Abstract:
A system and a method for selectively coating a substrate includes a removable mask including a magnetic member having a first surface contour shaped to conform to the outside surface of the substrate and a magnetizable member having a second surface contour shaped to conform to the inside surface of the substrate. The method for coating the substrate includes magnetically coupling a removable mask to at least one surface of the substrate; forming a coating of a coating material on the at least one surface of the substrate with the magnetically coupled removable mask using a bath containing the coating material; and selectively decoupling the removable mask from the at least one coated surface to reveal a portion of the coated surface without the coating.

Description:
BACKGROUND 
       [0001]    The subject matter disclosed herein relates generally to the field of manufacturing and, more particularly, to a removable magnetic mask for masking areas of a substrate to be coated or processed. 
       DESCRIPTION OF RELATED ART 
       [0002]    Typically, masking materials, such as vinyl adhesive tapes and lead tapes are used to prevent coatings from being deposited in areas that are covered with the masked material. For example, lead tape is used to mask flat areas of a metallic substrate in order to prevent deposition of copper plating. However, on flat areas, vinyl masking materials lift off during processing, thereby compromising the integrity of the coating process. Additionally, conductive and non-conductive coatings are applied through the coating process at different times and may need to be removed using chemicals. These chemicals pose an environmental risk during the coating process. An improved method of masking certain areas for applying coatings or other materials during processing would be well received in the field. 
       BRIEF SUMMARY 
       [0003]    According to one aspect of the invention, a method for selectively coating a substrate, includes magnetically coupling a removable mask to at least one surface of the substrate; forming a coating of a coating material on the at least one surface of the substrate with the magnetically coupled removable mask using a bath containing the coating material; and selectively decoupling the removable mask from the at least one coated surface to reveal a portion of the surface without the coating. 
         [0004]    According to another aspect of the invention, a system for coating a substrate having an inside surface and an outside surface includes a removable mask with a magnetic member having a first surface contour shaped to conform to the outside surface; and a magnetizable member having a second surface contour shaped to conform to the inside surface, the magnetizable member being sufficiently magnetizable to magnetically couple the removable mask to the outside surface to prevent a coating material from being deposited or plated between the removable mask and the outside surface during a deposition or plating process. 
         [0005]    According to another aspect of the invention, a selectively coated substrate made according to a process including the steps of magnetically coupling a removable mask to at least one surface of the substrate; forming a coating of a coating material on the at least one surface of the substrate with the magnetically coupled removable mask using a bath containing the coating material; and selectively decoupling the removable mask from the at least one coated surface to reveal a portion of the coated surface without the coating. 
         [0006]    Other aspects, features, and techniques of the invention will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0007]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which like elements are numbered alike in the several FIGURES: 
           [0008]      FIG. 1  is a view of an exemplary system according to an embodiment of the invention; 
           [0009]      FIG. 2  illustrates a cross-sectional view of a removable mask used for a ferrous substrate during a coating process according to an embodiment of the invention; 
           [0010]      FIG. 3  illustrates a cross-sectional view of a removable mask used for a non-ferrous substrate during a coating process according to an embodiment of the invention; 
           [0011]      FIG. 4  illustrates a flow chart for an exemplary process for coating a substrate using a removable mask according to an embodiment of the invention; and 
           [0012]      FIG. 5A  is a view of a copper plating bath for coating the substrate according to the process of  FIG. 4 ; and 
           [0013]      FIG. 5B  illustrates an exemplary view of a bath having chemicals to coat the substrate according to the process of  FIG. 4   
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Referring to the drawings,  FIG. 1  illustrates an exemplary system  100  with a rotary wing aircraft  102  having a removable mask  104  according to an embodiment of the invention. As illustrated, an aircraft skin such as on, for example, an aircraft door  106  on the rotary wing aircraft  102  may be selectively coupled to a removable mask  104 . The aircraft door  106  may be selectively coupled to mask  104  during certain aspects of fabrication of aircraft door  106 , for example acid etching, in order to prevent coatings or compositions from infiltrating to its surface. The removable mask  104  may be a two dimensional (2D) or three-dimensional (3D) structure formed into a particular shape in order to follow a contour of a surface of the structure being processed such as, for example, the aircraft door  106 . In an embodiment, the removable mask  104  may be formed from a flexible sheet or foil and be stamped out to take various shapes and sizes. In the example illustrated, the removable mask  104  is formed to match a 3D shape of the aircraft door  106  having contours and curvatures. In embodiments, the removable mask  104  may be an electromagnet that is magnetizable by flowing electric current through the removable mask  104 , or may be a permanent magnet made from a magnetic rare earth element or other magnetic material therein to adhere to the aircraft door  106  with a magnetic field. 
         [0015]      FIG. 2  depicts an embodiment of removable mask  104  of  FIG. 1  as used on a rigid structure  202  which is formed from a low-alloy ferrous substrate such as, for example, stainless steel or iron. As illustrated, removable mask  104  has a generally arcuate shape and having a thickness as selected or predefined by a user. In another embodiment, the removable mask  104  may be a 2D or 3D shape and may be formed to have an internal surface that follows a contour of an external or internal surface to which it is adhered. In the illustrated figure, the removable mask  104  has a generally arcuate shape and has an internal surface that follows a generally arcuate shape of external surface of rigid structure  202 . However, in embodiments, the removable mask  104  may have other 3D geometries without departing from the scope of the invention. As illustrated, removable mask  104  may be used during processing of the rigid structure  202  such as, for example, a section of a tail cone on rotary wing aircraft  102  ( FIG. 1 ). The removable mask  104  being formed from, in one example, a rare earth material may adhere to the ferrous material (i.e., magnetizable material) of rigid structure  202  during aspects of processing of the rigid structure  202  as is described in the embodiment of  FIG. 4 . 
         [0016]      FIG. 3  depicts an embodiment of removable mask  104  as used on a rigid structure  302  which is formed from a non-ferrous material such as, for example, an aluminum or magnesium alloy. As illustrated, removable mask  104  may be a permanent magnet which is formed from a rare earth material and is provided to magnetically couple to a magnetizable material  304  on an opposite surface of rigid structure  302 . The removable mask  104  being formed, in an example, from a rare earth magnet, magnetically holds the magnetizable material  304  against the inside surface of the rigid structure during processing of the rigid structure  302 . In embodiments, the removable mask  104  may be a 2D or 3D shape and may be formed to have an internal surface that follows a contour of an external or internal surface to which it is adhered. In the illustrated figure, the removable mask  104  has a generally arcuate shape and has an internal surface that follows a generally arcuate shape of external surface of rigid structure  302 . 
         [0017]      FIG. 4  illustrates an exemplary process  400  of processing a substrate such as, for example, a substrate made from an aluminum alloy according to an embodiment of the invention. As shown, the exemplary process is initiated by surface pre-treatment process  402  of the substrate during which the substrate undergoes various treatments to yield a surface character suitable for a subsequent electroplating and hardening process. The surface pre-treatment is not only used to remove dirt and organic contaminants from the surface of the aluminum alloy substrate, but also to remove an oxide or a hydroxide formed on the aluminum alloy substrate thereby permitting the surface of the substrate to be exposed for the copper plating process. 
         [0018]    According to one exemplary process, the surface pre-treatment process  402  includes removing surface contaminants using a suitable technique such as, in some non-limiting examples, solvent rinsing, vapor degreasing using trichloroethylene or other suitable solvents, solvent emulsion cleaning or the like in order to remove any grease or organic compounds. In an exemplary embodiment, a degreasing bath having an aqueous, non-silicate alkaline solution containing a surfactant may be utilized to clean the substrate. Following degreasing, the substrate is subject to a rinse in a water bath to remove solvents from its surface. In an embodiment, the substrate may be immersed in a second rinse in order to ensure that solvents are not present on the surface. Following water rinse, the substrate may be subjected to a solvent emulsion cleaning or the like in order to remove any grease or organic compounds. Following, solvent emulsion cleaning, the substrate is rinsed in a water bath and, in an embodiment, subjected to an acid etching. In acid etching, the substrate is immersed in an acid bath containing 30% by mass hydrochloric acid (HCL) for a predetermined time in order to remove an oxide layer from its surface. Following the acid bath, the substrate is rinsed in a water bath and dried in preparation for a copper plating process  404 . As will be appreciated by those of skill in the art, these surface pre-treatment procedures are susceptible to a wide array of alternatives. Thus, it is contemplated that any number of other procedures and practices may likewise be utilized such as, for example, by mechanical methods or by immersion or spray cleaner systems in order to perform the pre-treatment process of the substrate. Such pre-treatment may not be needed in all aspects of the invention, and different chemicals and processes may be utilized in other aspects. 
         [0019]    Following the surface pre-treatment process  402 , the pre-treated substrate is subjected to a copper plating process  404 . With further reference to  FIG. 5A , the removable mask  104  and/or  304  is attached to the substrate  202  or  302  at this point to protect one or both surfaces during the process  404 . In an embodiment, copper electroplating process  404  is a cathodic plating process performed in a bath of copper sulphate. The substrate is used as a cathode, copper as an anode  504 , while the copper sulphate is suspended in the bath. Copper plating  404  may be performed by applying a negative DC charge to the substrate through a battery  506 . The oppositely charged copper molecules in the bath are drawn to the cathodic substrate and deposit on the surface of the substrate that is not concealed by the removable mask  104  and/or  304 . The copper coated substrate is rinsed in water and dried. In an alternative embodiment, an anodic copper plating may also be used in lieu of cathodic copper plating. In this way, in the shown embodiment, portions of the surfaces are made conductive, and portions covered by the mask  104  and/or  304  are made non-conductive. While described in terms of copper plating, it is understood that other types of metal plating or deposition can be used. Further, the bath  502  can occur in a dedicated vat or tank  502 , or can be in the same bath or tank used in the pre-treatment process  402 . 
         [0020]    Next, in an embodiment, the copper plated substrate includes a corrosion inhibitive conversion coating process  406  with a trivalent chromium-containing layer in order to protect the surface from corrosion. As the conversion coating is conductive, areas of the substrate that are to be made non-conductive are covered with the removable mask  104  and/or  304 . As such, the mask  104  and/or  304  need not be applied in the coating process  404  where the plating is desired, and can be applied afterwards to block the application of subsequent layers in a subsequent process such as process  406 . The removable mask  104  and/or  304  prevents the conversion coating from infiltrating through it and coating the covered surface. With reference to  FIG. 5B , in an embodiment, removable mask  104  is attached to a first surface and a magnetizable material  304  is coupled at an opposite surface of the substrate at a location adjacent to an inside surface of the removable mask in order to selectively and frictionally hold the removable mask  104  to the aluminum alloy substrate. The substrate including the removable mask  104  and magnetizable material  304  is immersed in the treatment bath inside vat or tank  508 . The treatment bath includes an aqueous solution having a salt of hexafluorozirconic acid and a water soluble trivalent chromate compound, which is free of hexavalent chromium. In one exemplary embodiment, the trivalent chromate compound is trivalent chromium sulfate. The water soluble trivalent chromate compound is present in the aqueous solution in sufficient concentrations to coat the surfaces of the pre-treated heat exchanger with a uniform layer of trivalent chromium. In one exemplary embodiment, the aqueous solution can include Surtec 650, which is a commercially available liquid trivalent chromium based chemical available from CST-SurTec, Inc. In a non-limiting embodiment, the substrate is immersed for about 10 minutes at ambient temperature of about 30 degree Celsius (about 303 Kelvin) to about 40 degree Celsius (about 313 Kelvin) in order to induce the conversion coating on the surface. In other non-limiting embodiments, the aqueous solution may contain fluoride and fluoborate. It is to be appreciated that the acidic fluoride character of the conversion coating solution removes the native oxide films and replaces it with hydrated Al—Zr—O—F layer, which increases the hydrophilicity of the surface of the substrate and activates the surface for organic coating. In an embodiment, the conversion coated substrate is evaluated by visual inspection. While a specific process  406  is described above, it is understood that other chemicals, temperatures and timings can be used according to the specific application, and that process  406  need not be used in all aspects of the invention such as where a conversion coating is not needed. 
         [0021]    In an exemplary embodiment, following conversion coating process  406 , the substrate is subjected to substrate hardening process  408 . In an embodiment, the removable mask  104  is removed from the copper plated substrate prior to the copper plated substrate being inserted into a carburization chamber, although it is understood that the mask  104  and/or  304  could be left on in other aspects. In embodiments, the copper plated substrate may be carburized in a carburization chamber using a source of carbon and at an elevated temperature. In an embodiment, gas carburizing may be utilized at a temperature within the range of 900 degree Celsius (1173 Kelvin) to 950 degree Celsius (1253 Kelvin) using carbon monoxide gas as the carbon source. In another embodiment, liquid source may be used such as, for example, a molten salt of sodium cyanide and barium chloride is used. It is understood that the hardening process  406  is not required in all aspects, and that other temperatures and materials can be used according the specific application in other aspects. 
         [0022]    Lastly, the substrate surface is subjected to a surface post-treatment process  410  which may include removing chemical contaminants using a suitable technique such as, in some non-limiting examples, immersion in a water bath, solvent rinsing, vapor degreasing or other suitable solvents, solvent emulsion cleaning or the like in order to remove any compounds. It is understood that the post-treatment process  410  is not required in all aspects or can be provided at a separate facility. 
         [0023]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. While the description of the present invention has been presented for purposes of illustration and description, it is not intended to be exhaustive or limited to the invention in the form disclosed. Further, while described in the context of the manufacture of parts for a helicopter, it is understood that aspects can be used in other contexts in which a coating is to be selectively disposed on a surface, such as in semiconductor manufacturing. Many modifications, variations, alterations, substitutions, or equivalent arrangement not hereto described will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. Additionally, while the various embodiment of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.