Abstract:
A method for forming a composite structure is disclosed. The method includes four steps. Step one calls for applying a primer ( 104 ) to a surface ( 102 ) of a tool ( 100 ). Step two requires applying a coating ( 106 ) to primer ( 104 ). Step three calls for curing primer ( 104 ) and coating ( 106 ). The last step calls for forming the composite structure on tool ( 100 ). More specifically, primer ( 104 ) may be a powdered primer, and coating ( 106 ) may be a powdered fluorinated organic compound.

Description:
RELATED APPLICATIONS 
     This application is related to U.S. application Ser. No. 09/248,172, entitled “Acid Impervious Coated Metal Substrate Surface and Method of Production,” now U.S. Pat. No. 6,124,000, issued Sep. 26, 2000. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     This invention relates generally to the field of materials construction and, more specifically, to an apparatus and method for forming a composite structure. 
     BACKGROUND OF THE INVENTION 
     Composite structures are desirable in many industries for many applications. The aerospace industry, for example, uses composite structures extensively because, among other desirable attributes, composites have high strength-to-weight ratios. Because of the ever increasing use of composite structures throughout industry, manufacturers are continually searching for better and more economical ways of forming composite structures. 
     In the forming of composite structures many manufacturing steps are performed. One such step that is usually required is an elevated-temperature curing step. A composite structure is placed on a tool, which is normally the tool that was used to shape the composite structure, and then placed in an oven for a period of time. After the curing cycle the composite structure is removed from the tool. Most composite materials have a tendency to adhere to the tool, which may cause harm to the shape or surface of the composite structure when being removed. This is the reason release agents were developed. Before placing a composite structure on a tool, a release agent is applied to the tool surface to allow the composite structure to be easily removed from the tool after curing. This release agent needs to be reapplied to the tool before every curing cycle, which takes time. In addition, typical release agents are organic solvent-based, which emit pollution. Furthermore, some of the release agent transfers to the composite structure, which results in a time-consuming sanding step of the surface of the composite structure before painting. 
     The challenges in the field of forming composite materials continue to increase with demands for more and better techniques having greater flexibility and adaptability. Therefore, a need has arisen for a new apparatus and method for forming a composite structure. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, an apparatus and method for forming a composite structure is provided that substantially eliminates or reduces disadvantages and problems associated with previously developed apparatuses and methods. 
     An apparatus for forming a composite structure is disclosed. The apparatus comprises a tool having a surface that is substantially covered by a primer and a coating. More specifically, the primer may be a powdered primer, and the coating may be a powdered fluorinated organic compound. 
     A method for forming a composite structure is disclosed. The method comprises four steps. Step one calls for applying a primer to a surface of a tool. Step two requires applying a coating to the primer. Step three calls for curing the primer and coating that are applied to the tool. The last step calls for forming the composite structure on the tool. 
     In accordance with another aspect of the present invention, a method for forming a composite structure is disclosed. The method comprises six steps. Step one calls for cleaning a surface of a tool with an environmentally friendly solvent. Step two requires covering a peripheral portion of the surface with, for example, masking tape. The third step calls for applying a powdered primer to the uncovered portion of the surface. Step four calls for applying a powdered coating to the primer. Step five requires the curing of the primer and coating that are applied to the tool. The last step allows for forming the composite structure on the tool. 
     A technical advantage of the present invention is the elimination of having to apply a release agent each time a composite structure is cured. The powdered primer and powdered coating will result in a more durable tool that can be used for numerous curing cycles. This will save time and money. 
     Another technical advantage of the present invention is that emissions from traditional release agents will be eliminated. The powdered primer and powdered coating are environmentally friendly, and will allow a manufacturer to meet tightening environmental regulations. This will also eliminate any permit and compliance issues associated with the current use of release agents. 
     An additional technical advantage of the present invention is that the number of times a composite structure has to be sanded before being painted will be substantially reduced. This will save time and money. 
    
    
     Other technical advantages are readily apparent to one skilled in the art from the following figures, descriptions, and claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the invention, and for further features and advantages, reference s now made to the following description, taken in conjunction with the accompanying drawings, in which: 
     FIG. 1A is an elevation view of a tool useful in the practice of the present invention; 
     FIG. 1B is a fragmented view of a metallic tool useful in the practice of the present invention showing, in greater detail, the primer, coating, and surface of the metallic tool; 
     FIG. 1C is a fragmented view of a composite tool useful in the practice of the present invention showing, in greater detail, the primer, coating, and surface of the composite tool; and 
     FIG. 2 is a flowchart demonstrating one method of forming a composite structure in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The preferred embodiments of the present invention and its advantages are best understood by referring now in more detail to FIGS. 1A,  1 B,  1 C, and  2  of the drawings, in which like numerals refer to like parts. 
     FIG. 1A is an elevation view of a tool  100  useful in the practice of one embodiment of the present invention. Tool  100  has a surface  102  in which there is a primer  104  and a coating  106  applied thereto. Tool  100 , along with the applied primer  104  and coating  106 , is used for the forming of composite structures. Solely for convenience, tool  100  is shown in FIG. 1A to be separated into two halves, each half being constructed of a different material. As illustrated by FIG. 1A, Tool  100  may be constructed of a metallic material, or tool  100  may be constructed of a composite material. Other types of materials are also contemplated by the present invention. Furthermore, the shape of tool  100  as shown in FIG. 1A is only one of many shapes that are possible. Depending on the final composite structure desired, tool  100  can be any shape imaginable. 
     Surface  102  is the “working surface” of tool  100 . In other words, surface  102  is where the composite structure will be formed and, hence, where primer  104  and coating  106  will be applied. Surface  102  is normally prepared before the application of primer  104  and coating  106  by cleaning with an environmentally-friendly solvent, such as isopropyl alcohol. This solvent is then allowed to dry before the application of primer  104  and coating  106 . It may be, however, unnecessary to clean surface  102  depending on its initial condition. On the other hand, before cleaning surface  102  with a solvent, surface  102  may be abraded with, for example, a Scotchbrite and a jitter bug sander. In the case of tool  100  being constructed of a composite material, there may be an additional preparation step after cleaning the surface with a solvent. This would be a step of applying a surfactant solution, which may be any of a myriad of commercially-available soaps. This surfactant solution is also allowed to dry on surface  102  before application of primer  104  and coating  106 . 
     In another embodiment of the present invention, the preparation of surface  102  may also include a covering of the periphery of surface  102  with a tape  108 . Tape  108  may be a masking tape or any other tape that is adequate to protect the periphery of surface  102  when applying primer  104  and coating  106 . This covering of the periphery of surface  102  is for any subsequent sealant that would be used for vacuum bag forming of a composite structure. 
     FIG. 1B is a fragmented view of one embodiment of the present invention showing tool  100  constructed of metallic material. In this embodiment, primer  104  is a fluorinated powdered primer used for fluorinated compounds, and is used to obtain a good bond between coating  106  and tool  100 . As examples, primer  104  may be tetrafluoroethylene or an ethylene polymer blended with epoxy. Other fluorinated hydrocarbons are contemplated by the present invention for use as primer  104 . The thickness of primer  104  will generally be 2-3 mils. However, depending on the type of material used, and the method of application, other thicknesses are contemplated. Primer  104  is typically sprayed onto surface  102  of tool  100  by an electrostatic powder spray gun  110  as illustrated in FIG.  1 A. Electrostatic powder spray guns are well known in the art of material coatings. Other methods of applying primer  104  to surface  102  of tool  100  are contemplated by the present invention. 
     FIG. 1C is a fragmented view of another embodiment of the present invention showing tool  100  constructed of composite material. In this embodiment, primer  104  is a nylon-powdered primer. Nylon is used because it has release properties of its own. Other types of primer  104  are contemplated by the present invention. Once again, primer  104  is typically sprayed onto surface  102  of tool  100  by an electrostatic powder spray gun  110 . However, other methods of applying primer  104  are contemplated. 
     Referring to either FIG. 1B or FIG. 1C, coating  106  is shown. Coating  106  is used as the release agent when constructing a composite structure with tool  100 . Coating  106  is a fluorinated hydrocarbon in powdered form, and is commercially available. Examples of coating  106  are Dyher 820 by Whifford Inc., Teflon manufactured by DuPont and distributed by Intech, and Halar by Ausimont USA, Inc. Other types of fluorinated powdered hydrocarbons are also contemplated by the present invention. The thickness of coating  106  will generally be 2-3 mils. However, depending on the type of material used, and the method of application, other thicknesses are contemplated. A conventional corona electrostatic coating process, using electrostatic powder spray gun I  10 , may be used to apply coating  106  to primer  104 . Coating  106  will chemically or mechanically bond to primer  104  after application. Using powdered fluorinated hydrocarbons for coating  106  eliminates emission problems typical of the traditional release agents, such as Frecote 44NC, used in constructing composite structures. This will allow manufacturers to meet tightening environmental regulations, and will eliminate any permit and compliance issues associated with the use of traditional release agents. 
     After the application of both primer  104  and coating  106  to surface  102  of tool  100 , a curing cycle is typically performed. Tool  100  is coupled to a heat source, such as an oven, for a certain period of time depending on the type of coating  106  used. The temperature used in the curing process varies depending on the type of material used for tool  100 , but will generally be greater than approximately 450° F. Solely as an example, if Halar is used as a coating for tool  100  made of steel, tool  100  would be cured at approximately 535° F. for approximately twenty minutes. After the curing cycle, tool  100  is allowed to cool down to ambient temperature. Tool  100  is then ready for forming composite structures. 
     In an embodiment where tool  100  is made of composite material, as shown in FIG. 1C, the nylon-powdered primer will melt during the curing cycle, and the nylon will flow around the fluoropolymer particles contained in coating  106  and mechanically lock them into place. A durable coating  106  will result. No matter what type of material tool  100  is constructed of, a smooth, tack-resistant surface of coating  106  also results. This means that when forming a composite structure using tool  100 , many cycles of use can be accomplished before having to inspect surface  102  of tool  100  for recoating. This eliminates the traditional step of having to apply a release agent each time a composite structure is cured, which will save time and money. In addition, more time and money will be saved by the use of primer  104  and coating  106  because of the elimination of a sanding step that is typical with the use of traditional release agents. Using traditional release agents results in a transfer of some of the release agent into the composite tool being formed, which means the composite structure has to be sanded before being painted. With the present invention, there is no transfer of primer  104  and/or coating  106  to composite structures during the curing cycle. 
     FIG. 2 is a flowchart demonstrating one method of forming a composite structure in accordance with the present invention. In one embodiment, surface  102  of tool  100  is cleaned with an environmentally compliant solvent at step  200 . If tool  100  is constructed of composite material, as determined at decisional step  218 , then a surfactant solution is also applied to surface  102  and allowed to dry at step  220 . In any case, the next step is to cover a peripheral portion of surface  102  with tape  108  at step  202 . Then powdered primer  104  can be applied to the uncovered portion of surface  102  at step  204 . In the case of tool  100  being made of composite material, powder primer  104  will comprise a nylon-powdered primer. After the application of powdered primer  104 , coating  106 , which comprises a powdered fluorinated organic compound, is applied to primer  104  at step  206 . Tool  100  is then cured in an oven for a period of time at step  208  and a composite structure is coupled to tool  100  and formed at step  210 . 
     Although an embodiment of the invention and its advantages are described in detail, a person skilled in the art could make various alternations, additions, and omissions without departing from the spirit and scope of the present invention as defined by the appended claims.