of an anti-corrosion coating, which is applied by thermal spraying, wherein for thermal spraying an inert carrier gas is used with a reducing gas component.

In a corrosive attack, the aluminum-zinc coating goes into solution and protects the underlying material of the component, such as iron. The electrochemical potential of an aluminum-zinc coating thermally sprayed with the reducing gas component is higher than that of an aluminum-zinc coating thermally sprayed without a reducing gas component, for example under conventional air. The corrosion protection effect of the aluminum-zinc coating thermally sprayed with the reducing gas component is based on a combination of the cathodic protection of the aluminum-rich phases, a selective corrosion of the zinc associated with the formation of voluminous corrosion products (aluminum hydroxides and zinc hydroxides). These deposit in the pores, which increases the tightness of the coating. In a corrosive attack, the aluminum atoms in the outermost molecular layer are first oxidized because of their zinc-double affinity for oxygen. A zinc oxide does not start at this time. It forms aluminum oxides, which are surrounded by zinc atoms. When this is done with all the aluminum atoms in the first molecule layer, zinc oxide is also formed, which is easily soluble and "flushed" out of the surface. What remains is a firmly adhering, dense and very stable aluminum oxide layer that protects the underlying aluminum-zinc coating. In addition, cathodic action can be realized across gaps in the injured aluminum-zinc coating.

A prerequisite for the occurrence of these anti-corrosive properties is that the applied aluminum-zinc coating is not already oxidized by the process of application and that the oxide can form on the surface to achieve its full effect. at Methods of applying the aluminum-zinc coating without reducing gas component, for example with air, each particle is already oxidized before impacting the component. Aluminum-zinc coatings thermally sprayed with the reducing gas component form very pure aluminum-zinc coatings with a low oxide content.

Parameters of the thermal spraying determine to a greater extent the properties of the aluminum-zinc coating. The choice of the nozzle system, as well as parameters such as voltage, current or the type of carrier gas influence the spray particles in the detachment of electrodes and in their flight phase and thereby the aluminum-zinc coating formed therefrom. Finely atomised melt droplets mean at the same time a large specific surface and thus the promotion of the oxide content in the aluminum-zinc coating. This oxidation can be significantly reduced by using inert carrier gases with a reducing gas component.

Advantageously, a second coating, in particular one or more color layers, is applied via the aluminum-zinc coating. Thus, a corrosion protection system is produced from at least two layers. The aluminum-zinc coating according to the invention forms the first layer, a so-called primer. The second coating forms the second layer. The resistance of the corrosion protection can be further increased by the interaction of the first anti-corrosion coating and the second coating. The adhesion of the second coating is significantly improved by the presence of the anti-corrosion coating of the present invention, firstly compared to a "second" coating without an underlying anti-corrosion coating and secondly compared to an anti-corrosion coating which was not thermally sprayed with the reducing gas component.

The first layer "heals" by flowing damage, such as cracks. The second layer limits this flow of the first layer so that this "healing" can take place and the loss of material from the first layer is limited by the flow.

In the present invention, therefore, an anticorrosive coating containing an injection-metallized layer, applied to workpieces or components, which is in particular carried out so (process) technically that on this injection-metallized anticorrosive coating more (color) layers in downstream or upstream process steps be / were applied, so that from the interaction of spray-metallized layer and the other (color) layers, a high quality corrosion protection for the so coated workpieces or components results, which withstands the most challenging corrosive media and environmental conditions. For the application of the injection-metallized layer, the highest possible efficiency for application by the invention is made possible, and an oxidation of the anti-corrosion coating by the process of applying the anti-corrosion coating is prevented according to the invention.

Preferably, hydrogen is used as the reducing gas component. Further advantageously, nitrogen is used as the carrier gas. Particularly preferably, a hydrogen-nitrogen mixture is used. The proportion of the reducing gas component in the gas mixture is preferably between 0.1 and 10%, in particular between 2 and 4%.

Also a use of in the EP 1 674 590 A1 By the same applicant disclosed gas mixture containing hydrogen is conceivable. In that regard, reference is expressly made to this document with respect to the corresponding disclosure. In particular, such a gas mixture containing 3 to 7 vol.% Hydrogen, is suitable for a method according to the invention. However, in this invention, hydrogen has been used merely as a carrier gas to bind atmospheric oxygen (eg, from ambient air).

Also, a gas mixture according to the EP 2 186 593 A1 , also from the same applicant, is conceivable. In that regard, reference is expressly made to this document with respect to the corresponding disclosure. Such a gas mixture comprises a mixture of argon, helium, nitrogen, carbon dioxide or hydrogen or mixtures thereof with a gaseous hydrocarbon under normal conditions. In particular, this gas mixture contains doping amounts of NO and / or NO ₂ . In this invention, the mixtures are each used as a pure carrier gas. Preferably, an arc spraying is used for thermal spraying. In arc spraying two wires are melted in an arc and atomized by means of a carrier gas to spray particles and then transported to the component. The electric arc burns between the two wires, which are formed as anode and cathode. As wires therefore only electrically conductive materials come into question. The two wires can be made of the same or different materials. Instead of wires, two metallic tubes can also be used. The arc is normally generated between the two wire ends, which are fed to each other in the spray gun, by the application of a voltage with a contact ignition. Cored wires can also be processed, which makes it possible to additionally apply hard-wearing layers for wear protection, which contain, for example, oxides, nitrides, carbides or borides. For example, an aluminum-zinc coating can process up to 20kg per hour. Arc spraying has ideal conditions for the application of metallic anti-corrosion coating. Easy handling, use of favorable materials (through the use of wire), high application rate with high efficiency, as well as detection of large surfaces in a short time.

A thickness of the spray-metallized coating is preferably between 50 μm and 150 μm, in particular between 75 μm and 120 μm, more particularly 100 μm.

Preferably, the adhesion of the spray-metallized aluminum-zinc coating is on average between 7.0 and 8.0 MPa and the adhesion of the further (paint) layers on the spray-metallized layer itself or the anti-corrosion coating on the coated material is also on average between 7, 0 and 8.0 MPa.

Preferably, the anticorrosive coating is applied to components exposed to a seawater atmosphere (C5-M) or to a marine atmosphere (Im2), eg on oil rigs or on shore systems, and / or to components that have other corrosive chemical atmospheres (C5-I). are exposed, eg in chemical plants. The anti-corrosion coating is also suitable for components that are exposed to extreme climate, especially tropical climate, such as metallization of propane bottles for tropical climate.

In a particularly preferred embodiment of the invention, the anti-corrosion coating is applied to components of a wind turbine, in particular an offshore wind turbine. The anti-corrosion coating is particularly suitable for application to wind towers of wind turbines or offshore wind turbines. The anticorrosive coating can be applied in a particularly simple manner to components that are subject to high mechanical stress, such as flanges, ribs and attachment surfaces, according to the invention. Due to the adhesive strength and the longevity of the anti-corrosion coating applied according to the invention, maintenance intervals can be kept as long as possible.

The invention further relates to a use of a gas mixture containing a reducing gas component for applying an anti-corrosion coating to components, and to using an aluminum-zinc coating as an anti-corrosion coating for components. Embodiments of these uses of the invention will become apparent from the above description of the method according to the invention in an analogous manner.

Figur 1

ein Bauteil ohne Antikorrosionsbeschichtung,

Figur 2

ein Bauteil mit einer Aluminium-Zink-Beschichtung, die mit Luft als Trägergas aufgebracht wurde,

Figur 3

ein Bauteil mit einer mittels einer Ausführungsform eines erfindungsgemäßen Verfahrens aufgebrachten Aluminium-Zink-Beschichtung mit einem eine Aktivgaskomponente enthaltenden Gasgemisch als Trägergas und

Figur 4

einen vergrößerten Ausschnitt des Bauteils aus Figur 3, zur Verdeutlichung der Wirkung der mittels einer Ausführungsform eines erfindungsgemäßen Verfahrens aufgebrachten Aluminium-Zink-Beschichtung.

The invention will now be explained with reference to the accompanying drawings. In this show

FIG. 1

a component without anti-corrosion coating,

FIG. 2

a component with an aluminum-zinc coating applied with air as a carrier gas,

FIG. 3

a component with an aluminum-zinc coating applied by means of an embodiment of a method according to the invention with a gas mixture containing an active-gas component as the carrier gas and

FIG. 4

an enlarged section of the component FIG. 3 to illustrate the effect of by means of an embodiment of a According to the method applied aluminum-zinc coating.

The FIGS. 1 to 4 show the results of the laboratory tests and test series on which the invention is based.

In the course of laboratory tests, the corrosion protection effect of various duplex systems suitable for use on offshore wind turbines was investigated. Particular attention was paid to the design of the metallizations.

A sealer is used in the pore-rich arc sprayed anti-corrosion coatings to seal the anti-corrosion coating to prevent the ingress of moisture.

The different anticorrosive coatings were prepared for laboratory testing in accordance with ISO 20340 with an artificial breach (Ritz) of 30mm length and 2mm width (horizontal) to simulate damage to the anticorrosive system and subjected to a 25 week cyclic aging test. Assessment criteria for the quality of the different anti-corrosion coatings were the degree of corrosion of the scribe, as well as degree of blistering, degree of rust, degree of cracking, degree of exfoliation and degree of undercutting of the scribe.

Compared to anti-corrosion coatings, which were not applied by thermal spraying, in particular with a reducing gas component, a much better anti-corrosion behavior can be demonstrated. With regard to corrosion and influence on the connection with a color layer, furthermore, considerable differences of the different anti-corrosion coatings could be found.

The arc-sprayed aluminum-zinc coating with a coating thickness of 75μm showed the best results in the tests. Red rust formed here only near the Ritz. An arc-sprayed aluminum-zinc coating with a layer thickness of 50μm, however, begins after about 16 weeks with the formation of red rust.

In FIG. 1 shows a component without anti-corrosion coating, which has also been subjected to the laboratory tests described above. As in FIG. 1 can be seen, the component is coated without anticorrosive coating after 25 weeks with strong and deeply penetrating into the base material, emanating from the Ritz red rust.

In FIG. 2 is a 75μm thick aluminum-zinc coating shown, which was applied with air as the carrier gas by arc spraying and was also subjected to the laboratory tests described above. The protective aluminum-zinc coating shows (also after 25 weeks) an improvement over the component without anti-corrosion coating FIG. 1 , Although the aluminum-zinc coating protects the flat areas of the component, the Ritz still shows strong red rust formation, which continues into the area.

FIG. 3 shows the using a hydrogen-nitrogen gas mixture arc sprayed aluminum-zinc coating with 75μm layer thickness according to the invention, which has been subjected to the laboratory tests described above. It can be clearly seen that the Ritz is completely protected after 25 weeks and only slight oxide formation is present in some places. In FIG. 4 is a cut through the Ritz FIG. 3 shown. The almost white oxide layer on the surface washes into the defect and protects it. Also visible is the aluminum oxide layer protecting the underlying aluminum-zinc coating.

After the 25-week aging test, the different anti-corrosion coatings were subjected to tear tests to assess adhesion. Without anticorrosive coatings, the bond strength is at a mean of 3.4MPa. The aluminum-zinc coating applied by air as the carrier gas has an adhesive strength of 4.8 MPa. The best values are achieved by the aluminum-zinc coating applied by means of the hydrogen-nitrogen gas mixture. The adhesive strength of said aluminum-zinc coating is on average 7.6 MPa. The cause of these higher values is the better anchoring of the organic coating.

Claims (14)

A method for applying an anti-corrosion coating to components, wherein an aluminum-zinc coating is used at least as part of an anti-corrosion coating, characterized in that the aluminum-zinc coating is applied by thermal spraying, wherein for thermal spraying an inert carrier gas with a reducing gas component is used. A method according to claim 1, wherein on or under the aluminum-zinc layer, a further coating, in particular one or more color layers, is applied. A method according to claim 1 or 2, wherein hydrogen is used as the reducing gas component. The method of claim 1, 2 or 3, wherein nitrogen is used as the carrier gas. Method according to one of the preceding claims, wherein a hydrogen-nitrogen mixture is used as the injection gas mixture. Method according to one of the preceding claims, wherein for thermal spraying an arc spraying is used. Method according to one of the preceding claims, wherein the injection-metallized layer is applied alone or as part of an anti-corrosion coating to mechanically stressed areas to reduce wear and corrosion. Method according to one of the preceding claims, wherein a proportion of the reducing gas component of the gas mixture between 0.1% and 10%, in particular between 2% and 4%. Method according to one of the preceding claims, wherein a thickness of the spray-metallized coating between 50μm and 150μm, in particular between 75μm and 120μm, more preferably 100μm. Method according to one of the preceding claims, wherein the adhesion of the injection-metallized aluminum-zinc layer averages between 7.0 and 8.0 MPa and, as far as dependent on claim 2, the adhesion of the further layers on the spray-metallized layer itself or the anti-corrosion coating the coated material is on average between 7.0 and 8.0 MPa. Method according to one of the preceding claims, wherein the anti-corrosion coating is applied to components which are exposed to a corrosive atmosphere, in particular a seawater atmosphere or a maritime or chemical atmosphere. Method according to one of the preceding claims, wherein the anti-corrosion coating is applied to components of a wind turbine, in particular an offshore wind turbine. Use of a gas mixture containing a reducing gas component for applying an anti-corrosion coating to components, wherein the anti-corrosion coating is formed as an aluminum-zinc coating, and the anti-corrosion coating is applied by thermal spraying using an inert carrier gas containing the reducing gas component. Use of an aluminum-zinc coating as an anti-corrosion coating for components, characterized in that the anti-corrosion coating is applied by thermal spraying, wherein for thermal spraying an inert carrier gas is used with a reducing gas component.

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