Patent Application
20110003165
Not applicable.
Not applicable.
1. Field of the Invention
The invention relates generally to apparatus and methods relating to the application of coatings, and more particularly to a multilayer anti-corrosive coating for a metallic substrate such as an iron pipe.
2. Description of Related Art
Iron-based pipes have been used in transporting water from different sources for many years. Over time, these pipes exhibit corrosion and, depending on their use, may require frequent replacement. Replacing iron-based pipes is costly for the material, the labor, and the down-time to the consumer.
Cathodic protection is one technique used to control corrosion of a metal surface. This is done by making the surface to be protected the cathode of an electrochemical, or galvanic cell. This is most commonly done using alloys of zinc, magnesium and aluminum. These galvanic anodes are designed and selected to have a greater negative electrochemical potential than the metal they are protecting, which is typically steel. As the galvanic anode electrode corrodes, the anode material is consumed until it must be replaced.
Galvanizing, or more specifically hot-dip galvanizing is the process whereby steel is coated with a layer of metallic zinc. Galvanized coatings are extremely durable in most environments because of their barrier properties and cathodic protection. If, or when, the zinc coating is breached or scratched, exposing the steel surface, the zinc coating acts as an anode to form a galvanic cell, thereby protecting the steel from corrosion. This is also known as localized cathodic protection.
Coatings to iron-based pipes have also been developed utilizing epoxy compositions that result in good corrosion resistance. For example, thermoset polymers are widely used to protect steel pipes, concrete reinforcing bars (rebar), pipe connections, valves and the like from corrosion. The most commonly used thermoset polymer for this type of application is fusion bonded epoxy. Fusion bonded epoxy is typically applied to a steel pipe that is preheated to the application temperature where the fusion bonded epoxy transforms to a liquid. The liquid fusion bonded epoxy flows and solidifies on the pipe, pipe joint, and the like. Coating thickness of the fusion bonded epoxy is around 250 to 500 microns. However, the thickness of these coatings vary, are difficult to apply especially at the joints, and different coatings are required depending on the environmental exposure of the iron-based pipes.
With fusion bonded epoxy, any breach in the coating will result in corrosion of the coated material.
A multilayer coating that is corrosion resistant has a first coating layer on a substrate; a second coating layer deposited on the first coating layer; and a third coating layer deposited on the second coating layer; wherein the first coating layer is substantially a metal, the second coating layer is a mixture of the metal and a polymeric material, and the third coating layer is substantially the polymeric material.
The substrate can be any of iron, iron pipe, steel, copper, nickel, concrete, wood, wood products, fiberglass, ceramic, plastic, and any other metal or non-metal material that can be used as a substrate. The metal used for the first and second coating layers is at least one of zinc, aluminum, alloy of zinc-aluminum, magnesium, alloy of zinc-magnesium, alloy of aluminum-magnesium, indium, alloy of zinc-indium, alloy of aluminum-indium, alloy of magnesium-indium, gallium, alloy of zinc-gallium, alloy of aluminum-gallium, alloy of magnesium-gallium, alloy if indium-gallium, tellurium, alloy of zinc-tellurian, alloy of aluminum-tellurium; alloy of magnesium-tellurium, alloy of indium-tellurium, and alloy of gallium-tellurium.
In one embodiment, the substrate is iron pipe and the first coating layer comprises a metal that is anodic to the substrate, preferably 99% zinc or aluminum-zinc having a ratio of about 85% aluminum to about 15% zinc.
In one embodiment, the polymeric material comprises at least one of polyethylene, polypropylene, polyester, nylon, polytetrafluorethylene (PTFE), ethylene methacrylate acid copolymer (EMAA), a thermoplastic material and a thermoset material. In one embodiment the polymeric material is polyethylene or polypropylene.
The thickness of the multilayer coating varies with the thickness of the various layers. The thickness of the first coating layer is approximately 25 microns to approximately 200 microns; the thickness of the second coating layer is approximately 5 microns to approximately 200 microns; and the thickness of the third coating layer is approximately 5 microns to approximately 200 microns. In one embodiment, the thickness of the first coating layer is approximately 70-80 microns, the thickness of the second coating layer is approximately 20-30 microns, and the thickness of the third coating layer is approximately 95-105 microns.
In another embodiment, a method is provided for applying a multilayer coating and has the steps of first applying a first coating layer on a substrate; a second step of applying a second coating layer on the first coating layer; and a third step of applying a third coating layer on the second coating layer; wherein the first coating layer is substantially a metal, the second coating layer is a mixture of the metal and a polymeric material, and the third coating layer is substantially the polymeric material.
In one embodiment of the multilayer coating, the first coating layer, the second coating layer and the third coating layer are each applied sequentially using thermal spray. Additionally, the second coating layer may be applied as a mixture, or applied as separate materials that mix during the application processes. More specifically, the metal is applied utilizing a first application means, and the polymer material is applied utilizing a second application means, and the materials mix to form the second coating layer at the application site.
The method of providing the multilayer coating may also include the step of heating the substrate to approximately the fusing temperature of the metal when applying the first coating layer.
The method of providing the multilayer coating may also includes the step of heating the substrate to approximately the fusing temperature of the polymeric material when applying the third coating layer.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.
The present invention is further described in the detailed description which follows, in reference to the noted drawing by way of a non-limiting example of an exemplary embodiment of the present invention, and wherein:
The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.
The first coating layer 20 is substantially a metal layer that is applied using cold spray or thermal spray techniques. It is understood that thermal spray includes the use of various techniques, including, but not limited to, combustion flame, combustion wire, high velocity oxygen fuel (HVOF), high velocity liquid fuel (HVLF), high velocity air-fuel (HVAF), and plasma.
The metal 22 is typically at least one of zinc, aluminum, alloy of zinc-aluminum, magnesium, alloy of zinc-magnesium, alloy of aluminum-magnesium, indium, alloy of zinc-indium, alloy of aluminum-indium, alloy of magnesium-indium, gallium, alloy of zinc-gallium, alloy of aluminum-gallium, alloy of magnesium-gallium, alloy if indium-gallium, tellurium, alloy of zinc-tellurian, alloy of aluminum-tellurium, alloy of magnesium-tellurium, alloy of indium-tellurium, and alloy of gallium-tellurium. Other metals may also be considered. In one embodiment, the substrate 10 is iron pipe and the first coating layer 20 is a metal 22 that is anodic to the substrate 10. When this is the configuration, the metal 22 is preferably one of 99% zinc and aluminum-zinc having a ratio of about 85% aluminum to about 15% zinc, and the thickness 24 of the first coating layer is approximately 25 microns to approximately 200 microns. In another embodiment the thickness 24 of the first coating layer is approximately 70-80 microns.
In one embodiment the first coating layer 20 is applied utilizing thermal spray techniques, where the metal 22 is fed as a powder or a wire. The metal 22 is preferably applied at the fusing temperature of the anode, that is, for example, if the substrate 10 is an iron pipe and the metal 22 is zinc, the fusing temperature is approximately 850° F.
The second coating layer 30 is a mixture of the metal 22 and a polymeric material 32. The polymeric material 32 may be applied using thermal spray or cold spray techniques. The polymeric material 32 is at least one of polyethylene, polypropylene, polyester, nylon, polytetrafluorethylene (PTFE), ethylene methacrylate acid copolymer (EMAA), a thermoplastic material and a thermoset material. In one embodiment the polymeric material 32 is at least one of polyethylene and polypropylene. The thickness 34 of the second coating layer 30 is approximately 5 microns to approximately 200 microns. In another embodiment, the thickness 34 of the second coating layer 30 is approximately 20-30 microns.
The second coating layer 30 is preferably applied utilizing thermal spray techniques, where the polymeric material 32 is powder fed through a hopper. The polymeric material 32 is preferably applied at the fusing temperature of the polymeric material 32, that is, for example, at a temperature of approximately 450° F.
In one embodiment, the metal 22 and the polymeric material 32 are applied substantially simultaneously from two or more applicator guns, the mixing occurring at the deposition site.
The third coating layer 40 is made up essentially of the polymeric material 32. The polymeric material 32 may be applied using thermal spray or cold spray techniques. The polymeric material 32 is at least one of polyethylene, polypropylene, polyester, nylon, polytetrafluorethylene (PTFE), ethylene methacrylate acid copolymer (EMAA), a thermoplastic material and a thermoset material. In the preferred embodiment the polymeric material 32 is at least one of polyethylene and polypropylene. The thickness 44 of the third coating layer 40 is approximately 5 microns to approximately 200 microns. In the preferred embodiment, the third thickness 44 of the third coating layer is approximately 95-105 microns.
The third coating layer 40 is preferably applied utilizing thermal spray techniques, where the polymeric material 32 is powder fed through a hopper. The polymeric material 32 is preferably applied at the fusing temperature of the polymeric material 32, that is, for example, at a temperature of approximately 450° F. This is similar to the application of the polymeric material as part of the second layer.
The multi-layer coating 12 is applied to the substrate 10 by first applying the first coating layer 20 onto the substrate 10. This is followed by applying the second coating layer 30 onto the first coating layer. The second coating layer 30 is applied by spraying a mixture of the metal 22 used in the first layer 20 with a polymeric material 32.
It should be noted that the second coating layer 30 can be applied to the first coating layer 20 utilizing a single spray gun or a multiple spray gun method. When a two spray gun method is used, the metal 22 is sprayed from a first spray gun towards the outer surface of the first coating layer 20 while the polymeric material 32 is sprayed from a second spray gun towards the outer surface of the first coating layer 20. Mixing of the coating materials 22, 32 takes place, for example, prior to the coating material reaching the outer surface of the first coating layer 20 by firing the spray guns substantially simultaneously, or upon impact at the outer surface of the first coating layer 20.
In one embodiment, the polymeric coating material 32 is applied first to the outer layer of the first coating layer 20, and the metal coating material 22 embeds into the polymeric material 32 forming the second coating layer 30.
In another embodiment, the multiple spray guns release the coating materials 22, 32 substantially simultaneously to form the second coating layer 30.
It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.
This application is based upon U.S. Provisional Application No. 60/992,143 filed on Dec. 4, 2007, the disclosure of which is hereby incorporated-by-reference thereto in its entirety and the priority of which is claimed under 35 U.S.C. §119(e).
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US08/85396 | 12/3/2008 | WO | 00 | 9/14/2010 |
| Number | Date | Country | |
|---|---|---|---|
| 60992143 | Dec 2007 | US |
