CA2085852A1

CA2085852A1 - Flame sprayed composite coating

Info

Publication number: CA2085852A1
Application number: CA002085852A
Authority: CA
Inventors: James H. Reimer
Original assignee: Individual
Current assignee: Plastic Flamecoat Systems Inc
Priority date: 1991-12-23
Filing date: 1992-12-18
Publication date: 1993-06-24
Also published as: TW247290B; EP0549298A3; KR930012290A; EP0549298A2; MX9207501A; CN1073697A; JPH05345966A; BR9205092A

Abstract

ABSTRACT
A composite coating and method of application are provided that comprise flame spraying a layer of thermoplastic onto a substrate and thereafter flame spraying an overlying layer of another, higher melting powder such as metal onto the thermoplastic surface so as to embed unmelted particles of the higher melting powder in the thermoplastic.

Description

~r.,V~ r~;2 PFSI-20, 631 IN THE UNITED STA'rES PATENT AND ~ADEM~RK OFE'ICE

FL~ME SPRAYED COMPOSITE COATING

BACKGROUND OF THE INVENTION

1. Field of the Invention This invention relates to composite coatings applied by flame spraying to an underlying substrate.
More particularly, the invention relates to composite.
flame sprayed coatings comprising an intermediate plast.ic layer that is ~lame sprayed onto a substrate, and an overlying metal, metal-containing, or ceramic layer that is flame sprayed onto the plastic layer.

2. Description of Related Art : 10 Methods and apparatus for coating substrates, particularly metal, with a layer of thermoplastic . material by means of flame spraying have previously been .~ disclosed, for example, in United States Patent Nos.
4,632,309 and 4,934,595, and in pending United States ~: -15 Patent Application Ser. No. 07\760,866, filed September 16, l991o These methods and devices enable a user to melt powdered thermoplastic resin and apply it to a : substrate at coverage rates that make the process acceptable for applying protective coatings over a wide . variety of uses. Such uses can include, for.example, coating structural steel used in bridges or other construction, coating piping or vessels that may be subjected to corrosion, coating ship hulls to reduce the rate of barnacle formation and facilitate barnacle ~: 25 removal, and the like.
; Methods and apparatus for applying thin metal coatings to plastic substrates have also been disclosed.

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Most of such methods employ means -for melting, vaporizing or .ionizing the metal prior to applying .it to the surface of the su~strate. These coating processes are normally performed under carefully controlled conditions and require high temperatures -to melt or vaporize the metal.

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SUMMARY OF TIIE INVENTION
Accordi~cJ to -the present invention, a substrate coating and method of application are disclosed that utilize an intermediate layer of flame sprayed plastic in combination with an overlying layer of flame sprayed, powdered metal, metal-containing particles or ceramic particles. Preferred substrates are metal surfaces, although other substrates can also be used within the scope o~ the invention. Application of the coating disclosed herein does not require meltiny or ionization of the metal, metal-containing or ceramic particles used to form the overlying layer.
According to a preferred embodiment oE the method of the invention, powdered thermoplastic material, pre~erably ethylene methacrylic acid (EMAA) copolymer, is first flame sprayed onto a substrate to form an intermediate thermoplastic layer. The powder used to form the overlying layer is then heated in a flame sprayer device to a temperature greater than the melting point of the thermoplastic material comprising the intermediate layer, but lower than the melting point of the metal. The heated powder, preferably metal or a metal oxide, is then ~ sprayed over the thermoplastic intermediate layer, ; causing the powder particles to embed in the surface of - the thermoplastic. As the surface of the thermoplastic intermediate layer becomes fully coated with particles of the metal powder, additional metal will not adhere beGause the metal is not in a molten state.
The composite coatings of the invention can be specially adapted for uses such as corrosion-resistant, antifoulant or wear-resistant applications by selecting a powdered material for the overlying layer which exhibits the desired property.

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BRIEF DESCRIPTION OF THE DRAWINGS
The apparatus of the invention is further described and explai.ned in relation to the following figures of the drawings wherein:
Figure l is a photomicrograph of a cross-section taken through a substrate made in accordance with the present invention, wherein an aluminum substrate is coated with an intermediate layer of EMAA and an overlying layer of copper powder; and Figure 2 is a photomicrograph of a cross-section ~: taXen through a substrate made in accordance with the present invention, wherein an aluminum substrate is coated with an intermediate layer of EMAA and an overlying layer of tungsten carb.ide powder.

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s DESCRIPTION OF THE P~EFERRED EMBODIMENTS
Accorclirlg to the pre~ent invention, an improved spray coatilly is provided that comprises an intermediate layer comprising a major portion of a thermoplastic resin, and an overlying layer that comprises a major portion of a metal, metal-containing, or ceramic powder.
The spray coating of the invention can be applied to a wlde variety of substrate ma~erials to achieve desirable surface properties and characteristics.
Depending upon the particular substrate and the coating materials employed, such application can be performed in the field, at the use site, or in a plant. Exemplary substrates that can be coated in accordance with the present invention include metals, metal-containing materials, ceramic materials, cellulosic materials materials and polymeric materials, provided that such surfaces have been satisfactorily clean, brushed, or otherwise prepared as necessary to facilitate bonding of a thermoplastic intermediate layer to which an overlying layer of powdered metal, metal-containing or ceramic material can subsequently be applied. According to a preferred embodiment of the invention, the surface to be coated is prepared by sand blasting, if necessary, to an SSPC-6 specification to remove all dust and extraneous matter.
Following preparation of the substrate surface, a powdered thermoplastic material is applied to the substrate to form an intermediate surface coating preferably having a thickness ranging from about 8 to about 12 mils. Accordin~ to a particularly preferred embodiment of the invention, the intermediate surface coating is flame sprayed onto the substrate as disclosed in United States Patent No. 4,934,595, or in pending United States Patent Application Ser. No. 07\760,866, filed September 16, 1991! the entire specifications of which are incorporated by reference hereln.

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Suitable thermop]astic resins for use in forminy the intermediate layer of the coating clisclosed herein include, for example, EMAA, ethylene vinyl acetate (EVA) and polypropylene, although other similarly effective resins can likewise be used within the scope of the invention. Althouyh substrates to be coated as provided herein are preferably made of metal, substrates made of other materials can likewise be coated within the scope of the invention provided that the thermoplastic resin Elame sprayed onto the subs-trat:e to form the intermediate layer will adhere to the substrate surface.
After the substrate has been coated with the intermediate layer of thermoplastic resin, an overlying layer is applied that preferably comprises a major portion of a powdered metallic material. Although a metallic material is preferred for use in forming the overlying layer of the composite coating of the invention, it will be appreciated, however, that powdered metal-containing or ceramic materials can also be applied to a substrate using the methods disclosed herein, and the use of such materials likewise falls within the scope of the present invention. Metal-containing materials can include, for example, metal oxides, metal nitrides, and the like.
A preferred metallic material for use in forming the overlying layer of the subject composite coating is powdered copper, although other metallic materials such as, for example, aluminum, carbide, tungsten carbide, stellite, chromium, stainless steel, nickel, titanium, metal oxides, metal alloys, and the like, can also be used. According to a preferred embodiment of the invention, the metallic overlying layer is applied to the thermoplastic-coated substrate in the same manner as the thermoplastic layer, except that the powdered metal is substituted for the powdered thermoplastic, and a surface preparation step is not generally required. The overlying layer can be applied either before or after the -thermoplastic layer has cooled to ambient temperature.
Surface preparation, usu~lly just washiny, of the thermoplastic intermecliate layer should not be needed unless the plastic surface has been contaminated such as by oil or the like prior to application of the overlying layer.
The powdered metal, metàl-containing or ceramic particles used to form the overlying layer are preferably heated by combustion from the flame spray gun to a temperature greater than the melting point of the thermoplastic material used to form the intermediate layer of the composite coating, but less than the temperature that will char, ignite or otherwise degrade the thermoplastic, and less than the melting point of the powder particles. When heated to such temperature, the powder particles will become partially embedded in the surface of the thermoplastic layer when propelled against it by the force of the stream emanating from the flame spray gun coupled with a softening or melting of the thermoplastic at the surface of the intermediate layer due to the relatively greater temperature of the heated powder particles. Once the surface of the intermediate layer has been substantially covered by the partially embedded heated particles of the overlying layer, further spraying will typically result in the excess powder bouncing off and accumulating below the work surface.
Such excessive spraying can generally be minimized by advancing the flame spray gun to a new area as surface coverage is observed by visual monitoring.
Although the size of the thermoplastic particles used in flame spraying the intermediate layer can vary according to the type of material and substrate, the thermoplastic material, the temperature used in the flame spray gun, and the desired thickness of the intermediate layer, thermoplastic particle sizes ranging from about 40 ` mesh to about 120 mesh are preferred. Although the thickness of the intermediate layer of thermoplastic t~

m~terial will preferably rancJe rom about 8 to about 12 mils, it ~ill be understood that the preferred thickness c~n vary either above or below that range, depending upon factors such as, for example, the size, geometry and material of the substrate; the intended use; the use environment; the nature and amount of abrasion li~ely to be experienced during use; the type, particle size and thickness of the metal powder to be applied over the thermoplastic layer; and the like.
Similarly, the size of the powder particles used in flame spraying the overlying layer can vary according to the type of material, -the substrate, the intended use, the thermoplastic material, the temperatur~ used in the flame spr~y gun, and the desired thickness of the overlying layer. Preferably, the average particle size will have a maximum diameter that is less than or equal to the thickness of the intermediate layer onto which the ; particles are sprayed. Although the thickness of the overlying layer of metallic or ceramic material will preferably range from about one-to about ten mils, it will be understood that the preferred thickness can vary, depending upon factors such as the particle dimensions, the extent to which the particles are embedded in the intermediate layer, the intended use, the use environment, the amount and nature of any abrasion to which the coating will be subjected during use, and the like.
;~ Once the overlying layer of the subject composite coating has been applied, further processing can be done, if desired, to achieve particular finishes. Thus, for example, where the overlying layer comprises copper, the resultant flame sprayed metal surface can be polished to achieve a slick, shiny surface appearance.
If the overlying surface layer of the composite coating subsequently becomes scratched or damaged, repair is usually easily accomplished by spraying additional metal, metal-containing or ceramic powder onto the .

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g remaining thermop]astic ~aterial of the intermediate layer.
The composite coatings and coating method of the invention are further described and explained in relation to the following examples, with reference to the photomicrographs oE the accompanying figures.

Example 1 A test coupon of aluminum was prepared for use as a subs-trate by sandblasting the surface to a one to three mil anchor profile. The test coupon was then coated with an intermediate layer of PF 111 (a product designation of Plastic Flamecoat systems, Inc. for EMAA having a melting point of about 1600F, 710C.) by flame spraying the material onto the top surface of the aluminum to achieve a thermoplastic layer having a thickness of about ten mils. After allowing the thermoplastic-coated substrate to cool to ambient temperature, an overlying layer of powdered copper was flame sprayed onto the thermoplastic intermediate layer. The thickness of the overlying layer ;~ 20 was about three mils, and the powdered copper was heated to a temperature of about 300~F (1490C) by the flame spray gun prior to application to the coupon. The fuel gas used in the flame spray gun was propane. A cross-sectional cut was thereafter made through the coupon, and the structure of the cross-section is shown in the accompanying photomicrograph identified as Figure 1~ The substrate, intermediate and overlying layers referred to above are clearly visible in Figure 1.
, Example 2 A test coupon of aluminum was prepared for use as a substrate by sandblasting the surface to a one to three mil anchor pattern. The test coupon was then coated with an intermediate layer of PF 111 by flame spraying the material onto the top surface of the aluminum to achieve a thermoplastic layer having a thickness of about ten .

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powdered tungsten carbide was flame sprayed onto the thermoplastic intermediate layer. The thickness of the overlyinq layer was about three mils and the powdered tungsten carbide was heated to a temperature of about 3000F (149~C) by the flame spray.gun prior to application to the coupon. The fuel gas used in the flame spray gun was propane. A cross-sectional cut was thereafter made through the coupon, and the structure of the cross section is shown in the accompanying photomicrograph identified as Figure 2. The substrate, intermediate and overlying layers referred to above are clearly visible in Figure 2.
Other alterations and modifications of the invention will likewise become apparent to those of : ordinary skill in the art upon reading the present : disclosure, and it is intended that the scope of the invention disclosed herein be limited only by the broadest interpretation of the appended claims to which the inventor is legally entitled.

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Claims

1. A composite coating for a substrate, the coating comprising a first layer of thermoplastic that is flame sprayed onto the substrate, and a second layer of powdered metal that is flame sprayed onto the first layer.

2. The composite coating of claim 1 wherein the thermoplastic is selected from the group consisting of ethylene methacrylic acid, ethylene vinyl acetate and polypropylene.

3. The composite coating of claim 2 wherein the thermoplastic is ethylene methacrylic acid.

4. The composite coating of claim 1 wherein the powdered metal comprises a material selected from the group consisting of copper, aluminum, carbide, tungsten carbide, stellite, chromium, stainless steel, nickel, titanium, and alloys thereof.

5. The composite coating of claim 4 wherein the powdered metal comprises copper.

6. The composite coating of claim 1 wherein the substrate is a metallic surface.

7. The composite coating of claim 1 wherein the first layer has a thickness ranging from about eight mils to about 12 mils.

8. The composite coating of claim 7 wherein the thickness of the first layer is about ten mils.

9. The composite coating of claim 7 wherein the the second layer has a thickness that is up to about the thickness of the first layer.

10. The composite coating of claim 7 wherein the metal powder has an average particle size that does not exceed the thickness of the first layer.

11. A protective composite coating for a substrate, the coating made by flame spraying a first continuous layer of thermoplastic onto the substrate, and thereafter flame spraying a second continuous overlying layer of powder having a higher melting point than the first layer onto the first layer at a temperature greater than the melting point of the thermoplastic but less than the melting point of the powder so that the flame sprayed powder is partially embedded in the first layer, said powder being selected from the group consisting of metals, metal-containing materials, and ceramics.

12. The composite coating of claim 11 wherein the powder is selected from the group of metal-containing materials consisting of metal alloys, metal oxides and metal nitrides.

13. The composite coating of claim 12 wherein the powder is selected from the group of metals consisting of copper, aluminum, carbide, tungsten carbide, stellite, chromium, stainless steel, nickel, titanium and alloys thereof.

14. The composite coating of claim 11 wherein the powder comprises glass beads.

15. The composite coating of claim 11 wherein the thermoplastic is selected from the group consisting of ethylene methacrylic acid copolymer, ethylene vinyl acetate copolymer and polypropylene.

16. The composite coating of claim 15 wherein the thermoplastic is ethylene methacrylic acid copolymer.

17. The composite coating of claim 11 wherein the substrate is selected from the group consisting of metals, metal-containing materials, ceramic materials, cellulosic materials and polymeric materials.

18. The composite coating of claim 11 wherein the first layer has a thickness ranging from about eight mils to about 12 mils.

19. The composite coating of claim 18 wherein the the first layer has a thickness of about 10 mils.

20. The composite coating of claim 11 wherein the the second layer has a thickness up to about the thickness of the first layer.

21. The composite coating of claim 11 wherein the powder has an average particle size that does not exceed the thickness of the first layer.

22. A method for coating a substrate comprising the steps of:
a. cleaning the suface of the substrate;
b. providing a first powder comprising a major portion of a thermoplastic resin;
c. flame spraying the first powder onto the substrate to form a substantially continuous intermediate layer of thermoplastic resin having an outwardly facing surface opposite the substrate;
d. providing a second powder comprising a major portion of unmelted particles of a material selected from the group consisting of powdered metals, powdered metal-containing materials, and ceramics; and e. flame spraying the unmelted particles of the second powder onto the intermediate layer in such manner that a substantially continuous overlying layer is formed which comprises unmelted particles of the second powder embedded in the outwardly facing surface of the intermediate layer.

23. The method of claim 22 wherein the first powder is flame sprayed onto the substrate at a temperature greater than the melting point of the thermoplastic resin.

24. The method of claim 22 wherein the second powder is flame sprayed onto the substrate at a temperature greater than the melting point of the thermoplastic resin but less than the melting point of the major portion of the second powder.

25. The method of claim 22 comprising the additional step of cooling the intermediate layer prior to applying the overlying layer.

26. The method of claim 22 comprising the additional step of polishing the overlying layer.

27. The method of claim 22 wherein the second powder comprises an antifoulant material.

28. The method of claim 22 wherein the second powder comprises an abrasion-resistant material.

29. The method of claim 22 wherein the second powder comprises a corrosion-resistant material.